GB2343716A

GB2343716A - 0ne-chamber expansion-type exhaust silencer

Info

Publication number: GB2343716A
Application number: GB9926233A
Authority: GB
Inventors: Keiji Terada; Masato Iwata
Original assignee: Yutaka Giken Co Ltd
Current assignee: Yutaka Giken Co Ltd
Priority date: 1998-11-13
Filing date: 1999-11-08
Publication date: 2000-05-17
Anticipated expiration: 2019-11-08
Also published as: GB9926233D0; DE19953307A1; JP4098421B2; GB2343716B; JP2000145428A

Abstract

To improve the strength and the rigidity of a one chamber expansion type exhaust silencer, a supporting member 5 with a through hole 4 having an area of more than 1.5 times that of the cross-section of inlet pipe 2 is arranged into a shell 1 both end portions of which are closed by end plates 1a, 1b. The upstream end of inlet pipe 2 is fixed to end plate 1a, while the other end is fixed to supporting member 5. One end portion of outlet pipe 3, which may be formed into a U-shape, is fixed to supporting member 5, while the other end is fixed to end plate 1b. End plate 1b may have two walls 1c, 1d, the latter being punched with many holes and the space between them being filled with glass wool 6. Two supporting members 5 may be provided (fig.4). A partition 7 (figs. 5,7) may be provided to form, with end plate 1b, a resonance chamber 8 in communication with the inlet pipe. A straight-through silencer (12,fig.8) may be provided upstream of the expansion silencer. The area of through hole 4 being more than 1.5 times that of the cross-section of inlet pipe 2 enables the inside of shell 1 to function as one chamber, so that the deadening of sound in the low frequency zone can be made.

Description

AN EXHAUST SILENCER BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a one chamber expansion type of exhaust silencer, in particular to an exhaust silencer in which it is realized to increase the rigidity of a shell forming an exhaust silencer and to reasonably support a pipe connected with the shell.

2. Description of the Prior Art In an exhaust silencer for deadening exhaust sound of engine, as shown in Fig. 11, threshold frequency for effective silencing is set by applying a volume V per a chamber of silencer, a length Ll of inlet pipe, a length L2 of outlet pipe, a crosssectional area Sl of an inlet pipe, and a cross-sectional area S2 of an outlet pipe.

Accordingly, to increase volume V per a chamber of silencer makes possible to increase a length L2 of outlet pipe, by which exhaust sound of low frequency zone can be effectively deadened.

A one chamber expansion type of exhaust silencer 50 shown in Fig. 12 comprises a tube-shaped shell 51, an inlet pipe 52 arranged on the side of engine, and an outlet pipe 53 arranged on the side of the air, in which pipes 52,53 pass through end plates 51a covering both ends of a shell 51 and are fixed to the end plates 51a by means of welding and the like, respectively. In the exhaust silencer 50, a volume V of shell 51 which is made of one chamber can be increased, by which exhaust sound including low frequency zone can be effectively deadened. Further since exhaust gas introduced from inlet pipe 52 to shell 51 expands in the shell 51 and is exhausted through outlet pipe 53, the channel resistance of exhaust gas is decreased, by which the back pressure of engine can be decreased to improve the output of engine.

The above-mentioned exhaust silencer 50 has the advantage of having the silencing characteristic in wide frequency zone. On the other hand, the exhaust silencer has problems that since each pipe 52,53 is fixed only at one point to end plate 51a of shell 51, the strength and the rigidity of holding portions of the respective pipes 52,53 are small so that the exhaust silencer is worse in the durability, that since shell 51 is made of one chamber, the rigidity of tubular body forming the shell 51 is decreased so that the shell is apt to resonate, and that the thermal deformation of a member arranged on the inside of the shell is large.

A multistage expansion type of exhaust silencer 60 shown in Fig. 13 comprises a tube-shaped shell 61, an inlet pipe 62 arranged on the side of engine, an outlet pipe 63 arranged on the side of the air, separators 64,65 dividing the inside of the shell 61 into a plurality of chambers, and a pipe 66 for communicating the individual chambers with each other, in which pipes 62,63,66 are fixed to end plates 61a of shell 61 and separators 64,65, by means of welding and the like, respectively. In the exhaust silencer 60, since pipes 62,63,66 are fixed to two points of end plates 61a and separators 64,65, respectively, the strength and the rigidity of holding portions of pipes 62,63,66 are increased to improve the durability, the shell 61 is strengthened by separators 64,65 to not resonate, and further the thermal deformation of a member arranged on the inside of the shell is decreased.

