JP2000220534A - Egr gas cooling device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve fatigue failure resistance strength by arranging stress releasing means on a brazing part of at least an EGR gas flow-in side in brazing parts of a tube sheet and each heat transferring pipe, in the case where heat transferring pipe group is fixed to the tube sheets fixed in the vicinity of both end parts of an inner wall of a barrel pipe by means of brazing. SOLUTION: In a plurality of heat transferring pipes 20 in a multiple pipe type EGR gas cooling device, those both end parts are fixed to tube sheets 3 disposed in the vicinity of both end parts of an inner wall of a barrel pipe by means of brazing. In this case, a pipe enlarging part 20-1 is formed along a part positioned outward of an axial direction from a tip end part of a brazing material filet 5-1 in association with brazing 5 carried out after from a pipe end. A taper part 20-3 is formed along a primary pipe part 20-2 from the pipe enlarging part 20-1. The pipe enlarging part 20-1 and the taper part 20-3 are formed, and thereby, the maximum value tensile stress value on a surface of the heat transferring pipe 20 is reduced, a generating position of the maximum tensile stress value is shifted outward from a thin wall part of a brazing material filet 5-1 so as to improve fatigue failure resistance strength.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for cooling an EGR gas with a cooling liquid for an engine or a dedicated cooling water in a cooled EGR system.

[0002]

2. Description of the Related Art A part of exhaust gas is taken out of an exhaust system,
To return to the intake system of the engine and add it to the mixture,
EGR (Exhaust Gas Recircula)
Tion: exhaust gas recirculation). EGR is NOx
(Nitrogen oxides) generation, pump loss reduction, heat radiation loss to the cooling fluid due to lowering of combustion gas temperature, increase in specific heat ratio due to changes in working gas amount and composition, and reduction in cycle efficiency Since many effects such as improvement can be obtained, it is an effective method for improving the thermal efficiency of the engine while purifying the exhaust gas.

[0003] However, when the temperature of the EGR gas increases and the amount of the EGR gas increases, the heat effect of the EGR gas causes the EGR gas to increase.
It has been recognized that the durability of the valve may deteriorate, leading to premature breakage, the need for a water-cooled structure to prevent this, and the reduction in fuel efficiency due to the decrease in charging efficiency due to the rise in intake air temperature. I have. To avoid this,
2. Description of the Related Art A cooled EGR system that cools EGR gas with a coolant of an engine or the like is used. As a cooling device for the cooled EGR system, a multi-tube heat exchanger made of austenitic stainless steel is generally used.

As a multi-tube heat exchanger used in this case, as shown in FIG. 10, a cylinder having a cooling medium inlet 1-1 and a cooling medium outlet 1-2 at both ends is provided. Inside the tube 1, both ends of the heat transfer tube group 2 are fixed to a sheet metal tube sheet 3 by brazing, while the tube sheet 3 is arranged with its outer peripheral end fixed to the inner wall of the body tube 1 by brazing. , One end of the body tube 1 has E
An end cap 4 provided with a GR gas inlet 4-1 is fixed, and an EGR gas outlet 4 is provided at the other end.
The end cap 4 provided with 2 is fixed.

[0005]

In the above-described multi-tube heat exchanger, both ends of the tube sheet 3 and the heat transfer tube group 2 are fixed by brazing. When the crack grows and reaches the surface of the heat transfer tube, tensile stress concentrates on this portion, thereby causing a phenomenon in which circumferential fatigue fracture occurs in the heat transfer tube.

The inventor of the present invention has conducted various experiments on the circumferential fatigue fracture phenomenon and found that it is based on the following causes. That is, generally, the tube sheet is made of SUS 304 or SUSU 3 having a thickness of 1 to 3 mm.
16, while the heat transfer tube has an outer diameter of 4.5 to 8.0 mm,
SUS 304 or SU with a thickness of 0.3-0.7mm
SU 316 having a tensile strength of about 60
kgf / mm ² , and the fatigue strength is about 30 kgf / mm ² . On the other hand, a Ni-based brazing material is generally used as the brazing material, and the tensile strength of the brazing material is about 20 kgf / mm ^2.
And fatigue strength of about 10 kgf / mm ² .

