Fluid Dynamic-Pressure Bearing Device and Spindle Motor

A fluid dynamic-pressure bearing device comprising:

• a shaft;
• a hub from which the shaft extends toward the other end of the shaft in the axial direction and rotates with the shaft and includes a thrust bearing surface which extends outwardly in the radial direction from the one end of the shaft, an annular surface which extends outside of the thrust bearing surface outwardly in the radial direction, and a peripheral wall which surrounds the shaft and extends towards the other end;
• a fixed portion having a hole having a cylindrical inner peripheral surface, a thrust bearing surface formed to surround the opening of the hole at the one-end side and a flange surface faced with the annular surface outside of the thrust bearing surface, the shaft being rotatably inserted into the hole;
• a thrust dynamic-pressure generating grooves formed on one or both of the thrust bearing surface of the hub and the thrust bearing surface of the fixed portion;
• radial dynamic-pressure generating grooves formed on one or both of the outer peripheral surface of the shaft and the inner peripheral surface of the hole;
• a thrust narrow gap provided between the thrust bearing surface of the hub and the thrust bearing surface of the fixed portion which is faced to the thrust bearing surface of the hub;
• a radial narrow gap which is provided between the outer peripheral surface of the shaft and the inner peripheral surface of the hole that is faced to the outer peripheral surface of the shaft and is communicated with the thrust narrow gap at its one end;
• an annular gap which is provided between the flange surface and the annular surface during a rated rotation, is communicated at its inner periphery with the outer periphery of the thrust narrow gap and has a dimension greater than the dimension of the thrust narrow gap plus the average depth of the thrust dynamic-pressure generating grooves;
• a sealing gap which is formed between the outer peripheral surface of the fixed portion and the peripheral wall that is faced thereto and is communicated with the outer periphery of the annular gap;
• a lubricating liquid which fills the thrust narrow gap, the radial narrow gap and the annular gap substantially without causing interruptions and fills at least a portion of the sealing gap;
• a thrust dynamic-pressure bearing comprising the thrust narrow gap, the lubricating liquid retained within the gap and the thrust dynamic-pressure generating grooves for generating dynamic pressures in the lubricating liquid;
• and
• a radial dynamic-pressure bearing comprising the radial narrow gap, the lubricating liquid retained within the gap and the radial dynamic-pressure generating grooves for generating dynamic pressures in the lubricating liquid.