Title: Conical hydrodynamic pivot bearing
Abstract: A bearing having a conical hydrodynamic bearing section and a pivot bearing section. The bearing can be used with a spindle motor. The conical hydrodynamic bearing section is formed by the conical portion of the shaft and a correspondingly shaped cavity of the bearing sleeve. The pivot bearing section is located adjacently to the conical bearing section and is formed by the curved end face of the shaft and an endplate inserted into the cavity of the bearing sleeve.
Patent Number: 6,921,209 Issued on 07/26/2005 to Hoffmann, et al.
| Inventors:
|
Hoffmann; Joerg (Mettlach, DE);
Hafen; Martin (Spaichingen, DE);
Winterhalter; Olaf (Epfendorf, DE)
|
| Assignee:
|
Minebea Co., Ltd. (Nagano, JP)
|
| Appl. No.:
|
388731 |
| Filed:
|
March 12, 2003 |
Foreign Application Priority Data
| Aug 29, 2002[DE] | 102 39 886 |
| Current U.S. Class: |
384/110; 384/109 |
| Intern'l Class: |
F16C 032/06 |
| Field of Search: |
384/100,107,110,112,450,243,244,245,246,108,109
|
References Cited [Referenced By]
U.S. Patent Documents
| 4043612 | Aug., 1977 | Orcutt.
| |
| 4346946 | Aug., 1982 | Maruyama.
| |
| 4547081 | Oct., 1985 | Tanaka et al.
| |
| 4720198 | Jan., 1988 | DeBruyn.
| |
| 4934836 | Jun., 1990 | Tanaka et al.
| |
| 5598048 | Jan., 1997 | Dunfield et al.
| |
| 5667309 | Sep., 1997 | Nose.
| |
| 5855437 | Jan., 1999 | Lee.
| |
| 5947608 | Sep., 1999 | Kim.
| |
| 6020664 | Feb., 2000 | Liu et al.
| |
| 6069768 | May., 2000 | Heine et al.
| |
| 6127756 | Oct., 2000 | Iwaki et al.
| |
| 6371650 | Apr., 2002 | Goto et al.
| |
| 6406185 | Jun., 2002 | Lin.
| |
| 6520476 | Feb., 2003 | Chuang.
| |
| Foreign Patent Documents |
| 2815009 | Oct., 1979 | DE.
| |
| 07071448 | Mar., 1995 | JP.
| |
Primary Examiner: Hannon; Thomas R.
Attorney, Agent or Firm: Lutzker; Joel, Vishev; Anna, Schulte Roth & Zabel
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims priority from Fed. Rep. Of Germany Patent Application
No. DE10239886.0, filed on Aug. 29, 2002, and from U.S. Provisional Patent Application
Ser. No. 60/363,784, filed on Mar. 12, 2002.
Claims
1. A bearing comprising:
a sleeve having a first section, a second section and a third section, said sections
of said sleeve forming a cavity within said sleeve, said second section of said
sleeve extending from said first section of the sleeve to said third section of
the sleeve,
a shaft having a first section, a second section, a third section and a fourth
section, said third section of said shaft extending from said second section of
the shaft to said fourth section of the shaft; and
a fluid;
wherein
said shaft extends into said cavity within said sleeve, and a gap exists between
said shaft and said sleeve;
said fluid is contained in said gap;
said second section of said sleeve has a length extending from said first section
of said sleeve, and it has an inner radius perpendicular to said length that increases
as a function of a distance measured along said length from said first section
of said sleeve;
said third section of said shaft has a length extending from said second section
of said shaft, and it has a radius perpendicular to said length that increases
as a function of a distance measured along the length from said second section
of said shaft;
said third section of said shaft is positioned inside said second section of
said sleeve;
pressure generating grooves are formed on one of said second section of said
sleeve and said third section of said shaft;
said fourth section of said shaft has a length extending from said third section
of said shaft and it has a radius perpendicular to said length that decreases as
a function of a distance measured along the length from said third section of said
shaft until said radius of said fourth section of said shaft reaches zero at the
end of said length;
the fourth section of said shaft is positioned inside said third section of said
sleeve.
2. A bearing according to claim 1 wherein:
said shaft rotates.
3. A bearing according to claim 1 wherein:
said sleeve rotates.
