EXHAUST MUFFLER FOR VEHICLE

Abstract

An exhaust muffler for a vehicle includes a muffler body coupled to an exhaust pipe and a tailpipe coupled to the muffler body. The muffler body has a plurality of expansion chambers, an exit communication pipe that discharges exhaust to the tailpipe from one of the plurality of expansion chambers positioned in a most downstream part of an exhaust flow path, and a spark arrester arranged in the exit communication pipe. An exhaust flow path narrowing portion is provided at an entrance portion of the exit communication pipe.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an exhaust muffler for a vehicle. In particular, the present invention relates to a spark arrester provided in an exhaust muffler for a vehicle.

2. Description of the Related Art

Conventionally, an exhaust muffler for a vehicle including a spark arrester is known. In general, the spark arrester is formed by a mesh-like member made of metal.

Meanwhile, since the spark arrester is arranged in an exhaust flow path in the exhaust muffler and exposed to exhaust gas, it is required to be so durable that it does not deform under conditions of high temperatures and high back pressure with an exhaust pulse. Accordingly, the spark arrester is provided with a frame member for reinforcing a mesh-like member made of a metal mesh. Thus, the spark arrester is prevented from deforming under the foregoing conditions. There is Prior Technique Document JP 8-61046 A.

That is, the spark arrester is structured by a mesh-like member as a filter portion, and a frame member as a reinforcing portion for reinforcing the filter portion. Therefore, since the structure is complicated, manufacturing of the spark arrester is not easy and involves high costs.

SUMMARY OF THE INVENTION

The present invention is made in consideration of the foregoing problems, and an object thereof is to provide an exhaust muffler for a vehicle including a spark arrester, designing of which can be streamlined.

In order to achieve the object stated above, the present invention provides an exhaust muffler for a vehicle including a muffler body coupled to an exhaust pipe, and a tailpipe coupled to the muffler body. The muffler body includes a plurality of expansion chambers, an exit communication pipe that discharges exhaust to the tailpipe from one of the plurality of expansion chambers positioned in a most downstream part of an exhaust flow path, and a spark arrester arranged in the exit communication pipe. An exhaust flow path narrowing portion is provided at an entrance portion of the exit communication pipe.

With the structure described above, the spark arrester is not arranged in the expansion chamber but in the exit communication pipe. Further, the exhaust flow path narrowing portion is provided at the entrance portion of the exit communication pipe. Thus, the back pressure acting on the spark arrester can be reduced, whereby deformation due to back pressure of the spark arrester can be suppressed. As a result, the reinforce member can be dispensed with, and designing of the spark arrester can be streamlined.

With the exhaust muffler, preferably, the following structure can be employed.

(1) .The spark arrester is structured by a mesh-like member.

With the structure (1), since the spark arrester is structured by a mesh-like member, the productivity of the spark arrester can be improved and costs can be reduced.

Furthermore, since no reinforce member covers the surface of the spark arrester, the filter portion of the spark arrester can be secured for the entire surface. As a result, the spark arrester can be structured in a compact manner.

(2) The exhaust flow path narrowing portion is structured by a lid member that has a through hole and that is provided at an upstream portion of the exit communication pipe.

With the structure (2), the exhaust flow path narrowing portion can be easily formed. Further, as compared with the case where a tapered narrowing portion is formed, the exhaust flow path can be sharply narrowed, and the back pressure in the exit communication pipe can be more effectively reduced. Thus, deformation caused by the back pressure of the spark arrester can be further suppressed.

(3) In the structure (2), the opening area of the through hole is substantially identical to the cross-sectional area of the exhaust flow path at the upstream end of the exhaust pipe.

With the structure (3), while realizing a reduction in the back pressure, it becomes possible to secure the exhaust flow path of proper size, and to avoid a reduction in the engine performance attributed to an excessive increase in the back pressure.

(4) In the structure (2), the difference between the cross-sectional area being perpendicular to the exhaust flow path of the exit communication pipe and the cross-sectional area being perpendicular to the exhaust flow path of the spark arrester is substantially identical to an opening area of the through hole.

With the structure (4), it becomes possible to avoid an excessive increase in the diameter of the exit communication pipe, whereby the muffler body can be structured in a compact manner.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a left side view of a utility vehicle according to one embodiment;

FIG. 2 is a perspective view of an exhaust system;

FIG. 3 is a left side view of an exhaust muffler;

FIG. 4 is an exploded perspective view of the exhaust muffler;

FIG. 5 is a V-V cross-sectional view of the exhaust muffler shown in FIG. 3;

FIG. 6 is a VI-part enlarged view of the exhaust muffler shown in FIG. 5;

FIG. 7 is a VII-part enlarged view of the exhaust muffler shown in FIG. 5;

FIG. 8 is a vertical cross-sectional view of a spark arrester;

FIG. 9 is a IX-IX cross-sectional view of the exhaust muffler shown in FIGS. 5; and

FIG. 10 is a X-X cross-sectional view of the exhaust muffler shown in FIG. 5.

