TW201935816A - Outer disc type motor having fence type stator capable of reducing heat generation and lowering energy consumption by ensuring effective reduction of air gap and smoothness of magnetic path - Google Patents

Abstract

Provided is an outer disc type motor having a fence type stator, which includes a pivot shaft; a plurality of disc type outer rotors arranged in parallel, each including a disc body and an even number of permanent magnets, wherein the center of the disc body is vertically fixed to the pivot shaft, and the adjacent permanent magnets are evenly arranged in a manner of same polarities opposite to each other, while different magnetic polarities of the permanent magnets of the disc type outer rotor are opposite to each other; a fence type stator including a plurality of elongated iron cores respectively parallel to the axial direction and evenly arranged and distributed on a circular tube by taking the pivot shaft as a center, and having two polarities respectively corresponding to the permanent magnets, wherein the number of the iron cores is more than twice that of the permanent magnets and less than twice of that of the permanent magnets; and an enabling controller for providing an AC clock-driven signal so that each two adjacent clock-driven signals have a uniform phase difference, and the sum of the aforementioned phase differences of the fence type stator is a non-zero integral multiple of 360 degrees.

Description

Outer disk motor with fenced stator

An outer disk motor, especially an outer disk motor with a fence stator.

A common permanent magnet DC servo motor is a rotor with a permanent magnet installed on the periphery, and an armature coil at the core of the stator. Whether the current passes through the armature coil will generate heat due to resistance or during commutation. It is difficult to easily dissipate the sudden heat when the current is jumped in the medium. If it is applied to the direct drive system, the high heat at the rotor will be transmitted to the drive shaft. Under long-term use, it will gradually cause the deformation of the drive shaft. In contrast, As shown in FIG. 1, the permanent magnet AC servo motor 9 has a stator having an armature coil 91 disposed on the outer layer of the motor, and a permanent magnet 93 disposed on the core rotor, so it has better heat dissipation and higher power volume. ratio. Although some outer rotor motors overcome the heat dissipation problem of the armature coils, they are limited by the inner and outer layer-covered structure design, which reduces the elasticity of the strain in the face of problems such as output torque changes and installation space restrictions.

On the other hand, because the operation of the motor is mainly dependent on the attraction and repulsion of opposite poles of the magnetic force, the distribution of the magnetic field lines has a decisive influence on the operation of the motor. Because the magnetic reluctance of air is very high, if the iron core in the permanent magnet device and the coil, the lower the proportion of the path in the closed circuit, the longer the air area passing through, the magnetic resistance will be greatly increased, and the magnetic flux will be dispersed. The efficiency is also reduced. A conventional disc-type generator 8, as shown in FIG. 2, although the motor structure of the disc-type outer rotor 81 is disclosed, there is no proper answer to the aforementioned problems of heat generation and energy consumption. In addition, the number of permanent magnets and coils 83 If the target is not properly matched, the magnetic circuit will not work uniformly. In each cycle, the output may be uneven and the rotation may be uneven.

How to make the gap between the magnetic pole and the core of the permanent magnet narrow, and form a proper magnetic circuit, so that the magnetic flux is concentrated in the expected path to avoid divergence, and the time-varying driving signal is properly used to form an efficient interaction between the electromagnet and the permanent magnet Action, thereby improving the energy conversion efficiency of the motor, is the problem to be solved by the present invention.

An object of the present invention is to provide an outer disk motor having a fence type stator. The ratio of the number of stator iron cores to the number of permanent magnets in the rotor ensures that the air gap is effectively reduced, the magnetic path is smooth, and heat generation and energy consumption are reduced. efficacy.

Another object of the present invention is to provide an outer disk motor with a fence type stator, which utilizes the phase difference between the clock-type drive signals and cooperates with the proportional configuration of the iron core and the permanent magnet to make the overall magnetic drive of the motor uniform and run smoothly.

Yet another object of the present invention is to provide an outer disk motor having a fence type stator. The structure of the outer rotor of the disk prevents the stator with coil windings from being covered, which is easy to dissipate heat and smoothly extend the life of the motor assembly.

Another object of the present invention is to provide an outer disk motor having a fence type stator. A structure of a set of fence type stators is provided between every two disk type outer rotors arranged in parallel with each other, and the outer plate can be provided to the outer disk as required. The two outer sides of the rotor are coaxially expanded, so that the specifications of the single motor are not changed, and it can flexibly respond to the output torque and installation space requirements.

