U.S. patent application number 11/547641 was filed with the patent office on 2007-12-13 for dynamic bearing device.
Invention is credited to Toshiyuki Mizutani.
Application Number | 20070286538 11/547641 |
Document ID | / |
Family ID | 35125150 |
Filed Date | 2007-12-13 |
United States Patent
Application |
20070286538 |
Kind Code |
A1 |
Mizutani; Toshiyuki |
December 13, 2007 |
Dynamic Bearing Device
Abstract
A seal member is fixed to a predetermined position on an outer
peripheral surface of a shaft portion. During rotation of a shaft
member, a lower end surface of the seal member is opposed to an
upper end surface of a bearing sleeve through an intermediation of
a thrust bearing gap to form a second thrust bearing gap. An outer
peripheral surface of the seal member defines between itself and an
inner peripheral surface of an upper end portion of a housing a
seal space having a predetermined volume.
Inventors: |
Mizutani; Toshiyuki;
(Kuwana-shi, JP) |
Correspondence
Address: |
WENDEROTH, LIND & PONACK, L.L.P.
2033 K STREET N. W.
SUITE 800
WASHINGTON
DC
20006-1021
US
|
Family ID: |
35125150 |
Appl. No.: |
11/547641 |
Filed: |
April 7, 2005 |
PCT Filed: |
April 7, 2005 |
PCT NO: |
PCT/JP05/06847 |
371 Date: |
July 3, 2007 |
Current U.S.
Class: |
384/112 ;
29/898.02; 384/114 |
Current CPC
Class: |
Y10T 29/4968 20150115;
F16C 33/1075 20130101; Y10T 29/497 20150115; F16C 17/028 20130101;
F16C 33/107 20130101; Y10T 29/49703 20150115; F16C 17/107 20130101;
Y10T 29/49639 20150115; F16C 33/745 20130101 |
Class at
Publication: |
384/112 ;
029/898.02; 384/114 |
International
Class: |
F16C 17/10 20060101
F16C017/10; B21D 53/10 20060101 B21D053/10 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 9, 2004 |
JP |
2004-115695 |
Apr 9, 2004 |
JP |
2004-115704 |
Jan 25, 2005 |
JP |
2005-017068 |
Claims
1. A dynamic bearing device, comprising: a housing; a bearing
sleeve fixed inside the housing; a shaft member making a relative
rotation with respect to the housing and the bearing sleeve; a seal
member situated at one end of the housing; and a radial bearing
portion supporting the shaft member radially in a non-contact
manner by a dynamic pressure action of a fluid generated in a
radial bearing gap between the bearing sleeve and the shaft member,
characterized in that the seal member is provided on the shaft
member, with a seal space being provided beside an outer peripheral
surface of the seal member.
2. A dynamic bearing device, comprising: a housing; a bearing
sleeve fixed inside the housing; a shaft member making a relative
rotation with respect to the housing and the bearing sleeve; a seal
member situated at one end of the housing; and a radial bearing
portion supporting the shaft member radially in a non-contact
manner by a dynamic pressure action of a fluid generated in a
radial bearing gap between the bearing sleeve and the shaft member,
characterized in that the shaft member has a shaft portion inserted
into an inner peripheral surface of the bearing sleeve and a flange
portion provided on the shaft portion, that the seal member is
fixed to the shaft member, with a seal space being defined beside
an outer peripheral surface of the seal member, that the dynamic
bearing device includes a first thrust bearing portion provided
between one end surface of the seal member and one end surface of
the bearing sleeve opposed thereto, with the first thrust bearing
portion supporting the seal member and the shaft member in a thrust
direction in a non-contact manner by a dynamic pressure action of a
fluid generated in a thrust bearing gap, and that the dynamic
bearing device includes a second thrust bearing portion provided
between one end surface of the flange portion and another end
surface of the bearing sleeve opposed thereto, with the second
thrust bearing portion supporting the shaft member in the thrust
direction in a non-contact manner by a dynamic pressure action of
the fluid generated in a thrust bearing gap.
3. A dynamic bearing device according to claim 1, characterized in
that a tapered surface gradually diminished in diameter toward
outside of the housing is formed on the outer peripheral surface of
the seal member.
4. A dynamic bearing device according to claim 1, characterized in
that the seal member is fixed to the shaft member by an adhesive,
and that an adhesion position of at least one of the seal member
and the shaft member is provided with a recess to be filled with
the adhesive.
5. A dynamic bearing device, comprising: a housing; a bearing
sleeve fixed inside the housing; a shaft member making a relative
rotation with respect to the housing and the bearing sleeve; a seal
member situated at one end of the housing; and a radial bearing
portion supporting the shaft member radially in a non-contact
manner by a dynamic pressure action of a fluid generated in a
radial bearing gap between the bearing sleeve and the shaft member,
characterized in that the seal member is provided on the shaft
member, that one end surface of the seal member is opposed to one
end surface of the bearing sleeve through an intermediation of a
thrust bearing gap, and that an outer peripheral surface of the
seal member is provided with a tapered surface gradually diminished
in diameter toward outside of the housing and facing a seal
space.
6. A dynamic bearing device according to claim 1, characterized in
that the radial bearing portion has a dynamic pressure groove as a
dynamic pressure generating means.
7. A dynamic bearing device according to claim 1, characterized in
that the radial bearing portion is formed by a multi-arc
bearing.
8. A spindle motor for a disk device, comprising the dynamic
bearing device according to claim 1.
9. A method of manufacturing a dynamic bearing device comprising: a
housing; a bearing sleeve fixed inside the housing; a shaft member
having a shaft portion inserted into an inner peripheral surface of
the bearing sleeve and a flange portion provided on the shaft
portion; a seal member fixed to the shaft member; a radial bearing
portion supporting the shaft member radially in a non-contact
manner by a dynamic pressure action of a fluid generated in a
radial bearing gap between an inner peripheral surface of the
bearing sleeve and an outer peripheral surface of the shaft member;
a first thrust bearing portion supporting the seal member and the
shaft member in a thrust direction in a non-contact manner by a
dynamic pressure action of the fluid generated in a thrust bearing
gap between one end surface of the seal member and one end surface
of the bearing sleeve; and a second thrust bearing portion
supporting the shaft member in the thrust direction in a
non-contact manner by a dynamic pressure action of the fluid
generated in a thrust bearing gap between one end surface of the
flange portion and another end surface of the bearing sleeve, the
method comprising the steps of: inserting the shaft portion of the
shaft member into the inner peripheral surface of the bearing
sleeve and attaching the seal member to the shaft portion to
thereby interpose the bearing sleeve between the one end surface of
the seal member and the one end surface of the flange portion;
adjusting, after the step, an axial relative position of the shaft
portion and the seal member to define, between the bearing sleeve
and the one end surface of the seal member and between the bearing
sleeve and the one end surface of the flange portion, gaps of an
amount corresponding to a sum total of the thrust bearing gaps of
the first thrust bearing portion and the second thrust bearing
portion; fixing, after the step, the seal member to the shaft
portion; and accommodating an assembly including the bearing
sleeve, the shaft member, and the seal member assembled together by
the step in the housing.
