SWAGED TRI-FLOW MUFFLER
United States Patent 3841435
A swaged outer muffler shell with straight or offset bushings houses a three tube structure forming a tri-flow gas passage through the muffler.
US Patent References:
Silencer
Powers - September 1944 - 2357791
Retroverted passage type muffler with resonator chambers
Cary - October 1953 - 2656005
Muffler
Heath - July 1964 - 3141518
Muffler
Jettinghoff - June 1965 - 3191715
Muffler with two longitudinally separated chambers
Whitney - October 1965 - 3209861
Silencer
Powers - September 1944 - 2357791
Retroverted passage type muffler with resonator chambers
Cary - October 1953 - 2656005
Muffler
Heath - July 1964 - 3141518
Muffler
Jettinghoff - June 1965 - 3191715
Muffler with two longitudinally separated chambers
Whitney - October 1965 - 3209861
Application Number:
05/415284
Publication Date:
10/15/1974
Filing Date:
11/12/1973
View Patent Images:
Export Citation:
Assignee:
Tenneco Inc. (Racine, WI)
Primary Class:
Other Classes:
29/890.080
International Classes:
F01N1/02; F01N1/08; F01N1/08
Field of Search:
181/35C,49,53,54,57,59,61 29/157R,475
US Patent References:
Primary Examiner:
Wilkinson, Richard B.
Assistant Examiner:
Gonzales, John F.
Attorney, Agent or Firm:
Harness, Dickey & Pierce
Parent Case Data:
RELATED APPLICATION
This application is a continuation-in-part of my copending U.S. application, Ser. No. 329,395, filed Feb. 5, 1973, now abandoned and assigned to the assignee hereof.
Claims:
I claim
1. A muffler adapted for use in an internal combustion engine exhaust system comprising an elongated tubular monolithic shell having opposite ends reduced in diameter to form inlet and outlet bushings respectively, a plurality of transverse partitions located inside and supported on the wall of the shell, three parallel longitudinally extending open ended gas flow tubes supported in and structurally interconnecting the partitions so that the partitions and tubes form a subassembly, first and second of said tubes having offset portions extending respectively into said inlet and outlet bushings and being supported therein.
2. A muffler as set forth in claim 1 wherein said offset portions are welded to said bushings and said partitions have a slip fit with respect to the shell.
3. A muffler as set forth in claim 1 wherein there are three partitions subdividing the space inside the shell into four chambers, a first of said partitions acting with the inlet end of the shell to define a first chamber, a second of said partitions acting with the first partition to define a second chamber, a third of said partitions acting with the second partition to define a third chamber, said third partition acting with the outlet end of the shell to define a fourth chamber.
4. A muffler as set forth in claim 3 wherein at least one of the tubes has perforations along a portion of its length that is located in said second chamber.
5. A muffler as set forth in claim 4 including an open ended tuning tube mounted on the third partition and acoustically connecting the third chamber to the fourth chamber.
6. A muffler as set forth in claim 3 wherein said offset portions of said first and second tubes are located in said first and fourth chambers respectively.
7. A muffler as set forth in claim 6 wherein said first and second tubes open respectively into the third and the first chambers, the third of said tubes opening into the first and third chambers and extending through the second chamber.
8. A muffler as set forth in claim 7 wherein said third tube is perforated in said second chamber.
9. A muffler as set forth in claim 8 including a tuning tube mounted on the third partition and connecting the third chamber to the fourth chamber.
10. A muffler as set forth in claim 9 wherein said bushings extend at an angle to the longitudinal axis of the shell.
11. A muffler as set forth in claim 3 wherein said first tube opens into said second chamber, said second tube opens into said third chamber, and said first and third partitions having gas passage means therein for the flow of gas from the second chamber to the first chamber and from the fourth chamber to the third chamber, the third of said tubes opening at one end in the first chamber and at the other end in the fourth chamber and extending through said second and third chambers.
12. A muffler as set forth in claim 11 wherein said third tube has an array of perforations opening into at least one of said second and third chambers.
13. A muffler as set forth in claim 11 wherein said third tube is perforated and the perforations open into both said second and third chambers and provide means for limited bypass flow of gas between the tube and said chambers.
14. The method of making a muffler which comprises forming a subassembly of a plurality of partitions and three parallel tubes extending between and welded to the partitions, one of said tubes being an inlet tube and another being an outlet tube, said inlet and outlet tubes being bent to have offset ends, inserting said subassembly into said shell and providing said partitions with a slip fit on the inner wall of the shell, and swaging the ends of the shell down into bushings extending around and in contact with the offset ends of said inlet and outlet tubes.
