Abstract: An electric motor includes a configuration that directs at least a portion of an electric field generated by phase windings into a stator.

Abstract: A motor includes a stator and a rotor provided inside the stator. The stator includes a stator core, and a coil made of aluminum and wound around the stator core in distributed winding. The rotor includes a rotor core, and a first number of permanent magnets mounted in the rotor core. The coil of the stator is covered with varnish. The first number is greater than or equal to 6, and is less than or equal to 10. Each of the first number of permanent magnets of the rotor contains neodymium, iron, boron and dysprosium, and has a dysprosium content of 0% to 4% by weight.

Abstract: A motor includes a stator core, teeth respectively protruding from the stator core, and coils respectively wound onto the teeth n (n is an integer of 2 or greater) turns including first to n-th turns. Within each of ranges respectively wound with the coils onto the teeth in directions of protrusion of the teeth from the stator core, the first turn of each of the coil lies adjacent to a center of the motor. A k-th (k is an integer, 1<k?n) turn of each of the coils lies opposite to the center of the motor. The first turn when each of the coils is cut in a corresponding one of the directions of protrusion of the teeth from the stator core is greater in cross-sectional area than each of the k-th turn and the n-th turn.

Abstract: An apparatus includes a motor having a rotor; and a stator, where the rotor is located at least partially in a rotor receiving area of the stator, where the stator includes at least one coil winding and teeth, where the at least one coil winding is located on at least some of the teeth, where the teeth include a first set of the teeth and a second set of the teeth, where the teeth of the first set of teeth are longer in a radial direction from the rotor receiving area than the teeth of the second set of teeth.

Abstract: A servo valve torque motor apparatus including a pair of pole pieces; one or more permanent magnet(s) held between the pole pieces an armature supported between the pole pieces for rotation about an axis; the armature being for connection to a member that resists rotation of the armature; and a coil on the armature; wherein when an electrical current is passed through the coil the armature is rotated against the member; and wherein the magnet(s) is/are secured to the two pole pieces by mechanical fixings passing through holes in the magnet(s).

Abstract: A method of manufacturing a laminated stator core and a laminated stator core manufactured by the method, the method capable of forming a recess 21 over one or both of (a) a lateral portion of an ear piece C of the stator core sheet A to be formed adjacent to the stator core sheet B and (b) a peripheral portion of the annular yoke piece D continuing to the lateral portion, the peripheral portion beside the ear piece C; fitting one ear piece E of the stator core sheet B with a gap in the recess 21; and thereby improving a material yield when the stator core sheets 13 are formed from the strip material 14.

Abstract: The permanent magnet rotary electrical machine according to an embodiment includes a rotor core and a stator core. The rotor core is attached to a rotation shaft, and has permanent magnets. The stator core is disposed to face the rotor core in a radial direction of the rotation shaft, and has slots and coils. The slots are provided with coils. Here, the coils are wound in a concentrated winding. Besides, the number of slots per pole and phase q is a fraction satisfying the following relational expression (A).

Abstract: A stator core includes three split cores, each of the split cores including a core-back portion including an inner surface facing a rotor, a tooth base portion protruding radially inwards from the inner surface of the core-back portion and a pair of tooth overhang portions protruding from both sides of a tip end of the tooth base portion in a circumferential direction. The inner surface of the core-back portion including a pair of orthogonal surface regions extending from both sides of a base end of the tooth base portion in a direction orthogonal or substantially orthogonal to the tooth base portion, the orthogonal surface regions extending radially outwards beyond projection positions of tip ends of the tooth overhang portions when the tooth overhang portions are projected on an imaginary plane including the orthogonal surface regions in parallel or substantially in parallel to the tooth base portion.

Abstract: An object of the present invention is to provide a squirrel-cage induction motor with high efficiency. In a squirrel-cage induction motor including a stator in which stator windings are wound in a number of stator slots arranged at intervals in the vicinity of the inner periphery of a stator core and a rotor in which rotor conductors are embedded in a number of rotor slots arranged at intervals in the vicinity of the outer periphery of a rotor core and end rings are provided at both ends of the rotor core, the rotor core is formed of a plurality of blocks, an annular short-circuit ring is provided between respective blocks of the rotor core to short-circuit the rotor conductors, and laminated thickness of the rotor core is made larger than laminated thickness of the stator core.

