Abstract: There is provided a rotor core which increases the quality and reliability thereof by preventing the occurrence of a core separation of the rotor core. There is provided a rotor core including a plurality of substantially cylindrical core blocks which are stacked on each other; and a plurality of magnets, characterized in that a plurality of magnet holes extending in an axial direction are provided in the plurality of core blocks so as to extend over the plurality of core blocks in that the plurality of magnets are accommodated in each of the plurality of magnet accommodation holes and fixed therein with a resin, and in that an axial position of core block boundary planes where the plurality of core blocks are brought into abutment with each other and an axial position of magnet boundary planes where the plurality of magnets are brought into abutment with each other differ from each other.

Abstract: A method for manufacturing a laminated core is provided that makes positions of boundary parts of laminated blocks and improves an efficiency of a welding operation of the blocks. The above-described object is achieved by the method of manufacturing the laminated core 10 including a process that forms a plurality of blocks 12 having a plurality of welding parts 13 to 15 of different forms or colors at intervals of prescribed angles in the circumferential direction, a process that laminates the plurality of blocks 12 under a state that the blocks are rotated at intervals of the prescribed angles and a process that welds the welding parts 13 to 15 having the different forms or colors of the laminated blocks 12 to form integrally the plurality of blocks 12.

Abstract: An electric motor includes a stator having multiple magnetic poles and a rotor rotatably mounted to the stator. The rotor includes a shaft, a commutator and a rotor core fixed to the shaft; and windings wound on the rotor core and electrically connected to the commutator. The rotor core is formed by stacking a plurality of laminations. Each lamination includes an inner ring having a hole for fixing the shaft; an outer ring radially spaced from the inner ring; multiple teeth extending outwardly from the outer ring, and multiple ribs connecting the inner ring to the outer ring. Each rib has a width w measured in a circumferential direction of the lamination. The number of ribs is n. The width w and the number n satisfy the formula: 0.75?n×w2?64, where the width w is measured in millimeters.

Abstract: An alternator of high quality and high performance includes a rotor, a stator core arranged so as to surround the rotor and having a plurality of axially extending slots arranged at a predetermined circumferential pitch, and a stator having a stator winding fitted into the slots. The stator core includes element iron cores of a hexahedral shape which are deformed to curve, with their adjacent end faces being abutted and bonded to each other, each of the element iron cores being composed of thin steel plates laminated and integrated with one another, with concave and convex portions formed on the thin steel plates being fitting with each other. The concave and convex portions are formed on a borderline between a compressive region of the stator core at an inner diameter side thereof and a tensile region of the stator core at an outer diameter side thereof.

Abstract: The method for manufacturing a stator core includes: a punching step in which magnetic segments are punched out of an electromagnetic steel sheet that is coated with an organic insulating coating; a laminating step in which a laminated body is formed by laminating a predetermined number of the punched magnetic segments; a first preheating step in which a welding position on a wall surface of the laminated body is heated locally from a first end to a second end in a direction of lamination to decompose an organic component in the insulating coating thermally at the welding position; and a first welding step in which the welding position at which the organic component in the insulating coating is decomposed thermally is welded from the first end to the second end in the direction of lamination to interconnect and integrate the laminated magnetic segments.

Abstract: The invention relates to a method for the production of a soft magnetic core for generators and generator with a core of this type. To produce a core, a plurality of magnetically activated and/or magnetically activatable textured laminations is produced from a CoFeV alloy. This plurality of laminations is then stacked to form a core assembly. Then the core assembly, if consisting of magnetically activatable laminations, is magnetically activated. Finally, the magnetically activated core assembly is eroded to produce a soft magnetic core. A core of this type is suitable for a generator with a stator and a rotor for high-speed aviation turbines, the laminations in the core assembly being oriented in different texture directions relative to one another.

Abstract: In a stator manufacturing method to manufacture a stator in which divided-core assemblies are arranged in a cylindrical shape, each of which includes a divided-core member having a teeth portion on which a coil is wound. In this method, the divided-core assemblies are inserted in the cylindrical shape into a fixed mold, resin sheets containing glass fibers or carbon fibers are disposed on coil-end portions of the cylindrically-arranged divided-core assemblies, and a slide part of a movable mold applies pressure to and molds the resin sheets, thereby combining the divided core assemblies into a single unit. The movable mold is operated to position the divided-core assemblies in place by a cylindrical part and then apply pressure to and mold the resin sheets by the slide part.

