Patent Publication Number: US-2009232678-A1

Title: Heat dissipation fan

Description:
BACKGROUND  
     1. Technical Field 
     The present invention relates to a heat dissipation fan, and more particularly relates to a heat dissipation fan which has a good lubricating effect. 
     2. Description of Related Art 
     With the continuing development of the electronic technology, electronic packages such as CPUs (central processing units) are generating more and more heat that is required to be dissipated immediately. Heat dissipation fans are commonly used in combination with heat sinks for cooling CPUs. Performances of heat dissipation fans mostly depend on performances of bearings used in the heat dissipation fans. Good lubricating qualities of the bearings increase the life-span of the bearings. 
     A typical heat dissipation fan comprises a fan housing having a central tube extending upwardly therefrom, a bearing received in the central tube, a stator mounted around the central tube, 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 central tube has an opening defined at a top end thereof. The bearing is inserted into the central tube through the opening. Lubricating oil is injected into the central tube to lubricate the bearing and the shaft. A lubricating effect of the bearing and the shaft can be properly maintained when the heat dissipation fan is vertically mounted. However, when the heat dissipation fan is mounted in an upside-down manner, the lubricating oil will leak out of the central tube through the opening of the central tube and the amount of the lubricating oil in the bearing is thus gradually reduced. The friction between the shaft and the bearing is therefore increased due to a decrease of the lubricating oil, which results in uncomfortable noise or malfunction being generated. As a result, the performance of the heat dissipation fan deteriorates, and the life-span of the fan is accordingly shortened. 
     What is needed, therefore, is a heat dissipation fan which can reduce or eliminate a leakage of the lubricant oil from the bearing thereof. 
     SUMMARY 
     The present invention relates to a heat dissipation fan. According to an embodiment of the present invention, the heat dissipation fan includes a fan housing, a bearing assembly, a stator and a rotor. The fan housing includes a base and a central tube extending upwardly from a top surface of the base. The bearing assembly includes a bearing received in the central tube and defining a bearing hole therein, a porous wick element and a locking washer. The stator is mounted around the central tube. The rotor includes a shaft extending through the bearing hole of the bearing. The locking washer is mounted around the shaft and fixed on a top end of the central tube. The locking washer, the bearing and the shaft cooperatively form an oil reservoir in the top end of the central tube. The porous wick element is received in the oil reservoir and physically contacts with the bearing. 
     Other advantages and novel features of the present invention will become more apparent from the following detailed description of preferred embodiment when taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  an assembled, isometric view showing a heat dissipation fan in accordance with an embodiment of the present invention. 
         FIG. 2  is an exploded, isometric view of the heat dissipation fan of  FIG. 1 . 
         FIG. 3  is a view similar to  FIG. 2 , but shown in an up-side-down aspect. 
         FIG. 4  is a cross-section view of the heat dissipation fan of  FIG. 1 , taken along line IV-IV thereof. 
         FIG. 5  is an enlarged view of a circled portion V of  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENT 
     Reference will now be made to the drawings to describe the various present embodiments in detail. 
     Referring to  FIGS. 1-3 , a heat dissipation fan according to an embodiment includes a rotor  40 , a stator  30  in respect to which the rotor  40  is rotatable, a fan housing  10  receiving the rotor  40  and the stator  30  therein, and a bearing assembly  20 . 
     The fan housing  10  comprises a base  12  and a central tube  14  extending upwardly from a top surface of a central portion of the base  12 . The central tube  14  defines a central hole  142  therein and forms an open end at a top portion thereof. An annular recess  144  is formed on an inner circumference of the top portion of the central tube  14 . The annular recess  144  communicates with the central hole  142 . The top portion of the central tube  14  has an inner diameter which is larger than that of the other portion of the central tube  14 . A receiving concave  120  is formed on a bottom surface of the central portion of the base  12 . The receiving concave  120  faces opposite to the central hole  142  of the central tube  14  and is isolated from the central hole  142  of the central tube  14  by the base  12 . In other words, the receiving concave  120  is aligned with the central hole  142 , but does not communicate with the central hole  142 . 
