JP2000130963A - Double-pipe heat exchanger - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a double-pipe heat exchanger to prevent the occurrence of a crack due to thermal fatigue of a radiation fan. SOLUTION: An EGR cooler comprises an inner pipe 11 through the inner side of which cooling water flows; an outer pipe 12 surrounding the outer periphery of the inner pipe 11 apart therefrom and partitioning a flow part 13 between the inner pipe 11 and the inner pipe; and radiation fins securely contained in the inner pipe 11. The inner and outer pipes 11 and 12 forms a double piping structure, and the EGR cooler 10 cools cooling water flowing through a cooling section C wherein the outer periphery of the inner pipe 11 and cooling water in the flow passage 13 are brought into contact with each other. In the EGR cooler 10, an end part A on the cooling water inflow side of the radiation fin is positioned outside the cooling section C. Thus, the temperatures of the two ends of the radiation fin 16 and the temperature of the inner pipe 11 corresponding thereto are approximately the same as each other, a thermal stress generated at an outer peripheral part and a brazed part B is relaxed, and a crack due to thermal fatigue of the radiation fin 16 is prevented from occurring.

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.

[0003] As shown in FIGS. 4 and 5, an E is disposed in the exhaust passage (not shown) in the EGR device.
The GR cooler 50 has an inner tube 51 through which EGR gas flows, and an outer peripheral surface of the inner tube 51, the ends of which are fixed to the outer peripheral surface of the inner tube 51. It is configured as a double piping structure with an outer pipe 53 that partitions the flow passage 52. A radiation fin 54 for promoting heat transfer is housed in the inner tube 51, and the outer periphery of the radiation fin 54 is fixed to the inner periphery of the inner tube 51 by brazing.

[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]

However, since the outer periphery of the radiating fin 54 is constrained by the inner tube 51 cooled by the cooling water, the inner periphery of the radiating fin 54 and the flow passage 52 are connected through the inner tube 51. There is a large temperature difference between the outer peripheral portion and the outer peripheral portion that is in contact. In particular, the EG of the radiation fins 54
A very large temperature difference (300 to 500 ° C.) occurs between the central portion and the outer peripheral portion at the R gas inflow side end A. For this reason, a large thermal stress is generated particularly on the outer periphery and the brazing portion B at the EGR gas inflow side end A of the radiation fin. Therefore, a crack K may be generated on the outer periphery of the cooling fin 54 and the brazing portion B due to thermal fatigue.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a double-pipe heat exchanger capable of preventing a heat radiation fin from being cracked due to thermal fatigue. It is in.

[0007]

According to a first aspect of the present invention, a first cylindrical member through which a medium to be cooled is circulated and an outer periphery of the first cylindrical member are separated from each other to surround the first cylindrical member. A second tubular member defining a circulation section between the first tubular member and a heat dissipating member housed and fixed in the first tubular member;
And the second tubular member is configured as a double-pipe structure, and the double-pipe heat exchange cools the medium to be cooled passing through the coolable section where the outer periphery of the first tubular member and the cooling medium in the flow passage contact each other. The gist of the present invention is that at least the inflow side end of the medium to be cooled is located outside the coolable section among the both ends of the heat radiation member. (Operation) Therefore, according to the first aspect of the present invention, when the high-temperature medium to be cooled flows into the double-pipe heat exchanger, the heat radiating member is heated by the medium to be cooled, and the temperature of the heat radiating member rises. The heat of the heat dissipating member is transmitted to the first cylindrical member, and
The temperature of the tubular member also increases. Since the cooling water inflow side end of the heat radiation member is located outside the coolable section of the first cylindrical member, the cooling water inflow side end of the heat radiation member and the corresponding first cylindrical member are It rises to almost the same temperature.

[0008]

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 FIGS. 1-3, the EG of an internal combustion engine
A double-pipe heat exchanger (hereinafter, referred to as an “EGR cooler”) 10 disposed in the middle of an exhaust circulation passage (not shown) in the R apparatus 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.

An outer tube 1 serving as a second cylindrical member is provided on the outer periphery of the inner tube 11 so as to surround the outer periphery of the inner tube 11 at a distance.
2 are arranged. Both ends of the outer tube 12 are gradually reduced in diameter, and are 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. The EGR cooler 10 can cool the EGR gas passing through a coolable range C where the cooling water flowing through the flow passage 13 and the outer peripheral surface of the inner pipe 11 come into contact.

