Future Technologies against Turbocharger Noise Transferred to Exhaust Systems 2008-01-0891
Downsizing concepts have led to an increasing use of turbochargers in gasoline engines. Turbochargers are available with different tolerances, although, small tolerances come at a high cost. Affordable turbochargers with bigger tolerances cause high frequency airborne and structure-borne noise which leads to turbocharger noises such as howling and whistling. Some noises are synchronic with the speed of the turbine or multiples of it. They span the audible range up to 16 kHz, provided that the dominance is below 5 kHz. Other noises are e.g. caused by the resonance of the bearing from the turbine. They are mainly between 500 Hz and 1 kHz. The exhaust system is one of the components which is excited; the radiated noise is then transferred into the cabin.
Following Murphy's Law, when turbocharger noise occurs, it appears late within a development. One reason for this noise is part to part variation of the turbocharger. Unfortunately, structural resonances of the exhaust system are within the frequency range of turbocharger noise and will be excited in some cases. To avoid such disturbing noise, long and soft flexible elements are placed between the turbocharger and the exhaust line. However, these elements change the whole dynamic behavior of the exhaust line. In addition, they have to be implemented early within a development. Otherwise road load and engine vibrations cause durability issues. It is, therefore, necessary to have detailed knowledge of the dynamical behavior of these flexible elements to select them with view to turbocharger noise. This, however, is not yet provided by the flex element supplier for frequencies above 200 Hz.
For this reason new technologies are presented here to investigate and to decouple structure-borne noise.