JPH08189349A - Double exhaust pipe for engine - Google Patents

Abstract

PURPOSE: To improve temperature rise characteristics of exhaust gas and certainly eliminate thermal expansion difference between an outer pipe and an inner pipe. CONSTITUTION: A double exhaust pipe is composed of an outer pipe 1 and an inner pipe 2 made of material thinner than that of the outer pipe 1, and inserted into the outer pipe 1 with a clearance 12. In such a double exhaust pipe, each end of the outer pipe 1 and the inner pipe 2 are connected to a flange 3 arranged on an upstream end in a flowing direction of exhaust gas. A circular bent portion 5 prepared by bending a pipe wall inward or outward is formed on the inner pipe 2 near its end. A cylindrical member 8 whose leading end 8b is inserted into the inner pipe 2 without contact in the flowing direction of the exhaust gas. The leading end of the cylindrical member 8 is extended so as to surround the circular bent portion 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dual exhaust pipe for an engine, which is intended to keep the exhaust gas of a vehicle warm and to suppress heat radiation into the engine room.

[0002]

2. Description of the Related Art In automobiles, a catalyst is arranged downstream of an exhaust pipe to purify exhaust gas. In this case, in terms of purification efficiency, there is a problem when the engine is started. When the engine is started, both the catalyst and the exhaust gas have a low temperature. Therefore, since the catalyst temperature does not reach the activation temperature, a chemical change does not occur, and a situation occurs in which the unburned components in the exhaust gas cannot fully react.

In order to deal with this, a double exhaust pipe has been proposed in which the temperature of the exhaust gas is kept warm. In the double exhaust pipe, the inner pipe is concentrically arranged with a gap inside the outer pipe, and a hollow heat insulating layer is secured between the outer pipe and the inner pipe.

The double exhaust pipe secures the structural strength of the outer pipe, and the inner pipe forming the exhaust gas passage is made as thin as possible to reduce the heat capacity of the portion in contact with the exhaust gas. it can. Further, since the hollow heat insulating layer is provided between the inner pipe and the outer pipe, heat escape through the outer pipe can be reduced. Therefore, when the engine is started, the temperature of the inner wall of the exhaust pipe can be quickly raised, and the heat retention effect of the exhaust gas can be enhanced.

However, in the double exhaust pipe, since a large temperature difference occurs between the inner pipe and the outer pipe, it is necessary to adopt a structure in which the outer pipe holds the inner pipe while absorbing the difference in thermal expansion between the two.

Conventionally, as an example of such a structure, FIG.
The one shown in FIG. 12 is known.

FIG. 8 shows a double exhaust pipe disclosed in Japanese Utility Model Laid-Open No. 2-103122. In this double exhaust pipe, the end portion of the outer pipe 1 is elastically deformable in the radial direction and the axial direction.
It is fixed to the outer circumference of the inner pipe 2 via 1 and the connecting member 51 absorbs the difference in thermal expansion between the outer pipe 1 and the inner pipe 2.

FIG. 9 shows a double exhaust pipe described in JP-A-5-44460. In this double exhaust pipe, the outer pipe 1 is formed in a bellows shape, and the bellows portion absorbs a difference in thermal expansion between the outer pipe 1 and the inner pipe 2.

FIG. 10 shows a double exhaust pipe described in Japanese Utility Model Laid-Open No. 62-67922. In this double exhaust pipe, the outer pipe 1
One end of the inner pipe 2 is welded to the flanges 55 and 56 provided at both ends of the inner pipe 2 and the other end is press-fitted, and the thermal expansion difference between the outer pipe 1 and the inner pipe 2 is absorbed by sliding at the press-fitted fitting portion. I am trying.

FIG. 11 shows a double exhaust pipe described in Japanese Utility Model Laid-Open No. 56-67318. In this double exhaust pipe, the inner pipe 2
A spacer 58 is interposed in the gap between the outer tube 1 and the outer tube 1, and the spacer 58 absorbs the difference in thermal expansion between the outer tube 1 and the inner tube 2.

FIG. 12 shows a hollow double tube described in Japanese Utility Model Laid-Open No. 59-99117. In this double exhaust pipe, the inner pipe 2
A bent portion 59 is provided in a part of the outer tube 1, and the bent portion 59 absorbs the difference in thermal expansion between the outer tube 1 and the inner tube 2.

