Document O3nLDZbGX0BgDm3dYZ9REor8X

FILE NAME Brakes BRK DATE 1987 Apr 15 DOC BRK164 DOCUMENT DESCRIPTION EPA Report - Analysis of the Feasibility of Replacing Asbestos in Automobile and Truck Brakes FINAL REPORT I FS on = ANALYSIS OF THE FEASIBILITY OF REPLACING ASBESTOS IN AUTOMOBILE AND TRUCK BRAKES Prepared for the Environmental Protection Agency vane (ateae April 15 1987 by The American Society of Mechanical Engineers This is a report of an expert panel assembled by ASME to address the technical issues associated with the removal of asbestos from vehicle friction products This panel convened on December 3 and 4 1986 to discuss issues of vehicle safety friction material availability and performance and future trends in the development of asbestos friction products Panel Members Panel Chairman Dr. L. S. Skip Fletcher Associate Director Texas Engrg Experiment Station The Texas & University System 301 Engineering Research Center College Station TX 77843 409 845-7270 Members Mr. Arnold E. Anderson Ford Motor Company 20000 Rotunda Drive P.O. Box 2053 Dearborn MI 48121-2053 Mr. Robert Nelson Manager Technical Service ABEX Corporation 3001 West Big Beaver Suite Troy MI 48084 710 Mr. John Fobian Dr. Michael J. Rabins Director Automotive Engineering Assoc Graduate American Automobile Association Engrg Programs _ 8111 Gatehouse Road Wayne State University Falls Church VA 22047 731 Science Library Detroit MI 48202 Dr. Serge Gratch 32475 Bingham Road Mr. Richard Radlinski Birmingham MI 48018 Vehicle Stability & Control Branch Mr. Jerry McCullough Head Development Section Lyndon B. Johnson Space Center Houston TX 77058 Nat'l Hwy Traffic P.O. Box 37 East Liberty OH Safety 43319 Admin Dr. Ernest Rabinowicz Prof. of Mechanical Engrg Mass Institute of Technology Cambridge MA 02139 21 Draft Report Prepared by Mr. Mr. Scott Barber Jeff Hadden Mr. Joseph Hoess Mr. Keith Dufrane Mr. Jerry Francis Battelle Columbus Division 505 King Avenue Columbus Ohio 43201 TABLE OF CONTENTS EXECUTIVE SUMMARY AND CONCLUSIONS e @ e ' ' ' ' ' ' ' ' ' ' ' ' ' 8 Conclusions eo ee @ @ 8s #' ' @ e@ @ @ @ ' ' @ 28 @ 28 ' ' ' ' ' 28 8 @ eo ' @ @' @ @' #' ' ' ' ' @ e ee e@ e' e@ #' 8 @ Task 1. Determine Populations of Aftermarket Vehicle Classes and Brake System Designs in the United States Task 2. Conduct Dynamometer and Vehicle Qualification Tests on Asbestos Materials Using Representative Vehicles . 1 INTRODUCTION eo ' ' 8 @' ' 8 @ @ ' @' @' ' @ e' ' 8 8* #8 8 8 8 @ 6 2 REVIEW OF VEHICLE BRAKING SYSTEMS eo ' ' ee # e 8 e' 2 e# # # ee 6 12 2.1 Section Summary . 2. 6 6 we ew ee ee ee ee ee 12 2.2 Braking Performance Requirements .e ' @ ' # 8 ' 28 ee ee @ 13 2.3 Influence of Brake Friction Material Characteristics on Brake System Response . 1 we we we we ee 15 2.4 Influence of Brake Design on Brake Effectiveness .... 16 2.5 Influence of Brake Lining Drum Pressure 1 Distribution on Brake Effectiveness .......... 2.6 Issues of Friction Vibration and Brake Noise . ee 2.6.1 Stick Slip 2... e ee ee ee ee 2.6.2 Negative Slope of the Friction Velocity Curve . 1 2.6.3 Positive Mechanical Feedback .......... 2.7 Comparison of Wheel Disc Brake Systems With Front Wheel Rear Wheel Drum System ........ 3. EVALUATION OF FRICTION MATERIAL PERFORMANCE o ' ' ' ' # #' 8 r 3.1 Section Summary 2... 6 ew ee ee we ee ee ee 3.2 General Evaluation Criteria ........2...00888 TABLE OF CONTENTS Continued 3.2.1 Fade Resistance re r re 202 es 3.2.2 Fade Recovery ......0-.-02 [ 3.2.3 Delayed Fade 2... 2. ww we ee ee 3.2.4 Brake Effectiveness Versus Speed Characteristics ..........-. 1 3.2.5 Friction Stability ............ 3.2.6 Wet Friction 3.2.7 Moisture .......+.+... 1 Lining Sensitivity 3.2.8 Wear Rate ........0.6.2..2468- 3.2.9 Friction Material Qualification 3.3 Laboratory and Vehicle Friction Material Evaluation 3.3.1 Friction Assessment Screening Test FAST . 3.3.2 Friction Materials Test Machine FMTM . 3.3.3 Girling Scale Dynamometer 3.3.4 Full Brake Inertia Dynamometer ...... 1 3.4 Correlation of Laboratory Test Results With Vehicle Test Results 3.5 Federal Braking Requirements and Other Brake Tests 3.5.1 Federal Motor Vehicle Safety Standard 105 ccs 3.5.1.1 Stopping Distance Requirements . la 3.5.1.2 Parking Brake Requirements . 3.5.2 Federal Motor Vehicle Safety Standard 121 . mn 3.5.2.1 Vehicle Braking Experiments ... 3.5.2.2 Parking Brake Test ....... ii TABLE OF CONTENTS Continued 3.5.2.3 Dynamometer Testing for FMVSS 121 ... 48 3.5.3 Federal Motor Vehicle Safety Standard 135 . 48 3.5.3.1 Front Brake Biasing 49 3.5.3.2 Control Forces for Brake Application . 49 3.5.3.3 Parking Brake Performance ....... 49 3.5.4 SAE Recommended Practices for Evaluating Brake Systems and Friction Materials ...... PERFORMANCE ATTRIBUTES OF FRICTION MATERIALS NOW IN USE 4.1 Section Summary . . . . . . . . we ew we . . 4.2 Introduction to Friction Material Formulations .... 4.3 Asbestos Friction Materials 06-4 4.4 Asbestos Friction Materials 1 ... 2 eee eee 4.4.1 Semimetallic Friction Materials 4.4.2 Asbestos Organic Friction Materials .... 4.4.3 Sintered Metallic Friction Materials ...... 4.4.4 Carbon Friction Materials ........ 4.5 Aftermarket Vehicle Considerations 2... ees 4.5.1 Drum Brakes . . 1. 1 1 ew we ee ee ee ee 4.5.2 Disc Brakes . 2. 1 1 wwe ee wee ee we 4.5.3 Factors Affecting Substitution of Friction Materials 2... + ' ' oe ew ew we ww 4.6 Direct Comparison of OEM Brake Linings . 2... 1 and ee Aftermarket eee ee we th ee we ee 4.6.1 Dynamometer Test Data 1... ee eee ene 4.6.2 Vehicle Test Data 2... 2 ee we ee ee es TABLE OF CONTENTS Continued Page 4.7 Issues of Consumer Acceptability of wa Asbestos Materials . . 1 ee ew ew ee ew ee we es 71 REVIEW OF VEHICLES AFFECTED BY PROPOSED BAN ees 73 E Summary 2. 16 5.1 Section . 1 6 wee ee ee ee ee ee ee 73 ss 5.2 Brake System Trends in Passenger Cars Trucks and Equipment . 2... 1 ee ee ee ew ee eee 74 5.2.1 Passenger Cars 1 eee ee ee ee ee ee 74 5.2.2 Trucks . 2. 1 ee ee ee ee ee ee es 76 Highway 2... 5.2.2.1 Light Trucks . - 2. 2. 5.2.2.2 Medium Trucks 6 eee ee ee ee 6 2 ee ee ee 78 79 5.2.2.3 Heavy Trucks ee ee ee ee ee ws 80 5.2.3 Highway Trucks and Equipment .. 1... seuss 80 5.3 Current European and Japanese Experience in Brake . Design and Friction Material Selection Automobiles and Light Trucks . 1 ee ee eee ee ee ee ee ee 81 SUMMARY OF INDUSTRY RESPONSES TO PROPOSED BAN ... + sss 85 6.1 Section Summary 6 ww we ee ee eh ee ee ee ee 85 6.2 Concerns of Respondents to Issues of Brake Performance 85 6.3 Concern of Respondents to Issues of Friction Material Availability . 6. 6. ee ee ee ee ew ee ee es 88 6.4 Concerns of Respondents to Feasibility of the Proposed Phase Schedule . 2... ee ee ee eee es 89 1 REFERENCES 2... we ee ete ee ee ee ee ee 91 TR iv LIST OF FIGURES Figure Schematic of Generalized Braking System ......+.- rm Figure Forces Acting on Brake Shoes of Two Common Designs . E Figure Relationship Between Brake Effectiveness and Brake Design for Various Lining Friction Levels .......-.- Figure Effect of Lining Pressure Distribution on Brake 1 Effectiveness for a Leading Shoe Drum Brake .......- Figure Fade Characteristics of Good Friction Materials . 2... and Poor Brake 2 ee ew ee ee ee tt Figure Fade Recovery Characteristics of Good and Poor Brake Friction Materials 2... ee ee ee ee ew Figure Delayed Fade Characteristics of Friction Materials . Figure Speed Versus for Good and Braking Performance Characteristics Poor Friction Materials 2 ..... se. es Figure Friction Stability Characteristics of Both Good and Poor Friction Materials . 2... 1 2 ee ee ee ee Figure 10 Wet Braking Performance for Good and Poor Performance Braking Materials .. 2... 1 1 ee ee ewes Figure 11 Effect of Moisture Sensitivity on Performance . . 1. 2 6 ew ee ee Braking ee ee ee te Figure 12 Wear Performance for Braking Materials .......--s Figure 13 Schematic of Inertia Dynamometer 2... 22 ees Figure 14. Comparison of Dynamometer Test Results for Four 1 Figure 15 Different Friction Materials 12 x 3 Duo Servo Drum Brake 300 F After 1. - ee Burnish ee we we ees Vehicle Test Results Aftermarket Friction Comparing Materials the Performance of 1... 2 ee ee ewes LIST OF TABLES Page Table 1 Motor Vehicles Affected by Proposed Ban . 11 Table 2 Influence of Some Brake Lining Property Design Changes on Brake System Response With Modifications to Compensate ....... cee we ee 17 Table 3 Machines For Friction Material Evaluation Reference 3 vee ee we e e ee we ee 38 Table 4. Test and Performance Criteria Specified Under FMVSS 105 ....... Ce ee ee ee ee ee ee 46 Table 5 Selected SAE Vehicle Brake Test Codes +... 51 s es Table 6 Producers of Brake Linings for Light and Medium Vehicles 1. 6 1 2 ee ee eee ee ee ee 63 Table 7 Producers of Brake Linings for Heavy Vehicles 65 Table 8 New Vehicle Sales and Vehicle Registration For 1987 Ref 15 . 2 1 we wee ew ee ee ee 75 Table 9 List of 1984 American Automobiles Equipped With Wheel Disc Brakes Ref 16 2. ee ees ...... 77 Table 10 List of 1984 Manufactured Automobiles Equipped With Wheel Disc Brakes Ref 14 ....... 82 Table 11 List of 1984 Japanese Automobiles Equipped With Wheel Disc Brakes Ref 10 . 1... 2. 2 ee ee eee 84 Table 12 List of Respondents to Federal Register Notice Regarding Proposed EPA Action .. 1... 22 ee ee ees 86 Table 13 Summary of Respondent's Comments to Proposed EPA Plan 1 ww ew ee we ee tee ee ee ee es 87 LIST OF APPENDICES Appendix A. Vehicle and Dynamometer Test Procedures for Qualifying Friction Materials and Brake Systems Under FMVSS 105 and FMVSS 121 2... 1 1 we ee ees A vi Pe aol. 6 RB 1 ( LIST OF APPENDICES Continued Appendix B. Appendix C. Appendix D. Concerns of Respondents to Brake Performance .... Issues of 2.2. + ee eee ee ee . Concerns of Respondents to Issues of Friction Material Availability . 2... 2. 2 ee ee eee ew Concerns of Respondents Regarding Feasibility of Proposed Phase Schedule 2-5. ee ee eee 1 1 1 1 re T vii EXECUTIVE SUMMARY AND CONCLUSIONS Due to reported health problems associated with the use of asbestos the Office of Toxic Substances has proposed a regulation to ban the use of asbestos over a year phase period Since asbestos is Pee currently a critical constituent in some vehicle friction products the Environmental Protection Agency is interested in determining whether the 1 proposed ban could have adverse effects on vehicle braking safety In order to assess the potential effects of the proposed ban on = vehicle brake system operation and vehicle safety a panel of individuals knowledgeable in the various aspects of vehicle brakes and friction mate- rials was assembled by the American Society of Mechanical Engineers ASME The panel addressed technological issues associated with the removal of re60 asbestos from friction materials specifically 1 Identification of substitute brakes and systems 2 Influence of the ban on motor vehicle safety standards 3 Problems associated with replacing asbestos friction mate- rials in aftermarket vehicles and 4 Pace of research and commercialization and effects on phase This report addresses the technical issues related to the proposed ban considered by the panel to be the most important Conclusions The panel reached the following conclusions | mbteamnets 1 Because vehicle controllability during braking is strongly affected | by friction material performance unqualified substitution of friction ~~ materials in either vehicle disc pads or drum linings may have an adverse effect on vehicle brake balance and controllability Vehicle controllability during braking is affected by both driver ot and brake system performance Generally vehicle front braking ratios are adjusted on a model basis to provide optimal braking Too much braking on an axle results in premature wheel lock and this can lead to loss of steering control front lock or spin- * Information supporting this conclusion is presented in Chapter 2 of this report gREE PR 1 out rear lock While the effectiveness of disc brakes is directly proportional to disc friction levels the effectiveness of drum brakes can be greatly affected by changes in lining friction Friction materials that exhibit reduced effectiveness also can result in brakes having insufficient torque needed to stop the vehicle Different drum brake designs exhibit dramatic differences in effectiveness Brake effectiveness can also be affected by the friction proper- ties of the friction material For these reasons automobile and truck manufacturers have strongly opposed the immediate ban of asbestos in aftermarket friction materials for older vehicles 2 No simple bench tests are available to evaluate the performance 1 characteristics of friction materials or to demonstrate their compliance with Motor Vehicle Safety Standards The qualification of original equipment braking systems is regu- lated under Federal Motor Vehicle Safety Standards FMVSS 105 and 121. For many original equipment manufacturers these requirements represent minimal standards of performance and supplemental qualifi- cations are usually satisfied due to customer demand Satisfactory compliance with FMVSS 105 and 121 requires vehicle and inertial dyna- mometer test facilities to evaluate brake system performance on a model basis To test compliance with these requirements vehicle manufacturers submit braking systems and friction products to numerous a levelosf qualification tests Results obtained using scaled laboratory apparatus such as friction material testing machines FMTM or friction assessment screening test FAST machines have 1 been shown to correlate poorly with vehicle test results The performance of aftermarket friction materials is not regulated by law 1 * Information supporting this conclusion is presented in Chapter 3 of this report py 1 1 1 meme a P 3 3 Qualified asbestos friction materials are not yet available for all current applications asbestos friction material technology is advancing rapidly Several new asbestos car light truck and heavy vehicle brake systems have been released for OEM applications in the past 3 years More new vehicle brake systems will be released with asbestos friction materials for the 1988 model year Original equipment vehicle manufacturers in the United States and Europe are rapidly moving toward asbestos brake systems for all new cars light trucks and heavy trucks Adequate asbestos friction material formulations presently are not available for all vehicle systems However with present progress continuing most new passenger cars should be equipped with totally asbestos frictional systems by 1991 and most light trucks and heavy trucks with cam brakes by 1992. However a few volume new vehicle applications may not have acceptable asbestos friction materials at that time Heavy truck wedge brake blocks medium truck drum brake linings and many road vehicle brake linings may not be developed by 1992 New classes of asbestos friction materials have unique compo- sitions which may have unexpected unique failure modes are revealed failure mechanisms In many cases only through extensive vehicle testing 4 The substitution of unqualified asbestos friction materials in the aftermarket poses the largest potential safety issue et A large number of older vehicles in the United States have brake systems designed for asbestos friction products The use of unproven materials in place of proven asbestos materials in existing systems could result in a loss of vehicle controllability during braking Currently there are no required performance tests for aftermarket brake friction materials In addition most of the aftermarket non- * Information supporting this conclusion is presented in Chapter 4 of this report ** Information supporting this conclusion is presented throughout the report oe oe Fo [ 1 1 1 nee a 1 Y eT L asbestos material suppliers lack the facilities to evaluate their materials under dynamometer and vehicle braking test conditions asbestos friction materials that have been developed to date have provided some new and unexpected failure modes and mechanisms due to their unique combinations of new raw materials and manufacturimanunfactugring processes Mandating aftermarket asbestos friction materials for vehicles that were originally equipped with asbestos linings would lead to a potentially serious customer safety risk unless stringent friction material qualification specification tests are included 5 The majority of the automobiles sold in the United States now are fitted with front disc brakes and rear drum brakes and this trend will most likely continue for some time Because disc brakes maintain effectiveness at high braking speeds wheel disc brakes have been used in the past on high performance European vehicles designed to operate at high speeds on unregulated European highways This is one reason behind the European use of 4wheel disc systems In addition asbestos drum brake materials for automobile drum brakes have been difficult to qualify in the past For these reasons several European automakers use wheel disc brakes in conjunction with semimetallic pad materials as a means of eliminating asbestos Because of differences between qualification standards cost driver preference and driving conditions in the United States and Europe brakes American and Japanese automakers Suitable asbestos materials are are utilizing rear drum not available for all of these applications and industry substitution of asbestos materials in all existing brake designs would require considerable development It is unrealistic to assume that all automakers will redesign all passenger car and truck braking systems around disc brakes in order to utilize semimetallic materials The adoption of FMVSS 135 and the failure to qualify rear brake drum linings exhibiting consistent levels of friction over a wide * Information supporting this conclusion is presented in Chapter 5 of this report range of performance conditions may affect the design philosophy of American and Japanese automotive engineers Forced to ensure front bias in the system automakers may move to using less effective disc brakes on the rear and increasing the front braking ratio to ensure consistent performance if proven rear lining materials are oe not found FT 6 Industry gave mixed response to the proposed EPA action Numerous automobile truck and friction material manufacturers eS responded with written comments to the Federal Register announcement of the proposed EPA action While most of the automobile and truck manufacturers were optimistic about the future availability of 1 asbestos materials they were unanimous in their opposition to a proposed phase schedule in which the amount of allowable asbestos would be phased out over a year period Instead they favored a year lead time prior to any ban In addition they were unanimously opposed to banning containing materials for older aftermarket vehicles Although suitable substitutes have been found for automobile front disc brakes material qualification for rear automobile drum brakes and medium truck drum brakes is still in progress Friction product manufacturers gave mixed response to the issues One manufacturer indicated that for many applications suitable substi- tutes are available although for many vehicle applications no quali- fied materials exist Another manufacturer indicated that suitable ee on substitutes were produced by their company although no FMVSS 105 or FMVSS 121 qualification capabilities existed at their facility L Recommended Future Work eo Industry trends for the next 5 years appear to be directed toward the elimination of asbestos in all new vehicles For these applications the use qualified asbestos friction materials may not present a vehicle safety problem over the life of the friction product However the use * Information supporting this conclusion is presented in Chapter 6 of this report 6 of unqualified asbestos materials for the aftermarket still remains a safety issue If the eventual elimination of all asbestos in friction products is to be accomplished additional future studies are required Several possible research tasks are briefly outlined in the following sections | Task 1. Determine Populations of Aftermarket Vehicle Classes and Brake System Designs in the United States E ee The purpose of this task would be to determine and project over the next 10 years the general classes of brake designs found on older vehicles passenger cars and light trucks medium trucks and heavy trucks that will require aftermarket friction materials For example e it would be useful to determine how many passenger cars in the 3000-3500 lb weight range are fitted with servo drum brake and how many utilize trailing drum brakes In addition the population of vehicles having wheel brakes as opposed to rear wheel front wheel disc brakes could be determined Thus vehicle populations would be assessed with respect to weight range brake design and front braking balance This information would help the EPA to determine where the qualification of asbestos friction materials for the aftermarket would have the greatest impact on asbestos elimination For example if the results indicate that 80 percent of the passenger vehicles using asbestos materials are fitted with servo rear drum brakes and front disc brakes and are within the 3300-3800 lbs weight range then the requalification of asbestos materials for these vehicles would have the greatest impact on asbestos elimination Task 2. Conduct Dynamometer and Vehicle Qualification Tests on Asbestos Materials Using Representative Vehicles The purpose of this task would be to determine whether current asbestos materials could be safely used in aftermarket vehicles designed for use with asbestos friction products This task would draw upon the results of Task 