MAGNET, ELECTRIC MOTOR, AND METHOD OF MANUFACTURING MAGNET

Abstract

Provided is a magnet that allows the orientation direction of main and auxiliary pole pieces to be set precisely and enables easy fabrication of flux focusing permanent magnet units having a high magnetic flux density A magnet 22 includes permanent magnet units 22a each including a main pole piece 221 and auxiliary pole pieces 222. The main pole piece 221 is composed of permanent magnet sheets 221a with substantially the same thickness stacked in the thickness direction. The auxiliary pole pieces 222 are composed of permanent magnet sheets 222a with substantially the same thickness stacked in the thickness direction and arranged at positions adjacent to the main pole piece 221 with orientation directions different from the orientation direction of the main pole piece 221 thereby to focus the magnetic flux at the main pole piece 221.

Claims

1-7. (canceled)

8. A magnet comprising a permanent magnet unit comprising: a main pole piece including permanent magnet sheets with substantially same thickness stacked in a thickness direction; and an auxiliary pole piece including permanent magnet sheets with substantially same thickness stacked in the thickness direction, the auxiliary pole piece being positioned adjacent to the main pole piece in such a manner that an orientation direction of the auxiliary pole piece differs from an orientation direction of the main pole piece thereby to focus a magnetic flux at the main pole piece.

9. The magnet according to claim 8, wherein the permanent magnet sheets of the main pole piece and the permanent magnet sheets of the auxiliary pole piece have the same orientation direction.

10. The magnet according to claim 8, wherein the permanent magnet sheets of the main pole piece and the permanent magnet sheets of the auxiliary pole piece have same thickness.

11. The magnet according to claim 8, wherein at least one of the main pole piece and the auxiliary pole piece is further divided in a direction orthogonal to a thickness direction.

12. The magnet according to claim 8, wherein the permanent magnet unit is provided for each pole, is positioned along a thrust generation direction, and includes, in a portion of a core being a thrust generation element, a magnet holder including a wall-shaped part extending in a direction orthogonal to the thrust generation direction between the permanent magnet units, and an enlarged part extending from an end of the wall-shaped part in a direction overlaying a corner portion on an end side of each of the pennanent magnet units.

13. An electric motor comprising: a rotor including the magnet according to claim 8.

14. An electric motor comprising: a rotor including the magnet according to claim 9.

15. An electric motor comprising: a rotor including the magnet according to claim 10.

16. An electric motor comprising: a rotor including the magnet according to claim 11.

17. An electric motor comprising: a rotor including the magnet according to claim 12.

18. A method of manufacturing a magnet, comprising: constructing a main pole piece by cutting out a stacked body including a stack of permanent magnet sheets from a predetermined direction; and constructing an auxiliary pole piece by cutting out a stacked body including a stack of permanent magnet sheets having a same orientation as an orientation of the permanent magnet sheets of the main pole piece from a different direction, the auxiliary pole piece having an orientation direction different from an orientation direction of the main pole piece when the auxiliary pole piece is assembled at a position adjacent to the main pole piece.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] FIGS. 1A to 1C are partially enlarged cross-sectional views of an electric motor including magnets according to an embodiment of the present invention.

[0027] FIG. 2 is a perspective view of a permanent magnet unit of a magnet in FIG. 1.

[0028] FIGS. 3A to 3D illustrate the eddy currents generated in the permanent magnet unit.

[0029] FIGS. 4A to 4D illustrate a method of manufacturing the permanent magnet unit.

[0030] FIGS. 5A to 5C illustrate a method of manufacturing magnets according to the embodiment.

[0031] FIGS. 6A and 6B illustrate a method of manufacturing the magnets.

[0032] FIGS. 7A to 7C illustrate the magnetic flux flow generated in the magnets together and a comparative example.

[0033] FIGS. 8A and 8B illustrate a modification of the present invention.

[0034] FIG. 9 illustrates another modification of the present invention.

[0035] FIGS. 10A1 to 10B illustrate another modification of the present invention.

[0036] FIG. 11 illustrates another modification of the present invention.

[0037] FIG. 12 illustrates another modification of the present invention.

DETAILED DESCRIPTION

[0038] An embodiment of the present invention will be described below with reference to the drawings.

[0039] FIG. 1 illustrates an example of an application of the magnets according to the present invention to an electric motor or a motor M.