10. A dynamic bearing device according to claim 2, characterized in
that a tapered surface gradually diminished in diameter toward
outside of the housing is formed on the outer peripheral surface of
the seal member.
11. A dynamic bearing device according to claim 2, characterized in
that the seal member is fixed to the shaft member by an adhesive,
and that an adhesion position of at least one of the seal member
and the shaft member is provided with a recess to be filled with
the adhesive.
12. A dynamic bearing device according to claim 2, characterized in
that the radial bearing portion has a dynamic pressure groove as a
dynamic pressure generating means.
13. A dynamic bearing device according to claim 5, characterized in
that the radial bearing portion has a dynamic pressure groove as a
dynamic pressure generating means.
14. A dynamic bearing device according to claim 2, characterized in
that the radial bearing portion is formed by a multi-arc
bearing.
15. A dynamic bearing device according to claim 5, characterized in
that the radial bearing portion is formed by a multi-arc
bearing.
16. A spindle motor for a disk device, comprising the dynamic
bearing device according to claim 2.
17. A spindle motor for a disk device, comprising the dynamic
bearing device according to claim 5.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a dynamic bearing device
for supporting a rotary member in a non-contact manner by a dynamic
pressure action of a fluid (i.e., lubricating fluid) generated in a
bearing gap. The dynamic bearing device is suitable for use in: a
spindle motor for an information apparatus, for example, a magnetic
disk device, such as an HDD or an FDD, an optical disk device, such
as a CD-ROM, a CD-R/RW, or a DVD-ROM/RAM, or a magneto-optical disk
device, such as an MD or MO; a polygon scanner motor for a laser
beam printer (LBP); or a small motor for an electrical apparatus
such as an axial fan.
[0003] 2. Description of the Related Art
[0004] Apart from high rotational accuracy, an improvement in
speed, a reduction in cost, a reduction in noise, etc. are required
of the various motors mentioned above. One of the factors
determining such the requisite performances is a bearing for
supporting a spindle of the motor. Recently, as a bearing of this
type, use of a dynamic bearing superior in the above-mentioned
requisite performances has been considered, or such the dynamic
bearing has been actually put into practical use.
[0005] For example, in a dynamic bearing device to be incorporated
into the spindle motor of a disk drive apparatus, such as an HDD,
there are provided a radial bearing portion supporting a shaft
member radially in a non-contact manner and a thrust bearing
portion supporting the shaft member in a thrust direction in a
non-contact manner. As the radial bearing portion, there is used a
dynamic bearing provided with grooves (i.e., dynamic pressure
grooves) for dynamic pressure generation provided in an inner
peripheral surface of a bearing sleeve or in an outer peripheral
surface of the shaft member. As the thrust bearing portion, there
is used a dynamic bearing provided with dynamic pressure grooves
in, for example, both end surfaces of a flange portion of the shaft
member or in surfaces opposed thereto (e.g., an end surface of the
bearing sleeve and an end surface of a thrust member fixed to a
housing (see, for example, Patent Documents 1 and 2).
Alternatively, as the thrust bearing portion, there may be used a
bearing (i.e., a so-called pivot bearing) of a structure in which
one end surface of the shaft member is contact-supported by a
thrust plate (see, for example, FIG. 4 of Patent Document 2).
[0006] In general, the bearing sleeve is fixed to a predetermined
position of an inner periphery of the housing and, to prevent
leakage of the fluid (e.g., a lubricating oil) poured into an inner
space of the housing to the outside, a seal member is arranged at
an opening of the housing in many cases. The inner peripheral
surface of the seal member defines a seal space between itself and
the outer peripheral surface of the shaft member, and the volume of
the seal space is set to be larger than the amount by which the
lubricating oil filling the inner space of the housing undergoes a
change in volume through thermal expansion/contraction within a
temperature range of use. Thus, even when there is a change in the
volume of the lubricating oil as a result of a temperature change,
an oil level of the lubricant is always maintained within the seal
space (see Patent Document 1).
Patent Document 1: JP 2003-65324 A
Patent Document 2: JP 2003-336636 A
[0007] As described above, in the conventional dynamic bearing
device, the seal space is formed between the inner peripheral
surface of the seal member fixed at the opening of the housing and
the outer peripheral surface of the shaft member; if the seal space
is to have a function to absorb a change in the volume of the
lubricating oil due to a temperature change, it is necessary to
secure a relatively large axial dimension for the seal space (i.e.,
the seal member). Thus, from the design standpoint, it is necessary
to lower, within the housing, the position of the axial center of
the bearing sleeve relatively toward a bottom side of the housing,
with the result that the distance between the bearing center of the
radial bearing portion and the center of gravity of the rotary
member increases, which, depending upon the condition of use, etc.,
can lead to a shortage of load capacity with respect to a moment
load. Further, in a construction in which thrust bearing portions
are provided on both sides of the flange portion of the shaft
member, the axial distance between the two thrust bearing portions
becomes relatively smaller, with the result that the load capacity
of the thrust bearing portions with respect to the moment load
tends to be so much the lower. In particular, in a case of a
dynamic bearing device for use in a disk drive apparatus, as a
rotor (i.e., a rotary member to which a rotor hub, a rotor magnet,
a disk, a clamper, etc. are assembled) rotates, a relatively large
moment load acts on the shaft member, so the moment load resistance
is an important characteristic.
[0008] Further, in a dynamic bearing of this type, the thrust
bearing gap of the thrust bearing portion is under the influence of
component precision, assembly precision, etc., so it is difficult
to control the thrust bearing gap to a desired value. Under the
circumstances, there is nothing for it but to perform a complicated
assembly operation.
[0009] It is an object of the present invention to make it possible
to reduce the axial dimension of the above-mentioned seal space of
a dynamic bearing device of this type, thereby enhancing the load
capacity of the dynamic bearing device with respect to the moment
load or reducing the axial dimension of the dynamic bearing
device.
[0010] Another object of the present invention is to enhance the
load capacity of the thrust bearing portion with respect to the
moment load.
[0011] Still another object of the present invention is to provide
a method which makes it possible to easily set the thrust bearing
gaps of a dynamic bearing device of this type with high
accuracy.
SUMMARY OF THE INVENTION
[0012] To attain the above-mentioned objects, the present invention
provides a dynamic bearing device, including: a housing; a bearing
sleeve fixed inside the housing; a shaft member making a relative
rotation with respect to the housing and the bearing sleeve; a seal
member situated at one end of the housing; and a radial bearing
portion supporting the shaft member radially in a non-contact
manner by a dynamic pressure action of a lubricating oil generated
in a radial bearing gap between the bearing sleeve and the shaft
member, characterized in that the seal member is provided on the
shaft member, with a seal space being provided beside an outer
peripheral surface of the seal member.
