Prediction of wet band brake dynamic engagement behaviour - Part 2: experimental model validation

A wet (oil-lubricated) band brake in a vehicle automatic transmission system exhibits widely varying engagement behaviour under different operating conditions. In recent years, analytical evaluation of the band engagement behaviour has become increasingly important to improve automatic transmission shift quality. Thus. a mathematical tool which accurately captures band engagement physics is indispensable in a transmission design process. This paper describes experimental validation of the dynamic band engagement model which includes the physics of squeeze film, asperity deformation, porous oil diffusion., heat transfer and loading pressure distribution caused by a self-energizing mechanism. The model is implemented as a stand-alone computer program to predict the band engagement behaviour on an inertia absorption type band engagement test stand. Simulation results show good agreement with experimental torque profiles over a wide range of operating conditions. The model provides an analytical interpretation of the widely varying engagement behaviour resulting from the effects of oil temperature, friction material permeability and drum speed. The successful model validation demonstrates that the dynamic band engagement model serves as a valuable tool to assist band design and shift calibration processes of automatic transmission systems.