JPH1018839A - Double pipe exhaust manifold - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent occurrence of a crack at welded portions, and prevent deterioration of a catalytic converter caused by exhaust gas of a high temperature during operation at a high speed. SOLUTION: In a double pipe manifold, each of a branch pipe 2, an exhaust gas collecting portion 3 and an exhaust pipe 4 comprises a double pipe constituted of an inner cylinder 5 and an outer cylinder 6 which are spaced apart from each other, thereby discharging collected exhaust gas to a catalytic converter disposed downstream. In this case, the inner and outer cylinders 5, 6 are formed of respective pairs of bisected pipes 8, 9 and 11, 12, which are bisected from upstream toward downstream. The pair of bisected pipes 8, 9 constituting the inner cylinder 5 are provided with a plurality of welded portions A, in which seams are partly welded to each other, and not-welded portions B, in which seams are not welded. The not-welded portions B are formed at least at a bending point of an exhaust gas passage, in which exhaust gas collides against the inner wall of the inner cylinder 5 at a predetermined angle, at an inlet end on a cylinder head side, and at an outlet end on an exhaust pipe side. The pair of bisected pipes 11, 12 constituting the outer cylinder 6 are welded to each other over the entire seams thereof.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a double pipe exhaust manifold for collecting exhaust gas discharged from a plurality of exhaust ports of a cylinder head of an internal combustion engine and guiding the exhaust gas to an exhaust pipe.

[0002]

2. Description of the Related Art Generally, an exhaust pipe connected to an exhaust manifold of an internal combustion engine is provided with a catalytic converter for purifying exhaust gas. This catalytic converter is heated to a certain temperature or more by heat of exhaust gas. If it is not, the purification function cannot be sufficiently exerted. Therefore, at the start of operation, it is necessary to send exhaust gas having the highest possible temperature to the catalytic converter to warm the catalytic converter in a short time. However, at the start of operation, since the temperature of the exhaust gas is low, it is desirable to minimize the exhaust gas heat from the exhaust port of the cylinder head to the catalytic converter. Since the wall is thick, the heat capacity is large and the temperature does not easily rise, so that the temperature difference between the exhaust manifold and the exhaust gas is large at the start of operation, and the heat of the exhaust gas is easily taken away.

To cope with this, for example, as described in Japanese Patent Application Laid-Open No. 6-200755, a branch pipe of an exhaust manifold communicating with an exhaust port of a cylinder head and exhaust gas from the branch pipe are collected. And the collecting pipe leading to the exhaust pipe is a double pipe consisting of an inner cylinder and an outer cylinder, respectively.
By reducing the thickness of the inner cylinder, its heat capacity is reduced so that heat of exhaust gas is not deprived as much as possible.

FIG. 3 shows a double pipe exhaust manifold M of this type, which includes a plurality of branch pipes a projecting upstream so as to communicate with an exhaust port of a cylinder head (not shown).
It has an exhaust gas collecting part b for collecting the exhaust gas flowing through each branch pipe a, and an exhaust pipe c for discharging the exhaust gas collected in the exhaust gas collecting part b to a catalytic converter provided downstream. The ends of the branch pipe a and the discharge pipe c are provided with a flange d. This double-pipe exhaust manifold M is composed of a double pipe in which an inner cylinder e and an outer cylinder f are arranged at a distance from each other.

As described above, the double-pipe exhaust manifold M is formed by the double pipes of the inner cylinders e and g and the outer cylinders f and h. As shown in FIG. 4, the outer cylinders f and h are formed by welding a pair of half pipes i divided in two from the upstream side to the downstream side and welding the seam by welding. ing.

[0006]

As described above, in the double pipe exhaust manifold M, the inner cylinders e and g are usually formed by connecting a pair of half pipes i by welding.
Conventionally, since welding is performed over the entire length of the joint extending in the axial direction of the pair of half pipes i, there are the following problems.

