JP2004084481A - Exhaust pipe - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve warm-up performance of a catalyst device when exhaust gas temperature is in a low temperature range, and suppress thermal degradation of the catalyst device when exhaust gas temperature is in a high temperature range. <P>SOLUTION: An exhaust pipe 20 is arranged between an internal combustion engine and the catalyst device for purifying exhaust gas. The exhaust pipe 20 has a first route R1, a second route R2 defined in the first route R1, and a valve system 33 for opening and closing the first route R1 and the second route R2. The valve system 33 closes the first route R1 and opens the second route R2 when exhaust gas temperature is in a low temperature range, and opens the first route R1 and partly closes the second route R2 when exhaust gas temperature is in a high temperature range. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an exhaust pipe arranged between an internal combustion engine and a catalyst device for purifying exhaust gas.
[0002]
[Prior art]
BACKGROUND ART A vehicle equipped with an internal combustion engine is provided with a catalyst device for purifying exhaust gas discharged by combustion of the internal combustion engine. In such a catalyst device, there is a predetermined temperature range for exhibiting a satisfactory purifying function. If the temperature is below this temperature range, the purifying function of the catalytic device is reduced. It causes deterioration. Therefore, as an exhaust pipe for guiding the exhaust gas discharged from the internal combustion engine to the catalyst device, an exhaust pipe in which the passage of the exhaust gas is variable is disclosed in, for example, JP-A-2000-234739 or JP-A-2000-233471. No. pp. 147-64. These exhaust pipes have a double piping structure of an outer pipe and an inner pipe arranged in the outer pipe, and a space between an inner wall of the outer pipe and the inner pipe has a first passage through which exhaust gas passes. And the space in the inner pipe becomes the second path through which the exhaust gas passes. The outer tube is formed in a cylindrical shape having a uniform diameter, and the inner tube is formed in a cylindrical shape having a substantially uniform diameter except for the end on the discharge side. An opening / closing valve that can open and close the first path and the second path at the discharge end of the inner pipe is provided in the outer pipe, and the exhaust gas passes by switching the opening / closing valve according to the temperature range of the exhaust gas. The route can be switched. That is, when the exhaust gas temperature is in a low temperature range, the first route is closed and the second route is opened, and when the exhaust gas temperature is in a middle temperature range, both the first route and the second route are opened. Is in a high temperature range, the first path is opened and the second path is closed. Therefore, when the exhaust gas temperature is in a low temperature range, the catalyst can be warmed up by suppressing a decrease in the exhaust gas temperature by using the second path in the inner pipe as the exhaust gas passage. Further, when the exhaust gas temperature is in a high temperature range, the first path is a path through which the exhaust gas passes, whereby the exhaust gas temperature can be lowered and the catalyst can be cooled. Further, when the exhaust gas temperature is in the middle temperature range, the exhaust gas passage is set to the first path and the second path, so that both exhaust noise reduction and low exhaust pressure can be achieved.
[0003]
[Problems to be solved by the invention]
However, in the exhaust pipes described in the above publications, the inner pipe is formed in a cylindrical shape having a substantially uniform diameter except for the end on the discharge side. The portions are open at the center of the outer tube without being joined. Therefore, when the exhaust gas temperature is in a low temperature range, a large amount of low-temperature exhaust gas flows through the first path (the space between the outer pipe and the inner pipe) to lower the exhaust gas temperature, thereby warming up the catalyst device. Performance is reduced. Further, when the exhaust gas temperature is in a high temperature range, a large amount of the high-temperature exhaust gas also flows through the second path (the inner pipe), so that the exhaust gas temperature cannot be lowered, which may cause thermal degradation of the catalyst device. .
[0004]
The present invention has been made to solve the above problems, and an object of the present invention is to improve the warm-up property of the catalyst device when the exhaust gas temperature is in a low temperature range, and to improve the warming up performance of the catalyst device when the exhaust gas temperature is in a high temperature range. An object of the present invention is to provide an exhaust pipe capable of suppressing thermal deterioration of a catalyst device.
[0005]
[Means for Solving the Problems]
Hereinafter, the means for achieving the above object and the effects thereof will be described.
According to the first aspect of the present invention, there is provided an exhaust pipe arranged between an internal combustion engine and a catalyst device for purifying exhaust gas, wherein a first path, a second path disposed in the first path, A valve for opening and closing the first path and the second path, wherein the valve closes the first path and opens the second path when the exhaust gas temperature is in a low temperature range, and the exhaust gas temperature is high. When it is a zone, the first path is opened and a part of the second path is closed.