[0012]

By the way, FIG. 8 and FIG.
Since the double exhaust pipe shown in (1) uses the inner pipe 2 as a structural member, it cannot cope with the thinning of the inner pipe 2.

Further, the double exhaust pipe shown in FIG. 10 may not be able to smoothly absorb the difference in thermal expansion because an unreasonable force may act on the press-fitting fitting portion of the inner pipe 2.

Further, in the double exhaust pipe shown in FIG. 11, one end of the inner pipe 2 needs to be a free end in order to release the thermal expansion of the inner pipe 2, and the gap between the free end and the outer pipe is Exhaust gas may come and go, which may deteriorate the temperature rise performance of the exhaust gas.

The double exhaust pipe shown in FIG. 12 can absorb the difference in thermal expansion at the bent portion 59, but the exhaust gas flowing in the inner pipe 2 hits the bent portion 59 to increase the heat transfer coefficient. In addition, since the surface area of the pipe wall is increased at the bent portion 59, the heat of the exhaust gas escapes more, which may deteriorate the temperature raising performance of the exhaust gas.

In consideration of the above circumstances, the present invention provides an engine which can improve the temperature rise characteristic of exhaust gas at the time of starting the engine and can surely absorb the difference in thermal expansion between the outer pipe and the inner pipe. It is intended to provide a heavy exhaust pipe.

[0017]

The invention according to claim 1 comprises an outer pipe and an inner pipe which is formed thinner than the outer pipe and is inserted into the outer pipe with a gap therebetween. In the double exhaust pipe of the engine to be the passage, each end portion of the outer pipe and the inner pipe is joined to the flange arranged at the upstream end in the flow direction of the exhaust gas, and on the inner pipe close to the end portion, An annular curved portion is formed by bending the pipe wall inward or outward, and the flange is fitted with a cylindrical member having a tip inserted in the inner pipe in a non-contact manner along a flow direction of exhaust gas,
It is characterized in that the tip end of the cylindrical member is extended to a position covering the annular curved portion.

According to a second aspect of the present invention, there is provided the dual exhaust pipe for an engine according to the first aspect, wherein the inner space of the inner pipe and the inner pipe are within a range of the inner pipe covered by the cylindrical member. A double exhaust pipe for an engine, characterized in that a conduction hole is provided to connect a gap between the outer pipe and the outer pipe.

According to a third aspect of the present invention, there is provided the dual exhaust pipe for an engine according to the first or second aspect, wherein the cylindrical member is made of the same material and has the same thickness as the inner pipe, or the inner pipe. It is characterized by being formed of a material having a specific heat, a coefficient of thermal expansion and a wall thickness equivalent to those of.

A fourth aspect of the present invention is a double exhaust pipe for an engine according to any one of the first to third aspects, wherein the cylindrical member integrally has a flange portion protruding outward on an upstream end side. The flange portion is held between the flange and the other flange so as to be held at the inner position of the inner pipe.

According to a fifth aspect of the present invention, there is provided an engine including an outer pipe and an inner pipe which is formed thinner than the outer pipe and is inserted into the outer pipe with a gap, and the inner pipe serves as an exhaust gas passage. In a heavy exhaust pipe, the inner pipe is divided into an upstream side and a downstream side, and a support material is welded to the outer periphery of the downstream end of the upstream inner pipe, whereby a cylinder facing the downstream end of the upstream inner pipe. Is formed, and the upstream end of the downstream side inner pipe is slidably inserted and joined into this gap.

According to a sixth aspect of the present invention, there is provided a dual exhaust pipe for an engine according to the fifth aspect, wherein the support member is made of the same material and has the same thickness as the inner pipe, or is equivalent to the inner pipe. It is characterized by being formed of a material having a specific heat, a coefficient of thermal expansion, and a wall thickness.

According to a seventh aspect of the present invention, there is provided an engine having an outer pipe and an inner pipe which is thinner than the outer pipe and is inserted into the outer pipe with a gap, and the inner pipe serves as an exhaust gas passage. In the heavy exhaust pipe, the downstream end of the inner pipe is inserted into the central opening of the flange joined to the downstream end of the outer pipe in a non-contact manner and extends outward from the flange, and the outer peripheral side of the inner pipe. A tapered connecting member is provided on the inner pipe, the upstream end of the connecting member is welded to the outer circumference of the inner pipe, and the downstream end is welded to the flange so that the inner pipe is held by the flange through the connecting member. Further, an annular curved portion formed by bending the pipe wall inward or outward is provided between the upstream end and the downstream end of the connecting member.

