Study On Vibration Reduction Technologies For High Speed Cars

High speed vehicle is different from ordinary vehicle in its special dynamic environments. Higher speeds would increase excitation frequencies between wheels and rails, and therefore generate increased structure vibrations, wheel rail dynamic forces, and severe hunting oscilations. However, the requirements of safety, comfort, fast and convenience for passengers will never change. To achieve this goal, dynamic performance of high speed vehicles should have the following three basic qualifications. Hunting instability is not allowed in the high speed, good ride comfort should be assured in the high speed, low wheel/rail force and wear should be assured on the curve in the high speed. There is a fundamental design conflict between vehicle stability and curving performance. However, for the high speed railway, the curve radius on the main line is big enough that curving performance can be considered to be of minor status. Therefore, the problem of achieving high speed operation without hunting instability and with good ride comfort is investigated in this paper.To investigate the hunting instability of high speed railway vehicle, the vehicle is modeled as a rigid multi-body system composed of yaw damper components, air spring components, emergency spring components and traction motor components. In order to reduce the carbody vibration, simplified vertical model of the rigid-flexible coupling system, accurate three-dimensional model of the rigid-flexible coupling system, constrained carbody damping treatment model, and carbody piezoelectric structure model are established. Based on the proposed models, the following aspects are extensively studied.(1) With all nonlinearities in the model linearised or eliminated, eigenvalues and eigenvectors of the linearised equations are calculated with root locus analysis. It shows that two modes of hunting instability exist in the railway vehicle systems, one called carbody hunting and the other one called bogie hunting. Then, the effect of the secondary lateral suspension stiffness, secondary lateral suspension damping, secondary longitudinal stiffness, secondary longitudinal damping, primary longitudinal stiffness, wheel tread equivalent conicity, and carbody weight on hunting stability is investigated. Investigation results show that two modes of hunting instability may emerge in the railway vehicles due to different suspension parameters and wheel/rail conditions, which may be the mian factor to restrict high speed speed operation.(2) The influence of the primary longitudinal stiffness, primary lateral linear and nonlinear stiffness, value of equivalent conicity, shape of wheel profile, linear and nonlinear parameters of yaw damper, frequency and damping ratio of traction motor lateral motion, frequency and damping ratio of traction motor yaw motion, stiffness and friction coefficient of emergency spring, secondary lateral damping, and Kalker weighting coefficient on the critical speed is investigated extensively. Based on the simulation results, design principles of vehicle parameters in respect of hunting stability are proposed. At last, some of the theoretical analysis results are validated by the roller rig test.(3) Based on the study of vibration sources and transmission paths of the carbody lateral and vertical oscillations, the influence of the secondary lateral damper, the inter-car damper, and the secondary lateral semi-active suspension on the carbody lateral vibration, and the influence of the primary and secondary vertical damping, the air spring parameters, the mounting angle of yaw damper and the traction rod longitudinal stiffness on the carbody vertical vibration are investigated. Based on these researches, design principles of vehicle parameters in respect of ride comfort are proposed.(4) Differences between the rigid multi-body vehicle model and the rigid-flexible coupling vehicle model in hunting stability, ride comfort, and curving performance are presented. Then, the characteristic of carbody elastic vibration is revealed, and the vibration suppression mearsures are determined. Through reasonable assumptions, the formula of the loss factor for the carbody with constrained damping layers is derived. The influence of length, thickness, and elastic modulus of the constrained damping layers on the carbody elastic vibration is investigated by numerical simulation. At last, the piezoelectric shunt damping treatment on the outside sheathing of car body and the concept of an active vibration reduction system of a railway vehicle car body with offset piezoceramic stack actuators are simulated.(5) The application of the theoretical hunting stability analysis to a high speed passenger car with offensive vehicle hunting problem in the filed tests is presented. Causes and solutions for this problem is proposed based on the simulation results and test results.