Rotor for rotating electric machine

A rotor includes a rotor core having a plurality of pairs of magnet-receiving holes and a plurality of magnets respectively received in the magnet-receiving holes. Each pair of the magnet-receiving holes is arranged in a substantially V-shape opening radially outward and a center bridge formed between the two magnet-receiving holes of the pair. For each of the magnet-receiving holes, a protrusion is formed, at a position closer to a radially outer end than a radially inner end of the center bridge, so as to protrude from the center bridge inward of the magnet-receiving hole. Moreover, a magnetic flux barrier is formed at a radially innermost corner portion of the magnet-receiving hole and defined by a curved surface that includes three or more single-curvature surfaces having different curvatures. Among the single-curvature surfaces, the single-curvature surface which has the minimum curvature is positioned closest to the longitudinal axis of the rotor core.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based on and claims priority from Japanese Patent Application No. 2012-203247, filed on Sep. 14, 2012, the content of which is hereby incorporated by reference in its entirety into this application.

BACKGROUND

1. Technical Field

The present invention relates to rotors for rotating electric machines that are used in, for example, motor vehicles as electric motors and electric generators.

2. Description of Related Art

There are known rotors for rotating electric machines that are used in, for example, motor vehicles as electric motors and electric generators. Those rotors include a rotor core and a plurality of permanent magnets. The rotor core is configured to be disposed in radial opposition to a stator of the rotating electric machine. The rotor core has a plurality of pairs of magnet-receiving holes formed therein. Each pair of the magnet-receiving holes is arranged in a substantially V-shape that opens toward the stator side. Each of the permanent magnets is received in a corresponding one of the magnet-receiving holes of the rotor core. Further, for each pair of the magnet-receiving holes, the two corresponding permanent magnets which are respectively received in the two magnet-receiving holes of the pair are arranged so as to together form one magnetic pole of the rotor core.

Japanese Unexamined Patent Application Publication No. 2006-311730 (to be simply referred to as Patent Document 1 hereinafter) discloses a rotor for a rotating electric machine. In the rotor, each of the permanent magnets is arranged in the corresponding one of the magnet-receiving holes of the rotor core so that there is formed a gap between a radially-outer side surface of the permanent magnet and a wall surface of the corresponding magnet-receiving hole. The gap has a uniform width at a central portion in a width direction of the permanent magnet. Further, the gap has a greater width at end portions in the width direction of the permanent magnet than at the central portion. Consequently, with the above arrangement of the permanent magnets in the corresponding magnet-receiving holes of the rotor core, it is possible to prevent local stress concentration from occurring in the rotor core.

However, though Patent Document 1 discloses how to reduce stress concentration on a bridge connecting the permanent magnet and a q-axis core, it fails to disclose how to reduce stress concentration on a radially innermost portion of the corresponding magnet-receiving hole. The stress concentration on the radially innermost portion of the corresponding magnet-receiving hole occurs when the rotor core has a small cross-sectional area. In particular, when the rotor is used in a motor generator which has a gear or a large-diameter shaft provided radially inside of the rotor, the maximum stress induced in the radially innermost portion of the corresponding magnet-receiving hole is almost equal to that induced in the bridge. In addition, in the rotor disclosed in Patent Document 1, there is formed, at the radially innermost portion of the corresponding magnet-receiving hole, a protrusion for positioning the permanent magnet in the corresponding magnet-receiving hole. Consequently, due to the protrusion, a maximum thermal stress is also induced in the radially innermost portion of the corresponding magnet-receiving hole.

