US20030141042A1

US20030141042A1 - High thermal capability positive heat sink for rectifier assembly

Info

Publication number: US20030141042A1
Application number: US10/062,737
Authority: US
Inventors: Michael Bradfield; Stephen Alford
Original assignee: Delphi Technologies Inc
Current assignee: Delphi Technologies Inc
Priority date: 2002-01-31
Filing date: 2002-01-31
Publication date: 2003-07-31

Abstract

A heat sink structure is provided for a rectifier assembly of an air-cooled generator. The heat sink structure comprises a substantially annular base that defines a plane. The base has a plurality of cooling fins extending from it and which project from the plane. The base further has a plurality of cooling slots, which comprise cutouts of the fins. Additionally, the base has diode mounts, each of which is adapted to retain a respective diode in a thermally conductive manner, whereby heat from each respective diode is transferred to the base and to the cooling fins. Also provided is a method for manufacturing a heat sink structure. The method comprises the steps of configuring a sheet of thermally conductive material to include a substantially annular base, perforating the base to form contiguous fin projections, and bending the fin projections out of the base whereby fin shaped slots remain.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a heat sink structure for a rectifier assembly for an air-cooled generator, and a method of producing a heat sink structure for a rectifier assembly.

2. Discussion of the Related Art

It is known that excessive heat accumulation can cause the rectifier of an automotive generator to malfunction. Efforts therefore have been directed to cooling such rectifiers. In some cases, the cooling is provided by air, while in other cases, the cooling is provided by significantly more expensive and complicated liquid cooling techniques (e.g., using a water coolant). The prior art techniques for cooling the rectifier of a generator typically provide inadequate cooling (e.g., there may be a high thermal impedance between the heat sink of the rectifier assembly and the surrounding cooling environment, such as air). In particular, present production heat sinks are typically stamped aluminum plates with a variety of holes and opening configurations. These openings promote airflow through the rectifier and at the same time provide surface area for convective heat transfer.

One approach taken in the art involves casting or otherwise mounting a cooling fin arrangement to a heat sink base or other component of a rectifier assembly, as seen by reference to U.S. Pat. No. 3,684,944 issued to Evgrafov et al. Evgrafov et al. disclose a rectifier assembly with cooling fins that are cast or otherwise mounted on a base. However, the cooling fin arrangement of Evgrafov et al. has the disadvantage of higher manufacturing costs for parts produced by these manufacturing processes versus stamping.

Another approach taken in the art involves stamping cooling fins out of a base, as seen by reference to U.S. Pat. No. 5,640,062 to Yockey. Yockey discloses a stamped base with cooling fins that project radially out from it. However, because of the limitations of a flat, stamped heat sink, the amount of surface area that can be realized by the heat sink disclosed by Yockey is limited.

There is consequently a need in the art for a rectifier assembly for an air-cooled generator, a heat sink structure for use in such a rectifier assembly, and/or a method of producing a heat sink structure for a rectifier assembly to overcome the above described limitations.

SUMMARY OF THE INVENTION

It is a primary object of the present invention to overcome the foregoing problems and/or to satisfy at least one of the aforementioned needs. The invention provides a heat sink structure for use in a rectifier assembly for an air-cooled generator, and/or a method of manufacturing a heat sink structure for a rectifier assembly. The invention includes shear formed fins and slots which maximizes the available surface area of the heat sink. The invention is further efficiently manufactured by stamping and shear forming processes, as opposed to more expensive casting or extrusion methods.

To achieve this and other objects and advantages, the present invention provides a heat sink structure for a rectifier assembly of an air-cooled generator. The heat sink structure includes a substantially annular base that defines a plane. The structure includes a plurality of cooling fins that extend from the base and project out from the plane. The base further includes a plurality of cooling slots that are cutouts of the fins. The structure also includes diode mounts, each of which is adapted to retain a respective diode in a thermally conductive manner, whereby heat from each respective diode is transferred to the base and to said cooling fins, to provide a heat sink effect.

