A Study On The Influence Mechanism Of Wheel System On The Shimmy Of 4WID Electric Vehicles

The steering wheel shimmy refers to the continuous vibration of the wheel around the kingpin when the car is driving on a flat road,and this kind of vibration will be transmitted to the steering wheel through the steering system and even cause the obvious vibration of the whole vehicle.The complex vibration phenomenon is called shimmy.With the increasing demand of electric vehicles and the huge advantages of the 4WID(Four-Wheel-IndependentDrive)technology in the aspects of structure,response and energy saving,4WID electric vehicles have gradually become the mainstream of the development of electric vehicles.The in-wheel motors are also widely used in 4WID electric vehicle due to its high energy efficiency and compact structure.However,the introduction of in-wheel motors greatly increases the unsprung mass,deteriorstes the grounding conditions of the tire and the stability of the wheel,which in turn affects the shimmy of the vehicle.In order to study the influence of the characteristics of the wheel system on the shimmy of 4WID electric vehicle,this paper takes the 4WID electric vehicle independently developed by the laboratory as the research object.Firstly,a nonlinear dynamics method is used to establish the multi-degree of freedom theoretical model of the whole vehicle.The Hopf bifurcation characteristics of the system were analyzed by the nonlinear theory and the MATLAB software,and the influence of the wheel system characteristics on the bifurcation characteristics was studied.Then the virtual prototype model of the whole vehicle was established by using the multi-body dynamic software ADAMS/Car,and the typical simulation analysis was carried out.The influence of the unsprung mass and the other wheel system parameters on the vehicle motion state was studied,and the results were compared with the results of theoretical analysis.Finally,in order to verify the results of the simulation,a 4WID electric vehicle driven by inwheel motors was developed independently.It showed that the wheel system is the key factor affecting the wheel shimmy.To a certain extent,the critical speed of the Hopf bifurcation and the vibration amplitude of the steering wheel shimmy is affected.The unsprung mass is different from that of the other wheel system parameters.First,in the case where the unsprung mass increases,not only the speed range in which the self-excited shimmy occurs is expanded,but also the velocity range that will cause the self-excited shimmy to occur will be moved forward,that is,the speed at which the self-excited shimmy is excited will be reduced.Second,under the condition of spring mass increasing,the vibration amplitude at the occurrence of self-excited shimmy not only increases,but also has a linear relationship with the change of unspring mass.