U.S. patent number 3,648,803 [Application Number 04/868,283] was granted by the patent office on 1972-03-14 for exhaust system.
This patent grant is currently assigned to Walker Manufacturing Company. Invention is credited to Robert A. Heath, Ronald J. Martoia.
United States Patent |
3,648,803 |
Heath , et al. |
March 14, 1972 |
EXHAUST SYSTEM
Abstract
A simplified very low height sound attenuating muffler for
flowing gases is formed from an outer tube shaped into an oval
cross section to engage and be welded to a perforated
straight-through gas flow tube and then the ends of the outer tube
and selected intermediate portions are compressed into contact with
each other to form closures at opposite ends of the muffler and at
interior points which divide the muffler into chambers of various
volumes that may be keyed to the frequencies to be attenuated.
Inventors: |
Heath; Robert A. (Jackson,
MI), Martoia; Ronald J. (Jackson, MI) |
Assignee: |
Walker Manufacturing Company
(Racine, WI)
|
Family
ID: |
25351366 |
Appl.
No.: |
04/868,283 |
Filed: |
October 13, 1969 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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531245 |
Mar 2, 1966 |
|
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Current U.S.
Class: |
181/250 |
Current CPC
Class: |
F01N
1/02 (20130101); F01N 13/02 (20130101); F01N
13/1838 (20130101); F01N 13/185 (20130101); F01N
1/006 (20130101); F01N 1/023 (20130101); F01N
2470/02 (20130101); F01N 2470/10 (20130101); F01N
2450/22 (20130101); F01N 2450/20 (20130101); F01N
2490/155 (20130101) |
Current International
Class: |
F01N
7/18 (20060101); F01N 1/02 (20060101); F01N
7/00 (20060101); F01N 7/02 (20060101); F01N
1/00 (20060101); F01n 001/02 (); F01n 007/18 () |
Field of
Search: |
;181/48,47,54,59,61,63 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Tomsky; Stephen J.
Parent Case Text
RELATED APPLICATION
This application is a continuation of Ser. No. 531,245, filed Mar.
2, 1966.
Claims
We claim:
1. A silencing device comprised of an outer shell formed from an
elongate integral tubular member of a generally oval
cross-sectional contour, a straight through inner gas flow tube
extending the length of said outer shell and forming an exhaust gas
inlet at one end of said outer shell and an exhaust gas outlet at
the other end of said outer shell, opposite sides of the shell
being in engagement to form end closures at opposite ends of said
outer shell around said exhaust gas inlet and said exhaust gas
outlet, said outer shell being in engagement with opposite sides of
said inner tube along the full length thereof to define a
longitudinally extending space between each side of the tube and
each side of the shell, each of said spaces being subdivided into a
plurality of longitudinally spaced silencing chambers by means of
longitudinally spaced integral sections of the outer shell that are
in engagement with the respective side of the inner tube and with
each other to define partitions separating said silencing chambers,
said inner tube having spaced patches of perforations formed
therein so that substantially all of the silencing chambers have at
least one patch opening into it, at least one perforation patch
being spaced substantially from the opposite ends of the silencing
chamber into which it opens, said patch being confined to a
relatively short length of said inner tube for forming two
effective silencing subchambers within said silencing chamber
located on opposite sides of said patch, each of said effective
subchambers having a length substantially equal to the distance
between said patch and the respective opposite end of said
subchamber.
2. A silencing device comprised of an outer shell formed from an
elongate integral tubular member of a generally oval
cross-sectional contour, a straight through inner gas flow tube
extending the length of said outer shell and forming an exhaust gas
inlet at one end of said outer shell and an exhaust gas outlet at
the other end of said outer shell, opposite sides of the shell
being in engagement to form end closures at opposite ends of said
outer shell around said exhaust gas inlet and said exhaust gas
outlet, said outer shell being in engagement with opposite sides of
said inner tube along the full length thereof to define a
longitudinally extending space between each side of the tube and
each side of the shell, each of said spaces being subdivided into a
plurality of longitudinally spaced silencing chambers by means of
longitudinally spaced integral sections of the outer shell that are
in engagement with the respective side of the inner tube and with
each other to define partitions separating said silencing chambers,
said inner tube having spaced patches of perforations formed
therein so that substantially all of the silencing chambers have at
least one patch opening into it, and four chambers having said
perforate patches therein which are materially shorter in length
than the chambers whereby the chambers can be tuned to attenuate a
desired frequency.
