| Vehicle electronic stability Hydraulic Control Unit(HCU)is the executive arm of the Electronic Stability Control(ESC).The HCU includes high-speed solenoid valves to regulate wheel brake pressure,motors,plunger pumps and accumulators.The principle is that the hydraulic control unit accepts the instruction of the electronic stability control unit and regulates the on-off of the hydraulic circuit to control the braking force so as to ensure the stability of the vehicle.Under correct instruction,the working performance of ESC control unit and high-speed solenoid valve as core components have a direct impact on vehicle safety issues.Therefore,research on hydraulic control unit and high-speed solenoid valve is very important.The purpose of this paper is to carry out simulation testing and optimization control of the ESC hydraulic control unit,providing ideas for the design and optimization of the HCU.Firstly,analyze the overall physical structure of the hydraulic control unit.Then the two working condition of the hydraulic control unit is studied,including the execution state of the high speed on-off valves,motors and other components in the hydraulic control unit during active pressure regulation and passive pressure regulation.And the function of multiple check valves inside the hydraulic control unit and the high frequency PWM control of the high-speed solenoid valve as the main executive component are analyzed,which lays the foundation for the following simulation models and control methods.Next,build the simulation model of the HCU and analyze its dynamic characteristic.The premise of dynamic characteristic analysis is to study and analyze the mathematical physics model of each module in the hydraulic brake system,and then to establish AMESim simulation model including ABS system and ESC system according to mathematical physics model.Select the parameters of the model according to the actual situation.The influence of the change of main parameters on the characteristics of the increasing and decreasing pressure of ABS and ESC is simulated and analyzed.The curves of increase and decrease pressure under different parameters are obtained,which can provide a reliable hydraulic environment for the subsequent research of high-speed solenoid valves.Afterwards,the mechanism and system of high-speed solenoid valve is analyzed.Based on the principles of electromagnetics and fluid mechanics,the mathematical models of electromagnetic force,friction force and hydrodynamics of outflow valve and inflow valve are established.The time response characteristics of the electromagnetic force and the current under different duty cycles are studied.The influence of structural parameters such as valve inlet and outlet diameter,seat cone angle,pressure drop at both ends of valve and radius of spherical valve core on the steady flow force and transient flow force is analyzed.The Simulink model of high-speed solenoid valve is embedded into the AMESim model of ESC hydraulic brake system in the form of S-function to simulate the valve spool displacement response of high-speed solenoid valve under different PWM duty cycle control signals.Analyze the electromagnetic force and hydrodynamic force.Then the proportional opening function of high-speed solenoid valve is researched.The spool displacement and wheel cylinder pressure under different duty cycles are observed.The duty cycle range of proportional opening under different valve structure parameters is obtained to guide the direction of valve structure optimization.Finally,the Simulator manufactured by dSPACE was used as the pressure acquisition platform.The RapidECU manufactured by Huahai Company was used as a rapid prototyping controller,and the hardware-in-the-loop test bench was constructed by the signal line and the built hydraulic braking system.The correctness of the hydraulic control unit simulation model is verified by the test bench test.And the test results show that the hydraulic control unit has the functions of increase/hold/decrease pressure,and the conversion valve has the function of limiting the pressure in certain high-frequency PWM duty cycle range. |
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