JP6126564B2 - Exhaust pipe with catalyst installed in the vehicle - Google Patents

Description

  The present invention relates to an improvement in an exhaust pipe with a catalyst mounted on a vehicle.

  Various exhaust pipes with a catalyst for purifying exhaust gas mounted on a vehicle and exhausted from an internal combustion engine have been proposed (see, for example, Patent Document 1 (FIG. 4)).

  As shown in FIG. 4 of Patent Document 1, the exhaust pipe (31) (the numbers in parentheses indicate the symbols described in Patent Document 1. The same applies hereinafter) is an exhaust that forms an exhaust path (37) through which exhaust gas passes. A pipe (39), a reduction catalyst (38) interposed inside the exhaust pipe (39), and an axial direction of the exhaust pipe (39) extend so as to surround the exhaust pipe (39). A path forming member (33). That is, the exhaust pipe (31) is a member having a so-called double pipe structure.

  By the way, in the technique of Patent Document 1, the reduction catalyst (38) is disposed inside the exhaust pipe (39). Details of the mounting structure of the reduction catalyst (38) to the exhaust pipe (39) are disclosed. It has not been. For example, the exhaust pipe (39) and the path forming member (33) (hereinafter referred to as “cover member (33)”) at the joining relationship between the reduction catalyst (38) and the exhaust pipe (39) or at the position of the reduction catalyst (38). Details are not disclosed.

Usually, in order to fix the reduction catalyst (38) to the exhaust pipe (39), welding is performed. The weld bead has a height. In order to secure a space for accommodating the weld bead, it is necessary to increase the outer diameter of the cover member (33). As the outer diameter of the cover member (33) increases, the outer diameter of the exhaust pipe also increases.
In an exhaust pipe with a catalyst in which the outside of the catalyst is covered with a cover member, a technique that can keep the outer diameter of the exhaust pipe small is desired.

JP 2010-1738 A

  This invention makes it a subject to provide the technique which can restrain the outer diameter of an exhaust pipe small in the exhaust pipe with a catalyst with which the outer side of the catalyst is covered with the cover member.

The invention according to claim 1 is connected to an exhaust port of an internal combustion engine mounted on a vehicle to form an exhaust path, a catalyst is provided in the middle of the exhaust path, and an upstream pipe portion located upstream from the catalyst; An exhaust pipe with a catalyst mounted on a vehicle, wherein the downstream pipe portion located downstream from the catalyst is formed of a separate member, the catalyst is surrounded by a catalyst outer cylinder, and the outside of the catalyst outer cylinder is covered with a cover member. The cover member is welded to the catalyst outer cylinder at one end thereof, and the other end is welded to one of the upstream pipe portion or the downstream pipe portion. One end of the catalyst outer cylinder is welded to the cover member and the upstream pipe portion or the downstream pipe portion. The other of the pipe parts is welded and fixed, and the upstream pipe part and the downstream pipe part are connected with the same diameter as the outer diameter of the catalyst outer cylinder to form an exhaust path, and the other end of the catalyst outer cylinder is , Inside the cover member, on one of the upstream pipe part or the downstream pipe part Characterized in that it is combined with the support.

The invention according to claim 2 is characterized in that one end of the cover member is welded to the upstream pipe portion at the first welded portion, and the other end of the cover member is welded to the downstream pipe portion at the second welded portion. .

In the invention according to claim 3 , the catalyst outer cylinder is welded to the second welded portion, and the distance between the catalyst and the second welded portion is smaller than the distance between the catalyst and the first welded portion. And

The invention according to claim 4 is characterized in that the catalyst outer cylinder is welded to the first welded portion, and the distance between the catalyst and the first welded portion is larger than the distance between the catalyst and the second welded portion.

The invention according to claim 5 is characterized in that one of the upstream pipe part or the downstream pipe part, the cover member, and the catalyst outer cylinder are welded at a time.

The invention according to claim 6 is characterized in that the upstream pipe part and the downstream pipe part are single pipes, and the upstream pipe part, the downstream pipe part and the catalyst outer cylinder have substantially the same outer diameter.

In the invention according to claim 7 , the upstream pipe part and the downstream pipe part are each a double pipe having an inner pipe and an outer pipe, the outer diameter of the outer pipe of the upstream pipe part and the outer pipe of the downstream pipe part. The outer diameter is substantially the same.

In the invention according to claim 8 , an exhaust path is configured by connecting to an exhaust port of an internal combustion engine mounted on a vehicle, a catalyst is provided in the middle of the exhaust path, and an upstream pipe portion positioned upstream from the catalyst; An exhaust pipe with a catalyst mounted on a vehicle, wherein the downstream pipe portion located downstream from the catalyst is formed of a separate member, the catalyst is surrounded by a catalyst outer cylinder, and the outside of the catalyst outer cylinder is covered with a cover member. The cover member is welded to the catalyst outer cylinder at one end, and the other end is welded to one of the upstream pipe part or the downstream pipe part. One end of the catalyst outer cylinder is welded to the cover member and the upstream pipe part or the downstream pipe. The upstream pipe part and the downstream pipe part are connected to each other with the same diameter as the outer diameter of the catalyst outer cylinder to form an exhaust passage, and the upstream pipe part and the downstream pipe One end of the outer pipe of the pipe part has a throttle part and is upstream The other end of the outer pipe of the downstream pipe and the outer pipe of the downstream pipe has an extending portion extending in the axial direction of the downstream pipe, and the throttle is between the end of the cover member and the catalyst outer cylinder. The throttle part and the cover member are welded and fixed at this connection part.

  In the invention according to claim 1, one end of the catalyst outer cylinder is welded to the cover member and one of the upstream pipe portion and the downstream pipe portion. That is, one end of the catalyst outer cylinder was welded and fixed together with the exhaust pipe and the cover member.

  Temporarily, in the structure in which one end of the catalyst outer cylinder is welded to the exhaust pipe and the cover member is separately welded to the exhaust pipe, a built-up portion of a weld bead for fixing one end of the catalyst outer cylinder is formed inside the cover member. Therefore, it is necessary to increase the outer diameter of the cover member accordingly.

  In this regard, in the present invention, since one end of the catalyst outer cylinder is welded to the cover member and the exhaust pipe, the outer diameter of the cover member is increased by the build-up portion of the weld bead that fixes one end of the catalyst outer cylinder. Never become.

  Therefore, the outer diameter of the cover member can be kept small. If the outer diameter of the cover member is reduced, the appearance of the exhaust pipe with catalyst is enhanced. In addition, the catalyst can be warmed up early as the outer diameter of the cover member becomes smaller.

