Patent ID: 7374340
Filing Date: 2008-05-20
Classification: F16C

Abstract:
1. A fluid dynamic-pressure bearing comprising: a stationary assembly; a rotational assembly mounted to said stationary assembly so as to be rotatable, about a center axis of the bearing, relative to said stationary assembly, said rotational assembly and said stationary assembly defining a series of gaps therebetween, the gaps being open to each other so as to constitute a passageway; and lubricating fluid retained in the passageway formed by the series of gaps between said stationary assembly and said rotational assembly; wherein the gaps include a first gap delimited by and between first respective confronting surfaces of said station assembly and said rotational assembly, and at least one annular gap, comprising a second gap, delimited by and between respective peripheral surfaces of said stationary assembly and said rotational assembly, the respective peripheral surfaces confronting each other in the radial direction of the bearing, one of the first respective surfaces has dynamic pressure-generating grooves therein for inducing dynamic pressures in said lubricating fluid when the rotational assembly rotates relative to the stationary assembly about the center axis, the peripheral surfaces which delimit the second gap being oriented relative to one another such that the width of the second gap, as measured in the radial direction of the bearing, increases along the axial direction of the bearing in a direction away from the first gap, whereby said lubricating fluid is retained in the passageway between said second gap and at least said dynamic pressure-generating grooves, and an annular interface between the lubricating fluid and air is maintained within the second gap, and the passageway has a neck therein, the neck providing a constriction in the passageway between said dynamic pressure-generating grooves and said annular interface, and the neck forming part of one of the at least one annular gaps, whereby said neck increases the resistance of the lubricating fluid to flowing through said series of gaps from said dynamic pressure-generating grooves to thereby prevent said lubricating fluid from flowing out of the bearing.