Wheel cylinder pressure estimation for hydraulic braking system based on multi-model fusion of apply valve characteristic

Estimating the wheel cylinder pressure accurately with the hydraulic model of the apply valve is quite challenging due to the narrow linear control range of the pulse-width-modulation (PWM) apply valve in the hydraulic braking system. Considering this characteristic of the apply valve, this paper proposes a wheel cylinder pressure estimation method based on a fusion model through combing the linear and the switching hydraulic models. Firstly, the key parameters and the linear range of the apply valve are determined through experimental measurements, as well as the linear and the switching hydraulic models of the apply valve are established. Secondly, these two models are integrated using fuzzy rules to create a high-precision fusion hydraulic model that can accurately calculate the flow rate of the apply valve. Then, the wheel cylinder pressure is estimated by the measured P-V characteristic. Finally, the wheel cylinder pressure estimation-based pressure closed-loop test is carried out by the hardware-in-the-loop bench, and results indicate that the proposed method can significantly improve the dynamic accuracy of the hydraulic model-based wheel cylinder pressure estimation, with the estimation error below 0.5 MPa.