[0013] Here, as the fluid (i.e., lubricating fluid), it is also
possible to use a gas, such as air, apart from a liquid, such as a
lubricating oil (or lubricating grease) or a magnetic fluid.
[0014] In the above-mentioned construction, the seal space is
provided between the outer peripheral surface of the seal member
provided on the shaft portion and the inner peripheral surface of
one end portion of the housing, so, in securing, in the seal space,
a volume capable of absorbing a change in volume due to a change in
the temperature of the lubricating oil filling the inner space of
the housing, it is possible to make the axial dimension of the seal
space (i.e., seal member) smaller than that in the prior art. Thus,
it is possible to set, within the housing, the axial center
position of the bearing sleeve nearer to one end portion of the
housing than in the prior art (that is, to arrange the bearing
sleeve nearer to one end portion of the housing than in the prior
art, or to make the axial dimension of the bearing sleeve larger
than that in the prior art), whereby the distance between the
bearing center of the radial bearing portion and the center of
gravity of the rotary member is reduced, thereby enhancing the load
capacity with respect to the moment load. Further, in a case of
arranging the bearing sleeve nearer to one end portion of the
housing than in the prior art, it is possible to make the axial
dimension of the dynamic bearing device smaller than that in the
prior art.
[0015] TO attain the above-mentioned objects, the present invention
further provides a dynamic bearing device, including: a housing; a
bearing sleeve fixed inside the housing; a shaft member making a
relative rotation with respect to the housing and the bearing
sleeve; a seal member situated at one end of the housing; and a
radial bearing portion supporting the shaft member radially in a
non-contact manner by a dynamic pressure action of a fluid
generated in a radial bearing gap between the bearing sleeve and
the shaft member, characterized in that the shaft member has a
shaft portion inserted into an inner peripheral surface of the
bearing sleeve and a flange portion provided on the shaft portion,
that the seal member is fixed to the shaft member, with a seal
space being defined beside an outer peripheral surface of the seal
member, that the dynamic bearing device includes a first thrust
bearing portion provided between one end surface of the seal member
and one end surface of the bearing sleeve opposed thereto, with the
first thrust bearing portion supporting the seal member and the
shaft member in a thrust direction in a non-contact manner by a
dynamic pressure action of a fluid generated in a thrust bearing
gap, and that the dynamic bearing device includes a second thrust
bearing portion provided between one end surface of the flange
portion and another end surface of the bearing sleeve opposed
thereto, with the second thrust bearing portion supporting the
shaft member in the thrust direction in a non-contact manner by a
dynamic pressure action of the fluid generated in a thrust bearing
gap.
[0016] In addition to the above-mentioned effects, due to the
provision of the first thrust bearing portion and the second thrust
bearing portion so as to sandwich the bearing sleeve axially from
both sides, the axial distance between the two thrust bearing
portions is increased as compared with the construction in which
the thrust bearing portions are provided on both sides of the
flange portion, and the load capacity of the thrust bearing
portions with respect to the moment load is so much the higher.
[0017] The fixation of the seal member to the shaft member can be
effected by an appropriate fixing means, such as adhesion, a
combination of adhesion and press-fitting, or welding (ultrasonic
welding). When adopting adhesion (or a combination of adhesion and
press-fitting) as the fixing means, it is possible to provide a
recess to be filled with adhesive at an adhesion position of at
least one of the seal member and the shaft member. The recess may
be provided in the form of a circumferential groove or in the form
of one or a plurality of recesses arranged circumferentially. The
adhesive also fills the recess at the adhesion position and
solidifies, whereby the strength with which the seal member is
fixed to the shaft member is enhanced.
[0018] In the above-mentioned construction, the width (i.e., radial
dimension) of the seal space may be axially uniform; however, from
the viewpoint of enhancing the sealing property, it is desirable
for the seal space to be of a tapered configuration gradually
diminished in size toward the interior of the housing. That is,
when the seal space has the tapered configuration, the fluid in the
seal space is drawn in by capillary attraction in the direction in
which the seal space is diminished in size (i.e., toward the
interior of the housing). As a result, it is possible to
effectively prevent leakage of the fluid from the interior to the
exterior of the housing. As means for realizing such the
construction, there are available a means for forming, on the outer
peripheral surface of the seal member, a tapered surface gradually
diminished in diameter toward the exterior of the housing, and a
means for forming a tapered surface gradually diminished in
diameter toward the exterior of the housing on a surface opposed to
the outer peripheral surface of the seal member through the
intermediation of the seal space, for example, on the inner
peripheral surface of one end portion of the housing. In
particular, with the former means, the seal member rotates together
with the shaft member, whereby, in addition to the drawing-in
action due to the capillary attraction, it is also possible to
obtain a drawing-in action due to the centrifugal force during
rotation (i.e., a so-called centrifugal seal), so leakage of the
fluid from the interior to the exterior of the housing is more
effectively prevented.
[0019] To attain the above-mentioned objects, the present invention
further provides a dynamic bearing device, including: a housing; a
bearing sleeve fixed inside the housing; a shaft member making a
relative rotation with respect to the housing and the bearing
sleeve; a seal member situated at one end of the housing; and a
radial bearing portion supporting the shaft member radially in a
non-contact manner by a dynamic pressure action of a fluid
generated in a radial bearing gap between the bearing sleeve and
the shaft member, characterized in that the seal member is provided
on the shaft member, that one end surface of the seal member is
opposed to one end surface of the bearing sleeve through an
intermediation of a thrust bearing gap, and that an outer
peripheral surface of the seal member is provided with a tapered
surface gradually diminished in diameter toward outside of the
housing and facing a seal space.
[0020] In the dynamic bearing device constructed as described
above, the radial bearing portion may be formed by a dynamic
bearing provided with dynamic pressure grooves of an axially
inclined configuration, such as a herringbone-like configuration or
a spiral configuration, a dynamic bearing (i.e., multi-arc bearing)
in which the radial bearing gap is diminished in a wedge-like
fashion in one or both circumferential directions, or a dynamic
bearing (i.e., step bearing) in which a plurality of dynamic
pressure grooves in the form of axial grooves are provided at
predetermined circumferential intervals.
[0021] The dynamic bearing device constructed as described above
can preferably be used as a dynamic bearing device for a spindle
motor for use in an information apparatus, such as a disk
device.
