U.S. patent number RE30,306 [Application Number 06/020,758] was granted by the patent office on 1980-06-17 for air intake silencer.
This patent grant is currently assigned to Deere & Company. Invention is credited to Stephen A. Braun, James W. Moore.
United States Patent |
RE30,306 |
Moore , et al. |
June 17, 1980 |
Air intake silencer
Abstract
An air intake silencer includes a box-shaped expansion chamber
constructed of identically dimensioned, separable halves
respectively connected to a carburetor intake system and a tubular
intake member. In a basic form of the silencer, the tubular intake
member includes a metal tube mounted in the expansion chamber and
having a single elongate opening in communication with the interior
of the chamber, the tube being connected so as to form a
continuation of a hose located exteriorly of the chamber. For
obtaining more effective silencing, air distribution and filtering
the basic form of the silencer may be altered by dividing the
expansion chamber in half with a perforated baffle plate and/or by
substituting a perforated metal tube for the aforedescribed metal
tube.
Inventors: |
Moore; James W. (Horicon,
WI), Braun; Stephen A. (Horicon, WI) |
Assignee: |
Deere & Company (Moline,
IL)
|
Family
ID: |
26693821 |
Appl.
No.: |
06/020,758 |
Filed: |
March 15, 1979 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
684593 |
May 10, 1976 |
04093039 |
Jun 6, 1978 |
|
|
Current U.S.
Class: |
181/229; 181/239;
181/243; 181/272; 181/282; 220/4.24 |
Current CPC
Class: |
F02B
61/02 (20130101); F02M 35/1211 (20130101); F02M
35/1216 (20130101); F02M 35/162 (20130101) |
Current International
Class: |
F02B
61/00 (20060101); F02B 61/02 (20060101); F02M
35/12 (20060101); F01N 001/00 (); F02M
035/00 () |
Field of
Search: |
;181/229,239,243,264,272,282,269,245 ;220/4B,4D,4E,4R,8 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Hix; L. T.
Assistant Examiner: Fuller; Benjamin R.
Claims
We claim:
1. An expansion chamber for an air intake silencer, comprising:
upper and lower identically dimensional and configured chamber
halves; said upper chamber half including a closed top wall joined
to a depending wall means having a lower end defined by a first
flange and terminating in first plane inclined upwardly from a rear
location to a front location of the lower end; said lower chamber
half including a closed bottom wall joined to an upright wall means
having an upper end defined by a second flange and terminating in a
second plane which is parallel to the first plane; said first and
second flanges defining respective connection surface means which
cooperate to form a telescopic joint whereby the lower and upper
ends respectively of the depending and upright wall means are
releasably joined together; an air inlet opening means being
provided in the depending wall means of the upper chamber for
connection to a tubular inlet member; and an air outlet opening
means, for connection to carburetor intake means, being provided at
a forward location in the upright wall means of the lower chamber
at a level which places at least a portion of the outlet opening
means at a level above a rear location of the second flange whereby
easy access may be had to the air outlet opening means, when the
upper chamber half has been disconnected from the lower chamber
half, so that carburetor adjustments may be made by inserting a
tool through the outlet opening means.
2. The expansion chamber defined in claim 1 wherein a baffle plate
containing perforations is supported in the expansion chamber such
that one side of the plate cooperates with the upper chamber half
to form a first compartment while another side of the plate
cooperates with the lower chamber half to form a second
compartment.
3. The expansion chamber defined in claim 2 wherein said
perforations are positioned in a plurality of rows; each
perforation having a louvre extending thereabove and located on
said other side of the plate; and the louvres of adjacent rows of
said perforations being inclined toward each other.
4. The expansion chamber defined in claim 1 wherein the depending
and upright wall means respectively of the upper and lower chamber
halves each include a plurality of interior stiffener ribs; and
certain ribs of the upper chamber half extending from the closed
top wall and being respectively aligned with and connected to
certain ribs of the second chamber half extending from the closed
bottom wall whereby the expansion chamber includes stiffener ribs
which traverse the telescopic joint.