As a result of performing a vibration test on an EGR gas cooling device made of such a material, as shown in FIG.
It was found that it existed within the width 1 of the thin portion 1. That is, since the tube sheet 3 is rigid and does not move in the vibration direction, a surface tensile stress is generated in the heat transfer tube 2 from the end face of the tube sheet 3. By applying the vibration in this manner, a maximum tensile stress point appears on the surface of the heat transfer tube 2 on the tube sheet 3 side slightly from the tip end of the brazing material fillet 5-1, and the brazing material fillet 5-having a lower fatigue limit than the heat transfer tube 2. In FIG. 1, first, a crack c is generated, and then the crack c grows and reaches the surface of the heat transfer tube 2 by a notch effect.

[0008] This means that in the engine test conducted by the present inventor, the locations where the heat transfer tubes were fatigued and broken were all thin-walled portions of the brazing filler material slightly spaced from the tube sheet side portions. This fatigue fracture phenomenon was particularly remarkable in the brazing filler metal at the brazing portion on the EGR gas inflow side where the allowable stress was reduced.

An object of the present invention is to provide an EGR gas cooling device which has excellent durability reliability even under a vibration state of an engine or the like and can exhibit excellent fatigue fracture resistance.

[0010]

In order to solve the above-mentioned problems, an EGR gas cooling apparatus according to the present invention is provided near both ends of an inner wall of a body tube provided with a cooling medium inlet and a cooling medium outlet at both ends. A heat transfer tube group is fixedly arranged on the fixed tube sheet by brazing, and E
In a multi-tube type EGR gas cooling device having a structure in which an inlet and an outlet for the GR gas are provided, stress is applied to at least a brazing portion on the EGR gas inflow side of a brazing portion between the tube sheet and each heat transfer tube. A relief means is provided, and the stress relaxation means positions a maximum tensile stress point on an outer surface of the heat transfer tube in an axial direction outward from the brazing filler material portion. Things.

In the present invention, the stress relaxation means comprises an expanded portion and a tapered portion, a vertical rising portion and a tapered portion, or a thick portion formed near the end of the heat transfer tube. Is provided on at least one of the outer peripheral side and the inner peripheral side of the heat transfer tube, or the stress relaxation means is constituted by a sleeve externally or internally fitted near an end of the heat transfer tube, and the sleeve is provided on a free end side. And a slit portion on the free end side.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the accompanying drawings. FIG. 1 shows a first embodiment according to the first embodiment of the present invention.
FIG. 2 is a half sectional view showing a second embodiment according to the first embodiment of the present invention, and FIG.
FIG. 4 is a half sectional view showing a fourth embodiment according to the first embodiment of the present invention. FIG. 4 is a half sectional view showing a fourth embodiment according to the first embodiment of the present invention. FIG. 3A is a diagram showing a first example according to a second embodiment of the present invention, and FIG.
6A is a half sectional view, FIG. 6B is a perspective view, FIG. 6 is a view showing a second embodiment according to the second embodiment of the present invention, FIG. 6A is a half sectional view, FIG. 7A and 7B are views showing a third embodiment according to the second embodiment of the present invention, wherein FIG. 7A is a half sectional view, FIG. 7B is a perspective view, and FIG. FIG. 8A is a view showing the fourth embodiment, in which FIG.
(B) is a perspective view, FIG. 9 is a graph showing the surface stress distribution of the example of the present invention and the comparative example, 3 is a tube sheet,
20, 30, 40, 50, 60 are heat transfer tubes, 21, 31,
41 and 51 are sleeves.

