Abstract:
The device for generating a cooling air flow in a preferential flow direction for cooling electrical components, particularly LEDs, comprises a first and a second channel wall ( 34,36 ) having mutually confronting inner sides, and an oscillation drive means ( 42 ) for generating an oscillating movement of at least a partial region ( 38 ) of at least one of said channel walls ( 34,36 ) in the direction toward the other channel wall and away therefrom. The inner side of at least one of said two channel walls ( 34,36 ) has a surface structure ( 30 ) designed for anisotropic flow, which has a smaller flow resistance coefficient in the preferential flow direction ( 28 ) than in a direction extending at an angle to the preferential flow direction ( 28 ) and particularly in a direction extending opposite to the preferential flow direction ( 28 ).

Description:
RELATED CROSS-REFERENCING 
       [0001]    The present invention claims the priority of European Patent Application No. 10 174 853.1 filed on Sep. 1, 2010, the disclosure of which is incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a device for generating a cooling air flow in a preferential flow direction for cooling electrical components, particularly electro-optical components such as e.g. LEDs. The present invention particularly relates to the integration of a device of the above type into a cooling body for cooling electrical components, particularly electro-optical components such as e.g. LEDs. 
         [0004]    2. Description of the Prior Art 
         [0005]    On the sector of land and air vehicles, efforts have been under way for many years to install LEDs as a replacement of conventional illuminants of the type with filaments or of the gas discharge type. This trend is favored by the recent introduction of high-performance LEDs on the market, which due to their relatively high light intensity can also be used e.g. for headlights of automobiles and in aircraft. Further, there exist illumination applications wherein the light is switched on only for a short time, while, however, due to the power density and the available (cooling) surface, there is a risk of inadmissible overheating of the illuminant or lamp in the course of the typical operating period. This is the case e.g. in runway, turn-off, taxi, landing and take-off lights of aircraft equipped with LED illuminants. 
         [0006]    Presently, for cooling LED illuminants, use is made inter alia of passive systems, i.e. cooling bodies, by which the LEDS or the component parts heated by LED illuminants are exposed to the ambience via an enlarged surface. Also such cooling bodies, however, cannot prevent the risk of overheating of the LED illuminants. For this reason, in situations where a predetermined temperature limit has been reached, the LED illuminants will be dimmed so that the power input will be reduced, thus taking into consideration the fact that the current-carrying capacity of LEDs tends to decrease with increasing temperature. 
         [0007]    An apparatus for cooling an electronic device is described in EP-A-1 020 9121 A2 and includes a casing formed with a plurality of air intake/exhaust holes through which air will pass. A plate-type mobile member is installed to vibrate in said casing and divides an inner space of the case into an upper space and a lower space. An elastic support film is fixed in the casing to support the mobile member and has a bulged portion capable of being elastically deformed. A driving device is provided for vibrating the mobile member. By the vibration of the mobile member, air in the upper and lower spaces of the casing is exchanged with outside air through the air intake/exhaust holes which are each provided with valves. 
         [0008]    A valveless micropump is known from DE 42 23 019 C1. Further cooling devices for cooling e.g. electronic components are disclosed in each of WO-A-2010/044047, US-A-2007/0272392 and US-A-2006/0048918. 
         [0009]    It is an object of the invention to improve the cooling of electrical components, particularly electro-optical components such as e.g. LEDs, notably by providing a reliably operating device for generating a cooling air flow in a preferential flow direction for cooling the electrical components. 
       SUMMARY OF THE INVENTION 
       [0010]    According to the invention, the above object is achieved by a device for generating a cooling air flow in a preferential flow direction for cooling electrical components, particularly LEDs, wherein said device comprises
       a first and a second channel wall having mutually confronting inner sides, and   an oscillation drive means for generating an oscillating movement of at least a partial region of at least one of said channel walls in the direction toward the other channel wall and away therefrom,   the inner side of at least one of said two channel walls having a surface structure designed for anisotropic flow, said surface structure having a smaller flow resistance coefficient in the preferential flow direction than in a direction extending at an angle to the preferential flow direction and particularly in a direction extending opposite to the preferential flow direction.       
 
         [0014]    In accordance with the invention, an air flow is generated between two channel walls, notably in a preferential flow direction. In the context of the invention, the term “channel wall” is to understood as denoting a wall delimiting an air volume or, more generally, a fluid volume. The two channel walls provided according to the invention need not be connected to each other, so that the region between the channel walls can be open toward the ambience via at least one edge of each channel wall. Preferably, the two channel walls provided according to the invention are the parallel cooling plate elements of a cooling body. 
