WO2014167448A1

WO2014167448A1 - Heat sink, lighting device and heat sink manufacturing method

Info

Publication number: WO2014167448A1
Application number: PCT/IB2014/060212
Authority: WO
Inventors: Ya-Kuang Hsiao; Huaizhou LIAO; Hai Tao LIU
Original assignee: Koninklijke Philips N.V.
Priority date: 2013-04-07
Filing date: 2014-03-27
Publication date: 2014-10-16

Abstract

Disclosed is a heat sink (10) for a lighting device (200), the heat sink comprising a base portion (20) for engaging with the lighting device; an end portion (30); a first array of spatially separated first cooling fins (40) extending from the base portion to the end portion; a second array of spatially separated second cooling fins (50) extending from the base portion to the end portion; wherein the first array is arranged opposite the second array. A lighting device including such a heat sink and a method of manufacturing such a heat sink are also disclosed.

Description

HEAT SINK, LIGHTING DEVICE AND HEAT SINK MANUFACTURING METHOD

FIELD OF THE INVENTION

The present invention relates to a heat sink for a lighting device, a lighting device comprising such a heat sink and a method of manufacturing a heat sink.

BACKGROUND OF THE INVENTION

With a continuously growing population, it is becoming increasingly difficult to meet the world's energy needs as well as to control carbon emissions to kerb greenhouse gas emissions that are considered responsible for global warming phenomena. These concerns have triggered a drive towards more efficient energy consumption in an attempt to reduce energy consumption.

One such area of concern is lighting applications, either in domestic or commercial settings. There is a clear trend towards the replacement of traditional incandescent light bulbs, which are notoriously energy inefficient, with more energy efficient replacements. Indeed, in many jurisdictions the production and retailing of incandescent light bulbs has been outlawed, thus forcing consumers to buy energy-efficient alternatives, e.g. when replacing incandescent light bulbs.

A particular promising alternative is provided by solid state lighting (SSL) devices, which can produce a unit luminous output at a fraction of the energy cost of incandescent light bulbs. An example of such a SSL element is a light emitting diode.

One technical challenge with providing lighting devices based on SSL elements is that the performance of the SSL element, e.g. the LED, is temperature-dependent. At higher temperatures the performance of the SSL element can diminish, such that it is important to transfer the heat generated by the SSL element away from the SSL element, i.e. cool the SSL element. To his end, most lighting devices such as light bulbs include a heat sink to transfer the heat generated by the SSL elements, thereby effectively cooling the SSL elements and ensuring that the SSL elements performs as desired. However, a heat sink can significantly increase or even dominate the cost of the lighting device. As the relatively high cost of SSL-based lighting devices is one of the most important economic factors that hinder market penetration of such lighting devices, it is therefore desirable to be able to manufacture such a heat sink in a cost-effective manner.

An example of such a heat sink is disclosed in WO 201 1/124386 A1. The heat sink comprises a central heat dissipating body and a plurality of cooling ribs extending in a radial direction outwardly from the central heat dissipating body and in an axial direction away from this body. This heat sink is manufactured as a single integrated piece. However, its manufacture is still relatively complex and the limitations on the number of cooling ribs that can be integrated in the heat sink means that effective cooling may not be possible for lighting devices having a relatively large number of SSL elements. SUMMARY OF THE INVENTION

The present invention seeks to provide a heat sink that can be manufactured in a cost-effective manner and that can provide effective cooling in a lighting device.

The present invention further seeks to provide a lighting device including such a heat sink.

The present invention yet further seeks to provide a method of manufacturing such a heat sink.

According to an aspect of the present invention, there is provided a heat sink for a lighting device, the heat sink comprising a base portion for engaging with the lighting device; an end portion; a first array of spatially separated first cooling fins extending from the base portion to the end portion; a second array of spatially separated second cooling fins extending from the base portion to the end portion; wherein the first array is arranged opposite the second array.

By providing a double array of cooling fins that are opposite each other and are thermally coupled to the base portion, very efficient cooling of the lighting device can be realized. A further advantage is that the heat sink may be formed from a single sheet of heat-conductive material such as a metal, in a simple manufacturing process, thereby providing a cost-effective heat sink.

Although the shape of the cooling fins is not particularly limited, in an embodiment each first cooling fin has a first section extending from the base portion in a first direction and a second section extending from the first section to the end portion in a second direction; and each second cooling fin has a third section extending from the base portion in the second direction and a fourth section extending from the third section to the end portion in the first direction. This heat sink can be manufactured in a particularly straightforward manner, in particular when each first section has the same length as each third section, such that consequentially each second section has the same length as each fourth section because each first cooling fin has the same length as each second cooling fin.

