Rotating electrical machine and method for producing magnetic pole pieces

Abstract

Rotating electrical machine having a number of magnetic pole pieces (3) arranged at an oblique angle with respect to the direction in which the axis of rotation extends; and with a cylindrical fixing ring (7) to which the plurality of magnetic pole pieces (3) are mounted, wherein an insertion portion (8) on the outer periphery of the fixing ring (7) and an insertion portion (10) in the magnetic pole piece (3) are assembled to fix the magnetic pole piece (3) to the fixing ring (7); and a permanent magnet (1) is arranged in a groove between adjacent magnetic pole pieces (3) and the permanent magnet (1) has a shape in which an oblique angle is formed with respect to the direction of the axis of rotation when arranged between the magnetic pole pieces (3); characterized in that both the insertion portion (8) on the outer circumference of the fastening ring (7) and the insertion portion (10) in the magnetic pole piece (3) extend parallel to the direction in which the axis of rotation extends, wherein the magnetic pole piece (39) is made of a magnetic material and the fastening ring (7) is made of a non-magnetic material.

Description

BACKGROUND OF THE INVENTIONField of the InventionThe present invention relates to a rotating electric machine such as a motor or an electric generator and the like.Prior ArtIn conjunction with global warming, efficient rotating electrical machines such as motors and electric generators, and motor vehicles with small-size, high-torque rotating electrical machines are expected to be effective anti-global warming measures. Electric motors considered as the heart of industry consume about 70% of the electrical energy used in factories. That is, with an improvement in engine efficiency by a few percent, an energy saving on the order of several hundred thousand kilowatts of electric energy generated in power plants can be achieved.Electrification of individual parts of vehicles and increasing use of eco-friendly vehicles such as HEVs (hybrid electric vehicles) and EVs (electric vehicles) are measures against global warming in transport. For example, with an HEV that requires half of fuel as compared to conventional gasoline-powered vehicles, CO2 ausstoß is also substantially reduced. For example, in terms of vehicle electrification, by changing the power steering system from the conventional hydraulic system to an electromotive system, by avoiding idling effects, fuel consumption can be decreased by 3 to 5%, which also contributes to reduction of CO2 emissionen.Rare earth magnets such as neodymium magnets and samarium-cobalt magnets used in rotary electric machines have a permanent magnetic flux density three times that of conventional ferrite magnets, and have a strong attractive force. In recent years, therefore, in vehicle engines to be small-sized to generate a large torque and compressor engines for air conditioners requiring a high energy efficiency, permanent magnet rotors made of these rare earth magnets have been increasingly installed.The materials of these rare earth magnets are also referred to as rare metals. The amount available is much smaller for these materials than for the base metals such as iron or aluminum, and they can be degraded only in a few places. Rare earth magnets are therefore much more expensive than conventional ferrite magnets. Although rare earth metals have advantages in achieving high efficiency, small size, and large torque in rotating electric machines, there is a tendency to achieve the same motor characteristics without rare earth magnets in order to manufacture cheaper rotating electric machines.In view of this, in order to use ferrite magnets having a small magnetic coercive force and a low cost per unit weight, I-type inner permanent magnet rotor rotating electric machines have been proposed for generating attractive forces corresponding to those of neodymium magnets. However, I-type inner permanent magnet rotors have a small effective magnetic flux density and a large block torque (torque fluctuations when the rotating electric machine is slowly rotating and no electric power is supplied) because of the magnets embedded in the rotor, as compared with conventional surface permanent magnet rotors. It is therefore considered that I-type inner permanent magnet rotors are not suitable for rotary electric machines which are subject to high demands in terms of block torque, such as EPS motors (motors for electric power steering).Japanese Patent Publication JP 2009-50 099 A describes a technique in which, for "forming a rotor core, a permanent magnet rotor, and a permanent magnet synchronous rotary electric machine with a small power decrease of the rotary electric machine by the decrease of the magnetic flux density with an inclination that is easy to manufacture", "a rotor 1 inserts a permanent magnet 2 into a permanent magnet insertion groove 34 that extends obliquely to the axial direction of a rotor core 3 and in which adjacent magnets 2 are located with common poles facing each other. The rotor 1 is opposed with a space therebetween by a stator. The rotor 1 and the stator are supported so as to be rotatable relative to each other. With this structure, a high-performance permanent magnet motor without block torque is obtained."