An Investigation of Shaft Dynamic Effects on Gear Vibration and Noise Excitations

Transmission error has long been identified to be the main exciter of gear whine noise. This research effort seeks to investigate the mechanisms and principal controlling factors that affect the actual noise generation from a typical gearbox housing due to transmission error excitations. The insight gained is expected to help in identifying possible noise control procedures in typical gearing applications. The example gearbox of this paper is an aircraft auxiliary-drive idler gearbox run at low load so that transmission error is the primary mesh excitation. A limited set of dynamic noise and vibration data are collected in transient speed run-ups. A contact-mechanics gear-tooth model is used to predict the static transmission error at each mesh. A finite-element model of the shafting that incorporates complex shaft and bearing data is used to predict the shaft dynamics with the static transmission error at the gear mesh(es) as the sole excitation. The dynamic bearing forces that thus arise and excite the housing are predicted. A frequency-response based model is developed to model the intermediate stages between the bearing force excitation and the final sound radiation from the gearbox. Comparisons are made between the model predictions and experimental measurements. The major shaft modes are identified and parametric studies are performed to identify the effect of the major controlling factors in the noise generation process. In addition, the effect of mesh phasing on the shaft dynamics is studied to investigate the possibility of noise reduction through the selection of suitable phasing between the two meshes of the system.