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 120xc2x0 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.
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.
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 second resting radius. In the presently preferred embodiment according to this aspect of the invention, the second resting radius is about 80% of the first resting radius. Similarly, the outer edge of each of the openings preferably has a first operating radius when the axial gap motor-generator is at an operational speed, and the outer edge of each of the magnets has a second operating radius when the axial gap motor-generator is at the operational speed, wherein the first operational radius is substantially equal to the second operational radius.
Each of the magnets preferably is shaped relative to the corresponding one of the openings so that, when inserted into the corresponding one of the openings, the outer edge of the magnet and the outer edge of the corresponding one of the openings form an outer edge gap. In embodiments including the inner and side edges, the inner edge of the magnet and the inner edge of the opening form an inner edge gap, and each of the side edges of the magnet and the side edges of the corresponding one of the openings form a side edge gap.
Preferably, the axial gap motor-generator has an operational speed or operational speed range, and the outer edge of each of the magnets is dimensioned to conform or substantially conform to the outer edge of the corresponding one of the openings when the axial gap motor-generator is operated at the operational speed and the outer edge of the corresponding one of the openings is thereby deformed. In the preferred embodiment, a bonding material is disposed in a portion of the side edge gaps, but preferably is excluded from the inner and outer edge gaps.
The axial gap motor-generator preferably also includes a backiron assembly coupled to the rotor and rotatably mounted about the axis. The backiron assembly includes an attachment device rotatably disposed about the axis, and first and second couplers coupled to the attachment device. The first coupler is positioned on the first side of the rotor and the second coupler is positioned on the second side of the rotor. The backiron assembly also preferably includes first and second backiron plates disposed adjacent to but spaced from the windings of the stator assembly. The first backiron plate is coupled to the first coupler and is positioned on the first side of the rotor. The second backiron plate similarly is coupled to the second coupler and is positioned on the second side of the rotor. Each of the first and second couplers preferably comprises an annular tube. In the preferred embodiment, the attachment device is coupled to the rotor body. It may be threadably engaged with the rotor body.
In the preferred embodiment, the first rotor side is disposed in a first rotor plane and the second rotor side is disposed in a second rotor plane substantially parallel to the first rotor plane. In that embodiment, the first backiron plate is disposed in a first backiron plane and the second backiron plate is disposed in a second backiron plane. Preferably, the first and second backiron plates are disposed with respect to the first and second rotor planes when the rotor is at rest so that the first backiron plane is substantially parallel to the first rotor plane and the second backiron plane is substantially parallel to the second rotor plane when the axial gap motor is operated at the operational speed. Similarly, the first backiron plate preferably is disposed with respect to the first rotor plane when the rotor is at rest so that the first backiron plane forms an angle of about 1 to 3 degrees, and preferably about 2 degrees, with respect to the first rotor plane.
In like manner, in the preferred embodiment, the second rotor side is disposed in a second rotor plane; and the second backiron plate is disposed in a second backiron plane. In this embodiment, the second backiron plate is disposed with respect to the second rotor plane when the rotor is at rest so that the second backiron plane forms an angle of about 1 to 3 degrees, and preferably about 2 degrees, with respect to the second rotor plane. The first and second backiron plates preferably have a conical inclination toward the rotor.
In accordance with another aspect of the invention, an axial gap motor-generator is provided of the type coupled to a shaft having an axis of rotation. The motor-generator according to this aspect of the invention comprises magnetic field generating means for generating a magnetic field. The magnetic field generating means includes a force bearing means for bearing stress on the magnetic field generating means created when the axial gap motor-generator is operated at an operational speed. The motor-generator also includes rotor means for rotatably supporting the magnetic field generating means about the axis of rotation. The rotor means includes means for securing the magnetic field generating means to the rotor. The securing means includes means for conforming to the force bearing means when the axial gap motor-generator is operated at the operational speed. The motor-generator also includes stator means positioned adjacent to the magnetic field generating means for interacting with the magnetic field to generate an electric voltage.
Preferably but optionally, the rotor means further includes coupling means for coupling the rotor means to the shaft. The securing means preferably comprises means for bonding the magnetic field generating means to the rotor means. The bonding means preferably is excluded from the force bearing means.
The rotor means also preferably includes means for concentrating the magnetic field toward the stator means. The concentrating means includes means for aligning the concentrating means with the rotor means when the axial gap motor-generator is operated at the operational speed.
