Predictive Wheel Cylinder Pressure Control for Automotive Hydraulic Brake-by-Wire Systems

Abstract

High-speed on/off valve (HSV), characterized by its low cost, fast response, and strong robustness, has been extensively used in automotive hydraulic brake-by-wire systems. Studies on wheel cylinder pressure (WCP) control methods based on HSVs have been ongoing for a long time. To alleviate the calibration workload and avoid the usage of the pulsewidth modulation technique, this article proposes an intuitive and easy-to-implement predictive pressure control (PPC) method by directly taking advantage of the on/off nature of the HSV. First, considering the HSV as an ideal hydraulic switch with two states of on and off, the finite control combinations of the inlet and outlet valves are defined. Subsequently, the corresponding finite flow rate set WCP model is proposed. Second, the principle and design of the proposed PPC method are presented. Based on pressure measurements and disturbance observation, at every sampling instant, the WCPs are predicted by applying all control combinations to the finite flow rate set WCP model. These predictions are evaluated with a cost function that minimizes the pressure tracking error. Then, the control combination with minimum cost is selected and applied. Finally, a hardware-in-the-loop test bench is set up to implement and validate the proposed PPC method. The experimental results demonstrate that compared to a classic WCP control method based on the pulsewidth modulation technique, the proposed PPC method improves precision by at least 10% and 40% in the steady-state and dynamic pressure tracking experiments for normal braking demands, respectively.