U.S. patent application number 10/580966 was filed with the patent office on 2007-10-11 for fluid bearing device.
Invention is credited to Kenji Ito.
Application Number | 20070237438 10/580966 |
Document ID | / |
Family ID | 34708893 |
Filed Date | 2007-10-11 |
United States Patent
Application |
20070237438 |
Kind Code |
A1 |
Ito; Kenji |
October 11, 2007 |
Fluid Bearing Device
Abstract
Disclosed is a fluid bearing device in which a high adhesive
strength is ensured in fixing another member by adhesion to a resin
housing. A bearing sleeve is secured in position inside the resin
housing, and a shaft member is radially supported in a non-contact
fashion by a dynamic pressure action of lubricant generated in a
radial bearing clearance between the shaft member and the bearing
sleeve. A metal bracket for mounting the stator coil of a motor is
fixed by adhesion to the outer periphery of the housing, in which
the adhesion portion of the outer periphery of the housing to be
fixed to the bracket is roughened, setting the surface roughness to
0.5 .mu.mRa to 2.0 .mu.mRa.
Inventors: |
Ito; Kenji; (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: |
34708893 |
Appl. No.: |
10/580966 |
Filed: |
December 15, 2004 |
PCT Filed: |
December 15, 2004 |
PCT NO: |
PCT/JP04/19158 |
371 Date: |
February 22, 2007 |
Current U.S.
Class: |
384/118 ;
G9B/19.029 |
Current CPC
Class: |
F16C 35/02 20130101;
F16C 33/1075 20130101; Y10T 29/49703 20150115; F16C 2370/12
20130101; F16C 17/107 20130101; H02K 5/1675 20130101; Y10T 29/49636
20150115; Y10T 29/49639 20150115; F16C 33/107 20130101; G11B
19/2018 20130101 |
Class at
Publication: |
384/118 |
International
Class: |
F16C 17/00 20060101
F16C017/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 24, 2003 |
JP |
2003-427433 |
Claims
1. A fluid bearing device comprising: a housing; a bearing sleeve
secured in position inside the housing; a shaft member adapted to
rotate relative to the bearing sleeve; and a radial bearing portion
supporting the shaft member radially in a non-contact fashion with
an oil film formed in a radial bearing clearance between an inner
peripheral surface of the bearing sleeve and an outer peripheral
surface of the shaft member, with another member being fixed by
adhesion to the housing, wherein at least the housing is formed of
resin, and wherein, of the housing and the other member, an
adhesion portion of the one formed of resin has a surface roughness
of 0.5 .mu.mRa or more.
2. A fluid bearing device according to claim 1, wherein the
adhesion portion has a surface roughness of 2.0 .mu.mRa or
less.
3. A fluid bearing device according to claim 1, wherein the other
member fixed to the housing by adhesion is a bracket for mounting a
stator coil of a motor.
4. A fluid bearing device according to claim 1, wherein the other
member fixed to the housing by adhesion is a sealing member for
sealing up an opening of the housing.
5. A fluid bearing device according to claim 1, wherein the other
member fixed to the housing by adhesion is a thrust bush closing a
bottom portion of the housing.
6. A fluid bearing device according to claim 1, wherein the other
member fixed to the housing by adhesion is the bearing sleeve.
7. A motor comprising a fluid bearing device as claimed in claim 1;
a stator coil; and a rotor magnet.
8. A fluid bearing device according to claim 2, wherein the other
member fixed to the housing by adhesion is a bracket for mounting a
stator coil of a motor.
9. A fluid bearing device according to claim 2, wherein the other
member fixed to the housing by adhesion is a sealing member for
sealing up an opening of the housing.
10. A fluid bearing device according to claim 2, wherein the other
member fixed to the housing by adhesion is a thrust bush closing a
bottom portion of the housing.
11. A fluid bearing device according to claim 2, wherein the other
member fixed to the housing by adhesion is the bearing sleeve.
