JP2007315325A - Heat exchanger structure for egr cooler - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heat exchanger structure for an EGR cooler, using two heat exchangers for improving the whole heat exchanging efficiency while suppressing local boiling and preventing the degradation of durability. <P>SOLUTION: A tube assembly consists of a number of tubes having the same length and being long in the axial direction, which are lined in parallel in mutually spaced relation and supported at both ends by partition plates. It is stored in a cylindrical heat exchanger shell. A cooling water inlet pipe and a cooling water outlet pipe are provided on the heat exchanger shell. An EGR gas passage is formed in each tube, and the two heat exchangers with the built-in tubes use cooling water for cooling the outer peripheries of the tubes. The two heat exchangers are formed in one serial and concentric unit. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a heat exchanger structure of an EGR cooler in which two heat exchangers are arranged in the EGR gas flow direction so that cooling efficiency can be improved.

In recent years, with the tightening of exhaust gas regulations for diesel engines, the environment surrounding the EGR cooler has become severe, such as an increase in the temperature of the EGR gas, an increase in gas flow rate, and a decrease in the gas outlet temperature of the EGR cooler (an increase in heat dissipation). It is desired to increase the amount of heat and maintain high temperature durability.
In general, as shown in FIG. 5, an intercooler 2 and a radiator 3 are arranged in front of the diesel engine 1, an EGR cooler 4 or 6 is arranged in the rear, and a turbocharger 5 is arranged in the side. The turbocharger 5 is arranged so that the compressor 5a is directed from the front and the waste gas from the turbine 5b is discharged rearward.
In the normal EGR coolers 4 and 6, as shown in FIG. 6, a multi-tubular heat exchanger incorporating many circular tubes or a flat tube heat exchanger incorporating many flat tubes provided with radiating fins shown in FIG. The cooling water inlets 4a and 6a are provided at the end on the gas inlet side, the cooling water outlets 4b and 6b are provided at the end on the gas discharge side, and flanged headers 4c, 4d, 6c and 6d are provided, and the sizes of the flanges 4e, 4f, 6e, and 6f are determined so as to be bolted to the piping from the diesel engine 1 side.
As shown in FIG. 8, the internal structure of the EGR coolers 4 and 6 includes a plurality of tubes 4i,..., 4i, 6i,. A multi-tube heat exchanger or a flat type incorporating a tube assembly 7 supported by a partition plate for closing an end portion of 6g and outlet side partition plates 4h, 6h with a space between the tubes spaced apart from each other It is configured as a tube heat exchanger.
The relationship between the inlet and outlet of the exhaust gas to the EGR coolers 4 and 6 and the inlet and outlet of the cooling water is that the cooling water inlets 4a and 6a are provided at the end on the gas inlet side, and the cooling water outlet 4b is provided at the end on the gas outlet side. , 6b is provided (cocurrent flow cooling method) that is devised so that the flow flows evenly in the main body by the pressure of cooling water (Patent Document 1). There is also a cooling water inlet 4a, 6a provided on the gas discharge side and a cooling water outlet 4b, 6b provided on the gas inlet side (counterflow system) (Patent Document 2).

JP 2000-045883 A JP 2000-274990 A

[Problems of the prior art]
In the EGR coolers 4 and 6, the exhaust gas temperature becomes higher than 500 ° C. on the gas inlet side, and the cooling water inlet temperature is approximately 80 to 90 ° C. because the cooling water after cooling the diesel engine is used. Therefore, the temperature difference between the two fluids increases on the gas inlet side, and the cooling water may boil.
In order to suppress this boiling, the cooling water inlets 4a and 6a are provided at the gas inlet side ends of the EGR coolers 4 and 6, and the cooling water outlets 4b and 6b are provided at the gas outlet side ends. Some structures have a structure in which the flow is evenly diffused by the inflowing pressure. In this structure, the flow of EGR gas and cooling water is in the same direction. As the temperature rises, the temperature difference between the two fluids becomes smaller, and the amount of heat exchange decreases.
For these reasons, it is considered to divide into two in the longitudinal direction. However, if the same cooling water is used, the temperature on the inlet side does not change, and the piping system is branched on both the inlet side and the outlet side. As a result, the piping is complicated and the mounting work becomes difficult.

