Patent Application
20180142861
N/A
The present disclosure relates to heat sinks for solid state illumination systems, and more particularly pertains to compact module with air flow path directing warmed air to defog a headlamp lens cover.
While solid state light sources, e.g., light emitting diodes (LEDs) may generate less thermal energy compared to traditional bulbs (e.g., incandescent light bulbs), solid state light sources nevertheless generate thermal energy which should be managed in order to control the junction temperature. A higher junction temperature generally correlates to lower light output, lower luminaire efficiency, and/or reduced life expectancy.
Solid-state illumination systems include heat sinks to dissipate thermal energy away from the solid state light source in order to manage the junction temperature. A two-component heat sink is known in US Pat. Pub. 2014/0338878 (Tessnow). Other examples of heat sinks and air flow are in U.S. Pat. No. 7,683,395 (Huber); U.S. Pat. No. 9,115,861 (Sieme); U.S. Pat. No. 6,497,507 (Weber); U.S. Pat. No. 7,329,033 (Glovatsky); Pub. US2011/0310631 (Davis); and European EP 2 020 569 (Barthel); and German DE 10 2011 084 114 (Wais).
It is known that solid-state light-emitting diodes (LEDs) are efficient and used in automotive low beam and high beam headlamps. Higher power LEDs are now used in such applications, such as those sold by OSRAM Opto Semiconductors under the trade designation Oslon Black Flat S (Model KW HLL531.TE) which has 5 chips generating 2000 lumens and a 20 Watt thermal load (28 total electrical Watts, 8 Watts emitted as light). Such LEDs need relatively large heat sinks. Since it is desired that the headlamps are moveable so as to be aimed, the heat sinks are internal to a sealed housing. The heat sinks for such large thermal loads are large and heavy, consuming about 500 grams of aluminum, which presents a lampset packaging problem. Simultaneously, however, the thermal power of these LEDs is nonetheless too small to melt ice or defog lenses as was commonly done by the traditional but less efficient filament incandescent or halogen lamps. Even when using the higher power LEDs and passive heat sinks the radiated heat remains behind the headlamp housing's bezel which conceals the light source and the front lens cover stays relatively cool. Conventional solutions have involved hot air generating fans with complicated air ducts that required breaking holes into the bezel, undesirable from a standpoint of a vehicle manufacturer's styling goals.
Features and advantage of the claimed subject matter will be apparent from the following description of embodiments consistent therewith, which description should be considered in conjunction with the accompanying drawings, wherein:
By way of an overview, one aspect consistent with the present disclosure features an extruded heat sink as part of a vehicle solid-state lamp module cooling system that incorporates a fan to direct air across the heat-dissipating ribs.
The heat sink of the present disclosure provides numerous benefits and solves several problems. For example, while cast aluminum heat sinks are inexpensive and allow complex heat sink shapes, cast aluminum has a low thermal conductivity (e.g., about 90 W/mK) which may not be able to transfer enough thermal energy away from the solid state light source to maintain the desired junction temperature. While present inventors are aware of some cast aluminum heat sink material having a somewhat higher thermal conductivity (e.g., about 120 W/mK) than conventional cast aluminum, it is considered exotic and expensive, and for practical purposes extruded aluminum is considered to have a thermal conductivity about twice that of cast aluminum. Additionally, the low thermal conductivity of cast aluminum may require the cast aluminum heat to be unacceptably bulky and/or heavy. While extruded aluminum heat sinks have substantially higher thermal conductivity compared to cast aluminum heat sink (e.g., about 200 W/mK), extruded aluminum heat sinks suffer from limited design flexibility. For example, the shape of extruded aluminum heat sinks is generally limited to a symmetric shape unless post-extrusion machining (e.g., to include mounting holes and/or irregular shapes) is utilized. Unfortunately, the post-extrusion machining adds cost to the heat sink and can limit high volume production. Further details are disclosed in US Pat. Pub. 2014/0338878 (Tessnow), incorporated by reference herein.
The heat sink of the present disclosure solves certain disadvantages and limitations discussed above. The heat sink is preferably formed in two parts which are coupled together, each part being preferably of extruded aluminum component (and its relatively high thermal conductivity) and is able to effectively and efficiently spread the thermal energy of the solid state light source across the heat sink. A fan is arranged to direct air across heat dissipating ribs of each heat sink. Moreover, extruded aluminum heat sinks are relatively inexpensive, and expensive post-manufacture machining may be minimized because of the simplicity of joining the two pieces by drilling simple through-holes in each extruded heat sink to receive bolts, whereby two bolts join the two heat sinks together and to a housing, further reducing the manufacturing cost of the module.
Turning now to
First base 4 is disposed transverse to second base 24, such as being perpendicular, or substantially perpendicular, to second base 24. Thus first ribs 8 and second ribs 28 abut and collectively define continuous air flow paths that wrap around the rear faces (opposite first and second exposed surfaces 6, 26) of first and second heat sinks 2, 20.
