U.S. patent application number 12/594279 was filed with the patent office on 2010-03-11 for drum type washing machine.
This patent application is currently assigned to Panasonic Corporation. Invention is credited to Yoshio Kobayashi, Takeshi Kowa, Hu Li, Masahiko Morisaki, Hiroshi Murakami, Yukinori Nakagawa, Yuichiro Tashiro, Yuichi Yoshikawa.
Application Number | 20100058817 12/594279 |
Document ID | / |
Family ID | 39863567 |
Filed Date | 2010-03-11 |
United States Patent
Application |
20100058817 |
Kind Code |
A1 |
Yoshikawa; Yuichi ; et
al. |
March 11, 2010 |
DRUM TYPE WASHING MACHINE
Abstract
A drum type washing machine of the present invention is a
direct-drive washing machine including a washing-machine casing; a
rotating drum with its drum rotation shaft horizontal or inclined;
and a motor driving the rotating drum. The motor has a stator
including a coil wound in a toroidal winding form and first molding
resin; and a twin-type rotor including an outer rotor, an inner
rotor, and second molding resin integrally molding them.
Inventors: |
Yoshikawa; Yuichi; (Osaka,
JP) ; Li; Hu; (Osaka, JP) ; Morisaki;
Masahiko; (Osaka, JP) ; Murakami; Hiroshi;
(Osaka, JP) ; Tashiro; Yuichiro; (Osaka, JP)
; Kobayashi; Yoshio; (Osaka, JP) ; Kowa;
Takeshi; (Osaka, JP) ; Nakagawa; Yukinori;
(Osaka, JP) |
Correspondence
Address: |
Brinks Hofer Gilson & Lione/Panasonic
P.O. Box 10395
Chicago
IL
60610
US
|
Assignee: |
Panasonic Corporation
Kadoma-shi
JP
|
Family ID: |
39863567 |
Appl. No.: |
12/594279 |
Filed: |
April 8, 2008 |
PCT Filed: |
April 8, 2008 |
PCT NO: |
PCT/JP2008/000895 |
371 Date: |
November 12, 2009 |
Current U.S.
Class: |
68/139 |
Current CPC
Class: |
D06F 37/304 20130101;
H02K 1/278 20130101; H02K 21/16 20130101; H02K 1/2786 20130101;
H02K 21/222 20130101 |
Class at
Publication: |
68/139 |
International
Class: |
D06F 25/00 20060101
D06F025/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 11, 2007 |
JP |
2007-103648 |
Claims
1. A drum type washing machine comprising: a washing-machine casing
having an opening through which laundry is loaded and unloaded; a
rotating drum having a drum rotation shaft in a horizontal or
inclined direction relative to the casing; and a motor driving the
rotating drum, wherein the machine is a direct-drive washing
machine the drum rotation shaft of which is connected directly to a
motor shaft of the motor, and wherein the motor includes: a stator
having: a ring-like stator yoke; a plurality of outer teeth
projecting from the stator yoke in an outer circumferential
direction; a plurality, the equal number as the outer teeth, of
inner teeth projecting from the stator yoke in an inner
circumferential direction; a plurality of outer slots formed
between each of the outer teeth; a plurality of inner slots formed
between each of the inner teeth; a coil wire-connected to the
stator yoke between the outer slot and the inner slot in a shape of
a three-phase star or a delta, wound in a toroidal winding form;
and first molding resin integrally molding the stator yoke, the
outer slot, the inner slot, and the coil; and a twin-type rotor
having: an outer rotor disposed facing the outer teeth through a
given air gap; an inner rotor disposed facing the inner teeth
through a given air gap; second molding resin integrally molding
the outer rotor and the inner rotor; and the motor shaft connected
to the outer rotor and the inner rotor.
2. The drum type washing machine of claim 1, wherein the rotating
drum has a bottomed, cylindrical water receiving tub at an outer
circumference thereof, and the motor is fixed to a bottom of the
water receiving tub.
3. The drum type washing machine of claim 2, wherein the first
molding resin has a plurality of attaching portions, which are
fixed to the water receiving tub.
