Rotor core, rotor, and electric motor

Abstract

Multiple pairs of magnet slots and a plurality of first holes are formed in a rotor core according to the present invention. Each of the multiple pairs of magnet slots includes a first magnet slot and a second magnet slot. The first holes include a first portion corresponding to at least a portion of the area between the radially inner end of the first magnet slot and the radially inner end of the second magnet slot, and a second portion which is continuous with the first portion and which is located farther inward than the first portion in the radial direction of the rotor core.

Description

Rotor core, rotor and electric motor

[0001] The present disclosure relates to a rotor core, a rotor, and an electric motor.

[0002] The end face of the rotor core of a motor has multiple pairs of magnet slots arranged in a V-shape, with magnets inserted into each slot. Holes are often formed in the rotor core to reduce its weight and inertia (see, for example, Japanese Patent No. 6987310). However, if holes are formed inside each pair of V-shaped magnet slots, the flow of magnetic flux is obstructed, resulting in reduced torque.

[0003] Patent No. 6987310

[0004] To increase torque, it is conceivable to extend the V-shaped tips of each pair of magnet slots radially inward of the rotor core. However, this would reduce the area of ​​the rotor core where holes can be formed. As a result, it would be difficult to reduce weight and inertia. Furthermore, in this case, even if the rotor is inserted into the inner cylinder of the magnetizing yoke, it would be difficult to fully magnetize the portion of the magnet located radially inward, which would result in a decrease in torque.

[0005] Therefore, there is a demand for a lightweight rotor core, rotor, and electric motor that can reduce inertia and sufficiently magnetize without reducing torque.

[0006] According to a first aspect of the present disclosure, there is provided a rotor core, the rotor core being provided with a plurality of pairs of magnet slots extending in an axial direction of the rotor core, the plurality of pairs of magnet slots being arranged at equal intervals in a circumferential direction of the rotor core in a radial cross section of the rotor core, each pair of magnet slots including a first magnet slot inclined counterclockwise with respect to a radius of the rotor core and a second magnet slot inclined clockwise with respect to the radius of the rotor core, and in each pair of magnet slots, one end of the first magnet slot and one end of the second magnet slot and one end of the first magnet slot and one end of the second magnet slot are spaced apart from each other, and the other end of the first magnet slot and the other end of the second magnet slot are adjacent to each other radially inward of the rotor core than the one end of the first magnet slot and the one end of the second magnet slot, and further, a first hole is formed adjacent to each pair of magnet slots, and the first hole includes a first portion corresponding to at least a part of the area between the other end of the first magnet slot and the other end of the second magnet slot, and a second portion that is continuous with the first portion and is located radially inward of the rotor core than the first portion.

[0007] The objects, features, and advantages of the present disclosure will become more apparent from the following description of the embodiments taken in conjunction with the accompanying drawings.

[0008] 1 is an axial sectional view of an electric motor including a rotor core according to the present disclosure; FIG. 2 is a radial sectional view of a rotor core according to a first embodiment; FIG. 3 is a partial sectional view of an enlarged portion of FIG. 3; FIG. 4 is a radial sectional view of a rotor core similar to FIG. 2; FIG. 5 is another partial sectional view of the rotor core shown in FIG. 2; FIG. 6 is a partial sectional view of an enlarged portion of FIG. 6; FIG. 7 is a partial sectional view showing magnetic flux of an electric motor in the prior art; FIG. 8 is a diagram showing the relationship between time and torque of an electric motor in the prior art; FIG. 9 is a partial sectional view showing magnetic flux of an electric motor according to the first embodiment; FIG. 10 is a diagram showing the relationship between time and torque of an electric motor according to the first embodiment; FIG. 11 is a partial sectional view showing the magnetization rate of an electric motor in the prior art; FIG. 12 is a partial sectional view showing the magnetization rate of an electric motor according to the first embodiment;

[0009] Embodiments of the present disclosure will be described below with reference to the accompanying drawings. Corresponding components are designated by common reference numerals throughout the drawings. FIG. 1 is an axial cross-sectional view of an electric motor equipped with a rotor core according to the present disclosure. As shown in FIG. 1, the electric motor 1 includes a stator 9 and a rotor 10 rotatably supported by the stator 9. A first bearing 7 and a second bearing 8 are disposed on the inner peripheral surface of the stator 9. A shaft 5 passing through the rotor 9 is rotatably supported by the stator 9 via the first bearing 7 and the second bearing 8. A detector 6 for detecting the rotation speed of the shaft 5 is attached to one end of the stator 9.

[0010] Fig. 2 is a radial cross-sectional view of a rotor core according to the first embodiment. The rotor core 10a shown in Fig. 2 is generally ring-shaped with a through-hole in the center for the shaft portion 5. However, as will be described later, it is preferable that the outer peripheral surface of the rotor core 10a is not smooth. Furthermore, the rotor core 10a is typically formed by laminating multiple magnetic plates, such as iron plates, carbon steel plates, and electromagnetic steel plates, in the shape shown in Fig. 2, or by using a powder iron core.

[0011] The rotor core 10a is formed with a plurality of pairs of magnet slots 20 extending in the axial direction of the rotor core 10a at equal intervals in the circumferential direction. Each pair of magnet slots 20 includes a first magnet slot 21 inclined counterclockwise with respect to the radius of the rotor 10 and a second magnet slot 22 inclined clockwise with respect to the radius of the rotor 10. It is preferable that the absolute values ​​of the inclination angles with respect to the radius of the first magnet slot 21 and the second magnet slot 22 are equal to each other.

[0012] Figure 3 is a partial cross-sectional view of the rotor core shown in Figure 2. Permanent magnets 91 and 92 are inserted into magnet slots 21 and 22 of the rotor core 10a, respectively. Therefore, the magnet slots 21 and 22 are preferably substantially rectangular in shape to correspond to the shapes of the permanent magnets 91 and 92, and are preferably the same shape as each other. Note that for the purpose of simplification, the permanent magnets 91 and 92 may be omitted from the illustration.

