Unequal-thickness magnetic pole type magnetic gear composite motor

Abstract

The invention relates to the technical field of composite motors, and discloses an unequal-thickness magnetic pole type magnetic gear composite motor which comprises a low-speed rotor, a magnetism adjusting ring, a high-speed rotor and a stator which are coaxially arranged at intervals from outside to inside, air gaps are formed between adjacent structures, and the three layers are respectively an outer-layer air gap, a middle-layer air gap and an inner-layer air gap. The high-speed rotor comprises a cylindrical framework, an even number of unequal-thickness permanent magnets are evenly embedded in the side wall of the cylindrical framework at intervals, and each unequal-thickness permanent magnet is thick in the middle and thin on the two sides, so that a middle-layer air gap and an inner-layer air gap are uneven air gaps. By means of the non-uniform air gaps, the harmonic content of the middle-layer air gap and the inner-layer air gap is reduced, and the torque density of the composite motor is improved.

Description

Technical Field

[0001] The invention relates to the technical field of motors, and in particular to a unequal-thickness magnetic pole type magnetic gear composite motor. Background Art

[0002] With the rapid development of permanent magnet materials, magnetic gear transmission has been widely used. The magnetic gear composite motor cleverly utilizes the internal space of the magnetic gear and combines it with the permanent magnet synchronous motor, making the motor compact in structure and combining it with many advantages of magnetic gears. It also belongs to non-contact transmission and does not have the shortcomings of traditional mechanical gear reducers such as mechanical fatigue, wear, and the need for lubrication and maintenance. At the same time, it also has the advantages of long service life, low noise, and easy maintenance. Therefore, it has broad application prospects in the fields of wind power generation, robot joint motors and new energy vehicles.

[0003] According to the number of air gaps and the degree of coupling of the motor, motor structures with different topological structures are derived, which are mainly divided into three-layer air gap and two-layer air gap magnetic gear compound motors. Among them, the three-layer air gap magnetic gear compound motor makes full use of the internal space of the magnetic gear to install the permanent magnet motor in it. The hybrid magnetized magnetic gear structure in patent No. 201621094676.2 is a typical three-layer air gap magnetic gear compound motor after the permanent magnet motor is embedded. However, it has the problems of low magnetic steel utilization and large torque pulsation. For the two-layer air gap magnetic gear compound motor, as the air gap decreases, the magnetic gear part will become complicated, so that the magnetic field coupling will be more complicated, resulting in greater torque pulsation and motor loss. Summary of the invention

[0004] The invention provides a unequal thickness magnetic pole type magnetic gear composite motor, which solves the problems of low magnetic steel utilization rate and large torque pulsation of the existing composite motor.

[0005] The present invention can be achieved through the following technical solutions:

[0006] A unequal thickness magnetic pole type magnetic gear composite motor comprises a low-speed rotor, a magnetic adjustment ring, a high-speed rotor and a stator which are coaxially spaced from outside to inside, air gaps are formed between adjacent structures, and there are three layers in total, which are respectively recorded as an outer air gap, a middle air gap and an inner air gap. The high-speed rotor comprises a cylindrical skeleton, and an even number of unequal thickness permanent magnets are evenly spaced and embedded on the side wall of the cylindrical skeleton. Each of the unequal thickness permanent magnets is thick in the middle and thin at both sides, so that the middle air gap and the inner air gap are unequal air gaps.

[0007] Furthermore, Halbach array permanent magnets are affixed to the outer and inner sides of the side wall of the tubular frame between two adjacent unequal thickness permanent magnets. The Halbach array permanent magnets are all tangentially magnetized and are concentric with the tubular frame. The unequal thickness permanent magnets are all radially magnetized, and the radially inward and radially outward magnetization methods are alternately arranged.

[0008] Furthermore, the unequal thickness permanent magnet is in the shape of an elongated strip as a whole, similar to a rugby ball, with some arcuate surfaces exposed on the outside and inside of the side wall, and the curvature of the arcuate surface exposed on the outside is greater than that of the arcuate surface exposed on the inside.

[0009] Furthermore, the unequal thickness permanent magnet is in the shape of a long strip as a whole when viewed from the axial direction, and is thick in the middle and thin on both sides in the radial direction, similar to a rugby ball-shaped structure, and the curvature of the outer arc surface is greater than that of the inner arc surface.

