U.S. patent application number 09/818896 was filed with the patent office on 2002-05-02 for magnetizing method for a permanent-magnet motor.
Invention is credited to Asano, Yoshinari, Itoh, Hiroshi, Shinto, Masayuki.
Application Number | 20020050902 09/818896 |
Document ID | / |
Family ID | 15922425 |
Filed Date | 2002-05-02 |
United States Patent
Application |
20020050902 |
Kind Code |
A1 |
Asano, Yoshinari ; et
al. |
May 2, 2002 |
MAGNETIZING METHOD FOR A PERMANENT-MAGNET MOTOR
Abstract
In a method of magnetizing a material of a permanent magnet
portion provided in a rotor for a permanent-magnet motor, the
material of the permanent magnet portion is embedded inside the
rotor body, while the permanent magnet material has anisotropy in a
direction penetrating the permanent magnet portion in section, and
then the rotor is incorporated in a magnetizing unit and held in a
rotatable manner, and the permanent magnet material is magnetized
by flowing a magnetizing current through windings under the
condition that the rotor is rotatably held in the magnetizing unit.
Thus, the permanent magnet material is completely magnetized in a
normalized direction, and even if the rotor is shifted from the
normalized position, the rotor is retained back to the normalized
position by a magnet torque.
Inventors: |
Asano, Yoshinari;
(Takefu-shi, JP) ; Shinto, Masayuki; (Sabae-shi,
JP) ; Itoh, Hiroshi; (Takefu-shi, JP) |
Correspondence
Address: |
WENDEROTH, LIND & PONACK, L.L.P.
2033 K STREET N. W.
SUITE 800
WASHINGTON
DC
20006-1021
US
|
Family ID: |
15922425 |
Appl. No.: |
09/818896 |
Filed: |
March 28, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09818896 |
Mar 28, 2001 |
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09573853 |
May 19, 2000 |
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09573853 |
May 19, 2000 |
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09104221 |
Jun 25, 1998 |
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Current U.S.
Class: |
335/284 |
Current CPC
Class: |
H02K 15/03 20130101;
H01F 13/003 20130101 |
Class at
Publication: |
335/284 |
International
Class: |
H01F 007/20 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 27, 1997 |
JP |
9-171398 |
Claims
What is claimed is:
1. A method of magnetizing a material of a permanent magnet portion
provided in a rotor having a magnetic pole for a permanent-magnet
motor, comprising: embedding the material of the permanent magnet
portion inside the rotor body, said permanent magnet material
having anisotropy in a direction penetrating the permanent magnet
portion in section; incorporating the rotor in a magnetizing unit
to be held in a rotatable manner; and magnetizing the permanent
magnet material embedded in the rotor under the condition that the
rotor is rotatably held in the magnetizing unit.
2. The method as claimed in claim 1, wherein the direction in the
middle part of the anisotropy on each permanent magnet portion is
substantially parallel to the magnetic pole center line of the
rotor.
3. The method as claimed in claim 1, wherein each permanent magnet
portion has an inward convex arc shaped plate in sectional view
having radial anisotropy of which a concentrated center is
coincident with a center of the arc shaped permanent magnet portion
in each magnetic pole of the rotor to fabricate a reversed
salient-pole construction.
4. The method as claimed in claim 1, wherein a plurality of said
permanent magnet portions are radially arranged in section for each
magnetic pole of the rotor where the total number of the permanent
magnet portions is integer times of the total number of the
magnetic poles.
5. The method as claimed in claim 1, wherein said magnetizing unit
comprises a stator of a motor and at least one end of a rotating
shaft of the rotor is rotatably held by a bearing means in the
stator during the magnetizing operation.
6. The method as claimed in claim 1, wherein the magnetization of
the permanent magnet material embedded in the rotor body is carried
out by flowing electric current between two phases among the three
phases through windings provided on the magnetizing unit.