The invention according to claim 8 is the double exhaust pipe for an engine according to claim 7, wherein the connecting member is made of the same material and has the same thickness as the inner pipe, or is equivalent to the inner pipe. It is characterized by being formed of a material having a specific heat, a coefficient of thermal expansion, and a wall thickness.

[0025]

According to the first aspect of the present invention, the wall thickness of the inner tube is thin, so that the heat capacity of the inner tube is small and the wall temperature of the inner tube rises early. Therefore, the amount of heat transferred from the exhaust gas to the inner pipe is suppressed to a low level, the temperature drop of the exhaust gas is suppressed, and as a result, the inlet exhaust gas temperature of the catalyst installed on the downstream side in the exhaust gas flow direction can be increased. it can.

Further, when the exhaust gas hits the annular curved portion of the inner pipe directly, a large amount of heat of the exhaust gas is given to the inner pipe, which may slow the rise of the exhaust gas temperature. Since the curved part is completely covered by the cylindrical member,
Exhaust gas does not directly hit the annular curved portion, and a decrease in exhaust gas temperature is suppressed. Further, the difference in thermal expansion between the inner pipe and the outer pipe at high temperature is reliably absorbed by the deformation of the annular curved portion.

According to the second aspect of the invention, the pressure difference between the exhaust gas inside and outside the inner pipe is alleviated through the through hole provided in the inner pipe. Since this conduction hole is covered with a cylindrical member,
Exhaust gas hardly leaks to the outside of the inner pipe through the through hole.

In the invention of claim 3, there is no difference in thermal expansion between the cylindrical member and the inner tube.

According to the fourth aspect of the invention, the cylindrical member can be held by holding the flange portion when the flange is joined to the mating flange.

According to the invention of claim 5, since the downstream end of the upstream inner pipe and the upstream end of the downstream inner pipe are inserted and joined to each other, the thermal expansion of the inner pipe is absorbed without fear of exhaust gas leakage. be able to.

In the invention of claim 6, there is no difference in thermal expansion between the support material and the inner pipe.

In the invention of claim 7, since the inner pipe extends downstream of the flange toward the exhaust pipe, the exhaust gas does not come into direct contact with the flange, and the escape of heat of the exhaust gas through the flange is suppressed. In addition, since the inner pipe and the outer pipe are joined via the connecting member to separate the gap between the inner pipe and the outer pipe from the inner space of the inner pipe, the low temperature air from the gap between the inner pipe and the outer pipe is separated. The function of sucking out the exhaust gas is eliminated, and the decrease in exhaust gas temperature is reliably suppressed. Further, since the exhaust gas does not directly impinge on the welded portion of the connecting member and the inner pipe, the heat transfer coefficient of the exhaust gas does not increase, and in that respect also, the decrease of the exhaust gas temperature is suppressed. Further, when the temperature is high, the thermal expansion of the inner pipe and the outer pipe is absorbed by the deformation of the annular curved portion provided on the connecting member.

According to the invention of claim 8, there is no difference in thermal expansion between the connecting member and the inner pipe.

[0034]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is an external view of the double exhaust pipe of the first embodiment of the present invention applied to an exhaust manifold. Figure 2
FIG. 2 is a sectional view taken along the line II-II in FIG. 1, showing a structure on the exhaust gas inlet side. FIG. 3 is a cross-sectional view taken along the line III-III of FIG. 1, showing a structure in the middle of the double exhaust pipe.
FIG. 4 is a cross-sectional view taken along the line IV-IV in FIG. 1, showing the structure on the exhaust gas outlet side. In the figure, F indicates the flow direction of the exhaust gas.

As shown in FIGS. 2 to 4, inside the outer pipe 1 formed to be a strength member of the exhaust manifold, the outer pipe 1 is formed thinner than the outer pipe 1 (for example, 0.5 mm). The inner tubes 2 and 10 thus formed are concentrically inserted with a gap 12 therebetween. The inner pipe of this embodiment is the upstream inner pipe 2 on the way.
And the inner pipe 10 on the downstream side. The outer tube 1 is integrally formed, and flanges 3 and 13 having a sufficient thickness are welded to both ends thereof.