That is, since the double-pipe exhaust manifold M becomes extremely hot during operation, the inner tubes e and g are thermally deformed due to thermal expansion, and thermal stress is generated in the welded portion. This causes a crack in the welded portion. Had occurred. The cracks in the welded portion are particularly caused by the exhaust gas flowing into the branch pipe a from the exhaust port.
A portion j that collides with the inner wall of the exhaust gas collecting portion b;
That is, it is remarkable at the portion j where the flow path of the exhaust gas is bent.

Accordingly, an object of the present invention is to provide a double-pipe exhaust manifold which can prevent the occurrence of cracks in the welded portion by providing a non-welded portion in the inner cylinder.
Another object of the present invention is to provide a double-pipe exhaust manifold capable of preventing deterioration of a catalytic converter caused by high-temperature exhaust gas during steady-state operation, particularly during high-speed operation.

It is still another object of the present invention to provide a double pipe exhaust manifold which can reduce the number of welds in the inner cylinder and facilitate assembly.

[0010]

According to the first aspect of the present invention,
A branch pipe protruding upstream so as to communicate with each of a plurality of exhaust ports of a cylinder head of the internal combustion engine; an exhaust gas collecting portion for collecting exhaust gas flowing through each branch pipe; And a discharge pipe for discharging the collected exhaust gas to a catalytic converter provided on the downstream side. In the pipe exhaust manifold, the inner cylinder and the outer cylinder are composed of a pair of half tubes divided into two from the upstream side to the downstream side, and the pair of half tubes constituting the inner cylinder is partially welded at a joint thereof. It has a plurality of welded portions and a non-welded portion where welding is not performed, and the non-welded portion has at least a bending point of an exhaust gas flow path where exhaust gas hits the inner wall of the inner cylinder at an angle, and an inlet end on the cylinder head side. Section and the outlet end on the exhaust pipe side. Are a pair of half tube constituting the outer tube is characterized in that the seam is welded over its entire length.

(Function) In the first aspect of the present invention, the exhaust gas flowing out of the exhaust port of the cylinder head flows into the exhaust gas collecting portion through each branch pipe, and further flows out of the exhaust pipe through the discharge pipe. At the start of the operation, the temperature of the exhaust gas is low, but the heat capacity is small because the inner cylinder is thin, so that the temperature of the exhaust gas decreases only slightly. For this reason, the catalytic converter provided in the exhaust pipe is heated in a short time by the heat of the exhaust gas.

The temperature of the exhaust gas increases as time elapses from the start of operation, and the heat of the exhaust gas causes the inner cylinder to thermally expand. However, since this thermal expansion is absorbed by the flexibility of the non-welded portion of the inner cylinder, there is almost no possibility that a crack is generated in the welded portion of the inner cylinder. Such a thermal expansion is particularly remarkable in a portion exposed to a high-temperature atmosphere, that is, a portion opposed to the inlet of the branch pipe, which is a portion where the flow path of the exhaust gas is bent.

However, since a non-welded portion not welded is located at this portion, the thermal expansion due to the high-temperature exhaust gas is absorbed. Most of the exhaust gas that has flowed into the branch pipe from the exhaust port of the cylinder head flows out of the exhaust gas collecting section through the exhaust pipe to the exhaust pipe.However, since the non-welded part of the inner cylinder is not sealed, some exhaust gas It may leak to the side. However, since the outer cylinder is welded over its entire length, the outer cylinder has sufficient airtightness, so that exhaust gas does not leak outside the double pipe exhaust manifold.

[0014] Leakage of the exhaust gas to the outer cylinder side is not preferable because it causes a decrease in the temperature of the exhaust gas. However, since the engine speed is low and the back pressure is low at the time of idling in a cold start in which it is desired to rapidly raise the catalyst temperature, it is low. Leakage to the outer cylinder side is hardly a problem. It is more profitable to obtain the effect of preventing cracks due to the provision of the non-welded part, and at the time of long-term steady operation where the back pressure is high and some leakage to the outer cylinder side is expected. Alternatively, at the time of high-speed operation, there is no need to keep the temperature, and heat consumption due to leakage to the outer cylinder side has the advantage of preventing deterioration of the catalytic converter.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A double pipe exhaust manifold according to the present invention will be described below with reference to an embodiment shown in the drawings. In FIGS. 1 and 2, the double pipe exhaust manifold 1 includes a plurality of branch pipes 2, an exhaust gas collecting section 3, and a discharge pipe 4. A flange 10 is provided.

