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Development of Empirical Asperity Contact Model for Wet Friction Material
- Hiral Haria - Ford Motor Company ,
- Yuji Fujii - Ford Motor Company ,
- Gregory M. Pietron - Ford Motor Company ,
- Masatoshi Miyagawa - F.C.C. CO., LTD. ,
- Takahiro Tsuchiya - F.C.C. CO., LTD. ,
- Shinji Nakamura - F.C.C. CO., LTD. ,
- Matthew Wendel - F.C.C. CO., LTD. ,
- Hiroya Miyoshi - F.C.C. CO., LTD. ,
- Shiyang Hou - University of Michigan ,
- Pengchuan Wang - University of Michigan ,
- Nikolaos Katopodes - University of Michigan
ISSN: 2641-9637, e-ISSN: 2641-9645
Published April 02, 2019 by SAE International in United States
Citation: Haria, H., Fujii, Y., Pietron, G., Miyagawa, M. et al., "Development of Empirical Asperity Contact Model for Wet Friction Material," SAE Int. J. Adv. & Curr. Prac. in Mobility 1(2):771-781, 2019, https://doi.org/10.4271/2019-01-0346.
A wet clutch couples or decouples gear elements to alter torque paths in an automatic transmission system. During the gear shifting event, the clutch torque is directly transmitted to the output shaft. Hence, clutch torque heavily influences the dynamics of the transmission. In order to evaluate the behavior of the transmission early and efficiently, the development process increasingly relies on high-fidelity transmission system simulations with added complexity. However, a wet clutch continues to be modeled using Coulomb’s friction in a typical shift simulation. Its linear framework does not physically represent non-linear hydrodynamic effects due to the presence of oil layer during clutch engagement. To make up the lack of physics, Coulomb’s clutch model often requires extensive tuning to match actual shift behaviors. Alternatively, a squeeze film based clutch model, coupled with an asperity contact model, can be employed to represent hydrodynamic behaviors and enable the broader use of dynamic simulation models in transmission development. However, while the squeeze film model has been extensively studied over the years, the asperity contact model remains largely unexamined. In this research, the contact behaviors of the asperities are empirically characterized for a wet clutch friction material. The results are compared against the base theory of Greenwood-Williamson asperity contact model (GW model) which is commonly accepted in wet clutch modeling. The analysis shows that the key assumptions of GW model, specifically the elastic deformation of spherical asperity tip and Gaussian distribution of their heights, do not hold for clutch friction materials. A new empirical asperity contact model is developed for wet friction material based on asperity roughness characterization and microscopic contact area measurements. The empirical model provides an accurate representation of asperity behaviors in wet clutch modeling, as an alternative to the conventional GW model, for high-fidelity transmission system simulations. The modeling framework is also applicable to a broad range of friction materials used in dry clutches, brakes and other applications that are characterized with hard constituents embedded in an elastic matrix.