U.S. patent application number 14/724848 was filed with the patent office on 2015-09-17 for permanent magnet type rotary electric machine and electric power steering apparatus using the same.
This patent application is currently assigned to MITSUBISHI ELECTRIC CORPORATION. The applicant listed for this patent is Mitsubishi Electric Corporation. Invention is credited to Satoru AKUTSU, Toshihiro MATSUNAGA, Yusuke MORITA, Masatsugu NAKANO, Misa NAKAYAMA, Kazuhisa TAKASHIMA.
Application Number | 20150263571 14/724848 |
Document ID | / |
Family ID | 45810217 |
Filed Date | 2015-09-17 |
United States Patent
Application |
20150263571 |
Kind Code |
A1 |
NAKANO; Masatsugu ; et
al. |
September 17, 2015 |
PERMANENT MAGNET TYPE ROTARY ELECTRIC MACHINE AND ELECTRIC POWER
STEERING APPARATUS USING THE SAME
Abstract
Not less than two regions different in magnetic circuit design
are provided in a rotational axis direction of the rotor (30), the
regions being different by changing a cross-sectional shape in the
rotational axis direction in a cross-section perpendicular to a
rotational shaft (10) of the rotor (30) having the permanent
magnets (1) and the rotor core (2); the supplemental grooves (5)
are provided in axial partial regions of each of the teeth (7) of
the stator core (3); and the region in which the supplemental
groove (5) is provided is each partial region for each region
facing a region same in magnetic circuit design of the rotor (30).
This enables to reduce cogging torque generated by variations on
the rotor side.
Inventors: |
NAKANO; Masatsugu; (Tokyo,
JP) ; MATSUNAGA; Toshihiro; (Tokyo, JP) ;
MORITA; Yusuke; (Tokyo, JP) ; NAKAYAMA; Misa;
(Tokyo, JP) ; TAKASHIMA; Kazuhisa; (Tokyo, JP)
; AKUTSU; Satoru; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Mitsubishi Electric Corporation |
Tokyo |
|
JP |
|
|
Assignee: |
MITSUBISHI ELECTRIC
CORPORATION
Tokyo
JP
|
Family ID: |
45810217 |
Appl. No.: |
14/724848 |
Filed: |
May 29, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13697064 |
Nov 9, 2012 |
|
|
|
PCT/JP2010/065228 |
Sep 6, 2010 |
|
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14724848 |
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Current U.S.
Class: |
310/216.094 |
Current CPC
Class: |
H02K 1/276 20130101;
H02K 29/03 20130101; H02K 2213/03 20130101; H02K 1/146 20130101;
B62D 5/046 20130101; H02K 1/148 20130101; H02K 21/16 20130101; H02K
1/16 20130101; H02K 1/278 20130101 |
International
Class: |
H02K 1/14 20060101
H02K001/14; B62D 5/04 20060101 B62D005/04 |
Claims
1. A permanent magnet type rotary electric machine comprising: a
rotor having a plurality of magnetic poles composed of permanent
magnets and a rotor core; and a stator including armature windings
and a stator core which is provided with slots for incorporating
said armature windings and has a plurality of teeth facing said
rotor, each of said teeth of said stator core being provided with
supplemental grooves at portions facing said rotor, wherein not
less than two regions different in magnetic circuit design are
provided in a rotational axis direction of said rotor, the regions
being different by changing a cross-sectional shape in the
rotational axis direction in a cross-section perpendicular to a
rotational shaft of said rotor having said permanent magnets and
said rotor core; the supplemental grooves are provided in axial
partial regions of said tooth of said stator core; the region in
which the supplemental groove is provided is each partial region
for each region facing a same region in magnetic circuit design of
the rotor; and an axial end face of the supplemental groove is
located in an end face perpendicular to the rotational shaft
between the regions different in magnetic circuit design of said
rotor.
2. The permanent magnet type rotary electric machine according to
claim 1, wherein the region in which the supplemental groove is
provided is a region half of each axial length for each region
facing a same region in magnetic circuit design of the rotor.
3. The permanent magnet type rotary electric machine according to
claim 1, wherein a width Wd of the supplemental groove is larger
than an opening width Ws of the slot.
4. The permanent magnet type rotary electric machine according to
claim 1, wherein a depth Hd of the supplemental groove is larger
than a thickness Hs of an end portion of said tooth.
5. The permanent magnet type rotary electric machine according to
claim 1, wherein the supplemental groove is not provided in an
axial end portion of said stator core.
6. The permanent magnet type rotary electric machine according to
claim 1, wherein the supplemental groove is provided at one place
in a circumferential center portion of said stator core at a
portion in which the tooth faces said rotor.
7. The permanent magnet type rotary electric machine according to
claim 1, wherein when the number of poles of said magnetic poles of
said rotor is P and the number of the slots of said stator is S,
the following relationship is established: 0.75<S/P<1.5.
8. The permanent magnet type rotary electric machine according to
claim 1, wherein the number of poles P of said magnetic pole of
said rotor is 12n.+-.2n and the number of the slots S of said
stator is 12n, n being natural number.
9. The permanent magnet type rotary electric machine according to
claim 1, wherein the number of poles P of said magnetic pole of
said rotor is 9n.+-.n and the number of the slots S of said stator
is 9n, n being natural number.
10. A permanent magnet type rotary electric machine comprising: a
rotor having a plurality of magnetic poles composed of permanent
magnets and a rotor core; and a stator including armature windings
and a stator core which is provided with slots for incorporating
said armature windings and has a plurality of teeth facing said
rotor, each of said teeth of said stator core being provided with
supplemental grooves at portions facing said rotor, wherein the
plurality of said magnetic poles of said rotor are configured by
arranging not less than two groups of permanent magnets in a
rotational axis direction, respectively; the supplemental grooves
are provided in axial partial regions of said tooth of said stator
core; the region in which the supplemental groove is provided is
each partial region for each region facing not less than two groups
of said permanent magnets arranged in the rotational axis
direction; and an axial end face of the supplemental groove is
located in an end face perpendicular to the rotational shaft
between not less than two groups of said permanent magnets arranged
in the rotational axis direction.
11. The permanent magnet type rotary electric machine according to
claim 10, wherein the region in which the supplemental groove is
provided is a region half of each axial length for each region
facing not less than two groups of said permanent magnets arranged
in the rotational axis direction.
12. An electric power steering apparatus using the permanent magnet
type rotary electric machine as set forth in claim 1 as a driving
motor.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. application Ser.
No. 13/697,064, filed Nov. 9, 2012, which is a National Stage of
International Application No. PCT/JP2010/065228 filed Sep. 6, 2010,
the contents of all of which are incorporated herein by reference
in their entirety.
TECHNICAL FIELD
[0002] The present invention relates to a permanent magnet type
rotary electric machine which uses permanent magnets for field
system and an electric power steering apparatus using the same.
BACKGROUND ART
[0003] In recent years, a motor with small cogging torque has been
required for various applications such as industrial servo motors
and hoists for elevators. In focusing attention on such
applications for vehicles, an electric power steering apparatus has
become widespread for achieving an improvement in fuel consumption
and an improvement in steering performance. Cogging torque of a
motor for use in the electric power steering apparatus is
transmitted to a driver via gears; and therefore, reduction in
cogging torque of the motor is strongly desired in order to obtain
a smooth steering feeling. In response, one possible method to
reduce the cogging torque is to provide supplemental grooves in a
core of a stator. Such a method is disclosed in Patent Document 1,
Patent Document 2, and Patent Document 3.
RELATED ART DOCUMENT
Patent Document
[0004] Patent Document 1: Japanese Unexamined Patent Publication
No. 2001-25182
[0005] Patent Document 2: Japanese Unexamined Patent Publication
No. 2006-230116
[0006] Patent Document 3: Pamphlet of International Patent
Unexamined Publication No. WO2009/084151
DISCLOSURE OF THE INVENTION
Problems to be Solved by the Invention
[0007] The supplemental grooves are provided over the whole in a
rotational axis direction of the motor in a permanent magnet type
rotary electric machine of Patent Document 1; and therefore, a
problem exists in that the equivalent length of air gap becomes
longer and accordingly torque is reduced.
