U.S. patent number RE45,387 [Application Number 13/945,043] was granted by the patent office on 2015-02-24 for spindle motor having a fluid dynamic bearing system and a stationary shaft.
This patent grant is currently assigned to Minebea Co., Ltd.. The grantee listed for this patent is Minebea Co., Ltd.. Invention is credited to Martin Bauer, Martin Engesser, Jurgen Fleig, Thomas Fuss, Vladimir V. Popov, Guido Schmid, Stefan Schwamberger, Matthias Wildpreth, Olaf Winterhalter.
United States Patent |
RE45,387 |
Popov , et al. |
February 24, 2015 |
Spindle motor having a fluid dynamic bearing system and a
stationary shaft
Abstract
The invention relates to a spindle motor having a fluid dynamic
bearing system comprising axial and radial bearings that contains a
rotor component (14) which encloses a stationary shaft (12), which
in turn is connected at both its ends to axially aligned bearing
parts (16; 18) that are fashioned such that they form capillary
sealing gaps (32; 34), a recirculation channel (28) filled with
bearing fluid that connects the remote regions of the bearing to
each other, and an electromagnetic drive system (42, 44) for
driving the rotor component.
Inventors: |
Popov; Vladimir V.
(Villingen-Schwenningen, DE), Fleig; Jurgen (St.
Georgen, DE), Bauer; Martin (Villingen-Schwenningen,
DE), Schmid; Guido (Triberg, DE),
Winterhalter; Olaf (Epfendorf, DE), Wildpreth;
Matthias (Villingen-Schwenningen, DE), Fuss;
Thomas (Rottweil, DE), Engesser; Martin
(Donaueschingen, DE), Schwamberger; Stefan
(Villingen-Schwenningen, DE) |
Applicant: |
Name |
City |
State |
Country |
Type |
Minebea Co., Ltd. |
Nagano-ken |
N/A |
JP |
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Assignee: |
Minebea Co., Ltd. (Nagano-Ken,
JP)
|
Family
ID: |
40586050 |
Appl.
No.: |
13/945,043 |
Filed: |
July 18, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
12313898 |
Nov 25, 2008 |
7982349 |
Jul 19, 2011 |
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Foreign Application Priority Data
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Nov 30, 2007 [DE] |
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10 2007 058 150 |
Sep 19, 2008 [DE] |
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10 2008 048 079 |
Oct 21, 2008 [DE] |
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10 2008 052 469 |
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Current U.S.
Class: |
310/90 |
Current CPC
Class: |
F16C
33/1085 (20130101); F16C 33/745 (20130101); H02K
5/1677 (20130101); F16C 17/107 (20130101); F16C
2370/12 (20130101) |
Current International
Class: |
H02K
5/16 (20060101) |
Field of
Search: |
;310/90,51 ;384/100 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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102005005414 |
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Oct 2006 |
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DE |
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102007005516 |
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Aug 2008 |
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DE |
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102008052469 |
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Jun 2009 |
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DE |
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2003333798 |
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Nov 2003 |
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JP |
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2005304290 |
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Oct 2005 |
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JP |
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2006071087 |
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Mar 2006 |
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JP |
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200724199 |
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Feb 2007 |
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JP |
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2007155093 |
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Jun 2007 |
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JP |
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Primary Examiner: Nguyen; Hanh
Attorney, Agent or Firm: Cooper & Dunham LLP
Claims
The invention claimed is:
1. A spindle motor having a fluid dynamic bearing system
comprising: a stationary shaft (12; 212; 312) that is held directly
or indirectly in a baseplate (10, 210; 310), a rotor component (14,
114a; 214; 314a-c) rotatably supported with respect to the shaft
about a rotational axis (46; 246; 346), a bearing gap (20, 220;
320) open at both ends filled with a bearing fluid that separates
the adjoining surfaces of the shaft (12; 212; 312), the rotor
component (14, 114a; 214; 214a-c) and at least one first bearing
part (16, 216; 316) from one another, a first radial bearing (22a,
222a; 322a) and a second radial bearing (22b, 222b; 322b) formed
between the opposing axially extending bearing surfaces of the
shaft (12; 212; 312) and the rotor component (14, 114a; 214;
314a-c), an axial bearing (26, 226; 326) formed between the
opposing radially extending bearing surfaces of the rotor component
(14, 114a; 214; 314a-c) and the first bearing part (16, 216; 316)
connected to the baseplate, a recirculation channel (28; 128; 228;
328) filled with bearing fluid that connects the remote regions of
the bearing to each other, and an electromagnetic drive system (42,
44; 342, 244) for driving the rotor component, and characterized in
that the recirculation channel (28, 128; 228) ends in a gap (21)
radially outside of the bearing gap (20) of the axial bearing (26),
the width of the gap (21) being greater than the width of the
bearing gap (20).
2. A spindle motor according to claim 1, characterized in that the
rotor component consists of an inner, sleeve-shaped rotor component
(114a; 314a) and an outer cup-shaped rotor component (144b;
314b).
3. A spindle motor according to claim 2, characterized in that the
inner, sleeve-shaped rotor component (314a) is enclosed by a
further, sleeve-shaped rotor component (314c) on which the outer
cup-shaped rotor component (314b) is disposed.
4. A spindle motor according to claim 1, characterized in that it
only contains one rotating, mechanical rotor component (14; 214)
taking the form of a hub/bearing bush arrangement.
5. A spindle motor according to claim 1, characterized in that the
first bearing part (216) is integrally formed with the shaft (212)
as one piece.
6. A spindle motor according to claim 1, characterized in that a
second bearing part (18; 318) is integrally formed with the shaft
(12) as one piece.
7. A spindle motor according to claim 1, characterized in that the
rotor component (14, 114a; 214; 314a-c) has surfaces that are
fashioned such that, together with surfaces of the second bearing
part (18; 218; 318), they form a sealing gap (32; 232; 332) of a
capillary gap seal.
8. A spindle motor according to claim 1, characterized in that the
rotor component (14, 114a; 214; 314a-c) has surfaces that are
fashioned such that, together with surfaces of a first bearing part
(16; 216; 316), they form a sealing gap (34; 234; 334) of a
capillary gap seal.
9. A spindle motor according to claim 1, characterized in that the
recirculation channel (328) is disposed in the rotor component
(314a) or between the rotor components (314a, 314c) and connects
the sealing gap (334) radially outside the axial bearing (226) to a
section of the bearing gap (320) located radially outside a dynamic
pumping seal.
10. A spindle motor according to claim 1, characterized in that the
recirculation channel (28, 128; 228) is disposed at an incline to
the rotational axis (46), which, on rotation of the rotor
component, causes a centrifugal force to be exerted on the bearing
fluid held in the recirculation channel, the centrifugal force
transporting the bearing fluid through the recirculation channel
(28, 128; 228) in the direction of arrow (29).
11. A spindle motor according to claim 10, characterized in that
the recirculation channel (28, 128; 228) is inclined at an angle of
5 to 15 degrees with respect to the rotational axis (46).
12. A spindle motor according to claim 10, characterized in that
the centrifugal force exerted on the bearing fluid due to the
inclined recirculation channel (28, 128; 228) acts in the same
direction as a pumping force exerted on the bearing fluid due to an
overall pumping effect of the axial bearing (26; 126; 226; 326) and
the radial bearings (22a, 22b; 122a, 122b; 222a, 222b; 322a,
322b).
13. A spindle motor according to claim 12, characterized in that
the pumping force generated by the centrifugal force is directed to
the axial bearing (26).
