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The objectives of this work were to establish a method to diagnose the source of gear rattle and to evaluate the rattle objectively. The methods are described in detail, applied to two passenger cars as an example. Investigations were conducted into transmission rattle under transient conditions. By analysing the transmission casing vibration with respect to the engine flywheel angle, and presenting the data in the form of contour maps, it was shown that the two vehicles had different characteristics of gear impacts. Further measurements of the angular motion of each gear revealed the impact conditions at the input mesh in the transmission largely controlled the character of the rattle and were fundamentally different between the two vehicles. A rattle index was developed, based on the casing vibration under transient driving conditions.

Demand for lighter and smaller automotive transmissions is accelerating the need to accurately predict the helical gear root stress. In an effort to identify the maximum root stress of a in-mesh tooth, the load distribution along the contact line is investigated with 3-dimensional finite element models. Resultant data from the FEM analysis was utilized to derive a simple formula that aims to serve the same purpose. This formula takes into consideration three new factors on stress compensation, effective facewidth and stress concentration in addition to the tooth form commonly associated in stress calculations.