5. The expansion chamber defined in claim 4 wherein said certain
ribs of the upper and lower chamber halves each have end surfaces
which are located adjacent the telescopic joint; the end surfaces
of the certain ribs of the upper chamber half being coplanar with
each other, and the surfaces of the certain ribs of the lower
chamber half being coplanar with each other and parallel to the end
surfaces of the certain ribs of the upper chamber half; and a
perforated baffle plate mounted in said expansion chamber in
sandwiched relationship between the end surfaces of the certain
ribs of the upper chamber half and the end surfaces of the certain
ribs of the lower chamber half.
6. The expansion chamber defined in claim 5 wherein the end
surfaces of some of the certain ribs of the upper chamber half are
provided with pins projecting therefrom which are respectively
received in holes located in some of the end surfaces of some of
the certain ribs of the lower chamber half, and vice-versa, and
said baffle plate including passages respectively having the pins
of the upper and lower chamber halves extending therethrough.
.Iadd. 7. An air intake silencer for an internal combustion engine,
comprising: an expansion chamber of a generally rectangular box
configuration including top and bottom walls joined by front, rear
and opposite sidewalls; an air inlet opening provided in one of the
walls at an upper location in the box; an air outlet opening
provided in the front wall at a lower location in the box; and said
box being made up of upper and lower sections releasably joined at
a joint which, in side view, is inclined upwardly from a rear
location, at a level below that of at least a portion of the air
outlet opening, to a front location at a level above that of the
air outlet opening. .Iaddend..Iadd. 8. The air intake silencer
defined in claim 7 wherein a baffle plate containing perforations
is supported in the expansion chamber such that one side of the
plate cooperates with the upper section to form a first compartment
while another side of the plate cooperates with the lower section
to form a second compartment. .Iaddend..Iadd. 9. The air intake
silencer defined in claim 7 wherein the joint is composed of
cooperating interior surfaces; and said baffle plate being
sandwiched between and supported by said surfaces. .Iaddend.
Description
BACKGROUND OF THE INVENTION
The present invention relates generally to devices for muffling
noises emitted from the combustion air induction system of an
internal combustion engine.
Two-cycle internal combustion engines have seen increasing use in
the recreational vehicle market. The aspiration system of a
two-cycle engine causes air to be gulped into the carburetor system
and results in a loud noise having a frequency which is a function
of the engine speed. These factors have created a great deal of
interest in silencing two-cycle engine air induction systems.
Early air intake silencers merely consisted of enclosures, such as
a console or hood over the engine or a box around the carburetor
system, lined with sound absorbing material. While these
constructions worked very well at frequencies above 1500 Hertz,
they were marginally effective on low frequency intake noise and
often were constructed such that the sound absorption material
became saturated with fuel from carburetor spit-back.
As two-cycle engines became more powerful and thus, noisier, it
became necessary to make silencers which would muffle intake noise
in the frequency range below 1500 Hertz. Heretofore, this has been
done by constructing air intake silencers according to the
principles applied to exhaust mufflers. The simplest of these
exhaust muffler designs is a tail pipe attenuator, a low pass
acoustical filter which consists of an expansion chamber having a
length of pipe connected thereto. Studies show that this type of
silencer will attenuate noise only in certain limited frequency
ranges that are a function of the tail pipe length and that other
frequencies may actually be amplified. The studies also show that
the maximum degree of attenuation is determined by the volume of
the expansion chamber, the larger the chamber the greater the
attenuation. Because the intake noise harmonics shift in frequency
as the engine speed changes, it is impossible to design a simple
silencer, using tail pipe attenuator principles, with a broad
enough attenuation range to cover a substantial part of the
frequencies under 1500 Hertz. Accordingly, the most effective
silencers heretofore constructed have included several reactive
chambers tuned for different frequency ranges and many of these
silencers have had one or more of the disadvantages of being large,
complex, expensive and restrictive to air intake inflow which
adversely affects the carburetor process.
SUMMARY OF THE INVENTION
According to the present invention, there is provided a novel air
intake silencer and more particularly there is provided an intake
silencer which is effective on low frequency as well as high
frequency noise.
A broad object of the invention is to provide an intake silencer
which is of a relatively simple, inexpensive construction and which
effectively attenuates intake noise and at the same time permits
flow therethrough with minimum restriction and in a manner
compatible with the throttle control of the carburetor so as to not
seriously affect the carburetor process or the engine
performance.
Another object of the invention is to provide an air intake
silencer having a basic silencing structure to which additional
elements may be selectively added to gain more effective silencing
if desired.