[0010] Furthermore, the number of pole pairs of the high-speed rotor is n h , the number of pole pairs of the low-speed rotor is n l The number of magnetic adjustment blocks on the magnetic adjustment ring is p, and the relationship between them satisfies p=n l +n h , and the number of magnetic field pole pairs generated by the stator after power is applied is the same as the number of high-speed rotor pole pairs n h equal.

[0011] Furthermore, the magnetic tuning ring includes a main frame of a cylindrical structure, and a plurality of openings are evenly spaced along the axial direction of the side wall of the main frame, and a magnetic tuning block is embedded in each of the openings. Each of the magnetic tuning blocks is made of laminated silicon steel sheets, and the main frame is manufactured by 3D printing.

[0012] Furthermore, the low-speed rotor includes a back iron of a cylindrical structure, and a Halbach array permanent magnet is attached to the inner surface of the back iron;

[0013] The stator winding includes a stator yoke, and the stator winding is wound around the yoke part of the stator yoke.

[0014] The beneficial technical effects of the present invention are:

[0015] Compared with the prior art, it has the following beneficial effects:

[0016] (1) The unequal thickness pole type magnetic gear compound motor provided by the present invention has unequal thickness pole high-speed rotor permanent magnets using Halbach array unequal thickness olive-shaped poles. When the amount of permanent magnets is the same, it not only improves the output torque of the unequal thickness pole type magnetic gear compound motor, but also reduces the manufacturing cost and improves the sinusoidal nature of the air gap magnetic field. It also has a significant effect on suppressing the torque pulsation of the motor. Torque pulsation will increase the wear of the mechanical parts and accelerate the occurrence of failures. By reducing the torque pulsation, it is beneficial to the smooth operation of the motor and can extend the life of the motor and its driving equipment.

[0017] (2) The unequal-thickness magnetic pole type magnetic gear composite motor provided by the present invention uses a non-magnetic material PLA as the magnetic ring to manufacture the main frame part through 3D printing, making the motor lighter. Traditional manufacturing methods require expensive molds, while 3D printing does not rely on molds and is particularly suitable for small-batch production, which significantly reduces the initial production cost. The motor frame can also be designed and produced according to specific needs, making production more flexible. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic diagram of a radial cross section of the unequal thickness magnetic pole type magnetic gear compound motor of the present invention;

[0019] Figure 2 It is a schematic diagram of the structure of the low-speed rotor permanent magnet of the present invention;

[0020] Figure 3 It is a schematic diagram of the main frame structure of the magnetic tuning ring of the present invention;

[0021] Figure 4 It is a schematic diagram of the high-speed rotor structure of the present invention;

[0022] Figure 5 It is a schematic diagram of the stator structure of the present invention;

[0023] Figure 6 It is a schematic diagram of the structure of permanent magnets of unequal thickness in the high-speed rotor of the present invention;

[0024] Figure 7 It is a torque diagram of a high-speed rotor and a low-speed rotor of the unequal-thickness magnetic pole type magnetic gear compound motor of the present invention;

[0025] Figure 8 is a schematic diagram of the structure of the magnetic gear compound motor of Comparative Example 1;

[0026] Fig. 9 is a torque diagram of a high-speed rotor and a low-speed rotor of a magnetic gear compound motor of comparative example 1;

[0027] Fig.10 is a schematic diagram of the structure of the magnetic gear compound motor of Comparative Example 2;

[0028] Fig.11 is a torque diagram of a high-speed rotor and a low-speed rotor of a magnetic gear compound motor of comparative example 2;

[0029] Fig.12 It is a schematic diagram of the high-order harmonic changes corresponding to the rotating magnetomotive force generated by a composite motor corresponding to a high-speed rotor constructed by using equal-thickness permanent magnets in the prior art;

[0030] Fig.13 It is a schematic diagram of the change of high-order harmonics corresponding to the rotating magnetomotive force generated by the composite motor of the present invention;

[0031] Among them, 1-low-speed rotor; 11-back iron; 2-magnetic adjustment ring; 21-main frame; 22-opening; 3-high-speed rotor; 31-permanent magnets of unequal thickness; 32-cylindrical frame; 33-Halbach array permanent magnet; 4-stator; 41-stator yoke; 42-stator winding. DETAILED DESCRIPTION

[0032] The specific implementation of the present invention is described in detail below with reference to the accompanying drawings and preferred embodiments.

