Probability Considerations in Design Case Study- Analysis of Multi Plate Wet Clutch for Judder and Rattling

Most of the studies on judder and rattling in power train with multi plate wet clutches are focused on the slip-stick phenomena of the friction materials, lubrication used, thermo-elastic behavior of friction materials, tribology considerations, boundary layer, asperity contact theories and so on. In this paper, a different approach for problem solution is presented. This is based on the concept of mutual matching and differences seen in the behavior of mating components under different assembly boundary conditions, since a very small proportion of mass production exhibits judder and rattling. The clutch and the engine components are assembled in random orientation about the axis of rotation. The probability considerations are extended to explain the basic, root cause of variation on problem occurrence and inconsistency of problem repeatability, even though all the components are within design specifications. The effects of mutual matching of clutch assembly parts and possible variations during clutch fitment on an engine due to the geometric tolerances allowed are objectively evaluated through the design for assembly (DFA) considerations using solid models of parts. An approach towards the design of clutch actuating components for accommodating misalignments is suggested. A design leading to the complete solution to the problem is evolved. The validation of the design was executed with many permutations and combinations on the different assemblies and different engines. The design refinements were introduced based on the vehicle validations and test rig observations under various operating conditions.