Design And Simulation Of The Electrical Assistant-Power Steering System On Car

The electric motor provides the assistant power for the Electric Assistant-Power Steering (EPS) system directly, and the magnitude is controlled by Electrical Control Unit (ECU).The EPS reduces the driver's force put on the steering wheel when the vehicle is in the state of low speed, improves the agility function of manipulation system. When the vehicle is turned up from low speed shift to high one, the Electric Control Unit ensures steady steering road-feeling, improve the steady of vehicle when it is in the state of high speed, and the EPS has many virtues such as saving the fuel, no leaking, and is good for environment safety and so on, which can be realized by traditional hydraulic assistant-power steering and electric controlled hydraulic assistant-power steering system. And The EPS is a new high technology that has compact relationship with vehicle's development, it is also one of the developing direction of assistant- power steering technologies, has wide application foreground.In this paper, I have consulted many related books, technology literatures and data about EPS, have comprehended the basic working theory, that's when steer by manipulating the steering wheel, the torque sensor detects the torque operated on the steering shaft and give an electric signal, at the same time the vehicle speed sensor gets the speed of vehicle and gives an electric signal, too. According this two signals, ECU doing the logical calculation and analysis, get the goal electric current through the knowing assistance characteristic curve , and adjust it, give the electric motor an appropriate electric current to make corresponding torque, which will be operated on the steering organ through retarder framework to get steering that suit the state of vehicle.In this paper ,have introduced the main constitutes of EPS minutely , explain working theory and what type to choose of the main parts, includes the Electric Control Unit, Torque Sensor, Vehicle Sensor , current Sensor,Electric Motor and so on.The assistance characteristic of EPS means the law of assistant power changed with the state of vehicle. For the EPS, use the relation among the electric current, torque on steering wheel and vehicle speed to show its Assistance Characteristic. The Assistance Characteristic has important influence to the function of assistant power steering system, including the function of handiness, return ,road-feeling. According different type of vehicle, the assistance characteristic curve also has many kinds, and can be divided three kinds: line, fold ,curve. In this paper, I have brought forward a new assistance characteristic analysis scheme which is based upon the fuzzy control theory .When the signal of torque and vehicle speed have been transmitted into the ECU, first, ECU will decide the goal torque according the assistance characteristic ,then through the special control algorithm which is the content of control theory, make the actual torque follow the goal torque. In short , the course of realize the control strategy is deciding the goal torque and following.In this paper, use the Fuzzy Logic block of MATLAB to get assistance characteristic, when input the torque and vehicle speed, the goal electric current can be gotten, while most of control strategies usually get goal torque according special assistance characteristic chart when have known the size of torque input torque and vehicle. so the new control strategy in my paper has reduced the loops, save the room of system.The hardware circuit of EPS'S controller is constituted by DSP, input interface block of vehicle speed and torque sensor, battery voltage monitor block, electric current of motor monitor block, driving block of electric motor, malfunction diagnosis and display block and so on, the DSP is the core of controller, it collects the output signal of torque and vehicle speed sensor, drives the electric motor through the driving circuit of motor, achieve the function of safety monitor, malfunction check and display. It also provide working condition for the software.The main tasks of software of EPS include: system's initialization self-check, signal collection of torque and vehicle speed from sensors, the collection of monitor information about battery voltage and electric current of motor, output control of clutch,malfunction self-diagnosed, displayed and stored .The main programs are used to finish the initialization of system, include the initialization of block inside and outside the chip of DSP,enactment of halt task and priority, the start-up of safety monitor block , the start-up of state and malfunction display block and cooperate many tasks. The signal collection block includes two parts: torque signal collection and vehicle speed collection. Besides, in order to reduce the interference of signals from outside, design the numeral filter program. and also do reliability design to assure the system can work normally.In the last part, use the software ADAMS/view block to build a model, and build simulation model of EPS control system in MATLAB/Simulink. get the electrical current curve when the vehicle speed is 20km/h,40km/h,60km/h,80km/h,100km/h. use the mean referred in the chapter 3 to get the current value ,compare this two results, validate the correction and practicability of the model built in this paper. According the character of motor, get the assistance torque chart, and we can see that the EPS design in the paper can provide good assistance torque, make the steering handy, have good road feeling, and improve the active safety of vehicle, so the paper get original the design goal...