FLAT TUBE FOR HEAT EXCHANGER, HEAT EXCHANGER USING THE FLAT TUBE, AND METHOD OF MOLDING THE FLAT TUBE FOR THE HEAT EXCHANGER

Abstract

 The present invention provides a flat tube to be used in a heat exchanger that allows the heat exchanger to be provided as a compact unit and can be used as a universal part. The present invention also provides a heat exchanger that includes such flat tubes and a method for manufacturing the flat tubes. In flat tubes 5 and 6 each formed in the shape of a flat tube with two open ends and a fluid passage formed therein and having twisted portions near the open end portions 13 and 14 and open end portions 13 and 14 inserted at tube insertion holes 7 or 8 and 12 ranging along the central lines of a header pipe 2 or 3 and a header pipe 4, the open end portions 13 and 14 of the flat tube 5 (6) are offset relative to the central line of the flat tube extending along the length thereof to a specific extent so as to align the open end portion 13 (14) with a side edge of the flat tube 5 (6). This structure allows the heat exchanger to be provided as a compact unit and the flat tubes can be offered as universal parts.

Description

Technical Field

[0001] The present invention relates to a flat tube to be used in a heat exchanger, which has two open ends, is formed in the shape of a flat tube with a passage formed therein and has the opened ends thereof inserted at tube insertion holes formed at header pipes. More specifically, it relates to a flat tube for a heat exchanger, having twisted portions near the open end portions thereof. The present invention also relates to a heat exchanger that includes the flat tube described above and a method for forming the flat tube for a heat exchanger.

Background Art

[0002] A heat exchanger with a high pressure-withstanding specifications, which includes header pipes and flat tubes inserted and bonded at the header pipes, needs to assure the required pressure-withstanding strength by minimizing the diameters of the header pipes. This requirement is addressed in a structure in which the portions of flat tubes to be inserted and bonded at the header pipes near the open end portions are twisted by approximately 90° so as to align the open end portions along the longer side of the header pipes, tube insertion holes ranging along the axial direction are formed at the circumferential surfaces of the header pipes and the open end portions of the flat tubes are inserted and bonded at the tube insertion holes (patent reference literature 1). As a variation of this structure, the openings at the flat tubes may be offset relative to the central line of the flat tubes extending along the lengthwise direction (see patent reference literature 2).

Patent reference literature 1: Japanese Patent Publication No. 2002-521644

Patent reference literature 2: European Patent Publication No. EP 0845648A2

Disclosure of the Invention

Problems to be Solved by the Invention

[0003] However, if the twisted open end portions of the flat tubes are not sufficiently offset in a heat exchanger having header pipes disposed adjacent to each other and the flat tubes disposed so as to extend side-by-side, the flat tubes will have to be disposed over a significant interval from each other in order to allow their open ends to be inserted at the tube insertion holes at the header pipes. The dimensions of the heat exchanger unit at such a heat exchanger are bound to be significant. If, on the other hand, the open end portions are offset to an excessive extent, the adjacent header pipes will need to be disposed over a significant distance from each other, resulting in an increase in the external dimensions.

[0004] If the external dimensions of the heat exchanger are controlled by adjusting the extent of the open end offset in correspondence to each heat exchanger model, the flat tubes cannot be provided as universal parts and the manufacturing process and the assembly process are bound to become complex and laborious. Furthermore, the flat tube manufacturing process includes a step for twisting and offsetting the open end portions and, for this reason, it is not ideal for mass production.

[0005] Accordingly, primary objects of the present invention are to provide a flat tube to be used in a heat exchanger, which allows the external dimensions of the heat exchanger to be minimized and can be provided as a universal part, to provide a heat exchanger that includes such a flat tube and a method for forming a flat tube that is optimal for mass production.

Means for Solving the Problems

[0006] The present invention achieves the objects described above by providing the flat tube for a heat exchanger, formed in the shape of a flat tube with two open ends and a fluid passage formed therein, having twisted portions near the open end portions and having the open end portions inserted at tube insertion holes extending along central lines of header pipes, which is characterized in that the open end portions of the flat tube are each offset relative to a central line of the flat tube extending along the lengthwise direction and that the extent of the offset is set so that the open end portion is aligned with a side edge of the flat tube.

[0007] Thus, in a heat exchanger with header pipes disposed adjacent to each other, a sufficient distance between the open end portions of two flat tubes disposed side-by-side can be assured by turning the offset open ends outward and, at the same time, since the open ends are not set too far apart, the header pipes can be positioned close to each other. In addition, when two flat tubes disposed side-by-side are connected to a common header pipe, the open end portions can be set close to each other by turning the offset open ends inward so as to minimize the diameter of the common header pipe.

