Rotor and motor

A rotor includes a first rotor core, a second rotor core, a field magnet, and a back magnet. The first rotor core includes a disk-shaped first core base and a plurality of first claw-poles. The second rotor core includes a disk-shaped second core base and a plurality of second claw-poles. The field magnet has the first claw-poles function as first magnetic poles and the second claw-poles function as second magnetic poles. The back magnet is arranged along back surfaces of the first and second claw-poles. The back magnet is magnetized such that radially outer sections have the polarities that are the same as the first and second magnetic poles. The back magnet is formed integrally, has an annular shape, and is in contact with all of the back surfaces of the first and second claw-poles.

BACKGROUND OF THE INVENTION

The present invention relates to a rotor and a motor.

A rotor of a motor may have a so-called Lundell-type construction using a permanent magnet field and including a pair of rotor cores and a field magnet (refer to, for example, Japanese Laid-Open Utility Model Publication No. 5-43749). Each of the two rotor cores includes a plurality of claw-poles arranged along a circumferential direction. The two rotor cores are joined with each other. The field magnet is arranged between the two rotor cores so that the claw-poles of the two rotor cores alternately function as different magnetic poles.

In the rotor described in Japanese Laid-Open Utility Model Publication No. 5-43749, a back magnet (auxiliary magnet in the document) is arranged between the back surface of the claw-poles (inner circumferential surface of flange in the document) and the field magnet to reduce leakage flux. Further, as shown inFIG. 3of the document, the back magnet is annularly integrated, for example, to reduce the number of components.

In the rotor described above, the number of components is reduced by annularly integrating the back magnet. However, it is desirable that leakage flux be further suppressed.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a rotor and a motor capable of suppressing leakage flux without increasing the number of components.

One aspect of the present invention is a rotor including a first rotor core, a second rotor core, a field magnet, and a back magnet. The first rotor core includes a disk-shaped first core base and a plurality of first claw-poles arranged at equal intervals on an outer circumferential portion of the first core base. Each of the first claw-poles projects outward in a radial direction and extends in an axial direction. The second rotor core includes a disk-shaped second core base and a plurality of second claw-poles arranged at equal intervals on an outer circumferential portion of the second core base. Each of the second claw-poles projects outward in the radial direction and extends in the axial direction. Each of the second claw-poles is arranged between corresponding ones of the first claw-poles. The field magnet is arranged between the first core base and the second core base in the axial direction. The field magnet is magnetized in the axial direction so that the first claw-poles each function as a first magnetic pole and the second claw-poles each function as a second magnetic pole. The back magnet is arranged along a back surface of each of the first and second claw-poles. The back magnet is magnetized so that radially outer sections of the back magnet have polarities that are the same as the first and second magnetic poles. The back magnet is integrally formed, has an annular shape, and is in contact with all of the back surfaces of the first and second claw-poles.

A further aspect of the present invention includes a first rotor core, a second rotor core, a field magnet, and a back magnet. The first rotor core includes a disk-shaped first core base and a plurality of first claw-poles arranged at equal intervals on an outer circumferential portion of the first core base. Each of the first claw-poles projects outward in a radial direction and extends in an axial direction. The second rotor core includes a disk-shaped second core base and a plurality of second claw-poles arranged at equal intervals on an outer circumferential portion of the second core base. Each of the second claw-poles projects outward in the radial direction and extends in the axial direction. Each of the second claw-poles is arranged between corresponding ones of the first claw-poles. The field magnet is arranged between the first core base and the second core base in the axial direction. The field magnet is magnetized in the axial direction so that the first claw-poles each function as a first magnetic pole and the second claw-poles each function as a second magnetic pole. The back magnet is arranged along a back surface of each of the first and second claw-poles. The back magnet is magnetized so that radially outer sections of the back magnet have polarities that are the same as the first and second magnetic poles. The back magnet includes magnet blocks, the number of which is the same as the number of pole pairs. Each magnet block includes a first back magnet portion, arranged along the back surface of a corresponding one of the first claw-poles, and a second back magnet portion, arranged on the back surface of a corresponding one of the second claw-poles. The first back magnet portion and the second back magnet portion are adjacent in a circumferential direction and formed integrally. The first and second back magnet portions are in contact with all of the back surfaces of the first and second claw-poles.