1 by limiting the vehicle studies to these vehicles known to represent the majority of vehicles now in service In this way the study could be conducted in a more effective manner This experimental study would use dynamometer and vehicle tests to determine friction product effectiveness under vehicle service conditions The ability of brake systems and friction materials to satisfy Federal motor vehicle safety standards would also be assessed This second task would determine 1 whether safe effective substitute materials are available termarket applications and is among suppliers of after- file E F | Bet 4 = [ 1 1 ee Ee C 1. INTRODUCTION The Environmental Protection Agency under the authority granted by the Toxic Substance Control Act TSCA has proposed a ban on the pro- duction and importation of asbestos and containing products According to documents published in the Federal Register Vol 51 No. 19 Wednesday January 29 1986 the EPA has proposed several alternative approaches to eventually eliminate or drastically reduce the amount of asbestos used in the United States The proposed actions apply to products containing asbestos as well as raw asbestos mined or imported for incor- poration into products The proposed ban on asbestos would have a direct effect on fric- tion materials used in automotive truck transit bus and train brake systems At the present time many friction products contain asbestos Asbestos provides several performance attributes for the brake lining both during its intended use as well as during its manufacture and assem- bly Removal of asbestos from these materials raises the following . questions 1 Will asbestos friction products allow motor vehicles to meet current and proposed braking standards asbestos friction materials have added new complexicompl-exi- ties to brake system design and development because of their new different and sometimes unexpected functional properties Furthermore brake system development work becomes more difficult with the present shortage of fully evaluated documented asbestos brake lining formulations However fully asbestos formulations for passenger cars light trucks and heavy trucks have been produced and more have been released for production There is considerable controversy whether acceptable asbestos substitute friction materials have been found for some vehicle brakes in particular some of the larger passenger medium truck drum brakes 2 Will the use of asbestos materials require redesign of braking components such as actuation cylinders distribution valves and reservoirs and accumulators to permit safe use of asbestos brake linings This question arises due to the proposed requirement for applying asbestos friction materials to existing vehicles that have braking systems designed for use with containing friction materials When asbestos friction materials are installed in existing vehicle systems with no alteration of the rest of the braking system stopping distances may increase required brake actuation forces may increase resistance to fade may decrease and undesirable brake stability problems may arise It would appear to be prohibitively expensive to replace brake system components to accommodate friction materials with different frictional characteristics because of the extensive redesign and retesting required To assess the impact of the proposed ban the feasibility will have to be addressed for the direct replacement of asbestos brake linings on existing vehicles with asbestos friction materials 3 What schedule for asbestos phase can be implemented without compromising vehicle braking performance and safety This question arises due to the possibility that in some applications acceptable substitute materials may not be available because of performance manufacturability or profitability issues For some specialized vehicles the market for friction products may be so small as to restrict the profitability of developing and manufacturimanunfactguring suitable asbestos friction materials and required associated hardware Objectives of this study were 1 Define the technological to issues associated with the EPA's 10 plan to disallow the use of asbestos in automobile and truck braking systems Such issues would include Identification of substitute brakes and systems Influence of the ban on motor vehicle safety standards Problems associated with replacing asbestos brakes on existing vehicles with alternative materials and e Pace of research and commercialization as they affect the proposed time for phase of asbestos 2 Collect relevant technical information required to resolve those issues 3 Present the findings and conclusions of the study regarding those issues where the state of existing knowledge is suffi- cient to make a sound engineering judgement 4 Define the limits of current knowledge and identify priority research topics where available information is not sufficient to draw firm conclusions This report addresses these and other issues created by the proposed EPA action against asbestos Section 2 of the report describes vehicle braking systems now in use in both highway and highway vehicles Table 1 lists the general vehicle classifications using these braking systems and vehicle examples affected by the ban Section 3 of the for report describes how friction materials vehicle use under Federal Motor Vehicle are evaluated Standards and and qualified Society of Auto- motive Engineers SAE practices Section 4 describes the performance of the various friction products Section 5 covers vehicle applications affected by the proposed ban Finally Section 6 outlines the responses of the various industries to the EPA's proposed ban 11 TABLE 1. MOTOR VEHICLES AFFECTED BY PROPOSED BAN Vehicle Category On highway low weight Example Automobiles and light trucks On highway high weight Off highway Heavy trucks trailer combinations Buses Concrete mixers Tank trucks fi Logging trucks Mining trucks Agricultural equipment Representative Brake Systems 4 wheel drum Rear wheel drum wheel disc 4 wheel disc and front e Hydraulic cam air Wedge air Air disc drum drum drum cam air Air disc Wet oil drum disc 1 sae el _ 12 2 REVIEW OF VEHICLE BRAKING SYSTEMS 2.1 Section Summary A review of vehicle braking systems is presented in this section and includes discussions of the performance requirements factors influ- encing performance and general design characteristics of the main braking systems The main purpose of this section is to examine how vehicle braking performance is affected by the friction characteristics of both pad and lining materials This is of particular importance in the aftermarket in which asbestos materials may be replaced with asbestos materials having different frictional properties The main points of the section are Vehicle brakes must provide consistent and dependable per- formance over a wide range of environmental and operating conditions causing complex design and development challenges and necessitating performance tradeoffs Brake lining friction and wear characteristics along with thermal and mechanical properties all affect the brake torque output especially with factor drum brakes The performance of these brake American automobiles systems which are common on many is especially sensitive to the frictional properties of the brake lining material Vehicle controllability and stability during braking is depen- dent upon the stability and consistency of the brake system For example an alteration in the front braking balance due to a change in either the front or rear friction material may decrease vehicle controllability The use of friction materials having different wear stiffness friction or thermal expansion characteristics may cause a degradation in braking performance Structural and vibrational behavior of brake assemblies can be significantly affected by structural properties of the the frictional elastic and friction materials Brake squeal occurs when the brake and associated structural components are excited to vibrate due to friction Some friction materials naturally damp or dissipate the vibration while other mate- 14 HAYA As0yda01] /Paed5 ~ QVOY/ 3191HSOINVAD 3A buryouganbuoy ONS -1LNV ONDIVYS W3iSA WALSA BRAKE ave AIBWSYq + DYNAMICSDRIVER ASEMBLY ayve ONILVnoW W31SA , be joo4 4043 40 Y3AING SOIWVNAG ILVW3HOS SCHEMATICSHEMATICSCHEMATIC BRAKING = Jundl pauiseg Buiyorg9UDWU0) jonyoy BunjougJ@OUDaWIOLg id S,MaARaNOlid39u4d [OjUsWIAYSbuyosadQ Sud puo Ipu0d me ~ eo f 15 Accuracy of the driver's perception of the operating environment Dynamic response characteristics of the driver Predictability and reliability of the total brake system Vehicle characteristics and Response characteristics of the braking system In order to stop a vehicle safely the brake system should provide repeatable uniform deceleration for the same brake pedal input and provide braking force in proportion to pedal force Further vehicle path direction should be readily controllable by the driver during braking The limitation to decelerate a vehicle depends ultimately on tire traction which varies with wheel slip Maximum braking requires the brake torque to be just enough so that the resulting wheel generates peak traction force available at the tire interface Excessive brake torque causes a progressive increase in wheel slip and decrease in adhesion resulting in wheel lockup and skidding Skidding may produce an unsafe condition because directional control of the vehicle is reduced substantially and stopping distances may be increased wheel lockup during braking results in severe vehicle uncontrollability For this reason current European braking standards and proposed American braking standards require that in the event of wheel lock the front wheels must lock before the rear wheels To ensure this condition throughout the life of the friction material both front and rear brake system per- formance must not be altered by friction material wear or by other changes in the material friction characteristics Changes in the friction material properties either due to replacing the brake shoes materials or due to wear prior operating history with different friction temperature and load effects will change the response characteristics of the braking system 2.3 Influence of Brake Friction Material Characteristics on Brake System Response There are several scenarios in which an existing hydraulic or pneumatic system would require modification or redesign to accommodate changes in the properties of the brake friction material These are summarized in Table 2. As indicated in the table substitution of asbestos 16 friction materials for original asbestos linings requires characterization of the substitute material properties followed by an evaluation or verification of the performance of the existing brake system with the asbestos materials Due to brake system design differences this must be done on a model basis For new vehicles asbestos friction materials may be incorpor- ated into a new brake system design Depending on the characteristics of ee the asbestos friction materials compared with those of the asbestos materials the new brake system design could involve minor modifications I of existing designs or completely new brake components In order to achieve adequate braking performance brakes are designed primarily on the basis of wear stability brake or shoe factor ratio of brake torque to applied force and pedal travel These parameters are interrelated For example lining material thermal expansion may I require added running clearances to avoid parasitic drag This then results in the need for greater brake pedal travel which may lead to a master cylinder resizing If pedal forces then become too great a booster may need to be added or increased in size Some of these relations are dis- cussed in the following sections 2.4 Influence of Brake Design on Brake Effectiveness As mentioned previously it is important that a vehicle have the =. ability to be decelerated rapidly and controllably during emergency braking Thus the response of the vehicle to the driver's brake commands must be Co predictable repeatable and fast enough to stop the vehicle in a short distance but slow enough that the driver can respond effectively with subsequent corrective braking and steering commands e.g. to avoid skidding or fishtailing a force The and relationships between braking frictional the coefficients of friction have a strong torque applied influence on vehicle stability The parameter that most strongly affects the stability of brakes is the shoe or brake factor also called effectiveness The brake effec- tiveness is defined as the ratio of the brake friction torque to the applied force and is used commonly to describe the performance of brakes 17 TABLE 2 INFLUENCE OF SOME BRAKE CHANGES ON BRAKE SYSTEM DESIGN MODIFICATIONS TO LINING PROPERTY RESPONSE WITH COMPENSATE Change of Brake Lining Properties Lower Friction Coefficients d Front brakes - Rear brakes - Both front Higher Friction Coefficients - Front brakes - Rear brakes - Both front ae FrictonPropetis_. Poor Fade Characteristics - Green fade - Thermal fade - Water fade - Flash fade Inconsistent Friction Level - Green linings Usage history Wear depth Within batch batch nn hae Environmental Sensitivity - water vapor Cony - Road dust - Oily contaminants - Oxide effects menasiaen| t Lower Compression Modulus | ays Higher Compression Modulus Mechanil Propetis . Higher Thermal Expansion Growth Lower Tensile Strength Lower Toughness Potential Response of Brake System Greater Pedal Forces Required Leading to - Early rear skid - Early front skid - Low brake capacity Lower Brake Pedal Force Required Leading to - Early front skid - Early rear skid - Touchy pedal High Brake Pedal Force Required For - Initial hot brake - Any hot brake - Wet brakes - High speed stops Varied Brake Pedal Forces Needed With - New brake linings Temperature change Mileage driven Brake imbalance - car variations Brake Pedal Force Sensitive to - Humidity - Dust pickup - Road rain splash - Moist storage Higher Brake Pedal Travel Noise and Uneven Effectiveness Brake Dragging and Spotting Lining Fracture Cast Iron Scoring Handling Breakage Needed Design Modifications Larger Booster or Small Master Cyl - Big front w.C. > Big rear w.c. - system redesign Smaller Booster Big Master Cyl - Small front w.c. - Small rear w - System redesign Recalibrate Booster - Scorch Modify - Shield linings linings brakes - Modify linings Change Linings Redesign Brake - Modify linings - Modify linings Modify linings Improve process - QC improvement Change Linings Redesign Brake Modify linings Shield brakes Shield brakes Materials change Redesign Stiffen Actuation System Reduce Drum Stiffness Add Clearance or Thin Linings Use More Rivets Mold Linings Alter Processes 18 Figure 2a shows the forces acting in the shoes of a simple lead- trailing drum shoe causes it to brake As be further shown loaded the friction force on the leading against the drum increasing its effec- tiveness while the friction force on the trailing shoe causes it to oppose the application force decreasing its effectiveness In the servo design Figure 2b the friction force of the primary shoe is used to apply the secondary shoe thereby markedly amplifying the application referred to force The increase in brake loading due to friction as actuation and this phenomenon can be used to is increase the brake effectiveness This design has been and still is used extensively on American cars using containing brake linings Although the phenomenon of actuation can increase brake effectiveness the effectiveness is strongly influenced by the frictional properties of the lining material Figure 3 shows the relationship between brake effectiveness and lining friction coefficients for different drum brake designs and for an automobile disc brake servo drum brakes are widely used in American automobiles while leading systems are found on many transit buses and heavy trucks trailing systems are also found on most heavy trucks and on many automobiles Assuming a nominal friction coefficient of 0.4 a percent change in friction coeffi- coeffi- cient can alter the brake effectiveness by approximately 44 percent for a servo drum brake 33 percent for the trailing drum brake and eo only 12 percent for a disc brake Figure 3 also shows that for automobile oo rear drum brake systems friction materials qualified for use with duo- 1 servo systems may not systems Conversely perform satisfactorily when materials qualified for use used with trailing in trailing systems may precipitate rear wheel lock when used with a more effective servo system CEs Aftermarket friction materials from different manufacturers can exhibit a wide variance in friction characteristics This can lead to variable and unpredictable brake performance even with materials containing asbestos Under current law aftermarket friction materials do not have to meet Federal Motor Vehicle Safety Standards As more major OEM friction material suppliers phase out asbestos materials the burden of supplying materials for the aftermarket will fall on these secondary aftermarket suppliers Under the proposed ban on Pa PF -_ 19 Wheel Cylinder Trailing Shoe rors Hydraulic Force on Leading Shoe Leading Shoe Trailing Shoe Friction Force Shoe Return Spring Return Friction Force on Leading Shoe Trailing Shoe Pivots Away From Drum Shoe Pivots a trailing Application force Rotation Leading Shoe ~ Leading Shoe Pivots Toward Drum ae 1 radius Force transmitted through linkage Lee Drum rotation b servo FIGURE 2. FORCES ACTING ON BRAKE SHOES OF TWO COMMON DESIGNS 80 Drum Brakes Drum radius 5.5 70 Cylinder radius 3.0 Pin and link radius 4.6 ae 120 lining arcs located 30 from anchor pin A 60 Disc DriadsicusBr5a.k8e2s Mean pad radius 4.88 1 _= =_e Efectivns 40 Brake 30 -- 20 mmeoe servo Leading leading Leading ay, Trailing L>LY Disc ee] 1 | 1 fo) 0.1 0.2 0.3 0.4 0.5 0.6 Lining Coefficient of Friction | aoe FIGURE 3. RELATIONSHIP BETWEEN BRAKE EFFECTIVENESS AND BRAKE Tm DESIGN FOR VARIOUS LINING FRICTION LEVELS 21 asbestos linings the brake system engineer would have two choices First the drum brake could be redesigned and redeveloped for acceptable performance with asbestos linings Second the designer could wait for a lining formulation to be developed that can be used directly in existing drum brake designs This is a critical decision Redesign of a brake assembly is costly time consuming and probably unrealistic However waiting for the development of a suitable universal asbestos replacement friction material has yet to be made involves the risk of not having acceptable aftermarket components if asbestos brake linings are banned 2.5 Influence of Brake Lining Drum Pressure Distribution on Brake Effectiveness For drum brakes of the same design the use of different materials exhibiting similar friction coefficients is not sistent and even braking throughout the life of sufficient to the material ensure con- The use of a material that exhibits different wear or thermal properties can be suffi- cient to change the effectiveness of the brake system Figure 4 shows the variation in effectiveness for the same brake design but for different brake Tining pressure distributions Note that large changes of brake effectiveness are possible for the same value of friction coefficient due to the effect of lining pressure distribution Several factors can lead to uneven and inconsistent brake lining- brake drum pressure distribution but the most significant are wear and thermal distortion Wear tends to shift the center of pressure location Thus substitute friction materials with different wear rates from the original asbestos materials may also influence stability by changing the center of pressure A reduction in brake effectiveness or an increase in brake effectiveness leading to wheel lock could be possible conse- quences of improper friction material selection The profiles of the brake linings also are affected by thermal Ta distortion Brake lining expansion through the friction material thickness is often much greater for asbestos brake linings and these friction materials also tend to be much stiffer Therefore and pressure distributions will be different which the can contact geometry affect the friction 22 A Bao - Efectivns D a A Heel and toe Tapered biased Uniform Center contact en P oe C 11 Friction Coefficient FIGURE 4. EFFECT OF LINING PRESSURE DISTRIBUTION ON BRAKE EFFECTIVENESS FOR A LEADING SHOE DRUM BRAKE -WOD sion rates rates cause inconsistent braking performance performance especially with ayeuq varying varying brake temperatures voy adepsazULUOLZILAS 9YZ 7e pa ze uauab sanbuoz added added complication complication results from greater thermal expansion asayy rate compression compression stiffness many many asbestos asbestos friction materials materials This called spotting thermoelastic thermoelastic thermoelastic instability instability causes lining pressure pressure pressure distributions distributions become become localized resultant resultant high thermal thermal stresses and erratic friction values basic principles principles are simple but total system effects can extremely complex diweucp 4ayzyO pue For example one | particular particular particular lining location location have greater clamping clamping than average providing greater greater friction generation This causes causes location location expand , further increasing increasing excess excess load rate If lining wear rate rate this cycle can continue continue time leading formation formation hot spot Hot spotting spotting tends to ne speeds Since Since brake overlooked early early stages "ssa 20ud quawdo,aaap axeug ay} 40 Issues ued ZL SauaAas