A Multi-Physics Model for Wet Clutch Dynamics.

Abstract

A multi-physics model is developed for predicting the dynamic behavior of wet clutch engagement under realistic driving conditions. The transmission clutch plays a significant role in determining drivability and fuel economy. The present work overcomes previous limitations by constructing a detailed computational fluid dynamics model for wet clutch engagement. An open clutch model for single and multi-phase flow is developed. This model is used to provide the initial conditions for the dynamic engagement model. New extended boundary formulations are examined in order to reduce numerical errors at inlet and outlet boundaries. A new approach for squeeze-film flow is developed based on an iterative method. Given the external force responsible for plate movement, the squeeze velocity is computed by trial until the internal fluid stresses balance the external force. The latter are shown to have a major effect on squeeze-film flow and clutch engagement in general. The model also captures the flow in the micro-channels created by the grooves on the friction material surface and the flow through the porous friction material. The clutch engagement model combines the squeeze-film flow model with the influence of a rough surface on lubrication flow using the concept of flow factor, the mechanical contact based on the real contact area and the heat flux at the interface between the friction and separator using a virtual volume. A series of squeeze flow experiments were performed at the Ford Motor Company testing facility. The data are de-noised using standard statistical filters and then are used to validate the numerical results. Based on the comparison with the experimental data, the performance of the proposed model is found satisfactory. The wet clutch model developed in this research can become a baseline model for the prediction of the engagement behavior of a real wet clutch. When various material properties and further detailed geometric features are included, the present model may become an efficient alternative to laboratory testing and lead to designs that cannot be envisioned by other approaches.