Note: Descriptions are shown in the official language in which they were submitted.
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RD-18,554
PL~RAL-STAG~ FORM-r~OUN~ CQI~ wl~NG~ EQ~
A SwITCHED RELUCTANCE MOT~R
F~ld of the Inve~tion
This invention relates generally to stator pole
coil windings for switched reluctance mo~ors. More
particularly, this invention relates to form-wound coil
windings for a switched reluctance motor, each comprising
plural winding stages which are assembled sequentially.
Back~round of the Inve~tion
Switched reluctance motors (S~Ms) are doubly
salient machines; that is, they have multiple poles on both
the stator and the rotor. Moreover, there are coil windings
on the stator, but no windings or magnets on the rotor. In a
SRM, each motor phase comprises at least one pair of
diametrically opposite stator poles, each stator pole having
a coil winding wound thereon. The stator pole coil windings
comprising each motor phase winding are connected in series
or in parallel, so that when a phase winding is excited,
magnetic flux produced in the corresponding pair(s) of stator
poles combines additively. Upon excitation of a motor phase
by supplying current to the corresponding stator pole coil
windings, a magnetic force of attraction results between the
excited stator pole pair(s) and the nearest rotor poles,
thereby causing the rotor to rotate. Current is switched off
in the excited motor phase winding before the rotor poles
rotate past the aligned position; otherwise, the magnetic
force of attraction would produce a negative or braking
torque. Continuous rotation of the rotor is achieved by
sequentially switching on and off adjacent motor phases. To
excite the motor phases, undirectional current pulses
synchronized with rotor movement are supplied to the motor
phase windings by a converter. Exemplary SRM converters are
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RD-18,554
illustrated in commonly assigned U.S. Patent No. 4,684,867,
issued to T.J.E. Miller on August 4, 1987.
In general, during manufacture of a switched
reluctance motor, the coil windings are wound as
subassemblies and then applied to the stator poles.
Disadvantageously, this conventional stator assembly process
necessarily leaves unused spaced in each interpole region.
That is, in order for a coil being assembled onto a stator
pole to be able to clear adjacent windings that have been
assembled previously, the width of the coil is restricted.
As a result, for a particular SRM, maximum attainable flux,
and hence output torque and voltage, are limited.
Objects of the Invention
It is, therefore, an object of the present
invention to provide stator pole coil windings for a switched
reluctance motor which utilize a larger portion of the
interpole space than conventional coil windings, thereby
enabling production of increased flux per unit of current
and, thus, proportionately higher torque and voltage output.
Another object of the present invention is to
provide stator pole coil windings for a switched reluctance
motor which result in lower conductor losses per unit of
applied power than conventional coil windings.
Still another object of the present invention ls to
provide a method of making coil windings for a switched
reluctance motor, each of which utilize a larger portion of
the interpole space than conventional coil windings, thus
resulting in a more highly efficient motor.
Summarv of the Invention
The foregoing and other objects are achieved in a
plural-stage, form-wound coil winding for a switched
reluctance motor. In particular, in a two-stage form-wound
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RD-18, 554
coil winding, the first stage comprises an inner coil winding
which is rectangular in cross-section and fits directly, i.e.
closely, around a stator pole of the SRM. The second stage
comprises an outer coil winding which is also rectangular in
S cross-section and fits directly around the first coil
winding. The inner and outer coil windings are form-wound,
i.e., separately wound as subassemblies before application to
the stator poles.
During SRM stator assembly, each outer coil is
assembled around the respective stator pole. After all of
the outer coils have been assèmbled onto the stator, each
inner coil is then inserted into the corresponding outer
coil. The inner and outer coils on each stator pole are
connected in series to each other so as to preserve the same
general winding direction. Finally, the stator pole coil
windings comprising each motor phase winding are connected in
series or in parallel.
Brief Description of the Drawinas
The features and advantages of the present
invention will become apparent from the following detailed
description of the invention when read with the accompanying
drawings in which:
Figure 1 is a cross-sectional view of
conventional switched reluctance motor;
Figure 2 is a cross-sectional view of a SRM
illustrating the direction of current in an exemplary motor
phase winding and further illustrating the direction of
magnetic flux resulting therefrom; and
Figure 3 is a cross-sectional view of a switched
reluctance motor including stator pole coil windings in
accordance with the present invention.
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RD-18,554
Detailed Description of the Invention
Figure 1 is a cross-sectional view of a switched
reluctance motor ~SRM) 10 having conventional stator pole
coil windings. By way of example, SRM 10 is illustrated as a
three-phase machine, each motor phase comprising one pair of
S diametrically opposite stator poles. However, it is to be
understood that the principles of the present invention apply
to SRMs having any number of phases and, thus, any number of
stator poles.
