Heat exchanger and associated method

Abstract

A heat exchanger for cooling a machine fluid of a vehicle, and associated method. The heat exchanger can include a fluid inlet tank, a fluid outlet tank, and a plurality of heat transfer tubes connecting the inlet tank to the outlet tank. Each tube can include first and second substantially flat sidewalls, a plurality of internal webs extending between the first and second sidewalls, and a plurality of first dimples formed on the first sidewall, each first dimple formed over one of the webs.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent application Ser. No. 10/404,015 filed on Mar. 31, 2004 which claims the benefit of U.S. Provisional Application No. 60/375,920 filed on Apr. 25, 2002. The disclosures of these applications are incorporated by reference herein.

TECHNICAL FIELD

The present invention relates to the area of cooling of the fluids that are used in machinery such as engines, transmissions and other power equipment to lubricate components and/or transfer power.

INTRODUCTION

In the automotive industry it is necessary to cool the oil used in automatic transmissions. The automotive transmission fluid (ATF) reaches high temperatures in the operation of the transmission. These high temperatures need to be reduced to avoid breakdown of the fluid. A device called a transmission oil cooler is conventionally used for that purpose.

With reference to the simplified prior art view of FIG. 1, a typical transmission cooler 3 is illustrated in an automotive application. The exemplary application is shown to generally include an engine 4 and a transmission 5. The oil cooler 3 is typically located inside one of the tanks 2 of a radiator 1. The coolant inside the tanks 2 is used as the cooling medium for the oil cooler 3. This is possible despite the fact that the coolant itself is relatively hot, because the oil temperature is substantially higher. The temperature differential between the coolant in the radiator tank 2 and the oil in the oil cooler 3 is used to cool the oil. The oil circulates through hydraulic lines 6 between the transmission 5 and the oil cooler 3, and the oil gets cooled in the heat exchanger 3.

FIG. 2 illustrates one typical transmission oil cooler 3 in further detail. The oil cooler 3 is located inside the tank 2 of radiator 1. This type of oil cooler, which consists of concentric brass tubes between which the oil flows, is typically made by brazing, a high temperature process that requires expensive brazing equipment and complex process control. The result is a relatively expensive and heavy oil cooler. FIG. 2A shows the cross section of the oil cooler.

FIG. 3 shows a more modern transmission oil cooler 3′. The oil cooler 3′ is again located inside the tank 2 of radiator 1. This type of oil cooler 3′ is called a plate cooler, because it basically consists of several flat plates inside which the oil flows. Plate oil coolers are typically made using aluminum strips which are joined together along their perimeter in a brazing process. The use of flat plates leads to a better heat exchange performance than for a concentric tube cooler, but the result is still a relatively expensive and heavy oil cooler. The very large number and length of brazed joints creates many potential failure modes (leaks), which has a potential negative impact on the reliability of this oil cooler.

FIG. 4 shows an engine oil cooler 7 that can be used in addition to the previously shown transmission oil cooler 3. Some vehicles require both oil coolers. Virtually every vehicle with an automatic transmission requires a transmission oil cooler, and many high powered or high rpm engines require also an engine oil cooler. Typically the engine cooler and the transmission oil cooler are on two separate, independent cooling circuits. The engine oil circulating through the engine oil cooler 7 is typically cooled by placing the oil cooler 7 in a housing that contains coolant. Another possibility (not shown here) is to place the engine oil cooler in the second radiator tank (the first one is already occupied by the transmission oil cooler).

While known oil coolers have proven to be suitable for their intended purposes, a need remains in the pertinent art for a lightweight, low cost, highly reliable oil cooler and other heat exchanger with highly efficient heat transfer characteristics.

SUMMARY

The present teachings provide a heat exchanger for cooling a machine fluid of a vehicle. The heat exchanger can include a fluid inlet tank, a fluid outlet tank, and a plurality of heat transfer tubes connecting the inlet tank to the outlet tank. Each tube can include first and second substantially flat sidewalls, a plurality of internal webs extending between the first and second sidewalls, and a plurality of first dimples formed on the first sidewall. Each first dimple can be formed over one of the webs.

