The present disclosure relates to a pole piece device and a magnetic gear including the pole piece device. Background technology [0002] As a type of gear device, a magnetic gear that uses the attractive and repulsive forces of magnets to transmit torque and motion without contact, thereby avoiding problems such as wear, vibration, and noise caused by tooth contact. There is Among these magnetic gears, the magnetic flux modulation type (harmonic type) magnetic gear has an inner peripheral magnetic field and an outer peripheral magnetic field arranged concentrically (coaxially), and between these two magnetic magnetic fields. A magnetic pole piece device having a plurality of magnetic pole pieces (pole pieces) and a plurality of non-magnetic bodies arranged alternately in the circumferential direction (Patent Document 1 to 2). Then, the magnetic fluxes of the magnets of the two magnetic fields are modulated by the magnetic pole pieces to generate harmonic magnetic fluxes, and the two magnetic fields are synchronized with the harmonic magnetic fluxes. , the flux-modulated magnetic gear operates. [0003] For example, in a magnetic geared motor in which the magnetic flux modulation type magnetic gear and the motor are integrated, the magnetic field on the outer peripheral side is fixed and functions as a stator, and the magnetic field on the inner peripheral side is fixed to the high-speed rotor, The pole piece arrangement described above functions as a low speed rotor. By rotating the high-speed rotor by the magnetomotive force of the coil, the low-speed rotor rotates according to the reduction ratio determined by the ratio between the number of pole pairs of the high-speed rotor and the number of pole pairs of the low-speed rotor. As a magnetic geared motor, a type in which permanent magnets are installed in a high-speed rotor and a stator, and a type in which a permanent magnet is installed only in a high-speed rotor are known. prior art documents patent literature [0004] Patent Document 1: US Patent Application Publication No. 2018/0269770 Patent Document 2: Japanese Patent No. 5286373 SUMMARY OF THE INVENTION Problems to be Solved by the Invention [0005] As shown in Patent Document 1, the plurality of magnetic pole pieces provided in the above-described magnetic pole piece device are generally formed by stacking steel plates (magnetic steel plates) in a direction (axial direction) along the rotation axis of the magnetic pole piece device. However, there is a problem of reduced efficiency due to iron loss (eddy current loss) caused by axial leakage flux at the end of the pole piece. [0006] In view of the circumstances described above, it is an object of at least one embodiment of the present invention to provide a pole piece device in which axial leakage flux at the ends of the pole pieces is suppressed. Means to solve problems [0007] A pole piece device according to at least one embodiment of the present invention, A magnetic pole piece device disposed between an inner diameter side magnet field and an outer diameter side magnet field in a magnetic gear, A plurality of magnetic pole pieces arranged at intervals in the circumferential direction of the magnetic gear, Each of the plurality of magnetic pole pieces has a plurality of plate-shaped electromagnetic steel sheets having a longitudinal direction, Each of the plurality of electromagnetic steel sheets is laminated along the circumferential direction with the longitudinal direction along the axial direction of the magnetic gear. [0008] The magnetic gear according to at least one embodiment of the present invention is 　The inner diameter side magnet field, an outer diameter magnet field arranged on the outer diameter side with respect to the inner diameter magnet field; and the above-described magnetic pole piece device disposed between the inner diameter side magnet field and the outer diameter side magnet field. The invention's effect [0009] According to at least one embodiment of the present invention, a magnetic pole piece device is provided in which core loss (eddy current loss) due to axial leakage flux at the end of the magnetic pole piece is suppressed. Brief description of the drawing [0010] 1 is a schematic cross-sectional view perpendicular to the axial direction of a magnetic gear according to an embodiment of the present invention; FIG. 2 is a partially enlarged cross-sectional view of the magnetic gear shown in FIG. 1; FIG. 3 is a schematic diagram of a pole piece according to an embodiment of the present invention; FIG. 4A is a schematic diagram of a pole piece provided with a high thermal conductivity plate according to an embodiment of the present invention; FIG. 4B is a diagram