Note: Descriptions are shown in the official language in which they were submitted.
LIGHTWEIGHT HIGH POWER ELECTROMOTIVE DEVICE
FIELD OF THE INVENTION
This invention relates to a high power-to-weight
ratio electromotive device capable of operating as a motor,
alternator or generator.
BACKGROUND OF THE INVENTION
Electromotive devices are known for use both in
transforming electrical energy into mechanical power and
transforming mechanical power into electrical energy. In
both cases, the energy or power producing capability results
due to relative movement between a magnetic field and
electrically conductive elements.
Light weight motor, alternator and generator
devices are well known and some are capable of operation at
high speeds. However, many such devices are not capable of
producing high power at high speeds. For example, high
power density devices of 0.6 horsepower per pound of weight
are known for intermittent operation, but such devices are
incapable of continuous operation at high power densities in
excess of 1.0 horsepower per pound.
Prior electromotive devices are not capable of
simultaneous high speed and high torque operation, nor are
they capable of highly efficient operation.
Known electromotive devices which include a stator
and rotor arrangement can include magnetic elements on the
rotor (for example, see U.S. Patents Nos. 3,663,850;
3,858,071; or 4,451,749) or on the stator (U.S. Patents Nos.
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3,102,964; 3,312,846; 3,602,749; 3,729,642 or 4,114,057).
Furthermore, double sets of polar pieces can be utilized, as
in U.S. Patent No. 4,517,484.
In addition, a shell rotor has been suggested in
U.S. Patents Nos. 295,368; 3,845,338 and 4,398,167, with a
double shell rotor arrangement suggested in U.S. Patent No.
3,134,037.
Bundles of wires have been used in place of a
single conductor in the armature assemblies of motors for
high voltage and high current usage and/or to reduce current
flow loss due to skin effect, and heating due to eddy
currents; see U.S. Patents Nos. 497,001; 1,227,185;
3,014,139; 3,128,402; 3,538,364 or 4,321,494, or British
Patent No. 9,557. The plural wires are used with solid or
laminated cores, see U.S. Patents Nos. 3,014,139 or
3,128,402; or British Patent No. 9,557.
Some prior electromotive devices, such as that
described in U.S. Patent No. 3,275,863, have a power-to-
weight ratio of up to one horsepower per pound and U.S.
Patent No. 4,128,364 teaches using a gas, liquid, or a
mixture thereof to cool a motor to increase its power
handling capability.
Many of the preceding difficulties in achieving a
high power-to-weight ratio electromotive device have been
addressed by a dispersed conductor electromagnetic device
which is the subject of a co-pending U.S. Patent
Application, by the inventor of the present invention,
entitled "Lightweight High Power Electromagnetic
Transducer". The co-pending design utilizes a straight-
sided armature bar of powdered iron which allows full
exposure of the copper to the magnetic field. In addition,
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the powdered iron does not have the flux-carrying ability
that silicon iron does. To minimize the eddy current
effect, it utilizes extremely fine wire. The armature bars
are fabricated from powdered iron to further insure the 3-d
dispersion necessary to reduce/minimize back electromotive-
force (back EMF).
Unfortunately, this approach is inefficient in
terms of power-in versus power-out due to the resistance
characteristic of fine wire. This characteristic causes
significant energy loss in the form of heat at higher
operating levels, which translates into lost power and
efficiency. In addition, the straight bars do not lend
themselves to standard production automatic winding
techniques as the coils would slip outward from in between
the bars.
The power loss due to fine wire resistance is
compensated for by increasing the amount of permanent magnet
material beyond the saturation level of the iron bars.
Aside from the costs of additional material, the bulk of
this additional flux goes into the copper in the form of
eddy current loss and is dispersed, leaving very little gain
in power for the additional material investment. While the
preceding and other various arrangements have been used to
attempt to achieve a high power-to-weight ratio
electromotive device, they have not been completely
successful. In particular, the prior art does not teach the
necessity to disperse the conductors to enable high speed
operation. This is due, at least in part, to a widely
accepted theory that the magnetic field is relatively small
in the non-magnetic winding conductors. With conductors
built according to conventional teachings, it has been found
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that torque, at constant current, decreases with increasing
speed. This result is contrary to the conventional
expectation that torque will remain high as speed increases.
