JP7658715B2 - Sintered magnet for motor, manufacturing method thereof, and permanent magnet type synchronous motor - Google Patents

Description

This disclosure relates to a method for manufacturing a sintered magnet for a motor, a sintered magnet for a motor, and a permanent magnet type synchronous motor equipped with the sintered magnet for a motor.

Patent Document 1 discloses a method for manufacturing a permanent magnet synchronous motor (hereinafter sometimes simply referred to as a "motor") that rotates a rotor by passing a current through the windings of a stator. Specifically, Patent Document 1 discloses that an unprocessed surface (black skin portion) is left on each end of a number of sintered magnets embedded in the iron core of the rotor, and the sintered magnets are arranged so that the unprocessed surfaces are close to each other. The sintered magnets are arranged in such a way that the performance of the motor is not affected by variations in the magnetic properties of the unprocessed surfaces. The sintered magnets come in a variety of shapes, and are used by being embedded in openings provided in the iron core of the rotor.

Japanese Patent Application Publication No. 10-271723

The motor described in Patent Document 1 makes it possible to reduce the processing costs of sintered magnets, thereby enabling a reduction in price without compromising the performance of a permanent magnet synchronous motor.

There is a demand for the development of a manufacturing method for sintered magnets for motors that can further reduce manufacturing costs, sintered magnets for motors, and permanent magnet synchronous motors.

In one embodiment, the manufacturing method of a sintered magnet for a motor disclosed herein includes the steps of: a) preparing a sintered magnet having a convex first main surface, a second main surface opposite the first main surface, and a side surface; b) forming a reference plane on a portion of the first main surface by partially grinding the top of the first main surface of the sintered magnet; and c) forming a surface that defines the length and/or width of the sintered magnet by grinding at least a portion of the side surface of the sintered magnet, thereby producing a sintered magnet for a motor in which the first main surface includes the reference plane.

In one embodiment, the first major surface includes an unground surface.

In one embodiment, the unground surface has a curved shape on both sides of the reference plane.

In one embodiment, the method further includes a step d of forming another reference plane parallel to the reference plane on the second main surface by grinding at least a portion of the second main surface of the sintered magnet.

In one embodiment, steps b and d are performed simultaneously.

In one embodiment, step c is performed after step a.

In one embodiment, the method further includes a step e of processing the second main surface into a concave curved surface.

In one embodiment, the area of the reference plane on the first main surface is 50% or less of the area of the first main surface.

In one embodiment, the surface of the first main surface that is not ground is maintained in a black skin state formed by the sintering process.

In one aspect, the sintered magnet for motors disclosed herein is a sintered magnet for motors having a convex first main surface, a second main surface opposite the first main surface, and a side surface, the first main surface including a reference plane, and the side surface having a surface that defines the length and/or width of the sintered magnet for motors.

In one embodiment, the first major surface includes an unfinished surface.

In one embodiment, the unmachined surface has a curved shape on both sides of the reference plane.

In one embodiment, the second main surface of the sintered magnet includes another reference plane that is parallel to the reference plane.

In one embodiment, the second main surface has a concave curved surface.

In one embodiment, the area of the reference plane on the first main surface is 50% or less of the area of the first main surface.

In one embodiment, the permanent magnet synchronous motor of the present disclosure comprises a rotor and a stator, the rotor having an iron core and a plurality of permanent magnets fixed to the iron core, each of the plurality of permanent magnets being a sintered magnet for a motor as described above.

According to an embodiment of the present disclosure, a method for manufacturing sintered magnets for motors is provided that can improve the yield of magnet material and reduce the grinding process time without compromising motor performance. This makes it possible to reduce the manufacturing costs of high-performance sintered magnets for motors and permanent magnet synchronous motors.

FIG. 1 is a cross-sectional view that illustrates a schematic configuration example of a permanent magnet type synchronous motor having a conventional embedded magnet structure. 1A to 1C are cross-sectional views illustrating steps in a conventional method for producing a semi-cylindrical magnet. FIG. 2 is a perspective view showing examples of shapes of an embodiment (left side) of a sintered magnet for motors according to the present disclosure and a comparative example (right side). 1A and 1B are cross-sectional views showing examples of the shapes of an embodiment (left side) of a sintered magnet for motors according to the present disclosure and a comparative example (right side). 1A to 1C are cross-sectional process diagrams illustrating an embodiment of a method for producing a sintered magnet for motors according to the present disclosure. FIG. 11 is a perspective view showing a process of partially grinding the top portion of a first main surface of a sintered magnet. FIG. 2 is a perspective view that typically illustrates a step of forming a surface that defines the width of the sintered magnet by grinding the side surface of the sintered magnet. 1 is a cross-sectional view illustrating a schematic configuration example of a rotor core according to an embodiment of the present disclosure. 9 is a cross-sectional view showing a schematic state in which magnets are embedded in the rotor core of FIG. 8 . 1A to 1C are cross-sectional process diagrams illustrating an embodiment of a method for manufacturing a sintered magnet for motors (arch-shaped) according to the present disclosure. 1 is a cross-sectional view illustrating a schematic configuration example of a permanent magnet type synchronous motor according to an embodiment of the present disclosure.

