US007036207B2
`
`(12) United States Patent
`Neal
`
`(10) Patent No.:
`(45) Date of Patent:
`
`US 7,036,207 B2
`May 2, 2006
`
`(54) STATOR ASSEMBLY MADE FROM A
`PLURALITY OF TOROIDAL CORE
`SEGMENTS AND MOTOR USING SAME
`
`(75) Inventor: Griffith D. Neal, Alameda, CA (US)
`(73) Assignee: Encap Motor Corporation, Alameda,
`CA (US)
`
`(*) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`(21) Appl. No.: 09/798,511
`
`(22) Filed:
`(65)
`
`Mar. 2, 2001
`Prior Publication Data
`US 2002/0135263 A1
`Sep. 26, 2002
`
`(51) Int. Cl
`e vº._2 - e.
`(2006.01)
`H02K 15/06)
`(2006.01)
`H02K 1/14
`(52) U.S. Cl. ............................ 29/597; 29/596; 29/606:
`310/45; 310/218
`(58) Field of Classification Search .................. 29,596,
`29/598, 597, 605, 606, 732; 310/214, 216,
`310/45, 154, 156, 218
`See application file for complete search history.
`
`(56)
`
`References Cited
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`BE
`
`(Continued)
`OTHER PUBLICATIONS
`G.D. Neal et al. “Ceramic Filled Thermoplastic Encapsula
`-
`Design F
`for a BLDC Motor in a Disk Dirve”
`tion as a Design Feature for a
`Otor 1m a |)1Sk |)1rve
`IEEE 2000.*
`
`(Continued)
`-
`Primary Examiner—Eric Compton
`(74) Attorney, Agent, or Firm—Brinks Hofer Gilson &
`Lione
`(57)
`
`ABSTRACT
`
`A plurality of stator arc segments form a toroidal core for a
`stator assembly used to make a motor. In a preferred
`embodiment, a plurality of magnetic fields is created when
`electrical current is conducted through wire wound around
`poles on the toroidal core. A monolithic body of phase
`change material substantially encapsulates the conductors
`and holds the stator arc segments in contact with each other
`in the toroidal core. Hard disc drives using the motor, and
`methods of constructing the motor and hard disc drives are
`also disclosed.
`
`29 Claims, 6 Drawing Sheets
`
`Petitioners Exhibit 1007
`Page 1
`
`

`

`US 7,036,207 B2
`
`Page 2
`
`U.S. PATENT DOCUMENTS
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`
`OTHER PUBLICATIONS
`LNP Engineering Plastics, Advertisement entitled “Kon-
`duit™ Thermally Conductive Composites.” undated Q
`pages)
`y
`P
`°
`:
`LNP Engineering Plastics, Press Release entitled “LNP
`Introduces First-Ever Line of Thermally Conductive
`Compounds,” Jan. 28, 1999 (2 pages).
`Search Report for Patent Cooperation Treaty application No.
`PCT/US02/06508, Date of Mailing Jul. 12, 2002, 3 pages.
`
`* cited by examiner
`
`Petitioners Exhibit 1007
`
`Page 2
`
`Petitioners Exhibit 1007
`Page 2
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`

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`U.S. Patent
`U.S. Patent
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`May 2, 2006
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`1
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`Petitioners Exhibit 1007
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`92
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`AN
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`oo)WA
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`102
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`10G
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`107
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`Petitioners Exhibit 1007
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`US 7,036,207 B2
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`1
`STATOR ASSEMBLY MADE FROM A
`PLURALITY OF TOROIDAL CORE
`SEGMENTS AND MOTOR USING SAME
`
`FIELD OF THE INVENTION
`
`The present invention relates generally to a stator assem
`bly used in a motor. It relates particularly to a spindle motor
`such as used in a hard disc drive, and to the construction and
`arrangement of a stator assembly made from a plurality of
`arc segments.
`
`10
`
`BACKGROUND OF THE INVENTION
`
`2
`different points around the circle differs. Compared from the
`radius line of the circle, the grain orientation is sometimes
`aligned along the radius, sometimes transverse to it, and
`mostly at a varying angle to the radius. The un-aligned grain
`structure of conventional stators causes the magnetic flux
`values to differ in parts of the stator and thus the motor does
`not have consistent and uniform torque properties as it
`rotates.