  The present invention has been made in view of the above-mentioned problems in the prior art, and the technical problem specifically set in order to solve this problem is to suppress local boiling with two heat exchangers and to improve durability. It is an object of the present invention to provide a heat exchanger structure of an EGR cooler that can prevent a decrease in the temperature and increase the overall heat exchange efficiency.

In order to specify the heat exchanger structure of the EGR cooler in which the above-mentioned problems in the present invention can be effectively solved, all the matters recognized as necessary are covered and specifically configured as the problem solving means.
The first problem-solving means relating to the heat exchanger structure of the EGR cooler is that each tube is spaced from each other with a plurality of tubes having the same length in the axial direction and parallel to each other. The tube assembly supported by the partition plate is accommodated in a cylindrical heat exchanger outer shell, and a cooling water inlet pipe and a cooling water outlet pipe are provided in the heat exchanger outer shell. Two heat exchangers with built-in tubes that cool the outer periphery of each tube with cooling water are provided as EGR gas passages, and the two heat exchangers are integrated in series and concentrically.

The second problem-solving means relating to the heat exchanger structure of the EGR cooler is the heat exchange in which both ends of the outer shell of the heat exchanger are formed with fitting ends, one of which is a fitting hole and the other is a fitting shaft. Two heat exchangers are formed, and the two heat exchangers are connected in series and concentrically at the fitting end.
According to a third problem-solving means relating to the heat exchanger structure of the EGR cooler, a recess serving as a positioning member for a storage position is provided in the center of the cylindrical body serving as the outer shell of the heat exchanger, and the length of the tube assembly is determined. A tube assembly having a length that can be stored in a storage range from an end of the outer shell of the heat exchanger to a recess, and having a length that can be stored on both sides of the recess formed in the outer shell of the heat exchanger. And two heat exchangers are formed in the longitudinal direction.

Moreover, the 4th problem-solving means which concerns on the heat exchanger structure of an EGR cooler same as the above is characterized by welding and integrating the joined fitting end part.
Further, according to a fifth problem solving means relating to the heat exchanger structure of the EGR cooler, the tube assembly is configured such that both end portions of each tube and both partition plates supporting the both end portions are fixed by integral brazing. After the insertion into the exchanger outer shell, the partition plates and the heat exchanger outer shell are integrated by welding.

The sixth problem solving means according to the heat exchanger structure of the EGR cooler is characterized in that the tube is a cylindrical tube and the heat exchanger outer shell is a cylindrical shell.
The seventh problem-solving means according to the heat exchanger structure of the EGR cooler is characterized in that the tube is a flat tube and the heat exchanger outer shell is a square tube shell.

  In the first problem solving means related to the heat exchanger structure of the EGR cooler, two heat exchangers are integrated in series in the direction of EGR gas flow by integrating the two heat exchangers concentrically in series. The upstream side of the EGR gas flow becomes a high-temperature side heat exchanger, the downstream side becomes a low-temperature side heat exchanger, and on the high-temperature side, local boiling is suppressed to prevent deterioration of durability, On the low temperature side, the minimum temperature of the exhaust gas temperature of the EGR gas can be lowered to increase the overall heat exchange efficiency, facilitating the production, and the EGR cooler having two heat exchangers can be compactly integrated.

  In the second problem-solving means relating to the heat exchanger structure of the EGR cooler, the fitting end portions of the two identical heat exchangers can be easily fitted in series and concentrically and integrated in the EGR gas flow direction. Two heat exchangers can be formed, the upstream side of the EGR gas flow becomes the high temperature side heat exchanger, the downstream side becomes the low temperature side heat exchanger, and the high temperature side has local boiling To prevent the deterioration of durability and lower the minimum temperature of the exhaust gas temperature of the EGR gas on the low temperature side, thereby improving the overall heat exchange efficiency, facilitating manufacturing and having two heat exchangers EGR cooler can be put together compactly.

