Abstract:
A heat exchanger ( 20 ) includes a plurality of tubes ( 23 ) with a fluid flowing therein and header tanks ( 21 ) arranged at the longitudinal ends of the tubes ( 23 ) and comunicating with the plurality of the tubes ( 23 ). The header tanks ( 21 ) each include a core plate ( 27 ) coupled with the tubes ( 23 ) and a tank body ( 31 ) coupled to straight portions ( 29 ) holding the joints of the core plate ( 27 ) with the tubes ( 23 ) and forming an internal space of the tank together with the core plate ( 27 ). The cross section of the each header tank ( 21 ) configured of the core plate ( 27 ) and the tank body ( 31 ) is in the shape of an ellipse or a polygon similar to an ellipse, and the aspect ratio of the ellipse inscribed in the cross section of the header tank ( 21 ) is between 0.95 and 1.05 inclusive. Thus, the header tanks of the heat exchanger have a strength capable of sufficiently resisting an increased supercharge pressure.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     This invention relates to a heat exchanger having a pair of header tanks capable of having a sufficient strength so as to withstand even a high-pressure medium.  
         [0003]     2. Description of the Related Art  
         [0004]     The restriction of the exhaust gas emitted from large trucks is increasing more and more every year. At the same time, the supercharge pressure and temperature of the intercooler of large trucks have increased remarkably as shown in  FIG. 9 . As a heat exchanger of this intercooler, a vertically long header tank  11  having a rectangular cross section shown in  FIG. 10  is conventionally known. With the increase in supercharge pressure, however, this header tank  11  is deformed in an increased amount and may break under an excessively large load imposed on the root of the tubes. An example of this header tank is described in Japanese Unexamined Patent Publication No. 9-196594.  
       SUMMARY OF THE INVENTION  
       [0005]     The object of this invention is to solve the problem described above and provide a heat exchanger having a header tank capable of sufficiently resisting an increased supercharge pressure.  
         [0006]     In order to solve the aforementioned problem, according to a first aspect of the invention, there is provided a heat exchanger employing a means wherein an outside portion of a cross section of the header tank substantially perpendicular to a longitudinal direction thereof which extends from one joint to the other where the tube is connected with the core plate including the cross section of a tank body is in the shape an ellipse or a polygon similar to an ellipse, and wherein the aspect ratio of an ellipse inscribed in the outside portion is between 0.95 and 1.05 inclusive. With this heat exchanger, the stress concentration at the joints between the core plate and the tube can be prevented on the one hand, and the sectional shape of the portion reinforced in strength by the tubes is not required to be limited on the other hand, thereby improving the design freedom.  
         [0007]     Also, in order to solve the aforementioned problem, according to another aspect of the invention, there is provided a heat exchanger wherein the cross section of the header tank substantially perpendicular to a longitudinal direction of the header tank is in the shape of an ellipse or a polygon similar to an ellipse, and the aspect ratio of an ellipse inscribed in the header tank is between 0.93 and 1.05 inclusive.  
         [0008]     In this heat exchanger, a header tank is provided in which stress concentration at the joint between the core plate and the tubes can be prevented, and therefore which has sufficient strength to resist an increased supercharge pressure.  
         [0009]     In order to solve the aforementioned problem, according to still another aspect of the invention, there is provided a heat exchanger wherein straight portions each making up a joint margin are formed at the joint between the core plate and the tank body. Therefore, a more reliable header tank is provided in which the joint area between the core plate and the tank body can be positively secured.  
         [0010]     In order to solve the aforementioned problem, according to yet another aspect of the invention, there is provided a heat exchanger wherein a cap is coupled to the openings at the ends of the cylindrical header tank. When the core plate and the tank body are coupled to each other, therefore, a jig can be inserted from the openings and pressure can be applied from both inside and outside the header tank, thereby making possible a positive coupling.  
         [0011]     The reference numeral inserted in parentheses following the name of each means described above indicates an example of correspondence with a specific means described in the embodiments below.  
         [0012]     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. 
     
    
       [0013]     BRIEF DESCRIPTION OF THE DRAWINGS  
         [0014]      FIG. 1  is a front view schematically showing a heat exchanger according to an embodiment of the invention.  
         [0015]      FIG. 2  is a sectional view taken along line A-A in  FIG. 1 .  
         [0016]      FIG. 3  is a diagram showing the relation between the aspect ratio of the inscribed ellipse of the header tank and the stress exerted on the tube root.  
         [0017]      FIG. 4A  is a sectional view showing a header tank including a tank body having a semicircular cross section and a core plate having a cross section equivalent to one half of an octagon, wherein the straight portions of the tank body are located outside the straight portions, respectively, of the core plate.  
         [0018]      FIG. 4B  is a sectional view showing a header tank including a tank body having a semicircular cross section and a core plate having a cross section equivalent to one half of an octagon, wherein the straight portions of the tank body are located inside the straight portions, respectively, of the core plate.  
