Abstract:
A cooling device for cooling an electronic component, such as a power semiconductor, includes a cooling body which can be thermally coupled to the component, at least one sonotrode element for generating ultrasonic waves having a predetermined wavelength directed towards the cooling body, and a resonance tube that is associated with the sonotrode element and that is arranged between the sonotrode element and the cooling body, wherein a distance between the sonotrode element and the cooling body corresponds to an integral multiple of a quarter of a wavelength, such that a standing wave is formed between the at least one sonotrode element and the cooling body.

Description:
REFERENCE TO RELATED APPLICATIONS 
       [0001]    This is a U.S. national stage of application No. PCT/EP2013/057022 filed 3 Apr. 2013. Priority is claimed on German Application Nos. 102012205463.4 filed 3 Apr. 2012 and 102012215484.1 filed 31 Aug. 2012, the content of which are incorporated herein by reference in their entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The invention relates to a cooling device for cooling an electronic component comprising a power semiconductor. 
         [0004]    2. Description of the Related Art 
         [0005]    For cooling thermally demanding electronic components, such as power semiconductors, passive-convective cooling with the aid of a cooling body is often not sufficient. In such cases, it is therefore necessary for an air flow that is directed toward the cooling body to be additionally actively generated. 
         [0006]    Apart from the use of mechanical blowers that are both noisy and also prone to wear and tear, the use of ultrasonic transducers to this end is also known. Such transducers, such as piezoelectric sonotrodes, apart from the actual ultrasonic waves, also generate an air flow, referred to as ultrasonic wind, which is directed away from the transducer and which may be used for active cooling. 
         [0007]    In comparison with mechanical blowers, however, only a comparatively low throughput of air is generated with ultrasonic transducers. 
       SUMMARY OF THE INVENTION 
       [0008]    It is thus an object of the present invention to provide an improved cooling device which enables improved heat conveyance away from electronic components and, in particular, generates an increased throughput of air. 
         [0009]    This and other objects and advantages are achieved in accordance with the invention by providing a cooling device that is configured to cool an electronic component, in particular a power semiconductor. It displays at least one sonotrode element for generating ultrasonic waves of a predefined wavelength. The cooling device in accordance with the invention furthermore displays a tuned pipe that is assigned to the sonotrode element and that has a first opened end and a second opened end. In the cooling device in accordance with the invention, the sonotrode element is disposed so as to be closer to the first end than to the second end of the tuned pipe, or else the first end faces toward the sonotrode element. The distance from the sonotrode to the second end and/or from the first end to the second end substantially corresponds to an integral multiple of half of the wavelength. Alternatively or additionally to the respective distance, the flow path between the sonotrode and the second end and/or the flow path between the first end and the second end through the tuned pipe substantially corresponds to an integral multiple of half of the wavelength. 
         [0010]    It should be understood that a distance or flow path that substantially corresponds to an integral multiple of half of the wavelength may slightly deviate, i.e., in particular by at most one eighth, preferably by at most one sixteenth, of the wavelength, from the integral multiple of half of the wavelength. Ideally, the deviations from the integral multiple of half of the wavelength are at most one thirtysecondth of the wavelength. Particularly and preferably, the distance or the flow path, in the context of the production tolerance, exactly corresponds to an integral multiple of half of the wavelength. 
         [0011]    On account of this geometric arrangement, an antinode of the ultrasonic waves that are excited in a resonant manner by the sonotrode element is configured at the second end of the tuned pipe. A standing wave is thus generated between the sonotrode element and the second end of the tuned pipe, or between the first end and the second end of the tuned pipe. In the case of the cooling body in accordance with the invention, the oscillation conditions, as described above, thus correspond to those of an open organ pipe. 
         [0012]    On account of the ultrasonic field that oscillates in the tuned pipe, in comparison with arrangements that are free of a tuned pipe, a significantly increased flow speed of the flowing air is achieved at the second end of the tuned pipe. Consequently, heat transfer of a cooling body that is disposed so as to be close to the second end to the flowing air is significantly improved. 
