No abstract

Railway vehicles under certain conditions experience sustained lateral oscillations during which the wheel flanges bang from one rail to the other. It has been found that this behavior, called hunting, only occurs above certain critical forward velocities. Approximations to these critical velocities have been found from a stability analysis of the linear equations of motion for many different railway vehicle models. Hunting is characterized by violent motions that impose large loads on the vehicle and track, and bring several important nonlinear effects into play. This paper reports results of an analysis of nonlinear equations of motion written for two models of a railway truck. The influence of the nonlinear effects on stability is determined and the character of the hunting motion is investigated. One model represents a truck whose axle bearings are rigidly held in the truck frame while the truck frame is connected through a suspension system to a reference that moves along the track with constant velocity. The more complex model includes additional suspension elements between the axle bearings and truck frame. The effects of flange contact, wheel slip and Coulomb friction are described by nonlinear expressions. These results show the significant influence of flange contact on stability, and illustrate the effects of vehicle and track parameters such as rail adhesion, forward velocity, and wheel load on the forces and power dissipation at the wheel-rail interface.

This paper presents a survey of the research concerned with the dynamics of single, conventional railway vehicles. Attention is concentrated on analytical research and only that experimental research that has been performed in conjunction with analytical efforts. The often conflicting objectives for railway vehicle suspension design and the research done to understand the design implications of these objectives are discussed.

This study addresses the question of whether rail passenger vehicles with more sophisticated (and more expensive) suspensions can operate on rougher (and less expensive) track with an overall lower net cost for the guideway-vehicle system. Four suspensions, representing a range of performance and cost, are optimized for operation on the roughest possible track. The cost of each suspension and its guideway is estimated. Two of the advanced guideway-vehicle systems appear to result in an overall cost savings. However, because of uncertainties in the estimates of guideway maintenance cost, these conclusions are regarded as illustrative of our methodology rather than quantitatively reliable.

A constrained optimization algorithm to maximize the operating speed of a fifteen degree-of-freedom lateral dynamic model for a passenger railcar subject to random alignment irregularities is presented in this paper. The constraints placed on the optimization problem limit the passenger discomfort, primary and secondary suspension clearance, the wheel slippage, and secondary suspension stroke to practical values while traversing a curve. The optimization results demonstrate that the primary suspension system and the wheel conicity have the most profound influence on maximizing the critical speed where “hunting” begins. The maximum critical speed is insensitive to large variations in secondary yaw stiffness. The secondary lateral stiffness has less effect on the maximum critical speed than the primary lateral stiffness. Thus, the secondary stiffness can be chosen primarily to satisfy passenger ride comfort specifications. The maximum critical speed is quite sensitive to whether the wheel is new, slightly worn, or severely worn.