Abstract:
A heat exchanger such as a condenser for use in an automobile air-conditioning system is composed of a pair of header tanks, plural tubes connecting both header tanks, and fins made of a thin aluminum plate disposed between the tubes. Those components are all connected to one another by brazing to form a unitary body of the heat exchanger. A solder material for bonding the tubes and the header tanks is attached onto the inner surface of both header tanks to prevent the solder material from dispersing into the thin fins in the brazing process. Thus, the thin aluminum fins are protected against erosion due to the solder dispersed therein.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
         [0001]    This application is based upon and claims benefit of priority of Japanese Patent Application No. 2000-193155 filed on Jun. 27, 2000, the content of which is incorporated herein by reference.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to a heat exchanger having plural tubes connected to header tanks by brazing. This invention is adequately applicable to an automotive heat exchanger such as a condenser for use in an air-conditioner.  
           [0004]    2. Description of Related Art  
           [0005]    A condenser having plural tubes connected to header tanks disposed at both sides of the tubes is known hitherto. A cross-sectional view of a header tank to which a tube is connected in a conventional heat exchanger is shown in FIG. 3. Plural aluminum tubes  14  having refrigerant passages therein are connected to header tanks disposed at both ends of the tubes. In FIG. 3, only one tube  11  is shown and another tube is not shown. Aluminum fins (such fines  15  as shown in FIG. 1) are interposed between neighboring tubes, and the tubes and fines are laminated forming a condenser core.  
           [0006]    In the conventional condenser, the header tank  11  is composed of a first U-shaped plate  111  and a second u-shaped plate  112 , both connected to each other. The first U-shaped plate  111  is a clad plate having a core plate  111   a  and a solder layer  111   b  clad on the outer surface of the core plate  111   a . The second U-shaped plate  112  is also a clad plate having a core plate  112   a  and solder layers  112   b  and  112   c  which are clad on both inner and outer surfaces of the core plate  112   a . The fins  15  disposed between the tubes  14  and connected thereto are also made of solder-clad aluminum, while tubes  14  are made of bare aluminum. Each tube  14  having plural refrigerant passages therein are made by a drawing process.  
           [0007]    In the assembling process of the condenser, the tubes  14  and the fins  15  are alternately laminated, and the tubes  14  are inserted into both header tanks to form a unitary condenser unit. Flux “f” is coated on the solder layers  111   b  and  112   c  which are clad on the outer surface of the tube  11 . Then, the condenser unit is brazed in a furnace to melt the solder layers and to connect all the components to one another. In this brazing process, the solder layer  111   b  on the outer surface of the first plate  111  connects the tubes  14  to the first plate  111 , and the solder clad on the fins  15  connects the tubes  14  and fins  15  together.  
           [0008]    In the brazing process of the conventional condenser, the molten solder material is not only used for connecting the first plate  111  to the tubes  14  but also supplied to the fins  15  connected to the tubes  14 , because the solder layer  111   b  is located on the outer surface of the header tank  11 . Therefore, the solder from the first plate  111  is added to the clad solder on the fins  15 , and solder becomes too rich at the end portions of the fins  15  located close to the first plate  111 . In other words, much solder is dispersed into the end portions of the fins  15 , causing erosion in the fins  15 . Though the solder is also dispersed into the tubes  14 , the erosion problem is more harmful to the fins  15  because the fins  15  are much thinner than the tubes  14 .  
         SUMMARY OF THE INVENTION  
         [0009]    The present invention has been made in view of the above-mentioned problem, and an object of the present invention is to eliminate or at least suppress the solder dispersion into the tubes and especially into the fins in the brazing process, thereby avoiding the erosion due to the dispersed solder.  
           [0010]    A heat exchanger is composed of a pair of cylindrical header tanks (a first header tank and a second header tank), plural tubes connecting the pair of header tanks and plural corrugated fins disposed between the tubes in heat conductive relation. The heat exchanger may be used as a condenser for condensing over-heated refrigerant in an automotive air-conditioning cycle. The refrigerant supplied to the first header tank is distributed to the plural tubes and flows into the second header tank. The over-heated refrigerant is cooled down while flowing through the tubes, and the condensed refrigerant flows out from the second header tank.  
           [0011]    The tanks are formed by rounding a solder-clad aluminum plate, so that the solder layer is positioned in the inner surface of the cylindrical tanks. The solder layer serves as a material for connecting the tubes and the tanks in brazing. The tubes are drawn from a bare aluminum material, and the corrugated fins are made of a thin solder-clad aluminum plate. Flux to promote brazing is coated on the outer surface of the tubes. Then, all the components thus made are assembled to form a heat exchanger unit. The assembled heat exchanger unit is brazed in a furnace filled with nitrogen gas or inert gas. In the brazing process, the tubes and tanks are connected to each other by the molten solder layer clad on the inner surface of the tanks, while the corrugated fins are connected to the tubes by the molten solder on the surface of the corrugated fins.  
