JPH08277995A - Double exhaust pipe - Google Patents

Abstract

PURPOSE: To prevent reduction in strength of an inner pipe and deterioration in a catalyst due to high temperature by maintaining a heat retaining property of exhaust gas highly when an engine is started and suppressing excessive increase in temperature when temperature of the exhaust gas is increased because of high load running and the like. CONSTITUTION: In a double exhaust pipe consisting of an outer pipe 8, an inner pipe 7 arranged inside the outer pipe 8 while allowing a clearance 5 between them, and a supporting member 9 which is arranged between the outer pipe 8 and inner pipe 7 and hold the inner pipe 7 on the outer pipe 8 while absorbing relative deformation in the inner pipe 7 and the outer pipe 8, a projecting piece type rib 7a is arranged on the outer circumference of the inner pipe 7, and the rib 7a is free from contact with the outer pipe 8 when the temperature of the inner pipe 7 is low, while following deformation of the inner pipe 7, the rib 7a is displaced toward the outer pipe 8 side so as to be brought into contact with the outer pipe 8 when the temperature of the internal pipe 7 is increased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a double exhaust pipe for a vehicle, which can enhance the heat retention effect of exhaust gas at the time of engine start and activate the catalyst.

[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 is proposed in which the temperature of the exhaust gas is kept warm (Shokai 62-679).
No. 22, Japanese Utility Model Publication No. 56-65123, etc.). 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, since a large temperature difference occurs between the inner tube and the outer tube, it is necessary to take a structure in which the outer tube holds the inner tube while absorbing the difference in thermal expansion between the two.

Conventionally, as an example of such a structure, FIG.
Are known (see Japanese Utility Model Laid-Open No. 56-68318, Japanese Utility Model Laid-Open No. 5-19522, etc.). In this double exhaust pipe, in the air heat insulating layer 15 between the inner pipe 7 and the outer pipe 8,
Mesh ring (support member) woven from heat-resistant wire 1
By inserting 6, the inner tube 7 is held by the outer tube 8 while absorbing the difference in thermal expansion between the inner tube 7 and the outer tube 8.

[0006]

By the way, the increase in the heat retention of the exhaust gas brings about a good result in terms of activation of the catalyst at the time of cold start, but the temperature raising performance of the exhaust gas is increased.
If the exhaust gas temperature rises during high-load running or the like, there is a risk that the inner tube will become hot and the durability will be reduced, or that the catalyst will deteriorate at high temperatures. In particular, in the bent portion of the exhaust pipe and the gathered portion of the exhaust pipe, the influence of heat from the exhaust gas becomes large, which may cause a problem of thermal stress concentration.

In consideration of the above circumstances, the present invention can keep the heat retention of exhaust gas high at the time of engine start, and suppresses excessive temperature rise when exhaust gas temperature rises due to high load running or the like. It is an object of the present invention to provide a double exhaust pipe capable of preventing the decrease in strength of the inner pipe and the deterioration of the catalyst at high temperature.

[0008]

According to the invention of claim 1, an outer pipe, an inner pipe arranged with a gap in the outer pipe, and an inner pipe and an outer pipe arranged between the outer pipe and the inner pipe. In a double exhaust pipe consisting of a support member that holds the inner pipe to the outer pipe while absorbing the relative deformation of the inner pipe, the outer pipe of the inner pipe does not come into contact with the outer pipe when the inner pipe is cold, and the inner pipe becomes hot. It is characterized in that a protruding piece-shaped rib that comes into contact with the outer pipe by being displaced toward the outer pipe due to the deformation of the inner pipe when the rib becomes protruding is provided.

A second aspect of the present invention is the dual exhaust pipe according to the first aspect, wherein the rib is formed on a side of the inner pipe which is apt to be heated to a side which is deformed toward the outer pipe. I am trying.

A third aspect of the present invention is the double exhaust pipe according to the first or second aspect, wherein the pipe wall of the inner pipe at the portion where the rib is provided is flattened.

A fourth aspect of the present invention is the double exhaust pipe according to any one of the first to third aspects, in which heat conduction is conducted at a position where a rib of the outer pipe comes into contact with the portion of the outer pipe more than other portions. It is characterized in that a heat conducting member having a high rate is provided.

A fifth aspect of the present invention is the double exhaust pipe according to the fourth aspect, characterized in that the heat conducting member is attached to the outer pipe so as to be able to approach and separate from the rib.

