Patent Publication Number: US-6213196-B1

Title: Double heat exchanger for vehicle air conditioner

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application relates to and claims priority from Japanese Patent Application No. 11-276941 filed on Sep. 29, 1999, the contents of which are hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to heat exchangers, and particularly to a double heat exchanger having plural heat exchange cores. The present invention is suitably applied to a double heat exchanger combining a condenser of a refrigeration cycle for a vehicle air conditioner and a radiator for cooling engine coolant. 
     2. Related Art 
     Generally, in a double heat exchanger having plural heat exchange cores, a specification of one of the heat exchange cores does not necessarily conform to a specification of the other. Conventionally, a double heat exchanger has a condenser core and a radiator core in which a corrugated condenser fin and a corrugated radiator fin are integrally formed. In such a heat exchanger, when plural condenser tubes and plural radiator tubes are arranged in a vertical direction at the same pitch and a height of each of the radiator tubes is larger than that of each of the condenser tubes in the vertical direction, a height of the condenser fin disposed between adjacent condenser tubes needs to be larger than that of the radiator fin disposed between adjacent radiator tubes in the vertical direction. 
     However, since the condenser fin is integrally formed with the radiator fin, a longitudinal length of the condenser fin when flattened to a flat plate is necessarily equal to that of the radiator fin. Therefore, a height of the condenser fin can not be simply increased by increasing only the longitudinal length of the condenser fin. 
     JP-A-11-148795 discloses a double heat exchanger in which a height of a corrugated radiator fin is made larger than that of a corrugated condenser fin by setting a radius of curvature of each wave of the radiator fin smaller than that of each wave of the condenser fin. However, generally, in a multi-flow type heat exchanger having plural tubes, the tubes and plural fins are alternately layered to be tentatively assembled and then integrally brazed in a furnace. Therefore, when a radius of curvature of each wave of the condenser fin is different from that of the radiator fin, an amount of deformation of the condenser fin caused by a force of constraint applied to the condenser fin during an assembling process of the condenser fin and condenser tubes becomes different from that of the radiator fin, even if the condenser fin and the radiator fin are made of the same material and has the same plate thickness. As a result, a contact pressure between the condenser fin and each of the condenser tubes may be largely different from a contact pressure between the radiator fin and each of radiator tubes, thereby causing a fin-tube brazing failure. 
     Further, when a radius of curvature of each wave of the fin is decreased, a filler is restricted from being formed at a connection portion between the fin and the tube during brazing. Therefore, an area of heat transfer from the tube to the fin is decreased, thereby declining heat exchange performance of the heat exchanger. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing problems, it is an object of the present invention to provide a heat exchanger having first and second heat exchangers, in which a first corrugated fin of the first heat exchanger is integrally formed with a second corrugated fin of the second heat exchanger while a radius of curvature of each wave of the first fin is not largely different from that of the second fin. 
     According to the present invention, a heat exchanger has a first heat exchanger and a second heat exchanger disposed at a downstream air side of the first heat exchanger. The first heat exchanger has a plurality of first tubes through which a first fluid flows and a first fin disposed between adjacent first tubes to facilitate heat exchange between the first fluid and air. The first fin has a corrugated shape including a plurality of first upper folds, a plurality of first lower folds and a first wall portion which connects one of the first upper folds and one of the first lower folds next to each other. The second heat exchanger has a plurality of second tubes through which a second fluid flows and a second fin disposed between adjacent second tubes to facilitate heat exchange between the second fluid and air. The second tubes extend in substantially parallel with the first tubes. The second fin is integrally formed with the first fin to have a corrugated shape including a plurality of second upper folds, a plurality of second lower folds and a second wall portion which connects one of the second upper folds and one of the second lower folds next to each other. The first and second fins are partially connected to each other through a connection member. An inclination angle of the first wall portion is different from that of the second wall portion so that a height of the first fin becomes different from that of the second fin. 