15. The method of claim 14 including the step of bending the bushings at angles to the axis of the shell.
16. The method of making a muffler which comprises forming a subassembly of three partitions and three parallel tubes secured to the partitions, a first of said tubes being an inlet tube and a second being an outlet tube and said first and second tubes being welded respectively to first and second of said partitions, the third tube being welded to each of said partitions, said inlet and outlet tubes being bent to have offset ends, inserting said subassembly into said shell and providing said partitions with a slip fit on the inner wall of the shell, swaging the ends of the shell down into bushings extending around and in contact with the offset ends of said inlet and outlet tubes, and welding at least one of the bushings to a tube.
1. A muffler adapted for use in an internal combustion engine exhaust system comprising an elongated tubular monolithic shell having opposite ends reduced in diameter to form inlet and outlet bushings respectively, a plurality of transverse partitions located inside and supported on the wall of the shell, three parallel longitudinally extending open ended gas flow tubes supported in and structurally interconnecting the partitions so that the partitions and tubes form a subassembly, first and second of said tubes having offset portions extending respectively into said inlet and outlet bushings and being supported therein.
2. A muffler as set forth in claim 1 wherein said offset portions are welded to said bushings and said partitions have a slip fit with respect to the shell.
3. A muffler as set forth in claim 1 wherein there are three partitions subdividing the space inside the shell into four chambers, a first of said partitions acting with the inlet end of the shell to define a first chamber, a second of said partitions acting with the first partition to define a second chamber, a third of said partitions acting with the second partition to define a third chamber, said third partition acting with the outlet end of the shell to define a fourth chamber.
4. A muffler as set forth in claim 3 wherein at least one of the tubes has perforations along a portion of its length that is located in said second chamber.
5. A muffler as set forth in claim 4 including an open ended tuning tube mounted on the third partition and acoustically connecting the third chamber to the fourth chamber.
6. A muffler as set forth in claim 3 wherein said offset portions of said first and second tubes are located in said first and fourth chambers respectively.
7. A muffler as set forth in claim 6 wherein said first and second tubes open respectively into the third and the first chambers, the third of said tubes opening into the first and third chambers and extending through the second chamber.
8. A muffler as set forth in claim 7 wherein said third tube is perforated in said second chamber.
9. A muffler as set forth in claim 8 including a tuning tube mounted on the third partition and connecting the third chamber to the fourth chamber.
10. A muffler as set forth in claim 9 wherein said bushings extend at an angle to the longitudinal axis of the shell.
11. A muffler as set forth in claim 3 wherein said first tube opens into said second chamber, said second tube opens into said third chamber, and said first and third partitions having gas passage means therein for the flow of gas from the second chamber to the first chamber and from the fourth chamber to the third chamber, the third of said tubes opening at one end in the first chamber and at the other end in the fourth chamber and extending through said second and third chambers.
12. A muffler as set forth in claim 11 wherein said third tube has an array of perforations opening into at least one of said second and third chambers.
13. A muffler as set forth in claim 11 wherein said third tube is perforated and the perforations open into both said second and third chambers and provide means for limited bypass flow of gas between the tube and said chambers.
14. The method of making a muffler which comprises forming a subassembly of a plurality of partitions and three parallel tubes extending between and welded to the partitions, one of said tubes being an inlet tube and another being an outlet tube, said inlet and outlet tubes being bent to have offset ends, inserting said subassembly into said shell and providing said partitions with a slip fit on the inner wall of the shell, and swaging the ends of the shell down into bushings extending around and in contact with the offset ends of said inlet and outlet tubes.
15. The method of claim 14 including the step of bending the bushings at angles to the axis of the shell.
16. The method of making a muffler which comprises forming a subassembly of three partitions and three parallel tubes secured to the partitions, a first of said tubes being an inlet tube and a second being an outlet tube and said first and second tubes being welded respectively to first and second of said partitions, the third tube being welded to each of said partitions, said inlet and outlet tubes being bent to have offset ends, inserting said subassembly into said shell and providing said partitions with a slip fit on the inner wall of the shell, swaging the ends of the shell down into bushings extending around and in contact with the offset ends of said inlet and outlet tubes, and welding at least one of the bushings to a tube.
