Motor and vehicle drive device

Abstract

A motor according to an aspect of the present invention is a motor capable of switching the number of poles, and comprises: a rotor that can rotate about a central axis; and a stator that is positioned on the outer side of the rotor in the radial direction. The stator has a stator core facing the rotor with a gap therebetween in the radial direction, and a plurality of coil parts. The stator core has an annular core back part, and a plurality of tooth parts that protrude radially inward from the inner circumferential surface of the core back part, and are arranged along the inner circumferential surface of the core back part. The plurality of coil parts are attached to the plurality of tooth parts. The ratio of a radial dimension of the core back part to the minimum dimension of each of the tooth parts in a direction orthogonal to the radial direction is 142-352%.

Description

Motor and vehicle drive device

[0001] The present invention relates to a motor and a vehicle drive device.

[0002] 2. Description of the Related Art Induction motors are known that include a stator core having a plurality of teeth and a yoke that connects the plurality of teeth to one another (for example, Japanese Patent Laid-Open Publication No. 10-080077).

[0003] Japanese Patent Publication No. 10-080077

[0004] In the induction motor described above, efficiency can be improved by appropriately setting the yoke width and the tooth width. Since the output torque of an induction motor varies depending on the rotor rotation speed, induction motors used over a wide range of rotation speeds are configured to switch the number of poles depending on the rotor rotation speed. In an induction motor with such a configuration, the optimal widths of the yoke and the tooth widths vary depending on the number of poles, so using a stator core optimized for a specific number of poles may result in a decrease in output torque for other numbers of poles.

[0005] In view of the above circumstances, one aspect of the present invention aims to provide a motor capable of switching the number of poles and capable of increasing output torque, and a vehicle drive device.

[0006] One aspect of the motor of the present invention is a motor capable of switching the number of poles, comprising a rotor rotatable about a central axis and a stator positioned radially outward of the rotor. The stator has a stator core facing the rotor with a gap in the radial direction, and a plurality of coil portions. The stator core has an annular core back portion and a plurality of teeth portions that protrude radially inward from the inner circumferential surface of the core back portion and are arranged along the inner circumferential surface of the core back portion. The plurality of coil portions are attached to the plurality of teeth portions. The ratio of the radial dimension of the core back portion to the smallest dimension of each of the plurality of teeth portions in a direction perpendicular to the radial direction is 142% or more and 352% or less.

[0007] One aspect of the motor of the present invention is a motor capable of switching the number of poles, comprising a rotor rotatable about a central axis and a stator positioned radially outward of the rotor. The stator has a stator core facing the rotor with a gap in the radial direction, and a plurality of coil portions. The stator core has an annular core back portion and a plurality of teeth protruding radially inward from an inner circumferential surface of the core back portion and arranged along the inner circumferential surface of the core back portion. The plurality of coil portions are attached to the plurality of teeth. The ratio of the radial dimension of the core back portion to the maximum dimension of each of the plurality of teeth in a direction perpendicular to the radial direction is 48% or more and 114% or less.

[0008] One aspect of the motor of the present invention is a motor capable of switching the number of poles, comprising: a rotor rotatable about a central axis; and a stator positioned radially outward of the rotor. The stator has a stator core facing the rotor with a gap in the radial direction; and a plurality of coil portions. The stator core has an annular core back portion and a plurality of teeth protruding radially inward from an inner circumferential surface of the core back portion and arranged along the inner circumferential surface of the core back portion. The plurality of coil portions are attached to the plurality of teeth. The ratio of the radial dimension of the core back portion to the average of the minimum dimension of each of the plurality of teeth in a direction perpendicular to the radial direction and the maximum dimension of each of the plurality of teeth in a direction perpendicular to the radial direction is 72% or more and 172% or less.

[0009] One aspect of a vehicle drive device of the present invention includes the motor described above and a control device that switches the number of poles configured in the stator of the motor depending on the state of the vehicle.

[0010] According to one aspect of the present invention, in a motor and a vehicle drive device, a reduction in output torque can be suppressed in a motor that is capable of switching the number of poles.

[0011] FIG. 1 is a schematic cross-sectional view showing a motor according to an embodiment. FIG. 2 is a cross-sectional view showing a portion of the motor according to an embodiment, taken along line II-II of FIG. 1. FIG. 3 is a cross-sectional view showing a portion of a stator core according to an embodiment. FIG. 4 is a cross-sectional view showing a first state of a stator according to an embodiment. FIG. 5 is a cross-sectional view showing a second state of a stator according to an embodiment. FIG. 6 is a diagram showing an example of output torque of a motor according to an embodiment. FIG. 7 is a first diagram showing maximum output torque of a motor according to an embodiment. FIG. 8 is a first diagram showing integrated torque values ​​of a motor according to an embodiment. FIG. 9 is a second diagram showing maximum output torque of a motor according to an embodiment. FIG. 10 is a second diagram showing integrated torque values ​​of a motor according to an embodiment. FIG. 11 is a third diagram showing maximum output torque of a motor according to an embodiment. FIG. 12 is a third diagram showing integrated torque values ​​of a motor according to an embodiment.

[0012] In the following description, the Z-axis is indicated in the figures where appropriate. The Z-axis is the direction in which the central axis J of the motor in the embodiment described below extends. The central axis J shown in each figure is a virtual axis. In the following description, the direction in which the central axis J extends, i.e., the direction parallel to the Z-axis, is referred to as the "axial direction." The radial direction centered on the central axis J is simply referred to as the "radial direction." The circumferential direction centered on the central axis J is simply referred to as the "circumferential direction." The side of the axial direction toward which the arrow of the Z-axis points (+Z side) is referred to as the "upper side." The side of the axial direction opposite to the side toward which the arrow of the Z-axis points (-Z side) is referred to as the "lower side." Note that the terms "upper side" and "lower side" are simply names used to describe the relative positional relationships of the various components, and the actual positional relationships may be other than those indicated by these names.

[0013] The circumferential direction is indicated by the arrow θ in each drawing. The side of the circumferential direction toward which the arrow θ points is called the "one circumferential side." The side of the circumferential direction opposite to the side toward which the arrow θ points is called the "other circumferential side." The one circumferential side is the side that moves clockwise around the central axis J when viewed from above (+θ side). The other circumferential side is the side that moves counterclockwise around the central axis J when viewed from above (-θ side).

[0014] The motor 10 of this embodiment shown in FIG. 1 is a motor that is attached to equipment mounted on a vehicle. The equipment to which the motor 10 is attached may be an automatic transmission or a vehicle drive system that drives the axles of the vehicle. In this embodiment, the motor 10 is attached to the vehicle drive system. That is, the vehicle drive system includes the motor 10. The motor 10 includes a housing 11, a rotor 20, a stator 30, a control device 50, a first bearing 15, and a second bearing 16.

[0015] The housing 11 accommodates the rotor 20, the stator 30, the first bearing 15, and the second bearing 16. The control device 50 may be disposed inside the housing 11 or outside the housing 11. In this embodiment, the control device 50 is disposed outside the housing 11. The housing 11 has a tubular portion 12, an upper cover portion 13, and a first bearing holder 14. The tubular portion 12 has a cylindrical shape extending in the axial direction about the central axis J. The tubular portion 12 is open on the upper side. The tubular portion 12 has a side wall portion 12a, a lower wall portion 12b, and a second bearing holder 12c.

[0016] The side wall portion 12a has a cylindrical shape extending in the axial direction around the central axis J. The side wall portion 12a surrounds the rotor 20, the stator 30, the first bearing 15, and the second bearing 16 from the radially outer side. The upper end of the side wall portion 12a is the upper end of the cylindrical portion 12. An opening 12d that opens upward is provided at the upper end of the side wall portion 12a.

[0017] The lower wall portion 12b has an annular plate shape centered on the central axis J. The plate surface of the lower wall portion 12b faces the axial direction. The radially outer end of the lower wall portion 12b is connected to the lower end of the side wall portion 12a. The lower wall portion 12b is provided with a lower wall hole 12e that penetrates the lower wall portion 12b in the axial direction. When viewed in the axial direction, the lower wall hole 12e has a circular shape centered on the central axis J.

