Fixer

Abstract

This stator comprises: a stator iron core (11) including a back yoke (13) that is mounted around a shaft and surrounds a rotor (30), and a plurality of teeth (14) that are mounted at intervals in a circumferential direction of the shaft and attached to the back yoke (13); and a coil (12) wound around each tooth (14). Each of the teeth (14) has an inner peripheral surface facing the rotor (30), and includes a tip portion (14a) protruding forward and backward in a rotating direction of the rotor (30), and a base portion (14b) facing the back yoke (13). The inner peripheral surface (14c) includes a first region (14d), and a second region (14e). An average interval between the second region (14e) and an outermost trajectory of the rotor (30) is greater than an average interval between the first region (14d) and the outermost trajectory of the rotor (30).

Description

【Technical Field】 【0001】 The present disclosure relates to a stator of an electric motor or a generator. 【Background Art】 【0002】 To address environmental problems such as global warming, the concept of MEA (more electric aircraft), which is the electrification of aircraft equipment, is being promoted. As part of this, there is a demand for further smaller, lighter, and higher-power-density electric motors. For example, in order to improve the energy efficiency of an electric motor, it is known to adopt a rectangular flat wire with a rectangular cross-section. That is, a coil (rectangular flat coil) composed of rectangular flat wires is mounted on the electric motor, thereby improving the occupation ratio of the coil (see Patent Document 1). 【Prior Art Documents】 【Patent Documents】 【0003】 【Patent Document 1】 Japanese Patent Application Laid-Open No. 2021-158725 【Summary of the Invention】 【Problems to be Solved by the Invention】 【0004】 Generally, eddy currents are generated in the coil of an electric motor due to the magnetic flux from the rotor. When a rectangular flat coil is used for this coil, eddy current loss tends to increase due to the increase in its surface area. The increase in eddy current loss is one of the factors that reduce the energy efficiency of the electric motor. 【0005】 The present disclosure has been made in view of the above circumstances, and an object thereof is to provide a stator capable of improving the output density. 【Means for Solving the Problems】 【0006】 One aspect of the present disclosure is a stator comprising a back yoke provided around an axis and surrounding a rotor, and a stator core including a plurality of teeth spaced apart in the circumferential direction of the axis and attached to the back yoke, and a coil wound around each of the teeth, each of which has an inner circumferential surface facing the rotor and includes a tip portion projecting forward and backward in the rotational direction of the rotor, and a base portion facing the back yoke, wherein the inner circumferential surface includes a first region located forward in the rotational direction and a second region located backward in the rotational direction relative to the first region, and the average distance between the second region and the outermost trajectory of the rotor is greater than the average distance between the first region and the outermost trajectory of the rotor. 【0007】 The first region of the inner circumferential surface may include a first curved surface having a center of curvature radially inward from the inner circumferential surface, and the second region of the inner circumferential surface may include a second curved surface having a center of curvature radially outward from the inner circumferential surface. The inner circumferential surface may include a portion perpendicular to the radial direction. The tip of each tooth may be formed in a flared shape toward the rotor. The coil may be made of a wire having a rectangular cross-section. The back yoke may be provided with a groove into which the base of each tooth is inserted. [Effects of the Invention] 【0008】 According to this disclosure, it is possible to provide a stator capable of improving output density. [Brief explanation of the drawing] 【0009】 [Figure 1] Figure 1 is a cross-sectional view of an electric motor equipped with a stator according to an embodiment of this disclosure. [Figure 2] Figure 2 is a partial cross-sectional view of a tooth and its surrounding area according to an embodiment of the present disclosure. [Figure 3] Figure 3 is a cross-sectional view of a modified example of teeth according to the present disclosure. [Figure 4]Figure 4 shows the analysis results of the magnetic flux density distribution around the connection portion between the back yoke and the teeth. Figure 4(a) shows the magnetic flux density distribution of a comparative example where no groove is formed, and Figure 4(b) shows the magnetic flux density distribution of this embodiment where a groove is formed. [Modes for carrying out the invention] 【0010】 The following describes a stator 10 according to several embodiments of this disclosure. Common parts in each figure are denoted by the same reference numerals, and redundant explanations are omitted. For convenience of explanation, the Z-axis is defined as the reference axis of the entire stator 10, and the circumferential direction CD and radial direction RD are defined with respect to a point on the Z-axis. The stator 10 surrounds the outer circumference of the rotor 30. The rotor 30 rotates in the rotational direction TD with the Z-axis as its rotational axis. This rotational direction TD is counterclockwise in Figure 1. 