Gear Teeth Parameter Identification in Helicopter Planetary Gearbox Using Tachometer and Vibration Signals
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Abstract
Accurate identification of gear tooth counts in planetary gearboxes is essential for condition-based maintenance and health monitoring in gearbox systems. However, direct inspection of internal gear components—especially planet gears—is often infeasible due to the gearbox's enclosed structure and lack of documentation in aging or mixed fleets. This paper presents a methodology to estimate the number of gear teeth in bevel, sun, planet, and ring gears with fixed ring gear planetary gearboxes using vibration and tachometer signals. By applying Time Synchronous Averaging (TSA) and Fast Fourier Transform (FFT), we isolate gear mesh frequencies from noise and harmonics. Three case studies— UH60 Black Hawk, AS350, and Bell 407GXi main gearboxes—demonstrate the application of the technique. For bevel gear estimation, TSA is performed using the input shaft rate, allowing dominant frequency peaks to reveal the gear mesh. In planetary gears, TSA is applied using the output shaft rate. Candidate mesh frequencies are identified, with harmonics and known gear interactions used to eliminate false positives. The most plausible planetary mesh frequency is used to estimate the ring gear tooth count, from which the sun gear tooth count is inferred using the total gear ratio.
How to Cite
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Planetary Gear Box, Gear Teeth Estimation, HUMS, Helicopters, UH60
McFadden, P. D., & Smith, J. D. (1985). An Explanation for the Asymmetry of the Modulation Sidebands about the Tooth Meshing Frequency in Epicyclic Gear Vibration. Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science, 199(1), 65-70.
McFadden, P. D.(1986). Detecting Fatigue Cracks in Gears by Amplitude and Phase Demodulation of the Meshing Vibration. Journal of Vibration, Acoustics, Stress, and Reliability in Design, 108(2), 165-170. doi.org/10.1115/1.3269317
Cho, C., & Bechhoefer, E. (2025). Gearbox Casing Crack Detection based on Vibration Signals in Frequency and Time Domain. Vertical Flight Society 81th Annual Forum & Technology Display. doi.org/10.4050/F-0081-2025-28
Sawalhi, N., & Randall, R. B. (2014). Gear Parameter Identification in a Wind Turbine Gearbox using Vibration Signals. Mechanical Systems and Signal Processing, 42, 368-376. doi.org/10.1016/j.ymssp.2013.08.017
Bechhoefer, E., & He, D. (2016). Reducing Tachometer Jitter to Improve Gear Fault Detection. Annual Conference of the PHM Society 8 (1), Denver, Colorado
Bechhoefer, E. (2019). A Comprehensive Analysis of the Performance of Gear Fault Detection Algorithms. Proceedings of the Annual Conference of the PHM Society, 11(1). doi.org/10.36001/phmconf.2019.v11i1.823
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