Exhaust muffler

In an exhaust muffler using a double communicating tube as a communicating tube between expansion chambers, the exhaust muffler controls exhaust gas so as not to flow directly between intake and exhaust ports of an inner communicating tube and an outer communicating tube to thereby utilize the volume of the expansion chamber sufficiently. On one end side of the double communicating tube facing into a second expansion chamber, a distal end opening of the inner communicating tube functions as an intake port of an inside passage. A closing member for closing an end in the axial direction of an annular passage is provided in or in the vicinity of a distal end opening of the outer communicating tube. An exhaust port for opening the annular passage outwardly in the radial direction is provided between the closing member of the outer communicating tube and a first partition wall.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority under 35 USC 119 to Japanese Patent Application No. 2015-032510 filed Feb. 23, 2015 the entire contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an exhaust muffler.

2. Description of Background Art

An exhaust muffler is known wherein a partition wall is provided between expansion chambers with a communicating tube passing through the partition wall so as to provide communication between the expansion chambers. See, for example, Japanese Patent Application Laid-Open Publication No. 2006-207548. The communicating tube is a double tube formed of an outer communicating tube and an inner communicating tube. An inside passage within the inner communicating passage and an annular passage between the inner communicating tube and the outer communicating tube are formed as exhaust passages through which exhaust gases flow in opposite directions to each other. With this construction, in comparison with the case where a plurality of communicating tubes are arranged spaced apart from each other, an arrangement space for the plurality of communicating tubes (exhaust passages) is suppressed.

In the above mentioned exhaust muffler, an end portion of the inner communicating tube located in one end portion of the double communicating tube facing into one of the expansion chambers extends beyond a distal end opening of the outer communicating tube with both of distal end openings of the inner communicating tube and the outer communicating tube being located close to each other. The distal end opening of the inner communicating tube functions as an intake and exhaust port (an exhaust port in Japanese Patent Application Laid-Open Publication No. 2006-207548) of the inside passage, and the distal end opening of the outer communicating tube functions as an intake and exhaust port (an exhaust port in Japanese Patent Application Laid-Open Publication No. 2006-207548) of the annular passage. More specifically, an outlet of the outer communicating tube and an inlet of the inner communicating tube are directed in the same direction, and the inlet of the inner communicating tube is located in the exhaust direction of the outlet of the outer communicating tube, so that the exhaust gas flowing out of the outlet of the outer communicating tube easily enters the inlet of the inner communicating tube before it is expanded enough within the expansion chamber. Therefore, there is a possibility that the volume of the expansion chamber is not sufficiently utilized.

SUMMARY AND OBJECTS OF THE INVENTION

The present invention has been made in consideration of the above described circumstances, and an objective of an embodiment of the present invention is to provide an exhaust muffler having a double communicating tube as a communicating tube providing communication between expansion chambers and which controls the exhaust gas so as not to flow directly between intake and exhaust ports of an inner communicating tube and an outer communicating tube to thereby make it possible to sufficiently utilize the volume of the expansion chamber.

In order to achieve the above described object, according to an embodiment of the present invention, there is provided an exhaust muffler (10) comprising a cylindrical body (11), a partition wall (26) partitioning an interior of the cylindrical body (11) into a plurality of expansion chambers (31,32), and a communicating tube (40) passing through the partition wall (26), wherein the communicating tube (40) is in the form of a double communicating tube (40) consisting of an outer communicating tube (41) and an inner communicating tube (42), and an inside passage (44) within the inner communicating passage (42) and an annular passage (43) between the inner communicating tube (42) and the outer communicating tube (41) function as exhaust passages through which exhaust gases flow in opposite directions to each other, wherein on one end side of the double communicating tube (40) facing into one (32) of the expansion chambers (31,32), a distal end opening (42c) of the inner communicating tube (42) functions as an intake and exhaust port (48) of the inside passage (44), and wherein a closing portion (45) for closing an end in the axial direction of the annular passage (43) is provided in or in the vicinity of a distal end opening (41d) of the outer communicating tube (41). An outer circumferential intake and exhaust port (47) for opening the annular passage (43) outwardly in a radial direction is provided between the closing portion (45) of the outer communicating tube (41) and the partition wall (26).

