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  
       [0001]     1. Field of the Invention  
         [0002]     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.  
         [0003]     2. Description of the Related Art  
         [0004]     A conventional multiflow radiator, as shown in  FIG. 9 , includes a core portion J 4  having a plurality of tubes J 2  and fins J 3  coupled to the outer surface of the tubes J 2 , a header tank J 5  communicating with the plurality of the tubes J 2  and an insert J 6  arranged at the end of the core portion J 4  for reinforcing the core portion J 4 .  
         [0005]     The header tank J 5  is configured of a core plate J 5   a  coupled with the tubes J 2  and a tank body J 5   b  providing the internal space of the tank. The tubes J 2  and the insert J 6  are coupled to the core plate J 5   a  by brazing after being inserted into the header tank J 5 .  
         [0006]     In this radiator, if the temperature of the cooling water flowing in the tubes J 2  undergoes a change, the amount of thermal expansion of the tubes J 2  directly affected by the cooling water is different from that of the insert J 6  which is affected only indirectly.  
         [0007]     The difference in thermal expansion amount between the tubes J 2  and the insert J 6  due to the temperature difference is liable to generate a thermal stress due to the thermal distortion in the root (coupling) between the tube J 2  adjacent to the insert J 6  and the core plate J 5   a . As a result, repeated changes in temperature, and changes in thermal stress, pose a problem that the tubes J 2  in the neighborhood of the root may be broken.  
         [0008]     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).  
         [0009]     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  
       [0010]     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.  
         [0011]     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.  
         [0012]     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.  
         [0013]     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).  
         [0014]     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).  
         [0015]     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.  
         [0016]     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.  
         [0017]     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.  
         [0018]     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 ( 5   a ) with the tubes ( 2 ) fixed thereon and a tank body ( 5   b ) providing the internal space of the tank with the core plate ( 5   a ), 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.  
         [0019]     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 ( 5   a ). 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 ).  
         [0020]     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 ( 5   f ,  12   f ) 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.  
         [0021]     The through hole ( 5   f ,  12   f ) 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 ).  
         [0022]     Also, the through hole ( 5   f ,  12   f ) may be formed in the part of each core plate ( 5   a ) outside the tank body ( 5   b ) or a protrusion ( 12 ) may be formed outside each longitudinal end of the tank body ( 5   b ).  
         [0023]     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.  
         [0024]     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.  
         [0025]     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.  
         [0026]     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.  
         [0027]     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 ( 2   a ) 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 ( 73   a ,  73   b ), respectively, and the stress absorber constitutes a base portion-side expansion ( 74 ) having a substantially U-shaped cross section of the base portion ( 71 ).  
         [0028]     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.  
         [0029]     In this case, the base portion-side expansion ( 74 ) may be tilted with respect to the direction of air flow.  
         [0030]     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 ).  
         [0031]     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.  
         [0032]     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.  
         [0033]     As a result, the distance between the notch ( 73   a ) on the upstream side in the air flow and the notch ( 73   b ) 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 ).  
         [0034]     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.  
         [0035]     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.  
         [0036]     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.  
         [0037]     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.  
         [0038]     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 ( 2   a ) 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.  
         [0039]     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.  
         [0040]     According to a ninth aspect of the invention, there is provided a heat exchanger wherein only one end of the notch ( 76 ) is open.  
         [0041]     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.  
         [0042]     Alternatively, the two ends of the notch ( 76 ) may be open or connected to each other.  
         [0043]     Further, a plurality of the notches ( 76 ) may be formed.  
         [0044]     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.  
         [0045]     In addition, the plurality of the notches ( 76 ) can be tilted in directions different from the direction of air flow.  
         [0046]     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 ).  
         [0047]     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.  
         [0048]     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.  
         [0049]     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  
       [0050]      FIG. 1  is a front view showing a radiator  1  according to a first embodiment.  
         [0051]      FIG. 2A  is an enlarged view showing the essential parts of the radiator  1  according to the first embodiment.  
         [0052]      FIG. 2B  is an enlarged plan view of the fitting between the tank body  5   b  and the insert  6  as taken from the X direction in  FIG. 2A .  
         [0053]      FIG. 3A  is an enlarged view showing the essential parts of the radiator  1  according to a second embodiment.  