[0006]
Therefore, according to the above configuration, the exhaust gas passes through the second path by closing the first path when the exhaust gas temperature is in a low temperature range, so that a decrease in the temperature of the exhaust gas is suppressed, and the warming-up of the catalyst device is performed. Performance is improved. Further, by closing only a part of the second path when the exhaust gas temperature is in a high temperature range, the exhaust gas passes through the first path and the second path and is introduced into the catalyst device. The exhaust pressure can be prevented from rising while preventing the exhaust gas from hitting.
[0007]
As in the invention according to claim 2, the valve includes a first on-off valve capable of opening and closing the first path and a second on-off valve capable of opening and closing a part of the second path. be able to.
[0008]
According to a third aspect of the present invention, there is provided an outer pipe disposed between an internal combustion engine and a catalyst device for purifying exhaust gas, and an inner pipe disposed so as to have a gap between an inner wall of the outer pipe. In the exhaust pipe provided with: an enlarged diameter portion is provided at an end of the inner pipe on the side of the internal combustion engine.
[0009]
Therefore, according to the above configuration, the enlarged diameter portion is formed at the end of the inner pipe on the side of the internal combustion engine into which the exhaust gas flows. When the temperature of the exhaust gas is in a low temperature range, the flow rate of the exhaust gas is small and the exhaust gas is easily diffused. The warm-up property of the device is improved.
[0010]
According to a fourth aspect of the present invention, there is provided an outer pipe disposed between an internal combustion engine and a catalyst device for purifying exhaust gas, and an inner pipe disposed so as to have a gap between an inner wall of the outer pipe. In the exhaust pipe provided with, a heat radiation promoting means is formed on at least an outer wall of the outer pipe.
[0011]
Therefore, according to the above configuration, since the heat radiation promoting means is provided on at least the outer wall of the outer pipe, the cooling of the exhaust gas passing through the outer pipe when the exhaust gas temperature is in a high temperature range is promoted, and the heat of the catalyst device is increased. Deterioration is suppressed.
[0012]
According to a fifth aspect of the present invention, in the exhaust pipe according to the fourth aspect, the heat radiation promoting means is provided with irregularities on an outer wall of the outer tube to increase a surface area.
Therefore, according to the above configuration, it is possible to provide a simple configuration in which the outer wall of the outer tube is provided with irregularities to increase the surface area, and it is possible to suppress an increase in the size of the outer tube.
[0013]
According to a sixth aspect of the present invention, in the exhaust pipe according to the first or second aspect, a gap is provided between an outer pipe disposed between the internal combustion engine and the catalyst device and an inner wall of the outer pipe. An inner pipe arranged so as to have, the first path is a space formed between the outer pipe and the inner pipe, the second path is an inner space of the inner pipe, An enlarged diameter portion is provided at an end of the inner pipe on the side of the internal combustion engine.
[0014]
Therefore, according to the above configuration, in addition to the functions and effects of the first aspect of the present invention, when the exhaust gas temperature is in a low temperature range, more exhaust gas is introduced into the inner pipe by the enlarged diameter portion. The decrease is suppressed, and the warm-up property of the catalyst device is improved.
[0015]
According to a seventh aspect of the present invention, in the exhaust pipe according to any one of the first, second, and sixth aspects, a heat radiation promoting unit is formed on at least an outer wall of the outer pipe.
[0016]
Therefore, according to the above configuration, in addition to the function and effect of the invention of claim 6, since the heat radiation promoting means is provided on at least the outer wall of the outer tube, the exhaust gas passes through the outer tube when the exhaust gas temperature is in a high temperature range. The cooling of the exhaust gas is promoted, and the thermal degradation of the catalyst device is suppressed.
[0017]
According to an eighth aspect of the present invention, in the exhaust pipe according to the seventh aspect, the heat dissipation promoting means is provided with irregularities on an outer wall of the outer tube to increase a surface area.
Therefore, according to the above configuration, in addition to the operation and effect of the invention of claim 7, it is possible to provide a simple configuration in which the outer wall of the outer tube is provided with irregularities to increase the surface area, and the outer tube is enlarged. Can be suppressed.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment in which the present invention is embodied in an exhaust pipe provided in an exhaust system of an internal combustion engine for a vehicle will be described with reference to the drawings. FIG. 1 is a schematic diagram of an internal combustion engine system including an exhaust pipe of the present embodiment, and FIG. 2 is a cross-sectional view of the exhaust pipe of the present embodiment with a part of the exhaust pipe omitted.
