Electric motor

Abstract

To provide an electric motor with further improved torque and efficiency.SOLUTION: An electric motor includes a disk-shaped rotor core with a shaft line in the center, a plurality of permanent magnets arranged circumferentially inside the rotor core, and a stator surrounding the rotor core and the permanent magnets from the outer circumferential side. On the outer circumferential side of the permanent magnets in the rotor core, a plurality of outer slits are formed that extend from both ends in the circumferential direction of the permanent magnets toward the outer circumferential side of the permanent magnets in a direction that is closer to each other as they move toward the outer side in the radial direction. Thereby, it is possible to reduce leaked magnetic fluxes.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present disclosure relates to an electric motor.

Background Art

[0002] As a type of electric motor, a PMSM (Permanent Magnet Synchronous Motor) including a rotor having permanent magnets and a stator that covers the rotor from the outer peripheral side is known. As a specific example of this type of electric motor, the device described in Patent Document 1 below can be mentioned. In the electric motor according to Patent Document 1, permanent magnets are embedded inside the rotor core, and arc-shaped slits extending along the magnetic path of the permanent magnets are formed inside the rotor core. Thereby, it is said that the reluctance torque of the electric motor is reduced, and torque ripple and noise can be reduced.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, when the slit is simply arc-shaped as in the electric motor described in Patent Document 1 above, the flow of magnetic flux from the permanent magnet toward the stator is obstructed, and magnetic flux leakage increases. As a result, there is a risk of affecting the torque and efficiency of the motor.

[0005] The present disclosure has been made to solve the above problems, and an object thereof is to provide an electric motor with further improved torque and efficiency.

Means for Solving the Problems

[0006] In order to solve the above problems, the electric motor according to the present disclosure includes a disk-shaped rotor core centered on an axis, a plurality of permanent magnets arranged circumferentially inside the rotor core, and a stator that surrounds the rotor core and the permanent magnets from the outer peripheral side. On the outer peripheral side of the permanent magnets in the rotor core, a plurality of outer slits extending in a direction approaching each other are formed from both circumferential ends of the permanent magnets toward the radially outer side. Over the entire circumferential direction of the permanent magnet, The width of the outer slit increases as it approaches the central portion in the circumferential direction of the permanent magnet.

Advantages of the Invention

[0007] According to the present disclosure, an electric motor with further improved torque and efficiency can be provided.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Modes for Carrying Out the Invention

[0009] <First Embodiment> (Configuration of the Electric Motor) Hereinafter, the electric motor 100 according to the first embodiment of the present disclosure will be described with reference to FIGS. 1 and 2. As shown in FIG. 1, the electric motor 100 includes a rotor 1 extending along an axis Ac, and a stator 3 that covers the rotor 1 from the outer peripheral side.

[0010] (Configuration of the Rotor) The rotor 1 has a rotor core 11 and a permanent magnet 2. The rotor core 11 has a cylindrical shape centered on the axis Ac. Although not shown in detail, the rotor core 11 is formed into a cylindrical shape as a whole by stacking a plurality of thin steel plates.

[0011] A plurality of permanent magnets 2 are embedded inside the rotor core 11. More specifically, these permanent magnets 2 are arranged at intervals in the circumferential direction with respect to the axis Ac. Each permanent magnet 2 has a pair of unit magnets 21. Each unit magnet 21 has a plate shape with a rectangular cross-sectional shape when viewed from the direction of the axis Ac. By arranging these unit magnets 21 adjacent to each other in the circumferential direction, one permanent magnet 2 is formed. Details of the arrangement and orientation of the unit magnets 21 will be described later.

[0012] (Configuration of the stator) The stator 3 has a back yoke 31, teeth 32, a coil 33, and tooth tips 34. The back yoke 31 has an annular shape centered on the axis Ac. The outer peripheral surface of the back yoke 31 is fixed to the inner peripheral surface of a casing (not shown). A plurality of teeth 32 are provided on the inner peripheral side of the back yoke 31. These teeth 32 are arranged at equal intervals in the circumferential direction of the axis Ac along the inner peripheral surface of the back yoke 31. Each tooth 32 protrudes radially inward from the inner peripheral surface of the back yoke 31.