The present invention also provides a method of manufacturing a heat sink structure for a rectifier assembly. The method comprises the steps of configuring a sheet of thermally conductive material to include a substantially annular base, perforating the base to form fin projections contiguous with the base, and bending the fin projections out from said base whereby fin shaped slots remain in the base.

The expression “substantially annular”, as used in this disclosure, encompasses not only purely annular structures (i.e., O-shaped structures), but also C-shaped structures and other structures that approximate a purely annular shape.

Still other objects, advantages, and features of the present invention will become more readily apparent when reference is made to the accompanying drawings and the associated description contained herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view of a positive heat sink for a rectifier assembly according to a preferred embodiment of the present invention. [0013]
FIG. 2 is a sectional view of a positive heat sink and rectifier assembly according to a preferred embodiment of the present invention. [0014]
FIG. 3 is a cross-sectional view of an exemplary generator in which the rectifier assembly of FIGS. 1 and 2 has been mounted. [0015]
FIG. 4 is a graph demonstrating the high thermal capability of the present invention.[0016]

DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 illustrates, among other things, a [0017] heat sink structure 10 according to the preferred embodiment of the present invention. As will be described hereinafter, the heat sink structure 10 is particularly well suited for use as part of a rectifier assembly 12 (best shown in FIG. 2) of an air-cooled generator 100 (best shown in FIG. 3). The heat sink structure 10, however, can be used in other applications where similar benefits can be realized.
The exemplary [0018] heat sink structure 10 includes a substantially annular base 14, a cooling fin arrangement 16, a cooling slot arrangement 18, and a plurality of diode mounts 20. Base 14 is disposed about an axis 22, and generally lies in and defines a plane 24. Axis 22 intersects plane 24 at a center point 26 of base 14. Base 14 may be made out of any thermally conductive material, including 1100 aluminum.
[0019] Cooling fin arrangement 16 comprises a plurality of fins 28 that extend from the surface of the base 14. Cooling fin arrangement 16 consists of a plurality of fins 28 that are shear formed and bent up from the surface of base 14, projecting out of plane 24, extending substantially parallel to axis 22. In a preferred embodiment, cooling fins 28 are angularly spaced around base 14.
[0020] Cooling slot arrangement 18 consists of a plurality of slots 30 within base 14. Slots 30 are cutouts of fins 28. That is, slots 30 result from the shear forming and bending of fins 28. Like cooling fins 28, in the preferred embodiment slots 30 are angularly spaced around base 14. In such a configuration, slots 30 have a radially innermost edge, or end, 32 proximate to center point 26, a radially outermost edge, or end, 34 distal to center point 26, and radially extending edges 36 between inner and outer edges 32, 34. Cooling slot arrangement 18 is provided to allow convective heat transfer between base 14 and the atmosphere, or forced air currents 38 shown in FIG. 2.
As shown in FIG. 1, the radial extending [0021] edges 36 of each slot 30 are tapered toward each other at radial inner end 32. The angular spacing of slots 30, along with the radial extension of slots 30 and the tapered radially extending edges 36 allow for stamping die clearance during the shear forming of fins 28.
As shown in FIG. 2, each [0022] cooling fin 28 has a contiguous edge 40 with each corresponding slot 30. In the embodiment depicted in FIG. 2, edge 40 is contiguous with outer edge 34. However, it will be appreciated by those skilled in the art that edge 40 may be contiguous with inner edge 32 or radial edge 36.
Cooling fin and [0023] slot arrangements 16, 18 represent an improvement over prior art heat sink structures and methods of manufacturing the same. Many conventional heat sink structures are typically stamped out of thermally conductive material, and removing away a portion of the same so that a base with fin projections remains. Under the present invention disclosed herein, cooling fins 28 are shear formed so that little, if any, of base 14 is removed (i.e., there is little or no “waste” material). This maximizes the available surface area of base 14, while providing cooling fins 28 and slots 30, all of which enhance the desired heat sink, or cooling effect.
