Electric motor rotor

Abstract

A rotor 1 is provided so as to extend in the direction of a rotation center axis of an electric motor and is supported so as to be rotatable about the rotation center axis. The rotor 1 comprises: a plurality of permanent magnets 21, 22 arranged in the outer peripheral portion of the rotor 1 such that, in the outer peripheral portion, N-poles and S-poles, which are magnetic poles each extending parallel to the direction of the rotation center axis, are formed alternately in the circumferential direction of the rotor 1; an outer peripheral core 30 disposed facing middle portions that are portions of the outer peripheral surfaces of the permanent magnets excluding both end portions of the permanent magnets in the direction of the rotation center axis; and a pair of terminal cores 40 disposed at opposing end portions of the rotor 1 in the direction of the rotation center axis. The outer peripheral core 30 and the terminal cores 40 are formed from a magnetic material, and the maximum magnetic permeability of the terminal cores 40 is equal to or less than the maximum magnetic permeability of the outer peripheral core 30.

Description

[Technical field]

[0001] The present invention relates to a rotor for an electric motor. [Background technology]

[0002] For example, the following Patent Documents 1 to 3 describe a rotor of an electric motor (hereinafter simply referred to as a "rotor"). This rotor includes a rotor core and a plurality of permanent magnets. The rotor core is a cylindrical member formed by laminating approximately circular electromagnetic steel plates (iron core pieces). The rotor core is provided with a plurality of holes for respectively accommodating (embedding) the plurality of permanent magnets. These holes penetrate from one end face to the other end face of the rotor core. These holes are arranged at equal intervals in the circumferential direction of the rotor core.

[0003] The permanent magnet is a flat (rod-shaped) member extending parallel to the direction in which the central axis of rotation of the electric motor extends. The permanent magnet is magnetized in the thickness direction. That is, the front surface of the permanent magnet is a north pole and the back surface is a south pole. The permanent magnet is disposed within a hole in the rotor core. This forms multiple magnetic poles (north poles and south poles) at equal intervals around the rotor core. The rotor core is provided with multiple gaps (slits) at predetermined positions around each permanent magnet to reduce leakage magnetic flux. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2015 / 166532 [Patent Document 2] JP 2007-330027 A [Patent Document 3] JP 2018-117488 A Summary of the Invention

[0005] In the above conventional rotor, the position of the permanent magnets, the number of permanent magnets, the position of the air gap (magnetic path), etc. are optimized to improve the torque of the electric motor.

[0006] An object of the present invention is to provide a rotor that can improve the average torque of an electric motor (the average value of torque during one rotation of the rotor) compared to conventional methods.

[0007] In order to achieve the above-mentioned object, the rotor of an electric motor according to the present invention is an electric motor rotor that is extended in the direction of the central axis of rotation of an electric motor and supported rotatably around the central axis of rotation, and is equipped with a plurality of permanent magnets arranged on the outer periphery of the rotor so that N poles and S poles, which are magnetic poles each extending parallel to the direction of the central axis of rotation, are formed alternately in the circumferential direction of the rotor, an outer periphery core arranged to face each other in the middle part of the outer periphery of each permanent magnet, excluding both ends in the direction of the central axis of rotation, and a pair of terminal cores arranged at both ends of the rotor in the direction of the central axis of rotation. The outer core and the terminal core are made of magnetic material, and a first magnetic flux is formed in the middle of the longitudinal direction of the outer surface of the rotor by the action of the outer core, and a second magnetic flux is formed in the radial direction of the rotor by the action of the terminal core, and during the process in which the rotor rotates when the electric motor is operated, the maximum magnetic permeability of the terminal core is set to be less than or equal to the maximum magnetic permeability of the outer core so that the second torque generated by the action of the second magnetic flux decreases in the process in which the first torque generated by the action of the first magnetic flux increases.

[0008] In a rotor of an electric motor according to one aspect of the present invention, adjacent outer circumferential cores are connected to each other via connecting portions.

[0009] In a rotor for an electric motor according to another aspect of the present invention, the maximum magnetic permeability of the connection portion is equal to or less than the maximum magnetic permeability of the outer core.

