Fault-induced gear meshing modulation sideband extraction and evaluation for fault diagnosis of planetary gearboxes

Gearboxes, known for their compact size and stable transmission capability, are widely used as power transmission structures in various types of mechanical equipment, such as wind turbines, helicopters, and special vehicles. However, due to harsh and non-stationary working conditions, gear surfaces often deteriorate, leading to faults such as wear, pitting, and cracking. Therefore, it is vital to monitor the working status of gearboxes and diagnose gear faults as early as possible. Gear faults can induce characteristic modulation effects near the gear meshing frequency (GMF), resulting in the appearance of fault-induced sidebands in a vibration spectrum. Extraction of these sidebands allows for the diagnosis of gear faults in a gearbox. However, when faced with a planetary gearbox having a complex configuration, strong background noise and additional fault-unrelated sidebands can interfere with fault-induced sidebands, making accurate diagnosis difficult. To address these challenging issues, this paper proposes a novel fault-induced gear meshing modulation sideband extraction method. In the process, the sidebands directly related to the gear fault near the GMF are first identified and then extracted by a variational harmonic mode decomposition (VHMD) method. Accordingly, a fault-related gear meshing modulation component (GMMC) can be accurately reconstructed by summing up the extracted fault-induced sidebands. Using the GMMC, the gear fault severity can be assessed by evaluating its amplitude modulation (AM) effect. The superior performance of the proposed method is finally demonstrated by experimental data.