Patent ID: 6512316
Filing Date: 2003-01-28
Classification: F16C,G11B

Abstract:
In a spindle motor comprising: a first upright shaft (2) fixedly mounted on a base (1); a pair of a first upper ball bearing (3) and a first lower ball bearing (4) both rotatably mounted on said first upright shaft (2) and provided with a plurality of first balls (5a, 5b) between their first inner rings (3a, 4a) and their first outer rings (3b, 4b); a first sleeve (6) fitted to outer peripheral surfaces of said first outer rings (3b, 4b); and, a rotor hub (7) mounted on an outer peripheral surface of said first sleeve (6) so that said rotor hub (7) is rotatably supported on said base (1), the improvement wherein:said rotor hub (7) is provided with an axial center bore (8); said axial center bore (8) is provided with a pair of large-diameter bore portions in its opposite axial end portions together with a small-diameter bore portion (8a) which is axially interposed between said large-diameter bore portions; an inner diameter of said small-diameter bore portion (8a) is smaller than an outer diameter of said first sleeve (6); said axial center bore (8) of said rotor hub (7) is fitted to an outer peripheral surface of said first sleeve (6) in an insertion manner through a heating shrinkage fit process, so that said first sleeve (6) is subjected to a radially inwardly exerted pressure applied from outside to said first sleeve (6) to deform resiliently radially inwardly; whereby a small-diameter portion is formed in said first sleeve (6) to extend radially inwardly between said first outer rings (3b, 4b) of said first upper ball bearing (3) and said first lower ball bearing (4).