FR2819550A1 - Exhaust silencer for motorcycles comprises casing enclosing expansion chamber containing catalyst, partition dividing chamber into sections upstream and downstream from catalyst which has flange welded to internal surface of casing - Google Patents

Abstract

The exhaust silencer comprises a cylindrical casing (24) enclosing an expansion chamber (25) which contains a catalyst (72). A partition (53) divides the chamber into sections upstream and downstream from the catalyst. This has a flange (56) which is welded to the internal surface of the casing.

Description

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 The present invention relates to an exhaust silencer comprising a catalyst placed in an expansion chamber intended to allow the passage of exhaust gases so that they are purified by the catalyst, and more specifically it relates to a construction for connecting the components of the exhaust silencer.

 Document JP-A-5-187 217 describes a conventional exhaust silencer of this type.

 According to the aforementioned document, the exhaust silencer is intended to reduce the exhaust noise produced by the exhaust gases discharged by an internal combustion engine, and it comprises a shell-shaped member whose interior space is used as an expansion chamber intended to allow the passage of exhaust gases, a catalyst placed in the expansion chamber, and partition walls arranged in the expansion chamber and intended to partition the latter into upstream and downstream chambers of catalyst . The partition walls each have a main partition body which extends transversely to the expansion chamber and a cylindrical flange formed at an outer circumferential edge portion of the main body of the partition wall.

The outer circumferential surface of the flange is connected to the inner surface of the shell-shaped member by plug welding in a welding operation from the outside.

 When the internal combustion engine which has the exhaust silencer is in operation, the exhaust gases evacuated by the engine pass into the expansion chamber of the silencer and are evacuated to the atmosphere. When passing through the expansion chamber, the exhaust gases first penetrate upstream of the expansion chamber, which is upstream of the catalyst, then pass through the catalyst and downstream of the expansion chamber which is downstream of the catalyst. When passing through the expansion chamber, the exhaust gases

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 repeat a rebound and a contraction, and the vibration energy of the exhaust gases is attenuated by this repetition of a rebound and a contraction, so that the exhaust noise is reduced. The exhaust gases are then discharged to the atmosphere.

 During the passage through the catalyst, the exhaust gases are purified by chemical adsorption reactions on the catalyst, so that the exhaust gases then purified are evacuated to the atmosphere.

 In the conventional exhaust silencer described above, the locations at which the external circumferential surfaces of the flanges of the partition walls are connected to the internal surface of the shell-shaped member are located in the expansion chamber which constitutes the space internal of the shell-shaped organ, and the expansion chamber is a narrow space.

 Consequently, when it is wished to weld the external circumferential surfaces of the flanges to the internal surface of the shell-shaped member in its circumferential direction using the expansion chamber used as space for welding, it is found that this welding operation is extremely delicate.

 Plug welding is adopted for the solution of this problem, and it requires an operation from outside the shell-shaped member. However, this plug welding is intermittent welding and consequently, it risks producing a space between the internal surface of the shell-shaped member and the external circumferential surfaces of the flanges at locations on the circumference of each flange.

 Thus, as described above, in the case where the exhaust gases flow into the expansion chamber of the exhaust silencer, when the exhaust gases penetrate from the upstream side of the expansion chamber which is upstream of the catalyst, some of the exhaust gases may pass bypass around

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 of the catalyst and enter the downstream side of the muffler, downstream of the catalyst, through these spaces, following a shortcut. If there is thus a shortcut for the circulation of the exhaust gases in this way, the exhaust gases are evacuated to the atmosphere without being purified by the catalyst, in a manner which is obviously not desirable.

 The invention has been carried out taking into account the preceding situations, and its object is to allow the evacuation of purified exhaust gases which are cleaner to the atmosphere, since the exhaust gases are only evacuated to the atmosphere. after passing through an expansion chamber of an exhaust silencer, all the exhaust gases being purified by a catalyst placed in the expansion chamber.

 The object of the invention is also to facilitate the manufacture of an exhaust silencer produced as indicated above, even when access to the silencer is difficult.

 To this end, the invention relates to a muffler comprising: an envelope member whose internal space is used as an expansion chamber intended to allow the passage of exhaust gas, a catalyst placed in the expansion, and a partition wall placed in the expansion chamber and intended to partition the expansion chamber into upstream and downstream chambers relative to the catalyst, the partition wall comprising a main partition wall body intended to extend transversely to the expansion chamber and a cylindrical flange formed along a part of the external circumferential edge of the main body of the partition wall, and the external circumferential surface of the flange being connected to an internal surface of the casing member, and the outer circumferential surface of the flange is

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 firmly attached to the inner surface of the casing member around the entire circumference of the flange.

