U.S. patent application number 16/724688 was filed with the patent office on 2020-04-23 for manufacturing method for rotor core and manufacturing method for motor core.
This patent application is currently assigned to TOYOTA JIDOSHA KABUSHIKI KAISHA. The applicant listed for this patent is TOYOTA JIDOSHA KABUSHIKI KAISHA. Invention is credited to Toshimitsu TAKAHASHI, Mayumi TAKAZAWA, Shigeto TAKEUCHI.
Application Number | 20200127544 16/724688 |
Document ID | / |
Family ID | 60480137 |
Filed Date | 2020-04-23 |
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United States Patent
Application |
20200127544 |
Kind Code |
A1 |
TAKAHASHI; Toshimitsu ; et
al. |
April 23, 2020 |
MANUFACTURING METHOD FOR ROTOR CORE AND MANUFACTURING METHOD FOR
MOTOR CORE
Abstract
A manufacturing method for a rotor core included in a rotor of a
motor punches an electromagnetic steel sheet includes punching a
plurality of plates for rotor core from an electromagnetic steel
sheet; producing a rotor-core precursor by stacking up the plates
for rotor core; manufacturing a rotor core by annealing an outer
circumferential region of the rotor-core precursor at a first
predetermined temperature, and annealing an inner circumferential
region of the rotor-core precursor at a second predetermined
temperature; the first predetermined temperature being a
temperature at which grain growth of crystals of the
electromagnetic steel sheet is promoted; and the second
predetermined temperature being a temperature at which grain growth
of the crystals of the electromagnetic steel sheet is not
promoted.
Inventors: |
TAKAHASHI; Toshimitsu;
(Toyota-shi, JP) ; TAKEUCHI; Shigeto; (Toyota-shi,
JP) ; TAKAZAWA; Mayumi; (Okazaki-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
TOYOTA JIDOSHA KABUSHIKI KAISHA |
Aichi-ken |
|
JP |
|
|
Assignee: |
TOYOTA JIDOSHA KABUSHIKI
KAISHA
Aichi-ken
JP
|
Family ID: |
60480137 |
Appl. No.: |
16/724688 |
Filed: |
December 23, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
15806721 |
Nov 8, 2017 |
10554107 |
|
|
16724688 |
|
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H02K 15/12 20130101;
Y10T 29/49012 20150115; H02K 15/024 20130101; H02K 15/02
20130101 |
International
Class: |
H02K 15/12 20060101
H02K015/12; H02K 15/02 20060101 H02K015/02 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 25, 2016 |
JP |
2016-229199 |
Claims
1. A rotor core comprising: a stacked body formed of a plurality of
plates; an outer circumferential region positioned at an outer
circumferential side of the stacked body, and an inner
circumferential region positioned at an inner circumferential side
of the stacked body; a magnet slot provided in the outer
circumferential region; wherein the outer circumferential region is
an annular region extending from an outer circumferential contour
of the rotor core in a radially inward direction to a predetermined
position between the outer circumferential contour and a center
portion of the magnet slot; and an average grain size of crystals
in the outer circumferential region is larger than an average grain
size of crystals in the inner circumferential region.
2. The rotor core according to claim 1, wherein the average grain
size of the crystals in the outer circumferential region is 50
.mu.m or more, and the average grain size of the crystals in the
inner circumferential region is less than 50 .mu.m.
3. The rotor core according to claim 1, wherein the outer
circumferential region is a surface layer of the rotor core.
4. The rotor core according to claim 1, wherein a yield strength of
the inner circumferential region is larger than a yield strength of
the outer circumferential region by an amount of 70 MPa to 120
MPa.
5. The rotor core according to claim 1, wherein the outer
circumferential contour has a circular shape.
6. The rotor core according to claim 1, wherein the inner
circumferential region extends in a radially outward direction from
an inner circumferential contour of the rotor core to the
predetermined position located between the outer circumferential
contour and the center portion of the magnet slot.
7. The rotor core according to claim 1, wherein a portion of the
magnet slot is provided in the outer circumferential region and a
portion of the magnet slot is provided in the inner circumferential
region.
Description
INCORPORATION BY REFERENCE
[0001] This is a Continuation of application Ser. No. 15/806,721
filed on Nov. 8, 2017 (allowed), which claims priority to Japanese
Patent Application No. 2016-229199 filed on Nov. 25, 2016. The
entire disclosures of the prior applications are considered part of
the disclosure of the accompanying continuation application, and
are hereby incorporated by reference.
BACKGROUND
1. Technical Field
[0002] The present disclosure relates to a manufacturing method for
a rotor core included in a motor, and a manufacturing method for a
motor core including a rotor core and a stator core that are
included in a motor.
2. Description of Related Art
[0003] In the automobile industry, aiming at further enhancement of
driving performance of hybrid vehicles and electric vehicles,
developments of higher output performance, weight reduction, and
downsizing of drive motors have been promoted day after day.
Household electric appliance manufactures have been knuckling down
on further downsizing and higher performance of motors incorporated
in various household electric appliances.
[0004] In order to enhance the motor performance, how much various
losses caused inside motors can be reduced is a great issue. For
example, after electricity is inputted, a copper loss resulting
from a conductor resistance loss is caused in a coil composing a
motor, and an iron loss (or a high-frequency iron loss) resulting
from an eddy current loss or a hysteresis loss is caused to a rotor
and a stator, so that the motor efficiency and the torque
performance become deteriorated depending on these losses.