DETAILED DESCRIPTION OF THE INVENTION

First Embodiment

As shown inFIG. 1, a motor case2of a motor1includes a tubular housing3, which includes a closed end3a, and a front end plate4, which closes the open front end (left end as viewed inFIG. 1) of the tubular housing3. A circuit accommodation box5, which accommodates a power supply circuit of a circuit substrate and the like, is coupled to the back end (right end as viewed inFIG. 1) of the tubular housing3. A stator6is fixed to an inner circumferential surface of the tubular housing3. The stator6includes an armature core7, from which teeth inwardly extend in the radial direction, and a segment conductor (SC) winding8, which is wound around the teeth of the armature core7. A rotor11of the motor1includes a rotation shaft12and is arranged inside the stator6. The rotation shaft12is a non-magnetic metal shaft and supported to be rotatable by bearings13and14, which are respectively arranged on the closed end3aof the tubular housing3and the front end plate4.

As shown inFIGS. 2 and 3, the rotor11includes first and second rotor cores21and22, an annular magnet23(seeFIG. 3), and a back magnet24. The solid line arrows inFIGS. 2 and 4indicate the magnetization direction (from S pole toward N pole) of the magnets23and24.

As shown inFIGS. 2 and 3, the first rotor core21includes a generally disk-shaped first core base21aand a plurality of (five in the present embodiment) first claw-poles21barranged at equal intervals along an outer circumferential portion of the first core base21a. Each of the first claw-poles21bprojects outward in the radial direction and extends in the axial direction. Each first claw-pole21bincludes circumferential end faces21cand21dthat are flat surfaces and extend in the radial direction (not inclined relative to the radial direction as viewed from the axial direction). Further, each first claw-pole21bhas a sectoral cross-section in the radial direction. The angle between the circumferential end faces21cand21dof each first claw-pole21b, which is referred to as the circumferential angle, is set to be smaller than the angle of the interval between adjacent ones of the first claw-poles21bin the circumferential direction.

As shown inFIGS. 2 and 3, the second rotor core22, which has a shape identical to the first rotor core21, includes a generally disk-shaped second core base22aand a plurality of second claw-poles22barranged at equal intervals along an outer circumferential portion of the second core base22a. Each of the second claw-poles22bprojects outward in the radial direction and extends in the axial direction. Each second claw-pole22bincludes circumferential end faces22cand22dthat are flat surfaces and extend in the radial direction. Further, each second claw-pole22bhas a sectoral cross-section in the radial direction. The angle between the circumferential end faces22cand22dof each second claw-pole22b, which is referred to as the circumferential angle, is set to be smaller than the angle of the interval between adjacent ones of the second claw-poles22bin the circumferential direction. The second rotor core22is coupled to the first rotor core21so that the second claw-poles22bare arranged between the first claw-poles21b. The annular magnet23(seeFIG. 4) is arranged (held) between the first core base21aand the second core base22ain the axial direction. In this case, the circumferential end face21cof each first claw-pole21bextends parallel in the axial direction to the opposing circumferential end face22dof the adjacent second claw-pole22b. This forms a generally straight gap extending in the axial direction between the end faces21cand22d. Further, the other circumferential end face21dof each first claw-pole21bextends parallel in the axial direction to the opposing circumferential end face22cof the adjacent second claw-pole22b. This forms a generally straight gap extending in the axial direction between the end faces21dand22c.

As shown inFIG. 3, the annular magnet23has the same outer diameter as the first and second core bases21aand22a, that is, the first and second rotor cores21and22less the claw-poles21band22b. The annular magnet23is magnetized in the axial direction so that each first claw-poles21bfunctions as a first magnetic pole (N pole in the present embodiment) and each second claw-pole22bfunctions as a second magnetic pole (S pole in the present embodiment). Accordingly, the rotor11of the present embodiment has a so-called Lundell-type construction that uses the annular magnet23as a field magnet. In the rotor11, the first claw-poles21b, which function as the N poles, and the second claw-poles22b, which function as the S poles, are alternately arranged in the circumferential direction. There are a total of ten magnetic poles (five pole pairs). Since the number of pole pairs is an odd number of three or greater, claw-poles of the same polarity are not arranged at opposing positions separated by 180° in the circumferential direction in each rotor cores. This provides a shape that stabilizes magnetic vibration.