The present teachings also provide a method for making a heat exchanger for cooling a machine fluid. The method includes forming a plurality of tubes having first and second substantially flat sidewalls, coupling a first end of each tube to a fluid inlet tank, coupling a second end of each tube to a fluid outlet tank, forming webs between the first and second sidewalls of each tube, and forming a plurality of first dimples on the first sidewall of each tube, each first dimple formed over one of the webs.

Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:

FIG. 1 is a schematic illustration of a prior art transmission heat exchanger circuit;

FIG. 2 is a view of a prior art conventional heat exchanger of concentric tube design shown in partial section;

FIG. 2A is a cross-sectional view taken along the line 2A-2A;

FIG. 3 is a view of another prior art heat exchanger of plate design shown in partial section;

FIG. 4 is a schematic illustration of prior art engine heat exchanger and transmission heat exchanger circuits;

FIG. 5 is a top view of a heat exchanger according to the present teachings;

FIG. 6 is a side view of the heat exchanger of FIG. 5;

FIG. 6A is a cross-sectional view taken along the line 6A-6A;

FIG. 7 is a top view of a heat exchanger according to the present teachings;

FIG. 8 is a top view of a heat exchanger according to the present teachings;

FIG. 9 is a top view of a heat exchanger according to the present teachings;

FIG. 10A is a cross-sectional view of a heat transfer tube of a heat exchanger according to the present teachings;

FIG. 10B is a cross-sectional view of the tube of FIG. 10A taken along a line perpendicular to the line of the FIG. 10A cross-section;

FIG. 11A is a cross-sectional view of a tube of a heat exchanger according to the present teachings;

FIG. 11B is a cross-sectional view of the tube of FIG. 11A taken along the line perpendicular to the line of the FIG. 11A cross-section;

FIG. 12A is a cross-sectional view of a tube of a heat exchanger according to the present teachings;

FIG. 12B is a cross-sectional view of the tube of FIG. 12A taken along the line perpendicular to the line of the FIG. 12A cross-section;

FIG. 13 is a side view of a portion of a tube of a heat exchanger according to the present teachings;

FIG. 13A is a cross-sectional view taken along the line 13A-13A;

FIG. 14 is a top view of a heat exchanger according to the present teachings;

FIG. 15 is a side view of the heat exchanger of FIG. 14;

FIG. 16 is a top view of a heat exchanger according to the present teachings;

FIG. 17 is a side view of the heat exchanger of FIG. 16;

FIG. 18 is a top view of an air-cooled heat exchanger in accordance with the teachings of the present invention;

FIG. 19 is a side view of the heat exchanger of FIG. 18;

FIG. 20 is a side view of a heat exchanger according to the present teachings;

FIG. 21 is a top view of the heat exchanger of FIG. 20;

FIG. 22 is a cross-sectional view taken along the line 22-22 of FIG. 20; and

FIG. 23 is a cross-sectional view taken along the line 23-23 of FIG. 20.

DETAILED DESCRIPTION

The following description of various aspects of the invention is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. The present teachings are applicable, but are not limited to, the area of cooling of transmission oil and/or engine oil in automotive applications. The present teachings are, for example, also applicable to diverse areas such as railways, ships, aircraft, machine tool, power generation equipment and others.

