JPH06336921A - Exhaust tube of internal combustion engine - Google Patents

Abstract

PURPOSE:To improve the exhaust purifying performance by retraining the temperature decrease in exhaust gas in cold time and at the time of starting an engine, and provide both of improved exhaust purifying performance and vibration absorbing performance. CONSTITUTION:A part of thin thickness inner tube 21 is constituted of a thin thickness bellows 22. In a thick thickness outer tube 24, a clearance 29 is formed between the outer tube and the inner tube 21. In the outer tube 24, a spherical sliding joint 27 is formed, surrounding the bellows 22. The clearance 29 serves as a heat insulating air layer. The bellows 22 and the sliding joint 27 absorb the vibration of an engine.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust pipe of an internal combustion engine for automobiles.

[0002]

2. Description of the Related Art When an exhaust gas purification catalytic converter is installed in the exhaust system of an internal combustion engine, the temperature drop of the exhaust gas is suppressed during cold or engine start to accelerate the catalyst activation temperature reaching time and improve the exhaust gas purification performance. In order to improve it, there is a type in which an exhaust pipe connecting an internal combustion engine and a catalytic converter is dually configured with an inner pipe and an outer pipe, and a gap (a heat insulating layer) is formed between both pipes. Then, in the middle of such an exhaust pipe, a flexible pipe is provided as a vibration absorbing portion in order to block transmission of engine vibration to the exhaust pipe.

This structure is shown in FIG. Reference numeral 1 is a first double pipe, which is composed of an inner pipe 2 and an outer pipe 3. Reference numeral 4 denotes a flange welded to the upstream end (left end) of the double pipe 1, which is mounted on an engine (not shown). Reference numeral 5 is a flexible pipe including a bellows tube 6 and a wire mesh-like outer tab radar 7 and 8 is a second pipe composed of an inner pipe 9 and an outer pipe 10.
Of the double pipe, and a flange 11 is welded to its downstream end (right end).

The downstream end of the first double pipe 1 is fitted into the upstream end (left end) of the flexible pipe 5, and a band 12 is wound around the outer periphery of the upstream end of the flexible pipe 5, so that the double pipe 1,
The flexible pipe 5 and the band 12 are welded and fixed. Further, the upper end (left end) of the second double pipe 8 is fitted into the lower end (left end) of the flexible pipe 5, and the band 13
It is welded and fixed together.

Reference numeral 14 is a catalytic converter, and a flange 15 welded to its upstream end is connected to the downstream end of the second double pipe 8 via a flange 11.

[0006]

SUMMARY OF THE INVENTION In the above conventional technique,
Since the flexible pipe 5 does not have an airtight heat insulating layer, there is a problem in that heat escapes from this portion to the outside and radiates heat, which significantly impairs warm-up of the catalytic converter.

In addition, the two double tubes 1 and 8 are required, and the structure is complicated and the cost is high. Therefore, the present invention solves these problems and retains heat to improve the temperature rise of the catalyst and vibration (bending displacement).
It is an object of the present invention to provide an exhaust pipe having a simple double pipe structure capable of achieving both absorption.

[0008]

In order to achieve the above object, an exhaust pipe of an internal combustion engine according to the present invention is an inner pipe (21).
In the exhaust pipe in which a gap (29) is formed between the outer pipe (24) and the outer pipe (24), a bellows portion (22) is formed in a part of the inner pipe (21).
And the outer pipe (24) near the bellows portion (22) is formed into a spherical sliding joint (27).

The gap (29) may be filled with a heat insulating material.

[0010]

[Operation] Since the spherical sliding joint has a good sealability,
An air layer (gap) with high airtightness is formed between the outer tubes, and heat insulation (heat retention) is improved. At the same time, due to the structure of the sliding joint, the strength of the outer pipe can be increased and the plate thickness of the inner pipe can be reduced. As a result, the heat capacity of the inner pipe is reduced, the temperature decrease of the exhaust gas at the time of engine start is suppressed, the temperature rising property of the catalyst is improved, and the exhaust gas purification performance is improved. Moreover, the bellows of the thin plate absorbs the thermal stress in the axial direction caused by the difference in elongation due to the temperature difference between the inner tube and the outer tube.

In this way, both exhaust purification performance and vibration (bending displacement) absorption can be achieved. In the case where the gap is filled with the heat insulating material, it is possible to further improve the exhaust gas purification performance by improving the heat retention and the strength of the exhaust pipe.

