Patent Application
20110120110
This invention relates to the field of heat engines and in particular to a de-coupled displacement type Stirling engine wherein the displacer is not mechanically coupled to the power piston.
The sterling engine is a class of heat engines considered as a closed cycle system. The working gas is permanently contained within the system.
Displacement type Stirling engines, use an insulated mechanical displacer to push the working gas between the hot and cold sides of the cylinder. The displacer is large enough to insulate the hot and cold sides of the cylinder thermally. A large quantity of gas is displaced. There is a large enough of a gap between the displacer and the cylinder wall to allow gas to flow around the displacer easily.
These engines can operate at low temperature differentials because of the large volume of gas that is can expand to can push on the piston.
Typical low temperature differential Stirling engines may utilize a crank shaft attached to a flywheel. Typically, a single power piston is arranged within the same cylinder on the same shaft as a displacer piston. The displacer piston is a loose fit and does not extract any power from the expanding gas but only serves to shuttle the working gas from the hot heat exchanger to the cold heat exchanger. When the working gas is pushed to the hot end of the cylinder it expands and pushes the power piston. When it is pushed to the cold end of the cylinder it contracts and the momentum of the machine, enhanced by the flywheel, pushes the power piston the other way to compress the gas. The mechanism, in such a Sterling engine, can only move the displacer a short distance. This type of Sterling engine may not be effective at utilizing natural heat sources.
These prior art Sterling engines do not ensure the working gas has fully heated and cooled. Full heating and full cooling is defeated by the direct mechanical coupling of the power piston to the displacer piston. This limits the amount of work that can be performed.
In summary, the low temperature differential Stirling engine according to one aspect of the present invention may be characterized as including a sealed elongate hollow container such as a cylinder, having a corresponding elongate cavity therein containing a gaseous working fluid and a displacer slidably mounted in the cavity. The displacer is translatable along the cavity. The container has a hot end and an opposite cold end. Translation of the displacer along the cavity forces the working fluid into the hot or cold ends sequentially according to a Stirling cycle. The hot end of the container has a power piston conduit. The conduit is in fluid communication with a power piston cylinder containing a power piston slidably mounted therein. Thus the conduit is in fluid communication between the working fluid in the cavity in the hot end of the container and the power piston cylinder so that heated expansion of the working fluid in the hot end of the container produces a power stroke of the piston. The displacer is mechanically decoupled from said power piston.
An actuator is mounted substantially within the container. A corresponding processor provides logic control of the actuator. The actuator translates the displacer between the hot and cold ends according to, and so as to optimize, the Stirling cycle operating in the container.
Advantageously a power take-off is connected to the piston so as to produce useful work from the piston at least during the piston's power stroke. The power take-off may provide power to the actuator.
In one embodiment the actuator includes a motor operating to translate the displacer according to logic controls from the processor. The processor is advantageously adapted to maintain the position of the displacer in the hot end or in the cold end of the container until the working fluid is fully heated or cooled. A generator may provide power for driving the motor. The generator may be included as part of the power take-off so that the generator is driven by some of the power from the piston's power stroke. Thus the power take-off further includes a transmission producing useful work, including the generator.
In one embodiment the actuator includes a counter-balance weight counter-balancing the displacer to thereby reduce power requirements of the motor. In this embodiment the actuator further includes an elongate flexible member such as a cord, line, cable, etc suspending, on opposite ends thereof, the displacer and the counter-balance weight. The motor engages and drives the flexible member so as to vertically translate the counter-balanced displacer and weight.
In a further embodiment the actuator includes a screw which is driven by the motor. The screw helically engages the displacer with its helical threads to translate the displacer vertically.
Advantageously, the screw may be off-set from the centroidal axis of the displacer so as to inhibit rotation about a vertical axis of the displacer relative to the container when the container's cavity and the displacer are both cylindrical. Other means may be employed to inhibit such rotation of the displacer.
The processor may obtain displacer location information from micro switches, contacting the displacer, located on top or bottom of the cavity.
In another embodiment, the motor used to move the displacer may be a logic controlled stepper motor that has the angle of rotation controlled so that the displacer is location is controlled precisely.
In one embodiment the processor is adapted to maintain the position of the displacer according to active feedback to the processor of the thermodynamic status of the working fluid. Alternatively the processor may be adapted to maintain the position of the displacer according to a time value.
a is an enlarged view of a portion of
In the accompanying illustrations, like reference numerals denote corresponding parts in each view.
As seen in
A pulley bracket 16 is mounted to the cylinder head on end 10b of cylinder 10. Bracket 16 is mounted so as to position a concentrically inner most of end 16c of bracket 16 so as to lie substantially on axis B. The opposite end 16b of bracket 16, that is, the distal end, is aligned radially outwardly and/or orthogonally to axis B, flush along end 10b and adjacent cylindrical cylinder wall 10d. The distal end of bracket 16 is aligned longitudinally with the longitudinal axis C of channel 14a.