A more specific object is to provide an air intake silencer
including an expansion chamber constructed from identically
dimensioned and configured molded chamber halves fit together with
overlapping lips or flanges which allow a minimum of sound and air
leakage without requiring gasket material.
Still another object is to provide an air intake silencer which can
be adapted to a wide variety of different engines, carburetion
systems and locations in an engine compartment by constructing the
expansion chamber such that holes may be cut in various areas of
the walls thereof for connection to air inlet and outlet tubular
members.
Yet another object of the invention is to provide an air intake
silencer which can easily be removed or partially dismantled to
gain access to the carburetor system to service or adjust the
latter.
A more specific object of the invention is to provide an air intake
silencer having an expansion chamber which may be divided into two
compartments by means of a baffle plate having a plurality of
openings therein for effecting even air distribution to multiple
carburetor systems, providing filtering of incoming air and for
muffling high frequency noises coming from the engine intake system
by causing a non-linear distortion of the high amplitude sound
waves.
Still another object of the invention is to provide an air intake
silencer having a baffle plate, as described above, with the baffle
plate being easily installable and removable.
Yet another object of the invention is to provide an air intake
silencer having an expansion chamber to which is connected an
extended inlet which may optionally be formed by a first tube,
having only a single elongate opening therein to communicate air
into the chamber, or a second tube, having a plurality of louvred
openings therein to communicate air into the chamber.
These and other objects will become apparent from a reading of the
following description in conjunction with the appended
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic left rear perspective view of the forward end
of the snowmobile with parts broken away exposing an air intake
silencer constructed according to the principles of the present
invention.
FIG. 2 is a left side elevational view of the top half of the
expansion chamber of the silencer shown in FIG. 1.
FIG. 3 is a left side view of the chamber half shown in FIG. 2.
FIG. 4 is a left side elevational view of the bottom half of the
expansion chamber of the silencer shown in FIG. 1.
FIG. 5 is a right side view of the chamber half shown in FIG. 4 and
in addition showing the location that a single outlet might occupy
when the expansion chamber is coupled to an engine having a single
carburetor.
FIG. 6 is a top view of the chamber half shown in FIG. 5.
FIG. 7 is a view of one type of the tube which may be used to form
a part of the air inlet member and to form a cylindrical
compartment within the expansion chamber.
FIG. 8 is a view of the downstream side of a baffle plate which may
be mounted in the expansion chamber so as to divide the latter into
two compartments.
FIG. 9 is a right end view of the baffle plate shown in FIG. 8.
FIG. 10 is a view of a second type of tube which may be used in
lieu of the tube shown in FIG. 7.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The present invention is here described as being used to silence a
two-cycle internal combustion engine of a snowmobile, however, it
is to be understood that this is merely a representative
application of the invention and that it may be used to silence
four-cycle engines used on vehicles other than snowmobiles.
In the description that follows, terms such as right, left, top,
bottom, front, and rear are used throughout with reference to the
invention being positioned, as shown in FIG. 1, and to the normal
forward direction of travel of the vehicle.
Referring now to FIG. 1, therein is shown a forward portion of a
snowmobile 10. The snowmobile 10 is supported at its forward end by
a pair of ski assemblies 12 (only one shown) and at its rearward
end by a suspended drive track 14. The track 14 is driven by means
of an engine 16 coupled thereto by transmission means including a
variable speed primary clutch 18 coupled to a crankshaft extension
(not visible) of the engine 16, a secondary clutch 20 connected to
the clutch 18 by a drive belt 22 and coupled so as to impart
rotation to a countershaft 24, and track drive elements 26
connected to the countershaft 24 by a drive chain assembly (not
shown) located in a chain case 28.
Mounted on a rear surface of the engine 16 are right and left
carburetors 30 and 32, respectively. Provided for the purpose of
delivering air to and for silencing noise emitted from the
carburetors 30 and 32 is an air intake silencer 34. The silencer 34
includes a box-shaped expansion chamber 36 constructed of
identically dimensioned and configured upper and lower chamber
halves 38 and 40, respectively telescopically interconnected, as at
42, in a manner to be presently described. It is herenoted that
some sort of band or strap (not shown) would normally be engaged
with at least the upper half 38 so as to hold the latter downwardly
against the lower half 40, the latter normally being supported on a
support surface (not shown) of the snowmobile 10.
