JPH07224649A - Exhaust manifold structure - Google Patents

Abstract

PURPOSE:To prevent any crack due to thermal stress from occurring in a weld zone between a branch pipe and a manifold part even in the case where a thermal expansion coefficient between the branch pipe consisting of double pipes and this manifold part is varied each. CONSTITUTION:Both inner and outer pipes 22 and 24 of a branch pipe 20 relatively shiftable in the axial direction, while a downstream end of the inner pipe 22 is projected more than that of the outer pipe 24, and an exhaust gas inflow limiting means 40 is installed in an interval between a peripheral surface of the inner pipe 22 projected out of the outer pipe 24 and an inner wall surface of a manifold part 30, and an end face of the manifold part 30, where the outer pipe is inserted into, and the peripheral surface of the outer pipe 24 are joined together by means of a weld zone 42.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the structure of an exhaust manifold of an internal combustion engine, and more particularly to the structure of an exhaust manifold that guides exhaust gas to a collecting portion via a branch pipe composed of a double pipe.

[0002]

2. Description of the Related Art An exhaust manifold plays a role of collecting exhaust gas discharged from each combustion chamber of an engine body and sending the exhaust gas to an exhaust pipe. The upstream side is composed of a plurality of branch pipes and the downstream side is It is composed of a gathering section. Conventionally, an exhaust manifold has been known in which a branch pipe is a double pipe made of stainless steel and a collecting portion is a casting. The reason why the branch pipe is a double pipe is to suppress the decrease in the temperature of the exhaust gas and raise the catalyst bed temperature to improve the purification performance of the exhaust gas. For smoothing the exhaust pressure and reducing exhaust pressure loss and radiated noise.

A technique for inserting the downstream end of a branch pipe into a casting assembly and joining the end surface of the branch pipe and the outer peripheral surface of the branch pipe by welding is disclosed in, for example, JP-A-63-63. It is disclosed in Japanese Patent No. 170515. When the branch pipe is composed of a double pipe, the outer peripheral surface of the outer pipe inserted into the collecting portion is welded to the end surface of the collecting portion.

[0004]

However, when the branch pipe consisting of the double pipe is made of stainless steel and the collecting portion is made of casting, the thermal expansion coefficient of each member is different, so that the welded portion is excessively large. There is a problem that thermal stress acts. That is, when the welded portion is heated by the exhaust gas, the difference in thermal expansion between the outer tube and the gathered portion in the welded portion becomes large, and the thermal stress acting on the welded portion becomes excessive. for that reason,
Cracks may occur in the weld.

According to the present invention, even if the coefficient of thermal expansion of the branch pipe consisting of the double pipe and the collecting portion are different, by restricting the flow of the exhaust gas to the welding portion joining the branch pipe and the collecting portion,
An object of the present invention is to provide an exhaust manifold structure capable of preventing cracks due to thermal stress from occurring in a welded portion.

[0006]

According to an exhaust manifold structure for achieving the above object, a branch pipe through which exhaust gas discharged from an engine body flows is composed of a metal double pipe having an inner pipe and an outer pipe. In the exhaust manifold in which the downstream end portion of the branch pipe is inserted into a collecting portion made of a member having a coefficient of thermal expansion different from that of the branch pipe, and the collecting portion and the branch pipe are connected by welding, the inner pipe of the branch pipe is The outer pipe and the outer pipe are relatively movable in the axial direction, the downstream end of the inner pipe is projected more than the outer pipe, and the exhaust gas flows in between the outer peripheral surface of the inner pipe protruding from the outer pipe and the inner wall surface of the collecting portion. A limiting means is provided, and the end face of the assembly portion into which the outer pipe is inserted and the outer peripheral face of the outer pipe are welded all around.

[0007]

In the exhaust manifold structure according to the present invention,
Since the exhaust gas flows through the inner pipe of the branch pipe, the temperature of the inner pipe becomes high and the thermal expansion amount of the inner pipe becomes large. Since the outer tube is located on the outer circumference of the inner tube, the temperature rise is suppressed to a considerably small level and the amount of thermal expansion becomes small as compared with the inner tube. Since the inner tube and the outer tube can move relative to each other in the axial direction, even if the thermal expansion amount of the inner tube is larger than that of the outer tube, the inner tube can escape to the outer tube in the axial direction. It will be possible. Therefore, even if an outer pipe having a small amount of thermal expansion is welded to the collecting portion, a large thermal stress due to thermal expansion over the entire length of the outer pipe does not occur in the welded portion. Further, since the exhaust gas inflow limiting means is provided at the downstream end portion of the inner pipe, the exhaust gas discharged from the downstream end of the inner pipe into the collecting portion enters between the inner pipe and the outer pipe. It is not possible to limit the exhaust gas to the weld side. Therefore, the welded part is not significantly heated by the exhaust gas. Therefore, the difference in thermal expansion between the outer tube and the gathered portion in the welded portion becomes extremely small, and the occurrence of cracks in the welded portion due to thermal stress is prevented.