           [0012]    Since the solder layer is positioned on the inner surface of the cylindrical header tank, i.e., the aluminum plate forming the header tank is between the solder layer and the corrugated fin, the solder molten in the brazing process is prevented from dispersing into the fin even if the end portion of the fin is positioned close to the header tank. In addition, unnecessary dispersion of the molten solder into the tubes is also prevented. Thus, the fin made of a thin aluminum plate is protected against erosion due to excessive solder dispersed into the fin.  
           [0013]    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 following drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    [0014]FIG. 1 is a perspective view showing an entire structure of a condenser;  
         [0015]    [0015]FIG. 2 is a partial cross-sectional view showing a portion connecting a tube to a header tank in the condenser shown in FIG. 1, as an embodiment of the present invention; and  
         [0016]    [0016]FIG. 3 is a partial cross-sectional view showing a portion similar to that of FIG. 3 in a conventional condenser. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0017]    An embodiment of the present invention will be described with reference to FIGS. 1 and 2. First, referring to FIG. 1, the entire structure of a condenser  10  which is generally referred to as a multi-flow-type condenser will be described. The condenser  10  cools down and condenses overheated gaseous refrigerant supplied from a compressor (not shown) in an automotive air-conditioning system. The condenser  10  is composed of a condenser core  13  disposed between and connected to a pair of header tanks, a first header tank  11  and a second header tank  12 . The header tanks  11 ,  12  are made of aluminum and substantially cylinder-shaped.  
         [0018]    The condenser core  13  is composed of tubes  14 , corrugated fins  15 , both being alternately laminated, and side plates  19 ,  20  respectively disposed at the top and the bottom of the condenser core  13 . The condenser core  13  is connected between both header tanks  11 ,  12 , so that the tubes extend horizontally. The tube  14  is made by drawing aluminum into a flat shape having plural refrigerant passages therein. The fin  15  is made by bending a solder-clad aluminum plate into a corrugated shape. One end of each tube  14  is inserted into the first header tank  11  and the other end into the second header tank  12 , so that the inner spaces of both header tanks  11 ,  12  communicate with each other through the tubes  14 . The U-shaped side plate  19  is disposed at the top of the condenser core  13  and connected to the upper most fin  15 , while the other U-shaped side plate  20  is disposed at the bottom of the condenser core  13  and connected to the lower most fin  15 . Both side plates  19 ,  20  serve as condenser frames with which the condenser  10  is mounted on a vehicle body.  
         [0019]    A refrigerant inlet port  16  is provided at an upper portion of the first header tank  11 , while a refrigerant outlet port  17  is provided at a lower portion of the second header tank  12 . The refrigerant entering the first tank  11  through the inlet port  16 , is distributed to each tube  14 , enters the second header tank  12  through the tubes  14  and flows out from the outlet port  17 . Both ends of the first header tank  11  are closed with caps  113 ,  114 , respectively, and similarly both ends of the second header tanks  12  are closed with caps  123 ,  124 , respectively.  
         [0020]    The structure connecting the tubes  14  to the header tanks  11 ,  12  will be described in detail with reference to FIG. 2 that shows a cross-section II-II marked in FIG. 1. Since both header tanks  11 ,  12  have the same structure, the structure of the first header tank  11  will be described below as a representative of both header tanks  11 ,  12 . Reference numbers shown in parentheses in FIG. 2 denote components or portions of the second header tank  12  that correspond to those of the first header tank  11 .  
         [0021]    The first header tank  11  is composed of a first U-shaped plate  111  and a second U-shaped plate  112 , both being connected to each other to form a cylindrical inner space that serves as a refrigerant passage. A pair of caps  113 ,  114  close both ends of the inner passage. Plural openings (not shown), the number of which corresponds to the number of tubes  14 , are formed in the first header tank  11 , so that each tube  14  is inserted into the opening and connected thereto. The first plate  111  which is connected to the tubes  14  is a solder-clad aluminum plate having a core aluminum plate  111   a  and a solder layer  111   b  clad on the inner surface of the first plate  111 . The second plate  112  is a solder-clad aluminum plate having a core aluminum plate  112   a  and solder layers  112   b ,  112   c  clad on both surfaces of the second plate  112 . Both aluminum core plates  111   a ,  112   a  are made of an aluminum material such as A-3003, and the solder layers  111   b ,  112   b ,  112   c  are made of a solder material such as A-4045.  
