Dynamic modelling and vibration characteristic analysis of gear transmission system under the effect of time-varying misalignment from clearance of bearings

Gear misalignment error is one of the most common errors in manufacturing or assembling process, which leads to uneven distribution of contact stress and increased vibration and noise due to the biased load. It also influences the diagnosis of gear local defects due to the coupling effect of them. To address the gear misalignment errors caused by discrepancies in bearing clearance at both ends of shaft, a coupled gear-shaft-bearing nonlinear dynamic model with 24 DOF is developed. Effect of time-varying misalignment errors on the characteristics of contact, stiffness and vibration are analyzed. Simulations are performed to evaluate the vibration response of the gear transmission system under the excitation of time-varying misalignment from bearing clearances and gear spall. Results indicate that discrepancies of bearing clearances reduce the time-varying meshing stiffness of the gear pair, which generates additional vibration and affects the vibration responses of the gear transmission system. Time-varying misalignment from bearing clearance also contributes the rising of shaft rotating frequency, which results in difficulty to detect early spalling faults on gear surface. Verification experiments are conducted to assess the precision of the enhanced gear-shaft-bearing model. New indicators are proposed to defect the change of gear misalignment error due to bearing clearances. The proposed coupling model contributes to a deeper insight on condition monitoring strategies and early fault diagnosis methodologies for gear transmission systems.