Abstract:
A cooling fan includes a stator, a base supporting the stator, and a rotor positioned to rotate with respect to the stator. The base includes a bearing housing and a central hole defined in the bearing housing. The rotor includes a hub and a shaft extending from the hub. An end of the shaft is fixed in the hub, and another end of the shaft is extending in the central hole defined in the bearing housing. The bearing housing includes a main cylindrical portion and a protruding portion bent radially inward from a top end of the main portion, and the protruding portion thus serves as a lubricant retaining portion of the bearing housing.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The present disclosure relates to a cooling fan typically employed in an electronic device such as a computer, and more particularly to a cooling fan which has a bearing housing with a bent end in order to retain lubricant in the bearing housing. 
         [0003]    2. Description of Related Art 
         [0004]    With the continuing development of electronics technology, heat-generating electronic components such as CPUs (central processing units) are generating more and more heat when in operation. In typical devices that employ CPUs, the heat requires immediate dissipation. Cooling fans are commonly used in combination with heat sinks for cooling the CPUs. 
         [0005]    A typical cooling fan comprises a fan housing having a bearing housing extending upwardly therefrom, a bearing received in the bearing housing, a stator mounted around the bearing housing, and a rotor rotatable with respect to the stator. The rotor includes a hub and a shaft extending from the hub into the bearing. The bearing housing has an opening defined at a top end thereof. In assembly of the cooling fan, the bearing is inserted into the bearing housing through the opening. Lubricant is injected into the bearing housing to lubricate the bearing and the shaft. Traditionally, a discrete retaining ring is located at the top end of the bearing housing to retain the lubricant in the bearing housing, so as to maintain the lubrication of the bearing and the shaft. 
         [0006]    However, rotation of the rotor with respect to the stator during the working lifetime of the cooling fan is liable to cause the discrete retaining ring to loosen and become deformed. As such, there is a high risk of the lubricant leaking out of the bearing housing, resulting in increased friction between the shaft and the bearing. When this happens, the performance of the cooling fan deteriorates, and the lifespan of the cooling fan is shortened. 
         [0007]    What is needed, therefore, is an improved cooling fan which can overcome the above-described shortcomings 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is an assembled view of a cooling fan according to an exemplary embodiment of the present disclosure. 
           [0009]      FIG. 2  is essentially an exploded view of the cooling fan of  FIG. 1 , showing the parts prior to assembly of the cooling fan, including a bearing housing partly cut away for clarity. 
           [0010]      FIG. 3  is an enlarged view of a circled portion III of  FIG. 2 . 
           [0011]      FIG. 4  is an inverted view of  FIG. 2 . 
           [0012]      FIG. 5  is an abbreviated, cross-sectional view of the cooling fan of  FIG. 1 , taken along a line V-V thereof. 
           [0013]      FIG. 6  is an enlarged view of a circled portion VI of  FIG. 5 . 
           [0014]      FIG. 7  is an abbreviated, cross-sectional view of a cooling fan according to another exemplary embodiment of the present disclosure. 
           [0015]      FIG. 8  is an enlarged view of a circled portion VIII of  FIG. 7 . 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    Exemplary embodiments of a cooling fan in accordance with the present disclosure will now be described in detail below and with reference to the drawings. 
         [0017]      FIGS. 1 and 2  show a cooling fan  100  in accordance with an exemplary embodiment of the disclosure. The cooling fan  100  includes a fan housing  10 , a bearing assembly  20 , a stator  30 , and a rotor  50 . The rotor  50  surrounds the stator  30 . The stator  30  and the rotor  50  are received in the fan housing  10 . 
         [0018]    The fan housing  10  includes a plate  11 , a sidewall  13  extending vertically and upwardly from a circumferential edge of the plate  11 , and a bearing housing  14  extending vertically and upwardly from a center of the plate  11 . 
         [0019]    The plate  11  is flat, and an air inlet  111  is defined in a central portion of the plate  11 . In particular, the air inlet  111  occupies an annular area, and in this embodiment includes three centrosymmetric openings. Thus the plate  11  includes a base  113  located in a center of the air inlet  111 , and three connecting sheets  115  extending from a periphery of the base  113  to connect with portions of the plate  11  surrounding the air inlet  111 . In this embodiment, the base  113  and the connecting sheets  115  are integral portions of the plate  11 . 
         [0020]    The bearing housing  14  is formed on the center of the base  113 . In this embodiment, the bearing housing  14  is integrally formed with the base  113 . That is, the bearing housing  14  is integrally formed with the plate  11 , with the bearing housing  14  and the plate  11  being a single monolithic body of the same material. 
