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.

Description:
FIELD OF THE INVENTION  
       [0001]     The invention relates to air intake systems for recreational vehicles such as snowmobiles, all terrain vehicles (ATVs), and other similar vehicles. More particularly, the invention relates to air intake systems that reduce the transmission of noise from the engines of such vehicles.  
       BACKGROUND  
       [0002]     Snowmobiles are popular land vehicles used as transportation vehicles or as recreational vehicles in cold and snowy conditions. Snowmobiles typically employ an internal combustion engine to drive an endless track to provide propulsion. Noise generated by snowmobile engines can be emitted from either the exhaust or the air intake of the engine, detracting from the enjoyment of the user, as well as potentially creating an environmental nuisance. Methods of addressing exhaust noise are known in the art. Methods of reducing air intake noise exist, but such methods tend to reduce air flow to the engine, thereby reducing engine efficiency and hence performance. Further, such methods do not adequately address the need to suppress noise energy at particular frequencies associated with snowmobile engines. Therefore, a need exists to reduce the amount of engine noise that is emitted from the air intake of snowmobile engines, particularly at certain frequencies, while maintaining a high amount of air flow to the engine to maximize engine performance.  
       BRIEF SUMMARY OF THE INVENTION  
       [0003]     Some embodiments of the invention provide an air intake for a snowmobile that incorporates frequency selective noise attenuation while maintaining high air flow to the snowmobile engine. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0004]      FIG. 1  is a side view of a snowmobile.  
         [0005]      FIG. 2  is a front, top, left perspective view of an air intake duct within a housing.  
         [0006]      FIG. 3  is a left side view of an air intake duct within a housing.  
         [0007]      FIG. 4  is a top view of an air intake duct within a housing.  
         [0008]      FIG. 5  is a right side view of an air intake duct and baffle plates according to an embodiment of the invention.  
         [0009]      FIG. 6  is a bottom view of an air intake duct and baffle plates according to an embodiment of the invention.  
         [0010]      FIG. 7  is a detailed view of the perforated area of a perforated (sleeve) resonator according to an embodiment of the invention.  
         [0011]      FIG. 8  is a detailed view of the opening associated with a Helmholtz resonator according to an embodiment of the invention.  
         [0012]      FIG. 9  is a detailed view of the opening associated with a Helmholtz resonator according to an embodiment of the invention.  
         [0013]      FIG. 10  is a schematic view of an air intake duct with two Helmholtz resonators and one perforated sleeve resonator.  
         [0014]      FIG. 11  is a schematic view of an air intake duct with a plurality of Helmholtz resonators, with at least one perforated sleeve resonator between each pair of adjacent Helmholtz resonators.  
         [0015]      FIG. 12  is a schematic view of an air intake duct with a plurality of resonator volumes in accordance with an embodiment of the invention.  
         [0016]      FIG. 13  is a schematic view of an air intake duct with a plurality of resonator volumes in accordance with an embodiment of the invention.  
         [0017]      FIG. 14A  is a chart showing the noise attenuation frequency response curves of typical Helmholtz resonators and perforated sleeve resonators.  
         [0018]      FIG. 14B  is a chart showing the noise attenuation frequency response curves of two Helmholtz resonators in close proximity to each other.  
         [0019]      FIG. 14C  is a chart showing the noise attenuation frequency response curves of two Helmholtz resonators separated by a perforated sleeve resonator. 
     
    
     DETAILED DESCRIPTION  
       [0020]     The following detailed description should be read with reference to the drawings, in which like elements in different drawings are numbered identically. The drawings depict selected embodiments and are not intended to limit the scope of the invention. It will be understood that embodiments shown in the drawings and described above are merely for illustrative purposes, and are not intended to limit the scope of the invention as defined in the claims that follow.  