[0040] As illustrate in FIG. 1A, the motor M is an inner rotor type rotary electric machine including a shaft 1 provided with a rotor 2 or a mover that can rotate together with the shaft 1 and a stator 3 positioned around the outer periphery of the rotor 2.

[0041] The stator 3 includes a substantially cylindrical stator core 31, teeth 32 that are formed integrally on the stator core 31 at equal angular positions and extend toward the inner circumference, and coils 33 wound around the respective teeth 32. The coils 33 are connected to a power supply device (not illustrated) and generate a rotating magnetic field to rotate the rotor 2 by feeding power.

[0042] The rotor 2 is positioned on the inner circumference side of the stator 3 with a predetermined gap therebetween. The rotor 2 includes a substantially cylindrical rotor core 21 and a permanent magnet 22 positioned along the outer circumference of the rotor core 21.

[0043] The permanent magnet 22 is constructed in an annular shape by arranging a number of one-pole permanent magnet units 22a corresponding to the number of poles in the thrust generation direction, that is, in the circumferential direction of the rotor core 21. Each permanent magnet unit 22a consists of a main pole piece 221 and auxiliary pole pieces 222. As illustrated in FIG. 1B, the permanent magnet units 22a constitute a flux focusing magnet such as a Halbach array magnet. The main pole piece 221 is arranged so that the orientation direction indicated by the bold arrow points in the radial direction (R direction), which is the direction orthogonal to the thrust generation direction, while the auxiliary pole pieces 222 are arranged on both sides of the main pole piece 221 so that the orientation directions indicated by the bold arrows point toward the main pole piece 221, that is, in the direction at a predetermined angle (±α, where α is preferably an acute angle) to the radial direction. The orientation direction refers to the direction in which magnetization is easy. The permanent magnet is magnetized along the orientation directions. In FIG. 1 and other drawings, the orientation direction is indicated by a double-headed arrow, and the magnetization direction is indicated by a single-headed arrow.

[0044] The motor M of the present embodiment includes permanent magnet units 22a each including one main pole piece and two auxiliary pole pieces, and a multipole surface magnet type rotor 2 including a number of permanent magnet units 22a corresponding to the number of poles of the motor M.

[0045] The above permanent magnet arrangement provides a flux focusing magnet 22 such as a Halbach array magnet in which the magnetic flux is readily focused at the main pole pieces 221 compared to a parallel orientation magnet.

[0046] A permanent magnet motor has increased magnetic flux density, but also has eddy currents increased in proportion to the square of the magnetic flux due to armature reaction and the excitation frequency. Therefore, when the excitation frequency is increased to radio frequency or the magnetic flux is increased by increasing the current to increase the power density of the motor M, the accompanying increase in eddy currents becomes a problem. Increased eddy current losses lead to heat generation in the magnet 22 and reduced motor efficiency.

[0047] Accordingly, the present embodiment adopts a novel structure for the main pole piece 221 and the auxiliary pole pieces 222 in which multiple permanent magnet sheets 221a and 222a having the same orientation direction are stacked and divided in a direction different from the stacking direction to obtain the main pole pieces 221 and the auxiliary pole pieces 222, as necessary.

[0048] Specifically, the main pole piece 221 is constructed by stacking permanent magnet sheets 221a each having substantially the same thickness t1 in the circumferential direction orthogonal to the orientation direction (R±90 degrees), and each of the auxiliary pole pieces 222 is constructed by stacking permanent magnet sheets 222a having substantially the same thickness t2 in a direction orthogonal to the orientation direction (±α±90degrees). In the present embodiment, the permanent magnet sheets 221a and 222a are made of the same material, and their external dimensions are substantially identical, including their thicknesses t1 and t2. Even when the thicknesses t1 and t2 are different, the effect of adopting a stacked structure or divided structure is the same.

[0049] FIG. 2 illustrates the dimensional relationship between the main pole piece 221 and the auxiliary pole pieces 222. The longitudinal dimensions b1 and b2 of the main pole piece 221 and the auxiliary pole pieces 222, and the axial dimensions c1 and c2 of the main pole piece 221 and the auxiliary pole pieces 222 are set to be substantially identical (identical or approximately identical) to each other.

[0050] As illustrated in FIG. 1, the main pole piece 221 is further divided equally by a dividing surface 221x in a direction (radial direction) orthogonal to the thickness direction of the permanent magnet sheets 221a. In the illustrated example, the main pole piece 221 is divided in halves, but the main pole piece 221 may be divided into any number of sections. Although not illustrated, the auxiliary pole pieces 222 may also be divided in a similar manner.