[0008] In the flat tube for a heat exchanger, formed in the shape of a flat tube with two open ends and a fluid passage formed therein, having twisted portions near the open end portions and having the open end portions inserted at tube insertion holes ranging along central lines of header pipes and the open end portions thereof offset relative to the central line of the flat tube extending along the lengthwise direction, the measurement of the twisted portions taken along the length of the flat tube should be set within the range equal to or greater than the width of the flat tube and equal to or less than 1.3 times the width of the flat tube, so as to sustain the required level of heat exchanging performance while assuring sufficient durability.

[0009] The heat exchanger according to the present invention includes header pipes, flat tubes, each formed in the shape of a flat tube with two open ends and a fluid passage formed therein and having the open end portions thereof inserted at tube insertion holes formed at the header pipes, and fins disposed between the flat tubes set next to each other. The heat exchanger is characterized in that the tube insertion holes are formed as elongated holes ranging along the central lines of the header pipes, that portions of the flat tubes near the open end portions are twisted so as to match the shape of the elongated holes and the open end portions are offset relative to the central line of the flat tubes extending along the lengthwise direction and that the extent to which the open end portions are offset is set so as to align the open end portions with the side edges of the flat tubes. The heat exchanger adopting this structure can be provided as a compact unit.

[0010] More specifically, the header pipes include a first header pipe, a relay header pipe disposed so as to face opposite the first header pipe and a second header pipe disposed next to the first header pipe so as to face opposite the relay header pipe. The flat tubes include a plurality of first flat tubes disposed so as to communicate between the first header pipe and the relay header pipe and a plurality of second flat tubes disposed so as to communicate between the relay header pipe and the second header pipe. The open end portions of the first flat tubes inserted at the tube insertion holes at the first header pipe are offset toward the side edges of the first flat tubes further away from the second flat tubes, whereas the open end portions of the first flat tubes inserted at the tube insertion holes at the relay header pipe are offset toward the side edges of the flat tubes closer to the second flat tubes. The open end portions of the second flat tubes inserted at the tube insertion holes at the second header pipe are offset toward the side edges of the flat tubes further away from the first flat tubes, whereas the open end portions of the second flat tubes inserted at the tube insertion holes at the relay header pipe are offset toward the side edges of the second flat tubes closer to the first flat tubes.

[0011] Such a heat exchanger with a twin flow of coolant flowing in opposite directions can be provided as a compact unit.

[0012] The heat exchanger flat tube manufacturing method according to the present invention relates to a method for forming a flat tube used in a heat exchanger, formed in the shape of a flat tube with two open ends and a fluid passage formed therein and having twisted portions near the open end portions thereof, the open end portions inserted at tube insertion holes ranging along the central lines of header pipes and the open end portions offset relative to a central line of the flat tube extending along the lengthwise direction, characterized in that each open end of the flat tube and a portion of the flat tube away from the open end by a predetermined distance are clamped with chuck members and that the chuck member clamping the open end is made to slide along the offset direction while it rotates around an axis extending along the length of the flat tube.

[0013] In the method for forming a flat tube to be used in a heat exchanger, formed in the shape of a flat tube with two open ends and a fluid passage formed therein, having twisted portions near the open end portions, the open end portions inserted at tube insertion holes ranging along the central lines of header pipes and the open end portions offset relative to the central line of the flat tube extending along the lengthwise direction, each open end of the flat tube and a portion of the flat tube away from the open end by a predetermined distance may be clamped with chuck members, the chuck member clamping the open end may be made to slide along the clamping direction and then the chuck member may be made to rotate around an axis set along the central line of the flat tube extending along the lengthwise direction.

[0014] Alternatively, a portion of the flat tube away from an open end of the flat tube by a predetermined distance may be clamped with a chuck member, then the open end may be clamped with another chuck member while the open end is made to become displaced along the clamping direction and subsequently, the chuck member clamping the open end may be made to rotate around an axis set along the central line of the flat tube extending along the lengthwise direction.

[0015] As a further alternative, each open end of the flat tube and a portion of the flat tube away from the open end by a predetermined distance may be clamped with chuck members, the chuck member clamping the open end may be made to rotate around an axis extending along the length of the flat tube and then the chuck member may be made to slide along the offset direction.

[0016] The chuck member clamping the open end of the flat tube may be positioned close to the chuck member clamping the portion away from the open end by the predetermined distance while the chuck member clamping the open end rotates around the axis extending along the length of the flat tube so as to form a small twisted portion.

[0017] A predetermined range of clearance may be formed between the chuck member clamping the portion away from the open end of the flat tube by the predetermined distance and the flat tube.

[0018] Instead of the chuck member, a pair of rollers may be used to clamp the portion of the flat tube away from the open end by the predetermined distance.

[0019] The corners of the chuck member clamping the open end of the flat tube and the chuck member clamping the portion of the flat tube away from the open end by the predetermined distance, used to clamp the open end and the portion away from the open end by the predetermined distance and set on sides opposite from each other, may be beveled so as to prevent the chuck members from biting into the flat tube.