         [0013]    The first end of the tuned pipe is particularly expediently spaced apart from the sonotrode by a multiple of half of the wavelength, where the first and the second end of the tuned pipe moreover are spaced apart from one another by a multiple of half of the wavelength, or else the flow path between the first and the second end is a multiple of half of the wavelength. In this manner, resonances that are configured between the first and the second end, and between the sonotrode element and the second end, may be advantageously superimposed on one another and reinforced. 
         [0014]    In the cooling device in accordance with the invention, the sonotrode element is expediently disposed outside the tuned pipe and/or at the face side in relation thereto. In this manner, the sonotrode element is able to excite resonances in the tuned pipe in a particularly efficient manner. 
         [0015]    The cooling device in accordance with the invention furthermore advantageously comprises a cooling body that is couplable to the component and that is disposed so as to be close to the second end of the tuned pipe, in particular so as to be at the face side in relation thereto and/or so as to be outside of the tuned pipe. The air that exits from the tuned pipe and, in comparison to the prior art, which is significantly increased in its flow rate, may in this manner suitably expose the cooling body to heat-evacuating air. 
         [0016]    In the case of the cooling device in accordance with the invention, an air gap is preferably provided between the second end of the tuned pipe and the cooling body. On account thereof, an outflow of the air flow supplied by the ultrasonic wind is enabled. 
         [0017]    In the case of the cooling device in accordance with the invention, the distance between the sonotrode element and the second end of the tuned pipe and/or between the first and the second end of the tuned pipe and/or the flow path through the tuned pipe between the sonotrode and the second end of the tuned pipe and/or between the first and second end of the tuned pipe ideally corresponds to half and/or one and/or one and a half and/or two and/or two and a half and/or three wavelength(s). In practice, resonances can be efficiently excited in this manner. 
         [0018]    In the case of the cooling device in accordance with the invention, the diameter of the tuned pipe expediently substantially corresponds to the wavelength. In this case, resonances in the tuned pipe can be particularly easily excited. 
         [0019]    It should be understood that a diameter of the tuned pipe that substantially corresponds to the wavelength may also slightly deviate from the wavelength, i.e., in particular by at most one eighth of the wavelength, preferably by at most one sixteenth of the wavelength. Ideally, the deviations from the integral multiple of half of the wavelength are at most one thirtysecondth of the wavelength. 
         [0020]    In the case of the cooling device in accordance with the invention, the first end of the tuned pipe particularly preferably displays a cutting edge. By means of the cutting edge, the resonant effect of the tuned-pipe flow is reinforced at the inlet of the air flow, as in the case of an organ pipe. On account of the geometry of the cutting edge and/or of the first end of the tuned pipe and/or of the sonotrode element, the air flow is ideally channeled such that it exactly impinges the cutting edge, in particular via the at least one suitably provided flow-conducting means. 
         [0021]    In one preferred embodiment of the invention, a wall of the tuned pipe, at the first end on its inside, is inclined in relation to the longitudinal extent of the tuned pipe, suitably such that the wall, at the first end or toward the first end, tapers in a pointed manner. 
         [0022]    Alternatively or additionally, the wall of the first end of the tuned pipe, on its outer side, is inclined in relation to the longitudinal extent of the tuned pipe, suitably such that the wall, at the first end or toward the first end, tapers in a pointed manner. 
         [0023]    In one particularly preferred embodiment of the invention, in the case of the cooling device a flow-conducting structure, via which flowing air is conductible so as to impinge on the cutting edge, is additionally provided. 
         [0024]    The flow-conducting structure is expediently disposed and configured such that the flow-conducting structure displays at least one flow duct, where the cross-sectional face of the flow duct is reduced close to the cutting edge. The flow duct is expediently disposed so as to be axially aligned with the tuned pipe. The flow duct is suitably disposed on an end that is remote from the cutting edge, close to the sonotrode element. 