3. A device as set forth in claim 2 wherein said four chambers are
of four different lengths.
4. A device as set forth in claim 3 wherein the perforate patch in
at least one of the four chambers is located at an intermediate
point in the chamber which is spaced unequal distances from
opposite ends of the chamber.
Description
BRIEF SUMMARY OF THE INVENTION
Since modern motor vehicle design requires a high degree of engine
exhaust system silencing in a minimum of space, it is a principal
object of this invention to provide such a compact but highly
effective exhaust silencing system.
It is a further object of the invention to provide an improved
silencing device having a relatively low height and yet capable of
silencing a wide range of frequencies in a minimum overall
volume.
It is a still further object of this invention to provide a
silencing device having a relatively small number of components and
yet capable of silencing a large number or range of
frequencies.
It is another object of this invention to provide an improved
method for forming a silencing device that is capable of
attenuating a wide range of silent frequencies.
It is yet another object of this invention to provide an improved
method that lends itself to the low cost formation of a silencing
device for an internal combustion engine.
An exhaust system for an internal combustion engine includes at
least one silencing device embodying the invention disclosed
herein. The inventive silencing device is comprised of an outer
shell formed from an integral, elongated tubular member deformed
into a generally oval cross-sectional contour. An inner tube
extends the length of the outer shell and forms an exhaust inlet in
one end of the outer shell and an exhaust outlet in the other end
of the outer shell. Means form closures for opposite ends of the
outer shell around the exhaust gas inlet and exhaust gas outlet.
The outer shell is in engagement with the opposite sides of the
inner tube to define at least one longitudinally extending chamber
therebetween. The plurality of perforate openings in the inner tube
provide for gas communication with the chamber for silencing.
The method of forming an exhaust silencer of the type described in
the immediately preceding paragraph and embodying this invention
comprises the steps of deforming a relatively large diameter
tubular member into a substantially oval shape. A smaller diameter
tubular member is inserted into the larger diameter tubular member
with opposite sides in engagement with the deformed larger member
to define at least one silencing chamber between the members. End
closures are formed for the larger member around the smaller member
to enclose a chamber between the members. The opposite ends of the
smaller member forming exhaust gas inlet and outlet bushings in
respective ends of the silencer.
Other objects and advantages of this invention will become more
apparent as this description proceeds, particularly when considered
in conjunction with the accompanying drawings.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a top plan view of an automotive exhaust system embodying
this invention;
FIG. 2 is an enlarged cross-sectional view of one of the silencing
devices of the system in FIG. 1 taken substantially in the plane of
FIG. 1;
FIG. 3 is an enlarged cross-sectional view taken along the line
3--3 of FIG. 2;
FIG. 4 is an enlarged cross-sectional view, taken in the plane of
FIG. 1, showing another of the silencing devices;
FIG. 5 is an enlarged cross-sectional view taken along the line
5--5 of FIG. 4;
FIG. 6 is an enlarged cross-sectional view, taken in the plane of
FIG. 1, showing the remaining silencing device;
FIG. 7 is a cross-sectional view taken generally along the line
7--7 of FIG. 6;
FIG. 8 is a perspective view, with portions broken away, of a part
of the silencing device shown in FIGS. 2 and 3;
FIG. 9 is a cross-sectional view, in part similar to FIGS. 2 and 4
and showing another embodiment of the invention;
FIG. 10 is a cross-sectional view taken along the line 10--10 of
FIG. 9;
FIG. 11 is a cross-sectional view, in part similar to FIGS. 2, 4,
and 9, showing another embodiment of the invention;
FIG. 12 is a cross-sectional view, in part similar to FIGS. 2, 4,
9, and 11, showing a still further embodiment of the invention;
and
FIGS. 13 through 17 are views illustrating the method by which
silencing devices embodying this invention may be formed.
DETAILED DESCRIPTION OF THE INVENTION
Referring now in detail to FIG. 1, a portion of an internal
combustion engine is identified generally by the reference numeral
21. The engine has an exhaust manifold 22 from which exhaust gases
are delivered to an exhaust system embodying this invention and
identified generally by the reference numeral 23. If the engine 21
is of the V-type, a similar exhaust system may be provided for each
bank of cylinders or only one system may serve both banks. The
system 23 also may be used with an in-line engine.
