Axial gap induction motor

Abstract

To provide an axial gap induction motor having high volume and output per weight of the motor.SOLUTION: An axial gap induction motor includes rotors 60, 70 fixed to a rotary shaft 22, and a disk-like stator 51 arranged with a gap in a shaft direction of the rotary shaft between the rotors. A plurality of toroidal coils 53 for generating a rotating magnetic field are wound around the stator. On the rotor, a conductor 62 is arranged for generating rotation of the rotor with the rotating magnetic field. The conductor 62 is opposed to each portion of the toroidal coil 53 so as to generate rotating force by utilizing a magnetic field generated from all portions of the toroidal coil 53.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an axial gap induction motor having a gap between the stator and rotor in the axial direction of the rotating shaft, which makes it possible to improve the power density (power per volume or weight of the motor). [Background technology]

[0002] Induction motors are configured to supply alternating current to the stator windings to generate a rotating magnetic field, which induces current in the rotor conductors, generating a torque to rotate the rotor. Induction motors are asynchronous motors, meaning that the rotor rotates at a speed slightly slower than the speed of the rotating magnetic field. Axial gap induction motors have the advantages of being able to be miniaturized and not requiring the use of permanent magnets (hence, no need for rare earths), and therefore are widely used in industrial applications. Their use is also expanding in electric vehicles (EVs), hybrid electric vehicles (HEVs), drones, etc. (Non-patent document 1 below).

[0003] The cross-sectional view of the motor in Fig. 10(a) shows an induction motor with a single stator and double rotor structure as an example of a conventional axial gap induction motor. Two rotors 20 and 21 are fixed to a rotating shaft 22, and the stator 10 is disposed between the rotor 20 and the rotor 21 with a gap therebetween.

[0004] As shown in FIG. 10(b), the stator 10 includes a disk-shaped stator core 11 having a central hole 13 through which the rotating shaft 22 is inserted, and a plurality of toroidal coils 12 wound around one disk surface, the outer peripheral surface, the other disk surface, and the inner peripheral surface on the center hole side of the stator core 11. As shown in FIG. 11, the stator core 11 is formed with grooves (slots) 14 in which the toroidal coils 12 are each housed.

[0005] The slots 14 are provided to enable concentrated winding of the coil. By winding the coil in the slots 14, the coil end portion can be made smaller and interference with coils of other phases can be prevented.

[0006] A rotating magnetic field is generated by supplying three-phase AC currents of U-phase, V-phase, and W-phase to each of the multiple toroidal coils 12 wound around the stator core 11. Fig. 12 shows the arrangement of the toroidal coils 12 to which U-phase, V-phase, and W-phase currents are supplied for generating a rotating magnetic field when the motor has six poles.

[0007] On the other hand, rotors 20 and 21 are configured by forming slots 24 in rotor core 23 as shown in FIG. 13, and fitting conductors 25 shown in FIG. The conductor 25 attached to the rotor is sometimes called a "squirrel cage conductor."

[0008] In the axial gap induction motor of Fig. 10(a), when a current of any one of the U-phase, V-phase, or W-phase of a three-phase AC is supplied to each of the toroidal coils 12 of the stator 10 and a rotating magnetic field is generated, an electromotive force is generated in the conductor 25 of the rotors 20, 21 by this magnetic field, and a current flows in the conductor 25. Then, an electromagnetic force acts between this current and the rotating magnetic field, and the conductor 25 is pulled in the direction of the rotating magnetic field. As a result, the rotors 20, 21 rotate in the direction of the rotating magnetic field.

[0009] In order to increase the torque of an axial gap induction motor, individual axial gap induction motors are sometimes multiplexed, as shown in Figure 15. In Figure 15, five axial gap induction motors are multiplexed. [Prior art documents] [Non-patent literature]

[0010] [Non-Patent Document 1] Ryosuke Sakai, Masahiro Yoshida, Katsufumi Tajima, "Study on the Basic Design of Axial Gap Induction Motors", Magnetics / Motor Drive / Linear Drive Joint Research Meeting Materials, MAG-17-169, MD-17-111, LD-17-090, December 2017 Summary of the Invention [Problem to be solved by the invention]

[0011] An object of the present invention is to provide an axial gap induction motor that can increase the output (power density) per volume and weight of the motor. [Means for solving the problem]

[0012] The present invention provides an axial gap induction motor including a rotor fixed to a rotating shaft, and a stator having a central hole through which the rotating shaft is inserted and disposed with a gap between the rotor and the rotor in the axial direction of the rotating shaft, the stator having a stator core having a central hole and a plurality of toroidal coils wound around a flat surface of the stator core perpendicular to the axial direction of the rotating shaft and an outer peripheral surface and an inner peripheral surface parallel to the axial direction of the rotating shaft, each of the toroidal coils being supplied with a current so as to generate a rotating magnetic field, and the rotor having a conductor that generates a rotating force in the rotor by the rotating magnetic field generated by the toroidal coils, the conductor facing the portion of the toroidal coil on the flat surface of the stator core and also facing at least one of the portion of the toroidal coil on the outer peripheral surface of the stator core and the portion of the toroidal coil on the inner peripheral surface of the stator core. In this axial gap induction motor, torque is generated not only by the magnetic field generated from the toroidal coil portion on the flat surface of the stator, but also by the magnetic fields generated from the toroidal coil portion on the outer circumferential surface of the stator and the toroidal coil portion on the inner circumferential surface of the stator, thereby improving the power density of the motor.

