JPH09242538A - Double tube for automobile exhaust system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To facilitate bending work of a double tube by providing an outer tube having a bending portion and an inner tube having a bending portion and being thinner than the outer tube, forming a corrugated portion in an axial direction of the inner tube, and setting a maximum diameter of the corrugated portion smaller than the inner diameter of the outer tube. SOLUTION: A front tube 1 for leading exhaust gas from an exhaust manifold to a catalyst converter or the like is provided with an L-shaped main body of a double structure, in which an inner tube 3 is inserted into an outer tube 2, and flanges 4, 5 at both ends thereof. A bending portion 6 is formed on the outer tube 2, while a bending portion 7 is formed on the inner tube 3 in a position corresponding to the bending portion 6. In this case, the inner tube 3 is thinner than the outer tube 2, and a corrugated portion 9 is formed in the bending portion 7 by corrugating. A maximum diameter of the corrugated portion 9 is smaller than the inner diameter of the outer tube 2 such that the inner tube 3 cannot be brought into contact with the outer tube 2. Consequently, it is possible to efficiently absorb thermal expansion of the inner tube 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has one or more corrugated portions formed in the axial direction of an inner pipe, which facilitates bending work.
The present invention relates to a double pipe for an automobile exhaust system having a small heat capacity.

[0002]

2. Description of the Related Art An exhaust system for an automobile is provided with an exhaust manifold for discharging exhaust gas from an engine.
Further, a front tube or the like for guiding the exhaust gas from this exhaust manifold to a catalytic converter or the like is arranged. A front tube having a structure shown in FIG. 1 is introduced in Japanese Utility Model Laid-Open No. 19522/1993. The front tube 1 has an L-shaped main body having a double structure in which an inner tube 3 is inserted into an outer tube 2, and flanges 4 and 5 are attached to both ends of the main body. A bent portion 6 is formed on the outer tube 2, and a bent portion 7 is formed on the inner tube 3 at a position corresponding to the bent portion 6. The outer tube 2 and the inner tube 3 are fixed to the outer tube 2 at one end of the front tube 1. At the other end, the outer tube 2 and the inner tube 3 are not fixed,
The sliding member 8 is configured to be relatively movable.

In the front tube 1 of FIG. 1, when exhaust gas flows into the inner tube 3, the temperature of the inner tube 3 rises and the inner tube 3 thermally expands. The thermal expansion of the inner pipe 3 is absorbed by the relative movement of the inner pipe 3 and the outer pipe 2 via the sliding member 8. However, it is relatively difficult to reduce the thickness of the inner pipe 3 and bend it into a double pipe. Even if various measures are taken during bending, the wall thickness of the inner tube 3 is 0.6 m.
m is the limit. Since the manufacturing constraint is added to the wall thickness, the heat capacity of the inner pipe 3 cannot be reduced, and the inner pipe 3 does not quickly rise in temperature when the vehicle engine is started. As a result, the purification efficiency of the exhaust gas in the catalytic converter is reduced, so that an expensive catalyst whose efficiency is less likely to be reduced must be used.

Therefore, Japanese Patent Laid-Open No. 174020/1995 proposes a front tube using a bellows made of stainless steel as an inner tube. In this front tube, a corrugated portion 9 as shown in FIG. 2 is formed by a hydraulic bulge method on the bent portion 7 of the inner tube 3 which is thinner than the outer tube 2 by about 0.5 mm. There is. The inner pipe 3 has one end 1 on the upstream side.
It is fixed to the outer tube 2 at 0, and is slidable with respect to the outer tube 2 by the slide mechanism 12 at the downstream end 11. When the temperature of the inner pipe 3 rises, the inner pipe 3 thermally expands. The outer periphery of the corrugated portion 9 slides along the inner surface of the outer pipe 2 toward the non-fixed end side of the inner pipe 3 according to the thermal expansion of the inner pipe 3. That is, the thermal expansion of the inner pipe 3 is guided to the non-fixed side, and the thermal expansion of the inner pipe 3 is absorbed by the relative movement of the inner pipe 3 and the outer pipe 2 on the non-fixed side.

[0005]

By the way, in the front tube having the double tube structure, when exhaust gas emission starts by starting the engine, the inner tube 3 is moved only by the axial method (longitudinal direction) according to the temperature rise. Rather than thermal expansion in the radial direction. The thermal expansion in the radial direction comes into close contact with the inner wall surface of the outer tube 2 and acts as a resistance when the inner tube 3 slides toward the non-fixed side end portion of the outer tube 2, thereby smoothly sliding the inner tube 3. There is a risk that it will disturb the movement. Further, if the inner tube 3 or the corrugated portion 9 that has been thermally expanded in the radial direction comes into close contact with the inner wall surface of the outer tube 2, the function as a double tube will be impaired. The present invention has been devised to solve such a problem, in which a corrugated portion is formed by corrugation processing on the bent portion of the inner pipe so that the inner pipe does not contact the outer pipe. It is an object of the present invention to efficiently absorb the thermal expansion of the inner pipe by the structure for maintaining it and to provide a double pipe suitable as an exhaust system for automobiles.