Abstract: A small-size or micro electric machine and its stator iron core. Such machine comprises rotor assembly and stator assembly installed between front & rear end covers; the stator assembly also includes the stator iron core evenly set with multiple stator slots; the bottom width of the stator slot is as 7-10 times large as the opening width of the stator slot; the shoulder width of the stator slot is as 4-7 times large as the opening width of the stator slot; the slot bottom width of the stator slot is as 1.3-2.0 times large as the slot shoulder width of the stator slot. The said small-size or micro electric machine has advantages of lower input power, higher efficiency and higher output moment of force, that is a high-efficient and energy-saving electric machine.

Abstract: The device comprises a single circular row of permanent magnetic poles and a circular row of electromagnets, magnetic-force-conducting elements of which have central polar part and two lateral polar parts connected to the central polar part and spaced from opposing (in the direction which is essentially perpendicular to the rotation axis) sides of the central polar part. Winding is situated upon central polar part. The part of winding positioned between the polar parts of the magnetic-force-conducting element is more than half the length of the whole winding. Central polar part may have at least one groove. The distance between the centers of adjacent polar surfaces of the magnetic-force-conducting element is set depending on the angle between the magnetic poles in the circular row. The angular dimension of the polar surface of the lateral polar part depends on the angular dimension of the polar surface of the central polar part.

Abstract: A spindle motor of a disk drive apparatus includes a base unit, a stator core, a covered cylindrical rotor hub, a rotor magnet, and a bearing mechanism. The height of the stator core in an axial direction is about 50% or more and about 70% or less of the height of the stator. A torque constant Kt of torque generated between a stator and a rotor magnet is about 4 mN·m/A or more and about 6 mN·m/A or less. A motor constant Km is about 2 mN·m/(A·??) or more and about 4 mN·m/(A·??) or less.

Abstract: A power tool is provided including a housing and an electric motor disposed in the housing. The motor includes a stator having pole pieces mated together and field coils disposed on the pole pieces, the stator having an outside diameter. The motor also includes an armature having an outside diameter that is at least 0.625 of the outside diameter of the stator.

Abstract: A stator includes an iron core 3 in which a plurality of teeth 2 are connected into an integral body, and coil wires 5 each of which is wound in series around each set of a predetermined number of teeth included in the plurality of teeth. Each of the coil wires 5 is routed in a slanting direction between opposed faces of two adjacent teeth 2 in each set of the predetermined number of teeth 2, so that each of the coil wires makes a transition from a wire wound around one of them 2 to a wire wound around the other tooth 2.

Abstract: A brushless DC motor provided with nine slots and eight poles includes a stator including a stator core having pole teeth on the outer circumference thereof and a coil wound around each pole tooth; a rotor disposed at an outside position of the outer circumference of the stator via a gap and having a multiply magnetized permanent magnet with plural magnetic poles; a pole tooth surface formed at a portion of the pole tooth and facing an inner circumference of the rotor; a recessed portion formed on the pole tooth surface; and a slot formed between the adjacent pole teeth and extending a first angular range around a rotational center of the rotor; in which the recessed portion extends in a second angular range around the rotational center of the rotor, the second angular range is 1.2 to 3.0 times the first angular range, the recessed portion has a radial depth which is 0.

Abstract: A single-phase induction motor in which coils are wound around a plurality of teeth by a concentrated winding method is constructed such that an area of a smallest of all cross-sections of a core back element taken along planes which are parallel or substantially parallel to an axial direction is about 0.90 or more times an area of the smallest of all cross-sections of the teeth taken along planes which are parallel or substantially parallel to the axial direction, to prevent or minimize leakage of the magnetic flux.

Abstract: An electric machine having a stator surrounding a rotor with an air gap therebetween. The stator has slots in its inner margin for accommodating stator coil windings. Stator teeth defined by the slots have irregular shapes to modify a variable flux flow pattern in the air gap to reduce harmonic torque components with minimal effect on an average value of rotor torque.

Abstract: A motor comprises a stator having a plurality of magnetic poles disposed at first predetermined intervals along an outer periphery thereof, and a rotor having a permanent magnet with poles magnetized alternately to have different polarities at second predetermined intervals and disposed rotatably around the outer periphery of the stator with a predetermined gap. The magnetic poles of the stator has extended portions formed in a manner to extend from magnetic polar bases into a direction generally parallel to the permanent magnet, and the extended portions are formed of a high-permeability magnetic steel sheet with silicon content less than 3.0 wt-%.

