Abstract:
An exemplary heat dissipation fan includes a rotor and a stator. The rotor includes a hub, a central shaft extending down from a top end of the hub, the shaft having a free end far from the top end of the hub. A magnetic element attached to an inner periphery of the hub. The stator includes a stator core consisting layers of yokes, two insulation frames mounted at two opposite ends of the stator core and a coil wound around the insulation frames. An outer surface of the stator faces and is spaced from an inner surface of the magnetic element of the rotor with a clearance defined therebetween. A width of a bottom end of the clearance adjacent to the free end of the shaft being smaller than a width of a top end of the clearance.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The disclosure relates to electronic device cooling, and particularly to a heat dissipation fan providing stable rotation of a rotor thereof. 
         [0003]    2. Description of the Related Art 
         [0004]    With the continuing development of electronics technology, electronic packages such as CPUs (central processing units) employed in electronic devices are generating more and more heat. The heat requires immediate dissipation in order that the CPU and the electronic device can continue to operate stably. A heat dissipation fan is commonly used in combination with a heat sink for cooling the CPU. 
         [0005]    A conventional heat dissipation fan includes a stator, and a rotor having a hub with a plurality of blades extending from the hub. The stator establishes an alternating magnetic field interacting with a magnetic field of the rotor to drive the rotor to rotate. Thus the rotation of the blades generates a forced airflow, for cooling the CPU. The stator includes a bearing defining a bearing hole therein. The rotor has a shaft extending into the bearing hole and is thus rotatably supported by the bearing. 
         [0006]    However, during rotation of the rotor, the rotating blades generate an external air pressure which pulls the rotor to move upwardly along an axial direction away from the stator. When this happens, the rotor is said to be in a “floating” condition. The floating rotor is inclined to generate noise, which may be annoying or even unacceptable. 
         [0007]    What is desired, therefore, is a heat dissipation fan which can overcome the above-described shortcomings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is an isometric, assembled view of a heat dissipation fan according to an exemplary embodiment of the present disclosure. 
           [0009]      FIG. 2  is an exploded view of the heat dissipation fan of  FIG. 1 . 
           [0010]      FIG. 3  is similar to  FIG. 2 , but showing the exploded heat dissipation fan inverted. 
           [0011]      FIG. 4  is a cross-section of the heat dissipation fan of  FIG. 1 , taken along line IV-IV thereof. 
       
    
    
     DETAILED DESCRIPTION 
       [0012]    Reference will now be made to the figures to describe an embodiment of the present heat dissipation fan in detail. 
         [0013]    Referring to  FIGS. 1 and 2 , a heat dissipation fan includes a housing  10 , a rotor  30  and a stator  20 . The rotor  30  is rotatable about the stator  20 . 
         [0014]    The housing  10  is generally in the form of a hollow rectangular frame, and includes a top wall  11 , a bottom wall  12  parallel to and spaced from the top wall  11 , and an annular side wall  13  connected between the top wall  11  and the bottom wall  12 . An air inlet  40  is defined in a central portion of the top wall  11 . An air outlet  50  aligned with the air inlet  40  is defined in a central portion of the bottom wall  12 . The housing  10  also includes a base  121  located at a center of the air outlet  50 , a central tube  123  extending upward from the base  121 , and a plurality of ribs  122  extending radially from an outer periphery of the base  121  to connect an inner periphery of the bottom wall  12 . The central tube  123  defines a central hole  124  therein, and thus includes an open top end. The central hole  124  extends along an axial direction of the central tube  123  for receiving a bearing  14  therein. 
         [0015]    The stator  20  includes a stator core  22 , a plurality of coils  24  wound on the stator core  22 , a pair of insulation frames  26 , and a PCB (printed circuit board)  28  connected to the coils  24  electrically. In this embodiment, there are four coils  24 . Referring also to  FIGS. 3 and 4 , the stator core  22  is made of metallic material, and includes layered yokes  221  stacked along a bottom to top direction thereof. Referring back to  FIG. 2 , each of the yokes  221  includes an annular plate  223  and a plurality of T-shaped arms  224  extending outwardly from an outer periphery of the annular plate  223 . In the present embodiment, there are four arms  224 , which are equally spaced from each other along a circumference direction of the annular plate  223 . Inner diameters of the annular plates  223  of the yokes  221  are substantially the same. Outer edges of the arms  224  of each yoke  221  are located on a same imaginary circle, which has a common center with the annular plate  223 . A diameter of the imaginary circle is a diameter of the yoke  221 . The diameters of the yokes  221  are different from each other. 
         [0016]    More specifically, the diameters of the yokes  221  gradually decrease from a bottommost yoke  221  to a topmost yoke  221  along a stacking direction thereof. Accordingly, when the yokes  221  are stacked together to form the stator core  22 , a cylindrical receiving space  220  is defined in a central portion of the stator core  22  cooperatively by inner edges of the annular plates  223  of the yokes  221 ; and the outer edges of the arms  224  cooperatively define a tapered (frustoconical) outer surface  222 . The receiving space  220  is configured for receiving the central tube  123  therein. A diameter of the tapered outer surface  222  gradually decreases from a bottom end of the stator core  22  to a top end of the stator core  22 . That is, an outer size of the stator core  22  decreases gradually along an axial direction from the bottom end to the top end thereof. 
