motor

Abstract

The present invention provides a motor that can suppress back electromotive force at high speeds without reducing torque at low speeds. [Solution] The motor 100 comprises a stator 10 having a stator core 11 with teeth 11a and windings wound around the teeth 11a, and a rotor 20 equipped with permanent magnets 23. In the rotor 20, at least a portion of the part where the permanent magnets 23 embedded in the rotor 20 and the stator 10 face each other is provided with a non-magnetic portion 25.

Description

[Technical Field]

[0001] This disclosure relates to motors. [Background technology]

[0002] While most motors are used at a constant rotation speed in applications such as compressors and blowers, recent motors are used with controlled rotation speeds in a variety of applications. For example, the drive motors in hybrid vehicles are used in a wide range of operating speeds, from low to high. Also, servo systems, which are typical for FA (Factory Automation) motors, are driven at high acceleration / deceleration speeds and high speeds in order to quickly follow position commands. The increased power output and speed of motors are proving useful in high-end applications, and the market for these motors continues to expand. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-184461 [Overview of the project] [Problems that the invention aims to solve]

[0004] When the rotational speed exceeds a certain value, a phenomenon called voltage saturation occurs, in which the relationship between the back electromotive force generated by the motor and the power supply voltage reverses. To mitigate voltage saturation, one approach is to reduce the amount of magnetic flux in the field, which is the cause of the back electromotive force.

[0005] Therefore, a method is known to suppress the motor's back electromotive force and improve torque in the high-speed range by performing so-called flux weakening control. However, copper loss increases by the amount of d-axis current required for flux weakening control, reducing efficiency. Alternatively, it is conceivable to improve torque in the high-speed range by replacing the rotor's permanent magnets with permanent magnets with weaker magnetic force. However, this method reduces torque at low speeds. For example, Patent Document 1 proposes a control model that improves the instantaneous saturation of voltage in the step response by inserting a motor inverse model after the current controller.

[0006] The inventors of this invention believed that if they could realize a motor structure that can suppress back electromotive force at high speeds without reducing torque at low speeds, they could provide a motor with high torque and high output over a wide operating range using a general control system. [Means for solving the problem]

[0007] Therefore, the present disclosure aims to provide a motor that can suppress back electromotive force at high speeds without reducing torque at low speeds.

[0008] A motor relating to one aspect of this disclosure is A stator having a stator core with teeth and windings wound around the teeth, Equipped with a rotor with permanent magnets, In the rotor, at least a portion of the part where the permanent magnet embedded in the rotor faces the stator is provided with a non-magnetic portion.

[0009] According to one aspect of this disclosure, At least a portion of the stator may be made of a nonlinear soft magnetic material.

[0010] According to one aspect of this disclosure, The non-magnetic portion may be provided so as to obstruct the magnetic flux in the d-axis relative to the permanent magnet.

[0011] According to one aspect of the present disclosure, The non-magnetic portion may be provided asymmetrically with respect to the d-axis.

[0012] According to one aspect of the present disclosure, The rotor is configured by laminating a plurality of laminated iron core pieces, The plurality of laminated iron core pieces may be laminated such that the positions of the non-magnetic portions of adjacent laminated iron core pieces are shifted.

[0013] According to one aspect of the present disclosure, The rotor is configured by laminating a plurality of laminated iron core pieces, The plurality of laminated iron core pieces may be laminated such that the positions of the non-magnetic portions of adjacent laminated iron core pieces are symmetric with respect to the d-axis.

[0014] According to one aspect of the present disclosure, The non-magnetic portion may be provided so as to extend in the q-axis direction.

[0015] According to one aspect of the present disclosure, The non-magnetic portion, a d-axis flux barrier extending in the d-axis direction, and a q-axis flux barrier extending in the q-axis direction, may be provided.

Advantages of the Invention

[0016] According to the present disclosure, it is possible to provide a motor that can suppress the counter electromotive force during high-speed rotation without reducing the torque during low-speed rotation.

Brief Description of the Drawings

[0017] [Figure 1] FIG. 1 is a diagram showing a motor 100 according to a first embodiment of the present disclosure. [Figure 2] FIG. 2 is a graph showing BH curves of a general soft magnetic material and a non-linear soft magnetic material. [Figure 3] FIG. 3 shows an efficiency map of the motor 100 of the first embodiment shown in FIG. 1. [Figure 4] Figure 4 shows the motor 200 related to Reference Example 1. [Figure 5] Figure 5 is the efficiency map of motor 200 shown in Figure 4. [Figure 6] Figure 6 shows the motor 300 according to Reference Example 2. [Figure 7] Figure 7 is an efficiency map of the motor 300 shown in Figure 6. [Figure 8] Figure 8 shows the magnetic flux density distribution of motor 200 in Reference Example 1. [Figure 9] Figure 9 shows the magnetic flux density distribution of the motor 100 in the first embodiment. [Figure 10] Figure 10 shows the magnetic flux density distribution of motor 300 in Reference Example 2. [Figure 11] Figure 11 shows the rotor 20 of the motor 400 according to a modified example of the present disclosure. [Figure 12] Figure 12 shows a motor 500 according to the second embodiment of the present disclosure. [Figure 13] Figure 13 shows the efficiency map of the motor 500 of the second embodiment shown in Figure 12. [Figure 14] Figure 14 shows the magnetic flux density distribution of the motor 500 in the second embodiment. [Figure 15] Figure 15 shows a motor 600 according to the third embodiment of this disclosure. [Figure 16A] Figure 16A is an enlarged view of motor 200 in Reference Example 1, in which the q-axis flux barrier 601 is not provided. [Figure 16B] Figure 16B is an enlarged view of the motor 600 of the third embodiment, which is provided with a q-axis flux barrier 601. [Figure 17] Figure 17 is a comparison of the maximum torque of three types of motors: 200, 600, and 700. [Figure 18] Figure 18 shows the torque distribution generated on the rotor surface of motor 20 (a), motor 700 (b), and motor 600 (c) at a rotational speed of 15,000 rpm. [Figure 19A]Figure 19A shows the magnetic flux density distribution of motor 200 (a). [Figure 19B] Figure 19B shows the magnetic flux density distribution of motor 700 in (b). [Figure 19C] Figure 19C shows the magnetic flux density distribution of motor 600 (c). [Figure 20] Figure 20 is a comparison of the efficiencies of motor 200 (a), motor 700 (b), and motor 600 (c). [Figure 21] Figure 21 is a comparison of the losses of motor 600 in (a), motor 700 in (b), and motor 600 in (c). [Figure 22A] Figure 22A shows the eddy current loss of motor 200 (a). [Figure 22B] Figure 22B shows the eddy current loss of motor 700 in (b). [Figure 22C] Figure 22C shows the eddy current loss of motor 600 (c). [Figure 23] Figure 23 shows a motor 800 according to the fourth embodiment of this disclosure. [Modes for carrying out the invention]

