KR20160028285A - Magnetic gear having external pole piece member - Google Patents

Abstract

The present invention relates to a magnetic gear and, more specifically, to a magnetic gear which has a pole piece at an outside of rotors located spaced apart on a rotary shaft such that a structure of the magnetic gear can be simplified by reducing number of gaps and reduction of a torque transmissibility due to friction can be minimized by reducing number of bearings supporting the rotary shaft.

Description

Magnetic gear having an external pole piece member, wherein the pole piece is provided on the outside of the rotors,

The present invention relates to a magnetic gear, and more particularly, to provide a pole piece on the outer side of rotors located on a rotating shaft, thereby simplifying the structure by reducing the number of pores and reducing the number of bearing rings Thereby minimizing a reduction in the torque transmission rate due to abrasion.

Magnetic gear is a non-contact type gear unit that transmits power in a non-contact manner by using magnetic force. It has less noise and vibration than a gear that transmits power by physical contact, does not require lubricant injection and maintenance, And durability are high.

In addition, since magnetic gears can reduce energy loss, high efficiency driving is possible, and reliability and accurate peak torque can be transmitted.

Recently, efforts have been made to apply magnetic gears to various industries such as wind turbines, electric vehicles, and transmissions.

FIG. 1 shows a general magnetic gear, and FIG. 2 shows a vertical section of a general magnetic gear.

1 and 2, a conventional magnetic gear 10 mainly includes an inner rotor 11, an outer rotor 12, rotors 11 and 12 between an inner rotor 11 and an outer rotor 12, And a pole piece module (13) spaced apart from the pole piece module (13).

The inner rotor 11 includes a magnet 11a radially attached to the outside of the inner rotor 11b and the inner rotor 11b about a rotating shaft, (12a) and a magnet (12b) radially attached inside the outer rotor (12a) about a rotation axis, the pole piece module (13) having a plurality of pole pieces 13a.

The magnets of the inner rotor 11 and the outer rotor 12 are arranged such that the magnets having magnetic force in opposite directions to each other (in the direction toward the rotation axis and the direction opposite to the rotation axis) Two magnets with a magnetic force in the direction form a dipole.

In addition, when the pole piece module 13 is fixed, the inner rotor 11 and the outer rotor 12 rotate in opposite directions to each other. Depending on which rotor is the input shaft, a reduction gear or an accelerator .

The number of dipoles of the outer rotor 12 and the number of dipoles of the inner rotor 11 are expressed by the following equations the number of pole pieces 13a is determined.

[Mathematical expression a]

Here, N is the number _s, p ₁ is a bipolar number, p ₂ of the outer rotor 12 of the pole piece (13a) is the number of the bipolar inner rotor (11).

2, the number of poles of the magnet of the outer rotor 12 is 42 poles, the number of poles of the poles is 21 poles, the number of poles of the magnet of the inner rotor 11 is 4 poles and the number of poles of the poles is 2 poles, The number of poles of each rotor is 21 poles and 23 poles plus two poles.

Further, the gear ratio of the magnetic gear 10 is determined by the ratio of the number of dipoles of the rotors as shown in the following equation (b).

[Mathematical expression b]

In addition, the speed ratio of the rotors of the magnetic gear 10 is expressed by the following equation (c).

[Mathematical expression c]

The pole pieces 13a of the conventional magnetic gear 1 have outer rings 13aa and 13ab and outer rings 13aa and 13ab having the same central angle and different diameters, , And a straight line 13ad connecting the other ends.

However, due to the morphological limitations of these pole pieces 13a, the conventional magnetic gear 10 has a problem in that the gap between the outer rotor 12 and the pole piece module 13, between the inner rotor 11 and the pole piece module 13 The magnetic flux can not be concentrated on the air gap, resulting in a low torque transmission and a large torque ripple.

3 shows a vertical section of the conventional magnetic gear 10 in the direction of the rotation axis. The conventional magnetic gear 10 includes the inner rotor 11, the outer rotor 12, the pole piece module 13, And further comprises a housing 14, a pole piece module support member 15, an inner rotor support member 16, and an outer rotor support member 17.

The housing 14 defines an external configuration and the pole piece module support member 15 supports the pole piece module 13 so as to be spaced apart from the housing 14 inside the housing 14 .