14. A spindle motor according to claim 12, characterized in that
the centrifugal force is at least twice as big as the force exerted
on the bearing fluid due to the overall pumping effect of the axial
bearing (26) and the radial bearings (22a, 22b).
15. A spindle motor according to claim 1, characterized in that a
dynamic pumping seal (36; 236; 336) is formed between opposing
radially extending surfaces of the rotor component (14, 114; 214;
314) and a second bearing part (18; 218; 318) connected to the
shaft.
16. A spindle motor according to claim 15, characterized in that
the dynamic pumping seal (36; 236; 336) is formed between a
radially extending end face of the rotor component (14, 114a; 214;
314a) and an adjoining radially extending end face of the second
bearing part (18; 218; 318).
17. A spindle motor according to claim 15, characterized in that
the dynamic pumping seal (36; 236; 336) is disposed substantially
perpendicular and the sealing gap (32; 232; 332) of the gap seal
.Iadd.is .Iaddend.substantially parallel to the rotational axis
(46; 246; 346).
18. A spindle motor according to claim 1, characterized in that the
baseplate (10; 310) has a ferromagnetic ring (40; 340) that lies
axially opposite a rotor magnet (44; 344) of the electromagnetic
drive system and is magnetically attracted by this magnet and that
they generate a magnetic force that is directed in the opposite
direction to a bearing force generated by the axial bearing (26;
326).
19. A spindle motor according to claim .[.18.]. .Iadd.1.Iaddend.,
characterized in that the electromagnetic drive system comprises a
stator arrangement (42; 342) which is disposed at an axial offset
with respect to .[.the.]. .Iadd.a .Iaddend.rotor magnet (44; 344)
and generate a magnetic force that is directed in the opposite
direction to a bearing force generated by the axial bearing (26;
326).
20. A spindle motor according to claim 1, characterized in that
adjacent surfaces of the second bearing part (18) and the rotor
component 14 form a further axial bearing (25).
21. A spindle motor according to claim 1, characterized in that a
further bearing part (19) connected to the rotor component adjoins
the second bearing part (18), a pumping seal (36) being disposed
between the two bearing parts (18, 19) and a sealing gap being
disposed between the bearing part (19) and the shaft (12).
22. A spindle motor having a fluid dynamic bearing system
comprising: a stationary shaft (12; 212; 312) that is held directly
or indirectly in a baseplate (10, 210; 310), a rotor component (14,
114a; 214; 314a-c) rotatably supported with respect to the shaft
about a rotational axis (46; 246; 346), a bearing gap (20, 220;
320) open at both ends filled with a bearing fluid that separates
the adjoining surfaces of the shaft (12; 212; 312), the rotor
component (14, 114a; 214; 214a-c) and at least one first bearing
part (16, 216; 316) from one another, a first radial bearing (22a,
222a; 322a) and a second radial bearing (22b, 222b; 322b) formed
between the opposing axially extending bearing surfaces of the
shaft (12; 212; 312) and the rotor component (14, 114a; 214;
314a-c), an axial bearing (26, 226; 326) formed between the
opposing radially extending bearing surfaces of the rotor component
(14, 114a; 214; 314a-c) and the first bearing part (16, 216; 316)
connected to the baseplate, a recirculation channel (28; 128; 228;
328) filled with bearing fluid that connects the remote regions of
the bearing to each other, and an electromagnetic drive system (42,
44; 342, 244) for driving the rotor component, characterized in
that the recirculation channel (28, 128; 228) ends in a gap (21)
radially outside of the bearing gap (20) of the axial bearing (26),
and further characterized in that the width of the gap (21) is
greater than or equal to the width of the bearing gap (20) of the
axial bearing (26) plus the depth of the bearing patterns of the
axial bearing (26).
23. A spindle motor having a fluid dynamic bearing system
comprising: a stationary shaft (12; 212; 312) that is held directly
or indirectly in a baseplate (10, 210; 310), a rotor component (14,
114a; 214; 314a-c) rotatably supported with respect to the shaft
about a rotational axis (46; 246; 346), a bearing gap (20, 220;
320) open at both ends filled with a bearing fluid that separates
the adjoining surfaces of the shaft (12; 212; 312), the rotor
component (14, 114a; 214; 214a-c) and at least one first bearing
part (16, 216; 316) from one another, a first radial bearing (22a,
222a; 322a) and a second radial bearing (22b, 222b; 322b) formed
between the opposing axially extending bearing surfaces of the
shaft (12; 212; 312) and the rotor component (14, 114a; 214;
314a-c), an axial bearing (26, 226; 326) formed between the
opposing radially extending bearing surfaces of the rotor component
(14, 114a; 214; 314a-c) and the first bearing part (16, 216; 316)
connected to the baseplate, a recirculation channel (28; 128; 228;
328) filled with bearing fluid that connects the remote regions of
the bearing to each other, and an electromagnetic drive system (42,
44; 342, 244) for driving the rotor component, and a sealing gap
(32; 332) for sealing the bearing gap (20, 220; 320) which is
covered by an annular cover (30, 130; 330) connected to the rotor
component (14; 114a; 314c) that, together with the second bearing
part (18; 318), forms a labyrinth seal (48; 348).
24. A spindle motor according to claim 23, characterized in
.Iadd.that .Iaddend.the annular cover (330) is formed by the rotor
component.
25. A spindle motor according to claim 23, characterized in that
the sealing gap (32) is formed between an inner circumferential
surface of the cover (130) and an outer circumferential surface of
the second bearing part (18).
26. A spindle motor according to claim 23, characterized in that
the sealing gap (32; 332) is formed between an inner
circumferential surface/end face of the rotor component (14, 114a;
214; 314a; 314c) and an outer circumferential surface/end face of
the second bearing part (18; 218; 318).
27. A spindle motor according to claim 23, characterized in that
the sealing gap (34; 234; 334) is formed between an outer
circumferential surface of the rotor component (14, 114a; 214;
314a; 314c) and an inner circumferential surface of the first
bearing part (16; 216; 316).
28. A spindle motor according to claim 23, characterized in that
surfaces of the rotor component (14, 144a; 214) or the cover (130)
and the second bearing part (18; 218) forming the sealing gap (32;
232) extend substantially parallel to the rotational axis (46; 246)
or are inclined at an acute angle to the rotational axis.
29. A spindle motor according to claim 23, characterized in that
surfaces of the rotor component (14, 114a; 214; 314a; 314c) and the
first bearing part (16; 216; 316) forming the sealing gap (34; 234;
334) extend substantially parallel to the rotational axis (46; 246;
346) or are inclined at an acute angle to the rotational axis.
