1
FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
[See section 10, Rule 13]
PERMANENT MAGNET MOTOR
MITSUBISHI ELECTRIC CORPORATION, A CORPORATION ORGANISED AND
EXISTING UNDER THE LAWS OF JAPAN, WHOSE ADDRESS IS 7-3,
MARUNOUCHI 2-CHOME, CHIYODA-KU, TOKYO 100-8310, JAPAN
THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE
INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED.
2
DESCRIPTION
5 Technical Field
[0001]
The present application relates to a permanent magnet
motor.
Background Art
10 [0002]
To date, with regard to a rotor of a permanent magnet
motor, slits aligned so that neighboring intervals are
practically equal have been provided in a rotor core surface
of an IPM (interior permanent magnet) motor in order to improve
15 demagnetization resistance of a permanent magnet (for example,
refer to Patent Literature 1).
Also, with regard to a magnet-embedded rotor of an
existing motor, slits inclined in one direction of rotation
are provided in a rotor core surface of an IPM motor in order
20 to reduce torque ripple (for example, refer to Patent
Literature 2).
[0003]
The previously described kinds of existing IPM motors
have a main object of achieving an improvement in
25 demagnetization resistance or a reduction of torque ripple.
3
In the case of demagnetization resistance improvement, there
is no need to adopt a complicated structure wherein slits are
provided in a rotor surface as disclosed in Patent Literature
1, as it is sufficient to apply a permanent magnet with a high
coercive force. Also, in the case of torque 5 ripple reduction,
a structure having the kind of perfectly circular external
rotor form disclosed in Patent Literature 2 is a form such that
torque ripple worsens, so is not appropriate.
Generally, an IPM has greater demagnetization resistance
10 than a surface permanent magnet (SPM), and reluctance torque
can be utilized, because of which a small motor with a high
output can be realized by increasing an amount of current,
thereby increasing torque density.
Citation List
15 Patent Literature
[0004]
Patent Literature 1: JP-A-2006-081336
Patent Literature 2: JP-A-2006-014450
Summary of Invention
20 Technical Problem
[0005]
In this case, differing from an SPM, an IPM is such that
a face opposing a stator inner diameter forms a rotor core with
high magnetic permeability, because of which a magnetic flux
25 that crosses a magnetic pole surface in a circumferential
4
direction increases, and an air gap magnetic flux density is
more liable to become locally excessive compared with an SPM.
An existing permanent magnet motor is such that due to
a local increase in magnetic flux density in an air gap, an
electromagnetic excitation force proportional 5 to two times the
magnetic flux density acts, attempting to cause a stator to
transform, because of which there is a problem in that motor
vibration noise worsens. As reducing the motor current or
enlarging the air gap causes the torque density to decrease,
10 the advantages of reducing size and increasing output with
respect to an SPM are cancelled out.
[0006]
The application discloses technology for resolving the
heretofore described kind of problem, and has an object of
15 providing a permanent magnet motor such that a worsening of
motor vibration noise can be restricted while securing a
reduction in size and an increase in output, which are
advantages of an IPM.
Solution to Problem
20 [0007]
A permanent magnet motor disclosed in the present
application includes a stator, and a rotor disposed opposing
an inner side of the stator and having a field pole of a rotor
core in which a permanent magnet is embedded, wherein the field
25 pole has a radius smaller than an arc centered on a shaft of
5
the rotor, a multiple of slits are formed in the field pole,
the multiple of slits are disposed so that an interval between
a first central line positioned between a multiple of the slits
and a second central line positioned between a neighboring
multiple of the slits increases as the first 5 central line and
the second central line head toward an outer peripheral side
of the rotor core, and of the multiple of slits of the field
pole, a first slit disposed in a central position of the field
pole, and a second slit and a third slit disposed on either
10 side of the first slit, are disposed within 20% of a
circumferential direction width of the permanent magnet.
Advantageous Effects of Invention
[0008]
According to the permanent magnet motor disclosed in the
15 present application, a permanent magnet motor such that a
worsening of vibration noise of a motor can be restricted, while
securing a reduction in size and an increase in output, which
are advantages of an IPM, is obtained.
Brief Description of Drawings
20 [0009]
[Fig. 1] Fig. 1 is an axial direction sectional view of
a permanent magnet motor according to a first embodiment.
