Abstract:
A highly stable and durable fan bearing structure practical for small electronic device application is disclosed to include a bearing block, which has a stepped hub defining a vertically extending axle hole and an inside annular flange inside the axle hole at a distance away from the top opening of the axle hole, a fan blade assembly, which has permanent magnets mounted in a hollow base block thereof and an axle suspending in the hollow base block and inserted into the axle hole and coupled to the inside annular flange of the stepped hub and kept in coincidence with the central axis of the axle hole, and a stator module accommodated in the hollow base block of the fan blade assembly for acting against the permanent magnets to cause rotation of the fan blade assembly upon connection of an electric current.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to an electric fan and more specifically, to fan bearing structure in which the stepped hub has an inside annular flange for the coupling of the axle of the fan blade assembly to keep the axle in coincidence with the central axis of the axle hole of the stepped hub of the bearing block for smooth and stable rotation without noises. 
         [0003]    2. Description of the Related Art 
         [0004]    Following fast development of high technology, electronic devices are created having the characteristic of small size and high performance. In these electronic devices, small electronic components are installed in a limited area. In consequence, a big amount of heat energy is produced during the operation of a high-performance electronic device. Excessive high temperature may cause electronic ionization and thermal stress, resulting in low stability of the electronic device. Therefore, it is important to dissipate heat during the operation of an electronic device. Normally, a cooling fan and a heat sink are directly installed in an electronic device for quick dissipation of heat. 
         [0005]    Therefore, using a fan to dissipate heat from, for example, a CPU has become a requisite measure. A fan general uses a bearing to support the axle of the fan blade assembly, allowing rotation of the fan blade assembly at a high speed. Therefore, a bearing for this purpose must have the features of long working life, low noise level, low power loss and excellent heat dissipation effect. To achieve these objects, an excellent lubrication effect between the bearing and the axle of the fan blade assembly is needed. Excellent lubrication effect between the bearing and the axle of the fan blade assembly lowers friction during rotation of the axle relative to the bearing. Therefore, lubricating oil is commonly used and applied to the bearing and axle of a fan. However, lubricating oil may leak out of the bearing or evaporate if the fan is turned upside down or kept in a horizontal position during packing or delivery of the fan. Further, dust or impurities may enter a gap between the bearing and the axle, causing friction between the bearing and the axle during rotation of the axle. Friction between the bearing and the axle during rotation of the axle results in noises and vibration of the fan blade assembly. 
         [0006]      FIGS. 8 and 9  show a fan bearing structure according to the prior art. According to this design, the bearing A has a body A 1 , an expanded base A 2  at the bottom side of the body A 1 , an axle hole A 3  at the center of the body A 1 , and a plurality of hooks A 4  at the top side of the body A 1  around the axle hole A 3 . The hooks A 4  each have a protruding portion A 5 . After insertion of the axle B 1  of the fan blade assembly B into the axle hole A 3 , the protruding portions A 5  of the hooks A 4  are forced by the springy power of the material of the hooks A 4  into engagement with the annular groove B 2  around the periphery of the axle B 1 , thereby holding the axle B 1  to the bearing A and allowing rotation of the fan blade assembly B relative to the bearing A. 
         [0007]    The aforesaid fan bearing structure is still not satisfactory in function because of the following drawbacks:
   1. The bearing A must have a certain height for receiving the axle B 1  and supporting rotation of the axle B 1 . The design of the hooks A 4  further increases the height of the bearing A. To fit the height of the bearing A, the length of the axle B 1  is relatively increased. Thus, the fan blade assembly B cannot have a low profile for use in an electronic device having light, thin and small characteristics.   2. Because the hooks A 4  are disposed at the top side of the body A 1  around the axle hole A 3  and have the respective protruding portions A 5  suspending in the axle hole A 3 , the hooks A 4  may be permanently deformed or damaged accidentally during insertion of the axle B 1  into the axle hole A 3 , and the axle B 1  may be jammed in the axle hole A 3  of the bearing A in case the hooks A 4  are deformed or damaged.   3. The hooks A 4  have a thin wall of low strength. The clamping force of the hooks A 4  is low. During high-speed rotation of the axle B 1 , the axle B 1  may escape from the constraint of the hooks A 4  and may be unable to keep the axle B 1  in vertical, causing vertical displacement of the fan blade assembly B relative to the bearing A or damage of the hooks A 4 .   4. Because the hooks A 4  have a thin wall of low strength and provide a small clamping force. During high-speed rotation of the axle B 1 , the hooks A 4  may be unable to keep the axle B 1  in vertical, causing vibration of the fan blade assembly B, and vibration of the fan blade assembly B may damage the hooks A 4 .   5. The hooks A 4  are disposed at the top side of the body A 1  and spaced from one another around the axle hole A 3 . In case the hooks A 4  are not accurately positioned or deformed accidentally, the axle B 1  may rub against the hooks A 4  during its high-speed rotation, causing noises or damage of the hooks A 4 .   
