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

Rotor core, rotor, and motor

[0001] SUMMARY OF THE INVENTION Embodiments of the present invention relate 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 possible to rotate the V-shaped tips of each pair of magnet slots and extend them radially inward of the core. However, this reduces the area of ​​the rotor core where holes can be formed. As a result, it is difficult to reduce the weight and inertia.

[0005] Therefore, there is a need for a lightweight rotor core, rotor, and electric motor that can reduce inertia 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 the plurality of pairs 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 further comprising a first magnet slot and a second magnet slot inclined clockwise with respect to the radius of the rotor core between the first magnet slot and the second magnet slot in each pair of magnet slots. a rotor core having a plurality of holes formed therein extending in the axial direction of the rotor core, each of the plurality of holes in a radial cross section of the rotor core being composed of an approximately isosceles triangle with its apex angle pointing toward the center of the rotor core and an arc protruding radially outward from the base of the isosceles triangle, and at least a portion of the arc in the hole in the radial cross section of the rotor core being located radially outward from the rotor core with respect to a first line segment between a portion of the first magnet slot located at the outermost position of the rotor core and a portion of the second magnet slot located at the outermost position of the rotor core.

[0007] The objects, features and advantages of the present invention 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 according to a first embodiment of the present invention; FIG. 2 is a radial sectional view of a rotor of the electric motor according to the first embodiment; FIG. 3 is a first partially enlarged view of the rotor shown in FIG. 2; FIG. 4 is a second partially enlarged view of the rotor shown in FIG. 2; FIG. 5 is a third partially enlarged view of the rotor shown in FIG. 2; FIG. 6 is a partial sectional view showing magnetic flux of an electric motor in the prior art; FIG. 7 is a diagram showing the relationship between time and torque of an electric motor in the prior art; FIG. 8 is a partial sectional view showing magnetic flux of an electric motor according to the first embodiment; FIG. 9 is a diagram showing the relationship between time and torque of an electric motor according to the first embodiment; FIG. 10 is a radial sectional view of a rotor core of the electric motor according to the first embodiment;

[0009] Hereinafter, embodiments of the present invention will be described 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 according to a first embodiment of the present invention. 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 that passes through the rotor 9 is rotatably supported by the stator 9 via the first bearing 7 and the second bearing 8. A detector 6 that detects 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 the rotor of the electric motor according to the first embodiment. The rotor 10 shown in Fig. 2 is generally ring-shaped and has 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 10 is not smooth.

[0011] The rotor 10 is formed with a plurality of pairs of magnet slots 20 that extend in the axial direction of the rotor 10 and are equally spaced apart 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 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] Permanent magnets 21a and 21b are inserted into these magnet slots 21 and 22. 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 preferably the same shape as each other. Furthermore, it is preferable that the magnet slots 21 and 22 have additional notches or the like formed therein in order to easily insert and remove the permanent magnets 21a and 21b.

[0013] These magnet slots 21, 22 are arranged so as to converge toward each other toward the inside in the radial direction of the rotor 10. In other words, these magnet slots 21, 22 are formed so as to form a substantial V-shape. However, these magnet slots 21, 22 do not need to be connected to each other on the inside in the radial direction.

[0014] 2, the outer periphery of the rotor 10 is made up of a plurality of first outer periphery portions 11 and a plurality of second outer periphery portions 12 that connect each of 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 10. As can be seen from FIG. 2, the plurality of first outer periphery portions 11 correspond to the regions of the plurality of pairs of magnet slots 20. And the plurality of second outer periphery portions 12 each correspond to the region 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 peripheral portion 11 is located radially outward of the rotor 10 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 10. The entire first outer peripheral portion 11 is located inside a circle (shown by a dashed line in FIG. 8 , described later) whose radius is a line segment connecting the center O of the rotor 10 and the outermost portion of the first outer peripheral portion 11. Furthermore, it is preferable that the outermost portion of the second outer peripheral portion 12 be located radially outward of one pair of permanent magnets 21 b and the other pair of permanent magnets 21 a of the two pairs of magnet slots 20 adjacent to the second outer peripheral portion 12.

[0016] In this way, because the outer periphery of the rotor 10 is not a perfect circle, the change in the magnetic flux linkage is small when the electric 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, it is possible to improve the controllability of the electric motor 1 having the rotor 10.

[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.

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

[0019] 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, too, the outermost portions of the multiple first outer peripheral portions 11 are located radially outward of the rotor 10 relative to the outermost portions of the multiple second outer peripheral portions 12, so the outer periphery of the rotor 10 has a shape that is different from a perfect circle. Therefore, it can be seen that the same effect as described above can be obtained.

[0020] Furthermore, in a modification of the first embodiment (not shown), the first outer peripheral portion 11 may be located radially inward of the rotor 10 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.