[0018] The embodiments of this disclosure will be described below with reference to the drawings. For the sake of clarity, the description of components having the same reference numeral as those already described in the description of the embodiments will be omitted. Furthermore, the dimensions of the components shown in these drawings may differ from the actual dimensions of the components for the sake of clarity.

[0019] <First Embodiment> Figure 1 shows a motor 100 according to the first embodiment of the present disclosure. The motor 100 shown in Figure 1 is an IPMSM (Interior Permanent Magnet Synchronous Motor) with 3 phases, 6 poles, 45 slots, distributed windings, and a number of slots per pole per phase q = 2.5. The motor 100 is a rotating field type and comprises a stator 10 and a rotor 20 that is rotatable relative to the stator 10. The rotor 20 rotates around a rotation axis that extends perpendicular to the plane of the paper in Figure 1 relative to the stator 10. The number of phases, poles, number of slots, and winding method of the motor in the present disclosure are not limited to those shown.

[0020] The stator 10 includes a stator core 11 that is substantially ring-shaped. The stator core 11 has a ring-shaped back yoke 11b and a plurality of teeth 11a arranged on the inner circumference side of the back yoke 11b. The teeth 11a are portions that protrude radially inward from the inner circumferential end of the back yoke 11b. The plurality of teeth 11a are substantially the same shape as each other. A slot is provided between two adjacent teeth 11a.

[0021] A winding is placed in each slot. The winding is wound around each tooth 11a, and the winding forms a stator coil 12. Each stator coil 12 is wound around the teeth 11a by distributed winding. The stator coil 12 is excited by an alternating current from the outside.

[0022] The rotor 20 includes a rotor core 21 formed by laminating multiple electromagnetic steel sheets in the direction of the rotation axis. The rotor core 21 is a cylindrical member. The inner circumference hole of the rotor core 21 constitutes a shaft mounting hole 22. A drive shaft (not shown) is fixed to the shaft mounting hole 22. Rotation is transmitted to the object to be driven by the motor 100 via the drive shaft.

[0023] Multiple permanent magnets 23 are provided in the rotor core 21 of the rotor 20. The permanent magnets 23 are embedded inside slots provided in the rotor core 21. The permanent magnets 23 are flat and are substantially the same in size, material, and composition.

[0024] In the illustrated example, the multiple permanent magnets 23 are arranged at equal intervals along the circumference of a circle centered on the axis of rotation O, forming six poles that are 60° apart from each other. Therefore, The magnetomotive force on the stator coil 12 caused by each permanent magnet 23 is approximately the same. Furthermore, rotor gaps 24 extending radially outward are provided at both ends of each permanent magnet 23. There are no materials inside the rotor gaps 24; only air is present.

[0025] In the motor 100 of this first embodiment, the stator core 11 has a ring-shaped back yoke 11b made of non-oriented electrical steel sheet, which is a type of soft magnetic material, and a plurality of teeth 11a made of a nonlinear soft magnetic material. In this specification, a nonlinear soft magnetic material is defined as a material that does not magnetize (remains low magnetic flux density) until a certain magnetic field strength H acts upon it, but when the magnetic field strength H exceeds a certain value, the relative permeability μr increases and the magnetic flux density rises sharply. In Figure 1, the part made of the nonlinear soft magnetic material is shown. (Teeth 11a) is shown with hatching. In Figure 1, the hatching does not represent a general cross-section; the hatching on the stator core 11 indicates a portion composed of a nonlinear soft magnetic material. The hatching on the rotor core 21 indicates the permanent magnet 23.

[0026] Here, we will explain nonlinear soft magnetic materials in detail using Figure 2. Figure 2 is a graph showing the BH curves for a general soft magnetic material and a nonlinear soft magnetic material. In Figure 2, the horizontal axis represents the magnetic field strength H, and the vertical axis represents the magnetic flux density B. As shown in Figure 2, in general soft magnetic materials such as non-oriented electrical steel sheets, when the magnetic field strength H is near zero, the magnetic flux density B increases sharply when a magnetic field is applied. As the magnetic field strength H increases, it converges to the saturation magnetic flux density Bs. In other words, in general soft magnetic materials, the magnetic flux density B increases immediately when a magnetic field is applied, but as the magnetic field strength H increases, the rate of increase in magnetic flux density B becomes more gradual and converges to the saturation magnetic flux density Bs. Generally speaking, Materials with a high relative permeability μr (the slope of the graph in Figure 2) and a high saturation magnetic flux density Bs have been developed as soft magnetic materials. Furthermore, for electrical steel sheets, a type of soft magnetic material, it is generally desirable to have materials whose magnetic flux density B increases rapidly when a magnetic field is applied. In the following explanation, for the purpose of contrasting with nonlinear soft magnetic materials, such general soft magnetic materials that exhibit a rapid increase in magnetic flux density B even in weak magnetic fields will also be referred to as linear soft magnetic materials.