[0020] It is desirable that the bevel radius R be set so that R ≥ 0.5t is true with t representing the plate thickness of the flat tube.

Effect of the Invention

[0021] As described above, in the flat tube to be used in a heat exchanger according to the present invention, formed in the shape of a flat tube with two open ends and a fluid passage formed therein, having twisted portions formed near the open end portions and the open end portions inserted at tube insertion holes ranging along the central lines of header pipes, the open end portions of the flat tube are each offset relative to the central line of the flat tube extending along the length thereof by a specific extent so as to align the open end portions at a side edge of the flat tube. As a result, the external dimensions of the heat exchanger can be minimized and the flat tube can be provided as a universal part, thereby enabling simpler and less labor-intensive manufacturing and assembly.

[0022] In addition, by offsetting the twisted open end portions of the flat tube relative to the central line of the flat tube extending along the length thereof and setting the range of the twisted portions equal to or greater than the width of the flat tube and equal to or less than 1.3 times the width of the flat tube, the wasted area where fins cannot be mounted is reduced while assuring the required level of durability in the twisted portions.

[0023] While the flat tube described above needs to be formed by twisting the areas near the open end portions thereof around the axis extending along the length of the flat tube and offsetting the open end portions relative to the central axis of the flat tube extending along the length thereof, each open end and a portion of the flat tube away from the open end by the predetermined distance are each clamped via a chuck member during this process. As the open end of the flat tube and the portion of the flat tube away from the open end by the predetermined distance are clamped with the chuck members and the chuck member clamping the open end is made to slide along the offset direction while it rotates around the axis extending along the length of the flat tube, the range of material deformation is minimized.

[0024] In the method whereby each open end of the flat tube and a portion of the flat tube away from the open end by the predetermined distance are clamped with chuck members, the chuck member clamping the open end is made to slide along the offset direction and then the chuck member clamping the open end is made to rotate around an axis set along the central line of the flat tube extending along the length thereof, the portion of the flat tube away from the open end by the predetermined distance may be first clamped with the corresponding chuck member, the open end may then be clamped with the other chuck member while the open end is displaced along the offset direction and subsequently, the chuck member clamping the open end may be made to rotate around the axis set along the central line of the flat tube extending along the length thereof. Alternatively, the open end of the flat tube and the portion of the flat tube away from the open end by the predetermined distance may be clamped with chuck members, the chuck member clamping the open end may he made to rotate around the axis set along the length of the flat tube and then the chuck member clamping the open end may be made to slide along the offset direction. In either case, the chuck member movement is simplified and, thus, the mechanism is also simplified.

[0025] Furthermore, the chuck member clamping the open end of the flat tube may be positioned close to the chuck member clamping the portion away from the open end by the predetermined distance as the chuck member clamping the open end rotates around the axis set along the length of the flat tube. In this case, the extent to which the material is allowed to stretch is minimized and consequently, the material does not rupture readily. In addition, since the twisted area, which is not used in the heat exchange, is reduced, the area over which fins are mounted in the heat exchanger is increased, thereby assuring a greater heat exchanging area.

[0026] By creating a predetermined range of clearance between the chuck member used in conjunction with the portion away from the open end of the flat tube by the predetermined distance and the flat tube or by clamping the portion away from the open end by the predetermined distance with a pair of rollers instead of the chuck member, any stretching of the twisted portion can be absorbed with the whole flat tube.

[0027] By beveling the corners of the clamping portion of the chuck member used to clamp the open end of the flat tube and the chuck member used to clamp the portion away from the open end by the predetermined distance, which are located on sides opposite from each other, the chuck members are prevented from biting into the flat tube, and thus, the twisted portion does not become damaged.

Brief Description of the Drawings

[0028] 

FIG. 1 schematically illustrates the structure adopted in the heat exchanger according to the present invention, with FIG. 1(a) presenting a plan view of the heat exchanger, FIG. 1(b) presenting a front view of the heat exchanger, FIG. 1(c) showing the first and second header pipes and FIG. 1(d) showing the relay header pipe;

FIG. 2 shows the relationship between the header pipes and the flat tubes in a sectional view taken along line A-A in FIG. 1(b);

FIG. 3 shows one of the flat tubes in the heat exchanger, with FIG. 3(a) presenting a top view of the flat tube and FIG. 3(b) presenting a view of the flat tube taken along the horizontal direction;

FIGS. 4(a) to 4(c) show a first forming method that may be adopted to form a twisted portion near an open end of the flat tube;

FIGS. 5(a) to 5(d) show a second forming method that may be adopted to form a twisted portion near an open end of the flat tube;

FIGS. 6(a) to 5(d) show a third forming method that may be adopted to form a twisted portion near an open end of the flat tube;

