Transmission & clutch

Clutch
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[pic] Clutch for a drive shaft: The clutch disc (center) spins with the flywheel (left). To disengage, the lever is pulled (black arrow), causing a white pressure plate (right) to disengage the green clutch disc from turning the drive shaft, which turns within the thrust-bearing ring of the lever. Never will all 3 rings connect, with no gaps.

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Rear side of a Ford V6engine, looking at the clutch housing on the flywheel
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Single, dry, clutch friction disc. The splined hub is attached to the disc with springs to damp chatter.
A clutch is a mechanism for transmitting rotation, which can be engaged and disengaged. Clutches are useful in devices that have two rotating shafts. In these devices, one shaft is typically driven by a motor or pulley, and the othershaft drives another device. In a drill, for instance, one shaft is driven by a motor, and the other drives a drill chuck. The clutch connects the two shafts so that they can either be locked together and spin at the same speed (engaged), or be decoupled and spin at different speeds (disengaged).
Multiple plate friction clutch
This type of clutch has several driving members interleaved with severaldriven members. It is used in motorcycles and in some diesel locomotives with mechanical transmission. It is also used in some electronically-controlled all-wheel drive systems. This is the most common type of clutch on modern types of vehicles.
Vehicular
There are many different vehicle clutch designs but most are based on one or more friction discs, pressed tightly together or against aflywheel using springs. The friction material varies in composition depending on whether the clutch is dry or wet, and on other considerations. Friction discs once contained asbestos, but this has been largely eliminated. Clutches found in heavy duty applications such as trucks and competition cars use ceramic clutches that have a greatly increased friction coefficient; however, these have a "grabby"action and are unsuitable for road cars. The spring pressure is released when the clutch pedal is depressed thus either pushing or pulling the diaphragm of the pressure plate, depending on type, and the friction plate is released and allowed to rotate freely.
When engaging the clutch, the engine speed may need to be increased from idle, using the manual throttle, so that the engine does not stall(although in some cars, especially diesels, there is enough torque at idling speed that the car can move; this requires fine control of the clutch). However, raising the engine speed too high while engaging the clutch will cause excessive clutch plate wear. Engaging the clutch abruptly when the engine is turning at high speed causes a harsh, jerky start. This kind of start is necessary anddesirable in drag racing and other competitions where speed is more of an issue than comfort.
Wet and dry
A 'wet clutch' is immersed in a cooling lubricating fluid, which also keeps the surfaces clean and gives smoother performance and longer life. Wet clutches, however, tend to lose some energy to the liquid. A 'dry clutch', as the name implies, is not bathed in fluid. Since the surfaces of a wetclutch can be slippery (as with a motorcycle clutch bathed in transmission oil), stacking multiple clutch disks can compensate for the lower coefficient of friction and so eliminate slippage when fully engaged.
Operation in automobiles
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This plastic pilot shaft guide tool is used to align the clutch disk as the spring-loaded pressure plate is installed. The transmission's drive splines andpilot shaft have an identical shape. A number of such devices fit various makes and models of drivetrains
In a car the clutch is operated by the left-most pedal using a hydraulic or cable connection from the pedal to the clutch mechanism. Even though the clutch may physically be located very close to the pedal, such remote means of actuation (or a multi-jointed linkage) are necessary to...