Heat exchanger and method for manufacturing the same

Abstract: According to the present invention, a first tube (2) is constructed by connecting a plate material (21, 22) into a tubular shape. In the manufacturing process, after an inner fin (5) is disposed around an outer wall of a second tube (3), the first tube (2) is disposed around the second tube (3), and the first tube (2) and the second tube (3) are fixed by connecting the plate material (21, 22) in such a manner that the inner fin (5) is in contact with the both tubes (2, 3). In this way, the inner fin (5) and both tubes (2, 3) are certainly contacted closely to each other without enlarging the second tube (3).

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention: The present invention relates to a heat exchanger comprising the features of the preamble of claim 1. The invention also relates to a method for manufacturing a heat exchanger. 2. Description of Related Art: An oil cooler having an outer cylindrical pipe and an inner cylindrical pipe is structured, as shown in JP-U-58-52462, such that a passage through which an oil flows is formed between the outer cylindrical pipe and the inner cylindrical pipe and an inner fin is disposed in the passage. Generally, both pipes employ seamless pipes having no seam (connecting surface), which are produced by drawing or extruding, in view of a mechanical strength, a manufacturing cost, and the like. To improve a heat-exchange (cooling) efficiency, it is necessary to certainly contact the inner fin closely to both pipes. Therefore, generally, after the inner fin is inserted into the passage (gap), the inner cylindrical pipe is enlarged (this work is hereinafter referred to as "enlarging pipe work") by applying a pressure from an inside of the inner cylindrical pipe before being brazed, so that the inner fin certainly contacts both pipes closely. However, the enlarging pipe work needs a specific jig thereof. In addition, it is difficult to enlarge the inner cylindrical pipe uniformly; and therefore, a reduction of manufacturing cost of the oil cooler is disturbed. Further, it is actually difficult to inspect whether or not the inner fin certainly contacts both pipes closely after the enlarging pipe work is finished. Therefore, when the enlarging pipe work is improper, the inner fin and both pipes may be brazed to each other while forming a gap therebetween, and a deterioration of the heat-exchange efficiency and the durability may be caused. Furthermore, there is known from JP-A-03-071942 a heat exchanger as defined in the preamble of claim 1. This heat exchanger is 'constituted by an outer cylindrical pipe (first tube), an inner cylindrical pipe (second tube) and an inner fin disposed in a passage formed between the inner and outer cylindrical pipes. The outer pipe is provided with a connection portion extending in a longitudinal direction thereof for connecting side edge parts of the outer pipe material together. SUMMARY OF THE INVENTION The present invention has been accomplished in view of the above-mentioned problem, and an object of the present invention is to abolish the enlarging pipe work and to certainly contact the inner fin and both pipes closely while improving the durability of the tube arrangement. According to the present invention, the first and second tubes are formed in flat shape, both tubes having parallel wider sides and narrower sides; the first connection portion of the first tube is disposed on one of said narrower sides formed on the first tube; and the wider side of the first and second tubes provide a second connection portion connected partly and directly to the other. In this way, when the plate material of the first tube is connected, the first and second tubes are certainly connected to the inner fin closely without enlarging the second tube. Therefore, because it is not necessary to enlarge the second tube, a deterioration of a heat exchanging efficiency and a durability due to the improper work for enlarging the second tube can be prevented, with the result that the manufacturing cost of the heat exchanger can be reduced. Further, by forming the first and second tubes in flat shape and providing a second connection portion on a wider side of the first and second tubes, it is possible to effectively improve the durability of both tubes. BRIEF DESCRIPTION OF THE DRAWINGS - Additional objects and advantages of the present invention will be more readily apparent from the following detailed description of preferred embodiments thereof when taken together with the accompanying drawings in which: FIG. 1A is a perspective view showing an oil cooler according to a first embodiment of the present invention disposed in a tank of an oil cooler, and FIG. 1B is a perspective of the oil cooler according to the first embodiment; FIG. 2 is a cross sectional view of the oil cooler in a transverse direction according to the first embodiment; FIG. 3 is a disassembled perspective view of the oil cooler according to the first embodiment; FIG. 4 is an explanatory view showing