U.S. patent application number 10/107245 was filed with the patent office on 2002-10-17 for permanent magnet type rotary electric machine and electrically driven vehicle using the same.
This patent application is currently assigned to Hitachi, Ltd.. Invention is credited to Oda, Keiji, Shibukawa, Suetaro.
Application Number | 20020149289 10/107245 |
Document ID | / |
Family ID | 18495763 |
Filed Date | 2002-10-17 |
United States Patent
Application |
20020149289 |
Kind Code |
A1 |
Oda, Keiji ; et al. |
October 17, 2002 |
Permanent magnet type rotary electric machine and electrically
driven vehicle using the same
Abstract
A plurality of permanent magnets 6 are embedded in a cylindrical
rotor core 8 and arranged in a circumferential direction of the
rotor core 8. A pair of side rings 81 are mounted on the axial ends
of the rotor core 8. The outer diameter of each side ring 81 is set
smaller than the outer diameter of the rotor core 8. With this
structure, an eddy current generated in each side ring 81 can be
suppressed to thereby prevent abnormal heating and accordingly
prevent thermal demagnetization of the permanent magnets 6.
Inventors: |
Oda, Keiji; (Hitachinaka,
JP) ; Shibukawa, Suetaro; (Hitachinaka, JP) |
Correspondence
Address: |
CROWELL & MORING, L.L.P.
P.O. Box 14300
Washington
DC
20044-4300
US
|
Assignee: |
Hitachi, Ltd.
|
Family ID: |
18495763 |
Appl. No.: |
10/107245 |
Filed: |
March 28, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10107245 |
Mar 28, 2002 |
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09472519 |
Dec 27, 1999 |
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Current U.S.
Class: |
310/261.1 ;
310/156.08 |
Current CPC
Class: |
Y02T 10/64 20130101;
B60K 1/00 20130101; B60L 2240/423 20130101; Y02T 10/72 20130101;
Y02T 10/70 20130101; B60L 50/51 20190201; B60L 2240/425 20130101;
H02K 1/276 20130101; B60L 3/0061 20130101; B60L 50/66 20190201;
B60L 15/20 20130101; B60L 2240/36 20130101; B60L 2240/421
20130101 |
Class at
Publication: |
310/261 ;
310/156.08 |
International
Class: |
H02K 001/22; H02K
021/12 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 25, 1998 |
JP |
10-369970 |
Claims
What is claimed is:
1. A permanent magnet type rotary electric machine comprising: a
stator having a cylindrical stator core and a plurality of stator
windings wound on said stator core; and a rotor having a
cylindrical rotor core opposed to an inner circumferential surface
of said stator core with a given gap defined therebetween, a
plurality of permanent magnets embedded in said rotor core and
arranged in a circumferential direction of said rotor core, and a
pair of retainer plates mounted on the axial ends of said rotor
core; wherein the outer diameter of each of said retainer plates is
set smaller than the outer diameter of said rotor core.
2. A permanent magnet type rotary electric machine according to
claim 1, wherein the difference between the outer diameter of said
rotor core and the outer diameter of each of said retainer plates
is set to 1/2 or more of the difference between the inner diameter
of said stator core and the outer diameter of said rotor core.
3. A permanent magnet type rotary electric machine comprising: a
stator having a cylindrical stator core and a plurality of stator
windings wound on said stator core; and a rotor having a
cylindrical rotor core opposed to an inner circumferential surface
of said stator core with a given gap defined therebetween, a
plurality of permanent magnets embedded in said rotor core and
arranged in a circumferential direction of said rotor core, and a
pair of retainer plates mounted on the axial ends of said rotor
core; wherein each of said retainer plates is formed of a metal
material having a resistivity of 10 .mu..OMEGA.cm or higher.
4. A permanent magnet type rotary electric machine comprising: a
stator having a cylindrical stator core and a plurality of stator
windings wound on said stator core; and a rotor having a
cylindrical rotor core opposed to an inner circumferential surface
of said stator core with a given gap defined therebetween, a
plurality of permanent magnets embedded in said rotor core and
arranged in a circumferential direction of said rotor core, and a
pair of retainer plates mounted on the axial ends of said rotor
core; wherein the outer diameter of each of said retainer plates is
set smaller than the outer diameter of said rotor core, and each of
said retainer plates is formed of a metal material having a
resistivity of 10 .mu..OMEGA.cm or higher.
