Patent ID: 7015611

Claim:
A spindle motor having a rotation center axis, comprising: a stator assembly which comprises: a bracket having a through hole aligned with said rotation center axis and a cylindrical portion formed at a rim of said through hole; a stator fixed to said bracket; and a stator bearing which includes a stator bearing surrounding wall having an cylindrical shape, disposed on an inner face of said through hole and extending in the rotation center axial direction, and an annular flange projecting outward in the radial direction from an upper end of said stator bearing surrounding wall; a rotor assembly rotated about said rotation center axis, the motor assembly comprises: a shaft; a rotor upper wall portion fixed to an upper portion in the rotation center axial direction of said shaft; a rotor annular portion extending downward In the rotation center axial direction from an outer portion of said rotor upper wall portion; a yoke made of a magnetic material, having an approximately cylindrical shape and a flat endface being perpendicular to the center axis of said yoke, the distance to the edge of said flat endface measured from the center axis of said cylindrical yoke being smaller than that to the outer peripheral surface of said annular flange portion, a portion of said flat endface contacting a portion of said rotor annular portion and being fixed thereto, said annular flange, portion axially interposed between said flat endface of said yoke and said rotor upper wall portion; and a field magnet fixed to the outer peripheral portion of said yoke and facing the inner portion of said stator in the radial direction; a bearing section including a first clearance formed between an upper end face of said stator bearing and an lower face of said rotor upper wall portion, a lubricating fluid retained as a working fluid in said first clearance; and a taper seal area formed between an outer peripheral surrounding wall and the inner peripheral face of said yoke, in a clearance whose clearance dimension gradually increases downward in the axial direction from said flange, wherein said lubricating fluid forms a air-fluid boundary between the lubricating fluid and an air in said taper seal area.