A sixth aspect of the present invention is the double exhaust pipe according to any one of the first to fifth aspects, wherein the pipe wall of the inner pipe is bent and deformed around a portion of the inner pipe where the temperature tends to rise. It is characterized by forming beads.

The invention according to claim 7 is the double exhaust pipe according to any one of claims 1 to 6, wherein an extension piece as the support member is integrally formed on the rib, and the extension piece is internally formed. An inclined portion that is inclined with respect to the radial direction of the pipe and a sliding contact portion that slidably contacts the inner peripheral surface of the outer pipe are provided, and the extension piece is elastically deformed in the radial direction of the inner pipe. It is characterized in that it is arranged in the gap between the pipe and the inner pipe.

The invention according to claim 8 is the double exhaust pipe according to any one of claims 1 to 7, wherein the inner pipe is divided into a plurality of portions in the circumferential direction, and the side edge portion of the divided portion. It is characterized in that the rib is formed on the inner surface of the inner tube and the inner tube is formed by joining the ribs to each other.

According to a ninth aspect of the present invention, in the double exhaust pipe according to the eighth aspect, one of the ribs to be joined to each other is formed longer than the other rib, and the one rib wraps the other rib, It is characterized by crimping the ribs together in that state.

[0017]

According to the invention of claim 1, when the inner pipe has a low temperature, the ribs are not in contact with the outer pipe, so that the heat of the inner pipe does not escape to the outer pipe by heat conduction. Therefore, the exhaust gas flowing inside the inner pipe is kept warm. On the other hand, when the inner pipe has a high temperature, the rib contacts the outer pipe, so that heat of the inner pipe escapes to the outer pipe by heat conduction through the rib, and the inner pipe is cooled. Therefore, the temperature rise of the inner pipe is suppressed, and the strength of the inner pipe is prevented from lowering due to the heat effect. Further, since the inner pipe is cooled, the temperature of the exhaust gas flowing in the inner pipe is prevented from being excessively high, and the catalyst is prevented from being deteriorated at high temperature. The ribs also increase the strength of the inner tube itself.

According to the second aspect of the present invention, ribs are provided on a portion which is likely to be heated to a high temperature due to the influence of exhaust gas, for example, a bent portion or a collecting portion of the pipe, and the ribs are provided when the inner pipe has a high temperature. Since it comes into contact with the outer tube, it is possible to locally dissipate the heat of the part that easily becomes hot, and to prevent the heat of that part from rising.

According to the third aspect of the present invention, since the tube wall of the inner tube at the portion where the rib is provided is flattened, there is not much clearance between the inner tube and the outer tube, and a clearance is secured between the tip of the rib and the outer tube. Even if it is difficult, it is possible to secure a constant gap, and it is possible to achieve both the exhaust gas heat retention characteristic at low temperatures and the high heat suppression characteristic at high temperatures.

According to the invention of claim 4, when the rib is displaced according to the deformation of the inner pipe at a high temperature, the rib comes into contact with the heat conducting member. Therefore, heat transfer is promoted and the cooling effect of the inner pipe is enhanced.

According to the fifth aspect of the present invention, the distance between the rib and the heat conducting member can be adjusted by adjusting the position of the heat conducting member.

According to the sixth aspect of the invention, since the bead is provided around the portion where the temperature easily rises, the thermal stress due to the high temperature can be dispersed by the bead, and the concentration of the thermal stress can be relaxed.

In the invention of claim 7, the relative displacement between the inner pipe and the outer pipe is absorbed by the deformation of the inclined portion and the sliding contact portion sliding. Therefore, the strain energy repeatedly generated in the supporting member is reduced, and the durability of the supporting member is improved.

In the invention of claim 8, since the inner pipe is divided in the circumferential direction, the divided parts can be easily press-molded, and when the inner pipe has a thin wall thickness and is difficult to bend in the shape of the pipe. Also, even when the bending radius is small and it is difficult to bend, the bent portion and the collecting portion of the pipeline can be easily processed. Further, since there are ribs on the side edge portions of the divided portions, it is easy to join the divided portions to each other, and it is possible to increase the strength and quality of the inner pipe and minimize the welding deformation.

In the ninth aspect of the present invention, one rib is wrapped around the other rib and the mutual ribs are caulked, so that the airtightness of the rib joint is secured. Further, since welding is unnecessary, it is possible to manufacture a high-quality inner pipe without welding defects and welding deformation.

