Research On Matching Design And Control Of Distributed Steering System For In-Wheel Motor Electric Vehicle

The development of new energy vehicles is one of the important ways to solve the problems of environmental pollution,climate warming and energy shortage.In-wheel motor electric vehicle can realize independent and controllable driving torque of each wheel as well as efficient power transmission,which has become an important topic for new energy vehicles.With the continuous improvement of China’s automotive technology,the development of intelligent vehicles has received widespread attention.As an advanced steering system,steer-by-wire system has become one of the core components of the intelligent chassis system.Steer-by-wire system can achieve the ideal variable transmission ratio according to the driver’s demand,avoiding the adverse effect of the steering characteristics of fixed-ratio cars changing with vehicle speed on the driver’s driving experience.In addition,steer-by-wire system can also achieve active steering control,which can compensate and adjust the front wheel angle by controlling the steering motor to apply a superimposed front wheel angle independent of the driver’s operation when necessary.In-wheel motor electric vehicle uses in-wheel motor as the power source to drive the vehicle,and it is easy to combine the technologies such as steer-by-wire,which is of great significance to improve vehicle’s maneuvering stability.Accordingly,this paper takes in-wheel motor electric vehicle as the research object and completes the matching design of the distributed steer-by-wire system.In order to improve the handling stability of in-wheel motor electric vehicle,the ideal variable transmission ratio of steer-by-wire system and the active steering control were studied.The main research contents are as follows:(1)In order to improve the steering performance of in-wheel motor electric vehicle and realize the intelligent development of chassis system,a distributed steer-by-wire system scheme was proposed,which eliminated the mechanical connection between the left and right side wheels,and the steering process was driven by the left and right side steering motors.The steering system dynamics model was established based on Adams/View,added constraints and drives to each component of the steering system,and obtained the relationship between the demand thrust,speed and torque of key components in the steering process.The relationship between thrust,speed and torque of key components in the steering process was obtained,and the selection of steering motor and ball screw components was completed.To meet the high strength requirements of in-wheel motor electric vehicle steering knuckle,typical extreme conditions were selected for the strength verification of the steering knuckle.To address the problem that in-wheel motor electric vehicle steering knuckle was susceptible to resonate due to the vibration of the hub motor,a modal analysis of the steering knuckle was conducted to determine whether it will resonate.In order to avoid resonance of the steering knuckle and improve the economy of in-wheel motor electric vehicle,the topology optimization of the steering knuckle was carried out with the objectives of lightweighting and increasing the intrinsic frequency of the steering knuckle,while ensuring the strength of the steering knuckle.(2)An accurate vehicle dynamics model is the basis for completing the research on ideal variable ratio control and active steering control of in-wheel motor electric vehicle.The whole vehicle dynamics model was built based on MATLAB/Simulink,including the driver model,body model,steering system model,tire model,hub motor model and auxiliary calculation model.In order to verify the accuracy of the built in-wheel motor electric vehicle dynamics model,a vehicle dynamics model with the same parameters was built based on Car Sim,and the double shift line and angular step conditions were selected to verify the built wheel hub motor electric vehicle model.(3)The ideal variable transmission ratio was designed based on the constant transverse velocity gain method for steer-by-wire system,and then the optimal transverse velocity gain value was selected by using genetic algorithm to optimize the constant transverse velocity value,and the ideal variable transmission ratio curve was initially determined.To solve the problem of sudden change of the ideal variable transmission ratio curve at the critical speed,an improved S function was used to correct it,so as to avoid the sudden change of the ideal transmission ratio and the sudden change of the steering motor torque.In order to prevent the car from skidding or tailing on the road with low adhesion coefficient,the design of the ideal variable transmission ratio under different road adhesion coefficients was completed based on fuzzy control with different road adhesion coefficients as the research object.(4)In order to further improve the handling stability of the car,the active steering control of the steering system was studied.The linear two-degree-of-freedom vehicle model was selected as the reference model,and yaw rate and sideslip angle of the vehicle were selected as the control variables,based on the LQR algorithm to track and control the deviation values of the actual yaw rate and sideslip angle from the ideal value,the additional angle of rotation of the front wheel was calculated independently of the driver’s input,realized active steering control for steer-by-wire system.To verify the active steering control effect,the angular step,continuous sinusoidal and double-shifted line conditions were selected for simulation verification.