Patent Publication Number: US-6209202-B1

Title: Folded tube for a heat exchanger and method of making same

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to heat exchangers for motor vehicles and, more specifically, to a folded tube and method for making same for a heat exchanger in a motor vehicle. 
     2. Description of the Related Art 
     It is known to provide a tube for a heat exchanger such as a condenser in an air conditioning system of a motor vehicle. The tube typically carries a first fluid medium in contact with its interior while a second fluid medium contacts its exterior. Typically, the first fluid medium is a liquid and the second fluid medium is air. Where a temperature difference exists between the first and second fluid mediums, heat will be transferred between the two via heat conductive walls of the tube. 
     It is also known to provide corrugated fins or ribs in the interior of the tube to increase the surface area of conductive material available for heat transfer to cause turbulence of the fluid carried in the interior of the tube and to increase the burst strength of the tube. One known method of making such a tube is to physically insert a corrugated fin into the generally flattened tube after the tube has been manufactured. This is an extremely difficult process since the corrugated fin to be inserted into the tube is extremely thin and subject to deformation during the insertion process. 
     Another known method of forming a tube for a heat exchanger is to extrude the tube in an extrusion process. In this construction, internal ribs are formed during the extrusion. However, these extruded tubes are relatively expensive to produce. 
     Yet another known method of forming a tube for a heat exchanger is to provide a flat, elongated sheet with lugs and the ends of the sheet are folded to form the tube. The ends of the tube are then brazed. An example of such a tube is disclosed in U.S. Pat. No. 5,386,629. In this construction, the tube may have flow paths between the lugs having a hydraulic diameter of less than 0.050 inches. Hydraulic diameter is conventionally defined as the cross-sectional area of each of the flow paths multiplied by four and divided by a wetted perimeter of the corresponding flow path. While a hydraulic diameter of less than 0.050 inches optimizes heat transfer efficiency, it is relatively expensive to produce. 
     Although the above tubes have worked well, they suffer from the disadvantage that the extruded tubes are relatively costly to manufacture Another disadvantage of the above tubes is that the lugs are not folded and squeezed. Yet another disadvantage of the above tubes is that the hydraulic diameter of the flow paths are not greater than 0.050 inches, making them relatively expensive to produce. Therefore, there is a need in the art to provide a folded tube for a heat exchanger of a motor vehicle that overcomes these disadvantages. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention is a folded tube for a heat exchanger. A folded tube includes a base, a top spaced from and opposing the base, a first side interposed between the base and the top along one side thereof, and a second side interposed between the base and the top along another side thereof. The folded tube also includes at least one of the base and the top having at least one internal web having an initial web height and being compressed to extend the at least one internal web to a final web height greater than the initial web height and defining a plurality of fluid ports. 
     Also, the present invention is a method of making a folded tube for a heat exchanger. The method includes the steps of providing a generally planar sheet, folding the sheet, and forming at least one internal web having a first fold portion and a second fold portion. The method also includes the steps of compressing the at least one internal web to extend a height of the at least one internal web. The method further includes the steps of folding the sheet and forming a base and a top opposing the base and a first side interposed between the top and the base and a second side interposed between the top and the base such that the at least one internal web contacts either one of the top or the base to provide a plurality of fluid ports. 
     One advantage of the present invention is that a folded tube for a heat exchanger such as a condenser is provided for an air conditioning system of a motor vehicle for condensing liquid refrigerant. Another advantage of the present invention is that the folded tube is stamped and folded and is more economical to manufacture than an extruded tube. Yet another advantage of the present invention is that the folded tube can have multiple ports or flow paths with a hydraulic diameter greater than 0.070 inches, making it relatively inexpensive to manufacture. Still another advantage of the present invention is that the folded tube is able to meet performance requirements. 
     Other features and advantages of the present invention will be readily appreciated, as the same becomes better understood after reading the subsequent description taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an elevational view of a folded tube, according to the present invention, illustrated in operational relationship with a heat exchanger of a motor vehicle. 
     FIG. 2 is an enlarged perspective view of the folded tube of FIG.  1 . 
     FIG. 3 is an end view of the folded tube of FIG.  1 . 
