Rotary power converter

A rotary power converter apparatus for coupling power between a prime driver and plural generators. The apparatus includes a frame having a first and second bearing aligned along an axis of rotation and a rotor assembly supported thereby. The rotor assembly includes a shaft fabricated from a light weight material that is rotatably supported along the axis of rotation by the first and second bearings. There is a prime-driver rotor assembly, that has a magnetic structure supported by a light weight non-magnetic alloy hub that is fixed to rotate with the shaft. There are also plural generator rotor assemblies, each having a permanent magnet structure supported by a light weight non magnetic alloy hub also fixed to rotate with the shaft. A prime driver stator assembly is fixedly supported by the frame and aligned concentric with the prime driver rotor assembly to enable magnetic coupling of power therewith. There are also plural generator stator assemblies fixedly supported by the frame, and each aligned concentric with one of the plural generator rotor assemblies to enable magnetic coupling of power therewith.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to motor-generator sets. More specifically, the present invention relates to rotary machines driven by electric motor prime drivers coupled through lightweight, low inertia, rotor assemblies to plural electric generators.

2. Description of the Related Art

Power conversion is useful for converting the power output from a prime driver to one or more driven devices, which may vary the nature of the converted power. In the case of electrical power, the motor-generator set is an example of a power converter. Input electrical power is converted to rotary mechanical power using an electric motor. The mechanical power is coupled to a generator, which converts mechanical power back to electrical power. The rotary power conversion process enables a range of power characteristics to be changed. Among these is voltage, amperage, direct versus alternating current, frequency, current flow, and so forth. Modern systems employ electrical power characteristics that are more varied than the historic direct current power and fixed voltage power distribution alternating current power, 60 Hz, for example. Systems today operate over a wide range of voltages and frequencies, and also employ non-linear electrical characteristics. Non-linear characteristics include pulsed power controllers, such as pulse wide, pulse period, pulse amplitude, and other non-sinusoidal waveforms. Solid state power converters exists as well, such as DC-to-DC converters and so forth.

Rotary power converters exhibit certain beneficial characterizes and limitations as well. A high degree of electrical isolation is possible due to the mechanical coupling of the converted power. The input and output characteristics of the converted power are very flexible, and power systems of mixed types can be coupled together. Issues related to mechanical efficiency affect overall performance, and traditional design philosophies limit system designs that have historically been employed. With advancements in electrical and electronic technology, rotary power converters have lagged behind emerging technology. Yet, the rotary power converter can solve problems heretofore addressed with other technologies. Thus there is a need in the art for an advanced rotary power converter that addresses modern demands for flexibility, efficiency and the integration of various power system characteristics.

SUMMARY OF THE INVENTION

The need in the art is addressed by the apparatus of the present invention. The present invention teaches a rotary power converter apparatus for coupling power between a prime driver and plural generators. The apparatus includes a frame having a first and second bearing aligned along an axis of rotation and a rotor assembly supported thereby. The rotor assembly includes a shaft fabricated from a light weight material that is rotatably supported along the axis of rotation by the first and second bearings. There is a prime-driver rotor assembly, that has a magnetic structure supported by a light weight non-magnetic alloy hub that is fixed to rotate with the shaft. There are also plural generator rotor assemblies, each having a permanent magnet structure supported by a light weight non magnetic alloy hub also fixed to rotate with the shaft. A prime driver stator assembly is fixedly supported by the frame and aligned concentric with the prime driver rotor assembly to enable magnetic coupling of power therewith. There are also plural generator stator assemblies fixedly supported by the frame, and each aligned concentric with one of the plural generator rotor assemblies to enable magnetic coupling of power therewith.

In a specific embodiment of the foregoing apparatus, the shaft is fabricated from a material selected from aluminum, aluminum alloy, type 6061-T6 aluminum alloy, graphite, graphite alloy, ceramic, nanotube reinforced polymers, and carbon composites. In another embodiment, the first and second bearing are graphite alloy bearings. In another embodiment, the graphite alloy is Graphalloy brand graphite and metal alloy formed from molten metal, graphite and carbon.

In a specific embodiment of the foregoing apparatus, the prime-driver rotor magnetic structure is a multi-pole permanent magnet. In a refinement, the permanent magnet is a Neodymium-Iron-Boron rare-earth magnet. In another embodiment, the permanent magnet is encased with a circumferential reinforcing band about the outer periphery. In another embodiment, the prime-driver rotor magnetic structure is a magnetic induction structure.