12. A motor comprising a fluid bearing device as claimed in claim
2; a stator coil; and a rotor magnet.
13. A motor comprising a fluid bearing device as claimed in claim
3; a stator coil; and a rotor magnet.
14. A motor comprising a fluid bearing device as claimed in claim
4; a stator coil; and a rotor magnet.
15. A motor comprising a fluid bearing device as claimed in claim
5; a stator coil; and a rotor magnet.
16. A motor comprising a fluid bearing device as claimed in claim
6; a stator coil; and a rotor magnet.
17. A motor comprising a fluid bearing device as claimed in claim
8; a stator coil; and a rotor magnet.
18. A motor comprising a fluid bearing device as claimed in claim
9; a stator coil; and a rotor magnet.
19. A motor comprising a fluid bearing device as claimed in claim
10; a stator coil; and a rotor magnet.
20. A motor comprising a fluid bearing device as claimed in claim
11; a stator coil; and a rotor magnet.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a fluid bearing device.
This fluid bearing device is suitable for use as a bearing device
in the spindle motor of an information apparatus, for example, a
magnetic disc apparatus, such as an HDD or an FDD, an optical disc
apparatus, such as a CD-ROM, a CD-R/RW, or a DVD-ROM/RAM, or a
magneto-optical disc apparatus, such as an MD or an MO, the polygon
scanner motor of a laser beam printer (LBP), a color wheel for a
projector, or the small motor of an electric apparatus, such as an
axial flow fan.
[0003] 2. Related Background Art
[0004] Apart from high rotational accuracy, an improvement in
speed, a reduction in cost, a reduction in noise, etc. are required
of the motors as mentioned above. One of the factors determining
such requisite performances is the bearing supporting the spindle
of the motor. Recently, as such a kind of bearing, use of a dynamic
pressure bearing superior in the above requisite performances is
being considered or such a fluid bearing has been actually put into
practical use. This type of fluid bearing is roughly classified
into two categories: a dynamic pressure bearing equipped with a
dynamic pressure generating means for generating dynamic pressure
in a lubricant in a bearing clearance, and a circular bearing
equipped with no such dynamic pressure generating means (a bearing
whose bearing surface is of a circular configuration).
[0005] As an example of such a bearing device, JP 2000-291648 A
discloses a dynamic pressure bearing device for use in the spindle
motor of a disc drive apparatus, such as an HDD. In this bearing
device, a bearing sleeve is fixed to the inner periphery of a
housing formed as a bottomed cylinder, and a shaft member with a
flange portion protruding radially outwards is inserted into the
bore defined by the inner periphery of the bearing sleeve, wherein
a fluid dynamic pressure is generated in a radial bearing clearance
and a thrust bearing clearance formed between the rotating shaft
member and the stationary members (the bearing sleeve, the housing,
etc.), the shaft member being supported in a non-contact fashion by
this fluid dynamic pressure.
[0006] Incidentally, a spindle motor of this type rotates a shaft
member by an excitation force generated by a rotor magnet and a
stator coil; conventionally, the rotor magnet is, in many cases,
fixed to a member rotating with the shaft member (a disc hub or the
like), whereas the stator coil is fixed to a metal bracket (a motor
bracket) fixed to the outer periphery of the housing of a dynamic
pressure bearing device.
[0007] The fixation of the motor bracket and the housing is
generally effected by adhesion. Conventionally, the housing has
been formed of a soft metal, such as brass; since the adhesion is
effected between metal members, it has been possible to obtain a
necessary and sufficient adhesive force.
[0008] Recently, however, use of a resin housing is being
considered from the viewpoint of achieving a reduction in cost,
etc. In this case, it is impossible to obtain a sufficient adhesive
force for the connection between the resin housing and the motor
bracket. Thus, what matters here is how to attain a sufficient
adhesive force for the connection therebetween.
