Heat exchanger

Abstract

A heat exchanger comprises a core portion including a plurality of tubes with a heat medium flowing therein and fins coupled to the outer surface of the tubes for promoting heat exchange with the heat medium, a pair of header tanks extending in a direction perpendicular to the length or the tubes at the longitudinal ends of the tubes and communicating with the tubes, and a pair of inserts arranged substantially parallel to the length of the tubes at the ends of the core portion to receive the heat transmitted from the core portion and having the ends thereof supported on the header tanks, each header tank includes a core plate with the tubes fixed thereon and a tank body providing the internal space of the tank with the core plate, and the ends of each insert are arranged outside the internal space of the tank and the insert is movably fitted in the header tank and along the length thereof and is immovable in a direction perpendicular to the length thereof.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a heat exchanger or, in particular, to a heat exchanger effectively applicable to a multiflow radiator for cooling the cooling water of the internal combustion engine of an automotive vehicle.

2. Description of the Related Art

A conventional multiflow radiator, as shown in FIG. 9, includes a core portion J4 having a plurality of tubes J2 and fins J3 coupled to the outer surface of the tubes J2, a header tank J5 communicating with the plurality of the tubes J2 and an insert J6 arranged at the end of the core portion J4 for reinforcing the core portion J4.

The header tank J5 is configured of a core plate J5a coupled with the tubes J2 and a tank body J5b providing the internal space of the tank. The tubes J2 and the insert J6 are coupled to the core plate J5a by brazing after being inserted into the header tank J5.

In this radiator, if the temperature of the cooling water flowing in the tubes J2 undergoes a change, the amount of thermal expansion of the tubes J2 directly affected by the cooling water is different from that of the insert J6 which is affected only indirectly.

The difference in thermal expansion amount between the tubes J2 and the insert J6 due to the temperature difference is liable to generate a thermal stress due to the thermal distortion in the root (coupling) between the tube J2 adjacent to the insert J6 and the core plate J5a. As a result, repeated changes in temperature, and changes in thermal stress, pose a problem that the tubes J2 in the neighborhood of the root may be broken.

To cope with this problem, an anti-thermal distortion heat exchanger structure has been proposed in which a part of the insert is formed in a U-shaped spring structure so that the thermal distortion of the tubes is reduced while, at the same time, suppressing the reduction in rigidity of the core portion (Japanese Patent No. 2927711).

The anti-thermal distortion structure described in Japanese Patent No. 2927711, however, poses the problem that the thermal distortion is concentrated on, and can break, the spring structure.

SUMMARY OF THE INVENTION

In view of the situation described above, the object of this invention is to provide a heat exchanger in which the rigidity of the core portion is secured while, at the same time, the thermal distortion is absorbed.

The conventional multiflow radiator includes a core portion having a plurality of tubes, a header tank communicating with the plurality of the tubes and an insert arranged at the end of the core portion for reinforcing the core portion. Also, the header tank is configured of a core plate coupled with the tubes and a tank body providing an internal space of the tank. The tubes and the insert are inserted in the head tank and coupled to the core plate. Under these conditions, the tubes are held by equal forces by the insert through the fins.

In this radiator, the temperature of the cooling water flowing in the tubes may undergo a change. The amount of thermal expansion is different between the tubes directly affected by the cooling water and the insert affected indirectly by the cooling water. The difference in the amount of thermal expansion between the tubes and the insert is liable to generate thermal stress due to thermal distortion at the root (coupling) between as the core plate and the tubes adjacent to the insert. A repeated change in temperature and hence a repeated chance in thermal stress poses the problem that the tubes in the neighborhood of the root may be broken.

To obviate this problem, an anti-thermal distortion structure has been proposed in which the thermal distortion is absorbed by cutting the longitudinal central portion of the insert (Japanese Unexamined Patent Publication No. 11-325783).

In another conventional anti-thermal distortion structure that has been proposed, an expansion having a substantially semicircular cross section is formed on the insert and adapted to be deformed to absorb the thermal distortion (Japanese Unexamined Patent Publication No. 11-237197).

In the anti-thermal distortion structure proposed in Japanese Unexamined Patent Publication No. 11-325783, however, the notch of the insert reduces the strength to hold the tubes. In the case where the internal pressure in the tubes increases and the tubes expand under the pressure of the cooling water, the notch of the insert is locally deformed due to the pressure in the tubes. As a result, the portion of the tube adjacent to the notch is deformed by expansion and may break.

The anti-thermal distortion structure proposed by Japanese Unexamined Patent Publication No. 11-237197 also poses a similar problem to Japanese Unexamined Patent Publication No. 11-325783 due to the fact that the tube holding strength of the expansion of the insert is reduced.

In view of this fact, the object of the present invention is to provide a heat exchanger in which the thermal distortion is reduced while, at the same time, the pressure resistance performance is secured.

In order to achieve this object, according to a first aspect of the invention, there is provided a heat exchanger comprising a core portion (4) including a plurality of tubes (2) with a heat medium flowing therein and fins (3) coupled to the outer surface of the tubes (2) for promoting heat exchange with the heat medium, a header tank (5) extending in a direction perpendicular to the length of the tubes (2) at each longitudinal end of the tubes (2) and communicating with the tubes (2), and an insert (6) arranged substantially parallel to the length of the tubes (2) at the end of the core portion (4) to receive the heat transmitted from the core portion (4) and having the ends thereof supported on the header tank (5), wherein the header tank (5) includes a core plate (5a) with the tubes (2) fixed thereon and a tank body (5b) providing the internal space of the tank with the core plate (5a), and wherein the ends of the insert (6) are arranged outside the internal space of the tank and the insert (6) is movably fitted in the header tank (5) and along the length and immovable in a direction perpendicular to the length thereof.

As described above, the insert (6) is movable in the direction along the length thereof in which the thermal distortion occurs and is immovable in the direction perpendicular to the length of the insert (6). In the case where thermal distortion occurs, therefore, the insert (6) moves and prevents the thermal stress from being concentrated at the coupling (root) between the tubes (2) and the core plate (5a). On the other hand, the insert (6) is immovable in the direction perpendicular to the direction in which the thermal distortion occurs, and therefore the strength of the core portion (4) can be maintained. As a result, the thermal distortion can be absorbed while at the same time securing the rigidity of the core portion (4).

Specifically, the fitting between the header tank (5) and the insert (6) has an insertion structure in which the end of the insert (6) is inserted in a corresponding through hole (5f, 12f) formed in the corresponding header tank (5). At the same time, the fitting between the header tank (5) and the insert (6) has an anti-brazing structure. As a result, the insert (6) can be fitted in the header tank (5) and is movable in the longitudinal direction.