First, the structure on the upstream side in the exhaust gas flow direction (exhaust gas inlet side) will be described with reference to FIG.

The flange 3 at the upstream end has an annular fitting recess 3c at an inner peripheral corner of a surface 3b opposite to the flange joint surface 3a with respect to the engine exhaust port. The end portion of the outer tube 1 is curved and narrowed to an inner diameter slightly larger than the outer diameter of the inner tube 2, and the straight portion 1a formed by the narrowing is
The end portion of the outer tube 1 is welded to the flange 3 while being fitted to the inner peripheral surface of the fitting recess 3c of the flange 3 and the tip end surface of the linear portion 1a being abutted against the bottom surface of the fitting recess 3c. There is.

Further, at a position close to the flange 3 of the inner pipe 2, the pipe wall is locally curved outwardly in a semi-circular convex shape to form an annular curved portion 5 continuous over the entire circumference. There is. Further, on the inner pipe 2 closer to the flange 3 than the annular curved portion 5, a gap 12 between the inner pipe 2 and the outer pipe 1 and a conduction hole 6 that communicates with the inner space of the inner pipe 2 are provided.

The inner pipe 2 is formed in a straight cylindrical shape in which the portion closer to the flange 3 than the annular curved portion 5 is expanded, and the end of the expanded portion is a straight line of the end of the outer pipe 1. The fitting recess 3c of the flange 3 is inserted together with the end of the outer tube 1 into the portion 1a.
It is located inside and welded to the flange 3.

A base end portion 8a of a straight cylindrical collar 8 is fixed to the inner peripheral surface of the flange 3. The collar 8 is made of the same material and has the same thickness as the inner pipe 2, and the tip portion (downstream end portion) 8b is inserted into the inner pipe 2 along the flow direction of the exhaust gas. The tip 8b of this collar 8 is
It extends to the downstream side of the annular curved portion 5 formed in the inner pipe 2, and completely covers the conduction hole 6 and the annular curved portion 5. The collar 8 is formed to have a diameter slightly smaller than the diameter of the inner pipe 2, and on the downstream side of the annular curved portion 5, the inner pipe 2 and the collar 8 are formed.
Are opposed to each other in a non-contact manner with a slight gap 17 therebetween. The gap 17 extends from the downstream end 16 of the annular curved portion 5 to the tip of the collar 8 with a certain size, and has a certain length from the downstream end 16 of the annular curved portion 5 to the tip of the collar 8. Is secured.

Next, the structure between the upstream side and the downstream side will be described with reference to FIG.

At the connecting portion between the upstream inner pipe 2 and the downstream inner pipe 10, the same material as the inner pipe 2 is provided on the outer peripheral surface of the end of the upstream inner pipe 2.
A short tube-shaped support material 11 of the same meat quality is arranged. The support material 11 is formed to have a small diameter so that the upstream side is closely fitted to the outer circumference of the inner pipe 2, and the downstream side is equivalent to the wall thickness than that. It is formed to have a large diameter, and only the small diameter portion 11a on the upstream side thereof is fixed to the outer peripheral surface of the inner pipe 2 by welding, and the downstream side is faced between the large diameter portion 11b on the downstream side and the outer peripheral surface of the inner pipe 2. A cylindrical gap 14 is formed. This gap 14 is slightly larger than the wall thickness of the downstream inner pipe 10, and
An enlarged diameter tip portion 10a of the downstream inner pipe 10 having the same inner diameter as the upstream inner pipe 2 is slidably connected in the longitudinal direction of the pipe.

Next, the structure on the downstream side (exhaust gas outlet side) in the exhaust gas flow direction will be described with reference to FIG.

The flange 13 at the downstream end has a central opening 1
3 a is formed to be larger than the inner pipe 10 so that there is a gap between the outer pipe 3 a and the outer periphery of the downstream inner pipe 10. Outer tube 1
The downstream end of the flange 13 is curved and narrowed down to the diameter of the central opening 13a of the flange 13, and the narrowed linear portion 1b is fitted to the inner peripheral surface of the central opening 13a of the flange 13. It is welded to the flange 13.