30. A hard disk drive comprising a spindle motor for rotatably
driving at least a storage disk, and means for writing on and
reading data from the storage disk, the spindle motor having a
fluid dynamic bearing system and comprising: a stationary shaft
(12; 212; 312) that is held directly or indirectly in a baseplate
(10, 210; 310), a rotor component (14, 114a; 214; 314a-c) rotatably
supported with respect to the shaft about a rotational axis (46;
246; 346), .Iadd.a .Iaddend.bearing gap (20, 220; 320) open at both
ends filled with a bearing fluid that separates the adjoining
surfaces of the shaft (12; 212; 312), the rotor component (14,
114a; 214; 214a-c) and at least one first bearing part (16, 216;
316) from one another, a first radial bearing (22a, 222a; 322a) and
a second radial bearing (22b, 222b; 322b) formed between the
opposing axially extending bearing surfaces of the shaft (12; 212;
312) and the rotor component (14, 114a; 214; 314a-c), an axial
bearing (26, 226; 326) formed between the opposing radially
extending bearing surfaces of the rotor component (14, 114a; 214;
314a-c) and the first bearing part (16, 216; 316) connected to the
baseplate, a recirculation channel (28; 128; 228; 328) filled with
bearing fluid that connects the remote regions of the bearing to
each other, and an electromagnetic drive system (42, 44; 342, 244)
for driving the rotor component, characterized in that the
recirculation channel (28, 128; 228) ends in a gap (21) radially
outside of the bearing gap (20) of the axial bearing (26), and
further characterized in that the width of the gap (21) is greater
than or equal to the width of the bearing gap (20) of the axial
bearing (26) plus the depth of the bearing patterns of the axial
bearing (26).
31. A spindle motor having a fluid dynamic bearing system
comprising: a stationary shaft (12; 212; 312) that is held directly
or indirectly in a baseplate (10, 210; 310), a rotor component (14,
114a; 214; 314a-c) rotatably supported with respect to the shaft
about a rotational axis (46; 246; 346), a bearing gap (20, 220;
320) open at both ends filled with a bearing fluid that separates
the adjoining surfaces of the shaft (12; 212; 312), the rotor
component (14, 114a; 214; 214a-c) and at least one first bearing
part (16, 216; 316) from one another, a first radial bearing (22a,
222a; 322a) and a second radial bearing (22b, 222b; 322b) formed
between the opposing axially extending bearing surfaces of the
shaft (12; 212; 312) and the rotor component (14, 114a; 214;
314a-c), an axial bearing (26, 226; 326) formed between the
opposing radially extending bearing surfaces of the rotor component
(14, 114a; 214; 314a-c) and the first bearing part (16, 216; 316)
connected to the baseplate, a recirculation channel (28; 128; 228;
328) filled with bearing fluid that connects the remote regions of
the bearing to each other, and an electromagnetic drive system (42,
44; 342, 244) for driving the rotor component, characterized in
that the recirculation channel (28, 128; 228) is disposed in the
rotor component (14; 114a; 214) and connects a sealing gap (34)
radially outside the axial bearing (26) to a section of the bearing
gap (20) adjacent to a dynamic pumping seal (136).
Description
.Iadd.This application is an application for reissue of U.S. Pat.
No. 7,982,349, based on application Ser. No. 12/313,898 filed Nov.
25, 2008, and notice is hereby given under 37 CFR .sctn.1.177 that
more than one application for reissue of U.S. Pat. No. 7,982,349
has been filed, namely: (1) the instant reissue application Ser.
No. 13/945,043 (filed on Jul. 18, 2013), (2) first continuation
reissue application Ser. No. 13/946,142 (filed on Jul. 19, 2013 as
a continuation of reissue application Ser. No. 13/945,043), and (3)
second continuation reissue application Ser. No. 13/946,244 (filed
on Jul. 19, 2013 as a continuation of reissue application Ser. No.
13/945,043)..Iaddend.
BACKGROUND OF THE INVENTION
The invention relates to a spindle motor having a fluid dynamic
bearing system and a stationary shaft.
DESCRIPTION OF PRIOR ART
Spindle motors having a fluid dynamic bearing system are used, for
example, for driving hard disk drives and can generally be divided
into two different groups, that is to say designs: motors having a
rotating shaft and a bearing system usually open at only one end
(e.g. a single plate design) and motors having a stationary shaft.
An important advantage afforded by spindle motors having a
stationary shaft is the possibility of fastening the shaft at each
end, to the baseplate and to the motor housing respectively. This
gives these kinds of motors significantly greater structural
stiffness making them particularly suitable, for example, for hard
disk drives that have increased or special requirements, as occur
nowadays for many mobile applications with ever increasing data
densities along with vibrations occurring during normal operation.
Another important area of application is in hard disk drives that
require a particularly low level of operating noise, where greater
structural stiffness can especially reduce the transmission and
radiation of vibrations generated by the electromagnetic forces of
the motor.
In order to prevent bearing fluid from leaking out of the bearing,
the construction, and particularly the sealing, of a spindle motor
having a stationary shaft and a fluid dynamic bearing system open
at both ends are usually more complex than for a spindle motor
having a rotating shaft. For a bearing gap open at both ends, there
is moreover an increased risk of air penetrating into the bearing
gap and impairing the function of the bearing system. Measures have
therefore to be taken to prevent air from penetrating into the
bearing gap and/or to transport air out of the bearing gap or out
of the bearing fluid respectively.
SUMMARY OF THE INVENTION
It is the object of the invention to provide a spindle motor that
contains a fluid dynamic bearing system having a stationary shaft
fixed at both ends and that consists of only a few parts that are
relatively easy to manufacture. Another object is to facilitate the
discharge of any air bubbles found in the bearing gap.
This object is achieved by providing a spindle motor according to
the invention which comprises a stationary shaft that is held in a
baseplate, either directly or indirectly using an additional flange
member, a rotor component supported rotatably about a rotational
axis with respect to the shaft, a bearing gap open at both ends
that is filled with a bearing fluid and that separates the
adjoining surfaces of the shaft, the rotor component and at least
one first bearing part from one another, a first radial bearing and
a second radial bearing formed between the opposing axially
extending bearing surfaces of the shaft and the rotor component, an
axial bearing formed between the opposing radially extending
bearing surfaces of the rotor component and the first bearing part
connected to the baseplate, a recirculation channel filled with
bearing fluid that connects the remote regions of the bearing to
each other and an electromagnetic drive system for driving the
rotor component.
The invention also claims for a hard disk drive comprising such a
spindle motor for rotatably driving at least one storage disk.
Preferred embodiments and further advantageous characteristics of
the invention are revealed in the dependent claims.
In a preferred embodiment of the invention, the bearing system
comprises a total of only four mechanical components, three of the
components being stationary components and only one rotating,
mechanical rotor component taking the form of a hub/bearing bush
arrangement being provided. Such a small number of parts makes the
bearing system very simple to construct and in particular makes it
possible to manufacture the parts relatively easily and at low cost
and to machine them with low tolerance. It is possible to reduce
the number of parts still further by forming one of the two bearing
parts integrally with the shaft.
According to the invention, various sealing concepts are provided
for sealing the bearing gap that is open at both ends. In one
concept, the rotor component can have surfaces fashioned such that
they form a capillary gap seal together with the surfaces of a
bearing part. The gap seal can be formed between an inner
circumferential surface of the rotor component and an outer
circumferential surface of the respective bearing part. Conversely,
it is also possible for the gap seal to be formed between an outer
circumferential surface of the rotor component and an inner
circumferential surface of the bearing part. Depending on the
design and space situation in the bearing, the gap seal may be
aligned vertically or horizontally to the rotational axis. In the
case of spindle motors for high rotational speeds, it is preferable
if the capillary seal is disposed vertically so that the
centrifugal forces acting on the bearing fluid exert less influence
on the bearing fluid in the capillary seal.
Ideally, the walls defining the capillary seals are slanted so that
the capillary seal narrows in the direction of the bearing gap and
that the center line of the sealing gap extending in the direction
of the bearing gap has an increasingly large spacing to the
rotational axis in a radial direction, so that the fluid pressure
in the bearing fluid increases due to the centrifugal force that
acts in the direction of the bearing gap.
