Multi-limit Cyclic Shimmy Research Of Heavy-duty Truck With Dual Front-axle Steering

Dual front-axle steering system has simple structure, low cost, and can make truck achieve efficient steering with small radius. Dual front-axle system is widely used in many trucks, at the same time, the tires wear of dual front-axle wheel has also attracted attention. Shimmy can not only causes tire wear, but also cause self-excited vibration of the steering system, which affects the automobile’s handling stability and ride comfort. Therefore, on the basis of previous studies, this paper further research shimmy phenomenon of dual front-axle steering system, and analysis shimmy mechanism, and study the impact on the vehicle shimmy.In this paper, we studied the dynamic behavior of multi-limit cycle self-excited vibration of shimmy system by using the dry friction model with the negative slope characteristic. Considering nonlinear tire and dry friction, we established 9 degrees freedom shimmy differential equations. Firstly, the 9 degree of freedom system was analyzed qualitatively, and the 22 dimensional state equation of the system was reduced by using the center manifold theorem to obtain a two-dimensional plane system and analyzed it. Then the numerical calculation method was used to calculate the 9 degree of freedom system. The bifurcation behavior and the characteristic of multi-limit cycle were analyzed in detail. Then the vehicle dynamics model was established, and MATLAB software was used to numerical calculation of the vehicle model and to analyze the impact of the structural parameters on the vehicle vibration.Qualitative analysis showed that the polar coordinate expression of the Hopf normal form of the two-dimensional system has c=0, and the degradation Hopf bifurcation occurs at the bifurcation point. Numerical results showed that the dry friction model with the negative slope characteristic could induce multiple limit cycle in a certain range. Appropriate changes in the structural parameters of the system and dry friction torque, could effectively restrain system of self-excited shimmy, and also could prevent the truck from producing serpentine phenomenon.