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Gear whine in 1st and 2nd gears in a new rear wheel drive automatic transmission was identified as a potential customer dis-satisfier. Improvements to the vehicle system were implemented, but did not sufficiently reduce the noise. CAE modeling and hardware testing were used for gear tooth optimization, transmission system, driveline, and vehicle system studies. The planetary gears were re-designed with increased contact ratio, and significant interior noise reduction was achieved; but some vehicles still had excessive noise due to gear parameter variability from multiple sources. Using a DOE and statistical studies, a set of gear parameter targets were identified within the tolerances of the design, which achieved the program objectives for noise.

Numerous authors have previously published on the effects of system dynamics on gear noise in automotive applications [1,2]. It is now widely understood that the torsional compliances and inertias of propeller shafts and pinion gear sets are a controlling factor in final drive gear noise for rear wheel drive vehicles. Considerable progress has been achieved in using finite element simulations of the driveline dynamics to improve the system in regards to gear noise. However very few published results are available showing the application of dynamic simulation methods to automatic transmissions which require considerations of the complications due to epicyclical gear sets. This paper documents the successful application of finite element dynamics modeling methods to the prediction of gear noise from the gear set in a rear wheel drive automatic transmission. The model was used to investigate the effects of component inertias, stiffnesses, and resonances.