Optionally, the gap seal can be augmented by a dynamic pumping seal
which is formed between the opposing radially extending surfaces of
the rotor component and a second bearing part connected to the
shaft. The surfaces of the rotor component and of a bearing part
forming the seal having appropriate pumping patterns that, on
rotation of the bearing, generate a pumping effect on the bearing
fluid directed towards the interior of the bearing and that
compensate any counter pressure of all the bearing patterns thus
preventing bearing oil from leaking out of the bearing gap, despite
the adjacent gap seal or capillary seal respectively having a
comparatively short overall axial length.
To allow bearing fluid to circulate in the fluid bearing, the rotor
component comprises a recirculation channel which connects the
radially extending sections of the bearing gap or sealing gaps to
each other. The recirculation channel is preferably disposed such
that it connects the sealing gap radially outside the axial bearing
to a section of the bearing gap located radially within the upper
sealing gap or the dynamic pumping seal. In this case, the
recirculation channel is inclined, i.e. not parallel, to the
rotational axis. Using the recirculation channel, the sealing gap
radially outside the axial bearing can also be connected to a
section of the bearing gap located radially outside the dynamic
pumping seal.
In a preferred embodiment of the invention, the recirculation
channel is inclined at an acute angle to the rotational axis. Due
to the inclined recirculation channel a centrifugal force is
exerted on the bearing fluid when the rotor component is in
rotation. The centrifugal force within the recirculation channel
accelerates the bearing fluid in the same direction as does the
overall pumping force which is generated by the axial bearing and
the two radial bearings. The pumping force generated by the
centrifugal force is directed towards the axial bearing and
preferably twice as strong as the overall pumping force exerted on
the bearing fluid in the same direction and generated by the axial
bearing and the two radial bearings.
In one embodiment of the invention, the surfaces of the rotor
component and the bearing part, which form the capillary seal, are
preferably parallel to the rotational axis or inclined at an acute
angle to the rotational axis. The respective angles of the surfaces
defining the capillary gap have to differ in size, thus producing a
capillary seal having a tapered cross-section.
One embodiment of the invention provides for the capillary seal to
be covered by an annular cover connected to the rotor component,
the annular cover forming a labyrinth seal together with a bearing
part. This goes to improve the reliability that bearing fluid will
not leak out of the capillary seal. The annular cover may of course
also be disposed on the bearing part.
According to another embodiment of the invention, the cover may be
so formed and fixed onto or into the rotor component that its
inside circumference, together with an outside circumference of the
associated bearing part, defines the sealing gap of the capillary
seal.
The invention will now be described in more detail on the basis of
three embodiments with reference to the drawings. Further
advantages and characteristics of the invention can be derived from
the following description.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a section through a first embodiment of the spindle
motor according to the invention.
FIG. 2 shows a section through a second embodiment of the spindle
motor according to the invention.
FIG. 3 shows a section through a third embodiment of the spindle
motor according to the invention.
FIG. 4 shows a section through a fourth embodiment of the spindle
motor according to the invention.
FIG. 5 shows a section through a fifth embodiment of the spindle
motor according to the invention.
FIG. 6 shows a section through a sixth embodiment of the spindle
motor according to the invention.
FIG. 7 shows a section through a seventh embodiment of the spindle
motor according to the invention.
FIG. 8 shows a section through an eighth embodiment of the spindle
motor according to the invention.
FIG. 9 shows an enlarged view of the end region of the
recirculation channel located radially outside the axial
bearing.
FIG. 10 shows a section through a ninth embodiment of the spindle
motor according to the invention.
DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION
FIGS. 1 and 2 show two embodiments of a spindle motor according to
the invention that essentially have the same basic construction.
The spindle motors could be used for driving the storage disks of a
hard disk drive.
The spindle motor according to FIG. 1 comprises a baseplate 10 that
has a substantially central cylindrical opening in which a first
bearing part 16 is accommodated. The first bearing part 16 is
approximately cup-shaped in form and comprises a central opening in
which the shaft 12 is fixed. A second bearing part 18 is disposed
at an upper end of the stationary shaft 12, the second bearing part
18 being preferably annular in shape and formed integrally with the
shaft 12. The said components 10, 12, 16 and 18 form the stationary
components of the bearing system of the spindle motor. The shaft 12
has a tapped hole 52 at its upper end for the purpose of fixing it
to a housing cover 50 of the spindle motor or of the hard disk
drive respectively. The spindle motor comprises a single-piece
rotor component 14 that is disposed in a space formed by the shaft
12 and the two bearing parts 16, 18, rotatable with respect to
these components. The rotor component is approximately U-shaped in
cross-section. The upper bearing part 18 lies in an annular recess
in the rotor component 14. Adjoining surfaces of the shaft 12, the
rotor component 14 and the bearing parts 16, 18 are separated from
one another by a bearing gap 20 open at both ends that is filled
with a bearing fluid, such as bearing oil. The electromagnetic
drive system of the spindle motor is formed in a well-known manner
by a stator arrangement 42 disposed on the baseplate 10 and an
annular permanent magnet 44 enclosing the stator arrangement at a
spacing, the permanent magnet being disposed on an inner
circumferential surface of the rotor component 14.
The rotor component 14 of the spindle motor has a hollow
cylindrical section that is designed in such a way that its inside
circumference forms two cylindrical bearing surfaces that are
separated by a circumferential groove 24 in between. These bearing
surfaces enclose the stationary shaft 12 at a distance of only a
few micrometers while forming the bearing gap 20 and are provided
with suitable grooved patterns, so that, together with the
respective opposing bearing surfaces of the shaft 12, they form two
fluid dynamic radial bearings 22a and 22b.
A radially extending section of the bearing gap 20 adjoins the
lower radial bearing 22b, the radially extending section of the
bearing gap being formed by radially extending bearing surfaces of
the rotor component 14 and corresponding opposing bearing surfaces
of the bearing part 16. These bearing surfaces form a fluid dynamic
axial bearing 26 having bearing surfaces taking the form of
circular rings perpendicular to the rotational axis 46. The fluid
dynamic axial bearing 26 is marked in a well-known manner by
spiral-shaped grooved patterns that may be provided either on the
rotor component 14, on the bearing part 16 or on both parts. The
grooved patterns of the axial bearing 26 preferably extend over the
entire end face of the rotor component, i.e. from the inside rim to
the outer rim. This goes to produce a defined distribution of
pressure in the entire axial bearing gap and negative pressure
zones are avoided since fluid pressure continuously increases from
a radially outer to a radially inner position of the axial bearing.
Due to this radially-outwards declining pressure gradient, any
gases contained in the bearing fluid are transported radially
outwards. All the grooved patterns needed for the radial bearings
22a, 22b and for the axial bearing 26 are advantageously disposed
on the rotor component 14, which goes to simplify the manufacture
of the bearing, particularly the shaft 12 and the bearing part 16,
since all the patterns can be made in a single operation.
A sealing gap 34 proportionally filled with bearing fluid adjoins
the radial section of the bearing gap 20 in the region of the axial
bearing 26, the sealing gap 34 being formed by the opposing
surfaces of the rotor component 14 and the bearing part 16 and
sealing the end of the fluid bearing system on this side. The
sealing gap 34 comprises a radially extending section wider than
the bearing gap 20 that merges into a tapered section extending
almost axially which is defined by an outer circumferential surface
of the rotor component 14 and an inner circumferential surface of
the bearing part 16. Alongside its function as a capillary seal,
the sealing gap 34 acts as a fluid reservoir, making available the
amount of fluid necessary for the useful life of the bearing system
after fluid is lost from the bearing gap by evaporation. Moreover,
filling tolerances and any thermal expansion of the bearing fluid
can be compensated. The two surfaces on the rotor component 14 and
the bearing part 16 forming the tapered section of the sealing gap
34 may each be inclined inwards with respect to the rotational axis
46. On rotation of the bearing, this causes the bearing fluid to be
pressed towards the interior in the direction of the bearing gap 20
due to the centrifugal force.