First, the multi-tube EGR of the present invention shown in FIG.
In the case of a gas cooling device, an expanded portion 20-1 is formed from a pipe end to a portion located axially outward from a tip end portion of a brazing material fillet accompanying brazing performed later, and the expanded portion is formed. The two ends of the heat transfer tube 20 having the tapered portion 20-3 over the original tube portion 20-2 are connected to the tube sheet 3 made of sheet metal.
Is inserted into the mounting hole 3-1 drilled and brazed. In this case, the brazing material fillet 5-1 of the brazing part 5 is located at the expanded part 20-1.

The material of the heat transfer tube used in the present invention includes SUS304, SUS304L, SUS316, S
Austenitic stainless steel such as US316L and SUS321 is used, and the outer diameter is 6.35 mm or 5.
Although the length is usually about 120 mm to about 600 mm, the length is not particularly limited, and the body tube and tube sheet are made of the same material as described above. And E of such material
As a brazing material used for fixing the heat transfer tube 20 and the tube sheet 3 in the GR gas cooling device, for example, a Ni-based brazing material composed of Cr 7% by weight, B 3% by weight, Si 4% by weight, Fe 3% by weight, and the balance Ni is generally used. It is important to note that Japanese Patent Application Nos. 11-18364 and 11
The brazing material disclosed in No. -18465 is preferable because of having excellent sulfuric acid corrosion resistance.

As described above, in the embodiment shown in FIG.
By forming the expanded portion 20-1 and the tapered portion 20-3 near the end of the tube, the maximum tensile stress value on the surface of the heat transfer tube 20 is reduced, and the position where the maximum tensile stress value on the surface of the heat transfer tube 20 is generated Can be removed from the thin portion of the brazing material fillet 5-1 of the brazing portion 5, thereby obtaining an EGR gas cooling device having excellent fatigue fracture resistance even when used under a vibrating state. It has become possible.

Although the present invention is preferably applied to both brazed portions of both ends of the heat transfer tube and both tube sheets,
Since this fatigue fracture phenomenon is particularly remarkable in the brazing material fillet of the brazing portion on the EGR gas inflow side where the allowable stress is low, it is important to apply the method to at least the brazing portion on the EGR gas inflow side.

Next, the multi-tube EGR of the present invention shown in FIG.
In the case of a gas cooling device, a heat transfer tube 30 having a bulge portion 30-3 formed of a vertical rising portion 30-1 and a tapered portion 30-2 formed at an interval corresponding to the thickness of the tube sheet 3 from the pipe end. Are inserted into the mounting holes 3-1 formed in the sheet metal tube sheet 3 and brazed. Also in this case, the brazing material fillet 5-1 of the brazing portion 5 is located at the top of the bulge portion 30-3, so that the maximum tensile stress value on the surface of the heat transfer tube 30 is reduced, and The position where the maximum tensile stress value is generated on the surface can be removed outward from the thin-walled portion of the brazing filler material 5-1 of the brazing portion 5, thereby providing excellent fatigue fracture strength even when used under vibration. It has become possible to obtain an EGR gas cooling device having the above.

In the case of the multi-pipe type EGR gas cooling apparatus of the present invention shown in FIG. 3, the portion extending from the pipe end to the portion located axially outward from the brazing filler metal for brazing performed later is used. It inserts and brazes both ends of the heat transfer tube 40 having the thick wall portion 40-1 formed on the inner peripheral surface side into a mounting hole 3-1 formed in the tube sheet 3 made of sheet metal. Also in this case, the brazing material fillet 5-1 of the brazing portion 5
Is located in the thick portion 40-1, so that the maximum tensile stress value on the surface of the heat transfer tube 40 is reduced and the heat transfer tube 4
The position where the maximum tensile stress value occurs on the surface of No. 0 can be removed from the thin-walled portion of the brazing material fillet 5-1 of the brazing portion 5, and as a result, excellent fatigue fracture resistance even when used under vibration. It has become possible to obtain a strong EGR gas cooling device. In FIG. 3, reference numeral 40-2 denotes the thick portion 40.
-1 and a tapered wall formed between the original pipe portion 40-3.