[0013] The radially inner end of the tooth 32 is the tooth tip 34. The tooth tip 34 protrudes from both sides in the circumferential direction of the tooth 32. Also, a coil 33 is provided around the tooth 32. The coil 33 is formed by winding a copper wire or the like around the tooth 32 a plurality of times. By passing an electric current through this coil 33, the coil 33 is excited. The rotor 1 rotates around the axis Ac due to the electromagnetic force generated between this coil 33 and the permanent magnet 2.

[0014] (Configuration and arrangement of unit magnets) Next, with reference to FIG. 2, the detailed configuration of the rotor core 11 will be described. As shown in FIG. 2, a pair of unit magnets 21 forming the permanent magnet 2 extend in a direction of being spaced apart from each other in the circumferential direction as they go from the radially inner side to the radially outer side. That is, these unit magnets 21 are arranged in an inclined posture with respect to the radial direction.

[0015] Note that, between the pair of unit magnets 21, the poles of the surfaces facing the radially outer side are the same. On the other hand, between the adjacent permanent magnets 2, the poles are different from each other. That is, the permanent magnets 2 are arranged such that the N pole and the S pole alternate in the circumferential direction.

[0016] Furthermore, the unit magnet 21 has a variable magnet 21A located relatively radially inward and a fixed magnet 21B laminated on the radially outer side of the variable magnet 21A. The variable magnet 21A can change its magnetic force by magnetization or demagnetization. On the other hand, the fixed magnet 21B has a constant magnetic force. By controlling the energizing current of the coil 33, the magnetic force of the variable magnet 21A changes, making it possible to change the torque and efficiency of the motor 100.

[0017] (Configuration of the outer slit) A plurality of slits (outer slit 22, inner slit 23) are formed in the rotor core 11 to guide the magnetic flux generated from the above-described permanent magnet 2 (unit magnet 21). The outer slit 22 is formed on the radially outer side of the unit magnet 21. As an example, six outer slits 22 are formed at intervals in the circumferential direction. That is, three outer slits 22 are formed for each unit magnet 21.

[0018] These outer slits 22 extend in a direction of approaching each other as they go from both circumferential ends of the unit magnet 21 to the radially outer side. Also, these outer slits 22 extend linearly in a direction orthogonal to the outer surface (the surface facing the radially outer side) of the unit magnet 21. Here, the "orthogonal" mentioned herein represents a substantially orthogonal state, and design tolerances and manufacturing errors are allowed.

[0019] Furthermore, among these six outer slits 22, the closer the outer slit 22 is to the circumferential center of the permanent magnet 2, the larger its width becomes. That is, when taking the gap between a pair of unit magnets 21 as a reference, the first outer slit 22A that is closest to the circumferential direction from the gap has a larger width than the third outer slit 22C that is located outermost in the circumferential direction. Also, the second outer slit 22B formed between the first outer slit 22A and the third outer slit 22C has a larger width than the third outer slit 22C and a smaller width than the first outer slit 22A. Here, the "width" refers to the dimension in the plane direction orthogonal to the extending direction of the outer slit 22.

[0020] (Configuration of inner slit) A plurality of inner slits 23 are formed on the radially inner side of the permanent magnet 2. As an example, six inner slits 23 are formed at intervals in the circumferential direction. That is, three inner slits 23 are formed for each unit magnet 21.

[0021] As shown in FIG. 1 or FIG. 2, these inner slits 23 extend in a curved shape from one permanent magnet 2 (unit magnet 21) to the other permanent magnet 2 (unit magnet 21) among a pair of circumferentially adjacent permanent magnets 2. That is, a plurality of arc-shaped inner slits 23 are formed on the radially inner side of the permanent magnet 2.

[0022] Furthermore, among these inner slits 23, the closer the inner slit 23 is to the radially outer side, the smaller its width becomes. That is, the first inner slit 23A located closest to the radially inner side has a larger width than the third inner slit 23C located outermost in the radial direction. Also, the second inner slit 23B formed between the first inner slit 23A and the third inner slit 23C has a larger width than the third inner slit 23C and a smaller width than the first inner slit 23A. Here, the "width" refers to the dimension in the plane direction orthogonal to the extending direction of the inner slit 23.