 
         [0013]    Therefore, it is desirable to provide a fan bearing structure that eliminates the aforesaid problem. 
       SUMMARY OF THE INVENTION 
       [0014]    The present invention has been accomplished under the circumstances in view. According to one aspect of the present invention, the fan bearing structure comprises a bearing block, which has a stepped hub defining a vertically extending axle hole and an inside annular flange inside the axle hole, a fan blade assembly, which has permanent magnets mounted in a hollow base block thereof and an axle suspending in the hollow base block and inserted into the axle hole and coupled to the inside annular flange of the stepped hub in spot contact with the bottom wall of the stepped hub inside the axle hole and kept in coincidence with the central axis of the axle hole, and a stator module accommodated in the hollow base block of the fan blade assembly for acting against the permanent magnets to cause rotation of the fan blade assembly upon connection of an electric current. This design has the feature of low profile, practical for use in an electronic device having light, thin and small characteristics. 
         [0015]    According to another aspect of the present invention, the inside annular flange is disposed inside the axle hole at a distance away from the top opening of the axle hole such that when the axle of the fan blade assembly is inserted into the axle hole and coupled to the inside annular flange, the axle is stably coupled to the stepped hub for smooth and stable rotation relative to the stepped hub. Further, the stepped hub of the bearing block has vertical crevices that allows radial expansion of the stepped hub for accurate coupling of a neck of the axle to the inside annular flange of the stepped hub. 
         [0016]    According to still another aspect of the present invention, in addition to the function of allowing radial expansion of the stepped hub upon insertion of the axle, the vertical crevices of the stepped hub facilitate mold stripping, preventing damage of the inside annular flange by the mold when stripping the mold during fabrication of the bearing block. By means of the design of the vertical crevices, the formation of the inside annular flange on the inside wall of the stepped hub is simple. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  is an exploded view of a part of a fan bearing structure in accordance with a first embodiment of the present invention. 
           [0018]      FIG. 2  is an exploded view in section of the fan bearing structure in accordance with the first embodiment of the present invention. 
           [0019]      FIG. 3  is sectional assembly view of the fan bearing structure in accordance with the first embodiment of the present invention. 
           [0020]      FIG. 4  is an enlarged view of a part of  FIG. 3 . 
           [0021]      FIG. 5  is sectional side view of a fan bearing structure in accordance with a second embodiment of the present invention. 
           [0022]      FIG. 6  is a sectional side view of a fan bearing structure in accordance with a third embodiment of the present invention. 
           [0023]      FIG. 7  is an elevational view of a bearing block for a fan bearing structure in accordance with a fourth embodiment of the present invention. 
           [0024]      FIG. 8  is an elevational view of a bearing block for a fan bearing structure according to the prior art. 
           [0025]      FIG. 9  is a sectional assembly view of the fan bearing structure according to the prior art. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0026]    Referring to  FIGS. 1˜4 , a fan bearing structure of an electric fan in accordance with the present invention is shown comprised of a bearing block  1 , a stator module  2  and a fan blade assembly  3 . 
         [0027]    The bearing block  1  is made out of a porous, oil-containing and extensible plastic material, having a stepped hub  11  perpendicularly upwardly extending from the center of its top wall, and a plurality of mounting lugs  15  radially outwardly extending from its bottom side around the periphery. The stepped hub  11  has an axle hole  12  axially defined therein and extending to the topmost edge, an inside annular flange  121  extending around its inside wall within the axle hole  12  at a predetermined elevation, a plurality of vertical crevices  13  cut through its relatively bigger lower part in communication with the axle hole  12 , an outside stop flange  141  extending around the periphery of its relatively smaller upper part  14 , a coupling groove  142  extending around the periphery of its relatively smaller upper part  14  between the outside stop flange  141  and its relatively bigger lower part, and a plurality of vertical ribs  143  protruded from the periphery of its relatively smaller upper part  14 . Further, each mounting lug  15  has a mounting through hole  151 . 