4. A bearing according to claim 1
wherein said sleeve further comprises a fourth section located adjacently to
said third section of said sleeve;
wherein an end plate is inserted into said fourth section of said sleeve;
wherein said fourth section of said sleeve is contiguous with said third section
of said sleeve and forms an opening at the bottom end of said cavity within said
sleeve;
said endplate seals said opening; and
said shaft rotates on said endplate.
5. A bearing according to claim 1 wherein:
the inner radius of said second section of said sleeve has a value and it is
described by the following equation:
where
r
sl1 is the inner radius of said second section of said sleeve at
a particular point along its length;
A is the minimum value of the inner radius of said second section of said sleeve;
m is a constant positive value, and
Y is a distance measured from a lower end of said first section of said sleeve
to said particular point.
6. A bearing according to claim 5 wherein:
the radius of the third section of said shaft has a value and it is described
by the equation:
r
sh1 is the radius of the third section of shaft at a particular point
along its length;
D is the minimum value of the radius of the third section of said shaft;
Z is a distance measured from a lower end of said second section of said shaft
to said particular point;
f(Z) is a function of Z with a minimum value of zero;
the derivative of f(Z) with respect to Z is always positive; and
the second derivative of f(Z) with respect to Z is always negative.
7. A bearing according to claim 1 wherein:
the distance between the radius of said third section of said shaft and the inner
radius of said second section of said sleeve is constant over the entire length
of said third section of said shaft.
8. A bearing according to claim 7 wherein:
the inner radius of said second section of said sleeve has a value and it is
described by the following equation:
where
r
sl1 is the inner radius of said second section of said sleeve at
a particular point along its length;
A is the minimum value of the inner radius of said second section of said sleeve;
m is a constant positive value, and
Y is a distance measured from a lower end of said first section of said sleeve
to said particular point.
9. A bearing according to claim 7 wherein:
the radius of the third section of said shaft has a value and it is described
by the equation:
r
sh1 is the radius of the third section of said shaft at a particular
point along its length;
D is the minimum value of the radius of the third section of said shaft;
Z is a distance measured from a lower end of said second section of said shaft
to said particular point;
f(Z) is a function of Z with a minimum value of zero;
the derivative of f(Z) with respect to Z is always positive; and
the second derivative of f(Z) with respect to Z is always negative.
10. A bearing for a spindle motor comprising:
a shaft having an end portion, said end portion further comprising a conical
section and a convex section;
a bearing sleeve having a cavity that surrounds the shaft at a small radial distance;
and
an endplate inserted into an opening in said cavity and affixed to the bearing
sleeve;
wherein
a pivot bearing is provided between the endplate and the convex section of the
end portion of the shaft; and
a portion of said cavity is shaped in a complimentary fashion to said conical
section of said end portion of said shaft.
11. A hydrodynamic bearing, comprising:
a shaft further comprising a conical bearing portion and a pivot bearing portion
having a curved surface and located adjacently to said conical bearing portion;
a bearing sleeve having an internal cavity accommodating said shaft, said internal
cavity further comprising a conical cavity portion corresponding in shape to said
conical bearing portion of said shaft;
an endplate enclosing said internal cavity of said bearing sleeve; and
a plurality of dynamic pressure-generating grooves formed on one of an outer
surface of said conical bearing portion of said shall and an inner surface of said
conical cavity portion of said bearing sleeve,
wherein a conical hydrodynamic bearing is formed between said outer surface of
said conical bearing portion and said inner surface of said conical cavity portion,
and wherein a hydrodynamic pivot bearing is formed between said curved surface
of said pivot bearing portion and said endplate.
12. A bearing according to claim 11 further comprising:
a fluid dynamic journal bearing.
13. A hydrodynamic bearing comprising:
a conical hydrodynamic bearing section formed by a conical portion of a shaft
and a correspondingly shaped portion of a cavity of a bearing sleeve; and
a pivot bearing section located adjacently to the conical bearing section and
formed by a curved end face of the shaft and an endplate inserted into a bottom
portion of the cavity of the bearing sleeve.
Description
BACKGROUND OF THE INVENTION
The following invention relates to electronic spindle motors of the type used
in disk drives and in particular relates to improvements in fluid bearings for
such motors.
