Patent ID: 7567003

Claim:
A cooling fan comprising: a fan housing having a central tube extending upwardly therefrom, the central tube defining a central hole therein, and forming a recess in a top portion thereof, the recess communicating with the central hole, a diameter of the recess being greater than that of the central hole; a bearing impregnated with lubricant oil being received in the central hole of the central tube, an axial hole being defined in the bearing, a top end of the bearing being lower than a bottom of the recess of the central tube; a stator mounted around the central tube; a rotor comprising a hub having a shaft extending from the hub into the axial hole of the bearing, a slot being defined in a top end of the shaft near the hub, the bottom of the recess being higher than a top of the slot, and a bottom of the slot being higher than the top end of the bearing; and an oil retaining ring mounted around the shaft and being fixedly received in the recess of the central tube and abutting the bottom of the recess of the central tube, the slot of the shaft being located lower than a bottom of the retaining ring and higher than the top end of the bearing; wherein an oil buffer is defined among the shaft, the central tube, the bottom of the retaining ring and the top end of the bearing, and communicates with the slot, a depth of the oil buffer in an axial direction of the shaft being greater than that of the slot, the slot being configured for preventing lubricant oil which escapes from the bearing during operation of the cooling fan from continuously creeping up along the shaft.