`Another drawback with using circular steel pieces is that,
`especially for inward facing poles, it has been difficult to
`wind the wire windings tightly because of the cramped space
`to work inside of the laminated stator core. The cramped
`working space creates a lower limit on the size of the stator
`and thus the motor. The limited working space also results
`in a low packing density of wire. The packing density of
`wire coiled around the poles affects the amount of power
`generated by the motor. Increasing packing density increases
`the power and thus the efficiency of the spindle motor.
`An important factor in motor design is to reduce stack up
`tolerances in the motor. Stack up tolerances reduce the
`overall dimensional consistency between the components.
`Stack up tolerances refer to the sum of the variation of all the
`tolerances of all the parts, as well as the overall tolerance
`that relates to the alignment of the parts relative to one
`another. One source of stack up tolerances is from the
`circular stator body. Generally, the thickness of rolled steel
`is not uniform across the width of the roll. Sometimes the
`edges are thicker or thinner than the center. In a stator made
`from circular stamped pieces, the thickness of individual
`laminations are thus different from one side to the other.
`When stacked together, this creates a stack up tolerance
`problem. Furthermore, the circular stampings leave a lot of
`wasted steel that is removed and must be recycled or
`discarded.
`Another important factor in motor design is the lowering
`of the operating temperature of the motor. Increased motor
`temperature affects the electrical efficiency of the motor and
`bearing life. As temperature increases, resistive loses in wire
`increase, thereby reducing total motor power. Furthermore,
`the Arhennius equation predicts that the failure rate of an
`electrical device is exponentially related to its operating
`temperature. The frictional heat generated by bearings
`increases with speed. Also, as bearings get hot they expand,
`and the bearing cages get stressed and may deflect, causing
`non-uniform rotation reducing bearing life. This non-uni
`form rotation causes a further problem of limiting the ability
`of the servo system controlling the read/write heads to
`follow data tracks on the magnetic media. One drawback
`with existing motor designs is their limited effective dissi
`pation of the heat, and difficulty in incorporating heat sinks
`to aid in heat dissipation. In addition, in current motors the
`operating temperatures generally increase as the size of the
`motor is decreased.
`Manufacturers have established strict requirements on the
`outgassing of materials that are used inside a hard disc drive.
`These requirements are intended to reduce the emission of
`materials onto the magnetic media or heads during the
`operation of the drive. Of primary concern are glues used to
`attach components together, varnish used to insulate wire,
`and epoxy used to protect steel laminations from oxidation.
`In addition to such outgassed materials, airborne particu
`late in a drive may lead to head damage. Also, airborne
`particulates in the disc drive could interfere with signal
`transfer between the read/write head and the media. To
`reduce the effects of potential airborne particulate, hard
`drives are manufactured to exacting clean room standards
`
`15
`
`20
`
`25
`
`Computers commonly use disc drives for memory storage
`purposes. Disc drives include a stack of one or more
`magnetic discs that rotate and are accessed using a head or
`read-write transducer. Typically, a high speed motor such as
`a spindle motor is used to rotate the discs.
`In conventional spindle motors, stators have been made
`by laminating together stamped pieces of steel. These
`stamped pieces of steel are generally circular in nature, but
`also have “poles” extending either inwardly or outwardly,
`depending on whether the rotor is on the inside or surrounds
`the stator. The stamped pieces are laminated together and
`then coated with insulation. Wire is then wound around the
`poles to form stator windings.
`An example of a conventional spindle motor 1 is shown
`in FIG. 1. The motor 1 includes a base 2 which is usually
`made from die cast aluminum, a stator 4, a shaft 6, bearings
`30
`7 and a disc support member 8, also referred to as a hub. A
`magnet 3 and flux return ring 5 are attached to the disc
`support member 8. The stator 4 is separated from the base 2
`using an insulator (not shown) and attached to the base 2
`using a glue. Distinct structures are formed in the base 2 and
`the disc support member 8 to accommodate the bearings 7.
`One end of the shaft 6 is inserted into the bearing 7
`positioned in the base 2 and the other end of the shaft 6 is
`placed in the bearing 7 located in the hub 8. A separate
`electrical connector 9 may also be inserted into the base 2.
`Each of these parts must be fixed at predefined tolerances
`with respect to one another. Accuracy in these tolerances can
`significantly enhance motor performance.