[0026]

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

[First Embodiment] FIG. 1 is a vertical sectional view showing a high temperature state of a double exhaust pipe according to a first embodiment of the present invention, and FIG. 2 is a sectional view taken along the line II-II of FIG. . 3 is a perspective view showing a state before the inner pipe is assembled, FIG. 4 is a perspective view showing a state after the inner pipe is assembled, and FIG. 5 is a cross-sectional view showing a state in which the inner pipe is incorporated inside the outer pipe. It is a figure.

As shown in FIG. 1, the double exhaust pipe (herein, simply referred to as "exhaust pipe") 4 of this embodiment has a 90-degree bent portion (a portion which easily becomes hot) at a substantially central portion in the pipe length direction.
The outer pipe 8 is formed as a bent pipe having 4Y, and is formed thickly so as to have a function as a strength member in a casting or the like, and a gap (air heat insulating layer) 5 is provided inside the outer pipe 8. The inner pipe 7 is provided between the outer pipe 8 and the inner pipe 7, which is thinly formed of stainless steel or the like and constitutes an exhaust gas passage, and absorbs relative deformation of the inner pipe 7 and the outer pipe 8. Inner tube 7
And a support member 9 for holding the outer tube 8 on the outer tube 8.

To reduce the wall thickness of the inner pipe 7, the wall thickness of the inner pipe 7 is brought close to the exhaust gas temperature in a short time by decreasing the wall thickness to reduce the heat capacity, and the temperature of the exhaust pipe 4 is raised. This is to improve the effect. By doing so, as a result, the catalyst can be activated at the time of engine start.

The outer tube 8 as a strength member formed to be thick by casting or the like has integral flanges 8f at both ends,
The flange 8f is connected to the exhaust port of the engine, other exhaust pipes, a catalyst and the like.

As shown in FIG. 3, the inner tube 7 is divided into two (half-divided) in the circumferential direction by a cutting surface including the center line of the curved inner tube 7 (a cutting surface along the normal line of the curved portion). Has been done,
At each side edge of the divided part, outwardly, a predetermined height (width)
The rib 7a having a flange shape (projection piece shape) is formed.
Each rib 7a is continuously formed with a constant width along the longitudinal direction of the inner pipe 7, and is not formed in the vicinity of both ends of the inner pipe 7 due to the support members 9 being provided. As shown in FIG. 4, the inner pipe 7 is configured as a curved pipe having a circular cross section by overlapping the rib 7a with the rib 7a on the other side and welding the outer ends of the rib 7a (welded portion 13). There is.

The height H1 of the rib 7a in this case is 1.5.
It is set to about 3 mm. This value is determined from the relationship between the interval between the air heat insulating layers 5 (see FIG. 1) and the maximum deformation amount of the inner pipe 7, with the minimum value that can be formed by pressing. Generally, the air insulation layer 5 is preferably about 3 to 5 mm, and the deformation amount of the inner pipe 7 at high temperature is about 1 to 2 mm. Therefore, the maximum deformation amount of the inner pipe 7 is subtracted from the maximum value of the air insulation layer 5. The value (= 3 mm) is the maximum value of the height H1 of the rib 7a. Then, when the inner pipe 7 is at a low temperature, the rib 7a surely comes into non-contact with the outer pipe 8, and when the inner pipe 7 becomes hot, the outer end of the rib 7a becomes an inner wall of the outer pipe 8 due to the thermal expansion of the inner pipe 7. It comes in contact.

Both ends of the inner pipe 7 are free ends (see FIG. 1), and a support member 9 is provided on the outer peripheral surface of the inner pipe 7 which has become the free end. The support member 9, as shown in FIG.
A plurality of (three in this example) are arranged at equal intervals in the circumferential direction of the inner pipe 7. Each support member 9
Is a small-width thin plate material made of a metal material having high elasticity, and is fixed to the outer peripheral surface of the inner pipe 7 by welding (welding portion 11), and a base end portion 9a and an outer pipe 8 direction from the base end portion 9a. An inclined portion 9b extending in the longitudinal direction of the inner pipe 7 and inclined.
A sliding contact portion 9c is provided on the tip end side of the inclined portion 9b and slides on the inner peripheral surface of the outer tube 8 in a pressure contact state.

The base end 9a of the support member 9 is formed in a flat plate shape so as to be in close contact with the outer peripheral surface of the inner pipe 7, and the inclined portion 9b is
The pipe extends in a direction inclined with respect to the radial direction of the inner pipe 7, here, in a direction inclined outward of the pipe end of the inner pipe 7. Further, the sliding contact portion 9c is curved in a convex curved shape on the contact surface side. The support member 9 is disposed in the space heat insulating layer 5 between the outer pipe 8 and the inner pipe 7 as shown in FIG. 1 while being elastically deformed in the radial direction of the inner pipe 7. There is.

