Patent Publication Number: US-7594327-B2

Title: Heat exchanger and method of making the same

Description:
FIELD OF THE INVENTION 
     This invention relates to heat exchangers, and in more particular applications, to improved side plates for heat exchangers, as well as methods of making a heat exchanger. 
     BACKGROUND OF THE INVENTION 
     Many heat exchangers in use today, such as, for example, vehicular radiators, oil coolers, and charge air coolers, are based on a construction that includes two spaced, generally parallel headers which are interconnected by a plurality of spaced, parallel, flattened tubes. Located between the tubes are thin, serpentine fins. In the usual case, the outer most tubes are located just inwardly of side plates on the heat exchanger and serpentine fins are located between those outer most tubes and the adjacent side plate. 
     The side plates are typically, but not always, connected to the headers to provide structural integrity. They also play an important role during the manufacturing process, particularly when the heat exchanger is made of aluminum and components are brazed together or when the heat exchanger is made of other materials and some sort of high temperature process is involved in the assembly process. 
     More particularly, conventional assembly techniques involve the use of a fixture which holds a sandwiched construction of alternating tubes and serpentine fins. The outside of the sandwich, that is the outer layers which eventually become the sides of the heat exchanger core, is typically provided with side plates whose ends are typically connected mechanically to the headers. Pressure is applied against the side plates to assure good contact between the serpentine fins and the tubes during a joining process such as brazing to assure that the fins are solidly bonded to the tubes to maximize heat transfer at their points of contact. If this is not done, air gaps may be located between some of the crests of the fins and the adjacent tube which adversely affect the rate of heat transfer and durability, such as the ability to resist pressure induced fatigue and to withstand elevated pressures. 
     At the same time, when the heat exchanger is in use, even though the side plates may be of the same material as the tubes, because a heat exchange fluid is not flowing through the side plates but is flowing through the tubes, the tubes will typically be at a higher temperature than the side plates, at least initially during the start up of a heat exchange operation. 
     This in turn results in high thermal stresses in the tubes and headers. Expansion of the tubes due to relatively high temperatures tends to push the headers apart while the side plates, at a lower temperature, tend to hold them together at the sides of the core. All too frequently, this creates severe thermal stress in the heat exchanger assembly resulting in fracture or the formation of leakage openings near the tube to header joints which either requires repair or the replacement of the heat exchanger. 
     It has been proposed to avoid this problem, after complete assembly of the heat exchanger, by sawing through the side plates at some location intermediate the ends thereof so that thermal expansion of the tubes is accommodated by the side plates, now in multiple sections, which may move relative to one another at the saw cut. However, this solution adds an additional operation to the fabrication process and consequently is economically undesirable. 
     It has also been proposed to weaken the intermediate portion of the side plate by placing lines of weakening in the side plate, such as seen in U.S. Pat. No. 6,412,547 to Siler. However, this method requires the additional manufacturing steps of cutting openings and embossing lines of weakening in the side plates. 
     SUMMARY OF THE INVENTION 
     In accordance with one form of the invention, a side plate is provided for use with a heat exchanger. The heat exchanger includes a pair of spaced, generally parallel headers, a plurality of spaced, generally parallel tubes extending between and in fluid communication with an interior or the headers and fins extending between the tubes. The side plate includes first and second ends and an intermediate portion. At least one of the ends is shaped to provide at least one localized contact bonded to one of the headers. The intermediate portion has a width and extends between the ends. Each localized contact has a contact width that is less than ⅕ the width of the intermediate portion. 
     In accordance with one form, a side plate is provided for use with a heat exchanger. The heat exchanger includes a pair of spaced, generally parallel headers, a plurality of spaced, generally parallel tubes extending between and in fluid communication with an interior or the headers and fins extending between the tubes. The side plate includes first and second ends and an intermediate portion. At least one of the ends is shaped to provide at least one localized contact bonded to one of the headers. The intermediate portion has a width and extends between the ends. Each localized contact is sized to separate from the header under relatively low tension applied by the thermal expansion and contraction of the heat exchanger under normal operation conditions. 
     In one form, each of the first and second ends are shaped to provide at least one localized contact bonded to the headers. 
     In one form, the first end is V-shaped to provide one localized contacts. 
     According to one form, the first end is U-shaped to provide two localized contacts. 
     According to one form, peaks of the fins contact a bottom surface of the side plate. 
     In accordance with one form, the side plate also includes a tab extending substantially perpendicularly therefrom and contacts a side of the fins. 
     In one form, the tabs contact serpentine fins. 
     According to one form, the first end is bonded to a cylindrical header. 
     In accordance with one form, the localized contact is shaped to provide a line contact with the header. 
