Patent Publication Number: US-2003231968-A1

Title: Fan structure

Description:
BACKGROUND OF THE INVENTION  
       [0001] 1. Field of the Invention  
       [0002] The present invention generally relates to a fan structure.  
       [0003] 2. The Related Art  
       [0004] Fans have been widely used in removing heat from all kinds of devices that generate heat during their operation. Two major concerns of the fans are the noise caused by the operation of the fan and the airflow rate that can be induced by the fan. A conventional fan comprises a fixed frame and a rotary blade assembly rotatably supported in the frame by bearing. To enhance the overall performance of the fan, some particularly designed, sophisticated bearings are employed to reduce noise and to improve efficiency of the fan. However, such sophisticated bearings are expensive and thus increase the overall costs of the fan.  
       [0005] Thus, it is desired to have a fan structure of low costs but high performance to overcome the above-mentioned problems.  
       SUMMARY OF THE INVENTION  
       [0006] An object of the present invention is to provide a fan having a simple structure and thus low costs.  
       [0007] Another object of the present invention is to provide a fan structure having a high performance for efficiently driving airflow.  
       [0008] A further object of the present invention is to provide a fan structure, which eliminates the axial reciprocation of the fan blade assembly.  
       [0009] To achieve the above objects, in accordance with the present invention, there is provided a fan comprising a blade assembly rotatably supported in a frame. The blade assembly comprises a cylinder having an outer surface to which blades are mounted and an inner surface to which magnets are mounted. The blade assembly has an axle concentric with the cylinder. The frame comprises a casing made of silicone steel that is fixed inside the frame and supports a bearing device. The bearing device defines a central bore rotatably receiving the axle of the blade assembly therein with the cylinder of the blade assembly fit over and spaced from the casing. Windings of conductive wires are encased and fixed in the casing and surround the bearing device for being electrically powered to generate a magnetic field that interacts with the magnetic means of the blade assembly to rotate the blade assembly. The casing comprises opposite upper and lower disks with tabs extending between the upper and lower disks. The tabs extends from a circumference of the upper disk and have free ends fit into corresponding notches defined in the lower disk with a major surface of the tabs extending along a circumferential direction of the disks. Portions of the lower disk project beyond the tabs and are positioned in correspondence to the magnets of the blade assembly for magnetically attracting and thus maintaining the blade assembly in a close position with respect to the lower disk to eliminate “pump” action or axial reciprocation of the blade assembly.  
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0010] The present invention will be apparent to those skilled in the art by reading the following description of a preferred embodiment thereof, with reference to the attached drawings, in which:  
     [0011]FIG. 1 is a perspective view of a fan constructed in accordance with the present invention;  
     [0012]FIG. 2 is a cross-sectional view of the fan of the present invention with a blade assembly separated from a frame of the fan;  
     [0013]FIG. 3 is a cross-sectional view of the fan of the present invention;  
     [0014]FIG. 4 is a perspective view showing, in a separated manner, an upper silicon steel member and a lower silicon steel member of the fan of the present invention;  
     [0015]FIG. 5 is an assembled view of FIG. 4 with the upper and lower silicon steel members fixed together. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
     [0016] With reference to the drawings and in particular to FIGS. 1 and 2, a fan constructed in accordance with the present invention, generally designated with reference numeral  10 , comprises a frame  20  inside which a blade assembly  11  is rotatably supported and driven by magnetically induced forces.  
     [0017] Also referring to FIG. 3, the blade assembly  11  comprises a hollow cylinder  13  with an end closed and a concentric axle  15  extending from the closed end of the cylinder  13 . A plurality of blades  12  is mounted to and equally spaced along an outside surface of the cylinder  13 . Magnet means  14  comprising at least one ring magnet is fixed to an inside surface of the cylinder  13 .  
     [0018] The frame  20  comprises a bearing device  21  defining a central bore  22  for rotatably and snugly receiving the axle  15  therein whereby the blade assembly  11  is rotatably supported by the bearing device  21  in the frame  20 . Windings of conductive wires  23  are formed around the bearing device  21 . The conductive wires  23  are connected to an electrical power source (not shown) to receive electrical current therefrom. When the electrical current flows through the windings  23 , a magnetic field is induced which interacts with the magnet means  14  of the blade assembly  11  to drive the blade assembly  11 .  
     [0019] Also referring to FIGS. 4 and 5, the windings  23  are encased in a casing (not labeled) made of silicon steel. The casing is comprised of a lower member or base  40  and an upper member or cover  30  mounted together to encase the windings  23 . The lower member  40  is made in the form of a circular disk defining a plurality of notches  42  equally spaced along a circumference thereof. A hub  41  is formed on the lower member  40  for receiving the bearing device  21  therein.  
     [0020] The upper member  30  is made in the form of a circular disk having a surface area smaller than a surface area of the lower member  40 . Namely, the radius of the upper member  30  is smaller than the radius of the lower member  40 . The upper member  30  defines a central hole  31  substantially aligned with the hub  41  of the lower member  40 . A plurality of tabs  32  extends perpendicularly from a circumference of the upper member  30  and having free ends respectively corresponding to and fit into the notches  42  of the lower member  40 . The bearing device  21  is received in both the hole  31  of the upper member  30  and the hub  41  of the lower member  40  and supported by the upper and lower members  30 ,  40 .  
     [0021] Since the tabs  32  of the upper member  30  have a major surface extending in a circumferential direction of the windings  23  (namely the major surfaces of the tabs  32  defining a cylinder covering the windings  23  if the tabs  32  are extended in the circumferential direction), rather than in a radial direction as commonly observed in the conventional fan rotor, the surface area of the tabs  32  on which a driving force caused by the interaction between the magnetic field induced by the windings  23  and the magnet means  14  is effectively increased thereby substantially increasing the torque acting upon the blade assembly  11 .  
     [0022] Since the radius of the lower member  40  is greater than that of the upper member  30 , when the tabs  32  of the upper member  30  are fit into the corresponding notches  42  of the lower member  40 , the portions of the lower member  40  that are between adjacent notches  42  are located beyond the tabs  32  of the upper member  30  and corresponding, in position, to the ring magnet  14 . Thus, an attraction force is induced between the magnet means  14  and the lower member  40  to retain the blade assembly  11  close to the lower member  40  and consequently eliminating the so called “pump” action of the blade assembly  11 . (The “pump” action of the blade assembly  11  occurs when a fan is activated and the rotor or blade assembly moves axially and reciprocally with respect to the stator or frame.)  
     [0023] Since the hub  41  is integrally formed on the lower member  40 , additional bushing or collar is not necessary in retaining the bearing device  21  and the axle  15  in position. This simplifies the structure of the fan and reduces costs thereof.  
     [0024] In the embodiment illustrated, the upper member  30  has four tabs  32  which correspond to four poles of the fan. However, it is apparent to those having ordinary skills in the art to increase the number of the tabs  32  in two to count the poles number to six, eight and so on. Thus, operation stability can be easily maintained and the costs of material can be reduced.  
     [0025] Although the present invention has been described with reference to the preferred embodiment thereof, it is apparent to those skilled in the art that a variety of modifications and changes may be made without departing from the scope of the present invention which is intended to be defined by the appended claims.