a manufacturing process of the oil cooler according to the first embodiment; FIG. 5 is a cross sectional view showing a modification of the present invention; FIG. 6A is a cross sectional view in a longitudinal direction of an oil cooler according to a second embodiment of the present invention, and FIG. 6B is a cross sectional view taken along the line VII-VII of FIG. 6A; FIG. 7 is a cross sectional view taken along the line VIA-VIA of FIG. 6A FIGS. 8A and 8B are explanatory views showing a diffusion space formed in a passage; FIGS. 9A and 9B show a modification of a protrusion portion; FIGS. 10A and 10B show another modification of a protrusion portion; FIGS. 11A and 11B are disassembled perspective views of an oil cooler according to a third embodiment of the present invention; FIG. 12 is an explanatory view of a hole portion of a first tube and a burring portion of a second tube according to the third embodiment; FIG. 13 is a perspective view showing an oil cooler having a round tube. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments according to the present invention will be described hereinafter with reference to the drawings. A first embodiment of the present invention will be described. In this embodiment, an exchanger according to the present invention is applied to an oil cooler for cooling an engine oil lubricating in an engine (not shown), a hydraulic oil (ATF) for an automatic transmission, or the like (hereinafter simply referred to as "oil"). As shown in FIG. 1A, the oil cooler 1 is disposed in a tank 101 of a radiator 100 for cooling engine cooling water in such a manner that a longitudinal direction thereof is consistent with a longitudinal direction of the tank 101. FIG. 1B is an enlarged view of the oil cooler 1. FIG. 2 shows a cross section in a direction perpendicular to the longitudinal direction of the oil cooler 1 of the embodiment (a cross section in a transverse direction). In a first tube (outer cylindrical pipe) 2 formed in a flat shape, a second tube (inner cylindrical pipe) 3, a longitudinal direction of which is consistent with the first tube 2, is disposed. The first tube 2 is constructed by a first plate 21 and a second plate 22, which are formed into predetermined shapes by pressing plate materials made of aluminum. A connection portion (first connection portion) 2a for connecting both plates 21 and 22 extends in the longitudinal direction of the first tube 2. The second tube 3 is a seamless tube having no seam (connection portion), which is produced by drawing or extruding. At end portions in the transverse direction of the second plate 22, of the connection portion 2a of the second plate 22, as shown in FIG. 3, there are formed caulked protrusions (caulked portions) 22a at a left-right side of the paper sheet (only right side is shown), which protrudes toward the first plate 21. The caulked protrusions are folded toward the first plate 21 and plastically deformed so that both plates are fixed to each other by caulking. As shown in FIG. 2, between both tubes 21 and 22, there is formed a passage 4 through which the oil (fluid) flows. In the passage 4, there is disposed an offset type inner fin 5 in contact with both tubes 21 and 22 to facilitate a heat-exchange (cooling) of the oil. Each wall surface of the first tube 2 (both plates 21 and 22) and the second tube 3 is covered with a brazing material having a melting point lower than that of the aluminum. By the brazing material, the connection portions 2a of both plates 21 and 22 are connected, and both tubes 2 and 3 and the inner fin 5 are connected. In this embodiment, both tubes 2 and 3 are connected with the inner fin therebetween. As shown in FIG. 2, both tubes 2 and 3 are directly connected in the passage 4 by a concave portion (second connection portion) 2b formed in the first tube 2. A plurality of the concave portions (dimples) 2b stand in a line in series in the longitudinal direction of the first tube 2 while being depressed toward the second tube 3. Each bottom 2b 1 of the concave portions 2b are connected to the second tube 3. The concave portions 2b are integrally formed with both plates 21 and 22 by pressing. As shown in FIG. 1B, there are formed an inflow port 6 through which the oil introduced from the engine into the passage 4 and an outflow port 7 through which the cooled oil flows out. Next, a method for manufacturing the oil cooler according to the embodiment will be described. First, an inner fin 5 is disposed around the outer wall of the second tube 3 (first process), and the bottom portions 2b 1 of the concave portions 2b are connected to the second tube 2 by spot welding (see FIG. 4). Next, both plates 21 and 22 are contacted closely to the inner fin 5 in such a manner that the second tube 3 and the inner fin 5 are sandwiched from a vertical direction of the paper sheet, and the caulked protrusions 22a are folded, so that both plates 21 and 22 are fixed by caulking (FIG. 4B). Both plates 21 and 22, the second tube 3, and the inner fin 5 are brazed to one another while being