Abstract:
Heat exchangers, particularly brazed heat exchangers used in motor vehicle applications, are presented. The tubes of the heat exchangers are coated with a multi-layered clad of preferably at least four layers of material of metallic alloy base.

Description:
[0001]     This patent application claims priority of Provisional application No. 60/642,173 filed Jan. 7, 2005 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates to heat exchanger, and, particularly, brazed heat exchangers used in motor vehicle applications.  
       BACKGROUND OF THE INVENTION  
       [0003]     Heat exchangers have been constructed in a variety of ways in the prior art. In general, a heat exchanger will comprise a plurality of components that is assembled together by suitable joining techniques. Many techniques may be utilized, including mechanical assemblies and the like. In one preferred embodiment, one or more of the components of the heat exchanger such as the baffles, the end tanks, the tubes, fins, the inlets, the outlets, a bypass or combinations thereof may be attached to each other using brazing. Although various brazing techniques may be used, one technique often found in making heat exchangers is referred to as controlled atmosphere brazing. Controlled atmosphere brazing typically employs a brazing alloy for attaching components wherein the components are formed of materials with higher melting points than the brazing alloy. The brazing alloy is preferably positioned between components or surfaces of components to be joined and, subsequently, the brazing alloy is heated and melted (e.g., in an oven or furnace, and preferably under a controlled atmosphere). Upon cooling, the brazing alloy preferably forms a metallurgical bond with the components for attaching the components to each other. The brazing alloy may be provided as a cladding on one of the components of the heat exchanger. In such a situation, it is contemplated that the components may be formed of a material such as a higher melting point aluminum alloy while the cladding may be formed of a lower melting point aluminum alloy.  
         [0004]     The current art for radiator type heat exchangers typically utilize welded or folded tubes that consist of three layer clad brazing material. Prior art heat exchangers, and, in particular, radiators, had a maximum of three layers of alloys as attempts to have more layers often resulted in brazing issues.  
         [0005]     In most radiator type heat exchangers, the three layer clad material include an external brazing clad material, a base core material, and an internal clad material. The internal clad material is particularly used for brazing and/or corrosion protection. Four layer material compositions, such as that of U.S. Pat. No. 6,555,251, Kilmer et al, issued Apr. 29, 2003, do exist, but relate to some material composition specifics, but not the potential of applying specific four layers of alloys for heat exchanger applications. In radiator applications in particular, one limitation faced by both welded and folded radiator tubes is related to the depth of the heat exchanger parallel to the external fluid flow. Due to mechanical stress considerations, the maximum core depth that is utilized with a single tube row is less than 40 mm. For applications with a core depth of 40 mm or greater, two tube rows are utilized in order to reduce the internal pressure induced stress in the flat sections of the radiator tube. The usage of two tubes necessitates a space between the two tube rows to ensure manufacturability during both assembly and brazing.  
       SUMMARY OF THE INVENTION  
       [0006]     Heat exchangers of the present invention will typically include one or more tubes, one or more end tanks, one or more inlets and outlets, one or more baffles, one or more fins or a combination thereof. Depending upon the embodiment of the heat exchanger, various different shapes and configurations are contemplated for the components of the heat exchanger. For example, and without limitation, the components may be integral with each other or they may be separate. The shapes and sizes of the components may be varied as needed or desired for various embodiments of the heat exchanger. Preferred heat exchangers are, for example, radiator type heat exchangers and charge air coolers. Heat exchangers, and, especially, radiators, are surprisingly well suited to the use of an at least four-layer braze alloy to provide the advantages listed hereinabove.  
         [0007]     Various aspects of the present invention utilize a minimum of four layer alloy material that offers significant enhancements in performance, durability, and packaging of heat exchangers. As described above, a majority of the automotive radiators produced today utilize welded or folded tubes that utilize multi-layer braze clad material. The braze clad material usually includes an aluminum alloy, copper alloy, or similar core material in between two layers of modified compatible alloys. The modified alloys may be utilized for brazing, for corrosion protection, etc.  
         [0008]     Aspects of the present invention, for example, have a heat exchanger with a plurality of tubes, at least one tube consisting of a single welded tube with one or more brazed beads longitudinally extended down the length of the tube that effectively creates two or more flow channels, typically of less than 40 mm, while utilizing a single tube. These beads can, for example, be mechanically created by rolling the tube material to form one or more depressions of circular-shape, square or rectangular shape or any combination thereof separated by the thickness of the tube. Beads, in various aspects of the present invention, are forced against each other during the heat exchanger manufacturing process creating contact or a very small gap in between them. In such processes, the coolant side of the beads (internal side of the tube) is covered by a braze clad layer that, when exposed to a controlled atmosphere brazing process, as described above, will melt and create a metallurgical bond securing the beads together along the length of the tube. This eliminates the internal pressure stress concerns found in the prior art and reduces the overall package required for the radiator by eliminating the space required for the two tube rows.  