[0008] Furthermore, Patent Document 1, Patent Document 2, and
Patent Document 3 exert an effect to reduce cogging torque of the
number of pulsations and an integral multiple thereof of the least
common multiple of the number of poles and the number of slots;
however, a problem exists in that it is not possible to
sufficiently suppress a cogging torque component (a component which
pulsates the number of times corresponding to the number of slots
by one rotation of a rotor), the cogging torque component being
generated by variations on the rotor side, for example, an
attachment position error, a shape error, and/or variations in
magnetic characteristics of permanent magnets.
[0009] This invention has been made to solve the problem as
described above, and an object of the present invention is to
provide a permanent magnet type rotary electric machine which
reduces cogging torque and an electric power steering apparatus
using the same.
Means for Solving the Problems
[0010] According to the present invention, there is provided a
permanent magnet type rotary electric machine including: a rotor
having a plurality of magnetic poles composed of permanent magnets
and a rotor core; and a stator including armature windings and a
stator core which is provided with slots for incorporating the
armature windings and has a plurality of teeth facing the rotor.
Each of the teeth of the stator core is provided with supplemental
grooves at portions facing the rotor.
[0011] In the permanent magnet type rotary electric machine, not
less than two regions different in magnetic circuit design are
provided in a rotational axis direction of the rotor, the regions
being different by changing a cross-sectional shape in the
rotational axis direction in a cross-section perpendicular to a
rotational shaft of the rotor having the permanent magnets and the
rotor core; the supplemental grooves are provided in axial partial
regions of the tooth of the stator core; and the region in which
the supplemental groove is provided is each partial region for each
region facing a region same in magnetic circuit design of the
rotor.
Advantageous Effect of the Invention
[0012] The permanent magnet type rotary electric machine according
to the present invention can reduce cogging torque (component in
which the number of pulsations per one rotation of a rotor
corresponds to the number of slots), the cogging torque being
generated by variations on the rotor side, for example, an
attachment position error, a shape error, and/or variations in
magnetic characteristics of the permanent magnets.
[0013] Objects, features, aspects, and advantageous effects other
than the foregoing of the present invention will become more
apparent from the following detailed description of the present
invention for referring to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a cross-sectional view exemplarily showing a
permanent magnet type rotary electric machine according to
Embodiment 1 of the present invention;
[0015] FIG. 2 is a cross-sectional view taken along the line A1-A2
shown in FIG. 1;
[0016] FIG. 3 is a cross-sectional view taken along the line B1-B2
shown in FIG. 1;
[0017] FIG. 4 is a cross-sectional view taken along the line C1-C2
shown in FIG. 1;
[0018] FIG. 5 is a cross-sectional view taken along the line D1-D2
shown in FIG. 1;
[0019] FIG. 6 is a partial perspective view showing a stator core
according to Embodiment 1;
[0020] FIG. 7 is a perspective view showing a rotor according to
Embodiment 1; and
[0021] FIG. 8 is a partial perspective view showing a different
stator core according to Embodiment 1.
[0022] FIG. 9 is a perspective view showing a different rotor
according to Embodiment 1;
[0023] FIG. 10 is a partial cross-sectional view exemplarily
showing a permanent magnet type rotary electric machine including
the stator core of FIG. 6 and the rotor of FIG. 7;
[0024] FIG. 11 is a partial cross-sectional view exemplarily
showing a permanent magnet type rotary electric machine including a
stator core and the rotor of FIG. 7;
[0025] FIG. 12 is a partial cross-sectional view exemplarily
showing a permanent magnet type rotary electric machine including
the stator core of FIG. 8 and the rotor of FIG. 9;
[0026] FIG. 13 is a partial cross-sectional view exemplarily
showing a permanent magnet type rotary electric machine including a
stator core and the rotor of FIG. 9;
[0027] FIG. 14 is a cross-sectional view showing a rotor in the
case where an attachment position of a permanent magnet is out of
position from an ideally equally-spaced position;
[0028] FIG. 15 is an explanation view showing waveforms of a
cogging torque for a rotational angle of 30 degrees (mechanical
angle); and
[0029] FIG. 16 is an explanation view showing waveforms of a
cogging torque for a rotational angle 30 degrees (mechanical
angle).
[0030] FIG. 17 is an explanation view for comparing waveforms of
cogging torque of the present invention with that of a known
example (an supplemental groove is absent);
[0031] FIG. 18 is an explanation view showing frequency analysis
results of the cogging torque waveforms of FIG. 17;
[0032] FIG. 19 is an explanation view showing a histogram of
cogging torque of the known example;
[0033] FIG. 20 is an explanation view showing a histogram of
cogging torque of the present invention;
[0034] FIG. 21 is an explanation view showing an supplemental
groove and a slot opening portion;
[0035] FIG. 22 is an explanation view showing the relationship
between the width of an supplemental groove and cogging torque;
[0036] FIG. 23 is a cross-sectional view showing a permanent magnet
type rotary electric machine according to Embodiment 2; and
[0037] FIG. 24 is a cross-sectional view showing a different
example of a permanent magnet type rotary electric machine
according to Embodiment 2.
[0038] FIG. 25 is a cross-sectional view showing a further
different example of a permanent magnet type rotary electric
machine according to Embodiment 2;
[0039] FIG. 26 is a perspective view showing a rotor according to
Embodiment 3;
[0040] FIG. 27 is a partial perspective view showing a stator core
according to Embodiment 3;
[0041] FIG. 28 is a partial perspective view showing other example
of a stator core according to Embodiment 3;
[0042] FIG. 29 is a cross-sectional view showing a rotor according
to Embodiment 3;
[0043] FIG. 30 is a perspective view showing a rotor according to
Embodiment 4;
[0044] FIG. 31 is a partial perspective view showing a stator core
according to Embodiment 4;
[0045] FIG. 32 is a perspective view showing a different example of
a rotor according to Embodiment 4; and
[0046] FIG. 33 is a perspective view showing an electric power
steering apparatus according to Embodiment 5.
MODE FOR CARRYING OUT THE INVENTION
Embodiment 1
[0047] FIG. 1 shows a typical cross-sectional view in a plane
parallel to a rotational shaft and passing through the rotational
shaft on a permanent magnet type rotary electric machine of
Embodiment 1 of the present invention. Permanent magnets 1 are
mounted on the surface of a rotor core 2. Protrusion portions 8 are
provided near circumferential end portions of the permanent magnet
1 and the protrusion portions 8 are arranged so as to sandwich the
permanent magnets 1. In the case where each of the protrusion
portions 8 is arranged between the adjacent permanent magnets 1,
the protrusion portions 8 and the permanent magnets 1 are not
simultaneously illustrated in a cross-sectional view in a plane
parallel to a rotational shaft 10 and passing through the
rotational shaft 10; however, the protrusion portions 8 and the
permanent magnets 1 are simultaneously illustrated in FIG. 1 for
ease of understanding.
[0048] The rotational shaft 10 is press-fitted to the rotor core 2
and a rotor 30 is configured to be rotatable by bearings 11a, 11b.
A rotational angle sensor 14 that detects a rotational angle is
provided on the rotor 30. The rotational angle sensor 14 is formed
of, for example, a resolver or a Hall sensor and a magnet or an
encoder. A stator core 3 is provided so as to face the permanent
magnets 1; and, for example, the stator core 3 can be formed by
laminating magnetic steel sheets or formed of a dust core. Armature
windings 4 are wound around the stator core 3. A stator 40 is fixed
to a frame 13 by press-fitting, shrink-fitting, or the like and the
frame 13 is fixed to a housing 12.
[0049] Supplemental grooves 5 are provided at portions facing the
permanent magnets 1 of the stator core 3. Further, the supplemental
grooves 5 are provided at portions in a rotational axis direction.