Referring to FIG. 5, an exemplary heat exchanger, such as for example, an oil cooler, is illustrated and identified at reference character 10 according to an aspect of the present teachings. The heat exchanger 10 is shown to generally include first and second end tanks 12 and 14. The end tanks 12 and 14 can be round or circular in shape. The end tanks 12 and 14 can be connected by a plurality of heat transfer tubes 16. In the exemplary illustration of FIG. 5, the heat exchanger 10 is shown to include five such tubes 16, although any number of tubes 16 can be used. The tubes 16 may be brazed to the end tanks 12 and 14. The first end tank 12 defines a first port 18 as the inlet of oil to be cooled and the second end tank 14 defines a second port 20 as the outlet. Typically, the ends of the tanks 12, 14 can threaded or equipped with some type of connector that allows the connection to the hydraulic lines leading the oil. The complete heat exchanger 10 can be immersed in a cooling medium, such as radiator coolant, typically a mixture of 50% water and 50% glycol. The heat of the oil is transferred through the tube walls to the cooling medium, so that the temperature of the oil leaving the heat exchanger 10 is significantly lower than the temperature of the oil flowing into the heat exchanger 10.

FIG. 7 illustrates another exemplary heat exchanger 30 that includes three tubes 16 adapted for applications, for example, in which less heat transfer is required. FIG. 8 illustrates another exemplary heat exchanger 32 in which four tubes 16 are used. FIG. 9 illustrates another exemplary heat exchanger 34 with six tubes 16, for applications in which greater heat transfer is desirable.

Referring to FIG. 10A, an enlarged cross-section of one of the tubes 16 is illustrated. In the exemplary aspect of FIG. 10A, the tube 16 is shown to include a pair of sidewalls 38, and internal webs 40 connecting the sidewalls 38. The internal webs 40 are incorporated to provide strength to the tube 16 to meet the requirement of a high-pressure test that the heat exchanger 10 must pass for validation. FIG. 10B is a cross-sectional view of tube 16 of FIG. 10A taken along a line perpendicular to the cross-sectional line of FIG. 10A.

FIGS. 11A and 11B illustrate another exemplary aspect of the tubes 16 according to the present teachings. In this aspect, the tube 16 can include indentations 44 along the full width of the tube 16, alternately spaced on both sidewalls 38 of the tube 16. Turbulation of the flow through the tubes 16 occurs at each indentation 44, increasing the heat transfer.

Referring to FIGS. 12A and 12B, an exemplary tube 16 can include dimples 46 that are formed alternately on both sidewalls 38 of the tube 16 and located between the internal webs 40. The dimples 16 can be of round, circular, oval or other shapes as desired. Turbulation of the flow through the tubes 16 occurs at each dimple 46, increasing the heat transfer.

Referring to FIGS. 13 and FIGS. 13A, exemplary tubes 16 can include dimples 46 formed on one of the sidewalls 38 in a staggered or zigzag pattern. In the exemplary illustration of FIGS. 13 and 13A, the opposite sidewall 38 does not include any dimples 46.

Referring to FIGS. 14 and 15, an exemplary heat exchanger 50 according to the present teachings can include a plurality of tubes 16, with each tube defining a convoluted shape having convolutions 51. The multiple direction change of each tube 16 provides good turbulence for efficient heat transfer. The heat exchanger 50 can also include round, rectangular or otherwise shaped end tanks 12 and 14. Each tube 16 can also include turbulators 49, which are inserted within the passages of the tube 16, for providing additional turbulence. These turbulators 49 can be pieces of bent wire or bent metal strips, etc.

With reference to FIGS. 16 and 17, another exemplary heat exchanger 52 having convoluted tubes 16 can include first and second end tanks 54 and 56 that are rectangular in shape. Other shapes of end tanks 54, 56 can be used, such as oval, elliptical or of other polygonal or curved, as desired in a particular application.

Referring to FIGS. 18 and 19, an exemplary heat exchanger 60 that is air-cooled is illustrated. In contrast to the previously described heat exchangers 10, 30, 32, 50, 52, the heat exchanger 60 is not immersed in a cooling liquid, but instead it releases its heat to the surrounding air, similar to a typical engine radiator. The heat exchanger 60 can include fins 62 placed between tubes 16 to provide additional cooling surface. The heat exchanger 60 can include end tanks 54 and 56 that can be circular, round, rectangular, oval or any other shape desired.