[0005] In manufacturing of a stator core and a rotor core,
rotor-core plates and stator-core plates are obtained from an
electromagnetic steel sheet by punching the electromagnetic steel
sheet, multiple rotor-core plates are stacked up, and are then
squeezed and/or welded together so as to produce a rotor core, and
multiple stator-core plates are stacked up, and are then squeezed
and/or welded together so as to manufacture a stator core.
[0006] In order to enhance magnetic characteristics by reducing the
above iron losses in the stator core and the rotor core, there may
be applied a method of annealing both the stator core and the rotor
core at a predetermined temperature, while removing work strain
introduced by pressing or the like, and/or a method of promoting
grain growth of crystals forming the both cores, as with materials
such as semi-process materials that are supposed to be
annealed.
[0007] Unfortunately, it is known that there is a contradiction
that the magnetic characteristics are enhanced by grain growth of
the crystals in both the stator core and the rotor core through
annealing, while strengths (tensile strengths) of the cores become
deteriorated due to the grain growth of the crystals.
[0008] Reduction in iron loss of the stator core promotes
downsizing and energy saving of the motor. In the meantime, the
rotor core is a member rotating at such a high speed that a strong
centrifugal force acts on this member during its rotation, and thus
the rotor core is required to have a high strength strong enough to
resist this strong external force. Therefore, annealing the rotor
core becomes a factor of deterioration of strength, and thus it
cannot be said that this method is a preferable method; therefore,
a manufacturing method of annealing only a stator core without
annealing a rotor core might be applied in some cases. However, a
rotor core manufactured by this method cannot be expected to have
the above-described enhancement of magnetic characteristics.
[0009] To cope with this, Japanese Patent Application Publication
No. 2004-270011 discloses a manufacturing method for a non-oriented
electrical steel sheet having a high magnetic flux density that is
capable of simultaneously collecting rotor members and stator
members from an identical steel sheet, while attaining a high
magnetic flux density and a high strength in the rotor members as
well as attaining a high magnetic flux density and a low iron loss
in the stator members. Specifically, this method is a method that
carries out hot-rolled steel annealing in such a manner that a
crystal grain size becomes 50 .mu.m or more to 500 .mu.m or less in
order to manufacture of a non-oriented electrical steel sheet
having a high magnetic flux density whose steel-plate composition
is specified at a predetermined mass ratio.
SUMMARY
[0010] In the manufacturing method disclosed in JP 2004-270011 A,
since the non-oriented electrical steel sheet having a high
magnetic flux density is subjected to the hot-rolled steel
annealing, stator-core steel plates and rotor-core steel plates are
both annealed. Hence, in the rotor-core steel plates, although
enhancement of the magnetic characteristics can be expected, it is
concerned that deterioration of strength thereof might be caused,
as described above.
[0011] The present disclosure provides a manufacturing method for a
rotor core capable of manufacturing a rotor core excellent in
magnetic characteristics and having a high strength, and a
manufacturing method for a motor core capable of manufacturing a
stator core excellent in magnetic characteristics, in addition to
the above rotor core.
[0012] A manufacturing method for a rotor core according to the
present disclosure is a manufacturing method for a rotor core
included in a rotor of a motor, and the manufacturing method
includes: punching a plurality of plates for rotor core from an
electromagnetic steel sheet; producing a rotor-core precursor by
stacking up the plates for rotor core; manufacturing a rotor core
by annealing an outer circumferential region of the rotor-core
precursor at a first predetermined temperature, and annealing an
inner circumferential region of the rotor-core precursor at a
second predetermined temperature; the first predetermined
temperature being a temperature at which grain growth of crystals
of the electromagnetic steel sheet is promoted; and the second
predetermined temperature being a temperature at which grain growth
of the crystals of the electromagnetic steel sheet is not
promoted.
[0013] The manufacturing method for the rotor core of the present
disclosure is characterized by annealing the rotor-core precursor
produced by stacking up the plurality of plates for rotor core
formed of the electromagnetic steel sheet while providing a
difference in temperature during the annealing between the outer
circumferential region and the inner circumferential region of the
rotor-core precursor so as to manufacture the rotor core.
Specifically, the outer circumferential region is annealed at a
temperature at which grain growth of the crystals of the
electromagnetic steel sheet is promoted, and the inner
circumferential region is annealed at a temperature at which grain
growth of the crystals of the electromagnetic steel sheet is not
promoted.
[0014] Here, in the rotor core in a circular shape in a plan view,
the "outer circumferential region" denotes an outer circumferential
annular region ranging from an outer circumferential contour in a
circular shape to an inner region with a predetermined distance, or
the like, and the "inner circumferential region" denotes a region
at a center position excluding the outer circumferential region of
the rotor core, or the like.
[0015] The outer circumferential region may be defined as a range
where the iron loss is relatively great, that is, for example, a
range approximately 5 mm more inward from the outer circumferential
contour in a circular shape of the stator core. Here, the crystal
grains in the outer circumferential region are allowed to grow so
as to enhance the magnetic characteristics, to thereby effectively
reduce the iron loss in the rotor core.
