Abstract
This paper describes an investigation into engine idling noise induced by the timing gear train. A friction ring, as named by the authors, was introduced as a noise reduction technique to reduce the vibration of the gear. The friction ring was inserted into a groove inside the rim of the gear. The mechanism of reducing gear vibration by using the friction ring was analyzed, and it was proven that the installation of a friction ring reduced the gear vibration and hence the engine idling noise.