Research On The Precise Pressure Control Of Hydraulic Actuator Of Electronic Stability Control System

Electronic stability control system(ESC), an advanced automotive active safety system consisting of anti-lock brake system(ABS), traction control system(TCS) and active yaw control system(AYC), can prominently improve the vehicle safety performance. Hydraulic control unit(HCU) is the actuator of ESC. It is very important of controlling the brake cylinder pressure precisely by HCU to achieve expected ESC control effect. Thus it is significant to research on the precise pressure control of hydraulic actuator of ESC.Based on theoretical analysis, simulations and tests, hydraulic actuator controlled by pulse width modulation(PWM) is studied in detail in order to extend the effective range of duty ratio, realizing the precise pressure control of brake cylinder. The research is executed in three parts. Firstly the mathematic model of the high speed on-off valve is derived from the analysis of flow force, to analyze the relationship between valve structural parameters and flow force. The flow field of high speed on-off valve is simulated using the computational fluid dynamic(CFD) to amend the conclusion of the theoretical analysis, and the valve structural parameters are optimized according to the genetic algorithm, offering the theoretical references for extending the duty ratio of PWM. Secondly the simulation model of high speed on-off valve is established in MATLAB/Simulink, and then embedded in the HCU simulation model established in AMESim, resulting in the co-simulation model of hydraulic actuator. Finally the simulation model is verified by the hardware-in-loop tests, where effects of the valve structural parameters and carrier frequency on the pressure control are analyzed.It is indicated that the high speed on-off valve controlled by pulse width modulation(PWM) of high frequency can float at a certain orifice. The floating orifice can be adjusted by changing the duty ratio within a certain valid range to achieve the precise linear pressure control. Furthermore it is critical to increase the range of flow force for extending the effective range of duty ratio. The pressure difference, the valve seat angle and the throttle diameter of the high speed on-off valve have a significant effect on the flow force. At last some the effects of structural parameters of the high speed on-off valve on extending the range of the linear pressure control are proposed, serving as references for the precise control of pressure.