[0010] In another aspect of the present invention, a rotor of an electric motor includes a central core extending in the direction of the central axis of rotation and supported rotatably around the central axis of rotation, the plurality of permanent magnets are arranged on an outer peripheral surface of the central core, and the pair of terminal cores are arranged at both ends of the central core in the direction of the central axis of rotation.

[0011] In a rotor for an electric motor according to another aspect of the present invention, the terminal core has positioning portions that define positions of the permanent magnets in the circumferential direction of the outer periphery of the rotor.

[0012] In the rotor of the present invention, an outer core as a magnetic body is attached to the middle part of the permanent magnet in the longitudinal direction. Therefore, magnetic flux is concentrated in the middle part of the outer peripheral surface of the rotor in the longitudinal direction. Hereinafter, this magnetic flux is referred to as the "first magnetic flux". In other words, magnetic flux leakage to both end face sides in the longitudinal direction of the rotor is reduced. Although there is also magnetic flux (leakage magnetic flux (hereinafter referred to as the "second magnetic flux")) that flows from the permanent magnet to both end sides of the rotor, this magnetic flux is concentrated (shorted) in the terminal core as a magnetic body. In other words, the second magnetic flux tends to flow in the radial direction of the rotor, not in the circumferential direction of the rotor (see FIG. 6).

[0013] Here, in an electric motor to which the rotor according to the present invention is applied, the first torque generated in the rotor due to the action of the first magnetic flux and the second torque generated in the rotor due to the action of the second magnetic flux change in different ways (see FIG. 7). Specifically, in the process in which the first torque decreases, the second torque increases, and in the process in which the first torque increases, the second torque decreases. Thus, in an electric motor employing the rotor according to the present invention, the fluctuation in the torque generated in the rotor (the sum of the first torque and the second torque) is small, and the average torque is improved compared to an electric motor employing a conventional rotor. [Brief description of the drawings]

[0014] [Figure 1] 1 is a perspective view of a rotor according to an embodiment of the present invention; [Diagram 2] FIG. 2 is an exploded perspective view of the rotor of FIG. 1. [Diagram 3] FIG. 11 is a perspective view of a rotor according to a modified example of the present invention. [Figure 4] FIG. 4 is an exploded perspective view of the rotor of FIG. 3. [Diagram 5] 4 is a graph showing an example of the relationship between the magnetic field applied to the electromagnetic steel sheet and the dust core and the magnetic flux density. [Figure 6] FIG. 2 is a diagram showing the direction of magnetic field lines in a terminal core. [Figure 7]4 is a graph showing torque fluctuations. [Figure 8] 1 is a first table showing the improvement rate of average torque of an electric motor using a rotor of the present invention. [Figure 9] 2 is a second table showing the improvement rate of average torque of an electric motor using a rotor of the present invention. [Figure 10] 11 is a third table showing the improvement rate of the average torque of an electric motor using the rotor of the present invention. [Figure 11] 4 is a fourth table showing the improvement rate of the average torque of an electric motor using the rotor of the present invention. [Figure 12] 4 is a front view showing the positional relationship between the permanent magnets and the outer core (main body). FIG. [Figure 13] 13 is a front view showing an example in which a portion of the outer periphery of a terminal core is cut away. FIG. [Figure 14] 1 is a table showing the dimensions of each part. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] (Summary) Hereinafter, a "rotor 1 for an electric motor" (hereinafter simply referred to as "rotor 1") according to one embodiment of the present invention will be described. Here, a brief description will be given of the configuration of an electric motor to which rotor 1 is applied. The electric motor includes a stator. The stator is a cylindrical component. A plurality of teeth are formed on the inner peripheral surface of the stator. These teeth are arranged at equal intervals around the circumferential direction of the stator. A coil is attached to each tooth. In other words, an electric wire is wound around the teeth.

[0016] The rotor 1 is a cylindrical part. The rotor 1 is housed inside the stator. The rotor 1 and the stator are arranged coaxially. The rotor 1 has a plurality of magnetic poles (north and south poles) each extending parallel to its central axis of rotation. These magnetic poles are arranged at equal intervals around the circumference of the rotor 1. In this embodiment, the rotor 1 has eight magnetic poles (four north poles and four south poles). These north poles and south poles are arranged alternately around the circumference of the rotor 1. Power is supplied to the multiple coils of the stator in a predetermined order. This causes the rotor 1 to rotate relative to the stator.