5. A permanent magnet type rotary electric machine comprising: a
stator having a cylindrical stator core and a plurality of stator
windings wound on said stator core; and a rotor having a
cylindrical rotor core opposed to an inner circumferential surface
of said stator core with a given gap defined therebetween, a
plurality of permanent magnets embedded in said rotor core and
arranged in a circumferential direction of said rotor core, and a
pair of nonmagnetic members mounted on the axial ends of said rotor
core; wherein each of said nonmagnetic members is formed of a
nonmetal material.
6. A permanent magnet type rotary electric machine comprising: a
stator having a cylindrical stator core and a plurality of stator
windings wound on said stator core; and a rotor having a
cylindrical rotor core opposed to an inner circumferential surface
of said stator core with a given gap defined therebetween, a
plurality of permanent magnets arranged in a circumferential
direction of said rotor core, and a pair of retainer plates mounted
on the axial ends of said rotor core; wherein the outer diameter of
each of said retainer plates is set smaller than the outer diameter
of said rotor core.
7. A permanent magnet type rotary electric machine comprising: a
stator having a cylindrical stator core and a plurality of stator
windings wound on said stator core; and a rotor having a
cylindrical rotor core opposed to an inner circumferential surface
of said stator core with a given gap defined therebetween, a
plurality of permanent magnets arranged in a circumferential
direction of said rotor core, and a pair of retainer plates mounted
on the axial ends of said rotor core; wherein each of said retainer
plates is formed of a metal material having a resistivity of 10
.mu..OMEGA.cm or higher.
8. A permanent magnet type rotary electric machine comprising: a
stator having a cylindrical stator core and a plurality of stator
windings wound on said stator core; and a rotor having a
cylindrical rotor core opposed to an inner circumferential surface
of said stator core with a given gap defined therebetween, a
plurality of permanent magnets arranged in a circumferential
direction of said rotor core, and a pair of nonmagnetic members
mounted on the axial ends of said rotor core; wherein each of said
nonmagnetic members is formed of a nonmetal material.
9. An electrically driven vehicle comprising: a battery for
supplying a DC voltage; an inverter for converting said DC voltage
supplied from said battery into an AC voltage; and a permanent
magnet type rotary electric machine for outputting a drive torque
for driving said vehicle at said AC voltage; said permanent magnet
type rotary electric machine comprising: a stator having a
cylindrical stator core and a plurality of stator windings wound on
said stator core; and a rotor having a cylindrical rotor core
opposed to an inner circumferential surface of said stator core
with a given gap defined therebetween, a plurality of permanent
magnets embedded in said rotor core and arranged in a
circumferential direction of said rotor core, and a pair of
retainer plates mounted on the axial ends of said rotor core;
wherein the outer diameter of each of said retainer plates is set
smaller than the outer diameter of said rotor core.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a compact, lightweight,
high-torque permanent magnet type rotary electric machine suitable
for use at high temperatures, and also to an electrically driven
vehicle using the rotary electric machine.
[0002] A driving motor for use in an electrically driven vehicle,
especially, in an electric vehicle is desired to have a compact,
lightweight configuration and high efficiency, because the capacity
of a battery mounted on the electric vehicle is limited and it is
necessary to ensure a sufficient distance traveled by the capacity
of the battery once fully charged.
[0003] To make a motor compact and lightweight, it is desired to be
fit for high-speed rotation. Further, as a high-efficient motor, a
permanent magnet motor is recommendable rather than a DC motor and
an induction motor. In particular, as compared with a surface
magnet motor having permanent magnets on the outer circumferential
surface of a rotor, a so-called internal magnet motor having a
permanent magnet holding portion in a steel plate, e.g., a silicon
steel plate, having a permeability higher than that of permanent
magnets is suitable for the high-efficient motor. The reason is
that the internal magnet motor can be operated up to high speeds by
field weakening control and can be operated with high efficiency by
field weakening control.
[0004] Further, as compared with the rotor of the surface magnet
motor, the rotor of the internal magnet motor has an advantage such
that the rotational strength of the rotor is determined by the
strength of the silicon steel plate, resulting in high reliability
in high-speed rotation. An example of such a motor configuration is
disclosed in Japanese Patent Laid-open No. 3-138050.