[0051] In the permanent magnet having a stacked structure as illustrated in FIG. 3B, eddy currents flow through cross-sections that are each smaller than the cross-section of a mass of permanent magnet (main pole piece 221 and auxiliary pole pieces 222) illustrated in FIG. 3A through which an eddy current flows. By further dividing the permanent magnet as in FIG. 3C, the cross-sections through which the eddy currents flow becomes even smaller. As a result, the eddy current loss is smaller in the structure in FIG. 3B than in structure in FIG. 3A, and even smaller in the structure in FIG. 3C. This results in less heat generation in the magnet 22 and lower motor efficiency, thereby allowing greater currents to flow. Therefore, it is possible to increase the power density of the motor through an increase in excitation frequency by multipolarity.

[0052] As illustrated in FIG. 3D, the permanent magnet can be divided into multiple sections in the axial direction as well.

[0053] To achieve such a stacked structure of a main pole piece 221 and auxiliary pole pieces 222, the present embodiment adopts a method of manufacturing a magnet illustrated in FIG. 4.

[0054] First, as illustrated in FIG. 4A, thin permanent magnet sheets 221a (222a) are cut out from the permanent magnet block. After the permanent magnet sheets 221a (222a) are bonded together, as illustrated in FIG. 4B, main pole pieces 221 are cut out from the stacked body of the permanent magnet sheets 221a, as illustrated in FIG. 4C1, and auxiliary pole pieces 222 are cut out from the stacked body of the permanent magnet sheets 222a, as illustrated in FIG. 4C2.

[0055] To obtained a main pole piece 221, a quadrangle x1 having two sides extending along the stacking direction is obtained by cutting the stacked body from the small end direction. To obtained an auxiliary pole piece 222, a quadrangle x2 oblique to the stacking direction is obtained by cutting the stacked body from the small end direction.

[0056] Then, as illustrated in FIG. 4D, the main pole pieces 221 and the auxiliary pole pieces 222 are bonded together. Two main pole pieces 221 are bonded together to form one main pole piece 221 divided into two sections in the orientation direction. The number of divisions is only an example.

[0057] If a permanent magnet (main pole pieces 221 and auxiliary pole pieces 222) having different orientation directions can be made with one type of finishing jig, only one type of finishing jig will be needed, and the cost of making magnets including mold and processing costs can be reduced.

[0058] With regard to a magnetization process, as in the case of a conventional Halbach array magnet illustrated in FIG. 5A, if a main pole piece I orientated in the radial direction of a rotor 2 and auxiliary pole pieces II oriented in the circumferential direction of the rotor 2 are integrated, the orientation direction of the permanent magnet is not parallel to the magnetic field generated by magnetization coils. Consequently, a magnetic field appropriately passing through the main pole piece I and the auxiliary pole pieces II cannot be generated for magnetization of the permanent magnet.

[0059] In particular, in a multipole structure illustrated in FIG. 5A1, a magnetic field that passes through all of the main pole pieces I and the auxiliary pole pieces II with different orientation directions needs to be generated. As a result, it is difficult to fabricate coils that can generate such a magnetic field for magnetization.

[0060] In contrast, as illustrated in FIG. 5A2, if the main pole pieces I and the auxiliary pole pieces II are to be magnetized individually, the number of steps for magnetization increases. Also, during bonding of the main pole pieces I and the auxiliary pole pieces II to a rotor core 21, the magnetic attractive force and the repulsive force of the main pole pieces I and the auxiliary pole pieces II are intense and frequently cause an effect that makes the bonding process difficult.

[0061] Therefore, as illustrated in FIG. 5B, the orientation directions of the auxiliary pole pieces 222 are set to acute angles ±α to the orientation direction of the main pole piece 221. Then, as illustrated in FIG. 5C, the unmagnetized main pole piece 221 and auxiliary pole pieces 222 are bonded together to form a one-pole permanent magnet unit 22a. Finally, a magnetic field for magnetization is applied to each permanent magnet unit 22a.

[0062] The shape of the permanent magnet unit 22a in FIG. 5C is actually the fan shape illustrated in FIG. 6A since the permanent magnet unit 22a is arranged around the rotor core 21.