The through hole (5f, 12f) may alternatively be formed in the surface perpendicular to the length of the tubes (2). With the extension of the tubes (2), therefore, the header tank (5) can move relative to the insert (6), and the thermal stress can be prevented from being concentrated on the insert (6).

Also, the through hole (5f, 12f) may be formed in the part of each core plate (5a) outside the tank body (5b) or a protrusion (12) may be formed outside each longitudinal end of the tank body (5b).

According to a second aspect of the invention, there is provided a heat exchanger wherein the fins (3) and the inserts (6) are formed of a bare material not covered by a brazing material.

As a result, a fillet is not formed in the coupling between the fins (3) and each insert (6) and, therefore, the heat of the tubes (2) adjoining the insert (6) is hardly passed to the insert (6). Thus, the temperature difference between a first tube (2) adjoining the insert (6) and a second tube (2) adjoining the first tube (2) can be further reduced. In this way, the thermal distortion can be suppressed even more.

In order to achieve the object described above, according to a third aspect of the invention, there is provided a heat exchanger comprising a core portion (4) including a plurality of tubes (2) with a heat medium flowing therein, a pair of header tanks (5) extending in a direction perpendicular to the length of the tubes (2) at the longitudinal ends of the tubes (2) and communicating with the tubes (2), and a pair of inserts (6) arranged substantially parallel to the length of the tubes (2) in such a manner as to contact the core portion (4) at the ends of the core portion (4) and each having the ends thereof supported on the corresponding header tank (5), wherein, in order to absorb the stress generated along the length of each insert (6), a stress absorber (74, 76, 77) is formed over the distance from the upstream side to the downstream side of the insert (6) in the air flow in such a manner that the most upstream end and the most downstream end of the stress absorber (74, 76, 77) in the air flow are not superposed, one on the other, along the direction of air flow.

By forming the stress absorber (74, 76, 77) in the insert (6) as described above, the stress generated along the length of the insert (6) can be absorbed. Also, in view of the fact that the stress absorber (74, 76, 77) is formed with the most upstream and the most downstream ends thereof in the air flow not superposed one on the other along the direction of air flow, the stress absorber (74, 76, 77), i.e. the portion of the insert (6) having a weak force to hold the tubes (2) can be dispersed over the length of the tubes (2). In the case where the internal pressure of the tubes (2) increases, therefore, the insert (6) is prevented from being deformed locally by the stress absorber (74, 76, 77). In this way, the tubes (2) are prevented from being broken by expansion and deformation. As a result, the thermal distortion can be reduced while at the same time the pressure resistance performance is secured.

Each tube (2) may have a flat cross section in the direction of air flow, and the insert (6) may include a base portion (71) having a surface substantially parallel to the flat surface (2a) of the tube (2) and extending substantially in parallel to the length of the tube (2), and ribs (72) projected in a direction substantially perpendicular to the base portion (71) from the ends of the base portion (71) in the direction of air flow and are extended substantially parallel to the length of the tube (2), wherein the portions of the ribs (72) corresponding to the most upstream and the most downstream ends of the stress absorber are formed with notches (73a, 73b), respectively, and the stress absorber constitutes a base portion-side expansion (74) having a substantially U-shaped cross section of the base portion (71).

A “substantial U shape” is a shape configured of two substantially opposed parallel surfaces and a substantially arcuate bottom surface connected to the two surfaces, in which the bottom surface may include a horizontal portion. In other words, the cross section may be substantially channel-shaped.

In this case, the base portion-side expansion (74) may be tilted with respect to the direction of air flow.

According to a fourth aspect of the invention, there is provided a heat exchanger wherein the base portion-side expansion (74) is split into a plurality of portions in the direction of air flow, which are connected to each other through slits (75) formed in the cross section of the base portion (71).

As a result, the length of the base portion-side expansion (74) along the direction of air flow can be reduced by the length of the slits (75) in the direction of air flow, thereby improving the moldability.

According to a fifth aspect of the invention, there is provided a heat exchanger wherein a plurality of the base portion-side expansions (74) are not aligned.

As a result, the distance between the notch (73a) on the upstream side in the air flow and the notch (73b) on the downstream side in the air flow can be increased without increasing the angle that the base portion-side expansion (74) forms with the direction of air flow. Thus, the pressure resistance performance can be positively secured without deteriorating the moldability of the base portion-side expansion (74).

According to a sixth aspect of the invention, there is provided a heat exchanger wherein the plurality of the base portion-side expansions (74) are tilted in different directions from the direction of air flow.

This configuration can reduce the spring back at the time of molding the plurality of the base portion-side expansions (74) and thus improve the moldability.

According to a seventh aspect of the invention, there is provided a heat exchanger wherein the plurality of the base portion-side expansions (74) are arranged substantially parallel to the direction of air flow in such a manner as not be superposed one on another in the direction of air flow.

This configuration eliminates the need of tilting the base portion-side expansions (74) from the direction of air flow and therefore the moldability can be improved.

According to an eighth aspect of the invention, there is provided a heat exchanger wherein each tube (2) has a flat cross section in the direction of air flow and the insert (7) includes a base portion (71) having a surface substantially parallel to the flat surface (2a) of the tube (2) and extending in the direction substantially parallel to the length of the tube (2) and ribs (72) projected in the direction substantially perpendicular to the base portion (71) and extending in the direction substantially parallel to the length of the tube (2), and wherein the stress absorber is a notch (76), cut in the base portion (71), diagonal to the direction of air flow.

As a result, the stress absorber can be configured of only the notch (76) formed in the insert (7), and therefore the pressure resistance performance can be secured with a simple configuration.

According to a ninth aspect of the invention, there is provided a heat exchanger wherein only one end of the notch (76) is open.

This configuration leaves one of the ribs (72) intact and can avoid reducing a rigidity more than requires. As a result, the force to hold the tubes (2) can be increased. Thus, the thermal distortion can be reduced while, at the same time, positively securing the pressure resistance performance.

Alternatively, the two ends of the notch (76) may be open or connected to each other.

Further, a plurality of the notches (76) may be formed.

Furthermore, only one end of each of a plurality of notches (76) may be open, and the open ends of the plurality of the notches (76) may be arranged alternately between the upstream side and the downstream side of the base portion (71) in the air flow.

In addition, the plurality of the notches (76) can be tilted in directions different from the direction of air flow.

According to a tenth aspect of the invention, there is provided a heat exchanger wherein the notch (76) is formed in the base portion (71), the portion of the pair of the ribs (72) adjoining the notch (76) is formed with a U-shaped rib-side expansion (77) in the direction of air flow, and the stress absorber includes the rib-side expansion (77).

