Noise reduction technique for snowmobiles

Abstract

An air intake that reduces the transmission of noise from an internal combustion engine while maintaining high air intake flow rates. The air intake has a duct for delivering air to an internal combustion engine, and resonator volumes in communication with the inside of the duct, to selectively attenuate engine noise at certain frequencies and across certain frequency ranges.

1 . An air intake for an internal combustion engine, comprising: 
 a duct for directing air intake flow through an interior space in the duct towards an engine for use in internal combustion, the duct having an inlet and an outlet;    a housing surrounding the duct and defining an enclosed space between the duct and the housing; and    baffle plates extending outwardly from the duct to the housing and dividing the enclosed space into a plurality of resonator volumes, the duct having openings in walls of the duct, the openings establishing fluid communication paths between the interior space of the duct and the resonator volumes to form at least two Helmholtz resonators to attenuate sound pressure energy emanating from the internal combustion engine, the at least two Helmholtz resonators being insulated from each other.    
     
     
         2 . The air intake of  claim 1 , wherein the at least two Helmholtz resonators are separated by at least one of the resonator volumes to insulate the at least two Helmholtz resonators from each other.  
     
     
         3 . The air intake of  claim 1 , wherein a portion of the duct is perforated, the perforations establishing fluid communication paths between the interior space of the duct and at least one of the resonator volumes to form at least one sleeve resonator to attenuate sound pressure energy emanating from the internal combustion engine.  
     
     
         4 . The air intake of  claim 3 , wherein the at least one sleeve resonator is positioned between the at least two Helmholtz resonators to insulate the at least two Helmholtz resonators from each other.  
     
     
         5 . The air intake of  claim 1 , wherein the at least two Helmholtz resonators attenuate sound of different wavelengths.  
     
     
         6 . The air intake of  claim 1 , wherein the at least two Helmholtz resonators attenuate sound under 1000 Hz.  
     
     
         7 . The air intake of  claim 1 , wherein at least one of the openings for the at least two Helmholtz resonators faces in a different direction.  
     
     
         8 . An air intake for an internal combustion engine, comprising: 
 a duct for directing air intake flow through an interior space in the duct towards an engine for use in internal combustion, the duct having an inlet and an outlet;    the duct having openings in walls of the duct, the openings establishing fluid communication paths between the interior space of the duct and enclosed resonator volumes to form two separate Helmholtz resonators to attenuate sound pressure energy emanating from the internal combustion engine, the two Helmholtz resonators being insulated from each other.    
     
     
         9 . The air intake of  claim 8 , wherein the two Helmholtz resonators are separated by another resonator volume to insulate the two Helmholtz resonators from each other.  
     
     
         10 . The air intake of  claim 8 , wherein a portion of the duct is perforated, the perforations establishing fluid communication paths between the interior space of the duct and at least one of the resonator volumes to form at least one sleeve resonator that attenuates sound pressure energy emanating from the internal combustion engine.  
     
     
         11 . The air intake of  claim 10 , wherein the at least one sleeve resonator is positioned between the two Helmholtz resonators to insulate the two Helmholtz resonators from each other.  
     
     
         12 . The air intake of  claim 8 , wherein the two Helmholtz resonators are spaced apart a sufficient distance to insulate the two Helmholtz resonators from each other.  
     
     
         13 . The air intake of  claim 8 , further including a housing at least partially surrounding the duct and forming the enclosed resonator volumes between the duct and the housing.  
     
     
         14 . The air intake of  claim 8 , wherein the enclosed resonator volumes forming the two Helmholtz resonators are formed in part by the outside surface of the duct.  
     
     
         15 . The air intake of  claim 1 , wherein each of the at least two Helmholtz resonators is adapted to attenuate sound pressure energy at or around a particular frequency.  
     
     
         16 . The air intake of  claim 15 , wherein two or more baffle plates extend between the wall of the duct and the housing, dividing the enclosed space between the wall of the duct and the housing into three resonator volumes, and wherein the air intake includes two Helmholtz resonators.  
     
     
         17 . The air intake of  claim 16 , wherein the two Helmholtz resonators include a first resonator volume located nearest the air intake inlet and a third resonator volume located nearest the air intake outlet.  
     
     
         18 . The air intake of  claim 17 , further comprising at least one perforated area in the wall of the duct, wherein the at least one perforated area places the duct in fluid communication with a second resonator volume positioned between the first and third resonator volumes, forming a perforated sleeve resonator adapted to attenuate sound pressure energy emanating from the internal combustion engine over a range of frequencies.  
     
     
         19 . The air intake of  claim 17 , wherein the two Helmholtz resonators are adapted to attenuate sound pressure energy emanating from the internal combustion engine at frequencies at or around 125 hertz and 250 hertz.  
     
     
         20 . The air intake of  claim 18 , wherein the perforated sleeve resonator comprises two or more perforated areas.  
     
     
         21 . The air intake of  claim 18 , wherein the duct and the housing form a continuous air intake flow path for maximizing air flow and improving engine efficiency.  
     
     
         22 . The air intake of  claim 18 , wherein the two Helmholtz resonators are adapted to attenuate sound pressure energy emanating from the internal combustion engine at frequencies at or around 125 hertz and 250 hertz.  
     
     
         23 . The air intake of  claim 22 , wherein the Helmholtz resonator adapted to attenuate sound pressure energy at frequencies at or around 125 hertz includes the first resonator volume and the Helmholtz resonator adapted to attenuate sound pressure energy at frequencies at or around 250 hertz includes the third resonator volume.  
     
     
         24 . The air intake of  claim 23 , wherein the perforated sleeve resonator is adapted to attenuate sound pressure energy emanating from the internal combustion engine over a frequency range from about 275 hertz to about 1000 hertz.  
     
     
         25 . The air intake of  claim 23 , wherein the perforated sleeve resonator is adapted to attenuate sound pressure energy emanating from the internal combustion engine over a frequency range from about 300 hertz to about 600 hertz.  
     
     
         26 . A snowmobile having skis, an endless track propulsion mechanism, a steering column for turning the skis, an internal combustion engine for driving the endless track, and an air intake system for delivering air to the internal combustion engine, the air intake system comprising: 
 a duct for directing air intake flow through an interior space in the duct towards an engine for use in internal combustion, the duct having an inlet and an outlet;    a housing surrounding the duct and defining an enclosed space between the duct and the housing; and    baffle plates extending outwardly from the duct to the housing and dividing the enclosed space into a plurality of resonator volumes, the duct having openings in walls of the duct, the openings establishing fluid communication paths between the interior space of the duct and at least two of the resonator volumes to form at least two Helmholtz resonators to attenuate sound pressure energy emanating from the internal combustion engine, the duct further having a perforated portion establishing fluid communication between the interior space of the duct and at least one of the resonator volumes to form at least one sleeve resonator that attenuates sound pressure energy emanating from the internal combustion engine, wherein the at least two Helmholtz resonators are insulated from each other by the at least one sleeve resonator.