[0063] FIG. 6A illustrates each permanent magnet unit 22a, i.e., one main pole piece 221 and two auxiliary pole pieces 222 being magnetized individually. Adjacent permanent magnet units 22a are magnetized so that their S and N poles are opposite to each other. These permanent magnet units 22a are bonded to the rotor core 21 to achieve the bonding state illustrated in FIG. 6B.

[0064] This eliminates the trouble of magnetization and the magnetic influence between the permanent magnets, such as when each of the permanent magnets I to IX is magnetized before being bonded to the rotor core 21. This also eliminates the problem of generating an intense magnetic flux for magnetization, such as when all permanent magnets I to IX are magnetized at once after being bonded to the rotor core 21. As a result, the permanent magnets I to IX can be magnetized with an appropriate magnetic flux, and since the permanent magnet units 22a have already been bonded to the rotor core 21 one by one, there is only the influence of the magnetic effect between the permanent magnet units 22a and 22a, and the influence of magnetic attractive force and repulsion can be reduced as much as possible.

[0065] The permanent magnet units 22a each consisting of a main pole piece 221 and auxiliary pole pieces 222 are held in a magnet holder 210 of the rotor core 21 illustrated in FIG. 1. The magnet holder 210 has a wall-shaped part 210a and an enlarged part 210b. The wall-shaped part 210a is a single unit that protrudes from the cylindrical rotor core 21 at equal intervals in the radial direction orthogonal to the thrust generation direction and extends between the permanent magnet units 22a to the vicinity of the gap between the stator 3 and the rotor 2. The enlarged part 210b extends in the circumferential direction (in the direction forming a T-shape) of the rotor core 21 from the tip of the wall-shaped part 210a so as to overlay the corners of the auxiliary pole pieces 222 at the edge of the permanent magnet unit 22a. The enlarged part 210b mechanically holds the corners of the auxiliary pole pieces 222 of adjacent permanent magnet units 22a and 22a in the radial direction. The wall-shaped part 210a may serve to hold the permanent magnet units 22a in the circumferential direction.

[0066] In such a case, chamfered parts 222b are provided on the corner portions at the edges of the auxiliary pole pieces 222, and the enlarged part 210b is shaped along the chamfered parts 222b so that the outer circumferential surfaces 22a1 of the permanent magnet units 22a and the outer circumferential surface 210b1 of the enlarged part 210b are substantially flush. The chamfered parts 222b are surfaces tilting in the orientation directions of the auxiliary pole pieces 222 of the permanent magnet unit 22a, and the enlarged part 210b is tapered and shaped as an inverted triangle.

[0067] In the case of a parallel orientation magnet 22′ in FIG. 7A, short-circuiting through the magnet holder 210 is likely to occur by providing the magnet holders 210. In contrast, in the case of the flux focusing magnet 22 illustrated in FIG. 7B, holding by the magnet holders 210 having an enlarged part along the orientation direction causes the orientation directions of the auxiliary pole pieces to tilt toward the center of the magnetic pole even with the magnet holders 210, thereby preventing short circuiting through the magnet holder 210 and reducing magnetic flux leakage.

[0068] By holding the magnet 22 in this way with the magnet holders 210 that forms an integral part of the rotor core 21, the magnet 22 can be mechanically held by only the magnetic circuit components of the motor M. As a result, a cylindrical magnet holder part 210′ as illustrated in FIG. 7C is not needed. Since the enlarged part 210b is accommodated in the chamfered parts 222b, the gap length between the stator 3 and the rotor 2 is reduced, as illustrated in FIG. 1, to achieve the effect of increasing the fundamental wave component of the magnetic flux density due to the magnet 22.

[0069] As it is apparent from the original magnetic flux (parallel magnetic flux) other than the short-circuit magnetic flux H′ illustrated in FIG. 7A and the original magnetic flux (magnetic flux consisting of the main pole pieces 221 and the auxiliary pole pieces 222) other than the short-circuit magnetic flux H illustrated in FIG. 7B under the magnetic flux focusing structure such as a Halbach array, the effect of an increase in the fundamental wave component of the magnetic flux density due to the magnet 22 is achieved also by shifting the original magnetic flux toward the pole center.

[0070] When the fundamental wave component of the magnetic flux density by the magnet 22 increases in a motor having the same size and current due to the effect of the above two points, the torque increases because the torque is proportional to the product of the fundamental wave of the in-slot current, the fundamental wave of the magnetic flux density, and the motor product thickness.