Disc drive systems have been used in computers and other electronic devices
for many years for storage of digital information. Information is recorded on concentric
memory tracks of a magnetic disc medium, the actual information being stored in
the form of magnetic transitions within the medium. The discs themselves are rotatably
mounted on a spindle, the information being accessed by means of transducers located
on a pivoting arm which moves radially over the surface of the disc. The read/write
heads or transducers must be accurately aligned with the storage tracks on the
disc to ensure proper reading and writing of information; thus the discs must be
rotationally stable.
Electric spindle motors of the type used in disk drives conventionally rely
on ball bearings to support a rotary member, such as a rotating hub, on a stationary
member, such as a shaft. Ball bearings are wear parts and in time friction will
cause failure of the motor. In addition, ball bearings create debris in the form
of dust or fine particles that can find their way into "clean" chambers housing
the rotary magnetic disks which are driven by the motor. The mechanical friction
inherent in ball bearings also generates heat and noise, both of which are undesirable
in a disk drive motor.
Fluid dynamic bearings represent a considerable improvement over conventional
ball bearings in spindle drive motors. In these types of systems, lubricating fluid-either
gas or liquid-functions as the actual bearing surface between a stationary base
or housing in the rotating spindle or rotating hub of the motor. For example, liquid
lubricants comprising oil, more complex ferro-magnetic fluids or even air have
been utilized in hydrodynamic bearing systems.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a spindle motor with a fluid
dynamic pivot bearing which saves run-current and, therefore, reduces power consumption
of the spindle motor. The present inventions combines the benefit of increased
stability provided by hydrodynamic bearings with the benefit of low power consumption
provided by pivot bearings.
The present invention provides these benefits by providing a fluid dynamic conical
bearing with a pivot bearing for use in a spindle motor. The fluid dynamic conical
bearing resists both horizontal motion of the shaft and upward motion of the shaft,
while the pivot bearing resists downward motion of the shaft.
The above and other objects, aspects, features and advantages of the invention
will be more readily apparent from the description of the preferred embodiments
thereof taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention is illustrated by way of example and not limitation and the figures
of the accompanying drawings in which like references denote like or corresponding
parts, and in which:
FIG. 1 is a side cut-away view of an electronic spindle motor having a rotational
shaft, a fluid dynamic conical bearing, and a pivot bearing according to the first
embodiment of the present invention.
FIG. 2 is a side cut-away view of a bearing according to the second embodiment
of the present invention.
FIG. 3 is a side cut-away view of a bearing according to the third embodiment
of the present invention.
DETAILED DESCRIPTION
Reference will now be made in detail to the preferred embodiments of the
invention, examples of which are illustrated in the accompanying drawings. While
the invention will be described in conjunction with the preferred embodiments,
it will be understood that the described embodiments are not intended to limit
the invention specifically to those embodiments.
The first embodiment of the present invention is shown in FIG. 1. A Spindle motor
2 includes a bracket
4 which is to be mounted on a disk drive device
(not shown). A rotor
6 is arranged for rotation relative to bracket
4.
A sleeve
8 and a stator
10 are fixedly mounted on bracket
4.
Rotor
6 comprises a rotor hub
18 and a tubular shaft
20
fixed coaxially to rotor hub
18. A rotor magnet
12 is bonded to the
inner side of a circumferential wall of rotor hub
18. The outer side of
the circumferential wall of the rotor hub
18 is shaped to hold a magnetic
disk (not shown).
Stator
10 comprises a core
52 fixedly fitted to bracket
4
and coils
54 wound on the core
52. The stator
10 is radially
spaced by a small gap from and arranged opposite to the rotor magnet
12.
Sleeve
8 is a tubular member comprising four sections that are distinguished
from each other based upon their inner radii. First sleeve section
81 has
a constant inner radius A, except that, the inner radius of first sleeve section
81 increases slightly near the top surface of sleeve
8 to form a
capillary seal. Second sleeve section
82 has an inner radius that increases
linearly as the depth of the sleeve
8 increases so as to form a frustum
shaped conic section. The inner radius of second sleeve section
82 can be
described by the following equation: r
sl2=A+mY, where r
sl2
is the inner radius of second sleeve section
82, A is the inner radius of
first sleeve section
81, m is the rate of increase (slope) of the radius
of second sleeve section
82, and Y is the vertical distance below first
sleeve section
81. Third sleeve section
83 has a constant inner radius
B that is equal to the maximum radius of second sleeve section
82. Fourth
sleeve section
84 has a constant inner radius C that is greater than the
inner radius of third sleeve section
83. End plate
42 is fit into
fourth sleeve section
84 of Sleeve
8.
