Fault diagnosis of planetary gearboxes via torsional vibration signal analysis

Torsional vibration signals are theoretically free from the amplitude modulation effect caused by time variant vibration transfer paths due to the rotation of planet carrier and sun gear, and therefore their spectral structure are simpler than transverse vibration signals. Thus, it is potentially easy and effective to diagnose planetary gearbox faults via torsional vibration signal analysis. We give explicit equations to model torsional vibration signals, considering both distributed gear faults (like manufacturing or assembly errors) and local gear faults (like pitting, crack or breakage of one tooth), and derive the characteristics of both the traditional Fourier spectrum and the proposed demodulated spectra of amplitude envelope and instantaneous frequency. These derivations are not only effective to diagnose single gear fault of planetary gearboxes, but can also be generalized to detect and locate multiple gear faults. We validate experimentally the signal models, as well as the Fourier spectral analysis and demodulation analysis methods.

► The explicit torsional signal model of a planetary gearset with and without distributed faults is given.
► The explicit torsional signal model of a planetary gearset with local gear faults is given.
► The spectral characteristics of the torsional vibration models are derived.
► The spectral characteristics of amplitude- and frequency-demodulated signals are derived.
► The derived spectral characteristics are validated with experimental data.