| 摘要 |
A spindle motor of the present invention is capable of keeping its ball (5a, 5b)'s pre-load constant, because a sleeve (6) is capable of being resiliently deformed due to its resiliency, and therefore capable of constantly keeping a pre-load applied to the balls (5a, 5b) from inner and inner ring raceways of inner and outer rings (3a, 4a, 3b, 4b) of ball bearings (3, 4). In this motor, a rotor hub (7) has an axial center bore (8). This bore (8) is provided with: a large-diameter bore portions in its opposite axial ends; and, a small-diameter bore portion (8a) axially interposed between the large-diameter bore portions. An inner diameter of the small-diameter bore portion (8a) is smaller than an outer diameter of the sleeve (6). The axial center bore (8) of the hub (7) is fitted to an outer peripheral surface of the sleeve (6) in an insertion manner through a heating shrinkage fit process, so that the sleeve (6) is subjected to a radially inwardly exerted pressure applied from outside to resiliently deform radially inwardly. As a result, a small-diameter portion (6a) is formed in the sleeve (6) to extend radially inwardly between the outer rings (3b, 4b).
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