Rotor core, rotor, and electric motor

Abstract

The present invention provides a rotor core (10a) provided with a plurality of pairs of magnet slots (20) formed to assume a V shape. A plurality of holes (30) are formed between each pair of magnet slots. The hole (30) includes a general isosceles triangle (T, 31) with the vertex angle directed to the center of the rotor core and an arc (32) connected to the base of the isosceles triangle. At least a part of the arc is positioned, in a radial direction of the rotor core, on an outer side of a first line segment connecting outermost portions of the magnet slots.

Description

Technical Field

[0001] Embodiments of the present invention relate to a rotor core, a rotor, and an electric motor.

Background Art

[0002] On the end face of the rotor core of a motor, a plurality of pairs of magnet slots arranged in a V shape are formed, and magnets are inserted into each magnet slot. For the purpose of reducing the weight of the rotor core and reducing inertia, holes are formed in the rotor core (see, for example, Japanese Patent No. 6987310). However, when holes are formed inside each pair of magnet slots arranged in a V shape, the flow of magnetic flux is obstructed and the torque is reduced.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In order to increase the torque, it is conceivable to rotate the V-shaped tip portions in each pair of magnet slots and extend them inward in the radial direction of the core. However, in this case, the area of the rotor core where holes can be formed becomes small. As a result, it is difficult to reduce the weight and it is also difficult to reduce the inertia.

[0005] Therefore, a lightweight rotor core, rotor, and electric motor that can reduce inertia without reducing torque are desired.

Means for Solving the Problems

[0006] According to a first aspect of the present disclosure, a rotor core is provided, the rotor core having a plurality of pairs of magnet slots extending in the axial direction of the rotor core, the plurality of pairs of magnet slots being arranged at equal intervals in the circumferential direction of the rotor core in a radial cross-section of the rotor core, each pair of magnet slots of the plurality of pairs of magnet slots including a first magnet slot inclined counterclockwise with respect to the radius of the rotor core and a second magnet slot inclined clockwise with respect to the radius of the rotor core, further comprising a plurality of holes extending in the axial direction of the rotor core between the first magnet slot and the second magnet slot in each pair of magnet slots, each of the plurality of holes in a radial cross-section of the rotor core being a substantially isosceles triangle with its apex angle pointing toward the center of the rotor core and protruding radially outward from the base of the isosceles triangle semicircular A rotor core is provided, comprising an arc, wherein in the radial cross-section of the rotor core, at least a portion of the arc in the hole is located radially outward of the rotor core than a first line segment between a portion of the first magnet slot located at the outermost edge of the rotor core and a portion of the second magnet slot located at the outermost edge of the rotor core.

[0007] The object, features, and advantages of the present invention will become even clearer from the following description of embodiments related to the accompanying drawings. [Brief explanation of the drawing]

[0008] [Figure 1] This is a cross-sectional view in the axial direction of an electric motor according to the first embodiment of the present invention. [Figure 2] This is a radial cross-sectional view of the rotor of an electric motor according to the first embodiment. [Figure 3] Figure 2 is a first partial enlarged view of the rotor shown. [Figure 4] Figure 2 is a second magnified view of the rotor shown. [Figure 5] Figure 2 is a third magnified view of the rotor. [Figure 6A]This is a partial cross-sectional view showing the magnetic flux of an electric motor in the prior art. [Figure 6B] This diagram shows the relationship between time and torque in conventional electric motors. [Figure 7A] This is a partial cross-sectional view showing the magnetic flux of an electric motor based on the first embodiment. [Figure 7B] This figure shows the relationship between time and torque of an electric motor based on the first embodiment. [Figure 8] This is a radial cross-sectional view of the rotor core of an electric motor according to the first embodiment. [Modes for carrying out the invention]

[0009] Embodiments of the present invention will be described below with reference to the attached drawings. Throughout all drawings, corresponding components are denoted by the same reference numerals. Figure 1 is an axial cross-sectional view of an electric motor according to a first embodiment of the present invention. As shown in Figure 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 arranged on the inner circumferential surface of the stator 9. A shaft portion 5 that passes through the rotor 9 is rotatably supported by the stator 9 by the first bearing 7 and the second bearing 8. A detector 6 for detecting the rotational speed of the shaft portion 5 is attached to one end of the stator 9.