Description:
BRIEF SUMMARY OF THE INVENTION
It is the purpose of the invention to provide a durable, compact, highly effective muffler that may be used in an automotive exhaust system.
In one embodiment the invention accomplishes this purpose by means of a one piece outer shell or housing with offset bushings to provide durability and compactness and a three tube silencing structure plus a resonator structure inside the housing to provide highly effective, broad band sound attenuation. In another embodiment, the resonator structure is omitted and a long, perforated intermediate tube is utilized.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a longitudinal cross section through a muffler embodying the invention with the various tubes rotated into the plane of the section;
FIG. 2 is an end view of the muffler of FIG. 1 and showing the actual location of the tubes;
FIG. 3 is a longitudinal cross section through a second embodiment of the invention; and
FIG. 4 is an end view of the muffler of FIG. 3.
In the drawings, the symbol "x" designates a spotweld.
DESCRIPTION OF THE INVENTION
The muffler 1 comprises an outer shell 3 which is originally a seamless steel tube but which is swaged down at opposite ends to form reduced diameter inlet and outlet bushings 5 and 7, respectively. The inner ends of the bushings are preferably coaxial with the main, full diameter body 11 of the shell but, preferably, and as illustrated, the bushings are angled or offset in opposite directions a slight but equal amount to facilitate a neat installation in the exhaust system of a particular make automobile manufactured outside the United States. The shell is reduced down into the bushings after a tube and partition subassembly 13 is inserted.
The subassembly 13 comprises three longitudinally separated partitions 15, 17, and 19 which have annular peripheral flanges 21 that fit the inside surface of the shell main body portion 11 but are preferably not spotwelded or otherwise affixed to the shell whereby relative longitudinal adjustment between the partitions and shell may occur. Partition 15 has three openings as defined by necks 23, 25, and 27 and these are longitudinally aligned with three openings in partition 17 as defined by necks 29, 31, and 33. Partition 19 has two openings as defined by necks 35 and 37, and these are longitudinally aligned with necks 31 and 33 in partition 17. Imperforate open ended tube 39 is supported in and spotwelded to necks 23 and 29; perforate open ended tube 41 is supported in necks 25 and 31, being spotwelded to neck 25; imperforate open ended tube 43 is supported in and spotwelded to neck 35; and open ended imperforate tube 45 is supported in necks 27, 33, and 37, being spotwelded to necks 27 and 37. It will be appreciated that by virtue of the various weld connections between the symmetrically arranged tubes and partitions the parts are secured to each other and may be readily handled as the subassembly 13 for insertion into and positioning within the shell 3 prior to formation of bushings 5 and 7. After insertion, the spotwelding of the tubes to the bushings holds the subassembly in place. Differential expansion is accommodated by the slip fit of the partition in the shell and of tube 45 in partition 17.
The tube 39 has an offset or angled portion 47 terminating in an inlet opening 49 and the tube 45 has an offset or angled portion 51 terminating in an outlet opening 53 which is coaxial with opening 49 and with the axis of the shell 3. The end portions of the tubes defining openings 49 and 53 serve as jig and fixture means for the swaging of the ends of the shell 3 into the bushings 5 and 7, the shell being reduced in diameter into tight contact with the ends of the tubes so that the tubes and shell can be spotwelded together as indicated. After the swaging of the ends of the shell into bushings 5 and 7, the bushings can be offset or angled in opposite directions as shown, though spotwelding of the ends of the tubes to the bushings is preferably done prior to the offsetting.
The partitions divide the interior of shell 3 into a series of longitudinally adjacent chambers. Thus, partition 15 and the inlet end 55 of shell 3 form a chamber 57; partitions 15 and 17 form a chamber 59; partitions 17 and 19 form a chamber 61; and partition 19 and the outlet end 63 of the shell form a chamber 65. Chambers 57 and 61 serve as cross over chambers and also function to provide sound attenuation; chamber 59 serves as a resonator chamber for intermediate and high frequencies in combination with the perforations 67 in tube 41; and chamber 65 has a volume coordinated with the length and cross sectional area of tube 43 to serve as a Helmholtz resonator for attenuating a predetermined relatively low frequency of sound in the exhaust system.