     Therefore, a height of the first fin becomes different from that of the second fin while maintaining a radius of curvature of each of the first upper and lower folds of the first fin equal to that of each of the second upper and lower folds of the second fin. As a result, the first fin and the second fin respectively make contact with each of the first tubes and the second tubes with the substantially same contact pressure during an assembling process, thereby restricting a brazing failure between the first and second fins and each of the first and second tubes. Further, according to the present invention, each of the radius of curvature of the first and second fins becomes a relatively large value. Therefore, a fillet is sufficiently formed between the first and second fins and each of the first and second tubes, respectively, during a brazing process, and a heat exchange performance of the heat exchanger is restricted from declining. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     This and other objects and features of the present invention will become more readily apparent from a better understanding of the preferred embodiment described below with reference to the accompanying drawings, in which: 
     FIG. 1 is a schematic perspective view showing a double heat exchanger according to a preferred embodiment of the present invention; 
     FIG. 2 is a schematic perspective view showing the double heat exchanger according to the embodiment; 
     FIG. 3 is a partial sectional view showing the double heat exchanger according to the embodiment; 
     FIG. 4 is a schematic partial perspective view showing a fin of the double heat exchanger according to the embodiment; 
     FIG. 5 is a schematic partial perspective view showing the fin according to the embodiment; 
     FIG. 6 is a schematic partial front view showing the fin according to the embodiment; 
     FIG. 7 is a schematic partial front view showing a fin of a double heat exchanger according to a modification of the embodiment; and 
     FIG. 8 is a schematic partial front view showing a fin of a double heat exchanger according to another modification of the embodiment. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A preferred embodiment of the present invention is described hereinafter with reference to the accompanying drawings. In the embodiment, the present invention is applied to a double heat exchanger  100  having a condenser  110  of a refrigeration cycle for a vehicle air conditioner and a radiator  120  for cooling engine coolant which cools a water-cooled engine of a vehicle. In FIG. 1, the double heat exchanger  100  is viewed from an upstream air side with respect to air passing therethrough. In FIG. 2, the double heat exchanger  100  is viewed from a downstream air side, that is, from the engine. 
     As shown in FIG. 1, the double heat exchanger  100  has the condenser  110  which performs heat exchange between refrigerant circulating the refrigeration cycle and air passing through the condenser  110  so that refrigerant is cooled. The condenser  110  has plural condenser tubes  111  through which refrigerant flows, plural condenser fins  112  each of which is disposed between adjacent condenser tubes  111  to facilitate heat exchange between refrigerant and air and header tanks  113 ,  114  respectively disposed at right and left flow-path ends of the condenser tubes  111  in FIG. 1 to communicate with the condenser tubes  111 . Refrigerant in the header tank  113  is distributed into each of the condenser tubes  111 . After being heat-exchanged with air, refrigerant flowing through each of the condenser tubes  111  is collected into the header tank  114 . 
     As shown in FIG. 3, each of the condenser tubes  111  is formed into a flat shape by extrusion or drawing and has plural refrigerant passages  111   a  extending in a longitudinal direction of the condenser tubes  111  therein. Each of the condenser fins  112  is integrally formed with each of radiator fins  122  of the radiator  120 . 
     As shown in FIG. 2, the double heat exchanger  100  has the radiator  120  which performs heat exchange between engine coolant discharged from the engine and air passing through the radiator  120  so that engine coolant is cooled. The radiator  120  has plural radiator tubes  121  through which engine coolant flows, plural radiator fins  122  each of which is disposed between adjacent radiator tubes  121  to facilitate heat exchange between engine coolant and air and header tanks  123 ,  124  respectively disposed at left and right flow-path ends of the radiator tubes  121  in FIG. 2 to communicate with the radiator tubes  121 . Engine coolant flowing into the header tank  123  is distributed into each of the radiator tubes  121 . After being heat-exchanged with air, engine coolant flowing through each of the radiator tubes  121  is collected into the header tank  124 . 
     As shown in FIG. 3, each of the radiator tubes  121  is formed into a flat shape. A height h 2  of each of the radiator tubes  121  in a longitudinal direction of the header tanks  113 ,  114 ,  123  and  124  is larger than a height h 1  of each of the condenser tubes  111 . Preferably, h 1  is set to 0.8-1.4 mm, and h 2  is set to 1.0-1.6 mm. A width W 1  of each of the condenser tubes  111  in a direction in which air passes through the double heat exchanger  100  is substantially equal to a width W 2  of each of the radiator tubes  121 . Refrigerant flows through the condenser tubes  111  while changing from gas refrigerant to liquid refrigerant. Engine coolant flows through the radiator tubes  121  without phase change. Therefore, a cross-sectional area of flow of each of the radiator tubes  121  is preferably set larger than that of each of the condenser tubes  111 . 