The downstream inner pipe 10 has a downstream end 10b.
Extends through the central opening 13 a of the flange 13 to the outside of the flange 13. On the outer peripheral side of the inner pipe 10, a tapered cylindrical connecting member 9 having a diameter enlarged toward the downstream side is arranged, and an upstream end 9a of the connecting member 9 is fitted to the outer periphery of the inner pipe 10. Welded and fixed, downstream end 9b
Is fitted to the inner circumference of the central opening 13a of the flange 13 formed to be larger than the outer diameter of the inner pipe 10, and is welded to the flange 13 together with the straight portion 1b of the outer pipe 1. And
The inner pipe 10 is held by the flange 13 via the connecting member 9.

At a position close to the flange 13 of the connecting member 9, the tube wall is locally curved outwardly in a semi-circular convex shape so that the annular curved portion 1 is continuous over the entire circumference.
5 is formed. Since the connecting member 9 is welded to the outer surface of the inner pipe 10, the joining is easy, and the weld gas is not directly exposed to the exhaust gas.

The operation of the double exhaust pipe of the above embodiment will be described below.

First, the temperature rise of exhaust gas at the time of starting will be described.

The temperature of the outer pipe 1 and the inner pipe 2 of the double exhaust pipe before the engine is started is the same as the outside air temperature except immediately after the engine is stopped. After the engine is started, in the double exhaust pipe, the inner pipe 2 is first warmed by the exhaust gas flowing in the inner pipe 2. As a result, the wall temperature of the inner pipe 2 increases, but the temperature of the exhaust gas decreases by the amount of heat applied to the inner pipe 2.

In the double exhaust pipe of this embodiment, since the thickness of the inner pipe 2 is thin, the heat capacity of the inner pipe 2 is small and the wall temperature of the inner pipe 2 rises early. Therefore, the amount of heat transferred from the exhaust gas to the inner pipe 2 is suppressed to a low level, the temperature decrease of the exhaust gas is suppressed, and as a result, the inlet exhaust gas of the catalyst installed in the downstream of the double exhaust pipe of this embodiment. The temperature can be raised.

On the exhaust gas inlet side, as shown in FIG.
Although a part of the exhaust gas may flow out to the gap 12 between the inner pipe 2 and the outer pipe 1 through the through hole 6 provided in the inner pipe 2, the heat quantity of the exhaust gas may decrease, and the exhaust gas temperature may decrease. Since the collar 8 completely covers the conduction hole 6, exhaust gas is prevented from flowing out to the gap 12 between the inner pipe 2 and the outer pipe 1 through the small gap 17 between the collar 8 and the inner pipe 2.

When the exhaust gas directly impinges on the annular curved portion 5 of the inner pipe 2, the heat transfer coefficient of the exhaust gas at the downstream end 16 of the annular curved portion 5 increases, and the annular curved portion 5 further increases. As the heat transfer area of the inner pipe 2 increases, a large amount of heat of the exhaust gas is given to the inner pipe 2 and the wall temperature of the inner pipe 2 itself rises faster, but the exhaust gas temperature rises slower. Therefore, the early activation of the catalyst will be suppressed. However, in the double exhaust pipe of this embodiment, since the annular curved portion 5 is completely covered with the collar 8, the exhaust gas does not come into direct contact with the annular curved portion 5, and the exhaust gas temperature can be effectively lowered. Can be suppressed.

Further, the exhaust gas passing through the tip portion 8b of the collar 8 will flow into the inner pipe 2 on the downstream side thereof, but since the expansion of the flow passage diameter from the collar 8 to the inner pipe 2 is small, The effect of reducing the pressure due to the expansion of is reduced, and the decrease in the temperature of the exhaust gas due to this is suppressed.

On the other hand, at the connecting portion between the upstream inner pipe 2 and the downstream inner pipe 10 located in the middle of the double exhaust pipe, as shown in FIG. 3, a gap slightly larger than the wall thickness of the downstream inner pipe 10. 14
Since the tip of the downstream side inner pipe 10 is inserted and joined to the inner pipe 2, the exhaust gas flowing in the inner pipes 2 and 10 is
And does not flow into the gap 12 of the outer tube 1. Further, the low temperature air or the exhaust gas in the gap 12 is not sucked out, and the air flows to the downstream side without a temperature drop.

At the joint, there is a slight step immediately after the diameter-expanding tip 10a of the downstream inner pipe 10, but the step is very small, so the heat of the exhaust gas at this part is small. The increase in transmissivity is small, and the temperature of exhaust gas is hardly decreased.