heated in a furnace (second process). In this embodiment, the concave portions 2b and the second tube 3 are connected by welding; however, the bottom portions 2b 1 of the concave portions 2b are partially pressed by a punch or the like to such an extent that a cracking is not generated thereon, so that the concave portions 2b and the second tube 3 may be fixed easily by caulking (crimping). Next, features of the present invention will be described. According to the embodiment, because the first tube 2 is formed by connecting the first plate 21 and the second plate 22, when both plates 21 and 22 are connected, both tubes 2 and 3 are certainly contacted to the inner fin 5 closely. Therefore, it is not necessary to perform the enlarging pipe work after both tubes 2 and 3 and the inner fin 5 are temporarily assembled. Accordingly, it is possible to prevent the deterioration of the heat-exchange efficiency and the durability due to the improper enlarging pipe work. In addition, the yield of the oil cooler 1 can be improved, and the number of the manufacturing processes can be reduced, with the result that the manufacturing cost of the oil cooler 1 can be reduced. Even if a defective brazing is caused due to a faulty contact (gap) between both tubes 2 and 3 and the inner fin 5, because both tubes 2 and 3 are directly connected by the concave portions 2b, it is possible to prevent the durability of the oil cooler 1 from lowering excessively. Therefore, the reliability and the durability of the oil cooler 1 can be improved. As in this embodiment, when the shape of the tube is flat, a bending stress is applied to both tubes 2 and 3 by the pressure in the passage 4, in addition to the simple tensile stress. In this embodiment, because both tubes 2 and 3 are connected substantially at a center of the width direction (the large diameter direction of the flat shape) of both tubes 2 and 3, it is possible to effectively improve the durability of both tubes 2 and 3. As being apparent from the above description, if the number of the concave portions 2b, i.e., the number of the connection portions for directly connecting between both tubes 2 and 3, the durability of the oil cooler 1 can be improved. However, the durability is not determined only by the number of the concave portions 2b but varies by thicknesses of the both tubes 2 and 3, the size W in the width direction of the tube (see FIG. 2), and the like. Further, if the number of the concave portions 2b is increased simply, the number of processes for connecting the concave portion 2b to the second tube 3 increases, with the result that the manufacturing cost of the oil cooler 1 may increase. Therefore, it is necessary to determine the number of the concave portions 2b while being in harmony with the durability and the manufacturing cost. The inventors have examined the number of the concave portions 2b by using an average thickness of the tube in the oil cooler for a vehicle. As a result, it comes to the conclusion that a distance (pitch) P between the concave portions 2b is preferably 70 % - 200 % of the size W in the width direction. In this embodiment, each thickness of both tubes 2 and 3 is 0.6 mm, the size W in the width direction is 35 mm, and the pitch P is 35 mm. Further, in this embodiment, because the concave portions 2b are connected to the second tube 3 before both plates 21 and 22 are fixed by caulking, the inner fin 5 is pressed by both plates 21 and 22 toward the second tube 3, and the inner fin 5 is temporarily fixed to the second tube 3. Therefore, when both tubes 21 and 22 are fixed by caulking, it is prevented that the inner fin 5 moves (is displaced), so that a gap can be prevented from being formed between the inner fin 5 and both tubes 2 and 3. Accordingly, the yield of the oil cooler 1 can be improved, and the manufacturing cost can be reduced. Further, because both plates 2 and 3 are fixed by caulking before being brazed, it is not necessary to temporarily fix both plates 2 and 3 by a jig or the like. Therefore, the oil cooler 1 can be disposed in a furnace without being bound by the jig, and a large number of the oil coolers can be brazed per one brazing process as compared with when the oil cooler is bound by the jig. As a result, the manufacturing cost of the oil cooler 1 can be reduced. In the above-described embodiment, the first tube 2 is constructed by the first and second plates 21 and 22; however, as shown in FIG. 5, the first tube may be constructed by folding a single plate 23. Further, the process for fixing both plates 21 and 22 by caulking (caulked protrusion 22a) may be abolished. However, in this case, it is necessary to braze both plates 21 and 22 while being temporarily fixed by a jig or the like. In the above-described embodiment, the process for connecting the concave portions 2b is performed before the process for fixing both plates 21 and 22 by caulking; however, this process is abolished, and the concave portions 2b may be brazed simultaneously in the process for brazing both tubes 2 and 3 and the inner fin 