(12) United States Patent
`Neal et al.
`
`US00689.2439B1
`(10) Patent No.:
`US 6,892,439 B1
`(45) Date of Patent:
`May 17, 2005
`
`(54) MOTOR WITH STATOR MADE FROM
`LINEAR CORE PREFORM
`(75) Inventors: Griffith D. Neal, Alameda, CA (US);
`Albert D. Neal, Long Beach, 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.: 09/775,242
`:12, 21.
`(22) Filed:
`Feb. 1, 2001
`
`BE
`.
`EP
`EP
`FR
`JP
`JP
`JP
`JP
`SU
`SU
`WO
`WO
`WO
`WO
`
`FOREIGN PATENT DOCUMENTS
`870 878
`1/1979
`sº ; A1 ;
`0 747 943 A2 12/1996
`0 883 171 A1 12/1998
`2 647 958
`12/1990
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`12/1993
`10070870
`3/1998
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`1494,148
`7/1989
`WO 92/06532
`4/1992
`WO 96/20501
`7/1996
`WO 96/33533
`10/1996
`WO 97/39870
`10/1997
`
`(51) Int. Cl." ................................................ H02K 15/16
`
`OTHER PUBLICATIONS
`
`§ Hº search - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - jº LNP Engineering Plastics, Advertisement entitled “Kon
`
`- - - - - - - - - - - - - - - - - - - - - - - - - - - 31 0/179 21 6, 254
`2
`2
`
`duit" Thermally COnductive Composites,” undated (2
`pages).
`
`(56)
`
`References Cited
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`(Continued)
`
`
`
`(Continued)
`
`Primary Examiner—Joseph Waks
`(74) Attorney, Agent, or Firm—Steven P. Shurtz, Brinks
`Hofer Gilson & Lione
`(57)
`ABSTRACT
`A motor includes a stator having multiple conductors that
`create a plurality of magnetic fields when electrical current
`is conducted through the conductors. The stator has a pair of
`opposing end surfaces in contact with each other forming a
`toroidal core. A monolithic body of phase change material
`substantially encapsulates the conductors and holds said
`toroidal core in place. The stator is formed by laminating
`strips together to form a linear core preform, winding wire
`around poles extending from a side of the core preform, then
`rolling the preform to bring its two ends together to form the
`toroidal core. Hard disc drives using the motor, and methods
`of constructing the motor and hard disc drives are also
`disclosed.
`
`26 Claims, 7 Drawing Sheets
`
`PAGE 1 OF 16
`
`PETITIONERS' EXHIBIT 1108
`
`

`

`US 6,892,439 B1
`Page 2
`
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`OTHER PUBLICATIONS
`Product Information from Dupont Engineering Polymers
`itled “Electrical/Electronic Thermoplastic Encapsula
`entitle
`p
`p
`tion,” undated, Publ. Reorder No.: H-58633 (R, 96.7), 20
`pages.
`.
`.
`-
`-
`LNP Engineering Plastics, Press Release entitled “LNP
`Introduces First—Ever Line of Thermally Conductive Com
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`Equipment Running Longer,” Jul. 14, 1999, -http://www.b
`mworks.com/VIP.htm>, 1 page
`-
`~~:
`-
`•.
`..
`The Epoxylite Corporation, article from the Internet entitled
`“Vacuum Pressure Impregnation (VPI) Systems”, Nov. 19,
`1999,
`<http://www.epoxylite.com/EpoxyliteBquipmen
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`Neeltran Inc., article from the Internet entitled “Vacuum
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`w.neeltran.thomasregister.com/olc/neeltran/neel9.htm>
`2
`pages.
`Copy of Search Report for PCT Application No. US00/
`- -
`-
`-
`19870 filed on Jul. 19, 2000 which is for a corresponding
`PCT case filed by the assignee Encap Motors Corporation
`who is also the assignee of this US application.
`U.S. Appl. No. 09/470,424, filed Dec. 22, 1999.
`U.S. Appl. No. 09/470,425, filed Dec. 22, 1999.
`U.S. Appl. No. 09/470,426, filed Dec. 22, 1999.
`U.S. Appl. No. 09/470,427, filed Dec. 22, 1999.
`U.S. Appl. No. 09/470,428, filed Dec. 22, 1999.
`U.S. Appl. No. 09/470,429, filed Dec. 22, 1999.
`U.S. Appl. No. 09/470.430, filed Dec. 22, 1999
`S. Appl. No. 09/470,430, filed Dec. 22,
`-
`U.S. Appl. No. 09/470,431, filed Dec. 22, 1999.
`U.S. Appl. No. 09/470,432, filed Dec. 22, 1999.
`U.S. Appl. No. 09/470,433, filed Dec. 22, 1999.
`U.S. Appl. No. 09/470,434, filed Dec. 22, 1999.