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 rotor arrangement for an electric prime mover (6) of a motor vehicle has a rotor shaft (34), on which at least two laminate stacks (36, 38, 40, 42, 44, 46) are arranged. At least one laminate stack (36) is configured to enable a changed moment of inertia of this laminate stack (36) with respect to another laminate stack (38).

Abstract: A rotating electrical machine includes a rotor configured to rotate about an axis. The rotor includes a rotor lamination stack having a plurality of sheets pressed into a composite assembly in an axial direction and being radially divided into an inner mechanical part and an outer electrical part. A rotor winding is disposed in the electrical part of the rotor lamination stack. A stator is concentrically surrounding the rotor. A plurality of shear bolts is disposed in the mechanical part and configured to reach through the rotor lamination stack. A plurality of further bolts is disposed in the electrical part, the plurality of shear bolts and a plurality of further bolts being configured to press the plurality of sheets in the axial direction.

Abstract: The invention relates to an electrical machine (8), in particular an electric motor, suitable for the adjustment by external force of elements of a motor vehicle, essentially for driving a steering booster. The inventive electrical machine comprises a rotor (7) and a shaft (10), the rotor having a plurality of plates (5), wherein the plates (5) are premounted on the shaft either individually or as a plate assembly (6) or by means of a plurality of plate assemblies (6), the rotor (7) being connected to the shaft (10). The plates (5) have resilient lugs (3) for fixing the plates (5) and/or plate assemblies (6) to the shaft (10). Furthermore, the plates (5) of the plate assemblies (6) comprise centering lugs (1) which serve to radially center the plate assembly (6) relative to the shaft (10).

Abstract: A motor includes a rotation shaft, a stator, and a rotor. The stator includes an armature winding and a stator core including a main core portion with an axial stack of core sheets and a magnetic plate on an end thereof. Each core sheet includes a tooth formation portion around which the armature winding is wound. The magnetic plate includes a stacked portion and an axially extending portion. The stacked portion stacked on the axial end of the main core portion and includes an end located toward the rotor. The axially extending portion extends toward the outer side in the axial direction from the end of the stacked portion located toward the rotor and is opposed to the rotor in a radial direction of the motor. The axially extending portion is shaped to be magnetically skewed in a circumferential direction relative to the tooth formation portion and the stacked portion.

Abstract: A stator core is formed from a continuous strip of wound sheet stock material, in which the sheet stock material is converted from the sheet stock to a formed material including winding slot cutouts. This strip of formed material is then wound into the stator core, with the winding slot cutouts in the formed material maintained at a substantially constant width throughout most of the radial extent of the resulting winding slots in the finished article. However, one or more of the radially innermost and radially outermost layers may define winding slot cutouts that are wider than the other winding slot cutouts. Where several radial layers are altered in this way, the cutout widths are progressively expanded such that the resulting winding slot has terminal ends with edges that are effectively “radiused” or rounded, thereby protecting windings near the edge of such slots.

Abstract: The invention relates to a magnetic rotor core for an electric rotary machine, including a stack of magnetic laminations having some poles provided with pole tips, said core including a stack that comprises laminations of which at least one of the poles has at least one at least partially truncated pole tip, preferably a single pole tip.

Abstract: There is described a method and apparatus for forming a core for an electrical machine, in which a stamped metal strip (4a, 4b) is wound onto a mandrel (22), to form a helical winding. The diameter of the mandrel is then increased to apply tension to the wound strip, while the coils of the wound strip are held between clamps (24, 25). The coils of the wound strip are then fixed relative one to another (50, 51), while the coil is held at the increased diameter. The diameter of the mandrel is then reduced to disengage the laminated core from the mandrel. To produce a rotor or stator for an electrical machine, electrical coils are mounted in slots formed in the inner or outer surface of the core. The rotor or stator may then be incorporated into an electrical machine such as a motor or generator.

