The Study On Control Strategy Of Electric Power Steering

EPS system is a new type of power steering system,because of its energy-saving,environmental protection,simple structure,better stability,once launched,it will be highly regarded by many companies and research institutes.The performance of automobile steering is optimized by means of the motor installed in the steering system and electric control unit.At the time of turning vehicles electric control unit can receive the current state of the automobile information,and then feedback it to the steering system to provide the appropriate power.So the EPS can ensure steering light and sensitive at lower velocity and maintain stability at high speed.EPS has become a focus in the reasearch of the automotive power steering technology,and it will have broad market prospects.First of all,this paper reviews the development of automobile steering system and lists the specific advantages of it,and summarizes the research status about EPS at home and abroad.It is determined that the overall research contents of this paper.Secondly,on the basis of understanding the working principle and the structure,this thesis analyze the system dynamics and set up the dynamic model of them.Then the method of curve fitting for power curve designed and studied the power control strategy of EPS in order to get the vehicle ideal power curve at full speed.The complex power expression is transformed into the form of two product of one doller function(The product of the function of the speed induction coefficient and the moment)and the use of cftool to get the corresponding fitting curve and the system of the power curve through the experiment to get the relevant data.In addition,the return to center control strategy is also the focus of this paper.The method of trial and error to get the reasonable parameters is used and then design a PID controller of EPS.Use the trail and error method in the Carsim-Simulink and hardware in the loop platform to adjust the parameters of the controller.To ensure that the response of the system in the consistency and accuracy,the power compensation control and motor current control are added during the modeling process.Thirdly,the traditional steering system,the boosting motor,the power control module and the return control module is setted up in MATLAB/Simulink environment.And it is embedded in Casim-joint Simulink simulation platform.The input,output and testing condition are setted on the simulation process.The simulation results show that under the same conditions,to join the EPS system after the steering wheel torque values is less than no EPS system of torque values.These results proved the design of the EPS system on the steering portability was significant.After join the return to center control,the steering wheel can more quickly back to the middle position,basically eliminated the residual angle at low speed and the phenomenon of overshoot.It is also explained the feasibility of joint simulation in the study of EPS.Finally,the EPS system hardware in loop experiment platform and dSPACE-CarSimjoint simulation environment is built.The results show that the vehicle with EPS system in steering portability,return to center and stability are improved significantly compared with no EPS system.It is verified that the effectiveness of the EPS system,the correctness and validity of controller and the control strategy designed.