U.S. patent application number 09/471375 was filed with the patent office on 2001-11-22 for motor having a rotor with interior split-permanent-magnet.
Invention is credited to IKKAI, YASUFUMI, KONDO, YASUHIRO, NAKAMURA, TOMOKAZU, NISHIYAMA, NORIYOSHI, OGUSHI, MASAKI.
Application Number | 20010043020 09/471375 |
Document ID | / |
Family ID | 18493740 |
Filed Date | 2001-11-22 |
United States Patent
Application |
20010043020 |
Kind Code |
A1 |
NISHIYAMA, NORIYOSHI ; et
al. |
November 22, 2001 |
MOTOR HAVING A ROTOR WITH INTERIOR SPLIT-PERMANENT-MAGNET
Abstract
A motor includes a rotor with interior permanent magnets and a
stator with teeth wound by concentrated windings. The permanent
magnet is split along a plane oriented to the stator, and an
electrically insulating section is set between the spilt magnet
pieces. This structure allows the permanent magnet to be
electrically split thereby restraining the production of eddy
current. As a result, heat-production is damped thereby preventing
heat demagnetization of the permanent magnet.
Inventors: |
NISHIYAMA, NORIYOSHI;
(OSAKA, JP) ; NAKAMURA, TOMOKAZU; (OSAKA, JP)
; IKKAI, YASUFUMI; (HYOGO, JP) ; OGUSHI,
MASAKI; (NARA, JP) ; KONDO, YASUHIRO; (OSAKA,
JP) |
Correspondence
Address: |
WENDEROTH LIND & PONACK LLP
SUITE 800
2033 K STREET
WASHINGTON
DC
20006
US
|
Family ID: |
18493740 |
Appl. No.: |
09/471375 |
Filed: |
December 23, 1999 |
Current U.S.
Class: |
310/156.01 |
Current CPC
Class: |
H02K 1/276 20130101;
B60L 3/0061 20130101; Y02T 10/64 20130101; B60L 2240/423 20130101;
B60L 15/20 20130101; B60L 50/66 20190201; Y02T 10/72 20130101; Y02T
10/70 20130101; B60L 50/52 20190201; H02K 21/16 20130101; H02K
7/006 20130101; B60L 2240/36 20130101; H02K 1/2766 20130101 |
Class at
Publication: |
310/156.01 |
International
Class: |
H02K 021/12 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 25, 1998 |
JP |
10-369167 |
Claims
What is claimed is:
1. A motor comprising: a rotor having an interior permanent magnet;
and a stator having teeth wound by concentrated windings, wherein
the permanent magnet is split along a plane being oriented toward
said stator, and an electrically insulating section is put between
split magnet pieces.
2. The motor as defined in claim 1, wherein the permanent magnet is
coated by an electrically insulating material.
3. The motor as defined in claim 1, wherein the electrically
insulating section comprises epoxy resin.
4. The motor as defined in claim 1, wherein the electrically
insulating section is formed by air gap.
5. The motor as defined in claim 1, wherein the permanent magnet
comprises rare-earth-sintered magnet.
6. The motor as defined in claim 1 is controlled rotation thereof
by weakening-magnetic-field controlling method.
Description
FIELD OF THE INVENTION
[0001] The present invention relates generally to a motor having a
rotor with interior permanent magnets, more particularly it relates
to a motor with interior split-permanent-magnets, thereby restrains
eddy-current from occurring and prevents heat-demagnetization.
BACKGROUND OF THE INVENTION
[0002] FIG. 11 illustrates a rotor with interior permanent magnets
of a conventional motor. The motor has rotor 310 in which permanent
magnets 312 are embedded, and rotor 310 is disposed in a stator
(not shown) with concentrated windings, so that the motor can
driven by not only magnet torque but also reluctance torque. This
rotor is hereinafter referred to as a "rotor with interior
permanent magnets".
[0003] However this conventional motor has the following
problems:
[0004] Comparing with a motor with a distributed-winding stator, a
motor with a concentrated-winding stator subjects itself to greater
changes of magnetic flux interlinked with rotor 310 when the motor
rotates. As a result, a large eddy-current occurs in magnets 312
embedded in the rotor, and thus the motor with a
concentrated-winding stator is vulnerable to irreversible heat
demagnetization. Meanwhile, the distributed-winding stator is
structured in the following way: A slot is formed between two
stator-teeth, and a plurality of teeth thus form a plurality of
slots. Windings striding over at least one slot are provided, and
part of a winding of a phase exists between pitches of another
phase winding. The concentrated-winding stator, on the other hand,
is structured by providing a winding of one phase to one stator
tooth respectively.