The above-mentioned exhaust silencer 60 has the advantage of having the high strength and the durability. However, the exhaust silencer 60 has the problem that a volume per one chamber thereof is smaller than that of a one chamber expansion type of exhaust silencer 50, so that the silencing characteristic in the low frequency zone becomes worse. Particularly, for improving the silencing characteristic in the low frequency zone, it becomes necessary to increase a volume of expansion chamber so that the exhaust silencer 60 becomes large-sized.

As above-mentioned, a one exhaust expansion type of exhaust silencer has the advantage of having the preferable frequency characteristic on deadening exhaust sound. However, it has the problem that it is not preferable about the strength and the rigidity thereof. A multistage expansion type of exhaust silencer has the preferable properties of the strength and the rigidity. However, it has the problem that the silencing characteristic in the low frequency zone becomes worse.

BREF SUMMARY OF INVENTION It is one object of the invention to provide a one chamber expansion type of exhaust silencer in which while the silencing characteristic in the low frequency zone is kept, the strength and the rigidity is improved.

Inventors have known, from the results of various experiments made in order to solve the above-mentioned problem, that in order to improve the strength and the rigidity of holding portions of an inlet pipe and an outlet pipe to a shell in a one chamber expansion type of exhaust silencer, these pipes are preferably fixed at two points of an end plate and a portion other than the end plate, respectively, that in order to improve the rigidity of shell, the rigidity can be improved by increasing the thickness of material for a tubular body forming the shell or by providing a member brought into contact with shell inside the shell, and that in order to prevent excessive thermal expansion and thermal deformation of internal member of shell, it is necessary to arrange a member for constraining the internal member of shell in such an extent that the thermal expansion and thermal deformation thereof can be prevented.

Further, as to a member brought into contact with shell, a member brought into contact with an outer surface of the shell and a member brought into contact with an inner surface of the shell are thought. However, considering the support and fixing of the respective pipes and the prevention of the internal member of shell from thermally expanding and others, it is preferable that the above-mentioned member brought into contact with shell has a shape which is nearly equal to the cross-sectional shape, and is a supporting member which is able to support free ends of the respective pipes.

When the above-mentioned member brought into contact with shell is arranged on the inside of the shell, the rigidity and the strength of shell and each pipe can be improved. However, there is a fear that the function of a one chamber expansion type of exhaust silencer is lost. Therefore, an experiment was made on whether the inside of a shell can be fulfilled as one chamber, by forming the above-mentioned supporting member with a through hole for letting exhaust gas pass.

Fig. 9 is a schematic view for explaining an equipment for the above mentioned experiment, and Fig. 10 is a graph showing experimental results on measurement of the silencing level. In the experiment, an inlet pipe 2 and an outlet pipe 3 were arranged inside a shell 1, and a various supporting member 5 formed with a through hole 4 having an area of 0.5 to 3.0 times as large as the cross-sectional area of inlet pipe 2, respectively, were altematively attached. While a sound was produced from a speaker 71 disposed at the side of an inlet of inlet pipe 2, inlet sound pressure was measured through a microphone 72 provided on inlet pipe 2, and outlet sound pressure was measured through a microphone 73 disposed on the side of an outlet of outlet pipe 3, by which differences between both measurements were determined.

From the above-mentioned experimental result, it was seen that when the area of through hole 4 formed in supporting member 5 being 0.5 to 1.5 times of the crosssectional area of inlet pipe 2, the silencing level is drastically improved, but at 0.5 times, the silencing level is supersaturated, further, in 1.5 to 3.0 times, the silencing level is nearly constant in which great improvement is not found. Namely, even in case of a supporting member 5 having the same shape as that of the inside of shell 1, by forming the supporting member 5 with a through hole having an area of more than 1.5 times of the cross-sectional area of inlet pipe 2, the exhaust silencer can be fulfilled as a one chamber expansion type of exhaust silencer, notwithstanding that the rigidity of shell 1 can be improved and besides the strength and the rigidity of holding portions of each pipe 2,3.

Accordingly, the exhaust silencer according to this invention is characterized in that in a silencer having a shell and an inlet pipe for introducing exhaust gas into the shell, and an outlet pipe for exhausting exhaust gas from the shell, a supporting member is arranged inside the shell, wherein the outer peripheral surface of the supporting member is brought into contact with the inner surface of the shell, and the supporting member is formed with supporting hole for supporting at least one of the inlet pipe and the outlet pipe and with a through hole having an area of more than 1.5 times of the cross-sectional area of the inlet pipe.