showing the relationship between the tensile modulus and thermal conductivity of CRFP. FIG. 5 is a schematic diagram of a pole piece having rounded ends according to an embodiment of the present invention; FIG. 6 is a schematic diagram of a magnetic pole piece having permeability anisotropy according to an embodiment of the present invention; FIG. 7 is a schematic diagram of a magnetic pole piece including split magnetic steel sheets according to an embodiment of the present invention; FIG. 8 is a schematic diagram of a magnetic pole piece including split magnetic steel sheets according to an embodiment of the present invention, in which split positions are dispersed; FIG. 9 is a schematic diagram of a magnetic pole piece including a slit electromagnetic steel sheet according to an embodiment of the present invention; FIG. 10 is a schematic diagram of a magnetic pole piece including a slit electromagnetic steel sheet according to an embodiment of the present invention, in which notch positions are dispersed; FIG. 11 is a schematic diagram of magnetic pole pieces laminated by line welding according to an embodiment of the present invention. FIG. 12 is a schematic diagram of a pole piece including an inclined portion according to an embodiment of the present invention; FIG. 13 is a schematic diagram showing an inclination pattern of an inclined portion according to an embodiment of the present invention; FIG. 14 is a schematic diagram showing an inclination pattern of an inclined portion according to another embodiment of the present invention; FIG. MODE FOR CARRYING OUT THE INVENTION [0011] Several embodiments of the present invention will be described below with reference to the accompanying drawings. However, the dimensions, materials, shapes, relative arrangements, etc. of the components described as embodiments or shown in the drawings are not intended to limit the scope of the present invention, and are merely illustrative examples. No. For example, expressions denoting relative or absolute arrangements such as "in a direction", "along a direction", "parallel", "perpendicular", "center", "concentric" or "coaxial" are strictly not only represents such an arrangement, but also represents a state of relative displacement with a tolerance or an angle or distance to the extent that the same function can be obtained. For example, expressions such as "identical", "equal", and "homogeneous", which express that things are in the same state, not only express the state of being strictly equal, but also have tolerances or differences to the extent that the same function can be obtained. It shall also represent the existing state. For example, expressions that express shapes such as squares and cylinders do not only represent shapes such as squares and cylinders in a geometrically strict sense, but also include irregularities and chamfers to the extent that the same effect can be obtained. The shape including the part etc. shall also be represented. On the other hand, the expressions "comprising", "comprising", "having", "including", or "having" one component are not exclusive expressions that exclude the existence of other components. [0012] (Configuration of magnetic gear 9) FIG. 1 is a schematic cross-sectional view orthogonal to the axial direction b of the magnetic gear 9 according to one embodiment of the present invention. 2 is a partially enlarged cross-sectional view of the magnetic gear shown in FIG. 3, 4A and 5-14 are schematic diagrams of a pole piece 2 according to one embodiment of the invention. In the following description, the direction along the rotational direction of the magnetic gear 9 (magnetic pole piece device 1) is the circumferential direction a, and the direction along the rotational axis (axis line l) of the magnetic gear 9 (magnetic pole piece device 1) is the axis. A direction (radial direction) orthogonal to the circumferential direction a and the axial direction b will be described as a radial direction c. [0013] The magnetic gear 9 is a device that has a mechanism that uses the attractive force and repulsive force of a magnet to transmit torque without contact. The magnetic gear 9 shown in FIGS. 1 and 2 is of a magnetic flux modulation type (harmonic type), and as shown, the outer diameter side magnet field 7 having a cylindrical (annular shape, the same applies hereinafter) shape as a whole. (outer rotor), an inner diameter magnet field 8 (inner rotor) having an overall cylindrical or columnar shape, and a magnetic pole piece device 1 (center rotor) having an overall cylindrical shape. there is When the magnetic pole piece device 1 is arranged between the outer magnet field 7 and the inner magnet field 8, they are arranged