The invention discloses an outer disk motor with a fence type stator, comprising: at least one pivot shaft extending along an axial direction; at least two disk outer rotors arranged in parallel with each other, each The disk-type outer rotor includes a disk body and an even number of permanent magnets, respectively, and the disk body is vertically fixed to the pivot with its symmetrical center, and the permanent magnets are provided on the disk body with two magnetic poles on the disk body. Disk body, and each of the permanent magnets and the shortest distance point of the pivot are co-located on a circle centered on the pivot, and each two adjacent permanent magnets are connected in series with each other in the same polarity and opposite to the pivot The shafts are evenly arranged, and the different magnetic poles of the permanent magnets of the at least two adjacent disc-type outer rotors are arranged opposite to each other; at least one set of fence-type stators includes a plurality of elongated iron cores, each of which They are arranged parallel to each other and parallel to the axial direction, and are evenly distributed on a circular tube with the pivot as the center. Each of the foregoing iron cores of the aforementioned group of fence-type stators respectively corresponds to the two disks in close proximity to the two disks respectively. The number of the above-mentioned permanent magnets of the external rotor and the number of the iron cores are more than double and less than twice the number of the permanent magnets. The iron core is respectively wound with a coil winding for receiving an AC clock-type drive signal to magnetize the iron core; at least one rotor position sensing element for measuring the position of the permanent magnet of the disk-type outer rotor and outputting at least one position signal And an enabling controller, according to the aforementioned position signal received, providing the above-mentioned alternating-current clock-type driving signal to the above-mentioned coil winding, so that each of the clock-type driving signals of two adjacent said coil windings has respectively A uniform phase difference, and the sum of the foregoing phase differences between all adjacent coil windings of all the set of fence stators is a non-zero integer multiple of 360 degrees.

Since an outer disk motor with a fence stator in this case includes at least two disk outer rotors and at least one set of fence stators arranged in parallel with each other, the outer rotor and the stator are cleverly arranged with each other and at least one pivot shaft. On the one hand, the distance of the air gap is reduced, so that the magnetic flux mainly reaches the circuit through the iron core and the permanent magnet, and the magnetic resistance is greatly reduced; on the other hand, because the numbers of the permanent magnet and the iron core are matched with each other, they form a magnetic circuit and match each other With specific Phase-differenced clock-type driving signals make the rotor run smoothly. In addition, the external disk motor is easy to dissipate heat, and the life of the motor component is prolonged. Further expansion of the auxiliary disk outer rotor and auxiliary fence stator makes the invention unnecessary. By changing the specifications of the motor unit, the output torque can be flexibly adjusted to meet the needs of the installation space. In particular, every two adjacent permanent magnets on the outer rotor are arranged in the same polarity and opposite to the aforementioned pivot. Evenly arranged, and the disparate magnetic poles of the two permanent magnets of the disc-type outer rotor are arranged opposite to each other, and each core of the fence-type stator is proximate to the two permanent magnets corresponding to the two disc-type outer rotors respectively Combined with the structural features that the number of iron cores is more than double and less than twice the number of permanent magnets, each permanent magnet is just matched with a complete magnetic circuit, which effectively improves the energy conversion efficiency of the motor and achieves the effect of reducing heat generation and energy consumption. To achieve all of the above.

20‧‧‧ Enable Controller

12‧‧‧ Pivot

121‧‧‧circle

123, 123’‧‧‧ round tube

14, 81‧‧‧ disc outer rotor

141‧‧‧ plate body

93, 143, 143 ’, 143” ‧‧‧ permanent magnets

145‧‧‧Polymagnetism

16, 16’‧‧‧ Fence type stator

161, 161 ’, 161” ‧‧‧ iron core

163‧‧‧coil winding

165‧‧‧ non-magnetic stator base

18‧‧‧Rotor position sensing element

21‧‧‧ Fork

3‧‧‧Motor housing

9‧‧‧ permanent magnet AC servo motor

91‧‧‧ armature coil

8‧‧‧ Disc Generator

83‧‧‧coil

1‧‧‧outer disc motor

FIG. 1 is a schematic side view of a structure of a conventional motor having an outer rotor, and is used to explain the relative positional relationship between a motor stator and a rotor.