In the above-mentioned exhaust silencer, the inner surface of the shell is constrained by the outer peripheral surface of the supporting member being brought into contact with the inner surface of the shell so that the rigidity can be increased and the resonance of shell can be prevented, and further the generation of excessive thermal expansion and thermal deformation in the internal member of the shell can be prevented. Further, by holding the inlet pipe and the outlet pipe to two points of end plates of the shell and the supporting plate, both the strength and the rigidity of holding portions of these pipes can be increased.

In the above-mentioned exhaust silencer, at least one of inlet pipe and outlet pipe is preferably curved into a U-shape inside the shell. In such an exhaust silencer, a flow of exhaust gas and the silencer can be separated, by which a temperature of the silencer can be decreased, and a zone of frequency in which the deadening of sound can be possible can be widened so that the deadening of sound in the low frequency zone can be made.

Further, at least one of inlet pipe and outlet pipe is preferably formed with holes for passing exhaust gas on the side thereof directed to the inside of the shell. Further, it is preferable that the shell has end plates at both end portions thereof, at least one end plate of both the end plates is preferably comprised of acoustic material provided inside the at least one end plate and a plate formed with a plurality of small holes for securing the acoustic material. In such a exhaust silencer, an effective silencer can be formed by forming the structure in which a conventional multistage expansion type of exhaust silencer is combined with a one chamber expansion type of exhaust silencer.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings: Fig. 1 is a view for explaining the structure of an exhaust silencer according to a first embodiment of this invention; Fig. 2 is a view taken on line II-II in Fig. 1 for explaining a supporting member; Fig. 3 is a view taken on line III-III in Fig. 1 for explaining the inner surface of an end plate disposed on the back side of the exhaust silencer; Fig. 4 is a view for explaining a practical example of the exhaust silencer according to the first embodiment; Fig. 5 is a view for explaining a practical example of the structure in which the exhaust silencer according to the first embodiment is combined with a conventional silencer; Fig. 6 is a view for explaining the structure of an exhaust silencer according to a second embodiment of this invention; Fig. 7 is a view for explaining a practical example of the structure in which the exhaust silencer according to the second embodiment is combined with a conventional silencer; Fig. 8 is a view for explaining the structure of an exhaust gas silencer according to a third embodiment of this invention; Fig. 9 is a schematic view for explaining an equipment used in the silencing experiment; Fig. 10 is a graph of measured silencing level ; Fig. 11 is a view for showing an example of basic design in an exhaust silencer; Fig. 12 is a view for explaining a conventional one chamber expansion type of exhaust silencer; and Fig. 13 is a view for explaining a conventional multistage expansion type of exhaust silencer.

DETAILED DESCRIPTION Referring to Figs. 1 to 3, the structure of an exhaust silencer A according to the first embodiment is explained. The exhaust silencer A is comprised of a shell 1 having both end portions which is closed by end plates la, lb, an inlet pipe 2 for introducing exhaust gas exhausted from an engine into shell 1, an outlet pipe 3 for exhausting exhaust gas expanded inside the shell to the air, and a supporting member 5 formed with a through hole 4 having an area of more than 1.5 times of the cross-sectional area of inlet pipe 2 as shown in Fig. 2.

The shape and the volume of shell 1, the cross-sectional area of inlet pipe 2, the position of the supporting member 5 in the inside of shell 1 and others are previously determined in the stage of design according to the volume of exhaust gas and the frequency zone which is to be deadened.

The shell 1 is formed into a tube made of multilayer material by forming into a tubular shape a plate having the thickness which is previously set. End portions of the shell 1 are closed by end plates la, lb. Inlet pipe 2 passes through an end plate la, and the outlet pipe 3 passes through end plate Ib.

End plate 1b of shell 1 has a convex portion lc as a first plate, and is provided with a punching sheet ld formed with a large number of holes as a second plate on the side directed toward the inside of shell 1. A space is formed between convex portion lc and punching sheet ld, and the space is packed with glass wool 6 having the function of acoustic material. The punching sheet 1d of end plate lb is opposed to an end portion 2b of inlet pipe 2 positioned on the side of exhaust, in which since exhaust gas sent from an engine is received by glass wool 6 as acoustic material, the high effect of silencing can be shown.

