为了研究在途检测车辆运行的动态稳定性问题，在分析机车车辆动力学响应特点的基础上，基于响应信号的非平稳特征提出一种动态检测车辆运动稳定性的时变阻尼比的新方法。该方法的核心是对横向振动加速进行改进经验模式分解，得到信号的基本模式分量。分别对信号的基本模式分量进行归一化希尔伯特变换得到模式分量对应的瞬时频率和瞬时幅值，应用瞬时幅值和瞬时频率计算该模式下信号的时变阻尼比。由时变阻尼比的正负来判断车辆的运行稳定性，正的时变阻尼比表明车辆运行稳定，零或负时频阻尼比表明车辆运行失稳，负的时频阻尼比的绝对值大小表明了车辆失稳的严重程度。通过仿真算例和线路实测信号对该方法进行理论和试验验证，结果表明该方法能够从响应信号中准确、有效地捕捉系统稳定性的动态时变特征，为机车车辆运动稳定性的在途监测提供有效方法。

In order to dynamically detect vehicle motion stability during operation, as a new method of detecting vehicle motion stability, the time-varying damping ratio, is presented on the basis of the analysis of the dynamic response feature and the non-stationary characteristics of the response signals. The lateral vibration accelerations are decomposed by the IEMD(improved empirical mode decomposition) into a finite and often small number of IMF(intrinsic mode functions). The instantaneous frequency and the instantaneous amplitude of the intrinsic mode components are drawn through normalized Hilbert transform, respectively. The time-varying damping ratios under different intrinsic modes are computed by applying instantaneous amplitude and instantaneous frequency to judge the running stability of the vehicle. The zero or negative damping ratio indicates that the vehicle is unstable, the positive damping ratio shows that the vehicle keeps stable, the absolute value of the negative ratio means the severity of vehicle instability. Through the theoretical and experimental verification applying simulation and the measured signals, the results show the method can accurately and efficiently dynamically capture the time-varying characteristics of the system stability, with a powerful method for transit monitoring of vehicle running stability.