FIG. 2 is a schematic structural diagram of a conventional disc motor, which is used to explain its main constituent elements and their relative relationships.

FIG. 3 is a partially exploded perspective view of a first preferred embodiment of an outer disk motor with a fence type stator according to the present invention, illustrating the disk body and permanent magnet structure of the rotor.

FIG. 4 is a partially exploded perspective view of the embodiment of FIG. 3, illustrating a perspective view of a relative relationship between a non-magnetic stator base and a core-coil of a stator.

FIG. 5 is a schematic three-dimensional combination diagram of the permanent magnet and the core-coil of FIG. 4.

6 is an exploded perspective view of the permanent magnet and the core-coil of FIG. 5.

FIG. 7 is a schematic diagram of an actuated wheel of FIG. 3 applied to an electric bicycle.

FIG. 8 is a schematic diagram of an actuating wheel of FIG. 3 applied to a single fork electric bicycle.

FIG. 9 is a schematic diagram of a clock-type driving signal provided by the enable controller in the embodiment of FIG. 3, and illustrates the phase difference relationship of the clock-type driving signals received by adjacent coil windings.

FIG. 10 is a schematic side view of a magnetic field line distribution of the permanent magnet in the embodiment of FIG. 3. FIG.

FIG. 11 is a partially exploded perspective view of a second preferred embodiment of an outer disk motor with a fence stator according to the present invention.

The foregoing and other technical contents, features, and effects of the present invention will be clearly presented in the following detailed description of the preferred embodiments with reference to the drawings; in addition, in each embodiment, the same elements will be similar Labeled.

A first preferred embodiment of an outer disk motor with a fenced stator in this case, please refer to FIGS. 3 to 6 together. The aforementioned outer disk motor 1 has a pivot shaft 12 extending in an axial direction. For ease of explanation, the foregoing axial direction is defined here as the up-down direction along the figure, and two disc-type outer rotors 14 arranged in parallel with each other. Each disc-type outer rotor 14 includes a disc body 141 and an even number of permanent magnets, respectively. 143. In this example, six permanent magnets 143 are used as an example. In addition, the disk bodies 141 in this example are all circular disk-shaped, and are respectively fixed to the above-mentioned pivot shaft 12 vertically with their symmetrical centers.

In this example, the permanent magnets 143 described above are each slightly embedded in a flat curved shape and embedded in the disk body 141, and the two magnetic poles N and S of each permanent magnet 143 are not only provided at the disk body 141, but also Adjacent two permanent magnets 143 are arranged in such a manner that the N poles are close to each other or the S poles are close to each other. As can be easily understood by those familiar with this technical field, even if this The permanent magnets here are changed to other shapes such as horseshoe or rectangular. As long as the permanent magnets are arranged on the disk body 141 in the foregoing manner, the implementation of the present invention is still not hindered. And because the permanent magnet 143 in this example is curved, the curved shape of the magnet is such that the magnets and magnetic poles are uniformly arranged on a circle 121 with the pivot 12 as the center. In addition, the two The relative arrangement of the disc-shaped outer rotor 14 is such that the different magnetic poles of the permanent magnet 143 are opposed to each other.

The above-mentioned outer disc motor 1 further includes a set of fence-type stators 16. In this example, the set of fence-type stators 16 includes nine strip-shaped iron cores 161 of equal length, and each of the above-mentioned cores 161 has a length of 3.5. In centimeters, the iron core 161 in this example is explained as being composed of a plurality of silicon steel sheets, thereby reducing the eddy current effect, and is held by a non-magnetically permeable stator base 165. Of course, those with ordinary knowledge in the technical field of the present invention can arbitrarily choose, for example, die-casting of iron powder or other conventional magnetic conductors as the iron core, which will not hinder the implementation of this case. Each of the foregoing iron cores 161 is arranged parallel to each other along the above-mentioned axial direction, and is evenly distributed at a circular pipe 123 with the pivot axis 12 as the center. Since each of the iron cores 161 is uniformly arranged, each of the iron cores 161 and The angle between the connecting line of the pivot shaft 12 and the connecting line of the adjacent iron core 161 and the pivot shaft 12 is 30 degrees, and the two poles of each iron core 161 are close to the permanent magnets 143 corresponding to the two disk-type outer rotors 14 respectively. Since the number of iron cores 161 in this example is 1.5 times that of the permanent magnets 143, no matter how the permanent magnets 143 rotate to any position, they can correspond to two iron cores 161, and the two iron cores 161 are close to their N poles and The S pole makes the two permanent magnets 143 corresponding to each other of the upper and lower disk-type outer rotors 14 exactly form a complete magnetic circuit through the two iron cores 161 here.

