FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See section 10, rule 13)
“A DIRECT DRIVE WASHING MACHINE”
WHIRLPOOL OF INDIA LTD., an Indian
Company of Whirlpool House, Plot no. 40, Sector-
44, Gurgaon-122002, Haryana
The following specification particularly describes the invention and the
manner in which it is to be performed.
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FIELD OF THE INVENTION
The present invention generally relates to the field of washing machines. More specifically,
the present invention relates to a washing machine employing direct drive configuration.
BACKGROUND OF THE INVENTION
A conventional direct drive washing machine has an outer tub and a cylindrical basket type
drum which is disposed in the outer tub and rotates inside the outer tub. The tub is configured
to contain water (along with detergent) and the drum is rotated in the outer tub with laundry
loaded therein to wash the laundry. To enable the drum to rotate with respect to the outer tub,
a direct drive mechanism is provided.
In case of a direct drive configuration, washing machine would comprise a tub, a drum
rotatably mounted inside the tub, a shaft connected the drum and a direct drive motor
including a rotor assembly fastened to the shaft including magnets positioned in a
circumferential position, a stator assembly mounted on the rear side of the outer tub and a
casing for encompassing the said components. Although conventional direct drive washing
machines have been of tremendous success for years, there have been certain problems
associated with these washing machines which for a long time have not been resolved. One
of such problems in the conventional direct drive washing machines, the stator is mounted on
the rear side of the outer tub. Owing to the said location of the stator, there has been a space
constraint in the conventional washing machines and the overall washing capacity of the
outer tub gets limited. In recent years, the demand for a larger washing capacity has
increased. Thus, it is necessary to design such a washing machine which has a casing reduced
in size and an outer tub increased in capacity.
Another problem associated with the conventional direct drive washing machines is that the
rotor employed in the conventional direct drive washing machines consists of permanent
magnets which extend over the entire length of the rotor which increases the overall weight
of the direct drive washing machine. Due to increase in overall weight, the probability of
damages during transportation increases. As described above, due to the presence of the
permanent magnets, the overall weight of the washing machine increases, hence, additional
counter balance weight is required to reduce the vibration/displacement of the outer tub
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during the operation.
Therefore, there always existed a need in the art to provide a direct drive type washing
machine which overcomes the above mentioned problems and proves to be user friendly.
OBJECT OF THE INVENTION
The primary object of the present invention is to provide a direct drive washing machine with
increased washing capacity by effectively using the space between the casing and the outer
tub without increasing the size of the casing.
Another object of the present invention is to provide a direct drive washing machine with
reduced overall weight and increased efficiency.
Yet another objective of the present invention is to provide a direct drive washing machine
which can be easily transported and installed with minimal damages.
Yet another objective of the present invention is to provide a direct drive washing machine
which is economical, durable and user friendly.
SUMMARY OF THE INVENTION
Accordingly, the present invention provides a direct drive washing machine comprising a
casing; an outer tub placed inside the casing; at least one slotted stator mounted on the
periphery of the outer tub, said at least one slotted stator having a plurality of coils wound in
the slots so as to produce rowing magnetic field in a working condition; an inner drum
located inside the outer tub, the inner drum being provided with a pair of concentric strips of
electrical conductors wound on an outer circumference thereof, said inner drum along with
the pair of concentric strips co-operate with said at least one slotted stator to define an
induction motor to impart rotary motion to the inner drum.
BRIEF DESCRIPTION OF DRAWINGS
The features of the present invention are set forth with particularity in the appended claims.
The invention itself, together with further features and attended advantages, will become
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apparent from consideration of the following detailed description, taken in conjunction with
the accompanying drawings. One or more embodiments of the present invention are now
described, by way of example only, with reference to the accompanied drawings wherein like
reference numerals represent like elements and in which:
Figure 1 illustrates a sectional view of the direct drive washing machine in accordance with
an aspect of the present invention.
Figure 2 illustrates a pictorial view of direct drive washing machine in accordance with an
aspect of the present invention.
Figure 3 illustrates a sectional side view of the direct drive washing machine in accordance
with an aspect of the present invention.