[0027] In contrast, the nonlinear soft magnetic material that the inventor focused on shows that, when the magnetic field strength H is near zero, the magnetic flux density changes only slowly even when a magnetic field is applied. However, when the magnetic field strength H becomes a constant value Hk, the magnetic flux density B increases rapidly. Subsequently, as the magnetic field strength H increases, it converges to the saturation magnetic flux density Bs. In other words, the magnetic flux density B does not increase easily when a weak magnetic field below a certain value is applied to the nonlinear soft magnetic material, but when a strong magnetic field strength H above a certain value is applied, the magnetic flux density B increases rapidly. To put it another way, the nonlinear soft magnetic material has the characteristic that magnetic flux does not pass through easily even when a weak magnetic field strength H is applied, but magnetic flux passes through rapidly when a strong magnetic field strength H is applied. In Figure 2, the magnetic field strength at which magnetic flux passes through easily is shown as the rising magnetic field Hk. In the BH curve, the rising magnetic field Hk is This refers to the magnetic field strength at which the magnetic flux density of a nonlinear soft magnetic material reaches 25% of its saturation magnetic flux density. The stator 10 of the motor 100 shown in Figure 1 uses a nonlinear soft magnetic material with a rising magnetic field Hk of 6 kA / m. For parts not made of nonlinear soft magnetic material, non-oriented electrical steel sheet of designation (grade) 35H300 (manufactured by Nippon Steel Corporation) is used.

[0028] Returning to Figure 1, the rotor core 21 of the motor 100 in this first embodiment is provided with a non-magnetic portion 25. The non-magnetic portion 25 is a portion with a lower relative permeability compared to other parts. For example, the non-magnetic portion 25 can be made up of voids provided in the rotor core 21 as shown in the figure, or notches provided on the outer circumference of the rotor core 21. The non-magnetic portion 25 may be made up of air, or it may be made up of a non-metallic material with a low relative permeability, such as resin. Alternatively, the non-magnetic portion 25 may be made of a magnetic composite material with low iron loss.

[0029] At least a portion of the non-magnetic portion 25 is provided on the rotor 20 in the area where the permanent magnets 23 embedded in the rotor 20 face the stator 10. The non-magnetic portion 25 is positioned to interfere with the magnetic force acting between the permanent magnets 23 and the teeth 11a, and functions to weaken the magnetic force of the permanent magnets 23 on the teeth 11a. The non-magnetic portion 25 is provided to correspond to each permanent magnet 23. In the illustrated example, six non-magnetic portions 25 are provided for six permanent magnets 23.

[0030] Figure 3 shows the efficiency map of the motor 100 of the first embodiment shown in Figure 1. In Figure 3, the horizontal axis represents the rotational speed of the motor 100, and the vertical axis represents the torque of the motor 100. Contour lines connect operating conditions with equal efficiency. Reference Examples 1 and 2 will be described in order to discuss the characteristics of the motor 100 of the first embodiment.

[0031] Figure 4 shows the motor 200 according to Reference Example 1. As shown in Figure 4, the motor 200 is an embedded magnet synchronous motor that does not have a non-magnetic part 25 and does not have any parts made of nonlinear soft magnetic material. The number of poles, the number of slots, etc. are the same as the motor 100 of the first embodiment shown in Figure 1. The efficiency map of the motor 200 shown in Figure 4 is shown in Figure 5.

[0032] Figure 6 shows a motor 300 according to Reference Example 2. As shown in Figure 6, the motor 300 has a stator 10 that is made of a nonlinear soft magnetic material, but the rotor core 21 does not have a nonmagnetic part 25. In other respects, the motor 300 is the same as the motor 200 of Reference Example 1. The efficiency map of the motor 300 shown in Figure 6 is shown in Figure 7.

[0033] First, let's compare Figures 5 and 7. In other words, we will compare the motor 200 of Reference Example 1, which does not have a non-magnetic part 25 and does not have a nonlinear soft magnetic material in the stator core 11, with the motor 300 of Reference Example 2, which has a nonlinear soft magnetic material in the stator core 11.

[0034] As can be seen from Figures 5 and 7, the rotational speed is 3,000 min⁻¹. -1 In the following low-speed range, the torque of motor 200 in Reference Example 1 is 168 Nm, while the torque of motor 300 in Reference Example 2 is 163 Nm. In other words, the torque of motor 300 in Reference Example 2 in the low-speed range is slightly lower than the torque of motor 200 in Reference Example 1.

[0035] Rotation speed 10,000 min⁻¹ -1 At moderate speeds, the torque of motor 200 in Reference Example 1 is 37.4 Nm, while the torque of motor 300 in Reference Example 2 is 42.5 Nm. In other words, in the moderate speed range, the torque of motor 300 in Reference Example 2 is 13.6% higher than that of motor 200 in Reference Example 1 at the same rotational speed.

[0036] Furthermore, the high-efficiency range of motor 300 in Reference Example 2 is wider than that of motor 200 in Reference Example 1. Specifically, the upper limit of the rotational speed at which motor 200 in Reference Example 1 achieves 95% efficiency is 10,000 min⁻¹. -1 While it is less than that, the upper limit of the rotational speed at which 95% efficiency can be obtained for motor 300 in Reference Example 2 is 12,000 min⁻¹. -1 To that extent, the motor 300 in Reference Example 2 has improved efficiency in the low-torque, high-speed range compared to the motor 200 in Reference Example 1.