As shown inFIG. 4, the back magnet24is integrally formed with an annular shape and includes first back magnet portions25, second back magnet portions26, and continuous portions27arranged between the back magnet portions25and26. The back magnet24does not have recesses and projections in the radial direction. Thus, the back magnet24has an outer surface and an inner surface in the radial direction forming true circles as viewed in the axial direction.

Referring toFIGS. 2 to 4, the first back magnet portions25are arranged between back surfaces21e(radially inner surfaces) of the first claw-poles21band an outer circumferential surface22fof the second core base22a. Each first back magnet portion25, which has a sectoral cross-section in the radial direction, and is magnetized so that the section (radially outer side) that comes into contact with the back surface21eof the corresponding first claw-pole21bbecomes the N pole, which is the same polarity as the first claw-pole21b, and the section that comes into contact with the outer circumferential surface22fof the second core base22abecomes the S pole, which is the same polarity as the second core base22a.

The second back magnet portions26are arranged between back surfaces22e(radially inner surfaces) of the second claw-poles22band an outer circumferential surface21fof the first core base21a, as shown inFIGS. 2 to 4. Each second back magnet portion26has a sectoral cross-section in the radial direction, and is magnetized so that the section (radially outer side) that comes into contact with the back surface22eof the corresponding second claw-pole22bbecomes the S pole, and the section that comes into contact with the outer circumferential surface21fof the first core base21abecomes the N pole.

The first back magnet portions25and the second back magnet portions26each have a length in the axial direction set so that the first back magnet portions25and the second back magnet portions26extend from an axial end face of the rotor11to an axial position corresponding to where the annular magnet23is located. In other words, the first and second back magnet portions25and26have axial lengths that are substantially the same as the back surfaces21eand22eof the first and second claw-poles21band22b. Further, the first and second back magnet portions25and26are configured so that the back surfaces21eand22eof the first and second claw-poles21band22bentirely come into contact with the first and second back magnet portions25and26in the radial direction. As a result, when viewed from the radial direction, the back magnet24includes alternately arranged portions shifted back and forth toward one axial side (first back magnet portion25) and the other axial side (second back magnet portion26). In this manner, the back magnet24is zigzagged in the axial direction so that sets of a ridge and a valley, the number of which is the same as the number of pole pairs, are arranged continuously in the circumferential direction.

As shown inFIGS. 2 and 4, the continuous portions27extend continuously in the circumferential direction between the first back magnet portions25and the second back magnet portions26. As shown inFIG. 2, the continuous portion27is configured to be longer than the first and second back magnet portions25and26in the axial direction and have substantially the same axial length as the first claw-poles21band the second claw-poles22b.

A magnetization method of the back magnet24and the annular magnet23will now be described.

FIG. 6shows a first magnetizing device31that magnetizes the annular magnet23. The first magnetizing device31includes magnetizing portions31aand31bhaving different magnetic poles and respectively facing the upper and lower surfaces of the annular magnet23as viewed in the drawings. This magnetizes the annular magnet23in the thickness direction (axial direction) of the annular magnet23.FIGS. 5 and 6show a second magnetizing device32that magnetizes the back magnet24. The second magnetizing device32includes magnetizing portions32aand32bhaving different magnetic poles. The magnetizing portions32aand32bare arranged to face the back magnet24. The second magnetizing device32entirely magnetizes the back magnet24from an outer surface (radially outer surface) of the back magnet24. Specifically, the back magnet24is magnetized to form curved magnetic fluxes extending between adjacent back magnet portions25and26. In this manner, the back magnet24undergoes polar anisotropic orientation.

With regard to the magnetizing order of the annular magnet23and the back magnet24, simultaneous magnetization of the annular magnet23and the back magnet24is advantageous in that this would reduce magnetizing steps. However, by magnetizing the annular magnet23and the back magnet24at different timings, magnetic flux interference would not occur between the annular magnet23and the back magnet24. In particular, by first magnetizing the annular magnet23, magnetization of the annular magnet23would be ensured. By first magnetizing the back magnet24, magnetization of the back magnet24would be ensured.