7. The method as claimed in claim 1, wherein said permanent magnet
portion embedded in the rotor comprises four flat plates to form a
square shape in section view so that each permanent magnet plate
has anisotropy substantially parallel to the center line of the
magnetic pole of the rotor.
8. The method as claimed in claim 1, wherein said permanent magnet
portion embedded in the rotor comprises a pair of flat plates
coupled to each other for each magnetic pole of the rotor, said
coupled flat plates forming a generally V-character shape having a
vertex projected inward in section view at which said pair of
permanent magnet portions are joined.
9. The method as claimed in claim 8, wherein each permanent magnet
portion has anisotropy in a direction substantially parallel to the
transverse direction in section of the permanent magnet plate so
that the magnetic fluxes thereof are concentrated onto the center
of each magnetic pole.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention generally relates to a magnetizing
method for a permanent-magnet motor, and in particular to a method
of magnetizing a permanent-magnet material used in a rotor
structure of a permanent-magnet motor having reversed
salient-polarity to make effective use of a reluctance torque
together with a magnet torque.
[0003] 2. Description of the Prior Art
[0004] Conventionally, permanent-magnet motors are used as examples
of variable velocity motors in many cases. A permanent-magnet motor
has a rotor which includes plural pieces of permanent magnet. In
such a permanent-magnet type motor, a permanent magnet is formed by
e.g. molding a solid mass of magnetic powder material. Therefore,
the molded permanent magnet material has no magnetic polarity at an
initial stage of manufacturing process of a motor. Namely, by
effecting a magnetizing process of a permanent magnet material, the
magnetic polarity is given to the permanent magnet material for the
first time to form plural pieces of permanent magnet members.
[0005] When a magnetizing operation of a permanent magnet material
is carried out, a center axis of the resultant permanent magnet
member must be positioned in a normalized relationship in
accordance with an axis of magneto-motive force generated by a
magnetizing current flowing through windings located on a stator so
that the magnetic pole is fixed to a reference or normalized
position without any displacement. This alignment of the magnet
axis and the magneto-motive force axis was conventionally performed
by a mechanical construction.
[0006] If magnetization of the permanent magnet material is carried
out with a displacement between the magnet axis and the
magneto-motive force axis, the resultant magnetization is
insufficient in quantity, resulting in reduction of a driving
efficiency of a motor and causing an error in detecting a
rotational position of a rotor. Thus, the alignment of the magnet
axis and the magneto-motive force axis is essentially
necessary.
[0007] In a conventional magnetizing method for a rotor having
outward salient polarity as shown in FIG. 13, electric current for
alignment is applied from an alignment current source to flow
through windings on a stator to generate a magneto-motive force. In
the meanwhile, the rotor core 103 includes four pieces of permanent
magnet 106 for four polarized sections and joint members 108 of
electro-magnetic steel for coupling the adjoining permanent magnet
members to each other. In this construction, when the alignment
current is flown through the windings, the magneto-motive force
generated by the alignment current acts as an absorbing force for
absorbing the joint members. Thus, the rotor is rotated toward the
normalized position for establishing the alignment by the absorbing
action due to the magneto-motive force generated by the alignment
current. By this alignment operation, the magnet center axis is set
to a specified relationship of e.g. right angles with respect to
the axis of the magneto-motive force generated by the alignment
current.
[0008] Then, under the condition that the rotor is set in the
normalized position, the magnetization is carried out by applying a
magnetizing current from a magnetizing current source to flow
through the windings. In this magnetizing operation, the magnet
center axis can be coincident with the axis of the magneto-motive
force generated by flowing the magnetizing current through the
windings so that the rotor is maintained in the normalized
position.
[0009] In order to effectively take advantage of a magnet torque as
well as a reluctance torque, another conventional method of
magnetizing a permanent magnet material was developed for
fabricating a rotor having a reversed (i.e., inward) salient
polarity as shown in FIGS. 9 and 10. In this construction, the
material of the permanent magnet is firstly embedded in a rotor
body of a motor and then magnetized. It is noted here that the
reluctance torque is a component of the total torque when the motor
is operating synchronously. It results from the saliency of the
poles and is a manifestation of the poles attempting to align
themselves with the air-gap magnetic field.