[0037] (Effects due to nonlinear soft magnets) When the motor 200 in Reference Example 2 is driven in the low-torque, high-speed range, the amount of magnetic flux generated by the stator coil 12 is small, and the magnetic flux from the permanent magnets 23 of the rotor 20 becomes dominant. In this state, the strength of the magnetic field becomes smaller than the rising magnetic field Hk of the nonlinear soft magnetic material used in the teeth 11a, and the magnetic flux density of the teeth 11a becomes small. Therefore, even when the rotor 20 is operated at high speed, the induced voltage of the stator coil 12 becomes small. This suppresses copper loss in the stator coil 12. Furthermore, the magnetic flux density of the teeth 11a does not increase unless a magnetic field strength above a certain level acts on it. Therefore, the magnetic flux density of the teeth 11a in some areas that contribute to torque increases, while the magnetic flux density of other parts that do not contribute to torque can be kept low. This suppresses iron loss due to the teeth 11a that do not contribute to torque, and the overall efficiency can be increased. In other words, efficiency is increased in the low-torque, high-speed range.

[0038] Furthermore, when the motor is driven with high torque, the amount of current supplied to the stator coil 12 increases. In this state, the strength of the magnetic field acting on the teeth 11a is the sum of the magnetic flux of the permanent magnet 23 and the magnetic flux of the stator coil 12, which is greater than the rising magnetic field Hk of the nonlinear soft magnetic material, and the magnetic flux density of the teeth 11a increases. As a result, the motor 300 in Reference Example 2 can output high torque in the medium speed range.

[0039] Furthermore, if high torque output is desired, a high voltage is applied to the stator coil 12. In this state, a large magnetic field is applied to the stator coil 12. Therefore, whether the stator coil 12 is made of a linear soft magnetic material or a nonlinear soft magnetic material, the magnetic flux density of the stator coil 12 will be the same saturation magnetic flux density Bs. For this reason, the maximum torque of the motor 200 in Reference Example 2 will be the same as that of the motor 200 in Reference Example 1. In this way, by using a nonlinear soft magnetic material in at least a portion of the stator core 11, the efficiency of the motor can be increased.

[0040] Next, compare FIGS. 3 and 7. Rotation speed 3,000 min -1 In the following low speed region, the torque of the motor 300 of Reference Example 2 is 163 Nm, while the torque of the motor 100 of the first embodiment is 165 Nm. That is, the torque of the motor 100 of the first embodiment is increased in the low speed region as compared with the motor 300 of Reference Example 2.

[0041] Rotation speed 10,000 min -1 At a medium speed of about this level, the torque of the motor 300 of Reference Example 2 is 42.5 Nm, while the torque of the motor 100 of the first embodiment is 42.9 Nm. That is, in the medium speed region, at the same rotation speed, the torque of the motor 100 of the first embodiment is larger than the torque of the motor 300 of Reference Example 2.

[0042] Also, the high efficiency region of the motor 100 of the first embodiment is wider than the high efficiency region of the motor 300 of Reference Example 2. Specifically, the upper limit of the rotation speed at which 95% efficiency of the motor 300 of Reference Example 2 is obtained is about 12,000 min -1 whereas the upper limit of the rotation speed at which 95% efficiency of the motor 100 of the first embodiment is obtained is about 13,500 min -1 or so. That is, the motor 100 of the first embodiment realizes high torque in the low speed region and high efficiency in the high speed region. Also, the torque is higher than that of the motor 300 of Reference Example 2 in the high speed region, and is about the same as that of the motor 200 of Reference Example 1.

[0043] Next, the mechanism by which the motor 100 of the first embodiment exhibits the above-described effects will be described using FIGS. 8 and 9. FIG. 8 is a diagram showing the magnetic flux density distribution of the motor 200 of Reference Example 1. FIG. 9 is a diagram showing the magnetic flux density distribution of the motor 100 of the first embodiment. FIGS. 8 and 9 both show the rotation speed of 15,000 min -1The figure shows the magnetic flux density distribution when the rotor rotates counterclockwise. In the example shown in Figure 9, the non-magnetic portion 25 is located in a region of the rotor 20 that is clockwise from the d-axis. In Figures 8 to 10, darker colors indicate a higher magnetic flux density distribution.

[0044] As shown in Figure 8, the magnetic flux density of the teeth 11a of the motor 200 in Reference Example 1 is 1T or more. In particular, the magnetic flux density is high at the two teeth 11a located near the counterclockwise end and the clockwise end of the permanent magnet 23.

[0045] In contrast, the magnetic flux density of the teeth 11a of the motor 100 in the first embodiment shown in Figure 9 differs depending on the teeth 11a.

[0046] (Effects due to the non-magnetic part 25) Incidentally, when observing the magnetic flux density of each tooth 11a at a certain time during torque generation, it is found that there are teeth 11a that generate torque, teeth 11a that do not contribute to torque but have a high magnetic flux density, and teeth 11a that generate negative torque. Negative torque is the torque that acts on the rotor 20 to decelerate it. Among these, teeth 11a with zero or negative torque are the cause of various performance degradations such as torque damping, torque ripple, and losses.

[0047] Therefore, in the motor 100 of this first embodiment, a non-magnetic portion 25 is provided in at least a part of the rotor 20 where the permanent magnet 23 embedded in the rotor 20 and the stator 10 face each other. This non-magnetic portion 25 makes it difficult for the magnetic flux of the teeth 11a, which generate torque in the negative direction, to pass through. The operation of this non-magnetic portion 25 will be explained below.