FIG. 1 exemplifies the supplemental grooves 5 arranged at three
positions in the axis direction. Although description will be made
in detail later, axial positional relationship in which the
supplemental grooves 5 are provided is set according to the
protrusion portions 8.
[0050] Cross-sectional views in a plane perpendicular to the
rotational shaft 10 of FIG. 1 are shown in FIGS. 2, 3, 4, and 5.
FIGS. 2, 3, 4, and 5 are cross-sections taken along the lines
A1-A2, B1-B2, C1-C2, and D1-D2 shown in FIG. 1, respectively. In
these cross-sectional views, the permanent magnets 1 are attached
on the surface of the rotor core 2; and in these examples, the
number of poles (the number of magnetic poles) is 10. Further, the
permanent magnet 1 is semicylindrical in cross-sectional shape and
reduces harmonic components of magnetic flux to form induced
voltage into a sine wave shape; and accordingly, torque pulsations
are reduced. The rotor core 2 is provided with the protrusion
portions 8, each being formed by a part of the rotor core 2 and
made of the same material. The protrusion portions 8 serve to fix
and retain the permanent magnets 1 so as not to slip in a
circumferential direction.
[0051] Meanwhile, the stator core 3 of the stator 40 is provided
with slots 6, each for winding the armature winding 4. In an
example of FIG. 2, each of the armature windings 4 is intensively
wound around a tooth 7 extending in the radial direction of the
stator core 3; and the number of the slots is 12. The armature
winding is wound around all of the 12 teeth. Further, the number of
phases of the permanent magnet type rotary electric machine is 3;
and if they are expressed by U phase, V phase, and W phase, the
windings are arranged in the arrangement of U1+, U1-, V1-, V1+,
W1+, W1-, U2-, U2+, V2+, V2-, W2-, and W2+ as shown in FIG. 2. In
this case, signs + and - denote winding directions; and the winding
directions of + and - are opposite to each other. Further, U1+ and
U1- are connected in series and U2- and U2+ are also connected in
series. These two series circuits can be connected in parallel or
connected in series. The same applies to V phase and W phase.
Moreover, three phases can be connected in star connection or in
delta connection.
[0052] FIG. 2 is the cross-section taken along the line A1-A2 shown
in FIG. 1; and in the cross-section thereof, the supplemental
groove is not provided in the stator core 3 but the protrusion
portion 8 is provided in the rotor core 2. FIG. 3 is the
cross-section taken along the line B1-B2 shown in FIG. 1; and in
the cross-section thereof, the supplemental groove 5 is provided in
the stator core 3 and the protrusion portion 8 is provided in the
rotor core 2. FIG. 4 is the cross-section taken along the line
C1-C2 shown in FIG. 1; and in the cross-section thereof, the
supplemental groove 5 is not provided in the stator core 3 and the
protrusion portion 8 is not provided in the rotor core 2. FIG. 5 is
the cross-section taken along the line D1-D2 shown in FIG. 1; and
in the cross-section thereof, the supplemental groove 5 is provided
in the stator core 3 but the protrusion portion 8 is not provided
in the rotor core 2.
[0053] FIG. 6 is a partial perspective view showing the stator core
of the permanent magnet type rotary electric machine of FIG. 1.
FIG. 6 shows only one half, that is, six teeth out of the 12 teeth
for ease of understanding the present invention. The stator core 3
is provided with the teeth 7 radially extending and facing the
permanent magnets; and the supplemental grooves 5 are provided on
the surface of the end of each tooth 7, the Surface being faced to
the rotor. The supplemental grooves 5 are arranged at three
positions in the axis direction and the supplemental groove 5 near
the axial center is longer in axial length than other two
supplemental grooves 5.
[0054] FIG. 7 is a perspective view showing the rotor of the
permanent magnet type rotary electric machine of FIG. 1. Portions
in which the rotational shaft 10 is protruded from the end faces of
the rotor core 2 are omitted for simplicity. Furthermore, a
protective cover of the permanent magnet 1 is omitted. The
permanent magnets 1 are provided on the surface of the rotor core 2
and each of the protrusion portions 8 is provided between the
adjacent permanent magnets 1. Further, the protrusion portions 8
are provided on both axial end portions. In the case where the
protrusion portion 8 is formed of a magnetic material, the
configuration of magnetic circuit in a cross-section of a plane
perpendicular to the rotational shaft 10 is different between a
cross-section of a portion in which the protrusion portion 8 is
present and a cross-section of a portion in which the protrusion
portion 8 is not present.
[0055] If the protrusion portions 8 are present, effects exist in
that the protrusion portions 8 prevent the permanent magnets 1 from
being out of position in the circumferential direction and make the
permanent magnets 1 position easily; however, in the case where the
presence or absence of the protrusion portions 8 changes in the
axis direction or the size of the protrusion portion 8 changes in
the axis direction, a problem exists in that cogging torque
increases because the magnetic circuit is not uniform in the axis
direction. More particularly, cogging torque caused by variations
in attachment position, shape, and/or characteristics of the
permanent magnet 1 may increase. The present invention has an
object to provide the arrangement of the supplemental groove 5
capable of effectively reducing the cogging torque in the permanent
magnet type rotary electric machine including the rotor 30 that has
the configuration of at least two types of magnetic circuits.
[0056] Hereinafter, the arrangement of the supplemental groove 5
intended for reduction in cogging torque will be described in
detail. FIG. 10 is a cross-sectional view of the permanent magnet
type rotary electric machine of FIG. 1, that is, the permanent
magnet type rotary electric machine including the stator core of
FIG. 6 and the rotor of the FIG. 7 and exemplarily shows the
cross-sectional view in a plane passing through the rotational
shaft. In FIG. 10, symbols A and B are used to discriminate the
configuration of the magnetic circuit on the rotor 30 side. A
region in which the protrusion portion 8 is present is expressed by
A; and a region in which the protrusion portion is not present is
expressed by B. In this example, the protrusion portions 8 are
provided on both axial end portions; and therefore, arrangement is
made in the order of the region A, the region B, and the region A
from above toward the page space in FIG. 10. Further, the axial
length of these regions is illustrated by symbols Lr1, Lr2, and
Lr3, respectively. Meanwhile, in the stator 40 side, a region in
which the supplemental groove 5 is absent is expressed by X; and a
region in which the supplemental groove 5 is present is expressed
by Y. Arrangement is made in the order of X, Y, X, Y, X, Y, and X
from above toward the page space in FIG. 10. Further, the axial
length of these regions is illustrated by symbols Ls1, Ls2, Ls3,
Ls4, Ls5, Ls6, and Ls7, respectively.
[0057] A dashed line in FIG. 10 is a line showing a plane
perpendicular to the shaft. The same applies to FIG. 11, FIG. 12,
and FIG. 13. The dashed line in FIG. 10 shows that the position of
an axial end face of the protrusion portion 8 is the same as that
of an axial end face of the supplemental groove 5. For example, the
lower end face of the upper protrusion portion 8 toward the page
space corresponds to the lower end face of the upper supplemental
groove toward the page space. Incidentally, FIG. 10, FIG. 11, FIG.
12, and FIG. 13 show that the axial position on the stator side
corresponding to the axial position on the rotor side is the same
at the positions of the dashed line. In FIG. 10, a relation
equation of Lr1=Ls1+Ls2 is established. Similarly, relation
equations of Lr2=Ls3+Ls4+Ls5 and Lr3=Ls6+Ls7 are established.
[0058] Next, description will be made on a mechanism in which
cogging torque can be considerably reduced if the supplemental
grooves 5 are arranged as shown in FIG. 10. Ten permanent magnets 1
in the rotor in FIGS. 2 to 5 and FIG. 7 show examples in which the
attachment positions of the permanent magnets are equally spaced
and the cross-sectional shapes thereof are also the same. However,
in fact, variations in manufacture are possible. For example, even
when the permanent magnets 1 are accurately attached, the
attachment position of the permanent magnets 1 is not equally
spaced and may be out of position by approximately several .mu.m to
100 .mu.m in the circumferential direction. Meanwhile, there may be
assumed a case where a cross-sectional shape is not also an ideally
bilaterally symmetrical shape, one of the right and left
thicknesses increases, and the other thickness decreases. Such an
example is shown in FIG. 14.
