Hydrodynamic type bearing unit

Details Hydrodynamic type bearing unit Hydrodynamic type bearing unit

2000-10-26

2002-08-13

Hannon, Thomas R. (Department: 3682)

Bearings

Rotary bearing

Fluid bearing

Reexamination Certificate

active

06431757

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a hydrodynamic type bearing unit. This bearing unit is particularly suited to supporting a spindle of a spindle motor for use in information equipment including magnetic disk drives such as an HDD and an FDD, optical disk drives such as a CD-ROM and a DVD-ROM, and magneto-optical disks such as an MD and an MO, or a spindle of a polygon scanner motor for use in laser beam printers (LBPs).
2. Description of the Related Art
A spindle motor in various information equipment mentioned above requires high rotational accuracy, along with higher speeds, lower costs, lower noises, and the like. Among the components that determine these performance requirements is a bearing for supporting the spindle of that motor. For this type of bearing, a hydrodynamic type bearing having excellent properties as to the above-mentioned performance requirements has been recently studied for its use, or put into practical use.
For example, some hard disk drives (HDD), a kind of information equipment, include a bearing unit in which, as schematically shown in
FIG. 5
, both a radial bearing part
10
′ for supporting a spindle member
2
′ in the radial direction and a thrust bearing part
11
′ for supporting the spindle member
2
′ in the thrust direction are constituted by hydrodynamic type bearings. In this shown example, the spindle member
2
′ consists of a spindle
2
a
′ and a thrust disc
2
b
′ fixed to an end of the spindle
2
a
′. The rotation of the spindle member
2
′ creates other hydrodynamic pressures of oil, air, or the like in a bearing clearance Cr′ of the radial bearing part
10
′ and in bearing clearances CS
1
′ and CS
2
′ of the thrust bearing part
11
′, whereby the spindle member
2
′ is rotatably supported in both the radial and thrust directions without contact.
Recently, in contemplation of on-notebook-PC mounting and the like, there has been a growing demand that the above-described bearing unit
1
′ have more compact configuration, in particular a reduced axial dimension (lower profile). As a measure to be taken therefor, the radial bearing part
10
′ may be effectively reduced in axial length L′. The reduction of the axial length L′, however, is accompanied by a decrease of the radial bearing part
10
′ in bearing span (distance between axially-spaced hydrodynamic type bearings), producing a problem of lower bearing capacity against a moment load.
In particular, the thrust disc
2
b
′ and the spindle
2
a
′ conventionally involve forming errors in the perpendicularity therebetween and the like. To prevent the thrust disc
2
b
′ and the thrust bearing surfaces
11
a
′,
11
b
′ from contacting each other because of these errors, the thrust bearing clearances CS
1
′ and CS
2
′ are formed fairly large. When the spindle member
2
′ here is tilted by a moment load (as shown by double-dashed chain lines in FIG.
5
), however, most of the moment load is supported by the radial bearing part
10
′ (the top end thereof, in particular) while the thrust bearing part
11
′ exerts little moment supporting power. This decreases the moment load capacity of the entire bearing unit.
Moreover, when the bearing unit
1
′ is made thinner as described above, the diameter D′ of the thrust disc
2
b
′ becomes greater in relation to the axial length L′ of the radial bearing part
10
′. The moment load capacity of the entire bearing unit thus depends largely on the moment load capacity of the thrust bearing part
11
′. On the contrary, the conventional thrust bearing part
11
′ cannot provide a sufficient moment supporting power, and this has been a major obstacle to increase moment load capacity.
SUMMARY OF THE INVENTION
In view of the foregoing, an object of the present invention is to enhance the moment supporting power, in particular, of the thrust bearing part, and improve the moment load capacity of the entire hydrodynamic type bearing unit.
To achieve the foregoing object, a hydrodynamic type bearing unit according to the present invention comprises: a spindle member composed of a spindle and a flange portion; a radial bearing part for supporting the spindle member in a radial direction without contact by means of a hydrodynamic pressure occurring in a radial bearing clearance between the outer periphery of the spindle and a radial bearing surface opposed thereto; and a thrust bearing part for supporting the spindle member in a thrust direction without contact by means of hydrodynamic pressures occurring in thrust bearing clearances between the end faces of the flange portion and thrust bearing surfaces opposed thereto, wherein a relation between the radial bearing clearance and the thrust bearing clearances are set so that a moment load acting on the spindle member is supported by both of the radial bearing part and the thrust bearing part. Here, the spindle member tilted comes into contact at the outer periphery of its spindle with both axial ends of the radial bearing surface opposed thereto. In the meantime, the rims of both end faces of its flange portion also come into contact with the respective thrust bearing surfaces opposed thereto.
When the radial bearing clearance &dgr;
R
and the thrust bearing clearance &dgr;
A
satisfy the following expression:
(
D&dgr;
R
/L
)+&egr;≧&dgr;
A
≧D&dgr;
R
/L
(where D is the diameter of the flange portion, L is the axial length L of the radial bearing part, and &egr; is a machining error), both the radial bearing part and the thrust bearing part can secure a practically sufficient moment supporting power.
Here, the machining error &egr; may be 4 &mgr;m. The diameter D of the flange portion may be equal to or smaller than 10 mm.
In any of the configurations described above, the diameter of the flange portion is preferably greater than the axial length of the radial bearing part.
The nature, principle, and utility of the invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings in which like parts are designated by like reference numerals or characters.


REFERENCES:
patent: 5357162 (1994-10-01), Aiyoshizawa et al.
patent: 5707154 (1998-01-01), Ichiyama
patent: 6040648 (2000-03-01), Kawawada et al.
patent: 6059459 (2000-05-01), Ichiyama

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