         [0015]    According to the invention, it is provided that at least one of the two channel walls or an additional element between the two channel walls can at least in partial regions thereof be subjected to an oscillating movement. For this purpose, the device of the invention comprises an oscillation drive unit. Said partial region of at least one of the two channel walls (or of an element arranged between them) which can be subjected to an oscillating motion, will now oscillate in a direction extending orthogonally to the extension of the channel wall. Starting from a specific time and point along the air flow, the air will be urged away in all directions in a uniform manner, namely when impinging onto that channel wall in whose direction the oscillating partial region is presently moving. The inner side of at least one of the two channel walls (or the outer side of the element arranged between the channel walls) is provided with an anisotropic surface structure. Under the aspect of flow technology, this surface structure has an anisotropic effect on an air flow sweeping along the surface structure. This means that the surface structure has a lower flow resistance in the preferential flow direction than in a direction extending at an angle to the preferential flow direction and in a direction opposite to the preferential flow direction. Thus, by the effect of the integrated anisotropic surface structure, there is generated an anisotropic air drag coefficient or air-flow drag coefficient which will hinder the “air-wave” to propagate at a uniform speed and will guide the air into the preferential flow direction. Generated in this manner is a net volume and mass flow which preferably, in relation to the orientation of the device in the mounted state, will be guided upward, i.e. in the direction of the air flow generated by the natural convection. 
         [0016]    By the oscillation movement, there is first generated an air movement between the channel walls. In the region opposite the oscillating partial region, this air movement will be deflected, namely generally to all sides. By the effect of the anisotropic surface structure, the thus deflected air flow will now be largely deflected into the preferential flow direction, or, expressed in a different manner, the air will flow primarily in the preferential flow direction. On the whole, a net air flow is generated in the preferential flow direction. 
         [0017]    Thus, according to the arrangement proposed by the invention, the air movement oscillating orthogonally to the extension of the channel walls is deflected into an air movement between the two channel walls, said air movement between the two channel walls streaming at different rates in the most different directions parallel to the channel walls and between the latter while, however, due to the anisotropic surface structure, a net or preferential flow direction is obtained. When applying this concept to the cooling plate elements of a cooling body, the device according to the invention can enhance the natural convection in that the cooling plate elements are vertically oriented and the anisotropic surface structure is oriented in such a manner that the preferential flow direction is pointing upward. 
         [0018]    An essential advantage of the device of the invention resides in its reliable cooling effect, while the need for moving component parts, such as e.g. inlet and/or outlet valves operating in opposite senses to each other, is obviated (except for said oscillating partial region of at least one of the channel walls and respectively of an element arranged therebetween). Particularly, no active cooling devices such as e.g. ventilators are required. In aircraft industry, such active cooling measures are presently not admissible because it is feared that the cooling would be considerably impaired in case of a fallout of the active cooling devices such as e.g. ventilators and the like. Apart from the above advantage, the device of the invention and the cooling method of the invention will guarantee their functionality even under extreme ambient conditions. The influence of such ambient conditions or extreme external influences is to be expected on the landing gear of aircraft where the device would be exposed to aggressive media, dirt, flying stones or gravel, icing and vibration. A further advantage of the device of the invention is to be seen in that no complex electronic control process is required and that the oscillation drive unit can be fed directly by the vehicle or aircraft power supply system at different frequencies. The cooling concept provided by the invention is inexpensive and is easily put into practice under the constructional aspect while working with utmost reliability. 
         [0019]    At lower temperatures, the stiffness of the channel wall(s) will increase in those regions where said oscillating partial regions are located. Thereby, the effectiveness of the air movement is reduced, which, however, is not critical because lower temperatures will also require less cooling performance. At higher temperatures, by contrast, the flexibility of the oscillating partial regions of the channel wall(s) will increase, namely exactly when a maximum cooling performance is required. 
         [0020]    A further advantage of the device of the invention is to be seen in that the anisotropic surface structure results in an enlargement of the surface area of the channel wall(s). This is advantageous particularly if the anisotropic surface structure is provided on an element of the cooling body which is dissipating heat to the ambience. 
         [0021]    Apart from the above effects, a further considerable cooling effect is obtained by the feature that, by the (rectangular) deflection of the air flow in the area of the oscillating partial region of at least one of the channel walls and respectively of the element optionally arranged therebetween, the “aerodynamic boundary layer” on the channel wall and respectively on the oscillating partial region is substantially thinner. Herein, an “aerodynamic boundary layer” is to be understood as a nearly immobile air layer arranged directly on the surface of the channel wall and respectively the partial region. Since the movement of air in this region is normally very slight, there is thus only a limited heat exchange between the respective component part and the ambience. Thus, by reduction of the thickness of this effective boundary layer, the heat exchange is improved. By “breaking up” this boundary layer, as achieved by the functionality of the inventive device, the air flowing through the channels can become considerably warmer and thus can dissipate considerably more energy than would be the case in a purely “parallel” flow through the channels. 
