Permanent-magnet-embedded motor

This application is a U.S. national stage application of International Patent Application No. PCT/JP2014/065484 filed on Jun. 11, 2014, the disclosure of which is incorporated herein by reference.

The present invention relates to a permanent-magnet-embedded motor.

A general permanent-magnet-embedded motor includes a stator iron core, and a rotor which is arranged on an inside diameter side of the stator iron core and in which a permanent magnet is embedded in an inner part of a rotor iron core. The rotor iron core is formed by stamping of an electromagnetic steel sheet into a predetermined shape and by swaging and laminating of a plurality of stamped electromagnetic steel sheets. In the rotor iron core, magnet insertion holes are formed at substantially equal intervals in a circumferential direction according to the number of magnetic poles in the permanent magnet. Each magnet insertion hole is stretched in an axial direction and a permanent magnet is inserted into an inner part of each magnet insertion hole.

Here, an outer side surface in a radial direction of the permanent magnet inserted into each magnet insertion hole and an inner side surface in the radial direction thereof are connected to each other via a thin part formed between the magnetic poles of the permanent magnet. Then, magnetic flux generated in each permanent magnet passes through a core back of the stator iron core and goes back to the rotor iron core. However, a part of the magnetic flux from a surface of each permanent magnet becomes leakage flux that passes through the thin part, stays in the inner part of the rotor iron core, and goes back to the permanent magnet instead of going to the core back. That is, a part of the magnetic flux that goes out from one surface of each permanent magnet passes through the thin part and enters a different surface of the permanent magnet without passing through the stator iron core. Such leakage flux does not contribute to torque and becomes a factor of increasing an iron loss in the rotor. Thus, the leakage flux is preferably controlled as much as possible. In such a manner, since a thin part formed between the magnetic poles becomes a path of leakage flux, a width thereof is preferably as narrow as possible.

However, since centrifugal force during a high-speed rotation of the rotor of the permanent-magnet-embedded motor acts on the permanent magnet, centrifugal force that acts on each part of the rotor iron core becomes large in proportional to the square of the number of rotations in a case where an upper limit of the number of rotations of the rotor becomes higher. Thus, in the thin part of the rotor iron core, it is necessary to increase strength of a part that supports a surface on an outer side in a radial direction of the permanent magnet. For example, it is necessary to widen a width of the thin part in proportional to the square of the number of rotations.

As a method of improving the strength of the rotor iron core other than widening of the width of the thin part between the magnetic poles, it is considered to divide each of the permanent magnet, which configures each magnetic pole, and the magnet insertion hole into two or more in a circumferential direction and to provide a bridge, which connects an outer side in a radial direction of the rotor iron core and an inner side in the radial direction thereof, between the divided magnet insertion holes.

However, similarly to the above-described thin part between the magnetic poles, this bridge becomes a path of leakage flux and a width in a circumferential direction of the magnet is decreased for a width of the bridge. Thus, when the bridge is provided and the width in the circumferential direction of the magnet is decreased, there is a problem that an effective magnetic flux that contributes to torque is decreased and a size of the permanent-magnet-embedded motor is increased in order to cover the decrease.

As a method that does not depend on providing of a bridge, it is considered to use a steel sheet with mechanical strength higher than that of an electromagnetic steel sheet including silicon steel or Armco iron (hereinafter, referred to as “high-strength steel sheet”) in a rotor iron core. However, a high-strength steel sheet generally has an inferior magnetic characteristic, specifically an inferior iron loss characteristic, compared to an electromagnetic steel sheet. Thus, an iron loss in the rotor is increased greatly in a case where an electromagnetic steel sheet in the whole rotor iron core is replaced with the high-strength steel sheet. Thus, an iron core including an electromagnetic steel sheet is used in a part where the most of an iron loss in the whole rotor is generated, that is, a part on an outer side in a radial direction of a permanent magnet and an iron core including a high-strength steel sheet is used in the remaining part.