As a result, the supporting member 9 generates a radially outward protruding tension (elastic reaction force), and the protruding tension causes the sliding contact portion 9c formed on the free end side to move inside the outer tube 8. It is pressed against the peripheral surface. Therefore, as shown in FIG. 5, with the inner tube 7 maintaining the air heat insulating layer 5 at a predetermined interval between the inner tube 7 and the outer tube 8 at an arbitrary portion in the tube length direction, due to the protrusion tension of the support member 9, It is held by the outer tube 8. Further, in this state, a predetermined gap H2 is secured between the rib 7a and the outer tube 8 when the temperature is low.

The height of the support member 9 in the free state is set to be smaller than the radial dimension of the gap 5 between the inner pipe 7 and the outer pipe 8 in order to secure the pressure contact force to the inner peripheral surface of the outer pipe 8. 2 to
It is enlarged by about 1.0 mm. Then, by elastically deforming the support member 9 by this amount and inserting the support member 9 into the outer pipe 8, a projecting tension that presses against the inner peripheral surface of the outer pipe 8 is generated.

Next, the operation will be described.

When the exhaust gas temperature is low and the inner pipe 7 is at a low temperature, such as when the engine is started, the inner pipe 7 is not deformed so much that the ribs 7a are not in contact with the outer pipe 8 as shown in FIG. Therefore, the heat of the inner pipe 7 does not escape to the outer pipe 8 by heat conduction.
Therefore, the exhaust gas flowing inside the inner pipe 7 is kept warm,
Early activation of the catalyst is achieved.

On the other hand, when the temperature of the exhaust gas and the temperature of the inner pipe 7 become high, such as during high load running, the thermal deformation increases accordingly. At this time, the inner pipe 7 is thin, and the inner pipe 7
Due to a difference in temperature between the outer tube 8 and the outer tube 8, the inner tube 7 and the outer tube 8 have different thermal deformation modes, and the inner tube 7 is largely deformed with respect to the outer tube 8. The outer pipe 8 is deformed in the pipe length direction and the radial direction.

In the case of a bent pipe, the arrow (a) in FIG.
As shown in (b), the inlet and outlet of the exhaust pipe 4 are deformed in the longitudinal direction, but at the bent portion 4Y, as shown by an arrow (c), the outer circumferential direction of the bent portion 4 (the normal direction of the bent portion). )
Transforms into. Especially, in the bent portion 4Y of the exhaust pipe,
Since the high-temperature exhaust gas strongly hits the inner wall surface of the inner pipe 7, it is greatly affected by heat and is greatly deformed in the arrow (c) direction.

Then, the outer ends of the ribs 7a at that portion come into contact with the inner wall surface of the outer pipe 8, whereby the heat of the inner pipe 7 escapes to the outer pipe 8 by heat conduction. Therefore, the inner tube 7 is cooled, the stress concentration of the inner tube 7 is eased particularly at the bent portion 4Y, the strength reduction of the inner tube 7 due to the thermal influence is suppressed, and the reliability and durability of the inner tube 7 are reduced. improves. Further, by cooling the inner pipe 7, it is possible to prevent the exhaust gas flowing in the inner pipe 7 from excessively high temperature, so that the high temperature deterioration of the catalyst is prevented.

The relative deformation of the inner pipe 7 and the outer pipe 8 is absorbed as follows. That is, with respect to the deformation in the longitudinal direction, the inclined portion 9b of the support member 9 is elastically deformed along the longitudinal direction to be absorbed to some extent, but most of it exceeds the sliding contact portion 9c of the support member 9. Slides on the inner peripheral surface of the outer tube 8 in the longitudinal direction, so that the deformation is released. Further, with respect to the radial deformation, the inclined portion 9c of the support member 9 elastically deforms in the radial direction, and the sliding contact portion 9c moves along the inner peripheral surface of the outer pipe 8 in the longitudinal direction along with the deformation. By sliding, the displacement is released. Therefore, the deformation of the inner tube 7 is absorbed without generating large strain energy in the support member 9.

