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Vibration and noise spectra from automotive planetary transmissions commonly exhibit components at distinct frequencies around the gear mesh (tooth passing) frequency and its higher harmonics, called modulation sidebands. They constitute a significant portion of the vibration and noise generated by the transmission. Sidebands have influence on noise quality measures as well as having great potential to provide valuable clues in regards to gear tooth combinations, phasing of planets, manufacturing errors like eccentricity, run out present in the gear set. First critical step in designing and controlling the sideband activity of a planetary transmission is to develop a comprehensive model to predict modulation sidebands as well as describing the mechanisms causing sidebands. The paper describes the investigation of side bands, correlation with theoretical, analytical and test results and solution to minimize the noise.

Certain categories of vehicle users have very high expectations of comfort, with noise playing a major role in these requirements. Market research demonstrates that gear whine is an important failure mode for transmission NVH. French major OEM is developing new design methodologies which will guarantee improved NVH quality performance in all new gearbox designs. A transmission NVH simulation and analysis tool has been tested on pre-existing transmission designs to assess its capabilities in the prediction and resolution of gear whine problems. The software tool successfully predicted the vibration response of the current gearboxes. The validated model has been used to simulate parametric sensitivity of NVH performance and the software simulation tool is now part of the OEM's design and development process

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 favored 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.