By forming at least a notch (76) in the base portion (71) and the rib-side expansions (77) on a pair of the ribs (72) in this way, the stress generated along the length of each insert can be positively absorbed.

Incidentally, the reference numerals in parentheses, to denote the above means, are intended to show the relationships between the specific means which will be described later in an embodiment of the invention.

The present invention may be more fully understood from the description of preferred embodiments of the invention, as set forth below, together with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view showing a radiator 1 according to a first embodiment.

FIG. 2A is an enlarged view showing the essential parts of the radiator 1 according to the first embodiment.

FIG. 2B is an enlarged plan view of the fitting between the tank body 5b and the insert 6 as taken from the X direction in FIG. 2A.

FIG. 3A is an enlarged view showing the essential parts of the radiator 1 according to a second embodiment.

FIG. 3B is an enlarged plan view of the fitting between the tank body 5b and the insert 6 as taken from the X direction in FIG. 3A.

FIG. 4A is an enlarged view showing the essential parts of the radiator 1 according to a third embodiment.

FIG. 4B is an enlarged plan view of the fitting between the tank body 5b and the insert 6 as taken from the X direction in FIG. 4A.

FIG. 5A is an enlarged view showing the essential parts of the radiator 1 according to a fourth embodiment.

FIG. 5B is an enlarged plan view of the fitting between the tank body 5b and the insert 6 as taken from the X direction in FIG. 5A.

FIG. 6A is an enlarged view showing the essential parts of the radiator 1 according to fifth and sixth embodiments.

FIG. 6B is an enlarged plan view of the fitting between the tank body 5b and the insert 6 as taken from the X direction in FIG. 6A.

FIG. 7 is a bar chart comprising the temperature of the tubes and the inserts according to the prior art with that according to the seventh embodiment.

FIG. 8 is an enlarged view showing the essential parts of the radiator 1 according to a seventh embodiment.

FIG. 9 is an enlarged view showing the essential parts of the conventional radiator.

FIG. 10 is a front view of the radiator 1 according to an eighth embodiment.

FIG. 11A is a plan view showing the insert 6 according to the eighth embodiment.

FIG. 11B is a front view of FIG. 11A.

FIG. 12A is a plan view showing the insert 6 according to a ninth embodiment.

FIG. 12B is a front view of FIG. 12A.

FIG. 13A is a plan view showing the insert 6 according to a tenth embodiment.

FIG. 13B is a front view of FIG. 13A.

FIG. 14A is a plan view showing the insert 6 according to an eleventh embodiment.

FIG. 14B is a front view of FIG. 14A.

FIG. 15A is a plan view showing the insert 6 according to a twelfth embodiment.

FIG. 15B is a front view of FIG. 15A.

FIG. 16A is a plan view showing the insert 6 according to a thirteenth embodiment.

FIG. 16B is a front view of FIG. 16A.

FIG. 17A is a plan view showing the insert 6 according to a fourteenth embodiment.

FIG. 17B is a front view of FIG. 17A.

FIG. 18A is a plan view showing the insert 6 according to a fifteenth embodiment.

FIG. 18B is a front view of FIG. 18A.

FIG. 19A is a plan view showing the insert 6 according to a sixteenth embodiment.

FIG. 19B is a front view of FIG. 19A.

FIG. 20A is a plan view showing the insert 6 according to a seventeenth embodiment.

FIG. 20B is a front view of FIG. 20A.

FIG. 21 is a perspective view showing the insert 6 according to the seventeenth embodiment.

DESCRIPTION OF PREFERRED EMBODIMENTS

A first embodiment of the invention will be explained below with reference to FIGS. 1 and 2. The first embodiment is an application of a heat exchanger, according to this invention, to a radiator 1 for exchanging heat between the atmosphere (air) and the engine cooling water (heat medium) that has cooled an automotive engine. FIG. 1 is a front view of the radiator 1 according to the first embodiment, FIG. 2A an enlarged view of the essential parts of the first embodiment, and FIG. 2B an enlarged plan view of a fitting between a core plate 5a and one insert 6 taken from the X direction.

In FIG. 1, tubes 2 are where the engine cooling water flows. A plurality of the tubes 2 are formed flat, so that the direction of air flow (direction perpendicular to the page) coincides with the direction of the long diameter, and are arranged in parallel to each other in the horizontal direction so that the longitudinal direction coincides with the vertical direction thereof.

The flat surfaces 2a (FIG. 2A) on the two sides of each tube 2 are coupled with corrugated fins 3, whereby the heat transfer with the air is increased to promote the heat exchange between the engine cooling water and the air. The substantially rectangular heat exchange unit including the tubes 2 and the fins 3 is hereinafter referred to as a core portion 4.

A header tank 5 extends in the direction horizontal direction in this embodiment) perpendicular to the length of the tubes 2 at each longitudinal end (upper and lower ends in this embodiment) of the tubes 2 and communicates with the plurality of the tubes 2. Each header tank 5 includes a core plate 5a with the tubes 2 coupled by insertion thereinto and a tank body 5b providing the internal space of the tank with the core plate 5a. According to the first embodiment, the core plate 5a is formed of a metal (such as an aluminum alloy) and the tank body 5b is formed of resin.

As shown in FIG. 2A, packing (not shown), made of an elastic material such as rubber, is arranged in a groove 5c formed along the whole peripheral edge of the core plate 5a thereby to close the gap between the tank body 5b and the core plate 5a in liquid tight fashion. A plurality of hooks 5d are erected on the peripheral edge of the core plate 5a. By fixedly caulking the hooks 5d on the flange formed on the outer peripheral edge of the tank body 5b, the tank body 5b is assembled on the header plate 5a.

The tank body 5b is fixedly caulked on the core plate 5a by plastic deformation of a part of the core plate 5a pressed against the tank body 5b.

An insert 6 extending substantially parallel to the length of the tubes 2 to reinforce the core portion 4 is arranged at each end of the core portion 4. This insert 6 includes a base portion 6a having a surface substantially parallel to the flat surface 2a of the tubes 2 and extending in a direction substantially parallel to the length of the tubes 2, and ribs 6b projected in a direction (horizontal direction in this embodiment) substantially perpendicular to the base portion 6a and extending in a direction substantially parallel to the length of the tubes 2. In the insert 6, the ribs 6b are arranged at the ends of the base portion 6a in a direction perpendicular to the length of the base portion 6a. Thus, the cross section of the insert 6 is substantially channel-shaped with an open side far from the core portion 4. Also, the insert 6 is in contact with the core portion 4 from which heat is transferred.

A support structure for the core plate 5a and the insert 6 will be explained.