Although this double exhaust pipe is a thin curved pipe, since the inner pipe 7 is divided in the circumferential direction, it can be easily manufactured by pressing the divided portion and welding it later. You can In addition, ribs 7a are provided on the side edges of the divided portion.
Therefore, it is easy to join the divided pieces together. For example, when welding the outer end of the rib 7a, even if there is a large amount of penetration, no hole will be formed, so that the allowable range of current or the like can be set wide, and the welding speed can be increased to increase the heat input. By lowering the temperature, welding deformation can be suppressed to a small level. Therefore, automatic welding by a robot becomes possible, highly reliable welding can be performed, and high quality can be achieved.

The presence of the rib 7a improves the strength of the inner pipe 7. FIG. 7 shows the difference between the case where the rib 7a is not formed (a) and the case where the rib 7a is formed (b). Strain energy generated when a force P is applied (Mises stress)
In the case of (a), the force P
A large stress concentration is observed in the portion to which is applied, and that portion may be greatly deformed. However, in the case of (b), since the rib 7a is present, the stress is dispersed even if the force P is applied, The deformation of that part becomes small. In this way, since the inner tube 7 is strengthened due to the rib 7a,
Springback after press molding can be prevented, and high precision can be achieved by low distortion welding or the like. Further, since welding deformation can be reduced, there is an advantage that the welding jig and the like can be simplified and the correction process after welding can be reduced.

In order to bring the rib 7a and the outer tube 8 which are not in contact with each other at a low temperature into contact with each other only at a high temperature, the gap H2 between the rib 7a and the outer tube 8 shown in FIG. 5 must be properly secured. However, when the distance between the air insulating layers 5 is small, the gap H2
Is difficult to set to an appropriate value. In such a case, as shown in FIG. 6, the portion provided with the rib 7a is flattened, and the diameter D2 of the portion provided with the rib 7a is made smaller than the regular diameter D1. 8 intervals H
Set 2 to an appropriate value. As a result, the same effect as the above case can be obtained.

[Second Embodiment] The first embodiment has shown the case where the present invention is applied to a bent pipe, but in the second embodiment, the present invention is applied to an exhaust manifold. FIG. 8 is a sectional view showing the actual use state.

The exhaust manifold 24 of this embodiment has a collecting pipe portion (a portion where temperature rises easily) 24Y, one end of which is connected to the exhaust port 2 of the cylinder head 1 and the other end of which is connected to the catalyst 6. . The exhaust manifold 24 includes a thin inner pipe 7 forming an exhaust gas passage, a thick outer pipe 8 as a strength member arranged with an air heat insulating layer 5 on the outer side thereof, and an inner pipe 7 to the outer pipe 8. The outer tube 8 is connected to the cylinder head 1 via the gasket 3 with the bolt 12 and the other end is connected via the gasket 3 to the catalyst 6 with the bolt 12. . The outer pipe 8 is made of a cast product, and the inner pipe 7 is divided in half in the circumferential direction, and has ribs 7a along the side edges of the divided portions. When the inner pipe 7 is thermally expanded, the ribs 7 of the collecting pipe portion 24Y are
a contacts the outer tube 8. Other configurations are the same as those of the first embodiment.

In this exhaust manifold, the rib 7a is not in contact with the outer pipe 8 at a low temperature as in the first embodiment, so that the heat retention performance of the exhaust gas is secured. On the other hand, at a high temperature, the ribs 7a come into contact with the outer pipe 8 as the inner pipe 7 is deformed, so that the heat of the inner pipe 7 is released to the outer pipe 8 and the inner pipe 7 is cooled, and the exhaust gas is exhausted. The temperature rise of the gas is suppressed and high temperature deterioration of the catalyst is prevented.

[Third Embodiment] In the first embodiment described above, the rib 7a contacts the inner wall surface of the outer pipe 8 at high temperature to release the heat of the inner pipe 7 to the outer pipe 8. In the third embodiment, as shown in FIG. 9, a material having a higher thermal conductivity than the material of the outer tube 8 such as aluminum (copper, brass or the like) is provided at the position where the rib 7a of the bent portion 4Y is in contact. When the rib 7a is displaced outward, the screw rod 14 made of aluminum is fitted and fixed.
It contacts the tip 14b of the.