Permanent magnets (hereafter simply referred to as "magnets") are processed into various shapes and used for a variety of purposes. Rare earth magnets have excellent magnetic properties and are widely used. Among them, R-T-B sintered magnets (R is a rare earth element, and T is a transition metal element that always contains Fe), known as neodymium magnets, are widely used due to their excellent magnetic properties and relatively low material costs compared to other rare earth magnets (e.g. samarium cobalt magnets).

R-T-B based sintered magnets are manufactured using the following method.

First, a powder of an R-T-B alloy having the desired composition is prepared. The alloy powder is press-molded to produce a powder compact having the desired shape. The powder compact is sintered to obtain a sintered body. If necessary, the sintered body is subjected to heat treatment such as aging treatment. The sintered body is machined before or after the heat treatment to become a magnet of the desired size and shape. The magnet is then washed to remove grinding powder and grinding fluid (coolant) that have adhered to the magnet surface by the machining process. Various surface treatments may be performed to improve corrosion resistance, etc. After the magnetization process, the sintered body functions as a permanent magnet. For convenience, in this specification, the sintered body in the state before magnetization will also be broadly referred to as a "magnet."

The R-T-B sintered magnets produced in this way are widely used in permanent magnet synchronous motors. In such motors, for example, torque is generated by a rotating magnetic field formed by copper wire (windings) wound around the teeth of the stator. A number of R-T-B sintered magnets are attached to the rotor's iron core, which is made of a soft magnetic material. Permanent magnet synchronous motors are classified into surface magnet type and embedded magnet type. For example, embedded magnet type motors use sintered magnets embedded in each of a number of openings (holes or recesses) formed inside the rotor's iron core. If a gap with low magnetic permeability occurs inside the iron core, the magnetic resistance of the rotor increases and the motor's characteristics deteriorate. For this reason, the shape and size of the sintered magnet are precisely matched to the shape and size of the openings provided inside the rotor's iron core.

The openings for embedding magnets inside the rotor's iron core can have simple shapes surrounded by flat surfaces, or shapes that include curved surfaces, commonly referred to as "semi-cylindrical" or "arc-shaped". This is because precise control of the distribution of magnetic flux passing through the rotor while the motor is rotating is necessary to improve the motor's performance, making the shape and arrangement of the sintered magnets important. For this reason, sintered magnets are processed precisely over a long period of time, and the proportion of the shaved material tends to increase. This leads to a decrease in material utilization rate, or yield. After shaving off the magnet material containing expensive rare earth elements, it can be recycled from the grinding powder (sludge) and other materials, but this inevitably increases manufacturing costs.

Figure 1 is a cross-sectional view showing a schematic example of a permanent magnet synchronous motor with a conventional embedded magnet structure.

In the illustrated example, the motor 1000 is a permanent magnet synchronous motor having a rotor 500 and a stator 600.

The rotor 500 has an iron core 52 having a plurality of openings (holes or recesses) 50 extending along the rotation axis, and a plurality of permanent magnets (sintered magnets) 200 arranged in each of the openings 50. In FIG. 1, one permanent magnet (abbreviated simply as "magnet") 200 is shown in a state before being embedded in the opening 50 of the iron core 52. In reality, a magnet is embedded inside each opening 50. The rotor 500 in this example has four poles, and four magnets 200 are embedded. The magnets 200 are magnetized on the outside or inside in the radial direction of the rotor 500, and the north poles and south poles are arranged alternately along the circumferential direction on the peripheral surface of the rotor 500. The number of poles of the rotor 500 is not limited to four poles, and may be two poles or six poles or more.

The stator 600 has a number of teeth 64, each of which has a winding 62 around it. For example, a three-phase AC current flows through the windings 62 from an inverter circuit (not shown), and a magnetic flux is generated that penetrates the inside of the iron core 52 of the rotor 500 from the tips of the teeth 64. The interaction between the stator magnetic flux generated by the windings 62 and the rotor magnetic flux created by the magnets 200 enables the rotor 500 to rotate with the desired torque and speed.