4. The drum type washing machine of claim 1, wherein the stator
yoke has a plurality of through holes penetrating axiswise, and
wherein the first molding resin integrally molds the stator yoke,
the outer slot, the inner slot, the coil, and the through
holes.
5. The drum type washing machine of claim 4, wherein each of the
through holes is formed at an intersecting point of a straight line
connecting a rotation-direction center of the outer teeth to a
rotation-direction center of the inner teeth; and a center arc of
the stator yoke.
6. The drum type washing machine of claim 4, wherein the through
holes have circular or elliptical cross sections.
7. The drum type washing machine of claim 1, wherein the second
molding resin has a plurality of ventilating holes penetrating in a
direction of the motor shaft.
8. The drum type washing machine of claim 1, wherein the second
molding resin has a plurality of projections at a part thereof
facing the stator in a direction of the motor shaft.
9. The drum type washing machine of claim 1, wherein the second
molding resin has a plurality of ribs at a back side thereof.
10. The drum type washing machine of claim 1, wherein the number
(S) of the outer slots is equal to that of the inner slots, wherein
the outer rotor includes an outer rotor yoke and an outer permanent
magnet with the number of poles P, wherein the inner rotor includes
an inner rotor yoke and an inner permanent magnet with the number
of poles P, and wherein the number of slots S and the number of
poles P hold S:P=3:2N-1, where integer N is 1 or more, and a case
where 2N-1 is a multiple of 3 is excluded.
11. The drum type washing machine of claim 10, wherein the number
of slots S and the number of poles P hold S:P=3:5.
12. The drum type washing machine of claim 10, wherein at least one
of the outer permanent magnet and the inner permanent magnet is
embedded into an inside of the outer rotor yoke or the inner rotor
yoke.
Description
TECHNICAL FIELD
[0001] The present invention relates to a direct-drive drum type
washing machine including a rotating drum with its rotation central
axis horizontal or inclined, and a motor driving the rotating
drum.
BACKGROUND ART
[0002] For fully automatic washing machines of recent years,
direct-drive drum type washing machines with a drying function
added have been mainstream. A motor for driving a rotating drum of
such a washing machine, directly driving the rotating drum not
through a gear, needs to implement simultaneously low speed and
high torque (from 10 rpm to 100 rpm, 10 Nm or higher) for washing;
and high speed and low torque (1,000 rpm or higher) for dewatering.
While washing, at an extremely low speed, cogging torque (largely
influencing vibration and noise of the washing machine) of the
motor needs to be reduced.
[0003] As a technique implementing such a motor producing low speed
and high torque, a washing-machine motor is known as described in
patent literatures 1 and 2. A washing-machine motor described in
the patent literatures includes a stator, and a rotor arranged in
the outer circumference of the stator. However, as described in
patent literature 1, for a motor with a single stator and a single
rotor to produce high torque, the amount of the coil wound around
the stator, and/or the magnetic force of the rotor need to be
increased. Accordingly, the overall volume of the machine body
undesirably increases. Further, a washing-machine motor described
in patent literature 1 includes a coil wound around the stator by
concentrated winding method. Hence, this type of motor generates a
radial force higher than that including a coil wound by distributed
winding method. Herewith, noise and vibration while driving
undesirably increase.
[0004] Under the circumstances, to eliminate the above-described
problems, a motor as described in patent literature 2 is devised. A
motor described in patent literature 2 includes a hollow
cylinder-shaped stator having a coil produced by winding a wire
around teeth by concentrated winding method; an inner rotor
arranged leaving an even gap off the inner circumferential surface
of the stator; an outer rotor arranged leaving an even gap off the
outer circumferential surface of the stator. A motor with such a
structure described in patent literature 2 can use a force caused
by magnetic flux of the inner rotor and that of the outer rotor.
Accordingly, the motor can increase power density and produce high
torque in spite of its small size.
[0005] However, a motor described in patent literature 2 as well,
including a coil wound by concentrated winding method, generates a
high radial force. Herewith, vibration and noise undesirably
increase.
[0006] Hence, with a drum type washing machine including a
washing-machine motor as described in patent literatures 1 and 2,
it is undesirably difficult to simultaneously implement higher
capacitance, compactification, and noise reduction.