yOU SL abesn Vibration Issues Friction Friction Induced aq Al quaqzsaapeut Vibration and Noise Aemyfly wou Bur yeug Burunp Vehicle Bulunp und20 Vehicle braking components suorzed.iddeayxeuq qyBry yzim Sabesn ayeuq aunzeusdwa} MOL Vehicle braking systems generally generally include include include several structural structural structural cause calipers calipers pedal linkages linkages etc. Forces Forces generated generated during associated braking components high stresses these brake components components in vehicle- ea wos result from the components axles suspension suspension elements These These stresses stresses dynamic dynamic dynamic from Sufficiently braking torque well as thermal and nominal loads Sufficiently Sufficiently large dynamic and thermal stresses stresses superimposed in vehicle structures structures stresses might fractures fractures fatigue failures Ciel conditions conditions brake structures then could the dynamic dynamic behavior friction material result unsafe operating properties strongly influence influence ie properties determine magnitude vehicle structure structure braking because generated the friction magnitude magnitude and frequency braking braking these phenomena such brake uzim chatter groan produce structural vibrations of vehicle.com- vehicle.com- -uedxa jeuuayz saybry yzyM SLessazew UOL FIL AJ uoseauSLY} WOG Sabqiuasse ayeug wnup sabuet ay} ud Ayperoadsa eaveyoezUOd ayy 3e payeuauabh saquoy 74 24 ponents which may be either reduced or increased by substituting different brake friction materials The influence of a particular braking material on structural vibrations depends strongly upon the specific brake system design Therefore replacement materials should be evaluated carefully for critical vehicle applications Another structural consideration occurs in attaching the friction material to the brake shoe This can be done by riveting bonding or integrally molding the lining to the brake shoe asbestos linings generally are stiffer more brittle and more highly anisotropic i.e. their properties are sensitive to orientation which can provide attachment challenges Friction vibration and noise can occur under some condi- tions with vehicle braking systems The phenomenon has received consider- able attention and attempts are normally made to quantify the parameters that influence its initiation In the final analysis however this phe- nomenon is usually evaluated experimentally on a model basis Although the principle of sliding friction is extremely complicated and not totally understood at the present time it is known that friction is not a steady process Vibration occurs because of this variation in friction force in the related components It is also known that friction vibration occurs via several different yet distinct a: mechanisms It is possible to have more than one vibration mechanism active at a given time This makes brake vibration corrections were) complex generate Some asbestos friction materials friction excited oscillations for as tend to be more prone to yet uncertain reasons It 1 is felt that their generally greater energy storage modulus stiffness and lower energy loss modulus dampening are probable sources of greater re tendencies of rope in for vibration and noise Asbestos is much like a brake lining formulation although much finer many strands in size This is believed to provide the greater inherent dampening of asbestos friction [ materials Fiberglass aramid fiber Kevlar steel wool wolastonite and other asbestos reinforcing fibers typically are found as single solid elements contributing minimally to the lining damping To clarify some of the mechanisms of friction factor vibration the following sections discuss these mechanisms in more detail 25 2.6.1 Stick At low brake application speeds it is possible for the brake lining and drum or disc to stick together for a short time twisting up the vehicle suspension assembly breakaway value the When the restoring torque lining again slips against builds up to the static the disc This stick and slip cycle repeats rapidly generating brake chatter groan or squeal vibration This mechanism is attributed to a difference in the static and kinetic frictional torques and the spring restoring forces acting on brake components The stick mechanism produces a excited vibration with displacement characteristics similar to a shape form This is the usual mechanism for speed brake chatter although it can also exist in the form of a higher frequency squeal 2.6.2 Negative Slope of the Friction Velocity Curve This vibration inducing mechanism arises from a negative slope of the friction velocity curve characteristic of certain materials in specific speed ranges This causes instability in the system and excites vibrating components into nearly sinusoidal waveforms An explanation is based on observations that the brake drum or rotor surface roughness asperities require a finite amount of time to produce equilibrium deformation of the brake lining material The time that is available to deform the lining is decreased with increasing speed restricting the time to compress the asperities in the friction material Thermal effects such as interfacial softening and changes of the chemical composition of surface layers also have been offered as an explanation for the cause of the negative slope of friction versus velocity 2.7 Comparison of Wheel Disc Brake Systems With Front Wheel Rear Wheel Drum System The almost standard use of front wheel disc brakes for automobiles has been due to some performance characteristics provided by this design Because these brakes and the friction metallics can operate at higher materials used with them notably temperatures than drum brakes the 26 vehicle's braking balance can be shifted toward the front reducing the likelihood of rear wheel lock during severe braking conditions In addition since automobile front brakes are exposed to water disc brakes provide for more effective wet braking under many road conditions Many European automobiles imported to the United States have been OC fitted with wheel disc brakes There appears to be three reasons for implementing these brake systems First the effectiveness of disc brakes 1 is less affected by friction material performance than the effectiveness of drum brakes Since European safety standards require front brake biasing 1 to prevent rear wheel lock this situation is more readily ensured by using similar brakes on all four wheels and adjusting the front = _ pressure proportioning valve accordingly accomplished with vehicles outfitted with Front brake biasing can be rear drum brakes but the drum 4 brakes require friction materials that exhibit very stable friction eT, performance in order to ensure consistent performance Figure 3 Second in the absence of suitable asbestos linings some European manufacturers elected to use proven metallic materials and disc brakes as a means of eliminating asbestos Third in the United States there is a perceived performance advantage provided by the term wheel disc brakes and so such systems are usually provided on higher priced imports More inexpen- inexpensive automobiles produced for spread consumption in Europe Fiat VW Renault etc. are Rear wheel disc still equipped with rear wheel drum brakes brakes have disadvantages Currently used mate- rials metallics exhibit poor friction performance at low temperatures and optimum performance at high temperatures The effectiveness of the parking brake can be adversely affected since these brakes are usually applied when the brakes are hot and then required to hold as the brakes cool down Also the disc normal load for the parking brakes can decrease as the pads cool down and contract from their hot try The rear disc braking surfaces also are more prone to by mud and road debris thrown from the front wheels expanded geomecontamination wT =? _- a am Mikael wwe E 27 EVALUATION OF FRICTION MATERIAL PERFORMANCE 3.1 Section Summary The performance of friction materials as applied to automotive brake systems is reviewed in this section along with the pertinent friction material testing devices and relevant testing procedures and standards Main points presented are Friction materials are expected to perform satisfactorily over a wide range of operating and environmental conditions as an important element of the total brake system Many fade critical performance considerations such as recovery are sensitive both to the friction fade and material and to the brake system in which it is tested Therefore system testing is required for proper evaluation Friction stability can vary with both thermal and mechanical history Therefore short evaluations and those with narrow ranges of brake temperatures can produce incomplete data leading to erroneous conclusions on brake compatibility and performance Laboratory specimen test machines such as FAST and FMTM may be appropriate for quality control tests and material screening but they are not able to determine bility of substitute friction materials or to the accepta- compare differ- differ- ent friction materials Full brake inertial dynamometers properly instrumented and utilized can be used to screen friction materials and determine some component performance behavior Typically these large and expensive devices do not adequately simulate the airflow over the brake and the environmental conditions of vehicle service Good brakes are those with few minor faults Brake devel- opment testing therefore is time consuming and costly since a wide range of conditions must be evaluated in the process of brake development oer 1 1 | F 28 Federal Motor Vehicle Safety Standards FMVSS 105 121 and the proposed 135 are severe brake tests which are only one of many standards that new OEM vehicle brake systems must meet No standards need be met by aftermarket friction materials 3.2 General Evaluation Criteria Friction material performance for vehicle brake systems may be qualified by meeting the requirements of the Federal Safety Standards Society of Automotive Engineers SAE recommended practices along with brake component and vehicle manufacturers standards These experiments are directed to maximize safety dependability and customer satisfaction over a variety of brake operating conditions For new vehicles compliance with federal and state motor vehicle safety standards is only the starting point for acceptance of a brake system This section of the report discusses the criteria and techniques used to determine friction material suitability and performance Full evaluation of a friction material requires installation into a complete brake system It is only in the full brake system that many of the impor- tant brake lining attributes such as fade fade recovery environmental effects and varying service factors may be properly determined Vehicle brakes are required to operate under a wide range of conditions from steep downhill grades with a heavily loaded vehicle to minimal loads on interstate highways Vehicle brakes must be completely reliable nation and must be minimally affected by temperature wateorr contami- Brake actuation forces should be properly distributed and brake friction must be consistent throughout the life of the friction material Pedal actuation forces brakes should not exceed the capabilities of a wide range of drivers Vehicle braking performance can be closely related to loss of directional control in vehicles Under skidding conditions the tendency for wheel lockup in some brake systems can make controlling the vehicle more difficult Commercial vehicles with lower brake effectiveness have been shown to be less likely to encounter loss of control in accidents presumably due to lower usage speeds and reduced tendency for wheel lockup 2 ree ra = _- es fi" 29 Variation in the front brake balance due to changes in frictional performance may adversely affect safety through reduced directional control and stopping efficiency The subject of vehicle brake systems is discussed in more detail in Section 2 Section 3.2 of the report describes some of the more important friction material performance characteristics that are evaluated during original equipment manufacturer OEM brake system qualification experiments These include Fade Resistance Fade Recovery Delayed Fade Effectiveness Versus Speed Friction Stability Wet Friction Moisture Sensitivity and Wear Rate Each of these important performance characteristics will be highlighted in the following sections 3.2.1 Fade Resistance Brake fade refers to a loss of brake effectiveness generally as the result of excessive brake temperatures Such excessive temperatures may occur under hard brake usage conditions or under less stringent condi- tions should component cooling be restricted Brake fade may occur under particularly hazardous driving conditions such as descending steep and winding mountain roads Five types of brake fade have been described Thermal to high brake system bulk temperatures Delayed to resin migration during brake cooling Blister to effects of surface lining blisters Flash to high speed high torque demand braking and Water to partial lubrication from water contamination Figure 5 shows a performance comparison between a good friction material and a poor material The poorer friction material exhibits a more rapid drop of brake effectiveness compared with the better mate- rial Since poor brake fade behavior could also be exhibited by high quality materials if used in inappropriate brake applications brake lining fade behavior is meaningful primarily in the context of a particular brake lining brake and vehicle application It should be noted that although these curves are continuous the driver applies the brakes at discrete points along the curve If the last application happens to be on the knee of a performance curve then the next brake application will yield different and unexpected brake system response | 4 Oe Efectivns Good Poor 1 FIGURE 5. Brake Temperature FADE CHARACTERISTICS OF GOOD AND POOR BRAKE FRICTION MATERIALS t | Efectivenes : Efectivenes | Ef ectivenes Good (: Time Cooling Brake FIGURE 6 FADE RECOVERY CHARACTERISTICS OF GOOD AND POOR BRAKE FRICTION MATERIALS re: ra a a 9 _ 1 (Gewen, | ee eC eG fr F 31 3.2.2 Fade Recovery Fade recovery refers to the ability of the friction material to quickly regain normal effectiveness after fade This recovery is shown in Figure 6. As the brake cools with time after experiencing fade the friction level should return rapidly to approximately the fade level Poor friction materials may exhibit slow recovery compared with good friction materials and may produce either a decrease or increase of brake effectiveness as a lasting consequence of the fade 3.2.3 Delayed Fade Delayed fade is a phenomenon which may occur with some friction materials This phenomenon is illustrated in Figure 7. During fade recovery brake effectiveness may drop unexpectedly causing a temporary but potentially hazardous increase of required brake pedal force This delayed fade is insidious in that it is often totally unexpected It occurs well after a period of hard brake usage and usually with no warning signs 3.2.4 Brake Effectiveness Versus Speed Characteristics To ensure even braking over a wide range of stopping speeds the brakes on each axle should exhibit similar effectiveness characteristics at all vehicle speeds In general brake effectiveness decreases with increasing speed Consequently a brake application from 60 mph usually requires greater brake pedal effort than from 20 mph Good brake linings provide less speed spread or difference in effectiveness at different braking speeds and good brake systems employ friction materials that provide a proper balance of front brake effectiveness at any speed Figure 8 shows the general relationship between brake effectiveness and deceleration for brakes with poor and good speed spread performance As illustrated the effectiveness at 75 mph is markedly different from that at 25 mph for this brake using a relatively poor friction material Disc brakes are inherently less speed sensitive than factor drum brakes so they typically show less speed spread ve Mr 1 | ,E ww 7 32 Good f Effectiveness Effectiveness Effectiveness Efectivenes ( Efectivenes \ Poor Effectiveness \ Efectivenes \ \ FIGURE 7. Time Cooling Brake DELAYED FADE CHARACTERISTICS OF FRICTION MATERIALS | Efectivenes Efectivenes Effectiveness Efectivenes Ef ectivenes Ef ectivenes Ef ectivenes Good Poor -- FIGURE 8 al | | 25 50 75 100 Vehicle Speed SPEED VERSUS BRAKING PERFORMANCE CHARACTERISTICS FOR GOOD AND POOR FRICTION MATERIALS 1 ore 1 1 33 3.2.5 Friction Stability To ensure consistent vehicle braking performance the brake effectiveness characteristics should be stable throughout the life of the brake linings Figure 9 shows the difference between a poor material and a good material in this regard The brake effectiveness of poor friction materials can deteriorate with accumulated use history and wear as indicated On vehicles equipped with a balanced set of friction materials on all four brakes a gradual reduction in brake effectiveness may be marked only by a slight increase in pedal pressure to decelerate the vehicle but brake stability will be essentially unaffected However on vehicles employing two unmatched friction materials on the front and rear axles a shift in effectiveness of one braking axle relative to the other will alter braking balance and could adversely affect controllability of the vehicle during hard braking 3.2.6 Wet Friction The performance of vehicle brakes when wet is a significant safety concern Disc brakes usually are less affected by water than are drum brakes largely because of the lower inherent servo factor in disc brakes However both disc and drum brakes can show large effectiveness losses when wet As expected poor friction materials can provide a greater loss of effectiveness and take a considerably longer time to recover friction capability when wetted than experienced by good materials This is shown in Figure 10. Permeability heterogeneity and compression stiffness are some of the brake lining properties which determine wet friction response Complete understanding of this behavior is not known so full brake dynamometer and vehicle tests are used to establish the wet friction behaviors of a brake system 34 oe = , h Good Poor Efectivns 0 FIGURE 9. | | | 25 50 75 100 Lining Worn percent FRICTION STABILITY CHARACTERISTICS OF BOTH GOOD AND POOR FRICTION MATERIALS Good Poor Efectivns Wet Time FIGURE 10. WET BRAKING PERFORMANCE FOR GOOD AND POOR PERFORMANCE BRAKING MATERIALS 35 3.2.7 Moisture Sensitivity Friction materials are porous reinforced composites that are capable of absorbing atmospheric moisture when a vehicle is parked such as overnight For some friction materials this moisture has been shown to lower brake effectiveness temporarily leading to a phenomenon called morning sickness Other of the cast iron drum morning surface sickness effects result from when a vehicle is parked for rusting some time causing abnormally it is possible for high initial the friction brake effectiveness Under material to become rust- some conditions bonded to the the interface cast iron Substantial driving free and the rusted surface of torque may be required the brake drum or disc to break may generate a temporarily uneven brake torque Figure 11 effectiveness The depicts the ideal brake effect of moisture sensitivity assembly exhibits little or no on brake moisture sensitivity When present it usually persists for a few brake applications and disappears when brake heat drives the moisture from the brake lining or wear removes the surface rust 3.2.8 Lining Wear Rate Wear rates of friction materials depend upon temperature prior se0m, 28s use speed and load In general wear is directly proportional to applied normal load and speed At moderate brake drum and disc temperatures friction material wear rates are not affected greatly by temperature vie Sta However at high brake temperatures wear of the friction material may increase exponentially due to thermally induced degradation of the organic resin binder material Figure 12 shows representative wear performance for three differ- ent types of friction materials Low quality materials may utilize an inferior binder resin with poor heat resistance providing like that labelled A This may give acceptable wear rates a wear at low curve brake temperatures but rapid wear rates at higher brake temperatures OEM type materials behave like curve B and heavy duty brake linings wear like curve C Note this heavy lining does not improve wear life except at the higher brake temperatures 36 Poor h Good Efectivns Poor ecg Time From Cold Start FIGURE 11. EFFECT OF MOISTURE SENSITIVITY ON BRAKING PERFORMANCE ~~ She Rate | Wear ake Lining Temperature FIGURE 12. WEAR PERFORMANCE FOR BRAKING MATERIALS 38 TABLE 3. MACHINES FOR FRICTION MATERIAL EVALUATION REFERENCE 3 Apparatus General Test Procedure 1 Friction assessment screening test machine FAST 90 minute FAST QC test Friction materials test FMTM SAE J661a quality control machine test procedure 3 Girling scale dynamometer Simulated vehicle road test 4 Full brake inertia dynamometer Simulated vehicle road test Mihi rs oe 1 1 lent lisias tment 39 3.3.1 Friction Assessment Screening Test FAST The Friction Assessment Screening Test FAST machine was developed by Ford Motor Company specifically for rapid fingerprinting of friction material specimens It is used for plant quality control of clutch facings and brake linings and some specialized friction material screening and diagnostic tests A square specimen generally is used but lining samples up to square can be