 In addition, in the aforementioned exhaust silencer, the outer circumferential surface of the flange is welded to the inner circumferential surface of the shell-shaped member over its entire circumference, by projection of the laser beam.

 In addition, in the exhaust silencer, the laser beam is projected from outside the shell-shaped member.

 Other characteristics and advantages of the invention will be better understood on reading the description which follows of exemplary embodiments, made with reference to the attached drawings in which: FIG. 1 is an enlarged partial section of a silent pot exhaust of the motorcycle shown in Figure 2; Figure la is an enlargement of the circled part of Figure 1; Figure 2 is a side elevational view of a motorcycle; Figure 3 is a side elevational view, in partial longitudinal section, along line 3-3 of Figure 1; Figure 4 is a section along line 4-4 of Figure 1; Figure 5 is a rear view of a muffler; and Figure 6 is an exploded view of Figure 4.

 Reference is made to FIG. 2 in which the reference 1 designates a motorcycle of the type of a scooter provided with a saddle. The reference Fr designates the front.

 The motorcycle 1 has a chassis 2 which supports the body of the motorcycle 1, a front fork 3 supported at the front end of the chassis 2 so that this front fork 3 can be steered, a front wheel 4 supported at the lower end of the front fork 3, a handlebar 5 supported at the upper end of the

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 front fork 3, a drive unit 8 supported at the bottom of an intermediate portion of the chassis 2 in the front-rear direction of the chassis 2, so that it can pivot on a support shaft 7, a rear wheel 9 supported at a rear pivoting end of the drive unit 8, a damper 10 intended to cause the support of the pivoting end of the drive unit 8 at the rear part of the chassis 2, and a sheet metal 11 supported at the rear part of the chassis 2.

 The motorcycle 1 is placed on the surface 13 of a road, on its front and rear wheels 4 and 9. The driving force of the drive unit 8 is applied to the rear wheel 9 so that the motorcycle 1 can be move.

 The drive unit 8 comprises an internal combustion engine 15 supported by the chassis 2 and forming the drive source used for the bearing, a unit 16 forming a transmission, connected to the rear part of the engine 15 in integral form so that it supports the rear wheel 9 and transmits the energy from the engine 15 to the rear wheel 9, and a unit 17 for exhausting the exhaust gases E discharged by the engine 15 to the atmosphere.

 The internal combustion engine 15 has a casing 18 pivotally supported on the chassis 2 by the support shaft 7, and a cylinder 19 protruding above the casing 18. The exhaust unit 17 comprises a metal tube 20 of exhaust which first extends downwards from the cylinder 9 then turns backwards, in a position close to a rear part of the casing 18, then rises backwards. The exhaust unit 17 further comprises an exhaust silencer 21 connected to the extension end of the exhaust pipe 20 and formed by machined sheets constituting an overall body.

 We will now describe in detail the exhaust silencer 21.

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In FIGS. 1 to 5, the muffler 21 has an outer casing 24 defining the outer contour of the muffler, an inner casing 26 which is a shell-shaped member mounted in the outer casing 24 and the internal space is used as expansion chamber 25 intended to allow the passage of exhaust gases E, a space 28 formed between the external and internal envelopes 24, 26, a support member 27 placed in space 28 and welded to the outer casing 24 as well as the inner casing 26 so that the inner casing 26 is supported on the outer casing 24, through holes 30 and 31 formed in opposite parts of the outer casing 24 and in the internal casing 26 respectively, guide conduits 32 intended to pass through the holes 30, 31 so that communication takes place between the interior and the exterior of the expansion chamber 25, and a thermal insulation material and from r Noise reduction 33 formed of glass wool and loaded into the space 28.

plaques de fermeture 40 et 41 destinées à fermer une autre extrémité (extrémité arrière) de chacun des organes cylindriques 36 et 37. L'organe cylindrique 37 de l'enveloppe interne 26 a de multiples petites ouvertures 42 formées par poinçonnage. The outer casing 24 and the inner casing 26 comprise cylindrical members 36 and 37 connected to each other on the same axis 35, plates 38 and 39 for closing each end (the front end) of the cylindrical members 36 and 37 in the direction axial, and

closure plates 40 and 41 intended to close another end (rear end) of each of the cylindrical members 36 and 37. The cylindrical member 37 of the internal envelope 26 has multiple small openings 42 formed by punching.