Figure 4 illustrates a sectional view taken along the section line 2-2 depicted in Figure 1.
Figure 5A illustrates an enlarged view of the block shown in Figure 4 showing the
construction of rotor and slotted stator.
Figure 5B illustrates the slotted stator having plurality of coils wound thereupon.
Figure 6 illustrates the magnetic field being produced by the slotted stator.
Figure 7 illustrates a schematic view of the direct drive washing machine in accordance with
another aspect of the present invention.
Figure 8 illustrates a sectional front view and sectional side view of direct drive washing
machine in accordance with an aspect of the present invention.
Skilled artisans will appreciate that elements in the drawings are illustrated for simplicity and
have not necessarily been drawn to scale. For example, the dimensions of some of the
elements in the drawings may be exaggerated relative to other elements to help to improve
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understanding of embodiments of the present invention.
DETAILED DESCRIPTION
While the invention is susceptible to various modifications and alternative forms, specific
embodiment thereof has been shown by way of example in the drawings and will be
described in detail below. It should be understood, however that it is not intended to limit the
invention to the particular forms disclosed, but on the contrary, the invention is to cover all
modifications, equivalents, and alternative falling within the spirit and the scope of the
invention as defined by the appended claims.
Before describing in detail embodiments it may be observed that the drawings are showing
only those specific details that are pertinent to understanding the embodiments of the present
invention so as not to obscure the disclosure with details that will be readily apparent to those
of ordinary skill in the art having benefit of the description herein.
The terms “comprises”, “comprising”, or any other variations thereof, are intended to cover a
non-exclusive inclusion, such that a setup, device that comprises a list of components does
not include only those components but may include other components not expressly listed or
inherent to such setup or device. In other words, one or more elements in a system or
apparatus proceeded by “comprises… a” does not, without more constraints, preclude the
existence of other elements or additional elements in the system or apparatus.
The present invention generally relates to a direct drive washing machine. In particular, the
present invention relates to a user friendly direct drive washing machine with increased
washing capacity.
According to one aspect of the present invention, a direct drive washing machine comprising:
a casing; an outer tub placed inside the casing; at least one slotted stator mounted on the
periphery of the outer tub, said at least one slotted stator having a plurality of coils wound in
the slots so as to produce rowing magnetic field in a working condition; an inner drum
located inside the outer tub, the inner drum being provided with a pair of concentric strips of
electrical conductors wound on an outer circumference thereof, said inner drum along with
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the pair of concentric strips co-operate with said at least one slotted stator to define an
induction motor to impart rotary motion to the inner drum.
According to another aspect of the present invention, wherein said at least one slotted stator
is mounted along a circular path on the periphery of the said outer tub.
According to yet another aspect of the present invention, wherein said at least one slotted
stator is mounted along a length on the periphery of the said outer tub.
According to still another aspect of the present invention, wherein the pair of concentric
strips comprises a first strip of a low reluctance material and a second strip of a low
resistance material.
According to one aspect of the present invention, wherein said at least one slotted stator has
an arc shaped inner surface configured to be in close proximity of the inner drum.
According to another aspect of the present invention, wherein the arc shape of said at least
one slotted stator defines an angle of about 45 degrees.
According to yet another aspect of the present invention, wherein the plurality of coils wound
on said at lest one slotted stator is provided a single phase supply or a multi phase supply.
According to still another aspect of the present invention, wherein if a single phase supply is
provided, at least one of the said plurality of coils is connected to a capacitor.
According to one aspect of the present invention, wherein heat generated by said at least one
slotted stator is used for heating water flowing to the washing machine.
The following paragraphs describe the present invention with reference to figures 1-8.
Now turning to figure 1, a sectional view of the direct drive washing machine in accordance
with an aspect of the present invention is illustrated therein. The washing machine comprises
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of an outer tub (1) placed inside a casing/housing (2) and an inner drum (3) placed inside the
outer tub (1). The inner drum (3) is configured to rotate inside the outer tub (1). The outer tub
(1) is supported at its bottom by one or more supporting mechanisms (4). In an aspect of the
present invention, the supporting mechanism (4) may be a spring. In order to dampen the
oscillations in the outer tub, one or more oscillation dampening mechanisms (5) may connect
the outer tub (1) to the casing (2). In an aspect of the present invention, the oscillation
dampening mechanism (5) may be a damper.