[0059] FIG. 14 shows that the attachment position of the permanent
magnets is out of position from an ideally equally-spaced position
in a direction shown by an arrow. Further, a cross-sectional shape
is not also bilaterally symmetrical and a portion of a
semicylindrical apex moves in the arrow direction, which shows the
cross-sectional shape is not bilaterally symmetrical. As described
above, if variations occur in the rotor, cogging torque increases
and a component which pulsates the number of times same as the
number of slots per one rotation of the rotor appears. In the
example of Embodiment 1, the number of slots is 12; and therefore,
cogging torque appears 12 times by one rotation of the rotor, that
is, cogging torque appears at a period of 30 degrees (360
degrees/12=30 degrees) in mechanical angle.
[0060] FIGS. 15, 16 are views showing waveforms of a cogging torque
for a rotational angle of 30 degrees (mechanical angle). A waveform
shown by the curve A-X in FIG. 15 shows a cogging torque waveform
at the time when variations in the permanent magnets 1 are in a
state of FIG. 14 in the case where the stator 40 and the rotor 30
of the permanent magnet type rotary electric machine are equally
configured in "the presence of the protrusion portion and the
absence of the supplemental groove." Meanwhile, a waveform shown by
the curve A-Y shows a cogging torque waveform at the time when
variations in the permanent magnets 1 are in the state of FIG. 14
in the case where the stator 40 and the rotor 30 are equally
configured in "the presence of the protrusion portion and the
presence of the supplemental groove." It is observed that these
waveforms are large in component with a period of 30 degrees in
mechanical angle, which shows that the cogging torque is large.
[0061] Further, a waveform shown by an explanatory note "invention"
in FIG. 15 is a waveform of cogging torque when variations in the
permanent magnets 1 are in the state of FIG. 14 in the case where
"the presence of the protrusion portion and the absence of the
supplemental groove" and "the presence of the protrusion portion
and the presence of the supplemental groove" are simultaneously
provided, so that the waveform becomes an average waveform of two
waveforms. This waveform is extremely small in component with a
period of 30 degrees in mechanical angle and the cogging torque can
be considerably reduced. This makes phases of components with a
period of 30 degrees in mechanical angle invert by providing the
supplemental grooves 5 to cancel out cogging torque at the portion
in which the supplemental groove 5 is provided and cogging torque
at the portion in which the supplemental groove 5 is absent; and
accordingly, the cogging torque is considerably reduced.
[0062] Similarly, FIG. 16 shows cogging torque waveforms at the
time when variations in the permanent magnets 1 are in the state of
FIG. 14 in the case where a waveform shown by the curve B-X is in
"the absence of the protrusion portion and the absence of the
supplemental groove" and a waveform shown by the curve B-Y is in
"the absence of the protrusion portion and the presence of the
supplemental groove." Meanwhile, a waveform of the invention is a
waveform of cogging torque when variations in the permanent magnets
1 are in the state of FIG. 14 in the case where "the absence of the
protrusion portion and the absence of the supplemental groove" and
"the absence of the protrusion portion and the presence of the
supplemental groove" are simultaneously provided, so that the
waveform becomes an average waveform of two waveforms. This case
also shows that the waveform is extremely small in component with a
period of 30 degrees in mechanical angle, and therefore, the
cogging torque can be considerably reduced.
[0063] Further, attention needs to be paid that the A-X waveform of
FIG. 15 differs from the B-X waveform of FIG. 16 and the A-Y
waveform of FIG. 15 differs from the B-Y waveform of FIG. 16. This
shows that cogging torque cannot be sufficiently cancelled out in
the A-X waveform and the B-Y waveform and cogging torque cannot
also be sufficiently cancelled out in the B-X waveform and the A-Y
waveform. Therefore, in order to sufficiently reduce a component
with a period of 30 degrees in mechanical angle, the arrangement of
the supplemental groove 5 needs to consider the arrangement of the
protrusion portions 8, that is, magnetic circuit design on the
rotor 30 side needs to be considered. Consequently, if the
arrangement of the supplemental grooves is made as shown in FIG.
10, the A-X waveform and the A-Y waveform can be cancelled out in
the region of the axial length Lr1 and the region of the axial
length Lr3; and the B-X waveform and the B-Y waveform can be
cancelled out in the region of the axial length Lr2; and therefore,
the cogging torque can be considerably reduced. The axial length of
providing the supplemental groove 5 should be approximately 1/2
(for example, 1/2.+-.10%) of the axial length of the stator core,
and more preferably 1/2 (for example, 1/2.+-.5%).
[0064] Further, in FIG. 10, if the following is given:
Ls1=Ls2=Lr1/2,
Ls4=Ls3+Ls5=Lr2/2, and
Ls6=Ls7=Lr3/2,
the axial length of the regions of A-X is equal to that of the
regions of A-Y, and the axial length of the regions of B-X is equal
to that of the regions of B-Y; and therefore, it becomes a
configuration in which the effect of reduction in cogging torque
can be more exerted.
[0065] FIG. 17 is a view for comparing waveforms of cogging torque
of the configuration of FIG. 10 with cogging torque in the case
where the supplemental grooves 5 are not provided as a known
example. Standardization is made so that the maximum value of the
cogging torque of the known example is 100%. Dashed lines depict
the waveform of cogging torque of the known example and components
which pulsate 12 times by one rotation of the rotor are noticeably
observed. Meanwhile, the invention shown by a solid line is the
cogging torque waveform of the configuration of FIG. 10 and
confirmation can be made that cogging torque can be considerably
reduced. FIG. 18 is frequency analysis results of the cogging
torque waveforms of FIG. 17. The invention can considerably reduce
a 12th-order component of cogging torque caused by variations on
the rotor 30 side as compared to the known example.
[0066] The above has described the case where a pattern of
variations is as shown in FIG. 14. In order to verify the
advantageous effect of the invention, a histogram is created for
the 12th-order component of cogging torque (component in which the
number of pulsations corresponds to the number of slots) in a total
of 10,000 rotary electric machines on the assumption that random
variations occur in each of the ten permanent magnets. The results
are shown in FIG. 19 and FIG. 20. FIG. 19 is a histogram of the
known example and FIG. 20 is a histogram of the configuration of
FIG. 10 (the invention). A vertical axis is frequency; and a
horizontal axis is the amplitude of cogging torque and is shown in
percent value as in a vertical axis of FIG. 17. Comparison is made
on the assumption that variation conditions on the rotor 30 side
are the same. Cogging torque is widely distributed in FIG. 19 and
therefore a problem exists in that the cogging torque becomes large
according to the pattern of variations.
[0067] However, in the configuration of the invention, it shows
that the cogging torque is small regardless of the pattern of
variations in the permanent magnets 1 of the rotor 30. That is, the
permanent magnet type rotary electric machine with high robustness
against variations in manufacture on the rotor 30 side can be
obtained. The configuration of the known supplemental grooves is
targeted at the effect of reduction in component in which the
number of pulsations per one rotation of the rotor corresponds to
the least common multiple of the number of poles and the number of
slots; and therefore, the effect of reduction cannot be
sufficiently obtained for a component (component in which the
number of pulsations corresponds to the number of slots) generated
by the variations on the rotor 30 side.
