Electric motor with rotor structure to prevent defect due to stress caused by temperature change, and manufacturing process for this

Abstract

Manufacturing method of an electric motor (10) comprising a stator (18) and a rotor (14) configured to be rotated relative to the stator, the procedure includes the following steps: Forming a rotor core (26) by stacking magnetic steel plates (24); Aligning a plurality of permanent magnets (28) in one direction of a rotational axis of the rotor (14) and fixing the permanent magnets (28) to the magnetic steel plate (24) by means of adhesives; Positioning an engagement element (40) that melts at a temperature higher than the curing temperature of the adhesives between the permanent magnets (28) that are adjacent to each other in the direction of the axis of rotation; and Heating the rotor (14) after the adhesives have cured, so that the engagement element (40) melts and flows out between adjacent permanent magnets (28), wherein a thickness of the engagement element (40) in the direction of the axis of rotation is determined such that adjacent permanent magnets (28) which are bonded to the rotor core (26) within a manufacturing temperature range of the rotor (14) do not contact each other at a lower limit of an operating temperature of the electric motor.

Description

Background of the invention 1. Field of the invention

[0001] The present invention relates to an electric motor and a manufacturing method thereof, the electric motor having a rotor structure for preventing a defect such as bending of the rotor and breakage of a magnet due to thermal stresses of a magnetic steel plate, a shaft and the magnet, etc., constituting the rotor. 2. Description of the related art

[0002] Generally, the main components for constructing a rotor of a synchronous electric motor are a magnetic steel plate, a carbon steel shaft, and a permanent magnet. The rotor structure can include: an SPM (surface permanent magnet) structure, in which a permanent magnet is attached to a rotor surface; and an IPM (interior permanent magnet) structure, in which a permanent magnet is embedded in a magnetic electric plate.

[0003] In the prior art, an electric motor is required to have a large maximum output or maximum torque, but only a small moment of inertia. Therefore, when an electric motor is designed or manufactured, its rotor structure is usually configured to extend in the axial direction. In such an electric motor, a neodymium magnet (NdFeB) with a high magnetic force is often used. An adhesive is commonly used as a means for fixing the neodymium magnet to a core structure in which magnetic steel plates are stacked. A one-component thermosetting plastic adhesive is widely used as the adhesive.

[0004] To prevent stress on a rotor having a plurality of magnets, several techniques have been proposed. For example, JP 2002-78257 A discloses a rotor having a permanent magnet, and describes that "a motor of the invention comprises a plurality of poles and a rotor, wherein a gap is formed between adjacent permanent magnets of the poles. Even when the temperature is varied, the thermal stress between the permanent magnet and the rotor is reduced, thereby limiting component decoupling." Furthermore, it describes that "in the motor of the invention, the gap between adjacent permanent magnets is filled with an adhesive and beads."By filling the gap between permanent magnets with the adhesive and the bead of predetermined dimensions, the thickness between the adjacent permanent magnets can be constant, thereby easily controlling the dimension of the rotor.”

[0005] In contrast, JP 2011-205781 A discloses an electric motor with a permanent magnet and describes that "when a permanent magnet is inserted into a magnet insertion space formed in a rotor core, thin rubbers are temporarily attached to upper and lower ends in relation to the magnet insertion direction, and then the permanent magnets are sequentially inserted. After one or more magnets are inserted to stack the magnets in the rotation direction, the rotor core is attracted from both ends thereof such that pressure is exerted on the thin rubber on the end of the magnet, thereby forming a rotor structure."

[0006] In the prior art rotor, in which a neodymium magnet is bonded and fixed to a rotor core with a stacked magnetic steel plate, stress is generated due to the difference in linear expansion coefficients between the neodymium magnet and the iron constituting the rotor. After the two components with different linear expansion coefficients are bonded by an impregnating agent (or adhesive), when the temperature is varied from the point where the adhesive is cured, a difference occurs between the axial lengths of the iron and the magnet, thereby generating stress. Due to the stress, the following defects may occur. - the adhesive used to stick the magnet will break and the magnet may come off. - the rotor may bend due to unevenness of the adhesive. - the magnet can be broken. - a gap may form between the stacked magnetic steel plate.

[0007] In particular, in a rotor which is comparatively long in the axial direction, a plurality of magnets are stacked in the axial direction, and the defects described above may seriously occur according to its axial length.