Shaft
20 is also comprised of four sections. First shaft section
201
fits inside of and is rigidly connected to hub
18. Second shaft section
202 fits inside of first sleeve section
81, although second shaft
section
202 extends slightly below first sleeve section
202. Second
shaft section
202 has a constant radius F that is slightly less than the
radius A of first sleeve section
81. Third shaft section
203 extends
below second shaft section
202 and it fits within second sleeve section
82. The radius of third shaft section
203 is less than the radius
of second sleeve section
82. However, the radius of third shaft section
203 increases faster than the rate of increase of the radius of second sleeve
section
82 until approximately the mid point of second sleeve section
82,
after which the radius of third shaft section
203 increases slower than
the rate of increase of the radius of second sleeve section
82. Hence, the
distance between second sleeve section
82 and third shaft section
203
reaches a minimum at approximately the mid point of second sleeve section
82.
Fourth shaft section
204 extends below third shaft section
203 and
it begins at approximately the same height as third sleeve section
83. The
radius of fourth shaft section
204 decreases rapidly and it goes to zero
at the bottom of third sleeve section
83 at which point fourth shaft section
204 touches end plate
42.
The radius of third shaft section
203 can be described by the following
equation: r
s3=D+f
s3(Z), where r
s3 is the radius
of third shaft section
203, D is the radius of second shaft section
202,
Z is the vertical distance below second shaft section
202, and f
s3(Z)
is a constantly increasing function of Z. The derivative of f
s3(Z) with
respect to Z, which is equal to the derivative of the radius of third shaft section
203 with respect to Z, is always positive (df
s3(Z)/dZ=dr
s3/dZ>0).
Additionally, in the first embodiment, the second derivative of f
s3(Z)
with respect to Z is always negative (d
2f
s3(Z)/d
2Z=d
2r
s3/d
2Z<0)
and it is a continuous function.
The distance between second sleeve section
82 and third shaft section
203 is at its minimum when the rate of increase of the radius of third shaft
section
203 as a function of the vertical distance below second shaft section
202 (the derivative of f
s3(Z) with respect to Z) is equal to
the rate of increase of the radius of second sleeve section
82 (r
sl2-;r
s3
is a minimum when df
s3(Z)/dZ=m). Bearing stiffness can be adjusted by
varying the derivative of the rate of increase of the radius of third shaft section
203. The closer that d
2f
s3(Z)/d
2Z is to
zero the stiffer the bearing will be, provided that the minimum distance between
third shaft section
203 and second sleeve section
82 remains constant.
However, such increased stiffness results in greater energy losses.
The gap comprised of the spaces between sleeve
8, end plate
42
and shaft
20 is filled with an appropriate lubricating fluid. Pressure generating
grooves are formed either onto the surface of second sleeve section
82 or
onto the surface of third shaft section
203 to create a conical bearing.
The grooves are formed such that they are centered approximately at the point where
the distance between second sleeve section
82 and third shaft section
203
is a minimum (df
s3(Z)/dZ=m). Hence, the maximum pressure is generated
at that point.
Forth shaft section
204, end plate
42, and third sleeve section
203 form a pivot bearing. Downward motion of the rotor is resisted by the
physical contact of shaft
20 and end plate
42. Additionally, the
conical bearing provides stabilization of the rotor in the horizontal plane and
it also resists upward motion of the rotor. Hence, thrust bearings and journal
bearings are generally not required for this embodiment of the invention. However,
one or two journal bearings may be added to this embodiment by forming pressure
generating grooves onto the surface of either first sleeve section
81 or
second shaft section
202, if additional horizontal stabilization is required.
Additionally, pressure generating grooves can be placed on the bottom of the fourth
shaft section
204 or on the top of the end plate
42 to minimize material
contact between the shaft
20 and the end plate
42.
This first embodiment can be modified to allow for a fixed shaft rotating hub
arrangement. In such an arrangement, shaft
20 is press-fit into the end
plate
42 and sleeve
8 is affixed to the hub
18.
The second embodiment of the present invention is shown in FIG.
2. FIG.
2 shows the bearing portion of a spindle motor. It is comprised of sleeve
8,
shaft
20, and end plate
42.
