Rotor of a synchronous motor

Abstract

The present invention provides a rotor for a synchronous motor. The rotor of the synchronous motor includes a plurality of magnets fixed to the outer circumferential surface of a rotor core and a reinforcing member having a cylindrical shape. A sandwiching member is arranged between the magnets and the reinforcing member. The magnet has an outer circumferential surface with a central portion bulging outward in the circumferential direction. The sandwiching member is formed to cover the entire outer circumferential surface of the magnet. The outer circumferential surface of the sandwiching member has a circular shape when cut along a plane perpendicular to the axis of rotation, and is in close contact with the inner circumferential surface of the reinforcing member.

Description

Technical Field

[0001] The present invention relates to a rotor of a synchronous motor having a reinforcing member for pressing a magnet. Background Art

[0002] A synchronous motor includes a rotor that rotates about an axis of rotation and a stator disposed around the rotor. Synchronous motor rotors include those in which a rotor core forming a yoke and permanent magnets are alternately arranged circumferentially, and those in which permanent magnets are embedded within the rotor core. Furthermore, surface magnet rotors are known, in which multiple permanent magnets are circumferentially arranged on the outer surface of the rotor core.

[0003] In a surface-magnet rotor, radially outward forces act on the permanent magnets during rotor rotation. For example, these forces are due to the centrifugal force generated by the rotor's rotation and the magnetic attraction of the stator's magnetic field. Therefore, the permanent magnets must be fixed to the rotor core to prevent them from detaching from the rotor core even when subjected to radial forces for extended periods.

[0004] Conventional synchronous motors are known in which permanent magnets fixed to the surface of a rotor core are fixed from the outside by a cylindrical member (see, for example, Japanese Patent Application Laid-Open Nos. 2017-225316, 64-81634, and 2017-195751). Summary of the Invention

[0005] In synchronous motors using permanent magnets, torque pulsation may occur depending on the position of the stator core slots relative to the rotor's outer circumference. This torque pulsation is called cogging torque. Because cogging torque impedes smooth rotor rotation and causes noise and vibration, it is desirable to reduce it.

[0006] To reduce cogging torque, it is known to adjust the shape of the rotor surface facing the stator. For example, in a surface magnet rotor, each magnet can be formed so that its thickness in the center is greater than that at the circumferential ends. In other words, the magnet can be formed so that the diameter of the outer circumference of the central portion is greater than that of the outer circumferential surface of the end portions. The magnet has a shape in which the central portion bulges outward.

[0007] In rotors equipped with magnets that bulge outward at the center, a cylindrical member can also be used to press the magnets. However, because the cross-sectional shape of the outer circumference of the magnet is not circular, the cylindrical member is deformed into a shape that follows the outer circumference of the magnet. Therefore, compared to rotors with circular cross-sectional shapes of the outer circumference of the magnet, there is a problem of a weaker force pressing the magnets. In particular, in synchronous motors where the rotor rotates at high speed, the centrifugal force of the magnets increases, causing the magnets to detach from the rotor core. As a result, the position of the magnets relative to the rotor core may be offset.

[0008] In addition, the inner diameter of the cylindrical component used to fix the magnet is set according to the diameter of the central part and the diameter of the end of the magnet. Because the strength of the cylindrical component needs to be ensured, there is a limit to the range to which the inner diameter of the cylindrical component can be expanded. On the other hand, the dimensions of the shaft, rotor core, and magnet include manufacturing errors. Therefore, if the error obtained by adding the error of the shaft, the error of the rotor core, and the error of the magnet is larger on the positive side, the limit to which the inner diameter of the cylindrical component can be expanded is exceeded, and there is a possibility that the strength of the cylindrical component will be reduced.