[0016] On the other hand, the inner circumferential region of the
rotor core is a region where the crystal grains have not grown, so
that this region has a higher strength (tensile strength), and by
having this inner circumferential region, it is possible to ensure
a high strength of the rotor core.
[0017] In another aspect of the manufacturing method for the rotor
core according to the present disclosure, the second predetermined
temperature may be a temperature at which work strain during the
punching the plates for rotor core is removed.
[0018] During the punching process of the electromagnetic steel
sheet, the work strain is introduced in the rotor-core plates;
therefore, in the inner circumferential region, by annealing the
inner circumferential region at the temperature at which grain
growth of the crystals of the electromagnetic steel sheet is not
promoted and also at the temperature at which the work strain
introduced during the punching process is removed, it is possible
to cope with deterioration of magnetic characteristics in the inner
circumferential region due to the punching.
[0019] In another aspect of the manufacturing method for the rotor
core according to the present disclosure, the manufacturing method
for the rotor core may include: providing with insulating members
on at least a top surface and a bottom surface of the rotor-core
precursor; and placing and annealing the rotor-core precursor in an
annealing furnace while a side surface of the rotor-core precursor,
extending in a circumferential direction of the rotor-core
precursor, is exposed.
[0020] In the state in which the insulating members are disposed on
the top surface and the bottom surface of the rotor-core precursor
and the side surface extending in the circumferential direction of
the rotor-core precursor is exposed, for example, only the side
surface of this rotor core is exposed to the outside. If the
annealing is carried out in this state, the top and the bottom
surfaces of the rotor core are protected by the insulating members,
and thus only the side surface of the rotor core is directly heated
so that the temperature thereof is increased, and the heat is
gradually transferred from the side surface toward the inside of
the rotor core.
[0021] By terminating the annealing at a stage where the outer
circumferential region of the rotor-core precursor is annealed so
that the temperature thereof becomes increased up to a
predetermined temperature, it is possible to desirably promote
grain growth of the crystals of the electromagnetic steel sheet in
the outer circumferential region of the rotor-core precursor, and
also possible to suppress grain growth of the crystals of the
electromagnetic steel sheet in the inner circumferential region of
the rotor-core precursor.
[0022] It should be noted that when the top and the bottom surfaces
of the rotor-core precursor are covered by the insulating members,
the entire top and the entire bottom surfaces of the rotor-core
precursor may be covered by the insulating members, or only
portions of the top and the bottom surfaces corresponding to the
inner circumferential region of the rotor-core precursor may be
covered by the insulating members.
[0023] In another aspect of the manufacturing method for the rotor
core according to the present disclosure, the manufacturing method
for the rotor may further include using an internally-movable
annealing furnace. The internally-movable annealing furnace may
have a space for movement where the rotor-core precursor rollingly
moves. The internally-movable annealing furnace may include heating
units disposed around the space for movement. The manufacturing
method for the rotor may further include heating and annealing the
rotor-core precursor from a side surface of the rotor-core
precursor while the rotor-core precursor rollingly moves in the
space for movement under operation of the heating units.
[0024] By using the internally-movable annealing furnace including
the space for movement where the rotor-core precursor in a columnar
shape rollingly moves, and heating and annealing the rotor-core
precursor from the side surface thereof by the heating units while
the rotor-core precursor is allowed to rollingly move, it is
possible to efficiently anneal the outer circumferential region of
the rotor-core precursor. As a method of allowing the rotor-core
precursor to rollingly move, for example, such a method may be
employed that an annular gear is fixed to the rotor-core precursor,
and a long gear extending in the longitudinal direction in the
space for movement and slidable in the space for movement is
brought to mesh with the annular gear fixed to the rotor-core
precursor, and this long gear is brought to slide so as to allow
the rotor-core precursor to rollingly move in the space for
movement.
[0025] There may be employed a method that consecutively arranges a
pre-heating zone and a high-temperature heating zone in the
internally-movable annealing furnace, pre-heats the entire
rotor-core precursor up to a predetermined temperature during the
rolling movement of the rotor-core precursor in the pre-heating
zone maintained at a relatively low temperature, and subsequently
actively anneals the rotor-core precursor from the side surface
thereof during the rolling movement of the rotor-core precursor in
the high-temperature heating zone, to thereby promote grain growing
of the crystals in the outer circumferential region of the
rotor-core precursor.
[0026] The present disclosure is also directed to a manufacturing
method for a motor core including a rotor core included in a rotor
and a stator core included in a stator, and the manufacturing
method includes: punching a plurality of plates for rotor core and
a plurality of plates for stator core plates from an
electromagnetic steel sheet; producing a rotor-core precursor by
stacking up the plates for the rotor core; producing a stator-core
precursor by stacking up the plates for the stator core plates;
manufacturing a rotor core by annealing an outer circumferential
region of the rotor-core precursor at a first predetermined
temperature and annealing an inner circumferential region of the
rotor-core precursor at a second predetermined temperature so as to
produce a rotor core; manufacturing a stator core by annealing the
stator-core precursor; the first predetermined temperature being a
temperature at which grain growth of crystals of the
electromagnetic steel sheet is promoted; and the second
predetermined temperature being a temperature at which grain growth
of the crystals of the electromagnetic steel sheet is not
promoted.