FIGS. 7(a) to 5(d) show a fourth forming method that may be adopted to form a twisted portion near an open end of the flat tube;

FIGS. 8(a) to 5(d) show a fifth forming method that may be adopted to form a twisted portion near an open end of the flat tube;

FIG. 9 presents an example in which the second chuck member is positioned with a predetermined clearance 30 between itself and the flat tube during the process in which a twisted portion is formed near the open end of the flat tube;

FIG. 10 shows an example in which a pair of rollers are used in place of the second chuck member during the process in which a twisted portion is formed near the open end of the flat tube;

FIG. 11 shows an example in which the corners of the chuck members 21 and 22, via which the flat tube is clamped to form twisted portions 15 and 16, are beveled;

FIG. 12 presents a characteristics diagram of the relationship between the beveling radius and the twist width; and

FIG. 13 presents a characteristics diagram of the relationship among the twist width, the wasted area in the heat exchanger and the leak risk.

Explanation of Reference Numerals

[0029] 

1

heat exchanger

2

first header pipe

3

second header pipe

4

relay header pipe

5, 6

flat tube

13, 14

open end

15, 16

twisted portion

17

fin

Best Mode for Carrying Out the Invention

[0030] The following is an explanation of the best mode for carrying out the present invention, given in reference to the attached drawings.

[0031] A heat exchanger 1 in FIGS. 1 and 2 is used in a refrigerating cycle engaged in operation by using a high-pressure coolant, such as a CO2 coolant, sealed therein. The heat exchanger 1 includes first and second header pipes 2 and 3 disposed next to each other and a relay header pipe 4 disposed so as to face opposite the first and second header pipes 2 and 3. The first header pipe 2 and the relay header pipe 4 are made to communicate with each other via a plurality of first flat tubes 5, whereas the second header pipe 3 and the relay header pipe 4 are made to communicate with each other via a plurality of second flat tubes 6.

[0032] The first and second header pipes 2 and 3 each assume a tubular shape achieved by fitting a tube mounting plate 2b (3b) at a slit 4 (5) formed at the side surface of a pipe forming member 2a (3a) with a circular section. The two ends of each header pipe along the lengthwise direction are closed off by lids 2c (3c) inserted through notches 6 at the pipe forming member 2a (3a). At each tube mounting plate 2b or 3b, a plurality of tube insertion holes 7 (8) formed as elongated holes ranging along the lengthwise direction are present in a single straight row, as shown in FIG. 1(c).

[0033] Likewise, the relay header pipe 4 is formed by fitting a tube mounting plate 4b at a slit 9 formed at the side surface of a pipe forming member 4a with a circular section, with the two ends thereof along the lengthwise direction closed off with lids 4c inserted through notches 10 formed at the pipe forming member 4a. The pipe forming member 4a has a diameter greater than the diameters of the first and second header pipes 2 and 3, and the lateral width of the tube mounting plate 4b, too, is set greater than the lateral widths of the tube mounting plates 2b and 3b at the first and second header pipes 2 and 3. As shown in FIG. 1(d), a plurality of tube insertion holes 12, which are elongated holes ranging along the lengthwise direction, are formed at the tube mounting plate 4b in two straight rows.

[0034] The first flat tubes 5 and the second flat tubes 6 each have two open ends and a fluid passage formed therein. As shown in FIG. 3, the portions of each flat tube near its open ends 13 and 14 present on the two sides along the lengthwise direction are twisted by approximately 90° around an axis extending alone the length of the flat tube. In addition, the open end portions 13 and 14 are each offset relative to the central line of the flat tube extending along the length thereof to a specific extent so that the open end portion is aligned at a side edge of the flat tube 5 (6). One of the open end portions along the longer side of the flat tube 5 (6) is made to offset to a side opposite from the side to which the other open end portion is offset, so as to achieve point symmetry relative to the center of the flat tube.

[0035] One of the open end portions, i.e., the open end 13, at each first flat tube 5 is inserted at a tube insertion hole 7 at the first header pipe 2 and the open end portion 13 is also offset toward the side edge further away from the corresponding second flat tube 6. The other open end 14 of the first flat tube 5 is inserted at a tube insertion hole 12 at the relay header pipe 4 and the open end portion 14 is also offset toward the side edge closer to the corresponding second flat tube 6. In addition, one of the open end portions, i.e., the open end 14, at each second flat tube 5 is inserted at a tube insertion hole 8 at the second header pipe 3 and the open end portion 14 is also offset toward the side edge further away from the corresponding first flat tube 5. The other open end 13 of the first flat tube 5 is inserted at a tube insertion hole 12 at the relay header pipe 4 and the open end portion 13 is also offset toward the side edge closer to the corresponding second flat tube 6.