[0009] Furthermore, if the sum of the errors in the shaft, rotor core, and magnets is smaller on the negative side (larger in absolute value), sufficient pressure may not be applied to the magnets. Consequently, the magnets may become detached from the rotor core as the rotor rotates. Furthermore, considering the sum of the errors in the shaft, rotor core, and magnets reduces design tolerances, potentially making it difficult to manufacture magnets.

[0010] A technical solution disclosed herein provides a rotor of a synchronous motor, the rotor of the synchronous motor comprising: a rotor core that rotates around a rotation axis; a plurality of permanent magnets that are fixed to the outer peripheral surface of the rotor core; and a reinforcing member that has a cylindrical shape and is formed to press the permanent magnets toward the rotor core. A sandwiching member is arranged between the permanent magnet and the reinforcing member. The permanent magnet has an outer peripheral surface whose central portion bulges outward relative to a circle centered on the rotation axis when cut along a plane perpendicular to the rotation axis. The sandwiching member is formed to cover the entire outer peripheral surface of the permanent magnet. The outer peripheral surface of the sandwiching member is formed to follow a circle centered on the rotation axis when cut along a plane perpendicular to the rotation axis, and is in close contact with the inner peripheral surface of the reinforcing member. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 This is a cross-sectional view of the first rotor according to the embodiment, taken along a plane perpendicular to the rotation axis.

[0012] Figure 2 This is a cross-sectional view of the first rotor taken along a plane parallel to the rotation axis.

[0013] Figure 3It is an enlarged cross-sectional view of a portion of the first rotor where magnets are arranged.

[0014] Figure 4 This is a diagram illustrating cumulative errors associated with the radial dimension of the rotor.

[0015] Figure 5 It is an enlarged cross-sectional view showing a portion where magnets are arranged in the second rotor according to the embodiment.

[0016] Figure 6 It is an enlarged cross-sectional view of the portion between the magnets of the second rotor. DETAILED DESCRIPTION

[0017] Reference Figures 1 to 6 The rotor of the synchronous motor of the embodiment is described. The synchronous motor includes a stator and a rotor arranged inside the stator. The stator is formed by, for example, stacking a plurality of electromagnetic steel sheets in the direction in which the shaft extends. A plurality of coils are arranged along the circumferential direction of the stator. The synchronous motor of this embodiment is arranged inside the spindle head of a machine tool and is used to rotate the spindle of the machine tool. The rotor of the synchronous motor of this embodiment is a surface magnet type rotor in which permanent magnets are arranged on the surface of the rotor core.

[0018] Figure 1 5 is a cross-sectional view of the first rotor according to the present embodiment, taken along a plane perpendicular to the rotation axis. Figure 2 3 is a cross-sectional view of the first rotor according to the present embodiment, taken along a plane parallel to the rotation axis. Figure 2 It is along Figure 1 Cross-sectional view of the A-A line. Figure 1 and Figure 2 The first rotor 1 includes a shaft 11 that rotates around a rotation axis 31. The shaft 11 is formed in a cylindrical shape.

[0019] The rotor 1 includes a rotor core 12 fixed to the shaft 11. The rotor core 12 of the present embodiment has a cylindrical shape. The rotor core 12 rotates around the rotation axis 31. The rotor core 12 has an outer peripheral surface 12a having a circular shape when cut along a plane perpendicular to the rotation axis 31. The rotor core 12 is formed, for example, by stacking a plurality of electromagnetic steel sheets in the direction of the rotation axis 31. In addition, the rotor core 12 can be formed by a single component. For example, the rotor core 12 can be formed by cutting a magnetic component such as iron. The rotor core 12 is fixed to the shaft 11. In addition, the rotor core may also include a shaft. That is, the shaft 11 and the rotor core 12 of the present embodiment can be formed integrally by one component.

