Heat exchanger, tank for heat exchanger, and method of making the same

A tank for a heat exchanger includes an extruded tank section having a generally constant extrusion profile extending in a longitudinal direction from a first tank end to a second tank end. A first planar end cap is joined to the extruded tank section near the first tank end, and a second planar end cap is joined to the extruded tank section near the second tank end. Together, the extruded tank section and first and second end caps can at least partially define an internal tank volume. The first and second planar end caps are both arranged at non-perpendicular angles to the longitudinal direction.

BACKGROUND

Heat exchangers are used to transfer thermal energy from one stream of fluid at a first, higher temperature to another stream of fluid at a second, lower temperature. Oftentimes such heat exchangers are used to remove waste heat from a process fluid such as oil, coolant, or the like by transferring that heat to a flow of cooler air directed to pass through the heat exchanger.

In certain applications, the process fluid to be cooled is also at an operating pressure that is substantially greater than the ambient atmospheric pressure of the heat exchanger's surroundings. As a result, it becomes necessary for the heat exchanger to be designed to withstand the pressure forces that result from the process fluid passing through the heat exchanger. This can become challenging, especially in cases where the heat exchanger is to be used in large systems and machinery such as, for example, construction equipment, agricultural machines, and others. As the size of the machine or system increases, the flow rate of the process fluid also increases, necessitating larger heat exchangers to accommodate both the heat transfer requirements and the fluid flow rates. Such larger heat exchangers can have substantially large surface areas exposed to the pressure of the process fluid, especially in tank areas, and the force of the fluid pressure acting on these large surfaces can lead to destructive mechanical stresses in the heat exchanger structure.

An example of such a heat exchanger as known in the art is depicted inFIG. 1. The heat exchanger101is of a bar and plate construction, and can be used as, for example, an oil cooler for an off-highway vehicle such as an excavator, wheel loader, combine, etc. Oil to be cooled by the heat exchanger101travels through a plurality of channels provided within a heat exchanger core102, those channels alternatingly with channels for cooling air that is directed in a cross-flow orientation to the oil through the core102. Tanks103are provided at either end of the core102to direct the oil to and from the core102, and inlet/outlet ports106are provided at each of the tanks103to fluidly couple the heat exchanger101to the oil circuit.

The tanks103must be sized to be large enough to evenly distribute the flow of oil to the individual channels. As a result, substantially large surface areas within the tank are exposed to the typically high pressure of the oil, and must be designed to be capable of withstanding such forces. A typical tank construction for such high-pressure applications includes an extruded tank section104with an arcuate (e.g. cylindrical) internal profile in order to evenly distribute the forces resulting from the pressure loading. Flat end caps105are welded to the ends of the extruded tank section104in order to close off the ends of the tank103. Those flat end caps105must again be designed with a thickness that is suitable for withstanding the pressure forces imposed on them by the fluid in the tank103. Such a tank construction can be more economical than a tooled cast tank for low-volume manufacturing.

The inventors have found that, even when such heat exchangers have been designed with wall sections suitable for withstanding the elevated operating pressure of the intended application, the forces acting on the end caps can result in undesirable and damaging stresses in the remainder of the heat exchanger. Thus, there is still room for improvement.

SUMMARY

In some embodiment of the invention, a tank for a heat exchanger includes an extruded tank section having a generally constant extrusion profile extending in a longitudinal direction from a first tank end to a second tank end, a first planar end cap joined to the extruded tank section near the first tank end, and a second planar end cap joined to the extruded tank section near the second tank end. The extruded tank section and first and second end caps together at least partially define an internal tank volume. The first and second planar end caps are both arranged at non-perpendicular angles to the longitudinal direction.

In some embodiments the first end cap is at least partially recessed from the first tank end and the second end cap is at least partially recessed from the second tank end. Some embodiments include at least one mounting hole extending through the extruded tank section without passing through the internal tank volume, and in some such embodiments the mounting hole is located between the first planar end cap and the first tank end.