[0068] The configuration of FIG. 11 can also obtain an effect
similar to that of FIG. 10. FIG. 11 is an example in which the
arrangement of the protrusion portions 8 of the rotor core 2 is the
same as that of FIG. 10, but the arrangement of the supplemental
grooves 5 of the stator core 3 is different. The example is such
that the supplemental groove 5 provided in the region of Ls4 shown
in FIG. 10 is provided in regions of Ls3 and Ls5; and accordingly,
the supplemental grooves. 5 are arranged at two places in the axis
direction. The arrangement of such supplemental grooves 5 can also
obtain the effect of reduction in cogging torque by a mechanism
described in the example of FIG. 10. Furthermore, as in FIG. 10,
the axial length of providing the supplemental groove 5 should be
approximately 1/2 (for example, 1/2.+-.10%) of the axial length of
the stator core, and more preferably 1/2 (for example,
1/2=.sup.1=5%).
[0069] Further, it goes without saying that, in FIG. 11, if the
following is given:
Ls1=Ls2=Lr1/2,
Ls4=Ls3+Ls5=Lr2/2, and
Ls6=Ls7=Lr3/2,
the axial length of the regions of A-X is equal to that of the
regions of A-Y, and the axial length of the regions of B-X is equal
to that of the regions of B-Y; and therefore, it becomes a
configuration in which the effect of reduction in cogging torque
can be more exerted.
[0070] Although the examples in which the protrusion portions 8 are
arranged on both axial end portions are described in FIGS. 6, 7,
10, and 11, an application range of the present invention is not
limited to these examples. Other examples are shown in FIGS. 8 and
9. FIG. 8 is a partial perspective view showing a different stator
core of a permanent magnet type rotary electric machine according
to Embodiment 1. FIG. 8 shows one half, that is, six teeth out of
the 12 teeth for ease of understanding. FIG. 9 is a perspective
view showing a different rotor of a permanent magnet type rotary
electric machine according to Embodiment 1. Portions in which the
rotational shaft 10 is protruded from the end faces of the rotor
core 2 are omitted for simplicity. Furthermore, a protective cover
of the permanent magnet 1 is omitted. The permanent magnets 1 are
provided on the surface of the rotor core 2. Protrusion portions 8,
each being formed by a part of the rotor core 2 and made of the
same material, are provided between the adjacent permanent magnets
1 to fix and retain the permanent magnets 1. Further, the
protrusion portions 8 are provided at positions apart from both
axial end portions by a predetermined distance.
[0071] Cross-sectional views corresponding to these examples are
shown in FIG. 12 and FIG. 13. In FIG. 12 and FIG. 13, the
protrusion portions 8 of the rotor core are provided at two places
in the axis direction and the axial positions thereof are apart
from end portions by Lr1 or Lr5. With respect to the configuration
of such a rotor, FIG. 12 shows an example in which three
supplemental grooves 5 are arranged in the axis direction of the
stator core 3 and FIG. 13 shows an example in which two
supplemental grooves 5 are arranged. If the arrangement of the
supplemental grooves 5 is made as shown in FIG. 12, the A-X
waveform and the A-Y waveform can be cancelled out in a region of
an axial length Lr2 and a region of an axial length Lr4; and the
B-X waveform and the B-Y waveform can be cancelled out in a region
of axial lengths Lr1, Lr3, and Lr5; and therefore, the cogging
torque can be considerably reduced. The axial length of providing
the supplemental groove 5 should be approximately 1/2 (for example,
1/2.+-.10%) of the axial length of the stator core, and more
preferably 1/2 (for example, 1/2.hoarfrost.5%).
[0072] Further, in FIG. 12, if the following is given:
Ls1=Ls2=Lr1/2,
Ls3=Ls4=Lr2/2,
Ls5+Ls7=Ls6=Lr3/2,
Ls8=Ls9=Lr4/2, and
Ls10=Ls11=Lr5/2,
the axial length of the regions of A-X is equal to that of the
regions of A-Y, and the axial length of the regions of B-X is equal
to that of the regions of B-Y; and therefore, it becomes a
configuration in which the effect of reduction in cogging torque
can be more exerted.
[0073] Meanwhile, if the arrangement of the supplemental grooves 5
is made as shown in FIG. 13, the A-X waveform and the A-Y waveform
can be cancelled out in a region of an axial length Lr2 and a
region of an axial length Lr4; and the B-X waveform and the B-Y
waveform can be cancelled out in a region of axial lengths Lr1,
Lr3, and Lr5; and therefore, the cogging torque can be considerably
reduced. The axial length of providing the supplemental groove 5
should be approximately 1/2 (for example, 1/2.+-.10%) of the axial
length of the stator core, and more preferably 1/2 (for example,
1/2.+-.5%).
[0074] Further, in FIG. 13, if the following is (given:
Ls1=Lr1,
Ls2=Ls3=Lr2/2,
Ls7=Ls8=Lr4/2,
Ls4+Ls6=Ls1+Ls5+Ls9=(Lr1+Lr3+Lr5)/2, and
Ls9=Lr5,
the axial length of the regions of A-X is equal to that of the
regions of A-Y, and the axial length of the regions of B-X is equal
to that of the regions of B-Y; and therefore, it becomes a
configuration in which the effect of reduction in cogging torque
can be more exerted.
[0075] Although the examples shown in this time are those in which
the presence or absence of the protrusion portion of the rotor core
changes in the axis direction, the application of the present
invention is not limited to these examples. In the case where not
less than two types of regions different in magnetic circuit design
of the rotor are provided in the axis direction, for example, in
the case where the protrusion portions are not present but concave
portions are present between the adjacent permanent magnets, in the
case where the cross-sectional shape of the permanent magnet
changes, and the like, the supplemental grooves are provided in a
similar manner; and accordingly, cogging torque can be considerably
reduced.
[0076] As described above, in the rotor, if the configuration is
made such that not less than two regions different in magnetic
circuit design are provided in the axis direction, the regions
being different by changing at least one of a cross-sectional shape
in the rotational axis direction in a cross-section perpendicular
to the rotational shaft of the rotor core and a cross-sectional
shape in a cross-section perpendicular to the rotational shaft of
the permanent magnets; the supplemental grooves are provided in the
axial partial regions of the stator core; and the region in which
the supplemental groove is provided is each partial region for each
region facing a region same in magnetic circuit design of the
rotor, it becomes possible to considerably reduce cogging torque
(component in which the number of pulsations by one rotation of the
rotor corresponds to the number of slots), the cogging torque being
generated by variations on the rotor side, for example, an
attachment position error, a shape error, and/or variations in
magnetic characteristics of the permanent magnets. Incidentally,
the above mentioned region facing a region same in magnetic circuit
design of the rotor represents a stator side region corresponding
to a region same in magnetic circuit design of the rotor at the
time when the rotor side and the stator side are delimited in a
plane perpendicular to the shaft.
[0077] Further, if the configuration is made such that the region
in which the supplemental groove is provided is a half of each
axial length for each region facing a region same in magnetic
circuit design of the rotor, an effect is sufficiently exerted in
that cogging torque generated at the region in which the
supplemental groove is provided and cogging torque generated at the
region in which the supplemental groove is not provided are
cancelled out. Therefore, it becomes possible to more effectively
reduce cogging torque (component in which the number of pulsations
by one rotation of the rotor corresponds to the number of slots),
the cogging torque being generated by variations on the rotor side,
for example, an attachment position error, a shape error, and/or
variations in magnetic characteristics of the permanent
magnets.
[0078] If the configuration is made such that a region provided
with the protrusion portion in an axial portion of the rotor core
is present, positioning of the permanent magnets can be made
because of the presence of the protrusion portion; and therefore,
an effect exists in that the accuracy of the attachment position
improves. At the same time, the configuration is made such that the
supplemental groove is provided; and accordingly, this allows to
prevent cogging torque generated by the difference in magnetic
circuit design due to the protrusion portion from increasing, and
to effectively reduce cogging torque (component in which the number
of pulsations by one rotation of the rotor corresponds to the
number of slots) generated by variations on the rotor side.