Further, the multi-tube EGR of the present invention shown in FIG.
In the case of a gas cooling device, a heat transfer tube in which a thick portion 50-1 is formed on the outer peripheral surface side from a pipe end to a portion located in an axial direction outward from a brazing material fillet accompanying brazing performed later. 50 are inserted into the mounting holes 3-1 formed in the sheet metal tube sheet 3 and brazed. Also in this case, the brazing material fillet 5 of the brazing portion 5 is also used.
-1 is located in the thick portion 50-1, and the heat transfer tube 5
As a result, it was possible to obtain an EGR gas cooling device having excellent fatigue fracture resistance even when used in a vibrating state.

In FIG. 4, reference numeral 50-2 denotes a tapered wall formed between the thick portion 50-1 and the original tube portion 50-3.

As described above, FIGS. 3 and 4 show an embodiment in which the thick portion is provided on either the inner peripheral surface or the outer peripheral surface of the heat transfer tubes 40 and 50. However, the thick portion is provided inside the heat transfer tube. It goes without saying that it may be formed on both the peripheral surface and the outer peripheral surface.

In the above embodiment, the heat transfer tube is formed with an expanded portion and a tapered portion, a vertical rising portion and a tapered portion, or a thick portion near the end of the heat transfer tube, which are used as stress relaxation means. The present invention is not limited to such an embodiment, and the heat transfer tube is not subjected to any processing and a sleeve such as SUS 304, SUS 316, or the like, or a cross-section is substantially provided near the end of the heat transfer tube. It is also possible to form a stress relief unit by fitting a sleeve with a slit provided with a minute slit over the entire length in the axial direction so as to form a C-shape. Such an embodiment is described below with reference to FIGS.

First, in the case of the multi-tube type EGR gas cooling apparatus of the present invention shown in FIG. 5, both ends of the heat transfer tube 60 are inserted into mounting holes 3-1 formed in the sheet metal tube sheet 3. In addition, the cylindrical sleeve 21 is positioned so that one end surface 21-1 thereof is in contact with the side surface of the tube sheet 3, and the whole is brazed. In this case, the sleeve 21
Is set so that its free end face 21-2 is positioned axially outward from the side surface of the tube sheet 3 with respect to the brazing filler material for the brazing performed later, whereby the heat transfer tube 60 is formed. The maximum tensile stress value of the surface of the heat transfer tube 60 can be reduced, and the position where the maximum tensile stress value of the surface of the heat transfer tube 60 is generated can be removed outside the thin portion of the brazing filler material 5-1 of the brazing portion 5. Accordingly, it has become possible to obtain an EGR gas cooling device having excellent fatigue fracture resistance even when used under a vibration state. In order to disperse the tensile stress more effectively, the free end face 31-2 of the cylindrical sleeve 31 is tapered as shown in FIG.
It is preferable to form it.

In the case of the multi-tube type EGR gas cooling apparatus of the present invention shown in FIG. 7, both ends of the heat transfer tube 60 are inserted into mounting holes 3-1 formed in the tube sheet 3 made of sheet metal. A cylindrical sleeve 41 having a plurality of slits 41-3 extending in the axial direction so as to open toward the free end surface 41-2 is positioned such that one end surface 41-1 abuts against the side surface of the tube sheet 3. At the very least, the whole is brazed. In this case, the length of the sleeve 41 is set such that its free end face 41-2 is located axially outward from the side surface of the tube sheet 3 with respect to the brazing filleret 5-1 associated with brazing performed later. By setting the length, the maximum tensile stress value on the surface of the heat transfer tube 60 is reduced, and
The position of the maximum tensile stress value on the surface of the brazing material 5 can be removed outward from the thin portion of the brazing filler material 5-1 of the brazing part 5, and the surface tensile stress acting on the heat transfer tube 60 is reduced by the slit 41-3. EGR that has excellent fatigue fracture resistance even when used under vibration conditions
It has become possible to obtain a gas cooling device.