According to an embodiment of the present invention, on the one end side of the double communicating tube (40), the distal end opening (42c) of the inner communicating tube (42) functions as an intake port (48), and the outer circumferential intake and exhaust port (47) functions as an exhaust port (47).

According to an embodiment of the present invention, the closing portion (45) is provided with a closing member (45) of a plate shape which intersects with an axial direction of the double communicating tube (40), and the closing member (45) is arranged closer to the distal end opening (41d) of the outer communicating tube (41) than the partition wall (26).

According to an embodiment of the present invention, the outer circumferential intake and exhaust port (47) is arranged to be offset toward the partition wall (26) between the closing portion (45) and the partition wall (26).

According to an embodiment of the present invention, on the other end side of the double communicating tube (40) facing into the other expansion chamber (31) partitioned from the one expansion chamber (32) by the partition wall (26), an end portion of the outer communicating tube (41) is supported on an opposed wall (27) located on the opposite side of the other expansion chamber (31) from the partition wall (26).

According to an embodiment of the present invention, a second closing portion (27a) which closes the distal end opening (41c) of the outer communicating tube (41) located on the opposed wall (27) side is formed in the opposed wall (27), and a second outer circumferential intake and exhaust port (46) which opens the annular passage (43) outwardly in the radial direction is provided in the end portion of the outer communicating tube (41) located on the opposed wall (27) side.

According to an embodiment of the present invention, an end portion of the inner communicating tube (42) located on the opposed wall (27) side is supported on the opposed wall (27), and an end of the inner communicating tube (42) located on the partition wall (26) side is supported through the closing portion (45) on the outer communicating tube (41).

According to an embodiment of the present invention, another tube (35) which passes through the partition wall (26) is arranged below the double communicating tube (40), wherein the double communicating tube (40) has the inner communicating tube (42) of a circular cross section and the outer communicating tube (41) of a non-circular cross section, and the outer communicating tube (41) has a cross sectional shape of which a height dimension (H) in a vertical direction is smaller than a width dimension (W) in a horizontal direction.

According to an embodiment of the present invention, since, on one end side of the double communicating tube facing into one of the expansion chambers, the intake and exhaust port of the inner communicating tube is directed toward the axial direction, and the outer circumferential intake and exhaust port of the outer communicating tube is directed outwardly in the radial direction, the exhaust gas flowing out of the intake and exhaust port of one of the outer communicating tube and the inner communicating tube can be restrained from flowing directly into the intake and exhaust port of the other tube, in comparison with the case where the outer circumferential intake and exhaust port of the outer communicating tube is directed toward the axial direction similar to the intake and exhaust port of the inner communicating tube, whereby it can be expanded sufficiently within the expansion chamber. More specifically, the volume of the expansion chamber is sufficiently utilized whereby to be able to effectively perform noise reduction.

According to an embodiment of the present invention, since the exhaust gas discharged radially outwardly from the exhaust port of the outer communicating tube flows in such a way as to make a detour around the intake port of the inner communicating tube so as to be expanded within the expansion chamber, the exhaust gas flowing out of the outer communicating tube can be restrained from flowing directly into the inner communicating tube so as to be expanded sufficiently within the expansion chamber, so that the volume of the expansion chamber is sufficiently utilized whereby to be able to effectively perform noise reduction.

According to an embodiment of the present invention, in comparison with the case where the closing member terminating the annular passage is located in the vicinity of the partition wall, the length of the outer communicating tube is effectively utilized so that the length of the annular passage can be ensured and a range for providing the intake and exhaust port of the outer communicating tube can be ensured.

According to an embodiment of the present invention, since the outer intake and exhaust port and the distal end opening of the inner communicating tube are spaced apart from each other as far as possible, the exhaust gas flowing out of one of the intake and exhaust ports of the outer communicating tube and the inner communicating tube can be more effectively restrained from flowing directly into the other intake and exhaust port.