 The through holes 30 and 31 are formed in the parts of the closing plates 38 and 39. The guide pipe 32 inserted in the through holes 30 and 31 is used as an inlet pipe 45. The inlet pipe 45, at the the exterior of the outer casing 24 is connected to the extension end of the exhaust pipe 20. Another end of the inlet pipe 45 opens into the expansion chamber 25 so

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 that the exhaust gases E are introduced from the internal combustion engine into the expansion chamber 25 via the exhaust manifold 20. The other end of the inlet pipe 45 protrudes into the expansion chamber 25 and is supported by the internal envelope 26 using the other support member 46.

 The through holes 30 and 31 are formed in the other closure plates 40 and 41. The guide pipe 32 inserted in the through holes 30 and 31 is used as an outlet pipe 47. One end of the outlet pipe 47 in the axial direction opens into the expansion chamber 25, while the other end of the outlet pipe 47 opens to the outside of the external envelope 24 towards the atmosphere, and thus evacuates the exhaust gases E from the expansion chamber 25 towards the outside of the expansion chamber 25.

 The edges of the two through holes 30 and 31 are formed at a distance in an axial direction on each of the inlet pipes 45 and outlet 47, used as guide pipe 32. A portion 28a of the space 28 is placed between the front edges of the two through holes 30 and 31. The thickness of the part 28a of the space 28 is practically equal to the thickness of the other part of this space 28. The thermal insulation member 33 intended to reduce the noise is locked in part 28a.

 The total circumference of the edge of each through hole 30, formed in the closing plates 38 and 40 of the outer casing 24, is welded to the outer surface of an intermediate part of the guide pipe 32 in the longitudinal direction.

 The edge of each through hole 31 of each of the closure plates 39 and 41 of the inner casing 26 is connected to the outer surface of the intermediate part of the guide pipe 32 in the length direction. Although the above-mentioned connected parts are not welded, the connected parts can be welded at their circumference.

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Several partition walls 53 intended to partition the expansion chamber 25 into sectioned chambers 49 to 52, from first to fourth, are arranged in the axial direction of the exhaust silencer 21 in the direction of the axis 35. Each of the partition walls 53 has a main body 55 of partition wall placed in the expansion chamber 25 transversely, practically on the axis 35, and in the form of a disc practically. In addition, the partition wall 53 has a cylindrical flange 56 forming an outer periphery of the partition walls 53, formed in one piece along the outer periphery of the main body 55 of the partition wall and extending over a small distance in the axial direction. The external surface of the flange 56 is connected to the internal surface of the internal envelope 26 to be welded to this internal envelope 26.

 The first to fourth sectioned chambers 49 to 52 are arranged in this order in the direction from the inlet pipe 45 of the exhaust silencer 21 towards the outlet pipe 47. One end of the inlet pipe 45 opens out into the first partitioned chamber 49. A first communication line 58 is arranged so that it enters each of the partition walls 53, and is welded so that it is supported by the partition walls 53 and allows the communication of the first chamber partitioned 49 with the fourth partitioned chamber 52. A second communication line 59 is arranged, in the same way as the first communication line 58, being supported by the partition walls 53 so that the fourth partitioned chamber 52 communicates with the third partitioned room 51.

A third communication line 60 is arranged so that, like the first communication line 38, it is supported by the partition walls 53 and allows the third partitioned chamber 51 to communicate with the second partitioned chamber 50. A

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 end of the outlet pipe 47 in the axial direction opens into the second partitioned chamber 50.

 As indicated in the drawings, the outer casing 24 and the inner casing 26 are sectioned into two members 64 and 65 in the form of halves, each having a semicircular shape in section, so that an imaginary flat surface 63 which extends in the axial direction of the cylindrical members 36 and 37 and passes through the axis 35 which corresponds practically to the central position of the expansion chamber 25 is fixed as a limit. A sectioned end 64a of the casing 24 and a sectioned end 65a of the inner casing 26, which are opposite, are separated from each other in the direction of the imaginary flat surface 63. Another part 28b of the space 28 is formed between the two severed ends 64a and 65a. The thermal insulation member 33 which reduces noise is also enclosed in part 28b.

 The two opposite sectioned ends 64a of the two members 64 of the outer casing 24 are connected and welded to each other. The two opposite sectioned ends 65a of the two members 65 of the internal envelope 26 are superimposed and welded.

