JP7293690B2 - silencer - Google Patents

Description

The present invention relates to a silencer.

2. Description of the Related Art Conventionally, in a vehicle internal combustion engine, a structure has been proposed in which exhaust gas is discharged to the outside through a muffler (see, for example, Patent Document 1). In Patent Document 1, the internal space of a muffler as a silencer is partitioned into a plurality of expansion chambers by a plurality of partition walls. The expansion chambers are communicated with each other by pipes (communication pipes). As a result, the exhaust gas is repeatedly expanded and contracted by flowing through each expansion chamber, and noise is reduced.

Japanese Patent No. 5922334

However, in Patent Literature 1, repeated expansion and contraction of the exhaust gas causes a large pressure loss, resulting in a decrease in engine output. Thus, it has been known that there is a trade-off between the muffler's muffler performance and output improvement effect, and it is difficult to achieve both at the same time.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a noise reduction device capable of achieving both an excellent noise reduction effect and an improved output with a simple configuration.

A muffler according to one aspect of the present invention is a muffler connected to a vehicle engine through an exhaust pipe, and comprises a hollow tubular main body and a plurality of expansions in the inner space of the main body in the axial direction. an inlet pipe for introducing exhaust gas into an expansion chamber positioned upstream of the plurality of expansion chambers; and an expansion chamber positioned downstream of the plurality of expansion chambers. a discharge pipe that discharges to the outside, wherein the partition wall is formed with communication holes that communicate with the plurality of expansion chambers, and the downstream end of the introduction pipe and the upstream end of the discharge pipe are connected to each other. The open ends are bent and opened so as to face the connecting portion between the main body and the partition wall , and the respective open ends are arranged so as not to overlap the communicating holes when viewed in the axial direction . When the downstream end of the introduction pipe is projected toward the connection portion, the range in which the downstream end and the main body overlap is smaller than the width of the opening of the downstream end, and A ratio of the range in which the downstream end portion and the main body portion overlap with respect to the width is 0.75 or less, and the distance between the communicating hole and the exhaust pipe when the communicating hole is projected in the axial direction toward the exhaust pipe. The overlapping range of the upstream end is smaller than the opening width of the communicating hole, and the ratio of the overlapping range of the communicating hole and the upstream end to the opening width of the communicating hole is 0.75 or less. characterized by

Advantageous Effects of Invention According to the present invention, both excellent silencing effect and improved output can be achieved with a simple configuration.

2 is a right side view of the vehicle according to the embodiment; FIG. 1 is a cross-sectional view of a silencer according to an embodiment; FIG. FIG. 5 is a schematic diagram showing variations of the layout of the introduction tube; 4 is a graph showing the relationship between the overlapping ratio of the introduction pipe and the muffler body and the pressure loss. It is a schematic diagram which shows the variation of the layout of an exhaust pipe. 5 is a graph showing the relationship between the overlapping ratio of communicating holes and discharge pipes and pressure loss.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In addition, although an example in which the present invention is applied to a sports-type two-wheeled vehicle will be described below, the applicable object is not limited to this and can be changed. For example, the present invention may be applied to other types of vehicles, such as straddle-type vehicles such as buggy-type tricycles and four-wheel vehicles. In addition, regarding the directions, the front of the vehicle is indicated by an arrow FR, and the rear of the vehicle is indicated by an arrow RE. Also, in the following figures, a part of the configuration is omitted for convenience of explanation.

A schematic configuration of a vehicle according to the present embodiment will be described with reference to FIG. FIG. 1 is a right side view of the vehicle according to this embodiment.

As shown in FIG. 1, a vehicle 1 is a sports-type motorcycle, and is constructed by suspending (supporting) an engine 3 on a body frame 2 made of steel or aluminum alloy. The engine 3 is composed of, for example, a parallel four-cylinder engine. The engine 3 is configured by attaching a cylinder head 31 and a cylinder head cover 32 to the upper part of an engine case 30 in which a crankshaft (not shown) and the like are accommodated. An oil pan 33 is provided below the engine case 30 .

The vehicle body frame 2 is a twin-spar type frame formed by aluminum casting, and by suspending the engine 3 as described above, the vehicle body as a whole is configured to obtain rigidity. The body frame 2 as a whole has a shape extending from the front to the rear and curved downward at the rear end side.