For example, in a motor described in Patent Literature 1, a rotary shaft includes an iron core part on an outer side in a radial direction of a plurality of permanent magnets (hereinafter, referred to as “A part”) and an iron core part other than the A part (hereinafter, referred to as “B part”). The B part includes an iron core part on an inner side in a radial direction of each permanent magnet and an iron core part between magnetic poles. The A part includes silicon steel or Armco iron with a superior magnetic characteristic and the B part includes carbon steel with a mechanical strength higher than that of the A part. Then, the iron core part between the magnetic poles is formed in a T-shape. Hereinafter, the T-shaped iron core part will be referred to as an “engagement part.” The engagement part is extended from an outer peripheral part of the B part toward an outer side in a radial direction between the magnetic poles and has a leading end branching in a T-shape. Moreover, at a leafing end of the part branching in the T-shape, a recessed part to be engaged with a protruded part in an end part in a circumferential direction of the A part is formed. With this configuration, coming off of the iron core part of the A part from the rotary shaft due to the centrifugal force in a rotation of the rotary shaft is prevented.

Patent Literature 1: Japanese Patent Application Laid-Open No. 2008-154329

However, according to a conventional technology in Patent Literature 1, a method of reducing leakage flux is not disclosed in this literature although it is possible to improve centrifugal force resistant strength. That is, since a T-shaped engagement part becomes a path of leakage flux, there is a problem that it is not possible to control an increase in an iron loss and leakage flux although it is possible to improve centrifugal force resistant strength.

The present invention has been achieved in view of the above and it is an object of the present invention to obtain a permanent-magnet-embedded motor that can control an increase in an iron loss and leakage flux while securing mechanical strength for resisting centrifugal force.

In order to solve the above-mentioned problems and achieve the object, according to an aspect of the present invention, there is provided a permanent-magnet-embedded motor in which a plurality of magnets is embedded in a rotor iron core, wherein the rotor iron core includes: a plurality of first iron cores arranged on an outer side in a radial direction of each magnet; and a second iron core having mechanical strength higher than mechanical strength of each of the first iron cores and that includes an inner iron core arranged on an inner side in the radial direction of each of the magnets and a plurality of inter-magnetic pole iron cores formed integrally with the inner iron core and arranged between magnetic poles of each of the magnets, each of the inter-magnetic pole iron cores contacts an end part in a circumferential direction of each of the first iron cores and is formed from the end part in the circumferential direction of each of the first iron cores to the inner iron core, and a flux barrier is formed between each of the magnets and each of the inter-magnetic pole iron cores.

According to this invention, it is possible to control an increase in an iron loss and leakage flux while securing mechanical strength for resisting centrifugal force.

FIG. 1 is a longitudinal sectional view illustrating a schematic configuration of a permanent-magnet-embedded motor according to a first embodiment of the present invention.

FIG. 2 is an A-A sectional view of a rotor iron core illustrated in FIG. 1 .

FIG. 3 is a sectional view of a rotor in which a permanent magnet is embedded in a magnet insertion hole in FIG. 2 .

FIG. 4 is a view in which an inter-magnetic pole iron core and a periphery thereof illustrated in FIG. 3 are enlarged.

FIG. 5 is a sectional view of a rotor iron core of a permanent-magnet-embedded motor according to a second embodiment of the present invention.

FIG. 6 is a sectional of a rotor iron core of a permanent-magnet-embedded motor according to a third embodiment of the present invention.

Embodiments of a permanent-magnet-embedded motor according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

First Embodiment

FIG. 1 is a longitudinal sectional view illustrating a schematic configuration of a permanent-magnet-embedded motor 100 according to a first embodiment of the present invention. FIG. 2 is an A-A sectional view of a rotor iron core 5 illustrated in FIG. 1 . FIG. 3 is a sectional view of a rotor 1 in which a permanent magnet 7 is embedded in a magnet insertion hole 9 in FIG. 2 . FIG. 4 is a view in which an inter-magnetic pole iron core 5 B 2 and a periphery thereof illustrated in FIG. 3 are enlarged.

The permanent-magnet-embedded motor 100 includes the rotor 1 , a stator 2 , a frame 3 , and a bracket 4 .

The frame 3 is formed in a cylindrical shape with a bottom and one end in an axial direction of the frame 3 is formed in a flange shape toward an outer side in a radial direction. A flange part 3 a formed in the flange shape is arranged in such a manner as to be in contact with a flange part 4 a formed in the bracket 4 .

At a center part in the other end in the axial direction (bottom part) of the frame 3 , a protruded recessed part 3 c is formed toward an anti-load side of the rotor 1 (lower side in FIG. 1 ). In the recessed part 3 c , a bearing 10 to support a shaft 6 on the anti-load side of the rotor 1 is arranged.

