The present invention relates to a free-piston linear generator (FPLG) in which a reciprocating piston is a magnet that transfers energy generated by combustion or steam to an induction coil or coils wrapped around the engine cylinder.
In free-piston engines, power is not delivered to a crankshaft but is instead extracted through either exhaust gas pressure driving a turbine, through driving a linear load such as an air compressor for pneumatic power, or by incorporating a linear alternator directly into the pistons to produce electrical power. Free-piston linear generators typically use chemical energy from fuel to drive magnets through a stator and convert this linear motion into electric energy.
Several attempts have been made to design and produce a free-piston linear generator powered by internal combustion, examples of which are disclosed in U.S. Pat. No. 2,362,151A, WO 2007/035102 A1, WO 2017/109203 A1, DE102011117404B4, CN111206989B, and CN110529245B. All of these, however, require substantial mechanical complexity and have limited compression ratios in the engine, thereby limiting thermal efficiency.
The present invention is directed to a free-piston linear generator wherein the piston is a magnet propelled into reciprocating motion inside a non-conducting cylinder around which is wrapped one or more induction coils. The magnet-piston may be propelled into motion using either internal combustion of a diesel aerosol in a two-stroke or 4-stroke configuration, with ignition provided by compression, or by steam pressure provided by an external boiler. Sensor-controlled exhaust, fuel-intake, and air-intake valves are located at either end of the cylinder, although only a single intake valve would be required in a steam version. As the magnet-piston moves in the cylinder, the power stroke on one side of the magnet-piston is the compression stroke on the other side. The movement of the magnet-piston induces an electric current in the induction coil, by which energy is drawn from the engine as useful work. The flow of current through the coil is monitored by an ammeter, and the valves are actuated when the sinusoidal current flow approaches zero, which correlates with the end of travel of the magnet-piston. Sensor-controlled oil-injection ports are located at the center of the cylinder and are actuated when the current flow is at its maximum, which correlates with when the magnet piston is at the midpoint of the cylinder. Oil is thereby injected to lubricate the travel of the magnet-piston while minimizing the admixture of lubricating oil into the fuel-air mix during compression.
In accordance with an example of the present invention, a free piston linear induction generator comprises a first generator unit having at least one cylinder having an interior space and first and second ends, left and right end caps secured to the cylinder at the first and second ends, respectively, a single piston formed of a magnetic material disposed within the interior space of the cylinder, the piston dividing the interior space into a left interior space to the left of the piston, and a right interior space to the right of the piston, at least one conductive coil wound around the cylinder, input and exhaust valves on each of the left and right end caps, the valves controlled by a control unit, and an ammeter connected to the at least one conductive coil, the ammeter producing a current output indicative of a location of the piston within the cylinder, the valves controlled by the control unit based on the location of the piston, such that the piston moves in the cylinder in a reciprocating motion, from one end of the cylinder to the other, to thereby induce a current in the at least one conductive coil.
At least one oil-injection port is located in the cylinder and is adapted to inject lubricating oil into the cylinder based on the position of the piston within the cylinder. The oil-injection port is preferably located in the center of the cylinder, and the cylinder is preferably formed of stainless steel. The cylinder may be wrapped in a thin coating of an insulating material, which may be formed of silicone rubber. The left and right end caps may be curved inwardly toward the interior of the cylinder, and ends of the magnet may be correspondingly concave to accommodate the inwardly curved end caps. Preferably, the magnet is provided with rings to form a seal between the magnet and the cylinder, and the conductive coil may extend beyond the ends of the cylinder.
The magnet may be an Alnico magnet, and may be disposed in a housing with a cushioning layer made of a soft, insulating, non-magnetic material surrounded by a carbon steel shell. Alternatively, the piston may be made of carbon steel, and the at least one coil induces a magnetic field in the piston.
A valve-actuating coil may be fixed to each of the input and exhaust valves, and activated by the control unit to form an electromagnet, and the piston thereby acts to open and close the input and exhaust valves.
