Axial flux motor rotor

Abstract

The utility model provides an axial magnetic flux motor rotor, which comprises magnetic steel, a rotor iron core, reinforcing ribs and a fixed disc, the magnetic steel is arranged on at least one axial side of the rotor iron core, and a low flux density area is formed at the position of the rotor iron core far away from the magnetic steel; the reinforcing ribs penetrate through the low flux density area of the rotor iron core; the fixing disc is connected with the reinforcing ribs and used for fixing the reinforcing ribs. By arranging the reinforcing ribs in the low-flux-density area, the structural strength of the rotor core is improved, and eddy-current loss is avoided under the condition that the reinforcing ribs are made of metal materials.

Description

Technical Field

[0001] The utility model relates to the technical field of axial flux motors, in particular to an axial flux motor rotor. Background Art

[0002] Axial flux motors, also known as disc motors, have the advantages of small axial size, high torque density, high power density and high efficiency, and are widely used in electric vehicles, general industry and other fields. Axial flux motors include stators and rotors. Depending on the number of stators and rotors, axial flux motors are divided into single-stator single-rotor motors, dual-stator single-rotor motors and other motors. Taking the dual-stator single-rotor motor as an example, the rotor is held between the two stators.

[0003] refer to Figure 1 The rotor includes two layers of upper and lower magnetic steel 100 and a rotor core 500 located in the middle layer. The upper and lower magnetic steel 100 are surface mounted, and the rotor core 500 is usually made of magnetic conductive metal. Although the structural strength is improved, it will produce large eddy current losses and easily cause the magnetic steel to lose magnetism at high temperature.

[0004] The axial flux motor is developing towards high speed and high power density, which puts forward higher strength and performance requirements for the rotor structure of the axial flux motor. Based on this, there is an urgent need for an axial flux motor rotor with low eddy current loss while ensuring structural strength. Utility Model Content

[0005] The utility model aims to provide an axial flux motor rotor, which improves the structural strength and reduces the eddy current loss.

[0006] In order to achieve the above object, the utility model provides an axial flux motor rotor, comprising:

[0007] magnetic steel;

[0008] A rotor core, wherein at least one axial side of the rotor core is provided with a magnetic steel, and a low magnetic density area is formed at a position of the rotor core away from the magnetic steel;

[0009] A reinforcing rib, wherein the reinforcing rib passes through a low magnetic flux density area of ​​the rotor core;

[0010] A fixing plate is connected to the reinforcing rib and is used to fix the reinforcing rib.

[0011] As a preferred embodiment, the reinforcing ribs include:

[0012] Limiting plate;

[0013] A rod body is provided, wherein the rod body passes through the low magnetic density area of ​​the rotor core, and two ends of the rod body are respectively connected to a limit plate and the fixed disk, and the limit plate and the fixed disk are respectively limited and abutted against the radial sides of the rotor core.

[0014] As a preferred embodiment, the fixed plate comprises:

[0015] Upper plate;

[0016] A lower plate is connected to the upper plate and clamps the rod body of the reinforcing rib.

[0017] As a preferred embodiment, the lower plate is provided with a lower receiving groove, and the upper plate is provided with an upper clamping block, and the upper clamping block corresponds to the lower receiving groove one by one;

[0018] After the upper plate and the lower plate clamp the rod body of the reinforcing rib, the rod body is located in the lower accommodating groove, and the upper clamping block is embedded in the clamping groove provided in the rod body.

[0019] As a preferred embodiment, the upper plate and the lower plate are fixed by bolts, and the bolts and the lower receiving groove are spaced apart.

[0020] As a preferred embodiment, the fixing disk is located radially inside or outside the rotor core.

[0021] As a preferred embodiment, the reinforcing ribs are made of metal material.

[0022] As a preferred embodiment, it also includes:

[0023] An inner ring, the inner ring being arranged radially inward of the rotor core;

[0024] The outer ring is arranged on the radial outside of the rotor core, and the reinforcing ribs connect the inner ring and the outer ring.

[0025] As a preferred embodiment, the magnetic steel is spliced ​​along the circumferential direction;

[0026] Alternatively, the rotor core is provided with a magnetic steel slot, and the magnetic steel is arranged in the magnetic steel slot.