[Fig. 2A] Fig. 2A is a front view of a rotor of the
permanent magnet motor according to the first embodiment.
25 [Fig. 2B] Fig. 2B is a front view of the rotor of the
6
permanent magnet motor according to the first embodiment.
[Fig. 2C] Fig. 2C is a front view of the rotor of the
permanent magnet motor according to the first embodiment.
[Fig. 2D] Fig. 2D is a front view of the rotor of the
permanent magnet motor according to the 5 first embodiment.
[Fig. 2E] Fig. 2E is a front view of the rotor of the
permanent magnet motor according to the first embodiment.
[Fig. 3] Fig. 3 is a front view of a permanent magnet
motor in a comparative example.
10 [Fig. 4] Fig. 4 is a front view of a permanent magnet
motor in a comparative example.
[Fig. 5] Fig. 5 is a front view of a permanent magnet
motor in a comparative example.
[Fig. 6A] Fig. 6A is a drawing showing changes in
15 electromagnetic excitation force and torque when slits are
provided in a field pole.
[Fig. 6B] Fig. 6B is a drawing showing changes in
electromagnetic excitation force and torque when slits are
provided in the field pole.
20 [Fig. 6C] Fig. 6C is a drawing showing changes in
electromagnetic excitation force and torque when slits are
provided in a field pole.
[Fig. 7] Fig. 7 is a front view of a rotor of the permanent
magnet motor according to the first embodiment.
25 [Fig. 8] Fig. 8 is a drawing wherein analysis values
7
obtained using Fig. 6A to Fig. 6C are plotted, with a vertical
axis as electromagnetic excitation force and a horizontal axis
as a torque ripple value.
[Fig. 9] Fig. 9 is a drawing wherein data corresponding
to a second slit and a third slit neighboring 5 a first slit being
disposed in positions greater than 20% with respect to a
circumferential direction width of a permanent magnet are
separated from the data plotted in Fig. 8 and replotted.
[Fig. 10] Fig. 10 is a drawing wherein data corresponding
10 to the second slit and the third slit neighboring the first
slit being disposed in positions within 20% with respect to
the circumferential direction width of the permanent magnet
are separated from the data plotted in Fig. 8 and replotted.
Description of Embodiments
15 [0010]
Hereafter, a first embodiment will be described, based
on the drawings.
Identical reference signs in the drawings indicate
identical or corresponding components.
20 First Embodiment
Fig. 1 is an axial direction sectional view of a permanent
magnet motor according to the first embodiment. The permanent
magnet motor according to the first embodiment is used in, for
example, an electric power steering system.
25 As shown in Fig. 1, a permanent magnet motor (hereafter
8
referred to simply as “motor”) 1 includes a rotor 22 having
a rotor core 23 in whose interior a multiple of permanent
magnets 25 are disposed, and supported so as to rotate freely,
and a stator 12 provided across an air gap 50 on an outer side
of the rotor 22. Also, the stator 12 includes 5 a stator core
3 and a stator winding 5.
[0011]
The stator core 3 is formed by, for example, plate-form
electromagnetic steel sheets being stacked, and the
10 three-phase stator winding 5 is wound around the stator core
3 across an insulator 4 made of resin. The stator windings
5 of each phase are delta-connected by a winding terminal 7
housed in a terminal holder 6 made of resin. Furthermore, a
connection terminal 8 for connecting to a lead wire 2 is
15 attached to the winding terminal 7 of each phase. The
connection terminal 8 is attached to a connection terminal base
portion 9, and a nut 10 for attaching the lead wire 2 to the
connection terminal 8 is housed in an interior of the connection
terminal base portion 9.
20 [0012]
The stator core 3 is press-fitted into a frame 11 made
of iron, forming the stator 12 of the motor 1. There is a bottom
portion in one end portion of the frame 11, and a rear bearing
box portion 13 that houses a rear bearing 26 for supporting
25 one end of the rotor 22 is formed in a central portion of the
9
bottom portion. Another end portion of the frame 11 is opened,
and a spigot joint portion 14 for linking to a housing 17 of
the motor 1 is formed. A flange portion 15 having a screw
clamping portion for screwing the stator 12 to the housing 17
of the motor 1 is formed on an outer periphery 5 of the spigot
joint portion 14 of the frame 11. An O-ring-form frame grommet
16 for waterproofing is provided between the housing 17 of the
motor 1 and the flange portion 15 of the stator 12.