Each of the diode mounts [0024] 20 is adapted to retain a respective diode 42 in a thermally conductive manner. Heat from each respective diode 42 is transferred to the base 14 and to the cooling fin arrangement 16 to provide the desired heat sink effect. Preferably, press-fit diodes 42 are used. Such diodes 42 are generally known. Typically, they have a conductive housing 44 with a closed end (not shown) and an open end 46. The closed end, during installation of the diode 42, is press-fit into a correspondingly sized recess 20. The correspondingly sized recesses 20, in this regard, constitute the diode mounts 20. The diode material is contained within the conductive housing 44. The conductive housing 44 serves as either the anode or the cathode of the diode 42. Projecting out from the diode 42, through the open end 46 of the conductive housing 44, is an electrical diode terminal 48 that defines the opposite terminal to the conductive housing 44. This electrical diode terminal 48 defines the cathode if the conductive housing 44 serves as the anode, or defines the anode if the conductive housing 44 serves as the cathode. The diode terminal 48 that projects out from the open end 46 of the conductive housing 44 does not make electrical contact with the conductive housing 44.
One type of press-[0025] fit diode 50 allows current to flow into the a conductive housing 52, through the diode 50, and out through a diode terminal 54 that extends through an open end 56 of the conductive housing 52. Current, however, cannot pass in the reverse direction. Another type of press-fit diode 42 allows the current to flow into the diode terminal 48 that projects out from the open end 46 of the conductive housing 44, through the diode 42, and out from the conductive housing 44. Electrical current cannot flow in the reverse direction.
For the exemplary arrangement shown in FIGS. 1 and 2, the [0026] heat sink structure 10 is provided on the positive side rather than the electrical ground side of the rectifier assembly 12. Accordingly, it carries the positive-type of diodes 42.
As the flow of electrical current heats the press-[0027] fit diodes 42, 50, the press- fit diodes 42, 50 transfer this heat to their surroundings. Preferably, the diode mounts 20 of the heat sink structure 10 are defined by a circumferential wall of a recess 20 or hole in the base 14 of the heat sink structure 10. The heat from each diode 42 therefore is transferred to the heat sink structure 10. This heat, in turn, is readily transferred to air flowing about the heat sink structure 10. The increased surface area provided by the cooling fin arrangement 16 and cooling slot arrangement 18 enhances this transfer of heat.
The [0028] heat sink structure 10 can be manufactured in a relatively uncomplicated and inexpensive manner from a sheet of electrically and thermally conductive material. The sheet may be made of aluminum that is about 4 to 5 millimeters thick. A preferred method of manufacturing the heat sink structure 10 for a rectifier assembly 12, includes the steps of configuring the sheet of thermally conductive material to include a base 14 and perforating the base to form fin projections 28 that are contiguous with the base 14. The configuration of the sheet into base 14 may be done by conventional stamping techniques. As stated above, the perforation of fins 28 out of base 14 may be done by shear forming fins 28. The shear forming further forms substantially radially extending and angularly spaced slots 30 in the base 14.
[0029] Fins 28 are bent in a substantially axial direction, whereby each of the fins 28 is contiguous with an edge of slot 30. In a preferred embodiment shown in FIGS. 1 and 2, fins 28 are bent at an edge 40 contiguous with an outer edge 34 of slots 30. Under conventional methods, it is difficult to shear form fins with parallel sides, such as in a row. Under the method disclosed herein, the tapered edges 36 of each slot 30 permit each fin 28 to naturally clear the stamping die as the fin 28 is shear formed up.
While stamping is the preferred way of configuring the sheet, it is understood that alternative techniques, such as cutting, can be used. An advantage of the stamping process is that, in a single stamping operation, the [0030] base 14 can be provided with diode mounts 20 (e.g., in the form of recesses or holes) and/or additional holes and features (to be described hereinafter) that are used to accommodate other features of the heat sink structure 10 or of the rectifier assembly 12 in which the heat sink structure 10 is used.
The ability to use a stamping process in the manner described above greatly simplifies the overall manufacturing process and represents a significant savings in cost over other ways of providing heat sink structures. It also represents significant savings in the time required to manufacture each [0031] heat sink structure 10.
The diode mounts [0032] 20 and other features, of course, can be provided using alternative techniques (e.g., drilling, cutting, and the like). In this regard, they need not be made using the aforementioned stamping technique.
As illustrated in FIGS. 1 and 2, the present invention also provides the [0033] rectifier assembly 12 that includes the aforementioned heat sink structure 10. The exemplary rectifier assembly 12 is adapted for use in an air-cooled generator. An exemplary generator 100 is shown in FIG. 3 and will be described hereinafter. It is understood, however, that the exemplary rectifier assembly 12 can be applied to other uses.