[0071] When the magnetic flux density by the magnet 22 increases in a motor having the same size and torque due to the effect of the above two points, the current decreases and the copper loss decreases because the copper loss is proportional to the product of the square of the in-slot current and the winding resistance. Since a reduction in copper losses causes a reduction in motor input, such a reduction leads to an increase in motor efficiency or the ratio of output to input.

[0072] Furthermore, an increase in the magnetic flux density by the magnet 22 in a motor having the same size and current due to the effect of the above two points makes the motor product thickness smaller to make the motor M smaller and lighter.

[0073] In this way, reducing the gap length by eliminating the cylindrical magnet holder part 210′ or minimizing the short-circuiting of the magnetic flux by making the magnet 22 a flux focusing type like a Halbach array causes an increase in the magnetic flux density by the magnet 22, allowing an increase in torque, an increase in efficiency, and a reduction in size and weight.

[0074] Therefore, if the motor M is applied to a field in which miniaturization and weight reduction are important, such as a high-power density motor for aircrafts and automobiles, miniaturization and weight reduction can be achieved, and use as a motor that can operate even in a temperature environment with a large temperature difference is possible because of the above-described mechanical holding structure.

[0075] As described above, the magnet 22 of the present embodiment includes the permanent magnet units 22a each including a main pole piece 221 and auxiliary pole pieces 222. The main pole piece 221 is composed of the permanent magnet sheets 221a with substantially the same thickness stacked in the thickness direction. The auxiliary pole pieces 222 are composed of the permanent magnet sheets 222a with substantially the same thickness stacked in the thickness direction and arranged at positions adjacent to the main pole piece 221 with orientation directions different from the orientation direction of the main pole piece 221 thereby to focus the magnetic flux at the main pole piece 221.

[0076] In this way, by adopting main pole pieces 221 and auxiliary pole pieces 222 having a stacked structure of permanent magnet sheets 221a and 222a, the orientation directions can be set more accurately than main pole pieces 221 and auxiliary pole pieces 222 composed of lumps of permanent magnets, and a flux focusing type permanent magnet unit 22a having a high magnetic flux density can be easily and appropriately fabricated. Moreover, dividing the magnets reduces the eddy current and thereby reduces the eddy current loss. The resulting temperature drop achieves a high magnetic flux density as a flux focusing magnet such as a Halbach array. Thus, when applied to motors and the like, further miniaturization and higher output can be achieved.

[0077] At this time, the permanent magnet sheets 221a constituting the main pole piece 221 and the permanent magnet sheets 222a constituting the auxiliary pole pieces 222 have the same orientation direction with respect to the sheet coordinate system, so that the main pole piece 221 and the auxiliary pole pieces 222 can be easily fabricated.

[0078] Moreover, the permanent magnet sheets 221a constituting the main pole piece 221 and the permanent magnet sheets 222a constituting the auxiliary pole pieces 222 have the same thickness with respect to the sheet coordinate system, so that the main pole piece 221 and the auxiliary pole pieces 222 can be even more easily fabricated.

[0079] The main pole piece 221 is further divided in a direction orthogonal to the thickness direction, and thereby the surface generating eddy current loss becomes smaller. Therefore, the eddy current loss is reduced, the magnetic flux density is increased, and it becomes possible to further miniaturize and increase the output power when applied to motors and the like.

[0080] A portion of the external shape of the main pole piece 221 and the auxiliary pole pieces 222 have substantially the same dimensions. As a result, the process of matching the dimensions is simplified, and the fabrication of the permanent magnet unit 22a is facilitated.

[0081] The permanent magnet unit 22a is arranged along the thrust generation direction, and a portion of the rotor core 21 has magnet holders 210 each including a wall-shaped part 210a extending in the radial direction or a direction orthogonal to the thrust generation direction between the permanent magnet units 22a and 22a, and an enlarged part 210b extending from the end of the wall-shaped part 210a in a direction overlaying the corner portions on the end side of the auxiliary pole pieces 222 of the permanent magnet unit 22a.