         [0021]    The sidewall  13  includes an arc-shaped surrounding wall  131  surrounding a majority of the rotor  50 , a first air-guiding wall  133 , and a second air guiding wall  135 . The first air-guiding wall  133  and the second air-guiding wall  135  extend outwardly from two ends of the surrounding wall  131 , respectively. The first air-guiding wall  133  and the second air-guiding wall  135  are spaced from and parallel to each other, whereby an air outlet  134  is defined therebetween. 
         [0022]    The bearing housing  14  is a central tube and extends from the center of the base  113 . A central hole  140  vertical to the base  113  is defined in the bearing housing  14 . The bearing housing  14  has an opening defined at a top end of the central hole  140 . The central hole  140  has a uniform inner diameter throughout its axial length. 
         [0023]    Referring to  FIG. 3 , the bearing housing  14  includes a main portion  141 , and a protruding portion  145  extending upwardly from a top end of the main portion  141  away from the base  113 . 
         [0024]    The main portion  141  is cylindrical, and extends vertically and upwardly from the center of the base  113 . The protruding portion  145  extends upwardly from the center of the top end of the main portion  141 . The central hole  140  extends through the bearing housing  14  from a top end of the protruding portion  145  to a bottom end of the main portion  141  connecting the base  113 . Inner cylindrical surfaces of the main portion  141  and the protruding portion  145  are coplanar. The protruding portion  145  is cylindrical (or annular), and an outer diameter thereof is smaller than an outer diameter of the main portion  141 . 
         [0025]    The bearing assembly  20  includes a bearing  21  and a disk  23 . The bearing  21  is a sleeve bearing and made from sintered powder such as copper powder or ceramic powder. A plurality of pores (not shown) is defined in the bearing  21 , and the pores communicate with each other. The bearing  21  is received in the central hole  140  of the bearing housing  14  via the opening of the bearing housing  14 . The bearing  21  defines an axial hole  211  therein. A plurality of channels  213  is defined in the bearing  21 . Each channel  213  extending from a center of a top end of the bearing  21  radially outward to a peripheral side surface of the bearing  21 , and then down along a peripheral wall of the bearing  21  along a direction parallel to a axis of the bearing  21  to a bottom of the bearing  21 . Thus, each channel  213  is L-shaped, and innermost extremities of the channels  213  at the top end of the bearing  21  communicate with the axial hole  211  of the bearing  21 . The channels  213  are radially symmetrically arranged around the axis of the bearing  21 . With the above-described configuration, lubricant at the top of the axial hole  211  is guided to a top portion of the bearing  21 , and then returns to a bottom portion of the bearing  21  (see below). The disk  23  is made of wear-resistant material, and is located at a bottom end of the central hole  140 . 
         [0026]    The stator  30  includes an iron core  31 , a coil  33 , a circuit board  35 , and an insulating frame  37 . The insulating frame  37  encloses the iron core  31  therein. The coil  33  is twined around the insulating frame  37 . The circuit board  35  is located at a bottom end of the insulating frame  37  and electrically connected with the coil  33 . The core  31 , the insulating frame  37  and the circuit board  35  are arranged along a common axis. As such, a mounting hole  39  is commonly defined through the core  31 , the insulating frame  37  and the circuit board  35 . 
         [0027]    Referring to  FIG. 4 , the rotor  50  includes a hub  51 , a shaft  53 , a magnetic ring  55 , and a plurality of fan blades  57 . 
         [0028]    The hub  51  includes a circular base plate  511 , and a surrounding sidewall  513  extending vertically and upwardly from a circumferential edge of the base plate  511 . A fixing seat  5112  is formed in a center of the base plate  511 , and the fixing seat  5112  fixes a top end of the shaft  53  therein. A free end of the shaft  53  extends down away from the fixing seat  5112 . Preferably, the shaft  53  defines an annular slot  531  in a circumferential wall thereof, at a position near a top end of the shaft  53  close to the hub  51 . 
         [0029]    The magnetic ring  55  is attached to the inner surface of the sidewall  513 . The fan blades  57  extend radially and outwardly from a periphery of the hub  51 . An inner diameter of the magnetic ring  55  and an inner diameter of the hub  51  are both larger than an outer diameter of the iron core  31  and an outer diameter of the insulating frame  37 , so that the iron core  31  and the insulating frame  37  can be received in the magnetic ring  55  and the hub  51 . 
         [0030]    The hub  51  encloses the stator  30  and the magnetic ring  55  therein. The magnetic ring  55  is spaced from the iron core  31  and surrounds the periphery of the iron core  31 . 