  In the third problem solving means relating to the heat exchanger structure of the EGR cooler, two tube assemblies are built in both sides of the recess in the outer shell of the heat exchanger made of one cylinder, and each has a cooling water inlet pipe. And a cooling water outlet pipe, and two heat exchangers are integrally formed in series, so that the upstream side becomes a high temperature side heat exchanger and the downstream side becomes a low temperature side heat exchanger with respect to the flow of EGR gas. On the high temperature side, local boiling can be suppressed to prevent deterioration of durability, and on the low temperature side, the minimum temperature of the exhaust gas temperature of EGR gas can be lowered to increase the overall heat exchange efficiency, facilitating manufacturing. An EGR cooler having two heat exchangers can be put together in a compact manner.

In the fourth problem solving means related to the heat exchanger structure of the EGR cooler, the fitting end portions joined by the second problem solving means are integrated by welding, thereby increasing durability and sealing the whole. The degree of cooling can be increased.
In the fifth problem solving means relating to the heat exchanger structure of the EGR cooler, the tube assembly for forming the heat exchanger of the third problem solving means is integrally brazed with both partition plates supporting the ends of the tubes. After inserting into the heat exchanger outer shell, each partition plate and the heat exchanger outer shell are welded and integrated to increase durability and improve the degree of sealing, and the tube assembly is heated overall. Therefore, local thermal distortion does not occur, cooling efficiency can be increased, manufacturing can be facilitated and manufacturing cost can be reduced, and an EGR cooler having two heat exchangers can be compactly integrated. .

Hereinafter, the best embodiment according to the present invention will be described in detail.
However, this embodiment is specifically described for better understanding of the gist of the invention, and does not limit the content of the invention unless otherwise specified.
In addition, the same thing as a prior art example attaches | subjects the same code | symbol, and abbreviate | omits detailed description.

[First Embodiment]
As shown in FIG. 1, the EGR cooler 8 of the first embodiment is provided with two multi-tube heat exchangers of the same shape integrally molded by in-furnace brazing, one of which is a high temperature side heat exchanger 8a. The other is used as the low temperature side heat exchanger 8b.
The high temperature side heat exchanger 8a and the low temperature side heat exchanger 8b can be independently supplied with cooling water by welding the cooling water inlet 4a and the cooling water outlet 4b to the outer shell, respectively. Like that.
The outer shell has a concave-convex shape with one end portion as a convex end portion (fitting shaft) 10a and the other end portion as a concave end portion (fitting hole) 10b, which serve as fitting end portions. A fitting end portion (a fitting end portion having a shaft hole fitting shape) 10 is formed, and the convex side end portion 10a of the low temperature side heat exchanger 8b is inserted into the concave side end portion 10b of the high temperature side heat exchanger 8a. By doing so, it is possible to easily connect the EGR gas flow in series and concentrically. After the insertion, laser welding is performed at the fitting position to seal the fitting portion and to integrate as an EGR cooler.

The high temperature side heat exchanger 8a and the low temperature side heat exchanger 8b are both used as an EGR cooler having two heat exchangers by concentrically fitting individual heat exchangers formed by brazing together. Thus, the EGR gas that has passed through the high temperature side heat exchanger 8a immediately flows into the low temperature side heat exchanger 8b through the space of the fitting portion, so that the EGR gas is exchanged from the high temperature side heat exchanger 8a to the low temperature side heat exchange. In order to prevent the temperature from being lowered unnecessarily, the vessel 8b should flow evenly in the cross-sectional direction.
The high-temperature side heat exchanger 8a is cooled so that EGR gas and cooling water flow in the same direction, and the low-temperature side heat exchanger 8b is cooled so that EGR gas and cooling water flow oppositely. Pipe the water system.