         [0022]    According to an advantageous embodiment of the invention, it is provided that the anisotropic surface structure comprises a plurality of projections extending from the channel wall, each of said projections having a front side facing in a direction opposite to the preferential flow direction and a rear side facing in the preferential flow direction, and that the geometry of said front side of a protrusion is adapted to generate of a higher flow resistance coefficient than the geometry of said rear side of the protrusion. 
         [0023]    A possible embodiment of said anisotropic surface structure is to be seen in that said front sides of the protrusions are formed by front flanks and the rear sides of the protrusions are formed by rear flanks, and that said rear flanks are steeper than said front flanks. This is realized e.g. in that the protrusions extend substantially transversely to the preferential flow direction and form a sawtooth profile. 
         [0024]    As an alternative to the above serially arranged “ramps” extending transversely to the preferential flow direction and in combination forming a sawtooth profile, the anisotropic surface structure can also be realized by triangular or part-cylindrical protrusions. In case of triangular protrusions, these are arranged on the surface with their bases facing in a direction opposite to the preferential flow direction. In case of protrusions having a round or cylindrical circumferential surface in a partial region of their circumference while otherwise being flattened, these protrusions are to be arranged with their flattened portions facing in the preferential flow direction. As to the geometric configuration of the protrusions, it generally applies that, for fluid flowing over the surface structure, they offer a smaller flow resistance in the preferential flow direction than in a direction opposite to the preferential flow direction or, in broader terms, in a direction extending at an angle to the preferential flow direction. 
         [0025]    Until now, the invention has been described for the case that at least one of the two channel walls is provided with an oscillating partial region. Suitably, both channel walls comprise oscillating partial regions, while these oscillating partial regions are movable for oscillation in opposite senses. 
         [0026]    For the invention, it basically plays no role where exactly said anisotropic surface structure is arranged between the channel walls. Suitably, however, the channel wall which is movable in an oscillating manner should be provided with the anisotropic surface structure on its inner side. 
         [0027]    A further advantageous embodiment of the invention is characterized by a third channel wall having an inner side facing toward the two other channel walls, the second channel wall being arranged between the first and the third channel wall and having two (inner) sides opposite to the third and respectively the first channel wall, said two sides being provided with an anisotropic surface structure, with either (i) the second channel wall or (ii) the first and third channel wall or (iii) all three channel walls being movable in an oscillating manner. 
         [0028]    As an alternative, a further advantageous embodiment of the invention can be characterized by a third channel wall having an (inner) side facing toward the two other channel walls, the second channel wall being arranged between the first and the third channel wall and having two inner sides opposite to the third and respectively the first channel wall, said two inner sides being provided with an anisotropic surface structure, the inner faces of the first and the third channel wall being provided with a respective anisotropic surface structure, with either (i) the second channel wall or (ii) the first and third channel wall or (iii) all three channel walls being movable in an oscillating manner. 
         [0029]    In these two alternative embodiments of the invention, it can be additionally provided that the preferential flow directions in the two intermediate spaces between the second channel wall and the first and respectively the third channel wall are identical or opposite to each other. 
         [0030]    The oscillatable partial region of a channel wall and respectively of another element arranged between two channel walls is suitably formed as an elastic membrane operatively connected to the oscillation drive unit. The operative connection between the oscillation drive unit and the membrane can be provided, apart from the option of using a mechanical connection, particularly as a magnetic coupling wherein, in the latter case, the oscillation drive unit will generate a magnetic field and said membrane comprises a magnetic material which will be exposed to said magnetic field, wherein said membrane is movable in an oscillating manner as a result of magnetic and eddy-current effects. 
         [0031]    The oscillatable channel wall comprises on at least one of its sides, particularly externally of the membrane, said anisotropic surface structure. 