In accordance with another aspect of the invention, a rotor is provided for use in an axial gap motor-generator of the type coupled to a shaft having an axis of rotation. The rotor comprises a rotor body having an outer region. The rotor also 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 rotor 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 outer edge, the inner 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 openings. In embodiments including the inner edges and side edges, the inner edge of the magnets generally conforms to but is slightly smaller than the inner edge of the corresponding one of the openings, and the pair of side edges of the magnets generally conform to but are slightly smaller than the pair of side edges of the openings. Each of the magnets is shaped to be inserted into the corresponding one of the openings.
Preferably but optionally, the rotor further comprises an expandable hub for coupling the rotor to the shaft.
In the preferred embodiment of-the rotor according to this aspect of the invention, the outer edge of each of the openings has a first resting radius when the rotor is at rest. The outer edge of each of the magnets has a second resting radius when the rotor is at rest, wherein the first resting radius is larger than the second resting radius. The second resting radius in accordance with the preferred embodiments herein described is about 80% of the first resting radius.
The outer edge of each of the openings in the rotor preferably has a first operational radius when the rotor is at an operational speed. The outer edge of each of the magnets preferably has a second operational radius when the rotor is at the operational speed, wherein the first operational radius is substantially equal to the second operational radius.
Preferably, each of the magnets is shaped relative to the corresponding one of the openings so that, when inserted into the corresponding one of the openings, for embodiments including the inner and side edges, the inner edge of the magnet and the inner edge of the opening form an inner edge gap, each of the side edges of the magnet and the side edges of the corresponding one of the openings form a side edge gap, and the outer edge of the magnet and the outer edge of the corresponding one of the openings form an outer edge gap.
The rotor, like the motor-generator, has an operational speed or operational speed range. Preferably, the outer edge of each of the magnets is dimensioned to conform to the outer edge of the corresponding one of the openings when the rotor is operated at the operational speed and the outer edge of the corresponding one of the openings is thereby deformed.
In the preferred rotor, a bonding material is disposed in a portion of the side edge gaps. The bonding material preferably is excluded from the outer edge gap, and more preferably is excluded from the inner and outer edge gaps.
The rotor preferably includes a backiron assembly comprising an attachment device coupled to the rotor body and rotatably disposed about the axis, and first and second couplers coupled to the attachment collar. The first coupler is positioned on the first side of the rotor and the second coupler is positioned on the second side of the rotor. The backiron assembly further includes a first backiron plate coupled to the first coupler and positioned on the first side of the rotor, and a second backiron plate coupled to the second coupler and positioned on the second side of the rotor. Preferably, each of the first and second couplers comprises an annular tube. The attachment device preferably is coupled to the rotor body. Again, preferably, the attachment device is threadably engaged with the rotor body.
In the preferred embodiment, the first rotor side is disposed in a first rotor plane and the second rotor side is disposed in a second rotor plane substantially parallel to the first rotor plane. In this embodiment, the first backiron plate is disposed in a first backiron plane and the second backiron plate is disposed in a second backiron plane. The first and second backiron plates are disposed with respect to the first and second rotor planes when the rotor is at rest so that the first backiron plane is substantially parallel to the first rotor plane and the second backiron plane is substantially parallel to the second rotor plane when the rotor is operated at the operational speed.
Preferably, the first backiron plate is disposed in a first backiron plane, and the first backiron plate is disposed with respect to the first rotor plane when the rotor is at rest so that the first backiron plane forms an angle of about 1 to 3 degrees, and more preferably about 2 degrees, with respect to the first rotor plane. Similarly, preferably the second rotor side is disposed in a second rotor plane, the second backiron plate is disposed in a second backiron plane, and the second backiron plate is disposed with respect to the second rotor plane when the rotor is at rest so that the second backiron plane forms an angle of about 1 to 3 degrees, and more preferably about 2 degrees, with respect to the second rotor plane.
In accordance with another aspect of the invention, a rotor is provided for use in an axial gap motor-generator of the type coupled to a shaft having an axis of rotation. The rotor according to this aspect of the invention comprises magnetic field generating means for generating a magnetic field. The magnetic field generating means includes a force bearing means for bearing stress on the magnetic field generating means created when the axial gap motor-generator is operated at an operational speed. The rotor also includes means for securing the magnetic field generating means to the rotor. The securing means includes means for conforming to the force bearing means when the axial gap motor-generator is operated at the operational speed.
