(12) United States Patent
`Nitta et al.
`
`US00626.5804B1
`(10) Patent No.:
`US 6,265,804 B1
`(45) Date of Patent:
`*Jul. 24, 2001
`
`(54) ELECTRIC MOTOR WITH SPLIT STATOR
`CORE AND METHOD OF MAKING THE
`N
`N
`SAME
`
`(56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`(75) Inventors: Isamu Nitta, Yokahama; Kinya
`Hayashi, Toki, both of (JP)
`(73) Assignee: Kabushiki Kaisha Toshiba, Kanagawa
`(JP)
`
`(*) Notice:
`
`4,015,154 * 3/1977 Tanaka et al. ......................... 310/42
`4,365,180 * 12/1982 Licata et al. .....
`. 310/216
`4,665,329 * 5/1987 Raschbichler ...
`.... 310/13
`4,672,253 * 6/1987 Tajima et al. ....
`. 310/269
`4,818,911 * 4/1989 Taguchi et al. ...................... 310/259
`4,990,809 * 2/1991 Artus et al. .......................... 310/192
`5,592,731 * 1/1997 Huang et al. ...
`... 29/596
`This patent issued on a continued pros- sº : | Nº. et ! i.
`----- sº
`ecution application filed under 37 CFR
`2--> < 2
`&l?lå?å €l &ll.
`...................
`1.53(d), and is subject to the twenty year
`5,912,515 * 6/1999 Ackermann et al. .............. 310/67 R
`patent term provisions of 35 U.S.C.
`FOREIGN PATENT DOCUMENTS
`154(a)(2).
`4-29536
`1/1992 (JP).
`Subject to any disclaimer, the term of this
`* cited by examiner
`patent is extended or adjusted under 35
`Primary Examiner—Elvin Enad
`U.S.C. 154(b) by 0 days.
`Assistant Examiner—Dang Dinh Le
`(74) Attorney, Agent, or Firm—Pillsbury Winthrop LLP
`(57)
`ABSTRACT
`An electric motor includes a rotor and a stator including a
`plurality of unit cores each of which has two ends. The unit
`cores are disposed so that the ends of each unit core are
`adjacent to the ends of the neighboring unit cores respec
`tively. Each unit core includes a yoke section and a plurality
`of salient poles which are integral with the yoke section and
`on which windings are wound respectively. Adjacent por
`tions of the unit cores are selected so that magnetic fluxes
`passing through the respective adjacent portions are sub
`stantially the same.
`
`(21) Appl. No.: 09/391,450
`(22) Filed:
`Sep. 8, 1999
`(30)
`Foreign Application Priority Data
`Sep 8, 1998 (JP) ................................................. 10–253716
`Dec. 22, 1998 (JP) ...
`.... 10-364401
`Aug. 17, 1999
`(JP) ................................................. 11–230540
`(51) Int. Cl." .............................. H02K 1/12; H02K 1/06;
`H02K 1/00; H02K 1/04
`(52) U.S. Cl. .......................... 310/259; 310/217; 310/193;
`310/43
`(58) Field of Search ..................................... 310/269, 254,
`310/258, 259, 216, 217, 218, 179, 185,
`193, 43, 45; 29/596
`
`
`
`12 Claims, 14 Drawing Sheets
`
`NIDEC and HONDA - Ex. 1012
`Nidec Corporation and American Honda
`Motor Co., Inc. - Petitioners
`
`1
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`U.S. Patent
`US. Patent
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`Jul. 24, 2001
`Jul. 24, 2001
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`F I G. 1
`FIG.
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`2
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`U.S. Patent
`US. Patent
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`Jul. 24, 2001
`Jul. 24, 2001
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`Sheet 2 of 14
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`US 6,265,804 B1
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`F I G. 2
`FIG. 2
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`U.S. Patent
`US. Patent
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`Jul. 24, 2001
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`F I G. 3
`FIG. 3
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`U.S. Patent
`US. Patent
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`FIG. 4
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`U.S. Patent
`US. Patent
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`Jul. 24, 2001
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`F I G. 1 1
`FIG. 11
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`US 6,265,804 B1
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`1
`ELECTRIC MOTOR WITH SPLIT STATOR
`CORE AND METHOD OF MAKING THE
`SAME
`
`BACKGROUND OF THE INVENTION
`
`1. Field of the Invention
`
`This invention relates to an electric motor provided with
`a split stator core including a plurality of circumferentially
`disposed unit cores and a method of making such a motor.
