U.S. patent number 3,840,764 [Application Number 05/390,566] was granted by the patent office on 1974-10-08 for drive arrangement for a washing or dry cleaning machine.
Invention is credited to Manfred Burger.
United States Patent |
3,840,764 |
Burger |
October 8, 1974 |
DRIVE ARRANGEMENT FOR A WASHING OR DRY CLEANING MACHINE
Abstract
An eddy-current motor for driving the drum or basket of a
washing or dry cleaning machine, has a disc rotor coupled to the
drum and a stator having a plurality of rod-shaped electromagnets
whose windings are functionally interconnected in groups, each
group defining a different number of poles so that the drum may be
rotated at different speeds.
Inventors: |
Burger; Manfred (8023 Pullach,
DT) |
Family
ID: |
25763749 |
Appl.
No.: |
05/390,566 |
Filed: |
August 22, 1973 |
Foreign Application Priority Data
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Aug 25, 1972 [DT] |
|
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2241970 |
May 7, 1973 [DT] |
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2322859 |
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Current U.S.
Class: |
310/185; 310/114;
68/24; 310/268 |
Current CPC
Class: |
H02K
17/14 (20130101); D06F 37/304 (20130101); H02K
7/14 (20130101); H02K 17/16 (20130101) |
Current International
Class: |
D06F
37/30 (20060101); H02K 7/14 (20060101); H02K
17/16 (20060101); H02K 17/02 (20060101); H02K
17/14 (20060101); H02k 017/14 () |
Field of
Search: |
;310/166,268,112,113,114,184,185 ;318/243 ;68/23,24,23.7 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Duggan; D. F.
Attorney, Agent or Firm: Berman; Hans
Claims
What I claim is:
1. Cleaning apparatus comprising a housing, a drum member mounted
in said housing, and drive means for rotating said drum member, the
drive means including:
a. an eddy current rotor disc mounted on said housing for rotation
about an axis and including an induction disc of electrically
conductive, non-magnetic material, and a yoke disc of
ferro-magnetic material in intimate contact with said induction
disc;
b. a multi-pole stator mounted proximate said rotor disc in a
position to induce eddy currents in said induction disc,
1. said stator including a plurality of rod-shaped electromagnets
and at least one soft-iron yoke,
2. each electromagnet including a soft-iron core and an
electromagnetic winding thereabout,
3. said windings being arranged in a plurality of conductively
connected groups constituting respective pluralities of poles when
said windings are energized,
4. the number of poles constituted by a first one of said groups
being different from the number of poles constituted by a second
group,
5. each soft-iron core having a first pole end facing said
induction disc and a second pole end in abutting engagement with
said soft iron yoke,
6. the electromagnets associated with said first group being
radially spaced from said axis a first distance, and the
electromagnets associated with said second group being radially
spaced from said axis a second distance different from said first
distance; and
c. connecting means drivingly connecting said rotor disc to said
drum member.
2. Apparatus as set forth in claim 1, wherein the number of poles
constituted by said first group is smaller than the number of poles
constituted by said second group, and said first distance is
smaller than said second distance.
3. Apparatus as set forth in claim 1, wherein said rotor disc and
said stator are each annular and have respective radial widths
substantially equal to the radial dimension of said first pole
ends.
4. Apparatus as set forth in claim 1, wherein said connecting means
connect said rotor disc to said drum member for simultaneous
rotation about said axis.
5. Apparatus as set forth in claim 1, wherein said pole ends have a
cross section in a radial plane or generally trapezoidal shape.
