Joints with clearance always exist in steering mechanism of vehicles due to the machining tolerances, deformations and wear, which should not be neglected in modeling and analysis of vehicle shimmy system. Based on Lagrange equation method, a six-DOF dynamic model of vehicle shimmy system with consideration of multi-clearance joints was established. The model of movement pairs with clearance was built based on Hertzian contact law. The nonlinear cornering force of pneumatic tire was described based on PAC2002 tire model, and its parameters were obtained by an identification method based on experimental data. Then numerical examples were employed to evaluate the dynamic response of the shimmy system. The influence of multi-clearance joints on the response of shimmy was analyzed, and it is compared with that of one clearance joint. The acting mechanism of contact force between movement pairs was investigated, and global dynamic analysis was carried out by using point mapping method. Moreover, the dynamic mechanism for vehicle shimmy was investigated based on energy input. The conclusions can provide theoretic evidence for attenuation of vehicle shimmy, especially for those in-service vehicles.

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A novel parameter identification method for dynamics models of pneumatic tire was presented. The parameter identification process and methodology relate to Nelder-Mead algorithm, genetic algorithm and random value method. Based on experimental data and tire modeling of PAC2002, the lateral force parameters, longitudinal force parameters and aligning moment parameters were identified by using the presented identification approach. It can be found that the novel parameter identification approach is more accurate and efficient, which can provide theoretic evidence for tire modeling and analysis. Moreover, a software system that integrates the parameter identification methodology was compiled and developed by using MATLAB and C++, which can provide a quick and efficient parameter identification process for engineering application in the future.