Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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TITLE: SPHERICAL, DIRECT CURRENT, CAGE ROTOR
ELECTRIC MOTOR
Field of the Invention
The subject of the invention is a spherical, direct current,
cage rotor electric motor.
Background to the Invention
A very wide scale of direct current electric motors is known.
The direct current electric motors of the electric motor driven
vehicles constitute one large group of them.
The US-PS No. 4 948 998 describes a twin-commutator,
highly reliable direct current electric motor, provided with two
independent, parallel windings, arranged in the rotor core. Through
the bush systems located on both sides of the motor and through the
commutator, the windings can be used separately or together. The
rotor is cylindrical, non-self carrying and the stator contains field
windings.
The scheme of an open squirrel cage direct current electric
motor with commutators on both ends and with cylindrical iron cored
rotor is described in publication sheet EP 0 481 774 (A2). It is
suggested to use it primarily for large-current railway traction
motors, however, the description does not provide dispositions,
practical instructions or directions for the implementation of the
magnetic circuit, bearing support, cooling, etc.
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The 1989 product booklet of the ESCAP company
(Switzerland) describes direct current electric motors with low
moment of inertia and ironless rotor, where the self carrying,
cylindrical rotor is a so-called thread wound (compacted honeycomb)
coil. This arrangement reduces the effective torque by about 30% and
increases the length of the coil and its resistance in the same
proportion. The direct current electric motors of small inertia and
with ironless (hollow) self carrying rotors, described in the 1989
product-booklet of the Pacific Scientific company (USA, Illinois) are
similar to them.
From the US-PS No. 4 019 075 ironless rotor coils of
miniature direct current electric motors can be learned. The multiple-
wound lap windings have relatively large coil-heads, i.e. 'unused'
parts. The self-carrying rotors developed by them are cylindrical with
single-sided commutator.
Another cylindrical solution with single-sided commutator
can be learned from US-PS No. 4 181 966, in which case the field
magnet is located inside, while the soft magnet yoke is located
outside of the rotor.
The field magnets of the direct current electric motor with
cylindrical, ironless, self carrying rotor according to the solution of
US-PS No. 4 110 645 are located outside of the rotor, while the flux
conducting yoke is located within the rotor.
A cylindrical, direct current, electric motor is described also
in HU-PS No. 189 040, where the rotor of the implementation
according to Fig. 2 thereof is a disk shaped wire coil, with
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significant parasite coil-head wire lengths and masses. The double
rotor and the commutators on the rotors of the solution according to
Fig. 3 thereof are also disk shaped and made of printed circuits,
while the bushes are directed radially.
An electric motor partly similar to the latter, with a rotor
and commutator made of double printed circuit boards can be seen in
Fig. 1 of US-PS No. 4 082 971, with the difference that the two
rotors driving the same shaft have separate, independent stator
magnetic circuits, since aluminum spacers and housing parts are
located between the yokes.
Summary of the Invention
The need has arisen for low and medium current electric
motors of better efficiency.
I have set as an objective of my invention to reduce the
effect and mass of those components which increase the losses,
therefore decrease the efficiency, and to increase the power per
volume. .
The key for the solution was given by the recognition that
the source of the losses is primarily the exciting circuit of the motor,
its inhomogenity and dispersion and, on the other hand, the added
resistance loss caused by the relatively great length of the coil-heads
of the rotor.
To exclude the above mentioned deficiencies and to satisfy
the demands that have arisen, I have found a spherical arrangement
suitable.
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A solution for the optimal design of the exciting circuit is
the use of high energy, double-sided permanent magnets, preferably
made of alloys, the magnetic line of force of which is radial over a
relatively large angular range, a direct consequence of which is that
the (B) induction lines are perpendicular to the direction of the
current' (I), and further, to the generated force (F).
Shortly: it is easy to see the obvious fact that in case of the
rotor of a spherical shape motor, the requirement of perpendicularity
is satisfied at any point of the above mentioned angular range.
The second question, i.e. the design of the rotor is a more
complex problem. With other words: a meaningful increase of
efficiency can only be achieved by reducing the amount of energy
transformed into heat according to the I2R power formula. It can be
regarded solved by using a spherical shell shaped rotor, made of
copper profiles of relatively large cross section and strength which,
at the same time, is suitable for transmitting torque.
The objective of the invention was achieved by designing a
spherical, direct current, cage rotor electric motor, the stator of
which is composed of an inner part, made of a spherical, hollow, flux
conducting, soft magnetic yoke, and a surrounding outer part of
spherical shell shape, consisting of segmental parts or cast over the
inner part, and made of permanent magnet, the output axle is a
splined tubular shaft, protrudi..g through the hole of the inner part.