(Summary).From U.S. Pat. No. 4,658,167 A, a rotor for electric machines according to the preamble of claim 1 is arranged with a plurality of magnetic pole shoes arranged axially one behind the other, the outer arcs of which alternately overlap the two adjacent permanent magnets. US 2005 / 0 212 375 A1 discloses a rotor core having a magnetic pole shoe formed integrally with a fastening ring. Further prior art is described in the documents JP H01-270 757 A, MUELLER, G; PONICK, B: Fundamentals of electric machines. 9th Edition. Weinheim: WILEY-VCH Verlag GmbH & Co KGaA, 2006. S.236-239, ISBN 978-3-527-40524-4, DE 10 2004 047 311 A1, US 2009 / 0 026 872 A1, JP H08-9 599 A, US 2006 / 0 175 923 A1 and U.S. Pat. No. 6,392,324 B1.SUMMARY OF THE INVENTIONIn the technique described in Japanese Patent Publication JP 2009 050099 A, the rotor core 3 is composed of superposed members in which the groove 34 into which the permanent magnet 2 is inserted is located. In this structure, the entire rotor core 3 is made of the same material.When a part of the rotor (for example, the portion adjacent to the rotational axis on the inner periphery) is made of another material, the structure described in Japanese Patent Publication JP 2009-50 099 A cannot be used.It is therefore an object of the present invention to provide a rotary electric machine having a structure in which a plurality of magnetic pole shoes are arranged along the outer periphery of the rotational axis, whereby a rotary electric machine having a small block torque is to be produced by inclination of the magnetic pole shoes. It is a further object to provide a method for producing such magnetic pole shoes.The object is achieved by a rotating electric machine having the features of claim 1 and by a method having the features of claim 6.The rotary electric machine of the present invention comprises a plurality of magnetic pole shoes disposed at an oblique angle, and a cylindrical mounting ring for mounting the magnetic pole shoes, wherein both an insertion portion on the outer periphery of the mounting ring and an insertion portion included in the magnetic pole shoes extend along the rotation axis.By providing the oblique angle to the magnetic pole shoes, the rotating electric machine of the present invention having a rotor structure with a number of magnetic pole shoes can prevent occurrence of block torques. Since the portion where the fastening ring and the magnetic pole shoes are engaged with each other extends along the rotation axis, these components can be assembled dimensionally stable, resulting in a rigid rotor structure.Further technical problems, configurations and advantages result from the following description of embodiments.BRIEF DESCRIPTION OF THE DRAWINGSFIG. 1 is a rotor portion diagram of an I-type inner permanent magnet rotor. FIG. 2 is a diagram of the rotor portion of a conventional surface permanent magnet rotor. FIG. 3 is a magnetic flux diagram in an I-type inner permanent magnet rotor. FIG. 4 is an illustration of the means for securing the elements in a prior art I-type permanent magnet inner rotor. FIG. 5 is a perspective view of a fixing ring 7. FIG. 6 is a perspective view of a sheet metal part 9 for producing the fastening ring 7. FIG. 7 is a perspective view of a magnetic pole shoe 3. FIG. 8 is a perspective view of a permanent magnet 1. Fig. 9 is a perspective view showing that the magnetic pole piece 3 and the permanent magnet 1 are arranged in a circular manner. FIG. 10 is a diagram showing the method of inserting the fixing ring 7 into the magnetic pole piece 3. FIG. 11 is an illustration of another method of assembling the magnetic pole piece 3, the permanent magnet 1 and the fixing ring 7. FIG. 12 is a perspective view of a composite unit 13. FIG. 13 is an inner perspective view of a rotary electric machine including an I-type inner permanent magnet rotor 2 according to Embodiment 1. FIG. 14 is a perspective view of a stamping 21 for forming the magnetic pole shoe 3. FIG. 15 is a plan view of two kinds of punches for punching the die cut 21. FIG. 16 is a diagram for explaining the difference between the positions in punching a steel sheet. Fig. 17 is a perspective view showing how a number of the composite units 13 are put on each other. Fig. 18 is an illustration of a coil-type device related to the invention in place of the permanent magnet 