OBJECTIVES OF THE INVENTION
It is a primary obj ective of this invention to
provide an electromotive device which achieves a high power-
to-weight ratio by dispersing the electromotive windings to
minimize eddy currents within the coils.
It is a further obj ective of this invention to
provide an electromotive device which achieves a high power-
to-weight ratio by dispersing the electromagnetic field core
pieces to minimize eddy currents.
It is a still further obj ective of this invention
to provide an electromotive device which achieves a high
power-to-weight ratio by dispersing the electromotive
windings to minimize eddy currents within the coils and the
electromagnetic field core pieces to minimize eddy currents
generally.
It is another obj ective of this invention to
provide an electromotive device which achieves a high power-
to-weight ratio by shielding the electromotive windings with
field core piece extensions to minimize eddy currents within
the coils.
It is a primary obj ect of this invention to
provide an improved electromotive device.
It is another obj ect of this invention to provide
an improved electromotive device that is lightweight and
provides high power.
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It is still another object of this invention to
provide an improved electromotive device that operates at
high efficiency.
It is still another object of this invention to
provide an improved electromotive device having high power
density per unit weight.
It is still another object of this invention to
provide an improved electromotive device having a high
power-to-weight ratio.
It is still another object of this invention to
provide an improved electromotive device capable of
operating as a highly efficient motor, alternator or
generator.
It is still another object of this invention to
provide an improved electromotive device that is capable of
continuous operation at high power densities in excess of
one horsepower per pound.
It is still another object of this invention to
provide an improved electromotive device having an armature
assembly with dispersed conductors, different sections of
which have flux carrying elements positioned therebetween
with the conductors and flux carrying elements being formed
and positioned in a manner so as to create low opposing
induced currents.
It is still another object of this invention to
provide an improved electromotive device having an optimum
thickness armature assembly which represents a balance among
the effects of heat transfer to the cooling medium, heat
production from resistance heating and other sources, and
torque production.
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SUMMARY OF THE INVENTION
This invention provides an electromotive device
comprising: an inductor including a plurality of magnetic
flux conducting bars and electric windings disposed about
the bars for generating an electromagnetic field; the
electric windings comprising electrical conductors randomly
dispersed between the flux conducting bars; the bars
incorporating a geometry which shields the windings from the
magnetic fields within the electromotive device; a magnetic
field generator positioned adjacent to one side of the
inductor; a first flux return path on the side of the
magnetic field generator opposite the inductor; and a second
flux return path on the side of the inductor opposite the
magnetic field generator.
This invention provides an improved electromotive
device with a high power density per unit weight effected by
utilization of an armature assembly having a large diameter-
thin cross-section speculation ratio. This results in low
opposing induced currents, as well as low eddy currents, to
enable operation of the electromotive device at high
efficiency with high torque being maintainable during high
speed operation.
When the armature moves relative to a magnetic
flux producing assembly, eddy currents are established in
the electrically conductive portions of the armature and
these currents lead to heating and skin effects
(collectively known as eddy current losses). However, these
currents also produce another effect not recognized by the
prior art. They are opposing induced currents which alter
the magnetic flux pattern and act to reduce the torque with
speed increase. This power conversion reduction with speed
increase is minimized in this invention by dispersing the
conductors forming the windings.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the invention will now be described
by way of example, with reference to the accompanying
drawings, wherein:
Figure 1 is a side sectional view of a rotary
implementation of the electromotive device of this
invention.
Figure 2 is a sectional view taken through lines
2-2 of Figure 1.
Figure 3 is a partial isometric view of an
armature showing the arrangement of the dispersed conductors
and flux carrying elements of the electromotive device shown
in Figures 1 and 2.
Figure 4 is a diagram illustrating a typical
arrangement of a two layer winding formed by the dispersed
conductors and illustrating the flux carrying elements
positioned between turns of the windings.
Figure 5 is a single lamination stamping of
controlled grain ferrous metal which, when laminated in
mass, form "I" beam stator bars.
Figure 6 is a single lamination stamping of
controlled grain ferrous metal which, when laminated in
mass, form a plurality of modified "I" beam stator bars.
Figure 7 is a partial isometric view of an
armature showing the arrangement of the dispersed conductors
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and flux carrying elements of the electromotive device shown
in Figure 1.
