Apparatus for damping resonance in a conduit

Abstract

Method and apparatus for damping resonance in a conduit ( 10 ) utilized for transporting exhaust gases from an internal combustion engine. The resonance is damped by virtue of the conduit ( 10 ) being provided with at least one perforation ( 14 ) located at a distance from the outlet end ( 11 ) of the conduit.

1 . An apparatus for damping resonance in a conduit ( 10 ) for transporting exhaust gases from an internal combustion engine, which conduit ( 10 ) is provided with at least one perforation ( 14 ) located at a distance from the outlet end ( 11 ) of the conduit and at a point in the conduit ( 10 ) with a comparatively lower static pressure than downstream therefrom, the perforation ( 14 ) forming an acoustic connection between the interior of the conduit ( 10 ) and the surrounding atmosphere.  
     
     
         2 . The apparatus as recited in  claim 1 , wherein the lower static pressure in the vicinity of the perforation ( 14 ) is brought about by means of a reduction in the cross section of the conduit.  
     
     
         3 . The apparatus as recited in  claim 2 , wherein the reduction in the cross section of the conduit ( 14 ) is designed as a venturi.  
     
     
         4 . The apparatus as recited in  claim 2 , wherein the pipe portion ( 10   a ) designed as a venturi is covered on the outside with a sound-absorbing material.  
     
     
         5 . The apparatus as recited in  claim 4 , wherein the sound-absorbing material is covered by a perforated plate ( 17 ).  
     
     
         6 . The apparatus as recited in  claim 1 , wherein the lower static pressure in the vicinity of the perforation ( 14 ) is brought about by means of a change in direction of the gas flow in the conduit.  
     
     
         7 . The apparatus as recited in  claim 6 , wherein the change in direction of the gas flow is brought about by means of a curve of the conduit.  
     
     
         8 . The apparatus as recited in  claim 1 , wherein the perforations ( 14 ) are covered by means of a sound-permeable fabric ( 20 ) on the inside or outside of the conduit ( 10 ).  
     
     
         9 . A method for affecting acoustic attenuation of resonant exhaust noise produced by a combustion engine, said method comprising: 
 providing a combustion engine with an exhaust conduit having a length that causes a high magnitude resonant acoustic sound to be experienced in the exhaust conduit as the combustion engine passes through an exhaust resonance producing speed range; and    attenuating the magnitude of the high magnitude resonant acoustic sound at an outlet of the exhaust conduit by causing at least a portion of the high magnitude resonant acoustic sound to diffuse outside the exhaust conduit upstream of the outlet.    
     
     
         10 . The method as recited in  claim 9 , further comprising: 
 providing at least one aperture along the length of the exhaust conduit and arranging the aperture so that at least a portion of the high magnitude resonant acoustic sound diffuses therethrough.    
     
     
         11 . The method as recited in  claim 10 , further comprising: 
 locating the at least one aperture at a position along the length of the exhaust conduit where a negative pressure is normally developed inside the conduit in comparison to ambient pressure outside the conduit.