| 摘要 |
An object is to provide a bearing unit superior in reliability with no leakage of lubricating oil, and capable of reliably and less expensively solving the problem of shaft float during rotor rotation caused by imbalance of a pair of dynamic pressure generating grooves; and a rotation driving device having such bearing unit. Thus, it comprises a shaft (100) having an exposed end (160), an inner end (162) of smaller outer diameter disposed on the side opposite to the exposed end (160) and an intermediate level difference portion (170) of smaller outer diameter formed in a position between the exposed end (160) and the inner end (162), a thrust bearing (130) for rotatably supporting the inner end (162) of the shaft (100) with respect to the thrust direction, and a lubricating oil (150) held in a holding member (120) and filled between the shaft (100), a radial bearing (110) and the thrust bearing (130), the axial length (m) of the inner end (162) of the shaft (100) being smaller than the axial length (n) extending from the outer surface of the holding member (120) to the portion including the intermediate level difference portion (170) of the shaft (100).
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