`U.S. Appl. No. 09/738,268, filed Dec. 15, 2000.
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`Copy of corresponding application U.S. Ser. No. 09/798,511
`filed Mar. 2, 2001
`• 2–2
`-
`* cited by examiner
`
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`1
`MOTOR WITH STATOR MADE FROM
`LINEAR CORE PREFORM
`
`US 6,892,439 B1
`
`2
`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 body. 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 sheet
`steel is not uniform across the width of the sheet. Sometimes
`the edges are thicker or thinner than the center. In a stator
`made from circular stamped pieces, the thickness of indi
`vidual laminations are thus different from one side to the
`other. When stacked together, this creates a stack up toler
`ance 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
`uniform rotation causes a further problem of limiting the
`ability of the servo system controlling the read/write heads
`to follow the data tracks on the magnetic media. One
`drawback with existing motor designs is their limited effec
`tive dissipation 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
`and air filters are installed inside of the drive to reduce the
`contamination levels during operation.
`
`FIELD OF THE INVENTION
`The present invention relates generally to a motor. It
`relates particularly to a spindle motor such as used in a hard
`disc drive, and to the construction of the stator for the motor.
`
`10
`
`15
`
`20
`
`35
`
`25
`
`BACKGROUND OF THE INVENTION
`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
`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
`30
`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
`different points around the circle differs. Compared from the
`radius line of the circle, the grain orientation is sometimes
`
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`45
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`50
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`3
`One example of a spindle motor is shown in U.S. Pat. No.
`5,694,268 (Dunfield et al.) (incorporated herein by
`reference). Referring to FIGS. 7 and 8 of this patent, a stator
`200 of the spindle motor is encapsulated with an overmold
`209. The overmolded stator contains openings through
`which mounting pins 242 may be inserted for attaching the
`stator 200 to a base. U.S. Pat. No. 5,672,972 (Viskochil)
`(incorporated herein by reference) also discloses a spindle
`motor having an overmolded stator. One drawback with the
`overmold used in these patents is that it has a different
`coefficient of linear thermal expansion (“CLTE”) than the
`corresponding 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 damping some vibrations gener
`ated by energizing 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.
`Furthermore, none of these three prior art designs address
`the problem of variations in the thickness of steel used to
`make stator cores and the non-uniform grain structure in the
`steel compared to the magnet 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 stator assembly that includes a stator having multiple
`conductors that create a plurality of magnetic fields when
`electrical current is conducted through the conductors and a
`core having a pair of opposing end surfaces in contact with
`each other forming a toroidal shape; and a monolithic body
`of phase change material substantially encapsulating the
`conductors and the core and holding said core in a toroidal
`shape.
`In another aspect, the invention is a method of making a
`motor comprising: providing a linear stator core preform,
`wherein said core preform has a first end surface and a
`second end surface and poles extending along one side
`thereof; winding wire around said poles; forming a toroidal
`core by bringing the first end surface and the second end
`surface into contact with each other; and substantially
`encapsulating said toroidal core stator with a monolithic
`body of phase change material.
`In another aspect, the invention is a method of making a
`stator assembly for a motor that includes the steps of
`providing a linear core preform, having a first end surface
`and a second end surface and poles extending along one side
`thereof; winding wire around said poles; forming a toroidal
`core by bringing the first end surface and the second end
`surface into contact with each other; and substantially
`encapsulating said toroidal core and windings with a mono
`lithic body of phase change material to form the stator
`assembly.
`In yet another aspect, the invention is a method of making
`a motor that includes the steps of providing a linear core
`preform having two end surfaces and a plurality of poles
`
`4
`extending from one side; winding wire around the poles;
`forming a toroidal core by bringing the two end surfaces of
`the core preform adjacent to each other; clamping the
`toroidal core in an injection mold cavity to hold the toroidal
`shape; injection molding phase change material around said
`toroidal core to substantially encapsulate said toroidal core
`with a monolithic body of phase change material to form a
`stator assembly; and constructing the stator assembly into a
`motor.
`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.
`FIG. 2 is a perspective view of a core preform.
`FIG. 3a is a cross-sectional view of a stator core preform
`of FIG. 2 during a first stage of the rolling process.
`FIG. 3b is a cross-sectional view of a partially-rolled
`stator core preform of FIG. 3a during a second stage of the
`rolling process.
`FIG. 3c is a cross-sectional view of a substantially-rolled
`stator core preform of FIG. 3b during a third stage of the
`rolling process.
`FIG. 3d is a perspective-side view of a mandrel used in the
`rolling process in FIGS. 3a–3c.
`FIG. 4 is a perspective view of a rolled stator core preform
`of FIG. 3c forming a toroidal core.
`FIG. 5 is a perspective view of an encapsulated stator
`using the toroidal core 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. 7.