[0008] Fig. Figure 11 specifically describes the problems described above in a rotor according to the prior art. A rotor 50 as shown in Fig. The rotor shown in Figure 11 is an IPM rotor and includes a rotor core 54 formed by stacking an annular magnetic steel plate 52, a plurality of permanent magnets 56 embedded in the rotor core 54, and two end plates 58 that clamp the magnetic steel plate 52 from both sides in the axial direction. Each permanent magnet 56 is a neodymium magnet having a substantially smooth shape, and the shapes of the permanent magnets are identical to each other. The permanent magnets are formed as a plate extending in the axial direction of the rotor, and the plate is inserted into a slot 60 extending in the axial direction and formed in the rotor core 54. One main surface of each permanent magnet 56 is bonded to an inner surface of the slot 60 by means of a thermosetting resin adhesive (or impregnating agent) 62.

[0009] From the state of section (a) according to Fig. 11, when the temperature of the rotor core 54 (at least a portion of the rotor 54 near the adhesive 62) reaches a curing temperature of the adhesive 62, the magnetic steel plate 52 expands with a comparatively high linear expansion coefficient (for example, 12×10 -6 / K) in the substantially axial direction of the rotor 54 (in the horizontal direction), as shown in section (b) according to Fig. 11. In contrast, the axial size of the permanent magnet 56 is not significantly changed because a linear expansion coefficient of the permanent magnet 56 in the axial direction is significantly small (in the case of the neodymium magnet -0.5×10 -6 / K). In such a state, the adhesive 62 is cured, so that the permanent magnet 56 and the magnetic steel plate 52 are bonded.

[0010] Next, when the temperature of the rotor core 54 is lowered to a lower limit of the operating temperature of the electric motor, the magnetic steel plate 52 contracts in the substantially axial direction. In this regard, since the magnetic steel plate 52 is bonded and fixed to the permanent magnet 56, a portion of the magnetic steel plate 52 near the permanent magnet 56 does not contract, and a portion of the magnetic steel plate 52 near the outer surface or the center of the rotor core 54 contracts as the temperature decreases. As a result, a strain is generated and a stress exists in the rotor core 54, as shown in section (c) of FIG. Fig. 11. Furthermore, as shown in section (d) according to Fig. 11, due to the stress from the load, a crack 64 may occur in the magnetic steel plate 52, the rotor shaft may bend (not shown), and / or a crack or damage may occur in the permanent magnet 56.

[0011] In the technique according to JP 2002-78257 A, a gap is formed between the permanent magnets so that stress is not generated by the load due to the series of magnets. However, when such a technique is applied to the IPM structure, it is difficult to form a constant gap between the magnets in terms of the structure or its manufacturing. In contrast, when the technique is applied to the SPM structure, it is necessary to position the permanent magnets while placing a jig, etc., to form a constant gap between the magnets, and therefore, it is difficult to manufacture the structure.

[0012] Furthermore, JP 2002-78257 A describes that the adhesive is filled into the gap between the magnets, and polyethylene beads or silicone rubber beads are added to the adhesive. However, it is difficult to reliably fill the adhesive into the gap between the magnets because such a process depends on the property of the adhesive and the skill of a user. Furthermore, in the process, it is necessary to remove the adhesive that protrudes from the gap toward the surface of the magnet. Furthermore, if the beads are added to the adhesive, the property of the adhesive may be adversely affected. Since the distribution density of the beads in the adhesive may be uneven, the adhesive effect of the adhesive may become unstable.

[0013] In contrast, in the structure of JP 2011-205781 A, an elastic thin plate is attached to one surface of the magnet facing in the axial direction, and a clamping force is applied to the structure from both axial ends thereof by means of clamping plates, so that a compressive force is exerted on the elastic thin plate. However, in the structure of JP 2011-205781 A, adhesives are not used to fix the permanent magnets, and thus the structure is not intended to bear the stress due to the difference in linear expansion coefficients. Furthermore, the object of the invention of JP 2011-205781 A is to prevent the magnet from being damaged when the magnet is inserted and fixed in the rotor manufacturing process, and thus does not solve the defect of thermal stress.

[0014] JP 2010-259231 A discloses a manufacturing method for a magnetic pole in which a plurality of magnet pieces are obtained by breaking a magnetic body along predetermined breaking points and filling an insulating material into the resulting gaps. The insulating material comprises a mixture of non-conductive particles (such as glass beads) in an adhesive.