Figure 8 is a partially cutaway view similar to
that of Figure 2 but illustrating an alternative embodiment
of the electromotive device of this invention.
Figure 9 is a partially cutaway view similar to
that of Figure 2 but illustrating another alternative
embodiment of the electromotive device of this invention.
Figure 10 is a partial cutaway view similar to
10 that of Figure 2 but illustrating still another alternative
embodiment of the electromotive device of this invention.
Figure 11 is a side sectional view of an
alternative embodiment of the electromotive device as shown
in Figure 1, wherein the inductor is fixed to the shaft as
15 may be convenient in a brush commutated system.
Figure 12 is an exploded isometric view of still
another alternative embodiment of the electromotive device
of this invention, and illustrates a flat linear
implementation thereof.
Figure 13 is a graph illustrating the relationship
between torque and speed for a conventional electromotive
device b and for the electromotive device of this invention
a.
Figure 14 is a graph illustrating tested eddy
25 current, hysteresis and windage losses at different speeds
of one example of the electromotive device of this
invention.
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DESCRIPTION OF THE INVENTION
This invention provides a high power density (1 to
5 horsepower per pound) electromotive device incorporating
a large diameter-thin cross-section speculation ratio. This
is advantageous because, for a given number of magnets or
poles, the larger the diameter, the larger the
circumferential size can be. As diameter decreases, the
circumferential size of each magnet decreases until it is
virtually not seen or interacted with. Conversely, given a
fixed size magnetic pole, as diameter increases more
magnetic poles can be utilized, resulting in working of the
copper-iron-magnets more times per revolution, thereby
producing more power. Therefore, within limits, a reduction
in diameter results in loss of power and efficiency per unit
mass. In addition, according to basic physics, torque T is
directly proportional to the effective radius R of the
acting force F (T = R x F). AS the radius is doubled, the
torque arm and the amount of material producing torque are
also doubled, so power and torque increase as the square of
the radius.
In a typical electric motor, torque falls off
rapidly with increasing speed. This is primarily due to
"opposing induced currents" or "eddy current losses" in the
copper conductors and armature bars. The losses associated
with the windings or copper are caused by cross-leakage
between bars (made worse by radially long bars), direct
exposure of the copper to the magnetic field, and over
saturation of the armature bars due to an excess amount of
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permanent magnet material. These losses are minimized by
this invention.
Losses associated with bar-to-bar cross leakage
are reduced by designing the electromotive device of this
invention so that it incorporates radially short armature
bars.
Losses induced by the copper being directly
exposed to the magnetic field are reduced in the present
invention by an I-shaped armature bar acting as a shield to
the magnetic field.
Finally, losses caused by over saturation of the
armature bars are reduced by reducing the amount of
permanent magnet material such that the bars just "approach"
saturation. This is accomplished empirically as explained
later.
These three factors allow for much heavier wire to
be utilized without fear of eddy current losses. In the
invention, the cross-sectional area of wire may be approxi-
mately eight times that of prior designs. The heavier gauge
wire provides two significant functions; it significantly
reduces resistance heating due to its large cross-sectional
area increase and it provides more conductor (copper) per
available space. These two functions enable increased
efficiency and increased power output, respectively. In
addition, the armature bars themselves are constructed as a
lamination of several individual thin stampings, each
insulated one from the other. The insulation is a silicon
oxide by-product produced during the annealing process.
Because sheet metal stampings are utilized, the material
grain direction can be and is controlled in the radial
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direction Figure 6, thereby insuring a maximum flux carrying
capability.
The controllable dispersion characteristics
achieved via thin lamination grain control provides much
better performance than the powdered iron 3-d dispersion
solid bars in the co-pending application previously
referenced. The I-shaped lamination assembly armature bar
lends itself to conventional automatic winding techniques
when a special holding fixture is utilized.
The problem of losses associated with the windings
or copper caused by over saturation of inductor bars due to
an excess of permanent magnet material is addressed in the
present invention by providing the proper amount of
permanent magnet material so as to approach the saturation
level of the armature bars. This is accomplished by
empirical methodology to optimize the combination of copper,
iron, and permanent magnet materials to achieve optimum
power density and optimum efficiency through "saturation
approaching". Saturation or over-saturation is a serious
detriment to good performance. In the empirical method, a
very sensitive dynamometer was used to measure and plot
losses as a function of field. When copper eddy currents
were eliminated, there was no reduction in flux. Based on
the data obtained, flux conducting bars were fabricated from
a metal alloy having an iron content which creates a flux
carrying ability approximately equal to the flux saturation
point as determined by the electrical properties of the
design.