[0020] The rotor 1 has a plurality of magnets 13 fixed to the outer peripheral surface 12a of the rotor core 12. The magnets 13 of this embodiment are permanent magnets formed in a plate shape. The plurality of magnets 13 are arranged at equal intervals along the circumferential direction. The number of magnets 13 depends on the number of poles of the rotor 1. Any number of magnets can be fixed to the rotor core according to the number of poles of the rotor. Figure 1 In the example shown, a four-pole rotor is shown which is equipped with four magnets 13 . Figure 1 and Figure 2 The illustrated magnet 13 extends from one end portion to the other end portion of the rotor core 12 in the axial direction. The shape of the magnet 13 is not limited to this, and multiple magnets may be arranged in the direction extending along the rotation axis 31. For example, a pair of two magnets may be arranged along the direction of the rotation axis 31, and multiple pairs may be arranged in the circumferential direction.

[0021] The rotor 1 of this embodiment includes a reinforcing member 15, which is formed to press the magnet 13 toward the rotor core 12. The reinforcing member 15 of this embodiment presses the magnet 13 toward the rotation axis 31. The reinforcing member 15 has a cylindrical shape. A sandwiching member 14 is arranged between the magnet 13 and the reinforcing member 15. At least a portion of the sandwiching member 14 of this embodiment is arranged between the magnet 13 and the reinforcing member 15. The sandwiching member 14 is formed to cover all of the plurality of magnets 13. The reinforcing member 15 is formed to cover the sandwiching member 14. The reinforcing member 15 is formed to press the sandwiching member 14 toward the rotation axis 31. That is, a force compressed by the reinforcing member 15 is applied to the sandwiching member 14. The magnet 13 is pressed toward the rotation axis 31 by the sandwiching member 14.

[0022] The reinforcing member 15 of this embodiment is formed of fiber reinforced plastic (FRP). Examples of fiber reinforced plastic include carbon fiber reinforced plastic (CFRP) in which carbon fibers are added to plastic as a reinforcement material, and glass fiber reinforced plastic (GFRP) in which glass fibers are added to plastic as a reinforcement material.

[0023] Figure 3 1 is an enlarged cross-sectional view of a portion of a magnet of the first rotor according to this embodiment. Figure 3 This is a cross-sectional view taken along a plane perpendicular to the rotation axis 31. Figures 1 to 3 Magnet 13 has a circumferential center portion 13a and circumferential end portions 13b on either side. Magnet 13 has an inner circumferential surface 13c, which is radially inward of rotor 1, and an outer circumferential surface 13d, which is radially outward. Inner circumferential surface 13c is fixed to outer circumferential surface 12a of rotor core 12. Magnet 13 has circumferential end portions 13e on either side. Here, center portion 13a represents the midpoint of the circumferential length between end portions 13e.

[0024] The inner circumferential surface 13c of the magnet 13, when cut along a plane perpendicular to the rotation axis 31, has a shape that extends along a circle centered on the rotation axis 31. The diameter from the rotation axis 31 to the inner circumferential surface 13c at the center portion 13a is the same as the diameter from the rotation axis 31 to the inner circumferential surface 13c at the end portion 13b. The inner circumferential surface 13c of the magnet 13 is in close contact with the outer circumferential surface 12a of the rotor core 12.

[0025] In contrast, outer circumferential surface 13d of magnet 13 has a shape in which central portion 13a bulges outward relative to a circle centered on rotation axis 31. The diameter of central portion 13a, as indicated by arrow 81, from rotation axis 31 to outer circumferential surface 13d is greater than the diameter of end portion 13b, as indicated by arrow 82, from rotation axis 31 to outer circumferential surface 13d. In other words, central portion 13a of magnet 13 corresponds to the major diameter portion. End portion 13b of magnet 13 corresponds to the minor diameter portion. The thickness of magnet 13 at central portion 13a is greater than the thickness at end portion 13b.