By forming the end plate lb as above-mentioned, sound of exhaust at the high frequency zone can be absorbed. Further, the vibration of end plate lb can be prevented by strengthening the end plate lb with punching sheet ld.

The supporting member 5 has the shape of the outer peripheral surface which is equal to that of the inner surface of the shell 1, and a flange 5a formed along the outer periphery of the supporting member. Therefore, when the supporting member 5 is arranged inside the shell 1, the flange 5a is securely brought into contact with the inner surface of shell 1, by which the supporting member 5 can be kept at the fixed position without being moved inside the shell 1, while the rigidity of the shell can be increased and the excessive thermal expansion and thermal deformation of the internal member of shell 1 can be prevented by the supporting member constraining shell 1.

The supporting member 5 has, at a given position, a supporting hole 5b for supporting inlet pipe 2 formed into a nearly straight pipe which passes through the supporting member, a supporting hole 5c for supporting the outlet pipe 3 formed into a U-shape which passes through the supporting member, and a through hole 4 formed at a position which avoids these supporting holes Sb, 5c.

As above-mentioned, the area of through hole 4 is needed to be more than 1.5 times of the cross-sectional area of inlet pipe 2, and the upper limit of the area of the through hole 4 is such an area that the improvement in the rigidity of the shell 1 and the function of preventing the internal member of the shell 1 from being thermally expanded and deformed cannot be shown by the supporting member 5. However, as is obvious from the above-mentioned experimental results, since when the area of the through hole 4 becomes 1.5 times of the cross-sectional area of inlet pipe 2, the effect of silencing becomes saturated state, it is sufficient to be 1.5 to 3.0 times.

The inlet pipe 2 is formed as a pipe having the cross-sectional area previously determined according to the amount of exhaust of engine to which the exhaust silencer is applied. A length of the inlet pipe of from end plate la is previously set according to the low frequency zone to be deadened. An end portion of the inlet pipe 2 on the side of the upper stream seeing in the flowing direction of exhaust gas is fixed to end plate la of shell 1 by means of welding and the like. An end portion of the inlet pipe on the side of the lower stream is held by the supporting plate under the state the inlet pipe 2 passes through the supporting hole 5b of supporting plate 5, wherein the inlet pipe 2 is preferably fixed to the supporting plate 5b by means of welding and the like after inlet pipe 2 was made pass through supporting hole 5b.

Outlet pipe 3 has a portion formed into a U-shape which is inserted into the inside of the shell 1. An end portion thereof on the side of the upper stream seeing in the flowing direction of exhaust gas, which is projected from the supporting hole 5c formed in the supporting member 5, opens in the same direction as an outlet of inlet pipe 2 held by the supporting member 5. The middle portion of the portion formed into the U-shape passes through the supporting hole 5c of the supporting member 5, and is held by the supporting member 5. An end portion of the outlet pipe 3 on the side of the lower stream is fixed to the end plate lb.

In such a manner, the separation of a high temperature of exhaust gas from exhaust silencer A by forming outlet pipe 3 into a U-shape makes possible to decrease a temperature of the exhaust silencer A, by which the internal member of the shell 1 can be prevented from being excessively thermally expanded. Further, the frequency zone in which sound deadens can be more widened in such an extent that the deadening of sound in the low frequency zone can be also possible.

Inlet pipe 2, which an end portion on the side of the lower stream is held by supporting member 5, is fixed to the supporting member 5 in such a manner that the end portion is projected from a surface of the supporting member 5 by a given length.

On the other hand, an end portion of the outlet pipe 3 held by the supporting member 5 is positioned on the same surface as supporting member 5. Since the respective pipes 2, 3 are arranged in such a manner, exhaust gas introduced through the inlet pipe 2 into the shell flows in the direction shown by arrow a in the inside of the shell 1, and is exhausted through the outlet pipe 3 into the air.

A given part of the inlet pipe 2 (between a holding portion thereof held by the end plate la and another holding portion thereof held by the supporting member 5) is formed with a large number of holes 2a, so that the adjustment of flowing course of exhaust gas is possible by the formation of the holes 2a. However, the present invention is not restricted to that holes 2a are formed in the inlet pipe 2, but holes 2a may be formed on the side of the outlet pipe 3, or holes 2a may be formed in sides of the two of the inlet pipe 2 and the outlet pipe 3.

