Analysis On Instability Boundary Of Steering Situation And Yaw Stability Control Of Iwmev

Compared with the traditional centralized driving mode,In-wheel-motor electric vehicle(IWMEV)has simplified structure and can adjust driving torque independently of each wheel.So far,IWMEV has become the focus of electric vehicle research.For steering situation,improving steering performance and stability are two goals of yaw stability control.At present,in order to improve steering performance,research mainly uses the direct yaw torque control to tracking expected yaw.Due to the limitation of the road adhesion and the nonlinear characteristics of the tire,the vehicle would lose control and be instability in many extreme conditions.On the other hand,the rear drive has a better performance than the front drive when steering,but the rear drive has poor stability,easy to lose control.Focusing on the torque distribution problem between front and rear axles,this paper analyzes vehicle dynamics mechanism of steering instability and the instability boundary.Finally,this paper proposes a method of yaw stability control based on the torque distribution between front and rear axles to improve the steering performance and stability when steering.First,through simulation,this paper describes the improvement of the steering performance using the front and rear axle torque distribution and the phenomenon of vehicle instability.Then,the mechanism and main reason of vehicle steering instability are analyzed based on the vehicle dynamics model.Combined with the dynamic characteristics of vehicle instability,a method to identify the instability boundary is proposed.The method is simple in calculation and relies little on the vehicle state information,so is easy for application in real vehicles.Based on the steering-instability identification,this paper proposes a torque distribution method between the front and rear axle.The method makes fully use of the practical adhesion of each wheel to achieve more lateral force of the vehicle in order to improve the yaw performance.Meanwhile Combined with steering-instability identification,the stability can be guaranteed.Finally,this paper studys the yaw stability control method based on the torque distribution between axles.To track the expected yaw,a constrained model predictive controller was established after analyzing the design of the expected yaw.In the end,a rapid control prototype and a Hardware in loop test platform was established to verify the algorithm.