Bearings – Rotary bearing – Fluid bearing
Reexamination Certificate
2001-02-23
2004-03-30
Schwartz, Christopher P. (Department: 3683)
Bearings
Rotary bearing
Fluid bearing
Reexamination Certificate
active
06712513
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a fluid bearing device for information equipments, audio and video equipments, business machines. More particularly, the invention relates to a fluid bearing device suitable for magnetic hard disk drive (HDD), fan motor and so forth to be used in a notebook type personal computer or the like.
2. Description of the Related Art
As a typical conventional fluid bearing device of the type set forth above is a spindle motor for HDD, for example. A construction of the spindle motor will be discussed with reference to
FIG. 3
which is a section showing a construction of a spindle motor as the fourth embodiment of the present invention.
In the spindle motor, a cylindrical portion
101
a
is vertically extended from a base
101
. On the cylindrical portion
101
a
, a sleeve
102
is fixed. A shaft
103
is rotatably inserted into the sleeve
102
. On the upper end of the shaft
103
, a reversed cup-shaped hub
104
is integrally mounted. Between the shaft
103
and the sleeve
102
, a dynamic pressure fluid bearing portion is interposed.
Namely, on the lower end of the shaft
103
, a disk shaped thrust plate
105
is secured by press fitting. Both planar surfaces of the thrust plate
105
serves as thrust receiving surface
105
s
of a thrust fluid bearing S. To the thrust receiving surface
105
s
on the upper surface side, a lower end surface of the sleeve
102
as a counter part member is placed in opposition. The lower end surface of the sleeve
102
serves as the thrust bearing surface
102
s
of the thrust fluid bearing S.
On the other hand, below the thrust plate
105
, a counter plate
106
as another counter part member is arranged. The counter plate
106
is fixed to the base
101
. The upper surface of the counter plate
106
is placed in opposition to the thrust receiving surface
105
s
on the lower surface side of the thrust plate
105
to form thrust bearing surface
106
s
of the thrust fluid bearing S. At least one of the thrust receiving surfaces
105
s
and the thrust bearing surfaces
102
s
and
106
s
, a thrust fluid bearing S having a not shown herringbone type or spiral type groove for generating a dynamic pressure, is constructed.
Furthermore, on the outer peripheral surface of the shaft
103
, a pair of radial receiving surface
103
r
is formed. In opposition to the radial receiving surface
103
r
, a radial bearing surface
102
r
is formed on the inner peripheral surface of the sleeve
102
. At least one of the radial receiving surface
103
r
and the radial receiving surface
102
r
has a herringbone type groove
107
for generating dynamic pressure for example, to form a radial fluid bearing R.
On the outer periphery of the cylindrical portion
101
a
, a stator
108
is fixed. The stator
108
opposes with a rotor magnet
109
fixed on the lower side of the inner peripheral surface of the hub
104
over the entire circumference to form a drive motor M for driving the shaft
103
and the hub
104
for rotation in integral manner.
When the shaft
103
is driven to rotate, by pumping action of respective grooves for generating dynamic pressure of the thrust fluid bearing S and the radial fluid bearing R, dynamic pressure is generated in lubricant in bearing clearances of the fluid bearings S and R. The shaft
103
is supported in non-contact manner with the sleeve
102
and the counter plate
106
.
Such conventional spindle motor is constructed with a stainless steel having high Young's modules (Vickers hardness Hv=about 270) for certainly obtaining a joint strength by press fitting of the thrust plate
105
and the shaft
103
to assure impact resistance against external shock. The sleeve
102
and the counter plate
106
as counterpart member is constructed with a copper alloy of the same composition (e.g. free cutting brass of Vickers hardness Hv=about 150). On the other hand, the groove for generating dynamic pressure of the thrust fluid bearing S is processed by etching on both planar surfaces of the thrust plate
105
.
In the recent spindle motor for HDD, it has been required superior durability in starting and stopping for assuring reliability for a long period. Particularly, in case of dynamic pressure fluid bearing, it is inherent to cause mutual contact between the thrust bearing surface
106
s
and the thrust receiving surface
105
s
upon starting and stopping. Therefore, repeating of starting and stopping inherently cause wearing to increase wearing tip which can be bit in the bearing to degrade precision of rotation or in the worst case to cause failure of rotation.
Accordingly, it is important to prevent the thrust bearing surface
106
s
and the thrust receiving surface
105
s
from being damaged due to contact upon starting and stopping.
However, in the conventional thrust fluid bearing S, since the groove for generating dynamic pressure is in the thrust plate
105
which is formed with the stainless steel having high hardness, fine burr or bulge portion around the peripheral portion of the groove to be created during etching process, cannot be removed completely. Therefore, by repeating of starting and stopping, it is possible to damage the bearing surface (thrust bearing surface
102
s
and the thrust bearing surface
106
s
) of the counterpart member (sleeve
102
and counter plate
106
) formed with copper alloy having low hardness.
On the other hand, since the stainless steel is not good in cutting ability, difficulty is encountered in assuring dimensional precision to cause manufacturing ability.
SUMMARY OF THE INVENTION
Therefore, the present invention is to provide a fluid bearing device solving the problem in the conventional fluid bearing and superior in wear start-stop resistance and in manufacturing ability.
In order to accomplish the above-mentioned object, a fluid bearing device comprises:
a shaft having a flange portion;
a sleeve opposing to the shaft across a fluid bearing clearance of a radial fluid bearing;
a counterpart member opposing to at least one of plane of the flange portion across a fluid bearing clearance of a thrust bearing,
the flange portion and the sleeve portion being formed of copper alloy of mutually difference composition.
With the construction set forth above, the fluid bearing device according to the present invention facilitates certainly obtaining dimensional precision, achieves superior workability and mass-productivity since the flange portion and the sleeve are formed of copper alloy having high cutting ability.
Since the flange portion and the sleeve are formed with the copper alloys mutually having different compositions, high workability in formation of the dynamic pressure generating groove can be achieved for accomplishing high mass-production ability by machining the dynamic pressure generating groove on one of the flange portion and the sleeve having lower hardness. In addition, fine burr or bulged portion around the groove formed during machining of the groove, can be completely removed for successfully preventing damaging of the bearing surfaces of the member, to which the flange portion or the sleeve contact due to repeated staring and stopping of the bearing.
It is preferred that the composition of the copper alloys forming the flange portion and the sleeve are selected to that the difference of hardness in Vickers hardness Hv is greater than or equal to 50. Thus, the bearing surface of the member is hardly damaged to achieve high durability in starting and stopping. When the hardness of the flange portion and the sleeve is the same, the dynamic pressure generating groove may be formed in either one of or both of the flange portion and the sleeve.
On the other hand, in the fluid bearing device, a copper alloy forming the sleeve is a copper alloy having Vickers hardness Hv 180 or higher, and more preferably having Vickers hardness Hv 200 or higher.
Also, in the fluid bearing device of the present invention, the copper alloy can be any one of beryllium copper, high strength b
Higuchi Yukio
Ochiai Masayuki
Otsubo Takenobu
Sakatani Ikunori
Tanaka Katsuhiko
Crowell & Moring LLP
NSK Ltd.
Schwartz Christopher P.
Torres Melanie
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