In operation, an exhaust pipe (not shown) is attached to the inlet bushing 5 to conduct exhaust gas from an internal combustion engine to the open end of inlet pipe 39. The gas flows from pipe 39 to chamber 61 where it reverses direction to enter perforated tube 41 and flow to chamber 57. It reverses direction in chamber 57 and flows to outlet bushing 7 via outlet tube 45. A predetermined low frequency is attenuated by connection of tube 43 and chamber 65 to chamber 61. Gas at the outlet bushing 7 can flow to atmosphere via a tailpipe 67 secured to the bushing.
The three tube arrangement is known to produce very effective silencing and the shape and size of chamber 57 is thought to increase the usual attenuation. If desired, the portions of tubes 39 and/or 45 in chamber 59 may be perforated to provide acoustic communication as well as some cross bleeding for back pressure reduction.
Referring to the second embodiment shown in FIGS. 3 and 4, the muffler 101 comprises an outer shell 103 which is originally a seamless steel tube but which is swaged down at opposite ends to form reduced diameter inlet and outlet bushings 105 and 107, respectively. The inner ends of the bushings are preferably coaxial with the main, full diameter body 111 of the shell. The shell 103 is reduced down into the bushings after a tube and partition subassembly 113 is inserted.
The subassembly 113 comprises three longitudinally separated partitions 115, 117, and 119 which have annular peripheral flanges 121 that fit the inside surface of the shell main body portion 111 but are preferably not spotwelded or otherwise affixed to the shell whereby relative longitudinal adjustment between the partitions and shell may occur. Partition 115 has two openings as defined by necks 123 and 125, neck 123 being longitudinally aligned with an opening in otherwise imperforate partition 117 as defined by neck 127. Partition 119 has two openings as defined by necks 135 and 137, neck 135 being longitudinally aligned with neck 127. Imperforate open ended tube 139 is supported in and spotwelded to neck 123; perforate open ended tube 141 is supported in and spotwelded necks 123, 127, and 135; and imperforate open ended tube 143 is supported in and spotwelded to neck 137. The various weld connections between the symmetrically arranged tubes and partitions secure them to each other so that they may be readily handled as the subassembly 113 for insertion into and positioning within the shell 103 prior to formation of bushings 105 and 107. After insertion, the spotwelding of one or both tubes 139 and 143 to one or both bushings holds the subassembly in place. Differential expansion is accommodated by the slip fit of the partitions in the shell.
The tube 139 has an offset or angled portion 147 terminating in an inlet opening 149 and the tube 143 has an offset or angled portion 151 terminating in an outlet opening 153 which is coaxial with opening 149 and with the axis of the shell 103. The end portions of the tubes defining openings 149 and 153 may be used as jig and fixture means for the swaging of the ends of the shell 103 into the bushings 105 and 107, the shell being reduced in diameter into tight contact with the ends of the tubes so that the tubes and shell can be spotwelded together as indicated. The bushings can be offset or angled as in FIGS. 1-2, if desired.
The partitions divide the interior of shell 103 into a series of longitudinally adjacent chambers. Thus, partition 115 and the inlet end 155 of shell 103 form a chamber 157; partitions 115 and 117 form a chamber 159; partitions 117 and 119 form a chamber 161; and partition 119 and the outlet end 163 of the shell form a chamber 165. Tubes 139 and 145 project about halfway into the chambers 159 and 161, respectively. Tube 141 is preferably perforated along its entire length so that there is communication between the inside of the tube and chambers 159 and 161.
In operation, an exhaust pipe (not shown) is attached to the inlet bushing 105 to conduct exhaust gas from an internal combustion engine to the open end of inlet pipe 139. The gas flows from pipe 139 to chamber 159 where it reverses direction to flow through two holes formed by two necks 167 in partition 115 and flow to chamber 157. It reverses direction in chamber 157 and flows to chamber 165 via intermediate tube 141. The gas reverses direction in chamber 165 and flows through gas passage means in the form of two holes (not shown) in partition 119 formed by necks similar to necks 167 and flow into chamber 161. From there it reverses direction to flow out of the muffler via the outlet tube 143. The perforations in tube 141 permit cross bleeding from chamber 159 into the tube and from the tube into chamber 161 thereby tending to reduce back pressure.
The three tube arrangement is known to produce very effective silencing and the shape and size of end chambers 157 and 165 is thought to increase the usual attenuation.
It will be seen that the shells 3 and 103 with, if desired, offset bushings, are very compact. The shell is monolithic or one piece with no seams and is therefore particularly strong and corrosion resistant. The internal structure provides a high degree of attenuation over a wide range of frequencies. Modifications in the specific details shown may be made without departing from the spirit and scope of the invention.