`In operation, the disc stack is placed upon the hub. The
`stator windings are selectively energized and interact with
`the permanent magnet to cause a defined rotation of the hub.
`As hub 8 rotates, the head engages in reading or writing
`activities based upon instructions from the CPU in the
`computer.
`Manufacturers of disc drives are constantly seeking to
`improve the speed with which data can be accessed. To an
`extent, this speed depends upon the efficiency of the spindle
`motor, as existing magneto-resistive head technology is
`capable of accessing data at a rate greater than the speed
`offered by the highest speed spindle motor currently in
`production. The efficiency of the spindle motor is dependent
`upon the dimensional consistency or tolerances between the
`various components of the motor. Greater dimensional con
`sistency between components leads to a smaller gap between
`the stator 4 and the magnet 3, producing more force, which
`provides more torque and enables faster acceleration and
`higher rotational speeds.
`The conventional method of forming stators has a number
`of drawbacks. First, most steel is manufactured in rolled
`sheets and thus has a grain orientation. The grain orientation
`has an effect on the magnetic flux properties of the steel. In
`circular stamped pieces of steel, the grain orientation at
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
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`Petitioners Exhibit 1007
`Page 9
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`

`3
`and air filters are installed inside of the drive to reduce the
`contamination levels during operation.
`An example of a spindle motor is shown in U.S. Pat. No.
`5,694,268 (Dunfield et al.) (incorporated herein by refer
`ence). Referring to FIG. 5 of this patent, a stator of the
`spindle motor is encapsulated with an overmold 42. The
`overmolded stator 40 contains openings through which
`mounting pins 44 may be inserted for attaching the stator
`200 to a base. U.S. Pat. No. 5,672,972 (Viskochil) (incor
`porated herein by reference) also discloses a spindle motor
`having an overmolded stator. One drawback with the over
`mold used in these patents is that it has a different coefficient
`of linear thermal expansion (“CLTE”) than the correspond
`ing metal parts to which it is attached. Another drawback
`with the overmold is that it is not very effective at dissipating
`heat. Further, the overmolds shown in these patents are not
`effective in dampening some vibrations generated by ener
`gizing the stator windings.
`U.S. Pat. No. 5,806,169 (Trago) (incorporated herein by
`reference) discloses a method of fabricating an injection
`molded motor assembly. However, the motor disclosed in
`Trago is a step motor, not a high speed spindle motor, and
`would not be used in applications such as hard disc drives.
`Further, none of these three prior art designs address the
`problem of variation in the thickness of steel used to make
`the stator cores and the non-uniform grain structure in the
`steel compared to the magnetic flux in the stator during
`operation of the motor. Thus, a need exists for an improved
`high speed spindle motor, having properties that will be
`especially useful in a hard disc drive, overcoming the
`aforementioned problems.
`
`BRIEF SUMMARY OF THE INVENTION
`
`A high speed motor has been invented which overcomes
`many of the foregoing problems. In addition, unique stator
`assemblies and other components of a high speed motor
`have been invented, as well as methods of manufacturing
`motors and hard disc drives. In one aspect, the invention is
`a motor comprising: a plurality of stator arc segments
`forming a toroidal core, wherein each said stator arc segment
`has two end surfaces that are each in contact with an end
`surface of another stator arc segment to form a toroidal core;
`and a monolithic body of phase change material substan
`tially encapsulating the stator arc segments and holding said
`toroidal core in place.
`In another aspect the invention is a method of making a
`motor comprising: providing at least two stator arc segments
`each having a first end surface and a second end surface;
`aligning said stator arc segments to form a toroidal core,
`wherein each said end surface of one segment is in contact
`with an opposing end surface of another segment; and
`substantially encapsulating said toroidal core with a mono
`lithic body of phase change material and solidifying the
`phase change material to hold the stator arc segments
`together.
`In another aspect the invention is a method of making a
`motor comprising: providing four stator arc segments,
`wherein each stator arc segment has a first end surface and
`a second end surface; aligning said stator arc segments to
`form a toroidal core, wherein each said end surface of one
`segment is in contact with an opposing end surface of
`another segment; and substantially encapsulating said tor
`oidal core with a monolithic body of phase change material,
`wherein said substantially encapsulating is by injection
`molding said phase change material around said toroidal
`COre.
