Cascade-Free Predictive Wheel Slip Control With Discrete-Valued Inputs for Automotive Hydraulic Anti-Lock Braking Systems

The automotive hydraulic anti-lock braking systems (ABSs) employ cascaded wheel slip control (WSC) and pressure control and adopt the pulsewidth modulation technique to deal with discrete valve dynamics. Pursuing a simple and effective alternative, this article presents a cascade-free discrete-valued predictive WSC (DV-P-WSC) method. First, from a discrete on/off perspective, the finite control combinations of the inlet valve (IV) and the outlet valve (OV) are defined, corresponding to the pressure increase, decrease, and hold control actions. Then, the control-oriented wheel slip model with a discrete-valued input is presented. Second, a general DV-P-WSC scheme is proposed. At each sampling instant, the two-step-ahead wheel slip predictions corresponding to all control combinations are performed. These predictions are evaluated with a predefined cost function. The optimal prediction and its control combination are determined. Then, the optimal control combination is directly applied to the IV and OV. On this basis, a specific DV-P-WSC method design is illustrated, where an ultra-local approximation of the proposed wheel slip model is incorporated to reduce the influence of the inaccurate model. Finally, a hardware-in-the-loop (HIL) test bench is built to implement the proposed DV-P-WSC method. The comparative experiments validate the effectiveness and superiorities of the proposed DV-P-WSC method.