Vibration Characteristics Analysis And Fault Diagnosis Of Axle Box Bearing Of EMU

The axle box bearing is one of the core rotating parts in the running gear of EMU,its health status directly affects the reliability and safety of EMU.Under the high-speed and heavy-load conditions,the roller,inner and outer raceways are prone to failure because of the complex and strong wheel-rail excitation for a long time.Vibration signal is highly sensitive to bearing faults,but due to the influence of vibration transmission path,different measuring points on the axle box surface have different sensing ability to bearing faults.In addition,complex wheel-rail excitation will has a great impact on the impulse response caused by faults,which increase the difficulty of bearing fault diagnosis.In respect of the issues above,this thesis considers the dynamic interaction between the axle box bearing,the frame,and the wheel set,to establishe axle box flexible vehicle rigid-flexible coupling dynamic model.Considering the influence of wheel-rail excitation,the characteristics of roller-raceway contact load are simulated and analyzed.Under different bearing fault conditions,the vibration characteristics of the axle box are simulated and analyzed to determine the fault sensitive sensing points on the surface of the axle box.Furthermore,the influence of wheel-rail excitation on the vibration characteristics of sensitive sensing points is simulated and analyzed.The fault diagnosis method of axle box bearing based on vibration signal is researched and verified by experiment.The main research contents in this thesis include:1.A multi-rigid body dynamic model of the axle box bearing is established according to the structural parameters of the axle box bearing of EMU.Furthermore,according to the vehicle dynamics parameters,the wheelset,frame and other components were considered as rigid body,and the axle box was considered as flexible body.The axle box flexible vehicle rigid-flexible coupling dynamic model is established by using Recurdyn and Simpack multi-body dynamics software and Ansys finite element analysis software.2.The roller-raceway contact load are simulated and analyzed under wheel polygon,track irregularity,and wheel-rail comprehensive excitation conditions.The results show that the polygonal excitation of the wheel mainly produces periodic amplitude modulation on the contact load of the rolling elements in the load-bearing area.The track irregularities excitation will cause the fluctuations of the contact load in the load-bearing area and the non-load-bearing area to increase significantly.3.Through the simulation and analysis of the vibration characteristics of the axle box under various bearing failure states,the fault-sensitive sensing measuring points on the surface of the axle box are obtained.Furthermore,the influence of wheel-rail comprehensive excitation on the vibration characteristics of sensitive sensing measuring points is analyzed by simulation.The results show that the amplitude of fault impulse response is seriously non-stationary modulated by wheel-rail comprehensive excitation,which makes the effect of envelope spectrum analysis poor.4.A fault diagnosis method for axle box bearings based on average autocorrelation and optimized Variational Modal Decomposition is proposed.Firstly,the average autocorrelation algorithm is used to reduce the noise of the vibration signal;Then the inverse ratio of the fault characteristic frequency energy is served as the fitness function,and the Harris Hawk Optimization is used to optimize the key parameters of the Variational Modal Decomposition to achieve adaptive signal decomposition;Finally,the square envelope spectrum is used for fault diagnosis and analysis.The results show that this method can effectively eliminate the affect of random noise and extract the fault features of bearings stably and accurately.