The inner rotor support member 16 supports the inner rotor 11 on the inner side of the pole piece module supporting member 15 away from the pole piece module supporting member 15, And has an input shaft 11c exposed to one side.

The outer rotor support member 17 may also be configured to separate the outer rotor 12 from the housing 14 and the pole piece module 13 and away from the housing 14 and the pole piece module 13, And has an output shaft 12c exposed to the other side of the housing 14. [

Also, bearings 14a, 15a, 16a, 16b are provided between the stationary member and the rotating member. In detail, the bearings 14a, 15a, 16a and 16b may be radial bearings supporting a load acting perpendicular to the rotation axis of the rotating member.

The bearings 14a, 15a, 16a, and 16b may include a first outer rotor support bearing 14a that supports the output shaft 12c in the housing 14, a second outer rotor support bearing 14b that supports the pole piece module support member 15, A second outer rotor support bearing 15a for supporting the outer rotor support member 17, a first inner rotor support bearing 16a for supporting the input shaft 11c to the pole piece module support member 15, And a second inner rotor bearing (16b) supporting the inner rotor (11) on the rotor support member (17).

That is, since the conventional magnetic gear 10 includes the four bearings 14a, 15a, 16a, and 16b, the torque transmission rate due to the friction of the bearings is low.

In order for the rotors 11 and 12 to rotate inside the housing 14, a first gap a1 between the housing 14 and the inner rotor, the outer rotor 12, The second gap a2 between the pole piece module 13 and the inner rotor 11 and the third gap a3 between the pole piece module 13 and the inner rotor 11 must be present.

[Prior Art Literature]

[Patent Literature]

1. Korean Patent Publication No. 10-2013-0042564, magnetic gear device and retaining member

2. Korean Patent Publication No. 10-2014-0013087, magnetic gear device

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a magnetic gear having a simple structure which can reduce the number of voids.

It is another object of the present invention to provide a magnetic gear capable of reducing the number of bearings and minimizing the reduction in the torque transmission rate due to the friction of the bearings.

It is also an object of the present invention to provide a magnetic gear capable of improving torque transmission and lowering torque ripple by optimizing the shape of the pole piece to concentrate the magnetic flux in the gap, thereby improving power transmission rate and reliability.

The objects of the present invention are not limited to the above-mentioned objects, and other objects not mentioned can be clearly understood by those skilled in the art from the following description.

According to an aspect of the present invention, An output side rotor disposed on the rotation axis extension of the input side rotor and spaced apart from the input side rotor; And a pole piece module that surrounds the input side rotor and the output side rotor from the outside of the input side rotor and the output side rotor and has a plurality of pole pieces radially positioned on the rotation axis and transmits the magnetic force of the input side rotor to the output side rotor; Wherein the input side rotor and the output side rotor are located together inside the pole piece module and are spaced apart from the pole piece module.

In a preferred embodiment, the pole piece module includes a pole piece module support member for supporting the pole piece to maintain its radial position with respect to the rotation axis, and the magnetic gear is fixed to one side of the pole piece module support member An input shaft support bearing which is fixed to an input shaft of the input side rotor and which rotates the input side rotor while being spaced apart from the pole piece module; An output shaft support bearing which is fixed to the inside of the other side of the pole piece module support member and whose inner ring is fixed to the output shaft of the output side rotor and which rotates the output side rotor while being spaced apart from the pole piece module; And a rotor connection bearing that rotates the output shaft of the input side rotor and the input side rotor of the output side rotor while sliding so that the output side of the input side rotor and the input side of the output side rotor are supported on the rotation axis.

In a preferred embodiment, the cross-section of each of the pole pieces has a first arc, a second arc having the same center and center angles as the first arc and an inner diameter smaller than the inner diameter of the first arc, And a second figure surrounded by a line connecting one end and each other end of the second call and a third figure having the same position and inner diameter as the second call and the central angle being larger than the central angle of the second call, 3, the center position and the central angle are the same, the inner diameter is the fourth figure which is smaller than the inner diameter of the third call, and the shape in which the second figure surrounded by the line connecting the one end and the other end of the third call and the fourth call And the bisector positions of the second call and the third call are combined so as to overlap with each other.

In a preferred embodiment, the vertical distance (hereinafter, referred to as 'first vertical distance') between the fourth call and the third call is a vertical distance between the fourth call and the first call , &Quot; second vertical distance ") is larger than 13.5% and smaller than 23.5%.