[0022] To attain the above-mentioned objects, the present invention
further provides a method of manufacturing a dynamic bearing
device, including: a housing; a bearing sleeve fixed inside the
housing; a shaft member having a shaft portion inserted into an
inner peripheral surface of the bearing sleeve and a flange portion
provided on the shaft portion; a seal member fixed to the shaft
member; a radial bearing portion supporting the shaft member
radially in a non-contact manner by a dynamic pressure action of a
fluid generated in a radial bearing gap between an inner peripheral
surface of the bearing sleeve and an outer peripheral surface of
the shaft member; a first thrust bearing portion supporting the
seal member and the shaft member in a thrust direction in a
non-contact manner by a dynamic pressure action of the fluid
generated in a thrust bearing gap between one end surface of the
seal member and one end surface of the bearing sleeve; and a second
thrust bearing portion supporting the shaft member in the thrust
direction in a non-contact manner by a dynamic pressure action of
the fluid generated in a thrust bearing gap between one end surface
of the flange portion and another end surface of the bearing
sleeve, the method including the steps of: inserting the shaft
portion of the shaft member into the inner peripheral surface of
the bearing sleeve and attaching the seal member to the shaft
portion to thereby interpose the bearing sleeve between the one end
surface of the seal member and the one end surface of the flange
portion; adjusting, after the step, an axial relative position of
the shaft portion and the seal member to define, between the
bearing sleeve and the one end surface of the seal member and
between the bearing sleeve and the one end surface of the flange
portion, gaps of an amount corresponding to a sum total of the
thrust bearing gaps of the first thrust bearing portion and the
second thrust bearing portion; fixing, after the step, the seal
member to the shaft portion; and accommodating an assembly
including the bearing sleeve, the shaft member, and the seal member
assembled together by the step in the housing.
[0023] In the above-mentioned construction, the thrust bearing gaps
are set at the stage of previously assembling together the bearing
sleeve, the shaft member, and the seal member, so the thrust
bearing gaps can easily be set with high accuracy. After the
setting of the thrust bearing gaps, the operation of assembling the
components to each other is completed when the assembly including
the bearing sleeve, the shaft member, and the seal member is
accommodated in the housing, thus simplifying the assembling
operation.
[0024] According to the present invention, it is possible to
enhance the load capacity of a dynamic bearing device with respect
to the moment load, or to make the axial dimension of a dynamic
bearing device compact. Thus, it is possible to achieve a reduction
in the size of a spindle motor equipped with the dynamic bearing
device for use in an information apparatus, such as a disk
device.
[0025] Further, according to the present invention, it is possible
to enhance the load capacity of the thrust bearing portion with
respect to the moment load.
[0026] Further, according to the present invention, it is possible
to set a thrust bearing gap in a dynamic bearing device of this
type easily and with high accuracy.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] FIG. 1 is a sectional view of a spindle motor for an
information apparatus into which a dynamic bearing device according
to an embodiment of the present invention is incorporated.
[0028] FIG. 2 is a sectional view of a dynamic bearing device
according to a first embodiment of the present invention.
[0029] FIG. 3 is a sectional view of a bearing sleeve and diagrams
showing a lower end surface and an upper end surface thereof.
[0030] FIG. 4 is a diagram illustrating an assembly process.
[0031] FIG. 5 is a diagram illustrating an assembly process.
[0032] FIG. 6 is a diagram illustrating an assembly process.
[0033] FIG. 7 is a sectional view of a dynamic bearing device
according to a second embodiment of the present invention.
[0034] FIG. 8 is a sectional view of a dynamic bearing device
according to a third embodiment of the present invention.
[0035] FIG. 9 is a sectional view of a bearing sleeve and a diagram
showing a lower end surface thereof.
[0036] FIG. 10 is a top view of a housing.
[0037] FIG. 11 is a sectional view of another example of a radial
bearing portion.
[0038] FIG. 12 is a sectional view of still another example of the
radial bearing portion.
[0039] FIG. 13 is a sectional view of yet another example of the
radial bearing portion.
[0040] FIG. 14 is a sectional view of another example of the radial
bearing portion.
DETAILED DESCRIPTION OF THE INVENTION
[0041] In the following, an embodiment of the present invention
will be described with reference to the drawings.
[0042] FIG. 1 is a diagram conceptually showing a construction
example of an information apparatus spindle motor into which the
dynamic bearing device (i.e., fluid dynamic bearing device) 1
according to this embodiment is incorporated. The spindle motor is
used in a disk drive apparatus, such as an HDD, and is equipped
with: the dynamic bearing device 1 for rotatably supporting a shaft
member 2 in a non-contact manner; a rotor (i.e., disk hub) 3
mounted to the shaft member 2; and a stator coil 4 and a rotor
magnet 5 opposed to each other through the intermediation of, for
example, a radial gap. The stator coil 4 is mounted to the outer
periphery of a bracket 6, and the rotor magnet 5 is mounted to the
inner periphery of the disk hub 3. A housing 7 of the dynamic
bearing device 1 is fixed to the inner periphery of the bracket 6.
One or a plurality of disks D such as magnetic disks are retained
by the disk hub 3. When electricity is supplied to the stator coil
4, the rotor magnet 5 is rotated by an electromagnetic force
generated between the stator coil 4 and the rotor magnet 5, and
with this rotation, the disk hub 3 is rotated integrally with the
shaft 2.
[0043] FIG. 2 shows the dynamic bearing device 1 of a first
embodiment of the present invention. The dynamic bearing device is
composed of the housing 7, a bearing sleeve 8 fixed to the housing
7, the shaft member 2, and a seal member 9 fixed to the shaft
member 2.
[0044] Between an inner peripheral surface 8a of the bearing sleeve
8 and an outer peripheral surface 2a1 of a shaft portion 2a of the
shaft member 2, there are provided a first radial bearing portion
R1 and a second radial bearing portion R2 which are axially spaced
apart from each other. Further, a first thrust bearing portion T1
is provided between an upper end surface 8b of the bearing sleeve 8
and a lower end surface 9b of the seal member 9, and a second
thrust bearing portion T2 is provided between a lower end surface
8c of the bearing sleeve 8 and an upper end surface 2b1 of a flange
portion 2b of the shaft member 2. For the sake of convenience in
illustration, in the following description, a side on which a
bottom portion 7b of the housing 7 is situated will be referred to
as the lower side, and a side on which an opening of the housing 7
is situated (i.e., side opposite to the bottom portion 7b) will be
referred to as the upper side.
[0045] The housing 7 is formed as a bottomed cylinder, for example,
by injection molding of a resin material, and is equipped with a
cylindrical side portion 7a and the bottom portion 7b provided
integrally at the lower end of the side portion 7a. Further, a step
portion 7d is integrally formed at a position spaced apart axially
upwards from an inner bottom surface of the bottom portion 7b by a
predetermined dimension.
[0046] A resin forming the housing is mainly made of a
thermoplastic resin; for example, it is possible to use an
amorphous resin, such as polysulfone (PSF), polyether sulfone
(PES), polyphenyl sulfone (PPSU), or polyether imide (PEI), or a
crystalline resin, such as liquid crystal polymer (LCP),
polyetherether ketone (PEEK), polybutyrene terephthalate (PBT), or
polyphenylene sulfide (PPS). There are no particular limitations
regarding the filler to be used for the above resin; for example,
it is possible to use, as the filler, a fibrous filler, such as
glass fiber, a whisker-like filler, such as potassium titanate, a
scale-like filler, such as mica, or a fibrous or powdered
conductive filler, such as carbon fiber, carbon black, graphite,
carbon nanomaterial, or metal powder. These fillers may be used
singly or in the form of a mixture of two or more them. This
embodiment employs, as the material forming the housing 7, a resin
material obtained by mixing 2 to 8 wt % of carbon fiber or carbon
nanotube as the conductive filler with liquid crystal polymer (LCP)
as the crystalline resin.