         [0054]      FIG. 3B  is an enlarged plan view of the fitting between the tank body  5   b  and the insert  6  as taken from the X direction in  FIG. 3A .  
         [0055]      FIG. 4A  is an enlarged view showing the essential parts of the radiator  1  according to a third embodiment.  
         [0056]      FIG. 4B  is an enlarged plan view of the fitting between the tank body  5   b  and the insert  6  as taken from the X direction in  FIG. 4A .  
         [0057]      FIG. 5A  is an enlarged view showing the essential parts of the radiator  1  according to a fourth embodiment.  
         [0058]      FIG. 5B  is an enlarged plan view of the fitting between the tank body  5   b  and the insert  6  as taken from the X direction in  FIG. 5A .  
         [0059]      FIG. 6A  is an enlarged view showing the essential parts of the radiator  1  according to fifth and sixth embodiments.  
         [0060]      FIG. 6B  is an enlarged plan view of the fitting between the tank body  5   b  and the insert  6  as taken from the X direction in  FIG. 6A .  
         [0061]      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.  
         [0062]      FIG. 8  is an enlarged view showing the essential parts of the radiator  1  according to a seventh embodiment.  
         [0063]      FIG. 9  is an enlarged view showing the essential parts of the conventional radiator.  
         [0064]      FIG. 10  is a front view of the radiator  1  according to an eighth embodiment.  
         [0065]      FIG. 11A  is a plan view showing the insert  6  according to the eighth embodiment.  
         [0066]      FIG. 11B  is a front view of  FIG. 11A .  
         [0067]      FIG. 12A  is a plan view showing the insert  6  according to a ninth embodiment.  
         [0068]      FIG. 12B  is a front view of  FIG. 12A .  
         [0069]      FIG. 13A  is a plan view showing the insert  6  according to a tenth embodiment.  
         [0070]      FIG. 13B  is a front view of  FIG. 13A .  
         [0071]      FIG. 14A  is a plan view showing the insert  6  according to an eleventh embodiment.  
         [0072]      FIG. 14B  is a front view of  FIG. 14A .  
         [0073]      FIG. 15A  is a plan view showing the insert  6  according to a twelfth embodiment.  
         [0074]      FIG. 15B  is a front view of  FIG. 15A .  
         [0075]      FIG. 16A  is a plan view showing the insert  6  according to a thirteenth embodiment.  
         [0076]      FIG. 16B  is a front view of  FIG. 16A .  
         [0077]      FIG. 17A  is a plan view showing the insert  6  according to a fourteenth embodiment.  
         [0078]      FIG. 17B  is a front view of  FIG. 17A .  
         [0079]      FIG. 18A  is a plan view showing the insert  6  according to a fifteenth embodiment.  
         [0080]      FIG. 18B  is a front view of  FIG. 18A .  
         [0081]      FIG. 19A  is a plan view showing the insert  6  according to a sixteenth embodiment.  
         [0082]      FIG. 19B  is a front view of  FIG. 19A .  
         [0083]      FIG. 20A  is a plan view showing the insert  6  according to a seventeenth embodiment.  
         [0084]      FIG. 20B  is a front view of  FIG. 20A .  
         [0085]      FIG. 21  is a perspective view showing the insert  6  according to the seventeenth embodiment. 
     
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0086]     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  5   a  and one insert  6  taken from the X direction.  
         [0087]     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.  
         [0088]     The flat surfaces  2   a  ( 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 .  
         [0089]     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  5   a  with the tubes  2  coupled by insertion thereinto and a tank body  5   b  providing the internal space of the tank with the core plate  5   a . According to the first embodiment, the core plate  5   a  is formed of a metal (such as an aluminum alloy) and the tank body  5   b  is formed of resin.  
         [0090]     As shown in  FIG. 2A , packing (not shown), made of an elastic material such as rubber, is arranged in a groove  5   c  formed along the whole peripheral edge of the core plate  5   a  thereby to close the gap between the tank body  5   b  and the core plate  5   a  in liquid tight fashion. A plurality of hooks  5   d  are erected on the peripheral edge of the core plate  5   a . By fixedly caulking the hooks  5   d  on the flange formed on the outer peripheral edge of the tank body  5   b , the tank body  5   b  is assembled on the header plate  5   a.    
