The clutch plate consists of steel plate with a splined central hub. Annular friction facings are attached to the Steel plate by rivets. Special resins are also being used to find the friction facings. A simple clutch plate of this type is shown in figure.
With a solid clutch plate, described above, it becomes difficult to control the engagement of the clutch. A commonly used solution for this is the provision of axial cushioning interposed between the clutch plate and the friction facings. The curved cushioning spring segments are attached rigidly to the centre plate and the friction facings are rivated to this springs.
The waviness of the springs increases the free spring height. On engagement, the load applied first has to compress the spring segments to the Flat condition, resulting in a greater degree of clutch control (due to longer distance travelled at the clutch plate) and therefore smoother engagement.
This results in longer life of the clutch facing. Longer wear life is obtained because the friction materials contacts the pressure plate and flywheel under more uniform pressure, thereby allowing the uniform heat generation over the entire friction surface.
The wear of the clutch facing is more Rapid if localised spots contact the mating surfaces absorbing high amount of The generated heat, resulting in localised deterioration of the facing material. As the initial high spots fail, other high spots are created due to thermal expansion resulting in further wear.
Apart from the cushioning, the clutch plates are also provided with means of absorbing undesirable torsional vibrations. The clutch plate for this purpose, has to be made in two parts that is a central hub sub assembly and the outer facing the Rings assembly, the two being torsionally flexible with respect to each other.
The central hub assembly consists of a splined hub with radially placed slots in the flange of the hub. There are similar slots in each of the two plates situated on either side of the hub flange. Coil springs under slight compression are fitted in this slots, this provide a flexible torsional connection between the centre hub flange and the side plates, which are rivated to the main clutch plate by barrel rivets whose central portion of a larger diameter control the relative spacing between the side plates. Springs of various stiffnesses, with different sizes of slots in the plates can be provided to achieve the desired load angular deflection pattern.
Rubber blocks and Hydraulic systems also have been used in place of springs. Sometimes a friction drag is also provided between the hub and the clutch plate which provides a damping action as the coil springs recoil after a pulsation.
A large amount of heat is produced due to friction in the clutch and this heat must be dissipated effectively. A commonly used method to do this is to make the clutch plates perforated.
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