Specifically, the vehicle body frame 2 includes a main frame 21 extending rearward from a head pipe 20 in a bifurcated manner, and a body frame 22 extending downward from the rear end of the main frame 21 . A fuel tank (not shown) is arranged on the upper portion of the main frame 21 . A swing arm 10 is swingably supported at a substantially central portion of the body frame 22 in the vertical direction. The swing arm 10 extends rearward. A rear wheel 11 is rotatably supported at the rear end of the swing arm 10 .

A seat rail 23 extending rearward and upward is provided at the upper end of the body frame 22 . The seat rails 23 are provided with a rider seat and a pillion seat (both not shown).

A pair of left and right front forks are steerably supported on the head pipe 20 via a steering shaft (both not shown). A front wheel (not shown) is rotatably supported under the front fork.

An exhaust pipe 40 (exhaust pipe) is connected to each exhaust port of the cylinder head 31 as part of the exhaust device 4 . A plurality of exhaust pipes 40 (four in the present embodiment) extend downward from each exhaust port, are bent rearward in front and below the engine 3, are combined into one, and extend rearward of the vehicle. ing.

A chamber 41 as a silencer is connected to the rear end (downstream side) of the exhaust pipe 40 . A muffler joint pipe 42 extending rearward and upward is connected to the downstream end of the chamber 41 . A muffler 5 as a silencer is connected to the rear end of the muffler joint pipe 42 . The muffler 5 is arranged on the right side of the swing arm 10 and the rear wheel 11 so that the rear end side is raised.

Exhaust gas from the engine 3 is introduced into the chamber 41 through the exhaust pipe 40 and then discharged outside through the muffler joint pipe 42 and the muffler 5 . The exhaust gas is purified and muted within the muffler 5 .

Next, referring to FIG. 2, a noise reduction device according to this embodiment will be described. FIG. 2 is a cross-sectional view of the silencer according to this embodiment. Specifically, FIG. 2A is a cross-sectional view of the silencer according to this embodiment, and FIG. 2B is a schematic cross-sectional view of a simplified partial configuration of FIG. 2A. Note that the catalyst is omitted in FIG. 2B for convenience of explanation.

As shown in FIGS. 2A and 2B, the muffler 5 includes a hollow cylindrical muffler body 50 (main body) that forms an internal space of a predetermined shape (for example, a single cross-sectional shape in the axial direction) extending back and forth. . The muffler body 50 has a double tube structure in which an outer tubular portion 50a and an inner tubular portion 50b are overlapped. The tip portion of the muffler body 50 has a reduced diameter, and has an outer diameter corresponding to the outer diameter of an introduction pipe 52, which will be described later. A tail portion 50c is welded to the rear end portion of the muffler body 50 as a lid member. These configurations form a predetermined expansion space within the muffler body 50 .

The internal space of the muffler body 50 is partitioned into two expansion chambers in the longitudinal direction by a baffle plate 51 (partition wall). That is, the baffle plate 51 partitions the internal space of the muffler body 50 into two expansion chambers in the axial direction. Of the two expansion chambers, the space on the front side of the baffle plate 51 (the expansion chamber located on the upstream side) is the first expansion chamber S1, and the space on the rear side of the baffle plate 51 (the expansion chamber located on the downstream side) is the first expansion chamber S1. This is the second expansion chamber S2.

The baffle plate 51 has, for example, a disc shape corresponding to the cross-sectional shape of the muffler body 50 . The outer peripheral portion of the baffle plate 51 is welded along the inner peripheral surface of the muffler body 50 . Welding may be partial welding or all-around welding. A communication hole 51a is formed substantially in the center of the baffle plate 51 for communicating the two expansion chambers. The communication hole 51a is formed so as to pass through the baffle plate 51 in the thickness direction (front-rear direction).

An introduction pipe 52 for introducing exhaust gas into the first expansion chamber S<b>1 is provided at the tip of the muffler body 50 so as to pass through the muffler body 50 . The introduction pipe 52 is formed of a pipe having a circular cross section as a whole, and includes a straight pipe portion 52a extending in the axial direction of the muffler body 50, an enlarged diameter portion 52b increasing in diameter toward the downstream, and a honeycomb portion 52c forming a catalyst. and a bent portion 52d that bends the exhaust passage in a predetermined direction are joined by welding.

The straight pipe portion 52 a has an outer diameter smaller than that of the muffler body 50 and extends longitudinally along the axial direction so as to pass through the axial center of the muffler body 50 . A muffler joint pipe 42 (see FIG. 1) is connected to the tip of the straight pipe portion 52a. The rear end of the straight pipe portion 52a is inserted into the first expansion chamber S1.

