Research On Dynamic Characteristics And Its Application Of A Ball Bearing-Rigid Rotor System With A Local Defect

A rolling bearing is a key and critical element of light-duty rotation machineries such as an aero-engine.It is one of the elementary topics for the subproject“dual-rotor-bearing-casing system vibration transmission and fault source tracing”of“basic research on safe operation of aircraft engine（National Basic Research Program,973 Program）”.It is also one of the important issues for the“Major Projects of Aviation Engines and Gas Turbine”.Because the working condition becomes more and more complex and rigorous,as a key and weak link,the failure risk of a rolling bearing is becoming higher.To guarantee the good functioning of a rotating machine,bearing fault diagnosis is becoming more and more important.Besides,the study of fault mechanism plays a very elementary role for bearing diagnosis.The raceway local defects are most common fault types,and the local faults represented by wear and spalling account for a large proportion,study of this kind of bearing fault has important practical value.Different from the existing research on bearing local fault,the nonlinear vibration theory was used to study the vibration characteristics of fault bearing-rotor system through the perspective of the integration of bearing and rotor.The objective of this thesis focused on the raceway local fault in ball bearing by considering the experiment condition of our lab.There exsit three main excitations:varying compliance（VC）excitation,rotor exccentric excitation and pulse excitation.This thesis studied the dynamic response features and the influencing factors of a bearing-rigid rotor system,some new dynamic features and the application were discovered by analyzing theoretical and experimental results.The dynamic characteristics of a health ball bearing-rotor system was studied and the relationship between the VC vibration and bearing vibration signal was comfirmed.First,considering a balanced rotor,the HB-AFT was used to calculate the dynamic characteristics of the system,and the calculation results showed that the system existed VC resonance and light super-harmonic resonance.Second,considering the influence of the rotor unbalance excitation,the Runge-Kutta method was used to calculate the dynamic response of the system,the influence of the rolling element number and unbalanced excition force on dynamic characteristics was discussed.Calculation results illustrated that increase of ball number could reduce VC characteristics,parametric excitation property and some nonlinear phenomena;the characteristic response of the system related to VC vibration was reduced when rotor eccentric excitation force was big;the VC vibration showed similar results to the balanced rotor when the rotor eccentricity became small.At the same time,the calculation results also demonstrated that the response near the VC resonance zone contained abundant bearing vibration information.Assuming balanced rotor and outer raceway fault,the resonance characteristics and frequency-domain characteristics of a fault bearing-rotor system were studied.First,we compared the differences of two local defect models--geometric boundary（GB）model and pulse force（PF）model in view of dynamics.PF model could be expressed as the Fourier series form and be calculated by the HB-AFT with high calculation efficiency and simplicity for theoretical analysis,however,the GB model was based on the change of radial clearance which was not easy for mathematical approximation.In addition,the GB model could cause quasi-periodic problem to bring trouble for dynamic equation solving.On the consideration of rapid calculation and mechanism research,we thought the PF model had an advantage over the GB model.Then,the fault bearing-rotor system with different PF model were solved through HB-AFT,the calculation results illustrated that fault bearing-rotor system presented the obvious VC resonance and VC super-harmonic resonance under different parameters.The obvious super-harmonic resonance could be regarded as the dynamic fault feature by contrasting the healthy bearing-rotor system.These phenomena also demonstrated that the VC resonance zone and VC super-harmonic resonance zone were the sensitive zone for bearing vibration information.Besides,the low frequency-domain characteristics of a bearing-rotor system with outer race defect was analyzed,and we draw a conclusion that depending on the 2^nd defect and higher order defect harmonic frequency with amplitude condition was more reliable to judge a fault.Combining the envelop analysis,the application of dynamic characteristics of fault bearing-rotor system was provided.First,the dynamic characteristics of a bearing-rotor system with outer race local defect and inner race local defect were calculated.Second,the envelope analysis technique was introduced to analyze the effect of rotor speed on bearing vibration characteristic.The envelope analysis results presented a clear and rich bearing fault information in low-speed zones where the VC resonance zone existed while they presented a weak bearing fault information in high-speed range,the inner race defect was especially sensitive.Besides,the envelope analysis under different systemetic parameters and fault parameters also revealed similar results.Third,the corresponding mechanism of these phenomena were explained through analyzing the bearing force at different rotor speed conditions:the effect of the rotor eccentric in high-speed range changed the contact condition between the rolling element and raceway,which led to the decrease of bearing vibration information and vibration impulsive feature of the local defect.Combining the analysis above,the low-speed range where VC resonance zone existed was more suitable for signal acquisition.The verification of the theoretical results was carried out through experiment.First,the experiment results proved the VC resonance characteristics―the soft spring characteristics in vertical direction and coexist of hard and soft spring characteristics in horizontal direction;the weak 2^nd super-harmonic resonance was also detected.Second,in terms of bearing-rotor system with outer race defect,the experimental results confirmed that there were significant VC resonance and 2ⁿdd super-harmonic VC resonance;compared to the healthy system,the energy of outer race defect frequency and its harmonics increased;the statistic results also revealed that the 2^nd defect frequency were more apparent.Besides,the natural frequency of the bearing-rotor system was also detected in the frequency spectrum,which confirmed the explanation to the quasi-periodic phenomenon.Later,the obvious inner/outer defect frequency through the envelop analysis technique were obtained in the VC resonance zone for the application of vibration status,which demonstrated the effect of vibration status on the signal acquisition and the importance of signal acquisition rotor speed.The experimental results qualitatively confirmed the resonance characteristic,frequency characteristics and the reasonable rotor speed range for vibration signal acquisition of a fault bearing-rotor system.In conclusion,the nonlinear vibration theory and the experimental exploration was used to study the dynamic characteristics of a defective bearing-rigid rotor system,some new dynamic phenomena and corresponding mechanism were discovered in this paper.Besides,the application of these phenomena and mechanism were presented.The research results of this paper will have important theoretical and practical value.