WO2014061908A1

WO2014061908A1 - Double porosity-type power generator

Info

Publication number: WO2014061908A1
Application number: PCT/KR2013/007380
Authority: WO
Inventors: 이성근
Original assignee: Lee Seong Goun
Priority date: 2012-10-19
Filing date: 2013-08-16
Publication date: 2014-04-24
Also published as: KR101238855B1

Abstract

Disclosed is a double porosity-type power generator that reduces the occurrence of cogging torque. The double porosity-type power generator according to the present invention includes: a hollow outer side core, and a hollow armature that is disposed to be inserted into an inner side of the outer core and that is induced with voltage according to a change in magnetic flux; and a field magnet that is disposed to be inserted into the inside of the armature so as to generate a magnetic flux. The field magnet and the outer core are disposed so as to be separately rotatable, and the outer side core is linked to the rotation of the field magnet due to a magnetic force during the rotation of the field magnet.

Description

Dual air generator

The present invention relates to a double-pore type generator, and more particularly, to a double-pore type generator in which a cogging torque caused by an imbalance in the magnetic flux distribution of the voids in the generator is reduced.

The cogging torque in the generator is a torque generated by the force between the stator and the rotor trying to move in the direction of decreasing the magnetoresistance due to the unbalance of the magnetic flux distribution in the air gap. During the operation of the function to lower the power generation efficiency.

In particular, in wind power generation, it is important to reduce the wind speed at which the initial start-up is possible. In the synchronous generator, the initial starting wind speed decreases as much as the cogging torque is reduced. Therefore, the reduction of the cogging torque is a key problem in this field. In order to solve this problem, axial magnetic permanent magnet generator (AKA: AFPM) is applied coreless type without core, which reduces initial starting wind speed while reducing cogging torque. This falls and is not a fundamental solution.

The related art is disclosed in detail in the Republic of Korea patent "Coreless motor having a multi-stage rotor and a drive device using the motor", registration number 10-0947518.

On the other hand, the radial magnetic flux permanent magnet generator (aka: RFPM) having a core according to the prior art has the advantage of high efficiency and high output, but the cogging torque is large, there is a problem that does not start at low wind speed.

1 is a cross-sectional view of a generator according to the prior art, in which an armature capable of inducing a voltage in response to a change in magnetic flux between a field 920 generating a magnetic flux and a gap 940 is provided. It is fixed and placed inside.

When the field 920 is rotated to generate power in the structure according to the related art, due to the imbalance of the magnetic flux distribution on the air gap 940 between the field 920 and the core 932 due to the force to move toward the direction of less magnetic resistance. Maneuvering and driving are hindered, and this magnetic force is called cogging torque. In order to improve this, increasing the number of poles of the field 920 and the armature 910 or improving the structural unbalance of the

cores

931 and 932 can reduce the size of the cogging torque. This is not a solution.

An object of the present invention for solving the problems of the prior art described above is to provide a generator capable of fundamentally removing or reducing the cogging torque of the generator.

The object of the present invention is not limited to the above-mentioned object, and other objects which are not mentioned will be clearly understood from the following description.

Dual-porous generator according to an embodiment of the present invention described above is installed inside the hollow core and the outer core and the hollow armature and the inside of the armature is a voltage induced by the change of magnetic flux It includes a field generating the magnetic flux while being installed, the field and the outer core is installed so as to be individually rotated, the outer core is linked to the rotation of the field by the magnetic force during the rotation of the field It is characterized by.

Dual-porous generator according to another embodiment of the present invention, the inner core and the hollow core of the outer core, one side cross-section of the inner core and the outer core is structurally connected, the other side is open, rotatable Rotatably installed rotatable cores;

A hollow armature inserted into an inner core and an outer core of the rotatable core and having a voltage induced by a change in magnetic flux; And a field generating magnetic flux;

It includes. Here, the armature is wound around the inner core and the concentric winding is formed to be inclined at a predetermined angle with respect to the horizontal cross-section of the inner core at one angle, and the two poles are arranged in the field in the circumferential direction, the field is The rotation is interlocked by being fixed to the rotatable core.

