Effects of gears, bearings, and housings on gearbox transmission shafting resonances

Gear noise, comprised of tones centered around gear meshing frequencies, is transmitted through driveshafts, bearings, and transmission housings. Gear noise transmission is amplified, sometimes strongly, by modes of vibration of the shafting. The shafts of the input and output gears vibrate like beams at low to mid frequencies. The resonance frequencies and vibration patterns of these beam-like modes depend strongly on the shaft boundary conditions, which in turn depend on the impedances of the bearings, and of the transmission housing. In this paper, we present simulated and measured modes of the input and output shafts of a single stage spur gear system mounted in a rectangular metal gearbox. The impedances of the gears, bearings, and housing are added in sequence and the effects on the fundamental mode shapes and frequencies are shown. The bearing impedances have the largest effects on the shafting modes, increasing the resonance frequencies significantly, along with spreading the frequencies of similar mode types. Including the housing impedances at the bearing locations reduces slightly the spread of shaft mode frequencies.