The motion of crankshaft is transmitted to gearbox through clutch. Clutch is a device used in transmission system of motor vehicle to disengage or engage the engine with transmission system. The clutch is located between engine and gearbox. When the clutch is engaged, the power flows from the engine to rear wheels through transmission system and vehicle moves on the road. When clutch is disengaged, the power is not transmitted to rear wheels and vehicle stops while engine is still running. Clutch works on the principle of friction.
Requirements of Clutch:
- Clutch should be light in weight.
- Torque transmission should be large.
- The wearing surfaces should have long life.
- It should be easy to operate.
- It should be free from vibration and damping.
- It should be dynamically balanced.
The following are the main types of clutches are as follows;
- Single Plate Clutch.
- Multi-Plate Clutch.
- Centrifugal Clutch.
Single Plate Clutch
Single plate clutch is the most common type of clutch used in motor vehicles. It consists of single clutch plate mounted on splines of the clutch shaft. The front end of clutch shaft is resting in bearing of flywheel. The flywheel is mounted on the engine shaft. The pressure plate is connected to the flywheel through clutch spring and is free to slide on clutch shaft. When the clutch is engaged, the clutch plate is gripped between the flywheel and the pressure plate. Due to the friction between the flywheel and clutch plate and between clutch plate and pressure plate, clutch works as a single unit to transmit the power from engine shaft to clutch shaft.
When the clutch pedal is pressed, the pressure plate moves back against the spring force, which makes clutch plate free between flywheel and pressure plate. The flywheel keeps rotating along the engine shaft but due to disconnection clutch shaft stops. This disconnects the transmission system from engine. The clutch pedal is pressed as long, the clutch remains in disengaged position and when the clutch pedal is released clutch engages.
Centrifugal clutch is the type of clutch, the clutch pedal and springs are eliminated and power transmission takes place purely by centrifugal force on plate, which is used to apply required pressure on floating plate to keep clutch in engaged position. It is required to engage the load after the driving member has attained a particular speed, a centrifugal clutch is used. A centrifugal clutch is being increasingly used in an automobiles and machines. It works on the principle of centrifugal force.
In centrifugal clutch, the operation is automatic and depends upon the engine speed. It consists of a cylindrical drawn in which shoes slide in a radial direction and make contact through friction surfaces with the inner lining of the drum. As the shoe rotates, the centrifugal force holds them against the inner surface of the drum and torque transmitted. The shoes are held by the springs which just prevent contact with the drum until a specified speed of motion has been reached.
Multi-plate clutch consists of two friction plates having friction linings on both sides except the first plate which is adjacent to the flywheel. This plate is having friction lining on one side. The friction plates are connected on the top of flywheel. The friction plates are rotate with the flywheel and with driving shaft. The friction plates are also free to move axially. Those plates are supported on splines of the driven shaft and rotate with it. These plates are situated in between the friction plates and also slide axially.
When the clutch is engage, the spring will press the discs into contact with the friction plates and the power will be transmitted from the driving shaft to the driven shaft.
Multi-plate clutch may be dry or wet. When the clutch operated in oil bath, it is called as wet clutch. When the clutch operated dry, is called as dry clutch. The multi-plate clutch is used when a large torque is to be transmitted such as in case of motor cars and machine tools.