The dual-gauge generator according to another embodiment of the present invention is composed of an inner core and a hollow outer core, one end surface of the inner core and the outer core is structurally connected, and the other side is a fixed core open ; A hollow armature inserted between the inner core and the outer core of the stationary core so as to be rotatable and inducing a voltage according to a change in magnetic flux; And a field generating magnetic flux; It includes. Here, the armature is wound around the inner core and the concentric winding is formed in one or more poles inclined at a predetermined angle with respect to the horizontal cross-section of the inner core, two poles are arranged in the field in the circumferential direction, the field and the The stationary core is fixed and installed so that the armature rotates.

According to the present invention, the cogging torque of the generator can be fundamentally removed or reduced, so that the generator can be easily started and the efficiency can be increased. In particular, when used as a wind power generator can lower the initial maneuvering wind speed has an advantage in the utilization of wind resources.

1 is a cross-sectional view of a generator according to the prior art.

2 is a partial airflow flux flow diagram of a generator according to the invention.

3 is a perspective view of an armature in accordance with an embodiment of the present invention.

4 is a cross-sectional view of an armature in accordance with an embodiment of the present invention.

5 is a perspective view of a rotatable core according to an embodiment of the present invention.

6 is a cross-sectional view of a rotatable core according to an embodiment of the present invention.

7 is a perspective view of a fixed core according to one embodiment of the present invention.

8 is a sectional view of the stationary core according to an embodiment of the present invention.

9 is a perspective view of a sliding core according to an embodiment of the present invention.

10 is a cross-sectional view of the sliding core according to an embodiment of the present invention.

11 is a cross-sectional view of a dual-gap generator with an inner field according to one embodiment of the present invention.

12 is a cross-sectional view of a dual-gap generator with an outer field according to another embodiment of the present invention.

Figure 13 is a cross-sectional view of a dual air gap generator having both internal and external fields according to another embodiment of the present invention.

14 is a cross-sectional view of a generator with a rotatable core in accordance with another embodiment of the present invention.

15 is a cross-sectional view of a generator with a stationary core in accordance with another embodiment of the present invention.

16 is a cross-sectional view of a generator with a sliding core according to another embodiment of the present invention.

17 is a perspective view and a side view of an inclined concentric winding according to an embodiment of the present invention.

Advantages and features of the present invention and methods for achieving them will be apparent with reference to the embodiments described below in detail together with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but will be implemented in various forms, and only the embodiments are to make the disclosure of the present invention complete, and those skilled in the art to which the present invention pertains. It is provided to inform the full scope of the invention. Meanwhile, the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. In this specification, the singular forms also include the plural unless specifically stated otherwise in the phrases. Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Hereinafter, the dual-pore type generator according to the embodiments of the present invention will be described with reference to FIGS. 2 to 16.

Dual-porous generator according to the embodiments of the present invention is composed of the armature 110, the field 120 and the core 130, and rotates by connecting the field 120 and the core 130 structurally or magnetically By interlocking with each other, it is possible to realize a reduction in cogging torque that has hindered starting in the conventional structure.

2 is a flow diagram of a partial magnetic flux generation of the generator according to the present invention, there is a field 120 for generating a magnetic flux, and the field 120 with the gap 141 between the field 120 and induced voltage in accordance with the change of the magnetic flux 150 There is an armature 110 that can be made, and there is a core 130 with the armature 110 and the gap 142 in between.

The magnetic flux 150 generated by the field 120 flows through the

pores

141 and 142 and the armature 110 to the core 130. (Where the polarity is reversed, the magnetic flux will change direction.)

At this time, if the relative position between the armature 110 and the field 120 is changed, the relative position also changes between the armature 110 and the magnetic flux 150, so that a voltage proportional to the magnitude of the change is induced in the armature 110. do.

At this time, the cogging torque is generated in the form of a magnetic force that prevents the change of the relative position between the field 110 and the core 130, so when the core 130 is interlocked with respect to the rotation of the field 120, Changes can be eliminated or reduced so that no cogging torque can be generated or reduced.

In this embodiment, the armature 110 is disposed between the field 120 and the core 130, and the pores are formed between the armature 110 and the field 120 and between the armature 110 and the core 130, respectively. When structurally connecting the 120 and the core 130, the change in the relative position is eliminated while the cogging torque is not generated. In addition, when the field 120 rotates, the core 130 is attracted to the magnetic force to be interlocked with the field 120 to reduce the change in relative position, thereby reducing the occurrence of cogging torque.

3 to 10 look at one embodiment of a component for realizing the above principle.

