United States Patent [191
`Clark
`
`[54] DISCOIDAL DYNAMO-ELECTRIC
`MACHINE
`
`[75] Inventor: Peter Bruce Clark, Auckland, New
`Zealand
`
`[73] Assignee: Cadac Limited, Auckland, New
`Zealand
`
`424,332
`[21] Appl. No.:
`Jan. 28, 1994
`[22] PCI‘ Filed:
`PCT/NZ94/00005
`[86] PCI‘ No.:
`Apr. 24, 1995
`§ 371 Date:
`§ 102(e) Date: Apr. 24, 1995
`[87] PCI‘ Pub. No.: WO94/19859
`
`PCI‘ Pub. Date: Sep. 1, 1994
`Foreign Application Priority Data
`
`[30]
`
`Feb. 17, 1993 [NZ] New Zealand ......................... .. 245928
`May 6,1993 [NZ] New Zealand ......................... .. 247564
`
`[51] Int. Cl.6 .......................... .. H02K 1/22; H02K 21/12;
`H02K 1/12
`[52] US. Cl. ......................... .. 310/268; 310/156; 310/254
`[58] Field of Search .,. ................................ .. 310/154, 156,
`310/268, 261, 254, 179
`
`[56]
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`Hllllllllllll||||||||llllllllllllllllll'llllll|l||||l|||llllllll'lllllllll
`US00565L880A
`l
`5,656,880
`Aug. 12, 1997
`
`[11] Patent Number:
`[45] Date of Patent:
`
`4,228,384 10/1980 Arnold, Jr. et a1. .................. .. 318/254
`
`4,629,920 12/1986 Hermann ............................... .. 310/156
`
`4,633,149 12/1986 Welterlin ............................... .. 318/254
`
`4,677,335
`
`6/1987 Ueda et a1. ........................... .. 310/268
`
`4,710,667 1211987 Whitely ................................. .. 310/268
`
`4,820,949 4/1989 Mizobuchi et a1. .................... .. 310/90
`
`5,184,040
`5,396,140
`
`2/1993 Lim ................ ..
`3/1995 Goldie et a1.
`
`310/114
`.. 310/268
`
`Primary Examiner-—Steven L. Stephan
`Assistant Examiner-—Michae1 Wallace, Jr.
`Attorney, Agent, or Firm-Young & Thompson
`
`[57]
`
`ABSTRACT
`
`A discoidal dynamo-electric machineshas a discoidal stator
`carrying a number of meandering copper windings imbed
`ded in a substrate having a magnetic permeability of less
`than 20 relative to air, and a discoidal rotor mounted on a
`central shaft so that the rotor can be positioned close to and
`rotates in a plane parallel to that of the stator. The rotor has
`a circular array of permanent magnets mounted on a backing
`plate of mild steel, each of the magnets having a trapezoidal
`or a truncated sector of a circle shape, the magnets being
`closely spaced around the rotor to provide a series of closely
`apposed and alternating permanent magnetic poles.
`
`4,167,692
`
`9/1979 Sekiya et a1. ......................... .. 318/138
`
`16 Claims, 3 Drawing Sheets
`
`3030
`
`9/1/2
`
`BMW-1014
`Page 1 of 7
`
`

`

`
`
`BMW-1014
`Page 2 of 7
`
`

`

`US. Patent
`
`Aug. 12, 1997
`
`Sheet 2 0f 3
`
`5,656,880
`
`22.2 I‘ 202
`
`IMMIMMMMMMMMMMMMIIHMMWMMMMMMMIII
`
`-
`
`205
`
`205 A
`
`Q) N
`02
`
`Fig3
`
`BMW-1014
`Page 3 of 7
`
`

`

`U.S. Patent
`US. Patent
`
`Aug. 12, 1997
`Aug. 12, 1997
`
`Sheet 3 0f 3
`Sheet 3 of 3
`
`5,656,880
`5,656,880
`
`
`
`BMW-1014
`
`Page 4 of7
`
`BMW-1014
`Page 4 of 7
`
`