6. Cleaning apparatus comprising a housing, a drum member mounted
in said housing, and drive means for rotating said drum member, the
drive means including:
a. an eddy current rotor disc mounted on said housing for rotation
about an axis, said rotor disc including a ferromagnetic yoke disc
having two oppositely directed, radial faces, and first and second
electrically conducting, non-magnetic induction discs in intimate
contact with said faces respectively;
b. first and second multi-pole stators on respective axial sides of
said rotor disc, said stators being mounted proximate said first
and second induction discs respectively for inducing eddy currents
in the associated proximate discs,
1. each stator including a soft iron yoke and a plurality of
rod-shaped electromagnets, each electromagnet including a soft-iron
core and an electromagnetic winding thereabout,
2. the windings of the electromagnets of each stator being
conductively connected in at least one group and constituting a
plurality of poles,
3. the number of poles in the group of windings of said first
stator being different from the number of poles in the group of
windings of said second stator,
4. each of said soft-iron cores having a first pole end facing the
associated induction disc and said soft-iron yoke; and
c. connecting means drivingly connecting said rotor disc to said
drum member.
7. Apparatus as set forth in claim 6, wherein the soft-iron core of
said first and second stators are radially equidistant from said
axis.
8. Apparatus as set forth in claim 6, wherein said rotor disc and
said stators are each annular, having respective radial widths
substantially equal to the radial dimension of said first pole
ends.
9. Apparatus as set forth in claim 1, wherein the cores associated
with the windings of each group are equiangularly spaced about said
axis.
10. Apparatus as set forth in claim 9, wherein each winding of one
group is separated from each angularly adjacent winding of said one
group by at least one winding of each of the other groups.
11. Apparatus as set forth in claim 1, wherein said stator further
includes a support and fastening means releasably fastening each of
said electromagnets to said support.
Description
BACKGROUND OF THE INVENTION
a. Field of the Invention
This invention relates to automatic washing and dry cleaning
machines. More particularly, this invention relates to an improved
eddy-current drive arrangement for such machines.
B. Discussion of the Prior Art
Known automatic washing and dry cleaning machines typically include
a rotatably mounted drum or basket in which the clothes to be
cleaned are placed during operation of the machine.
Means are provided to rotate the basket during the cleaning and
drying cycles and such means may comprise an a.c. motor or, as
disclosed in U.S. Pat. No. 3,194,032 which issued July 13, 1965 to
J. W. Von Brimer, an eddy-current linear actuator motor may be
used. As disclosed in the Von Brimer patent, the eddy-current motor
comprises a disc-shaped rotor mounted to the basket for
simultaneous rotation therewith. More specifically the rotor
comprises an induction disc of non-magnetic, electrically
conductive material in intimate contact with a yoke disc of
ferromagnetic material. A stator having a plurality of poles each
comprising a plurality of electro-magnetic windings, is positioned
adjacent the rotor in such a position as to induce eddy-currents in
the rotor. The windings are arranged in groups and means are
provided to vary the number of poles in each group. Thus, when the
groups of windings are supplied with alternating current of
differing phases the stator generates pulsating, phase-shifted
magnetic fields offset circumferentially relative to the rotor. The
superposition of the pulsating magnetic fields results in a
rotating, travelling field which causes the rotor to turn, by
induction.
The speed at which the rotor rotates depends upon the speed of the
travelling magnetic field which, in turn, depends on the number of
poles per group of windings about the circumference of the rotor.
By varying the number of poles in each group of windings the
rotation speed of the rotor may be changed. This is particularly
important in washing and dry-cleaning machines which require a
relatively low speed for washing and a higher speed for spinning
and drying.
To provide this speed changing capability the stator of machines
such as disclosed in U.S. Pat. No. 3,194,032 is provided with a
plurality of laminations having notches into which the conductors
of the winding groups are placed. This technique, well known in the
electric motor industry, permits the rated current to flow in each
winding group when the stator is rotating at the rated speed. The
rated current is, of course, substantially smaller than the current
which flows when the rotor is held stationary.
This property, which is desirable in conventional electric motors,
is undesirable in eddy current motors used in washing and dry
cleaning machines. Because of the complex, and therefore expensive,
shape of the stator laminations, the stator must be dimensioned
sparingly for its current carrying ability.