`2. Description of the Prior Art
`For the purpose of effective utilization of steel material,
`the prior art has provided an annular split stator core formed
`by disposing a plurality of circumferentially split unit cores
`into a generally circularly or squarely annular configuration.
`More specifically, when annular steel sheets which are to be
`stacked into a stator core are punched out of steel sheets,
`portions of each steel sheet outside and inside the annular
`configuration are left unused. The above-mentioned annular
`split stator core provided by the prior art is directed to a
`reduction in such unused portions of the steel sheets.
`However, a location of portions of the unit cores adjacent
`to each other is selected at random. This results in unbalance
`
`in magnetic attractive forces acting between the unit cores,
`whereupon vibration and noise are produced.
`Each of a number of steel sheets stacked together into a
`unit core is formed by punching a silicon steel sheet having
`a surface treated for electrical insulation by a press. The
`punching sometimes results in warpage and/or burrs in ends
`of the silicon steel sheet. In a stator core formed by annularly
`disposing a plurality of unit cores, when the unit cores
`adjacent to each other are displaced in the direction of stack
`of the steel sheets or when one or more steel sheets have the
`
`warpage and/or burrs, the steel sheets of each unit core are
`electrically short-circuited by the ends of the steel sheets of
`the other unit core. This results in eddy currents flowing in
`the direction of stack of steel sheets in the unit core, so that
`an iron loss is increased.
`
`SUMMARY OF THE INVENTION
`
`Therefore, an object of the present invention is to provide
`an electric motor in which the unbalance in the magnetic
`attractive forces acting between the unit cores can be
`restrained so that the vibration and noise are prevented, and
`a method of making the motor.
`Another object is to provide an electric motor which is
`provided with a stator core including a plurality of unit cores
`and in which the iron loss can be reduced.
`
`The present invention provides an electric motor com-
`prising a rotor and a stator including a plurality of unit cores
`each of which has two ends. The unit cores are disposed so
`that the ends of each unit core are adjacent to the ends of the
`neighboring unit cores respectively. Each unit core includes
`a yoke section and a plurality of salient poles which are
`integral with the yoke section and on which concentrated
`windings are wound. In this construction, each unit core is
`disposed so that the yoke section thereof is adjacent to the
`yoke sections of the neighboring unit cores and so that the
`salient poles thereof are separate from the salient poles of the
`neighboring unit cores. Further,
`the salient poles are
`arranged circumferentially with a regular pitch. Further, a
`number of the salient poles of each unit core is equal to a
`number of phases of the windings multiplied by any integer.
`Additionally, each of the portions of the unit cores adjacent
`to each other is set so as to assume an angular position where
`a multiple obtained by multiplying a pitch angle of the
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`salient poles agrees with a multiple obtained by multiplying
`a pitch angle of magnetic poles of the rotor.
`Upon excitation of the windings of the above-described
`motor, a rotating magnetic field is generated so that the rotor
`is rotated. An amount of magnetic flux passing through each
`yoke section changes momentarily as the rotor is rotated.
`However, when a plurality of salient poles are provided so
`as to correspond to each of the phases, the yoke sections of
`the stator core have at an interval of a predetermined angle
`portions where amounts of magnetic flux passing there-
`through become the same. In the present
`invention,
`the
`number of salient poles of each unit core is determined so
`that the interval of the predetermined angle coincides with
`the adjacent portions of the unit cores. Accordingly, the
`amounts of magnetic flux passing through the respective
`adjacent portions of the unit cores become approximately
`the same although changing momentarily. Consequently,
`when the adjacent portions of the unit cores are located so
`as to correspond to positions where the magnetic fluxes
`passing the respective yoke sections are substantially the
`same, the magnetic attractive forces acting between the unit
`cores can be balanced to be canceled, whereupon occurrence
`of the vibration and noise due to the magnetic attractive
`forces can be prevented.