[0023] (Function and effect)

[0024] According to the above configuration, a plurality of outer slits 22 are formed on the outer peripheral side of the permanent magnet 2 in the rotor core 11. Further, these outer slits 22 extend in a direction approaching each other as they go radially outward. Since the outer slits 22 are gaps, the magnetic resistance is larger than that of the rotor core 11 itself. Therefore, the magnetic flux generated by the permanent magnet 2 is guided in the extending direction of the outer slits 22 while avoiding the outer slits 22. In other words, the magnetic flux is guided in a direction approaching each other as it goes radially outward. Thereby, the magnetic flux can be converged toward the teeth 32 of the stator 3. As a result, the leakage magnetic flux can be further reduced.

[0025] Here, as shown in FIG. 2, the direction along the magnetic field of the permanent magnet 2 is defined as the d-axis, and the direction orthogonal to this d-axis is defined as the q-axis. In order to increase the reluctance torque, there is a demand to reduce the magnetic resistance in the d-axis direction. In the above configuration, among the plurality of outer slits 22, the width of the outer slit 22 becomes larger toward the circumferential center of the permanent magnet 2. In other words, the ratio occupied by the rotor core 11 itself becomes smaller toward the circumferential center. Thereby, the width of the magnetic path in the circumferential center can be reduced, and the magnetic resistance (that is, the magnetic resistance in the above-described d-axis direction) can be further reduced. As a result, it becomes possible to increase the reluctance torque or to more smoothly demagnetize or magnetize the permanent magnet 2.

[0026] Furthermore, since the width of the outer slit 22 is small at both ends in the circumferential direction of the permanent magnet 2, the ratio occupied by the rotor core 11 itself is large. Thereby, the strength of the rotor core 11 can be ensured. Also, by increasing the ratio occupied by the rotor core 11 itself in this way, it is possible to make it difficult for magnetic saturation to occur.

[0027] In addition, according to the above configuration, the pair of unit magnets 21 extend in a direction in which they are separated from each other in the circumferential direction as they face the radially outer side. That is, these unit magnets 21 face the circumferential center portion. For this reason, the direction in which the outer slit 22 extends can be made closer to the direction of the magnetic flux generated by the unit magnet 21. As a result, the leakage magnetic flux can be further reduced.

[0028] Also, according to the above configuration, the outer slit 22 extends linearly in a direction orthogonal to the outer surface of the unit magnet 21. That is, the direction of the magnetic flux generated by the unit magnet 21 and the direction in which the outer slit 22 extends can be made closer to each other. As a result, the leakage magnetic flux can be more effectively reduced.

[0029] Furthermore, according to the above configuration, among the plurality of inner slits 23, the width becomes smaller as the inner slit 23 on the radially outer side is reached. Thereby, the magnetic resistance in the q-axis direction can be increased. As a result, it becomes possible to increase the reluctance torque of the permanent magnet 2, or to perform demagnetization or magnetization of the permanent magnet 2 more smoothly.

[0030] In addition, according to the above configuration, the permanent magnet 2 has a variable magnet 21A. By applying magnetization (or demagnetization) to this variable magnet 21A by a stator for magnetization, the magnetic force of the entire permanent magnet 2 can be changed. Thereby, it becomes possible to operate the electric motor 100 as a variable magnetic force motor.

[0031] The first embodiment of the present disclosure has been described above. Note that various changes and modifications can be made to the above configuration without departing from the gist of the present disclosure. For example, in the first embodiment above, an example in which the permanent magnet 2 has a variable magnet 21A has been described. However, it is also possible to adopt a configuration in which the permanent magnet 2 does not have a variable magnet 21A and is integrally formed only by a fixed magnet 21B.

[0032] <Second Embodiment> Next, a second embodiment of the present disclosure will be described with reference to FIG. 3. Note that the same components as those in the first embodiment described above are denoted by the same reference numerals, and detailed descriptions thereof are omitted. As shown in the figure, in this embodiment, a protrusion 11P is provided on the outer peripheral surface 11S of the rotor core 11. The protrusion 11P is provided at a portion corresponding to the permanent magnet 2 in the circumferential direction on the outer peripheral surface 11S. The protrusion 11P has a smaller radius of curvature than other portions on the outer peripheral surface 11S and protrudes in an arc shape toward the radially outer side. A plurality of such protrusions 11P are formed at equal intervals over the entire circumference of the outer peripheral surface 11S.

[0033] According to the above configuration, it is possible to reduce the harmonic magnetic flux while maintaining the magnetic flux in the d-axis direction. As a result, torque fluctuations (torque ripple) and the noise based on this can be further reduced.