The preferred embodiments of the invention use a
hollow cross-sectional arrangement which lends itself to
multiple concentric elements or multiple-motors-within-a
-
motor. These could be operated concurrently to maximize
power density per available space, or individually in a
staged manner (like shifting gears in a transmission).
The cross-sectional arrangement features two
radiating and convecting surfaces for removing heat from the
armature (conventional designs have one). Thus the motor
can be driven at higher power levels for longer durations
without overheating.
The invention can be used as brush-commutated
motor or brushless, both in radial and linear
configurations. It can be used as a DC generator or an AC
alternator. The use depends on whether an electrical signal
is conveyed to the armature to create a force, causing
movement of the magnetic flux producing structure relative
to the armature, or whether the magnetic flux producing
structure is moved relative to the armature.
An exemplary embodiment of the electromotive
device is illustrated in Figure 1. This embodiment includes
an outer cylindrical housing 43 which is completed by front
45 and rear end plates 46 secured at opposite ends of the
cylindrical housing.
A shaft 51 includes a central portion 52 extending
through the cylindrical housing. The shaft is mounted in
the end plates 45 and 46, respectively, by means of bearings
57 and 58 so that the central portion 52 of the shaft is
coaxially positioned with respect to the cylindrical
housing. The reduced diameter rear portion 60 of the shaft
is mounted in bearing 58 and the front portion 62 of the
shaft extends through the front bearing 57 and end plate 45.
The end plates, 45 and/or 46 may include air
intake and exhaust apertures 66 and 67. These apertures
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allow cooling air to flow through the housing. In addition,
an aperture 68 is positioned to allow armature conductor
connections through end plate 46. In some environments in
which the device cannot operate in a gas (air) medium,
liquid coolant, such as oil, is used. In such cases, the
housing is sealed to retain the liquid.
The rotor 70 has a double shell configuration
provided by inner and outer spaced cylinders 72 and 73 which
extend normally from the ring connection portion 75. The
inner cylinder 72 is secured to the shaft centre section 62
by a pair of hubs 54 and 55 to hold the double shell
coaxially inside the cylindrical housing 43.
Figure 2 is a portion of a cross-sectional view
taken along lines 2-2 of Figure 1. It more clearly
illustrates that the inner cylinder 72 of rotor 70 includes
a magnetic flux return path in the form of a shell, 32,
which is preferably a lamination of rings of silicon iron or
some other magnetically permeable, low hysteresis loss
magnetic material supported by the cylindrical section 72
extending from the hubs 54 and 55. The cylinders 72 and 73
and connecting ring 75 are formed of any suitable material,
including iron.
The outer cylinder 73 comprises a magnetic flux
return path, 33, which may be solid iron or some other
permeable, low hysteresis loss magnetic material and a
plurality of magnetic elements 30 are mounted on the inner
surface of return path 33. In the exemplary embodiment, the
magnets 30 are permanent magnets preferably formed of
neodymium boron ferrite (NdFeB), but they may be formed of
barium ferrite ceramic (BaFe Ceramic), smarmy cobalt (SmCo),
or the like. Permanent magnets are used in the illustrated
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exemplary embodiment but they could be replaced with
electromagnets.
Returning to Figure 1, the stator inductor 82 is
fixed with respect to housing 43. It is mounted on the rear
end plate 46 so that the rotor 70 rotates around the common
axis of the stator 82 and the housing 43. The stator 82 is
a stationary cylindrical shell encompassed by the inner and
outer cylinders 72 and 73 of the rotor.
The stator 82 includes electrical conductors 84 of
Figures 2 and 3 which are randomly dispersed between stator
bars 86. Dispersed conductors 84 are preferably a bundle of
relatively large (for an electromotive device) diameter
insulated copper wires wound into a linking pattern with the
opposite ends of the wire bundles connected to connectors 89
which extend through aperture 68 in end plate 46 of Figure
1. The use of dispersed, large diameter windings enables
the resultant electromotive device to achieve a high power-
to-weight ratio because (1) the dispersed windings minimize
eddy currents within the coils and (2) the large diameter
wire reduces the number of field generating elements for a
given power factor which also reduces eddy currents within
the coils.