[0033] like Figure 1 and 2 As shown, the present invention provides a unequal thickness magnetic pole type magnetic gear composite motor, which has a low-speed rotor 1, a magnetic adjustment ring 2, a high-speed rotor 3 and a stator 4 from the outside to the inside, which are coaxially nested, and air gaps are formed between adjacent structures, with a total of three layers, which are respectively recorded as an outer layer air gap, a middle layer air gap and an inner layer air gap. The high-speed rotor 3 includes a cylindrical skeleton 32, and an even number of unequal thickness permanent magnets 31, such as four, are evenly spaced and embedded on the side wall of the cylindrical skeleton 32. Each unequal thickness permanent magnet 31 is thick in the middle and thin on both sides, so that the middle layer air gap and the inner layer air gap are uneven air gaps. In this way, with the help of uneven air gaps, the harmonic content of the middle layer air gap and the inner layer air gap is reduced, and the torque density of the composite motor is improved.

[0034] The magnetic field energy stored in the composite motor is approximately the magnetic field energy in the motor air gap and permanent magnet, that is,

[0035]

[0036] The magnetic field energy W depends on the structural size of the motor, the performance of the permanent magnet, and the relative position between the stator and the rotor. The distribution of the air gap flux density along the armature surface can be approximately expressed as

[0037]

[0038] In the formula, B r (θ), h m (θ) and δ(θ,α) are the distributions of the permanent magnet remanence, the effective air gap length, and the permanent magnet magnetization direction length along the circumferential direction, respectively.

[0039] From the geometric relationship, the thickness of the permanent magnet in the radial magnetization direction is

[0040]

[0041] The air gap flux density of the motor can be expressed as

[0042]

[0043] Where: H c is the coercive force of the permanent magnet; μ0 is the magnetic permeability of air; μ r is the relative magnetic permeability; g is the air gap; H r (θ) is the thickness of the permanent magnet in the magnetization direction. It can be seen from the above formula that when the permanent magnet material is determined, if the thickness change in the magnetization direction of the permanent magnet is close to sine, the sinusoidality of the air gap flux density can be improved.

[0044] Therefore, the permanent magnets of the high-speed rotor in the composite motor of the present invention adopt a unequal thickness structure, and the relative magnetic permeability of the permanent magnets is approximately equal to 1. The air gap magnetic flux density expression of the motor is:

[0045]

[0046] The rotating magnetic force generated by the motor is

[0047]

[0048] Where: F μ is the amplitude of the μth harmonic of the permanent magnet, μ=1, 3, 5…; ω is the rotor rotation angular frequency; p is the number of permanent magnet pole pairs.

[0049] F μ It can be expressed as

[0050]

[0051] Where: H r (θ) is the height of the permanent magnet in the magnetizing direction; α p Polar arc coefficient

[0052] The influence of high-order harmonics on the change of magnetomotive force is small and can be ignored. The present invention only considers the harmonic amplitude of the permanent magnet before the 9th harmonic. Fig.12 , Fig.13 It can be seen that the amplitude of the motor of the present invention at the 1st harmonic is significantly higher than that of the unimproved motor, which is helpful to improve the output torque. At the same time, its harmonic amplitude shows a stable downward trend, without rebound fluctuation, and the operation is more stable; while the amplitude of the unimproved motor at the 5th harmonic does not decrease but increases, and the amplitude of the 9th harmonic increases again after the 7th harmonic amplitude decreases significantly, showing a large fluctuation. rThe change of (θ) will make the magnetomotive force generated by the motor more stable.

[0053] From the above analysis, it can be seen that the thickness of the permanent magnet in the magnetization direction will affect the air gap flux density and magnetomotive force distribution. The torque pulsation is mainly the cogging torque generated by the interaction between the permanent magnet, the stator and the magnetic ring. The output torque is the mechanical torque output by the motor, which is usually related to the magnetic field strength, the position of the rotor and the load condition in the motor. The magnetomotive force is the ability of the motor to generate a magnetic field. The greater the magnetomotive force, the stronger the magnetic field strength, which in turn leads to an increase in magnetic flux and the final output torque. Therefore, there is a direct correlation between the variation amplitude of the magnetomotive force and the stability of the torque pulsation. Significant changes in the magnetomotive force often lead to large fluctuations in the torque output, that is, the stability of the torque pulsation is reduced. On the contrary, when the change of the magnetomotive force is relatively gentle, the fluctuation of the torque will also decrease accordingly, thereby maintaining a higher stability. Therefore, the reasonable selection of the unequal thickness of the inner and outer arc surfaces of the permanent magnet can make the air gap flux density of the motor close to the sine, reduce the harmonic content, and reduce the torque pulsation.