On the exhaust gas outlet side, as shown in FIG.
Since the downstream side inner pipe 10 extends to the exhaust pipe side downstream from the flange 13, the exhaust gas does not come into direct contact with the flange 13, and the escape of heat of the exhaust gas through the flange 13 is suppressed.

Further, since the inner pipe 10 and the outer pipe 1 are welded by the connecting member 9 and the gap 12 between the inner pipe 10 and the outer pipe 2 and the inner space of the inner pipe 10 are isolated from each other, the low temperature from the gap 12 is reduced. It is possible to reliably suppress the decrease of the exhaust gas temperature by eliminating the air sucking action. Further, since the exhaust gas does not directly impinge on the welded portion of the connecting member 9 and the inner pipe 10, the heat transfer coefficient of the exhaust gas does not increase, and in that respect also, the decrease of the exhaust gas temperature is suppressed.

Next, when the exhaust gas and the exhaust pipe are sufficiently warmed when driving in urban areas, due to the difference in heat capacity and surface temperature due to the difference in wall thickness between the inner pipe 2 and the outer pipe 1, the inner pipe 2, 10
A difference in thermal expansion occurs between the outer tube 1 and the outer tube 1.

That is, since the outer tube 1 is not directly exposed to the exhaust gas, has a low surface temperature, and has a large wall thickness, it has a large heat capacity, and therefore the thermal expansion is smaller than that of the inner tubes 2 and 10. On the other hand, the inner pipe 2, which is directly exposed to high-temperature exhaust gas and has a small heat capacity due to its thin wall, has a high temperature and undergoes large thermal expansion.

The difference in thermal expansion between the inner tubes 2 and 10 and the outer tube 1 is
It can be absorbed by the deformation of the annular curved portions 5 and 15 provided on the upstream side and the downstream side and the slide of the plug-in type connecting portion of the upstream inner pipe 2 and the downstream inner pipe 10 on the way, which causes a difference in thermal expansion. It is possible to reliably prevent damage to the inner tubes 2 and 10.

Further, the deformation of the inner tubes 2 and 10 is repeated due to the pressure difference due to the temperature difference of the gas between the inner space of the inner tubes 2 and 10 and the gap 12 between the inner tubes 2 and 10 and the outer tube 1. However, since the inner space of the inner pipes 2 and 10 communicates with the outer space by the through hole 6 provided in the upstream inner pipe 2, the exhaust gas pressure in the inner pipes 2 and 10 and the gap The pressure in 12 is leveled and the inner tubes 2 and 10 are prevented from being deformed.

Since the diameter of the through hole 6 is small, even if it is provided on the exhaust gas outlet side, the action of sucking out the gas from the gap 12 is low, and the exhaust gas temperature immediately after the engine is started cannot be greatly lowered. No, but it is preferable to install it on the entrance side.

From the above, when the double exhaust pipe of this embodiment is used, the heat retention performance of the exhaust gas is enhanced, and thereby the catalyst activity at the time of starting the engine is enhanced. Also, the surface temperature of the outer tube 1 can be kept low even under high load conditions,
It is possible to suppress an increase in the ambient temperature in the engine room. Therefore, the cost and weight of parts can be reduced, and the heat resistance performance can be improved especially in a hot place.

Further, even when running under high load, the inner pipe 2,
10 can absorb the difference in thermal expansion between the outer tube 1 and the inner tube 2,
Even if 10 is made as thin as possible, the risk of breakage can be eliminated.

Next, another embodiment of the present invention in which the structure on the exhaust gas inlet side is modified will be described.

In the second embodiment shown in FIG. 5, the diameter of the upstream end portion 19 of the annular curved portion 5 of the inner pipe 2 is reduced, and the portion from that portion to the upstream end of the inner pipe 2 is formed in a taper shape with an enlarged diameter. are doing.
According to this, the upstream end 19 of the annular curved portion 5 and the inner pipe 2
Since it is possible to reduce the clearance 17a between the collar 8 and the inner tube 2, it is possible to prevent the exhaust gas from flowing to the flange 3 side through the clearances 17 and 17a between the collar 8 and the inner pipe 2, and to escape the heat of the exhaust gas. Can be further suppressed.