The tip of the enlarged diameter portion 52b is welded to the rear end of the straight pipe portion 52a. The diameter-enlarged portion 52b tapers toward the rear, which is the downstream side. A honeycomb portion 52c is welded to the rear end of the enlarged diameter portion 52b. The honeycomb portion 52c has the same axial direction as the muffler body 50 and is formed in a columnar shape. The outer diameter of the honeycomb portion 52c is larger than the outer diameter of the straight pipe portion 52a. The honeycomb portion 52c is composed of, for example, a three-way catalyst, and adsorbs pollutants (carbon monoxide, hydrocarbons, nitrogen oxides, etc.) in the exhaust gas and converts them into harmless substances (carbon dioxide, water, nitrogen, etc.). and purify.

A bent portion 52d is welded to the rear end of the honeycomb portion 52c. The bent portion 52d is bent rearward and downward while maintaining the outer diameter of the honeycomb portion 52c. For example, the bent portion 52d is bent rearward and downward at an angle of 45 degrees with respect to the axial direction of the honeycomb portion 52c (the straight pipe portion 52a or the enlarged diameter portion 52b). Although the details will be described later, the bent portion 52d is bent such that the open end (downstream end) on the downstream end side faces the connecting portion W between the muffler body 50 and the baffle plate 51 . Further, the open end of the bent portion 52d is arranged so as not to overlap the communicating hole 51a when viewed in the axial direction.

Further, at the rear end portion of the muffler body 50, a discharge pipe 53 for discharging the exhaust gas from the second expansion chamber S2 to the outside is provided so as to pass through the tail portion 50c. The discharge pipe 53 is formed of a pipe having a circular cross section and extends in the axial direction of the muffler body 50 . The discharge pipe 53 has an outer diameter smaller than that of the muffler body 50 and extends longitudinally along the axial direction so as to pass through the axial center of the muffler body 50 . The distal end of the discharge pipe 53 enters the second expansion chamber S2. The rear end of the discharge pipe 53 protrudes outward through the tail portion 50c.

The upstream end of the discharge pipe 53 is bent forward and downward to be open. For example, the discharge pipe 53 is bent forward and downward at an angle of 45 degrees with respect to the extending direction (axial direction). Although the details will be described later, the discharge pipe 53 is bent such that its open end (upstream end) faces the connecting portion W between the muffler body 50 and the baffle plate 51 . Further, the open end portion is arranged so as not to overlap the communicating hole 51a when viewed in the axial direction. In addition, the introduction pipe 52 and the discharge pipe 53 are arranged so as to face each other with the communication hole 51a of the baffle plate 51 interposed therebetween.

In this way, the downstream end of the introduction pipe 52 and the upstream end of the discharge pipe 53 are bent in a predetermined direction and are open, and the open ends of the introduction pipe 52 and the discharge pipe 53 are connected to the muffler body 50 respectively. and the baffle plate 51.

Note that FIG. 2A shows a case where a honeycomb portion 52c is provided as a catalyst in the middle of the introduction pipe 52. As shown in FIG. However, in FIG. 2B, for the sake of convenience, the enlarged diameter portion 52b and the honeycomb portion 52c are omitted, and the introduction pipe 52 is represented only by the straight pipe portion 52a and the bent portion 52d. This is because the presence or absence of the catalyst is irrelevant to the explanation of the exhaust flow in the muffler 5 .

By the way, in the muffler 5 attached to the vehicle engine, it has been conventionally required to achieve both noise reduction performance and output improvement. However, there is a trade-off between noise reduction performance and output improvement, and it is difficult to achieve both at the same time. For example, it is preferable to reduce the pressure loss in the muffler to prevent output reduction. From the standpoint of silencing, it is also necessary to achieve silencing over a wide range of high and low frequencies. In particular, it is conceivable to mute the sound in the high-frequency range.

Therefore, the inventors of the present invention focused on the communication structure between the plurality of expansion chambers in the muffler and the internal piping layout in order to achieve both the improvement of the noise reduction performance and the improvement of the output, and arrived at the present invention. Specifically, the inventors of the present invention made the exhaust flow in the upstream expansion chamber of the plurality of expansion chambers laminar, thereby minimizing the pressure loss and reflecting the exhaust gas on the muffler wall surface the number of times. was found to be able to reduce noise in the high-frequency range by increasing the Furthermore, the inventors of the present invention have found that by turbulent part of the exhaust gas flowing into the expansion chamber on the downstream side of the plurality of expansion chambers, it is possible to reduce noise in the low frequency band and high frequency band. rice field. In this case, directing part of the exhaust gas to the exhaust outlet makes it possible to prevent the pressure loss from increasing more than necessary. Then, the conditions for laminarization and turbulence of the exhaust flow described above were derived by analysis.

