Emissions and fuel consumption are key development goals in modern vehicle engines. To use down-sizing and down-speeding the best way, an optimized charging strategy for the combustion engine is necessary. Due to their higher overall efficiency, compared with mechanical charging systems, exhaust gas turbocharging has become a technical standard of today’s vehicle engines. Especially in the upper and middle class vehicles the acoustic comfort is an important unique selling point and must not be affected by turbocharging. The constant tone is one of the relevant noise phenomena of turbochargers. His origins are natural-modes of the rotor radial bearings. Because of that an experimental investigation is significantly more complex in comparison with other noises at the turbocharger. The investigations are carried out on a turbocharger of a 2.0l gasoline engine with a waste-gate for boost pressure control. The turbocharger is mounted acoustic-decoupled from the engine to avoid unwanted interactions which distorts the results. Displacement sensors were applied inside turbocharger housing and were used to measure the displacement path of the rotor on compressor- and turbine-side. Also sensors to measure the radial bearing bush speeds are applied. The studies show a direct relationship between the rotational speeds of the floating bush bearing and the constant-tone phenomenon in air- and structure-borne noise. Simultaneous to the constant-tone occurrence also a change in the oscillation mode of the rotor can be observed. Furthermore the influence of the oil temperature, the oil supply pressure and the air mass flow were investigated.