         [0028]    The stator module  2  comprises a circuit board  21 , an electrically insulative bracket  22  fixedly provided at the top side of the circuit board  21 , a through hole  23  vertically extending through the electrically insulative bracket  22  and the circuit board  21 , a plurality of silicon steel plates  24  fastened to the outside wall of the electrically insulative bracket  22  and partially extended to the inside of the through hole  23 , and a plurality of windings  25  wound on the silicon steel plates  24 . 
         [0029]    The fan blade assembly  3  comprises a hollow base block  31 , a downwardly extending accommodation open chamber  32  defined within the hollow base block  31 , a plurality of fan blades  311  radially extending from the hollow base block  31  and equiangularly spaced around the periphery of the hollow base block  31 , magnetic devices, for example, permanent magnets  33  fixedly mounted inside the accommodation open chamber  32 , and an axle  34  fixedly fastened to the hollow base block  31  and downwardly suspending in the accommodation open chamber  32  at the center. The axle  34  has rounded bottom end  342  and a neck  341  adjacent to the rounded bottom end  342 . 
         [0030]    During installation of the present invention, the stator module  2  is capped on the bearing block  1  to receive the stepped hub  11  in the through hole  23  and to have the silicon steel plates  24  be coupled to the coupling groove  142  of the stepped hub  11  and stopped at the bottom side of the outside stop flange  141  and prohibited from vertical displacement relative to the bearing block  1 . At this time, the vertical ribs  143  of the bearing block  1  are stopped against the silicon steel plates  24  to stop the stator module  2  from rotation relative to the bearing block  1 . 
         [0031]    Thereafter, the fan blade assembly  3  is capped on the stator module  2  and the bearing block  1  to have the electrically insulative bracket  22  of the stator module  2  be received in the accommodation open chamber  32  with the permanent magnets  33  aimed at the windings  24  at the electrically insulative bracket  22  and to have the axle  34  be pivotally inserted into the axle hole  12  of the bearing block  1 , and then the mounting through holes  151  of the mounting lugs  15  are affixed to the fan blade assembly  3 . When inserting the axle  34  into the axle hole  12  of the stepped hub  11  during installation, the extensible material property of the bearing block  1  allows the rounded bottom end  342  of the axle  34  to be moved downwardly over the inside annular flange  121  to have the neck  341  of the axle  34  be coupled to the inside annular flange  121  and the rounded bottom end  342  of the axle  34  in spot-contact with the bottom wall of the stepped hub  11  inside the axle hole  12 , thereby allowing rotation of the fan blade assembly  3  relative to the stator module  2  and the bearing block  1 . 
         [0032]    Further, the vertical crevices  13  of the stepped hub  11  allow radial expansion of the stepped hub  11  upon insertion of the axle  34 , and facilitate mold stripping, preventing damage of the inside annular flange  121  by the mold when stripping the mold during fabrication of the bearing block  1 . By means of the design of the vertical crevices  13 , the formation of the inside annular flange  121  on the inside wall of the stepped hub  11  is simple. 
         [0033]    By means of a spot contact between the rounded bottom end  342  of the axle  34  and the bottom wall of the bearing block  1  inside the axle hole  12  and the coupling between the inside annular flange  121  of the stepped hub  11  and the neck  341  of the axle  34 , the axle  34  is constantly kept in coincidence with the central axis of the axle hole  12  of the stepped hub  11  of the bearing block  1 , assuring smooth and stable rotation of the fan blade assembly  3  relative to the stator module  2  and the bearing block  1 . Further, because the bearing block  1  is made out of a porous oil-containing plastic material, the bearing block  1  provides an oil film for protection between the axle  34  and the inside wall of the axle hole  12 , preventing friction noises or friction heat during rotation of the fan blade assembly  3  relative to the stator module  2  and the bearing block  1 . Therefore, the invention eliminates the drawbacks of the prior art design that requires a lubricating oil maintaining design and a sufficient supply of a lubricating oil, and achieves high rotation precision and high-speed rotation stability. 
         [0034]    When an electric current passes through the silicon steel plates  24  and the windings  25  at the circuit board  21  of the stator module  2 , the windings  25  induce a magnet field. By means of magnetic repelling action between the windings  25  and the permanent magnets  33 , the fan blade assembly  3  is rotated relative to the stator module  2  and the bearing block  1 . By means of the coupling between the inside annular flange  121  of the stepped hub  11  and the neck  341  of the axle  34 , the axle  34  is constantly kept in the coincidence with the central axis of the axle hole  12  of the stepped hub  11  of the bearing block  1 , assuring smooth and stable rotation of the fan blade assembly  3  relative to the stator module  2  and the bearing block  1 . 