In an embodiment, the first cooling fins are spatially separated by respective first gaps and the second cooling fins are spatially separated by respective second gaps, and wherein each first cooling fin faces a second gap and each second cooling fin faces a first gap. In other words, the first gaps may have been created by the formation of the second cooling fins and the second gaps may have been created by the first cooling fins.

In a particularly advantageous embodiment, the first cooling fins and the second gaps have a first width; the second cooling fins and the first gaps have a second width; and the first width and the second width are each in a range of 1.5 to 4.0 mm. Preferably, the first width is equal to the second width. It has been found through thermodynamical modelling that a heat sink having cooling fins obeying the aforementioned width constraints has a heat dissipation efficiency that is several times higher than most conventional heat sinks.

The heat sink may have any suitable shape, such as a linear shape or an annular shape. An annular-shaped heat sink may be advantageously used in light bulbs. The heat sink of the present invention is not limited to two arrays of cooling fins. In an embodiment, the heat sink further comprises a third array of spatially separated third cooling fins extending from the base portion to the end portion. This further improves the heat transfer capacity of the heat sink, although this may increase manufacturing complexity.

In accordance with another aspect of the present invention, there is provided a lighting device comprising at least one lighting element and the heat sink according to an embodiment of the present invention, wherein the at least one lighting element engages with the base portion of the heat sink. Such a lighting device benefits from lower overall manufacturing costs due to the relatively cheap heat sink, which therefore increases the marketability of the lighting device.

The at least one lighting element may be arranged on a carrier such as a printed circuit board, said carrier being supported by the base portion. The at least one lighting element preferably is a solid state lighting element; the at least one lighting element more preferably is a light emitting diode.

In accordance with yet another aspect of the present invention, there is provided a method of manufacturing a heat sink for a lighting device, the method comprising providing a sheet of a heat-conductive material; making a plurality of incisions in the heat-conductive material, thereby defining a base portion, an end portion opposite the base portion and a plurality of fins extending from said base portion to said end portions, said fins being separated by said incisions; forming a first array of fins extending between the base portion and the end portion by forcing a first plurality of fins out of the plane of the sheet; and forming a second array of fins extending between the base portion and the end portion by forcing a second plurality of fins out of the plane of the sheet, such that the first array is arranged opposite the second array. This method produces the heat sink of the present invention in a simple manner, thereby providing a cost-effective heat sink.

The steps of forming the first array and the second array preferably are performed simultaneously to further reduce the complexity of the manufacture of the heat sink, which by way of non-limiting example may be manufactured from an oblong or annular sheet.

In an alternative embodiment, the sheet may be bent to form an annular heat sink. This is a particularly cost-effective embodiment of manufacturing an annular heat sink.

BRIEF DESCRIPTION OF THE EMBODIMENTS

Embodiments of the invention are described in more detail and by way of non-limiting examples with reference to the accompanying drawings, wherein:

FIG. 1 schematically depicts a portion of a heat sink according to an embodiment of the present invention;

FIG. 2 and 3 schematically depict different aspects of the heat sink of FIG.

1 ;

FIG. 4 schematically depicts a heat sink according to another embodiment of the present invention;

FIG. 5 schematically depicts a method of manufacturing a heat sink according to an embodiment of the present invention; and

FIG. 6 schematically depicts a lighting device according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

It should be understood that the Figures are merely schematic and are not drawn to scale. It should also be understood that the same reference numerals are used throughout the Figures to indicate the same or similar parts.

FIG. 1 schematically depicts a portion of an annular heat sink 10 according to an embodiment of the present invention. The annular heat sink 10 is shown in its entirety in FIG. 4. The heat sink 10 is made of a heat-conducting material, such as a metal. Aluminium is particularly preferred as it is a relatively cheap metal that can be easily processed, e.g. because it is relatively soft and pliable, but other suitable metals will be immediately apparent to the skilled person. The heat sink 10 comprises a base portion 20 for engaging with the lighting device, in particular, the base portion 20 may be brought into contact with one or more solid state lighting (SSL) elements. For instance, the SSL elements may be arranged on a carrier such as a printed circuit board, which carrier may be placed on the base portion 20 such that the base portion 20 supports the carrier. Generally, the base portion 20 is thermally coupled to the one or more SSL elements such that the heat generated by the SSL elements is transferred to the heat sink 10 through the base portion 20.