According to an embodiment of the present invention, the number of component parts is reduced and the outer communicating tube can be supported at both ends. Therefore, the support of the outer communicating tube can be stabilized as compared with cantilever support of the outer communicating tube, and the positioning and assembly of the outer communicating tube can be easily performed. In addition, the outer communicating tube can be extended long whereby to heighten a noise reduction effect.

According to an embodiment of the present invention, the other end side of the outer communicating tube is closed while being supported, and the exhaust gas flows in such away as to spread within the other expansion chamber. Therefore, the volume of the other expansion chamber also is utilized sufficiently, so that the noise reduction can be effectively performed.

According to an embodiment of the present invention, the number of component parts is reduced and the inner communicating tube can be supported at both ends. Therefore, the support and assembly of the inner communicating tube can be stabilized as compared with cantilever support, and the inner communicating tube can be extended long whereby to heighten the noise reduction effect.

According to an embodiment of the present invention, the double communicating tube and another tube are vertically arranged side by side, so that the width in the horizontal direction of the exhaust muffler can be reduced and the height in the vertical direction of the exhaust muffler can be reduced as much as possible. In addition, although the thickness in the radial direction of the annular passage varies in accordance with the positions in the circumferential direction due to the inner communicating tube of circular cross section and the outer communicating tube of non-circular cross section, a passage area can be ensured while reducing the height of the exhaust muffler as much as possible by reducing the thicknesses of both side parts in the height direction of the annular passage and increasing the thicknesses of both side parts in the width direction thereof.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the present invention will be described hereunder with reference to accompanying drawings.

In the following description, the orientation such as “front,” “rear,” “left,” “right” or the like shall be identical with an orientation of a vehicle (two-wheeled motorcycle) to be referred to below unless otherwise specified. In addition, an arrow FR indicates a forward direction of the vehicle and an arrow UP indicating an upward direction of the vehicle.

Referring toFIG. 1, a two-wheeled motorcycle110includes a pair of left and right main frames112extending from a head pipe111obliquely downwardly to the rear of the vehicle with a swing arm114extending from a rear part of the main frames112through a pivot shaft113to the rear of the vehicle. A rear wheel116is rotatably mounted on a rear part of the swing arm114. A front fork117is mounted on the head pipe111in a rotatable (steerable) manner with a front wheel118rotatably mounted on a lower part of the front fork117. A handle is mounted on an upper end of the front fork117for steering the front wheel118. A down tube122extends downwardly from a neighboring part of the head pipe111and then rearwardly of the vehicle so as to be connected to a lower end of the rear part of the mainframe112. An internal combustion engine123is arranged between the down tube122and the main frame112located above the down tube122with an exhaust pipe124extending forwardly of the vehicle from the internal combustion engine123, then turning rearwardly so as to pass through the right side in the vehicle width direction of the internal combustion engine123and passes through between the pair of main frames112so as to extend to the rear of the vehicle. An exhaust muffler10is connected to a rear end of the exhaust pipe124.

The internal combustion engine123is a water-cooled four-stroke cycle gasoline engine. A fuel tank125for the internal combustion engine123is supported on the main frames112in a rearward position of the head pipe111. A radiator126for the internal combustion engine123is arranged along the down tube122.

The motorcycle110is an off road vehicle which has a large upward and downward stroke amount of the wheel, so that a front fender127is located in a sufficiently higher position than the front wheel118and a rear fender128is located in a sufficiently higher position than the rear wheel116.

Details of the exhaust muffler10will be described with reference toFIGS. 2 to 7. An arrow N in the drawing indicates the flow of the exhaust gas in the exhaust muffler10.

The exhaust muffler10is connected to the rear end of the exhaust pipe124which discharges the exhaust gas from the internal combustion engine123toward the rear of the vehicle (seeFIG. 1). The exhaust muffler10is formed in the shape of a cylinder which is inclined rearwardly upwardly with respect to the horizontal direction and extends linearly. An arrow FR' in the drawing indicates a forward direction in the axial direction of the cylinder of the exhaust muffler10(the axial direction of the muffler), and an arrow UP' indicates an upward direction lying at right angles to the axial direction of the muffler.