[Equation 1]

Where alpha is the first vertical distance and L _pr is the second vertical distance.

The central angle of the fourth arc is less than 40% of the central angle of the virtual arc connecting the first calls of the two pole pieces with one pole piece interposed therebetween (hereinafter referred to as a reference angle) Bigger and smaller than 50%.

&Quot; (2) "

Where beta is the central angle of the fourth arc and N _p is the number of pole pieces.

In a preferred embodiment, a line connecting the first call and the second call in the first figure is a curve concave toward the center of the first figure (hereinafter, referred to as a 'concave curve').

In a preferred embodiment, the length from the bisecting position of the virtual line segment connecting the both ends of the concave curve (hereinafter, referred to as 'first virtual line segment') to the concave curve in the vertical direction (Hereinafter, referred to as " second virtual line segment ") vertically connected to the fourth arc at one end of the concave curve, Is greater than 30% and less than 40% of the length up to a virtual line segment connecting the bisection position of the arc and the bisection position of the fourth line (hereinafter, referred to as 'third virtual line segment').

In a preferred embodiment, the concave length is calculated by the following equation (3).

&Quot; (3) "

Where D _pi is the inner diameter of the fourth arc, D _po is the inner diameter of the first arc, and N _p is the number of pole pieces.

The present invention further provides a multiple type magnetic gear comprising at least two magnetic gears, wherein the output side rotor of the first magnetic gear is directly coupled to the input side rotor of the second magnetic gear do.

The present invention has the following excellent effects.

First, according to the magnetic gear of the present invention, since the pole piece module also serves as a housing, the rotors can be rotated with only one gap in the pole piece module, so that the structure is very simple.

Further, according to the magnetic gear of the present invention, since the rotors can be rotated in a noncontact manner by only three bearings, there is an advantage that the decrease in the torque transmission rate due to the friction of the bearings can be minimized.

Further, according to the magnetic gear of the present invention, by optimizing the shape of the pole piece to concentrate the magnetic flux in the gap, the torque transmission is improved and the torque ripple is reduced, thereby improving the power transmission rate and reliability.

Further, according to the multiple type magnetic gear of the present invention, there is an effect that a large torque ratio can be provided even with a small volume by directly connecting two magnetic gears.

1 is a view showing a general magnetic gear,
2 is a vertical sectional view of a general magnetic gear,
3 is a vertical cross-sectional view of a general magnetic gear in the direction of the rotation axis,
4 is a view showing a magnetic gear according to an embodiment of the present invention,
5 is a vertical sectional view of a magnetic gear according to an embodiment of the present invention.
FIG. 6 is a vertical cross-sectional view of a magnetic gear according to an embodiment of the present invention,
7 is a view showing an example of a pole piece of a magnetic gear according to an embodiment of the present invention,
8 is a view for explaining the shape of a pole piece of a magnetic gear according to an embodiment of the present invention,
9 to 11 are diagrams for explaining a variable for determining the shape of a pole piece of a magnetic gear according to an embodiment of the present invention,
12 is a view for explaining a multiple type magnetic gear according to another embodiment of the present invention.

Although the terms used in the present invention have been selected as general terms that are widely used at present, there are some terms selected arbitrarily by the applicant in a specific case. In this case, the meaning described or used in the detailed description part of the invention The meaning must be grasped.

Hereinafter, the technical structure of the present invention will be described in detail with reference to preferred embodiments shown in the accompanying drawings.

However, the present invention is not limited to the embodiments described herein but may be embodied in other forms. Like reference numerals designate like elements throughout the specification.

4 and 5, the magnetic gear 100 according to the present invention includes an input side rotor 110, an output side disposed apart from the input side rotor 110 on an extension line of the rotation axis c of the input side rotor 110, A rotor 120, and a pole piece module 130 surrounding the input side rotor 110 and the output side rotor 120.

The input side rotor 110 includes an input side rotor 111 and a magnet 112 which is radially attached to the outside of the input side rotor 111 about a rotational axis c.

The output side rotor 120 includes an output side rotor 121 and a magnet 122 radially attached to the outside of the output side rotor 121 about a rotation axis c.

The gear ratio of the magnetic gear 100 is determined by the ratio of the number of dipoles of the input side rotor 110 and the output side rotor 120, as shown in Equation (b).