[0027] As a preferred embodiment, the magnetic steels are respectively arranged on both sides of the rotor core in the axial direction, and the low magnetic density area of ​​the rotor core corresponds to the center position of the magnetic steels.

[0028] Compared with the prior art, this technical solution has the following advantages:

[0029] By arranging the reinforcing ribs in the low magnetic flux density area, not only the structural strength of the rotor core is improved, but also when the reinforcing ribs are made of metal, eddy current loss will not occur.

[0030] The fixing plate fixes the reinforcing ribs so that the reinforcing ribs are kept in the low magnetic density area of ​​the rotor core. At the same time, the fixing plate supports the rotor core to further improve the structural strength.

[0031] The present invention is further described below with reference to the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 is a structural schematic diagram of an existing rotor;

[0033] Figure 2 This is an exploded view of the first embodiment of the axial flux motor rotor of the utility model;

[0034] Figure 3 A schematic diagram of the magnetic field flow direction of the first embodiment of the axial flux motor rotor of the utility model;

[0035] Figure 4 It is a structural schematic diagram of the rotor core in the first embodiment of the axial flux motor rotor of the utility model;

[0036] Figure 5 It is a schematic structural diagram of the outer ring of the first embodiment of the axial flux motor rotor of the utility model;

[0037] Figure 6 This is a schematic diagram of the structure of the inner ring of the first embodiment of the axial flux motor rotor of the utility model;

[0038] Figure 7 It is a structural schematic diagram of the upper disk in the first embodiment of the axial flux motor rotor of the utility model;

[0039] Figure 8 It is a structural schematic diagram of the lower plate in the first embodiment of the axial flux motor rotor of the utility model;

[0040] Fig. 9 This is a schematic diagram of the structure of the reinforcing ribs in the first embodiment of the axial flux motor rotor of the utility model;

[0041] Fig.10 This is an exploded view of the second embodiment of the axial flux motor rotor of the utility model;

[0042] Fig.11 A schematic diagram of the magnetic field flow direction of the second embodiment of the axial flux motor rotor of the utility model;

[0043] Fig.12It is a schematic structural diagram of the rotor core in the second embodiment of the axial flux motor rotor of the utility model;

[0044] Fig.13 This is a schematic diagram of the structure of the magnetic steel in the second embodiment of the axial flux motor rotor described in the present invention.

[0045] In the figure: 100 magnetic steel, 110 axially magnetized magnetic steel, 120 tangentially magnetized magnetic steel, 100a chamfered portion, 200 screws, 300 inner ring, 310 inner through hole, 320 inner connecting hole, 400 outer ring, 410 outer through hole, 420 outer connecting hole, 500 rotor core, 500a low magnetic density area, 500b high magnetic density area, 510 magnetic steel slot, 511 slot oblique portion, 520 core through hole, 600 reinforcing rib, 610 rod portion, 620 limiting plate, 630 slot, 700 fixing plate, 710 upper plate, 711a block, 720 lower plate, 721a lower accommodating groove, 800 bolts, 1000 mounting hole. DETAILED DESCRIPTION

[0046] The following description is used to disclose the utility model so that those skilled in the art can implement the utility model. The preferred embodiments described below are only examples, and those skilled in the art can think of other obvious variations. The basic principles of the utility model defined in the following description can be applied to other embodiments, variations, improvements, equivalents, and other technical solutions that do not deviate from the spirit and scope of the utility model.

[0047] First embodiment

[0048] like Figure 2 and Figure 3 As shown, the axial flux motor rotor comprises:

[0049] Magnetic steel 100;

[0050] A rotor core 500, wherein a magnetic steel 100 is disposed on at least one axial side of the rotor core 500, and a low magnetic density region 500a is formed at a position of the rotor core 500 away from the magnetic steel 100;

[0051] A reinforcing rib 600, wherein the reinforcing rib 600 passes through the low magnetic flux density region 500a of the rotor core 500;

[0052] A fixing plate 700 , wherein the fixing plate 700 is connected to the reinforcing rib 600 and is used to fix the reinforcing rib 600 .