Preferably, the chamber halves 38 and 40 are cast or molded from a
plastic material such as acrylonitrile butadiene styrene
(abbreviated, ABS) however, any material which would prevent sound
transmission through the walls thereof would be suitable. It will
be appreciated that a cost savings in the manufacture of the
expansion chamber 36 may be realized due to the fact that the
halves 38 and 40 can be made from the same die or mold.
Air is admitted into the expansion chamber 36 by means of a tubular
member 44 having an open upper end 46 from which it extends first
downwardly and then leftwardly through an opening 48 (FIG. 2) in a
right side wall 50 of and into engagement with an inner surface of
a left side wall 52 of the upper chamber half 38 with that part of
the member 44 which is inside the chamber 36, in effect, acting as
a tubular compartment therein which extends the range of
frequencies over which the silencer is effective beyond that
possible with only the chamber 36 and the part of the member 44
exteriorly of the chamber 36. The open end 46 of the tubular member
44 is located in a plenum chamber or void 54 partly bounded by a
hood portion 56 and an instrument panel 58. The members forming the
chamber 54 may be lined with sound absorbing material (not shown)
for additional silencing.
The tubular member 44 includes a first section in the form of a
hose 60 (FIG. 1) located entirely outside of the chamber 36 and a
second section having only a right end located outside of the
chamber 36 and connected to the hose 60. The second section of the
member 44 is preferably made of metal and may either be like a tube
62 (FIG. 7) or like a tube 64 (FIG. 10) with the selection of the
tubes 62 and 64 depending upon their respective abilities in
filtering, distributing and silencing in a given application of the
intake silencer 34.
The tubes 62 and 64 are each cylindrical and each has a support
strap 66 welded in its left end, each strap 66 supporting a
threaded stud 68 which is located along the longitudinal axis of a
respective one of the tubes 62 and 64. When either of the tubes 62
and 64 installed, the stud 68 will project through a hole 70,
provided in the left side wall 52 of the upper chamber half 38, and
will receive a nut 72 (FIG. 1). A resilient seal 74 is received on
a right end portion of each of the tubes 62 and 64 and each is for
the purpose of sealing the space between the periphery of the
opening 48 and a respective one of the tubes 62 and 64. The only
difference between the tubes 62 and 64 is that the portion of the
tube 62 adapted to be located between the walls 50 and 52 of the
upper chamber half 38 is provided with but a single elongate
opening 76 extending lengthwise of the tube 62, through which air
flows into the chamber 36, while the corresponding portion of the
tube 64 is provided with a plurality of openings or perforations 78
respectively having a plurality of louvres 79 associated therewith.
It is herenoted that the opening 76 and the openings 78 act to give
the effect of tubes of various lengths so as to extend the range of
sound frequencies over which the tube is effective for
silencing.
The openings 78 are arranged in rows and the louvres 79 associated
with the openings 78 of adjacent rows are inclined towards each
other to effect intermixing of air flowing through the openings of
adjacent rows. The louvres also serve to trap a volume of air in
the vicinity of the holes and this function together with that of
intermixing the air has been found to increase the silencing
effectiveness of the silencer.
Air leaves the expansion chamber 36 via a pair of transversely
spaced hoses 80 (only the left hose is shown) which respectively
couple the intake of the carburetors 30 and 32 to right and left
openings 82 and 84 (FIG. 5) provided in a forward wall 86 of the
lower chamber half 40. It is to be understood that the openings 82
and 84 may be spaced differently if necessary to accommodate
connection to other dual carburetor configurations or that only a
single opening 88, for example, (see dashed lines in FIG. 5) would
be cut in the wall 86 if the carburetor system consisted of only a
single carburetor.
It is herenoted that for the purpose of providing easy access to
the air intakes of the carburetors 30 and 32 via the openings 82
and 84 and the hoses 80, the respective lower and upper ends of the
upper and lower chamber halves 38 and 40 are constructed to
terminate in respective planes which are parallel to each other and
to the telescopic joint 42 which inclines upwardly and from rear to
front as viewed from the side. This results in the forward wall 86
of the lower chamber half 40 being higher than a rear wall 90 and,
as can best be seen in FIG. 5, the openings 82 and 84 are located
in the wall 86 so as to be at least partially above the level of
the top of the rear wall 90 so as to permit a tool to be inserted
through the openings 82 and 84 to aid in adjusting the carburetors
30 and 32.