  In the invention according to claim 2, one end and the other end of the cover member are welded to the upstream pipe portion and the downstream pipe portion, respectively. That is, since the cover member can be used as a connecting member between the upstream pipe portion and the downstream pipe portion, the number of parts of the exhaust pipe with catalyst can be reduced.

In the invention which concerns on Claim 3, the distance between the 1st welding part located in the upstream of a catalyst and a catalyst is large compared with the distance between the 2nd welding part located in the downstream of a catalyst, and a catalyst.
Temporarily, depending on the position of the weld bead of the 1st welding part arrange | positioned upstream of a catalyst, the heat capacity of an exhaust pipe changes in the upstream of a catalyst. If the heat capacity on the upstream side of the catalyst changes, it may be difficult to obtain favorable purification characteristics.

  In this regard, in the present invention, since the distance between the catalyst and the second welded portion is smaller than the distance between the catalyst and the first welded portion, the influence due to the absorption of exhaust heat caused by the weld bead of the first welded portion is suppressed. be able to. As a result, the purification characteristics of the catalyst can be easily brought close to the desirable characteristics.

  In the invention which concerns on Claim 4, the distance between the 1st welding part located in the upstream of a catalyst and a catalyst is large compared with the distance between the 2nd welding part located in the downstream of a catalyst, and a catalyst. Thereby, when warming up a catalyst, the influence by absorption of the exhaust heat by the weld bead of the 1st welding part located in the upstream of a catalyst can be suppressed. As a result, the purification characteristics of the catalyst can be easily brought close to the desirable characteristics.

  In the invention which concerns on Claim 5, a downstream pipe part, a cover member, and a catalyst outer cylinder are welded at once. Since the three members are welded at a time, the welding length is shortened and the number of welding steps can be reduced. As a result, the manufacturing cost of the exhaust pipe with catalyst can be suppressed.

  In the invention according to claim 6, the upstream pipe part, the downstream pipe part, and the catalyst outer cylinder have substantially the same outer diameter. Thus, the external appearance of the exhaust pipe can be enhanced by setting the outer diameters of the respective pipes to be substantially the same.

  In the invention which concerns on Claim 7, both an upstream pipe part and a downstream pipe part are double pipes, and the outer diameter of an upstream pipe part and the outer diameter of a downstream pipe part are substantially the same. If the outer diameters of the upstream pipe part and the downstream pipe part are substantially the same, the outer diameter of the upstream pipe part and the outer diameter of the downstream pipe part are different from each other, particularly in the connecting part with the catalyst outer cylinder. The diameter change becomes inconspicuous. As a result, the appearance of the exhaust pipe can be improved.

  In the invention which concerns on Claim 8, a throttle part, an extension part, and a catalyst outer cylinder are weld-fixed by the connection part provided in a throttle part. That is, since welding is performed at the connecting portion provided in the narrowed portion, it is possible to suppress protrusion of the build-up portion of the weld bead. As a result, the appearance of the exhaust pipe can be improved.

1 is a right side view of a motorcycle according to the present invention. It is a right view of the exhaust apparatus which concerns on this invention. FIG. 3 is a sectional view taken along line 3-3 in FIG. 2. It is a figure explaining welding a catalyst support | carrier and a cover member to a downstream pipe part in FIG. It is a figure explaining welding an upstream pipe part to a catalyst carrier and a cover member in FIG. It is a figure explaining the welding structure of the exhaust pipe with a catalyst concerning an example and a comparative example. FIG. 7 is a cross-sectional view taken along line 7-7 in FIG. It is a figure explaining welding an upstream side exhaust pipe to a downstream side exhaust pipe in FIG. FIG. 9 is a sectional view taken along line 9-9 in FIG. 2. FIG. 3 is an enlarged view of 10 parts in FIG. 2. FIG. 11 is a cross-sectional view taken along line 11-11 in FIG. 2. It is sectional drawing of the exhaust pipe with a catalyst which concerns on 2nd Example. It is sectional drawing of the exhaust pipe with a catalyst which concerns on 3rd Example.

  Hereinafter, embodiments of the present invention will be described in detail. In the drawings and examples, “up”, “down”, “front”, “rear”, “left”, and “right” respectively indicate directions viewed from the driver who rides the motorcycle.

First, Embodiment 1 of the present invention will be described with reference to the drawings.
As shown in FIG. 1, a motorcycle 10 includes a body frame 11, a front wheel steering section 15 that supports a front wheel 13 so as to be steerable on the front portion of the body frame 11, and a body frame behind the front wheel steering section 15. 11, an internal combustion engine 17 as a drive source suspended from the vehicle 11, a rear wheel suspension unit 16 that supports the rear wheel 14 in a swingable manner on the vehicle body frame 11 behind the internal combustion engine 17, and a vehicle body behind the front wheel steering unit 15. This is a saddle-ride type vehicle that includes a fuel tank 18 and a seat 19 that are attached to the frame 11 in the front-rear direction, and an occupant sits on the seat 19.

  The vehicle body frame 11 forms a head pipe 21 that supports the front wheel steering unit 15 so as to be steerable, and a downward bent portion 22 that extends slightly inclined downward from the head pipe 21 toward the rear of the vehicle and then bends downward. However, the main frame 23 that extends downward and supports the internal combustion engine 17 and the fuel tank 18, the down frame 24 that extends from the head pipe 21 obliquely downward in the vehicle width direction, and the lower bent portion of the main frame 23. A seat rail 26 that extends rearward of the vehicle to support the seat 19 while forming an upper bent portion 27 that extends rearward from the vehicle 22 and bends upward in the middle, and between the upper bent portion 27 of the seat rail 26 and the main frame 23. The main element is the support frame 28 passed to the above.

  The front wheel steering unit 15 includes a steering handle 31, a front fork 32 extending downward from the steering handle 31 with a predetermined caster angle, and a front wheel 13 rotatably supported on the lower end of the front fork 32. It is a component. The rear wheel suspension 16 includes a swing arm 33 extending from the lower part of the main frame 23 toward the rear of the vehicle, the rear wheel 14 rotatably supported on the rear end of the swing arm 33, and the swing arm 33 and the seat rail 26. The rear cushion 34 delivered is a component.