 Referring now to Figures 1,3 and 4 the support member 27 is placed in the vicinity of the flange 56 which constitutes the outer periphery of the partition wall 53, in the direction of the surface of the inner wall 26, more precisely in the axial direction of the cylindrical member 37 of the internal envelope 26 in the direction of the axis 35.

 The support member 27 occupies an offset position closer to one end (rear) among the two ends of the exhaust silencer 21 in the axial direction of the cylindrical members 36 and 37.

 As indicated in FIGS. 1, 3, 4 and 6, the thermal insulation member 33 intended to reduce noise is sectioned in the form of a first member 68 adjacent to the rear end and other members 69 and

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 70 adjacent to the other end (front) in the axial direction of the cylindrical members 36 and 37, so that the support member 27 is fixed at the limit. In addition, the other members 69 and 70 are sectioned in the second member 69 placed between each member 64 forming a half (straight half 64 in FIG. 6) among the two members 64 of the external envelope 24 and the member 65 forming one half of the internal envelope 26 and which is inserted in the member 64. In addition, the other members 69 and 70 include the third member 70 inserted in the member 64 forming the other half (left half 64 in the figure 6) of the outer casing 24 and into the member 65 forming a half of the inner member 26 which is inserted into the member 64 forming the half. Thus, the thermal insulation member 33 intended to reduce noise is sectioned in the form of three members 68 to 70, from a first to a third.

 In FIGS. 1, 3 and 4, the exhaust silencer 21 includes a catalyst 72 placed in the expansion chamber 25. The catalyst 72 is placed in the axial (longitudinal) direction of the inlet pipe 45 in the chamber expansion valve 25, so that the catalyst 72 is turned towards the opening of the inlet pipe 45. In addition, the catalyst 72 is mounted in a first connection pipe 58 and is supported on the internal wall 26 by the intermediate this connecting pipe 58 and the aforementioned respective walls 53 of partitioning.

 The catalyst 72 is a so-called "triple" catalyst and it promotes reactions on the surface of the catalyst 72 by chemical adsorption reactions, so that the exhaust gases E circulating in the passage of the first connection pipe 58 are purified by passage through the catalyst. It should be noted that, although the catalyst 72 is supported directly on the first connecting pipe 58, it can also be supported directly by the partition walls 53.

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In FIG. 1, the external circumferential surface of the partition wall 53 (A) of the respective partition walls 53 which divide the expansion chamber 25 into an upstream side (first partitioned chamber 49) which is upstream of the catalyst 72 and a downstream side (second to fourth partitioned chambers 50 to 52) which is downstream of the catalyst 72, is firmly fixed to an internal surface of the internal envelope over the entire circumference.

 More specifically, the external circumferential surface of the flange 56 of the partition wall 53 (A) is welded to the internal circumferential surface of the internal envelope 26 by welding with a laser beam 73a projected by an apparatus 73 for projecting a beam laser, so that, as described below, the flange 56 is firmly fixed to the inner casing 26 over the entire outer circumference of the flange 56. In this case, the laser beam 73a is projected from outside the inner casing 26.

 In FIGS. 1 to 3, a metal thermal insulation member 74 is arranged so that it covers an edge of the through hole 31 formed in the closing plate 41 of the internal envelope 26 so that the outlet pipe 47 can pass from the interior of the fourth partitioned chamber 52 of the expansion chamber 25, and the thermal insulation member 74 is supported by the outlet pipe 47.

 In addition, a protective member 75 comprising a metal pipe is placed on the outer casing 24 so that it completely covers, from the outside of the projecting pipe, a part of the downstream side of the outlet pipe 47 which protrudes outside the outer casing 24. The protective member 75 covers an outer surface with a through hole edge 30 at its base portion and is welded to an outer surface of the closure plate 40 of the outer envelope 24 at the same part.

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The method of forming the exhaust silencer 21 will now be described.

 We refer to Figure 6; the inlet pipe 45 and the other support member 46 are welded to each other. The outlet pipe 47, the communication pipes 58 to 60 and the partition walls 53 are welded to each other. In addition, the members 64 and 65 forming the halves of the outer casing 24 and the inner casing 26 are produced.

 Then, the inlet pipe 45, the other support member 46, the outlet pipe 47, the communication pipes 58 to 60 and the partition walls 53 are surrounded by the two members 65 in the form of halves. The cylindrical member 37 of the internal envelope 26, the other support member 46 and the flange 56 of each of the partition walls 53 are welded in a plug from the outside. The two opposite sectioned ends 65a of the two members 65 forming the halves of the outer casing 26 are connected and welded to each other. In this case, a semicircle of each through hole 31 is formed in each member 65. As the two members 65 forming the halves surround the aforementioned elements, the inlet pipe 45 and the outlet pipe 47 are brought into a state in which the inlet pipe 45 and the outlet pipe 47 are inserted into each through hole 31 (see FIG. 6).