As shown in FIG. 2, sleeve
8 is a tubular member comprising four sections
that are distinguished from each other based upon their inner radii. First sleeve
section
81 has a constant inner radius A, except that the inner radius of
first sleeve section
81 increases slightly near the top surface of sleeve
8 to form a capillary seal. Second sleeve section
82 has an inner
radius that increases linearly as the depth of the sleeve
8 increases so
as to form a conic section. The inner radius of second sleeve section
82
can be described by the following equation: r
Sl2=A+mY, where r
Sl2
is the inner radius of second sleeve section
82, A is the inner radius of
first sleeve section
81, m is the rate of increase (slope) of the radius
of second sleeve section
82, and Y is the vertical distance below first
sleeve section
81. Third sleeve section
83 has a constant inner radius
B that is equal to the maximum radius of second sleeve section
82. Fourth
sleeve section
84 has a constant inner radius C that is greater than the
inner radius of third sleeve section
83. End plate
42 is fit into
fourth sleeve section
84 of Sleeve
8.
As shown in FIG. 2, shaft
20 is also comprised of four sections. First
shaft section
201 fits inside of and is rigidly connected to hub
18.
Second shaft section
202 fits inside of first sleeve section
81,
although second shaft section
202 extends slightly below first sleeve section
202. Second shaft section
202 has a constant radius F that is slightly
less than the radius A of first sleeve section
81. Third shaft section
203
extends below second shaft section
202 and it fits within second sleeve
section
82. The radius of third shaft section
203 is less than the
radius of second sleeve section
82 by a constant amount. Hence, the distance
between second sleeve section
82 and third shaft section
203 is constant
over the entire length of third shaft section
203. Fourth shaft section
204 extends below third shaft section
203 and it begins at approximately
the same height as third sleeve section
83. The radius of fourth shaft section
204 decreases rapidly and it goes to zero at the bottom of third sleeve
section
83 at which point fourth shaft section
204 touches end plate
42.
The radius of third shaft section
203 can be described by the following
equation: r
s3=D+f
s3(Z), where r
s3 is the radius
of third shaft section
203, D is the radius of second shaft section
202,
Z is the vertical distance below second shaft section
202, and f
s3(Z)
is a constantly increasing function of Z. The derivative of f
s3(Z) with
respect to Z, which is equal to the derivative of the radius of third shaft section
203 with respect to Z, is a constant positive value (df
s3(Z)/dZ=dr
s3/dZ>0).
Additionally, in the second embodiment, the second derivative of f
s3(Z)
with respect to Z is always zero (d
2f
s3(Z)/d
2Z=d
2r
s3/d
2Z=0).
The gap comprised of the spaces between sleeve
8, end plate
42
and shaft
20 is filled with an appropriate lubricating fluid. Pressure generating
grooves are formed on the surface of second sleeve section
82 or onto the
surface of third shaft section
203 to create a conical bearing. Fourth shaft
section
204, end plate
42, and third sleeve section
83 form
a pivot bearing. In the second embodiment, the conical bearing provides stabilization
to the rotor in the horizontal plane and it also resists upward motion of the rotor.
Downward motion of the rotor is resisted by the pivot bearing. Hence, thrust bearings
and journal bearings are generally not required for this embodiment of the invention.
However, as shown on FIG. 2, pressure generating grooves
21 are included
on second shaft section
202 to form a journal bearing and provide additional
horizontal stabilization. Additionally, pressure generating grooves may be placed
on the bottom of the fourth shaft section
204 or on the top of the end plate
42 to minimize material contact between the shaft
20 and the end
plate
42.
The primary difference between embodiment 2 and the bearing of embodiment 1 is
that the derivative of the rate of increase of the radius of third shaft section
203 with respect to the vertical distance below second shaft section
202
is equal to zero (d
2f
s3(Z)/d
2Z=d
2r
s3/d
2Z=0),
which is the limiting case from embodiment 1.
The third embodiment of the present invention is shown in FIG.
3. FIG.
3 shows the bearing portion of a spindle motor. It is comprised of sleeve
8,
shaft
20, and end plate
42.