The [0034] exemplary rectifier assembly 12 may be used with a dual three-phase winding generator. It therefore is adapted to hold two sets of three (i.e., six) negative-side diodes 50 and two sets of three (i.e., six) positive-side diodes 42. Each stator phase of the generator 100 is associated with one of the positive-side diodes 42 and one of the negative-side diodes 50. More specifically, each negative-side diode 50 is electrically connected between the generator's electrical ground (e.g., its housing) and a respective stator phase winding so that electrical current can flow from the electrical ground into the respective stator phase winding, but not in the reverse direction. Each positive-side diode 42, by contrast, is connected between the rectifier's output terminal 58 (i.e., the terminal that typically is connected to a positive terminal of the battery or other device to be charged) and a respective stator phase winding so that electrical current can flow from the respective stator phase winding to the rectifier's output terminal, but not in the reverse direction. In FIG. 1, the bolt 58 defines the rectifier's output terminal.
The [0035] exemplary rectifier assembly 12 includes a substantially annular support 60 adapted to hold negative-side diodes 50 in such a way that (1) a ground terminal of each negative-side diode 50, (i.e., the conductive housing 52 thereof) is electrically connected to the support 60; (2) a phase terminal (i.e., terminal 54) of each negative-side diode 50 remains electrically connectable to a respective one of several stator output phases from the generator 100; and (3) the negative-side diodes 50 are thermally connected to the support 60 so that heat from the negative-side diodes 50 is transferred to the support 60, to provide a heat sink effect.
The [0036] annular support 60 preferably includes six negative-side recesses 62 on the support 60. Each of the negative-side recesses 62 is adapted to receive a press-fit version of the negative-side diodes 50 in such a way that walls of the negative-side recesses 62 press-fittingly retain the negative-side diodes 50. The annular support 60 is further provided with cooling slots 64, positioned in line with cooling slots 30, to allow air currents 38 to flow through and cool the rectifier assembly 12.
The substantially annular [0037] heat sink structure 10 is similarly thermally and electrically conductive. The heat sink structure 10 is adapted to hold positive-side diodes 42 in such a way that (1) a positive terminal (i.e., the conductive housing 44) of each positive-side diode 42 is electrically connected to the heat sink structure 10; (2) a phase terminal (i.e., terminal 48) of each positive-side diode 42 remains connectable to a respective phase output from a respective one of the stator output phases from the generator 100; and (3) the positive-side diodes 42 are thermally connected to the heat sink structure 10 so that heat from the positive-side diodes 42 is transferred to the heat sink structure 10, to provide a heat sink effect.
The [0038] heat sink structure 10, as indicated above, preferably includes a plurality of positive-side recesses 20 on the heat sink structure 10. Each positive-side recess 20 is adapted to receive a press-fit version of the positive-side diodes 42 in such a way that walls of the positive-side recesses 20 press-fittingly retain the positive-side diodes 42.
The [0039] heat sink structure 10 is spaced apart from the annular support 60. The heat sink structure 10 is further provided with passage holes 68. Passage holes 68 are positioned above negative side diodes 50 and are provided to provide access to each diode terminal 54 that extends through an open end 56 of the conductive housing 52.
The [0040] rectifier assembly 12 is farther provided with a terminal assembly 70 for electrically connecting phase leads (not shown) from the stator to the diodes 42, 50. Terminal assembly 70 may be mounted to the periphery of heat sink structure 10, as shown in FIG. 1. Terminal assembly 70 comprises a cover 72 made of an electrically insulating material, such as plastic. Embedded in the plastic cover are six insert molded metallic terminal strips 74. Strips 74 are electrically isolated from each other. Strips 74 correspond to the two sets of three phase windings from the stator. Strips 74 are made of an electrically conductive metal, preferably copper.
Each [0041] terminal strip 74 is electrically connected to a crimping wing 76. Crimping wings 76 serve as terminals for the ends of phase leads (not shown). Each terminal strip 74 is further electrically connected to a pair of diode terminals, consisting of a diode terminal 48 from a positive diode 42 and a diode terminal 54 from a negative diode 50. In the embodiment shown in FIGS. 1 and 2, each terminal strip 74 is connected to a first copper strap 76 which is soldered to a diode terminal 48 from a positive diode and a second copper strap 80 that is soldered to a diode terminal 54 that extends through its passage hole 68 from negative diode 52.
As shown in FIG. 2 (but absent in FIG. 1), a slotted [0042] cover 82 can be provided over the rectifier assembly 12 to protect the rectifier assembly 12, while allowing air to flow through the rectifier assembly 12. The slotted cover 82, for example, can be made of plastic using conventional injection molding techniques. The cover 82 preferably is substantially annular.
