Clutch control

Clutch control refers to the act of controlling the speed of a vehicle with a manual transmission by partially engaging the clutch plate, using the clutch pedal instead of (or in conjunction with) the accelerator pedal. The purpose of a clutch is in part to allow such control; in particular, a clutch provides transfer of torque between shafts spinning at different speeds. In the extreme, clutch control is used in performance driving, such as starting from a dead stop with the engine producing maximum torque at high RPM.

With the clutch pedal completely pressed or a motorcycle's lever pulled entirely towards you, there is no direct link between the engine and the driveshaft, so no power can pass from the engine to the driveshaft and wheels. With the pedal entirely released, there is full contact between the engine and the driveshaft, via the clutch plate, which means that the engine can apply power directly to the driveshaft. However, it is possible to have the clutch plate partially engaged, allowing the clutch to slip. As a result, only a fraction of the power from the engine reaches the driveshaft which is commonly known as Half clutch.

There are benefits to the use of clutch control in specific circumstances:

When a car is in first gear, small variations in engine speed translate to large changes in acceleration and engine braking. However, with a combination of clutch control and careful use of engine speed, a much smoother ride can be achieved by allowing the clutch to slip. Variations in engine revs are not immediately translated into changes in drive shaft rotation speed, but rather the friction on the clutch plate allows the drive shaft to gradually equalize with the speed of the engine.

Once the car reaches a suitable speed, the clutch can be fully engaged and speed can then be controlled either by varying the engine speed or by partially disengaging the clutch again if necessary.

This particular use of clutch control is frequently taught to learning drivers as a way to control acceleration when pulling away from a complete stop or when driving at very slow speeds while minimizing the chance of stalling the engine.

When pulling away on an uphill slope the chance of stalling the engine is greater, and as a result it can be beneficial to engage the clutch more slowly than normal while revving higher than normal.

In countries such as Singapore, learner drivers who wish to drive stick or manual transmission cars would have to drive off a manual transmission car from a complete stop on a steep slope to pass their driving test and get their driving licence.

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Wikipedia