As shown inFIG. 2, the exhaust muffler10includes a cylinder body11which has a linearly extending cylindrical appearance. The cylinder body11has a double pipe structure consisting of an outer cylinder21and an inner cylinder22located in an inside of the outer cylinder21. The outer cylinder21and the inner cylinder22are formed in predetermined cross sectional shapes, respectively. An annular clearance23is formed between an inner circumference of the outer cylinder21and an outer circumference of the inner cylinder22. Into this annular clearance23there is filled a sound absorbing material such as glass wool or the like, for example.

To a front end of the cylinder body11, there is connected a front cap12of a tapered shape which is tapered forwardly. To a rear end of the cylinder body11, there is connected a tail cap13provided with a rear end surface which is downwardly inclined with respect to a rear end surface orthogonal to the axial direction of the muffler.

A rear end opening of the front cap12is axially aligned with a front end opening of the outer cylinder21of the cylinder body11and joined thereto by welding or the like. A front pipe14which is connected to the exhaust pipe124passes through and is supported on the front end opening of the front cap12. An outer circumferential surface of the front pipe14and the front end opening of the front cap12are joined together by welding or the like.

On an outer circumference of an upper portion of an intermediate part of the cylinder body11, there is provided a mounting bracket90for mounting the intermediate part on a vehicle body frame of the motorcycle110. The exhaust muffler10is mounted on the vehicle body of the motorcycle110in such a manner that a front end portion of the front pipe14is connected to and supported on a rear end portion of the exhaust pipe124and an upper side of the intermediate part of the cylinder body11is mounted through the mounting bracket90on the vehicle body frame (seeFIG. 1).

A front end portion of the inner cylinder22of the cylinder body11is supported on an inner portion of the outer cylinder21through a supporting ring25. A front end opening of the inner cylinder22opens into a space within the front cap12. A rear end portion of the inner cylinder22is supported on the outer cylinder21through an outer circumferential rib24aof an end plate24which lies at right angles to the axial direction of the muffler.

A first partition wall26of a plate shape extends orthogonal to the axial direction of the muffler and is provided in a region close to a front of an intermediate part in the axial direction of the inner cylinder22. A second partition wall27of a plate shape which extends orthogonal to the axial direction of the muffler is provided in a region close to a rear in the axial direction of the inner cylinder22. In the interior of the exhaust muffler10, a first expansion chamber31is defined between the first partition wall26and the second partition wall27, a second expansion chamber is defined in front of the first partition wall26, and a third expansion chamber33is defined between the second partition wall27and the end plate24.

The front pipe14has a front part which is substantially the same diameter as the exhaust pipe124and a rear part which is formed in a rearwardly spreading taper shape. A rear end of the front pipe14is connected to an exhaust gas inlet tube body35which extends in parallel with the cylinder body11. The exhaust gas inlet tube body35extends across the second expansion chamber32and passes through a lower part of the first partition wall26. A rear end portion of the exhaust gas inlet tube body35faces into the first expansion chamber31. An exhaust gas purifying catalyser CAT is retained in an interior of the exhaust gas inlet tube body35. More specifically, the exhaust gas inlet tube body35forms a casing for the exhaust gas purifying catalyser CAT. An exhaust port36located in a rear end of the exhaust gas inlet tube body35opens rearwardly in the vicinity of a front end of the first expansion chamber31.

A double communicating tube40extends in parallel with the cylinder body11and is supported on the first partition wall26and the second partition wall27. The double communicating tube40is arranged directly above the exhaust gas inlet tube body35. The double communicating tube40includes an outer communicating tube41and an inner communicating tube42which are arranged spaced apart from each other. The outer communicating tube41passes through the first partition wall26and provides communication between the first expansion chamber31and the second expansion chamber32. The inner communicating tube42passes through the first partition wall26and the second partition wall27so as to provide communication between the second expansion chamber32and the third expansion chamber33. An inside passage44in an interior of the inner communicating tube42and an annular passage43between the inner communicating tube42and the outer communicating tube41are formed as passages through which the exhaust gas flows in opposite directions.

