NIDEC and HONDA - Ex. 1002
`Nidec Corporation and American Honda
`Motor Co., Inc. - Petitioners
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`“Express Mail" mailing label number
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`EL 594 257 797 US
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`Date of Deposit:
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`March 5, 2003
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`Our Case No. 8864/33
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`IN THE UNITED STATES PATENT AND TRADEMARK OFFICE
`APPLICATION FOR UNITED STATES LETTERS PATENT
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`INVENTOR:
`
`GRIFFITH D. NEAL
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`TITLE:
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`ATTORNEYS:
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`STATOR ASSEMBLY MADE FROM A
`MOLDED WEB OF CORE
`SEGMENTS AND MOTOR USING
`SAME
`
`STEVEN P. SHURTZ
`REG. NO. 31,424
`BRINKS HOFER GILSON & LIONE
`P.O. BOX 10395
`CHICAGO, ILLINOIS 60610
`(312) 321-4200
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`STATOR ASSEMBLY MADE FROM A MOLDED WEB OF CORE
`SEGMENTS AND MOTOR USING SAME
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`REFERENCE TO EARLIER FILED APPLICATION
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`The present application is a continuation-in-part of Application Serial
`No. 09/798,511, filed March 2, 2001, and entitled Stator Assembly Made From
`A Plurality Of Toroidal Core Arc Segments And Motor Using Same, whichis
`hereby incorporated by reference.
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`FIELD OF THE INVENTION
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`The presentinvention relates generally to a stator assembly usedin a
`dynamoelectric machine such as a motoror a generator.
`It relates particularly
`to a spindle motor such as usedin a hard disc drive, and to the construction
`and arrangementof a stator assembly made fromaplurality of arc segments.
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`BACKGROUND OF THE INVENTION
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`Computers commonly usedisc drives for memory storage purposes.
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`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 bylaminating
`together stamped pieces of steel. These stamped piecesof 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 whichis 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 magnet3 andflux return ring 5 are attached to the disc support
`member 8. The stator 4 is separated from the base 2 using an insulator (not
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`shown) and attached to the base 2 using a glue. Distinct structures are
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`formed in the base 2 and the disc support member 8 to accommodatethe
`bearings 7. One endofthe shaft 6 is inserted into the bearing 7 positionedin
`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 mayalso beinserted into the
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`base 2.
`Eachof these parts mustbe fixed at predefined tolerances with respect
`to one another. Accuracyin these tolerancescan significantly enhance motor
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`performance.
`In operation, the disc stack is placed upon the hub. The stator
`windings are selectively energized and interact with the permanent magnetto
`cause a defined rotation of the hub. As hub 8 rotates, the head engagesin
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`reading or writing activities based upon instructions from the CPU in the
`computer.
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`Manufacturers of disc drives are constantly seeking to improve the
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`speed with which data can be accessed. To an extent, this speed depends
`uponthe 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
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`dimensional consistency between components leads to a smaller gap
`betweenthe stator 4 and the magnet3, producing more force, which provides
`more torque and enablesfaster acceleration and higher rotational speeds.
`The conventional method of forming stators has a numberof
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`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 piecesof steel, the grain
`orientation differs at different points around the circle. Compared from the
`radius line of the circle, the grain orientation is sometimes aligned along the
`radius, sometimes transverseto it, and mostly at a varying angle to the radius.
`The un-aligned grain structure of conventional stators causes the magnetic
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`flux values to differ in parts of the stator, and thus the motor does not have
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`consistent and uniform torque properties as it rotates.
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`Another drawbackwith using circular steel piecesis that, especially for
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`inward facing poles, it has beendifficult to wind the wire windings tightly
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`because of the cramped spaceto workinside of the laminated stator core.
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`The cramped working space creates a lower limit on the size of the stator and
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`thus the motor. The limited working space also results in a low packing
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`density of wire. The packing density of wire coiled around the poles affects
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`the amount of power generated by the motor.
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`Increasing packing density
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`increases the power and thus the efficiency of the spindle motor.