[0010] Figure 2 is a radial cross-sectional view of the rotor of an electric motor according to the first embodiment. The rotor 10 shown in Figure 2 is substantially ring-shaped with a through hole for the shaft portion 5 in the center. However, as will be described later, it is preferable that the outer surface of the rotor 10 is not smooth.

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

[0012] Permanent magnets 21a and 21b are inserted into these magnet slots 21 and 22, respectively. Therefore, the magnet slots 21 and 22 are preferably substantially rectangular in shape to correspond to the shapes of the permanent magnets 21a and 21b, and are identical in shape to each other. Furthermore, it is preferable that additional notches or the like are formed in the magnet slots 21 and 22 in order to easily insert and remove the permanent magnets 21a and 21b.

[0013] These magnet slots 21 and 22 are arranged to converge toward each other radially inward from the rotor 10. In other words, these magnet slots 21 and 22 are formed in a roughly V-shape. However, these magnet slots 21 and 22 do not need to be connected to each other radially inward.

[0014] Furthermore, in Figure 2, the outer circumference of the rotor 10 is composed of a plurality of first outer circumference portions 11 and a plurality of second outer circumference portions 12 that connect each of the plurality of first outer circumference portions 11. In other words, the plurality of first outer circumference portions 11 and the plurality of second outer circumference portions 12 are arranged alternately in the circumferential direction of the rotor 10. As can be seen from Figure 2, the plurality of first outer circumference portions 11 correspond to the respective regions of the plurality of pairs of magnet slots 20. The plurality of second outer circumference portions 12 correspond to the regions between two adjacent pairs of magnet slots 20 among the plurality of pairs of magnet slots 20.

[0015] Furthermore, the outermost portion of the first outer circumference portion 11 is located radially outward of the rotor 10 than the outermost portion of the second outer circumference portion 12. In other words, multiple first outer circumference portions 11 as convex portions and multiple second outer circumference portions 12 as concave portions are alternately arranged in the circumferential direction of the rotor 10. The entire first outer circumference portion 11 is located inside a circle (shown by a dashed line in Figure 8, described later) whose radius is the line segment connecting the center O of the rotor 10 and the outermost portion of the first outer circumference portion 11. Preferably, the outermost portion of the second outer circumference portion 12 is located radially outward of the rotor 10 than one pair of permanent magnets 21b and the other pair of permanent magnets 21a of two pairs of magnet slots 20 adjacent to the second outer circumference portion 12.

[0016] Thus, since the outer periphery of the rotor 10 is not a perfect circle, the change in the magnetic flux linkage number becomes small when the motor 1 having the rotor 10 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, the controllability of the motor 1 provided with the rotor 10 can be enhanced.

[0017] Also, in FIG. 2, each of the outermost portions of the first outer peripheral portion 11 is composed of 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 surely located inside the aforementioned circle and becomes smooth.

[0018] And each of the outermost portions of the second outer peripheral portion 12 is composed of at least one straight line. In the illustrated embodiment, the outermost portion of the second outer peripheral portion 12 includes a straight line substantially parallel to one side of the permanent magnets 21a of one pair and one side of the permanent magnets 21b of the other pair among the two pairs of magnet slots 20 adjacent to the second outer peripheral portion 12.

[0019] In an embodiment not shown, the outermost portion of the first outer peripheral portion 11 may be composed of at least one straight line, and the outermost portion of the second outer peripheral portion 12 may be composed of at least one curve. Further, both the outermost portion of the first outer peripheral portion 11 and the outermost portion of the second outer peripheral portion 12 may be composed of 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 composed of at least one curve. Further, at least one of the outermost portion of the first outer peripheral portion 11 and the outermost portion of the second outer peripheral portion 12 may be composed of at least one straight line and at least one curve. Even in such a case, since the outermost portions of the plurality of first outer peripheral portions 11 are located radially outside the outermost portions of the plurality of second outer peripheral portions 12 with respect to the rotor 10, the outer periphery of the rotor 10 has a shape different from a perfect circle. Therefore, it can be understood that the same effects as described above can be obtained.

[0020] Furthermore, in a modified example of the first embodiment (not shown), the first outer peripheral portion 11 may be located radially inward of the rotor 10 than the second outer peripheral portion 12. Even in this case, the same effects as described above can be obtained and it falls within the scope of the first embodiment.