Further, in order to add to the flux circulation the conductors of
the several groups of windings must be placed in the notches of the
laminations in such a manner that conductors placed in the same
notch must all conduct current in the same direction. Thus, the
circuitry required to establish the several groups of windings
becomes exceedingly complex and expensive. This is particularly
true if the windings are to be arranged so that the number of poles
in each group may be selectively altered.
Conventional machines of this type are driven by an electric motor
which is a compact and independently operated unit, typically
mounted on a stand and having a rotor shaft journaled therein. In
order to reduce the initial cost of such a washing or dry cleaning
machine it is customary to select the smallest possible motor which
will do the job, because the cost of the motor is a significant
factor in the overall machine cost. The load on the motor depends
largely on the weight and distribution of the clothes in the
basket. Centrifugal forces exerted on the basket cause substantial
additional loads on the motor, particularly during acceleration and
deceleration thereof. Peak motor loads may thus occur which are
several orders of magnitude larger than the rated load.
Conventional washing and dry-cleaning machines are therefore
equipped with extensive over-load protection devices.
With eddy current motors, however, because the rated current is
substantially smaller than the current which flows with a
stationary basket, particularly complicated measures are required
to prevent overload of the stator during start-up. Also, it is
impossible to provide electromagnetic braking of the drum, for
example by interchanging the phases of two groups of windings, and
if the speed of rotation of the drum is to be changed a complex
control arrangement is needed.
SUMMARY OF THE INVENTION
These and other problems are solved by the instant invention whose
basic object is to simplify the above described basket drive
arrangement and to render the drive insensitive to overloads.
In a first embodiment of the invention this object is attained by
making the pole windings rod magnets each comprising an
electromagnetic winding wound on a soft iron core. The iron cores
have first pole ends positioned proximate the induction disc and
second pole ends abuttingly engaging a soft iron yoke. The iron
cores which comprise the groups of windings of differing pole
numbers are radially spaced at different distances from the axis of
rotation of the rotor.
It will be appreciated that not only is it easier to wind a rod
magnet than a gapped core magnet but, because of a rod magnet's
simpler structure, it is more readily overdimensioned than a
conventional slotted magnet. The soft iron cores can, therefore, be
positioned in front of the rotor with optimum utilization of the
given shape of the washer basket, without concern for any increase
in the rated current. The invention thus provides a basket drive
which requires little space and which does not substantially exceed
the space required for the basket itself. Further, the rod magnet
windings may be safely operated at current levels which approach
the stationary rotor current experienced during start up. Thus, the
speed control circuiting for the basket is considerably
simplified.
The energizing current may be switched on or off at any rotary
speed between zero and rated speed without any special safety
precautions for avoiding overloads in the stator windings. Because
of the high moment of inertia of the basket, it is sufficient to
provide two limiting values of rotary speed and to monitor these
speeds, for example, by a tachometer-generator mechanically
switching the energizing current on and off when these limiting
values are passed. It is thus unnecessary to provide speed control
by means of thyristors or the like, which are expensive at the
relatively high current levels involved. The basket drive of this
invention is, therefore, particularly suited for washing and dry
cleaning machines which require rotary speed ranges to be
maintained during the washing cycle as well as the spinning cycle.
The direction of rotation may be changed, if desired, for example,
by interchanging the phases of the two groups of windings to
reverse the direction of the rotating travelling field. Because the
rated current and the current with a stalled basket are of the same
order of magnitude, the basket drive according to the invention may
be used to brake the rotating basket. The mechanical brakes
heretofore employed with such machines may therefore be omitted.
Because the size limitations imposed on eddy-current motors of the
type disclosed in U.S. Pat. No. 3,194,032 are not present in the
instant invention, cooling the rotorpresents no special
problem.