[0027] The manufacturing method for the motor core of the present
disclosure is a method of manufacturing both the rotor core and the
stator core (both are referred to collectively as a motor core)
included in the motor, and is characterized by manufacturing the
rotor core by a common method to the above-described manufacturing
method for the rotor core.
[0028] By punching a common electromagnetic steel sheet so as to
obtain the rotor-core plates and the stator-core plates from this
electromagnetic steel sheet, it is possible to reduce a waste
portion of the electromagnetic steel as little as possible, thus
enhancing a yield rate of the materials.
[0029] In the second step, the entire stator-core precursor is
annealed at a temperature at which the grain growth of the crystals
is promoted so as to enhance the magnetic characteristics.
[0030] The rotor core manufactured by the manufacturing method of
the present disclosure has excellent magnetic characteristics and a
high strength, and the stator core manufactured by the same method
also has excellent magnetic characteristics; thus these motor cores
are used for manufacturing of motors having an excellent
performance.
[0031] Further, in the manufacturing method for the motor core
according to the present disclosure, as another aspect of the
manufacturing method, the second predetermined temperature may be a
temperature at which work strain during the punching the plates for
rotor core and the plates for stator core is removed.
[0032] In the another aspect of the manufacturing method for the
motor core according to the present disclosure, in the second step,
the manufacturing method for the motor core may include providing
with insulating members on at least a top surface and a bottom
surface of the rotor-core precursor; and placing and annealing the
rotor-core precursor and the stator-core precursor in the annealing
furnace while a side surface of the rotor-core precursor, extending
in a circumferential direction of the rotor-core precursor, is
exposed.
[0033] For example, the rotor-core precursor is disposed inside the
stator-core precursor, and these core precursors are both placed in
the common annealing furnace so as to simultaneously anneal these
both core precursors, to thereby efficiently carry out the
annealing using the minimally small annealing furnace.
[0034] In another aspect of the manufacturing method for the motor
core according to the present disclosure, the manufacturing method
for the motor core may further include using an internally-movable
annealing furnace. The internally-movable annealing furnace may
have a space for movement where the rotor-core precursor rollingly
moves. The internally-movable annealing furnace may include heating
units disposed around the space for movement. The manufacturing
method for the motor core may further include heating the
rotor-core precursor from a side surface of the rotor-core
precursor while the rotor-core precursor rollingly moves in the
space for movement under operation of the heating units; and
placing and annealing the stator-core precursor in a different
annealing furnace.
[0035] While the rotor-core precursor is allowed to rollingly move
in the space for movement in the internally-movable annealing
furnace, the side surface of the rotor-core precursor is
continuously and directly heated by the heating units disposed
around the space for movement, to thereby efficiently anneal the
rotor-core precursor from the side surface (the outer
circumferential region) thereof. On the other hand, the stator-core
precursor is placed in the different annealing furnace so as to be
annealed such that the grain growth of the crystals is promoted
through the entire stator-core precursor, to thereby produce a
stator core excellent in magnetic characteristics.
[0036] As can be appreciated from the above description, according
to the manufacturing method for the rotor core and the
manufacturing method for the motor core according to the present
disclosure, there is provided a difference in temperature during
the annealing between the outer circumferential region and the
inner circumferential region of the rotor-core precursor, the outer
circumferential region is annealed at a temperature at which the
grain growth of the crystals of the electromagnetic steel sheet is
promoted, and the inner circumferential region is annealed at a
temperature at which the grain growth of the crystals of the
electromagnetic steel sheet is not promoted, to thereby manufacture
the rotor core excellent in magnetic characteristics and having a
high strength, thus also manufacturing the motor core including
such a rotor core.
BRIEF DESCRIPTION OF THE DRAWINGS
[0037] Features, advantages, and technical and industrial
significance of exemplary embodiments of the disclosure will be
described below with reference to the accompanying drawings, in
which like numerals denote like elements, and wherein:
[0038] FIG. 1 is a schematic view explaining a first step of a
manufacturing method for a rotor core of the present
disclosure;
[0039] FIG. 2 is a schematic view explaining the first step of the
manufacturing method, subsequent to FIG. 1;
[0040] FIG. 3 is a schematic view explaining an embodiment 1 of a
second step of the manufacturing method for the rotor core;
[0041] FIG. 4 is a view explaining heating control flows of an
outer circumferential region and an inner circumferential region of
a rotor-core precursor, during annealing;
[0042] FIG. 5 is a schematic view explaining an embodiment 2 of the
second step of the manufacturing method for the rotor core;
[0043] FIG. 6 is a perspective view of a manufactured rotor
core;
[0044] FIG. 7 is a schematic view explaining a first step of a
manufacturing method for a motor core of the present
disclosure;
[0045] FIG. 8 is a schematic view explaining the first step of the
manufacturing method, subsequent to FIG. 7;
[0046] FIG. 9 is a schematic view explaining a second step of the
manufacturing method for the motor core;
[0047] FIG. 10 is a view explaining heating control flows of a
stator-core precursor, and the outer circumferential region and the
inner circumferential region of the rotor-core precursor, during
annealing;
[0048] FIG. 11 is a perspective view of a manufactured motor
core;
[0049] FIG. 12 is a view showing experiment results identifying a
relation between annealing temperatures and strengths of rotor
cores after annealing;
[0050] FIG. 13 is a view showing experiment results identifying a
relation between annealing temperatures and iron losses of the
rotor cores after the annealing; and
[0051] FIG. 14 is a view showing experiment results regarding iron
losses and strengths of an embodiment example and comparative
examples.