SUMMARY OF THE INVENTION
[0009] In view of this, it is an object of the present invention to
achieve an enhancement in the adhesive strength for the connection
between a resin housing and another member, such as a motor
bracket.
[0010] In order to achieve this object, a fluid bearing device
according to the present invention includes: a housing; a bearing
sleeve secured in position inside the housing; a shaft member
adapted to rotate relative to the bearing sleeve; and a radial
bearing portion supporting the shaft member radially in a
non-contact fashion with an oil film formed generated in a radial
bearing clearance between an inner peripheral surface of the
bearing sleeve and an outer peripheral surface of the shaft member,
with another member being fixed by adhesion to the housing, in
which at least the housing is formed of resin, and in which, of the
housing and the other member, an adhesion portion of the one formed
of resin has a surface roughness of 0.5 .mu.mRa or more.
[0011] Usually, a resin product is formed by injection molding. The
molding surface of the mold for injection molding is
mirror-finished, so that the surface roughness of the resin product
obtained is approximately 0.1 .mu.mRa, which is markedly lower than
that of a metal product. By intentionally roughening the surface of
the adhesion portion of a resin product thus obtained by injection
molding to 0.5 .mu.mRa or more, when connecting the housing and the
other member by adhesion, adhesive enters the voids defined by the
surface protrusions and recesses resulting from the surface
roughening to thereby provide an anchoring effect, so that it is
possible to ensure a high adhesion strength. This helps to ensure a
high anti-impact property between the resin housing and the member
to be connected therewith, so that it is possible to form the
housing of resin and to provide a fluid bearing device superior in
durability and reliability. Apart from the adhesion portion of the
housing (the portion of the housing to be connected to some other
member by adhesion), such surface roughening can also be effected
on the adhesion portion of the other member (the portion of the
other member to be connected to the housing by adhesion) when the
other member is formed of resin.
[0012] On the other hand, when the adhesion portion is roughened to
an excessive degree, a deterioration in the releasability of the
molded product results at the time of molding. In view of this, it
is desirable for the surface roughness of the adhesion portion to
be not more than 2.0 .mu.mRa, more preferably, not more than 1.5
.mu.mRa.
[0013] There are no particular limitations regarding the kind of
resin of which the housing is to be formed as long as it is a
thermoplastic resin. Examples of the resin that can be used include
amorphous resins, such as polysulfone (PSF), polyether sulfone
(PES), polyphenyl sulfone (PPSF), and polyether imide (PEI), and
crystalline resins, such as liquid crystal polymer (LCP),
polyetheretherketone (PEEK), polybutyrene terephthalate (PBT), and
polyphenylene sulfide (PPS).
[0014] It is also possible to add filler to the above-mentioned
resins as needed. There are no particular limitations regarding the
kind of filler used. Examples of the filler that can be used
include a fibrous filler such as glass fiber, a whisker-like filler
such as potassium titanate, a scaly filler such as mica, and a
fibrous or powder-like conductive filler such as carbon fiber,
carbon black, graphite, carbon nanomaterial, and metal powder. Such
filler may be used singly, or two or more kinds of filler may be
mixed with each other.
[0015] There are no particular limitations regarding the function,
structure, configuration, etc. of the other member to be connected
with the housing by adhesion, and its material may be metal or one
of the resin materials as mentioned above. Apart from the outer
peripheral surface of the housing, this other member maybe
connected by adhesion to various parts of the housing, such as the
inner peripheral surface or the bottom portion thereof. Instead of
performing it on the adhesion portion alone, it is also possible to
perform the surface roughening on the entire surface of the member
including the adhesion portion.
[0016] There are no particular limitations regarding the adhesive
used for the connection by adhesion of the housing and the other
member; it is selected from among various types of adhesive,
including epoxy type adhesives, urethane type adhesives, acrylic
type adhesives, etc. according to the resin material used and the
kind of material of the other member to be connected thereto by
adhesion.
