Abstract:
A bearing assembly includes a sleeve bearing ( 2 ) having a mating portion ( 22 ) and a center bore ( 20 ), a shaft ( 1 ) disposed in the center bore, and a rotary block ( 3 ) mounted on the shaft and being rotatable therewith. A gap exists between the inner circumferential surface of the bearing and the outer circumferential surface of the shaft to allow the shaft to be capable of rotate in the bore without scrapping the bearing. The rotary block includes a mounting portion ( 30 ) engaging with the mating portion of the bearing, whereby the rotary block is rotatably supported on the bearing.

Description:
TECHNICAL FIELD 
   The present invention relates to a bearing system, and particularly to an improvement of bearing assembly used for fans. 
   BACKGROUND 
   With the improvement of operation speed of recent electric devices such as data storage devices, the speed of the reading-writing and locating is accelerated accordingly. Thus, more and more heat is generated. In order to maintain the electric devices work normally, the heat generated by the electric devices must be dissipated rapidly. Fans act an important role during the heat dissipation. The design and lifetime of bearings in the fans determine the performance and the life of the fans. 
   An example of a conventional bearing structure is shown in  FIG. 8 . The bearing structure comprises a rotary shaft  1   a  and a stationary bearing  2   a  which defines a central bore  3   a  for receiving the shaft  1   a.  A small gap is formed between the shaft  1   a  and the bearing  2   a  for holding lubricating oil therein. However, when the gap is too narrow, the lubricating oil will be extruded out of the gap so that large-area dry friction exists between the shaft  1   a  and the bearing  2   a . This results in the bearing structure wearing out to thereby reduce the lifetime of the bearings structure and generate undesired noise. On the contrary, when the gap is significantly wide, the shaft  1   a  is prone to sway radially or unsteadily to generate noise as well. 
   A new bearing structure that overcomes the above-mentioned disadvantages is desired. 
   SUMMARY OF THE INVENTION 
   Accordingly, an object of the present invention is to provide a bearing assembly which has a long lifespan and generates less noise. 
   To achieve the above-mentioned object, a bearing assembly in accordance with the present invention comprises a sleeve bearing having a mating portion and a center bore, a shaft disposed in the center bore, and a rotary block mounted on the shaft and being rotatable therewith. A gap exists between the inner circumferential surface of the bearing and the outer circumferential surface of the shaft to allow the shaft to rotate in the bore without friction existing between the shaft and the bearing. The rotary block comprises a mounting portion engaging with the mating portion of the bearing, whereby the rotary block is rotatably supported on the bearing. 
   Other objects, advantages and novel features of the present invention will be drawn from the following detailed description of the preferred embodiments of the present invention with attached drawings, in which: 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an exploded, isometric view of a bearing system used in a fan in accordance with the first embodiment of the present invention; 
       FIG. 2  is an enlarged view of a rotary block and a sleeve bearing of the bearing system of  FIG. 1 , viewed from another aspect; 
       FIG. 3  is a cross-sectional view of the bearing system assembled in the fan of  FIG. 1 ; 
       FIG. 4  is an isometric view of a rotary block and a sleeve bearing of the bearing system in accordance with the second embodiment of the present invention; 
       FIG. 5  is an isometric view of a rotary block and a sleeve bearing of the bearing system in accordance with another embodiment of the present invention; 
       FIG. 6  is a cross-sectional assembled view of  FIG. 5 ; 
       FIG. 7A  is an axial plan view of a shaft and a rotary block in accordance with another embodiment of the invention; 
       FIG. 7B  is an axial plan view of a shaft and a rotary block in accordance with another embodiment of the invention; and 
       FIG. 8  is a cross-sectional view of a conventional bearing structure. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   Referring to  FIG. 1 , a bearing system is used in a fan. The fan includes a rotor  8 , a stator  80 , a bearing system, a ring  14  and a frame  82 . The bearing system includes a shaft  1 , two sleeve bearings  2 , two rotary blocks  3  and a coil spring  4 . The frame  82  comprises a central tube  84 . An annular shoulder  86  (shown in  FIG. 3 ) is formed on the inner surface of the central tube  84 . 
   The shaft  1  has a column shape with two vertical sections cut away symmetrically from two opposite sides thereof. A semispherical-shaped guiding portion  10  is formed at a distal end of the shaft  1 . An annular slot  12  is defined in the vicinity of the guiding portion  10  for receiving the ring  14 . The shaft  1  is provided with absorbent material  5  (shown in  FIG. 3 ) for holding lubricating oil. 
   Referring to  FIG. 2 , the sleeve bearing  2  is made of ceramic or other sintered material. A plurality of internal wicking structure such as slits or round holes is formed inside of the bearing  2 . Each bearing  2  comprises a circumferential wall  21 , a mating portion  22  formed at the top of the circumferential wall  21  and a central bore  20 . The mating portion  22  defines an annular recess  24 . A plurality of slots  26  communicating with the annular recess  24  is defined in and extends through each bearing  2 . The internal diameter of the central bore  20  is larger than the external diameter of the shaft  1 . 
