Engine Noise Reduction for Lower External Noise Levels of Passenger Cars

Using a Porsche 944 engine, measures for noise reduction are presented, which significantly improve the vehicle's external noise emission. Based upon a detailed noise analysis, noise-emitting engine components could be determined and the noise was quantified and assigned to the various sources. The engine noise level was lowered by primary measures, by modification of the solid-born sound propagation in the engine, as well as by sound neutralization. Particularly efficient were modifications to the crank gear, crankcase, valve gear, oil sump, intake manifold, alternator, and toothed belt drive. It was found that light alloy engines require other priorities, as compared to iron-block engines. The engine noise could be reduced by more than 10 dBA compared to the original version. The exterior noise, measured in accordance with 81/334 EWG (with modified intake and exhaust systems) could be lowered by 4 dBA. The subjective ratings clearly confirmed the measured improvements. Since the vehicle in its production version already remains well under todays legal noise levels, there is a good chance to comply also with future, more severe, noise legislation, without a complete engine encapsulation. However, this will require increased development expenditure