Investigation of system dynamics considering gear–bearing coupling under multiple fault modes

To diagnose the fault forms of key components in the drive system of aircraft engine accessories, it is necessary to accurately grasp the changes in their vibration characteristics. Targeting a certain aircraft gear–bearing drive system as the research object, this work adopted the lumped mass method to establish its nonlinear dynamic model and differential equation, considering the vibration coupling of key components such as spiral bevel gears, spur gears, and bearings. The typical fault modes of gears were introduced, and the time-domain and frequency-domain system features were analyzed as characteristic indicators for fault diagnosis, assuming the spur gear and spiral bevel gear were simultaneously in a typical fault mode. The results revealed that under pitting failure, the vibration acceleration values of these key components were mostly in the range of 0.1–1.2 m/s 2 , showing multiple peaks with elevated amplitudes between 2000 and 5000 Hz; some frequency points exhibited higher amplitudes that approached 1.2 m/s 2 . Under the condition of wear, the vibration characteristics of these key components underwent coordinated variations, with obvious peaks of 0.77 and 0.57 m/s 2 appearing at the second harmonic of the two types of gears, respectively, causing the system to enter the “cascading wear” stage and forming a degradation cycle of vibration–wear coupling. During fatigue crack failure, the high-order harmonic components of these key components were enhanced, with significant peaks appearing at 2 and 3 times the mesh frequency. These findings offer an accurate numerical basis for fault diagnosis and self-maintenance design of aircraft engine accessory drive systems. Moreover, the presented methodological framework provides a valuable reference for analyzing the nonlinear vibration characteristics resulting from gear–bearing coupling under other typical fault mode combinations.