In the exhaust silencer A formed as above-mentioned, the effect of silencing in the low frequency can be expected as a one chamber expansion type of exhaust silencer, and further the strength of holding portion of the respective pipes 2,3 is improved and the rigidity thereof is increased to prevent the resonance of the shell.

Furthermore, the durability of the silencer can be improved.

Fig. 4 is a view for explaining a practical example of the above-mentioned exhaust silencer A. In the drawing, two supporting members 5 are arranged inside a shell 1, wherein an inlet pipe 2 of nearly straight pipe and an outlet pipe formed into a U-shape pass through supporting members 5 and are held by the supporting members.

In the exhaust silencer A formed as above-mentioned, it is possible that the respective pipes 2,3 are held to the supporting members with the higher holding strength and the higher rigidity is shown. Further since two supporting members 5 are provided in the silencer, the shell 1 can be firmly constrained by these supporting members so that the higher rigidity can be shown.

Fig. 5 is a view for explaining an example of type in which the abovementioned exhaust silencer A is combined with a conventional exhaust silencer. In (a) of Fig. 5, a partition plate 7 is arranged inside a shell 1 of exhaust silencer A, by which a resonance chamber 8 is formed between a partition plate 7 and an end plate lb, and the resonance chamber 8 is communicated with an end portion of an inlet pipe 2.

Further, in (b) of Fig. 5, an expansion chamber 9 is formed by arranging partition plate 7 in a shell 1 of the exhaust silencer, and a large number of holes 3a are formed on the side of an outlet pipe 3 corresponding to the expansion chamber 9.

Even in the respective exhaust silencer formed as above-mentioned, the respective exhaust silencer show advantages of a one chamber expansion type of exhaust silencer A so that the effect of silencing can be shown in the wide frequency zone.

Then, referring to Fig. 6, the structure of an exhaust silencer B according to the second example is explained. In Fig. 6, the same marks are affixed to the same parts and the same functioning parts as in the above-mentioned example, of which explanation is omitted.

In exhaust silencer B shown in (a) of Fig. 6, an outlet pipe 10 formed into a nearly straight pipe is used instead of the outlet pipe 3 formed into a U-shape in the above-mentioned exhaust silencer A. Namely the exhaust silencer B has the same structure as that of the exhaust silencer A except the outlet pipe 10.

In the exhaust pipe B, a supporting member 5 lies toward an end plate la, in which an end portion of an inlet pipe 2 and an end portion of an outlet pipe 10 pass through supporting plate 5 and are held by the supporting plate. In the exhaust silencer B formed in such a manner, exhaust gas introduced through inlet pipe 2 into the inside of shell 1 flows through a through hole 4 formed in supporting member 5 and is exhausted from the outlet pipe to the air, in the course of exhaust gas flowing in the direction shown by arrow b.

Even in the exhaust silencer B formed as above-mentioned, the exhaust silencer B shows advantages of a one chamber expansion type of exhaust silencer so that the effect of silencing can be shown in the wide frequency zone.

(b) of Fig. 6 shows a practical example of the exhaust silencer B, wherein two supporting members 5 are arranged inside a shell 1. In the exhaust silencer formed in such a manner, it is possible that the respective pipes 2,10 are held to the supporting members with the higher holding strength and the higher rigidity is shown. Further since two supporting members 5 are provided in the silencer, the shell 1 can be firmly constrained by these supporting members so that the higher rigidity can be shown.

Fig. 7 is a view for explaining a silencer in which the exhaust silencer B is combined with a conventional exhaust silencer. In (a) of Fig. 7, a partition plate 7 is arranged in a shell 1 of the exhaust silencer, by which a resonance chamber 8 is formed between the partition plate 7 and an end plate lb, and the resonance chamber 8 is communicated with end portion of inlet pipe 2. Further, in (b) of Fig. 7, an expansion chamber 9 is formed by arranging a partition plate 7 in shell 1 of the exhaust silencer, and a large number of holes 10a are formed on the side of an outlet pipe 10 corresponding to the expansion chamber 9.

Even in the respective exhaust silencer formed as above-mentioned, the respective exhaust silencers show advantages of a one chamber expansion type of exhaust silencer A so that the effect of silencing can be shown in the wide frequency zone.

Fig. 8 is a view for explaining the structure of an exhaust silencer C according to the third example of the present invention. In Fig. 8, the same marks are affixed to the same parts and the same functioning parts as in the above-mentioned example, of which explanation is omitted.