More specifically, in the annular passage44within the outer communicating tube41which provides communication between the first expansion chamber31and the second expansion chamber32, the exhaust gas flows from a rear end side to a front end side. In the inside passage44within the inner communicating tube42which provides a communication between the second expansion chamber32and the third expansion chamber33, the exhaust gas flows the front end side to the rear end side. Hereinafter, a rear end portion of the outer communicating tube41is referred to as an intake side tube end portion41a, and a front end portion of the outer communicating tube41is referred to as an exhaust side tube end portion41b. Moreover, a front end portion of the inner communicating tube42is referred to as an intake side tube end portion42a, and a rear end portion of the inner communicating tube42is referred to as an exhaust side tube end portion42b. In addition, in the outer communicating tube41, a range of a predetermined width located forwardly from the intake side tube end portion41ais referred to as an intake region having a plurality of small holes (intake port)46a, and a range of a predetermined width located rearwardly from the exhaust side tube end portion41bis referred to as an exhaust region having a plurality of small holes (exhaust port)47a.

A front part of the outer communicating tube41passes through the first partition wall26, and the exhaust region is arranged within the second expansion chamber32. The front part of the outer communicating tube41is supported on the first partition wall26while passing through it.

As shown inFIG. 5, the first partition wall26has an upper supporting hole26aon which the outer communicating tube41and a front part of the double communicating tube40are supported while passing therethrough, and a lower supporting hole26bon which a rear end portion of the exhaust gas inlet tube body35is supported while passing therethrough. These two supporting holes26a,26bare formed as a continuously connected opening26cso as to make the distance between the double communicating tube40on the upper side and the exhaust gas inlet tube body35on the lower side as small as possible. With this construction, the exhaust muffler10is made small in size in the height direction.

The exhaust gas inlet tube body35has a circular shape in cross section. On the other hand, the outer communicating tube41of the double communicating tube40has a flat substantially pentagonal shape in cross section of which a vertical width is reduced. The cross sectional shape of the outer communicating tube41has a height dimension H in the vertical direction which is smaller than a width dimension W in the horizontal direction. Also in this point, the exhaust muffler is made small in size in the height direction. The width dimension W in the horizontal direction of the cross sectional shape of the outer communicating tube41is set to be not more than a width dimension (diameter) in the horizontal direction of the cross sectional shape of the exhaust gas inlet tube body35located below the outer communicating tube41, whereby to prevent the exhaust muffler10from being increased in size in the horizontal direction.

The inner communicating tube42having a circular cross sectional shape is inserted into the outer communicating tube41of the above cross sectional shape so that the annular passage43is formed between the inner communicating tube42and the outer communicating tub41. A width of the annular passage43in the radial direction orthogonal to the axial direction of the annular passage43varies in accordance with positions in the circumferential direction of the annular passage43. Therefore, the annular passage43is formed with a narrow region in the radial direction (upper and lower regions on the outside of the inner communicating tube42) and a wide region in the radial direction (left and right regions on the outside of the inner communicating tube42).

As shown inFIGS. 2 and 6, in the intake side tube end portion42aof the inner communicating tube42, an intake port48is formed by a distal end opening42cof the inner communicating tube42.

As shown inFIGS. 2 and 7, in the exhaust side tube end portion42bof the inner communicating tube42, an exhaust port49is formed by a distal end opening42dof the inner communicating tube42.

On the other hand, a distal end opening41dof the exhaust side tube end portion41bof the outer communicating tube41is closed with a closing member45into which the intake side tube end portion42aof the inner communicating tube42is inserted so as to be supported by the closing member45. An exhaust port47on the distal end side of the outer communicating tube41is formed by a plurality of small holes47awhich open radially outwardly in the exhaust region. Although the closing member45may be arranged in a more recessed side (side closer to the first partition wall26) than the distal end opening41d, it is preferable that it is arranged closer to the distal end opening41d than the first partition wall26so as to ensure the length of the annular passage43and to ensure the exhaust region.