Further, it can be noticed that at least one slotted stator (6) is mounted on a periphery of the
outer tub (1). The said at least one slotted stator (6) is mounted on an outer periphery of the
outer tub (1). Owing to the said location of at the least one slotted stator (6), the overall
washing capacity of the outer tub (1) increases (as illustrated in figure 2 with reference
numeral 7). Furthermore, the inner drum (3) located inside the outer tub (1) is provided with
a pair of concentric strips (8) of electrical conductors on an outer circumference thereof. The
inner drum (3) is supported along its rear wall using a shaft and drum support (9). The casing
(1) is provided with a door (10) for providing access to the inner drum (3). Further, a bellow
(11) is provided in the door (10) so as to prevent water from leaking through the door (10) in
a working condition.
As said above, the pair of concentric strips (8) is mounted on the outer periphery of the inner
drum (3). Now referring to figure 3, which shows the inner drum (3) along with the pair of
concentric strips (8). The pair of concentric strips (8) is provided with a first strip (8a) and a
second strip (8b) of electrical conductors mounted on the outer circumference thereof. The
first strip (8a) of electrical conductor is made of a low reluctance material and the second
strip (8b) of electrical conductor is made of a low resistance material. Particularly, the first
strip (8a) of electrical conductor which is closest to the inner drum (3) comprises steel wires
of diameter 3mm which is wounded concentrically on the inner drum (3). The second strip
(8b) made up of aluminium sheet of thickness 1mm is in turn wound on the first strip (8a) in
a concentric manner such that a 1-2 mm air gap is maintained between the slotted stator (6)
and the aluminium strip (8b). The first (8a) and second strips (8b) are wound in a manner so
as to cover the entire length and width of the slotted stator (6).
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Referring to figure 4, at least one slotted stator (6) mounted on the periphery of the outer tub
(1) comprises a core made of stacked sheets of steel and is provided with a plurality of slots
which can accommodate a plurality of coils so as to produce rowing magnetic field in a
working condition. In an aspect of the present invention as illustrated in figure 4, the slotted
stator (6) is provided with 12 slots and accommodates 6 wound coils. The slotted stator (6)
has an arc shaped inner surface to be in close proximity with the inner drum (3) and in an
aspect of the present invention (as illustrated in figure 4), the arc sector has an angle of about
45 degrees.
In an aspect of the present invention, the plurality of coils wounded on the at least one slotted
stator (6) are made of copper wires with 120 turns in slots 1-7, 2-8, 3-9, 4-10, 5-11, 6-12 as
illustrated in figures 5A and 5B. Thus, 6 double stranded coils are used and 24 terminals are
taken out. Coil pitch in such stator is 22.5 degrees mechanical. Holes (12) has also been
provided for precisely mounting the at least one slotted stator (6) on the outer tub (1) with an
air gap of 1-2 mm.
Coming to the working principle, the plurality of coils wound on the at least one slotted
stator (6) when energized tend to produce a rowing magnetic field (13) i.e. main magnetic
flux (as illustrated in figure 6). When the generated magnetic flux cuts the second strip of
electrical conductor i.e. the aluminium sheet (8b), swirls of eddy currents are created. This in
turn creates the magnetic field that opposes the relative motion between the main magnetic
field and the aluminium sheet (8b). This creates a torque in the rotor (the inner drum (3)
along with the pair of concentric strips (8a, 8b)) so that it also moves along with the rowing
magnetic field. The first strip (8a) of electrical conductor of low reluctance i.e. the steel wires
confesses the main magnetic flux emerged from the at least one slotted stator (6) to itself and
ensures that the main magnetic flux cuts the second strip (8b) of electrical conductor i.e. the
aluminium sheet. The first strip (8a) of electrical conductor i.e. the steel wires acts as a
magnetic shield so that there will not be any magnetic attraction inside the inner drum (3).