Abstract: A specific force capacity thrust bearing and a method for producing such a design for a particular application are disclosed. The magnetic flux density in the stator material is maximized by varying cross-sectional area normal to the flux path. After a set of initial parameters are chosen, the design can be improved upon by changing the design variables and then verifying the force capacity using a finite element program. By linking the finite element program to a model of the geometry and using some basic algorithms, it is possible to automatically iterate until an optimal design is reached. The resulting design has a much higher force capacity than designs typical of the prior art.

Abstract: A motor comprising a stator having a plurality of magnetic poles disposed in a circumferential direction along an outer periphery thereof, a rotor disposed rotatably around the outer periphery of the stator, and a magnet disposed in a circumferential direction along an inner periphery of the rotor. The stator is formed by laminating sheet-like plates. A plurality of the sheet-like plates including an outermost layer of this laminated body comprises a flat portion substantially perpendicular to the magnet, and an extended portion bent to a direction substantially parallel to the magnet. A part of the sheet-like plate having the extended portion disposed to the outermost side is formed into a thickness smaller than thicknesses of the other parts.

Abstract: A turbogenerator (10) has a rotor (11) having a cylindrical rotor body (13), which at each of the two ends merges into a shaft end (14), and in a middle section has the electromagnetically active region (23) of the rotor (11), in which the rotor (11) is assembled from a plurality of rotor parts which are interconnected and arranged in series on the rotor axis (19). With such a rotor, lower losses and temperatures in the end region of the rotor, and overall a higher limit rating or a broadened output range, become possible as a result of the fact that the rotor body (13) in the active region (23) is formed of an easily magnetizable material, especially a first steel, and in that the end sections of the rotor body (13) which are located outside the active region (23) and the shaft ends (14) are formed of a material with reduced magnetizability or of a non-magnetic material, especially a second steel.

Abstract: A stator assembly for use in a superconducting generator operated at frequencies up to 10 Hz is disclosed. The stator assembly includes a ferromagnetic stator winding support having a plurality of teeth defining slots, the slots configured to receive and support stator windings. The stator winding support is formed so that the ratio of the sum of the widths of the slots to the sum of the widths of the teeth and slots is in the range of 0.65 to 0.90.

Abstract: A stator 13 on whose outer circumference a plurality of magnetic poles 13a are arranged is mounted on a substrate 11, and a rotor 14 is rotatably disposed around the stator. The inner circumferential face of the rotor is provided with a magnet 15 magnetized to have alternately opposite polarities in a direction opposing the stator, and magnetized to have alternately opposite polarities in a direction opposing the substrate. The outer circumferential ends of the magnetic poles of the stator are provided with a first extended portion 13c that extends from a magnetic pole base 13d to the substrate side, and a second extended portion 13b that extends from the magnetic pole base to a side opposite the substrate side. A face of the substrate opposing the rotor is provided with a FG pattern 19 outside the outer circumferential face of the stator such that the FG pattern opposes the magnet.

Abstract: A rotor 14 is rotatably disposed around a stator 13 that is provided with a plurality of magnetic poles 13a. The inner circumferential face of the rotor is provided with a magnet 15 on whose face opposing the stator main magnetization is performed, and on whose face opposing the substrate FG magnetization is performed. The outer circumferential ends of the magnetic poles of the stator are provided with extended portions 13b and 13c that vertically extend from the magnetic pole base 13d. A face of the substrate opposing the rotor is provided with a FG pattern 19 opposing the magnet 15. The FG pattern is disposed on an outer side in a radial direction of the outer circumferential face of the stator.

Abstract: A rotor 14 is rotatably disposed around a stator 13 that is provided with a plurality of magnetic poles 13a. The inner circumferential face of a rotor frame 14b of the rotor is provided with a magnet 15 magnetized to have alternately opposite polarities in a direction opposing the stator, and magnetized to have alternately opposite polarities in a direction opposing a substrate. The outer circumferential ends of the magnetic poles of the stator are provided with a first extended portion 13c that extends from a magnetic pole base 13d to a substrate 11 side, and a second extended portion 13b that extends from the magnetic pole base to a side opposite the substrate side. A face of the substrate opposing the rotor is provided with a FG pattern 19.

Abstract: A motor having a rotor whose outer surface conforms to a non-degenerate quadric surface, and a matching stator.