`

`1
`DISCOIDAL DYNAMO-ELECTRIC
`MACHINE
`
`TECHNICAL FIELD OF THE INVENTION
`
`This invention relates to the ?eld of dynamo-electric
`machines; particularly brushless direct-current electric
`machines (BDCMs) and more particularly to those BDCMs
`constructed in the pancake, or discoidal style.
`
`5
`
`BACKGROUND
`A BDCM type of electric motor (or generator) confers a
`number of advantages over prior-art slotted armature
`motors, such as deletion of the sliding contacts at a
`commutator, absence of cogging, lighter weight, and higher
`e?iciency. Most BDCMs are constructed in a pattern involv
`ing apposed (ie side by side) cylindrical surfaces between
`which the interaction of magnetic forces operating in a radial
`direction provides a torque. There is however a need for an
`efficient economical motor having a ?attened, discoidal
`shape.
`
`15
`
`OBJECT
`It is an object of the present invention to provide an
`improved discoidal dynamo-electric machine, or one which
`will at least provide the public with a useful choice.
`
`25
`
`STATEMENT OF THE INVENTION
`In one aspect the invention provides a discoidal dynamo
`electric machine having a discoidal stator and a discoidal
`rotor mounted on a central shaft so that the rotor can be
`positioned close to and rotate in a plane parallel to that of the
`stator, wherein the rotor has a circular array of permanent
`magnets thereon providing a series of closely apposed and
`alternating permanent magnetic poles.
`Preferably the rotor is made of iron or steel, or another
`ferromagnetic material.
`Preferably the windings meander on a repetitive series of
`radial paths, the number of such paths being preferably equal
`to the number of poles.
`Because the magnetic poles are closely spaced around the
`rotor it is preferred that there is an even number of between
`8 and 64 poles, in its most preferred form of the invention
`there are about 28 poles.
`In another aspect the invention provides a BDCM using
`ferrite magnets together with a relatively wide air gap
`between rotor and stator.
`In a third aspect this invention provides a pancake or
`discoidal BDCM in which the windings are upon or within
`a substrate having a magnetic permeability of less than 20,
`relative to air.
`In a related aspect a ferromagnetic material having a
`permeability of over 20 may be placed beneath the windings.
`Preferably this material is selected from a range including
`powdered ferrite, iron tape, iron wire, or iron sand.
`Preferably the magnets are strontium-ferrite and each has
`a trapezoidal or sector shape.
`In a related aspect a ferromagnetic material having a
`permeability of over 20 may be placed beneath the windings.
`Preferably this material is selected from the group compris
`ing powdered ferrite. iron or steel tape. iron or steel wire, or
`iron sand.
`
`35
`
`45
`
`55
`
`DRAWINGS
`These and other aspects of this invention, which should be
`considered in all its novel aspects, will become apparent
`
`65
`
`5,656,880
`
`2
`from the following description, which is given by way of
`example only, with reference to the accompanying drawings,
`in which:
`FIG. 1a: is an illustration of the face of a ?rst rotor for a
`preferred dynamoelectric machine.
`FIG. 1b: is an illustration of the face of a ?rst stator for
`use with the rotor of FIG. 1a.
`FIG. 2: is a sectional view on a radius through the rotor
`and stator of a motor of the present invention.
`FIG. 3: is a sectional view along a tangent cutting the
`magnet array, showing ?ux lines and windings for the rotor
`and stator of a motor in accordance with FIG. 2.
`FIG. 4: is a surface view of the stator of a 28-pole motor.
`FIG. 5: is a surface view of the rotor of a 28-pole motor.
`FIG. 6: is a surface view of part of a stator having
`magnetic-?eld sensors.
`First Embodiment—FlGS. 1-3
`This ?rst embodiment of a dynamo-electric machine will
`be described with reference to a brushless DC Motor com
`prising two disks in a stack, one-a stator (120, 205,
`303)——?xed to mountings (not illustrated) and the other—a
`rotor (100, 204, 305)—capable of rotation about its center
`on a shaft 201, which is preferably mounted on bearings 121,
`202.
`Generally there will be an array of windings 122, 301. 302
`placed on one face of the stator/?xed disk, and an array of
`closely spaced permanent magnets 102, 102' .
`.
`. will be
`placed on one face of the rotor. This arrangement avoids the
`need for wiping contacts to transfer electricity; however the
`comparatively lower rotational inertia of a disk carrying
`windings plus the possibility of providing a ?xed backing
`plate of a ferromagnetic substance having high permeability,
`to lead the ?ux lines more directly through the windings,
`may lead to further embodiment having a magnet array on
`a stator and windings on the rotor disk.
`In general the ferrite magnets 102 . . . 203, 307, and 308
`will be mounted as a circular array and presenting alternate
`poles on the exposed surface (as shown in FIG. 10) using
`preferably adhesive means on a substantially ?at plate of
`mild steel 100, 204, which will complete the magnetic
`circuit between one pole and its neighbours (as shown in
`FIG. 3—300 and in more detail at 306. Preferably the plate of
`mild steel will be ?rmly attached to the rotatable drive shaft
`201 of the motor.
`Preferably the permanent magnets of this invention are
`ferrite magnets. The optimum number of poles is believed to
`be 20, although a greater or lesser even integer number of
`poles may be preferred. For example a greater number may
`be preferred in the event that this motor is constructed with
`a wider diameter.
`Preferably each ferrite magnet is in the shape of a ?at
`tened cube, having one pair of elongated sides. Optionally
`each magnet may be provided with one or more fastening
`holes or engagement means, capable of engaging with
`corresponding members placed on the surface of the mild
`steel disk. Fastening means are not shown in the radial
`section 200.
`Preferably each ferrite magnet is shaped in the form of a
`truncated sector of a circle, as shown (102) in FIG. 1a,
`having an angle of 18 degrees between its sloping sides in
`the case of a 20-pole motor in order to maintain the preferred
`con?guration of motors of this type; namely closely apposed
`magnetic poles along the elongated sides of each magnet.
`Other angles will be preferred for other numbers of poles. If
`only rectangular magnets are available, the condition of
`
`BMW-1014
`Page 5 of 7
`
`