Although the torque produced by a rod magnet motor according to
this invention decreases with decreased spacing of the soft iron
cores from the rotor axis, an embodiment has been found
advantageous in which, if the number of poles in each group of
windings is different, the group having the smallest number of
poles is positioned closest to the axis of rotation. However, when
it is desired to attain the greatest possible torque for a given
size basket drive, for example where a particularly high spinning
speed is required, another embodiment of the invention includes a
rotor having two induction discs on either side of a common yoke
disc. As in the previous embodiment, the pole magnets are rod
magnets wound on soft iron cores, and the cores associated with one
group of windings comprising a first number of poles are on one
side of the rotor while the other group of windings comprising a
second number of poles are on the other side of the rotor. The
first pole ends of the cores are positioned proximate their
respective induction discs while the second pole ends engage a soft
iron yoke. Preferably, the soft iron cores on both sides of the
rotor are equidistant from the axis of rotation.
In another embodiment of the invention, the soft iron cores are
positioned at equal distances from adjacent cores associated with
the same group of windings. Preferably, the cores are also
positioned at equal distances from adjacent iron cores associated
with groups of windings of equal numbers of poles. This embodiment
is distinguished by a greatly improved freedom from vibration of
the rotor, particularly when the cores are circumferentially
distributed about the rotor.
When the cores are located relatively far from the axis of
rotation, it is mechanically advantageous to make the induction
disc, yoke disc and/or the soft iron yoke similar in shape and to
give them a radial width substantially equal to the radial
dimensions of the pole ends of the soft iron cores.
In order to reduce iron losses it is advantageous to make the yoke
disc, soft iron yoke and/or the soft iron cores laminar,
conventional transformer laminations being suitable. When the yoke
disc and/or the soft iron yoke are annular, they may be formed by
winding a ribbon of transformer lamination.
The shape of the fundamental magnetic wave may be improved by
providing the pole ends of the iron cores which are adjacent the
induction disc with pole pieces which reduce the air gap between
pole ends of adjacent iron cores, in the direction of the rotor
circumference. This expedient improves the torque and such pole
pieces have an approximately trapezoidal cross-section parallel to
the induction disc. The windings of the rod magnets in a given
group may be connected in series or in parallel, but a series
connection is preferred.
In a particularly advantageous embodiment of the invention, two rod
windings of one group are separated from each other by a rod
winding from each of the other groups. In this arrangement all rod
windings will contribute to the total flux, and the flux of one
winding will not cancel that of another.
In order to prevent sealing problems with respect to any fluid
which may be present in the drum, it is preferred to construct the
machine in such a manner that the eddy-current rotor is mounted
within the machine housing. This is entirely possible with the
instant invention because the rotor requires little space and thus,
does not significantly increase the volume of the housing. Keeping
the housing volume low is important, particularly, in dry cleaning
machines, because of the unavoidable loss of solvent vapor which
occurs each time the housing is opened, such losses being directly
porportional to the housing volume.
Although dry cleaning solvents are corrosive, the electromagnets
need not be encapsulated if the magnets are positioned at least
partly outside of the machine housing. When the electromagnets are
provided with pole pieces which pass through the housing and form a
portion of the housing wall, the pole pieces may be positioned
close to the rotor, thereby enhancing the induction effect.
The invention and its mode of operation will now be described with
reference to the drawings.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a simplified, cross-sectional view of an illustrative
basket-drive according to the invention, together with other
elements of a washing or drycleaning machine;
FIG. 2 is another view of the apparatus shown in FIG. 1 taken in
section on line II--II;
FIGS. 3a and 3b are circuit diagrams of groups of motor windings in
the basket drive of FIG. 1;
FIG. 4 is a cross-sectional view of another embodiment of the
invention;
FIG. 5 is a plan view of a portion of the stator pole pieces in
FIG. 4;
FIG. 6 is a cross-sectional view of an additional embodiment of the
invention; and
FIG. 7 is a cross-sectional view of yet another embodiment of the
invention, taken through its axis of rotation.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows a washing or drycleaning machine 1 having a housing 2
provided with an access door 3 and enclosing a drum or basket 5 for
the goods to be washed or drycleaned. The basket is rotatably
supported in a bearing 7 and is connected with an eddy-current
rotor disc 11 of the basket drive motor by a horizontal shaft 9,
the disc 11 also being rotatably supported by the bearing 7. A
stator 13 carrying a plurality of magnetic windings is located
proximate the rotor 11 in such a position as to induce an
electromagnetic field in the rotor.