on the same axis l (coaxial) and are spaced apart from each other in the radial direction c by a certain distance. are arranged with an interval (air gap G) of . That is, the outer magnet field 7 is arranged radially outside (on the outer diameter side) of the inner magnet field 8 . Also, the pole piece device 1 is arranged between the inner diameter magnet field 8 and the outer diameter magnet field 7 . The outer magnet field 7, the inner magnet field 8 and the pole piece device 1 are arranged concentrically. [0014] In addition, as shown in FIG. 2, the outer diameter side magnetic field 7 and the inner diameter side magnetic field 8 are circumferentially spaced (equally spaced) in a cross section cut along the radial direction c of the magnetic gear 9. It has a magnetic pole pair (71, 81) such as a permanent magnet consisting of a plurality of N and S poles spaced apart. Specifically, the outer diameter magnet field 7 has a plurality of magnetic pole pairs 71 and a support member 72 that supports the plurality of magnetic pole pairs 71 . On the cylindrical inner peripheral surface of the outer magnet field 7, a plurality of magnetic pole pairs 71 are arranged so that the magnetic poles face the radial direction c, and the N poles and S poles are alternately arranged along the circumferential direction. It is installed over the entire circumference so as to be replaced. Similarly, the inner diameter magnet field 8 has a plurality of magnetic pole pairs 81 and a cylindrical support member 82 that supports the plurality of magnetic pole pairs 81 . A plurality of magnetic pole pairs 81 are arranged on the cylindrical outer peripheral surface of the inner diameter magnet field 8 along the entire circumference along the circumferential direction a in the same manner as described above. The magnetic pole piece device 1 also has a plurality of magnetic pole pieces 2 (pole pieces) arranged at intervals (equal intervals) over the entire circumference in the circumferential direction a. Then, for example, when the inner diameter side magnet field 8 is rotated, the magnetic flux of the inner diameter side magnet field 8 is modulated by the magnetic pole piece of the pole piece device 1, and the magnetic pole is changed by the action of the modulated magnetic field and the outer diameter side magnet field 7. Rotational torque is generated in the single device 1 . [0015] 2, the magnetic pole piece device 1 includes an outer peripheral cover member 52 and an inner peripheral cover member 53 which are arranged outside and inside in the radial direction c so as to sandwich the plurality of magnetic pole pieces 2. may have. The outer peripheral cover member 52 and the inner peripheral cover member 53 are members each having a cylindrical shape, and the diameter of the inner peripheral cover member 53 is smaller than the diameter of the outer peripheral cover member 52 . Therefore, when the inner peripheral cover member 53 is coaxially arranged inside the outer peripheral cover member 52, a cylindrical space is formed over the entire circumference between the inner peripheral surface of the outer peripheral cover member 52 and the outer peripheral surface of the inner peripheral cover member 53. It is formed. In this cylindrical space, a plurality of long magnetic pole pieces 2 are arranged with their longitudinal directions along the axial direction b and spaced from each other in the circumferential direction a. At this time, the space between each of the plurality of magnetic pole pieces 2 (inter-adjacent space 54) may be a space, or a non-magnetic material may be provided. However, the magnetic pole piece device 1 may not have the two cover members described above, and may include a non-magnetic material placed between each of the plurality of magnetic pole pieces 2 . [0016] In the embodiment shown in FIGS. 1 and 2, the magnetic gear 9 (flux modulation type magnetic gear) is integrated with the motor to form a magnetic geared motor. More specifically, as shown in FIG. 2, in the magnetic geared motor, a plurality of coils 73 are installed in the outer magnet field 7 to form a stator. Rotate the magnetic field 8 (high-speed rotor). As a result, the magnetic pole piece device 1 (low-speed rotor) rotates in accordance with the reduction ratio determined by the ratio of the number of pole pairs of the magnetic pole pairs 71 of the outer magnet field 7 to the number of pole pairs of the magnetic pole pairs 81 of the inner magnet field 8. It is designed to rotate. [0017] In addition, a cooling medium such as air or water is supplied to the magnetic geared motor to protect the above components from the heat generated during operation. In the embodiment shown in FIGS. 