Research On Coordinated Control Method Of Active Front Steering And Direct Yaw-moment For Vehicle

All along,the active safety is one of the hot issues in the automotive industry.As the chassis system becomes larger and larger,the coupling problem between subsystems becomes more and more serious.Integrated chassis control can not only solve the interference between vehicle dynamics,but also optimize the vehicle performance.And in the environment of environmental protection and energy problems,electric cars are more and more popular.Compared with traditional cars,electric wheel-drive electric cars have the unique advantage of being able to independently control the torque of each wheel,which is more conducive to the integrated control of each chassis system.Active front wheel steering(AFS)and direct yaw moment(DYC)are also future development trends,so it is of practical engineering significance to integrate them in electric vehicles.In this paper,the hub-driven electric vehicle is taken as the research object,aiming at the coupling interference problem of AFS and DYC subsystems under certain operating conditions,AFS and DYC controllers are established respectively.The phase plane method is used to analyze the vehicle stability,establish the coordination controller,design the coordination control strategy,and assign the weight to the subsystem,so as to improve the safety and stability of the vehicle.The main research contents are as follows:1.For the car model without electric wheel drive in CarSim,it is necessary to modify the traditional vehicle model,including vehicle body parameters,transmission system,suspension system and tire model,and conduct policy comparison and verification between the improved model and the original model to ensure its correctness,which can be used for subsequent research.2.Based on AFS analysis of vehicle stability,a non-linear full-dimensional state observer is designed to estimate the vehicle’s center of mass sideslip angle.Based on this,a sliding mode variable structure control theory is used to build an AFS controller and handle its chattering.CarSim / Simulink is used to set the angular step and double-shift line conditions to verify it.The results prove the effectiveness of the control strategy.3.The fuzzy sliding mode theory is used to design the double-layer DYC controller.The upper layer obtains the total yaw moment required to maintain the stability of the vehicle,and the lower layer is a torque distributor.The phase plane method is used to analyze the stability of the vehicle.The phase plane stability boundary is determined according to the influence of vehicle speed,front wheel rotation angle and road adhesion coefficient on vehicle stability.This design coordinates the controller.Through CarSim / Simulink joint simulation,comparing the stability control effects of AFS single control,DYC single control and two systems coordinated control,it is proved that the AFS and DYC coordinated control strategy designed in this paper can control the vehicle in comparison with two subsystems alone a safer range,the stabilization effect is better.