[0026] The shape of the outer peripheral surface 13d, in which the central portion 13a bulges outward, can be set using any method. In this embodiment, the shape of the outer peripheral surface 13d when cut along a plane perpendicular to the rotation axis 31 is an arc. The shape of the outer peripheral surface 13d is determined by offsetting the position of the center of the arc of the outer peripheral surface 13d from the rotation axis 31. In the cross-sectional shape, the center of the arc of the inner peripheral surface 13c becomes the rotation axis 31. In contrast, the center of the arc of the outer peripheral surface 13d is the point 32 offset outward from the rotation axis 31. Thus, in this embodiment, the curvature of the inner peripheral surface 13c is different from the curvature of the outer peripheral surface 13d. In this embodiment, the radius of curvature of the outer peripheral surface 13d is smaller than the radius of curvature of the inner peripheral surface 13c. In addition to the above, for example, a function such as a hyperbolic cosine function can also be used to set the cross-sectional shape of the outer peripheral surface 13d.

[0027] The sandwiching member 14 of this embodiment is formed to cover at least the outer peripheral surface 13d of the magnet 13. The sandwiching member 14 is formed to cover the entire outer peripheral surface 13d of the magnet 13. In other words, the sandwiching member 14 is formed to cover the central portion 13a and the end portions 13b, and the diameter from the rotation axis 31 to the outer peripheral surface 13d at the central portion 13a is different from the diameter from the rotation axis 31 to the outer peripheral surface 13d at the end portions 13b.

[0028] In the first rotor 1, the sandwiching member 14 is disposed between the outer circumferential surface 13d of the magnet 13 and the inner circumferential surface 15a of the reinforcement member 15, as well as between circumferentially adjacent magnets 13. Furthermore, the sandwiching member 14 is formed to fill the entire area surrounded by the outer circumferential surface 12a of the rotor core 12, the inner circumferential surface 15a of the reinforcement member 15, the outer circumferential surface 13d of the magnet 13, and the end surface 13e. Therefore, the thickness of the sandwiching member 14 at the end 13b of the magnet 13 is greater than the thickness at the center 13a. The outer circumferential surface 14a of the sandwiching member 14, when cut along a plane perpendicular to the rotation axis 31, is formed along a circle centered on the rotation axis 31. Specifically, the outer circumferential surface 14a of the sandwiching member 14 is formed concentrically with the outer circumferential surface 12a of the rotor core 12. Furthermore, the sandwiching member 14 extends from one end surface of the rotor core to the other end surface along the direction of the rotation axis 31.

[0029] The sandwiching member 14 can be formed of a non-magnetic material. In this embodiment, the sandwiching member 14 is formed of resin. For example, the sandwiching member 14 can be formed of epoxy resin. In addition to resin, the sandwiching member 14 can also be formed of ceramics or non-magnetic metal.

[0030] In this embodiment, the outer peripheral surface 14a of the sandwiching member 14 is formed to have a circular cross-sectional shape when cut along a plane perpendicular to the rotation axis 31. Although the thickness of the magnet 13 is not constant along the circumferential direction, it can be pressed with the same force as if the outer peripheral surface 13d of the magnet 13 had a circular cross-sectional shape. In other words, even if the thickness of the magnet 13 is not constant along the circumferential direction, the pressing force does not decrease.

[0031] For example, in the absence of the sandwiching member 14, the magnet 13 contacts the reinforcing member 15. The reinforcing member 15 is deformed into a shape along the outer peripheral surface 13d of the magnet 13, and the pressing force on the magnet 13 is reduced compared to the case where the cross-sectional shape of the outer peripheral surface 13d of the magnet 13 is circular. Therefore, when the rotor 1 rotates and centrifugal force acts, the magnet 13 is easily detached from the rotor core 12 at the end 13b. As a result, there is a case where the magnet 13 leaves the rotor core 12 and the position of the magnet 13 relative to the rotor core 12 is offset. However, in this embodiment, the magnet 13 can be pressed with the same pressing force as when the cross-sectional shape of the outer peripheral surface 13d of the magnet 13 is circular, and the magnet 13 can be effectively suppressed from detaching from the rotor core 12.