[0018] The second bearing holder 12c protrudes upward from the outer edge of the lower wall hole 12e. The second bearing holder 12c is cylindrical and has a center on the central axis J. The second bearing holder 12c opens upward. The second bearing 16 is held on the inner circumferential surface of the second bearing holder 12c.

[0019] The upper cover portion 13 has a disk shape centered on the central axis J. The plate surface of the upper cover portion 13 faces the axial direction. The upper cover portion 13 is fixed to the upper end of the cylindrical portion 12. The upper cover portion 13 closes the opening 12d from above.

[0020] The first bearing holder 14 is fixed to a portion of the inner circumferential surface of the side wall portion 12a that is above the rotor 20 and the stator 30. The first bearing holder 14 has a substantially annular shape centered on the central axis J. The first bearing 15 is held on the inner circumferential surface of the first bearing holder 14.

[0021] The rotor 20 is rotatable about a central axis J. The rotor 20 includes a rotor core 21, a conductive member 24, and a shaft 26.

[0022] The rotor core 21 has a substantially annular shape centered on the central axis J. The rotor core 21 surrounds the shaft 26 from the radially outer side. The rotor core 21 is magnetic. For example, the rotor core 21 is a laminated steel plate formed by stacking multiple electromagnetic steel plates in the axial direction. As shown in FIG. 2 , the rotor core 21 has a rotor main body 22 and multiple rotor protrusions 23.

[0023] The rotor main body 22 has a substantially circular ring shape centered on the central axis J. A shaft 26 passes through the rotor main body 22 in the axial direction. The inner circumferential surface of the rotor main body 22 is fixed to the shaft 26. In this way, the shaft 26 is fixed to the rotor core 21.

[0024] Each of the multiple rotor protrusions 23 protrudes radially outward from the rotor main body 22. Each rotor protrusion 23 faces the stator 30 with a radial gap therebetween. The rotor protrusions 23 are arranged at intervals along the outer peripheral surface of the rotor main body 22. In this embodiment, the rotor core 21 has 34 rotor protrusions 23. The number of rotor protrusions 23 included in the rotor core 21 may be 33 or less, or 35 or more. Although not shown, in this embodiment, each rotor protrusion 23 is positioned toward one circumferential side (+θ side) as it extends downward. Each rotor protrusion 23 extends in a direction facing between the axial direction and the circumferential direction. Each rotor protrusion 23 may be positioned toward the other circumferential side (−θ side) as it extends downward. Each rotor protrusion 23 has a protrusion main body portion 23a and a protrusion umbrella portion 23b.

[0025] The protruding main body portion 23a protrudes radially inward from the outer peripheral surface of the rotor main body portion 22. When viewed in the axial direction, the protruding main body portion 23a has a generally rectangular shape with its long sides extending radially. The protruding main body portions 23a are spaced apart from one another along the circumferential direction. The protruding umbrella portion 23b is connected to the radially outer end of the protruding main body portion 23a. The protruding umbrella portion 23b extends in the circumferential direction. The surface of the protruding umbrella portion 23b facing radially outward is arc-shaped with the center axis J as its center. The end of the protruding umbrella portion 23b on one circumferential side (+θ side) is located on one circumferential side of the radially outer end of the protruding main body portion 23a. The end of the protruding umbrella portion 23b on the other circumferential side (-θ side) is located on the other circumferential side of the radially outer end of the protruding main body portion 23a. The protruding umbrella portions 23b are arranged at intervals from one another in the circumferential direction.

[0026] As shown in Fig. 1, the conductive member 24 is attached to the rotor core 21. The conductive member 24 is electrically conductive. The conductive member 24 may be made of a metal material such as aluminum. The conductive member 24 has a first end ring 24a and a second end ring 24b. As shown in Fig. 2, the conductive member 24 has a plurality of shaft portions 24c.

[0027] Each of the first end ring 24a and the second end ring 24b has an annular plate shape centered on the central axis J. A shaft 26 passes through each of the first end ring 24a and the second end ring 24b in the axial direction. The first end ring 24a is disposed above the rotor core 21. The first end ring 24a is attached to the surface of the rotor core 21 facing upward. The second end ring 24b is disposed below the rotor core 21. The second end ring 24b is attached to the surface of the rotor core 21 facing downward.

[0028] Each of the multiple shaft portions 24c connects the first end ring 24a and the second end ring 24b. As shown in FIG. 2, when viewed from the axial direction, each shaft portion 24c is substantially rectangular. The shaft portions 24c are spaced apart along the circumferential direction. The shaft portions 24c are disposed between the protruding main body portions 23a that are adjacent to each other in the circumferential direction. When viewed from the circumferential direction, each shaft portion 24c overlaps with the rotor core 21. Although not shown, in this embodiment, each shaft portion 24c is positioned toward one circumferential side (+θ side) as it extends downward. In other words, each shaft portion 24c extends in a direction facing between the axial direction and the circumferential direction. Each shaft portion 24c may be positioned toward the other circumferential side (−θ side) as it extends downward.

[0029] As shown in FIG. 1 , the shaft 26 has a generally cylindrical shape extending in the axial direction about the central axis J. The shaft 26 passes axially through the rotor core 21. The shaft 26 is fixed to the inner circumferential surface of the rotor core 21. An upper portion of the shaft 26 is supported by the first bearing 15 so as to be rotatable about the central axis J. A lower portion of the shaft 26 is supported by the second bearing 16 so as to be rotatable about the central axis J. As a result, the rotor 20 is rotatable about the central axis J. The lower end of the shaft 26 protrudes outside the housing 11 through the lower wall hole 12 e. A driven member (not shown) is attached to the lower end of the shaft 26, and the rotation of the rotor 20 is transmitted to the driven member.

[0030] The first bearing 15 rotatably supports an upper portion of the shaft 26. The second bearing 16 rotatably supports a lower portion of the shaft 26. In this embodiment, the first bearing 15 and the second bearing 16 are ball bearings. The first bearing 15 and the second bearing 16 may be rolling bearings other than ball bearings, or may be plain bearings.

[0031] The stator 30 is located radially outside the rotor 20. The stator 30 surrounds the rotor 20 from the radial outside. The stator 30 faces the rotor 20 with a gap in the radial direction. The stator 30 is fixed to the inner circumferential surface of the side wall portion 12a. The stator 30 has a stator core 31, an insulator 37, and a plurality of coil portions 38.

[0032] The stator core 31 has a generally annular shape extending in the axial direction about the central axis J. The stator core 31 faces the rotor 20 in the radial direction with a gap therebetween. The stator core 31 is magnetic. For example, the stator core 31 is a laminated steel plate formed by stacking multiple electromagnetic steel plates in the axial direction. As shown in FIG. 2 , the stator core 31 has a core back portion 32 and multiple stator protrusions 33.

[0033] The core back portion 32 has an annular shape centered on the central axis J. In the present embodiment, the core back portion 32 has a substantially circular shape centered on the central axis J. As shown in FIG. 1 , the outer peripheral surface of the core back portion 32 is fixed to the inner peripheral surface of the side wall portion 12 a. This fixes the stator 30 to the housing 11. In the following description, as shown in FIG. 3 , the radial dimension of the core back portion 32 may be referred to as the width Wb of the core back portion 32. More specifically, the radial dimension between the inner peripheral surface of the core back portion 32 between adjacent stator protrusions 33 and the outer peripheral surface of the core back portion 32 is referred to as the width Wb of the core back portion 32. In the present embodiment, the width Wb of the core back portion 32 is constant in the circumferential direction. However, if the width Wb of the core back portion 32 is not constant in the circumferential direction, the minimum radial dimension is defined as the width Wb of the core back portion 32.