SUMMARY

According to exemplary embodiments, a rotor for a rotating electric machine is provided which includes a rotor core and a plurality of magnets. The rotor core has a longitudinal axis and a plurality of pairs of magnet-receiving holes formed therein. Each pair of the magnet-receiving holes is arranged in a substantially V-shape that opens toward a radially outer periphery of the rotor core. Each of the magnets is received in a corresponding one of the magnet-receiving holes of the rotor core. For each pair of the magnet-receiving holes of the rotor core, the two corresponding magnets which are respectively received in the two magnet-receiving holes of the pair are arranged so as to together form one magnetic pole of the rotor. The rotor core further has, for each pair of the magnet-receiving holes, a corresponding center bridge that extends in a radial direction of the rotor core between the two magnet-receiving holes of the pair to separate them from each other. For each of the magnet-receiving holes, there are also formed a protrusion and a magnetic flux barrier in the rotor core. The protrusion protrudes from the corresponding center bridge inward of the magnet-receiving hole, so as to position the corresponding magnet received in the magnet-receiving hole. The protrusion is positioned closer to a radially outer end of the corresponding center bridge than a radially inner end of the corresponding center bridge. The magnetic flux barrier is positioned at a radially innermost corner portion of the magnet-receiving hole and defined by a curved surface that includes three or more single-curvature surfaces having different curvatures. Among the single-curvature surfaces, the single-curvature surface which has the minimum curvature is positioned closest to the longitudinal axis of the rotor core.

With the above configuration, the protrusion for positioning the corresponding magnet, which would be provided at the radially innermost corner portion of the magnet-receiving hole according to the prior art, is offset radially outward of the radial center position of the corresponding center bridge. Consequently, the influence of the protrusion on generation of centrifugal stress (i.e., stress induced by centrifugal force) in the corresponding center bridge is reduced, thereby preventing excessive stress concentration from occurring in the corresponding center bridge.

Moreover, among the single-curvature surfaces of the curved surface defining the magnetic flux barrier, it is easiest for centrifugal stress to concentrate on the single-curvature surface which has the minimum curvature. However, the single-curvature surface with the minimum curvature is located away from the corresponding center bridge. Consequently, it is possible to distribute stress concentration in the rotor core. In other words, it is possible to prevent excessive stress concentration from occurring in the rotor core.

Furthermore, with the above configuration, the protrusion, at which a maximum thermal stress may occur, is positioned away from the radially innermost corner portion of the magnet-receiving hole. Consequently, thermal stress concentration will not occur at the same areas of the rotor core as centrifugal stress concentration. As a result, it is possible to reduce the total stress concentration in the rotor core.

In one exemplary embodiment, the curved surface which defines the magnetic flux barrier includes first to third continuous single-curvature surfaces. The first single-curvature surface has a first radius of curvature and its center of curvature located radially outside of the curved surface. The second single-curvature surface has a second radius of curvature and its center of curvature located radially outside of the curved surface. The third single-curvature surface has a third radius of curvature and its center of curvature located radially outside of the curved surface. Among all the single-curvature surfaces included in the curved surface, the second single-curvature surface has the minimum curvature and is positioned closest to the longitudinal axis of the rotor core.

Further, the curved surface which defines the magnetic flux barrier also includes a fourth single-curvature surface that connects the third single-curvature surface and a radially inner-side wall surface of the magnet-receiving hole. The fourth single-curvature surface has a fourth radius of curvature and its center of curvature located radially inside of the curved surface.

In another exemplary embodiment, the curved surface which defines the magnetic flux barrier includes, on each of opposite sides of the single-curvature surface which has the minimum curvature, a plurality of continuous single-curvature surfaces having different curvatures.

It is preferable that for each of the magnet-receiving holes of the rotor core, there is formed, radially outside of the protrusion, a second magnetic flux barrier for causing a magnetic short circuit along the corresponding center bridge.

DESCRIPTION OF EMBODIMENTS

Exemplary embodiments will be described hereinafter with reference toFIGS. 1-4. It should be noted that for the sake of clarity and understanding, identical components having identical functions throughout the whole description have been marked, where possible, with the same reference numerals in each of the figures and that for the sake of avoiding redundancy, descriptions of the identical components will not be repeated.

First Embodiment

FIG. 1shows the overall configuration of a rotor10according to a first embodiment.

The rotor10is designed to be used in an electric motor (not shown) for a motor vehicle. The motor includes, in addition to the rotor10, a housing, a stator and a rotating shaft, all of which are not shown in the figures. The housing is configured to receive both the rotor10and the stator therein such that the rotor10is disposed radially inside the stator. That is to say, the motor is of an inner rotor type. The rotating shaft is rotatably supported at opposite ends thereof by the housing via a pair of bearings (not shown). The rotor10is configured to be fixedly fitted on the rotating shaft so as to rotate along with the rotating shaft.