DETAILED DESCRIPTION OF THE INVENTION

Embodiment

[Overall Structure]

In the following, with reference to the accompanying drawings, a description will be given of one embodiment of the present invention. Note that, for the sake of convenience in describing, the following description is based on the premise that the front-rear direction of a vehicle is applied to the front-rear direction of the exhaust muffler and other components, and that the right-left direction in connection with the vehicle-width direction (the right and left sides as seen from the rear of the vehicle) as seen from the passengers on the vehicle is applied to the right-left direction of the exhaust muffler and other components.

FIG. 1 is a left side view of a utility vehicle according to the present embodiment, with shell constituent members such as doors being removed. As shown in FIG. 1, the utility vehicle includes: a right and left pair of front wheels 11 on the front side and a right and left pair of rear wheels 12 on the rear side; a passenger space 14 surrounded by a ROPS 13, between the front wheels 11 and the rear wheels 12; and a rear deck 15 on the rear side of the passenger space 14. The ROPS 13 is an abbreviation for a rollover protective structure.

In the passenger space 14, a floor panel 16 forming the floor surface, a front seat 17, and a rear seat 18 are provided. Below the rear seat 18, an engine 20 is stored. In front of the engine 20, an exhaust portion 21 for discharging exhaust gas is provided. To the exhaust portion 21, an exhaust system 1 is connected, and the exhaust gas discharged from the engine 20 is purified by the exhaust system 1 with exhaust noises being cancelled, and discharged into the air.

[Exhaust System 1]

With reference to FIG. 2, a description will be given of the exhaust system 1. FIG. 2 is a perspective view of the exhaust system 1, together with the engine 20 and a transmission 22. As shown in FIG. 2, the exhaust system 1 includes an exhaust pipe 7 fixed to an exit portion of the exhaust portion 21 via a flange 71, and an exhaust muffler 2 being fixed by welding to the downstream end portion of the exhaust pipe 7. The exhaust muffler 2 is arranged at the substantially center portion in the vehicle-width direction and below the rear deck 15 (see FIG. 1). The exhaust muffler 2 is mounted on an exhaust muffler mounting portion 24 mounted at an upper portion of the transmission 22, via an exhaust muffler mounting apparatus 8.

The exhaust muffler mounting portion 24 has a support bracket 241 fixed to the upper portion of the transmission 22, and rod engaging portions 242 fixed by welding to the top face of the support bracket 241. The rod engaging portions 242 are provided to form a right and left pair, and each provided with a rubber damper 242a having a bore penetrating in the front-rear direction. Into the bore of the rubber damper 242a, a rod 82 of the exhaust muffler mounting apparatus 8 is inserted in the front^-rear direction, whereby the exhaust muffler 2 is held.

[Exhaust Pipe 7]

The exhaust pipe 7 extends from the flange 71, via a pipe 70 being curved to detour the engine 20 from the left side toward the rear side, and reaches the exhaust muffler 2 via an entrance cone portion 73. On the outer surface of the pipe 70, a heat shield plate 72 is attached, whereby heat is prevented from dissipating from the surface of the pipe 70 to the surrounding components. To the entrance cone portion 73, a sensor mounting boss 74 (see FIG. 3) for mounting an exhaust gas sensor is provided.

[Exhaust Muffler 2]

With reference to FIGS. 3 to 7, a description will be given of the exhaust muffler 2. FIG. 3 is a left side view of the exhaust muffler 2. FIG. 4 is an exploded perspective view of the exhaust muffler 2. FIG. 5 is a V-V cross-sectional view of FIG. 3. FIG. 6 is a VI-part enlarged view of FIG. 5. FIG. 7 is a VII-part enlarged view of FIG. 5. In FIG. 4, a sleeve portion 30 and the downstream side cover 34 are partially transparent to show the internal structure, and the exhaust muffler mounting apparatus 8 is not shown.

As shown in FIG. 3, the exhaust muffler 2 includes a muffler body 3, a spark arrester 5 mounted on the rear portion of the muffler body 3, and the exhaust muffler mounting apparatus 8 mounted on the bottom portion of the muffler body 3. As shown in FIG. 4, a gasket 9 is assembled between the spark arrester 5 and the muffler body 3.

(Muffler Body 3)

The muffler body 3 has a shell formed by the sleeve portion 30, an upstream side cover 33 closing the upstream side opening of the sleeve portion 30, and a downstream side cover 34 closing the downstream side opening of the sleeve portion 30. At the upstream side cover 33, an exhaust entrance portion 332 connected to the entrance cone portion 73 of the exhaust pipe 7 (see FIG. 2) is formed. At the downstream side cover 34, an exhaust exit portion 342 to which a spark arrester 5 is connected is formed.

In the muffler body 3, an upstream side separator 35 and a downstream side separator 36 are provided. A second expansion chamber 38 is formed between the upstream side cover 33 and the upstream side separator 35, and a first expansion chamber 37 is formed between the upstream side separator 35 and the downstream side separator 36. By the provision of the downstream side separator 36, the downstream side of the exhaust muffler body 3 becomes the double structure, and a heat insulation chamber (or a sound shield chamber) 39 is formed between the downstream side separator 36 and the downstream side cover 34. That is, in the muffler body 3, the second expansion chamber 38, the first expansion chamber 37, and the heat insulation chamber 39 are formed in turn from the front side.