The generator of the present invention may be operated as an internal combustion generator, in which case the input and exhaust valves on each of the left and right end caps are comprised of fuel intake, air intake and exhaust valves. An inner conductive coil and an outer conductive coil are provided and preferably extend beyond the ends of the cylinder. The fuel intake valves are adapted to receive a combustible fuel, such that (i) when the right interior space is compressed as the magnet moves toward and approaches the right endcap, the exhaust valve in the left endcap opens, allowing exhaust in the left interior space to vent, the air intake valve in the left endcap opens to allow air into the left interior space, and the fuel is ignited in the right interior space thereby driving the piston toward the left endcap, and (ii) when the left interior space is compressed as the magnet moves toward and approaches the left endcap, the exhaust valve in the right endcap opens, allowing exhaust in the right interior space to vent, the air intake valve in the right endcap opens to allow air into the right interior space, and the fuel is ignited in the left interior space thereby driving the piston toward the right endcap. The generator would thus operate in a two-stroke cycle. The generator preferably includes a current source adapted to apply a current to one of the inner and outer conductive coils to thereby drive the piston toward one of the endcaps to compress and ignite fuel in one of the interior spaces, to thereby start the generator.
In accordance with another example of the present invention, a second generator unit, substantially identical to the first generator unit, is also provided, and first and second current sources are adapted to supply one of the inner and outer conductive coils in the respective first and second generator units, to thereby drive the pistons in the first and second generator units synchronously, such that the pistons run in tandem. When one of the first and second generator units is undergoing an intake/compression stroke, the other of the first and second generator units is undergoing a power/exhaust stroke, and when one of the first and second generator units is undergoing a power/compression stroke, the other of the first and second generator units is undergoing an intake/exhaust stroke, to thus operate in a four-stroke cycle.
In accordance with another example of the present invention, the generator the input valves are adapted to allow a source of steam to enter their respective interior spaces, and the exhaust valves are adapted to allow steam in their respective interior space to exit therefrom, to thereby run the generator as a steam-powered generator.
These and other objects, aspects and examples of the present invention will be described with reference to the following drawing figures, of which:
As shown in
The present invention can be operated as an internal combustion engine or a steam engine. In the internal-combustion version, and as shown in
The operation of the internal combustion version will be described with reference to
The accelerating magnetic field produced by the reciprocating motion of the magnet-piston 12 induces an alternating electrical current in the induction coils 24, 26, which are wrapped around the outside of the cylinder. The current can be applied to load 30,
In order to maximize the energy captured, it is better, space and weight considerations permitting, to have multiple layers of induction coils around the cylinder. Maximizing the energy captured will also reduce electrical interference with other electronic devices in the vicinity. It is also better, space constraints permitting, to have the induction coils extend beyond the ends of the cylinder itself, since the magnetic field of the magnet-piston would also extend beyond the end-of-travel of the magnet-piston itself.
Preferably, at least two coils are provided, one of which is adapted to actively move the magnet-piston within the cylinder, by applying a current from a source 36,
Oil ports 28a,
There are two major advantages to this system. First is its relative mechanical simplicity: the only moving parts in the generator are the valves and the magnet-piston itself. The bigger advantage, however, is that the cylinder can be arbitrarily long, which in turn means that the compression ratios can be arbitrarily large. Consequently, the thermal efficiency of the generator can potentially be extremely high. This is possible because energy is extracted through electrical induction instead of mechanically. Mechanical extraction of useful work, as in a conventional engine, would require more moving parts and would also create space constraints that would limit compression ratios.
A potential problem of the 2-stroke internal combustion generator is that, as with a typical two-stroke diesel engine, exhaust is accomplished by the remaining pressure in the chamber once the piston reaches top-dead center, since there is still a large pressure differential between the gas inside the combustion chamber and the surrounding air. However, as compression ratios rise, and thermal efficiency rises with them, the pressure differential between the waste gases inside the combustion chamber, when the piston reaches the end of its travel, and the surrounding air, goes to zero.
As such, when using the present invention, particularly with a long cylinder to maximize thermal efficiency, it may be preferable to utilize a 4-stroke cycle, with two (or a multiple thereof) substantially identical, separate generators 10, having functionally similar components, including the cylinder, endcaps, magnet-piston, coils, and valves, running side-by-side, adjacent to each other. The two separate generators may appropriately share, or have a separate, ammeter 30, control 34, current source 36 and actuators 38, under the control of control 34, which will be readily understood in view of the description herein.
