Characteristic Analysis Of Hollow Worn Tread Of High Speed Emu And Its Impact On Vehicle Stability

Nowadays,the total length of China's high-speed railway network has approached30,000 kilometers,exceeding the total mileage of high-speed railways in all other countries.High speed EMU(Electric Multiple Units)has the characteristic of large train density,highloads operation and faster operation speed.Then the wheel/rail damage was also far more serious than that of ordinary railway vehicles.Therefore,wheel/rail wear of EMU running on high-speed railway line shows new characters mainly presented as hollow worn tread and wheel polygon.Hollow worn tread would degrade lateral stability of vehicles and wheel polygon would deteriorate vertical vibrations of vehicles and threat reliability of components.This thesis aims at the issue of bogie lateral instability for certain type of EMU on several high-speed railway lines,evaluating influences of hollow worn tread on vehicle lateral stability.Wheel/Rail contact geometric relationship is one of the main factors dominating vehicle dynamic performance.In practical application and maintenance process,the nominal equivalent conicity(transverse displacement of wheelset is 3 mm)is selected as the inspection index,but it is found that wheels with same normal equivalent conicity would have different wheel/rail interactions.Thus a new evaluation method was proposed: based on statistics,the wheel/rail contact condition was identified with“nonlinear factor”.This thesis developed vehicle dynamic model and wheel wear prediction model,based on multi-body system dynamic theory?wheel/rail rolling contact theory and wheel/rail contact wear method,analysed the effects of nonlinear characteristics of equivalent conicity curve and hollow worn wheel false flange effect on vehicle stability combining the worn tread data of field test,and researched on prediction of hollow worn wheel simultaneously.Researches of this thesis mainly consist of following parts:(1)Considering the limitation of normal equivalent conicity,a method of nonlinear equivalent conicity was applied to analyse the nonlinear characteristics of equivalent conicity curve.A new evaluation method was proposed based on statistics data,and the wheel/rail contact condition was identified with “nonlinear factor” derived by equivalent conicity range from 1 mm to 6 mm.It is an effective method to evaluate the relationship between wheel/rail nonlinear contact condition and vehicle dynamic performance.(2)Researches were conducted on depth of tread wear,depth of hollow wear and width of hollow wear,based on field tests of hollow worn tread profiles and the collection of the data of profile parameters during one wheel maintenance period.A vehicle dynamic model was developed considering hollow worn profiles for evaluating how hollow worn profiles would affect vehicle dynamic behaviours.It was found that when the depth of hollow wear reaching certain level,local wheel/rail geometric matching is similar to flange contact,which would increase lateral impact and form the “False Flange Effect”;the tread with larger depth of hollow wear has a larger wheel/rail impact.The indicators,such as the width of the worn zone and worn depth have less influence on the wheel/rail impact.With further research,it is found that the“False Flange Effect”is bound up with the nonlinear characteristics of equivalent conicity curve;the“False Flange Effect”of hollow worn tread with larger nonlinear equivalent conicity is obviously stronger.(3)According to this model,the impact of different operation mileage on vehicle dynamics performance was analyzed.While the vehicle operating at a high speed,the lateral vibration frequency caused by hollow worn tread is close to the natural vibration frequency of the frame,which will induce lateral coupled vibration of bogie and exceeding of the limit criteria.In addition,after computer simulation,the result shows that hollow worn tread mainly affects the of wheel/rail lateral impact,such as derailment coefficient,axle lateral force and other indicators.On the contrary,the wheel/rail vertical shock,such as wheel/rail vertical force and loading rate of wheel reduction wheel,has little influence.Via field test and simulation analysis,it is found that hollow worn tread is the main cause of frame instability alarm.Using rail grinding and wheel re-profiling could observably improve lateral stability of bogie;meanwhile,lathe process improvement,rail profile and wheel tread optimizing,reasonable matching of suspension parameters of EMU train should be carried out simultaneously,then the lateral performance of bogie can be improved and the bogie lateral alarms will be eliminated eventually.(4)A wheel/rail wear prediction model was established based on Archard wear theory.Combining with the fitting line conditions and bogie parameters,the abrasion process of hollow worn tread was simulated,meanwhile compared with the measured data of wear depth.The influence of different bogie parameters and line conditions on hollow worn tread was analyzed.The bogie parameters have less influence on hollow worn tread,while line condition and track irregularity have remarkable effects on tread wear.