[0021] As shown in Figure 2, the end face of the rotor 10 has multiple holes 30 that extend in the axial direction of the rotor 10 and are formed at equal intervals in the circumferential direction. Figure 3 is a first partial enlarged view of the rotor shown in Figure 2. As can be seen from Figures 2 and 3, each of the multiple holes 30 is formed in the region of the rotor 10 corresponding to the first outer peripheral portion 11. More precisely, the holes 30 are formed between the first magnet slot 21 and the second magnet slot 22 of a pair of magnet slots 20. The shape of the holes 30 will be described later.

[0022] Similarly, multiple sets of holes 41 and 42 extending in the axial direction of the rotor 10 are formed at equal intervals in the circumferential direction on the end face of the rotor 10. As can be seen from Figures 2 and 3, each of the multiple sets of holes 41 and 42 is formed in the region of the rotor 10 corresponding to the second outer peripheral portion 12. Furthermore, hole 41 is formed radially outward from hole 42 of the rotor 10, and hole 41 is smaller than hole 42. In one example, hole 41 is circular, and hole 42 is oval, with its width decreasing from the radially inside to the outside of the rotor 10. Alternatively, at least one of holes 41 and 42 may be oval or elliptical.

[0023] The shape of the holes 30 will now be described. As shown in Figure 3, each of the holes 30 consists of a first portion 31 and a second portion 32 located radially outward from the rotor 10 than the first portion 31. The centerlines of the first portion 31 and the second portion 32 are located on one radius R of the rotor 10. In this specification, "radius R" is a portion of the straight dashed line in Figure 8, which will be described later, that extends from the center O of the rotor 10 and passes through the centerline of the holes 30. In other words, "radius R" is the line segment connecting the center O of the rotor 10 and the edge of the first outer circumference portion 11 from the center O.

[0024] As shown in Figure 3, the first part 31 is in the shape of an approximately isosceles triangle T, with its vertex angle pointing towards the center O of the rotor 10. The second part 32 is in the shape of a circular arc, such as a semicircular arc, projecting radially outward from the base of the isosceles triangle T of the rotor 10. Preferably, the first part 31 and the second part 32 are smoothly connected to each other.

[0025] The reason for specifying "approximately isosceles triangle" is to include cases that differ from a perfect isosceles triangle, such as when the vertex of the isosceles triangle T is rounded, when each of the two hypotenuses 33 of the isosceles triangle T is composed of multiple straight lines, or when each of the two hypotenuses 33 of the isosceles triangle T contains a curve. Furthermore, the arc as the second part 32 may be longer or shorter than the arc of a semicircle. Also, the arc as the second part 32 may be an elliptical arc.

[0026] In Figure 3, in one pair of magnet slots 20, a portion of the first magnet slot 21 located on the outermost side of the rotor 10 is denoted as "X", and a portion of the magnet slot 22 located on the outermost side of the rotor 10 is denoted as "X'". At least a portion of the arc representing the second portion 32, for example, point A, is located radially outward from the line XX' of the rotor 10.

[0027] Thus, since at least a portion of the hole 30 is located radially outward from the rotor 10 than the straight line XX', the length of the hole 30 along radius R is longer than the length of one surface of the permanent magnets 21a and 21b facing the hole 30 (corresponding to the width of the permanent magnets). Therefore, in the first embodiment, a large hole 30 can be formed, which in turn makes the rotor 10 lighter and allows for higher speeds of the electric motor 1. Furthermore, because the second portion 32 is an arc, the flow of magnetic flux is not obstructed when the electric motor 1 with the rotor 10 is driven.

[0028] As mentioned above, it is preferable that the first outer peripheral portion 11 in which the hole 30 is formed protrudes radially outward from the rotor 10 than the second outer peripheral portion 12. In this case, the hole 30 can be made even longer radially from the rotor 10 by the protruding portion of the first outer peripheral portion 11. Therefore, it can be seen that the hole 30 can be made larger and the rotor 10 can be made lighter.

[0029] Figure 4 is a second enlarged view of the rotor shown in Figure 2. In Figure 4, each hypotenuse 33 of the first portion 31 of the hole 30 has a first straight section 33a extending from the base of a roughly isosceles triangle T, and a second straight section 33b extending from the distal end of the first straight section 33a toward point B, the vertex angle of the roughly isosceles triangle T. As can be seen by referring to Figures 3 and 4, the first straight section 33a is connected to the second portion 32. The intersection point B between the two second straight sections 33b may also be rounded.