tested The small flat sample assures rapid specimen seating to the flat cast iron test disc inch thick diameter Quality control QC tests run for 90 minutes with the friction drag held to a constant value With a constant rubbing speed 880 rpm and constant friction drag the horsepower dissipated is also constant providing repeatable temperature histories 70 to 560 F for QC QC tests are often run on every batch of friction material as the linings are finished at their manufacturing sites However the small FAST specimen precludes confidently making correlations of laboratory performance with full brake behavior Thus this machine is used primarily for routine brake lining QC testing Specialized characterization test procedures are mostly proprietary and require exper- tise for proper evaluation While this machine reportedly has been used to perform friction material screening tests it never has been recommended as a substitute for scale brake evaluations 3.3.2 Friction Materials Test Machine FMTM This apparatus developed by T. P. Chase of General Motors uses an shaped square specimen of brake lining material which is forced against the internal surface of a rotating inch diameter cast iron brake drum Auxiliary heaters and air blowers are used to provide controlled brake drum heating and cooling rates The FMTM is also used for quality control testing SAE has developed a recommended practice SAE J661a that is classified as a quality control test procedure on the FMTM This test requires more test time and expense than the FAST QC procedure since it includes simulated burnish wear effectiveness fade and recovery procedures It is used more for ne 1 _ pe r, 1 1 Om F 40 periodic QC surveillance testing than for routine production batch testing General Motors and others also have developed specialized testing procedures for evaluating brake lining materials on the FMTM Based on the SAE J661a procedure a brake lining friction rating specification has been required by some states for many years However this brake lining rating system has been shown to be clearly inadequate for meaningful comparative testing with different types of classes of friction materials The SAE recommended practice J866 revised in March 1985 includes this caution against such uses Note It is emphasized that this recommended practice does not establish friction requirements for brake linings nor does it designate significant characteristics of brake linings which must be considered in overall brake performance Due to other factors that include brake system design and operating environment the friction coefficients obtained from this recommended practice cannot be reliably used to predict brake system performance Technical papers have pointed out that laboratory specimen tests such as those which use the FMTM do not provide acceptable correlation with actual vehicle or brake dynamometer service when asbestos or asbestos linings are evaluated Different classes of asbestos brake linings such as asbestos organic NAO and semimetallic semimet provide conflicting trends as well as different absolute values of friction on the Chase Machine 3.3.3 Girling Scale Dynamometer The Girling Scale Dynamometer is an apparatus which employs scaled brake components A small brake disc is mounted on the end of a rotating shaft which carries inertia discs sized to ensure that the scaled disc pad will absorb the same amount of energy per unit area as a sized brake disc pad The friction sample is pneumatically loaded against the rotating disc and a torque control system is used to produce a repetitive constant deceleration drag Some brake characteristics scale by geometry and others are governed by absolute physical size Consequently experience is required 41 when using a scale device to be assured that the scaling process itself has not altered performance characteristics of the brake assembly Therefore this device as well as the other specimen test devices can produce good test results only when utilized by a person with expertise in such specialized tests 3.3.4 Full Brake Inertia Dynamometer A full brake dynamometer simulates vehicle braking by mounting a complete brake assembly to a large rotating inertially loaded shaft The shaft's inertial loading is usually adjusted to simulate the actual road inertia Figure 13 shows a schematic of an inertial dynamometer Brake inertial dynamometers are designated by the number of ends stations or brake assemblies that can be tested at one time Most are single ended for testing a single brake Double dynamometers while capable of simultaneous testing of two brakes often are used as single brake dynamometers so one test assembly can be installed as the other is being tested Only a few ended brake dynamometers have been built It is difficult on multiple station dynamometers to control the air flow for balanced brake cooling Most brake dynamometers place the brake assemblies in closed ducts both aminiatel to expedite cooling and to control smoke and odor Since faster cooling t rates hasten testing most dynamometer tests have much greater air flow [rey and resultant cooling rates than are found in road testing Consequently brake dynamometers are used mostly for controlled wear tests basic effectiveness tests initial recovery tests and parking brake neal tests Full brake dynamometers are available in a range of sizes with end inertial capacities ranging from minicar to maxitruck There are no standards so almost every unit is different Dynamometer rh differences in test results can be significant even for carefully matched linings and brakes tested to the same inertia parative brake lining test data is preferably loading obtained Consequently comfrom a single brake dynamometer Much of the data difference between various dynamometers results from using brake lining thermocouples to control the brake test as required 42 = t [WIE Quid a Bad ONbIOL | 2g IOLJY SpIOYUMA]4 PenCew]s \ SsopurAd2A MALIWOVNAG oneIpA TTT ~_ . i, VILYSNI Iq 40 an) sy B - dynamometer Flywhels ous Motor Hydraulic gt were ayeIg ANI : INERTIA DYNAMOMETER | a3 I 7_ ' | 43 in the FMVSS 121 dynamometer procedure and as specified in most other procedures Significant brake drum temperature variations occur with semimet and semimetallic linings compared with conventional asbestos materials when control is by the lining temperature Even different formulations of the same general type exhibit test drum temperature differences especially if they vary in metallic content Current brake testing practice now favors measurement of the cast iron temperature for test control In this way differences of lining thermal conductivity do not significantly alter the temperature of the major heat sink the drum or disc mass Drum temperature measurement requires infrared pyrometry or thermocouple slip assemblies Most good brake dynamometers now permit one or both of these instrument refinements Burnishing conditions also affect the test results with most drum brake linings and blocks being sensitive to their initial usage history When drum temperature control of the burnishing operation is provided the test results are clearly better - It now appears possible with proper instrumentation and good control on the burnishing procedure to perform meaningful friction material screening tests on full brake dynamometers Except for replicating airflow over the brake and environmental conditions such as water and dust contamination full brake dynamometers now can closely duplicate most vehicle service braking conditions and are invaluable for brake diagnostic testing They can be excellent for initial brake lining screening tests However they are not sufficient to fully evaluate the acceptability of substitute brake linings 3.4 Correlation of Laboratory Test Results With Vehicle Test Results Numerous studies have been done to determine the correlation rr between laboratory friction material test results and actual vehicle test 4,5,6,7,8 In general the only good analogy of a vehicle brake is the brake itself Consequently there are no specimen or scale test devices that can consistently yield test data that correlates with full vehicle performance data This does not mean that such laboratory tests are useless that they should not be used to predict field perform- om 1 11 11 44 ance behavior They can and have been used to screen friction material for undesirable performance flaws Even tests on full brake dynamometers are difficult to correlate with road vehicle brake performance unless careful instrumentation and test controls are used It should be possible to correlate full brake dynamometer test results with road data without need for questionable cor- rection factors This has been attempted by published by few but not yet verified by anyone 3.5 Federal Braking Requirements and Other Brake Tests As indicated in previous sections the qualification of vehicle brake systems and friction materials can involve numerous experiments to determine effectiveness stability fade resistance moisture sensitivity wet friction and other performance parameters Some of the brake performance criteria are determined by Federal Motor Vehicle Standards 10583 and proposed 135 for hydraulic brakes 121 for air brakes while other performance standards are determined principally by the standards of the vehicle and friction product manufacturers This section of the report discusses the Federal Motor Vehicle Safety Standards now in effect and proposed for hydraulic and air brakes In addition some of the numerous SAE brake test procedures used to evaluate brake system and friction product performance will be discussed 3.5.1 Federal Motor Vehicle Safety Standard 105 This federal standard mandates hydraulic and parking brake performance under specific vehicle operating conditions Under the provisions of this standard vehicles under 10,000 lbs gross vehicle weight are tested to one set of procedures while vehicles over 10,000 lbs gross vehicle weight are tested to a different set of procedures General specifications are designed around stopping distances for braking with minimal tire skidding Brake use tends to modify friction material performance For this reason specifications are listed for new burnished and conditioned burnished friction materials 45 FMVSS 105 outlines braking requirements for vehicles braking under level straight dry clean pavement conditions Requirements for vehicle wet braking as well as parking brake performance on grades are also outlined Table 4 lists the general categories of tests and the evaluation criteria used to determine brake performance Specific braking requirements are outlined in the following section 3.5.1.1 Stopping Distance Requirements FMVSS 105 outlines a series of tests for brake effectiveness and dictates required stopping distances without wheel lock for passenger cars vehicles passenger cars with GVWR of less than 8,000 lbs vehicles weighing between 8,000 and 10,000 lbs and vehicles with a GVWR of greater than 10,000 lbs The procedures describe required performance for new brake linings and for burnished linings that have accumulated a specified history of brake per- formance Performance requirements for partially disabled brake systems also are outlined Appendix A lists the procedures for evaluating braking system stopping distances under normal braking duty The performance under brake fade conditions is determined by measuring the brake pedal force required to stop the vehicle under severe braking conditions 3.5.1.2 Parking Brake Requirements The vehicle parking brake must be capable of holding the vehicle stationary for 5 minutes on a grade 30 percent for cars 20 percent for light trucks and vehicles over 10,000 lbs This can be accomplished in part by using the transmission to brake the vehicle provided the parking mechanism in the transmission must be engaged before the ignition key can be removed With respect to replacement friction materials the ability of alternative materials to provide static friction levels sufficient to satisfy these criteria can only be assessed by actual vehicle tests 46 TABLE 4. TESTS AND PERFORMANCE CRITERIA SPECIFIED UNDER FMVSS 105 Test Performance Criteria Effectiveness Stopping Distance Fade tests Pedal force and deceleration pmrewn 3 Wet brakes Pedal force and deceleration eee 4 Parking brake Pedal force force 1 oy 71 General Test Conditions Before and after GVWR and empty With and without Before and after Before and after burnish failures spike stops fade Pedal force needed to hold required deceleration in repeated stops to heat brakes Pedal force during cool down recovery Did brakes return to normal Pedal force needed deceleration after wet Did brakes return to hold brakes are to normal Hold on grade with specified application force 47 3.5.2 Federal Motor Vehicle Safety Standard 121 Federal Motor Vehicle Safety Standard 121 lists the performance requirements for air braking systems These systems are commonly used in heavy trucks trailer combinations road vehicles and transit buses This federal standard specifies requirements for stopping distance brake effectiveness fade and recovery brake actuation time brake release time and parking brake operation For these vehicles brake loading can vary considerably depending upon the service conditions and cargo load carried by the This truck or trailer section of the report will be concerned with stopping dis- tance requirements and dynamometer experiments needed to determine these requirements Currently under FMVSS 121 only intercity and transit buses are required to meet stopping distance requirements All other vehicles are exempt and do not require vehicle tests to satisfy FMVSS 121 3.5.2.1 Vehicle Braking Experiments Vehicle braking tests are conducted on level surfaces exhibiting different friction properties as indicated by pavement skid numbers to a generally dry concrete surface For example an while a 30 skid 80 skid number refers number refers to a wet polished concrete surface Vehicle loads are adjusted to replicate heavy loaded or light unloaded conditions Brakes are evaluated by braking the vehicle from 60 mph and 30 mph on a dry surface with a skid number of 81 and by braking the vehicle on a wet surface with a skid number of 30. Both dry and wet pavement braking are conducted under empty and fully loaded conditions Braking road test procedures for FMVSS 121 are listed in Appendix A. Note that in contrast with FMVSS 105 no decelerations are designated Road tests with new brakes are preceded by a brake burnishing wed procedure consisting of lining temperatures are 500 brake applications restricted to 500 F - 50 During burnishing F Note that brake brake drum hi temperature is not controlled 3.2.4 In addition to the regular system brakes the vehicles must have emergency braking systems capable of stopping the vehicle in the event of partial brake system failure This requirement is similar to the FMVSS 48 105 requirements describing brake operation in the event of partial loss of hydraulic fluid 3.5.2.2 Parking Brake Test The parking brakes for trucks E buses and tractor combinations must be capable of holding the vehicle on a 20 percent grade on a concrete surface under both empty or FS fully loaded conditions in both directions Initial brake application can be achieved using air or hydraulic activators Once actuated the application braking loads must be maintained solely by mechanical means 1 3.5.2.3 Dynamometer Testing for FMVSS 121. FMVSS 121 describes _ procedures for inertia dynamometer evaluation of friction materials These procedures require the installation of a complete air brake assembly on the inertia dynamometer Since stopping distance requirements cannot be measured using an inertia dynamometer brake performance is determined by measuring brake torques and deceleration rates as a function of air pressure in the actuator Dynamometer inertia is determined by using the inertial equivalent to the vehicle load on each axle The dynamometer test sequence for determining brake retardation brake power and brake recovery is listed in Appendix A. Trailers are only required to pass brake retardation requirements Service line pressure and calculated brake retardation factor are used to determine acceptability of the materials 3.5.3 Proposed Motor Vehicle Vehicle Safety Standard 135 This standard would replace FMVSS 105 for hydraulic brakes for passenger cars only It contains a shortened test procedure designed to be more harmonized with European regulations Requirements posed by the new standard which may affect friction material qualification are described in the following sections This proposed standard can be found in Federal Register May 10 1985 Vol 50 No. 91 pp 19744 through 19760. Later revisions are in FR Jan 14 1987 Vol 52 No. 9 pp 1474 through 1474 49 3.5.3.1 Front Brake Biasing Under FMVSS 135 standard brake balancing would have to be adjusted to ensure that in the event of a braking situation resulting in wheel lock the front wheels will lock first for both a lightly vehicle and a loaded vehicle Currently oF FMVSS 105 does not specify a wheel lock sequence The braking situation involves careful selection of friction materials exhibiting exhibiting stable repeat- ra able friction performance coupled with a properly adjusted proportioning valve A vehicle designed witgh front braking could become unsafe 1 over time if the brake balance significantly changed sey 3.5.3.2 Control Forces for Brake Application Under the proposed standards the allowable pedal forces required to brake the vehicle under specified stopping conditions will be reduced Lower control forces may necessitate redesign of brake components on some cars to provide greater mechanical advantage particularly to meet the requirements for performance 7 with a failed power assist unit 3.5.3.3 Parking Brake Performance Under the proposed standard the test gradient would be reduced from 30 percent to 20 percent and a } dynamic parking test has been added The allowable control force for applying the brake would be reduced This particular requirement may not place additional restrictions on friction material performance A grade reduction ee from 30 percent to 20 percent represents a 30 percent reduction in load applied via gravity in the direction of slope In contrast the proposed ee reduction in allowable control force for the parking brake is between 10 and 20 percent e e 3.5.4 SAE Recommended Practices for Evaluating Brake Systems and Friction Materials The Society of Automotive Engineers SAE has developed about 26 recommended practices for checking the performance of brake lining systems These standards cover automobile truck and trailer brake system tests using both vehicles and dynamometers Prior to the adoption of FMVSS 105 and 121 the SAE procedures were intended to give some suggested standard guidelines to brake system 50 evaluations The enactment of FMVSS 105 as a requirement for brake system certification shifted the emphasis of these SAE procedures to the role of supplementary tests that could be used to further qualify vehicle brakes and braking systems Table 5 lists some of the SAE brake test code procedures Various SAE documents outline test procedures while others outline performance requirements for various vehicle classes TH 5] ayeg TZ61/6 T961/9 ELOI/E peaoudy PaspAas Pasprad PaspAas - - - ES6T/S TABLE SELCTED VEHICLE TEST CODES Descripton psuhoewn syonay Comhaenvtes Coments psuueed syany SOLIPYA evaluting with vehicle Aqnp Le} procedure perfomancerecomende vehiclepractice sabuseg3ybel IvaWOD material procedure 400d Intende to tests conditonsconditons conditions light {uaqwoeudp FMVS perfomance duty e by PUD 4ysaq up yas aaey procedur inexpnsive cursoy BLIYIA cursory cars , inexpensive in QEvBE Pasenger designddesigned staions cursoy Pasengr vehicles test eyquay) inertia brakescursory state dynamoetr uMoYysYLM A, state vehicle vehicle inspection stations inspection 3VS Aaeay $0 samodyo sd UOLZeAs0dauewso0j As0qegy SAE dynamoetrdynamoetr UOLSIBA dual- re procedure sad version version SAE inertia J843b pue dynamoetr light Pasengerduty dynamoetr Buysn 40j -lenp aouewsjadJazwoeuAp auewsojyuad Jazwoeudp Gupyenga Buyzenta Hupzenta asnpadou aunprdou aunparosd aunprdou aunpasoud e}4azew sa_2pyasyonugwayshs wazsks waqsks ud} yd soy udsag soy soy 1 4592 03 soy apod yp, dn 7saq 359} yosued Bupqes aL 353) Ip YaA YMAD UO} sabused ,eqsaul e,quoy 3121 JD} Asoqegy Asozeg) Asozeqgy u0Lzd) as 4 ue 49A ayeug asn-ul axeug pue 00'0I pua ayeug apo) avs e19C 299e pevec toze eter osnet ogee SBUYN 52 4.0 PERFORMANCE ATTRIBUTES OF FRICTION MATERIALS NOW IN USE 4.1 Section Summary This section presents some performance characteristics of known asbestos and asbestos friction materials and discusses the feasibility of replacing the asbestos brake linings that are currently used Main points brought out in this section include Friction materials are proprietary formulations made from specific fillers combinations and friction of binder modifiers resins reinforcing agents to provide acceptable performance in some brake applications Chrysotile asbestos friction products have been highly developed and refined over the past 80 years Their field performance attributes are well known asbestos friction materials presently are under intensive development but decade Limited most have been conceived within the field service data is available past Four classes of asbestos friction products exist non- asbestos organic NAO bonded metallic semimetallic sintered metallic and carbon Only the semimetallic we whe and NAO materials have shown promise for common automotive brake lining applications Semimetallic linings are