[0019]
As shown in FIG. 1, an intake manifold 11 is provided on an intake side of a gasoline engine (hereinafter, simply referred to as an engine) 10 as an internal combustion engine, and air introduced through an air cleaner is passed through the intake manifold 11 to the engine. 10 is supplied.
[0020]
An exhaust manifold 12 is provided on the exhaust side of the engine 10, and a start catalyst 13 having a three-way catalyst as one of the catalytic converters is connected downstream of the exhaust manifold 12. The start catalyst 13 is for quickly purifying harmful gases in the combustion gas discharged from the engine 10 in a cold state immediately after the start of the engine 10. Generally, in order for a catalytic converter to function, it must be heated to a predetermined temperature or higher. The start catalyst 13 is connected to the vicinity of the engine 10 (exhaust manifold 12) so as to be warmed by the combustion gas at an early stage.
[0021]
An underfloor catalytic converter 14, which is another catalytic device, is connected to the downstream side of the start catalyst 13 via an exhaust pipe 20 of the present embodiment. The underfloor catalytic converter 14 is for purifying harmful gases in the combustion gas discharged from the engine 10 when the engine 10 is warm.
[0022]
A muffler (not shown) is connected to the downstream side of the underfloor catalytic converter 14 via an exhaust pipe 15.
In the exhaust system configured as described above, exhaust gas discharged from the engine 10 flows through the exhaust manifold 12, the start catalyst 13, the exhaust pipe 20, the underfloor catalytic converter 14, the exhaust pipe 15, and the muffler to the outside. Is discharged. The exhaust gas flowing in this way is purified of the harmful gas in the start catalyst 13 and the underfloor catalytic converter 14, and is silenced in the muffler.
[0023]
Next, the structure of the exhaust pipe 20 of the present embodiment for connecting the start catalyst 13 and the underfloor catalytic converter 14 will be described with reference to FIGS.
As shown in FIG. 2, the exhaust pipe 20 of the present embodiment has a gap between an outer pipe 22 disposed between the start catalyst 13 and the underfloor catalytic converter 14 and an inner wall of the outer pipe 22. And an inner pipe 24 arranged to have a double pipe structure.
[0024]
The outer pipe 22 is a pipe having a substantially circular cross section, and has a substantially constant diameter from the start catalyst 13 side to the underfloor catalytic converter 14 side. As shown in FIG. 5, a large number of dimples 22a are formed in the outer tube 22 in the section from the end (upstream end) on the side of the start catalyst 13 to the middle part, as a means for promoting heat radiation. Due to these dimples 22a, irregularities are formed on the inner and outer walls of the outer tube 22, and the surface area of the outer tube 22 is increased, so that the cooling of the exhaust gas passing through the first path R1 in the outer tube 22 can be promoted. At both ends of the outer tube 22, mounting flanges 23a and 23b for connecting to the start catalyst 13 and the underfloor catalytic converter 14 are provided.
[0025]
The inner pipe 24 is a section from the end (upstream end) on the start catalyst 13 side, which is an end on the engine 10 side, to an intermediate section, and a section from the intermediate section to an end (downstream end) on the underfloor catalytic converter 14 side. In the section, it is arranged so as to form a gap with the inner wall of the outer tube 22. That is, in the inner pipe 24, a section from the upstream end to the intermediate portion is formed as a circular portion 25 which is substantially coaxial with the outer pipe 22 and has a smaller diameter than the outer pipe 22. As shown in FIG. 4, an enlarged diameter portion 25 a is formed at the end of the circular portion 25 on the start catalyst 13 side, and the diffusion of the exhaust gas toward the outer pipe 22 is performed by the enlarged diameter portion 25 a. This suppresses the introduction of exhaust gas into the inner pipe 24. In the middle portion of the inner tube 24, a gradually changing portion 26 whose cross section gradually changes from a substantially circular shape and finally becomes a substantially semicircular shape, a semicircular portion 27 having a substantially semicircular cross section, A gradually changing portion 28 which gradually changes from a semicircle and finally becomes substantially circular is formed. As shown in FIG. 6, the semicircular portion 27 is arranged so that the arc portion contacts the inner wall of the outer tube 22. The cross-sectional shape of the void except for the semicircular portion 27 from the cross section of the outer tube 22 is substantially the same as the semicircular portion 27 (semicircular shape). As shown in FIG. 2, in the inner tube 24, a section from the intermediate portion to the downstream end is formed as a circular portion 29 which is substantially coaxial with the outer tube 22 and has a smaller diameter than the outer tube 22. The plate thickness of the inner tube 24 is set to be smaller than the plate thickness of the outer tube 22, and the heat capacity of the inner tube 24 is small.