         [0091]     The tank body  5   b  is fixedly caulked on the core plate  5   a  by plastic deformation of a part of the core plate  5   a  pressed against the tank body  5   b.    
         [0092]     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  6   a  having a surface substantially parallel to the flat surface  2   a  of the tubes  2  and extending in a direction substantially parallel to the length of the tubes  2 , and ribs  6   b  projected in a direction (horizontal direction in this embodiment) substantially perpendicular to the base portion  6   a  and extending in a direction substantially parallel to the length of the tubes  2 . In the insert  6 , the ribs  6   b  are arranged at the ends of the base portion  6   a  in a direction perpendicular to the length of the base portion  6   a . 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.  
         [0093]     A support structure for the core plate  5   a  and the insert  6  will be explained.  
         [0094]     According to the first embodiment, the ends of the core plate  5   a  are extended outward of the tank body  5   b . Specifically, the ends of the core plate  5   a  assembled on the tank body  5   b  are exposed. Each end of the core plate  5   a  is formed with a through hole  5   f  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 .  
         [0095]     The base portion  6   a  of the insert  6  is bent in an opposed relation to the groove  5   c  of the core plate  5   a , after which the end of the base portion  6   a  (hereinafter referred to the insert end portion  6   c ) is extended toward the through hole  5   f  of the core plate  5   a  and, with the insert end portion  6   c  inserted in the through hole  5   f , is fitted to the core plate  5   a . In other words, the fitting between the core plate  5   a  and the insert  6  constitutes an insertion structure.  
         [0096]     The fitting between the core plate  5   a  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  5   f  and the portion of the insert end portion  6   c  corresponding to the through hole  5   f . As a result, the fitting between the core plate  5   a  and the insert  6  is not brazed.  
         [0097]     According to the first embodiment, the tubes  2 , the fins  3 , the core plates  5   a  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  5   a  and the inserts  6  are all bonded by brazing except for the fitting between each core plate  5   a  and the corresponding insert  6 .  
         [0098]     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  5   a  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).  
         [0099]     In  FIG. 1 , a cooling water inlet  7   a  is connected to the outlets side of the engine cooling water, and a cooling water outlet  6   b  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 .  
         [0100]     Next, a method of fabricating the radiator  1  according to the first embodiment will be briefly explained.  
         [0101]     The fins  3 , the tubes  2  and each insert  6  are assembled as shown in  FIG. 2A  and the insert end portion  6   c  is inserted into the through hole  5   f . 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  5   a  and the insert  6  is not brazed in view of the fact that the brazing material on the inner wall of the through hole  5   f  of the core plate  5   a  and the part of the insert end portion  6   c  corresponding to the through hole  5   f  is cut off.  
         [0102]     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.  
         [0103]     As described above, the fitting between the core plate  5   a  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  5   a . 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.  
         [0104]     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.  
         [0105]      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  5   a  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  5   f  and the insert end portion  6   c , so that the inner wall of the through hole  5   f  and the insert end portion  6   c  are kept out of direct contact with each other.  
         [0106]     As a result, the fitting between the core plate  5   a  and the insert  6  is prevented from being brazed, and therefore effects similar to those of the first embodiment are achieved.  
         [0107]     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.  
         [0108]      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  5   a  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  5   f  is formed by burring the brazing material surface (the surface clad with the brazing material) outside.  
         [0109]     As a result, the brazing material surface of the core plate  5   a  and the insert end portion  6   c  are kept out of contact with each other. At the same time, the brazing material on the portion of the insert end portion  6   c  corresponding to the through hole  5   f  is cut off and, therefore, the fitting between the core plate  5   a  and the insert  6  is prevented from being brazed. Thus, effects similar to those of the first embodiment are produced.  
         [0110]     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.  
         [0111]      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  5   a  and the insert  6  taken from the X direction in  FIG. 5A . As shown in  FIG. 5A , the insert end portion  6   c  according to the fourth embodiment is inserted in the through hole  5   f  with the brazing material surface bent inward.  