[0015] US 2009 / 0 174 273 A1 discloses manufacturing methods for a rotor in which a magnet is fixed in a rotor core by injecting molten resin into a slot using an injection molding process. This is done under the assumptions that a dimension between an end surface of the rotor core and an end surface of the permanent magnet forms an interval, and that a minimum value of a gap dimension between an inner surface of the slot and a side surface of the permanent magnet allows complete filling of the gap.

[0016] The Wikipedia article "Lost-wax casting," published on April 7, 2012, covers common lost-wax casting processes. Further prior art is cited in the publications JP 2000-324 736 A, JP H05-135 976 A, JP 2012-029 343 A, JP 2009-296 696 A, JP 2003-164 085 A, DE 10 2009 027 916 A1, US 6 359 359 B1, JP 2010-141 989 A, US 5 936 323 A, and DE 10 2009 054 584 A1. SUMMARY OF THE INVENTION

[0017] Therefore, the object of the invention is to provide an electric motor having a rotor structure and a manufacturing method thereof, wherein a stress due to a temperature change does not occur and a manufacturing problem does not occur.

[0018] According to the invention, a manufacturing method for an electric motor is provided according to the independent claim. Developments are presented in the dependent claims.

[0019] Preferably, there is provided an electric motor comprising a stator and a rotor configured to be rotated relative to the stator, the rotor comprising: a rotor core formed by stacking magnetic steel plates; a plurality of permanent magnets aligned in a direction of a rotation axis of the rotor, the permanent magnets being bonded and fixed to the magnetic steel plate by adhesives; and an engaging member positioned between the permanent magnets adjacent to each other in the direction of the rotation axis, wherein a thickness of the engaging member in the direction of the rotation axis is determined such that adjacent permanent magnets bonded to the rotor core do not contact each other within a manufacturing temperature range of the rotor at a lower limit of an operating temperature of the electric motor.

[0020] Preferably, the engagement element is elastically or plastically deformable.

[0021] Preferably, the permanent magnets are bonded and fixed in a magnet insertion hole formed in the rotor core and extending in the direction of the rotation axis.

[0022] Preferably, the permanent magnets are bonded and fixed to a surface of the rotor core.

[0023] Preferably, there is provided a manufacturing method of an electric motor including a stator and a rotor configured to be rotated relative to the stator, the method comprising the steps of: forming a rotor core by stacking magnetic steel plates; aligning a plurality of permanent magnets in a direction of a rotation axis of the rotor and fixing the permanent magnets to the magnetic steel plate by adhesives; and positioning an engaging member between the permanent magnets adjacent to each other in the direction of the rotation axis, wherein a thickness of the engaging member in the direction of the rotation axis is determined such that adjacent permanent magnets bonded to the rotor core within a manufacturing temperature range of the rotor do not contact each other at a lower limit of an operating temperature of the electric motor.

[0024] Preferably, the method further comprises the step of further heating the rotor after the adhesives have cured so that the engaging element melts and flows from between adjacent permanent magnets.

[0025] Preferably, the method comprises the step of alternately inserting the permanent magnet and the engaging member into a magnet insertion hole formed in the rotor core.

[0026] Preferably, the method comprises the step of previously adhering the engaging element to an end face of the permanent magnet opposite in the direction of the rotation axis. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The above and other objects, features and advantages of the invention will become more apparent from the following description of the preferred embodiments of the invention with reference to the accompanying drawings.

[0028] They show: Fig. 1 is a view of a schematic structure of an electric motor according to an embodiment of the invention; Fig. 2 an axial cross-sectional view of a rotor of the electric motor according to Fig. 1; Fig. 3 is a view showing an example in which an engaging member positioned between permanent magnets is a sheet member; Fig. 4 is a view showing an example in which the engaging member is a silicon resin or a urethane foam applied to the permanent magnet, Fig. 5 is a view showing an example in which the engaging member is made of foamed polystyrene beads; Fig. 6 is a view showing an example in which the engaging member is a corrugated metal or resin; Fig. 7 is a view showing a manufacturing method of the rotor according to Fig. 2 describes; Fig. 8 is a view showing another manufacturing method of the rotor according to Fig. 2 describes; Fig. 9 is a view showing a function and an effect of the engaging element of the rotor according to Fig. 2 describes; Fig. 10 is a view of a schematic structure of an electric motor according to another embodiment of the invention; and Fig. 11 is an axial cross-sectional view of a rotor of an electric motor of the prior art, comprising a section (a) showing a state before curing of adhesives, a section (b) showing a state in which the temperature of the rotor is increased to a curing temperature of the adhesives, a section (c) showing a state in which the temperature of the rotor is reduced from the state of section (b) to a lower limit of an operating temperature of the motor, and a section (d) showing a state in which a part of the stacked magnetic steel plates is broken. DETAILED DESCRIPTION