not readily applicable to drum brakes except for heavy truck brake blocks dab e asbestos organic linings offer the best potential for most automotive friction material applications However development of NAO materials is hampered by a lack of under- standing of the new raw materials specifically their spe- cial processing requirements and their service perform- ance behavior Since lining formulation is a proprietary process there is very little information interchange on asbestos lining technology No performance requirements exist for aftermarket friction products Consequently asbestos brake linings are 53 commercially available but they lack field service data to assure satisfactory performance for the full range of automotive applications 4.2 Introduction to Friction Material Formulations ee Little has been published about the specific formulations of 6 friction materials since they are considered to be proprietary compositions by the friction material manufacturers This section of the report reviews eS the more common forms of both asbestos and asbestos lining materials and presents data regarding performance under vehicle or simulated vehicle 1 braking conditions Friction materials for automobiles contain four general types 1 of ingredients reinforcing usually fibers friction modifiers fillers and binders Most automotive friction materials use thermosetting resins in their binder systems These resins often of the step Novo- lac phenolic type and generally modified for both processing and functional purposes provide the matrix to bond the various constituents together Internal pressures generated during processing and fade testing can reach 1000 psi eratures so binder resins require good tensile Binder resins provide more than just strength at elevated temp- structural attributes to the brake lining Thermal stability friction level fade fade recovery dimensional stability wear life and other performance characteristics of the brake lining are determined at least in part by the choice and amount of binder resin a] Reinforcing agents provide the structural elements to support the friction material in service Brake linings experience a range of mn loadings that require strength stiffness and toughness The reinforcing agents contribute to the stiffness and strength of the friction material EEE? composite attributes Usually these agents are to the brake lining such fibrous as wear and most often resistance and provide other improved dimen- sional stability Since chrysotile asbestos has been used as a reinforcing agent in friction materials for about 80 years its performance attributes are fairly well known Chrysotile asbestos was chosen because of its unique combination of physical thermal mechanical tribological processing os Fe _ anes, se es wee e 11 54 and economic properties It is a unique mineral processed to provide the desired fiber length distribution and fiber openness degree of fiber fluffing or opening of the fiber bundles needed for specific applications Usually two or more grades of chrysotile asbestos are blended to produce the desired properties for the brake lining asbestos friction materials use a blend from several hundred potential fiber and other structural agents that have been tried in brake linings No one fiber replaces asbestos so a fiber cocktail is developed to provide the needed processing structural functional and permeability attributes for the brake lining at an acceptable Friction modifiers and fillers as the cost names suggest are added to provide the needed performance modifications and cost control to the binder system Hundreds of organic and inorganic constituents may be used in varying amounts distributions and particle sizes to achieve the intended results Since friction material formulation is more of an art than science it is common for these materials to be sequentially added to the formulation to correct different performance shortcomings in the lining development process The asbestos friction materials have four developmental classes asbestos organic NAO semimetallic semimet sintered metallic and carbon Semimetallic and NAO linings appear to be the best suited for most automotive brake applications but all four types will be discussed in Section 4.4 4.3 Asbestos Friction Materials Asbestos has been used in brake linings and other friction pro- ducts since the turn of the century when metals leather and wood no longer were adequate The predominant type of asbestos used in brake linings is chrysotile a hydrated magnesium silicate The ultimate chrysotile fibril is about one millionth of an inch in diameter so a fiber bundle about the size of a human hair may contain a million fibrils The larger fiber bundles a friction material called crudes Smaller fibers constitute especially the visible asbestos when fully wetted by in the binder resin are lengths and fiber virtually diameters impossible to see in the brake lining Many are used in making the asbestos friction 55 materials usually by selection of an appropriate commercial grade or grades and by proper blending Asbestos provides many desirable attributes to the linings both in manufacture and in service usage During the mixing and molding process asbestos helps to hold the materials together This is referred to as green strength in the E preforming and molding operations During molding and also during usage the asbestos provides permeability to the lining letting internally generated volatiles escape before they can produce high internal pressures and possibly blister or crack the brake linings _= Chrysotile asbestos being hydrated loses this water as the temperature rises At around 650 degrees Celsius about 1200 degrees F this dehydroxylation causes about a percent weight loss to the asbestos At slightly higher temperatures the chrysotile asbestos converts to an amorphous or glassy phase One common product of this conversion is called forsterite In this converted phase the chrysotile asbestos normally has been transformed from a fiber to a very fine powder At very high temperatures forsterite can deposit in smeared layers over the disc or drum braking surfaces but this is quite uncommon and undesired Each vehicle application requires friction materials exhibiting different frictional and mechanical properties Passenger car and light truck drum brake linings called segments usually contain from 30 to 70 percent by weight of asbestos If held together with a liquid resin these are referred to as wet mixes Such materials are commonly rollmolded to their basic sectional shape but also may be formed by extrusion or other molding processes When a powdered binder resin is used the mix is referred to as a dry mix These generally require an initial molding or briquetting operation to produce the required shape Both are cured by heat in a process that is both time and temperature dependent A wide range of friction wear and other properties can be built into such materials particularly with over 70 years of formulation development time Asbestos provides good static friction properties important to drum brakes with integral parking brakes and is easily formed by many processes to make durable and dimensionally stable segments Passenger car and light truck disc brake linings are almost exclusively made with powdered binder resins in dry mix processes that FT 1 noway 1 oO , 56 involve being individually molded to nearly final dimensions Asbestos content usually is a bit lower and longer fiber lengths are used in disc brake linings because of their greater temperatures and pressures in service usage The asbestos is permeability or breathing characteristic of chrysotile important to disc brakes to prevent rapid friction loss with increasing temperatures and during hard high speed stops Heavy truck drum brake linings are called blocks and are gener- ally molded in slabs Longer fiber length asbestos and added crude fiber content is needed in these blocks for reasons similar to those for disc brakes Truck blocks are thick about 0.75 inches 19 mm so they require sufficient as well as permeability to from hard brake release usage volatile materials from Inadequate breathing manufacturing causes blistered or delaminated brake linings Truck refined over the years with special brake blocks formulations have been continuously for most of the unique usage conditions 4.4 Asbestos Friction Materials Less than twenty years have been devoted to the development of asbestos brake linings with the most intensive effort over the past ten years Various alternative fibers have been studied since cotton was replaced by asbestos 80 years ago However none provided the requisite performance to challenge asbestos until the semimetallic linings were developed for hard service disc brake usage in the 1970's Concerns about asbestos fiber toxicity increasingly stringent air quality standards and rising insurance costs all stimulated the development of substitute materials Substantial progress appears to have been made in the past few years as many new vehicle models have been released with fully asbestos brake systems Several aftermarket friction products have been advertised as asbestos but little is known of their actual service performance characteristics Dynamometer and vehicle performance test data for asbestos friction materials are not available so a complete evaluation of these materials was not possible A variety able for aftermarket applications No of asbestos materials is avail- replacement friction materials except qualified OEM linings are known to have undergone qualification 57 tests under FMVSS 105. In addition most aftermarket suppliers lack the facilities required to conduct FMVSS 105 and FMVSS 121 test procedures The following discussion though not complete provides at least an introduction to the different types of asbestos friction materials hUPe that are presently available or under development Some of their basic functional characteristics are also given when sufficient information was | available ET Despite substantial engineering efforts asbestos replacement friction materials are not available at a proven quality and performance SR level that is equivalent to that of the original brake linings for vehicles which originally were released with asbestos brake linings asbestos friction materials technology is advancing rapidly 1 with many new car light truck heavy truck and road brake systems being released for new vehicle production Materials are under development for all four general classes 4.4.1 Semimetallic Friction Materials Semimetallic and resin bonded metallic RBM are all names for this popular class of friction material Semimetallics utilize steel wool some form of iron powder graphite binder resin and various other con- stituents in their formulations eee Semimetallics have been used as disc brake linings on passenger cars and light trucks for about a decade Presently they are the most common friction material used with original equipment manufacturer OEM disc brakes in the United States Although originally produced with a e e asbestos backing layer most semimetallic linings now use no backing layer or one of a asbestos organic NAO composition Semimetallic linings also have had limited usage in heavy truck drum and disc brakes ee These friction materials are usually pressed to finished dimensions Consequently they are not readily made into drum brake seg- E ments due to the needed large lining curvature Since semimetallics also tend to be low in strength and stiffness they are better suited to the thicker disc brake lining and heavy truck block configurations Semimetallic linings have several unique performance character- istics For one they have a high initial wear rate at least until a 58 ferrous transfer layer is built up onto the drum or disc cast iron surface This formation is rapid at high temperatures but can be quite slow for brakes that operate at low temperatures low speed and light pressures Lining wear life is greatest for moderate temperature service Poor lining life can result from very low usage temperatures so brakes are often designed to run hotter with semimetallic linings Most friction materials have a lower friction level at higher rubbing speeds but semimets do not These materials have nearly constant friction levels from about 30 mph to beyond 100 mph providing potential front brake balancing difficulties for some systems While the friction is nearly constant at high speeds the lining wear rate is not Semimetallic linings have high wear rates per unit work done at higher rubbing speeds Thus they seldom are used for racing car applications Water affects many friction materials greatly but has very little influence on semimetallics accompanied by oil Water and oil can act to reduce the friction of semimet materials in contact with cast iron discs Since road splashing generally contains some oil this can cause a loss of friction Disc brakes are less water sensitive than are most drum brakes and often run warm enough to dry quickly so water effects usually are not critical or long lasting Cool and humid ambient air conditions affect semimetallic linings significantly causing a temporarily low brake effectiveness called morning sickness 4.4.2 Asbestos Organic Friction Materials asbestos organic NAO materials utilize a combination of fibers and other ingredients to fulfill the functions that chrysotile fibers had performed in asbestos linings Aramid DuPont's Kevlar fiberglass mineral wool wollastonite steel wool and processed mineral fiber are some of the common reinforcement fibers used along with the binder resin and various fillers and friction modifiers in NAO brake linings NAO brake lining formulations presently are used in some OEM drum brake applications for passenger cars and light trucks and increas- 59 ingly are used in brake blocks on heavy truck drum brakes NAO disc brake linings have been released for many OEM disc brake applications Development efforts of NAO drum brake segments for the remaining OEM appli- cations remains active art This class of friction materials offers the greatest hope as an effective asbestos replacement but also provides the greatest problems rn" to develop Literally hundreds of fibers and reinforcing agents have been used generally in combination with several others Finding the best combination for lining processability friction level friction sta- te bility wear life fade resistance recovery contamination sensitivity and mechanical properties is a formidable task even using statistically =o designed experiments Since there is essentially no technical communication or cooperation among the lining suppliers each is working virtually 1 independently at this task It appears likely that new NAO materials will be developed that are superior to the best of the asbestos linings Presently NAO materials tend to be hard brittle low in perme- ability highly anisotropic and prone to hot spot blister and crack in service 4.4.3 Sintered Metallic Friction Materials Usually sintered these heavy materials typically are of @inewsen iron or copper base but they may generally contain inorganic filler and friction modifiers as minor constituents Sintered ferrous drum brake linings were released for a few OEM 1 passenger car applications two decades ago They tend to be environmentally sensitive both to temperature and moisture which limits commercial appli- 1 cations However they are used for special service aftermarket automo- biles some severe service commercial vehicles and aircraft disc brake CC applications Sintered copper friction materials have been used in heavy duty brakes and clutches metal forming a bronze can perform well in hard for around three decades Often with another and a refractory such as mullite these materials service usage However they too are environmentally 1 1 1 " E 60 sensitive and can cause severe galvanic corrosion in wet environments when used against the typical grey cast iron countersurface materials Aircraft disc brakes and heavy duty tractor clutches are present uses for the sintered bronze friction materials No known new application of these relatively old and well developed friction materials has resulted from the search for asbestos substi- tutes largely due to their cost and sensitivity to light environmental conditions 9 4.4.4 Carbon Friction Materials fiber These materials are space composites of carbon graphite held in a matrix of amorphous carbon using a costly and con- suming manufacturing process Military aircraft race cars and some commercial aircraft now sometimes use the carbon friction materials for both the stationary and rotating elements of disc brakes High cost and environmental sensi- tivity limit additional applications 4.5 Aftermarket Vehicle Considerations 4.5.1 Drum Brakes Brake design also affects the suitability of using some friction materials The servo drum brake used in older U.S. vehicles usually employs two different types of linings with different friction properties on a single brake to maximize overall brake performance Aftermarket friction materials must be capable of replicating original design friction levels and friction stability to achieve acceptable vehicle braking performance The trailing drum brake used on the rear axle of the smaller front wheel drive vehicles does not require friction materials new with such stringent friction stability properties In both applications 61 the static friction properties of the material are important due to the use of rear drum brakes as parking brakes 4.5.2 Disc Brakes Disc brakes generally operate at higher temperatures than do drum brakes and the friction material used for this application must exhibit stable friction behavior over a wide temperature range U.S. passenger cars and friction materials light truck disc were designed to brakes which used asbestos phenolic operate at lower temperatures than do present linings vehicles that generally had use semimetallic higher friction linings These asbestos especially at the lower brake temper- temper- atures than do the semimetallic linings 4.5.3 Factors Affecting Substitution of Friction Materials vehicles The use designed of asbestos materials for asbestos linings as direct substitutes may be restricted for in the following reasons 1 Braking balance between front and rear brakes may be adversely affected With few exceptions semimetallic and NAO linings oo presently available are for the use only asbestos friction materials on disc brakes Use of semimetallic SE linings would cially at the decrease the front brake effectiveness espe- lower temperatures Since many of the front brakes were designed to operate at lower temperatures than are optimal for semimetallics the semimetallic linings 1 would not provide proper friction and wear behavior for many users The available NAO rear brake linings differ in their Th friction properties especially in the low temperature region and also may be humidity sensitive Front brake balance at low temperature could be unsatisfactory 62 unless matched front and rear linings both were installed during brake servicing Regrettably many users have only one set of linings replaced at a time This offers a substantial opportunity for unbalanced braking between the front and rear brakes No known balanced asbestos brake lining sets are available for the aftermarket applications that originally were asbestos The front balance with replacement asbestos linings probably will be sensitive to the brake temperature vehicle speed and brake line pressure 2 Parking brake capacity may be reduced Many of the asbestos organic NAO drum brake linings provide low effectiveness at low temperatures In addition they also generally have high thermal expansion coefficients and are stiffer in compression This can lead to a loss of parking brake capacity both from the lower effectiveness values and from larger losses of input cable forces due to lining contraction 3 No meaningful brake lining effectiveness ratings exist NAO friction materials are currently produced domes- tically in both brake pad and brake drum configurations Tables 6 and 7 list current U.S. producers of brake pads and linings for passenger cars and the manufacturers of NAO brake trucks linings for Only light a third of and medium vehicles are outfitted with the facilities needed to evaluate friction products under true vehicle test conditions or simulated vehicle tests full brake inertia dynamometers Similarly only a third of the manufacturers of heavy vehicle drum brake evaluating blocks have appropriate test facilities for their NAO friction materials All of these suppliers rate their linings using a rating methodology that has been shown to be deficient see Section 3.2.2 Re] ~ JaYseUWT SusMoy puesnoy saonpud sozaqse IPE upeqyuo. uortliu0S-0rsped qees -}wasayeug -Oud 2s}p -04dyquow pue WNP W9 Sadayd sad 403 Le IYsyonp T unup paonp W30 osty Jaw AND saho}dw3 002 02 ! V/N 08*b /N /N 006 002 oot V/N Asbestos Location Location voy Li (suey ^'l Sd tw) 1op Pads v/N Linings 0S 8 million V/N OYN and xX X SIDNIAWHIGW ayeug sbuy wnig uy X X x X soqasy ONY X Xx xX x X asbestos JHOIT OWN X Od OH Speg SONIET aftermarket X x x ~} aftermaketa724g was JXvda 4819 40 drun X X X Xx X aftermarket X X x X X Xx Xx lining SYZINGOd Aftermarket 2 aftermkt qayseuw3z 79y40W1975e qayxsewaze Jayewsgz qayuewsqy Jay74PU9z 40 Jayseuz pajuodw, paysewaz * 9 4OJ pue SyINuy F18VL aftermarket pue pue aftermarket ysawop ILyad OEM Wi0se W30 pue pue wi0 w30 AL sew WIO wnt pue soy sued ad se awOos paw W30Ze Dd}Sa] pue wI0 yy) and NL 1) Ay YW Aftermakt *psaoyzes SL 10 Aftermaket Sapbuy CN AN Ho HO OL Lp LpAuap SAO4L u0QUas] uozkeq u0zheg soy Aueg es (uoyspar