Metal working – Method of mechanical manufacture – Electrical device making
Reexamination Certificate
2001-04-19
2004-06-22
Tugbang, A. Dexter (Department: 3729)
Metal working
Method of mechanical manufacture
Electrical device making
C029S596000, C029S592100, C310S049540, C310S045000, C310S216055, C310S261100, C310S262000
Reexamination Certificate
active
06751842
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the construction of a machine rotor, in particular, it relates to the construction of rotors for high-speed, controlled-pole electric machines. For purposes of this application, the term high-speed machine shall mean a rotating machine wherein the rotational speed and the diameter of the rotating portion of the machine are such as, in their combination, to give rise to centrifugal forces of such magnitude acting upon the rotating portion of the machine as to require explicit consideration in the design and construction of the machine.
2. Description of Related Art
A controlled-pole electric machine includes a rotor and a stator, each held in position by a frame in such a fashion as to permit continuous mechanical rotation of the rotor relative to the stator.
Typically in controlled-pole machines, the adjacent surfaces of the rotor and the stator are of nominally cylindrical form, each of diameter similar to but not identical to the diameter of the other, the axes of these cylindrical surfaces being coaxial with each other such that the surface of the rotor passes in close fixed proximity to the surface of the stator during rotation of the rotor about this axis; the clearance region between said surfaces being otherwise known as the airgap. Controlled-pole machines may be of external rotor construction having the rotor outside the airgap such that the rotor surrounds the stator, or they may be of internal rotor construction having the rotor inside the airgap such that the stator surrounds the rotor.
A controlled-pole rotor includes an annular layer of permanent magnetic material, one surface of which, absent certain restraining materials which are a part of the invention described herein, is adjacent to and defines one boundary of the airgap; the magnetic material is usually mounted upon a core of high magnetic permeability, low eddy current and magnetic hysteresis loss material and attached to a rotating mechanical shaft. The permanent magnetic material in controlled-pole machines typically comprises a ferrite based, fired ceramic material having very low electrical conductance, high remanent magnetization, and a coercive force tailored to its controlled-pole usage.
A controlled-pole stator usually includes a structure of high magnetic permeability, low eddy current and magnetic hysteresis loss material having a number of slots running nominally axially along its airgap surface in which are inserted windings consisting of a number of electrical conductors; said electrical conductors often comprising, in part, several multi-turn coils, and being rotationally positioned and electrically interconnected so as to achieve the desired electrical, magnetic and mechanical characteristics. Certain of these windings, otherwise known as the main windings, are of such a number, positioning, and electrical connection as to be comparable in their function to the windings of a conventional fixed-pole electric machine. Certain other of these windings, otherwise known as the exciter windings and which are unique and essential to the controlled-pole machine, are of such a number, positioning, and electrical connection as to permit controlling the direction and magnitude of the magnetization of the rotor's permanent magnetic material during operation of the machine.
During the rotor's rotation, the permanent magnetic material of the rotor passes in close proximity to the stator, and in consequence of this motion and of the passage of an alternating current of appropriate magnitude through the exciter winding, the rotor's permanent magnet layer is magnetized into a pattern of radially directed, alternating north and south magnetic poles, the effective rotational speed of said magnetic poles thereby being in synchronization with the alternating currents in the exciter winding irrespective of the rotational mechanical speed of the rotor. Subsequently, in the case of the machine's functioning as a motor; these north and south magnetic poles in passing in close proximity to the main windings interact with the magnetic field produced by alternating currents in the main windings supplied from an external source thereby producing a rotor torque; or, in the case of the machine's functioning as a generator, an alternating pattern of north and south magnetic poles is produced in the rotor's magnetic layer in a manner similar to that described for the case of the motor, and an externally supplied torque causes the rotor's north and south magnetic poles to pass in close proximity to the main windings thereby inducing an alternating current in the main windings and thence to any externally connected electrical load, said main winding currents being synchronous with the currents in the exciter windings irrespective of the rotational mechanical speed of the rotor. In both cases, the alternating current in the exciter windings and the alternating currents in the main windings are caused to be synchronized with each other through the controlling of the rotor's magnetic poles and are independent of the speed of mechanical rotation of the rotor, thus permitting the delivery of continuous, smooth torque independent of speed in the case of the machine's functioning as a synchronous motor, or the continuous delivery of a constant frequency alternating electrical current independent of speed in the case of the machine's functioning as a synchronous alternator.
It is common to construct the rotor's permanent magnet layer from a number of individual pieces of magnetic material assembled in mosaic-like fashion in one or more annular layers to form the desired composite magnetic cylinder, the individual pieces typically being bonded to each other and to the underlying high permeability core by means of a bonding agent such as a high strength epoxy.
The operation of a rotor of this form of construction as a controlled-pole rotor creates several conditions which, in a manner or degree not material to operation of a fixed-pole machine and not obvious to those skilled in the art of fixed-pole or controlled-pole machines, present opportunity for inventive enhancement or which rise to the level of becoming problematic and compelling of inventive solution. This is particularly true in a machine of internal rotor construction having the rotor inside the airgap such that the stator surrounds the rotor,
One such instance arises from the substantial thickness of the annular magnetic material layer of the internal rotor which results when two adjacent cylindrical surface layers of the magnetic material of the rotor have significantly different diameters and, as a consequence, significantly different surface areas. In the controlled-pole machine, it is common for these respective cylindrical surface areas to differ by twenty percent or more. This condition also obtains for the cylindrical surface of the high permeability core of the stator adjacent to the airgap and for the cylindrical surface of the high permeability core of the rotor underlying the magnetic material layer. During operation of the controlled-pole machine, substantially all the magnetic flux produced within the stator core by the currents in the various stator windings and the magnetic flux produced by the rotor's layer of magnetic material traverses and is contained within the high permeability core of the stator, the airgap, the rotor's magnetic material layer, and the high permeability core of the rotor. The combination of all these circumstances, that is substantially constant total quantity of magnetic flux traversing said regions, and said surfaces varying in area according to their distance from the axis of rotation, results in a condition wherein the magnetic flux density varies throughout the volume of the magnetic material layer of the rotor according to the distance from the axis of rotation.
Additionally, while the magnetic flux produced by currents in the main winding typically traverses the magnetic layer in a ra
Barber Ronnie J.
Roesel, Jr. John F.
Precise Power Corporation
Sacco & Associates PA
Tugbang A. Dexter
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