Influence Of Suspension Nonlinear Characteristics On Shimmy Of 4WID Electric Vehicle

The development of four-wheel independent drive(4WID)electric vehicles(EVs)has led to significant changes in modern vehicles.The introduction of the hub motor simplifies the transmission structure,improves the transmission efficiency and facilitates vehicle control.At the same time,it also increases the unsprung mass,resulting in deterioration of the overall ride comfort of the vehicle and the contact condition between tires and road.Besides,it also increases the coupling effect of the vertical vibration of the suspension and the shimmy of the steering system,make the global problem of vehicle shimmy more complicated and uncertain.In this paper,mainly focuses on the four-wheel hub motor drive model,establishes a 5-DOF model with a suspension system,and systematically studies the nonlinear characteristics of the suspension and the main pin gap and dry friction non-smooth nonlinear factors on the phenomenon of shimmy,and took the lead in launching the whole vehicle shuffling road experiment in the field of shimmy.The main tasks of this paper are as follows:First,for a new type of 4WID electric vehicle driving the electric vehicle,a 5DOF front-wheel-shimmy model including an independent suspension system was established based on the Lagrange equation,qualitative and quantification analysis was performed.Firstly,based on the characteristics of the new 4WID car and the main factors affecting the shimmy,a 5DOF shimmy model consisting of the left and right front wheel around the kingpin swing angle,the left and right suspension around the longitudinal axis,and the steering wheel angle was established using Lagrange.Then,the 5DOF front-wheel-shimmy model is completed by combining the tire's dynamic cornering characteristics and the tire rolling constraint equation.Finally,according to the quantitative analysis of the model,the conclusion is drawn that the introduction of the hub motor leads to the increase of the speed range of the shimmy phenomenon and the increase of the amplitude value of the same speed slewing.Scond,consider the impact of a typical nonlinear suspension system on the 4WID electric vehicle,a new type of automotive shimmy.Based on the above 5DOF model,the nonlinear damper and nonlinear spring in the nonlinear suspension system are considered and the corresponding dynamic model is established.The simulation results show that the nonlinear suspension has a great influence on the phenomenon of vehicle shimmy,resulting in a multiple limit cycle phenomenon.Third,the effect of vertical suspension coupling due to linear suspension on the phenomenon of shimmy is discussed.Special consideration is given to the vertical lateral coupling effect of the linear suspension system and a corresponding coupling model is established.The influence of the linear suspension and the coupled suspension on the oscillation phenomenon is compared and analyzed.The results show that the coupling in the suspension has a slight forward movement in the post-critical velocity in the oscillation range,and it has a very early amplitude for the formation of the oscillation.Great influence.Secondly,the suspension cross arm that influences the coupling action has an inhibitory effect on the suspension of the suspension around the longitudinal axis of the vehicle.Fourth,consideration was also given to non-smooth non-linear factors such as kingpin motion gap and dry friction.The Discontinuous two-state gap amplitude model and Couloumb dry friction model of static friction model was established respectively,and both of them were quantitatively analyzed.The results show that both of them have a greater impact on the shimmy.With the increase of the main pin gap,the interval of the shimmy speed increases and the amplitude increases.As the dry friction increases,the interval and amplitude of the shimmy speed decrease rapidly.Finally,a 4WID electric vehicle shimmy experimental vehicle platform was built,and the entire vehicle road experiment was first conducted in the field of shimmy.First of all,according to the purpose of the vehicle and the experimental requirements to determine the overall performance of the vehicle and the key structure of the form design,and then the key subsystems and components of the safety and experimental performance of the simulation analysis and verification.Finally,the corner sensor and wheel speed sensor required for the experiment are installed on the vehicle,and the entire vehicle bench test and on-road operation are performed.On the basis of the above,a series of road-shuffling experiments for the entire vehicle at different speeds were performed,and the theoretical model was verified based on the experimental results,indicating that the established theoretical model was reliable and correct.