As shown inFIGS. 1 and 2, the rotor10includes a rotor core11, a plurality of permanent magnets13embedded in the rotor core11, and a filler14filled in void spaces formed between the rotor core11and the permanent magnets13. That is to say, in the present embodiment, the rotor10is configured as an Interior Permanent Magnet (IPM) rotor.

The rotor core11is formed, by axially laminating a plurality of annular magnetic steel sheets, into a hollow cylindrical shape. Consequently, at the radial center of the rotor core11, there is formed a through-hole11a, in which the rotating shaft is to be fixedly fitted so as to rotate together with the rotor core11.

The permanent magnets13are embedded in the rotor core11so as to form a plurality of magnetic poles of the rotor10on the radially outer periphery of the rotor core11. The magnetic poles are equally spaced in the circumferential direction of the rotor core11at predetermined intervals so that the polarities of the magnetic poles alternate between north and south in the circumferential direction. In addition, in the present embodiment, the number of the magnetic poles of the rotor10is equal to, for example, 12 (i.e., 6 north poles and 6 south poles).

More specifically, in the present embodiment, the rotor core11has a plurality (e.g., 12) of pairs of magnet-receiving holes12formed in the vicinity of the radially outer periphery of the rotor core11. Each of the magnet-receiving holes12extends in the axial direction of the rotor core11so as to penetrate the rotor core11in the axial direction. Further, each of the magnet-receiving holes12has a cross section perpendicular to the longitudinal axis O of the rotor core11, the shape of which is a variation of a rectangle.

In addition, it should be noted that though there is shown only one pair of the magnet-receiving holes12inFIGS. 1 and 2, the plurality of pairs of the magnet-receiving holes12are equally spaced in the circumferential direction of the rotor core11at predetermined intervals.

Moreover, in the present embodiment, each pair of the magnet-receiving holes12is arranged so as to form a substantially V-shape that opens toward the radially outer periphery of the rotor core11. Further, for each pair of the magnet-receiving holes12, there is formed a corresponding center bridge15of the rotor core11which extends in a radial direction of the rotor core11to separate the two magnet-receiving holes12of the pair from each other. The corresponding center bridge15is provided for causing magnetic flux saturation and thereby impeding formation of a magnetic circuit between the two magnet-receiving holes12.

Furthermore, for each pair of the magnet-receiving holes12, the two magnet-receiving holes12of the pair are symmetrically formed with respect to the corresponding center bridge15; the width directions of the two magnet-receiving holes12respectively coincide with the extending directions of the two sides of the substantially V-shape formed by the two magnet-receiving holes12. In addition, both the longitudinal directions of the two magnet-receiving holes12are parallel to the longitudinal axis O of the rotor core11.

Each of the permanent magnets13is inserted in a corresponding one of the magnet-receiving holes12of the rotor core11so as to extend in the axial direction of the rotor core11. Further, each of the permanent magnets13has a substantially rectangular cross section perpendicular to the axial direction of the rotor core11(i.e., the direction of the longitudinal axis O of the rotor core11). That is to say, in the present embodiment, each of the permanent magnets13has a substantially cuboid shape.

Moreover, for each pair of the magnet-receiving holes12of the rotor core11, the two permanent magnets13which are respectively inserted in the two magnet-receiving holes12of the pair are arranged so that the polarities (north or south) of the two permanent magnets13are the same on the radially outer periphery of the rotor core11. Consequently, the two permanent magnets13together form one of the magnetic poles of the rotor10on the radially outer periphery of the rotor core11. In addition, as shown inFIG. 1, when viewed along the axial direction of the rotor core11, the two permanent magnets13are symmetrically arranged and extend obliquely with respect to a centerline C1of the magnetic pole; the centerline C1extends in the radial direction, along which the corresponding center bridge15of the rotor core11is formed, and bisects the magnetic pole in the circumferential direction of the rotor core11. Consequently, the two permanent magnets13also together form a substantially V-shape that opens radially outward (i.e., toward the radially outer periphery of the rotor core11).

