Research On Fault Mechanism And Diagnosis Method Of The Gear Transmission System Of Urban Railway Vehicle

The gear transmission system is an essential component of urban railway vehicles,and its health state is closely related to the safety of train operation.In 2015,Beijing subway trains found more than twenty spalling on the tooth surface of the gear.Although the fault mode of the gear transmission system is different,it can lead to an adverse effect on the safety and dynamic performance of urban railway vehicles.Underestimate the impact of the failure of gear components,which may cause the systemic failure of the traction transmission system,leading to serious disaster.Urban railway vehicle wheelset and gear are coaxially assembled.On the one hand,the gear transmission system is subject to high-frequency vibration impact of gear teeth meshing,on the other hand,it is subject to the non-linear contact of the wheel and rail and the vibration elements such as primary suspension and secondary suspension.The impact of vibration is different from the general gear transmission system,and the dynamic characteristics and nonlinear behavior are very complicated.Besides,considering that the gear transmission system of urban railway vehicles works in a non-stationary environment that changes at all times,it is difficult to implement its fault diagnosis using general signal processing methods.Therefore,there is an urgent need to conduct in-depth research on the dynamics,failure mechanisms,and diagnostic methods of the gear transmission system of the urban railway vehicle.Given the above problems,the main research work of the paper is as follows:(1)Based on the potential energy method,a calculation model for the time-varying meshing stiffness of the profile-shifted involute spur gear is established.The study found that the modified coefficient has a more significant impact on the overall meshing stiffness of the gear.Based on this,the longitudinal-vertical dynamic model of urban railway vehicle was established,and the Shanghai subway track spectrum suitable used for urban railway vehicle dynamics analysis was introduced.The model was validated in comparison with experimental data.The proposed meshing stiffness model of profile-shifted involute spur gear meshing stiffness model covers the meshing stiffness model of standard involute spur gear,which can be widely used in industry;the proposed longitudinal-vertical dynamic model of urban railway vehicle can be used to evaluate dynamic indicators of urban railway vehicle considering gear meshing excitation.(2)According to the meshing stiffness model of the profile-shifted involute spur gear,the model for the tooth root crack,spalling,and tooth surface wear failure is further derived.For tooth root cracks,spalling and tooth surface wear,the effects of different fault severities on the time-varying meshing stiffness are analyzed,and the time-domain response and the power spectrum differences of the meshing forces with varying levels of fault are investigated.The sensitive feature of time-domain and frequency-domain features have been acquired,and the evolutionary trends of each component have been obtained.(3)Analyze the external excitation of the gear-wheelset system of urban railway vehicle under traction,coasting,and braking conditions in detail and establish planar dynamic models with and without consideration of wheel-rail adhesion.It is found that the error between analytical speed obtained by the cumulative integral method and numerical speed achieved by the proposed planar dynamic model is small enough,and the model has good speed tracking ability.On this basis,the torsional time-frequency characteristics,slip velocity time histories,wheel-rail normal force,adhesive force,and intermittent contact characteristics under the traction condition,the coasting condition,and the braking condition are analyzed,respectively.The investigation finds that the performance of the intermittent contact characteristics and these dynamic responses in the three conditions are closely related.(4)For nonlinear dynamics of the transient process of the forced vibration system,a quasi-steady analysis method based on the "slicing" idea is proposed.The Single-degree-of-freedom model is obtained based on the urban railway vehicle gear-wheelset two-degree-of-freedom torsional vibration model using order reduction and dimensionless technique.Through the quasi-steady analysis,the productive nonlinear behavior evolution process of the gear-wheel pair system that changes with the speed under traction conditions is revealed.By comparing the results of the time-frequency analysis,it is found that there is a one-to-one correspondence between the bifurcation and chaotic behavior of the gear torsional vibration system and the time-frequency characterization of the signal,which provides theoretical support for a variety of frequency-response behaviors appearing in condition monitoring.(5)Based on the research results of fault mechanism and dynamic characteristics under various operating conditions,aiming at the fault diagnosis of non-stationary signals of gearboxes,a dislocated time-frequency representation method that can not only increase the sample size but also characterize the trend of continuous signal changes is proposed,and Alex Net is used to perform deep transfer diagnosis of faults in gear transmission systems.The study found that the dislocated CWT representation has better performance in deep transfer diagnosis.At the same time,by increasing the overlap rate in dislocated time-frequency representation,the accuracy of transfer diagnosis can be effectively improved,helping deep networks to achieve a more accurate classification of different working conditions and faults.Finally,the proposed algorithm is verified through experimental research,and intelligent faults under multiple operating conditions have been successfully implemented on the test bench of the gear transmission system of the urban railway vehicle.The research results will provide a theoretical basis for the actual fault diagnosis of the gear transmission system of urban railway vehicles,and have decisive significance for the maintenance of urban rail transit equipment.