Abstract:
An electronics cooling system comprises a tubular fan duct and an electronics housing. The fan duct includes has a fan duct casing containing a fan with rotor blades and stator vanes. The electronics housing is mounted directly on the tubular fan duct, such that the electronics housing and the fan duct casing together enclose an interior space. A cooling airflow path extends from a high-pressure region of the tubular fan duct, through an inlet hole into the interior space, and out a bleed hole into a surrounding environment. The electronics cooling system further comprises three electronics mounts within the interior space. A first electronics mount is located immediately adjacent to the inlet hole, on the fan duct. A second electronics mount is located immediately radially outward of the stator vanes, on the fan duct. A third electronics mount is located immediately adjacent to the bleed hole, on the housing.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a continuation in part of Pal et al. U.S. patent application Ser. No. 13/050,509, filed Mar. 17, 2011, which is hereby incorporated by reference. Pal et al. U.S. patent application Ser. No. 13/052,837, filed Mar. 21, 2011, is also incorporated by reference. 
     
    
     BACKGROUND 
       [0002]    The present invention relates generally to electronics cooling, and more particularly to air cooling for a fan motor controller. 
         [0003]    Fans are commonly used to dissipate heat from electronic components, thereby avoiding component failure and extending component lifetimes. Some electronic components in aircraft, including motor controllers, are commonly located in motor controller housings mounted on fan housings. Electronics installed in these motor controller housings are conventionally cooled with airflow circulated by the nearby fan. Some such cooling systems divert relatively cool air from a region of the fan duct downstream of the fan, and pass this air through the housing before releasing it into the environment at a vent in the housing. Other conventional cooling systems take in air from the environment for cooling by means of an outlet in the casing, and draw this air through the housing by means of an air passage from the housing to a region of the fan duct immediately upstream of the fan. In aircraft, the fan which provides cooling airflow may be a part of an air management system. The amount of air utilized for cooling is typically small compared to the total airflow volume of the fan—usually on the order of 2%—and thus does not disrupt normal fan functions, such as cabin or lavatory air circulation or for electronics bay cooling. 
         [0004]    Conventional fan motor controller assemblies comprise a box-like fan motor controller housing with a flat base mounted to an adjacent cylindrical fan duct via an intervening thermal interface which adds to the cost and weight of the total assembly. In addition, many fan motor controller housings include machined fins arranged near high-heat components to increase heat dissipation surface area. These fins also increase the cost and weight of the total assembly. 
         [0005]    It is generally desirable that the spatial footprint of fan motor controller hardware be as small as possible. Any increase to the packing density of heat generating electronics, however, necessitates corresponding improvements to heat dissipation, to avoid excessive component degradation. There exists, therefore, a need for fan motor controller housings capable of increased cooling at lower cost and weight. 
       SUMMARY 
       [0006]    The present invention is directed toward an electronics cooling system comprising a tubular fan duct and an electronics housing. The fan duct includes a fan duct casing containing a fan with rotor blades and stator vanes. The electronics housing is mounted directly on the tubular fan duct, such that the electronics housing and the fan duct casing together enclose an interior space. A cooling airflow path extends from a high-pressure region of the tubular fan duct, through an inlet hole into the interior space, and out a bleed hole into a surrounding environment. The electronics cooling system further comprises three electronics mounts within the interior space. A first electronics mount is located immediately adjacent to the inlet hole, on the fan duct. A second electronics mount is located immediately radially outward of the stator vanes, on the fan duct. A third electronics mount is located immediately adjacent to the bleed hole, on the housing. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is a perspective view of a fan motor controller assembly. 
           [0008]      FIG. 2  is a cross-sectional view of the fan motor controller assembly of  FIG. 1 . 
           [0009]      FIG. 3  is a perspective view of a fan duct of the fan motor controller assembly of  FIG. 1 . 
           [0010]      FIG. 4  is a transparent perspective view of the fan motor controller assembly of  FIG. 1 , depicting components within a fan motor controller housing. 
           [0011]      FIGS. 5A and 5B  are perspective views of one panel of the fan motor controller housing of  FIG. 4 , from two angles. 
           [0012]      FIG. 6  is a transparent perspective view of another panel of the fan motor controller housing of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0013]      FIG. 1  is a perspective view of fan motor controller assembly  10 . Fan motor controller assembly  10  comprises housing  12  and fan duct  14 . Housing  12  is a boxlike structure containing motor controller electronic components which generate heat. Housing  12  is formed of a rigid, thermally conductive material, such as aluminum. Fan duct  14  is a substantially cylindrical duct containing a fan (see  FIG. 2 ) which forces air in an airflow direction, when active, thereby creating regions of high and low relative pressure within fan duct  14  (see  FIG. 2 , below). Fan duct  14  may, for example, be an aluminum duct for an aircraft air management system, such as a cabin or lavatory air duct or an electronics cooling air supply. 