[0007] [Patent literature 1] Japanese Patent Unexamined Publication
No. 2007-089282
[0008] [Patent literature 2] Japanese Translation of PCT
Publication No. 2005-521378
SUMMARY OF THE INVENTION
[0009] A drum type washing machine of the present invention
includes a washing-machine casing having an opening through which
laundry is loaded and unloaded; a rotating drum having its drum
rotation shaft in a horizontal or inclined direction relative to
the casing; and a motor driving the rotating drum. The washing
machine is a direct-drive one in which the drum rotation shaft is
directly connected to the motor shaft.
[0010] The stator of the motor includes a ring-like stator yoke;
plural outer teeth projecting from the stator yoke in the outer
circumferential direction; plural (the equal number as outer teeth)
inner teeth projecting from the stator yoke in the inner
circumferential direction; plural outer slots formed between each
outer teeth; and plural inner slots placed between each inner
teeth. The stator further includes a coil connected to the stator
yoke between the outer slot and the inner slot in a shape of
three-phase star or delta, wound in a toroidal winding form; and
first molding resin integrally molding the stator yoke, outer slot,
inner slot, and coil.
[0011] Further, the rotor of the motor is twin-type and includes an
outer rotor disposed facing the outer teeth through a given air
gap; an inner rotor disposed facing the inner teeth through a given
air gap; second molding resin integrally molding the outer rotor
and the inner rotor; and a motor shaft connected to the outer rotor
and the inner rotor.
[0012] With a drum type washing machine of the present invention
according to the structure, the capacity of laundry can be
increased to a maximum extent in spite of its small size, and
vibration and noise are reduced to implement low noise allowing
night-time operation. Additionally, the invention improves
resistance to water and drip to implement a highly reliable washing
machine.
BRIEF DESCRIPTION OF DRAWINGS
[0013] FIG. 1 is a sectional view of a drum type washing machine
according to an embodiment of the present invention.
[0014] FIG. 2 is a perspective view of motor 5 of the drum type
washing machine according to the embodiment of the present
invention.
[0015] FIG. 3 is an explanatory perspective view showing the stator
and the rotor of motor 5 of the same, disassembled.
[0016] FIG. 4 is an explanatory perspective view of the same,
viewed from a different direction.
[0017] FIG. 5 is a sectional view of motor 5 of the same.
[0018] FIG. 6 is a sectional view showing a cross section in FIG.
5, taken along line 6-6.
[0019] FIG. 7 is a graph showing relationship between the width of
a teeth tip and cogging torque in motor 5 of the same.
[0020] FIG. 8 is a graph showing relationship between a rotational
position (electrical angle) and induced voltage of the rotor of
motor 5 of the same.
[0021] FIG. 9 is a graph showing relationship between a rotational
position (electrical angle) and a radial force of the rotor of
motor 5 of the same.
[0022] FIG. 10 is a graph showing relationship between a rotational
position (electrical angle) and cogging torque of the rotor of
motor 5 of the same.
[0023] FIG. 11 is a graph showing power density of motor 5 of the
same, for each type of motor.
[0024] FIG. 12 is a graph showing relationship between the number
of poles and a torque constant of motor 5 of the same.
[0025] FIG. 13 schematically shows circumstances of currents
flowing through coil 15 of motor 5 of the same.
REFERENCE MARKS IN THE DRAWINGS
[0026] 1 Washing-machine casing [0027] 1a Opening [0028] 2 Rotating
drum [0029] 3 Water receiving tub [0030] 4 Drum rotation shaft
[0031] 5 Motor [0032] 9 Lid [0033] 10 Stator [0034] 11 Stator core
[0035] 12 Outer teeth [0036] 13 Inner teeth [0037] 14 Stator yoke
[0038] 15 Coil [0039] 16 Outer slot [0040] 17 Inner slot [0041] 18
Through hole [0042] 20 Inner rotor [0043] 21 Inner rotor yoke
[0044] 22 Inner permanent magnet [0045] 30 Outer rotor [0046] 31
Outer rotor yoke [0047] 32 Outer permanent magnet [0048] 41 First
surface [0049] 42 Second surface [0050] 51 First molding resin
[0051] 52 Second molding resin [0052] 60 Attaching portion [0053]
61 Motor shaft [0054] 62 Rib [0055] 64 Ventilating hole [0056] 65
Projection [0057] 71 Straight line connecting the center in the
rotation direction of the outer teeth to the center in the rotation
direction of the inner teeth [0058] 72 Center arc of stator
yoke
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0059] Hereinafter, a description is made of an embodiment of the
present invention in reference to some drawings. FIG. 1 is a
sectional view of a drum type washing machine according to the
embodiment of the present invention.
