Research On Vibration Characteristics Simulation And Compound Fault Feature Extraction Of Train Axle Box System Under Complex Excitation

As one of the most important parts of the high-speed train rotation system,the axle box bearing mainly supports the rotation of the system and provides additional damping to make the system operate stably.Axle box bearing,as the key to transfer traction power,is susceptible to the excitation caused by the complex status of wheelset.In particular,wheelset is disturbed by wheel-rail wear,wheel polygon and operation line environment,which leads to dynamic uncertainty of its excitation.This makes the vibration response of axle box bearing more complicated.The vibration characteristics and characteristic evolution rule of axle box bearings change with the excitation action,which makes it difficult to monitor,identify and predict the health status of the axle box system.It is the main idea to study the dynamic behavior and vibration characteristics of the axle box system by separating the wheelset from the axle box bearing and establishing a comprehensive multi-degree-of-freedom model of the axle box bearing system,which considers the dynamic coupling between components,and then adding the established model to the vehicle-track coupling dynamic model.This is beneficial to further explore the influence mechanism of external excitation source of axle box bearing.In this paper,the vibration and contact problems related to high-speed train axle box system are taken as the research objects,and a vehicle-track coupling dynamic model containing axle box system is constructed,and the vibration characteristics of high-speed train axle box system under complex excitation conditions are studied.Finally,the bench test of bearing fault is carried out,and the method of compound fault characteristic extraction of wheelset/bearing is studied.The main work is as follows:(1)Based on the classical vehicle-track coupling dynamics theory and tapered roller bearing dynamics calculation method,a vehicle-track coupling dynamics model containing axle box system is established.The differential equation of rail vibration and the structural mode of wheelset are calculated and analyzed.The dynamic coupling relationship between wheel and rail is described in detail through the wheel/rail contact model.The dynamic coupling equations between axle box and frame as well as between frame and car body are analyzed and derived respectively.The axle box system is closely combined with the vehicletrack coupling system.Based on this model,the influence of track geometry irregularities on the vibration characteristics of the axle box system is analyzed,and the vibration response characteristics of the axle box system under typical excitation conditions are studied by combining with the typical polygonal model of wheelset.(2)Based on the axle box system-vehicle-track coupling dynamic model containing wheelset faults,the influence of different polygonal wear order,amplitude,length of flat scar and wheelset diameter on the dynamic characteristics of axle box system are analyzed.Based on the safety evaluation and health management of wheels,the safety threshold of wheel wear which can ensure the normal operation of high-speed trains is given.In the meanwhile,it provides theoretical basis for the design,operation and maintenance of high-speed train axle box system.(3)Based on the multi-body dynamics software,the axle box system-vehicle-track coupling dynamics model containing bearing outer race faults and roller faults is established.In view of the local defects and faults of axle box bearings that often occur in the service process of high-speed trains,that is,outer race faults and roller faults as model excitation,the safety threshold of corresponding defects is given by analyzing the influence of different defect widths of outer race and roller for axle box bearing and the influence of compound defect excitation for bearing outer race and wheel flat scar on vibration characteristics of axle box system,which provides the foundation for the health monitoring of axle box system.(4)The bench test of wheelset/bearing composite defects is carried out,and the method of wheelset/bearing compound fault characteristic extraction is studied based on axle box vibration signals.A feature extraction method for wheelset/bearing compound faults based on VMD is proposed.The proposed method avoids the problem of optimal selection of modal number K in VMD,and achieves adaptive decomposition of VMD independent of prior knowledge,which can effectively extract compound fault features in complex electromechanical systems.