  When the high temperature side heat exchanger 8a is used as a parallel flow, and the water is spread by using the dynamic pressure when cooling water flows in to suppress local boiling, the tubes 4i,..., 4i that are EGR gas passages are exposed. In the low-temperature side heat exchanger 8b, if the EGR gas temperature is set to 200 ° C. or lower, preferably around 150 ° C., the counter flow is counteracted. By doing so, it can be cooled effectively, the efficiency as a heat exchanger can be kept high, and the gas temperature at the EGR gas outlet can be lowered further.

[Function and effect]
In the EGR cooler of the first embodiment configured as described above, the heat exchange efficiency is improved and the durability is lowered by integrally configuring the two heat exchangers of the high temperature side and the low temperature side in the flow direction of the EGR gas. And the operating rate of each heat exchanger can be improved. By integrating two identically formed heat exchangers, productivity can be improved, compact formation can be facilitated, assembly can be facilitated, and cost can be reduced.

[Second Embodiment]
As shown in FIG. 2, the EGR cooler 8 according to the second embodiment includes a recess 9c provided in the center of the cylindrical body forming the heat exchanger outer shell (9a, 9b) with respect to the flow of EGR gas. Two heat exchangers are formed by installing tube assemblies 7 and 7 having the same shape on both sides of the tube, and the upstream side of the recess 9c with respect to the flow of EGR gas is a high temperature side heat exchanger 8a. The downstream side is used as the low temperature side heat exchanger 8b. The high temperature side heat exchanger 8a and the low temperature side heat exchanger 8b are respectively provided with a cooling water inlet 4a and a cooling water outlet 4b in the outer shells 9a and 9b of the heat exchangers 8a and 8b, respectively. Allow cooling water to be supplied to either of the streams.

The heat exchanger outer shells 9a and 9b of the EGR cooler 8 form a concave portion 9c that serves as a positioning member that is recessed until the entire circumference comes out to the inner side of the inner wall surface toward the center at the central portion. From the other end, the tube assembly 7 on the high temperature side is inserted until the tube assembly 7 on the low temperature side comes into contact with the recess 9c.
For this reason, dimensions such as the lengths of the outer shells 9a and 9b and the positions of the recesses 9c and the lengths of the tube assemblies 7 and 7 are automatically adjusted so as to reach the necessary insertion depth by contacting the recesses 9c. It is determined in advance.
The tube assemblies 7 and 7 are integrally formed by brazing in the furnace, and then inserted into the outer shells 9a and 9b. The outer shells 9a and 9b are inserted into the partition plates 6a and 6b of the tube assemblies 7 and 7, respectively. Two heat exchangers integrated in series and concentrically with the EGR gas are formed by laser welding at the arrangement position.

The high temperature side heat exchanger 8a and the low temperature side heat exchanger 8b are both formed by fitting the integrally brazed tube assemblies 7 and 7 to the outer shells 9a and 9b, and both are used for one EGR cooler. It becomes a heat exchanger.
The EGR gas that has passed through the high temperature side heat exchanger 8a is formed by the recess 9c and immediately flows into the heat exchanger 8b dedicated to the low temperature side through the space between the partition plates 4g and 4h of the tube assemblies 7 and 7. Thus, the temperature of the EGR gas is prevented from being unnecessarily lowered.
And the piping of a cooling water system | strain is made so that the high temperature side heat exchanger 8a may become a parallel flow, and the low temperature side heat exchanger 8b becomes a countercurrent.

  If the high-temperature side heat exchanger 8a is used as a parallel flow and the dynamic pressure when cooling water flows in is used to improve the spread of water and suppress local boiling, any of the tubes 4i,. In the heat exchanger 8b dedicated to the low temperature side, the EGR gas temperature is set to 200 ° C. or lower, preferably about 150 ° C. The flow can be effectively cooled, the efficiency as a heat exchanger can be kept high, and the gas temperature can be lowered at the EGR gas outlet.

