A clutch is a mechanical device that provides for the transmission of power from one component to another when engaged, but can be disengaged.In the simplest application, clutches are employed in devices which have two rotating shafts. In these devices, one shaft is typically attached to a motor or other power unit while the other shaft provides output power for work to be done. In a motor vehicle, the clutch is used to connect the drive from the engine to the transmission and the driving wheels.
The pressure plate moves closer to the fly wheel and the plate effect of the spring incresase. the movement requires the relase bearing to the moved back to give clearance between these two components.
The clutch is located between the engine and the gearbox, as disengaging it is required to change gear. Although the gearbox does not stop rotating during a gear change, there is no torque transmitted through it, thus less friction between gears and their engagement dogs. The output shaft of the gearbox is permanently connected to the final drive, then the wheels, and so both always rotate together, at a fixed speed ratio. With the clutch disengaged, the gearbox input shaft is free to change its speed as the internal ratio is changed. Any resulting difference in speed between the engine and gearbox is evened out as the clutch slips slightly during re-engagement.
Clutches in typical cars are mounted directly to the face of the engine's flywheel, as this already provides a convenient large diameter steel disk that can act as one driving plate of the clutch.