         [0014]    As depicted, housing  12  is a five-sided structure comprised of one top panel  16 , two front/rear panels  18 , and two side panels  20 . Top panel  16  and side panels  20  are substantially rectangular, while front/rear panels  18  are shaped to conform to the cylindrical shape of the adjacent surface of fan duct  14 . In the depicted embodiment, front/rear panels  18  are eight-sided panels. In other embodiments, front/rear panels  18  may have other shapes which conform to the surface of fan duct  14 . In some embodiments, both front/rear panels  18  are identical, as are both side panels  20 . In other embodiments, each panel may exhibit minor differences, such as in the location of cooling or attachment holes (discussed below). Like fan duct  14 , panels  16 ,  18 , and  20  are formed of a rigid thermal conductor such as aluminum or aluminum alloy. In some embodiments each panel  16 ,  18 , or  20  is a separate piece. In other embodiments some subset of panels  16 ,  18 , and  20  may be cast or welded together in one piece. 
         [0015]    Housing  12  forms a closed interior space together with fan duct  14 . Housing  12  may be bolted or welded to fan duct  14 . In some embodiments, one or more of panels  16 ,  18 , or  20  are removable, allowing access to electronic components inside housing  12 . Fan duct  14 , although substantially cylindrical, includes a flat side portion coinciding with the location of housing  12 , as depicted and described below with respect to  FIG. 3 . 
         [0016]      FIG. 2  is a cross-sectional view of motor controller assembly  10  through section line  2 - 2  of  FIG. 1 . Motor controller assembly  10  includes housing  12  and fan duct  14 , as explained above. Fan duct  14  contains rotor blades  22  and stator vanes  24  situated within duct casing  26 . Although only one stage of rotor blades  22  and stator vanes  24  is shown, some embodiments may include multiple stages of alternating rotor blades and stator vanes. Housing  12  has interior space  28  formed by duct casing  26  and panels  16 ,  18 , and  20 , as discussed above with respect to  FIG. 1 . The portion of duct casing  26  which bounds interior space  28  includes, in some embodiments, a substantially flat surface which deviates from the generally cylindrical shape of fan duct  14 , as described and depicted below with respect to  FIG. 3 . Fan duct  14  is fluidly connected to the interior space  28  by inlet holes  30   a  and  30   b  (collectively referred to as inlet holes  30 ), and interior space  28  is fluidly connected to the environment by bleed holes  32 . Inlet holes  30  are cast or drilled holes through the exterior of fan duct  14  at high-pressure locations. Air from inlet holes  30  is diverted out of fan duct  14  into interior space  28  to cool electronics. A plurality of bleed holes  32  are located on panels  18  and  20  to reject air from interior space  28 . Bleed holes  32  are strategically located to draw air through electronic components, as described below with respect to  FIGS. 4 ,  5 A,  5 B, and  6 . Air diverted from fan duct  14  by inlet holes  30   a  and  30   b  enters and circulates throughout interior space  28 , cooling electronic components therein before exiting through bleed holes  32 . Air is expelled from bleed holes  32  to the surrounding environment (at low relative pressure). In some embodiments, bleed holes  32  may also be present in panel  16 . 
         [0017]    Housing  12  houses and provides cooling for various heat-producing electronic components, including insulated gate bipolar transistor (IGBT) module  100 , auto-transformer rectifier unit (ATRU)  102 , inter-phase transformers (IPTs)  104 , and inductor  106 . In many embodiments, additional electronic components such as printed wiring boards of various kinds are also situated in housing  12  for cooling. In addition, some electronic components are mounted on side panels  20 , as described below with respect to  FIGS. 4 and 6 . As depicted, IGBT module  100  and ATRU  102  are mounted on duct casing  26 , and are cooled by a combination of direct air cooling (convection) from air bled into interior space  28  by inlet holes  30 , and indirect air cooling (conduction) through duct casing  26  into the primary air stream of fan duct  14 . IPTs  104 , inductor  106 , and other components mounted on panels  16 ,  18 , and  20  are cooled primarily through direct air cooling, as described below with respect to  FIGS. 4 ,  5 A,  5 B, and  6 . 
         [0018]    IGBT module  100  is mounted directly on fan duct casing  26 . IGBT module  100  is cooled convectively by direct air flow from inlet hole  30   a , and conductively through fan duct casing  26  and stator vane  24  via indirect air cooling utilizing the primary air stream of fan duct  14 . In the depicted embodiment there are six inlet holes  30   a , each which Stator vanes  24  serve as cooling fins, providing increased surface area for heat dissipation into the air stream of fan duct  14 . 