[0029] Fig. 1 shows a schematic structural view of an electric motor 10 according to an embodiment of the invention. The rotor 10 includes a rotor 14 into which a shaft 12 (i.e., a rotation axis) is inserted, a stator 18 formed by stacking annular magnetic steel plates 16, and a housing 22 that includes the rotor 14 and the stator 18 and rotatably supports the shaft 12 by means of a support 20. Since components other than the rotor 14 may be conventional, a detailed description thereof will be omitted.

[0030] Fig. 2 shows the rotor 14 of the electric motor 10 according to Fig. 1. The rotor 14 according to Fig. 2 is a rotor with an IPM structure in which permanent magnets are embedded. The rotor 14 includes a rotor core 26 formed by stacking annular magnetic steel plates 24, a plurality of permanent magnets 28 embedded in the rotor core 26, and two end plates 30 that sandwich or clamp the magnetic steel plates from both axial sides. For example, each permanent magnet 28 is a neodymium magnet with a substantially flat shape, and preferably, each magnet has the same shape. As shown in Fig. As shown in Figure 2, the permanent magnets 28 are aligned in the direction of the rotation axis (specifically, one end face of each permanent magnet faces each other to form a magnet plate extending in the direction of the rotation axis of the rotor) and are inserted into a magnet insertion hole or slot 32 formed in the rotor core 26 and extending in the direction of the rotation axis. Main surfaces 34 and 36 of each permanent magnet 28 are bonded to an inner surface of the slot 32 using a thermosetting plastic adhesive (or impregnating agent) 38. Each permanent magnet 28 does not contact the other, and a deformable engaging member 40 is positioned between the end faces of the magnets.

[0031] The engaging member 40 is an elastically or plastically deformable member, and the thickness of the engaging member 40 in the direction of the rotation axis of the rotor is determined such that adjacent permanent magnets 28 bonded to the rotor core 26 within a manufacturing temperature range of the rotor do not contact each other at a lower limit of an operating temperature of the electric motor, as will be described below.

[0032] Fig. 3 to 6 show various examples of an engaging element 40. First, Fig. 3 shows an example in which the engaging element is an elastically or plastically deformable sheet-like member 40a, such as rubber or resin. The sheet-like member 40a is bonded to the axial end surface of the permanent magnet 28 using an adhesive, etc., and functions as the engaging element.

[0033] Fig. Figure 4 shows an example in which the engagement element is a liquid resin 40b that exhibits elasticity after curing, like rubber. The liquid resin 40b is applied to the axial end surface of the permanent magnet 28 using a spatula 42, etc., and functions as the engagement element after curing.

[0034] Fig. Figure 5 shows an example in which the engaging element consists of elastically or plastically deformable beads 40c, such as expanded polystyrene. The beads 40c are bonded to the axial end surface of the permanent magnet 28 using an adhesive, etc., and function as the engaging element.

[0035] Fig. 6 shows an example in which the engaging element is a corrugated plate element 40d formed by corrugating a resin plate or a metal plate so that the plate has a certain elasticity. The corrugated plate element 40d is bonded to the axial end surface of the permanent magnet 28 using an adhesive, etc., and functions as the engaging element.

[0036] About the examples according to Fig. 3 to 6, a resin having a comparatively low melting point higher than a curing temperature of the adhesive (ie, the electric motor is not adversely affected at the melting point), a metal such as tin (which has a melting point of 232 °C), or a low melting point metal (e.g., an alloy having a melting point of 138 °C containing bismuth, tin, lead, and cadmium) may be used as the engaging element.In other words, when a member that melts at a temperature higher than the curing temperature of the adhesive (or the impregnating agent) is used in a process of heating and curing the adhesive, the engaging member can be melted by further increasing the temperature after curing the adhesive so that the engaging member flows between the permanent magnets, whereby a suitable gap or space can be formed between the permanent magnets.

