EP2275738B1 - Cooling element for a semiconductor light source of a motor vehicle lighting device - Google Patents

Description

The invention relates to a cooling element for a semiconductor light source of a lighting device of a motor vehicle according to the preamble of claim 1, as from the document DE 10 2007 024 962 A known.

Moreover, the invention relates to a method for producing such a cooling element according to the preamble of the independent method claim.

Such a cooling element has a cooling body arranged for the release of heat to the environment and a flange plate designed for thermal coupling of the semiconductor light source and for fastening the cooling element to the illumination device.

Semiconductor light sources are currently increasing used in lighting devices of motor vehicles. After the use was initially limited to signal lights such as brake and turn signals, it is currently being begun to use semiconductor light sources for headlight functions, so for lighting the vehicle environment. An example of this is an LED headlamp for the Audi R8 (LED = Light Emitting Diode) supplied by the Applicant.

Unlike halogen or gas discharge lamps, LEDs emit cold light. The radiation itself thus contains no heat radiation components which would be comparable to the corresponding proportions of a halogen lamp or gas discharge lamp. Nevertheless, even when operating LEDs, losses of about 80% occur. This means that 80% of the electrical energy used for operation is released as heat loss and the LED heat up. This is problematic because important properties of LEDs such as their luminous flux, color, forward voltage and lifetime are highly temperature dependent. The temperature of the semiconductor light sources must therefore be within narrow, fixed limits by a predetermined thermal operating point. In particular, the LEDs must be protected against overheating.

Depending on the manufacturer, the maximum permissible chip temperature is between 125 ° C and 185 ° C. Exceeding the respective maximum temperature results in destruction of the LED. Since only about 20% of the electrical energy used is converted into light, headlamp heat losses occur, which can reach values between 20 watts and 40 watts.

To reliably dissipate these occurring in the LED chip loss heat outputs without impermissibly high LED temperatures To be able to use cooling concepts are applied, which provide in particular large-scale aluminum or copper cooling elements of the type mentioned above to absorb the heat loss through the flange plate and deliver to the environment via serving as heat sink ribs and other surface-enlarging structures.

Often, the cooling requirements are so high that normal convective cooling is no longer sufficient and a constant cooling air flow must be forced with a fan.

As a heat sink mainly aluminum heat sinks are used, which are manufactured either by the die casting, continuous casting or extrusion process.

Continuous casting and extruded heat sinks are used on the one hand because of the better thermal properties of the aluminum alloys available for these processes. On the other hand, these methods allow significantly finer structures, i. There are particularly high and thin cooling fins or cooling pins produced with which, because of their large surface, particularly effective heat sink with low thermal resistance can be represented at the same time compact design.

The disadvantage is that these methods are poorly suited to mold the usually required centering and fasteners with. In addition, these heatsinks often require a costly machining post-processing of individual functional surfaces, such as the connection surface for the LED.

On the other hand, heat sinks produced using the die-casting process enable particularly complex shapes. Thereby Functional elements and functional surfaces can be easily integrated, as fastening and centering elements can be easily molded.

In contrast, only relatively short and thick cooling fins can be produced in the die casting process, which suffers from the efficiency of the heat sinks. Furthermore, die-cast alloys have inferior thermal conductivity compared to continuous casting or extrusion alloys. Mostly, these heatsinks require much larger volumes compared to continuous casting or extrusion heatsinks.

Various attempts have been made to combine the advantages of die-cast and extruded parts or die-cast and continuous cast parts. Here, continuous casting or extruded heat sinks were mounted on die-cast holding elements. In such mounting solutions, however, it is difficult to ensure a good thermal connection between the components to be joined: Even if the connecting surfaces are machined consuming on flatness in the range of 0.01 mm, the remaining air gaps and the associated thermal resistances are not large tolerable fluctuations.

Against this background, the object of the invention is to specify a cooling element of the type mentioned above, which combines the advantages of the die casting process - great freedom in shaping - with the advantages of extruded or continuously cast heat sinks - namely, low thermal resistances. With regard to the method aspects, the object of the invention is to specify a method for producing such a cooling element.

This object is achieved in each case with the features of the independent claims.

The invention is characterized in particular by the fact that the cooling element is a composite part of a casting and an inserted during casting of the casting in the mold insert, wherein the flange plate is the casting and the heat sink is the insert.

By inserted during casting of the casting in the mold insert of the inserted as an insert heat sink is encircled by the melt to be poured as a casting flange plate so that the casting shrinks on cooling on the insert and the insert thus encloses form-fitting. As a result, in particular a very good thermal connection between the two parts is ensured without disturbing air gaps which disadvantageously increase the thermal resistance.