Especially as the overall thickness of the motor in this example is not more than 6 cm, the thickness is actually only about 5 cm, and the thickness of the disc outer rotor 14 is about 0.5 cm, which makes the gap between the iron core 161 and the permanent magnet 143 quite narrow. Smaller than the thickness of the disc outer rotor 14, making the magnetic circuit The portion passing through the air is very short, and the magnetic lines of force of the permanent magnet 143 will pass through the iron core 161 densely, so the magnetic resistance will be greatly reduced. Of course, those skilled in the art can understand that in order to constitute the corresponding magnetic circuit, the number of the aforementioned iron cores of the present invention must be a positive integer that exhibits a radial symmetrical distribution with respect to the above-mentioned pivot axis, and the number is greater than twice the number of the permanent magnets. And less than twice.

Each of the aforementioned iron cores 161 is wound with a coil winding 163 for receiving an alternating-current clock-type driving signal S1 to magnetize the aforementioned iron core 161; when a certain pole of the permanent magnet 143 has just passed the corresponding end portion of the iron core 161, the iron The core end is formed with the same magnetism as the magnetic pole to exert the thrust of repulsion of the same polarity, and to provide the attraction of opposite polarity attraction when the opposite magnetic pole approaches; until the next magnetic pole approaches, the magnetic end of the core 161 begins to weaken After returning to zero, the phase is changed, and the next magnetic pole is driven to continue to run with the opposite magnetism. Since the number of permanent magnets 143 is not equal to the number of iron cores 161, in order to generate the maximum driving torque, not only must the position of the permanent magnets 143 of the disc outer rotor 14 be accurately obtained, but also each coil winding 163 be provided with a phase difference. Clock drive signal.

Therefore, the rotor position sensing element 18 as shown in FIG. 9 measures and outputs a position signal to the enable controller 20, and the enable controller 20 provides an AC signal based on the received position signal. The clock-type driving signal S1 to the coil winding 163 of the fence stator 16, so that the clock-type driving signals S1 of every two adjacent coil windings 163 have a uniform phase difference, and all of the group of fence-type stators 16 The sum of the aforementioned phase differences between all adjacent coil windings 163 of N is a non-zero integer multiple of 360 degrees. Therefore, each core 161 will be driven by a clock-type driving signal that matches the rotation speed of the disc-type outer rotor 14, and the clock-type driving signals received by the adjacent cores 161 are respectively 120 degrees as in this example. The phase difference is such that after three iron cores are separated from each other, the clock driving signal received by the fourth iron core will be equal to the first iron core, and after the nine iron cores are surrounded, the sum of the phase differences in this example It is 1080 degrees. In this example, 18 cases of the above-mentioned rotor position sensing element are explained as Hall Element, those skilled in the art to which the present invention pertains may select other suitable elements for simple transformation.

In this example, the fence stator 16 further includes a non-magnetically permeable stator base 165 to hold each iron core 161. The non-magnetically permeable stator base 165 is further provided with a set of ball bearings at the upper and lower ends of the drawing. (Not shown), so that the above-mentioned pivot shaft 12 can smoothly pivot in the non-magnetic stator base 165. And the disc-type outer rotor 14 and the fence-type stator 16 can be relatively pivotally combined. As shown in FIG. 7, because the motor in this example is used as an actuating wheel of an electric bicycle, the disc outer rotor 14 can be directly coupled to the tire of the wheel, and the non-magnetic stator base 165 is further connected to a motor housing 3. It is then connected to the front fork 21 of the electric bicycle to protect the fence stator (not shown) from accidental collision or contact due to external force, which may cause damage to the core 161 or the coil winding 163 or short-circuit burnout. Of course, even if the front fork is changed to a rear fork, or to a single-sided front fork 21 as shown in FIG. 8, the implementation of the present invention is not hindered.