In a specific embodiment of the foregoing apparatus, the rotor assembly alloy hubs are crossed drilled to reduce weight. In another embodiment, the rotor assembly alloy hubs are fabricated from a material selected from aluminum, aluminum alloy, type 6061-T6 aluminum alloy, graphite, graphite alloy, ceramic, nanotube reinforced polymers, and carbon composites.

In a specific embodiment of the foregoing apparatus, the prime driver stator assembly is a multi-pole electromagnet assembly wound upon a laminate magnetic material core. In another embodiment, the plural generator stator assemblies are multi-pole electromagnets assemblies wound upon laminate magnetic material cores. In another embodiment, the prime driver and generator stators are multi-pole electromagnets, and the number of poles in the plural generator stator assemblies is greater than the number of poles in the prime driver stator assembly.

In a specific embodiment of the foregoing apparatus, plural isolation plates are interspersed between the prime driver stator assembly and the plural generator stator assemblies. In a specific embodiment, the plural isolation plates are lightweight thermally and electrically conductive plates effective at isolating electrical and radio frequency energy. The plural isolation plates may be CoolPoly brand isolation plates.

In a specific embodiment of the foregoing apparatus, the number of the plural generator rotor assemblies and the number of the plural generator stator assemblies is greater than three. In another embodiment, the prime-driver rotor assembly and the prime driver stator assembly are configured as a multi-pole brushless DC motor, the apparatus further includes a pulse width modulated DC servo drive coupled to energize the multi-pole brushless DC motor. In another specific embodiment, the outputs of the plural generator stator assemblies are combined in parallel or series to sum the power output therefrom. In a refinement to the foregoing apparatus, a portion of the power output from the plural generator stator assemblies is fed back to the prime driver stator assembly.

DESCRIPTION OF THE INVENTION

While the present invention is described herein with reference to illustrative embodiments for particular applications, it should be understood that the invention is not limited thereto. Those having ordinary skill in the art and access to the teachings provided herein will recognize additional modifications, applications, and embodiments within the scope hereof, and additional fields in which the present invention would be of significant utility.

The present invention overcomes the problems in the prior art through teachings directed to an advanced rotary power converter that addresses modern demands for flexibility, efficiency and the integration of various power system characteristics in a compact, lightweight and power efficient apparatus. An illustrative embodiment of the invention is comprised of set of three or more permanent magnet rotors disposed upon a lightweight shaft supported by two or more bearings. Each rotor is supported on a lightweight, non magnetic hub and rotates within a stator having a wire wound iron laminate core, and each is configured to function as either a motor or a generator. The apparatus provides increased efficiency of the motor-generator energy transfer and the coupling of plural generators to a single prime driver along a single drive shaft.

The drive shaft and rotor hubs in the illustrative embodiment are fabricated from aluminum alloy to minimize weight and inertia of the rotating structure. In addition, excess material is removed from the hubs to minimize rotational mass. Two bearings rotatably support the drive shaft along a horizontal axis, however, additional bearings can be added to stabilize the rotating structure at speed and under load. The bearings are fabricated from a commercial material called “Graphalloy”, which is a graphite/metal alloy that is formed from molten metal, graphite and carbon. Graphalloy is a uniform, solid, self-lubricating, bushing and bearing material. Graphalloy yields a low coefficient of friction, thereby minimizing resistance to the rotation of the drive shaft and rotor assembly. The bearings and drive shaft are supported above a base plate by two bearing mounts.

Each of the rotors is a permanent magnet rotor that is coupled to the drive shaft by a hub that is fabricated from type 6061-T6 aluminum alloy and cross drilled to remove unnecessary material, thereby minimizing weight and inertia of the rotating structure. The rotor magnets are all phenolic-coated high-gauss (rated at 50M and RIE 1100) Neodymium-Iron-Boron rare-earth magnets (hereinafter “NdFeB”). The magnets are cemented together to form a two inch diameter rotor, which is then bound by a type303stainless steel circumferential band. The arrangement and polarization of the magnets presents eight or sixteen poles along the circumference of each rotor. The motor rotor is configured with eight poles and the generator rotors are configured with sixteen poles each. The decreased number of poles in the prime driver, motor, produces a higher shaft velocity during operation. The illustrative embodiment employs one motor and four generators, however, the scope of the present invention contemplates a six generator structure and even an undetermined plural number of generators can be mounted along the single drive shaft.