The casting of the flange plate achieves the important advantages of the great freedom of design in the case of the flange plate. The use of the heat sink as an insert allows in particular the use of extruded or continuously cast heat sink. As a result, the invention combines the advantages of lower thermal resistances of a heat sink with the advantages of a large freedom of form in the flange without having to accept disadvantageously large thermal contact resistance between flange plate and heat sink in purchasing.

The advantage of low thermal resistances is achieved, in particular, with an embodiment which extends through at least one by a continuous casting or Extruded molding produced heat sink made of an aluminum, copper or magnesium alloy.

Alternative embodiments of the cooling element with at least one magnesium die-cast heat sink have the advantage that lower wall thicknesses and thus more filigree cooling fins can be realized than in Al diecasting. In addition, the low density allows significant weight savings.

Heat sinks designed with stamping and bending technology have cost advantages, especially with large quantities. In addition, cooling elements with particularly small wall thicknesses (and weight) can be represented.

Since the complexity of the parts is significantly limited by the manufacturing process, it is particularly possible here to connect several heat sink elements by casting with the material of the flange plate to form a complex composite heat sink. A further preferred embodiment therefore provides a plurality of separate heat sinks, which are connected by the casting to a composite heat sink.

It is also preferred that the casting has molded functional surfaces during casting. This reduces the manufacturing effort and at the same time improves the heat transfer through the flange plate, since thermal contact resistance, which could occur through air gaps, can be avoided.

For a good heat dissipation from the power dissipation producing LED, it is particularly advantageous that the casting has a set up for thermal coupling of the semiconductor light source bearing surface as a molded functional surface.

It is also preferred that the composite part has during encapsulation of the insert with embedded metallic functional parts. By embedding these functional parts in particular a dimensionally accurate and firm mechanical connection of these parts is achieved with the flange plate. This applies in particular to centering elements and / or fastening elements for the semiconductor light source and / or for an optical element and / or for the attachment of the cooling element in the illumination device. Examples of such elements are screw and / or bearing bushes and / or at least centering pins and / or threaded studs and / or bearing pins as centering and / or as fasteners.

A particularly preferred refinement is characterized in that the heat sink has a heat sink carrier plate and a heat release side adapted to emit heat to the environment, with a surface which is enlarged by first structures (eg, by pins and / or ribs) and one for insertion in a mold of the casting arranged heat receiving side, wherein the heat receiving side of the heat sink has second surface-enlarging structures that are embedded in the casting.

As second surface-enlarging structures ribs, in particular dovetail-shaped profiled ribs, and / or pins and / or openings and / or outbreaks in the heat sink carrier plate are preferred, wherein the heat sink carrier plate on the set up for insertion into the mold of the casting Heat absorption side is arranged.

With regard to the method aspects of the invention, there is an advantage in that the production cost is lower than that for those on a continuous casting or extrusion press heatsink required effort for the machining of functional surfaces.

Further advantages will be apparent from the dependent claims, the description and the attached figures.

It is understood that the features mentioned above and those yet to be explained below can be used not only in the particular combination indicated, but also in other combinations or alone, without the scope of the present invention being defined by the appended claims leave.

drawings

Figur 1

ein bekanntes Druckguss-Kühlelement;

Figur 2

eine Draufsicht auf eine Funktionsfläche eines Ausführungsbeispiels der Erfindung;

Figur 3

ein Querschnitt durch den Gegenstand der Figur 2;

Figur 4

eine Ausgestaltung eines Kühlkörper-Einlegeteils; und

Figur 5

eine weitere Ausgestaltung eines Kühlkörper-Einlegeteils.

Embodiments of the invention are illustrated in the drawings and are explained in more detail in the following description. In each case, in schematic form:

FIG. 1

a known die-cast cooling element;

FIG. 2

a plan view of a functional surface of an embodiment of the invention;

FIG. 3

a cross section through the subject of FIG. 2 ;

FIG. 4

an embodiment of a heat sink insert part; and

FIG. 5

a further embodiment of a heat sink insert.

In detail, the shows Fig. 1 a perspective view of a conventional die-cast cooling element 10 with cooling fins 12 and a flange plate 14. The flange plate 14 has molded fasteners such Screw-on eyes 16 and screw domes 18 and centering elements such as centering pins 20, 22 and a mounted semiconductor light source 24. The elements 16, 18, 20, 22, 24 are arranged on a functional surface 26. The semiconductor light source is an arrangement 28 of an LED or a plurality of LEDs, which is mounted on a base element 30 and is mechanically and thermally connected to the flange plate 14 of the cooling element 10 via the base element 30.

Due to its production as a one-piece produced in a single casting process die-cast cooling element 10, the molded-on cooling fins 12, which represent the heat sink of the known cooling element 10, inevitably made relatively coarse. In the presentation of the FIG. 1 this is expressed by the comparatively rough design of each individual cooling rib 12 and the comparatively small number of eight cooling ribs 12 given given dimensions of the cooling element 10.