In the example of FIG. 1, the magnet 200 has a "semi-cylindrical" cross-sectional shape, and extends with the same cross-sectional shape in the direction of the rotation axis of the rotor 500. The shape of the magnet 200 is not limited to a "semi-cylindrical" shape. The shape and size of the magnet 200 match the shape and size of the opening 50 of the iron core 52. To produce such a magnet 200, for example, the processing described below has been performed.

Referring to Figure 2, a conventional method for producing a semi-cylindrical magnet 200 will be described.

First, as shown in step S1 of FIG. 2, a magnet 200 having a cross section larger than the final cross section of the magnet is prepared. Specifically, a powder compact of a magnetic material is sintered by powder metallurgy to obtain a sintered magnet 200. This sintered magnet 200 has a convex first main surface 10, a second main surface 20 opposite to the first main surface 10, and four side surfaces 30. Next, the first main surface 10 of the sintered magnet 200 is processed so that the plane indicated by line A-A in step S2 is exposed as a reference surface. This processing is called "reference surface processing." In this way, a flat reference plane 10S is formed on the first main surface 10 as shown in step S3. In addition, a reference surface that defines the length and width of the sintered magnet 200 is also formed by polishing the side surface 30 of the sintered magnet 200.

"The length and/or width of the sintered magnet" refers to the size of the sintered magnet in a direction parallel to the reference surface. Furthermore, the "plane defining the length and/or width of the sintered magnet" is typically perpendicular to the reference surface of the first main surface.

After this, in step S4, the entire first main surface 10 is shaped to form the curved surface 10R shown by the dashed line. This shaping is required to form the curved surface 10R with high dimensional accuracy. Hereinafter, the processing of the sintered magnet 200 into a curved shape may be referred to as "shape processing." In this way, in step S5, a sintered magnet 200 is obtained that has the shape and size of the opening 50 of the rotor 500 as shown in FIG. 1.

According to the conventional processing method described above, in order to perform the shaping process, it is necessary to prepare the magnet 200 in step S1 in a large size (ensuring a machining allowance for the shaping process). This results in a decrease in yield (material utilization rate) in both steps S2 and S4. Furthermore, there is also the problem that the process time is long because high-precision processing is performed using a processing machine that performs the shaping process.

The inventors have been working hard to find a solution to these problems, and have investigated the relationship between the processed shape of sintered magnets and motor performance. They have discovered that even if the first main surface of a sintered magnet is not processed and a part of the surface is left unprocessed, as long as there is a flat reference surface in the center of the first main surface, it is possible to realize a sintered magnet that can be properly embedded in a rotor with almost no deterioration in motor performance, and have completed the present invention. This makes it unnecessary to reserve a machining allowance for processing, and therefore the yield (material utilization rate) can be significantly improved. Furthermore, the machining allowance during processing of the reference surface is reduced, and processing is no longer necessary, which shortens the process time.

The following describes an embodiment of a sintered magnet for motors according to the present disclosure.

First, let us refer to Figures 3 and 4. The left side of Figure 3 is a perspective view showing an example of the shape of an embodiment of a sintered motor magnet according to the present disclosure, and the right side of Figure 3 is a perspective view showing an example of the shape of a conventional sintered motor magnet. In Figure 3, arrows are drawn indicating the length L and width W of the sintered motor magnet 100. Figure 4 is a cross-sectional view showing an example of the shape of the present embodiment (left side) and a comparative example (right side). In Figure 4, an arrow is drawn indicating the thickness T of the sintered motor magnet 100.

As shown in Figures 3 and 4, the sintered motor magnet 100 in this embodiment has a convex first main surface 10, a second main surface 20 opposite the first main surface 10, and a side surface 30. The first main surface 10 includes a reference plane 10S, and the side surface 30 has surfaces 30W, 30L that define the length and/or width of the sintered motor magnet 100. In this way, no "shape processing" has been performed on the sintered motor magnet 100.

