Fluid dynamic bearing device, motor, and disk drive device

A fluid dynamic bearing device comprising:

• a shaft disposed along a center axis extending vertically;
• a sleeve including a through hole into which the shaft is inserted, the sleeve cylindrically extending in an axial direction around the shaft;
• a thruster disposed below the shaft in the axial direction to close an opening in a lower end of the sleeve;
• a plurality of dynamic pressure grooves defined in at least one of an outer peripheral surface of the shaft and an inner peripheral surface of the sleeve;
• and
• a lubricating oil present among the shaft, the sleeve, and the thruster;
• wherein
• the shaft includes:
• a shaft main body extending along the center axis in a columnar shape;
• and
• a shaft flange extending outward in a radial direction from a lower end of the shaft main body;
• the inner peripheral surface of the sleeve includes:
• a first inner peripheral surface facing an outer peripheral surface of the shaft main body in the radial direction;
• and
• a second inner peripheral surface that at least partially faces an outer peripheral surface of the shaft flange in the radial direction;
• the sleeve includes:
• a sleeve inner lower surface that connects a lower end of the first inner peripheral surface and an upper end of the second inner peripheral surface and that at least partially faces the shaft flange in the axial direction;
• and
• at least one circulation hole that passes through an inside of the sleeve and that is open in the sleeve inner lower surface;
• and
• at least a portion of the second inner peripheral surface of the sleeve is defined by an inclined surface extending downward in the axial direction, and inclined radially outward, from a portion above the thruster in the axial direction and on a radially outer side of the lower opening of the circulation hole.