FIG. 2 shows an embodiment of a cooling element 32 according to the invention in a plan view of a functional surface 26. In the plan view, the cooling element 32, not different from the known cooling element 10 and therefore has in particular those already in connection with the FIG. 1 explained functional surface 26 with molded fasteners in the form of screw-on eyes 16 and screw domes 18 and centering in the form of centering pins 20, 22 and a mounted with a base member 30 to the functional surface 26 semiconductor light source 24 with an LED array 28. The base element 30 is centered by the centering pins 22 in a predetermined position on the functional surface 26 and by fasteners 34, for example by screws or through to the functional surface 26th molded rivet pins, fixed to the flange plate 14.

The centering pins 20 and the fastening elements 16, 18 serve for centering and mounting the cooling element 32 in a lighting device (not shown) for a motor vehicle and / or for mounting an optical element (not shown) and / or a shutter arrangement. In one embodiment, the illumination device is a headlight or a light module of a headlight. The optical element is a reflector arranged for focusing the light of the LED array 28 or a lens arranged for this purpose.

FIG. 3 shows a section along line III, III cut through the cooling element 32 of the FIG. 2 , In contrast to the conventional one-piece die-cast cooling element 10 of FIG. 1 is the cooling element 32 as an exemplary embodiment of a cooling element according to the invention a composite part of a casting 36 and an inserted during casting of the casting 36 in the mold insert 38. Here, the flange plate, the casting 36 and the heat sink, the insert 38. In the following, therefore, both the flange as well as the casting of a cooling element 32 according to the invention designated by the reference numeral 36. Analogously, both the insert part and the heat sink identical to the insert part are designated by the reference numeral 38 below. The insert is an extrusion or continuous casting heat sink, a magnesium die-cast heat sink, a heat sink designed as a punched-bent part or an arrangement of a plurality of such heat sink.

As already mentioned, continuous casting and extrusion processes allow the use of alloys better thermal properties than alloys suitable for die casting. In addition, continuous casting and extrusion processes enable the production of significantly finer structures. That is, these methods allow production of heat sinks 38 with, for example, particularly high and / or thin cooling fins or cooling pins. Due to the resulting large surface can be particularly effective heat sink 38 with low thermal resistance, ie produce high thermal conductivity, at the same time compact dimensions. This will be the subject of FIG. 3 by the number of cooling structures 46, which is higher by a factor of about 1.5 than the number eight of the cooling fins 12 of the conventional die-cast cooling element 10 of the FIG. 1 ,

In magnesium diecasting, smaller wall thicknesses and thus more filigree cooling fins can be realized than in die-cast aluminum. In addition, the low density of magnesium die-casting allows significant weight savings. It is disadvantageous that no rivet pegs can be molded onto magnesium die-cast parts, since magnesium die-casting can not be deformed sufficiently plastically. Even screw connections can not be realized without further ado because of the high reduction potential of magnesium (electrochemical voltage series: -2.38 volts, for comparison: aluminum: -1.66 volts). Special aluminum screws or screws with special coatings may be required.

Heat sinks designed with stamping and bending technology have cost advantages, especially with large quantities. In addition, cooling elements with particularly low wall thicknesses and thus particularly low weight can be represented. Because the complexity of running in stamping and bending technology Heatshrills is significantly limited by the manufacturing process, it is particularly possible here to connect several heat sink sub-elements by casting with the material of the casting to form a complex composite heat sink.

In the production of the cooling element 32, a part of the heat sink 38 is placed in a mold or die-casting tool and encapsulated with the material of the flange plate 36. The material is preferably aluminum, an aluminum alloy, a magnesium alloy, a copper alloy or an alloy having a plurality of these materials.

When encapsulating some or all required functional surfaces are molded with the same and some or all metallic functional parts such as centering and mounting elements for the LED array 28 and / or the base element and / or the optics and / or the diaphragm arrangement and in a preferred embodiment / or the attachment in the lighting device with the liquid flange material encapsulated and embedded in the flange plate. The functional surface provided for the thermal coupling of the LED arrangement 28 is in the process cast as flat as possible and only a surface roughness having the lowest possible surface roughness.

The einzugießende heat sink 38 has in the embodiment that in the FIG. 3 a heat sink support plate 40 and a heat dissipating side 42 provided for discharging heat to the environment, and a heat receiving side 44 adapted for insertion into a mold of the casting.