         [0031]    Referring to  FIGS. 5 and 6 , when assembling the cooling fan  100 , the disk  23  is inserted into and located at the bottom of the central hole  140 . The bearing  21  is inserted into the central hole  140 . The top end of the bearing  21  is lower than the top end of the protruding portion  145 , and the bottom end of the bearing  21  abuts against the disk  23 . Then, the protruding portion  145  of the bearing housing  14  is bent radially and inwardly to form a lubricant retaining portion  1451 . The lubricant retaining portion  1451  is annular, and defines a through hole  1453  in the center thereof. The through hole  1453  communicates with the central hole  140 , and is aligned with the axial hole  211 . An inner diameter of the through hole  1453  and an inner diameter of the axial hole  211  are both slightly larger than an outer diameter of the shaft  53 . The free end of the shaft  53  is extended through the through hole  1453  of the lubricant retaining portion  1451  and the axial hole  211  of the bearing  21  sequentially, to abut against the disk  23 . In this embodiment, the lubricant retaining portion  1451  is formed by hot-melting the protruding portion  145  sufficiently to allow it to be bent. 
         [0032]    The lubricant retaining portion  1451  is located between the bottom end of the fixing seat  5112  and the slot  531 . An upper surface of the lubricant retaining portion  1451  is near and spaced from the bottom end of the fixing seat  5112 , to define a gap  1500  therebetween. The gap  1500  helps ensure that the fixing seat  5112  does not interfere with the lubricant retaining portion  1451 . The slot  531  is located in the central hole  140 , and completely below the lubricant retaining portion  1451 . 
         [0033]    An annular narrow space  1600  is defined between the inner edges of the lubricant retaining portion  1451  and a periphery of the shaft  53 . The space  1600  helps ensure that the shaft  53  rotates within the lubricant retaining portion  1451  without friction. Preferably, as indicated above, the lubricant retaining portion  1451  is located above the slot  531 , surrounding the shaft  53 . Alternatively, the lubricant retaining portion  1451  can extend into the slot  531  (see  FIGS. 7 and 8 ). 
         [0034]    Furthermore, the lubricant retaining portion  1451 , the bearing  21  and the shaft  53  cooperatively form a lubricant reservoir  60  above the top portion of the bearing  21 . During operation, the rotor  50  is driven to rotate by the interaction between an alternating magnetic field established by the outer cores  31  of the stator  30  and the magnetic ring  55  of the rotor  50 . Lubricant creeps up along the rotating shaft  53  under the influence of the centrifugal force generated by the rotation of the shaft  53 , and then escapes to the lubricant reservoir  60  through in a very small cylindrical clearance  1700  located between the bearing  21  and the shaft  53 . When the lubricant reaches the top end of the bearing  21 , the lubricant escapes into the lubricant reservoir  60 . As indicated above, the lubricant reservoir  60  is cooperatively defined between the top end of the bearing  21 , the lubricant retaining portion  1451  and the shaft  53 . The slot  531  of the shaft  53  prevents the lubricant from continuously creeping up along the shaft  53 . Since the lubricant reservoir  60  is almost or substantially hermetically sealed by the retaining portion  1451 , the retaining portion  1451  can prevent the lubricant from leaking out of the lubricant reservoir  60 . In addition, the lubricant in the lubricant reservoir  60  is guided by the channels  213  to return to the bottom portion of the bearing  21 , which helps maintain the lubrication of the bearing  21  and the shaft  53 . 
         [0035]    In summary, the lubricant retaining portion  1451  is formed by bending the protruding portion  145  of the bearing housing  14  which is formed integrally with the base  113 . Therefore no discrete retaining ring or locking disk is needed to prevent the lubricant from leaking out of the lubricant reservoir  60 , which increases the efficiency of assembling the cooling fan  100  and reduces costs. Furthermore, because the lubricant retaining portion  1451  is located below the fixing seat  5112  with the upper surface of the lubricant retaining portion  1451  being spaced by the gap  1500  from the fixing seat  5112 , the bottom end of the fixing seat  5112  does not interfere with the lubricant retaining portion  1451  when the rotor  50  is rotating relative to the bearing  21  at high speed. Moreover, with the narrow space  1600 , the shaft  53  does not interfere with the inner edges of the lubricant retaining portion  1451 . 
         [0036]    It is to be understood, however, that even though numerous characteristics and advantages of the embodiments have been set forth in the foregoing description, together with details of the structures and functions of the embodiments, the disclosure is illustrative only, and 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.