[0034] As shown in FIG. 2 , each of the multiple stator protrusions 33 protrudes radially inward from the core back portion 32. Each stator protrusion 33 faces the rotor 20 with a radial gap therebetween. The stator protrusions 33 are arranged at intervals along the inner circumferential surface of the core back portion 32. In this embodiment, the stator core 31 has 36 stator protrusions 33. The number of stator protrusions 33 included in the stator core 31 may be 35 or less, or 37 or more. Each stator protrusion 33 has a tooth portion 34 and an umbrella portion 35.

[0035] Each tooth 34 protrudes radially inward from the core back portion 32. The teeth 34 are spaced apart from one another along the inner circumferential surface of the core back portion 32. As shown in FIG. 3 , when viewed from the axial direction, each tooth 34 has a generally trapezoidal shape whose dimensions in a direction perpendicular to the radial direction decrease toward the radially inner side. In the following description, the direction perpendicular to the axial direction and the radial direction may be referred to as a first direction D1. Each tooth 34 has a first portion 34a, a second portion 34b, and a third portion 34c.

[0036] The first portions 34a are the radially inner ends of the teeth 34. The dimensions of the teeth 34 in the first direction D1 are smallest at the first portions 34a. That is, the minimum dimension of the teeth 34 in the first direction D1, i.e., the direction perpendicular to the radial direction, is the dimension of the first portions 34a in the first direction D1. In the following description, the minimum dimension of the teeth 34 in the first direction D1, i.e., the dimension of the first portions 34a in the first direction D1, may be referred to as the minimum width Wmin of the teeth 34. In this embodiment, a first ratio R1, which is the ratio of the width Wb of the core back portion 32, i.e., the radial dimension of the core back portion, to the minimum width Wmin of the teeth 34, is 142% or more and 352% or less. Preferably, the first ratio R1 is 185% or more and 288% or less.

[0037] The second portions 34b are the radially outer ends of the teeth 34. The dimensions of the teeth 34 in the first direction D1 are greatest at the second portions 34b. That is, the maximum dimension of the teeth 34 in the first direction D1 is the dimension of the second portions 34b in the first direction D1. In the following description, the maximum dimension of the teeth 34 in the first direction D1, i.e., the dimension of the second portions 34b in the first direction D1, may be referred to as the maximum width Wmax of the teeth 34. In this embodiment, a second ratio R2, which is the ratio of the width Wb of the core back portion 32, i.e., the radial dimension of the core back portion, to the maximum width Wmax of the teeth 34, is 48% or greater and 114% or less. Preferably, the second ratio R2 is 63% or greater and 95% or less.

[0038] The third portion 34c is a portion of the tooth portion 34 between the first portion 34a and the second portion 34b in the radial direction. In this embodiment, the radial distance between the third portion 34c and the first portion 34a is the same as the radial distance between the third portion 34c and the second portion 34b. The dimension of the third portion 34c in the first direction D1 is the average dimension of the minimum width Wmin and the maximum width Wmax of the tooth portion 34. In other words, the dimension of the third portion 34c in the first direction D1 is the average dimension of the minimum dimension of the tooth portion 34 in a direction perpendicular to the radial direction and the maximum dimension of the tooth portion 34 in the direction perpendicular to the radial direction. In the following description, the dimension of the third portion 34c in the first direction D1 may be referred to as the average width Wave of the tooth portion 34. In this embodiment, a third ratio R3, which is the ratio of the width Wb of the core back portion 32, i.e., the radial dimension of the core back portion, to the average width Wave of the teeth 34, i.e., the average dimension of the minimum dimension of the teeth 34 in the direction perpendicular to the radial direction and the maximum dimension of the teeth 34 in the direction perpendicular to the radial direction, is 72% or more and 172% or less. Preferably, the third ratio R3 is 94% or more and 143% or less.

[0039] The umbrella portion 35 is connected to the radially inner end of the tooth portion 34. That is, the umbrella portion 35 is connected to the first portion 34a. The umbrella portion 35 extends in the circumferential direction. The surface of the umbrella portion 35 facing radially inward is arc-shaped with the center axis J as its center. As shown in FIG. 2 , the umbrella portion 35 faces the rotor core 21 with a radial gap. The end of the umbrella portion 35 on one circumferential side (+θ side) is located on one circumferential side of the first portion 34a. The end of the umbrella portion 35 on the other circumferential side (-θ side) is located on the other circumferential side of the first portion 34a. The umbrella portions 35 are spaced apart from one another in the circumferential direction. Note that the stator core 31 does not necessarily have to have the umbrella portion 35.

[0040] The insulator 37 shown in FIG. 1 insulates the stator core 31 from the coil portion 38. The insulator 37 has insulating properties. In this embodiment, the insulator 37 is made of resin. The insulator 37 is attached to each stator protrusion 33. Note that instead of the insulator 37, insulating paper may be placed between the stator core 31 and the coil portion 38.

[0041] Each of the multiple coil portions 38 is attached to a corresponding tooth portion 34 via an insulator 37. Although not shown in the figure, in this embodiment, each coil portion 38 is attached across multiple teeth portions 34. An alternating current is supplied to each coil portion 38 from an external power source (not shown). When the alternating current is supplied to each coil portion 38, multiple magnetic poles are formed in the stator core 31. That is, multiple magnetic poles are formed in the stator 30. Magnetic flux flows from each magnetic pole formed in the stator 30 into the rotor protrusion 23 of the rotor core 21. Furthermore, as described above, because each coil portion 38 shares an alternating current, when the magnetic force of each magnetic pole formed in the stator 30 fluctuates, the magnetic field around each shaft portion 24c of the conductive member 24 fluctuates, generating an induced current in each shaft portion 24c. Furthermore, when the induced current flowing through each shaft portion 24c fluctuates due to the fluctuation in the magnetic field around each shaft portion 24c of the conductive member 24, a magnetic flux is generated in each rotor protrusion 23. When an alternating current is supplied to each coil portion 38, a magnetic force is generated between the stator core 31 and the rotor core 21 in the circumferential direction, causing the rotor 20 to rotate about the central axis J.

[0042] The control device 50 controls the current supplied to each coil unit 38. The control device 50 is electrically connected to an external power source (not shown) and each coil unit 38. In this embodiment, the control device 50 generates a six-phase AC current from the current supplied from the external power source (not shown) and controls the AC current supplied to each coil unit 38. In this embodiment, the control device 50 controls the AC current supplied to each coil unit 38, thereby changing the number of magnetic poles configured in the stator 30 between four and eight. That is, the number of magnetic poles configured in the stator 30 is variable between four and eight. In other words, the motor 10 is capable of switching the number of poles. Furthermore, the control device 50 is capable of switching the number of poles configured in the stator 30 depending on the state of the vehicle. In the following description, the magnetic state of the stator 30 when four magnetic poles are configured in the stator 30 is referred to as a first state C1. Furthermore, the magnetic state of the stator 30 when eight magnetic poles are configured in the stator 30 is referred to as a second state C2. That is, in this embodiment, the magnetic state of the stator 30 can be changed between a first state C1 and a second state C2 by the control device 50.

[0043] As shown in FIG. 4 , in the first state C1, the stator 30 is configured with four magnetic poles M1. The magnetic poles M1 are configured to be spaced apart from one another in the circumferential direction. Each magnetic pole M1 is configured at a portion connecting four of the four stator protrusions 33 and the core back portion 32. The magnetic poles M1 that are configured adjacent to one another in the circumferential direction are magnetically connected via the core back portion 32. The four magnetic poles M1 include two north magnetic poles Mn1 and two south magnetic poles Ms1. The two north magnetic poles Mn1 are configured to face each other in the radial direction across the central axis J. The two south magnetic poles Ms1 are configured to face each other in the radial direction across the central axis J. The north magnetic poles Mn1 and south magnetic poles Ms1 are configured to alternate in the circumferential direction.

