高速下轿车转向系非线性振动的分岔特性

Bifurcation Characteristics on Nonlinear Vibration of Its Steering System When Car Running at a High Speed

当轿车以80 km·h–1及以上速度行驶时,将会出现严重的前轮摆振现象。针对轿车高速行驶状态中出现的摆振问题建立轿车转向系统4自由度非线性动力学模型,计及转向连杆的弹性作用,将该动力学模型简化为弹簧阻尼元件,综合考虑轮胎非线性侧向力、转向横拉杆铰链间隙,以及主销处的干摩擦等非线性因素,在车轮具有失衡量的情况下分析转向系统的非线性动力学特性,数值计算动力学系统的分岔图、Poincaré映射、频谱图,得到转向系统随动态参数变化的分岔规律和运动规律,基于施米特正交化方法计算振动系统的最大Lyapunov指数谱和特定分岔点的各维指数,确定系统的运动状态,划分系统的失稳区间,为转向系统动态参数的设计与优化以及非线性摆振的主动控制与被动控制提供了理论依据。

Severe shimmy of a car＇s front wheel occurs when it runs at 80 km？h–1 or higher speed.In allusion to this shimmy problem,a 4 degrees of freedom nonlinear dynamic model of automotive steering is established.During modeling,the elastic function of steering link rod is taken over and the link rod is looked at spring-damper unit.Nonlinear factors including lateral force of tire,clearance of steering link rod,coulomb friction of the pin etc.are added to this model.Under the condition that unbalance mass exists in the wheel,the nonlinear dynamic characteristics of steering system are analyzed.Bifurcation rules of the steering system are obtained by using the method of Poincaré mapping and frequency chart analysis.The Lyapunov exponent spectrum is calculated by Schmidt method.Unstable areas are divided and movement status is made certain.All the numerical results can provide the theoretical support for design or optimization of steering system dynamic parameters and active or passive control of nonlinear shimmy.