`Each unit core preferably includes the salient poles the
`number of which is represented as CM(Nt/CD(Nt, Np), Nf)
`where CM(A, B) is a common multiple of integers A and B,
`CD(A, B) is a common divisor of integers A and B, Nt is a
`total number of salient poles of a stator, which is equal to or
`larger than 2, Np is a total number of magnetic poles of a
`rotor, which is equal to or larger than 2, and Nf is the number
`of winding phases.
`In a case where the positions where the magnetic fluxes
`passing through the yoke sections are substantially the same
`are obtained when a rotor used With the above-described
`
`stator has a plurality of magnetic poles, a total number of
`magnetic poles of the rotor is preferably equal to the number
`of unit cores multiplied by any positive number, in addition
`to the condition that the number of salient poles of each unit
`core is equal to the number of winding phases multiplied by
`any positive integer.
`The number of unit cores is obtained when a divisor
`
`common to the above-mentioned total numbers Nt and Np is
`found. Accordingly, when the total number Np is divided by
`the number of unit cores, the least number of salient poles
`that can be provided on a single unit core is obtained.
`Accordingly, the number of salient poles of each unit core
`can be obtained from a multiple common to the least number
`of salient poles and the total number Nf of winding phases.
`The salient poles preferably have different shapes of distal
`ends and arranged in a pattern in which said salient poles
`having the different shapes of distal ends adjoin each other,
`the pattern being repeated circumferentially. The number of
`the salient poles of each unit core is equal to a common
`multiple to a number of the distal end shapes of the salient
`poles and the number of winding phases.
`In the above-described arrangement pattern of the salient
`poles, the arrangement pattern of salient poles of each unit
`core needs to correspond to those in the adjacent unit cores
`in addition to the condition that the number of salient poles
`of each unit core is equal to the number of winding phases
`multiplied by any positive integer. This is met when the
`number of salient poles is a common multiple to the number
`of types of distal ends of the salient poles and the number of
`winding phases. In this case, the multiple is preferably a
`least common multiple.
`
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`US 6,265,804 B1
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`3
`The invention also provides an electric motor comprising
`a rotor and a stator core including a plurality of unit cores
`each of which has two ends. The unit cores are disposed so
`that the ends of each unit core are adjacent to the ends of the
`neighboring unit cores with electrically insulating clearance
`maintaining members being interposed therebetween,
`respectively. Each unit core is formed by stacking a number
`of steel sheets each of which has a surface to which a
`treatment for electrical insulation is applied. Since the ends
`of the adjacently disposed unit cores are separated from each
`other by the clearance maintaining members, the ends can be
`insulated from each other such that eddy current loss is
`reduced.
`In a preferred form, the clearance between the ends of
`each unit core and the neighboring unit cores is set to be in
`a range between 0.01 and 0.15 mm.
`BRIEF DESCRIPTION OF THE DRAWINGS
`Other objects, features and advantages of the present
`invention will become clear upon reviewing the following
`description of the preferred embodiments, made with refer
`ence to the accompanying drawings, in which:
`FIG. 1 is a plan view of a stator core of an electric motor
`of a first embodiment in accordance with the present inven
`tion;
`FIG. 2 is a plan view of a stator core and a rotor of an
`electric motor of a second embodiment in accordance with
`the invention;
`FIG. 3 is a plan view of an assembly of a rotor and stator
`core of an electric motor of a third embodiment in accor
`dance with the invention;
`FIG. 4 is a view similar to FIG. 3, showing a modified
`form of the third embodiment;
`FIG. 5 is an enlarged transverse sectional plan view of
`connecting portions of unit cores in an electric motor of a
`fourth embodiment in accordance with the invention;
`FIG. 6 is a plan view of the motor of the fourth embodi
`ment;
`FIG. 7 is an enlarged longitudinal sectional plan view of
`the connecting portions of the motor shown in FIG. 6;
`FIG. 8 is a graph showing the relationship between the
`clearance between the ends of the unit cores and the iron
`loss;
`FIG. 9 is a transverse sectional plan view of an electric
`motor of a fifth embodiment in accordance with the inven
`tion;
`FIG. 10 is a partially enlarged transverse sectional plan
`view of the motor shown in FIG. 9;
`FIG. 11 is a transverse sectional plan view of a molding
`die, showing a method of making the motor shown in FIG.
