Cooling Fan

Abstract

A cooling fan includes a fan frame, a stator unit and an impeller. The fan frame includes a balancing member having a shaft-coupling portion. A lateral wall portion is formed on the balancing member and includes an air inlet and an air outlet. The stator unit has a base plate and a coil unit. The impeller has a permanent magnet and a shaft rotatably coupled with the shaft-coupling portion. An air gap is formed between the permanent magnet and the coil unit. A first annular reference plane extends through the outer annular face of the permanent magnet, and a second annular reference plane extends through the inner annular face of the permanent magnet. A magnetic attraction range is formed between the balancing member, the permanent magnet and the first and second annular reference planes. The balancing member is at least partially shaded from the permanent magnet by the base plate.

What is claimed is: 
     
         1 . A cooling fan comprising:
 a fan frame having a balancing member, wherein the balancing member comprises a shaft-coupling portion, wherein a lateral wall portion is formed along an outer periphery of the balancing member, and wherein the lateral wall portion comprises an air inlet and an air outlet;   a stator unit having a base plate and a coil unit; and   an impeller having a shaft and a permanent magnet, wherein the shaft is rotatably coupled with the shaft-coupling portion, wherein an air gap is formed between the permanent magnet and the coil unit of the stator unit,   wherein a first annular reference plane is defined as extending through the outer annular face of the permanent magnet in an axial direction of the impeller, wherein a second annular reference plane is defined as extending through the inner annular face of the permanent magnet in the axial direction of the impeller, wherein a magnetic attraction range is formed between the balancing member, the permanent magnet, the first annular reference plane and the second annular reference plane, and wherein the balancing member is at least partially shaded from the permanent magnet by the base plate.   
     
     
         2 . The cooling fan as claimed in  claim 1 , wherein the air gap is an axial air gap. 
     
     
         3 . The cooling fan as claimed in  claim 1 , wherein the air gap is a radial air gap. 
     
     
         4 . The cooling fan as claimed in  claim 1 , wherein the base plate has an outer periphery located in the magnetic attraction range. 
     
     
         5 . The cooling fan as claimed in  claim 1 , wherein the base plate has an outer periphery located outside the magnetic attraction range. 
     
     
         6 . The cooling fan as claimed in  claim 1 , wherein the coil unit is formed on a surface of the base plate, wherein the base plate is a layout board, and wherein the coil unit is electrically connected to a driving circuit. 
     
     
         7 . The cooling fan as claimed in  claim 1 , wherein the stator unit further comprises at least one silicon steel plate and an insulation bobbin, wherein a driving circuit is arranged on a surface of the base plate to form a circuit board, wherein the insulation bobbin is coupled with the at least one silicon steel plate, and wherein the coil unit is in the form of an enamel copper wire wound around the insulation bobbin. 
     
     
         8 . The cooling fan as claimed in  claim 1 , wherein the base plate forms one or more pairs of opposing notches on an outer periphery thereof. 
     
     
         9 . The cooling fan as claimed in  claim 1 , wherein the base plate forms one or more pairs of opposing truncated edges on an outer periphery thereof. 
     
     
         10 . The cooling fan as claimed in  claim 1 , further comprising a cover plate coupled with the lateral wall portion of the fan frame, wherein the cover plate includes a through-hole axially aligned with the air inlet of the lateral wall portion. 
     
     
         11 . The cooling fan as claimed in  claim 1 , wherein the balancing member includes at least one secondary air inlet.