The operation of the rotor11of the first embodiment will now be described.

The rotor11of the motor1of the first embodiment includes the back magnet24, which is integrally formed with an annular shape. The first and second back magnet portions25and26of the back magnet24have the same axial length as the back surfaces21eand22eof the first and second claw-poles21band22b. Thus, when the back magnet24including the first and second back magnet portions25and26is coupled to the first and second rotor cores21and22, the first and second back magnet portions25and26automatically come into contact with all of the back surfaces21eand22e. This further suppresses leakage flux.

The first embodiment has the advantages described below.

(1) The leakage flux is suppressed by using the back magnet24. Further, the first and second back magnet portions25and26of the back magnet24come into contact with all of the back surfaces21eand22eof the claw-poles21band22b. This further suppresses generation of leakage flux. Moreover, the back magnet24is formed integrally with an annular shape. This decreases the number of components.

(2) The back magnet24is a polar anisotropic magnet and thus generates strong magnetic fluxes directed in specific directions at the claw-poles21band22b. The back magnet24thus effectively obtains rotor torque.

(3) The back magnet24of the first embodiment is free from recesses and projections in the radial direction. In other words, the back magnet24is formed so that the radially outer surface and the radially inner surface are true circles as viewed from the axial direction. The back magnet24thus has a simple shape and may easily be magnetized by the magnetizing device32.

Second Embodiment

A second embodiment of the present invention will now be described with reference toFIGS. 11 to 17. The second embodiment differs from the first embodiment in the structure of the back magnet24. Thus, only the structure of the back magnet24will be described below in detail.

As shown inFIGS. 11 to 13B, the back magnet24includes a plurality of (five in the present embodiment) magnet blocks29. The number of magnet block portions is the same as the number of pole pairs. Each magnet block29includes a first back magnet portion25and a second back magnet portion26that are integrally formed.

As shown inFIGS. 14 and 15, the magnet blocks29are arranged in the circumferential direction with a predetermined gap K provided between one another in the circumferential direction. As shown inFIG. 15, the magnet blocks29are arranged so that hypothetical circles extending along the inner and outer circumferential surface of the magnet blocks29form substantially true circles as viewed from the axial direction.

As shown inFIGS. 11 to 13B, the first back magnet portion25of each magnet block29is arranged between the back surface21e(radially inner side) of a first claw-pole21band the outer circumferential surface22fof the second core base22a. The first back magnet portion25has a sectoral cross-section in the radial direction, and is magnetized so that the section (radially outer side) that comes into contact with the back surface21eof the first claw-pole21bbecomes the N pole, which is the same polarity as the first claw-pole21b, and the portion that comes into contact with the outer circumferential surface22fof the second core base22abecomes the S pole, which is the same polarity as the second core base22a. The first back magnet portion25of the second embodiment is formed to be wider in the circumferential direction that the back surface21eof the corresponding first claw-pole21b.

As shown inFIGS. 11 to 13A, the second back magnet portion26of each magnet block29is arranged between the back surface22e(radially inner side) of the second claw-pole22band the outer circumferential surface21fof the first core base21a. The second back magnet portion26has a sectoral cross-section in the radial direction, and is magnetized so that the section (radially outer side) that comes into contact with the back surface22eof the second claw-pole22bbecomes the S pole, and the portion that comes into contact with the outer circumferential surface21fof the first core base21abecomes the N pole. The second back magnet portion26of the second embodiment is formed to be wider in the circumferential direction than the back surface22eof the second claw-pole22b.

Referring toFIGS. 11 and 12, the first back magnet portions25and the second back magnet portions26each have a length in the axial direction set so that the first back magnet portions25and the second back magnet portions26extend from an axial end face of the rotor11to an axial position corresponding to where the annular magnet23is located. In other words, the first and second back magnet portions25and26have axial lengths that are substantially the same as the back surfaces21e,22eof the first and second claw-poles21band22b. Further, the first and second back magnet portions25and26are configured so that the back surfaces21eand22eof the first and second claw-poles21band22bentirely come into contact with the first and second back magnet portions25and26in the radial direction.

