Research On Chassis Comprehensive Motion Control For Intelligent In-Wheel Motor Drive Electric Vehicles

Nowadays,with the rapid growth of vehicle population,traffic accidents,energy consumption and environmental pollution are becoming increasingly prominent.As the introduction of the ban on the sale of fuel vehicles in various regions of the world,the research on pure electric vehicle technology has received increasing attention from major auto companies and scientific research institutions.In the form of the drive system,the In-Wheel Motor Drive electric vehicle using four in-wheel motors to drive four wheels directly and omitting the drive system completely,has the competitive advantages of compact structure,short transmission chain,high efficiency,which will provide more degrees of freedom in the chassis design,dynamic control and the layout of vehicles.Therefore,this kind of vehicles have increasingly become a research hotspot at home and abroad.In addition,another trend in the present automobile industry is “intelligent vehicles”.Various advanced Intelligent Drive Assist system are becoming standard configuration for high-end models of many car brands,such as lane keeping,adaptive cruise and self-parking,and so on.Semi-autonomous driving and conditional self-driving intelligent vehicles have also entered the road test phase.Among the key technologies for intelligent vehicles,motion control is the basic of self-driving.In this paper,the chassis comprehensive motion control of in-wheel motor drive electric vehicles is studied to realizing reliable autonomous driving for this special vehicle platform.Considering the characteristics of the in-wheel motor drive electric vehicles,this paper has employed Carsim and Matlab/Simulink software to complete the construction of the vehicle model.Among them,the vehicle motion dynamics model is provided by Carsim,and its transmission system has been modified to meet the chassis structure of in-wheel drive platform.The in-wheel motor model is built in Simulink.On the one hand,the structure and work principle of the brushless DC motor have been analyzed,then in-wheel motor drive control strategy based on PWM modulation has been established.On the other hand,the principle of energy feedback control of brushless DC motor has been studied,then the energy feedback control strategy based on half-bridge chopping wave is established.Additionally,based on the operating characteristics of the EHB system,a simplified second order hydraulic model is established by the least square method.This paper decouples the comprehensive chassis motion control of intelligent vehicle into longitudinal motion control and lateral motion control.For the longitudinal motion control,an active cruise control strategy was designed,where the idea of preview control is used to improve the tracking accuracy and safe ty,and the auto-tuning of control parameters is achieved through fuzzy theory.Then,on the premise of ensuring the safety and reliability of the system,the regenerative braking control is taken into account in the active cruise control to enhance the energy efficiency of the vehicle so as to extend the driving range.Using four typical working conditions including the speed control,distance control,front vehicle cut-in and front vehicle cut-out,the tracking accuracy and reliability of the active cruise strategy have been verified via simulations.In the lateral motion control,the trajectory tracking of the vehicle and the direct yaw moment control problem are mainly discussed.The trajectory tracking of the vehicle is achieved by using the optimal preview control,where the lateral error at the preview point is used as a feedback signal.In order to improve the accuracy of trajectory tracking and the steering stability of the vehicle,a direct yaw moment control strategy based on the differential drive/brake of the in-wheel motors has also been designed.At the same time,to enhance the reliability of the vehicle,fault tolerance control when one in-wheel motor breakdown occurs is also realized by the direct yaw moment control strategy.The simulation results show that the control effect and reliability of the algorithm are both satisfactory during the angle step steering condition and double lane change condition.