Hydrodynamic bearing device, spindle motor, and recording and reproducing apparatus

1. A hydrodynamic bearing device, comprising:

a shaft;

a sleeve configured to rotate relative to the shaft, the sleeve having an inner peripheral surface opposing an outer peripheral surface of the shaft at a distance in a radial direction so as to form a first gap therebetween;

a sealing member provided as one with the sleeve, having an inner peripheral surface opposing an outer peripheral surface of the shaft at a distance in a radial direction so as to form a second gap therebetween, and having an end face opposing one side end face of the sleeve at a distance in an axis direction so as to form a third gap therebetween;

a thrust flange provided in close proximity to an end of the shaft, having a diameter larger than that of the shaft, and having an end face opposing the other side end face of the sleeve at a distance in an axis direction so as to form a fourth gap therebetween;

at least one connecting channel between the third gap and the fourth gap to connect the third gap and the fourth gap therebetween; and

a lubricating fluid retained in at least the first gap, the third gap, the fourth gap, and the connecting channel;

a radial dynamic pressure bearing is formed in the first gap,

an interface between the lubricating fluid and the atmosphere is formed in the second gap, and

a radial clearance A of the first gap, a radial clearance B of the second gap, and an axis direction clearance C of the third gap satisfy a relationship

A<B<C.

2. The hydrodynamic bearing device of claim 1 , wherein dynamic pressure generated by the radial dynamic pressure bearing is generated in a direction such that the lubricating fluid flows from the first gap towards the second gap or the third gap.

3. The hydrodynamic bearing device of claim 1 , wherein a thrust dynamic pressure bearing is formed in the fourth gap.

4. The hydrodynamic bearing device of claim 3 , wherein dynamic pressure generated by the radial dynamic pressure bearing or the thrust dynamic pressure bearing is generated in a direction such that the lubricating fluid flows from the first gap towards the second gap or the third gap.

5. A hydrodynamic bearing device, comprising:

a shaft;

a sleeve configured to rotate relative to the shaft, the sleeve having an inner peripheral surface opposing an outer peripheral surface of the shaft at a distance in a radial direction so as to form a first gap therebetween;

a sealing member provided as one with the sleeve, having an inner peripheral surface opposing an outer peripheral surface of the shaft at a distance in a radial direction so as to form a second gap therebetween, and having an end face opposing one side end face of the sleeve at a distance in an axis direction so as to form a third gap therebetween;

a thrust plate opposing the other side end face of the sleeve at a distance in an axis direction so as to form a fourth gap therebetween and sealing one opening end of the sleeve;

at least one connecting channel between the third gap and the fourth gap to connect the third gap and the fourth gap; and

a lubricating fluid retained in at least the first gap, the third gap, the fourth gap, and the connecting channel;

a radial dynamic pressure bearing is formed in the first gap,

an interface between the lubricating fluid and the atmosphere is formed in the second gap, and

a radial clearance A of the first gap, a radial clearance B of the second gap, and a third axis-direction clearance C satisfy a relationship

A<B<C.

6. The hydrodynamic bearing device of claim 5 , wherein dynamic pressure generated by a radial hydrodynamic groove is generated in a direction such that the lubricating fluid is flown from the first gap towards the second gap or the third gap.

7. A hydrodynamic bearing device, comprising:

a shaft having a cylindrical section and a small diameter cylindrical section, the small diameter cylindrical section being provided via a step surface in close proximity to one end section of the cylindrical section and having a diameter smaller than the outer diameter of the cylindrical section;

a sleeve configured to rotate relative to the shaft, the sleeve having an inner peripheral surface opposing an outer peripheral surface of the cylindrical section of the shaft at a distance in a radial direction so as to form a first gap therebetween;

a sealing member provided as one with the sleeve, having an inner peripheral surface opposing an outer peripheral surface of the small diameter cylindrical section of the shaft at a distance in a radial direction so as to form a second gap therebetween, and having an end face opposing both the step surface of the shaft at a distance in an axis direction so as to form a fifth gap therebetween and one side end face of the sleeve at a distance in an axis direction so as to form a third gap therebetween;

a thrust flange provided in close proximity to the other end side of the shaft, having an end face opposing the other side end face of the sleeve at a distance in an axis direction so as to form a fourth gap therebetween, and having a diameter larger than that of the cylindrical section of the shaft;

at least one connecting channel between the third gap and the fourth gap to connect the third gap and the fourth gap; and

a lubricating fluid retained in at least the first gap, the third gap, the fourth gap, and the connecting channel;

a radial dynamic pressure bearing is formed in the first gap,

an interface between the lubricating fluid and the atmosphere is formed in the fifth gap, and

a radial clearance A of the first gap, an axis direction clearance D of the fifth gap, and an axis-direction clearance C of the third gap satisfy a relationship

A<D<C.