The exhaust system 23 is comprised of a first silencing device 24
having an inlet bushing 25 that is connected by means of an exhaust
inlet pipe 26 to the engine exhaust manifold 22. An outlet bushing
27 of the first silencing device 24 is connected to an inlet
bushing 28 of a second silencing device 29 by means of a short
length of pipe 31. The second silencing device 29 has an outlet
bushing 32 that is connected to an inlet bushing 33 of a third
silencing device 34 by means of a pipe section 35. An outlet
bushing 36 of the third silencing device 34 is connected to a short
tailpipe 37 for discharge of the silenced exhaust gases to the
atmosphere.
Referring now specifically to FIGS. 2, 3, and 8, the first
silencing device 24 is comprised of an outer shell 38 which, as
will be discussed below, is comprised of a relatively large
diameter integral tubular member that is deformed into a generally
oval cross-sectional shape. Contained within the outer shell 38 is
an inner tube 39 that is engaged on opposite sides thereof by the
deformed portion of the outer shell 38 (FIG. 3). Since the
remaining portion of the outer shell 38 is not in engagement with
the inner tube 39, a pair of chambers are formed on opposite sides
of the silencing device 24.
One side of the outer shell 38 is formed with integral pinched-in
sections 41, 42, 43, 44, 45, 46 and 47 formed by permanently
deforming the portion of the outer shell 38 on the respective side
of the silencing device 24 so that the outer shell sides sealingly
engage the inner tube 39 around approximately 180.degree. of its
circumference. In addition, the facing surfaces of the outer shell
38 at the pinched-in sections 41 through 47 engage each other to
form, in effect, partitions that divide the chamber at one side of
the device 24 into a plurality of longitudinally spaced silencing
chambers 51, 52, 53, 54, 55, 56, 57 and 58. The chambers 51 and 58
at opposite ends of the silencing device 24 are closed by
pinched-in sections 59 and 61 of the outer shell 38 which form
closures for the opposite ends of this side of the silencing device
24 in the same manner as the pinched-in sections 41 through 47 form
partitions.
The side opposite the chambers 51 through 58 of the outer shell 38
is formed with pinched-in sections 62, 63 and 64 that define
longitudinally spaced silencing chambers 65, 66, 67 and 68. The
pinched-in sections 63 and 64 are similar in configuration to the
sections 41 through 47 in that they engage the inner tube 39 around
one-half of its circumference and form partitions between the
chambers 66, 67 and 68.
An intermediate tube 69 extends parallel to the inner tube 39
through the pinched-in section 62 and is affixed, as by spot welds
indicated by the X's, to the inner tube 39. The opposite ends of
the intermediate tube 69 open into the chambers 65 and 66. Opposing
faces 71 of the outer shell 38 pinched-in section 62 engage the
intermediate pipe 69 and adjacent side of the inner tube 39 so as
to form a complete partition between the chambers 65 and 66. The
intermediate tube 69, however, extends through the partition thus
formed and provides for fluid communication between the chambers 65
and 66. The outer end of the chamber 65 is closed by means of a
pinched-in section 72 similar to the sections 59 and 61 at opposite
side of the device. In a like manner, the rear end of the chamber
68 is closed by means of a pinched-in section 73.
At the inlet end of the first silencing device 24, the exhaust gas
inlet bushing 25 is formed by a pipe having a reduced diameter
section 74 that terminates at an outstanding flange 75. The
pinched-in sections 59 and 72 of the outer shell 38 engage the
reduced diameter section 74 completely around its circumference so
as to form effective closure for this end of the outer shell 38.
The inner tube 39 is slidingly received in the reduced diameter
section 74 and may be affixed to it, as by the spot welds noted by
the x's in the drawing. In a like manner, the outlet bushing 27 at
the opposite end of the first silencing device 24 is formed by a
pipe having an enlarged diameter portion 76 that is sealingly
engaged around its periphery by the pinched-in sections 61 and 73.
The opposite end of the inner tube 39 is received within the outlet
bushing portion 76 and may be affixed to it, as by spot welds
indicated by the reference numeral X. If desired, the opposite
sides of all or any of the pinched-in sections may be further spot
welded to each other.