[0053] The rotor core 500 is provided with an axial side of the magnetic steel 100, and an air gap surface is formed between it and the stator, that is, a magnetic circuit is formed on the axial side of the rotor core 500 where the magnetic steel 100 is provided, and a low magnetic density area 500a is formed at a position of the rotor core 500 away from the magnetic steel 100. By arranging the reinforcing ribs 600 in the low magnetic density area 500a, not only the structural strength of the rotor core 500 is improved, but also when the reinforcing ribs 600 are made of metal, eddy current loss will not occur. The fixing plate 700 fixes the reinforcing ribs 600 so that the reinforcing ribs 600 are kept in the low magnetic density area 500a of the rotor core 500, and the fixing plate 700 supports the rotor core 500 to further improve the structural strength.

[0054] When the magnetic steel 100 is disposed on only one axial side of the rotor core 500, the assembled axial flux motor rotor can be applied to a single-stator single-rotor axial flux motor or a single-stator dual-rotor axial flux motor.

[0055] When the magnetic steel 100 is respectively arranged on both sides of the rotor core 500 in the axial direction, the assembled axial flux motor rotor can be applied to a double-nail single-rotor axial flux motor, as shown in FIG. Figure 4 At this time, the low magnetic flux density area 500a is formed in the middle of the axial direction of the rotor core 500. Figure 3 The low magnetic flux density zone 500a of the rotor core 500 corresponds to the center position of the magnetic steel 100. Specifically, the low magnetic flux density zone 500a is located in the middle position of the axial direction of the rotor core 500 and corresponds to the center of the axially magnetized magnetic steel 110. The magnetic flux density of the low magnetic flux density zone 500a of the rotor core 500 is 0 to 0.8T.

[0056] The high magnetic flux density area 500 b of the rotor core 500 corresponds to a position between the axial magnetization magnetic steel 110 and the tangential magnetization magnetic steel 120 , and the magnetic flux density of the high magnetic flux density area 500 b of the rotor core 500 is 1.8-2.5T.

[0057] The magnetic flux density of the rotor core 500 gradually increases from the low magnetic flux density area 500a to the adjacent high magnetic flux density area 500b. Figure 3, in the process of splicing two adjacent magnetic steels 100, two tangentially magnetized magnetic steels 120 are arranged between the axially magnetized magnetic steels 110 of the two magnetic steels 100, wherein the junction of the tangentially magnetized magnetic steels 120 and the axially magnetized magnetic steels 110 corresponds to the rotor core 500 which is a high magnetic density area 500b, and the magnetic density of the rotor core 500 gradually decreases from the high magnetic density area 500b to the splicing of the two tangentially magnetized magnetic steels 120. It should be noted that the magnetic density of the rotor core 500 corresponding to the splicing of the two tangentially magnetized magnetic steels 120 is greater than the magnetic density of the low magnetic density area 500a. The magnetic density, also known as the magnetic flux density, refers to the number of magnetic lines of force passing vertically through a unit area.

[0058] like Figure 4 As shown, the rotor core 500 is disc-shaped and is provided with a core through hole 520 through which the reinforcing rib 600 passes. The core through hole 520 can penetrate the radial inner side and the radial outer side of the rotor core 500 so that the reinforcing rib 600 passes through the rotor core 500 radially.

[0059] The rotor core 500 may be formed by winding silicon steel sheets to reduce eddy current loss. Of course, the rotor core 500 is pressed from amorphous materials, and the amorphous materials include soft magnetic materials.

[0060] like Figure 2 , Figure 4 and Fig. 9 As shown, the reinforcing rib 600 comprises:

[0061] Limiting plate 620;

[0062] The rod body 610 passes through the low magnetic density area 500a of the rotor core 500. The two ends of the rod body 610 are respectively connected to the limit plate 620 and the fixed disk 700. The limit plate 620 and the fixed disk 700 are respectively limited and abutted against the radial sides of the rotor core 500.

[0063] The rod body 610 passes through the core through hole 520 of the rotor core 500 located in the low magnetic density area 500a, and the limiting plate 620 and the fixing plate 700 are respectively limited and abutted against the radial sides of the rotor core 500 to fix the rod body 610 in the core through hole 520.