Please refer to FIG. 9 together. When the outer disc motor 1 is located above the axial direction of the disc outer rotor 14 and the permanent magnets 143 of the permanent magnets 143 are arranged in a series of SN, NS, SN,... On the disk body 141, the magnetic poles of the permanent magnets 143 of the disk-type outer rotor 14 which are relatively below the above-mentioned axial direction are arranged from the left to the right in a series arrangement in the NS, SN, NS,... 141. At this time, if a magnetic pole driven and induced by an iron core 161 is exactly the same as the magnetic pole of the permanent magnet 143 which is in close proximity, the permanent magnet 143 is pushed by the iron core 161 along the tangential direction of the circle 121 due to the repulsion of the magnetic poles. That is, the above-mentioned outer disc rotor 14 is pushed and rotated by the above-mentioned fence stator 16. In this example, the same push / pull action is generated every 120 degrees on a circle 121 circle, so that the above-mentioned outer disc motor 1 Each phase can generate three times the push / pull force.

In this example, the ratio of the number of the foregoing iron cores 161 to the number of the permanent magnets 143 is 3: 2. That is, every three of the foregoing iron cores 161 correspond to two permanent magnets 143, respectively, and three sets of such corresponding combinations are formed around the disk body 141. As shown in FIG. 10, the above-mentioned iron cores 161 and the corresponding permanent magnets 143 are in close proximity. The shortest distance is smaller than the thickness of the disk body, so that the corresponding iron core 161 and the permanent magnet 143 form a good magnetic flux circuit. At the same time, considering the introduction of the clock drive signal, when the permanent magnet 143 rotates with the rotor and commutates the inductive poles exactly in the core 161, the magnetic lines of force of the permanent magnet 143 pass through the core 161, causing hysteresis loss (Hysteresis Losses) are reduced, which in turn reduces the heating of the magnetic conductor, which also reduces the consumption of electrical energy, which increases the overall conversion efficiency of the motor.

When the disk-type outer rotor 14 is driven to rotate by the above-mentioned fence-type stator 16, the original correspondence relationship between the iron core 161 and the permanent magnet 143 is changed, and the same-pole repulsion force that the original magnetic pole was subjected to is gradually changed due to the rotation of the rotor. A magnetic pole is attracted by a different magnetic pole. At this time, the rotor position sensing element 18 will sense the change in the position of the permanent magnet 143 of the disc outer rotor 14 and further output a position signal to the enable controller 20. According to the received position signal, the enabling controller 20 is researched to judge whether the rotation speed of the disc-type outer rotor 14 is changed, and decide whether the frequency of the AC clock drive signal needs to be increased or decreased.

In this embodiment, in order to further reduce the distance of the air gap and to concentrate the magnetic field lines of the permanent magnets, one position is installed at each position where the poles of the permanent magnet 143 which are opposite to each other and are close to the fence stator 16 are opposite to each other. As shown in FIG. 6, the polycondensing magnets 145 are, in this example, a flat cylindrical permanent magnet. Each of the polycondensing magnets 145 attracts the magnetic poles of the corresponding permanent magnets, and assumes the passage of magnetic lines of force, further narrowing. The air gap between the permanent magnet 143 and the iron core 161 reduces the magnetic resistance and improves the conversion efficiency.

Of course, this magnetic concentrating magnet is not necessarily provided. In order to simplify the structure and reduce the manufacturing cost, as shown in the second preferred embodiment of the present invention, the permanent magnet 143 ′ and the adjacent The gap between the permanent magnets is narrowed, and at the same time, the distance between the permanent magnet 143 'and the iron core 161' arranged along the virtual circular tube 123 'is reduced, so that the magnetic resistance between the rotor and the fence stator 16' is reduced. In addition, the above-mentioned permanent magnets need only be arranged in pairs uniformly, and are not limited to 6, and the number of iron cores in the fence stator need only conform to an integer between one and two times the number of the above-mentioned permanent magnets. That is, the key lies in the above-mentioned clock-type driving signals. The sum of the phase differences between them is an integer multiple of 360 degrees, and the phase differences between every two adjacent coils are the same as each other and change with the rotation speed.

