Abstract:
A fan comprises a hub and a stator coil disposed with the hub. A first set of blades is disposed about the hub. Second blades are disposed on an interior of the hub. An opening is provided through the face of the hub. When the fan is operating, a flow of air passes through the opening which is then captured by the second blades and redirected across the stator coils to provide cooling.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS  
       [0001]     The present application claims priority from U.S. Provisional Application Ser. No. 60/755,746, filed Dec. 29, 2005, and is fully incorporated herein by reference for all purposes. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     The present invention relates generally to cooling fans, and in particular to a fan configured to cool the stator windings of a motor component of the cooling fan.  
         [0003]      FIG. 7  shows an exploded cross-sectional view of components comprising a conventional cooling fan. The figure shows a base  702  that is part of the cooling fan housing (not shown) onto which a stator is mounted. Typically, the base  702  includes a small printed circuit board for the electronics which control motor operation. Power and control wires (not shown) run from the printed circuit board for connection to an external power source and to a computer. The stator assembly comprises a coil subassembly  704  comprising some number of individually activated coils wound about a bearing liner  706 . A rotor assembly is positioned around the stator coil  704 . The rotor assembly includes a yoke  708  which is shaped like a cup that fits around the stator coil  704 . An axle  710  is axially connected to the interior of the yoke  708 . A number of permanent magnets  712  are fixedly mounted about the interior periphery of the yoke  708 . When the yoke  708  is assembled with the stator assembly, the axle  708  is received within the bearing liner  706  and the permanent magnets  712  are disposed around the coil subassembly  704 . The axle  710  rests on a bearing surface neat the bottom of the bearing liner  706 . An impeller  714 , comprising a hub  716  and some number of fan blades  718  attached to the hub, fits over the yoke  708  and is connected to the yoke.  
         [0004]     Rotation of the rotor assembly results in suitably timed activation and deactivation of the coils in the coil subassembly  704 . The fan blades  718  are typically configured so that the resulting flow of air is toward the rotor assembly (inlet airflow) and away from the stator assembly (outlet airflow).  
         [0005]     The motor essentially comprises the coil subassembly  704  and the permanent magnets  712 . Due to the constant flow of current in the stator windings of the motor, the stator windings of a cooling fan motor can get quite hot.  
       BRIEF SUMMARY OF THE INVENTION  
       [0006]     Embodiments of the present invention include secondary blades disposed in the interior of the hub of a fan, in addition to the primary blades of the fan. The secondary blades blow air through openings provided in the yoke of the stator. The air flow through the stator provides significant cooling of the stator windings, thus allowing for the motor to run at higher speeds and higher torque levels. The secondary blades can be configured to achieve desired levels of cooling. Lab results have shown substantial temperature reductions, ranging from 5° C. to 40° C. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]      FIGS. 1 and 2  show an embodiment of an impeller according to the present invention.  
         [0008]      FIG. 3  illustrates a schematic cross-sectional view of a hub embodiment according to the present invention.  
         [0009]      FIG. 4  illustrates a schematic cross-sectional view of a fan assembly embodied according to the present invention.  
         [0010]      FIG. 5  is perspective view of a fan embodied in accordance with the present invention, showing openings formed in the yoke of the fan.  
         [0011]      FIGS. 6A-6E  illustrate various configurations of openings in a yoke in accordance with the present invention.  
         [0012]      FIG. 7  shows an exploded view of components comprising a conventional cooling fan. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0013]      FIGS. 1 and 2  illustrate the basic components of an impeller  114  according to an illustrative embodiment of the present invention. The impeller  114  comprises a hub  116  to which fan blades  118  are attached. For purposes of identification, these blades  118  are referred to as primary blades. The direction of inlet air flow is toward an inlet facing surface  120  of the hub  116  when the impeller  114  is operated. The primary blades  118  are configured to capture a portion of the inlet air flow to create a primary flow  1 A in the axial direction, which flows around the hub  116 . Consequently, the primary blades  118  can also be referred to as axial blades.  
         [0014]     Referring to  FIGS. 1-3 , an opening  122  is provided through the inlet facing surface of the hub  116 . As a result of having a hub opening  122 , a secondary flow component  1 B of the inlet air flow is created. The interior of the hub  116  includes a set of secondary blades  218 . In this particular illustrative embodiment of the present invention, the secondary blades  218  are disposed about an interior surface  320  opposite the inlet facing surface  120 . As will be explained in more detail, the secondary flow  1 B is captured by the secondary blades  218  and is radially distributed in the volume of space in the interior of the hub  116 . For this reason, the secondary blades  218  can also be referred to as radial blades. The secondary blades  218  depicted in the figures are schematic in nature. The actual shape of the secondary blades  218 , their size, numbers, and so on can be optimized for specific dimensions of the fan components. In addition, any suitable material can be used for the secondary blades  218  and can be the same or different material as used to make the primary blades  118 .  
