Document 1QZdzrMBK04J9GNgeDna5ygEj

Bottossd tpusd prcpe'tionol to angina spisd Spsad-droop ttrtr,..^ jL r-Spoad-dtooptsrSf Spaodar Spring X-Spssd'Oroopttrsr Spsadar rod- 1^,'Pomtr piston yControtport* tint Fust to tngios Fast control I f uotua 1 Simple combination of 0 boll hood and a direct-connected A Speed-drooo lever U uaeri m pilot Volvo ho. but on. oquillbhum poiltloo, I. unilobln * d,oop lo .loblll.e the octlon -Pw hyd^TTM '<*, ..... \1DIESEL GOVERNORS--III | How Hydraulic Governors Give Betti , .'TM, rP toL. Apr,,ovld. p.rmonIkn. ,!p~fitdteddrwoiothp A' lAodcdtiolnocInMo...simPpilloet hvyodlr,,aumlico.s.p.adedo-d..r,oolpocgoov.e.r.noIru.dl ufrlionwg MB- liitrol for Modern Diesel Engines Using pressurized oil on a power piston in creases power available to actuate engine's fuel valve, gives closer control of speed, per mits adjustment of unit's speed droop. Heve ore your basic facts on this type of governor By EDGAR J KATES, Consulting Cnginsor, Nut York, M. Y. Last montu wo uv that meehani.cal governors have certain disadvantages that may preclude their use (or some services. Poor sensitivity, small power output unless governor Is excessively Urge, and unavoidable speed droop are Included in these disadvantages Of course they are unimportant in some applications. But for engines needing more sensitive control, greater power for movement of fuel-control mecha nism, or identical speed (or all loads, hydraulic governors often prove better. Let's see why this is so. Hydraulic governor* have more parts and are more expensive than mechani cal types but they have these advan tages: They (1) are more sensitive (2) have greeter power to move en gine's fuel-control mechanism (3) can be made Isochronous (identical speed for all loads). In these governors the power that moves engine throttle does nor come from the speed-measuring device. In stead, It comes from a hydraulic power piston, or servomotor. This is a piston acted on by a fluid under pressure, gen erally oil pressurized by o pump. By using an appropriate piston size end oil pressure tho power output at the governor's output shaft (work capac ity) can be made sufficient to operate promptly the fuel-changing mechanism of the largest engines. Spaed-measuring device, through its speeder rod, is attached to * small cy lindrical valve, called the pilot valve. This valve slides up and dova to? bushing containing pons, which e--*^ oil flow to and from the servoBkotsf?! Force needed to slide the pilot extremely small and a small bill budl is able to control i large aatocst^j] power st the servomotor. - -juiff Elementary hydraulic governor, Rg 1, has the land (raised portion) pf-lbl pilot valve equal in width to ibe'porw When governor operates ot control] speed the land closes port, shuttlngd. oil flow, If governor speed falls, because eltcfl crease of engine load, the flyweigiifl move in and lire pilot valve moves dojoj This opens the port to the power phuT end connects it to a supply ol oil ofli*2 pressure. The oil nets on the power w ton, forcing it up to increase the'f^j flow. [f governor speed rises, becatnenj*,j decrease of engine load, the flyweights move out and pilot valve moves up- TjuJ opens port from power piston to a drib leading to the sump. Spring sb#| power piston force* piston down to oj crease fuel supply to engine. *3? Note that port stays closed only;*.*, one certain speed, end that throlds 4?; he in any position from full losd to "ft! load at this speed. Ideally. the engine should run at exaetly $51 same speed at any load and the l0,.e5g nor woutd be called Isochronous. Unfortunately, a simple hydrss^.^j INOINEfllNO AND MANAGEMENT SECTION jnalst liko this has a serious defect, jnrStug iu practical use. It is injjgfeimstable. That is, it moves j82uilly, making unnecessary cor* Sm^tioas. In other words, It hunts. SuM^whst causes this. witting is caused by the unavoidable tBffig'bctween tho moment the govsrSSrfrui and the moment the engine reads' Engine cannot instantly come Bjifyu^lhe speed colled for by the ggind speed is below governor ____ [rioted, pilot valve is moving WwTpjston to increase fuel supply. Qfctime engine speed rises to control SnHwith pilot valve centered and gwojof power piston stopped, fuel tn&hu already keen increased too Sjjh^Eagine speed, therefore, confees.to rise. This overspeeding opens ^Wt valve the other woy to decreaso ^ftipply, But by the lime engine 5<d!fs11a to the right value, the fuel EJtwhsi again traveled too far. Ensjjhltn undertpeeds and the whole Iwjepests indefinitely. Some means agthflhing governor must be added |5Sg<ie satisfactory operation. Orp. To obtoln stability, W/hydrsulic governors employ the gppk of speed droop. It gives stav&heeauje engine throttle can take position for any one speed, load change causes a speed && resulting governor action ceases st the point that gives the amount of fuel needed for the new load. In this way, speed droop prevents unnecessary governor movement end over-correction of fuel supply (hunting) : .Note, however, that to -prevent hunt ing the speed droop must be enough to take care of the unavoidable delay while the engine is responding to governor action. U droop is insufficient, some hunting still occurs while engine is re turning to its steady speed after the first momentary speed change. Hydraulic governors may be built with cither permanent or temporary speed droop, depending on their appli cation. Governors with permanent speed droop are not isochronous. Permanent spaed droop can be ob tained in several ways. One of these. Fig. 2, is to connect a lever between the power piston and speeder spring so speed setting is decreased as fuel sup ply is Increased. Reducing speeder spring force lowers engine speed; in creasing spring force raises engine speed, Powcn, Mar, p 73. Speed-droop lever. Fig. 2, performs this function in (his governor. Let's trace action of a hydraulic gov ernor with permanent speed droop, Fig. 3. In It a simple pilot-valve plunger, attached to the end of the speeder rod, slides In e hushing having drilled con trol ports. Oil lines from these ports connect to both sides of a power piston ENGINEERING AND MANAGEMENT SECTION on the fuel-control rod. Valve poila ere just closed when the ball arms are Jo a vertical position with engine running at desired speed and load.. Load Increase. When load is applied to engino its speed decreases. As speed lalU, bell arms move in. Fig. 4, lowering pilot-valve plunger. This opens the porta, allowing oil under pressure to flow through the lower port to under side of power piston to force it op end increase fuel supply. Oil on top of pis ton flows out of upper port and escapes from top of bushtng to a sump. As power piston moves up, It pushes speed-droop lever up, reduoing speeder spring force. Reduced force allows ball arms to move out, raising the pilotvalve plunger end slewing the further upward movement of power piston. When ball arms reach the vertical posi tion, control ports are closed and power piston stops moving upward. Since speeder-spring force is reduced as fuel or load increases, a balance is reached with feu flyweight force, that is, with lower engine speed. Reduction of engine steady speed caused by load increase is the speed droop. Note that speed-droop lever prevents over-correc tion of fuel (hunting) by stopping power-piston corrective movement be fore the engine returns to Its previous running speed. load Decrease. As load drops, engine speed rises. Governor bell arms move