Research On Coordinated Control Of Active Rear-Wheel Steering And Direct Yaw Moment For Distributed Drive Electric Vehicle

The distributed drive electric vehicle has the advantages of energy conservation,environmental protection and high transmission efficiency,and each wheel torque is independently controllable,which provides favorable hardware conditions for vehicle handling and stability control.However,under extreme conditions,low adhesion road coefficient,large sideslip angle steering and motor out torque limit make the tire force easy to reach saturation,which makes it difficult to fully guarantee the vehicle dynamic stability with a single direct yaw moment control(DYC)mode.Active Rear Wheel Steering(ARS)control can further improve the ground adhesion performance of tires and effectively reduce the vehicle’s tail flick or roll under dangerous conditions.Therefore,this paper takes the distributed drive electric vehicle as the research object,and designs and integrates the coordinated control strategy of active rear wheel steering and direct yaw moment.The main work is as follows:A three degree of freedom dynamic mathematical model of the distributed drive electric vehicle is established,and the mechanical properties of the tire are estimated using the magic tire model.On this basis,through linearization,a two degree of freedom reference model of the vehicle is established.The power transmission system and steering system of the vehicle dynamics model are set in Car Sim software,and a distributed drive electric vehicle model with rear wheel steering is built.The motor drive controller,rear wheel steering controller and vehicle dynamics controller are respectively established in Matlab/Simulink software,Finally,a joint simulation platform for dynamic control of distributed drive electric vehicles is built.The influence mechanism of yaw rate and sideslip angle on vehicle handling stability is analyzed.The model predictive control strategy of active rear wheel steering is designed,and the simulation experiments of double lane shifting and serpentine working conditions are carried out.Compared with the traditional front wheel steering control and the active rear wheel steering based on LQR,the results show that under certain working conditions,the designed active rear wheel steering MPC strategy can provide the lateral yaw correction torque for vehicle stability control,effectively restrain the vehicle centroid sideslip angle,improve vehicle stability and maneuverability,but under dangerous working conditions such as low adhesion road surface and high speed big steering,The control ability of active rear wheel steering is limited due to the rapid saturation of tire cornering force.The vehicle handling stability judgment method based on phase plane theory is studied.The vehicle dynamics control area is divided into stable area,unstable area and coordinated control area.The active rear wheel steering and direct yaw moment coordinated control system is designed with a hierarchical structure.In the upper coordination controller,the fuzzy control algorithm is used to obtain the boundary coefficient of the coordination control area,which provides an accurate basis for the intervention of the stability controller,and then determines the control weight of the active rear wheel steering and the direct yaw moment.In the lower controller,the sliding mode control algorithm is used to calculate the additional yaw moment.Finally,according to the control weight assigned by the upper layer,the rear wheel steering angle and the direct yaw moment are coordinated.The analysis of joint simulation results shows that the proposed coordinated control can achieve accurate tracking of ideal yaw rate,reduce the impact of longitudinal speed on stability,give full play to the respective advantages of active rear wheel steering and direct yaw moment control modes,and improve the vehicle stability control margin.