[0021] As shown in Fig. 2, a plurality of holes 30 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. Fig. 3 is a first enlarged partial view of the rotor shown in Fig. 2. As can be seen from Figs. 2 and 3, each of the plurality of holes 30 is formed in an area of ​​the rotor 10 corresponding to the first outer peripheral portion 11. Strictly speaking, the hole 30 is formed between the first magnet slot 21 and the second magnet slot 22 of a pair of magnet slots 20. The shape of the hole 30 will be described later.

[0022] Similarly, multiple sets of holes 41, 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, 42 is formed in a region of the rotor 10 corresponding to the second outer peripheral portion 12. Furthermore, hole 41 is formed radially outward of hole 42 and is smaller than hole 42. In one example, hole 41 is circular, and hole 42 is elliptical, the width of which decreases from the inner to the outer radial direction of the rotor 10. Alternatively, at least one of holes 41, 42 may be elliptical or oval.

[0023] The shape of the holes 30 will be described below. As shown in FIG. 3 , each of the holes 30 is composed of a first portion 31 and a second portion 32 located radially outward of the first portion 31 of the rotor 10. The center lines of the first portion 31 and the second portion 32 are located on one radius R of the rotor 10. Note that the "radius R" in this specification is a portion of the straight dashed line that extends from the center O of the rotor 10 and passes through the center line of the hole 30 in FIG. 8 , which will be described later. In other words, the "radius R" is the line segment that connects the center O of the rotor 10 and the edge of the first outer peripheral portion 11.

[0024] 3, the first portion 31 has a shape of a substantially isosceles triangle T with its apex angle pointing toward the center O of the rotor 10. The second portion 32 has a shape of an arc, for example a semicircular arc, that protrudes from the base of the isosceles triangle T toward the outside in the radial direction of the rotor 10. It is preferable that the first portion 31 and the second portion 32 are smoothly connected to each other.

[0025] The reason for using the term "approximately isosceles triangle" is to include cases that differ from a perfect isosceles triangle, such as when the apex 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 includes a curve. Furthermore, the arc serving as the second portion 32 may be longer or shorter than the arc of a semicircle. Furthermore, the arc serving as the second portion 32 may be the arc of an ellipse.

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

[0027] In this way, at least a portion of the hole 30 is located radially outward of the straight line XX' of the rotor 10, and therefore the length of the hole 30 on the radius R is longer than the length of one surface of the permanent magnets 21a, 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 results in a reduction in the weight of the rotor 10 and an increase in the speed 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 having the rotor 10 is operating.

[0028] As described above, it is preferable that the first outer peripheral portion 11 in which the holes 30 are formed protrudes radially outward of the rotor 10 more than the second outer peripheral portion 12. In this case, the holes 30 can be formed longer in the radial direction of the rotor 10 by the protruding portion of the first outer peripheral portion 11. Therefore, it will be understood that the holes 30 can be made larger and the rotor 10 can be made lighter.

[0029] Figure 4 is a second enlarged partial 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 line portion 33a extending from the base of the approximately isosceles triangle T and a second straight line portion 33b extending from the distal end of the first straight line portion 33a toward a point B at the apex of the approximately isosceles triangle T. As can be seen with reference to Figures 3 and 4, the first straight line portion 33a is connected to the second portion 32. In addition, the intersection point B between the two second straight line portions 33b may be rounded.

[0030] In Fig. 4, the first straight line portion 33a and the second straight line portion 33b intersect at an intersection C. As can be seen by referring to Figs. 3 and 4, the intersection C is located substantially outside the isosceles triangle T with respect to the hypotenuse corresponding to the intersection C. In other words, the angle formed by the radius R and the first straight line portion 33a shown in Fig. 4 is smaller than the angle formed by the radius R and the second straight line portion 33b.

[0031] Therefore, the first portion 31 having the above-described shape is larger than the first portion 31 as a perfect isosceles triangle T. Therefore, the hole 30 can be made larger, and the rotor 10 can be made correspondingly lighter. Furthermore, the second straight portion 33b extends from the vicinity of point B so as to enlarge the hole 30, while the first straight portion 33a extends so as to prevent the hole 30 from becoming larger. In other words, it is preferable that the hole 30 is formed so as 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 excessively large and prevents the flow of magnetic flux from being obstructed on the radially outer side of the rotor 10.

[0032] Furthermore, in Figure 4, in a pair of magnet slots 20, the portion of the first magnet slot 21 that is closest to the radius R is designated as "Y", and the portion of the second magnet slot 22 that is 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'. The vertex B may be located at the intersection of the line YY' and the radius R, or may be located radially inward of the line YY' of the rotor 10. In this way, because the end of the hole 30 located radially inward of the rotor 10 is located near the line YY', the hole 30 can be made larger, and as a result, the rotor 10 can be made lighter.