[0060] Washing-machine casing 1 of the drum type washing machine
has bottomed, cylindrical water receiving tub 3 arranged therein in
a state inclined downward from the front side of body 1 toward the
back side. The inside of this water receiving tub 3 rotatably
supports bottomed, cylindrical rotating drum 2 so that its drum
rotation shaft 4 is inclined downward from the front side of
washing-machine casing 1 toward the back side.
[0061] The front side of washing-machine casing 1 has opening 1a
formed therein for loading and unloading laundry. Then, opening 1a
is provided with lid 9 made of material such as glass for opening
and closing opening 1a.
[0062] The outside of the bottom of water receiving tub 3 has motor
shaft 61 of motor 5 directly connected thereto on the same axis as
drum rotation shaft 4 of rotating drum 2. Motor 5 can control
rotation speed and a rotation direction of rotating drum 2. Motor 5
is fixed to water receiving tub 3 at attaching portion 60 (to be
described later) formed on the outer circumference of motor 5 with
attaching means such as screws (not shown).
[0063] FIG. 2 is a perspective view of motor 5 of a drum type
washing machine according to the embodiment of the present
invention. FIGS. 3 and 4 are explanatory perspective views of
stator 10 of motor 5, and a twin-type rotor including inner rotor
20 and outer rotor 30, disassembled. FIGS. 3 and 4 are perspective
views viewed from different directions.
[0064] Motor 5 is composed of stator 10, inner rotor 20 facing the
internal diameter side of stator 10; and outer rotor 30 facing the
external diameter side.
[0065] Stator 10 is covered with first molding resin 51 over the
substantially whole surface. Inner rotor 20 and outer rotor 30 are
integrally molded with second molding resin 52. The outer
circumference of stator 10 has five attaching portions 60 arranged
thereon at uniform intervals in the rotation direction. These first
molding resin 51 of stator 10 and second molding resin 52 of the
rotor are integrally molded by being inserted into a resin-molding
mold, respectively.
[0066] Second molding resin 52 of the rotor has plural ventilating
holes 64 penetrating in the direction of motor shaft 61. Second
molding resin 52 is provided thereon with plural projections 65 at
the part facing stator 10 in the direction of motor shaft 61.
Consequently, while inner rotor 20 and outer rotor 30 are rotating,
heat generated from stator 10 is agitated. Then, hot airflow occurs
in the rotation direction between stator 10, inner rotor 20, and
outer rotor 30. This hot airflow flows out through ventilating hole
64 to discharge heat inside motor 5. Further, the back side of
second molding resin 52 is provided thereon with plural ribs 62.
Accordingly, required strength can be secured while reducing the
amount of molding resin.
[0067] FIG. 5 is a sectional view of motor 5, and FIG. 6 is a
sectional view showing a cross section in FIG. 5, taken along line
6-6. Stator core 11 composing stator 10 includes substantially
ring-like stator yoke 14; outer teeth 12 projecting from stator
yoke 14 in the outer circumferential direction; and inner teeth 13
(the equal number as outer teeth 12) projecting from stator yoke 14
in the inner circumferential direction. Stator core 11 further has
outer slot 16 formed between each outer teeth 12; and inner slot 17
formed between each inner teeth 13. Then, stator 10 further has
plural coils 15 wire-connected in a shape of three-phase star or
delta by toroidal winding method wound around stator yoke 14 placed
between outer slot 16 and inner slot 17, by concentrated winding
method.
[0068] Here, with motor 5 according to this embodiment, both inner
rotor 20 and outer rotor 30 have 20 poles and 12 slots,
respectively. The combination of 20 poles and 12 slots brings about
the same effect as that by distributed winding in coil arrangement
as later described in detail (refer to FIG. 8).