     The stator  30  comprises a stator core  33  consisting of several layers of yokes, stator coils  35  wound around the stator core  33  to establish an alternating magnetic field, and a PCB (printed circuit board)  31  electrically connected with the stator coils  35 . To avoid the coils  35  from electrically contacting with the stator core  33 , upper and lower insulating frames  37  are used to cover the stator core  33  and electrically insulate the stator coils  35  from the stator core  33 . 
     The rotor  40  comprises a hub  42  forming downwardly a shaft seat  46  at a central portion thereof, a plurality of fan blades  44  extending radially outwardly from an outer periphery of the hub  42 , an annular magnet  45  adhered to an inner surface of the hub  42 , and a shaft  47  retained in and extending downwardly from the shaft seat  46 . The shaft  47  defines an annular slot  471  in a circular circumference thereof, at a position near a top end of the shaft  47  which locates adjacent to the hub  42 . A cylindrical protrusion  48  extends downwardly from the hub  42 , wherein the protrusion  48  surrounds and spaces a distance from the shaft seat  46 . The protrusion  48  and the shaft seat  46  cooperatively define an annular chamber  480  therebetween. 
     The bearing assembly  20  comprises a wear pad  21 , a bearing  23 , a porous wick element  24 , a locking washer  25  and a magnetic unit  27 . The bearing  23  is a sleeve bearing and made from sintering powders such as copper powders or ceramic powders. A plurality of pores (not shown) are defined in the bearing  23  and communicate with each other. The bearing  23  is received in the central hole  142  of the central tube  14  via the open end of the central tube  14 . The bearing  23  defines an axial hole  231  therein for extension of the shaft  47  therethrough. A circular cavity  232  is formed in a top portion of the bearing  23 . The cavity  232  communicates with the axial hole  231 . Thus, the top portion of the bearing  23  has an inner diameter which is larger than that of the other portion of the bearing  23 . Two channels  234  are axially defined in an outer surface of the bearing  23 . The channels  234  communicate with the axial hole  231  of the bearing  23  for guiding oil at the top portion of the bearing  23  to return back to a bottom portion of the bearing  23 . 
     The porous wick element  24  is cylindrically-shaped in configuration. The porous wick element  24  is made of a porous material, such as polyurethane foam plastic, foamed metal or sponge. The porous wick element  24  is received in the cavity  232  of the bearing  23 . More specifically, a bottom surface and an outer circumference surface of the porous wick element  24  are interferentially and physically respectively attached to a top surface and a side surface of the bearing  23  defining the cavity  232 . A plurality of pores (not shown) are defined in the porous wick element  24  and communicate with each other. 
     The locking washer  25  is made of a material having high strength, high abrasion resistance and low friction factor, such as nylon. Referring to  FIGS. 4-5 , the locking washer  25  comprises a cylindrical mounting portion  251 , a retaining ring  253  extending inwardly from a top end of the mounting portion  251 , and a flange  255  extending upwardly and perpendicularly from a top surface of the retaining ring  253 . The flange  255  offsets inwardly a distance with respect to the mounting portion  251 . An inner diameter of the flange  255  is greater than an inner diameter of the retaining ring  253 . 
     The mounting portion  251  has an outer diameter substantially equals to the diameter of the annular recess  144  of the central tube  14 . The retaining ring  253  extends horizontally from the top end of the mounting portion  251  towards the slot  471  of the shaft  47 , and substantially covers the open end of the central tube  14 . The retaining ring  253  defines an inner hole  250  in a middle portion for extension of the shaft  47  therethrough. A diameter of the inner hole  250  of the retaining ring  253  is slightly larger than a diameter of an outer surface of the shaft  47  at the slot  471 , but smaller than a diameter of the other portion of the shaft  47 . Thus, the retaining ring  253  of the locking washer  25  is engaged in the slot  471  of the shaft  47  to limit an axial movement of the shaft  47 . A narrow gap is defined between an inner circumferential surface of the retaining ring  253  and the outer surface of the shaft  47  defining the slot  471 , in order to avoid an interference between the shaft  47  and the retaining ring  253  during rotation of the shaft  47 . The flange  255  and the mounting portion  251  are staggered to each other, thereby forming a step  254  on the top surface of the retaining ring  253  above the mounting portion  251 . In other words, the step  254  is formed between the mounting portion  251  and the flange  255 . A diameter of the flange  255  is smaller than a diameter of the protrusion  48  of the hub  42 . The flange  255  extends upwardly from the top surface of the retaining ring  253  into the annular chamber  480 . 