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`An important factor in motor design is to reduce stack up tolerancesin
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`the motor. Stack up tolerances reduce the overall dimensional consistency
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`between the components. Stack up tolerancesrefer to the sum of the
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`variation of all the tolerancesofall the parts, as well as the overall tolerance
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`that relates to the alignment of the parts relative to one another. One source
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`of stack up tolerances is from the circular stator body. Generally, the
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`thickness of rolled steel is not uniform across the width of the roll. Sometimes
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`the edges are thicker or thinner than the center.
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`In a stator made from
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`circular stamped pieces, the thicknesses of individual laminations are thus
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`different from one side to the other. When stacked together, this creates a
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`stack up tolerance problem. Furthermore, the circular stampingsleave a lot of
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`wasted steel that is removed and must be recycled or discarded.
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`Another important factor in motor design is the lowering of the
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`operating temperature of the motor.
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`Increased motor temperature affects the
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`electrical efficiency of the motor and bearinglife. As temperature increases,
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`resistive loses in wire increase, thereby reducing total motor power.
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`Furthermore, the Arhennius equation predicts that the failure rate of an
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`electrical device is exponentially related to its operating temperature. The
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`frictional heat generated by bearings increases with speed. Also, as bearings
`get hot they expand, and the bearing cages get stressed and maydeflect,
`causing non-uniform rotation, reducing bearinglife. This non-uniform rotation
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`causesa further problem oflimiting the ability of the servo system controlling
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`the read/write heads to follow data tracks on the magnetic media. One
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`drawbackwith existing motor designsis their limited effective dissipation of
`the heat, and difficulty in incorporating heat sinksto aid in heat dissipation.
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`In
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`addition, in current motors the operating temperatures generally increase as
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`the size of the motor is decreased.
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`Manufacturers have established strict requirements on the outgassing
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`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
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`attach components together, varnish used to insulate wire, and epoxy used to
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`protect steel laminations from oxidation.
`in addition to such outgassed materials, airborne particulate in a drive
`may lead to head damage. Also, airborne particulates in the disc drive could.
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`interfere with signal transfer between the read/write head and the media. To
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`reducethe effects of potential airborne particulate, hard drives are
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`manufactured to exacting clean room standards andair filters are installed
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`inside of the drive to reduce the contamination levels during operation.
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`An example of a spindle motor is shown in U.S. Patent No. 5,694,268
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`(Dunfield et a/.) (incorporated herein by reference). Referring to FIG. 5 ofthis
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`patent, a stator of the spindle motor is encapsulated with an overmold 42.
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`The overmolded stator 40 contains openings through which mounting pins 44
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`may be inserted for attaching the stator 200 to a base. U.S. Patent
`No. 5,672,972 (Viskochil) (incorporated herein by reference) also discloses a
`spindle motor having an overmolded stator. One drawback with the stators
`described in these patentsis this difficulty in winding wire on the poles.
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`Another drawbackis the height of the lamination stacks. Further, the
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`overmolds shownin these patents are not effective in dissipating heat or
`dampening somevibrations generated by energizing the stator windings.
`U.S. Patent No. 5,806,169 (Trago) (incorporated herein by reference)
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`discloses a methodoffabricating an injection molded motor assembly.
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`However, neither the Trago design nor the other prior art designs address the
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`problems of winding wire, variation in the thickness of steel used to make the
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`stator cores and the non-uniform grain structure in the steel compared to the
`magnetic flux in the stator during operation of the motor.
`Some of these problems have been addressed by motor manufacturing
`methods in which individual stator arc segments are made and woundwith
`wire to form poles, and these segments are then assembled to form a
`complete stator. While this process allows for higher packing density, it has
`several drawbacks. Somehowtheindividual segments have to be assembled
`and held in place to form the stator.
`In addition, the individual wires of the
`different poles have to be connected togetherfor the poles that are of the
`same phase. These numerouswires tend to get in the way during the
`assembly process, slowing down the manufacturing process.