Abstract: A ring motor (1) as a direct drive, particularly for vertical mills or rod mills, has a stator (6) and a rotor (12) configured as a rotating milling body (10), wherein the stator (6) has at least two different excitation systems, and the milling body (10) has only a toothed structure, which electromagnetically interacts with the excitation systems of the stator (6) and thus brings about a rotation of the milling body (10).

Abstract: Disclosed is a stator core including a core back fixedly inserted onto an outer surface of a stationary member, a plurality of teeth protruding from the core back in an outer diameter direction, wherein a coil is wound around the plurality of teeth so as to allow magnetic flux from a magnet to flow to the teeth, front end portions defining outer edges of the teeth, respectively, and body portions defining a length of the teeth and having a width increasing from the core back toward the front end portions, respectively.

Abstract: This invention relates to a three-phase square-wave permanent magnet brushless DC motor for solving problems of the existing square-wave permanent Magnet Motor and sine-wave permanent magnet motor. In this invention, the number 2P of magnetic poles on the said rotor core is 8; the slot number Z of the said stator core is 12, accordingly there are 12 teeth, including three big teeth, three medium teeth and six small teeth; the ratio of their mechanical angles is 50° (±5°) for big teeth: 40° (±5°) for medium teeth: 15° (±5°) for small teeth, and the sum of the mechanical angles of one big tooth, one medium tooth and two small teeth must be 120°. Three-phase concentrated windings are respectively wound on the big teeth and the medium teeth, in which there are only two concentrated windings for each phase, thus there are only 6 concentrated windings for the three-phase motor.

Abstract: The present invention relates to a motor having a stator with a magnetized rotor rotatably positioned in the stator. The stator and the rotor each have at least two magnetic poles. At least one of the stator poles has a different area confronting the poles of the rotor than the other stator poles. An air gap is positioned between each of the at least two stator poles and at least two rotor poles. The distance of the air gap between each stator pole and each rotor pole is different. A coil is wound upon a bobbin which is placed about at least one of the stator poles. Altering the confronting area of the stator poles allows a larger bobbin and coil to be placed about the stator pole.

Abstract: A brushless motor has a stator and a rotor. The stator has a stator core with a plurality of inwardly extending salient poles and windings wound about the salient poles. The rotor has a shaft, a rotor core fixed onto the shaft, and magnets inserted in the rotor core for forming magnetic poles of the rotor. Each of the salient poles has a pole shoe with a pole face that extends along a circumferential direction confronting the rotor core and being spaced from the rotor core by an air gap. In a radial cross section of the motor, each of the magnetic poles of the rotor has an effective dimension (W) which is about 0.85 times to 1.2 times of the chord length (L) of each pole face.

Abstract: An object of the present invention is to provide a squirrel-cage induction motor with high efficiency. In a squirrel-cage induction motor including a stator in which stator windings are wound in a number of stator slots arranged at intervals in the vicinity of the inner periphery of a stator core and a rotor in which rotor conductors are embedded in a number of rotor slots arranged at intervals in the vicinity of the outer periphery of a rotor core and end rings are provided at both ends of the rotor core, the rotor core is formed of a plurality of blocks, an annular short-circuit ring is provided between respective blocks of the rotor core to short-circuit the rotor conductors, and laminated thickness of the rotor core is made larger than laminated thickness of the stator core.

Abstract: A stator for an electrical machine, in particular a rotary current generator, is proposed, in which the stator (36) is made by the flat-packet technique and comprises at least one stator iron (10) and a stator winding (30), and the stator iron (10) has a substantially annular-cylindrical shape, and the stator iron (10) has an axial direction (a) which is oriented in the direction of a cylinder axis, and the stator iron (10) has an end face, oriented in the direction of the cylinder axis and defining a slot area (ANut), and a ratio (A) formed of the slot area (ANut) and the end face area amounts to between 0.4 and 0.8.

Abstract: The permanently excited synchronous machine (1) includes a rotor (3) and a stand (2) which contains a three-branched winding system (8) which comprises tooth coils. The stand (2) has a total of three or six grooves (5) and a tooth (6, 7) is formed there between. A total of three tooth coils (9) are arranged in the grooves (5) and each coil is associated with one of the three winding phases. The number of user pole pairs (pN) is four or five. The rotor (3) has twice as many user pole pairs (pN) of permanent magnets (18) which are evenly distributed on the periphery.