According to the first embodiment, the ends of the core plate 5a are extended outward of the tank body 5b. Specifically, the ends of the core plate 5a assembled on the tank body 5b are exposed. Each end of the core plate 5a is formed with a through hole 5f in the direction perpendicular to the length of the header tank 5 on the surface of the header tank 5 substantially perpendicular to the length of the tubes 2.

The base portion 6a of the insert 6 is bent in an opposed relation to the groove 5c of the core plate 5a, after which the end of the base portion 6a (hereinafter referred to the insert end portion 6c) is extended toward the through hole 5f of the core plate 5a and, with the insert end portion 6c inserted in the through hole 5f, is fitted to the core plate 5a. In other words, the fitting between the core plate 5a and the insert 6 constitutes an insertion structure.

The fitting between the core plate 5a and the insert 6 constitutes an anti-brazing structure. Specifically, the brazing material is cut off from the inner wall portion of the through hole 5f and the portion of the insert end portion 6c corresponding to the through hole 5f. As a result, the fitting between the core plate 5a and the insert 6 is not brazed.

According to the first embodiment, the tubes 2, the fins 3, the core plates 5a and the inserts 6 making up base members are all formed of an aluminum alloy, and aluminum such as A4045 is used as a filler material for brazing. The tubes 2, the fins 3, the core plates 5a and the inserts 6 are all bonded by brazing except for the fitting between each core plate 5a and the corresponding insert 6.

According to the first embodiment, each tube 2 is clad (covered) with a brazing material (filler material), and so is the surface of the core plate 5a near to the care portion 4. The fins 3 are formed of an aluminum material not clad with the brazing material (hereinafter referred to as a bare material).

In FIG. 1, a cooling water inlet 7a is connected to the outlets side of the engine cooling water, and a cooling water outlet 6b is connected to the inlet side of the engine cooling water. Pins 8 are protruded members for assembling the radiator 1 on the vehicle body, i.e. a carrier (radiator supporter or front end panel) not shown. Cap 9 is a pressure-type radiator cap, and plug 10 constitutes a cock for closing the drain port to drain off the engine cooling water from the radiator 1.

Next, a method of fabricating the radiator 1 according to the first embodiment will be briefly explained.

The fins 3, the tubes 2 and each insert 6 are assembled as shown in FIG. 2A and the insert end portion 6c is inserted into the through hole 5f. This assembly, while being maintained in its state by a jig such as a wire, is heated in a furnace thereby to braze the fins 3, the tubes 2 and the insert 6. In the process, the fitting between the core plate 5a and the insert 6 is not brazed in view of the fact that the brazing material on the inner wall of the through hole 5f of the core plate 5a and the part of the insert end portion 6c corresponding to the through hole 5f is cut off.

In assembling the fins 3, the tubes 2 and the insert 6, the fins 3 are pressed and elastically deformed, so that even in the case where the thickness of the fins 3 is reduced by brazing, the fins 3 and the tubes 2 can be kept in contact with each other.

As described above, the fitting between the core plate 5a and the insert 6 makes up an insertion structure while, at the same time, it is prevented from being brazed. As a result, the insert 6 is made movable in the direction (along the length of the insert 6) in which the thermal distortion occurs, while the movement of the insert 6 is restricted in the direction perpendicular to the direction in which the thermal distortion occurs. At the time of thermal distortion, therefore, the movement of the insert 6 prevents the thermal stress from being concentrated at the coupling of the tube 2 and the core plate 5a. On the other hand, the insert 6 is not moved in a direction perpendicular to the direction in which thermal distortion occurs and, therefore, the strength of the core portion 4 is maintained. Thus, while securing the rigidity of the core portion 4, the thermal distortion can be absorbed.

Next, a second embodiment of the invention will be explained with reference to FIG. 3. The second embodiment is different front the first embodiment in the anti-brazing structure. In FIG. 3, component parts similar or identical to those of the first embodiment are designated by the same reference numerals, respectively, and not described again.

FIG. 3A is an enlarged view of the essential parts of the radiator 1 according to the second embodiment, and FIG. 3B an enlarged plan view of the fitting between the core plate 5a and the insert 6 as taken from the X direction in FIG. 3A. As shown in FIG. 3A, according to the second embodiment, a collar 11 of bare material is interposed between the through hole 5f and the insert end portion 6c, so that the inner wall of the through hole 5f and the insert end portion 6c are kept out of direct contact with each other.

As a result, the fitting between the core plate 5a and the insert 6 is prevented from being brazed, and therefore effects similar to those of the first embodiment are achieved.

Next, a third embodiment of the invention will be explained with reference to FIGS. 4A, 4B. The third embodiment is different from the first embodiment in the anti-brazing structure. In FIGS. 4A, 4B, component parts similar or identical to those of the first embodiment are designated by the same reference numerals, respectively, and not described again.

FIG. 4A is an enlarged view of the essential parts of the radiator 1 according to the third embodiment, and FIG. 4B an enlarged plan view of the fitting between the core plate 5a and the insert 6 as taken from the X direction in FIG. 4A. As shown in FIG. 4A, according to the third embodiment, the through hole 5f is formed by burring the brazing material surface (the surface clad with the brazing material) outside.

As a result, the brazing material surface of the core plate 5a and the insert end portion 6c are kept out of contact with each other. At the same time, the brazing material on the portion of the insert end portion 6c corresponding to the through hole 5f is cut off and, therefore, the fitting between the core plate 5a and the insert 6 is prevented from being brazed. Thus, effects similar to those of the first embodiment are produced.

Next, a fourth embodiment of the invention will be explained with reference to FIG. 5. The fourth embodiment is different from the first embodiment in the anti-brazing structure. In FIG. 5, component parts similar or identical to those of the first embodiment are designated by the same reference numerals, respectively, and not described again.

FIG. 5A is an enlarged view of the essential parts of the radiator 1 according to the fourth embodiment, and FIG. 5B an enlarged plan view of the fitting between the core plate 5a and the insert 6 taken from the X direction in FIG. 5A. As shown in FIG. 5A, the insert end portion 6c according to the fourth embodiment is inserted in the through hole 5f with the brazing material surface bent inward.

As a result, the brazing material surface of the insert 6 and the inner wall surface of the through hole 5f are kept out of contact with each other. Also, as the brazing material on the inner wall surface of the through hole 5f is cut off, the fitting between the core plate 6a and the insert 6 is prevented from being brazed. Thus, effects similar to those of the first embodiment can be obtained.

Next, a fifth embodiment of the invention will be explained with reference to FIGS. 6A, 6B. The fifth embodiment is different from the first embodiment in that the insert 6 is fitted in the tank body 5. In FIG. 6, component parts similar or identical to those of the first embodiment are designated by the same reference numerals, respectively, and not described again.

