Abstract:
An improved heat exchanger includes an integral side piece/end cap structure for closing the ends of tanks and providing a side piece for each side of the heat exchanger and includes connecting strands between an end cap section and a side piece section that are weak, allowing the breakage thereof prior to excessive thermal stresses being placed on tube to the header joints. Also disclosed is the use of clips on end cap section and/or tank ends together with a tab on the end cap section which may be used to self-fixture of the components during assembly.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates to a heat exchanger, and more particularly, to a heat exchanger whose components are assembled to one another by soldering or brazing, for example, aluminum heat exchangers.  
       BACKGROUND OF THE INVENTION  
       [0002]     Heat exchangers for vehicles as, for example, radiators or charge air coolers, conventionally include a plurality of parallel, spaced, flat tubes that extend between header plates with tube slots which sealingly receive the ends of the flat tubes. Serpentine fins are disposed between adjacent ones of the tubes and collecting tanks are assembled in sealed relation to header plates on sides thereof opposite the tubes. As is typical with the heat exchangers utilizing the serpentine fins, to facilitate assembly, side pieces are located along each side of the heat exchanger core and extend between corresponding ends of the two headers to sandwich a serpentine fin against an endmost tube in the core. Frequently, the heat exchangers are made from aluminum in which appropriate part surfaces are clad with a braze alloy to allow the components to be assembled together by a brazing process. It is likewise possible to make copper or copper/brass heat exchangers using solder in lieu of a braze alloy.  
         [0003]     It has been proposed in German patent application No. DE 102 37 769.3 to make the tanks of such heat exchangers out of channel-like material. Closure caps are fitted to the ends of the tanks and the same may be formed separately or integrally with the side pieces. For example, one side piece may have two closure caps formed thereon, one on each end of the side piece, to be fitted to the tank end at the corresponding end of each header plate.  
         [0004]     A typical problem that occurs in the production of such heat exchangers is that the heat exchanger must be assembled from its individual parts in preparation for brazing or soldering. This means constituents must be temporarily fastened until the joining process is completed. Currently, various fixtures or jigs are used for the purpose and clamp the heat exchanger in assembled relation. The heat exchanger remains clamped until the soldering or brazing process is completed.  
         [0005]     In order to minimize or eliminate the need for such fixtures, there have been proposed various expedients whereby parts of the heat exchanger itself are provided with integral fastening devices which eliminate one or more fixtures or jigs. By way of example, reference is made to U.S. Pat. No. 6,131,286 dated Oct. 17, 2000 which discloses a tab and slit instruction for temporarily holding two metal pieces together during a joining process. This type of pre-assembly fastening is problematical in the fabrication of heat exchangers because of the required slit. In heat exchangers, the slit and the protrusion must be joined absolutely tightly or else the heat exchanger will leak.  
         [0006]     In addition, so-called “thermal cycling” that occurs during the operation of heat exchangers, often leads to breaks. Thermal cycling occurs, for example, in a vehicle when the engine is operating when the heat exchanger runs at relatively high temperature and when the engine is turned off, the heat exchanger cools to ambient temperature. Temperature gradients also lead to the same problem. Even in operation with the heat-exchange fluids at constant pressures, the side pieces in heat exchangers and the endmost tubes in the core tend to run cooler than those in the center of the core.  
         [0007]     In either event, thermal stresses arise and typically are concentrated at the tube to header joints. Of course, if the thermal stress leads to cracks at tube to header joints, the heat exchanger begins to leak and frequently will require some sort of repair which can be expensive and which can lead to extensive down time for the apparatus with which the heat exchanger is used.  
         [0008]     The present invention is directed to solving one or more of the above problems.  
       SUMMARY OF THE INVENTION  
       [0009]     It is the principal object of the invention to provide a new and improved heat exchanger. More specifically, one object of the invention is to provide a heat exchanger that may be readily manufactured with little or no use of jigs or fixtures in the pre-assembly process.  
         [0010]     It is also a principal object of the invention to provide a heat exchanger that is less susceptible to failure or leakage due to thermal cycling or thermal gradients.  
