Electric motor and method for manufacturing electric motor

Abstract

According to the present invention, in a pole piece in which the magnetization direction among a plurality of magnets is oriented in the radial direction with respect to an axis, the pinch angle, which is the angle that is formed by a pair of straight lines extending circumferentially inward along the end surfaces on both peripheral sides of the pole piece when viewed from the axial direction, is set greater than the angle that is formed by a pair of straight lines extending from the axis to the end surfaces on both peripheral sides. The circumferential-direction dimension of the pole piece is such that a virtual circle equal to the magnet width, which is a value obtained by dividing the circumferential length by the number of the magnets arranged in the circumferential direction, is positioned more radially inward than the radially central portions of the magnets.

Description

Electric motor and method for manufacturing electric motor

[0001] This application claims priority to Japanese Patent Application No. 2023-222382, filed on December 28, 2023, the contents of which are incorporated herein by reference.

[0002] One type of electric motor known as an outer rotor type is known. This type of electric motor mainly comprises a stator arranged on the inner periphery and an outer rotor that covers the stator from the outer periphery. A coil is built into the stator, and a magnet is built into the inner periphery of the rotor body of the outer rotor. The outer rotor is supported so that it can rotate around the axis of the stator. When current is supplied to the coil, an electromagnetic force is generated between the coil and the magnet, causing the outer rotor to rotate around the axis.

[0003] Here, a magnet arrangement known as a Halbach array has been put into practical use for outer rotors. In this arrangement, the magnetization direction of multiple magnets arranged circumferentially, as viewed from the axial direction, gradually changes in a rotating manner from one magnet on one side to the other (see, for example, Patent Document 1 below). In this arrangement, magnets whose magnetization direction faces radially relative to the axis are called pole pieces, and magnets arranged between a pair of adjacent pole pieces are sometimes called transition pieces. To arrange these fan-shaped magnets (pole pieces and transition pieces) with a constant radial width in a circular pattern on the inner circumferential surface of the rotor body with sufficiently narrow gaps between the magnets, due to geometric constraints, it is necessary to manufacture the outer rotor by inserting some or all of the magnets in the axial direction.

[0004] US Patent Application Publication No. 2020 / 0358345

[0005] However, because magnets that are already magnetized are affected by the magnetic forces of other magnets around them, there is room for improvement in the arraying techniques that involve the process of inserting some or all of the magnets axially, as described above.

[0006] The present disclosure provides an electric motor that is easier to manufacture and has high performance, and a method for manufacturing the electric motor.

[0007] The electric motor according to the present disclosure is an electric motor comprising: a stator having a circular cross section centered on an axis and incorporating a coil; and an outer rotor having a cylindrical shape centered on the axis and covering the stator from the outer periphery side, wherein the outer rotor has a rotor body and a plurality of magnets arranged in a Halbach pattern circumferentially on the inner periphery side of the rotor body, and among the plurality of magnets, in a pole piece whose magnetization direction faces radially relative to the axis, when viewed from the axial direction, an angle formed by a pair of straight lines extending toward the inner periphery along both end faces in the circumferential direction of the pole piece is set to be larger than the angle formed by a pair of straight lines extending from the axis to the outer periphery end portions of the end faces on both sides in the circumferential direction, and the radial position of an imaginary circle where the circumferential dimension of the pole piece is equal to the magnet width, which is a value obtained by dividing the circumferential length by the number of magnets arranged in the circumferential direction, is located radially inward of the center of the magnet in the radial direction.