Note that a wave washer 12 is arranged between a bottom surface of the recessed part 3 c (seating surface part 3 b ) and the bearing 10 . Since the wave washer 12 biases an outer ring of the bearing 10 in the axial direction, it is possible to apply precompression to the bearing 10 and to control a vibration of the shaft 6 .

The bracket 4 is formed in a cylindrical shape and one end in the axial direction of the bracket 4 is formed in a flange shape toward an outer side in a radial direction. The flange part 4 a formed in the flange shape is arranged in such a manner as to be in contact with the flange part 3 a formed in the frame 3 .

At the center part in the other end in the axial direction of the bracket 4 , a protruded recessed part 4 c is formed toward a load side of the rotor 1 (upper side in FIG. 1 ). In the recessed part 4 c , a bearing 11 to support a shaft 6 on the load side of the rotor 1 is arranged. At the center of a bottom surface of the recessed part 4 c (seating surface part 4 b ), a hole 4 d for insertion of the shaft 6 on the load side of the rotor 1 is formed.

A fastening member is inserted into the flange part 3 a and the flange part 4 a and the fastening member is fastened after the bracket 4 is provided in such a manner to cover an opening part of the frame 3 , whereby the bracket 4 is fixed to the frame 3 .

The stator 2 includes a ring-shaped stator iron core 13 and a winding wire 14 to which electric power from the outside is suppled. The stator 2 is fixed to an inner side of the frame 3 , for example, by a method of shrinkage fitting or the like.

The stator iron core 13 is formed by laminating of a plurality of electromagnetic steel sheets, each of which is stamped into a predetermined shape, in the axial direction. On an inner peripheral side of the stator iron core 13 , a plurality of teeth (not illustrated) is provided at equal intervals in a circumferential direction.

Around each tooth, the winding wire 14 is wound via an insulator (not illustrated). Then, the rotor 1 is arranged with a predetermined gap 15 on an inside diameter side of the stator 2 .

The rotor 1 includes a ring-shaped rotor iron core 5 , the shaft 6 , a plurality of permanent magnets 7 (magnet), and an end sheet 8 .

The rotor 1 is arranged with the gap 15 on the inside diameter side of the stator 2 . At the center of the rotor 1 , the shaft 6 is provided.

In the rotor iron core 5 included in the rotor 1 , a plurality of magnet insertion holes 9 (see FIG. 2 ) corresponding to the number of magnetic poles is arranged.

Each magnet insertion hole 9 is a space surrounded by an inner side surface in a radial direction 5 A 3 of a first iron core 5 A, an outer side surface in a radial direction 5 B 1 a of a second iron core 5 B, and a flux barrier 16 (all of which will be described later) and formed as a hole for insertion of a magnet. Each magnet insertion hole 9 is extended in the axial direction in such a manner as to pierce through both ends of the rotor iron core 5 .

An inner iron core 5 B 1 includes a plurality of protrusions 5 B 1 b (see FIG. 4 ) to regulate movement of each permanent magnet 7 . Each protrusion 5 B 1 b is formed in both end parts in the circumferential direction on the outer side surface in a radial direction 5 B 1 a of the inner iron core 5 B 1 . Since the end surface in a circumferential direction 7 c of each permanent magnet 7 is held with each protrusion 5 B 1 b when the protrusion 5 B 1 b is provided in such a manner, it is possible to hold the permanent magnet 7 immovable during driving.

However, when the protrusions 5 B 1 b are provided, the protrusions 5 B 1 b become the shortest flux path of magnetic flux generated by the winding wire 14 . When the permanent magnet 7 is crossed in an opposite direction of a direction of magnetization of the permanent magnet 7 , irreversible demagnetization is easily caused. Thus, a height in the radial direction of each protrusion 5 B 1 b is as low as possible in a range in which each permanent magnet 7 can be held.