[0036] In the flat areas between the individual first flat tubes 5 and the flat areas between the individual second flat tubes 6 excluding the areas over which the twisted portions 15 and 16 are formed near the open end portions on the two sides, corrugated fins 17 are disposed. Next to the flat tubes on the two ends of the layered assembly, side plates 18 each having a U-shaped section are disposed via fins 17 over the flat areas. It is to be noted that the fins disposed between the first flat tubes 5 and the fins disposed between the second flat tubes 6 may be formed separately or may be formed as integrated parts.

[0037] Accordingly, a fluid having flowed into the first header pipe 2 is distributed into the first flat tubes 5, exchanges heat with the air passing through the fins 17 and is then collected into the relay header pipe 4. It then makes a U-turn inside the relay header pipe 4, is distributed into the second flat tubes 6, exchanges heat with the air passing through the fins 17 again, is collected into the second header pipe and flows out through the second header pipe 3. Thus, twin flows of coolant along opposite directions are achieved through the first flat tubes 5 and the second flat tubes 6. In addition, by allowing the air to travel from the side where the second flat tubes 6 are present, the air is made to flow along the direction opposite from the direction of the coolant flow through the flat tubes.

[0038] In addition, since the open end portions 13 and 14 of the flat tube 5 (6) are offset so as to align with the side edges of the flat tube 5 (6) (the open end portion near the first and second header pipes 2 and 3 is offset so as to align with the outer side edge and the open end portion near the relay header pipe 4 is offset so as to align with the inner side edge). Thus, the open end 13 and 14 of the flat tubes 5 and 6 on the side where the first and second header pipes 2 and 3 are present can be inserted at the tube insertion holes without having to set the first and second header pipes 2 and 3 over a significant distance from each other. In other words, the first and second header pipes can be disposed right next to each other. In addition, the open end portions of the first and second flat tubes 5 and 6 on the side where the relay header pipe 4 is present can be set close enough to each other, to allow the diameter of the relay header pipe to assume a smaller value. As a result, the heat exchanger with twin coolant flows in opposite directions can be provided as a compact unit. In addition, identical universal flat tubes can be used as the first and second flat tubes. Namely, universal parts can be used as the first and second flat tubes and this simplifies the manufacturing process and the assembly process. Thus, the flat tubes according to the present invention facilitate mass production.

[0039] Any of the following forming methods may be adopted to mass produce flat tubes described above having portions thereof near the open end portions twisted and the open end portions thereof offset.

[0040] In a first forming method shown in FIG. 4, each open end (13 or 14) of a flat tube (5 or 6) achieving predetermined dimensions and a portion 20 away from the open end by a predetermined distance are respectively clamped by a first chuck member 21 and a second chuck number 22, as shown in FIG. 4(a). Then, as shown in FIG. 4(b), the first chuck member 21 clamping the open end (13 or 14) is made to slide along the offset direction while the first chuck member rotates around an axis set along the length of the flat tube 5 (6) so as to twist the area near the open end (13 or 14) by approximately 90°, as shown in FIG. 4(c) and align the open end portion (13 or 14) at a side edge of the flat tube (5 or 6) as shown in FIG. 4(c). The twisting step and the offsetting step are executed concurrently and the speeds with which the individual steps are executed are controlled so that the twisting motion and the offsetting motion start simultaneously and end simultaneously.

[0041] In this forming method, the deformation attributable to the twisting motion of the portion near the open end (13 or 14) of the flat tube (5 or 6) and the deformation attributable to the offsetting motion occur at the same time, allowing the overall deformation of the material constituting the twisted portion (15 or 16) to occur over the minimum possible range. In other words, no redundant deformation occurs.

[0042] In a second forming method shown in FIG. 5, the flat tube (5 or 6) achieving predetermined dimensions is clamped at two positions, i.e., at an open end (13 or 14) and a portion 20 away from the open end by a predetermined distance, via a first chuck member 21 and a second chuck member 22 respectively, as shown in FIG. 5(a). Then, as shown in FIG. 5(b), the first chuck member 21 clamping the open end (13 or 14) is made to slide along the clamping direction and then the first chuck member is made to rotate around an axis set along the central line of the flat tube (5 or 6) extending along the length thereof, as shown in FIG. 5(c). As a result, the portion near the open end (13 or 14) becomes twisted by approximately 90° and the open end portion (13 or 14) becomes aligned at the side edge of the flat tube (5 or 6), as shown in FIG. 5(d).

[0043] In this forming method, the first chuck member is made to rotate around the axis set along the central line of the flat tube (5 or 6) extending along the length thereof after sliding the first chuck member 21 and, as a result, the movement of the chuck member 21 is simplified, which, in turn, allows the mechanism to be simplified.

