Abstract: A hydraulic dynamic bearing has a rotor comprised of a flanged shaft having a thrust ring portion and a cylinder portion, a hub attached to the flanged shaft, and a rotor magnet attached to an inner peripheral face of a skirt portion of the hub. A stator rotatably supports the rotor and comprises a bearing sleeve to which are attached stator coils, and a stator base plate that supports the sleeve. A gap exists between confronting surfaces of the flanged shaft and the bearing sleeve, and lubricating oil is sealed in the gap. Thrust dynamic pressure generating grooves are formed in one or both faces of the thrust ring, and the grooves are in the form of a herringbone pattern having radial inner groove sections and outer groove sections. The depth of the inner groove sections is shallower than that of the outer groove sections, and the depths of both groove sections are constant. The optimum inner-to-outer groove depth ratio is 0.6 to 0.7.

Abstract: [Problem] In a hydraulic dynamic bearing comprising a flanged shaft having a thrust ring portion and a cylinder portion, a single bag-like stepped sleeve, a presser ring and a lubricating oil sealed in a fine gap including a thrust gap formed between these bearing constituting members, the lubricating oil in a thrust dynamic pressure generating groove is prevented from being subjected a negative pressure in the vicinity of an inlet. [Means for Resolution] In case of a spiral pattern, the thrust dynamic pressure generating groove G2 is formed such that its depth becomes gradually deep from a side at which a flow velocity of the lubricating oil flowing through the thrust gap is low toward a side at which it is high. Further, in case of a herringbone pattern, the thrust dynamic pressure generating groove G2 is formed such that its depth becomes shallow in an inner peripheral face side than a return point R of the pattern and deep in an outer peripheral face side. An optimum groove depth ratio is 0.6 to 0.7.

Abstract: A double sleeve type dynamic bearing comprises a fixed shaft having at least one end fixedly mountable to an apparatus in which the bearing is utilized, a rotary sleeve arranged coaxially with the fixed shaft so that a first fine gap is formed therebetween, a fixed sleeve arranged coaxially with the rotary sleeve so that a second fine gap is formed therebetween, and a lubrication oil filled in the fine gaps. The first fine gap and the second fine gap each have an open end exposed to air outside the bearing and an opposite end that is not exposed to the air, the opposite ends being in communication with each other. A holding member holds the fixed shaft and the fixed sleeve and is disposed adjacent to a lower end surface of the rotary sleeve to form a third fine gap between the holding member and the lower end surface of the rotary sleeve. The third fine gap is formed with a thrust dynamic pressure producing groove, and opposite ends of the first and second fine gaps meet each other through the third fine gap.

Abstract: The present invention is a double sleeve type fluid dynamic pressure bearing, comprising a fixed shaft having respective ends to be fixed to a utilized apparatus; a rotary sleeve arranged to provide a first fine gap between an inner peripheral surface thereof and an outer peripheral surface of the fixed shaft, a fixed sleeve arranged to provide a second fine gap between an inner peripheral surface thereof and an outer peripheral surface of the rotary sleeve, a holder member arranged to cooperate with a lower end surface of the rotary sleeve to provide a third gap, and wherein the first fine gap and the second fine gap are formed with radial dynamic pressure producing grooves while the third fine gap is formed with a thrust dynamic pressure producing groove, the first, second and third fine gaps being filled with lubrication oil, the first fine gap and the second fine gap having one ends made as opening ends contacting with the air and the other ends made as closed ends communicated with each other through the