Clutches are a physical disconnect between the engine and the wheels of the car. More specifically, it disconnects the flywheel (connected to the engine) from the gearbox (connected to the wheels). This allows the engine to spin independently of the wheels, which is necessary for starting and stopping.
In more detail…the engine spins the flywheel, which is basically a plate at the rear of the engine (transverse engine mounting aside). This spinning plate presses against the clutch, which is essentially another spinning plate but connected to the gearbox. When you press the clutch pedal in, the clutch plate moves backwards, coming out of contact with the flywheel. When you let the clutch pedal out, the clutch plate is pressed forward by a spring, applying pressure to the flywheel and eventually spinning up/down to the same rpm via friction.
The classification of clutches can be done on the basis of several parameters.
On the basis of presence of lubricant-
In this type of clutches, the lubricant is not applied and hence the torque transmitting of these clutches is better.
In this type of clutches, the lubricant is applied to dissipate the heat from the frictional surfaces in contact. The torque transmitting capacity is slightly reduced due to a decreased coefficient of friction between the contact surfaces due to the presence of the lubricant.
On the basis of number of plates-