`
`US 7,036,207 B2
`
`4
`In yet another aspect, the invention is a combination of
`stator arc segments and a carrier used to support said stator
`arc segments during a winding operation comprising a
`plurality of stator arc segments, and: a plurality of cavities
`to hold and support said stator arc segments, wherein said
`cavities are spaced apart a distance X, wherein the distance
`X is the length of uncoiled wire necessary to align said stator
`arc segments to form a toroidal core.
`The invention provides the foregoing and other features,
`and the advantages of the invention will become further
`apparent from the following detailed description of the
`presently preferred embodiments, read in conjunction with
`the accompanying drawings. The detailed description and
`drawings are merely illustrative of the invention and do not
`limit the scope of the invention, which is defined by the
`appended claims and equivalents thereof.
`
`BRIEF DESCRIPTION OF SEVERAL VIEWS OF
`THE DRAWINGS
`
`FIG. 1 is an exploded, partial cross-sectional and perspec
`tive view of a conventional high speed motor of the prior art.
`FIG. 2 is a perspective view of a stator arc segment.
`FIG. 3 is a perspective view of a combined carrier
`assembly and stator arc segments of FIG. 2.
`FIG. 4 is a perspective view of stator arc segments of FIG.
`2 with windings thereon ready to be formed into a toroidal
`COre.
`FIG. 5 is a perspective view of an injection molded stator
`assembly using the stator arc segments of FIG. 4.
`FIG. 6a is a cross-sectional view of the toroidal core of
`FIG. 4 in an injection mold assembly, prior to injecting a
`phase change material.
`FIG. 6b is a cross-sectional view of the toroidal core of
`FIG. 4 in an injection mold assembly, after injecting a phase
`change material.
`FIG. 7 is an exploded, partial cross-sectional and perspec
`tive view of a high speed motor using the encapsulated stator
`of FIG. 5.
`FIG. 8 is an exploded, partial cross-sectional and perspec
`tive view of a high speed motor and disc assembly made
`with the motor of FIG. 7.
`FIG. 9 is a cross-sectional view of the motor of FIG. 8.
`
`DETAILED DESCRIPTION OF THE DRAWINGS
`AND PREFERRED EMBODIMENTS OF THE
`INVENTION
`
`A preferred embodiment of a high speed motor of the
`present invention and portions of the motor at different
`stages of manufacture are shown in FIGS. 2–7 and 9. By
`“high speed” it is meant that the motor can operate at over
`5,000 rpm. The spindle motor 100 is designed for rotating a
`disc or stack of discs in a computer hard drive. Motor 100
`is formed by using an injection molded stator assembly 40,
`that is formed by injection molding a plurality of stator arc
`segments 20 aligned to form a toroidal core 17. Although the
`embodiment described here uses four arc segments, one of
`ordinary skill in the art will understand that two, three or any
`greater number of arc segments may be used. The preferred
`motor of the present invention is smaller, has a grain
`structure that is more uniformly aligned, allows for greater
`packing density of wire and reduces waste of steel in the
`manufacturing process as compared with conventional
`motors used for disc drives, thereby increasing power and
`reducing stack up tolerances and manufacturing costs and
`producing other advantages discussed below.
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`50
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`Petitioners Exhibit 1007
`Page 10
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`

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`US 7,036,207 B2
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`Referring to FIG. 2, a stator arc segment 20 is first
`constructed, using steel laminations 11. The stator arc seg
`ment 20 is made of steel pieces that are stamped out of rolled
`steel. The stamped steel pieces are arc segments, but also
`have poles 21 extending inwardly or outwardly depending
`on whether the rotor is inside or surrounds the stator. In the
`embodiment shown in FIG. 2, the poles 21 are shown
`extending inwardly. The stamped pieces are then coated with
`epoxy which provides insulation and laminates the pieces
`together to form a stator arc segment 20.
`As shown in FIG. 3, the stator arc segments 20 are then
`preferably placed in a carrier 30. The carrier 30 has a
`plurality of cavities 32 that hold the stator arc segments 20
`in place. In a preferred embodiment, the space between the
`cavities is equivalent to the length of wire needed to travel
`from a point on one pole 21a to the next pole 21b in the same
`phase of windings following the arc of the stator arc seg
`ments 20. The carrier 30 shown in FIG. 3 shows an alter
`native embodiment where the space between the cavities is
`not necessarily equivalent to the length of wire needed to
`travel from a point on one pole 21a to the next pole 21b. By
`precisely aligning the stator arc segments 20, the carrier 30
`greatly enhances the efficiency for winding wire 15 around
`the poles 21 and manufacturing stators.