The first back magnet portion25and the second back magnet portion26of each magnet block29have substantially the same axial length. The first back magnet portion25and the second back magnet portion26are separated from each other shifted in the axial direction. Thus, the magnet block29has steps when viewed from the radial direction. As a result, the arrangement of the magnet blocks29in the circumferential direction alternately arranges the first back magnet portions25and the second back magnet portions26in the circumferential direction with steps formed in the axial direction.

As viewed from the axial direction, the radially outer surfaces of the first back magnet portions25and the second back magnet portions26have the same curvature. Further, the radially inner surfaces of the first back magnet portions25and the second back magnet portions26have the same curvature.

The magnetization method of the back magnet24and the annular magnet23of the second embodiment shown inFIGS. 16 and 17is similar to the first embodiment will not be described.

The operation of the rotor11of the second embodiment will now be described.

The rotor11of the motor1of the second embodiment includes the back magnet24that is formed integrally with an annular shape. The first and second back magnet portions25and26of the back magnet24have the same axial lengths as the back surfaces21eand22eof the first and second claw-poles21band22b. Thus, when the back magnet24including the first and second back magnet portions25and26is coupled to the first and second rotor cores21and22, the first and second back magnet portions25and26automatically come into contact with all of the back surfaces21eand22e. This further suppressing leakage flux. Moreover, the back magnet24is formed by the magnet blocks29, each including a set of the first and second back magnet portions25and26. Thus, each magnet block29may easily be magnetized.

In addition to advantages (1) and (2) of the first embodiment, the second embodiment has the following advantage.

(4) The back magnet24of the second embodiment free from recesses and projections in the radial direction. Thus, the back magnet24is formed so that the radially outer surfaces of the first back magnet portion25and the second back magnet portion26in each magnet block29are arcuate and have the same curvature as viewed in the axial direction. Further, the radially inner surfaces of the first back magnet portion25and the second back magnet portion26in each magnet block29are arcuate and have the same curvature as viewed in the axial direction. In this manner, the magnet block29of the back magnet24has a simple shape and may easily be magnetized by the magnetizing device32.

Referring toFIGS. 7 to 9, in the first embodiment, inter-pole magnets28may be arranged between adjacent ones of the first claw-poles21band the second claw-poles22bin the circumferential direction. The inter-pole magnets28are magnetized in the circumferential direction so that sections of the same polarity face each other between the inter-pole magnets28and the first and second claw-poles21band22b. Thus, the section of each inter-pole magnet28located closer to the first claw-pole21bfunctions as the N pole, and the section of each inter-pole magnet28located closer to the second claw-pole22bfunctions as the S pole. This structure suppresses the generation of leakage flux between the claw-poles.

The second embodiment may also include inter-pole magnets arranged between the first claw-poles21band the second claw-poles22bin the circumferential direction (not shown). This structure also suppresses the generation of leakage flux between the claw-poles.

In the first and second embodiments, the back magnet24is configured by the polar anisotropic magnet but may be formed by a different type of anisotropic magnet. Further referring toFIGS. 10 and 18, the first back magnet portions25and the second back magnet portions26of the back magnet24may be magnetized in the radial direction.

The back magnet24may be formed by, for example, a sintered magnet or a bond magnet (plastic magnet, rubber magnet, or the like). This allows for the back magnet24to be formed through, for example, either one of compression molding and injection molding and allows for different manufacturing processes. Further, the back magnet24may be manufactured using a versatile material such as ferrite magnet, SmFeN magnet, SmCo magnet, neodymium magnet, and the like. Moreover, any of various types of magnets may be used as the inter-pole magnet28.

In the first and second embodiments, a single annular magnet23is used as the field magnet. Instead, a permanent magnet may be divided into segments that are arranged between the first and second core bases21aand22ain the axial direction around the rotation shaft12.

In the first and second embodiments, the first and second rotor cores21and22and the armature core7may be formed, for example, by stacking magnetic metal plates or molding a magnetic powder.

In the first and second embodiments, coils may be wound around the teeth of the stator6in a concentrated winding or a distributed winding.