A fluid dynamic bearing device rotatably supports a shaft member through an oil film formed in a bearing clearance. The fluid dynamic bearing device is one having characteristics such as high-speed rotation operation, excellent rotational accuracy, and quietness. In recent years, by taking advantage of those characteristics, the fluid dynamic bearing device is suitably used as a bearing device for a motor to be mounted to various electrical apparatuses such as information equipment. Specifically, as a bearing device for a motor, the fluid dynamic bearing device can be suitably used in the following: a spindle motor for an information apparatus such as a magnetic disk drive such as an HDD, an optical disk drive for a CD-ROM, CD-R/RW, DVD-ROM/RAM, or the like, or a magneto-optical disk drive for an MD, MO, or the like; a polygon scanner motor of a laser beam printer (LBP); or a fan motor.
As a fluid dynamic bearing device of this type, one having a structure is well-known in which a bearing sleeve made of a sintered metal is fixed along an inner periphery of a housing of a bottomed cylindrical shape, and an axial member is inserted along an inner periphery of the bearing sleeve so that a radial bearing clearance is formed between an outer peripheral surface of the axial member and an inner peripheral surface of the bearing sleeve. In the housing, a seal member is disposed adjacently to the bearing sleeve in an axial direction thereof, and a seal space is formed in which an lubricant oil is filled between an inner peripheral surface of the seal member and an outer peripheral surface of the axial member. As a result, leakage of the lubricant oil filled inside the housing is prevented owing to a capillary effect.
Well-known example of the housing and the seal member includes a machined product of a free-cutting brass (refer to Patent Document 1, for example).
Further, as a fluid dynamic bearing device of this type, one illustrated in FIG. 16 is well-known. In a fluid dynamic bearing device 70 illustrated in the figure, a bearing sleeve 78 is fixed along an inner periphery of a housing 77, and an axial member 72 is inserted along an inner periphery of the bearing sleeve 78 so that radial bearing portions 75 and 76 are provided in a radial bearing clearance formed between an outer peripheral surface of the axial member 72 and an inner peripheral surface of the bearing sleeve 78. Further, an annular seal member 79 is fixed along an inner periphery of an opening of the housing 77, and a seal space is formed between the seal member 79 and the axial member 72. For cost reduction of the fluid dynamic bearing device, it is desirable that the number of components be as small as possible, and the configurations of the members be as simple as possible. Accordingly, in the fluid dynamic bearing device 70 illustrated in the figure, the housing 77 is formed in a bottomed cylindrical shape (cup shape) in which a side portion and a bottom portion thereof are formed integrally with each other, and an inner periphery of the side portion is formed in a cylindrical surface straight over the entire axial length (refer to Patent Documents 2 and 3, for example).
Still further, as examples of the fluid dynamic bearing device of this type, Patent Document 4 describes one in which a housing made of a resin is used, and Patent Document 5 describes one in which a bearing sleeve made of a resin is used. As described above, employment of the housing and bearing sleeve made of a resin achieves the reduction in material cost.    Patent Document 1: JP 2003-172336 A    Patent Document 2: JP 2003-232353 A    Patent Document 3: JP 2003-239974 A    Patent Document 4: JP 2005-282779 A    Patent Document 5: JP 2005-163858 A