3 to 4 are a perspective view and a cross-sectional view of the armature according to an embodiment of the present invention, which has a hollow shape, and a winding 111 for winding a voltage therein is wound therein, and the winding 111 is It is molded so that it can be supported and is connected to the output line 112.

The winding 111 has a required pole number and polarity, and has a loop shape surrounding the magnetic flux 150 radiated in a direction perpendicular to the central axis of the armature 110 to induce a voltage corresponding to the change of the magnetic flux 150. You can.

As the thickness of the armature 110 increases, the density of the magnetic flux 150 of the

air gaps

141 and 142 is lowered, so that the efficiency is poor. Therefore, the winding 111 is twisted as thin as possible and then formed between the field 120 and the core 130. It is important.

17 is a perspective view and a side view of an inclined concentric winding of an armature according to an embodiment of the present invention, which relates to a winding method of winding the armature winding 111 thinly and surrounds the field 320 or the inner core 320. While winding while winding, the concentric windings 340 are wound to be inclined at an angle with respect to the horizontal section of the field 320 or the inner core 320.

In the concentric winding 340, as the inclination angle θ increases, the output voltage during power generation increases, while the length of the winding increases, and the inclination angle θ with respect to the horizontal section of the field 320 or the inner core 320 is increased. It is practical to wind up in the range of 20 to 80 degrees.

The concentric windings 340 may be configured as a plurality of poles by winding the winding as well as one pole, the concentric windings 340 formed of one winding makes a single-phase output, concentric formed of three windings The windings 340 produce a three-phase output, by adjusting the arrangement phase of the concentric windings 340 to create a phase difference between the output voltages of each phase.

In the case where the inclined concentric winding 340 is adopted as the armature winding 111, the number of poles of the field 120 corresponding to the poles should be two poles, which is viewed in the circumferential direction of the field 120 from the armature 110 side. It means that there should be one N pole and one S pole.

Since the armature adopting the inclined concentric winding 340 has a characteristic of two poles, if a field having a pole number other than the two poles is combined, a magnetic flux is canceled, the output voltage is distorted, and efficiency is lowered. There is no

5 to 6 are a perspective view and a cross-sectional view of a rotatable core according to an embodiment of the present invention, the inner core 131 having a shape that can also function as a rotating shaft, the hollow core in a form surrounding the inner core 131 There is an outer core 132, the inner core 131 and the outer core 132 is a structure that one side is structurally connected and rotated together, the other side is open to the inner core 131 and the outer core 132 The armature 110 can be disposed while having the

gaps

141 and 142 between them. The inner core 131 may also serve as a rotation axis, or may have a separate rotation axis in the center of the inner core 131.

The arrangement of the magnetic bodies in the constituents of the

cores

131 and 132 increases the density of the magnetic flux 150 of the

voids

141 and 142, thereby improving efficiency.

7 to 8 are a perspective view and a cross-sectional view of a fixed core according to an embodiment of the present invention, since the inner core 131 is relatively short compared to the rotary core of FIGS. Since there is no difference, components that perform substantially the same functions as the rotatable cores of FIGS. 5 to 6 will be referred to by reference numerals, and detailed description thereof will be omitted.

9 to 10 are a perspective view and a cross-sectional view of a sliding core according to an embodiment of the present invention, there is a hollow outer core 132 that can be inserted by placing the armature 110 and the field 120, the generator There is a frame 210 forming an outer portion of the frame 210, there is a bearing 220 for supporting the outer core 132 to rotate inside the frame 210.

Hereinafter, the field 120 applied to the present invention will be described with reference to FIGS. 11 to 13.

11 is a cross-sectional view of a generator having an inner field according to an embodiment of the present invention, Figure 12 is a cross-sectional view of a generator having an outer field according to another embodiment of the present invention, Figure 13 is another embodiment of the present invention Sectional view of a generator with both internal and external fields.

In FIGS. 11-13, the armature 110 is centered between the armature 110 and the

pores

141 or 142 with the armature 110 or the gap between the armature 110 and the

pores

141, 142. It can be arrange | positioned at both sides, and is fixed to the adjacent

field side cores

131 and 132, respectively, and is a structure which can change a relative position with the armature 110.

Since the field 120 should have a function of generating the magnetic flux 150, it may use a permanent magnet or an electromagnet.