pazeuodl *duoy Kuedwoy *duo) x) xaqy puag AGG*auy $407K aupesoy $107W ("Atqg aa sz YOLQIEAY INpoud [euay 022q) [e4auypueyu) auseuy 0) [Bays 65oWur sea] H UO, ZILA *swazsk UANZON OFNy *duo) ayeug Jul 64 S}UuaWwUO) "pBGL LIGHT AND Y/N Gas sakojdw3 *S M Products Location |e) LocationLocation Location V/N Pads Products Lop yzLM NAO boone 40 Taphnock OYN f4079a41g al PA sBuy SUd}Ze4aAO. S319TH3A wnaguty OEM X X X soyaqsy WNIO3IN S,p4emMpue x Walkerton aL ~ OWN X x X suo} szonpud 1H917 sped provided 1986 company Primaryrepsentaives of SyoNpsg esoduoj x X Products Telphone and Sales Corporations Ward x Xx Ward's 00IS JO SHAINGOd S4Osar0ug 3 e qaysew7y yasewW4I9zY qayxuewiazs qey74wITY *su0pQeIb1qNgAvepuoras 407234} 9 zayuew pue JIVE W30 pue S$,Puem ee Puen H Sapyequsda AuewpJd uo} WA er 3ze YA UPALeG Dee 907 vd -40 saXkojdwa Auedwod In Kaans =Q y20ued) Aemabpiy u03491eMaude Aq pue 9861 ewnLeda pap} 491 sales aoud DA} *582un0s Auedwo} 09 OLS ZOWO apshayg s YNny 830 L4eg ey UOEL $3 up BayaFIP 2Npoud saunb 4 Sahojdwz 002 Y/N = 861saypesvoy (suey ral V/N tp) top 65 oov ooe 002 v/N Se 8I el ad V/N V/N oor S V/N V/N Location Location Location Location Market x Winchestr x x TNClevland SJTDINAAVIH Ridgway PA X OEM Xx x X V/N x xX x X V/N x YO4 SONIT , xX X X X X X V/N X x AVG LLL SUZINGOd4O Worth , 3S1d ayeug twa aftermarket Xx L qaxseuU3zy aftermaket qayxsewazje qayxseuq *Jaysew9z Jayxsewazje qaysewqy Jaysewzy qayueizs 58 qaxuey x FIGVL App pue pue pue pue acy Asey pue pue pue pue pue w30 W30 wid w30 udpw wad w30 w30 wa0 N v/N WA0 NI YA NL Crawfordsvile Crawfordsvile 4aqSyouLA aftermaket NI] NI XL vd AemBbpy uoqz6;uAH @LzSeoMaN A 2404 aApyequsda 1) AK / OL AX X1 HO *psoj7e49s uonbay 6ur.2auK LpASPsojmeuy uozsnoy SOLPASHNOT eul pay Auedwos Aq papi a_spie)7eu0d aduepsg UO}I} doy aftermarketaftermarket aftermaket udp 1340d pue Buy -Sskgsuzy Jeg Buy4201g 09 pul pO4g "pOtd acud repsentaive repsentaive xpu}ag Aavaysato ua uy XH usNzAN $374eg bug ayeug sua URIS paum axe4g 65w yuewAey ospueys JauLed saunbi4 109 09 44 y 66 This test with 1 inch square specimens can give particularly misleading friction data for some NAO and semimet brake linings The brake lining or disc system is a tribological system in which alterations in either the pad surface or the rotor surface affect system frictional behavior Under elevated temperatures cast iron surfaces can form iron oxides or develop transfer films which exhibit lower coefficients of friction than do plain cast iron surfaces The abrasive nature of asbestos friction materials acts to continually remove these surface films thus restoring system friction and metallics on the other hand depend on a transfer brake effectiveness film that is known to exhibit low friction under cold and moist conditions 4.6 Direct Comparison of OEM and Aftermarket Brake Linings Complete brake dynamometer and vehicle performance data are not generally available to use for comparisons of different friction materials making it difficult to support or refute claims made about the availability of acceptable asbestos replacement brake linings When available interpretation and The next evaluation of the test data can be difficult two sections present both dynamometer data and vehicle test data that highlight observed performance limitations posed by the use ew of asbestos friction materials mea 4.6.1 Dynamometer Test Data One example set of data follows which supports the claim that no acceptable asbestos friction materials have yet been developed E for certain drum brakes In this case a full brake dynamometer was used to test four different sets of drum brake linings on a inch servo drum brake with a inch lining width Identical procedures and matching test components were used so the brake linings were the only known variables 67 The linings tested have been coded a condition for the availability of this test data For simplicity of presentation only the initial lining burnish test data is shown Figure 14a shows this data for Lining A a NAO drum brake lining | set The test data is presented as brake line pressure versus equivalent fn. . vehicle speed The brake line pressure relates to the amount of brake pedal effort exerted All brake stops after stop were performed from E the same initial brake drum temperature of 300 degrees F. All of the stops were from the same initial speed 40 mph and controlled to provide an equivalent of 8 feet per second per second deceleration normal braking application Note the wide range of pressures required to make the same stop Even after 100 burnish applications the required hydraulic pressures varied by a factor of two for adjacent stops Also the required i a brake pressures for this normal type of brake stop were almost to the limit for the power brake booster Brake lining A would this brake assembly However be unacceptable for any this lining formulation OEM was brake usage on released for production application on a smaller brake and attendant different smaller drum thinner linings lining A met brake all of With a the service requirements for an OEM brake lining This demonstrates how the accept- ability of a friction material is not just dependent upon the properties of the brake lining but also depends on the specific choice of brake vehicle and use conditions B was Figure 14b shows performance curves for a NAO material B. a candidate NAO material but was not released for production Lining It ee used a different asbestos fiber system from that used in A. This lining provided on average higher brake effectiveness but with a greater GuV= range of brake application pressures for the same illustrated here other test data for this lining test Although show it to have not an unde- era sirable morning sickness with first few cold stops A lining very like high this initial effectiveness for the on the rear drum brakes used with a semimetallic front disc brake lining would provide a vehicle brake system with a very strong tendency for rear wheel lockup skidding when cold 68 Ov Of W30 Yaidy gq 4 er OO < SO}aqsy 6bur y Ol Pp SIWNLW Ov NOILUS | Of UOLYINPOAg 01-0 i O02 Q SOPaqsy LN3Y41G bulury ydw | ai pads *4S9} wNOd ne 40-100 UL (Lt O SLINSIY Suaqun Ob aiya, 110 434) | Oe quajoinby g ayvua doys _- ! 02 Surut] LS4aL wha we OWN | mph 40 OATS 4 . Lining Asbestos saAund Lining Lining x 4O y uO ZL |. DIFFERENTDIFFERENT DIFERNT FRICTON MATERIALS MATERIALS OVN 1 Ol e +930N PL 0 JYNI4 isd QC} 'aanssauy sult) ayD4g 69 Figure 14c shows performance curves for a material C. Lining C a premium quality aftermarket asbestos lining set has been used for many years Note the narrow band of brake line pressures for this burnish sequence In particular the stops from 40 through 100 were virtually identical This consistency of brake effectiveness although not guaranteed by the use of asbestos friction materials is not yet available from any known NAO drum brake lining on this size of drum brake Lining C had slightly higher about 25 percent lining wear rates than the two asbestos materials shown Figure 14d shows performance curves for asbestos material D. Lining D was the OEM released material for this brake system It had the highest average effectiveness of the four linings and also the narrowest band of brake line pressures In this case the second 100 burnish data was included to illustrate the consistency of performance that can be obtained from this brake About 45 brake applications were required to obtain steady frictional behavior After these the test data were very repeatable and the variation of effectiveness with speed was quite acceptable for a servo drum brake 4.6.2 Vehicle Test Data For a vehicle test study conducted by the National Highway and Traffic Safety Administration NHTSA the performance of aftermarket brake linings was compared to the performance of OEM linings The experiments were conducted using a compact size passenger car equipped with front disc brakes with metallic pads and servo drum brakes on the rear Twenty different aftermarket rear drum linings were obtained by purchasing them from automotive service centers and automobile parts outlet stores These materials were identified with a letter code of A through W. Experiments were conducted under conditions similar to those specified in FMVSS 105 see Appendix A To generate data representative of OEM lining performance 10 sets of qualified linings were also obtained and tested to generate a comparison baseline ee 0'0 FS psil9'0 es Efectivnsa4 _ 7 oehch}ht Pea J Lining vee sete Aftermarket Lining Code a 30 mph burnish rear brake effectiveness results ift-lb/pe! i I , Efectivr Gamage Sor 2 Ots ] er C. . ee Aftermarket Lining Cade 30 mph post burnish rear effectiveness results brake 0 peit Efectivns a ec FP " SE Aftermarket Aftermarket Lining Code b 60 mph burnish rear brake effectiveness results 1/1 Efectivens I 1/1 os a bec epe Pe^'aetsetererpenestre&v Aftermarket Aftermarket Lining Cade d 60 mph post burnish rear brake effectiveness results FIGURE 15. VEHICLE TEST RESULTS COMPARING THE PERFORMANCE OF AFTERMARKET FRICTION MATERIALS REF 12 15 71 Figure 15 shows the measured brake effectiveness for the various aftermarket linings under four different test conditions At least two separate sets and as many as four separate sets of the same linings were tested variations in performance are illustrated by the range in effective- CU ness exhibited among and 15d indicate the different sets of identical wide range of effectiveness materials variability Figures 15c among the aftermarket materials Lining material R exhibited the highest vari- FR ability in effectiveness This material was the only asbestos material tested of the 23 aftermarket materials tested This data is consistent 1 with the dynamometer test results presented in Figure 14 The remaining 22 test results also illustrate how wide variations in effectiveness can _=_ exist even for asbestos materials 4.7 Issues of Consumer Acceptability of Asbestos Materials Consumer acceptability of asbestos friction materials as with asbestos friction materials will be affected by material wear per- formance and by the could lead to sooty tendency to induce brake noise Excessive brake wear tire sidewalls while brake noise continues to be an annoyance to many consumers _- Some brake materials used for front disc brakes have created a dirty wheel syndrome from wear debris Also known as dusting this situation arises when fine sooty wear debris is deposited on the outside wheel and the surfaces This situation makes routine tire main- tenance more undesirable since the black film is tenacious and usually makes the car owner's hands dirty To prevent this situation some car owners switch to aftermarket disc pads that are advertised as being dusting resistant Auto owners apparently assume that these materials are equally effective as braking materials as other materials more prone to dusting Aluminum shields are also available to shroud the disc and prevent debris from being deposited on the outer wheel surfaces These a shields are mounted between the disc and wheel of the brake and wheel assembly First the Two adverse situations may arise from the use of such shrouds discs may operate at higher temperatures due to the decreased 72 convection and radiation from the disc surface Second the wheel lug nuts may eventually loosen due to plastic deformation of the aluminum shroud in the vicinity of the lugs The dirty wheel syndrome has been reported more often by owners of German luxury automobiles such as BMW and Mercedes for many years Owners of such vehicles tend to be more fastidious about the car's appear- ce ance than owners of other less expensive vehicles which utilize other materials It is now becoming more of a problem on American and Japanese cars as more asbestos materials are utilized 86 Nevertheless the various techniques used by owners to eliminate ma; the problem more clearly illustrate the public's viewpoint that brakes are largely unaffected by consumer neglect or tampering tampering vehicle quali- fied asbestos materials that exhibit excessive brake squeal or dusting 1 could be replaced by materials provided by an unregulated aftermarket supplier that need not meet any certification ee 8 Ont ene | i 73 REVIEW OF VEHICLES AFFECTED BY PROPOSED BAN 5.1 Section Summary The purpose of this section was to examine the various vehicle classes using friction materials and identify trends in braking systems in the various vehicle classses The following observations were made The overwhelming majority of American passenger cars are now designed with front disc brakes and rear drum brakes There is not a significant trend toward wider use of wheel disc brakes American manufacturers are directing efforts toward developing suitable asbestos lining materials for rear automotive drum brakes Because disc brakes maintain effectiveness at high braking speeds wheel disc brakes have been used in Europe on some high performance vehicles before asbestos became a concern Now some European manufacturers use wheel disc brakes and metallic brake pads as a means of eliminating asbestos from passenger cars Differences in consumer acceptance brake wear between Europe and the United and brake noise may restrict States the use specifically of wheel disc systems in the United States Trends in light truck braking systems follow those in passenger cars Most medium trucks drum brakes on all American European and Japanese use four wheels Acceptable qualified sub- stitutes for current asbestos lining materials have not been found in many cases These drum brake systems use segments a thin lining material similar in geometry to automobile brake linings However the relatively severe braking requirements of this application prevent a simple retrofit of automobile materials to the medium truck market A r small percentage of medium trucks are now being produced with disc brakes and metallic pads Acceptable substitutes found in some cases in for the asbestos materials have been heavy truck segment These Oe [ [ _ _- eames ae L tri 74 brake systems use thick molded brake blocks which are bolted or riveted to shoes Some asbestos materials have been found to exhibit sufficient mechanical strength and frictional properties for this application 5.2 Brake System Trends in Passenger Cars Trucks and Equipment For this study motor vehicles have been divided into three classes passenger cars highway trucks and highway vehicles Motorcycles transit buses and trains and aircraft have not been included The overwhelming majority of vehicles in the United States are as expected passenger cars Table 8 The majority of the 1984 American passenger cars were fitted with a drum and front disc brake system 33 percent of 1984 imported automobiles were fitted with wheel disc brake systems Medium and heavy trucks continue to use traditional drum brakes Light trucks use front disc brakes with rear drum brakes 5.2.1 Passenger Cars Passenger cars are the largest single market for friction products in the U.S. As indicated previously there were about 130 million regis- tered passenger cars in 1984 in the United States Prior to 1965 almost all American passenger cars were equipped with wheel drum brakes with asbestos linings In 1965 some vehicles Lincoln Continental and disc brakes Widespread Chevrolet Corvette were use of front disc brakes equipped with front across most product lines of American manufacturers began in the early 1970s There are a substantial number of vehicles that have drum brake systems designed for use with asbestos friction materials In 1984 there were still 11.5 million cars in operation that were manufactured prior to 1970 and the majority of these presumably were fitted with wheel drum brakes Prior to 1982 the majority of automobiles with wheel disc brakes had been designed for use with asbestos brake pads Since the mean with life of passenger cars is now about 7.6 years automobiles fitted brakes designed for use with asbestos friction products will continue to be in operation for several more years Vehicles manufactured in 1986 75 TABLE 8. NEW VEHICLE SALES AND VEHICLE REGISTRATION FOR 1984 REF 15 U.S. Calendar Year Sales Millions amg, ese wwe Passenger Cars 10.4 Domestic Imported 8.0 2.4 On Highway Trucks 4.1 Light Medium Heavy 3.8 0.06 0.20 oe Highway Vehicles Farm equipment Construction equipment 0.17 0.05 * 1986 estimate ** 1985 estimate rea 76 with asbestos friction materials can be expected to require aftermarket brake components for at least another 11 years Current American automobiles are almost exclusively designed with front wheel disc brakes As shown in Table 9 American manufacturers do not appear to be embracing wheel disc brakes as a means of changing the braking characteristics of automobiles Currently American manufacturers appear to be retaining rear wheel drum brakes These brakes are attractive for the following reasons 1 Easier implementation of parking brake mechanism 2 Less susceptability to debris 3 Less susceptibility to corrosion 4 Less weight and 5 At the present under American Less cost time there appears to driving speeds to rear be no wheel distinct performance advantage disc brakes other than reduced time required for maintenance The use of rear disc brakes also simplifies the setting of front braking balance The current trend among American automakers is to implement asbestos brake lining and brake pad materials in new major model changeovers redesigned Brake systems on existing models are never routinely New models such as the Ford Taurus are equipped with semi- metallic front disc brake pads and asbestos organic rear drum linings Rather than redesign brake systems with wheel disc brakes using semi- metallic pads American automobile manufacturers have elected to retain rear drum brakes and direct development efforts toward new asbestos rear drum linings Qualification of asbestos materials through vehicle testing may take 2 years or longer assuming a suitable material exists for a specific vehicle application The redesign of a vehicle's rear brake system from drum brakes to disc brakes could take 5 to 7 years with little guarantee of significantly improved performance 5.2.2 Highway Trucks highway trucks are generally classified with respect to gross vehicle weight class i.e. by the vehicle curb weight plus cargo Trucks can be considered single chassis vehicles or can be used in trailer 77 | Te BE TABLE 9. LIST OF 1985 AMERICAN AUTOMOBILES EQUIPPED WITH WHEEL DISC BRAKES REFERENCE 16 1 Number of Units Sold With Wheel Disc Brakes Percentage of output General Motors 164,301 Ford 46,608 Chrysler 0 eee American Motors Corporation Volkswagen of America ae Honda 0 82,797 0 = 3.6 2.7 0 0 100 0 tT a 1 mer | PAGE , 78 combinations Eight weight classes currently exist although for the purposes of this study the following classifications are used Classification Light Medium Heavy GVW Class Group 1 Group 2 Group 3 Group 4 Group 5 Group 6 Group 7 Group 8 GVW Range lbs 6,000 and less 6,001 and 10,000 10,001 - 14,000 14,001 - 16,000 16,001 - 19,500 19,501 - 26,000 26,001 - 33,000 33,001 - over New truck registrations for 1984 indicate that light trucks make up approximately 94 percent of the total truck population which reflects the popularity of small pick trucks and mini vans In contrast medium trucks account for about 1 percent of the population while heavy trucks make up the remaining 5 percent The following sections outline current in vehicle brake materials for the three classes brake systems of highway and trends trucks 5.2.2.1 Light Trucks The light truck designation refers to both pick trucks and compact vans used in light hauling and passenger transport About 3.9 million light trucks were sold in 1984 in the U.S. As of 1984 almost 31 million light trucks were registered in the United States Trends in light truck braking systems follow closely those of passenger cars In 1984 in the United States were more than 94 percent of light trucks manufactured equipped with front wheel disc brakes Ford and GM brakes 1987 light trucks are using variable proportioning valves for or lock systems to improve braking under a wide range of rear truck loads Calibration of a variable proportioning valve is affected by changes in rear brake lining material In this respect trucks brakes are following European passenger car trends in that design steps are being taken to ensure front wheel brake biasing re FY Bavren 1 1 1 | ae 79 Many light truck brakes manufactured in the United states are now using asbestos semimetallic materials in the front disc brakes and asbestos organic linings for the rear drum brakes In 1986 the Ford Aerostar and Ranger models were fitted with all asbestos friction materials The automotive industry is in the process of converting existing light truck models Although over to asbestos friction products new truck brake systems appear to be heading toward asbestos friction materials a large population of older vehicles requiring aftermarket friction products still exists Between 1970 and 1982 the median age of light trucks was 7.1 years 5.2.2.2 Medium Trucks The medium truck designation generally refers to single chassis trucks with a lbs These trucks usually are used as GVW of between 14,001 lbs and 26,000 enclosed delivery trucks or open flat trucks Manufacturers usually provide the engine train cab and chassis which are custom modified to suit the customers needs Brake systems on this truck classification can be either hydraulic or air operated depending upon customer selection and intended service The majority of the systems are hydraulic due to lower initial costs associated with these systems In 1982 there were 1.4 million medium trucks in service in the United