In each magnet insertion hole 9 , permanent magnets 7 with different polarities are arranged alternately in the circumferential direction. The number of poles of the permanent magnets 7 is six (see FIG. 3 ) in the rotor 1 illustrated as an example. However, the number of magnetic poles of the permanent magnets 7 is not limited to this. Also, a sectional surface of each permanent magnet 7 illustrated in FIG. 3 has a tabular rectangle shape. However, a shape of each permanent magnet 7 is not limited to this and a different shape may be included according to a purpose of reducing a noise or improving demagnetization resistance. In such a case, a shape of the inner side surface in a radial direction 5 A 3 of the first iron core 5 A or a shape of the outer side surface in a radial direction 5 B 1 a of the inner iron core 5 B 1 of the second iron core 5 B is formed as a shape corresponding to a shape of each permanent magnet 7 .

To both end surfaces of the rotor iron core 5 , disk-shaped end sheets 8 are respectively attached (see FIG. 1 ). Each end sheet 8 is to prevent the permanent magnets 7 inserted into each magnet insertion hole 9 from falling off.

As a method of fixing each end sheet 8 to each end surface of the rotor iron core 5 , for example, a method of providing a through hole in each of the rotor iron core 5 and the end sheet 8 and fasting a bolt to the through hole or swaging a rivet in the through hole may be used other than welding or adhesion.

As a different method, a method of providing a spigot structure on abutting surfaces of each end surface of the rotor iron core 5 and each end sheet 8 and attaching the end sheet 8 to the end surface of the rotor iron core 5 may be used. In the spigot structure, for example, a recessed part is formed on a surface of the rotor iron core 5 which surface faces each end sheet 8 , a protruded part is provided on a surface of each end sheet 8 which surface faces the rotor iron core 5 , and the protruded part and the recessed part are fitted to each other.

At a center part in the radial direction of the rotor iron core 5 , a shaft fitting hole 18 is provided. To the shaft fitting hole 18 , the shaft 6 to transmit rotation energy is fitted by shrinkage fitting or pressure fitting. The shaft 6 has a cylindrical shape and the shaft fitting hole 18 has a shape corresponding to this.

Both end parts of the shaft 6 fitted to the shaft fitting hole 18 are supported rotatably by the bearing 11 arranged in the bracket 4 and the bearing 10 arranged in the frame 3 .

As illustrated in FIG. 2 , the rotor iron core 5 includes a plurality of first iron cores 5 A and a second iron core 5 B.

Each first iron core 5 A is formed by stamping and laminating of a plurality of electromagnetic steel sheets having silicon steel or Armco iron with a superior magnetic characteristic. Each first iron core 5 A is arranged on an outer side in the radial direction of each permanent magnet 7 (see FIG. 3 ).

The second iron core 5 B is formed by stamping and laminating of a plurality of high-strength steel sheets having carbon steel or the like with mechanical strength higher than that of the electromagnetic steel sheets of each first iron core 5 A.

The second iron core 5 B includes an inner iron core 5 B 1 and a plurality of inter-magnetic pole iron cores 5 B 2 . The inner iron core 5 B 1 is arranged on an inner side in the radial direction of each permanent magnet 7 and each inter-magnetic pole iron core 5 B 2 is formed integrally with the inner iron core 5 B 1 and is arranged between magnetic poles 17 of each permanent magnet 7 .

As illustrated in FIG. 4 , the first iron cores 5 A and the second iron core 5 B are arranged in such a manner that an outer peripheral surface 5 B 2 a of each inter-magnetic pole iron core 5 B 2 and an outer peripheral surface 5 A 1 of each first iron core 5 A are on the same circumference when each permanent magnet 7 is arranged.

Each inter-magnetic pole iron core 5 B 2 includes a trunk part 5 B 21 extended from the inner iron core 5 B 1 to the outer side in the radial direction and two branch parts 5 B 22 that are an end part of the trunk part 5 B 21 which part branches into two and is in contact with an end part in a circumferential direction 5 A 2 of each first iron core 5 A. In such a manner, each inter-magnetic pole iron core 5 B 2 is formed from the inner iron core 5 B 1 to the end part in a circumferential direction 5 A 2 of each first iron core 5 A in such a manner as to regulate positions in the radial direction and the circumferential direction of each first iron core 5 A. A shape of a sectional surface of each inter-magnetic pole iron core 5 B 2 is a T-shape.