`

`5,656,880
`
`10
`
`3
`closely apposed magnetic poles may be approximated by
`increasing the number of poles.
`Preferably the ferrite magnets are magnetised across their
`wide faces. so that the entire exposed surface of a mounted
`magnet is either a North or a South pole. as shown in FIGS.
`la and 3.
`A second ?at plane (the stator) preferably composed of a
`rigid. non-conducting material (120, 205, 303) is provided to
`serve as a support for the windings. Preferably this material
`has a low magnetic permeability, less than 20 relative to air
`(where air is taken as =1), and is thick enough to separate the
`?elds generated by the windings from any nearby conduct
`ing or ferromagnetic substances in order to (a) minimize
`losses due to hysteresis and eddy currents, and (b) minimize
`losses due to unnecessarily high inductance. Windings may
`be attached to this surface by (for example) adhesives or
`embedment in grooves. In any case, the windings will
`preferably be potted in a substantially rigid matrix of a
`?ame-retardant plastics material (as 304). such as an epoxy.
`a polyurethane. or a silicone rubber. and any one of a number
`of commercial products (e.g. “ YNITE” (a trade mark of Du
`Pont)) designed for electric appliances may be selected.
`A preferred option for this type of motor is the use of a
`backing. behind the windings, of ferromagnetic material
`which serves to direct the lines of ?ux through the windings
`without much effect on their inductance. One preferred
`backing is shown as 205A in FIG. 2. representing a section
`through a number of turns of a 4 mm wide steel tape wound
`on itself outwards from near the center of the stator (like the
`turns of tape in an audio tape cassette). Optionally many
`turns of iron wire may be wound so as to occupy a
`comparable space. This ferromagnetic material is preferably
`moulded into the plastics matrix, so that it is held ?rmly and
`magnetostrictive noise is minimized
`Preferably the motor windings are wound in a three-phase
`con?guration, which may be star, delta. or remain as sepa
`rate windings depending on the preferred method for ener
`gisation of the windings. The windings are preferably Wound
`in copper wire. although other fabrication techniques such as
`stamping from a sheet. or primed-circuit techniques may be
`employed. A preferred winding con?guration is a rosette
`shape as per 122 in FIG. lb (where one turn of one phase is
`shown), in which the radius lines will generate a magnetic
`?eld capable of interaction with the ?ux emanating from the
`magnets. and the inner and outer perimeter lines are simply
`connections. Assuming three electrical phases, windings of
`each phase are offset by (120/pole number) degrees from the
`adjacent phase. FIG. 3 shows the winding pattern in more
`detail. 301 shows three groups (phases) of ingoing
`windings—qas wires-in section, and 302 shows three
`groups (phases) of outgoing windings. again in section.
`In order to sequence the energisation of the windings. in
`order to create a torque. a controller having solid-state
`switches is preferred. Such controllers are commonly used
`in motor systems employing the BDCM family and are
`well-known to those skilled in the relevant arts. and may be
`synchronised to the position of rotation by Hall-effect or
`other magnetic sensors. optical sensors. or more preferably
`by sensing the back-EMF voltages generated during motion
`in un-energised windings. Some applications including trac
`tion applications may use magnetic sensors such as Hall
`e?’ect sensors and FIG. 6 shows at 600 a part of a stator
`assembly, bearing three magnetic sensors at 601. 602. and
`603. Three sensors are usually su?icient. The sensors are
`65
`mounted in the shoulder section of the slots of the stator. A