         [0011]     An exemplary embodiment of the invention achieves the foregoing objects in heat exchangers that include a pair of parallel headers, each having spaced tube slots aligned with tube slots in the other header. Tubes extend between aligned ones of the tube slots in the headers and fins extend between the tubes. Side pieces on opposed sides of the heat exchanger embrace the fins thereat and extend substantially between the corresponding ends of the headers. A pair of channel-tanks, one for each header, is fitted to the corresponding header oppositely of the tubes and end caps having bent edges embracingly and sealingly closing opposite ends of each tank are provided. The end caps are integral extensions of each end of each side piece to form end cap/side pieces. The heat exchanger is characterized by a reduction in cross section of each end cap/side piece adjacent each end of each header of at least about 50%. Each such reduction is defined by at least one cutout adjacent each end of each header.  
         [0012]     In a preferred embodiment, fasteners are provided for securing the end caps to the tank ends during assembly of the heat exchanger.  
         [0013]     In a highly preferred embodiment, each of the cross section reductions is at least about 80% of the cross section, and the end caps and side pieces remain integral about the cutout or cutouts through the retention of a connecting strand or a small number of connecting strands extending across the cutout(s) from the side piece to the integral end cap at each end of each side piece.  
         [0014]     In one embodiment, the heat exchanger is formed of aluminum and is assembled by brazing. The connecting strand or strands are sized to be readily severed if necessary.  
         [0015]     In a preferred embodiment, the fasteners include resilient, U-shaped clips on the end cap bent edge or on the ends of the tanks. Preferably, the clips are integrally formed of projections on the components.  
         [0016]     In a preferred embodiment, the fasteners also include a tab on each end cap which is bendable to overlie an adjacent end of the tank.  
         [0017]     In one embodiment, the U-shaped clips each include a sloped extremity on at least one of the legs thereon to serve as a pilot surface for receipt of a corresponding end of the tank or a corresponding bent edge of the end caps.  
         [0018]     In one embodiment, the cutout(s) defines a central connecting strand extending between each side piece and the associated end cap, while in another embodiment, the cutout(s) defines two spaced, off-center connecting strands extending between each side piece and the associated end caps.  
         [0019]     Other objects and advantages will become apparent from the following specification taken in connection with the accompanying drawings. 
     
    
     DESCRIPTION OF THE DRAWINGS  
       [0020]      FIG. 1  is a fragmentary, perspective view of a side piece for a heat exchanger made according to the invention;  
         [0021]      FIG. 2  is a view similar to  FIG. 1 , but of a modified embodiment;  
         [0022]      FIG. 3  is similar to  FIGS. 1 and 2 , but illustrates a third embodiment;  
         [0023]      FIG. 4  is similar to  FIGS. 1-3 , inclusive, but illustrates a fourth embodiment;  
         [0024]      FIG. 5  is an enlarged, fragmentary view of one corner of a heat exchanger;  
         [0025]      FIG. 6  is a side elevation taken from the left of  FIG. 5 ;  
         [0026]      FIG. 7  is a fragmentary sectional view taken approximately along the line  7 - 7  in  FIG. 5 ;  
         [0027]      FIG. 8  is a sectional view taken approximately along the line  8 - 8  in  FIG. 5 ;  
         [0028]      FIG. 9  is a vertical section of the structure shown in  FIG. 5 ;  
         [0029]      FIG. 10  is an exploded view of the structure of  FIG. 5 ;  
         [0030]      FIG. 11  is a view similar to  FIG. 10  but of a modified embodiment of the invention;  
         [0031]      FIG. 12  is a fragmentary, elevational view of a corner of a heat exchanger made according to the invention;  
         [0032]      FIG. 13  is a sectional view taken approximately along the line  13 - 13  in  FIG. 12 ; and  
         [0033]      FIG. 14  is a sectional view taken approximately along the line  14 - 14  in  FIG. 12 . 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0034]     As alluded to previously, the heat exchanger of the present invention is ideally suited for vehicular use as, for example, a vehicular radiator or charge air cooler. However, no limitation to vehicular use, or to a radiator, or charge air cooler is intended because those skilled in the art will recognize that the heat exchanger of the invention may be used in a variety of environments and for a variety of purposes. For example, the same could be utilized in a heating system for a building, or the like. In any event, no limitation to a particular environment of use or to a particular use is intended except insofar as expressly stated in the appended claims.  