[0017] (composition) Next, a description will be given of the configuration of the rotor 1. The rotor 1 includes a central core 10, a plurality of permanent magnets 20 (four permanent magnets 21 and four permanent magnets 22), an outer circumferential core 30, and a pair of terminal cores 40, 40, as shown in FIG.

[0018] The central core 10 is a cylindrical part as shown in Fig. 2. The central core 10 is a laminated body formed by stacking a plurality of disk-shaped core pieces 11. The core pieces 11 are formed by punching out an electromagnetic steel sheet (base material).

[0019] A punched hole PH1 is formed in the center of the core pieces 11. The punched hole PH1 has a circular shape. When the core pieces 11 are stacked, the punched holes PH1 communicate with each other. That is, a through hole TH1 is formed in the center of the central core 10, penetrating from one end face to the other end face in its longitudinal direction (extension direction of the central axis). A shaft (output shaft of an electric motor) (not shown) is inserted and fixed in this through hole TH1.

[0020] The permanent magnet 20 is a narrow plate-like part extending parallel to the extension direction of the central axis (rotation central axis) of the central core 10. The permanent magnet 20 is curved to follow the outer peripheral surface of the central core 10. That is, one surface of the permanent magnet 20 in the plate thickness direction is a convex surface, and the other surface is a concave surface. The permanent magnet 20 is magnetized in the plate thickness direction. That is, the convex surface side of the permanent magnet 21 is an N pole, and the concave surface side is an S pole. On the other hand, the convex surface side of the permanent magnet 22 is an S pole, and the concave surface side is an N pole. On the outer peripheral surface of the central core 10, the permanent magnets 21 and the permanent magnets 22 are alternately arranged in the circumferential direction. As a result, the above-mentioned eight magnetic poles (four N poles and four S poles) are arranged on the outer peripheral surface of the central core 10.

[0021] The outer core 30 has a plurality of plate-shaped main body portions 31 arranged to face the surfaces (convex surfaces) of the permanent magnets 21, 22, and a connection portion 32 connecting adjacent main body portions 31, 31. The main body portions 31 are made of a magnetic material, and the connection portion 32 is made of a non-magnetic material. The main body portions 31 are made of, for example, the same electromagnetic steel plate as the central core 10. The connection portion 32 is made of, for example, a synthetic resin material (for example, polyphenylene sulfide resin). The main body portions 31 extend parallel to the central axis of the central core 10. The length Lc of the main body portions 31 is shorter than the length Lm of the permanent magnets 21, 22 (see FIG. 12). The width Wc of the main body portions 31 is narrower than the width Wm of the permanent magnets 21, 22. The main body portions 31 are curved to fit the convex surfaces of the permanent magnets 21, 22. The main body 31 is disposed (bonded) facing the center of the permanent magnets 21, 22. That is, the intermediate portion in the longitudinal direction of the permanent magnets 21, 22 is covered by the outer core 30, and both ends in the longitudinal direction of the permanent magnets 21, 22 are exposed. In the above example, adjacent main body portions 31 are connected via the connecting portion 32. That is, the outer core 30 has a ring shape. The main body portion 31 and the connecting portion 32 may be formed as separate parts and connected to each other. In addition, a part (a part corresponding to the connecting portion 32) of the ring-shaped part made of electromagnetic steel sheet may be irradiated with laser light to modify and demagnetize the part. In addition, as shown in FIG. 3 and FIG. 4, the connecting portion 32 may be omitted, and each main body portion 31 may be bonded to the surface of the permanent magnets 21, 22.

[0022] The terminal core 40 is a disk-shaped component. The outer diameter of the terminal core 40 is larger than the outer diameter of the center core 10. A through hole TH2 is provided in the center of the terminal core 40. The inner diameter of the through hole TH2 is the same as the inner diameter of the through hole TH1. The terminal cores 40, 40 are attached to both end faces of the center core 10 in the longitudinal direction. The terminal cores 40, 40 and the center core 10 are arranged coaxially.