[0005] The motor configuration disclosed in this publication is
such that permanent magnets are embedded in a rotor core formed of
a magnetic material having a permeability higher than that of the
permanent magnets, and that auxiliary magnetic poles composed of
the permanent magnets and the rotor core are arranged in a
circumferential portion of the rotor core. By forming such an
internal magnet configuration that the permanent magnets are
embedded in the rotor core formed of a magnetic material having a
permeability higher than that of the permanent magnets, field
weakening control can be performed and the motor can be operated
with high efficiency up to a high-speed region.
[0006] However, the motor configuration disclosed in the above
publication has no consideration on a fixing method for the
permanent magnets, especially, on a fixing method for the permanent
magnets in the axial direction of the rotor core. Although the
above publication describes that the permanent magnets are bonded
in holes, there is a possibility that the permanent magnets may
axially escape from the holes because of a reduction in adhesive
strength by bonding only in the case of a rotary electric machine
to be operated at high temperatures.
[0007] To cope with this problem, a pair of retainer plates (which
will be hereinafter referred to as side rings) for preventing the
escape of the permanent magnets are mounted on the axial ends of
the rotor. Each side ring is formed of a nonmagnetic material to
prevent short of magnetic flux. However, in the case that each side
ring is formed of a metal material, an eddy current is generated in
each side ring by a change in magnetic flux from stator windings,
because of conductivity of the metal material, causing abnormal
heating of each side ring. Accordingly, there is a possibility of
high-temperature demagnetization of the permanent magnets due to
the heat from each side ring.
SUMMARY OF THE INVENTION
[0008] It is accordingly an object of the present invention to
provide a permanent magnet type rotary electric machine which can
prevent thermal demagnetization of the permanent magnets to thereby
effect a reduction in size and weight and a high torque.
[0009] It is another object of the present invention to provide an
electrically driven vehicle using the permanent magnet type rotary
electric machine.
[0010] According to an aspect of the present invention, the outer
diameter of each of a pair of retainer plates mounted on the axial
ends of a rotor core is set smaller than the outer diameter of the
rotor core, thereby suppressing the generation of an eddy current
in each retainer plate due to magnetic flux from stator
windings.
[0011] Preferably, the difference between the outer diameter of the
rotor core and the outer diameter of each retainer plate is set to
1/2 or more of the difference between the inner diameter of the
stator core and the outer diameter of the rotor core.
[0012] According to another aspect of the present invention, each
retainer plate is formed of a metal material having a resistivity
of 10 .mu..OMEGA.cm or higher, thereby suppressing the generation
of an eddy current in each retainer plate due to magnetic flux from
the stator windings.
[0013] According to a further aspect of the present invention, the
outer diameter of each retainer plate is set smaller than the outer
diameter of the rotor core, and each retainer plate is formed of a
metal material having a resistivity of 10 .mu..OMEGA.cm or higher,
thereby suppressing the generation of an eddy current in each
retainer plate due to magnetic flux from the stator windings.
[0014] According to a still further aspect of the present
invention, each retainer plate is a nonmagnetic member formed of a
nonmetal material, thereby suppressing the generation of an eddy
current in each retainer plate due to magnetic flux from the stator
windings.
[0015] According to a still further aspect of the present
invention, there is provided an electrically driven vehicle
comprising a battery for supplying a DC voltage; an inverter for
converting the DC voltage supplied from the battery into an AC
voltage; and a permanent magnet type rotary electric machine for
outputting a drive torque for driving the vehicle at the AC
voltage. The permanent magnet type rotary electric machine in this
electrically driven vehicle is the permanent magnet type rotary
electric machine according to the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is an axial sectional view of a permanent magnet type
rotary electric machine according to a preferred embodiment of the
present invention;
[0017] FIG. 2 is a cross section taken along the line A-A in FIG.
1;
[0018] FIG. 3 is an enlarged view of a portion B shown in FIG. 1;
and
[0019] FIG. 4 is a perspective view showing a schematic
configuration of an electric vehicle using the permanent magnet
type rotary electric machine of the present invention.
EXPLANATION OF REFERENCE NUMERALS
[0020] 1: rotary electric machine 2: stator 3: rotor 4: stator core
5: stator windings 6: permanent magnets 8: rotor core 81: side
rings 9: rotating shaft 10: housing 11: end bracket 12:
bearings
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0021] There will now be described a permanent magnet type rotary
electric machine and an electrically driven vehicle using the same
according to a preferred embodiment of the present invention with
reference to the drawings.