Further, the muffler body 3 is provided with an entrance communication pipe 40 communicatively connecting between the exhaust entrance portion 332 and the first expansion chamber 37, and an exit communication pipe 41 communicatively connecting between the second expansion chamber 38 and the exhaust exit portion 342.

Next, a specific description will be given of the constituent elements of the muffler body 3.

Upstream Side Cover 33

The upstream side cover 33 has a front wall 331, an exhaust entrance portion 332 formed at the substantially left half surface of the front wall 331, and an upstream side cover flange portion 333 projecting rearward from the circumference of the front wall 331. At the substantially right half surface of the front wall 331, a substantially X-shaped reinforcing bead 331a projecting frontward is formed. Formation of the reinforcing bead 331a improves the surface stiffness of the front wall 331, whereby vibration noises (chattering noises) of the front wall 331 are suppressed. Furthermore, as the reinforcing bead 331a is formed so as to project frontward, the volume of the muffler body 3 increases.

As shown in FIG. 5, the exhaust entrance portion 332 has a burring-like opening shape projecting frontward, and has its front portion externally fitted to the outer circumference face of the entrance communication pipe 40. The front end portion of the exhaust entrance portion 332 is positioned rearward than the front end portion of the entrance communication pipe 40.

Referring back to FIG. 4, the upstream side cover flange portion 333 has an upstream side inner sleeve holding portion 333a projecting rearward from the periphery of the front wall 331, and an upstream side outer sleeve holding portion 333c projecting rearward from the upstream side inner sleeve holding portion 333a via an upstream side step portion 333b. The upstream side outer sleeve holding portion 333c is positioned radially outward than the upstream side inner sleeve holding portion 333a.

Downstream Side Cover 34

The downstream side cover 34 has a rear wall 341, an exhaust exit portion 342 formed at the substantially right half surface of the rear wall 341 and a downstream side cover flange portion 343 projecting frontward from the periphery of the rear wall 341. At the substantially left half surface of the rear wall 341, a substantially X-shaped reinforcing bead 341a projecting rearward is formed. Formation of the reinforcing bead 341a improves the surface stiffness of the rear wall 341, whereby vibration noises (chattering noises) of the rear wall 341 are suppressed. Furthermore, as the reinforcing bead 341a is formed so as to project rearward, the volume of the muffler body 3 increases.

The exhaust exit portion 342 has a gasket mounting face 342a formed in a concave manner frontward from the rear wall 341, an exhaust exit opening 342b bored at the gasket mounting face 342a, and a spark arrester mounting portion 342c provided on the rear wall 341 radially outward than the gasket mounting face 342a.

The downstream side cover flange portion 343 has a downstream side inner sleeve holding portion 343a projecting frontward from the periphery of the rear wall 341, and a downstream side outer sleeve holding portion 343c further projecting frontward from the downstream side inner sleeve holding portion 343a via a downstream side step portion 343b. The downstream side outer sleeve holding portion 343c is positioned radially outward than the downstream side inner sleeve holding portion 343a.

Sleeve portion 30

As shown in FIG. 5, the sleeve portion 30 includes an outer sleeve 31, an inner sleeve 32 positioned as being distanced from the outer sleeve 31 radially inwardly, and a sound absorption chamber 42 formed between the outer sleeve 31 and the inner sleeve 32. A sound absorbing material 43 is enclosed in the sound absorption chamber 42. The sound absorbing material 43 has, for example, a two-layer structure, and is structured by stainless steel wool arranged on the inner sleeve 32 side and glass wool arranged on the outer sleeve 31 side. Note that, the sound absorbing material 43 may be formed in a single-layer structure.

The outer sleeve 31 is a cylindrical element formed of a steel plate being wound in an elliptical manner, the abutting ends of which are joined to each other by welding. The outer sleeve 31 extends from the upstream side outer sleeve holding portion 333c to the downstream side outer sleeve holding portion 343c. The front portion of the outer sleeve 31 is fixed by welding to the rear end peripheral portion of the upstream side outer sleeve holding portion 333c, and the rear portion of the outer sleeve 31 is fixed by welding to the front end peripheral portion of the downstream side outer sleeve holding portion 343c.

The inner sleeve 32 is a cylindrical element formed of a steel plate being wound in an elliptical manner, the abutting ends of which are joined to each other by welding. The inner sleeve 32 extends from the upstream side inner sleeve holding portion 333a to the downstream side inner sleeve holding portion 343a. The front portion of the inner sleeve 32 has its outer circumferential cylindrical face internally fitted to the upstream side inner sleeve holding portion 333a so as to be slidable in the front-rear direction (that is, in the longitudinal direction of the muffler body 3). On the other hand, the rear portion of the inner sleeve 32 is fixed by welding at several portions in the circumferential direction, as being interposed between the downstream side separator flange portion 362 and the downstream side inner sleeve holding portion 343a.

