Patent ID: 8083480

Claim:
A cooling fan comprising: a fan housing having a shaft seat extending downwardly therefrom; a shaft having a top end being fixedly connected to the shaft seat of the housing and a free end extending downwardly from the shaft seat; a stator being fixedly mounted around the shaft seat of the fan housing; a rotor comprising: a hub having a plurality of blades extending radially and outwardly therefrom; and a fixing tube extending upwardly from the hub, the fixing tube having an open top end and a closed bottom end, a fixing hole being defined in the fixing tube communicating with the open top end; and a sleeve bearing being fixedly received in the fixing hole of the fixing tube to rotate with the rotor during operation of the cooling fan, a bearing hole being defined in the sleeve bearing for extension of the free end of the shaft therethrough; wherein the open top end of the fixing tube is higher than a top end of the sleeve bearing; wherein the shaft defines an annular slot in a circular circumference thereof, near the top end of the shaft adjacent to the shaft seat of the fan housing, the slot being located higher than the top end of the sleeve bearing and between the top end of the sleeve bearing and the open top end of the fixing tube; and wherein an oil retaining ring is fixedly mounted in the open top end of the fixing tube to enclose the open top end of the fixing tube, and an oil buffer is defined among the fixing tube, the sleeve bearing, the oil retaining ring and the shaft.