Abstract:
A cooling fan for cooling a heat source includes a frame ( 10 ), a stator ( 20 ) mounted in the frame, a rotor ( 30 ) rotatably attached in the frame, a cover ( 40 ) fixed on the frame, and a pair of bearings ( 50, 60 ) received in the cover and the frame respectively. The rotor includes an impeller and a shaft ( 36 ) inserted through the impeller, wherein the shaft has an upper portion being received in one of the pair of bearings in the cover, and a lower portion being received in another one of the pair of bearing in the frame; thus, a vibration of the shaft can be prevented by supports of the pair of bearings, and the rotor is able to maintain a stable rotation, as the cooling fan is in a high speed operation.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a cooling fan, and more particularly to a cooling fan having a pair of bearings for providing a stable operation to the cooling fan. 
         [0003]    2. Description of Related Art 
         [0004]    With continuing development of the electronic technology, electronic components such as CPUs generate more and more heat that is required to be dissipated immediately. A heat sink is often mounted on the electronic component for absorbing heat therefrom, and a fan is also provided to further remove heat from the heat sink with its forced airflow. 
         [0005]    Conventionally, the fan includes a frame, a stator attached in the frame, a bearing received in the stator, and a rotor rotatably mounted to the stator. The rotor includes an impeller and a shaft extending downwardly from the impeller, wherein a lower portion of the shaft is enclosed by the bearing. When the fan operates, the impeller is rotated around the shaft with a support provided by the bearing. 
         [0006]    However, the shaft only has the lower portion received in the bearing, while an upper portion thereof is not supported by any structure, which leads the impeller fixed on a upper portion of the shaft is prone to perform a vibration when the impeller is in a high speed rotation. This vibration would cause the fan to have an unstable operation that may generate a noise and reduce a lifetime of the fan. 
         [0007]    What is needed, therefore, is a heat dissipating device which can overcome the above-mentioned disadvantages. 
       SUMMARY OF THE INVENTION 
       [0008]    A cooling fan for cooling a heat source includes a frame, a stator mounted in the frame, a rotor rotatably attached in the frame, a cover fixed on the frame, and a pair of bearings received in the cover and the frame respectively. The rotor includes a impeller and a shaft inserted through the impeller, wherein the shaft has an upper portion being received in one of the pair of bearings in the cover, and a lower portion being received in another one of the pair of bearing in the frame; thus, a vibration of the shaft can be prevented by supports of the pair of bearings, and the rotor is able to maintain a stable rotation, when the cooling fan is in a high speed operation. 
         [0009]    Other advantages and novel features of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings, in which: 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    Many aspects of the present apparatus can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present apparatus. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. 
           [0011]      FIG. 1  is a view of a vertical section of a cooling fan in accordance with a preferred embodiment of the present invention; 
           [0012]      FIG. 2  is an isometric view of a cover of the cooling fan of  FIG. 1 ; and 
           [0013]      FIG. 3  is an isometric view of the cooling fan of  FIG. 1  with the cover being removed for clarity. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0014]    As shown in  FIG. 1 , a cooling fan in accordance with a preferred embodiment of the present invention for cooling a heat source (not shown), comprises a frame  10 , a stator  20  disposed in the frame  10 , a rotor  30  rotatably installed on the stator  20 , a cover  40  secured on the frame  10  to cover the stator  20  and the rotor  30 , and a pair of bearings  50 ,  60  respectively contained in a bottom of the frame  10  and in the cover  40 . 
         [0015]    Referring to  FIGS. 1 and 3 , the frame  10  is used for being fixed on a structure (not shown) for mounting the cooling fan thereon. The frame  10  comprises a square lower plate  12 , a square upper plate  14  parallel to the lower plate  12 , and an annular sidewall  16  sandwiched between and interconnecting the lower plate  12  and the upper plate  14 . Each of the upper plate  14  and the lower plate  12  has four circular holes  120 ,  140  defined in four corners thereof respectively. Four grooves  142  are defined near the four circular holes  140  of the upper plate  14  respectively, each of which defines a threaded hole  1420  at a bottom face thereof. A circular through hole  18  is defined through the upper plate  14  and the lower plate  12  for forming a cylindrical space to receive the stator  20  and the rotor  30  therein. A collar  122  is formed in a central area of a bottom of the through hole  18  with a plurality of ribs  123  extending outwardly and radially from a circumferential periphery of the collar  122  to connect with the sidewall  16 , thereby securing the collar  122  to the sidewall  16 . The collar  122  has a hollow tube  124  extending upwardly and perpendicularly from a center area of a top face thereof for accommodating a lower one, in this embodiment, the bearing  50  of the pair of bearings  50 ,  60  therein. An annular wall  126  is formed outwardly and horizontally around a lower portion of the tube  124 . An annulus  128  extends inwardly and vertically from an inner face of the tube  124  and opposite to the annular wall  126 . 
