Permanent magnet rotor

Details Permanent magnet rotor Permanent magnet rotor

2003-01-17

2004-05-25

Mullins, Burton (Department: 2834)

Electrical generator or motor structure

Dynamoelectric

Rotary

C310S156480, C310S156560, C310S261100

Reexamination Certificate

active

06741003

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a permanent magnet rotor in a permanent magnet type rotary electric device such as, for example, a permanent magnet electric motor or a permanent magnet generator, and particularly relates to an embedded magnet type permanent magnet rotor, suited for use in an inner rotor type permanent magnet rotary electric device for effecting decreased torque ripples and cogging torque.
2. Description of the Related Art
A conventional embedded magnet type permanent magnet rotor has been disclosed, for example, in Laid Open Japanese Patent Application Hei-11-262205 or Hei-11-206075, and is illustrated in
FIG. 12
herein. The permanent magnet rotor is illustrated in
FIG. 12
with respect to the shape of one pole of the rotor in end view. The rotor has a rotor core
1
formed with a plurality of slits
2
A,
2
B,
2
C in multiple layers. Each of the slits
2
A,
2
B,
2
C has an end face in the shape of an arc. The arc is configured such that the longitudinal ends of the arc are located in the vicinity of the outside circumferential surface of the rotor core
1
and such that the longitudinal middle portion of the arc is located radially inwardly of the end portions. Each slit
2
A,
2
B,
2
C extends to the opposite end of the rotor core
1
in the axial direction (i.e., perpendicular to the plane of FIG.
12
), and each slit has the same cross sectional shape through its length as the shape of the end face shown in FIG.
12
.
In order to form a permanent magnet rotor
10
having a rotor core
1
with permanent magnets embedded, bond magnet (plastic magnet) may be filled in the slits
2
A,
2
B,
2
C and solidified. That is, the bond magnets in the slits
2
A,
2
B,
2
C are formed by injection molding. Preferably, the bond magnet is filled in a magnetic field. Alternatively, permanent magnets are machined respectively in the shapes of the slits
2
A,
2
B,
2
C, and are fitted in the slits
2
A,
2
B,
2
C. As shown in the permanent magnet rotor
10
of
FIG. 12
, bridges
3
of a certain thickness are formed between the longitudinal ends (portions close to the outside circumferential surface of the rotor core
1
) of the slits
2
A,
2
B,
2
C and the outside circumferential surface of the core
1
. Thus, the radially outer portions of the rotor core
1
proximate to each slit
2
A,
2
B,
2
C (i.e., the portions of the rotor core proximate to the outside circumferential surface of each slit) and the radially inner portions of the rotor core
1
(i.e., the portions of the rotor core on the center axis side of each slit) will not be perfectly separated by the slits
2
A,
2
B,
2
C. Rather, the bridges provide magnetic paths between the portions of the rotor core on either side of each of the slits
2
A,
2
B,
2
C.
In the conventional permanent magnet rotor
10
described above, the distribution of magnetic flux density formed in the clearance between the rotor and the stator when the rotor is assembled in a rotary electric device is shown in FIG.
13
. As illustrated, the distribution of the flux density is in the shape of approximately a rectangular wave, so that the distortion factor is large. The large distortion factor results in increased torque ripples and cogging torque.
SUMMARY OF THE INVENTION
The embodiments of the present invention are directed to a permanent magnet rotor that has decreased torque ripples and cogging torque.
One aspect of the present invention is an embodiment of a permanent magnet rotor having a rotor core that comprises a plurality of magnetic poles. The rotor core includes a plurality of permanent magnets embedded in slit sections formed in layers for each magnetic pole. The layers comprise a radially innermost layer, a least one intermediate layer, and a radially outermost layer. The radially innermost layer and the at least one intermediate layer each include at least one vacant slit section in which no permanent magnet is embedded. The vacant section in the radially innermost layer is larger than the vacant slit section in the intermediate layer. The permanent magnets embedded in the slit sections in each layer generate magnetic flux. The permanent magnets embedded in the slit sections of the radially innermost layer generate more magnetic flux than the permanent magnets embedded in the slit sections of the at least one intermediate layer.
In accordance with certain preferred embodiments of this aspect of the present invention in which the vacant slits are provided in the foregoing configuration, the amount of total magnetic flux generated by each permanent magnet layer when the rotor is assembled in a rotary electric device is larger for a radially inward layer than for a radially outward layer. Therefore, the distribution of magnetic flux density formed in the clearance between the rotor and the stator has a stepped shape that is closer to a sinusoidal wave rather than to a rectangular wave. Thus, compared with a conventional permanent magnet rotor, the distortion factor of the waveform of induced voltage is decreased. Torque ripples, cogging torque, noises and vibrations are also decreased.
Another aspect of the present invention is an embodiment of a permanent magnet rotor having a rotor core that comprises a plurality of magnetic poles. The rotor core includes a plurality of permanent magnets embedded in slit sections formed in layers for each magnetic pole. The layers comprise a radially innermost layer, at least one intermediate layer, and a radially outermost layer. The permanent magnets in the radially innermost layer, the at least one intermediate layer and the radially outermost layer are selected to have residual flux densities. The residual flux density of the permanent magnet in the at least one intermediate layer is greater than the residual flux density in the radially innermost layer. The residual flux density of the permanent magnet in the radially outermost layer is greater than the residual flux density of the permanent magnet in the at least one layer. The total magnetic flux generated by the permanent magnet in the radially innermost layer is greater than the total magnetic flux generated by the permanent magnet in the at least one intermediate layer. The total magnetic flux generated by the permanent magnet in the at least one intermediate layer is greater than the total magnetic flux generated by the permanent magnet in the radially outermost layer.
In particularly preferred embodiments in accordance with this aspect of the present invention, at least one of the layers of slit sections has at least one vacant slit in which no permanent magnet is embedded.
In certain preferred embodiments in accordance with this aspect of the present invention, the shape of the distribution of magnetic flux density formed in the clearance between the rotor and the stator can be made closer to a sinusoidal wave than to a rectangular wave, without having any vacant slits, so that magnets can be embedded more efficiently in the rotor core to facilitate size reduction.
Another aspect of the present invention is an embodiment of a permanent magnet rotor having a rotor core that comprises a plurality of magnetic poles. The rotor core includes a plurality of permanent magnets embedded in slit sections formed in layers for each magnetic pole. The layers comprise a radially innermost layer, at least one intermediate layer, and a radially outermost layer. Each layer has a respective mean residual magnetic flux density determined by the kind of permanent magnet in each layer and by a length of the permanent magnet in each layer. At least one of the layers comprises a plurality of slit sections. The plurality of slit sections in the at least one of the layers comprise at least a first kind of permanent magnet having a first residual magnetic flux density and at least a second kind of permanent magnet having a second residual magnetic flux density different from the first residual magnetic flux density. The at least one of the layers has a mean residual magnetic flux density deter

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