Numerical Investigation of Friction Material Contact Mechanics in Automotive Clutches 2020-01-1417
A wet clutch model is required in automotive propulsion system simulations for enabling robust design and control development. It commonly assumes a Coulomb’s model for simplicity, even though it does not physically represent viscous torque transfer. A Coulomb friction coefficient is treated as a tuning parameter in simulations to match vehicle data for targeted conditions. The simulations tend to deviate from actual behaviors for different drive conditions unless the friction coefficient is adjusted repeatedly. Alternatively, a complex hydrodynamic model, coupled with a surface contact model, is utilized to enhance the fidelity of system simulations for broader conditions. The theory of elastic asperity deformation is conventionally employed to model clutch surface contact. However, the recent examination of friction material shows that elasticity modulus of surface fibers significantly exceeds contact load, implying no deformation of fibers. This article investigates the friction material contact mechanics through numerical simulations. A surface model is constructed based on microscopic examination of material topography and properties. FEM simulation is conducted to examine the interactions between surface fibers and surrounding medium under loaded conditions. The change in real contact area with respect to nominal surface pressure correlates qualitatively between simulations and experiments. The numerical study provides new insight into frictional material contact mechanics that is not directly observable. It also supports the assumptions behind the empirical fiber contact model that is recently introduced to enhance hydrodynamic clutch models.
Hiral Haria, David Popejoy, Rachel Divinagracia, Yuji Fujii, Masatoshi Miyagawa, Takahiro Tsuchiya, Shinji Nakamura, Matthew Wendel, Nikolaos Katopodes
Ford Motor Company, FCC Co., Ltd., University of Michigan