`U.S. Patent No. 6,049,153 to Nishiyama describes the use of crimping
`or welding to attach segments together. This process deforms the steel and
`reducesthe level of magnetic flux produced by the laminations. The process
`also requires numerouswire interconnections when the poles are wound as
`discrete components, and it does not offer improvements in wire routing.
`U.S. Patent No. 5,729,072 to Hirano describes the use of welding or an
`adhesive to hold the segments together. A disadvantage of this approachis
`that the stator poles must be handled as separate elements during stator
`construction. This requires complicated assembly equipment and a slow
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`manufacturing process.
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`U.S. Patent No. 6,265,804 to Nitta describes the use ofplastic
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`insulation in combination with segmented stators. This approach does not
`improve on the problem of how to assemble andhold the individual segments
`in place, nor doesit aid in connecting the various wires.
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`U.S. Patent No. 6,167,610 to Nakahara describes a method of making
`a rotary motor wherea length of steel strip has thin portions between blocks
`of pole teeth. Wire is wound onthe pole teeth while the steel strip is straight.
`Later the thin sections are bentto allow the poles to form a stator. One
`problem with this design is that when the thin portions are bent, the stress on
`the steel reducesthe flux capacity of the connecting steel, forming the back
`iron. Also, the stamping of such a length of steel strip would be expensive
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`and result in large amount of scrap. Thus, a need exists for a method of
`making motors overcoming the aforementioned problems.
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`BRIEF SUMMARYOF THE INVENTION
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`A method of making stator assemblies has been invented which
`overcomes manyof the foregoing problems.
`In addition, unique stator
`assemblies and other components of a motor have been invented.
`In one
`aspect, the invention is a stator assembly comprising a plurality of discrete
`stator segments eachat least partially encased with a phase change material,
`wherein the phase change material also comprises a bridge between adjacent
`segmentsto link adjacent segmentsinto a continuousstrip; and the linked
`stator segments being arranged and secured together to form the stator
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`assembly.
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`In a second aspect, the invention is a combination of stator arc
`segments anda flexible carrier used to link said stator arc segments during a
`winding operation comprising: a) a plurality of stator arc segments; and b) a
`phase change material constituting said flexible carrier adhered to the stator
`arc segments which links said segments in a uniform and predetermined
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`position with respect to one another.
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`In another aspect the invention is a method of making a stator
`assembly comprising: a) providing at least two stator arc segments linked
`together by a phase change material and each constituting a pole and having
`a first side surface and a second side surface; b) winding wire on the poles; c)
`aligning said stator arc segments to form a toroidal core, wherein each said
`side surface of one segmentis in contact with an opposing side surface of
`another segment; and d) substantially encapsulating said toroidal core with a
`monolithic body of phase change material to form said stator assembly.
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`In another aspect the invention is a method of making a stator
`assembly comprising: a) providing at least two stator arc segmentslinked
`together by a phase change material and each providing a pole and having a
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`first side surface and a second side surface; b) winding wire on each pole of
`each arc segment; c) aligning said stator arc segments to formatoroidal core,
`wherein each said side surface of one segmentis in contact with an opposing
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`side surface of another segment; and d) placing a retaining member on the
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`exterior of the toroidal core to unitize the structure.
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`In yet another aspect, the invention is a series of discrete stator
`segments each substantially encapsulated with, and linked together by
`bridges made from, an injection molded thermoplastic material.
`With the unique linked but discrete segment assemblies, wire can be
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`wound around the poles with a high packing density, yet at the same time the -
`segments can be maintainedin their proper order so that one continuous piece
`of wire can be used to wind all poles in the same series or phase, makingit
`unnecessary to later connect wires from individual windings to one another. The
`invention provides the foregoing and other features, and the advantagesof the
`invention will become further apparentfrom the following detailed description of
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`the presently preferred embodiments, read in conjunction with the
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`accompanying drawings. The detailed description and drawings are merely
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`illustrative of the invention and do notlimit the scope of the invention, which is
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`defined by the appendedclaims and equivalents thereof.
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`BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS
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`FIG. 1 is an exploded, partial cross-sectional and perspective view of a
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`conventional prior art high speed motor.