         [0025]    The flow-conducting structure preferably displays at least one flow-conducting pipe and at least one flow-limiting device that interacts with the flow-conducting pipe so as to form at least one flow duct. The conducting pipe is preferably disposed so as to be axially aligned with the tuned pipe. In one expedient embodiment of the invention, the flow-limiting device is a funnel, cone, or truncated cone, which is disposed so as to be axially aligned with the tuned pipe and lies within the conducting pipe, and which toward the tuned pipe widens along the longitudinal axis of the flow-conducting pipe and is preferably configured in a solid manner. In this manner, an outlet opening of the flow-conducting pipe in the radial direction may overlap with the cutting edge. In this manner, a particularly good exposure of the cutting edge to the flow is achieved. 
         [0026]    The throughput of air generated by the ultrasonic transducers, and thus the cooling power, may be improved by suitable measures as have been described above. 
         [0027]    Even having a reinforced throughput of air of the solution in accordance with the invention, as described above, in the case of active cooling using ultrasonic transducers, on account of the configuration of a static air barrier layer on the surface of the cooling body, the heat transfer on the moving air flow of the ultrasonic wind is, however, occasionally limited. 
         [0028]    By means of the cooling device in accordance with the invention, which is described in the following, at least to the extent that they do not correspond to the features described above, may be alternatively or additionally available to the features of the cooling device in accordance with the invention as described above, an in comparison further improved thermal evacuation of electronic components is enabled. 
         [0029]    Such a cooling device in accordance with the invention for cooling an electronic component, i.e., a power semiconductor, comprises a cooling body that is thermally coupled to the component, at least one sonotrode element for generating ultrasonic waves of a predefined wavelength that are directed toward the cooling body, and a tuned pipe that is assigned to the sonotrode element and that is disposed between the sonotrode element and the cooling body. Here, it is provided in accordance with the invention that a distance between the sonotrode element and the cooling body corresponds to an integral multiple of a quarter of the wavelength. 
         [0030]    On account of this geometric arrangement, wave nodes are configured on the surface of the cooling body. As a result, a static wave is thus generated between the sonotrode element and the cooling body. In contrast to the arrangement described above, the oscillation conditions thus no longer correspond to those of an open organ pipe but rather a covered organ pipe. 
         [0031]    On account of the oscillating ultrasonic field, the thickness of the stagnant barrier layer on the surface of the cooling body is substantially reduced, such that the thermal transfer to the flowing air is significantly improved. Turbulences that significantly facilitate the thermal exchange between the cooling body and the air may be formed, in particular, in the region of the barrier layer, such that the cooling efficiency of such a device is particularly good. 
         [0032]    In a further embodiment of the invention, an air gap is provided between a cooling-body end of the tuned pipe and the cooling body. On account thereof an outflow of the air flow that is supplied by the ultrasonic wind is enabled. The gap width here may be suitably selected; it is possible, for example, for a gap width of quarter of the ultrasonic wavelength to be chosen, such that an antinode is present at the opening of the tuned pipe. 
         [0033]    It is furthermore expedient to provide at least one flow-conducting element in a surface region of the cooling body which faces toward the cooling-body side end of the tuned pipe. On account thereof, the outflow of the ultrasonic wind may be controlled in a targeted manner. This is particularly advantageous when a plurality of sonotrode elements and assigned tuned pipes are to be used. By way of a suitable configuration of the flow-conducting elements, a negative influence of the individual air flows of the sonotrode elements on one another may be prevented. 
         [0034]    In one possible embodiment, the flow-conducting element is configured for diverting by 180° an air flow that enters in the direction of a surface normal of the surface of the cooling body. The ultrasonic wind here is thus dissipated in a counter-parallel manner to its direction of entry. This is particularly expedient in combination with an air dissipation duct that runs parallel to the tuned pipe and that guides the air flow away from the surface of the cooling body in a perpendicular manner. 
         [0035]    However, an alternative embodiment in which the flow-conducting element is configured for diverting by 90° an airflow that enters in the direction of a surface normal of the surface of the cooling body is particularly space-saving. 