[0010] FIGS. 9 and 10 show an example of a conventional magnetizing
method for a permanent-magnet type motor to have a reversed
salient-polarity construction effectively taking advantage of a
reluctance torque along with a magnetic torque. In this
construction, plural permanent magnet material portions 52a and 52b
are embedded for each pole section inside a rotor core 51 of a
rotor 50. The rotor core 51 is essentially composed of high
permeable materials such as e.g. iron or formed by laminating
electro-magnetic steel plates. Then, the embedded permanent magnet
materials 52a and 52b are magnetized by applying a magnetizing
current from a magnetizing current source (not shown) flowing
through windings 21 provided on a stator 20.
[0011] The rotor 50 is rotated on a rotating shaft 54, generating a
magnet torque and reluctance torque due to a rotational magnetic
field generated by the current flowing through the windings 21 on
the stator 20. Thus, the magnetization of the permanent magnet
materials 52a and 52b embedded in the rotor 50 is carried out by
flowing electric current between e.g. R-phase and S-phase of the
three phases through the windings 21 while the rotor 50 is fixed to
a normalized position specified for accurate and complete
magnetization as shown in FIGS. 9 and 10.
[0012] In this magnetizing operation, however, if the rotor is
displaced in position even only slightly from the normalized
position, the reluctance torque acts as a rotating force to rotate
the rotor 50, which undesirably causes a shift in position of the
rotor to result in insufficient magnetization.
[0013] In order to avoid this problem, the rotor 50 is incorporated
in a motor 1 as shown in FIG. 11, with its shaft end 53 being
securely regulated in position by providing a securing jig member
55 for preventing the rotor from rotating.
[0014] Alternatively, as shown in FIG. 12, the rotor 50 is
incorporated in a cylindrical magnetizing yoke 4 with the shaft end
53 fixed in position to a securing jig member 56 for preventing
rotation of the rotor.
[0015] However, in the mechanical alignment of the magnet axis and
the magneto-motive force axis in these conventional magnetizing
methods mentioned above, as the magnetizing current is required to
have a large value of several tens or several hundreds times larger
than the rated current value, therefore the rotational force of the
rotor 50 by the reluctance torque is very strong. Accordingly,
there has been a problem that the securing jig member for
preventing rotation of the rotor is undesirably damaged, or a
mechanism for transferring a driving force from the rotating shaft
is damaged in some cases.
SUMMARY OF THE INVENTION
[0016] The present invention has been developed with a view to
substantially solving the above described disadvantages.
Accordingly, an essential objective of the present invention is
therefore to provide a noble magnetizing method for a
permanent-magnet motor.
[0017] In order to achieve the above objective, according to an
aspect of the present invention, a method of magnetizing a material
of a permanent magnet portion provided in a rotor having a magnetic
pole for a permanent-magnet motor, comprises:
[0018] embedding the material of the permanent magnet portion
inside the rotor body, where the permanent magnet material has
anisotropy in a direction penetrating the permanent magnet portion
in section;
[0019] incorporating the rotor in a magnetizing unit to be held in
a rotatable manner; and
[0020] magnetizing the permanent magnet material embedded in the
rotor under the condition that the rotor is rotatably held in the
magnetizing unit.
[0021] By this method of the arrangement, the anisotropy is given
to the permanent magnet material to have magnetic properties which
differ in various directions for the rotor of the permanent-magnet
motor, and a shaft core of the rotor is rotatably positioned on the
rotation center axis, so that permanent magnet material is
magnetized in a normalized direction, and even if the rotor
position is shifted from the normalized position during the
magnetizing operation, the rotor position is retained back to the
normalized position by a magnet torque, thus completely magnetizing
the permanent magnet material.
[0022] In an aspect of the present invention, the direction in the
middle part of the anisotropy on each permanent magnet portion is
substantially parallel to the magnetic pole center line of the
rotor, and each permanent magnet portion has an inward convex arc
shaped plate in sectional view having radial anisotropy in each
magnetic pole of the rotor to fabricate a reversed salient-pole
construction to thereby effectively take advantage of a magnet
torque together with a reluctance torque.
[0023] By this method, a reluctance torque is effectively used and
the permanent magnet material can be completely magnetized with
ease even for a high efficient motor.
[0024] According to another aspect of the present invention, the
magnetizing unit comprises a stator of a motor and at least one end
of a rotating shaft of the rotor is rotatably held by a bearing
means provided in the stator during the magnetizing operation.
[0025] By this method of the arrangement, the magnetization can be
performed in the incorporated condition of the rotor before the
motor is loaded, and therefore there is no need of providing a
securing jig member for preventing rotation of the rotor, thus
improving productivity of a motor.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] These and other objects and features of the present
invention will become clear from the following description taken in
conjunction with the preferred embodiments thereof with reference
to the accompanying drawings, in which:
[0027] FIG. 1 is a sectional view of a motor with a rotor set to a
normalized position according to an embodiment of the present
invention;
[0028] FIG. 2 is a schematic view of a motor incorporated with a
rotor according to an embodiment of the present invention;
[0029] FIG. 3 is a circuit diagram showing a magnetizing current
supply construction according to an embodiment of the present
invention;
[0030] FIG. 4 is a graph showing a waveform of a magnetizing
current according to an embodiment of the present invention;
[0031] FIG. 5 is a sectional view of a motor with a rotor shifted
from a normalized position according to an embodiment of the
present invention;
[0032] FIG. 6 is a schematic view of a magnetizing yoke
incorporated with a rotor according to an embodiment of the present
invention;
[0033] FIG. 7 is a sectional view of a motor according to another
embodiment of the present invention;
[0034] FIG. 8 is a sectional view of a motor according to further
another embodiment of the present invention;
[0035] FIG. 9 is a sectional view of a motor showing a conventional
magnetizing method;
[0036] FIG. 10 is a sectional view of a motor showing a
conventional construction of windings;
[0037] FIG. 11 is a schematic view of a motor incorporated with a
rotor showing a conventional magnetizing method;
[0038] FIG. 12 is a schematic view of a magnetizing yoke
incorporated with a rotor showing a conventional magnetizing
method; and
[0039] FIG. 13 is a sectional view of a conventional salient-pole
type motor.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0040] Before the description proceeds, it is noted that, since the
basic structure of the preferred embodiment is similar to that of
the conventional one, like parts are designated by the same
reference numerals throughout the accompanying drawings.
[0041] The following describes a preferred embodiment of a
magnetizing method for a permanent-magnet motor with reference to
FIGS. 1 to 8.
[0042] In a method of magnetizing a permanent magnet material for a
permanent-magnet motor, as shown in FIG. 1, permanent magnet
materials 12a and 12b are embedded around a rotating shaft 14
inside a rotor core body 11 to form one or more permanent magnet
portions symmetrically for e.g. four pole sections in section view.
In this embodiment, e.g. two pieces of permanent magnet material
portions 52a and 52b are radially arranged in each pole section. As
the permanent magnet materials, although almost any kind of steel
capable of being hardened by heat treatment may be used, it is
preferable to use iron-powder compact materials especially produced
for this purpose, or other materials, for example, hardened alloys,
ceramic, and the like work-hardened materials.
[0043] The rotor core body 11 is essentially formed of high
permeable materials such as e.g. iron or formed by laminating a
plurality of electromagnetic steel plates, and the permanent magnet
materials 12a and 12b embedded in the rotor core body 11 are
magnetized to fabricate a rotor 10 having a reversed
salient-polarity to make effective use of a reluctance torque
together with a magnetic torque. In this arrangement, by applying a
magnetizing current from a magnetizing current supply source, the
rotor 10 is rotated with the rotating shaft 14 while a magnetic
torque and reluctance torque are generated due to a rotational
magnetic field generated by the windings 21 provided on a stator 20
of the motor. Thus, the windings 21 provide e.g. four pole sections
having a three-phase construction.
[0044] In a preferred embodiment, although two or more pieces of
the embedded permanent magnet portions 12a and 12b are arranged in
a radial direction in the rotor core body for each pole section,
one permanent magnet material portion may be formed in each pole
section. Each permanent magnet material portion has an inward
convex arc shaped plate in sectional view to have a reversed
salient-polarity.
[0045] In this construction, an anisotropic material is used as the
permanent magnet material portions to have anisotropy in radial
directions as shown by arrow marks 15 which are oriented in
directions penetrating the permanent magnet portions in section
where the center line of the anisotropy marks 15 on each permanent
magnet portion is substantially parallel to the magnetic pole
center line m (m') of the rotor and the concentrated radial center
of the anisotropy marks 15 is coincident with the radial center of
the arc shaped permanent magnet portions in each pole section.
Thus, a rotor is fabricated to have a reversed salient-pole
construction in which the magnetic polarization properties differ
in different directions. Ferrite or rare-earth materials may be
used as an anisotropic material for the permanent magnet so long as
the material has an anisotropy property when performing a
magnetization operation.
[0046] The magnetization of the permanent magnet materials 12a and
12b embedded in the rotor core 11 is carried out by flowing a
magnetizing electric current between two phases, e.g., R-phase and
S-phase of the three phases through the windings 21 provided on the
stator 20 under the condition that the rotor 10 is incorporated in
a motor shown in FIG. 2.
[0047] In this magnetizing operation shown in FIG. 2, there is not
provided any securing jig member for preventing rotation of the
rotor but the rotating shaft 14 of the rotor 10 is freely rotatable
by providing a bearing means 5 in the condition that the center
axis of the shaft is fitted to the rotation axis of the rotor
whereas the shaft end 13 is not fixed nor loaded but made freely
rotatable.
[0048] In this embodiment, as shown in FIG. 3, the magnetizing
electric current is flown e.g. from the R-phase to the S-phase by
connecting a terminal 2 to a magnetizing power source (not shown)
in a magnetizing circuit. In a usual arrangement, electric charge
is held by a capacitor 3, and when a switch 7 is closed on, the
electric current is instantaneously flown through the windings 21,
where the magnetizing current instantaneously increases to a peak
value Imax and attenuates as shown by a current waveform in FIG.
4.
[0049] In this arrangement, according to a general theory in a
rotor structure having a reversed salient-polarity, a force (F)
acting as a shifting force to shift the rotor in rotational
position from the normalized position is equal to a sum of a magnet
torque (TM) and a reluctance torque (TR), that is represented
by:
F=TM+TR
[0050] where the magnet torque (TM) and reluctance torque (TR) are
represented as following equations:
TM=-c.sub.1I.psi.sin 2.theta.
TR=c.sub.2I.sup.2.psi.sin 4.theta.
[0051] where c.sub.1 and c.sub.2 are positive constants, I is
electric current, .psi. is magnetic flux, and .theta. is a shifted
(mechanical) angle of a rotor from the normalized position.
[0052] In this connection, when .theta.=0, namely, when the rotor
is precisely located in the normalized position, no magnet torque
nor reluctance torque is generated and then the rotor is in a
stationary condition (i.e., F=0). However, as shown in FIG. 5, when
the rotor is slightly shifted in position from the normalized
position by a minute angle .theta. (>0), the reluctance torque
becomes positive (TR>0) but the magnet torque remains TM=0
because the magnetization amount is zero (i.e., .psi.=0) at the
initial stage before the magnetization is effected. Therefore, the
shifting force becomes positive (F>0), acting as a rotating
force to further shift the rotor in position. In the meanwhile,
since the permanent magnet materials 12a and 12b have anisotropy
15, the magnetization proceeds although incompletely and the
magnetic flux is gradually increased to be positive (.psi.>0).
