Patent Publication Number: US-6668916-B2

Title: Flat tube block heat exchanger

Description:
FOREIGN PRIORITY 
     This application claims priority to DE 101 47 192.0, a German patent application filed Sep. 25, 2001, pursuant to 35 U.S.C. §119(a)-(d). 
     FIELD OF THE INVENTION 
     This invention pertains to heat exchangers for vehicles and more particularly to such heat exchangers that include a block of heat exchange elements including flat tubes. 
     BACKGROUND OF THE INVENTION 
     Flat tube block heat exchangers have rows of flat tubes that may be alternated with corrugated fins. The ends of the flat tubes provide flow paths between tanks located at the opposite ends of the flat tubes and the flat tubes extend from one header plate to another header plate at the opposite end of the flat tubes. Typically, the flow paths created by the flat tubes extend generally perpendicular to the header plates at the ends of the tubes. The header plates are manufactured and supplied separately from the flat tubes and are typically made from relatively heavy materials. Further, the header plates occupy space at the collection tanks located at either end of the flat tube block heat exchanger. 
     Headerless flat tubes have been formed by placing two tube halves adjacent to one another where the ends of the tube halves have been deformed such that the broad sides may be connected. Drawn or welded tubes have been slit in their narrow sides in order to deform the ends and connect the broad sides. In both cases the connected broad sides form a “peak-and-valley” surface that is not conducive to directing flow from a transverse direction into the flat tubes. Examples of heat exchangers with these types of flat tubes are disclosed in German Patent Application Nos. DE 100 16 113.8 and DE 100 19 268.8, both of which are incorporated herein by reference. 
     While these constructions can perform satisfactory for their intended purpose, there is always room for improvement. For example, the pressure loss of the medium flowing through the collection tanks and flat tubes of a block heat exchanger could be reduced in order to improve their application opportunities, especially in the vehicle field. 
     BRIEF SUMMARY OF THE INVENTION 
     In one form, the invention provides a heat exchanger that includes a pair of collection tanks spaced opposite each other. The tanks are fluidly connected by a plurality of flat tubes that provide flow paths between the tanks. The flat tubes have opposing ends that correspond to one of the tanks and each end has two broad sides and two narrow sides. Each broad side has an inner surface and is deformed to expose the inner surface. The exposed inner surfaces of each flat tube are bonded to the exposed inner surface of any adjacent flat tube to define a fluid barrier with the corresponding tank. 
     In one form, each of the narrow sides is connected to an edge of the corresponding tank. 
     According to one form, the deformed broad sides have two bends of about 90° with the bonded inner surfaces arranged in parallel orientation to the broad sides of any adjacent flat tube. Alternatively, the flat tubes are arranged in oblique orientation relative to a longitudinal axis of the flat tubes and the broad sides have a first bend of about 90° and a second bend that corresponds to the angle of the oblique orientation. In another alternative, the deformed broad sides are curved to expose the inner surface with a cross-section that is semicircular or semielliptical. 
     According to one form, the bonded broad sides define a plurality of fluid inflow funnels to the flat tubes. 
     According to one form, the flat tubes are formed from two half-shells. 
     In one form, each of the narrow sides includes a cut extending parallel to a longitudinal axis of the flat tubes, the cut separates the broad sides at the tube end. 
     In one form, each of the narrow sides includes two cuts that separate the broad sides at the tube ends and define a tab in each narrow side. In one form, the tab is bent inward into the flat tube. 
     In yet another form of the invention, a heat exchanger includes a pair of tanks spaced opposite each other, the tanks are fluidly connected by a plurality of spaced apart flat tubes to provide flow paths between the tanks. Each flat tube has opposing ends corresponding to one of the tanks, each end has a first broad side, a second broad side, and two narrow sides, each broad side has an inner surface and an outer surface. Each first broad side being deformed to expose the inner surface of the first broad side, and each of the exposed inner surfaces of each first broad side is bonded to the outer surface of any adjacent second broad side to define a fluid barrier with corresponding tank. 