     According to one form, a method is provided for making a heat exchanger. The method includes the steps of: 
     assembling the components of a heat exchanger core in a fixture to have a pair of spaced parallel headers, spaced tubes extending between the headers, a side plate extending between the headers at a side of the core, and serpentine fins located between adjacent tubes and between the side plate and an outermost one of the tubes; 
     locating the side plate between the headers overlying an outermost one of said fins by abutting at least one localized contact formed on an end of the plate against one of the headers; 
     bonding the localized contact to the header during a bonding process for the core; and 
     subjecting the heat exchanger to operating temperatures resulting in the breaking of the bond between the localized contact and the header. 
     In one form, the bonding step includes bonding the localized contact at each end of the side plate. 
     Other objects, advantages, and features will become apparent from a complete review of the entire specification, including the appended claims and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side view of a heat exchanger and side plate assembly; 
         FIG. 2  is a top view an embodiment of an end of a side plate bonded to a header; 
         FIG. 3  is a is a side view of  FIG. 2 ; 
         FIG. 4  is a top view of another embodiment of an end of a side plate bonded to a header; 
         FIG. 5  is a side view of  FIG. 4 ; 
         FIG. 6  is a top view of yet another embodiment of an end of a side plate bonded to a header; 
         FIG. 7  is a side view of  FIG. 6 ; 
         FIG. 8  is a top view of yet another embodiment of an end of a side plate bonded to a header; 
         FIG. 9  is a side view of  FIG. 8 ; and 
         FIG. 10  is a side view similar to  FIGS. 3 ,  5 ,  7  and  9 , but showing an alternate embodiment of an end contact. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention will be described hereinafter as a vehicular radiator, such as, for example, a radiator for a large truck. However, it should be understood that the invention is applicable to radiators used in other contexts, for example, a radiator for any vehicle or for stationary application as an internal combustion engine driven generator. The invention is also useful in any of the many types of heat exchangers that utilize side plates to hold serpentine fins against parallel tubes extending between spaced headers, such as, for example, oil coolers and charge air coolers. Accordingly, no limitation to any particular use is intended except insofar as expressed in the appended claims. 
     Referring to  FIG. 1 , a typical heat exchanger of the type of concerned includes spaced, parallel header plates  10 ,  12 , between which a plurality of flattened tubes  14  extend. The tubes  14  are spaced from one another and their ends are brazed or welded or soldered to and extend through slots, not shown, in the headers  10  and  12  so as to be in fluid communication with the interior of a tank  16  fitted to each of the headers  10 ,  12 . In this regard, it is to be noted that as used herein, the term “header” collectively refers to the header plates  10 ,  12 , to the headers  10 ,  12  with the tanks  16  secured thereon, or integral header and tank constructions known in the art as, for example, made by tubes or various laminating procedures. Side plates  18 ,  20  flank respective sides of the heat exchanger construction and extend between the headers  10 ,  12  and are metallurgically bonded thereto. 
     Between the spaced tubes  14 , and between the endmost tube  14  and an adjacent one of the side plates  18 ,  20  are ambient air fins, such as conventional serpentine fins  22 . However, while conventional serpentine fins  22  are shown, it should be understood that in some applications it may be desirable to use plate fins that extend essentially perpendicular to the longitudinal axes of the tube with the end edges of the plate fins being overlayed by the side plates  18  and  20 . As is well known, the fins  22  may be formed of a variety of materials. Typical examples are aluminum, copper and brass. However, other materials can be used as well depending upon the desired strength and heat exchange efficiency requirements of a particular application. 
     In a highly preferred embodiment of the invention, all of the just described components, with the possible exception of the tanks  16  which may be formed of plastic, are formed of aluminum or aluminum alloy and are braze clad at appropriate locations so that an entire assembly is illustrated in  FIG. 1  may be placed in a brazing oven and the components all brazed together. In the usual case, prior to brazing, an appropriate fixture is employed to build up a sandwich made up of the tubes  14  alternating with the serpentine fins  22  and capped at each end by the side plates  18  and  20 . The headers  10 , 12  are fitted to the ends of the tubes  14  so as to allow the tubes  14  to communicate with the interior of the headers  10 , 12  and/or tanks  16 . Specifically, the ends of the tubes  14  may be inserted into openings (not shown) in the headers  10 , 12  and brazed thereto. 
     Each side plate  18 , 20  includes first and second ends  30 , 32  and an intermediate portion  34  extending between the ends  30 , 32 . The intermediate portion preferably has a width W that is the same or nearly the same as the width of the fins  22 . At least one of the ends  30 , 32  is shaped to provide at least one localized contact  36  bonded to one of the headers  10 , 12 , as best seen in  FIGS. 2 ,  4  and  6 . 
     Referring to  FIG. 2 , the end  30  may include more than one localized contact  36 . As shown in  FIG. 2 , two localized contacts  36  are bonded to the header  10 . Alternatively, as seen in  FIG. 6 , there is one localized contact  36  located on the end  30 . Each localized contact  36  is bonded to the header  10  through such processes as brazing, soldering, welding and other methods known in the art. The localized contact  36  may be shaped as a point so as to provide a line of contact with the header  10 , as best seen in  FIGS. 3 ,  5  and  7 . 
