Research On The Assistant Motor Control Strategy Of EPS In A Sedan Using Simulation Methods

EPS (Electric Power Steering System), which was developed in order to meet steering handiness at low speed and road feeling at high speed, completely abandoned the hydraulic mechanism, is a power steering system which adopts motor to provide assist torque, which is controlled by ECU (Electric Control Unit), according to the velocity of the vehicle and the torque of the steering wheel. Torque that is exported by motor is translated by steering system gearing and can be used to help driver steer. Because of their great predominance, it has been increasingly applied in a wide variety of vehicles, and gradually has a trend to replace the hydraulic power steering system. In the EPS system, the core technology is focus on hardware and software two aspects: hardware mainly refers to the motor and deceleration; software refers to motor's control strategy.The thesis focused on the model of EPS steering system and motor's control strategy. The following is the mainly content of the thesis:Chapter one introduces development process of power steering system, development actuality at home and abroad, structure and principle, the key components, advantages, key technology and the direction of development of EPS.Chapter two is about to how to build the model of steering system of EPS and the whole vehicle. According to the actual electric power steering system structure, EPS model is built using reduced-order modeling methods; Secondly, the software Simscape is introduced, which is an expansion module of Simulink in MATLAB 2007a; moreover, the simulation model of EPS steering system is built using the Simscape software; Thirdly, vehicle system dynamics software—Carsim is introduced, and build the vehicle simulation model; Finally, the steering system simulation model and vehicle model get together and make up of the thesis simulation model. At last, using sinusoidal test, the normal steady rotation test and aligning test is to test the model. Chapter three is about to the matching and model of assisted motor. Firstly, the thesis analyzes and discusses installation location of the motor and style; secondly, it brings some requires about the size of motor,the output torque and steering speed; Thirdly, according to the assist characteristic of the original hydraulic steering, motor's torque and steering speed, the motor electrical parameters are designed. Following, introduc the software SimPowerSystems, and also use the software to build the equivalent simulation model of a brush DC motor, at last gain the mechanical properties of motor; finally, the motor simulation model is improved, and gains the final simulation model.Chapter four is about to joint simulation of EPS assist system. According to the steering handiness and road feeling, ideal steering wheel torque that the driver needs is introduced. Secondly, there are three kinds curve forms of EPS system's assist characteristic: straight-line, broken-line and curve. Moreover, in order to coordinate the relation between steering maneuverability and road feeling, the assist curve should vary with vehicle speed, namely the speed-varied straight-line assist characteristic. At last, according to the characteristic of speed-varied straight-line and in situ steering hydraulic assist curve, the EPS's speed coefficient of speed-varied straight-line assist characteristic is gained using the joint simulation model of the vehicle model and assisted model. The thesis can obtain speed-varied straight-line assist characteristic quadratic fit of throught speed coefficient of speed-varied straight-line assist characteristic in order to implement assist control of the motor.Chapter five is about to the simulation research of the motor's control strategy. Firstly, the control methods of the EPS's assist characteristic is analysed and introduced, which considers basic control and compensate control. Moreover, basic control is composed of assisted control, align control and damp control; compensate control is composed of friction compensation, inertia compensation and damp compensation. Secondly, the thesis adopts current control of the motor in order to implement the motor's control target, namely D-value of goal current and current of a measurement proceeds PID control. At the same time, the drive of the motor is finished by voltage, so the control of motor must add a voltage's feedforward control in order to drive motor. Thirdly, the motor's sumulation model obtains using the joint of the vehicle model and motor model, and is validated by simulation. At last, the thesis does some simulation researches, including assist control, dynamic following characteristic align control and damp control in the steering system.Chapter six is the conclusions and the further work. Firstly, sum up thesis work. Secondly, point out the shortage of the thesis and the future research direction.