Study On Differential Drive Assist Steering And Yaw Moment Control For The In-wheel Motor Electric Vehicle

With the trend of energy conservation,environmental protection and safety proving to be the three major themes of current automobile development,electric vehicles have become the focus of automotive industry.In-wheel Motor Electric Vehicle(IEV)integrates the drive motor and wheel into a whole,which not only greatly simplifies or eliminates the traditional mechanical transmission device,but also provides a new type of vehicle driving mode.With the development of power electronic technology,this driving form can control the torque of each wheel independently,rapidly and accurately.It would not only realize the chassis dynamic control of traditional vehicle conveniently,but also could develop new functions and technologies that are difficult to be realized in traditional vehicles.In order to make full use of the unique advantage of IEW,it is of great significance to develop fine control systems to improve the vehicle maneuver stability.Therefore,this article mainly launches the research from the following several aspects.(1)Establish a IEV dynamic model.To provide a fundamental for the research in following chapters,a vehicle model with seven degrees of freedom including longitudinal,lateral,yaw motion of vehicle and the rotation of the four wheels and other related sub models containing the tire model,steering system model,driver model and motor model is developed.Moreover,the vehicle model is verified by CarSim vehicle dynamics software.(2)Research on differential drive assist steering(DDAS)control.Firstly,the basic principle of DDAS is analyzed;Secondly,after summary of the advantages and disadvantages of the three kinds(straight line,broken line and curve type)of power assisted characteristic curves,a DDAS is proposed based on the curve type assisted characteristic with quadratic curve.Finally,the simulation analyses are carried out through three different steering wheel angle input and initial speed.(3)Study on vehicle direct yaw moment control(DYC).In order to solve the problem of yaw stability and track keeping in the extreme condition,a yaw moment sliding mode controller based on vehicle yaw rate and sideslip angle is presented.Aiming at the chattering problem of sliding mode control and integrating all advantages of sliding mode control and fuzzy logic control,a fuzzy sliding model control strategy is employed.In addition,a nonlinear sliding mode observer(SMO)with simple structure and fast calculation is set up to deal with the problems that the vehicle sideslip angle and tire force are difficult to measure directly.The SMO and DYC are verified by simulation.(4)DDAS and DYC joint control.According to the researches above and the systematic summary of the relationship between DDAS and DYC,a joint control method is proposed,considering the DYC in the whole with which DDAS is satisfied priority in the local.Last but not least,the joint control system is verified through the simulation of serpentine and lemniscate tests with driver-vehicle closed-loop system.