The 4-stroke cycle will be described with reference to
When using two cylinders or a multiple thereof in a 4-stroke configuration, it will be necessary to run a current through the innermost induction coil of any cylinder not undergoing a power stroke (in
In
As an alternative to internal combustion, the present invention could also be used as a steam engine. In this configuration, only two valves, an intake valve 22d and an exhaust valve 22e,
In general, in all of the embodiments discussed above, the cylinder itself is preferably constructed of a material strong enough to withstand heat and pressure inherent in its operation, but it would also preferably be made of a material with low electrical conductivity, to thereby minimize energy loss due to inducing an electrical current in the cylinder, while also reducing the risk of sparking. For example, stainless steel would provide an acceptable mixture of strength, heat resistance, and low conductivity, while also not being too expensive.
Another possibility would be a ceramic material, and while there have been some experiments with ceramic engines, the problem with ceramics, while strong, heat-resistant, and with a high electrical resistivity, is that they tend to be brittle, thus limiting the ability of the cylinder to withstand the frequent pressure changes required. Another option might be a polymer, and there has been some work to develop a polymer engine, as in U.S. Pat. No. 4,726,334A. Polymers generally have very high electrical resistivity but may lack the required strength and heat resistance and can be combustible. Still another option would be a densified wood of the kind developed by a team led by Liangbing Hu at the University of Maryland. This material is reportedly of comparable strength to steel, while also having a high electrical resistivity without being brittle. It is, however, reportedly also prone to much greater thermal expansion than steel and may also be combustible. Nevertheless, ceramics, polymers, densified wood or other materials might also be suitable, especially as further advances are made in materials science and engineering. The ideal material would be high in strength, heat resistance, and electrical resistance, while low in brittleness. As presently understood, the material that best meets these criteria without being an experimental material for use in an engine would probably be stainless steel.
As shown in
Efficiency can be improved by wrapping the cylinder 14 in a thin coating of an insulating material 14a, as shown in
Care should be taken to ensure that the magnet-piston does not lose its charge when exposed to heat or subject to impact, and to avoid breaking under physical stress. Alnico magnets, although not as strong magnetically as rare earth magnets, particularly neodymium, may be preferred, as they are more resistant to heat, are generally less brittle, and less expensive than rare earth magnets. As shown in
Alternatively, the piston could be made of carbon steel. It would then be possible to turn the piston into an electromagnet by running a direct current through the innermost induction coil, thereby inducing a magnetic field in the piston. The engine would then function as before, with the gas-pressure-driven reciprocating motion of the magnet piston inducing an alternating current in the outer induction coils. The potential problems here are, first, that the movement of the electromagnet-piston would interfere with the direct current in the innermost induction coil, thereby interfering with the induced magnetic field, and second, that some of the energy generated by the engine would have to be used to power the electromagnet, reducing net energy production. Nevertheless, this would be an option in applications where the lifespan of the magnet was most essential.
Finally, the valves 22 can be standard solenoid-actuated valves, but a simpler expedient would be to use a coil 40 installed on, and fixed to, each valve-shaft, as shown in
While the foregoing is directed to exemplary embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof. The examples disclosed herein are for exemplary purposes only and should not be construed as limiting the present invention, which is defined in the following claims.
This application is a continuation of U.S. patent application Ser. No. 18/236,013, filed Aug. 21, 2023, the entire disclosure of which is hereby incorporated by reference.
Number | Name | Date | Kind |
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2362151 | Ostenberg | Nov 1944 | A |
7431474 | Mah | Oct 2008 | B2 |
8729717 | Durrett et al. | May 2014 | B2 |
10815878 | Rainey | Oct 2020 | B2 |
20130025570 | Sturman | Jan 2013 | A1 |
Number | Date | Country |
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111206989 | May 2020 | CN |
110529245 | May 2021 | CN |
2007035102 | Mar 2007 | WO |
2017109203 | Jun 2017 | WO |
WO-2020011790 | Jan 2020 | WO |
WO-2022180629 | Sep 2022 | WO |
Entry |
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Machine Translation of WO2022180629A1 Pdf File Name: “WO2022180629A1_Machine_Translation.pdf”. |
Machine Translation WO2020011790A1 Pdf File Name: “WO2020011790A1_Machine_Translation.pdf”. |
Number | Date | Country | |
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Parent | 18236013 | Aug 2023 | US |
Child | 18370184 | US |