`9;
`FIGS. 12 to 15 are plan views of an electric motor of a
`sixth embodiment in accordance with the invention, show
`ing the steps of making the motor;
`FIG. 16 is an exploded perspective view of the stator and
`holding frames employed in the motor of the fourth embodi
`ment;
`FIG. 17 is a sectional view taken along line 17—17 in
`FIG. 16; and
`FIG. 18 is a sectional view taken along line 18—18 in
`FIG. 16.
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`A first embodiment of the invention will be described with
`reference to FIG. 1. The invention is applied to an electric
`
`4
`motor of the inner rotor type in which a rotor is disposed
`inside a stator. Referring to FIG. 1, a split stator core 1 of the
`motor is shown. The split stator core 1 comprises three unit
`cores 2. Each unit core 2 is made by stacking a number of
`punched silicon steel sheets. Outer circumferential faces of
`ends of each unit core 2 adjacent to ends of the other unit
`cores 2 are welded together to be connected to each other. As
`a result, each end of each unit core is adjacent to one of the
`ends of the neighboring unit core with a minute clearance
`therebetween.
`Each unit core 2 includes a yoke section 3 and three
`salient poles 4a to 4c extending from the yoke section 3.
`Windings are wound on the salient poles 4a to 4c of each
`unit core 2 into a concentric winding (not shown) so that the
`salient poles 4a to 4c are in phase with those of the other unit
`cores 2 respectively. More specifically, windings of phase a
`are wound on the three salient poles 4a respectively and
`windings of phase b are wound on the three salient poles 4b
`respectively. Further, windings of phase c are wound on the
`three salient poles 4c respectively. Thus, three-phase wind
`ings are wound on the stator core 1 and the number of salient
`poles and the number of winding phases are equal to each
`other in each unit core 2.
`In the stator core 1 constructed as described above, each
`of portions of each unit core 2 adjacent to the respective
`neighboring unit cores 2 is located between the salient poles
`4a and 4c or between phase a and c windings. In other
`words, winding phase arrangement patterns at both sides of
`all the adjacent portions are the same.
`In the above-described stator core 1, the yoke sections 3
`where amounts of magnetic flux passing through them are
`substantially the same exist at an interval of a predetermined
`angle when the windings of the respective phases are wound
`on the salient poles 4a to 4c. The interval is represented as
`a pitch angle of salient poles, the number of which is
`obtained by multiplying the number of winding phases by a
`positive number. Accordingly, when the stator core 1 is
`constructed as described above, the number of winding
`phases is 3, and the number of salient poles of each unit core
`2 is 3 and is equal to the number of winding phases
`multiplied by any positive number (1 in the embodiment).
`Consequently, the stator core 1 is split so that amounts of
`magnetic flux passing through the adjacent portions become
`the same. A rotor (not shown) is provided inside the stator
`core 1 so that the motor is constructed.
`According to the above-described embodiment, the adja
`cent portions of the unit cores 2 are positioned at intervals
`of the number of salient poles which is obtained by multi
`plying the number of winding phases by a positive number.
`Consequently, since magnetic attractive forces acting
`between the unit cores 2 constituting the stator core 1 are
`approximately equal to each other, occurrence of vibration
`and noise due to unbalance of the magnetic attractive forces
`between the unit cores 2 can be prevented.
`The above-mentioned positive number in 1 in the embodi
`ment and consequently, the stator core can be divided into
`the largest number of unit cores 2. Accordingly, the material
`for the iron core can effectively be used. Further, since only
`the locations of the adjacent portions of the unit cores 2 need
`to be determined when the invention is to be put into
`practice, the invention can be realized without an increase in
`the manufacturing cost.