When the magnetization further proceeds and absolute value of TM
becomes larger than the value of TR, the force F=TM+TR becomes
negative (i.e., F<0), and thus the rotor is restored back toward
the normalized position (i.e., point of .psi.=0) in an attenuation
manner as the rotor is freely rotatable. Once the rotor position is
settled to the normalized position, the magnetization of the
permanent magnet materials is precisely effected at the normalized
position of the rotor since then, ensuring the complete and
accurate magnetization.
[0053] In a modified embodiment, as shown in FIG. 6, the rotor 10
is incorporated in the magnetizing yoke 4 instead of a motor and
the shaft core of the rotor is fitted to the rotation axis in the
condition that the rotor is freely rotatable by providing a bearing
means 5 in a jig member 6 in the vicinity of at least one end
portion 13. In this construction, the magnetizing current is flown
through windings (not shown) provided on the yoke 4.
[0054] In another modified embodiment as shown in FIG. 7, e.g. four
flat plates of the permanent magnet material 32 are embedded in a
rotor core body 31 to form a square shape in section view so that
each permanent magnet plate has anisotropy represented by arrow
marks 35 oriented in a direction penetrating the permanent magnet
plate in section and substantially parallel to the center line m
(m') of the magnetic pole of the rotor 30.
[0055] In this arrangement, since the permanent magnet portion 32
is formed of flat plate, the manufacturing process can be precisely
performed at a low cost with high accuracy, allowing to provide a
high reliable motor, suppressing irregularity in size thereof.
Moreover, when the permanent magnet portion is made of rare-earth
materials having anisotropy, a large amount of magnetic flux can be
generated with a less amount of magnet, which allows to make a
motor small in size.
[0056] In further another modified embodiment as shown in FIG. 8, a
pair of permanent magnet material portions 42a and 42b are embedded
for one pole section in a rotor core body 41. Each pair of
permanent magnet portions 42a and 42b are coupled to each other to
form a generally V-character shape plate having a vertex or tip end
42c thereof projected inward in section view at which the two
permanent magnet portions 42a and 42b are joined. In this
construction, each permanent magnet portion is provided with
anisotropy represented by arrow marks 45 generally oriented in a
direction penetrating the permanent magnet plate in section so that
the magnetic fluxes are concentrated to the center of each magnetic
pole of the rotor.
[0057] In these embodiments described above, although the
magnetizing current is flown between the R-phase and S-phase of the
windings in a magnetizing operation, the current may be flown
between any other two phases, for example, between T phase and a
short-circuited point of the R and S phases, so long as the rotor
position is generally fitted to the normalized position.
[0058] Moreover, the present invention is not limited to the above
described embodiments, and a driving way of a motor, arrangement of
the windings and a type of a motor may be changed to various
modifications within the scope of the present claimed
invention.
[0059] As apparent from the above description, according to a first
aspect of the present invention, even when a reluctance torque acts
on the rotor to cause a shift in position during a magnetizing
operation, the rotor position is restored back toward the
normalized position by a magnet torque because of the anisotropy of
the permanent magnet material so that the magnetization is
completely carried out with high accuracy.
[0060] According to a second aspect of the present invention, the
magnetization can be carried out in a state of a rotor incorporated
with a permanent magnet material before a motor is provided with a
load. Thus, the magnetization can be carried out without providing
any securing jig member for preventing rotation of a rotor, which
improves productivity of a motor.
[0061] According to a third aspect of the present invention, a
reluctance torque is effectively used and the permanent magnet
material can be completely magnetized with ease even for a high
efficient motor.
[0062] Although the present invention has been fully described in
connection with the preferred embodiments thereof with reference to
the accompanying drawings, it is to be noted that various changes
and modifications are apparent to those skilled in the art. Such
changes and modifications are to be understood as included within
the scope of the present invention as defined by the appended
claims unless they depart therefrom.
* * * * *