Vibration monitoring threshold of turboprop engine reducer

In order to meet the requirements of undertaking the gear hub fault diagnosis of a turboprop aero-engine without decomposition, a complete machine vibration test system was designed and built. 18 times of complete machine vibration tests were accomplished on the factory bench and out-field aircrafts by using the test system and 2 times of tests were applied based on a specially ordered aero-engine reducer with simulated faults. Aiming at real characteristics of the faults, two methods were used to analyze the signal data, and the monitoring threshold value was confirmed according to the 3σ rule. Based on IIR digital filter theory, the characteristic sub-band was extracted and a comparative analysis of measured signals was carried out. The first level gear tooth meshing frequency in gear hub (1736 Hz) and the gear tooth meshing frequency (6458.5 Hz) were defined as the feature frequencies and the threshold value of the characteristic sub-band was determined. According to the Hilbert demodulation theorem, vibration signals of the reducer were demodulated. The amplitudes of the modulated signals were analyzed comparatively and the threshold value for demodulated characteristic monitoring was confirmed. The demodulation characteristic monitoring thresholds were calculated according to four times the rotating frequency of the planetary gear fram (71.7 Hz) which is of obvious difference under different conditions of the engine. ©, 2015, Chinese Vibration Engineering Society. All right reserved.