Since the inner sleeve 32 is held in this manner, the relative elongation between the outer sleeve 31 and the inner sleeve 32 can be tolerated. That is, when exhaust gas flows inside the exhaust muffler body 3, the outer sleeve 31 and the inner sleeve 32 thermally expand in accordance with their respective temperatures. Meanwhile, the sleeve portion 30 has a double structure made up of the outer sleeve 31 and the inner sleeve 32, and furthermore, the sound absorbing material 43 is arranged between the outer sleeve 31 and the inner sleeve 32. Accordingly, the outer sleeve 31 and the inner sleeve 32 are different from each other in temperature. More specifically, the temperature of the inner sleeve 32 facing the first and second expansion chambers 37 and 38 and the heat insulation chamber 39 is higher than that of the outer sleeve 31 being exposed to the air. Therefore, the thermal expansion amount of the inner sleeve 32 is greater than that of the outer sleeve 31.

At this time, the upstream side cover 33 and the downstream side cover 34 become away from each other in accordance with the thermal expansion amount of the outer sleeve 31, and the inner sleeve 32 having its rear portion fixed to the downstream side cover 34 shifts with the downstream side cover 34. On the other hand, the front portion of the inner sleeve 32 slides over the upstream side inner sleeve holding portion 333a of the upstream side cover 33 and thermally expands freely, irrespective of the displacement of the upstream side cover 33 corresponding to the thermal expansion amount of the outer sleeve 31. That is, the relative elongation of the outer sleeve 31 and the inner sleeve 32 is tolerated.

Further, the inner sleeve 32 is provided with many pores 322 that establish communication between the sound absorption chamber 42 and the second expansion chamber 38. Further, as shown in FIG. 6 in an enlarged manner, at the front end portion of the inner sleeve 32, a bent portion 321 that is inwardly bent is formed. Formation of the bent portion 321 allows the inner sleeve 32 to be easily assembled to the upstream side inner sleeve holding portion 333a. Specifically, allowing the bent portion 321 to abut on the entrance portion of the upstream side inner sleeve holding portion 333a, the inner sleeve 32 can be guided and assembled to the upStream side inner sleeve holding portion 333a.

Thus, for example in the case where the upstream side cover 33 is fixed by welding to the outer sleeve 31 and thereafter the inner sleeve 32 is assembled from the downstream side of the outer sleeve 31, the tip portion of the inner sleeve 32 can be easily fitted to the upstream side inner sleeve holding portion 333a at the bottom while being guided by the bent portion 321. That is, the inner sleeve 32 can be easily fitted to the upstream side inner sleeve holding portion 333a at the bottom that cannot easily be visually recognized.

Upstream Side Separator 35

Referring back to FIG. 5, the upstream side separator 35 has an upstream side partition wall 351 that partitions the inner circumferential side of the inner sleeve 32 into the first expansion chamber 37 and the second expansion chamber 38, and an upstream side separator flange portion 352 projecting rearward from the periphery of the upstream side partition wall 351. At the upstream side partition wall 351, a burring-like entrance communication pipe mounting portion 351a and an exit communication pipe mounting portion 351b projecting rearward, and a burring-like communication hole 351c projecting frontward (see FIG. 4) are formed. The upstream side separator 35 is fixed by welding at several portions in the circumferential direction to the inner circumferential face of the inner sleeve 32 via the upstream side separator flange portion 352.

Downstream Side Separator 36

The downstream side separator 36 has a downstream side partition wall 361 that partitions the inner circumferential side of the inner sleeve 32 into the first expansion chamber 37 and the expansion chamber 39, and a downstream side separator flange portion 362 projecting rearward from the periphery of the downstream side partition wall 361. At the downstream side partition wall 361, a burring-like exit communication pipe mounting portion 361a projecting rearward is formed. The downstream side separator 36 is fixed to the downstream side inner sleeve holding portion 343a by welding, together with the rear portion of the inner sleeve 32 as described above, at several portions in the circumferential direction via the downstream side separator flange portion 362.

Entrance Communication Pipe 40

The entrance communication pipe 40 is made of a straight tubular pipe member having a constant diameter, and extends rearward from the exhaust entrance portion 332, to the rear side of the entrance communication pipe mounting portion 351a. In the entrance communication pipe 40, a catalyst 6 is arranged. As shown in FIG. 7 in an enlarged manner, the front end portion of the exhaust entrance portion 332 and the front end portion of the entrance communication pipe 40 are arranged stepwise on the outer circumference of the entrance cone portion 73, and these three components are integrally joined by a common welding bead W1. Referring back to FIG. 5, the rear portion of the entrance communication pipe 40 is joined by welding at several portions in the circumferential direction to the entrance communication pipe mounting portion 351a.

Catalyst 6

The catalyst 6 is structured by a first catalyst 61 and a second catalyst 62, in each of which a honeycomb carrier made of metal is supported noble metal. The second catalyst 62 has its downstream side end face substantially matched with the downstream end portion of the entrance communication pipe 40. The first catalyst 61 is arranged to be away on the upstream side by a prescribed distance relative to the second catalyst 62.

