Patent Application
20130154423
The present disclosure generally relates to an axial flux alternator, and more particularly to a flux augmentation ring that may enhance alternator efficiency at an efficient cost.
Axial flux alternators convert mechanical energy into electrical energy through the use of magnetic inductance principles. Mechanical energy, generated by a wind turbine for example, is transferred to an input shaft, which spins a rotor(s) containing an array of permanent magnets. Rotation of the magnets causes alternating magnetic fields to pass over coils of wire affixed to stators, thereby creating a voltage potential in the wire through magnetic inductance. The electricity generated by the axial flux alternator is then used by electronic devices or is stored for later use.
Axial flux alternators share some common limitations. Power efficiency is, in part, dependent upon the strength of magnetic flux fields contained therein. Many of these devices rely on a large number of magnets (often arranged on multiple rotors) to create strong magnetic flux fields to increase power efficiency. However, a significant increase in the cost of rare-earth magnets is quickly making these arrangements less cost efficient, especially for larger designs. Moreover, attractive forces between these magnets can create undesirable axial warping forces on magnet rotors. Additionally, many axial flux alternators experience cogging forces that limit low torque applications. Furthermore, designs using ferrous stator materials often experience eddy current back forces that result in energy loss through heat dissipation and magnetic drag on the rotors. Still further, some components of axial flux alternators may suffer from warping caused by electromagnetic forces generated between rotors and stators therein. Additionally, warping forces may be generated in designs that use only one side of magnets, often mounted on a ferritic substrate, to help vector more field strength in the direction of stator coils. Warping can become increasingly problematic as the diameter of the alternator increases. It can be costly to strengthen these components to resist warping forces.
The present disclosure is directed to an axial flux alternator that may comprise one or more rotors, each rotor comprising one or more magnets; one or more stators, each stator comprising one or more coils of electrically conductive material; one or more flux augmentation rings comprising a ferrous material; wherein the one or more rotors, one or more stators, and one or more flux augmentation rings may be arranged about a common axis with predetermined spacing between each; wherein the one or more magnets, one or more conductive coils, and at least a portion of the one or more flux augmentation rings may be arranged at a substantially similar radial distance from the common axis; and wherein the one or more rotors may be rotatable about the common axis.
In various embodiments, the one or more rotors may comprise non-ferrous materials. In an embodiment, the one or more magnets may be embedded within the one or more rotors. In another embodiment, the one or more magnets may be arranged in a pattern with alternating polarities on a given rotor.
In various embodiments, the one or more stators may comprise non-ferrous materials. In various embodiments, the one or more stators may comprise dielectric materials. In an embodiment, the dielectric materials may be arranged in multiple layers. In another embodiment, the one or more stators may comprise materials configured to reduce the build up of Lenz force therein.
In various embodiments, the one or more flux augmentation rings may comprise steel material. In an embodiment, a given flux augmentation ring may be rotationally coupled with an adjacent rotor.
In various embodiments, the one or more stators may comprise slots to facilitate winding of the coils. In an embodiment, adjacent slots may have necked regions arranged in alternating orientations. In another embodiment, the one or more coils may be wound about the slots in an over/under pattern configured to minimize warping forces on the one or more stators. In yet another embodiment, at least one of the one or more stators may comprise coils on opposite surfaces of the stator.
In an embodiment, at least one of the one or more stators may be disposed between a rotor and a flux augmentation ring. In another embodiment, axial flux alternator may have a 2:1 or greater ratio of magnets to coils.
In another aspect, the present disclosure is directed to an axial flux alternator that may comprise one or more flux augmentation rings comprising a ferrous material; one or more magnets configured to travel along a predetermined path, at least a portion of the path being offset from and aligned substantially parallel to at least a portion of the flux augmentation ring; one or more coils of electrically conductive material disposed between the flux augmentation ring and the predetermined path; wherein the flux augmentation ring may be configured to draw a magnetic flux field from the one or more magnets; and wherein as the one or more magnets travel along the predetermined path, the magnetic flux field crosses the one or more conductive coils thereby creating a voltage potential therein.
In various embodiments, the one or more magnets and correspondingly aligned portions of the one or more flux augmentation rings move together. In an embodiment, the movement of the one or more magnets and correspondingly aligned portions of the one or more flux augmentation rings substantially eliminates cogging.