The cage rotor is a spherical surface of revolution surrounding and
enclosing the ferromagnetic stator of sandwich structure angular-
symmetrically, which is composed of copper profiles, arched along
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the planes parallel to the geometric axis of the splined tubular shaft,
the insulated hub-parts of which are fixed to the splined tubular shaft
by means of screw type clamping bushes, the ends of the copper
profiles are machined into planes perpendicular to the geometric axis
of the splined tubular shaft, and which form disk shape commutators,
to the commutators bushes, preferably made of bronze-graphite or
mercury, are resiliently coupled, whose terminals are formed as plug-
socket holders or clamping screws. The inner part of the stator can be
of meridian lattice structure. The caged rotor can have a form
different from spherical, e.g. ellipsoid of rotation, eventually a
discus form, nevertheless, it must be a body of rotation. The
equatorial of the cage rotor has the shape of a torus, and' it is
provided with a fiber glass reinforced heat resistant plastic stiffener
ring, which is concentrically surrounded by segmented permanent
magnetic main poles, which in turn are surrounded by the shell
structure of soft magnetic yokes made of two hemispherical-like
parts that are pressed to one another at their edges, which in turn are
surrounded by a light metal alloy, for example aluminum, hollow
casing containing openings, and between the stator and the splined
tubular shaft, and between the casing and the splined tubular shaft
bearings, preferably roller bearings, and sealing elements are
arranged. Within the splined tubular shaft, in the range of the
geometric center of the motor, larger openings, and at the planes of
the commutators, smaller openings and gilled air-inlet ports forming
carburatter chokes are formed.
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The casing can be made of two hemispherical parts provided
with ventilating openings, and they can be fixed together by, for
example, bolts, however, a spherical plastic net or lattice work of
appropriate strength can also be used. From the outer mantle of the
caged rotor, at the dividing plane, air-outlet channels having a
tangential outlet end sections are formed in the permanent magnetic
main poles, in the soft magnetic yoke shell structure, as well as in
the casing parts. Tangential baffles are arranged at the outlet part of
said end section.
Brief Description of the Drawings
The spherical, direct current, cage rotor electric motor
according to the invention is described below in more details, by an
example embodiment, and with the help of the attached drawing, in
which in Figure 1 the cross section of the motor is seen; in Figure 2 a
more detailed cross section is shown.
Detailed Description
The motor thus has a splined tubular shaft 1, which has, at
its larger diameter middle section, a stator, which comprises a
spherical, hollow inner part 2 made of a flux conducting soft
magnetic yoke, and a permanent magnetic outer part 3 surrounding
said inner part 2, which consists of segmental parts or which is cast
onto the inner part 2. The stator is surrounded by an angular-
symmetric, spherical shell surface of revolution shaped cage rotor 6,
which is made of copper profiles, preferably profiled plates or rods,
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that are arched in planes parallel to the geometric axis 13 of the
splined tubular shaft 1, the ends of the profiles constitute, at the
splined tubular shaft 1, the commutators 10A, IOB, ... of disk
segment shape, which are machined into a plane perpendicular to the
geometric axis I3 of the splined tubular shaft 1. Close to the
commutators 10A, 10B, ...brushes llA, 11B of disk segment shape
sit resiliently, made preferably of bronze-graphite, the terminals
14A, 14B of which are formed as plug-socket holders or clamping
screws. The insulated hub parts 4A, 4B; SA, SB are fixed onto the
splined tubular shaft 1 by means of the screw type clamping bushes
21A, 21B. ,
At its biggest diameter, i.e. equatorically, the caged rotor 6
is strengthened by a ring 7 made of insulating material, preferably
fiber glass reinforced heat resistant plastic, which is press molded
by forming air channels) therein simultaneously - onto the cage
rotor 6, already mounted on the stator. The cage rotor 6 is surrounded
by permanent magnetic main poles 8 shaped as spherical shell
segments, bordered by planes parallel to the geometric axis 13 of the
splined tubular shaft 1, the permanent magnetic main poles 8 in turn
are surrounded, also in the shape of a spherical shell, by the shell
structure of soft magnetic yokes 9, split along the biggest diameter
('equator'). The direction of the developing magnetic field in the
space between the permanent magnetic main poles 8 of the assembled
' motor is radial.
Finally, the outer part of the spherical, direct current, cage
rotor electric motor is composed of by the casing parts 12A and 12B,
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which, too, are spherical, fixed together by bolts at their biggest
diameter, provided with gill-openings and preferably are webbed on
their outside, and made of light metal alloy, for example aluminum.
Instead of the casing parts 12A and 12B, a spherical plastic
web or lattice work can also be used.