[0008] The electric motor according to the present disclosure is an electric motor comprising: a stator having a circular cross section centered on an axis and incorporating a coil; and an outer rotor having a cylindrical shape centered on the axis and covering the stator from the outer periphery, wherein the outer rotor has a rotor body and a plurality of magnets arranged in a Halbach array circumferentially on the inner periphery of the rotor body, the plurality of magnets having pole pieces whose magnetization directions face radially relative to the axis, and transition pieces arranged between a pair of circumferentially adjacent pole pieces, and further comprising a first adhesive layer bonding the outer periphery of the pole pieces to the inner periphery of the rotor body, and a second adhesive layer provided on the circumferential end faces of the transition pieces or the transition piece and the pole piece, bonding the transition pieces to each other or the transition piece and the pole piece in the circumferential direction, wherein the second adhesive forming the second adhesive layer has a higher elongation rate than the first adhesive forming the first adhesive layer.

[0009] The method for manufacturing an electric motor according to the present disclosure is a method for manufacturing the above-mentioned electric motor, and includes the steps of preparing the rotor body, attaching the pole pieces at circumferential intervals on the inner surface of the rotor body, forming a transition piece assembly by circumferentially joining the transition pieces together, and fitting the transition piece assembly from the inner side between the pole pieces on the inner surface of the rotor body.

[0010] According to the present disclosure, it is possible to provide an electric motor that can be manufactured more easily and has high performance, and a method for manufacturing the electric motor.

[0011] Fig. 1 is a cross-sectional view showing the configuration of an electric motor according to an embodiment of the present disclosure; Fig. 2 is an enlarged view of an outer rotor according to an embodiment of the present disclosure; Fig. 3 is an explanatory diagram showing dimensions of each part of the outer rotor according to an embodiment of the present disclosure; Fig. 4 is a flowchart showing each step of a method for manufacturing an electric motor according to an embodiment of the present disclosure; Fig. 5 is an explanatory diagram showing a state of each step in a method for manufacturing an electric motor according to an embodiment of the present disclosure; Fig. 6 is an explanatory diagram showing a state of another step in a method for manufacturing an electric motor according to an embodiment of the present disclosure; Fig. 7 is a graph showing the relationship between electrical angle and torque.

[0012] (Configuration of Electric Motor) Hereinafter, an electric motor 1 according to an embodiment of the present disclosure and a method for manufacturing the electric motor 1 will be described with reference to FIGS. 1 to 7 .

[0013] As shown in Fig. 1, the electric motor 1 includes a stator 10, an outer rotor 20, and a casing (not shown). The stator 10 has a stator body 11 and a plurality of coils 12. The stator body 11 has a cylindrical or columnar shape centered on the axis X. The plurality of coils 12 are arranged on the outer periphery of the stator body 11. As an example, the coils 12 extend in a radial direction relative to the axis X, and are arranged at equal intervals in the circumferential direction.

[0014] (Configuration of Outer Rotor) The outer rotor 20 is supported so as to be rotatable about the axis X relative to the stator 10, which is a stationary body. The outer rotor 20 has a rotor body 21 and a plurality of magnets 22. The rotor body 21 is cylindrical and has its center on the axis X, and covers the stator 10 from the outer periphery with a gap between them. A plurality of magnets 22 are arranged on the inner circumferential surface of the rotor body 21. These magnets 22 are rectangular when viewed from the direction of the axis X, and are arranged in the circumferential direction.

[0015] When a current is supplied to the coil 12 of the stator 10, an electromagnetic force is generated between the coil 12 and the magnet 22. The outer rotor 20 is rotated around the axis X by this electromagnetic force.

[0016] (Magnet Arrangement) As shown in Figure 2, the multiple magnets 22 are arranged in a so-called Halbach array. When viewed from the axial direction X, the magnetization direction of the magnets 22 changes clockwise or counterclockwise from the magnet 22 on one side of the circumferential direction to the magnet 22 on the other side. The example in Figure 2 shows a configuration in which the magnetization direction changes in 45° increments. The tip of the arrow in the figure indicates the south pole side, and the base end indicates the north pole side. By adopting a Halbach array, it is possible to improve the torque of the electric motor 1 having the outer rotor 20.