[0030] In Figure 4, the first straight section 33a and the second straight section 33b intersect at intersection point C. As can be seen by referring to Figures 3 and 4, intersection point C is located outside the approximately isosceles triangle T with respect to the hypotenuse corresponding to intersection point C. In other words, the angle between radius R and the first straight section 33a shown in Figure 4 is smaller than the angle between radius R and the second straight section 33b.

[0031] Therefore, the first part 31 having the shape described above is larger than the first part 31 as a perfect isosceles triangle T. Consequently, the hole 30 is made larger, and the rotor 10 can be made lighter by that amount. Furthermore, the second straight section 33b extends from the vicinity of point B to enlarge the hole 30, while the first straight section 33a extends to suppress the enlargement of the hole 30. In other words, it is preferable that the hole 30 is formed to be larger on the radially inner side of the rotor 10 and smaller on the radially outer side of the rotor 10. This prevents the hole 30 from becoming extremely large and suppresses obstruction of the magnetic flux flow on the radially outer side of the rotor 10.

[0032] Furthermore, in Figure 4, in a pair of magnet slots 20, a portion of the first magnet slot 21 closest to radius R is designated as "Y," and a portion of the second magnet slot 22 closest to the same radius R is designated as "Y'." The vertex B on the apex side of the approximately isosceles triangle T is located near the line YY'. Vertex B may be located at the intersection of line YY' and radius R, or it may be located radially inward of line YY' from the rotor 10. In this way, the end of the hole 30 located radially inward of the rotor 10 is located near line YY', so the hole 30 can be enlarged, and as a result, the rotor 10 can be made lighter.

[0033] Furthermore, it is preferable that vertex B is located radially outward from the line YY' of the rotor 10. This ensures the strength of the rotor 10. This configuration is particularly preferable when the rotor 10 is formed by stacking multiple magnetic plates in the axial direction of the rotor 10, as it ensures the strength of the multiple magnetic plates.

[0034] Furthermore, Figure 5 is a third enlarged view of the rotor shown in Figure 2. In the example shown in Figure 5, the maximum width L2 of the hole 30 perpendicular to the radius R (see Figures 3 and 4) roughly corresponds to the base of the approximately isosceles triangle T mentioned above. Preferably, this maximum width L2 is 1 / 3 or less of the length L1 of the straight line XX'. This prevents the hole 30 from becoming excessively large while suppressing obstruction of the magnetic flux flow on the radially outer side of the rotor 10.

[0035] Furthermore, the line segment L3 shown in Figure 5 is the length between the edge 5a of the through hole in the rotor 10 into which the shaft portion 5 is inserted and the outermost portion of the rotor 10, and represents the length of a portion of the radius R mentioned above. The line segment L4 represents the length between the outermost portion of the hole 30 in the radial direction of the rotor 10 and the outermost portion of the rotor 10 in the radial direction. In other words, the line segment L4 is the shortest distance between the first outer circumference portion 11 and the second portion 32 of the hole 30.

[0036] In Figure 5, it is preferable that the length of line segment L3 is less than 10 times the length of line segment L4. In one example, the length of line segment L3 is 10 times the length of line segment L4. In such a case, it is possible to maintain a large hole 30 while suppressing obstruction of the magnetic flux flow on the radially outer side of the rotor 10.

[0037] Here, Figure 6A is a partial cross-sectional view showing the magnetic flux of a conventional electric motor, and Figure 7A is a partial cross-sectional view showing the magnetic flux of an electric motor based on the first embodiment. The electric motor 1' shown in Figure 6A includes a stator 9' and a rotor 10'. On the other hand, the electric motor 1 shown in Figure 7A includes a stator 9 and the aforementioned rotor 10. The structures of rotors 10 and 10' are well known, so their explanation is omitted. As can be seen by comparing Figure 6A and Figure 7A, even when holes 30, 41, and 42 are formed as in electric motor 1, the flow of magnetic flux is not obstructed by holes 30, etc. Furthermore, electric motor 1 is lighter than electric motor 1' due to the presence of holes 30, 41, and 42.

