Abstract:
An air induction housing having a perforated wall which simultaneously provides ample air entry into the air induction housing and excellent intake noise attenuation. The size, number and arrangement of the perforations is selected such that ample airflow is provided and audibility of intake noise is minimized, based upon simultaneous optimization of: providing a plurality of perforations which collectively have an opening size that accommodates all anticipated airflow requirements; sizing each of the perforations such that the airflow demand involves an airflow speed through each perforation that is below a predetermined threshold at which perforation airflow noise is generated; and arranging the perforation distribution in cooperation with configuring of the air induction housing to provide a highest level of intake noise attenuation.

Description:
TECHNICAL FIELD 
     The present invention relates to air induction housings used in the automotive arts for air intake and air filtration for supplying intake air to an internal combustion engine. More particularly, the present invention relates to an air induction housing having a perforated wall for simultaneously providing air intake and sound (acoustic) attenuation. 
     BACKGROUND OF THE INVENTION 
     Internal combustion engines rely upon an ample source of clean air for proper combustion therewithin of the oxygen in the air mixed with a supplied fuel. In this regard, an air induction housing is provided which is connected with the intake manifold of the engine, wherein the air induction housing has at least one air induction opening for the drawing-in of air, and further has a filter disposed thereinside such that the drawn-in air must pass therethrough and thereby be cleaned prior to exiting the air induction housing on its way to the intake manifold. 
     Problematically, a consequence of the combustion of the fuel-air mixture within the internal combustion engine is the generation of noise (i.e., unwanted sound). A component of this noise is intake noise which travels through the intake manifold, into the air induction housing, and then radiates out from the at least one air induction opening. The intake noise varies in amplitude across a wide frequency spectrum dependent upon the operational characteristics of the internal combustion engine, and to the extent that it is audible to passengers of the motor vehicle, it is undesirable. 
     As shown at  FIG. 1 , a solution to minimize the audibility of intake noise is to equip an air induction housing  10  with an externally disposed resonator  12  connected to the air induction housing by an externally disposed snorkel  14 . The air induction housing  10  has upper and lower housing components  16 ,  18  which are sealed with respect to each other, and are also selectively separable for servicing a filter media (not shown) which is disposed thereinside. An induction duct  20  is connected to the induction housing and defines an air induction opening  22  for providing a source of intake air to the air induction housing at one side of the filtration media, as for example by being interfaced with the lower housing component  18 . An intake manifold duct  24  is adapted for connecting with the intake manifold of the internal combustion engine, and is disposed so as to direct the intake air at the other side of the filtration media out of the air induction housing  10 , as for example via the upper housing component  16 . 
     One end of the snorkel  14  is connected to the induction duct  20  adjacent the air intake opening  22 . The other end of the snorkel  14  is connected to the resonator  12 , which is essentially an enclosed chamber. Each end of the snorkel  14  is open so that intake noise may travel between the induction duct  20  and the resonator  12 . The resonator  12  is shaped and the snorkel  14  configured (as for example as two snorkel tubes  14   a ,  14   b ) such that the intake noise passing through the induction duct toward the air intake opening in part passes into the resonator and then back into the induction duct so as to attenuate the intake noise by frequency interference such that the audibility of the intake noise exiting the air intake opening is minimized. 
     While the prior art solution to provide attenuation of intake noise does work, it does so by requiring the inclusion of an externally disposed snorkel and resonator combination which adds expense, installation complexity and packaging volume accommodation. 
     Accordingly, what is needed is to somehow provide attenuation of intake noise as an inherent feature of the air induction housing so as to thereby minimize expense, complexity and packaging volume. 
     SUMMARY OF THE INVENTION 
     The present invention is an air induction housing having a perforated wall which simultaneously provides ample air entry into the air induction housing and excellent intake noise attenuation, while attendantly minimizing expense and complexity of fabrication and assembly, as well as packaging volume. 
     The air induction housing having a perforated sound attenuation wall according to the present invention includes an air induction housing having an internally disposed filtration media, and is preferably characterized by mutually selectively sealable and separable housing components; an intake manifold duct interfaced therewith adapted for connection to the intake manifold of an internal combustion engine; and a perforated sound attenuation wall integrated with the air induction housing and characterized by a plurality of perforations formed of the air induction housing, itself. The air induction housing may be of any configuration and is suitably shaped to suit a particular motor vehicle application. 