Furthermore, the configuration is made such that the supplemental
grooves are not provided at axial end portions as shown in FIGS. 6
and 8; and accordingly, a portion having a large gap formed with
respect to the rotor at each axial end portion can be reduced as
compared to the case where the supplemental grooves are provided at
the axial end portions. This increases an effect that prevents
foreign particles from entering into the gap portion between the
stator and the rotor.
[0079] Next, the shape of the supplemental groove will be
described. FIG. 21 is a view for explaining the width of the
supplemental groove Wd, the depth of the supplemental groove Hd,
the width of a slot opening Ws, and the thickness of a tooth end
portion Hs. In the structure of the present invention, phases of
components in which the number of cogging torque pulsations
corresponds to the number of slots are inverted at a portion in
which the supplemental groove is provided and a portion in which
the supplemental groove is not provided to obtain a cancelling out
effect; and therefore, the selection of the shape of the
supplemental groove has an influence on the size of the effect.
FIG. 22 is a graph in which a horizontal axis is the ratio of the
width of the supplemental groove Wd to the width of the slot
opening Ws and a vertical axis is overall values of the cogging
torque at the time when variations occur in the rotor.
[0080] As compared to the case where Wd/Ws=0, in other words, the
supplemental groove is not provided; if Wd/Ws.gtoreq.1.0, the
cogging torque is not more than 1/2 of the case where the
supplemental groove is not provided. Further, if Wd/Ws.gtoreq.1.25,
the cogging torque is 0.001 Nm that is an extremely small value. If
the cogging torque due to variations of the rotor is suppressed to
this extent, for example, in the case where a rotary electric
machine is incorporated in an electric power steering apparatus (to
be described later), an effect is obtained in that a driver can
obtain good steering feeling without feeling cogging torque.
[0081] If Wd/Ws.gtoreq.1.0, phases of components in which the
number of cogging torque pulsations corresponds to the number of
slots can be inverted by changing components of permeance
pulsations due to the slots of the stator core; and therefore,
cogging torque at the portion in which the supplemental groove 5 is
provided and cogging torque at the portion in which the
supplemental groove is absent can be cancelled out each other. In
the case where one supplemental groove is provided,
Wd/Ws.gtoreq.1.0 can be used; and in the case where not less than
two supplemental grooves are provided, Wd/Ws.gtoreq.1.0 can be used
by defining the total of the widths of all the supplemental grooves
provided in the tooth as Wd; and accordingly, similar effects can
be obtained.
[0082] Further, the depth of the supplemental groove Hd is
preferably larger than the thickness of the tooth end portion Hs.
Also, phases of components in which the number of pulsations
corresponds to the number of slots can be inverted by changing the
component of permeance pulsations due to the slots of the stator
core. It becomes possible to sufficiently exert an effect that
cancels out the above mentioned cogging torque the portion in which
the supplemental groove is provided and cogging torque at the
portion in which the supplemental groove is absent.
[0083] Patent Document 1, Patent Document 2, and Patent Document 3
disclose examples in which two or not less than two supplemental
grooves are provided in each tooth in the circumferential
direction; however, in Embodiment 1, one supplemental groove is
provided at a circumferential center portion in each tooth. A
cogging torque Sth-order component (S is the number of slots)
generated by variations on the rotor side is largely involved with
an Sth-order component of permeance pulsations due to the slots of
the stator; however, an effects exists in that it is easy to change
an amplitude and a phase of the Sth-order component of the
permeance pulsations by providing one supplemental groove. When the
number of the supplemental grooves is smaller, the average length
of gap becomes shorter. Therefore, one supplemental groove is
provided at the circumferential center portion and only at an axial
portion; and accordingly, degradation of torque during load
application can be minimized.
[0084] In Embodiment 1, the supplemental groove has a shape formed
by cutting out the core in a rectangular shape, but the
supplemental groove is not limited to this shape. For example, it
goes without saying that similar effects can be obtained by a shape
formed by cutting out the core in an arc-like shape, cutting out in
a triangle shape, and the like. Furthermore, the permanent magnet
type rotary electric machine with 10 poles and 12 slots shown in
Embodiment 1 is larger in the winding factor of a fundamental wave
than that with the number of poles:the number of slots=2:3, which
has been conventionally and widely used; and therefore, the rotary
electric machine in Embodiment 1 is suitable for use in small size
and high output machines. In addition, as compared to a rotary
electric machine with the same number of slots, the least common
multiple of the number of poles and the number of slots is 60 in
the case of 10 poles and 12 slots, and 24 in the case of 8 poles
and 12 slots; and accordingly, the rotary electric machine with 10
poles and 12 slots is smaller in cogging torque of order of the
least common multiple. However, a problem exists in that cogging
torque caused by variations on the rotor side of the rotary
electric machine with 10 poles and 12 slots is larger than that
with 8 poles and 12 slots and robustness against variations in
manufacture is low. However, the problem can be solved by
Embodiment 1; and therefore, there can be obtained a permanent
magnet type rotary electric machine which achieves small size and
high output, and reduction in cogging torque caused by variations
in manufacture at the same time.
[0085] Embodiment 1 shows the example in which the protrusion
portions are provided on the rotor core. If the protrusion portions
are present; effects exist in that positioning of the permanent
magnets can be made and the permanent magnets can be prevented from
being out of position in the circumferential direction; whereas, a
problem exists in that a cogging torque Sth-order component (S is
the number of slots) becomes large due to the difference of
magnetic circuit design. However, Embodiment 1 can solve the
problem and can achieve the effects of positioning the permanent
magnets and preventing the permanent magnets from being out of
position in the circumferential direction, and the reduction in the
cogging torque Sth-order component at the same time.
Embodiment 2
[0086] Embodiment 1 describes the example in which the number of
poles (the number of magnetic poles) is 10 and the number of slots
is 12; however, the present invention is not limited to this
example. In the case of the combination of the following
relationship
0.75<S/P<1.5,
where, P is the number of poles and S is the number of slots in a
permanent magnet type rotary electric machine, there is known a
small size and high torque permanent magnet type rotary electric
machine in which the winding factor is high and magnetic flux of
permanent magnets is efficiently used as compared to the case of
S/P=0.75 and S/P=1.5 described in Patent Document 1, Patent
Document 2, and Patent Document 3.
[0087] Further, the least common multiple of the number of poles
and the number of slots are large; and therefore, it is also known
that a cogging torque component which pulsates the number of times
corresponding to the least common multiple of the number of poles
and the number of slots by one rotation of a rotor is small as
compared to the case of S/P=0.75 and S/P=1.5. Meanwhile, a problem
exists in that a cogging torque Sth-order component (component
which pulsates the number of S times by one rotation of the rotor)
is large and robustness against variations on the rotor side is
low, the cogging torque Sth-order component being generated by
variations on the rotor side, for example, an attachment position
error, a shape error, and/or variations in magnetic characteristics
of the permanent magnets. Therefore, this problem needs to be
solved in the permanent magnet type rotary electric machine to be
mass-produced as in the case where the rotary electric machine is
incorporated in an electric power steering apparatus.
[0088] Then, if the present invention is applied to the permanent
magnet type rotary electric machine having the combination of the
following relationship
0.75<S/P<1.5,
this enables to increase robustness against variations on the rotor
side and to reduce the cogging torque Sth-order component.
[0089] Among the permanent magnet type rotary electric machines
satisfying the following relationship
0.75<S/P<1.5,
FIG. 23 shows an example having P=14 and S=12, FIG. 24 shows an
example having P=8 and S=9, and FIG. 25 shows an example having
P=10 and S=9.
[0090] One supplemental groove 5 is provided in each tooth. FIGS.
23, 24, and 25 are cross-sectional views each showing a
cross-sectional view of portions in which the supplemental grooves
5 are provided. Although there are portions in which the
supplemental grooves 5 are not provided according to an axial
position as in Embodiment 1, such a drawing is omitted. If such a
configuration is made, the winding factor is high; and therefore,
both effects can be achieved at the same time, one effect being a
small size and high torque and the other effect being high in
robustness against variations on the rotor side.
[0091] Furthermore, the same effect can be obtained with the
combination of an integral multiple of the number of poles and the
number of slots. Therefore, when expressed generally including the
number of poles P=10 and the number of slots S=12, the same effects
can be obtained if the following is given:
the number of poles P=12n.+-.2n and the number of slots S=12n,
and
the number of poles P=9n.+-.n and the number of slots S=9n,
where n is natural number.
Embodiment 3
[0092] The aforementioned embodiments are the examples of the
surface magnet type in which the permanent magnets are attached on
the surface of the rotor core; however, the present invention can
be applied, but not limited to this example. FIG. 26 is a magnet
embedded type structure in which permanent magnets 1 are embedded
in a plurality of opening portions 9 (FIG. 29) provided inside a
rotor core 2 in a rotational axis direction. A rotational shaft 10
is inserted in the rotor core 2. The permanent magnets 1, each
having a flat shape, are embedded in the rotor core 2 to constitute
a plurality of magnetic poles. Further, the rotor core 2 includes
concave grooves 2a each provided on a surface portion at an axial
portion between the adjacent magnetic poles along the magnetic
poles. A cross-sectional view having the concave grooves 2a is
shown in FIG. 29. The permanent magnet 1 is embedded in the opening
portion 9 of the rotor core 2 and non-magnetic air gap portions 9a
are provided on the right and the left of the permanent magnet 1.
Further, a core portion 2b between the magnetic poles is provided
in a magnetic path portion of the rotor core 2 provided between the
adjacent permanent magnets 1.
[0093] A cross-sectional shape in a cross-section perpendicular to
the rotational shaft 10 of the rotor core 2 changes in the axis
direction as is apparent from FIG. 26. The shape is configured such
that the concave groove 2a is provided in a region shown by A and
the concave groove is not provided in a region shown by B. The
cross-sectional shape changes in the order of A, B, A, and B in the
axis direction to arrange regions different in magnetic circuit
design. Further, the axial length of these regions is expressed by
Lr1, Lr2, Lr3, and Lr4. As described above, the structure different
in magnetic circuit design in the axis direction is made; and
accordingly, a 6th-order torque ripple in electrical angle and
cogging torque of an order corresponding to the least common
multiple of the number of poles and the number of slots can be
reduced by using a cancelling out effect. In FIG. 26, cogging
torque and torque ripple in the region A and cogging torque and
torque ripple in the region B can be cancelled out.
[0094] However, cogging torque caused by variations on the rotor
side, for example, an attachment position error, a shape error,
and/or variations in magnetic characteristics of the permanent
magnets may become large. But, this problem can be solved by
providing a stator core structure to be described below.
[0095] FIG. 27 and FIG. 28 are partial perspective views each
showing only one tooth of the stator core for ease of
understanding. In this case, description will be made using the
perspective views, although the description has been made by
cross-sectional views as shown in FIGS. 10 to 14 in Embodiment 1.
The permanent magnet type rotary electric machine of Embodiment 3
is a configuration example of 10 poles and 12 slots in which twelve
stator cores 3 of FIG. 27 are arranged in the circumferential
direction so as to surround outside the rotor of FIG. 26.
Furthermore, the positional relationship between the rotor 30 and
the stator core 3 is a positional relationship in which axial end
portions substantially correspond or correspond to each other.
[0096] In the stator core 3 of FIG. 27 and in a region facing the
region A in which the concave groove 2a of the rotor core 2 is
provided, the stator core 3 is composed of two types of regions, a
region X in which the supplemental groove 5 is not present and a
region Y in which the supplemental groove 5 is present. A region
facing the region B in which the concave groove 2a is not present
is also composed of two types of regions, the region X in which the
supplemental groove 5 is not present and the region Y in which the
supplemental groove 5 is present. If such a configuration is made,
it becomes possible to considerably reduce cogging torque by using
the cancelling out effect as described in Embodiment 1. The axial
length of providing the supplemental groove 5 should be
approximately 1/2 (for example, 1/2.+-.10%) of the axial length of
the stator core, and more preferably 1/2 (for example,
1/2.+-.5%).
[0097] Further, in FIGS. 26 and 27, if the following is given:
Ls1=Ls2=Lr1/2,
Ls3=Ls4=Lr2/2,
Ls5=Ls6=Ls3/2, and
Ls7=Ls8=Lr4/2,
as described in Embodiment 1, the axial length of the regions of
A-X is equal to that of the regions of A-Y, and the axial length of
the regions of B-X is equal to that of the regions of B-Y; and
therefore, it becomes a configuration in which the effect of
reduction in cogging torque can be more exerted.
[0098] Also in the stator core 3 of FIG. 28 and in a region facing
the region A in which the concave groove 2a is provided, the stator
core 3 is composed of two types of regions, a region X in which the
supplemental groove 5 is not present and a region Y in which the
supplemental groove 5 is present. A region facing the region B in
which the concave groove 2a is not present is also composed of two
types of regions, the region X in which the supplemental groove 5
is not present and the region Y in which the supplemental groove 5
is present. The axial length of providing the supplemental groove 5
should be approximately 1/2 (for example, 1/2.+-.10%) of the axial
length of the stator core 3, and more preferably 1/2 (for example,
1/2.+-.5%).
[0099] Further, in FIGS. 26 and 28, if the following is given:
Ls1=Ls2/2=Lr1/2,
Ls2/2=Ls3/2=Lr2/2,
Ls3/2=Ls4/2=Lr3/2, and
Ls4/2=Ls5=Lr4/2,
the axial length of the regions of A-X is equal to that of the
regions of A-Y, and the axial length of the regions of B-X is equal
to that of the regions of B-Y; and therefore, it becomes a
configuration in which the effect of reduction in cogging torque
can be more exerted.
[0100] If such a configuration is made, cogging torque does not
considerably increase even when the position of the permanent
magnets is out of position in the opening portions provided in the
rotor core and the characteristics vary. That is, robustness is
high against variations on the rotor side and a cogging torque
Sth-order component can be reduced (S denotes the number of slots
of the stator core). Further, the shape of the opening portion 9 of
the rotor core is designed to be large in the horizontal direction
of the permanent magnet. In the case where the air gap portion 9a
is formed on the right and left sides of the permanent magnet when
the permanent magnet is inserted, the magnetic path portion of the
rotor core provided between the adjacent permanent magnets, that
is, the core portion 2b between the magnetic poles can be narrow;
and therefore, leakage flux can be reduced and a rotary electric
machine with small size and high torque can be obtained.
[0101] However, a problem exists in that the air gap portion is
present on the right and left sides of the permanent magnet; and
therefore, the position of the permanent magnet is out of position
and an Sth-order component of cogging torque increases. However, if
the configuration provided with the stator core of the present
invention, effects are exerted in that robustness is high against
variations on the rotor side and the cogging torque Sth-order
component can be reduced. Further, a structure different in
magnetic circuit design in the axis direction is made; and
accordingly, a 6th-order torque ripple in electrical angle and
cogging torque of an order corresponding to the least common
multiple of the number of poles and the number of slots can be
reduced.
Embodiment 4
[0102] Embodiments 1 to 3 describe the configuration of the
permanent magnet type rotary electric machines in which not less
than two regions different in magnetic circuit design are provided
in a rotational axis direction, the regions being different by
changing at least one of a cross-sectional shape in the rotational
axis direction in a cross-section perpendicular to the rotational
shaft of the rotor core and a cross-sectional shape in a
cross-section perpendicular to the rotational shaft of the
permanent magnets; however, a different configuration example will
be described in this case. FIG. 30 is a perspective view of a rotor
in which permanent magnets 1 are provided on a surface portion of a
rotor core 2 and the number of poles is 10. The permanent magnets 1
are arranged in two groups in the axis direction and are formed
with stepwise skew.
[0103] As described above, in the rotor 30 which is configured by
not less than two groups of permanent magnets arranged in the axis
direction, variations in shape, attachment positions, and the like
of the permanent magnets shown in FIG. 14 may be largely changed
between not less than two groups of the permanent magnets 1
arranged in the axis direction.