         [0112]     As a result, the brazing material surface of the insert  6  and the inner wall surface of the through hole  5   f  are kept out of contact with each other. Also, as the brazing material on the inner wall surface of the through hole  5   f  is cut off, the fitting between the core plate  6   a  and the insert  6  is prevented from being brazed. Thus, effects similar to those of the first embodiment can be obtained.  
         [0113]     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.  
         [0114]      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  5   b  and the insert  6  taken from the X direction in  FIG. 6A . As shown in  FIG. 6A , each longitudinal end of the tank body  5   b  is formed with a protrusion  12  outside of the tank body  5   b . The protrusion  12  is formed of resin and is molded integrally with the tank  5   b.    
         [0115]     The protrusion  12  is formed with a through hole  12   a . The through hole  12   a  is configured to be fitted on the core plate  5   a  with the insert end portion  6   a  inserted in the through hole  5   f.    
         [0116]     As described above, by fitting the insert end portion  6   c  in the protrusion  12  of the tank body  5   b  of resin, the fitting between the insert  6  and the tank body  5   b  is prevented from being brazed and, therefore, effects similar to the first embodiment are achieved.  
         [0117]     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  5   b  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.  
         [0118]     According to the sixth embodiment, the tank body  5   b  and the protrusion  12  are formed of a metal (such as aluminum alloy), and the protrusion  12  is formed integrally with the tank body  5   b . Also, the brazing material on the fitting between the tank body  5   b  and the insert  6 , i.e. the inner wall portion of the through hole  12   a  and the portion of the insert end portion  6   c  corresponding to the through hole  12   a  is cut off.  
         [0119]     As described above, the insert  6  is fitted in the protrusion  12  of the tank body  5   b  and the brazing material on the fitting between the tank body  5   b  and the insert  6  is cut off thereby to prevent the brazing. Thus, effects similar to those or the first embodiment are achieved.  
         [0120]     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.  
         [0121]      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  2 A, the tube adjacent to the first tube  2 A a second tube  2 B, and the tube adjacent to the second tube  2 B a third tube  2 C.  
         [0122]     In the prior art, the coupling between the tube J 2  or the insert J 6  (base portion J 6   a ) and the fins J 3 , 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 J 2 A is liable to be deprived of heat by the insert J 6  to cause an increased temperature difference between the first tube J 2 A and the second etude J 2 B.  
         [0123]     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  2 A is not easily deprived of heat by the insert  6 . As shown in  FIG. 7 , therefore, the temperature difference between the first tube  2 A and the second tube  2 B can be decreased. Thus, the thermal distortion can be reduced.  
         [0124]     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  6   c  corresponding to the through holes  5   f ,  12   a  is cut off according to the first to third and sixth embodiments, and the insert end portion  6   c  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  6   c  corresponding to the through holes  5   f ,  12   a  may be coated with an anti-brazing agent.  
         [0125]     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.  
         [0126]     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  6   c  corresponding to the through hole  5   f ,  12   a  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  5   f  and the insert end portion  6   c  according to the second embodiment, and the through hole  5   f  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  5   f ,  12   a.    
         [0127]     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.  
         [0128]     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.  
         [0129]     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 .  
         [0130]     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  5   a  coupled with the tubes  2  inserted therein and a tank body  5   b  providing the internal space of the tank with the core plate  5   a.    
         [0131]     The header tank  5  includes a cooling water inlet  7   a  connected to the cooling water cutlet side of the engine (not shown) and a cooling water outlet  7   b  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 .  
         [0132]      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  2   a  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 .  
         [0133]     The pair of the ribs  72  of the insert  6  are formed with notches  73   a ,  73   b , 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  73   a ) formed in the rib  72  on the upstream side in the air flow and the notch (hereinafter referred to as the downstream side notch  73   b ) 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.  
         [0134]     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 .  
         [0135]     As shown in  FIG. 11A , the base portion-side expansion  74  is formed to connect the upstream-side notch  73   a  and the downstream-side notch  73   b  and is arranged diagonally to the direction of air flow.  
         [0136]     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.  
         [0137]     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 .  
         [0138]     Thus, the thermal distortion is reduced and the pressure resistance performance is secured at the same time.  
         [0139]     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 .  
         [0140]     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 .  
         [0141]     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  74   a  and the one arranged downstream in the air flow a second base portion-side expansion  74   b.    