The stator 13 is equipped with a plurality of rod magnet windings
17 each of which is wound about a soft iron core 15 releasably
fastened to a carrier 19 by a non-magnetic bolt, not illustrated,
but common to the several illustrated embodiments of the invention.
When the rod magnet windings, which are spaced from each other
about the circumference of the rotor 11, are supplied with
alternating currents offset in phase, the windings 17 produce
magnetic fields which are also offset in phase relative to each
other, which, when superimposed on each other, produce an angularly
travelling field. Because of the eddy current induced in an
induction disc 21 associated with the rotor 11, which is positioned
in front of the windings 17, rotor 11 will turn.
The magnetic circuit in each core 15 is closed at one end through a
soft iron yoke disc 23 in the rotor 11, and at the other end
through an annular, soft iron yoke 25. In the first embodiment, the
cores, as well as the soft iron yokes, are comprised of stacked
laminations. Advantageously, the soft iron yokes 25 may be formed
from annularly wound strips of transformer lamination material.
Some of the magnet windings 17 and cores 15 are omitted from FIG. 1
for the sake of clarity, but FIG. 2 gives a complete view of the
stator 13 in section along the line II -- II in FIG. 1.
As shown, the stator 13 is comprised of two separate annular
portions 27,29. The speed of rotation of the basket during spinning
and during washing is determined by the number of poles in the
stator portions 27,29 respectively. In the embodiment illustrated
in FIG. 2, the first stator portion 27 has four poles, and the
second portion 29 has eight poles. While an adequately high
spinning speed is generally reached with four poles on the stator
portion 27, rotary speeds low enough for washing are preferably
produced by more than eight poles, the number shown in the drawing
being eight for the convenience of pictorial representation only.
The cores 15 and the corresponding core windings 17 on each stator
portion 27,29 are equally spaced from each other and are equally
spaced from the axis of rotation.
FIG. 3a illustrates the series connection of the windings 17 on the
eight-pole, second stator portion 29 which are arranged in groups
31. Three groups 31 are provided to supply the second stator
portion 29 with three-phase AC. Four windings 17, uniformly
distributed about the circumference of the rotor 11, are serially
connected in each group 31. Respective windings 17 of the two other
groups are circumferentially interposed between each pair of
adjacent windings 17 in one group 31, in uniform sequence. The
groups 31 have respective terminal connections U,V,W and X,Y,Z by
means of which the groups may be connected to a suitable
three-phase supply system in either a Y or delta connection. FIG.
3b shows the circuit diagram for the four-pole, first stator
portion 27 and is analogous to the circuit shown in FIG. 3a. FIG.
3b differs from FIG. 3a essentially in having only two windings 17
serially connected in each group 33.
FIG. 4 shows another embodiment of the invention, analogous
elements being provided with the same reference numbers as in the
figures described above, augmented by 100. As shown, the rotor 111
comprises a circular ring and is connected to the shaft 109 for
rotation by a hub 135 which is made from a minimum of material to
avoid imbalance. First and second stator portions 127, and 129
respectively are positioned on either side of the rotor 111, and
each has a different number of poles. The magnetic flux generated
by the rod windings 117 in the cores 115, and in the annular yokes
125 is closed in a circuit including the annular yoke disc 123. In
this embodiment, a pair of induction discs 121 are mounted on
either side of the yoke disc 123.
FIG. 5 illustrates another arrangement for the pole ends of the
cores 15 which are adjacent to the induction disc 23. The pole ends
are equipped with generally trapezoidal-shaped pole pieces 200 to
improve the torque produced by the motor. The pole pieces 200
provide an airgap of uniform width a between adjacent soft iron
cores 15, the air gap a being greater than the spacing of the pole
pieces 200 from the induction disc.