Abstract: In a vehicle AC generator, a stator core (42) is formed by laminating thin steel sheets, the stator core (42) being provided with a plurality of slot portions (43) which accommodate a stator winding (41) and tooth portions (44) which define adjacent ones of the slot portions; the stator winding (41) is disposed in the slot portions to constitute a stator (4); the stator core (42) is filled with varnish (45) between laminates of each tooth (44) at least in an inner diameter end surface region which faces the rotor (3) and is coated with epoxy resin varnish (46) on the tooth surface of the inner diameter end surface region to form an anti-rust film.

Abstract: A thin spindle motor having a stator core with sufficient swaging strength even using thin magnetic steel sheets is provided, whereby the magnetic loss and the power consumption of the spindle motor are reduced. The stator core is formed by laminating plural stator laminations with a thickness of 0.1 to 0.2 mm and joined by a swaging portion. The swaging portion has an approximately rectangular shape having long sides extending along a radial direction when viewed from an axial direction. The swaging portion has a cross section with a middle portion parallel to the radial direction and a slope portion at the both sides when viewed from a circumferential direction, thereby forming a recess. The recess has a depth that is less than the thickness of the stator lamination whereby the swaging portion does not cut the stator lamination.

Abstract: A laminated rotor and an electric machine including the laminated rotor are disclosed. In an embodiment, a rotor comprises a plurality of stacked laminations, wherein each lamination includes a plurality of radially extending slots arranged about a circumference of each of the plurality of laminations, and the plurality of radially extending slots in successive laminations in the stack are aligned. A stud member passes longitudinally through at least one hole in the lamination stack, and a plurality of coils are positioned within the plurality of slots. Fewer than all of the plurality of slots have a coil positioned therein, leaving at least three slots empty. Balance members may be placed in the slots that do not have a coil positioned therein to balance the rotor.

Abstract: A rotor includes a core made of a laminated steel sheet assembly including a plurality of laminated magnetic steel sheets each having a flat plate shape, the core including a through hole at a rotation center, a shaft inserted in a through hole of the core, an inner-peripheral-side welded part located on an inner peripheral side of the core, the welded part being a welded section joining between adjacent steel sheets and joining the laminated steel sheet assembly to the shaft over a laminating direction, and an outer-peripheral-side welded part located on an outer peripheral side of the core and in an end part in the laminating direction, the welded part being a welded section joining between some of the magnetic steel sheets, the joined steel sheets including a steel sheet forming an end face of the core in the laminating direction.

Abstract: A lamination assembly having a lamination stack including a plurality of lamination members, and at least one inter-lamination thermal transfer member coupled to at least one of the plurality of lamination members. The at least one inter-lamination thermal transfer member establishes a heat dissipation path from the lamination stack.

Abstract: An embedded magnet type electric motor rotor (10) including with a core (11) which is formed by laminating a plurality of electrical steel sheets, magnets (M) which are arranged in a plurality of magnet slots (30) which are formed in a circumferential direction of the core, and non-core parts (35, 36) which are positioned in clearances between the magnet slots and the magnets which are arranged in the magnet slots, wherein in the rotor, reinforcing parts (40) which reinforce the core in an axial direction are provided at least at two non-core parts of the core.

Abstract: An electric motor is provided, including a stator having two electromagnetic poles diametrically opposite each other, a rotor including a rotor core configured for being rotatably mounted with a shaft for rotation relative to the stator. The rotor core is formed by stacking a plurality of laminations each of which has a central hole and a plurality of generally radially extending teeth. The stator and the rotor have geometric attributes such that: R1=G*0.9968, wherein G is defined as thickness of a field yoke, and R1 is defined as a distance from an outside edge of a central hole to bases of the teeth. A compressor assembly is also provided that employs the present motor.

Abstract: A rotor for an induction motor has a plurality of central laminations defining a central bore extending along an axis. End laminations are at each axial end of the central laminations. Metal is within gaps formed between lamination teeth. The end laminations have teeth extending radially outwardly from a central ring portion. A bore is formed in a face of the end laminations facing outwardly, and adjacent to where the teeth connect into the central ring portion. A motor and method are also described.