 In this case, the plug welding of the cylindrical member 37 on the flange 56 of the partition wall 53 (A) is intended for temporary welding of the elements, and, after this temporary plug welding, the cylindrical member 37 and the partition wall 53 (A) are finally welded by the laser beam 73a projected by the apparatus 73.

 The support member 27 is then welded to the external surface of each member 65 forming one half of the internal envelope 26. Next, the thermal insulation member 33 intended to reduce noise is placed between the

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 outer surface of each member 65 of the inner casing 26 and each member 64 of the outer casing 24 which covers the member 65. Each member 64 is intended to cover a member 65. The two opposite sectioned ends 64a of the two members 64 forming the halves of the outer casing 24 are connected and welded to each other. In this case, a semicircle of the through hole 30 is formed in the plate 38 for closing each member 64. As the two members 64 cover the member 65, the inlet pipe 45 is put in a state in which this pipe 45 is inserted into the through hole 30. The inserted part of the inlet pipe 45 is welded. On the other hand, the through hole 30 is formed in the two members 64. This hole 30 and the outlet pipe 47 are brought into cooperation before the covering of the member 65. The engaged part is welded, while the protective member 75 is welded to each member 64.

 The formation of the exhaust silencer 21 is thus completed.

 We refer again to FIG. 1; when the internal combustion engine 15 is running, the exhaust gases E discharged from the engine 15 can first pass through the inlet pipe 45 and then into the first partitioned chamber 49. Then, the exhaust gases E circulate in the first communication line 58, the fourth partitioned chamber 52, the second communication line 59, the third partitioned chamber 51, the third communication line 60 and the second partitioned chamber 50, in that order.

 During the circulation of the exhaust gases E in the exhaust silencer 21, these exhaust gases E rapidly and repeatedly undergo expansion and contraction. The vibration energy of the exhaust gases E is attenuated by the actions of the space 28 placed between the external envelope 24 and the internal envelope 26, small openings 42 and the thermal insulation member 33, which reduces the

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 noise. The vibration energy can then pass through the outlet pipe 47, to be evacuated towards the outside of the exhaust silencer 21.

 Consequently, the exhaust gases E undergo a noise reduction due to the previous actions in the exhaust silencer 21 and are evacuated to the atmosphere.

 The exhaust gases E have a high temperature.

In particular, since the catalyst 72 for purifying the exhaust gases E by chemical adsorption reactions is located in the expansion chamber 25, the reactions with the catalyst 72 cause a further rise in the temperature of the exhaust gases E .

 Although the heat of the exhaust gases E at high temperature in the expansion chamber 25 is transmitted to the external surface of the external casing 24 by the internal casing 26, the heat transmission is prevented by the thermal insulation 33 intended to reduce noise.

 Consequently, the change in coloration of the external surface of the external envelope 24 under the action of the high temperatures of the exhaust gases E can be avoided.

 Furthermore, as described above, the external circumferential surface of the flange 56 of the partition wall 53 (A) is firmly fixed to the internal surface of the internal casing 26 over the entire circumference of the flange 56.

 In this construction, in the case where the exhaust gases E pass into the expansion chamber 25 formed in the exhaust silencer 21, when the exhaust gases E penetrate from the upstream side of the expansion chamber 25 which is upstream of the catalyst 72, these exhaust gases E, even in part, cannot penetrate downstream of the expansion chamber 25 which is downstream of the catalyst through the space between the internal circumferential surface of the internal envelope 26 and the outer circumferential surface of the flange 56, so

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 that all the exhaust gases E pass well through the catalyst 72 placed in the expansion chamber 25.

 Consequently, since all the exhaust gases E are safely purified by the catalyst 72, the exhaust gases are discharged into the atmosphere in a purified state.

 In addition, as described above, the external circumferential surface of the flange 56 is welded to the internal circumferential surface of the internal envelope 26 over its entire circumference, by projection of the laser beam 73a by the apparatus 73 over the entire circumference of the flange 56 .

 As this arrangement ensures a robust fixing of the external circumferential surface of the flange 56 to the internal circumferential surface of the internal envelope 26 in a certain manner, all the exhaust gases E pass through the catalyst 72 in the same way.

