The Dynamic Features Of The Urban Railway Vehicles Under Wheel Flat And Out Of Round Faults

As one of the important means of transportation for urban travel,the operation safety of urban railway vehicles is more of the top priority.With the increase of subway operation mileage,the wheelset will cause wheel failure due to sudden load change or fatigue in actual operation,which threatens the driving safety.Wheel abrasions and non-roundness are common faults in the operation of urban rail vehicles.The occurrence of wheel abrasions will cause periodic impulse impact on the vehicle during operation,which will have a great impact on the vehicle's transmission system,frame,body and other components,and even cause accidents such as derailment caused by wheel and rail separation.As a harmonic periodic fault,the wheel irregularity also affects the key parts of the vehicle.And because of the existence of two kinds of faults in the process of vehicle ride stability,comfort has a greater impact.In order to ensure the safe operation of vehicles,this paper studies and analyzes the dynamic characteristics generated by common wheel faults.The research results can not only provide theoretical basis for fault diagnosis and reliability analysis,but also provide reference for on-site rotation repair and operation maintenance.The main work and conclusions of this paper are as follows:1.In this paper,based on the vehicle track coupling dynamics model,the vehicle dynamics model with wheel failure and flat scar fault was established,and the transmission system and gear system were added.The above parts are considered as rigid bodies,the contact between wheel and rail and the contact between gear teeth is considered as local elasticity,and the equation of the problem is derived and solved by d 'alembert's principle.According to the model and the analysis of the calculation results,the amplitude of the gear box's response to the vertical vibration of the track irregularity is close to that of the wheelset,and the excitation effect is greater than that of the motor.In addition,when the vehicle is running at low speed,the torsional vibration of the gear system is greatly affected by the internal excitation of the gear.When the speed is high,the torsional vibration acceleration of the gear system is greatly affected by the excitation of the track irregularity,and the internal and external excitation of the gear system ACTS at the same time.2.Urban rail vehicles can be divided into idling,traction and braking conditions in the actual operation.This paper discusses the influence of the above wheel faults on the time-frequency domain of each component of the vehicle dynamics model under the variable speed condition.Due to the action of the basic resistance,the amplitude declines steadily and weakly under the condition of inactive movement.Under the traction condition,the amplitude changes greatly and the impact frequency of wheel abrasions increases obviously.Compared with the constant torque area,the fast change of fault frequency in the constant power area is due to the action of the traction force,which makes the vehicle speed increase faster.3.The length of wheel abrasion is positively correlated with traction.With the increase of speed,the flat scar will be transformed from periodic excitation to random excitation.Through the above analysis,the contribution to the amplitude can be determined from the speed andfault length.The effect of length on the impact amplitude is greater than that of speed on the impact amplitude.4.When the wheel failure is not circular,the fault features are not obvious.The short-time Fourier transform(STFT)of the time-domain signal containing the fault of the wheel is not enough to obtain the fault characteristics of the time frequency,which needs to be further processed.After analysis and calculation,it is found that the spectral reconstruction is suitable for fault feature extraction of the impulse type excitation,and the variational mode decomposition can be used to deal with the fault characteristics of the wheel.Under the three working conditions,the comparison shows that the failure of non-circular wheels in traction condition is more likely to cause the vibration of gear box and the increase of vertical vibration acceleration response amplitude than that of non-circular wheels in idling condition.5.Output the calculated results and analyze the regular vibration characteristics with statistical indicators,and analyze the vibration characteristics with load spectrum.Through the analysis of the statistical characteristics of the calculated results,it is found that when the dynamic statistical index is used to represent the fault characteristics of flat scar,the index fluctuates less under the condition of idle operation.For the wheel abrasion fault,the peak-to-peak value is more suitable to describe the wheel flat scar fault;For the non-circular fault of the wheel,the two indexes of p2 and fr1 can be used to calculate and evaluate the statistical characteristics of the non-circular fault of the wheel.Through the analysis of the load spectrum,it is found that the cycle times of wheel abrasions are mainly dominated by the speed and the operation points are concentrated,while the wheel irregularity is mainly dominated by the fault depth and the fault order and the operation points are scattered.And the two kinds of faults in idling and braking conditions,although the speed has been reduced,but the number of cycles is still on the rise.