In the illustrated embodiment, the first main surface 10 includes an unground surface 10N. The unground surface 10N has a curved shape on both sides of the reference plane 10S. Such a curved shape is not formed by the above-mentioned shape processing, but is a shape formed by sintering a powder compact whose shape has been adjusted by pressing. The unground surface 10N is typically an "unprocessed surface". Therefore, the surface 10N is maintained in a black skin state formed by the sintering process. In this disclosure, the term "grinding" refers to the physical removal of magnet material from the surface of a sintered magnet using a grinding stone or the like to form a "shape", and broadly includes "polishing". A part or all of the unground surface 10N may be subjected to some kind of "surface treatment". This surface treatment includes chemical or physical treatment for improving weather resistance, deposition of a metal layer such as plating, application of resin, etc. In addition, the removal of unintentional protrusions or attached unnecessary matter on a part of the unground surface 10N is not included in "grinding" and may be performed as necessary. Furthermore, when performing surface treatments such as plating or resin coating, processing to improve adhesion (e.g., shot blasting, barrel polishing, etc.) is not included in "grinding" and can be performed as necessary.

In a preferred embodiment, the area of the reference plane 10S on the first main surface 10 is 50% or less of the area of the first main surface 10, and more preferably 40% or less. The width of the reference plane 10S is, for example, about 1 mm or more and about 5 mm or less. If the width of the reference plane 10S is smaller than this, it will not function adequately as a reference surface, and if it is larger than this, material and grinding time will be wasted.

The sintered magnet for motor 100 shown in Figures 3 and 4 has a reference surface 30L that defines the length L of the sintered magnet 200, and a reference surface 30W that defines the width W of the sintered magnet 200.

Next, a method for manufacturing a sintered magnet for a motor according to an embodiment of the present disclosure will be described with reference to FIG. 5. FIG. 5 is a process cross-sectional view for explaining an embodiment of a method for manufacturing a sintered magnet for a motor according to the present disclosure.

First, in step a, a sintered magnet 100 is prepared having a convex first main surface 10, a second main surface 20 opposite the first main surface 10, and a side surface 30. In this example, the second main surface 20 is a substantially flat surface. According to the present disclosure, compared to the conventional method described above, it is not necessary to prepare a cross section larger than the final cross section of the magnet. In other words, when the final magnet size is the same, the size of the sintered magnet 100 prepared can be made smaller than that of the conventional method (magnet 200). This can improve the yield (material utilization rate). For example, in the case of R-T-B sintered magnets, by eliminating the shape processing, it is possible to achieve an improvement in yield (material utilization rate) of 5% or more, typically 10% or more.

In step b, the top of the first main surface 10 of the sintered magnet 100 is partially ground to form a reference plane 10S on a part of the first main surface 10. In this example, the grinding process is performed until the surface indicated by the dashed line B-B in FIG. 5 is exposed. According to the embodiment of the present disclosure, compared to step S2 in the conventional method, it is not necessary to secure a machining allowance for the shape processing, so the machining allowance for the processing in step b is reduced and the process time can be shortened. In this way, the thickness T of the sintered magnet 100 reaches the design value. Note that when the top of the first main surface 10 is partially ground, the second main surface 20 may be ground at the same time. By grinding the second main surface 20, another reference plane parallel to the reference plane 10S is formed on the second main surface (step d). This allows the thickness T of the sintered magnet 100 and the length and/or width dimensions in the next step c to be specified with higher accuracy.

Next, in step c, at least a portion of the side surface 30 of the sintered magnet 100 is ground to form a surface that defines the length L and/or width W of the sintered magnet 200. In this example, grinding is performed until the surface indicated by the dashed lines C1-C1 and C2-C2 in FIG. 5 is exposed. Although the surface 30W that defines the width W of the sintered magnet 100 is shown in FIG. 5, a surface that defines the length L of the sintered magnet 100 may also be formed. In this manner, the manufacturing method of the sintered magnet for motors in the embodiment of the present disclosure produces a sintered magnet whose first main surface includes a reference plane as the sintered magnet for motors. In other words, the process of processing into a curved shape (shape processing) (step S4) is not performed.

Figure 6 shows a schematic example of the configuration of a processing machine 700 that can be used for the grinding process in step b. This processing machine 700 is equipped with a pair of rotating grinding wheels 70. The grinding wheels 70 face each other in parallel. Each grinding wheel 70 has a flat grinding layer. Such a grinding wheel 70 can be produced by electrolytic deposition of diamond abrasive grains (grain size 100 μm to 200 μm). In order to obtain high processing accuracy, the grinding wheels 70 need to be replaced with new parts as necessary.