States 14,15 Current manufacturers and marketers of medium trucks in the United States are Ford General Motors Chrysler Mack and Mercedes and others These manufacturers typically purchase axle and brake assem- blies from foundation axle and brake manufacturers and assemble them along with the engine and chassis into the finished truck These brake systems brakes are almost exclusively drum brakes on both These brakes use strip linings similar to the front and rear automotive drum brakes However due to the more severe braking conditions found in these trucks qualified asbestos materials have not been found for some medium trucks Disc brakes for medium trucks are now under development although the number now in service is very small Some of the advantages cited for truck disc brakes are light weight and increased ease of maintenance However problems with excessive rotor and pad temperatures continue to limit their use in potentially severe braking conditions European medium 80 trucks produced by IVECO Italy and Scania Sweden are exclusively fitted with hydraulically actuated drum 17,18,19 5.2.2.3 Heavy Trucks The heavy truck designation refers to Pe either chassis trucks or segmented trailers having a GVWR of greater than 26,000 lbs In general the single chassis trucks have hydraulically brake systems while the brakes of tractor Ps combinations are generally air actuated Large truck brake systems are almost exclusively drum type Ps either of the trailing type Figure 3a or the leading leading leading type For these severe braking requirements thick block segments rather than thin strips of friction materials are bolted or riveted to shoes Some success has been achieved in qualifying asbestos block materials - for heavy truck applications This success has been due in part to the ability to mold the asbestos materials into rigid blocks possessing sufficient mechanical strength The use of disc brakes in the heavy truck market has received some attention centered around but the the use overwhelming majority of of drum brakes Because the systems drum brakes is still still offer some performance advantages over disc brakes a complete conversion to disc brakes in this vehicle market is not expected Qualification of asbestos materials for truck and trailer service is progressing through the combined efforts of foundation brake 1 manufacturers truck manufacturers and friction product manufacturers Most of the aftermarket friction product manufacturers do not possess the 1 facilities to evaluate the performance of their products under vehicle service conditions 5.2.3 Highway Trucks and Equipment i Farm equipment and construction equipment have braking needs TI TI different from those of highway trucks Braking speeds will be lower and required brake torques will be higher Examples of highway equipment include road scrapers road graders excavators haulers cranes mobile drilling rigs and other large 81 pieces of equipment Farm equipment can range from small tractors to large harvesting combines Qualification of friction products for these applications is usually the responsibility of the foundation brake manufacturer and the equipment manufacturer since no Federal braking requirements exist Materials found to perform satisfactorily through years of customer and manufacturers experience are rarely changed since the usage conditions and PS equipment change only slightly The development of qualified asbestos replacements for this market segment may be difficult due to the extended time required for development coupled with the relatively small market represented by the farm and construction equipment industry 1 5.3 Current European and Japanese Experience in Brake Design and Friction Material Selection Automobiles and Light Trucks The bulk of the European import automobile and truck market is comprised of vehicles manufactured in Germany Great Britain France Sweden and Italy As indicated previously most of the recent imported European automobiles are fitted with front semimetallic asbestos friction pads wheel There disc is a brakes strong which trend use among European automakers to use materials Table 10 lists wheel disc the European brakes along with automakers and the semimetallic percentage of their product lines that are equipped with wheel disc brakes Although the percentage of new European wheel disc brake imports is high 80 percent the total number of units imported is small compared with United States automobile production European drivers have different preferences with respect to brake performance than do American drivers In general Europeans are more tolerant of brake squeal and brake wear than are American drivers and materials judged acceptable from a standpoint of stopping performance alone may not be acceptable to the American public In addition the European safety standards are different from those in the United States but are difficult to compare directly Generally the EEC regulations allow lower levels of braking efficiency than do the United States regu- lations but they do require brake balance is front bias calculations to show that the design intent i.e. front wheels lock first The emphasis atanaend a Sha a, [ [ -- 82 TABLE 10. LIST OF 1984 MANUFACTURED AUTOMOBILES EQUIPPED WITH WHEEL DISC BRAKES REF 14 Number of Units Sold in the U.S. Percentage With Wheel Disc Brakes Germany Mercedes Volkswagen BMW Audi Porsche Great Britain Jaguar France Renault Peugeot Italy Alfa Romeo 58,017 64,405 64,525 54,590 14,708 18,044 10,277 14,792 3,399 100 100 58.6 15 100 100 0 100 100 Sweden Volvo Saab TOTAL 96,422 100 25,146 100 424,325 83 83 of front biasing makes wheel disc brakes attractive because the effectiveness of disc brakes are less affected by slight changes in friction material performance Automakers can help ensure that the brakes are front biased in spite of unforseen friction product behavior by using proportioning proportioning valves to force the front discs to handle most of the vehicle braking States Virtually all of the Japanese automobiles imported to the United are fitted with front disc brakes although some models are also equipped with wheel disc brakes Table 11 lists the percentages of Japanese vehicles equipped with wheel disc brakes In 1984 only 20 percent of the 1 million units sold in the United States were so equipped The eventual adoption of FMVSS 135 and the failure to qualify rear automotive brake drum linings exhibiting consistent levels of friction over a wide of American bias in the disc brakes range of performance conditions may affect the design philosophy and Japanese automobile engineers Forced to ensure front system automakers may eventually move to using effective on the rear axle and increasing the front braking ratio to ensure consistent system performance if proven rear drum lining materials are not found = rmac ae 1 Eee 1 1 E E 84 TABLE 11 LIST SOLD WITH OF 1984 JAPANESE AUTOMOBILES IN THE UNITED STATES EQUIPPED WHEEL DISC BRAKES REF 10 Number of Units Sold JAPAN Honda Nissan Toyota Subaru Mitsubishi Isuzu Mazda TOTAL 374,819 372,633 306,900 148,880 39,104 17,233 128,197 1,387,766 Percentage With Wheel Disc Brakes 17.9 32.7 24.9 0 0 0 20 85 6.0 SUMMARY OF INDUSTRY RESPONSES TO PROPOSED BAN 6.1 Section Summary Various concerns representing automobile manufacturers truck and equipment manufacturers friction product producers and environmental groups responded with written comments to the Environmental Protection Agency's proposal outlined in the Federal Register Table 12 lists the respondents In general respondents commented on numerous facets of the proposal but the comments most pertinent to this study were those dealing with issues of brake performance application availability and feasibility of the proposed phase schedule The comments of respondents have been categorized in the following sections with respect to the issues addressed Table 13 summarizes in a very general sense the responses of the various industries and groups to the main features of the proposed EPA ban oe 6.2 Concerns of Respondents to Issues of Brake Performance The comments of the respondents to this issue are summarized in Appendix B. The automobile and truck manufacturers were consistent in their opposition to the proposed ban on asbestos in aftermarket friction products These manufacturers contend that vehicle safety may be compromised if unproven friction products are used in place of vehicle products containing asbestos One truck manufacturer Navistar claims that brake and friction product qualification can take up to 48 months so the time and cost of qualifying materials for other aftermarket products would be prohibitive Some manufacturers question the term performance of some asbestos materials and subsequently feel that further development will be necessary before cated that friction a phase can be feasible Ford Motor Company indiproducts must be qualified under long term conditions more stringent than federal motor vehicle safety standards in order to determine the sensitivity of materials to spotting and morning sickness Rockwell International inferred that current asbestos TABLE 12 LIST OF RESPONDENTS TO FEDERAL REGISTER NOTICE REGARDING PROPOSED EPA ACTION Automobile Manufacturers Japanese Automakers Toyota Technical Center U.S.A. Inc. Subaru of America Inc. American Honda Motor Company Inc. Mitsubishi Motors Corporation Nissan Research and Development Inc. American Automakers Chrysler Corporation General Motors Corporation Ford Motor Company American Motors Corporation European Automakers Volkswagen of America Mercedes of North America Austin Rover Group Limited Inc. Trade Associations Automobile Importers of America Inc. National Automobile Dealers Association [ Motor Vehicle Manufacturers Association Environmental Lobbyists National Resources Defense Council Inc. Truck and Equipment Manufacturers Foundation Brake and Axle Manufacturers Rockwell International Truck Frame and Chassis Builders Navistar International Corporation Freightliner Corporation Farm Equipment John Deere and Company Friction Product Manufacturers OEM Compounders Bendix Corporation Abex Corporation Aftermarket Suppliers Wagner Scan Original Quality Inc. Trade Association Friction Materials Standards Inst Fiber Suppliers DuPont 87 PROSED S$0}agse $0 UMOQ JawOlL}ud RESPONDETS RaESuPONtDENTS LLEM ULYZLM MOU quausuOnd PROSED of aSPUd ueid Performance Perfomance ue,d Substiute Substiue Feasibility Availbty NV AQLseay Perfomance materials S3NQLYS Propsed Phase aftermaket Availbty Phase Down forfor materials disc 1d ueq ueg front Automobile older materials disc plan e should should brakes brakes e down Manufctres OL Truck Manufctre Product Manufctres ed = ET FT8VL ISLP wnup brakes brakes not lead aftermkt older suficently qualifeddrum BLQeyaeto down materials aftermaket for materials road aftermarket for Aj materials uo a, should on phase plan quar should be and available vehicles qualified not exmpt should avilabe lead eLuazew avilabe as sayeuq sayeuqdiysn eyewt pue yak AuewaAey | e |e e qualifcation qualification qualifcton godperformance than asbetosasbetosyduiaxa years materials be have Allied awos materials [| uo al ScanavilabePac aplicatons substitutes available jo Scan Scan - se Scan (xt subtiues ubstiutes for imediate imediate Suanzoesy Jaunzoepuy_ Cd aqowLy,n ponude, quadinb3 uIOLzIL qonpod Sn4auunzeIe maAterUiaGls szLAqo) Fh _ 1" 88 materials designated for highway heavy applications give unaccep- table performance and durability Friction product manufacturers gave mixed reports concerning product performance Bendix indicated that development work was still progressing and substitute formulations need to be evaluated using vehicle tests and dynamometer tests Scan on the other hand claimed to have products available for all no house inertia dynamometer heavy or vehicle vehicle applications although test facilities are available at Pac's facility for qualification of materials 6.3 Concern of Respondents to Issues of Friction Material Availability The comments of the respondents to this issue are summarized in Appendix asbestos C. U. S. and Japanese automobile manufacturers indicate that nonfront disc brake pads are now being used extensively on new car models Chrysler indicated that all but one vehicle manufactured by Chrysler is fitted with metallic front brake pads while General Motors acknowledged that for front disc brakes asbestos replacement materials are now available for new model cars Asbestos rear drum brake materials are still not available for automotive applications Volkswagen indicated that in model year 1987 all products will be fitted with asbestos linings while Daimler indicated that new 300 series models will be fitted with asbestos friction materials Daim- Benz did indicate that brake systems of other vehicles in their product line are undergoing lengthy and extensive redesign and requalification to be fitted with asbestos materials Since most heavy duty truck and equipment brakes use drum brakes the concerns of truck and equipment manufacturers were different from those of the automobile manufacturers Since truck life is considerably longer than automobile life aftermarket availability for older vehicles remains a strong concern Freightliner and Rockwell indicated that friction product suppliers have been unable to provide qualified for heavy highway and highway applications asbestos linings John Deere indi- 89 cated that replacement materials have not been qualified for use in tractor transmission clutches and axle brakes Friction product manufacturers gave mixed reports concerning the availability of asbestos materials for the various applications Allied Bendix indicated that they had been successful in developing asbes- Pe free products for some applications tions currently remain without qualified although many asbestos vehicle applica- materials Scan- 1 Pac all and DuPont both indicated that substitute materials applications although Scan has concentrated on are available for providing materials for aftermarket heavy vehicle applications However both Scan and DuPont lack the facilities to conduct vehicle or dynamometer tests required 1 for FMVSS certification 6.4 Concerns of Respondents to Feasibility of the Proposed Phase Schedule The comments of the respondents to this issue are summarized in Appendix D. ters voiced The automobile industry both domestic manufacturer and imporunanimous concern over the proposed timetable for asbestos phase The following were major points made by this industry 1 The years 1981 1982 and 1983 were years of severe recession in the automobile industry Therefore asbestos quotas based on asbestos usage during these years are excessively eel restrictive 2 The proposed rating is unfair to auto importers who voluntarily EE restricted imports during 1981 1982 and 1983 3 Option , which allows a five lead time to develop and qualify new asbestos materials is preferable than the proposed staggered phase effort 4 If FMVSS 135 is adopted more lead time may be required depend- E ing upon exact provisions of FMVSS Truck and equipment manufacturers 135 whose products rely upon drum brake materials were opposed to the proposed immediate reduction in allow- able asbestos in friction materials Navistar Freightliner and Wagner supported a plan in which most asbestos use was banned time Modifications of this provision would allow the after a year lead use of asbestos in 90 materials for which no replacement material was qualified John Deere requested an exemption for all materials used inside such as clutches and sealed axle brake units used on a machine housing John Deere tractors The friction product manufacturers gave mixed reports concerning the proposed alternatives phase schedule Bendix indicated that for original equipment materials will be available reliable within 5 years DuPont and Scan on the other hand indicated that acceptable substitute materials now exist Both companies lack the facilities to qualify materials and systems under Federal safety standards The National Resources Defense Council NRDC supports an immediate ban on all asbestos in friction products both new and aftermarket They contend that viable substitutes are available today pus . 91 REFERENCES 1 Newcomb T. P. and Spurr R. T. Braking of Road Vehicles Robert Bentley Inc. Cambridge Massachusetts 1969 FS 2 Starks H. J. Loss of Directional Control in Accidents Involving Commercial Vehicles 1963 Symposium on Control of Vehicles Inst Mech Engrs London 8 [ 3 Anderson A. Wear of Brake Materials from Wear Control Handbook M. B. Peterson W. A. Winer Editors ASME New York New York Preston J. D. and Forthofer R. J. Correlation of Vehicle Dyna- a mometer and Other Laboratory Tests for Brake Friction Materials SAE Paper No. 710250 Warrendale Pennsylvania Tsang P. Jacko M. and Rhee K. Comparison of Chase and Inertial Brake Dynamometer Testing of Automotive Friction Materials 1985 _ Wear of Materials Conference ASME 1985 New York Burkman A. J. and Highley F. H. Laboratory Evaluation of Brake Lining Materials Paper NO 670510 Warrendale Pennsylvania Preston J. D. Inertia Dynamometer Evaluation of Brake Lining Materials SAE Paper No. 730192 Warrendale Pennsylvania Steis D. E. Inertia Brake Dynamometer Testing Techniques for FMVSS 121 SAE Paper No. 751010 Warrendale Pennsylvania Anderson A. Ford Motor Company personal communication 10 Substitution Analysis for Asbestos Brake Linings for Road Vehicles prepared by ICF Inc. for Ms. Amy Moll Environmental ESE Protection Agency Washington D.C. 11 Data provided by A. Anderson Ford Motor Company 12 Flick M. A. Radlinski R. W. and Kirkbride R. L. The Effect of Aftermarket Linings on Braking Efficiency SAE paper 870267 February en 1987 Warrendale Pennsylvania 13 Fobian J. AAA American Automobile Association personal oe. communication } 14 Ward's Automotive Yearbook 1985 Ward's Communication's Detroit Michigan 15 Motor Vehicle Manufacturers Figures 1985 Associate MVMA Motor Vehicle Fact and 16 Automotive News 1986 Market Data Book Issue April 30 1986 1 _ 1 92 17 Aoki K. Japanese Track Brake Philosophy Worldwide Braking Trends Medium and Heavy Duty Trucks SAE 1984 Warrendale Pennsylvania 18 Thoms E. European Brake Philosophy Worldwide Braking Trends Medium and Heavy Duty Trucks SAE 1984 Warrendale Pennsylvania 19 RothVegel K. and Denzler U. European Brake Philosophies for Commercial Vehicles in the Range From 6 to 16 Tons FVS Worldwide Braking Trends Medium and Heavy Duty Trucks SAE 1984 Warrendale Pennsylvania res) pee i [ APPENDIX A Vehicle and Dynamometer Test Procedures for Qualifying Friction Materials and Brake Systems Under FMVSS 105 and FMVSS 121 eae Ri A TABLE A SUMMARY OF TEST PROCEDURES FOR FMVSS 105 Cm No. Sequence ra 1 Instrumentation Check | [ee 2 First preburnish Effectiveness test om, 3 Burnish brake linings at GVWR epmen) 1 4 Second effectiveness Rivne test 5 First reburnish Procedure Stopping Distance Per Vehicle Group ft A B C D Check instrumentation by making not more than 10 stops from 30 mph at a deceleration of not more than 10 sec Make 6 stops from 30 mph then make 6 stops from 60 mph 57 65 69 88 216 242 0 = 267 = 388 Procedure of 10,000 1 lbs Vehicles or less with GVWR Make 200 stops from 40 mph at a deceleration rate of 12 sec Use approximately 1 mile rest interval in between brake applications Procedure 2 Vehicles with GVWR of over 10,000 lbs Make 500 snubs at 10 sec maintain brake temperatures less than 500 F Make 6 stops from 30 mph then make 6 stops from 60 mph then make 4 stops from 80 mph GVWR > 10,000 lbs 54 204 57 57 216 = 194 81 388 Make 35 stops from 40 mph at a deceleration rate of 12 sec 6 Test parking brake Measure force required to actuate hand brake lever Position vehicle on incline and observe position ability Note Unless otherwise specified brakes on hottest axle are between 150-200 F at start of test stops 2 TABLE - SUMMARY OF TEST PROCEDURES FOR FMVSS 105 Continued No. Sequence FE 7 Third effectiveness test Gi 8 Partial failure a. ore Procedure Empty and loaded conditions evaluated under 20 percent and light trucks and vehicles over 10,000 lbs and 30 percent grades passenger cars Make 6 stops from 60 mph under lightly conditions Under lightly conditions disable either the front brakes or rear brakes Make 4 stops from 60 mph Restore disabled half disable 2nd half repeat Repeat procedure at GVWR stops for vehicles Stopping Distance Per Vehicle Group ft A B C 0 194 216 242 =388 456 517 517 613 9 Inoperative brake power and power assist units Disable power assist Make 4 stops from 60 at GVWR only mph variable requirements 10 First fade and recovery at GVWR 1 yr Procedure 1 - Vehicles With GVWR 10,000 or Less baseline fade recovery Make 3 stops from 30 mph at 10 sec sec deceleration and measure control force readings Make 5 stops from 60 mph at 15 sec sec deceleration followed by 5 stops stops at maximum attainable deceleration between 5 sec and 15 sec at 0.4 mile intervals Drive 1 mile at 30 mph to prepare for recovery tests Make 5 stops from 30 mph at 10 sec sec deceleartion at 1 mile intervals Note Unless otherwise specified brakes on hottest axle are between 150-200 F at start of test stops A TABLE 1 SUMMARY OF TEST PROCEDURES FOR FMVSS 105 Continued No. Sequence Procedure Stopping Distance Per Vehicle Group ft A B C D Procedure 2 Vehicle With GVWR of More Than 10,000 Lbs FS While in neutral make 3 snubs baseline from 40 mph to 20 mph at 10 sec sec deceleration a fade While in neutral make 10 snubs from 40 to 20 mph at 10 sec sec deceleration at 30 second intervals =a Drive 1.5 miles at 40 mph to prepare for recovery tests recovery While in neutral make 5 snubs from 40 mph to 20 mph at 