     Additionally, the ends  30 , 32  may take a variety of shapes to provide the desired localized contacts  36 . For example, in  FIG. 6 , the end  30  is generally V-shaped whereas in  FIG. 2 , the end  30  is generally U-shaped. In this regard, it should be appreciated that the U-shaped end  30  in  FIG. 2  can provide self-centering of the side plate  18 , 20  with respect to the corresponding header  10 , 12  because if the side plate  18 , 20  is slightly off from center, one of the two prongs of the U-shape will touch the header first and will glide on the header surface until the other point of the U-shaped end  30  touches the header. By way of further example, in  FIG. 8 , the end  30  has a “multi toothed” or “saw toothed” shape providing four of the point contacts  36 , only two of which in the illustrated embodiment actually contact the corresponding header  10 , 12 . Such a design allows for lateral misalignment of the side plate  18 , 20  to the respective header  10 , 12  while still ensuring that at least one or more of the point contacts  36  will abut the corresponding header  10 , 12 . This also helps to ensure that the header-to-header spacing or distance is kept within the desired tolerances even when the side plate  18 , 20  moves laterally during brazing, becoming off-centered. The actual shape of the ends  30 , 32  and of the associated localized contact(s)  36  can be adjusted as required or desired. 
     Specifically, the localized contact  36  can be shaped to accommodate a variety of header shapes. Referring to  FIG. 2 , the header  10  is cylindrical. However, it should be understood by those skilled in the art that the headers  10 , 12  may take a variety of other shapes and geometries such as rectangular, triangular or other shapes and geometries understood by those skilled in the art. 
     Furthermore, while  FIGS. 2-7  depict only one end  30  of the side plate  18  as having at least one localized contact  36 , it should be readily understood by those skilled in the art that both ends  30 , 32  can be shaped to have at least one localized contact  36  bonded to the respective header  10 , 12 . Similarly, each side plate  18 , 20  may have each respective first and second ends  30 , 32  include at least one localized contact  36 . 
     The side plates  18 , 20  may optionally include one or more tabs  40  to help maintain the position of the fins  22  as seen in  FIGS. 4-7 . As seen in  FIGS. 4  (in phantom) and  5 , the tab  40  preferably extends substantially perpendicularly from the side plate  18 , 20  to retain the fins. The tab  40  contacts a side  42  of the fins  22  while a bottom surface  44  of the side plate  30  contacts peaks  46  of the fins  22 . The tab  40  can be used to help maintain the location of outermost ones  48  of fins  22  during assembly. Additionally, multiple tabs  40  can be used as seen in  FIGS. 6  (in phantom) and  7 . 
     During assembly and operation, the localized contacts  36  are intended to be bonded to the respective headers  10 , 12 , but sized to subsequently break that bond and separate from the header during normal operation from relatively low tension applied by the thermal expansion and contraction of the heat exchanger. The localized contacts  36  preferably have a width that is at least less than ⅕ the width W of the intermediate portion  34 , and preferably are shaped as a point to provide a line of contact with the header  10 , with the length of the line contact being defined by the thickness of the side plate  18 , 20 . As yet a further alternative, the end  30 , 32  can be coined so as to reduce the local thickness of the side plate  18 , 20  to provide either a shortened line of contact or, as best seen in  FIG. 10 , an essentially point contact. The relatively smaller width of the localized contact  36  allows the contact  36  and the respective header  10 , 12  to separate under the above described operation of the heat exchanger. In this regard, the separation can occur in a number of ways, for example, by breaking of the bond joint between the contact  36  and the respective header  10 , 12 , by breaking of the end  30  at or adjacent the bond joint, or by a combination of these two. This allows the tubes  14  to expand and contract according to temperature changes during normal operation, without binding caused by the side plates  18 , 20  being joined to the headers  10 , 12 . It should be easily appreciated that it is preferred for the breaking of the bond at the localized contact  36  to occur without damaging the header  10 , 12  to the point that a leak path is created. 
     The heat exchanger may be manufactured as discussed below. The main components of the heat exchanger core can be assembled in a fixture (not shown) to hold the core. The headers  10 , 12  can be placed at opposite ends of the fixture with layers of tubes  14  and fins  22  stacked and located between the headers  10 , 12 . The fins  22  are stacked between adjacent tubes  14 . Additionally, fins  22  are located adjacent the top-most and bottom most tubes  14 . The side plates  18 , 20  are located between the headers overlying the outermost ones  48  of the fins  22  by abutting at least one localized contact  36  formed on one of the ends  30 , 32  of the plate  18 , 20  against one of the headers  10 , 12 . The localized contact  36  is then bonded to the header  18 , 20  during a bonding process for the core. Subsequently, the heat exchanger can be subjected to operating temperatures resulting in the breaking of the bond between the localized contact  36  and the header  18 , 20 .