Conductors 84 are formed into a bundle throughout
the armature with each turn of the wire windings having a
flux carrying element or stator bar 86 therebetween. A
typical winding is schematically illustrated in Figure 4.
The flux carrying elements, stator bars 86, are
preferably a lamination of a plurality of silicon iron
sheets. Figure 5 illustrates the configuration of a single
layer or sheet of a laminated stator bar. The extensions 34
at the four corners give the bar an "I" beam cross-sectional
configuration and provide increased surface area for cooling
as well as flux shielding for the windings. These two
advantages over the prior art are further features which
enable the resultant electromotive device to achieve a high
power-to-weight ratio. Shielding the electromotive windings
from the magnetic fields within the motor minimizes eddy
currents within the coils. This and the increased cooling
heat exchange surface allows higher current flow which
increases field strength without increasing eddy currents in
the windings.
The use of stampings such as illustrated in Figure
5 allow the grain direction within the metal forming the bar
to be controlled. Thus a bar may be produced with a grain
direction as illustrated in Figure 5 wherein the grain
direction is parallel to the primary flux path through the
stator bar. This reduces heat generation because of the
reduced level of resistance to magnetic flux. A random
grain pattern provides maximum resistance which leads to
maximum heat generation and a uniform grain pattern reduces
resistance and its resultant heat. A grain pattern
following the direction of flux minimizes resistance and
heating. Thus a controlled grain inductor bar construction
allows higher flux densities without increased heating.
This increases the efficiency of the device and aids in
reaching the stated objectives of the invention.
Figure 6 illustrates an alternative shape for each
layer of the laminated induction core or stator bar. In
this embodiment, all of the bars share a common central
section which simplifies stamping, laminating and assembly.
When used as a motor at constant current, the
torque output of this invention can be maintained nearly
-
constant even with increases in rotor speed, as illustrated
in Figure 13 by line a. This is unlike prior art devices
wherein torque drops off rapidly with increased speed, as
indicated in Figure 13 by line b. The combination of high
torque and high speed, achieved in the electromotive device
of this invention, results in a high power-to-weight ratio.
The stator 82 (formed by the dispersed conductors
84 and flux carrying members 86) is closely spaced with
respect to magnets 30 positioned about the inner surface of
the cylindrical flux return path 33, and also closely spaced
with respect to the laminated cylindrical flux return path
32, as shown in Figures 2 and 7. As previously explained
and illustrated, cylindrical sections 72 and 73 provide
support for the inner and outer magnetic flux return paths
32 and 33. Typical flux paths have been illustrated in
Figure 2. As shown, these flux paths are loops, each of
which penetrates the inductor or stator, twice passing
through the flux carrying members 86. The flux carrying
members are dimensioned to create a thick induction to
maintain a high flux density which is essential to high
torque. Thus, as illustrated in Figure 7, the dimension of
the flux conducting bars 86 along the axis parallel to the
primary flux path through the bars is short relative to the
longitudinal axis of the bars which is parallel to the major
axis of the electric windings 84 disposed about the bars for
generating an electromagnetic field.
As indicated in Figure 8, the electromotive device
may be configured with magnets 80 on the outer surface of
the inner cylindrical section 72 rather than on the inner
surface of the outer cylindrical section 73. In Figure 9,
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the electromotive device is configured with magnets 80 on
both inner and outer sections 72 and 73.
In Figure 10, two cylindrical stators 82 encompass
both sides of magnets 80. In addition, while not
specifically shown, it is also to be realized that the
electromotive device could be configured by placing
additional layers of stator-rotor elements radially inwardly
and/or outwardly of that shown in the figures.
The electromotive device of this invention thus
includes a magnetic flux producing assembly having at least
one pair of poles which can be embodied by using permanent
magnets or electromagnets, and an inductor assembly which
intercepts the magnetic flux produced by the magnetic flux
producing assembly and has an alternating structure of
conductive windings and flux carrying elements. A winding
can be used as the principal component of the inductor with
the winding consisting of bundles of separate dispersed
conductors. The use of dispersed conductors of large
diameter wire permits high speed rotation of the rotor when
used in conjunction with winding flux shielding, flux
carrying elements.
