Figure 13-2.-Exploded and cross-sectional views of a plate clutch.or power takeoff units. These units may be used to(disc). The driver of the automobile controls theoperate accessory attachments. The propeller shafts andclutch assemblies of these power trains are very muchlike those used to drive the wheels.THE CLUTCHThe clutch is placed in the power train of motorizedequipment for two purposes:First, it provides a means of disconnecting thepower of the engine from the driving wheels andaccessory equipment. When you disengage the clutch,the engine can run without driving the vehicle oroperating the accessories.Second, when you start the vehicle, the clutchallows the engine to take up the load of driving thevehicle or accessories gradually and without shock.Clutches are located in the power train between thesource of power and the operating unit. Usually, they areplaced between the engine and the transmissionassembly, as shown in figure 13-1.Clutches generally transmit power from theclutch-driving member to the driven member byfriction. Strong springs within the plate clutch (fig. 13-2)gradually bring the driving member (plate), secured tothe engine flywheel, in contact with the driven memberpressure of the springs through use of the clutch. If thedriver only applies light pressure, little friction takesplace between the two members, which permits theclutch to slip. As the driver increases pressure, frictionalso increases and less slippage occurs. When thedriver’s foot releases pressure from the clutch pedal andapplies full spring pressure, the driving plate and drivendisc move at the same speed. All slipping then stopsbecause of the direct connection between the drivingand driven shafts.In most clutches, a direct mechanical linkage existsbetween the clutch pedal and the clutch release yokelever. Many late model vehicles and some larger unitsthat require greater pressure to release the spring use ahydraulic clutch release system. A master cylinder (fig.13-3), similar to the brake master cylinder, attaches tothe clutch pedal. A cylinder, similar to a single-actingbrake wheel cylinder, connects to the master cylinder byflexible pressure hose or metal tubing (fig. 13-3). Theslave cylinder connects to the clutch release yoke lever.Movement of the clutch pedal actuates the clutch mastercylinder. Hydraulic pressure transfers this movement tothe slave cylinder, which, in turn, actuates the clutchrelease yoke lever.We use various types of clutches. Most passengercars and light trucks use the previously mentioned plate13-2
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