A positive output terminal (e.g., bolt [0043] 58) of the generator 100 is electrically connected to the heat sink structure 10. The connection to the battery or other device to be charged by the generator 100 can be made via this positive output terminal (e.g., bolt 58). Heat sink structure 10 can further be configured to a voltage rectifier 84 for the rectifier assembly 12.
The substantially annular shape of the [0044] exemplary rectifier assembly 12 advantageously corresponds with the typical shape of a generator housing. It also advantageously provides an internal opening to accommodate the rotor shaft 121 of a typical generator 100.
With reference to FIG. 3, it can be seen how conveniently the [0045] rectifier assembly 12 fits within a generator housing 100 and around the rotor shaft 121 of the generator 100. A conventional alternator 100 is illustrated in FIG. 3 sometimes referred to herein as a generator. Alternator 100 has a rotor assembly generally designated by the reference numeral 120 and stator assembly generally designated by the reference numeral 115. The rotor assembly 120 includes a shaft 121 supporting all rotating magnetic circuit structures thereof including conventional pole- members 116A and 116B, rotor core 117 and field coil 118 wound upon bobbin 112. Additionally, all other non-magnetic circuit rotating structures are carried thereby, including air circulation fans 119 and 127 located at axially opposite sides of the pole-members. Fan 127 is formed from sheet metal stock and spot welded to pole-member 116B while fan 119 is formed from an appropriate thermoplastic material and heat staked to tower extensions (not shown) from the field coil bobbin 112. The shaft 121 in turn is rotatably supported within a housing 126 by a pair of bearings 123 and 122.
The [0046] support 60 and generator housing 126 preferably are formed integrally as an aluminum die cast. The heat sink structure 10 preferably is a stamped and formed aluminum plate that is provided using the manufacturing method described above. Other materials and manufacturing techniques, of course, can be used in lieu of, or in addition to, the foregoing exemplary materials and techniques.
Since the [0047] rectifier assembly 12 and the heat sink structure 10 thereof occupy a significant amount of the usable space around the rotor shaft 121, and since they fill that space with a large surface area, the heat from the diodes 42, 50 is dissipated in a very efficient manner. To further enhance this efficiency, fans 119 and 127 propel air through the spaces separating the rectifier assembly 12. In particular, fans 119 and 127 propel air through the fins 28 and slots 30. An efficient and compact heat sink structure therefore is provided.
The foregoing [0048] exemplary rectifier assembly 12 advantageously uses relatively inexpensive and uncomplicated parts, is provided using relatively inexpensive and uncomplicated manufacturing and assembling techniques, and despite these expedients, provides a very effective cooling action in conjunction with air flowing over and through the rectifier assembly 12.
FIG. 4 presents a [0049] graph 200 demonstrating the high thermal capability of the present invention. First, graph 200 plots generator speed 202 (x-axis) against diode temperature 204 (left y-axis) for generators operating at an ambient temperature of 125 degrees Celsius, and generating an output voltage of 13V. Graph 200 shows the diode temperatures for positive diodes 206 and negative diodes 208 operating on current production rectifier assemblies. Diodes 206, 208 reach temperatures as high as about 222 degrees Celsius and 212 degrees Celsius, respectively. In contrast, graph 200 shows the diode temperatures for positive diodes 210 and negative diodes 212 operating on a rectifier assembly with a heat sink according to the invention disclosed herein. Under the improved heat sink structure, diodes 210, 212 only reach temperatures of about 185 and 195 degrees Celsius, respectively.
[0050] Graph 200 also plots generator speed 202 (x-axis) against generator output in amps (right y-axis) for generators operating under the above operating conditions. Graph 200 shows that production output for rectifier assemblies under the present invention 218 is nearly equal to output for conventional generators 216.
While the [0051] exemplary rectifier assembly 12 is adapted to hold six negative-side diodes 50 and six positive-side diodes 42 so that it can be readily used with two (2) independent three-phase rectifier circuits (e.g., generator 100), it is understood that the invention is not limited to such an arrangement. The rectifier assembly 12 can be modified to hold more or fewer negative-side diodes 50 and/or positive-side diodes 42, depending upon the intended application of the rectifier assembly 12.
While the present invention has been described with reference to certain preferred embodiments and implementations, it is understood that various modifications and variations will no doubt occur to those skilled in the art to which this invention pertains. These and all other such variations which basically rely of the teachings through which this disclosure has advanced the art are properly considered within the scope of this invention. [0052]

