Research On The Control And Coordination Method For 4WID-4WIS Electric Vehicle

The four-wheel independent driving and four-wheel independent steering(4WID-4WIS)electric vehicle is equipped with four in-wheel-motors and four steering motors,which is different from the electric vehicle that only replaces engine with motor.Compared with traditional vehicles,the 4WID-4WIS electric vehicle has more controllable degrees of freedom,and this makes it have unexampled advantages in the view of the saving energy control and the handling stability control.However,this also means that the dynamics control system for the 4WID-4WIS electric vehicle which has a crucial impact on the vehicle performance needs a completely new design and research.Based on the vehicle handling stability,the paper focuses on the research of four-wheel steering(4WS)control system,4WIS control system,4WID control system and 4WID-4WIS coordination control system.The detailed content of this paper includes a few aspects:(1)The 4WID-4WIS electric vehicle dynamics model that contains the 8-DOF vehicle body dynamics model,the GIM tire model,the driving system model and the steering system is established.Meanwhile,a driver model named YAT driver model is proposed based on the yaw angle tracking.The test results prove the rationality and validity of the model.The established 4WID-4WIS electric vehicle dynamics model lays a foundation for later studies.(2)A radial basis function(RBF)neural network controller for 4WS system is designed by applying the theory of artificial neural network.The designed RBF controller has been trained by using the direct off-line training method and the off-line training and on-line revising method separately.In the process of the direct off-line training,a ?feedforward+feedback? data acquisition unit is proposed for the collection of training data.In the process of off-line training and on-line revising,a closed-loop direct training system and a RBF identifier are designed.The former is used for the off-line training,and the latter is used for the on-line revising.The experiment and analysis are shown that,the proposed RBF controller for 4WS system has good control effect on the side slip angle,but less control effect on the yaw rate.Because 4WS system has only one control output that makes it difficult to satisfy two control objectives well.(3)The study is extended to the 4WIS system which could overcome the shortcoming of 4WS system.After establishing the ideal vehicle dynamic model,a 4WIS LQR controller for model following purpose is designed by using optimal control theory.Then,from perspective of vehicle dynamics,a steering angle adjustment strategy based on vehicle steering state is proposed by analyzing the 4WIS vehicle dynamic characteristics.The proposed adjustment strategy can improve the utilization of the lateral tire force.Based on the correspondence between the LQR control parameters and control outputs,the wheel steering angle adjustment strategy is mapped to the control parameters adjustment strategy.With the help of expert control theory and genetic algorithm(GA),a GA-based LQR control parameter adjuster is designed.With the help of fuzzy control logic,a fuzzy logic LQR control parameter adjuster is also designed.Two varying parameter LQR(VLQR)control systems are established by combining the model following LQR controller with different control parameter adjuster.Simulation results demonstrate that the VLQR control systems are both have a better control effect,which can meet the side slip angle control objective and the yaw rate control objective simultaneity.Besides,the proposed control systems have strong robustness and good capability of preventing lateral disturbance.(4)A 4WID control system has been put forward,which includes the functionalities of vehicle speed control and assist steering control.The coordinated control strategy between 4WID system and 4WIS system is further studied.According to the wheel steering angle adjustment strategy of 4WIS system,an assist steering additional torque allocation strategy of 4WID system is proposed.The proposed allocation strategy will not affect the 4WIS system and not change vehicle speed when the assist steering function of 4WID system works.Through the additional torque allocation strategy,the coordination between 4WID system and 4WIS system is implemented.Furthermore,an acceleration slip regulation based on the slip threshold is designed,which can solve wheel's skid and improve the function of the 4WID-4WIS coordinated control system.Simulation results demonstrate that the 4WID-4WIS coordinated control system has a great effect on improving vehicle handling stability,keeping lane under extreme condition and acceleration slip,and enhances the vehicle driving and steering safety very significant.(5)Hardware-in-loop simulation platform includes NI PXI real-time system hardware,AC servo motors and their drivers,angle sensors,data acquisition cards,drive/brake pedal,steering wheel and photoelectric encoder is established.A few tests about the established hardware-in-loop simulation platform and 4WID-4WIS coordinated control system hardware-in-loop simulation have been completed.The results show that the established hardware-in-loop simulation platform is running well and it can be used for the real-time environment test of 4WID-4WIS dynamics control system.The 4WID-4WIS coordinated control system has ideal control effects in real-time environment,and can effectively improve vehicle handling stability.