[0013] In addition, in this axial gap induction motor, the stator core has a disk shape.

[0014] In the axial gap induction motor of the present invention, the stator core may have a square cross-sectional shape. The cross-sectional area of ​​the stator core can be maximized by making the cross-section square when the perimeter of the cross-section is constant. This allows it to handle higher drive voltages and reduce drive current for higher efficiency. It also allows the length of the coil wound around the stator core to be minimized, which reduces copper loss for higher efficiency and a reduction in winding weight.

[0015] In the axial gap induction motor of the present invention, a slot is provided at the mounting position of the toroidal coil in the stator core.

[0016] In the axial gap induction motor of the present invention, slots are provided at the mounting positions of the conductors of the rotor core.

[0017] In the present invention, the axial gap induction motor is multiplexed by being arranged on the same shaft. Effect of the Invention

[0018] The axial gap induction motor of the present invention has a high power density. Analysis using a finite element analysis model confirmed that the maximum power output was improved by 80% or more compared to conventional devices. [Brief description of the drawings]

[0019] [Figure 1] FIG. 1A is a cross-sectional view of an axial gap induction motor according to an embodiment of the present invention, FIG. 1B is a diagram showing a stator thereof, and FIG. 1C is a diagram showing a rotor thereof. [Diagram 2] (a) is a plan view of a stator core of the present invention, (b) is a cross-sectional view of the stator core taken along line AA, and (c) is a cross-sectional view of the stator core taken along line BB. [Diagram 3] (a) is a plan view of a rotor core of the present invention, (b) is a cross-sectional view of the rotor core taken along line AA, and (c) is a cross-sectional view of the rotor core taken along line BB. [Figure 4]FIG. 1A is a plan view of a conductor to be attached to a rotor of the present invention; FIG. 1B is a cross-sectional view of the conductor taken along the line AA of the conductor; FIG. 1C is a cross-sectional view of a conductor according to a modified example of the present invention; and FIG. 1D is a cross-sectional view of a conductor according to another modified example of the present invention. [Diagram 5] FIG. 1A is a cross-sectional view of an axial gap induction motor according to a modified example of the present invention, FIG. 1B is a stator thereof, and FIG. 1C is a rotor thereof. [Figure 6] A diagram showing the specification data of an analysis model using finite element analysis [Figure 7] Diagram showing the geometry of the analysis model [Figure 8] A diagram showing (a) the relationship between rotation speed and power, (b) the relationship between rotation speed and torque, (c) maximum power and torque, and (d) the maximum power density per weight and volume of the motor, obtained by analysis using the finite element analysis method. [Figure 9] FIG. 1 is a diagram showing a multiplexed structure of an axial gap induction motor according to the present invention. [Figure 10] (a) A cross-sectional view of a conventional axial gap induction motor, (b) its stator, and (c) its rotor. [Figure 11] Diagram showing a conventional stator core [Figure 12] Stator toroidal coil layout [Figure 13] Diagram showing a conventional rotor core [Figure 14] A diagram showing a conductor mounted on a conventional rotor, (a) a plan view, and (b) a cross-sectional view. [Figure 15] A diagram showing the multiplexing structure of a conventional axial gap induction motor. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Fig. 1 shows an axial gap induction motor 50 according to an embodiment of the present invention. Fig. 1(a) is a cross-sectional view thereof, in which a stator 51 is disposed between rotors 60 and 70. Fig. 1(b) shows the stator 51 configured by mounting a toroidal coil 53 in the slots of a stator core 52. Fig. 1(c) shows a rotor 60 (70) configured by mounting a conductor 62 in the slots of a rotor core 61.

[0021] FIG. 2(a) shows a stator core 52, its AA cross-sectional view (cross-sectional view of the slot position where the toroidal coil 53 is mounted) is shown in FIG. 2(b), and its BB cross-sectional view of a position where no slot exists is shown in FIG. 2(c). The shape of the stator 51 differs from that of the conventional stator 10 (Figures 10(b) and 11) in that slots 54 are provided on the outer peripheral surface 521 and inner peripheral surface 522 of the stator core 52 so that the toroidal coil 53 does not protrude from the outer peripheral surface 521 and inner peripheral surface 522 of the stator core 52 (or so that the amount of protrusion is reduced).