Abstract: The axial gap type motor according to the present invention is provided with: a rotor and a first stator and a second stator, wherein the first and second stators includes an annular back yoke and a plurality of teeth which is provided on the annular back yoke at predetermined intervals in a peripheral direction so as to protrude toward the rotor in the direction of the rotation axis; the peripheral pitch of the plurality of teeth of the first and second stators are equal to each other; and in a case where the first stator and the second stator which sandwich the rotor therebetween in the direction of the rotation axis are seen from one side in the direction of the rotation axis, facing surfaces of the teeth of the first and second stators which face to the rotor are formed so as not to overlap completely each other.

Abstract: A motor for driving an actuator used such as for a throttle valve of an automobile engine and an optical axis controller of an automobile headlight. In two cup-shaped rotor yokes each provided with an internal diameter enlarged part at its opening, a ring-shaped joint material with an external diameter fitting into this internal diameter enlarged part is inserted into the internal diameter enlarged part to form a rotor yoke assembly. A motor is available with high durability against vibration and shock owing to high accuracy in dimensions, lightweight, and high rigidity of the rotor.

Abstract: An electric motor has a stator, and a rotor disposed within the stator. The stator has a set of stator laminations and a set of windings held in position by the set of stator laminations. The rotor is arranged to rotate about an axis. The set of stator laminations is arranged into a stack. Each stator lamination includes an outer section, and a set of teeth coupled to the outer section. Each tooth of the set of teeth extends from that outer section toward the axis. Each tooth has (i) a first end which is proximate to the outer section and distal to the axis, and (ii) a second end which is proximate to the axis and distal to the outer section. A width of the first end of each tooth is substantially greater than a width of the second end of each tooth.

Abstract: A motor includes a stator, a rotor, a shaft (50) and two end caps (10, 40), which are assembled together. According to the precision requirements, the outer circumference of the rotor core (20), and the outer circumference, the inner bore (33), the end surfaces of the stator core (30) are subjected to grind. The ground rotor core (20) is nested in the ground stator core inner bore (33), wherein the punched outer diameter of the rotor core (20) is equal to the punched diameter of the inner bore (33) of the stator core (30). The shaft (50) is pressed directly into the shaft bore of the rotor core (20) so as to tightly fit with the shaft bore of the rotor core (20).

Abstract: A rotor 14 is rotatably disposed around a stator 13 that is provided with a plurality of magnetic poles 13a. The inner circumferential face of the rotor is provided with a magnet 15 on whose face opposing the stator main magnetization is performed, and on whose face opposing the substrate FG magnetization is performed. The outer circumferential ends of the magnetic poles of the stator are provided with extended portions 13b and 13c that vertically extend from the magnetic pole base 13d. A face of the substrate opposing the rotor is provided with a FG pattern 19 opposing the magnet 15. The FG pattern is disposed on an outer side in a radial direction of the outer circumferential face of the stator.

Abstract: A stator 13 on whose outer circumference a plurality of magnetic poles 13a are arranged is mounted on a substrate 11, and a rotor 14 is rotatably disposed around the stator. The inner circumferential face of the rotor is provided with a magnet 15 magnetized to have alternately opposite polarities in a direction opposing the stator, and magnetized to have alternately opposite polarities in a direction opposing the substrate. The outer circumferential ends of the magnetic poles of the stator are provided with a first extended portion 13c that extends from a magnetic pole base 13d to the substrate side, and a second extended portion 13b that extends from the magnetic pole base to a side opposite the substrate side. A face of the substrate opposing the rotor is provided with a FG pattern 19 outside the outer circumferential face of the stator such that the FG pattern opposes the magnet.

Abstract: A rotor 14 is rotatably disposed around a stator 13 that is provided with a plurality of magnetic poles 13a. The inner circumferential face of a rotor frame 14b of the rotor is provided with a magnet 15 magnetized to have alternately opposite polarities in a direction opposing the stator, and magnetized to have alternately opposite polarities in a direction opposing a substrate. The outer circumferential ends of the magnetic poles of the stator are provided with a first extended portion 13c that extends from a magnetic pole base 13d to a substrate 11 side, and a second extended portion 13b that extends from the magnetic pole base to a side opposite the substrate side. A face of the substrate opposing the rotor is provided with a FG pattern 19.

Abstract: A rack-assist type electric power steering device (10) uses a motor (1) as a drive source. The stator (11) of the motor (1) includes a stator core (13) having ring-like yoke portion (16) and teeth (17) projecting from the yoke portion (16) in the inner direction. In the stator core (13), the ratio (Wy:Wt) between the width (Wy) of the yoke portion (16) in the radial direction and the width (Wt) of the teeth (17) in the circumferential direction is 1:1.4 to 1.8.

