Vibrodiagnostics of turboprop engine gearbox wear

The peculiarities of the structure of the vibration spectrum of the turboprop engine differential gear in the case of wear of the central gear teeth are discussed and a technique of vibration diagnostics of the defect is proposed in the paper. It is found that the wear leads to multiple harmonics, including tooth harmonics, in the broadband vibration maxima spectrum. The frequency of the first harmonic of the series is determined by multiplying the speed of rotation of the outer central gear by the number of the worn teeth. It has been shown that increased intensity of one of the components of this series is the cause of the fatigue failure of a rotor blade of one of the compressor stages. Comparative analysis of the autospectra, the spectrum peaks of the spectrum envelope and the data of cascade demodulation show that in this case the autospectra is most informative. On the basis of the statistics of reworked gearboxes and a gearbox with the level of wear twice the norm threshold values were obtained for two of the most informative spectral components. These values make it possible to identify the gear unit with inadmissible degree of wear of its teeth. Statistical analysis of gear vibration of the repaired items revealed the presence of a component that characterizes relative beating of the outer central gear and satellites. It was found that its intensity differs from engine to engine by more than an order of magnitude. The impact of this beating is considered to be one of the main causes of increased wear. The investigation of the effect of this factor on the development of the defect is determined as the line of further research.