The inner pipe 39 is provided with a first series of louvered
openings 77 that extend completely around its circumference and
substantially the full length of the chambers 51 and 65. The first
series of louvered openings provides for communication of the
exhaust gases flowing through the inner tube 39 into the chambers
51 and 65. A second series of louvered openings 78 is formed around
approximately 180.degree. of the inner tube 39 in the area between
the pinched-in sections 41 and 46 of the outer shell 39. The
louvered openings 78 thus provide for communication of the exhaust
gases with the chambers 52 through 56. A third series of louvered
openings 79 are formed around the circumference of the inner tube
39 between the pinched-in sections 46 and 63 and the pinched-in
sections 61 and 73. The louvered openings 79 thus provide for
exhaust gas communication with the chambers 57, 58, 67 and 68.
The louvered openings into the chambers 51 through 58, 67 and 68
cause these chambers to function as high frequency sound
attenuating chambers known in the art as "spit chambers." These
chambers will attenuate a relatively broad band of high frequency
noises, the band determined by the volume of individual chambers
and the size and spacing of the louvered openings into them. By
altering the volumes of the chambers 51 through 58, 67 and 68 as
well as the spacing and size of the louvers 77, 78 and 79, a broad
band of high frequency ranges may be attenuated within the
silencing device 24.
The chamber 65 will also function somewhat as a spit chamber due to
the number of louvered openings into it. The exhaust pressure
pulses in the chamber 65 will be transmitted through the tuning
neck formed by the intermediate tube 69 into the chamber 66 which
is otherwise closed. Thus, the chamber 66 and the tuning neck 69
act as a Helmholtz tuner for attenuating a desired frequency. The
louvered openings 77 broad band this tuner to some extent.
Preferably, the louvered opening 77 in the chamber 65 is located at
an anti-node of the frequency silenced by the Helmholtz tuner.
Referring now in detail to FIGS. 4 and 5, the silencing device 29
is similar in some respects to the silencing device 24 and includes
an outer shell 81 that is formed from a large diameter piece of
tubing that is permanently deformed into a generally oval shape and
through which an inner tube 82 extends. The inner tube 82 is
engaged on diametrically opposite sides by the outer shell 81 so as
to form two separate chambers on opposite sides of the device 29.
The chambers are divided into a plurality of longitudinally spaced
chambers by pairs of pinched-in sections 83, 84, 85 and 86. As in
the silencing device 24, the pinched-down sections 83-87 form
partitions that isolate sound attenuating chambers 92 through 99,
101 through 104 from each other. As in the preceding embodiment,
the opposite ends of the pipe 81 are telescopically received within
the inlet bushing 28 and the outlet bushing 32. End closures for
the respective ends of the silencing device 29 are formed by
pinched-in sections, indicated generally by the reference numeral
105.
A first series of louvered openings 106 are formed around the
circumference of the inner pipe 81 for substantially the full
length of the chambers 92 through 96 and 98, 99, 100, 102 and 103.
Thus, these chambers function as spit chambers for attenuating high
frequency sounds. These chambers may have the same or different
volumes but in the depicted embodiment each of the respective pairs
have the same volume. The inner pipe 82 has a second bank of
louvered openings 107 formed around its circumference and opening
into the chambers 97 and 104. The louvered openings 107 do not
extend the full length of the chambers 97 and 104 and these
chambers function as quarter wave length tuners for silencing a
predetermined frequency and all odd harmonics of this predetermined
frequency. The frequency tuned is equivalent to the frequency that
has a wave length equal to one-quarter of the length of the tuning
chamber, in this case the distance from the center of the louvered
openings 107 to the closed end formed by the pinched-in sections
105. Although the chambers 97 and 104 have the same lengths, it is
to be understood that different lengths may be employed by changing
the location of either of the pairs of pinched-in sections 87 or
105.