8. The hydrodynamic bearing device of claim 7 , wherein dynamic pressure generated by a radial hydrodynamic groove is generated in a direction such that the lubricating fluid is flown from the first gap towards the fifth gap or the third gap.

9. The hydrodynamic bearing device of claim 7 , wherein a thrust dynamic pressure bearing is formed in the fourth gap.

10. The hydrodynamic bearing device of claim 9 , wherein dynamic pressure generated by the radial dynamic pressure bearing or the thrust dynamic pressure bearing is generated in a direction such that the lubricating fluid is flown from the first gap towards the fifth gap or the third gap.

11. A hydrodynamic bearing device, comprising:

a shaft having a cylindrical section and a small diameter cylindrical section, the small diameter cylindrical section being provided via a step surface in close proximity to one end section of the cylindrical section and having a diameter smaller than the outer diameter of the cylindrical section;

a sleeve configured to rotate relative to the shaft, the sleeve having an inner peripheral surface opposing an outer peripheral surface of the cylindrical section of the shaft at a distance in a radial direction so as to form a first gap therebetween;

a sealing member provided as one with the sleeve, having an inner peripheral surface opposing an outer peripheral surface of the small diameter cylindrical section of the shaft at a distance in a radial direction so as to form a second gap therebetween, and having an end face opposing both the step surface of the shaft at a distance in an axis direction so as to form a fifth gap therebetween and one side end face of the sleeve at a distance in an axis direction so as to form a third gap therebetween;

a thrust plate opposing the other side end face of the sleeve at a distance in an axis direction so as to form a fourth gap therebetween and sealing one opening end of the sleeve;

at least one connecting channel between the third gap and the fourth gap to connect the third gap and the fourth gap; and

a lubricating fluid retained in at least the first gap, the third gap, the fourth gap, and the connecting channel;

a radial dynamic pressure bearing is formed in the first gap,

an interface between the lubricating fluid and the atmosphere is formed in the fifth gap, and

a radial clearance A of the first gap, an axis direction clearance D of the fifth gap, and an axis direction clearance C of the third gap satisfy a relationship

A<D<C.

12. The hydrodynamic bearing device of claim 11 , wherein dynamic pressure generated by the radial dynamic pressure bearing is generated in a direction such that the lubricating fluid flows from the first gap towards the fifth gap or the third gap.

13. A hydrodynamic bearing device having a hydrodynamic bearing using a lubricating fluid, comprising:

a shaft;

a sleeve configured to rotate relative to the shaft, the sleeve having an inner peripheral surface opposing an outer peripheral surface of the shaft at a distance in a radial direction so as to form a first gap therebetween; and

a sealing member provided as one with the sleeve such that a second gap is formed between the sealing member and the shaft and having an end face opposing one side end face of the sleeve at a distance in an axis direction so as to form a third gap therebetween;

an interface between the lubricating fluid and the atmosphere is formed in the second gap, and

a relationship is such that the first gap size<the second gap size<the third gap size.

14. The hydrodynamic bearing device of claim 13 , wherein the second gap is a radial clearance formed between an outer peripheral surface of the shaft and an inner peripheral surface of the sealing member.

15. The hydrodynamic bearing device of claim 13 , wherein:

the shaft is formed with an end face facing in the axis direction; and

the second gap is an axis direction clearance formed between an end face of the shaft and an end face of the sealing member.

16. The hydrodynamic bearing device of claim 13 , wherein:

a radial dynamic pressure bearing is formed in the first gap; and

dynamic pressure generated by the radial dynamic pressure bearing is generated in a direction such that the lubricating fluid flows from the first gap towards the second gap or the third gap.

17. A spindle motor comprising the hydrodynamic bearing device of claim 13 .

18. A recording and reproducing apparatus comprising the spindle motor of claim 17 .