Patent Application
20120086213
The invention relates to electric power generators in general and, more particularly to electric power generators that include ferrofluid bearings to permit smooth rotation.
Electric power generators are well-established devices in which mechanical energy is converted to electrical energy through the magnetoelectric effect. Electric current flows through a conductor when magnetic flux changes, typically by moving the conductor through a magnetic field. Various sources of mechanical energy for the required motion are commonly used such as steam (generated by fossil or nuclear fuel), water, compressed air, and wind. Typical electric generators have a rotating part known as the rotor, and a stationary part known as the stator. The conductors are in the form of conductor coils/windings and may be positioned on either the rotor or the stator. Similarly, the magnets that provide the magnetic field (either permanent magnets or electromagnets) may be positioned on either the rotor or the stator.
Because the rotor rotates relative to the stator, electric generators, as with many machines having rotating parts, use bearings between the relatively rotating parts. However, conventional ball bearings have high rotational torque at low rotational speeds and lower rotational torque at high rotational speeds. Frictional heat is generated that can degrade lubricants used with the ball bearings as well as degrading the bearings themselves. Further, at high rotational speeds, ball bearings can vibrate which causes problems at close design tolerances.
Thus there is a need in the art for improved electric generators having improved bearings to ensure smooth operation over a long operating lifetime.
The present invention uses ferrofluid bearings in a variety of configurations to ensure smooth relative rotation between one or more stators and one or more rotors. The invention also uses ferrofluid bearings to center the rotor in order to maintain proper alignment between the rotor(s) and the stator(s).
In one embodiment, the electric generator includes first and second stators, each stator including plural magnets separated by a yoke of magnetizable materials. The magnets are configured such that the direction of magnetization alternates between adjacent magnets whereby magnetic flux is concentrated in the magnetizable materials. In one embodiment the magnetic flux is directed substantially perpendicular to the plane of the stator. A rotor configured to rotate in a horizontal plane is positioned between the stators. The rotor includes plural coils in which current is induced during rotation from passing through the magnetic fields generated by the stators.
A first set of ferrofluid bearings is positioned between the first stator and the rotor and a second set is positioned between the rotor and the second stator. A third set of ferrofluid bearings are positioned adjacent to the periphery of the rotor and configured to center the rotor. The rotor periphery can be the inner periphery or the outer periphery.
Alternatively, the magnets may be positioned on the rotor and the coils on the stator.
In one embodiment, the electric generator of the present invention is used with a wind collection apparatus to provide the mechanical energy required for electric power generation.
Turning to the drawings in detail,
Rotor 20 includes plural wire coils 22 in which current is induced during rotation from passing through the magnetic fields generated by the stators. The wire coils are embedded in a polymeric material 24 and, optionally, do not have a core to prevent formation of eddy currents. The rotor has a vertical axis and rotates in a horizontal plane in the various FIGS.
To enable relative motion between the rotor and the stators and to center the rotor, a variety of ferrofluid bearings are positioned in the electric generator 100. Ferrofluid bearings are based on ferrofluid materials. Ferrofluids are colloidal suspensions of magnetic or magnetizable particles such as iron oxide particles having a typical particle size between 30 and 150 angstroms. A surfactant (such as oleic acid, tetramethylammonium hydroxide, citric acid, and soy lecithin) adsorbs at one end to a particle and at the other end to a carrier fluid (typically a lubricant such as a synthetic hydrocarbon or a synthetic ester). This ensures separation of the particles even in the presence of a strong magnetic field. In the presence of a magnetic field, the ferrofluid moves to the region of highest magnetic flux and is contained in that region even in the case of high loads, thus bearings can be made from ferrofluids without the need for special containment seals.
Ferrofluid properties, such as viscosity and saturation magnetization, are determined by particle composition, particle size, particle concentration, and selection of the carrier fluid and the surfactant. For use in bearing applications, the higher the saturation magnetization, the greater the load that the ferrofluid bearing can support. For embodiments of the present invention, a saturation magnetization of approximately 50 mT to 60 mT is typically selected. To minimize sliding friction, a low viscosity carrier fluid is selected. For the embodiments of the present invention, typical viscosity values are less than 40 centipoise. Unlike mechanical bearings, ferrofluid bearing stiffness scales with rotation speed because of the hydrodynamic effect of the lubricant carrier liquid.
Ferrofluid materials are commercially available from Ferrotec Corporation (Nashua, N.H., USA).
Because ferrofluids move to the region of highest magnetic flux, as seen in
Depending upon the load-bearing requirements of the different sets of bearings 30, 40, and 50, the ferrofluid bearings are customized based on magnet 12 size and strength, magnetizable material 14 size, and selection of the components of the ferrofluid, as discussed above.
Depending on the volume of ferrofluid used, the ferrofluid bearings take on different configurations. For example, as seen in
As seen in
Although the embodiment of
A lightweight dielectric housing 90 holds electric generator 100 and also houses magnets 52 for side ferrofluid bearings 50 (best seen in
In one embodiment of the present invention, the electric generator 100 has mechanical energy imparted to it by wind force. To cause the rotor to rotate and generate electricity, wind drives fan blades 60 (
As seen in
In one embodiment, the electric generator of the present invention is housed in a wind collection apparatus. The wind collection apparatus is an omnidirectional wind collector which concentrates and accelerates wind from an inlet and sends the wind upward through fan blades 60 to cause rotation of the rotor. Further details of the wind collection apparatus are disclosed in co-pending, commonly-assigned U.S. patent application Ser. No. ______ (Attorney Docket No. P3452US00), filed concurrently with the present application and the disclosure of which is incorporated by reference herein. However, it is understood that the electric generator of the present invention can use other forms of mechanical energy to drive the rotor such as steam power and water power.
While the foregoing invention has been described with respect to various embodiments, such embodiments are not limiting. Numerous variations and modifications would be understood by those of ordinary skill in the art. Such variations and modifications are considered to be included within the scope of the following claims.