FIG. 8 shows a multi-tube EGR according to the present invention.
In the case of the gas cooling device, both ends of the heat transfer tube 60 are inserted into the mounting holes 3-1 formed in the sheet metal tube sheet 3;
And a frusto-conical sleeve 51 with its bottom end face 51-1
Is positioned so as to contact the side surface of the tube sheet 3 and brazing is performed as a whole. Also in this case, the length of the sleeve 51 is set such that the top free end surface 51-2 is positioned axially outward from the brazing filleret 5-1 accompanying the brazing performed later from the side surface of the tube sheet 3. By setting the maximum length, the maximum tensile stress value on the surface of the heat transfer tube 60 is reduced, and the position where the maximum tensile stress value on the surface of the heat transfer tube 60 is generated is determined by the brazing material fillet 5-1 of the brazing portion 5.
EGR with excellent fatigue fracture resistance even when used under vibration conditions
It has become possible to obtain a gas cooling device. In FIGS. 5 to 8, reference numeral 6 denotes a brazing portion between the free end face of each sleeve and the heat transfer tube 60, and the brazing portion 6 is a brazing portion because the sleeve follows the movement of the heat transfer tube 60. Unlike No. 5, it is hardly affected by surface tensile stress.

In the embodiments shown in FIGS. 5 to 8, the sleeves 21, 31, 41 and 51 are externally fitted to the outer peripheral surface of the heat transfer tube 60, but the inner peripheral surface near the end of the heat transfer tube is shown. It goes without saying that the same function and effect as described above can be exerted even if these sleeves are internally fitted and brazed.

[0027]

Next, examples of the present invention will be described together with comparative examples. [Example 1] A mounting hole 3-1 having an inner diameter of 7.0 mm was formed in a SUS 304 tube sheet 3 having a thickness of 1.5 mm. On the other hand, SUS 304 having an outer diameter of 6.35 mm and a wall thickness of 0.4 mm is used so that the original tube portion 20-2 has the structure shown in FIG.
The heat transfer tube 20 is formed with an expanded tube portion 20-1 having a length of 6.5 mm and an outer diameter of 7.0 mm from the end of the tube, and a tapered portion 20-3 having a width of 2.0 mm. did.

The expanded portion 20-1 of the heat transfer tube 20 having the above-described configuration is inserted into the mounting hole 3-1 of the tube sheet 3 to insert 7% by weight of Cr, 3% by weight of B, 4% by weight of Si, and 3% by weight of Fe3.
The brazing was carried out with a Ni-based brazing filler metal consisting of wt% and the balance being Ni. As a result, the heat transfer tubes 2
0 mm in the axial direction of the brazing filler material 5-
1 was formed.

The free end of the sample tube obtained in this manner was multiplied by 100 G, and the distribution of the tensile stress value on the surface of the heat transfer tube at that moment was analyzed by the finite element method (FEM). It is shown in FIG.

[Embodiment 2] The same materials as in Embodiment 1 above,
Mounting hole 3 with inner diameter 6.35 mm in tube sheet 3 of dimensions
-1 was drilled. On the other hand, a heat transfer tube 30 made of SUS 304 having an outer diameter of 6.35 mm and a thickness of 0.4 mm having an outer diameter of 7.35 mm at a position 1.5 mm from the end of the tube so as to have the structure shown in FIG.
Bulge part 30-3 having a width of 5 mm and a width of 5 mm
A brazing material similar to that of the first embodiment is formed by inserting an end into the mounting hole 3-1 and bringing the vertical rising portion 30-1 of the bulge portion 30-3 into contact with the side surface of the tube sheet 3. Brazed by As a result, the tube sheet 3
, A brazing filler material 5-1 was formed in the axial direction of the heat transfer tube 30 over 0.5 mm. The free end of the sample tube obtained in this way was multiplied by 100 G, and the distribution of the tensile stress value on the surface of the heat transfer tube at that moment was analyzed by FEM.
FIG. 9 shows the analysis result.