[0034] The second embodiment of the present disclosure has been described above. Note that various changes and modifications can be made to the above configuration without departing from the gist of the present disclosure.

[0035] As a modification common to each embodiment, it is also possible to adopt the configuration shown in FIG. 4. This figure shows an example in which one plate-shaped magnet is used as the permanent magnet 2b. Even with such a configuration, it is possible to obtain the same operational effects as those described in the above embodiments.

[0036] <Supplementary Note> The electric motors described in each embodiment are understood as follows, for example.

[0037] (1) The electric motor 100 according to the first aspect includes a disk-shaped rotor core 11 centered on the axis Ac, a plurality of permanent magnets 2 arranged in the circumferential direction inside the rotor core 11, and a stator 3 surrounding the rotor core 11 and the permanent magnets 2 from the outer peripheral side. On the outer peripheral side of the permanent magnet 2 in the rotor core 11, a plurality of outer slits 22 extending in a direction approaching each other from both circumferential ends of the permanent magnet 2 toward the radially outer side are formed.

[0038] According to the above configuration, a plurality of outer slits 22 are formed on the outer peripheral side of the permanent magnet 2 in the rotor core 11. Further, these outer slits 22 extend in a direction approaching each other as they go radially outward. Since the outer slits 22 are gaps, the magnetic resistance is larger than that of the rotor core 11 itself. For this reason, the magnetic flux generated by the permanent magnet 2 is guided in the extending direction of the outer slits 22 while avoiding the outer slits 22. In other words, the magnetic flux is guided in a direction approaching each other as it goes radially outward. Thereby, the magnetic flux can be converged toward the teeth 32 of the stator 3. As a result, the leakage magnetic flux can be further reduced.

[0039] (2) In the electric motor 100 according to the second aspect, the width of the outer slit 22 increases toward the center in the circumferential direction of the permanent magnet 2.

[0040] Here, the direction along the magnetic field of the permanent magnet 2 is defined as the d-axis, and the direction orthogonal to this d-axis is defined as the q-axis. In order to increase the reluctance torque, there is a demand to reduce the magnetic resistance in the d-axis direction. In the above configuration, among the plurality of outer slits 22, the width of the outer slit 22 increases toward the center in the circumferential direction of the permanent magnet 2. In other words, the proportion occupied by the rotor core 11 itself becomes smaller toward the center in the circumferential direction. Thereby, the width of the magnetic path in the circumferential direction center can be reduced, and the magnetic resistance (that is, the magnetic resistance in the above-described d-axis direction) can be further reduced. As a result, it becomes possible to increase the reluctance torque or to more smoothly demagnetize or magnetize the permanent magnet 2. Furthermore, since the width of the outer slit 22 is small at both ends in the circumferential direction of the permanent magnet 2, the proportion occupied by the rotor core 11 itself is large. Thereby, the strength of the rotor core 11 can be ensured. Also, by increasing the proportion occupied by the rotor core 11 itself in this way, it is possible to make it difficult for magnetic saturation to occur.

[0041] (3) In the electric motor 100 according to the third aspect, the permanent magnet 2 has a pair of unit magnets 21 that extend in a direction in which they are separated from each other in the circumferential direction as they extend from the inner side to the outer side in the radial direction.

[0042] According to the above configuration, the pair of unit magnets 21 extend in a direction in which they are separated from each other in the circumferential direction as they extend toward the outer side in the radial direction. That is, these unit magnets 21 are each directed toward the central portion in the circumferential direction. For this reason, the direction in which the outer slit 22 extends and the direction of the magnetic flux generated by the unit magnet 21 can be brought closer. As a result, the leakage magnetic flux can be further reduced.

[0043] (4) In the electric motor 100 according to the fourth aspect, the plurality of outer slits 22 linearly extend in a direction orthogonal to the outer surface of the unit magnet 21.

[0044] According to the above configuration, the outer slit 22 linearly extends in a direction orthogonal to the outer surface of the unit magnet 21. That is, the direction of the magnetic flux generated by the unit magnet 21 and the direction in which the outer slit 22 extends can be brought closer. As a result, the leakage magnetic flux can be more effectively reduced.

[0045] (5) In the electric motor 100 according to the fifth aspect, a plurality of inner slits 23 that extend in a curved shape from one of the pair of permanent magnets 2 toward the other permanent magnet 2 are formed on the inner circumferential side of the permanent magnet 2 in the rotor core 11, and the width of the inner slit 23 becomes smaller as it goes toward the outer side in the radial direction.