         [0016]    The pair of bearings  50 ,  60  can be oil-containing bearings, or ball bearings. The lower bearing  50  of the pair of bearings  50 ,  60  is received in the tube  124  of the frame  10  in such a manner that a bottom face of the lower bearing  50  of the pair of bearings  50 ,  60  contacts a top face of the annulus  128  on the tube  124 , and an outer face of the lower bearing  50  contacts the inner face of the tube  124 . The lower bearing  50  of the pair of bearings  50 ,  60  defines a cylindrical passage (not labeled) therein, which is located coaxially with the tube  124 . 
         [0017]    The stator  20  is disposed in the frame  10  and comprises a circular base  22  contacting a top face of the annular wall  126 , and a plurality of coils  24  installed on the base  22  for exerting an alternating magnet field when an alternating current is given to the stator  20 . The base  22  defines a hole (not labeled) therein to enable the stator  20  to be sleeved onto the tube  124 . 
         [0018]    The rotor  30  is received in the through hole  18  of the frame  10 . The rotor  30  comprises a hub  32 , a permanent magnetic sleeve  38  installed into the hub  32 , a plurality of blades  34  extending radially and outwardly from a circumference of the hub  32 , and a shaft  36  inserted through the hub  32 . The hub  32  comprises a disk (not labeled) and an annular flange (not labeled) extending downwardly and perpendicularly from a rim of the disk. A central area of a top face of the disk is concaved to form a cavity  320  in the hub  32 . The shaft  36  is inserted through a center of the disk of the hub  32  with an upper portion thereof extending beyond the center of the disk and partly exposed within the cavity  320 ; and a lower portion inserted into the passage of the lower bearing  50  of the pair of bearings  50 ,  60  so as to be confined by the lower bearing  50  of the pair of bearings  50 ,  60 , whereby the lower portion of the shaft  36  is supported to be prevented from vibration. The shaft  36  defines a recess (not labeled) near a bottom portion thereof for being snapped by the annulus  128  of the frame  10 , thus preventing the rotor  30  from falling off from the frame  10 . The magnetic sleeve  38  has an annular configuration contacting an inner circumference of the flange of the hub  32 , wherein the magnetic sleeve  38  surrounds the shaft  36  and has a lower portion opposing to the coils  24  of the stator  20 . 
         [0019]    Also referring to  FIG. 2 , the cover  40  rests on the frame  10  to sandwich the rotor  30  and the stator  20  with the frame  10 . The cover  40  has four straight beams  42  connect with each other to construct a square configuration therefor. A circular plate  44  is formed in a central area of the cover  40  corresponding to the disk of the hub  32  in a manner such that the circular plate  44 , the disk, and the collar  122  are in alignment with each other. Four beams  48  connect the circular plate  44  with the four beams  42  respectively, wherein the four beams  48  are distributed evenly around the circular plate  44 , so that four identical openings  480  each having a shape similar to a square, are defined between the circular plate  44  and the four beams  42 ,  48 . A hollow, tubular body  46  extends downwardly and perpendicularly from a bottom face of the circular plate  44 , thereby to form a cylindrical space  460  together with the circular plate  44 . The tubular body  46  has an exterior diameter less than a diameter of the cavity  320  in the hub  32 , and a height larger than that of the cavity  320 , whereby the tubular body  46  can be partly accommodated in the cavity  320  with its top portion located beyond the hub  32 . Four locking feet  420  are formed downwardly and perpendicularly from four corners of the cover  40  respectively corresponding to the four threaded holes  1420  of the frame  10 . The cover  40  is fixed on the frame  10  by fitting the four locking feet  420  into the four threaded holes  1420  of the frame  10  respectively, and putting the tubular body  46  into the cavity  320  of the hub  32  with a gap defined between the circular plate  44  and a top face of the shaft  36  for preventing an interference from occurring between the shaft  36  and the cover  40 . When the fan is assembled completely, the circular plate  44 , the tubular body  46 , the pair of bearings  50 ,  60 , the hub  32 , the magnetic sleeve  38 , the hollow tube  124 , and the collar  122  would be coaxial with each other. 
         [0020]    The upper bearing  60  of the pair of bearings  50 ,  60  is installed into the cylindrical space  460  of the cover  40  with its top face contacting the bottom face of the circular plate  44  securely, its outer face contacting an inner face of the tubular body  46  of the cover  40 , and its inner face contacting an outer face of the upper portion of the shaft  36 , whereby the upper portion of the shaft  36  is confined to be prevented from a vibration when the rotor  30  is in rotation. 
         [0021]    In use, when an electric power is given to the cooling fan, the coils  24  of the stator  20  generates the alternating magnet field that interacts with the magnetic sleeve  38  of the rotor  30 , thereby driving the rotor  30  to rotate around the shaft  36  in a high speed. Due to the lower portion and the upper portion of the shaft  36  being supported by the lower one  50  and the upper bearing  60  of the pair of bearings  50 ,  60 , respectively, vibrations caused by unsymmetric forces acting on two ends of the shaft  36  can be prevented. Therefore, the cooling fan can operate in a stable condition without noise generated, and the lifetime of the cooling fan is prolonged accordingly. 
         [0022]    It is believed that the present invention and its advantages will be understood from the foregoing description, and it will be apparent that various changes may be made thereto without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the examples hereinbefore described merely being preferred or exemplary embodiments of the invention.