[0013] The magnet slots 20 of each pair are arranged to converge toward each other radially inward of the rotor core 10a. In other words, the magnet slots 21, 22 are formed to form a substantial V-shape. In the present disclosure, the angle formed by the magnet slots 21, 22 of each pair of magnet slots 20 is an obtuse angle, for example, 120°. Note that these magnet slots 21, 22 do not need to be connected to each other radially inward of the rotor core 10a.

[0014] Furthermore, in FIG. 2 , the outer periphery of the rotor core 10a is composed of a plurality of first outer periphery portions 11 and a plurality of second outer periphery portions 12 connecting the plurality of first outer periphery portions 11. In other words, the plurality of first outer periphery portions 11 and the plurality of second outer periphery portions 12 are arranged alternately in the circumferential direction of the rotor core 10a. As can be seen from FIG. 2 , each of the plurality of first outer periphery portions 11 roughly corresponds to a respective region of each of the plurality of pairs of magnet slots 20. Strictly speaking, each of the first outer periphery portions 11 corresponds to the other end 21x of the magnet slot 21 and the other end 22x of the second magnet slot 22 on the radially inner side of the rotor core 10a. The plurality of second outer periphery portions 12 correspond to the regions between two adjacent pairs of magnet slots 20 among the plurality of pairs of magnet slots 20. Strictly speaking, the aa of the second outer periphery portion 12 corresponds to one end 21y of the magnet slot 21 and one end 22y of the second magnet slot 22 on the radially outer side of the rotor core 10a.

[0015] Furthermore, the outermost portion of the first outer peripheral portion 11 is located radially outward of the rotor core 10a relative to the outermost portion of the second outer peripheral portion 12. In other words, a plurality of first outer peripheral portions 11 as convex portions and a plurality of second outer peripheral portions 12 as concave portions are alternately arranged in the circumferential direction of the rotor core 10a. The entire first outer peripheral portion 11 is located within a circle whose radius is the line segment connecting the center O of the rotor core 10a and the outermost portion of the first outer peripheral portion 11. In Figure 5, which is a radial cross-sectional view of the rotor core similar to Figure 2, the aforementioned circle is indicated by a dashed line.

[0016] In this way, because the outer periphery of the rotor core 10a is not a perfect circle, the change in the magnetic flux linkage is small when the electric motor 1 having the rotor core 10a is driven, and as a result, it is possible to prevent the cogging torque and torque ripple from increasing. Therefore, in the first embodiment of the present invention, it is possible to improve the controllability of the electric motor 1 having the rotor core 10a.

[0017] 2, each of the outermost portions of the first outer peripheral portion 11 is formed by at least one curve. In one example, the first outer peripheral portion 11 is defined by the formula r = D - E / cos(Fθ) (D, E, and F are positive numbers). In this case, the first outer peripheral portion 11 is positioned reliably within the aforementioned circle and is smooth. Each of the outermost portions of the second outer peripheral portion 12 may be formed by at least one straight line.

[0018] In an embodiment not shown, the outermost portion of the first outer peripheral portion 11 may be formed by at least one straight line, and the outermost portion of the second outer peripheral portion 12 may be formed by at least one curved line. Furthermore, both the outermost portion of the first outer peripheral portion 11 and the outermost portion of the second outer peripheral portion 12 may be formed by at least one straight line, or both the outermost portion of the first outer peripheral portion 11 and the outermost portion of the second outer peripheral portion 12 may be formed by at least one curved line. Furthermore, at least one of the outermost portions of the first outer peripheral portion 11 and the second outer peripheral portion 12 may be formed by at least one straight line and at least one curved line. In such a case, the outermost portions of the first outer peripheral portions 11 are positioned radially outward of the rotor core 10a relative to the outermost portions of the second outer peripheral portions 12, so that the outer periphery of the rotor core 10a has a shape other than a perfect circle. Therefore, it can be seen that the same effect as described above can be obtained.

[0019] Furthermore, in a modification of the first embodiment (not shown), the first outer peripheral portion 11 may be located radially inward of the rotor core 10a relative to the second outer peripheral portion 12. Even in such a case, the same effects as those described above can be obtained, and this is included in the scope of the first embodiment.

[0020] As shown in Fig. 2, a plurality of first holes 31 extending in the axial direction of the rotor core 10a are formed at equal intervals in the circumferential direction on the end face of the rotor core 10a. As can be seen from Figs. 2 and 3, each of the plurality of first holes 31 is formed in a region of the rotor core 10a corresponding to the first outer circumferential portion 11. Strictly speaking, the first holes 31 are formed on one radius of the rotor core 10a between the first magnet slot 21 and the second magnet slot 22 of a pair of magnet slots 20. The shape of the first holes 31 will be described later.

[0021] A plurality of second holes 32 are formed at equal intervals in the circumferential direction in the end face of the rotor core 10a. Each of the second holes 32 is formed on the same radius as mentioned above. Therefore, the first holes 31 and the second holes 32 are arranged side by side on the same radius of the rotor core 10a. Therefore, as can be seen from FIG. 3 , the second holes 32 are formed radially outward of the rotor core 10a than the first holes 31. Strictly speaking, the first holes 31 are formed radially inward of the pair of magnet slots 20 in the rotor core 10a, and the second holes 32 are formed radially outward of the pair of magnet slots 20 in the rotor core 10a. The shape of the second holes 32 will be described later.

[0022] Furthermore, as can be seen from Figure 2, multiple sets of third holes 33 and fourth holes 34 are formed at equal intervals around the circumferential direction of the rotor core 10a. Sets of third holes 33 and fourth holes 34 are formed between two adjacent pairs of magnet slots 20 out of the multiple pairs of magnet slots 20. The third holes 33 and the fourth holes 34 are arranged side by side on the same radius of the rotor core 10a. The third holes 33 are formed radially outward of the fourth holes 34 on the rotor core 10a. The shapes of the third holes 33 and the fourth holes 34 will be described later.