With such a processing machine 700, the thickness T of the sintered magnet 100 can be adjusted by grinding both sides of the sintered magnet 100 that are in contact with the sintered magnet 100 with the grinding wheels 70. Meanwhile, FIG. 7 shows a schematic diagram of the grinding process in step c. This grinding process can be performed by a processing machine 800 having a configuration similar to that of the processing machine 700 in FIG. 6. The processing machine 800 can adjust the width W of the sintered magnet 100 by grinding the side surfaces of the sintered magnet 100 with a pair of rotating grinding wheels 80. The width W of the sintered magnet 100 may be adjusted using the same processing machine 700 by changing the spacing between the grinding wheels 70 of the processing machine 700.

These grinding processes are not limited to these devices, and grinding devices of other configurations may be used. Grinding of the length L of the sintered magnet 100 can also be performed using a known processing machine. Grinding to form these flat processed surfaces is easier than "shape processing" to obtain a curved shape. The processing machines exemplified in Figures 6 and 7 can grind both sides of the sintered magnet 100 simultaneously, but grinding may also be performed one side at a time. Grinding fluid is supplied to the grinding portion during grinding.

In this way, a sintered magnet 100 is obtained in which the first main surface 10 includes a reference plane 10S. As shown in the bottom row of FIG. 5, the first main surface 10 includes an unground surface 10N. The unground surface 10N has a curved shape on both sides of the reference plane 10S. This curved surface is typically an unprocessed surface, and is maintained in a black skin state formed by the sintering process. The reference plane 10S in this embodiment differs from a conventional reference plane during manufacturing in that it retains a planar shape even when the magnet is finally embedded in a motor and used.

The magnets manufactured in this way are magnetized and then used to manufacture permanent magnet synchronous motors. The embedding process into the rotor is explained below.

Figure 8 is a cross-sectional view showing a schematic configuration example of the iron core 52 of the rotor 500 in this embodiment. Figure 9 is a cross-sectional view showing a schematic state in which the magnet 100 is embedded in the iron core of Figure 8.

The iron core 52 in FIG. 8 has multiple openings 520. Each opening 520 has a planar portion 10F facing the reference plane 10S on the first main surface 10 of the sintered magnet 100, a planar portion 20F facing the second main surface 20 of the sintered magnet 100, and a planar portion 30F facing the side surface 30W of the sintered magnet 100.

As shown in FIG. 9, a gap G may be formed between the unground surface 10N of the sintered magnet 100 and the iron core 52. This gap G is designed to absorb any "variations" that may occur in the shape or dimensions of the surface 10N for each sintered magnet 100, and to prevent physical interference between the surface 10N and the iron core 52. The unground surface 10N of the sintered magnet 100 is typically an unprocessed surface, so it has a high degree of surface roughness and is prone to "variations" in shape and dimensions depending on the state of sintering.

In the example shown in FIG. 9, the position of the unground surface 10N of the sintered magnet 100 is close to other adjacent sintered magnets 100. The surface 10N may have been oxidized by the sintering process or subsequent heat treatment, and the magnetic properties of the surface region may be deteriorated compared to the magnetic properties inside the sintered magnet 100. For this reason, it was previously considered necessary to remove the black skin portion with deteriorated magnetic properties by grinding. The inventor, without being bound by such technical common sense, has found that a decrease in motor performance can be avoided even if the black skin is left on 50% or more of the area of the first main surface 10 of the sintered magnet 100.

The shape of the sintered magnet 100 in the embodiment of the present disclosure is not limited to a "cylindrical" shape, but may also be a "bow" shape.

An embodiment for obtaining a bow-shaped sintered magnet will be briefly described with reference to Figure 10. Figure 10 is a process cross-sectional view for explaining an embodiment of a manufacturing method for a sintered magnet for a motor according to the present disclosure.

First, in step a, a sintered magnet 100 is prepared, which has a convex first main surface 10, a second main surface 20 opposite the first main surface 10, and a side surface 30. In a cross section of this sintered magnet 100, the first main surface 10 is convex and the second main surface 20 is concave.

In step b, the top portion of the first main surface 10 of the sintered magnet 100 is partially ground to form a reference plane 10S on a portion of the first main surface 10. In this example, the grinding process is performed until the surface indicated by the dashed line B-B in FIG. 5 is exposed. In this way, the thickness T of the sintered magnet 100 reaches the design value. When the top portion of the first main surface 10 is partially ground, the second main surface 20 may be ground simultaneously or separately to form another reference plane parallel to the reference plane 10S on the second main surface (step d).