[0013]
10 The housing 17 of the motor 1 is formed by a die casting
of an aluminum alloy, and a front bearing box 18 that houses
a front bearing 27 for supporting one end of the rotor 22 is
formed in a central portion. Also, a resolver mounting portion
20 for attaching a resolver 19, which is a rotation sensor for
15 detecting an angle of rotation of the rotor 22, is formed in
a vicinity of the front bearing box 18 of the housing 17. A
mounting spigot joint portion 21 for attaching the motor 1 to
a mating instrument is provided in an end portion of the housing
17 on a side opposite to a side on which the stator 12 is
20 attached.
[0014]
The rotor 22 includes the rotor core 23, which is formed
by electromagnetic steel sheets attached to an iron shaft 24
being stacked. Further, either end of the shaft 24 is supported
25 by the rear bearing 26 and the front bearing 27 so as to rotate
10
freely. A boss 28, which is coupling for linking to a mating
instrument, is attached to a front side end portion of the shaft
24.
[0015]
Fig. 2A and Fig. 2B are front views 5 of a rotor of a
permanent magnet motor according to the first embodiment.
Also, Fig. 2B is an enlarged view of Fig. 2A. As shown in Fig.
2A and Fig. 2B, the multiple of permanent magnets 25 are
embedded in a circumferential direction in the rotor core 23
10 of the rotor 22. The multiple of permanent magnets 25 are
housed and fixed in a multiple of permanent magnet mounting
holes 47 disposed at equal intervals in the circumferential
direction in the rotor core 23, and a gap portion 45 is formed
on either side of the permanent magnet 25. Fig. 2A and Fig.
15 2B are centered on the rotor 22. Therefore, a depiction of
the stator 12 provided across the air gap 50 on an outer
periphery of the rotor 22 is omitted. The stator 12 has the
stator core 3, which has a multiple of teeth 48 and a multiple
of slots (not shown), and an armature winding (not shown) wound
20 around the teeth 48 and housed in the slots.
[0016]
Rather than being a perfect circle centered on the shaft
24, the rotor core 23 in the first embodiment has a floral form,
and a multiple of slits 41 are formed in a field pole 40 of
25 the rotor core 23 in which the permanent magnet 25 is embedded.
11
The field pole 40 has a radius smaller than an arc centered
on the shaft 24, which is attached on an inner side of the rotor
22. Also, of the multiple of slits 41, a central slit B in
a center of the field pole 40 is such that a longitudinal axial
direction (longitudinal direction) thereof 5 is disposed in a
radial direction of the rotor core 23 or a radial direction
of an outer periphery of the floral form field pole 40.
[0017]
Also, the rotor core 23 of the field pole 40 is between
10 the slits 41, and central lines 42 between the slits 41 are
set so as to spread farther apart the nearer the central lines
42 come to an outer peripheral side. That is, the slits 41
are provided so that an interval between a first central line
42a between the slits 41 and a second central line 42b between
15 the neighboring slits 41 gradually increases as the first
central line 42a and the second central line 42b head toward
the outer peripheral side of the rotor 22. For example, seven
slits 41 are disposed in each field pole 40 (= one magnetic
pole portion). Also, an odd number of slits 41 are disposed
20 axisymmetrically sandwiching the central slit B disposed in
the center of the field pole 40, and lengths of the slits 41
are axisymmetrically the same. A circumferential direction
width of the permanent magnet 25 is greater than a radial
direction width, and the permanent magnet 25 is of a flat plate
25 magnet form.
12
[0018]
Also, a connection portion 44 is provided in order to
integrate the field pole 40 divided by the slits 41. The field
pole 40 divided by the slits 41 is integrated by the connection
portion 44. The connection portion 44 5 is configured of a
connection portion (field pole upper side) 44a or a connection
portion (field pole lower side) 44b.
Also, Fig. 2C to Fig. 2E are front views of a rotor of
a permanent magnet motor that is another example according to
10 the first embodiment. In Fig. 2C, a form of the permanent
magnet 25 is a curved form, but structures excepting the
permanent magnet 25 and a form of a permanent magnet mounting
hole are the same as the structures in Fig. 2A.