The pole piece module 130 also encloses the input side rotor 110 and the output side rotor 120 from the outside of the input side rotor 110 and the output side rotor 120, And a plurality of pole pieces 131 positioned at a predetermined position.

That is, the input side rotor 110 and the output side rotor 120 are located together inside the pole piece module 130.

The pole piece module 130 is spaced apart from the input side rotor 110 and the output side rotor 120, respectively.

The pole piece module 130 transmits the magnetic force generated by the rotation of the input side rotor 110 to the output side rotor 120 to rotate the output side rotor 120.

In addition, the number of the pole pieces 131 satisfies the above-mentioned formula (a).

4 and 5 illustrate that the magnetic gear 100 of the present invention is a cylindrical rotary type magnetic gear, it can be manufactured as a disk rotating type, a flat plate linear type, and a cylindrical linear type. (See, for example, Patent Reference can be made to the disk rotation type, flat plate linear type, and cylindrical linear type of Document 1).

6, the magnetic gear 100 of the present invention includes a pole piece module supporting member 132 for holding the pole piece 131 in a radial shape, And a plurality of bearings (140, 150, 160) for supporting the bearings.

The pole piece module supporting member 132 supports the pole pieces 131 in a radial position and constitutes the pole piece module 130 together with the pole pieces 131.

That is, the pole piece module 130 may serve as a housing outside the rotors 110 and 120.

The bearings 140, 150 and 160 are fixed to the inside of one side of the pole piece module supporting member 132 and the inner race is supported by an input shaft support bearing 140 fixed to the input shaft 113 of the input side rotor 110, The outer ring is fixed to the inside of the other side of the pole piece module supporting member 132 and the inner ring is fixed to the output shaft 123 of the output side rotor 120 and the output side rotor 120 is fixed to the pole piece module 130 And the output shaft 114 of the input side rotor 110 and the input shaft 124 of the output side rotor 120 are supported on the rotation axis c so that the input side rotor 110, And a rotor connecting bearing 160 for rotating the output shaft 114 of the output shaft 110 and the input shaft 124 of the output shaft 120 while sliding on each other.

The output shaft support bearing 150 and the input shaft support bearing 140 are each provided with a radial bearing receiving a load acting perpendicular to the rotation axis c and the rotor connection bearing 160 And is provided with a thrust bearing receiving a thrust parallel to the rotation axis c.

That is, since the magnetic gear 100 of the present invention requires only three bearings as compared with the conventional magnetic gear 10, it is possible to reduce the reduction of the torque transmission rate due to the friction of the bearings.

Since the magnetic gear 100 of the present invention requires only one gap a4 between the rotors 110 and 120 and the pole piece module 130 as compared with the conventional magnetic gear 10, It is easy to manufacture, can reduce manufacturing cost, and can easily control the size of the gap.

7 is a sectional view showing an example of a pole piece 130 of a magnetic gear 100 according to an embodiment of the present invention. The pole piece 13a of the magnetic gear 10 can concentrate the magnetic flux .

8, the pole piece 131 of the magnetic gear 100 of the present invention has a shape of a bar parallel to the rotation axis c and has a vertical section of the first figure 131a and the second figure 131b And has a shape joined in a planar manner.

The first figure 131a has a first arc 131aa which is a curved line and the first arc 131aa and the center c have the same position and a central angle 1 and their inner diameters d2 are equal to each other. A second line 131ab that is smaller than the inner diameter d1 of the first line 131aa, a line 131ac that connects one ends of the first line 131aa and the second line 131ab, And a line 131ad connecting the other end of the second arc 131ab and the other end of the second arc 131ab.

In other words, the inner radius d2 / 2 of the second arc 131ab is smaller than the inner radius d1 / 2 of the first arc 131aa, the curvatures are equal to each other, and the position of the center c is And coincides with the position of the rotation axis (c).

The lines 131ac and 131ad connecting the first line 131aa and the second line 131ab are curved toward the center of the first graphic pattern 131a .

The second figure 131b has the same position and inner diameter d2 as the second arc 131ab and the center c and the central angle 2 is equal to the central angle 1 of the second arc 131ab. The inner diameter d3 is equal to the inner diameter d2 of the third row 131ba and the inner diameter d2 of the third row 131ba is the same as that of the third row 131ba, A line 131bd connecting one end of the third call 131b and the fourth call end 131bb and a line 131bb connecting the third call end 131ba and the fourth call end 131bb, And a line 131bc that connects the other ends of the two electrodes 131a and 131b.

