Structure Borne Noise Prediction Techniques 900019

The Noise Vibration Harshness (=NVH) behaviour of engines or power units is the one of the predominant factors for market acceptance of vehicles.
To reach this goal it is necessary to reduce the absolute noise level and also the noise level in specific frequency ranges. In diesel engines the predominant noise or vibrations are caused by combustion. This excitation is transferred via the crank train and bearings to the outer noise radiating engine surfaces. For gasoline engines this transfer path is also important. In such engines noise is created in the area of the main bearings by vibrations of the crankshaft.
In this paper a new prediction technique for the above mentioned vibration transfer problems which was developed at AVL during the last three years is described. The work was carried out in cooperation with AUDI AG and VW AG, West Germany.
This prediction technique is based on nonlinear Finite Element (FE) calculation methods and includes hydrodynamic calculation of the engine bearings. The results are obtained by a time history calculation of the response of the engine model due to the excitation forces of gas and inertia loads. After the comparison of the calculated results with experimental results from a test rig investigation, measurement and calculation were carried out to a 5-cyl. gasoline engine. During this investigation some remarkable results were obtained, leading to a better understanding of the vibration transfer from the rotating crankshaft to the engine surface.


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