Permanent magnets can be selected in a variety of poles, materials and shapes according to the design needs, and since the permanent magnet is a magnetic material, there may be no field-side core (131 or 132).

When the field 120 is composed of an electromagnet, additional devices or structures, such as a slip ring and a brush structure for supplying an excitation current to the field winding and the field winding, or an exciter and a rectifier for supplying electricity in a contactless manner, are required. Do.

The technologies required to adopt permanent magnets or electromagnets have been widely known from the prior art, and are materials, structures, and devices that are widely used in existing generators, and detailed descriptions thereof will be omitted since they are far from the basic gist of the present invention. .

However, the specification of the use of the terms of the core (130, 131, 132) is required in the present specification, in the generator, the terms stator and rotor are generally distinguished terms in terms of movement, and the terms field and armature are in terms of electromagnetic function As a distinction term, the rotor may be a field or an armature in some cases. Similarly, in the generator to which the present invention is applied, unlike the prior art, the armature 110 and the core 130 are separated from each other, and the field 120 is structurally located inside or outside and may be fixed or rotated so that the core ( 131, 132 may also have a number of cases, so the name cannot be unified from a single point of view. Therefore, the structural core is classified into the inner core 131 and the outer core 132, and in terms of movement, it is divided into the rotary core (131, 132) and the fixed core (131, 132) and the sliding core (132), in terms of electromagnetic function With the armature 110 as the center, the field 120 side will be referred to as the field-side core, and the opposite side will be referred to as the armature-side core. The cogging torque associated with the basic idea of the present invention is the field 120 and the armature-side core 131 or 132).

Hereinafter, a generator having a rotatable core and a generator having a fixed core will be described with reference to FIGS. 14 to 16.

14 is a cross-sectional view of a generator having a rotatable core according to another embodiment of the present invention, FIG. 15 is a cross-sectional view of a generator having a fixed core according to another embodiment of the present invention, and FIG. Cross section of a generator with a sliding core according to another embodiment.

14 is a cross-sectional view of a generator with a rotatable core according to another embodiment of the present invention.

Referring to FIG. 14, a generator having a rotatable core according to another embodiment of the present invention includes an inner core 131 and a hollow outer core 132, and includes an inner core 131 and an outer core ( One side cross-section of the 132 is structurally connected, the other side is open, rotatably installed rotatable core (131, 132), the inner core 131 and the outer core 132 of the rotatable core (131, 132) It is inserted and is composed of a hollow armature 110 of the voltage induced by the change of the magnetic flux, and the field 120 for generating the magnetic flux.

Here, the hollow armature 110 is fixed to the bracket 230, the output line 112 from the armature is connected to the output terminal 113 outside the generator. The armature 110 may be attached to other fixing parts such as the frame 210 instead of the bracket 230 according to a design need. The

rotatable cores

131 and 132 installed to be rotatable are arranged with the armature 110 and the

gaps

141 and 142 interposed therebetween, and the field 120 is fixed to the inner core 131, and the outside of the generator is framed. 210 and the bracket 230 and the like.

In addition, the armature 110 may be wound around the inner core 131, a concentric winding formed at one or more poles inclined at a predetermined angle with respect to the horizontal cross-section of the inner core 131, wherein the field 120 has two poles It is preferable to arrange in the circumferential direction.

Bearing 220 and the like can be used between the fixed portion and the rotating portion, the installation position and the number can be changed as necessary in a range that does not violate the spirit of the present invention.

When the rotary shaft 240 rotates due to the external force of the generator, the

rotary cores

131 and 132 structurally connected thereto and the field 120 rotate together, and the magnetic flux 150 generated by the field 120 also rotates together. Done. At this time, since the change of the magnetic flux occurs when viewed from the fixed armature 110 side, the voltage is induced in the winding 111.

Meanwhile, the field 120 and the outer core 132 are structurally connected and rotate together, so there is no change in relative position, so that cogging torque is not generated.

Referring to FIG. 15, a generator having a fixed core according to another embodiment of the present invention includes an inner core 131 and a hollow outer core 132, and includes an inner core 131 and an outer core 132. One end of the cross-section is structurally connected, the other side is fixed to the fixed core (131,132) formed to open, and inserted into the middle of the inner core 131 and the outer core 132 of the fixed core (131,132) to be installed rotatably It is composed of a hollow armature 110, the voltage is induced in accordance with the change of the magnetic flux, and the field 120 for generating the magnetic flux.