  The internal combustion engine 17 includes a crankcase 37, a cylinder portion 38 that is inclined slightly forward from the upper surface of the crankcase 37 and extends upward, and an intake port 42 formed in the rear wall 38b of the cylinder portion 38 (FIG. 2). And an exhaust device 40 connected to an exhaust port 41 (see FIG. 2) formed in the front wall 38a of the cylinder portion 38. The front part of the crankcase 37 is attached to a front hanger 43 provided at the lower part of the down frame 24, and the rear part of the crankcase 37 is attached to a rear hanger 44 provided at the lower part of the main frame 23 so as to be suspended from the vehicle body frame 11. Is done. A guard frame 45 that guards the internal combustion engine 17 is attached to the down frame 24.

Next, the exhaust device will be described in detail.
The exhaust device 40 mounted on the motorcycle 10 extends forward from the front wall 38 a of the cylinder portion 38, bends downward, extends obliquely downward along the crankcase 37, and then extends along the lower end of the crankcase 37. An exhaust pipe 47 extending rearward, a catalyst unit 48 interposed in the middle of the exhaust pipe 47 and positioned in front of the crankcase 37, and inserted and connected from the rear end of the exhaust pipe 47 in a direction in which the swing arm 33 extends. The silencer 49 extends along the swing arm 33 at substantially the same height. A stay member 51 for attaching the exhaust device 40 to the rear hanger 44 on the vehicle side is provided at an intermediate portion in the longitudinal direction of the exhaust device 40.

  As shown in FIG. 2, the exhaust device 40 is connected to the exhaust port 41 of the internal combustion engine 17 and constitutes an exhaust path 52. The exhaust path 52 includes an exhaust pipe 47 and a silencer 49 connected to the downstream side of the exhaust pipe 47. A catalyst 53 is provided in the middle of the exhaust path 52. The exhaust pipe 47 extending from the exhaust port 41 includes an upstream exhaust pipe 35 and a downstream exhaust pipe 36 connected to the rear end of the upstream exhaust pipe 35, and a silencer is provided at the downstream end of the downstream exhaust pipe 36. 49 are connected. The catalyst 53 is accommodated on the upstream exhaust pipe 35 side.

Next, the detailed structure of the catalyst accommodated in the upstream side exhaust pipe and the peripheral portion will be described. In the following drawings, white arrows indicate the direction in which exhaust gas flows.
As shown in FIG. 3, the upstream side exhaust pipe 35 is a catalyst-equipped exhaust pipe 47 </ b> A in which a catalyst 53 is provided. The upstream side exhaust pipe 35 includes a catalyst outer cylinder 54 in which the catalyst 53 is accommodated, an upstream pipe part 55 located upstream from the catalyst outer cylinder 54, and a downstream pipe part 56 located downstream from the catalyst outer cylinder 54. It consists of. Each of the upstream pipe portion 55 and the downstream pipe portion 56 is composed of separate members. The outside of the catalyst 53 is covered with a cover member 57.

  In the exhaust pipe with catalyst 47 </ b> A, the catalyst unit 48 includes a catalyst 53, a cylindrical catalyst outer cylinder 54 that holds the catalyst 53, and a cover member 57 that covers the outside of the catalyst 53. The catalyst 53 has a cylindrical honeycomb structure. The cover member 57 extends along the axial direction of the catalyst outer cylinder 54 and has a cover diameter-reducing portion 61 in the vicinity of one end 57a and a cover diameter-increasing portion 62 in the vicinity of the other end 57b. The catalyst 53 and the catalyst outer cylinder 54 are surrounded with a gap of.

  An upstream pipe portion 55 is inserted into the inner peripheral surface 54 bu on the upstream side of the catalyst outer cylinder 54, and a downstream pipe portion 56 is inserted into the inner peripheral surface 54 au on the downstream side of the catalyst outer cylinder 54. The other end 57 b (upper end) of the cover member 57 is welded to the outer peripheral surface of the upstream pipe portion 55, and one end 57 a (lower end) of the cover member 57 is welded to the outer peripheral surface of the downstream pipe portion 56. Specifically, the other end 57 a (rear end) of the cover member 57 is welded to one end 54 a (rear end) of the catalyst outer cylinder 54 and is also welded to the outer peripheral surface of the downstream pipe portion 56.

  A portion where one end 57 b (front end) of the cover member 57 is welded to the upstream pipe portion 55 is referred to as a first weld portion 65, and the other end 57 a (rear end) of the cover member 57 is welded to the downstream pipe portion 56. 2 welds 66. The second welded portion 66 includes a welded portion for welding between one end 54 a (rear end) of the catalyst outer cylinder 54 and the cover member 57, and between the one end 54 a (rear end) of the catalyst outer cylinder 54 and the downstream pipe portion 56. It is the part where the welded part that welds is continuous. Note that the other end 54 b (front end) of the catalyst outer cylinder 54 is slidably supported by the upstream pipe portion 55.

  Here, the distance B1 between the lower end of the catalyst 53 and the second welded portion 66 is smaller than the distance A1 between the upper end of the catalyst 53 and the first welded portion 65 (B1 <A1). The upstream pipe part 55 and the downstream pipe part 56 are both single pipes, and the outer diameter D1 of the upstream pipe part 55, the outer diameter D2 of the downstream pipe part 56, and the outer diameter Ds of the catalyst outer cylinder 54 are substantially the same. .

Next, in FIGS. 4 to 5, a manufacturing method of the exhaust pipe with catalyst described in FIG. 3 will be described.
FIG. 4A is a diagram for explaining that the catalyst outer cylinder with the cover member temporarily welded is inserted into the downstream pipe portion, and FIG. 4B is the downstream of the catalyst outer cylinder with the cover member temporarily welded. It is a figure explaining having inserted in the pipe part. FIG. 4C is an enlarged view of part 4 (c) of FIG. 4B. FIG. 4D is a diagram illustrating that the catalyst outer cylinder and the cover member are fillet welded to the downstream pipe portion according to the embodiment. FIG. 4E is a diagram illustrating the downstream pipe portion according to the comparative example. It is a figure explaining that the catalyst outer cylinder and the cover member were fillet welded on the entire circumference. Fillet welding is a welding means that welds the corners of two surfaces that are substantially perpendicular to each other. In this embodiment, the corners of the stacked metal members (steel plates) are welded.

  As shown in FIG. 4A, a cover member 57 is inserted into the catalyst outer cylinder 54 to which the catalyst 53 is attached, and the cover member 57 is temporarily welded in the vicinity of the end portion 54a (lower end) of the catalyst outer cylinder 54. To do. The temporary welding is usually spot-welded at two or three locations in the circumferential direction. The end portion 54a (lower end) of the catalyst outer cylinder 54 and the end portion 57a (lower end) of the cover member 57 are not aligned (aligned), and the end portion 57a (lower end) of the cover member 57 is not in contact with the catalyst outer cylinder. Spot welding is performed in a state of being arranged so as to be shifted to the catalyst side by a length s1 from the end portion 54a (lower end) of 54. Next, the catalyst outer cylinder 54 to which the cover member 57 is temporarily fixed is inserted into the downstream pipe portion 56 in the direction of arrow a.