An abutting surface in a circumferential direction 5 B 22 a of a leading end part 5 B 22 A of each branch part 5 B 22 is in contact with an abutting surface in a circumferential direction 5 A 22 of each first iron core 5 A and an abutting surface in a radial direction 5 B 22 b of the leading end part 5 B 22 A of each branch part 5 B 22 is in contact with an abutting surface in a radial direction 5 A 21 of each first iron core 5 A when each permanent magnet 7 is arranged. That is, the leading end part 5 B 22 A of each branch part 5 B 22 is formed in such a manner as to regulate a position in the circumferential direction of each first iron core 5 A and a position in the radial direction thereof.

With a configuration in such a manner, even in a case where centrifugal force acts on each first iron core 5 A and each permanent magnet 7 due to a rotation of the rotor 1 , it is possible to securely prevent each first iron core 5 A and each permanent magnet 7 from coming off from the rotor iron core 5 due to the centrifugal force.

Between each permanent magnet 7 and each inter-magnetic pole iron core 5 B 2 , the flux barrier 16 that is a gap for preventing short-circuiting of magnetic flux is formed. In the rotor iron core 5 in FIG. 3, 12 flux barriers 16 are formed.

As illustrated in FIG. 4 , for example, each flux barrier 16 is formed from abutting surfaces of each first iron core 5 A and each inter-magnetic pole iron core 5 B 2 to an end surface in a circumferential direction 7 c of each permanent magnet 7 . Note that the abutting surfaces of each first iron core 5 A and each inter-magnetic pole iron core 5 B 2 mean abutting surfaces in the radial direction of each first iron core 5 A and each inter-magnetic pole iron core 5 B 2 and abutting surfaces in the circumferential direction of each first iron core 5 A and each inter-magnetic pole iron core 5 B 2 . Also, the abutting surfaces in the radial direction mean an abutting surface in a radial direction 5 A 21 of each first iron core 5 A and an abutting surface in a radial direction 5 B 22 b of each inter-magnetic pole iron core 5 B 2 . The abutting surfaces in the circumferential direction mean an abutting surface in a circumferential direction 5 A 22 of each first iron core 5 A and an abutting surface in a circumferential direction 5 B 22 a of each inter-magnetic pole iron core 5 B 2 .

In such a manner, the rotor iron core 5 according to the present embodiment includes the plurality of first iron cores 5 A including an electromagnetic steel sheet with a superior magnetic characteristic, the second iron core 5 B including a high-strength steel sheet with high mechanical strength, and the flux barrier 16 . Hereinafter, an effect of that will be described.

An outer side surface in a radial direction 7 a and an inner side surface in a radial direction 7 b of each permanent magnet 7 arranged in each magnet insertion hole 9 are connected to each other via the inter-magnetic pole iron core 5 B 2 formed between the magnetic poles 17 of the permanent magnets 7 . For example, magnetic flux generated in each permanent magnet 7 passes through the stator iron core 13 (see FIG. 1 ) and goes back to the rotor iron core 5 . However, a part of magnetic flux that goes out from each permanent magnet 7 passes through the inter-magnetic pole iron cores 5 B 2 and becomes leakage flux that does not contribute to a torque.

On the other hand, since centrifugal force during a high-speed rotation of the rotor 1 acts on the permanent magnets 7 and the first iron cores 5 A, the rotor iron core 5 needs to have mechanical strength for resisting the centrifugal force. In a case where a high-strength steel sheet is used in the whole rotor iron core 5 , an iron loss in the rotor is increased compared to a case where a general electromagnetic steel sheet that is not a high-strength steel sheet is used although it is possible to satisfy mechanical strength for resisting the centrifugal force in a high-speed rotation of the rotor 1 .

In view of such a problem, the rotor iron core 5 according to the present embodiment includes the plurality of first iron cores 5 A including an electromagnetic steel sheet with a superior magnetic characteristic, the second iron core 5 B including a high-strength steel sheet with high mechanical strength, and the flux barrier 16 .

According to the rotor iron core 5 configured in such a manner, it is possible to control an increase in an iron loss in the rotor since the first iron cores 5 A in which the most of the iron loss in the whole rotor is generated include an electromagnetic steel sheet.

Also, since the inter-magnetic pole iron cores 5 B 2 to support the centrifugal force that acts on the first iron cores 5 A and the permanent magnets 7 include a high-strength steel sheet, it is possible to improve centrifugal force resistant strength.