     The wear pad  21  is made of high abrasion resistant material. The wear pad  21  is mounted in a bottom end of the central hole  142  of the central tube  14 , for supporting a bottom end of the shaft  47 . 
     The magnetic unit  27  comprises a magnetic yoke  273  and a columned magnet  271 . The magnetic yoke  273  is cup-shaped, having a close end and an opposite open end. An axial cross-sectional view of the magnetic yoke  273  is “U” shaped. The magnetic yoke  273  encloses the magnet  271  therein, along with a top surface of the magnet  271  exposed out of the magnetic yoke  273 . Bottom surface and side surface of the magnet  271  are affixed to an inner surface of the magnetic yoke  273  to connect the magnet  271  and the magnetic yoke  273  together. 
     When assembled, the bearing  23  is mounted into the central tube  14 , and the shaft  47  is rotatably received in the bearing  23 . The porous wick element  24  is received in the cavity  232  of the bearing  23 . The mounting portion  251  is pressingly fitted in the annular recess  144  of the central tube  14 . The top portion of the central tube  14  is bent inwardly to form a pressing portion  145  abutting on the step  254  of the retaining ring  253  for keeping the locking washer  25  and the bearing  23  in the central tube  14 . The retaining ring  253  of the locking washer  25 , the bearing  23  and the shaft  47  cooperatively form an oil reservoir  50  at the top portion of the bearing  23 . The porous wick element  24  is received in the oil reservoir  50 . The magnet  271  and the magnetic yoke  273  are both received in the receiving concave  120  of the base  12  of the fan housing  10 , wherein the top surface of the magnet  271  faces to the bottom end of the shaft  47 . 
     During operation, the rotor  40  is driven to rotate by the interaction between the alternating magnetic field established by the coils  35  of the stator  30  and the magnet  45  of the rotor  40 . The lubricating oil creeps up along the rotating shaft  47  under the influence of the centrifugal force generated by the rotation of the shaft  47  and then escapes to the oil reservoir  50  through a clearance defined between the top end of the bearing  23  and the shaft  47 . The slot  471  of the shaft  47  prevents the oil from continuously creeping up along the shaft  47 . Since the oil reservoir  50  is almost hermetically sealed by the retaining ring  253 , the retaining ring  253  can prevent the lubricating oil from leaking out of the oil receiver  50 . 
     As the porous wick element  24  defines a plurality of pores therein, the porous wick element  24  can absorb the lubricating oil accumulated in the oil receiver  50 , thereby further preventing the lubricating oil from leaking out of the oil receiver  50 . The porous wick element  24  then returns the lubricating oil back to the bearing  23  under a capillary force generated by the pores of the bearing  23 . The porous wick element  24  can absorb the lubricating oil in the oil reservoir  50  and prevent the lubricating oil from leaking out of oil reservoir  50  whether the heat dissipation fan is positioned in a top side up manner, a lain down manner, or an upside-down manner according to requirements. Preferably, the pores defined in the porous wick element  24  have an average pore size lager than that of the pores defined in the bearing  23 , which makes the bearing  23  generate a larger capillary force than the porous wick element  24  to accelerate the lubricating oil flowing back to the bearing  23  from the porous wick element  24 . Thus, the lubricating oil is kept from leaking out of the bearing  23 . Good lubrication of the bearing  23  and the shaft  47  is thus consistently maintained, thereby improving the quality and life-span of the heat dissipation fan. 
     Moreover, the flange  255  of the locking washer  25  can further prevent the lubricating oil from leaking out of the oil reservoir  50 . The bottom surface and the side surface of the magnet  271  are covered by the magnetic yoke  273 , which prevents magnetic energy from leaking out from the magnetic yoke  273 . Thus, the magnet  271  can generate a magnetic attraction force which attracts the shaft  47  to always maintain in contact with the wear pad  21  and prevents the shaft  47  from floating along an axial direction of the bearing  23 . The axially upward movement of possible floating of the rotor  40  during operation of the heat dissipation fan is avoided, whereby the rotor  40  is maintained to rotate steadily. 
     It is to be understood, however, that even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function 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 invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.