Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2000-05-08
2003-10-14
Ramirez, Nestor (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
Reexamination Certificate
active
06633106
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to electrical generators and motors, and more specifically, to axial gap motor-generators and related components, systems and methods.
2. Description of the Related Art
A need has existed for some time for small, light weight and efficient electrical machines that are capable of handing substantial power outputs without the need for elaborate external cooling systems. Applications for such devices include power conversion systems or subsystems for satellites, military vehicles and weapon systems, and the like.
There has been a need for power conversion systems that can operate at high rotational speeds. There also has been a need for power conversion systems that generate relatively little heat. This feature can be important in applications such as space-based power systems, wherein heat dissipation can be quite limiting and thermal accumulation can degrade system performance and lifetime. Thermal generation also can be problematic with such applications as military weapon system power conversion subsystems. Excess thermal energy generated during power conversion, aside from constituting an unwanted loss of precious energy, can result in unwanted thermal signatures that can be utilized by hostile parties to identify and possibly target the platform. The generation of unwanted thermal energy also may be disadvantageous in that removal of such energy may require active cooling. This requirement can place unwanted demands on space, weight, power and energy resources.
Axial gap motor-generators have been used or proposed in some applications in which high power density and low thermal generation have been desired. Axial gap motor-generators offer a number of advantages over more traditional power conversion devices. Axial gap motor-generators can be advantageous when operated at high rotational rates, for example, in that they can provide high energy densities and relatively high power outputs while generating relatively little thermal energy loss.
Axial gap motor-generators, however, have not been without limitations. One such limitation is that, at the high rotational speeds often needed for sufficiently high power output levels, low heat loss levels, and low cooling requirements, for example, 10,000, and as high as 40,000 to 50,000 revolutions per minute (RPM), mechanical stresses are so substantial that failures are common. A number of approaches have been proposed for addressing such limitations.
One of the undesirable stresses placed on the system at high rotational speeds involves the substantial mechanical stress placed on the magnets used in the rotor. As the rotor spins at high speeds, the forces on the magnets are quite substantial. High efficiency magnets capable of generating the large magnetic field strengths required for high performance applications, such as neodymium-iron-boron magnets, are relatively brittle. Impact loading can cause them to crack and disintegrate at high rotational speeds. Their ability to accommodate tension forces is particularly limited.
Another limitation of axial gap motor-generators has been that, at the relatively high rotational speeds required for advanced power conversion systems, they have a limited ability to accommodate the structural deformations that occur as the device reaches its intended operational speed or speed range. Substantial flexure between the rotor and related components, for example, can change the geometry of the components responsible for converting power and the resultant magnetic field strength, thus causing inefficiencies and energy losses. Excessive flexure in some instances can result in unwanted contacting of moving components, which can result in destruction of the motor-generator.
Axial gap motor-generators also have been limited in that the performance of the magnets typically used in such machines is degraded substantially by elevated temperatures. The practical threshold for neodymium magnets and similar rare earth permanent magnets, for example, is about 120° C. Beyond that temperature range, their performance begins to degrade substantially and permanently. Thus, there is a need for axial gap motor-generators that have relatively contained operating temperatures so that the integrity and performance of the magnets can be preserved when the device operates at high speeds, e.g., in excess of 40,000 RPM.
A further limitation in many known axial gap motor-generators involves the presence of undesirable and problematic vibrations that arise in the device. These vibrations usually are attributable to the high speed rotation of the rotor assembly, and small asymmetries or variations in material densities, dimensions, etc.
OBJECTS OF THE INVENTION
Accordingly, an object of the present invention according to one aspect is to provide an axial gap motor-generator that is capable of operating effectively at high angular velocities, e.g., in excess of 10,000 RPM.
Another object of the invention according to another aspect is to provide an axial gap motor-generator that preserves the integrity of the magnets used in the device, even at relatively high rotational speeds.
Another object of the invention according to another aspect is to provide an axial gap motor-generator that can withstand substantial mechanical stress and deformation without significant adverse impact on the operation and efficiency of the device.
Another object of the invention according to a further aspect is to provide an axial gap motor-generator that effectively avoids undesirable thermal energy accumulation.
Another object of the invention according to still another aspect is to provide an axial gap motor-generator that limits unwanted vibrations in the device during high speed operation.
Another object of the invention is to provide related methods.
Additional objects and advantages of the invention will be set forth in the description that follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations pointed out in the appended claims.
SUMMARY OF THE INVENTION
To achieve the foregoing objects, and in accordance with the purposes of the invention as embodied and broadly described in this document, an axial gap motor-generator is provided, of the type coupled to a shaft having an axis of rotation. The motor-generator comprises a rotor having a rotor body rotatably disposed about the shaft and having an outer region. The rotor includes a plurality of openings disposed in the outer region and spaced from one another. Each of the openings includes an outer edge, and preferably but optionally an inner edge and a pair of side edges. The motor-generator also includes a plurality of magnets equal in number to the openings. Each of the magnets includes an outer edge, and preferably but optionally an inner edge and a pair of side edges corresponding respectively to the inner edge, the outer edge, and the pair of side edges of a corresponding one of the openings. The outer edge of the magnets generally is non-conformal to and is slightly smaller than the outer edge of the corresponding one of the openings. Each of the magnets is shaped to be inserted into the corresponding one of the openings. A stator assembly is positioned adjacent to the rotor. The stator assembly includes windings positioned to be adjacent to the magnets when the rotor is rotated.
Preferably, the axial gap motor-generator according to this aspect of the invention further includes an expandable hub between the rotor and the shaft.
The rotor also may include a rim around the outer region. The rim may comprise, for example, a composite material.
The outer edge of each of the openings preferably has a first resting radius when the axial gap motor-generator is at rest, and the outer edge of each of the magnets has a second resting radius when the axial gap motor-generator is at rest, wherein the first resting radius is larger than the s
Addison Karen
Ramirez Nestor
Sullivan Law Group
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