The branch pipes 2 branch off from the exhaust gas collecting section 3 and protrude upstream, and are connected to the exhaust ports of a cylinder block (not shown) via flanges 10, respectively. The discharge pipe 4 is connected to an exhaust pipe (not shown) connected to the downstream side, and discharges exhaust gas flowing down to the exhaust gas collecting section 3 to the exhaust pipe. The double pipe exhaust manifold 1 has an inner cylinder 5
And the outer tube 6 are arranged at a distance from each other.

The space between the inner cylinder 5 and the outer cylinder 6 forms a heat insulating layer 7. The heat insulating layer 7 may be a simple space or a heat insulating material filled in a gap between the inner cylinder 5 and the outer cylinder 6. In the former case, the air forms the heat insulating layer. FIG. 2 shows a double pipe exhaust manifold 1
FIG. 2 is a cross-sectional view of a portion of the branch pipe 2 taken along the line II. In the case of the double pipe exhaust manifold 1, the heat insulating layer 7 is a space.

The sectional view of the portion of the discharge pipe 4 along the line II-II is the same as FIG. Thus, the inner cylinder 5 and the outer cylinder 6
The reason why the heat insulating layer 7 is formed in between the above is that at the start of the operation, it is necessary to prevent the temperature of the exhaust gas from lowering so that the exhaust gas having the highest possible temperature flows to the catalytic converter (not shown).

The inner cylinder 5 is formed by joining a pair of half pipes 8 and 9 divided in half from the upstream side to the downstream side. The joints extending in the axial direction of the pair of half pipes 8 and 9 are welded only at a plurality of portions. In other words, only a few joints extending in the axial direction are spot-welded. The pair of half tubes 8 and 9 have the same shape and structure as the conventional half tube i shown in FIG.

Then, the welded portion A which is spot-welded
Is located at a position where the exhaust gas does not strike the inner wall of the inner cylinder 5 at an angle, that is, at a portion Y where the exhaust gas flows parallel to the inner wall of the inner cylinder 5, while the non-welded portion B where welding is not performed 5 and an inlet end of the inner cylinder 5 on the cylinder head side.

As described above, the reason why the non-welded portion B is provided in the inner cylinder 5 is that when the inner cylinder 5 thermally expands, a thermal stress is generated in the welded portion A and a crack is generated in this portion. If there is, this thermal expansion is absorbed by the shape deformation of the non-welded portion B, so that the thermal stress generated in the welded portion A is very small and does not reach the point where a crack is generated in the welded portion A. This is for absorbing the thermal expansion of.

The reason why the welding portion A is selected as the portion Y where the exhaust gas flows in parallel to the inner wall of the inner cylinder 5 is that the portion X where the exhaust gas strikes the inner wall of the inner cylinder 5 at an angle is particularly suitable for the inner cylinder. This is to avoid such a portion X because the thermal expansion of No. 5 is large and a crack is easily generated in the welded portion A. on the other hand,
Similarly to the inner cylinder 5, the outer cylinder 6 also includes a pair of half tubes 11 and 12 divided into two from the upstream side to the downstream side.
The pair of half tubes 11 and 12 are connected to each other by welding over the entire length of the joint extending in the axial direction differently from the inner cylinder 5. In FIG. 1, C indicating a peripheral portion of the outer cylinder 6 by a thick line represents a welded portion.

That is, since the outer cylinder 6 has its seam welded over its entire length, airtightness is sufficiently maintained. Therefore, no problem occurs even when the non-welded portion B exists between the pair of half pipes 8 and 9 by making the inner cylinder 5 have only a few welds. Even if the exhaust gas leaks from the non-welded portion B of the inner cylinder 5 to the outer cylinder 6 side, the exhaust gas does not leak outside the double pipe exhaust manifold 1 because the outer cylinder 6 is completely airtightly maintained. Because.

