Development of Reduction Method for Whirl Noise on Turbocharger

The whirl noise on turbochargers is generated by the self-induced vibration of the oil film in the bearing system. The noise is characterized by its frequency behavior that doesn't increase proportionately to the turbo shaft speed. It tends to be felt annoying. In this paper, to improve the whirl vibration, a statistical analysis approach was applied to the bearing specifications. The results from experiments showed that the bearing clearances played an important role in the reduction of the whirl vibration. To further investigate into this phenomenon, the shaft oscillation behavior was measured. And a vibration simulation program for the turbocharger bearing system was also developed. As the results, it was concluded that suppressing the shaft oscillation with a parallel mode could reduce the whirl vibration and the ‘different-clearance’ combination, in which the different bearing clearance specification was applied to the compressor and turbine side, could reduce the whirl vibration further than the conventional ‘same-clearance’ bearing set.