[Function and effect]
In such an EGR cooler of the second embodiment, two heat exchangers of the high temperature side and the low temperature side are integrally formed in the flow direction of the EGR gas, thereby improving the heat exchange efficiency and reducing the durability. The operating rate can be improved.
By accommodating the two heat exchangers in the cylindrical body forming one outer shell, it is possible to form a compact, facilitate assembly, improve productivity, and reduce cost.

[Third Embodiment]
As shown in FIG. 3, the EGR cooler 18 of the third embodiment is a flat tube having the same shape in the outer shell (19 a, 19 b) integrally formed by brazing in the furnace and having a substantially rectangular cross section. Two square heat exchangers (18a, 18b) incorporating a large number of 6i,..., 6i are prepared, and one is used as the high temperature side heat exchanger 18a and the other is used as the low temperature side heat exchanger 18b. .
The high temperature side heat exchanger 18a and the low temperature side heat exchanger 18b can be independently supplied with cooling water by welding the cooling water inlet 6a and the cooling water outlet 6b to the outer shell, respectively. Like that.
The outer shell is used for fitting opposite ends with one end as a convex end (fitting shaft side end) 10a and the other end as a concave end (fitting hole side end) 10b. A fitting end portion (fitting end portion for fitting a shaft hole) 20 having an uneven shape as an end portion is formed, and the convex side of the low temperature side heat exchanger 18b is formed on the concave side end portion 20b of the high temperature side heat exchanger 18a. By inserting the end portion 20a, it can be easily connected in series and concentrically to the flow of EGR gas. After the insertion, laser welding is performed at the fitting position to seal the fitting portion and to integrate as an EGR cooler.

The high temperature side heat exchanger 18a and the low temperature side heat exchanger 18b are both used as an EGR cooler having two heat exchangers by concentrically fitting individual heat exchangers formed by brazing together. Thus, the EGR gas that has passed through the high temperature side heat exchanger 18a immediately flows into the low temperature side heat exchanger 18b through the space of the fitting portion, so that the EGR gas is exchanged from the high temperature side heat exchanger 18a to the low temperature side heat exchanger. It is made to flow evenly in the cross-sectional direction to the vessel 18b and not to unnecessarily decrease the temperature.
The high temperature side heat exchanger 18a is cooled so that EGR gas and cooling water flow in the same direction, and the low temperature side heat exchanger 18b is cooled so that EGR gas and cooling water flow in opposite directions. Pipe the water system.

  When the high temperature side heat exchanger 18a is used as a parallel flow and the dynamic pressure at the time when the cooling water flows in is used to improve the spread of the water and suppress the local boiling, the flat tubes 6i,. When the low temperature side heat exchanger 18b is set such that the EGR gas temperature is set to 200 ° C. or lower, preferably about 150 ° C., in the low temperature side heat exchanger 18b, countercurrent flows. Thus, the cooling can be effectively performed, the efficiency as the heat exchanger can be kept high, and the gas temperature at the EGR gas outlet can be lowered.

[Function and effect]
In the EGR cooler 18 of the third embodiment configured as described above, the heat exchange efficiency is improved by integrally configuring the two heat exchangers 18a and 18b on the high temperature side and the low temperature side in the EGR gas flow direction, A decrease in durability can be suppressed, and the operating rate of each heat exchanger 18a, 18b can be improved. By integrating two identically formed heat exchangers 18a and 18b, productivity can be improved and the heat exchangers 18a and 18b can be formed compactly, making assembly easy and reducing costs.