     The size, number and arrangement of the perforations is selected, per the configuration of the air induction housing and the airflow requirements of the internal combustion engine, such that a multi-faceted synergy is achieved whereby: 1) ample airflow is provided through the perforations to supply the internal combustion engine with required aspiration over a predetermined range of engine operation, and 2) audibility of intake noise is minimized. The multi-faceted synergy is based upon simultaneous optimization of three facets: 1) providing a plurality of perforations which collectively have an area that accommodates all anticipated airflow (aspiration) requirements of a selected internal combustion engine; 2) minimizing the diameter while simultaneously adjusting the area of the perforations such that the airflow demand of the internal combustion engine involves an airflow speed through each perforation that is below a predetermined threshold at which the perforation airflow noise generated by the flow of the air through the perforations is acceptably inaudible; and 3) arranging the perforation distribution in cooperation with configuring of the air induction housing to provide a highest level of intake noise attenuation (i.e., minimal audibility). 
     A significant aspect of the present invention is that the intake noise attenuation is accomplished inherently by the air induction housing, itself, obviating need for any external components of any kind (as for example an external snorkel and resonator combination of the prior art). 
     Accordingly, it is an object of the present invention to provide an air induction housing having a perforated wall which simultaneously provides ample air entry into the air induction housing and excellent intake noise attenuation, while attendantly minimized are expense and complexity of fabrication and assembly, as well as packaging volume. 
     This and additional objects, features and advantages of the present invention will become clearer from the following specification of a preferred embodiment. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a prior art air induction housing including an external snorkel and resonator combination for attenuating intake noise. 
         FIG. 2A  is a graphical representation of two acoustic (sound) waves 180 degrees out of phase with respect to each other such that the acoustic waves are in destructive interference. 
         FIG. 2B  is a schematic representation of how sound attenuation is believed to be provided by an air induction housing having a perforated sound attenuation wall according to the present invention. 
         FIG. 3  is a perspective view of an air induction housing according to the present invention. 
         FIG. 4  is a perspective view of a lower housing component of an air induction housing having a perforated sound attenuation wall, which, in combination with the upper housing of  FIG. 3 , was analogously used for providing certain test plots in  FIGS. 9 and 10 . 
         FIG. 5  is a front side view of the lower housing of  FIG. 4 . 
         FIG. 6  is a rear side view of the lower housing of  FIG. 4 . 
         FIG. 7  is a left side view of the lower housing of  FIG. 4 . 
         FIG. 8  is a top plan view of the lower housing of  FIG. 4 . 
         FIG. 9  is a graph of engine RPM versus sound level for several air induction housings according to the present invention per  FIG. 3  and analogously per  FIGS. 4 through 8 , each having a selected perforated sound attenuating wall; for a prior art air induction housing with external snorkel and resonator combination per  FIG. 1 ; and for an exemplar base line. 
         FIG. 10  is a graph of airflow rate versus air pressure loss for a prior art air induction housing with external snorkel and resonator combination per  FIG. 1 , and for an air induction housing having a perforated sound attenuating wall according to the present invention per  FIG. 3  and analogously per  FIGS. 4 through 8 . 
         FIG. 11  is a flow chart of an algorithm for optimizing acoustic attenuation of intake noise by the air induction housing having a perforated sound attenuating wall according to the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the Drawing,  FIGS. 2A through 11  depict various aspects of an air induction housing having a perforated sound attenuation wall according to the present invention. 
       FIGS. 2A and 2B  show principles of physics under which it is believed an air induction housing having a perforated sound attenuation wall according to the present invention provides acoustic (sound) attenuation of intake noise, without resort to an external snorkel and resonator combination as used in the prior art. 
       FIG. 2A  demonstrates the principle of destructive interference of acoustic (sound) waves. In this case, acoustic wave A is 180 degrees out of phase with acoustic wave B. As a result, if acoustic waves A and B have the same amplitude, then they completely cancel one another by destructive interference, the result being line C of zero amplitude. 
     Turning attention next to  FIG. 2B , a schematic representation of air induction housing having a perforated sound attenuating wall  100  according to the present invention is depicted, including an air induction housing  102 , an intake manifold duct  108  and a perforated wall  110  having a plurality of perforations  112  (holes or apertures) formed therein. Operationally, intake noise N from the engine passes into the air induction housing  102  via the intake manifold duct  108 , enters into the interior space  114  of the air induction housing passing through a filtration media  116  disposed within the air induction housing, and strikes the perforated wall  110 . The noise N strikes the perforated wall as an incident acoustic wave Ni, and is reflected as a reflected acoustic wave Nr which is 180 degrees out of phase with respect to the incident acoustic wave, whereby the incident and reflected acoustic waves mutually undergo destructive interference. 
     Further, under another principle, it is believed that to the extent the diameter D of the perforations  112  is less than any acoustic wave length λ of the noise (see  FIG. 2A ), then these acoustic waves cannot exit the perforations. Accordingly, the level of sound emitted from the perforations exterior to the air induction housing  100  is acceptably inaudible to the occupants of the motor vehicle. 
     A mathematical theory believed to describe the foregoing description is as follows. 
     A reflection coefficient, R, is used to describe the ratio of the reflected wave to that of the incident wave (see  Acoustics of Ducts and Mufflers with Application to Exhaust and Ventilation System Design , by M. L. Munjal, published by John Wiley &amp; Sons, 1987:
 
