The fluid dynamic bearings system of the invention provides a device
located in a non-grooved low pressure region located at some point in the
overall fluid circulation path of the fluid dynamic bearing to collect
and trap any air bubbles which may be found in the fluid of the
hydrodynamic bearing. More specifically, the air extraction device of the
invention comprises a shallow angle V-shaped region which is located in
fluid communication with but not in a grooved region of the hydrodynamic
bearing. In summary, according to the present invention the hydrodynamic
bearing comprises a shaft with a thrust plate at or near at least one end
thereof. The thrust bearings are formed on the upper and lower surfaces
of the thrust plate (301) and journal bearing (320) on the shaft or
facing sleeve surface. Lubricant lies between each of these surfaces and
facing surface of a sleeve (312) or counter-plate (308) which overlies
the thrust bearing, and fluid lies in all these regions. In the region on
the outer surface of the counter-plate distant from the shaft (322) and
facing the counter-plate (308) a countersink (340) is formed on the axial
face of the thrust plate (301) and end of bearing shaft with a shallow
angle such that the force of surface tension forms a meniscus between the
air and the lubricant along the surface of the countersink angle period.
Lubricant circulation path-holes (380,382) are provided from, this
countersink region to the region at the junction between the shaft and
the thrust plate which also between the journal bearing and the thrust
bearing. Thus the fluid can pass through these circulation holes
extending from the journal and thrust plate up to the countersink region,
and form a capillary seal on either side of the countersink region
adjacent the thrust bearing. As an alternative, the shallow angled region
may also be located on the outer diameter of the thrust plate or on the
shaft adjacent the journal bearing.