Research On Multiple Limit Cycles In Shimmy Induced By Dry Friction Of Suspension And Steering System

Modern suspension and steering system of vehicle is a complex mechanism withmulti-degree of freedom. Because of the elasticity of the suspension and steeringmechanism, the steering wheel may shimmy continuously around the kingpin inducedby an external excitation. Steering system shimmy may also lead to vibration of the fullvehicle, which may has significantly negative impacts on the handling stability. Due tothe hysteretic effect of dry friction, the suspension and steering system may presentmultiple limit cycles responses under different external excitations. In other words, themagnitude of initial excitation has an impact on the amplitude of shimmy. The researchon that issue has not been deep enough.In order to research on multiple limit cycles induced by dry friction and to get itsinfluence on handling stability of the vehicle, the Stefanski-Wojewoda friction modelwhich can describe the hysteretic effect is introduced. A simplified model of a domesticsedan as the prototype is established, and numerical calculation is performed with theuse of Matlab/simulink. This paper’s main research contents are as follows:(1)A single wheel shimmy model considering the kingpin friction is established.And the effects of the angular stiffness of the front wheel around the kingpin, the casterangle and the dry friction torque on the multiple limit cycles shimmy are found.(2)A four degree of freedom steering system shimmy model with independentsuspension considering the steering system friction is established. And the effects of theangular stiffness between the front wheel and the middle rock arm, the caster angle andthe dry friction torque on the multiple limit cycles shimmy are found.(3)A vehicle motion model with seven degree of freedom considering the steeringsystem shimmy is established. And the effects of steering system shimmy on the vehiclehandling stability are found.It shows that dry friction hysteresis effect may induce multiple limit cyclesresponses within a certain range. With the change of parameters of the system, theamplitude of shimmy can be controlled and the slalom phenomenon of the vehicle underslightly initial excitation may be avoided.