The material of the inner cylinder 5 is, for example, 1
SUS430 (JIS standard) having a composition of 8Cr is typical, and SUS409 and 410 (JIS standard) having a composition of 13Cr are typical examples of the material of the outer cylinder 6. In addition, the double pipe exhaust manifold 1 includes a branch pipe 2
And the exhaust gas collecting part 3 and the discharge pipe 4 are formed by integral molding. However, it is not always necessary to form the integral molding, and the separately formed branch pipe 2, the exhaust gas collecting part 3 and the discharge pipe 4 are welded. May be combined.

Next, the operation of the embodiment of the present invention will be described. The exhaust gas flowing out of the exhaust port of the cylinder head (not shown) flows into the exhaust gas collecting section 3 from each branch pipe 2, and further flows out of the exhaust pipe 4 to an exhaust pipe (not shown).
At the start of the operation, the temperature of the exhaust gas is low, but the heat capacity is small because the inner cylinder 5 is thin, so that heat absorption by the inner cylinder 5 is small and the temperature of the exhaust gas is slightly reduced. Therefore, a catalytic converter (not shown) provided in the exhaust pipe is heated in a short time by the heat of the exhaust gas.

The temperature of the exhaust gas rises as time elapses from the start of operation, and the heat of the exhaust gas causes the inner cylinder 5 to thermally expand and deform. If the joint of the inner cylinder is welded over its entire length as in the conventional example, the welded portion cannot be thermally deformed freely, and thermal stress is generated inside. When the thermal stress exceeds the welding strength of the welded portion, a crack is generated in the welded portion.

However, in the embodiment of the present invention, this thermal expansion is absorbed as a shape deformation in the non-welded portion B of the inner cylinder 5, so that the thermal expansion is prevented from being concentrated on the welded portion A. There is almost no possibility that a crack is generated in the welded portion A. Such a thermal expansion is caused by a part exposed to a particularly high-temperature atmosphere, such as a part X of the exhaust gas collecting part 3 which is directly hit by exhaust gas flowing into the branch pipe 2 from an exhaust port (not shown) of the cylinder head. This is remarkable at a portion X where the road is bent.

However, since the non-welded portion B, which is not welded, is located at the portion X, the thermal expansion at the portion X where the exhaust gas hits directly is absorbed as thermal deformation of the non-welded portion B. Most of the exhaust gas flowing into the inner cylinder 5 from the exhaust port of the cylinder head flows out to an exhaust pipe (not shown). However, since the inner cylinder 5 is provided with the non-welded portion B, a part of the exhaust gas is The non-welded portion B flows out to the outer cylinder 6 side. However, since the joint of the outer cylinder 6 is welded over the entire length, the outer cylinder 6 has sufficient airtightness, so that the exhaust gas does not leak outside the double pipe exhaust manifold 1.

It is to be noted that a part of the exhaust gas leaking from the non-welded portion B toward the outer cylinder 6 lowers the exhaust gas temperature.
At the time of operation rotation where it is desired to introduce exhaust gas into the catalytic converter while maintaining the exhaust temperature as much as possible, since the engine rotation is in an idling state, the amount of exhaust is small, and the non-welded state in which the plate-thickness portion abuts the plate-thickness portion Even in the part B, there is almost no exhaust gas leaking from here to the outer cylinder 6 side.

On the other hand, at the time of engine steady operation, since the catalytic converter has already risen to the activation temperature, the amount of exhaust gas increases with the steady operation of the engine, so that the amount of exhaust gas leaking to the outer cylinder 6 increases. Even if the exhaust gas temperature is reduced by that amount, there is no problem. Since the catalytic converter accelerates catalyst deterioration and lowers durability when the temperature reaches a certain level or more, it is preferable to lower the exhaust gas temperature.