[0012]

1 (a), 1 (b) and 1 (c) show a first embodiment of the present invention, in which the present invention is applied to a front pipe directly below an engine. Reference numeral 21 is a thin-walled inner tube having a circular cross section, and a thin-walled bellows 22 is also connected to a part thereof. A band 23 connects the bellows 22 to the inner pipe 21. 24
Is a thick outer tube, which is composed of a first outer tube 25 and a second outer tube 26. The outer tubes 25, 26 are formed so that the portion surrounding the bellows 22 is formed in a spherical shape and can slide on each other. To form a sliding joint 27.

The spherical portions of the first outer pipe 25 and the second outer pipe 26 constituting the sliding joint 27 are slidably fitted to each other. In FIG. 1 (a), there is a gap between these spherical portions, but this is exaggerated for clarity of illustration. The parts are slidably and closely fitted together.

A flange 28 is provided at the upstream end of the first outer pipe 25.
Are welded. Also, inside the upstream end of the outer pipe 25,
An end portion 22 obtained by expanding the upstream cylindrical portion 22a of the bellows 22.
b is welded. A downstream side of the spherical portion of the second outer pipe 26 is configured to surround the inner pipe 21 by forming a gap 29 with the inner pipe 21.

Reference numeral 30 denotes an annular wire mesh spot welded to the outer periphery of the downstream end of the inner pipe 21. The wire mesh 30 is slidably held between the outer pipe 26 and the outer pipe 26.
It does not necessarily have to be slidable, and the inner and outer tube ends may be fixed. Reference numeral 31 is a connection flange welded to the downstream end of the outer pipe 26. 32 is a catalytic converter, 33 is a flange for connection welded to the upstream end of the catalytic converter 32,
It is connected to the flange 31.

The inner tube 21 and the bellows 22 have a wall thickness of 0.8 mm and 0.3 mm, respectively, and the outer tubes 25 and 26 have a wall thickness of 1.2 mm. 2A and 2B show a second embodiment of the present invention, in which a cylindrical inner pipe 34 is provided inside the upstream portion of the dual structure exhaust pipe of the first embodiment. The inner pipe 34 has its upstream end expanded, and is welded and fixed to the first outer pipe 25 and the upstream end 22b of the bellows 22. The inner pipe 34 prevents exhaust gas from the engine from directly hitting the bellows 22. Therefore, the temperature rise of the bellows 22 is suppressed and the life thereof is extended. In addition, the exhaust gas is less likely to directly hit the inside of the bellows 22 and obstruct the flow of the bellows 22, thus preventing generation of abnormal noise.

Although not shown, in the invention of claim 2, the gap 29 between the inner pipe and the outer pipe is filled with a heat insulating material to improve the heat retention (heat insulating) property and the strength of the exhaust pipe. I am trying.
In addition to the above-described embodiment, only the bellows and the spherical sliding joint portion are made as a joint unit separately from the double tubular portion, and the joint unit is joined and connected to the double tubular portion. You can do it.

[0018]

Since the exhaust pipe of the internal combustion engine of the present invention is constructed as described above, the strength can be improved by using a thick material for the outer pipe, and the inner pipe and the bellows can be thinned accordingly. The heat capacity can be reduced. Further, since the spherical sliding joint has good airtightness, it has good heat retention (heat insulation). Therefore, not only the strength and the vibration absorption can be improved, but also the exhaust purification performance is improved.

Furthermore, the axial thermal stress caused by the difference in elongation due to the temperature difference between the inner tube and the outer tube is absorbed by the thin bellows, and the durability is improved.

[Brief description of drawings]

FIG. 1 is a first embodiment of the present invention, (a) is a schematic longitudinal sectional view, (b) is an enlarged view of a B portion of FIG. 1 (a), and (c) is an enlarged view of a C portion of FIG. .

FIG. 2 is a second embodiment of the present invention, in which (a) is a schematic vertical cross-sectional view, and (b) is an enlarged view of a portion B in FIG. 2 (a).

FIG. 3 is a schematic vertical sectional view of the prior art.

[Explanation of symbols]

21 ... Inner pipe, 22 ... Bellows part (bellows), 24 ... Outer pipe, 27 ... Sliding joint, 29 ... Gap.

Claims (2)

[Claims] 1. An exhaust pipe in which a gap is formed between an inner pipe and an outer pipe, a bellows portion is provided in a part of the inner pipe, and the outer pipe near the bellows portion is formed into a spherical sliding joint. An exhaust pipe of an internal combustion engine characterized by being formed. 2. The exhaust pipe for an internal combustion engine according to claim 1, wherein the gap is filled with a heat insulating material.