At the other end of the fluid bearing system, the rotor component
14 adjoining the upper radial bearing 22a is designed such that it
forms a radially extending surface that, together with a
corresponding opposing surface of the bearing part 18, forms a
narrow gap whose width is wider than the width of the bearing gap
20 in the region of the radial bearing. In the region of this gap,
a dynamic pumping seal 36 can optionally be disposed that is marked
by suitable pumping patterns taking the form of spiral grooves on
the surfaces of the rotor component 14, the bearing part 18 or
both, and seals the fluid bearing system at this end. The pumping
seal 36 widens at the outer end and leads into a sealing gap 32
preferably having a tapered cross-section. The sealing gap 32
extends substantially axially and is defined by the opposing
surfaces of the rotor component 14 and the bearing part 18 that are
preferably inclined inwards with respect to the rotational axis 46.
On rotation of the bearing, this causes the bearing fluid to be
pressed towards the interior in the direction of the bearing gap 20
due to the centrifugal force. The sealing gap 32 may be covered by
an annular cover 30. The cover 30 is held in an annular groove 38
in the rotor component 14 and bonded in place, for example.
Together with the end of the shaft 12, the cover 30 forms a
labyrinth seal 48, by means of which the exchange with air and thus
the evaporation of bearing fluid is reduced. This goes to improve
the reliability that bearing fluid will not leak out of the sealing
gap 32. The annular cover may also of course be disposed on the
shaft 12 and form a labyrinth seal with the rotor component 14.
In order to fulfill the described functions and to ensure a simple
motor assembly, the two bearing parts 16, 18, which are fixedly
connected to the shaft 12 by means, for example, of an integral
design or by pressing, bonding or welding, must of course be
suitably designed. It may be particularly favorable to design one
of the two bearing parts, part 16 for example, to be cup-shaped
with a raised rim, so that, together with an opposing surface of
the rotor component 14, it forms a sealing gap 34 of a capillary
gap seal at its inner circumferential surface, and at the outside
circumference it can be connected to the baseplate 10. On the other
hand, the simplest possible design for the bearing parts 16, 18 may
be advantageous, such as a chamfered or even a straight circular
disk, like bearing part 18 for example.
To ensure continuous flushing of the bearing system with bearing
fluid, the rotor component 14 is provided with a recirculation
channel 28. The recirculation channel 28 connects the radial
section of the sealing gap 34 located radially outside the axial
bearing 26 to a radially extending section of the bearing gap
radially within the dynamic pumping seal 36, i.e. the section of
the bearing gap between the pumping seal 36 and the first radial
bearing 22a. The recirculation channel 28 can be easily realized,
for example, by drilling through the rotor component 14 at an angle
to the rotational axis 46 of the motor. In doing so, the
recirculation channel 28 is inclined at an angle of approximately
10 degrees to the rotational axis 46. The upper end of the
recirculation channel 28 lies radially within the pumping seal 36.
This means that in the region of the opening of the recirculation
channel 28 higher pressure prevails than, for example, in the
sealing gap 32, so that any air bubbles found in the bearing gap in
the region of the opening of the recirculation channel 28 are
transported radially outwards due to the falling pressure gradient,
whereas the bearing fluid is transported radially inwards due to
the effect of the pumping seal 36. The inclined arrangement of the
recirculation channel 28 and the different pressure conditions at
the opposing ends of the recirculation channel 28 favor the
discharge of air bubbles out of the bearing fluid.
The radial bearings each consist of a number of half-sine-shaped
bearing grooves that pump the bearing fluid axially upwards or
downwards respectively. Due to the varying lengths of the bearing
grooves, asymmetric shaped radial bearings are produced that have
an overall pumping direction, which, even in the case of a bearing
bore that, due to manufacturing tolerances, deviates from a
cylindrical shape and is slightly tapered in the region of the
radial bearing gap, is always directed axially upwards in the
direction of the second bearing part 18. The axial bearing 26
preferably has spiral-shaped bearing grooves that pump the bearing
fluid radially inwards. When the bearing is in operation,
centrifugal forces act on the bearing fluid found within the
recirculation channel, so that it is pressed axially downwards thus
producing a recirculation of bearing fluid within the fluid
bearing.
Since the entire rotor of the spindle motor (apart from magnet 44
and a cover 30 where applicable) preferably consists of only the
rotor component 14, the position tolerance with respect to the
fluid bearing of the rotor surfaces, which act, for example, as
supporting surfaces for the storage disks of a hard disk drive, is
better than for a rotor consisting of several parts, and the
mechanical stability is considerably greater. Moreover, the
functional surfaces (bearing surfaces) of the fluid bearing system,
all of which are located on one part, preferably the rotor
component 14, can be relatively easily manufactured to the required
precision. In particular, compared, for example, to a considerably
smaller bearing bush of a conventional design, the rotor component
14 can be relatively easily clamped into a chuck and the final
processing of almost all the bearing surfaces can be carried out
without having to rechuck. What is more, it is now possible to
dispense with the assembly of the rotor from several separate
parts, which is difficult particularly for small form factors and
inevitably associated with stoppages, and where the separate parts
together have to incorporate all the functional surfaces necessary
for a fluid bearing system with the required precision and
additional, specially designed close-tolerance connecting
regions.
Because the bearing is mounted in the first bearing part 16, which
acts as a flange for connection to the baseplate 10, it is possible
to mount the fluid bearing as a structural unit, to fill it with
bearing fluid and to test it before the fluid bearing is connected
as a structural unit to the baseplate 10.
Since the spindle motor has only one fluid dynamic axial bearing 26
that generates a force in the direction of the second bearing part
18, a corresponding counterforce or preload force has to be
provided that holds the bearing system in axial balance. For this
purpose, the baseplate 10 may have a ferromagnetic ring 40 that
lies axially opposite the rotor magnet 44 and is magnetically
attracted by the rotor magnet. This magnetic force of attraction
acts in opposition to the force of the axial bearing 26 and keeps
the bearing axially stable.
As an alternative or in addition to this solution, the stator
arrangement 42 and the rotor magnet 44 may be disposed at an axial
offset with respect to one another in such a way that the rotor
magnet 44 is disposed axially further away from the baseplate 10
than the stator arrangement 42. Through the magnetic system of the
motor, an axial force is thereby built up that acts in the opposite
direction to the axial bearing 26.
The outer cup-shaped part of the rotor component 14 is provided for
the purpose of attaching the storage disks 58 of the hard disk
drive. The annular disk-shaped storage disks 58 rest on a lower,
radially outwards aligned collar of the rotor component 14 and are
separated from one another by spacers 60. The storage disks 58 are
held by a holding piece 54 that is fixed by means of screws in
tapped holes 56 in the rotor component 14.
In FIG. 2 a spindle motor is illustrated in which identical
components or components having the same functions as those in FIG.
1 are provided with the same reference numbers. The spindle motor
according to FIG. 2 essentially differs from the spindle motor
according to FIG. 1 by having a two-piece rotor component and a
different design for the upper seal. Substantially the same
description applies to FIG. 2 as for the spindle motor in FIG.