[0064] The fixed disk 700 may be located on the radial inner side of the rotor core 500, and the limiting plate 620 is located on the radial outer side of the rotor core 500, wherein the limiting plate 620 is arc-shaped, and the area of ​​the limiting plate 620 is larger than the area of ​​the core through hole 520, that is, the rod body 610 is inserted into the core through hole 520 radially from the outside to the inside, and the limiting plate 620 abuts against the radial outer side of the rotor core 500, and then the rod body 610 is fixed by the fixed disk 700 to the radial inner part of the rotor core 500, so as to realize the fixation of the reinforcing rib 600. Of course, the fixing disk 700 may be located on the radially outer side of the rotor core 500, and the limiting plate 620 may be located on the radially inner side of the rotor core 500, that is, the reinforcing rib 600 is radially penetrated through the core through hole 520 of the rotor core 500 from the inside to the outside, and the fixing disk 700 is arranged on the radially outer side of the rotor core 500 to fix the reinforcing rib 600.

[0065] like Figure 2 , Figure 7 and Figure 8 As shown, the fixing plate 700 includes:

[0066] Upper plate 710;

[0067] The lower plate 720 is connected to the upper plate 710 and clamps the rod body 610 of the reinforcing rib 600 .

[0068] The upper plate 710 and the lower plate 720 overlap from top to bottom along the axial direction to clamp the reinforcing rib 600. The upper side surface of the lower plate 720 is provided with a plurality of lower receiving grooves 721a arranged at intervals in a circumference, and the lower side surface of the upper plate 710 is provided with a plurality of upper clamping blocks 711a arranged at intervals in a circumference, and the upper clamping blocks 711a correspond to the lower receiving grooves 721a one by one, that is, one upper clamping block 711a is provided in each lower receiving groove 721a.

[0069] refer to Figure 2 and Figure 8 The lower accommodating groove 721a passes through the outer edge of the lower plate 720. When the upper plate 710 and the lower plate 720 clamp the rod body 610 of the reinforcing rib 600, the rod body 610 is located in the lower accommodating groove 721a, and the upper clamping block 711a is embedded in the clamping groove 630 opened in the rod body 610 to achieve clamping and fixing. After that, the upper plate 710 and the lower plate 720 can be fixed by bolts 800, etc., and the fixing is convenient and quick.

[0070] refer to Figure 2The number of the reinforcing ribs 600 and the bolts 800 are both multiple, and can be selected based on factors such as structural strength. The bolts 800 fixed between the upper plate 710 and the lower plate 720 are spaced apart from the lower receiving groove 721a.

[0071] like Figure 2 , Figure 5 and Figure 6 As shown, the axial flux motor rotor also includes:

[0072] An inner ring 300, wherein the inner ring 300 is arranged radially inward of the rotor core 500;

[0073] The outer ring 400 is disposed on the radially outer side of the rotor core 500 , and the reinforcing rib 600 connects the inner ring 300 and the outer ring 400 .

[0074] The inner ring 300 and the outer ring 400 can be made of steel to improve the structural strength. The height of the inner ring 300 and the outer ring 400 are equal, and are equal to the sum of the heights of the rotor core 500 and the upper and lower layers of the magnetic steel 100, ensuring the radial limiting ability of the inner ring 300 and the outer ring 400 to the magnetic steel 100.

[0075] refer to Figure 5 and Figure 6 , the inner ring 300 is provided with an inner through hole 310, the outer ring 400 is provided with an outer through hole 410, and the inner through hole 310 and the outer through hole 410 are used for the reinforcing rib 600 to pass through. It can be seen that the cross-sectional shapes of the core through hole 520 of the rotor core 500, the inner through hole 310 of the inner ring 300, the outer through hole 410 of the outer ring 400, and the rod 610 of the reinforcing rib 600 are adapted to each other, for example, in a square or circular shape, and the size, shape, and size can be designed according to electromagnetic simulation and structural strength.

[0076] The limiting plate 620 of the reinforcing rib 600 abuts against the outer wall of the outer ring 400, and the rod body 610 of the reinforcing rib 600 sequentially penetrates the outer ring 400, the rotor core 500 and the inner ring 300 until being fixed by the fixing plate 700 located on the inner wall of the inner ring 300. At this time, the fixing plate 700 supports the inner ring 300 to further improve the structural strength.

[0077] like Figure 2 and Figure 3 As shown, the magnetic steel 100 is circumferentially spliced ​​on the same axial side of the rotor core 500, and can be mounted on the rotor core 500 in a surface mounting manner. A mounting hole 1000 is formed between two adjacent magnetic steels 100, and the axial flux motor rotor also includes:

[0078] The screws 200 penetrate the mounting holes 1000 and are respectively connected to the inner ring 300 and the outer ring 400 to limit the rotor core 500 in the circumferential direction and the axial direction.