FIG. 6A is an enlarged view of the essential parts of the radiator 1 according to the fifth embodiment, and FIG. 6B an enlarged plan view of the fitting between the tank body 5b and the insert 6 taken from the X direction in FIG. 6A. As shown in FIG. 6A, each longitudinal end of the tank body 5b is formed with a protrusion 12 outside of the tank body 5b. The protrusion 12 is formed of resin and is molded integrally with the tank 5b.

The protrusion 12 is formed with a through hole 12a. The through hole 12a is configured to be fitted on the core plate 5a with the insert end portion 6a inserted in the through hole 5f.

As described above, by fitting the insert end portion 6c in the protrusion 12 of the tank body 5b of resin, the fitting between the insert 6 and the tank body 5b is prevented from being brazed and, therefore, effects similar to the first embodiment are achieved.

Next, a sixth embodiment of the invention will be explained with reference to FIGS. 6A, 6B. The sixth embodiment is different from the fifth embodiment in that the tank body 5b is formed of metal. In FIGS. 6A, 6B, component parts similar or identical to those of the fifth embodiment are designated by the same reference numerals, respectively, and not described again.

According to the sixth embodiment, the tank body 5b and the protrusion 12 are formed of a metal (such as aluminum alloy), and the protrusion 12 is formed integrally with the tank body 5b. Also, the brazing material on the fitting between the tank body 5b and the insert 6, i.e. the inner wall portion of the through hole 12a and the portion of the insert end portion 6c corresponding to the through hole 12a is cut off.

As described above, the insert 6 is fitted in the protrusion 12 of the tank body 5b and the brazing material on the fitting between the tank body 5b and the insert 6 is cut off thereby to prevent the brazing. Thus, effects similar to those or the first embodiment are achieved.

Next, a seventh embodiment of the invention is explained with reference to FIGS. 7, 8. The seventh embodiment is different from the first embodiment in that both the fins 3 and the inserts 6 are formed of a bare material. In FIGS. 7, 8, component parts similar or identical to those of the first embodiment are designated by the same reference numerals, respectively, and are not described again.

FIG. 7 is a bar chart comparing the temperature of the tubes and the inserts between the prior art and the seventh embodiment, and FIG. 8 an enlarged view showing the essential parts of the radiator 1 according to the seventh embodiment. In FIG. 8, the tube adjacent to the insert 6 is called a first tube 2A, the tube adjacent to the first tube 2A a second tube 2B, and the tube adjacent to the second tube 2B a third tube 2C.

In the prior art, the coupling between the tube J2 or the insert J6 (base portion J6a) and the fins J3, as shown by the black parts in FIG. 9, is formed with a fillet (solid mass of a filler material) and is firmly brazed. As shown in FIG. 7, therefore, the first tube J2A is liable to be deprived of heat by the insert J6 to cause an increased temperature difference between the first tube J2A and the second etude J2B.

The seventh embodiment, on the other hand, has a similar configuration to the first embodiment, and uses a bare material for the insert 6. As shown in FIG. 8, therefore, each coupling between the fin 3 and the insert 6 is not formed with a fillet. As a result, the first tube 2A is not easily deprived of heat by the insert 6. As shown in FIG. 7, therefore, the temperature difference between the first tube 2A and the second tube 2B can be decreased. Thus, the thermal distortion can be reduced.

Other embodiments are explained below. As described above, in order to prevent the brazing of the fitting between the header tank 5 and the insert 6, the brazing material on the portion of the insert end portion 6c corresponding to the through holes 5f, 12a is cut off according to the first to third and sixth embodiments, and the insert end portion 6c is bent with the brazing material surface inside according to the fourth embodiment. The invention, however, is not limited to these configurations. For example, the portion of the insert end portion 6c corresponding to the through holes 5f, 12a may be coated with an anti-brazing agent.

Also, a clad material may be used for the fins 3 and a bare material For the insert 6. Although the fins 3 and the insert 6 are brazed, the fitting between the header tank 5 and the insert 6 is not brazed. Thus, effects similar to the first embodiment can be produced.

In a similar fashion, in order to prevent the brazing of the fitting between the header tank 5 and the insert 6, the brazing material on the portion of the insert end portion 6c corresponding to the through hole 5f, 12a is cut off according to the first to fourth and sixth embodiments, the collar member 11 of a bare material is interposed between the through hole 5f and the insert end portion 6c according to the second embodiment, and the through hole 5f is formed by burring according to the third embodiment. The intention, however, is not limited to these configurations, but an anti-brazing agent may be coated on the inner wall of the through hole 5f, 12a.

An eighth embodiment of the invention is explained below with reference to FIGS. 10, 11. This embodiment is an application of the heat exchanger according to this invention to the radiator 1 for exchanging heat between the air and the cooling water (heat medium) that has cooled the vehicle engine. FIG. 10 is a front view of the radiator 1 according to the eighth embodiment.

In FIG. 10, the cooling water flows in the tubes 2. Each tube 2 is flat so that the direction of air flow (direction perpendicular to the page) coincides with the direction of the long diameter, and a plurality of the tubes 2 are arranged in parallel to each other in vertical direction in such a manner that the longitudinal direction thereof coincides with the horizontal direction.

The flat surfaces on the two sides of each tube 2 are coupled with the corrugated fins 3, whereby the heat transfer area with the air is increased to promote the heat exchange between the cooling water and the air. The substantially rectangular heat exchange unit including the tubes 2 and the fins 3 is hereinafter referred to as the core portion 4.

The header tank 5 extends in the direction (vertical direction in this embodiment) perpendicular to the length of the tubes 2 at each longitudinal end (horizontal ends in this embodiment) of the tubes 2 and communicates with a plurality of the tubes 2. The header tank 5 includes a core plate 5a coupled with the tubes 2 inserted therein and a tank body 5b providing the internal space of the tank with the core plate 5a.

The header tank 5 includes a cooling water inlet 7a connected to the cooling water cutlet side of the engine (not shown) and a cooling water outlet 7b connected to the cooling water inlet side of the engine. Also, an insert 6 for reinforcing the core portion 4 extends in the direction substantially parallel to the length of the tubes 2 at each end of the core portion 4.

FIG. 11A is a plan view showing the insert 6 according to the eighth embodiment, and FIG. 11B a front view of FIG. 11A. As shown in FIGS. 11A, 11B, the insert 6 includes a base portion 71 having a surface substantially parallel to the flat surface 2a of the tubes 2 and extending in the direction substantially in parallel to the length of the tubes 2 and a pair of ribs 72 projected from the ends of the base portion 71 along the air flow in the direction (direction of tube stack) substantially perpendicular to the base portion 71 and extending in a direction substantially parallel to the length of the tubes 2.