[0044] In a third forming method shown in FIG. 6, a portion 20 of the flat tube (5 or 6) assuming predetermined dimensions, which is away from an open end (13 or 14) by a predetermined distance, is clamped with a second chuck member 22, as shown in FIG. 6(a). Then, as shown in FIG. 6(b), the open end (13 or 14) is clamped with the first chuck member 21 as it is displaced along the clamping direction by using the clamping force of the first chuck member 21. Next, the first chuck member 21 is made to rotate around an axis set along the central line of the flat tube (5 or 6) extending along the length thereof, as shown in FIG. 6(c). As a result, the portion near the open end (13 or 14) becomes twisted by approximately 90° and the open end portion (13 or 14) becomes aligned at a side edge of the flat tube (5 or 6), as shown in FIG. 6(d).

[0045] In this forming method, the open end (13 or 14) is displaced by the clamping force imparted from the first chuck member 21, and then, the first chuck member 21 is made to rotate around the axis set along the central line of the flat tube (5 or 6) extending along the length thereof to offset the open end portion. Thus, the movements of the chuck members 21 and 22 are further simplified, which, in turn, allows the mechanism to become further simplified.

[0046] In a fourth forming method shown in FIG. 7, the flat tube (5 or 6) achieving predetermined dimensions is clamped at two positions, i.e., at an open end (13 or 14) and the portion 20 away from the open end by the predetermined distance via the first chuck member 21 and the second chuck member 22 respectively, as shown in FIG. 7(a). Then, as shown in FIG. 7(b), the first chuck member 21 clamping the open end (13 or 14) is made to rotate around an axis set along the central line of the flat tube (5 or 6) extending along the length thereof. Subsequently, the first chuck member 21 is made to slide along the offset direction, as shown in FIG. 7(c) so as to twist the portion of the flat tube near the open end portion (13 or 14) by approximately 90° and align the open end (13 or 14) at a side edge of the flat tube (5 or 6), as shown in FIG. 7(d).

[0047] In the forming method described above, the first chuck member 21 is first rotated around the axis set along the central line of the flat tube (5 or 6) extending along the length thereof and then is made to slide. As a result, the movements of the chuck members 21 and 22 are simplified, which, in turn, allows the structure of the mechanism to be simplified.

[0048] In a fifth forming method shown in FIG. 8, the flat tube (5 or 6) achieving predetermined dimensions is clamped at two positions, i.e., at an open end (13 or 14) and a portion 20 thereof away from the open end by a predetermined distance, via a first chuck member 21 and a second chuck member 22 respectively, as shown in FIG. 8(a). Then, as shown in FIG. 8(b), the first chuck member 21 clamping the open end (13 or 14) is made to slide along the offset direction while it rotates around an axis set along the length of the flat tube (5 or 6) and, at the same time, the first chuck member 21 is positioned in close proximity to the second chuck member 22. As a result, the portion near the open end (13 or 14) becomes twisted by approximately 90° and the open end portion (13 or 14) becomes aligned at a side edge of the flat tube (5 or 6), as shown in FIG. 8(c). The twisting step and the offsetting step are executed concurrently, and the speeds with which the individual steps are executed are controlled so that the twisting motion and the offsetting motion start and end simultaneously.

[0049] The forming method described above minimizes the extent to which the material stretches, which, in turn, reduces the occurrence of material rupture. In addition, the dimensions of the twisted portions 15 and 16 (the twist width L), which are not used for the heat exchange, are minimized. This, in turn, assures a greater area in the heat exchanger 1 over which the fins 17 are mounted, thereby increasing the heat exchanging area.

[0050] It is to be noted that the first chuck member 21 may be positioned in close proximity to the second chuck member 22 while twisting the open end 13 (14) around the axis set along the length of the flat tube 5 (6) in any of the forming methods described above.

[0051] In addition, while the second chuck member 22 is used to clamp the portion 21 away from either the open end 13 (14) at the flat tube 5 (6) in the examples described above, a predetermined range of clearance 30 may be set between the second chuck member 22 and the flat two 5 (6), as shown in FIG. 9 or a pair of rollers 31, instead of the second chuck member 22, may be used to clamp the portion 20, as shown in FIG. 10.

[0052] In either case, the portion 20 away from the open end 13 (14) by the predetermined distance is not directly clamped by the chuck, which, in turn, allows any stretching of the flat tube (5 or 6) resulting from the twisting step or the offsetting step to be absorbed over the entire flat tube. As a result, any reduction in the wall thickness due to stretching of the material or rupture over the area that would otherwise be clamped by the chuck member can be prevented.

