The exterior noise of vehicles is primarily determined by the sound radiated by the power unit. Lower noise levels have been reached through improved knowledge, but this reduction is not sufficient to meet current stringent standards. A complete enclosing of the power unit is an efficient approach to the problem. An economic solution for passenger cars is to enclose the engine compartment in a sound proof manner. This approach has been adopted in the past by Avl and d is discussed in this paper. One of the design characteristics is that the cooling system is placed outside the enclosure so that optimum sound insulation of the engine is obtained. With prototype vehicles using an improved exhaust muffler system a noise reduction of 8 dba in the ISO pass by acceleration test can be achieved. The external noise measured when the engine is idling, especially in front of the vehicle, is up to 12 dba lower. Sound levels within the enclosure are usually higher than in the non enclosed case; however, this does not necessarily result in a deterioration in passenger comfort. Because of the closed engine compartment, sound radiated downwards, reflected on the road surface and transmitted back into the passenger compartment is depressed. Therefore, with an additional treatment of the firewall an even lower interior noise can be achieved in the middle and high frequency range, whereas at low frequencies when the transmission of structural vibrations is dominating, the influence of the enclosure can be neglected. For the covering abstract of the conference see TRIS 451834. (TRRL)

Media Info

  • Features: Figures; Photos; References;
  • Pagination: p. 121-130

Subject/Index Terms

Filing Info

  • Accession Number: 00451849
  • Record Type: Publication
  • Source Agency: Transport Research Laboratory
  • Files: ITRD, TRIS
  • Created Date: May 31 1986 12:00AM