         [0021]     A snowmobile  10  in accordance with some embodiments of the invention is shown in  FIG. 1 . Generally, snowmobile  10  includes a longitudinally extending chassis  12  having a front portion  14  and a rear portion  16 . The chassis  12  supports and mounts several vehicle components, including an engine  18 , a seat  20 , a drive track  22 , a pair of steerable skis  24 , and a body assembly  26 . In some embodiments, the chassis  12  supports the engine  18  proximate the front portion  14  and the seat  20  proximate the rear portion  16 . The seat  20  is adapted to accommodate a rider in straddle fashion, and the engine  18  powers the drive track  22  operatively connected to the chassis  12  proximate the rear portion  16 . Engine  18  can be an internal combustion engine, for example a two-stroke or four-stroke engine, that uses air and fuel to provide the combustion products. Means for supporting a rider&#39;s feet extending longitudinally below opposite lateral sides of the seat  20  may be provided. In some embodiments, the means may include footrests  28  that extend longitudinally below opposite lateral sides of the seat  20 .  
         [0022]     The chassis front portion  14  may be suitable for mounting the pair of steerable skis  24  and supporting the body assembly  26 . The body assembly  26  may contain the engine  18 . A steering post  30  is operatively connected to the pair of skis  24 . Means for rotating the steering post  30  to effect steering may be provided, and the means for rotating may be supported by the steering post  30 . In some embodiments, the means for rotating may include a steering control, such as handlebars  32 , supported by the steering post  30 .  
         [0023]      FIG. 2  shows a perspective view of an air intake duct  100  mounted within an air intake housing  200  for the delivery of air to an internal combustion engine for a snowmobile  10 . Air intake duct  100  includes air inlet  102  for receiving incoming air into air intake duct  100 , air outlet  104  for the delivery of air to an internal combustion engine, and wall  106 , which forms a continuous flow path from air inlet  102  to air outlet  104 . The shape of air intake duct  100  can be any suitable shape, such as rectangular, cylindrical, or elliptical, to account for manufacturing and/or packaging considerations. Air intake housing  200  is shown cut-away to show internal details. A space  156  is defined by the enclosed volume between the outer surface of wall  106  and the inner surface of air intake housing  200 . Baffle plates  140  extend outwardly from air intake duct  100 , and are oriented generally perpendicular to the direction of air flow through air intake duct  100 . Baffle plates  140  thereby divide space  156  into three resonator volumes  150 ,  152 ,  154 .  
         [0024]     Two of the resonator volumes can form Helmholtz resonators for the air intake duct  100  by providing fluid communication through openings  120 ,  130  (see  FIGS. 3-5 ) in the wall  106  of the air intake duct  100  between each of the two resonator volumes and the space within the air intake duct  100 . The Helmholtz resonators function to attenuate noise energy from the engine at certain frequencies. The particular frequency attenuated by each such Helmholtz resonator is a function of several physical parameters including the radius of the opening, the length of the “neck” of the opening, the volume of the resonator volume, and the speed of sound. A typical Helmholtz resonator can function to sharply attenuate noise energy in a relatively narrow range of frequencies. However, if two Helmholtz resonators are placed in close proximity to each other, the “sharpness” of the frequency response of each will be lessened such that a broader range of frequencies will be attenuated, but to a lesser degree. (“Sharpness,” as used here, roughly corresponds to the “Q” of a resonant circuit, a ratio that is inversely proportional to the bandwidth of the frequency response.) Increasing the distance between two Helmholtz resonators tends to “insulate” them from this effect, i.e., the separation tends to cause the Helmholtz resonators to act somewhat independently of each other, thereby focusing the attenuation response around two frequencies of interest. The insulating effect may be provided or enhanced by including, for example, other physical structures in the space that separates the two Helmholtz resonators.  