     FIG. 4 is an enlarged view of a portion of the folded tube in circle  4  of FIG.  2 . 
     FIG. 5 is an enlarged view of a portion of the folded tube in circle  5  of FIG.  2 . 
     FIG. 6 is an end view of another embodiment, according to the present invention, of the folded tube of FIG.  1 . 
     FIG. 7 is an enlarged view of a portion of the folded tube in circle  7  of FIG.  6 . 
     FIG. 8 is an end view of yet another embodiment, according to the present invention, of the folded tube of FIG.  1 . 
     FIG. 9 is an end view of still another embodiment, according to the present invention, of the folded tube of FIG.  1 . 
     FIG. 10 is an end view of still yet another embodiment, according to the present invention, of the folded tube of FIG.  1 . 
     FIGS. 11A through 11D are views illustrating steps of a method, according to the present invention, of making the folded tube. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT(S) 
     Referring to the drawings and in particular FIG. 1, one embodiment of a heat exchanger  10 , such as a condenser for an air conditioning system (not shown), is shown for a motor vehicle (not shown). The heat exchanger  10  includes a plurality of generally parallel folded tubes  10 , according to the present invention, extending between oppositely disposed headers  14 , 16 . The heat exchanger  10  includes a fluid inlet  18  for conducting cooling fluid into the heat exchanger  10  formed in the header  14  and an outlet  20  for directing cooling fluid out the heat exchanger  10  formed in the header  16 . The heat exchanger  10  also includes a plurality of convoluted or serpentine fins  22  attached to an exterior of each of the tubes  12 . The fins  22  are disposed between each of the tubes  12 . The fins  22  conduct heat away from the tubes  12  while providing additional surface area for convective heat transfer by air flowing over the heat exchanger  10 . It should be appreciated that, except for the folded tube  12 , the heat exchanger,  10  is conventional and known in the art. It should also be appreciated that the folded tube  12  could be used for heat exchangers in other applications besides motor vehicles. 
     Referring to FIGS. 2 through 5, the folded tube  12  extends longitudinally and is substantially flat. The folded tube  12  includes a base  24  being generally planar and extending laterally. The folded tube  12  also includes a top  26  spaced from the base  24  a predetermined distance and opposing each other. The top  26  is generally planar and extends laterally. The folded tube  12  includes a first side  28  interposed between the base  24  and the top  26  along one side thereof. The first side  28  is generally arcuate in shape. The folded tube  12  also includes a second side  30  interposed between the base  24  and the top  26  along the other side and opposing the first side  28 . The folded tube  12  has a generally rectangular cross-sectional shape. It should be appreciated that the folded tube  12  may have any suitable cross-sectional shape. 
     Referring to FIG. 4, the second side  30  is generally arcuate in shape and formed from a first end  32  of the base  24  and a second end  34  of the top  26 . The first end  32  is generally arcuate in shape and has a recess  36  formed by a shoulder  38  extending inwardly. The second end  34  is generally arcuate in shape and overlaps the first end  32  and terminates in the recess  36  to produce a substantially flush outer periphery of the second side  30 . The first side  28  has a single wall thickness while the second side has a double wall thickness for extra strength against stone chips while driving the motor vehicle. Preferably, the wall thickness for the folded tube  12  has a maximum of 0.35 millimeters. It should be appreciated that the base  24 , top  26 , first side  28  and second side  30  form a hollow channel or interior for the folded tube  12 . 
     Referring to FIGS. 2,  3  and  5 , the folded tube  12  includes at least one, preferably a plurality of internal webs  40  extending from either one of or both the base  24  and top  26  to form a plurality of ports or flow paths  42  in the interior of the folded tube  12 . In the embodiment illustrated, the base  24  has two internal webs  40  spaced laterally and extending longitudinally and upwardly. The top  26  has three internal webs  40  spaced laterally and extending longitudinally and downwardly. The internal webs  40  extend in alternate directions such that one of the internal webs  40  on the base  24  is disposed between a pair of internal webs  40  on the top  26  to form six ports  42 . It should be appreciated that the number of internal webs  40  can be varied to produce the number of ports  42  desired. 