Further still, in Fig. 2D, a form of the rotor core 23
15 opposing a bridge portion 43 is a perfectly circular form 46,
but structures excepting this form are the same as the
structures in Fig. 2A.
Also, in Fig. 2E, a form of the slit 41 is trapezoidal,
but structures excepting the form of the slit 41 are the same
20 as the structures in Fig. 2A.
[0019]
Fig. 3 to Fig. 5 are front views of a permanent magnet
motor in a comparative example. Fig. 3 to Fig. 5 show the teeth
48 of the stator 12 provided across the air gap 50 on the outer
25 side of the rotor 22. In Fig. 3, the external form of the rotor
13
22 is the perfectly circular form 46, because of which torque
ripple increases. Also, in Fig. 4, no slit 41 is provided in
the rotor core 23, because of which a magnetic flux 49 crossing
the field pole 40 of the rotor core 23 flows, and magnetic flux
density in a region A of the air gap 50 increases. 5 Also, in
Fig. 5, the intervals between the slits 41 become smaller the
nearer to the outer peripheral side of the rotor core 23, and
there is no longer an advantage of the magnetic flux density
of the air gap 50 being dispersed because of the slits 41.
10 [0020]
Meanwhile, in the first embodiment, a particularly
noticeable advantage can be exhibited with poles and slots such
as 10 poles and 12 slots, 14 poles and 12 slots, or 14 poles
and 18 slots, wherein a mode such that a low order
15 electromagnetic excitation force mode is small and vibration
noise is liable to increase, for example, a secondary mode all
round, occurs.
One of the slits 41 is in the center of the field pole
40. The center of the field pole 40 is the place in which a
20 sectional area of the field pole 40 with respect to the crossing
magnetic flux 49 is greatest and the magnetic flux 49 flows
most easily, and an advantage in that the magnetic flux 49 is
interrupted by the slit 41 is obtained.
[0021]
25 Also, the number of slits 41 formed in the field pole
14
40 is desirably five to seven per field pole 40 (= one magnetic
pole portion) in a case of, for example, 10 poles and 12 slots
and a diameter of in the region of 40 to 50. The reason is
that when increasing the number of slits 41 until magnetic
saturation occurs in the field pole 40, 5 an advantage of
restricting vibration noise is easily obtained, but the slits
41 form magnetic resistance, and torque decreases. Also,
another reason is that when considering a circumferential
direction width of the field pole 40, a slit width, and a slit
10 interval (an interval in the region of the thickness of the
electromagnetic steel plates of the rotor core 23 is needed),
forming more than five to seven slits when punching with a press
or the like to fabricate the slits 41 is difficult, and the
like.
15 [0022]
Fig. 6A to Fig. 6C are drawings wherein amounts of change
in electromagnetic excitation force and torque in a structure
when slits are provided in a field pole and amounts of change
in electromagnetic excitation force and torque in a structure
20 (an assembly B) wherein slits are not provided in a field pole
are plotted. In Fig. 6A to Fig. 6C, a graph on which the amounts
of change in electromagnetic excitation force and torque are
plotted is shown on the left side, and a front view of a form
of the assembly B, wherein slits are not provided in the field
25 pole, is shown on the right side. Also, Fig. 7 is a front view
15
of a rotor of a permanent magnet motor according to the first
embodiment.
[0023]
To describe more specifically, an assembly A with
specifications designed using an optimum 5 design tool of
electromagnetic field analysis wherein five or seven slits 41
are disposed in the 10 pole, 12 slot motor 1 shown in Fig. 7,
and a position (a distance L between slits) and an angle θ of
the slits 41 are caused to change, so that a secondary component
10 (a component causing transformation to an ellipse), which is
a main component of electromagnetic excitation force that
causes vibration noise in the stator core 3 or the frame 11,
is minimal, and the assembly B with specifications such that
the slit 41 is not disposed in the field pole 40, which is the
15 reference for slit design, are plotted in Fig. 6A to Fig. 6C.
[0024]
In Fig. 6A to Fig. 6C, a vertical axis shows an
electromagnetic excitation force change rate, and a horizontal
axis shows an amount of torque change. With an electromagnetic
20 excitation force value of the assembly B, which has no slit
41, as 100, the vertical axis shows as a percentage (%) to what
level the electromagnetic excitation force can decrease with
respect to 100 owing to slit design. Also, with a torque amount
of the assembly B, which has no slit 41, as 0, the horizontal
25 axis shows to what extent the torque amount changes owing to
16
slit design.