Specifically, in this embodiment, the internal space of the muffler body 50 is partitioned into two front and rear expansion chambers (a first expansion chamber S1 and a second expansion chamber S2) by the baffle plate 51. , and the discharge pipe 53 is arranged in the second expansion chamber S2 on the downstream side. A single communication hole 51a is formed in the baffle plate 51 as a structure for communicating these two expansion chambers. Furthermore, in each expansion chamber, the downstream end side of the introduction pipe 52 and the upstream end side of the discharge pipe 53 are bent in a predetermined direction so as to separate from the communication hole 51a. More specifically, the introduction pipe 52 and the discharge pipe 53 are bent so that their respective open ends face the connecting portion W between the muffler body 50 and the baffle plate 51 . Furthermore, the open ends of the introduction pipe 52 and the discharge pipe 53 are arranged so as not to overlap the communication hole 51a when viewed in the axial direction.

According to these configurations, by shifting the open ends of the introduction pipe 52 and the discharge pipe 53 from the communication hole 51a, part of the exhaust gas flows directly downstream (the discharge pipe 53). , the other portion diffuses into the expansion chamber. Since the exhaust gas directly led to the exhaust pipe 53 has a small pressure loss, an increase in output is expected. On the other hand, the exhaust gas diffused into each expansion chamber is reflected multiple times by the wall surface, thereby making it possible to obtain a silencing effect. As a result, it is possible to achieve both an improvement in silencing performance and an improvement in output.

Further, since the honeycomb portion 52c is arranged as a catalyst in the middle of the introduction pipe 52, the honeycomb portion 52c can be effectively warmed by the exhaust gas filled in the first expansion chamber S1. As a result, it is possible to promote early activation of the catalyst and improve exhaust gas purification performance.

Further, as a structure for communicating the two expansion chambers, a communicating hole 51a is adopted instead of a baffle pipe. As a result, the number of parts and the welding process can be reduced, and the muffler 5 can be realized with a simple configuration.

Further, the point of harmony between the improvement in noise reduction performance and the improvement in output is determined by the positional relationship between the introduction pipe 52 and the baffle plate 51 and the positional relationship between the communication hole 51 a and the discharge pipe 53 . In the first expansion chamber S1, as shown in FIG. 2, the end of the introduction pipe 52 projected toward the baffle plate 51 is denoted by A. Then, the introduction pipe 52 (bending portion 52d) is bent so that A is larger than a. That is, when the downstream end of the bent portion 52d, which is the open end of the introduction pipe 52, is projected toward the connection portion W, the overlapping range a of the bent portion 52d and the muffler body 50 is the opening width A of the bent portion 52d. less than

According to this configuration, by increasing the number of times the exhaust gas is reflected off the wall surface in the first expansion chamber S1, it is possible to effectively muffle noise, especially in a high frequency band. Although the details will be described later, the ratio (a/A) of the overlapping range a between the bent portion 52d and the muffler body 50 to the opening width A of the bent portion 52d is preferably 0.75 or less.

Further, in the second expansion chamber S2, if the range obtained by projecting the communicating hole 51a in the axial direction is B, and the range B corresponding to the open end of the discharge pipe 53 is b, then B is larger than b. The discharge pipe 53 is bent at . That is, when the communication hole 51a is projected toward the discharge pipe 53 in the axial direction, the range b in which the communication hole 51a and the upstream end portion of the discharge pipe 53 overlap is larger than the opening width B of the communication hole 51a. is also small.

According to this configuration, part of the exhaust gas can be guided directly to the exhaust pipe 53 within the second expansion chamber S2. Therefore, even if the exhaust gas is diffused into the two expansion chambers, excessive pressure loss can be prevented, and both noise reduction performance and engine output can be achieved. Although the details will be described later, the ratio (b/B) of the range b where the communicating hole 51a and the upstream end of the discharge pipe 53 overlap with respect to the opening width B of the communicating hole 51a is preferably 0.75 or less. .