  FIG. 4B shows a state in which the catalyst outer cylinder 54 to which the cover member 57 is temporarily fixed is inserted into the downstream pipe portion 56.

  As shown in FIG. 4C, the second welded portion 66 is subjected to full fillet welding. In the figure, the hatched portion with chain lines is the portion where fillet welding is performed.

  As shown in the embodiment of FIG. 4D, fillet welding is performed on the second welded portion 66. While the weld bead 67 melts into any of the downstream pipe portion 56, the catalyst outer cylinder 54, and the cover member 57, the three parts are firmly fixed to each other. By performing fillet welding among the cover member 57, the catalyst outer cylinder 54, and the downstream pipe portion 56, the catalyst outer cylinder 54 and the cover member 57 can be reliably joined to the downstream pipe portion 56. That is, the downstream pipe portion 56, the cover member 57, and the catalyst outer cylinder 54 are welded at a time by the second welding portion 66.

  As shown in the comparative example of FIG. 4E, the end portion 57aa (rear end) of the cover member 57 protrudes from the end portion 54a (rear end) of the catalyst outer cylinder 54. When fillet welding is performed on the downstream pipe portion 56, the catalyst outer cylinder 54, and the cover member 57 in this positional relationship, the downstream pipe portion 56 and the cover member 57 are welded, but the catalyst outer cylinder 54 and the downstream side are welded. The pipe portion 56 and the catalyst outer cylinder 54 and the cover member 57 are not welded.

  Returning to FIG. 4D, in the present invention, the position of the end portion 57 a (rear end) of the cover member 57 that covers the catalyst outer tube 54 with respect to the end portion 54 a (rear end) of the catalyst outer tube 54. Is slightly shortened, so that the downstream pipe portion 56, the catalyst outer cylinder 54, and the cover member 57 can be securely fixed by welding.

  FIG. 5A is a diagram for explaining that the upstream pipe portion is inserted into the catalyst outer cylinder with the cover member temporarily fixed, and FIG. 5B is a diagram for explaining that the upstream pipe portion is inserted into the cover member. It is. FIG. 5C is an enlarged view of part 5 (c) of FIG. 5B. FIG. 5D is a diagram for explaining that the upstream pipe portion is fillet welded to the cover member according to the embodiment.

As shown in FIG. 5A, the upstream pipe portion 55 is inserted in the direction of the arrow m in the catalyst outer cylinder 54 and the cover member 57 welded to the downstream pipe portion in FIG.
FIG. 5B shows a state where the upstream pipe portion 55 is inserted into the catalyst outer cylinder 54 and the cover member 57. At this time, the end of the upstream pipe portion 55 is inserted into the other end 54 b (front end) of the catalyst outer cylinder 54.

As shown in FIG. 5C, the end portion of the cover member 57 is subjected to fillet welding on the entire circumference of the upstream pipe portion 55 to form a first weld portion 65. In the figure, the hatched portion is the portion to be welded.
In the embodiment of FIG. 5 (d), the first welded portion 65 that is fillet welded on the entire circumference is shown. The weld bead 68 melts into both the upstream pipe portion 55 and the cover member 57, and the upstream pipe portion 55 and the cover member 57 are firmly fixed to each other.

Next, the operation of the exhaust pipe with catalyst described above will be described.
FIG. 6A is a cross-sectional view of the exhaust pipe with catalyst according to the embodiment, and FIG. 6B is a cross-sectional view of the exhaust pipe with catalyst according to the comparative example.

In the embodiment of FIG. 6A, one end 54 a (rear end) of the catalyst outer cylinder 54 is welded to one end 57 a (rear end) of the cover member 57 and the downstream pipe portion 56.
In the comparative example of FIG. 6B, in the exhaust pipe 47Ab with the catalyst, the ends 54a and 54b (rear end and front end) of the catalyst outer cylinder 54 are not welded to the cover member 57B. A weld bead 69 of a welded portion that welds between the end portion 54a (rear end) and the exhaust pipe (downstream pipe portion 56) is provided outside the catalyst outer cylinder 54 and inside the cover member 57B. In such a structure, it is necessary to increase the outer diameter of the cover member 57B that covers the catalyst outer cylinder 54 by the height of the build-up portion of the weld bead 69 of the weld portion.

  In addition, the welded portion between the downstream pipe portion 56 and the end portion 54a (rear end) of the catalyst outer cylinder 54 and the welded portion between the downstream pipe portion 56 and the cover member 57B are not integrated but separately provided at different positions. Therefore, when the same length of the catalyst 53 is used, the length Lb of the cover member 57B is longer than the length La of the cover member 57 in FIG. 6A (La <Lb).

  Returning to FIG. 6A, in the present invention, one end 54a (rear end) of the catalyst outer cylinder is welded to the cover member 57 and the exhaust pipe (downstream pipe portion 56). Since the three members including the one end 54a (rear end) of the catalyst outer cylinder, the cover member 57, and the exhaust pipe (downstream pipe portion 56) can be welded at a time, the welding cost can be reduced.

  Further, it is not necessary to set the outer diameter of the cover member 57 in consideration of the build-up height of the weld bead welded to the catalyst outer cylinder 54. Therefore, the outer diameter of the cover member 57 can be kept small. If the outer diameter of the cover member 57 is reduced, the appearance of the catalyst-equipped exhaust pipe 47A can be improved. In addition, the catalyst can be warmed up early as the outer diameter and length of the cover member 57 become smaller.

  Further, since the welded portion between the downstream pipe portion 56 and the end portion 54a (rear end) of the catalyst outer cylinder 54 and the welded portion between the downstream pipe portion 56 and the cover member 57 are integrally provided, the same length is provided. When the catalyst 53 is used, the length La of the cover member 57 can be made shorter than the length Lb of the cover member 57 in FIG. 6B (La <Lb). As a result, the catalyst unit 48 can be reduced in size.

  Returning to FIG. 3, one end 57 a (rear end) and the other end 57 b (front end) of the cover member 57 are welded to the downstream pipe portion 56 and the upstream pipe portion 55, respectively. That is, since the cover member 57 can be used as a connecting member between the downstream pipe portion 56 and the upstream pipe portion 55, the number of parts of the catalyst-equipped exhaust pipe 47A can be reduced.