[Fourth Embodiment]
As shown in FIG. 4, the EGR cooler 18 of the fourth embodiment includes a recess 19 c provided in the center portion with respect to the flow of EGR gas inside the cylindrical body forming the heat exchanger outer shell (19 a, 19 b). Tube assemblies 7 and 7 using flat tubes 6i,..., 6i having the same shape are provided on both sides to form two heat exchangers 18a and 18b, and upstream of the recess 19c with respect to the flow of EGR gas. Is used as the high temperature side heat exchanger 18a, and the downstream side is used as the low temperature side heat exchanger 18b. The high temperature side heat exchanger 18a and the low temperature side heat exchanger 18b are respectively provided with a cooling water inlet 6a and a cooling water outlet 6b in the outer shells 19a and 19b of the heat exchangers 18a and 18b, respectively. Allow cooling water to be supplied to either of the streams.

The heat exchanger outer shells 19a and 19b of the EGR cooler 18 form a concave portion 19c that serves as a positioning member that is recessed until the entire circumference comes out from the inner wall surface toward the center at the central portion. From the other end, the tube assembly 7 on the high temperature side is inserted until it contacts the recess 19c.
For this reason, dimensions such as the lengths of the outer shells 19a and 19b and the positions of the recesses 19c and the lengths of the tube assemblies 7 and 7 are automatically adjusted to reach the required insertion depth by contacting the recesses 19c. It is determined in advance.
The tube assemblies 7 and 7 are integrally formed by brazing in the furnace, and then inserted into the outer shells 19a and 19b. The outer shells 19a and 19b are inserted into the partition plates 6g and 6h of the tube assemblies 7 and 7, respectively. By performing laser welding at the arrangement position, two heat exchangers 18a and 18b integrated in series and concentrically with the EGR gas are formed.

Both the high temperature side heat exchanger 18a and the low temperature side heat exchanger 18b are formed by fitting the integrally brazed tube assemblies 7 and 7 to the outer shells 19a and 19b, and both are used for one EGR cooler. It becomes a heat exchanger.
The EGR gas that has passed through the high temperature side heat exchanger 18a is formed by the recess 19c and immediately flows into the low temperature side dedicated heat exchanger 18b through the space between the partition plates 6h and 6g of the tube assemblies 7 and 7. Thus, the temperature of the EGR gas is prevented from being unnecessarily lowered.
And the piping of a cooling water system | strain is made so that the high temperature side heat exchanger 18a may become a parallel flow, and the low temperature side heat exchanger 18b may become a countercurrent.

  When the high-temperature side heat exchanger 18a is used as a parallel flow and the dynamic pressure when cooling water flows in is used to improve the spread of water and suppress local boiling, any of the tubes 6i,. In the low-temperature side heat exchanger 18b, if the EGR gas temperature is set to 200 ° C. or lower, preferably around 150 ° C., the counter flow is counterflowed. By doing so, it can be effectively cooled, the efficiency as a heat exchanger can be kept high, and the gas temperature can be lowered at the EGR gas outlet.

[Function and effect]
In such an EGR cooler of the fourth embodiment, the heat exchanger 18a, 18b of the high temperature side and the low temperature side are integrally formed in the flow direction of the EGR gas, thereby improving the heat exchange efficiency and durability. It is possible to suppress the decrease in the operating rate and improve the operating rate.
Since the two heat exchangers 18a and 18b are accommodated in one cylindrical body that forms the outer shell (19a and 19b), the heat exchanger 18a and 18b can be formed compactly, facilitate assembly, and improve productivity. Cost can be reduced.

[Another aspect]
Such an embodiment is specifically described in order to facilitate understanding of the gist of the invention, but does not limit the content of the invention, and is not particularly described (including design content). The embodiment is not limited, and may be changed as appropriate. In this sense, some other embodiments that meet the spirit of the invention are shown below.

Although the high temperature side heat exchangers 8a and 18a are cocurrent, and the low temperature side heat exchangers 8b and 18b are countercurrent, they are not necessarily formed in such a form, but both may be cocurrent or countercurrent. If the piping is easy without lowering the heat exchange efficiency, it can be used.
In this way, it can be divided into two heat exchangers 8a, 8b or heat exchangers 18a, 18b, and the post-process including assembly can be processed efficiently, improving work efficiency, reducing costs and Any configuration that contributes to improving heat exchange efficiency can be used.