[0047] The shaft member 2 is formed, for example, of a metal
material, such as stainless steel, or in a hybrid structure
composed of metal and a resin, and is equipped with the shaft
portion 2a and the flange portion 2b provided integrally or
separately at the lower end of the shaft portion 2a. Further, in
this embodiment, a recess, for example, a circumferential groove
2a2, is formed at a predetermined position of the outer peripheral
surface 2a1 of the shaft portion 2a to which the seal member 9 is
fixed.
[0048] The bearing sleeve 8 is formed as a cylinder of a porous
material composed of a sintered metal, in particular, a porous
material composed of a sintered metal whose main component is
copper. The bearing sleeve 8 is fixed to a predetermined position
of an inner peripheral surface 7c of the housing 7. It is also
possible for the bearing sleeve 8 to be formed not only of the
sintered metal, but also of some other metal material, which is not
the porous material, for example, of a soft metal such as
brass.
[0049] On an inner peripheral surface 8a of the bearing sleeve 8,
there are provided axially separated upper and lower two regions
constituting the respective radial bearing surfaces of the first
radial bearing portion R1 and the second radial bearing portion R2.
In the two regions, there are respectively formed dynamic pressure
grooves 8a1 and 8a2 of a herringbone configuration as shown, for
example, in FIG. 3. The upper dynamic pressure grooves 8a1 are
formed axially asymmetrically with respect to an axial center m
(i.e., axial center of the region between the upper and lower
inclined groves), and an axial dimension X1 of the region on the
upper side of the axial center m is larger than an axial dimension
X2 of the region on the lower side of the axial center m. Further,
in an outer peripheral surface 8d of the bearing sleeve 8, there is
formed one or a plurality of axial grooves 8d1 extending over the
entire axial length of the bearing sleeve. In this example, three
axial grooves 8d1 are formed at constant intervals in a
circumferential direction.
[0050] Dynamic pressure grooves 8b1 of a spiral configuration as
shown, for example, in FIG. 3, are formed in an upper end surface
8b of the bearing sleeve 8 constituting the thrust bearing surface
of the first thrust bearing portion T1. Similarly, dynamic pressure
grooves 8c1 of a spiral configuration as shown, for example, in
FIG. 3, are formed in a lower end surface 8c of the bearing sleeve
8 constituting the thrust bearing surface of the second thrust
bearing portion T2.
[0051] The seal member 9 is formed in a ring-like shape, for
example, of a soft metal material, such as brass, or some other
metal material, or a resin material, and is fixed, for example, by
adhesive, to a predetermined position of the outer peripheral
surface 2a1 of the shaft portion 2a. During rotation of the shaft
member 2, a lower end surface 9b of the seal member 9 is opposed to
the upper end surface 8b of the bearing sleeve 8 through the
intermediation of a predetermined thrust bearing gap to form the
first thrust bearing portion T1. An outer peripheral surface 9a of
the seal member 9 forms between itself and an inner peripheral
surface 7a1 of the upper end portion (i.e., opening) of the housing
7 a seal space S having a predetermined volume. The seal space S is
formed beside the outer peripheral surface 9a of the seal member 9,
so, in securing in the seal space S a volume capable of absorbing a
change in volume due to a change in the temperature of the fluid
filling the inner space of the housing 7, it is possible to make an
axial dimension of the seal space S (i.e., the seal member 9)
smaller than that in the prior art. Thus, it is possible, for
example, to make the axial length of the bearing sleeve 8 larger
than that in the prior art and transfer the axial center m of the
dynamic pressure grooves 8a1 of the first radial bearing portion R1
to the upper end surface 8b side, or to make an axial dimension of
the bearing sleeve 8 smaller than that in the prior art. When the
former measure is taken, an axial distance between the axial center
m of the dynamic pressure grooves 8a1 of the first radial portion
R1 and the axial center of the dynamic pressure grooves 8a2 of the
second radial bearing portion R2 increases, so it is possible to
achieve an enhancement in the load capacity with respect to a
moment load. On the other hand, when the latter measure is taken,
it is possible to make the axial dimension of the dynamic bearing
device smaller than that in the prior art.
[0052] In this embodiment, the outer peripheral surface 9a of the
seal member 9 is equipped with a tapered surface 9a1 gradually
diminished in diameter toward the exterior of the housing 7, so the
seal space S exhibits a tapered configuration gradually diminished
in size toward the interior of the housing 7. During rotation of
the shaft member 2, the fluid in the seal space S is drawn in a
direction in which the seal space S is narrowed (i.e., in a
direction of the interior of the housing) by a drawing-in action
due to capillary attraction and a drawing-in action due to a
centrifugal force during the rotation. As a result, leakage of a
lubricating oil from the interior of the housing 7 is effectively
prevented.
[0053] The dynamic bearing device 1 of this embodiment is
assembled, for example, by the following process.
[0054] First, the shaft member 2, the bearing sleeve 8, and the
seal member 9 are assembled together. As shown, for example, in
FIG. 4, the bearing sleeve 8 is attached to the shaft portion 2a of
the shaft member 2 placed on the upper surface of a base 10, and
the lower end surface 8c of the bearing sleeve 8 is brought into
contact with the upper end surface 2b1 of the flange portion 2b.
Then, after applying an adhesive, for example, a thermosetting
adhesive, to the shaft portion 2a, the seal member 9 is attached to
the shaft portion 2a, and the lower end surface 9b of the seal
member 9 is brought into contact with the upper end surface 8b of
the bearing sleeve 8, whereby the bearing sleeve 8 is interposed
between the lower end surface 9b of the seal member 9 and the upper
end surface 2b1 of the flange portion 2b.
[0055] Next, the thrust bearing gaps are set. The setting of the
thrust bearing gaps is effected by adjusting the relative axial
positions of the shaft member 2 and the seal member 9. For example,
in the above-mentioned state, that is, in a state in which the
lower end surface 8c of the bearing sleeve 8 is in contact with the
upper end surface 2b1 of the flange portion 2b and the lower end
surface 9b of the seal member 9 is in contact with the upper end
surface 8b of the bearing sleeve 8 (i.e., state in which there is
no thrust bearing gap), the shaft member 2 is caused to make a
relative movement in the axial direction with respect to the
bearing sleeve 8 and the seal member 9 by an amount corresponding
to the sum total .delta. of the thrust bearing gap of the first
thrust bearing portion T1 (indicated by symbol .delta.1) and the
thrust bearing gap of the second thrust bearing portion T2
(indicated by symbol .delta.2) (=.delta.1+.delta.2).