The exhaust region is arranged closer to the first partition wall26than the closing member45. The intake side tube end portion42aof the inner communicating tube42is located in the vicinity of the distal end opening41dof the exhaust side tube end portion41bof the outer communicating tube41closed with the closing member45. More precisely, the intake side tube end portion42aof the inner communicating tube42is arranged in such a way as to project a little forwardly from the distal end opening41dof the exhaust side tube end portion41bof the outer communicating tube41. More specifically, the exhaust region is arranged spaced apart from the intake side tube end portion42aof the inner communicating tube42as far as possible. The intake side tube end portion42aof the inner communicating tube42is supported on an inner circumference of the exhaust side tube end portion41bof the outer communicating tube41through the closing member45.

Further, the intake side tube end portion41aof the outer communicating tube41is closed with a second closing portion27aof the second partition wall27into which the exhaust side tube end portion42bof the inner communicating tube42is inserted so as to be supported by the second closing portion27a. The second closing portion27ais formed in the shape of an annular projection which projects forwardly around the circumference of a passing-through portion of the inner communicating tube42. A distal end opening41cof the intake side tube end portion41aof the outer communicating tube41is fitted onto and butted against an outer circumference of the second closing portion27afrom the front side. With this construction, the position in the forward and rearward direction of the outer communicating tube41is fixed, and the intake side tube end portion41ais supported on the second partition wall27in a closing state. An intake port46on the rear end side of the outer communicating tube41is formed with the plurality of small holes46awhich open radially outwardly in the intake region. The intake region is arranged close to the second partition wall27so as to ensure the length of the annular passage43.

The exhaust side tube end portion42bof the inner communicating tube42is arranged in such a way as to project a little rearwardly from the distal end opening41cof the intake side tube end portion41aof the outer communicating tube41and the second partition wall27. The exhaust side tube end portion42bof the inner communicating tube42is supported on an inner circumference of the second closing portion27aof the second partition wall27.

As shown inFIG. 2, the exhaust port49of the inner communicating tube42faces and opens into an upper part of the third expansion chamber33. A tail pipe15of an upwardly convexed curve shape is inserted into and supported on an upper part of the end plate24. The tail pipe15has a front end opening which opens downwardly. The front end opening of the tail pipe15functions as an intake port16and is arranged below the exhaust port49of the inner communicating tube42within the third expansion chamber33. The intake port16of the tail pipe15is arranged spaced apart from the exhaust port49of the inner communicating tube42, so that the volume of the third expansion chamber33is effectively utilized to thereby heighten the noise reduction effect.

The tail pipe15has a rear end opening which opens downwardly to the rear. The rear end opening of the tail pipe15opens in the outward direction of the muffler so as to function as an exhaust port17of the whole of the exhaust muffler10. In addition, by dispensing with the end plate24, the tail pipe15and the third expansion chamber33, the exhaust port49of the inner communicating tube42may be used as an exhaust port of the whole of the exhaust muffler10in such a way as to open in the outward direction of the muffler.

First, the exhaust gas introduced into the front pipe14from the exhaust pipe124is purified by the exhaust gas purifying catalyser CAT within the exhaust gas inlet tube body35and then, passes through in the order of the first expansion chamber31, the second expansion chamber32and the third expansion chamber33while flowing in such a way as to turn around within the cylinder body11, so that it is cooled down and reduced in pressure so as to lower or reduce the exhaust heat and the exhaust noise. Thereafter, the exhaust gas is discharged from the exhaust port17of the tail pipe15.

The exhaust gas flowing into the first expansion chamber31from the exhaust gas inlet tube body35is expanded and reduced in pressure within the first expansion chamber, and thereafter, flows into the annular passage43from the intake port46of the outer communicating tube41located on the rear end side of the double communicating tube40. The exhaust gas within the annular passage43then flows forwardly along the annular passage43, and then, flows outwardly in the radial direction (not rearwardly in the axial direction) into the second expansion chamber32from the exhaust port47of the outer communicating tube41located on the front end side of the double communicating tube40.