         [0019]    Air diverted from fan duct  14  flows through and around ATRU  102 , providing direct air cooling. In one embodiment, ATRU  102  may be a light-weight transformer supported by a support structure mounted on duct casing  26 , as described in U.S. patent application Ser. No. 13/050,509, from which this application is a continuation in part. In other embodiments ATRU  102  may be a conventional transformer assembly in thermal potting. ATRU  102  includes air channels through which air from a high-pressure region of fan duct  14  can pass to cool ATRU  102 . In some embodiments these air channels meet with inlet holes  30   b , such that the pressure differential between interior space  28  (low relative pressure) and the high-pressure region of fan duct  14  (high relative pressure) draws cooling air through ATRU  102 . 
         [0020]    By mounting IGBT module  100  and ATRU  102  directly on fan duct casing  26 , fan motor controller assembly  10  is able to provide adequate cooling to both components without relying on a heavy thermal interface between electronic components and fan duct  14 . In addition, utilizing stator vanes  24  as cooling fins obviates the need for a separate finned heat exchanger, further reducing mass without decreasing cooling capacity. 
         [0021]      FIG. 3  is a perspective view of fan duct  14 , depicting fan duct casing  26  with inlet holes  30  (including inlet holes  30   a  and inlet holes  30   b ), flat pedestal  34 , thermal interface  36 , and attachment holes  38 . As described above with respect to  FIGS. 1 and 2 , fan duct casing  26  forms the exterior of fan duct  14 , and inlet holes  30  provide cooling airflow through interior space  28  (see  FIG. 2 ). Attachment holes  38  are rivet or screw holes which allow front/rear panels  18  and side panels  20  to be bolted to fan duct casing  26 . In some embodiments, some panels  18  or  20  may be removable by unscrewing bolts or screws from attachment holes  38 . As mentioned previously, some panels  18  or  20  may be welded into place on fan duct casing  26 . 
         [0022]    Flat pedestal  34  provides a conductive platform for electronic components such as IGBT  100  and ATRU  102 . By casting flat pedestal  34  into fan duct casing  26 , fan motor controller assembly  10  is able to eschew the conventional separate flat electronics platform connected to a cylindrical surface of fan duct casing  26  by a heavy thermal interface. Flat pedestal  34  thus provides more direct conductive cooling of electronic components, while allowing the total mass of fan motor controller assembly  10  to be reduced. Some embodiments of fan motor controller assembly  10  further include one or more thermal interface layers  36 , which may for instance be conventional thermal pads of a conductive material such as Thermstrate. Thermal interface layers  36  are thin and lightweight, and form a thermal interface between electronic components and fan duct casing  26  which does not significantly increase the mass of fan motor controller assembly  10 . 
         [0023]      FIG. 4  is a transparent perspective view of fan motor controller assembly  10 , depicting components mounted in interior space  28  on panels  18  and  20 , including IPTs  104 , inductor  106 , differential mode (DM) inductors  108 , resistors  110 , capacitors  112 , and a plurality of printed wiring boards and other electronic components. Fan motor controller assembly  10  comprises housing  12  and fan duct  14  as described previously. Housing  12  is formed of top panel  16 , two front/rear panels  18 , and two side panels  20 , and is penetrated by bleed holes  32  (including bleed holes  32   a ,  32   b ,  32   c , and  32   d ). IPTs  104  and inductor  106  are mounted on one front/rear panel  18 , while DM inductors  108 , resistors  110 , and capacitors  112  are mounted on one side panel  20 . These components are cooled both by conductive dissipation through panels  18  or  20 , and by direct air flow across or through the electronic components. Some components, such as capacitors  112 , need little or no cooling. Other components, such as IPTs  104  and inductor  106 , must be able to dissipate large amounts of heat to minimize component degradation. Bleed holes  32  in panels  16 ,  18 , and  20  expel air from interior space  28 , thereby producing a continuous cooling air flow from fan duct  14 , through interior space  28 , and into the environment. In particular, bleed holes  32   a  expel air though top panel  16 , bleed holes  32   b  and  32   c  expel air through front/rear panels  18  (see  FIGS. 5A and 5B , below), and bleed holes  32   d  expel air through side panels  20  (see  FIG. 6 , below). Bleed holes  32   b  are located at the mounting positions of IPTs  104  to draw air through IPTs  104  for increased direct air cooling. Bleed holes  32   c  are located at the mounting position of inductor  106  to similarly draw air through inductor  106  for direct air cooling. Bleed holes  32   d  are located near fan duct  14 , and provide airflow through side panels  20 , but are not located at the mounting positions of DM inductors  108  or resistors  110 , as these components require less cooling than IPTs  104  or inductors  106 . In general, bleed holes  32  draw air through the electronic components which much dissipate the most heat, while other components mounted on panels  16 ,  18 , and  20  are cooled only by general airflow within and through interior space  28 . Bleed holes  32  are thus strategically located to provide airflow directly through components in need of the most cooling. In the depicted embodiment, bleed holes  32   a ,  32   b , and  32   d  and inlet holes  30   a  are circular holes 0.2 in. (5.1 mm) in diameter, bleed holes  32   c  are circular holes 0.125 in. (3.2 mm) in diameter, and inlet holes  30   b  are 0.312×0.188 in. (7.9×4.8 mm) kidney-shaped holes. Qualitatively, the sizes of inlet holes  30  are selected to provide adequate cooling airflow for motor controller electronics without impairing the operation of the fan by diverting excessive air. Inlet holes  30  only divert approximately 2% of airflow through fan duct  14 , negligibly affecting the operation of the fan. Although the size of bleed holes  32  is not as critical, both inlet holes  30  and bleed holes  32  must be large enough to avoid clogging with dust or debris, yet small enough to concentrate airflow around heat-producing electronics. Bleed holes  32  secondarily provide means to expel moisture from fan motor controller assembly  10  during startup. 