[0044] In each N magnetic pole Mn1, magnetic flux flows from the radially outer side to the radially inner side in each tooth 34n, and the magnetic flux flows from each tooth 34n into the rotor core 21. The magnetic flux flowing into the rotor core 21 flows from the rotor core 21 to each tooth 34s in each S magnetic pole Ms1. The magnetic flux flowing into each tooth 34s flows from the radially inner side to the radially outer side in each tooth 34s and flows into each tooth 34n of each N magnetic pole Mn1 via the core back portion 32. As a result, the magnetic flux of each magnetic pole M1 forms a magnetic loop circulating through the stator core 31 and the rotor core 21. Therefore, as described above, when an AC current is supplied to each coil portion 38, a magnetic force directed in the circumferential direction is generated between the stator core 31 and the rotor core 21, causing the rotor 20 to rotate about the central axis J. In the first state C1, the magnetic flux flowing through the core back portion 32 is the sum of the magnetic fluxes flowing through the two tooth portions 34. Therefore, in the first state C1, the magnetic flux flowing through the core back portion 32 is greater than the magnetic flux flowing through each tooth portion 34.

[0045] As shown in FIG. 5 , in the second state C2, the stator 30 is configured with eight magnetic poles M2. The magnetic poles M2 are configured with a circumferential gap between them. Each magnetic pole M2 is configured by two stator protrusions 33 and a portion of the core back portion 32 that connects the two stator protrusions 33. The magnetic poles M2 that are configured adjacent to each other in the circumferential direction are magnetically connected via the core back portion 32. The eight magnetic poles M2 include four north magnetic poles Mn2 and four south magnetic poles Ms2. The north magnetic poles Mn2 and south magnetic poles Ms2 are configured alternately in the circumferential direction.

[0046] In each N magnetic pole Mn2, magnetic flux flows from the radially outer side to the radially inner side in each tooth 34n, and the magnetic flux flows from each tooth 34n into the rotor core 21. The magnetic flux flowing into the rotor core 21 flows from the rotor core 21 into each tooth 34s of each pair of S magnetic poles Ms2 configured adjacent to each other in the circumferential direction. The magnetic flux flowing into each tooth 34s flows from the radially inner side to the radially outer side in each tooth 34s and flows via the core back portion 32 into each tooth 34n of each pair of N magnetic poles Mn2 configured adjacent to each other in the circumferential direction. As a result, the magnetic flux of each magnetic pole M2 forms a magnetic loop circulating through the stator core 31 and the rotor core 21. Therefore, as described above, when an AC current is supplied to each coil portion 38, a magnetic force directed in the circumferential direction is generated between the stator core 31 and the rotor core 21, causing the rotor 20 to rotate about the central axis J. In the second state C2, magnetic flux flows through one tooth portion 34 in the core back portion 32. Therefore, in the second state C2, the magnetic flux flowing through the core back portion 32 is the same as the magnetic flux flowing through each tooth portion 34. In the second state C2, the magnetic flux flowing through each tooth portion 34 is greater than the magnetic flux flowing through each tooth portion 34 in the first state C1. In addition, in the first state C1, the magnetic flux flowing through the core back portion 32 is greater than the magnetic flux flowing through the core back portion 32 in the second state C2.

[0047] The above description has been given of the amount of magnetic flux flowing through the core back portion 32 and each of the teeth 34 in each of the first state C1 and the second state C2 of the stator core 31 having 36 stator protrusions 33. Even if the number of stator protrusions 33 in the stator core 31 and the number of stator protrusions 33 constituting each of the magnetic poles M1 and M2 differ from those in this embodiment, the amount of magnetic flux flowing through the core back portion 32 in the first state C1 will be relatively large, and the amount of magnetic flux flowing through each of the teeth 34 in the second state C2 will be relatively large.

[0048] Figure 6 is a diagram showing an example of the output torque of the motor 10 of this embodiment. The horizontal axis of Figure 6 represents the rotation speed Nr of the rotor 20. The vertical axis of Figure 6 represents the output torque Tm of the motor 10. The first output torque S1 is the output torque of the motor 10 in the first state C1, i.e., when the stator 30 is configured with four magnetic poles M1. The second output torque S2 is the output torque of the motor 10 in the second state C2, i.e., when the stator 30 is configured with eight magnetic poles M1.

[0049] The first output torque S1 is substantially constant from the low rotation speed Nr to the first rotation speed Nr1, and decreases as the rotation speed Nr increases when the rotation speed Nr exceeds the first rotation speed Nr1. The second output torque S2 is substantially constant from the low rotation speed Nr to the second rotation speed Nr2, which is a rotation speed lower than the first rotation speed Nr1, and decreases as the rotation speed Nr increases when the rotation speed Nr exceeds the second rotation speed Nr2. The second output torque S2 is greater than the first output torque S1 at rotation speeds Nr lower than the first rotation speed Nr1 and lower than a third rotation speed Nr3, which is a rotation speed higher than the second rotation speed Nr2. The second output torque S2 is smaller than the first output torque S1 at rotation speeds Nr higher than the third rotation speed Nr3. Therefore, when the rotor 20 is rotated at a low speed lower than the third rotation speed Nr3, the number of poles of the stator 30 is set to eight, and when the rotor 20 is rotated at a high speed higher than the third rotation speed Nr3, the number of magnetic poles of the stator 30 is set to four, thereby increasing the output torque of the motor 10 from the low speed range to the high speed range. In this embodiment, the maximum torque Tmax of the motor 10 is the maximum torque of the first output torque S1.

[0050] As described above, at rotational speeds Nr lower than the third rotational speed Nr3, the second output torque S2 is greater than the first output torque S1. Here, the torque obtained by integrating the torque difference between the second output torque S2 and the first output torque S1 at rotational speeds Nr lower than the third rotational speed Nr3 is referred to as the first torque integrated value T1. The first torque integrated value T1 corresponds to the area surrounded by the second output torque S2 and the first output torque S1 at rotational speeds Nr lower than the third rotational speed Nr3. The first torque integrated value T1 is the torque obtained by changing the magnetic state of the stator 30 from the first state C1 to the second state C2. Therefore, the larger the first torque integrated value T1, the more effective it is to switch the number of poles of the stator 30 from four to eight by the control device 50 at rotational speeds Nr lower than the third rotational speed Nr3.

[0051] As described above, at rotational speeds Nr greater than the third rotational speed Nr3, the second output torque S2 is smaller than the first output torque S1. The torque obtained by integrating the torque difference between the first output torque S1 and the second output torque S2 at rotational speeds Nr greater than the third rotational speed Nr3 is referred to as the second torque integrated value T2. The second torque integrated value T2 corresponds to the area surrounded by the first output torque S1 and the second output torque S2 at rotational speeds Nr greater than the third rotational speed Nr3. The second torque integrated value T2 is the torque obtained by changing the magnetic state of the stator 30 from the second state C2 to the first state C1. Therefore, the larger the second torque integrated value T2, the more effectively the control device 50 can switch the number of poles of the stator 30 from eight to four at rotational speeds Nr greater than the third rotational speed Nr3.

[0052] The sum of the first torque accumulation value T1 and the second torque accumulation value T2 is referred to as a total torque accumulation value Tsum. The larger the total torque accumulation value Tsum, the more effective it is for the control device 50 to determine whether switching the number of poles of the stator 30 between four and eight.

[0053] FIG. 7 is a first diagram showing the maximum torque Tmax of the motor 10 of this embodiment. The horizontal axis of FIG. 7 represents the first ratio R1, i.e., the ratio of the width Wb of the core back portion 32 to the minimum width Wmin of the teeth portion 34. In this embodiment, stator cores 31 with different first ratios R1 are manufactured by varying the minimum width Wmin of the teeth portion 34 and the width Wb of the core back portion 32 while maintaining the outer diameter, inner diameter (the diameter of an imaginary circle connecting the tips of the multiple umbrella portions 35), number of stator protrusions 33, and cross-sectional area of ​​the stator core 31 constant. Furthermore, the volume of each stator core 31 with a different first ratio R1 is constant. The larger the first ratio R1 of a stator core 31, the narrower the minimum width Wmin of the teeth portion 34 and the wider the width Wb of the core back portion 32. The vertical axis of FIG. 7 represents the maximum torque Tmax of the motor 10. The maximum torque Tmax increases as the first ratio R1 increases when the first ratio R1 is less than approximately 250%, and decreases as the first ratio R1 increases when the first ratio R1 is equal to or greater than approximately 250%. When the first ratio R1 is less than 142%, the width Wb of the core back portion 32 becomes too small, resulting in too little magnetic flux passing through the core back portion 32. As a result, too little magnetic flux flows between the stator core 31 and the rotor core 21, and the magnetic force between the stator core 31 and the rotor core 21 becomes too small. Therefore, the maximum torque Tmax becomes too small.