Between the hollow inner part 2 and outer part 3 of the
stator and the splined tubular shaft 1, roller bearings 16A and 16B
and bearing boxes 18A, 18B, provided with bores, and between the
casing parts i2A, 12B and the splined tubular shaft 1 roller bearings
17A, 17B and sealing elements 19A, 19B are arranged. in the range
of the geometric axis of the splined tubular shaft large openings are
formed. The bores of the bearing boxes 18A, 18B connect the
openings 15 with the space of the cage rotor 6.
For the operation of the spherical, direct current, cage rotor
electric motor according to the invention it is preferable to use
compressed air, which coming from one (or both) ends) of the
splined tubular shaft 1, traveling within it, enters the interior of the
motor by passing through the openings 15 of the splined tubular shaft
1 in the range of its geometric center, as well as through the smaller
openings 20A, 20B, provided in the splined tubular shaft 1 at the
planes of the commutators 10A, IOB, then it leaves the motor
through the bores of the bearing boxes 18A, 18B and through the (not
shown) gill-open ~ngs of the casing parts 12A, 12B.
In Figure 2, naturally, the same reference numbers refer to
the same elements. Furthermore, at the planes of the commutators
10A, lOB carburatter chokes 22A, 22B, and from the outer mantle of
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the caged rotor 6, at the dividing plane, air-outlet channels 23A, 23B
having tangential outlet end sections are formed in the permanent
magnetic main poles 8, in the soft magnetic yoke shell structure 9, as
well as in the casing parts 12A, 12B. The paths of the air flow 24A,
24B are shown by dashed lines.
The operation of the spherical, direct current, cage rotor
electric motor according to the invention is the following:
Similarly to the known motors, its operation is based on the
fact that a force acts on a conductor in which a current flows and
placed in a magnetic field.
When a current flows in the conducting elements 6A, 6B, ...
of the cage rotor 6, shown in the figure, in the direction indicated by
the arrow, then a force acts on the left hand side arched conducting
element 6A, upwards from the plane of the sheet, and on the right
hand side arched conducting element 6B downwards from the plane
of the sheet, as a direct result of which is that the cage rotor 6
attempts to rotate the splined tubular shaft 1 counter clockwise.
If the direction of the current is reversed, the cage rotor 6
will rotate clockwise.
It is easy to see, that if the direction of the current is
reversed at each half rotation, the continuity of the rotation can be
maintained. Following the path of the air flow, it is easy to see as
well that the motor acts at the same time as a centrifugal blower or
turbine of double-side inlet, provided with meridian baffles.
All electromotive force is the result of an energy
transformation E. The matter is that there is another fundamental and
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simple relationship between the electricity, mentioned before, and
the magnetism, which is invariant with the known physical laws, and
can be developed into a new equation, which gives the following
relationship of energy equilibrium for spherical motors and
generators:
2~Mn = EI = I2rw
If I is given in A, r in m, w in s~l, then the induced
electromotive force E is obtained in V, and the whole magnetic
torque exerted by the motor is obtained in Nm.
The advantages of the spherical, direct current, cage rotor
electric motor, constituting the subject of my invention, are the
following:
- Independent of their geometric sizes, the efficiency of all
spherical, direct current, cage rotor electric motors is the same,
which exceeds 90%;
- The spherical shape of the rotor and the strong magnetic
field, which is practically radial over a large angular range, makes it
possible that the improductive length of the wires is the smallest
possible, and there is no coil-head;
- The moment of inertia of the self carrying 6 cage rotor is
small and, further, there is no wattless component arising from the
coil-heads, therefore the motor is especially suitable for fast (for
example servo) drives;
- Because of the higher efficiency, motors of smaller mass
and volume can be produced, which are especially advantageous in
case of airborne systems, for example, on aircraft, satellites, etc.;
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- The reliability of the motor is higher, and the life of the
bushes is longer, due to the double commutator and brush system;
- By means of higher current open cage rotors and by
increasing the number of brushes and the number of copper profiles
or rods, i.e. the conducting elements, constituting the caged rotor,
the pulsation of the shaft-torque can be reduced, which makes the use
of inertia masses other than the strengthening ring unnecessary in
case of, for example, tired vehicles, motor cycles, cars, etc.;
- Due to the practically closed magnetic field, the
detrimental parasitic magnetic radiation of the motor can be
significantly reduced, which is advantageous, for example, in case of
airborne systems;
- It is easy to use, in connection with the motor, different
kind of semiconductor pulse-width modulated choppers (realized by
tyristors, GTO tyristors, transistors and POWER-MOSFET elements);
- The ironless caged rotor also acts as a centrifugal blower
or turbine of double-side inlet, provided with meridian baffles;
- The splined tubular shaft makes it possible to use the
motor as a single-flow propeller turbine, for example in case of
sport aircraft.