[0005] The reason why the motor having the concentrated-winding
stator is vulnerable to heat-demagnetization is detailed
hereinafter.
[0006] It is well known that eddy current loss "W.sub.e" is
proportionate to a square of maximum operable magnetic-flux-density
"B.sub.m", and this relation can be expressed in the following
equation.
W.sub.e=P.sub.i/t={1/(6.rho.)}.pi..sup.2f.sup.2B.sub.m.sup.2t.sup.2[W/m.su-
p.3]
[0007] where
[0008] P.sub.t=power consumption
[0009] t=plate width interlinking with the magnetic flux
[0010] .rho.=resisting value proper to the permanent magnet
[0011] f=exciting frequency
[0012] Since the motor having the concentrated-winding stator is
subjected to greater changes in magnetic flux running through the
rotor, the maximum operable magnetic-flux-density "B.sub.m" in the
above equation becomes greater and thus eddy-current-loss "W.sub.e"
grows larger.
[0013] If a motor has the concentrated winding stator, and yet, the
permanent magnets are stuck onto an outer wall of the rotor, the
changes in magnetic-flux-density is not so large that the
heat-demagnetization due to the eddy-current-loss is negligible. In
the motor having the concentrated winding stator and a rotor in
which the permanent magnets are embedded, the space between the
magnet and the outer circumference of rotor core 314 forms a path
for the magnetic-flux to flow. The density of magnetic-flux from
the stator changes depending on the position of stator teeth with
regard to the magnets, so that magnitude of changes in the
magnetic-flux-density at the path is increased. As a result,
eddy-current occurs in magnets 312 embedded in rotor 310, thereby
heating the magnet to produce irreversible
heat-demagnetization.
SUMMARY OF THE INVENTION
[0014] The present invention addresses the problems discussed above
and aims to provide a motor having a rotor with
interior-permanent-magnets. This rotor produces the less
eddy-current and can prevent the heat-demagnetization in the
permanent magnets embedded in the rotor.
[0015] The motor of the present invention comprises the following
elements:
[0016] a rotor in which permanent magnets are embedded, and
[0017] a stator of which teeth wound by windings in a concentrated
manner.
[0018] The permanent magnets are split in respective sides facing
the stator, and insulating sections are inserted into respective
gaps between respective split magnets. This structure splits the
magnets electrically thereby restraining the eddy-current from
occurring and then suppressing the heat-demagnetization in the
magnets embedded into the rotor.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is a cross section illustrating a motor, having a
rotor with interior permanent magnets, in accordance with a first
exemplary embodiment of the present invention.
[0020] FIG. 2 is a perspective view of the permanent magnets to be
embedded into the rotor of the motor shown in FIG. 1.
[0021] FIG. 3 is a perspective view of permanent magnets to be
embedded into a rotor of a motor in accordance with a second
exemplary embodiment of the present invention.
[0022] FIG. 4 is a perspective view of permanent magnets to be
embedded into a rotor of a motor in accordance with a third
exemplary embodiment of the present invention.
[0023] FIG. 5 is a cross section illustrating a rotor of a motor,
in which "I" shaped permanent magnets are embedded, in accordance
with a fourth exemplary embodiment of the present invention.
[0024] FIG. 6 is a cross section illustrating a rotor of a motor,
in which permanent magnets are embedded, in accordance with a fifth
exemplary embodiment.
[0025] FIG. 7A is a perspective view of permanent magnets to be
embedded into the rotor of the motor in accordance with the fifth
exemplary embodiment.
[0026] FIG. 7B is a front view of the permanent magnets shown in
FIG. 7A.
[0027] FIG. 8A is a perspective view of permanent magnets to be
embedded into a rotor of a motor in accordance with a sixth
exemplary embodiment.
[0028] FIG. 8B is a front view of the permanent magnets shown in
FIG. 8A.
[0029] FIG. 9 is a perspective view of permanent magnets to be
embedded into a rotor of a motor in accordance with a seventh
exemplary embodiment.
[0030] FIG. 10 is a block diagram of an electric vehicle in which
the motor of the present invention is mounted.
[0031] FIG. 11 is a cross section illustrating a conventional motor
having a rotor with interior permanent magnets.
DETAILED DESCRIPTION OF THE INVENTION
[0032] Exemplary embodiments of the present invention are
demonstrated hereinafter with reference to the accompanying
drawings.
[0033] (Exemplary Embodiment 1)
[0034] FIG. 1 is a cross section illustrating a motor, having a
rotor with interior permanent magnets, in accordance with the first
exemplary embodiment of the present invention, and FIG. 2 is a
perspective view of the permanent magnets to be embedded into the
rotor of the same embodiment.
[0035] In FIG. 1, motor 10 includes rotor 14 with interior
permanent magnets 12, and stator 15 facing to rotor 14 via annular
space. Respective teeth 17 of stator 15 are wound by windings 18 in
a concentrated manner, i.e. concentrated windings are provided to
respective teeth.
[0036] Rotor 14 comprises the following elements:
[0037] a rotor core laminated with a plurality of steel plates;
[0038] permanent magnets 12 embedded into slots axially provided;
and
[0039] a rotating shaft 16 extending through a center of the rotor
core.
[0040] Respective magnets 12 have a shape protruding toward the
center of rotor core. As such, the magnets are embedded into the
rotor so that rotor 4 can produce respective directions for
magnetic flux to flow with ease and with difficulty. An inductance
ratio in respective directions can be thus obtained, and it is
called a salient pole rate.
[0041] A rotor polarity is formed between magnet 12 and an outer
wall of the rotor core to which magnets 12 face. The magnetic-flux
from the permanent magnet flows with ease through the section
covering the rotor polarity, and this flowing direction is called
"d axis". On the other hand, the magnetic-flux flows with
difficulty through a section covering a boundary between two
adjacent magnets, and this flowing direction is called "q
axis".
[0042] Stator 15 is formed by linking twelve stator-blocks 19 to
each other in an annular shape. Each stator block 19 comprises
teeth 17 wound by winding 18 in the concentrated manner, and the
blocks are welded to form a ring. In the case of a three-phase and
eight-pole motor, for instance, windings provided to a first four
teeth every three teeth out of 12 teeth are coupled with each other
thereby forming phase "U". In the same manner, the windings
provided to the second four teeth on the right side of the
respective first four teeth discussed above are coupled with each
other thereby forming phase "V". Further, the windings provided to
the third four teeth on the left side of the first four teeth are
coupled with each other thereby forming phase "W". Stator 15 thus
forms three-phase with concentrated windings.
[0043] In motor 1 constructed above, the magnetic flux generated by
magnet 12, i.e. the magnetic flux produced by the
rotor-magnetic-poles, travels to teeth 17 of the stator via the
annular space thereby contributing to the torque production. This
motor has the salient-pole-rate and controls the current-phases to
be optimal by current thereby driving itself not only by the magnet
torque but also by the reluctance torque.
[0044] One of the features of the present invention is a method of
embedding the permanent magnets into the rotor. Magnets 12 to be
embedded into rotor 14 in the first exemplary embodiment are
detailed hereinafter.
[0045] As shown in FIG. 2, each magnet 12 is split into two magnet
pieces 13 in the axial direction of rotor 14. Each two magnet
pieces 13 are embedded into one single hole provided to rotor 14,
thereby forming each magnet 12. Epoxy resin of electrically
insulating, used as a coating material, is applied to the overall
surface of each magnet piece 13. If magnet pieces 13 are
stacked-up, each piece is electrically insulated and they can form
an independent circuit. A space between respective stacked-up
magnet pieces 13 is not less than 0.03 mm corresponding to the
thickness of coating material applied to the magnet pieces.
[0046] The two magnet pieces 13 are embedded adjacently with each
other into the hole of the rotor core so that magnet 12 is split
into two sections facing to stator 15. Respective magnet pieces 13
are arranged in the following way: Respective magnetic-fluxes
generated from two magnet pieces embedded in one hole flow in the
same direction with regard to the outer wall of the rotor to which
these two magnet pieces face. Another pair of magnet pieces
embedded into a hole adjacent to the hole discussed above generate
the magnetic flux in the direction reversed to the direction of the
magnetic flux discussed above. For instance, two magnetic pieces
embedded into one hole face to the outer wall of the rotor with
poles "N", then another pair of magnet pieces embedded into the
hole adjacent to this hole should face to the outer wall with poles
"S".
[0047] The space between the two magnet pieces is not necessarily
resin, and it can be any electrically-insulating-materials
including air-gap.
[0048] Magnet 12 is split by a plane facing toward stator 15,
thereby reducing the eddy current produced in magnet 12. The plane
extends from the rotor center toward the stator. This is because of
the following reason:
[0049] Since teeth 17 are wound by concentrated windings 18, stator
15 receives greater changes in the density of magnetic-flux
supplied from teeth 17. The maximum operable magnetic-flux-density
B.sub.m expressed in the equation discussed previously thus grows
greater. This change in the magnetic-flux-density produces the eddy
current in each magnet 12. In this first exemplary embodiment, each
magnet 12 embedded in rotor 14 is split into two magnet pieces 13,
and epoxy resin--which is non-magnetic material--is put between
these two pieces, thereby dividing magnet 12 not only physically
but also electrically. As a result, the production of eddy current
is restrained by narrowing the width "t" of plate interlinking with
the magnetic flux in the equation discussed previously.