1.DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTSConventional I-type Inner Permanent Magnet RotorAs a comparative example, a conventional I-type inner permanent magnet rotor will be described below, and thereafter the structure of the rotary electric machine according to the present invention will be described.FIG. 1 shows the rotor portion of an I-type inner permanent magnet rotor. I-type interior permanent magnet rotors are used when attractive forces equivalent to those of neodymium magnets are to be generated with ferrite magnets having a small magnetic coercive force and a low cost per unit weight.In I-type inner permanent magnet rotors, a segment magnet 1 is disposed so that the longitudinal direction of the segment magnet 1 is aligned in the radial direction of the rotor 2. The inner circumferential surface of the stator is located on the outer circumferential side of the rotor 2, and magnetic pole shoes 3 made of a magnetic material such as magnetic steel sheet are disposed between the segment magnets 1 arranged in the circumferential direction.FIG. 2 shows the rotor portion of a conventional surface permanent magnet (SPM) motor. In surface permanent magnet motors, the magnets 1 are arranged in the circumferential direction of the rotor 2, that is, the inner circumferential surface of the stator is located on the outer circumferential side of the rotor 2.In the I-type inner permanent magnet rotor shown in Fig. 1, the longitudinal dimensions of the magnet 1 may be larger than in the conventional surface permanent magnet rotor shown in Fig. 2. The attractive force of I-type inner permanent magnet rotors can also be obtained by using ferrite magnets whose magnetic coercive force is only one third that of rare earth magnets by increasing the surface area of the magnets against the rare earth magnets to three times that of rare earth magnet rotors. Although the volume of the magnets increases as the surface area of the magnets increases, the cost of the rotating electric machine is lower because the cost per unit weight is low.Fig. 3 shows the magnetic flux in an I-type inner permanent magnet rotor. Fig. 3(a) shows the magnetic flux when the inner peripheral surface 4 of the permanent magnet 1 is made of a magnetic material. Fig. 3(b) shows the magnetic flux when the inner peripheral surface 4 is not made of a magnetic material.In an I-type inner permanent magnet rotor, the magnetic pole shoes 3 are fixedly attached to the inner peripheral portion 4 of the rotor without mutual contact. When the inner peripheral portion 4 of the rotor is made of a magnetic material, a redundant magnetic flux is formed between the inner peripheral portion 4 of the rotor and the permanent magnet 1, as shown in FIG. 3(a). As a result, the magnetic flux between the stator 5 and the permanent magnet 1 is reduced. It may therefore be that the desired torque is not always achieved. On the other hand, if the inner peripheral portion 4 of the rotor is made of members made of a non-magnetic material, the redundant magnetic flux can be reduced by the inner peripheral portion 4 of the rotor and the magnetic flux between the stator 5 and the permanent magnet 1 can be utilized more effectively, thereby increasing the attractive force.Fig. 4 shows the manner of fixing the elements in an existing I-type inner permanent magnet rotor. In FIG. 4, the magnetic pole shoes 3 and the permanent magnets 1 are alternately arranged in the circumferential direction, the whole body being made of a synthetic resin 6 (a non-magnetic material), and a rotation axis for forming the rotor being provided. The resin 6 may be, for example, PBT (polybutylene terephthalate), PPS (polyphenylene sulfide), a thermoplastic resin such as LCP (liquid crystal polymer), or a thermal curing resin such as BMC (bulk molding compound).The redundant magnetic flux shown in Fig. 3(a) can be suppressed by fixing the magnetic pole shoes 3 and the permanent magnet 1 by the resin 6. However, such a structure is serious in rigidity and thermal strength. The present invention therefore includes a structure for an I-type interior permanent magnet rotor having a reduced redundant magnetic flux and increased rigidity.Embodiment 1: Configuration of Rotating Electric MachineReferring to FIGS. 5 to 13, the individual elements of a rotary electric machine in an embodiment 1 of the present invention and the assembly thereof will be described below. The rotating electric machine according to the present invention has a structure in which the magnetic pole shoes 3 and the permanent magnet 1 are attached to the outer periphery of a fixing ring 7.FIG. 5 is a perspective view of the fixing ring 7. the fixing ring 7 shown in FIG. 5 is made of a non-magnetic metal such as aluminum (A 5052, A 2017, A 7075 according to JIS (Japanese Industrial Standard) or stainless steel (SUS 