The clutch is an element which makes a temporary connection between gear box and vehicle engine. It transmits not only engine torque, but also ensures comfort and drivability during slippage. One of the main functions of clutch disc is to transmit the engine torque while absorbing vibrations. It allows a soft gradual reengagement of torque transmission. The cushion disc which is located between two clutch facings has wavy surface, thus it behaves like a spring during engagement and disengagement. The axial elastic stiffness of the clutch disc is obtained by a cushion disc. The load-deflection curve is obtained by compressing clutch disc between two plates, representing pressure plate and flywheel. The wavy shape of the cushion disc provides progressive stiffness curve of the clutch disc.

The cushion disc participates in drivers comfort during engagement of the clutch. The comfort depends on the limits of the progressive stiffness curve. Outside the limits of this cushion function, the clutch engagement would be harsh and uncomfortable for the driver. Besides, engine torque may not be transmitted during the later service lifetime and the life of the clutch might be decreased. In the case cushion disc has no cushioning function, then the engine might be stopped. Additionally, improper cushioning function causes heat and deform of the pressure plate and it also decreases the transmitted engine torque. Therefore, cushion disc has to have certain cushioning characteristics in order to overcome these problems.

In this study, the optimum shape design of cushion disc was performed using an evolutionary optimization algorithm. Differential evolution algorithm was selected as the optimization method because it guarantees the global optimum. Design of experiment method has been employed to construct the response surface that approximates the behavior of the objective function inside a certain design space. Three shape parameters of cushion disc have been selected. The objective of the shape optimization is to find the optimum shape parameters that provide the target stiffness curve. After solving the optimization problem with differential evolution method, optimum shape parameters of cushion disc have been found for two case studies. A Pascal code based differential evolution optimization code was developed for shape optimization and Ansys finite element software was used for calculating stiffness curve of cushion disc.

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