[0017] Examples of the other member to be connected to the housing
by adhesion include a bracket for mounting a stator coil, a sealing
member for hermetically sealing an opening of the housing, a thrust
bush for closing the bottom portion of the housing, and a bearing
sleeve.
[0018] Since it uses a resin housing, a motor having a dynamic
pressure bearing device as described above, a stator coil, and a
rotor magnet is inexpensive. Further, since a sufficient level of
adhesive strength is ensured, the motor exhibits high impact
resistance and is superior in durability and reliability.
[0019] According to the present invention, it is possible to ensure
a strong adhesive force for the connection by adhesion between the
resin housing and the other member, making it possible to improve
the fluid bearing device in terms of durability and
reliability.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 is a sectional view of a spindle motor for an
information apparatus with a dynamic pressure bearing incorporated
therein;
[0021] FIG. 2 is a sectional view of the dynamic pressure
bearing;
[0022] FIG. 3 is a sectional view of a bearing sleeve to be used in
the dynamic pressure bearing device;
[0023] FIG. 4 is a plan view of the housing as seen from the
direction of the arrow B in FIG. 2;
[0024] FIG. 5 is a sectional view of a spindle motor for an
information apparatus with a dynamic pressure bearing according to
another embodiment incorporated therein;
[0025] FIG. 6 is a sectional view of a dynamic pressure bearing
device according to another embodiment of the present invention;
and
[0026] FIG. 7 is a diagram showing test results obtained through
measurement, showing the relationship between the surface roughness
of the housing adhesion portion and the adhesive strength.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0027] In the following, embodiments of the present invention will
be described with reference to FIGS. 1 through 7.
[0028] FIG. 1 conceptually shows an example of the construction of
a spindle motor for an information apparatus with a dynamic
pressure bearing device 1, supporting a shaft member 2 with a
dynamic pressure oil film, incorporated therein. This spindle motor
is used in a disc drive device, such as an HDD, and contains the
dynamic pressure bearing device 1, a disc hub 3 mounted to a shaft
member 2, and a stator coil 4 and a rotor magnet 5 that are opposed
to each other through the intermediation, for example, of 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 disc hub 3. As described below, the dynamic pressure bearing
1 has a housing 7 fixed by adhesion to the inner periphery of the
bracket 6. The disc hub 3 retains one or a plurality of discs D,
such as magnetic discs (see FIG. 5). When the stator coil 4 is
energized, the rotor magnet 5 is rotated by an electromagnetic
force between the stator coil 4 and the rotor magnet 5, whereby the
disc hub 3 and the shaft member 2 constitute rotary members to
rotate integrally.
[0029] FIG. 2 is an enlarged view of the dynamic pressure bearing
device 1. This dynamic pressure bearing device 1 consists of as
main components the housing 7 formed as a bottomed cylinder with
one end open, a bearing sleeve 8 fixed to the inner periphery of
the housing 7, and the shaft member 2.
[0030] In this dynamic pressure bearing 1, there are provided,
between the inner peripheral surface 8a of the bearing sleeve 8 and
the outer peripheral surface 2a of the shaft member 2, a first
radial bearing portion R1 and a second radial bearing portion R2
axially spaced apart from each other. Further, a thrust bearing
portion TI is formed between the upper end surface 7d of the
housing 7 and the opposing lower end surface 3a of the disc hub
(rotor) 3 fixed to the shaft member 2. In the following
description, for the sake of convenience, the bottom portion 7b
side of the housing 7 will be referred to as the lower side, and
the side opposite to the bottom portion 7b will be referred to the
upper side.
[0031] The housing 7 is formed as a bottomed cylinder by injection
molding of a resin material consisting, for example, of liquid
crystal polymer (LCP) as a crystalline resin with 2 to 8 wt % of
carbon nanotube as a conductive filler added thereto, and is
equipped with a cylindrical side portion 7a and the bottom portion
7b formed integrally at the lower end of the side portion 7a.