Hence, the rotor i.e. inner drum (3) along with pair of concentric strips (8a, 8b) co-operate
with said at least one slotted stator (6) to define an induction motor to impart rotary motion to
the inner drum (3). In the working condition, the at least one slotted stator (6) mounted on the
periphery of the outer tub (1) produces heat. When the water is supplied to the outer tub (1),
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it absorbs the heat thus produced. It may be noted that the inner drum (3) is provided with
plurality of perforations so that warm water from the outer tub (1) flows into the inner drum
(3) wherein the laundry is being washed. Thus, the heat energy being produced by the at least
one slotted stator (6) is imparted to the water being supplied to the outer tub (1).
To achieve high torque and high efficiency, it is possible to mount more than one slotted
stators (6) on the periphery of the outer tub (1). It may be noted that the at least one of slotted
stators (6) can be mounted along a circular path on the periphery of the outer tub (1) as
illustrated in figure 7. Although not illustrated in the drawings, it is also possible to mount
more than one of slotted stators (6) along a length on the periphery of the outer tub (1)
according to another embodiment of the present invention. Further, it is possible to easily and
effectively switch between the high speed low torque mode and low speed high torque mode
with a single set of winding by changing the poles, the turns and the resistance of the
plurality of coils wounded on the at least one slotted stator by means of taps and some power
electronics. Furthermore, it is possible to provide either a single phase supply or a multi
phase supply to the plurality of coils wounded on the at least one slotted stator (6). It may be
noted that if a single phase supply is provided, the at least one of the said plurality of coils is
connected to a capacitor. Since the winding is made of separate coils, it is possible to connect
the same in several fashions to operate in three phase as well as single phase and also with
pole changing capability.
Figure 8 illustrates a sectional front view of a horizontal axis direct drive washing machine in
according with an aspect of the present invention. Although the description and drawings
illustrates a horizontal axis washing machine, it is possible to implement the direct drive
mechanism taught in the present invention to other types of direct drive washing machines
such as vertical axis direct drive washing machine.
The invention will be better understood with the experimental results described hereafter,
given for illustration only.
Prototype I:
The prototype machine has been constructed with the following specifications.
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No of phases = 3
No of poles = 2
Synchronous speed = 375rpm
Rated voltage = 70V
Rated current = 6A
Assumed efficiency = 0.5
Assumed power factor = 0.5
Assumed airgap length = 1mm
No of stator slots = 12
No of stator turns = 100
No of slots / pole / phase = 2
Stator Weight = 6.6kg
Machine Dimensions
Arc radius = 0.249m
Length of the machine = 0.07m
Airgap length = 5mm
Rotor steel thickness = 3mm
Rotor Aluminium thickness = 1mm
Load Performance
Full load speed = 107rpm
Full load Torque = 12.3Nm
Operating frequency = 50 Hz
Voltage applied = 45V
Current drawn = 5A
Power factor = 0.4
Full load power input = 160W
Prototype II:
The prototype II machine has been constructed with the following specifications for 1ϕ
operation:
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No of phases = 2 (made from 1ϕ supply with capacitors)
No of poles = 2
Synchronous speed = 375rpm
Rated voltage = 230V
Rated current = 2A
Assumed airgap length = 1mm
No of stator slots = 12
No of stator turns = 240
No of slots / pole / phase = 3
Stator Weight = 6.8kg
Machine Dimensions
Arc radius = 0.249m
Length of the machine = 0.065m
Airgap length = 2mm
Rotor steel thickness = 3mm
Rotor Aluminium thickness = 1mm
Operational Performance
Operating frequency = 50 Hz
Voltage applied = 200V
Current drawn = 1.6A
Power factor = 0.99
Capacitor used = 20μF
Power input = 320W
Speed = 235rpm
Maximum speed achieved = 550rpm at 640W (100 Hz)
Stator and Rotor Resistance:
R1 = 22.5Ω
R2 = 22.5Ω
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The Rotor resistance seems to be too high. If the rotor resistance is too high then the slip at
which the maximum torque occurs tends to increase. Hence the maximum torque point in the
torque speed characteristics is shifted to the left.