Distance L1 between the upstream side end face of the first catalyst 61 and the downstream side end face of the second catalyst 62 is sufficiently shorter than length L2 of the entrance communication pipe 40. For example, distance L1 is set to be substantially half as great as L2. That is, in front of the first catalyst 61 in the entrance communication pipe 40, a space having a substantially identical inner diameter as the outer diameter of the first catalyst 61 is formed over a prescribed length.

The first catalyst 61 and the second catalyst 62 are fixed by brazing to the inner circumferential face of the entrance communication pipe 40.

Exit Communication Pipe 41

The exit communication pipe 41 has a straight tubular pipe member 411 having a constant diameter, and a lid member 412 joined by welding to the front end portion of the pipe member 411. The pipe member 411 extends from the front of the exit communication pipe mounting portion 351b to immediately before the exhaust exit portion 342 via the exit communication pipe mounting portion 361a. Note that, the central axis of the pipe member 411 is substantially identical to the central axis of the exhaust exit opening 342b. The rear end position of the pipe member 411 is set so as not to be in contact with the exhaust exit portion 342, in consideration of the shape tolerance, the assembly tolerance, the thermal expansion amount and the like of each component.

At the lid member 412, a burring-like opening 412a projecting frontward is formed. The exit communication pipe 41 is fixed by welding at several portions in the circumferential direction to the exit communication pipe mounting portion 351b of the upstream side separator 35 at a slightly frontward position than the central portion in the front-rear direction of the pipe member 411. Further, the exit communication pipe 41 is fixed by welding at several portions in the circumferential direction, on the rear portion of the pipe member 411, to the exit communication pipe mounting portion 361a of the downstream side separator 36.

(Spark Arrester 5)

Next, a description will be given of the spark arrester 5 with reference to FIGS. 8 to 10. FIG. 8 is a vertical cross-sectional view of the spark arrester 5. FIG. 9 is a IX-IX cross-sectional view of FIG. 5. FIG. 10 is a X-X cross-sectional view of FIG. 5. As shown in FIG. 8, the spark arrester 5 includes a spark arrester body portion 51 for capturing soot or carbon in exhaust gas, a tailpipe 52 for discharging the exhaust gas having passed through the spark arrester body portion 51 into the air, a spark arrester flange 53 for mounting the spark arrester 5 to the exhaust exit portion 342 (see FIG. 4), an inner circumferential ring 54 for coupling the spark arrester body portion 51 and the tailpipe 52 to each other, and an outer circumferential ring 55 for fixing the spark arrester body portion 51 to the inner circumferential ring 54.

The spark arrester body portion 51 is in a shape of a sleeve whose front end portion is closed while being open rearward. The circumference of the spark arrester body portion 51 is formed by having a mesh-like member made of metal cylindrically wrapped around such that its opposite peripheries overlap each other, and by fixing the overlapped peripheries at several portions by spot welding. Then, as shown in FIG. 9, the front portion of the spark arrester body portion 51 is formed by folding four sides of the circumferential portion inwardly, and fixing the substantially center portion of the overlapped mesh-like member by spot welding.

Referring back to FIG. 8, the tailpipe 52 is a pipe-like member, which extends rearward, and then curves diagonally downward. Thus, exhaust gas is caused to be discharged from the rear end portion of the tailpipe 52 in the rearward diagonally downward direction, that is, toward the ground.

The spark arrester flange 53 includes a substantially triangular base plate 531 (see FIG. 4), a sidewall 532 provided to stand rearward from the periphery of the base plate 531, and a tailpipe mounting portion 533 provided at the substantially center portion of the base plate 531 so as to project rearward. Near each vertex of the substantially triangle base plate 531, a spark arrester mounting hole 531a is bored. As shown in FIG. 4, by allowing a bolt 10 to penetrate through the spark arrester mounting hole 531a so as to screw to the spark arrester mounting portion 342c, the spark arrester 5 is removably fixed to the exhaust exit portion 342. Further, as shown in FIG. 5, the spark arrester body portion 51 is positioned in the exit communication pipe 41 in the state where the spark arrester 5 is fixed to the muffler body 3.

Referring back to FIG. 8, the outer circumferential ring 55 is a cylindrical element opening in the front-rear direction, and is fitted to the outer circumferential portion of the spark arrester body portion 51 with its rear end portion substantially matched with the rear end portion of the spark arrester body portion 51. The inner circumferential ring 54 is a cylindrical element that opens in the front-rear direction and that is structured to be longer in the longitudinal direction than the outer circumferential ring 55. The inner circumferential ring 54 is fitted to the inner circumferential portion of the spark arrester body portion 51 while being substantially matched with the front end portion of the outer circumferential ring 55. That is, the rear end portion of the inner circumferential ring 54 is positioned on the rear side of the spark arrester body portion 51.