         [0036]    In this case, the entering ultrasonic wind is thus dissipated toward the periphery of the cooling body. It is particularly expedient here for the flow-conducting element to extend up to a peripheral region of the surface of the cooling body. 
         [0037]    The flow-conducting element, in the surface, of the cooling body, here may configure a sunken duct the width of which substantially corresponds to the diameter of the tuned pipe. A helical geometry of the flow-conducting element, which extends to the periphery of the cooling body, is also possible. Depending on the arrangement of the individual sonotrode elements, other geometries may also be expedient. 
         [0038]    Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0039]    The invention and its embodiments are described in more detail in the following by means of the drawing, in which: 
           [0040]      FIG. 1  shows a schematic sectional illustration of a cooling device in accordance with the invention; 
           [0041]      FIG. 2  shows a schematic sectional illustration of a further exemplary embodiment of a cooling device in accordance with the invention, having a tuned pipe with a cutting edge; 
           [0042]      FIG. 3  shows a schematic sectional illustration of a further exemplary embodiment of a cooling device in accordance with the invention having a tuned pipe with a cutting edge; 
           [0043]      FIG. 4  shows a schematic sectional illustration of a further exemplary embodiment of a cooling device in accordance with the invention having a tuned pipe with a cutting edge; 
           [0044]      FIG. 5  shows a schematic sectional illustration of a further exemplary embodiment of a cooling device in accordance with the invention having a tuned pipe with a cutting edge and a flow-conducting structure; 
           [0045]      FIG. 6  shows a schematic sectional illustration of the exemplary embodiment of the cooling device in accordance with the invention, of  FIG. 1 ; 
           [0046]      FIG. 7  shows a schematic sectional illustration of a further exemplary embodiment of a cooling device in accordance with the invention; 
           [0047]      FIG. 8  shows a schematic sectional illustration of the cooling device of  FIG. 6 , with a depiction of the thermal insulation layer on the surface of the cooling device; 
           [0048]      FIG. 9  shows a schematic sectional illustration of the exemplary embodiment of the cooling device in accordance with the invention of  FIG. 7 , with a depiction of the thermal insulation layer on the surface of the cooling body; 
           [0049]      FIG. 10  shows a perspective view of an exemplary embodiment of a cooling device in accordance with the invention having a plurality of sonotrodes; 
           [0050]      FIG. 11  shows a schematic sectional illustration of an exemplary embodiment of a cooling device in accordance with the invention having a flow duct for dissipating the heated air, which runs parallel to the tuned pipe; 
           [0051]      FIG. 12  shows a perspective view of a cooling body having flow-conducting elements, for use in an exemplary embodiment of a cooling device in accordance with the invention; and 
           [0052]      FIG. 13  shows a perspective view of an alternative cooling body having flow-conducting elements for use in an exemplary embodiment of a cooling device in accordance with the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0053]    The cooling device  10  illustrated in  FIG. 1  serves for actively cooling a semiconductor component (not explicitly illustrated in  FIG. 1 ). The cooling device  10  comprises a piezoelectric sonotrode  12  and a cooling body  30  that is thermally coupled to the semiconductor. Between the sonotrode  12  and the cooling body  30  a circular-cylindrical tuned pipe  16  having a first  50  and a second opened end  55  is disposed such that the first opened end  50  points toward the sonotrode  12  and the second opened end  55  of the tuned pipe  16  points toward the cooling body  30 . 
         [0054]    In the illustration shown, the sonotrode  12  emits ultrasonic waves having a predefined wavelength into the first end  50  of the tuned pipe  16 . Here, the length L of the tuned pipe  16  corresponds to substantially one and a half wavelengths. In other exemplary embodiments that are not specifically illustrated, the length L of the tuned pipe  16  is another integral multiple of half of the wavelength. The first end  50  of the tuned pipe  16  is spaced apart from the sonotrode  12  by half of a wavelength, the distance a. On account of this arrangement and configuration, standing ultrasonic waves are configured both between the first end  50  and the second end  55  of the tuned pipe  16  and also between the sonotrode  12  and the second end  55  of the tuned pipe  16 . Here, the diameter D of the tuned pipe  16  corresponds to one wavelength. On account of the diameter, the configuration of standing waves is thereby significantly supported. 