Here, the armature 110 is installed to be rotatable, and the fixed

cores

131 and 132 are disposed inside and outside the armature 110 with the

gaps

141 and 142 interposed therebetween, and the field 120 is fixed to the inner core 131. The bracket 230 is installed on one side of the axial direction. The armature 110 installed to be rotatable is equipped with a slip ring 114 and a brush 115, and the output line 112 of the armature 110 is connected to the slip ring 114 so that the armature 110 may be connected thereto. Induced by the voltage is a structure that can be delivered to the output terminal 113 outside the generator.

When the rotating shaft 240 rotates due to the external force of the generator, the armature 110 structurally connected thereto rotates together, and the magnetic flux 150 generated from the fixed field 120 is fixed so that the armature 110 rotates. When viewed from the side of the magnetic flux changes occur, the voltage is induced in the winding 111.

On the other hand, because the field 120 and the outer core 132 disposed inside are fixed in a structurally connected state, there is no change in relative position, so that cogging torque is not generated.

16 is a generator with a sliding core according to another embodiment of the present invention.

Referring to Figure 16, the generator having a sliding core according to another embodiment of the present invention, the hollow core outer core 132, the inner core 132 is inserted into the installation, according to the change in the magnetic flux A hollow armature 110 in which voltage is induced, and is inserted into the armature 110 is installed, and consists of a field 120 for generating a magnetic flux.

Here, the hollow outer core 132 is connected to the frame 210 through the bearing 220 is a structure capable of individual rotation.

In addition, the hollow armature 110 is located inside the outer core 132, is fixed to both brackets 230, the output line 112 from the armature is connected to the output terminal 113 outside the generator It is. The armature 110 may be attached to other fixing parts such as the frame 210 instead of the bracket 230 according to a design need.

The field 120 is located inside the armature, and is structurally fixed to the inner core 131 connected to the rotational shaft so that the rotation is possible. In the absence of the inner core 131, the field 120 is the rotational shaft 240 ) Is fixed immediately. Such a field can be either a permanent magnet or an electromagnet.

The outer periphery of the generator is made of a frame 210 and the bracket 230, and the bearing 220, etc. can be used for the connection of the fixed part and the rotating part, the installation position if necessary in a range that does not violate the spirit of the present invention. And quantity can be changed.

When the rotary shaft 240 rotates due to the external force of the generator, the inner core 131 and the field 120 which are structurally connected thereto rotate together, and the magnetic flux 150 generated by the field 120 also rotates together. In the fixed arrangement of the armature 110, since the change in the magnetic flux occurs, the voltage is induced in the winding 111.

On the other hand, cogging torque is generated between the field 120 and the inner core 132 disposed inside, and when the cogging torque at the start is greater than the force corresponding to the static friction force of the outer core 132, the outer core 132 is the field ( 120 is rotated by the rotation, the rotation of the outer core 132 is coupled to the rotation of the field 120 but rotates with a degree of slip corresponding to the rotation friction force.

By the above operation, the cogging torque generated at the start of the generator is limited below the torque corresponding to the static frictional force of the outer core 132, and the cogging torque corresponds to the rotational friction force of the outer core 132 at the time of operation of the generator. By the function to maintain the level to the level is improved the starting and operating characteristics of the generator.

This operation is similar to the principle of an induction motor in which the rotor is rotated by an induction current induced in the rotor winding in response to the rotor field made by the stator. The present invention reduces the input of the driving rather than restraining the rotor of the induction motor. In addition, when the outer core 132 is interlocked with the rotation of the field 120, the relative speed between the field 120 and the outer core 132 is reduced, thereby reducing the iron loss generated in the outer core 132 and the efficiency is improved.

By reducing the electrical resistance of the rotor winding through which the induction current flows in the induction motor in such a way as to increase the above effect, the induction current flows through the outer core 132 of the present invention as the input of the driving state is reduced and the efficiency is improved. Including the sieve as a constituent component or disposing the sieve at a predetermined position reduces the electrical resistance, thereby improving the efficiency.

The material of the electric circuit disposed on the outer core 132 may be a copper or aluminum component having a low electrical resistance, the shape of the conductor, including the squirrel, winding or hollow cylindrical structure used in the induction motor Any structure that reduces the electrical resistance to induced current induced in the core 132 can be applied.