[0023] The first hole 31 will now be described. As shown in Fig. 3, the first hole 31 is a substantially isosceles triangle with an acute apex angle. The apex side of the substantially isosceles triangle is located radially outward from the rotor core 10a, and the base side of the substantially isosceles triangle is located radially inward from the rotor core 10a. The base of the substantially isosceles triangle is perpendicular to one radius of the rotor core 10a.

[0024] The reason for using the term "approximately isosceles triangle" is that it encompasses cases that differ from a perfect isosceles triangle, such as when the apex of the isosceles triangle is rounded, when each of the two hypotenuses of the isosceles triangle is made up of multiple straight lines, or when each of the two hypotenuses of the isosceles triangle includes a curve. The same applies to the other holes 32, 33, and 34.

[0025] Figure 4 is an enlarged partial cross-sectional view of a portion of Figure 3. As can be seen from Figures 3 and 4, first hole 31 is composed of a first portion 31a including the acute angle of a substantially isosceles triangle and a second portion 31b including the base of the substantially isosceles triangle. First portion 31a has a shape similar to first hole 31. The boundary line between first portion 31a and second portion 31b is preferably parallel to the base.

[0026] 4, the boundary line between the first portion 31a and the second portion 31b corresponds to a portion of a line segment L0 that connects, on the radially inner side of the rotor core 10a, the other end 21x of the first magnet slot 21 and the other end 22x of the second magnet slot 22. Strictly speaking, the line segment L0 connects a portion of the other end 21x of the first magnet slot 21, which is located at the radially innermost position of the rotor core 10a, and a portion of the other end 22x of the second magnet slot 22, which is located at the radially innermost position of the rotor core 10a.

[0027] It is preferable that the other end 21x of the first magnet slot 21 and the hypotenuse of the approximately isosceles triangle adjacent thereto are approximately parallel to each other. Similarly, it is preferable that the other end 22x of the first magnet slot 22 and the hypotenuse of the approximately isosceles triangle adjacent thereto are approximately parallel to each other.

[0028] In this manner, the first hole 31 in the present disclosure is formed adjacent to the region between the first magnet slot 21 and the first magnet slot 22. The first portion 31a of the first hole 31 is formed between the other end 21x of the first magnet slot 21 and the other end 22x of the second magnet slot 22. Furthermore, the second portion 31b of the first hole 31 is formed radially inward of the rotor core 10a relative to the first portion 31a.

[0029] In other words, the first hole 31 according to the present disclosure necessarily includes the second portion 31b in addition to the first portion 31a formed between the first magnet slot 21 and the second magnet slot 22. Therefore, in the present disclosure, it is possible to form a large first hole 31. As a result, it is possible to reduce the weight of the rotor core 10a and increase the speed of the electric motor 1.

[0030] 3, a gap 21g is formed on one end 21y of the first magnet slot 21. The gap 21g is formed so as to partially protrude from the end 21y along the length of the first magnet slot 21. A gap 22g of a similar shape is formed on one end 22y of the second magnet slot 22.

[0031] Furthermore, a gap 21p is formed on the other end 21x side of the first magnet slot 21. Similarly, a gap 22p is formed on the other end 22x side of the second magnet slot 22. The gaps 21p, 22p partially protrude from the other ends 21x, 22x along the length portions of the first magnet slot 21 and the second magnet slot 22.

[0032] Such gaps 21g, 21p of the first magnet slot 21 and 22g, 22p of the second magnet slot 22 serve as flux barriers that suppress magnetic flux leakage from both longitudinal ends of the magnets 91, 92 to the rotor core. The gaps 21g, 22g, 21p, 22p also serve to facilitate the insertion and removal of the permanent magnets 91, 92 into the corresponding magnet slots 21, 22. Furthermore, the formation of the aforementioned gaps 21g, 21p, 22g, 22p reduces the weight of the rotor core 10a.

[0033] In Figure 4, line segment L0' is shown connecting a portion of the other end 21x of the first magnet slot 21 on the radially outer side of the rotor core 10a to a portion of the other end 22x of the second magnet slot 22 on the radially outer side of the rotor core 10a. As can be seen from Figure 4, portions of the air gaps 21p and 22p each protrude beyond line segment L0' radially outward of the rotor core 10a. In other words, the air gaps 21p and 22p are formed to protrude from the other ends 21x and 22x in both a direction perpendicular to the length of the first magnet slot 21 and the second magnet slot 22 and in the length direction of the magnet slots 21 and 22, respectively. Note that the air gaps 21p and 22p are connected to the first magnet slot 21 and the second magnet slot 22, respectively. As can be seen from the figure, the air gaps 21p and 22p do not communicate with each other.

[0034] As shown in FIG. 4 , the shortest distance between the gap 21p at the other end 21x of the first magnet slot 21 and the first hole 31 is defined as distance a. The shortest distance between the gap 22p at the other end 22x of the second magnet slot 22 and the first hole 31 is also defined as distance a'. The shortest distance between the other end 21x of the first magnet slot 21 and the first hole 31 is also defined as distance a'. The shortest distance between the other end 22x of the second magnet slot 22 and the first hole 31 is also defined as distance a'. The distance a can be equal to or less than half, preferably equal to or less than one-fourth, of the distance a'. In a typical example, the distances a are greater than 0 and equal to or less than 1 millimeter.

[0035] As described above, the angle between the magnet slots 21, 22 is an obtuse angle, and in such cases, it is difficult for the electric motor 1 equipped with the rotor core 10a to output high torque. However, the rotor core 10a of the present disclosure is formed with the first holes 31 and air gaps 21p, 22p of the shape and dimensions described above. This reduces magnetic flux leakage when the electric motor 1 is running, and therefore the electric motor 1 can maintain high torque even when the angle between the magnet slots 21, 22 is an obtuse angle. Furthermore, by forming the first holes 31 and air gaps 21p, 22p, the weight of the rotor core 10a can be reduced.

