Research On Coordinated Control Of Straight Driving Stability Of Four-Wheel Independent Drive Electric Vehicle

With the rapid increase of the annual output and the quantity of the global automobile,the energy crisis and the environmental pollution have become the two worldwide difficult problems which puzzle the mankind,so the development of the new generation electric vehicle has become the hot spot of the automobile research and development.The four-wheel independent drive electric vehicle is a kind of electric vehicle with a very broad prospect of development.It has the advantages of independent control of four-wheel drive torque,easy measurement of torque and speed,high transmission efficiency and so on.It is beneficial for the coordinated distribution of vehicle driving force and dynamic control,and it is suitable for the miniaturization and intelligent development of electric vehicles.In this thesis,the four-wheel independent drive electric vehicle is taken as the research object,and the coordinated control of the vehicle straight driving stability is studied.Firstly,the vehicle dynamics model of four-wheel independent drive electric vehicle is established by the vehicle dynamics software CarSim.According to the vehicle dynamic performance index,the matching calculation of wheel hub motor is carried out,and then the motor model is established in MATLAB/Simulink software.Through the CarSim-Simulink joint simulation platform,the straight driving ability of the vehicle is verified,which lays a foundation for the subsequent vehicle control system.Secondly,the straight driving stability of four-wheel independent drive electric vehicle is introduced,from the longitudinal and lateral force situation of the whole vehicle analyzes the causes of the straight driving deviation,and from the point of slip rate analyzes the vehicle driving stability.The factors that affect the vehicle’s straight driving stability and the corresponding conditions are classified and summarized.The yaw rate and slip rate are selected as the control variables of the coordinated control system.Thirdly,aiming at eliminating the influence of the motor torque control error and different road surface on the vehicle straight driving stability,a four-wheel independent drive electric vehicle straight driving stability coordinated control system is designed.The control system is composed of two parts: the upper controller based on PID algorithm and the sliding mode variable structure algorithm and the lower controller based on rules.The upper controller includes a speed following controller,an additional yaw torque controller and a driving anti-slip controller.The lower controller is a torque coordination allocation controller.Then,the dynamics model of the whole vehicle and the straight driving stability coordinated control system are integrated,and a four-wheel independent drive electric vehicle joint simulation platform based on CarSim-Simulink is built.The two side hub motors can’t provide equal torque and different adhesion coefficient road surface conditions are used for simulation analysis.The simulation results show that the vehicle single wheel slip rate is controlled within 0.15,and the yaw rate is controlled within 0.3(/s).Thus,the straight driving stability of the vehicle can be effectively guaranteed.Finally,the real-time simulation platform based on dSPACE is used to verify the reliability and real-time performance of the control algorithm,the real-time simulation results show that the algorithm has good real-time performance and reliability.