At that time, the exhaust gas flows outwardly in the radial direction from the exhaust port47of the outer communicating tube41, so that it goes away from the intake port48of the inner communicating tube42within the second expansion chamber32. Therefore, the exhaust gas flowing out of the exhaust port47is restrained from flowing immediately into the intake port48without being expanded sufficiently within the second expansion chamber32, whereby the volume of the second expansion chamber32is effectively utilized and the noise reduction is efficiently performed. Since the exhaust gas is dispersed by a group of the multiple small holes47aformed as the exhaust port47of the outer communicating tube41and flows into the second expansion chamber32, the noise reduction effect is still more heightened.

As described above, in the exhaust muffler10of the above embodiment, on the front end side of the double communicating tube40facing into the second expansion chamber32, the distal end opening42cof the inner communicating tube42is formed as the intake port48of the inside passage44. In (or in the vicinity of) the distal end opening41dof the outer communicating tube41, there is provided the closing member45for closing the end in the axial direction of the annular passage43. Between the closing member45of the outer communicating tube41and the first partition wall26, there is provided the exhaust port47for opening the annular passage43outwardly in the radial direction.

With this construction, since, on the front end side of the double communicating tube40facing into the second expansion chamber32, the intake port48of the inner communicating tube42is directed toward the axial direction, and the exhaust port47of the outer communicating tube41is directed outwardly in the radial direction, the exhaust gas flowing out of the exhaust port47of the outer communicating tube41can flow in such a way so as to take a long way around the intake port48of the inner communicating tube42to thereby be expanded. At the same time, the exhaust gas flowing out of the exhaust port47of the outer communicating tube41can be restrained from flowing directly into the intake port48of the inner communicating tube42in comparison with the case where the exhaust port47of the outer communicating tube41is directed toward the axial direction similar to the intake port48of the inner communicating tube42, so that it can be expanded sufficiently within the expansion chamber32. More specifically, the volume of the second expansion chamber32is utilized sufficiently whereby to be able to effectively perform the noise reduction. Further, since the double communicating tube40combining two communicating tubes is provided, the arrangement space for the communicating tubes can be reduced whereby to make it possible to increase the degree of freedom in arrangement of the communicating tubes, in comparison with the case where two communicating tubes are arranged spaced apart from each other in a side by side relationship.

Further, in the above exhaust muffler10, the closing member45is formed in a plate shape which intersects with the axial direction of the double communicating tube40, and arranged closer to the distal end opening41dof the outer communicating tube41than the first partition wall26. Therefore, in comparison with the case where the closing member45terminating the annular passage43is located in the vicinity of the first partition wall26, the length of the outer communicating tube41can be effectively utilized so that the length of the annular passage43can be ensured and the range for providing the exhaust port47of the outer communicating tube41can be ensured.

In the above exhaust muffler10, since the exhaust port47of the outer communicating tube41is arranged in such a way so as to be offset toward the first partition wall26between the first partition wall26and the closing member45, the exhaust port47and the distal end opening42cof the inner communicating tube42are spaced apart from each other as far as possible, so that the exhaust gas flowing out of the exhaust port47of the outer communicating tube41can be more effectively restrained from flowing directly into the intake port48of the inner communicating tube42.

In the above exhaust muffler10, on the rear end side of the double communicating tube40facing into the first expansion chamber31partitioned from the second expansion chamber32by the first partition wall26, the end portion of the outer communicating tube41is supported on second partition wall27located on the opposite side of the first expansion chamber31from the first partition wall26. With this construction, the number of component parts is reduced and the outer communicating tube41can be supported at both ends. Therefore, the support of the outer communicating tube41can be stabilized as compared with the cantilever support of the outer communicating tube41, and the positioning and assembly of the outer communicating tube41can be easily performed. In addition, the outer communicating tube41can be extended long whereby to heighten a noise reduction effect.