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`FIG. 2 is perspective view of a stator arc segmentbeing loaded into an
`injection mold priorto injecting a phase change material to make a limited
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`series of stator arc segments of the present invention.
`FIG. 3 is a perspective, partial cross-sectional view of an encapsulated
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`stator arc segmentof FIG. 2.
`FIG. 4 is a perspective view of the encapsulated stator arc segmentof
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`FIG. 2.
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`FIG. 5 is a perspective view of a series of encapsulated stator arc
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`segments of FIGS. 2-4 linked together by a thermoplastic webbing.
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`FIG. 6 is a perspective view of the series of stator arc segments of
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`FIG. 5 during wire winding.
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`FIG. 7 is a perspective view of an injection molded stator assembly
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`using the linked serial of webbed stator arc segments of FIG. 6.
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`FIG. 8a is a cross-sectional view of a toroidal core made from the
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`linked series of stator arc segments after the wire winding shownin FIG. 5 in
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`an injection mold assembly, prior to injecting a phase change material.
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`FIG. 8b is a cross-sectional view of the toroidal core of FIG. 8a in an
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`injection mold assembly after injecting a phase change material, resulting in
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`the stator assembly of FIG. 7.
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`FIG. 9 is an exploded, partial cross-sectional and perspective view of a
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`motor using the encapsulated webbedstator of FIG. 7.
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`FIG. 10 is a perspective view of a stator assembly of a second
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`embodimentof the present invention using a steel bandto unitize the webbed
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`stator arc segments.
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`DETAILED DESCRIPTION OF THE DRAWINGS AND PREFERRED
`EMBODIMENTSOF THE INVENTION
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`A preferred embodiment of a motor of the present invention and
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`portions of the motorat different stages of manufacture are shownin FIGS. 2-
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`7 and 9. The spindle motor 100 (FIG. 9) is designed for rotating a disc or
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`stack of discs in a computer hard drive. Motor 100 is formed by using an
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`injection molded stator assembly 40, that is formed by injection molding a
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`plurality of stator arc segments 20 (FIG. 2) aligned to form a toroidal core 17
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`(FIG. 7). Although the embodiment described here usesindividual arc
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`segments, oneof ordinary skill in the art will understand that groups of two,
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`three or any greater numberof arc segments may be used. The preferred
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`motor of the present invention may be smailer, has a grain structure that is
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`more uniformly aligned, and allows for greater packing density of wire and
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`reduces waste of steel in the manufacturing process, as compared with
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`conventional motors, thereby increasing power and reducing stack up
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`tolerances and manufacturing costs and producing other advantages
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`discussed below.
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`Referring to FIG. 2, a stator arc segment 20is first constructed, using
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`steel laminations 11. The stator arc segment 20 is made of steel pieces that
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`are stamped out of rolled steel. The stamped steel pieces are arc segments,
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`but also have a pole 21 extending inwardly or outwardly depending on
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`whether the rotor is inside or surrounds the stator.
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`In the embodiment shown
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`in FIG. 2, the pole 21 is shown extending inwardly. The stamped pieces are
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`then coated with encapsulating material 22 which provides electrical insulation
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`and laminates the pieces together to form a stator arc segment 20, and links
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`other arc segments into a continuous strip via webbing 23.
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`The encapsulating material 22 is preferably formed of a phase change
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`material, meaning a material that can be used in a liquid phase to envelope
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`the stator, but which later changes to a solid phase. There are two types of
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`phase change materials that will be most useful in practicing the invention:
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`temperature activated and chemically activated. A temperature activated
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`phase change material will become molten at a higher temperature, and then
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`solidify at a lower temperature. However, in order to be practical, the phase
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`change material must be molten at a temperature that is low enough thatit
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`can be used to encapsulate a toroidal core. Preferred phase change
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`materials will be changed from a liquid to a solid in the range of about 200 °F
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`to about 700 °F, more preferably in the range of about 550 °F to about 650 °F.