[0056] To be more specific, as shown, for example, in FIG. 5, an
assembly put together in the state as described above is placed on
an upper surface of a jig 11 provided with a step portion 11a of a
predetermined depth W2, with the lower end surface 8c of the
bearing sleeve 8 being in contact with the upper surface of the jig
11 and the flange portion 2b being accommodated in the step portion
11a. In this state, the shaft member 2 is pressed from above to be
allowed to make a relative movement in the axial direction with
respect to the bearing sleeve 8 and the seal member 9 by the
predetermined amount 5. In this case, when the depth W2 of the step
portion 11a is accurately controlled with respect to an axial
dimension W1 of the flange portion 2b such that a relationship of
W2=W1+.delta. is obtained, it is possible to set the thrust bearing
gap .delta.(=.delta.1+.delta.2) easily and with high accuracy
solely by pushing the shaft member 2 forward until the lower end
surface 2b2 of the flange portion 2b abuts a bottom surface 11a1 of
the step portion 11a. Thus, the operation and device related to the
setting of the thrust bearing gap are simplified. Alternatively, it
is also possible to set the thrust bearing gap
.delta.(=.delta.1+.delta.2) by setting the depth of the step
portion such that a relationship of W2>W1+.delta. is obtained
and by controlling an axial relative movement amount of the shaft
member 2.
[0057] Alternatively, the setting of the thrust bearing gap can be
effected by using as a reference the upper end surface 8b of the
bearing sleeve 8 when the lower end surface 8c of the bearing
sleeve 8 is in contact with the upper end surface 2b1 of the flange
portion 2b and adjusting the axial position of the seal member 9
such that the lower end surface 9b of the seal member 9 is brought
to a position where the lower end surface 9b is axially spaced
apart from the upper end surface 8b by an amount corresponding to
the above-mentioned sum total .delta.(=.delta.1+.delta.2). Such the
positional adjustment in the axial direction of the seal member 9
can be effected easily and with high accuracy, for example, by
allowing a spacer, whose width is accurately controlled to a
dimension equal to the above-mentioned sum total .delta., to be
interposed between the upper end surface 8b of the bearing sleeve 8
and the lower end surface 9b of the seal member 9.
[0058] After setting the thrust bearing gap (.delta.) through
adjustment of the axial relative position of the shaft portion 2
and the seal member 9, the seal member 9 is fixed to the shaft
portion 2a at that position. In this embodiment, the seal member 9
is fixed by adhesion to the shaft portion 2a through heat treatment
(baking) of the thermosetting adhesive applied to the shaft portion
2a. At this time, the adhesive applied to the shaft portion 2a also
fills a circumferential groove 2a2 in the outer peripheral surface
2a1 and solidifies therein, whereby the adhesion strength for the
seal member 9 with respect to the shaft member 2 is enhanced.
[0059] Next, as shown in FIG. 6, the assembly put together by the
above process and composed of the shaft member 2, the bearing
sleeve 8, and the seal member 9 is inserted into the inner
peripheral surface 7c of the housing 7, and the lower end surface
8c is brought into contact with the step portion 7d of the housing
7; in this state, the outer peripheral surface 8d of the bearing
sleeve 8 is fixed to the inner peripheral surface 7c of the housing
7. The fixation of the bearing sleeve 8 to the housing 7 can be
effected by an appropriate means, such as adhesion, press-fitting,
a combination of adhesion and press-fitting, or welding (such as
ultrasonic welding). In the drawing, 5 is considerably exaggerated
in dimension.
[0060] When the assembly is completed as described above, the shaft
portion 2a of the shaft member 2 is inserted into the inner
peripheral surface 8a of the bearing sleeve 8, and the flange
portion 2b is accommodated in the space portion between the lower
end surface 8c of the bearing sleeve 8 and the inner bottom surface
of the bottom portion 7b of the housing 7. Further, the seal space
S having a predetermined volume is defined between the outer
peripheral surface 9a of the seal member 9 and the inner peripheral
surface 7a1 of the upper end portion of the housing 7. After that,
the inner space of the housing 7 sealed by the seal member 9,
inclusive of inner voids of the bearing sleeve 8, is filled with a
fluid, such as a lubricating oil. An oil level of the lubricating
oil is constantly maintained within a range of the seal space
S.
[0061] During rotation of the shaft member 2, regions of the inner
peripheral surface 8a of the bearing sleeve 8 constituting the
radial bearing surfaces (i.e., two upper and lower regions) are
respectively opposed to the outer peripheral surface 2a1 of the
shaft portion 2a through the intermediation of a radial bearing
gap. Further, a region of the upper end surface 8b of the bearing
sleeve 8 constituting the thrust bearing surface is opposed to the
lower end surface 9b of the seal member 9 through the
intermediation of a thrust bearing gap, and a region of the lower
end surface 8c of the bearing sleeve 8 constituting the thrust
bearing surface is opposed to the upper end surface 2b1 of the
flange portion 2b through the intermediation of a thrust bearing
gap. As the shaft member 2 rotates, a dynamic pressure of the
lubricating oil is generated in the radial bearing gap, and the
shaft portion 2a of the shaft member 2 is supported radially and
rotatably in a non-contact manner by an oil film of the lubricating
oil formed in the radial bearing gap. As a result, there are formed
the first radial bearing portion R1 and the second radial bearing
portion R2 supporting the shaft member 2 radially and rotatably in
a non-contact manner. At the same time, a dynamic pressure of the
lubricating oil is generated in the thrust bearing gaps, and the
shaft member 2 and the seal member 9 are supported rotatably in the
thrust direction in a non-contact manner by oil films of the
lubricating oil formed in the thrust bearing gaps. As a result,
there are formed the first thrust bearing portion T1 and the second
thrust bearing portion T2 supporting the shaft member 2 rotatably
in the thrust direction in a non-contact manner. The thrust bearing
gap (indicated by .delta.1) of the first thrust bearing portion T1
and the thrust bearing gap (indicated by .delta.2) of the second
thrust bearing portion T2 are controlled accurately in the
above-described assembly step such that a relationship of
.delta.=.delta.1+.delta.2 is obtained, so it is possible to obtain
a stable thrust bearing function.
[0062] Further, as described above, the dynamic pressure grooves
8a1 of the first radial bearing portion R1 are formed
asymmetrically in the axial direction with respect to the axial
center m, with the axial dimension X1 of the region on the upper
side of the axial center m being larger than the axial dimension X2
of the region on the lower side thereof (see FIG. 3). Thus, during
rotation of the shaft member 2, the lubricating oil drawing force
(i.e., pumping force) due to the dynamic pressure grooves 8a1 is
larger in the upper region than in the lower region. Due to this
difference in drawing force, the lubricating oil filling the gap
between the inner peripheral surface 8a of the bearing sleeve 8 and
the outer peripheral surface 2a1 of the shaft portion 2a flows
downwards, and circulates through the route: the thrust bearing gap
of the second thrust bearing portion T2.fwdarw.the axial grooves
8d1.fwdarw.the thrust bearing gap of the first thrust bearing
portion T1 before being drawn into the radial bearing gap of the
first radial bearing portion R1 again. In this way, the lubricating
oil flows and circulates through the inner space of the housing 7,
whereby it is possible to prevent a phenomenon in which the
pressure of the lubricating oil in the inner space locally becomes
a negative pressure, making it possible to eliminate the generation
of bubbles as a result of the generation of a negative pressure,
and leakage of the lubricating oil, generation of vibration, etc.
due to the generation of bubbles. Further, if, for some reason,
bubbles are allowed to be mixed into the lubricating oil, the
bubbles are discharged into the atmosphere through the oil surface
(gas-liquid interface) of the lubricating oil in the seal space S
when they circulate with the lubricating oil, so it is possible to
more effectively prevent the adverse effects of the bubbles.