1.
In FIG. 2, the rotor component 114 is formed in two pieces and
comprises an inner, approximately cylindrical rotor component 114a
and an outer approximately cup-shaped rotor component 114b. The
inner rotor component 114a encloses the shaft 12 and, together with
the shaft, forms the two radial bearings 22a, 22b. An end face of
the inner rotor component 114a lies opposite a radial surface of
the first bearing part 16 and, together with the first bearing part
16, forms the axial bearing 26. The dynamic pumping seal 36 is
formed by an end face of the inner rotor component 114a and an
opposing surface of the second bearing part 18, at least one of the
two surfaces being provided with pumping patterns. Outside the
pumping seal 36, the sealing gap 32 adjoins, which is defined by an
inner circumferential surface of a cup-shaped cover 130 and an
outer, chamfered circumferential surface of the second bearing part
18. The cover 130 is mounted on the end face of the inner rotor
component 114a and welded, for example, to this component. An
annular labyrinth gap 48 remains between an inside edge of the
cover 130 and the bearing part 18 (or the shaft 12 respectively),
the labyrinth gap additionally sealing the capillary seal towards
the outside.
The sealing gap 34 adjoining the axial bearing 26 is defined by the
outside circumference of the inner rotor component 114a and the
inside circumference of the cup-shaped first bearing part 16. The
recirculation channel 128 extends within the inner rotor component
114a and connects the sealing gap 34 in the region of the outside
diameter of the axial bearing 26 to a section of the bearing gap
radially within the pumping seal 36. The recirculation channel 128
is inclined at an angle of approximately 10 degrees with respect to
the rotational axis 46.
The inner rotor component 114a takes on the function of a bearing
bush and the outer, cup-shaped rotor component 114b has the
function of a hub that carries the magnet 44 of the drive system
and the components to be driven, such as the storage disks 58, as
described in conjunction with FIG. 1.
FIG. 3 shows an enlarged section through a bearing system of a
spindle motor according to the invention. In this embodiment, the
shaft 212 and the first bearing part 216 are integrally formed as
one piece. The rotor component 214 is disposed rotatable about the
rotational axis 246 in an annular space formed by the shaft 212 and
the first bearing part 216. The first bearing part 216 is fixedly
connected at its outside circumference to the base 210 of the
motor. Two radial bearings 222a, 222b are disposed between bearing
surfaces on the inside circumference of the rotor component 214 and
on the outside circumference of the shaft 212 and separated from
one another by an axial section of the bearing gap 220. An axial
bearing 226 is disposed along a radial section of the bearing gap
220, the axial bearing being formed by bearing surfaces on the end
face of the rotor component 214 or on a bottom surface of the first
bearing part 216 respectively. The axial section of the bearing gap
220 merges into a sealing gap 232 that has a radially extending
section and an axially extending section and is defined by surfaces
of a second bearing part 218 disposed on the shaft 212 and the
opposing surfaces of the rotor component 214.
The sealing gap 232 is partially filled with bearing fluid and
forms a tapered gap seal. A cover to cover the sealing gap and to
restrain the bearing fluid is not provided here. In the region of
the sealing gap 232, one or more pumping seals 236 or 237 may be
disposed that are located in the horizontally or in the vertically
extending gap between the second bearing part 218 and the
respective opposing surface of the rotor component 214 and that
transport the bearing fluid found in the sealing gap 232 towards
the interior in the direction of the axial section of the bearing
gap 220. Another sealing gap 234, which additionally acts as a
fluid reservoir, is provided adjoining the radial section of the
bearing gap 220. The sealing gap 234 is part of a gap that is
defined by the outside diameter of the cylindrical part of the
rotor component 214 and the inside diameter of the first bearing
part 216. A recirculation channel 228 is provided in the rotor
component 214, the recirculation channel connecting the respective
open ends of the bearing gap 220 to each other. This embodiment of
the spindle motor is characterized by the small number of necessary
components. The other components of the spindle motor, such as the
drive system and the holding piece for the storage disks, are not
illustrated in FIG. 3.
The recirculation channel is preferably inclined by 5-15 degrees
with respect to the rotational axis. Alternatively, the
recirculation channel can also be aligned largely parallel to the
rotational axis 46. The bearing grooves of the axial bearing 26,
226 preferably run from the radially inner bearing bore to the
radially outer region of the capillary seal 34. Both the axial
bearing patterns 26, 226 as well as the pumping patterns of the
pumping seals 36, 236, 237 are preferably formed on the surface of
the rotor component 14, 114a, 214. The pumping patterns of the
pumping seals 36, 236 extend in a radial direction again preferably
from the radially inner region of the bearing bore next to the
shaft to the region of the sealing gap 32, 232. In addition or as
an alternative, an axially extending pumping seal 237 may be
disposed in the region of the sealing gap 232, as illustrated in
FIG. 3.
FIG. 4 shows a further embodiment of a spindle motor according to
the invention having a baseplate 310 in which a first bearing part
316 is accommodated. The first bearing part 316 comprises a central
opening in which a shaft 312 is fixed. The shaft 312 has a step
that acts as a stopper and rests on the surface of the bearing part
316. The step enables the axial distance between the two bearing
parts 316 and 318 to be very precisely and reproducibly adjusted.
At an upper end of the stationary shaft 312, a second bearing part
318 is disposed that is preferably integrally formed with the shaft
312 as one piece. The spindle motor comprises a multipart rotor
component that has an inner rotor component 314a which is disposed
in a space formed by the shaft 312 and the two bearing parts 316,
318, rotatable with respect to the shaft. The upper bearing part
318 is accommodated in an annular recess in the rotor component
314a. Adjoining surfaces of the shaft 312, the rotor component 314a
and the bearing parts 316, 318 are separated from one another by a
bearing gap open at both ends 320 that is filled with a bearing
fluid, such as bearing oil. The rotor component 314a is enclosed by
an outer, cup-shaped rotor component 314b that carries at its
inside circumference an annular permanent magnet 344 forming part
of the electromagnetic drive system. A stator arrangement 342 is
disposed on the baseplate 310, the stator arrangement lying
opposite the permanent magnet 344.
The inner rotor component 314a has a hollow cylindrical bore at
whose inside circumference two cylindrical bearing surfaces are
formed that are separated by a circumferential groove 324 lying in
between. These bearing surfaces enclose the stationary shaft 312 at
a distance of only a few micrometers while forming the bearing gap
320 and are provided with grooved patterns, so that together with
the respective opposing bearing surfaces of the shaft 312, they
form two fluid dynamic radial bearings 322a and 322b.
A radially extending section of the bearing gap 320 adjoins the
bearing gap in the region of the lower radial bearing 322b, the
radially extending section of the bearing gap 320 separating the
radially extending bearing surfaces of the rotor component 314a and
the corresponding opposing bearing surfaces of the bearing part 316
from one another. The bearing surfaces of the above-mentioned
components form a fluid dynamic axial bearing 326 that is marked in
a well-known manner by spiral-shaped grooved patterns that are
formed on one or both bearing surfaces.
A sealing gap 334 proportionally filled with bearing fluid adjoins
the radial section of the bearing gap 320 in the region of the
axial bearing 326, the sealing gap 334 being formed by opposing
surfaces of the rotor component 314a and the bearing part 316 and
sealing the lower end of the bearing gap. The sealing gap 334
comprises a radially extending section wider than the bearing gap
320 that merges into a tapered, almost axially extending section
that is defined by an outer circumferential surface of the rotor
component 314a and an inner circumferential surface of the bearing
part 316. The sealing gap 334 further acts as a fluid reservoir and
serves to compensate filling tolerances, loss of bearing fluid
through evaporation and thermal expansion of the bearing fluid.