It is a longitudinal section showing a multi-tube heat exchanger used in a 1st embodiment of an EGR cooler by the present invention. It is a longitudinal cross-sectional view which shows the multi-tube heat exchanger used by 2nd Embodiment same as the above. It is a longitudinal cross-sectional view which shows the flat tube type heat exchanger used by 3rd Embodiment same as the above. It is a longitudinal cross-sectional view which shows the flat tube type heat exchanger used by 4th Embodiment same as the above. It is a system system | strain diagram of the conventional EGR cooler. It is an expansion perspective view which shows the multitubular heat exchanger used with the conventional EGR cooler. It is side surface explanatory drawing which shows the multitubular heat exchanger used with the conventional EGR cooler. It is a perspective explanatory view which shows a flat tube type heat exchanger used in a conventional EGR cooler partially broken.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Diesel engine 2 Intercooler 3 Radiator 4 EGR cooler 4a, 6a Cooling water inlet 4b, 6b Cooling water outlet 4g, 6g (Inlet side) Partition plate 4h, 6h (Outlet side) Partition plate 4i Tube 6i (Flat) tube 5 Turbo Charger 5a Compressor 5b Turbine 7 Tube assemblies 8a, 18a High temperature side heat exchangers 8b, 18b Low temperature side heat exchangers 9a, 19a Outer shells 9b, 19b (for high temperature side heat exchangers) Outer shells (for low temperature side heat exchangers) 9c, 19c Concave portion 10, 20 Concave end portion (gender end portion)
10a, 20a Convex side end (fitting shaft)
10b, 20b Concave end (fitting hole)
18 EGR cooler 19 (heat exchanger) outer shell

Claims (7)

  Heat exchange is formed in a cylindrical shape from a tube assembly in which many tubes of the same length in the axial direction are parallel and each tube is spaced from each other and both ends of each tube are supported by partition plates. A cooling water inlet pipe and a cooling water outlet pipe are provided in the outer shell of the heat exchanger, and each tube has an EGR gas passage and the outer periphery of each tube is cooled by cooling water. A heat exchanger structure of an EGR cooler comprising two heat exchangers, wherein the two heat exchangers are integrated in series and concentrically.   Two heat exchangers are formed at both end portions of the outer shell of the heat exchanger, each of which has a fitting end portion where one is a fitting hole and the other is a fitting shaft, and the two heat exchangers are fitted to the fitting portion. 2. The heat exchanger structure for an EGR cooler according to claim 1, wherein the ends are connected in series and concentrically.   A recess serving as a positioning member is provided in the center of the cylindrical body that is the outer shell of the heat exchanger so that the length of the tube assembly is within the storage range from the end of the outer shell of the heat exchanger to the recess. A tube assembly having a length that can be stored, and a tube assembly having a length that can be stored on each side of the recess formed in the outer shell of the heat exchanger is built in to form two heat exchangers in the longitudinal direction. The heat exchanger structure of the EGR cooler according to claim 1, wherein the heat exchanger structure is an EGR cooler.   The heat exchanger structure of an EGR cooler according to claim 2, wherein the joined fitting end portions are integrated by welding.   In the tube assembly, both end portions of each tube and both partition plates supporting the both end portions are fixed by integral brazing and inserted into the heat exchanger outer shell, and then both the partition plates and the heat exchanger outer shell are inserted. And a heat exchanger structure for an EGR cooler according to claim 3, wherein:   4. The heat exchanger structure of an EGR cooler according to claim 3, wherein the tube is a cylindrical tube, and the outer shell of the heat exchanger is formed into a cylindrical shell.   4. The heat exchanger structure of an EGR cooler according to claim 3, wherein the tube is a flat tube and the outer shell of the heat exchanger is formed as a square tube shell.

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