[0048] Here, we focus on one permanent magnet 23 and discuss the magnetic flux density of eight teeth 11a located near the permanent magnet 23. As shown in Figure 1, the imaginary line extending radially from near the center of the permanent magnet 23 is called the d-axis. The imaginary line extending radially from the position between adjacent permanent magnets 23 is called the q-axis. The eight teeth 11a discussed here can also be said to be teeth 11a located between the two q-axes. For convenience, we will call the first tooth 11a1 located at the counterclockwise end of the eight teeth 11a, and the tooth 11a located at the clockwise end the eighth tooth 11a8.

[0049] The first tooth 11a1 is assumed to generate a magnetic force that attracts the permanent magnet 23, thereby generating torque that accelerates the rotor 20. However, unlike this first embodiment, in the motor 200 of Reference Example 1 shown in Figure 8, which does not have a non-magnetic part 25, a similar magnetic flux density acts on the eighth tooth 11a8, causing the eighth tooth 11a8 to attract the permanent magnet 23. The magnetic force that the eighth tooth 11a8 exerts on the permanent magnet 23 slows down the rotor 20, which rotates counterclockwise.

[0050] However, as shown in Figures 1 and 9, a non-magnetic section 25 is provided near the clockwise end of the rotor 20 of the motor 100 in this first embodiment to weaken the magnetic force acting from the permanent magnet 23 to the stator 10. In other words, the non-magnetic section 25 is provided to make it difficult for the magnetic flux of the eighth tooth 11a8, which generates negative torque, to pass through. As a result, the magnetic flux density of the eighth tooth 11a8 does not easily become high.

[0051] Thus, with the motor 100 of this first embodiment, the magnetic force that accelerates the rotor 20 in a counterclockwise direction between the permanent magnet 23 and the first tooth 11a1 is maintained, while the magnetic force that decelerates the rotor 20 in a counterclockwise direction between the permanent magnet 23 and the eighth tooth 11a8 is reduced. For this reason, the motor 100 of this first embodiment can output higher torque at the same speed as the motor 200 of Reference Example 1 and the motor 300 of Reference Example 2.

[0052] Furthermore, the magnetic flux generated by the field magnetomotive force linked to the windings only has an effective component that contributes to positive torque, while other magnetic flux densities are suppressed. As a result, back electromotive force is less likely to be generated even at high rotational speeds. In other words, voltage saturation due to high-speed driving is improved, and high torque can be output. Furthermore, since the motor 100 of this first embodiment does not require the use of permanent magnets with particularly weak magnetic force, it can output high torque even at low rotational speeds.

[0053] Furthermore, the stator 10 of the motor 100 in this first embodiment shown in Figure 9 has a larger area of ​​low magnetic flux density overall compared to the stator 10 of the motor 200 in Reference Example 1 shown in Figure 8. Therefore, iron loss is less likely to occur. Also, because there are many regions with low magnetic flux density, the amount of magnetic flux linked to the stator coil 12 is reduced, and back electromotive force is suppressed. This effect of suppressing back electromotive force becomes more pronounced as the motor 100 rotates at high speed. Thus, according to the motor 100 of this first embodiment, it is possible to provide a motor that can suppress back electromotive force at high speeds without reducing torque at low speeds.

[0054] In this first embodiment, at least a portion of the teeth 11a is made of a nonlinear soft magnetic material whose magnetic flux density does not increase unless a strong magnetic field is applied, so the magnetic flux density of the eighth tooth 11a8 is even less likely to increase.

[0055] Furthermore, while Figures 1 and 9 illustrate an example in which the teeth 11a are made of a nonlinear soft magnetic material and the nonmagnetic portion 25 of the void is provided near the clockwise end of the permanent magnet 23, the disclosure is not limited to this. By providing a nonlinear soft magnetic material in at least a portion of the stator 10, the magnetic flux density will not increase unless a certain level of magnetic field strength is applied. This allows the magnetic flux density in parts that do not contribute to torque to be kept low. As a result, iron loss due to the teeth 11a, which do not contribute to torque, can be suppressed, and overall efficiency can be increased. In other words, by providing a nonlinear soft magnetic material in at least a portion of the stator 10, the efficiency of the motor 100 can be increased.

[0056] The non-magnetic portion 25 may be provided so as to obstruct the magnetic flux along the d axis with respect to the permanent magnet 23. Furthermore, it is preferable that the non-magnetic portion 25 is provided asymmetrically with respect to the d axis with respect to one permanent magnet 23, as shown in Figure 9. In the illustrated example, the non-magnetic portion 25 is not provided on the part of the rotor 20 located in the counterclockwise direction of the d axis, but is provided on the part of the rotor 20 located in the clockwise direction of the d axis. As a result, when the rotor 20 rotates counterclockwise, characteristics such as improved torque and efficiency are enhanced compared to when it rotates counterclockwise.

[0057] Figure 10 shows the magnetic flux density distribution of the motor 300 of Reference Example 2. As shown in Figure 10, at least a part of the stator 10 is made of a nonlinear soft magnetic material, but in the motor 300 of Reference Example 2, in which the rotor 20 does not have a non-magnetic part 25, the magnetic flux density of the entire stator 10 is reduced while the magnetic flux density near the first tooth 11a1 is increased. However, compared to the motor 100 of the first embodiment shown in Figure 9, the effect of reducing the magnetic flux density of the eighth tooth 11a8 is not sufficient. Therefore, the effect of reducing the magnetic flux density of the eighth tooth 11a8 by providing a non-magnetic part 25 on the rotor 20 can be confirmed.

