Dynamic Modeling And Vibration Characteristic Analysis Of Inter-Shaft Bearing Multi-faults

The inter-shaft bearing is the key component of the aero-engine rotor system,which is prone to failure due to its harsh working environment,large dynamic load and poor lubrication conditions.Once the fault occurs,it will affect the normal work of the engine.This paper further reveals the mechanism of inters-shaft bearing fault and obtains the variation rule of characteristic parameters of inters-shaft bearing fault.This lays a foundation for the study of monitoring and diagnosis methods of aero-engine inter-shaft bearing fault.At present the theory of inter-shaft bearing fault is not perfect,especially the mechanism of multi-faults of inter-shaft bearing is unclear.Firstly,based on the nonlinear Hertz contact theory,the time-varying displacement excitation function was used to describe the simultaneous faults in the inter-shaft bearing,and a dynamic model of the inter-shaft bearing was established.Secondly,on the basis of the single-fault model,the time-varying displacement excitation of the multi-faults was further derived,and the 4-DOF dynamic model of the multi-faults was established.Finally,according to the actual working condition of the inter-shaft bearing,an inter-shaft bearing fault test bench was built to simulate the inter-shaft bearing.By comparing the experimental data with the dynamic numerical simulation results,it is found that the error between the simulation results and the experimental results of fault characteristic frequency is less than 1%,which verifies the validity of the dynamic model.Based on the multi-faults model,the influence of defect width,radial load and speed ratio on characteristic parameters of typical faults was analyzed.The results show that the vibration signals of the inner and outer ring multi-faults contain both inner and outer ring fault information.The vibration signals of the inner ring multi-faults and the outer ring multi-faults appear the phenomenon of pulse superposition in the time domain diagram.With the increase of defect width,radial load and speed ratio,both the peak value and the root mean square value tend to increase,but the kurtosis factor changes in a complicated way.When the bearing is in fault mode,the kurtosis factor is always larger than 3,while the waveform factor is not sensitive to the fault.The peak value is not as stable as the root mean square value in the variation of defect width and speed ratio,so it is more suitable in the fault diagnosis of impact load.