【正文】 nd hoses and a lever of the clutch release yoke shaft. The main cylinder acmodates a piston with a cup. The pneumatic booster serves to decrease the pedal force required to disengage the clutch. The booster includes two housings with the servo diaphragm clamped in between. The housing acmodates pneumatic, hydraulic and servo plungers. When the clutch pedal is pushed, the fluid pressure from the main cylinder is transmitted through the pipelines and hoses to the hydraulic and servo plungers of the pneumatic booster.The servo arrangement is intended for automatic change of the air pressure in the pneumatic cylinder proportionally to the force applied to the pedal. The plunger moves with the diaphragm, the outlet valve closes and the inlet valve opens thus admitting the pressed air to the pneumatic plunger piston. The forces created by the pneumatic and hydraulic plungers are added together and are applied through the push rod to the release yoke shaft lever, the lever turns the shaft and the release yoke shaft disengaging the clutch. After the clutch pedal is released,the outlet valve opens and the inlet closes. Under the action of the springs thepistons return the plungers to the initial position and the air from the cylinder is let out to the atmosphere. Automatic clutches were used in certain . and European cars. American MotorsEstick clutch eliminated the need for physical operation of the clutch pedal. A German car maker engineered an automatic clutch system called Hydrak, which consisted of a fluid flywheel connected to a single, dry disk clutch.In the EStick set up, the pressure plate levers engage the clutch disk rather than release them. Also, the clutch remains disengaged until a servo unit is applied by oil pressure when the shift lever is placed in gear with the engine running.The Hydrak unit also begins operation when the lever is in gear. This activates a booster unit, which disengages the clutch disk. The hydraulic clutch parts are bridged over by a freewheel unit, which goes into action when the speed of the rear wheels is higher than the speed of the engine. A special device controls ingagement of the mechanical clutch, depending on whether the rear axle is in traction or is pushed by car momentum. A moreorless unusual clutch pressure plate setup is used on late model Chrysler and American Motors cars. Called a semicentrifugal clutch, the pressure plate has six cylindrical rollers which move outward under centrifugal force until they contact the cover. As engine speed increases, the rollers wedge themselves between the pressure plate and cover so that the faster the clutch rotates, the greater the pressure exerted on the pressure plate and disk. Automobile TransmissionA transmission is a speed and power changing device installed at some point between the engine and driving wheel of the vehicle. It provides a means for changingthe ratio between engine rpm ( revol utions per minute) and driving wheels rpm to best meet each particular driving situation. Given a level road ,an automobile without a transmission could be made to move by accelerating the engine and engaging the clutch. However, a start under these conditions would be slow, noisy and unfortable. In addition, it would place a tremendous strain on the engine and driving parts of the automobile.So in order to get smooth starts and have power to pass and climb hills, a power ratio must be provided to multiply the torque and turning effort of the engine. Also required is a speed ratio to avoid the need for extremely high engine rpm at high road speeds. The transmission is geared to perform these functions.The transmission is designed for changing the torque transmitted from the enginecrankshaft to the propeller shaft, reversing the vehicle movement and disengaging the engine from the drive line for a long time at parking or coasting. A higher to rque should be applied to the wheels to set an automobile in motion or move uphill with a full load than to keep it rolling after it gets under way on level stretches of the road, when inertia is high and tractive resistance is low. To meet these variable torque requirements, special gear boxes are used. Such gear boxes are called fixedratio transmissions.In a gear train consisting of a driving gear and a driven gear,