[0032] In particular, in a synchronous motor in which the rotor 1 rotates at high speed, the centrifugal force is large. The centrifugal force increases in proportion to the square of the rotation speed. Therefore, when the rotor 1 rotates at high speed, the magnet 13 easily separates from the rotor core 12. However, in the rotor 1 of the present embodiment, since the magnet 13 can be fully pressed against the rotor core 12, the separation of the magnet 13 can be suppressed. The rotation speed of the high-speed rotation of the synchronous motor can be exemplified as 10,000 rpm or more. The synchronous motor of the present embodiment is a motor for rotating the main shaft of a machine tool, and rotates at high speed. The rotor 1 of the present embodiment is suitable for a synchronous motor in which such a shaft 11 rotates at high speed.

[0033] Figure 4 The figure showing the manufacturing error is shown in FIG. Each component is manufactured so that the dimensions are within the tolerance range set at the time of design. The manufacturing error may cause the overall dimension to be larger or smaller. Figure 4 , exemplifies a case where the overall size increases. In the rotor 1 of this embodiment, dimensional errors occur when the shaft 11 is manufactured. For example, an error occurs in the diameter of the outer circumferential surface 11a of the shaft 11. Furthermore, an error occurs in the diameter of the outer circumferential surface 12a of the rotor core 12 when the rotor core 12 is manufactured. Furthermore, an error occurs in the thickness when the magnet 13 is manufactured. The error in the diameter of the outer circumferential surface 13d of the magnet 13 (the diameter from the axis of rotation 31 to the outer circumferential surface 13d) is the sum of the error in the diameter of the outer circumferential surface 11a of the shaft 11, the error in the diameter of the outer circumferential surface 12a of the rotor core 12, and the error in the thickness of the magnet 13. When the error of the shaft 11 is larger on the positive side, the error of the rotor core 12 is larger on the positive side, and the error in the thickness of the magnet 13 is larger on the positive side, the error in the diameter of the outer circumferential surface 13d of the magnet 13 becomes very large. In other words, the cumulative error increases.

[0034] In this embodiment, as described later, after the sandwiching member 14 is formed on the outer peripheral surface 13d of the magnet 13, the reinforcing member 15 having an inner diameter set according to the diameter of the outer peripheral surface 14a of the sandwiching member 14 is attached to the outer peripheral surface 14a of the sandwiching member 14.

[0035] In a rotor that does not include the sandwiching member 14, the inner diameter of the reinforcing member is set so as to be able to supply the required pressing force, based on the diameter of the outer peripheral surface 13d at the end 13b of the magnet 13 and the diameter of the outer peripheral surface 13d at the center 13a. For example, the inner diameter of the reinforcing member can be set as follows: the required pressing force can be supplied to the outer peripheral surface having a diameter between the diameter of the outer peripheral surface 13d at the end 13b and the diameter of the outer peripheral surface 13d at the center 13a. However, when the diameter of the reinforcing member 15 is expanded, there is a limit to the amount of expansion. For example, a reinforcing member formed of fiber-reinforced plastic has a range within which the inner diameter can be increased. If the cumulative error is large, the range within which the inner diameter can be increased is exceeded, and there is a possibility that the strength of the reinforcing member 15 will be reduced.

[0036] Furthermore, if the error in shaft 11 is significantly negative, the error in rotor core 12 is significantly negative, and the error in magnet 13 thickness is significantly negative, the radial dimension of outer circumferential surface 13d of magnet 13 becomes significantly smaller (the absolute value of the error increases). Therefore, in a rotor without interposing member 14, the force exerted by reinforcing member 15 on magnet 13 may be weakened. As a result, magnet 13 may become detached from rotor core 12 as the rotor rotates.