         [0024]      FIGS. 5A and 5B  are perspective views of a one front/rear panel  18  of housing  12 .  FIG. 5A  provides an exterior view of front/rear panel  18 , while  FIG. 5B  shows the interior side of front/rear panel  20 . Front/rear panel  18  has bleed holes  32   b  and  32   c , and supports IPTs  104  and inductor  106 . 
         [0025]    Each IPT  104  comprises a plurality of wrapped cores  114  separated by spaces  116 , which coincide with bleed holes  32   b . Pressure differential between the environment (low relative pressure) and interior space  28  (high relative pressure) draws cooling air through spaces  116  and out via bleed holes  32   b . This airflow directly through IPTs  104  provides increased cooling over convection cooling from general air circulation within interior space  28 . 
         [0026]    Front/rear panel  18  includes inductor mount  40 , a platform to which inductor  106  is attached for cooling. Inductor mount  40  includes a plurality of inductor air passages  42  which extend from interior space  28  to bleed holes  32   c . Air is drawn from interior space  28  through air passage  42  and out bleed holes  32   c  via the previously discussed pressure differential between the environment and interior space  28 . The flow of cooling air through inductor air passages  42  provides increased cooling for inductor  106  over convection cooling from general air circulation within interior space  28 . 
         [0027]    The positioning of bleed holes  32   b  and  32   c  draws air through spaces  116  and inductor air passages  42 , increasing possible heat dissipation from IPTs  104  and inductor  106  without significantly increasing the mass of fan motor controller assembly  10 . 
         [0028]      FIG. 6  is a transparent perspective view of one side panel  20  of housing  12 . Side panel  20  has bleed holes  32   d , and supports DM inductors  108 , resistors  110 , and capacitors  112 . Capacitors  112  produce negligible heat. DM inductors  108  and resistors  110  are substantial heat producers which must be cooled to avoid component damage and minimize deterioration. Unlike IPTs  104  or inductor  106 , DM inductors  108  and resistors  110  are cooled only by circulated airflow within interior space  28 ; bleed holes  32   d  are located near the intersection of side panel  20  and fan duct casing  26 , and therefore do not draw cooling air through DM inductors  108  or resistors  110 . In alternative embodiments for which additional cooling is desired, electronic components and bleed holes  32   d  could be relocated to coincide, as described with respect to bleed holes  32   b  and  32   c  in  FIGS. 5A and 5B . In the depicted embodiment, bleed holes  32   a ,  32   b ,  32   c , and  32   d  collectively provide air circulation through interior space which directly cools heat-producing electronic components. air circulation through interior space 
         [0029]    Fan motor controller assembly  10  provides convection and conduction cooling for electronic components including IGBT module  100 , ATRU  102 , IPTs  104 , inductor  106 , DM inductors  108 , and resistors  110 . Hotter components are cooled by airflow directed through or adjacent to the components via inlet holes  30   a  and  30   b , and bleed holes  30   b  and  30   c . IGBT module  100  and ATRU  102 , which produce the most heat of electronic components within fan motor controller assembly  10 , are in direct thermal contact with fan duct casing  26  of fan duct  14 , wherein stator vanes  24  act as cooling fins to dissipate heat over a large surface area. The location of components, inlet holes, and bleed holes in fan motor controller assembly  10  provides increased cooling over the prior art, while concentrating components in a smaller space, with reduced weight. 
         [0030]    While the invention has been described with reference to an exemplary embodiment(s), it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.