Abstract: A fluid dynamic bearing is provided. A structure in which a shaft member and an annular member fitted about the shaft member are rotatably supported by a bearing member and an annular member on the bearing member has a fifth gap for storing a lubricating fluid and supplying it to a second gap below the annular member on the shaft member and a third gap around its outer periphery through a fourth gap. The fourth and fifth gaps are tapered to produce a capillary drawing force toward the third and second gaps, so that the lubricating fluid may be supplied effectively from the fifth gap to the second and third gaps. This makes it possible to suppress any sudden formation of a reduced pressure upon exposure to impact or vibration to prevent the leakage of any lubricating fluid caused by the generation of bubbles, while making up for the loss of any lubricating fluid by vaporization.

Abstract: A fluid dynamic bearing is provided. A structure in which a shaft member and an annular member fitted about the shaft member are rotatably supported by a bearing member and an annular member on the bearing member has a fifth gap for storing a lubricating fluid and supplying it to a second gap below the annular member on the shaft member and a third gap around its outer periphery through a fourth gap. The fourth and fifth gaps are tapered to produce a capillary drawing force toward the third and second gaps, so that the lubricating fluid may be supplied effectively from the fifth gap to the second and third gaps. This makes it possible to suppress any sudden formation of a reduced pressure upon exposure to impact or vibration to prevent the leakage of any lubricating fluid caused by the generation of bubbles, while making up for the loss of any lubricating fluid by vaporization.

Abstract: A magnet 5 is disposed radially outward to a fitting portion 8. Thereby, an armature 3 to be disposed so as to face the magnet 5 may be arranged radially outward. It is possible to keep a large space for the arrangement of a fluid bearing to be disposed radially inward to the armature, and, as a result, the fluid bearing having a large size may be used. The large sized fluid bearing 40 is used for keeping a high mechanical strength, avoiding a fear that the fluid bearing 40 would be damaged when it receives a shock, and also avoiding the reduction in rotational speed of the magnetic disk 7, the degradation of accuracy in the writing and reading operation of magnetic data and the generation of a noise or a vibration The fluid bearing 40 is used to reduce a friction even if the motor is rotated at a high speed, which may reduce the power consumption.

Abstract: In a ball bearing, a shielding plate (5), which is injection-molded into one piece from a polyacetal resin which is adequate in all of rigidity, Flexibility and resiliency, is interposed between an inner race (1) and an outer race (2) in a side off the bearing to protect the interior of the bearing from dust and moisture. In assembling, the shielding plate ( 5 ) has its outer peripheral portion resiliently deformed and fitted into an inner annular groove (2a) of the outer race (2), and does not affect the outer race (2) in dimension thereof at all after completion of the assembling.