     Each of the internal webs  40  extends longitudinally and has a first portion  44  and a second portion  46 . The internal web  40  is formed by folding the first fold portion  44  and second fold portion  46  of the base  24  and/or top  26  back on itself for an initial predetermined internal web height and a predetermined internal web width or thickness. In the embodiment illustrated, the initial predetermined internal web height is approximately 0.7812 mm with a uniform initial predetermined internal web width of approximately 0.68 mm. It should be appreciated that the initial predetermined web thickness is uniform. 
     After the internal web  40  is initially formed, it is compressed or laterally extruded by a conventional process such as coining to extend the height of the internal web  40 . In the embodiment illustrated, the internal web  40  has a final predetermined internal web height (h) and predetermined internal web width or thickness (w). In the embodiment illustrated, the final predetermined web height (h) is approximately 1.345 mm and the final predetermined internal web thickness (w) is approximately 0.38 mm at its peak and approximately 0.68 mm at its base. The final internal web  40  is tapered at a predetermined angle. The predetermined angle is zero to seven degrees and, in the embodiment illustrated, preferably the predetermined angle is approximately 6.363 degrees. It should be appreciated that the taper angles are a result of the lateral extrusion. It should also be appreciated that the internal webs  40  have a non-uniform thickness. It should further be appreciated that the internal webs  40  maintain a predetermined distance or spacing between the base  24  and the top  26 . 
     The folded tube  12  has the internal webs  40  laterally spaced to provide the ports  42  with a predetermined hydraulic diameter. The hydraulic diameter is defined as the cross-sectional area of each of the flow paths or ports  40  multiplied by four and divided by a wetted perimeter of the corresponding flow path or port  42 . With the present invention, the hydraulic diameter of the ports range up to and beyond 0.070 inches. The hydraulic diameter is preferably smaller than 0.050 inches but heat transfer efficiency of the tubes of the present invention remain high even when they hydraulic diameter is greater than 0.070 inches. For example, the port  42  may have a cross-sectional area of 3.71 mm and a wetted perimeter of 8.25 mm for a hydraulic diameter of 0.0708 inches or 1.798 mm. 
     The folded tube  12  has its inner and outer surfaces coated with a known brazing material. As a result, the brazing material flows between the first end  32  of the base  24  and the second end  34  of the top  26  by capillary flow action to braze the ends together. Also, the brazing material flows between the peak of the internal webs  40  and the base  24  and top  26  to braze them together. 
     Referring to FIGS. 6 and 7, another embodiment  112 , according to the present invention, of the folded tube  12  is shown. Like parts of the folded tube  12  have like reference numerals increased by one hundred (100) . The folded tube  112  has the internal webs  140  extending from the base  124  and top  126  and spaced laterally such that the internal webs  140  on the base  124  and top  126  contact each other. The folded tube  112  also includes a partition  150  extending from the top  126  to the base  124  and which defines a pair of the adjacent ports  142 . The partition  150  includes a pair of opposing, connecting bend portions  152  disposed at a predetermined radius of curvature toward one another. Each of the bend portions  152  includes a leg portion  154  depending from each of the bend portions  152  and which contact the base  124  at terminal ends  156 . The terminal ends  156  can be either flat or include a bent over portion  157 . A braze seam  158  is disposed at the top of the partition  150  along the longitudinal length of the folded tube  112 . It should be appreciated that the partition  150  can be formed similar to that disclosed in U.S. Pat. No. 5,597,837. 
     Referring to FIG. 8, another embodiment  212 , according to the present invention, of the folded tube  12  is shown. Like parts of the folded tube  12  have like reference numerals increased by two hundred (200). The folded tube  212  has a partition  250  similar to the partition  150  of FIG. 6 extending from the top  226  to the base  224  and which defines a pair of the adjacent ports  242 . The folded tube  212  also has the internal webs  240  extending from the base  224  and the top  226  in an alternating manner similar to the internal webs  40  of FIG.  1 . 