The motor and generator stators in the illustrative embodiment are independently supported from a base plate, and each is centered on one of aforementioned rotors. Other types of support structures, housings and integrated machines which are known to those skilled in the art are equally applicable to the teachings herein. Each stator is fabricated from iron laminates stamped with the appropriate number of magnetic poles and wound in a three-phase sequence. The motor stator is wound with twelve poles and the generator stator is wound with twenty-four poles. The inside diameter of the laminate cores/poles is 2.245″, allowing clearance for the 2.015″ outside diameter rotors. The motor stator includes three Hall-effect sensors positioned to detect rotation for feedback to a prime drive controller.

The motor is disposed near the center of the drive shaft and the generators are positioned on either side thereof. Although other arrangements are possible and fall within the scope of the present invention. An isolating plate is disposed between the motor and each of the generators. In the illustrative embodiment, a “Coolpoly” brand polymer plate is positioned to isolate electrical and radio frequency energy from coupling between the motor and generator stages of the system. Coolpoly is a lightweight polymer that is thermally and electrically conductive. The main drive shaft of the prototype has sufficient length to support the requisite number of generators. Coolpoly is available from Cool Polymers, Inc., located in Warwick, R.I.

In the illustrative embodiment, the prime driver is a brushless direct current motor with a stator wound with a three-sequence progressive phase arrangement, and a permanent magnet rotor. The motor is driven by a three-phase pulse width modulated DC servo drive, which is a variable speed drive that gathers feedback from the three Hall effect sensors. In the illustrative embodiment, an Advanced Motion Controls, of Camarillo Calif., model B25A20AC servo controller is employed. However, any suitable motor drive could be employed in the invention, including simple connection to AC power mains using an AC induction motor as the prime driver of the system, or other electromechanical rotational machines that are known to those skilled in the art. The DC servo motor drive is powered from 120 Vac nominal wall outlet power in the illustrative embodiment.

The advancements in the art provided through the teachings of the present invention are applicable to a wide variety of motor-generator rotary power converter system arrangements. The bearings, shaft and rotor hubs are fabricated from very lightweight alloys, polymers, graphite, and other high strength and lightweight materials. Non-magnetic materials are used to enhance lightweight characteristics, which is contrary to conventional use of ferrites and other magnetically permeable materials. The lightweight rotor assembly enables operation of the apparatus at much higher rotational velocities than are conventionally applied. A circumferential reinforcing band is provided about the rotor magnets to enable them to withstand higher centrifugal forces. A single prime drive is coupled to plural generators through a single, solid, drive shaft that is supported on low friction bearings. The apparatus of the present invention is widely sealable from huge machines capable of converting tens of megawatts to “nano” sized devices that can be incorporated into man-portable appliances. The outputs of the plural generators can be wound for varying voltages and currents, including AC, DC, and non-linear waveforms, which can be integrated in series, parallel of other combinations, as are known to those skilled in the art Battery reserve power can be integrated into the system to sustain operation when mains power is unavailable, and the batteries can be charged by one or more of the plural generators in a feedback configuration. The advantageous aspects of the apparatus of the present invention are realized through the use of lightweight rotor components and low friction assemblies with multiple rotor-stator assemblies driven on a single shaft. This approach enables multiple generator sets to be simultaneously driven by a single prime driver, with low inertia characteristics advantageously employed to allow compact proportions, high-speed operation with rapid acceleration. Multiple outputs can be independently configured to the requisite voltage and phase characteristics.

Reference is directed toFIG. 1andFIG. 2, which are a side view and top view drawing, respectively, of motor-generator rotary power converter2according to an illustrative embodiment of the present invention. The illustrative embodiment is shown in prototype form, and therefore employs an open frame structure built-up from a base plate4. A pair of bearing mounts6support a pair of rotary bearings8along an axis of rotation of a drive shaft10. The base plate4and bearing mounts6are fabricated from lightweight aluminum alloy, which also exhibit excellent heat conduction characteristics. The bearings8are Graphalloy brand graphite alloy bearings that exhibit very low friction and excellent thermal characteristics. The bearings8are supported by the bearing mounts6, which in turn, rotationally support the drive shaft10. Five rotor-stator assemblies12,14,16,18,20are disposed along the length of drive shaft10. Rotor-stator assembly16is the prime driver of the shaft10, and, rotor-stator assemblies12,14,18,20are configured as permanent magnet generators. Because of the intense electrical and magnetic fields associated with operation of the rotor-stator assemblies, the present inventions employs isolation assemblies22,24,26,28disposed between each pair of adjacent rotor-stator assemblies12,14,1618,20. The rotor-stator assemblies and isolation assemblies will be more fully descried hereinafter.