Preferably, the rotor includes coupling means for coupling the rotor to the shaft. The securing means preferably comprises means for bonding the magnetic field generating means to the rotor means. Preferably, where a bonding means is used, it is excluded from the force bearing means. The rotor preferably also includes means for concentrating the magnetic field toward the stator means. The concentrating means includes means for aligning the concentrating means with the rotor means when the axial gap motor-generator is operated at the operational speed.
In accordance with another aspect of the invention, a magnet is provided for use in a rotor of an axial gap motor-generator of a type coupled to a shaft having an axis of rotation. The rotor includes a plurality of openings, each of the openings including an outer edge. The magnet according to this aspect of the invention comprises an outer edge corresponding to the outer edge of a corresponding one of the openings. The outer edge of the magnet generally is non-conformal to and is slightly smaller than the outer edge of the openings. The magnet is shaped to be inserted into and to substantially conform to a corresponding one of the openings. The magnet is shaped relative to the corresponding one of the openings so that, when inserted into the corresponding one of the openings, the outer edge of the magnet is non-conformal with the outer edge of the opening when the rotor is in a rest state, and the outer edge of the magnet is conformal with or substantially conformal with the outer edge of the opening when the rotor is in an operational state.
In accordance with another aspect of the invention, a backiron assembly is provided for use in an axial gap motor-generator of a type coupled to a shaft having an axis of rotation and having a rotor with first and second sides. The backiron assembly comprises an attachment device disposed about a backiron assembly axis corresponding to the axis of rotation. The backiron assembly also includes first and second couplers coupled to the attachment device. The first coupler is positioned on the first side of the rotor and the second coupler is positioned on the second side of the rotor when the backiron assembly is operated with the rotor. The backiron assembly further includes first and second backiron plates coupled to the first and second couplers respectively and are positioned on the first and second sides respectively of the rotor when the backiron assembly is operated with the rotor.
Each of the first and second couplers preferably comprises an annular tube. In the preferred embodiment according to this aspect of the invention, the attachment device is threaded for engagement with the rotor.
The backiron assembly is designed to operate at an operational speed. In the preferred embodiment, the first rotor side is disposed in a first rotor plane and the second rotor side is disposed in a second rotor plane substantially parallel to the first rotor plane. In this embodiment, the first backiron plate is disposed in a first backiron plane and the second backiron plate is disposed in a second backiron plane, and the first and second backiron plates is disposed with respect to the first and second rotor planes when the backiron assembly is operated with the rotor and the rotor is at rest so that the first backiron plane is substantially parallel to the first rotor plane and the second backiron plane is substantially parallel to the second rotor plane when the backiron assembly is operated at the operational speed.
Preferably, the first backiron plate is disposed in a first backiron plane, and the first backiron plate is disposed with respect to the first rotor plane when the backiron assembly is operated with the rotor and the rotor is at rest so that the first backiron plane forms an angle of about 1 to 3 degrees, and more preferably about 2 degrees, with respect to the first rotor plane. Similarly, the second backiron plate is disposed in a second backiron plane, and the second backiron plate is disposed with respect to the second rotor plane when the backiron assembly is operated with the rotor and the rotor is at rest so that the second backiron plane forms an angle of about 1 to 3 degrees, and more preferably about 2 degrees, with respect to the second rotor plane. The first and second backiron plates preferably have a conical inclination toward the rotor when the backiron assembly is coupled to the rotor and the backiron assembly is at rest.
In accordance with another aspect of the invention, a backiron assembly is provided for use in an axial gap motor-generator of a type coupled to a shaft having an axis of rotation having a rotor with first and second sides and a stator assembly. The backiron assembly comprises attachment means disposed about a backiron assembly axis corresponding to the axis of rotation for attaching the backiron assembly to the rotor, first and second magnetic field concentrating means positioned on the first and second sides respectively of the rotor when the backiron assembly is operated with the rotor for concentrating a magnetic field from the rotor to the stator assembly, and first and second coupling means for coupling the respective first and second magnetic field concentrating means to the attachment means.