[0032] As shown in FIG. 4, dynamic pressure grooves 7d l of, for
example, a spiral configuration, are formed in the upper end
surface 7d constituting the thrust bearing surface of the thrust
bearing portion T1. These dynamic pressure grooves 7d l are formed
at the time of formation of the housing 7 by injection molding.
That is, at the pertinent position of the mold for forming the
housing 7 (the position where the upper end surface 7d is to be
formed), there is previously prepared by machining a groove pattern
for forming the dynamic pressure grooves 7d1, and, at the time of
formation of the housing 7 by injection molding, the shape of the
groove pattern is transferred to the upper end surface 7d of the
housing 7, whereby it is possible to form the dynamic pressure
grooves 7d1 simultaneously with the formation of the housing 7 by
molding.
[0033] Further, the housing 7 has, in the outer periphery of the
upper portion thereof, a tapered outer wall 7e gradually diverging
upwards. Between this tapered outer wall 7e and an inner wall 3b1
of a flange portion 3b provided on the disc hub 3, there is formed
a tapered sealing space S gradually diminishing upwards. During
rotation of the shaft member 2 and the disc hub 3, this sealing
space S communicates with the outer side of the thrust bearing
clearance of the thrust bearing portion T1.
[0034] The shaft member 2 is formed as a shaft with a uniform
diameter of a metal material, such as stainless steel. The disc hub
3 is fixed to the shaft member 2 by thread engagement as shown in
the drawing, or some other appropriate means, such as press-fitting
or adhesion.
[0035] The bearing sleeve 8 is formed in a cylindrical
configuration using a porous material consisting of, for example, a
sintered metal, in particular, a sintered metal whose main
component is copper, and is fixed to a predetermined position of
the inner peripheral surface 7c of the housing 7 by, for example,
adhesion or ultrasonic welding.
[0036] On the inner peripheral surface Ba of the bearing sleeve 8,
formed of a sintered metal, there are provided upper and lower
areas constituting the radial bearing surfaces of the first radial
bearing portion R1 and the second radial bearing portion R2 so as
to be axially spaced apart from each other, and, in these two
areas, there are respectively formed dynamic pressure grooves 8a l
and 8a 2 of a herringbone-like configuration (or a spiral
configuration) as shown, for example, in FIG. 3. In the radial
bearing portions R1 and R2 shown, the upper dynamic pressure
grooves 8a1 are formed axially asymmetrical with respect to the
axial center m (the axial center of the region between the upper
and lower inclined grooves), and the axial dimension X1 of the
region above the axial center m is larger than the axial dimension
X2 of the region below the same. Further, on the outer peripheral
surface 8d of the bearing sleeve 8, there is formed one or a
plurality of axial grooves 8d1 so as to extend over the entire
axial length thereof.
[0037] The shaft member 2 is inserted into the bore defined by the
inner peripheral surface 8a of the bearing sleeve 8. When the shaft
member 2 and the disc hub 3 are at rest, there respectively exist
minute gaps between the lower end surface 2b of the shaft member 2
and the inner bottom surface 7b1 of the housing 7 and between the
lower end surface 8c of the bearing sleeve 8 and the inner bottom
surface 7b1 of the housing 7.
[0038] The inner space, etc. of the housing 7 are filled with
lubricant. That is, inclusive of the inner pores of the bearing
sleeve 8, the lubricant fills the clearance between the inner
peripheral surface 8a of the bearing sleeve 8 and the outer
peripheral surface 2a of the shaft member 2, the clearance between
the lower end surface 8c of the bearing sleeve 8 and the lower end
surface 2b of the shaft member 2 and the inner bottom surface 7b1
of the housing 7, the axial grooves 8d1 of the bearing sleeve 8,
the clearance between the upper end surface 8b of the bearing
sleeve 8 and the lower end surface 3a of the disc hub 3, the thrust
bearing portion T1, and the sealing space S.