5. In the above-described embodiment, the concave portions 2b are provided in the first tube 2, and both tubes 2 and 3 are directly connected to each other; however, convex portions protruding toward the first tube 2 are provided on the second tube 3, top ends of the convex portions may be connected to the first tube 2. Further, the top ends of the convex portions and the bottom portions 2b 1 may be respectively connected. In the above-described embodiment, the concave portions 2b are formed in a line in series in the longitudinal direction of the first tube 2; however, the present invention is not limited thereto, but the concave portions 2b may be formed alternately. A second embodiment of the present invention will be described with reference to FIGS. 6A to 8B. In the second embodiment, parts and components similar to those in the first embodiment are shown with the same reference numerals. In FIGS. 6A and 6B, an inflow port 6 for introducing the oil discharged from the engine into the passage 4 is formed at one end of the passage 4, and an outflow port 7 through which cooled oil flows out toward the engine is formed at the other end of the passage 4. The inflow port 6 and the outflow port 7 are open in a direction perpendicular to the longitudinal direction of the passage 2, i.e., toward the rear side of the vehicle. Brackets 8 and 9 made of aluminum are brazed to the first tube 2 and form the inflow port 6 and the outflow port 7, respectively, to fix the oil cooler 1 in the tank 101 of the radiator 100. Joint portions 8a and 9a to be connected to oil pipes (not shown) from the engine are connected to the brackets 8 and 9 from the outside of the tank 101 of the radiator 100. At least at a portion of the second tube 3, facing the inflow port 6, as shown in FIGS. 6A and 6B, there is formed a protrusion portion 10 protruding (elevated) toward the inflow port 6 in a spherical shape, integrally with the second tube 3. A spherical surface 10a of the protrusion portion 10 constructs a deflection wall for deflecting the oil having flowed from the inflow port 6 into a direction having a component in an opposite direction with the outflow port 7. The direction having a component in an opposite direction with the outflow port 7 is of a direction which is different from a main flow of the oil in the passage 4 and of a direction where the oil is diffused entirely in the passage 4. The inner fin 5 is not disposed at an end portion of the passage 4 and a portion where the protrusion portion 10 is formed. An opening diameter  1 of the inflow port 6 is substantially equal to a diameter  2 of the protrusion portion 10 at a lower side thereof. Considering the brazing performance and assembling performance of the brackets 8 and 9 into the first tube 2, the diameter  2 is smaller than the size W in the width direction (the size in a direction perpendicular to the longitudinal direction of the passage 4). Next, features of this embodiment will be described. According to this embodiment, the oil flowing from the inflow passage 6 is deflected into the direction having the component in the opposite direction with the outflow port 7, as shown in FIGS. 6A and 6B, and the oil is diffused entirely in the passage 4, so that the oil can be distributed entirely in the passage 4. In FIG. 6A, a flow of the oil is shown by large arrows. In this embodiment, as described above, because the oil is diffused entirely in the passage 4 to improve the cooling efficiency of the oil cooler 1, if the position of the protrusion portion 10 is improper, it is difficult to improve the cooling efficiency sufficiently. As a result of various examinations by the inventors, it comes to the conclusion that a top end portion of the protrusion portion 10 is preferably positioned at a portion in correspondence with a center of the outflow port 6. Further, if the length of the protrusion portion 10 (the distance from the second tube 3 to the top portion of the protrusion portion) is large, pressure loss (flow resistance) when the oil passes is large, with the result that the cooling efficiency may be deteriorated. As a result of further examinations by the inventors, to improve the cooling efficiency without causing the increase of the large pressure loss, it comes to the conclusion that a protrusion length h is preferably equal to or less than 50 % of a height (size of the inner diameter of the passage 4 parallel to the protruding direction of the protrusion portion 10) H of the inner diameter of the passage 4. As means for diffusing the oil flowing from the inflow port 6 entirely into the passage 4, as shown in FIGS. 8A and 8B, a diffusion space 11 having no inner fin 5 may be formed at a portion in the passage 4, in correspondence with the inflow port 6. However, in such a construction, there occur another problems that a total surface area of the inner fin 5 decreases and a connecting force for connecting between both tubes 2 and 3 through the inner fin 5 lowers to deteriorate the pressure resistance. In contrast, according to this embodiment, because