         [0035]     With the foregoing in mind, several embodiments of the invention will now be described.  
         [0036]     Turning first to  FIGS. 8, 9 , and  10 , a typical heat exchanger embodying the invention is shown fragmentarily. The same includes two, spaced, parallel header plates  20  (only one of which is shown) having upturned side edges  22  along its length. Elongated tube slots  24  extend transversely to the length of each header plate  20  from end to end thereof, and in turn receive the ends  26  of a plurality of flattened tubes  28  which extend between corresponding tube slots  24  in the two headers.  
         [0037]     An open-ended, open-bottomed channel-like tank, generally designated  30 , includes a base  32  with depending sides  34 . The sides  34  extend about the remote surfaces of the flanges  22  as well as about the bent edge  36  of an end cap part  38  of a combination side piece/end cap construction, generally designated  40 . One or more ports  42  will be located in the tank, typically in one of the sides  34 , for connection into the system with which the heat exchanger is used.  
         [0038]     As seen in  FIGS. 9 and 10 , the side piece/end cap assembly  40  includes an end piece section  44  in addition to the end cap section  38 . As perhaps best viewed in  FIG. 9 , the side piece section  44  sandwiches a serpentine fin  46  against the endmost one of the tubes  28 . Typically, this structure will be provided on both sides of the case. Additional serpentine fins  46  extend between adjacent ones of the tubes  28  as well.  
         [0039]     The foregoing description basically describes only a single quadrant of a typical heat exchanger. Those skilled in the art will recognize that a complete heat exchanger will include two of the header plates  20  that are spaced in parallel with the tubes  28  running between the two header plates  20  as mentioned previously. It will also include two of the tanks  30 , one for each header plate, and two of the side piece/end caps  40 , one on each side of the heat exchanger for sandwiching one of the fins  46  against the endmost tube  28  on each side of the heat exchanger. Further, as there will be two of the tanks  30 , one assembled to each of the header plates  20 , there will be a total of four of the end cap sections  38 , one for each end of each of the two tanks  30 .  
         [0040]     In the usual case, all of the components will be made of aluminum and, where required, provided with braze clad material, i.e., an aluminum brazing alloy having a melting point somewhat less than the melting point of the aluminum of which the components are formed. In some cases, the braze cladding will be on only one side of the component, while in other cases, it may be on both sides of the component. In some cases, a component may not be braze clad at all. By way of example, the tank  30  must be joined to the end caps  38  as well as to the header plate flanges  22 . If braze cladding is located on the remote surfaces of the two flanges  22 , that is, the two that face away from each other, as well as on the innermost side of the side piece/end cap  40 , then the tank  30  may be free of braze cladding because braze cladding will always be present at the interfaces of the header plate flanges  22  and the facing surface of the bent edge  36  of the end cap piece  38 . In addition, this will results in braze cladding being located on the inner side of the side piece section of the end cap/side piece structure  40  for bonding to the adjacent serpentine fin  46 .  
         [0041]     Turning now to  FIGS. 1-4 , four different forms of the end cap/side piece assembly  40  will be described. In each case, each side piece section  44  is formed integrally with two end cap sections  38 , with there being one end cap section  38  at each end of the side piece section  44 . Two sections  38  and  44  are separated by one or more cutouts  50 . In the embodiment of  FIG. 1 , cutouts  50  are separated by a single connecting strand  52  which is located centrally of the side piece/end cap assembly  40 . In contrast, cutouts  54  are arranged to define two, off-center connecting strands  56  in the embodiment of  FIG. 2 .  
         [0042]      FIG. 3  includes non-centered, multiple connecting strands  56  separated by cutouts  54  like the embodiment of  FIG. 2  while the embodiment of  FIG. 4  includes a single, central connecting strand  52  and cutouts  50  as in the embodiment of FIG.  1 .  
         [0043]     In all cases, the side piece/end cap structures  40  are integrally formed, that is, formed of a single piece of metal as by stamping. The side piece sections  44  include flanges  60  that are directed toward the endmost tube on the corresponding side of the core and serve to confine the serpentine fin  46  that is sandwiched against the endmost tube  28  by the side piece section  44  to aid in assembly.  