Here, with reference to FIG. 3 to FIG. 6, the point of harmony between the improvement of the noise reduction performance and the improvement of the output will be described. FIG. 3 is a schematic diagram showing variations of the layout of the introduction tube. FIG. 4 is a graph showing the relationship between the overlap ratio of the introduction pipe and the muffler body and the pressure loss. FIG. 5 is a schematic diagram showing a variation of the layout of the discharge pipe. FIG. 6 is a graph showing the relationship between the overlapping ratio of communicating holes and discharge pipes and pressure loss. In this embodiment, the harmony point is derived by performing analysis while changing the layout of the introduction pipe and the exhaust pipe.

First, the flow of exhaust gas when the overlapping ratio (a/A) of the introduction pipe 52 and the muffler body 50 is changed by changing the projection length of the introduction pipe 52 in the first expansion chamber S1 will be described. Figures 3A-C show examples where a/A = 25%, 75% and 100%. As analysis conditions, b/B is fixed in each figure, and the engine speed and engine displacement are also fixed.

As shown in FIG. 3A, under the condition of a/A=25%, the exhaust gas collides with the connecting portion W between the baffle plate 51 and the muffler body 50 when flowing into the first expansion chamber S1 from the bent portion 52d. and flow forward. The exhaust gas flows upward and rearward along the inner wall of the muffler body 50 while hitting the inner wall of the muffler body 50 several times, and flows into the second expansion chamber S2 through the communicating hole 51a.

As shown in FIG. 3B, under the condition of a/A=75%, part of the exhaust gas that collides with the connecting portion W flows forward along the wall surface of the muffler body 50 as in FIG. Part of it turns upward along the baffle plate 51 and flows forward.

As shown in FIG. 3C, under the condition of a/A = 100%, most of the exhaust gas that collides with the connection portion W is bent upward along the wall surface of the baffle plate 51 and directed forward. flow in.

Further, as shown in FIG. 4, the pressure loss is relatively small when a/A is 75% or less, whereas the pressure loss increases rapidly when a/A exceeds 75%. This is because when a/A is 75% or less, the exhaust gas flow is laminar, so the number of reflections to the wall surface of the muffler body 50 is effectively increased while the pressure loss does not become too large. Because it is possible. Therefore, both noise reduction performance (especially high frequency band) and output improvement are achieved. On the other hand, when a/A exceeds 75%, the direction of flow of the exhaust gas changes and turbulence rapidly progresses, which can be a cause of a rapid increase in pressure loss. As a result, the engine output will decrease. Thus, a/A is preferably 75% or less.

Next, the flow of exhaust gas when the overlapping ratio (b/B) of the communication hole 51a and the discharge pipe 53 is changed by changing the height position of the discharge pipe 53 in the second expansion chamber S2 will be described. Figures 5A-C show examples where b/B = 25%, 75% and 100%. In addition, in FIG. 5C, for the sake of convenience, the discharge pipe 53 is not bent. Further, as analysis conditions, a/A is fixed in each drawing, and the engine speed and the engine displacement are also fixed. Further, in FIG. 5, since the flow of the first expansion chamber S1 is common, description thereof will be omitted.

As shown in FIG. 5A, under the condition of b/B=25%, part of the exhaust gas that has flowed into the second expansion chamber S2 through the communication hole 51a directly flows into the exhaust pipe 53, and the other part It flows rearward and upward, collides with the wall surface in the second expansion chamber S2, and is diffused.

As shown in FIG. 5B, most of the exhaust gas flows directly into the exhaust pipe 53 under the condition of b/B=75%. However, part of the exhaust gas flows rearward and upward at locations that do not overlap the open end of the discharge pipe 53 when viewed from the axial direction of the communication hole 51a.

As shown in FIG. 5C, under the condition of b/B=100%, almost all of the exhaust gas directly flows into the exhaust pipe 53 and is exhausted to the outside.

Also, as shown in FIG. 6, when b/B is 75% or less, the pressure loss gradually decreases as b/B increases. It converges to a constant value with almost no change. This is because when b/B is 75% or less, the exhaust gas can be separated into two types: one that flows directly to the exhaust pipe 53, and the other that diffuses in the second expansion chamber S2. Therefore, the flow of the exhaust gas can be made turbulent in the second expansion chamber S2, and exhaust noise in the low frequency band and the high frequency band can be reduced. On the other hand, when b/B exceeds 75%, most of the exhaust gas is directly discharged to the outside through the exhaust pipe 53, so the flow of the exhaust gas cannot be turbulent, and the exhaust gas is forced into the second expansion. As a result of not being diffused in the chamber S2, the silencing performance is degraded. Thus, b/B is preferably 75% or less.