The heat sink carrier plate 40 is preferably wholly or partly cast in the casting 36. The heat release side 42 has an increased surface area by first structures 46 such as pins and / or ribs to improve the heat dissipation to the environment. The heat receiving side 44 of the heat sink 38 has second surface enlarging structures 48 embedded in the casting 36. As second surface-enlarging structures are preferably ribs, in particular dovetail-shaped profiled ribs and / or pins and / or openings (the material penetrating recesses) and / or outbreaks (reaching into the material, but not completely penetrating the material recesses) is used.

The second surface-enlarging structures 48 enlarge the form-fitting surface between the insert 36 and the casting 38. As a result, a firm connection without air gaps between the two components 36, 38 is achieved. The resulting composite part offers great design freedom thanks to the casting process. The casting process offers the possibility of embedding further metallic functional parts, for example screw and bearing bushings, centering pins and bearing bolts.

At the same time, the good thermal properties correspond to those of the extruded or continuous casting heat sink. In contrast to screwed, riveted or glued heat sink assemblies, insulating air layers between the parts can be reliably excluded. The production cost is lower when casting, especially for larger quantities, as would be required for the subsequent machining of the functional surfaces on the extrusion or continuous casting heat sink. The cooling element 32 with the features of the invention enables the saving of additional holding and Fasteners.

The FIGS. 4 and 5 show embodiments of heat sinks with carrier plates in each case in perspective view. It shows FIG. 4 an embodiment in which both the first surface-enlarging structures 46 on the heat-emitting side 42 and the second surface-enlarging structures 48 on the heat receiving side 44 are pins. FIG. 5 shows an embodiment in which both surface-enlarging structures 46/48 are formed as ribs. It is understood, however, that differently shaped structures can also be used on both sides of the carrier plate 40.

Claims (13)

1. A cooling element (32) for a semiconductor light source (24) of a motor vehicle, having a cooling body (38) arranged for emitting heat to the surroundings and having a flange plate (36) arranged for thermally coupling the semiconductor light source (24) and for securing the cooling element (32) to the lighting device, characterized in that the cooling element is a composite part comprising one cast part and one insert part (38) that is inserted into the casting mold when the cast part is being cast, the flange plate (36) being the cast part and the cooling body (38) being the insert part.
2. The cooling element (32) of claim 1, characterized by at least one cooling body (38) of an aluminum, copper or magnesium alloy, produced by a continuous casting or extrusion process.
3. The cooling element (32) of claim 1, characterized by at least one cooling body (38) embodied as a diecast magnesium cooling body (38) or as a stamped and bent part.
4. The cooling element (32) of one of the foregoing claims, characterized by a plurality of separate cooling bodies, which are joined together as one composite cooling body by means of the cast part (36).
5. The cooling element (32) of claim 1 or 2, characterized in that the cast part (36) has function faces (26) that are integrally formed on in the casting operation.
6. The cooling element (32) of claim 3, characterized in that the cast part (36) has, as the integrally formed-on function face (26), a support face arranged for thermally coupling the semiconductor light source (24).
7. The cooling element (32) of one of the foregoing claims, characterized in that in the casting of the insert part (38) integrally with the material comprising the cast part (36), it has metal function parts that are embedded jointly with it.
8. The cooling element (32) of claim 5, characterized by at least one centering element and/or at least one securing element for the semiconductor light source (24) and/or for at least one optical element and/or for securing the cooling element (32) in the lighting device.
9. The cooling element (32) of claim 6, characterized by at least one screw-in bush and/or and least one bearing bush and/or at least one centering pin (20, 22) and/or at least one threaded stay bolt and/or at least one bearing bolt as the centering element and/or as the securing element.
10. The cooling element (32) of one of the foregoing claims, characterized in that the cooling body (38) has a cooling body carrier plate (40) and a heat emission side (42) for emitting heat to the surroundings, this side having a surface area that is increased by means of first structures (46), and a heat absorption side (44) arranged for insertion into a casting mold of the cast part (36), the heat absorption side (44) of the cooling body (38) having second surface-area-increasing structures (48), which are embedded in the cast part (36).
11. The cooling element (32) of claim 8, characterized in that the second surface-area-increasing structures (48) are ribs, in particular ribs of swallowtail-like profile, and/or pins and/or through openings and/or blind openings in the cooling body carrier plate (40), and the cooling body carrier plate (40) is located on the heat absorption side (44) that is arranged for insertion into the casting mold of the cast part (36).
12. A method for producing a cooling element (32) for a semiconductor light source (24) of a motor vehicle, having a cooling body (38) arranged for emitting heat to the surroundings and having a flange plate (36) arranged for thermally coupling the semiconductor light source (24) and for securing the cooling element (32) to the lighting device, characterized in that one part of the cooling body (38) is inserted into a casting mold arranged for casting the flange plate (36) and is cast integrally with the material of the flange plate (36).
13. The method of claim 12, characterized by an aluminum, magnesium or copper alloy as the material comprising the flange plate (36).

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