In accordance with another aspect of the invention, an apparatus is provided for coupling a shaft and bearing assembly to a housing. The apparatus comprises an inner sleeve for coupling to the shaft and bearing assembly. The inner sleeve has an exterior surface and a pair of longitudinal edges. Each of the longitudinal edges includes a plurality of stanchions. The apparatus also includes an outer sleeve for coupling to the housing. The outer sleeve has an interior surface and a pair of longitudinal edges. Each of the outer sleeve longitudinal edges includes a plurality of outer sleeve stanchions corresponding in number and location to the inner sleeve stanchions and thereby forming a plurality of stanchion pairs. The inner sleeve is disposed within the outer sleeve to form an annular cavity between the exterior surface of the inner sleeve and the interior surface of the outer sleeve. The apparatus further includes a vibration absorbing material disposed in the annular cavity. The vibration absorbing material may assume a variety of different forms, as disclosed in greater detail below. The apparatus also includes a plurality of couplers. Each of the couplers corresponds to one of the stanchion pairs. Each of the couplers couples the corresponding stanchion pair together. In the preferred embodiment according to this aspect of the invention, each of the couplers comprises a C flexure.
In accordance with another aspect of the invention, an apparatus is provided for coupling a shaft and bearing assembly to a housing. The apparatus comprises outer sleeve means for coupling to the housing, and inner sleeve means disposed annularly within the outer sleeve means for coupling to the shaft and bearing assembly. The outer and inner sleeve means form an annular gap. The annular gap comprises vibration absorbing means for absorbing vibrations between the outer and inner sleeve means. The outer and inner sleeve means include coupling means for coupling the outer and inner sleeves to one another. The coupling means comprises stanchion means and fastening means for fastening the stanchion means to one another.
In accordance with another aspect of the invention, a method is provided for securing a magnet in a rotor having an opening with an outer edge, wherein the outer edge of the opening has a deformed shape when the rotor is in an operational state. The method comprises providing the magnet with an outer edge corresponding to the outer edge of the opening and sized to fit within the opening, and shaping and dimensioning the outer edge of the magnet so that the outer edge of the magnet substantially conforms to the outer edge of the opening when the outer edge of the opening has the deformed shape. The method optionally but preferably includes excluding a bonding material from the outer edge of the magnet.
In accordance with yet another aspect of the invention, a method is provided for rotating a rotor about an axis of rotation. The method comprises providing the rotor with a rotor body having an outer region and a plurality of openings disposed in the outer region and spaced from one another. Each of the openings includes an outer edge.
The method also includes disposing a magnet into each of the openings. Each magnet includes an outer edge corresponding to the outer edge of the openings. The outer edge of the magnets generally is non-conformal to and is slightly smaller than the outer edge of the openings. Each of the magnets is shaped to be inserted into a corresponding one of the openings.
The method further includes rotating the rotor to an operational speed so that the outer edge of the openings deform to thereby conform to the shape of the outer edge of the magnets.
Preferably, the opening providing step of the method includes shaping the outer edge of each of the openings to conform to a first resting radius when the rotor is at rest, and the magnet providing step includes shaping the outer edge of each of the magnets to conform to a second resting radius when the rotor is at rest, wherein the first resting radius is smaller than the second resting radius. Preferably but optionally, the second resting radius is about 80% of the first resting radius. Also preferably but optionally, the opening providing step includes shaping the outer edge of each of the openings to conform to a first operational radius when the rotor is at an operational speed, and the magnet providing step includes shaping the outer edge of the magnets to conform to a second operational radius when the rotor is at the operational speed, wherein the first operational radius is substantially equal to the second operational radius.
In accordance with another aspect of the invention, a method is provided for rotating a rotor having first and second rotor sides and a backiron assembly having first and second backiron plates. The method comprises positioning the first and second backiron plates at an angle with respect to the respective first and second rotor sides when the rotor and backiron are at rest. Preferably, the angle is about 1 to 3 degrees, and more preferably about 2 degrees. Also preferably, the angle is selected so that the first and second backiron plates are substantially parallel with respect to the respective first and second rotor sides when the rotor and backiron plates are rotating at an operational speed.
In accordance with still another aspect of the invention, a system is provided for converting power. The system comprises a shaft assembly, a flywheel coupled to the shaft assembly (optionally a plurality of such flywheels, and preferably two), and an axial gap motor-generator coupled to a shaft having an axis of rotation. The motor-generator preferably comprises an axial gap motor-generator as described above.