  Further, the distance (A1) between the first welded portion 65 located on the upstream side of the catalyst 53 and the catalyst 53 is larger than the distance (B1) between the second welded portion 66 located on the downstream side of the catalyst 53 and the catalyst. (B1 <A1).

  Temporarily, depending on the position of the weld bead of the 1st welding part arrange | positioned upstream of a catalyst, the heat capacity of an exhaust pipe changes in the upstream of a catalyst. If the heat capacity on the upstream side of the catalyst changes, it may be difficult to obtain favorable purification characteristics.

  In this regard, in the present invention, the distance (B1) between the catalyst 53 and the second welded portion 66 is smaller than the distance (A1) between the catalyst 53 and the first welded portion 65 (B1 <A1). The influence due to the absorption of the exhaust heat caused by the weld bead of the first welded portion 65 can be suppressed. As a result, the purification characteristics of the catalyst 53 can be easily brought close to the desirable characteristics.

  Further, the downstream pipe portion 56, the cover member 57, and the catalyst outer cylinder 54 are welded at a time. Since the three members are welded at a time, the weld length is shortened. As a result, the number of welding processes can be reduced. As a result, the manufacturing cost of the catalyst-equipped exhaust pipe 47A can be suppressed.

  Furthermore, the outer diameter D1 of the upstream pipe portion 55, the outer diameter D2 of the downstream pipe portion 56, and the outer diameter Ds of the catalyst outer cylinder 54 are substantially the same. The outer diameter of the exhaust pipe except for the cover member 57 surrounding the catalyst outer cylinder 54 is substantially the same, and as described above, the expansion of the outer diameter of the cover member 57 due to the height of the weld bead can be kept low. The appearance of the exhaust pipe can be improved.

  Further, in this embodiment, the plate thickness is sufficiently small with respect to the outer diameter of the upstream pipe portion 55, the plate thickness is sufficiently small with respect to the outer diameter of the catalyst outer cylinder 54, and the outer diameter of the downstream pipe portion 56. Since it can be considered that the plate thickness is sufficiently small, the inner diameter of the upstream pipe portion 55, the inner diameter of the catalyst outer cylinder 54, and the inner diameter of the downstream pipe portion 56 can be regarded as substantially the same. In this way, by making the inner diameter of the upstream pipe portion 55, the inner diameter of the catalyst outer cylinder 54, and the inner diameter of the downstream pipe section 56 substantially the same, the exhaust gas is biased to the entire catalyst 53 in the catalyst outer cylinder 54. It works without any problem and can improve the purification efficiency. Furthermore, the disturbance of the exhaust gas on the upstream side and the downstream side of the catalyst 53 can be minimized, the exhaust resistance can be reduced, and the exhaust efficiency can be further increased.

Next, the structure of the connecting portion where the upstream side exhaust pipe and the downstream side exhaust pipe are connected will be described.
As shown in FIG. 7, the exhaust pipe 47 includes an upstream exhaust pipe 35 connected to the exhaust port 41 (see FIG. 2), and a downstream exhaust pipe 36 connected to the downstream end of the upstream exhaust pipe 35. Consists of. The upstream exhaust pipe 35 is a single pipe, and the downstream exhaust pipe 36 is a double pipe composed of an inner pipe 71 and an outer pipe 72. The outer diameter D2 of the upstream exhaust pipe 35 (single pipe) and the outer diameter D3 of the downstream exhaust pipe 36 (double pipe) are substantially the same. Combustion gas discharged from the internal combustion engine 17 (see FIG. 2) passes only inside the inner pipe 71 of the downstream exhaust pipe 36.

  A part of the exhaust pipe (upstream exhaust pipe 35) is a single pipe, a part of the exhaust pipe (downstream exhaust pipe 36) is a double pipe, and the outer diameters D2 and 2 of the single pipe (upstream exhaust pipe 35) are as follows. Since the outer diameter D3 of the heavy pipe (downstream exhaust pipe 36) is set to be substantially the same, the exhaust pipe as a whole has a balanced shape. As a result, the appearance of the exhaust pipe 47 can be improved.

  Further, the combustion gas discharged from the internal combustion engine 17 (see FIG. 2) passes only through the inner pipe 71. If the inner diameter of the inner pipe 71 is not formed with a welded portion that affects the exhaust characteristics such as a weld overlay, the exhaust characteristics of the exhaust gas are not affected and the exhaust characteristics can be made favorable.

Next, a manufacturing method of the connection portion and the like will be described with reference to FIG.
FIG. 8A is a diagram for explaining that the downstream exhaust pipe having the outer pipe temporarily welded to the inner pipe is inserted into the upstream exhaust pipe, and FIG. 8B is a diagram illustrating the inner pipe of the downstream exhaust pipe. It is a figure explaining having inserted in the upstream exhaust pipe. FIG. 8C is an enlarged view of a portion 8 (c) of FIG. 8B, and FIG. 8D is a diagram for explaining that the portion of FIG. 8C is fillet welded.

  As shown in FIG. 8A, the outer pipe 72 is inserted into the inner pipe 71 in the downstream exhaust pipe 36. The front end (upstream end) of the inner pipe 71 is made to protrude from the front end (upstream end) of the outer pipe 72 so that the downstream exhaust pipe 36 can be inserted into the rear end of the upstream exhaust pipe 35 in a subsequent process. And the upstream end 72a of the outer side pipe | tube 72 is temporarily welded to the inner side pipe | tube 71, maintaining the state.

  Next, the inner pipe 71 of the downstream exhaust pipe 36 is inserted into the upstream exhaust pipe 35 in the direction of the arrow n in the figure. The inner tube 71 includes a normal portion 63 that is located inward of the outer tube 72 with a predetermined clearance, an inclined portion 64 that expands radially outward from the normal portion 63 and extends forward, It consists of an enlarged diameter portion 73 that extends forward from the inclined portion 64 and serves as a region to be inserted into the upstream side exhaust pipe 35.

  As shown in FIG. 8 (b), the enlarged diameter portion 73 constituting the inner pipe 71 of the downstream exhaust pipe 36 is inserted inside the upstream exhaust pipe 35. Here, the interval between the rear end (downstream end) of the upstream exhaust pipe 35 and the front end (upstream end) of the outer pipe 72 constituting the downstream exhaust pipe 36 is set to s2.