[0036] During magnetization, the rotor 10 is placed inside the magnet yoke (not shown) with the magnets 91, 92 inserted into all of the magnet slots 21, 22. At this time, the portions of the magnets 91, 92 located radially inside the rotor 10 are located far from the magnetizing yoke. For this reason, it is difficult to sufficiently magnetize the portions of the magnets 91, 92, particularly when the angle between the first magnet slot 21 and the second magnet slot 22 is acute.

[0037] However, compared to when the angles between the magnet slots are acute angles, in the present disclosure, the angles between the magnet slots 21, 22 are obtuse angles, so the other ends 21x, 22x of the magnet slots 21, 22 are located relatively close to the outer circumferential surface of the rotor core 10a. Therefore, in the present disclosure, it is relatively easy to magnetize even the portions of the magnets 91, 92 located near the other ends 21x, 22x of the magnet slots 21, 22. In other words, because the angles between the magnet slots 21, 22 can be made obtuse, this has the added advantage of making it easier to magnetize the magnets. This will be discussed later using Figures 10A and 10B.

[0038] Next, the second holes 32 will be described. As shown in Figure 3, the first holes 31 and the second holes 32 are arranged side by side on the same radius of the rotor core 10a. The first holes 31 are formed radially inward of the pair of magnet slots 20 on the rotor core 10a, and the second holes 32 are formed radially outward of the pair of magnet slots 20 on the rotor core 10a.

[0039] The second hole 32 is composed of a first portion 32 a and a second portion 32 b located radially outward of the rotor core 10 a relative to the first portion 32 a. The boundary line between the first portion 32 a and the second portion 32 b of the second hole 32 is preferably parallel to the base of the substantially isosceles triangle of the first hole 31.

[0040] As shown in FIG. 3 , the first portion 32a has a generally isosceles triangle shape with its apex angle pointing toward the center O of the rotor core 10a. The apex angle of the generally isosceles triangle of the first portion 32a is preferably acute and larger than the apex angle of the generally isosceles triangle of the first portion 31a of the first hole 31. The second portion 32b has an arc shape, such as a semicircular arc, that protrudes from the base of the isosceles triangle radially outward from the rotor core 10a. The first portion 32a and the second portion 32b are preferably smoothly connected to each other. In other words, at the connection point between the first portion 32a and the second portion 32b, the hypotenuse of the generally isosceles triangle of the first portion 32a and the tangent to the second portion 32b are preferably equal to each other. The arc of the second portion 32b may be longer or shorter than the semicircular arc. The arc of the second portion 32b may also be an elliptical arc.

[0041] 3, a first line segment L1 is a line segment connecting one end 21y of the first magnet slot 21 and one end 22y of the second magnet slot 22 on the radially outer side of the rotor core 10a. Strictly speaking, the first line segment L1 connects a portion of the end 21y of the first magnet slot 21 located at the radially outermost position of the rotor core 10a to a portion of the end 22y of the second magnet slot 22 located at the radially outermost position of the rotor core 10a. As can be seen from FIG. 3, the boundary line B1 between the first portion 32a and the second portion 32b of the second hole 32 is preferably parallel to the first line segment L1 and located radially inward of the first line segment L1 on the rotor core 10a.

[0042] In other words, at least a portion of the second portion 32b of the second hole 32 is located radially outward of the rotor core 10a relative to the first line segment L1. Therefore, in the present disclosure, a large second hole 32 can be formed, resulting in a reduction in the weight of the rotor core 10a and an increase in the speed of the electric motor 1. Furthermore, because the second portion 32b is an arc, the flow of magnetic flux is not obstructed when the electric motor 1 having the rotor core 10a is operating. Note that, in order to increase the area of ​​the second hole 32, the boundary line B1 may be located on the first line segment L1, or the boundary line B1 may be located radially outward of the first line segment L1 relative to the rotor core 10a.

[0043] As described above, it is preferable that the first outer peripheral portion 11 in which the second holes 32 are formed protrudes radially outward of the rotor core 10a more than the second outer peripheral portion 12. In this case, the second holes 32 can be formed further radially outward of the rotor core 10a by the protruding portion of the first outer peripheral portion 11. Therefore, it will be understood that the second holes 32 can be made larger, and the rotor core 10a can be made lighter accordingly.

[0044] 4, distance b is the shortest distance between gap 21p at the other end 21x of first magnet slot 21 and second hole 32. Distance b is also the shortest distance between gap 22p at the other end 22x of second magnet slot 22 and second hole 32. These distances b are measured from parts of gaps 21p, 22p that extend radially outward from rotor core 10a beyond line segment L0' to second hole 32.

[0045] The distance b can be equal to or less than half, preferably equal to or less than one-fourth, of the distance a'. In a typical example, the distance a is greater than 0 and equal to or less than 1 mm. This can provide the same effect as described above.

[0046] Next, the third hole 33 will be described. Figure 6 is another partial cross-sectional view of the rotor core shown in Figure 2. As shown in Figure 6, one pair of magnet slots 20a includes a first magnet slot 21a and a second magnet slot 22a. The other pair of magnet slots 20b includes a first magnet slot 21b and a second magnet slot 22b. The third hole 33 is formed between the second magnet slot 22a of the magnet slot 20a and the first magnet slot 21b of the magnet slot 20b.

[0047] 6, the third holes 33 are each formed into a substantially isosceles triangle, such as an obtuse isosceles triangle, with its apex angle 33a defined by a circular arc. The apex angle 33a of the substantially isosceles triangle of the third holes 33 faces radially outward from the rotor core 10a. Furthermore, it is preferable that the two hypotenuses of the substantially isosceles triangle of the third holes 33 are parallel to the second magnet slots 22a and the first magnet slots 21b, respectively.