[0082] The structure to hold the permanent magnet unit 22a in the enlarged part 210b allows the permanent magnet to be held only by the magnetic circuit components of the motor. At this time, by providing the chamfered parts 222b at the corner portions of the auxiliary pole pieces 222 of the permanent magnet unit 22a to accommodate the enlarged part 210b, it is possible to avoid an increase in the gap length between the stator 3 and the mover 2 when applied to motors and the like. When the corner portions are held down by the enlarged part 210b, flux leakage through the enlarged part 210b is reduced in the case of a flux focusing magnet such as a Halbach array compared with a parallel orientation magnet, so that the permanent magnet unit 22a can be appropriately held without greatly impairing the magnetic flux density.

[0083] The chamfered parts 222b are surfaces tilting along the orientation direction of the auxiliary pole pieces 222 constituting the permanent magnet unit 22a, and the enlarged part 210b has a tapered shape along the tilting surfaces. Therefore, even when the magnet holder 210 is provided, the magnetic flux does not easily flow through the magnet holder 210 to the rotor core 21, and thus the fundamental wave component of the magnetic flux density by the magnet can be increased.

[0084] When such a magnet is applied to the rotor 2 of the motor M, a multipole surface magnet type rotor 2 that is compact and lightweight with high torque and high efficiency can be appropriately constructed, and its use as a motor for aircraft or the like can be greatly expected.

[0085] Through a method of manufacturing a magnet, the main pole piece 221 and the auxiliary pole pieces 222 are constructed. The main pole piece 221 is constructed by cutting a stacked body made by stacking the permanent magnet sheets 221a in a predetermined direction. The auxiliary pole pieces 222 are constructed by cutting a stacked body made by stacking the permanent magnet sheets 222a having an orientation direction that is the same as that of the permanent magnet sheets 221a of the main pole piece 221 in a different direction so that the auxiliary pole pieces 222 have an orientation direction different from that of the main pole piece 221 in a motor coordinate system when assembled at positions adjacent to the main pole piece 221.

[0086] In this way, the main pole piece 221 and the auxiliary pole pieces 222 having small eddy current losses and different orientation directions when assembled can be easily fabricated in a similar fabrication process. From the point of view of the fabrication method in which the permanent magnet sheets 221a and 222a having the same orientation with respect to the sheet coordinate system are cut out from different directions, the thickness of the permanent magnet sheets 221a and 222a need not be the same, and the materials of the permanent magnet sheets 221a and 222a need not be the same.

[0087] When the same jig is used for cutting out the main pole piece 221 and the auxiliary pole pieces 222, a main pole piece 221 and auxiliary pole pieces 222 having the same dimensions can be easily fabricated.

[0088] Post-processing such as chamfering, etc., may be performed on the cut-out main pole piece 221 and auxiliary pole pieces 222, if necessary. Even when the final forms are different, the manufacturing process can be simplified by using common processing steps up to a certain point.

[0089] Although an embodiment of the present invention was explained above, the specific configuration of each component is not limited to those in the embodiment described above.

[0090] The thickness t1 of the permanent magnet sheets 221a of the main pole piece 221, and the thickness t2 of the permanent magnet sheets 222a of the auxiliary pole pieces 222 may be different.

[0091] The magnetic material for the main pole piece 221 and the auxiliary pole pieces 222 may be different. Between the main pole piece 221 and the auxiliary pole pieces 222, by selecting a material having high coercivity for whichever is easily demagnetized and a material having high residual magnetic flux density for whichever is difficult to demagnetized, the magnet 22 can have a high residual magnetic flux density and is difficult to demagnetize.

[0092] In the present embodiment, the main pole piece 221 is divided in the radial direction and the auxiliary pole pieces 222 are not divided, but as illustrated in FIG. 8A, the auxiliary pole pieces 222 may be divided in a direction orthogonal to the orientation direction. By increasing the number of dividing surfaces 222x, eddy current losses can be reduced more.

[0093] As illustrated in FIG. 8B, second auxiliary pole pieces 223 may be added. In the illustrated example, the orientation direction of the second auxiliary pole pieces 223 is orthogonal to the orientation direction of the main pole piece 221 but alternatively may be an oblique direction (for example, 30, 45, 60, or other degrees). By increasing the number of auxiliary pole pieces 222 and 223 so that the magnetic flux is focused at the main pole piece 221, the magnetic flux density of the magnet can be brought closer to the fundamental component or sine wave. The added auxiliary pole pieces 223 also have dividing surfaces 223x that reduce eddy current losses.