DETAILED DESCRIPTION OF EMBODIMENTS
[0052] Hereinafter, with reference to drawings, a manufacturing
method for a rotor core and a manufacturing method for a motor core
of the present disclosure will be described.
[0053] FIG. 1 and FIG. 2 are schematic views explaining a first
step of the manufacturing method for a rotor core of the present
disclosure in order, FIG. 3 is a schematic view explaining an
embodiment 1 of a second step of the manufacturing method for the
rotor core, and FIG. 4 is a view explaining heating control flows
of an outer circumferential region and an inner circumferential
region of a rotor-core precursor during annealing. FIG. 5 is a
schematic view explaining an embodiment 2 of the second step of the
manufacturing method for the rotor core.
[0054] As shown in FIG. 1, a broad electromagnetic steel sheet S is
punched with a not-illustrated press machine or the like so as to
produce multiple rotor-core plates 1, each formed in a disk shape
having a predetermined diameter, from the electromagnetic steel
sheet S. As an example of the electromagnetic steel sheet S, an
electromagnetic steel sheet of a so-called fine grain material
whose average grain size of crystals forming the electromagnetic
steel sheet is within a range of approximately 20 to 30 .mu.m may
be applied, or an electromagnetic steel sheet of a so-called normal
grain-size material whose average grain size of crystals is 50
.mu.m or more may be applied.
[0055] Next, as shown in FIG. 2, the multiple produced rotor-core
plates 1 are stacked up, and are squeezed and/or welded together,
or the like so as to produce a rotor-core precursor 10'.
[0056] Here, the rotor-core precursor 10' has a columnar shape, and
includes a side surface 10'd extending in the circumferential
direction, a top surface 10'e, a bottom surface 10'f The rotor-core
precursor 10' further includes magnet slots having the number
corresponding to the number of magnetic poles; in an example
illustrated in drawing, one magnet pole is composed of three
permanent magnets not illustrated, and two magnet slots 10'a in a
substantially inverted V-shape in a plan view and a single magnet
slot 10'b, a longitudinal direction of which is arranged in the
circumferential direction between these magnet slots 10'a, are
formed. However, there may be various manners of the magnet slots,
such as a manner of composing a single magnetic pole by a permanent
magnet disposed in a single magnet slot 10'b, and a manner of
composing a single magnetic pole by permanent magnets disposed in
two magnet slots 10'a in a substantially inverted V-shape. In
addition, a shaft slot 10'c is formed at a center position of the
rotor-core precursor 10'. These magnet slots 10'a, 10'b and the
shaft slot 10'c may be formed in the rotor-core plates 1 before
being stacked up, or may be so formed as to extend from the top
surface 10'e to the bottom surface 10'f after the respective
rotor-core plates 1 are stacked up (the above is a first step).
[0057] In the second step, the rotor-core precursor 10' produced in
the first step is annealed at different temperatures respectively
in the outer circumferential region thereof and in the inner
circumferential region thereof so as to manufacture the rotor core.
This second step will be described with reference to FIGS. 3, 4,
5.
[0058] First, the embodiment 1 of the second step will be described
with reference to FIG. 3 and FIG. 4. As shown in FIG. 3, insulating
members I are respectively placed on the top surface 10'e and the
bottom surface 10'f of the rotor-core precursor 10', while the side
surface 10'd extending in the circumferential direction of the
rotor-core precursor 10' is exposed to the outside, and the
rotor-core precursor 10' in this state is placed in an annealing
furnace K1 in which heating units H are incorporated.
[0059] The heating units H are operated so as to heat the
rotor-core precursor 10' from the side surface 10'd thereof (in
directions X) in the annealing furnace K1.
[0060] Specifically, in the annealing furnace K1, heat input from
the top surface 10'e and the bottom surface 10'f of the rotor-core
precursor 10' is suppressed by the insulating members I, while heat
input from the side surface 10'd thereof exposed to the outside is
actively carried out. Hence, in the rotor-core precursor 10', the
annealing progresses from the side surface 10'd thereof.
[0061] In this annealing process, the heating control flows of the
outer circumferential region and the inner circumferential region
of the rotor-core precursor shown in FIG. 4 are carried out.
[0062] In FIG. 4, a temperature T1 (a first predetermined
temperature) indicates an upper limit value of a temperature range
where grain growth of crystals forming the electromagnetic steel
sheet is promoted; a temperature T2 (a second predetermined
temperature) indicates an upper limit value of a temperature range
where grain growth of the crystals thereof is not promoted; and a
temperature T3 indicates a lower limit value of a temperature range
where work strain introduced in the rotor-core plates 1 during the
punching of the electromagnetic steel sheet S can be removed.
[0063] During the annealing process, the heating control is carried
out in the outer circumferential region of the rotor-core precursor
10' such that the temperature of the outer circumferential region
is increased up to the temperature T1 at time t1, and the outer
circumferential region is annealed at the temperature T1 for a
predetermined time period until time t2. On the other hand, the
heating control is carried out in the inner circumferential region
of the rotor-core precursor 10' such that the inner circumferential
region is annealed while the temperature thereof is gradually
increased up to the temperature T2 at the time t2. The heating is
terminated at a stage of the time t2, and a cooling control to cool
the annealing furnace K1 is carried out (the above is the
embodiment 1 of the second step).
