| High-speed railways in China have been developed rapidly in past ten years,and thousands of high-speed trains have been put into operation with good condition in the overall states of the railway vehicles.However,some abnormal vibration phenomenon of the vehicles which may cause train delay in some extent and make passengers feel discomfort was also found in the actual line operation.It was found that the hunting motion of the high speed train plays an important role in the abnormal vibration problems.In this paper the main problems found in long term operation of some high speed trains,like the bogie instability alarm,carbody shaking,carbody swaying,have been investigated.From the perspective of improving the wheel-rail contact geometry,a wheel tread profile design method is proposed,and a new tread profile is generated based on the existing EMU wheel profile.Through numerical simulation analysis,lab test,on-track test and application on a large amount of trains,it can be proved that the newly designed tread profile can effectively improve the vehicle hunting stability.The main research work in this paper is as follows:(1)From the aspects of simulation,on-track test and mechanism research,the abnormal vibration problems of bogie instability,vehicle body swaying and shaking during the field operation of a high-speed EMUs are systematically analyzed.It is found that the poor matching of the wheel-rail contact geometric relationship is the main cause,and the solution measures such as suspension system parameter optimization are summarized with their shortcomings discussed.(2)The poor matching of wheel-rail geometry is the main reason for the abnormal vibration problem related to the hunting stability occurred on high-speed EMUs.Based on the measured rail profiles in different states in China,the wheel-rail contact geometry using the measured wheel and rail profiles are analyzed.Then a concept of designing the equivalent conicity for specific zones on the wheel tread is proposed.The wheel tread is divided into normal working area,high taper area and low taper area,so as to realize the matching relationship between different areas and carry out the overall profile design.(3)A wheel tread profile is designed for high-speed EMUs.According to the aforementioned EMUs operation problems and the tread profile design concept proposed in this work,the parameters such as the equivalent taper,contact point distribution and contact angle of different sections of the tread are designed,and then the sections are connected to obtain the overall tread profile.For the new design tread and prototype tread,the wheel-rail contact geometry relationship and contact stress under various working conditions were compared and analyzed to verify the feasibility of the new design tread.(4)A three-dimensional nonlinear dynamic model of a high-speed EMU vehicle is established,taking into account multiple measured rail profiles.Vehicle dynamics simulation with new design tread is carried out and compared with the vehicle dynamic performance under prototype tread conditions.The related indicators such as vehicle motion stability,operational safety and stability are investigated.It is found that the new design tread has good dynamic performance under various working conditions,and the dynamic performance of the new design tread is better than the prototype tread.(5)In order to study the on-track adaptability of the new tread and the change of suspension parameters of the bogie,an index named equivalent conicity dispersion is used to describe the change of distribution of the equivalent conicity under different high-speed railways.The matching analysis between the rail profile of the actual abnormal vibration section of the vehicle and the improved tread surface are carried out,and the sensitivity of the improved tread scheme to the track gauge and the bogie suspension parameters are analyzed and improved by using dynamics simulations.(6)The rolling vibration rig tests for the newly designed tread were carried out to verify the improving effect of the new tread on the dynamic performance of the vehicle.Further,four groups of EMUs were selected for on-track running performance tests after using the new tread profile.The evolution of tread wear,bogie stability,vehicle stability and vibration characteristics were investigated with vehicle operation mileage.Following the previous field results,another 33 trains were selected to carry out application assessment and tracking tests for further validation and promotion.The wheel tread wear with the running distance and service environments such as different routes,different seasons,and different speeds are analyzed.Lab tests,on-track tests and field application assessment tests show that the new design tread can effectively guarantee the dynamic performance of the high-speed EMUs,and solve the vehicle hunting issue and the abnormal vibration problems caused by the prototype tread.The new tread profile significantly extends the wheel tread reprofiling cycle,and extend the service life of the wheel.(7)According to the requirements of maintenance and other operation experience,an economic maintenance program of wheel reprofiling is proposed with 13 thin-flange wheel profiles designed.The calculations of the vehicle dynamics performance,the strength of the wheel,wheel-rail contact geometry,ballast pass check,etc.,were carried out for different thin-flange profiles,and the experimental verification of the thin-flange profiles was carried out in combination with the EMU field application assessment.The results show that the thin-flange wheel profiles can significantly reduce the single repair amount of the tread,effectively improve the service life of the wheel and reduce the operation and maintenance cost of the high-speed EMUs.(8)Concerned on the vehicle abnormal vibration in the filed operation of high-speed EMUs,this wok proposed a design concept of wheel tread profile through controlling the equivalent conicity on various tread zones.A new wheel tread profile is generated with the economical thin-flange profiles provided for practical wheel profile reprofiling.The new tread has been verified through lab tests,on-track tests and field application tests,and used on the Chinese standard EMUs at speed 300 km/h and above.It solves the abnormal vibration problems such as vehicle hunting,vehicle swaying and car body shaking issues caused by the prototype tread.It furtherly significantly improves the repair mileage,extends the service life of the wheels and reduces the operating and maintenance costs of high-speed EMUs.This work shows important theoretical significance and engineering application merit. |
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