         [0032]    As already mentioned above, the device of the invention can be suitably integrated into the cooling plate elements of a cooling body. Thus, in this case, the two channel walls are formed by two adjacent cooling plate elements of the cooling body. If the device of the invention comprises three channel walls as provided according to one of its preferred embodiments, these channel walls are formed by three adjacent cooling plate elements. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0033]    A full and enabling disclosure of the present invention, including the best mode thereof, enabling one of ordinary skill in the art to carry out the invention, is set forth in greater detail in the following description, including reference to the accompanying drawing in which 
           [0034]      FIG. 1  is a lateral view of an LED light for an aircraft, 
           [0035]      FIG. 2  is a rear view of the LED light with a cooling body arranged thereon, 
           [0036]      FIG. 3  is a front perspective view of the light, 
           [0037]      FIG. 4  is a horizontal sectional view taken along the plane IV in  FIGS. 2 and 3 , 
           [0038]      FIGS. 5 and 6  illustrate the generation of the air flow in the preferential flow direction between respectively two cooling plate elements of the cooling body, these Figures showing the cooling body in sectional view taken at the level of line V in  FIG. 1 , 
           [0039]      FIG. 7  is a sectional view taken along line VII-VII in  FIG. 1 , i.e. a plan view onto the anisotropic surface structure with sawtooth profile according to the views in  FIGS. 2 ,  5  and  6 , 
           [0040]      FIG. 8  is a plan view of the anisotropic surface structure according to a an alternative embodiment, and 
           [0041]      FIG. 9  is a plan view of the anisotropic surface structure according to a further alternative embodiment. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0042]    In  FIGS. 1 to 3 , an LED aircraft light  10  is shown in lateral, rear and perspective view. Said aircraft light  10  comprises a housing  12  provided with a receiving chamber  14 . In said receiving chamber  14 , a plurality of LEDs  16  are arranged whose light will be fed into (TIR) light conductors  18  which in turn will radiate this light to the outside via a lighting plate or a transparent cover  20 . It should be noted that the use of TIR is not absolutely necessary for the invention. Within the framework of the invention, also other LED illuminants with or without light-conducting optical elements can be used. 
         [0043]    In the present embodiment, said LEDs  16  are high-performance LEDs and are held on a common support plate  22 . Said support plate  22  is in thermally conductive contact with a cooling body  24  which can form said housing  12 —or a part thereof—of aircraft light  10  and which comprises individual cooling plate elements  26 . Said cooling body  24  is provided with a device for generating, between said cooling plate elements  26 , air flows in a preferential flow direction  28  (see the flow arrows in  FIGS. 2 ,  3 ,  5 ,  6  and  7 ). 
         [0044]    For this purpose, two of said cooling plate elements  26  are on both of their sides provided with anisotropic surface structures  30 . These two cooling plate elements  26  are hereunder referred to by the term “channel wall”  32 , the two adjacent cooling plate elements  26  being referred to as the first and second channel walls  34 , 36 . Said channel wall  32  is then the third channel wall. In addition to the anisotropic surface structures  30 , the third channel walls  32  comprise partial regions  38 , arranged to be moved in an oscillating manner, in the form of membranes  40  which can be brought into oscillating movements with the aid of an oscillation drive means  42 . Said oscillation drive means  42  are electro-magnetic coils  43  provided to generate alternating magnetic fields to which said membranes  40  are exposed. Due to magnetism and eddy-current effects, the membranes  40  will be caused to oscillate transversely to the extension of the channel walls  32 , 34 , 36 . For this purpose, the membranes  40  are provided with magnetically sensitive materials. 
         [0045]    With reference to  FIGS. 5 and 6 , the functionality of said device for generating air flows between the channel walls  32 , 34 , 36  will be described hereunder. The coil  43  will be driven by an electronics unit  44 , and the magnetic field of coil  43  will have an alternately attractive and repulsive effect on membrane  40 .  FIG. 5  shows the situation where the membrane is attracted. In this situation, the air volume at  46  will be moved in the direction toward channel wall  36  where the air will be deflected in all directions. Since channel wall  32  comprises, on its side facing toward channel wall  36 , the anisotropic surface structure  30 , the major part of the deflected air flow will be conveyed in the direction of arrows  48 , 50 , i.e. in the preferential flow direction  28 . The anisotropic surface structure  30  comprises a plurality of protrusions  52  which in the present embodiment are respectively wedge-shaped and which together form a sawtooth profile. Each protrusion comprises a flat flank  54  and a steep flank  56 . With respect to the preferential flow direction  28 , said flat flank  54  is arranged upstream of said steep flank  56 . When viewed in the preferential flow direction  28 , protrusions  52  are positioned both upstream and downstream of the membrane, the latter being arranged substantially centrally on channel wall  32 . Thus, under the aspect of flow technology, the protrusions  52  arranged upstream of membrane  40  will have a different effect on the air flow from that of the protrusions  52  arranged downstream of membrane  40 . The protrusions  52  arranged upstream of membrane  40  will offer a higher flow resistance to the air flow deflected on channel walls  36  than the protrusions  52  arranged down-stream of membrane  40 . Thus, in other words, the major portion of the air flow deflected on channel wall  36  due to the deflective capacity of membrane  40  will flow in the preferential flow direction  28 ; only a small portion (see arrows  58 ) will flow e.g. oppositely to the preferential flow direction. 