Furthermore, in the present embodiment, for each of the magnet-receiving holes12of the rotor core11, there is formed a first protrusion20that protrudes from the corresponding center bridge15of the rotor core11inward of the magnet-receiving hole12, so as to position the corresponding permanent magnet13in the circumferential direction of the rotor core13on the corresponding center bridge15side. Further, the first protrusion20is offset radially outward from a radial center position of the corresponding center bridge15. In other words, the first protrusion20is positioned closer to the radially outer end than the radially inner end of the corresponding center bridge15. Moreover, at the two corner portions of the magnet-receiving hole12respectively on opposite sides of the first protrusion20, there are respectively formed first and second magnetic flux barriers16and17. Consequently, a first wall surface12aof the magnet-receiving hole12, which extends perpendicular to the width direction of the magnet-receiving hole12on the centerline C1side, is formed only at a distal end of the first protrusion20.

The first magnetic flux barrier16is formed at the corner portion12c(to be referred to as the radially innermost corner portion12chereinafter) between the first wall surface12aand a second wall surface12bof the magnet-receiving hole12; the second wall surface12bextends in the width direction of the magnet-receiving hole12on the radially inner side. The first magnetic flux barrier16is defined by a curved surface that includes three or more single-curvature surfaces having different curvatures.

More particularly, in the present embodiment, as shown inFIG. 3, the curve surface includes first to fourth continuous single-curvature surfaces16a-16d. The first single-curvature surface16a(A-B) has a radius of curvature R1and its center of curvature P1located radially outside of the curved surface. The second single-curvature surface16b(B-C) has a radius of curvature Rb1and its center of curvature P2located radially outside of the curved surface. The third single-curvature surface16c(C-D) has a radius of curvature R3and its center of curvature P3located radially outside of the curved surface. The fourth single-curvature surface16d(D-E) has a radius of curvature R4and its center of curvature P4located radially inside of the curved surface.

Among the curvatures of the first to the fourth single-curvature surfaces16a-16d, the curvature of the second single-curvature surface16bis the minimum. Moreover, among the first to the fourth single-curvature surfaces16a-16d, the second single-curvature surface16bis positioned closest to the longitudinal axis O of the rotor core11. Therefore, it is easiest for centrifugal stress (i.e., stress induced by centrifugal force) to concentrate on the second single-curvature surface16bamong the first to the fourth single-curvature surfaces16a-16d. However, the second single-curvature surface16bis arranged away from the corresponding center bridge15on which it is also easy for centrifugal stress to concentrate. Consequently, with the above arrangement, it is possible to distribute stress concentration in the rotor core11.

Furthermore, the fourth single-curvature surface16d, which is provided between the third single-curvature surface16cand the second wall surface12bof the magnet-receiving hole12, is convex radially outward while the third single-curvature surface16cis convex radially inward. That is, the third and fourth single-curvature surfaces16cand16dare formed so as to be respectively convex toward opposite directions. Consequently, it is possible to smoothly connect the third single-curvature surface16cand the second wall surface12bof the magnet-receiving hole12with the fourth single-curvature surface16d.

In addition, the first single-curvature surface16amay be connected to the first protrusion20via any suitable flat or curved surface.

The second magnetic flux barrier17is formed at the corner portion between the first wall surface12aand a third wall surface12dof the magnet-receiving hole12; the third wall surface12dextends in the width direction of the magnet-receiving hole12on the radially outer side. The second magnetic flux barrier17is provided for causing a magnetic short circuit along the centerline C1of the magnetic pole (or along the corresponding center bridge15). In addition, the second magnetic flux barrier17is formed so as to protrude radially outward from the third wall surface12dof the magnet-receiving hole12at a predetermined circumferential width and by a predetermined height.

Moreover, at the end of the second wall surface12bof the magnet-receiving hole12on the opposite side to the corresponding center bridge15, there is formed a second protrusion21for positioning the corresponding permanent magnet13in the circumferential direction of the rotor core11on the opposite side to the corresponding center bridge15. Further, on the radially outside of the second protrusion21, there is formed a third magnetic flux barrier18.