【0011】 The stator 10 and rotor 30 constitute the electric motor 1. Figure 1 is a cross-sectional view of the electric motor 1 equipped with the stator 10 according to this embodiment. This figure shows a cross-section of the electric motor 1 perpendicular to the Z-axis. The electric motor may be a DC motor such as an electromagnet field commutator motor, or an AC motor such as a permanent magnet synchronous motor. The stator 10 and rotor 30 can also constitute a generator such as a permanent magnet synchronous generator. 【0012】 The stator 10 comprises a stator core 11 and a coil 12. The stator core 11 comprises a back yoke 13 and a plurality of teeth 14. The back yoke 13 is positioned around the Z-axis as the central axis and surrounds the rotor 30. The stator core 11 and the coil 12 are housed in a casing (not shown). 【0013】 Multiple grooves 15 are formed on the inner circumferential surface 13a of the back yoke 13. The grooves 15 extend along the Z-axis. The width Wg of the grooves 15 along the circumferential direction CD (see Figure 2) is such that it accommodates the base 14b of the teeth 14 and allows the teeth 14 to slide along the Z-axis. The depth Dg of the grooves 15 along the radial direction RD is set to a value that provides a larger contact area between the back yoke 13 and the teeth 14 than when the teeth 14 are mounted on the inner circumferential surface 13a without grooves 15. For example, the depth Dg of the grooves 15 is set to half or more of the thickness Ty of the back yoke 13. 【0014】 Figure 2 is a partial cross-sectional view of the tooth 14 and its surrounding area. As shown in Figure 2, a projection 16 is formed on the bottom surface 15a of the groove 15. The projection 16 has a cross-sectional shape complementary to the cross-sectional shape of the dovetail groove 18 (described later) formed on the base 14b of the tooth 14, and extends along the Z-axis. The base 14b of the tooth 14 is inserted into the groove 15 from a direction along the Z-axis. At this time, the projection 16 on the back yoke 13 side engages with the dovetail groove 18 on the tooth 14 side. In addition, two adjacent teeth 14 attached to the back yoke 13 form a slot 17 between them (see Figure 1). The slot 17 is a space for housing the coil 12. 【0015】 As shown in Figure 1, multiple teeth 14 are arranged at intervals in the circumferential direction CD and extend from the back yoke 13 toward the Z axis (i.e., radially inward). This spacing (pitch) is equal to the spacing (pitch) of the grooves 15 formed in the back yoke 13. The teeth 14 are attached to the back yoke 13 by the engagement of the projections 16 and the grooves 15, and the two are magnetically coupled. This engagement also prevents the teeth 14 from falling out of the grooves 15. 【0016】 As shown in Figure 2, the teeth 14 have a tip portion 14a facing the rotor 30 and a base portion 14b facing the back yoke 13. The tip portion 14a protrudes forward and backward in the rotational direction (to both sides of the circumferential direction CD). In other words, the tip portion 14a has a first flange portion 20 that protrudes forward in the rotational direction TD of the rotor 30 (i.e., in the counterclockwise direction in Figure 1) and a second flange portion 21 that protrudes backward in the rotational direction TD. As an example, the tip portion 14a according to this embodiment is formed in a flared shape toward the rotor 30. That is, the tip portion 14a includes a portion in which the width along the circumferential direction CD increases as it approaches the rotor 30. This makes it possible to suppress an excessive increase in magnetic resistance within the tip portion 14a. 【0017】 The two side surfaces 14f, 14f of the tip portion 14a facing the circumferential direction CD may be concave surfaces that are recessed toward the vicinity of the intersection line between the center surface P of the teeth 14 and the inner circumferential surface 14c of the teeth 14, or they may be planes through which a perpendicular line passes near the vicinity of the intersection point (shown as a dotted line in the figure). In either case, the maximum width of the tip portion 14a along the circumferential direction CD is longer than the width of the base portion 14b along the circumferential direction CD. 