[0069] As described above, stator 10 is integrally molded with
first molding resin 51 after coil 15 is wound. The purpose is to
fix coil 15 to stator core 11 and to prevent moisture and drips.
Motor 5 is used for a washing machine, and thus improving
moisture-proof and drip-proof properties is particularly important.
In addition, when integrally molding with first molding resin 51 in
this way, the effect is expected in that molding resin 51 absorbs
vibration to reduce vibration and noise of the entire washing
machine.
[0070] Stator yoke 14 of stator core 11 has plural through holes 18
formed therein penetrating axiswise. When coil 15 is integrally
molded with first molding resin 51, molding resin 51 is filled into
outer slot 16, inner slot 17, first surface 41 (upper side in FIG.
6) of stator yoke 14, second surface 42 (lower side in FIG. 6) of
stator yoke 14, and through holes 18. With such a structure, first
molding resin 51 on first surface 41 of stator yoke 14 is to be
connected to first molding resin 51 on second surface 42 through
first molding resin 51 filled into through holes 18. Hence, even if
first molding resin 51 on first surface 41 and first molding resin
51 on second surface 42 are formed thinly to downsize the motor,
exfoliation is prevented owing to molding resin 51 filled into
through holes 18 being connected. Here, attaching portions 60 are
formed on second surface 42 from first molding resin 51.
[0071] Each of through holes 18 is provided at the intersecting
point of straight line 71 connecting the rotation-direction centers
of outer teeth 12 and inner teeth 13, passing through the
rotation-direction centers; and center arc 72 of stator yoke 14.
The shape of a cross section of through hole 18 is preferably
circular or elliptical, which is because the fluidity of the
molding resin material is increased.
[0072] The radial length of through hole 18 is preferably
0.5.+-.10% that of stator yoke 14. This is because a longer one
causes magnetic saturation in stator yoke 14 to decrease the motor
torque; a shorter one causes lower fluidity of the molding resin
when molding to decrease the strength. Here, the shape of a cross
section of through hole 18 is not limited to circular or
elliptical, but quadrangle, rectangle, triangle, or the like may be
used as appropriate.
[0073] First molding resin 51 and second molding resin 52 are
ideally unsaturated polyester resin containing a filler, which is
because the resin is excellent in fluidity during molding and in
strength after molding.
[0074] FIG. 7 is a graph showing relationship between the width of
a teeth tip and cogging torque. The broken line in the figure
represents relationship between the width of a tip of inner teeth
13 and cogging torque, where only inner rotor 20 is assumed to be
present. The solid line represents relationship between the width
of a tip of outer teeth 12 and cogging torque, where only outer
rotor 30 is assumed to be present.
[0075] FIG. 7 proves that to minimize the cogging torque, the width
of a teeth tip needs to be increased. In FIG. 7, the cogging torque
becomes lower particularly near 14.5 degrees and 19.3 degrees. In
such a case, the length (the pitch of teeth at their part with the
maximum width) of a slot open becomes shorter, and thus the amount
of first molding resin 51 filled into a slot open decreases. In
this embodiment, however, first molding resin 51 filled into plural
through holes 18 penetrating axiswise of stator yoke 14 connects
first molding resin 51 on first surface 41 to first molding resin
51 on second surface 42. Herewith, even if the amount of first
molding resin 51 filled into a slot open decreases, a strong fixing
strength of first molding resin 51 on stator core 11 is
implemented.
[0076] Outer rotor 30 is disposed facing outer teeth 12 through a
given air gap. Similarly, inner rotor 20 is disposed facing inner
teeth 13 through a given air gap.
[0077] Outer rotor 30 includes outer rotor yoke 31, and plural
outer permanent magnets 32 embedded into outer rotor yoke 31. Outer
rotor yoke 31 has magnetic steel sheets laminated thereon punched
into a given shape to form a magnetic circuit.
