Synchronous reluctance type rotary electric machine

A synchronous reluctance type rotary electric machine of an embodiment has a rotor core. The rotor core includes a plurality of poles, multi-layered hollow parts having a convex shape toward a side radially inward formed for each pole in cross section, and a bridge formed between each of the hollow parts and an outer circumferential surface thereof. When a boundary between two adjacent poles is a pole boundary, a groove is formed on at least one of both sides sandwiching the pole boundary at positions other than on the pole boundary on the outer circumferential surface of the rotor core.

FIELD

Embodiments described herein relate generally to a synchronous reluctance type rotary electric machine.

BACKGROUND

A synchronous reluctance type rotary electric machine includes a rotor and a stator. The rotor includes a shaft rotatably supported and extending in an axial direction at a center of the rotating shaft, and a rotor core externally fitted and fixed to the shaft. The stator includes a stator core having a plurality of teeth disposed on an outer circumference of the rotor core to be spaced apart from the rotor core and disposed to be spaced apart from each other in a circumferential direction, and multipole multiphase armature windings respectively wound around the plurality of teeth.

Multi-layered hollow parts having a convex shape toward a side radially inward are formed for each pole in the rotor core. When the hollow parts are formed in this manner, a direction in which magnetic flux easily flows and a direction in which magnetic flux does not easily flow are formed in the rotor core. Thus, the synchronous reluctance type rotary electric machine rotates the shaft using a reluctance torque generated by the hollow parts.

Incidentally, it is conceivable that synchronous reluctance type rotary electric machines be applied in various fields, and thus yet higher output and reduction in size are required. Due to this, synchronous reluctance type rotary electric machines are desired to have a higher capacity and a higher rotation speed. On the other hand, when hollow parts are formed in a rotor core, the rotor core is likely to be deformed. Therefore, when the rotor core is rotated at a high-speed, there is a likelihood that the rotor core will be deformed by a centrifugal force generated by the high-speed rotation.

Here, when a thickness at a portion called a bridge formed between both ends in a longitudinal direction of the hollow part and an outer circumferential surface of the rotor core is set to be thick, a rotor core can be made difficult to deform. However, when a thickness of the bridge is set to be thick, there is a likelihood of generating magnetic flux leakage at the bridge portion (magnetic circuit). For this reason, a desired reluctance torque is not easily obtained, and there is a likelihood that torque characteristics of the synchronous reluctance type rotary electric machine will deteriorate.

DETAILED DESCRIPTION

A synchronous reluctance type rotary electric machine of an embodiment has a rotor core. The rotor core includes a plurality of poles, multi-layered hollow parts having a convex shape toward a side radially inward formed for each pole in cross section, and a bridge formed between each of the hollow parts and an outer circumferential surface thereof. When a boundary between two adjacent poles is a pole boundary, a groove is formed on at least one of both ends sandwiching the pole boundary at positions other than on the pole boundary on the outer circumferential surface of the rotor core.

Hereinafter, a synchronous reluctance type rotary electric machine of an embodiment will be described with reference to the drawings.

FIG. 1is a partial cross-sectional perspective view illustrating a synchronous reluctance type rotary electric machine (hereinafter simply referred to as a rotary electric machine)1.

As shown inFIG. 1, the rotary electric machine1includes a housing2, a stator3fixed in the housing2, and a rotor4supported to be rotatable around a rotation axis O in the housing2. In the following description, a direction parallel to the rotation axis O will be simply referred to as an axial direction, a direction of revolving around the rotation axis O will be simply referred to as a circumferential direction, and a radial direction perpendicular to the rotation axis O will be simply referred to as a radial direction.

The housing2includes a substantially cylindrical frame5and bearing brackets6and7which close openings5aand5bat both ends in the axial direction of the frame5. Each of the bearing brackets6and7is formed in substantially a disc shape. Bearings8and9for rotatably supporting the rotor4are respectively provided substantially at centers in the radial direction of the bearing brackets6and7.