  As shown in FIG. 8C, fillet welding is performed all around the inner pipe 71, the outer pipe 72, and the upstream exhaust pipe 35 of the downstream exhaust pipe 36 so as to fill the interval s2. In the figure, the hatched portion with chain lines is the portion where fillet welding is performed.

  As shown in FIG. 8D, fillet welding is performed on the entire circumference so as to fill the interval s2, and the upstream side exhaust pipe 35, the inner pipe 71, and the outer pipe 72 are welded together. The inner pipe 71 has an enlarged diameter portion 73 in a region inserted into the upstream exhaust pipe 35, and the enlarged diameter portion 73 and the upstream exhaust pipe 35 are welded.

  Referring also to FIG. 7, the upstream side exhaust pipe 35, the inner pipe 71 and the outer pipe 72 are welded together. Since the three members of the upstream side exhaust pipe 35, the inner pipe 71, and the outer pipe 72 are welded together, the number of processing steps can be reduced, and the welding cost can be reduced. Further, since the weld bead 70 is formed at the stepped portion 75 between the outer peripheral surface 71g of the inner pipe 71 and the upstream side exhaust pipe 35, the protrusion of the weld bead 70 becomes inconspicuous and the appearance of the exhaust pipe 47 is improved. it can.

  An enlarged diameter portion 73 is provided in the inner pipe 71, and the enlarged diameter portion 73 and the upstream side exhaust pipe 35 are welded. If the enlarged diameter portion 73 is closely attached to the inner surface 35u of the upstream side exhaust pipe 35, the inner pipe 71 can be reliably welded to the upstream side exhaust pipe 35 while suppressing the amount of welding material used.

  Returning to FIG. 2, in the exhaust pipe 47, the catalyst is accommodated in the upstream exhaust pipe 35 (single pipe) that has a larger sectional area of the inner diameter than the downstream exhaust pipe 36, and thus the capacity of the catalyst 53 is secured. However, it is possible to suppress an uncomfortable appearance.

Next, the structure of the exhaust pipe connecting portion where the exhaust pipe and the silencer are connected will be described.
As shown in FIG. 9, the downstream exhaust pipe 36 of the exhaust pipe 47 has a double pipe structure including the inner pipe 71 and the outer pipe 72 as described above. An outer tube restricting portion 74 having a smaller outer diameter than the other portions of the outer tube 72 is provided, and the inner tube 71 is slidably supported by the outer tube restricting portion 74.

  The exhaust pipe connecting part 78 where the silencer 49 is welded to the outer pipe 72 of the exhaust pipe 47 is upstream of the outer pipe restricting part 74, and the outer pipe 72 and the inner pipe 71 are separated in the radial direction. The portion 76 is provided.

  The downstream end 71b of the inner pipe 71 is closed by a lid 79, and a plurality of holes 81 for diffusing exhaust gas are provided in the vicinity of the downstream end 71b. The exhaust gas flows to the silencer 49 through a large number of holes 81.

  As shown in FIG. 10, fillet welding is performed on the entire periphery of the silencer connecting portion 78 where the silencer 49 is welded to the outer pipe 72 of the exhaust pipe 47. Since the exhaust pipe 47 and the silencer 49 are connected by such a welded structure, for example, a connecting band, a fastening member, and the like can be omitted. As a result, the number of parts can be reduced.

  Referring also to FIG. 9, in the structure in which the silencer 49 is connected to an exhaust pipe (downstream exhaust pipe 36) having a double pipe structure composed of an inner pipe 71 and an outer pipe 72, an exhaust pipe (downstream exhaust pipe 36). The silencer 49 is welded to the outer tube 72 of FIG. The silencer 49 is welded to the outer tube 72 at a portion 76 where the outer tube 72 and the inner tube 71 are separated in the radial direction.

  If the silencer is welded to the inner pipe of the exhaust pipe, a weld bead may be formed on the inner surface of the inner pipe depending on the welding conditions. If a weld bead is formed on the inner surface of the inner pipe, the exhaust characteristic of the exhaust device 40 may change due to the weld bead.

  In this regard, in the present invention, the welded portion applied to the silencer coupling portion 78 that connects the exhaust pipe 47 and the silencer 49 is provided between the outer tube 72 and the silencer 49, and the inner tube There is no concern that a weld bead is formed on the inner surface of 71. Therefore, it is unlikely that the exhaust characteristics due to welding will change. As a result, the exhaust characteristics can be stabilized.

The combustion gas passes only through the inner pipe 71. Unless a welded portion that affects the exhaust characteristics such as a weld overlay is formed on the inner diameter of the inner pipe 71, the exhaust characteristics of the exhaust gas flowing through the inner pipe 71 are not affected, and the exhaust characteristics can be made favorable. it can.
Furthermore, since the inner tube 71 is slidably supported by the outer tube restricting portion 74 of the outer tube 72, the number of support members in the silencer 49 can be reduced.

  Referring also to FIG. 2, in the exhaust pipe 47, the catalyst 53 is accommodated in the upstream exhaust pipe 35 (single pipe) that can easily ensure a larger cross-sectional area of the inner diameter than the downstream exhaust pipe 36. Compared with the case where the catalyst is arranged in the exhaust pipe (double pipe), it is possible to suppress the discomfort in appearance while securing the capacity of the catalyst 53.

Next, the stay member that supports the exhaust device on the vehicle body side will be described.
As shown in FIG. 11, the exhaust pipe 47 has a stay member 51 attached to the vehicle. The stay member 51 is a portion where the outer pipe 72 and the inner pipe 71 are separated from each other in the radial direction. 72 is fixed by welding.

  The stay member 51 is welded to the outer tube 72. Since the stay member 51 is welded to the outer tube 72, in the region where the outer tube 72 and the inner tube 71 are separated in the radial direction, the inner surface 71 u of the inner tube 71 separated from the outer tube 72 by a predetermined amount is used. There is no concern that the weld bead is formed, and the influence on the inner surface 71u of the inner tube 71 can be ignored. Therefore, there is no fear of affecting the exhaust characteristics of the exhaust gas passing through the exhaust pipe.

Next, Example 2 according to the catalyst unit of the present invention will be described with reference to the drawings.
As shown in FIG. 12, the upstream side exhaust pipe 35 includes a catalyst outer cylinder 54 in which the catalyst 53 is accommodated, an upstream pipe portion 55 located on the upstream side of the catalyst outer cylinder 54, and a catalyst in which the catalyst 53 is accommodated. It consists of the downstream pipe part 56 located downstream from the outer cylinder 54. The upstream pipe portion 55 and the downstream pipe portion 56 are each constituted by separate members, and the outside of the catalyst 53 is covered with a cover member 57.