[0006]

In order to achieve the object, a double pipe for an automobile exhaust system of the present invention has an outer pipe having a bent portion and a bend at a position corresponding to the bent portion. A portion is formed, the inner pipe having a thickness smaller than that of the outer pipe, and one or more corrugated portions formed in the pipe axial direction of the inner pipe,
The maximum diameter of the corrugated portion is smaller than the inner diameter of the outer tube. The corrugated portion is preferably formed by corrugation and has a reduced diameter so that the inner tube does not come into contact with the outer tube. For the outer pipe and the inner pipe, for example, stainless steel pipes are used.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The double pipe according to the present invention is used as an inner pipe 3 which is thinner than the outer pipe 2. As the outer tube 2 and the inner tube 3, it is preferable to use a stainless steel tube having excellent corrosion resistance and heat resistance. Since a thin stainless steel pipe is used for the inner pipe 3, the inner pipe 3 quickly rises in temperature when the engine of the automobile is started, and high-temperature exhaust gas can be sent to the catalytic converter in a short time, improving the purification efficiency. To do. As shown in FIG. 3, a corrugated corrugated portion 9 is formed in the bent portion 7 of the inner pipe 3 by corrugation. As the corrugating method, for example, the method introduced in Japanese Patent Publication No. 49-43069 is adopted. When the corrugated portion 9 is formed by corrugating, the maximum diameter portion 13 having an outer diameter equal to or smaller than the original diameter of the inner pipe 3 is formed without forming a bulging portion as in hydraulic bulging. Is formed. That is, the corrugated portion 9 is basically the inner tube 3 having a reduced diameter.

As described above, when corrugation is performed, the corrugated portion 9 has a smaller peak diameter than the hydraulic bulge method, and contact with the outer tube 2 is reliably prevented. Further, in corrugating, contrary to the hydraulic bulge method, the wall thickness of the corrugated portion 9 becomes thicker than the wall thickness of the raw pipe. Therefore, when using a raw pipe having the same wall thickness, the corrugated portion 9 formed by corrugation has higher reliability of the welded portion. Outer tube 2
The upstream end 10 and the downstream end 11 are reduced in diameter. The end of the inner pipe 3 is fixed to the upstream end 10.
With respect to the downstream side end portion 11, the inner pipe 3 is provided via the sliding member 8.
The downstream end of the is provided slidably. Alternatively, since corrugation processing is suitable for corrugation processing with a small pitch and a large number of peaks, even if the inner tube 3 is fixed to the outer tube 2 without using the sliding member 8 as shown in FIG. The thermal expansion of the inner pipe 3 is sufficiently absorbed.

When a plurality of bent portions are required, a plurality of corresponding corrugated portions are provided. The method and apparatus introduced by the present inventors in JP-A-7-214182 are suitable for forming a plurality of corrugated portions. Further, as shown in FIG. 5, the corrugated portions 14 and 15 may be formed in the inner pipe 3 at a place other than the bent portion 7. The corrugated portions 14 and 15 improve the flexibility of the inner pipe 3 and more efficiently absorb the thermal expansion of the inner pipe 3. When the inner pipe 3 having the corrugated portion 9 formed therein is inserted into the outer pipe 2,
A gap 14 is formed between the outer pipe 2 and the inner pipe 3. The gap 14 absorbs the thermal expansion of the inner pipe 3 in the radial direction. That is, the inner pipe 3 does not come into contact with the inner wall surface of the outer pipe 2 and prevents smooth sliding of the inner pipe 3 along the pipe axis direction due to contact resistance. Further, the outer periphery of the corrugated portion 9 does not come into contact with the inner wall surface of the outer tube 2 to generate an abnormal sound. Moreover, since the inner pipe 3 is kept in a non-contact state with the outer pipe 2, the temperature of the exhaust gas in the inner pipe 3 is prevented from being lowered by the heat transfer from the inner pipe 3 to the outer pipe 2. Although the gap 14 is hollow in FIGS. 3 to 5, it may be filled with a heat insulating and sound insulating material such as glass wool. By filling the heat insulating and sound insulating material, the sound wave vibration radiated to the outside is attenuated, and the temperature drop of the exhaust gas flowing in the inner pipe 3 is further prevented.

[0010]

As described above, the double pipe for an automobile exhaust system of the present invention has a structure in which the inner pipe having the bent portion corrugated by corrugation is inserted into the outer pipe. Bending as a pipe is facilitated, and contact of the inner pipe with the outer pipe can be prevented with high accuracy. Further, since the corrugated portion is thicker than the raw pipe, the reliability of the welded portion is increased. Moreover, since the thin-walled stainless steel pipe is used as the inner pipe, the heat capacity of the inner pipe becomes small, the inner pipe heats up quickly when the automobile engine is started, and high-temperature exhaust gas can be sent to the catalytic converter. As a result, purification efficiency is improved.

[Brief description of drawings]

FIG. 1 Conventional double pipe for automobile exhaust system

[Fig. 2] Conventional double pipe for automobile exhaust system using stainless steel bellows

FIG. 3 is a dual pipe for an automobile exhaust system according to the present invention.

FIG. 4 is a dual pipe for an automobile exhaust system according to the present invention, which does not use a sliding member.

FIG. 5: Double pipe for automobile exhaust system in which a corrugated portion is formed in the non-bent portion

[Explanation of symbols]

1: Front tube 2: Outer tube 3: Inner tube
4, 5: Flange 6: Bent portion of outer pipe 7: Bent portion of inner pipe 8: Sliding member 9: Corrugated portion 10: Upstream end of inner pipe 11: Downstream end of inner pipe 12: Slide mechanism 13: Maximum diameter part 14: Gap 15, 16: Corrugated part

Claims (2)

[Claims] 1. An outer tube having a bent portion, an inner tube having a bent portion formed at a position corresponding to the bent portion, the inner tube having a thinner wall than the outer tube, and an axial direction of the inner tube. A double pipe for an automobile exhaust system, comprising: one or more corrugated processed portions formed in 1. and a maximum diameter of the corrugated processed portions being smaller than an inner diameter of the outer pipe. 2. The double pipe for an automobile exhaust system according to claim 1, wherein the corrugated portion according to claim 1 is formed by corrugation and has a reduced diameter.