[0058] <Variation> Furthermore, the motor 100 described above tends to perform better in a specific rotation direction. Therefore, the motor 400 may be configured as shown in Figure 11. In the modified motor 400 of this disclosure, a plurality of laminated iron core pieces constituting the rotor 20 are stacked such that the positions of the non-magnetic portions 25 of adjacent laminated iron core pieces are offset in the stacking direction. Figure 11 is a diagram showing the rotor 20 of the motor 400 according to the modified motor of this disclosure.

[0059] The modified motor 400 shown in Figure 11 has a first laminated core piece 26 and a second laminated core piece 27. Similar to the example shown in Figure 1, the first laminated core piece 26 does not have a non-magnetic portion 25 in the clockwise direction of the d-axis, but it does have a non-magnetic portion 25 in the counterclockwise direction of the d-axis. The second laminated core piece 27, conversely to the first laminated core piece 26, has a non-magnetic portion 25 in the clockwise direction of the d-axis, but does not have a non-magnetic portion 25 in the counterclockwise direction of the d-axis. These first laminated core piece 26 and second laminated core piece 27 are laminated in the direction of the rotation axis of the motor 400.

[0060] In this configuration, the positions of the non-magnetic portions 25 of adjacent laminated core pieces 26 and 27 in the direction of the rotation axis (lamination direction) are offset. With this type of motor 400, regardless of the direction of rotation, the back electromotive force at high speeds is suppressed without reducing the torque at low speeds.

[0061] Furthermore, as shown in Figure 11, it is preferable that the non-magnetic portions 25 of adjacent laminated iron core pieces 26 and 27 are not simply misaligned, but rather that they are laminated so that the positions of the non-magnetic portions 25 of adjacent laminated iron core pieces 26 and 27 are symmetrical with respect to the d-axis.

[0062] <Second Embodiment> In the motor 100 of the first embodiment described above, the rotor 20 has a non-magnetic portion 25 and at least a part of the stator 10 is made of a nonlinear soft magnetic material. However, as in the motor 500 of the second embodiment described below, the rotor 20 does not have to have a non-magnetic portion 25 and the stator 10 does not have to be made of a nonlinear soft magnetic material.

[0063] Figure 12 shows a motor 500 according to a second embodiment of the present disclosure. As shown in Figure 12, the motor 500 has a non-magnetic portion 25 provided in at least a part of the rotor 20 where the permanent magnets 23 embedded in the rotor 20 face the stator 10. The stator 10 is entirely made of non-oriented electrical steel sheet that is not a nonlinear soft magnetic material.

[0064] Figure 13 shows the efficiency map of motor 500. As shown in Figure 13, the maximum torque in the low-speed range is 168N, indicating that the torque does not decrease during low-speed rotation. Furthermore, the maximum torque of the motor 500 in the second embodiment in the high-speed range is about the same as that of the motor 200 in Reference Example 1.

[0065] Furthermore, the upper limit of the rotational speed at which the motor 500 of the second embodiment achieves 95% efficiency is approximately 11,000 min-1, which is greater than the upper limit of approximately 95,000 min-1 at which the motor 200 of Reference Example 1 achieves 95% efficiency. In other words, the motor 500 of the second embodiment also achieves high torque in the low-speed range and high efficiency in the high-speed range. The maximum torque of the motor 500 of the second embodiment at a rotational speed of 10,000 min-1 is 41 N·m, which is a 9.6% increase compared to the maximum torque of 37.4 N·m at a rotational speed of 10,000 min-1 in Reference Example 1. Thus, it was confirmed that, in the motor 500 of the second embodiment, the back electromotive force at high speeds can be suppressed without reducing the torque at low speeds.

[0066] Figure 14 shows the magnetic flux density distribution of the motor 500 of the second embodiment. In Figure 14, darker colors indicate a higher magnetic flux density distribution. As can be seen by comparing the motor 200 of Reference Example 1 in Figure 8 with the motor 500 of the second embodiment in Figure 14, in the motor 500 of the second embodiment, the magnetic flux density near the first tooth 11a1 is maintained while the magnetic flux density near the eighth tooth 11a8 is reduced. Therefore, in the motor 500 of the second embodiment, back electromotive force at high speeds can be suppressed without reducing torque at low speeds.

[0067] <Third Embodiment> By the way, in the first and second embodiments described above, an elliptical non-magnetic portion 25 having its major axis in the d-axis direction was described, but the present disclosure is not limited thereto. Figure 15 is a diagram showing a motor 600 according to the third embodiment of the present disclosure. At least a part of the stator 10 of the motor 600 according to the third embodiment is made of a nonlinear soft magnetic material. As shown in Figure 15, in this embodiment, a non-magnetic portion 25 extending in the q-axis direction is provided. The illustrated non-magnetic portion 25 is a slit extending from the right side (clockwise end) of the permanent magnet 23 to just before the surface of the rotor 20, and a slit extending from the left side (counterclockwise end) of the permanent magnet 23 to just before the surface of the rotor 20. In the following description, this non-magnetic portion 25 extending in the q-axis direction will be referred to as the q-axis flux barrier 601.

[0068] Figures 16A and 16B are diagrams illustrating the operation of the q-axis flux barrier 601. Figure 16A is an enlarged view of motor 200 of Reference Example 1, which is not provided with the q-axis flux barrier 601. Figure 16B is an enlarged view of motor 600 of the third embodiment, which is provided with the q-axis flux barrier 601. In Figures 16A and 16B, the rotor 20 is assumed to rotate counterclockwise.

[0069] (Increased torque) As shown in Figure 16A, we focus on the magnetic flux passing through the first tooth 611 and the second tooth 612, which are adjacent in a certain circumferential direction. It should be noted that the first tooth 611 referred to here has no relation to the first tooth 11a1 mentioned earlier. The magnetic flux passing from the first tooth 611 through the rotor 20 to the second tooth 612 imparts a positive (counterclockwise) torque to the rotor 20, as well as a negative torque. Specifically, in the illustrated example, the magnetic flux passing from the first tooth 611 to the rotor 20 imparts a positive torque to the rotor 20, but the magnetic flux passing from the rotor 20 to the second tooth 612 imparts a negative torque.

