Patent ID: 6920013

Claim:
A spindle motor comprising: a shaft; a unilaterally open-ended cylindrical bearing member having a bearing hole into which said shaft is inserted and a closed-end surface axially opposing the inserted-end face of said shaft; a rotor that rotates together with said shaft and has a circular flat face extending radially outward from the circumferential surface of said shaft; a series of bearing clearances filled with oil, formed in between said bearing member, said shaft, and the flat face of said rotor; a thrust bearing section provided with dynamic-pressure-generating grooves contoured to impart on the oil pressure acting radially inward during rotation of said rotor, and formed in between the end face along the open end of said bearing member and the flat face of said rotor; a radial bearing section provided with dynamic-pressure-generating grooves contoured to impart on the oil pressure acting inward from either end axially during rotation of said rotor, and formed in between the inner peripheral surface of said bearing hole and the circumferential surface of said shaft; a communicating passage formed in said bearing member so that one end of said communicating passage opens on said thrust bearing section radially inwardly therein and so that either axial end of a one of said bearing clearances being formed in between the inner peripheral surface of said bearing hole and the circumferential surface of said shaft communicative through said passage, for balancing pressure within said bearing clearances; and an annular protruding portion being formed on at least one of the end face of the bearing member and the flat face of the rotor at a radially inward portion of the thrust bearing section.