`Wire 15 is then wound around the poles 21 of the stator
`arc segments 20 using a spool winder 34 that has a set of
`needles 35 that wind wire around the poles 21. The wire 15
`is wound around one pole 21 and is then wound around
`another pole 21 in its phase until all poles 21 in the same
`phase are wound with the same wire 15. Poles 21 in other
`phases are also similarly wound. Having only arc segments,
`rather than a full toroidal core, and placing the arc segments
`20 in the carrier 30 makes it much easier for needle 35 to
`wind wire 15 around poles 21. Using this method, a wire
`packing density of about 60 percent to about 80 percent can
`be achieved.
`As shown in FIG. 4, the individual stator arc segments 20
`are then removed from the carrier and aligned to form a
`40
`magnetically inducible toroidal core 17 having a plurality of
`poles 21 thereon, and wire windings 15 which serve as
`conductors. To form the toroidal core 17, an end surface 16
`of each stator arc segment 20 is aligned and brought into
`contact with a corresponding end surface 19 of another
`stator arc segment 20. The wire 15 between the poles 21 of
`different stator arc segments 20 is also aligned in the toroidal
`core 17, following the arc of the stator arc segments 20. As
`a result, the wire in the toroidal core 17 is taught. After the
`wire is wound so that one set of three leads is terminated
`together to create the common ground 46, and the other ends
`of the wire, are for each of the three phases form the leads
`47a, 47b and 47c by which current is supplied to the
`windings. The conductors induce or otherwise create a
`plurality of magnetic fields in the core when electrical
`current is conducted through the conductors. In this embodi
`ment, a magnetic field is induced in each of the poles 21.
`As shown in FIG. 5, the toroidal core 17 is then encap
`sulated in a body 42. Together the toroidal core 17 and the
`body 42 make up an injection molded stator assembly 40.
`The body 42 is preferably a monolithic body. Monolithic is
`defined as being formed as a single piece. The body 42
`substantially encapsulates the toroidal core 17. Substantial
`encapsulation means that the body 42 either entirely sur
`rounds the toroidal core 17, or surrounds almost all of it
`except for minor areas of the toroidal core 17 that may be
`exposed. However, substantial encapsulation means that the
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`body 42 and toroidal core 17 are rigidly fixed together, and
`behave as a single component with respect to harmonic
`oscillation vibration.
`The body 42 is preferably formed of a phase change
`material, meaning a material that can be used in a liquid
`phase to envelope the stator, but which later changes to a
`solid phase. There are two types of phase change materials
`that will be most useful in practicing the invention: tem
`perature activated and chemically activated. A temperature
`activated phase change material will become molten at a
`higher temperature, and then solidify at a lower temperature.
`However, in order to be practical, the phase change material
`must be molten at a temperature that is low enough that it
`can be used to encapsulate a toroidal core. Preferred phase
`change materials will be changed from a liquid to a solid in
`the range of about 200°F. to about 700°F., more preferably
`in the range of about 550° F to about 650° F. The most
`preferred temperature activated phase change materials are
`thermoplastics. The preferred thermoplastic will become
`molten at a temperature at which it is injection-moldable,
`and then will be solid at normal operating temperatures for
`the motor. An example of a phase change material that
`changes phases due to a chemical reaction, and which could
`be used to form the body, is an epoxy. Other suitable phase
`change materials may be classified as thermosetting mate
`rials.
`The preferred method of developing the monolithic body
`42 comprises designing a phase change material to have a
`coefficient of linear thermal expansion such that the phase
`change material contracts and expands at approximately the
`same rate as the metal laminations of the toroidal core 17.
`For example, the preferred phase change material should
`have a CLTE of between 70% and 130% of the CLTE of the
`core of the stator. The phase change material should have a
`CLTE that is intermediate the maximum and minimum
`CLTE of the toroidal core and other motor components
`where the body is in contact with those other components
`and they are made of a different material than the core. Also,
`the CLTE’s of the body and toroidal core should match
`throughout the temperature range of the motor during its
`operation. An advantage of this method is that a more
`accurate tolerance may be achieved between the body and
`the components of the toroidal core because the CLTE of the
`body matches the CLTE of the toroidal core components
`more closely. Most often the toroidal core components will
`be metal, and most frequently steel and copper. Other motor
`parts are often made of aluminum and steel.