On the other hand, the outer core 132, which is a sliding core, is preferably composed of a ferromagnetic material such as silicon steel or soft iron, which is magnetic in a magnetic field, but may include a permanent magnet.

However, when the permanent magnet is included in the outer core 132, the magnetic flux density of the void may be increased, but the rotation between the magnetic flux by the field 120 and the magnetic flux by the permanent magnet of the outer core 132 may not be harmonized. In this case, a phenomenon in which the synthesized magnetic flux may be distorted may need to be designed so that slip between the field 120 and the outer core 132 is small.

As described above, it can be seen that by adopting the dual-porous generator structure according to the present invention, it is possible to fundamentally prevent the occurrence of cogging torque or reduce the cogging torque.

In general, in order to increase the output of the generator to increase the magnetic flux density of the air gap or to increase the rotational speed, in the structure according to the prior art there is a problem that the cogging torque increases in proportion to the increase in output, while the structure according to the present invention In the generator adopting the cogging torque does not occur even if the output is raised, even if cogging torque is generated is limited at a certain level. Therefore, it can be seen that the effect of the present invention is increased as the magnetic flux density is high or the high power generator having high rotation speed.

Those skilled in the art will appreciate that the present invention can be embodied in other specific forms without changing the technical spirit or essential features of the present invention. Therefore, it should be understood that the embodiments described above are exemplary in all respects and not restrictive. The scope of the present invention is shown by the following claims rather than the detailed description, and all changes or modifications derived from the claims and their equivalents should be construed as being included in the scope of the present invention.

Claims

Outer core in hollow form;

A hollow armature inserted into the outer core and configured to induce a voltage according to a change in magnetic flux; And

Is inserted into the inside of the armature, the field for generating a magnetic flux; including,

The field and the outer core are individually installed to be rotatable,

And the outer core is linked to the rotation of the field by magnetic force when the field is rotated.
The method of claim 1,

The armature is wound with one or more concentric windings wound around the field inclined at an angle with respect to the horizontal cross section of the field,

Double pole type generator, characterized in that the two poles are arranged in the circumferential direction.
The method of claim 1,

The field is a dual-pole generator, characterized in that selected from permanent magnets or electromagnets.
The method of claim 1,

The outer core is a permanent magnet or dual-porous generator, characterized in that the permanent magnet is partially included.
The method of claim 1,

Wherein said outer core is a ferromagnetic material that is magnetic in a magnetic field.
The method of claim 5

The outer core includes a double-porous generator, characterized in that the conductor to reduce the electrical resistance to the induced current induced by the change in the magnetic flux according to the rotation of the field.
An inner core and an outer core having a hollow shape, one end surface of the inner core and the outer core being structurally connected, and the other side being open, the rotatable core rotatably installed;

A hollow armature inserted between the inner core and the outer core of the rotatable core and having a voltage induced by a change in magnetic flux; And

Including magnetic fields to generate magnetic flux;

The armature is wound around the inner core and the concentric winding wound formed at least one pole inclined at a predetermined angle with respect to the horizontal cross-section of the inner core,

The field has two poles arranged in the circumferential direction,

The field is fixed to the rotary core of the dual-gap generator, characterized in that the rotation is interlocked.
The method of claim 7, wherein

The field generator is selectively fixed to an outer circumferential surface of the inner core or an inner circumferential surface of the outer core, or fixed to the outer circumferential surface of the inner core and the inner circumferential surface of the outer core, respectively.
An inner core and an outer core having a hollow shape, one end surface of the inner core and the outer core being structurally connected, and the other side of which is a fixed core;

A hollow armature inserted between the inner core and the outer core of the stationary core so as to be rotatable and having a voltage induced by a change in magnetic flux; And

Including magnetic fields to generate magnetic flux;

The armature is wound around the inner core and the concentric winding wound formed at least one pole inclined at a predetermined angle with respect to the horizontal cross-section of the inner core,

The field has two poles arranged in the circumferential direction,

And said field and said fixed core are fixed and said armature rotates.
The method of claim 9,

And the field is selectively fixed to an outer circumferential surface of the inner core or an inner circumferential surface of the outer core, or fixed to an outer circumferential surface of the inner core and an inner circumferential surface of the outer core, respectively.