[0046] Here, the direction along the magnetic field of the permanent magnet 2 is defined as the d-axis, and the direction orthogonal to this d-axis is defined as the q-axis. In order to increase the reluctance torque, there is a requirement to reduce the magnetic resistance in the d-axis direction and increase the magnetic resistance in the q-axis direction. According to the above configuration, among the plurality of inner slits 23, the width of the inner slit 23 on the radially outer side is smaller. Thereby, the magnetic resistance in the q-axis direction can be increased. As a result, it becomes possible to increase the reluctance torque of the permanent magnet 2, or to demagnetize or magnetize the permanent magnet 2 more smoothly.

[0047] (6) In the motor 100 according to the sixth aspect, a portion of the outer peripheral surface 11S of the rotor core 11 corresponding to the permanent magnet 2 in the circumferential direction has a smaller radius of curvature than other portions of the outer peripheral surface 11S of the rotor core 11 and protrudes radially outward.

[0048] According to the above configuration, a portion of the outer peripheral surface 11S of the rotor core 11 corresponding to the permanent magnet 2 in the circumferential direction has a smaller radius of curvature than other portions and protrudes radially outward. Thereby, while maintaining the magnetic flux in the d-axis direction, the harmonic magnetic flux can be reduced. As a result, torque fluctuations (torque ripple) and the noise based thereon can be further reduced.

[0049] (7) In the motor 100 according to the seventh aspect, the permanent magnet 2 includes a variable magnet 21A capable of changing the magnetic force by magnetization or demagnetization, and a fixed magnet 21B provided on the radially outer side of the variable magnet 21A and having a constant magnetic force.

[0050] According to the above configuration, the permanent magnet 2 has a variable magnet 21A. By applying magnetization (or demagnetization) to the variable magnet 21A by a stator for magnetization, the magnetic force of the entire permanent magnet 2 can be changed. Thereby, it becomes possible to operate the motor 100 as a variable magnetic force motor.

Explanation of Reference Numerals

[0051] 100 Electric motor 1 Rotor 2, 2b Permanent magnet 3 Stator 11 Rotor core 11P Protrusion 11S Outer peripheral surface 21 Unit magnet 22 Outer slit 22A First outer slit 22B Second outer slit 22C Third outer slit 23 Inner slit 23A First inner slit 23B Second inner slit 23C Third inner slit 31 Back yoke 32 Teeth 33 Coil 34 Tooth tip Ac axis

Claims

1. A disk-shaped rotor core centered on an axis, a plurality of permanent magnets arranged circumferentially inside the rotor core, a stator that surrounds the rotor core and the permanent magnets from the outer peripheral side, and comprising, on the outer peripheral side of the permanent magnet in the rotor core, a plurality of outer slits are formed that extend in a direction approaching each other from both circumferential ends of the permanent magnet toward the radially outer side, An electric motor in which the width of the outer slit increases as it approaches the circumferential center of the permanent magnet throughout the circumferential direction of the permanent magnet.

2. The permanent magnet has a pair of unit magnets that extend in a direction separating from each other in the circumferential direction from the radially inner side to the outer side, The electric motor according to claim 1, wherein the length of the outer slit increases as it approaches the circumferential center of the permanent magnet.

3. The electric motor according to claim 2, wherein the plurality of outer slits extend linearly in a direction orthogonal to the outer surface of the unit magnet.

4. On the inner peripheral side of the permanent magnet in the rotor core, a plurality of inner slits are formed that extend curvilinearly from one of the pair of adjacent permanent magnets in the circumferential direction toward the other permanent magnet, The electric motor according to any one of claims 1 to 3, wherein the width of the inner slit decreases as it goes radially outward.

5. The portion of the outer peripheral surface of the rotor core corresponding to the permanent magnet in the circumferential direction has a smaller radius of curvature than other portions of the outer peripheral surface of the rotor core and protrudes radially outward. The electric motor according to any one of claims 1 to 4.

6. The permanent magnet is, a variable magnet capable of changing the magnetic force by magnetization or demagnetization, and a fixed magnet provided on the radially outer side of the variable magnet and having a constant magnetic force. The electric motor according to any one of claims 1 to 5.

Images