Flow-valve modelling and wheel-slip control are investigated for an automotive hydraulic braking system which uses flow valves to supply brake fluid into the wheel cylinder and on/off valves to exhaust the brake fluid. First, the model of the flow valve is built using an experiment method, since its mechanism is difficult to analyse. Furthermore, because of the intrinsic difference between the two distinct valves, a special control problem is raised concerning how to realize wheel-slip control by using a unified strategy. Considering the essential characteristics of the two valves, a hybrid control approach, which contains an ordinary, continuous, state feedback function and a supervisory logic rule, is explored. Then, one feasible solution is obtained based on Lyapunov theory in the Filippov framework, so that the convergence of the control system is strictly guaranteed in theory. The controller has few tuning parameters and it is simple to tune. Illustrative hardware-in-the-loop simulation tests are carried out. The results show that both braking efficiency and ride quality are achieved, even if there are errors in the actuator control as well as in estimation of vehicle speed.
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