As described above, according to the present embodiment, it is possible to achieve both an excellent silencing effect and an improved output with a simple configuration.

In the above embodiment, the parallel four-cylinder engine 3 has been described as an example, but the configuration is not limited to this. For example, the engine 3 may be composed of a single-cylinder engine, a two-cylinder engine, a three-cylinder engine, or an engine with five or more cylinders, and the arrangement of each cylinder can be changed as appropriate.

Further, in the above embodiment, the muffler 5 is arranged on the right side of the vehicle, but the configuration is not limited to this. The muffler 5 may be arranged on the left side of the engine 3 .

Further, in the above embodiment, the internal space of the muffler body 50 is divided into two expansion chambers by the baffle plate 51, but the configuration is not limited to this. The internal space of the muffler body 50 may be divided into three or more expansion chambers.

In the above embodiment, the single communication hole 51a is formed in the baffle plate 51, but the configuration is not limited to this. A plurality of communication holes 51 a may be formed in the baffle plate 51 . Further, as a configuration for communicating a plurality of expansion chambers, a communicating pipe may be welded to the baffle plate 51 instead of the communicating hole 51a.

In addition, in the above-described embodiment, a/A is changed by changing the projection length of the introduction pipe 52 into the first expansion chamber S1, but it is not limited to this structure. For example, a/A may be changed by changing the vertical height position of the introduction pipe 52 with respect to the muffler body 50 and the bending angle of the introduction pipe 52 (bending portion 52d). Similarly, in the second expansion chamber S2, b/B may be changed by changing the bending angle of the discharge pipe 53. FIG.

In addition, although a plurality of embodiments and modifications have been described, other embodiments of the present invention may be a combination of the above-described embodiments and modifications in whole or in part.

Moreover, the embodiments of the present invention are not limited to the above-described embodiments, and various changes, substitutions, and modifications may be made without departing from the spirit of the technical idea of the present invention. Furthermore, if the technical idea of the present invention can be realized in another way due to advances in technology or another derived technology, that method may be used. Therefore, the claims cover all embodiments that can be included within the scope of the technical concept of the present invention.

INDUSTRIAL APPLICABILITY As described above, the present invention has the effect of being able to achieve both an excellent noise reduction effect and an improved output with a simple configuration, and is particularly useful as a noise reduction device for a motorcycle.

3: Engine 5: Muffler (silencing device)
40: Exhaust pipe (exhaust pipe)
41: Chamber 42: Muffler joint pipe 50: Muffler body (main body)
51: Baffle plate (partition wall)
51a: communication hole 52: introduction pipe 52a: straight pipe portion 52b: enlarged diameter portion 52c: honeycomb portion (catalyst)
52d: Bent portion 53: Discharge pipe A: Opening width B of introduction pipe: Opening width B of communication hole S1: First expansion chamber S2: Second expansion chamber W: Connection portion between main body and partition wall a: Introduction pipe and main body b: the range where the communication hole and the discharge pipe overlap

Claims (2)

A silencer connected to a vehicle engine through an exhaust pipe,
a hollow cylindrical main body;
a partition wall that divides the internal space of the main body into a plurality of expansion chambers in the axial direction;
an introduction pipe for introducing exhaust gas into an expansion chamber positioned upstream among the plurality of expansion chambers;
a discharge pipe for discharging exhaust gas from an expansion chamber located downstream of the plurality of expansion chambers,
a communication hole is formed in the partition wall to communicate with the plurality of expansion chambers,
The downstream end portion of the introduction pipe and the upstream end portion of the discharge pipe are bent and opened so that their open ends face the connecting portion between the main body portion and the partition wall . is arranged so as not to overlap the communicating hole when viewed from the axial direction ,
When the downstream end of the introduction pipe is projected toward the connection portion, the range in which the downstream end and the main body overlap is smaller than the width of the opening of the downstream end, and A ratio of the range in which the downstream end portion and the main body portion overlap with respect to the width is 0.75 or less,
A range in which the communicating hole and the upstream end portion of the exhaust pipe overlap when the communicating hole is projected toward the exhaust pipe in the axial direction is smaller than the opening width of the communicating hole, and is smaller than the opening width of the communicating hole. A muffler , wherein a ratio of a range in which the communication hole and the upstream end overlap with respect to a width is 0.75 or less . 2. A muffler according to claim 1 , wherein a catalyst is provided in the middle of said introduction pipe.

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