         [0046]    On that side of membrane  40  which in the situation according to  FIG. 5  is facing away from oscillation drive unit  42 , an underpressure will be generated, thus now causing air to flow from all sides along channel wall  34  toward the center of the wall. These individual air flows in turn will be exposed to the anisotropic surface structure  30  of channel wall  32  which will have the same effect as described above. The major portion of the inflowing air will flow in the direction of arrow  60 , i.e. in the preferential flow direction  28  while e.g. only a smaller portion (see arrow  62 ) will flow oppositely to the preferential flow direction  28 . 
         [0047]      FIG. 6  shows the situation in which the membrane  40  is repelled by the oscillation drive unit  42 . With reference to the arrows  48 ,  50  and  58 , it can be seen also here that the major portion of the air will flow in the preferential flow direction  28 . A corresponding situation will occur on the other side of membrane  40 , which side is facing toward the oscillation drive unit  42 . 
         [0048]    In the light  10  according to this embodiment, the above described mechanism has a dual effect, as evident e.g. from  FIG. 2 . This because the cooling body  24  is provided with two cooling plate elements  26  and respectively channel walls  32  which comprise anisotropic surface structures  30 . 
         [0049]      FIG. 7  is a plan view of the anisotropic surface structure  30 . 
         [0050]    Illustrated in  FIGS. 8 and 9  are two alternative embodiments of anisotropic surface structures  30 ′, 32 ″. As far as the other components of the lighting device which are shown in  FIGS. 8 and 9  are identical with the components of the lighting device according to  FIGS. 1 to 7 , they are marked by the same reference numerals in  FIGS. 8 and 9  as in  FIGS. 1 to 7 . 
         [0051]    In  FIG. 8 , the anisotropic surface structure  30 ′ comprises individual projections  52 ′ which in plan view have the shapes of partial circles. Said projections  52 ′ comprise flattened sides  56 ′ oriented toward the preferential flow direction  28 , and convexly curved sides  54 ′ oriented in a direction opposite to the preferential flow direction  28 . Also by this arrangement and orientation of the projections  52 ′, there is formed a surface structure  30 ′ which, for air flowing along the surface, offers a smaller flow resistance in the preferential flow direction  28  than in a direction opposite to the preferential flow direction  28 . 
         [0052]    In  FIG. 9 , the projections  52 ″ of the anisotropic surface structure  30 ″, when seen in plan view, have a triangular shape wherein the bases  56 ″ are oriented toward the preferential flow direction  28  while the tips  54 ″ are oriented in a direction opposite to the preferential flow direction  28 . Again, there is formed a surface structure  30 ″ having an anisotropic effect under the aspect of flow technology, which, for air flowing along the surface, offers a smaller flow resistance in the preferential flow direction  28  than in a direction opposite to the preferential flow direction  28 . 
         [0053]    In the lighting device  10  according to the above described embodiments, the mechanism for generating air flows between the cooling plate elements of the cooling body in the preferential flow direction, can be provided as just a single unit or as a plural number of units and/or be used e.g. in combination with other cooling mechanisms and measures for prevention of overheating of the LEDs. According to  FIGS. 4 ,  5  and  6 , the cooling body comprises a chamber filled with a PCM material  70 . The PCM material  70 , as long as it is in a solid state of aggregation, will in a first phase serve for cooling the LEDs. As soon as the PCM material  70  has taken up a quantity of heat so large that the material has fully transitioned into the liquid state of aggregation, its cooling effect has been exhausted and the further cooling can be performed by the cooling mechanism described further above in that, between the cooling plate elements, an air flow is generated in the preferential flow direction  28  for supporting the normal air flow by convection from below to above. Should the cooling performance not be sufficient, the LEDs may be dimmed to prevent them from overheating. 
         [0054]    Although the invention has been described and illustrated with reference to specific illustrative embodiments thereof, it is not intended that the invention be limited to those illustrative embodiments. Those skilled in the art will recognize that variations and modifications can be made without departing from the true scope of the invention as defined by the claims that follow. It is therefore intended to include within the invention all such variations and modifications as fall within the scope of the appended claims and equivalents thereof.