         [0055]    These standing waves configure in each case an antinode  20  on the second end  55 . On account thereof, apart from the ultrasonic oscillation per se, the air flow generated by the sonotrode  12 , i.e., ultrasonic wind, in the direction of the arrows  22  is reinforced. 
         [0056]    As is illustrated in the exemplary embodiments illustrated in  FIGS. 2 to 5 , the excitement of the standing waves is further improved in that a cutting edge  51 ′,  51 ″,  51 ′″ that allows an improved excitement of the air flowing into the pipe is provided on the first end  50 ′,  50 ″,  50 ′″,  50 ″″. 
         [0057]    As shown for example in  FIG. 2 , the cutting edge  51 ′ here is configured such that the wall of the tuned pipe  16 ′, at the first end  50 ′ of the tuned pipe  16 ′, on the inside, is inclined in relation to the direction of the longitudinal extent L of the tuned pipe  16 ′, specifically such that the wall, at the first end  50 ′, tapers in a pointed manner toward the sonotrode  12 . 
         [0058]    Alternatively, the wall of the tuned pipe  16 ′, at the first end  50 ″ of the tuned pipe  16 ″, on the outer side, may be inclined in relation to the direction of the longitudinal extent L of the tuned pipe  16 ″ such that the wall tapers in a pointed manner at the first end  50 ″ and thus forms a cutting edge  51 ″ ( FIG. 3 ). 
         [0059]    As illustrated in  FIG. 4 , the wall of the tuned pipe  16 ′″, at the first end  50 ′″ of the tuned pipe, both on the inner side and also on the outer side, may also furthermore be inclined so as to taper in a pointed manner in relation to the direction of the longitudinal extent L of the tuned pipe  16 ′″ and thus form a cutting edge  51 ′″. 
         [0060]    In the arrangement illustrated in  FIG. 5  (which otherwise corresponds to the arrangement illustrated in  FIG. 3 ) a flow-conducting structure  57 , by which flowing air can be conducted so as to impinge on a cutting edge  51 ″, is provided in the case of the cooling device. In principle, cutting edges as illustrated in  FIG. 2  or  4  may also be present in further exemplary embodiments which are not specifically illustrated. 
         [0061]    The flow-conducting structure  57  displays a flow-conducting pipe  60  that is disposed so as to be axially aligned in relation to the tuned pipe  16 ″″ and so as to be between the sonotrode  12  and the tuned pipe  16 ″″. The flow-conducting structure  57  furthermore displays a solid funnel  65  that is disposed within the flow-conducting pipe  60  and which widens along the flow-conducting pipe  60  toward the tuned pipe  16 ″″. A flow duct  80  is thus configured between the funnel  65  and the flow-conducting pipe  60 . Close to the tuned pipe  16 ″″ this flow duct  80  displays an outlet opening  70  having a reduced cross-sectional face, from which air flowing through the flow-conducting structure  57  may flow out. This outlet opening  70  of the flow-conducting structure  57  in the radial direction overlaps with the cutting edge  51 ″. 
         [0062]    Cooling devices.  10  in accordance with the invention, as have been described above and illustrated in  FIGS. 6 and 8  can be employed for actively cooling semiconductor components. As already described above, such cooling devices comprise a piezoelectric sonotrode  12  and a cooling body (henceforth, and in the figures described in the following, and in the further description identified by the reference sign  14  instead of the reference sign  30 ) which is thermally coupled to the semiconductor, between which a tuned pipe  16  is disposed. 
         [0063]    At the cooling-body end (henceforth, and in the figures described in the following, and in the further description identified by the reference sign  18  instead of the reference sign  55 ) of the tuned pipe, an antinode  20  of the ultrasonic oscillation generated by the sonotrode  12  is configured here. On account thereof, apart from the ultrasonic oscillation per se, the air flow generated by the sonotrode  12 , i.e., ultrasonic wind, in the direction of the arrows  22  is reinforced. 