     Further, as shown in FIGS. 1 and 2, a pair of side plates  130  are respectively disposed at upper and lower ends of the condenser  110  and the radiator  120  for reinforcing the condenser  110  and the radiator  120 . The tubes  111 ,  121 , the fins  112 ,  122 , the header tanks  113 ,  114 ,  123 ,  124  and the side plates  130  are integrally brazed. 
     Next, the condenser and radiator fins  112 ,  122  are described in detail with reference to FIGS. 3-6. As shown in FIGS. 3-6, the condenser fin  112  and the radiator fin  122  are integrally formed by rolling. As shown in FIGS. 4 and 5, the condenser fin  112  is bent into a corrugated shape having plural upper folds  112   b  and plural lower folds  112   c.  Each of the upper folds  112   b  and the lower folds  112   c  is formed into a rectangular wave shape to have a flat portion  112   a  extending in substantially parallel with a longitudinal direction of the condenser and radiator tubes  111 ,  121 . Further, the condenser fin  112  has plural wall portions  112   d  each of which connects one of the upper folds  112   b  and one of the lower folds  112   c  disposed next to each other. Similarly, the radiator fin  122  is bent into a corrugated shape having plural upper folds  122   b,  plural lower folds  122   c,  plural flat portions  122   a  and plural wall portions  122   d.    
     Each of the wall portions  112   d,    122   d  has plural louvers  112   e,    122   e  each of which is formed by cutting and raising a part of the wall portions  112   d,    122   d,  respectively. The louvers  112   e,    122   e  disturb a flow of air passing by the condenser and radiator fins  112 ,  122  and restrict a temperature boundary layer from growing. Further, as shown in FIGS. 4 and 5, plural connection portions f are formed to partially connect the condenser fin  112  and the radiator fin  122  while creating a predetermined gap W 3  therebetween. The connection portions f are disposed at intervals of several upper folds  112   b,    122   b.  As shown in FIG. 6, an inclination angle θ 1  of each of the wall portions  112   d  is made different from an inclination angle θ 2  of each of the wall portions  122   d.    
     The gap W 3  is set to a value larger than a plate thickness of the condenser fin  112  and the radiator fin  122  and is set so that each of the connection portions f is distorted to absorb a difference between an inclination angle θ 1  and an inclination angle θ 2 . Further, as shown in FIGS. 4 and 5, plural slits s are formed between the condenser fin  112  and the radiator fin  122  due to the gap W 3 . Heat transfer from the radiator  120  to the condenser  110  is restricted by the slits s. 
     According to the embodiment, an inclination angle θ 1  of the condenser fin  112  is made different from an inclination angle θ 2  of the radiator fin  122 . The condenser fin  112  and the radiator fin  122  have the same fin pitch so that a distance between adjacent upper folds  112   b  is equal to a distance between adjacent upper folds  122   b,  and a longitudinal length of the condenser fin  112  when flattened is equal to that of the radiator fin  122 . As a result, as shown in FIG. 6, a length L 1  of each of the flat portions  112   a  of the condenser fin  112  becomes smaller than a length L 2  of each of the flat portions  122   a  of the radiator fin  122  in a longitudinal direction of the condenser and radiator tubes  111 ,  121 . L 1  and L 2  are dimensions of portions of each of the condenser and radiator fins  112 ,  122  extending in parallel with a longitudinal direction of the tubes  111 ,  121 , respectively. Further, a height H 1  of the condenser fin  112 , that is, a height difference between an upper end of each of the upper folds  112   b  and a lower end of each of the lower folds  112   c,  becomes larger than a height H 2  of the radiator fin  122 . 