Abstract: A method for manufacturing a radial centering surface on an outer circumference of an annular laminated core of a stator comprises the steps of forming a stator with a hollow cylinder from strip-shaped laminations, preloading the stator axially before and during cutting, creating centering surfaces on an outer circumferential of the stator by using at least two cutting tools.

Abstract: A fan stator structure includes a stator assembly having at least one first silicon steel sheet and at least one second silicon steel sheet. The second silicon steel sheet has a base section and at least one magnetic conductive section extending from the base section. The first and second silicon steel sheets are stacked to form the stator assembly. By means of the first and second silicon steel sheets, the position of the magnetic force center of the stator assembly so as to reduce noise and wear ratio and prolong the lifetime of the fan.

Abstract: A rotating electric machine includes a rotor configured to rotate about an axis. The rotor includes a rotor laminate stack having layered laminations pressed in an axial direction to form a composite, the rotor laminate stack being radially divided into an inner mechanical region and an outer electrical region. A rotor winding is disposed in the electrical region of the rotor laminate stack. A stator concentrically surrounds the rotor. A press plate is configured to press the layered laminations in the axial direction, the press plate being radially divided into a separate inner press plate and a separate outer press plate so as to correspond to the radial division of the rotor laminate stack.

Abstract: A generator, for example of a wind turbine, includes two end plates and a plurality of stator laminate plates arranged between the two end plates, is described. Each laminate plate and each end plate comprise a number of cooling holes which are located such that the cooling holes of the laminate plates and the cooling holes of the end plates are aligned with each other to form a number of cooling ducts by the stator material itself. Furthermore, a method for cooling a laminated stator of a generator is described having a cooling fluid guided via a tubing from a cooling fluid reservoir into at least one a partly open cooling duct in the laminated stator.

Abstract: A rotor (10) for a generator, especially for a turbogenerator, is assembled from a plurality of separate rotor elements (11, 12) which are arranged one behind the other in the rotor axis (18), wherein the rotor elements (11, 12) abut on connecting faces and are welded to one another, forming circular weld seams (17) which concentrically encompass in each case an annular central gap (37) with a predetermined gap width. In order to achieve a maximum magnetically active volume with mechanical stresses which are as low as possible, on the outer circumference of the gap (37) the gap merges into a widening cavity (38) which is adjacent to the weld seam (17).

Abstract: A marking (7) that indicates inherent information about a stator (2), is formed of recesses inscribed at a predetermined position on the outer circumferential surface of a laminated iron core (21) of the stator (2), by melting a magnetic thin plate with a laser beam. The marking (7) is formed of recesses in the outer circumferential surface of the laminated iron core (21), i.e., in the outer circumferential surface, at the laminated side of the magnetic thin plate, of the laminated iron core (21). Accordingly, friction or the like does not peel off the marking.

Abstract: A stator core includes a first lamination and a second lamination. The first lamination is formed from a plurality of first segments and has a plurality of first mounting ears. The second lamination is formed from a plurality of second segments and has a plurality of second mounting ears. The first lamination and the second lamination are aligned with a common axis and are rotated about the common axis such that the first lamination is not aligned with the second lamination.

Abstract: Disclosed is a core including a plurality of core layers in a laminated structure formed through one-directional press shearing and having an insulating layer formed on the surface thereof prevented from being damaged by burrs formed through the press shearing when a winding coil is wound on and around the core, and a motor having the core. The core for a motor includes: a plurality of core plates having a laminated structure formed through one-directional press shearing; and a chamfered portion formed on at least some of the corners of a face opposed to one face of the core plate to which force is applied by the press shearing.

Abstract: The method for manufacturing a stator core includes: a punching step in which magnetic segments are punched out of an electromagnetic steel sheet that is coated with an organic insulating coating; a laminating step in which a laminated body is formed by laminating a predetermined number of the punched magnetic segments; a first preheating step in which a welding position on a wall surface of the laminated body is heated locally from a first end to a second end in a direction of lamination to decompose an organic component in the insulating coating thermally at the welding position; and a first welding step in which the welding position at which the organic component in the insulating coating is decomposed thermally is welded from the first end to the second end in the direction of lamination to interconnect and integrate the laminated magnetic segments.