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

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

[0035] 5 is the length between the edge 5a of the through hole of the rotor 10, into which the shaft portion 5 is inserted, and the outermost portion of the rotor 10, and indicates the length of a portion on the radius R. The line segment L4 indicates 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 peripheral portion 11 and the second portion 32 of the hole 30.

[0036] 5, the length of line segment L3 is preferably shorter 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 this case, the hole 30 can be kept large while preventing the flow of magnetic flux from being obstructed radially outside the rotor 10.

[0037] Here, FIG. 6A is a partial cross-sectional view showing the magnetic flux of a conventional electric motor, and FIG. 7A is a partial cross-sectional view showing the magnetic flux of a motor based on the first embodiment. The electric motor 1' shown in FIG. 6A includes a stator 9' and a rotor 10'. On the other hand, the electric motor 1 shown in FIG. 7A includes a stator 9 and the aforementioned rotor 10. The structure of the rotors 10 and 10' is well known, so a description thereof will be omitted. As can be seen by comparing FIGS. 6A and 7A, even if holes 30, 41, and 42 are formed as in the electric motor 1, the flow of magnetic flux is not obstructed by the holes 30 or the like. Furthermore, the electric motor 1 is lighter than the electric motor 1' by the amount of the holes 30, 41, and 42 formed.

[0038] Furthermore, FIG. 6B is a graph showing the relationship between time and torque of a motor according to the prior art, and FIG. 7B is a graph showing the relationship between time and torque of a motor according to the first embodiment. In these figures, the horizontal axis represents time, and the vertical axis represents torque of motors 1 and 1'. In FIG. 6B, the maximum torque of motor 1' is between 100 Nm and 101 Nm. In contrast, in FIG. 7B, the maximum torque of motor 1 is between 91.5 Nm and 92 Nm. In other words, even when holes 30, 41, and 42 are formed, the decrease in torque is suppressed to less than 10%.

[0039] In this way, even when the holes 30, 41, and 42 are formed, the torque is not significantly reduced and a practical torque can be generated. It will be apparent to those skilled in the art that the same effect can be obtained even when only the hole 30 is formed in the first embodiment.

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

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

[0042] 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.

[0043] 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 Magnet slot 21 First magnet slot 22 Second magnet slot 21a, 21b Permanent magnet 30 Hole 31 First portion 32 Second portion 33 Hypotenuse 33a First straight portion 33b Second straight portion 41, 42 Hole T Approximately isosceles triangle

Claims

1. A rotor core, The rotor core is 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 are disposed 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 of the plurality of pairs of magnet slots includes 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; Further, 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 a radial cross section of the rotor core, each of the plurality of holes is formed into a substantially isosceles triangle with an apex angle directed toward a center of the rotor core and an arc protruding from a base of the isosceles triangle toward the outside in the radial direction of the rotor core, A rotor core, wherein at least a portion of the arc in the hole in a radial cross section of the rotor core is located radially outward of the rotor core more than a first line segment between a portion of the first magnet slot located at the outermost position of the rotor core and a portion of the second magnet slot located at the outermost position of the rotor core.

2. The outer periphery of the rotor core is composed of a plurality of first outer periphery portions and a plurality of second outer periphery portions connecting the plurality of first outer periphery portions, the first outer circumferential portions correspond to respective regions of the pairs of magnet slots; The second outer circumferential portions each correspond to an area between two adjacent pairs of magnet slots among the plurality of pairs of magnet slots, The rotor core according to claim 1 , wherein an outermost portion of the first outer circumferential portions is located radially outward of the rotor core relative to an outermost portion of the second outer circumferential portions.

3. The first outer periphery portions are formed of at least one curve, The rotor core according to claim 2 , wherein the second outer circumferential portions are formed by at least one straight line.

4. Each of the two hypotenuses of the approximately isosceles triangle has a first straight line portion extending from the base and a second straight line portion extending from a distal end of the first straight line portion toward an apex angle of the approximately isosceles triangle, 3 . The rotor core according to claim 1 , wherein an intersection between the first straight portion and the second straight portion is located outside the approximately isosceles triangle with respect to the hypotenuse corresponding to the intersection.

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

6. A through hole for a shaft portion to be inserted into the rotor core is formed, A rotor core as described in claim 1 or 2, wherein the length of a third line segment located on the radius of the rotor core and connecting the outer edge of the through hole to the first outer peripheral portion is shorter than 10 times the distance from the first outer peripheral portion to the arc on the third line segment.

7. A rotor core according to claim 1 or 2, A shaft portion inserted into the rotor core; a magnet inserted into each of the pairs of magnet slots of the rotor core.

8. A rotor according to claim 7; and a stator disposed around the rotor.