Abstract
The paper deals with the noise emission of the three engine groups used in the four most important vehicle groups:
h heavy duty diesel engines used in lorries and busses
h smaller medium duty diesel engines used in vans and private motor cars
h light duty petrol engines used in private motor cars
For these engine groups the paper presents
h the development of engine noise emission during the last 30 years,
h the present acoustical state of the art and
h the development of engine noise emission expected during the next years.
To quantify the progress in noise emission decrease and simultaneous maximum power increase the ¡§acoustical efficiency¡§ is used.
During the seventies and eighties the acoustical efficiencies of (for example) heavy duty diesel production engines could be reduced from 4-10 10-6 to 1-2 10-6. To realize this noise reduction typical measures were acoustical optimization of the combustion process (often by turbocharging), speed reduction and sometimes blower optimization. In the nineties additionally the reduction of the noise excitation in the timing gear train and the acoustical structure optimization became more and more important. Thereby the acoustical efficiencies of heavy duty diesel production engines could be reduced to 0.25-0.4 10-6 today.
In spite of all the acoustical progress in the past a further noise reduction will be possible and necessary in the future, too: The author expects a further noise level reduction of around 3dB(A) within the next ten years. The paper deals with the possibilities to reach this further engine noise reduction; some examples are
h common rail injection systems, which reduce the noise excitation especially in the timing gearing trains of heavy duty diesel engines,
h bedplate or underplate constructions, which stiffen the lower parts of engine blocks and thereby reduce the noise emission of crankcases and oilpans or
h encapsulating, isolating or high damping plastic parts, which can be used to diminish the noise emission of engine parts like oilpans, intake pipes or covers drastically.