As shown, SRM 10 includes a rotor 14 rotatable in
either a forward or reverse direction within a stationary
stator lS. Rotor 14 has two pairs of diametrically opposite
rotor poles 16a-16b and 18a-18b. Stator lS has three pairs
of diametrically opposite stator poles 20a-20b, 22a-22b, and
24a-24b. Conventionai stator pole coil windings 26a, 26b,
lS 28a, 28b, 30a and 30b, respectively, are wound on stator
poles 20a, 20b, 22a, 22b, 24a and 24b, respectively. The
stator pole coil windings on each pair of opposing or
companion stator pole pairs are connected in series or
parallel to form a motor phase winding. As shown in Figure
2, the current I in each phase produces a magnetic flux
linkage by generating flux in the directions indicated by
arrows 32 and 34. For example, as shown, windings 26a and
26b are connected in series so that current I flows in the
direction indicated.
As hereinabove stated, during manufacture of a
typical SRM, the stator pole coil windings are wound as
subassemblies, hereinafter designated form-wound coil
windings, and then applied to the respective stator poles.
The number of turns and type of conductor used to make the
coil windings for a particular SRM depend upon the intended
application therefor. For windings comprised of a relatively
low number of turns of a heavy gauge conductor, the windings
are each formed into a predetermined coil shape corresponding
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RD-18,554
to the size of the respective stator poles, the stiffness of
the heavy gauge conductor retaining the shape of the coil
after the conductors have been form-wound. The conductors
comprising the form-wound coil are tightly packed.
S Alternatively, depending upon the SRM and its intended use, a
form-wound coil can be wound from many turns of a light gauge
conductor, provided that the turns are wrapped around a non-
metallic bobbin to retain the coil shape.
In order to apply the form-wound coil windings to
the stator poles, as hereinabove described, there is a
maximum coil width W1 which allows sufficient clearance for
assembly of the adjacent coil windings. Thus, a significant
portion of each interpole space 36 is unoccupied by coil
windings, as illustrated in Figure 1. This limitation on
lS usable interpole space, in turn, restricts maximum attainable
flux and, hence, output torque and voltage.
Figure 3 shows a SRM 38 employing the two-stage
stator pole coil windings of the present invention. Each
stator pole coil winding comprises an outer coil winding 40a,
40b, 42a, 42b, 44a and 44b, respectively, and an inner coil
winding 50a, 50b, 52a, 52b, 54a and 54b, respectively. The
outer coil winding and inner coil winding comprising each
stator pole coil winding are form-wound separately. To
maximize use of each interpole space 36, the inner and outer
windings each preferably have a substantially rectangular
cross-section, as illustrated. Moreover, for equivalent-
sized SRMs, the width Wl of the inner coil winding of the
present invention is preferably equal to that of the
conventional coil winding shown in Figure 1. Also like the
conventional coil winding, the inner coil is sized to fit
directly, i.e. closely, around the corresponding stator pole.
With the inner coil winding dimensions as hereinabove
described, the height H2 of the outer coil winding is
required to be less than the height Hl of the inner coil
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RD-18,554
wlnding, as shown in Figure 3. The outer coil winding is
sized to fit directly around the corresponding inner coil
winding, and the width W2 of the outer coil winding is
limited by the clearance necessary for assembly, to be
described hereinafter in detail.
In accordance with the present invention, during
SRM stator assembly, outer coil windings 40a, 40b, 42a, 42b,
44a and 44b are applied to stator poles 20a, 20b, 22a, 22b,
24a and 24b, respectively, before any inner coil windings are
applied thereto. With each outer coil winding in place about
the corresponding stator pole, each inner coil winding 50a,
50b, 52a, 52b, 54a and 54b is inserted into an outer coil
winding 40a, 40b, 42a, 42b, 44a and 44b, respectively, while
being fitted directly around the corresponding stator pole.
Each outer coil winding is then connected in series to the
respective inner coil winding to preserve the same general
winding direction. Lastly, the diametrically opposite stator
pole coil windings are connected in series or parallel, as
desired, so that the resulting magnetic flux patterns are
similar to those of the conventional SRM, as illustrated in
Figure 2.
By utilizing the two-stage stàtor pole coil
windings of the present invention, magnetic flux production
is significantly increased. Hence, torque and voltage output
per unit of current are proportionately increased, thereby
resulting in a more efficient SRM. Additionally, by
employing the two-stage windings according to the present
invention, so as to utilize a significantly larger portion of
the interpole space, conductor losses per unit of applied
power are decreased, thus further enhancing SRM efficiency.
While the preferred embodiments of the present
invention have been shown and described herein, it will be
obvious that such embodiments are provided by way of example
only. Numerous variations, changes and substitutions will
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RD-18, 554
occur to those of skill in the art without departing from the
invention herein. For example, a three-stage coil winding
comprising an inner coil winding, a first outer coil winding
and a second outer coil winding may be constructed in
S accordance with the present invention. To assemble a stator
comprising a three-stage coil winding, the winding stages are
applied to the stator poles sequentially as follows: all
first outer coil windings; all second outer coil windings;
and, lastly, all inner coil windings. In like fashion, the
principles of the present invention may be extended to four
winding stages and so forth. Accordingly, it is intended
that the invention be limited only by the spirit and scope of
the appended claims.
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