In this case, the outer wall of the outer tube 8 is previously provided with the screw hole 8
h is opened, and the screw portion 14a of the screw rod 14 made of aluminum is screwed into the screw hole 8h, and the screw rod 14 can be moved toward and away from the rib 7a. When setting the screwed position, first set the rib 7
Screw the screw rod 14 until it hits a. Then, the screw rod 14 is unscrewed by an appropriate amount so that the gap between the rib 7a and the tip of the screw rod 14 can be adjusted. That is, even when the air insulating layer 5 becomes large, a predetermined gap is always secured between the rib 7a and the tip of the screw rod 14 by performing an operation of once applying the screw rod 14 to the rib 7a and then returning it by an appropriate amount. You can

This clearance can be adjusted appropriately by the screwing amount of the screw rod 14, so that the inner pipe 7 can be adjusted depending on the temperature rise.
The timing of escaping the heat of can be changed appropriately. That is, the temperature at which the rib 7a is brought into contact with the threaded rod 14 and the heat of the inner tube 7 is released can be controlled by operating the threaded rod 14 from the outside.

In this embodiment, the rib 7a contacts the aluminum screw rod 14 at high temperature, so that heat conduction is promoted and the cooling efficiency of the inner pipe 7 is improved.

The screw hole 8h provided in the outer pipe 8 can be used as a positioning dowel at the time of core molding when the inner pipe 7 is manufactured by casting. Furthermore, it can be used as a hole for sand removal during casting, and the number of steps for repairing sand clogging can be reduced.

[Fourth Embodiment] FIG. 10 schematically shows the structure of the inner pipe 4 of the fourth embodiment of the present invention. The support member 9 is not shown. The assembling mode to the outer tube is exactly the same as that of the first embodiment.

In the inner pipe of this embodiment, a substantially annular shape (the vicinity of the rib 7a is omitted) is provided on the outer peripheral wall side of the bent portion 4Y against which high-temperature exhaust gas hits so as to surround the central portion of the bent portion 4Y. Beads 7b are formed. The bead 7b is formed as an arcuate cross section that is convex outward.

As described above, since the beads 7b are provided so as to surround a portion where thermal stress is likely to concentrate at high temperature, the thermal stress due to high temperature can be dispersed by the beads 7b and the concentration of thermal stress can be relaxed. Therefore, the reliability and durability of the inner pipe 7 can be improved.

[Fifth Embodiment] FIG. 11 shows the structure of an inner pipe 7 according to a fifth embodiment of the present invention. This inner tube 7 is shown in FIG.
As shown in (a), it is configured as a collecting pipe, and a bead 7b is formed so as to sandwich the collecting pipe portion 24Y. The method of combination with the outer tube is the same as in the first or second embodiment. The shape of the bead 7b is shown in FIG. 11 (c).
As shown in, the cross section is arcuate and its height H3
However, the rib height is H1-0.5 to 1 mm. This is to prevent the bead 7b from coming into contact with the outer tube 8 first. Thereby, the concentration of thermal stress generated in the collecting pipe portion 24Y of the inner pipe 7 can be dispersed, so that the reliability and durability of the inner pipe 7 are improved.

[Sixth Embodiment] Next, a sixth embodiment of the present invention will be described. FIG. 12 shows the inner pipe 7 used in the double exhaust pipe of the sixth embodiment. In this inner tube 7, the rib 7a
Is formed over the entire length of the inner pipe 7, and an extension piece 19 projecting outward in the radial direction of the inner pipe 7 is integrally formed on one of the ribs 7a facing each other at the end thereof. The extension piece 19 is used as a support member and is formed into a strip plate shape having an appropriate length.

FIG. 13 shows a state in which the inner pipe 7 is incorporated in the outer pipe 8. The extension piece 19 as a supporting member is bent and deformed in the circumferential direction of the inner pipe 7, extends the inclined portion 19b in the tangential direction of the inner pipe 7, and has a sliding contact portion 19c at the tip thereof.
Is slidably contacted with the inner peripheral surface of the outer tube 8. Since the inclined portion 19b in this case extends in the tangential direction of the inner pipe 7, it is inclined in the circumferential direction with respect to the radial direction (radius) of the inner pipe 7.

The length of the extension piece 19 is such that when the inner tube 7 is inserted into the outer tube 8, the sliding contact portion 19 at the tip of the extension piece 19 is inserted.
It is set such that c is elastically deformed inward by an appropriate amount. While elastically deforming the extension piece 19 in this manner, the inner tube 7 is replaced by the outer tube 8
When inserted inside, the sliding contact portion 19c at the tip of the extension piece 19
Comes into pressure contact with the inner peripheral surface of the outer pipe 8 with a protruding tension, whereby the inner pipe 7 is held by the outer pipe 8.