[0023] A plurality of (eight) protrusions 41 are provided on the outer peripheral edge of one surface of the terminal cores 40. These protrusions 41 are arranged at equal intervals in the circumferential direction of the terminal core 40. The terminal cores 40 are bonded to both end surfaces of the center core 10 so that the protrusion 41 of one terminal core 40 faces the protrusion 41 of the other terminal core 40. An end of the permanent magnet 21 (22) is arranged between two protrusions 41 adjacent to each other in the circumferential direction of the terminal core 40. That is, the protrusions 41 function as a positioning portion (a portion to prevent misalignment) of the permanent magnet 21 (22).

[0024] The terminal core 40 is made of a dust core (or an electromagnetic steel sheet). The maximum magnetic permeability of the terminal core 40 is equal to or less than the maximum magnetic permeability of the main body 31 of the outer core 30 (the maximum value of the gradient of the graph showing the relationship between the magnetic field and the magnetic flux density shown in FIG. 5).

[0025] (Action and Effects) As described above, the main body 31 of the outer core 30 as a magnetic body is attached to the middle part of the permanent magnets 21, 22 in the longitudinal direction. Therefore, the magnetic flux is concentrated in the middle part of the outer peripheral surface of the rotor 1 in the longitudinal direction. Hereinafter, this magnetic flux is referred to as the "first magnetic flux". In other words, the magnetic flux leakage to both end face sides in the longitudinal direction of the rotor 1 is reduced. Although there is also magnetic flux (leakage magnetic flux (hereinafter referred to as the "second magnetic flux")) that flows from the permanent magnets 21, 22 to both end sides of the rotor 1, these magnetic fluxes are concentrated (short-circuited) in the terminal cores 40, 40 as a magnetic body. That is, as shown in FIG. 6, the second magnetic flux does not flow in the circumferential direction θ of the rotor 1, but tends to flow in the radial direction R of the rotor 1 over the entire circumference of the terminal core 40.

[0026] FIG. 7 shows the results of a computer simulation of the change in the first torque T1 generated in the rotor 1 by the action of the first magnetic flux and the change in the second torque T2 generated in the rotor 1 by the action of the second magnetic flux (the relationship between the rotation angle of the rotor 1 and the first torque T1 and the second torque T2). As shown in the figure, the first torque T1 and the second torque T2 change in different ways. Specifically, in the process in which the first torque T1 decreases, the second torque T2 increases, and in the process in which the first torque T1 increases, the second torque T2 decreases. This effect is achieved by providing the protrusion 41 between the end of the permanent magnet 21 and the end of the permanent magnet 22. Therefore, in the electric motor using the rotor 1, the fluctuation in the torque generated in the rotor 1 (the sum of the first torque T1 and the second torque T2) is small, and the average torque Tm is improved compared to an electric motor using a conventional rotor.

[0027] Furthermore, in conventional rotors, when stacking the core pieces that make up the rotor core, it is necessary to align the positions of punched holes, slits, etc. Misalignment of these parts can cause a decrease in the torque of the electric motor, so high manufacturing precision is required for the rotor core. In contrast, in this embodiment, the core pieces 11 that make up the center core 10 have a simpler shape (number of punched holes) than conventional core pieces, making it easier to manufacture the center core 10.

[0028] (Example) Next, the results of a comparison (improvement rate of the average torque Tm (result of computer simulation)) between the average torque Tm of an electric motor using a conventional rotor X and the average torque Tm of electric motors using rotors Y1 and Y2 according to the embodiments of the present invention are shown in Fig. 8. In addition, the results of a comparison between the average torque Tm of an electric motor using rotor X and the average torque Tm of electric motors using rotors Z1 and Z2 according to comparative examples of the present invention are also shown in the same figure.

[0029] Like the conventional rotor, the rotor X has a rotor core made of laminated electromagnetic steel sheets. Permanent magnets are disposed in holes provided on the outer periphery of the rotor core. The electromagnetic steel sheets constituting the rotor core of the rotor X are "50A600" as specified in JIS C 2552-1986.

[0030] In the outer cores 30 of the rotors Y1, Y2, adjacent main body portions 31 are not connected via connecting portions 32, and each main body portion 31 is bonded to the surface of the permanent magnets 21, 22. In other words, there is an air gap between the permanent magnets 21, 22 (between the magnetic poles and outside thereof). Furthermore, the terminal cores 40, 40 of the rotor Y1 are made of the same electromagnetic steel sheet as the main body portion 31. "50A600" is used as the electromagnetic steel sheet that makes up the main body portion 31 and the terminal cores 40 of the rotor Y1.

[0031] On the other hand, the terminal cores 40, 40 of the rotor Y2 are composed of dust cores. That is, in the rotor Y1, the maximum magnetic permeability of the main body 31 and the terminal core 40 is the same. On the other hand, in the rotor Y2, the maximum magnetic permeability of the terminal core 40 is smaller than that of the main body 31. As the electromagnetic steel sheet constituting the main body 31 of the rotor Y2, "50A600" in JIS C 2552-1986 is adopted. The terminal core 40 of the rotor Y2 is an injection molded body (dust core) in which pure iron powder is contained in polyphenylene sulfide resin material. The content (volume ratio) of pure iron powder in the dust core is about 50%.

[0032] In the rotors Z1 and Z2, the entire outer core 30 is made of electromagnetic steel sheet ("50A600"). That is, not only the main body 31 but also the connection portion 32 is made of electromagnetic steel sheet ("50A600"). The end core 40 of the rotor Z1 is made of electromagnetic steel sheet ("50A600") like the rotor Y1, and the end core 40 of the rotor Z2 is made of a dust core like the rotor Y2.

[0033] As shown in the figure, the average torque Tm could be improved when rotors Y1 and Y2 were used in which the portions of the outer core 30 located between the magnetic poles and on the outside thereof were non-magnetic and the maximum magnetic permeability of the terminal core 40 was equal to or less than the maximum magnetic permeability of the main body 31. Furthermore, compared to the case of using rotor Y1 in which the maximum magnetic permeability of the terminal core 40 is equal to the maximum magnetic permeability of the main body 31, the average torque Tm could be improved more significantly when rotor Y2 in which the maximum magnetic permeability of the terminal core 40 is smaller than the maximum magnetic permeability of the main body 31 was used. On the other hand, the average torque Tm could not be improved in rotors Z1 and Z2 in which the portions of the outer core 30 located between the magnetic poles and on the outside thereof were magnetic.

[0034] Next, FIG. 9 shows the improvement rate of the average torque Tm when the rotors Y1a to Y1e having different dimensions (length Lc and width Wc (see FIG. 12 and FIG. 14)) of each part of the main body 31 are adopted. The rotors Y1a to Y1e have their main body 31 and terminal cores 40 made of electromagnetic steel sheets, similar to the rotor Y1 shown in FIG. 8. The length Lc and width Wc of the main body 31 of the rotors Y2a to Y2e and the length Lm and width Wm of the permanent magnets 21, 22 are as shown in FIG. 14. The portions of the outer core 30 of the rotors Y1a to Y1e that are located between and outside the magnetic poles are air gaps.

[0035] Next, FIG. 10 shows the improvement rate of the average torque Tm when the rotors Y2a and Y2b having different dimensions (length Lc and width Wc (see FIG. 14)) of each part of the main body 31 are adopted. The rotors Y2a and Y2b have their main body 31 made of electromagnetic steel sheets and their terminal cores 40 made of dust cores, similar to the rotor Y2 shown in FIG. 8. The length Lc and width Wc of the main body 31 of the rotors Y2a and Y2b, and the length Lm and width Wm of the permanent magnets 21, 22 are as shown in FIG. 14. The portions of the outer cores 30 of the rotors Y2a and Y2b that are located between and outside the magnetic poles are air gaps.

[0036] In addition, the figure shows the improvement rate of the average torque Tm when a rotor YA is adopted in which the main body 31 is made of an electromagnetic steel plate, the terminal core 40 is made of a dust core, and the connection portion 32 is made of the same dust core as the terminal core 40. Furthermore, the figure shows the improvement rate of the average torque Tm when a rotor YB is adopted in which the main body 31 and the terminal core 40 are made of an electromagnetic steel plate, and both ends in the longitudinal direction of the main body 31 are connected by connection portions 32 made of the same electromagnetic steel plate as the main body 31. The length Lc and width Wc of the main body portions 31 of the rotors YA and YB and the length Lm and width Wm of the permanent magnets 21 and 22 are the same as those of the rotor Y2b.

[0037] In the above embodiment, the terminal core 40 has a disk shape, but as shown in FIG. 13, an arc-shaped cutout portion CP may be provided on the outer periphery of the terminal core 40, facing the end faces of the permanent magnets 21 and 22. FIG. 11 shows the improvement rate of the average torque Tm when the rotor YC to rotor YG equipped with such a terminal core 40 are used. The radius Rc2 and central angle Xm of the inner periphery of the cutout portion CP, as well as the radius Rc1 of the terminal core 40 and the central angle Xc of the sector portion located between the adjacent cutout portions CP, are as shown in FIG. 14. The material of the outer periphery core 30 and the terminal core 40 of the rotor YC is the same as that of the rotor Y1c. The material of the outer periphery core 30 and the terminal core 40 of the rotor YD is the same as that of the rotor YB. The material of the outer periphery core 30 and the terminal core 40 of the rotor YE is the same as that of the rotor Y2b. The material of the outer periphery core 30 and the terminal core 40 of the rotor YF is the same as that of the rotor YA. The material of the outer circumferential core 30 and the end core 40 of the rotor YG is the same as that of the rotor Z2.

[0038] As described above, by optimizing the dimensions of the main body 31 relative to the dimensions of the permanent magnets 21, 22, it is possible to reduce the ripple (fluctuation range) of the first torque T1 and the second torque T2 and maximize the average torque Tm. In principle, it is preferable that the maximum magnetic permeability of the connection portion 32 is smaller than the maximum magnetic permeability of the main body 31. However, even if the maximum magnetic permeability of the main body 31 and the connection portion 32 are the same, there are cases where the average torque Tm can be improved by devising the shape of the terminal core 40 (see rotor YG in FIG. 11). [Explanation of symbols]

[0039] REFERENCE SIGNS LIST 1...rotor, 10...center core, 21, 22...permanent magnet, 30...peripheral core, 31...main body, 32...connection, 40...terminal core, 41...projection, CP...notch (positioning portion), T1...first torque, T2...second torque, Tm...average torque

Claims

1. A rotor of an electric motor that is extended in a direction of a rotation central axis of the electric motor and supported rotatably around the rotation central axis, a plurality of permanent magnets arranged on an outer periphery of the rotor such that N poles and S poles, which are magnetic poles extending parallel to the direction of the central axis of rotation, are alternately formed in a circumferential direction of the rotor; an outer core disposed to face an intermediate portion of an outer peripheral surface of each of the permanent magnets, excluding both ends in the direction of the central axis of rotation; a pair of terminal cores disposed at both ends of the rotor in the direction of the central axis of rotation; Equipped with The outer core and the end core are made of a magnetic material, A first magnetic flux is formed in a middle portion of the outer peripheral surface of the rotor in the longitudinal direction by the action of the outer peripheral core, and a second magnetic flux is formed in a radial direction of the rotor by the action of the terminal core, In a process in which the rotor rotates during operation of the electric motor, the maximum magnetic permeability of the end core is set to be equal to or less than the maximum magnetic permeability of the outer core so that a second torque generated by the action of the second magnetic flux decreases in a process in which a first torque generated by the action of the first magnetic flux increases. Electric motor rotor.

2. 2. The rotor of an electric motor according to claim 1, Adjacent outer cores are connected to each other via connection parts. Electric motor rotor.

3. 3. The rotor of an electric motor according to claim 2, The maximum magnetic permeability of the connection portion is equal to or less than the maximum magnetic permeability of the outer core. Electric motor rotor.

4. A rotor for an electric motor according to any one of claims 1 to 3, a central core extending in the direction of the central axis of rotation and supported rotatably around the central axis of rotation; The plurality of permanent magnets are disposed on an outer circumferential surface of the central core, The pair of terminal cores are disposed at both ends of the central core in the direction of the central axis of rotation. Electric motor rotor.

5. 2. The rotor of an electric motor according to claim 1, The terminal core has a positioning portion that defines the positions of the plurality of permanent magnets in the circumferential direction of the outer periphery of the rotor. Electric motor rotor.

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