In another aspect, the present disclosure is directed to an axial flux alternator that may comprise one or more rotors rotatable about an axis, each rotor comprising one or more magnets; one or more flux augmentation rings comprising a ferrous material, each flux augmentation ring being substantially centered about the axis and offset from an adjacent rotor; one or more stators centered about the axis, each stator being disposed between one of the one or more rotors and one of the one or more flux augmentation rings, each stator comprising one or more electrically conductive coils; wherein the one or more magnets, one or more conductive coils, and at least a portion of the one or more flux augmentation rings may be arranged at a substantially similar radial distance from the common axis; an input source that may be capable of transferring mechanical energy to the one or more rotors; and an output source that may be capable of receiving electrical energy from the one or more coils; wherein the input source may drive rotation of the one or more rotors, providing for magnetic fields spanning between the one or more magnets and the one or more flux augmentation rings to cross the one or more conductive coils, thereby generating electrical energy that is transferred to the output source.
In an embodiment, the one or more coils may be connected in series for single-phase power takeoff. In another embodiment, subsets of the one or more coils may be wired in series for multi-phase power takeoff.
For a more complete understanding of this disclosure, reference is now made to the following description, taken in conjunction with the accompanying drawings, in which:
Referring to
While rotors 20 may be made of any suitable material, they are preferably constructed of non-ferrous materials. Unlike ferrous rotors—which may pull magnetic flux radially from magnets 30, thereby inhibiting axial flux projection across stator coils 60—non-ferrous rotors would not. Additionally, rotors 20 may be made lighter by using non-ferrous materials. Other suitable materials for rotors 20 will be readily apparent to those skilled in the art. In one embodiment, rotors 20 may be fixedly connected to a shaft or similar structure 23 that is rotatable about central axis 21. Rotors 20 may be centered about central axis 21 and may be connected to a shaft 23 by flange 24 or any other suitable mechanism, including but not limited to friction, adhesive, welding, pins, or clamps. Shaft 23, and rotors 20 connected thereto, may be rotated by any mechanism, including but not limited to any device that extracts energy from its surroundings. Those of ordinary skill in the art will recognize that, in accordance with the present disclosure, rotors 20 may be fixedly connected to any alternative support structure using any mechanism so long as rotation of rotors 20 about central axis 21 may be achieved.
Rotor 20 may comprise one or more magnets 30. Magnets 30 may be any material capable of carrying a permanent magnetic charge. Magnets comprised of alloys of rare earth metals such as neodymium (NdFeB) and/or samarium cobalt (SmCo) are frequently used in the art, as are non rare earth permanent magnets such as those composed of ferrite. Other suitable magnetic materials will be readily apparent to those skilled in the art. Magnets 30 may be of any suitable shape and size, including but not limited to circular, rectangular, and wedge shapes. One or more magnets 30 may be mounted to each rotor 20, and may be distributed with substantially equal spacing and in a substantially symmetric pattern to maintain favorable balance as rotor 20 spins about central axis 21. In one embodiment, magnets 30 may be affixed to an outer surface of rotor 20. In another embodiment, magnets 30 may be embedded in rotors 20. Such a construction would allow both sides of magnets 30 to project substantially similar axial flux fields in opposite axial directions, thus enabling a single rotor 20 to project magnetic flux axially across stators 50 located on opposite sides of rotor 20. This embodiment has the added benefit of balancing both axial and radial loads on the rotor. Embedding magnets 20 may also avoid radial displacement of magnets 20 due to centrifugal forces by enabling the magnets 20 to be held in place by the tensile strength of the rotor material. Embedding magnets 20 also helps to balance magnetic forces pulling axially on each side of the rotor. A thin layer of adhesive and dielectric material, such as fiberglass, carbon fiber, aluminum, titanium, or other suitable non-conductive substance may cover the magnets 30. Circular patterns of magnets 30 may be used, but the present disclosure should be understood to encompass other suitable distributions.
Referring now to
Referring now to
Preferably, stators 50 may be made of any non-ferrous material. Stators 50 comprised of non-ferrous materials may avoid heat losses and rotational drag commonly associated with ferrous stator cores. Stators 50 made of ferrous material often experience eddy current back-force, or Lenz force, due to the buildup of opposing magnetic fields within the ferrous material. This back-force can lead to energy loss, both through heat dissipation and the drag on nearby rotors 20. In various embodiments, stators 50 are made of dielectric materials. In an embodiment, stators 50 comprise multiple thin layers of dielectric materials including, but not limited to glass-reinforced plastics, such as Garolite. Each may be insulated with a thin layer of dielectric material, such as varnish. An advantage of such a construction is that Lenz forces do not build up as much in thin layers. In another embodiment, stainless steel stator substrate, such as high-silicon steel or austenitic (non-magnetic) stainless steel, may be used. Other suitable materials for stators 50 will be readily apparent to those skilled in the art including, but not limited to wood, nylon, and ceramics. In one embodiment, stators 50 may extend from and/or be fixedly connected to an external housing by welding, mounting brackets, friction fit, or any other suitable attachment mechanism. One skilled in the art will recognize that the particular structure used to support the various components comprising axial flux alternator is not limited by the aforementioned embodiment. Any suitable support structure that allows for alignment and relative rotation of the various components of axial flux alternator 10 according to the present disclosure is recognized as being included herein.