[0048] Furthermore, the portions of the third hole 33 corresponding to the two diagonal angles of the approximately isosceles triangle may be omitted, and the hypotenuse and the base may be connected near the base. In FIG. 6, the portions corresponding to the diagonal angles are configured as right angles. Alternatively, the portions corresponding to the diagonal angles may be configured as arcs. By forming the third hole 33 in this manner, the flow of magnetic flux is not obstructed.

[0049] Furthermore, a protrusion 33b protruding radially inward of the rotor may be formed from the base of the substantially isosceles triangle of the third hole 33. The protrusion 33b is preferably formed at approximately the center of the base of the substantially isosceles triangle.

[0050] Figure 7 is an enlarged partial cross-sectional view of a portion of Figure 6. Figure 7 mainly shows the second magnet slot 22a of one pair of magnet slots 20a and the first magnet slot 21b of the other pair of magnet slots 20b. A line segment connecting the other end 22x of the second magnet slot 22a and the other end 21x of the first magnet slot 21b on the radially inner side of the rotor core 10a is designated as a second line segment L2. Strictly speaking, the second line segment L2 connects a portion of the other end 22x of the second magnet slot 22a located at the radially innermost position of the rotor core 10a to a portion of the other end 22y of the first magnet slot 21b located at the radially innermost position of the rotor core 10a. In this case, the entire third hole 33 is located radially outward of the second line segment L2 on the rotor core 10a.

[0051] As shown in Figure 7, the third holes 33 are formed in an area surrounded by the second magnet slot 22a in one pair of magnet slots 20a, the first magnet slot 21b in the other pair of magnet slots 20b, and the second line segment L2. In other words, the third holes 33 are not formed on or near the second line segment L2. This ensures the strength of the rotor core 10a. Furthermore, it can be seen that the flow of magnetic flux is not obstructed when the electric motor 1 including the rotor core 10a is operating.

[0052] 7, the third hole 33 is formed between the second magnet slot 22a of one pair of magnet slots 20a and the first magnet slot 21b of the other pair of magnet slots 20b. The shortest distance between the third hole 33 and the first magnet slot 21b is greater than the shortest distance c between the third hole 33 and the second magnet slot 22a.

[0053] The shortest distance c is preferably at least half the thickness t of the magnets 91, 92. In a typical example, the shortest distance is at least 2 millimeters. When the third holes 33 are located at a distance from the magnets 91, 92 that is at least half the thickness t of the magnets 91, 92, the magnetization described above can be performed without being affected by the third holes 33.

[0054] 7, a line segment connecting one end 22y of the second magnet slot 22a and one end 21y of the first magnet slot 21b on the radially inner side of the rotor core 10a is defined as a third line segment L3. Strictly speaking, the third line segment L3 connects a portion of one end 21y of the first magnet slot 22a located at the radially innermost position of the rotor core 10a with a portion of one end 22y of the second magnet slot 21b located at the radially innermost position of the rotor core 10a.

[0055] The third line segment L3 and the second line segment L2 are parallel to each other. The third hole 33 has a dimension d on the center line between the second magnet slot 22a and the first magnet slot 21b, which corresponds to the radius of the rotor core 10a. Dimension d does not necessarily have to be on the center line of the third hole 33. Furthermore, the dimension between the second line segment L2 and the third line segment L3 is defined as dimension e. In such a case, dimension e is preferably at least twice dimension d.

[0056] The reason for the shape and arrangement of the third holes 33 is to ensure the strength of the regions between the third holes 33 and the second magnet slots 22 a and first magnet slots 21 b, and to smooth the flow of magnetic flux. Furthermore, in a motor 1 equipped with such a rotor core 10 a, it is possible to reduce inertia.

[0057] Next, the fourth hole 34 will be described. As can be seen from FIG. 7 , the third hole 33 and the fourth hole 34 are juxtaposed on a radius of the rotor core 10a that passes through the center between the second magnet slot 22a in one pair of magnet slots 20a and the first magnet slot 21b in the other pair of magnet slots 20b. A set consisting of the third hole 33 and the fourth hole 34 is formed between two adjacent pairs of magnet slots 20a, 20b out of the multiple pairs of magnet slots 20. The third hole 33 and the fourth hole 34 may be formed line-symmetrically with respect to the radius. Furthermore, the fourth hole 34 is formed radially inward of the rotor core 10a from the second line segment L2.

[0058] The fourth hole 34 has a generally oval or elliptical shape, with its major axis parallel to the line segment L2. Furthermore, the fourth hole 34 preferably has protrusions 34a and 34b extending along the aforementioned radius. As shown in FIG. 7 , the protrusion 34a extends radially outward from the rotor core 10a, and the protrusion 34b extends radially inward from the rotor core 10a. By forming these protrusions 34a and 34b, the fourth hole 34 can be enlarged, thereby reducing the weight of the rotor core 10a. Note that one of the protrusions 34a and 34b may be omitted.

[0059] Here, Fig. 8A is a partial cross-sectional view showing the magnetic flux of a motor according to the prior art, and Fig. 9A is a partial cross-sectional view showing the magnetic flux of a motor equipped with a rotor core according to the first embodiment. The motor 1' shown in Fig. 8A includes a stator 9' and a rotor 10'. The rotor 10' does not have the first hole 31 to the fourth hole 34 formed therein. On the other hand, the motor 1 shown in Fig. 9A includes a stator 9 and the rotor 10 described above. The structures of the rotors 10 and 10' are well known, so a description thereof will be omitted.

[0060] 8A and 9A, even when the first through fourth holes 31 through 34 are formed as in the case of the electric motor 1, the flow of magnetic flux is not obstructed by the first holes 31, etc. Furthermore, the electric motor 1 is lighter than the electric motor 1' by the amount corresponding to the first through fourth holes 31 through 34 formed therein.

