JP2000161871A - Double piping type heat exchanger - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve reliability, use life, and cooling efficiency, and reduce parts number, manufacturing processes, and manufacturing cost. SOLUTION: An EGR cooler 10 is constructed as a double piping structure composed of an inner tube 11 and an outer tube 12. A heat radiation fin 11a is formed integrally with the inner tube 11 at an intermediate portion of the inner tube 11. The heat radiation fin 11A is formed radially of the inner tube 11 with a cross section formed substantially radially. More specifically, there is formed a concave portion 11b recessed in a center direction of the inner tube 121 at an equal angular interval from an outer peripheral surface of the inner tube 11 while there is formed a convex portion 11c protruded in a center direction of the inner tube 11 at an equal angular interval from an internal peripheral surface of the inner tube 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a double-pipe heat exchanger for cooling high-temperature exhaust gas extracted from an exhaust system, for example, in an exhaust gas recirculation system for an internal combustion engine.

[0002]

2. Description of the Related Art Conventionally, in order to reduce nitrogen oxides in exhaust gas of an internal combustion engine, a part of the exhaust gas is taken out from an exhaust system (exhaust manifold) and recirculated to an intake system (intake manifold). A recirculation device (hereinafter, referred to as an “EGR device”) is known. The EGR device has a double-pipe heat exchanger (hereinafter, referred to as "EGR gas") for cooling high-temperature exhaust gas (hereinafter, referred to as "EGR gas") taken out of an exhaust system before re-introducing it into an intake system.
"GR cooler". ) Is provided.

[0005] As shown in FIGS. 5 and 6, an E is disposed in the exhaust passage (not shown) in the EGR device.
The GR cooler 50 has an inner pipe 51 through which EGR gas flows, and an outer peripheral surface of the inner pipe 51 which is enclosed and fixed at both ends to an outer peripheral surface of the inner pipe 51. It has a double piping structure with an outer pipe 53 that partitions the annular flow passage 52. As shown in FIG. 6, a radiation fin 54 for promoting heat transfer is housed and fixed in the inner tube 51.

[0004] Cooling water is supplied to the outer pipe 53 through the flow passage 52.
And a discharge pipe 56 for discharging the cooling water in the flow passage 52. Cooling water for cooling the internal combustion engine is introduced into the flow passage 52 through an inlet pipe 55.
The cooling water flows through the flow passage 52, and flows through a discharge pipe 56 to a cooling water circulation circuit (not shown) of the internal combustion engine.
Is returned to. Heat exchange is performed between the high-temperature EGR gas and the cooling water via the inner pipe 51. As a result, EGR
The gas is cooled and reintroduced into the intake system of the internal combustion engine.

[0005]

By the way, high-temperature EG
When the R gas hits the radiation fins 54, the radiation fins 54
Causes thermal expansion. At this time, since the outer periphery of the radiation fin 54 is constrained by the inner tube 51 cooled by the cooling water, there is a gap between the central portion of the radiation fin 54 and the outer peripheral portion in contact with the flow passage 52 via the inner tube 51. Large temperature differences occur. Therefore, a large thermal stress is generated in the radiation fins 54. Due to this large thermal stress, the heat radiation fins 54 are creeped (heated) and deformed.
There is a possibility that a crack due to thermal fatigue may be generated on the outer periphery and the brazing portion of 4.

Further, the radiation fins 54 are formed by creep deformation.
A gap is formed between the heat radiation fin 54 and the inner tube 51, and the noise of the heat radiation fin 54 due to rattling in the inner tube 51 is generated. In addition, when the brazing portion is corroded,
There is a possibility that the inner tube 51 may be separated from the inner peripheral surface and fall off.

[0007] These are problems in improving the reliability and service life of the double-pipe heat exchanger. The high-temperature EGR gas is cooled by heat exchange between the EGR gas and the cooling water via the radiation fins 54 and the inner pipe 51. That is, the heat of the high-temperature EGR gas is first taken by the radiating fins 54 and is transmitted from the radiating fins 54 to the inner tube 51. Then, the heat transmitted to the inner pipe 51 is transmitted to the cooling water flowing through the flow passage 52 and is discharged. Therefore, no matter how much the shape of the radiation fin 54 (that is, the shape that can effectively exchange heat with the EGR gas),
There is a problem that the improvement of the cooling efficiency is limited by the presence of the inner tube 51.

