Abstract As automotive technology has been developed, gear whine has become a prominent contributor for cabin noise as the masking has been decreased. Whine is not the loudest source, but it is of high tonal noise which is often highly unpleasant. The gear noise originates at gear mesh. Transmission Error acts as an excitation source and these vibrations pass through gears, shafts and bearings to the housing which vibrates to produce noise on surrounding air. As microgeometry optimization target to reduce the fundamental excitation source of the noise, it has been favoured method to tackle gear whine noise, especially for manual transmission. However, practicality of microgeometry optimization for the planetary gear system has been still in question, because of complex system structure and interaction among multi mesh gear sets make it hard to predict and even harder to improve. In this paper, successful case of whine noise improvement by microgeometry is presented. System level simulation model with accurate details of actual test system condition such as clearances, measured microgeometry and test rig condition were constructed. The vibration at the accelerometer locationat the housing was predicted using the model. The comparison of the result to test result showed very good correlation. Especially, the absolute housing vibration level matched very well, which allowed engineers to use the simulation result during optimization process to make decision quickly without having to run the actual test to know if the improvement was sufficient enough to meet the vibration target. Microgeometry optimization was done for all gear set in the rear planetary. The predicted result of vibration showed 3 m/s2 reduction at the target speed range under target torque condition. The noise test result confirmed that the noise was reduced by 5∼ 6 dBA and the design target could be satisfied Keywords Transmission NVH, Whine, Micro geometry optimization, System modelling, Planetary 6 Speed Automatic Transmission Vibration Magnitude Prediction and Whine Noise Improvement through Transmission System Modeling2011-01-1553 Published 05/17/2011 Won Shin Romax Technology, Ltd. Ashish Kanase Romax Solutions Pvt Ltd. Sungwook Hwang, Sangbum Baek and Hyutae Shim Hyundai Motor Company Seiwoong Oh Romax Technology, ltd Copyright © 2011 SAE International doi:10.4271/2011-01-1553Downloaded from SAE International by University of Wisconsin - Madison , Sunday, September 09, 20181. Introduction With the advancement in automotive technology, gear whine has become a prominent contributor for cabin noise as the masking has been decreased. Whine is not the loudest source, but it is of high tonal noise which is often highly unpleasant. The gear noise originates at gear mesh. Transmission Error [1] acts as an excitation source and these vibrations pass through gears, shafts and bearings to the housing which vibrates to produce noise in surrounding air and structure- borne noise via the mounts on the casing. As microgeometry optimization target to reduce the fundamental excitation source of the noise, it has been favoured method to tackle gear whine noise, especially for manual transmission [ 2]. However, applying similar direct methods to planetary system has not been practical, because of the complexity of the system structure which consists of coupled multi mesh condition making it hard to predict and even harder to optimize. The paper discusses such practical method in reducing gear whine noise of a 6 speed FF automatic transmission by microgeometry optimization of a planetary gear set. At first, challenges in applying microgeometry optimization to planetary gear set are presented. This is followed with suggestions to overcome the challenges in modelling and optimization. The result includes the validation of simulation result by vibration testing to prove the fidelity of the approach. Finally, the result of the numerical optimization is presented