         [0044]     The embodiments of  FIGS. 1 and 2  have identical end cap sections  38 . As mentioned previously, each end cap section  38  is surrounded on three sides by a bent edge  36  about which one end of a tank  30  is abutted to be sealingly bonded thereto. As seen in  FIGS. 1 and 2 , integral, U-shaped clips  62  extend from the bent edge  36  away from the tank (see also  FIG. 8 ) with an outer leg  64  directed back toward the tank to resiliently clip on the end of the tank. This serves to fasten the tank  30  to the end cap section  38  during brazing or soldering.  
         [0045]     To facilitate fitting of the end of the tank  30  into the clips  62 , a sloped or slanted surface extension  66  extends away from the end cap section  38  and is located on one side of the leg  64  to serve as a pilot to guide the lower end of a corresponding side  34  of the tank  30  into the proper location and retain it by the resilience of the material of which the clip  62  is made.  
         [0046]     Each of the embodiments of  FIGS. 1 and 2  also includes, on the part  70  of the bent edge  36  remote from the side piece section  44  adjacent the part  70  of the bent side  36  a tab  72  which can be bent and deformed over the wall  32  of the tank as best seen in  FIG. 6 . The tab  72  thus serves to hold the wall  32  in firm engagement with the surface  70  during the brazing process to assure a leak-free joint.  
         [0047]     An embodiment of the invention utilizing the side piece/end cap assemblies  40  shown in  FIGS. 3 and 4  is illustrated in  FIGS. 11-14 . In this case, U-shaped spring clips  80  are integrally formed on each end  82  of each tank  39 , and specifically the sidewalls  34  thereof. As seen in  FIG. 13 , each of the U-shaped clips  80  includes an outwardly flared or sloped surface for the clips  80  to allow them to be fitted to outward projections on both sides of each end cap section  38 . That is, the flared sections  84  serve the same purpose, in the embodiment of  FIGS. 11-14  as the slope surfaces  66  of the clips  64  in the earlier illustrated embodiments using the assemblies  40  of  FIGS. 1 and 2 .  
         [0048]     The tab  72  is retained in the embodiment of  FIGS. 10-14 .  
         [0049]     It is to be particularly noted that connecting strands  52 ,  56 , and the various embodiments typically may be such that there is a slight offset of the end cap section  38  from the side piece section  44 . As can be seen, for example, in  FIGS. 5 and 9 , it is not unusual for the side piece section  44  to be located outwardly of the end of the header adjacent thereto, and the offset accommodates so locating the various components.  
         [0050]     Importantly, the cutouts  50 ,  54  provide a weak spot at the point whereat the side piece sections  44  would be connected directly to the header  20  or connected via the connection to the end cap section  38  and ultimately to the header  20  through the tank  30 . It is this area whereat substantial thermal stress can exist and is transmitted to the tube to header joints. Because the connecting strands are relatively thin, as can be seen in the drawings, they may readily fracture to relieve thermal stresses as required. To achieve the desired relief in such circumstances, it is highly desirable that the cross-sectional area of the piece of metal of which each assembly  40  is formed be reduced by at least 50% at the cutouts  50  or  54 . Preferably, the cross section reduction is at least about 80%. The side of the reduction is measured in a plane transverse to the length of each side piece/end cap assembly.  
         [0051]     Moreover, ideally, the connecting strands  52 ,  56  are sized so that they may easily be intentionally severed if desired, following brazing or soldering. In fact, it is only necessary that the connecting strands  52 ,  56  be of sufficient cross-sectional area as to provide some support for the end cap sections on the side piece section  44  during pre-assembly using the clips  62 ,  80  and the tab  72  during pre-assembly prior to brazing or soldering. Thus, it will be seen that the invention provides a heat exchanger that eliminates or minimizes thermal stresses at two of the header joints that may cause failure due to thermal cycling and/or thermal gradients. Furthermore, unique use of the clips and tabs eliminates the need for special fixtures or jigs to hold the components making up the heat exchanger in assembled relation prior to soldering or brazing, thereby minimizing the cost of fixturing during assembly.