【0018】 The tip portion 14a of the tooth 14 has a first side portion 20a and a second side portion 21a. The first side portion 20a is part of the first flange portion 20 and is located furthest forward in the rotational direction TD of the rotor 30. That is, the first side portion 20a is located furthest downstream (far left in Figure 2) in the rotational direction TD. The first side portion 20a may be formed continuously with the inner circumferential surface 14c as part of the inner circumferential surface 14c, or it may be formed as the end face of the first flange portion 20 facing forward in the rotational direction TD. 【0019】 The second side portion 21a is part of the second flange portion 21 and is located furthest rearward in the rotational direction TD. That is, the second side portion 21a is located furthest upstream (furthest right in Figure 2) in the rotational direction TD. Similar to the first side portion 20a, the second side portion 21a may be formed continuously with the inner circumferential surface 14c as part of the inner circumferential surface 14c, or it may be formed as the end face of the second flange portion 21 facing rearward in the rotational direction TD. 【0020】 The tip portion 14a of the tooth 14 has an inner peripheral surface 14c facing the rotor 30. The inner peripheral surface 14c extends from the first side portion 20a to the second side portion 21a. The inner peripheral surface 14c includes a first region 14d and a second region 14e. The first region 14d is located forward in the rotational direction TD and extends from the first side portion 20a toward the second side portion 21a. The second region 14e is located rearward of the first region 14d in the rotational direction TD and extends from the first region 14d to the second side portion 21a. 【0021】 The average distance between the second region 14e and the outermost locus of the rotor 30 is greater than the average distance between the first region 14d and the outermost locus of the rotor 30. Here, the average distance is a value obtained by averaging the shortest distances from each position in a region to the outermost locus of the rotor 30 during rotation along the circumferential direction CD (rotational direction TD). For example, when the cross-section of the rotor 30 is a perfect circle, the outermost locus of the rotor 30 coincides with the outer peripheral surface 30a of the rotor 30. In any case, the second region 14e includes more portions that are farther from the rotor 30 than the first region 14d. 【0022】 For convenience of explanation, in a cross-section orthogonal to the Z-axis, a connection point (boundary) C between the first region 14d and the second region 14e is defined. The connection point C is located on the center plane P of the tooth 14. The extension plane of the center plane P passes through the Z-axis. In other words, the Z-axis is included in the extension plane of the center plane P. Note that the position of the connection point C is not limited to being on the center plane P. 【0023】 The first region 14d may include the first curved surface 14da. The first curved surface 14da has at least one center of curvature radially inward from the inner circumferential surface 14c. Here, having a center of curvature radially inward (or radially outward) means that the line segment connecting a point on the first curved surface 14da to the center of curvature extends radially inward (or radially outward) from the point on the first curved surface 14da. For example, the first curved surface 14da has only one center of curvature, which lies on the Z-axis. In this case, the first curved surface 14da is arc-shaped, and the first curved surface 14da and the outermost trajectory of the rotor 30 (e.g., the outer circumferential surface 30a) are located concentrically. That is, the distance from the first curved surface 14da to the outermost trajectory of the rotor 30 is constant at each position on the first curved surface 14da along the circumferential direction CD. The inner circumferential surface 14c also includes a portion perpendicular to the radial direction RD at the connection point C. In this embodiment, since the connection point C is located on the central plane P, the inner circumferential surface 14c is perpendicular to the central plane P of the teeth 14. In this embodiment, the first region 14d is represented as the first curved surface 14da, which is a smooth arc-shaped curve in a cross section perpendicular to the Z axis (rotational axis). However, the first curved surface 14da may be represented as a curve formed by bending and connecting a plurality of curves whose respective centers of curvature are located radially inward in a cross section perpendicular to the Z axis (rotational axis). That is, the first curved surface 14da as a whole forms a curved surface with centers of curvature located radially inward, and may also have a plurality of curved surfaces (not shown) that are bent and connected at their connection points. 