Patent ID: 8587895

Claim:
A bearing mechanism, comprising: a shaft portion arranged about a center axis extending in an up-and-down direction, the shaft portion including a cylindrical outer circumferential surface; a sleeve portion arranged to rotate about the center axis, the sleeve portion including a through-hole arranged to accommodate the shaft portion; a lower opposing portion extending radially outward from a lower portion of the shaft portion, the lower opposing portion including an upper surface axially opposed to a lower end surface of the sleeve portion through a lower thrust gap; a lower outer ring-shaped portion whose relative position is fixed with respect to the lower opposing portion, the lower outer ring-shaped portion including a cylindrical or substantially cylindrical inner circumferential surface arranged to surround at least a portion of an outer circumferential surface of the sleeve portion; and an upper opposing portion extending radially outward from the shaft portion at an upper side of the sleeve portion, the upper opposing portion including a lower surface axially opposed to an upper end surface of the sleeve portion through an upper thrust gap; wherein a radial dynamic-pressure bearing portion is defined in a radial gap between the outer circumferential surface of the shaft portion and an inner circumferential surface of the sleeve portion; a lower thrust dynamic-pressure bearing portion is defined in the lower thrust gap; a lower seal portion is defined in a lower seal gap between the outer circumferential surface of the sleeve portion and the inner circumferential surface of the lower outer ring-shaped portion; an upper seal portion is defined in an upper seal gap joined to the upper thrust gap; the sleeve portion includes a lower portion including a large-diameter portion and a small-diameter portion positioned below the large-diameter portion, the small-diameter portion being smaller in diameter than the large-diameter portion; the sleeve portion further includes a communication path joined to the upper seal gap, the communication path including an opening portion opened in or near a border between the large-diameter portion and the small-diameter portion; the lower opposing portion includes an outer peripheral portion including an outer periphery protrusion portion radially opposed to an outer circumferential surface of the small-diameter portion and axially opposed to a lower surface of the large-diameter portion; a straight line interconnecting an outer edge of a lower surface of the small-diameter portion and an outer edge of the lower surface of the large-diameter portion on a cross section including the center axis extends across the outer periphery protrusion portion; a circulation path including the lower thrust gap, the radial gap, the upper thrust gap, and the communication pass communicates with the lower seal gap and the upper seal gap; and a lubricant is filled in the circulation path, the lower seal gap, and the upper seal gap.