[0026]
The inner tube 24 thus configured is held by a plurality of supports 30 arranged in the circular portions 25 and 29 so as to have a gap between the inner tube 24 and the inner wall of the outer tube 22. As shown in FIGS. 3 and 4, the support 30 includes a pair of hollow elastic supports 31, and the two elastic supports 31 are joined to the inner wall of the outer tube 22 with their ends abutting each other. ing. An auxiliary member 32 that slidably surrounds the circular portion 25 of the inner tube 24 is provided inside the two elastic supports 31. As the auxiliary member 32, a wire mesh formed by knitting a wire can be used.
[0027]
In the exhaust pipe 20 configured as described above, the space between the inner wall of the outer pipe 22 and the inner pipe 24 is the first path R1 through which the exhaust gas passes, and the space inside the inner pipe 24 is the passage of the exhaust gas. This is the second route R2.
[0028]
Further, the exhaust pipe 20 is provided with a valve mechanism 33 for switching a path through which exhaust gas passes at a portion corresponding to the semicircular portion 27 of the inner pipe 24. As shown in FIG. 6, the valve mechanism 33 penetrates the semicircular portion 27 of the outer pipe 22 and the inner pipe 24, and is rotatably provided via a pair of upper and lower bearings 35; A first opening / closing valve 36 attached to the support shaft 34 in R1 and a second opening / closing valve 37 attached to the support shaft 34 in the second path R2. The first on-off valve 36 and the second on-off valve 37 are mounted around the support shaft 34 with a phase difference of 90 degrees. The first on-off valve 36 is formed in a substantially semicircular shape, and can open and close the first path R1. The second on-off valve 37 can open and close a part of the second path R2 in the inner tube 24. Therefore, when the first on-off valve 36 is arranged so as to close the first path R1, the second on-off valve 37 is arranged so as to open the second path R2. When the first on-off valve 36 is arranged to open the first path R1, the second on-off valve 37 is arranged to close a part of the second path R2.
[0029]
A drive arm 34 a provided at an end of the support shaft 34 is connected to an actuator 38 driven by a command signal of an electronic control unit (hereinafter, referred to as an ECU) 40. Therefore, based on the operation of the actuator 38, the first on-off valve 36 and the second on-off valve 37 rotate via the support shaft 34, and the first path R1 and the second path R2 are opened and closed.
[0030]
The ECU 40 includes a well-known CPU, ROM, RAM, input / output ports, and the like, and inputs a detection signal of an air flow meter 42 that detects an intake air amount to the engine 10. When the amount of intake air to the engine 10 is large, the amount of air-fuel mixture to be burned increases and the exhaust gas temperature becomes a high temperature range. And the exhaust gas temperature falls into a low temperature range. Therefore, the temperature of the exhaust gas discharged from the engine 10 can be estimated based on the intake air amount detected by the air flow meter 42.
[0031]
Then, the ECU 40 receives a detection signal from the air flow meter 42 and controls the actuator 38 according to the detection signal to switch the exhaust gas passage in the exhaust pipe 20 between the first path R1 and the second path R2. Specifically, it is determined whether the current exhaust gas temperature belongs to a low temperature range or a high temperature range based on the intake air amount detected by the air flow meter 42. When the ECU 40 determines that the exhaust gas temperature is in the low temperature range, the ECU 40 controls the actuator 38 such that the first on-off valve 36 closes the first path R1 and the second on-off valve 37 opens the second path R2. If the ECU 40 determines that the exhaust gas temperature is in the high temperature range, the ECU 40 operates the actuator 38 so that the first on-off valve 36 opens the first path R1 and the second on-off valve 37 closes only a part of the second path R2. Control.