         [0009]     In a preferred method of making the heat exchangers of the present invention, the flat tubes of the heat exchanger are formed from flat sheet braze material and at least one portion is formed approximately normal to the wide portion (major axis) and parallel to the minor axis of the tube. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  shows a cross section view of a tube with a four layer, coated material useful in automotive heat exchanger applications, in accordance with an aspect of the present invention.  
         [0011]      FIG. 2  shows the post-braze configuration of a four layer coated material used in a heat exchanger, including internal braze joint, in accordance with an aspect of the present invention.  
         [0012]      FIG. 3  shows a tube of a heat exchanger with center beads and dimples, in accordance with an aspect of the present invention.  
         [0013]      FIG. 4  shows a tube of a heat exchanger with center beads and no dimples, in accordance with an aspect of the present invention.  
         [0014]      FIGS. 5   a  and  5   b  are typical radiator design post brazing wherein are shown tubes, fins, end tanks, and the like, capable of being made using a four layer clad, at least four-layer braze alloys, in accordance with an aspect of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0015]     Various embodiments of the present invention, heat exchangers with tubes have features such that the creation of a mechanical or electromechanical or any other type of device, further allows the tube bead to be stopped prior to the end of the tube resulting in a continuous brazing surface in the tube/header joint. By providing such a surface, various aspects of the present invention, therefore reduce the possibility that, a small gap will exist in between the header flange and the tube resulting in a no-braze condition and a leak path.  
         [0016]     In preferred embodiments of the present invention, a tube bead can also extend to the end of the tube. In heat exchanger with tanks and headers, a header flange can be formed to create an hourglass-shape tube slot to mate tubes comprising at least one tube bead, thereby resulting in a continuous brazing surface in the tube/header joint.  
         [0017]     In various embodiments of the present invention, a braze joint is formed in the tube comprising a preferably four or more layer braze alloy material, consisting of an external braze alloy, an aluminum alloy core base material, an internal corrosion coat (clad), i.e. any type of clad that can resist internal corrosion or chemical or electrical attack and/or degradation, and an internal brazing clad, all of which preferably comprise aluminum alloys.  
         [0018]     In particular embodiments of the present invention, a heat exchanger is provided with a core thickness of 40 mm or greater with enhanced performance and structural durability, in a more compact package.  
         [0019]     Other examples of various embodiments of the present invention have a heat exchanger that comprises a single welded radiator tube utilizing a four or more layer braze alloy material, comprising an external braze layer, a core alloy material layer, an internal corrosion resistant layer, and an internal braze layer, to form the overall clad.  
         [0020]     The tube is preferably formed through a normal rolling process, with or without dimples, with one or more beads down the length of the tube on both flat surfaces such that the beads contact each other inside the tube. The tubes are then assembled into a radiator core consisting of a parallel arrangement of tubes and fins and brazed using standard brazing practices to create braze joints including the joint at the point of contact for the two beads.  
         [0021]     In the preferred embodiments of the present invention, there is a significant increase in heat transfer efficiency in the same or smaller package size versus heat exchangers, and, especially, radiators, that do not have an at least four layer clad. In general, the package size can be reduced by 20% while maintaining or improving overall performance.  
         [0022]     In various embodiments of the present invention, a heat exchanger consists of electro-welded tubes with a center bead, with or without dimples, more preferably, with dimples, and an unformed tube end or tube end where the beads and dimples do not continue all the way to the end of the tube (unformed or bead-free), in the area of the tube to header interface (see  FIG. 3  and  FIG. 4 ).  
         [0023]     Referring to  FIG. 1 , tube material is coated with a four layer tube coating material: Layer # 1  (D)—External Braze Clad; Layer # 2  (C)—Core Alloy Material; Layer # 3  (B) or (B′)—Internal Corrosion Protection Clad, Layer # 4  (A)—Internal Brazing Clad. Internal side of the tube (I side) and external side of the tube (E side) are indicated.  