[0079] Since the screw 200 is built inside the magnetic steel 100 and is located in the magnetic circuit area, the screw 200 is made of a non-magnetic metal material to avoid an increase in eddy current loss.

[0080] refer to Figure 5 and Figure 6 The inner ring 300 is provided with an inner connection hole 320, and the outer ring 400 is provided with an outer connection hole 420. The screw 200 passes through the outer connection hole 420 on the outer ring 400 and the mounting hole 1000, and is screwed with the inner connection hole 320 to achieve the fixation of the three.

[0081] like Figure 2 The circumferential dimension of the magnetic steel 100 gradually increases from the inside to the outside along the radial direction, that is, the magnetic steel 100 is fan-shaped or trapezoidal.

[0082] refer to Figure 2 and Figure 3 The magnetic steel 100 can be formed by splicing one axial magnetized magnetic steel 110 and two tangential magnetized magnetic steels 120 , wherein the axial magnetized magnetic steel 110 is located between the two tangential magnetized magnetic steels 120 .

[0083] The magnetizing direction of the axial magnetized magnetic steel 110 is axial, and the magnetizing direction of the tangential magnetized magnetic steel 120 is tangential. Among the two adjacent left and right magnets 100, the magnetizing directions of the two tangential magnetized magnetic steels 120 of the left magnet 100 are tangential and respectively face the axial magnetized magnetic steel 110. The magnetizing directions of the two tangential magnetized magnetic steels 120 of the right magnet 100 are tangential and respectively face away from the axial magnetized magnetic steel 110, and a Halbach magnetic pole array is performed. The Halbach magnetic pole array structure has the characteristics of better sinusoidality of the motor air gap magnetic density waveform, high magnetic density amplitude, small rotor core thickness, and improved torque density.

[0084] When assembling the axial flux motor rotor, the magnetic steel 100 can be first arranged on both axial sides of the rotor core 500, and then the inner ring 300 and the outer ring 400 can be arranged radially inside and outside the rotor core 500, so that the magnetic steel 100 is radially limited between the inner ring 300 and the outer ring 400, and then the screw 200 is sequentially passed through the outer ring 400, the mounting hole 1000 between the magnetic steel 100, and the inner ring 300 to achieve fixation, and the reinforcing rib 600 is sequentially passed through the outer ring 400 and the rotor core 500 until the tail of the reinforcing rib 600 passes through the inner ring 300, and then the tail of the reinforcing rib 600 is clamped and fixed by the upper plate 710 and the lower plate 720 of the fixing plate 700 to complete the assembly of the axial flux motor rotor.

[0085] Second embodiment

[0086] like Figures 10 to 12 As shown, the axial flux motor rotor of the second embodiment is different from that of the first embodiment in that the rotor core 500 is provided with a magnetic steel slot 510 , and the magnetic steel 100 is disposed in the magnetic steel slot 510 .

[0087] refer to Fig.12 and Fig.13 The magnetic steel slot 510 penetrates the radial inner side and the radial outer side of the rotor core 500, so that the magnetic steel 100 can be inserted into the magnetic steel slot 510 in the radial direction. The magnetic steel slot 510 is consistent with the cross section of the magnetic steel 100, for example, it is rectangular. The magnetic steel 100 with a rectangular cross section is easy to process, which improves the material utilization rate and reduces the amount of magnetic steel to reduce costs. The shape of the magnetic steel slot 510 can also be made into a desired shape according to electromagnetic needs, and different processing methods can be used, such as winding first and then cutting to form the magnetic steel slot 510.

[0088] The magnetic steel slot 510 is provided with a slot bevel portion 511 near the axial side of the rotor core 500 , and the magnetic steel 100 is provided with a chamfered portion 100 a adapted to the slot bevel portion 511 to prevent the magnetic steel 100 from axial displacement.

[0089] like Fig.12 The magnetic steel slots 510 on both axial sides of the rotor core 500 correspond one to one, and the core through holes 520 are located between the corresponding magnetic steel slots 510. When the reinforcing ribs 600 are inserted into the core through holes 520, the structural strength can still be guaranteed.

