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Wet Multi plate clutch Construction
A multi plate clutch has more number of clutch plates. A typical clutch consist of the following components: Clutch basket or cover, clutch hub, drive (friction) plates, driven (steel) plates, pressure plate and the clutch springs. These can be seen in the picture.
The clutch housing is attached to the engine crank shaft flywheel. The pressure plate is fixed on the flywheel through the clutch springs. The engine flywheel turns the clutch housing. The inner circumference of the clutch basket is splined to carry the thin metal plates. The clutch basket splines engage the tabs on the friction drive plates. This sources the clutch housing and the drive plates to rotate together. Additionally they are free to slide axially within the clutch basket.
Interleaved with the drive plates, there are many number of driven plates. These driven friction plates have inner splines. These splines engage with the outer splines on the clutch hub. As such, the driven friction plates can slide on the clutch hub. The clutch hub is linked to the input shaft of the transmission gear box.
The drive plates and the driven plates are firmly pressed together by the pressure plate due to the clutch springs. The drive plates, driven plates and the strong clutch coil springs are assembled within the clutch basket.
Working of Multi Plate Clutch
During clutch engagement, spring pressure forces the pressure plate towards engine flywheel. This causes the friction plates and the steel driven plates to be held together. Friction locks them together tightly. Then the clutch basket, drive plates, driven plates, clutch hub and the gearbox input shaft all spin together as one unit. Now power flows from the clutch basket through the plates to the inner clutch hub and into the main shaft of the transmission.
The clutch gets released or disengaged when the clutch pedal is pressed. This causes the clutch pressure plate to be moved away from the drive and driven plates, overcoming the clutch spring force. This movement of the pressure plate, relieves the spring pressure holding the drive and driven plates together. Then the plates float away from each other and slip axially. Thus, the clutch shaft speed reduces slowly. Finally, the clutch shaft stops rotating. Power is no longer transferred into the transmission gearbox.
Multi plate clutches are used widely in motorcycles and scooters. The multiple plate clutch is used in some types of epicycle gearboxes. A multi plate clutch provides a very compact, yet a high friction coupling between the engine and the gearbox. With multiple plates, the friction surface area, strength and friction in the engaged clutch are increased. The increased friction surfaces, increases the torque transmission capacity of the clutch.
Depending upon the power output of the engine, and the weight of the vehicle, four to eight sets of plates (four to eight drive plates and four to eight driven plates) may be housed in the clutch basket.
The multi plate clutch may be of dry type or wet type. When the clutch functions in atmosphere, it is called a dry clutch. When the clutch operates in an oil bath, it is named as a wet clutch.
Some multi plate clutches work dry. Then the driving plates are lined on each side with a friction fabric. A dry clutch can withstand high temperatures and permits frequent gear shifts without much loss of power initiated by heat. A dry clutch should never come in contact with oil. In dry clutches, seals are used to inhibit entry of oil into the clutch basket. Oil will source clutch slippage and will ruin the clutch friction discs.
Most multiple clutches run in an oil bath. Wet clutches are used for several reasons: Debris resulting from clutch wear can be drained with the oil and trapped by the oil filter. Oil helps the clutch to run cool. In the case of two wheelers, since the primary drive requires lubrication, it is less costly to use a wet clutch.
A wet clutch operates smoother and uses more plates. Some clutches have alternative steel and bronze plates running in an oil bath and are quire smaller in diameter for minimal inertia.