Also, the flux barrier 16 has a function of narrowing down a width of a flux path in which leakage flux passes. That is, the flux barrier 16 has a function of narrowing down a width in the circumferential direction of the trunk part 5 B 21 in which the leakage flux passes and of narrowing down a width in the radial direction of each of the branch parts 5 B 22 in which the leakage flux passes. In other words, the flux barrier 16 has a function of increasing effective magnetic flux. With this configuration, short-circuiting of magnetic flux in an end part in the circumferential direction of each permanent magnet 7 is prevented and it becomes easy for the magnetic flux to move to the stator 2 (see FIG. 1 ), whereby it is possible to increase generated torque.

Note that by adequately setting a length and a width of the flux barrier 16 extended in the circumferential direction along each of the branch parts 5 B 22 , it is possible to bring the magnetic flux flowing on the surface of the rotor iron core 5 closer to a sinusoid, to reduce an iron loss in the rotor, and to reduce a noise.

Also, the branch parts 5 B 22 may be configured in the following manner. In FIG. 4 , when the number of magnetic poles is P, angular velocity (maximum angular velocity) of a rotation of the rotor 1 is ω, a sheet thickness of each high-strength steel sheet included in the second iron core 5 B is t, strength of each high-strength steel sheet is σ y , mass of a pair of a first iron core 5 A having a thickness corresponding to this sheet thickness t and a permanent magnet 7 in one pole is m, a distance from a position of a center of gravity G of this pair to a center of a shaft C is r, and a width in a radial direction of a branch part 5 B 22 at a position away for a certain distance x in the circumferential direction from an abutting surface in a circumferential direction 5 B 22 a of a leading end part 5 B 22 A of the branch part 5 B 22 toward an inter-magnetic pole iron core 5 B 2 is h, the width in the radial direction h of the branch part 5 B 22 is set in such a manner as to satisfy an expression (1).

With the setting in such a manner, it is possible to satisfy mechanical strength for resisting centrifugal force in a high-speed rotation of the rotor 1 . For example, in a case where a distribution of magnetic flux density on the surface of the rotor iron core 5 (deviation from sinusoid) is ignored and the width in the radial direction h of the branch part 5 B 22 is made as narrow as possible, the width in the radial direction h of the branch part 5 B 22 is determined by an expression (2) with a safety factor as α (α is value larger than 1).

Note that the value of the safety factor α is set in consideration of a material characteristic, a variation in production, or the like. Also, as the strength σσ y of each high-strength steel sheet, yield stress is generally used. In a case where fatigue becomes a problem (case where the number of rotations changes frequently), a fatigue limit is used.

Here, a reason why the width in the radial direction h of the branch part 5 B 22 is set in such a manner as to satisfy the expression (1) at the certain distance x will be described.

An amount of centrifugal force F that acts on the pair of the first iron core 5 A having a thickness corresponding to the above-described sheet thickness t and the permanent magnet 7 in one pole becomes the largest when the rotor 1 rotates at the maximum angular velocity co and is expressed by an expression (3).

[Math 3]

F=m·r·ω 2   (3)

Since the centrifugal force F in the expression (3) is supported by two branch parts 5 B 22 on both of right and left sides of the first iron core 5 A, force f that works in the radial direction of a leading end part 5 B 22 A of each branch part 5 B 22 is expressed by an expression (4) in a case where an angle formed by a line that connects the center of a shaft C and the position of the center of gravity G and a line that connects the center of a shaft C and the leading end part 5 B 22 A of the branch part 5 B 22 (abutting surface in circumferential direction 5 B 22 a ) is θ (unit is rad).

Generally, since a length in the circumferential direction of the branch part 5 B 22 is set adequately short compared to a length in the circumferential direction of one magnetic pole, the angle θ can be assumed as an expression (5).

Thus, the expression (4) is expressed as an expression (6).

From the expression (3) and the expression (6), the force f is expressed by an expression (7).

As described above, since the length in the circumferential direction of the branch part 5 B 22 is generally adequately short compared to the length in the circumferential direction of one magnetic pole, the branch part 5 B 22 having a thickness corresponding to the sheet thickness t can be assumed as a cantilever in which a concentrated load (force f) is applied to the leading end part 5 B 22 A. A bending moment M at the above-described position in the certain distance x is expressed by an expression (8).

[Math 8]

M=f·x   (8)

From the expression (7) and the expression (8), the bending moment M is expressed by an expression (9).

