Patent ID: 8016488

Claim:
A fluid dynamic bearing device, comprising: a housing opened at both ends thereof, the housing being provided with large diameter portions at both end portions thereof; bearing sleeves accommodated in the housing so as to be axially spaced apart from each other; a shaft member inserted along inner peripheries of the bearing sleeves, the shaft member having protruding sections which are provided at both ends of the shaft member and protrudes to an outer diameter side of the shaft member; radial bearing portions supporting the shaft member in a non-contact manner in a radial direction by a dynamic pressure action of a lubricant fluid, which is generated in radial bearing gaps between inner peripheral surfaces of the bearing sleeves and an outer peripheral surface of the shaft member; thrust bearing portions provided between end surfaces of the protruding sections of the shaft member and end surfaces of the bearing sleeves, the thrust bearing portions supporting the shaft member in a non-contact manner in a thrust direction by a dynamic pressure action of the lubricant fluid generated in thrust bearing gaps; a spacer portion, which protrudes further radially inwardly than outer peripheral surfaces of the bearing sleeves, is provided between the bearing sleeves axially spaced apart from each other, the spacer portion being formed integrally with the housing; and seal spaces formed on outer periphery sides of the protruding sections of the shaft member, wherein axial fluid paths are formed between an inner peripheral surface of the housing and the outer peripheral surfaces of the bearing sleeves, and wherein each of the end surfaces of the bearing sleeves is axially protruded above a step surface of the large diameter portion of the housing by a predetermined dimension, thereby an axial gap portion having an axial dimension, which is larger than the thrust bearing gap, is formed between the end surface of the protruding section of the shaft member and the step surface of the large diameter portion of the housing, the axial gap portion communicating to the axial fluid path and the thrust bearing gap at an inner diameter side of the axial gap portion and to the seal space at an outer diameter side of the axial gap portion.