US Patent 7922446 Cooling fan with balance structure

A cooling fan includes a fan housing (30) having a central tube (34) extending upwardly therefrom; the central tube has a bottom, annular protrusion (31). A bearing (61) is received in the central tube and mounted on the protrusion. A stator (20) is mounted around the central tube. A rotor (10) includes a shaft (18) having a free end (186) extending through the bearing and defining a notch (184) therein. A locking washer (63) engages into the notch of the shaft to limit movement of the shaft along an axial direction thereof. A balance structure (62) is arranged between the locking washer and the bearing. The balance structure is made of magnet and exerts a downwardly pulling force on the shaft to prevent the rotor from moving upwardly when the rotor is rotated.