GDN-21 DYNAMIC VIBRATION ANALYSIS OF HELICAL GEAR SYSTEM(GEAR DYNAMICS AND NOISE)

Through the improvement of gear parameter design and manufacturing processes directed at reducing transmission error, the gear noise level has been continually reduced in recent years. Demands for reducing gear noise are continually becoming more stringent, but the improvement of transmission error of gear pairs for gear noise reduction is nearing its limit. It has become increasingly difficult to estimate gear noise on the basis of transmission error, especially in high-frequency bands. In addition to these usual methods, there is a greater need to recognize the gear train itself as a transmitter of vibration and adopt approaches in which improvements are made to the gear train for the purpose of reducing gear noise. In this paper we present a new method of analyzing the vibration of a helical gear system, which makes it possible to predict the influence of the entire gear train (consisting of the gear blanks, shafts, bearings and the gears themselves) on gear noise. To reproduce as closely as possible the real operating condition of a helical gear system, we have developed a model with twelve degrees of freedom. It is represented by two equivalent masses coupled with the tooth mesh stiffness. In this method, the equivalent masses and the equivalent stiffness of gear trains were estimated with simplified finite element models. It was verified that the gear vibrations simulated with this method correlated well with measured gear noise. In this vibration analysis, it was found that the influence of the gear train as a whole on gear noise was as great as that of the gears themselves and that gear vibration was more sensitive to tooth surface modifications than transmission error. One of the tooth surface modifications that was effective in reducing gear vibration is described. In addition, a simplified prediction of the high-frequency gear noise level made with this method is presented.