In step c, at least a portion of the side surface 30 of the sintered magnet 100 is ground to form a surface that defines the length L and/or width W of the sintered magnet 200. Grinding is performed until the surface indicated by the dashed lines C1-C1 and C2-C2 in FIG. 10 is exposed. As a result, a surface (reference plane) 30W that defines the width W of the sintered magnet 100 is formed. Note that a surface (reference plane) that defines the length L of the sintered magnet 100 can also be formed by grinding the other side surfaces 30.

Next, in step e, the second main surface 20 is processed to remove the black skin from the second main surface 20 and form the curved surface 20R (processed into a concave curved surface).

In this way, a sintered magnet for motors is obtained in which the first main surface 10 includes an unground surface 10N, and the entire second main surface 20 is ground. The unground surface 10N has a curved shape on both sides of the reference plane 10S, and the cross section of the sintered magnet 100 is arch-shaped overall. Note that the shape processing (step e) for the second main surface 20 may be omitted.

The present invention is effective when applied to rare earth sintered magnets of various compositions. The effect is particularly notable in the case of hard magnet materials that are difficult to grind. Furthermore, the adverse effects of leaving the sintered surface unprocessed without grinding can be relatively negligible when the original magnetic performance is high. For this reason, the present invention exerts excellent effects when applied to high-performance rare earth magnets containing Dy or Tb.

Figure 11 is a cross-sectional view showing a schematic configuration example of a permanent magnet synchronous motor according to an embodiment of the present disclosure. The permanent magnet synchronous motor 1100 in this example includes a rotor 500 and a stator 600, and the configuration of the stator 600 is basically the same as that of the motor 1000 in Figure 1. However, the motor 1100 in this embodiment is a surface-mount type in which the sintered magnet 200 in the above embodiment is fixed to the surface of the iron core 52 of the rotor 500. The sintered magnet 200 according to the present disclosure can be used in both embedded and surface-mount motors.

The sintered magnet for motors and the manufacturing method thereof, as well as the permanent magnet type synchronous motor disclosed herein, can be widely used in, for example, electric vehicles, hybrid vehicles, etc. They can also be used in generators.

10: first main surface, 10S: reference plane, 20: second main surface, 30: side surface, 50: opening, 52: core, 62: winding, 64: teeth, 100: sintered magnet, 200: sintered magnet, 500: rotor, 600: stator, 1000: permanent magnet type synchronous motor

Claims (9)

A step a of preparing a sintered magnet having a convex first main surface, a second main surface opposite to the first main surface, and a side surface;
a step b of forming a reference plane on a part of the first main surface by partially grinding a top portion of the first main surface of the sintered magnet;
a step c of grinding at least a portion of the side surface of the sintered magnet to form a surface defining a length and/or a width of the sintered magnet;
Including,
the first main surface includes an unground surface, the unground surface having a curved shape on both sides of the reference plane;
A method for manufacturing a sintered magnet for a motor, comprising the steps of: producing a sintered magnet for a motor, the first main surface of which includes the reference plane, the area of the reference plane in the first main surface being 50% or less of the area of the first main surface, and the surface of the first main surface that is not ground being maintained in a black skin state formed by a sintering process. The method for manufacturing a sintered magnet for a motor according to claim 1 further includes a step d of forming another reference plane parallel to the reference plane on the second main surface by grinding at least a portion of the second main surface of the sintered magnet. The method for producing a sintered magnet for a motor according to claim 2, in which steps b and d are carried out simultaneously. The method for producing a sintered magnet for a motor according to any one of claims 1 to 3, in which step c is carried out after step a. The method for manufacturing a sintered magnet for a motor according to any one of claims 1 to 3 further includes a step e of processing the second main surface into a concave curved surface. A sintered magnet for motors having a convex first main surface, a second main surface opposite to the first main surface, and a side surface,
the first main surface includes a reference plane and an unmachined surface, the unmachined surface having a curved shape on both sides of the reference plane;
the side surface has a surface that defines the length and/or width of the sintered motor magnet,
a sintered magnet for a motor , wherein an area of the reference plane on the first main surface is 50% or less of an area of the first main surface, and the unprocessed surface is maintained in a black skin state due to sintering . The sintered magnet for a motor according to claim 6 , wherein the second main surface of the sintered magnet includes another reference plane parallel to the reference plane. 8. The sintered magnet for motors according to claim 6 , wherein the second main surface has a concave curved surface. A permanent magnet type synchronous motor including a rotor and a stator,
The rotor includes an iron core, a plurality of permanent magnets fixed to the iron core,
having
A permanent magnet type synchronous motor, wherein each of the plurality of permanent magnets is the sintered magnet for motor according to any one of claims 6 to 8 .

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