 Consequently, since all the exhaust gases E are certainly purified by the catalyst 72, they are evacuated to the atmosphere in a very clean state.

 In addition, as described above, the laser beam 73a is intended to be projected from the outside of the internal envelope 26.

 This arrangement allows the flange 56 to be welded to the internal casing 26 with a wide space formed outside the internal casing 26, and it is therefore not necessary to use a narrow space inside the relaxation room 25.

 Consequently, even if the exhaust silencer is made so that it evacuates highly purified exhaust gases to the atmosphere as described above, the manufacture of the exhaust silencer having this construction can be easy.

 It should be noted that, although the exhaust silencer has been described with the aforementioned construction, it may not include the outer casing 24. In addition, no plug welding is necessary between

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 the internal envelope 26 and the partition wall 53 (A).

 In addition, the other support members 46 and the partition walls 53 other than the wall 53 (A) can be welded to the internal casing 26 by the laser beam 73a, as can the partition wall (53 (A) .

 The structure produced according to the invention has the following effects.

 In the first aspect of the invention, the exhaust silencer comprises a member forming an envelope whose internal space is used as an expansion chamber allowing the passage of exhaust gases, a catalyst is placed in the expansion chamber , and the partition walls are placed in the expansion chamber so that they partition the latter into chambers placed upstream and downstream of the catalyst respectively, the partition walls each comprising a main partition wall body intended for s' extend transversely to the expansion chamber and a cylindrical flange formed along an outer circumferential edge of the main body of the partition wall, so that the outer circumferential surface of the flange can be connected to the inner surface of the member casing and the outer circumferential surface of the flange is firmly attached to the inner surface of the casing member over the entire cir flask conference.

 Thanks to this construction, when exhaust gases flow into the expansion chamber of the exhaust silencer, and the gases penetrate on the upstream side of the expansion chamber which is upstream of the catalyst, the exhaust cannot penetrate, even partially, on the downstream side of the expansion chamber, downstream of the catalyst, by passage between the internal circumferential surface of the internal casing and the external circumferential surface of the flange, so that it is certain that all exhaust

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 pass through the catalyst placed in the expansion chamber.

 Consequently, since all the exhaust gases are certainly purified by the catalyst, the exhaust gases discharged into the atmosphere are very purified.

 Furthermore, as described above, the external circumferential surface of the flange is welded to the internal circumferential surface of the internal envelope over its entire circumference by projection of a laser beam from an apparatus suitable for the complete circumference of the flange.

 As this operation firmly fixes the outer circumferential surface of the flange to the inner circumferential surface of the inner casing with certainty, all the exhaust gases pass in the same way through the catalyst.

 Consequently, since all the exhaust gases E are definitely purified by the catalyst, the exhaust gases discharged into the atmosphere are very purified.

 In addition, as described above, the laser beam can be projected from the outside of the outer envelope.

 This arrangement allows the welding of the flange on the internal envelope in the wide space formed outside the internal envelope, so that it is not necessary to use the narrow space formed inside from the relaxation room.

 Consequently, even if the exhaust silencer is made for the discharge of purified exhaust gases into the atmosphere as described above, the manufacture of the exhaust silencer can be easy thanks to this construction.

 Of course, various modifications can be made by those skilled in the art to the pots which have just been described solely by way of nonlimiting example without departing from the scope of the invention.

Claims (3)

 CLAIMS 1. Exhaust silencer, characterized in that it comprises: a casing member (24, 26) whose internal space is used as an expansion chamber (25) intended to allow the passage of gas from exhaust, a catalyst (72) placed in the expansion chamber (25), and a partition wall (53) placed in the expansion chamber (25) and intended to partition the expansion chamber (25) into upstream and downstream chambers with respect to the catalyst, the partition wall comprising: a main body (55) of partition wall intended to extend transversely to the expansion chamber (25), and a cylindrical flange (56) formed along a part outer circumferential edge of the main body of the partition wall, and in that the outer circumferential surface of the flange (56) is connected to an inner surface of the casing member (24,26), and the outer circumferential surface flange (56) is firmly attached to the internal surface of the casing member (24, 26) over the entire circumference of the flange.  2. muffler according to claim 1, characterized in that the outer circumferential surface of the flange (56) is welded to the inner circumferential surface of the casing member (24,26) over its entire circumference by projection a laser beam (73a).  3. Exhaust silencer according to claim 1, characterized in that the laser beam (73a) is projected from outside the envelope member (24,26).