The Study Of Wheelset Longitudinal Vibration And Its Influences On Wheel Tread Wear

For many years, the study of railway vehicle system dynamics was focused on vehicle lateral performance in order to achieve higher velocities and greater comfort. In the last two decades, however, increasing attention has been paid to vehicle system vertical dynamics,because of its significance for track structure vibration, noise, vehicle/track/bridge relationships and rail corrugation. In contrast, train longitudinal dynamics is of relevance mainly to problems involving interactions between different vehicles and has nothing to do with wheel/rail behaviour, whereas locomotive longitudinal dynamics is principally important with regard to the influence of the torsional rigidity of the transmission system on wheel/rail adhesion at starting, to prevent wheelset sliding and idling. In the study of vehicle system dynamics, the effects of wheelset longitudinal dynamics have long been neglected,because it has little to do with the studies mentioned above, or in other words, the influences of wheelset longitudinal dynamics to vehicle system dynamics still not been noticed yet.Usually, in the study of vehicle system dynamics, a common strategy is to posit the vehicle running on a stationary random road profile with a constant travel speed. Actually, there is a small random velocity flutter around wheelset nominal forward speed. The mechanism of wheelset longitudinal vibration cannot be fully reflected if the effect of small random velocity was not taken into consideration; therefore, wheelset forward speed is regarded as a dynamic variation in our research. This article argues, however, the behavior of wheelset longitudinal dynamics may be one of the important factors to cause abnormal vehicle jitter or wheel abnormal wear as well as some particular wavelength rail corrugation.Wheelset longitudinal vibration is a research category that belong to vehicle system longitudinal dynamics, compared with lateral and vertical dynamics, the study of wheelset longitudinal dynamics is still at an early stage, but it contains a wealth of content and its mechanism is very complicated, the research is of great significance to high-speed and heavy loading vehicles. This study focuses mainly on the mechanism of wheelset longitudinal vibration and its influence on periodical wheel tread wear. Combining wheelset longitudinal vibration with wheel/rail contact parameters vibration, it provides a new method to study the problem of some locomotives' peoridical wheel tread wear, and proposes the concrete measures to solve this problem. On the whole, the main content of this paper can be divided into three parts: the study of wheel/rail longitudinal friction model, the study of wheelset longitudinal vibration and its influences on wheel tread periodical wear. The specific research content as follows:1. By analysing the changing rules of wheel/rail creep curve in aspects of wheel/rail material strain, with account of wheelset longitudinal vibration, a longitudinal wheel/rail friction model is created, that fit our study. This model is composed of an elastic spring, a viscous damper and a friction element in series, among them the first two elements are frequency and amplitude dependence, in order to capture the characteristics of wheel/rail longitudinal vibration in small creepage; while, as for the friction element, it is mainly used to simulate the case in big creepage which considered the friction coefficient as the function of wheel/rail longitudinal creepage.2. This friction model is then incorporated into a vibration analysis of a wheelset coupled with a single-wheelset longitudinal dynamical model. In small creepage, dynamic responses of wheelset longitudinal vibration have been made under harmonic, impulse and random track irregularity excitation; the PSD of the single-wheelset system considering the effects of small randomly-varying velocity has been studied using perturbation method at the steady state, while, as for the unsteady state, we propose a method for studying wheelset longitudinal vibration PSD by the wavelet analysis method; wheelset longitudinal vibration under time-varying parameter (primary longitudinal stiffness) has been studied using DWT(Distrete Wavelet Transform) and CWT (Continuous Wavelet Transform) . The stability of wheel/rail self-excit vibration has been studied in big creepage, as well as the influence of primary stiffness and damping.3. In aspects of wheelset longitudinal vibration, this paper studys the mechanism of the formation of wheel tread wear in its initial stage and the development process of wheel tread periodical wear. This paper combines the problems of vehicle system dynamics and wheel/rail wear together, to deal with the impacts of wheelset longitudinal vibration on wheel/rail contact conditions and its mechanical properties, and meanwhile, the influence of wheelset longitudinal vibration on wear consumption and wear depth is simuated and analyzed.