         [0025]     In some embodiments, such as the one shown in  FIG. 2 , resonator volume  152  is positioned between two Helmholtz resonator volumes  150 ,  154 . Fluid communication may be provided between resonator volume  152  and the inside of air intake duct  100  through a perforated area  110  in the top portion of air intake duct  100 . Perforated area  110  may thereby form a “perforated sleeve” type resonator which may insulate the two Helmholtz resonators from interacting with each other, as described above. Similarly, a perforated area  112  (see  FIG. 6 ) may be located in the bottom portion of air intake duct  100 . A perforated sleeve type resonator typically functions to attenuate noise energy to a lesser degree, and over a relatively broad range of frequencies, as compared with a Helmholtz resonator. Physical parameters such as the number, size, and shape of the holes, the depth of the duct wall  106 , and the volume of the associated resonator volume, affects the frequency and attenuation characteristics of the perforated sleeve type resonator.  
         [0026]      FIG. 3  is a left, side view of the air intake duct  100  mounted within housing  200 , providing a cross sectional view of the three resonator volumes  150 ,  152 ,  154 . Helmholtz resonator opening  120  is shown protruding from the bottom portion of air intake duct  100 , providing fluid communication between the first resonator volume  150  and the inside of air intake duct  100 .  
         [0027]      FIG. 4  is a top view of air intake duct  100  positioned within air intake housing  200 . Helmholtz resonator opening  130  is seen protruding from the right side of air intake duct  100 , providing fluid communication between third resonator volume  154  and the space within air intake duct  100 .  
         [0028]      FIG. 5  is a right side view of air intake duct  100 , showing baffle plates  140  mounted thereto. As shown in  FIG. 5 , Helmholtz resonator openings  120 ,  130  are spaced longitudinally at or near the air inlet  102  and air outlet  104 , respectively. The perforated area  110 , as well as perforated area  112  (not shown), are located between Helmholtz resonator openings  120 ,  130  in the top and bottom portions of wall  106  of air intake duct  100 . Baffle plates  140  are shown for separating the resonator volumes  150 ,  152 , and  154 , such that the noise attenuation effect of each of the three resonator volumes is made to function substantially independently of the effect created by the other two resonator volumes. The larger volume of resonator volume  150  (relative to resonator volume  154 ) would tend to make the Helmholtz resonator associated with volume  150  attenuate noise energy at lower frequencies than the Helmholtz resonator associated with opening  130 , assuming other factors (such as the length of the neck portion of the openings  120 ,  130 , and the diameter of openings  120 ,  130 ) are held constant.  
         [0029]      FIG. 6  is a bottom view of air intake duct  100  showing a detailed description of perforated area  112 . The particular pattern and arrangement of perforations shown is for illustrative purposes. As would be known by a person of ordinary skill in the art, the pattern and arrangement of perforations may be varied to achieve a somewhat different noise response without departing from the scope of the invention.  
         [0030]      FIG. 7  is a close up view of perforated area  110  or  112 , showing the relative spacing and positioning of the apertures that comprise perforated areas  1   10 ,  112 .  
         [0031]     FIGS.  8 ( a ) and  8 ( b ) are two views of Helmholtz resonator opening  120 . Similarly, FIGS.  9 ( a ) and  9 ( b ) provide views of Helmholtz resonator opening  130 . For illustrative purposes only, the relative lengths of the openings  120 ,  130  is shown. The longer “neck” portion of opening  120  (relative to opening  130 ) would tend to make the Helmholtz resonator associated with opening  120  attenuate noise energy at lower frequencies than the Helmholtz resonator associated with opening  130 , assuming other factors (such as the volume of the respective resonator volumes  150 ,  154 , and the diameter of openings  120 ,  130 ) are held constant.  
         [0032]      FIG. 10  is a schematic diagram of an air intake duct  100  according to an embodiment of the invention.  FIG. 10  shows two Helmholtz resonators and a perforated sleeve resonator in fluid communication with the space inside air intake duct  100 . The parameters that define the frequency response characteristics of each Helmholtz resonator are indicated in  FIG. 10 , namely, the Helmholtz resonator volumes V 1 , V 2 , the length of the neck portions L 1 , L 2  between the air intake duct  100  and the resonator volumes V 1 , V 2 , and the radius of the openings r 1 , r 2 . Similarly, the parameters that define the frequency characteristic of the perforated sleeve resonator are indicated as resonator volume V s , hole depth d s , hole radius r s , and the number of holes n s .  