[0064] Here, the outer circumferential region of the rotor-core
precursor 10' is a region supposed to have significant
deterioration of magnetic characteristics due to an iron loss in
the finished rotor core, and for example, an annular range 5 mm
inward from the side surface 10'd can be specified as the outer
circumferential region. On the other hand, the inner
circumferential region of the rotor-core precursor 10' is an inner
region of the rotor-core precursor 10' excluding this outer
circumferential region.
[0065] Next, the embodiment 2 of the second step will be described
with reference to FIG. 5. In this embodiment, as shown in FIG. 5,
there is used an internally-movable annealing furnace K2 provided
with a space for movement MS where the rotor-core precursor 10'
rollingly moves, and also provided with heating units H on the
right and the left of the space for movement MS.
[0066] In the internally-movable annealing furnace K2, a
pre-heating zone YZ, a high-temperature heating zone HZ, a cooling
zone CZ are continuously arranged; and a long gear G2 slidable in
the space for movement MS is also provided. The insulating members
I are fixed to the top and the bottom surfaces of the rotor-core
precursor 10', an annular gear G1 is fixed to one of the insulating
members I, and the gear G1 and the gear G2 are brought to mesh with
each other. The long gear G2 is brought to slide (in a direction Z)
by a not-illustrated driving unit so as to allow the rotor-core
precursor 10' to rollingly (in a direction Y1) travel (in a
direction Y2) via the gear G1 from the pre-heating zone YZ, and the
high-temperature heating zone HZ, to the cooling zone CZ in the
space for movement MS. While the rotor-core precursor 10' is
rollingly (in the direction Y1) moving (in the direction Y2) in the
pre-heating zone YZ maintained at a relatively low temperature, the
entire rotor-core precursor 10' is pre-heated up to a predetermined
temperature. The rotor-core precursor 10' has a columnar shape, and
only the side surface 10'd thereof is exposed toward the heating
units H, so that the side surface 10'd of the rotor-core precursor
10' is directly heated (in the directions X), and thus the input
heat progresses from the side surface 10'd of the rotor-core
precursor 10'.
[0067] Next, the pre-heated rotor-core precursor 10' enters the
high-temperature heating zone HZ. As the heating units H located in
the high-temperature heating zone HZ, halogen heaters may be
employed, for example, so as to carry out heating at a higher
temperature than that in the pre-heating zone YZ. In the
high-temperature heating zone HZ, a higher-temperature heat than
that in the pre-heating zone YZ is inputted from the side surface
10'd of the rotor-core precursor 10' that is rollingly moving, so
that the annealing in the outer circumferential region of the
rotor-core precursor 10' progresses. After the rotor-core precursor
10' is annealed in the high-temperature heating zone HZ, the
rotor-core precursor 10' moves into the cooling zone CZ so as to be
cooled here. In the second step shown in FIG. 5, the heating
control shown in FIG. 4 is also carried out (the above is the
embodiment 2 of the second step).
[0068] As described above, the rotor core 10 shown in FIG. 6 is
manufactured by the method according to the first step and the
embodiment 1 or the embodiment 2 of the second step. Here, the
rotor core 10 includes the magnet slots 10a, 10b and the shaft slot
10c, and also includes an outer circumferential region 10A where
the crystals have grown in a predetermined width range w from a
side surface 10d thereof, and an inner circumferential region 10B
where the crystals have not grown, which is located inward of the
outer circumferential region 10A.
[0069] In the outer circumferential region 10A, the magnetic
characteristics become higher because the grain growth of the
crystals is promoted, so that the iron loss can effectively be
reduced. In addition, the inner circumferential region 10B is a
region having a higher strength (tensile strength) because the
grain growth of the crystals is not promoted. Accordingly, the
rotor core 10 becomes a core excellent in magnetic characteristics
and having a high strength.
[0070] FIGS. 7, 8 are schematic views explaining a first step of a
manufacturing method for a motor core of the present disclosure in
order; FIG. 9 is a schematic view explaining a second step of the
manufacturing method for the motor core; and FIG. 10 is a view
explaining heating control flows of the stator-core precursor, the
outer circumferential region and the inner circumferential region
of the rotor-core precursor during the annealing.
[0071] First, as shown in FIG. 7, the electromagnetic steel sheet S
is punched to obtain multiple sets of stator-core plates 2 and
rotor-core plates 1 from the electromagnetic steel sheet S, where
each rotor-core plate 1 is obtained from an inner region of each
corresponding stator-core plate 2 of the same single set, to
thereby produce predetermined sets of the stator-core plates 2 and
the rotor-core plates 1. In this manner, each stator-core plate 2
and each rotor-core plate 1 obtained from the inner region of each
corresponding stator-core plate 2 are produced by punching the
electromagnetic steel sheet S, to thereby reduce a waste portion of
the electromagnetic steel S as little as possible, thus enhancing
the yield rate of the materials.
