Multi Plate Clutch (Spring Type)

You would be aware of the fact that multi plate clutches are extensively used in bikes rather than cars. Instead, single plate clutches are deployed in cars. The reason for the multi plate clutches not being deployed in cars is:

Since the space is constricted in bikes, the value of R is small and due to the flanges and bolts, the value of r also cannot be changed beyond a limit. The smaller radius transmits lesser torque. Single plate clutch has a bigger value for R and hence more amount of torque is transmitted.

Why don’t cars have multi plate clutch?

The bigger the diameter of the clutch, the more the torque can be transferred through it. This can be proved based on the torque equation:

T = N * µ * W * (R+r)/2

T- Torque

N- Number of contacting surfaces

µ- co-efficient of friction

W- Normal force acting on clutch

R- Outer radius of clutch

r- Inner radius of clutch

Design of Multi plate clutch (spring type):

Multi plate clutch is made of several friction discs, unlike the single plate clutch that has only one friction disc with 2 friction surfaces are used to transmit power from the engine to the transmission.

Multi plate clutches consist of a series of friction discs (3 to 6) that are splined to a clutch shaft. Each friction disc has a friction surface on either side to increase the co-efficient of friction of the clutch. The clutch shaft is connected to the engine flywheel.

Steel discs are placed between the friction discs. The steel discs have external teeth that sit and lock within the clutch housing. The clutch housing transmits the power to the gearbox.

The entire friction discs and steel discs assembly is known as a clutch pack. A pressure plate is placed at the end of the clutch pack. The pressure plate engages the entire clutch pack together due to the force of the coil springs. The coil springs apply spring force on the pressure plate, which in turn applies pressure on the clutch pack.

Working of Multi plate clutch (spring type):

The clutch pack is pressed together with the help of spring force. When the clutch pedal is released, the rotation of friction discs will result in the rotation of steel discs and vice-versa.

When the clutch pedal is pressed, the friction and steel discs are no longer engaged and they start rotating freely without transmitting any power to the transmission.  

Most of the bikes use wet type multi plate clutch in order to avoid overheating of the clutch.