In some embodiments the generally constant extrusion profile includes first and second opposing, generally planar external surfaces joined by a third generally planar external surface perpendicular to the first and second generally planar external surfaces, and a cylindrical internal surface. Each of the first and second planar end caps includes an elliptical edge corresponding to a conic section of the cylindrical internal surface.

In some embodiments of the invention, a method of making a tank for a heat exchanger, includes: extruding a tank section having a generally constant extrusion profile extending in a longitudinal direction; cutting the extruded tank section to predetermined lengths along the longitudinal direction; forming flat end caps from a sheet of material, each of the flat end caps having first and second opposing faces spaced apart by a thickness of the material; inserting a first flat end cap within one of the predetermined lengths of the extruded tank section so that the longitudinal direction is at a non-zero angle to the first and second opposing faces of the first flat end cap; inserting a second flat end cap within that one predetermined length of the extruded tank section so that the longitudinal direction is at a non-zero angle to the first and second opposing faces of the second flat end cap; and joining the first and second flat end caps to the extruded tank section.

In some embodiment of the invention, a heat exchanger includes a plurality of fluid flow channels extending in parallel from a wall, and a tank sealingly joined to the wall to together define a tank volume. Internal surfaces of the tank volume are exposed to pressure forces from the fluid passing through the plurality of fluid flow channels. The tank includes an extruded tank section having a generally constant extrusion profile extending in a longitudinal direction from a first tank end to a second tank end, a first planar end cap joined to the extruded tank section near the first tank end and arranged at a non-perpendicular angle to the wall, and a second planar end cap joined to the extruded tank section near the second tank end and arranged at a non-perpendicular angle to the wall.

DETAILED DESCRIPTION

A heat exchanger1embodying the present invention is shown inFIGS. 2, 3, and7, and can provide durability advantages over other known heat exchangers when used in high-pressure applications such as oil cooling, charge-air cooling, and the like. For purposes of description, reference will be made to the heat exchanger1as being an air-cooled oil cooler to be used for the cooling of engine oil, but it should be understood that the invention can find applicability in other heat exchanger applications as well.

The heat exchanger1is of a bar-plate construction, with a brazed heat exchanger core2defining alternating passages for the flow of oil and cooling air. As best seen inFIG. 3, the core2is formed by stacking flat separator plates11spaced apart alternatingly by long bars9and short bars10to define alternating oil passages8and air passages7. The oil passages8, bounded by long bars9arranged at opposing air inlet and outlet faces of the heat exchanger1, extend in the heat exchanger width direction. The air passages7, bounded by short bars10arranged at opposing tank ends of the heat exchanger1, extend in the heat exchanger depth direction, so that the oil passages8and air passages7are arranged to be perpendicular to one another, resulting in a cross-flow heat exchange orientation. Oil inserts20are arranged between the separator plates11in the oil passages8, and air fins21are arranged between the separator plates11in the air passages7. The oil inserts20and air fins21provide heat transfer enhancement through additional heat exchange surface area and flow turbulation for their respective fluids, as well as provide structural support to the separator plates in order to withstand the pressurization forces imposed by the fluids. The core2is bounded by side plates22at both the top and bottom ends of the stack.

Flat sides of the short bars10, ends of the long bars9, and edges of the separator plates11and side plates22together form a generally planar wall13at each tank end of the core102. Inlet and outlet tanks3are welded to the walls13to provide inlet and outlet manifolding for the oil flowing through the oil passages8. Details of a representative tank3are shown inFIGS. 4-6, and will now be described in greater detail with reference to those figures andFIGS. 2, 3, and 7.

In order to withstand the elevated pressure forces imposed by the oil or other pressurized fluid traveling through the heat exchanger1, the tank3is formed as a welded assembly, preferably of an aluminum alloy, although other metals could be substituted if required for the application. The tank3is of a box-like construction, with three of the sides provided by an extruded tank section4, the profile of which is shown inFIG. 5. The extruded tank section4extends in a longitudinal direction (indicated by the double-ended arrow labeled “L” inFIG. 4) and includes a pair of opposing sides18spaced apart to define a tank width approximately equal to the depth of the heat exchanger core2, joined by a third side19to form the outer perimeter of the box-like tank. A fluid inlet or outlet port6is provided through one of the side walls18, although such a port6could alternatively be provided through the side wall19. A cylindrical surface16is provided in the interior of the tank section4extending along the length direction L so that internal pressure forces are resolved primarily as membrane stresses in the tank section4, rather than as bending stresses. Such a configuration can provide enhanced durability to the tank3when the fluid passing through the channels8of the heat exchanger1is at a pressure that is substantially elevated over the ambient pressure.