[0008]

1 and 2 show a first embodiment of the present invention, and FIG. 3 shows a second embodiment of the present invention. First, the configuration and operation common to each embodiment will be described with reference to FIGS. 1 and 2 of the first embodiment. However, the same reference numerals are used for the common components throughout the respective embodiments.

First Embodiment FIGS. 1 and 2 show an exhaust manifold applied to a four-cylinder engine. As shown in FIG. 2, the exhaust manifold 2 is roughly divided into a flange portion 10, a branch pipe 20, and a collecting portion 30. The flange portion 10 is fastened to a cylinder head (not shown). Flange part 10
The four branch pipes 20 that guide the exhaust gas G discharged from each exhaust passage of the cylinder head to the collecting portion 30 are connected to the.

The branch pipe 20 is composed of a double pipe consisting of an inner pipe 22 and an outer pipe 24. Inner tube 22 and outer tube 2
4 is made of stainless steel having heat resistance and corrosion resistance. A holding member 29 extending in the circumferential direction is provided between the inner pipe 22 and the outer pipe 24. Holding member 29
Is composed of a wire mesh ring obtained by pressing wire-shaped stainless steel into a ring shape by press molding. As a result, the inner pipe 22 and the outer pipe 24 are arranged with a predetermined distance. The inner pipe 22 has a floating structure that is relatively movable in the axial direction with respect to the outer pipe 24. The holding member 29 is movable in the axial direction. The wall thickness of the inner pipe 22 is smaller than the wall thickness of the outer pipe 24. This is to reduce the heat capacity of the inner pipe 22 by reducing the wall thickness.

The upstream end portion of the outer pipe 24 is connected to the flange portion 10 by welding. The collecting portion 30 located on the downstream side of the branch pipe 20 is made of cast iron or cast steel as a casting which is a member having a coefficient of thermal expansion different from that of the branch pipe 20. The gathering portion 30 is formed by casting, since the gathering portion 30 gathers the exhaust gas G from each branch pipe 20 into one and has a smoother flow path shape than a structure in which steel plates are joined by welding. This is because the exhaust pressure loss and the radiation noise can be reduced. A plurality of connection holes 32 into which each branch pipe 20 is inserted and a discharge hole 34 into which an exhaust pipe (not shown) is inserted are formed in the collecting portion 30.

The branch pipe 20 is provided in the connection hole 32 of the collecting portion 30.
The downstream end of is inserted. The outer peripheral surface of the downstream end portion of the outer pipe 24 inserted into the connection hole 32 is the end surface 36 of the collecting portion 30.
And a full-circumferential weld 42. The downstream end of the inner pipe 22 projects more than the downstream end of the outer pipe 24. The outer peripheral surface 22a of the inner pipe 22 protruding from the outer pipe 24 and the collecting portion 3
A gasket 40 as an exhaust gas inflow restriction means extending in the circumferential direction is provided between the inner wall surface 32a of the zero connection hole 32 and the inner wall surface 32a. The gasket 40 is composed of, for example, the wire mesh ring described above. Gasket 4
0 indicates that the exhaust gas G discharged into the collecting portion 30 is the inner pipe 22.
It has a function of limiting the flow toward the welded portion 42 side between the outer pipe 24 and the outer pipe 24. The gasket 40 is movable in the axial direction.

A plurality of protrusions 27a, 27b and 27c which bulge outward in the radial direction are formed at the downstream end of the inner pipe 22. The tips of the protrusions 27a, 27b, 27c are not in contact with the inner peripheral surface of the outer tube 24. The gasket 40 includes the protrusion 27a on the most downstream side and the protrusion 2 adjacent to the protrusion 27a.
It is located between 7b. The gasket 40 is prevented from excessive movement in the axial direction by the protrusions 27a and 27b located on both sides. The holding member 29 is also prevented from excessive movement in the axial direction by the projection 27b located upstream of the gasket 40 and the projection 27c located further upstream thereof.

Next, the operation common to each embodiment will be described with reference to FIGS. 1 and 2. Exhaust gas G discharged from the combustion chamber of the engine body (not shown) is discharged to the exhaust manifold 2 via the exhaust passage of the cylinder head (not shown). The exhaust gas G flowing into the exhaust manifold 2 is guided to the collecting portion 30 through the inside of the inner pipe 22 of each branch pipe 20. Therefore, the temperature of the inner pipe 22 increases due to the heat received from the exhaust gas G, and the inner pipe 22 thermally expands particularly in the axial direction. In this case, since the inner pipe 22 is movable in the axial direction with respect to the outer pipe 24, the inner pipe 22 can be released in the axial direction with respect to the outer pipe 24.

Since the inner tube 22 and the outer tube 24 are maintained at a constant interval by the holding member 29, the inner tube 22 and the outer tube 24 are
An air layer A is formed between the inner pipe 22 and the outer pipe 24.
The heat radiation to the is reduced. Therefore, the outer tube 24 is the inner tube 2
Compared with No. 2, the temperature rise is small and the amount of thermal expansion in the axial direction is small. Therefore, even if the outer pipe 24 having a small thermal expansion amount is welded to the flange portion 10 and the collecting portion 30, a large thermal stress due to thermal expansion over the entire length of the outer pipe 24 does not occur in the welded portion 30. Further, since the heat radiation from the inner pipe 22 to the outer pipe 24 is reduced, the decrease in the temperature of the exhaust gas G is suppressed, the activation of the catalyst in the cold state is promoted, and the purification performance of the exhaust gas G is improved. To be enhanced.