It is the purpose of the invention to provide a durable, compact, highly effective muffler that may be used in an automotive exhaust system.
In one embodiment the invention accomplishes this purpose by means of a one piece outer shell or housing with offset bushings to provide durability and compactness and a three tube silencing structure plus a resonator structure inside the housing to provide highly effective, broad band sound attenuation. In another embodiment, the resonator structure is omitted and a long, perforated intermediate tube is utilized.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a longitudinal cross section through a muffler embodying the invention with the various tubes rotated into the plane of the section;
FIG. 2 is an end view of the muffler of FIG. 1 and showing the actual location of the tubes;
FIG. 3 is a longitudinal cross section through a second embodiment of the invention; and
FIG. 4 is an end view of the muffler of FIG. 3.
In the drawings, the symbol "x" designates a spotweld.
DESCRIPTION OF THE INVENTION
The muffler 1 comprises an outer shell 3 which is originally a seamless steel tube but which is swaged down at opposite ends to form reduced diameter inlet and outlet bushings 5 and 7, respectively. The inner ends of the bushings are preferably coaxial with the main, full diameter body 11 of the shell but, preferably, and as illustrated, the bushings are angled or offset in opposite directions a slight but equal amount to facilitate a neat installation in the exhaust system of a particular make automobile manufactured outside the United States. The shell is reduced down into the bushings after a tube and partition subassembly 13 is inserted.
The subassembly 13 comprises three longitudinally separated partitions 15, 17, and 19 which have annular peripheral flanges 21 that fit the inside surface of the shell main body portion 11 but are preferably not spotwelded or otherwise affixed to the shell whereby relative longitudinal adjustment between the partitions and shell may occur. Partition 15 has three openings as defined by necks 23, 25, and 27 and these are longitudinally aligned with three openings in partition 17 as defined by necks 29, 31, and 33. Partition 19 has two openings as defined by necks 35 and 37, and these are longitudinally aligned with necks 31 and 33 in partition 17. Imperforate open ended tube 39 is supported in and spotwelded to necks 23 and 29; perforate open ended tube 41 is supported in necks 25 and 31, being spotwelded to neck 25; imperforate open ended tube 43 is supported in and spotwelded to neck 35; and open ended imperforate tube 45 is supported in necks 27, 33, and 37, being spotwelded to necks 27 and 37. It will be appreciated that by virtue of the various weld connections between the symmetrically arranged tubes and partitions the parts are secured to each other and may be readily handled as the subassembly 13 for insertion into and positioning within the shell 3 prior to formation of bushings 5 and 7. After insertion, the spotwelding of the tubes to the bushings holds the subassembly in place. Differential expansion is accommodated by the slip fit of the partition in the shell and of tube 45 in partition 17.
The tube 39 has an offset or angled portion 47 terminating in an inlet opening 49 and the tube 45 has an offset or angled portion 51 terminating in an outlet opening 53 which is coaxial with opening 49 and with the axis of the shell 3. The end portions of the tubes defining openings 49 and 53 serve as jig and fixture means for the swaging of the ends of the shell 3 into the bushings 5 and 7, the shell being reduced in diameter into tight contact with the ends of the tubes so that the tubes and shell can be spotwelded together as indicated. After the swaging of the ends of the shell into bushings 5 and 7, the bushings can be offset or angled in opposite directions as shown, though spotwelding of the ends of the tubes to the bushings is preferably done prior to the offsetting.
The partitions divide the interior of shell 3 into a series of longitudinally adjacent chambers. Thus, partition 15 and the inlet end 55 of shell 3 form a chamber 57; partitions 15 and 17 form a chamber 59; partitions 17 and 19 form a chamber 61; and partition 19 and the outlet end 63 of the shell form a chamber 65. Chambers 57 and 61 serve as cross over chambers and also function to provide sound attenuation; chamber 59 serves as a resonator chamber for intermediate and high frequencies in combination with the perforations 67 in tube 41; and chamber 65 has a volume coordinated with the length and cross sectional area of tube 43 to serve as a Helmholtz resonator for attenuating a predetermined relatively low frequency of sound in the exhaust system.