Reference is directed toFIG. 3,FIG. 4, andFIG. 5, which are an end view, side view, and top view drawing, respectively of the prime driver rotor-stator assembly16according to an illustrative embodiment of the present invention.FIG. 3ais an end view detail of the rotor assembly42used in the rotor-stator assembly16. The prime driver16is configured as an eight-pole brushless DC motor that employs a three-phase, twelve-pole stator in the illustrative embodiment. The stator consists of a laminated iron magnetic core34that is stamped for twelve electromagnetic poles35. The poles35are energized with ‘A’, ‘B’, and ‘C’ phase windings36,38,40that are wound about the poles35in a repeating sequence. The iron laminate core34is supported above the base plate4by stator support30, which is fabricated from lightweight aluminum alloy in the illustrative embodiment. The stator support30is attached to the base plate4using threaded fasteners32. The rotor assembly42is rotatably supported within the stator core34by the drive shaft10. Three Hall effect sensors37,39,41are positioned in alignment with the three phases for providing feedback to a DC servo drive controller as to the position and velocity of the rotor during operation.

FIG. 3ais a detailed side view of the rotor assembly42. An aluminum rotor hub44is attached to drive shaft10and supports the eight rotor magnets48. The rotor magnets48are cemented together and to the rotor hub44. In addition, a circumferential band50holds the plural magnets48against centrifugal force during high-speed operation. The band50is fabricated from type303stainless steel in the illustrative embodiment, however other suitable high strength materials can be employed, as will be appreciated by those skilled in the art. In the illustrative embodiment, the shaft10and hub44are fabricated from type 6061-T6 aluminum alloy and are cross drilled with plural holes46to reduce mass. Other lightweight and non-magnetic materials are contemplated as well, including aluminum, aluminum alloys, graphite, graphite alloy, ceramic, nanotube reinforced polymers, and carbon composites, and other similar materials known to those skilled in the art. The rotor hub44is effective at conducting heat away form from the rotor stator assembly16during operation. The hub44may be attached to the shaft10using a key-set, splined, compression, set-screw, cement, or other means as are known to those skilled in the art.

Reference is directed toFIG. 6,FIG. 7, andFIG. 8, which are an end view, side view, and top view drawing, respectively of the generator rotor-stator assemblies12,14,18,20according to an illustrative embodiment of the present invention.FIG. 6ais an end view detail of the rotor assembly66used in the generator assemblies. The generators12,14,18,20are configured as sixteen pole three-phase permanent magnet generators that employ a three-phase, twenty-four pole stator in the illustrative embodiment. The stator consists of a laminated iron magnetic core56that is stamped for twenty-four electromagnetic poles58. The poles58are energized with ‘A’, ‘B’, and ‘C’ phase windings60,62,64that are wound about the poles58in a repeating sequence. The iron laminate core56is supported above the base plate4by stator support52, which is fabricated from lightweight aluminum alloy in the illustrative embodiment. The stator support52is attached to the base plate4using threaded fasteners54. The rotor assembly66is rotatably supported within the stator core56by the drive shaft10.

FIG. 6ais a detailed side view of the rotor assembly66. An aluminum rotor hub68is attached to drive shaft10and supports the sixteen rotor magnets72. The rotor magnets72are cemented together and to the rotor hub68. In addition, a circumferential band71holds the plural magnets72against centrifugal force during high-speed operation. The band71is fabricated from type303stainless steel in the illustrative embodiment, however other suitable high strength materials can be employed, as will be appreciated by those skilled in the art. In the illustrative embodiment, the shaft10and hub68are fabricated from type 6061-T6 aluminum alloy and are cross drilled with plural holes70to reduce mass. Other lightweight and non-magnetic materials are contemplated as well, including aluminum, aluminum alloys, graphite, graphite alloy, ceramic, nanotube reinforced polymers, and carbon composites, and other similar materials known to those skilled in the art. The rotor hub68is effective at conducting heat away form the rotor stator assemblies12,14,18,20during operation. The hub68may be attached to the shaft10using a key-set, spline, compression, set-screw, cement, or other means as are known to those skilled in the art.