[0070] As shown in Figure 16B, when the q-axis flux barrier 601 is provided, the amount of magnetic flux flowing between the first teeth 611 and the second teeth 612 and the rotor 20 can be restricted. In other words, as shown in Figure 16A, when the q-axis flux barrier 601 is not provided, the amount of magnetic flux entering the rotor 20 from the first teeth 611 and the amount of magnetic flux leaving the rotor 20 for the second teeth 612 are equal. However, as shown in Figure 16B, when the q-axis flux barrier 601 is provided, the amount of magnetic flux entering the rotor 20 from the first teeth 611 and the amount of magnetic flux leaving the rotor 20 for the second teeth 612 can be made different. In this way, the amount of magnetic flux can be controlled by the q-axis flux barrier 601 and the positive torque can be increased. Furthermore, by adjusting the position and size of the q-axis flux barrier 601, the effect of increasing the positive torque can be enhanced.

[0071] (Increase in maximum torque) Figure 17 is a comparison of the maximum torques of three types of motors 200, 600, and 700. In Figure 17, (a) shows motor 200 of Reference Example 1, which is an embedded magnet synchronous motor that does not have a q-axis flux barrier 601 and does not have any parts made of nonlinear soft magnetic material; (b) shows embedded magnet synchronous motor 700, which has a q-axis flux barrier 601 but does not have any parts made of nonlinear soft magnetic material; and (c) shows motor 600 of the third embodiment. Figure 17 shows the maximum torque that motors 600 of (a) to (c) can generate under the conditions of a phase current of 600V or less and a phase current of 300A or less.

[0072] As shown in Figure 17, motor 700 in (b) has increased maximum torque in the low-speed rotation region of 1000 rpm compared to motor 200 in (a). Motor 600 of the third embodiment in (c) exhibits performance equivalent to (b) in the low-speed rotation region, and further increases the maximum torque compared to motor 700 in (b) in the high-speed rotation region of 20000 rpm or higher.

[0073] (Improvement of torque distribution) Figure 18 shows the torque distribution generated on the rotor surface of motor 200 (a), motor 700 (b), and motor 600 (c) at a rotational speed of 15,000 rpm. Hereafter, motor 200 (a), motor 700 (b), and motor 600 (c) in Figures 18 to 21 are synonymous with motor 200 (a), motor 700 (b), and motor 600 (c) in Figure 17.

[0074] As mentioned earlier, the torque generated at the end of the teeth is increased in the positive direction by the q-axis flux barrier 601. For this reason, at an electrical angle of 45 degrees, motor 700 (b) has a greater positive torque than motor 200 (a). Furthermore, at an electrical angle of 60 degrees, motor 600 (c) has an even greater positive torque than motor 700 (b). This is because the positive torque increased by the q-axis flux barrier 601 is further increased as the magnetic flux becomes more concentrated by the nonlinear soft magnetic material. Furthermore, Figure 18 shows that, at an electrical angle of 115 degrees, motor 700 (b) and motor 600 (c) exhibit reduced negative torque compared to motor 200 (a).

[0075] (Improvement of magnetic flux density) Figure 19A shows the magnetic flux density distribution of motor 200 (a). Figure 19B shows the magnetic flux density distribution of motor 700 (b). Figure 19C shows the magnetic flux density distribution of motor 600 (c). In Figures 19A to 19C, darker colors indicate a higher magnetic flux density distribution. As can be seen by comparing Figure 19A and Figure 19B, by providing the q-axis flux barrier 601, the magnetic flux can be concentrated on the first tooth 611 (the tooth that contributes to the positive torque) through which the magnetic flux is to be passed, and the magnetic flux to the second tooth 612 (the tooth that contributes to the negative torque) through which the magnetic flux is not to be passed can be reduced. As can be seen by comparing Figure 19B and Figure 19C, the magnetic flux density of the second tooth 612 through which the magnetic flux is not to be passed can be further reduced by using a nonlinear soft magnetic material. This can increase the efficiency of the motor 600.

[0076] Figure 20 compares the efficiency of motor 200 (a), motor 700 (b), and motor 600 (c). As shown in Figure 20, motor 600 (c) achieves higher efficiency than motor 200 (a) and motor 700 (b) in the high-speed rotation region.

[0077] Figure 21 compares the losses of motor 600 (a), motor 700 (b), and motor 600 (c). As shown in Figure 21, motor 700 (b) and motor 600 (c) concentrate the magnetic flux on the first tooth 611 through which they want the magnetic flux to pass (see Figure 16B), resulting in smaller stator tooth losses than motor 200 (a).

[0078] Furthermore, as will be described later, the q-axis flux barrier 601 improves demagnetization at the ends of the permanent magnet 23, so motor 700 in (b) and motor 600 in (c) have smaller eddy current losses than motor 200 in (a). Note that in Figure 21, motor 200 in (a) cannot be operated at 15,000 to 30,000 rpm, so its losses are shown as 0 for the time being. Similarly, motor 700 in (b) cannot be operated at 30,000 rpm, so its losses are shown as 0 for the time being.

[0079] Returning to Figures 16A and 16B, in the example shown in Figures 16A and 16B, non-magnetic portions 25 extending in the circumferential direction are provided at both ends of the permanent magnet 23. These non-magnetic portions 25 extending in the circumferential direction at both ends of the permanent magnet 23 are called the first flux barrier 602.