[0050] (Exemplary Embodiment 2)
[0051] FIG. 3 is a perspective view of permanent magnets to be
embedded into a rotor of a motor in accordance with the second
exemplary embodiment of the present invention. This second
embodiment differs from the first one in the way of splitting the
magnet, and others stay the same.
[0052] In the first embodiment, the magnet is split into two pieces
in the axial direction, however magnet 22 in this second embodiment
is split into five pieces in the axial direction, and this produces
the same advantage as the first embodiment has done.
[0053] (Exemplary Embodiment 3)
[0054] FIG. 4 is a perspective view of permanent magnets to be
embedded into a rotor of a motor in accordance with the third
exemplary embodiment of the present invention. This third
embodiment differs from the first one in the way of splitting the
magnet, and others stay the same.
[0055] In the first embodiment, the magnet is split into two pieces
in the axial direction, however magnet 32 in this third embodiment
is split into three pieces in a vertical direction with regard to
the axial direction, and this produces the same advantage as the
first embodiment has done.
[0056] The first, second and third embodiments prove that the
magnets split into pieces along planes facing to the stator can
restrain the production of eddy current.
[0057] (Exemplary Embodiment 4)
[0058] FIG. 5 is a cross section illustrating a rotor of a motor,
in which "I" shaped permanent magnets are embedded, in accordance
with the fourth exemplary embodiment of the present invention. This
fourth embodiment differs from the previous embodiments 1-3 in the
shape of magnet. In the previous embodiments, the magnet is in a
"V" shape; however, magnet 42 in the fourth embodiment is shaped in
a letter of "I".
[0059] In FIG. 5, each magnet 42 formed by two magnet pieces
aligned in an "I" shape is inserted into each hole provided in
rotor 44. Electrically insulating material is put between the two
pieces, this insulating material can be air gap. The fourth
embodiment can produce the same advantage as the first embodiment
has done.
[0060] Regarding the shape of the magnet, the embodiments 1-3
employ "V" shape, and this fourth one employs "I" shape; however,
the shape can be an arc being bowed toward the rotor center.
[0061] (Exemplary Embodiment 5)
[0062] FIG. 6 is a cross section illustrating a rotor of a motor,
in which permanent magnets are embedded, in accordance with the
fifth exemplary embodiment. FIG. 7A is a perspective view of the
permanent magnets to be embedded into the rotor of the motor in
accordance with the fifth exemplary embodiment, and FIG. 7B is a
front view of the permanent magnets shown in FIG. 7A.
[0063] In FIG. 6, permanent magnets 52 are embedded in rotor 54,
and rotary shaft 56 extends through the rotor center. This motor
has a stator (not shown) disposed around rotor 54 via annular
space.
[0064] Magnet 52 is formed by laminating a plurality of
rare-earth-sintered-magnet pieces. Air gaps 58 are provided between
respective magnetic pieces. Magnet 52 is bowed toward the rotor
center.
[0065] Magnet 52 is further detailed with reference to FIGS. 7A and
7B.
[0066] Magnet 52 comprises rare-earth-sintered magnet. In general,
the rare-earth-sintered magnet is coated on its surface in order to
avoid corrosion. Magnet 52 is formed by laminating six pieces of
this rare-earth-sintered magnet. Two or more than two protrusions
are provided on the respective faces laminated so that air gaps 58,
as insulating layers, are provided to each magnet piece. The total
area of the protrusions formed on each magnet piece should be
smaller than the area of the face laminated, e.g. not more than 10%
of the face laminated. The number of magnet pieces is not limited
to six but other plural numbers are acceptable as far as they can
provide air gaps between each magnet pieces.
[0067] As such, since magnet 52 has insulating layers (air gaps)
between respective magnet pieces making up magnet 52, it is
difficult for current to run through magnet 52. As a result, the
production of eddy current is restrained. Meanwhile, magnet 52
employs a conductive coating material to avoid corrosion; however,
the material can be insulating one, further, respective air gaps
can be filled with insulating resin thereby enhancing the strength
of magnet 52. The protrusions formed on each magnet piece can be
made from another material and disposed on each magnet piece.
Electrically insulating material among others for forming the
protrusions can produce the advantage distinctly.
[0068] (Exemplary Embodiment 6)
[0069] FIG. 8A is a perspective view of permanent magnets to be
embedded into a rotor of a motor in accordance with the sixth
exemplary embodiment, and FIG. 8B is a front view of the permanent
magnets shown in FIG. 8A.
[0070] This sixth embodiment differs from the fifth one in a way
splitting the magnet, and others stay the same.
[0071] In the fifth embodiment, the magnet is split into six pieces
in the axial direction; however, magnet 62 in this sixth embodiment
is split into three pieces in a vertical direction with regard to
the axial direction. The sixth embodiment can produce the same
advantage as the fifth one has done.
[0072] (Exemplary embodiment 7)
[0073] FIG. 9 is a perspective view of permanent magnets to be
embedded into a rotor of a motor in accordance with the seventh
exemplary embodiment of the present invention.
[0074] This sixth embodiment differs from the fifth one in a way
splitting the magnet, and others stay the same.
[0075] In the fifth embodiment, the magnet is split into six pieces
in the axial direction; however, magnet 72 in this seventh
embodiment is split into three pieces in a rotating direction, and
a center piece of the three pieces is further split into five
pieces in the axial direction. The seventh embodiment can produce
the same advantage as the fifth one has done.
[0076] When rare-earth-sintered magnet is used as interior
permanent magnets in the rotor, splitting the magnet effects the
advantage distinctly because the rare-earth-sintered magnet has
less electrical resistance and is easier for current to run through
comparing with a ferrite magnet. (The specific resistance of the
ferrite magnet is not less than 10.sup.-4 .OMEGA..multidot.m, and
that of the rare-earth-sintered magnet is ca. 10.sup.-6
.OMEGA..multidot.m.) In other words, when the same magnitude of
change in the magnetic-flux-density is applied from outside to the
magnet, the rare-earth-sintered magnet allows the eddy current to
run through more than 100 times in volume than the ferrite magnet
does. Thus the split of such magnet effectively restraints the
production of eddy current.
[0077] A driving control of the motor is demonstrated hereinafter,
this motor includes the rotor with the interior magnet of the
present invention.
[0078] A motor with a stator wound by concentrated windings
produces greater changes in the magnetic-flux-density when the
motor is driven under weakening-magnetic-field control. Because in
the motor having a rotor with interior permanent magnets, the
magnetic-flux runs through the space between the magnets and the
outer circumference of the rotor core, and thus the magnetic-flux
is distributed unevenly between the rotor and the stator.
[0079] The weakening-magnetic-field control applies inverse
magnetic-filed to the motor so that the magnetic-flux produced by
the magnet can be counteracted, therefore, this control method
produces greater changes in the magnetic-flux than a regular
control method does. Further the inverse magnetic-field narrows
tolerance for irreversible demagnetization, and this produces a
possibility of heat demagnetization at a temperature which is a
matter of little concern in a normal condition. The
weakening-magnetic-field-control thus produces distinctly an
advantage of damping the heat generated by the eddy current.
[0080] It is preferable to restrain the production of eddy current
as well as the heat-generation from the eddy current by splitting
the magnet, and this shows distinctly its effect when the motor is
under weakening-magnetic-field-control.
[0081] The motor used in the embodiments discussed above is an
inner-rotor type, i.e. a rotor is disposed inside a stator,
however, an outer-rotor type, i.e. a rotor is disposed outside a
stator, and a linear motor, i.e. a rotor moves linearly with regard
to a stator, produce the same advantages.
[0082] As the exemplary embodiments discussed previously prove that
the motor with interior permanent magnets of the present invention
can restrain the production of eddy current and damp the heat
demagnetization because the magnet is electrically split and thus
an area of each magnet facing to the stator becomes narrower. The
motor under the weakening-magnetic-field control can further damp
the heat demagnetization.
[0083] (Exemplary Embodiment 8)
[0084] FIG. 10 is a block diagram of an electric vehicle in which
the motor of the present invention is mounted.
[0085] Body 80 of the electric vehicle is supported by wheels 81.
This vehicle employs a front-wheel-drive method, so that motor 83
is directly connected to front-wheel-shaft 82. Motor 83 includes a
stator being wound by concentrated windings and having interior
permanent magnets as described in the exemplary embodiments
previously discussed. Controller 84 controls the driving torque of
motor 83, and battery 85 powers controller 84 and further powers
motor 83. Motor 83 is thus driven, which then rotates wheels
81.
[0086] In this eighth embodiment, the motor is employed to drive
the wheels of the electric vehicle. The motor can be employed also
to drive wheels of an electric locomotive.
* * * * *