Patent Publication Number: US-8123475-B2

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 having an improved bearing assembly. 
     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 requires immediate dissipation. Heat dissipation fans are commonly used in combination with heat sinks for cooling CPUs. 
     A conventional heat dissipation fan includes a fan frame having a central tube extending upwardly from a base thereof, 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. An annular recess is defined in a top portion of the central tube and above a top end of the bearing. 
     When assembled, lubricating oil is injected into the central tube to lubricate the bearing and the shaft, and an oil retaining ring around the shaft is pressingly fitted in the annular recess of the central tube. Then, the top portion of the central tube is bent inwardly via a hot-melting tool to form a pressing portion abutting on a top surface of the oil retaining ring, and therefore an interior oil space of the central tube is almost hermetically sealed by the retaining ring for preventing the lubricating oil from leaking out of the central tube. However, when there is a requirement to replace the bearing received in the central tube, the original fan frame must be totally discarded as the hot-melting connection between the retaining ring and the central tube of the fan frame, which results in increasing cost of the heat dissipation fan. Additionally, the assembly of the retaining ring is completed via the hot-melting tool, which increases a complexity of the assembly process of the heat dissipation fan. 
     It is thus desirable to provide a heat dissipation fan which can overcome the described limitations. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an isometric, assembled view of a heat dissipation fan according to an exemplary embodiment. 
         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 an enlarged view of a circled portion IV of  FIG. 3 . 
         FIG. 5  is a cross-section of the heat dissipation fan of  FIG. 1 , taken along line V-V thereof. 
         FIG. 6  is an enlarged view of a circled portion VI of  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made to the drawing figures to describe the present heat dissipation device in detail. 
     Referring to  FIGS. 1-3 , a heat dissipation fan includes a rotor  40 , a stator  30  in respect to which the rotor  40  is rotatable, a fan frame  10  receiving the rotor  40  and the stator  30  therein, and a bearing assembly  20 . 
     The fan frame  10  includes a base  12  and a central tube  14  extending upwardly from a central portion of the base  12 . The central tube  14  has a central hole  142  extending therethrough along an axis thereof, and thus forms an open top end and an open bottom end at two opposite ends, respectively. A pressing portion  145  protrudes radially and inwardly from the open top end of the central tube  14 . Thus, the central tube  14  has an inner diameter at the pressing portion  145  smaller than the inner diameter at the other portion of the central tube  14 . A receiving concave  122  is concaved from a bottom surface of the central portion of the base  12 . The receiving concave  122  is coaxial with the central hole  142  of the central tube  14  and communicates with the central hole  142 . A diameter of the receiving concave  122  is larger than the inner diameter of the central tube  14 . Referring to  FIG. 4 , a top wall  1221  is formed by the base  12  at the bottom end of the central tube  14 , and is located between the receiving concave  122  and the central hole  142 . The top wall  1221  is annular and horizontal. A sidewall  1223  is formed by the base  12  around the receiving concave  122 , interconnecting an outer periphery of the top wall  1221  and an inner periphery of the bottom surface of the base  12 . 
     A plurality of first locking units  146  extend downwardly from an inner periphery of the top wall  1221 , and are evenly disposed along a circumferential direction of the top wall  1221 . There are four first locking units  146  provided in this preferred embodiment. Each of the first locking units  146  includes a fixing pole  1461  extending downwardly from the top wall  1221  and a hook  1463  extending outwardly from a bottom end of the pole  1461  towards the sidewall  1223 . Each of the hooks  1463  faces the sidewall  1223 , and spaces a distance from the sidewall  1223 . 
     The bearing assembly  20  includes a locking washer  21 , a bearing  23 , a porous wick element  24 , a wear pad  29 , a magnetic unit  27 , and an oil sealing cover  26 . The bearing  23  is a sleeve bearing and made from sintering powers 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 . The bearing  23  defines an axial hole  231  therein for extension of a shaft  47  of the rotor  40  therethrough. The shaft  47  defines an annular slot  471  in a circumferential surface  470  thereof, at a position near a top end of the shaft  47 . A circular cavity  232  is formed in a top portion of the bearing  23  with a diameter larger than that of the axial hole  231 . 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 , and therefore an annular step surface  233  is formed at the top 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 circumferential surface of the porous wick element  24  are interferentially and intimately attached to the step surface  233  of the bearing  23  and an inner circumferential surface of the top end of the bearing  23  surrounding the cavity  232 , respectively. A plurality of pores (not shown) are defined in the porous wick element  24  and communicate with each other. 