A section modulus Z at the position in the certain distance x is expressed by an expression (10).

A maximum value σ max of stress at the position in the certain distance x is expressed by an expression (11).

From the expression (9), the expression (10), and the expression (11), the maximum value σ max of the stress is expressed by an expression (12).

The maximum value σmax of the stress needs to be lower than the strength σ y of each high-strength steel sheet at an arbitrary position of the branch part 5 B 22 . Thus, the value of the certain distance x needs to satisfy an expression (13).

When being written with respect to the width in the radial direction h, the expression (13) is expressed by an expression (14) and the expression (1) is acquired from the expression (14).

Note that each flux barrier 16 of the present embodiment is formed from the abutting surfaces of each first iron core 5 A and each inter-magnetic pole iron core 5 B 2 to the end surface in a circumferential direction 7 c of each permanent magnet 7 . However, for example, a flux barrier 16 may be formed only in a region 16 a (see FIG. 4 ) between the end surface in a circumferential direction 7 c of each permanent magnet 7 and the trunk part 5 B 21 . Also, a flux barrier 16 may be formed only in a region 16 b between a leading end part in a circumferential direction 5 A 23 of each first iron core 5 A and each branch part 5 B 22 .

In such a manner, even in a case where a flux barrier 16 is formed in a region that is a part of a region from the abutting surfaces of each first iron core 5 A and each inter-magnetic pole iron core 5 B 2 to the end surface in a circumferential direction 7 c of each permanent magnet 7 , it is possible to control an increase in an iron loss and leakage flux compared to the above-described conventional technology while securing mechanical strength for resisting centrifugal force.

As described above, the rotor iron core 5 of the permanent-magnet-embedded motor 100 according to the present embodiment includes: the plurality of first iron cores 5 A formed by laminating of a plurality of electromagnetic steel sheets and arranged in an outer side in the radial direction of each permanent magnet 7 ; and the second iron core 5 B formed by laminating of a plurality of electromagnetic steel sheets (high-strength steel sheet) with mechanical strength higher than mechanical strength of the plurality of electromagnetic steel sheets of the first iron cores 5 A and that includes the inner iron core 5 B 1 arranged on an inner side in the radial direction of each permanent magnet 7 and the plurality of inter-magnetic pole iron cores 5 B 2 formed integrally with the inner iron core 5 B 1 and arranged between the magnetic poles 17 of each permanent magnet 7 , wherein each inter-magnetic pole iron core 5 B 2 is formed from the end part in a circumferential direction 5 A 2 of each first iron core 5 A to the inner iron core 5 B 1 in such a manner as to regulate a position of each first iron core 5 A, and the flux barrier 16 is formed between each permanent magnet 7 and each inter-magnetic pole iron core 5 B 2 .

In such a manner, since the first iron cores 5 A in which the most of an iron loss in the whole rotor is generated includes the electromagnetic steel sheets, it is possible to control an increase in the iron loss in the rotor. Also, since the inter-magnetic pole iron cores 5 B 2 to support the centrifugal force that acts on the first iron cores 5 A and the permanent magnets 7 include the high-strength steel sheets, it is possible to improve centrifugal force resistant strength. That is, it is possible to improve the centrifugal force resistant strength and to control an increase in an iron loss at the same time. Also, since it is possible to increase effective magnetic flux by the flux barriers 16 , it is possible to increase generated torque.

Also, each flux barrier 16 is formed from abutting surfaces of each first iron core 5 A and each inter-magnetic pole iron core 5 B 2 to the end surface in a circumferential direction 7 c of each permanent magnet 7 . With this configuration, it is possible to control an increase in leakage flux compared to a case where a flux barrier 16 is formed only in a region that is a part of a region from the abutting surfaces of each first iron core 5 A and each inter-magnetic pole iron core 5 B 2 to the end surface in a circumferential direction 7 c of each permanent magnet 7 .

The inner iron core 5 B 1 includes a plurality of protrusions 5 B 1 b formed in both end parts in the circumferential direction of the outer side surface in a radial direction 5 B 1 a in contact with each permanent magnet 7 and that regulates a position of each permanent magnet 7 . Each flux barrier 16 is formed from the abutting surfaces of each first iron core 5 A and each inter-magnetic pole iron core 5 B 2 to each protrusion 5 B 1 b . With this configuration, since the end surface in a circumferential direction 7 c of each permanent magnet 7 is held by each protrusion 5 B 1 b , it is possible to hold the permanent magnet 7 immovable during driving and to control an increase in leakage flux.

