Vibro-Acoustic Effects of Friction in Gears: An Experimental Investigation

Amongst various sources of noise and vibrations in gear meshing, transmission error and sliding friction between the teeth are two major constituents. As the operating conditions are altered, the magnitude of these two excitations is affected differently and either of them can become the dominant factor. In this article, an experimental investigation is presented for identifying the friction excitation and to study the influence of tribological parameters on the radiated sound. Since both friction and transmission error excitations occur at the same fundamental period of one meshing cycle, they result in similar spectral contents in the dynamic response. Hence specific methods like the variation of parameters are designed in order to distinguish between the individual vibration and noise sources. The two main tribological parameters that are varied are the lubricant and the surface finish characteristics of gear teeth. Additionally, the test matrix included a wide range of meshing conditions such as gear tooth geometry, operating speed and external load torque. The analysis is conducted both in terms of the radiated sound and the dynamic forces transmitted through the bearings of the gearbox housing. Some of the results are evaluated against theoretical models that predict the dynamic response of gears and the housing. A qualitative discussion is presented on strategies for noise prediction from the knowledge of gear geometry, gear dynamic models, properties of sliding surfaces and sound radiating characteristics of gearbox housing.