     The locking washer  21  includes an annular retaining ring  213  and a flange  214  extending upwardly and perpendicularly from a top surface of the retaining ring  213 . The retaining ring  213  defines an inner hole in a middle portion for extension of the shaft  47  therethrough. A diameter of the inner hole of the retaining ring  213  is slightly larger than a diameter of the circumferential surface  470  of the shaft  47  at the slot  471 , but smaller than a diameter of the other portions of the shaft  471 . Thus, the retaining ring  213  of the locking washer  23  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  213  and the circumferential surface  470  of the shaft  47  defining the slot  471 , in order to avoid an interference between the shaft  47  and the retaining ring  213  during rotation of the shaft  47 . The flange  214  offsets inwardly a distance with respect to an outer periphery of the retaining ring  213 . That is, an outer diameter of the retaining ring  213  is larger than an outer diameter of the flange  214 , thereby forming a step  215  on the top surface of the retaining ring  213  adjacent to the outer periphery of the retaining ring  213 . A width of the step  215  substantially equals to a width of the pressing portion  145  of the central tube  14 . The retaining ring  21  substantially seals the open top end of the central tube  14  with the pressing portion  145  abutting on the step  215  of the retaining ring  213 , for blocking the locking washer  21 , the bearing  23 , the wear pad  29 , the magnetic unit  27  and the oil sealing cover  26  from slipping out of the central tube  14  via the open top end. 
     The magnetic unit  27  includes a magnetic yoke  273  and a columned magnet  271 . The magnetic yoke  273  is cup-shaped, and an axial cross-sectional view of the magnetic yoke  273  is “U” shaped. The magnetic yoke  273  encloses the magnet  271  therein, with a top surface of the magnet  271  exposed out of the magnetic yoke  273 . 
     The wear pad  29  is made of high abrasion resistant material. The wear pad  29  is mounted at a bottom end of the bearing  23  for supporting the bottom end of the shaft  47 . 
     The oil sealing cover  26  includes an oil lid  28  and a sealing ring  25 . Referring back to  FIG. 2 , the oil lid  28  includes a circular bottom wall  281 , an annular wall  282  extending upwardly and perpendicularly from the bottom wall  281 , a plurality of protruding members  283  formed on an inner circumferential surface of the annular wall  282  and a plurality of second locking units  285 . A diameter of the bottom wall  281  of the oil lid  28  substantially equals to the diameter of the receiving concave  122 . Thus, the oil lid  28  can be fitly received in the receiving concave  122 . The second locking units  285  are configured for detachably interlocking with the first locking units  146 , respectively, to mount the oil lid  28  in the receiving concave  122  of the base  12  to thereby seal the open bottom end of the central tube  14 . The second locking units  285  are defined in the bottom wall  281  and evenly disposed along a circumferential direction of the bottom wall  281 . Each of the second locking units  285  includes a through hole  2851  immediately adjacent to an outer periphery of the annular wall  282  and a fastening strip  2853  formed by the bottom wall  281  and located at a position radially outwards of the through hole  2851 . The through hole  2851  is for receiving a corresponding pole  1461  of the first locking unit  146  therein, and the fastening strip  2853  is for clasping a corresponding hook  1463  of the first locking unit  146  thereof. 
     The protruding members  283  are evenly disposed along the circumferential direction of the annular wall  282 . Each of the protruding members  283  extends along an axial direction of the annular wall  282 , and forms an inclined guiding surface  2830  on a top side thereof. A top portion of the annular wall  282  has an outer diameter which is smaller than that of a bottom portion of the annular wall  282 , thereby forming a supporting surface  284  at a junction of the top portion and the bottom portion of the annular wall  282 . The outer diameter of the top portion of the annular wall  282  substantially equals to the diameter of the central hole  142  of the central tube  14 . The sealing ring  25  has an inner diameter substantially equals to the outer diameter of the top portion of the annular wall  282 , and has an outer diameter slightly larger than the outer diameter of the bottom portion of the annular wall  282 . 
