Transmission Error and Noise Emission of Spur Gears: A Theoretical and Experimental Approach

Noise reduction is becoming a more and more important target for industrial gearboxes. The achievement of this goal requires a precise identification of gear noise sources, because only a good understanding of the phenomena involved in gear noise can give to the designer the tools to conceive gears with reduced acoustic emission, avoiding the time consuming and expensive “trial and error” procedure [1]. The variable component of Transmission Error (TE) is commonly recognized as one of the most important sources of gear noise. TE is mainly caused by teeth deflections under load and by manufacturing and assembly errors. The usual approach to these problems is to conceive profile modifications and crowning that absorb deformations and errors, in order to reduce TE and consequently noise. Since the correlation between gear TE and noise is complicated, profile modifications are often designed on the basis of past field experience, while software tools to predict TE as a function of tooth modifications are of great help. Nevertheless, such software tools must be validated through experimental tests. A software based on a simplified model of gear meshing, that takes into account manufacturing errors and profile modifications, has been developed and validated by means of a new test rig, specifically conceived for TE, vibrations and noise emission measurements. The rig has been designed and installed in the Laboratories of the Department of Mechanical Engineering, Politecnico di Milano. In this paper software simulations, TE predictions, TE and acoustic measurements are described and discussed. TE has been predicted and measured for two different gear sets, with the same macro-geometry (module, teeth number, center distance) and different micro-geometry (profile modifications); acoustic emission has also been measured. TE measurements show a good agreement with the theoretical predictions. The measurements made with the new test rig confirm the close correlation between TE and the level of acoustic emission.