1-2, as shown in FIG. 2, the cooling medium is provided at one end of each of the air gaps G formed on the inner and outer peripheral sides of the pole piece device 1, respectively. It is supplied so as to flow from one side toward the other end. In addition, the cooling medium is similarly supplied to the gap formed between the outer diameter side magnet field 7 and a housing (not shown) positioned on the outer peripheral side thereof. A gas such as air may be supplied to the gap between the outer magnet field 7 and the housing (not shown), or a water-cooled pipe may be installed, and cooling water or the like may be supplied to the water-cooled pipe. may be distributed. [0018] Although the case where the magnetic gear 9 is a magnetic geared motor has been described as an example, the magnetic gear 9 can also operate as a magnetic geared generator. In this case, the magnetic pole piece device 1 (center rotor) rotates as the inner diameter magnet field 8 (inner rotor) rotates. pole piece device More about this source textSource text required for additional translation information Send feedback Side panels History Saved Contribute 5,000 character limit. Use the arrows to translate more.The operation differs depending on whether 1 is a magnetic geared motor or a magnetic geared generator, but the structure of the device is the same. [0019] (Configuration of magnetic pole piece device 1) In the magnetic gear 9 (flux modulation type magnetic gear) having the above configuration, as shown in FIGS. of electromagnetic steel sheets 3. More specifically, each electromagnetic steel sheet 3 is a plate member formed by processing a soft magnetic material into a plate shape. It has a short side and a predetermined length (thickness) in a thickness direction orthogonal to each of the longitudinal direction and the short side direction. At least part of the surface of each electromagnetic steel sheet 3 may be coated with an insulating film. [0020] As shown in FIG. 3, in each magnetic pole piece 2, each of the plurality of magnetic steel sheets 3 is laminated along the circumferential direction a with its longitudinal direction along the axial direction b. That is, the stacking direction of the plurality of electromagnetic steel sheets 3 in each magnetic pole piece 2 is the direction along the circumferential direction a (thickness direction of the electromagnetic steel sheets 3) when arranged in the magnetic pole piece device 1 . Therefore, when arranged in the magnetic pole piece device 1, the ends of the magnetic pole pieces 2 in each of the axial direction b and the radial direction c are formed into slits by laminating a plurality of electromagnetic steel plates 3. . Therefore, it is possible to reduce core loss (eddy current loss) due to leakage flux at the end of each pole piece 2 in the axial direction b. In the case where each magnetic steel sheet 3 has the above-described insulating coating, the presence of the insulating coating between adjacent magnetic steel sheets 3 in a laminated state makes it possible to further suppress the above-described iron loss. . [0021] In the embodiments shown in FIGS. 3 to 14, the electromagnetic steel sheet 3 is a rectangular plate member whose longitudinal direction and transverse direction are perpendicular to each other. The length of each magnetic steel plate 3 in the longitudinal direction corresponds to the length of the outer magnet field 7 and the inner magnet field 8 in the axial direction b. The length of each electromagnetic steel plate 3 in the lateral direction is arranged between the outer magnet field 7 and the inner magnet field 8 with the lateral direction of each electromagnetic steel plate 3 along the radial direction c. It has a length that enables formation of an appropriate air gap G over the entire circumference of each of the inner and outer circumferences of the pole piece device 1 when the magnetic pole piece device 1 is formed. In addition, the thickness of each electromagnetic steel sheet 3 is shorter than the length in its longitudinal direction and lateral direction. Each magnetic pole piece 2 is formed by integrating a plurality of magnetic steel sheets 3 in a laminated state by, for example, welding or an adhesive. [0022] According to the above configuration, each magnetic pole piece 2 provided in the magnetic pole piece device 1 is arranged along the circumferential direction of the magnetic gear 9 with its longitudinal direction along the axial direction of the magnetic gear 9 (magnetic pole piece device 1). It is formed of a plurality of laminated electromagnetic steel sheets 3 . As a result, iron loss (eddy current loss) due to leakage flux at the end of each magnetic pole piece 2 in