Research On Optimal Distribution Algorithm Of Steering Force Angle Of Four-wheel Independent Steering/Drive Electric Vehicle

Environmental pollution and energy crisis are problems that cannot be ignored in today's world.In order to alleviate the pressure of environment and energy,the new energy vehicle(electric vehicle)industry was developed rapidly,and four-wheel independent steering/driving electric vehicle(4WISD-EV)appeared,which has more controllable freedom.4WISD-EV four-wheel's force and angle are independently controllable,so that it can be flexibly adjusted to achieve the optimal target performance.This paper aims at the comprehensive optimization of 4WISD-EV's low-speed steering mobility,medium and high speed steering stability and full-speed tire wear,and studies the design of its force and angle optimal allocation algorithm.Firstly,a vehicle Co-simulation model based on Carsim and Simulink software was built.According to the actual driving condition of the vehicle,the Carsim road test model was built and the Co-simulation interface was set up.The simulink model of steering and driving motors were built.Joining Carsim's vehicle body model and simulink's motors model,the whole vehicle Co-simulaion model was built complete.Secondly,a monorail vehicle dynamics model with additional rear wheels was bulit,and a rear wheel steering angle switching control algorithm was proposed.Through the kinematic analysied of the monorail model,the rear wheel steering angle switching control algorithm was studied,and the driver's steering operation was converted into the pre-allocated monorail model's front and rear wheel steering angle,which laied a foundation for the four-wheel independent steering force and angle distribution algorithm.Thirdly,the four-wheel independent steering angle distribution algorithm was studied.Based on the in-depth study of Ackerman angle distribution principle,an ackerman four-wheel steering angle distribution relationship was derived,which changes the instant center.And an all speed optimal ackerman angle distribution algorithm(ASOA)was proposed.The ASOA algorithm was verified by simulation under the low,medium and high speed,and evaluated the simulation results with the evaluation criteria of handling stability.The results proved that the ASOA algorithm has good optimization effect on low-speed steering mobility and mid-high speed steering stability,but it has shortcoming in tire wear optimization.Finally,the four-wheel independent steering angle and force optimal distribution algorithm was studied.Aiming at the problem of insufficient optimization of tire lateral force by ASOA algorithm,the influencing factors of tire lateral force during vehicle motion were analyzed.According to the idea of side offset compensation,an improved ASOA algorithm was proposed to distribute the four-wheel steering angles,and took the improved ASO A algorithm as the four-wheel steering angle acquisition modle.Based on the improved ASOA algorithm and the minimum load distribution rule of tires,an optimal ackerman force and angle distribution algorithm based on minimum load(OABML)was proposed.Under the constant steering angle input,the OABML algorithm was verified by simulation at the low,medium and high speed.Simulation results show that the OABML algorithm can effectively optimize the low speed steering mobility,medium-high speed steering stability and tire wear of 4WISD-EV.