1.5 mile _ intervals 11 Second reburnish Make 35 stops from 40 mph at a deceleration rate of 12 sec -- -- -- 12 Second fade and recovery at GVWR Repeat procedure for first fade and recovery except increase fade stops to 15 for vehicles < 10,000 lbs GVWR and to 20 for vehicles > 10,000 GVWR 13 Third reburnish ee =e 14 Fourth effectiveness test at GVWR _- Make 35 stops from 40 mph at a deceleration rate of 12 sec Make 6 stops from 30 mph then make 6 stops from 60 mph Make 4 stops from 80 mph vehicles with GVWR < 10,000 lbs Make 4 stops from 95 or 100 mph passenger cars only i -- -- 57 216 65 242 65 267 88 388 Note Unless otherwise specified brakes on hottest axle are between 150-200 F at start of test stops 4 SUMMARY OF TEST PROCEDURES FOR FMVSS 105 Continued No. OR Sequence 15 Water recovery | at GVWR _&x= 16 Spike stops at GVWR Procedure Make 3 stops from 30 mph at 10 sec deceleration Drive at 5 mph for 2 minutes through a inch deep water trough Leave water trough accelerate to 30 mph Make 5 stops from 30 mph at a deceleration of 10 sec Make 10 successive stops from 30 mph using a control force of 200 lbs applied in not more than 0.08 sec Make 6 stops from 60 mph Stopping Distance Per Vehicle Group ft A B C D 216 242 267 = 388 Vehicle Group Description A - passenger cars C - vehicles with 8000 < 10,000 B - passenger cars with GVWR of less than 8000 lbs D - vehicles with GVWR > 10,000 school buses over 10,000 lbs must meet all requirements All other vehicles over 10 K have to meet partial failure 8 and inoperative brake 9 requirements only Note Unless otherwise specified brakes on hottest axle are between 150-200 F at start of test stops eees eT nya A rs _rPh TABLE 2 SUMMARY OF ROAD TEST all vehicles except PROCEDURES FOR FMVSS 121 school buses are 1 exempt from these requirements 1 4 enma Sequence Procedure Burnish brake linings Road tests > effectiveness e Make 500 brake applications at 10 ft deceleration 1 mile intervals or 500 F brake temperatures Readjust brakes if necessary Under GVWR and unloaded make following stops From 20 From 60 From 20 brakes mph mph mph with with with service brakes service brakes emergency e From 60 mph with emergency brakes These stops to be conducted on dry and wet pavement A 1 [ === TABLE A SUMMARY OF DYNAMOMETER TEST PROCEDURES FOR FMVSS 121 tractors trucks buses trailers _ Sequence Procedure Evaluation Criteria Burnish brake linings all vehicles Brake effectiveness retardation factor trailers only Fade and recovery all vehicles Make 200 stops from 40 mph at 10 sec e Make 200 additional stops from 40 mph at 10 sec e Make 7 consecutive stops from 50 mph with increasing brake air chamber pressure e Decelerate from 50 mph to 15 mph at 9 sec at 72 second intervals deceleration rate repeat 10 times e Hot stop from 20 mph at 14 sec e Make 20 consecutive stops from 30 mph at 12 sec deceleration rate at 60 second intervals Brake temperatures T 315 F < T < 385 F Brake temperatures T 450 < T550 T550 T550 e Calculated brake retardation force force at each air chamber pressure e Service air pressure must be below 100 psi e No pressure limit e Service air pressure must be below 85 psi and above 20 psi PS. [ [ APPENDIX B CONCERNS OF RESPONDENTS TO ISSUES OF BRAKE PERFORMANCE 1 b B Automobile Manufacturers Mitsubishi Replacement parts should be exempt Must evaluate and consider - Adoption of larger brake booster - Increase of pad area - Adoption of ventilated disc brakes - Adoption of larger brakes e FMVSS 135 proposed by NHTSA is considered to be more stringent than FMVSS 105 Judder is currently a problem for clutches Chrysler Aftermarket materials for older vehicles should be exempt for safety reasons General Motors Aftermarket is serious concern for safety reasons Therefore aftermarket for older vehicles should be exempt Essential that EPA collaborate with NHTSA on this rulemaking Considering safety we are obligated to continue production of parts for servicing vehicles throughout their useful life Example of System Changes That Might Occur with a Lining Change Assume that a replacement lining has 20 percent less friction than the original A larger wheel cylinder would be specified to achieve the required torque output A larger wheel cylinder results in more fluid displacement and may require a master cylinder change to obtain the proper pedal travel Larger master cylinder may make pedal effort too high necessitating a booster change Testing of the vehicle may indicate insufficient parking brake capability due to the reduced friction necessitating a park brake cable change Increased cable forces may result in parking brake strut buckling during abuse tests necessitating a foundation brake redesign Nar parte 1 auew ot, | F- Mercedes Exemption indispensible for replacement parts FMVSS is in the process of being reconsidered by NHTSA impact may cause further delays A safe braking system is a well balanced design Influencing one of its parameters alone e.g. by replacing asbestos in friction materials necessitates reconsideration of the complete system Immediate availability of substitutes is not given for all applications Ford Complex - issues must be researched including Thermomechanical stability spotting and banding Brake fluid displacement Fluid boil metallic and metallic linings Morning sickness effects due to moisture Different friction levels Exemption for parts replacement for older vehicles Austin Group Unrealistic lead times Friction materials have a major effect on safety Exempt replacement parts for vehicles produced before rule goes into effect Toyota e Oppose applying rule to replacement parts for earlier models National Automobile Dealers Association Shouldn't rush brake development work OSHA standards cover danger to maintenance people AMC FMVSS more stringent braking requires are currently under study 3 Motor Vehicles Manufacturers Association The safety and effectiveness of motor vehicle braking will be reduced e The cost in terms of deaths and dollars from motor vehicle braking losses should be included with the potential impact assessment e Problems with new friction materials - Rotor scoring - Noise - Lining cracks - Absence of consistent and reliable braking performance data e Safety must not be compromised Truck and Equipment Manufacturers Wagner CAFE requirements - Resulted in significant redesign of vehicle and brakes - But current vehicle population of CAFE must be operated safely There are presently no data on brake performance from actual vehicle tests using - metallic disk brake friction materials - New substitutes Safety - health effects do not consider the safety related risks associated with possible inferior braking performance e No or little available test data Navistar e Need both fleet tests and dynamometer tests to qualify friction mate- rials - Dynamometer tests run per FMVSS Fleet tests run per IH Fleet Test Phase Qualification takes about 48 months Freightliner Technical problems to be can be used universally calculated further before asbestos linings Wear rate - At extremely high temperature 4 Speed sensitivity - Generally less sensitivity at low speeds than at high speeds Static friction characteristics - Much lower and can create difficulty in complying with Federal MVSS for parking Durability - Some are more susceptible to cracking and crumbling Low speed noise and chatter Heat Conduction and corrosion resistance - needs further evaluation Rockwell International Brake tests used to qualify materials Our internal test requirements Requirements of our brake customers FMVSS - highway air SAE 1152 - highway vehicle SAE 1473 - highway vehicle Specific industry standards for - Agriculture - Rail - Military specifications highway heavy duty applications e. Unacceptable durability and performance problems Higher friction requirements for highway vehicles Several asbestos lining characteristics require more development including - Low unburnished performance - Low burnish performance - Greater speed sensitivity at speeds 30mph Changes in FMVSS's can have a monumental to new brake lining materials impact when attempting conversion John Deere Agricultural industrial and garden tractors have much longer lives than traditional consumer products Therefore service is demanded for several decades Major concerns are - Identical friction coefficient fixed design - High safety risks risk concept - Low replacement part volume - Sizeable inventory of old agricultural tractors routinely provide service parts for machines build 20 to 35 years ago 5 Friction Product Manufacturers Bendix Bendix Direct substitution of new materials for asbestos fibers resulted in - Poor friction levels - Friction instability - Increased noise - Front vehicle brake imbalance Substitute formulations need to be evaluated ~ Vehicle tests J843d - Inertia dynamometer tests using Scan Industrial friction products - for asbestos friction products performance is the same as or better than asbestos friction products Now use SAE J661a to evaluate materials - Coefficient of friction versus - Wear test at 900 F 1 1 L E E E APPENDIX C CONCERNS OF RESPONDENTS TO ISSUES OF FRICTION MATERIAL AVAILABILITY 1 1 i - Automobile Manufacturers General Motors OK for front disc brakes replacements available No substitute for rear drum brakes . Especially difficult problem for heavy trucks Chrysler Currently all metallic front containing but one vehicle that Chrysler manufactures has semidisc brake pads However even these require an asbesunderlayer material for cushioning affect Brake design criteria - FMVSS - Lining life of 50,000 - Noise free operation miles - Controlled laboratory tests narrow field of candidates - Field tests Forcing the use vehicle safety of asbestos materials will compromise motor Mitsubishi Replacement parts should be exempt change of related parts New materials may require a design No substitute as yet for rear drum brake linings Honda Should address any vehicle manufactured after the effective date applicable to replacement parts Not Retrofitting would require replacing other parts and is not effective and reduces safety Volkswagen Will have beginning asbestos in 1987 model brake year linings across its entire product line Mercedes Rear brake pads and parking brake linings are asbestos free on all Mercedes passenger cars 2 New series are currently equipped with asbestos brake pads on all wheels Currently have asbestos clutch linings on all cars The other asbestos containing systems would have to be redesigned so as to accommodate asbestos friction materials This process of redesigning and testing is extremely time consuming and has not yet led to results that satisfy our criteria The problems encountered are basically the following The brake factor level as compared to customarily approved linings is either too high or too low The brake factor scatters a permissible range a function of miles travelled speed and temperature Hi wear of pads and discs Insufficient mechanical strength High thermal conductivity Low corrosion resistance These problems are less significant for rear brakes because the requirements regarding rear brakes are different from those for front brakes Ford No practical substitutes for - servo car and light truck drum brake linings - Engine manifold gaskets Motor vehicle safety must not be compromised Even a slight increase in traffic fatalities would eliminate any benefits erin American Motors Corporation Allow the use of asbestos in replacement parts for existing vehicles E Wagner Truck and Equipment Manufacturers d Considerably more progress made in manufacturing asbestos pads for disc brakes than for strip linings for drum brakes Some manufacturers of strip friction for drum brakes who restrict sale of asbestos material to OEM customer No aftermarket sales Drum brakes have changed to self energizing need higher coeffi- | LEl oc E - Bendix Bendix Bendix has in fact been successful in developing asbestos products for select applications but not all applications Aftermarket is of most concern Automobile front disc brakes is a very severe application for front wheel drive cars Rear disc brakes - may be able to use a effective asbestos organic disc pad asbestos organic drum brake linings first installed on US 1984 light trucks and then on 1986 passenger cars Some of this technology has recently been transferred to use on medium size trucks Friction Materials Standards Institute metallic disc brake pads are now on front brakes of passenger cars and light trucks most have them Aircraft brakes are asbestos asbestos developed for - Clutch facings in _7 Passenger cars heavy duty area The industry is working - Light medium - trailer on substitutes for and heavy truck drum blocks segments Scan Manufacture asbestos friction materials for industrial application asbestos products since 1977 - Lawn and garden tractors Snowmobiles Snow throwers Industrial clutches Electric brakes winches Asbestos products perform as well than asbestos products as and in most cases better Federal Express fleet of 390 IVECO vans have shown good results last 4x as long 4 25 vehicles - Heavy duty truck fleet 18 wheels better performance than asbestos lining 60 percent longer life School bus transit buses DuPont Viable - substitutes in friction products are currently available Automotive disk and drum brake linings Truck brake blocks Industrial brakes reinforced with aramid and other fibers 75 percent of new cars have asbestos brake linings Clutch manual transmission in use in Europe asbestos; Automatic transmission in use in U.S. DuPont believes substitutes are available for gaskets also Environmental Lobbyists National Resources Defense Council metallic disk brakes are in - In U.S. GM - In Europe Saab Volvo use and Jaguar DuPont - aramid products In Sweden is it illegal free brake is certified facturer of free brakes to replace brakes on vehicles if an asbestos- as satisfactory by the brake or vehicle manunew cars sold in Sweden are equipped with asbes- Nissan Need longer lead time - Light vehicle front brakes -- at least 5 years Light vehicle rear brakes -- at least 6 years Light trucks -- impossible to say Clutch linings -- at least 6 years Rule should not apply to replacement parts Rule should only apply to major vehicles redesigned as new models are introduced EPA should devise a flexible exemption procedure Chrysler Believe they can comply with time table of Alternative 2 except for trucks Truck brakes will be asbestos at end of year period specified in Alternative 2 EPA should publish guidelines for exemptions Exempt aftermarket Proposed schedule Product Category Time Construction products clothing 2 years Passenger car brakes all transmission ee applications 7 years way All other cases in motor vehicles 12 years Modification of Alternative 2 represents most practical approach General Motors Brake testing process can require up to 5 years Exempt aftermarket replacement for older vehicles In 1979 GM made goal to eliminate asbestos from brakes by 1985 - Largely met on front disc brakes - Not met on rear drum brakes due to - squeal - wear - friction stability 70 percent reduction is too severe after first year 3 e Recommend that a ban not take effect until after a period 10 years and that the EPA permanently exempt aftermarket brake linings Volkswagen e Beginning in 1987 model year no asbestos brake linings on VW E Proposes Fixed Time Limits for new vehicles E Product Clutch FTL 4 years Transmission 4 years [ Gaskets Front disc brake pads 4 years light duty 4 years 1 Rear drum brake lining light duty 6 years Medium and heavy duty brakes 10 years Exemption allowed if asbestos substitutes not available No permits needed Exempt replacement parts Mercedes e Ban only after 5 years Including possibility of exceptions - Indispensible with respect to replacement parts e Gaskets particularly cylinder head gaskets may need even longer lead time Alternative 1 is preferable over Alternative 2 e If FMVSS is revised this might result in further delays Introduce changes during model redesign Ford supports reasonable fixed time table for removal of asbestos pro- ducts coupled with a procedure for exempting where no reasonable alter- natives exist e Exemption for parts replacement Austin Anticipates lead time of 5 years to remove asbestos from its vehicles 4 Unrealistic lead times Alternatives 1 or 2 would be more equitable Exempt spare parts for earlier models we Toyota Opposed to applying rule for replacement parts to earlier models FT Against proposed phase over 10 years Prefer staged ban - Friction products year lead time - Gaskets year lead time 1- Insulators year lead time National Automobile Dealers Association EPA should consider a simple streamlined model ban on new vehicle parts Avoid regulating replacement parts EPA should consider - Ban beginning in a given model year for new vehicles - No regulation of replacement parts EPA and manufacturer should determine year of ban on different products American Motors Corporation Recommends hem - More realistic timetable o- - develop guidelines for exemption e EPA should ban asbestos use in specific products such as disc brakes rather than a product category such as friction material Develop guidelines for exemptions Lead time needs can only be adequately addressed under a specific regulation This is major reason AMC opposes the phase scheme proposed by EPA Motor Vehicles Manufacturers Association 11 Schedule for implementation must be contingent upon the availability of suitable substitute materials so that safety and braking performance are not compromised Lead times proposed are unrealistic MVMA supports an exemption process for essential uses without substitutes - MVMA supports an exemption process for essential uses without substi- tutes EPA should propose exemption procedure ee Exemptions for aftermarket required MVMA requests that EPA allow at least two full years between promulgation and the effective date of any regulatory action [ Individual member companies will provide additional comments on this matter of timing Truck and Equipment Manufacturers 1 Wagner Phase proposed in Option 3 10 year period represents too great a highway safety risk Brake strip friction material must be exempted from Option 3 and 5 year options 1 and 2 Recommend EPA establish mechanism for exemption procedure Request 1 an exemption on drum brake strip lining and 2 extension of year ban option for disc brake pads used on older vehicles Navistar 3-1 to 4 years any product lead time to develop and incorporate new material into year not enough lead time for brake linings Exemption required for replacement parts Navistar supports Alternative 1 5 years if certain modifications are made III T I T T T T ET II T - e Alternative 2 - comments same as for Alternative 1 fi Recommends - Lead time of 5 years plus 5 year phase Freightliner e Oppose EPA's primary proposal to immediately begin to phase out asbestos as impractical and practically impossible Support EPA's alternate proposal number 1 which provides 5 years before asbestos friction products would be banned Requests EPA proceed with Alternative 1. Allows friction materials to remain on the market for 5 adequate time for all commercial vehicle applications Rockwell Proposed schedule for phase - Within a reasonable period asbestos will replace asbestos po in most of the heavy duty or highway truck and trailer market - Definitive time constraints cannot be expected to phase out or ban asbestos linings for heavy highway vehicles with severe brake requirements and a few very heavy duty on- highway truck applications until higher friction asbestos qualification materials are developed John Deere A first reduction of 70 percent is too fast to reallocate asbestos for critical remaining uses - Most reductions contemplated by the regulations took place during the base years - Life cycle tests require 6 months of lab tests plus 2 years of field tests The regulation does not consider the necessity of providing quality service parts for repair of existing machinery e Recommendation - Exemptions be provided for asbestos used inside a machine housing - 70 percent reduction be changed as follows for new parts T Year 1 2 3 10 Percent 40 50 70 100 - Replacement parts over long period of time 7 Friction Parts Manufacturers DuPont Europe is ahead of U.S. in conversion of disc brake and manual clutches to substitutes / Viable substitutes are currently available for any application in friction products and gaskets - Substitutes are technically equivalent or superior - Initial cost is generally higher but this is offset by increased value in use Allied Believe safe reliable alternatives will be developed for all original equipment friction materials within 5 years of the effective date of regulation 10 years for aftermarket New model vehicles is best time to introduce these products Friction Materials Standards Institute Need time to develop and test satisfactory products Particular problem for aftermarket Highway safety in paramount An immediate ban cannot be supported because of the importance of safe braking systems on the nation's highway Original Quality Will take many years to develop a racing substitute at temperatures between 350 C and 1000 C. 5 to 10 years or even longer for current racing disc brake pads e We favor a disc pad ban in 10 years Scan Pac They already have acceptable material for industrial and automotive light through heavy trucks buses road construction farms etc. 8 Environmental Lobbyists National Resources Defense Council Ban on the use of asbestos in the brakes of all new cars and trucks and in all replacement brakes in existing motorized vehicles Replacements are available today 17