[0017] Of the multiple magnets 22, the magnets 22 whose magnetization direction is oriented radially relative to the axis X are called pole pieces 31. In the example of FIG. 2 , the magnetization direction changes by 45°, so three other magnets 22 are arranged between the pole pieces 31. These three magnets 22 are each called a transition piece 32. The magnetization direction of the magnets 22 that make up the transition piece 32 is not radial, but circumferential, or inclined at 45° relative to the radial direction. Note that a set of three transition pieces 32 may be referred to as a transition piece assembly 40 below.

[0018] The pole piece 31 and the transition piece 32 are both bonded to each other with an adhesive and fixed to the inner circumferential surface of the rotor body 21 with the same adhesive. A first adhesive layer 51 is interposed between the outer circumferential surface of the pole piece 31 and the inner circumferential surface of the rotor body 21. The first adhesive layer 51 is a layer formed by hardening the first adhesive. On the other hand, a second adhesive layer 52 is interposed between the magnets 22, i.e., between the transition pieces 32 or between the transition piece 32 and the pole piece 31. The second adhesive layer 52 is a layer formed by hardening the second adhesive. The second adhesive has a higher elongation rate and a lower elastic modulus than the first adhesive. A silicone-based elastic adhesive is suitable as the second adhesive to achieve these properties. This type of adhesive exhibits an elongation rate of, for example, 100% or more. An acrylic-based adhesive is suitable as the first adhesive. It is known that this type of adhesive generally has a low elongation rate of a few percent, but has higher strength and elastic modulus than the second adhesive.

[0019] (Shape of Magnets) Next, the detailed shape of each magnet 22 will be described with reference to FIG. 3 . As shown in the figure, the pole piece 31 and the transition piece 32 have different shapes when viewed from the axis X. Here, the angle formed by a pair of straight lines extending toward the inner periphery along both circumferential end faces of the pole piece 31 is referred to as the "included angle θ1." The angle formed by a pair of straight lines extending from the axis X to the outer periphery end of each circumferential end face of the pole piece 31 is referred to as the "axial angle θ2." The included angle θ1 is set larger than the axial angle θ2. Therefore, the circumferential end faces of adjacent pole pieces 31 are either parallel to each other or spread apart toward the inner periphery. The included angle θ1 is equal to 360° divided by the number of poles.

[0020] Furthermore, a pair of corners on the outer periphery of the pole piece 31 are each chamfered to form a notch 60 (see FIG. 2). As the notch 60, in addition to the curved chamfer shown in FIG. 2, a so-called C-chamfer can be used. By forming these notches 60, a triangular gap is formed between the pole piece 31 and the inner periphery of the rotor body 21. This gap is filled with the above-mentioned layer of adhesive. On the other hand, no notch 60 is formed at the pair of corners on the inner periphery.

[0021] Of the three transition pieces 32 constituting the transition piece assembly 40, a pair of transition pieces 32 located on opposite circumferential sides have a different shape from the remaining transition piece 32. These transition pieces 32 located on both circumferential sides are referred to as "end pieces 41." Of the two circumferential surfaces of the end piece 41, the surface facing the pole piece 31 is parallel to the circumferential end face of the pole piece 31 when viewed from the direction of the axis X. Note that "parallel" here refers to substantial parallelism, and slight deviations are permitted. The piece located in the center of the circumferential direction (center piece 42), excluding the end piece 41, is rectangular. Furthermore, cutouts 60 are also formed at a pair of corners on the outer periphery of these transition pieces 32 (see FIG. 2). On the other hand, no cutouts 60 are formed at a pair of corners on the inner periphery, or cutouts smaller than the cutouts 60 on the outer periphery are formed. Note that the cutouts 60 are preferably arc-shaped.

[0022] Here, the value obtained by dividing the sum of the circumferential dimensions of the multiple magnets 22 by the number of magnets 22 is defined as the "magnet width W." An imaginary circle when the magnet width W is equal among the multiple magnets 22 is defined as the "imaginary circle A." As shown in Figure 3, the radial position through which imaginary circle A passes is located radially inward of the radial center of the magnet 22.

[0023] (Method of Manufacturing Electric Motor) Next, a method of manufacturing the above-mentioned electric motor 1, in particular a method of manufacturing the outer rotor 20, will be described with reference to Figures 4 to 6. As shown in Figure 4, this manufacturing method includes step S1 of preparing the rotor body 21, step S2 of arranging the pole pieces 31, step S3 of constructing the transition piece assembly 40, and step S4 of attaching the pole piece 31 assembly to the rotor body 21.

[0024] In step S1, the prefabricated rotor body 21 is placed on, for example, a workbench. It is desirable that, in this state, marks or guides for positioning the pole pieces 31 are formed on the inner circumferential surface of the rotor body 21. Such marks may be, for example, protrusions protruding toward the inner circumferential side. Next, in step S2, the pole pieces 31 are arranged on the inner circumferential surface of the rotor body 21 (see FIG. 5). The pole pieces 31 are arranged at intervals in the circumferential direction according to the marks or guides. Next, in step S3, the transition piece assembly 40 is assembled. Specifically, the transition piece assembly 40 is constructed by joining the pair of end pieces 41 and one center piece 42 described above. In step S4, the transition piece assembly 40 is fitted into the gap between the pair of pole pieces 31 (see FIG. 6). This completes the outer rotor 20. The outer rotor 20 and the stator 10 are then housed in a casing, and other accessories are attached to complete the electric motor 1.

[0025] (Effects) Conventionally, when manufacturing an outer rotor 20 in which sector-shaped magnets 22 (pole pieces 31 and transition pieces 32) with a uniform radial thickness are arranged circumferentially with sufficiently narrow gaps, a process is required in which some or all of the magnets 22 are inserted axially into the rotor body. However, because already-magnetized magnets 22 are affected by the magnetic forces of other surrounding magnets 22, when inserting and arranging multiple magnets 22 axially as described above, it has been difficult to maintain a uniform thickness of the adhesive that bonds the magnets to the rotor body or between the magnets and in the gaps between them, thereby maintaining adhesive strength. In other words, there is room for improvement in the conventional method. To solve this problem, the present embodiment employs the above-described configurations and manufacturing method.

[0026] According to the above configuration, the angle formed by a pair of straight lines extending toward the inner periphery along both circumferential end faces of the pole piece 31 is set to be larger than the angle formed by a pair of straight lines extending from the axis X to both circumferential end faces of the pole piece 31. As a result, the circumferential end faces of a pair of adjacent pole pieces 31 extend parallel to each other toward the inner periphery, or extend so as to move away from each other toward the inner periphery. Therefore, when other magnets 22 are arranged between the pole pieces 31, the possibility of physical interference between the other magnets 22 and the pole piece 31 can be reduced. Therefore, it is possible to arrange only the pole piece 31 first, and then easily arrange the other magnets 22. This makes it possible to manufacture the outer rotor 20 more easily and in a shorter period of time.

[0027] In addition, because the sandwich angle of the pole pieces 31 is relatively large, if the pole pieces 31 attempt to fall off the rotor body 21 due to the magnetic field generated by the Halbach array magnets, the pole pieces 31 are sandwiched between the other magnets 22 arranged between the pole pieces 31 from both circumferential sides toward the outer periphery. This prevents the pole pieces 31 from falling off. As a result, the electric motor 1 can be operated more stably. Alternatively, by setting the rotor rotation speed higher, the output of the electric motor 1 can be increased, i.e., the weight of the electric motor 1 can be reduced for the same output.

[0028] Furthermore, the radial position of an imaginary circle where the circumferential length of the pole piece 31 is equal to the circumferential length divided by the number of magnets arranged circumferentially is located radially inward relative to the radial center of the magnet 22. This has the effect of optimizing the circumferential distribution of magnetic flux density on the inner periphery of the rotor magnet formed by the Halbach array magnets with different shapes, making it possible to suppress torque fluctuations (torque ripple) when the outer rotor 20 is rotated (see the solid line graph in FIG. 7 ; the dashed line graph shows conventional torque fluctuations). Therefore, it is possible to provide an electric motor 1 that can stably generate high torque regardless of rotation speed.

[0029] With the above configuration, the end faces on both circumferential sides of the transition piece 32 are parallel to the circumferential end faces of the pole piece 31 when viewed from the direction of the axis X, bringing the pole piece 31 and the transition piece 32 as close as possible to each other. On the other hand, if there are gaps or air gaps between the magnets 22, the magnetic force will decrease accordingly, which may affect the performance of the electric motor 1. With the above configuration, it is possible to reduce this possibility and provide an electric motor 1 with higher performance.

[0030] Here, because the magnetization direction of the pole pieces 31 is oriented in the radial direction, a radial load is mainly applied when the electric motor 1 is in operation. For this reason, it is desirable that the first adhesive layer 51 that joins the pole pieces 31 to the outer rotor 20 have a considerable degree of adhesive strength. On the other hand, the centrifugal force generated when the outer rotor 20 rotates causes the rotor body 21 to deform slightly so that it spreads out on both sides in the circumferential direction. For this reason, the magnets 22 are affected by the circumferential tensile force that accompanies the deformation of the rotor body 21, more than by the influence of the magnetic force.

[0031] However, with the above configuration, the first adhesive forming the first adhesive layer 51 that bonds the pole pieces 31 to the rotor body 21 has a high elastic modulus, a low elongation rate, and high adhesive strength. Therefore, even when a radial load is applied to the pole pieces 31, they do not lift or peel off from the rotor body 21. Furthermore, the second adhesive layer 52 that bonds the magnets 22 together circumferentially has a higher elongation rate and a lower elastic modulus than the first adhesive. Therefore, as the rotor body 21 expands in the circumferential direction, the adhesive can expand and follow the expansion of the circumferential gaps between the magnets 22. This reduces the possibility of misalignment of the magnets 22 in the outer rotor 20 or defects in the adhesive layer that secures the magnets 22, regardless of whether the motor is started, running, or stopped. This enables the motor 1 to continue operating stably for a long period of time. Furthermore, by setting the rotor rotation speed higher, the output of the motor 1 can be increased, i.e., the weight of the motor 1 can be reduced for the same output.

[0032] According to the above configuration, the two outer corners of the magnet 22 have cutouts 60 that are larger than the remaining two inner corners. This reduces the possibility of the magnet 22 interfering with other magnets 22 that are already placed when the magnet 22 is placed on the rotor body 21. Furthermore, during assembly, excess adhesive flows into the cutouts 60, allowing the thickness of the adhesive layer between the circumferential end faces of the magnet 22 and between the magnet 22 and the rotor body 21 to be adjusted to the desired thickness. This improves the adhesive quality of the magnet 22 and further increases the adhesive fixation strength of the magnet. As a result, the electric motor 1 can continue to operate stably at even higher rotation speeds and torques.

[0033] Here, a conventional method has been to spread the adhesive in the gaps while sliding some or all of the magnets 22 on the inner circumferential surface of the rotor body 21. However, this method results in friction between the magnets 22 and the inner circumferential surface of the rotor body 21, and in particular, it is not possible to maintain a uniform thickness of the adhesive in the gaps between the magnets 22 and the rotor body 21, which poses the risk of insufficient adhesive strength.

[0034] However, according to the above method, the pole pieces 31 are first attached to the rotor body 21, and then the step of fitting the transition piece assembly 40 between the pole pieces 31 is performed. Therefore, the Halbach array can be completed simply by inserting the transition piece assembly 40 from the radially inner side between the pole pieces 31 that have been positioned previously. This reduces the possibility of the magnets 22 and the inner circumferential surface of the rotor body 21 rubbing against each other. Therefore, it is possible to minimize the risk of insufficient adhesive strength of the magnets 22.

[0035] (Other Embodiments) Although the embodiments of the present disclosure have been described in detail above with reference to the drawings, the specific configuration is not limited to this embodiment, and design changes and the like within the scope that does not deviate from the gist of the present disclosure are also included.

[0036] Furthermore, the number of magnets 22, the number of coils 12, and the rate of change of magnetization direction (i.e., the number of poles) described in the above embodiment are merely examples, and can be changed as appropriate depending on the design and specifications. In any case, the same effects as those described above can be obtained.

[0037] Furthermore, the materials of the first adhesive and the second adhesive are merely examples, and any adhesive substance that has a significant difference in elongation rate can be used.

[0038] <Additional Notes> The electric motor 1 and the method for manufacturing the electric motor 1 described in each embodiment can be understood, for example, as follows.

[0039] (1) A first aspect of the electric motor 1 is an electric motor 1 including a stator 10 having a circular cross section centered on an axis X and incorporating a coil 12, and an outer rotor 20 having a cylindrical shape centered on the axis X and covering the stator 10 from the outer periphery side, the outer rotor 20 including a rotor body 21 and a plurality of magnets 22 arranged in a Halbach array in the circumferential direction on the inner periphery side of the rotor body 21, and among the plurality of magnets 22, pole pins whose magnetization direction faces a radial direction relative to the axis X are arranged in a Halbach array. In the pole piece 31, when viewed from the direction of the axis X, the angle formed by a pair of straight lines extending inward along the end faces on both sides of the circumferential direction of the pole piece 31 is set to be larger than the angle formed by a pair of straight lines extending from the axis X to the outer ends of the end faces on both sides of the circumferential direction, and the radial position of an imaginary circle where the circumferential length of the pole piece 31 is equal to the length obtained by dividing the circumferential length by the number of magnets arranged in the circumferential direction is located radially inward of the radial center of the magnet 22.

[0040] According to the above configuration, the angle formed by a pair of straight lines extending inward along both circumferential end faces of the pole piece 31 is set to be larger than the angle formed by a pair of straight lines extending from the axis X to both circumferential end faces of the pole piece 31. Therefore, when other magnets 22 are arranged between the pole pieces 31, the possibility of physical interference between these other magnets 22 and the pole piece 31 can be reduced.

[0041] (2) The electric motor 1 according to a second aspect is the electric motor 1 of (1), wherein the plurality of magnets 22 further includes a transition piece 32 arranged between a pair of circumferentially adjacent pole pieces 31, and the circumferential end face of the pole piece 31 adjacent to the transition piece 32 and the circumferential end face of the transition piece 32 are parallel to each other when viewed from the direction of the axis X.

[0042] According to the above configuration, the circumferential end face of the transition piece 32 is parallel to the circumferential end face of the pole piece 31 when viewed from the direction of the axis X, and the pole piece 31 and the transition piece 32 are brought as close as possible to each other.

[0043] (3) The electric motor 1 according to a third aspect is the electric motor 1 of (2), further comprising a first adhesive layer 51 that bonds the outer peripheral surface of the pole piece 31 to the inner peripheral surface of the rotor body 21, and a second adhesive layer 52 that is provided on the end surfaces of the transition pieces 32 or the transition piece and the pole piece facing in the circumferential direction and bonds the magnets 22 to each other or the transition piece and the pole piece in the circumferential direction, and the second adhesive that forms the second adhesive layer 52 has a higher elongation rate than the first adhesive that forms the first adhesive layer 51.

[0044] According to the above configuration, the first adhesive forming the first adhesive layer 51 that bonds the pole piece 31 to the rotor body 21 has a lower elongation rate, a higher elastic modulus, and a higher adhesive strength than the second adhesive forming the second adhesive layer 52 that bonds the transition pieces 32 together and the transition pieces 32 to the pole piece 31 in the circumferential direction. Therefore, even when a radial load is applied to the pole piece 31, the pole piece 31 does not lift up or peel off from the rotor body 21. Furthermore, the second adhesive layer 52 that bonds the magnets 22 together in the circumferential direction has a higher elongation rate and a lower elastic modulus than the first adhesive. Therefore, as the adhesive present in the gap expands, it can expand and follow the expansion of the circumferential gap between the magnets 22 that occurs as the rotor body 21 expands in the circumferential direction.

[0045] (4) The electric motor 1 according to the fourth aspect is an electric motor 1 according to any one of the aspects (1) to (3), in which the two corners facing the outer periphery of the magnet 22 have cutouts 60 formed therein that are larger than the remaining two corners facing the inner periphery.

[0046] According to the above configuration, the two outer corners of the magnet 22 have cutouts 60 that are larger than the remaining two inner corners. This reduces the possibility that the magnet 22 to be placed will interfere with other magnets 22 that are already placed when the magnet 22 is placed on the rotor body 21.

[0047] (5) A fifth aspect of the electric motor 1 is an electric motor 1 including a stator 10 having a circular cross section centered on an axis X and incorporating a coil 12, and an outer rotor 20 having a cylindrical shape centered on the axis X and covering the stator 10 from the outer periphery side, the outer rotor 20 including a rotor body 21 and a plurality of magnets 22 arranged in a Halbach array in the circumferential direction on the inner periphery side of the rotor body 21, the plurality of magnets 22 including a pole piece 31 whose magnetization direction faces a radial direction relative to the axis X, and a pair of the pole pieces 31 adjacent to each other in the circumferential direction. The rotor body 21 further comprises a first adhesive layer 51 that bonds the outer peripheral surface of the pole piece 31 to the inner peripheral surface of the rotor body 21, and a second adhesive layer 52 that is provided on the circumferential end surfaces of the transition pieces 32 or the transition pieces 32 and the pole pieces 31, and bonds the transition pieces 32 to each other or the transition pieces 32 and the pole pieces 31 in the circumferential direction, wherein the second adhesive that forms the second adhesive layer 52 has a higher elongation rate than the first adhesive that forms the first adhesive layer 51.

[0048] According to the above configuration, the first adhesive forming the first adhesive layer 51 that bonds the pole piece 31 to the rotor body 21 has a smaller elongation rate, a higher elastic modulus, and a higher adhesive strength than the second adhesive forming the second adhesive layer 52 that bonds the magnets 22 together in the circumferential direction. Therefore, even when a radial load is applied to the pole piece 31, it will not lift up or peel off from the rotor body 21. Furthermore, the second adhesive layer 52 that bonds the magnets 22 together in the circumferential direction has a larger elongation rate and a smaller elastic modulus than the first adhesive. Therefore, as the adhesive present in the gap expands, it can expand and follow the expansion of the circumferential gap between the magnets 22 that occurs as the rotor body 21 expands in the circumferential direction.

[0049] (6) The electric motor 1 according to a sixth aspect is the electric motor 1 of (1), in which the included angle is a value of 360° / number of poles.

[0050] According to the above configuration, when other magnets 22 are arranged between the pole pieces 31, the possibility of physical interference between these other magnets 22 and the pole pieces 31 can be further reduced.

[0051] (6) The electric motor 1 according to the sixth aspect is a manufacturing method of the electric motor 1 described in (2), and includes the steps of preparing the rotor body 21, attaching the pole pieces 31 at intervals in the circumferential direction on the inner surface of the rotor body 21, joining the transition pieces 32 together in the circumferential direction to form a transition piece assembly 40, and fitting the transition piece assembly 40 between the pole pieces 31 on the inner surface of the rotor body 21 from the inner side.