The heat sink 10 further comprises an end portion 30 and a first array of first cooling fins 40 extending from the base portion 20 to the end portion 30. A detail of the first array of first cooling fins 40 is shown in FIG. 2. The first cooling fins 40 are spatially separated from each other by first gaps 45. The heat sink 10 further comprises a second array of second cooling fins 50 extending from the base portion 20 to the end portion 30. A detail of the second array of second cooling fins 50 is shown in FIG. 3. The second cooling fins 50 are spatially separated from each other by second gaps 55. The first array of first cooling fins 40 and the second array of second cooling fins 50 are arranged opposite each other, thereby defining an air-filled cavity 60 that is delimited by the first array and the second array. In other words, in the heat sink 10 according to the present invention, an imaginary surface extends from the base portion 20 to the end portion 30, wherein the first array and the second array are located on opposite sides of the imaginary surface. The imaginary surface may be the plane of a sheet material from which the heat sink 10 is formed.

The provision of at least two arrays of cooling fins 40, 50 that are separated by an air-filled cavity 60 ensures that a higher density of cooling fins 40, 50 can be integrated in the heat sink 10, with the air-filled cavity 60 ensuring sufficient convection of air through the air gaps 45 and 55, such that the cooling fins 40, 50 can provide effective cooling of the one or more lighting elements engaging with the base portion 20 of the heat sink 10. The first cooling fins 40 and the second cooling fins 50 may have any suitable shape, e.g. an arched shape. However, in an advantageous embodiment, the first cooling fins 40 and the second cooling fins 50 have an angled shape. The first cooling fins 40 have first portion 42 extending from the base portion 20 in a first direction and a second section 44 extending from the first section 42 to the end portion 30 in a second direction, wherein the angle is defined between the first section 42 and the second section 44. The second cooling fins 50 each have a third section 52 extending from the base portion 20 in the second direction and a fourth section 54 extending from the third section 52 to the end portion 30 in the first direction, wherein the angle is defined between the third section 52 and the fourth section 54. In other words, the first section 42 is oriented in parallel with the fourth section 54 and the second section 44 is oriented in parallel with the third section 52. Although each cooling fin 40, 50 is shown to contain a single angle, it should be understood that the cooling fins 40, 50 may have any suitable number of angles.

In an embodiment, the first section 42 and the fourth section 54 have the same length, i.e. the junction between the first section 42 and the second section 44 and the junction between the third section 52 and the fourth section 54 are equidistant to the base portion 20.

In a preferred embodiment, the heat sink 10 is formed from a single sheet of a heat-conductive metal, e.g. a metal such as aluminium or the like as previously explained. This yields a particular cost-effective heat sink 10. The annular heat sink 10 shown in FIG. 1 and 4 is a non-limiting example of a heat sink 10 according to the present invention made from a single sheet of metal. In this preferred embodiment, each first cooling fin 40 is located opposite a second gap 55 and each second cooling fin 50 is located opposite a first gap 45. In other words, each first cooling fin 40 is released from a second gap 55 and each second cooling fin 50 is released from a first gap 45. The first array of first cooling elements 40 and the second array of second cooling elements 50 are located on opposite sides of the plane of the sheet material.

In an embodiment, the first cooling fins 40 have a first width and the second cooling fins have a second width, wherein the first width and the second width are individually selected from a range of 1 .5-4.0 mm. Preferably, the first cooling fins 40 are separated by a gap 45 having the second width and the second cooling fins 50 are separated by a gap 55 having the first width. The first width may be same as the second width or may be different to the second width. Preferably, the first width is the same as the second width.

It has been found from thermodynamical simulations that when the first cooling fins 40 and the second cooling fins 50 each have a width selected from the range of 1.5 - 4.0 mm, the heat sink 10 has a heat dissipation capacity of about five times the heat capacity of many conventional heat sinks, thus providing effective cooling of a lighting device thermally coupled to the base portion 20 of the heat sink. It has been found that if the fins have a width outside this range, the efficiency of the heat sink 10 rapidly reduces.

In particular, when the heat sink 10 is formed from a single sheet of a heat conducting material such as a metal, the gaps 45 and 55 also have a width in the range of 1.5 - 4.0 mm because a cooling fin of the array of cooling fins opposite such a gap has been released from such a gap, i.e. a first cooling fin 40 has been released from a second gap 55 and a second cooling fin 50 has been released from a first gap 45. It has been found through thermodynamic simulation that when the widths of the cooling fins 40, 50 and the widths of the gaps 45, 55 all lie within this range, the heat dissipation capacity of the heat sink 10 is excellent.