         [0017]    The insulation frames  26  are mounted to top and bottom ends of the stator core  22 , respectively. Each insulation frame  26  includes an annular portion  262 , and a plurality of claws  264  extending outwardly and radially from an outer periphery of the annular portion  262 . The annular portion  262  corresponds to the annular plates  223  of the yokes  221 , and the claws  264  correspond to the arms  224  of the yokes  221 . Thus there are four claws  264 , which are equally spaced from each other along a circumference direction of the annular portion  262 . The coils  24  wind around the claws  264  of the insulation frames  26  and corresponding portions of the arms  224  to establish an alternating magnetic field in operation of the heat dissipation fan. The insulation frames  26  space the coils  24  from the stator core  22 , thereby preventing the coils  24  from coming into electrical contact with the stator core  22 . The PCB  28  with electronic components mounted thereon is electrically connected to the coils  24  to control electrical current flowing through the coils  24 . 
         [0018]    The rotor  30  includes a hub  32  having a shaft  321  extending downward and perpendicularly from a central portion thereof, a plurality of blades  36  extending radially from an outer side of the hub  32 , and a magnetic element  34  adhered to an inner side of the hub  32 . The shaft  321  has a fixed end  322  connected with the hub  32  and a free end  323  away from the hub  32 . The magnetic element  34  is annular shaped (i.e., shaped like a hollow cylinder). An inner diameter of the magnetic element  34  is slightly larger than the largest outer diameter of the stator core  22 . An outer diameter of the magnetic element  34  is slightly larger than an inner diameter of the hub  32 , such that the magnetic element  34  can be interferentially fitted into the hub  32 . The magnetic element  34  can be a permanent magnet, or a magnetizing magnet which is made of non-magnetic material magnetized to create a persistent magnetic field. 
         [0019]    When the heat dissipation fan is assembled, the stator  20  is mounted around the central tube  123 , with the PCB  28  located on the base  121  of the housing  10 . The rotor  30  is positioned over the stator  20 , and is assembled to the stator  20  via the shaft  321  being rotatably received in the bearing  14 . An inner surface  140  of the magnetic element  34  faces and is spaced from the tapered outer surface  222  of the stator core  22 , with a generally annular clearance  60  defined therebetween. A width of the clearance  60  increases along an axial direction from the bottom end of the stator core  22  to the top end of the stator core  22 . That is, a distance between the tapered outer surface  222  of the stator core  22  and the inner surface  140  of the magnetic element  34  increases along the axial direction from the bottom end of the stator core  22  to the top end of the stator core  22 . Thus, a magnetic attracting force formed between the stator core  22  and the magnetic element  34  increases along the axial direction from the top end of the stator core  22  to the bottom end of the stator core  22 . 
         [0020]    In this embodiment, along the axial direction of the stator core  22 , the distance between the top end of the stator core  22  and the magnetic element  34  is largest, and the distance between the bottom end of the stator core  22  and the magnetic element  34  is smallest, such that the magnetic attracting force formed between the top end of the stator core  22  and the magnetic element  34  is smallest and the magnetic attracting force formed between the bottom end of the stator core  22  and the magnetic element  34  is largest. 
         [0021]    During operation of the heat dissipation fan, the rotor  30  is driven to rotate by the interaction of the alternating magnetic field established by the coils  24  of the stator  20  and the magnetic field of the magnetic element  34  of the rotor  30 . Thus rotation of the rotor  30  generates a forced airflow for cooling electronic packages, such as CPUs. 
         [0022]    Due to the magnetic attracting force formed between the stator core  22  and the magnetic element  34  decreasing along the axial direction from the bottom end of the stator core  22  to the top end of the stator core  22 , a larger magnetic attraction force acting on the magnetic element  34  is generated by the bottom end of the stator core  22 . When rotation of the rotor  30  generates an external air pressure tending to pull the rotor  30  upwardly along the axial direction thereof, simultaneously, the bottom end of the stator core  22  attracts the magnetic element  34  of the rotor  30  and tends to pull the rotor  30  downwardly along the axial direction thereof. That is, the greater magnetic attraction of the bottom end of the stator core  22  counteracts the effect that the external air pressure would otherwise have on the rotor  30 . Thus axially upward movement and floating of the rotor  30  during operation of the heat dissipation fan is avoided, and any problem of noise generated by floating of the rotor  30  is correspondingly avoided. 
         [0023]    It is to be further understood that even though numerous characteristics and advantages have been set forth in the foregoing description of embodiments, together with details of the structures and functions of the embodiments, the disclosure is illustrative only; and that changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the disclosure to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.