[0054] FIG. 8 is a first diagram showing the torque accumulation value of the motor 10 of this embodiment. The horizontal axis of FIG. 8 represents the first ratio R1. The vertical axis of FIG. 8 represents the torque accumulation value. The first torque accumulation value T1 increases as the first ratio R1 increases when the first ratio R1 is less than 142%. However, once the first ratio R1 exceeds approximately 142%, the first torque accumulation value T1 decreases as the first ratio R1 increases. As described above, the magnetic flux flowing through each tooth 34 in the second state C2 is greater than the magnetic flux flowing through each tooth 34 in the first state C1. Therefore, as the first ratio R1 increases, the minimum width Wmin of each tooth 34 narrows, which increases the magnetic flux leakage from each tooth 34 in the second state C2. As a result, the magnetic flux flowing between the stator core 31 and the rotor core 21 decreases, resulting in a decrease in the second output torque S2. Therefore, when the first ratio R1 becomes larger than approximately 142%, the first torque integrated value T1 decreases as the first ratio R1 increases.

[0055] The second torque integrated value T2 increases as the first ratio R1 increases when the first ratio R1 is 352% or less, and remains substantially constant when the first ratio R1 is greater than 352%. As described above, the magnetic flux flowing through the core back portion 32 in the first state C1 is greater than the magnetic flux flowing through the core back portion 32 in the second state C2. Therefore, when the width Wb of the core back portion 32 narrows as the first ratio R1 decreases, magnetic flux is more likely to leak from the core back portion 32 in the first state C1. This reduces the magnetic flux flowing between the stator core 31 and the rotor core 21, thereby reducing the first output torque S1. Therefore, when the first ratio R1 is 352% or less, the second torque integrated value T2 decreases as the first ratio R1 decreases.

[0056] When the first ratio R1 is less than approximately 250%, the total torque integrated value Tsum increases as the first ratio R1 increases. When the first ratio R1 is approximately 250% or greater, the total torque integrated value Tsum decreases as the first ratio R1 increases. When the first ratio R1 is less than approximately 250%, the decrease in the second torque integrated value T2, which decreases as the first ratio R1 decreases, is greater than the increase in the first torque integrated value T1, which increases as the first ratio R1 decreases. Therefore, the total torque integrated value Tsum decreases as the first ratio R1 decreases. Furthermore, when the first ratio R1 is approximately 250% or greater, the decrease in the first torque integrated value T1, which decreases as the first ratio R1 increases, is greater than the increase in the second torque integrated value T2, which increases as the first ratio R1 increases. Therefore, the total torque integrated value Tsum decreases as the first ratio R1 increases. When the first ratio R1 is equal to or greater than 142% and equal to or less than 352%, the total torque integrated value Tsum can be prevented from becoming too small, and the total torque integrated value Tsum can be increased. When the first ratio R1 is equal to or greater than 185% and equal to or less than 288%, the total torque integrated value Tsum can be increased more suitably.

[0057] As shown in FIG. 7 , the first ratio R1 at which the maximum torque Tmax is maximized is in the range of 237% to 288%. Also, as shown in FIG. 8 , the first ratio R1 at which the total integrated torque value Tsum is maximized is in the range of 185% to 237%. That is, in this embodiment, the first ratio R1 at which the maximum torque Tmax is maximized is different from the first ratio R1 at which the total integrated torque value Tsum is maximized. Even in this case, if the first ratio R1 is in the range of 185% to 288%, the maximum torque Tmax and the total integrated torque value Tsum can be maximized or close to their maximum values, thereby enhancing the effect of switching the number of poles. This allows the first ratio R1 to be appropriately selected in the range of 185% to 288% based on the desired specifications of the motor 10 and on the manufacturing aspects of the motor 10. In particular, when optimizing the effect of switching the number of poles, it is desirable to set the first ratio R1 in the range of 185% to 237%.

[0058] According to this embodiment, in the motor 10 capable of switching the number of poles, the stator 30 includes a stator core 31 that faces the rotor 20 across a radial gap, and multiple coil portions 38. The stator core 31 includes an annular core back portion 32 and multiple teeth 34 that protrude radially inward from the inner circumferential surface of the core back portion 32 and are arranged along the inner circumferential surface of the core back portion 32. The multiple coil portions 38 are attached to the multiple teeth 34. The first ratio R1, i.e., the ratio of the radial dimension of the core back portion 32 to the minimum dimension of each of the multiple teeth 34 in a direction perpendicular to the radial direction, is 142% or more and 352% or less. As described above, if the first ratio R1 is less than 142%, the width Wb of the core back portion 32 becomes too narrow, resulting in too little magnetic flux passing through the core back portion 32. As a result, too little magnetic flux flows between the stator core 31 and the rotor core 21, resulting in too little maximum torque Tmax. Furthermore, when the first ratio R1 is greater than 352%, as described above, the minimum width Wmin of each tooth portion 34 becomes too narrow, making it easier for magnetic flux to leak from each tooth portion 34 in the second state C2. This results in too little magnetic flux flowing between the stator core 31 and the rotor core 21, resulting in a small second output torque S2. Consequently, the first torque integrated value T1 becomes too small, resulting in too little total torque integrated value Tsum. This makes it difficult to enhance the effectiveness of switching the number of poles of the stator 30. In contrast, in this embodiment, the first ratio R1 is greater than or equal to 142% and less than or equal to 352%, preventing the width Wb of the core back portion 32 from becoming too narrow. This prevents the magnetic flux passing through the core back portion 32 from becoming too small. This prevents the magnetic flux flowing between the stator core 31 and the rotor core 21 from becoming too small, thereby increasing the maximum torque Tmax. Furthermore, since the minimum width Wmin of each tooth 34 can be prevented from becoming too narrow, in the second state C2, it is easy to prevent magnetic flux from leaking from each tooth 34. This makes it possible to prevent the magnetic flux flowing between the stator core 31 and the rotor core 21 from becoming too small.Therefore, as described above, the first torque integrated value T1 can be prevented from becoming too small, thereby increasing the total torque integrated value Tsum. This increases the effect of switching the number of poles of the stator 30. Therefore, the effect of switching the number of poles of the stator 30 can be increased while increasing the maximum torque Tmax. This increases the output torque of the motor 10, which is capable of switching the number of poles. Furthermore, it increases the output torque of a vehicle drive device equipped with the motor 10.

[0059] According to this embodiment, the first ratio R1, i.e., the ratio of the radial dimension of the core back portion 32 to the minimum dimension of each of the multiple teeth 34 in a direction perpendicular to the radial direction, is 185% or more and 288% or less. Therefore, the width Wb of the core back portion 32 can be more effectively prevented from becoming too narrow, and the magnetic flux passing through the core back portion 32 can be more effectively prevented from becoming too small. This can more effectively increase the maximum torque Tmax. Furthermore, the minimum width Wmin of each tooth 34 can be more effectively prevented from becoming too narrow, and therefore, in the second state C2, magnetic flux leakage from each tooth 34 can be more effectively prevented. This can more effectively increase the total torque integrated value Tsum, and more effectively enhance the effect of switching the number of poles of the stator 30. Therefore, the effect of switching the number of poles of the stator 30 can be more effectively enhanced while more effectively increasing the maximum torque Tmax. Therefore, the output torque of the motor 10 capable of switching the number of poles can be more effectively increased.

