A Time Efficient Thermal and Hydrodynamic Model for Multi Disc Wet Clutches

Wet Clutches are used in automotive powertrains to enable compact designs and efficient gear shifting. During the slip phase of engagement, significant flash temperatures arise at the friction disc to separator interface because of dissipative frictional losses. An important aspect of the design process is to ensure the interface temperature does not exceed the material temperature threshold at which accelerated wear behavior and/or thermal degradation occurs. During the early stages of a design process, it is advantageous to evaluate numerous system and component design iterations exposed to plethora of possible drive cycles. A simulation tool is needed which can determine the critical operational conditions the system must survive for performance and durability to be assured. This paper describes a time-efficient multiphysics model developed to predict clutch disc temperatures with a runtime in the order of minutes. It consists of a simplified 1D numerical model of heat conduction and storage within the clutch pack. A novel analytical interfacial model considers the effects of hydrodynamics and frictional heat generation at the sliding interface, including radial groove and squeeze flows, to calculate the heat transfer between the clutch surfaces and the fluid. The model has been validated against experiments. The assumptions made are demonstrated to be prudent as the presented model is shown to closely predict the disc and interface temperatures. Finally, the model is exercised to examine the effect of varying clutch plate number on temperature during an urban drive cycle.