US20050016717A1

US20050016717A1 - Heat exchanger

Info

Publication number: US20050016717A1
Application number: US10/885,961
Authority: US
Inventors: Berhnhard Lamich; Viktor Brost
Original assignee: Modine Manufacturing Co
Current assignee: Modine Manufacturing Co
Priority date: 2003-07-22
Filing date: 2004-07-07
Publication date: 2005-01-27
Also published as: EP1500892A2; EP1500892A3; DE10333150A1

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

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

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.
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.
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.
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.
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.
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.
The present invention is directed to solving one or more of the above problems.

SUMMARY OF THE INVENTION

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.
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.
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.
In a preferred embodiment, fasteners are provided for securing the end caps to the tank ends during assembly of the heat exchanger.
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.
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.
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.
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.
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.
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.
Other objects and advantages will become apparent from the following specification taken in connection with the accompanying drawings.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a fragmentary, perspective view of a side piece for a heat exchanger made according to the invention;
FIG. 2 is a view similar to FIG. 1, but of a modified embodiment;
FIG. 3 is similar to FIGS. 1 and 2, but illustrates a third embodiment;
FIG. 4 is similar to FIGS. 1-3, inclusive, but illustrates a fourth embodiment;
FIG. 5 is an enlarged, fragmentary view of one corner of a heat exchanger;
FIG. 6 is a side elevation taken from the left of FIG. 5;
FIG. 7 is a fragmentary sectional view taken approximately along the line 7-7 in FIG. 5;
FIG. 8 is a sectional view taken approximately along the line 8-8 in FIG. 5;
FIG. 9 is a vertical section of the structure shown in FIG. 5;
FIG. 10 is an exploded view of the structure of FIG. 5;
FIG. 11 is a view similar to FIG. 10 but of a modified embodiment of the invention;
FIG. 12 is a fragmentary, elevational view of a corner of a heat exchanger made according to the invention;
FIG. 13 is a sectional view taken approximately along the line 13-13 in FIG. 12; and
FIG. 14 is a sectional view taken approximately along the line 14-14 in FIG. 12.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

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.
With the foregoing in mind, several embodiments of the invention will now be described.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
The tab 72 is retained in the embodiment of FIGS. 10-14.
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.
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.
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.

Claims

1. A heat exchanger comprising:

a pair of parallel headers each having spaced tube slots aligned with tube slots in the other header;

tubes extending between aligned ones of the tube slots in said headers;

fins extending between the tubes;

side pieces on opposed sides of the heat exchanger embracing said fins thereat and extending substantially between corresponding ends of the headers;

a pair of channel-like tanks, one for each header, fitted to the corresponding header oppositely of the tubes; and

end caps having bent edges embracing and sealingly closing opposite ends of each said tank, said end caps being integral extensions of each end of each side piece to form end cap/side pieces and 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 defined by at least one cutout thereat.

2. A heat exchanger comprising:

tubes extending between aligned ones of the tube slots in said headers;

fins extending between the tubes;

a reduction in cross section of each end cap/side piece adjacent each end of each header of at least about 50%, each defined by at least one cutout thereat; and

fasteners for securing said end caps to said tank ends during assembly of the heat exchanger.

3. The heat exchanger of claim 2 wherein each said reduction is at least about 80% of said cross section and said end caps and side pieces remain integral about said cutout(s) through the retention of a connecting strand or a small number of connecting strands extending across said cutout(s) from the side piece to the integral end caps on each end of each side piece.

4. The heat exchanger of claim 3 wherein said heat exchanger is formed of aluminum and is assembled by brazing, said connecting strands being sized to be readily severed if necessary.

5. The heat exchanger of claim 2 wherein said fasteners include resilient U-shaped clips on said end cap bent edge or said ends of said tanks.

6. The heat exchanger of claim 2 wherein said fasteners include a tab on each end cap bendable to overly and engage an adjacent end of said tank.

7. The heat exchanger of claim 5 wherein said U-shaped clips each includes a sloped extremity on at least one of the legs thereon to serve as a pilot surface for receipt of a corresponding end of said tanks or a corresponding bent edge of said end caps.

8. The heat exchanger of claim 2 wherein said cutout(s) defines a central connecting strand extending between each side piece and the associated end caps.

9. The heat exchanger of claim 2 wherein said cutout(s) defines two spaced off center connecting strands extending between each side piece and the associated end caps.