         [0019]      FIG. 4C  is a sectional view showing a header tank including a tank body having a semicircular cross section and a core plate having a cross section equivalent to one half of an octagon, wherein the straight portions of both the tank body and the core plate are extended radially outward.  
         [0020]      FIG. 5  is a sectional view of a header tank having an octagonal cross section.  
         [0021]      FIG. 6  is a sectional view showing the shape or a header tank on the side nearer to the tube than the tube root.  
         [0022]      FIG. 7  is a perspective view showing a header tank having, at each end thereof, an opening covered with a cap.  
         [0023]      FIG. 8A  is a perspective view showing a header tank having a pseudo-circular outer peripheral portion and an outer peripheral portion larger in aspect ratio.  
         [0024]      FIG. 8B  is a sectional view showing a pseudo-circular outer peripheral portion of a header tank also having an peripheral portion larger in aspect ratio.  
         [0025]      FIG. 8C  is a sectional view showing an outer peripheral portion larger in aspect ratio or a header tank also having a pseudo-circular peripheral portion.  
         [0026]      FIG. 9  is a diagram showing recent increases in supercharge pressure and temperature of the intercooler for large trucks.  
         [0027]      FIG. 10  is a sectional view showing a vertically long rectangular conventional header tank. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0028]     Embodiments of the invention are explained below with reference to FIGS.  1  to  8 C.  
         [0029]     FIGS.  1  to  6  are diagrams showing a first embodiment of the invention. In  FIG. 1 , reference numeral  20  designates a heat exchanger. Heat exchanger  20  includes a plurality of tubes  23  with a pair of header tanks  21  juxtaposed at the ends thereof.  
         [0030]     The header tanks  21 , made of copper, iron or stainless steel high in strength at high temperatures and capable of being processed as a thin metal sheet, each have a core plate  27  coupled with each tube  23  at tube root  25  as shown in  FIG. 2 . Each core plate  27  has a substantially semicircular cross section, and is formed with a straight portion  29  at each end thereof as a brazing or welding margin. The core plate  27  is also provided with a Tank body  31  having a substantially semicircular cross section. Tank body  31  also has straight portions  33  as joints with the core plate  27 . The core plate  27  and the tank body are assembled with the straight portions  29 ,  33  coupled by brazing and welding, respectively. The header tanks  21  thus assembled are formed in such a manner that the cross section thereof is in contact with an ellipse.  
         [0031]     The ellipse  35  inscribed in the cross section of each header tank  21  is explained in more detail. The inscribed ellipse  35  is assumed to be in contact with an ordinary cross section of the header tank not connected with a pipe or a bracket.  
         [0032]     Assume that the intersection between the center line E along the center line of the tube  23  of the header tanks  21  and the inner wall surface of the tank body  31  is designated as A, the intersection between the center line E and the core plate  27  as B and the middle point of the line segment AB as 0. Also, assume that the intersections between the center line F passing through the point 0 in the direction perpendicular to the center line E and the inner wall surface of the header tank  21  as C, D, respectively. Then, the ellipse having the center at point 0 and one of the line segment AB=a and the line segment CD=b as a long axis and the other as a short axis constitutes an inscribed ellipse  35 .  
         [0033]     The ratio a/b between the long, and short axes of the inscribed ellipse  35  is preferably between 0.95 and 1.05 inclusive. The reason for this is shown by way of the graph of  FIG. 3 . The abscissa represents the aspect ratio a/b of the inscribed ellipse, and the ordinate represents the maximum stress exerted on the tube root, assuming that the aspect ratio is 100 when the aspect ratio a/b=1. As can be understood from this graph, the maximum stress exerted on the tube root is increased for an aspect ratio a/b of not more than 0.95 or not less than 1.05. As a result, the plate thickness is required to be increased and the machining becomes difficult, leading to higher costs. Thus, the aspect ratio a/b is desirably between 0.95 and 1.05 inclusive.  
         [0034]     As stated above, the header tanks  21  or the heat exchanger described above have a substantially circular cross section with an aspect ratio a/b of between 0.95 and 1.05 inclusive, and therefore concentration of stress on the tube root can be prevented. Also, in view of the fact that the core plate  27  and the tank body  31  are formed with the straight portions  29 ,  33 , respectively, which are brazed and welded, sufficient coupling strength is obtained. Even in a high-pressure medium, therefore, sufficient strength can be secured without increasing the thickness, thereby suppressing an increase in weight and cost.  
         [0035]     In the case where the inscribed ellipse  35 , with a substantially circular cross section having the ratio a/b between the long and short axes thereof, of not less than 0.95 and not more than 1.05 the thickness of the heat exchanger is increased, which somewhat disadvantageously requires consideration of the interference with the radiator when mounted on the vehicle. A vertically long cross section, however, would require a considerable increase in thickness in order to maintain the strength, resulting in an increased weight. Therefore, a substantially circular cross section can advantageously reduce both the thickness and the weight, for a lower cost.  
