Cooling fan with balance structure

A cooling fan comprising:

• a fan housing having a central tube extending upwardly therefrom;
• a bearing received in the central tube, and defining a bearing hole therein;
• a stator mounted around the central tube;
• a rotor having a shaft extending through the bearing hole of the bearing, at least one notch being defined in an end of the shaft;
• and
• at least one balance structure being mounted around the shaft with a top higher than the at least one notch of the shaft and a lower portion facing and surrounding an upper portion of the notch, the at least one balance structure exerting a downwardly attractive, magnetic force on the shaft,
• wherein the shaft defines two notches at two opposite ends thereof, and the at least one balance structure comprises upper and lower balance structures respectively arranged on two opposite ends of the bearing and mounted around the shaft with lower portions of the upper and lower balance structures facing upper portions of the notches of the shaft, respectively.