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`The most preferred temperature activated phase change materials are
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`thermoplastics. The preferred thermoplastic will become molten at a
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`temperature at whichit is injection-moldable, and then will be solid at normal
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`operating temperatures for the motor. An example of a phase change
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`material that changes phases due to a chemical reaction, and which could be
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`used to form the body, is an epoxy. Other suitable phase change materials
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`may beclassified as thermosetting materials.
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`As shownin FIG. 2 the segments 20 can be placed in a multi-cavity
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`mold 28 to increase productivity.
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`In the preferred embodimentthe individual
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`laminations 11 making up the segments are not interconnected but loosely
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`stacked together before insertion into the mold 28. After the thermoplastic
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`solidifies, the overmolded segments are ejected from their cavities. New
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`laminations are inserted into the cavities and the process repeats.
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`In the
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`preferred embodiment, a continuous strip of segments is formed bylinking the
`webbing from successive molding operation. This is done by designing the
`tool to insert a section of the plastic webbing of the outermost segment
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`molded in the prior cycle with the new laminations to be molded. When the
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`plastic encapsulates the new segments it can mechanically lock with or,
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`depending upon design, re-melt, the webbing from the prior cycle, thus
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`making a continuous strip, as shown in FIG. 5. The series has segments 20
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`with poles 21A, 21B and 21C arranged next to one another as theywill be in
`the finished stator assembly.
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`The stator arc segments 20 are preferably molded into a continuous
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`In the
`strip where the webbing acts as a carrier to link the segments together.
`preferred embodiment the encapsulating material 22 forms wire retaining
`flanges 24 to prevent wire from slipping off the pole.
`In a preferred
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`embodiment, winding posts 25 as well as webbing 23 allow orientation of wire
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`as it transfers across multiple poles.
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`By precisely aligning the stator arc segments 20, the webbing 23 can
`also be used to guide the wire between commonphasepoles, thus
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`eliminating the need for interconnections commonly used on segmented
`stator motors. This greatly enhancesthe efficiency for winding wire 15 around
`the poles 21 and significantly reducesthe cost.
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`The webbing can be deflected to allow the gap between adjoining
`poles to be increased as is shownin FIG. 6. This allows wire 15 to be wound
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`aroundthe poles 21 of the stator arc segments 20 using a fly winder 34 that
`has a set of needles 35. The wire 15 is wound around one pole 21 and is
`then wound around anotherpole 21 in its phase until all poles 21 in the same
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`phase are wound with the samewire 15. Poles 21 in other phases are also
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`similarly wound. Having only arc segments, rather than a full toroidal core,
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`and spreading the spacing betweenthe adjoining seqments for needle 35 to
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`wind wire 15 around poles 21, allows a wire packing density of more than 80
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`percent to be achieved.
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`A length of connected stator segments 20 corresponding to the number
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`of poles 21 required to produce the motor are cut from the continuousstrip.
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`The strip is then rolled into a magnetically inducible toroidal core 17 having a
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`plurality of poles 21 thereon, and wire windings 15 which serve as conductors.
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`To form the toroidal core 17, a side surface 16 of each stator arc segment 20
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`is aligned and broughtinto contact with a corresponding side surface of
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`anotherstator arc segment 20.
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`In certain embodiments where a reduction in
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`eddy currents is desirable, it may be preferable to separate faces 16. This
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`could be done by usinga thin film of encapsulation material 22 over the side
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`surfaces 16, or the edges 19 of the insulator end surface (FIG. 4) could be
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`usedto create the gap. The wire 15 between the poles 21 of different stator
`arc segments20is also alignedin the toroidal core 17, following the arcof the
`stator arc segments 20. Asa result, the wire in the toroidal core 17 is taught.
`As shownin FIG. 7, the toroidal core 17 is then encapsulatedin 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. Wires 44 extend out of the
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`body 42 for connection to the power source used to supply the motor.
`Substantial encapsulation means that the body 42 either entirely surrounds
`the toroidal core 17, or surrounds almostall of it except for minor areas of the
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`toroidal core 17 that may be exposed. However, substantial encapsulation
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`means that the body 42 and toroidal core 17 arerigidly fixed together, and
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`behave as a single componentwith respect to harmonic oscillation vibration.