Furthermore, the filler14is filled in all of the gaps between the wall surfaces of the magnet-receiving hole12and the corresponding permanent magnet13and the first to the third magnetic flux barriers16-18, thereby fixing the corresponding permanent magnet13in the magnet-receiving hole12. That is, the first to the third magnetic flux barriers16-18are filled with the filler14. In addition, the filler14is made of a nonmagnetic material, such as epoxy resin.

After having described the configuration of the rotor10according to the present embodiment, advantages thereof will be described hereinafter.

In the present embodiment, the rotor10includes the hollow cylindrical rotor core11and the permanent magnets13. The rotor core11has the longitudinal axis O and the plurality of pairs of the magnet-receiving holes12formed therein. Each pair of the magnet-receiving holes12are arranged in the substantially V-shape that opens toward the radially outer periphery of the rotor core11. Each of the permanent magnets13is received in the corresponding one of the magnet-receiving holes12of the rotor core11. For each pair of the magnet-receiving holes12, the two permanent magnets13which are respectively received in the two magnet-receiving holes12of the pair are arranged so as to together form one magnetic pole of the rotor10. The rotor core11further has, for each pair of the magnet-receiving holes12, the corresponding center bridge15that extends in the radial direction of the rotor core11between the two magnet-receiving holes12of the pair to separate them from each other. For each of the magnet-receiving holes12, there are also formed the first protrusion20and the first magnetic flux barrier16in the rotor core11. The first protrusion20protrudes from the corresponding center bridge15inward of the magnet-receiving hole12, so as to position the corresponding magnet13received in the magnet-receiving hole12. The first protrusion20is positioned closer to the radially outer end of the corresponding center bridge15than the radially inner end of the corresponding center bridge15. The first magnetic flux barrier16is positioned at the radially innermost corner portion12cof the magnet-receiving hole12and defined by the curved surface that includes three or more single-curvature surfaces having different curvatures. Among the single-curvature surfaces, the second single-curvature surface16bwhich has the minimum curvature is positioned closest to the longitudinal axis O of the rotor core11.

With the above configuration, the first protrusion20, which would be provided at the radially innermost corner portion12cof the magnet-receiving hole12according to the prior art, is offset radially outward from the radial center position of the corresponding center bridge15. Consequently, the influence of the first protrusion20on generation of centrifugal stress in the corresponding center bridge15is reduced, thereby preventing excessive stress concentration from occurring in the corresponding center bridge15.

Moreover, with the above configuration, it is easiest for centrifugal stress to concentrate on the second single-curvature surface16bamong the single-curvature surfaces of the curved surface defining the first magnetic flux barrier16. However, the second single-curvature surface16bis located away from the corresponding center bridge15. Consequently, it is possible to distribute stress concentration in the rotor core11. In other words, it is possible to prevent excessive stress concentration from occurring in the rotor core11.

Furthermore, with the above configuration, the first protrusion20, at which a maximum thermal stress may occur, is positioned away from the radially innermost corner portion12c. Consequently, thermal stress concentration will not occur at the same areas of the rotor core11as centrifugal stress concentration. As a result, it is possible to reduce the total stress concentration in the rotor core11.

Moreover, in the present embodiment, the curved surface which defines the first magnetic flux barrier16includes the first single-curvature surface16ahaving the radius of curvature R1and its center of curvature P1located radially outside of the curved surface, the second single-curvature surface16bhaving the radius of curvature Rb1and its center of curvature P2located radially outside of the curved surface, and the third single-curvature surface16chaving the radius of curvature R3and its center of curvature P3located radially outside of the curved surface.

With the above configuration, it is possible to easily realize the first magnetic flux barrier16having the above-described advantageous effects.

In the present embodiment, the curved surface which defines the first magnetic flux barrier16further includes the fourth single-curvature surface16dbetween the third single-curvature surface16cand the second wall surface12bof the magnet-receiving hole12. The fourth single-curvature surface16dhas the radius of curvature R4and its center of curvature P4located radially inside of the curved surface.

With the above configuration, the third and fourth single-curvature surfaces16cand16dare respectively convex toward opposite directions. Consequently, it is possible to smoothly connect the third single-curvature surface16cand the second wall surface12bof the magnet-receiving hole12with the fourth single-curvature surface16d.