FIG. 2is a cross-sectional view perpendicular to the rotation axis O illustrating a configuration of a portion of the rotary electric machine1. InFIG. 2, a quarter sector of the rotary electric machine1, that is, only a quarter-circumference circumferential angular region is shown.

As shown inFIGS. 1 and 2, the stator3includes a substantially cylindrical stator core10. An outer circumferential surface of the stator core10is internally fitted and fixed to an inner circumferential surface of the frame5. A radial center of the stator core10coincides with the rotation axis O.

Also, the stator core10can be formed by laminating a plurality of electromagnetic steel sheets or by compression-molding a soft magnetic powder. On an inner circumferential surface of the stator core10, a plurality of teeth11protruding toward the rotation axis O and disposed at regular intervals in the circumferential direction are integrally molded. The teeth11are formed to have a substantially rectangular cross section. A plurality of slots12are formed at regular intervals in the circumferential direction so that one slot12is disposed between adjacent teeth11. Through these slots12, armature windings13arc wound around each of the teeth11.

FIG. 3is a perspective view illustrating the rotor4.

As shown inFIGS. 2 and 3, the rotor4is disposed on a side radially inward from the stator core10. The rotor4includes a rotating shaft14extending in the axial direction and a substantially columnar rotor core15externally fitted and fixed to the rotating shaft14.

The rotor core15can be formed by laminating a plurality of electromagnetic steel sheets or by compression-molding a soft magnetic powder. An outer diameter of the rotor core15is set such that a predetermined air gap G is formed between each of the teeth11and the rotor core15facing each other in the radial direction. Also, a through hole16penetrating in the axial direction is formed at a radial center of the rotor core15. The rotating shaft14is press-fitted or the like to the through hole16, and thereby the rotating shaft14and the rotor core15rotate integrally.

Further, four layers of hollow parts (flux barriers)21,22,23, and24(a first hollow part21, a second hollow part22, a third hollow part23, and a fourth hollow part24) are formed to be aligned in the radial direction in each of the quarter-circumference circumferential angular region of the rotor core15. That is, the first hollow part21is formed on an outermost side in the radial direction, and the second hollow part22, the third hollow part23, and the fourth hollow part24are aligned in this order from the first hollow part21toward the side radially inward. Thus, the fourth hollow part24is disposed on the side furthest inward in the radial direction.

Also, each of the hollow parts21to24is formed to follow a flow of a magnetic flux formed when the armature windings13are energized. That is, each of the hollow parts21to24is formed to be curved so that a center thereof in the circumferential direction is positioned furthest inward in the radial direction (to have a convex shape toward the side radially inward). Thereby, a direction in which the magnetic flux easily flows and a direction in which the magnetic flux does not easily flow are formed in the rotor core15. In the following description, a longitudinal direction of each of the hollow parts21,22,23, and24when viewed from a direction of the rotation axis O (substantially a lateral direction inFIG. 2) will be simply referred to as a longitudinal direction of the hollow parts21,22,23, and24in some cases.

Here, in the present embodiment, a direction in which the magnetic flux easily flows is referred to as a q-axis. Also, a direction extending in the radial direction that is electrically and magnetically perpendicular to the q axis is referred to as a d-axis. That is, each of the hollow parts21to24forms a multilayer structure in the radial direction along the d-axis.

More specifically, regarding the q-axis direction in the rotor core15, a direction in which a flow of the magnetic flux is not interrupted by each of the hollow parts21to24is referred to as the q-axis. That is, a positive magnetic potential (for example, an N pole of a magnet is brought close thereto) is given to an arbitrary circumferential angular position on an outer circumferential surface15aof the rotor core15. Also, a negative magnetic potential (for example, an S pole of a magnet is brought close thereto) is given to another arbitrary circumferential angular position shifted by one pole (90 degrees in mechanical angle in the present embodiment) with respect to the positive magnetic potential. Then, when positions of such positive magnetic potential and negative magnetic potential are shifted from each other in the circumferential direction, a direction from the rotation axis O toward an arbitrary position when a majority of the magnetic flux flows is defined as the q-axis. Then, the longitudinal direction of each of the hollow parts21to24is the q-axis.