[0037] In contrast, the first rotor 1 of this embodiment includes a sandwiching member 14. The sandwiching member 14 is formed to cover the outer peripheral surface 13d of the magnet 13, and the outer peripheral surface 14a of the sandwiching member 14 is formed to have a circular cross-sectional shape. Therefore, the reinforcing member 15 can press the sandwiching member 14 and the magnet 13 toward the rotation axis 31 with the same force as when the outer peripheral surface 13d of the magnet 13 has a circular cross-sectional shape.

[0038] The sandwiching member 14 in the first rotor 1 is formed so as to cover the magnet 13 at its center portion 13a and end portions 13b. The sandwiching member 14 is preferably formed thick enough to offset the maximum dimensional variations due to design tolerances of the shaft 11, the rotor core 12, and the magnet 13. This configuration allows the thickness of the sandwiching member 14 to partially absorb manufacturing variations in the shaft 11, the rotor core 12, and the magnet 13.

[0039] Furthermore, as will be described later, the sandwiching member 14 can be formed so that the cross-sectional shape of the outer peripheral surface 14a of the sandwiching member 14 is along a circle centered on the rotation axis 31. As a result, it is possible to suppress the force applied to the magnet 13 from being reduced compared to the case where the cross-sectional shape of the outer peripheral surface 13d of the magnet 13 is circular. In addition, by adjusting the thickness of the sandwiching member 14 based on the inner diameter of the reinforcing member 15, the pressing force applied to the magnet 13 can be adjusted to an appropriate range.

[0040] In this embodiment, reinforcement member 15 is made of fiber-reinforced plastic. This structure allows magnet 13 to be secured by a lightweight, high-strength reinforcement member. Because fiber-reinforced plastic is lightweight, the centrifugal force during rotor 1 rotation is reduced. Therefore, reinforcement members made of fiber-reinforced plastic are suitable for rotors 1 that rotate at high speeds.

[0041] The material of the reinforcing member is not limited to a material containing resin, and can be formed of a non-magnetic material. For example, the reinforcing member can be formed of a non-magnetic metal. For example, the reinforcing member can also be formed of non-magnetic stainless steel or copper. The inner diameter of the reinforcing member formed of metal increases when heated. That is, the diameter of the reinforcing member can be easily expanded. Next, the rotor core to which the magnet and the sandwiching member are fixed is arranged inside the reinforcing member. Thereafter, by cooling the reinforcing member, the rotor core can be fixed inside the reinforcing member. In this way, the rotor core can be fixed inside the reinforcing member by shrink fitting. The reinforcing member formed of metal can easily fix the rotor core inside the reinforcing member.

[0042] Next, a method for manufacturing the rotor of this embodiment will be described. Figure 1 and Figure 3 First, multiple magnets 13 are fixed to the outer circumferential surface 12a of the rotor core 12. Next, a cylindrical frame member having a shape corresponding to that of the reinforcement member 15 is prepared. The inner circumferential surface of the frame member is formed from a material that has mold release properties from the resin. The frame member can be formed from metal, for example.

[0043] Next, the rotor core 12 to which the magnets 13 are fixed is inserted into the interior of such a frame member. The inner diameter of the frame member is preferably larger than the inner diameter of the reinforcing member 15. Next, the area surrounded by the frame member, the magnets 13, and the rotor core 12 is filled with a material to become the sandwich member 14. In this embodiment, the resin before curing is poured in. In the manufacturing method of the first rotor 1, in addition to the area between the magnets 13 and the frame member, the area between the magnets 13 is also filled with resin without a gap. Next, the material to become the sandwich member 14 is cured. In the form of this embodiment, the sandwich member 14 is formed by curing the resin. The rotor core 12 to which the magnets 13 and the sandwich member 14 are fixed can be formed.

[0044] Next, the outer peripheral surface 14a of the sandwiching member 14 is cut so that its cross-sectional shape becomes a circle centered on the rotation axis 31. At this time, the cutting is performed so that the diameter of the outer peripheral surface 14a of the sandwiching member 14 is within the designed tolerance range. The cutting is performed so that the diameter of the outer peripheral surface 14a of the sandwiching member 14 corresponds to the diameter of the inner peripheral surface 15a of the reinforcing member 15. For example, the cutting can be performed so that the diameter of the outer peripheral surface 14a of the sandwiching member 14 is slightly larger than the diameter of the inner peripheral surface 15a of the reinforcing member 15. A machine tool or the like can be used for the cutting process of the sandwiching member 14.

[0045] Next, the reinforcing member 15 is attached to the outside of the outer peripheral surface 14a of the sandwiching member 14. At this time, since the diameter of the outer peripheral surface 14a of the sandwiching member 14 is larger than the diameter of the inner peripheral surface 15a of the reinforcing member 15, the entire outer peripheral surface 14a of the sandwiching member 14 can be pressed. The magnet 13 is pressed with sufficient force through the sandwiching member 14.

[0046] Thus, the rotor manufacturing method of this embodiment includes a forming step of forming a sandwiching member to cover at least the entire outer circumference of the permanent magnet, and a cutting step of cutting the outer circumference of the sandwiching member. In the forming step, the sandwiching member is formed so that its outer diameter is larger than the inner diameter of the reinforcement member. In the cutting step, the sandwiching member is cut so that, when cut along a plane perpendicular to the rotation axis, its outer circumference forms a circle centered on the rotation axis. This manufacturing method allows the outer diameter of the sandwiching member to correspond to the inner diameter of the reinforcement member. The thickness of the sandwiching member can offset the cumulative error resulting from the sum of the errors in the shaft 11, the rotor core 12, and the thickness of the magnet 13. As a result, it is possible to prevent the reinforcement member 15 from exceeding its maximum diameter expansion due to large manufacturing errors, thereby reducing its strength. Furthermore, it is possible to prevent the pressing force on the magnet 13 from weakening. Furthermore, the radial length constrained by the reinforcement member 15 can be set within an appropriate range.

[0047] In particular, magnets are difficult to form with high dimensional accuracy. In the rotor of this embodiment, since the shape of the outer peripheral surface of the sandwiching member can be adjusted, the design tolerance of magnet 13 can be set larger. As a result, magnet 13 can be manufactured more easily. Furthermore, the manufacturing cost of rotor 1 can be reduced.

[0048] Furthermore, the outer peripheral surface 14a of the insert member 14 of this embodiment can be easily machined with high precision using a machine tool or the like. Therefore, it is sufficient to prevent the enlarged size (radial length of the enlarged diameter) of the reinforcing member 15 from being excessive. In other words, it is sufficient to prevent the diameter from being excessively enlarged. This can prevent the reinforcing member 15 from exceeding its maximum expansion limit and damaging it.

[0049] In the first rotor 1 of this embodiment, the sandwiching member 14 is disposed throughout the region surrounded by the rotor core 12, magnets 13, and reinforcement member 15. The sandwiching member is not limited to this configuration and may be formed to cover at least the entire outer circumference of the permanent magnet.

[0050] Figure 5 is an enlarged cross-sectional view of a portion of the magnets of the second rotor of this embodiment. In the second rotor 2, a sandwiching member 16 is formed for each magnet 13. The sandwiching member 16 is formed to fill the area between the outer circumferential surface 13d of the magnet 13 and the inner circumferential surface 15a of the reinforcement member 15. Furthermore, a cavity 21 is formed between circumferentially adjacent magnets 13.