         [0015]      FIG. 4  shows an assembly in accordance with an illustrative embodiment of the present invention, comprising the impeller  114  and a motor sub-assembly. Though the illustrated embodiment shows a brushless DC motor, it will be appreciated that other motor configurations can be used. The motor sub-assembly comprises a rotor component comprising a yoke  408  and an annular-shaped magnet  412  that is fixedly disposed in an interior of the yoke. The motor sub-assembly further comprises a stator component comprising stator coils  404  which are maintained in a fixed position. Typically the stator coils  404  are affixed to a portion of the housing of the fan.  
         [0016]     The rotor component is fixed within the interior volume of the hub  116  of the impeller  114 . This assemblage of impeller and rotor component can be referred to variously as the fan rotor, rotor assembly, or simply the rotor. The yoke  408  includes a shaft  410  (or axle) which rotatably supports the fan rotor assembly. The shaft  410  serves as an axis of rotation about which the rotor assembly rotates during operation of the fan.  
         [0017]     As mentioned above, the resulting air flow during fan operation includes a secondary flow component  1 B through opening  122 . As can be seen in  FIG. 4 , the secondary blades  218  rotate as the hub  116  spins during operation of the fan. The secondary flow  1 B is captured by the rotating secondary blades  218  and is radially directed into the interior volume of the hub  116 . Openings  428  formed in the yoke  408  permit the radially directed air flow (indicated the by the arrows) to pass into the interior volume of the yoke within which is contained the stator coils  404 . The resulting flow of air across the stator coils  404  carries away heat produced by the current flowing through the coils during fan operation. So long as the fan is operating, the secondary blades  218  will continue to capture a portion of the inlet airflow and direct through the openings in the yoke  408  to provide a continuous cooling effect.  
         [0018]     Although the stator coils are a main source of heat, it is noted that the printed circuit board that is usually provided at the base of the fan (e.g.,  702 ,  FIG. 7 ) typically include heat generating electronic components. It will be appreciated that the flow of air passing across the stator coils will also pass over and around the printed circuit board, and thus carry away some of the heat generated by the printed circuit board. Generally, the heat that accumulates within the yoke  408 , regardless of its sources, will be carried away in large part by the airflow created by the secondary blades  218  of the present invention.  
         [0019]     Conventional cooling techniques simply provide an opening in the hub and openings in the yoke. Air flow across the stator coils results from the flow created by the primary blades. However, the flow created by the primary blades is directed largely across the primary blades. The flow component through the hub and yoke openings is relatively minor. By comparison, the secondary blades provided according to the present invention create a significantly greater flow of air across the stator coils and thus significantly increases the cooling effect. Consequently, the motor can be run at higher speeds and higher torque levels since the additional heat created by the increase in current through the coils can be dissipated.  
         [0020]     It might be desirable to vary the amount of cooling effect that the secondary blades  218  provide. For example, hotter running fan motors of course would require more cooling, while cooler fan motor applications may require lesser cooling. The amount of cooling is varied by varying the amount of airflow across the motor and electronics. A primary design parameters include blade camber angle, blade stagger angle, blade chord, and number of blades.  
         [0021]     An example of a fan constructed according to the present invention is shown in  FIG. 5 . This type of fan is typically found in computer equipment such as desktop personal computers, network switching equipment, and so on, and other electronic equipment such as copying machines, overhead projection devices, and such. It can be appreciated that most fans can be adapted according to the present invention can be readily adapted for use generally with electronic devices where adequate heat dissipation is important.  
         [0022]     Referring now to  FIG. 5 , a housing  502  serves to contain the components of the fan. Though not shown the stator coils  404  shown in  FIG. 4  are typically mounted to the struts extending from the housing, which in  FIG. 5  would be found at the bottom of the housing  502 . The hub  116  (and its fan blades  118 ) fit within the housing  502 .  FIG. 5  shows the opening  122  formed through the inlet facing surface of the hub  116 . A portion of the yoke  408  is shown exposed through the opening  122 . Shown in dashed lines are openings  428  formed through the yoke  408  to provide a path for the flow of air into the interior of the yoke.  FIG. 5  shows the openings  428  in the yoke  408  to be circular in shape. However, it should be appreciated that other shaped openings are possible, as illustrated in  FIGS. 6A-6E , for example. Some of the secondary blades  218  are illustrated (see dashed lines) disposed about the interior of hub  116  in accordance with the present invention.  
         [0023]      FIGS. 6A-6E  show various top-view configurations of openings in the yoke. The figure is a top view looking down at the inlet facing surface of the yoke. In addition to circular-shaped openings as shown in  FIG. 5 , the openings can be slotted openings ( FIG. 6A ). The slots can overlap as shown in  FIG. 6B . The openings can be arcuate slots ( FIG. 6C ), rectangular slots ( FIGS. 6A and 6D ), and so on.  FIG. 6D  shows radially-directed openings in the yoke. For example, slots may be arranged in a radial manner relative to the center of the yoke. Openings can be large openings such as the pie-shaped openings shown in  FIG. 6E .  1241  It is also understood that the examples and embodiments described herein are for illustrative purposes only and that various modifications or changes in light thereof will be suggested to persons skilled in the art and are to be included within the spirit and purview of this application and scope of the appended claims.