Research On Steering Control Strategy Of Electric Vehicle Driven By In-wheel Motors

In recent years,the global car ownership is almost blowout.The global problems such as energy crisis and environmental pollution are becoming more and more serious.The development of new energy vehicles instead of traditional internal combustion engine cars has become an irreversible trend.The research of electric vehicles is very forward-looking in the automotive industry.Electric vehicles driven by in-wheel motors are regarded as an important direction in development of electric vehicles and have attracted much attention in recent years.This drive scheme removed the transmission system of traditional vehicles.The power is directly transmitted to the wheels,which improves the layout of the chassis,improves the transmission efficiency and reduces the power loss.Moreover,the wheels are independently controllable,which greatly improves the steering flexibility,maneuverability and safety of the vehicle.It has attracted people's great attention.Because the electric vehicle driven by in-wheel motors has no traditional mechanical differential,the research on electronic differential steering system is an unavoidable problem in the development of the electric vehicle driven by in-wheel rmotors.Moreover,the electric vehicle driven by in-wheel motors can achieve more forms of steering mode due to four wheels independently controlled.The excellent electronic differential can greatly improve the steering flexibility and stability of vehicle,which is very important for the safe driving of vehicle.In this paper,aiming at the low speed steering flexibility and high speed steering safety,a steering differential control strategy with its own advantages combining speed tracking method and torque compensation method are put forward.Through a large number of reading domestic and foreign literature,the current research status and development trend of the electronic differential control system are summarized and the research direction of the combination of speed and torque control is determined.Then,according to the relevant knowledge and dynamic indexes of automobile dynamics,the dynamic parameters of the vehicle are matched and calculated.Next,the three-phase asynchronous motor simulation model,the front wheel steering model and the heterodromous steering model are established by MATLAB/Simulink software and the principle of skew steering and the principle of pivot steering are analyzed.Through 4 parallel PI controllers,a double closed-loop control of rotate speed and current is applied,and a simulation experiment is carried out aiming at low speed with steering flexibility as control target.The results show that each motor can follow the theoretical speed well,achieve good control results and improve the steering flexibility of the vehicle under the control technology of this paper.In the end,aiming at the shortage of the current speed tracking method under middle and high speed conditions,a two-time torque compensation control strategy based on slip rate is designed.Simulation shows this method improves the traditional method that only according to the slip rate as the basis of torque distribution.A two-time torque compensation control strategy in this paper is that,firstly,the torque is pre distributed according to the ratio of the vertical load of each wheel to the total mass of th e car,and then the torque is compensated by the fuzzy controller according to the slip rate of each wheel.The road recognition controller,whole vehicle dynamics model with 7 degrees of freedom,Dugoff tire model and torque distribution controller are established.The road recognition controller is added to the Dugoff tire model,and the tire forces under different road conditions are obtained.The steering characteristics of vehicles driving in middle and high speed under various road conditions are studied and the simulation results are good.The results show that the method reduces the sensitivity of the driving torque to the slip rate,makes the vehicle more stable and efficient in steering,and has better steering performance and safety.The research methods and research results in this paper can provide a useful reference for the research on actual steering control strategy of electric vehicles.