考虑轮胎非线性约束的汽车摆振系统建模及行为特征分析

Modeling and Dynamic Behaviour Characteristic Analysis of Vehicle Shimmy System with Consideration of Tire Nonlinear Constraint

为更加全面地分析汽车摆振系统动力学稳定性及行为特征,结合改进的拉格朗日方程建立整车12自由度摆振系统动力学模型,并在轮胎单点接触模型的基础上,推导得到轮胎线性及非线性两种约束方程。根据系统状态矩阵,分别考察两种轮胎约束下的系统平衡点及其稳定性随车速的变化情况,并通过系统特征向量研究汽车摆振系统模态特性,分析轮胎参数对系统失稳模态的影响规律。研究表明,轮胎拖距和主销后倾角的减小可以提升系统稳定性,从而抑制汽车摆振。此外,以高斯白噪声为输入建立B级随机路面激励时域模型,进而研究随机路面激励下的摆振系统行为特征,并着重探讨轮胎非线性约束及参数对汽车摆振动力学的影响。研究发现,轮胎非线性约束虽然对摆振系统的失稳参数域没有影响,但会使得摆振幅值有所减小,且轮胎垂向载荷变化越大,两种轮胎约束下的摆振幅值差异就越大。因此,当轮胎垂向载荷变化较大时,轮胎垂向载荷对松弛长度和接地印迹的影响应该给予重视。

In order to more comprehensively analyse the dynamic stability and behaviour characteristic of vehicle shimmy system,a 12 degree-of-freedom dynamic model of vehicle shimmy system is established according to the modified Lagrange equations.Based on the single point contact tire model,the tire linear and nonlinear constraint equations are derived.According to the state matrix of vehicle shimmy system,the equilibrium and its stability of the shimmy system for two kinds of tire constraint equations are investigated respectively.The modal characteristic of the vehicle shimmy system is studied by using the system eigenvector,the influence of tire parameters on the instability mode of the system is also analyzed.The research shows that the reduction of the tire pneumatic trail and caster angle can improve the system stability,thus restraining vehicle shimmy.In addition,the Gaussian white noise is used as input to establish a time-domain model of B-grade random road roughness excitation.Then,the behaviour characteristic of the shimmy system under the random road roughness excitation is studied and the effects of the nonlinear constraint and parameters of the tire on vehicle shimmy dynamics are discussed.It is found that although the tire nonlinear constraint has little influence on the instability parameter region of the shimmy system,the shimmy amplitude is decreased.The larger the change of the tire vertical load,the larger the difference of the shimmy amplitude between two kinds of tire constraint equations.Therefore,when the change of the tire vertical load is large,the influence of the tire vertical load on the relaxation length and contact patch should be taken seriously.