[0078] Similarly, inner rotor 20 includes inner rotor yoke 21, and
plural inner permanent magnets 22 embedded into inner rotor yoke
21. Inner rotor yoke 21 has magnetic steel sheets laminated thereon
punched into a given shape to form a magnetic circuit. Here, outer
rotor 30 and inner rotor 20 do not include a rotor frame,
respectively. Accordingly, the weight and manufacturing
worker-hours can be reduced. Further, the amount equivalent to the
volume of a frame can be covered with second molding resin 52,
thereby absorbing vibration.
[0079] The description is made of the case where outer permanent
magnet 32 and inner permanent magnet 22 are embedded into their
respective rotor yokes (what is called magnet-embedded type), but
either one of them may be disposed on the surface of the rotor yoke
(what is called surface-magnet type). However, either one of them
needs to be of magnet-embedded type in order to implement high
torque and high power with the aid of reluctance torque.
[0080] As described above, outer rotor 30 and inner rotor 20 are
inserted into a resin-molding mold to be integrally molded with
second molding resin 52. Then, they are integrally connected to
motor shaft 61. Energizing coil 15 with a given current rotates
outer rotor 30 and inner rotor 20 integrally. With outer rotor 30
and inner rotor 20 thus structured integrally, motor 5 provides
higher torque and higher power than typical inner- and outer-rotor
motors.
[0081] FIG. 8 is a graph showing relationship between a rotational
position (electrical angle) and induced voltage of the rotor. FIG.
8 shows experimental results for rotors where relationship between
the number of slots S and the number of poles P holds S:P=3:2N-1
(excluding a case where 2N-1 is a multiple of 3).
[0082] FIG. 8 proves that if S:P=3:2N-1 (excluding a case where
2N-1 is a multiple of 3) holds, a substantially sine wave is
produced same as that with a coil by distributed winding method.
Further, the waveform of the induced voltage is a sine wave,
thereby restraining noise and vibration of motor 5 in the same way
as by distributed winding method.
[0083] Here, a description is made of the reason why a
substantially sine wave is produced same as that with a coil by
distributed winding method when S:P=3:2N-1 (excluding a case where
2N-1 is a multiple of 3) holds.
[0084] FIG. 13 schematically shows circumstances of a current
flowing through coil 15. Coil 15 is wound sequentially in the order
of U phase, V phase, and W phase. Reverse currents flow through
coils 15 wound around adjacent slots. That is to say, when a
current is flowing through a U-phase coil 15 from inner slot 17 to
outer slot 16, another current flows through adjacent V-phase coil
15 from outer slot 16 to inner slot 17. Yet another current flows
through W-phase coil 15 adjacent to V-phase coil 15 from inner slot
17 to outer slot 16.
[0085] With such a structure, reverse currents are to flow through
U-phase coil 15 and next U-phase coil 15, which thus the currents
shown by broken lines are to flow in a pseudo manner. The currents
shown by the broken lines are the same as those with a distributed
coil. Accordingly, when S:P=3:2N-1 (excluding a case where 2N-1 is
a multiple of 3) holds, the currents flow in the same way as those
by distributed winding method, which produces a substantially sine
wave same as that by distributed winding method.
[0086] FIG. 9 shows relationship between a rotational position
(electrical angle) and radial force of the rotor. The solid line in
FIG. 9 represents a motor (twin-rotor motor by toroidal winding
method) according to this embodiment; the broken line represents a
single-rotor motor by distributed winding method.
[0087] FIG. 9 proves that the twin-rotor motor by toroidal winding
method provides a radial force lower than the distributed-winding,
single-rotor motor. This is assumed to be because mutually
canceling out vibration of the inner rotor and that of the outer
rotor can reduce the radial force.
[0088] Such effect of radial force reduction is exerted
particularly in a direct-drive washing machine rotating at a low
speed (10 to 100 rpm) for washing. This is because cogging is
likely to influence noise and vibration of the washing machine due
to slow rotation.
[0089] FIG. 10 shows relationship between a rotational position
(electrical angle) and cogging torque of the rotor of a twin-rotor
motor by toroidal winding method. In the figure, the thin broken
line represents cogging torque by inner rotor 20; the thin solid
line, by outer rotor 30; and the central bold solid line, cogging
torque of entire motor 5 produced by combining the above
torques.