[0054] The number of pole pairs of the high-speed rotor is n h , the number of pole pairs of the low-speed rotor is n l The number of magnetic adjustment blocks on the magnetic adjustment ring is p, and the relationship between them satisfies p=n l +n h , and the number of magnetic field pole pairs generated by the stator after power is applied is the same as the number of high-speed rotor pole pairs n h equal.

[0055] Halbach array permanent magnets 33 are attached to the outer and inner sides of the side wall of the cylindrical frame 32 between two adjacent unequal thickness permanent magnets 31. The Halbach array permanent magnets 33 are all tangentially magnetized, and the unequal thickness permanent magnets 31 are all radially magnetized, and the radially inward and radially outward magnetization modes are alternately arranged, such as Figure 4 As shown, the arrow is the magnetization direction of the permanent magnet, wherein the Halbach array permanent magnet 31 is a tangentially magnetized sector-shaped magnetic steel surface attached to the inner and outer sides of the cylindrical frame and concentric with the cylindrical frame. The materials selected for the unequal thickness permanent magnet 31 and the Halbach array permanent magnet 33 are NdFe35 neodymium iron boron permanent magnets with large magnetic energy and not prone to demagnetization, and the magnetization method is to change at a 90° angle.

[0056] The unequal thickness permanent magnet is in the shape of a long strip as a whole when viewed axially, and is thick in the middle and thin on both sides in the radial direction, similar to a rugby ball-shaped structure, and the curvature of the outer arc surface is greater than that of the inner arc surface. Compared with the traditional tile-shaped permanent magnets of equal thickness, the outer arc surface of the unequal thickness permanent magnet of the present invention adopts an eccentric circle to inscribe the existing arc-shaped permanent magnet, and takes the arc of the eccentric circle as the outer arc of the unequal thickness permanent magnet to ensure that the minimum air gap distance remains unchanged, and changes the degree of inward curvature. The deviation distance between the center of the outer circle and the center of the rotating shaft of the composite motor is h, such as 10-13mm, and the radius of the eccentric circle of the outer arc is R7; similarly, the center of the inner arc surface is determined at the deviation distance H from the center of the rotating shaft of the composite motor, and the H value can be set to 95-100mm, and the inner arc surface radius R8 is taken as the minimum distance of the inner air gap between the stator and the high-speed rotor, such as Figure 6 As shown, increasing the magnetic pole deviation distance within a certain range can optimize the torque ripple.

[0057] We can evenly space a plurality of openings on the side wall of the cylindrical skeleton along its axial direction. The opening is a wedge-shaped structure with a larger outside and a smaller inside. Of course, the two side surfaces of the corresponding unequal thickness permanent magnets are also inclined surfaces inclined inwardly, so that the unequal thickness permanent magnets can be embedded in the openings. The edge positions can be sealed with glue. After embedding, part of the arcuate surfaces of the unequal thickness permanent magnets are exposed on the outside and inside of the side wall respectively, and the curvature of the arcuate surface exposed on the outside is greater than that of the arcuate surface exposed on the inside.

[0058] Permanent magnets of unequal thickness are installed between the opening slots of the cylindrical skeleton at different center angles required by the high-speed rotor according to the different pole pairs of the high-speed rotor. The thickness of the permanent magnet is the largest when the position angle is θ=0°, and the thickness of the permanent magnet gradually decreases toward both ends, and the magnetic field is more concentrated, making the inner air gap and the middle air gap uneven. The thickness change according to the magnetization direction of the permanent magnet will affect the distribution of the air gap magnetic flux and magnetomotive force, which can make the air gap magnetic flux of the motor close to sinusoidal, reduce the harmonic content, and suppress the torque pulsation of the motor.