【0024】 The second region 14e may include the second curved surface 14ea. The second curved surface 14ea has at least one center of curvature radially outward from the inner circumferential surface 14c. That is, the second curved surface 14ea is curved in the opposite direction to the curvature direction of the outermost trajectory of the rotor 30 (e.g., the outer circumferential surface 30a), and is formed in an inverse arc shape relative to the first curved surface 14da. Therefore, the distance between the second curved surface 14ea and the outermost trajectory of the rotor 30 gradually increases as it approaches the second side portion 21a from the connection point C. This rate of increase is greater the closer it is to the second side portion 21a. In this embodiment, the second region 14e is represented as the second curved surface 14ea by a smooth arc-shaped curve in a cross section perpendicular to the Z-axis (rotation center axis). However, the second curved surface 14ea may also be represented by a curve formed by connecting multiple curves, each with its center of curvature located radially outward in a cross section perpendicular to the Z-axis (rotation center axis). That is, the second curved surface 14ea as a whole forms a curved surface with a center of curvature located radially outward, and may also have a plurality of curved surfaces (not shown) that are bent and connected at their connection points. 【0025】 Furthermore, the surface shape of the first region 14d is not limited to such an arc-shaped surface, and can be defined arbitrarily as long as the above-mentioned distance relationship is satisfied. For example, the first region 14d may be composed of one or more planes. That is, the first region 14d may be represented by one or more straight lines in a cross section perpendicular to the Z-axis (rotation center axis). In the latter case, the first region 14d may have multiple planes (not shown) that are bent and connected at their connection points so as a whole form a curved surface with a center of curvature located radially inward. 【0026】 Similarly, the second region 14e may also consist of one or more planes. That is, the second region 14e may be represented by one or more straight lines in a cross section perpendicular to the Z-axis (axis of rotation). In the latter case, the second curved surface 14ea may have multiple planes (not shown) that are bent and connected at their connection points so as a whole form a curved surface with a center of curvature located radially outward. 【0027】 The coil 12 is wound around the teeth 14 and housed in the slot 17. The coil 12 is made of wire having a rectangular cross-section. That is, the coil 12 is a so-called rectangular coil. The coil 12 is stacked radially RD while being wound around the teeth 14. The wire used for the coil 12 is often a plate or flat bar with a predetermined thickness. However, for convenience, these are referred to as "wire". 【0028】 As described above, the teeth 14 include a flared tip portion 14a. In other words, the width of the slot 17 along the circumferential direction CD narrows as it approaches the rotor 30. Therefore, the coil 12 has a width and thickness that matches the shape of this slot 17. That is, as shown in Figure 2, the width Ws of the wire along the circumferential direction CD is narrower for wires wound closer to the rotor 30. However, the thickness Ts of the wire along the radial direction RD is thicker for wires wound closer to the rotor 30. 【0029】 Eddy current losses in the wire tend to increase with windings closer to the rotor 30. Therefore, the wire width Ws is narrowed for windings closer to the rotor 30 to reduce the magnetic flux passing through the wire. On the other hand, the wire thickness is increased for windings closer to the rotor 30 to suppress the increase in electrical resistance. By setting the width and thickness in this way, excessive increases in eddy current losses and copper losses are suppressed while increasing the space factor within the slot 17, thereby improving efficiency. 【0030】 As described above, the width Ws and thickness Ts of the wire in the coil 12 change with each turn. When manufacturing such a coil 12, for example, a strip-shaped conductor having a desired width Ws and thickness Ts is formed with each turn. These conductors are stacked in the direction of thickness Ts and joined in a spiral pattern. The parts of these conductors other than the joined parts are insulated from each other. The coil 12 is pre-assembled on the teeth 14 and attached to the back yoke 13 together with the teeth 14. Note that since the change in the width Ws and thickness Ts of the wire near the back yoke 13 is relatively small, the width Ws and thickness Ts may remain constant for a predetermined number of turns. 