`
`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. 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 linear stator core preform
`20 aligned to form a toroidal core 17. Although the embodi
`ment described here uses a flat linear stator core preform 20,
`
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`5
`one of ordinary skill in the art will understand that the stator
`core preform does not initially have to be flat, and may have
`some curvature. The motor of a preferred embodiment of the
`invention is smaller, has a grain structure that is 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.
`Referring to FIG. 2, a linear stator core preform 20 is first
`constructed, using steel laminations (not shown). The stator
`core preform 20 comprises of steel pieces that are stamped
`out of a rolled steel. The stamped steel pieces are linear and
`flat, 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 core preform 20. The
`stator core preform also has two end surfaces 16, 19.
`As shown in FIG. 2, wire 15 is then wound around the
`poles 21 of the stator core preform 20 using a spool winder
`34. The spool winder 34 has a set of needles 35 that make
`it easier to 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 in other phases are also
`similarly wound. Using this method, a wire packing density
`of about 60 percent to about 80 percent can be achieved.
`As shown in FIGS. 3a–3c, the stator piece is then rolled
`using a rolling apparatus. A preferred rolling apparatus is a
`diacro roll form machine. FIGS. 3a–3c show the positions of
`the stator core preform and the rolling apparatus at various
`stages in the rolling process. The rolling apparatus has a
`mandrel 70, wheel 72 and pins 74 and 76. The mandrel 70
`is circular and has a diameter that is equal to the inner
`diameter (D in FIG. 5) of toroidal core 17. As shown in FIG.
`3d, the wheel 72 is circular and has flanges 75 that hold the
`side edges of the stator piece in place and prevent spiraling
`of the stator piece during rolling. For rolling, the linear stator
`core preform 20 is positioned in the rolling apparatus so that
`the poles 21 face mandrel 70, as illustrated in FIG. 3a.
`Wheel 72 then rolls around the circumference of mandrel 70,
`as illustrated in FIG. 3b. As wheel 72 rolls, the core preform
`is also rolled and is held in place with the mandrel 70 by the
`wheel 72 and pins 74, 76. When the wheel 72 substantially
`circumscribes the mandrel 70 and approaches pin 74, pin 74
`is removed and pin 76 holds the stator piece in contact with
`mandrel 70 at a position behind wheel 72, as shown in FIG.
`3c. Wheel 72 then rolls further to fully circumscribe the
`mandrel 70 and complete the rolling process.
`As shown in FIG. 4, the end surfaces 16, 19 of the rolled
`preform stator 20 are aligned to form a magnetically induc
`ible toroidal core 17 having a plurality of poles 21 thereon,
`and wire windings 15 which serve as conductors. To form
`the toroidal core, end surface 16 of the stator core preform
`20 is aligned and brought into contact with end surface 19
`by placing and clamping the stator core preform 20 in an
`injection mold cavity. The toroidal core is shaped like a
`toroid and has a rectangular vertical cross-section. The wire
`15 between the poles 21 is also aligned in the toroidal core
`17, following the curvature of the toroidal core 17. As a
`result, the wire 15 in the toroidal core 17 is taught. The wire
`is wound so that one set of three leads is terminated together
`to create the common, and the other end of the stator has
`three phases. The conductors induce or otherwise create a
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`plurality of magnetic fields in the core when electrical
`current is conducted through the conductors. In this
`embodiment, 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 a 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 encap
`sulates the toroidal core 17. Substantial encapsulation means
`that the body either entirely surrounds the toroidal core 17,
`or surrounds almost all of it except for minor areas of the
`stator that may be exposed. However, substantial encapsu
`lation means that the 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 ecapsulate a toroidal core. Preferred tem
`perature activation of 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 materials.
`The method of developing the monolithic body 42 com
`prises designing a phase change material to have a coeffi
`cient 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 where the body is in contact with different
`materials. 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 compo
`ments 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 or 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
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`between about 0.8×107° in?in” F. and about 1.2×107° in?in.”
`F. throughout the range of 0–250° F (When the measured
`CLTE of a material depends on the direction of
`measurement, the relevant CLTE for purposes of defining
`the present invention is the CLTE in the direction in which
`the CLTE is lowest.)
`The CLTE of common solid parts used in a motor are as
`follows:
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`Steel
`Aluminum
`Ceramic
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`0.8
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`12,12-polyamide, 6,12-polyamide, and polyamides contain
`ing aromatic monomers, polybutylene terephthalate, poly
`ethylene terephthalate, polyethylene napththalate, polybuty
`lene napththalate, aromatic polyesters, liquid crystal
`polymers, polycyclohexane dimethylol terephthalate,
`copolyetheresters, polyphenylene sulfide, polyacylics,
`poly propylene, polyethylene, poly a ce tals,
`polymethylpentene, polyetherimides, polycarbonate,
`polysulfone, polyethersulfone,