it is not necessary to provide the diffusion space 11, the above-described problems do not occur, so that the cooling efficiency of the oil cooler 1 can be improved. Further, by employing the simple construction in which the protrusion portion 10 is integrally formed with the second tube 3, the cooling efficiency of the oil cooler 1 can be improved. Therefore, the increase of the manufacturing cost of the oil cooler 1 according to the improvement of the cooling efficiency can be improved. If the inner fin 5 is disposed at the portion where the protrusion portion 10 is formed, the cross section of the passage 4 is reduced by the protrusion portion 10, and the pressure loss by the inner fin 5 increases, with the result that the cooling efficiency of the oil cooler 1 may deteriorate. In this embodiment, because the inner fin 5 is not disposed at the portion where the protrusion portion 10 is formed, the pressure loss in the passage 4 can be prevented from increasing excessively. Further, in this embodiment, the inner fin 5 is not disposed at the end portion of the passage 4 to avoid the concave portion 2b connected to the second tube 3. In the above-described embodiment, the deflection wall is constructed by the spherical surface 10a of the protrusion portion 10; however, the protrusion portion 10 may be formed in a trigonal pyramid (see FIGS. 9A and 9B) or a quadrangular pyramid (see FIGS. 10A and 10B). In the above-described embodiment, the oil cooler 1 is disposed in the tank 101 of the radiator 1; however, may be disposed in an engine. A third embodiment of the present invention will be described. As shown in FIGS. 11A and 11B, the second tube 3 is constructed by two separate plates 31 and 32, and the inner fin 5 is constructed by two inner fins 51 and 52. In both plates 31 and 32, there are formed burring portions 31a and 32a protruding toward the first tube 2, in correspondence to the bottom portion 2b 1 of the first tube 2. The bottom portion 2b 1 has a hole portion 2b 2 for receiving the burring portion 31a through a hole portion 51a formed in the inner fin 5. The outer plate 21 and the inner plate 31 are assembled as a first assembly in such a manner that the burring portion 31a is inserted into the hole portion 2b 2 of the bottom portion 2b 1 , and then the burring portion 31a and the hole portion 2b 2 are liquid-tightly connected by enlarging the burring portion 31a outwardly as shown in FIG. 12. Each size of the burring portion 31a and the hole portion 2b 2 are set in advance to be in contact closely with each other when connected. The burring portion 31a and the hole portion 2b 2 may be connected by caulking or welding. Similarly, the outer plate 22 and the inner plate 32 are assembled as a second assembly to construct the oil cooler 1. Next, the first assembly and the second assembly are assembled by caulking the connection portion 22a. - According to this embodiment, because the second tube 3 is constructed by separate plates 31 and 32, it is easy to manufacture the plates 31 and 32 by pressing, with the result that the manufacturing cost of the second tube 3 can be reduced as compared with when the pipe material (which is produced by extruding or an electric resistance welded tube) is employed. Further, it is possible to assemble the oil cooler 1 in one direction. Further, as a comparative example, and also already known in the prior art, there is shown in FIG. 13 an oil cooler 1 having a round tubular shape.

Claims: A heat exchanger (1), comprising: a first tube (2) formed by connecting a plate material (21, 22) into a tubular shape, said first tube (2) having a first connection portion (2a) extending in a longitudinal direction thereof, for connecting an end portion of the plate material; a second tube (3) disposed in said first tube (2), in parallel with said first tube (2), to form a passage (4) therewith, through which a fluid passes; and an inner fin (5) disposed in said passage (4) in contact with said first tube (2) and said second tube (3), said inner fin (5) being for facilitating a heat-exchange of the fluid, characterized in that , said first tube (2) and said second tube (3) are formed in flat shape, both said tubes having parallel wider sides and narrower sides, said first connection portion (2a) is disposed on one of said narrower sides formed on said first tube (2), and said wider side of said first tube and said wider side of said second tube provide a second connection portion (2b, 2b2, 31a, 32a) connected partly and directly to the other. The heat exchanger (1) according to claim 1, wherein said first connecting portion (2a) has a caulked portion (22a) for fixing said end portion of the plate material (21, 22) by caulking. The heat exchanger (1) according to claim 1 or 2, wherein said first tube (2) is formed by connecting two plate materials (21, 22). The heat exchanger (1) according to one of claims 1 to 3, wherein said second tube (3) is formed by connecting two plate materials (31, 32). The heat exchanger according to one of claims 1 to 4, further