[0052] According to the above method, the pole pieces 31 are first attached to the rotor body 21, and then the step of fitting the transition piece assembly 40 between the pole pieces 31 is performed. Therefore, the Halbach array can be completed simply by inserting the transition piece assembly 40 from the radially inner side between the pole pieces 31 that have been positioned previously.

[0053] According to the present disclosure, it is possible to provide an electric motor that can be manufactured more easily and has high performance, and a method for manufacturing the electric motor.

[0054] DESCRIPTION OF SYMBOLS 1... Electric motor 10... Stator 11... Stator body 12... Coil 20... Outer rotor 21... Rotor body 22... Magnet 31... Pole piece 32... Transition piece 40... Transition piece assembly 41... End piece 42... Center piece 51... First adhesive layer 52... Second adhesive layer 60... Notch portion X... Axis

Claims

1. A motor comprising a stator having a circular cross-section centered on an axis and incorporating a coil, and an outer rotor having a cylindrical shape centered on the axis and covering the stator from the outer peripheral side, wherein the outer rotor has a rotor body and a plurality of magnets arranged in a Halbach array in the circumferential direction on the inner peripheral side of the rotor body. Among the plurality of magnets, in a pole piece whose magnetization direction faces the radial direction with respect to the axis, the scissor angle, which is the angle formed by a pair of straight lines extending inward in the circumferential direction along the end faces on both circumferential sides of the pole piece as viewed from the axial direction, is set larger than the angle formed by a pair of straight lines extending from the axis to the outer peripheral ends of the end faces on both circumferential sides. The radial position of a virtual circle whose diameter is equal to the circumferential dimension of the pole piece divided by the number of magnets arranged in the circumferential direction (magnet width) is located radially inside the central portion of the magnet in the radial direction.

2. The plurality of magnets further have a transition piece arranged between a pair of adjacent pole pieces in the circumferential direction, and the circumferential end faces of the pole piece adjacent to the transition piece and the circumferential end face of the transition piece are parallel as viewed from the axial direction X. The motor according to claim 1.

3. The motor further comprises a first adhesive layer that bonds the outer peripheral surface of the pole piece and the inner peripheral surface of the rotor body, and a second adhesive layer that is provided on the circumferentially facing end faces of the transition pieces or between the transition piece and the pole piece and bonds the transition pieces or the transition piece and the pole piece in the circumferential direction. The second adhesive forming the second adhesive layer has a larger elongation rate than the first adhesive forming the first adhesive layer. The motor according to claim 2.

4. Notches larger than the remaining two corners facing the inner peripheral side are formed at two corners facing the outer peripheral side of the magnet. The motor according to any one of claims 1 to 3.

5. A motor comprising a stator having a circular cross-section centered on an axis and incorporating a coil, and an outer rotor having a cylindrical shape centered on the axis and covering the stator from the outer peripheral side, wherein the outer rotor includes a rotor body, a plurality of magnets arranged in a Halbach array in the circumferential direction on the inner peripheral side of the rotor body, the plurality of magnets having a pole piece whose magnetization direction faces the radial direction with respect to the axis and a transition piece arranged between a pair of adjacent pole pieces in the circumferential direction, a first adhesive layer bonding the outer peripheral surface of the pole piece and the inner peripheral surface of the rotor body, and a second adhesive layer provided on the end surfaces facing the circumferential direction of the transition pieces or between the transition piece and the pole piece and bonding the transition pieces or the transition piece and the pole piece in the circumferential direction, and the second adhesive forming the second adhesive layer has a greater elongation rate than the first adhesive forming the first adhesive layer.

6. The motor according to claim 1, wherein the nipping angle is a value of 360° / number of poles.

7. A method of manufacturing the motor according to claim 2, the method including the steps of preparing the rotor body, attaching the pole pieces at intervals in the circumferential direction on the inner peripheral surface of the rotor body, forming a transition piece assembly by bonding the transition pieces in the circumferential direction, and fitting the transition piece assembly into the space between the pole pieces on the inner peripheral surface of the rotor body from the inner peripheral side.

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