[0104] In this case, a problem exists in that, unless' the
supplemental grooves of the stator core are appropriately provided,
a cancelling out effect cannot be obtained to increase cogging
torque. Therefore, the problem is solved by the following
configuration in the present invention.
[0105] As shown in FIG. 30, regions in the rotational axis
direction corresponding to the permanent magnets 1 arranged in two
groups in the rotational axis direction are expressed by M1 and M2.
Further, the axial length of these regions is expressed by Lr1 and
Lr2. Meanwhile, FIG. 31 is a partial perspective view showing only
one tooth out of twelve teeth of the stator core. A region in which
an supplemental groove 5 is not provided is expressed by X and a
region in which the supplemental groove 5 is provided is expressed
by Y; and arrangement is made in the order of X, Y, X, and Y. Each
axial length is expressed by Ls1, Ls2, Ls3, and Ls4.
[0106] If states of variations in shape of the permanent magnets,
variations in attachment position, and the like are different
between M1 and M2, cogging torque increases; and therefore, a
structure is designed such that both the presence and absence of
the supplemental groove 5 are provided in each region M1 and M2. If
such a structure is given, a cancelling out effect in the regions
of M1-X and M1-Y and a cancelling out effect in the regions of M2-X
and M2-Y are sufficiently exerted; and therefore, a cogging torque
Sth-order component (S denotes the number of slots of the stator
core) can be reduced even when variations in shape, an attachment
position error, and/or variations in magnetic characteristics of
the permanent magnets largely change between not less than two
groups of the permanent magnets arranged in the axis direction. The
axial length of providing the supplemental groove should be
approximately 1/2 (for example, 1/2.+-.10%) of the axial length of
the stator core, and more preferably 1/2 (for example,
1/2.+-.5%).
[0107] Further, in FIGS. 30 and 31, if the following is given:
Ls1=Ls2=Lr1/2 and
Ls3=Ls4=Lr2/2,
the axial length of the region of M1-X is equal to that of the
region of M1-Y, and the axial length of the region of M2-X is equal
to that of the region of M2-Y; and therefore, it becomes a
configuration in which the effect of reduction in cogging torque
can be more exerted.
[0108] FIG. 30 is an example in which the permanent magnets 1 are
segment magnets, but the application the present invention is not
limited to this example. FIG. 32 is an example in which two ring
shaped magnets are arranged in the axis direction. Ring shaped
permanent magnets include some magnets that have not radial
anisotropy, polar anisotropy, and anisotropy; however, an Sth-order
component of cogging torque (S denotes the number of slots of the
stator core) may generate by variations in orientation and
variations in magnetization. As in the example of FIG. 30, in the
case where a variation state is different between the permanent
magnets arranged in the axis direction, a problem exists in that,
unless the supplemental grooves of the stator core are
appropriately provided, a cancelling out effect cannot be obtained
to increase cogging torque. Therefore, if the supplemental grooves
are arranged as the stator core of FIG. 31, it becomes a
configuration in which the effect of reduction in cogging torque
can be more exerted. Embodiment 4 shows the example in which two
supplemental grooves are arranged in the axis direction; however,
it goes without saying that similar effects are exerted even in the
case of not less than three supplemental grooves. Further, similar
effects are obtained even in a structure other than the
configuration of FIG. 31, for example, a region in which the
supplemental groove is not provided is expressed by X and a region
in which the supplemental groove is provided is expressed by Y; and
arrangement is made in the order of X, Y, Y, and X.
[0109] FIG. 30 and FIG. 31 describe the examples in which the
number of poles (the number of magnetic poles) is 10 and the number
of slots is 12; however, Embodiment 4 is not limited to these
examples. In the case of the combination of the following
relationship
0.75<S/P<1.5,
where, P is the number of poles and S is the number of slots of a
permanent magnet type rotary electric machine, there is known a
small size and high torque permanent magnet type rotary electric
machine in which the winding factor is high and magnetic flux of
permanent magnets is efficiently used as compared to the case of
S/P=0.75 and S/P=1.5 described in Patent Document 1, Patent
Document 2, and Patent Document 3.
[0110] Further, the least common multiple of the number of poles
and the number of slots are large; and therefore, it is also known
that a cogging torque component which pulsates the number of times
corresponding to the least common multiple of the number of poles
and the number of slots by one rotation of a rotor is small as
compared to the case of S/P=0.75 and S/P=1.5. Meanwhile, a problem
exists in that a cogging torque Sth-order component (component
which pulsates the number of S times by one rotation of the rotor)
is large and robustness against variations on the rotor side is
low, the cogging torque Sth-order component being generated by
variations on the rotor side, for example, an attachment position
error, a shape error, and/or variations in magnetic characteristics
of the permanent magnets. Therefore, this problem needs to be
solved in the permanent magnet type rotary electric machine to be
mass-produced as in the case where the rotary electric machine is
incorporated in an electric power steering apparatus. Then, if
[0111] Embodiment 4 is applied to the permanent magnet type rotary
electric machine having the combination of the following
relationship
0.75<S/P<1.5,
this enables to increase robustness against variations on the rotor
side and to reduce the cogging torque Sth-order component.
[0112] Furthermore, the supplemental groove is provided at one
place in a circumferential center portion of the tooth of the
stator core in FIG. 31; and therefore, there can be obtained an
effect in that degradation of torque is smaller than the known
example. Therefore, it becomes possible to achieve small size and
high torque and to increase robustness at the same time; and
accordingly, there can be obtained special effects by the
configuration of Embodiment 4, the special effects being those that
cannot be obtained by Patent Document 1, Patent Document 2, and
Patent Document 3.
Embodiment 5
[0113] FIG. 33 is a conceptual view showing a vehicular electric
power steering apparatus using the permanent magnet type rotary
electric machine of Embodiments 1 to 4. In FIG. 33, the electric
power steering apparatus includes a column shaft 23 which is for
transmitting a steering force from a steering wheel 22. The column
shaft 23 is connected to a worm gear 24 whose detail is omitted but
only a gearbox is shown in the drawing. The worm gear 24 transmits
the output (torque, the number of rotations) of a driving motor 20
controlled by a controller 21 while changing a rotational direction
at a right angle, simultaneously decelerates, and increases assist
torque. Reference numeral 25 denotes a handle joint that transmits
the steering force and also changes the rotational direction. 26
denotes a steering gear whose detail is omitted but only a gearbox
is shown in the drawing. The steering gear 26 decelerates the
rotation of the column shaft 23 and simultaneously converts to
linear motion of a rack 27 to obtain a predetermined displacement.
This linear motion of the rack 27 moves wheels to enable the
vehicle to change its direction or the like.
[0114] In such electric power steering apparatus, the pulsation of
torque generated by the driving motor 20 is transmitted to the
steering wheel 22 via the worm gear 24 and the column shaft 23.
Therefore, in the case where the driving motor 20 generates large
torque pulsation, smooth steering feeling cannot be obtained.
However, the permanent magnet type rotary electric machine of
Embodiments 1 to 4 is incorporated as the driving motor 20 of the
electric power steering apparatus of Embodiment 5; and accordingly,
torque pulsation can be reduced. Therefore, the steering feeling in
the electric power steering apparatus can be improved.
[0115] Furthermore, the driving motor for the electric power
steering apparatus is mass-produced; and therefore, a problem
exists in that robustness of cogging torque against variations in
manufacture needs to be improved. In response, the permanent magnet
type rotary electric machine described in Embodiments 1 to 4 is
mounted and accordingly a cogging torque component caused by
variations in the rotor can be considerably reduced; and therefore,
an effect is exerted in that the robustness improves.
[0116] Various modifications and alternations of this invention can
be achieved to those skilled in the art without departing from the
scope and spirit of this invention, and it should be understood
that this is not limited to the respective illustrative embodiments
set forth in the description.
* * * * *