The pair of the ribs 72 of the insert 6 are formed with notches 73a, 73b, respectively, cut inward in the direction of the tube stack from the outer end of the ribs 72 in the direction of the tube stack. Also, the notch (hereinafter referred to the upstream side notch 73a) formed in the rib 72 on the upstream side in the air flow and the notch (hereinafter referred to as the downstream side notch 73b) formed in the rib 72 on the downstream side in the air flow are arranged in such a manner as not be superposed, one on the other, in the direction of air flow.

The base portion 71 of the insert 6 is formed with a base portion-side expansion 74. The base portion-side expansion 74 is formed by expanding the cross section of the base portion 71 substantially into a U shape in the direction of the tube stack. Also, the base portion-side expansion 74 is so configured to be deformed to absorb the tension or compression stress generated along the length of the insert 6.

As shown in FIG. 11A, the base portion-side expansion 74 is formed to connect the upstream-side notch 73a and the downstream-side notch 73b and is arranged diagonally to the direction of air flow.

As explained above, the base portion 71 of the inset 6 is formed with the base portion-side expansion 74 having a substantially U-shaped cross section, and therefore the stress generated along the length of the insert can be absorbed.

Also, by arranging the base portion-side expansion 74 diagonally to the direction of air flow, the stress absorber of the insert 6, i.e. the portion of the insert 6 weak in the force to hold the tube 2 can be dispersed over the length of the tube. As a result, in the case where the internal pressure of the tube 2 increases, the base portion-side expansion 74 of the insert 6 can be prevented from being locally deformed. Thus, the tube 2 is prevented from being deformed by expansion thereby preventing the breakage of the tube 2.

Thus, the thermal distortion is reduced and the pressure resistance performance is secured at the same time.

Next, a ninth embodiment of the invention will be explained with reference to FIGS. 12A, 12B. In FIGS. 12A, 12B, component parts similar or identical to those of the eighth embodiment are designated by the same reference numerals, respectively, and are not described again. FIG. 12A is a plan view showing the insert 6 according to the ninth embodiment, and FIG. 12B a front view of FIG. 12A.

As shown in FIGS. 12A, 12B, the base portion 71 of the insert 6 according to this embodiment is formed with a slit 75. According to this embodiment, the slit 75 is arranged with the length thereof substantially parallel to the length of the tubes 2.

Also, the base portion-side expansion 74 is split into two parts in the direction of air flow. Of the two base portion-side expansions 74 thus split, the one arranged upstream in the air flow is called a first base portion-side expansion 74a and the one arranged downstream in the air flow a second base portion-side expansion 74b.

The two base portion-side expansions 74a, 74b are connected to each other through the slit 75. Also, the two base portion-side expansions 74a, 74b are arranged out of alignment. According to this embodiment, the two base portion-side expansions 74a, 74b are connected to the longitudinal ends, respectively, of the slit 75.

As a result, effects similar to those of the eighth embodiment are produced.

Further, in view of the fact that the base portion-side expansion 74 is split into two parts in the direction of air flow and the two base portion-side expansions 74a, 74b thus split are connected to each other through the slit 75, the length of the base portion-side expansion 74 can be reduced by the length of the slit 75 in the direction of air flow. As a result, the moldability is improved.

Also, in view of the fact that the two base portion-side expansions 74a, 74b are not arranged in alignment, the distance between the upstream-side notch 73a and the downstream-side notch 73b in the air flow can be increased without changing the angle of the base portion-side expansion 74 with respect to the direction of air flow. As a result, the pressure resistance performance can be positively secured without reducing the moldability of the base portion-side expansion 74.

Next, a tenth embodiment of the invention will be explained with reference to FIGS. 13A, 13B. In FIGS. 13A, 13B, component parts similar or identical to those of the ninth embodiment are designated by the same reference numerals, respectively, and not described again. FIG. 13A is a plan view showing the insert 6 according to the tenth embodiment, and FIG. 13B a front view of FIG. 13A.

As shown in FIG. 13A, the two base portion-side expansions 74a, 74b according to this embodiment are tilted in opposite directions with respect to the direction of air flow.

More specifically, the end of the slit 75 connected with the first base portion-side expansion 74a is arranged nearer to the downstream-side notch 73b than to the upstream-side notch 73a in the direction of the length of the tube. The end of the slit 75 connected with the second base portion-side expansion 74b, on the other hand, is arranged farther from the upstream-side notch 73a than from the downstream-side notch 73b in the direction along the length of the tube.

As a result, effects similar to those of the ninth embodiment are produced.

Further, in view of the fact that the two base portion-side expansions 74a, 74b are tilted in opposite directions in the direction of air flow, the spring back when molding the base portion-side expansions 74a, 74b can be reduced for an improved moldability.

Next, an eleventh embodiment of the invention will be explained with reference to FIGS. 14A, 14B. In FIGS. 14A, 14B, component parts similar or identical to those of the ninth embodiment are designated by the same reference numerals, respectively, and are not described again. FIG. 14A is a plan view showing the insert 6 according to the eleventh embodiment, and FIG. 14B a front view of FIG. 14A.

As shown in FIGS. 14A, 14B, the base portion 71 of the insert 6 according to this embodiment is formed with two slits 75. According to this embodiment, the two slits 75 are arranged with the length thereof substantially parallel to the length of the tubes. Of the two slits 75, the one arranged on the upstream side in the air flow is called a first slit 75a and the one arranged downstream side in the air flow a second slit 75b.

The base portion-side expansion 74 is split into three parts in the direction along the air flow. The resultant three base portion-side expansions 74a to 74c are arranged substantially parallel to the direction of air flow in such a manner as not to be superposed, one on another, in the direction of air flow. Of the three base portion-side expansions 74, the one arranged upstream in the air flow is called a first base portion-side expansion unit 74a, the one arranged downstream in the air flow a second base portion-side expansion 74b, and the one arranged between the first base portion-side expansion 74a and the second base portion-side expansion 74c a third base portion-side expansion 74c.

As shown in FIG. 14A, the three base portion-side expansions 74a to 74c are coupled to each other through the two slits 75a, 75b. More specifically, one end of the first slit 75a along the tube length is connected to the first base portion-side expansion 74a, and the other end thereof to the third base portion-side expansion 74c. The downstream end of the third base portion-side expansion 74c alone the direction of air flow is connected to one end of the second slit 75b along the tube length, and the other end thereof to the second base portion-side expansion 74b.

As a result, effects similar to those of the ninth embodiment are produced.

Further, in view of the fact that the three base portion-side expansions 74a to 74c are formed substantially in parallel to the direction of air flow in such a manner as not to be superposed, one on another, in the direction of air flow, the base portion-side expansion 74 is not required to be tilted from the direction of air flow, and therefore the moldability is improved.