In the EGR cooler 50, after the inner pipe 51 and the outer pipe 53 have a double pipe structure, a radiation fin 54 previously formed in a radial cross section is inserted into the inner pipe 51, and the radiation fin 54 is It has been fixed in the inner tube 11 by brazing, which has many reliability and quality control items. Therefore, there is a problem that the number of parts and the number of manufacturing steps increase, and the manufacturing cost increases.

The present invention has been made to solve the above problems, and an object of the present invention is to improve reliability, service life, and cooling efficiency, and to reduce the number of parts, the number of manufacturing steps, and the manufacturing cost. To provide a double-pipe heat exchanger that can perform the heat treatment.

[0010]

According to a first aspect of the present invention, a first cylindrical member through which a medium to be cooled flows is separated from an outer periphery of the first cylindrical member. And a second pipe member that surrounds and surrounds the first pipe member to define a flow path for the cooling medium between the first pipe member and the second pipe member. The gist is that the heat radiating part is integrally formed.

According to a second aspect of the present invention, in the double-pipe heat exchanger according to the first aspect, the heat radiating portion is a concavo-convex portion formed to have a substantially radial cross section in a radial direction of the first cylindrical member. The gist is that there is.

According to the first aspect of the present invention, when the medium to be cooled hits the heat radiating portion, the heat radiating portion can be freely thermally expanded without being restricted by other members. That is, a large thermal stress is hardly generated in the heat radiating portion, and it is possible to prevent a crack from being generated due to the thermal stress or thermal fatigue. In addition, as compared with the related art, it is possible to completely eliminate problems such as rattling of the heat radiating portion, generation of abnormal noise, and falling off due to creep deformation. Furthermore, compared with the prior art, another member for the heat radiating portion is not required, and it is not necessary to manufacture the heat radiating portion by another member alone, and the heat radiating portion of another member is welded or soldered to the first cylindrical member. There is no need to attach. As a result, the reliability and service life of the double-pipe heat exchanger can be improved, and the number of parts, the number of manufacturing steps, and the manufacturing cost can be reduced.

According to the second aspect of the present invention, the first aspect is provided.
In addition to the effect of the invention described in (1), the contact area between the heat radiating portion and the cooling medium or the medium to be cooled, that is, the heat transfer area between the cooling medium and the medium to be cooled is increased. In addition, the heat of the medium to be cooled is taken by the convex portion of the heat radiating portion, and is directly transmitted to the cooling medium flowing in the concave portion of the heat radiating portion to be discharged. As a result, the cooling efficiency of the double-pipe heat exchanger can be improved.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is embodied in an exhaust gas recirculation device for an internal combustion engine (hereinafter, referred to as an "EGR device") will be described with reference to the drawings.

As shown in FIG. 1 and FIG.
A double-pipe heat exchanger (hereinafter, referred to as an “EGR cooler”) 10 provided in the middle of an exhaust circulation passage (not shown) in the GR device has a cooling medium taken out from the exhaust system of the internal combustion engine inside. Pipe 1 as a first cylindrical member through which high-temperature exhaust gas (hereinafter, referred to as “EGR gas”) flows
1 is provided.

The inner tube 11 is made of a material having high heat resistance and corrosion resistance, for example, a stainless steel material, and has an outer periphery formed as a second cylindrical member so as to surround the outer periphery of the inner tube 11 at a distance. A tube 12 is arranged. The outer tube 12
Are gradually reduced in diameter and fixed to the outer peripheral surface of the inner tube 11 by welding or the like. A flow passage 13 is formed between the outer peripheral surface of the inner tube 11 and the inner peripheral surface of the outer tube 12 for flowing cooling water as a cooling medium having an annular cross section. That is, the EGR cooler 10 is configured as a double pipe structure of the inner pipe 11 and the outer pipe 12.

The outer pipe 12 is provided with an introduction pipe 14 for introducing cooling water into the flow path 13 and a discharge pipe 15 for discharging cooling water in the flow path 13. Cooling water for cooling the internal combustion engine is supplied to the flow passage 13 through an introduction pipe 14, and the cooling water flows through the flow passage 13, and then flows through a discharge pipe 15 to a cooling water circulation circuit (not shown in the drawing) of the internal combustion engine. )
Is returned to. Therefore, the EGR cooler 10 can cool the EGR gas passing through the coolable section C where the cooling water flowing through the flow passage 13 and the outer peripheral surface of the inner pipe 11 are in contact.