Referring now to FIGS. 6 and 7, the silencing device 34 is designed
to attenuate a broad band of low and intermediate frequencies and
also includes a spit chamber device for attenuating high frequency
sounds. The device 34 has an inner tube 111 that is slidably
received at its opposite ends in the inlet and outlet bushings 33
and 36 and may be affixed, as by spot welding, to one or both of
them. An outer shell 112 of generally circular configuration is
necked down at each end and affixed, as by a circumferential weld,
to the bushings 33 and 36. A volume 113 or chamber is formed
between the outer shell 112 and inner tube 111 which functions as
sound attenuating expansion chamber. A plurality of louvered
openings 114 are formed along a major portion of the length of the
inner tube 111 around the circumference. These openings allow
exhaust gas to flow into the chamber 113 for attenuating a broad
band of low and intermediate frequencies.
A shell 115 also encircles the rearwardmost end of the inner tube
111 to define a second tuning volume 116 within the device 112. A
bank of louvers 117 is formed in the portion of the inner tube 114
within the shell 115 so that the chamber 116 acts as a high
frequency attenuating spit chamber.
It has been found that the described system will effectively
attenuate substantially all objectionable noises from a certain
design of automotive engine. The silencing devices 24 and 29 are
particularly effective in this regard inasmuch as they provide a
plurality of different tuning devices within a relatively small
overall height. That is, they include various size spit chambers,
quarter wave length tuners and Helmholtz tuners. It is to be
understood that various modifications may be made in the depicted
devices, for example, changing the volume of the individual
chambers by altering the location of the pinched-in sections which
define the partitions between the chambers. In the devices 24 and
29 the inner tube was centrally disposed within the outer shell so
as to define two rows of chambers on either side of the device. If
desired, the inner tube could be offset to one side of the outer
shell so as to provide different volume for the chambers at each
side or to provide a single row of chambers having larger volumes
if even more offset is desired. Such a device is shown in FIGS. 9
and 10 and is identified generally by the reference numeral
121.
The silencing device 121 is comprised of an outer shell 122 which,
as in the devices 24 and 29, is formed from a large diameter piece
of integral tubing that is deformed into a generally oval
cross-sectional shape. An inner tube 123 is disposed at one side of
the outer shell 122 and has an outer diameter that substantially
conforms to the arcuate side of the outer shell 122. The inner tube
extends beyond one end of the outer shell 122 and is formed with an
outwardly flared portion 124 that forms an inlet bushing. The
opposite end of the inner tube 123 extends beyond the opposite end
of the outer shell 122 and forms a reduced diameter outlet bushing
125.
An elongated volume is formed at the one side of the outer shell
122 adjacent the inner tube 123 and the ends of this volume are
closed by pinched-in sections 126 and 127 that form closures for
the respective ends of the outer shell 122 as in the previously
described embodiments. In addition, a plurality of pinched-in
sections 128, 129 and 130 are formed at longitudinally spaced
positions to divide the chamber into a plurality of silencing
chambers 131, 132, 133 and 134. One-half of the circumference of
the inner tube 123 may be provided with a bank of louvers 135 that
extends substantially the full length of the outer shell 122. The
chambers 131 through 134 will function as broad banded silencing
devices for intermediate and high frequency sounds. As in the
previously described embodiments, the volumes of these chambers may
be altered and the size and number of the louvered openings into
each chamber may be selected so as to accomplish the desired degree
of tuning.
A still further embodiment of the invention is shown in FIG. 11
wherein a silencing device is identified generally by the reference
numeral 141. As in the previously described embodiments, the
silencing device 141 comprises a generally oval elongated outer
shell 142 in which an inner tube 143 is positioned. The inner tube
143 is centrally disposed so as to provide two longitudinally
extending chambers on opposite sides thereof that are separated by
the contact between the outer shell 142 and the diametrically
opposite sides of the inner tube 143. Exhaust gas inlet and outlet
bushings 144 and 145 are formed in any suitable manner at the
opposite ends of the inner tube 143 externally of the outer shell
142. The opposite ends of the outer shell 142 are closed, as by
pinched-in sections 146 of the same type described in the preceding
embodiments.
In this embodiment, the volume at one side of the device 141 is
divided into two longitudinally spaced chambers 147 and 148 by
means of a pinched-in section 149. The chamber at the opposite side
of the device 141 is divided into two chambers 151 and 152 by means
of a pinched-in section 153 of the outer shell 142. Although in
this embodiment the chambers 147 and 151 and the chambers 148 and
152 have the same volumes, different volumes could be provided by
appropriately positioning the pinched-in sections 149 and 153. In
addition, a greater number of chambers could be provided if
desired.