The extruded first heat sink component 2 is formed from any suitable first material which includes any alloy thereof that can be extruded. The extruded second heat sink component 20 is formed from any suitable second material, including an alloy thereof, which can be extruded. Preferably first heat sink component 2 and first ribs 8 are formed from a first aluminum material which includes any aluminum alloy that can be extruded. Preferably second heat sink component 20 and second ribs 28 are formed from a second aluminum material which includes any aluminum alloy that can be extruded. The second aluminum material may be the same as or different than the first aluminum material, but is preferably the same aluminum material. Examples of the first and/or second aluminum materials may include, but are not limited to, AA 6061 (as designated by the Aluminum Association), AA 6063, or the like. Of course, these are just examples, and the present disclosure is not limited to any particular aluminum material unless specifically claimed as such. The use of aluminum materials for both the extruded first heat sink component 2 and the second heat sink component 20 allows the lamp module cooling system 10 of the present disclosure to be manufactured inexpensively compared to other heat sink designs while still allowing the heat sinks 2, 20 to dissipate enough heat for use in high-power solid state lighting applications with limited space and/or weight constraints. Having both first and second heat sinks 2, 20 formed of aluminum rather than one of aluminum and e.g. the other of a different material, e.g. copper, avoids adjacent materials having different electrode potentials, thus minimizing the likelihood of galvanic corrosion.
It could be considered ideal if it were possible to form the combined shape of first and second heat sinks 2, 20 as one integral piece, but the complex shape and, in preferred embodiments, near 90-degree angle from their mutually orthogonal arrangement likely prevents such a piece from being extruded integrally. Furthermore, if such an integral piece were molded, as noted above, existing cast aluminum or cast magnesium would have a significantly lower thermal conductivity than extruded aluminum, and even if that shape could be integrally molded, the thin fins on both surfaces could not wrap around so costly and extremely precise post-mold machining would be required.
The extruded heat sink components 2, 20 may have any profile which can be extruded. For example, first and second heat sinks 2, 20 may have the same cross-sectional profile along at least one dimension (e.g. the same cross-sectional profile along the length). For example, the first and second heat sinks 2, 20 include one or more ribs or fins 8, 28 extending outward to increase the surface area of the respective first and second heat sink 2, 20 to dissipate thermal energy. The heat-dissipating fins 8, 28 are co-extruded with respective bases 4, 24 of the first and second heat sink components 2, 20.
Fan 40 is in fluid communication with first heat sink 2 and second heat sink 20. Fan 40 has fan air inlet 44 and fan air outlet 42. Fan 40 is preferably an axial fan, though in other embodiments fan 40 could be configured as a radial fan. Fan 40 is preferably disposed with its air outlet 42 in confronting relation to second heat sink 20, in particular to heat dissipation second ribs 28 which form flow channels. In other embodiments, not shown, fan 40 could be disposed with air outlet 42 in confronting relation to first heat sink 2, such as in confronting relation to heat dissipation first ribs 8. In a preferred embodiment fan 40 is coupled to housing 30 in which it is securely held at a rearward cavity region 34 thereof, housing 30 being attached by bolts 18 to hold first and second heat sinks 2, 20. Fan 40 can provide sufficient airflow of about 9 cfm (cubic feet per minute) operating at full voltage (12V) and provides enough flow that the lamp module cooling system 10 still operates well at low voltage (9V) conditions. Fan 40 can be mounted to housing 30 with additional screws but in a preferred embodiment housing 30 has a receptacle or receiving cavity 34 at a rearward location that accommodates fan 40 with second heat sink 20, such as by shape or slight friction fit. Housing 30 is molded of suitable thermoplastic material such as polycarbonate or other high-temperature resistant plastic. Housing 30 has mounting regions to couple to vehicle headlamp frame 120.
As shown in
With components mounted in operational relationship shown in
As shown in
In operation, outlet flow 54 of warm air to lens cover 100 reduces relative humidity and allows condensation on front lens 100 to be absorbed by the air and transported to cooler section, thereby defogging lens cover 100.
In an embodiment in which first and second heat sinks 2, 20 are extruded from aluminum (such as aluminum of density 2.7 g/cm3), the ribs can be advantageously small, and matched to the footprint of axial fan 40 given the available vertical clearance behind bezel 110 in a top-mount system as depicted in
In appropriate situations, lamp module cooling system 10 can be used not only with a reflector optic 130 but also with a lens optics if the bezel is so constructed that air can go around the lens to be directed at lens cover 100.
While the principles of the present disclosure have been described herein, it is to be understood by those skilled in the art that this description is made by way of example and not as a limitation as to the scope of the embodiments. The features and aspects described with reference to particular embodiments disclosed herein are susceptible to combination and/or application with various other embodiments described herein. Such combinations and/or applications of such described features and aspects to such other embodiments are contemplated herein. Other embodiments are contemplated within the scope of the present invention in addition to the exemplary embodiments shown and described herein.
Modifications and substitutions by one of ordinary skill in the art are considered to be within the scope of the present invention, which is not to be limited except by the following claims.
The following is a list of reference numeral used in the specification:
