WO2024241779A1 - Electric motor - Google Patents

Abstract

The present invention reduces the cogging torque of an electric motor. This electric motor comprises: a stator (20) constructed by joining a plurality of split cores (21) by welding; and a rotor disposed so as to face the stator (20). In at least one of a plurality of joining portions (J) between the plurality of split cores (21), the ratio of weld portions in a second region (R2) is smaller than the ratio of weld portions (22) in a first region (R1), where the first region (R1) represents regions from the axial ends of the stator (20) to the ends of continuous weld portions (22) closest thereto, and the second region (R2) represents a region other than the first region (R1) and includes the axial center portion of the stator (20).

Description

Electric motor

This disclosure relates to electric motors.

　Conventionally, electric motors equipped with a stator made up of multiple split cores are known (for example, see Patent Document 1). The electric motor of Patent Document 1 is equipped with a stator and a rotor, and the stator is made up of multiple split cores joined by welding. The multiple split cores are joined at their contact points by laser welding along the axial direction of the stator.

JP 2002-95192 A

However, even if multiple split cores are assembled with high precision, the heat of laser welding can reduce the precision of the inner surface of the stator (i.e., the inner surface of the teeth portion of the stator). If the precision of the inner surface of the stator decreases, the cogging torque of the motor increases. In such a situation, one of the objectives of this disclosure is to reduce the cogging torque of the motor.

One aspect of the present disclosure relates to an electric motor. The electric motor includes a stator formed by welding a plurality of split cores together, and a rotor disposed opposite the stator. A region from the axial end of the stator to the end of the closest continuous weld is defined as a first region, and a region other than the first region, including the axial center of the stator, is defined as a second region, and in at least one of the multiple joints between the plurality of split cores, the proportion of welds in the second region is smaller than the proportion of welds in the first region.

The motor disclosed herein can reduce the cogging torque of the motor.

1 is a perspective view of an electric motor according to an embodiment of the present disclosure. FIG. 1 is a side view of an electric motor according to an embodiment of the present disclosure. 1 is a cross-sectional perspective view of an electric motor according to an embodiment of the present disclosure. FIG. 1 is a front view of an electric motor according to an embodiment of the present disclosure. FIG. 2 is a perspective view of a stator according to an embodiment of the present disclosure. 1 is a perspective view showing an arrangement of a plurality of split cores constituting a stator according to an embodiment of the present disclosure before being joined together. 11 is a perspective view showing the arrangement of the split cores after being joined together in a stator according to an embodiment of the present disclosure. FIG. 1 is a perspective view showing a stator and a frame when the stator according to an embodiment of the present disclosure is inserted into the frame and the stator is shrink-fitted. FIG. FIG. 2 is a side view of a stator according to an embodiment of the present disclosure. FIG. 11 is a side view of a stator according to a first modified example of an embodiment of the present disclosure. FIG. 11 is a side view of a stator according to a second modified example of the embodiment of the present disclosure.

Embodiments of electric motors according to the present disclosure are described below using examples. However, the present disclosure is not limited to the examples described below. In the following description, specific numerical values and materials may be given as examples, but other numerical values and materials may be applied as long as the effects of the present disclosure are obtained.

The electric motor according to the present disclosure is a device that converts electrical energy into mechanical energy (particularly, rotational energy) and may be, for example, an inner rotor type three-phase synchronous motor. The electric motor according to the present disclosure includes a stator and a rotor.

Below, the electric motor according to the present disclosure will be specifically described with reference to the drawings. Among the components of the electric motor described below, those components that are not essential to the electric motor according to the present disclosure may be omitted. Note that the drawings shown below are schematic and do not accurately reflect the shape or number of actual components.

<<Embodiment>>
(1) Electric motor 10
An electric motor 10 according to an embodiment of the present disclosure will be described with reference to Figs. 1 to 4. Fig. 1 is a perspective view of the electric motor 10 according to an embodiment of the present disclosure (hereinafter referred to as the present embodiment). Fig. 2 is a side view of the electric motor 10 according to the present embodiment. Fig. 3 is a cross-sectional perspective view of the electric motor 10 according to the present embodiment. Fig. 4 is a front view of the electric motor 10 according to the present embodiment.

The electric motor 10 of this embodiment is an inner rotor type three-phase synchronous motor, but is not limited to this. As shown in Figures 1 to 4, the electric motor 10 includes a stator 20, a rotor 30, a housing 40, and a shaft 50. As shown in Figure 2, the electric motor 10 further includes a bearing 60. The housing 40 includes an upper plate 40a, a frame 40b, and a bottom plate 40c.

When viewed from the direction along the axis 50, the housing 40 has a top plate 40a and a bottom plate 40c each having a rectangular shape with four corners cut out. The top plate 40a has a circular hole 40d in its center. The axis 50 passes through hole 40d. The bottom plate 40c has a hole 40e in its center. Note that the shapes of holes 40d and 40e are not limited to circles, and may be oval, rectangular, hexagonal, etc. Also, hole 40e does not have to be present, and does not have to pass through the bottom plate 40c.

The stator 20 is fixed to the frame 40b, and the rotor 30 is fixed to the shaft 50, and rotates integrally with the shaft 50. The shaft 50 has a cylindrical shape with a step. The bearing 60 is a part having a cylindrical shape, and is attached to the shaft 50 so that the shaft 50 can rotate. The shaft 50 is also attached to the housing 40 via the bearing 60. The "bottom plate" is also called an "end plate." In FIG. 2, the various parts built into the housing 40 are indicated by dashed lines.

FIG. 3 is a cross-sectional perspective view of the electric motor 10 shown in FIG. 2, cut along a plane perpendicular to the shaft 50 and including the line segment III-III. Note that the illustration of the bottom plate 40c is omitted in FIG. 3.

FIG. 4 shows a front view of the electric motor 10 shown in FIG. 1 with the top plate 40a removed. Note that the bearing 60 is omitted in FIG. 4.

In Figures 1 to 4 and the figures shown below, the direction parallel to the rotation axis of the rotor 30 of the electric motor 10 is the Z axis, the direction perpendicular to one side surface 40f of the rectangular frame 40b is the X axis, and the direction perpendicular to the X and Z axes is the Y axis. The X, Y, and Z axes form an orthogonal coordinate system. The rotation axis of the rotor 30 and the center of the shaft 50 are coincident. In other words, the center of the shaft 50 is parallel to the Z axis. Note that "top" and "bottom" are not limited to "top" and "bottom" in the vertical direction, but are used in a relative sense.

With the X-axis, Y-axis, and Z-axis defined as above, Figure 2 is a side view seen from the positive direction of the X-axis. Also, Figure 4 is a front view seen from the positive direction of the Z-axis.

As shown in Figures 2 to 4, the stator 20 is shrink-fitted to the frame 40b. The top plate 40a, the frame 40b, and the bottom plate 40c are made of aluminum or an aluminum alloy.

(2) Rotor 30
The rotor 30 is disposed opposite the stator 20. In this embodiment, the rotor 30 is disposed inside the stator 20, but is not limited to this. The rotor 30 has a rotor core 31 and a plurality of permanent magnets 32 (ten in this example) embedded in the rotor core 31 and arranged in a spoke shape. The rotor core 31 is made of a plurality of laminated electromagnetic steel plates. Each permanent magnet 32 is made of a rare earth sintered magnet.

In addition, the rotor core 31 may be made of a powder magnetic core, in addition to being made of multiple laminated electromagnetic steel plates.

The rotor 30 may have a rare earth magnet. Rare earth magnets generally have a high residual magnetic flux density, and a motor 10 using a rotor 30 having such a magnet can obtain a high magnetic flux density. For motors 10 with such high magnetic flux density, the effects of the invention disclosed herein can be exerted strongly. The rare earth magnet may be, for example, a neodymium magnet, but is not limited to this.

The rotor 30 has multiple permanent magnets 32 arranged in a spoke shape. In an electric motor 10 using a rotor 30 having multiple permanent magnets 32 arranged in a spoke shape (hereinafter also referred to as a spoke rotor), a high magnetic flux density can be obtained. For an electric motor 10 equipped with such a spoke rotor, the effects of the invention according to the present disclosure can be exerted strongly. The number of multiple permanent magnets 32 is not particularly limited, and may be, for example, 8 or more and 12 or less.

(3) Stator 20
Next, the stator 20 will be described. FIG. 5 is a perspective view of the stator 20 according to this embodiment. The stator 20 is formed by combining a plurality of split cores 21 (12 in this embodiment). Each split core 21 is formed of a plurality of laminated electromagnetic steel sheets. Each split core 21 has a yoke portion 21a and a teeth portion 21b protruding from the yoke portion 21a. Each split core 21 may be formed of a powder magnetic core in addition to being formed of a plurality of laminated electromagnetic steel sheets. The stator 20 has an outer peripheral surface 20a on its outer periphery and an inner peripheral surface 20b on its inner periphery. The central axis of the stator 20 coincides with the central axis of the rotor 30 and is parallel to the Z axis. On the outer peripheral surface of the stator 20, the edge in the Z axis positive direction is referred to as a first edge 20c, and the edge in the Z axis negative direction is referred to as a second edge 20d.

(4) Method of manufacturing the stator 20 and method of fixing the stator 20 to the frame 40b A method of manufacturing the stator 20 according to this embodiment and a method of fixing the stator 20 to the frame 40b will be described. FIG. 6 is a perspective view showing the arrangement of the split cores 21 constituting the stator 20 according to this embodiment before being joined. FIG. 7 is a perspective view showing the arrangement of the split cores 21 in the stator 20 according to this embodiment after the split cores 21 are joined. FIG. 8 is a perspective view showing the stator 20 and the frame 40b when the stator 20 according to this embodiment is inserted into the frame 40b and the stator 20 is shrink-fitted. In FIG. 6 to FIG. 8, the XYZ orthogonal coordinate system is defined so that the central axis of the stator 20 is parallel to the Z axis.

As shown in FIG. 6, multiple (12 in this embodiment) split cores 21 are arranged in a circular ring shape. Next, the circumferential ends of the multiple split cores 21 are irradiated with laser light, and the split cores 21 are joined by laser welding to obtain the stator 20 shown in FIG. 7.

The number of split cores 21 is not particularly limited and may be, for example, 8 or more and 16 or less. Each split core 21 may have a yoke portion 21a and teeth portions 21b protruding from the yoke portion 21a.

After obtaining the stator 20 shown in FIG. 7, the stator 20 is inserted into the frame 40b and shrink-fitted as shown in FIG. 8, and the stator 20 is fixed to the frame 40b.

(5) Welded portion 22 of stator 20
Regarding the stator 20 of the electric motor 10 of this embodiment, the welded portions 22 of the multiple split cores 21 will be described. Fig. 9 is a side view of the stator 20 of this embodiment, showing the welded portions 22 of the multiple split cores 21. Fig. 9 is a side view as viewed from the positive direction of the X-axis.

As shown in FIG. 9, the region from both ends of the stator 20 along the Z axis, i.e., the first edge 20c or the second edge 20d, to the end of the closest continuous weld 22 along the Z axis direction is defined as the first region R1, and the region other than the first region R1 including the central portion of the stator 20 along the Z axis direction is defined as the second region R2.

Here, "continuous weld 22" refers to a weld 22 formed across three or more electromagnetic steel sheets in the axial direction when the stator 20 is composed of electromagnetic steel sheets. In contrast, in this specification, a weld formed across two or less electromagnetic steel sheets in the axial direction is referred to as a "spot weld," and spot welds are not included in continuous welds. For example, if the weld 22 closest to the axial end of the stator is a spot weld, that spot weld is not taken into consideration in the definition of the first region.

In the above definition, if the first region R1 and the second region R2 overlap each other, the second region is given priority. In other words, depending on the length and arrangement of each weld 22, the "axial center of the stator" may be included in the "region from the axial end of the stator 20 to the end of the closest continuous weld 22." In such a case, priority is given to the region including the "axial center of the stator" being the second region R2, and this region is treated as the second region R2.

In all of the multiple joints (boundaries) J between the multiple split cores 21, the proportion of welded portions in the second region R2 is smaller than the proportion of welded portions 22 in the first region R1. In this embodiment, the second region R2 does not include welded portions 22. Note that, in at least one of the multiple joints J, it is sufficient that the proportion of welded portions in the second region R2 is smaller than the proportion of welded portions 22 in the first region R1.

The first regions R1 are located near both ends of the stator 20 in the Z-axis direction. The welds 22 of each first region R1 extend along the Z-axis direction of the stator 20.

In the axial direction of the stator 20, the ratio of the length of each first region R1 to the length of the second region R2 may be, for example, 1/4 or more, 1/2 or less, or may be approximately 1/3. For example, when the ratio is 1/3, the ratio of the axial lengths of one first region R1, the second region R2, and the other first region R1 is 1:3:1.

The welded portion of the first region R1 may extend along the axial direction of the stator. Since the boundary between adjacent split cores extends along the axial direction of the stator, this configuration allows the entire welded portion to contribute to the bonding of adjacent split cores. Therefore, the bonding strength between multiple split cores can be effectively increased. The welded portion of the first region R1 may extend in a direction that intersects with the axial direction of the stator.

The first regions R1 may be disposed near both ends of the stator in the axial direction. With this configuration, the bonding strength between the multiple split cores can be easily ensured in the two first regions R1.

The first region R1 may be located only near one axial end of the stator. With this configuration, since there is only one first region R1, the time required to perform welding can be reduced.

(6) First Modification A first modification of the stator 20 included in the electric motor 10 according to the embodiment of the present disclosure will be described. Fig. 10 is a side view of the stator 20 according to the first modification of the electric motor 10 of the present embodiment, and is a diagram showing the welded portions 22 of the multiple split cores 21. Fig. 10 is a side view as viewed from the positive direction of the X-axis.

As shown in FIG. 10, in the stator 20 according to the first modified example of the electric motor 10 of this embodiment, the first region R1 is disposed only in the vicinity of the first edge 20c of the stator 20. The other configurations are the same as those of the above embodiment.

In other words, the second region R2 does not have to include the welded portion 22. In this case, the proportion of the welded portion 22 in the second region R2 is 0%, and the cogging torque of the electric motor 10 can be further reduced. Note that the second region R2 may include the welded portion 22.

(6) Second Modification A second modification of the stator 20 included in the electric motor 10 according to the embodiment of the present disclosure will be described. Fig. 11 is a side view of the stator 20 of this embodiment, showing the welded portions 22 of the multiple split cores 21. Fig. 11 is a side view as viewed from the positive direction of the X-axis.

As shown in FIG. 11, the stator 20 according to the second modified example of the electric motor 10 of this embodiment has welds 22 formed in the second region R2 as well. Here, the proportion of welds 22 in the second region R2 is smaller than the proportion of welds 22 in the first region R1. The "proportion of welds 22" will be explained later. The rest of the configuration is the same as in the above-mentioned embodiment 1.

(7) Effects and Other Advantages of the Electric Motor 10 According to the Present Disclosure The effects and other advantages of the electric motor 10 according to the present disclosure will be described below.

The electric motor 10 includes a frame 40b into which the stator 20 is shrink-fitted. As a result of the shrink-fitting, the outer peripheral surface of the stator 20 is subjected to a compressive force by the inner peripheral surface of the frame 40b, which contracts. This improves the roundness of the outer peripheral surface 20a of the stator 20, and therefore the precision of the inner peripheral surface 20b of the stator 20. This effect is particularly useful in the second region R2, where the proportion of welded portions 22 is small. Furthermore, the improved precision of the inner peripheral surface of the stator can further reduce the cogging torque of the motor. The frame 40b may be made of aluminum or an aluminum alloy, for example.

The "roundness of the outer peripheral surface 20a of the stator 20" refers to the degree to which, for a cylindrical surface including the outer peripheral surface 20a of the stator 20, the axis of the cylindrical surface coincides with the central axis of the stator, and the circle formed by cutting the cylindrical surface along a plane perpendicular to the central axis of the stator 20 is close to being a perfect circle. Additionally, the "accuracy of the inner peripheral surface 20b of the stator 20" refers to the degree to which, for a cylindrical surface including the inner peripheral surface 20b of the stator 20, the axis of the cylindrical surface coincides with the central axis of the stator 20, and the circle formed by cutting the cylindrical surface along a plane perpendicular to the central axis of the stator 20 is close to being a perfect circle.

As a feature of the electric motor 10 according to the present disclosure, in at least one of the multiple joints J between the multiple split cores 21, the ratio of the welded portion 22 in the second region R2 is smaller than the ratio of the welded portion 22 in the first region R1. Here, the "ratio of the welded portion 22" refers to the ratio of the length of the welded portion to the length of each region in the axial direction of the stator 20 (if multiple welded portions exist, the total length of each welded portion). In other words, the ratio of the welded portion 22 in the first region R1 refers to the ratio of the length of the welded portion 22 to the entire length of each of the first regions R1 in the positive direction of the Z axis or the negative direction of the Z axis, measured along the Z axis direction. The ratio of the welded portion 22 in the second region R2 refers to the ratio of the length of the welded portion 22 to the entire length of the second region R2, measured along the Z axis direction. For example, if the length of the first region R1 is 100 mm and the length of the welded portion 22 in the first region R1 is 50 mm, in the axial direction of the stator 20, the ratio of the welded portion 22 in the first region R1 is 50%.

With this configuration, the effect of heat during laser welding on the accuracy of the inner circumferential surface 20b of the stator 20 is suppressed in the second region R2. The second region R2 is a region including the axial center of the stator 20, i.e., a region where the magnetic flux density is relatively high in the axial direction of the stator 20. In other words, the first region R1, which is a region including the axial end of the stator 20, has a lower magnetic flux density than the second region R2. This difference in magnetic flux density occurs because of the presence of magnetic flux leakage at the axial end of the motor 10. Since the accuracy of the inner circumferential surface 20b of the stator 20 is maintained high in the second region R2, which is a region where the magnetic flux density is relatively high, the cogging torque of the motor 10 can be reduced. On the other hand, the bonding strength between the multiple split cores 21 can be sufficiently ensured by welding in the first region R1.

Note that since there are multiple split cores 21, there are also multiple joints J between the split cores 21. Here, the ratio of the axial dimension of the second region R2 to the axial dimension of the first region R1 between the multiple joints J may be the same or different. Furthermore, the ratio of the welded portion 22 in the first region R1 between the multiple joints J may be the same or different. Similarly, the ratio of the welded portion 22 in the second region R2 between the multiple joints J may be the same or different. Furthermore, the ratio of the welded portion 22 in the second region R2 to the ratio of the welded portion 22 in the first region R1 between the multiple joints J may be the same or different. Note that in this specification, the joint J means the boundary at the joint between the split cores 21, and is a different concept from the welded portion 22. In that sense, the "multiple joints J between the multiple split cores 21" can also be rephrased as "multiple boundary portions between the multiple split cores 21".

In all of the multiple joints J, the proportion of welded portions 22 in the second region R2 may be smaller than the proportion of welded portions 22 in the first region R1. In this case, the above-mentioned cogging torque reduction effect can be further enhanced.