In this double exhaust pipe, when the inner pipe 7 is deformed in the radial direction, the inclined portion 19b of the extension piece 19 is elastically deformed in the circumferential direction to absorb the deformation of the inner pipe 7. Also,
When the inner pipe 7 is deformed in the longitudinal direction, the sliding contact portion 19c
Slides on the inner peripheral surface of the outer pipe 8 in the longitudinal direction to absorb the deformation of the inner pipe 7.

Further, according to this embodiment, since the extension piece 19 as a supporting member is integrally formed with the rib 7a, it is not necessary to separately provide a supporting member, and the number of parts can be reduced and the cost can be reduced. .

[Seventh Embodiment] Next, a seventh embodiment of the present invention will be described. FIG. 14 is a perspective view showing a state before assembling the inner pipe of this embodiment, and FIG. 15 is a front view showing a state where the inner pipe is assembled.

In this embodiment, among the ribs of the inner pipe 7 to be joined to each other, one rib 7d is formed longer than the other rib 7a, and the longer rib 7d is bent to form the shorter rib. 7a and wraps both ribs 7 in that state
A and 7d are fixed by crimping each other.

According to this structure, the shorter rib 7a is
Since the caulking is performed while being wrapped in the longer rib 7d, the airtightness at the mating portion of the ribs 7a and 7d can be kept good. Therefore, in assembling the inner pipe 7, it becomes possible to eliminate the welding process, and by eliminating welding defects, deformation, residual stress, etc., it is possible to produce a high-quality inner pipe without manufacturing variations. Further, the welding jig and the correction process after welding can be eliminated. In addition, since one rib 7d wraps the other rib 7a, the outer ends of the ribs are rounded and the contactability with the outer tube 8 is improved,
Heat conduction is promoted.

[Other Examples] In addition to the supporting member used in the above-mentioned examples, the mesh used in the conventional example may be used as the supporting member.

Further, in the above embodiment, the rib is formed on substantially the entire side edge of the divided portion, but it may be provided only on the side displaced in the outer tube direction. Alternatively, it may be provided only at the bent portion. Further, when the inner pipe is not of the split type, only ribs having the same function as described above may be provided.

[0068]

As described above, according to the first aspect of the present invention, when the temperature of the exhaust gas is low such as when the engine is started, the heat of the inner pipe is hard to escape to the other side, and the effect of keeping the temperature of the exhaust gas is improved. Increase. Therefore, early activation of the catalyst can be achieved.
Also, when the exhaust gas temperature and the inner pipe temperature are high, such as during high-load running, the ribs contact the outer pipe to release the heat of the inner pipe to the outer pipe, so the inner pipe is cooled and is affected by heat. The decrease in strength of the inner pipe is suppressed. In addition, the presence of the ribs increases the strength of the inner pipe itself, thereby improving the reliability and durability of the inner pipe. Further, since the exhaust gas temperature is lowered by cooling the inner pipe, deterioration of the catalyst at high temperature is prevented.

According to the second aspect of the present invention, the heat of the portion which easily becomes high in temperature can be locally released, so that the concentration of thermal stress can be relaxed and the durability can be improved.

According to the third aspect of the present invention, even when there is not much gap between the outer pipe and the inner pipe, the gap between the tip of the rib and the outer pipe can be set to an appropriate value. Therefore, it is possible to achieve both the exhaust gas heat retention characteristics at low temperatures and the high heat suppression characteristic at high temperatures.

According to the invention of claim 4, it is possible to promote the escape of heat from the inner pipe at high temperature, and to improve the characteristics at high temperature (preventing strength deterioration due to cooling of the inner pipe and high temperature of the catalyst due to lowering of exhaust gas temperature). (Performance related to deterioration prevention) can be improved.

According to the invention of claim 5, the distance between the rib and the heat conducting member can be adjusted. Therefore, at what temperature is the rib contacting the heat conducting member and the heat of the inner tube is released? You can control.

According to the sixth aspect of the present invention, the concentration of thermal stress in the portion where the temperature tends to rise can be alleviated, and the reliability and durability of the inner pipe can be improved.

According to the invention of claim 7, since the supporting member is integrally formed with the rib, it is not necessary to separately provide a supporting member, the number of parts can be reduced, and the cost can be reduced. Also, since the sliding contact part slides according to the relative displacement of the inner pipe and the outer pipe,
The strain energy repeatedly generated in the supporting member can be reduced, and the durability of the supporting member can be improved.

According to the invention of claim 8, even if there is a bent portion or a gathered portion, it can be easily processed, and the quality can be improved.

