Bearings – Rotary bearing – Fluid bearing
Reexamination Certificate
2000-03-24
2001-06-19
Mullins, Burton (Department: 2834)
Bearings
Rotary bearing
Fluid bearing
C310S090000, C384S112000
Reexamination Certificate
active
06247848
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a ring-like hydraulic dynamic bearing having axial dynamic pressure portions and a radial dynamic pressure portion contiguous to each other and to a spindle motor using the hydraulic dynamic bearing.
As a bearing for a spindle motor for a hard disk device, there is used a hydraulic dynamic bearing having a shaft portion and a bearing portion for supporting the bearing portion. The hydraulic dynamic bearing is formed with dynamic pressure generating grooves at either one of opposed faces of the shaft and bearing portions and is formed with a layer of a lubricant at high pressure in a very small clearance disposed between the shaft and bearing portions so that during rotation of the shaft portion noncontact rotation of the shaft portion is realized.
FIG. 8
is a sectional view showing a conventional ring-like hydraulic dynamic bearing. A ring-like hydraulic dynamic bearing
100
is provided with a shaft portion
103
constituted by fixing a ring
102
to an end portion
101
A of a shaft main body
101
by press fitting and a bearing portion
104
supporting the shaft portion
103
and is constituted such that the ring
102
at the shaft portion
103
rotatably contained in a recess portion
105
A of a main body
105
of the bearing portion
104
is prevented from coming out from the recess portion
105
A by a circular disk-like thrust holding member
106
.
An upper face
102
A and a lower face
102
B of the ring
102
are respectively formed with axial dynamic pressure generating grooves G
1
and G
2
and a peripheral face
102
C of the ring
102
is formed with radial dynamic pressure generating grooves G
3
.
A lubricant for generating dynamic pressure is held between the shaft portion
103
and the bearing portion
104
and accordingly, when the shaft portion
103
is rotated, axial dynamic pressure is generated between the upper face
102
A and the circular disk-like thrust holding member
106
by the axial dynamic pressure generating grooves G
1
and axial dynamic pressure is generated between the lower face
102
B and a bottom face of the recess portion
105
A by the axial dynamic pressure generating grooves G
2
. Further, radial dynamic pressure is generated between the peripheral face
102
C and an inner peripheral face of the recess portion
105
A by the radial dynamic pressure generating grooves G
3
. As a result, axial dynamic pressure bearings and a radial dynamic pressure bearing which are lubricant layers at high pressure are formed between the shaft portion
103
and the bearing portion
104
to thereby enable to rotate the shaft portion
103
by noncontact rotation.
As described above, according to the conventional ring-like radial dynamic bearing, there is constructed the constitution in which the radial dynamic pressure generating face and the axial dynamic pressure generating faces are contiguous to each other and accordingly, the following problem is posed. That is, when the shaft portion
103
is rotated, by the axial dynamic pressure generating grooves G
1
, the axial dynamic pressure generating grooves G
2
and the radial dynamic pressure generating grooves G
3
which are respectively formed at the upper face
102
A, the lower face
102
B and the peripheral face
102
C of the ring
102
, the lubricant is drawn to central portions of the respective dynamic pressure generating faces and negative pressure is produced at portions of the upper face
102
A and the peripheral face
102
C contiguous to each other and portions of the lower face
102
B and the peripheral face
102
C contiguous to each other. As a result of producing the negative pressure caused by mutual interference, air bubbles are liable to produce at the portions of the dynamic pressure generating faces contiguous to each other which hamper flow of the lubricant and accordingly, there causes a drawback in which sufficient dynamic pressure is not generated and the bearing rigidity is deteriorated.
SUMMARY OF THE INVENTION
Hence, it is an object of the invention to provide a hydraulic dynamic bearing capable of resolving the above-described problem in the conventional technology and to a spindle motor using the hydraulic dynamic bearing.
In order to resolve the above-described problem, according to an aspect of the invention, there is proposed a hydraulic dynamic bearing which is a ring-like hydraulic dynamic bearing comprising a shaft portion constituted by fixing a ring to an end portion of a shaft main body thereof and a bearing portion supporting the shaft portion via the ring wherein a radial dynamic pressure bearing portion and axial dynamic pressure bearing portions are formed contiguously to each other between the ring and the bearing portion and wherein spaces for storing a lubricant for generating dynamic pressure are provided along portions of the radial dynamic pressure bearing portion and the axial dynamic pressure bearing portions contiguous to each other.
When relative rotational motion is caused between the shaft portion and the bearing portion, the lubricant at the respective dynamic pressure bearing portions is drawn to respective central portions of the shaft and bearing portions to thereby generate required dynamic pressure. Therefore, at regions of the radial dynamic pressure bearing portion and the axial dynamic pressure bearing portions contiguous to each other, the lubricant is going to reduce. However, owing to the lubricant stored in the spaces provided along the portions of the two dynamic pressure bearing portions contiguous to each other, the reduction does not amount to produce mutual interference between the two dynamic pressure bearing portions and mutual operation between the two dynamic pressure bearing portions is alleviated. As a result, at the portions of the two dynamic pressure bearing portions contiguous to each other, generation of negative pressure is restrained and air bubbles can be restrained from generating in the lubricant and accordingly, the bearing rigidity can be made higher than that in the conventional bearing.
The radial dynamic pressure bearing can be formed by providing dynamic pressure generating grooves at an outer peripheral face of the ring or an inner face of the bearing portion opposed thereto. The axial dynamic pressure bearing can be formed by providing the dynamic pressure generating grooves at at least one of plane portions contiguous to an outer peripheral face of the ring. Alternatively, the dynamic pressure generating grooves may be formed at inner faces of the bearing portion opposed to the plane portions.
The spaces for storing the lubricant can be provided by forming ring-like recess portions at boundary regions between the outer peripheral face of the ring and the planes contiguous thereto. A sectional shape of the recess portion may be that of a circular arc or an arbitrary stepped shape of an L-like type.
According to another aspect of the invention, there is proposed a constitution in which a clearance is provided between an end face of the shaft main body and the bearing portion opposed thereto and paths for communicating the clearance with the atmosphere are formed at an inner peripheral face of the ring to thereby enable to circulate the lubricant by the clearance and the paths.
According to the constitution, in the case in which there is constructed a constitution in which axial dynamic pressure is generated between the plane portion on the end face side of the shaft main body in the plane portion of the ring and the bearing portion, even when the lubricant disposed in the clearance is drawn to the ring side in generating the dynamic pressure, owing to the lubricant circulating to the clearance by passing through the paths communicating with the atmosphere, the negative pressure can effectively be prevented from generating in the clearance. As a result, the dynamic pressure is excellently generated at the plane portion and the bearing rigidity can further be promoted.
Further, in either of the cases, the spaces for storing the lubricant are not limited to the
Goto Hiromitsu
Iwaki Tadao
Kawawada Naoki
Nitadori Koji
Ohki Shigeru
Adams & Wilks
Mullins Burton
Seiko Instruments Inc.
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