With automobiles powered by internal combustion engines, the total vehicle noise is due to the noise contributed by the exhaust system, the air intake, the engine and transmission surfaces, the cooling fan, the vehicle body and the tires. The exhaust system, the cooling fan and the power unit represent the most critical sources of the vehicle noise since they predominate at the typical medium speed driving pattern within populated areas - an operating condition which is also simulated with the presently enforced vehicle noise regulations. The exhaust noise can be reduced by improving the existing mufflers. The cooling fan noise can be lowered with systems which are optimized acoustically and aerodynamically. The noise of the power unit and particularly that of the engine, however, cannot be sufficiently reduced without changing the engine design concept. Because of the structural design and the operating principle of internal combustion engines, a significant reduction of their surface noise can only be achieved by isolating all the external engine surfaces from the vibrations of the load carrying inner engine structure. With existing engines this concept is realized by means of a complete encasing of the engine by a noise attenuating enclosure which is vibration isolated against the engine. With newly designed engines, however, this concept can be realized by integrating the noise attenuating enclosure into the engine structure. Depending on the type of vehicle and the maintenance requirements it is possible to integrate some parts of the vehicle body with the engine enclosure. With the measures described above, the achievable reduction of the noise emitted by an automobile is in the range of 12 dba. /Author/TRRL/

  • Corporate Authors:

    International Federation of Auto Techniques Engs

    3 Avenue du President Wilson
    F 75116 Paris,   France 
  • Authors:
    • Thien, G E
    • Fachbach, H A
  • Publication Date: 0


  • English

Media Info

  • Pagination: 1 p.

Subject/Index Terms

Filing Info

  • Accession Number: 00163331
  • Record Type: Publication
  • Source Agency: Transport and Road Research Laboratory (TRRL)
  • Report/Paper Numbers: Analytic
  • Files: ITRD, TRIS
  • Created Date: Apr 12 1978 12:00AM