[0022] On the other hand, in the axial gap induction motor 50 according to an embodiment of the present invention, the conductor 62 of the rotor 60 shown in FIG. 1(c) is attached to the rotor 60 so as to face each portion of the toroidal coil 53 of the stator 51 (i.e., the portion on the two disc surfaces of the stator core 52, the portion on the outer circumferential surface of the stator core 52, and the portion on the inner circumferential surface of the stator core 52) via a gap.

[0023] Fig. 3 shows the rotor core 61, and Fig. 3(a) shows its plan view. Fig. 3(b) shows a cross-sectional view (AA cross-sectional view) of the rotor core 61 at the position of the slot 64 where the conductor 62 is attached, and Fig. 3(c) shows a cross-sectional view (BB cross-sectional view) of the rotor core 61 at a position where the radial portion of the conductor 62 does not exist. The rotor core 61 is provided with a wall portion 65 that runs around the inner periphery, and a wall portion 66 that runs around the outer periphery.

[0024] FIG. 4 shows a conductor 62 attached to a rotor core 61, with FIG. 4(a) being a plan view and FIG. 4(b) being a cross-sectional view taken along line AA. The conductor 62 of the rotor 60 is arranged inside the slot 64 provided at the slot position of the rotor core 61, along the wall surface of the inner wall portion 65 to which one end of the slot 64 is connected, and along the wall surface of the outer wall portion 66 to which the other end of the slot 64 is connected (see Figure 1 (a)).

[0025] In addition, the radial length of the stator 51 equipped with the toroidal coil 53 is set so that a predetermined gap is maintained with respect to each of the conductors 62 of the rotor 60 provided on the wall surface of the inner side wall portion 65 and the conductors 62 of the rotor 60 provided on the wall surface of the outer side wall portion 66. The stator 51 is arranged so that half of its axial thickness fits between the inner side wall portion 65 and the outer side wall portion 66 of one rotor 60, and the remaining half fits between the inner side wall portion 65 and the outer side wall portion 66 of the other rotor 70 (see FIG. 1(a)).

[0026] Therefore, the conductor 62 provided on the rotor 60 faces the portion of the toroidal coil on one of the disk surfaces of the stator 51 at the portion indicated by 1 in FIG. 4(b), faces half of the portion of the toroidal coil on the inner surface of the stator 51 at the portion indicated by 2 in FIG. 4(b) (the conductor portion provided on the wall surface of the inner side wall portion 65 of the rotor 60), and faces half of the portion of the toroidal coil on the outer surface of the stator 51 at the portion indicated by 3 in FIG. 4(b) (the conductor portion provided on the wall surface of the outer side wall portion 66 of the rotor 60). In FIG. 4(b), reference numeral 4 denotes a portion that abuts against the top surface of wall portion 65, and reference numeral 5 denotes a portion that abuts against the top surface of wall portion 66.

[0027] Similarly, the portion indicated by 1 of the conductor 62 provided on the other rotor 70 faces the portion of the toroidal coil on the other disc surface of the stator 51, the conductor provided on the wall surface of the inner side wall portion 65 of the rotor 70 (portion 2 of the conductor 62) faces the remaining half of the portion of the toroidal coil on the inner surface of the stator 51, and the conductor provided on the wall surface of the outer side wall portion 66 of the rotor 70 (portion 3 of the conductor 62) faces the remaining half of the portion of the toroidal coil on the outer surface of the stator 51.

[0028] Therefore, all parts of the toroidal coil face the conductors 62 of the rotors 60 and 70, and the magnetic field generated from all parts of the toroidal coil is used to generate torque of the axial gap induction motor. As a result, the power density of the motor is increased.

[0029] FIG. 5 shows a first modified example of an axial gap induction motor of the present invention. In this axial gap induction motor, the cross-sectional shape of stator core 51 is set to a square. Therefore, the cross-sectional area of ​​the stator core can be maximized when the perimeter of the cross section is constant. The larger the cross-sectional area of ​​the stator core is, the higher the drive voltage of the motor can be, and the lower the drive current can be, thereby achieving high efficiency. Furthermore, by making the cross section of stator core 51 square, the length of the coil wound around the stator core can be shortened, which reduces copper loss, resulting in higher efficiency and a reduction in winding weight.