In the present embodiment, for each of the magnet-receiving holes12of the rotor core11, there is also formed, radially outside of the first protrusion20, the second magnetic flux barrier17for causing a magnetic short circuit along the corresponding center bridge15.

Consequently, with the second magnetic flux barrier17, the total area in which stress occurs is increased, thereby reducing stress concentration on the corresponding center bridge15. Moreover, it is possible to enhance magnetic flux saturation at the corresponding center bridge15, thereby improving the performance of the motor.

Second Embodiment

This embodiment illustrates a rotor10which has almost the same configuration as the rotor10according to the first embodiment; accordingly, only the differences therebetween will be described hereinafter.

In the first embodiment, for each of the magnet-receiving holes12of the rotor core11, there is formed, at the radially innermost corner portion12cof the magnet-receiving hole12, the first magnetic flux barrier16which is defined by the curved surface that includes the first to the fourth continuous single-curvature surfaces16a-16d(seeFIG. 3).

In comparison, in the present embodiment, as shown inFIG. 4, for each of the magnet-receiving holes12of the rotor core11, there is formed, at the radially innermost corner portion12cof the magnet-receiving hole12, a first magnetic flux barrier116. The first magnetic flux barrier116is defined by a curved surface that includes first to sixth continuous single-curvature surfaces16e-16jhaving different curvatures.

The first single-curvature surface16e(G-H) has a radius of curvature R5and its center of curvature P5located radially outside of the curved surface. The second single-curvature surface16f(H-I) has a radius of curvature R6and its center of curvature P6located radially outside of the curved surface. The third single-curvature surface16g(I-J) has a radius of curvature Rb1and its center of curvature P7located radially outside of the curved surface. The fourth single-curvature surface16h(J-K) has a radius of curvature R8and its center of curvature P8located radially outside of the curved surface. The fifth single-curvature surface16i(K-L) has a radius of curvature R9and its center of curvature P9located radially outside of the curved surface. The sixth single-curvature surface16j(L-M) has a radius of curvature R10and its center of curvature P10located radially inside of the curved surface.

Among the curvatures of the first to the sixth single-curvature surfaces16e-16j, the curvature of the third single-curvature surface16gis the minimum. Moreover, among the first to the sixth single-curvature surfaces16e-16j, the third single-curvature surface16gis positioned closest to the longitudinal axis O of the rotor core11. Therefore, it is easiest for centrifugal stress to concentrate on the third single-curvature surface16gamong the first to the sixth single-curvature surfaces16e-16j. However, the third single-curvature surface16gis arranged away from the corresponding center bridge15on which it is also easy for centrifugal stress to concentrate. Consequently, with the above arrangement, it is possible to distribute stress concentration in the rotor core11.

Furthermore, in the present embodiment, on one side (i.e., the first protrusion20side) of the third single-curvature surface16g, there are provided the first and second single-curvature surfaces16eand16f. On the other side (i.e., the second wall surface12bside) of the third single-curvature surface16g, there are provided the fourth, fifth and sixth single-curvature surfaces16h,16iand16j.

That is to say, in the present embodiment, the curved surface which defines the first magnetic flux barrier116includes, on each of opposite sides of the third single-curvature surface16gwhich has the minimum curvature, a plurality of continuous single-curvature surfaces having different curvatures.

With the above configuration, it is possible to more suitably vary the curvatures of the single-curvature surfaces included in the curved surface defining the first magnetic flux barrier116, thereby more reliably reducing stress concentration on the curved surface.

While the above particular embodiments have been shown and described, it will be understood by those skilled in the art that various modifications, changes, and improvements may be made without departing from the spirit of the invention.

For example, in the previous embodiments, the invention is directed to the rotor10for a vehicular motor. However, the invention can also be applied to a rotor for an electric generator or a rotor for a motor generator that can selectively function either as an electric motor or as an electric generator.

In particular, for a rotor which is used in a rotating electric machine with a gear or a large-diameter shaft provided radially inside of the rotor, remarkable local stress concentration may occur at the radially innermost corner portion of each of the magnet-receiving holes of the rotor core. Therefore, when the present invention is applied to such a rotor, it is possible to maximally achieve the advantageous effects of the invention as described in the previous embodiments.