Vibration diagnostic method based on improved intrinsic time-scale decomposition and energy operator demodulation for fault diagnosis of helicopter planetary gearboxes

Planetary gearboxes play a significant role in helicopter transmission system. Fault diagnosis of planetary gearboxes is a key topic for health monitoring and maintenance of helicopter. The vibration signals of faulty planetary gearboxes have complicated spectral structures due to its distinctive and complex structure and time-variant running operation condition, leading to the difficulty in fault diagnosis of planetary gearboxes. Considering that both the amplitude envelope and the instantaneous frequency of vibration signals are associated with the characteristic frequency of the faulty gear, we propose a vibration diagnostic method using the amplitude and frequency demodulation analysis. First, the vibration signal was decomposed into several proper rotation components (PRs) and a trend component by the improved intrinsic time-scale decomposition (IITD) method. Then the energy operator method was exploited to estimate the amplitude envelope and instantaneous frequency of the PR which contained obvious impacts. Finally, by analyzing the dominant peaks in the Fourier spectra of the demodulated amplitude envelope and instantaneous frequency with the theoretical characteristic frequency of each gear, we can diagnose planetary gearbox faults. The effectiveness of the proposed method is demonstrated by simulated signal analysis, and is validated by experimental signal analysis of a lab planetary gearbox with sun gear faults including a chipped tooth and a missing tooth.