[0063] Further, the inward drawing force (i.e., pumping force) for
the lubricating oil due to the dynamic pressure grooves 8b1 of the
first thrust bearing portion T1 also acts on the lubricating oil in
the radial bearing gap of the first radial bearing portion R1, so
even if the above-mentioned difference in drawing force in the
first radial bearing portion R1 is relatively small, it is possible
to secure a satisfactory flowing circulation of the lubricating
oil. As a result, it is possible to reduce the axial asymmetry of
the dynamic pressure grooves 8a1 of the first radial bearing
portion R1 as compared with that in the prior art; for example, it
is possible to diminish the axial dimension X1 of the upper region
of the dynamic pressure grooves 8a1 as compared with that in the
prior art and transfer the axial center m of the dynamic pressure
grooves 8a1 to the upper end surface 8b side, or to diminish the
axial dimension of the bearing sleeve 8. When the former measure is
taken, the axial distance between the axial center m of the dynamic
pressure grooves 8a1 of the first radial bearing portion R1 and the
axial center of the dynamic pressure grooves 8a2 of second radial
bearing portion R2 increases, so it is possible to achieve an
enhancement in the load capacity with respect to the moment load.
On the other hand, when the latter measure is taken, it is possible
to reduce the axial dimension of the dynamic bearing device as
compared with that in the prior art.
[0064] FIG. 7 shows a dynamic bearing device 21 according to a
second embodiment of the present invention. The dynamic bearing
device 21 of this embodiment differs from the dynamic bearing
device 1 of the first embodiment described above in that the
bearing sleeve is composed of an upper bearing sleeve 81 and a
lower bearing sleeve 82, with a spacer member 83 being interposed
between them. The spacer member 83 is formed in a ring-like shape
of a soft metal material, such as brass, or some other metal
material, or a resin material, and, unlike the upper bearing sleeve
81 and the lower bearing sleeve 82, has no porous texture.
[0065] The first radial bearing portion R1 is provided between an
inner peripheral surface 81a of the upper bearing sleeve 81 and the
outer peripheral surface 2a1 of the shaft portion 2a of the shaft
member 2, and the second radial bearing portion R2 is provided
between an inner peripheral surface 82a of the lower bearing sleeve
82 and the outer peripheral surface 2a1 of the shaft portion 2a.
Further, the first thrust bearing portion T1 is provided between an
upper end surface 81b of the upper bearing sleeve 81 and the lower
end surface 9b of the seal member 9, and the second thrust bearing
portion T2 is provided between a lower end surface 82c of the lower
bearing sleeve 82 and the upper end surface 2b1 of the flange
portion 2b of the shaft member 2. Formed in the lower end surface
of the upper bearing sleeve 81 is an annular groove (i.e.,
V-groove) for distinguishing the upper bearing sleeve from the
lower bearing sleeve 82. In an outer peripheral surface 81d of the
upper bearing sleeve 81, an outer peripheral surface 82d of the
lower bearing sleeve 82, and the outer peripheral surface of the
spacer member 83, there are respectively formed one or a plurality
of axial grooves 81d1, 82d1, and 83d which respectively extend over
the entire axial lengths of the axial grooves. The axial grooves
81d1, 82d1, and 83d are formed in alignment in circumferential
phase, and communicate axially with each other.
[0066] Since the spacer member 83 with no porous texture is
interposed between the upper bearing sleeve 81 and the lower
bearing sleeve 82, the total amount of lubricating oil filling the
inner space of the housing 7 can be less than that in the dynamic
bearing device 1 of the above-mentioned embodiment (for, the
interior of the spacer member 83 is impregnated with no lubricating
oil). On the other hand, the change in volume as a result of
thermal expansion/contraction of the lubricating oil is
proportional to the total amount of lubricating oil filling the
inner space of the housing 7, so, due to the reduction in the total
oil amount, it is possible to reduce the volume of the seal space
S. Thus, in the dynamic bearing device 21 of this embodiment, it is
possible to further reduce the axial dimension of the seal space S
(thus, the seal member 9). Otherwise, this embodiment is the same
as the first embodiment, so a redundant description thereof will be
omitted.
[0067] FIG. 8 shows a dynamic bearing device 31 according to a
third embodiment of the present invention. The dynamic bearing
device 31 of this embodiment differs from the dynamic bearing
device 1 of the first embodiment in that the first thrust bearing
portion T1 is provided between the lower end surface 8c of the
bearing sleeve 8 and the upper end surface 2b1 of the flange
portion 2b of the shaft member 2, and that the second thrust
bearing portion T2 is provided between the inner bottom surface 7b1
of the bottom portion 7b of the housing 7 and the lower end surface
2b2 of the flange portion 2b.
[0068] As shown in FIG. 10, dynamic pressure grooves 7b2 of, for
example, a spiral configuration, are formed in the inner bottom
surface 7b1 of the bottom portion 7b constituting the thrust
bearing surface of the second thrust bearing portion T2. The
dynamic pressure grooves 7b2 are formed at the time of the
injection molding of the housing 7. That is, a groove pattern for
forming the dynamic pressure grooves 7b2 is formed by machining at
a predetermined position (i.e., position where the inner bottom
surface 7b1 is to be formed) of the mold for molding the housing 7,
and the configuration of the groove pattern is transferred to the
inner bottom surface 7b1 of the housing 7 at the time of the
injection molding of the housing 7, whereby it is possible to form
the dynamic pressure grooves 7b2 simultaneously with the molding of
the housing 7. Further, the step portion 7d is integrally formed at
a position spaced apart from the inner bottom surface (thrust
bearing surface) 7b1 axially upwards by a predetermined distance
x.
[0069] Further, as shown in FIG. 9, dynamic pressure grooves 8c1 of
a spiral configuration as shown, for example, in FIG. 3(b), are
formed in the lower end surface 8c of the bearing sleeve 8
constituting the thrust bearing surface of the first thrust bearing
portion T1. No dynamic pressure grooves are formed in the upper end
surface 8b of the bearing sleeve 8. The upper end surface 8b of the
bearing sleeve 8 is opposed to the lower end surface 9b of the seal
member 9 through the intermediation of a gap larger than the thrust
bearing gap.