Stators 50 may comprise one or more wire coils 60. Wire coils 60 may be used, in combination with the rotating magnetic fields created by rotors 20, to generate electrical energy. Due to the alternating radial arrangement of the magnet poles on rotor 20, the magnetic field flips each time a magnet 30 passes over a coil 60. The more rapidly the field flips, the more voltage is created. Coils 60 may include any type of conductive wire, such as copper, twisted into a series of concentric loops.
Coils 60 may be coupled with stator 50 in any suitable manner. Referring to
The number of coils 60 used in axial flux alternator 10 is a matter of design choice, as is the size, length, and gauge of the wire used for coils 60. For instance, various design constraints such as overall physical size of axial flux alternator 10 and the desired electrical output of axial flux alternator 10 may affect the number, size, length, and gauge of wire coils 60. Typically, the greater the number of loops contained in a coil 60, the more voltage may be captured. Higher gauge wire can typically carry more current than similar wire of a lower gauge; however, higher gauge wire also typically occupies additional space than similar wire of a lower gauge, thus potentially limiting the number of loops contained in a coil 60 of a given size.
Coils 60 may be formed of wire enshrouded by a non-conductive insulator. Any type of non-conductive insulator is suitable, but one embodiment may utilize thin non-conductive enamel that helps to insulate each loop in coil 60 from one another, but does not occupy the amount of space required by a traditional rubber insulator. One of skill in the art will recognize that a desired balance between wire gauge (∝ current) and number of loops (∝ voltage) may be selected depending on the application for which axial flux alternator 10 will be used. In one embodiment, coils 60 are of substantially similar dimensions, comprise substantially similar gauge wire and number of loops, and are arranged in substantially similar geometric patterns on each stator 50.
One of ordinary skill will further recognize that a desired ratio of magnets 30 to coils 60 used in axial flux alternator 10 may be selected based on several design factors, including but not limited to the desirability of phasing. Moreover, depending on the application, all coils 60 on a given stator 50 may be connected in series, effecting “single-phase” power-takeoff; or, subsets of coils 60 may be wired in series to effect “multi-phase” power-takeoff. In single-phase operation, power from all coils 60 is collected simultaneously. While this configuration has the advantage of simplicity, such phasing may yield a large pulse of power that may, in turn, result in vibrations. Unless mitigating measures are taken, these vibrations could potentially damage or decrease performance of axial flux alternator 10 and any turbine connected thereto. In multi-phase operation, coils 60 may be wired in series in smaller subgroups. While one subgroup produces peak power, the other two may be declining in power or at zero power. In this configuration, overall power take-off may be substantially equivalent to that of single-phase operation, large pulses may be avoided and smoother power collection may occur. In an embodiment, multi-phase operation may be achieved by running individual stators in single-phase power-takeoff. In various embodiments, axial flux alternator 10 may comprise two magnets 30 per coil 60, or greater. In an embodiment, axial flux alternator 10 may comprise a 4:1 ratio of magnets 30 per coil 60, or greater. In single-phase configurations, in an embodiment magnets 30 may align with opposite sides of each coil, thereby maximizing the flux sine wave. One of ordinary skill in the art will understand that design choices of this nature do not affect the scope of the present disclosure.
Axial flux alternators typically feature alternating arrangements of rotors and stators as shown in
Referring now to
Referring now to
Although the present disclosure and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the disclosure as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present disclosure. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.
This application claims priority to U.S. Provisional Patent Application No. 61/570,782, entitled AXIAL FLUX ALTERNATOR WITH ONE OR MORE FLUX AUGMENTATION RINGS, filed Dec. 14, 2011, which is hereby incorporated by reference for all purposes.
| Number | Date | Country | |
|---|---|---|---|
| 61570782 | Dec 2011 | US |