[0060] FIG. 9 is a second graph showing the maximum torque Tmax of the motor 10 of this embodiment. The horizontal axis of FIG. 9 represents the second ratio R2, i.e., the ratio of the width Wb of the core back portion 32 to the maximum width Wmax of the teeth portion 34. In this embodiment, stator cores 31 with different second ratios R2 are manufactured by varying the maximum width Wmax of the teeth portion 34 and the width Wb of the core back portion 32 while maintaining the outer diameter, inner diameter, number of stator protrusions 33, and cross-sectional area of ​​the stator core 31 constant. Furthermore, the volume of each stator core 31 with different second ratios R2 is constant. Therefore, the larger the second ratio R2 of a stator core 31, the narrower the maximum width Wmax of the teeth portion 34 and the wider the width Wb of the core back portion 32. The vertical axis of FIG. 9 represents the maximum torque Tmax of the motor 10. In this embodiment, the relationship between the second ratio R2 and the maximum torque Tmax is similar to the relationship between the first ratio R1 and the maximum torque Tmax described above, and therefore redundant description may be omitted. When the second ratio R2 is less than approximately 75%, the maximum torque Tmax increases as the second ratio R2 increases. When the second ratio R2 is approximately 75% or greater, the maximum torque Tmax decreases as the second ratio R2 increases. When the second ratio R2 is less than 48%, the width Wb of the core back portion 32 becomes too small, resulting in too little magnetic flux passing through the core back portion 32. This results in too little magnetic flux flowing between the stator core 31 and the rotor core 21, and therefore the maximum torque Tmax becomes too small.

[0061] FIG. 10 is a second diagram showing the torque accumulation value of the motor 10 of this embodiment. The horizontal axis of FIG. 10 represents the second ratio R2. The vertical axis of FIG. 10 represents the torque accumulation value. In this embodiment, the relationships of the first torque accumulation value T1, the second torque accumulation value T2, and the total torque accumulation value Tsum with respect to the second ratio R2 are similar to the relationships of the first torque accumulation value T1, the second torque accumulation value T2, and the total torque accumulation value Tsum with respect to the first ratio R1 described above, and therefore, redundant explanations may be omitted. When the second ratio R2 is less than 48%, the first torque accumulation value T1 increases as the second ratio R2 increases. When the second ratio R2 is greater than 48%, the first torque accumulation value T1 decreases as the second ratio R2 increases. When the maximum width Wmax of each tooth 34 is narrowed, magnetic flux is more likely to leak from each tooth 34 in the second state C2, and the second output torque S2 is reduced. Therefore, when the second ratio R2 is greater than 48%, the first torque integrated value T1 decreases as the second ratio R2 increases.

[0062] The second torque integrated value T2 increases as the second ratio R2 increases when the second ratio R2 is 114% or less, and remains substantially constant when the second ratio R2 is greater than 114%. As described above, when the width Wb of the core back portion 32 is narrowed, magnetic flux is more likely to leak from the core back portion 32 in the first state C1, which reduces the first output torque S1. Therefore, when the second ratio R2 is 114% or less, the second torque integrated value T2 decreases as the second ratio R2 decreases.

[0063] The total torque integrated value Tsum increases as the second ratio R2 increases when the second ratio R2 is less than approximately 75%, and increases as the second ratio R2 increases when the second ratio R2 is approximately 75% or greater. Note that when the second ratio R2 is 48% or greater and 114% or less, the total torque integrated value Tsum can be prevented from becoming too small, and the total torque integrated value Tsum can be increased. Furthermore, when the second ratio R2 is 63% or greater and 95% or less, the total torque integrated value Tsum can be more suitably increased.

[0064] As shown in FIG. 9 , the second ratio R2 at which the maximum torque Tmax is maximized is in the range of 79% to 95%. Also, as shown in FIG. 10 , the second ratio R2 at which the total integrated torque value Tsum is maximized is in the range of 63% to 79%. Therefore, if the second ratio R2 is in the range of 63% to 95%, the maximum torque Tmax and the total integrated torque value Tsum can be maximized or close to their maximum values, thereby enhancing the effect of switching the number of poles. In particular, to optimize the effect of switching the number of poles, it is desirable to set the second ratio R2 in the range of 63% to 79%.

[0065] According to this embodiment, the second ratio R2, i.e., the ratio of the radial dimension of the core back portion 32 to the maximum dimension of each of the multiple teeth 34 in a direction perpendicular to the radial direction, is 48% or more and 114% or less. As described above, when the second ratio R2 is less than 48%, the width Wb of the core back portion 32 becomes too narrow, resulting in too little magnetic flux passing through the core back portion 32. As a result, too little magnetic flux flows between the stator core 31 and the rotor core 21, resulting in too little maximum torque Tmax. Furthermore, when the second ratio R2 is greater than 114%, as described above, the minimum width Wmin of each tooth 34 becomes too narrow, resulting in more magnetic flux leakage from each tooth 34 in the second state C2. As a result, too little magnetic flux flows between the stator core 31 and the rotor core 21, resulting in a small second output torque S2. Therefore, the first torque accumulated value T1 becomes too small, and the total torque accumulated value Tsum becomes too small. This makes it difficult to enhance the effect of switching the number of poles of the stator 30. In contrast, in the present embodiment, the second ratio R2 is 48% or more and 114% or less, which prevents the width Wb of the core back portion 32 from becoming too narrow. This prevents the magnetic flux passing through the core back portion 32 from becoming too small. This prevents the magnetic flux flowing between the stator core 31 and the rotor core 21 from becoming too small, thereby increasing the maximum torque Tmax. Furthermore, this prevents the maximum width Wmax of each tooth portion 34 from becoming too narrow, which makes it easier to prevent magnetic flux leakage from each tooth portion 34 in the second state C2. This prevents the magnetic flux flowing between the stator core 31 and the rotor core 21 from becoming too small. Therefore, as described above, the first torque accumulated value T1 can be prevented from becoming too small, thereby increasing the total torque accumulated value Tsum. This increases the effect of switching the number of poles of the stator 30. Therefore, the effect of switching the number of poles of the stator 30 can be increased while increasing the maximum torque Tmax. Therefore, the output torque can be increased in the motor 10 that can switch the number of poles. Furthermore, the output torque can be increased in a vehicle drive device that includes the motor 10.

[0066] According to this embodiment, the second ratio R2, i.e., the ratio of the radial dimension of the core back portion 32 to the maximum dimension of each of the multiple teeth 34 in a direction perpendicular to the radial direction, is 63% or more and 95% or less. Therefore, the width Wb of the core back portion 32 can be more effectively prevented from becoming too narrow, and the magnetic flux passing through the core back portion 32 can be more effectively prevented from becoming too small. This can more effectively increase the maximum torque Tmax. Furthermore, the maximum width Wmax of each tooth 34 can be more effectively prevented from becoming too narrow, and therefore, in the second state C2, magnetic flux leakage from each tooth 34 can be more effectively prevented. This can more effectively increase the total torque integrated value Tsum, and more effectively enhance the effect of switching the number of poles of the stator 30. Therefore, the effect of switching the number of poles of the stator 30 can be more effectively enhanced while more effectively increasing the maximum torque Tmax. Therefore, the output torque of the motor 10 capable of switching the number of poles can be more effectively increased.