         [0022]    The tubes  14  made of a bare aluminum material such as A-1050 are manufactured in a drawing process. The fins  15  are made of a solder-clad aluminum plate having a core plate made of aluminum such as A-3003 and a solder layer such as A-4045 clad on the core plate. The caps  113 ,  114  and side plates  19 ,  20  are made of bare aluminum such as A-3003. The refrigerant inlet port  16  and the refrigerant outlet port  17  are also made of bare aluminum.  
         [0023]    A process of manufacturing the condenser  10  will be explained below. All the components of the condenser  10  are manufactured using the solder-clad aluminum material or the bare aluminum, respectively. Then, flux is coated on the second plate  112  ( 122 ), the caps  113 ,  114  ( 123 ,  124 ), the tubes  14 , and the side plates  19 ,  20 , in a coating process such as immersion coating or roll coating. Then, the coated flux is dried. As the flux, a mixture of non-corrosive flux (e.g., fluorides such as a mixture of KALF 4  and K 2 Al 6 ) and a binder for improving flux adhesion (e.g., acrylic resin substantially composed of 2-ethylhexyl methacrylate) may be used. Alternatively, silicon (Si) may be further mixed with the mixture of the flux and the binder to improve brazing ability.  
         [0024]    Then, the components, including the first header tank  11 , the second header tank  12 , tubes  14 , fins  15 , side plates  19 ,  20 , and inlet and outlet ports  16 ,  17 , are all assembled to form a condenser unit  10  shown in FIG. 1. The assembled unit is kept in a jig to keep its unitary form. The unit kept in the jig is heated in a brazing furnace filled with nitrogen gas or inert gas up to a melting point of the solder material. Thus, all the components of the condenser  10  are connected to one another by brazing, forming a unitary body of the condenser  10 .  
         [0025]    In the brazing process, the first plates  111 ,  121  and the tubes  14  are connected to each other by the solder layers  111   b ,  121   b  clad on the inside surfaces of the first plates  111 ,  121  under the flux coated on the tubes  14 . Since the solder layers  111   b ,  121   b  are positioned inside the header tanks  11 ,  12 , i,e., fins  15  are separated by the core plates  111   a ,  121   a  from the solder layers  111   b ,  121   b  the solder is prevented from flowing to the fins  15 . Therefore, excessive solder supply to the fins  15  are avoided, and the end portions of the fins  15  may be positioned closer to the header tanks  11 ,  12 .  
         [0026]    In a conventional manufacturing process, flux “f” (shown in FIG. 3) necessary for brazing is coated after its assembling process by spraying or other methods. Accordingly, the flux is coated not only on necessary portions but also on other portions, and thereby a large amount of flux is consumed. On the contrary to the conventional process, in the process of the present invention, the flux required for brazing (connections between the first plates  111 ,  121  and tubes  14 , and between the tubes  14  and fins  15 ) is supplied from the tubes  14 . The flux required is coated on the tubes  14  before the assembling process. Therefore, the flux is coated only on the necessary portions and the unnecessary consumption of the flux is avoided.  
         [0027]    Application of the present invention is not limited to the condenser described above, but it can be applied to other heat exchangers such as automotive radiators. Though the solder-clad aluminum is used for the components requiring brazing in the foregoing embodiment, a solder material in a paste state may be coated on aluminum components, or silicon (Si) that promotes brazing may be coated on the aluminum components. The material of the components is not limited to aluminum, but the components may be made of an aluminum alloy. Though the flux required for brazing the first plates  111 ,  121  and the tubes  14  is coated on the tubes  14  in the foregoing embodiment, it is possible to additionally coat the flux on the solder layers  111   b ,  121   b , if necessary. Alternatively, the flux may be coated only on the solder layers  111   b ,  121   b  without coating it on the tubes  14 .  
         [0028]    Though the first plates  111 ,  121  having the solder layers clad on the inside surfaces thereof are used in the foregoing embodiment, it is also possible to additionally clad a sacrificial corrosion layer (e.g., A-7072 or A-3003 including 1 weight-percent Zn) on the outer surfaces of the first plates  111 ,  121 . Though the tubes  14  having plural passages therein formed by drawing are used in the foregoing embodiment, they may be replaced with tubes formed by presswork.  
         [0029]    While the present invention has been shown and described with reference to the foregoing preferred embodiment, it will be apparent to those skilled in the art that changes in form and detail may be made therein without departing from the scope of the invention as defined in the appended claims.