[Embodiment 3] The same materials as in Embodiment 2 above,
As shown in FIG. 3, the mounting holes 3-1 of the tube sheet 3 in which the mounting holes 3-1 having the same size and the same inner diameter are formed have the same material and outer diameter as those of the second embodiment, and 6.5 from pipe end
0.7 mm thick so that the inner peripheral surface side is thick
Thick portion 40-1 and tapered surface 40-3 over 2 mm
Then, the end portion of the heat transfer tube 40 having the following was inserted and brazed with the same brazing material as in Example 1. As a result, a brazing filler material 5-1 was formed from the side surface of the tube sheet 3 in the axial direction of the heat transfer tube 40 by 0.5 mm. 100G is applied to the free end of the sample tube thus obtained, and the distribution of the tensile stress value on the surface of the heat transfer tube at that moment is analyzed by FEM. The analysis result is shown in FIG.

[Embodiment 4] The same materials as in Embodiment 1 above,
The mounting hole 3-1 of the tube sheet 3 having the dimensions and the same inner diameter as the inner diameter has the same material as that of the first embodiment and the outer diameter of the original pipe portion 50-3. Further, as shown in FIG. 4, a transmission having a thick portion 50-1 having a thickness of 0.7 mm and a tapered surface 50-2 having a thickness of 2 mm so that the outer peripheral surface is thicker over 6.5 mm from the pipe end. The end of the heat tube 50 was inserted and brazed with the same brazing material as in Example 1.
As a result, the brazing filler material 5-1 was formed from the side surface of the tube sheet 3 to 0.5 mm in the axial direction of the heat transfer tube 50. 100G is applied to the free end of the sample tube thus obtained, and the distribution of the tensile stress value on the surface of the heat transfer tube at that moment is analyzed by FEM. The analysis result is shown in FIG.

Comparative Example A tube sheet having the same material and dimensions as those of the second embodiment and having the same inner diameter as that of the second embodiment is provided with the same material and outer diameter as those of the second embodiment. And
The end of the heat transfer tube having a uniform thickness was inserted and brazed with the same brazing material as in Example 1. As a result, a brazing filler material was formed from the side surface of the tube sheet over 0.5 mm in the axial direction of the heat transfer tube. 100G is applied to the free end of the sample tube thus obtained, and the distribution of the tensile stress value on the surface of the heat transfer tube at that moment is analyzed by FEM. The analysis result is shown in FIG.

As can be seen from FIG. 9, Embodiments 1 and 2 of the present invention
And 4, the maximum value of the surface tensile stress generated in the brazing filler material is significantly reduced as compared with the comparative example, and the position where the maximum tensile stress is generated is located outside the 0.5 mm portion which is the thin portion of the brazing filler material. In Example 2, although the position where the maximum tensile stress was generated was in the thin portion of the brazing filler material, the maximum value was extremely significantly reduced, so that the durability against vibration was improved. .

[0035]

As described above, according to the present invention, the maximum tensile stress point generated by the vibration of the heat transfer tube shifts from the inside of the brazing filler metal having a low fatigue limit to the surface of the heat transfer tube having a high fatigue limit. Circumferential fatigue destruction of the heat transfer tube due to vibration from the thin portion of the brazing material fillet of the brazing portion between the heat transfer tube and the tube sheet is effectively prevented, and EG
It has become possible to provide an EGR gas cooling device in which the durability reliability against vibration applied to the R gas cooling device has been significantly improved.

[Brief description of the drawings]

FIG. 1 is a half sectional view showing a first embodiment according to the first embodiment of the present invention.

FIG. 2 is a half sectional view showing a second embodiment according to the first embodiment of the present invention.

FIG. 3 is a half sectional view showing a third embodiment according to the first embodiment of the present invention.

FIG. 4 is a half sectional view showing a fourth embodiment according to the first embodiment of the present invention.