     In another form, the invention provides a method for manufacturing a heat exchanger includes the steps of: cutting a plurality of flat tube ends to separate each tube end into a pair of broad sides; deforming each of the broad sides to expose an inner surface of the broad side; abutting the exposed inner surface of each of the broad sides to an exposed inner surface of an adjacent broad side of another tube; affixing a tank on the flat tube ends; and bonding the adjacent broad sides to each other and the flat tube ends to the tanks. 
     In one form, each flat tube end includes a pair of narrow sides in the flat tube end, and the bonding step includes bonding the narrow sides of the flat tube ends to the tank. 
     In yet another form, a method is provided for manufacturing a heat exchanger and includes the steps of: cutting a plurality of flat tube ends to separate each tube end into a pair of broad sides; deforming each of the broad sides to expose an inner surface of the broad side; abutting the exposed inner surface of one of the broad sides to an outer surface of an adjacent broad side; affixing a tank on the flat tube ends; and bonding the adjacent broad sides to each other and the flat tubes with the tanks. 
     In one form, each flat tube end includes a pair of narrow sides in the flat tube end and the bonding step includes bonding the narrow ends of the flat tube ends to the tank. 
     Objects and advantages of the invention, as well as additional inventive features, will be apparent from the description of the invention provided herein and in the associated figures and appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a heat exchanger embodying the invention. 
     FIG. 2 is perspective view of a row of bonded flat tubes embodying the present invention. 
     FIG. 3 is a side elevation of a row of bonded flat tubes embodying the present invention. 
     FIG. 4 is a side elevation of a row of bonded flat tubes embodying the present invention. 
     FIG. 5 is a top view of an individual flat tube. 
     FIGS. 6A-6H are schematic depictions of the steps of a deformation process embodying the present invention. 
     FIGS. 7A-7C are schematic depictions of a process to form a rectangular cross-section of the flat tube end. 
     FIGS. 8A-8E are schematic depictions of another flat tube end deformation process. 
     FIGS. 9A-9E are schematic depictions of another flat tube end deformation process. 
     FIG. 10 is a cross-sectional view of a row of bonded flat tubes deformed by the process depicted in FIGS. 9A-9E. 
     FIG. 11 is a top view of an individual flat tube. 
     FIG. 12 is a side elevation of a row of bonded flat tubes according to an embodiment of the invention. 
     FIG. 13 is an enlarged view taken from line X in FIG.  12 . 
     FIG. 14 is a side elevation of a row of bonded flat tubes according to an embodiment of the invention. 
     FIG. 15 is an enlarged view taken from line X in FIG.  14 . 
     FIG. 16 shows a partial section of a row of bonded flat tubes according to an embodiment of the invention. 
     FIG. 17 shows a modification of the embodiment depicted in FIG.  16 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A heat exchanger  10  embodying the present invention is represented in FIG.  1  and depicts a collection tank  12  with side walls  14  that contact a row of flat tubes  16 . A second tank (not shown) contacts the row of flat tubes  16  opposite the collection tank  12 . The flat tubes  16  may be formed by welding, soldering or brazing two half shells together, or the flat tubes  16  may be drawn or extruded. As best seen in FIG. 3, heat exchange elements, such as corrugated ribs or serpentine fins  30  are preferably placed between rows of flat tubes  16 . 
     Each of the flat tubes  16  has narrow sides  18  and broad sides  20 . The ends  22  of the flat tubes  16  are deformed to expose an inner surface  24  of each broad side  20 . As best seen in FIG. 3, in one form the deformed flat tubes  16  are held together by bonding the inner surface  24  of one broad side  20  to the inner surface  24  of the broad side  20  of an adjacent flat tube  16 . The bonded flat tubes  16  define a fluid barrier with the corresponding tank  12  that can eliminate the need for a separate header plate on the tank  12 . The deformed ends  22  define a relatively flat surface  25  and fluid inflow funnels  26  that provide a fluid inlet to the flat tubes  16 . The flat surface can reduce pressure loses in comparison to the “peak and valley” configurations discussed in the Background section. Preferably, the narrow sides  18  of the flat tubes  16  are bonded to the edges  14  of the tanks  12 . Any suitable bonding technique, such as brazing, soldering, or welding, can be employed for any of the bonded connections or joints mentioned herein. The collection tank  12  may be closed on the ends transversing the tube ends  22  by several means well known in the art. 