[0070] The thrust bearing gap of the first thrust bearing portion
T1 (indicated by symbol .delta.1) and the thrust bearing gap of the
second thrust bearing portion T2 (indicated by symbol 52) can be
controlled with high accuracy such that a relationship of
x-w=.delta.1+.delta.2 is obtained, where x is the axial dimension
from the inner bottom surface 7b1 to the step portion 7d of the
housing 7, and w is the axial dimension of the flange portion 2b of
the shaft member 2.
[0071] In the third embodiment, when the second bearing portion T2
is formed by a so-called pivot bearing, the shaft member 2 used is
one having no flange portion 2b (i.e., one with a straight
configuration). In this case, it is also possible for the seal
member 9 to be formed integrally with the shaft portion 2a of the
shaft member 2. Otherwise, this embodiment is the same as the first
embodiment, so a redundant description thereof will be omitted.
[0072] The above-mentioned embodiments adopt a construction in
which a dynamic pressure action of a lubricant oil is generated by
dynamic pressure grooves of a herringbone-like or a spiral
configuration formed in the radial bearing portions R1, R2 and the
thrust bearing portions T1, T2; the present invention, however, is
not restricted to this construction.
[0073] For example, it is also possible to adopt a so-called step
bearing or a multi-arc bearing as the radial bearing portions R1,
R2.
[0074] FIG. 11 shows an example of a case in which one or both of
the radial bearing portions R1, R2 are formed by step bearings. In
this example, a plurality of dynamic pressure grooves 8a3 in the
form of axial grooves are provided at predetermined circumferential
intervals in the region of the inner peripheral surface 8a of the
bearing sleeve 8 constituting the radial bearing surface.
[0075] FIG. 12 shows an example of a case in which one or both of
the radial bearing portions R1, R2 are formed by multi-arc
bearings. In this example, the region of the inner peripheral
surface 8a of the bearing sleeve 8 constituting the radial bearing
surface is composed of three arcuate surfaces 8a4, 8a5, and 8a6
(i.e, so-called three-arc bearing). Respective centers of curvature
of the three arcuate surfaces 8a4, 8a5, and 8a6 are offset by the
same distance from the axial center O of the bearing sleeve 8
(i.e., the shaft portion 2a). In each of regions defined by the
three arcuate surfaces 8a4, 8a5, and8a6, the radial bearing gap has
a configuration gradually diminished in a wedge-like fashion in
both circumferential directions. Thus, when the bearing sleeve 8
and the shaft portion 2a make a relative rotation, the lubricating
oil in the radial bearing gap is forced into the gradually
diminished minimum gaps according to the direction of the relative
rotation to undergo an increase in the pressure thereof. Due to the
dynamic pressure action of the lubricating oil, the bearing sleeve
8 and the shaft portion 2a are supported in a non-contact manner.
It is also possible to form, in the border portions between the
three arcuate surfaces 8a4, 8a5, and 8a6, axial grooves called
separation grooves, which are one step deeper.
[0076] FIG. 13 shows another example of the case in which one or
both of the radial bearing portions R1, R2 are formed by multi-arc
bearings. In this example also, the region of the inner peripheral
surface 8a of the bearing sleeve 8 constituting the radial bearing
surface is formed by three arcuate surfaces 8a7, 8a8, and 8a9
(i.e., so-called three-arc bearing); in each of regions defined by
the three arcuate surfaces 8a7, 8a8, and 8a9, the radial bearing
gap has a configuration gradually diminished in a wedge-like
fashion in one circumferential direction. A multi-arc bearing of
this construction is sometimes referred to as a tapered bearing.
Further, in the border portions between the three arcuate surfaces
8a7, 8a8, and 8a9, there are formed axial grooves 8a10, 8a11, and
8a12 called separation grooves, which are one step deeper. Thus,
when the bearing sleeve 8 and the shaft portion 2a make a relative
rotation in a predetermined direction, the lubricating oil in the
radial bearing gap is forced into a minimum gap diminished in
wedge-like fashion to undergo an increase in the pressure thereof.
Due to the dynamic pressure action of the lubricating oil, the
bearing sleeve 8 and the shaft portion 2a are supported in a
non-contact manner.
[0077] FIG. 14 shows another example of the case in which one or
both of the radial bearing portions R1, R2 are formed by multi-arc
bearings. In this example, in the construction shown in FIG. 10,
predetermined regions 0 on the minimum gap side of the three
arcuate surfaces 8a7, 8a8, and 8a9 are formed by concentric arcs
whose center of curvature coincides with the axial center O of the
bearing sleeve 8 (i.e., the shaft portion 2a). Thus, in each
predetermined region .theta., the radial bearing gap (i.e., minimum
gap) is constant. A multi-arc bearing of this construction is
sometimes referred to as a tapered flat bearing.
[0078] While the multi-arc bearings of the above-mentioned examples
are so-called three-arc bearings, this should not be construed
restrictively; it is also possible to adopt a so-called four-arc
bearing, a five-arc bearing, and further, a multi-arc bearing
formed by six or more arcuate surfaces. In the case in which the
radial bearing portion is formed by a step bearing or a multi-arc
bearing, it is possible to adopt, apart from the construction in
which two radial bearing portions are axially spaced apart from
each other as in the case of the radial bearing portions R1, R2, a
construction in which one radial bearing portion is provided to
extend over the vertical region of the inner peripheral surface 8a
of the bearing sleeve 8.
[0079] Further, one or both of the thrust bearing portions T1, T2
may be formed, for example, by a so-called step bearing, a
so-called wave-type bearing (with an undulated step pattern), etc.,
in which a plurality of dynamic pressure grooves in the form of
radial grooves are provided at predetermined circumferential
intervals in the region constituting the thrust bearing
surface.
[0080] While in the above-mentioned embodiments a lubricating oil
is used as the fluid filling the interior of the dynamic bearing
device 1 and generating a dynamic pressure in the radial bearing
gap between the bearing sleeve 8 and the shaft member 2 and in the
thrust bearing gaps between the bearing sleeve 8, the shaft member
2, and the seal member 9, it is also possible to use some other
fluid capable of generating a dynamic pressure in the bearing gaps,
for example, a gas such as air, or a magnetic fluid.
[0081] Further, while in the above-mentioned embodiments the radial
bearing surface is formed on the inner peripheral surface 8a of the
bearing sleeve 8, it is also possible to form the radial bearing
surface on the surface opposed thereto through the intermediation
of the radial bearing gap, that is, on the outer peripheral surface
2a1 of the shaft portion 2a. Further, while in the above examples
the thrust bearing surfaces having dynamic pressure grooves are
formed on the end surfaces 8b, 8c of the bearing sleeve, it is also
possible to form the thrust bearing surfaces on the surfaces
opposed thereto through the intermediation of the thrust bearing
gaps, that is, on the lower end surface 9b of the seal member 9 and
on the upper end surface 2b1 of the flange portion 2b of the shaft
member 2.
* * * * *