Also, the assembly B, with the specifications that are
the reference for slit design, is such that some forms of the
rotor 22 from an almost perfectly circular form to a practically
floral form are selected by changing the arc radius 5 of the field
pole 40, and taken to be proof showing that a tendency to be
described below has universality, regardless of the design of
the assembly B. Specifically, the form of the assembly B shown
on the right side of Fig. 6A corresponds to, for example, the
10 floral form rotor 22 wherein the arc radius of the field pole
40 is small. Also, the form of the assembly B shown on the
right side of Fig. 6C corresponds to, for example, the rotor
22 with the almost perfectly circular form wherein the arc
radius of the field pole 40 is large. Also, the form of the
15 assembly B shown on the right side of Fig. 6B corresponds to
the rotor 22 having an arc radius of the field pole 40 midway
between the form of the assembly B shown on the right side of
Fig. 6A and the form of the assembly B shown on the right side
of Fig. 6C.
20 [0025]
Fig. 6A to Fig. 6C are drawings wherein torqueelectromagnetic
excitation force curves C joining the
assemblies B shown in Fig. 6A to Fig. 6C and assemblies A
designed with slits based on each assembly B are plotted as
25 exponential functions using the least squares method. Each
17
curve C is a curve that gradually approaches 71%, and shows
that electromagnetic excitation force can be considerably
reduced by slit design to a maximum of a 71% level. Also, when
an electromagnetic excitation force corresponding to a general
time constant that is an index indicating a 5 convergence speed
from the assembly B that is the reference to 71% is taken to
be 81% or less, it can be said that the electromagnetic
excitation force can converge to a sufficiently small value
in the assembly A owing to slit design.
10 [0026]
Fig. 8 is a drawing wherein analysis values obtained
using the specifications of each of Fig. 6A to Fig. 6C are
plotted, with a vertical axis as electromagnetic excitation
force and a horizontal axis as a torque ripple value. In Fig.
15 8, triangular, diamond, and square plotting forms shown in
assembly B are the form of one of the assemblies B, in which
no slit is provided in the field pole 40, shown on the right
side in Fig. 6A to Fig. 6C, but no particular correspondence
relation between the plotting form and the form of the assembly
20 B is specified here. The same applies to the assembly A.
[0027]
It is found that the assembly A is an assembly such that
torque ripple decreases and also, conversely, worsens with
respect to the assembly B, in which no slit 41 is provided in
25 the field pole 40, as shown in Fig. 8. Torque ripple worsening
18
in comparison with the assembly B, which is the reference, due
to slit design is because no balance is achieved between
electromagnetic excitation force and torque ripple, and
vibration noise caused by frame vibration and shaft vibration
cannot be restricted, and it goes without 5 saying that
specifications such that torque ripple is equal to or less than
that of the assembly B are specifications such that a clear
advantage of achieving a balance between electromagnetic
excitation force and torque ripple is obtained. Furthermore,
10 to focus on this point, it is clear that the plotted data are
divided into an assembly A1, wherein the electromagnetic
excitation force value is somewhat high, and an assembly A2.
[0028]
Fig. 9 is a drawing wherein data corresponding to a second
15 slit 41b and a third slit 41c neighboring a first slit 41a in
the rotor 22 shown in Fig. 7 being disposed in positions greater
than 20% with respect to a circumferential direction width W
of the permanent magnet 25 are separated from the data plotted
in Fig. 8 and replotted. Also, Fig. 10 is a drawing wherein
20 data corresponding to the second slit 41b and the third slit
41c neighboring the first slit 41a in the rotor 22 shown in
Fig. 7 being disposed in positions within 20% with respect to
the circumferential direction width W of the permanent magnet
25 are separated from the data plotted in Fig. 8 and replotted.
25 [0029]
19
Herein, when data wherein distances L are each set so
that the second slit 41b and the third slit 41c neighboring
the first slit 41a in the rotor 22 shown in Fig. 7 are disposed
in positions greater than 20% with respect to the
circumferential direction width W of the permanent 5 magnet 25
are separated and replotted in Fig. 9, and data wherein the
distances L are each set so that the second slit 41b and the
third slit 41c are disposed in positions within 20% are
separated and replotted in Fig. 10, it is clear that Fig. 8
10 depends on the dispositions of the second slit 41b and the third
slit 41c with respect to the magnet width W.