If the individual fins 40, 50 have a width exceeding 4.0 mm, the heat transfer from the fins to the surrounding air becomes less efficient due to the viscosity of the air. The friction between the air and the fin surface will capture hot air around the fin surface, just like an isolating layer, and reduce the heat dissipation efficiency. If the individual fins 40, 50 have a width smaller than 1.5 mm, the heat transfer from the fins to the surrounding air becomes less efficient due to the fact that consequently the gaps 45, 55 also have a width of less than 1.5 mm such that the air flow through the first array of first cooling fins 40 and through the second array of second cooling fins 50 becomes restricted, such that an insufficient air flow is achieved to effectively cool the heat conductive cooling fins 40, 50 of the heat sink 10. However, it should be understood that in an alternative embodiment (not shown), a first cooling fin 40 and a second cooling fin 50 may combine to form a closed body such as an oblong body, which body may be mounted between the base portion 20 and the end portion 30, in which case a heat sink 10 is formed from a plurality of separate and spatially separated bodies mounted between a separate base portion 20 and a separate end portion 30. A heat sink 10 according to this embodiment has the same beneficial thermal characteristics as the heat sink shown in FIG. 1 and 4 but is more expensive to manufacture.

The heat sink 10 shown in FIG. 1 -4 has an annular shape by way of non- limiting example only. It should be understood that the heat sink 10 may have any suitable shape, such as a linear shape.

FIG. 5 schematically depicts a method of manufacturing a heat sink 10 according to an embodiment of the present invention. The method begins in step (a) with the provision of a sheet 100 of a heat-conductive material. A metal sheet 100 is particularly suitable. The metal may be aluminium, which is cheap and pliable, or any other suitable metal may be used.

In step (b), a plurality of cuts or incisions 1 10 are made through the sheet 100. The incisions extend from a portion of the sheet 100 defining the base portion 20 to a portion of the sheet 100 defining the end portion 30 are preferably are equidistantly spaced to define a plurality of cooling fins 40, 50 extending from the base portion 20 to the end portion 30. The cuts or incisions 1 10 may be made in the sheet 100 in any suitable manner, e.g. by cutting or slicing the sheet 100.

In step (c), the first array of first cooling fins 40 extending between the base portion 20 and the end portion 30 and the second array of second cooling fins 50 extending between the base portion 20 and the end portion 30 are formed by forcing the first cooling fins 40 and the second cooling fins 50 out of the plane of the sheet 100, such that the first array is arranged opposite the second array, i.e. the first array and the second array are formed on opposites sides of the plane of the sheet 100. The first array and the second array are preferably formed simultaneously, although this is not essential. The cooling fins 40, 50 may be forced out of the plane of the sheet 100 to any suitable depth, e.g. a sheet 100 having first cooling fins 40 extending to 2 mm above the plane of the sheet 100 and having second cooling fins 40 extending to 2 mm below the plane of the sheet 100.

The sheet 100 may optionally be bent into an annular shape to provide the heat sink 10 as shown in FIG. 4. This bending step preferably is performed after the formation of the first cooling fins 40 and the second cooling fins 50.

At this point, it is noted that the spacing of the incisions 1 10 defines the width of the cooling fins 40, 50. For instance, a single pattern of equidistant incisions 1 10 yields a heat sink 10 in which the first cooling fins 40 and the second cooling fins 50 have the same width. Alternatively, an alternating spacing pattern of incisions 1 10 may be chosen in which the first cooling fins 40 have a first width and the second cooling fins 50 have a second width. In any embodiment, it is preferred that the first cooling fins 40 and the second cooling fins 50 have a width in the range of 1.5 - 4.0 mm as already explained in more detail above.

This also means that the first gaps 45 and the second gaps 55 each have a width in this range, as a first gap 45 is formed by the release of a second cooling fin 50 from the sheet 1 10 and a second gap 55 is formed by the release of a first cooling fin 50 from the sheet 1 10, such that first gaps 45 have the same width as the second cooling fins 50 and the second gaps 55 have the same width as the first cooling fins 40.

FIG. 6 schematically depicts a non-limiting example embodiment of a lighting device 200 of the present invention. The lighting device 200 comprises the heat sink 10 according to an embodiment of the present invention and one or more SSL elements 220 thermally coupled to the base portion of the heat sink 10. The one or more SSL elements 220 may be LEDs. The SSL elements 220 may be mounted on a carrier (not shown), such as an annular carrier. The carrier for instance may be a printed circuit board. The carrier may be supported by the base portion of the heat sink 10. In case of the lighting device 200 comprising a plurality of SSL elements 220, the SSL elements 220 may be the same SSL elements or may be different SSL elements 220, such as a mixture of different colour SSL elements, e.g. red and white LEDs, and/or different colour temperature white LEDs, and so on.