         [0064]    As shown in  FIG. 8 , the thermal evacuation from the cooling body  14  is occasionally hampered by a barrier layer  24  of stagnant air. 
         [0065]    In order to attenuate the configuration of the barrier layer  24 , in the further exemplary embodiment of a cooling device  26  in accordance with the invention, shown in  FIGS. 7 and 9 , the distance between the sonotrode  12  and the surface  28  of the cooling body  14  is selected such that it is an integral multiple of quarter of the wavelength of the ultrasound generated by the sonotrode  12 . 
         [0066]    On account thereof an oscillation node  31  is created on the surface  28  of the cooling body  14 . A standing wave is thus configured between the sonotrode  12  and the surface  28 . The standing wave reduces the extent of the barrier layer  24 , such that the barrier layer  24  displays a significantly smaller thickness than in the cooling devices  10  which have been described above. On account of the standing wave, in particular, turbulences in the region of the surface  28 , which counteract the formation of a barrier layer and improve the thermal evacuation from the cooling body  14 , are generated. 
         [0067]      FIG. 10  shows a perspective view of a cooling device  26  without the cooling body  14 . The cooling device  26  comprises a plurality of piezoelectric sonotrodes  12  that are enclosed between electrodes  32 ,  34 . The tuned pipes  16  assigned to the sonotrodes  12  are collectively received in a block  36  and, for the sake of clarity, not all identified. 
         [0068]    Together with the tuned pipes  16 , further flow ducts  38  that are likewise not all identified are introduced into the block  36 . The flow ducts  38 , in interaction with the flow-conducting elements  40  on the surface  28  of the cooling body  14 , serve for dissipating heated air from the surface  28 . 
         [0069]    As depicted in  FIG. 11 , the entering ultrasonic wind, after exiting from the tuned pipe  16  and when impinging the flow-conducting element  40 , is deflected by 180° and guided into the flow duct  38 , such that the heated air is evacuated from the cooling body  14 . On account thereof, it is in particular avoided that the air flows, which are generated by adjacent sonotrodes  12 , influence one another in a negative manner. Uniformly good heat dissipation is thus generated across the entire surface of the cooling body  14 . 
         [0070]      FIGS. 12 and 13  show alternative embodiments of the flow-conducting elements  40  on the surface  28  of the cooling body  14 . In the embodiment of  FIG. 12 , the flow conducting elements  40  are configured as sunken ducts that extend from the mouth regions  42  of the tuned pipes (not shown) toward the periphery  44  of the cooling body  14 . The ducts here display a width that corresponds to about the diameter of the tuned pipes  16 . 
         [0071]    In the embodiment depicted in  FIG. 13 , the flow-conducting elements  40  are configured as raised webs on the surface  28  of the cooling body  14 , which extend from a center  46  of the surface  28  along helical paths to the periphery  44  of the cooling body. 
         [0072]    It should be understood that the disclosed embodiments of invention are not limited to the geometries of the flow-conducting elements  40  shown in  FIGS. 11 to 13 . Depending on the configuration of the cooling body  14  and the amount of air and/or heat to be evacuated, other embodiments may also be expedient. 
         [0073]    Thus, while there have been shown, described and pointed out fundamental novel features of the invention as applied to a preferred embodiment thereof, it will be understood that various omissions and substitutions and changes in the form and details of the devices illustrated, and in their operation, may be made by those skilled in the art without departing from the spirit of the invention. For example, it is expressly intended that all combinations of those elements and/or method steps which perform substantially the same function in substantially the same way to achieve the same results are within the scope of the invention. Moreover, it should be recognized that structures and/or elements and/or method steps shown and/or described in connection with any disclosed form or embodiment of the invention may be incorporated in any other disclosed or described or suggested form or embodiment as a general matter of design choice. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto.