JPH09296723A - Double tube - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ensure the durability and reliability of a double tube. SOLUTION: Respective branch pipes 2a, 2b and 2c of an exhaust manifold 1 are composed of double tubes having inner tubes 6a, 6b and 6c, outer tubes 7a, 7b and 7c, and insulating layers therebetween 10a, 10b and 10c. The respective inner tubes 6a, 6b and 6c are fixed, at their fixed-support parts 8a... on their upstream ends, to the outer tubes 7a, 7b and 7c, and are slidably supported, at their sliding-support parts 9a, 9b and 9c on their downstream ends, by the outer tubes 7a, 7b and 7c. The inner tubes 6a, 6b and 6c and the outer tubes 7a, 7b and 7c are enlarged outward at their portions respectively corresponding to and contacting with the sliding-support parts 9a, 9b and 9c.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a double tube.

[0002]

2. Description of the Related Art Conventionally, an exhaust double pipe for an internal combustion engine having an inner pipe and an outer pipe, in which an annular heat insulating layer is formed between the inner pipe and the outer pipe, is known. There is. In this exhaust double pipe, the heat radiation amount of the exhaust gas from the exhaust double pipe is made as small as possible so that the catalyst provided downstream of the exhaust double pipe is quickly heated by the exhaust gas.

However, when the double pipe is constructed in this way, a large temperature difference occurs between the inner pipe and the outer pipe, and thus a large thermal expansion difference occurs between the inner pipe and the outer pipe. Therefore, each inner pipe is fixed to the corresponding outer pipe at the fixed support portion provided at the upstream end, and is supported slidably in the axial direction by the outer pipe at the slide support portion provided at the downstream end. An exhaust double pipe is known (see JP-A-6-101468). As described above, when the inner tube is supported by the outer tube so as to be slidable in the axial direction, the difference in thermal expansion in the axial direction can be absorbed.

[0004]

However, in the above-described exhaust double pipe, the inner pipe and the outer pipe located in the sliding support portion extend parallel to the axis of the branch pipe, and therefore, the inner pipe and the outer pipe. There is a problem that it is not possible to absorb a large difference in thermal expansion in the radial direction between them, resulting in undesirable stress concentration in the inner pipe, which may cause plastic deformation or cracks in the inner pipe. There is a point.

[0005]

In order to solve the above-mentioned problems, according to the present invention, there is provided a double pipe having an inner pipe and an outer pipe, each inner pipe being fixed to an outer pipe at a fixed support portion. In a double pipe axially slidably supported by the outer pipe in a sliding support portion provided at one end of the double pipe, the inner pipe and the outer pipe located in the sliding support portion are directed outward. Have expanded. That is, both the axial thermal expansion difference and the radial thermal expansion difference between the inner pipe and the outer pipe are absorbed.

[0006]

FIG. 1 shows a case where the present invention is applied to a branch pipe of an exhaust manifold of an internal combustion engine. However, the invention can also be applied to double tubes for other applications. Referring to FIG. 1, an exhaust manifold 1 includes three branch pipes 2a, which are connected to corresponding cylinders of an internal combustion engine.
2b and 2c are provided. These branch pipes 2a, 2b, 2c are connected to an engine body (not shown) via a common flange 3. The branch pipes 2a, 2b, 2c are connected to a common collecting pipe 4, and the collecting pipe 4 is connected via a flange 5 to a catalytic converter (not shown) containing a catalyst.

As shown in FIG. 1, each branch pipe 2a, 2b,
2c is composed of a double tube. That is, the branch pipe 2a includes an inner pipe 6a and an outer pipe 7a, the branch pipe 2b includes an inner pipe 6b and an outer pipe 7b, and the branch pipe 2c includes an inner pipe 6c and an outer pipe 7c. Each of the branch pipes 2a, 2b, 2c includes an outer pipe 7a, 7b,
7c is fixed to the flange 3 and the collecting pipe 4 by being joined to the flange 3 at the upstream end and to the collecting pipe 4 at the downstream end, for example, by welding.

The inner pipes 6a, 6b, 6c are respectively provided with corresponding outer pipes 7 in annular fixed support portions 8a, 8b, 8c.
It is fixed to a, 7b, 7c by welding, for example. Also,
The inner pipes 6a, 6b, 6c are annular sliding support portions 9a, 9
b and 9c, the corresponding outer tubes 7a, 7b, 7
It is slidably supported in the axial direction by c. Therefore, the inner tubes 6a, 6b, 6c move undesirably,
Alternatively, it is prevented from vibrating.

In this embodiment, each fixed support portion 8a,
The inner tubes 6a, 6b, 6c are directly supported by the outer tubes 7a, 7b, 7c at 8b, 8c and the respective sliding support portions 9a, 9b, 9c, that is, the inner tubes 6a, 6b, 6c and the outer tubes. The inner pipes 6a, 6b, 6c are supported by the outer pipes 7a, 7b, 7c without an intermediate member interposed between 7a, 7b, 7c.

In the example shown in FIG. 1, the fixed support portions 8a, 8a
b and 8c are inner pipes 6a, 6b and 6c and outer pipes 7a and 7c.
Slide support portions 9a, 9b, 9c are provided at the upstream ends of b, 7c, and at the downstream ends of the inner pipes 6a, 6b, 6c and the outer pipes 7a, 7b, 7c, respectively. In each of the branch pipes 2a, 2b, 2c, the temperature at the upstream end adjacent to the engine body is lower than that at the downstream end. Therefore, as in this embodiment, the fixed support portions 8a, 8b, 8c are connected to the branch pipes 2a, 2b, 2c.
By providing it at the upstream end, the weld is prevented from being significantly deteriorated.

As shown in FIG. 1, the axis L of the branch pipe 2b.
The length of b and the length of the axis Lc of the branch pipe 2c are set to be substantially equal to each other, while the length of the axis La of the branch pipe 2a is set to be longer than the lengths of the axes Lb and Lc of the branch pipes 2b and 2c. ing. The wall thicknesses of the outer tubes 7a, 7b, 7c are set to be substantially equal to each other. On the other hand, the wall thicknesses of the inner pipes 6b and 6c are set to be substantially equal to each other.
Is set to be larger than the wall thickness of the inner tubes 6b and 6c. Furthermore, the thickness of the inner pipes 6a, 6b, 6c is the outer pipe 7
It is set to be smaller than the wall thickness of a, 7b, and 7c.

Still referring to FIG. 1, each inner tube 6a, 6
b and 6c and the corresponding outer pipes 7a, 7b and 7c are arranged apart from each other.
b, 6c and the outer heat insulating layer 10 between the outer pipes 7a, 7b, 7c
a, 10b, 10c are provided respectively. In this embodiment, the heat insulation layer is formed of an air layer, but the inner pipe 6a,
The space between 6b, 6c and the outer tubes 7a, 7b, 7c may be filled with another fluid or granular material to form the heat insulating layer.

A curved portion 11 is usually provided in a branch pipe having a relatively long axial length such as the branch pipe 2a. However, when such a curved portion 11 is provided, the bending rigidity of the branch pipe 2a in the curved portion 11 becomes low. Therefore, the branch pipe 2a in the bending portion 11 has an elliptical cross section, whereby the bending portion 1
The bending rigidity of the branch pipe 2a in No. 1 is prevented from being lowered.

By the way, when the engine is started, especially when it is cold-started, the catalyst downstream of the exhaust manifold 1 may not reach its activation temperature. Even if the exhaust gas is guided to the catalyst in this state, the exhaust gas is satisfactorily purified. You may not be able to. Therefore, in the exhaust manifold of FIG. 1, the inner pipes 6a, 6
b, 6c and the outer tubes 7a, 7b, 7c between the heat insulation layers 10a, 1
0b and 10c are provided so that the heat quantity of the exhaust gas radiated through the exhaust manifold 1 is reduced. Further, the inner tubes 6a, 6b, 6c are made relatively thin so that the heat capacities of the inner tubes 6a, 6b, 6c are made large, and the outer tubes 7a, 7b, 7c are made relatively thick. The heat capacities of these outer pipes 7a, 7b, 7c are made small, so that the exhaust manifold 1
The temperature drop of the exhaust gas flowing inside is reduced. As a result, it is possible to quickly raise the temperature of the catalyst to the activation temperature, and thus to ensure good purification of exhaust gas.