By allowing the rear end portion of the spark arrester body portion 51 to be inserted between the inner circumferential ring 54 and the outer circumferential ring 55, and fixing the inner circumferential ring 54 and the outer circumferential ring 55 to each other by spot welding, the spark arrester body portion 51 made of a mesh-like member is surely fixed to the inner circumferential ring 54 and the outer circumferential ring 55 each being a plate-like member.

At the rear portion of the inner circumferential ring 54, the tailpipe 52 is fitted to the inner circumferential side, and the tailpipe mounting portion 533 of the spark arrester flange 53 is fitted to the outer circumferential side. The rear end portion of the tailpipe mounting portion 533 is positioned slightly frontward relative to the rear end portion of the inner circumferential ring 54. Thus, the rear end portion of the tailpipe mounting portion 533 and the rear end portion of the inner circumferential ring 54 are arranged stepwise on the outer circumference face of the tailpipe 52, and these three components are integrally joined by a common welding bead W2.

Here, with reference to FIGS. 9 and 10, a description will be given of a cross-sectional area of the exhaust flow path defined by the spark arrester 5 and the exit communication pipe 41. Firstly, with reference to FIG. 9, the opening area S1 of the opening 412a is designed to be substantially identical to the cross-sectional area S2 (see FIG. 2) of the exhaust flow path at the upstream end of the exhaust pipe 7. Further, with reference to FIG. 10, the inner diameter of the pipe member 411 is set such that the difference between the cross-sectional area S3 being perpendicular to the exhaust flow path of the pipe member 411 and the cross-sectional area S4 being perpendicular to the exhaust flow path of the spark arrester body portion 51 becomes substantially identical to the opening area S1 (see FIG. 9) of the opening 412a. That is, for the cross-sectional area of the exhaust flow path defined by the spark arrester 5 and the exit communication pipe 41, the cross-sectional area S2 of the exhaust flow path at the upstream end of the exhaust pipe 7 is secured.

(Exhaust Muffler Mounting Apparatus 8)

Next, a description will be given of the exhaust muffler mounting apparatus 8. As shown in FIG. 9, the exhaust muffler mounting apparatus 8 includes a metal-made rod support plate 81 fixed by welding to the outer circumference face of the outer sleeve 31, and a right and left pair of metal-made rods 82 fixed by welding to the bottom end portion of the rod support plate 81. The rod support plate 81 has a first inclined portion 811 extending from the right lower portion of the outer sleeve 31 in the diagonally left downward direction, a second inclined portion 812 extending from the left lower portion of the outer sleeve 31 in the diagonally right downward direction, and a horizontal portion 813 that connects between the bottom ends of the first and second inclined portions 811 and 812 and that extends substantially horizontally. The rods 82 extend in the front-rear direction.

The first and second inclined portions 811 and 812 are respectively provided with reinforcing beads 811a and 812a provided in the direction being away from the outer sleeve 31 in a concave manner. Further, the horizontal portion 813 is provided with rod mounting portions 813a for mounting the rods 82 and a reinforcing bead 813b provided in a concave manner toward the outer sleeve 31. The rod mounting portions 813a are formed as a right and left pair. The reinforcing bead 813b is formed over the joining portion of the horizontal portion 813 and the first and second inclined portions 811 and 812. Provision of the reinforcing beads 811a, 812a, and 813b improves rigidity of the rod support plate 81.

Further, since the reinforcing beads 811a and 812a are provided in a concave manner in the direction being away from the outer sleeve 31, the reinforcing beads 811a and 812a are prevented from abutting on the outer surface of the outer sleeve 31, whereby the first and second inclined portions 811 and 812 can easily conform to the outer surface of the outer sleeve 31. Thus, the first and second inclined portions 811 and 812 can be more surely fixed by welding to the outer sleeve 31.

Further, since the reinforcing bead 813b is provided in a concave manner toward the outer sleeve 31, the reinforcing bead 813b is prevented from abutting on the outer surface of the rods 82, whereby the rod mounting portions 813a can easily conform to the outer surface of the rods 82. Thus, the rods 82 can be more surely fixed by welding to the rod mounting portions 813a.

As shown in FIG. 2, by allowing the right and left pair of rods 82 to be inserted into the bores of the rubber dampers 242a of the exhaust muffler mounting portion 24 mounted on the transmission 22 from the rear side toward the front side, the exhaust muffler 2 can be surely held above the transmission 22.

The exhaust system 1 has its front portion fixed to the exhaust portion 21 of the engine 20 via the flange 71, and has its rear portion fixed to the exhaust muffler mounting portion 24 provided to the transmission 22 via the exhaust muffler mounting apparatus 8. Further, the transmission 22 is fixed to the engine 20 so as not to be relatively displaced. That is, since the exhaust system 1 including the front portion and the rear portion is fixed to the identical vibration system, it is not necessary to take into consideration of the relative displacement that occurs when the front portion and the rear portion are fixed to separate vibration systems. Thus, the exhaust system 1 is strongly fixed.