【0031】 Figure 3 is a cross-sectional view of one modified example of the tooth 14. As shown in this figure, the tip portion 14a of the tooth 14 may have a shape in which the width along the circumferential direction CD changes in steps as it approaches the rotor 30. For example, as shown in Figure 3, the tip portion 14a has a first portion 14g having an inner circumferential surface 14c, a first side portion 20a, and a second side portion 21a, and a second portion 14h located closer to the base portion 14b than the first portion 14g. The width of the second portion 14h along the circumferential direction CD is equal to the width Wb of the base portion 14b. On the other hand, the first portion 14g is provided with a first flange portion 20 having a first side portion 20a and a second flange portion 21 having a second side portion 21a, and the width Wp of the first portion 14g is greater than the width of the second portion 14h. However, even in this modified example, the average distance between the second region 14e of the inner circumferential surface 14c and the outermost trajectory of the rotor 30 is greater than the average distance between the first region 14d of the inner circumferential surface 14c and the outermost trajectory of the rotor 30. The thickness of the first portion 14g along the radial direction RD is set to a value that makes magnetic saturation less likely to occur, depending on the assumed magnetic flux. 【0032】 The magnetic resistance between the rotor and the teeth decreases as the distance between them decreases. Therefore, the rotor's magnetic flux can be increased by bringing the teeth closer to the rotor. As a result, torque can be increased. However, if the magnetic flux in the teeth increases excessively, magnetic saturation occurs within the teeth, increasing the leakage flux through the windings. As a result, eddy current losses in the windings increase. Also, generally, the magnetic flux in the teeth tends to be larger on the side where the rotor's magnetic flux is approaching and smaller on the side where the rotor's magnetic flux is moving away. 【0033】 The tip portion 14a of the teeth 14 according to this embodiment has an inner circumferential surface 14c in which the average distance between the second region 14e and the outermost trajectory of the rotor 30 is greater than the average distance between the first region 14d and the outermost trajectory of the rotor 30. In other words, considering the rotation of the rotor 30, the second flange portion 21 is located on the side where the magnetic flux of the rotor 30 approaches (i.e., the side where the magnetic flux penetrating the interior is large), and the first flange portion 20 is located on the side where the magnetic flux of the rotor 30 moves away (i.e., the side where the magnetic flux penetrating the interior is small). 【0034】 Consequently, the magnetic resistance between the second flange 21 and the rotor 30 increases, suppressing magnetic saturation within the second flange 21. This reduces leakage flux and decreases eddy current losses within the coil 12. For example, if a rectangular coil is used as the coil 12, eddy current losses become dominant among the losses within the coil 12. By reducing these eddy current losses, the total losses within the coil 12 can be effectively reduced. 【0035】 However, increasing the average distance between the second region 14e and the outermost trajectory of the rotor 30 reduces the torque obtained by the second flange 21. To compensate for this, the average distance between the first region 14d and the outermost trajectory of the rotor 30 is made closer than the average distance between the second region 14e and the outermost trajectory of the rotor 30. As a result, the magnetic resistance between the first flange 20 and the rotor 30 decreases compared to the magnetic resistance between the second flange 21 and the rotor 30, and the magnetic flux of the rotor 30 passing through the first flange 20 increases. Since the magnetic flux passing through the first flange 20 is relatively small compared to the magnetic flux passing through the second flange 21, magnetic saturation in the first flange 20 is less likely to occur than in the second flange 21. Therefore, by bringing the first side portion 20a closer to the rotor 30 than the second side portion 21a, it is possible to increase torque by taking in magnetic flux while suppressing the occurrence of magnetic saturation within the first flange portion 20. 【0036】 Thus, in this embodiment, the first side portion 20a of the first flange portion 20 and the second side portion 21a of the second flange portion 21 are positioned to compensate for each other's increases and decreases in torque and eddy current losses. As a result, the power density can be improved and the motor can be miniaturized compared to an electric motor of the same size. 【0037】 Due to the need to assemble the coil 12 inside the back yoke 13, the teeth 14 and the back yoke 13 are separated. Consequently, a small gap is inevitably formed where the two connect, and this gap increases magnetic resistance. This increase in magnetic resistance leads to an increase in leakage flux, which in turn increases eddy current losses in the wires of the rectangular coil near the back yoke 13. 