     As seen in FIGS. 2-6 and  8 , in some embodiments the broad sides  20  of the flat tubes ends  22  are deformed into two bends  28  of about 90° with the bonded inner surfaces  24  arranged roughly in parallel orientation to the broad sides  20  of any adjacent flat tube  16 . Alternatively, the inner surfaces  24  of the flat tubes  16  are arranged in an oblique orientation relative to the longitudinal axis  29  of the flat tubes  16  and the broad sides  20  have a first bend of about 90° and a second bend corresponding to the angle of the oblique orientation. 
     In the embodiment depicted in FIG. 3, a section of each of the narrow sides  18  has been removed or reshaped such that each broad side  20  has an narrowed end  32  with little or no corresponding narrow side  18 . Each narrowed end  32  has a portion  36  of the exposed inner surface  24  that is bonded to the portion  36  of the broad side  20  of an adjacent flat tube  16 . 
     In another embodiment, the tube ends  22  of FIG. 4 include tabs  40  formed from the narrow sides  18  of the flat tubes  16 . The tabs  40  are bent toward the inside of the flat tubes  16  and folded against the inner surface  24 . Alternatively, the tabs  40  may be eliminated by pinching or similar deformation. However, when the tabs  40  on narrow sides  18  are folded inward the resulting connection to the edges  14  of the tanks  12  is improved. Rigidity of the narrow sides  18  is increased by the bonding of the edges  14  of the tank  12 . 
     FIGS. 6-10 illustrate steps that may be taken to manufacture the tubes  16 . As best seen in FIGS. 6A and 7A, the tube end  22  may begin with a rectangular cross section having rounded corners  41  between the narrow sides  18  and the broad sides  20 . If this is the case, it is preferred that the corners be formed more sharply by inserting a tool (not shown) into the end  22  to form a rectangular cross section having sharp corners  41 , as seen in FIGS. 6B,  7 B and  7 C. A shoulder  42  is formed in the tube  16  as a byproduct of the insertion of the tool. The rectangular cross section creates more favorable conditions for bonding the narrow sides  18  to the side walls  14  of the tank  12  tightly and permanently. Next, as best seen in FIG. 6C, the narrow side  18  of each end  22  of the flat tubes  16  are cut, off-center, at  43  to separate the tube into a pair of broad sides  20   a ,  20   b  and form tabs  40  from the narrow sides  18 . As seen in FIGS. 6D and 6E, the broad sides  20   a ,  20   b  are bent to form right angle bends  28  relative to the longitudinal axis  29  of the flat tube  16 . The end  32  is formed by remounting or reshaping a section of each of the narrow sides  18 , as seen in FIG.  6 F. As seen in FIG. 6G, each broad side  20   a ,  20   b  is bent a second time to form a second right angle bend  28  that positions a portion of the broad side  20   a ,  20   b  generally parallel to the longitudinal axis  29  of the flat tube  16 . As seen in FIG. 6H, the tabs  40  are preferably folded inside the tube  16  against the narrow sides  18 . The cutting and deformation of the flat tube ends  22  may be carried out with a deformation machine equipped with a progressive die in which a finished deformed flat tube  16  is ejected with each stroke. 
     As shown in FIGS. 9A-9E, after the cuts  43  are formed, the separated broad sides  20   a ,  20   b  may alternatively be bent into a semi-circle  44  or semi-ellipse with ends  32  that are bent into a generally perpendicular orientation to the longitudinal axis  29  of the flat tube  16 . As with the embodiment of FIGS. 6A-H, a section of each of the narrow sides  18  may be removed or reshaped to form the end  32 . The tab  40  is preferably folded and bent inside the flat tube  16 , as seen in FIG.  9 E. As seen in FIG. 10, the narrowed ends  32  are abutted to the ends  32  of any adjacent flat tubes  16  to form the fluid barrier with the corresponding tank  12 . A wavy surface  25  is formed by the abutting of the ends  32  of the tubes  16  in this manner. 