Further, since the exhaust muffler 2 is held by the rubber dampers 242a as being inserted in the front-rear direction via the rods 82, thermal elongation of the exhaust system 1 in the front-rear direction, dimensional variations in the front-rear direction of each component of the exhaust system 1, or assembly variations of each component are absorbed in an excellent manner.

(Gasket 9)

As shown in FIG. 4, the gasket 9 is a disc-like seal member exhibiting excellent heat resistance. The gasket 9 seals against leakage of exhaust gas from between the gasket mounting face 342a of the exhaust exit portion 342 and the base plate 531 of the spark arrester flange 53.

[Flow of Exhaust Gas]

Next, a description will be given of the flow of exhaust gas in the exhaust system 1. Firstly, as indicated by arrow A in FIG. 2, exhaust gas discharged from the exhaust portion 21 of the engine 20 passes through the exhaust pipe 7 and arrives at the exhaust muffler 2. At this time, the exhaust gas enters from the entrance cone portion 73 of the exhaust pipe 7 and arrives at the exhaust entrance portion 332 (see FIG. 3). Here, as indicated by arrow B in FIG. 5, since the entrance cone portion 73 has a cone shape whose diameter widens rearward, the exhaust gas passing through the entrance cone portion 73 arrives at the exhaust entrance portion 332 while substantially uniformly diffusing in the radial direction.

Next, as indicated by arrow C in FIG. 5, the exhaust gas flows into the entrance communication pipe 40. Since the catalyst 6 is arranged as being away by a prescribed length from the upstream side end portion of the entrance communication pipe 40, the exhaust gas is further diffused in the radial direction while proceeding in the entrance communication pipe 40 until it arrives at the catalyst 6. As a result, at the upstream side end face of the catalyst 6, the exhaust gas that is substantially evenly distributed in the radial direction arrives.

Next, as indicated by arrow D in FIG. 5, the exhaust gas purified by the catalyst 6 arrives at the first expansion chamber 37. At this time, the temperature of the exhaust gas increases by the oxidation-reduction reaction of the catalyst 6. As the exhaust gas expands in the first expansion chamber 37, the back pressure and the exhaust noises are reduced. Note that, since the heat insulation chamber 39 is provided via the downstream side separator 36, the exhaust gas having passed through the catalyst 6 and achieving high temperatures is blocked by the heat insulation chamber 39, and therefore will not blow in the downstream side cover 34. Thus, the downstream side cover 34 is prevented from achieving high temperatures, and durability of the downstream side cover 34 is enhanced.

Further, around the first expansion chamber 37, the sound absorption chamber 42 where the sound absorbing material 43 is arranged is provided via the inner sleeve 32. Therefore, the exhaust noises emitted from the first expansion chamber 37 are prevented from passing through the sleeve portion 30 and emitted to the outside of the exhaust muffler 2.

Next, as indicated by arrow E in FIG. 5, the exhaust gas passes through a pair of communication holes 351c (see FIG. 4) provided at the upstream side separator 35, and arrives at the second expansion chamber 38. The exhaust gas has its flow regulated when it passes through the communication holes 351c, whereby the back pressure and the exhaust noises are further reduced. Then, the exhaust gas having passed through the communication holes 351c is expanded in the second expansion chamber 38, and the back pressure and the exhaust noises are even more reduced. In addition, since the second expansion chamber 38 communicates, through the pores 322, with the sound absorption chamber 42 formed around the second expansion chamber 38, the exhaust noises in the second expansion chamber 38 are absorbed by the sound absorbing material 43 arranged in the sound absorption chamber 42. Thus, the exhaust noise is still even more reduced.

Next, as indicated by arrow F in FIG. 5, the exhaust gas passes through the opening 412a of the lid member 412 and flows into the exit communication pipe 41. The opening 412a is burring shaped, and is smaller than the passage diameter of the pipe member 411. Therefore, when the exhaust gas flows into the exit communication pipe 41 from the second expansion chamber 38, the exhaust flow path is sharply narrowed by the opening 412a, whereby the back pressure and the exhaust noises of the exhaust gas are effectively reduced.

Note that, since the opening area S1 (see FIG. 9) of the opening 412a is formed to be substantially as great as the cross-sectional area S2 (see FIG. 2) of the exhaust flow path in the upstream end portion of the exhaust pipe 7, the exhaust flow path is prevented from excessively narrowed by the opening 412a, and the exhaust flow path of proper size is secured.

Next, as indicated by arrow G in FIG. 5, the exhaust gas flows into the inner circumferential side of the spark arrester body portion 51 from the outer circumferential portion of the spark arrester body portion 51. When the exhaust gas passes through the spark arrester body portion 51, soot, carbon and the like in the exhaust gas are captured by the mesh-like member of the spark arrester body portion 51.

Since the spark arrester body portion 51 is arranged in the exit communication pipe 41 being separated from the first and second expansion chambers 37 and 38, the back pressure with an exhaust pulse in the first and second expansion chambers 37 and 38 will not act on the spark arrester body portion 51. Further, since the back pressure is effectively reduced by the opening 412a of the lid member 412, the back pressure acting on the spark arrester body portion 51 is sufficiently reduced.

