A dynamic model for brake pedal feel analysis in passenger cars

Abstract

The brake system of a passenger car is a complex system composed of an assembly of mechanical parts, such as springs and rubber parts, and structures filled with gas and other liquids. In order to predict the brake pedal feel of a passenger car, a dynamic model of a brake system during application of the brake pedal was proposed; this considered and modelled the physical structures and the working processes of the key components. The model takes into account not only the spring preloads and the frictional forces in the booster and the master cylinder but also the reaction disc features and the variation in the bulk modulus of the brake fluid. When the pedal travel is regarded as the input, the boundary conditions for the dynamic equations of the brake system components are strictly defined. Also, bench experiments for the booster and the master cylinders were designed for parameter identification; the effectiveness of the component models was validated under conditions including with and without vacuum assist and with and without brake fluid. On the basis of these experiments, the static and dynamic characteristics of the brake pedal feel were simulated using the static model and the dynamic model of the brake system. Then, vehicle road experiments were carried out. With the assessment index of a three-quadrant diagram covering the pedal travel, the pedal force and the master cylinder pressure, as well as a four-quadrant diagram covering the pedal travel, the pedal force, the master cylinder pressure and the longitudinal deceleration of the vehicle, the results from the simulations and the experiment were compared and analysed. We conclude that this novel model of a brake system can accurately predict the brake pedal feel characteristics of passenger cars and can be used for brake system design and adjustment.