Research On The Dynamics And Simulation Of Front Wheel Shimmy Of A 7-DOF Electric Wheel Vehicle

With the emergence of electric wheeled vehicle,the structure of vehicles has changed.The introduction of the hub motor simplifies the transmission structure,thereby improving the transmission efficiency.However,the corresponding increase in the unsprung mass affects the operation stability and smoothness of the overall vehicle.Therefore,this dissertation mainly focuses on the shimmy problem of electric wheeled vehicle,orderly establishing the shimmy dynamics models of SDOF,4-DOF and 7-DOF,then systematically studying the shimmy characteristics under the influence of different parameters.Based on the 7-DOF shimmy dynamic model,the co-simulation model and the bench test are established.The results of co-simulation and bench test are compared with those of numerical simulation models,which further verifies the correctness of the shimmy dynamic model.What follows is the main work of this dissertation:1.This dissertation analyzes the causes and harms of front wheel shimmy of electric wheeled vehicle,and discusses the sources of shimmy interference and the conditions of self-excited shimmy and forced shimmy.By comparatively analyzing several classic tire models and dry friction models,the appropriate tire lateral force model and dry friction model are selected,which provides a basis for establishing the front wheel shimmy dynamic model.2.Based on the mechanism of shimmy,the shimmy system is properly simplified,and then the shimmy dynamics models of SDOF,4-DOF and 7-DOF are established.The kinematics differential equation and state equation of the shimmy system are derived based on the dynamic model.The stability of the shimmy system is calculated and analyzed through the Hopf theorem.And then,the dynamic model is numerically simulated to study the influence of internal and external parameters on the shimmy characteristics of the system.3.The co-simulation model is established on the basis of the 7-DOF shimmy dynamic model.The vehicle model is established through Carsim,and the subsystem model of the independent suspension is built by Simulink,and then the co-simulation model of the both is established.By comparing the co-simulation results with the Matlab numerical simulation results,it is found that the amplitude and bifurcation characteristics of the two shimmies are basically consistent,which verifies the validity of the established 7-DOF shimmy model.4.On the basis of the dynamic model and the co-simulation model,a shimmy test bench is built.The shimmy conditions under different parameters are tested and recorded on the bench.Finally,the experimental results are compared with the numerical simulation results of Matlab.It is found that the amplitude and bifurcation characteristics of the two shimmies are basically consistent,which proves that the dynamic model and simulation model established in this paper are effective and reliable.