Considering the stability of vehicle system, static instability and dynamic instability are two different instability problems. Because of the dynamic coupling between car and trailer, the problem of dynamic stability of car-trailer combination (CTC) is more obvious. This instability is called body sway or flutter in engineering, its boundary is often described by dynamic critical speed (v_crit). It has been proved by experiments that the steering system characteristics have an important impact on the dynamic stability of CTC, but the specific mechanism is not clear. In this paper, the characteristic and influence of steering subsystem are studied for the first time. Firstly, a 6-DOF nonlinear dynamic model of CTC is established by Lagrange equation. The steering subsystem characteristics, incl. stiffness, damping, rotational inertia, and dry friction, are considered in theoretical modeling. On this basis, the influences of steering characteristics, especially the dry friction, on v_crit and axle cornering stiffness of CTC are analyzed. Simulation results show that the v_crit can increase by 16% and 23.2% respectively via adjusting the steering stiffness and the sliding friction factor. Therefore, a fine selection of steering subsystem characteristics can effectively improve the dynamic stability and safety of CTC. The research results of this paper can provide reference for the design of steering system considering dynamic stability.

考虑到车辆系统的稳定性，静态不稳定和动态不稳定是两个不同的不稳定问题。由于汽车和挂车之间的动态耦合，车拖组合（CTC）的动态稳定性问题更加明显。这种不稳定性在工程中称为体摇摆或颤振，其边界常用动态临界速度（v _crit）。实验证明，转向系统特性对CTC的动态稳定性有重要影响，但具体机制尚不清楚。本文首次对转向子系统的特性及影响进行了研究。首先，利用拉格朗日方程建立了CTC的6自由度非线性动力学模型。转向子系统特性，包括 在理论建模中考虑了刚度、阻尼、转动惯量和干摩擦。在此基础上，分析了转向特性，尤其是干摩擦对CTC的v _crit和车桥侧偏刚度的影响。仿真结果表明v _crit通过调整转向刚度和滑动摩擦系数可以分别提高16%和23.2%。因此，精细选择转向子系统特性可以有效提高CTC的动态稳定性和安全性。本文的研究结果可为考虑动态稳定性的转向系统设计提供参考。