304, SUS 305 according to JIS). In the production of the fastening ring 7 as a solid element, production methods such as machining, extrusion or casting are used. At the outer peripheral portion of the fixing ring 7, an insertion portion 8 into which the magnetic pole piece 3 is inserted is provided. The insertion portion 8 has a groove-like or protruding shape corresponding to the shape of the insertion portion on the magnetic pole piece 3. The central hole 14 for inserting a shaft 15 will be described later.FIG. 6 is a perspective view of a plate member 9 for manufacturing the fixing ring 7. the fixing ring 7 can be manufactured by stacking plate members 9 made of a non-magnetic material as shown in FIG. 6 in the direction of the rotation axis. The insertion portion 8 is formed on the outer peripheral portion of the sheet metal part 9 in the same manner as in FIG. 5. The sheet metal parts 9 can be joined together by cold forging or welding, for example.FIG. 7 is a perspective view of the magnetic pole piece 3. In this structure, the permanent magnet 1 is disposed between adjacent magnetic pole shoes 3 such that the magnetic flux is inclined with respect to the rotational axis.On the rotation axis side of the magnetic pole piece 3 (the portion attached to the fixing ring 7), an insertion portion (protrusion) 10 for fixing is attached in the insertion portion 8 of the fixing ring 7. The insertion portion 10 of the magnetic pole piece 3 and the insertion portion 8 of the fixing ring 7 are formed in parallel to the direction of the rotation axis. Thus, the magnetic pole piece 3 can be inserted in the longitudinal direction of the fixing ring 7, thereby making the assembly easy. As long as it does not make the assembling difficult, it is not necessary that the insertion portion 10 of the magnetic pole piece 3 and the insertion portion 8 of the fixing ring 7 are parallel to the rotation axis. For example, they may be inclined by a few degrees to the axis of rotation. That is, the insertion portion 10 of the magnetic pole piece 3 and the insertion portion 8 of the fixing ring 7 should extend at least in the direction of the rotational axis. On the outer peripheral surface of the magnetic pole piece 3 (the side opposite to the portion attached to the fixing ring 7), there are provided ridges 11 for preventing the permanent magnet 1 from protruding on the outer periphery of the rotor. Instead of the webs 11, grooves can also be provided into which wedges are inserted.The magnetic pole piece 3 can be formed by bonding powdery magnetic materials by sintering or bonding agents (adhesives), or by punching and stacking magnetic steel sheets with insulation coating and then fixing (by cold forging or welding). The manufacturing method of punching and stacking will be described later.FIG. 8 is a perspective view of the permanent magnet 1, and the permanent magnet 1 has a shape in which an oblique angle is formed with respect to the direction of the rotational axis when the magnetic pole shoes 3 are disposed. The permanent magnet 1 can be manufactured by machining sintered magnets or by casting bonded magnets after mixing magnetic powder with resin.Fig. 9 is a perspective view of the annular arrangement of the magnetic pole piece 3 and the permanent magnet 1, and it can be seen that the permanent magnet 1 is inclined with respect to the direction of the rotational axis in accordance with the oblique shape of the magnetic pole piece 3. In FIG. 9, the magnetic pole shoes 3 are not attached to the fixing ring 7.Fig. 10 shows the operation of inserting the fixing ring 7 into the magnetic pole shoes 3. In the state shown in Fig. 9, the insertion portion 10 of the magnetic pole shoe 3 and the insertion portion 8 of the fixing ring 7 are aligned with each other and then assembled along the rotational axis. Since both the insertion portion 10 of the magnetic pole piece 3 and the insertion portion 8 of the fixing ring 7 are parallel (or substantially parallel) to the rotational axis, this operation can be easily performed. In order that the permanent magnet 1 does not damage, the magnetic pole piece 3, the permanent magnet 1 and the fixing ring 7 may be fixed with adhesive.Fig. 11 shows another method of assembling the magnetic pole shoes 3, the permanent magnets 1 and the fixing ring 7. Then, the insertion portion 10 of the magnetic pole piece 3 and the insertion portion 8 of the fixing ring 7 are aligned with each other and assembled in the same manner as in Fig. 10. These members are then placed in a mold and bonded magnets are injection formed in the grooves 12 formed by the magnetic pole piece 3 and the mounting ring 7.Fig. 12 is a perspective view of the composite unit 13, and as described above, there is obtained a composite unit 13 in which the magnetic pole shoes 3 are rigidly attached to the mounting ring 7 at