On the other hand, a direction in which a flow of the magnetic flux is interrupted by each of the hollow parts21to24, that is, a direction magnetically perpendicular to the q-axis is referred to as the d-axis. In the present embodiment, a direction parallel to a direction in which two rotor core portions separated into a region close to the rotation axis O and a region away from the rotation axis O by each of the hollow parts21to24face each other is the d-axis. Also, when the hollow parts21to24are formed in multiple layers (four layers in the present embodiment) as in the present embodiment, a direction in which the layers overlap is the d-axis. In the present embodiment, the d-axis is not limited to being electrically and magnetically perpendicular to the q-axis and may intersect the q-axis with a certain degree of angular width (for example, about 10 degrees in mechanical angle) from the perpendicular angle.

As described above, the rotor core15is configured to have four poles, and four layers of the hollow parts21to24are formed for each pole (a quarter-circumference circumferential angular region of the rotor core15). Then, one pole is a region between the q-axes.

In the following description, the d-axis is referred to as a pole center C1. The q-axis (both ends in the circumferential direction of the quarter-circumference circumferential angular region) serves as a boundary between two adjacent poles and is therefore referred to as a pole boundary E1.

That is, each of the hollow parts21to24is formed to be curved toward the side radially inward so that the pole center C1thereon is positioned furthest inward in the radial direction. Also, each of the hollow parts21to24is formed to be curved so that both ends thereof in a longitudinal direction are respectively positioned on outer circumferential portions of the rotor core15when viewed from the axial direction. Then, each of the hollow parts21to24is formed to follow the pole boundary E1as a position thereon becomes closer to both ends in the longitudinal direction and to be perpendicular to the pole center C1as a position thereof becomes closer to a center in the longitudinal direction.

Bridges26,27,28, and29(a first bridge26, a second bridge27, a third bridge28, and a fourth bridge29) are respectively formed between both ends in the longitudinal direction of each of the hollow parts21to24and the outer circumferential surface15aof the rotor core15in the q-axis direction.

The bridges26,27,28, and29means those formed close to the outer circumferential portion of the rotor core15in each of the hollow parts21to24in a range in which thicknesses thereof rapidly change (this range is referred to as a bridge range).

A first groove31is formed over the entire outer circumferential surface15aof the rotor core15in the axial direction in two fourth bridges29which are in a lowermost layer among the four bridges26to29. Also, a second groove32is formed over the entire outer circumferential surface15aof the rotor core15in the axial direction in two second bridges27positioned next to bridges which are in an uppermost layer (the first bridges26).

FIG. 4is an enlarged view of a portion A ofFIG. 2.

As shown inFIG. 4, the first groove31is formed within a range of the fourth bridge29. A groove depth H1of the first groove31is set to gradually increase toward the pole boundary E1. Also, the fourth bridge29is formed such that a side surface29a close to the fourth hollow part24is positioned radially inward toward the pole boundary E1. Thereby, a thickness T1in the q-axis direction of the fourth bridge29is formed to be substantially constant throughout. Also, the first groove31is formed such that an inner side surface31aclose to the pole boundary E1is substantially parallel to the pole boundary E1.

Thus, as shown in detail inFIG. 3, the first groove31is formed on both ends sandwiching the pole boundary E1at positions other than on the pole boundary E1on the outer circumferential surface15aof the rotor core15. In other words, a ridge part33extending in the axial direction is formed on the pole boundary E1and the first groove31is formed on both circumferential sides of the ridge part33on the outer circumferential surface15aof the rotor core15. Since the inner surface31aof the first groove31is substantially parallel to the pole boundary E1, a cross-sectional shape of the ridge part33perpendicular to the axial direction has substantially a rectangular shape.

