The clutch has three main functions:

(1) Make sure the car starts smoothly. After the engine is started and before the car starts, the driver first steps on the clutch pedal to separate the clutch from the engine and the transmission system, and then shift the transmission into gear, and then gradually release the clutch pedal to gradually engage the clutch. In the process of engagement, the resistance moment of the engine increases gradually. Therefore, step on the accelerator pedal gradually, that is, gradually increase the fuel supply to the engine, so that the engine speed is always kept at the minimum stable speed without stalling. At the same time, as the clutch engagement is gradually increased, the torque transmitted from the engine to the driving wheel through the transmission system will gradually increase. When the traction force is enough to overcome the starting resistance, the car starts to move from static and gradually accelerates.

(2) Smooth shifting is achieved. In the process of vehicle driving, in order to adapt to the changing driving conditions, the transmission system often needs to change different gears to work. In order to realize gear shifting of gear transmission, it is generally to move gears or other gear shifting mechanisms to push one gear pair out of the original gear, and then make another gear pair into operation. Before shifting, it is necessary to step on the clutch pedal to interrupt the power transmission, so that the meshing pair of the original gear can be disengaged, and the speed of the meshing part of the meshing pair of the new gear will gradually tend to be synchronized. In this way, the impact when entering the meshing can be greatly reduced, so as to realize smooth shifting.

(3) Prevent overloading of the drive train. If there is no clutch during emergency braking, the engine will sharply reduce its speed due to its rigid connection with the transmission system. As a result, all moving parts will produce a great inertia moment. The relative motion between the active part and the driven part of the clutch can be used to eliminate the load that exceeds the bearing capacity of the transmission system and reduce the damage to the parts