the axial direction b can be reduced, and the efficiency of the magnetic gear 9 provided with such a magnetic pole piece device 1 can be improved. be able to. [0023] In addition, the number of laminated magnetic steel sheets 3 required to form the magnetic pole piece 2 can be reduced compared to the case where a plurality of magnetic steel sheets 3 are laminated along the axial direction. Therefore, it is possible to improve the dimensional accuracy of the magnetic pole pieces 2 after lamination (dimensional error after lamination=error in the lamination direction length of each magnetic steel plate×number of laminated sheets). In addition, since the number of laminated magnetic steel sheets 3 is small in this way, it is possible to reduce the deviation of the end face of each magnetic steel sheet 3 when a plurality of magnetic steel sheets 3 are laminated when manufacturing the magnetic pole piece 2. For example, when fixing by pressure clamping and wire welding, application of wire welding fixation can be easily performed. When a plurality of electromagnetic steel sheets 3 are laminated along the axial direction, long fastening bolts made of non-magnetic material such as titanium alloy are used, but such bolts are no longer necessary, and the number of parts and cost can be reduced. [0024] Next, several other embodiments of the magnetic pole piece 2 (pole piece) described above will be described with reference to FIGS. 4A to 14, respectively. 4A, 5 to 14, and the magnetic pole piece device 1, each magnetic pole piece 2 has a longitudinal direction, a transverse direction, and a thickness direction of each magnetic steel plate 3, respectively, in an axial direction b, a radial direction c, and a circumferential direction. are arranged along the direction a. [0025] FIG. 4A is a schematic diagram of a pole piece 2 with a high thermal conductivity plate 4 according to one embodiment of the present invention. FIG. 4B is a diagram showing the relationship between the tensile modulus and thermal conductivity of CRFP. In some embodiments, each of the plurality of magnetic pole pieces 2 is disposed between at least a pair of adjacent magnetic steel plates 3 in the plurality of stacked magnetic steel plates 3, as shown in FIG. 4A. A high thermal conductivity plate 4 having a thermal conductivity higher than that may be further provided. The high thermal conductivity plate 4 has a plate shape with a longitudinal direction, as shown in FIG. 4A. The high thermal conductivity plate 4 is made of, for example, ceramics with high thermal conductivity such as aluminum, copper, or silicon nitride, which have higher thermal conductivity than iron, or pitch-based or PAN (polyacrylonitrile)-based carbon fiber reinforced plastic (hereinafter referred to as CFRP), and the like. [0026] In the embodiment shown in FIG. 4A, the high thermal conductivity plate 4 is a rectangular plate having long sides and short sides having the same length as the electromagnetic steel sheet 3, the longitudinal direction and the short side direction being orthogonal to each other. It is a component. Moreover, the thickness of the high thermal conductivity plate 4 is equal to or less than the thickness of the electromagnetic steel plate 3 . However, the present invention is not limited to this embodiment, and the dimensions (long side and short side lengths, thickness) of the high thermal conductivity plate 4 may be set arbitrarily. [0027] In addition, in the embodiment shown in FIG. 4A, the high thermal conductivity plate 4 is made of pitch-based CFRP. As shown in FIG. 4B, the thermal conductivity of CFRP depends on the tensile elastic modulus (Young's modulus), and tends to increase as the tensile elastic modulus increases. Specifically, the thermal conductivity of pitch-based CFRP is greater than iron at a tensile modulus of about 400 GPa (gigapascals). In the range of about 400 GPa to about 600 GPa, there is not much difference from that of PAN-based CFRP, and the rate of increase (slope) of thermal conductivity with respect to tensile elastic modulus has a substantially constant magnitude. However, the rate of increase in the thermal conductivity of pitch-based CFRPs can be greater when the tensile modulus is between about 600 GPa and about 800 GPa, and even more sharply above about 800 GPa to at least about 950 GPa. have been discovered. For example, the thermal conductivity of pitch-based CFRP is comparable to aluminum at a tensile modulus of about 800 GPa and exceeds copper at a tensile modulus of about 900 GPa. [0028] Therefore, in some embodiments, the high thermal conductivity plate 4 may be made of pitch-based CFRP. More specifically, the high heat conductive plate 4 may be formed