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`The preferred method of developing the monolithic body 42 comprises
`designing a phase change material to have a coefficient of linear thermal
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`expansion such that the phase change material contracts and expands at
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`approximately the same rate as the metal laminations of the toroidal core 17.
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`For example, the preferred phase change material should have a CLTEof
`between 70% and 130% of the CLTEof the core of the stator. The phase
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`change material should have a CLTEthat is intermediate the maximum and
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`minimum CLTE of the toroidal core and other motor components where the
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`bodyis in contact with those other components and they are made of a
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`different material than the core. Also, the CLTE’s of the body and toroidal
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`core should match throughout the temperature range of the motor during its
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`operation. An advantage of this methodis that a more accurate tolerance
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`may be achieved between the body and the components of the toroidal core
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`because the CLTE of the body matches the CLTEofthe toroidal core
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`components more closely. Most often the toroidal core componentswill be
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`metal, and most frequently steel and copper. Other motor parts are often
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`made of aluminum andsteel.
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`Most thermoplastic materials have a relatively high CLTE. Some
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`thermoplastic materials may have a CLTE at low temperatures that is similar
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`to the CLTE of metal. However, at higher temperatures the CLTE does not
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`match that of the metal. A preferred thermoplastic material will have a CLTE
`of less than 2 x 10°in/in/°F, more preferably less than 1.5 x 10°in/in/°F,
`throughout the expected operating temperature of the motor, and preferably
`throughout the range of 0-250°F. Most preferably, the CLTE will be between
`about 0.8 x 10° in/in/°F and about 1.2 x 10°in/in/°F throughout the range of
`0-250°F. (When the measured CLTE of a material depends onthe direction
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`of measurement, the relevant CLTE for purposesof defining the present
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`invention is the CLTE in the direction in which the CLTE is lowest. However,
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`if a material has a rate of expansion in one direction that is more than five
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`times greater than the expansionrate in one of the other directions, then the
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`CLTEfor purposesof defining the present invention is average of the CLTEs
`in each of the three X, Y and Z directions.
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`The CLTE of common solid parts used in a motorare as follows:
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`Steel
`Aluminum
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`Ceramic
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`23°C
`0.5
`0.8
`
`0.3
`
` (x10°in/in/°F)
`
`250°F
`0.8
`1.4
`
`0.4
`
`20
`
`25
`
`30
`
`14
`
`14
`
`

`

`
`
`-13-
`
`Of course,if the motor is designed with two or moredifferentsolids,
`such as steel and aluminum components, the CLTE of the phase change
`material would preferably be one that was intermediate the maximum CLTE
`
`and the minimum CLTE ofthe different solids, such as 0.65 in/in/°F at room
`temperature and 1.1 x10°in/in/°F at 250°F.
`
`Onepreferred thermoplastic material, Konduit OTF-212-11, which
`includes aluminum oxide asa filler at level of about 55%, was madeinto a
`thermoplastic body and tested forits coefficient of linear thermal expansion by
`a standard ASTMtest method.
`It was found to have a CLTEin the range of —
`30 to 30°C of 1.09x10°in/in/°F in the X direction and 1.26x10°in/in/°F in both
`the Y and Z directions, and a CLTEin the range of 100 to 240°C of 1.28x10°
`in/in/°F in the X direction and 3.16x10°in/in/°F in both the Y and Z directions.
`(Hence, the relevant CLTEsfor purposesof defining the invention are
`1.09 x 10° in/in/°F and 1.28 x 10° in/in/°F.) Another similar material, Konduit
`PDX —0-988, was found to have a CLTEin the range of —30 to 30°C of
`1.1x10°infin/°F in the X direction and 1.46x10°in/in/°F in both the Y and Z
`directions, and a CLTEin the range of 100 to 240°C of 1.16x10°in/in/°F in
`the X direction and 3.4x10°in/in/°F in both the Y and Z directions. By
`contrast, a PPS type polymer, (Fortron 4665) waslikewise tested. Whileit
`had a low CLTEin the range of —30 to 30°C (1.05x10°in/in/°F in the X
`direction and 1.33x10°in/in/°F in both the Y and Z directions), it had a much
`higher CLTEin the range of 100 to 240°C (1.94x10°in/in/°F in the X direction
`and 4.17x10°in/in/°F in both the Y and Z directions).