That is, according to the first embodiment, the
previously undifferentiated assembly A1 and assembly A2 can
be differentiated between by focusing on achieving a balance
15 between electromagnetic excitation force and torque ripple,
and specifications such that electromagnetic excitation force
can be further reduced can be selected.
[0030]
The first embodiment is such that, taking 20% with
20 respect to the circumferential direction width W of the
permanent magnet 25 as a threshold, torque ripple is reduced,
and a form of the rotor 22 that reduces electromagnetic
excitation force can be adopted, by the first slit 41a disposed
in a central position of the field pole 40, and the second slit
25 41b and the third slit 41c disposed on either side of the first
20
slit 41a, being disposed within 20% of the circumferential
direction width of the permanent magnet 25. As a result of
this, the motor 1 according to the first embodiment is such
that a worsening of vibration noise can be reduced.
Also, the multiple of slits 41 are 5 disposed so that
electromagnetic excitation force, which forms a main component
when a spatial order is a minimum order of two or more, decreases
to 81% or less with respect to a case where a rotor core with
no slit is adopted as a reference. Further still, the multiple
10 of slits 41 are disposed in a state such that torque ripple
is equal to or less than the torque ripple of a rotor core with
no slit with respect to a case where the rotor core with no
slit is adopted as a reference.
Embodiments can be combined, and each embodiment can be
15 modified or eliminated as appropriate.
Reference Signs List
[0031]
1 motor, 2 lead wire, 3 stator core, 4 insulator, 5 stator
winding, 6 terminal holder, 7 winding terminal, 8 connection
20 terminal, 9 connection terminal base portion, 10 nut, 11 frame,
12 stator, 13 rear bearing box portion, 14 spigot joint portion,
15 flange portion, 16 frame grommet, 17 housing, 18 front
bearing box, 19 resolver, 20 resolver mounting portion, 21
mounting spigot joint portion, 22 rotor, 23 rotor core, 24 shaft,
25 25 permanent magnet, 26 rear bearing, 27 front bearing, 28 boss,
21
40 field pole, 41 slit, 41a first slit, 41b second slit, 41c
third slit, 42 central line, 42a first central line, 42b second
central line, 43 bridge portion, 44 connection portion, 44a
connection portion (field pole upper side), 44b connection
portion (field pole lower side), 45 gap portion, 5 46 perfectly
circular form, 47 permanent magnet mounting hole, 48 teeth,
49 magnetic flux, 50 air gap
22
We Claim :
[Claim 1]
A permanent magnet motor, comprising:
5 a stator; and
a rotor disposed opposing an inner side of the stator
and having a field pole of a rotor core in which a permanent
magnet is embedded, wherein
the field pole has a radius smaller than an arc centered
10 on a shaft of the rotor,
a multiple of slits are formed in the field pole, the
multiple of slits are disposed so that an interval between a
first central line positioned between a multiple of the slits
and a second central line positioned between a neighboring
15 multiple of the slits increases as the first central line and
the second central line head toward an outer peripheral side
of the rotor core, and
of the multiple of slits of the field pole, a first slit
disposed in a central position of the field pole, and a second
20 slit and a third slit disposed on either side of the first slit,
are disposed within 20% of a circumferential direction width
of the permanent magnet.
[Claim 2]
The permanent magnet motor according to claim 1, wherein
25 the second and third slits are disposed axisymmetrically with
respect to the first slit.
[Claim 3]
The permanent magnet motor acc
2, wherein an external form of the rotor is a floral form.
5 [Claim 4]
The permanent magnet motor according to any one of claim
1 to claim 3, wherein the multiple of slits are disposed so
that electromagnetic excitation force
component when a spatial order is a minimum order of two or
10 more, decreases to 81% or less with respect to a case where
the rotor core that has no slit is adopted as a
[Claim 5]
The permanent magnet motor according to any one of
1 to claim 4, wherein the multiple of slits are disposed in
15 a state such that torque ripple is equal to or less than torque
ripple of the rotor core that has no slit
case where the rotor core that has no slit is adopted as a
reference.