Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
1999-05-10
2001-02-20
Enad, Elvin (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S112000, C310S049030, C310S178000, C310S180000, C310S164000, C310S165000, C310S254100, C310S261100
Reexamination Certificate
active
06191517
ABSTRACT:
FIELD AND BACKGROUND OF THE INVENTION
The present invention relates to electrical machinery and, more particularly, to brushless synchronous electrical generators and motors.
FIGS. 1A
,
1
B and
1
C illustrate the terms used herein to define the geometries of rotary machines and their electrical windings.
FIG. 1A
shows a right circular cylinder
11
, and the corresponding radial, azimuthal, and axial directions. As used herein, a “toroidal” winding is a winding, around a cylinder or torus, that is always perpendicular to the axial direction, and a “poloidal” winding is a winding that is at least partly parallel to the axial direction.
FIG. 1B
shows a torus
12
partially wound with a toroidal winding
13
.
FIG. 1C
shows a torus
14
partially wound with a poloidal winding
15
.
In a conventional synchronous AC electric generator, the rotor winding is connected to a DC current source via rings and brushes. As the rotor is rotated, the magnetic field created by the DC current rotates along with the rotor, inducing an AC electromagnetic force (EMF) in the stator winding. The same design is commonly used for synchronous electric motors: AC current in the stator winding creates a rotating magnetic field that interacts with the rotor's direct magnetic field, causing the rotor armature to rotate.
This design suffers from several inefficiencies. First, the rings and the brushes wear out over time and must be replaced. Second, parts of the stator winding, called “winding ends”, protrude beyond the armature. These winding ends do not participate in the generation of electrical current in a generator, or in the generation of torque in a motor; but, unless the windings are made of superconductors, the winding ends contribute to resistance losses. In addition, the associated magnetic fields create eddy currents in electrical conductors outside of the armatures. These eddy currents are an additional drain on the power output of a generator or the power input of a motor.
The reason that rings and brushes are needed in the conventional synchronous machine design is to provide electrical power from a stationary DC current source to a moving rotor winding. There also are brushless designs, one of which, a synchronous induction machine, is illustrated schematically in cross-section in FIG.
2
. An axially slotted cylinder
32
, made of a ferromagnetic material such as iron, is rigidly mounted on a shaft
30
, and rotates within a stationary armature
34
. Armature
34
is geometrically in the form of an annulus, with a cylindrical central hole to accommodate slotted cylinder
32
, and an interior equatorial slot to accommodate an annular, toroidally wound coil
36
. In cross section, armature
34
looks like two opposed U's, as shown. What appear as the arms of the U's are actually two toroidal disks. A set
38
of windings are wound poloidally in slots on the inner periphery of these two disks. Conventionally there are three interleaved windings in set
38
, making the synchronous induction machine of
FIG. 2
a three-phase machine.
A DC current is supplied to toroidal coil
36
, creating a magnetic field around slotted cylinder
32
and windings
38
. Because cylinder
32
is slotted and ferromagnetic, as cylinder
32
rotates, the geometry of the magnetic field changes, inducing an AC EMF in poloidal windings
38
. Conversely, an AC current introduced to poloidal windings
38
generates a time-varying magnetic field that applies a torque to cylinder
32
, causing cylinder
32
to rotate.
The design of
FIG. 2
eliminates the need for rings and brushes, but still has the inefficiencies associated with having winding ends that protrude outside the effective zone of electromagnetic induction. In addition, this design is inherently wasteful of space. Coils
36
and
38
must be separated spatially (as shown schematically in
FIG. 2
) to minimize eddy current losses.
There thus is a widely recognized need for, and it would be highly advantageous to have, an electrical machine (generator or motor) with only stationary windings, arranged geometrically for maximum efficiency.
SUMMARY OF THE INVENTION
According to the present invention there is provided an electrical machine including: (a) a rotor, free to rotate about a rotor axis and including a first magnetically interactive projection extending radially outward from the rotor axis; and (b) a stator including: (i) a first plurality of magnetically interactive stator cores extending radially outward from a first common center located on the rotor axis, and (ii) a structure for magnetically linking the first projection of the rotor to a radially outward end of each of the stator cores as the first projection sweeps past each the stator core as the rotor rotates.
According to the present invention there is provided an electrical machine including: (a) a rotor, free to rotate about a rotor axis and including a first magnetically interactive projection extending radially outward from the rotor axis; and (b) a stator including: (i) a first plurality of magnetically interactive stator cores extending radially outward from a first common center located on the rotor axis, and (ii) a second plurality of magnetically interactive stator cores, like in number to the stator cores of the first plurality and extending radially outward from a common center located on the rotor axis and different from the first common center; the common centers defining a stator axis coincident with the rotor axis, the stator cores of the first plurality being positioned azimuthally around the stator axis at substantially equal angular separations, the stator cores of the second plurality being positioned azimuthally around the stator axis at substantially equal angular separations, the stator cores of the second plurality being displaced azimuthally with respect to the stator cores of the first plurality.
As used herein, the term “magnetically interactive material” means a material that interacts strongly with a magnetic field, for example a ferromagnetic material or a ferrimagnetic material. Parts of the present invention that are made of, or include, a magnetically interactive material are herein called “magnetically interactive”. The preferred magnetically interactive materials of the present invention are soft ferromagnetic materials such as magnetic steel, and magnetically interactive insulators, such as ferrite. If electrically conductive materials such as magnetic steel are used, the parts constructed thereof preferably are constructed so as to suppress energy-wasting eddy currents. For example, these parts may be laminated of alternating layers of magnetic steel and an insulator.
The present invention is similar to the synchronous induction machine of
FIG. 2
, but the windings and armatures are arranged so that all, or almost all, of the length of the windings actively participate in the energy transformation process. The present invention is based on a stator armature that includes at least one set of magnetically interactive stator cores projecting radially away from a common center. A stator winding is wound toroidally around each stator core. A rotor rotates about an axially directed rotor axis that runs through the common center. Rigidly attached to the radially outward end of each stator core is a magnetically active crossbar that runs parallel to the rotor axis. The rotor includes at least one magnetically interactive projection, a radially outward surface of which sweeps past radially inward surfaces of the crossbars as the rotor rotates, thereby linking the projection magnetically to the radially outward ends of the stator cores.
Preferably, the rotor includes two such projections, with the stator cores axially between the two projections.
A mechanism is provided for generating a magnetic field in the rotor. In one preferred embodiment of the present invention, this mechanism includes one or more toroidal windings concentric with the rotor axis. In another preferred embodiment of the present invention, this mechanism includes permanent magne
Enad Elvin
Friedman Mark M.
S. H. R. Limited BVI
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