Note that, in the exit communication pipe 41, the passage area of the exhaust flow path formed around the spark arrester body portion 51, that is, the difference between the cross-sectional area S3 (see FIG. 10) of the pipe member 411 and the cross-sectional area S4 (see FIG. 10) of the spark arrester body portion 51, is set to be substantially identical to the opening area S1 (see FIG. 9) of the opening 412a of the lid member 412. Thus, while securing the passage area of the exhaust flow path in the exit communication pipe 41, an excessive increase in the diameter of the pipe member 411 is avoided.

Finally, as indicated by arrow H in FIG. 5, the exhaust gas flows into the tailpipe 52, and is discharged from the rear end portion of the tailpipe 52 into the air. In this manner, the exhaust gas discharged from the exhaust portion 21 (see FIG. 2) of the engine 20 arrives at the exhaust muffler 2. Then, the exhaust gas is purified in the exhaust muffler 2, and discharged from the tailpipe 52 into the air with fully suppressed exhaust noises.

[Effects of Embodiment]

(1) The spark arrester body portion 51 is arranged in the exit communication pipe 41 separated from the first and second expansion chambers 37 and 38, and the lid member 412 having the opening 412a as the exhaust flow path narrowing portion is provided at the upstream end portion of the exit communication pipe 41. Accordingly, the back pressure and the exhaust pulse acting on the spark arrester body portion 51 can be reduced. This can suppress deformation of the spark arrester body portion 51. As a result, a reinforce member for reinforcing the spark arrester body portion 51 made of a mesh-like member can be dispensed with, and designing of the spark arrester can be streamlined.

(2) The spark arrester body portion 51 is structured solely by the mesh-like member without any reinforce member and, therefore, productivity of the spark arrester body portion 51 can be improved and a reduction in costs can be achieved.

(3) The spark arrester body portion 51 is structured without any reinforce member. Thus, since the surface of the spark arrester body portion 51 is not shielded by the reinforce member, the filter portion of the spark arrester body portion 51 can be secured for the entire surface. As a result, an increase in size of the spark arrester body portion 51 can be avoided, and the spark arrester body portion 51 can be structured in a compact manner.

(4) The exhaust flow path narrowing portion can be easily formed by the burring-like opening 412a provided at the lid member 412. In particular, as compared with the case where the tapered narrowing portion is formed as the exhaust flow path narrowing portion, the exhaust flow path can be sharply narrowed, whereby the back pressure and the exhaust pulse in the exit communication pipe 41 can be more effectively reduced. Thus, deformation of the spark arrester body portion 51 can further be suppressed.

(5) The opening area S1 of the opening 412a as the exhaust flow path narrowing portion is substantially identical to the cross-sectional area S2 of the exhaust flow path at the upstream side end portion in the exhaust pipe 7. Thus, while realizing a reduction in the back pressure at the upstream side end portion of the exit communication pipe 41, it becomes possible to secure the exhaust flow path of proper size and to avoid a reduction in engine performance caused by an excessive increase in the back pressure.

(6) The inner diameter of the pipe member 411 is set such that the difference between the cross-sectional area S3 being perpendicular to the exhaust flow path of the pipe member 411 and the cross-sectional area S4 being perpendicular to the exhaust flow path of the spark arrester body portion 51 becomes substantially identical to the opening area S1 of the opening 412a. Thus, an excessive increase in the size of the pipe member 411 can be avoided, whereby the muffler body 3 can be structured in a compact manner.

The present invention is not limited to the embodiment described above, and various modifications can be employed in the range not departing from the claims.

Claims

1. An exhaust muffler for a vehicle comprising:

a muffler body coupled to an exhaust pipe; and

a tailpipe coupled to the muffler body;

wherein the muffler body includes: a plurality of expansion chambers; an exit communication pipe that discharges exhaust to the tailpipe from one of the plurality of expansion chambers positioned in a most downstream part of an exhaust flow path; an exhaust flow path narrowing portion at an upstream end of the exit communication pipe; and a spark arrester body arranged at a downstream side of the exhaust flow path narrowing portion in the exit communication pipe.

2. The exhaust muffler for a vehicle according to claim 1, wherein

the spark arrester body comprises a mesh-like member.

3. The exhaust muffler for a vehicle according to claim 1, wherein

the exhaust flow path narrowing portion is comprises a lid member having a through hole, the lid member being provided at an upstream portion of the exit communication pipe.

4. The exhaust muffler for a vehicle according to claim 3, wherein

an opening area of the through hole is substantially equal to a cross-sectional area of an exhaust flow path at an upstream end of the exhaust pipe.

5. The exhaust muffler for a vehicle according to claim 3, wherein

a difference between a cross-sectional area perpendicular to an exhaust flow path of the exit communication pipe and a cross-sectional area perpendicular to an exhaust flow path of the spark arrester is substantially equal to an opening area of the through hole.

6. The exhaust muffler for a vehicle according to claim 1, wherein an upstream end of the spark arrester body is spaced apart from the exhaust flow path narrowing portion.