`FIG. 2 illustrates a second embodiment in which the
`invention is applied to a permanent magnet motor of the
`inner rotor type. The stator core 5 comprises four unit cores
`6. Each unit core 6 includes a yoke section 7 and three
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`US 6,265,804 B1
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`5
`salient poles 8a to Sc extending from the yoke section.
`Windings are wound on the salient poles 8a to Sc of each
`unit core 6 into a concentric winding (not shown) so that the
`salient poles 8a to Sc are in phase with those of the other unit
`cores 6 respectively. More specifically, three-phase windings
`are wound on the stator core 5 and the number of salient
`
`poles and the number of winding phases are equal to each
`other in each unit core 6.
`
`Arotor 9 comprises a yoke 10 serving as a magnetic path
`and eight permanent magnets 11 mounted on an outer
`circumferential face of the yoke 10. A total number of
`magnetic poles of the rotor 9 is 8 and the number of unit
`cores 6 of the stator core 5 is 4. Accordingly,
`the total
`number of magnetic poles of the rotor 9 in exactly divisible
`by the number of unit cores 6 of the stator core 5. Further,
`the number of magnetic poles opposed to each one of the
`unit cores 5 is 2.
`
`Each of the adjacent portions of each unit core 6 and each
`neighboring unit core 6 is formed into the shape of a dovetail
`and is located between the salient poles 8a and 8c. Further,
`winding phase arrangement patterns at both sides of all the
`adjacent portions are the same. Moreover, patterns of oppo-
`sition between the salient poles and the permanent magnets
`at all the adjacent portions of the unit cores 6 are also the
`same. The reason for this is that the salient poles 8a to Sc are
`opposed to a magnetic pole 11 of the rotor 9 at the same
`position represented by an electrical angle. This means that
`the iron core is split so that amounts of magnetic flux passing
`through the adjacent portions become the same.
`In order that amounts of magnetic flux passing through
`the adjacent portions may become the same, the number of
`salient poles per unit core is represented as CM(Nt/CD(Nt,
`Np), Nf) where CM(A, B) is a common multiple of integers
`A and B, CD(A, B) is a common divisor of integers A and
`B, Nt is a total number of salient poles of a stator, which is
`equal to or larger than 2, Np is a total number of magnetic
`poles of a rotor, which is equal to or larger than 2, and Nf
`is the number of winding phases.
`More specifically, in a case where the positions where the
`magnetic fluxes passing through the respective yoke sections
`are substantially equal to each other are obtained when a
`rotor used with the above-described stator has a plurality of
`magnetic poles, the total number of magnetic poles of the
`rotor 9 is required to be equal to the number of unit cores
`multiplied by any positive number, in addition to the con-
`dition that the number of salient poles of each unit core 6 is
`equal to the number of winding phases multiplied by any
`positive integer.
`The number of unit cores is obtained when a divisor
`
`common to the above-mentioned total numbers Nt and Np is
`found. Accordingly, when the total number Np is divided by
`the number of unit cores, the least number of salient poles
`that can be provided on a single unit core is obtained.
`Accordingly, the number of salient poles of each unit core
`can be obtained from a common multiple to the least number
`of salient poles and the total number Nf of winding phases.
`According to the second embodiment, in the permanent
`magnet motor of the inner rotor type, the adjacent portion
`between each unit core 6 and each neighboring one is
`located so that the total number of magnetic poles of the
`rotor 9 is divided out by the number of unit cores 6 of the
`stator core 5 and so that the winding phase arrangement
`patterns at both sides of all the adjacent portions are the
`same. Even when the magnetic attractive forces act between
`the unit cores 6 constituting the stator core 5, the forces are
`approximately equal to each other. Consequently, occur-
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`rence of vibration and noise due to unbalance of the mag-
`netic attractive forces between the unit cores 6 can be
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`prevented.
`Further, in the case where the least common multiple is
`found when a common multiple to the least number of
`salient poles and the total number Nf of winding phases is
`obtained, the least number of salient poles of each unit core
`is obtained. Since this means that the stator core can be split
`into the largest number of unit cores 6, the material for the
`iron core can effectively be used.