Referring to FIGS. 20-23, another aspect of a heat exchanger constructed in accordance with the present teachings is illustrated and generally identified at reference character 100. For automotive applications, the heat exchanger 100 can be mounted within one of the tanks of the radiator that is used to cool the engine of the vehicle. The heat exchanger 100 can be, for example, an automotive transmission oil cooler, or other type of cooler. The heat exchanger 100 can generally include first and second end tanks 12 and 14. The end tanks 12 and 14 can be connected by a plurality of heat transfer tubes 102. The tubes can be extruded from aluminum or otherwise made from different materials. In some applications, the tubes 102 can be rigid and/or substantially flat. The tubes 102 can be brazed or otherwise suitably attached to the tanks 12 and 14 in a manner well-known in the art. As described above, the heat of the oil can be transferred through the tube walls to the cooling medium, so that the temperature of the oil leaving the heat exchanger 100 is significantly lower than the temperature of the oil flowing into the heat exchanger 100. Dimples or indents 104 can be formed on each sidewall of each heat transfer tube 102 to improve heat exchange.

The required cooling efficiency of a transmission oil cooler is generally higher than the efficiency required for other automotive cooling devices, such as radiators. For such applications, the dimples 104 of the heat exchanger 100 can be configured to improve the thermal capacity of the tubes 102 to meet applicable requirements. According to the present teachings, the dimples 104 can deep enough to provide adequate turbulation without tearing or fracturing the sidewalls of the tubes 102. The associated dimpling process is adapted to be repeatable and consistent and avoids variability in the cooling performance of the heat exchangers 100. The dimples 104 are configured such that they do not affect the ability of the heat exchanger 100 to withstand pressures of the order of 500 psi.

Referring to FIGS. 20, 22 and 23, an exemplary arrangement of dimples 104 according to the present teachings is illustrated. A plurality of first dimples 104a formed on a first sidewall 38a of the tube 102 is illustrated in solid lines. A plurality of second dimples 104b formed on a second sidewall 38b of the tube 102 is illustrated in phantom lines. The first and second dimples 104a, 104b are formed directly over alternating webs 40a, which are shortened to accommodate the depth of the dimples 104a, 104b. The dimples 104a, 104b can be formed centrally relative to the respective webs 40a, 40b. The first dimples 104a on the first sidewall 38a can be shifted relative to the second dimples 104b on the second sidewall 38b by one web, such that the webs 40a corresponding the first dimples 104a alternate with the webs 40b that support the second dimples 104b. In particular, each first dimple 104a is centered over a first web 40a and extends to two adjacent second webs 40b on each side of the first web 40a. Similarly, each second dimple 104b is centered over a second web 40b and extends to two adjacent first webs 40a on each side of the second web 40b. Forming the first and second dimples 104a, 104b directly over one of the first and second webs 40a, 40b allows the formation of much larger dimples that can extend nearly to the adjacent web on either side of the web central to the dimple without any tearing of sidewall metal. The dimples 104a, 104b can be formed very consistently because the webs 40a, 40b provide metal restraint on the punch used for the forming. The dimples 104a, 104b can be round, circular, oval, rectangular or have ay other shape.

Referring to FIG. 22, two fluid flow passages 117 bounded by first and second webs 40a, 40b are formed between each of the first dimples 104a and the second sidewall 38b. Referring to FIG. 23, two fluid flow passages 117 bounded by first and second webs 40a, 40b are also formed between the second dimples 104b and the first sidewall 38a. Each fluid flow passages 117 can have a substantially triangular shape, with one side following the curve defined by the corresponding dimple 104a, 104b. The second dimples 104b can be offset transversely by one web 40b from the webs 40a that are central to first dimples 104a. The arrangement of the first and second dimples 104a, 104b defines a continuing and very frequent change in fluid flow passage position and area, and creates enough turbulence to meets the critical criteria for transmission oil coolers.