[0094] As illustrated in FIG. 9, the enlarged part 210b of the magnet holder 210 of the rotor core 21 may not be embedded in the magnet 22. In this way, the magnetic flux density by the magnet 22 is increased because the magnet corner portions do not need to be chamfered. However, when the corner portions of the auxiliary pole pieces are not chamfered, the magnetic flux from the corner portions of the auxiliary pole pieces to the stator core 31 can easily pass through the gap between the stator 3 and the rotor 2 through the enlarged part 210b of the magnet holder 210. As a result, the permeability through the gap between the stator 3 and the rotor 2 increases, the inductance increases, and the power factor decreases, so that the application is possible to an acceptable extent.

[0095] Furthermore, as illustrated in FIG. 10A1, a magnet holding surface 210b1 of the enlarged part 210b constituting the magnet holder 210 tapers parallel to the magnetization direction of the auxiliary pole piece 222 constituting the permanent magnet unit 22a. In this way, it is difficult for the magnetic flux H to pass through the enlarged part 210b constituting the magnet holder 210, and the fundamental wave component of the original magnetic flux density can be increased.

[0096] As a comparative example, FIG. 10A2 illustrates the case where the magnet holding surface 210b2 of the enlarged part 210b constituting the magnet holder 210 is positioned at an angle to the magnetization direction. In this way, the magnetic flux H easily passes through the enlarged part 210b constituting the magnet holder 210, and the fundamental wave component of the original magnetic flux density decreases.

[0097] In this way, the tapered shape of the magnet holder 210 illustrated in FIG. 10A1 is more effective in preventing short-circuiting of the magnetic flux in terms of the magnetic flux density than the shape of the magnet holder 210 illustrated in FIG. 10A2. However, the effective area for holding the magnet is smaller, and the force for holding the magnet is smaller, so the application is effective to the extent permitted.

[0098] As illustrated in FIG. 10B, the wall-shaped part 210a constituting the magnet holder 210 may be made into an intermittent structure (comb-shaped) along the direction of the motor shaft m by notching or thinning. This reduces the volume of the magnetic body in the gap between the stator 3 and the rotor 2 illustrated in FIG. 1, so that the inductance is reduced, and the power factor can be improved.

[0099] The rotor core 21 and the permanent magnet units 22a may be bonded into a holding structure by applying an adhesive agent to the contact surface of the wall-shaped part 210a constituting the magnet holder 210 illustrated in FIG. 11 and the auxiliary pole pieces 222 or the contact surface of the outer circumference of the rotor core 21 and the main pole piece 221 or the auxiliary pole pieces 222. By filling the gaps between the permanent magnet units 22a and the rotor core 21 with an adhesive agent, collision due to variation of the gap caused by the linear expansion coefficient difference or dimensional tolerance can be prevented between the permanent magnet units 22a and the rotor core 21.

[0100] Since the wall-shaped part 210a of the magnetic pole holder 210 is positioned between the permanent magnet units 22a and 22a (the auxiliary pole pieces 222 and 222) in this way, the permanent magnet units 22a can be easily held. Therefore, when it is possible to hold the magnet by bonding or the like, the magnet holder 210 can be composed of only the wall-shaped part 210a, as illustrated in FIG. 11, and the enlarged part can be eliminated to increase the suppression effect of short-circuit magnetic flux.

[0101] When the present invention is applied to an outer rotor type motor, the motor may be assembled by bonding the main pole pieces and the auxiliary pole pieces to the inner periphery of the rotor core.

[0102] Furthermore, the magnet including the permanent magnet units of the present invention or its fabrication method may be applied to a stator and a mover of linear electric machines such as linear motors.

[0103] As illustrated in FIG. 12, when the present invention is applied to a linear electric machine, the main pole pieces 221 of the magnet units 22a are oriented in a direction orthogonal to the thrust generation direction, which is the extension direction of the core 21, and the auxiliary pole pieces 222 of the magnet units 22a are oriented in a direction that forms a predetermined angle (±α, where α is preferably an acute angle) to the orientation direction of the main pole pieces 221. In such case, magnet holders similar to the magnet holders 210 in the above embodiment may be positioned between the magnet units 22a and 22a.

[0104] Various other modifications may be applied to other configurations without departing from the gist of the present invention.

TABLE-US-00001 Reference Signs List A electric motor (motor) 2 rotor 3 stator 21 rotor core 22 magnet 22a permanent magnet unit 210 magnet holder 210a wall-shaped part 210b enlarged part 221 main pole piece 222 auxiliary pole piece 221a, 222a permanent magnet sheet