     Referring to FIG. 9, another embodiment  312 , according to the present invention, of the folded tube  12  is shown. Like parts of the folded tube  12  have like reference numerals increased by three hundred (300). The folded tube  312  has a partition  350  similar to the partition  150  of FIG. 6 extending from the top  326  to the base  324  and which defines a pair of the adjacent ports  342 . The folded tube  312  also has the internal webs  340  extending only from the base  324  to the top  326 . The internal webs  344  are similar to the internal webs  40  of FIG.  1 . It should be appreciated that the internal webs  240  extend from only one side of the folded tube  312  and may extend from the top  326  to the base  324 . 
     Referring to FIG. 10, another embodiment  412 , according to the present invention, of the folded tube  12  is shown. Like parts of the folded tube  12  have like reference numerals increased by four hundred (400). The folded tube  412  has a first side  428  and a second side  430  similar to the first side  28  and second side  30  of FIG.  1 . The folded tube  412  also has the internal webs  440  extending between the base  424  to the top  426 . The internal webs  344  are similar to the internal webs  40  of FIG. 1 except that the internal webs  444  may include recesses  460  or projections  462  to enhance fluid flow through the ports  442 . It should be appreciated that the internal webs  440  can have a uniform or non-uniform width and may extend from the top  426  or the base  424 . 
     Referring to FIGS. 11A through 11D, a method, according to the present invention, of the making the folded tube  12  is shown. The method includes the steps of providing a generally planar sheet  70  of elongate, deformable material coated with a braze material forming the base  24  and top  26  having their respective ends  32  and  34  edges along a longitudinal length thereof as illustrated in FIG.  11 A. The ends  32  and  34  of the base  24  and top  26  can be either flat or arcuate as illustrated in FIGS. 2 through 4. Alternatively, for the folded tube  112 ,  212  and  312 , the ends can be formed as illustrated in FIGS. 6 through 9. The method includes the step of folding the sheet  70  from the lateral sides to initially form the internal webs  40  with the first fold portion  44  and second fold portion  46  to an initial predetermined web height and width as illustrated in FIG.  11 B. The method also includes the step of compressing the internal webs  40  by lateral extrusion to extend the internal webs  40  to a final predetermined web height and width as illustrated in FIG.  11 C. The step of compressing also includes the step of forming a taper or tapered angle on the internal webs  40  and coining the internal radiuses. The method includes the step of folding the ends  32  and  34  toward one another until they meet to form the first side  28  and second side  30  and ports  42  as illustrated in FIG.  11 D. The method includes the step of connecting the ends  32  and  34  together as illustrated in FIG.  2 . The method includes the step of brazing the folded tube  12  by heating the folded tube  12  to a predetermined temperature to melt the brazing material to braze the ends  32  and  34  and the internal webs  44  to the base  24  and/or top  26 . The folded tube  12  is then cooled to solidify the molten braze material to secure the ends  32  and  34  together and the internal webs  44  and the base  24  and top  26  together. It should be appreciated that, instead of the ends  32  and  34 , the partition  150 , 250 , 350  of the folded tube  112 , 212 , 312  may be formed according to the steps disclosed in U.S. Pat. NO. 5,579,837, the disclosure of which is hereby incorporated by reference. It should also be appreciated that the folded tube  412  may be formed as described above for the folded tube  12  except that the projections  462  or recesses  460  are formed during the step of compressing by the lateral extrusion. 
     Accordingly, the folded tube  12 , 112 , 212 , 312 , 412  is a cost reduction over current tubes. The folded tube  12 , 112 , 212 , 312 , 412  has internal webs  40 , 140 , 240 , 340 , 440  that are folded and squeezed to maintain a predetermined distance between the top  26 , 126 , 226 , 326 , 426  and base  24 , 124 , 224 , 324 , 424 . The folded tube  12 , 112 , 212 , 312 , 412  also has the internal webs  40 , 140 , 240 , 340 , 440  forming ports  42 , 142 , 242 , 342  with a hydraulic diameter preferably greater than 0.050 inches. 
     The present invention has been described in an illustrative manner. It is to be understood that the terminology which has been used is intended to be in the nature of words of description rather than of limitation. 
     Many modifications and variations of the present invention are possible in light of the above teachings. Therefore, within the scope of the appended claims, the present invention may be practiced other than as specifically described.