[0022] FIG. 1 is an axial sectional view of a permanent magnet type
rotary electric machine (which will be hereinafter referred to
simply as a rotary electric machine) 1 according to a preferred
embodiment of the present invention, and FIG. 2 is a cross section
taken along the line A-A in FIG. 1. The rotary electric machine 1
is composed generally of a stator 2 and a rotor 3.
[0023] The stator 2 is composed of a cylindrical housing 10, an end
bracket 11 fixed to the housing 10 by bolts, a cylindrical stator
core 4 fixed to the inner circumferential surface of the housing
10, and a plurality of stator windings 5 wound on the stator core
4.
[0024] The rotor 3 is composed of a cylindrical rotor core 8, a
plurality of permanent magnets 6 inserted in a plurality of holes 7
formed in the rotor core 8 near its outer circumferential surface,
a rotating shaft 9 fixed to the rotor core 8 at its central
portion, and a pair of side rings 81 mounted on the axial opposite
ends of the rotor core 8 for retaining the rotor core 8 and the
permanent magnets 6. The rotating shaft 9 is rotatably supported at
its opposite ends to a pair of bearings 12 fixed to the end bracket
11 and the housing 10. The end bracket 11 is screwed to be fixed to
the housing 10 of the rotator 2 side. Each of the permanent magnets
6 is arcuate as shown in FIG. 2, and they are arranged in the
circumferential direction of the rotor core 8 with a given pitch.
However, the shape of each permanent magnet 6 is merely
illustrative and not limitative in the present invention.
[0025] Each side ring 81 is formed of a nonmagnetic material to
prevent short of the magnetic flux generated by the permanent
magnets 6. In the case that each side ring 81 is formed of a
nonmagnetic metal material, it is affected by a change in the
magnetic flux generated by the stator windings 5 because of the
conductivity of the metal material, resulting in generation of an
eddy current in each side ring 81 to cause abnormal heating of each
side ring 81. This heat is transmitted to the permanent magnets 6
to possibly demagnetize the permanent magnets 6. Particularly in
the case that each permanent magnet 6 is a rare-earth magnet, it
has such a characteristic that demagnetization tends to occur at
high temperatures. Therefore, it is necessary to prevent heating of
each side ring 81, thereby preventing a reduction in performance of
the rotary electric machine.
[0026] To reduce the influence of a change in magnetic flux from
the stator windings 5 and thereby suppress the generation of an
eddy current, the outer diameter of each side ring 81 is set
smaller than the outer diameter of the rotor core 8.
[0027] Such a diameter difference will now be described in more
detail with reference to FIG. 3 which is an enlarged view of a
portion B shown in FIG. 1. The difference between the outer
diameter D2 of the rotor core 8 and the outer diameter D3 of each
side ring 81 is set preferably to 1/2 or more of the difference
between the inner diameter D1 of the stator core 4 and the outer
diameter D2 of the rotor core 8.
[0028] The reason for this setting will now be described.
[0029] In considering the influence of an eddy current on each side
ring 81 as a force F acting between the stator core 4 and the rotor
core 8, the following equation holds.
F=k.multidot.1/.delta..sub.1.sup.2 (1)
[0030] where .delta..sub.1 is the difference between the inner
diameter D1 of the stator core 4 and the outer diameter D2 of the
rotor core 8, and k is the constant determined by a shape, a
voltage input to the stator, etc.
[0031] Eq. (1) also holds for the difference .delta..sub.2 between
the outer diameter D2 of the rotor core 8 and the outer diameter D3
of each side ring 81, so that the relation between F and
.delta..sub.2 is shown in Table 1.
1TABLE 1 .delta..sub.2 F Ratio of decrease in F to .delta..sub.2
0.5 4 k -- the same as .delta..sub.1 0.6 2.8 k 70% 0.75 1.8 k 45%
1.5 times .delta..sub.1 1.00 1.0 k 25% 1.25 0.64 k 16%
[0032] As understood from Table 1, the influence of an eddy current
generated in each side ring 81 due to the magnetic flux generated
by the stator windings 5 can be reduced to a half or less by
setting .delta..sub.2 to a value 1.5 times or more .delta..sub.1,
i.e., by setting the difference between the outer diameter D2 of
the rotor core 8 and the outer diameter D3 of each side ring 81 to
1/2 or more of the difference between the inner diameter D1 of the
stator core 4 and the outer diameter D2 of the rotor core 8.
