Design And Pressure Control Of Integrated Electro-Hydraulic Brake System

The brake system that has a great impact on ride comfort and handling stability is one of the most important subsystems of the car,which is the execution unit of Advanced Driving Assistant System and Automatic Driving System as well.This paper concentrates on the design and pressure control of integrated electro-hydraulic brake(I-EHB)system,including the hydraulic circuit design,the feed-back design of pedal sensation simulator,the decoding of linear inductive position sensor,the pressure control based on cascade PID control and integral sliding mode control.The contents of this paper are:(1)Three programs of electro-hydraulic brake system are designed and those basic brake function,failure backup braking,advantages and disadvantages are discussed.I-EHB system is the final one in consideration of brake comfort and the difficulty of development.A pedal sensation simulator is designed to have the same characteristic of pedal force versus displacement as the traditional brake system by optimized the stiffness of its two springs.The linear inductive position sensor of I-EHB system is decoded based on Geortzel algorithm,and the algorithm efficiency and linear range of the sensor are tested.(2)The magnetic force and inductance of coils of the valves are calculated by Maxwell software,including isolated valve(normally open valve)and control valve(normally closed).In AMESim software,the models of both valves are built,in order to get the dynamic characteristic of them.The duty cycles of the PWM voltage signals which are loaded on the coils are 40% at the very beginning,and after 10 ms,they are calculated by the inlet side pressure of both valves,which aim at responding quickly and reducing the heat generated by the coils.(3)A fifth-order model for I-EHB system is derived from its mechanical and hydraulic subsystems.The model is simpilfied and linearized at equilibrium states of 20,50,80 bar,and then the third-order transfer functions of the I-EHB system are derived,which are verified by AMESim software.The friction of I-EHB system is analyzed based on Stribeck friction mode and the control-oriented model of I-EHB system is derived by simplification.(4)In order to reduce the impact of the deadzone in the servo master cylinder,A cascade controller composed by position and pressure control is designed based on PID control.While the friction is ignored,with the cascade controller in which the PID parameters are tuned based on the I-EHB system transfer functions,the response time of the pressure in the servo master cylinder is less than 80 ms and the overshoot is within 6%,which helps improving the braking safety and comfort of the I-EHB system.Based on the control-oriented model,the integral sliding mode controller is designed and simulated in Matlab/Simulink.With the friction as external disturbance,under the control of integral sliding mode controller the response time of the pressure in the servo master cylinder in a little more compared to the cascade PID controller,but less overshoot and better Robust performance.