 R≡|R|e   jθ ,  (1)
 
where |R| and θ are the amplitude and phase of the reflection coefficient, respectively.
 
     The amplitude and phase of the reflection coefficient at an opening, i.e., the perforations, is described by the following equations:
 
| R|≅ 1−0.14 k   o   2   r   o   2   (2)
 
θ=π−tan −1 (1.2 k   o   r   o ),  (3)
 
where k o  is an initial wave number in a non-viscous fluid (i.e., air) and r o  is the radius of the enclosure (i.e., the air induction housing, itself).
 
     From equations (2) and (3), it is determined that the perforations of the perforated wall reflect the incident acoustic wave (of the engine intake noise) almost fully but with opposite phase as a reflected acoustic wave. Therefore, very little sound is emitted from the perforations because the reflected acoustic wave and subsequent incoming acoustic wave cancel one another by destructive interference. 
     Further, given a diameter, D, of the perforations, and given a smallest acoustic wave length, λ min , of the vast majority of the noise N, to the extent that D&lt;λ min , all the acoustic waves having λ satisfying λ min &lt;λ cannot exit the perforations. Accordingly, a minimum perforation diameter, D, is preferred. 
     However, a minimum diameter, D, of the perforations can produce noise as the airflow swiftly passes therethrough, as for example audibly detected as a howl, hiss or whistle. It is preferable that the Mach number, M, through the perforations be less than about 0.125, where M is defined by:
 
 M=v/s,   (4)
 
where s is the speed of sound in air and v is defined by:
 
 v =Ψ/(ρ A   P ),  (5)
 
where Ψ is the maximum intake air mass flow rate of an internal combustion engine operational range divided by the number of perforations, ρ is the density of air, and A P  is the area of each perforation.
 
     Referring now to  FIG. 3 , an exemplary configuration of an air induction housing with a perforated sound attenuating wall  100 ′ is depicted. 
     The air induction housing  102 ′ has upper and lower housing components  104 ,  106  which are selectively sealable and separable with respect to each other (as for example via peripherally disposed clips) for servicing a filter media (not shown, but indicated at  FIG. 2B ) which is disposed thereinside. An intake manifold duct  108 ′ is adapted for connecting with the intake manifold of an internal combustion engine, and its connection with the air induction housing is disposed so as to direct the intake air at one side of the filtration media out of the air induction housing  102 ′, as for example via the upper housing component  104 . A perforated wall  110 ′ is integrated with the air induction housing, wherein the perforations  112 ′ thereof collectively define an air induction opening for providing a source of intake air to the air induction housing  102 ′ at the other side of the filtration media, as for example by being interfaced with the lower housing component  104 . 
       FIGS. 4 through 8  depict views of a lower housing component  106 ′ of the induction housing of  FIG. 3 , having a perforated wall  110 ′ and perforations  112 ′, wherein  FIG. 8  is a plan view showing internal ribbing features  118 . The lower housing component  106 ′ was interfaced with the upper housing component  104  of  FIG. 3 , and the perforations thereof varied in diameter, number and distribution from that shown for testing, the results of which are shown in Table I and at  FIGS. 9 and 10 . 
     Turning attention to  FIG. 9 , a graph  120  of engine RPM versus emitted sound level of intake noise is shown. Plot  122  is a base requirement for sound emission. Plot  124  is the sound emitted by a prior art air induction housing with snorkel and resonator, as per that of  FIG. 1 . Plots  126 ,  128 ,  130 , and  132  are for an air induction housing with perforated sound attenuating wall according to the present invention as per that of  FIG. 3  and analogously per that of  FIGS. 4 through 8 , wherein plot  126  is for 10 circular perforations each of 27.5 mm diameter, plot  128  is for 103 circular perforations each of 10 mm diameter, plot  130  is for 200 circular perforations each of 7.2 mm diameter and plot  132  is for 10,000 circular perforations each of 1.02 mm diameter. It is seen that the present invention provides low sound level emission, in each plot better than the prior art, and better than the base line requirement. Further the best result is seen to be provided with the smallest diameter perforations. 
     Turning attention next to  FIG. 10 , a graph  140  of airflow rate versus air pressure loss is shown. Plot  142  is for a prior art air induction housing with snorkel and resonator as per that of  FIG. 1 , and plot  144  is for an air induction housing with perforated sound attenuating wall according to the present invention as per that of  FIG. 3  and analogously per that of  FIGS. 4 through 8 , having 73 perforations. It will be seen the results are comparable, whereby it is interpreted that the present invention provides air pass-through that is better than the prior art. 
     Table I shows data taken for various internal combustion engines, various selected perforation numbers and diameters for each engine, and the resulting Mach numbers associated with each of the perforation diameters and numbers selected. 
     