Further, since the inner cylinder 5 is welded at several locations, the double pipe exhaust manifold 1 can be easily assembled.
In addition, since the welded portion A is provided at the portion Y where the exhaust gas does not contact the inner wall of the inner cylinder 5 at an angle, cracks are less likely to be generated at the welded portion A, and thus the durability is not impaired. As described above, in the embodiment of the present invention,
Since the non-welded portion B is provided in the inner cylinder 5, the thermal expansion of the inner cylinder 5 due to exhaustion is absorbed by the shape deformation of the non-welded portion B, so that the thermal stress in the welded portion A is reduced.
As a result, the occurrence of cracks in the welded portion A is prevented.

The provision of the non-welded portion B has no effect on idling operation such as at the start of operation. However, when the exhaust amount is increased and the exhaust temperature is high as in the steady engine operation, the non-welded portion B is not affected. Exhaust gas from part B
Because the temperature of the exhaust gas decreases by leaking to the side,
During steady-state operation, particularly during high-speed operation, deterioration of the catalytic converter due to high-temperature exhaust gas is prevented.

[0033]

According to the first aspect of the present invention, since the non-welded portion is provided in the inner cylinder, the thermal expansion of the inner cylinder due to the exhaust heat is absorbed by the shape deformation at the non-welded portion. The thermal stress in the portion is reduced, and as a result, the occurrence of cracks in the welded portion is prevented.

In particular, since the joint of the inner cylinder is welded only at a plurality of locations, thermal expansion is easily absorbed, and the welded portion is provided at a portion where the exhaust gas flows in parallel, that is, at a portion where the exhaust gas does not hit at an angle. Has been
Problems such as crack generation hardly occur. Further, at the time of steady operation, particularly at the time of high-speed operation, since the temperature of the exhaust gas is lowered by the exhaust gas leaking from the non-welded portion to the outer cylinder side, deterioration of the catalytic converter due to the high-temperature exhaust gas is prevented.

Further, since the inner cylinder has several welds, it is easy to assemble the double pipe exhaust manifold, and the welded portion is provided at a position where the exhaust gas does not hit the inner wall of the inner cylinder at an angle. Cracks are less likely to occur in the welded portion, so that durability is not impaired even if there are several welds.

[Brief description of the drawings]

FIG. 1 is a front view showing a double pipe exhaust manifold according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view taken along the line 〓-〓 (line 〓-〓) of FIG. 1;

FIG. 3 is a front view of a conventional double pipe exhaust manifold.

FIG. 4 is a perspective view of a half pipe constituting the exhaust manifold shown in FIG. 3;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Double pipe exhaust manifold 2 Branch pipe 3 Exhaust gas collecting part 4 Discharge pipe 5 Inner cylinder 6 Outer cylinder 8, 9 Half pipe of inner cylinder 11, 12 Half pipe of outer cylinder A Welding part of inner cylinder B Inner cylinder Non-welded part C Welded part of outer cylinder

Claims (1)

[Claims] 1. A branch pipe (2) projecting upstream so as to communicate with a plurality of exhaust ports of a cylinder head of an internal combustion engine, and exhaust gas flowing through each branch pipe (2) is collected. An exhaust gas collecting part (3) and a discharge pipe (4) for discharging the collected exhaust gas to the downstream side are provided, and these are arranged with an inner cylinder (5) and an outer cylinder (6) spaced from each other. In a double-pipe exhaust manifold configured with a double pipe and discharging the collected exhaust to a catalytic converter provided on the downstream side, the inner cylinder (5) and the outer cylinder (6) are divided into two parts from the upstream side to the downstream side. Halved pipes (8, 9, 11, 1)
The pair of half pipes (8, 9) constituting the inner cylinder (5) are composed of a plurality of welded portions (A) with partially welded joints thereof and a non-welded portion (B) where welding is not performed. And the non-welded portion (B) has at least an inflection point of the exhaust gas flow path at which the exhaust gas hits the inner wall of the inner cylinder (5) at an angle, an inlet end on the cylinder head side, and an outlet on the exhaust pipe side. A pair of half pipes (11, 12) provided at the end and constituting the outer cylinder (6) are:
A double pipe exhaust manifold characterized by its seams being welded over its entire length.