中文摘要：

在分析国内外脱轨研究现状的基础上，总结出脱轨研究中存在如下主要问题。（1）现有预防脱轨标准对实际列车脱轨没有控制作用。（2）不明原因列车脱轨机理不明确。（3）列车脱轨计算存在3个根本问题：①列车-轨道（桥梁）时变系统振动方程组的建立与求解未满足轮轨位移衔接条件；②仅以轨道横向不平顺作为列车-轨道（桥梁）时变系统横向振动的激振源，未考虑根本激振源——轮轨接触状态的影响；③仅以轨道不平顺的随机性和按时不变系统随机振动分析理论，

英文摘要：

The major problems existing in the derailment studies are summarized according to analysis of the research status about train derailment in China and other countries of the world. （1） The current criteria for preventing derailment cannot assure that derailment will not occur. （2） It is not clear for train derailment mechanism. （3） There exist three fundamental problems in the calculation of train derailment as follows： （1） The connecting condition of displacement between wheel and rail cannot be satisfied in establishment and solution of vibration equation group of train-track （bridge） time variant system. （2） Only the lateral track irregularity is regarded as the exciting source of lateral vibration of train track （bridge） time-variant system. The true exciting source, i. e. the wheel and rail contact status is neglected. （3） The random lateral vibra tion of train-track （bridge） time-variant system is analyzed according to the random track irregularity and analysis theory of random vibration of time-in variant system. But the maximum responses of lat eral vibration of train-track （bridge） time-variant system cannot be calculated, and furthermore train deraiment cannot be forecasted. The thinking and methods for solving these problems are also introduced. The train derailment mechanism, which is the result of losing stability in lateral vibration status of train-track （bridge） time variant system, is proposed for the first time by analysis of characteristics of self-excitation of train vibration and losing stability in self-excitation vibration status of train derailment. So the key to analyzing train derailment is to analyze the stability of lateral vibration of train-track （bridge） time-variant system. The following conclusions are made by summarizing the existing analysis theory of stability of static and dynamic system. （1） Because of the characteristics of time-variant and self-excitation of train track （bridge） system, the stability of lateral