When the amount of heat radiation from the exhaust manifold 1 is reduced in this way, the temperature of the inner pipes 6a, 6b, 6c becomes significantly higher than the temperature of the outer pipes 7a, 7b, 7c, and as a result, the inner pipes The axial thermal expansion amount of 6a, 6b, 6c becomes significantly larger than the axial thermal expansion amount of the outer tubes 7a, 7b, 7c. Therefore, for example, the inner pipes 6a, 6b, 6
If both ends of c are welded and fixed to the outer pipes 7a, 7b, 7c, the inner pipes 6a, 6b, 6c and the outer pipes 7a, 7b, 7c have a difference in the amount of axial thermal expansion between the inner pipes 6a, 6b, 6c. For example, stress concentrates and acts on the welded portion, the curved portion, etc., so that the inner pipes 6a, 6b, 6c are plastically deformed or the inner pipe 6 is deformed.
Cracks may occur in a, 6b, and 6c.

Therefore, sliding support portions 9a, 9b, 9c are provided at the downstream ends of the branch pipes 2a, 2b, 2c, and the inner pipes 6a, 6b, 6c are axially moved in the sliding support portions 9a, 9b, 9c. , The outer tubes 7a, 7b, 7c are supported so as to be movable relative to each other. That is, when the temperature of the branch pipes 2a, 2b, 2c becomes high and the thermal expansion amount of the inner pipes 6a, 6b, 6c in the axial direction becomes larger than that of the outer pipes 7a, 7b, 7c, the inner pipes 6a, 6b
While being supported by the outer pipes 7a, 7b, 7c, 6b, 6c can slide in the sliding support portions 9a, 9b, 9c in the axial direction. As a result, the inner pipes 6a, 6b, 6c are replaced by the outer pipe 7.
By moving relative to a, 7b, and 7c, the difference in thermal expansion in the axial direction is absorbed. Therefore, it is possible to prevent the stress concentration portions from being generated in the inner pipes 6a, 6b, 6c.

However, as described at the beginning, the inner pipe 6
A large thermal expansion difference also occurs in the radial direction between a, 6b, 6c and the outer tubes 7a, 7b, 7c. Therefore, the inner pipes 6a, 6b, 6c located on the sliding support portions 9a, 9b, 9c
When the outer pipes 7a, 7b, 7c extend parallel to the axis of the branch pipe, this large difference in thermal expansion in the radial direction cannot be absorbed. As a result, the inner tubes 6a, 6b, 6c
Undesired stress concentration occurs in the inner pipes 6a, 6b, 6c
May plastically deform or crack the inner tube.

When the inner tubes 6a, 6b, 6c are slidably supported by the outer tubes 7a, 7b, 7c in this manner, the inner tube 6 tends to extend in the axial direction by thermal expansion.
The internal stress of a, 6b, 6c causes the sliding support portions 9a, 9b,
The outer peripheral surface of the inner pipes 6a, 6b, 6c and the outer pipe 7 in 9c
The inner pipes 6a, 6b, 6c become the outer pipes 7a, 7b, 7c only when the frictional force between the inner peripheral surfaces of a, 7b, 7c becomes larger.
Begins to move relative to. In other words, the inner pipe 6a,
Unless the internal stress of 6b and 6c overcomes the frictional force, the inner pipe 6
a, 6b, 6c do not move relative to each other. However, as described above, the inner tubes 6a, 6b, 6c and the outer tubes 7a, 7b, 7
If a large difference in thermal expansion in the radial direction occurs between c, the sliding support 9
The surface pressure between the inner pipes 6a, 6b, 6c located at a, 9b, 9c and the outer pipes 7a, 7b, 7c increases, and the frictional force increases. In this case, the inner pipes 6a, 6b and 6c are plastically deformed due to stress concentration regions or the inner pipes 6a, 6b and 6c are deformed.
There is a risk of cracking in c.