     Rather than being bent into a generally parallel orientation relative to the longitudinal axis  29  of the flat tubes  16 , the ends  32  may be retained in a generally perpendicular orientation relative to the longitudinal axis  29  of the flat tubes  16 , as seen in FIG.  12 . In that case, the ends  32  of adjacent flat tubes  16  are arranged one on top of the other with an exposed inner surface  24  bonded to an exposed outer surface  46  of any adjacent tube  16 . Optionally, a prefixation  48  can be formed in the narrowed end  32 , as shown in FIG. 13 to impart temporary holding of the tubes  16  before assembly with the tanks  12  and bonding of the assembled heat exchanger. The prefixation  48  is produced with a tool (not shown) that partially interlaces the adjacent ends  32 . The prefixation may also be introduced by other means. The previously described embodiments may also include such prefixation. 
     Alternatively, as seen in FIG. 14, rather than removing a section from the narrow sides  18  of both sides  20   a ,  20   b , a section of the narrow sides  18  of only one broad side  20   a  are removed or reshaped to form the end  32  while the opposite broad side  20   b  remains intact. The end  32  of the broad side  20   a  is placed under the intact broad side  20   b  of an adjacent flat tube  16  and a prefixation  58  is preferably formed in the abutted broad sides  20   a ,  20   b  as best seen in FIG.  15 . 
     Further examples of the tubes  16  are depicted in FIGS. 16 and 17. The cut away broad sides  20   a ,  20   b  are bent so as to generally form a semi-circle  64  when one end  32  is abutted to an adjacent end  32 , resulting in a wavy surface  25 , rather than a flat surface  25  as in FIGS. 3 and 4. Optionally, one or both of the abutting ends  32  may be further bent, for example into the bend  50  depicted in FIG. 17, to improve the bonding connection between the flat tubes  16 . The bend  50  serves as a prefixation. 
     An alternative process for manufacturing the tubes  16  is depicted in FIGS. 8A-8E. The narrow sides  18  of each of the ends  22  of the flat tubes  16  are cut centrally at  41  to separate each end  22  into the broad sides  20   a ,  20   b , as seen in FIG.  8 B. As seen in FIG. 8C, the broad sides  20   a ,  20   b  are bent to form right angle bends  28  relative to the longitudinal axis  29  of the flat tube  16 . A section of each of the narrow sides  18  is removed or reshaped forming the thin end  32 . As seen in FIG. 8E, each of the broad sides  20   a ,  20   b  is bent a second time to form a second right angle bend  28  that positions a portion of the broad side  20   a ,  20   b  generally parallel to the longitudinal axis  29  of the flat tube  16 . 
     The flat tubes  16  can be used in a variety of heat exchangers, for example in coolant coolers or air-cooled charge coolers with, for example, the embodiment of FIG. 6 being preferred for air-cooled charge coolers and the embodiment of FIG. 8 being preferred for coolant coolers. 
     Once the ends  22  of the flat tubes  16  have been deformed, the flat tubes  16  are bonded to one another and bonded to the tanks  12 . In a preferred embodiment, the entire heat exchanger including the tubes  16 , fins  30 , and tanks  12  are produced from solder-coated aluminum sheet. The resulting fluid barrier with the tanks  12  has either an almost flat surface  25  or a wavy surface  25  facing the collection tank  12 , which can provide reduced pressure losses over configurations currently known. The connection between the broad sides  20  should extend the entire width of the broad side  20 . The flat tube ends  22  are generally rectangular and therefore the broad sides  20  do not taper along the end  22  in the direction of the cut  41 . The rectangular shape eliminates any pressure loss from such tapering. 
     Another manufacturing method according to the invention for heat exchangers  10  with flat tubes  16  made of half shells is conducted by deforming the ends  22  of the half shells of the flat tubes  16  prior to assembling the fins  30  and the opposite half shell. The half shells are bonded to form flat tubes  16  during the same process that bonds the rows of fins  30  to the flat tubes  16  and bonds the exposed inner surfaces  24  of the deformed half shells to one another. 
     The use of any and all examples, or exemplary language (e.g., “such as” or “for example”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless expressly recited in a claim. 
     While some potential advantages and objects have been expressly identified herein, it should be understood that some embodiments of the invention may not provide all, or any, of the expressly identified advantages and objects. 
     Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Of course, variations of those preferred embodiments will become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.