An electric motor 18 having a corresponding driven shaft 18a is mounted on one side of the radially on the inner end 16a of bracket 16 so as to extend driven shaft 18a through a corresponding aperture in end 16a and so as to dispose the driven shaft 18a through the aperture to protrude from bracket 16 opposite to motor 18. A pulley 20 is mounted on the distal end 16b of bracket 16 so as to protrude from bracket 16 on the same side of bracket 16 as driven shaft 18a. A cord 22 or other substantially non-resilient elongate flexible member such as for example a line or cable is mounted at its end 22a to end 14b of displacer 14 so as to place end 22a of cord 22 substantially on longitudinal axis B. The protruding end of driven shaft 18a also lies on longitudinal axis B, and thus, with cord 22, between end 22a and driven shaft 18a, is substantially coaxial with longitudinal axis B. Cord 22 extends from where it is wrapped over driven shaft 18a to pulley 20. Cord 22 wraps over pulley 20 and extends then substantially along longitudinal axis C to where the opposite end of cord 22, namely end 22b, is mounted to counter weight 24, and in particular to end 24a of counter weight 24. Counter weight 24 is journalled in channel 14a and free to translate along channel 14a in direction D in counter balancing oppositely disposed translation relative to displacer 14 as displacer 14 translates in direction A. Counter weight 24 may be substantially equal in weight to displacer 14 so that, with counter weight 24 tethered to displacer 14 by cord 22, translating cord 22 over driven shaft 18a and pulley 20 may be done with relatively little torque applied by motor 18 to rotate driven shaft 18a in direction E. Cylinder 10 is oriented vertically, that is, so that longitudinal axis B is vertical. Displacer 14 may thus be elevated so as to bring end 14b towards end 10b as counter weight 24 is correspondingly lowered along channel 14a.
Power piston 26 is freely mounted within power piston cylinder 12 so as to freely translate in direction F to accomplish work when driven upwardly by the pressure of the working fluid, for example, air, contained within the hot end of cylinder 10, that is, upper cavity 10a between displacer 14 and end 10b of cylinder 10.
In one example, which is not intended to be limiting, of removing work from the upward power stroke of power piston 26 in power piston cylinder 12, a rack gear 28 may be mounted to the upper end 26a of piston 26 and extend vertically therefrom so as to engage linearly aligned gear teeth 28a with the corresponding teeth 30a on one-way ratchet gear 30. One-way ratchet gear 30 is mounted on a shaft 32 by means of a one-way ratchet mechanism 34, itself mounted onto shaft 32. A large gear or flywheel 36 is also mounted onto shaft 32. As rack gear 28 is driven upwardly in direction G, gear 30 is rotated in direction H, thereby, by the one-way drive of ratchet 34, also rotating flywheel 36 in direction I on shaft 32.
When the pressure under power piston 26, that is, within the upper cavity 10a within cylinder 10, is reduced by the operation of the sterling cycle, and power piston 26 retracts downwardly along power piston cylinder 12, rack gear 28 is lowered and, by the operation of one-way ratchet 34, gear 30 free-wheels in a direction in opposite to direction H without interfering with the rotation of gear 36 in direction I. Rotation of gear 36 in direction I drives a generator shaft 38a which causes the corresponding generator 38 to generate electricity to power motor 18 as governed by a processor 19. Processor 19 is a logic controller for the operation of motor 18.
The above described arrangement produces a positive net work which may be extracted from the rotation of gear 36.
Although not intending to be limiting, the cold or heat sink end 10c of cylinder 10 may be mounted in a geo-thermal arrangement so as to produce a temperature differential between the heat sink end, and the ambient temperature or hot end which may be the upper end 10b of cylinder 10.
One such geo-thermal arrangement could be a cylinder mounted in a hole where, in winter, the hot end is placed well below the frost line. The cold end sticks out of the hole. In this arrangement, the cold side would become the hot side and the hot side would become the cold side in summer.
As will be understood by those skilled in the art, the illustration of
For the operation of the Stirling cycle, end 10b of cylinder 10 is thus placed into heat while the other end 10c is placed in cold. In one embodiment, 10b end of the cylinder could be placed in a hole in the ground to take advantage of a geo-thermal difference in temperature between for example ambient air temperature above ground and the temperature in the hole for example where one end of the cylinder could be below the frost line.
The steps of operation are as follows;
During this operation the power piston is used to power a generator. A small portion of the generated electricity is used to power the motor and logic controller.
Having the logic controller wait until the gas is fully heated and cooled, increases the work produced during the cycle. Cycles that rely on a flywheel or spring mechanically linked to the piston and/or displacer to control the cycle of time of operation, do not necessarily allow enough time for the working gas to cool or heat.
As stated above, typically low temperature differential Stirling engines have a small displacer movement. In order for the device to be placed in a thermal well for geothermal electricity generation, the displacer movement must be much larger. This is accomplished with the present design.
It can be seen by someone skilled in the art that the displacer may be actuated by a motor and logic controller and also by other means than the one presented here. Therefore this invention is not intended to be limited to this mechanical configuration.
The Sterling engine may be pressurized so that larger loads may be moved by the heating or cooling of the gas.
In the alternative embodiment of
Displacer 46 is translated along the length of the hollow cavity 48a which extend along the hollow cylinder 48, cavity 48a including accumulator 48b.
As with the embodiment of
The displacer screw mechanism including threads 42a and threaded nut or collar 44 is offset from the centroid axis M of displacer 46 so that the offset mass of displacer 46 resists rotating of displacer 46 relative to cylinder 48 as the displacer screw is rotated so as to raise or lower displacer 46.
As will be apparent to those skilled in the art in the light of the foregoing disclosure, many alterations and modifications are possible in the practice of this invention without departing from the spirit or scope thereof. Accordingly, the scope of the invention is to be construed in accordance with the substance defined by the following claims.
This application claims priority from U.S. Provisional Patent Application Ser. No. 61/279,088 filed Oct. 16, 2009 and entitled Logic Controlled Stirling Engine.
| Number | Date | Country | |
|---|---|---|---|
| 61279088 | Oct 2009 | US |