of pitch-based CFRP having a tensile modulus of elasticity of 700 GPa to 950 GPa or 850 GPa or more, for example, 700 GPa or more. When pitch-based or PAN-based CFRP is used as the high heat conductive plate 4, it has a tensile modulus of elasticity higher than that of the electromagnetic steel sheet 3, such as a tensile modulus of 400 GPa or more. I wish I could. [0029] As already explained, in the magnetic gear 9, a cooling medium such as cooling air is supplied to each air gap G between the pole piece device 1 and each of the outer magnet field 7 and the inner magnet field 8. may be In this case, since the cooling medium supplied to the air gap G flows along the air gap G along the axial direction, the heated magnetic pole piece 2 is cooled from both ends in the radial direction c of the magnetic pole piece 2 that are in contact with the air gap G. However, if the thermal conductivity inside the pole piece 2 is low, the heat will stay inside the pole piece 2, resulting in poor cooling performance. However, by actively conducting the heat of the electromagnetic steel sheets 3 in the radial direction c by using the high heat conduction plates 4 installed between the plurality of electromagnetic steel sheets 3, the cooling effect of the two air gaps G is improved. It is possible to [0030] According to the above configuration, the plurality of magnetic steel sheets 3 in each of the plurality of magnetic pole pieces 2 are laminated while sandwiching at least one high thermal conductivity plate 4 therebetween. As a result, the magnetic pole pieces 2 can be cooled more uniformly and efficiently by the high thermal conductivity plates 4 placed between the plurality of electromagnetic steel plates 3, and the air on the inner and outer peripheral sides of the magnetic pole piece device 1 can be cooled. Cooling of each pole piece 2 by the cooling medium passing through the gap G can be performed more efficiently. [0031] Further, for example, when the high thermal conductivity plate 4 is formed of CFRP as described above, in some embodiments, as shown in FIG. Hereinafter, at least a portion may have a portion in which the fiber direction D) is along the radial direction c. In the embodiment shown in FIG. 4A, the high thermal conductivity plate 4 is oriented with the fiber direction D along the radial direction c in any of the axial directions b, from end to end in the radial direction c of the high thermal conductivity plate 4, and all are oriented along the radial direction c. [0032] However, the present invention is not limited to this embodiment. In some other embodiments, the high thermal conductivity plate 4 may have the fiber direction D oriented along the radial direction c at least in a portion including the center in the longitudinal direction. For example, the fiber direction D is along the axial direction b from at least one end, such as the end of the high heat conduction plate 4 on the side to which the cooling medium is supplied in the axial direction b, to a predetermined range along the axial direction b. can be As a result, the heat of the pole piece 2 can be easily conducted along the axial direction b. [0033] According to the above configuration, the CFRP fibers that make up the high thermal conductivity plate 4 are at least partially oriented along the radial direction c. Heat is better conducted along the fiber direction D. Thus, having the fiber direction D of the CFRP along the radial direction in the high thermal conductivity plate 4 cools the pole piece 2 more effectively than if the fiber direction D were oriented along other than the radial direction c. can be done. [0034] However, the present invention is not limited to this embodiment. In some other embodiments, the fiber direction D of the high thermal conductivity plate 4 made of CFRP may be other than the radial direction c. For example, fibers may be oriented in a mesh. [0035] FIG. 5 is a schematic diagram of a pole piece 2 having rounded ends according to one embodiment of the present invention. In some embodiments, as shown in FIG. 5 , each of the plurality of magnetic steel sheets 3 forming the magnetic pole piece 2 has a body portion 31 having a predetermined radial height H1 and a An end portion provided on at least one side of the main body portion 31 and having a radial height H2 smaller than the radial height H1 of the main body portion 31 (H1>H2) (hereinafter referred to as a small height end portion 32) and may contain With this configuration, the bulge of magnetic flux lines from the ends of the magnetic pole pieces 2 formed by laminating the small height ends 32 of the plurality of electromagnetic steel sheets 3 to the outside becomes small, and the leakage