In other words, the inner diameters d2 / 2 of the second arc 131ab and the inner diameters d2 / 2 of the third arc 131ba are the same, and the inner radius d2 / 2 of the third arc 131ba is the same Is larger than the inner radius (d3 / 2) of the arc 131bb.

The lines 131bc and 131bd connecting the ends of the third and fourth circles 131ba and 131bb are preferably straight lines.

The first figure 131a and the second figure 131b are arranged such that the bisection position c1 of the second arc 131ab and the bisection position c1 of the third arc 131ba overlap each other So that the cross-sectional shape of the pole piece 131 is formed.

9 to 11 illustrate variables for determining the shape of a pole piece of a magnetic gear according to an embodiment of the present invention, and the shape of the pole piece 131 is largely divided into three variables.

9, the first variable is a distance of a straight line perpendicular to the third and fourth lines 131ba and 131bb (hereinafter, referred to as 'first vertical distance').

Further, the first vertical distance? Is set to 13.5 占 퐉 (L _pr ', hereinafter referred to as' second vertical distance') between the fourth line 131bb and the first line 131aa, % And smaller than 23.5%.

That is, the first vertical distance? Is designed to satisfy the following equation (1).

Next, referring to FIG. 10, the second variable is the central angle (?) Of the fourth number 131bb.

The central angle beta of the fourth line 131bb is greater than the angle of the first arcs 131'aa and 131'aa of the two pole pieces 131 'and 131' Is greater than 40% and less than 50% of the central angle of the virtual arc connecting the opposite end of the arc (β ', hereinafter referred to as the' reference angle ').

That is, the central angle β of the fourth number 131bb is designed at an angle ranging from 40% to 50% of the reference angle β 'as shown in the following equation (2).

Where N _p is the number of pole pieces.

11, the third variable is a vertical bisecting point c2 at a bisecting position c2 of a virtual line segment l1 (hereinafter, referred to as a first virtual line segment) connecting both ends of a concave curve 131ac. (Hereinafter, referred to as a "concave length") to one of the concave curves 131ac.

The concave length may be defined by virtual line segments l2 and l3 perpendicularly connected to the fourth line 131bb at one end 131ac 'of the one concave curve 131ac on the first line 131aa side, (C4) of the first call (131aa) and the bisection position (c5) of the fourth call (131bb) in the vertical direction at the bisection position (c3) (Hereinafter, referred to as a 'reference length') to an imaginary line segment (? 3, hereinafter referred to as a third virtual line segment)

That is, the concave length? Is designed within the range of 30% to 40% of the reference length? 'As shown in Equation 3 below.

Here, D _pi is the inner diameter d3 of the fourth arc 131bb, D _po is the inner diameter d1 of the first arc 131aa, and N _p is the number of the pole pieces 131.

In Equation 3, denominator refers to the reference length y ', which is defined as a straight line passing through points c5 and c4 with the first imaginary line segment l3 being the x axis on a rectangular coordinate system centered on the origin c. And the y-axis coordinate value of the intersection of the straight line passing through the points c3 and c6. However, the reference length? 'Can be calculated by various methods.

12 is a view for explaining a multiple type magnetic gear according to another embodiment of the present invention.

Referring to FIG. 12, a multiple type magnetic gear 200 according to another embodiment of the present invention is formed by connecting a plurality of magnetic gears 100 according to an embodiment of the present invention by direct connection.

In FIG. 12, a dual type magnetic gear is shown in which two magnetic gears 100 and 100 'are directly connected. However, three or more magnetic gears may be directly connected.

In the case of the dual type, the output shaft 123 of the first magnetic gear 100 is connected to the input shaft 113 'of the second magnetic gear 110'.

When power is transmitted from the first magnetic gear 100 to the second magnetic gear 100 ', the second magnetic gear 100' is transmitted from the second magnetic gear 100 'to the first magnetic gear 100' When power is transmitted, it acts as an accelerator.

The gear ratio of the input side rotor 110 and the output side rotor 120 of the first magnetic gear 100 is 1:10 and the input side rotor 110 'and the output side rotor of the second magnetic gear 100' 120 'has a gear ratio of 1:10, the total gear ratio becomes 1: 100 and the torque ratio becomes 1: 100.

