Patent ID: 7578621
Filing Date: 2009-08-25
Classification: F16C,H02K

Abstract:
1. A fluid dynamic-pressure bearing device comprising: a shaft rotatable about a central axis, whereby the device has an axial direction corresponding to the direction of the central axis, and a radial direction perpendicular to the central axis; a hub having a hub-thrust bearing surface which extends from an outer peripheral surface of the shaft outwardly in the radial direction, and a hub annular surface which extends outwardly from the hub-thrust bearing surface; a fixed portion into which the shaft extends, the fixed portion having an inner peripheral surface facing and spaced from the outer peripheral surface of the shaft in the radial direction such that a radial gap having first and second ends, opposite one another in the axial direction, exists between the inner and outer peripheral surfaces, a fixed-portion upper thrust bearing surface facing and spaced from the hub-thrust bearing surface in the axial direction such that an upper thrust gap exists between the fixed-portion upper thrust and hub-thrust bearing surfaces, the upper thrust gap open to the radial gap at the first end of the radial gap, and a flange surface facing and spaced from the hub annular surface in the axial direction such that an annular gap exists between the flange and hub annular surfaces, and the fixed portion delimiting a communicating path open to and extending between the upper thrust gap and the second end of the radial gap, whereby a passageway in the form of a loop is formed within the device by the radial gap, the communicating path, and the thrust gap; and a contiguous body of lubricating liquid occupying the radial gap, the upper thrust gap, the communicating path, and the annular gap, and wherein at least one of the outer peripheral surface of the shaft and the inner peripheral surface of the fixed portion has radial dynamic-pressure generating grooves extending therein, the radial dynamic-pressure generating grooves being configured to generate pressure, acting in the radial direction, in the lubricating liquid in the radial gap during rotation of the shaft, whereby the lubricating liquid occupying the radial gap and the radial dynamic-pressure generating grooves constitute a radial dynamic-pressure bearing which supports the shaft for rotation about the central axis, at least one of the hub-thrust bearing surface and the fixed-portion upper thrust bearing surface has upper thrust dynamic-pressure generating grooves therein, the thrust dynamic-pressure generating grooves being configured to generate dynamic pressure, acting in the axial direction, in the lubricating fluid in the upper thrust gap during rotation of the shaft, whereby the lubricating liquid occupying the upper thrust gap and the thrust dynamic-pressure generating grooves constitute a thrust dynamic-pressure bearing which supports the hub in the axial direction during rotation of the shaft, the dynamic-pressure bearings are configured to generate a net pressure, acting in one direction of the loop formed by the passageway, in the lubricating liquid during rotation of the shaft, whereby the dynamic-pressure bearings circulate the lubricating liquid along the passageway during the rotation of the shaft, and an axial dimension of the annular gap is larger than the sum of an axial dimension of the upper thrust gap and the average depth of the upper thrust dynamic-pressure generating grooves, the axial dimension of the annular gap being a width of the annular gap between the hub annular surface and the flange surface as measured in the axial direction, and the axial dimension of the upper thrust gap being a width of the upper thrust gap between the hub-thrust bearing surface and the fixed-portion upper thrust bearing surface as measured in the axial direction.