Reference is directed toFIG. 9,FIG. 10, andFIG. 11, which are an end view, side view and top view drawing, respectively, of the isolation assemblies22,24,26,28according to the illustrative embodiment of the present invention. Isolation is achieved using a CoolPoly plate74, described hereinbefore. The plate74is sized to cover the stator windings. The plate74may be re-shaped76to suite the physical requirement of the apparatus housing, etc. In the illustrative embodiment, the plate74is attached to an isolation support78. The isolation plate74has a hole80formed therein to clear the shaft10and other components of the apparatus. The isolation plate support78is attached to the base plate4using threaded fasteners84. In the illustrative embodiment, the isolation plate support78is fabricated from type 6061 T6 aluminum alloy. In the illustrative embodiment, each of the isolation plate supports78also serves as an intermediate bearing support. Thus, an intermediate Graphalloy bearing82is supported by each isolation plate support78. The additional bearings82serve to stabilize the drive shaft10during high speed and high torque operation of the power converter.

Reference is directed toFIG. 12, which is a functional diagram of a rotary power converter according to an illustrative embodiment of the present invention.FIG. 12is a generalized view of a power converter according to the teachings of the present invention. The drive shaft95is forced to rotate by a prime driver rotor100, which is magnetically driven by a prime drive stator winding92. The stator winding92is powered be a prime driver power supply90. Virtually any electromotive rotor-stator technology known to those skilled in the art is applicable to the teachings of the present invention. The rotor100may be of the permanent magnet variety or may be an induced magnetism type of rotor, such as are used in alternating current induction motors, including squirrel cage motors. The shaft95urges the rotation of plural generator rotors96,98,102,104. Each of these rotors is magnetically coupled to a corresponding stator coil106,108,110,112. Each of these stator coils is electrically coupled to a corresponding load114,116,118,120. The lightweight characteristics of the shaft and rotors, through the use of non-magnetic materials enables high speed operation, low rotational moment, and quick acceleration and adaptation to varying loads. The present invention contemplates the use of a wide range of stator technologies known to those skilled in the art including HTS stators, Meschcon stators, E-Cycle Stators, and Thingap stators. Both magnetic core and coreless stators may be employed.

Reference is directed toFIG. 13, which is a functional diagram of a rotary power converter using three-phase stator assemblies according to an illustrative embodiment of the present invention.FIG. 13generally corresponds to the earlier described illustrative embodiment, with the addition of components to enable direct current loads. The shaft125is driven by a prime driver rotor-stator130. The rotor-stator used three-phase windings with corresponding Hall effect sensors132. All of these elements are coupled to an Advanced Motion Controls model B25A20AC Series Brushless Servo Amplifier124. The servo-amp124is supplied by AC power from the mains power supply122. The servo amp124enables variable speed drive of the prime driver130under synchronous operation by virtue of the Hall effect sensors132angular position feedback. Hall effect sensors are an illustrative application, other position sensing technologies can be employed as well, including optical-detectors and other sensors known to those skilled in the art. The shaft125couples power to the plural generators126,128,134,136, which are labeled “GEN A”, “GEN B”, “GEN C”, and “GEN D”, respectively. Each generator is a three-phase AC permanent magnet generator. Three phase bridge rectifiers138,140,142,144are coupled to the respective generators, and provide direct current to the corresponding loads. The loads146,148,150,152are labeled “LOAD A”, “LOAD B”, “LOAD C”, and “LOAD D”, corresponding to the generator names. Any type of DC load can be driven by the system.

Reference is directed toFIG. 14, which is a functional diagram of a rotary power converter using power integration and feedback according to an illustrative embodiment of the present invention.FIG. 12is a generalized view of a three-phase power converter according to an illustrative embodiment of the present invention. The drive shaft171is forced to rotate by a prime driver rotor166, which is magnetically driven by prime drive stator windings164. The stator windings164are powered be a prime driver power supply156. The shaft171urges the rotation of plural generator rotors160,162,168,170. Each of these rotors is magnetically coupled to a corresponding stator coil172,174,175,178. Each of these stator coils is electrically coupled to a load182through a power integration circuit180. The power integration circuit180combines the power output from the generators to drive the load182and to feedback power to the driver power supply156. A power reserve158is tapped to the feedback line and enables interruption of mains power supply154. The power reserve may be a storage battery bank, a capacitor bank, an inductor bank, and inertia storage device, or other electric power storage means that is known to those skilled in the art.