[0030] Moreover, Figs. 4(c) and 4(d) show rotor conductors of an axial gap induction motor according to a second modified example in which the shape of the rotor conductor is simplified. In the rotor conductor 621 shown in Fig. 4(c), the portion indicated by 2 in the conductor 62 in Fig. 4(b) is omitted. Also, in the rotor conductor 622 shown in Fig. 4(d), the portion indicated by 3 in the conductor 62 in Fig. 4(b) is omitted. Therefore, in the motor having the conductors 621 and 622, the magnetic field generated by the toroidal coil that can be used to generate torque is reduced compared to the motor having the conductor 62 in FIG. 4(b). However, even when conductors 621 and 622 are used, the magnetic field available for torque generation is greater than in a conventional axial gap induction motor, making it possible to increase the power density of the motor.

[0031] Next, the results of an analysis performed by finite element analysis to confirm the effects of the present invention will be described.

[0032] In this analysis, the torque outputs of an analytical model having a conventional structure and an analytical model having a structure of the present invention are determined and compared. 6 shows the specification data for each analysis model. In the analysis model of the present invention, the stator core 52 is inserted between the inner peripheral side wall 65 and the outer peripheral side wall 66 of the rotor core 61, so that the outer diameter of the rotor core 61 is larger than that of the analysis model of the conventional structure, and the inner diameter of the rotor core 61 is smaller than that of the analysis model of the conventional structure. FIG. 7 shows the overall shape of the analytical model and the shapes of each part constituting the analytical model.

[0033] FIG. 8(a) shows the results of an analysis of the relationship between the rotation speed and the motor output of each analysis model. FIG. 8(b) shows the results of an analysis of the relationship between the rotation speed and torque of each analysis model.

[0034] FIG. 8(c) shows the maximum output and maximum torque values ​​of each analytical model obtained from FIG. 8(a) and FIG. 8(b), as well as the ratio of the values ​​of the analytical model of the present invention when the values ​​of the conventional analytical model are set to 1.00. FIG. 8(d) shows the maximum power density per weight and the maximum power density per volume for each analytical model.

[0035] From the analysis results shown in FIG. 8, it can be seen that the output and torque of the axial gap induction motor of the present invention are improved by 80% or more compared to the conventional axial gap induction motor driven under the same operating conditions.

[0036] Furthermore, the axial gap induction motor of the present invention may have a multiplexed configuration in which a plurality of motors are stacked in the axial direction, as shown in FIG. In the case of a multiplexed motor, if one of the motors fails, power can be cut off to the failed motor while power continues to flow to the remaining motors, allowing for continuous operation and resulting in highly reliable motors.

[0037] Here, the rotor wall portions 65, 66 have been described as being cylindrical and respectively encircling the inner and outer circumferences of the rotor, but the rotor wall portions 65, 66 may also be formed to correspond to the positions at which the slots 64 are formed. [Industrial Applicability]

[0038] The axial gap induction motor of the present invention has the advantages of being small and having high torque density, and can be used in products in a wide range of industrial fields, including electric vehicles (EVs), hybrid electric vehicles (HEVs), drones, etc. [Explanation of symbols]

[0039] 10 Stator 11 Stator core 12 Toroidal coil 13 Center hole 14 Slots 20 Rotors 21 Rotor 22 Rotation axis 23 Rotor core 24 Slots 25 Conductor 50 Axial Gap Induction Motor 51 Stator 52 Stator core 521 Outer surface 522 Inner surface 53 Toroidal coil 54 Slots 60 rotors 61 Rotor core 62 Conductor 621 Conductor 622 Conductor 64 Slots 65 Wall 66 Wall 70 Rotor

Claims

1. A rotor fixed to a rotating shaft; a stator having a central hole through which the rotating shaft is inserted and disposed between the rotor and the stator with a gap provided in the axial direction of the rotating shaft; An axial gap induction motor comprising: the stator includes a stator core having the central hole, and a plurality of toroidal coils wound around a flat surface of the stator core perpendicular to an axial direction of the rotating shaft, and around an outer peripheral surface and an inner peripheral surface parallel to the axial direction of the rotating shaft, Each of the toroidal coils is supplied with a current to generate a rotating magnetic field; the rotor has a conductor that generates a rotational force in the rotor by the rotating magnetic field generated by the toroidal coil, an axial gap induction motor, wherein the conductor faces a portion of the toroidal coil on the flat surface of the stator core, and also faces at least one of a portion of the toroidal coil on the outer circumferential surface of the stator core and a portion of the toroidal coil on the inner circumferential surface of the stator core.

2. 2. The axial gap induction motor according to claim 1, The stator core has a disk shape.

3. 2. The axial gap induction motor according to claim 1, The stator core has a square cross-sectional shape.

4. 4. An axial gap induction motor according to claim 1, The stator core has a slot at a mounting position of the toroidal coil.

5. 5. An axial gap induction motor according to claim 1, An axial gap induction motor, wherein the rotor core has slots at positions where the conductors are attached.

6. A multiplexed motor in which a plurality of axial gap induction motors according to any one of claims 1 to 5 are arranged on the same shaft.

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