FIG. 6 shows another drive according to the invention in a washing
or drycleaning machine. The reference numerals of elements
analogous to elements in FIG. 1 are augmented by 200. A basket 205
is fastened in overhung relationship on a shaft 209 journaled in a
bearing 207 in a wall of the machine housing opposite the access
door 203, the shaft 209 being rotatably sealed in the machine
housing 202. An induction disc 221 is fastened on a hub 214 so that
its two opposite rotor surfaces are freely accessible. The disc 221
is caused to rotate by releasably mounted electromagnets 218
arranged in front of the disc and drives the basket 205 by means of
a speed-changing transmission 238 which connects the hub 214 to the
shaft 209. The electromagnets 218 have soft iron cores 215 which
are provided with windings 217 and pole pieces 216 on each of the
two terminal poles which are opposite a radial face of the disc
221. The windings 217 are supplied with AC having an offset phase
relationship. The cores 215 of the windings 217, which may be
combined into groups each having a different number of poles, may
be circumferentially offset, relative to one other, in uniform
sequence with respect to the disc 221. However, an arrangement
including features of the apparatus shown in FIGS. 1 and 2 is also
possible in which the second stator portion 29, for example, is
positioned in front of the disc 221, in addition to the
electromagnets 218. Depending on the number of poles in each group
of windings, the transmission 238 may be a speed-reducing or
speed-increasing transmission. The transmission 238 may be a belt
transmission or a gear transmission, or it may be constituted by
planetary gearing installed directly in the disc 221.
Elements shown in FIG. 7 corresponding to analogous elements in
FIG. 1 are provided with the same reference numerals augmented by
300. FIG. 7 shows a washing or drycleaning machine whose basket or
drum 305 is guided and supported in a housing 302 by means of a
plurality of guide rollers 308. The rollers permit rotary movement,
but axially secure the basket 305. A group of rod-shaped
electromagnets 318 is mounted on a wall 340 of the machine housing
302, opposite the access door 303. The magnets pass through the
wall 340 and consist of soft iron cores 315 enveloped by windings
317. The ends of the magnets 318 remote from the housing 302 are in
contact with a common yoke plate 319 of ferromagnetic material,
such as soft iron. The pole ends of the cores 315 in the housing
302 face an induction disc 321 fastened to a radial wall 346 of the
basket 305, a soft iron disc 323 being axially interposed between
the disc 321 and the wall 346. The cores 315 jointly with the plate
319 and the disc 323 constitute a closed path for magnetic flux,
the flux intersecting the induction disc 321 which may consist of
copper, aluminum or any other electrically conductive, non-magnetic
material.
The drive arrangements described above are particularly suitable
for washing and drycleaning machines of a size adequate for
industrial application although with suitable modifications they
may also be used in domestic machines. The first stator portion of
such a machine will typically have four poles, and thereby permit a
spinning rate of from 300 to 800 RPM when exited by AC current of
50HZ. The second stator portion will typically have 30 poles and
thus permit a rotary washing speed of from 5 to 60 RPM. The
necessary energizing current for such machines is of the order of
50 to 300 amps.
As previously discussed, it is possible to make either the
induction disc or the yoke disc, or preferably both, annular in
shape. The radius of each annulus preferably is the same as the
radius of the basket. When the induction and yoke discs are
annular, then the stator should also be annular. The radial width
of the rotor need be no larger than the radial dimension of the
pole-ends of the stator cores.
Also, the rotor need not necessarily be a separate element from the
disc or drum. It is perfectly feasible to use a portion of the drum
itself as the rotor, either by fabricating the entire drum from
some suitable electrically conductive material or by fastening a
suitable member directly to the drum. One skilled in the art may
make various changes to the elements and layout of parts shown,
without departing from the spirit and scope of the invention.
* * * * *