an oblique angle. As long as it is required, a ring-like holding member (not shown) is disposed on the edge surface in the axial direction of the components so that the permanent magnets 1, the magnetic pole shoes 3 and the fixing ring 7 do not come apart. The shaft 15 (not shown) is inserted into the opening 14 of the fastening ring 7. For connecting these members, knurling (pushing projections on the surface of the shaft 15 into the inner periphery of the opening 14), press fitting, fitting (in which 12 no fitting grooves are shown), and the like can be used. With these methods, the I-type inner permanent magnet rotor is formed.FIG. 13 is a perspective view of the inside of a rotary electric machine including the I-type inner permanent magnet rotor 2 of Embodiment 1. The I-type inner permanent magnet rotor 2 is supported on both sides by bearings 17. The stator 16 is formed by stamping a magnetic steel sheet into a cylindrical shape having a number of slots (slits) 18 on the inner periphery and stacking and fixing the steel sheets; protecting the prongs by resin insulators; and connecting the lead wires 20 of the coil 19 to form an electric circuit. When an electric current flows through the lead wires 20 of the coil 19, the coil 19 generates a rotating magnetic field on the inner circumferential surface of the stator core 5. The rotating magnetic field and the permanent magnets 1 (not shown) of the I-type inner permanent magnet rotor 2 cooperate to provide synchronous rotation.Heretofore, the structure of the rotary electric machine in Embodiment 1 has been described. A method of manufacturing the magnetic pole shoes 3 at an oblique angle will be described below.Embodiment 1: Production Method for Magnetic Pole Shoes 3FIG. 14 shows a perspective view of a stamped part 21 for the magnetic pole shoes 3. By laying stamped parts 21 one on top of the other, a magnetic pole shoe 3 is formed. In order to align the inner peripheral side of the magnetic pole piece 3 (the portion attached to the fixing ring 7) parallel to the rotation axis and thus form an oblique angle only on the outer peripheral side, the following method is adopted.FIG. 15 is a plan view showing two kinds of punches for punching the die 21, and the dies 21 can be formed by punching a magnetic steel sheet and the like using these punches in the sequential formation. FIG. 15(A) shows a punch for forming the inner peripheral portion of the die cut 21, and FIG. 15(B) shows a punch for forming the protruding shapes of the die cut 21.Fig. 16 shows the differences in the position where the steel sheet is punched. To form the oblique angle on the magnetic pole piece 3, the punch of Fig. 15(B) is rotated each time a sheet is stamped. In each position of the steel sheet, the outer circumferential section of the stamped part 21 thereby shifts in the circumferential direction by a specific angle. When the stamped parts 21 are placed one on the other, the oblique angle is then produced at the outer circumferential section of the magnetic pole shoe 3. The stamper of Fig. 15(A) is used in all layers in the same position. In all layers, the inner circumferential section of the stamped part 21 is thus located at the same position. The inner peripheral portion of the magnetic pole shoes 3 is therefore oriented parallel to the rotational axis.When the insertion portion 10 of the magnetic pole piece 3 is oriented approximately parallel to the direction of the rotational axis, the possible oblique angle is limited by the size and shape of the magnetic pole piece 3. In the I-type inner permanent magnet rotor 2 of Embodiment 1, the oblique angle is limited to less than half of the angle between adjacent magnetic pole shoes 3. When the oblique angle is above this threshold value, it exceeds the size of the insertion portion 10.Embodiment 1: ConclusionsAs described, the rotary electric machine according to Embodiment 1 comprises an I-type inner permanent magnet rotor 2 having a small block torque by forming an oblique angle on the magnetic pole piece 3 and permanent magnet 1. By forming the insertion portion 10 of the magnetic pole piece 3 and the insertion portion 8 of the fixing ring 7 parallel to the rotation axis, these members can be easily assembled, thereby increasing the rigidity.Embodiment 2Fig. 17 is a perspective view of the process of stacking a plurality of composite units 13, and as described in Embodiment 1, the oblique angle of the magnetic pole piece 3 is less than half the angle between adjacent magnetic pole pieces 3.Related DeviceFig. 