Research On Optimal Torque Vectoring Control For Lateral Stability Of Dual-motor Drive Vehicles

With the reduction of fossil fuels and the aggravation of environmental pollution,in the automotive industry,distributed drive electric vehicles have gradually become a research hot topic for their advantages of environment-friendly,high transmission efficiency,compact structure and independent control of driving wheels.Meanwhile,with the independent controlling of driving wheels,it also poses great challenges on the lateral stability control of distributed vehicles.Most of the current researches of vehicle stability control strategy focus on improving lateral stability of the vehicle by controlling the yaw moment through differential braking.However,the control strategies based on differential braking deteriorate the longitudinal performance.Besides,due to tire nonlinearity,the robustness of the control methods based on two degree of freedom(2DOF)vehicle model is poor.Thus,according to the nonlinearity of a dual-motor drive electric vehicle,an optimal torque vectoring control(TVC)system based on the approximate linear quadratic regulator(LQR)optimal control is proposed and analyzed in this thesis.The structure of the control system consists of three parts,i.e.pre-processor,model following controller and post-processor.Pre-processor estimates the vehicle motion state parameters and an accurate Magic Formula tire model is obtained.A nonlinear vehicle model with changing lateral stiffness is built in the model following controller.An optimal control system with a gain scheduling method based on CG longitudinal velocity and lateral acceleration is developed as well.In the post-processor,a torque vectoring control is proposed considering the constraints of motor peak torque and tire friction circle.Finally,co-simulations of LabVIEW and CarSim under different driving maneuvers show that yaw rate and longitudinal velocity responses are improved.Meanwhile,Hardware-in-the-Loop(HIL)test platform and simulated driving experiments are established to verify the effectiveness of the designed optimal torque vectoring control system in real-time.In summary,a nonlinear vehicle model based on Magic Formula tire model is built in this thesis,and an optimal TVC system for dual-motor drive vehicle is proposed,which can significantly improve the lateral stability and longitudinal performance of the vehicle simultaneously.The HIL experiments prove that the proposed control system has good practical value in stability control.In the future,the real racing car tests are expected.