         [0035]      FIG. 5  is sectional side view of a fan bearing structure in accordance with a second embodiment of the present invention. According to this embodiment, the bearing block  1  has a bottom center recess  16  in vertical alignment with the axle hole  12 , and a magnet  161  mounted in the bottom center recess  16  to attract the axle  34  in the axle hole  12 , keeping the axle  34  constantly in coincidence with the central axis of the axle hole  12  of the stepped hub  11  of the bearing block  1  and assuring smooth and stable rotation of the fan blade assembly  3  relative to the stator module  2  and the bearing block  1 . 
         [0036]      FIG. 6  is a sectional side view of a fan bearing structure in accordance with a third embodiment of the present invention. This embodiment is substantially similar to the embodiment shown in  FIG. 5 , with the exception that the magnet  161  is directly mounted in the axle hole  12  at the bottom side to support and attract the rounded bottom end  342  of the axle  34 , keeping the axle  34  constantly in coincidence with the central axis of the axle hole  12  of the stepped hub  11  of the bearing block  1  and assuring smooth and stable rotation of the fan blade assembly  3  relative to the stator module  2  and the bearing block  1 . 
         [0037]      FIG. 7  is an elevational view of a bearing block for a fan bearing structure in accordance with a fourth embodiment of the present invention. The bearing block  1  is shaped like a disk, having a plurality of mounting lugs  15  spaced around the periphery, each mounting lug  15  having a mounting through hole  151  for fixation to the fan blade assembly (not shown) with a respective fastening device to prohibit relative displacement between the bearing block  1  and the fan blade assembly, and a plurality of arched slots  152  cut through the top and bottom walls and equiangularly spaced around the stepped hub  11  for the flowing of air to dissipate heat. 
         [0038]    As indicated above, the present invention provides a fan bearing structure, which has the following features and benefits:
   1. The axle  34  of the fan blade assembly  3  is inserted into the axle hole  12  of the bearing block  1  with the neck  341  of the axle  34  coupled to the inside annular flange  121  of the stepped hub  11  of the bearing block  1 , keeping the axle  34  in coincidence with the central axis of the axle hole  12  of the stepped hub  11  of the bearing block  1  constantly and assuring smooth and stable rotation of the fan blade assembly  3  relative to the stator module  2  and the bearing block  1 .   2. The inside annular flange  121  is disposed at a distance far from the top opening of the axle hole  12  to support the axle  34  in coincidence with the central axis of the axle hole  12  of the stepped hub  11  of the bearing block  1 ; the vertical crevices  13  allows radial expansion of the stepped hub  11  to facilitate installation of the axle  34  in the axle hole  12  of the stepped hub  11 , assuring positive coupling between the neck  341  of the axle  34  and the inside annular flange  121  of the stepped hub  11  for stable rotation of the fan blade assembly  3  relative to the stator module  2  and the bearing block  1 .   3. In addition to the function of allowing radial expansion of the stepped hub  11 , the vertical crevices  13  of the stepped hub  11  also facilitate mold stripping, preventing damage of the inside annular flange  121  by the mold when stripping the mold during fabrication of the bearing block  1 . By means of the design of the vertical crevices  13 , the formation of the inside annular flange  121  on the inside wall of the stepped hub  11  is simple.   4. The silicon steel plates  24  of the stator module  2  are coupled to the coupling groove  142  and stopped at between the outside stop flange  141  and relatively bigger lower part of the stepped hub  11  to prohibit vertical displacement of the stator module  2  relative to the bearing block  1 , and the vertical ribs  143  of the stepped hub  11  are stopped against the silicon steel plates  24  to prohibit rotation of the stator module  2  relative to the bearing block  1 .   5. The bearing block  1  is made out of a porous and oil-containing plastic material, providing an oil film for protection between the axle  34  and the inside wall of the axle hole  12  and preventing friction noises or friction heat during rotation of the fan blade assembly  3  relative to the stator module  2  and the bearing block  1 .   
 
         [0044]    A prototype of fan bearing structure has been constructed with the features of  FIGS. 1˜7 . The fan bearing structure functions smoothly to provide all of the features disclosed earlier. 
         [0045]    Although particular embodiments of the invention have been described in detail for purposes of illustration, various modifications and enhancements may be made without departing from the spirit and scope of the invention. Accordingly, the invention is not to be limited except as by the appended claims.