       
         
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE I 
               
               
                   
               
               
                   
                 Inlet area (mm 2 ) 
                 Perforation 
                 Number of 
                   
                   
               
               
                 Engine Type 
                 (per best practice) 
                 diameter (mm) 
                 perforations 
                 Flow Rate (g/s) 
                 Mach Number 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 4 cylinder 
                 2968 
                 5 
                 152 
                 140 
                 0.111 
               
               
                   
                   
                 10 
                 38 
                   
                 0.111 
               
               
                   
                   
                 15 
                 17 
                   
                 0.111 
               
               
                   
                   
                 20 
                 10 
                   
                 0.106 
               
               
                   
                   
                 30 
                 5 
                   
                 0.094 
               
               
                   
                   
                 40 
                 3 
                   
                 0.088 
               
               
                   
                   
                 50 
                 2 
                   
                 0.085 
               
               
                 6 cylinder 
                 5959 
                 5 
                 304 
                 240 
                 0.095 
               
               
                   
                   
                 10 
                 76 
                   
                 0.095 
               
               
                   
                   
                 15 
                 34 
                   
                 0.095 
               
               
                   
                   
                 20 
                 19 
                   
                 0.096 
               
               
                   
                   
                 30 
                 9 
                   
                 0.090 
               
               
                   
                   
                 40 
                 5 
                   
                 0.091 
               
               
                   
                   
                 50 
                 3 
                   
                 0.096 
               
               
                 8 cylinder 
                 8247 
                 5 
                 420 
                 300 
                 0.086 
               
               
                   
                   
                 10 
                 105 
                   
                 0.086 
               
               
                   
                   
                 15 
                 47 
                   
                 0.086 
               
               
                   
                   
                 20 
                 27 
                   
                 0.084 
               
               
                   
                   
                 30 
                 12 
                   
                 0.084 
               
               
                   
                   
                 40 
                 7 
                   
                 0.081 
               
               
                   
                   
                 50 
                 5 
                   
                 0.073 
               
               
                 8 cylinder high 
                 8247 
                 5 
                 420 
                 450 
                 0.129 
               
               
                 performance engine 
                   
                 10 
                 105 
                   
                 0.129 
               
               
                   
                   
                 15 
                 47 
                   
                 0.129 
               
               
                   
                   
                 20 
                 27 
                   
                 0.126 
               
               
                   
                   
                 30 
                 12 
                   
                 0.126 
               
               
                   
                   
                 40 
                 7 
                   
                 0.121 
               
               
                   
                   
                 50 
                 5 
                   
                 0.109 
               
               
                   
               
             
          
         
       
     