[0059] like Figure 2 As shown, the low-speed rotor 1 includes a back iron 11 of a cylindrical structure, and a Halbach array permanent magnet is also posted on the inner surface of the back iron. Of course, the fixation between the two can also be achieved by riveting or other methods. The material used for the Halbach array permanent magnet is NdFe35 neodymium iron boron permanent magnet with large magnetic energy and not prone to demagnetization. The magnetization method is a Halbach array changed by 90°, and the number of pole pairs of the low-speed rotor can be set to 10 pairs.

[0060] like Figure 3As shown, the magnetic adjustment ring 2 is composed of a main frame 21 of a cylindrical structure and a plurality of magnetic adjustment blocks, which can be fixed to the fixed end cover of the motor by bolts. The main frame 21 can be made of non-magnetic material PLA through 3D printing, making the motor lighter; the magnetic adjustment block 22 is made of laminated silicon steel sheets and embedded in the main frame 21. A plurality of openings 22 can be evenly spaced on the side wall of the main frame along its axial direction, and the magnetic adjustment blocks are correspondingly embedded in the openings 22.

[0061] like Figure 5 As shown, the stator 4 includes a stator yoke 41 and a stator winding 42. The stator yoke 41 is made of silicon steel material and can be 4-stage 12-slot. The stator winding 42 is wound on its yoke. The stator winding 42 adopts distributed winding. After the winding is energized, the motor can generate a two-stage rotating magnetic field, which is the same as the number of pole pairs of the unequal thickness permanent magnets on the high-speed rotor 3.

[0062] The working principle of the present invention is as follows:

[0063] When the unequal thickness magnetic pole type magnetic gear compound motor is running, current is passed through the stator winding 42 in the stator 4, which will generate a rotating magnetic field with two poles. The rotating magnetic field is coupled with the radially magnetized unequal thickness permanent magnets 31 and the tangentially magnetized Halbach array permanent magnets 33 on the high-speed rotor 3, driving the high-speed rotor 3 to rotate at high speed. At this time, the high-speed rotating permanent magnets on the high-speed rotor 3 generate a rotating magnetic field, and the magnetic field is modulated by the magnetic adjustment block 22 on the magnetic adjustment ring 2. The number of pole pairs of the rotating magnetic field generated after modulation by the magnetic adjustment block 22 is the same as the number of pole pairs of the Halbach array permanent magnets on the low-speed rotor 1. The rotating magnetic field transmits the rotation to the low-speed rotor, and the low-speed rotor is connected to the output shaft end cover by bolts. Finally, the low-speed shaft outputs torque to the outside.

[0064] The unequal thickness magnetic pole type magnetic gear composite motor of the present invention has two rotors. The high-speed rotor of the internal unequal thickness magnetic pole adopts the unequal thickness olive-shaped magnetic pole of the Halbach array, which improves the sinusoidal property of the air gap magnetic flux density. The external low-speed rotor adopts the traditional concentric Halbach array magnetized permanent magnet. The high-speed rotor and the low-speed rotor form a magnetic field in the air gap. The magnetic field is modulated by the magnetic modulation ring to realize the deceleration operation of the motor. The reduction ratio of the motor is G, and its expression is: G=n l n h The unequal thickness magnetic pole structure greatly improves the utilization rate of permanent magnets, increases the output torque of the motor, and reduces the torque pulsation of the motor.

[0065] like Figure 7As shown, when the unequal thickness magnetic pole type magnetic gear compound motor of the present invention is running in a steady state, the torque of the high-speed rotor 3 and the low-speed rotor 1 is as follows, from which it can be seen that the maximum output torque Tmax of the low-speed rotor is 57.0115Nm, and the minimum output torque Tmin is 53.3628Nm.

[0066] Comparative Example 1

[0067] A commonly used magnetic gear compound motor, such as Figure 8 As shown, it is basically the same as embodiment 1, except that the permanent magnets on the high-speed rotor use concentric Halbach magnetization permanent magnets. The input and output torque diagrams are shown in FIG. Fig. 9 As shown, Fig. 9 It can be seen that the maximum output torque of the low-speed rotor is Tmax=33.8741Nm, and the minimum output torque is Tmin=25.1164Nm.