[0053] Furthermore, it is desirable to bevel the corners of the chuck members 21 and 22 over the areas used to clamp the flat tube to form the twisted portions 15 and 16, as shown in FIG. 11. It is desirable that the radius R of the beveled areas be set so that R ≥ 0.5t with t representing the plate thickness of the flat tube. While the chuck members do not bite into the flat tube even if the radius of the beveled areas is small, as long as the flat tube is twisted over a significant width range, the chuck members 21 and 22 are bound to bite into the flat tube to rupture or crack the flat tube over the clamped areas when the twist width (the measurement of the twisted portions taken along the length of the flat tube) L (see FIG. 3) is small, unless the radius of the beveled areas is increased. Accordingly, while a limit point exists, at which the twist width L needs to be increased as the bevel radius becomes smaller, as shown in FIG. 12, rupture and cracking over the twisted portions 15 and 16 can be prevented by setting the beveling radius R within the range described above.

[0054] In addition, it is desirable that twist width (the measurement of the twisted portions taken along the length of the flat tube) L (see FIG. 3) of the twisted portions 15 and 16 near the open end portions of the flat tube 5 (6) be set within a range of equal to or greater than the tube width W and equal to or less than 1.3 times the tube width W (1.0 W ≤ L ≤ 1.3 W). Once L becomes smaller than 1.0 W, the material stretches to a greater extent, which readily causes rupture and cracking of bent areas and increases the risk of fluid leak within the tube (see FIG. 13). Thus, L must be set equal to or greater than the tube width W in order to eliminate the risk of leak. If, on the other hand, the twist width becomes excessively large, the area where fins cannot be mounted increases. In other words, the size of wasted area that does not contribute to heat exchange increases. Accordingly, L should be set within the range described above by taking into consideration the minimum requirement for heat exchanging performance, so as to ensure that the heat exchanging performance is sufficient while eliminating the risk of a leak.

Claims

1. A flat tube (5,6) for a heat exchanger (1), formed in the shape of a flat tube with two open ends (13,14) and a fluid passage formed therein, having twisted portions (15,16) near the open ends (13,14) and having the open ends inserted at tube insertion holes (7,8,9) extending along central lines of header pipes (2,3,4), characterized in:

that said open end portions (13,14) of said flat tube (5,6) are each offset relative to a central line of said flat tube (5,6) extending along the lengthwise direction; and

that the extent of the offset is set so that said open end portion (13,14) is aligned with a side edge of said flat tube (5,6).

2. A flat tube (5,6) for a heat exchanger (1), formed in the shape of a flat tube with two open ends (13,14) and a fluid passage formed therein, having twisted portions (15,16) near the open ends (13,14) and having the open ends inserted at tube insertion holes (7,8,9) extending along central lines of header pipes (2,3,4), characterized in:

that said open end portions of said flat tube are each offset relative to a central line of said flat tube extending along the lengthwise direction; and

that the measurement of said twisted portions (15,16) taken along the length of said flat tube (5,6) is set within a range equal to or greater than the width of said flat tube (5,6) and equal to or less than 1.3 times the width of said flat tube (5,6).

3. A heat exchanger comprising header pipes (2,3,4), flat tubes (5,6), each formed in the shape of a flat tube with two open ends (13,14) and a fluid passage formed therein and having the open ends (13,14) thereof inserted at tube insertion holes (7,8,9) formed at said header pipes (2,3,4), and fins (17) disposed between said flat tubes (5,6) set next to each other, characterized in:

that said tube insertion holes (7,8,9) are formed as elongated holes ranging along the central lines of said header pipes (2,3,4);

that portions of said flat tubes (5,6) near the open ends (13,14) are twisted so as to match the shape of the elongated holes and said open end portions (13,14) are offset relative to a central line of said flat tubes (5,6) extending along the lengthwise direction; and

that the extent to which said open end portions (13,14) are offset is set so as to align said open end portions (13,14) with the side edges of said flat tubes (5,6).

4. A heat exchanger according to claim 3, characterized in:

that said header pipes (2,3,4) include a first header pipe, a relay header pipe disposed so as to face opposite said first header pipe (2) and a second header pipe (3) disposed next to said first header pipe (1) so as to face opposite the relay header pipe (4);

that said flat tubes (5,6) include a plurality of first flat tubes (5) disposed so as to communicate between said first header pipe (2) and the relay header pipe (4) and a plurality of second flat tubes (6) disposed so as to communicate between said relay header pipe (4) and said second header pipe (3);

that said open end portions of said first flat tubes (5) inserted at said tube insertion holes (4) at said first header pipe (2) are offset toward the side edges of said first flat tubes (5) further away from said second flat tubes (6), whereas said open end portions of said first flat tubes (5) inserted at the two poles at said relay header pipe (4) are offset so as to open on the side edges of said first flat tubes (5) closer to said second flat tubes(6) ; and

that said open end portions of said second flat tubes (6) inserted at said tube insertion holes (5) at said second header pipe (3) are offset toward the side edges of said second flat tubes (6) further away from said first flat tubes (5), whereas said open end portions (13,14) of said second flat tubes (6) inserted at said tube insertion holes (9) at said relay header pipe (4) are offset toward the side edges of said second flat tubes (6) closer to said first flat tubes (5).