comprising: means (8) for forming an inflow port (6) at one end in a longitudinal direction of the passage (4), for introducing the fluid into said passage (4), said inflow port (6) being open in a direction substantially perpendicular to the longitudinal direction of said passage (4); means (9) for forming an outflow port (7) at the other end in the longitudinal direction, through which the fluid in the passage (4) flows out; and a deflection member (10a) disposed in said passage (4), for deflecting the fluid flowing from said inflow port (6) into a direction having a component in an opposite direction with said outflow port (7). The heat exchanger (1) according to claim 5, wherein said deflection member (10a) is disposed to face said inflow port (6). The heat exchanger (1) according to claim 5 or 6, wherein said deflecting member (10a) includes a protrusion portion (10) protruding from an outer wall of said first tube (2) toward said inflow port (6). The heat exchanger (1) according to claim 7, wherein said protrusion portion (10) has a top end portion positioned in correspondence with a center of said inflow port (6). The heat exchanger (1) according to claim 7 or 8, wherein said protrusion portion (10) has a protrusion length being equal to or less than 50% of an inner diameter of said passage (4), parallel to a protrusion direction of said protrusion portion (10). The heat exchanger (1) according to one of claims 1 to 3 and 5 to 9, wherein said second tube (3) is formed by connecting a plate material (31, 32), said second tube (3) has a connection portion for connecting an end portion of the second plate material (31, 32), and said connection portion is located on said narrower side of said second tube (3). The heat exchanger according to claim 10, wherein said second connection portion (2b2, 31a, 32a) is provided by a hole portion (2b2) formed on said plate material (21, 22) of said first tube (2) and an insertion portion (31a, 32a) formed on said plate material of said second tube (3), the insertion portion (31a, 32a) being fixedly connected into said hole portion (2b2). The heat exchanger (1) according to one of claims 1 to 11, wherein said second connection portion (2b) is provided by a concave portion formed in said first tube (2). The heat exchanger (1) according to claim 11 or 12, wherein, said first tube (2) is formed by connecting two of said plate materials (21, 22), said second tube (3) is formed by connecting two of said plate materials (31, 32), said inner fin (5) includes a first inner fin (51) disposed between said wider sides of said first and second tubes, and a second inner fin (52) disposed between said wider sides of said first and second tubes. The heat exchanger (1) according to one of claims 1 to 13, wherein said second connection portion (2b, 2b2, 31a, 32a) is located between both longitudinal ends of said tubes. The heat exchanger (1) according to one of claims 1 to 14, wherein said second connection portion (2b, 2b2, 31a, 32a) is one of a plurality of second connection portions arranged with intervals (P). The heat exchanger (1) according to one of claims 1 to 15, wherein said inner fin (5) has a hole portion (51a) through which said second connection portion (2b, 2b2, 31a, 32a) is located. A method for manufacturing a heat exchanger (1) having a first tube (2) formed by connecting a plate material (21, 22) into a flat tubular shape, a second tube (3) having a flat tubular shape, and an inner fin (5), said method comprising: disposing said inner fin (5) on the outside of said second tube (3) ; disposing said plate material (21, 22) of said first tube on the outside of said inner fin (5) ; and connecting said plate material (21, 22) at a narrower side of the first tube by forming a first connection portion extending along a longitudinal direction of said first tube (2) so as to form said first tube (2), in such a manner that said inner fin (5) is contact with said first tube (2) and said second tube (3), characterized in that , the method further comprises: connecting a part of said plate material (21, 22) on a wider side of said first tube (2) directly to a part of a material of said second tube (3) to form a second connection portion (2b, 2b2, 31a, 32a) before said connecting step of said plate material is completed. The method for manufacturing a heat exchanger (1) according to claim 17, characterized by further comprising a step of forming a concave portion (2b) on said plate material (21, 22), the concave portion being formed to provide said second connection portion. The method for manufacturing a heat exchanger (1) according to claim 17, characterized by further comprising a step of connecting plate material (31, 32) of said second tube (3) after said connecting step of said second connection portion (2b2, 31a, 32a).

Inventors: SAKANE TAKAAKI, UCHIKAWA AKIRA, YAMANAKA YASUTOSHI, SAKANE, TAKAAKI, UCHIKAWA, AKIRA, YAMANAKA, YASUTOSHI
Applicants: DENSO CORP, DENSO CORPORATION
Application year: 1997
Main classification: F28D7
IPC codes: F28F9, F28F13, F28D9, F28D7