[0068] Comparative Example 2

[0069] A magnetic gear compound motor, such as Fig.10 As shown, the magnetic gear part adopts the hybrid magnetized magnetic gear structure in Chinese Patent No. 201621094676.2, which is basically the same as Example 1, except that the high-speed rotor adopts concentric Halbach magnetized permanent magnets and the low-speed rotor adopts concentric radial magnetized permanent magnets. The input and output torque diagrams are shown in FIG. Fig.11 As shown, Fig.11 It can be seen that the maximum output torque of the low-speed rotor is Tmax=33.9104Nm, and the minimum output torque is Tmin=25.4208Nm.

[0070] In summary, by comparing and analyzing the simulation results of the present invention and the two comparative examples, under the same amount of permanent magnets, the torque of the unequal thickness magnetic pole type magnetic gear composite motor of the present invention is significantly improved, which is 68.3% and 68.1% higher than the two comparative examples respectively; the torque pulsation torque of the unequal thickness magnetic pole type magnetic gear composite motor of the present invention is also significantly improved, which is 14.8% and 14.3% higher than the two comparative examples respectively. Therefore, the motor of the present invention has a larger output torque and smaller torque pulsation.

[0071] Although specific embodiments of the present invention are described above, those skilled in the art should understand that these are merely examples and that various changes or modifications may be made to these embodiments without departing from the principles and essence of the present invention. Therefore, the scope of protection of the present invention is limited by the appended claims.

Claims

1. A magnetic gear compound motor with unequal thickness magnetic poles, characterized in that: The invention comprises a low-speed rotor, a magnetic adjustment ring, a high-speed rotor and a stator which are coaxially arranged from outside to inside, and air gaps are formed between adjacent structures, with a total of three layers, which are respectively recorded as an outer air gap, a middle air gap and an inner air gap. The high-speed rotor comprises a cylindrical skeleton, and an even number of unequal thickness permanent magnets are evenly embedded on the side wall of the cylindrical skeleton. Each of the unequal thickness permanent magnets is thick in the middle and thin at both sides, so that the middle air gap and the inner air gap are uneven air gaps.

2. The unequal thickness magnetic pole type magnetic gear compound motor according to claim 1, characterized in that: Halbach array permanent magnets are attached to the outer and inner sides of the side wall of the cylindrical frame between two adjacent unequal thickness permanent magnets. The Halbach array permanent magnets are all tangentially magnetized and are concentric with the cylindrical frame. The unequal thickness permanent magnets are all radially magnetized, and the radially inward and radially outward magnetization methods are alternately arranged.

3. The unequal thickness magnetic pole type magnetic gear compound motor according to claim 2, characterized in that: The unequal thickness permanent magnet is in the shape of an elongated strip as a whole, similar to a rugby ball, with some arcuate surfaces exposed on the outside and inside of the side wall, and the curvature of the arcuate surface exposed on the outside is greater than that of the arcuate surface exposed on the inside.

4. The unequal thickness magnetic pole type magnetic gear compound motor according to claim 3, characterized in that: The unequal thickness permanent magnet is in the shape of a long strip as a whole when viewed from the axial direction, and is thick in the middle and thin on both sides in the radial direction, similar to a rugby ball-shaped structure, and the curvature of the outer arc surface is greater than that of the inner arc surface.

5. The unequal thickness magnetic pole type magnetic gear compound motor according to claim 1, characterized in that: The number of pole pairs of the high-speed rotor is n h , the number of pole pairs of the low-speed rotor is n l The number of magnetic adjustment blocks on the magnetic adjustment ring is p, and the relationship between them satisfies p=n l +n h , and the number of magnetic field pole pairs generated by the stator after power is turned on is the same as the number of high-speed rotor pole pairs n h equal.

6. The unequal thickness magnetic pole type magnetic gear compound motor according to claim 1, characterized in that: The magnetic tuning ring includes a main frame of a cylindrical structure, and a plurality of openings are evenly spaced along the axial direction on the side wall of the main frame. A magnetic tuning block is embedded in each of the openings, and each of the magnetic tuning blocks is made of laminated silicon steel sheets. The main frame is manufactured by 3D printing.

7. The unequal thickness magnetic pole type magnetic gear compound motor according to claim 1, characterized in that: The low-speed rotor comprises a back iron of a cylindrical structure, and a Halbach array permanent magnet is attached to the inner surface of the back iron; The stator winding includes a stator yoke, and the stator winding is wound around the yoke part of the stator yoke.

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