18 shows a non-inventive device in which a coil is used instead of the permanent magnet 1. In such a case, a bobbin 23 made of synthetic resin is put on the magnetic pole piece 3 from above and below, the put bobbin 23 is wound (not shown), and the wound bobbin 23 is assembled with the fixing ring 7. Thus, a brushless DC motor having a concentratedly wound rotor with an oblique angle can be produced. By separating the magnetic pole piece 3 from the mounting ring 7, a high density winding can be applied. The oblique angle on the magnetic pole shoe 3 allows torque fluctuations to be reduced.The present invention is not limited to the described embodiments, but various modifications are possible. The description of the embodiments is directed to a detailed explanation for a good understanding of the present invention, and it is not necessary that the present invention contain all the described components. The configuration of one embodiment may be partially replaced with the configuration of another embodiment. The configuration of one embodiment can also be supplemented by the configuration of another embodiment. A part of the configuration of an embodiment may be supplemented, omitted, or supplemented by another configuration.DESCRIPTION OF SYMBOLS1: Permanent magnet, 2: rotor, 3: magnetic pole shoe, 4: inner rotor periphery, 5: stator, 6: synthetic resin, 7: fastening ring, 8: insertion portion, 9: sheet metal part, 10: insertion portion, 11: web, 12: groove, 13: assembled unit, 14: opening, 15: shaft, 16: stator, 17: bearing, 18: slot, 19: coil, 20: lead wire, 21: stamped part, 23: coil body.

Claims

A rotary electric machine comprising: a plurality of magnetic pole shoes (3) arranged at an oblique angle with respect to the direction in which the rotational axis extends; and a cylindrical fixing ring (7) to which the plurality of magnetic pole shoes (3) are attached, wherein an insertion portion (8) at an outer periphery of the fixing ring (7) and an insertion portion (10) in the magnetic pole shoe (3) are assembled to fix the magnetic pole shoe (3) to the fixing ring (7); and a permanent magnet (1) is arranged in a groove between adjacent magnetic pole shoes (3), and the permanent magnet (1) has a shape in which an oblique angle is formed with respect to the direction of the rotational axis in the arrangement between the magnetic pole shoes (3); characterized in that both the insertion portion (8) at the outer periphery of the fixing ring (7) and the insertion portion (10) in the magnetic pole piece (3) extend parallel to the direction in which the rotation axis extends, the magnetic pole piece (39) being made of a magnetic material and the fixing ring (7) being made of a non-magnetic material.The rotary electric machine according to claim 1, wherein the magnetic pole shoe (3) is formed by stacking magnetic sheet members made of a magnetic material.The rotary electric machine according to claim 1, wherein a number of the composite units are stacked together from magnetic pole shoes (3) attached to the outer periphery of the fixing ring (7) along the rotation axis; each of the composite units being arranged such that the inclination of the magnetic pole shoes (3) in the composite units continuously passes over the composite units.The rotating electric machine according to claim 1, wherein the fixing ring (7) is made of a non-magnetic metal.The rotary electric machine according to claim 4, wherein the fixing ring (7) is made of at least one of the non-magnetic metals according to A 5052, A 2017, A 7075, SUS 304 and SUS 305 JIS.A method of manufacturing a magnetic pole piece (3) radially attached to the outer periphery of a fixing ring (7) of a rotary electric machine with a permanent magnet (1) disposed between magnetic pole pieces (3), comprising a first step of punching out a central portion of a magnetic sheet metal part from a magnetic material to form an insertion portion (10) in an edge portion of the magnetic pole piece (3) closer to a rotational axis than another edge portion; a second step of punching the magnetic sheet metal part to form a protrusion in an edge portion of the magnetic pole piece (3) farther from the rotational axis than another edge portion; and a third step of stacking a plurality of sheet metal parts with the insertion portion (10) and the protrusion; wherein in the first step the sheet metal parts are stamped each time at the same location and in the second step the sheet metal parts are stamped each in a position which is displaced in the direction of rotation of the axis of rotation by a specific angle of rotation, so that after the mounting of the magnetic pole shoes (3) on the fastening ring (7) the insertion portion (10) of the magnetic pole shoes (3) extends parallel to the direction in which the axis of rotation extends and a groove for receiving a permanent magnet (1) is formed between adjacent magnetic pole shoes (3), wherein the permanent magnet (1) has a shape in which an oblique angle is formed with respect to the direction of the axis of rotation when the magnetic pole shoes (3) are arranged between.

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