Study On Modeling And Simulation Of Electric Power Steering System

Steering performance is one of the most significant driving performances,has been emphasized since the first automobile was born.The development of steering system experienced four phrases:Mechanical Steering(MS),Hydraulic Power Steering(HPS),Electric Hydraulic Power Steering(EHPS) and Electric Power Steering(EPS).The electric power steering system (abbreviated as EPS) has the advantages of saving energy,protecting environment,active safety and advanced handling and stability performance,will be equipped in intermediate cars,sports cars and sport utility vehicles(SUV),not only limited in mini cars and economical cars.The EPS not only provides assist power when automobile runs at low speed,but also plays a key role when it runs at high speed,and EPS types become more and function becomes strong.Modeling of the electric power steering system was studied,and design of its control strategy was analyzed in the paper.To begin with,based on automobile dynamics modeling theory,work principle and components of EPS were researched;and mechanical steering parts,assist motor and retard gear model were built,which were combined with three-freedom car model and Fiala tire model,in order to compose the total model for EPS assist-characteristic simulating analysis.And then,for establishing desired assist motor current and achieving it,steering wheel torque and motor velocity were chosen as control variables , and the PD(Proportion and Deviation) control strategy was designed . Line-type assist characteristic was analyzed theoretically,and the value law of EPS control strategy parameters was found in terms of steering agility,steering feel and return-ability.Three kinds of typical steering tests including static steering,on-center steering and steering wheel returning with release were simulated,and simulation results indicate that control strategy can achieve expectation.With EPS,the driver steers the steering wheel more easily,and his steering feel becomes better and obvious as speed increases;when the steering wheel returns without hands on at high speed,it returns to its initial position smoothly and quickly.Therefore,automobile active safety and handling and stability are both improved.Finally,in order to build a more real and accurate car model,based on system multi-body dynamic theory,the multi-body dynamic car model including pinion and rack steering system,front macpherson suspension system,rear multi-link suspension system,magic formula tires and FF(Front Front) driving power system was developed in the environment of ADAMS/ Car software.The accuracy of car model was verified after stability corning test was simulated and done.To simulate complex control system,electric control unit(ECU),motor and gear system block diagram were built in the environment of MATLAB/Simulink software.After I/O(input and output) interface was defined,car model and control system model can be co-simulated.Steering performance of the car with or W/O(without) EPS was analyzed and studied,through simulating the whole model though the lemniscate test,on-center steering tests and steering wheel return-ability tests.