     It is seen from Table I that a wide range of perforation diameters can achieve a desired small Mach number. It is to be further noted that, per the above theoretical discussion, for purposes of acoustic (sound) attenuation, the smaller the perforation diameter the better. However, as mentioned hereinabove, it is necessary to adjust the area of the perforations so that the airflow (more specifically, the maximum airflow demanded of the internal combustion engine) passing through the perforations does not, itself, create undesirable noise, wherein it is preferred that the Mach number be under about 0.125 in order to achieve this result. 
     Thus, from Table I, it is possible to find best perforation parameters (by “best” is meant relative to the test results summarized in Table I, in that other tests may provide other “best” results): for the 4 cylinder engine is a perforated wall having 152 perforations of 5 mm diameter and having a Mach number equal to 0.111, best for the 6 cylinder engine is a perforated wall having 304 perforations of 5 mm diameter and having a Mach number equal to 0.095, best for the 8 cylinder engine is a perforated wall having 420 perforations of 5 mm diameter and having a Mach number equal to 0.086. The best for the high performance 8 cylinder engine may be a perforated wall having 420 perforations of 5 mm diameter and having a Mach number equal to 0.129, in that a Mach number of 0.129 may be acceptable (as empirically ascertained) in that engine application. 
     Turning attention now to  FIG. 11 , depicted are the steps associated with an algorithm  200  for expositing a method for optimizing the air induction housing with a sound attenuating perforated wall according to the present invention. 
     At Block  202 , the algorithm is initialized. At Block  204 , the engine airflow rate requirement of a selected internal combustion engine is determined. At Block  206 , the necessary inlet area, A I , is determined such that back pressure is not an issue for the operation of the internal combustion engine, per the determination at Block  204 . Once this area is determined, preferably about one percent (1%) is added thereto in order to account for entrance/exit airflow losses. This inlet area is the starting point for determining the number of perforations (based on average perforation area) of the perforated wall of the air induction housing. 
     Next, at Block  208 , a minimum perforation diameter is selected using an empirical best estimation to provide a perforation area, A P . Next, at Block  210 , the number, n, of perforations is calculated, wherein n=A I /A P . The smaller the perforation diameter, the better the noise attenuation benefit, as there are more waves reflected back into the box, as discussed hereinabove. However, the minimum area (and therefore diameter) of the perforations is limited by the Mach number, M, of the airflow through the perforations when at the maximum airflow rate, as discussed hereinabove. 
     Next, at Block  212 , the Mach number, M, for the airflow through the perforations when at the maximum mass flow rate is calculated using, for example, equations (4) and (5). At Decision Block  214 , inquiry is made whether the Mach number is less than, by way of preference, about 0.125. If the answer to the inquiry is no, then the algorithm returns to Block  208 , whereat a new minimum perforation diameter is selected, larger than that previously selected (that is, assuming the first chosen minimum diameter was a true minimum, otherwise various larger and smaller diameters can be tried to find the minimum). However, if the answer to the inquiry is yes, then the algorithm advances to Block  216 . 
     At Block  216 , the configuration of the air induction housing is determined. In so doing, taken into account are the packaging requirements for accommodation within the engine compartment, as well as a best estimation for providing acoustic attenuation, for example, per equations (2) and (3). The shape may be any suitable and/or necessary shape, as for example an irregular polygonal shape as for example shown at  FIGS. 3 through 8 , a regular polygonal shape, spherical shape, cylindrical shape, pyramidular shape, or some combinational shape thereof, etc. Next, at Block  218 , a distribution of the perforations is selected based upon an empirical best estimate. The spacing between the perforations should be maximized to ensure the best possible wave reflection (and thus sound attenuation). The spacing between the perforations is limited by the air induction housing size, per the number of perforations and the perforation area. 
     Next, at Decision Block  220 , inquiry is made, for example by use of empirical testing of a modeled air induction housing, whether the sound attenuation is a maximum (i.e., sound emission at the perforations is a minimum). If the answer to the inquiry is no, then the algorithm returns to Block  218 , wherein any possible reconfiguration of the air induction housing is made (if packaging constraints allow), and the perforation distribution is again reselected. However, if the answer to the inquiry at Decision Block  220  is yes, then the algorithm advances to Decision Block  224 . 
     At Decision Block  224 , inquiry is made whether the amount of sound attenuation is acceptable based upon a predetermined base line (as for example plot  122  of  FIG. 9 ). If the answer to the inquiry is no, then the algorithm returns to Block  216  to continue optimization of sound attenuation. However, if the answer to the inquiry at Decision Block  224  is yes, then fabrication of an air induction housing with a sound attenuating perforated wall according to the present invention may be performed with confidence. 
     It is to be understood that the perforations may have any shape or differing shapes, any area or differing areas, any diameter or differing diameters, and have uniform or non-uniform spacing therebetween, the perforated wall may be located anywhere or generally everywhere of the air induction housing, and that multiple layers of the perforated wall my be utilized, all for the purpose of tuning the intake noise emitted from the air induction system to a desired level of attenuation (acceptably inaudible) at the perforations. 
     To those skilled in the art to which this invention appertains, the above described preferred embodiment may be subject to change or modification. Such change or modification can be carried out without departing from the scope of the invention, which is intended to be limited only by the scope of the appended claims.