Research on vibration spectral structures of planetary gearboxes based on a universal equation of phenomenological modeling

A variety of factors such as time-varying transfer paths, planet shifts, etc., can induce additional modulation sidebands in the spectrum of planetary gearboxes. Most of previous work only considers the effect of a single factor on the sidebands, while these factors may occur at the same time and the corresponding results are not studied. Moreover, although all of these factors can result in additional sidebands, it is unclear that which the most important factor is, and brings difficulty to the fault diagnosis of planetary gearboxes. Aiming at this issue, a universal equation of phenomenological models of planetary gearboxes is developed in this paper to predict the importance of a certain factor in arising modulation sidebands. This model extends the previous phenomenological models which only contain a single factor of sideband formation and can describe the spectral structures of planetary gearboxes with multiple factors considered simultaneously. Effects of multiple factors including time-varying transfer paths, planet shifts and load sharing ratios on the modulation sidebands are analyzed. Furthermore, arbitrary one, two and multiple factors are introduced in the established phenomenological model to make a comparison between these factors. It is found that when the unequal load sharing among planet gears is not severe, a planet shift can result in abundant frequency components more prominently. Finally, the formation mechanisms of modulation sidebands are derived and some experimental validations are carried out to prove the effectiveness of proposed model.