`single turn of windings is shown as the dotted line 604. This
`
`55
`
`15
`
`20
`
`25
`
`35
`
`45
`
`4
`arrangement provides sensors at a spacing suitable for 60
`degree timing purposes. while sensors may be placed in
`alternate slots for 120 degree timing.
`A housing resistant to foreign bodies is preferred.
`although it is conceivable that a motor of this type could be
`integrated into the housing of an appliance such as--for
`example——a clothes washing machine. because it has been
`found that cylindrical topographies for motors of this type
`(our subset of BDCMs) may be constructed with a relatively
`large air gap between stator and rotor. and hence the amount
`of play found in an operating appliance such as a washing
`machine may not be excessive.
`Embodiment 2—28-pole motor
`This prototype embodies the features of the example
`above. but more closely speci?es some operating parameters
`suitable for a discoidal motor for use in a direct drive
`washing machine.
`The 28-pole motor has a stator comprising copper wind
`ings on a former, between a backing of (preferably) steel
`tape wound radially (like the tape in an audio cassette) and
`the magnet array on the rotor. Iron or steel wire is an optional
`alternative to the tape. The whole stator assembly is pref
`erably embedded in a therrnoplastics material such as
`“RYNITE”—a DuPont ?ame-retardant thermoplastic devel
`oped for electrical appliances.
`The rotor comprises a steel backing plate, 330 mm in
`diameter and on its “magnetic surface”—the surface
`apposed to the copper windings—it carries 28 strontium
`ferrite magnets. preferably of grade 8H. These are magne
`tised in place, after adhesive mounting, so that alternate
`north and south poles are produced on the surface and ?ux
`lines emanate from the surface and curve back into the
`nearest opposite pole. The thickness of each magnet is 9.5
`mm; the outside radius is 37 mm, the inside radius is 24 mm.
`and the radial length is 48 mm. Optionally the rotor may be
`provided with a turned rim to help prevent magnets from
`being displaced by centripetal forces. Also the magnet can
`be a one piece ring magnet or a number of closely spaced or
`contacting arc magnets.
`There is typically an air gap of 1.5 mm between the rotor
`and the stator. This is signi?cantly greater than the usual air
`gap to be found in an induction motor. and provides more
`tolerance during manufacture and for play or wear within
`bearings. Optionally this air gap may be increased—even
`during a cycle of operations-in order to decrease the
`coupling of the motor
`The characteristics of the windings are: Three-phase
`windings of 1 mm insulated copper wire. ten turns per pole.
`for a total of 280 turns. The line-to-line resistance is 2.3
`ohms; the line-to-line inductance is 4 millihenries. A full lap
`winding technique is used
`The characteristics of the magnetic ?eld may be inferred
`in a pragmatic way from the above Windings characteristics
`together with the performance details of the motor-its
`back-HVIF (k.V) is 130 volts per thousand RPM; and its
`torque coefficient is 1.2 Nm per A.
`This preferred embodiment is illustrated in FIG. 4.
`wherein 400 represents the winding array on a moulded
`stator, having ribs (e.g. 401) separating individual windings
`(402); there being three groups of windings per pole in this
`three-phase machine. The central aperture 403 is surrounded
`by part of the stator plate, bearing mounting holes.
`In FIG. 5. 500 depicts the rotor bearing 28 magnets 501.
`alternately presenting a south pole 502 and a north pole 503
`to the windings. 504 is a central aperture at which the rotor
`plate is fastened to the spindle of the motor (not shown).
`
`BMW-1014
`Page 6 of 7
`
`