`FIG. 3 illustrates a third embodiment in which the inven-
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`tion is applied to a permanent magnet motor of the outer
`rotor type wherein a rotor is disposed outside a stator. A
`stator core 12 comprises six unit cores 13. Each unit core 13
`is made by stacking a number of punched silicon steel
`sheets. Each unit core 13 includes a yoke section 14 and six
`salient poles 15a to 15f integrally extending from the yoke
`section. The unit cores 13 are embedded in a layer of a resin
`such as PPS resin by insert molding. Windings are wound an
`the salient poles 15a to 15f of each unit core 13 into a
`concentric winding (not shown) so that the salient poles 15a
`to 15f are in phase with those of the other unit cores 13
`respectively. Further, two windings belong to the same phase
`two salient poles apart, that is, the windings on paired salient
`poles 15a and 15d belong to phase U. The windings on
`paired salient poles 15b and 156 belong to phase V and the
`windings on paired salient poles 15C and 15f belong to phase
`W. Thus, two sets of three-phase windings are wound on
`each unit core 13. The paired salient poles belonging to the
`same phase have different patterns of combination of a
`radius from the center of rotation to the distal end of the
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`salient pole and a circumferential width of the distal end of
`the salient pole. In this case, each of the salient poles 15a,
`15c and 156 has a smaller radius and a larger circumferential
`width, whereas each of the salient poles 15b, 15d and 15f has
`a larger radius and a smaller circumferential width. More
`specifically, there are two types of shapes of distal ends
`defined by the radius of the salient pole and the circumfer-
`ential width of the distal end of the salient pole, and these
`two types are arranged alternately. Accordingly, when the
`arrangement of the two types of shapes of distal ends is one
`arrangement pattern,
`the number of salient poles in the
`arrangement pattern is 2 in each unit core 13. The number of
`winding phases 3 and the product or the number of salient
`poles and the number of winding phases is 6, which number
`agrees with the number of salient poles of each unit core 13.
`Arotor 16 is provided outside the stator core 12. The rotor
`16 comprises twenty-six permanent magnets 17 connected
`to one another. South pole magnets are shown by slant lines
`in FIG. 3, whereas no slant lines are given to north pole
`magnets. In this case, the number of magnetic poles can be
`divided by the number of unit cores since the number of unit
`cores 13 of the stator core 12 is 6 and the number of
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`magnetic poles of the rotor 16 in 24.
`Each adjacent portion of the unit cores 13 is located
`between the salient poles 15a and 15f and accordingly, the
`phase arrangement patterns of the windings at both sides of
`all the adjacent portions are the same. Further, the arrange-
`ment patterns of the shapes of distal ends of the salient poles
`at both sides of all the adjacent portions are also the same.
`As a result, amounts of magnetic flux passing through the
`respective adjacent portions are the same.
`Although the phase arrangement patterns of the windings
`are the same with respect to the salient poles 15c and 15d,
`the arrangement pattern of the shapes of distal ends of the
`salient pole differs from that in the salient poles 15a and 15f.
`
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`

`

`US 6,265,804 B1
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`Accordingly, no adjacent portion of the unit cores is pro
`vided between the salient poles 15c and 15d since a mag
`netic circuit with respect to the salient poles 15a and 15d
`differs from that with respect to the salient poles 15a and 15f
`such that amounts of magnetic flux are not the same.
`According to the third embodiment, even when the distal
`ends of the salient poles 15a to 15f of the stator core 1 have
`different shapes in the permanent magnet motor of the outer
`rotor type, the stator core 12 has the portions where the
`amounts of magnetic flux are the same. Accordingly, the
`adjacent portions of the unit cores are set at the portions
`respectively such that occurrence of vibration and noise due
`to unbalance of the magnetic attractive forces between the
`unit cores can be prevented.