The rotor component 314a at the other end of the bearing gap 320 is
designed such that it forms a radially extending surface that,
together with a corresponding opposing surface of the bearing part
318, forms a narrow gap whose width is wider than the width of the
bearing gap 320 in the region of the radial bearing. In the region
of this gap, a dynamic pumping seal 336 is provided that is marked
by suitable pumping patterns taking the form of spiral grooves on
the surfaces of the rotor component 314a or the bearing part 318
respectively and that seals the fluid bearing system at this end of
the bearing gap. On the other side of the pumping seal 336, a
sealing gap 332 having a tapered cross-section is provided that
extends substantially axially and is defined by the surfaces of the
rotor component 314a and the bearing part 318. The sealing gap 332
is covered by an annular cover 330 that is formed as part of the
outer rotor component 314b. Together with an end face of the
bearing part 318, the cover 330 forms a labyrinth seal 348 to
provide an additional seal for the sealing gap 332.
To ensure continuous flushing of the bearing system with bearing
fluid, a recirculation channel 328, such as an axial bore, is
disposed in the rotor component 314a. The recirculation channel 328
connects a section of the sealing gap 334 radially outside the
axial bearing 326 to a radially extending section of the bearing
gap radially outside the dynamic pumping seal 336.
Since the spindle motor has only one fluid dynamic axial bearing
326 that exerts a force in the direction of the second bearing part
318, a corresponding counterforce or preload force has to be
provided that keeps the bearing system in axial balance. For this
purpose, a ferromagnetic ring 340 is disposed on the baseplate 310,
the ferromagnetic ring 340 lying axially opposite the rotor magnet
344 axial and being magnetically attracted by the rotor magnet 344.
This magnetic force of attraction acts in opposition to the force
of the axial bearing 326 and keeps the bearing axially in
balance.
In FIG. 5, a modified embodiment of the spindle motor is shown that
differs in various ways from the spindle motor in FIG. 4.
The first way in which it differs from the spindle motor in FIG. 4
is that the rotor component consists of three parts: an inner,
sleeve-shaped rotor component 314a, a similarly sleeve-shaped rotor
component 314c enclosing the first component 314a and the outer
rotor component 314b. The inner rotor component illustrated in FIG.
4 is basically formed in two pieces and consists of the components
314a and 314c. The recirculation channel 328 is formed between the
two rotor components 314a and 314c, taking the form, for example,
of a channel-shaped groove at the outside circumference of
component 314a or at the inside circumference of component
314c.
Another difference is in the design of the shaft 312 that no longer
has a step in the region of the lower bearing part 316, but rather
is perfectly cylindrical.
The upper sealing gap 332 that extends between an inside
circumference of the rotor component 314c and an outside
circumference of the bearing part 318 is covered by a cover 330,
which, however, is formed as a separate, annular component. The
cover 330 is fixed to the rotor component 314c or the outer rotor
component 314b respectively. A capillary seal 348 is formed between
the cover 330 and the end face of the bearing part 318, just as in
the embodiment according to FIG. 4.
A further important difference in the bearing of FIG. 5 is that
instead of an upper pumping seal a second axial bearing 327 is now
provided. This axial bearing 327 is formed by an end face of the
rotor component 314a and an opposing bearing surface of the bearing
part 318. The axial bearing is marked by grooved patterns and forms
a counter bearing to the lower axial bearing 326. The two axial
bearing 326 and 327 operate in opposition to one another and keep
the bearing in axial balance, making a magnetic preload, as
provided in FIG. 4, no longer necessary.
FIG. 6 shows an embodiment of a spindle motor that is very similar
to the embodiment of FIG. 4. The first difference between the
spindle motor according to FIG. 6 and the spindle motor according
to FIG. 4 is that the recirculation channel 328 is not made
parallel to the rotational axis 346, but rather inclined at an
angle of approximately 5 degrees to the rotational axis 346. The
recirculation channel 328 thus connects a region of the lower
sealing gap 334 to a radially extending region of the bearing gap
radially outside an upper fluid dynamic axial bearing 327. The
fluid dynamic axial bearing 327 acts in opposition to the lower
fluid dynamic axial bearing 326 and constitutes a second difference
to the spindle motor according to FIG. 4 in which only a lower
fluid dynamic axial bearing was provided. Due to the two fluid
dynamic axial bearings 326 and 327, no magnetic preload is
necessary for the spindle motor according to FIG. 6.
FIG. 7 shows a spindle motor that is likewise very similar to the
spindle motor of FIG. 4. The spindle motor according to FIG. 7
comprises a greatly widened lower shaft end having a large
diameter, which is inserted into the lower bearing part 316. The
wider foot end of the shaft ensures greater stiffness. The inner
end face of the widened section of the shaft 312 together with an
end face of the rotor component 314a now forms the axial bearing
326 as well as parts of the radial section of the sealing gap 334.
Moreover, the upper bearing part 318 is not formed integrally with
the shaft, but rather as an annular part fixed separately to the
end of the shaft 312. In contrast to the spindle motor of FIG. 6,
for example, no upper axial bearing is provided but rather the
sealing effect of the sealing gap 332 in this region is supported
by a pumping seal 336 that is disposed between the end face of the
rotor component 314a and of the bearing part 318.
A magnetic preload that acts in the opposite direction to the force
of the axial bearing 326 is generated by a ferromagnetic ring 340
that lies opposite the rotor magnet 344 and attracted by this
magnet.
FIG. 8 shows a section through a spindle motor whose construction
corresponds substantially to the spindle motor of FIG. 2. Thus the
basic description of the spindle motors of FIGS. 1 and 2 applies to
the spindle motor of FIG. 8, identical components or components
having the same functions being indicated by the same reference
numbers.
As in the spindle motor of FIG. 2, a bearing part 18 is also
disposed at the upper end of the shaft 12 that is formed integrally
with the shaft 12 as one piece. Moreover, a pumping seal 136 for
sealing the sealing gap 32 is provided that is disposed between an
outside circumference of the bearing part 18 and an inside
circumference of a recess in the bearing bush 114a. The pumping
patterns of the pumping seal 136 that pumps in an axial direction
into the interior of the bearing are preferably disposed on the
inside circumference of the bearing bush 114a. Because the pumping
seal 136 is disposed between axially extending surfaces, the
diameter of the bearing part 18 can be decreased, by means of which
the diameter of the annular gap between the underside of the
bearing part 18 and an opposing surface of the bearing bush 114a is
also decreased.
A recirculation channel 128 is provided in the bearing bush 114a,
the recirculation channel 128 starting at the radially extending
annular gap between the underside of the bearing part 18 and an
opposing surface of the bearing bush 114a runs at an angle of
approximately 10 degrees to the rotational axis 46 and connects the
topside of the bearing to the underside and leads into a radially
outer region of the lower axial bearing 26. The recirculation
channel 128 thus ends outside the axial bearing gap 20 between the
axial bearing gap 20 and the sealing gap 34.