[0067] FIG. 11 is a third diagram showing the maximum torque Tmax of the motor 10 of this embodiment. The horizontal axis of FIG. 11 represents the third ratio R3, i.e., the ratio of the width Wb of the core back portion 32 to the average width Wave of the teeth 34. In this embodiment, stator cores 31 with different third ratios R3 are manufactured by varying the average width Wave of the teeth 34 and the width Wb of the core back portion 32 while maintaining the outer diameter, inner diameter, number of stator protrusions 33, and cross-sectional area of ​​the stator core 31 constant. Furthermore, the volume of each stator core 31 with a different third ratio R3 is constant. Therefore, the larger the third ratio R3 of a stator core 31, the narrower the average width Wave of the teeth 34 and the wider the width Wb of the core back portion 32. The vertical axis of FIG. 11 represents the maximum torque Tmax of the motor 10. In this embodiment, the relationship between the third ratio R3 and the maximum torque Tmax is similar to the relationship between the first ratio R1 and the maximum torque Tmax described above, and therefore redundant description may be omitted. When the third ratio R3 is less than approximately 125%, the maximum torque Tmax increases as the third ratio R3 increases. When the third ratio R3 is approximately 125% or greater, the maximum torque Tmax decreases as the third ratio R3 increases. When the third ratio R3 is less than 72%, the width Wb of the core back portion 32 becomes too small, resulting in too little magnetic flux passing through the core back portion 32. As a result, too little magnetic flux flows between the stator core 31 and the rotor core 21, and the maximum torque Tmax becomes too small.

[0068] FIG. 12 is a third diagram showing the torque accumulation value of the motor 10 of this embodiment. The horizontal axis of FIG. 12 represents the third ratio R3. The vertical axis of FIG. 12 represents the torque accumulation value. In this embodiment, the relationships of the first torque accumulation value T1, the second torque accumulation value T2, and the total torque accumulation value Tsum with respect to the third ratio R3 are similar to the relationships of the first torque accumulation value T1, the second torque accumulation value T2, and the total torque accumulation value Tsum with respect to the first ratio R1 described above, and therefore, redundant explanations may be omitted. When the third ratio R3 is less than 94%, the first torque accumulation value T1 increases as the third ratio R3 increases. When the third ratio R3 is greater than 94%, the first torque accumulation value T1 decreases as the third ratio R3 increases. When the average width Wave of each tooth 34 becomes narrower, magnetic flux is more likely to leak from each tooth 34 in the second state C2, and the second output torque S2 becomes smaller. Therefore, when the third ratio R3 becomes greater than 94%, the first torque integrated value T1 decreases as the third ratio R3 increases.

[0069] The second torque integrated value T2 increases as the third ratio R3 increases when the third ratio R3 is 172% or less, and remains substantially constant when the third ratio R3 is greater than 172%. As described above, when the width Wb of the core back portion 32 is narrowed, magnetic flux is more likely to leak from the core back portion 32 in the first state C1, which reduces the first output torque S1. Therefore, when the third ratio R3 is 172% or less, the second torque integrated value T2 decreases as the third ratio R3 decreases.

[0070] The total torque integrated value Tsum increases as the third ratio R3 increases when the third ratio R3 is less than 94%, and increases as the third ratio R3 increases when the third ratio R3 is 94% or greater. When the third ratio R3 is 72% or greater and 172% or less, the total torque integrated value Tsum can be prevented from becoming too small, allowing the total torque integrated value Tsum to be increased. Furthermore, when the third ratio R3 is 94% or greater and 143% or less, the total torque integrated value Tsum can be more suitably increased.

[0071] As shown in FIG. 11 , the third ratio R3 at which the maximum torque Tmax is maximized is in the range of 119% to 143%. Also, as shown in FIG. 12 , the third ratio R3 at which the total torque integrated value Tsum is maximized is in the range of 94% to 119%. Therefore, if the third ratio R3 is in the range of 94% to 143%, the maximum torque Tmax and the total torque integrated value Tsum can be maximized or close to their maximum values, thereby enhancing the effect of switching the number of poles. In particular, to optimize the effect of switching the number of poles, it is desirable to set the third ratio R3 in the range of 94% to 119%.

[0072] According to this embodiment, the third ratio R3, i.e., the ratio of the radial dimension of the core back portion 32 to the average of the minimum dimension of the teeth 34 in a direction perpendicular to the radial direction and the maximum dimension of the teeth 34 in a direction perpendicular to the radial direction, is 72% or more and 172% or less. As described above, when the third ratio R3 is less than 72%, the width Wb of the core back portion 32 becomes too narrow, resulting in too little magnetic flux passing through the core back portion 32. As a result, too little magnetic flux flows between the stator core 31 and the rotor core 21, resulting in too little maximum torque Tmax. Furthermore, when the third ratio R3 is greater than 172%, as described above, the minimum width Wmin of each tooth 34 becomes too narrow, resulting in more magnetic flux leakage from each tooth 34 in the second state C2. As a result, too little magnetic flux flows between the stator core 31 and the rotor core 21, resulting in too little total torque integrated value Tsum. This makes it difficult to enhance the effect of switching the number of poles of the stator 30. In contrast, in the present embodiment, the third ratio R3 is greater than or equal to 72% and less than or equal to 172%, which prevents the width Wb of the core back portion 32 from becoming too narrow. This prevents the magnetic flux passing through the core back portion 32 from becoming too small, thereby increasing the maximum torque Tmax. Furthermore, this prevents the average width Wave of each tooth portion 34 from becoming too narrow, which makes it easier to prevent magnetic flux from leaking from each tooth portion 34 in the second state C2. As described above, this prevents the first torque accumulation value T1 from becoming too small, thereby increasing the total torque accumulation value Tsum. This enhances the effect of switching the number of poles of the stator 30. This enhances the effect of switching the number of poles of the stator 30 while increasing the maximum torque Tmax. This allows the motor 10, which is capable of switching the number of poles, to more suitably increase its output torque. Furthermore, this allows the output torque to be increased in a vehicle drive device including the motor 10.

[0073] According to this embodiment, the ratio of the radial dimension of the core back portion 32 to the third ratio R3 is 94% or more and 143% or less. Therefore, the width Wb of the core back portion 32 can be more effectively prevented from becoming too narrow, and the magnetic flux passing through the core back portion 32 can be more effectively prevented from becoming too small. This can more effectively increase the maximum torque Tmax. Furthermore, the average width Wave of each tooth portion 34 can be more effectively prevented from becoming too narrow, and therefore, in the second state C2, leakage of magnetic flux from each tooth portion 34 can be more effectively prevented. This can more effectively increase the total torque integrated value Tsum, and more effectively enhance the effect of switching the number of poles of the stator 30. Therefore, the effect of switching the number of poles of the stator 30 can be more effectively enhanced while more effectively increasing the maximum torque Tmax. Therefore, the output torque of the motor 10 capable of switching the number of poles can be more effectively increased.

[0074] According to this embodiment, the number of poles configured in the stator 30 can be changed to 4 or 8. Therefore, as described above, when the rotor 20 is rotated at a low speed, the number of poles of the stator 30 is set to 8, and when the rotor 20 is rotated at a high speed, the magnetic poles of the stator 30 are set to 4, thereby increasing the output torque from the low speed range to the high speed range in the motor 10 in which the number of poles can be changed.

[0075] The present invention is not limited to the above-described embodiment, and other configurations and methods may be adopted within the scope of the technical concept of the present invention. For example, the number of poles of the stator is not limited to the present embodiment, and may be, for example, three or six, or five or ten. Furthermore, the stator core may be a stator core used in a motor with an outer rotor configuration, in which the stator core is disposed radially inside the rotor and the teeth protrude radially outward.

[0076] The shape of the umbrella portion is not limited to that of this embodiment, and may be other shapes, such as a substantially rectangular shape that protrudes in the circumferential direction when viewed from the axial direction.

[0077] A motor to which the present invention is applied is used, for example, in a vehicle drive system that rotates the axle of a vehicle. In such applications, motor torque is required when the vehicle is starting and when the vehicle is running at low speeds, and motor rotation speed is required when the vehicle is running at high speeds. Therefore, by switching the number of poles configured in the stator of the motor according to the vehicle state, a control device can maintain high torque and rotation speed output characteristics even in various vehicle states. This is expected to contribute to the vehicle's lifespan and cruising range. The control device may be, for example, an on-board ECU or a controller directly mounted on the vehicle drive system.

[0078] Regardless of the above, the use of the motor to which the present invention is applied is not particularly limited. For example, the motor may be mounted in a vehicle for an application other than a vehicle drive device, or may be mounted in equipment other than a vehicle. The configurations described above in this specification can be combined as appropriate within a range that does not contradict each other.