Therefore, in this embodiment, as shown in FIGS. 2A and 2B, the inner pipes 6a, 6b, 6c and the outer pipes 7a, 7b, which are located on the respective sliding support portions 9a, 9b, 9c,
7c is widened toward the outside, that is, in the relative movement direction of the inner pipes 6a, 6b, 6c with respect to the outer pipes 7a, 7b, 7c. In other words, the sliding support parts 9a, 9b, 9
inner pipes 6a, 6b, 6c and outer pipes 7a, 7 located at c
b and 7c are expanded toward the exhaust downstream side. As a result, when the inner tubes 6a, 6b, 6c are thermally expanded in the axial direction and also in the radial direction, the inner tubes 6a, 6b, 6c are axially and radially directed along the outer tubes 7a, 7b, 7c. It comes to slide outward. That is, the inner tubes 6a, 6
It is possible to absorb not only the difference in thermal expansion in the axial direction but also the difference in thermal expansion in the radial direction between b, 6c and the outer tubes 7a, 7b, 7c.

FIG. 2A shows the sliding support portion 9a of the branch pipe 2a, and FIG. 2B shows the sliding support portions 9b and 9c of the branch pipes 2b and 2c. When the curvature of the branch pipes 2b and 2c is relatively small, as shown in FIG. 2 (B), the inner pipes 6b and 6c and the outer pipes 7b and 7c located on the slide supporting portions 9b and 9c are respectively separated. Axes Lb, Lc over the entire circumference
On the other hand, only THETA is inclined. That is, the taper angles of the inner pipes 6b, 6c and the outer pipes 7b, 7c located on the slide support portions 9b, 9c with respect to the axes Lb, Lc are THE.
It is called TA.

When the curved portion 11 is provided like the branch pipe 2a, stress F acts on the inner pipe 6a due to thermal expansion of the inner pipe 6a located upstream of the curved portion 11. This stress F also acts on the inner pipe 6a positioned on the sliding support portion 9a while maintaining the direction. In this case, the sliding support portion 9
Similarly to b and 9c, if the taper angles of the inner pipe 6a and the outer pipe 7a are constant over the entire circumference, between the curved outer portion 6ao of the inner pipe 6a located on the curved outer side with respect to the axis La and the curved outer portion 7ao of the outer pipe 7a. The surface pressure becomes undesirably high, and the curved inner portion 6ai of the inner tube 6a located on the curved inner side with respect to the axis La on the other hand may be separated from the curved inner portion 7ai of the outer tube 7a and may not be able to support the inner tube 6a well.

Therefore, as shown in FIG. 2 (A), the curved inner portion 6ai of the inner pipe 6a located on the sliding support portion 9a.
And the taper angle of the curved inner portion 7ai of the outer tube 7a is set to a relatively small THETAI, and the taper angles of the curved outer portion 6ao of the inner tube 6a and the curved outer portion 7ao of the outer tube 7a located in the sliding support portion 9a are compared. Big THETAO
Stipulated in. As a result, the branch pipe 2a having the bend b11
Also in the above, it is possible to favorably absorb the difference in thermal expansion between the inner pipe 6a and the outer pipe 7a in the axial direction and the radial direction.

That is, all the sliding support parts 9a, 9
b and 9c, the inner tubes 6a, 6b, 6c and the outer tubes 7a, 7c
It is possible to satisfactorily absorb the difference in thermal expansion between the b and 7c in the axial direction and the radial direction, and prevent the friction force between the inner pipes 6a, 6b and 6c and the outer pipes 7a, 7b and 7c from increasing. be able to. Therefore, it is possible to prevent plastic deformation or cracks in the inner pipes 6a, 6b, 6c, and thus improve the durability and reliability of the exhaust manifold 1.