[0051] The second rotor 2 can be manufactured using the same manufacturing method as the first rotor 1. In this manufacturing method, the magnets 13 are also fixed to the rotor core 12. The rotor core 12, with the magnets 13 fixed thereto, is placed inside a pre-formed frame member. The frame member used to form the second rotor 2 has a wall portion formed along the end surface 13e of the magnets 13. The area surrounded by this wall portion, the outer circumferential surface 13d of the magnets 13, and the inner circumferential surface 15a of the reinforcement member 15 is filled with a material that will serve as a sandwich member. For example, resin is used. The sandwich member material is then cured to form a sandwich member for each magnet. For example, curing the resin forms a sandwich member 16 for each magnet 13. Next, using a machine tool or the like, the sandwich member 16 is cut so that its outer circumferential surface 16a extends along a circle centered on the rotation axis 31. The rotor core 12, with the magnets 13 and sandwich member 16 fixed thereto, is then secured inside the reinforcement member 15.

[0052] Figure 6 : FIG2 is an enlarged cross-sectional view illustrating the function of the second rotor of this embodiment. Figure 6 The curvature radius of the rotor is less than Figure 5 The curvature radius of the rotor is described in terms of the curvature radius of the rotor. In the second rotor 2, a cavity 21 is formed between the magnets 13. In the region where the sandwiching member 16 is disposed, the reinforcing member 15 has a curved portion 15b formed along the outer peripheral surface 16a of the sandwiching member 16, with a circular arc cross-sectional shape. Meanwhile, in the region where the cavity 21 is formed, a flat portion 15c extending in a planar shape is formed.

[0053] Because stress is generated at the boundary between the curved portion 15b and the flat portion 15c, the second rotor 2 has a characteristic of being weaker than the first rotor 1. However, in the second rotor 2, as in the first rotor 1, magnets 13 can be pressed with a sufficient force compared to a case without the intervening member 16. The other functions and effects of the second rotor 2 are the same as those of the first rotor 1, and therefore will not be described again.

[0054] The motor of this embodiment is a motor for rotating a main shaft of a machine tool, but the present invention is not limited to this form, and the rotor of this embodiment can be applied to any motor, and is particularly suitable for a motor with a relatively high rotation speed as described above.

[0055] According to one aspect of the present disclosure, it is possible to provide a rotor for a synchronous motor that is easy to manufacture and can suppress separation of magnets.

[0056] In each of the above-mentioned manufacturing steps, the order of the steps can be appropriately changed within the range in which the functions and effects are not changed.

[0057] The above embodiments can be combined as appropriate. In the above figures, the same or equivalent parts are marked with the same reference numerals. In addition, the above embodiments are examples and do not limit the invention. In addition, the embodiments include changes to the embodiments shown in the claims.

Claims

1. A rotor of a synchronous motor, characterized in that: The rotor of the synchronous motor comprises: a rotor core that rotates about an axis of rotation; a plurality of permanent magnets fixed to the outer peripheral surface of the rotor core; and a reinforcing member having a cylindrical shape and formed to press the permanent magnet toward the rotor core, A sandwiching member is arranged between the permanent magnet and the reinforcing member, The permanent magnet has an outer peripheral surface whose central portion bulges outward relative to a circle centered on the rotation axis when cut along a plane perpendicular to the rotation axis. The sandwiching member is formed to cover the entire outer peripheral surface of the permanent magnet, The outer peripheral surface of the sandwiching member is formed along a circle centered on the rotation axis when cut along a plane perpendicular to the rotation axis, and is in close contact with the inner peripheral surface of the reinforcing member. The sandwiching member is arranged in the area between the entire outer peripheral surface of the permanent magnet and the reinforcing member, and a cavity is formed in the entire area between the circumferentially adjacent permanent magnets. The reinforcing member is formed to press the sandwiching member toward the rotation axis, and has a flat portion extending in a planar shape in a region where the hollow portion is formed.

2. The rotor of the synchronous motor according to claim 1, wherein: The sandwiching member is formed of resin.

3. The rotor of a synchronous motor according to claim 1 or 2, wherein: The reinforcing member is formed of fiber-reinforced plastic.

4. The rotor of a synchronous motor according to claim 1 or 2, wherein: The reinforcing member is formed of a non-magnetic metal.

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