[0037] Next, a manufacturing process of the motor with IPM structure as shown in Fig. 2, with reference to Fig. 7 and Fig. 8. First, in the embodiment according to Fig. 7, the engaging element 40 is preliminarily attached or applied to one axial end of the permanent magnet 28, and the permanent magnet 28 is sequentially inserted into the slot 32 formed in the stack of magnetic steel plates 24 (in the illustrated embodiment, five permanent magnets are inserted into one slot 32). Then, a thermosetting resin adhesive is impregnated between the inner surface of the slot 32 and the main surface of the permanent magnet 28, and the rotor core 26 is heated to the curing temperature of the adhesive or higher to bond and fix the permanent magnet 28 to the rotor core 26.

[0038] In the embodiment according to Fig. 8, the engaging element 40 is not pre-attached or applied to the axial end of the permanent magnet, as in Fig. 7, but instead the permanent magnet 28 and the engaging element 40 are inserted alternately into the slot 32. In this regard, it is not necessary to attach the engaging element 40 to the permanent magnet 28. Then, similar to the embodiment according to Fig. 7, a thermosetting plastic adhesive is impregnated between the inner surface of the slot 32 and the main surface of the permanent magnet, and the rotor core 26 is heated to the curing temperature of the adhesive or more to bond and fix the permanent magnet 28 to the rotor core 26.

[0039] Next, the function of the engaging element 40 positioned between the permanent magnets 28 will be explained with reference to Fig. 9. A section (a) according to Fig. Fig. 9 shows a part of the rotor core 26 before the curing of the adhesive 38 impregnated between the inner surface of the slot 32 and the main surface of the permanent magnet 28 (generally at normal temperature). From the state of section (a) according to Fig. 9, when the temperature of the rotor core 26 (at least a periphery of the adhesive 38) is increased to the annealing temperature of the adhesive 38, the magnetic steel plate 24 expands with a comparatively high linear expansion coefficient (e.g., 12×10 -6 / K) mainly in the direction of the rotation axis (or in the left-right direction), while the permanent magnet 28 has a significantly low linear expansion coefficient relative to the magnetic steel plate 24 (e.g. -0.5×10 -6 / K in the case of a neodymium magnet) changes little in its dimensions in the axial direction, as shown in a section (b) according to Fig. 9 shown.

[0040] In the state of section (b) according to Fig. 9, the adhesive 38 is cured, and then the permanent magnet 28 and the magnetic steel plate 24 are bonded together.

[0041] Then, when the temperature of the rotor core 26 is lowered to a lower limit of an operating temperature of the electric motor, the magnetic steel plate 24 contracts mainly in the direction of the rotation axis, while the permanent magnet 28 changes little in its dimension. Furthermore, since the permanent magnet 28 is bonded and fixed to the magnetic steel plate 24, as shown in a section (c) according to Fig. 9, an axial distance between permanent magnets 28 is reduced (more precisely, a distance between the axial end faces of adjacent permanent magnets 28 is reduced). Further, the deformable engaging element 40 is applied between the end faces of the permanent magnets 28, as described above, a stress of the rotor core 26 acts by the compressive deformation of the engaging element 4 in the axial direction, whereby the Fig. 11 can be avoided. In addition, the thickness of the engaging element 40 is determined such that adjacent permanent magnets 28 do not contact each other at the lower limit of the operating temperature of the electric motor, as shown in section (c) according to Fig. 9 shown.

[0042] Although the magnetic steel plate 24 is also rotated to the extent in the radial direction of the rotor (the vertical direction in Fig. 9) due to the temperature change, the thermal stress in the radial direction of the rotor does not pose a problem because the permanent magnet 28 has a relatively high linear expansion coefficient in a magnetization direction (or in a direction of easy magnetization), that is, in the radial direction of the rotor (e.g. 6.5×10 -6 / K in the case of a neodymium magnet).