The lighting device 200 may further comprise a reflective element 240 for redirecting the luminous output of the one or more SSL elements 220 towards an exit window of the lighting device 200. The reflective element 240 may have any suitable shape.

The lighting device 200 may include additional optical elements, e.g. a beam shaping element to shape the luminous output of the lighting device 200. A non-limiting example of such a beam shaping element is a microlens array.

The lighting device may for instance be a light bulb such as a spot light bulb. Non-limiting examples of such spot light bulbs include sizes such as E27, MR1 1 , MR16, GU10, AR1 1 1 , Par30 Par38, BR30, BR40, R20, R50, and so on.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word "comprising" does not exclude the presence of elements or steps other than those listed in a claim. The word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The invention can be implemented by means of hardware comprising several distinct elements. In the device claim enumerating several means, several of these means can be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Claims

1. A heat sink (10) for a lighting device (200), the heat sink comprising:

a base portion (20) for engaging with the lighting device;

an end portion (30);

a first array of spatially separated first cooling fins (40) extending from the base portion to the end portion;

a second array of spatially separated second cooling fins (50) extending from the base portion to the end portion;

wherein the first array is arranged opposite the second array.

2. The heat sink (10) of claim 1 , wherein the heat sink is formed from a single sheet (100) of heat-conductive material.

3. The heat sink (10) of claims 1 or 2, wherein:

each first cooling fin (40) has a first section (42) extending from the base portion (20) in a first direction and a second section (44) extending from the first section to the end portion (30) in a second direction; and

each second cooling fin (50) has a third section (52) extending from the base portion (20) in the second direction and a fourth section (54) extending from the third section to the end portion in the first direction.

4. The heat sink (10) of claim 3, wherein each first cooling fin (40) has the same length as each second cooling fin (50), and wherein each first section (42) has the same length as each fourth section (54).

5. The heat sink (10) of any of claims 1 -4, wherein the first cooling fins (40) are spatially separated by respective first gaps (45) and the second cooling fins (50) are spatially separated by respective second gaps (55), and wherein each first cooling fin faces a second gap and each second cooling fin faces a first gap.

6. The heat sink (10) of claim 5, wherein:

the first cooling fins (40) and the second gaps (55) have a first width;

the second cooling fins (50) and the first gaps (45) have a second width; and

the first width and the second width are each in a range of 1.5 - 4.0 mm.

7. The heat sink (10) of claim 6, wherein the first width is equal to the second width.

8. The heat sink (10) of any of claims 1 -7, further comprising:

a third array of spatially separated third cooling fins extending from the base portion (20) to the end portion (30); wherein third array faces at least one of the first array and the second array.

9. A lighting device (200) comprising at least one lighting element (220) and the heat sink (10) of any of claims 1 -8, wherein the at least one lighting element engages with the base portion (20) of the heat sink.

10. The lighting device (200) of claim 9, wherein the at least one lighting element (220) is a solid state lighting element arranged on a carrier, said carrier being supported by the base portion (20).

1 1 . A method of manufacturing a heat sink for a lighting device, the method comprising:

providing a sheet (100) of a heat-conductive material;

making a plurality of incisions (110) in the heat-conductive material, thereby defining a base portion (20), an end portion (30) opposite the base portion and a plurality of cooling fins (40, 50) extending from said base portion to said end portions, said fins being separated by said incisions; forming a first array of first cooling fins (40) extending between the base portion and the end portion by forcing a first plurality of cooling fins out of the plane of the sheet; and

forming a second array of second cooling fins (50) extending between the 5 base portion and the end portion by forcing a second plurality of cooling fins out of the plane of the sheet, such that the first array is arranged opposite the second array.

12. The method of claim 1 1 , wherein the first cooling fins (40) and the second o cooling fins (50) each have a width in the range of 1.5 - 4.0 mm.

13. The method of claim 12, wherein the first cooling fins (40) and the second cooling fins (50) have the same width. 5

14. The method of any of claims 1 1 -13, wherein the steps of forming the first array and the second array are performed simultaneously.

15. The method of any of claims 1 1 -14, further comprising bending the sheet (100) into an annular heat sink (10).

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