[0039] During rotation of the shaft member 2 and the disc hub 3,
the (upper and lower) areas of the inner peripheral surface 8a of
the bearing sleeve 8 constituting the radial bearing surfaces are
opposed to the outer peripheral surface 2a of the shaft member 2
respectively through the intermediation of the radial bearing
clearances. The area of the upper end surface 7d of the housing 7
constituting the thrust bearing surface is opposed to the lower end
surface 3a of the disc hub 3 through the intermediation of the
thrust bearing clearance. As the shaft member 2 and the disc hub 3
rotate, a dynamic pressure of lubricant is generated in the radial
bearing clearances, and the shaft member 2 is supported radially
and rotatably in a non-contact fashion by oil films formed within
the radial bearing clearances. As a result, there are formed the
first radial bearing portion R1 and the second radial bearing
portion R2 supporting the shaft member 2 and the disc hub 3
radially and rotatably in a non-contact fashion. At the same time,
a dynamic pressure of lubricant is generated in the thrust bearing
clearance, and the disc hub 3 is rotatably supported in the thrust
direction in a non-contact fashion by an oil film formed within the
thrust bearing clearance, whereby there is formed the thrust
bearing portion T1 supporting the shaft member 2 and the disc hub 3
rotatably in the thrust direction in a non-contact fashion.
[0040] As shown in FIG. 1, a bracket 6 formed of metal, preferably
a light alloy, such as aluminum alloy, is fixed by adhesion to the
outer peripheral surface 7f of the side portion 7a of the housing
7. After the adhesion, the outer peripheral surface 7f of the
housing 7 (exclusive of the tapered outer wall 7e) and the inner
peripheral surface 6a of the bracket 6 are firmly connected to each
other by the adhesion filling the adhesion gap.
[0041] In the present invention, to ensure the requisite adhesive
strength for the housing 7 and the bracket 6, the surface of the
housing 7 is formed as a surface (a roughened surface) having a
center line average roughness of 0.5 .mu.mRa or more as defined in
JIS B0601. An examination by the inventor of the present invention
showed that a surface roughness less than 0.5 .mu.mRa does not
provide a sufficient adhesive strength. As far as only adhesive
strength is concerned, there is no need to particularly set an
upper limit to the surface roughness; however, when the surface
roughness is in excess of 2.0 .mu.mRa, it is rather difficult to
release the molded product from the mold after injection molding,
thus obstructing successive molding. Thus, it is desirable for the
surface roughness of the adhesion portion to be not less than 0.5
.mu.mRa but not more than 2.0 .mu.mRa (preferably not more than 1.5
.mu.mRa). It is not always necessary for the entire surface of the
housing 7 to be within the above-mentioned surface roughness range;
it suffices if at least the surface roughness of the adhesion
portion of the bracket 6 is within the above-mentioned range. When
fixing the bearing sleeve 8 by adhesion to the inner peripheral
surface 7c of the housing 7, a similar effect can be obtained by
forming the adhesion portion of the housing inner peripheral
surface 7c as a roughened surface as described above.
[0042] The surface roughening of the adhesion portion of the
housing 7 can be effected at low cost by, for example, performing
injection molding after roughening the mirror-finished molding
surface of the mold by shot blasting, sand paper or the like. For
instance, by roughening the molding surface of the mold to
approximately 1.0 .mu.mRa, it is possible to achieve a surface
roughness of 0.8 .mu.mRa in the resultant product obtained by
molding. Apart from such previous surface roughening of the mold,
it is also possible to form the surface of the adhesion portion as
a roughened surface by performing an appropriate surface roughening
processing on the housing surface after the injection molding.