A radiating fin 11a as a heat radiating portion is formed integrally with the inner tube 11 at an intermediate portion of the inner tube 11 as a flow passage forming portion. The radiating fins 11a are shown in FIG.
As shown in FIG. 3, the inner tube 11 is formed to have a substantially radial cross section (substantially star-shaped cross section) in the radial direction, and has a predetermined length in the tube axis direction of the inner tube 11 (in the present embodiment, both ends are formed). (The length located in the coolable section C).
At this time, the inner pipe 11 is spaced at equal angular intervals from the outer peripheral surface of the inner pipe 11.
Is formed in the center direction of the inner tube 11, while a concave portion 11b protruding toward the center direction of the inner tube 11 is formed at equal angular intervals from the inner peripheral surface of the inner tube 11. Has become.

As a method for manufacturing the inner tube 11 including the radiation fins 11a, for example, there is a method using hydraulic pressure (hydroforming). That is, a method in which a heat transfer fin 11a is transcribed is made, and the round tube is inflated by applying water pressure to conform to the mold.

It should be noted that it may be manufactured by a plastic working method called flow forming for working gears of a hub. Further, the round tube may be manufactured by a forming method of drawing out the roll tube with a roll or a die.

At this time, since the circumference of the radiation fin 11a is longer than the circumference of the original tube of the inner tube 11, the radiation fin 11a
The thickness t1 of the portion a is thinner than the original tube thickness t2 of the inner tube 11. In addition, the original pipe wall thickness t2 of the inner pipe 11 is set to a minimum thickness at which the outer pipe 12 can be fixed to the outer peripheral surface of the inner pipe 11 by welding or brazing.

Now, high-temperature EGR gas flows into the inner pipe 11 of the EGR cooler 10, and as shown in FIG.
When the GR gas comes into contact with the projection 11c of the radiation fin 11a, the heat of the high-temperature EGR gas is transferred to the projection 1c of the radiation fin 11a.
1c and is transmitted to the concave portion 11b of the radiation fin 11a. The heat transmitted to the recess 11b is
The heat is transmitted to the cooling water flowing in the inside 1b and discharged. That is,
The high-temperature EGR gas is cooled by heat exchange between the EGR gas and the cooling water via the radiation fins 11a of the inner pipe 11.

Accordingly, the double-pipe heat exchanger (EGR cooler) 10 of the present embodiment has the following features. (1) In the present embodiment, a radiation fin 11 a is formed integrally with the inner tube 11 at an intermediate portion of the inner tube 11. Therefore,
When the high-temperature EGR gas hits the radiating fins 11a, the radiating fins 11a can be thermally expanded freely without being restrained by other members as compared with the related art. In other words, the heat radiation fins 11a are less likely to generate large thermal stress therein, and can prevent the occurrence of cracks due to thermal stress or thermal fatigue.

Further, as compared with the prior art, it is possible to completely eliminate problems such as rattling of the radiating fins 11a due to creep deformation, generation of unusual noise, and falling off. As a result, the reliability and the service life of the double-pipe heat exchanger 10 can be improved.

(2) In the present embodiment, a radiation fin 11a is formed integrally with the inner tube 11 at an intermediate portion of the inner tube 11. The radiation fins 11a are formed in a substantially radial cross section (substantially star-shaped cross section) in the radial direction of the inner tube 11. At this time, a concave portion 11b is formed to be recessed from the outer peripheral surface of the inner pipe 11 at an equal angular interval in the center direction of the inner pipe 11, while the central direction of the inner pipe 11 is formed at an equal angular interval from the inner peripheral surface of the inner pipe 11. A protruding portion 11c is formed. That is, the radiation fin 11a
Contact area between the cooling water and EGR gas, that is, cooling water and EGR gas
The heat transfer area with the GR gas is increased.

Therefore, the heat of the high-temperature EGR gas is taken away by the projections 11c of the radiation fins 11a and directly
The heat is transmitted to the cooling water flowing in the concave portion 11b of FIG. As a result, the cooling efficiency of the double-pipe heat exchanger 10 can be improved.