`

`5,656,880
`
`20
`
`25
`
`30
`
`35
`
`40
`
`5
`Further variations on these embodiments include (but are
`not limited to) '(a) versions having a stator bearing non
`rotating windings located substantially symmetrically
`between two rotors. and optionally each rotor bears, adjacent
`to the stator, magnets having poles opposite to those of the
`opposing rotor, so that magnetic ?eld lines lie perpendicular
`to the windings, or (b) one rotor is a ferromagnetic substance
`that directs the magnetic ?eld of the magnets on the other
`rotor through the windings.
`Finally it will be appreciated that various other alterations
`or modi?cations may be made to the foregoing without
`departing from the scope of this invention as set forth in the
`following claims.
`I claim:
`1. A discoidal dynamo-electric machine having a discoi
`dal stator and a discoidal rotor mounted on a central shaft so
`that the rotor can be positioned close to and rotate in a plane
`parallel to that of the stator with a gap therebetween,
`a plurality of permanent magnetic poles mounted on or in
`a surface of the discoidal rotor facing the stator,
`said stator having a plurality of wound poles on or in a
`substrate of the stator, wherein a majority of said
`wound poles are positioned on or in that surface of the
`stator which faces said rotor so that the wound poles are
`adjacent said gap,
`and the permanent magnetic poles are closely spaced in
`the form of a circular array around the rotor surface
`such that there are short substantially semi-circular
`magnetic ?ux paths between adjacent permanent mag
`netic poles, said short magnetic ?ux paths extending in
`a region intersected by said majority of said wound
`poles whereby said majority of said wound poles
`intersect substantially all of the magnetic ?ux paths
`substantially at right angles thereto, said region having
`a magnetic permeability of less than 20 relative to air
`and being substantially non-conducting.
`2. A discoidal dynamo-electric machine as claimed in
`claim 1. wherein the substrate of the stator has a magnetic
`permeability of less than 20 relative to air.
`3. A discoidal dynamo-electric machine as claimed in
`claim 1, wherein there are no less than 8 and no more than
`64 permanent magnetic poles on said rotor.
`4. A discoidal dynamo-electric machine as claimed in
`claim 1, wherein there are about 28 permanent magnetic
`poles on said rotor.
`5. A discoidal dynamo-electric machine as claimed in
`claim 1, wherein the gap between said rotor and said stator
`is about 1.5 mm.
`_
`6. A discoidal dynamo-electric machine as claimed in
`claim 1, wherein the stator has an array of windings which
`meander on a repetitive series of radial paths, the number of
`such paths being equal to the number of permanent magnetic
`poles.
`7. A discoidal dynamo-electric machine as claimed in
`claim 1, wherein the windings are upon or within a substrate
`having a magnetic permeability of less than 20, relative to
`arr.
`
`45
`
`50
`
`6
`8. A discoidal dynamo-electric machine as claimed in
`claim 6 wherein the permanent magnetic poles are provided
`by a plurality of high strength magnets each shaped in the
`form of a truncated sector of a circle so that they maintain
`close spacing between adjacent magnets in the circular array.
`9. A discoidal dynamo-electric machine as claimed in
`claim 1, wherein the rotor is formed from a ferromagnetic
`material.
`10. A discoidal dynamo-electric machine as claimed in
`claim 1, wherein the rotor is formed from a mild steel plate.
`11. A discoidal dynamo-electric machine as claimed in
`claim 1, wherein said ferromagnetic material is selected
`from the group comprising powdered ferrite, iron or steel
`tape, iron or steel wire, and iron sand.
`12. A discoidal dynamo-electric machine having a discoi
`dal stator and a discoidal rotor mounted on a central shaft so
`that the rotor can be positioned close to and rotate in a plane
`parallel to that of the stator with a gap therebetween, a
`plurality of permanent magnetic poles mounted on or in a
`surface of the discoidal rotor facing the stator,
`said stator having a plurality of wound poles on or in a
`substrate of the stator, wherein a majority of said
`wound poles are positioned on or in that stu'face of the
`stator which faces said rotor so that the wound poles are
`adjacent said gap, and a ferromagnetic material having
`a permeability of over 20 relative to air is situated
`adjacent the wound poles,
`and the permanent magnetic poles are closely spaced in
`the form of a circular array around the rotor surface
`such that there are short magnetic ?ux paths between
`adjacent permanent magnetic poles, said relatively
`short magnetic ?ux paths between adjacent permanent
`magnetic poles, said short magnetic ?ux paths extend
`ing through a region intersected by said majority of said
`wound poles whereby said majority of said wound
`poles intersect substantially all of the magnetic ?ux
`paths substantially at right angles thereto.
`13. A discoidal dynamo-electric machine as claimed in
`claim 12. wherein there are no less than 8 and no more than
`64 permanent magnetic poles on said rotor.
`14. A discoidal dynamo-electric machine as claimed in
`claim 12, wherein there are about 28 permanent magnetic
`poles on said rotor.
`15. A discoidal dynamo-electric machine as claimed in
`claim 12, wherein the gap between the rotor and stator is
`about 1.5 mm.
`16. A discoidal dynamo-electric machine as claimed in
`claim 12, wherein the stator has an array of windings which
`meander on a repetitive series of radial paths, a number of
`such paths being equal to the number of permanent magnetic
`poles.
`
`BMW-1014
`Page 7 of 7
`
`