[0090] With motor 5 according to the embodiment, inner rotor 20 and
outer rotor 30 are structured so that the phase of cogging torque
by inner rotor 20 is inverted from that by outer rotor 30. The peak
value of cogging torque by inner rotor 20 is made roughly equal to
that by outer rotor 30. With such a structure, cogging torque of
entire motor 5 can be significantly reduced by mutually canceling
out cogging torque by inner rotor 20 and that by outer rotor 30, as
shown in FIG. 10.
[0091] FIG. 11 shows power density of a motor by each type. Here,
power density refers to power per volume of a motor. In FIG. 11, A
represents an inner single-rotor motor; B, outer single-rotor
motor; C, concentrated-winding twin-rotor motor; and D,
toroidal-winding twin-rotor motor according to the embodiment. A
hollow part shows the density of power by the inner rotor; a
hatched part, by the outer rotor.
[0092] FIG. 11 shows that power density of D is the highest. As
compared D to A, D has an inner slot area smaller than A, and thus
the power density of the inner rotor decreases. D, however, has an
outer rotor, and thus exceeds A in overall power density. FIG. 11
shows that D has a power density 1.9 times that of A.
[0093] As compared D to B, D has an outer slot area smaller than B,
and thus the power density of the outer rotor decreases. D,
however, has an inner rotor, and thus exceeds B in overall power
density. FIG. 11 shows that D has a power density 1.5 times that of
B.
[0094] These circumstances show that a washing machine with motor D
has a laundry capacity 1.9 times that with motor A; a washing
machine with motor D has a laundry capacity 1.5 times that with
motor B. In other words, if D, A, and B have an equal power, D can
be downsized by 50% by volume compared to A; 35%, to B.
[0095] As compared D to C, magnetic flux content passing through
rotor yoke D exceeds that through rotor yoke C, when the volumes of
both yokes are equal. Accordingly, the overall power density of D
exceeds that of C. FIG. 11 shows that D has a power density 1.4
times that of C.
[0096] FIG. 12 shows relationship between the number of poles and a
torque constant. In FIG. 12, the bold solid line shows experimental
results of a motor with S:P=3:2N-1 (excluding a case where N is a
multiple of 3). The thin broken line shows experimental results of
a motor with S:P=3:2N (conventional, typical case). The thin solid
line shows experimental results of a motor with other than the
above. FIG. 12 proves that a motor with S:P=3:2N-1 has an excellent
torque constant particularly for more than 20 poles. Specifically,
what is ideal is the combination of the number of slots S=12 and
the number of poles P=20 (i.e. S:P=3:5) described in the
embodiment.
[0097] The motor described hereinbefore includes a stator having a
coil wound in a toroidal winding form; and a twin-type rotor with
an outer rotor and an inner rotor, and thus can produce high torque
in spite of its small size as well as reducing noise and vibration
while driving. The motor includes first molding resin integrally
molding the stator yoke, outer slot, inner slot, and coil; and
second molding resin integrally molding the outer rotor and inner
rotor, thereby reducing the weight and manufacturing worker-hours
as compared to a case where molding is performed by using a frame.
Further, the amount equivalent to the volume of a frame can be
covered with molding resin, thereby absorbing vibration.
[0098] Moreover, the stator yoke has plural through holes formed
penetrating through both end surfaces thereof, and the molding
resin for a stator integrally molds the stator yoke, outer slot,
inner slot, coil, and through holes, thereby connecting molding
resin on both end surfaces of the stator yoke with molding resin
filled in the through holes, which prevents the molding resin
covering the stator from exfoliating off the stator.
[0099] Further, with the number of slots S and the number of poles
P holding S:P=3:2N-1, the waveform of the induced voltage is a sine
wave, thereby restraining noise and vibration of the motor.
[0100] With a drum type washing machine including the motor, the
capacity of laundry can be increased to a maximum extent in spite
of its small size, and vibration and noise are reduced to implement
low noise allowing night-time operation. Additionally, as the
invention has the structure covering main portions of motor with
molding resin, the invention improves resistance to water and drip
to implement a highly reliable washing machine.
INDUSTRIAL APPLICABILITY
[0101] A drum type washing machine according to the present
invention is useful as a washing machine producing high torque in
spite of its small size, and reducing noise and vibration while
driving.
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