[0043] Fig. 10 shows another embodiment of an electric motor rotor according to the invention, namely a rotor 114 with an SPM structure in which permanent magnets are attached to one surface of the structure. The rotor 114 has a rotor core 126 formed by stacking annular magnetic steel plates 124, a plurality of permanent magnets 128 embedded in the rotor core 126, and two end plates 130 that sandwich or clamp the magnetic steel plates 124 from both axial sides. For example, each permanent magnet 128 is a neodymium magnet with a substantially smooth shape, and preferably each magnet has the same shape. As shown in Fig. As shown in Figure 10, the permanent magnets 128 are aligned in the direction of the rotation axis (specifically, one end face of each magnet faces each other to form a curved magnetic plate extending in the direction of the rotation axis of the rotor) and are bonded to an outer side surface of the rotor core 126. Specifically, among main surfaces 134 and 136 of each permanent magnet 128, the concave main surface 136 is bonded to the substantially cylindrical side surface of the rotor core 126 by means of a thermosetting plastic adhesive 138. Each permanent magnet 128 does not contact the other, and a deformable engaging element 140 is positioned between the end faces of the magnets.

[0044] In adhering the permanent magnets 128 to the outer surface of the rotor core 126, a plurality of permanent magnets 26 connected to each other via the engaging element 140 between them (as indicated by reference numeral 128a according to Fig.10), may be bonded to the rotor core 126. Alternatively, each permanent magnet 128 having the engaging element 140 at one end thereof may be sequentially bonded to the rotor core 126.

[0045] The engaging element 140 and its function may be the same as those of the engaging element 40 described from the perspective of the rotor with an IPM structure, and thus a detailed description thereof will be omitted. As such, the invention can be applied to both the IPM structure in which the permanent magnet is embedded in the rotor core and the SPM structure in which the permanent magnet is bonded and fixed to the outer surface of the rotor core.

[0046] Although the permanent magnet was described as a neodymium magnet in the embodiment, the invention is not limited to this. For example, the permanent magnet may be a ferrite magnet. The invention can be applied to a case where the linear expansion coefficients of the permanent magnet and the magnetic steel plate (iron) are different in the direction of the rotation axis.

[0047] According to the invention, even if the temperature of the rotor is lowered from the temperature at which the permanent magnet is bonded to the rotor so that a difference occurs in the axial direction between the magnetic steel plate and the permanent magnet, the difference is absorbed by the deformation of the engaging member positioned between the permanent magnets, whereby the disadvantage such as damage to the rotor can be avoided.

[0048] In the invention, it is not necessary to provide a gap between aligned magnets as in the prior art, and the magnets are aligned in the axial direction and bonded to the rotor surface as well in the SPM structure.

[0049] Therefore, there's no need to intentionally create a gap between the magnets. Furthermore, there's no need to use a special adhesive. Moreover, when adhering the permanent magnet, it's only necessary to bond the permanent magnet to the rotor core, so there's no need to bond the magnets together. Therefore, the adhesive doesn't scatter or protrude, and there's no need to wipe off the scattered adhesive.

[0050] The element present between the aligned permanent magnets, at least until the adhesive has cured, is removed during the manufacturing process, creating a space between the magnets. Therefore, even if the rotor has a relatively long length in the axial direction, stress and tension are not retained, preventing the rotor from bending. Furthermore, breakage of the permanent magnet and the adhesive can be prevented.

Claims

[1] Manufacturing method of an electric motor (10) comprising a stator (18) and a rotor (14) configured to be rotated relative to the stator, the method comprising the steps of: Forming a rotor core (26) by stacking magnetic steel plates (24); Aligning a plurality of permanent magnets (28) in a direction of a rotation axis of the rotor (14) and fixing the permanent magnets (28) to the magnetic steel plate (24) by means of adhesives; Positioning an engaging element (40) which melts at a temperature higher than a curing temperature of the adhesives between the permanent magnets (28) which are adjacent to one another in the direction of the rotation axis; and Heating the rotor (14) after the adhesive has cured so that the engaging element (40) melts and flows out between adjacent permanent magnets (28), wherein a thickness of the engaging element (40) in the direction of the rotation axis is determined such that adjacent permanent magnets (28) bonded to the rotor core (26) within a manufacturing temperature range of the rotor (14) do not contact each other at a lower limit of an operating temperature of the electric motor. [2] A manufacturing method according to claim 1, wherein the method comprises the step of: alternately inserting the permanent magnet (28) and the engaging member (40) into a magnet insertion hole (32) formed in the rotor core (26). [3] A manufacturing method according to claim 1, wherein the method comprises the step of: previously adhering the engaging member (40) to an end face of the permanent magnet (28) opposite in the direction of the rotation axis.

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