| The brake system is an important subsystem that has a great impact on the driving stability and safety of the car,which is one of the key execution units of smart cars and their active safety systems.This thesis concentrates on the design and control method of the electro-hydraulic brake(EHB)system,including the design of solenoid valves,pedal sensation simulator and pressure sensor,the derivation of mathematical model and simulation of the EHB,the pressure controller design of the EHB,the modeling and co-simulation of anti-lock brake(ABS)system based on EHB.The contents of this thesis are:(1)The scheme of EHB is designed,and the hydraulic principle and implementation method of EHB in the brake-by-wire and fail-back brake modes are discussed.The solenoid valve is modeled,and the electromagnetic and flow fields are simulated with Maxwell and Fluent software.The dynamic characteristic simulation model is established on the Simulink software and verified by experiments.The hydraulic characteristics test bench of the solenoid valve is built,and the minimum opening,closing and maintaining duty and current are tested.Taking pedal force-stroke characteristic curve of 3-step slope as the design goal,a combined spring-type passive pedal simulator is designed.The pressure value of the pressure sensor is analyzed to verify and guarantee the test accuracy of pressure sensor with the hydraulic test bench.(2)The mathematical models of the motor-piston subsystem and servo cylinder-solenoid valve-wheel cylinder subsystem of EHB are established.The second-order transfer function is obtained after linearization of mathematical models above.Considering the nonlinear characteristics of the solenoid valve and wheel cylinder,the nonlinear model of EHB is obtained.The correctness of the linear model and the nonlinear model is verified with Amesim software.In addition,the influence of system structure parameters on the performance of EHB system is also analyzed.(3)To solve the problems of large step pressure response overshoot in the linear model of EHB,a variable parameter pressure controller is designed.To solve the problems such as the pressure dead zone in EHB and the premature intervention of the motor torque during variable parameter PID control,and considering the control characteristics of motor,a multi-loop pressure control method is designed.The experimental bench of EHB is built to verify the effectiveness of the multi-loop control method.(4)The wheel speed calculation method of the wheel speed sensor in the automobile anti-lock brake system is given,and the correctness of this method is verified with Simulink software.Considering the complete dynamic characteristics and constraints of the EHB,the third-order transfer function of the motor torque and slip rate is obtained.An anti-lock brake control method based on Youla parameters is designed.A co-simulation model of Carsim and Simulink is established,and the feasibility of the EHB applied to the anti-lock brake system of the car is verified. |
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