[0061] Furthermore, the angle formed by the first magnet slot 21' and the second magnet slot 22' of the pair of magnet slots 20' in Fig. 8A is an acute angle, for example, 60°. Therefore, the number of magnets 91', 92' inserted into the first magnet slot 21' and the second magnet slot 22', respectively, is greater than the number of magnets 91, 92 shown in Fig. 9A.

[0062] The diameter of the rotor 10' shown in Fig. 8A is equal to the diameter of the rotor 10 shown in Fig. 9A. However, the width W0 of the magnets 91', 92' shown in Fig. 8A is, for example, 31.4 mm, whereas the width W1 of the magnets 91, 92 shown in Fig. 9A is, for example, 22.5 mm.

[0063] In this manner, the present disclosure allows for fewer magnets 91, 92 and smaller dimensions than the prior art. As a result, it will be appreciated that the electric motor 1 can be significantly lighter than the electric motor 1'. In the illustrated embodiment, the total weight of the magnets 91, 92 of the electric motor 1 is, for example, approximately 28% less than the total weight of the magnets 91', 92' of the electric motor 1'.

[0064] Furthermore, FIG. 8B is a diagram showing the relationship between time and torque in a conventional electric motor, and FIG. 9B is a diagram showing the relationship between time and torque in the electric motor of the first embodiment. In these figures, the horizontal axis represents time, and the vertical axis represents torque for electric motors 1 and 1'. In FIG. 8B, the maximum torque value for electric motor 1' is between 100 Nm and 101 Nm. In contrast, in FIG. 9B, the maximum torque value for electric motor 1 is between 91.5 Nm and 92 Nm. In other words, even when first through fourth holes 31 through 34 are formed, the torque reduction is kept to less than 10%.

[0065] In this way, even when the first hole 31 to the fourth hole 34 are formed in the rotor 10, a practical torque can be generated without a significant decrease in torque. It will be apparent to those skilled in the art that a similar effect can be obtained even when only one of the first hole 31 to the fourth hole 34 is formed.

[0066] Furthermore, the ratio of the D-phase current to the stall current in motor 1 and motor 1' is expressed as a percentage as follows:

[0067] From this table, it can be seen that while the limit was exceeded at a rotation speed of 2500 rpm for electric motor 1, stable operation is possible even when the rotation speed is increased to, for example, 3000 rpm for electric motor 1. The reason for this is that the D-phase current for electric motor 1 is relatively small. Furthermore, copper loss, which increases in proportion to the square of the load current, is also suppressed in electric motor 1 compared to electric motor 1'. For this reason, electric motor 1 of the present disclosure is capable of higher speed rotation.

[0068] 10A is a partial cross-sectional view showing the magnetization rate of a motor according to the prior art, and FIG. 10B is a partial cross-sectional view showing the magnetization rate of a motor according to the first embodiment. These figures show three levels of magnetization rate, with the higher the magnetization rate, the darker the color of the corresponding region. Specifically, the low magnetization rate region (magnetic flux density 0.0 T to 1.7 T) is shown in white, the medium magnetization rate region (magnetic flux density 2.2 T to 3.3 T) is shown in light color, and the high magnetization rate region (magnetic flux density 3.5 T to 5.0 T) is shown in dark color.

[0069] In the prior art electric motor 1' shown in FIG. 10A, only portions of the magnets 91', 92' located radially outward of the rotor 10' are magnetized, while the remaining portions of the magnets 91', 92' located radially inward are not. Because the angle between the first magnet slots 21 and the second magnet slots 22 into which the magnets 91', 92' are inserted is acute, the distance between the other ends of the magnets 91', 92' located radially inward of the rotor 10' and the outer surface of the rotor 10' is long. For this reason, in the prior art, even if the rotor 10' is placed inside a magnetizing yoke (not shown), it is difficult to magnetize the other ends of the magnets 91', 92'. Therefore, in the prior art, the magnetization rate of the magnets 91', 92' is approximately 30%.

[0070] 10B, the magnets 91, 92 are magnetized over almost their entire surfaces, and the magnetization rate of the magnets 91, 92 is approximately 100%. In other words, in the present disclosure, even if the rotor 10 is placed inside the inner cylinder of a magnetizing yoke (not shown), the magnets 91, 92 can be sufficiently magnetized up to the other ends of the magnets 91, 92 on the radially inner side of the rotor 10. Therefore, in the present disclosure, in which the angle formed by the first magnet slot 21 and the second magnet slot 22 is an obtuse angle, the magnets 91, 92 can be reliably magnetized.

[0071] In the present disclosure, it is sufficient that the first hole 31 and the gaps 21p, 22p are formed, and it is not necessary to form the second hole 32 to the fourth hole 34. Furthermore, a configuration in which at least one of the second hole 32 to the fourth hole 34 is formed in addition to the first hole 33 and the gaps 21p, 22p is also included in the scope of the present disclosure.

[0072] Therefore, in at least one embodiment, by forming the first holes 31, etc., the weight of the rotor 10 can be reduced, and it is possible to reduce inertia while sufficiently magnetizing the rotor 10 without a significant decrease in torque. In other words, it is possible to provide a lightweight rotor 10 that can reduce inertia and sufficiently magnetize the rotor 10 without a decrease in torque. Therefore, it is possible to achieve high acceleration of the electric motor 1 having the rotor 10.

[0073] Although the embodiments of the present disclosure have been described in detail, the present disclosure is not limited to the individual embodiments described above. Various additions, substitutions, modifications, partial deletions, etc. are possible to these embodiments without departing from the gist of the invention or the concept and spirit of the present invention derived from the content of the claims and their equivalents. For example, in the above-described embodiments, the order of each operation and the order of each process are shown as examples and are not limited to these. The same applies when numerical values ​​or mathematical formulas are used in the description of the above-described embodiments. Furthermore, appropriate combinations of several of the above-described embodiments are within the scope of the present disclosure.

