A wet (oil-lubricated) band brake is a critical component in the operation of automatic transmission systems in automotive applications. Its engagement characteristics significantly affect the quality of automatic shifting. During the automatic transmission design process, it is important to characterize band engagement behaviour accurately under a wide range of operating conditions. This paper describes a mathematical model which predicts the dynamic engagement behaviour of the wet band brake. The space-time-dependent model includes the effects of squeeze film, asperity deformation, porous oil diffusion, heat transfer and loading pressure distribution caused by a self-energizing mechanism. The model can be readily implemented and efficiently executed on a computer as a standalone program or as a subroutine for automatic transmission shift simulations. Knowledge of band engagement obtained through the model is expected to lead to improved band design and automatic transmission shift calibration processes.

A wet (oil-lubricated ) band brake in a vehicle automatic transmission system exhibits widely varying engagement behaviour under diVerent 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 lm, asperity deformation, porous oil diVusion, heat transfer and loading pressure distribution caused by a selfenergizing 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 pro les over a wide range of operating conditions. The model provides an analytical interpretation of the widely varying engagement behaviour resulting from the eVects 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.

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