Components of A Clutch System
A clutch is a mechanical device used to provide an interruptible connection between the engine and the manual transmission or transaxle. It is a key element in the transmission system and is located between the back of the engine and the front of the transmission.
Functions of a Clutch
- Transmitting torque from the engine to the drivetrain.
- Engaging the gears when the vehicle is in motion without causing damage to the gear wheels.
A clutch assembly consists of many parts, but here are the major components:
1. Clutch release mechanism
This is a set of interrelated components that allow the operator to control the clutch. It consists of the clutch fork, clutch pedal assembly, cable or hydraulic circuit and a mechanical linkage.
There are currently two types of clutch release mechanism:
The manual clutch release mechanism is divided into two categories.
A clutch linkage mechanism – this mechanism uses rods and levers to transfer motion from the pedal to the fork. Movement of the pedal shoves the pushrod on the bell crank causing the bell crank to reverse the forward movement of the clutch pedal.
The cable mechanism – this mechanism uses a steel cable to transfer clutch pedal action to the clutch fork. The cable is usually connected to the clutch fork with the other end of the cable fastening to the upper end of the clutch pedal.
A hydraulic mechanism uses a hydraulic circuit to transfer pedal movement to the clutch fork. It is made of a master cylinder, a slave cylinder, and hydraulic lines. When the pedal is pressed, hydraulic pressure is created in the master cylinder, actuating the slave cylinder. This forces the slave cylinder to move the clutch fork.
2. Clutch release fork
The clutch fork, also known as a release arm or clutch arm, is the heart of clutch operation. It transfers motion from the release mechanism to the clutch release bearing and pressure plate. The clutch fork protrudes through a square hole in the bell house. It features a rubber boot which is designed to keep dirt and debris from entering the clutch housing.
3. Release bearing
The release bearing, also known as the throw-out bearing, is connected to one of the clutch fork mechanism and rides on the diaphragm spring. It either pulls or pushes the pressure plate diaphragm spring to connect or disconnect the grip of the pressure plate on the clutch disc when the pedal is pressed or released. The bearing also reduces pressure between the release fork and the pressure plate levers.
There are two major types of bearings:
• Hydraulic bearings
- these types of bearings operate on hydraulic pressure produced by a master cylinder. Hydraulic bearings are easy to install and provide maximum reliability as they don’t use a slave cylinder and the stock mechanical bearing.
• Manual bearings
– the manual throw-out bearing snaps over the end of the clutch fork. The movement of the clutch fork causes the bearing to slide along the transmission hub sleeve.
4. Clutch disc
The clutch disc is fixed between the pressure plate and the flywheel providing a connecting link between the transmission and the engine. It is made of friction material on both sides that make/break contact with the pressure plate surfaces and the flywheel. This friction surface allows for smooth engagement and disengagement.
Clutch discs are categorised as wet or dry systems. Wet clutch discs are immersed in engine oil which keeps the surfaces clean. They offer smoother performance and tend to have a long, service-free life. Dry clutches, on the other hand, are not bathed in a lubricating fluid and use friction to engage the performance clutch.
This component is connected to the engine’s crankshaft. Its face is made of iron and is precision machined to a smooth surface. Flywheels provide a mounting surface for the clutch cover and store and release energy pulses from the crankshaft.
6. Pressure plate
This spring-loaded device is bolted to the clutch flywheel. Its main function is to engage and disengage the flywheel and the clutch disc. There are two types of pressure plates:
• The diaphragm type
- this pressure plate uses a diaphragm spring to hold the clutch assembly together. The diaphragm spring is a round, conical disc of spring steel. Its pie-shaped segments run from the outer edge to the centre and provide clamping force against the pressure plate.
• Coil spring type
– the coil spring type uses several small coil springs instead of a single diaphragm spring. This type of pressure plate has release levers hinged inside the plate to move the face of the pressure plate away from the flywheel and the clutch disc. It also has small clip-type springs that fit around the release levers and a cover that holds the assembly together.