Modeling, Simulation And Test Of Electric Power Steering System

Electric Power Steering System is one of the most important subsystem in the modern automobile, as well as the safety part of the vehicle. At the beginning, according to reaserch some relevant document, introduced 5 types of steering system which are the mechanical steering system, mechanical and hydraulic power steering system, electric hydraulic power steering system, electric power steering system and power steering by wire system. Then analyzed each of the steering system structure and working principle, through the horizontal comparison between steering system, analyzed the advantage and development prospect of electric power steering system. Put the advantage of electric power steering system as the starting point of this paper.The main research object of this paper is Column Mounted Electric Power Steering System, and introduced the structure principle, control strategy, mathematical modeling, simulation and experimental analysis.Fistly, analyzed the dynamic route of EPS, then simplified EPS parts based on this route, got the simplified model, steering mechanism, torque sensors, power motor, output shaft, intermediate shaft and pinion and rack, then established the mathematical model for all of the parts. According to the input and output characteristics of electric power steering system, chose the handwheel torque and motor torque and the road random signal as state function input variables, and chose the steering wheel rotate angle, handwheel rotating speed, the displacement of rack, rack linear velocity, angle of motor rotor, the rotating speed of the motor as the state function output variables. Obtained the state function for the EPS after simulataneous each equations.Secondly, analyzed the three kinds of dynamical characteristics of electic steering system, which are linear type, folding type and curve type of dynamical characteristics curve. After the power characteristic curve was obtained by analysis and calculation of maximum current of assist motor, minimum handwheel torque and current, designed two current controller to control the current value in terms of the velocity of the vehicle and the handwheel input torque. Introduced the control strategy, especially fuzzy control and PID control. Analyzed the advantages and disadvantages from the simulation curves.Built target current controller simulation model, assist motor simulation model, EPS input and out put simulation model in Matlab/Simulink, and analyzed the simulation curve, confirmed the results have reached the design requirements. Then built the simulation model of EPS by connect each one of the models. Set different input paramaters, such as vehicle speed and handwheel torque, to verify the performance of the simuliation model. The result curves showed the model can meet the requirement of the control strategy design.Finally, analyzed the test requirements for an EPS products. Introduced and run the friction test, assist characteristics test and motor performance test. Evaluated the model performance by the test results and the evaluation range, to decide whether EPS could meet the design requirements.