The mouth region of the recirculation channel 128 is illustrated in
FIG. 9 in an enlarged view. It can be seen that the recirculation
channel 128 ends radially outside the bearing gap 20 of the axial
bearing 26. In the mouth region of the recirculation channel 128,
the bearing gap 20 widens to form a gap 21 which then merges
radially outwards into the sealing gap 34. Due to the inclined
arrangement of the recirculation channel 128 in the rotating
bearing part 114a, a centrifugal force is exerted on the bearing
fluid found in the recirculation channel 128. This centrifugal
force transports the bearing fluid in the direction of arrow 29,
i.e. starting from the axial gap in the region of the upper bearing
part 18 through the recirculation channel 128 to gap 21 in the
region of the lower bearing part 16. Gap 21 has a larger gap width
than the bearing gap 20, so as to allow the bearing fluid to flow
unimpeded out of the recirculation channel 128. The axial bearing
26 has bearing patterns that transport the bearing fluid in the
direction of the shaft 12 in the direction shown by arrow 27. The
radial bearings 22a and 22b generate an overall pumping effect
upwards in the direction of arrow 23 to bearing part 18, by means
of which the bearing fluid is then transported to the opening in
the recirculation channel 128 where the cycle starts over again.
The bearing fluid thus flows in the recirculation channel 128 in
the same direction as the net pumping direction of the bearing,
i.e. of the axial bearing 26 and the two radial bearings 22a, 22b.
The pumping seal 136 lies outside this cycle and pumps into the
interior of the bearing in the direction of the recirculation
channel 128.
The lower radial bearing 22b is made distinctly asymmetric and all
in all pumps the bearing fluid upwards, whereas the upper radial
bearing 22a is made symmetric or slightly asymmetric.
The pumping action on the bearing fluid generated by the
centrifugal force within the recirculation channel is preferably
substantially larger than the overall pumping action on the bearing
fluid in the same direction generated by the thrust bearing and the
two radial bearings. Because of the relatively large pumping action
generated by the inclined recirculation channel, a directed pumping
action generated by the axial bearing or the two radial bearings
may not be necessary to maintain circulation of the bearing fluid
within the bearing gap. In this case, the thrust bearing and/or the
two radial bearings can comprise bearing grooves that are almost
symmetrical and generate a pumping action of about the same
strength in both directions of the bearing gap.
Any air trapped in the bearing fluid that is found within the
recirculation channel 128 is transported upwards by the centrifugal
effect in the direction of the radial gap located between the
bearing bush 114a and the bearing part 18. Due to the continuous
increase in pressure brought about by the pumping seal 136 seen
from the upper sealing gap 32 in the direction of the interior of
the bearing, the air is subsequently forced out of the bearing via
the upper sealing gap 32.
The bearing patterns of the axial bearing 26 are preferably given a
spiral shape and formed in the bearing bush 114a, and extend
continuously from the inner bore next to the shaft 12 to the outer
rim of the bearing bush 114a.
A spindle motor as illustrated in FIGS. 8 and 9 is preferably used
for driving 2.5 inch hard disk drives. This kind of spindle motor
has, for example, a shaft diameter of 2.5 mm and a bearing bush
114a diameter of approximately 6 mm. The bearing patterns of the
axial bearing 26 have a depth, for example, of 15 .mu.m and, when
the motor is in operating status, the bearing gap 20 in the region
of the axial bearing 26 has a width, for example, of 10 to 15
.mu.m. The width of the axial bearing gap is defined by the
fly-height of the bearing. The gap width of the gap 21 in the mouth
region of the recirculation channel 128 is, for example, 30
.mu.m.
The gap width of gap 21 is preferably greater than or equal to the
fly-height (width of the axial bearing gap in operation) plus the
depth of the axial bearing patterns. Thanks to the inclined
recirculation channel 128, the circulation of bearing fluid in the
bearing gap is positively supported. This also applies accordingly
to the spindle motors illustrated in FIGS. 1-3 and 6.
FIG. 10 shows a section through a spindle motor whose construction
corresponds substantially to the spindle motor of FIG. 1. Thus the
basic description of the spindle motor of FIG. 1 applies to the
spindle motor of FIG. 10, identical components or components having
the same functions being indicated by the same reference
numbers.
The spindle motor illustrated in FIG. 10 has an upper bearing part
18 disposed on the shaft 12. The upper bearing part 18, encircled
by the bearing gap 20 filled with bearing fluid, is seated in a
recess in the rotor component 14. Together with an adjoining
surface of the rotor component 14, a lower surface of the bearing
part 18 forms an axial bearing 25 that operates in opposition to
the axial bearing 26 on the underside of the bearing. The axial
bearing 25 is marked by grooved patterns that are disposed on the
surface of the bearing part 18 and/or on the corresponding surface
of the rotor component 14. The grooved patterns generate a pumping
effect on the bearing fluid in the bearing gap 20 that is directed
towards the interior of the bearing, i.e. in the direction of the
radial bearings 22a, 22b.
A further bearing part 19 adjoins the upper end face of the bearing
part 18, the bearing part 19 being fixedly connected to the rotor
component 14. The two bearing parts 18, 19 are separated from each
other by a radially extending gap in whose course the dynamic
pumping seal 36 is disposed. The pumping seal 36 is marked by
pumping patterns pumping radially outwards and taking the form of
spiral grooves on the surfaces of bearing part 18 and/or bearing
part 19 and seals the fluid bearing system at this end. The gap in
the region of the pumping seal 36 extends radially inwards, changes
its course in an axial direction and merges into an axially
extending sealing gap 32 preferably having a tapered cross-section.
The sealing gap 32 is defined by the opposing surfaces of the shaft
12 and the bearing part 19. The sealing gap 32 is located at the
smallest diameter of the bearing and may be covered by an annular
cover 30. The cover 30 is held in an annular groove 38 of the rotor
component 14 and fixed there, for example, by being bonded, pressed
in or (laser) welded. The cover 30, together with the end of the
shaft 12, forms a labyrinth seal 48, by means of which the exchange
with air and thus the evaporation of bearing fluid is
decreased.
IDENTIFICATION REFERENCE LIST
10 Baseplate 12 Shaft 14; 114a, 114b Rotor component 16 First
bearing part 18 Second bearing part 19 Bearing part 20 Bearing gap
21 Gap 22a, 22b Radial bearing 24 Groove 25 Axial bearing 26 Axial
bearing 27 Direction of arrow 28; 128 Recirculation channel 29
Direction of arrow 30, 130 Cover 32 Sealing gap 34 Sealing gap 36,
136 Pumping seal 38 Annular groove 40 Ferromagnetic ring 42 Stator
arrangement 44 Magnet 46 Rotational axis 48 Labyrinth seal 50
Housing cover 52 Tapped hole (shaft) 54 Holding piece 56 Tapped
hole (rotor component) 58 Storage disks 60 Spacer 210 Baseplate 212
Shaft 214 Rotor component 216 First bearing part 218 Second bearing
part 220 Bearing gap 222a, 222b Radial bearing 226 Axial bearing
228 Recirculation channel 232 Sealing gap 234 Sealing gap 236
Pumping seal 237 Pumping seal 246 Rotational axis 310 Baseplate 312
Shaft 314, 314a, 314b Rotor component 314c Rotor component 316
First bearing part 318 Second bearing part 320 Bearing gap 322a,
322b Radial bearing 324 Groove 326 Axial bearing 327 Axial bearing
328 Recirculation channel 330 Cover 332 Sealing gap 334 Sealing gap
336 Pumping seal 340 Ferromagnetic ring 342 Stator arrangement 344
Magnet 346 Rotational axis 348 Labyrinth seal
* * * * *