FIGS. 5A and 5B are views showing a first embodiment according to a second embodiment of the present invention, wherein FIG. 5A is a half sectional view and FIG. 5B is a perspective view.

FIGS. 6A and 6B are views showing a second embodiment according to the second embodiment of the present invention, wherein FIG. 6A is a half sectional view, and FIG. 6B is a perspective view.

FIGS. 7A and 7B are views showing a third embodiment according to the second embodiment of the present invention, wherein FIG. 7A is a half sectional view and FIG. 7B is a perspective view.

FIGS. 8A and 8B are views showing a fourth embodiment according to the second embodiment of the present invention, wherein FIG. 8A is a half sectional view and FIG. 8B is a perspective view.

FIG. 9 is a graph showing surface stress distributions of an example of the present invention and a comparative example.

FIG. 10 is a schematic cross-sectional view of a conventional EGR gas cooling device including a multi-tube heat exchanger.

11A and 11B are diagrams for explaining a crack in a brazing filler material of a conventional brazing portion, in which FIG. 11A is a cross-sectional explanatory view showing a crack occurrence position, and FIG. 11B is a graph showing a distribution state of tensile stress.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Body pipe 1-1 Cooling medium inflow port 1-2 Cooling medium inflow port 2 Heat transfer tube group 3 Tube sheet 3-1 Mounting hole 4 End cap 4-1 EGR gas inflow port 4-2 EGR gas outflow port 5, 6 Brazing part 5-1 Brazing material fillet 20, 30, 40, 50, 60 Heat transfer tube 20-1 Expanding part 20-2 Original pipe part 20-3 Tapered part 30-1 Vertical rising part 30-2 Tapered part 30-3 Bulge part 40-1, 50-1 Thick part 40-2, 50-2 Taper part 40-3, 50-3 Original pipe part 21, 31, 41, 51 Sleeve 21-1, 21-2, 31-2 , 41-2, 51-1,
51-2 End surface 31-3 Tapered surface 41-3 Slit

[Procedure amendment]

[Submission date] April 19, 1999 (1999.4.1
9)

[Procedure amendment 1]

[Document name to be amended] Drawing

[Correction target item name] All figures

[Correction method] Change

[Correction contents]

FIG.

FIG. 2

FIG. 3

FIG. 4

FIG. 5

FIG. 6

FIG. 7

FIG. 8

FIG. 9

FIG. 10

FIG. 11 ────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] May 10, 1999 (1999.5.1
0)

[Procedure amendment 1]

[Document name to be amended] Drawing

[Correction target item name] FIG.

[Correction method] Change

[Correction contents]

FIG. 11

Claims (6)

[Claims] A heat transfer tube group is fixedly arranged by brazing on a tube sheet fixed near both ends of an inner wall of a body tube provided with a cooling medium inlet and a cooling medium outlet at both ends. In a multi-tube type EGR gas cooling device having a structure in which an EGR gas inlet and an outlet are provided at both ends of a body tube, at least an EGR gas inflow side of a brazing portion between the tube sheet and each heat transfer tube. An EGR gas cooling device characterized in that a stress relaxation means is provided at the brazing portion. 2. The EGR gas cooling device according to claim 1, wherein the stress relaxation means locates the maximum tensile stress point on the outer surface of the heat transfer tube in the axial direction outward from the brazing material fillet portion. . 3. The stress relaxation means according to claim 1, wherein the heat transfer tube comprises an expanded portion and a tapered portion, a vertical rising portion and a tapered portion, or a thick portion formed near the end of the heat transfer tube. An EGR gas cooling device as described in the above. 4. The EGR gas cooling device according to claim 3, wherein the thick portion is provided on at least one of an outer peripheral side and an inner peripheral side of the heat transfer tube. 5. The EGR gas cooling device according to claim 1, wherein said stress relieving means comprises a sleeve externally or internally fitted near an end of said heat transfer tube. 6. The EGR gas cooling device according to claim 5, wherein the sleeve has a tapered wall on a free end side or a slit on a free end side.