FIG. 5is an enlarged view of a portion B ofFIG. 2.

As shown inFIG. 5, the second groove32is formed on the second bridge27. A groove depth H2of the second groove32is set to gradually increase toward the pole center C1. Also, the second bridge27is formed such that a side surface27aclose to the second hollow part22is positioned radially inward toward the pole center C1. Thereby, a thickness T2in the q-axis direction of the second bridge27is formed to be substantially constant throughout.

Further, thicknesses of the first bridge26and the third bridge28in the q-axis direction are also formed to be substantially constant throughout.

Incidentally, each of the bridges26to29is a portion for making it difficult for the rotor core15to be deformed and is also a portion which causes magnetic flux leakage.

Hereinafter, a stress applied to the bridges26to29in a rotor core (hereinafter referred to as a conventional rotor core) in which the second groove32and the first groove31are not respectively formed in the second bridge27and the fourth bridge29will be described. Further, since the conventional rotor core is the same as the rotor core15of the present embodiment except for a configuration in which each of the grooves31and32is not formed, a description will be provided assuming that parts in the conventional rotor core the same as those in the rotor core15of the present embodiment are denoted by the same reference signs so that the description can be more easily understood.

FIG. 6is a distribution diagram for a stress applied to the rotor core15when the conventional rotor core15is rotated at a high speed.

As shown in dotted hatching inFIG. 6, when the conventional rotor core15is rotated at a high speed, a stress is applied to the bridges26to29. This is because a centrifugal force applied to the rotor core15between each of the hollow parts21to24when the rotor core is rotated is received by each of the bridge26to29. Here, it can be confirmed that hardly any stress due to high-speed rotation of the rotor core15is applied to a portion corresponding to the first groove31and a portion corresponding to the second groove32(for both, refer toFIG. 2) of the present embodiment.

That is, also when the first groove31and the second groove32are formed, the difficulty in deforming the rotor core15hardly changes. In addition to this, magnetic saturation occurs easily in the second bridge27and the fourth bridge29according to the first groove31and the second groove32being formed, and magnetic flux leakage can be suppressed.

Therefore, according to the above-described embodiment, the rotor core15can be made difficult to deform and torque characteristics of the rotary electric machine1can be improved.

Also, the first groove31is formed on both ends sandwiching the pole boundary E1at positions other than on the pole boundary E1on the outer circumferential surface15aof the rotor core15. In other words, the ridge part33extending in the axial direction is formed on the pole boundary E1and the first groove31is formed on both circumferential sides of the ridge part33on the outer circumferential surface15aof the rotor core15. Therefore, sufficient saliency (salient pole ratio, reluctance ratio between the d-axis and the q-axis) of the rotor core15can be secured while forming the first groove31. Therefore, the torque characteristics of the rotary electric machine1can be reliably improved.

Further, the first groove31and the second groove32are formed over the entire outer circumferential surface15aof the rotor core15in the axial direction. Therefore, the magnetic flux leakage at the second bridge27and the fourth bridge29can be reliably suppressed.

Also, a sufficient strength around the fourth bridge29in the rotor core15can be secured by forming the first groove31within the range of the fourth bridge29. Therefore, the rotor core15can be more reliably made difficult to deform while suppressing magnetic flux leakage.

Further, in the above-described embodiment, a case in which the first groove31is formed within the range of the fourth bridge29has been described. However, it is not limited thereto, and the first groove31may be formed beyond the range of the fourth bridge29.

Also, a case in which the first groove31is formed such that the inner side surface31aclose to the pole boundary E1is substantially parallel to the pole boundary E1has been described. However, it is not limited thereto, and the inner side surface31amay be formed to be inclined with respect to the pole boundary E1. Accordingly, the cross-sectional shape of the ridge part33perpendicular to the axial direction is not limited to a rectangular shape, and for example, the cross-sectional shape thereof perpendicular to the axial direction may be a trapezoidal shape that is tapered toward an outer side in the radial direction.