`Effective use of a material for the iron core has recently
`been required in the development of motors with large
`diameters. Three-phase motors are mainly used and have a
`number of salient poles per phase. Further, a plurality of
`types of salient poles are arranged so as to be adjacent to
`each other as a countermeasure for the vibration. The
`number of salient poles in each arrangement pattern is often
`2 which is the least natural number exceeding 1. In such a
`case, the largest number of unit cores can be obtained in the
`third embodiment when the iron core is split into unit cores
`each or which includes six salient poles, which number is the
`least common multiple to the number of energizing phases
`and the number of salient poles in each arrangement pattern.
`FIG. 4 illustrates a modified form of the third embodiment
`shown in FIG. 3. A stator core 18 comprises three unit cores
`19. Each unit core 19 includes a yoke section 20 and twelve
`salient poles 20a to 201 integrally extending from the yoke
`section. Windings are wound on the salient poles 20a to 201
`of each unit core 19 into a concentric winding (not shown)
`so that the salient poles 20a to 201 are in phase with those
`of the other unit cores 19 respectively. Further, each one
`winding and the winding two salient poles apart belong to
`the same phase, that is, the windings on paired salient poles
`20a and 20d belong to phase U. The windings on paired
`salient poles 20b and 20e belong to phase V and the
`windings on paired salient poles 20c and 20h belong to
`phase W, and so on. Thus, four sets of three-phase windings
`are wound on each unit core 19. The paired salient poles
`belonging to the same phase have different patterns of
`combination of a radius from the center of rotation to the
`distal end of the salient pole and a circumferential width of
`the distal end of the salient pole. In this case, each of the
`salient poles 20a, 20e and 20i has a smaller radius and a
`larger circumferential width, whereas each of the salient
`poles 20b, 20f and 20j has a larger radius and a smaller
`circumferential width. Each of the salient poles 20c, 20g and
`20k has a larger radius and a larger circumferential width.
`Each of the salient poles 20d, 20h and 201 has a smaller
`radius and a smaller circumferential width. More
`specifically, there are four types of shapes of distal ends
`defined by the radius of the salient pole and the circumfer
`ential width of the distal end of the salient pole, and the
`salient poles are arranged so that each one type is adjacent
`to another type. Accordingly, when the arrangement of the
`four types of shapes of distal ends is one arrangement
`pattern, the number of salient poles in the arrangement
`pattern is 4 in each unit core 13. The number of winding
`phases is 3 and the product of the number of salient poles
`and the number of winding phases in 12, which number
`agrees with the number of salient poles of each unit core 19.
`In this arrangement, too, the number of magnetic poles of the
`rotor 16 can be divided up by the number of unit cores.
`Each adjacent portion of the unit cores 19 is located
`between the salient poles 20a and 201 and accordingly, the
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`phase arrangement patterns of the windings at both sides of
`all the adjacent portion are the sane. Further, the arrange
`ment patterns of the shapes of distal ends of the salient poles
`at both sides of all the adjacent portions are also the same.
`As a result, amounts of magnetic flux passing through the
`respective adjacent portions of the unit cores 19 are the
`SãIIlê.
`Although the phase arrangement patterns of the windings
`are the same with respect to the salient poles 20c and 20d,
`the salient poles 20f and 20g and the salient poles 20i and
`20j, the arrangement pattern of the shapes of distal ends of
`the salient pole differs from that in the salient poles 20a and
`201. Accordingly, no adjacent portion of the unit cores is
`provided between each of the above-mentioned pairs of
`salient poles since amounts of magnetic flux are not the
`SãIIlê.
`FIGS. 5 to 8 illustrate a fourth embodiment of the
`invention. Referring to FIG. 6, a permanent magnet motor
`21 of the inner rotor type is shown. A rotor 22 of the motor
`21 includes a rotational shaft 23 to which a rotor yoke 24 is
`mounted. Permanent magnets 25 serving as magnetic field
`means are mounted on the rotor yoke 24. A stator 26
`comprises a stator core 27 and salient poles 29b extending
`from the stator core. Windings 28 are wound on the salient
`pole 29b respectively. The rotor 22 and the stator 26 are
`assembled together so that the permanent magnets 25 and
`the windings 28 are radially opposed to each other respec
`tively.
`The stator care 27 includes three unit cores 29 connected
`to one another. Each unit core 29 is made by stacking a
`