Next, a twelfth embodiment of the invention will be explained with reference to FIGS. 15A and 15B. In FIGS. 15A and 15B, the component parts similar or identical to those of the eighth embodiment are designated by the same reference numerals, respectively, and not described any more. FIG. 15A is a plan view showing the insert 6 according to the twelfth embodiment, and FIG. 15B a front view of FIG. 15A.

As shown in FIGS. 15A and 15B, the insert 6 according to this embodiment is formed with a notch 76. The notch 76 is formed by cutting the base portion 71 diagonally from one end to the other end in the direction of air flow in such a manner as to be tilted from the direction of air flow. As a result, the upstream and downstream ends of the notch 76 in the air flow are prevented from being superposed, one on the other, in the direction of air flow.

According to this embodiment, the notch 76 is formed continuously from the upstream end to the downstream end of the base portion 71 in the air flow. Also, the notch 76 is formed continuously in the ribs 72. More specifically, the portion of each rib 72 adjacent to the end of the notch 76 is notched substantially in parallel to the direction along the tube stack. According to this embodiment, therefore, the insert 6 is completely separated by the notch 76.

As described above, by forming the notch 76 in the base portion 71 of the insert 6, the stress generated along the length of the insert 6 can be absorbed.

Also, in view of the fact that the notch 76 is arranged diagonally with respect to the direction of air flow, the stress absorber of the insert 6, i.e. the portion of the insert 6 having little strength to hold the tube 2 can be dispersed along the tube length. In the case where the internal pressure of the tube 2 increases, therefore, the tube 2 is prevented from being locally deformed by expansion, thereby making it possible to prevent the tube 2 being broken.

Thus, the thermal distortion can be reduced while, at the same time, the pressure resistance performance is secured.

Further, in view of the fact that the stress generated along the length of the insert 6 can be absorbed simply by forming the notch 76 in the insert 6, the pressure resistance performance can be secured with a sample configuration.

Next, a thirteenth embodiment of the invention will be explained with reference to FIGS. 16A and 16B. In FIGS. 16A and 16B, component parts similar or identical to those of the twelfth embodiment are designated by the same reference numerals, respectively, and are not described again. FIG. 16A is a plan view showing the insert 6 according to the thirteenth embodiment, and FIG. 16B a front view of FIG. 16A.

As shown in FIGS. 16A and 16B, only one end (the upstream end in the air flow in this embodiment) of the notch 76 according to this embodiment is open. More specifically, one end of the notch 76 in the direction of air flow is connected to an end of the base portion 71 in the direction of air flow, and the other end (the downstream end in the air flow in this embodiment) of the notch 76 is located within the base portion 71. In other words, according to this embodiment, the insert 6 is not completely separated by the notch 76.

As described above, by opening only one end of this notch 76, one rib 72 is left intact and, therefore, an undesired rigidity reduction can be avoided. As a result, the force to hold the tubes 2 can be increased, thereby reducing the thermal distortion while, at the same time, positively securing the pressure resistance performance.

Next, a fourteenth embodiment of the invention will be explained with reference to FIGS. 17A and 17B. In FIGS. 17A and 17B, component parts similar or identical to those of the thirteenth embodiment are designated by the same reference numerals, respectively, and are not described again. FIG. 17A is a plan view showing the insert 6 according to the fourteenth embodiment, and FIG. 17B a front view of FIG. 17A.

As shown in FIGS. 17A and 17B, the base portion 71 of the insert 6 according to this embodiment is formed with three parallel notches 76. The three notches 76 are all formed by cutting the base portion 71, from the upstream end toward the downstream end thereof in the air flow.

By forming the three notches 76 in the base portion 71 in this way, the stress generated in the direction along the length of the insert 6 can be positively absorbed. Thus, the thermal distortion can be reduced while, at the same time, the pressure resistance performance is secured.

Next, a fifteenth embodiment of the invention will be explained with reference to FIGS. 18A and 18B. In FIGS. 18A and 18B, component parts similar or identical to those of the fourteenth embodiment are designated by the same reference numerals, respectively, and are not described again. FIG. 18A is a plan view showing the insert 6 according to the fifteenth embodiment, and FIG. 18B a front view of FIG. 18A.

As shown in FIGS. 18A and 18B, the base portion 71 of the insert 6 is formed with three parallel notches 76. According to this embodiment, the notch 76a arranged outside and along the tube length is formed by cutting the base portion 71, from the upstream end toward the downstream end in the air flow. The notch 76b arranged inside in the direction of tube stack, on the other hand, is formed by cutting the base portion 71 from the downstream end to the upstream end in the air flow.

As a result, effects similar to those of the fourteenth embodiment described above are achieved.

Next, a sixteenth embodiment of the invention will be explained with reference to FIGS. 19A and 19B. In FIGS. 19A and 19B, component parts similar or identical to those of the fourteenth embodiment are designated by the same reference numerals, respectively, and are not described again. FIG. 19A is a plan view showing the insert 6 according to the sixteenth embodiment, and FIG. 19B a front view of FIG. 19A.

As shown in FIGS. 19A and 19B, the base portion 71 of the insert 6 according to this embodiment is formed with four notches 76. Of the four notches 76, two (hereinafter referred to as first notch portions 76c) are formed by cutting the base portion 71, from the upstream end toward the downstream end in the air flow. The two other notches (hereinafter referred to as a second notch portion 76d), other than the first notch portion 76c, on the other hand, are formed by cutting the base portion 71, from the downstream end toward the upstream end in the air flow.

The two notches of the first notch portion 76c are arranged substantially parallel to each other. The two notches of the second notch portion 76d, on the other hand, are tilted in the opposite direction to the first notch portion 76c in the direction of air flow. Also, the two notches of the second notch portion 76d are arranged substantially in parallel to each other.

As a result, effects similar to those of the fourteenth embodiment described above are produced.

Next, a seventeenth embodiment of the invention will be explained with reference to FIGS. 20A, 20B. In FIGS. 20A, 20B, component parts similar or identical to those of the twelfth embodiment are designated by the same reference numerals, respectively, and are not described again. FIG. 20A is a plan view showing the insert 6 according to the seventeenth embodiment, and FIG. 20B a front view of FIG. 20A. FIG. 21 is a perspective view showing the insert 6 according to the seventeenth embodiment.

As shown in FIGS. 20A, 20B and 21, the ends of the notch 76 (hereinafter referred to as the rectangular portions 760) in the direction of air flow according to this embodiment are substantially rectangular and larger than the other parts of the notch 76. Also, the portion of each rib 72 adjacent to the corresponding rectangular portion 760 is formed with a rib-side expansion 77 of the rib 72 having a substantially U-shaped cross section. According to this embodiment, the rib-side expansions 77 are formed inward of the insert 6 in the direction of air flow.