As described above, according to the present disclosure, the cogging torque of the electric motor 10 can be reduced by reducing the proportion of the welded portion 22 in the region of high magnetic flux density (second region R2).

The electric motor 10 disclosed herein can be used, for example, in small electric motors for toys and models, as well as in electric motors for driving automobiles and trains, and can also be used in large electric motors such as those used in factories and power plants.

Additional Notes
The above description of the embodiments discloses the following techniques.

(Technique 1)
a stator formed by welding a plurality of split cores together;
a rotor disposed opposite the stator;
A region from an axial end of the stator to an end of a continuous weld closest thereto is defined as a first region, and a region other than the first region including an axial center portion of the stator is defined as a second region,
an electric motor, in which, in at least one of a plurality of joints between the plurality of split cores, a proportion of the weld in the second region is smaller than a proportion of the weld in the first region.

(Technique 2)
The electric motor according to claim 1, wherein in all of the plurality of joints, a proportion of the welded portion in the second region is smaller than a proportion of the welded portion in the first region.

(Technique 3)
The electric motor according to claim 1 or 2, wherein the second region does not include a welded portion.

(Technique 4)
The electric motor according to any one of claims 1 to 3, wherein the rotor has a rare earth magnet.

(Technique 5)
The electric motor according to any one of claims 1 to 4, wherein the rotor has a plurality of permanent magnets arranged in a spoke shape.

(Technique 6)
The electric motor according to any one of claims 1 to 5, further comprising a frame to which the stator is shrink-fitted.

(Technique 7)
The electric motor according to any one of techniques 1 to 6, wherein the welded portion in the first region extends along the axial direction of the stator.

(Technique 8)
The electric motor according to any one of claims 1 to 7, wherein the first region is arranged on both axial ends of the stator.

(Technique 9)
The electric motor according to any one of claims 1 to 7, wherein the first region is disposed only on one axial end side of the stator.

The electric motor of the present disclosure can be used, for example, as a small electric motor for toys or models, as an electric motor for driving automobiles or trains, and also as a large electric motor for use in factories or power plants. In this way, the electric motor of the present disclosure is industrially useful.

10: Motor 20: Stator 20a: Outer circumferential surface 20b: Inner circumferential surface 20c: First edge 20d: Second edge 21: Split core 21a: Yoke portion 21b: Teeth portion 22: Welded portion 30: Rotor 31: Rotor core 32: Permanent magnet 40: Housing 40a: Top plate 40b: Frame 40c: Bottom plate 40d, 40e: Hole 50: Shaft 60: Bearing J: Joint portion R1: First region R2: Second region

Claims (9)

a stator formed by welding a plurality of split cores together;
a rotor disposed opposite the stator;
A region from an axial end of the stator to an end of a continuous weld closest thereto is defined as a first region, and a region other than the first region including an axial center portion of the stator is defined as a second region,
an electric motor, in which, in at least one of a plurality of joints between the plurality of split cores, a proportion of the weld in the second region is smaller than a proportion of the weld in the first region. The electric motor of claim 1, wherein in all of the multiple joints, the proportion of welds in the second region is smaller than the proportion of welds in the first region. The electric motor according to claim 1 or 2, wherein the second region does not include a welded portion. The electric motor according to claim 1 or 2, wherein the rotor has a rare earth magnet. The electric motor according to claim 1 or 2, wherein the rotor has a plurality of permanent magnets arranged in a spoke shape. The electric motor according to claim 1 or 2, further comprising a frame to which the stator is shrink-fitted. The electric motor according to claim 1 or 2, wherein the welded portion of the first region extends along the axial direction of the stator. The electric motor according to claim 1 or 2, wherein the first region is disposed on both axial ends of the stator. The electric motor according to claim 1 or 2, wherein the first region is disposed only on one axial end side of the stator.

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