As the quietness of vehicles has been continually improved in recent years, there have been stronger requirements to reduce transmission gear noise and thereby improve transmission quality.So far efforts to achieve quieter gears have generally focused on ways of reducing the excitation forces of individual gears. In addition to these traditional methods, there is a greater need today to adopt a new approach to gear noise reduction in which improvements are made to the gear train itself as the transmitter of vibration in the transmission.This paper describes the systematic approach taken to reduce the overall gear noise of the new RE4F04A four-speed automatic transaxle.The cross-sectional view is shown in Fig. 1.The vibration characteristics of this automatic transaxle were first identified by finite element analysis, and an investigation was made of a gear train structure that would be effective in reducing gear noise. The effect of structural modifications on reducing gear noise was then verified experimentally. By modifying the gear train structure, the overall gear noise level was substantially reduced, resulting in a much quieter transmission unit.It was also found that the stiffness of the transaxle case at locations supporting the gear train bearings affected gear train vibration characteristics, which in turn influenced gear noise. The effect of changes in support stiffness on gear noise levels is also described.