As shown in FIG. 3, sleeve
8 is a tubular member comprising four sections
that are distinguished from each other based upon their inner radii. First sleeve
section
81 has a constant inner radius A, except that the inner radius of
first sleeve section
81 increases slightly near the top surface of sleeve
8 to form a capillary seal. Second sleeve section
82 has an inner
radius that increases as the depth of sleeve
8 increases. However, the rate
of increase of the inner radius of second sleeve section
82 decreases as
the depth of sleeve
8 increases. Third sleeve section
83 has a constant
inner radius B that is equal to the maximum radius of second sleeve section
82.
Fourth sleeve section
84 has a constant inner radius C that is greater than
the inner radius of third sleeve section
83. End plate
42 is fit
into fourth sleeve section
84 of Sleeve
8.
The inner radius of second sleeve section
82 can be described by the following
equation: r
sl2=D+f
sl2(Y), where r
Sl2 is the radius
of second sleeve section
82, D is the radius of first sleeve section
81,
Y is the vertical distance below first sleeve section
81, and f
sl2(Y)
is a constantly increasing function of Y. The derivative of f
s3(Y) with
respect to Y, which is equal to the derivative of the radius of second sleeve section
82 with respect to Y, is always positive (df
sl2(Y)/dY=dr
sl2/dY>0).
Additionally, in the third embodiment, the second derivative of f
sl2(Y)
with respect to Y is always negative (d
2f
s3(Z)/d
2Z=d
2r
s3/d
2Z<0)
and it is a continuous function.
As shown in FIG. 3, shaft
20 is also comprised of four sections. First
shaft section
201 fits inside of and is rigidly connected to hub
18.
Second shaft section
202 fits inside of first sleeve section
81,
although second shaft section
202 extends slightly below first sleeve section
202. Second shaft section
202 has a constant radius F that is slightly
less than the radius A of first sleeve section
81. Third shaft section
203
extends below second shaft section
202 and it fits within second sleeve
section
82. The radius of third shaft section
203 increases as the
depth of third shaft section
203 increases. However, the rate of increase
of the radius of third shaft section
203 decreases as the depth of third
shaft section
203 increases. The radius of third shaft section
203
is less than the radius of second sleeve section
82 by a constant amount
for the entire length of third shaft section
203. Fourth shaft section
204
extends below third shaft section
203 and it begins at approximately the
same height as third sleeve section
83. The radius of fourth shaft section
204 decreases rapidly and it goes to zero at the bottom of third sleeve
section
83 at which point fourth shaft section
204 touches end plate
42.
The radius of third shaft section
203 can be described by the following
equation: r
s3=D+f
s3(Z), where r
s3 is the radius
of third shaft section
203, D is the radius of second shaft section
202,
Z is the vertical distance below second shaft section
202, and f
s3(Z)
is a constantly increasing function of Z. The derivative of f
s3(Z) with
respect to Z, which is equal to the derivative of the radius of third shaft section
203 with respect to Z, is always positive (df
s3(Z)/dZ=dr
s3/dZ>0).
Additionally, in the first embodiment, the second derivative of f
s3(Z)
with respect to Z is always negative (d
2f
s3(Z)/d
2Z=d
2r
s3/d
2Z<0)
and it is a continuous function.
In the third embodiment, the gap comprised of the spaces between sleeve
8,
end plate
42 and shaft
20 is filled with an appropriate lubricating
fluid. Pressure generating grooves are formed either onto the surface of second
sleeve section
82 or onto the surface of third shaft section
203
to create a conical bearing. The conical bearing provides stabilization to the
rotor in the horizontal plane and it also resists upward motion of the rotor. The
placement of the grooves determines the relative strength of the horizontal stabilization
and the upward stabilization (the thrust and journal components of the conical
bearing). A higher placement of the grooves results in relatively greater resistance
to upward movement of the shaft, while a lower placement of the grooves results
in relatively greater horizontal stabilization. Additionally, fourth shaft section
204, end plate
42, and third sleeve section
83 form a pivot
bearing, which resists downward motion of the shaft by the physical contact of
shaft
20 with end plate
42. Hence, thrust bearings and journal bearings
are generally not required for this embodiment of the invention. However, as shown
on FIG. 3, pressure generating grooves
21 are included on second shaft section
202 to form a journal bearing and to provide additional horizontal stabilization.
Additionally, pressure generating grooves can be placed on the bottom of the fourth
shaft section
204 or on the top of the end plate
42 to minimize material
contact between the shaft
20 and the end plate
42.
*