         [0142]     The two base portion-side expansions  74   a ,  74   b  are connected to each other through the slit  75 . Also, the two base portion-side expansions  74   a ,  74   b  are arranged out of alignment. According to this embodiment, the two base portion-side expansions  74   a ,  74   b  are connected to the longitudinal ends, respectively, of the slit  75 .  
         [0143]     As a result, effects similar to those of the eighth embodiment are produced.  
         [0144]     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  74   a ,  74   b  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.  
         [0145]     Also, in view of the fact that the two base portion-side expansions  74   a ,  74   b  are not arranged in alignment, the distance between the upstream-side notch  73   a  and the downstream-side notch  73   b  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 .  
         [0146]     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 .  
         [0147]     As shown in  FIG. 13A , the two base portion-side expansions  74   a ,  74   b  according to this embodiment are tilted in opposite directions with respect to the direction of air flow.  
         [0148]     More specifically, the end of the slit  75  connected with the first base portion-side expansion  74   a  is arranged nearer to the downstream-side notch  73   b  than to the upstream-side notch  73   a  in the direction of the length of the tube. The end of the slit  75  connected with the second base portion-side expansion  74   b , on the other hand, is arranged farther from the upstream-side notch  73   a  than from the downstream-side notch  73   b  in the direction along the length of the tube.  
         [0149]     As a result, effects similar to those of the ninth embodiment are produced.  
         [0150]     Further, in view of the fact that the two base portion-side expansions  74   a ,  74   b  are tilted in opposite directions in the direction of air flow, the spring back when molding the base portion-side expansions  74   a ,  74   b  can be reduced for an improved moldability.  
         [0151]     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 .  
         [0152]     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  75   a  and the one arranged downstream side in the air flow a second slit  75   b.    
         [0153]     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  74   a  to  74   c  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  74   a , the one arranged downstream in the air flow a second base portion-side expansion  74   b , and the one arranged between the first base portion-side expansion  74   a  and the second base portion-side expansion  74   c  a third base portion-side expansion  74   c.    
         [0154]     As shown in  FIG. 14A , the three base portion-side expansions  74   a  to  74   c  are coupled to each other through the two slits  75   a ,  75   b . More specifically, one end of the first slit  75   a  along the tube length is connected to the first base portion-side expansion  74   a , and the other end thereof to the third base portion-side expansion  74   c . The downstream end of the third base portion-side expansion  74   c  alone the direction of air flow is connected to one end of the second slit  75   b  along the tube length, and the other end thereof to the second base portion-side expansion  74   b.    
         [0155]     As a result, effects similar to those of the ninth embodiment are produced.  
         [0156]     Further, in view of the fact that the three base portion-side expansions  74   a  to  74   c  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.  
         [0157]     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 .  
         [0158]     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.  
         [0159]     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 .  
         [0160]     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.  
         [0161]     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.  
         [0162]     Thus, the thermal distortion can be reduced while, at the same time, the pressure resistance performance is secured.  
         [0163]     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.  
         [0164]     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 .  
         [0165]     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 .  
         [0166]     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.  
         [0167]     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 .  
         [0168]     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.  
         [0169]     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.  
         [0170]     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 .  
         [0171]     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  76   a  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  76   b  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.  
         [0172]     As a result, effects similar to those of the fourteenth embodiment described above are achieved.  
         [0173]     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 .  
         [0174]     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  76   c ) 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  76   d ), other than the first notch portion  76   c , on the other hand, are formed by cutting the base portion  71 , from the downstream end toward the upstream end in the air flow.  
         [0175]     The two notches of the first notch portion  76   c  are arranged substantially parallel to each other. The two notches of the second notch portion  76   d , on the other hand, are tilted in the opposite direction to the first notch portion  76   c  in the direction of air flow. Also, the two notches of the second notch portion  76   d  are arranged substantially in parallel to each other.  
         [0176]     As a result, effects similar to those of the fourteenth embodiment described above are produced.  
         [0177]     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.  
         [0178]     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.  
         [0179]     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.  
         [0180]     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.  
         [0181]     As a result, thermal distortion is positively reduced while at the same time the pressure resistance performance is secured.  
         [0182]     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.  
         [0183]     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 .  
         [0184]     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.  
         [0185]     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.  
         [0186]     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.