(3) In the present embodiment, a radiation fin 11a is formed integrally with the inner tube 11 by plastic working at an intermediate portion of the inner tube 11. Therefore, another member for the radiation fins 11a is not required as compared with the related art. In addition, there is no need to manufacture the radiation fins 11a independently, and it is not necessary to weld or braze the radiation fins 11a to the inner tube 11.

As a result, the number of parts, the number of manufacturing steps, and the manufacturing cost of the double-pipe heat exchanger 10 can be reduced. (4) In the present embodiment, since the circumference of the radiating fin 11 a is longer than the circumference of the inner tube 11, the radiating fin 11 a
The thickness t1 of the portion a is thinner than the original tube thickness t2 of the inner tube 11. Therefore, the heat transfer distance in the radiation fin 11a is shortened, that is, the efficiency of heat exchange by the radiation fin 11a is improved.

As a result, the cooling efficiency of the double-pipe heat exchanger 10 can be improved. The above embodiment may be modified as follows. In the above embodiment, the radiation fins 11a are formed to have a substantially radial cross section (substantially star shape) in the radial direction of the inner tube 11, but the radiation fins 11a have a substantially radial cross section (substantially star shape). However, the present invention is not limited to this, and may be implemented, for example, by forming a cross section in a substantially gourd shape. In this case, substantially the same effects as in the above embodiment can be obtained.

In the above embodiment, the radiation fins 1
When formed in the radial direction of the inner tube 11 and having a substantially radial cross section (substantially star-shaped cross section), the concave portion 11b is recessed at an equal angular interval from the outer peripheral surface of the inner tube 11 toward the center of the inner tube 11. On the other hand, the projections (or peaks) 11c protruding from the inner peripheral surface of the inner pipe 11 at equal angular intervals in the center direction of the inner pipe 11 were formed. However, the recesses 11b or the projections 11c were formed. You may implement so that it may be formed in a non-equiangular interval. In this case, substantially the same effects as in the above embodiment can be obtained.

In the above embodiment, the inner tube 11 is made of a stainless steel material. However, the material is not limited to the stainless steel material. You may implement with an alloy etc. In this case, substantially the same effects as in the above embodiment can be obtained.

In the above embodiment, the double-pipe heat exchanger 10 is used for cooling the EGR gas of the internal combustion engine, but is used for cooling not the gas such as the EGR gas but the liquid. You may. Even in this case, the same effect as in the above embodiment can be obtained.

In the above embodiment, the EGR cooler 10 is constituted by the cylindrical inner pipe 11 and the outer pipe 12.
For example, the inner tube 11 and the outer tube 12 may have a rectangular or elliptical cylindrical shape. Even in this case, the same effect as in the above embodiment can be obtained.

[0034]

According to the first aspect of the present invention, the reliability and service life of the double-pipe heat exchanger are improved,
The number of parts, the number of manufacturing steps, and the manufacturing cost can be reduced.

According to the invention described in claim 2, according to claim 1
In addition to the effects of the invention described in (1), the cooling efficiency of the double-pipe heat exchanger can be improved.

[Brief description of the drawings]

FIG. 1 is a front sectional view of an EGR cooler according to the present invention.

FIG. 2 is a perspective view of an inner tube of the EGR cooler.

FIG. 3 is a sectional view taken along line AA in FIG. 1;

FIG. 4 is a sectional view taken along line BB in FIG. 1;

FIG. 5 is a front sectional view of a conventional EGR cooler.

FIG. 6 is a sectional view taken along line DD in FIG. 5;

[Explanation of symbols]

10 EGR cooler (double-pipe heat exchanger), 11 Inner tube as first cylindrical member, 11a Radiating fins as radiator, 11b concave portion, 11c convex portion, 12 as second cylindrical member Outer tube, 13 ... flow passage.

Claims (2)

[Claims] 1. A first cylindrical member through which a medium to be cooled flows, and a flow path for a cooling medium defined between the first cylindrical member and the first cylindrical member. A double-pipe heat exchanger, comprising: a heat transfer section integrally formed with a flow passage forming portion of the first pipe member. . 2. The double-pipe heat exchanger according to claim 1, wherein the heat radiating portion is a concavo-convex portion formed to have a substantially radial cross section in a radial direction of the first cylindrical member. Heavy piping type heat exchanger.