Main parts of clutch

Clutch has consisted of number of parts; [1]

1. Clutch plate
2. Clutch shaft or input shaft
3. Pressure plate assembly
4. Release bearing
5. Clutch linkages

Fig 1: Clutch-main-parts

Clutch plate: The clutch plate is a steel plate covered with frictional material that fits between the flywheel and the pressure plate. In the center of the plate is the hub, which is splined to fit over the splines of the input shaft. [1]

Fig 2: Clutch-plate

When the clutch is engaged, the disc is firmly squeezed between the flywheel and pressure plate. So the power from the engine is transmitted by the plate's hub to the transmission's input shaft.

A clutch plate has frictional material riveted or bonded to both sides. Grooves are cut across the face of the friction facings to allow for smooth clutch action, increased cooling and a place for the dust to go as the clutch plate wears. [1]

Asbestos wire-woven material was the most common facing for clutch plates. Due to recent awareness of the health hazards resulting from asbestos, new lining materials such as paper based materials that are strengthened by the addition of cotton and brass particles and wire. These increase the torsional strength of the facings and prolong the life of the clutch plate. The torsional dampener springs circle the center hub. This type of clutch plate is called "flexible clutch is engaged, the springs cushion the sudden loading by Hexing and allowing some twist between the hub and plate. Stop pins limit this torsional movement to approximately 3/8 inch. Different  types of clutch friction lining material should discuss later. [1]

Clutch shaft (input-shaft): The clutch shaft projects from the front of the transmission. The clutch plate will be splined to the clutch shaft. When the clutch is engaged, the clutch plate drives the transmission's input shaft through these splines. [1]

Fig 3: Clutch-shaft or input-shaft

Pressure plate assembly: The pressure plate squeezes the clutch plate onto the flywheel when the clutch is engaged and moves away from the plate when the clutch is disengaged. These actions allow the clutching transmit or not transmit the engine's torque to the transmission.

Fig 4: Pressure-plate-assembly

A pressure plate assembly includes a clutch cover (or clutch housing), release bearing, a pressure plate and a spring The spring used in most pressure plates is a single Belleville spring or diaphragm type spring, however a few use multiple coil springs, The clutch cover is a large bell-shaped metal casting that is fitted to the flywheel of the engine and rotates with the flywheel. [1]

Release bearing (or) throw-out bearing: The clutch release bearing is a ball type bearing and is usually sealed and pre-lubricated to provide smooth and quiet operation as they move against the pressure plate to disengage the clutch. [1]

Clutch linkages: Clutches are normally operated by either mechanical or hydraulic linkages.

(a) Mechanical linkages: Two types of mechanical linkages are used: the cable type and the shaft and lever type. The shaft and lever clutch linkage has many parts and pivot points and transfers the movement of the clutch pedal to the release bearing via shafts, levers, and bell cranks. This action causes the release bearing to move against the pressure plate. [1]

Fig 5: Mechanical-clutch-linkage

A cable-type clutch linkage is simple and lightweight. However, cables will gradually stretch and can break due to electrolysis. When the clutch pedal is depressed, the cable pulls on the clutch fork, which causes the release bearing to move against the pressure plate.

(b) Hydraulic linkage: In this type of clutch, the movement of the clutch pedal is converted by the master cylinder into a hydraulic pressure which is then transmitted to the clutch release fork via the slave cylinder. It consists of a master cylinder, a slave cylinder, and an oil reservoir. When the clutch pedal is depressed, the fluid under pressure from the master cylinder reaches the slave cylinder. The slave cylinder is mounted on the clutch itself. The fluid actuates slave cylinder push rod which further operates the clutch release fork to disengage the clutch. [1]

Fig 6: Hydraulic-linkages

The hydraulic system is designed to multiply the driver's efforts so that a light force applied to the foot pedal produces a much greater force on the clutch fork. A small piston in the master cylinder travels a relatively long distance with only a low input force. This moves larger piston in the slave cylinder a relatively small distance but produces a greater force to disengage the clutch. [1]

Flywheel: an important part of the engine is also the main driving member of the clutch. It is heavy, or has a large mass, which creates inertia. It is normally made of nodular or gray-cast iron, which has high graphite content (about 3%) to lubricate the engagement of the clutch. On a running engine, the crankshaft speeds up as a cylinder fires, then slows due to internal engine friction until the next cylinder fires. The flywheel absorbs some of the heat created by clutch operation by acting as a heat sink for the clutch friction disc. The face on the transmission side of the flywheel has a smooth, machined area that creates the application surface for the clutch friction disc. This surface must be properly finished to allow adequate slippage as the clutch engages and disengages, and to prevent slippage when the clutch is engaged.

Next Article: "Types of friction lining materials"

References:

[1] Automobile Engineering By Er AK Babu & Er Ajit Pal Singh, S. Chand & Co Pvt Ltd, New Delhi, ISBN 81-219-9770-4, Code:10A 560, 2013, 2014, “Clutch” p.177-185.