At one end of the outer shell 142, the inner tube 143 is provided
with a relatively short bank of louvered openings 154 that open
into the chamber 151. The openings 154 extend around one-half or
less of the circumference of the inner tube 143 and open only into
the chamber 151. Thus, the chamber 151 functions as a quarter wave
length tuner for silencing the frequency having a wave length
approximately equal to four times the distance from the center of
the bank of louvers 154 to the pinched-in section 153. On its
opposite side, the inner tube 143 has a short bank of louvers 155
that open only into the chamber 147. The bank of louvers 155 is
positioned between the ends of the chamber 147 so that the chamber
147 in effect acts as two quarter wave length tuners within a
single chamber. These tuners silence the frequencies having wave
lengths equal to four times the distance from the center of the
bank of louvers 155 to each of the pinched-in sections 146 and
149.
A relatively short bank of louvers 156 is formed in the portion of
the inner tube 143 opening into the chamber 152 and adjacent the
pinched-in section 153. Thus, the section 152 acts as a relatively
high frequency quarter wave length tuner. A somewhat longer bank of
louvers 157 is formed on the opposite side of the inner tube 143
opening into the chamber 148. This device will attenuate a somewhat
broader band of frequencies in the chamber 152.
As in the previously described embodiments, the device 141 shown in
FIG. 11 is susceptible of incorporating certain other features and
the frequencies tuned may be changed by altering the volumes of the
respective chambers or the locations of the louvers that open into
each of the chambers and the number of louvers. Other forms of flow
passages than louvered openings may be employed, but the louvered
openings have the effect of broadening the range of frequencies
silenced by a specific tuner.
As has been noted in the embodiment shown in FIG. 11, the chambers
147 and 151 and the chambers 148 and 152 have the same volume.
Different volumes may be employed by changing the locations of the
pinched-in sections, as shown in FIG. 12. In this embodiment, a
silencing device, indicated generally by the reference numeral 161,
is comprised of an outer shell 162 and an inner tube 163 with
pinched-in sections 164, 165, 166, 167, 168 and 169 forming end
closures and dividing the space between the outer shell 162 and
inner tube 163 into four discrete silencing chambers 171, 172, 173
and 174. The chambers 171 through 174 each have different volumes.
As in the embodiment shown in FIG. 11, banks of louvers 175, 176,
177 and 178 open into the chambers 171 through 174, respectively.
The chambers 172 through 174 each function as quarter wave length
tuners and the chamber 171 function as two quarter wave length
chambers due to the eccentric location of the louvers 175.
The method of forming the silencing devices identified generally by
the reference numerals 24, 29, 121, 141 or 161, will now be
described by particular reference to FIGS. 13 through 17. As has
been previously noted, the outer shells of these devices are formed
by taking a large diameter tubular member, indicated generally by
the reference numeral 191 in FIG. 13, and permanently deforming it
into an elongated oval shape, indicated generally by the reference
numeral 192 (FIG. 14). Any suitable bending machine may be used for
this purpose. A cylindrical inner tube 193 having an outer diameter
substantially equal to the height of the deformed section 192 is
then inserted into the deformed outer shell 192. Depending upon
whether one or two longitudinal rows of silencing chambers are
provided, the tube 193 is centrally disposed within the deformed
outer shell 192, offset slightly to one side thereof or positioned
at one side thereof. The tube 193 is formed with the louvers that
will open into the respective silencing chambers before insertion
into the outer shell 192, although in some instances the louvers
may be formed after assembly.
The outer shell 192 is then permanently deformed to provide
pinched-in sections 194, 195, 196, 197, 198 and 199. The pinched-in
sections may be formed simultaneously in pairs or singly by means
of a suitable bending press. If the sections are aligned, as the
sections 194 and 195, it is most convenient to form them
simultaneously (FIG. 16). At the same time the pinched-in sections
194 through 199 are formed, the opposing surfaces of the outer
shell 192 may be spot welded together. The spot welding may be done
later or may be omitted altogether.
The sections 196, 197, 198 and 199 form the end closures for the
muffler and the sections 196 and 197 form the intermediate
partitions.
While it will be apparent that the preferred embodiments of the
invention disclosed are well calculated to fulfill the objects
above stated, it will be appreciated that the invention is
susceptible to modification.
* * * * *