[0032]
Next, the operation of the exhaust pipe 20 of the present embodiment will be described. First, when the intake air amount is small, for example, immediately after the start of the engine, the ECU 40 determines that the current exhaust gas temperature is in a low temperature range based on a detection signal from the air flow meter 42. Based on this determination, the ECU 40 rotates the support shaft 34 by a predetermined amount via the actuator 38, and closes the first path R1 by the first on-off valve 36 and opens the second path R2 by the second on-off valve 37. Position. Then, the exhaust gas that has passed through the exhaust manifold 12 and the start catalyst 13 enters through the upstream end opening of the first path R1 and the upstream end opening of the second path R2, respectively. Since the exhaust gas is closed, the exhaust gas cannot pass through the first path R1 and stays in the first path R1. On the other hand, since the second path R2 is opened by the second on-off valve 37, the exhaust gas flows to the underfloor catalytic converter 14 through the second path R2. Here, the inside of the inner tube 24, which is the second route R2, has a high heat insulating property because the circular portions 25 and 29 and the gradually changing portions 26 and 28 are covered by the outer tube 22 with a gap. Moreover, the inner tube 24 is formed of a material having a small thickness and has a small heat capacity. Therefore, the exhaust gas is hardly cooled in the process of passing through the second route R2. Therefore, the temperature of the exhaust gas that has reached the underfloor catalytic converter 14 is sufficiently high, and the catalyst activity can be promptly increased immediately after the engine is started.
[0033]
Further, when the intake air amount is large, such as during normal running after a short time has elapsed since the start of the engine 10, the ECU 40 determines that the current exhaust gas temperature is in the high temperature range based on the detection signal from the air flow meter 42. . Based on this determination, the ECU 40 rotates the support shaft 34 by a predetermined amount via the actuator 38, opens the first path R1 by the first on-off valve 36, and closes a part of the second path R2 by the second on-off valve 37. Position where Then, the exhaust gas that has passed through the exhaust manifold 12 and the start catalyst 13 flows into the underfloor catalytic converter 14 through both the first path R1 and the second path R2. For this reason, compared with the case where the exhaust gas temperature is in a low temperature range, the cross-sectional area of the passage through which the exhaust gas can pass increases, and the rise in the back pressure of the exhaust gas is suppressed. Further, the first path R1 is surrounded by the outer pipe 22, and since the outer pipe 22 is cooled by the outside air, the exhaust gas that has passed through the first path R1 is appropriately cooled and has passed through the second path R2. The exhaust gas is mixed with the underfloor catalytic converter 14 before reaching an appropriate temperature. Therefore, the temperature of the catalyst of the underfloor catalytic converter 14 does not become high enough to cause thermal degradation.
[0034]
As described in detail above, according to the exhaust pipe 20 of the present embodiment, the following effects can be obtained.
In the present embodiment, when the temperature of the exhaust gas led to the exhaust pipe 20 is in a low temperature range, the exhaust gas passes through the second path R2 in the inner pipe 24 by closing the first path R1 in the outer pipe 22. Therefore, a decrease in the temperature of the exhaust gas can be suppressed, and the warm-up property of the underfloor catalytic converter 14 is improved. When the temperature of the exhaust gas led to the exhaust pipe 20 is in a high temperature range, only part of the second path R2 in the inner pipe 24 is closed, so that the exhaust gas passes through the first path R1 and the second path R2. Since the gas passes through the underfloor catalytic converter 14 and is introduced into the underfloor catalytic converter 14, it is possible to prevent a high-temperature exhaust gas from hitting the catalyst and also prevent a rise in exhaust pressure.
[0035]
In the present embodiment, the enlarged diameter portion 25a is formed at the end on the side of the start catalyst 13 into which the exhaust gas of the inner pipe 24 flows. When the temperature of the exhaust gas guided to the exhaust pipe 20 is in a low temperature range, the flow rate of the exhaust gas is small and the exhaust gas is easily diffused. However, since the exhaust gas is more introduced into the inner pipe 24 by the enlarged diameter portion 25a, A decrease in the exhaust gas temperature is suppressed, and the warm-up property of the underfloor catalytic converter 14 is improved.
[0036]
In the present embodiment, since a large number of dimples 22a are provided on the outer wall of the outer pipe 22 of the exhaust pipe 20 as heat dissipation promoting means, the temperature of the exhaust gas guided to the exhaust pipe 20 is high. The cooling of the exhaust gas passing through the outer pipe 22 can be promoted, and the thermal degradation of the underfloor catalytic converter 14 can be suppressed.
[0037]
In addition, in the present embodiment, cooling of the exhaust gas can be promoted by a simple configuration in which the outer pipe 22 is provided with irregularities called dimples 22a to increase the surface area, and the outer pipe 22 can be prevented from being enlarged. it can.
[0038]
The embodiment is not limited to the above, but may be modified as follows.
In the above embodiment, the heat dissipation promoting means is formed by increasing the surface area by forming irregularities called dimples 22a on the outer tube 22. However, grooves extending in the circumferential direction with respect to the inner and outer walls of the outer tube 22 and spiral grooves are provided. May be formed to increase the surface area.