  The upstream pipe portion 55 of the exhaust pipe 47 is inserted into the inner peripheral surface on the upstream side of the catalyst outer cylinder 54, and the downstream pipe portion 56 of the exhaust pipe 47 is inserted into the inner peripheral surface on the downstream side of the catalyst outer cylinder 54, The other end 57 b (upper end) of the cover member 57 is welded to the pipe portion 55, and one end 57 a (lower end) of the cover member 57 is welded to the downstream pipe portion 56. In addition, one end 54 a (lower end) of the catalyst outer cylinder 54 is slidably supported by the downstream pipe portion 56. Here, one end and the other end refer to end portions on opposite sides.

  A portion where the other end 57 b (upper end) of the cover member 57 is welded to the upstream pipe portion 55 is referred to as a first weld portion 65, and a portion where one end 57 a (lower end) of the cover member 57 is welded to the downstream pipe portion 56 is second. When the welded portion 66 is used, the first welded portion 65 includes a welded portion that welds between the other end 54b (upper end) of the catalyst outer cylinder 54 and the cover member 57, and the other end 54b (upper end) of the catalyst outer cylinder 54. The welded portion that welds the upstream pipe portion 55 is continuous. That is, the other end 54 b (upper end) of the catalyst outer cylinder 54 is welded and fixed to the cover member 57 and the upstream pipe portion 55.

  The major difference from the first embodiment is that the other end 54 b (upper end) of the catalyst outer cylinder 54 is welded to the first welding portion 65, and one end 54 a (lower end) of the catalyst outer cylinder 54 is slidable on the downstream pipe portion 56. There are no other significant differences.

  In the present invention, the other end 54 b (upper end) of the catalyst outer cylinder is welded to the cover member 57 and the upstream pipe portion 55. Since the three members can be welded at a time, the welding length can be shortened. As a result, the welding cost can be reduced. Further, it is not necessary to consider the build-up height of the weld bead that is welded to the catalyst outer cylinder 54. Therefore, the outer diameter of the cover member 57 can be kept small. When the outer diameter of the cover member 57 is reduced, the appearance of the catalyst-equipped exhaust pipe 47A is enhanced. In addition, the catalyst can be warmed up early as the outer diameter of the cover member 57 becomes smaller.

  Further, the distance (A2) between the catalyst 53 and the first welded portion 65 is larger than the distance (B2) between the catalyst 53 and the second welded portion 66 (B2 <A2). Thereby, when warming up the catalyst 53, the influence by the absorption of the exhaust heat in the weld bead of the first welded portion 65 located on the upstream side of the catalyst 53 can be suppressed. As a result, the purification characteristics of the catalyst 53 can be easily brought close to the desirable characteristics.

  Further, the outer diameter D1 of the upstream pipe portion 55, the outer diameter D2 of the downstream pipe portion 56, and the outer diameter Ds of the catalyst outer cylinder 54 are substantially the same. Thus, the external appearance of the exhaust pipe can be improved by setting the outer diameter of each pipe to be substantially the same and keeping the outer diameter of the cover member 57 small. In addition, there is no significant difference from the operation and effect of the first embodiment, and the description is omitted.

A third embodiment of the catalyst unit of the present invention will be described with reference to the drawings.
As shown in FIG. 13, in the upstream side exhaust pipe 35, a catalyst outer cylinder 54 in which the catalyst 53 is accommodated, an upstream pipe portion 55 positioned on the upstream side of the catalyst outer cylinder 54, and a catalyst in which the catalyst 53 is accommodated. It consists of the downstream pipe part 56 located downstream from the outer cylinder 54. The upstream pipe section 55 has an inner pipe 171 and an outer pipe 172, and the downstream pipe section 56 is a so-called double pipe having an inner pipe 271 and an outer pipe 272.

  The upstream pipe portion 55 and the downstream pipe portion 56 are each constituted by separate members, and the outside of the catalyst 53 is covered with a cover member 57. The cover member 57 is a cylindrical member extending along the axial direction of the catalyst outer cylinder 54, and no clearance is provided between the catalyst outer cylinder 54 and the cover member 57.

  The upstream pipe portion 55 of the exhaust pipe 47 is inserted into the inner peripheral surface 54ua on the upstream side of the catalyst outer cylinder 54, and one end 54a (lower end) of the catalyst outer cylinder 54 is slidably supported by the cover member 57, and the cover member The downstream pipe portion 56 of the exhaust pipe 47 is joined to the rear end of the 57. The other end 57 b (upper end) of the cover member 57 is welded to the upstream pipe portion 55, and one end 57 a (lower end) of the cover member 57 is welded to the downstream pipe portion 56.

  In the upstream pipe part 55, the end part 172 b (lower end) of the outer pipe 172 has a throttle part 77. The throttle portion 77 has a connection portion 83 that is connected so as to sandwich the end portion 54b (upper end) of the catalyst outer cylinder 54, and at this connection portion 83, the throttle portion 77 and the upper end 57b of the cover member are fixed by welding. The In the downstream pipe part 56, the end part 272 a (upper end) of the outer pipe 272 has an extending part 80 that extends in the axial direction of the downstream pipe part 56. At the extended portion 80, the end portion 272a (upper end) of the outer tube 272 and the lower end 57a of the cover member are fixed by welding.

  The main differences from the first embodiment are that the upstream pipe portion 55 and the downstream pipe portion 56 are both double-pipe structures, the connection portion 83 is provided with a throttle portion 77, and the cover member 57 is expanded in diameter. There is no portion and a reduced diameter portion, and there is no clearance (gap) between the cover member 57 and the catalyst outer cylinder 54.

  Here, the outer diameter D11 of the outer pipe 172 of the upstream pipe section 55, the outer diameter D21 of the outer pipe 272 of the downstream pipe section 56, and the outer diameter Ds1 of the cover member 57 are substantially the same. In this way, the upstream pipe 55, the cover member 57, and the downstream pipe 56 have substantially the same outer diameter, so that the upstream pipe 55 and the downstream pipe 56 have a double-pipe structure. Therefore, it is difficult to notice the change in the outer diameter of the exhaust pipe, and it can be made close to a single diameter exhaust pipe. In addition, since welding is performed at the connecting portion 83 provided in the throttle portion 77, the protrusion of the build-up portion of the weld bead can be suppressed. As a result, the appearance of the exhaust pipe can be improved.