Second Embodiment

FIG. 5 is a sectional view of a rotor iron core 5 of a permanent-magnet-embedded motor 100 according to a second embodiment of the present invention. As illustrated in FIG. 5 , in the rotor iron core 5 of the second embodiment, a direction of easy magnetization 19 (direction in which direction of crystal axis of material included in electromagnetic steel sheet is the most likely to be magnetized) of each electromagnetic steel sheet included in a first iron core 5 A is set in a radial direction in addition to the configuration of the first embodiment.

Although being changed slightly due to relative positions (phase) in a circumferential direction of the first iron core 5 A and a tooth of a stator iron core 13 and a conductive state of a winding wire 14 , a direction of magnetic flux passing through the first iron core 5 A faces a substantially radial direction in the whole phase. Thus, when the direction of easy magnetization 19 of each electromagnetic steel sheet included in the first iron core 5 A is set to the radial direction and a magnetic characteristic is improved, it is possible to improve efficiency of a magnetic circuit and to decrease an iron loss. Thus, it is possible to improve efficiency and an output of the permanent-magnet-embedded motor 100 .

Note that a direction of magnetic flux on an inner side in the radial direction of the permanent magnet 7 is not changed according to a phase. However, the magnetic flux on the inner side in the radial direction of the permanent magnet 7 faces various directions. Thus, it is preferred that a magnetic characteristic of a high-strength steel sheet included in a second iron core 5 B does not have directionality.

Third Embodiment

FIG. 6 is a sectional view of a rotor iron core 5 of a permanent-magnet-embedded motor 100 according to a third embodiment of the present invention. In the rotor iron core 5 of the third embodiment, a leading end part 5 B 22 A of each branch part 5 B 22 is formed in such a manner that a position thereof before an arrangement of each permanent magnet 7 is on an inner side in a radial direction of a position thereof after the arrangement of each permanent magnet 7 so as to bias an abutting surface in a radial direction 5 B 22 b of a first iron core 5 A with biasing force toward the inner side in the radial direction when each permanent magnet 7 is arranged.

In FIG. 6 , a leading end part 5 B 22 A- 1 indicated by a solid line indicates a state before an arrangement of each permanent magnet 7 and a leading end part 5 B 22 A- 2 indicated by a dotted line indicates a state after the arrangement of each permanent magnet 7 .

In such a manner, an inter-magnetic pole iron core 5 B 2 of the third embodiment is formed in such a manner that a position of the leading end part 5 B 22 A of each branch part 5 B 22 thereof before an arrangement of each permanent magnet 7 is on the inner side in the radial direction of a position thereof after the arrangement of each permanent magnet 7 .

Accordingly, when each permanent magnet 7 is inserted into each magnet insertion hole 9 illustrated in FIG. 2 , the leading end part 5 B 22 A is deformed from the position indicated by the solid line to the position indicated by the dotted line. Here, to each branch part 5 B 22 , force of moving the position of the leading end part 5 B 22 A thereof toward the position indicated by the solid line is applied. This force biases the first iron core 5 A placed on the inner side in the radial direction of the leading end part 5 B 22 A in a direction of an axial center. Thus, the first iron core 5 A can be in contact with the permanent magnet 7 with predetermined pressing force. That is, after assembly of the first iron core 5 A, a second iron core 5 B, and the permanent magnet 7 , the permanent magnet 7 is elastically sandwiched between the first iron core 5 A and the second iron core 5 B and is tightly fixed between the first iron core 5 A and the second iron core 5 B. Thus, it is possible to reduce a noise or vibration during driving and to prevent the permanent magnet 7 from being broken or cracked.

Note that the configuration described in each of the above embodiments is an example of a configuration of the present invention. It is obvious that it is possible to make a combination with a different known technology or to modify a configuration within the spirit and the scope of the preset invention, for example, by omitting a part.

As described above, the present invention can be applied to a permanent-magnet-embedded motor and is specifically useful as an invention that can control an increase in an iron loss and leakage flux while securing mechanical strength for resisting centrifugal force.