A Research On Method Of Pressure Control Of Integrated Electro-Hydraulic Brake System

This paper chooses the Integrated Electro-Hydraulic Brake System(I-EHB)as the research object in order to meet the increasing demands on brake system.The working principle of IEHB system under different braking conditions is analyzed and a mathematical model of I-EHB system with variable load is derived from its mechanical and hydraulic subsystems.Then the model is linearized at equilibrium state and its correctness is verified.Since the system load is variable during braking,a PID-based scheduling controller is designed,a test bench for the IEHB system is built and the effectiveness of the PID-based scheduling control method is verified by hardware-in-the-loop tests.Based on the solenoid valve flow test bench,the relationship between flow and pressure of normally open valve is obtained from test,which provides a basis for simplifying the throttling characteristics of solenoid valve.A scheduling controller based on sliding mode control is designed,which optimizes the motor output torque and improves the anti-disturbance capability.(1)The working principle of I-EHB system under different braking conditions is analyzed.Both mathematical models of I-EHB system with four wheel cylinders and two wheel cylinders are established and verified by AMESim software.The effect of motor torque constant,damping coefficient,piston diameter and equivalent contact stiffness on the dynamic response of the I-EHB system is analyzed.A model of internal leakage is established and the influence of the servo cylinder’s structural parameters on the leakage is investigated.(2)As the system load is variable when braking,a PID-based scheduling controller is designed,which could be switched according to different workloads.The simulation results show that,compared to PID controller,PID-based scheduling controller is able to reduce pressure response time to less than 110 ms with zero overshoot under step input.(3)The PID-based scheduling controller can solve the variable-load I-EHB pressure control problem well,but large motor output torque is required.A scheduling controller based on sliding mode is designed,compared to scheduling PID controller,the scheduling controller based on slide mode control results in a shorter pressure response time and reduces the motor torque by more than 0.7N·m.The ABS control strategy is designed based on sliding mode control method.The results of the simulation on road with adhesion coefficients of 0.7 and 0.4 show that the designed control strategy makes the slip rate fluctuate less and is closer to the optimal one,and shorten the braking distance.(4)Hardware-in-the-loop tests based on the I-EHB system bench are performed to verify the effectiveness of the PID-based scheduling control method under pressure input and pedal displacement input.A flow-pressure test of normally-open solenoid valve is conducted and the relationship between the pressure and flow of the valve is obtained,which provides a basis for linearizing the throttling characteristics of the valve.