A gasket 40 is provided at the downstream end of the inner pipe 22.
Since the inner pipe 22 is provided with the
The exhaust gas G discharged into the exhaust gas 0 cannot enter between the inner pipe 22 and the outer pipe 24, and the exhaust gas G is welded to the welded portion 42.
It is blocked from turning to the side. Therefore, the welded portion 42 is not significantly heated by the exhaust gas G. Therefore, the difference in the amount of thermal expansion between the outer tube 24 and the collecting portion 30 in the welded portion 42 becomes extremely small, and the occurrence of cracks in the welded portion 42 due to thermal stress is prevented.

Second Embodiment FIG. 3 shows a second embodiment of the present invention. In the first embodiment, the configuration and operation common to those in the second embodiment have been described. Therefore, only the configuration and operation unique to the second embodiment will be described here.

As shown in FIG. 3, the inner wall surface 3 of the collecting portion 30.
A heat insulating material 50 is coated on the surface 8. Insulation 50
The heat of the exhaust gas G flowing into the collecting portion 30
It has the function of suppressing a large loss of zero. In the second embodiment configured in this way, the collecting unit 30
Since the inner wall surface 38 of the exhaust gas G is covered with the heat insulating material 50, the amount of heat transfer of the exhaust gas G flowing into the collecting portion 30 to the collecting portion 30 becomes small, and the decrease in the temperature of the exhaust gas G is suppressed.

Therefore, the activation of the catalyst in the cold state can be promoted further than in the first embodiment, and the purification performance of the exhaust gas G can be enhanced. Further, since the amount of heat transferred to the collecting portion 30 is small, it is possible to lower the temperature of the welding portion 42 as compared with the case of the first embodiment. Therefore, the weld 4
2, the difference in the amount of thermal expansion between the outer tube 24 and the collecting portion 30 can be further reduced, and the welded portion 42 caused by the thermal stress can be reduced.
The generation of cracks is reliably prevented. In addition to the above-mentioned embodiment,
As the exhaust gas inflow limiting means, the inner pipe 22 of the branch pipe 20 is used.
A protrusion that contacts the inside of the collecting portion 30 is formed near the tip of the collecting portion 30 side, or a protrusion is provided inside the collecting portion 30 to form a maze with the protrusion on the inner pipe 22 side of the branch pipe 20. Then, the inflow of exhaust gas to the welded portion 42 may be restricted.

[0020]

According to the present invention, the inner pipe and the outer pipe of the branch pipe can be moved relative to each other in the axial direction, the downstream end of the inner pipe is projected more than the outer pipe, and the inner pipe of the outer pipe is projected. Exhaust gas inflow restriction means was provided between the outer peripheral surface and the inner wall surface of the collecting part, and the end surface of the collecting part into which the outer pipe was inserted and the outer peripheral surface of the outer pipe were welded all around, so that the exhaust gas was discharged into the collecting part. Exhaust gas can be restricted from entering between the inner pipe and the outer pipe, and heating of the welded portion by the exhaust gas can be significantly suppressed. Therefore, the difference in thermal expansion between the outer pipe and the gathered portion in the welded portion can be made extremely small, and the occurrence of cracks in the welded portion due to thermal stress can be prevented. As a result, exhaust gas leakage due to the occurrence of cracks in the welded portion can be reliably avoided. Further, since the thermal stress generated in the welded portion can be reduced, it is not necessary to perform elaborate welding for increasing the joint strength, and the welding material cost can be reduced.

[Brief description of drawings]

FIG. 1 is an enlarged sectional view of an essential part of an exhaust manifold structure according to a first embodiment of the present invention.

FIG. 2 is an overall perspective view of the exhaust manifold of FIG.

FIG. 3 is an enlarged cross-sectional view of a main part of an exhaust manifold structure according to a second embodiment of the present invention.

[Explanation of symbols]

 2 Exhaust manifold 20 Branch pipe 22 Inner pipe 24 Outer pipe 30 Collecting part 40 Gasket as exhaust gas inflow limiting means 42 Welding part 50 Insulating material

Claims (1)

[Claims] 1. A branch pipe through which exhaust gas discharged from an engine body flows is composed of a metal double pipe consisting of an inner pipe and an outer pipe, and the downstream end of the branch pipe is thermally expanded with the branch pipe. In an exhaust manifold which is inserted into a collecting part made of members having different ratios, and the collecting part and the branch pipe are connected by welding, the inner pipe and the outer pipe of the branch pipe are relatively movable in the axial direction, and the inner pipe is The downstream end of the outer pipe is projected from the outer pipe, and exhaust gas inflow limiting means is provided between the outer peripheral surface of the inner pipe protruding from the outer pipe and the inner wall surface of the collecting part, and the end face of the collecting part into which the outer pipe is inserted. Exhaust manifold structure characterized in that the outer peripheral surface of the outer pipe is welded all around.