Cooling fan

Abstract

A cooling fan includes a fan housing (10) having a central tube (14) extending upwardly therefrom, a bearing (30) received in the central tube, a stator (40) mounted around the central tube, and a rotor (20). The rotor includes a hub (22), a magnet (28) adhered to the hub, and a shaft (24) extending from the hub into the bearing. The stator includes a stator core (42) having a ring-shaped main body (420) and a plurality of claws extending radially and outwardly from the main body, coils (44) being wound on the claws, and a PCB (426) being electrically connected to the coils. At least one balancing structure (100) made of magnetizable material extends from the printed circuit board corresponding to a position between two adjacent claws of the stator core and exerts a downwardly attractive, magnetic force on the magnet.

1 . A cooling fan comprising:
 a fan housing having a central tube extending upwardly therefrom;   a bearing received in the central tube;   a rotor comprising a hub, a magnet fixed to an inner side of the hub, and a shaft extending from a central portion of the hub into the bearing;   a stator mounted around the central tube, comprising a stator core having a circular shaped main body and a plurality of claws extending radially and outwardly from the main body, coils being wound on the claws, and a printed circuit board being electrically connected to the coils; and   at least one balancing structure extending from the printed circuit board corresponding to a position between two adjacent claws of the stator core, the at least one balancing structure being made of magnetizable material and exerting a downwardly attractive, magnetic force on the magnet of the rotor, whereby the shaft is pulled downwardly by the at least one balancing structure.   
   
   
       2 . The cooling fan of  claim 1 , wherein the at least one balancing structure comprises a plurality of poles each arranged between a respective pair of adjacent claws. 
   
   
       3 . The cooling fan of  claim 1 , wherein the stator core has four claws, and the at least one balancing structure comprises four poles arranged between the claws. 
   
   
       4 . The cooling fan of  claim 1 , wherein each claw comprises a linear-shaped portion extending from the main body and an arc-shaped portion formed at an outer end of the linear-shaped portion, the arc-shaped portions being concentric, a gap being defined between two adjacent arc-shaped portions, the at least one balancing structure being located corresponding to the gap. 
   
   
       5 . The cooling fan of  claim 1 , wherein the at least one balancing structure is not higher than the stator. 
   
   
       6 . The cooling fan of  claim 1 , wherein the at least one balancing structure has a cross section being one of the following shape: circular, square, triangular, polygonal or irregular. 
   
   
       7 . The cooling fan of  claim 1 , wherein the at least one balancing structure is made of one of the following materials: steel, iron, iron alloy, nickel, silicon steel, permalloy and ferrite. 
   
   
       8 . The cooling fan of  claim 1 , wherein the at least one balancing structure comprises a plurality of poles being arranged between the claws, the poles being symmetrical to an axis of the stator. 
   
   
       9 . The cooling fan of  claim 1 , wherein the at least one balancing structure is fixedly connected to the printed circuit board by soldering or interference fit. 
   
   
       10 . The cooling fan of  claim 1 , wherein a shaft seat is formed at the central portion of the hub receiving one end of the shaft therein, and the bearing comprises a pair of ball bearings arranged at two opposite ends of the central tube, a conical-shaped coil spring being arranged between top one of the bearings and the shaft seat, a bottom end of the spring abutting against the top one of the bearings and having a diameter relatively smaller than that of a top end of the spring abutting against the shaft seat. 
   
   
       11 . A cooling fan comprising:
 a fan housing having a central tube extending upwardly from a base of the fan housing;   a bearing fixedly received in the central tube;   a stator mounted around the central tube, the stator having a printed circuit board and a plurality of magnetizable poles on the printed circuit board; and   a rotor having a hub, a magnet attached to the hub, and a shaft extending from the hub through the bearing in the central tube;   wherein the magnetizable poles of the stator interact with the magnet of the rotor to force the magnet and thus the shaft of the rotor to have a tendency to move downwardly.   
   
   
       12 . The cooling fan of  claim 11 , wherein the stator has a stator core comprising a plurality of claws extending radially and outwardly from a central main body of the stator core, the magnetizable poles of the stator each being located between two neighboring claws.