Abstract: A rotor includes a plurality of salient poles, each of which is formed by a plurality of plate members including steel plates that are stacked together, provided extending in a radial direction and around which a coil is wound. The plurality of salient poles has auxiliary salient poles that protrude from the salient poles between two salient poles that are adjacent to one another. The auxiliary salient poles are formed by only a first plate member that is a portion of plate members that forms the salient poles.

Abstract: A brushless motor comprises a rotor and a stator comprising a plurality of core plates laminated on one another. The core plates include a plurality of teeth portions. The plurality of core plates includes a first core plate and a second core plate, a combination of magnetic resistances of the teeth portions of the first core plate being adjusted at a first condition, and a combination of magnetic resistances of the teeth portions of the second core plate being adjusted at a second condition. Magnetic resistances of magnetic paths formed by the plurality of laminated teeth portions are adjusted to be same by adjusting a ratio of a number of the first core plates to a number of the second core plates.

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: Disclosed herein is a laminated core used for a motor including an electric motor, wherein the core is formed of a soft magnetic composite and has a structure in which one or more unit laminates are laminated. Since the core is fabricated by laminating soft magnetic composites, the mechanical strength of the core formed of the soft magnetic composites can be improved.

Abstract: Electrical machines, for example transverse flux machines and/or commutated flux machines, may be configured to achieve increased efficiency, increased output torque, and/or reduced operating losses via use of laminated materials, for example laminated materials configured with cuts and/or segmentations. Segmentations may also assist with manufacturability, mechanical retention of components, and the like.

Abstract: The present invention relates to an electromagnetic coil structure for being mounted on a magnetic core. Such a magnetic core is for instance a part of a rotating electric machine or of a magneto electronic angle sensor. The present invention further relates to a belonging magnetic core and to a magneto electronic angle sensor, in particular a reluctance resolver. Furthermore, the present invention relates to a method for fabricating such an angle sensor. The coil structure (106) comprises at least one electrically conductive winding formed as a flat conductive track (110), and at least one flexible electrically insulating carrier (112) for carrying said winding. Said coil structure has at least one opening (108) for receiving a magnetic flux guiding element (104) of said core. The circumferential surface of the core whereto said electromagnetic coil structure (106) is mounted has a polygonal shape.

Abstract: A coil back yoke has laminated structure in which a plurality of annular components are stuck together along the axis direction of a cylinder, the annular component is formed of a soft magnetic body and has structure in which a plurality of divided annular components having a shape divided along the circumferential direction of an annular ring are stuck together in an annular shape, and, to prevent joint portions formed in the annular components by sticking together the divided annular components along the circumferential direction of the annular ring from lining up on a straight line parallel to the axis direction of the cylinder, the joint portions of at least a part of the plurality of annular components are stuck together while being shifted along the circumferential direction of the annular ring with respect to the joint portions of the other annular components.

Abstract: A method for securing the end sections of an annular laminated article, such as a stator core, which includes a plurality of serially joined sections, each section formed of a plurality of stacked, planar laminas. The article is initially manufactured in a liner form, and is then formed into an annular form with the end sections disposed adjacent one another. At least one tab associated with one of the end sections is displaced by a forming tool into a corresponding cavity of the other of the end sections to secure the end sections together. In another embodiment, a pair of tabs each associated with one of the end sections are respectively displaced toward one another and into corresponding respective cavities each associated with the other of the end sections to secure the end sections together.

Abstract: A stir-welded rotor includes a stack of laminations, where each of the laminations defines a plurality of spaced-apart slots arrayed on an outer circumference. A conductor bar may be registered with each of the spaced-apart slots of the stack of laminations, with each conductor bar including a first metal portion and a second metal portion having substantially dissimilar compositions.

Abstract: A rotor for an electrical inductor motor or an induction generator includes a core having spaces formed in the core. The rotor also has a first end ring. The first end ring has a first hub portion. A first ring is connected to the first hub portion by first spokes. The rotor also has a second end ring. The second end ring has a second hub portion. A second ring is connected to the second hub portion by second spokes. The first end ring is secured to the core. The second end ring is rotated a predetermined amount so the first spokes are misaligned with the second spokes. The second end ring is connected to the first end ring and the core. The core, the first end ring and the second end ring form a substrate. An aluminum conductor is cast to the substrate. The aluminum conductor fills in the spaces and around the first and second spokes to form a cast rotor.

