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THE CLUTCH The clutch is placed in the power train of motorized equipment for two purposes: First, it provides a means of disconnecting the power of the engine from the driving wheels and accessory equipment. When you disengage the clutch, the engine can run without driving the vehicle or operating the accessories. Second, when you start the vehicle, the clutch allows the engine to take up the load of driving the vehicle or accessories gradually and without shock. Clutches are located in the power train between the source of power and the operating unit. Usually, they are placed between the engine and the transmission assembly, as shown in figure 13-1. Clutches generally transmit power from the clutch-driving member to the driven member by friction. Strong springs within the plate clutch (fig. 13-2) gradually bring the driving member (plate), secured to the engine flywheel, in contact with the driven member (disc). The driver of the automobile controls the pressure of the springs through use of the clutch. If the driver only applies light pressure, little friction takes place between the two members, which permits the clutch to slip. As the driver increases pressure, friction also increases and less slippage occurs. When the drivers foot releases pressure from the clutch pedal and applies full spring pressure, the driving plate and driven disc move at the same speed. All slipping then stops because of the direct connection between the driving and driven shafts. In most clutches, a direct mechanical linkage exists between the clutch pedal and the clutch release yoke lever. Many late model vehicles and some larger units that require greater pressure to release the spring use a hydraulic clutch release system. A master cylinder (fig. 13-3), similar to the brake master cylinder, attaches to the clutch pedal. A cylinder, similar to a single-acting brake wheel cylinder, connects to the master cylinder by flexible pressure hose or metal tubing (fig. 13-3). The slave cylinder connects to the clutch release yoke lever. Movement of the clutch pedal actuates the clutch master cylinder. Hydraulic pressure transfers this movement to the slave cylinder, which, in turn, actuates the clutch release yoke lever. We use various types of clutches. Most passenger cars and light trucks use the previously mentioned plate
Figure 13-3.-Master cylinder, slave cylinder, and connections for standard hydraulic clutch. clutch. The plate clutch is a simple clutch with three plates, one of which is clamped between the other two. Figure 13-2 shows exploded and cross-sectional views of a plate clutch. SINGLE-DISK CLUTCH The driving members of the single-disk clutch consist of the flywheel and the driving (pressure) plate. The driven member consists of a single disk, splined to the clutch shaft and faced on both sides with friction material. When the clutch is fully engaged, the driven disc is firmly clamped between the flywheel and the driving plate by the pressure of the clutch springs. That results in a direct, nonslipping connection between the driving and driven members of the clutch. In this position, the driven disc rotates the clutch shaft to which it is splined. The clutch shaft is connected to the driving wheels through the transmission, propeller shaft, final drive, differential, and live axles.
Figure 13-4.-Double-disk clutch-exploded view.
Figure 13-5.-Four-speed truck transmission.
Figure 13-6.-Power flow through a four-speed transmission. The double-disk clutch (fig. 13-4) is basically the same as the single-plate disk clutch except that another driven disk and intermediate driving plate are added. |
 
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