In one aspect, the cross-sectional dimensions of the heat transfer tubes 102 can be, for example, about 2.8 mm by 34 mm, and the spacing between adjacent webs 40 can be about 2.5 mm.

It will be appreciated from the above description that the present teachings provide a lightweight, low cost, highly reliable heat exchanger with highly efficient heat transfer characteristics. Further, the heat exchanger can increase reliability and reduces/eliminates potential failure modes, such as leaks. Extruded aluminum tubes can be used as part of the heat transfer mechanism. Extruded tubes simplify the manufacturing process, and reduce or eliminate potential failure modes (leaks), which directly impact reliability, production cost, testing cost and warranty costs. The use of extruded tubes dramatically reduces the need to join surfaces through brazing in a watertight and oil tight manner. Since every joint in a pressurized heat exchanger is always a potential failure mode, the elimination or reduction in the number of joints provides a major reliability advantage.

Further increase in the heat transfer capability of the heat exchanger can be provided by modifying the extruded tubes, for instance, by bending or convoluting them or creating dimples in them in order to increase turbulence in the tubes. Further increase the heat transfer capability of the heat exchanger can be provided by modifying the cross-section of the extruded tubes in ways that increase heat exchange.

The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.

Claims

1. A heat exchanger for cooling a machine fluid of a vehicle, the heat exchanger comprising:

a fluid inlet tank;

a fluid outlet tank; and

a plurality of heat transfer tubes connecting the inlet tank to the outlet tank, wherein each tube comprises: first and second substantially flat sidewalls; a plurality of internal webs extending between the first and second sidewalls; and a plurality of first dimples formed on the first sidewall, each first dimple formed over one of the webs.

2. The heat exchanger of claim 1, wherein the first dimples are formed over alternate webs of the tube.

3. The heat exchanger of claim 2, further comprising a plurality of second dimples formed on the second sidewall of each tube, each second dimple formed over one of the webs.

4. The heat exchanger of claim 3, wherein the second dimples are offset laterally by one web relative to the first dimples.

5. The heat exchanger of claim 1, wherein each first dimple is formed substantially centrally relative to the corresponding web.

6. The heat exchanger of claim 4, wherein each of first and second dimples are formed substantially centrally relative to the corresponding webs.

7. The heat exchanger of claim 1, wherein each first dimple defines a pair of fluid flow passages between the first dimple and the second sidewall.

8. The heat exchanger of claim 3, wherein each second dimple defines a pair of fluid flow passages between the second dimple and the first sidewall.

9. The heat exchanger of claim 6, wherein the dimples have shapes selected from the group consisting of oval, square, rectangular, polygonal, circular and rounded.

10. The heat exchanger of claim 1, adapted for immersion in a cooling liquid.

11. The heat exchanger of claim 1, adapted for air-cooling.

12. The heat exchanger of claim 1, wherein the tubes are connected to the inlet and outlet tanks by brazing.

13. The heat exchanger of claim 1, wherein the tubes are extruded from aluminum.

14. The heat exchanger of claim 1, further comprising cooling fins positioned between the tubes.

15. The heat exchanger of claim 1, wherein the machine fluid comprises transmission fluid.

16. A method for making a heat exchanger for cooling a machine fluid, the method comprising:

forming a plurality of tubes having first and second substantially flat sidewalls;

coupling a first end of each tube to a fluid inlet tank;

coupling a second end of each tube to a fluid outlet tank;

forming webs between the first and second sidewalls of each tube; and

forming a plurality of first dimples on the first sidewall of each tube, each first dimple formed over one of the webs.

17. The method of claim 16, further comprising forming the first dimples over alternate webs.

18. The method of claim 17, further comprising forming a plurality of second dimples on the second sidewall of each tube over alternate webs of the tube.

19. The method of claim 18, wherein forming the second dimples comprises offsetting the second dimples laterally by one web relative to the first dimples.

20. The heat exchanger of claim 1, wherein the first and second dimples are formed substantially centrally relative to the corresponding webs.