Motion periods of sun gear dynamic fault meshing positions in planetary gear systems

Abstract Special assembly manner provides planetary gearboxes unique transmission characteristics, meanwhile brings the diagnostic complexity via a fixed sensor due to the irregular dynamic nature of gear fault meshing positions. This paper proposes a systematic scheme to explore the motion periods of the sun gear fault meshing positions in a planetary gearbox, namely tidal periods. The generalized expressions to the tidal periods are derived and validated through the operational mechanism of a planetary gearbox. The tidal periods are incorporated into simulated signal models so that the unique influences to the vibration responses of a planetary gearbox are revealed. Some previously uncleared and uninterpreted fault-related sidebands can, therefore, be properly interpreted. Moreover, a tidal period is proved to be a minimized time duration that embrace complete fault induced information. Through simple statistical analysis of experimental data under different operating speeds, a minimum required data length for a proper fault diagnosis is recommended based on the analysis of a tidal period. The tidal period is an intrinsic nature due to the operational property of a planetary gearbox.