When the ridge part33is formed as described above, the fourth bridge29can be more reliably made difficult to deform and sufficient saliency of the rotor core15can be secured.

Further, a case in which the first groove31is formed on both sides sandwiching the pole boundary E1at positions other than on the pole boundary E1on the outer circumferential surface15aof the rotor core15has been described.

However, it is not limited thereto, and the first groove31need only be formed on at least one of both sides sandwiching the pole boundary E1. In this case, although the ridge part33is not formed on the pole boundary E1, since the magnetic flux leakage of the fourth bridge29in which the first groove31is formed can be suppressed, the rotor core15can be made difficult to deform and torque characteristics of the rotary electric machine1can be improved.

Also, in the above-described embodiment, a case in which the second groove32is formed on the second bridge27in addition to the first groove31formed on the fourth bridge29on the outer circumferential surface15aof the rotor core15has been described. However, it is not limited thereto, and the second groove32may not be formed in the second bridge27as shown inFIG. 7. Even with such a configuration as above, since the magnetic flux leakage of the fourth bridge29can be suppressed, the rotor core15can be made difficult to deform and torque characteristics of the rotary electric machine1can be improved.

Further, a case in which the first groove31and the second groove32are formed over the entire rotor core15in the axial direction has been described. However, it is not limited thereto, and a plurality of first grooves31and second grooves may be formed at intervals in the axial direction. Even in such a case, the magnetic flux leakage of the fourth bridge29and the second bridge27can be reduced compared to a case in which the first groove31and the second groove are not formed.

Further, in the above-described embodiment, a case in which the rotor core15is configured to have four poles has been described. However, it is not limited thereto, and the rotor core15may be configured to have four or more poles.

Further, a case in which the rotor core15has four layers of hollow parts21to24formed in each quarter-circumference circumferential angular region (for each pole) has been described. However, it is not limited thereto, and a plurality of hollow parts with four or more layers may be formed. Even in the case in which four or more layers of hollow parts are formed, a groove corresponding to the first groove31is formed on at least one of both sides sandwiching the pole boundary E1at positions other than on the pole boundary E1. Also, it is preferable to form a groove corresponding to the second groove32on the outer circumferential surface15aof a bridge (second bridge27) positioned next to a bridge closest to the pole center C1(first bridge26).

Also, in the above-described embodiment, a case in which each of the hollow parts21to24is formed to be curved so that a center thereof in the circumferential direction is positioned furthest inward in the radial direction (to have a convex shape toward the side radially inward) has been described. However, it is not limited thereto, and each of the hollow parts21to24need only be formed in a convex shape toward the side radially inward. That is, each of the hollow parts21to24may not be formed to be curved.

According to at least any one embodiment described above, sufficient saliency of the rotor core15can be secured while suppressing the magnetic flux leakage in the fourth bridge29by forming the first groove31on both sides sandwiching the pole boundary E1at positions other than on the pole boundary E1on the outer circumferential surface15aof the rotor core15. Therefore, torque characteristics of the rotary electric machine1can be reliably improved.

Also, the first groove31is formed such that the groove depth H1gradually increases toward the pole boundary E1. Further, the second groove32formed on the second bridge27is formed such that the groove depth H2gradually increases toward the pole center C1. Therefore, torque characteristics of the rotary electric machine1can be improved while making the rotor core15difficult to deform.

Also, the first groove31and the second groove32are formed over the entire outer circumferential surface15aof the rotor core15in the axial direction. Therefore, the magnetic flux leakage in the second bridge27and the fourth bridge29can be reliably suppressed.

Further, a sufficient strength around the fourth bridge29in the rotor core15can be secured by forming the first groove31within the range of the fourth bridge29. Therefore, the rotor core15can be more reliably made difficult to deform while suppressing magnetic flux leakage.