`In addition to having a desirable CLTE, the preferred phase change
`materialwill also have a high thermal conductivity. A preferred thermoplastic
`material will have a thermal conductivity of at least 0.4 watts/meter°K using
`ASTMtest procedure 0149 and tested at room temperature (23°C).
`In the present embodiment, the phase change material used to make
`the body 42is preferably a thermally conductive but non-electrically
`conductive plastic.
`In addition, the plastic preferably includes ceramicfiller
`particles such as aluminum oxide or boron nitride that enhance the thermal
`conductivity, while reducing the coefficient of linear thermal expansion of the
`
`10
`
`15
`
`20
`
`25
`
`30
`
`15
`
`15
`
`

`

`-14-
`
`plastic. Thefiller will preferably comprise about 30% or more of the phase
`change material, more preferably about 45% or more, and most preferably
`about 55% or more. A preferred form of plastic is polypheny! sulfide (PPS)
`sold under the tradename “Konduit” by LNP. Grade OTF-212-11 PPSis
`particularly preferred, using a roughly 55 weight percentage of aluminum
`oxide asa filler. Examples of other suitable thermoplastic resins include, but
`are notlimited to, thermoplastic resins such as 6,6-polyamide, 6-polyamide,
`4,6-polyamide, 12,12-polyamide, 6,12-polyamide, and polyamidescontaining
`aromatic monomers, polybutylene terephthalate, polyethylene terephthalate,
`polyethylene napththalate, polybutylene napththalate, aromatic polyesters,
`liquid crystal polymers, polycyclohexane dimethylol terephthalate,
`copolyetheresters, polyphenylenesulfide, polyacylics, polypropylene,
`polyethylene, polyacetals, polymethylpentene, polyetherimides,
`polycarbonate, polysulfone, polyethersulfone, polyphenylene oxide,
`polystyrene, styrene copolymer, mixtures and graft copolymers of styrene and
`rubber, and glass reinforced or impact modified versions of such resins.
`Blendsof these resins such as polyphenylene oxide and polyamide blends,
`and polycarbonate and polybutylene terephthalate, may also be usedinthis
`invention.
`
`Of course, two different phase change materials can be usedfor the
`encapsulating material 22 and the body 42. The encapsulating material 22
`will normally be a reaily stiff, high temperature thermoplastic, whereas, the
`body 42 will normally be made of a more compliant thermoplastic.
`As shownin FIG. 8a, to encapsulate the toroidal core 17 and form body
`42, the series of stator arc segments with windings already appliedisfirst
`clamped andheld 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 segments during molding.
`It is likely that more than the four pins 61
`shownin FIG. 8a will be needed to do this. Molten phase-change materialis
`theninjected 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
`
`10
`
`15
`
`20
`
`25
`
`30
`
`16
`
`16
`
`

`

`
`
`-15-
`
`retract as shownin FIG. 8b, and the phase change materialfills in the area
`vacated asthe pins retract. The phase change materialis 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
`aspectratio of the toroidal core 17. Preferably the injection molding operation
`is controlled in the manner described in U.S. Patent Application Serial No.
`09/983,002, filed October 17, 2001, which is hereby incorporated by reference
`in its entirety.
`
`10
`
`15
`
`20
`
`The injection molded stator assembly 40 is then used to construct the
`rest of the motor 100 (FIG. 9). The 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 shownin FIG. 9, 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 103is fixed to the inside of the
`hub 108 onaflange so asto be in operable proximity to the stator assembly.
`The magnet 103 is preferably a permanent magnet, as described below.
`Referring to FIG. 9, 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 46 co