Claims

What is claimed is:

1. A heat sink structure for a rectifier assembly of an air-cooled generator, said heat sink structure comprising:

a substantially annular base, said base defining a plane;

a plurality of cooling fins extending from said base and projecting out from said plane;

a plurality of cooling slots in said base, said slots comprising cutouts of said fins; and

diode mounts, each of which is adapted to retain a respective diode in a thermally conductive manner, whereby heat from each respective diode is transferred to said base and to said cooling fins, to provide a heat sink effect.

2. The heat sink structure of claim 1, wherein said cooling fins project substantially perpendicular to said plane.

3. The heat sink structure of claim 1, wherein said slots further comprise angularly spaced radial slots in said base, said slots having an inner edge proximate to the center of said substantially annular base, an outer edge distal to the center of said substantially annular base, and radially extending edges between said inner and outer edges.

4. The heat sink structure of claim 3, wherein each of said fins is contiguous with said base.

5. The heat sink structure of claim 4, wherein each of said fins are contiguous with said outer edge of each of said slots.

6. The heat sink structure of claim 3, wherein said radially extending edges of each slot taper toward each other at a radial end of each slot.

7. The heat sink structure of claim 3, wherein each of said diode mounts is defined by a circumferential wall of a recess or hole in said base.

8. The heat sink structure of claim 7, wherein said wall is adjacent said outer edge of said slot.

9. The heat sink structure of claim 1, wherein said base comprises an aluminum base.

10. A method of manufacturing a heat sink structure for a rectifier assembly, said method comprising the steps of:

configuring a sheet of thermally conductive material to include a substantially annular base;

perforating said base to form fin projections contiguous with said base; and

bending said fin projections out from said base whereby fin shaped slots remain in said base.

11. The method of claim 10, wherein the step of configuring said sheet of thermally conductive material comprises the step of stamping a substantially annular base from a metal sheet.

12. The method of claim 10, wherein the step of perforating said base further comprises shear forming fins in said base.

13. The method of claim 12, wherein the step of shear forming further comprises shear forming substantially radially extending and angularly spaced slots in said base.

14. The method of claim 13, further comprising the step of shear forming slots each of which having radially extending edges that taper toward each other at a radial end of each slot.

15. The method of claim 14, wherein the step of bending said fins comprises the step of bending said shear formed fins in a substantially axial direction, whereby each of said fins is contiguous with an edge of said slot.

16. The method of claim 15, wherein the step of bending said fin further comprises the step of bending each of said fins at an edge contiguous with an edge of said slot, said edge being radially distal from the center of said substantially annular base.