[0072] Subsequently, as shown in FIG. 8, the multiple produced
rotor-core plates 1 are stacked up, and are then squeezed and/or
welded together, or the like so as to produce the rotor-core
precursor 10'; and at the same time, the multiple produced
stator-core plates 2 are stacked up, and are then squeezed and/or
welded together, or the like so as to produce the stator-core
precursor 20' (the above is the first step).
[0073] Next, as shown in FIG. 9, with respect to the rotor-core
precursor 10', as similar to the case of FIG. 3, the insulating
members I are disposed on the top surface 10'e and the bottom
surface 10'f of the rotor-core precursor 10', and the rotor-core
precursor 10' in a state of being disposed inside the stator-core
precursors 20' is placed in the annealing furnace K1 in which the
heating units H are incorporated. In this manner, since both the
rotor-core precursors 10' and the stator-core precursors 20' are
annealed at the same time with the rotor-core precursors 10'
disposed inside the stator-core precursors 20', it is possible to
design the annealing furnace K1 to be as small as possible, and
also efficiently carry out the annealing.
[0074] In order to promote the annealing of the entire stator-core
precursor 20', no insulating members are placed thereon. In order
to adjust the heights of the rotor-core precursor 10' and the
stator-core precursor 20' to each other, the stator-core precursor
20' is placed on a seat D.
[0075] In the annealing furnace K1, the heating units H are
operated so as to heat the stator-core precursors 20' from the top
surface and the side surface thereof (in the directions X), and
also heat the rotor-core precursors 10' from the side surfaces 10'd
thereof via a space between the rotor-core precursors 10' and the
stator-core precursors 20' (in the directions X).
[0076] Accordingly, in the annealing furnace K1, the heat input
from the top surface 10'e and the bottom surface 10'f of the
rotor-core precursor 10' is suppressed by the insulating members I,
while the heat input from the side surface 10'd exposed to the
outside is actively carried out; and in the stator-core precursor
20', the heat input is actively carried out from the side surface
and the top surface thereof exposed to the outside; therefore, the
annealing progresses on the respective surfaces.
[0077] In this annealing process, there are carried out the heating
control flows of the stator-core precursor, and of the outer
circumferential region and the inner circumferential region of the
rotor-core precursor shown in FIG. 10.
[0078] In FIG. 10, the temperature T1 indicates an upper limit
value of a temperature range where grain growth of the crystals
forming the electromagnetic steel sheet is promoted; the
temperature T2 indicates an upper limit value of a temperature
range where the grain growth of the crystals is not promoted; and
the temperature T3 indicates a lower limit value of a temperature
range where work strain introduced in the rotor-core plates 1
during the punching process of the electromagnetic steel sheet S
can be removed.
[0079] During the annealing process, the heating control is carried
out in the outer circumferential region of the rotor-core precursor
10' such that the temperature of the outer circumferential region
is increased up to the temperature T1 at the time t1, and the outer
circumferential region is annealed at the temperature T1 for a
predetermined time period until the time t2; and the heating
control is carried out in the inner circumferential region of the
rotor-core precursor 10' such that the inner circumferential region
is annealed while the temperature thereof is gradually increased up
to the temperature T2 at the time t2. The heating control is
carried out on the stator-core precursor 20' such that the
temperature of the stator-core precursor 20' is increased up to the
temperature T1 at the time t3 earlier than the time t1, and the
stator-core precursor 20' is annealed at the temperature T1 for a
predetermined time period until the time t2. Then, the heating is
terminated at the stage of the time t2, and the control to cool the
annealing furnace K1 is carried out (the above is the second
step).
[0080] As described above, by the manufacturing method according to
the first step and the second step, a motor core 30 composed of the
rotor core 10 and the stator core 20 is manufactured, as shown in
FIG. 11.
[0081] Here, as shown in FIG. 6, the rotor core 10 includes the
magnet slots 10a, 10b and the shaft slot 10c, and also includes the
outer circumferential region 10A where the crystal grains have
grown in the predetermined width range w from the side surface 10d,
and the inner circumferential region 10B where the crystal grains
have not grown, which is located inward of the outer
circumferential region 10A. This outer circumferential region 10A
provides high magnetic characteristics, and the inner
circumferential region 10B ensures a high strength.
[0082] In the meantime, the stator core 20 has higher magnetic
characteristics because the crystal grains have grown through the
entire stator core 20, so that the stator core 20 becomes a core
whose iron loss is reduced.
[0083] Accordingly, it is possible to manufacture the rotor core 10
excellent in magnetic characteristics and having a high strength;
and furthermore, it is also possible to manufacture the stator core
20 excellent in magnetic characteristics.
[0084] Also in the second step of the manufacturing method for this
motor core, there may also be employed a method of using the
internally-movable annealing furnace K2 shown in FIG. 5 when the
rotor-core precursors 10' is annealed, and using the annealing
furnace K1 shown in FIG. 9 when the stator-core precursor 20' is
annealed.