Comparison between Actual and Expected speed:
Neglecting the core losses and considering copper losses alone
At
F=50hz
V=200v
I=1.6A
Expected speed=280 rpm
Actual speed achieved=235rpm
At
F=50hz
V=230v
I=1.8A
Expected speed=294 rpm
Actual speed achieved=260rpm
At
F=100hz
V=280v
I=2.3A
Expected speed=579 rpm
Actual speed achieved=550rpm
Observation:
V=230
I = 1.8A (at 260 rpm)
I = 1.94A (at 0 rpm (rotor blocked))
As the load increases the current also has to increase. The blocked rotor current must be very
much higher than that of the no load. But in this case it is just 0.14A. This justifies that the
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air turbulence is very high thus while the machine is running the air friction also increases as
the speed increases offering more load torque.
The Prototype II is also tested with the change in poles the turns and the Resistance of the
coil of the stator by means of taps.
Feature Prototype I Prototype II
No of phases 3 1/2/3
No of poles 2 2/6
Synchronous speed 375 125/375
No of stator turns 120 120/240
No of slots / pole / phase 2 1/2/3
Outcome:
1. The Machine is able to run in 1, 2 and 3 phase supplies.
2. The Machine is able to supply wash load of 8 kg (Towels 2.5kg + water packets 5.5kg) by
consuming 750W at 60 rpm at 50 Hz.
3. The machine is able to supply continuously 20Nm (Brake drum type load) @ 20rpm with a
power of 1.7KW at 50 Hz.
4. The machine is able to run at 1000 rpm at 200 Hz.
ADVANTAGES OF THE PRESENT INVENTION
The present invention has following advantages:
i) The present invention increases the overall washing capacity of the direct drive
washing machine.
ii) In the present invention, stator itself acts as a dead weight. Hence, additional counter
balance weight is not required to reduce the vibration/displacement of outer tub
during the operation. Thus reducing the overall weight of the direct drive washing
machine.
iii) With the present invention, the direct drive washing machine can be easily
transported and installed with minimal damages.
iv) The present invention provides an economical, durable and user friendly direct drive
washing machine.
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While the particular preferred embodiments of the present invention have been shown and
described, it will be obvious to those skilled in the art that changes and modifications may be
made without departing from the teachings of the invention. It is therefore contemplates that
the present invention cover any and all modifications, variations or equivalents that fall
within the scope of the basic underlying principles disclosed above and claimed herein.
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We claim:
1. A direct drive washing machine comprising:
a casing;
an outer tub placed inside the casing;
at least one slotted stator mounted on the periphery of the outer tub, said at least
one slotted stator having a plurality of coils wound in the slots so as to produce rowing
magnetic field in a working condition;
an inner drum located inside the outer tub, the inner drum being provided with a pair
of concentric strips of electrical conductors wound on an outer circumference thereof, said
inner drum along with the pair of concentric strips co-operate with said at least one slotted
stator to define an induction motor to impart rotary motion to the inner drum.
2. The direct drive washing machine as claimed in claim 1, wherein said at least one
slotted stator is mounted along a circular path on the periphery of the said outer tub.
3. The direct drive washing machine as claimed in claim 1, wherein said at least one
slotted stator is mounted along a length on the periphery of the said outer tub.
4. The direct drive washing machine as claimed in claim 1, wherein the pair of
concentric strips comprises a first strip of a low reluctance material and a second strip of a
low resistance material.
5. The direct drive washing machine as claimed in claim 1, wherein said at least one
slotted stator has an arc shaped inner surface configured to be in close proximity of the inner
drum.
6. The direct drive washing machine as claimed in claim 5, wherein the arc shape of
said at least one slotted stator defines an angle of about 45 degrees.
7. The direct drive washing machine as claimed in claim 1, wherein the plurality of
coils wound on said at lest one slotted stator is provided a single phase supply or a multi
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phase supply.
8. The direct drive washing machine as claimed in claim 7, wherein if a single
phase supply is provided, at least one of the said plurality of coils is connected to a capacitor.
9. The direct drive washing machine as claimed in claim 1, wherein heat generated
by said at least one slotted stator is used for heating water flowing to the washing machine.