[0039]
-In the said embodiment, a radiation fin may be provided to the outer wall of the outer tube 22, and it may be a radiation promotion means. In this case, the dimple 22a may or may not be provided.
[0040]
In the above embodiment, a temperature sensor for detecting the temperature of the exhaust gas is provided upstream of the underfloor catalytic converter 14, and the ECU 40 controls the valve mechanism 33 based on the detection result to set the path through which the exhaust gas passes through the first path. The switching may be performed between the route R1 and the second route R2.
[0041]
In the above embodiment, the valve mechanism 33 including the first opening / closing valve 36 and the second opening / closing valve 37 for switching the path through which the exhaust gas passes on the discharge side of the exhaust pipe 20 is provided. It may be formed at an arbitrary position of the tube 20. For example, it may be formed on the engine side of the exhaust pipe 20.
[0042]
In the above embodiment, the first opening / closing valve 36 and the second opening / closing valve 37 of the valve mechanism 33 are configured to be attached to the same support shaft 34, but the first opening / closing valve 36 and the second opening / closing valve 37 are separately supported. It may be configured to be attached to a shaft.
[Brief description of the drawings]
FIG. 1 is a schematic diagram of an engine system including an exhaust pipe according to an embodiment.
FIG. 2 is a cross-sectional view in which a part of an exhaust pipe of the embodiment is omitted.
FIG. 3 is a sectional view taken along line 3-3 in FIG. 2;
FIG. 4 is an enlarged sectional view of an engine side portion of an exhaust pipe.
FIG. 5 is a sectional view taken along line 5-5 in FIG. 2;
FIG. 6 is a sectional view of a valve mechanism portion of the exhaust pipe according to the embodiment.
[Explanation of symbols]
15, 20 ... exhaust pipe, 22 ... outer pipe, 22a ... dimple as heat dissipation promoting means, 24 ... inner pipe, 25, 29 ... circular section, 25a ... enlarged diameter section, 26, 28 ... gradually changing section, 27 ... half Circle part, 33 ... Valve mechanism, 34 ... Support shaft, 36 ... First on-off valve, 37 ... Second on-off valve, 38 ... Actuator, 40 ... Electronic control device (ECU), R1 ... First path, R2 ... Second Route.

Claims (8)

In an exhaust pipe arranged between the internal combustion engine and a catalyst device for purifying exhaust gas,
A first path, a second path disposed in the first path, and a valve that opens and closes the first path and the second path,
The valve closes the first path and opens the second path when the exhaust gas temperature is in a low temperature range, and opens and closes the first path when the exhaust gas temperature is in a high temperature range. An exhaust pipe characterized in that a part of the exhaust pipe is closed. The exhaust pipe according to claim 1,
The exhaust pipe according to claim 1, wherein the valve includes a first on-off valve capable of opening and closing the first path, and a second on-off valve capable of opening and closing a part of the second path. An outer pipe disposed between the internal combustion engine and a catalyst device for purifying exhaust gas, and an exhaust pipe including an inner pipe disposed so as to have a gap between the inner wall of the outer pipe,
An exhaust pipe, wherein an enlarged diameter portion is provided at an end of the inner pipe on the side of the internal combustion engine. An outer pipe disposed between the internal combustion engine and a catalyst device for purifying exhaust gas, and an exhaust pipe including an inner pipe disposed so as to have a gap between the inner wall of the outer pipe,
An exhaust pipe, wherein a heat radiation promoting means is formed on at least an outer wall of the outer pipe. The exhaust pipe according to claim 4,
The exhaust pipe according to claim 1, wherein the heat radiation promoting means has an uneven surface provided on an outer wall of the outer pipe to increase a surface area. The exhaust pipe according to claim 1 or 2,
An outer pipe disposed between the internal combustion engine and the catalyst device; and an inner pipe disposed so as to have a gap between inner walls of the outer pipe, wherein the first path includes the outer pipe. A space formed between the inner pipe and the inner pipe, wherein the second path is an inner space of the inner pipe;
An exhaust pipe having an enlarged diameter portion provided at an end of the inner pipe on the side of the internal combustion engine. In the exhaust pipe according to any one of claims 1, 2, and 6,
An exhaust pipe, wherein a heat radiation promoting means is formed on at least an outer wall of the outer pipe. The exhaust pipe according to claim 7,
The exhaust pipe according to claim 1, wherein the heat radiation promoting means has an uneven surface provided on an outer wall of the outer pipe to increase a surface area.

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