In the case of conductors of large cross-section
or conductive flux carrying elements of large cross-section,
as used at least in some prior known devices, as the
frequency of the magnetic field reversal increases, the
magnitude of the induced currents in the bars increases, and
the induced currents react with the magnetic field to create
a resisting torque which opposes the increase of rotational
speed. Thus, known shell type devices are inherently
limited to low speed by the reaction torque, and cannot be
rotated at high speed and are therefore not suitable, for
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example, for use as traction motors in most practical
applications. However, by shielding the windings from the
generated magnetic flux and isolating the flux created
within the windings, induced currents are limited and the
foregoing impediments to high-speed/high-torque operation
are eliminated.
When used as a motor, a means to displace (i.e.,
rotate) the magnetic field relative to the armature at high
speed must be provided so that electric power can be
converted into mechanical power in a manner similar to that
used by known motors. This can be accomplished by
connecting connectors 89 of the armature 82 in Figure 1 to
a current source.
When used as an alternator or generator, an
actuator rotates shaft 51 which rotates rotor 70 to induce
a voltage in conductors 84 and thereby generate an
electrical current flow from conductors 84 to a load via
connector 89.
While not specifically shown, it is to be
understood that the inductor includes necessary electric
commutation devices, including those devices wherein
commutation is performed electronically (as in a brushless
DC motor, for example), as well as those devices which
employ rectifiers instead of commutation (as is often used
in power generating applications). A hall device, 21 of
Figure 7, may be used in conjunction with a magnetic ring 22
to sense the passing of an inductor bar or pole piece, to
produce the required timing data.
Figure 11 illustrates an embodiment of the
electromotive device of this invention in which the inductor
82 is an armature. It is connected to shaft 52 by mounting
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disk 101, and inner and outer cylinders 72 and 73 are fixed
to the housing 43. In this embodiment, the inductor becomes
the rotor with electric power being communicated to it by
means of brushes or slip rings 102 (with brushes being
utilized in the case of a DC machine, and slip rings being
utilized in the case of an AC machine). The embodiment
shown in Figure 11 is preferred for some applications,
particularly in the case of a DC commutated machine.
This invention has a significant advantage over a
conventional motor by utilization of a minimum amount of
iron which undergoes flux reversal. That is, only the iron
in the flux carrying elements in the armature is subject to
the reversing flux as each pole is passed, and thus low
hysteresis losses are experienced, as shown in Figure 14.
In addition, the effects of flux leakage are reduced so that
all of the armature windings experience the total flux
change and thus are equally useful at producing torque.
This invention has significant heat transfer
advantages through the use of "I" beam shaped stator bars,
as shown in Figure 5. They make it possible to provide
cooling to both the inner and outer surfaces of the
inductor. As a result, the superior high power to weight
ratio is further enhanced.
By the principles of heat transfer, heat buildup
in an inductor, with constant surface temperature and
uniform internal heating per unit volume, depends on the
square of its thickness. For example, compare an "I" beam
armature 0.25 inches thick (as is possible in this
invention) to a solid rotor, five inches in diameter (as is
common in known devices). The heat buildup in such known
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devices is 400 times greater than that experienced by this
invention.
The electromotive device of this invention can be
produced in several topological variations of the basic
design. In addition to the rotating cylindrical shell
configuration, by changing the orientation of the magnets
and the windings, the motor can be made to produce a linear
motion. Other variations (not shown) include pancake and
conical configurations.
Figure 12 illustrates a linear reciprocating
implementation of the electromotive device of this invention
in which the structure is flat. As shown, magnets 113 are
mounted on flat lower return plate 114. Inductor 115 is
provided with dispersed conductors 116 and flux carrying
elements 117 in the same manner as described hereinabove
with respect to the other embodiments illustrated except
that the inductor is essentially flat rather than
cylindrical. An upper return plate 118 is also provided,
and inductor 115 is movable linearly with respect to, and
between, lower and upper plates 114 and 118 by means of
rollers 120 mounted on the edges of upper plate 118 and
rollers 121 mounted in roller mounting boxes 111 (carried by
lower plate 114).