         [0024]     A coated tube is prepared having a coating with four layers. The layers preferably comprise elements in the quantities listed below:  
         [0025]     Table 1: Composition control range for each layer of the four layer coated tubes (wt %):  
                                                                                                                         Si   Fe   Cu   Mn   Mg   Cr   Zn   Ti   Zr                                    B′   0.7 (Si + Fe)       0.1   0.1   0.1       0.8 to                                           1.3       A   6.8 to 8.2   0.80    0.25   0.1           0.2       B   0.8   0.3       1.6           1.5       0.15       C   0.6   0.7   0.05 to   1.0 to           0.1                   0.2   1.5                  
 
         [0026]     Referring to  FIG. 2 , tube walls ( 21 ) are provided, with braze joint ( 23 ) between tube walls, and bead ( 22 ) in final product for use in heat exchanger (not shown) where the bead ( 22 ) is fully brazed.  
         [0027]     Referring to  FIG. 3  and  FIG. 4 , at least two flow channels are formed. Unformed tune ends ( 31 ,  41 ) are shown on tubes ( 30 ,  40 ) with dimples ( 33 ) on one of the tubes with center bead ( 32 ), and none on tube of  FIG. 4  with center bead ( 42 ). Beads ( 32 ,  42 ) form a metallurgical bond, such as braze bond, induction bond, vibration bond, or the like, preferably a braze bond, securing both sides of the tube together.  
         [0028]     In various embodiments of the present invention internal bead braze joint allows the use of a single welded tube. A single welded tube provides for good manufacturability of product. Manufacturing improvements provided by various aspects of the present invention include reduced assembly time due to a reduced number of parts and enhanced braze ability in the tube to header joint due to the continuous interface between the header flange and the tube. In various embodiments, the presence of an internal bead provides structural stability of the radiator core for high demand applications.  
         [0029]     Internal corrosion tests of radiators with four-layer tube material were completed. For example, tube material forming a coat is provided as a four layer clad or coat. In at least one layer, 10% external aluminum brazing alloy aluminum core alloy is found; in at least one other layer, 10% internal corrosion protection aluminum alloy is found, in at least one other layer, 5% internal aluminum brazing alloy waterside is found.  
         [0030]     In four layers coats clad as described above, the results show only very light pitting: for example, −18 micron average pit depth as compared to 52 micron combined liner thickness; −23 micron maximum pit depth as compared to 52 micron combined liner thickness.  
         [0031]     The various layers of the material tube coat (clad) of the present invention have compositions that may be the same or different, depending on the layer. Table I shows four layers with relative amount based on weight percent of various elements such as Si, Fe, Cu, MN, Mg, Cr, Zn, Ti and Zr. In Table I, areas left blank indicate undetectable, insignificant or inconsequential amount of the material necessary to be present in that layer or clad coat. In  FIG. 1 , for example, for 5% mineral layer (D) minimized impact on the layer of (C) provides corrosion resistance; layers (D) or (A) with reduced Si dilution effect in brazing process to maximize the corrosion resistance; with layer C, in combination provides the four layers with highest corrosion potential after brazing.  
         [0032]     At least one layer, B layer, the potential for having the layer comprise B′ alloy, is also perceived as one of the aspects present invention.  
         [0033]     Referring to  FIG. 5   a  is shown a heat exchanger ( 50 ) having coated tubes ( 51 ) and tanks with headers ( 52 ) post brazing, with fins ( 53 ). Referring to  FIG. 5   b  are tubes ( 56 ,  57 ,  58 ), having four layers ( 59   a - c ,  60   a - c ,  61   a - c ,  62   a - c ) forming the clad of the tubes.  
         [0034]     In one aspect of the present invention, a method for making a multiple layer cladded heat exchanger is provided comprising the steps of: obtaining tubes that include a metal or metallic alloy comprising four layer clad material; arranging the tubes in alternating rows with secondary heat exchange fin surfaces to form a matrix; compressing the matrix; assembling headers to the matrix; and brazing the assembled header and matrix such that metallurgical bonds form throughout the matrix.  
         [0035]     Unless stated otherwise, dimensions and geometries of the various structures depicted herein are not intended to be restrictive of the invention, and other dimensions or geometries are possible. In addition, while a feature of the present invention may have been described in the context of only one of the illustrated embodiments, such feature may be combined with one or more other features of other embodiments, for any given application. It will also be appreciated from the above that the fabrication of the unique structures herein and the operation thereof also constitute methods in accordance with the present invention.  
         [0036]     The preferred embodiments of the present invention have been disclosed. A person of ordinary skill in the art would realize, however, that certain modifications would come within the teachings of the invention. Therefore, the following claims should be studied to determine the true scope and content of the invention.