In Fig. 8, in the exhaust silencer C, an inlet pipe 11 is curved into a U-shape.

The inlet pipe 11 passes through an end plate la and extends to a supporting member 5.

Further, the inlet pipe passes through the supporting member 5, thereafter, the top of the inlet pipe formed into a U-shape is held by the supporting member 5. Further, an outlet pipe 10 is formed into a straight pipe in such a manner as in the second example, wherein an end thereof is held by supporting member 5, while a given portion on the side of another end of the outlet pie 10 is held by an end plate lb.

A chamber 12 is mounted around a portion of the inlet pipe 11 on the side of the upper stream seeing in the direction of exhaust gas, and a portion of inlet pipe 11 corresponding to the chamber 12 is provided with a large number of holes 12a.

Therefore, the function of silencing at the first stage against exhaust gas exhausted from an engine can be shown by chamber 12.

In the exhaust silencer C formed as above-mentioned, a length of the inlet pipe (LI shown in Fig. 11) can be increased. Therefore, the effect of silencing in the low frequency zone can be expected as a one chamber expansion type of exhaust silencer by appropriately setting the threshold frequency for effective silencing. Further, the strength of holding portion of the respective pipes 11,10 is improved and the rigidity thereof is increased to prevent the resonance of the shell. Furthermore, the durability of the silencer can be improved.

Further, inlet pipe 11 of the exhaust silencer C acts as the outlet pipe of chamber 12, by which it becomes possible to appropriately set the threshold frequency for effective silencing.

As above-mentioned in detail, in an exhaust silencer according to the present invention, since a supporting member, which is formed with a through hole having an area of more than 1.5 times of the cross-sectional area of an inlet pipe, is arranged in a shell, an end portion of the inlet pipe and an end portion of an outlet pipe are held by the supporting member, and the outer peripheral surface of the supporting member is brought into contact with the inner surface of the shell, the strength of holding portions of the respective pipes and the rigidity thereof can be improved, by which the rigidity of the shell can be increased by constraining the shell by the supporting member so that the resonance of the shell can be prevented and the shell can be prevented from excessively thermally expanded and deformed.

In particular, by forming the supporting member with a through hole, notwithstanding the existence of the supporting member inside the shell, the exhaust silencer of the present invention can act as a one chamber expansion type of exhaust silencer. Therefore, the effect of silencing in the low frequency zone can be shown.

Further, since the exhaust silencer of the present invention can be operated as a one chamber expansion type of exhaust silencer, comparing the exhaust silencer of the present invention with a multistage expansion type of exhaust silencer, supposing that both the silencers have the same volume, the resistance of flowing course of exhaust gas can be sharply reduced so that the performance of output of engine can be improved. Further, when both the silencers have the same resistance of flowing course of exhaust gas, each pipe can be sharply reduced in size, and the amount of damping can be improved. Further when both the silencers have the same amount of damping, each pipe can be sharply reduced in size, and the volume of the shell can be sharply reduced to be small-sized and to make light-weight.

Claims

What is claimed is: 1. An exhaust silencer comprising: a shell; an inlet pipe for introducing exhaust gas into said gas; an outlet pipe for exhausting exhaust gas from the shell; and a supporting member arranged into said shell in such a manner that the outer peripheral surface of the supporting member is brought into contact with the inner surface of said shell, wherein said supporting member has a supporting hole for supporting at least one of the inlet pipe or the outlet pipe and a through hole with an area of more than 1.5 times of the cross-sectional area of the inlet pipe.
2. An exhaust silencer as claimed in claim 1, wherein at least one pipe of the inlet pipe and the outlet pipe is curved into a U-shape.
3. An exhaust silencer as claimed in claim 2, wherein the at least one of the inlet pipe and the outlet pipe is formed with a plurality of small holes in the side of a portion of the at least one pipe disposed inside the shell.
4. An exhaust silencer as claimed in claim 3, wherein the at least one of the inlet pipe and the outlet pipe is curved into a U-shape.
5. An exhaust silencer as claimed in claim 1, wherein the at least one plate of both end plates provided at both end portions of the shell is composed of a first plate forming an outer surface of the at least one plate and a second plate with a plurality of small holes forming an inner surface of the at least one plate, and acoustic material is provided between the first plate and the second plate.
6. An exhaust silencer as claimed in claim 5, wherein the plate composed of the first plate and the second plate is opposed to an end portion of the inlet pipe.