As described above, by forming the notch 76 in the base portion 71 and the rib-side expansions 77 of the pair of the ribs 72, the stress generated in the direction along the length of the insert can be positively absorbed.

Also, the diagonal arrangement of the notch 76, with respect to the direction of air flow, makes it possible to disperse the stress absorber of the insert 6, i.e. the portion of the insert 6 having a weak force to hold the tubes 2, over the length of the tube. As a result, in the case where the internal pressure of the tube 2 increases, the tube 2 is prevented from being locally expanded and deformed, thereby making it possible to prevent the tube 2 from being broken.

As a result, thermal distortion is positively reduced while at the same time the pressure resistance performance is secured.

Finally, other embodiments will be described. Although the embodiments described above are an application of the invention to the cross-flow radiator in which the cooling water flows in horizontal direction. Nevertheless, this invention is applicable also to the down-flow radiator in which the cooling water flows vertically.

Also, this invention is not limited to the embodiments described above in which the stress absorber, of the insert 6, is not in contact with the core portion 4. As an alternative, the stress absorber of the insert 6 may be in contact with the core portion 4.

Further, unlike in the fourteenth and fifteenth embodiments described above in which three notches 76 are formed in the base portion 71, two or four or more notches 76 may be formed.

In similar fashion, in spite of the fact that the base portion 71 is formed with four notches 76 according to the sixteenth embodiment, two or three or not less than five notches may be formed with equal effect.

While the invention has been described by reference to specific embodiments chosen for purposes of illustration, it should be apparent that numerous modifications could be made thereto, by those skilled in the art, without departing from the basic concept and scope of the invention.

Claims

1. A heat exchanger comprising:

a core portion including a plurality of tubes with a heat medium flowing therein and fins coupled to the outer surface of the tubes for promoting heat exchange with the heat medium;

a pair of header tanks extending in the direction perpendicular to the length of the tubes at the longitudinal ends of the tubes and communicating with the tubes; and

a pair of inserts arranged substantially parallel to the length of the tubes at the ends of the core portion to receive the heat transmitted from the core portion and having the ends thereof supported on the header tanks;

wherein each of the header tanks includes a core plate with the tubes fixed thereon and a tank body providing the internal space of the tank with the care plate, and

wherein the ends of each insert are arranged outside the internal space of the header tank and the insert is movably fitted in the header tank and along the length thereof.

2. A heat exchanger according to claim 1,

wherein the fitting between the header tank and the insert has an insertion structure in which an end or the insert is inserted in the through hole formed in the header tank.

3. A heat exchanger according to claim 2,

wherein the through hole is formed in the surface perpendicular to the length of the tubes.

4. A heat exchanger according to claim 1,

wherein the fitting between the header tank and the insert has an anti-brazing structure.

5. A heat exchanger according to claim 2,

wherein the longitudinal ends of the core plate extend outside of the tank body, and

wherein each of the through holes is formed in the portion of the core plate outside the tank body.

6. A heat exchanger according to claim 2,

wherein each longitudinal end of the tank body is formed with an outward protrusion, and

wherein the through hole is formed in the protrusion.

7. A heat exchanger according to claim 1,

wherein the fins and the inserts are formed of a bare material not covered by a brazing material.

8. A heat exchanger comprising:

a core portion including a plurality of tubes with a heat medium flowing therein;

a pair of header tanks extending in a direction perpendicular to the length of the tubes at the longitudinal ends of the tubes and communicating with the tubes; and

a pair of inserts arranged substantially parallel to the length of the tubes, and in such a manner as to contact the core portion at the ends of the core portion to transfer the heat from the core portion, and hating the ends thereof supported on the header tanks;

wherein a stress absorber to absorb the stress generated along the length of each insert is formed in the insert;

wherein the stress absorber is formed over each insert from the upstream side to the downstream side in the air flow; and

wherein the stress absorber is arranged in such a manner that the most upstream end and the most downstream end thereof in the air flow are not superposed, one on the other, along the direction of air flow.

9. A heat exchanger according to claim 8,

wherein each insert includes a base portion having a surface substantially parallel to the flat surfaces of the tubes and extending substantially parallel to the length of the tubes, and a pair of ribs are projected in a direction substantially perpendicular to the base portion from the ends of the base portion in the direction of air flow and are extended substantially parallel to the length of the tubes;

wherein the portions of the ribs corresponding to the most upstream end and the most downstream end of the stress absorber are formed with notches, respectively; and

wherein each stress absorber constitutes a base portion-side expansion of the base portion having a substantially U-shaped cross section.

10. A heat exchanger according to claim 9,

wherein the base portion-side expansion is formed diagonally with respect to the direction of air flow.

11. A heat exchanger according to claim 9,

wherein the base portion-side expansion is split into a plurality of parts in the direction of air flow, and

wherein the plurality of the base portion-side expansions are coupled to each other through slits formed in the base portion.

12. A heat exchanger according to claim 11,

wherein the plurality of the base portion-side expansions are not arranged in alignment.

13. A heat exchanger according to claim 11,

wherein the plurality of the base portion-side expansions are tilted in different directions with respect to the direction of air flow.

14. A heat exchanger according to claim 11,

wherein the plurality of the base portion-side expansions are arranged substantially parallel to the direction of air flow in such a manner as not to be superposed, one on another, in the direction of air flow.

15. A heat exchanger according to claim 8,

wherein the tubes each have a flat cross section in the direction of air flow, and

wherein each insert includes a base portion having a surface substantially parallel to the flat surface of the tubes and extending in the direction substantially parallel to the length of the tubes and a pair of ribs projected in the direction substantially perpendicular to the base portion and extending in the direction substantially parallel to the length of the tubes, and

wherein the stress absorber is a notch cut in the base portion diagonally to the direction of air flow.

16. A heat exchanger according to claim 15,

wherein only one end of the notch is open.

17. A heat exchanger according to claim 15, comprising a plurality of notches.

18. A heat exchanger according to claim 15, comprising a plurality of notches each having only one open end;

wherein the open ends of the plurality of the notches are arranged on the base portion and alternate between the upstream side and the downstream side in the air flow.

19. A heat exchanger according to claim 17,

wherein the plurality of the notches are tilted in different directions with respect to the direction of air flow.

20. A heat exchanger according to claim 15,

wherein the notch is formed in the base portion, the portion of each of the pair of the ribs adjoining the corresponding notch is formed with a U-shaped rib-side expansion in the direction of air flow, and each stress absorber includes the corresponding rib-side expansion.