In the above exhaust muffler10, the second closing portion27awhich closes the distal end opening41c of the outer communicating tube41located on the second partition wall27side is formed in the second partition wall27, and the intake port46which opens the annular passage43outwardly in the radial direction is provided in the end portion of the outer communicating tube41located on the second partition wall27side. With this construction, since the other end side of the outer communicating tube41is closed while being supported, and the exhaust gas flows in such a way so as to spread within the first expansion chamber31, the volume of the other expansion chamber also can be utilized sufficiently, so that the noise reduction can be effectively performed.

In the above exhaust muffler10, since the end portion of the inner communicating tube42located on the second partition wall27side is supported on the second partition wall27, and the end of the inner communicating tube42located on the first partition wall26side is supported through the closing member45on the outer communicating tube41, the number of component parts can be reduced and the inner communicating tube42can be supported at both ends. Therefore, the support and assembly of the inner communicating tube42can be stabilized as compared with the cantilever support, and the inner communicating tube42can be extended long whereby to heighten the noise reduction effect.

In the above exhaust muffler10, the exhaust gas inlet tube body35which passes through the first partition wall26is arranged below the double communicating tube40. The double communicating tube40has the inner communicating tube42of a circular cross section and the outer communicating tube41of a non-circular cross section, and the outer communicating tube41has a cross sectional shape of which the height dimension H in a vertical direction is smaller than the width dimension W in a horizontal direction. With this construction, the double communicating tube40and the exhaust gas inlet tube body35are vertically arranged in a side by side relationship, so that the width in the horizontal direction of the exhaust muffler10can be reduced and the height in the vertical direction of the exhaust muffler10can be reduced as much as possible. In addition, although the thickness in the radial direction of the annular passage43varies in accordance with the positions in the circumferential direction due to the inner communicating tube42of circular cross section and the outer communicating tube41of non-circular cross section, the passage area can be ensured while reducing the height of the exhaust muffler as much as possible by reducing the thicknesses of both side parts in the height direction of the annular passage43and increasing the thicknesses of both side parts in the width direction thereof.

In addition, in comparison with the case where the thickness in the radial direction of the annular passage43is constant, the thickness in the radial direction of the annular passage43increases or decreases locally in accordance with the positions in the circumferential direction. Therefore, the pressure loss of the exhaust gas becomes smaller in the part in which the thickness in the radial direction of the annular passage43increases, so that a good exhaust gas flow of the whole annular passage43can be obtained.

The present invention is not limited to the above described embodiment. For example, on one end side of the double communicating tube40facing into one of the expansion chambers, the distal end opening42cof the inner communicating tube42may be formed as an exhaust port, and the outer circumferential opening of the outer communicating tube41may be formed as an intake port. Moreover, the closing portion for closing the end in the axial direction of the annular passage43is not limited to the separate closing member45but may be configured to close the annular passage43by joining the end of the outer communicating tube41to the inner communicating tube42by squeezing the end of the outer communicating tube41, for example. In addition, the outer circumferential opening of the outer communicating tube41is not limited to punching holes but may be formed in a slit shape or a net shape.

Further, the outer communicating tube41may be configured to be supported only by the first partition wall26in a cantilever fashion such that the outer communicating tube41terminates at a position forwardly of the second partition wall27so as not to be supported by the second partition wall27. In this case, the outer circumferential opening of the outer communicating tube41located in the end part of the second partition wall27is dispensed with, and the distal end opening41cof the outer communicating tube41is used as the intake port of the annular passage43.

In addition, the exhaust muffler of the present invention is not limited to the exhaust muffler for the two-wheeled motorcycle, but may be applied to the exhaust muffler for a three-wheeled vehicle (the vehicle having one front wheel and two rear wheels or two front wheels and one rear wheel) or a four-wheeled vehicle.

It should be understood that the construction in the above embodiment is to be taken as an example of the present invention and that various changes and modifications may be made in the invention without departing from the spirit and scope thereof