[0043] The present invention is not restricted to the dynamic
pressure bearing device as shown in FIGS. 1 and 2 by way of
example; as long as the housing 7 is formed of resin, the present
invention is applicable to various types of dynamic pressure
bearing device. FIG. 5 shows an example thereof, in which the shaft
member 2 is composed of a shaft portion 2c and an outwardly
protruding flange portion 2d; a thrust bearing surface is formed on
either one end surface of the flange portion 2d or the end surface
of the bearing sleeve 8 opposed thereto, and on either the other
end surface of the flange portion 2d or the bottom portion 7b of
the housing 7 opposed thereto, whereby there are formed a first
thrust bearing portion T1 and a second thrust bearing portion T2
vertically spaced apart from each other (The radial bearing
portions R1 and R2 are not shown). In this embodiment also, the
outer peripheral surface 7f of the resin housing 7 is fixed by
adhesion to the inner peripheral surface of the bracket 6; by
roughening the outer peripheral surface 7f of the housing 7 prior
to adhesion as described above, it is possible to obtain a high
adhesive strength for the connection between the housing 7 and the
bracket 6. In this dynamic pressure bearing device 1, a sealing
member 9 sealing the opening at the upper end of the housing 7 can
be fixed by adhesion to the inner peripheral surface of the housing
7. In this case, the portion of the inner peripheral surface of the
housing 7 connected to at least the sealing member 9 may be
roughened in a manner as described above.
[0044] FIG. 6 shows an example in which, in the dynamic pressure
bearing device shown in FIG. 5, the bottom portion 7b of the resin
housing 7 is formed by a thrust bush 10, which is a separate
component. In this case, the thrust bush 10 is fixed by adhesion to
a large-diameter inner peripheral surface 7c1 formed in the inner
periphery of the housing 7; by roughening this large-diameter inner
peripheral surface 7c1 in a manner as described above, it is
possible to achieve a high adhesive strength. While, in the example
shown, a sealing portion 7g is integrally formed at the upper end
of the housing, it is also possible for this sealing portion 7g to
be formed as a separate sealing member 9 (see FIG. 5), fixing it by
adhesion to the inner periphery of the housing 7 roughened
beforehand.
[0045] In the above-described examples the adhesion portion of the
housing 7 is subjected to surface roughening; however, when the
member to which the housing 7 is to be fixed (e.g., the bracket 6,
the bearing sleeve 8, the sealing member 9, or the thrust bush 10)
is formed of resin, it is also possible for the adhesion portion of
that member to be subjected to surface roughening.
[0046] Further, while in the above embodiments the thrust bearing
portions T1 and T2 are both formed as dynamic pressure bearings,
the present invention is also applicable to a case in which these
thrust bearing portions are formed as contact type pivot
bearings.
[0047] The radial bearing portions R1 and R2 can also be formed by
multi-arc bearings. FIG. 8A shows an example thereof, in which a
plurality of arcuate surfaces 81 are formed in the areas of the
inner peripheral surface Ba of the bearing sleeve 8 constituting
the respective radial bearing surfaces of the first radial bearing
portion R1 and the second radial bearing portion R2 (also referred
to as the "tapered bearings"). The arcuate surfaces 81 are
eccentric arcuate surfaces whose centers are offset from the
rotation axis O by the same distance, and are formed at equal
intervals in the circumferential direction. Between the eccentric
arcuate surfaces 81, there are formed axial separation grooves
82.
[0048] By inserting the shaft member 2 into the bore defined by the
inner peripheral surface 8a of the bearing sleeve 8, the radial
bearing clearances of the first and second radial bearing portions
R1 and R2 are formed between the eccentric arcuate surfaces 81 and
separation grooves 82 of the bearing sleeve 8 and the circular
outer peripheral surface 2a of the shaft member 2. Of the radial
bearing clearances, the areas opposed to the eccentric arcuate
surfaces 81 constitute wedge-like clearances 83 gradually reduced
in clearance width in one circumferential direction. The
width-reducing direction of the wedge-like clearances 83 coincides
with the rotating direction of the shaft member 2.
[0049] FIGS. 8B and 8C show other embodiments of the multi-arc
bearings forming the first and second radial bearing portions R1
and R2.