FIG. 3 shows another embodiment. In FIG. 3, components similar to those of the embodiment of FIG. 1 are designated by the same numbers. Although only the slide support portion 9a of the branch pipe 2a is shown in FIG. 3, the other slide support portions 9b and 9c can be similarly configured. In the embodiment described above, the sliding support 9
The inner pipes 6a, 6b, 6c located at a, 9b, 9c and the outer pipes 7a, 7b, 7c are directly supported. On the other hand, in this embodiment, as shown in FIG. 3, the intermediate member 12 is inserted between the inner pipe 6a and the outer pipe 7a located in the sliding support portion 9a. The intermediate member 12 is held in the intermediate member holding hole 13 formed in the outer pipe 7a.

The intermediate member 12 is formed of, for example, wire mesh or glass wool. The intermediate member 12 is for surely supporting the inner pipe 6a, for example, and the good supporting action of the inner pipe 6a is maintained by the intermediate member 12 even if the entire branch pipe 2a vibrates greatly. Further, by inserting the intermediate member 12, it is possible to reduce the amount of heat transfer from the inner pipe 6a to the outer pipe 7a in the sliding support portion 9a, and thus it is possible to ensure the heat insulation performance of the branch pipe 2a.

By the way, when the inner pipe 6a and the outer pipe 7a located on the slide support portion 9a are formed substantially parallel to the axis La, if the intermediate member 12 is inserted between the inner pipe 6a and the outer pipe 7a, By the radial thermal expansion of 6a, the intermediate member 1
Undesirably large compressive stress acts on 2. As described above, the temperature around the sliding support portion 9a is considerably high, and when a large compressive stress acts on the intermediate member 12 at such a high temperature, deterioration of the intermediate member 12 progresses extremely rapidly, which is not preferable.

On the other hand, in the present embodiment, the inner pipe 6a and the outer pipe 7a located on the slide support portion 9a are expanded outward, and therefore the gap between the inner pipe 6a and the outer pipe 7a is increased. The distance D can be maintained substantially constant regardless of the amount of thermal expansion of the inner pipe 6a. As a result, it is possible to prevent the stress acting on the intermediate member 12 from increasing when the inner pipe 6a thermally expands in the radial direction. Therefore, the intermediate member 12
Can be reduced. As a result, a good supporting action of the inner pipe 6a and a good heat insulating performance of the branch pipe 2a can be maintained.

In the embodiments described so far, the fixed support portions 8a, 8b, 8c of the branch pipes 2a, 2b, 2c are formed at the upstream ends of the corresponding branch pipes 2a, 2b, 2c, respectively. However, these fixed support parts 8a, 8b, 8
The c may be formed at the intermediate portion between the upstream end and the downstream end of the corresponding branch pipes 2a, 2b, 2c. Alternatively, the fixed support portion is provided at the downstream end of the branch pipes 2a, 2b, 2c, and the slide support portion 9 is provided.
You may form a, 9b, 9c in an upstream end.

Further, in the embodiments described so far, one fixed support portion and one sliding support portion are provided for each branch pipe. However, a plurality of fixed supports and a plurality of sliding supports may be provided for each branch pipe.

[0030]

The durability and reliability of the double pipe can be ensured.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an entire exhaust manifold.

FIG. 2 is a partially enlarged view of a sliding support portion.

FIG. 3 is a partial enlarged view of a slide support portion according to another embodiment.

[Explanation of symbols]

 1 ... Exhaust manifold 1a ... 1st branch pipe group 1b ... 2nd branch pipe group 2a, 2b, 2c ... Branch pipe 4 ... Collecting pipe 6a, 6b, 6c ... Inner pipe 7a, 7b, 7c ... Outer pipe 8a, 8b, 8c ... Fixed support part 9a, 9b, 9c ... Sliding support part 10a, 10b, 10c ... Thermal insulation layer 12 ... Elastic member La, Lb, Lc ... Axis line

Claims (1)

[Claims] 1. A double pipe having an inner pipe and an outer pipe, wherein each inner pipe is fixed to an outer pipe at a fixed supporting portion, and the sliding pipe is provided at one end of the double pipe. A double pipe in which an outer pipe is slidably supported in the axial direction, and an inner pipe and an outer pipe located in a sliding support portion are expanded outward.