magnetic flux in the axial direction b is reduced. can be reduced. [0036] In the embodiment shown in FIG. 5, the radial height H1 of the main body portion 31 of each electromagnetic steel sheet 3 is constant, and both ends of the main body portion 31 in the longitudinal direction are connected to the small height end portions 32 described above. It has become. More specifically, each of the end portions of each electromagnetic steel sheet 3 has an arcuate shape (round shape) having a predetermined radius of curvature when viewed from the circumferential direction a side. Both ends of the magnetic pole piece 2 are formed in an arc shape by stacking the magnetic steel sheets 3 . [0037] However, the present invention is not limited to this embodiment. In some other embodiments, the small height end portion 32 of each electromagnetic steel plate 3 has a rectangular shape when viewed from the circumferential direction a side, and the corners of the end portion are cut linearly. It may have a missing shape. In some other embodiments, when viewed from the circumferential direction a side, it may be formed in a convex shape in the axial direction b, and by reducing the area at the tip, magnetic flux leakage in the axial direction is reduced. It becomes possible to [0038] According to the above configuration, each electromagnetic steel plate 3 has a radial height H2 of at least one end portion (small height end portion 32) in the longitudinal direction (axial direction b) equal to the radial height H2 of the main body portion 31. smaller than H1. This makes it possible to reduce the leakage flux at the end of the pole piece 2. More about this source textSource text required for additional translation information Send feedback Side panels History Saved Contribute 5,000 character limit. Use the arrows to translate more., iron loss (eddy current loss) at the end of the pole piece 2 can be suppressed. [0039] In the above-described embodiments, in some embodiments, at least one of the plurality of magnetic pole pieces 2 is a first magnetic pole piece 2a composed of a plurality of electromagnetic steel plates 3 having the small height end portion 32. Also good. Then, as shown in FIG. 5, a cover member 33 having a thermal conductivity higher than that of the electromagnetic steel plate 3 may be attached to the small height end portion 32 of the first magnetic pole piece 2a. Since the cover member 33 has a high thermal conductivity, the heat of the electromagnetic steel sheet 3 is easily conducted to the cover member 33, and cooling of the magnetic pole piece 2 (electromagnetic steel sheet 3) can be facilitated. [0040] In the embodiment shown in FIG. 5, the cover member 33 has a square shape when the magnetic pole piece 2 to which the first magnetic pole piece 2a is mounted is viewed from any of the circumferential direction a, the axial direction b, and the radial direction c. It has a shape like The cover member 33 is made of pitch-type CFRP, and is made so that the fiber direction D is aligned with the radial direction c when attached to the first magnetic pole piece 2a. [0041] However, the present invention is not limited to this embodiment. In some other embodiments, the shape of the cover member 33 is arbitrary so long as it can be attached to the low end 32 of the first pole piece 2a, and the end of the first pole piece 2a is It may have a shape that is not visually recognized as a square. The material of the cover member 33 may also have a higher thermal conductivity than the electromagnetic steel plate 3. For example, the same material as that of the high thermal conductivity plate 4 may be used. The direction D may be a direction other than the radial direction c. [0042] According to the above configuration, the end portion of the magnetic pole piece 2 formed of the plurality of magnetic steel sheets 3 having the small height end portion 32 has a higher thermal conductivity than the magnetic steel plate 3 at the end portion on the small height end portion 32 side. A cover member 33 formed of, for example, a pitch-based CFRP block is attached. Thereby, the cooling performance of the pole pieces 2 can be further improved. [0043] FIG. 6 is a schematic diagram of a pole piece 2 having anisotropy in magnetic permeability according to one embodiment of the present invention. In some embodiments, as shown in FIG. 6, the magnetic permeability of each of the plurality of magnetic steel sheets 3 forming the pole piece 2 may have anisotropy. Specifically, when the magnetic permeability along the longitudinal direction of each of the plurality of electromagnetic steel sheets 3 is P1, and the magnetic permeability along the lateral direction is P2, the relationship of P1