   The rotary block  3  is made of ceramic or other sintered material. Each block  3  defines a central bore having a profile mating with the shaft  1  and a mounting portion  30  for engaging with the mating portion  22  of the bearings  2 . An annular flange  32  protrudes from the mounting portion  30  as an extension corresponding to the annular recess  24 . The cross section of the flange  32  is trapezoid. The flange  32  is adapted to be received in the recess  24  to form a linear contact between the flange  32  and the recess  24  when the rotary block  3  engages with the bearing  2 . 
   Referring also to  FIG. 3 , the stator  80  is fixed around the central tube  84  of the frame  82 . The rotor  8  pivotably surrounds the stator  80 . The coil spring  4 , the rotary blocks  3 , the bearings  2  and the adsorbent material  5  are disposed on the shaft  1 . The inner surface of the central tube  84  firmly snatches the outer surface of the bearings  2  to maintain the bearings  2  to be stationary in the tube  84 . The shoulder  86  of the central tube  84  is located between the two bearings  2  to prevent the bearings  2  from moving in the axial direction of the tube  84 . A cavity is formed between the shaft  1 , the tube  84  and the pair of bearings  2 . The coil spring  4  is disposed between the rotor  8  and the upper one of the blocks  3  for providing the blocks  3  and the bearings  2  with a preset engaging pressure therebetween, whereby the blocks  3  maintains stationary relative to the bearings  2  in the axial direction of the shaft  1  when the blocks  3  rotate with the shaft  1 . Alternatively, the coil spring  4  is disposed between the lower rotary block  3  spacing from the rotor  8  and the ring  14  the size of which is enlarged enough to support the coil spring  4 . The mounting portion  30  of each rotary block  3  confronts the mating portion  22  of the corresponding bearing  2 . The flange  32  of each block  3  enters in the annular recess  24  of the corresponding bearing  2  to cause the bearing  2  to rotatably hold the block  3  and the shaft  1 . The absorbent material  5  is disposed on the shaft  1  in the cavity. Alternatively, the absorbent material  5  is disposed on the inner surface of the shoulder  86 . The lubricating oil stored in the absorbent material  5  is pulled out when the material  5  rotates with the shaft  1  and pours into gap between contact areas of the bearings  2  and the blocks  3  through the slots  26  and internal wicking structure of the bearings  2  during the operation of the fan. A gap exists between the inner circumferential surfaces of the bearings  2  and the outer circumferential surface of the shaft  1  to allow the shaft  1  to rotate in the bearings  2  without friction between the shaft  1  and the bearings  2 . Linear contact between the flange  32  of the block  3  and the bearing  2  in the annular recess  24  results in minor friction generated between the block  3  and the bearing  2  due to their relative movement, and friction therebetween reduces dramatically in comparison with prior arts. 
     FIG. 4  shows the second embodiment of a block  3 ′ of a bearing assembly of the present invention. The block  3 ′ forms a mounting portion  30 ′. A plurality of bulges  34 ′ extends from the mounting portion  30 ′ for slidingly engaging in the corresponding annular recess  24  of the bearings  2 . 
     FIG. 4  shows the second embodiment of a block  3 ′ of a bearing assembly of the present invention. The block  3 ′ forms a mounting portion  30 ′. A plurality of bulges  34 ′ extends from the mounting portion  30 ′ for slidingly engaging in the corresponding annular recess  24  of die bearings  2 . 
     FIG. 5  and  FIG. 6  show a rotary block  6  and a sleeve bearing  7  of the bearing system in accordance with another embodiment of the present invention. The bearing  7  defines an annular recess  74 . A plurality of balls  78  is partly received in the recess  74 . The rotary block  6  defines a mounting portion  60 . An annular groove  64  is defined in the mounting portion  60  for cooperating with the recess  74  to receive the balls  78  when the mating portion  60  engages directly with the bearing  7 . The bottom surface of the annular groove  64  contacts with the balls  78  when the rotary block  6  is disposed tightly next to the bearing  7 . The balls  78  are rotatable in the annular groove  64  and the annular recess  74  when the shaft  1  rotates relative to the bearings  2 . 
     FIG. 7A  and  FIG. 7B  show alternative configurations of the shalt  1  and the block. The shall has a non-cylindrical cross section. Referring to  FIG. 7A , in an axial plan view, the cross section of the shaft comprises a plurality of lobes formed on the outer peripheral of the shaft. Referring to  FIG. 7B , the shalt has a column shape with one section cut away from one side thereof. The block has a corresponding bore for receiving the shaft therein. 
   In the bearing assembly described above, the bearings  2  and  7  are spaced from each other by means of the shoulder  86  of the central tube  84 . Alternatively, the sleeve bearings  2  and  7  are integrally made without the shoulder  86  located therebetween. 
   It is understood that the invention may be embodied in other forms without departing from the spirit thereof. The above-described examples and embodiments are to be considered in all respects as illustrative and not restrictive, and the invention is not to be limited to the details given above.