In operation, an exhaust pipe (not shown) is attached to the inlet bushing 5 to conduct exhaust gas from an internal combustion engine to the open end of inlet pipe 39. The gas flows from pipe 39 to chamber 61 where it reverses direction to enter perforated tube 41 and flow to chamber 57. It reverses direction in chamber 57 and flows to outlet bushing 7 via outlet tube 45. A predetermined low frequency is attenuated by connection of tube 43 and chamber 65 to chamber 61. Gas at the outlet bushing 7 can flow to atmosphere via a tailpipe 67 secured to the bushing.
The three tube arrangement is known to produce very effective silencing and the shape and size of chamber 57 is thought to increase the usual attenuation. If desired, the portions of tubes 39 and/or 45 in chamber 59 may be perforated to provide acoustic communication as well as some cross bleeding for back pressure reduction.
Referring to the second embodiment shown in FIGS. 3 and 4, the muffler 101 comprises an outer shell 103 which is originally a seamless steel tube but which is swaged down at opposite ends to form reduced diameter inlet and outlet bushings 105 and 107, respectively. The inner ends of the bushings are preferably coaxial with the main, full diameter body 111 of the shell. The shell 103 is reduced down into the bushings after a tube and partition subassembly 113 is inserted.
The subassembly 113 comprises three longitudinally separated partitions 115, 117, and 119 which have annular peripheral flanges 121 that fit the inside surface of the shell main body portion 111 but are preferably not spotwelded or otherwise affixed to the shell whereby relative longitudinal adjustment between the partitions and shell may occur. Partition 115 has two openings as defined by necks 123 and 125, neck 123 being longitudinally aligned with an opening in otherwise imperforate partition 117 as defined by neck 127. Partition 119 has two openings as defined by necks 135 and 137, neck 135 being longitudinally aligned with neck 127. Imperforate open ended tube 139 is supported in and spotwelded to neck 123; perforate open ended tube 141 is supported in and spotwelded necks 123, 127, and 135; and imperforate open ended tube 143 is supported in and spotwelded to neck 137. The various weld connections between the symmetrically arranged tubes and partitions secure them to each other so that they may be readily handled as the subassembly 113 for insertion into and positioning within the shell 103 prior to formation of bushings 105 and 107. After insertion, the spotwelding of one or both tubes 139 and 143 to one or both bushings holds the subassembly in place. Differential expansion is accommodated by the slip fit of the partitions in the shell.
The tube 139 has an offset or angled portion 147 terminating in an inlet opening 149 and the tube 143 has an offset or angled portion 151 terminating in an outlet opening 153 which is coaxial with opening 149 and with the axis of the shell 103. The end portions of the tubes defining openings 149 and 153 may be used as jig and fixture means for the swaging of the ends of the shell 103 into the bushings 105 and 107, the shell being reduced in diameter into tight contact with the ends of the tubes so that the tubes and shell can be spotwelded together as indicated. The bushings can be offset or angled as in FIGS. 1-2, if desired.
The partitions divide the interior of shell 103 into a series of longitudinally adjacent chambers. Thus, partition 115 and the inlet end 155 of shell 103 form a chamber 157; partitions 115 and 117 form a chamber 159; partitions 117 and 119 form a chamber 161; and partition 119 and the outlet end 163 of the shell form a chamber 165. Tubes 139 and 145 project about halfway into the chambers 159 and 161, respectively. Tube 141 is preferably perforated along its entire length so that there is communication between the inside of the tube and chambers 159 and 161.
In operation, an exhaust pipe (not shown) is attached to the inlet bushing 105 to conduct exhaust gas from an internal combustion engine to the open end of inlet pipe 139. The gas flows from pipe 139 to chamber 159 where it reverses direction to flow through two holes formed by two necks 167 in partition 115 and flow to chamber 157. It reverses direction in chamber 157 and flows to chamber 165 via intermediate tube 141. The gas reverses direction in chamber 165 and flows through gas passage means in the form of two holes (not shown) in partition 119 formed by necks similar to necks 167 and flow into chamber 161. From there it reverses direction to flow out of the muffler via the outlet tube 143. The perforations in tube 141 permit cross bleeding from chamber 159 into the tube and from the tube into chamber 161 thereby tending to reduce back pressure.
The three tube arrangement is known to produce very effective silencing and the shape and size of end chambers 157 and 165 is thought to increase the usual attenuation.
It will be seen that the shells 3 and 103 with, if desired, offset bushings, are very compact. The shell is monolithic or one piece with no seams and is therefore particularly strong and corrosion resistant. The internal structure provides a high degree of attenuation over a wide range of frequencies. Modifications in the specific details shown may be made without departing from the spirit and scope of the invention.