[0033] When the eddy current becomes a half, the loss W is reduced
to 1/4 in accordance with the following equation.
W=I.sup.2.multidot.R (2)
[0034] where R is the electrical resistance.
[0035] Accordingly, a temperature rise of each side ring 81 is also
reduced to 1/4.
[0036] Thus, the influence of the eddy current is reduced in
proportion to the square of a distance, so that it is preferable to
maximize the difference .delta..sub.2 between the outer diameter of
the rotor core 8 and the outer diameter of each side ring 81.
[0037] It is sufficient to use a nonmagnetic material as the
material of each side ring 81. However, if the nonmagnetic material
is a material having a relatively low resistivity, such as copper
and aluminum, the amperage of the eddy current is large.
Accordingly, a nonmagnetic metal material having a relatively high
resistivity of 10 .mu..OMEGA.cm or higher, such as stainless steel,
is preferable as the material of each side ring 81.
[0038] An increase in resistivity means an increase in electrical
resistance R in the following equation.
I=E/R (3)
[0039] where E is the voltage induced to each side ring.
[0040] In comparing aluminum (resistivity: 2.8 .mu..OMEGA.cm) and
stainless steel (resistivity: 10 .mu..OMEGA.cm), the resistivity of
stainless steel is higher than the resistivity of aluminum by 3.6
times. Accordingly, the amperage in stainless steel becomes
{fraction (1/3.6)} of the amperage in aluminum, and a temperature
rise in stainless steel can be reduced to {fraction (1/13)} of that
in aluminum.
[0041] More preferably, the above-mentioned two features are
combined. That is, the outer diameter of each side ring 81 is set
smaller than the outer diameter of the rotor core 8, and the
material of each side ring 81 is a metal material such as stainless
steel having a resistivity of 10 .mu..OMEGA.cm or higher, thereby
enhancing the effect.
[0042] Further, if the operating temperature condition and the
rotational strength of the rotary electric machine 1 are allowed, a
nonmetal material such as resin may also be used as the material of
each side ring 81. The resistivity of a resin material is much
higher than that of a metal material, so that no eddy current flows
in each side ring 81, thereby eliminating abnormal heating. In the
case of applying a resin material to the opposite ends of the rotor
core 8 to configure the side rings 81, a method of mounting
platelike members of resin on the opposite ends of the rotor core 8
and a resin molding method of molding the opposite ends of the
rotor core 8 with resin may be realized.
[0043] Having thus described a specific preferred embodiment
employing an internal rotor, the present invention is applicable
alto to a rotary electric machine employing an external rotor or
the like having a structure such that both sides of magnets are
sandwiched by a pair of side rings.
[0044] Further, the rotary electric machine of the present
invention is effective in the case that it is used as a drive motor
for an electrically driven vehicle.
[0045] As an example of the electrically driven vehicle using the
rotary electric machine of the present invention as a drive motor,
a schematic configuration of an electric vehicle is shown in FIG.
4. The electric vehicle includes a rotary electric machine 10
according to the present invention, a battery 20 for supplying a DC
voltage, an inverter 30 for converting the DC voltage supplied from
the battery into an AC voltage, and a control unit 40 for
controlling a drive torque and a rotating speed of the rotary
electric machine 10. Accordingly, the drive wheels of the vehicle
are driven by the rotary electric machine 10 with a given torque
and rotating speed controlled by the control unit 40.
[0046] The rotary electric machine of the present invention can
suppress a temperature rise as compared with a conventional rotary
electric machine. Accordingly, the rotary electric machine of the
present invention can be reduced in size to contribute to
mountability on the vehicle and weight reduction of the vehicle,
thereby improving the performance of the vehicle.
[0047] According to the present invention, thermal demagnetization
of the permanent magnets can be prevented to thereby effect a
reduction in size and weight of the permanent magnet type rotary
electric machine and also effect a high torque thereof.
[0048] Further, by applying the permanent magnet type rotary
electric machine of the present invention to an electrically driven
vehicle, the vehicle can be reduced in weight to thereby improve
the performance of the vehicle.
* * * * *