         [0033]      FIG. 11  is a schematic diagram of an air intake duct  100  showing a plurality of Helmholtz resonators in accordance with an embodiment of the invention. As shown, at least one perforated sleeve resonator is positioned longitudinally between each pair of adjacent Helmholtz resonators. As would be obvious to one of ordinary skill in the art, the openings of the Helmholtz resonators could be oriented to project from different directions around the periphery of wall  106 , for example, to facilitate packaging and manufacturing constraints of the vehicle.  
         [0034]      FIG. 12  is a schematic diagram of an air intake duct in fluid communication with a plurality of longitudinally spaced resonator volumes that are separated from one another by a wall or baffle plate between each pair of adjacent resonator volumes. As shown, the resonator volumes share a common housing with each other, but are separated from the air intake duct and have openings providing the fluid communication path between the air intake duct and each respective resonator volume.  
         [0035]      FIG. 13  is a schematic diagram of an air intake duct  100  and a plurality of resonator volumes that are formed in part by the outer surface of the wall  106  of the air intake duct  100 . As shown, the resonator volumes cover a portion of the outer wall  106  of air intake duct  100 , but do not extend circumferentially around the entire air intake duct  100 . As would be obvious to one having ordinary skill in the art, the resonator volumes shown in  FIGS. 11-13  could be combined to form alternate embodiments of the invention without departing from the scope of the technique described herein. As would also be obvious to one having ordinary skill in the art, any of the resonator volumes shown in  FIGS. 11-13  could be extended circumferentially to surround the entire outer wall  106  of air intake duct  100 , or any portions thereof.  
         [0036]      FIG. 14A  is a frequency response curve, showing the noise attenuation characteristics of a typical Helmholtz resonator, as well as a typical perforated sleeve resonator. As shown, the Helmholtz resonator frequency response curve provides a relatively high degree of attenuation over a relatively narrow frequency range centered on the Helmholtz resonator frequency, F H , which is determined in part by the volume, neck length, and hole radius of the particular Helmholtz resonator. The noise attenuation characteristic of the perforated sleeve resonator is also shown in  FIG. 14A . As shown, the perforated sleeve resonator provides a relatively lesser degree of attenuation over a relatively broader range of frequencies than the Helmholtz resonator. This is indicated in  FIG. 14A  by the dashed frequency response curve of the perforated sleeve resonator, having a lower peak attenuation at frequency F s , and exhibiting a generally bell-shaped response. The frequency response curve of the perforated sleeve resonator shown in  FIG. 14A  is provided for illustration, not limitation, and may be influenced by factors such as the air intake flow rate, among other factors.  
         [0037]      FIG. 14B  is illustrative of a problem experienced when using more than one Helmholtz resonator in a given structure. As shown in  FIG. 14B , the placement of two Helmholtz resonators in close proximity to each other in a particular structure will cause a lesser degree of attenuation and a broader range of frequencies attenuated.  
         [0038]      FIG. 14C  shows a frequency response curve achieved by separating two adjacent Helmholtz resonators in a structure by placing at least one sleeve resonator between the two Helmholtz resonators, which isolates the Helmholtz resonators from each other to a certain degree by adding to the distance between the two Helmholtz resonators and causing them to act somewhat independently of each other.  
         [0039]     Thus, embodiments of the Noise Reduction Technique For Snowmobiles are disclosed. One skilled in the art will appreciate that the technique can be practiced with embodiments other than those disclosed. The disclosed embodiments are presented for purposes of illustration and not limitation, and the invention is limited only by the claims that follow.