Investigation On Fault Feature Evolution Of Planetary Gearbox With Typical Tooth Damages

The gear damages in a planetary gearbox can hardly be detected because of the unclear fault mechanism.Aiming at this challenging issue,the present thesis conducts a series of studies on the internal excitation characteristics induced by gear damages,the evolution rule of dynamic characteristics,the evolution mechanism of fault features and the damage identification from the perspective of dynamics.It can provide a solid theoretical foundation and effective technical means for the damage identification and the condition monitoring of planetary gearboxes.The main contents and contributions are as following:By considering the characteristics of gear damage modes of distributed wear and local crack,the models for calculating the meshing stiffness and the error displacement excitation of damaged gears are developed to investigate the influences of distributed wear and local crack of the sun gear on the internal excitations of the system.The relationships between the internal excitations and the gear damage modes as well as the damage states are revealed.The excitation principles of gear damage modes to the system are clarified,which lays a foundation for dynamic modeling and analysis of planetary transmissions.The bridge between the gear damages and the dynamic characteristics as well as the signal characteristics is constructed.The results show that the internal excitations of various gear damage modes are quite different,depending on the damage distribution characteristics and the damage states.With the internal excitations induced by the gear damages,a lateral-torsional-coupled dynamic model is established to predict the dynamic responses of a single stage planetary gear train under faulty conditions.The dynamic characteristics and the signal features of the system with distributed wear damage and local crack damage of the sun gear are studied.The response mechanism of gear damages in the vibration signals and the evolution rule of the dynamic characteristics of the system are revealed,which can provide a theoretical foundation for fault feature extraction and quantitative characterization,damage modes identification and state detection.It is found that the vibration signals in different damage modes and damage states have significant differences.With the help of the spectrum structure analysis,the fault features can be distinguished for typical damage modes according to frequency components,sideband spacing and the evolution rule of the corresponding amplitude.The superposition of signals from various vibration sources and the vibration transfer principle are studied,based on which a resultant vibration signal model is developed to simulate the actual vibration signals collected by transducers installed on the case of planetary gearbox.The effects of the vibration superposition,the time-varying vibration transfer path and the background noise are included in the signal model.Based on the model,the influences of typical damage modes and damage states of the sun gear on the characteristics of vibration signals are investigated.The general method is proposed for fault feature extraction and quantitative characterization.According to the fault features of each damage mode,the typical damage modes of the sun gear are diagnosed and identified.The proposed quantitative indicators of fault features can accurately reflect the damage state of the sun gear,based on which the evolution rule of fault features is revealed.The state detection of the typical damage modes of the sun gear can be realized.Based on the fault simulation bench of gear drivetrain,the experimental tests are performed under various damage modes and states of the sun gear.The comparison between the experimental results and the numerical simulation results verifies the correctness of the theoretical modeling and analysis.