5. A method for forming a flat tube (5,6) used in a heat exchanger (1), formed in the shape of a flat tube with two open ends (13,14) and a fluid passage formed therein and having twisted portions (15,16) near said open end portions (13,14) thereof, said open end portions (13,14) inserted at tube insertion holes (7,8,9) ranging along central lines of header pipes (2,3,4) and said open end portions (13,14) offset relative to a central line of said flat tube (5,6) extending along the lengthwise direction, characterized in:

that each opened end of said flat tube (5,6) and a portion of said flat tube away from the open end by a predetermined distance are clamped with a chuck member (21) ; and

that said chuck member (21) clamping the open end is made to slide along the offset direction while said chuck member (21) rotates along an axis extending along the length of said flat tube (5,6).

6. A method for forming a flat tube (5,6) used in a heat exchanger (1), formed in the shape of a flat tube (5,6) with two open ends (13,14) and a fluid passage formed therein and having twisted portions (15,16) near said open end portions (13,14) thereof, said open end portions (13,14) inserted at tube insertion holes (7,8,9) ranging along central lines of header pipes (2,3,4) and said open end portions (13,14) offset relative to a central line of said flat tube (5,6) extending along the lengthwise direction, characterized in:

that each open end of said flat tube (5,6) and a portion of said flat tube (5,6) away from the open end by a predetermined distance is clamped with chuck members (21,22); and

that the chuck member (21,22) clamping the open end (13,14) is made to slide along the clamping direction and then said chuck member (21,22) is made to rotate around an axis set along the central line of said flat tube (5,6) extending along the lengthwise direction.

7. A method for forming a flat tube (5,6) used in a heat exchanger (1), formed in the shape of a flat tube (5,6) with two open ends (13,14) and a fluid passage formed therein and having twisted portions (15,16) near said open end portions (13,14) thereof, said open end portions (13,!4) inserted at tube insertion holes (7,8,9) ranging along central lines of header pipes (2,3,4) and said open end portions (13,14) offset relative to a central line of said flat tube (5,6) extending along the lengthwise direction, characterized in:

that a portion of said flat tube (5,6) away from an open end of said flat tube (5,6) by a predetermined distance is clamped with a chuck member (22), then the open end is clamped with another chuck member (21) while the open end is made to become displaced along the clamping direction and subsequently, said chuck member (21) clamping the open end is made to rotate around an axis set along the central line of said flat tube (5,6) extending along the lengthwise direction.

8. A method for forming a flat tube (5,6) used in a heat exchanger (1), formed in the shape of a flat tube (5,6) with two open ends (13,14) and a fluid passage formed therein and having twisted portions (15,16) near said open end portions (13,14) thereof, said open end portions (13,14) inserted at tube insertion holes (7,8,9) ranging along central lines of header pipes (2,3,4) and said open end portions (13,14) offset relative to a central line of said flat tube (5,6) extending along the lengthwise direction, characterized in:

that each open end (13,14) of said flat tube (5,6) and a portion of said flat tube away from the open end by a predetermined distance is clamped with chuck members (21,22); and

that the chuck member (21) clamping the open end is made to rotate around an axis extending along the length of said flat tube (5,6) and then said chuck member (21) is made to slide along the offset direction.

9. A method for forming a flat tube to be used in a heat exchanger according to any of claims 5 through 8, characterized in:

that said chuck member (21) clamping the open end (13,14) of said flat tube (5,6) is positioned close to the chuck member (22) clamping said portion of said flat tube (5,6) away from the open end (13,14) by the predetermined distance while said chuck member (21) clamping the open end rotates around the axis extending along the length of said flat tube (5,6).

10. A method for forming a flat tube (5,6) to be used in a heat exchanger (1) according to any of claims 5 through 9, characterized in:

that a predetermined range of clearance is formed between said chuck member (21) clamping said portion away from the open end of said flat tube (5,6) by the predetermined distance and said flat tube (5,6).

11. A method for forming a flat tube (5,6) to be used in a heat exchanger (1) according to any of claims 5 through 9, characterized in:

that said portion of said flat tube (5,6) away from the open end by the predetermined distance is clamped by a pair of rollers (31) instead of said chuck member.

12. A method for forming a flat tube (5,6) to be used in a heat exchanger (1) according to any of claims 5 through 9, characterized in:

that corners of said chuck member (21) clamping the open end (13,14) of said flat tube (5,6) and said chuck member (22) clamping said portion of said flat tube (5,6) away from the open end (13,14) by the predetermined distance, used to clamp the open end and said portion away from the open end by the predetermined distance and set on sides opposite from each other are beveled.

13. A method for forming a flat tube (5,6) to be used in a heat exchanger (1) according to claim 12, wherein:

the bevel radius R is set so that R ≥ 0.5t is true with t representing the plate thickness of said flat tube (5,6).

Drawing