  Further, since the outer pipe 172 of the upstream pipe portion 55, the end portion 54b (upper end) of the catalyst outer cylinder 54, and the one end 57b (upper end) of the cover member 57 are integrally welded, the welding length can be shortened. In addition, since the upstream pipe portion 55 located on the upstream side of the catalyst 53 has a double-pipe structure, the heat retention effect of the exhaust gas is enhanced, and the purification performance can be improved if the heat retention effect is enhanced.

In this embodiment, the end of the outer tube of the upstream tube portion, the narrowed portion is formed, the end portion of the downstream pipe portion, but extending portion is formed, the end of the outer tube of the downstream pipe portion A throttle part is formed in the part, a connection part is provided in the throttle part, the throttle part and the cover member are welded and fixed at this connection part, and an extension part is formed at the end of the upstream pipe part Is fine.

  Although the present invention is applied to a motorcycle in the embodiment, it can also be applied to a tricycle and can be applied to a general vehicle.

  The present invention is suitable for a motorcycle provided with an exhaust pipe with a catalyst.

  DESCRIPTION OF SYMBOLS 17 ... Internal combustion engine, 41 ... Exhaust port, 52 ... Exhaust path, 53 ... Catalyst, 54 ... Catalyst outer cylinder, 55 ... Upstream pipe part, 56 ... Downstream pipe part, 57 ... Cover member, 65 ... 1st weld part, 66 2nd welding part, 77 ... Restriction part, 80 ... Extension part, 83 ... Connection part, 171 ... Inner pipe | tube, 172 ... Outer pipe | tube, 271 ... Inner pipe | tube, 272 ... Outer pipe | tube.

Claims (8)

An exhaust path (52) is configured by connecting to an exhaust port (41) of an internal combustion engine (17) mounted on the vehicle, and a catalyst (53) is provided in the middle of the exhaust path (52). The catalyst (53) The upstream pipe part (55) located on the further upstream side and the downstream pipe part (56) located on the downstream side of the catalyst (53) are each constituted by separate members, and the catalyst (53) is constituted by a catalyst outer cylinder (54). ) And an exhaust pipe with catalyst mounted on a vehicle in which the outside of the catalyst outer cylinder (54) is covered with a cover member (57),
The cover member (57) is welded to the catalyst outer cylinder (54) at one end thereof, and the other end is welded to one of the upstream pipe portion (55) or the downstream pipe portion (56),
One end of the catalyst outer cylinder (54) is welded and fixed to the cover member (57) and the other of the upstream pipe part (55) or the downstream pipe part (56), and the upstream pipe part ( 55) and the downstream pipe portion (56) are connected with the same diameter as the outer diameter (DS) of the catalyst outer cylinder (54) to form the exhaust passage (52) ,
The other end of the catalyst outer cylinder (54) is fitted and supported by the one of the upstream pipe part (55) or the downstream pipe part (56) inside the cover member (57). A catalyst-equipped exhaust pipe mounted on a vehicle. One end of the cover member (57) is welded to the upstream pipe portion (55) at the first weld portion (65),
The other end of the cover member (57) is catalyst-exhaust pipe is mounted on a vehicle of claim 1 Symbol mounting, characterized in that it is welded the downstream pipe portion (56) at the second welding unit (66) . The catalyst outer cylinder (54) is welded to the second welded part (66),
The vehicle according to claim 2 , wherein a distance between the catalyst (53) and the second welded part (66) is smaller than a distance between the catalyst (53) and the first welded part (65). Exhaust pipe with catalyst. The catalyst outer cylinder (54) is welded to the first weld (65),
The vehicle according to claim 2 , wherein a distance between the catalyst (53) and the first welded part (65) is larger than a distance between the catalyst (53) and the second welded part (66). Exhaust pipe with catalyst. The one of the upstream pipe portion (55) or the downstream pipe portion (56), the cover member (57), and the catalyst outer cylinder (54) are welded at a time. catalyst-exhaust pipe is mounted on a vehicle according to any one of 1-4. The upstream pipe part (55) and the downstream pipe part (56) are single pipes,
The said upstream pipe part (55), the said downstream pipe part (56), and the said catalyst outer cylinder (54) are mutually the outer diameters substantially the same, The any one of Claims 1-5 characterized by the above-mentioned. Exhaust pipe with catalyst mounted on the vehicle.   The upstream pipe part (55) and the downstream pipe part (56) are double pipes each having an inner pipe (171, 271) and an outer pipe (172, 272), and the upstream pipe part (55). 2. The exhaust pipe with catalyst mounted on a vehicle according to claim 1, wherein the outer diameter of the outer pipe (172) and the outer diameter of the outer pipe (272) of the downstream pipe portion (56) are substantially the same. . An exhaust path (52) is configured by connecting to an exhaust port (41) of an internal combustion engine (17) mounted on the vehicle, and a catalyst (53) is provided in the middle of the exhaust path (52). The catalyst (53) The upstream pipe part (55) located on the further upstream side and the downstream pipe part (56) located on the downstream side of the catalyst (53) are each constituted by separate members, and the catalyst (53) is constituted by a catalyst outer cylinder (54). ) And an exhaust pipe with catalyst mounted on a vehicle in which the outside of the catalyst outer cylinder (54) is covered with a cover member (57),
The cover member (57) is welded to the catalyst outer cylinder (54) at one end thereof, and the other end is welded to one of the upstream pipe portion (55) or the downstream pipe portion (56),
One end of the catalyst outer cylinder (54) is welded and fixed to the cover member (57) and the other of the upstream pipe part (55) or the downstream pipe part (56), and the upstream pipe part ( 55) and the downstream pipe portion (56) are connected with the same diameter as the outer diameter (DS) of the catalyst outer cylinder (54) to form the exhaust passage (52),
The upstream pipe part (55) and the downstream pipe part (56) are double pipes each having an inner pipe (171, 271) and an outer pipe (172, 272), and the upstream pipe part (55). The outer diameter of the outer pipe (172) and the outer diameter of the outer pipe (272) of the downstream pipe portion (56) are substantially the same,
One end of the outer pipe (172) of the upstream pipe part (55) and the outer pipe (272) of the downstream pipe part (56) has a throttle part (77),
The other end of the outer pipe of the upstream pipe section (55) and the outer pipe of the downstream pipe section (56) has an extending section (80) extending in the axial direction of the downstream pipe section (56). And
The throttle part (77) has a connection part (83) connected so as to sandwich the one end of the catalyst outer cylinder (54) between the end (57b) of the cover member (57),
At the connecting portion (83), catalyst-exhaust pipe where the throttle portion (77) and said cover member (57) is mounted on the vehicles you characterized in that it is welded.

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