A radiating fin 16 as a radiating member is housed and fixed to the inner tube 11. The radiating fins 16 are formed to have a substantially radial cross section (substantially star-shaped cross section) in the radial direction of the inner tube 11 and have a predetermined length in the tube axis direction of the inner tube 11. It is fixed to the inner peripheral surface.

That is, the radiation fin 16 is formed by bending a single metal plate such as stainless steel (for example, SUS304) having high heat resistance, high corrosion resistance and high thermal conductivity into a wave shape (approximate bellows shape) by pressing or the like. Each mountain part 16a of the one
Is rounded (corrugated cylindrical shape) so as to be in contact with the inner peripheral surface of the inner tube 11, and inserted into the inner tube 11. And
The heat radiation fins 16 are such that the outer surface of each ridge 16a is
1 is fixed to the inner peripheral surface of the inner tube 11 by brazing to the inner peripheral surface.

The length of the radiating fins 16 is set to be longer than the "coolable section C" in which the inner tube 11 can be directly cooled by the cooling water. It is arranged to be located. That is,
The end A of the radiating fin 16 at the highest temperature of the EGR gas inflow is disposed in a section where the outer peripheral surface of the inner tube 11 is in contact with the atmosphere. In a section where the outer peripheral surface of the inner pipe 11 is in contact with the atmosphere, the inner pipe 11 is not cooled by the cooling water, so that the temperature of the inner pipe 11 is substantially the same as the temperature of the EGR gas flowing inside. To rise.

When high-temperature EGR gas flows into the inner tube 11 of the EGR cooler 10 and the EGR gas comes into contact with the radiating fins 16, heat of the high-temperature EGR gas is taken by the radiating fins 16 and 11 is transmitted. Then, the heat transmitted to the inner pipe 11 is transmitted to the cooling water flowing through the flow passage 13 and is discharged. That is, the high-temperature EGR gas flows between the radiation fin 16 and the inner pipe 1 between the EGR gas and the cooling water.
The heat is exchanged through 1 to be cooled.

The inner tube 11 corresponding to the end A of the radiating fin 16 on the EGR gas inflow side is located outside the coolable section C and is not cooled by the cooling water. Therefore, the inner pipe 11
When the high-temperature EGR gas flows into the inside, the temperature of the inner pipe 11 corresponding to this rises with the temperature rise of the end A of the radiation fin 16 on the EGR gas inflow side. Then, the temperature of the end portion A of the radiating fin 16 on the EGR gas inflow side and the corresponding temperature of the inner tube 11 are substantially the same. That is, the temperature between the outer peripheral portion and the central portion of the EGR gas inflow side end A of the radiation fin 16 is made uniform. Therefore, the thermal stress generated in the outer peripheral portion of the radiation fin 16 and the brazing portion B is reduced. That is, cracks due to thermal fatigue of the outer peripheral portion of the heat radiation fin 16 and the brazed portions A and B are prevented.

Therefore, according to the present embodiment, the following effects can be obtained. (1) The length of the radiating fins 16 is set between the cooling water and the inner pipe 1.
1 was set longer than the coolable section C in contact with the outer peripheral surface, and the radiation fins 16 were arranged such that both ends thereof were located outside the coolable section C. Therefore, the radiation fins 16
And the corresponding temperature of the inner tube 11 becomes substantially the same, so that the thermal stress generated in the outer peripheral portion of the radiating fin 16 and the brazing portion B is reduced. Therefore, it is possible to prevent the heat radiation fin 16 from being cracked due to thermal fatigue.

(2) Since the heat radiation fins 16 are merely positioned at both ends outside the coolable section C, the heat radiation fins 16 can be prevented from cracking due to thermal fatigue with a simple structure.

(3) The radiation fins 16 are formed of a metal plate having high heat resistance and high corrosion resistance. Therefore, oxidative corrosion of the radiation fins 16 due to corrosive EGR gas can be suppressed as much as possible, and the product life of the EGR cooler 10 can be improved.

