Patent ID: 7922446

Claim:
A cooling fan comprising: a fan housing having a central tube extending upwardly therefrom; a bearing received in the central tube, the bearing defining a bearing hole therein and a plurality of channels in an outer circumferential surface thereof; a stator mounted around the central tube; a rotor comprising a hub having a shaft extending therefrom, the shaft having a free end far from the hub, the free end of the shaft extending through the bearing hole of the bearing and defining a notch therein; and a balance structure being mounted around the shaft with a top higher than the notch of the shaft and a lower portion facing an upper portion of the notch, the balance structure exerting a downwardly attractive, magnetic force on the shaft, wherein the balance structure is column shaped, a cross section of the balance structure is polygonal-shaped, and a gap is defined between each side of the balance structure and an inner circumferential surface of the central tube, the gap communicating with the channels of the bearing.