Research On Integrated Control Strategy For Chassis Of Four-in-Wheel Drive Electric Vehicle Under Combined Condition

Nowadays,low pollution and high efficiency electric vehicles have gradually become the main research direction in the automotive field,and become an indispensable part to solve the energy crisis and environmental pollution problems caused by traditional fuel vehicles.In recent years,Four-in-Wheel Drive Electric Vehicle has become a hot spot in the field of electric vehicle research because of the advantages of independent four-wheel drive,high controllable degree of freedom,high transmission efficiency and rapid torque response.However,the traditional research on handling stability of four-wheel drive electric vehicle mostly focuses on vehicle stability under pure cornering condition.Under compound condition,the coupling effect of tire cornering and longitudinal sliding will inevitably lead to significant changes in vehicle dynamic characteristics,resulting in changes in vehicle stability region.Therefore,this paper studies the chassis integrated control strategy of four-wheel drive electric vehicle in two directions of "analysis of vehicle handling and stability under composite conditions" and "integrated control of vehicle side longitudinal chassis under composite conditions".In this paper,a three-dimensional trajectory analysis method is proposed for the analysis of vehicle handling stability under side longitudinal sliding composite conditions.Combined with the sliding mode variable structure control theory,an integrated chassis control strategy is designed to comprehensively improve the vehicle handling stability under composite conditions.The specific research contents are as follows:Firstly,the vehicle dynamics model and simulation model are established.Based on two degree of freedom vehicle model,wheel model and Uni Tire tire model,this paper analyzes the expected goal under composite working conditions;The whole vehicle simulation model is built based on Car Sim software,which is used for the dynamic simulation of the software in the loop of the four-wheel drive electric vehicle;Secondly,aiming at the problem of vehicle handling and stability under composite conditions,a three-dimensional trajectory analysis method for vehicle stability analysis under composite conditions is proposed.Furthermore,the stability judgment criteria of three-dimensional trajectory are constructed,and the nonlinear variation law of vehicle stability region with vehicle speed,longitudinal acceleration,road surface adhesion coefficient and tire slip rate is revealed.Furthermore,the weight of dynamic yaw moment control is designed on the basis of three-dimensional trajectory,which lays a theoretical foundation for the research of chassis integrated control strategy;Then,based on the three-dimensional trajectory diagram,combined with the sliding mode variable structure controller,the integrated control strategy of four-wheel drive electric vehicle chassis is designed.In the upper layer,the longitudinal slip rate sliding mode controller and the lateral center of mass slip angle yaw rate sliding mode controller are designed,and the dynamic yaw moment weighting coefficient based on threedimensional trajectory diagram is used to optimize the additional yaw moment according to the control objective;According to the yaw moment determined by the upper layer,the lower layer realizes the torque distribution under the composite working condition,and finally improves the handling stability of the vehicle under the composite working condition.The performance of the proposed chassis integrated control strategy under the two working conditions of low attached road turning acceleration and separated road acceleration is evaluated.Finally,in order to further analyze and verify the performance and real-time performance of the control algorithm,the hardware in the loop dynamic simulation platform of four-wheel drive electric vehicle is built by using d SPACE,Autobox and other hardware.The platform is used to verify the integrated control strategy of the chassis under compound working conditions.The hardware in the loop simulation adopts two working conditions: accelerating steering and emergency braking.The results show that the control algorithm meets the real-time requirements.Under the side longitudinal sliding condition,the chassis integrated control strategy designed in this paper can control the slip rate within the optimal slip ratio range,and effectively avoid the vehicle instability caused by tire slip;Under the emergency braking condition,the control algorithm can maintain the good maneuverability of the vehicle under the condition of maximum acceleration braking.