[0050] Of these, in the embodiment shown in FIG. 8B, the
construction shown in FIG. 8A is modified such that predetermined
areas .theta. on the minimum clearance side of the eccentric
arcuate surfaces 81 are formed by concentric arcs which have the
rotation axis O as their centers. Thus, in each predetermined area
.theta., the radial bearing clearance (minimum clearance) is fixed.
A multi-arc bearing thus constructed is also referred to as a
tapered flat bearing.
[0051] In FIG. 8C, the areas of the inner peripheral surface 8a of
the bearing sleeve 8 constituting the radial bearing surfaces are
formed by three arcuate surfaces 81, with the centers of the three
arcuate surfaces 81 being offset by the same distance from the
rotation axis O. In each of the areas defined by the three
eccentric arcuate surfaces 81, the radial bearing clearance is
configured so as to be gradually diminished in both circumferential
directions.
[0052] While the multi-arc bearings of the first and second radial
bearing portions R1 and R2 described above are all three-arc
bearings, this should not be construed restrictively; it is also
possible to adopt a so-called four-arc bearing, five-arc bearing,
or, further, a multi-arc bearing with six arcs or more. Further,
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 and R2, it is also possible to adopt a
construction in which a single radial bearing portion is provided
so as to extend over the upper and lower areas of the inner
peripheral surface of the bearing sleeve 8.
[0053] Further, while in the above embodiment multi-arc bearings
are adopted as the radial bearing portions R1 and R2, it is also
possible to adopt a bearing of some other type. For example,
although not shown, it is also possible to use, in the area of the
inner peripheral surface 8a of the bearing sleeve 8 constituting
the radial bearing surface, a step bearing in which there are
formed dynamic pressure grooves in the form of a plurality of axial
grooves.
[0054] FIG. 7 shows test results obtained through measurement,
indicating the relationship between the surface roughness of the
housing adhesion portion and the adhesive strength. In this test,
the housing 7 used was one having a separate thrust bush 10 at the
bottom (see FIG. 6), and the extraction load of the thrust bush 10
was measured by gradually increasing the load in the thrust
direction applied to the thrust bush 10. The adhesive used was an
epoxy type adhesive (Epotec 353ND manufactured by Epoxy Technology,
Co.).
[0055] As is apparent from FIG. 7, in an ordinary injection-molding
product which had undergone no surface roughening (0.1 .mu.mRa),
the adhesive strength was 400N, whereas, by effecting surface
roughening on the adhesion portion to 0.5 .mu.mRa, the adhesive
strength was enhanced by approximately 25% to become 500 N, thus
satisfying the impact load level (1000 G) required of a dynamic
pressure bearing device. a surface roughness of 1.0 .mu.mRa, the
adhesive strength was 600 N, thus making it clear that a surface
roughness in excess of this would result in the adhesive strength
reaching a level of saturation. On the other hand, as stated above,
at a surface roughness in excess of 2.0 .mu.mRa, the releasability
in the injection molding deteriorates. Thus, as can also be seen
from the test results, it is desirable for the surface roughness of
the adhesion portion to be 0.5 .mu.mRa or more. On the other hand,
it is desirable for the upper limit of the surface roughness to be
2.0 .mu.mRa or less, preferably, 1.5 .mu.mRa or less.
[0056] It should be noted that when, as described above, the
bearing sleeve 8 is formed of an oil-impregnated sintered metal,
vacuum impregnation with lubricant is often effected. This vacuum
impregnation is effected by incorporating the bearing sleeve 8 into
the housing 7 and immersing the whole in oil; conventionally, even
if degreasing is effected on the housing 7 after such immersion in
oil, it has been impossible, in many cases, to obtain a sufficient
adhesive strength in the subsequent step of connecting the other
member by adhesion. In the present invention, in contrast, it is
possible to obtain a high adhesive strength even after such
immersion in oil. This proves the present invention to be
especially suitable for a bearing device in which the bearing
sleeve 8 is formed of an oil-impregnated sintered metal.
* * * * *