In the third embodiment shown in FIG. 6, the position of the inner peripheral surface of the central opening 3d of the flange 3 is enlarged to the position of the inner peripheral surface of the annular recess 3c (see FIG. 2) of the first embodiment. Color 8
Instead of the above, a cap 18 having a cylindrical portion 18a and a collar portion 18b having the same material and the same thickness as the inner tube 2 is used. Then, the flange portion 18b of the cap 18 is sandwiched between the flange 3 and another flange, whereby the cylindrical portion 18a is formed.
Is held at the same position as the collar 8 of the first embodiment. Further, in the cap 18, the cylindrical portion 18a and the collar portion 18b are
And are continuous by a smooth curved portion 18c.

According to this embodiment, the curved portion 18c of the cap 18 can completely cover the welded portions of the respective ends of the inner pipe 2 and the outer pipe 1 to the flange 3, so that the heat of the exhaust gas is prevented. The escape can be further suppressed. Also,
Since the fitting concave portion 3c on the inner peripheral portion of the flange 3 is eliminated, the manufacturing becomes easy.

In the fourth embodiment shown in FIG. 7, the outer tube 1, the inner tube 2 and the collar 8 are fitted together at the inner periphery of the central opening 3d of the flange 3 and welded together. . in this case,
In order to match the diameter of the collar 8, the diameter of the end portion of the outer pipe 1 and the diameter of the end portion of the inner pipe 2 are also narrowed down to the diameter of the collar 8 and welded to the flange 3. In this embodiment, the outer tube 1, the inner tube 2 and the collar 8 are welded together at the same portion, which facilitates manufacturing.

[0071]

As described above, according to the invention of claim 1, since the inner pipe is provided with the annular curved portion, the difference in thermal expansion between the thin inner pipe and the outer pipe can be reliably absorbed. Further, since the annular curved portion is covered with the cylindrical member, it is possible to suppress an increase in the heat transfer coefficient of the exhaust gas in the annular curved portion and an increase in the heat transfer area of the inner pipe, and to reduce the exhaust gas temperature after the engine is started early. It can be increased to promote early activation of the catalyst.

According to the second aspect of the present invention, by the conduction hole,
Since the pressure difference between the inside and the outside of the inner pipe is alleviated, the repeated deformation of the inner pipe due to the pressure difference can be suppressed.

According to the third aspect of the invention, since there is no difference in thermal expansion between the cylindrical member and the inner tube, there is no risk of contact between the two during thermal expansion, and heat escape due to contact can be suppressed.

According to the invention of claim 4, it is not necessary to weld the cylindrical member to the inner circumference of the flange, which facilitates the production and suppresses the escape of heat from the welded portion.

According to the fifth aspect of the present invention, the expansion joint of the downstream end of the upstream inner pipe and the upstream end of the downstream inner pipe can absorb the thermal expansion of the inner pipe while suppressing the leakage of exhaust gas. it can. As a result, the temperature of the exhaust gas after the engine is started can be raised early, and the catalyst can be activated early.

According to the invention of claim 6, there is no difference in thermal expansion between the support material and the inner pipe, so that no undue stress is generated between the two and the connection between the upstream inner pipe and the downstream inner pipe is prevented. The durability is improved.

According to the invention of claim 7, since the inner pipe and the outer pipe are joined through the connecting member having the annular curved portion, the difference in thermal expansion between the inner pipe and the outer pipe is caused by the annular curved portion. In addition to being able to reliably absorb, it is possible to eliminate the sucking action of the low-temperature air from the gap between the inner pipe and the outer pipe, and as a result, the exhaust gas temperature after the engine is started can be raised early,
It is possible to promote early activation of the catalyst.

According to the invention of claim 8, the difference in thermal expansion between the connecting member and the inner tube is eliminated, so that no undue force is applied to the inner tube and the durability is improved.

[Brief description of drawings]

FIG. 1 is an external view of an exhaust manifold to which a first embodiment of the present invention is applied.

FIG. 2 is a sectional view taken along the line II-II of FIG.

FIG. 3 is a sectional view taken along the line III-III of FIG.

4 is a sectional view taken along the line IV-IV in FIG.

FIG. 5 is a cross-sectional view showing the structure on the exhaust gas inlet side of the second embodiment of the present invention.

FIG. 6 is a sectional view showing a structure of an exhaust gas inlet side of a third embodiment of the present invention.