The telescopic joint 42 is formed by interfitting certain surfaces
of a peripheral flange 92, (FIG. 2) at the bottom of the upper
chamber half 38, with certain surfaces of a peripheral flange 94,
(FIG. 4) at the top of the lower chamber half 40. Specifically, the
flange 92 includes interior and exterior recessed surfaces 96 and
98, respectively, defining inner and outer downwardly facing
shoulders 100 and 102, the surface 96 extending across a forward
wall 104 of and rearwardly halfway along the right and left side
walls 50 and 52 of the upper chamber half 38, and the surface 98
extending across a rearward wall 106 of and forwardly halfway along
the right and left side walls 50 and 52. Similarly, the flange 94
includes exterior and interior recessed surfaces 108 and 110,
respectively, defining upwardly facing shoulders 112 and 114, the
surface 108 extending across the front wall 86 of and rearwardly
halfway along right and left side walls 116 and 118, respectively,
of the chamber half 40, and the surface 110 extending across the
rear wall 90 of and forwardly halfway along the right and left side
walls 116 and 118 of the chamber half 40. The recessed surfaces 96
and 98 of the upper chamber half 38 respectively telescopically
embrace the recessed surfaces 108 and 110 of the lower chamber half
40 when the chamber halves 38 and 40 are joined, as shown in FIG.
1, the shoulders 100 and 102 then being respectively engaged with
the shoulders 112 and 114.
For the purpose of preventing the walls of the expansion chamber 36
from pulsating and radiating noise in response to intake noise
pulses impinging thereupon, they are constructed with stiffener
means molded integrally with the interior thereof. Specifically,
the upper chamber half 38 includes a top wall 120 and arranged
perpendicular to and having upper ends integral with the wall 120
are right front and rear ribs 122 and 124 respectively, formed
integrally with the right side wall 50, left front and rear ribs
126 and 128, respectively, formed integrally with the left side
wall 52, and front and rear ribs 130 and 132, respectively, formed
integrally with the front and rear walls 104 and 106. It is
herenoted that in order to provide a flat wall in which outlet
openings such as the openings 82, 84 and 88 may be cut, the walls
86 and 106 have relatively large unstiffened areas. Noise
transmission through these areas may be diminished by applying a
thin sheet of viscoelastic or other suitable damping material (not
shown) to the walls 104 and 106 by means of an adhesive, as is
conventional in the art.
Additional stiffening is provided by a plurality of gussets 134
joined to the top wall 120 and respectively to the ribs 122-132.
All of the ribs except for rib 132 have downwardly facing lower end
surfaces, which are coplanar with each other.
Right and left downwardly projecting pins 136 and 138 are
respectively located centrally in the end surfaces of the right and
left front ribs 122 and 126; and upwardly extending holes 140 and
142 are respectively located centrally in the end surface of the
right and left rear ribs 124 and 128.
Similarly, the lower chamber half 40 includes a bottom wall 144 and
arranged perpendicular to and having lower ends integral with the
wall 116 are right front and rear ribs 146 and 148, respectively,
formed integrally with the right side wall 116, left front and rear
ribs 150 and 152, respectively, formed integrally with the left
side wall 118, and front and rear ribs 154 and 156, respectively,
formed integrally with the front and rear walls 86 and 90. With the
exception of front rib 154, all of the ribs of the chamber half 40
have upwardly facing upper end surfaces, which are coplanar with
each other. Right and left downwardly extending holes 158 and 160
are respectively located centrally in the end surfaces of the right
and left front ribs 146 and 150; and upwardly projecting pins 162
and 164 are respectively centrally located in the end surfaces of
the right and left rear ribs 148 and 152.
When the halves 38 and 40 are brought together, as shown in FIG. 1,
the right and left front ribs 122 and 126 of the half 38 are
respectively aligned with the right and left front ribs 146 and 150
of the half 40 and the pins 136 and 138 are respectively received
in the holes 158 and 160; and the right and left rear ribs 124 and
128 of the half 38 are aligned with the right and left rear ribs
148 and 152 of the half 40 and the pins 162 and 164 are
respectively received in the holes 140 and 142.