Reference is directed toFIG. 15, which is a functional diagram of a rotary power converter using power rectification and feedback according to an illustrative embodiment of the present invention.FIG. 15generally corresponds to the earlier described illustrative embodiment, with the addition of components to isolate the load and to switch the mains power and battery reserve power. The shaft195is driven by a prime driver rotor-stator198. The rotor-stator used three-phase windings with corresponding Hall effect sensors200. All of these elements are coupled to an Advanced Motion Controls model B25A20AC Series Brushless Servo Amplifier186. The servo-amp186is supplied by AC power from the mains power supply184though a power switch185. The servo amp186enables variable speed drive of the prime driver198under synchronous operation by virtue of the Hall effect sensors200angular position feedback. The shaft195couples power to the plural generators194,195,202,204, which are labeled “GEN A”, “GEN B”, “GEN C”, and “GEN D”, respectively. Each generator is a three-phase AC permanent magnet generator. Three phase bridge rectifiers206,208,210,212are coupled to the respective generators, and provide direct current output. Isolation rectifiers214,216,28,220prevent power feedback between the other components to avoid power loss through motoring of the generators. The four outputs are combined and coupled to the direct current load222. Any type of DC load can be driven by the system. A portion of the output power is fed back to the servo drive186. Reserve battery188is coupled via switch190to the feedback loop, thereby enabling battery reserve operation when mains power or sufficient feedback power is unavailable.

Reference is directed to Figure, which16is a functional diagram of a rotary power converter300according to an illustrative embodiment of the present invention. The illustrative embodiment demonstrates a characteristic of the advancement in the art through utilization of low-mass, lightweight materials and low friction bearings, which is the use of a remarkable number or rotor-stator assemblies in a single converter apparatus. A single shaft302supports seven rotor-stator assemblies304,306,308,310,312,314,316. The central rotor stator assembly310is configured as a driver unit, which is driven by a driver power supply318. The remaining rotor stator assemblies are all configured as generators304,306,308,312,314,316. Each of these generators is coupled to a corresponding load320,322,324,326,328,330, respectively. Each of these generators and loads can be independently configured to provide a requisite power demand, including direct current at various voltages, alternative current at various voltages, various numbers of phases, and any other power configuration known to those skilled in the art.

Reference is directed toFIG. 17, which is a functional diagram of a rotary power converter350according to an illustrative embodiment of the present invention. The embodiment inFIG. 17takes the plural rotor-stator assembly aspect of the present invention to an even more flexible configuration, which is suitable for scaling to very compact proportions. A single drive shaft352rotatably supports nine rotor-stator assemblies354,356,358,360,362,364,366,368,370. The central rotor stator assembly362is configured as a driver unit, which is driven by a driver power supply372. The remaining rotor stator assemblies are all configured as generators354,356,358,360,364,366,368,370. Each of these generators is coupled to a corresponding load372,374,376,378,380,382,384,386, respectively. Each of these generators and loads can be independently configured to provide a requisite power demand.

Reference is directed toFIG. 18,FIG. 19, andFIG. 20, which are a side sectional view, end sectional view and end view, respectively, of a rotary power converter224according to an illustrative embodiment of the present invention. The embodiment shown is suitable for industrial application, and is exemplary of the many possible configurations achievable through utilization of the teachings herein. An industrial enclosure226has plural cooling fins228extending from the exterior thereof. The drive shaft238extends through the end wall of the enclosure226and drives a cooling fan230. A fan shroud232directs the cooling air from an inlet hole260in the fan shroud232and over the cooling fins228. The plural rotor-stator assemblies240,242,2444,246,248are in thermal contact with the interior of the housing226, and thereby conduct heat away from the rotor-stator assemblies during operation. Plural isolation plates252,254,256,258are disposed between the rotor-stator assemblies so as to provide the aforementioned isolation. A very space-efficient and compact apparatus is thereby achieved.

Thus, the present invention has been described herein with reference to particular embodiments for particular applications. Those having ordinary skill in the art and access to the present teachings will recognize additional modifications, applications and embodiments within the scope thereof.

It is therefore intended that the appended claims cover any and all such applications, modifications and embodiments within the scope of the present invention.