     Referring to  FIG. 5 , when assembled, the locking washer  21  is firstly mounted into the central tube  14  via the open bottom end of the central tube  14  through the receiving concave  122  at the base  12  of the fan frame  10 , and then the bearing  23  with the porous wick element  24  received in the cavity  232  thereof is mounted into the central tube  14  via the open bottom end. The pressing portion  145  of the central tube  14  abuts on the step  215  of the retaining ring  213  of the locking washer  21  for holding the locking washer  21  and the bearing  23  in the central tube  14 . The shaft  47  extending through the inner hole of the retaining ring  213  is rotatably received in the bearing  23 . The retaining ring  213  of the locking washer  21 , the bearing  23  and the shaft  47  cooperatively form an oil reservoir  50  thereamong, which is positioned at the top portion of the bearing  23 . The porous wick element  24  is received in the oil reservoir  50 . 
     The oil sealing cover  26  is detachably connected to the base  12  of the fan frame  10  via the second locking units  285  of the oil lid  28  interlocked with the first locking units  146  located in the receiving concave  122  of the central tube  14 , for sealing the open bottom end of the central tube  14 . Referring to  FIG. 6 , the bottom wall  281  of the oil lid  28  is pressingly fitted in the receiving concave  122 . The poles  1461  of the first locking units  146  extending downwardly form the top wall  1221  traverse through the through holes  2851  of the bottom wall  281 , respectively, and the hooks  1463  clasp bottom sides of the fastening strips  2853 . The top surface of the bottom wall  281  tightly contacts with a bottom surface of the top wall  1221 . The annular wall  282  extends upwardly into the central hole  142  of the central tube  14  and abutting the bottom end of the bearing  23 . The wear pad  29  and the magnetic unit  27  are received in the annular wall  282  of the oil lid  28 , wherein the protruding members  283  provide a close contact between an outer circumferential surface of the magnetic unit  27  and the inner circumferential surface of the annular wall  282 . The wear pad  29  covers the top surface of the magnet  271  and contacts the bottom end of the shaft  47 . The sealing ring  25  is mounted around the top portion of the annular wall  282  and seated on the supporting surface  284 . The sealing ring  25  is pressingly fitted between an inner circumferential surface of the bottom portion of the central tube  14  and an outer surface of the top portion of the annular wall  282 . Accordingly, the oil sealing cover  26  completely covers the open bottom end of the central tube  14 . The oil sealing cover  26  and the central tube  14  cooperatively form a receiving room having a sealed bottom end for receiving the washer locker  21 , the bearing  23 , the shaft  47 , the wear pad  29  and the magnetic unit  27  therein. 
     During operation, the rotor  40  is driven to rotate by the interaction between the alternating magnetic field established by the stator  30  and the rotor  40 . The magnet  271  of the magnetic unit  27  can generate a magnetic attraction force which attracts the shaft  47  to always maintain in contact with the wear pad  29  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. 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 a 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  213 , the retaining ring  213  can prevent the lubricating oil from leaking out of the oil reservoir  50 . The plurality of pores of the porous wick element  24  can absorb the lubricating oil accumulated in the oil reservoir  50 , thereby further preventing the lubricating oil from leaking out of the oil reservoir  50 . The lubricating oil is then returned back to the bearing  23  from the oil reservoir  50  under a capillary force generated by the pores of the bearing  23 , thus to accelerate the lubricating oil flowing back to the sealed bottom end for circulation. 
     As the oil sealing cover  26  and the central tube  14  cooperatively forming the receiving room which has the sealed bottom end, the lubricating oil flowing back to the bearing  23  is prevented from leakage out of the central tube  14  through the open bottom end thereof. The lubricating oil is blocked from leaking out of the central tube  14 , and 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. On the other hand, as the oil sealing cover  26  is detachably connected to the open bottom end of the central tube  14  via the second locking units  285  of the oil lid  28  interlocked with the first locking units  146 , the bearing assembly  20  can be mounted into/taken out of the central tube  14  via the open bottom end of the central tube  14 . The pressing portion  145  of the central tube  14  is formed by an injection molding of the fan frame  10 , and no hot-melting tool is needed. Moreover, when one part of the bearing assembly  20  is needed to be replaced or repaired, the second locking units  285  of the oil sealing cover  26  can be disengaged form the first locking units  146  of the open bottom end of the central tube  14  easily. Then, the oil sealing cover  26  is dismounted form the open bottom end of the central tube  14 . The oil sealing cover  26  is separated from the base  12  of the fan frame  10 , and the damaged part of the bearing assembly  20  can be replaced. 
     It is to be understood, however, that even though numerous characteristics and advantages of the disclosure 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.