In order to provide an air filter, to provide for even air
distribution to the openings 82 and 84 and to increase the noise
silencing effectiveness of the silencer 34, the chamber 36 may be
divided into two compartments by means of a rectangular baffle
plate 166 (FIGS. 8 and 9). The plate 166 is dimensioned so that it
may be supported in sandwiched relationship between the coplanar
lower surfaces of the ribs 122-130 of the upper chamber half 38 and
the coplanar upper surfaces of the ribs 146-152 and 156 of the
lower chamber half 40. When the plate 166 is so installed, front
right and left notches 168 and 170, respectively will receive the
pins 136 and 138 while rear right and left notches 172 and 174,
respectively, will receive the pins 162 and 164. For the purpose of
conveying air between the upper and lower chambers 38 and 40,
respectively, the plate 166 is provided with a plurality of rows of
perforations 176. Associated with each of the perforations 176 is a
louvre 178 and it is to be noted that the louvres 178 in adjacent
rows are inclined towards each other. The plate 166 is to be
installed in the chamber 36, as described above, with the louvres
178 located on the lower side of the plate 166 so that streams of
air passing through the perforations 176 of adjacent rows will be
deflected toward each other by the louvres 178. The intermixing of
these streams of air aids in attenuating sound waves directed
toward the perforations 176.
The operation of the air intake silencer 34 is as follows. Assuming
the silencer 34 to be in a basic form wherein only the tube 62 is
located in the chamber 36, engine 16 will act to cause air to be
sucked into the intakes of the carburetors 30 and 32 from the
expansion chamber 36 via the openings 82 and 84 and the hoses 80.
This air is of course, immediately replaced by air which is drawn
into the chamber 36 from the void 54 via the hose 60 and tube 62,
with the air entering the chamber 36 via the elongate opening 76 in
the tube 62. In the event that the air exiting from the opening 76
does not arrive evenly distributed at the openings 82 and 84, the
flow may be "tuned" for such even distribution by rotating the tube
62 so as to redirect the air exiting from the opening 76.
Sound waves emitted from the carburetor intakes will impinge
against the walls of the expansion chamber 36 and will be precluded
from transmission therethrough due to the stiffness of the walls
effected by the ribs 122-132 and 146-156. If additional prohibition
of noise transmission is desired, thin sheets of commercially
available noise damping material may be glued on the exterior of
the chamber 36 where desired.
If air filtering and more sound wave attenuation is desired, the
perforated tube 64 may be substituted for the tube 62, in which
case the perforations 78 serve to filter incoming air and the
perforations 78 and louvres 79 serve to produce the increased
attenuation by mixing incoming air flow and by trapping small
volumes of air adjacent the perforations. The principles of the
attenuation attributable to the openings 78 and louvres 79 is quite
complex but the effect of the openings 78 and louvres is readily
discernible on standard noise measuring instruments.
If still further air filtering and attenuation and a more even
distribution of air to the carburetor system is desired, the baffle
plate 166 may be installed in the chamber 36. Because the plate 166
further compartmentalizes the chamber 36, sound wave frequencies,
in addition to those attenuated by the undivided chamber 36, are
attenuated with the additional frequencies being a function of the
volumes of the two compartments. The perforations 176 and louvres
178 will also act to filter and distribute incoming air and act to
further attenuate sound waves impinging on the plate 166, due to
the air flow mixing and air volume trapping functions thereof.
Of importance is the fact that no matter what form of the invention
is used, there will always be sufficient air flow to the
carburetors 30 and 32 for the engine 16 to operate properly.
Also, it will be appreciated that access to the carburetors 30 and
32 may be easily attained by removing the air silencers 34
therefrom by disconnecting the hoses 80 and that access to the
intakes of the carburetors 30 and 32 for the purpose of adjusting
the same by inserting a tool in the intakes thereof, may be easily
attained by removing the upper chamber half 38 from the lower
chamber half 40.
Further, it will be appreciated that inasmuch as the halves 38 and
40 are identically dimensioned and formed, they can be made on the
same die or mold, so as to reduce manufacturing costs, and that
inlet and outlet openings can then be added therein as desired.
While the tube 64 and baffle plate 166 are here shown as having
louvred openings, it is to be understood that a large variety of
openings or perforations may be provided in them without any
appreciable sacrifice in the filtering, air distribution and noise
attenuation functions of the tube 64 and baffle plate 166.
* * * * *