         [0036]      FIGS. 4A  to  4 C and  5  are diagrams showing other examples of the first embodiment.  
         [0037]      FIGS. 4A  to  4 C showing cross sections of a header tank including a semicircular cross section of the tank body and a half octagonal cross section of the core plate. The octagonal cross section has the corners thereof connected at a smooth angle. In the header tank  41  shown in  FIG. 4A , the straight portions  45  of the tank body  43  are coupled with the outside of the straight portions  49  of the half octagonal core plate  47 . In the header tank  51  shown in  FIG. 4E , on the other hand, the straight portions  55  of the tank body  53  are coupled with the inside of the straight portions  59  of the half octagonal core plate  37 . In the header tank  61  shown in  FIG. 4C , the straight portions  65 ,  69  of the tank body  63  having a semicircular cross section and the core plate  67  having a half octagonal cross section, respectively, extend radially outward, and the extensions thereof are coupled to each other.  
         [0038]     The header tank  71  shown in  FIG. 5  is in the shape of an octagon including a tank body and a core plate, in which the straight portions  75  of the tank body  73  are coupled to the inside of the straight portions  79  of the core plate  77 .  
         [0039]     The header tanks shown In  FIGS. 4A, 4B ,  4 C,  5  have a cross section in the shape of a polygon similar to the ellipse or a combination of an ellipse and a polygon similar to the ellipse. The polygon, however, is desirably at least a pentagon. The reason for this is that in the case where the polygon has less than five corners, the angle between the tube and the core plate at the tube root may assume a substantially right angle as shown in  FIG. 10 , for increased root stress, depending on the peripheral position of the polygon with respect to the tube. Also, a number of corners less than 5 would reduce the inside angle of the corners and concentrate stress.  
         [0040]     The portion of the header tank having a cross section In the shape of a polygon similar to an ellipse, therefore, is not necessarily limited to an octagon as in the embodiments described above, but may be a pentagon, a hexagon, a nonagon or a decagon.  
         [0041]     Also, the cross section of the header tank portion nearer to the tube than the tube root is not necessarily in contact with the inscribed circle. Specifically, as shown in  FIG. 6 , the portion of the header tank  91  nearer to the tube than the tube roots A, B does not necessarily project into contact with the inscribed ellipse  35  like the core plate  57  of the header tank  51  shown in  FIG. 4B , but the tube roots A and B mats be connected to each other in a region inside the inscribed circle  35  like the core plate  93  shown in  FIG. 6 . This is by reason of the fact that the portion between the tube roots A and B is reinforced by the tube  23  and has sufficient strength without being in contact with the inscribed circle  35 .  
         [0042]      FIG. 7  is a diagram showing a second embodiment of the invention having a structure in which an opening  81  is formed at the end of the header tank  51  and covered by a cap  83 . By so doing, the tank body  53  and the core plate  57  can be coupled to each other by inserting a jig from the opening  81  and closely attaching by pressing the straight portions  55 ,  59  against each other from both inside and outside.  
         [0043]     Generally, aluminum materials can be welded to each other in spite of a small clearance which may exist between them. On the other hand, in the case of a clearance at the weld zone of brass or stainless steel, welding is known to be difficult due to zinc being present in the structure of the former and due to the oxide film formed on the surface of the latter.  
         [0044]     In the header tank  51  having the cap  83  according to this embodiment, the welding zone can be closely attached by inserting a jig even when welding brass or stainless steel, thereby resulting in highly reliable welding work.  
         [0045]      FIG. 8A  shows a header tank  101  according to a third embodiment of the invention. Header tank  101  includes a similar core plate  57  to the one shown in  FIG. 4B , and the tank body  103  is fixedly welded on the core tank  57 . The tank body  103  has first tank outer peripheral portions  153  having a pseudo-circular cross section (aspect ratio of 1.95 to 1.05) as shown in  FIG. 8B , and second tank outer peripheral portions  105  having a larger aspect ratio (1.2, for example) than the first tank outer peripheral portion  153  as shown in  FIG. 8C . The first tank outer peripheral portions  152  and the second tank outer peripheral portions  105  alternate with each other to thereby form the tank body  103 .  
         [0046]     In view of the fact that the tank body  103  of the header tank  101  has the first tank outer peripheral portions  153  having a pseudo-circular cross section (aspect ratio of 1.95 to 1.05) and the second tank outer peripheral portions  105  having a larger aspect ratio (1.2, for example) than the first tank outer peripheral portions  153 , as described above, the rigidity of the tank as a whole is improved and deformation thereof suppressed, thereby reducing root stress.  
         [0047]     The shapes of the first tank outer peripheral portions  153  and the second tank outer peripheral portions  105  are applicable to the common portion other than where a pipe, a mounting bracket, etc. are arranged. Also, the aspect ratio of the shape of the second tank outer peripheral portions  10  is not limited to and can assume any value other than 1.2.  
         [0048]     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.