In particular, when the output power of the motor composed of only two disc-type outer rotors and a set of fence stators is insufficient, this embodiment is further below the disc-type outer rotor under the original drawing, and more along the coaxial direction of the pivot. Adding a set of auxiliary fence type stators and auxiliary plate type outer rotors having the same structure as the aforementioned disc type outer rotor and the above-mentioned fence type stator and having a common pivot configuration, the auxiliary fence type stator being magnetized by the enabling controller described above, For easy understanding, only the iron core 161 "of the auxiliary fence-type stator and the permanent magnet 143" of the auxiliary disc-type outer rotor are shown here to increase the overall torque output. Due to the above number of core-coil configurations, a complete magnetic field line path of the permanent magnet can be provided, so that the magnetic resistance is greatly reduced, and the rotating movement of the permanent magnet can periodically reduce the hysteresis during the excitation of the core by the AC signal. The heat generation and energy loss caused by the hysteresis phenomenon are reduced, so that the motor disclosed in the present invention has a low heat generation and high energy conversion efficiency during operation, and achieves the above-mentioned invention objectives beyond the prior art.

However, the above are only the preferred embodiments of the present invention, and cannot be used to limit the scope of the present invention. Any simple equivalent changes and modifications made in accordance with the scope of the patent application and the content of the invention specification of the present invention should be applied. Still within the scope of the invention patent.

Claims (8)

An outer disk motor with a fence stator includes: at least one pivot shaft extending along an axial direction; at least two disk outer rotors arranged in parallel with each other, each of the aforementioned disk outer rotors includes a disk body and An even number of permanent magnets, and the disk body is fixed to the pivot axis vertically with its symmetrical center, the permanent magnets are respectively installed on the disk body with two magnetic poles on the disk body, and each of the permanent magnets and the The shortest distance points of the pivots are located on a circle centered on the pivots. Each two adjacent permanent magnets are connected in series with the same polarity and aligned uniformly with respect to the pivots. Dissimilar magnetic poles of the aforementioned permanent magnets of the disk-type outer rotor are arranged opposite each other; at least one set of fence-type stators includes a plurality of elongated iron cores, and each of the foregoing iron cores is arranged parallel to each other along the above-mentioned axial direction and is uniform. Distributed in a circular tube with the pivot as the center, each of the aforementioned iron cores of the aforementioned group of fence-type stators is respectively divided into two poles. The permanent magnets corresponding to the two disk-type outer rotors are close to each other, and the number of the iron cores is more than twice and less than twice the number of the permanent magnets. Each of the foregoing iron cores is respectively wound with a coil winding for receiving an alternating current. A pulse-type driving signal magnetizes the aforementioned iron core; at least one rotor position sensing element for measuring the position of the permanent magnet of the disc-type outer rotor and outputting at least one position signal; and an enabling controller based on the foregoing received The position signal provides the above-mentioned alternating-current clock-type driving signal to the above-mentioned coil winding, and each clock-type driving signal of two adjacent coil windings has a uniform phase difference, and all The sum of the aforementioned phase differences between all adjacent coil windings is a non-zero integer multiple of 360 degrees. The outer disk motor with a fence stator as described in item 1 of the scope of the patent application, wherein each of the aforementioned iron cores is a plurality of silicon steel plates. The outer disk motor with a fence stator according to item 1 of the scope of the patent application, wherein the fence stator further includes a non-magnetically permeable stator base holding the iron cores. The outer disk motor with a fence stator as described in item 1 of the patent application scope further includes a motor housing connected to the fence stator. According to the outer disk motor with a fence stator according to item 1 of the scope of patent application, the length of the iron core is not more than 3.5 cm, and the overall thickness of the outer disk motor is not more than 6 cm. The outer disk motor with a fence stator according to item 1 of the scope of the patent application, wherein the rotor position sensing element is a Hall element. The outer disk motor with a fence stator as described in item 1 of the scope of the patent application, further includes an auxiliary disk outer rotor that is parallel to the above-mentioned disk outer rotor and has the same structure as the aforementioned disk outer rotor and is arranged in a coaxial manner. The aforementioned auxiliary disc-type outer rotor is disposed outside the two disc-type outer rotors; a set of auxiliary fence-type stators disposed between one of the aforementioned two disc-type outer rotors and the auxiliary disc-type outer rotor, the auxiliary fence-type The stator and the above-mentioned fence-type stator have the same structure and are arranged in a common pivot. The auxiliary fence-type stator is magnetized by the enabling controller described above. According to the outer disk motor with a fence stator according to item 1 of the scope of the patent application, the shortest distance between the iron core and the permanent magnet corresponding to the nearest is smaller than the thickness of the disk body.