Thursday, December 20, 2012

Care Care: Understanding the clutch system

The automotive clutch is used to connect and disconnect the engine and manual (hand shifter) transmission or transaxle. The clutch is located between the back of the engine and the front of the transmission. Basically, the essentials to the performance of a clutch are:

• sure engagement
• smooth engagement
• efficient gear change
• absorption of noise and vibration
• durability

The clutch works on the principle that power flow from one unit to another unit can be controlled with a drive disc and a driven disc. In an automotive clutch, one disc is fastened to the rear of the engine crankshaft, and the other disc is attached to the input shaft of the transmission. When both discs are not connected the crankshaft can rotate while the transmission input shaft remains stationary. However, when the transmission disc is forced into the spinning disc on the crankshaft, both discs spin together. Power flow is thus transferred out of the engine and into the transmission.

Clutch operation is effected by a system of springs and plates. When the driver presses the clutch pedal, the clutch release mechanism pulls or pushes on the clutch release fork (please see diagrams.) The fork moves the bearing into the centre of the pressure plate. This causes the pressure plate face to pull away from the clutch disc, releasing the disc from the flywheel. As a result, the engine crankshaft can now turn without turning the clutch disc and transmission input shaft.

When the clutch pedal is released by the driver, spring pressure inside the pressure plate pushes forward on the clutch disc. It locks the flywheel, disc, pressure plate, and transmission input shaft together. The engine again rotates the transmission input shaft, transmission gears, drive train and wheels of the car.

The splines in the centre of the clutch disc mesh with splines on the transmission input shaft. This makes the input shaft and disc turn together. However, the clutch disc is free to slide back and forth on the shaft. The clutch cover assembly is bolted to the engine flywheel and its sole function is to engage and disengage the clutch plate to and from the face ofthe flywheel. It does so by exerting pressure against the facings of the clutch plate. During an engagement, the latter is firmly held against the flywheel and revolves with the flywheel without slipping. In disengaging the clutch plate, the clutch cover assembly releases its pressure, allowing the clutch plate to operate independently of the flywheel.


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