     Therefore, the height H 1  of the condenser fin  112  is made different from the height H 2  of the radiator fin  122  while maintaining a radius of curvature r 1  of a connection portion  112   f  of the condenser fin  112  equal to a radius of curvature r 2  of a connection portion  122   f  of the radiator fin  122 . The connection portion  112   f  is disposed between one of the upper folds  112   b  and one of the wall portions  112   d  disposed next to each other or between one of the lower folds  112   c  and one of the wall portions  112   d  disposed next to each other. The connection portion  122   f  is disposed between one of the upper folds  122   b  and one of the wall portions  122   d  disposed next to each other or between one of the lower folds  122   c  and one of the wall portions  122   d  disposed next to each other. As a result, when the double heat exchanger  100  is tentatively assembled, a contact pressure between the condenser fin  112  and each of the condenser tubes  111  is made equal to a contact pressure between the radiator fin  122  and each of the radiator tubes  121 . Therefore, brazing failure between the condenser fin  112  and each of the condenser tubes  111  or between the radiator fin  122  and each of the radiator tubes  121  is restricted. Preferably, a difference ΔH between H 1  and H 2  is set to 0.1-1.0 mm, and a difference ΔL between L 1  and L 2  is set to 0.05-0.5 mm so that the condenser and radiator fins  112 ,  122  makes contact with each of the condenser and radiator tubes  111 ,  121  by a sufficiently large contact area, respectively. 
     Further, according to the embodiment, each of a radius of curvature r 1  of the condenser fin  112  and a radius of curvature r 2  of the radiator fin  122  is set to a relatively large value. As a result, a fillet is sufficiently formed at a connection portion between each of the condenser tubes  111  and the condenser fin  112  and a connection portion between each of the radiator tubes  121  and the radiator fin  122 . Therefore, heat exchange performance of the double heat exchanger  100  is restricted from declining. 
     Moreover, as shown in FIG. 6, since the inclination angle θ 1  of the condenser fin  112  is made different from the inclination angle θ 2  of the radiator fin  122 , each of the wall portions  112   d  of the condenser fin  112  is shifted from each of the wall portions  122   d  of the radiator fin  122  when viewed from an upstream air side. Therefore, a temperature boundary layer generated at an end portion of each of the wall portions  112   d  disposed at an upstream air side of each of the wall portions  122   d  is disturbed by each of the wall portions  122   d.  As a result, the temperature boundary layer is restricted from growing, and a heat transfer rate between air and refrigerant or air and engine coolant is improved. 
     Each of the condenser fin  112  and the radiator fin  122  may be formed into a corrugated shape having plural sine-wave folds, instead of the rectangular-wave folds. In such a case, the flat portions  112   a,    122   a  are not formed, and each of the upper folds  112   b,    122   b  and the lower folds  112   c,    122   c  has a uniform radius of curvature. Further, each of the slits s may be formed into a linear shape by cutting in a line between the condenser fin  112  and the radiator fin  122  so that an extremely small gap is formed between the condenser fin  112  and the radiator fin  122 . In such a case, the connection portions f need to be formed at intervals of several upper folds  112   b,    122   b  to make the inclination angle θ 1  different from the inclination angle θ 2 . However, when the slits S are formed to secure the predetermined gap W 3  between the condenser fin  112  and the radiator fin  122  as shown in FIGS. 4 and 5, the connection portions f may be formed between each of the wall portions  112   d,    122   d.    
     As shown in FIG. 7, each of the flat portions  112   a,    122   a  may be curved to have a radius of curvature R 1 , R 2  larger than the radius of curvature r 1 , r 2 , respectively. Further, as shown in FIG. 8, when the connection portions f are formed at intervals of several upper folds  112   b,    122   b,  a fin pitch P 1  of the condenser fin  112  between adjacent upper folds  112   b  may be different from a fin pitch P 2  of the radiator fin  122  between adjacent upper folds  122   b  between adjacent connection portions f. As a result, the inclination angle θ 1  of the condenser fin  112  becomes different from the inclination angle θ 2  of the radiator fin  122  between adjacent connection portions f, and the height H 1  of the condenser fin  112  becomes different from the height H 2  of the radiator fin  122 . In this case, each of the condenser fin  112  and the radiator fin  122  may be formed into a corrugated shape having plural rectangular wave folds or sine wave folds. 
     Although the present invention has been fully described in connection with preferred embodiments thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications will become apparent to those skilled in the art. Such changes and modifications are to be understood as being within the scope of the present invention as defined by the appended claims.