Get the facts right on the clutch in your automobile

A clutch is a device that has two rotating shafts, one of which is driven by a motor or pulley while the other drives another device. In a car, you need a clutch because the engine spins all the time, but the car’s wheels do not. In order for a car to stop without stalling the engine, the wheels need to be disconnected from the engine. A clutch allows us to smoothly engage a spinning engine to a non-spinning transmission by controlling the slippage between them.

There are many clutch designs for automobiles but most are based on one or more friction discs, pressed tightly together or against a flywheel using springs. The friction material varies in composition depending on whether the clutch is of the dry or wet type.

Wet clutches are immersed in oil for cooling while dry clutches do without it. Using oil means that there is some amount of ‘slippage’, but this can be overcome by using multiple clutch plates to increase friction. Clutches found in heavy duty applications such as trucks and competition cars use ceramic and these have a greatly increased friction coefficient. These have a “grabby” action, unsuitable for road cars.

When engaging the clutch, the engine speed may need to be increased from idle, using the manual throttle, so the engine does not stall. In some cars, especially diesels, there is enough torque at idling speed so that the car can move. This requires fine control of the clutch.

However, raising the engine speed too high will cause excessive clutch plate wear. Engaging the clutch abruptly when the engine is turning at high speed causes a harsh and jerky start. This kind of start is necessary and desirable in drag racing and other competitions where speed is more important than comfort.