US Patent 7567003 Cooling fan

A cooling fan includes a fan housing (30) having a central tube (34) extending upwardly thereof, a bearing (60) received in the central tube, a stator (20) mounted around the central tube, a rotor (10) including a hub (12) having a shaft (18) extending from the hub into the bearing, and a oil retaining ring (40) mounted around the shaft. A slot (180) is defined in a top end (182) of the shaft of the rotor near the hub to prevent the escaping oil from continuously creeping out along the shaft. The slot is located between the retaining ring and the bearing. The bearing has a plurality of channels (68) defined in an outer surface thereof, for guiding the escaping oil to return to an oil reservoir defined in a bottom of the central tube.