Document KJaDgkdYKJyVdMvK7aXa12Lj0

FINAL REPORT 77'' '' /tfr f ik ^v/ ^ O', Chr*~l on OF THE FEASIBILITY OF REPLACING IN AUTOMOBILE AND TRUCK BRAKES Prepared for the Environmental Protection Agency April 15, 1987 by The American Society of Mechanical Engineers HWBUI0013411 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 per formance, and future trends in the development of asbestos-free friction products. Panel Members Panel Chairman Dr. L. S. (Skip) Fletcher Associate Director Texas Engrg. Experiment Station The Texas AiM.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.0. Box 2053 Dearborn, MI 48121-2053 Mr. Robert Nelson Manager, Technical Service ABEX Corporation 3001 West Big Beaver Rd/Suite 710 Troy, HI 48084 Mr. John Fobian Director, Automotive Engineering American Automobile Association 8111 Gatehouse Road Falls Church, VA 22047 Dr. Serge Gratch 32475 Bingham Road Birmingham, MI 48018 Mr. Jerry McCullough Head, Development Section Lyndon B. Johnson Space Center Houston, TX 77058 Dr. Michael J. Rabins Assoc. Dean-Graduate Engrg. Programs Wayne State University 731 Science Library Detroit, MI 48202 Mr. Richard Radlinski Vehicle Stability & Control Branch Nat'l Hwy Traffic Safety Admin. P.0. Box 37 East Liberty, OH 43319 Dr. Ernest Rabinowicz Prof, of Mechanical Engrg. Mass. Institute of Technology Cambridge, MA 02139 Draft Report Prepared by: Mr. Scott Barber Mr. Jeff Hadden Mr. Josep Hoess Mr. Keith Dufrane Mr. Jerry Francis Battelle Columbus Division 505 King Avenue Columbus, Ohio 43201 HWBUI0013412 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 10-year phase-down period. Since asbestos is currently a critical constituent in some vehicle friction products, the Environmental Protection Agency is interested in determining whether the 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 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-ou 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: (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 and brake system performance. Generally, vehicle front-to-rear braking ratios are adjusted on a per-model basis to provide optimal braking. Too much braking on an axle results in premature wheel lock-up, and this can lead to loss of steering control (front lock-up) or spin- * Information supporting this conclusion is presented in Chapter 2 of this report. 2 out (rear lock-up). While the effectiveness of disc brakes is directly proportional to pad-disc friction levels, the effectiveness of drum brakes can be greatly affected by changes in lining-drum 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 effective ness. 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-top tests are available to evaluate the performance characteristics of friction materials or to demonstrate their compliance with Kotor 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 per-model basis. To test compliance with these requirements, vehicle manufacturers submit braking systems and friction products to numerous levels of qualification tests. Results obtained using scaled-down laboratory apparatus, such as friction material testing machines (FMTM) or friction assessment screening test (FAST) machines, have been shown to correlate poorly with vehicle test results. The per formance of aftermarket friction materials is not regulated by law. Information supporting this conclusion is presented in Chapter 3 of this report. HWBUI0013414 (3) Qualified, non-asbestos friction materials are not yet available for all current applications*. Non-asbestos friction material technology is advancing rapidly. Several new asbestos-free 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 non-asbestos friction materials for the 1988 model year. Original equipment vehicle manufacturers in the United States and Europe are rapidly moving toward asbestos-free brake systems for all new cars, light trucks, and heavy trucks. Adequate non-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 non-asbestos frictional systems by 1991, and most light trucks and heavy trucks with S-cam brakes, by 1992. However, a few low-volume new vehicle applications may not have acceptable non-asbestos friction materials at that time. Heavy truck wedge brake blocks, medium truck drum brake linings .and many off-road vehicle brake linings may not be developed by 1992. New classes of non-asbestos friction materials have unique compo sitions which may have unexpected failure mechanisms. In many cases, unique failure modes are revealed only through extensive vehicle testing. (4) The substitution of unqualified non-asbestos friction materials in the aftermarket poses the largest potential safety issue**. 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 4 asbestos material suppliers lack the facilities to evaluate their materials under dynamometer and vehicle braking test conditions. Non-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 manufacturing processes. Mandating aftermarket non-asbestos friction materials for vehicles that were originally equipped with asbestos-based 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, 4-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, non-asbestos drum brake materials for automobile drum brakes have been difficult to qualify in the past. For these reasons, several European automakers use 4-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, American and Japanese automakers are utilizing rear drum brakes.' Suitable non-asbestos materials are not available for all of these applications, and industry-wide substitution of non-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 HWBUI0013416 5 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-to-rear braking ratio to ensure consistent performance, if proven rear lining materials are not found. (6) Industry gave mixed response to the proposed EPA action*. Numerous automobile, truck, and friction material manufacturers 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 asbestos-free materials, they were unanimous in their opposition to a proposed phase-down schedule in which the amount of allowable asbestos would be phased out over a 10-year period. Instead, they favored a 5-year lead time prior to any ban. In addition, they were unanimously opposed to banning asbestos-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 substitutes were produced by their company, although no FMVSS 105 or FMVSS 121 qualification capabilities existed at their facility. Recommended Future Work 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 non-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. HWBUI0013417 6 of unqualified non-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 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, it would be useful to determine how many passenger cars in the 3000-3500 lb weight range are fitted with duo-servo drum brake and how many utilize leading-trailing drum brakes. In addition, the population of vehicles having 4-wheel drum-brakes as opposed to rear wheel drum-front wheel disc brakes could be determined. Thus, vehicle populations would be assessed with respect to weight range, brake design, and front-to-rear braking balance. This information would help the EPA to determine where the quali fication of non-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 duo-servo rear drum brakes and front disc brakes, and are within the 3300-3800 lbs weight range, then the requalification of non-asbestos materials for these vehicles would have the greatest impact on asbestos elimination. Task 2. Conduct Dynamometer and Vehicle Qualification Tests on Non-Asbestos Materials Using Representative Vehicles The purpose of this task would be to determine whether current non-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 HWBUI0013418 7 to represent the majority of vehicles now in service. In this way, the study could be conducted in a more cost-effective manner. This experimental study would use dynamometer and vehicle tests to determine friction product effectiveness under vehicle service condi tions. The ability of brake systems and friction materials to satisfy Federal motor vehicle safety standards would also be assessed. This second task would determine (I) whether safe effective substitute materials are available for some aftermarket applications and (2) what range of effectiveness currently exists among suppliers of after market non-asbestos materials. i {? { HWBUI0013419