[0074] The following supplementary notes are further disclosed regarding the above-described embodiments and modifications: (Supplementary Note 1) A rotor core (10a), wherein a plurality of pairs of magnet slots (20) extending in the axial direction of the rotor core (10a) are formed in the rotor core (10a), the plurality of pairs of magnet slots (20) are arranged at equal intervals in the circumferential direction of the rotor core (10a) in a radial cross section of the rotor core (10a), and each pair of magnet slots (20) of the plurality of pairs of magnet slots (20) includes a first magnet slot (21) inclined counterclockwise with respect to a radius of the rotor core (10a) and a second magnet slot (22) inclined clockwise with respect to the radius of the rotor core (10a), In each pair of magnet slots (20), one end of the first magnet slot (21) and one end of the second magnet slot (22) are spaced apart from each other, and the other end of the first magnet slot (21) and the other end of the second magnet slot (22) are adjacent to each other radially inward of the rotor core (10a) relative to the one end of the first magnet slot (21) and the one end of the second magnet slot (22); and a first hole (31) is formed adjacent to each pair of magnet slots (20), and the first hole (31) includes a first portion (31a) corresponding to at least a part of the area between the other end of the first magnet slot (21) and the other end of the second magnet slot (22), and a second portion (31b) continuous with the first portion (31a) and located radially inward of the rotor core (10a) relative to the first portion (31a). (Appendix 2) A rotor core (10a) according to Appendix 1, wherein gaps (21p, 22p) are formed at the other end of the first magnet slot (21) and the other end of the second magnet slot (22), and the gaps (21p, 22p) partially protrude radially outward from the rotor core (10a) beyond a line segment (L0') connecting the other end of the first magnet slot (21) at the radially outer side of the rotor core (10a) and the other end of the second magnet slot (22) at the radially outer side of the rotor core (10a).(Appendix 3) A rotor core (10a) according to appendix 1 or 2, wherein the distance (a) between the gap (21p) formed at the other end of the first magnet slot (21) and the first hole (31) is equal to or less than half of the distance (a') between the other end of the first magnet slot (21) and the first hole (31), and the distance (a) between the gap (22p) formed at the other end of the second magnet slot (22) and the first hole (31) is equal to or less than half of the distance (a') between the other end of the second magnet slot (22) and the first hole (31). (Supplementary Note 4) The rotor core (10a) according to any one of Supplements 1 to 3, wherein the outer periphery of the rotor core (10a) is composed of a plurality of first outer periphery portions (11) and a plurality of second outer periphery portions (12) connecting each of the plurality of first outer periphery portions (11), the plurality of first outer periphery portions (11) corresponding to the regions of each of the plurality of pairs of magnet slots (20), the plurality of second outer periphery portions (112) corresponding to the regions between two adjacent pairs of magnet slots (20a, 20b) of the plurality of pairs of magnet slots (20), and the outermost portions of the plurality of first outer periphery portions (11) are located radially outward of the rotor core (10a) relative to the outermost portions of the plurality of second outer periphery portions (12). (Supplementary Note 5) The rotor core (10a) according to any one of Supplements 1 to 4, wherein the plurality of first outer periphery portions (11) are composed of at least one curve, and the plurality of second outer periphery portions (12) are composed of at least one straight line. (Appendix 6) A rotor core (10a) according to any one of Appendices 1 to 5, further comprising a second hole (32) formed adjacent to each pair of magnet slots (20), and each of the first holes (31) and each of the second holes (32) being juxtaposed in the radial direction of the rotor core (10a).(Supplementary Note 7) The rotor core (10a) according to any one of Supplementary Notes 1 to 6, wherein each of the second holes (32) is composed of a substantially isosceles triangle in a radial cross section of the rotor core (10a) whose apex angle (32a) faces the center of the rotor core (10a) and an arc protruding from the base of the isosceles triangle radially outward of the rotor core (10a), and at least a portion of the arc of the second hole (32) is located radially outward of the rotor core (10a) with respect to a first line segment (L1) connecting the one end of the first magnet slot (21) and the one end of the second magnet slot (22) on the radially outward side of the rotor core (10a). (Appendix 8) A rotor core (10a) according to any one of Appendices 1 to 6, wherein the distance (b) between the gap (21p) formed at the other end of the first magnet slot (21) and the second hole (32) is equal to or less than half of the distance (a') between the other end of the first magnet slot (21) and the first hole (31), and the distance (b) between the gap (22p) formed at the other end of the second magnet slot (22) and the second hole (32) is equal to or less than half of the distance (a') between the other end of the second magnet slot (22) and the first hole (31). (Appendix 9) A rotor core (10a) according to any one of Appendices 1 to 8, wherein a third hole (33) is formed between two adjacent pairs of magnet slots (20a, 20b) of the plurality of pairs of magnet slots (20), and the third hole (33) is formed radially outward of the rotor core (10a) of a second line segment (L2) connecting the other end of the second magnet slot (22a) in one pair of magnet slots (20a) of the two pairs of magnet slots (20a, 20b) and the other end of the first magnet slot (21b) in the other pair of magnet slots (20b) of the two pairs of magnet slots (20a, 20b). (Appendix 10) A rotor core (10a) according to any one of Appendices 1 to 9, wherein the distance (c) between the third hole (33) and the first magnet slot (21) or the second magnet slot (22) is equal to or greater than half the thickness (t) of the magnet to be inserted into the first magnet slot (21) or the second magnet slot (22).(Appendix 11) The rotor core (10a) according to any one of Appendices 1 to 10, wherein a distance (e) between a third line segment (L3) connecting one end of the second magnet slot (22a) in one pair of magnet slots (20a) of the two pairs of magnet slots (20a, 20b) to one end of the first magnet slot (21b) in the other pair of magnet slots (20b) of the two pairs of magnet slots (20a, 20b) and the second line segment (L2) is at least twice the length (d) of the third hole (33) in the radial direction of the rotor core (10a). (Supplementary Note 12) A rotor core (10a) according to any one of Supplements 1 to 11, further comprising fourth holes (34) formed radially inward of the rotor core (10a) relative to the third holes (33), and each of the third holes (33) and each of the fourth holes (34) being juxtaposed in the radial direction of the rotor core (10a). (Supplementary Note 13) A rotor (10) comprising: the rotor core (10a) according to any one of Supplements 1 to 12; magnets (91, 92) inserted into each of the pairs of magnet slots (20), (20); and a shaft portion (5) inserted into the rotor core. (Supplementary Note 14) An electric motor (1) comprising: the rotor (10) according to Supplementary Note 13; and a stator (9) arranged around the rotor (10).