[0080] As shown in Figure 16A, if the q-axis flux barrier 601 is not provided, the magnetic flux passing between the first flux barriers 602 of the rotor 20 enters the permanent magnet 23 from the radially inner surface. The magnetic flux that penetrates the permanent magnet 23 then proceeds toward the teeth 611, 612. In particular, the magnetic flux also passes through the ends of the permanent magnet 23.

[0081] However, as shown in Figure 16B, when the q-axis flux barrier 601 is provided, the magnetic flux does not enter the region between the first flux barrier 602 and the q-axis flux barrier 601, and as a result penetrates the central region of the permanent magnet 23 and bypasses the ends of the permanent magnet 23. Therefore, demagnetization at the ends of the permanent magnet 23 is improved. For example, if the magnetic flux density at the ends of the permanent magnet 23 in motor 200 (a) is 2 [T], under the same conditions it is reduced to approximately 1.8 [T] in motor 700 (b) and approximately 1.7 [T] in motor 600 (c). Similarly, if the magnitude of the magnetic field at the ends of the permanent magnet 23 in motor 200 (a) is 500 [kA / m], under the same conditions it is improved to approximately 450 [kA / m] in motor 700 (b) and approximately 420 [kA / m] in motor 600 (c).

[0082] Figure 22A shows the eddy current loss of motor 200 (a). Figure 22B shows the eddy current loss of motor 700 (b). Figure 22C shows the eddy current loss of motor 600 (c). In Figures 22A to 22C, darker colors indicate a higher magnetic flux density distribution. As can be seen by comparing Figure 22A and Figure 22B, at the end of the permanent magnet 23, the q-axis flux barrier 601 reduces the flux linkage and thus the eddy current loss. As can be seen by comparing Figure 22B and Figure 22C, at the end of the permanent magnet 23, the nonlinear soft magnetic material further reduces the eddy current loss that was already reduced by the flux linkage due to the q-axis flux barrier 601.

[0083] As described above, motors 700 and 600, which have the q-axis flux barrier 601, exhibit high maximum torque over a wide range of rotational speeds (Figure 17), high efficiency (Figure 20), and low losses (Figure 21). Furthermore, these characteristics of maximum torque, efficiency, and losses are further improved by the fact that at least the stator 10 is composed of a nonlinear soft magnetic material.

[0084] Figure 23 shows a motor 800 according to the fourth embodiment of the present disclosure. As shown in Figure 23, a non-magnetic portion 25 may be provided near both ends of the permanent magnet 23, comprising a d-axis flux barrier 801 extending in the d-axis direction and a q-axis flux barrier 802 extending in the q-axis direction. The d-axis flux barrier 801 and the q-axis flux barrier 802 may be provided in a continuous manner. In the illustrated example, q-axis flux barriers 802 are provided at both ends of the permanent magnet 23, and the d-axis flux barriers 801 extend from each q-axis flux barrier 802 in directions away from each other. As described above, various motor characteristics can be improved with this configuration as well. For example, a motor 800 equipped with both a d-axis flux barrier 801 and a q-axis flux barrier 802 has higher maximum torque and efficiency over a wide range of rotational speeds compared to a motor equipped only with a d-axis flux barrier 801 or a motor equipped only with a q-axis flux barrier 802. In the motor 800 according to the fourth embodiment of this disclosure, at least a portion of the stator 10 may also be made of a nonlinear soft magnetic material.

[0085] While embodiments of this disclosure have been described above, it goes without saying that the technical scope of this disclosure should not be interpreted restrictively by the description of these embodiments. These embodiments are merely examples, and it will be understood by those skilled in the art that various modifications to the embodiments are possible within the scope of the invention described in the claims. The technical scope of this disclosure should be determined based on the scope of the invention described in the claims and the scope of its equivalents. [Explanation of Symbols]

[0086] 10 staters 11 Stator Core 11a Teeth 11a1 First Teeth 11a8 Eighth Teeth 11b Back yoke 12 Stator Coil 20 rotors 21 Rotor Core 22 shaft mounting holes 23 Permanent Magnets 24 Rotor gap 25 Non-magnetic part 26 First layered iron core piece 27 Second laminated iron core piece 100, 200, 300, 400, 500, 600, 700, 800 motors 601 q-axis flux barrier 602 First Flux Barrier 611 First Teeth 612 Second Teeth 801 d-axis flux barrier 802 q-axis flux barrier

Claims

1. A stator having a stator core with teeth and windings wound around the teeth, Equipped with a rotor with permanent magnets, A motor in which a non-magnetic portion is provided in at least a part of the rotor where the permanent magnet embedded in the rotor faces the stator.

2. The motor according to claim 1, wherein at least a portion of the stator is made of a nonlinear soft magnetic material.

3. The motor according to claim 1, wherein the non-magnetic portion is provided so as to obstruct the magnetic flux in the d-axis with respect to the permanent magnet.

4. The motor according to claim 1, wherein the non-magnetic portion is provided asymmetrically with respect to the d-axis.

5. The rotor is constructed by stacking multiple laminated iron core pieces, The motor according to claim 1, wherein the plurality of laminated core pieces are stacked such that the positions of the non-magnetic portions of adjacent laminated core pieces are offset.

6. The rotor is constructed by stacking multiple laminated iron core pieces, The motor according to claim 1, wherein the plurality of laminated core pieces are stacked such that the positions of the non-magnetic portions of adjacent laminated core pieces are symmetrical with respect to the d-axis.

7. The motor according to claim 1 or 2, wherein the non-magnetic portion is provided so as to extend in the q-axis direction.

8. The non-magnetic portion is A d-axis flux barrier extending in the d-axis direction, A motor according to claim 1 or 2, comprising a q-axis flux barrier extending in the q-axis direction.

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