[0085] In order to estimate respective characteristics of a test
body of a rotor core produced by the manufacturing method of the
present disclosure (an embodiment example), of a test body of a
rotor core without being subjected to the annealing (a comparative
example 1), of a test body of a rotor core entirely annealed at
750.degree. C. (a comparative example 2), and of a test body of a
rotor core entirely annealed at 850.degree. C. (a comparative
example 3), the present inventors and others conducted such an
experiment that test specimens were cut out from a steel sheet of a
raw material, and the test specimens were subjected to the same
heating treatment as those of the rotor cores. The test body of the
embodiment example was made by simulating a rotor core having a
diameter of 150 mm in a plan view wherein an annular range of 5 mm
from the outer circumference thereof is defined as the outer
circumferential region, and a region inward of the outer
circumferential region is defined as the inner circumferential
region, the outer circumferential region was annealed at 800 to
850.degree. C., and the inner circumferential region was annealed
at 650 to 750.degree. C. Each of the test bodies was made by using
rotor-core plates obtained by punching an electromagnetic steel
sheet, which was a fine grain material having an average grain size
of less than 50 .mu.m. Here, it is understood that the grain growth
of the crystals in the electromagnetic steel sheet is not promoted
within the temperature range of 750.degree. C. or less, and work
strain introduced during the punching process is removed within the
temperature range of 650.degree. C. or more. In the present
experiment, with respect to the strengths of the test bodies,
tensile test specimens were produced from fine grain materials
having different annealing temperatures, and yield strengths of the
respective test specimens were measured when a tensile test was
carried out by using a tensile tester. Similarly, an iron loss test
was conducted by measuring iron losses of test specimens cut out
from the fine grain materials having the different annealing
temperatures.
[0086] In the present experiment, the strengths and the iron losses
of the above embodiment example and the comparative examples 1 to 3
were verified, and there was conducted a test in which rotor-core
precursors were produced, and these rotor-core precursors were
annealed at various annealing temperatures, and yield strengths and
iron losses of the respective materials after being annealed at the
various annealing temperatures were measured. FIG. 12 shows test
results regarding the annealing temperatures and the yield
strengths (Yp) of the respective materials, and FIG. 13 shows test
results regarding the annealing temperatures and the iron losses of
the respective rotor cores. Numerical values on the vertical axis
of FIG. 12 indicate decrease in the yield strengths of the
respective rotor cores formed of a fine grain material, from yield
strengths thereof before the annealing to yield strengths thereof
after the annealing. A strength indicated by a broken line in FIG.
12 indicates a yield strength of a normal grain-size material.
Numerical values on the vertical axis of FIG. 13 indicate iron
losses of the respective rotor cores formed of the fine grain
material after the annealing in terms of proportions relative to
100 when an iron loss result of each rotor core formed of the fine
grain material before the annealing is defined to be 100.
[0087] As shown in FIG. 12, it is verified that the strength of
each rotor core after the annealing greatly changes from the
annealing temperature 750.degree. C., more specifically, it is
verified that the strength of each rotor core greatly drops in the
annealing temperature range of 750.degree. C. or more. Accordingly,
if focusing on only the strength of the rotor core, it is
preferable to adjust the annealing temperature to be lower than
750.degree. C.
[0088] Here, a range to which the embodiment example is applied is
shown in the drawing. In the rotor core according to the embodiment
example, the outer circumferential region thereof is annealed at
800 to 850.degree. C., and the inner circumferential region thereof
is annealed at 650 to 750.degree. C. In the rotor core according to
the embodiment example, a difference in annealing temperature is
provided between the outer circumferential region and the inner
circumferential region, and the inner circumferential region is
annealed at a temperature lower than the 750.degree. C., to thereby
ensure a high strength of the rotor core.
[0089] As shown in FIG. 13, it is verified that the iron loss of
each rotor core after the annealing greatly changes from the
annealing temperature of 750.degree. C., more specifically, the
iron loss of each rotor core greatly drops in the annealing
temperature range of 750.degree. C. or more. Accordingly, if
focusing on only the iron loss of the rotor core, it is preferable
to adjust the annealing temperature to be higher than 750.degree.
C.
[0090] In the rotor core according to the embodiment example, a
difference in annealing temperature is provided between the outer
circumferential region and the inner circumferential region, and
the outer circumferential region is annealed at a temperature
higher than 750.degree. C., to thereby ensure excellent magnetic
characteristics having a high iron-loss reduction effect.
[0091] FIG. 14 is a view showing test results regarding iron losses
and strengths of respective rotors of the embodiment example and
the comparative examples 1 to 3. In this drawing, a strength A
indicates that decrease of the yield strength from that before the
annealing in FIG. 12 is approximately 0 MPa to 20 MPa, and a
strength B indicates approximately 20 MPa to 40 MPa, and a strength
C indicates more than 40 MPa, respectively.
[0092] As shown in FIG. 14, it is verified that the comparative
example 3 and the embodiment example both of which were entirely
annealed at 850.degree. C. exhibit significant decrease in iron
loss to the same extent (approximately 87) if the comparative
example 1 is defined to be 100; and it is seen that with respect to
the strength, the embodiment example has a strength substantially
the same as that of the comparative example 1 that was not
annealed. That is, it is verified that with the manufacturing
method of the present disclosure that carries out the annealing the
outer circumferential region and the inner circumferential region
using the different annealing temperatures, it is possible to
obtain the rotor core excellent in magnetic characteristics and
having a high strength.
[0093] As described above, the embodiments of the present
disclosure have been described in detail with reference to the
drawings, but specific configurations are not limited to the
embodiments, and design changes and the like which are made within
a range not departing from the scope of the disclosure are included
in the disclosure.
* * * * *