In other words, when the conventional magnetic gear 10 is designed to have a torque ratio of 1: 100, the number of dipoles of the outer rotor must be 100 times larger than the number of dipoles of the inner rotor. (200) is advantageous in that a high torque ratio can be realized by using two magnetic gears.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation in the present invention. Various changes and modifications will be possible.

100: magnetic gear 110: input side rotor
111: input side rotor 112, 122: magnet
113: input shaft 120: output side rotor
121: output side rotor 130: pole piece module
131: pole piece 132: pole piece module supporting member
140: input shaft support bearing 150: output shaft support bearing
160: rotor connection bearing

Claims (9)

Input side rotor;
An output side rotor disposed on the rotation axis extension of the input side rotor and spaced apart from the input side rotor; And
A pole piece module which surrounds the input side rotor and the output side rotor from the outside of the input side rotor and the output side rotor and has a plurality of pole pieces radially positioned on the rotation axis and transmits the magnetic force of the input side rotor to the output side rotor; Including,
Wherein the input side rotor and the output side rotor are located together inside the pole piece module and are spaced apart from the pole piece module.
The method according to claim 1,
Wherein the pole piece module includes a pole piece module support member for supporting the pole pieces to maintain a radial orientation relative to the rotation axis,
An input shaft supporting bearing which is fixed to one side of the pole piece module supporting member and whose inner ring is fixed to an input shaft of the input side rotor and rotates while the input side rotor is spaced apart from the pole piece module;
An output shaft support bearing which is fixed to the inside of the other side of the pole piece module support member and whose inner ring is fixed to the output shaft of the output side rotor and which rotates the output side rotor while being spaced apart from the pole piece module; And
Further comprising a rotor coupling bearing that rotates the output shaft of the input side rotor and the input side rotor of the output side rotor while sliding so that the output side of the input side rotor and the input side of the output side rotor are supported on the rotation axis.
The method according to claim 1,
The cross-section of each of the pole pieces,
A first arc and a second arc having the same center position and center angle as the first arc and having an inner diameter smaller than the inner diameter of the first arc and a second arc having a first arc and a second arc, A first figure surrounded by a line,
And a center angle of the second arc is equal to a center angle of the second arc, a central angle of the third arc is greater than a central angle of the second arc, a central position and a center angle of the third arc are the same, and an inner diameter of the fourth arc is smaller than an inner diameter of the third arc And a second figure surrounded by a line connecting one end and each other end of the third and fourth arcs,
Wherein a bisecting position of the second arc and a bisecting position of the third arc are combined to each other so as to overlap with each other.
The method of claim 3,
The vertical distance between the fourth call and the third call (hereinafter, referred to as a 'first vertical distance') may be expressed by the following equation (1) Quot;) is greater than 13.5% and less than 23.5%.
[Equation 1]

Where alpha is the first vertical distance and L _pr is the second vertical distance.
The method of claim 3,
The central angle of the fourth arc is larger than 40% of the central angle of the virtual arc connecting the first calls of the two pole pieces with one pole piece interposed therebetween (hereinafter referred to as a reference angle) Magnetic gear characterized by less than 50%.
&Quot; (2) "

Where beta is the central angle of the fourth arc and N _p is the number of pole pieces.
The method of claim 3,
Wherein a line connecting the first call and the second call in the first figure is a curve concave toward the center of the first figure (hereinafter, referred to as 'concave curve').
The method according to claim 6,
(Hereinafter referred to as a "concave length") in the vertical direction at the bisecting position of a virtual line segment connecting the both ends of the concave curve (hereinafter, referred to as a "first virtual line segment"),
(2) of the first arc in the vertical direction at a bisecting position of a virtual line segment (hereinafter, referred to as a second virtual line segment) connected at a first call side end of the concave curve in a direction perpendicular to the fourth arc Of the length to a virtual line segment (hereinafter, referred to as a 'third virtual line segment') connecting the bisection positions of the fourth arc.
8. The method of claim 7,
Wherein the concave length is calculated by the following equation (3).
&Quot; (3) "

Where D _pi is the inner diameter of the fourth arc, D _po is the inner diameter of the first arc, and N _p is the number of pole pieces.
A magnetic bearing assembly comprising at least two magnetic gears according to any one of claims 1 to 8,
Wherein the output side rotor of the first magnetic gear is directly connected to the input side rotor of the second magnetic gear, among the magnetic gears.

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