[0038] Furthermore, Figure 6B shows the relationship between time and torque of a conventional electric motor, and Figure 7B shows the relationship between time and torque of an electric motor based on the first embodiment. In these figures, the horizontal axis represents time, and the vertical axis represents the torque of electric motors 1 and 1'. In Figure 6B, the maximum torque of electric motor 1' is between 100 Nm and 101 Nm. In contrast, in Figure 7B, the maximum torque of electric motor 1 is between 91.5 Nm and 92 Nm. In other words, even when holes 30, 41, and 42 are formed, the torque reduction is kept to less than 10%.

[0039] Thus, even when holes 30, 41, and 42 are formed, the torque does not decrease significantly, and a practical torque can be generated. Furthermore, it will be obvious to those skilled in the art that a similar effect can be obtained even when only hole 30 is formed in the first embodiment.

[0040] Therefore, in the first embodiment of the present invention, the rotor 10 can be made lighter by forming holes 30, etc., and the inertia can be reduced without a significant decrease in torque. In other words, a lightweight rotor 10 that can reduce inertia without a decrease in torque can be provided. Consequently, it becomes possible to increase the acceleration of the electric motor 1 having the rotor 10.

[0041] Furthermore, Figure 8 is a radial cross-sectional view of the rotor core of an electric motor according to the first embodiment. The rotor core 10a of the rotor 10 shown in Figure 8 is obtained by removing all the permanent magnets 21a, 21b and the rotor 5 from the rotor 10 shown in Figure 2. The other elements shown in Figure 8 are the same as those described with reference to Figure 2. Such a rotor core 10a shown in Figure 8, and the electric motor 1 shown in Figure 1, etc., are also included in the scope of the first embodiment of the present invention.

[0042] While embodiments of this disclosure have been described in detail, this disclosure is not limited to the individual embodiments described above. These embodiments can be added, replaced, modified, or partially deleted in various ways, without departing from the spirit of the invention or the idea and intent of the invention derived from the claims and their equivalents. For example, the order of operations and processes in the embodiments described above are given as examples only and are not limited thereto. The same applies when numerical values ​​or mathematical formulas are used in the description of the embodiments described above. Furthermore, combining some of the embodiments described above as appropriate is within the scope of this disclosure. [Explanation of symbols]

[0043] 1 electric motor 5. Shaft section 9 Stator 10 rotors 10a Rotor core 11 First outer peripheral part 12 Second outer peripheral part 20 Magnetic Slots 21 First Magnet Slot 22 Second Magnet Slot 21a, 21b permanent magnet 30 holes 31 Part 1 32 Second part 33 Hypotenuse 33a First straight section 33b Second straight section 41, 42 holes T approximately isosceles triangle

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. Furthermore, a plurality of holes extending in the axial direction of the rotor core are formed between the first magnet slot and the second magnet slot in each pair of magnet slots. In the radial cross-section of the rotor core, each of the plurality of holes is composed of a substantially isosceles triangle whose apex angle points toward the center of the rotor core, and a semicircular arc projecting radially outward from the base of the isosceles triangle. A rotor core in which, in the radial cross-section of the rotor core, at least a portion of the arc in the hole is located radially outward of the rotor core than the first line segment between a portion of the first magnet slot located at the outermost edge of the rotor core and a portion of the second magnet slot located at the outermost edge of the rotor core.

2. 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.

3. The aforementioned multiple first outer portions are composed of at least one curve. The rotor core according to claim 2, wherein the plurality of second outer peripheral portions are composed of at least one straight line.

4. Each of the two hypotenuses of the aforementioned approximately isosceles triangle has a first straight section extending from the base and a second straight section extending from the distal end of the first straight section toward the vertex angle of the aforementioned approximately isosceles triangle. The rotor core according to claim 1 or 2, wherein the intersection point between the first straight section and the second straight section is located outside the substantially isosceles triangle with respect to the hypotenuse corresponding to the intersection point.

5. The rotor core according to claim 1 or 2, wherein the length of the base of the substantially isosceles triangle is 1 / 3 or less of the length of the first line segment.

6. A through hole is formed in the rotor core for the shaft portion to be inserted, The rotor core according to claim 2, wherein the length of the third line segment, which is located on the radius of the rotor core and connects the outer edge of the through hole to the first outer circumference, is shorter than 10 times the distance from the first outer circumference to the arc on the third line segment.

7. A rotor core according to claim 1 or 2, The shaft portion inserted into the rotor core, A rotor comprising magnets inserted into each of the plurality of pairs of magnet slots of the rotor core.

8. The rotor according to claim 7, An electric motor comprising a rotor and a stator arranged around the rotor.

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