Abstract: A motor comprises a stator having a plurality of magnetic poles disposed at first predetermined intervals along an outer periphery thereof, and a rotor having a permanent magnet with poles magnetized alternately to have different polarities at second predetermined intervals and disposed rotatably around the outer periphery of the stator with a predetermined gap. The magnetic poles of the stator has extended portions formed in a manner to extend from magnetic polar bases into a direction generally parallel to the permanent magnet, and the extended portions are formed of a high-permeability magnetic steel sheet with silicon content less than 3.0 wt-%.

Abstract: A stator core that includes a pair of poles separated by an air gap. Each pole includes a first side adjacent the air gap and a second opposite side remote from the air gap. A pole arc is formed in the first side and an arcuate mounting recess is formed in the second side of each pole. Additionally, an electric machine that includes the stator core.

Abstract: A horizontal axis washing machine includes a clothing receptacle rotated by a 4 pole rotor. A 36 slot stator having an interior bore with an interior diameter receives the 4 pole rotor in magnetic coupling relation and capable of operating within a flux weakening range of at least 5:1. The stator has a ratio of an interior diameter to a minimum exterior diameter greater than or equal to 0.63:1.

Abstract: A rotating electrical machine comprises a stator and a rotor; the stator comprising a stator core having teeth and slots, and stator windings disposed in the slots, wherein the stator core is made of laminated steel sheets, teeth and slots of the steel sheet are made by etching, and the thickness of the steel sheet is between 0.05 mm and 0.30 mm. Specifically, it is preferable that the steel sheet used herein be a silicon steel sheet containing crystalline particles.

Abstract: Disclosed is an interior permanent magnet type brushless direct current (BLDG) motor including a stator having a plurality of slots wound in a distributed winding manner, and a rotor positioned in the stator, configured to rotate with respect to the stator, and having a rotor core, a plurality of permanent magnets inserted in the rotor core and a plurality of flux barriers, wherein a flux barrier angle of the rotor is determined by multiples of twenty as an electrical angle and the multiples of twenty relates to a number of slots of the stator.

Abstract: In a stator core composed of a powder compacted magnetic body, a yoke part comprises a protrusion protruding from an axial end face of a tooth. The tooth has an axial length gradually decreases towards an outside along the radial direction of the stator core, and a circumferential length which gradually increases towards an outside along the radial direction of the stator core. In one of the cross sections of stator core perpendicular to a radial direction, the height difference between axial end faces of the yoke part and the tooth is substantially equal to an axial length of a coil end part. Further, a cross-sectional area of the tooth perpendicular to the radial direction is substantially maintained constant along the radial direction, and the cross-sectional area is secured at a junction between the tooth and the yoke part, while half of the cross-sectional area is secured in a circumferential cross section of the yoke part.

Abstract: An induction motor embodiment includes a stator defining a stator bore, the stator including a stator yoke having a stator yoke thickness and a plurality of stator teeth, the teeth having a common length, with each of the stator teeth including a stator tooth center portion that extends from a stator tooth bottom portion proximal the yoke to a stator tooth tip portion, with adjacent stator teeth defining a stator slot between them, each stator slot having a stator slot bottom that extends along a stator slot bottom length. In the embodiment, the center portion has a stator tooth width that is less than or equal to one half the stator slot bottom length. In the embodiment, the stator tooth width is smaller than a stator slot opening width distance. In the embodiment, a ratio of stator yoke thickness to stator tooth width is at least 5:1. A rotor is rotably mounted in the stator.

Abstract: In a stator core having “N” slots, a tooth-width centerline of a linear yoke and a first extension line extended horizontally from a center of rotary shaft toward the linear yoke form a first angle. Assume there are first point on the first extension line at a first distance from the center, a second extension line drawn at a second distance horizontally from the center toward the linear yoke and extended vertically toward arc-shaped yokes, and a third extension line drawn from the center toward teeth ends of the linear yokes with angle “K”. The second and third extension line intersect at a second point. A line between the first and second points intersects with the first extension line, thereby forming the first angle. In this structure, 0<a<b, and (360/2N?60/2N)°<K<(360/2N+60/2N)° are established, where “a”, “b” are the first and the second distances respectively.