[0090] like Fig.11As shown, the magnetic steel 100 is divided into tangential magnetized magnetic steel and axial magnetized magnetic steel. The tangential magnetized magnetic steel and the axial magnetized magnetic steel are arranged at intervals. The magnetizing direction of the axial magnetized magnetic steel is axial, and is also divided into upward or downward. The magnetizing direction of the tangential magnetized magnetic steel is tangential, and is also divided into left or right. For details, please refer to Fig.11 , and then realize the Halbach magnetic pole array.

[0091] In summary, by arranging the reinforcing rib 600 in the low magnetic flux density area 500a, not only the structural strength of the rotor core 500 is improved, but also when the reinforcing rib 600 is made of metal, eddy current loss will not occur. The fixing plate 700 fixes the reinforcing rib 600 so that the reinforcing rib 600 remains in the low magnetic flux density area 500a of the rotor core 500, and the fixing plate 700 supports the rotor core 500 to further improve the structural strength.

[0092] The embodiments described above are only used to illustrate the technical ideas and features of the utility model, and their purpose is to enable technicians in this field to understand the content of the utility model and implement it accordingly. The patent application scope of the utility model cannot be limited only by this embodiment, that is, any equivalent changes or modifications made according to the spirit disclosed by the utility model still fall within the patent scope of the utility model.

Claims

1. An axial flux motor rotor, characterized in that: include: Magnetic steel (100); A rotor core (500), wherein a magnetic steel (100) is disposed on at least one axial side of the rotor core (500), and a low magnetic flux density region (500a) is formed at a position of the rotor core (500) away from the magnetic steel (100); A reinforcing rib (600), wherein the reinforcing rib (600) passes through a low magnetic flux density region (500a) of the rotor core (500); A fixing plate (700), wherein the fixing plate (700) is connected to the reinforcing rib (600) and is used to fix the reinforcing rib (600).

2. The axial flux motor rotor according to claim 1, characterized in that: The reinforcing rib (600) comprises: Limiting plate (620); A rod body (610), wherein the rod body (610) passes through the low magnetic density area (500a) of the rotor core (500), and the two ends of the rod body (610) are respectively connected to a limit plate (620) and a fixed disk (700), and the limit plate (620) and the fixed disk (700) are respectively limited and abutted against the radial sides of the rotor core (500).

3. The axial flux motor rotor according to claim 1, characterized in that: The fixing plate (700) comprises: Upper plate (710); A lower plate (720) is connected to the upper plate (710) and clamps the rod body (610) of the reinforcing rib (600).

4. The axial flux motor rotor according to claim 3, characterized in that: The lower plate (720) is provided with a lower accommodating groove (721a), and the upper plate (710) is provided with an upper clamping block (711a), and the upper clamping block (711a) corresponds one-to-one to the lower accommodating groove (721a); After the upper plate (710) and the lower plate (720) clamp the rod body (610) of the reinforcing rib (600), the rod body (610) is located in the lower receiving groove (721a), and the upper clamping block (711a) is embedded in the clamping groove (630) provided in the rod body (610).

5. The axial flux motor rotor according to claim 4, characterized in that: The upper plate (710) and the lower plate (720) are fixed by bolts (800), and the bolts (800) and the lower receiving groove (721a) are arranged at intervals.

6. The axial flux motor rotor according to claim 1, characterized in that: The fixing plate (700) is located radially inside or outside the rotor core (500).

7. The axial flux motor rotor according to claim 1, characterized in that: The reinforcing rib (600) is a reinforcing rib made of metal material.

8. The axial flux motor rotor according to claim 1, characterized in that: Also includes: An inner ring (300), the inner ring (300) being arranged radially inward of the rotor core (500); The outer ring (400) is arranged on the radially outer side of the rotor core (500), and the reinforcing rib (600) connects the inner ring (300) and the outer ring (400).

9. The axial flux motor rotor according to claim 1, characterized in that: The magnetic steel (100) is spliced ​​along the circumferential direction; Alternatively, the rotor core (500) is provided with a magnetic steel slot (510), and the magnetic steel (100) is arranged in the magnetic steel slot (510).

10. The axial flux motor rotor according to claim 1, characterized in that: The magnetic steel (100) is respectively arranged on both axial sides of the rotor core (500), and the low magnetic density area (500a) of the rotor core (500) corresponds to the central position of the magnetic steel (100).

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