`Most thermoplastic materials have a relatively high
`CLTE. Some thermoplastic materials may have a CLTE at
`low temperatures that is similar to the CLTE of metal.
`However, at higher temperatures the CLTE does not match
`that of the metal. A preferred thermoplastic material will
`have a CLTE of less than 2x10 ° in/in/* F., more preferably
`less than 1.5×107 in/in/* F., throughout the expected oper
`ating temperature of the motor, and preferably throughout
`the range of 0–250° F. Most preferably, the CLTE will be
`between about 0.8×10Tin/in/* F. and about 1.2×10Tin/in/9
`F. throughout the range of 0–250° F. (When the measured
`CLTE of a material depends on the direction of measure
`ment, the relevant CLTE for purposes of defining the present
`invention is the CLTE in the direction in which the CLTE is
`lowest.)
`
`Petitioners Exhibit 1007
`Page 11
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`

`

`7
`The CLTE of common solid parts used in a motor are as
`follows:
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`US 7,036,207 B2
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`8
`polypropylene, polyethylene, polyacetals, polymethylpen
`tene, polyetherimides, polycarbonate, polysulfone, poly
`ethersulfone, polyphenylene oxide, polystyrene, styrene
`copolymer, mixtures and graft copolymers of styrene and
`rubber, and glass reinforced or impact modified versions of
`such resins. Blends of these resins such as polyphenylene
`oxide and polyamide blends, and polycarbonate and poly
`butylene terephthalate, may also be used in this invention.
`As shown in FIG. 6a, to encapsulate the toroidal core 17
`and form body 42, the toroidal core 17 is first clamped and
`held in place by pins 61 in an injection mold cavity 66. The
`injection mold cavity 66 is very effective and maintains the
`toroidal shape of the toroidal core 17. Molten phase-change
`material is then injected into the molding cavity 66 with an
`extrusion screw (not shown) until the pressure inside the
`cavity reaches a predetermined molding pressure. After
`injecting the molten phase change material, the pins 61
`retract as shown in FIG. 6b. The phase change material is
`then allowed to cool and solidify into a monolithic body 42
`that substantially encapsulates the toroidal core 17. The
`preferred thickness of the body 42 depends on the aspect
`ratio of the toroidal core 17.
`The injection molded stator assembly 40 is then used to
`construct the rest of the spindle motor 100 (FIG. 7). The
`spindle motor 100 includes a hub 108, which serves as a disc
`support member, the stator assembly 40, a base 102, a shaft
`106 and bearings 107.
`As shown in FIG. 7, a shaft 106 is connected to the hub
`or disc support member 108 and is surrounded by bearings
`107, which are adjacent against the base 102 of the motor.
`A rotor or magnet 103 is fixed to the inside of the hub 108
`on a flange so as to be in operable proximity to the stator
`assembly. The magnet 103 is preferably a permanent mag
`net, as described below.
`Referring to FIG. 7, the bearings 107 include an upper
`bearing 46 and a lower bearing 48. Also, each bearing 107
`has an outer surface 50 and an inner surface 52. The outer
`surface 50 of the upper bearing contacts the hub 108 and the
`outer surface 50 of the lower bearing 48 contacts the lower
`support base 102. The inner surfaces 52 of the bearings 107
`contact the shaft 116. The bearings are preferably annular
`shaped. The inner surfaces 52 of the bearings 107 may be
`press fit onto the shaft 16. A glue may also be used. The outer
`surface 50 of the bearings 107 may be press fit into the
`interior portion of the base 102. A glue may also be used.
`The bearings in the embodiment shown in FIG. 7 are ball
`bearings. Alternatively other types of bearings, such as
`hydrodynamic or combinations of hydrodynamic and mag
`netic bearings, may be used. The bearings are typically made
`of stainless steel.
`The shaft 106 is concentrically disposed within the inte
`rior portion of the stator assembly 40 and the base 102. The
`bearings 107 surround portions of the shaft 106. As
`described above, the inner surfaces 52 of the bearings