[0075] REFERENCE SIGNS LIST 1 Electric motor 5 Shaft portion 9 Stator 10 Rotor 10a Rotor core 11 First outer peripheral portion 12 Second outer peripheral portion 20, 20a, 20b Pair of magnet slots 21, 21a, 21b First magnet slot 21g, 21p Air gap 22, 22a, 22b Second magnet slot 22g, 22p Air gap 31 First hole 31a First portion 31b Second portion 32 Second hole 32a First portion 32b Second portion 33 Third hole 33a Apex angle 33b Protrusion 34 Fourth hole 34a, 34b Protrusion 91, 92 Magnet L0, L0' Line segment L1 First line segment L2 Second line segment L3 Third line segment

Claims

1. It is a rotor core, The rotor core has multiple pairs of magnet slots formed therein, extending in the axial direction of the rotor core. The plurality of pairs of magnet slots are arranged at equal intervals in the circumferential direction of the rotor core in the radial cross-section of the rotor core. Each pair of magnet slots in the plurality of pairs of magnet slots includes a first magnet slot that is inclined counterclockwise with respect to the radius of the rotor core and a second magnet slot that is inclined clockwise with respect to the radius of the rotor core. In each pair of magnet slots, one end of the first magnet slot and one end of the second magnet slot are spaced apart from each other, and the other end of the first magnet slot and the other end of the second magnet slot are adjacent to each other radially inward from the rotor core than the one end of the first magnet slot and the one end of the second magnet slot. Furthermore, a first hole is formed adjacent to each pair of magnet slots, The rotor core comprises a first hole including a first portion corresponding to at least a part of the region between the other end of the first magnet slot and the other end of the second magnet slot, and a second portion continuous with the first portion and located radially inward of the rotor core than the first portion.

2. A gap is formed between the other end of the first magnet slot and the other end of the second magnet slot, The rotor core according to claim 1, wherein the gap partially protrudes radially outward from the rotor core beyond the line segment connecting the other end of the first magnet slot on the radially outward side of the rotor core and the other end of the second magnet slot on the radially outward side of the rotor core.

3. The distance between the gap formed at the other end of the first magnet slot and the first hole is less than or equal to half the distance between the other end of the first magnet slot and the first hole. The rotor core according to claim 2, wherein the distance between the gap formed at the other end of the second magnet slot and the first hole is less than or equal to half the distance between the other end of the second magnet slot and the first hole.

4. The outer circumference of the rotor core is composed of a plurality of first outer circumference portions and a plurality of second outer circumference portions that connect each of the plurality of first outer circumference portions. The plurality of first outer peripheral portions correspond to the respective regions of the plurality of pairs of magnet slots, The plurality of second outer peripheral portions correspond to the regions between two pairs of adjacent magnet slots among the plurality of pairs of magnet slots, The rotor core according to claim 1, wherein the outermost portion of the plurality of first outer peripheral portions is located radially outward of the rotor core than the outermost portion of the plurality of second outer peripheral portions.

5. The aforementioned multiple first outer portions are composed of at least one curve. The rotor core according to claim 4, wherein the plurality of second outer peripheral portions are composed of at least one straight line.

6. Furthermore, a second hole is formed adjacent to each pair of magnet slots. The rotor core according to claim 1, wherein each of the first holes and each of the second holes are arranged side by side in the radial direction of the rotor core.

7. Each of the second holes is composed of a substantially isosceles triangle in the radial cross-section of the rotor core, with its apex angle pointing towards the center of the rotor core, and an arc projecting radially outward from the base of the isosceles triangle. The rotor core according to claim 6, wherein at least a portion of the arc of the second hole is located radially outward of the rotor core than the first line segment connecting one end of the first magnet slot and one end of the second magnet slot, on the radially outward side of the rotor core.

8. The distance between the gap formed at the other end of the first magnet slot and the second hole is less than or equal to half the distance between the other end of the first magnet slot and the first hole. The rotor core according to claim 6, wherein the distance between the gap formed at the other end of the second magnet slot and the second hole is less than or equal to half the distance between the other end of the second magnet slot and the first hole.

9. A third hole is formed between two adjacent pairs of magnet slots among the aforementioned plurality of pairs of magnet slots. The rotor core according to claim 1, wherein the third hole is formed radially outward of the rotor core than the second line segment connecting the other end of the second magnet slot in one of the two pairs of magnet slots and the other end of the first magnet slot in the other pair of magnet slots.

10. The rotor core according to claim 9, wherein the distance between the third hole and the first magnet slot or the second magnet slot is more than half the thickness of the magnet to be inserted into the first magnet slot or the second magnet slot.

11. The rotor core according to claim 9, wherein the distance between the third line segment connecting one end of the second magnet slot in one of the two pairs of magnet slots and one end of the first magnet slot in the other pair of magnet slots and the second line segment is at least twice the length of the third hole in the radial direction of the rotor core.

12. Furthermore, a fourth hole is formed radially inward of the rotor core compared to the third hole. The rotor core according to claim 9, wherein each of the third holes and each of the fourth holes are arranged radially to the rotor core.

13. A rotor core according to claim 1 or 2, Magnets inserted into each of the aforementioned multiple pairs of magnet slots, A rotor comprising a shaft portion inserted into the rotor core.

14. The rotor according to claim 13, An electric motor comprising a rotor and a stator arranged around the rotor.