[0079] The present technology can be configured as follows: (1) A motor capable of switching the number of poles, the motor including: a rotor rotatable about a central axis; and a stator positioned radially outward of the rotor, the stator having a stator core facing the rotor across a radial gap, and a plurality of coil portions, the stator core having an annular core back portion and a plurality of teeth protruding radially inward from an inner circumferential surface of the core back portion and arranged along the inner circumferential surface of the core back portion, the plurality of coil portions being attached to the plurality of teeth, a ratio of a radial dimension of the core back portion to a minimum dimension of each of the plurality of teeth in a direction perpendicular to the radial direction being 142% or more and 352% or less. (2) The motor described in (1), wherein a ratio of a radial dimension of the core back portion to a minimum dimension of each of the plurality of teeth in a direction perpendicular to the radial direction is 185% or more and 288% or less. (3) The motor according to (1) or (2), wherein a ratio of a radial dimension of the core back portion to a minimum dimension of each of the plurality of teeth in a direction perpendicular to the radial direction is 185% or more and 237% or less. (4) A motor capable of switching the number of poles, comprising: a rotor rotatable about a central axis; and a stator positioned radially outward of the rotor, wherein the stator has a stator core facing the rotor with a gap in the radial direction, and a plurality of coil portions, the stator core having an annular core back portion and a plurality of teeth protruding radially inward from an inner peripheral surface of the core back portion and arranged along the inner peripheral surface of the core back portion, the plurality of coil portions being attached to the plurality of teeth, wherein a ratio of a radial dimension of the core back portion to a maximum dimension of each of the plurality of teeth in a direction perpendicular to the radial direction is 48% or more and 114% or less. (5) The motor according to (4), wherein a ratio of the radial dimension of the core back portion to a maximum dimension of each of the plurality of teeth in a direction perpendicular to the radial direction is 63% or more and 95% or less. (6) The motor according to (4) or (5), wherein a ratio of the radial dimension of the core back portion to a maximum dimension of each of the plurality of teeth in a direction perpendicular to the radial direction is 63% or more and 79% or less.(7) A motor capable of switching the number of poles, comprising: a rotor rotatable about a central axis; and a stator positioned radially outward of the rotor, wherein the stator has a stator core facing the rotor across a radial gap, and a plurality of coil portions, wherein the stator core has an annular core back portion and a plurality of teeth portions that protrude radially inward from an inner peripheral surface of the core back portion and are arranged along the inner peripheral surface of the core back portion, wherein the plurality of coil portions are attached to the plurality of teeth portions, and wherein a ratio of a radial dimension of the core back portion to an average dimension of a minimum dimension of each of the plurality of teeth portions in a direction perpendicular to the radial direction and a maximum dimension of each of the plurality of teeth portions in a direction perpendicular to the radial direction is 72% or more and 172% or less. (8) The motor according to (7), in which a ratio of the radial dimension of the core back portion to an average of a minimum dimension of each of the plurality of teeth in a direction perpendicular to the radial direction and a maximum dimension of each of the plurality of teeth in a direction perpendicular to the radial direction is 94% or more and 143% or less. (9) The motor according to (7) or (8), in which a ratio of the radial dimension of the core back portion to an average of a minimum dimension of each of the plurality of teeth in a direction perpendicular to the radial direction and a maximum dimension of each of the plurality of teeth in a direction perpendicular to the radial direction is 94% or more and 119% or less. (10) The motor according to any one of (1) to (9), in which the number of poles configured in the stator is variable between four and eight. (11) A vehicle drive device comprising the motor according to any one of (1) to (10) and a control device that switches the number of poles configured in the stator depending on the state of the vehicle.

[0080] 10...motor, 20...rotor, 30...stator, 31...stator core, 32...core back portion, 34...teeth portion, 38...coil portion, J...central axis, Wave...average width of teeth portion (average dimension of the minimum dimension in a direction perpendicular to the radial direction of the teeth portion and the maximum dimension in a direction perpendicular to the radial direction of the teeth portion), Wb...width of core back portion (radial dimension of the core back portion), Wmax...maximum width of teeth portion (maximum dimension in a direction perpendicular to the radial direction of the teeth portion), Wmin...minimum width of teeth portion (minimum dimension in a direction perpendicular to the radial direction of the teeth portion)

Claims

1. A motor capable of switching the number of poles, comprising: a rotor rotatable about a central axis; and a stator located radially outside the rotor, wherein the stator has a stator core facing the rotor with a gap in the radial direction, and a plurality of coil portions, wherein the stator core has an annular core back portion and a plurality of teeth portions protruding radially inward from an inner surface of the core back portion and arranged along the inner surface of the core back portion, wherein the plurality of coil portions are attached to the plurality of teeth portions, and a ratio of the radial dimension of the core back portion to the smallest dimension of each of the plurality of teeth portions in a direction perpendicular to the radial direction is 142% or more and 352% or less.

2. The motor according to claim 1, wherein the ratio of the radial dimension of said core back portion to the minimum dimension of each of said plurality of teeth portions in a direction perpendicular to the radial direction is 185% or more and 288% or less.

3. The motor according to claim 1, wherein the ratio of the radial dimension of the core back portion to the minimum dimension of each of the plurality of teeth portions in a direction perpendicular to the radial direction is 185% or more and 237% or less.

4. A motor capable of switching the number of poles, comprising: a rotor rotatable about a central axis; and a stator located radially outside the rotor, wherein the stator has a stator core facing the rotor with a gap in the radial direction, and a plurality of coil portions, wherein the stator core has an annular core back portion and a plurality of teeth portions protruding radially inward from an inner surface of the core back portion and arranged along the inner surface of the core back portion, wherein the plurality of coil portions are attached to the plurality of teeth portions, and a ratio of the radial dimension of the core back portion to the maximum dimension of each of the plurality of teeth portions in a direction perpendicular to the radial direction is 48% or more and 114% or less.

5. The motor according to claim 4, wherein a ratio of the radial dimension of said core back portion to the maximum dimension of each of said plurality of teeth portions in a direction perpendicular to the radial direction is 63% or more and 95% or less.

6. The motor according to claim 4, wherein a ratio of the radial dimension of said core back portion to the maximum dimension of each of said plurality of teeth portions in a direction perpendicular to the radial direction is 63% or more and 79% or less.

7. A motor capable of switching the number of poles, comprising: a rotor rotatable about a central axis; and a stator located radially outward of the rotor, wherein the stator has a stator core facing the rotor with a gap in the radial direction, and a plurality of coil portions, wherein the stator core has an annular core back portion and a plurality of teeth portions protruding radially inward from an inner peripheral surface of the core back portion and arranged along the inner peripheral surface of the core back portion, wherein the plurality of coil portions are attached to the plurality of teeth portions, and a ratio of the radial dimension of the core back portion to the average dimension of the minimum dimension of each of the plurality of teeth portions in a direction perpendicular to the radial direction and the maximum dimension of each of the plurality of teeth portions in a direction perpendicular to the radial direction is 72% or more and 172% or less.

8. A motor as described in claim 7, wherein a ratio of the radial dimension of the core back portion to an average dimension of the minimum dimension of each of the multiple teeth portions in a direction perpendicular to the radial direction and the maximum dimension of each of the multiple teeth portions in a direction perpendicular to the radial direction is 94% or more and 143% or less.

9. A motor as described in claim 7, wherein a ratio of the radial dimension of the core back portion to an average dimension of the minimum dimension of each of the multiple teeth portions in a direction perpendicular to the radial direction and the maximum dimension of each of the multiple teeth portions in a direction perpendicular to the radial direction is 94% or more and 119% or less.

10. The motor according to any one of claims 1 to 9, wherein the number of poles configured in the stator is variable between four and eight.

11. A vehicle drive device comprising: a motor according to any one of claims 1 to 9; and a control device that switches the number of poles configured in the stator depending on the state of the vehicle.

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