The tank3further includes a pair of planar end caps5arranged at opposing ends15of the extruded tank section4. The planar end caps5are arranged to be non-perpendicular to the longitudinal direction of the extruded tank section4. As best seen inFIG. 7, the deviation from perpendicular can be expressed in terms of an angle θ, and in at least some preferable embodiments the deviation from perpendicular is at least 55°. The planar end caps5can be economically produced by cutting the desired profile from a sheet of metal material by, for example, laser cutting or water jet cutting. The desired profile of the end cap5can include an elliptical edge24that corresponds to a conic section of the cylindrical surface16of the extruded tank section4, when that cylindrical surface16is intersected by a plane at the desired angle of deviation from perpendicular. Such a profile will enable a repeatable and closely matched alignment between the end cap5, at the desired angle, and the extruded tank section4so as to allow for joining of the end cap5and the tank section4by welding or other similar joining processes. In some embodiments, welding of the end cap5to the extruded tank section4is simplified by placing a weld bead17on the inwardly facing side of the tank4, i.e. on that side which eventually faces the internal volume14of the tank3.

The inventors have found that arranging the end caps5at such a non-perpendicular angle to the longitudinal direction of the extruded tank section4leads to a reduction of tensile stress within the flow inserts20at the tank mounting wall13. As pressure forces are exerted by the fluid within the internal volume14onto the flat surfaces of the end caps5, these pressure forces result in tensile stresses in the longitudinal direction L within the wall13. The inventors have found that, when the end caps are oriented to be perpendicular to the longitudinal direction (as in the prior art heat exchanger101), such tensile stresses can result in structural fatiguing of the inserts20and, consequently, an inability to maintain the shape of the flow channels8, resulting in pressure failure of the heat exchanger. Such undesirable results have in the past been addressed by adding multiple gussets between the perpendicular end cap and the internal tank walls. However, such added parts introduce undesirable cost and complexity to the manufacturing process.

By angling the end caps5, the pressure forces (indicated by the arrows labeled “P” inFIG. 7) act on the faces of the end cap at an angle to the longitudinal direction L, that angle being of the same value as the angle θ at which the end cap5is oriented. The resultant stresses imposed upon the heat exchanger1by those pressure forces will include a component that acts in the longitudinal direction within the wall13and imposes the damaging tensile stresses upon the inserts20, that component of the pressure force being decreased as the angle θ increases. Through computational analysis, the inventors have determined that the resultant stresses in the inserts20(which are known to be the weak spot with respect to tank pressurization) are substantially reduced over a comparative design with a gusseted perpendicular end cap.

In some embodiments of the invention, mounting features for the heat exchanger101are incorporated within the footprint of the tanks3. Mounting holes12can be machined into the extruded tank section3(such as by drilling, milling, or other machining processes). Such a mounting hole12can be advantageously located within the triangular region between the end cap5and the corresponding end15of the tank section3, so that mounting hardware can pass through the mounting hole12without needing to pass through the internal volume14of the tank3, thereby avoiding the possibility of fluid leakage through the mounting hole12. In some preferable embodiments, the mounting hole12passes through both side walls18of the extruded tank section4, so that mounting hardware such as a bolt or the like can pass through the tank3in order to secure the heat exchanger101. In some embodiments, a cylindrical tube can be inserted through the mounting hole12and welded to the tank3in order to provide further support for the mounting.

Various alternatives to the certain features and elements of the present invention are described with reference to specific embodiments of the present invention. With the exception of features, elements, and manners of operation that are mutually exclusive of or are inconsistent with each embodiment described above, it should be noted that the alternative features, elements, and manners of operation described with reference to one particular embodiment are applicable to the other embodiments.