The length of the radiating fins 16 is set to be longer than the coolable section C, and the radiating fins 16 are arranged such that both ends thereof are located outside the coolable range C. For this reason, no matter which side of the EGR cooler 10 allows the cooling water to flow, the radiation fins 16 do not crack due to thermal fatigue.

The above embodiment may be modified as follows. In the present embodiment, the length of the radiation fins 16 is set to be longer than that of the coolable section C, and both ends are disposed outside the coolable section C. However, as shown in FIG. The length of the radiation fin 16 may be arbitrarily changed as long as at least the EGR gas inflow side end A of the radiation fin 16 is located outside the coolable section C. In this case, EG
The R gas outflow side end does not need to be located outside the coolable section C by passing the cooled EGR gas. Even in this case, the inner pipe 11 corresponding to the end A of the EGR gas inflow side where the temperature is the highest in the radiation fin 16 is the same.
And the temperature of the radiation fin 16 becomes substantially the same.
The thermal stress generated at the GR gas inflow side end A is reduced, and the generation of cracks due to thermal fatigue of the radiation fins 16 can be prevented.

In this embodiment, only one radiating fin 16 is arranged in the inner tube 11, but as shown in FIG. 4, the radiating fin 16 is divided into a plurality of They may be spaced apart to have.
In this way, the inner tube 11 and the outer tube 12 can be arbitrarily bent between the radiation fins 16 according to the installation location of the EGR cooler 10.

In the present embodiment, the EGR cooler 10 is used for cooling the EGR gas of the internal combustion engine. However, the EGR cooler 10 may be used for cooling a liquid instead of a gas such as the EGR gas. Even in this case, the same effect as that of the present embodiment can be obtained.

In the present 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 an arbitrary shape such as a square tube or an elliptic tube. Even in this case, the same effect as that of the present embodiment can be obtained.

Next, technical ideas other than the claimed invention which can be understood from the present embodiment will be described below together with their effects. An exhaust gas recirculation apparatus comprising the double-pipe heat exchanger according to claim 1.

The double-pipe heat exchanger according to claim 1, wherein the heat radiating member is formed of a metal plate having high heat resistance, high corrosion resistance and high thermal conductivity. In this way, the heat radiation member can be prevented from being deteriorated by the medium to be cooled, and the product life of the double-pipe heat exchanger can be improved.

The double-pipe heat exchanger according to claim 1, wherein the heat radiating member is divided into a plurality. Even in this case, the same effect as the effect described in claim 1 can be obtained.

[0028] A double-pipe heat exchanger in which the length of the heat radiating member is set to be longer than the coolable section, and the heat radiating members are arranged such that both ends thereof are located outside the coolable range. With this configuration, no crack is generated in the heat dissipating member due to thermal fatigue, regardless of which side of the double-pipe heat exchanger allows the medium to be cooled.

[0029]

According to the first aspect of the present invention, the thermal stress generated at the cooling medium inflow side end of the heat radiating member is reduced, and the generation of cracks due to thermal fatigue of the heat radiating member can be prevented.

[Brief description of the drawings]

FIG. 1 is a front sectional view of an EGR cooler according to an embodiment.

FIG. 2 is a sectional view taken along line 1-1 in FIG. 1;

FIG. 3 is a front sectional view of an EGR cooler according to another embodiment.

FIG. 4 is a front sectional view of an EGR cooler according to another embodiment.

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

FIG. 6 is a sectional view taken along line 2-2 in FIG. 5;

[Explanation of symbols]

10 EGR cooler (double-pipe heat exchanger), 11 inner pipe (first cylindrical member), 12 outer pipe (second cylindrical member), 13 ...
Flow passages, 14: introduction pipe, 15: discharge pipe, 16: radiation fins (radiation members).

Claims (1)

[Claims] 1. A first cylindrical member through which a medium to be cooled is circulated, and an outer periphery of the first cylindrical member is separated from the first cylindrical member, and a cooling medium flow portion is defined between the first cylindrical member and the first cylindrical member. And a heat dissipating member housed and fixed in the first cylinder member, wherein the first and second cylinder members are configured as a double pipe structure, and an outer periphery of the first cylinder member is provided. A double-pipe heat exchanger that cools a medium to be cooled passing through a coolable section in which the cooling medium in the flow path contacts the cooling medium. Is a double-pipe heat exchanger located outside the section where cooling is possible.