FIG. 7 is a sectional view showing the structure of an exhaust gas inlet side of a fourth embodiment of the present invention.

FIG. 8 is a cross-sectional view of a first conventional example.

FIG. 9 is a sectional view of a second conventional example.

FIG. 10 is a cross-sectional view of a third conventional example.

FIG. 11 is a cross-sectional view of a fourth conventional example.

FIG. 12 is a cross-sectional view of a fifth conventional example.

[Explanation of symbols]

 1 Outer pipe 2 Upstream inner pipe 3,13 Flange 5,15 Annular curved part 6 Conducting pore 8 Collar (cylindrical member) 8b Tip part 9 Connecting member 9a Upstream end 9b Downstream end 10 Downstream inner pipe 10b Downstream end 11 Support material 12 Gap 14 Gap 18a Cap's cylindrical part (cylindrical member) 18b Cap's collar part F Exhaust gas flow direction

Claims (8)

[Claims] 1. A double exhaust pipe for an engine, comprising an outer pipe and an inner pipe which is thinner than the outer pipe and is inserted into the outer pipe with a gap, wherein the inner pipe serves as an exhaust gas passage. An annular ring in which the ends of the outer pipe and the inner pipe are joined to a flange arranged at the upstream end in the flow direction of the exhaust gas, and the pipe wall is curved inward or outward on the inner pipe close to the end. A curved portion is formed, and a cylindrical member having a tip inserted into the inner pipe in a non-contact manner along the exhaust gas flow direction is attached to the flange, and the tip of the cylindrical member covers the annular curved portion. Double exhaust pipe of the engine characterized by being extended to. 2. The double exhaust pipe of the engine according to claim 1, wherein the inner space of the inner pipe, the inner pipe, and the outer pipe are within a range of the inner pipe covered by the cylindrical member. A double exhaust pipe for an engine, which is provided with a through hole that communicates with the gap. 3. The double exhaust pipe of the engine according to claim 1, wherein the cylindrical member is made of the same material and has the same thickness as the inner pipe,
Alternatively, a dual exhaust pipe for an engine, which is formed of a material having a specific heat, a coefficient of thermal expansion, and a wall thickness that are equivalent to those of the inner pipe. 4. The double exhaust pipe for an engine according to claim 1, wherein the cylindrical member integrally has a flange portion projecting outward at an upstream end side, and the flange portion is A double exhaust pipe for an engine, which is held at an inner position of the inner pipe by being sandwiched between the flange and another flange. 5. A double exhaust pipe of an engine, comprising an outer pipe and an inner pipe which is thinner than the outer pipe and is inserted into the outer pipe with a gap, wherein the inner pipe serves as an exhaust gas passage, The inner pipe is divided into an upstream side and a downstream side, and a support material is welded to the outer circumference of the downstream end of the upstream side inner pipe to form a cylindrical gap facing the downstream side at the downstream end of the upstream side inner pipe. The double exhaust pipe of the engine is characterized in that the upstream end of the downstream inner pipe is slidably inserted and joined into this gap. 6. The double exhaust pipe of the engine according to claim 5, wherein the support member is made of the same material and has the same wall thickness as the inner pipe, or has the same specific heat and thermal expansion as the inner pipe. A double exhaust pipe for an engine, which is characterized by being made of a material having a high rate and a high wall thickness. 7. A double exhaust pipe of an engine, comprising an outer pipe and an inner pipe which is thinner than the outer pipe and is inserted into the outer pipe with a gap, wherein the inner pipe serves as an exhaust gas passage. The downstream end of the inner pipe is inserted into the central opening of a flange joined to the downstream end of the outer pipe in a non-contact manner, extends outwardly of the flange, and has a tapered connection to the outer peripheral side of the inner pipe. A member is provided, the upstream end of the connecting member is welded to the outer periphery of the inner pipe, the downstream end is welded to the flange, and the inner pipe is held by the flange via the connecting member; A double exhaust pipe for an engine, wherein an annular curved portion formed by bending a pipe wall inward or outward is provided between the upstream end and the downstream end of the connecting member. 8. The double exhaust pipe of the engine according to claim 7, wherein the connecting member is made of the same material and has the same thickness as the inner pipe,
Alternatively, a dual exhaust pipe for an engine, which is formed of a material having a specific heat, a coefficient of thermal expansion, and a wall thickness that are equivalent to those of the inner pipe.