Abstract: A rotor for a rotating electrical machine suppresses demagnetization of permanent magnets without deteriorating motor characteristics, is low-cost, and is highly reliable. The rotor has a plurality of rotor cores that are stacked together, a plurality of permanent magnets axially divided by the rotor cores and circumferentially arranged on each of the rotor cores, to circumferentially form magnetic irregularities, and a rotor blank made of nonmagnetic material arranged between those of the rotor cores that are adjacent to each other.

Abstract: A bulk material formed on a surface is provided. The bulk material includes a plurality of adhered domains of metal material, substantially all of the domains of the plurality of domains of metal material separated by a predetermined layer of high resistivity insulating material. A first portion of the plurality of domains forms a surface. A second portion of the plurality of domains includes successive domains of metal material progressing from the first portion. Substantially all of the domains in the successive domains each include a first surface and a second surface, the first surface opposing the second surface, the second surface conforming to a shape of progressed domains, and a majority of the domains in the successive domains in the second portion having the first surface comprising a substantially convex surface and the second surface comprising one or more substantially concave surfaces.

Abstract: The present invention provides a method for manufacturing a stator configured to ensure insulation properties between a conductor and an armature core while preventing a manufacturing cost from increasing and preventing a space factor from lowering. In an edge-removing step, a plurality of independent edge-removing punches, which correspond to one slot S or two or more slots S press and chamfer a corner portion of an axial opening edge of the slot in an axial end core sheet of the armature core.

Abstract: A resolver includes a disc-shaped rotor provided with a detection coil pattern formed in flat shape and a stator formed in flat plate shape placed to concentrically fact the rotor in an axial direction and configured such that a planar first excitation coil pattern to which a cosine wave is supplied and a planar second excitation coil pattern to which a sine wave is supplied, the first and the second patterns being laminated. The first and second excitation coil patterns are placed to face the detection coil pattern. An insulation layer is formed with insulating coating material between the first and second excitation coil patterns.

Abstract: An electric induction motor assembly includes a rotor assembly and a stator assembly. The rotor assembly includes an exposed bar rotor comprising a plurality of axially stacked, punched-to-size rotor laminations. The stator assembly includes a plurality of axially stacked, punched-to-size stator laminations. Each of the laminations presents an axial thickness of less than 0.024 inches. The rotor assembly and the stator assembly cooperatively define a radially extending air gap between a radially outer periphery of the rotor assembly and a radially inner periphery of the stator assembly that is less that 0.012 inches.

Abstract: An electric motor with a stator and a rotor, the stator and/or the rotor comprising a soft magnetic core comprising a lamination stack, is characterised, in that the lamination stack has a composition of 35% by weight?Ni?50% by weight, 0% by weight?Co?2% by weight, 0% by weight?Mn?1.0% by weight, 0% by weight?Si?0.5% by weight and 0.5% by weight?Cr?8% by weight and/or 0.5% by weight?Mo?8% by weight, residual iron and unavoidable impurities, where 0.5% by weight?(Mo+Cr)?8% by weight.

Abstract: A rotor assembly is assembled by providing an elongated rectangular strip of material having a first edge and a second edge defining a width, cutting the elongated rectangular strip to form a first patterned strip having a first side corresponding to the first edge, winding the first patterned strip portion around the perimeter of the rotor core such that the first edge is adjacent to the perimeter and the patterned strip portion forms a continuous laminated ring structure. Two laminated ring structures can be cut from a single strip, thereby reducing waste material and forming a strong structure.

Abstract: In an embedded magnet motor, radial magnets and first inclined magnets form north poles. The radial magnets and second inclined magnets form south poles. Core sheets each include preformed radial accommodating slots the number of which is expressed by P/2. Some of the preformed radial accommodating slots are short slots and the rest are long slots. The short slots are located at some parts of each radial accommodating slot along the axial direction. Radially inner ends of the short slots restrict the radial magnets from moving radially inward.