According to the ninth aspect of the present invention, one rib is wrapped around the other rib and the mutual ribs are caulked. Therefore, the airtightness of the inner tube can be ensured and welding is not required. The occurrence of welding defects and welding deformation can be prevented, and quality can be improved. Further, since one rib wraps the other rib, the outer ends of the ribs are rounded, the contactability with the outer tube is improved, and heat conduction is promoted.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view showing a state of a double exhaust pipe of a first embodiment of the present invention at a high temperature.

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

FIG. 3 is a perspective view showing a state before assembling the inner tube of the embodiment.

FIG. 4 is a perspective view showing a state after the inner tube is assembled.

FIG. 5 is a transverse cross-sectional view showing a state in which the inner tube is incorporated in the outer tube.

FIG. 6 is a cross-sectional view showing a modified example of FIG.

FIG. 7 is an explanatory diagram of strength of the inner pipe of the embodiment.

FIG. 8 is an overall sectional view showing a usage state of a double exhaust pipe of a second embodiment of the present invention.

FIG. 9 is a vertical sectional view of a double exhaust pipe according to a third embodiment of the present invention.

FIG. 10 is a configuration diagram of an inner pipe in a fourth embodiment of the present invention, (a) is a side view and (b) is a rear view.

FIG. 11 is a configuration diagram of an inner pipe in a fifth embodiment of the present invention, (a) is a side view, (b) is a front view, and (c) is an enlarged sectional view of a bead portion.

FIG. 12 is an exploded perspective view of an inner pipe before assembling according to a sixth embodiment of the present invention.

FIG. 13 is a front view showing a state in which the inner tube is incorporated in the outer tube.

FIG. 14 is an exploded perspective view of an inner tube of the seventh embodiment of the present invention before assembling.

FIG. 15 is a front view showing a state after the inner tube is assembled.

FIG. 16 is a vertical cross-sectional view showing a main part of a conventional double exhaust pipe.

[Explanation of symbols]

 7 Inner pipe 7a Rib 7b Bead 7d Longer rib 8 Outer pipe 9 Support member 14 Screw rod (heat conduction member) 19 Extension piece 19b Inclined portion 19c Sliding contact portion

Claims (9)

[Claims] 1. An outer pipe, an inner pipe disposed with a gap in the outer pipe, and the inner pipe disposed between the outer pipe and the inner pipe while absorbing relative deformation of the inner pipe and the outer pipe. In a double exhaust pipe consisting of a support member for holding the inner pipe to the outer pipe, the outer pipe of the inner pipe is not in contact with the outer pipe when the inner pipe has a low temperature, and the inner pipe deforms when the inner pipe has a high temperature. The double exhaust pipe is characterized in that a rib in the form of a protruding piece is provided so as to come into contact with the outer pipe by being displaced to the outer pipe side with the above. 2. The double exhaust pipe according to claim 1, wherein the rib is formed on a side of the inner pipe where the temperature easily rises, which is deformed toward the outer pipe. trachea. 3. The double exhaust pipe according to claim 1, wherein the pipe wall of the inner pipe at the portion where the rib is provided is flattened. 4. The double exhaust pipe according to any one of claims 1 to 3, wherein the ribs of the outer pipe are in contact with each other and have a higher thermal conductivity than other portions of the outer pipe. Double exhaust pipe characterized by having a member. 5. The double exhaust pipe according to claim 4, wherein the heat conducting member is attached to an outer pipe so as to be able to approach and separate from a rib. 6. The double exhaust pipe according to claim 1, wherein a bead is formed by bending and deforming a pipe wall of the inner pipe around a portion of the inner pipe where the temperature is likely to rise. A double exhaust pipe characterized by that. 7. The double exhaust pipe according to claim 1, wherein an extension piece as the support member is integrally formed on the rib, and the extension piece is provided in a radial direction of the inner tube. A slanting portion that is inclined with respect to the outer pipe and a sliding contact portion that slidably contacts the inner peripheral surface of the outer pipe are provided, and the extension piece is elastically deformed in the radial direction of the inner pipe. A double exhaust pipe characterized by being placed in a gap. 8. The double exhaust pipe according to claim 1, wherein the inner pipe is divided into a plurality of pieces in the circumferential direction, and the rib is formed on a side edge portion of the divided portion. A double exhaust pipe, wherein the inner pipe is formed by joining the ribs to each other. 9. The double exhaust pipe according to claim 8, wherein one of the mutually joining ribs is formed longer than the other,
A double exhaust pipe characterized in that the one rib is wrapped in the other rib and the ribs are caulked together in this state.