【0038】 In this embodiment, a groove 15 is formed in the inner circumferential surface 13a of the back yoke 13 into which the base 14b of the teeth 14 is inserted. As described above, the depth Dg of the groove 15 is set to a value that provides a larger contact area between the back yoke 13 and the teeth 14 than when the teeth 14 are attached to the inner circumferential surface 13a without the groove 15. In other words, the area in which the back yoke 13 and the teeth 14 are in contact with or facing each other increases. This reduces the magnetic resistance between the back yoke 13 and the teeth 14. As the magnetic resistance decreases, the leakage flux decreases, and the eddy current loss in the wires of the rectangular coil near the back yoke 13 can be reduced. 【0039】 Figure 4 shows the analysis results of the magnetic flux density distribution around the connection portion between the back yoke and the teeth. Figure 4(a) shows the magnetic flux density distribution of a comparative example in which the groove 15 is not formed, and Figure 4(b) shows the magnetic flux density distribution of this embodiment in which the groove 15 is formed. As shown in Figure 4(a), a gap GG exists between the back yoke 113 and the teeth 114 that increases magnetic resistance. Due to the presence of the gap GG, the magnetic flux of the teeth 114 is initially concentrated near the base of the projection 112 that is inserted into the groove 115 of the back yoke 113. Furthermore, since it is assumed that the gap GG also occurs at the tip 112a of the projection 112 and the bottom surface 115a of the groove 115, the direction of the concentrated magnetic flux is forcibly deflected in the circumferential direction. Such concentration and deflection of magnetic flux can be a factor in increasing leakage flux. 【0040】 On the other hand, in this embodiment shown in Figure 4(b), a gap GG that increases magnetic resistance may exist between the back yoke 13 and the teeth 14. However, due to the increased contact area between the two, the magnetic resistance decreases, the magnetic flux is moderately dispersed in the direction indicated by the arrow, and excessive concentration of the magnetic flux is suppressed. Consequently, leakage flux decreases, and eddy current losses in the coil 12 decrease. Therefore, the power density can be improved. 【0041】 The coil 12 may be constructed from a circular cross-section wire wound using a well-known method. However, if the coil 12 is constructed from a rectangular coil, the occupancy rate within the slot 17 can be increased compared to when the coil 12 is constructed from a circular cross-section wire. 【0042】 This disclosure is not limited to the embodiments described above, but includes all modifications within the meaning and scope of the claims as indicated by the claims. [Explanation of Symbols] 【0043】 1…Electric motor, 10…Stator, 11…Stator core, 12…Coil, 13…Back yoke, 13a…Inner surface, 14…Teeth, 14a…Tip, 14b…Base, 14c…Inner surface, 14d…First region, 14da…First curved surface, 14e…Second region, 14ea…Second curved surface, 14f…Side, 14g…First part, 14h…Second part, 15…Groove, 15a…Bottom surface, 16…Protrusion Part, 17...Slot, 18...Dovetail groove, 20...First flange, 20a...First side, 21...Second flange, 21a...Second side, 30...Rotor, 30a...Outer circumference, 112...Protrusion, 112a...Tip, 113...Back yoke, 114...Teeth, 115...Groove, 115a...Bottom surface, C...Connection point (boundary), CD...Circumferential direction, GG...Gap, P...Center surface, RD...Radial direction, TD...Rotational direction

Claims

[Claim 1] A stator core comprising a back yoke provided around the shaft and surrounding the rotor, and a plurality of teeth provided at intervals in the circumferential direction of the shaft and attached to the back yoke, The coil wound around each of the teeth and Equipped with, Each of the aforementioned teeth is Having an inner circumferential surface facing the rotor, and a tip portion that protrudes forward and backward in the rotational direction of the rotor, The base facing the back yoke and Includes, The aforementioned inner circumferential surface is A first region located forward in the aforementioned rotational direction, A second region located behind the first region in the rotational direction and Includes, The average distance between the second region and the outermost trajectory of the rotor is greater than the average distance between the first region and the outermost trajectory of the rotor. The first region of the inner circumferential surface includes a first curved surface having a center of curvature radially inward from the inner circumferential surface. The second region of the inner circumferential surface includes a second curved surface having a center of curvature radially outward from the inner circumferential surface. stator. [Claim 2] The inner circumferential surface includes a portion perpendicular to the radial direction. The stator according to claim 1. [Claim 3] The tip of each of the teeth is flared toward the rotor. The stator according to claim 1 or 2. [Claim 4] The coil is made up of electric wires having a rectangular cross-section. The stator according to claim 1 or 2. [Claim 5] The back yoke is provided with grooves into which the base of each of the teeth is inserted. The stator according to claim 1 or 2.

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