Most light vehicles use a single-plate clutch to transmit torque from the engine to the transmission input shaft.
The flywheel is the clutch driving member. The clutch unit is mounted on the flywheel’s machined rear face, so that the unit rotates with the flywheel.
The clutch unit consists of - a friction-type disc, with 2 friction facings and a central splined hub. - a pressure plate assembly, consisting of a pressed steel cover, a pressure plate with a machined flat face, and a segmented diaphragm spring. And a release bearing and operating fork.
The friction disc is sandwiched between the machined surfaces of the flywheel and the pressure plate when the pressure plate is bolted to the outer edge of the flywheel face.
The clamping force on the friction facings is provided by the diaphragm spring. Unloaded, it is a dished shape. As the pressure plate cover tightens, it pivots on its fulcrum rings, and flattens out to exert a force on the pressure plate, and the facings.
The transmission input shaft passes through the center of the pressure plate. Its parallel splines engage with the internal splines of the central hub, on the friction disc.
With engine rotation, torque can now be transmitted from the flywheel, through the friction disc, to the central hub, and to the transmission.
When the clutch pedal is depressed, the movement is transferred through the operating mechanism, to the operating fork and the release bearing.
The release bearing moves forward and pushes the center of the diaphragm spring towards the flywheel.
The diaphragm pivots on its fulcrum rings causing the outer edge to move in the opposite direction and act on the pressure-plate retraction clips. The pressure plate disengages, and drive is no longer transmitted.
Releasing the pedal allows the diaphragm to re-apply its clamping force and engage the clutch, and drive is restored.