Nested planetary gear trains, which consist of two integrated co-axial single-stage planetary gearsets, have recently been widely implemented in automobile transmissions and various other applications. In the current study, a non-destructive vibrational and acoustical monitoring technique is developed to detect a common type of gear grinding defect for a complex nested gear train structure. A nested gear train which has an unground pinion with unpolished teeth profile is used to exemplify the developed methodology. An experimental test stand with an open and vertical mounting configuration has been designed to acquire both vibrational and acoustical data. The measured data are investigated using several signal processing techniques to identify unground pinions in the gear system. A general frequency spectrum analysis is performed initially, which is then followed by a peak finding algorithm to identify the peaks in the spectrum. The peak frequency that matches the gear meshing frequency is selected for a further narrowband demodulation analysis. A Hilbert transform based demodulation filtering are then performed on the bandpass filtered signals around each selected frequency to obtain the corresponding instantaneous amplitude and phase signals. These demodulated signals for the gear train with unground gears appear to be different from that with normal gears, which can be used to detect whether grinding defect occurs in a gear train. Furthermore, the frequency spectra of these instantaneous phase and the amplitude signals are shown to exhibit peaks at the rotational frequency of the carrier where the unground pinion is mounted. This information allows the detection the location of the unground gear. The repeatability of results has been confirmed by multiple tests on the experimental setup designed in the current work. It can be concluded that the narrowband demodulation technique can be leveraged to develop an autonomous system for identifying imperfect pinions in a nested planetary gear system.
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