Patent Publication Number: US-10774783-B2

Title: Liquid piston stirling engine with linear generator

Description:
BACKGROUND OF THE INVENTION 
     This application relates generally to the field of electrical power generation and more particularly to electrical generation by Stirling engines. Even more particularly, the application relates to Stirling engines driving a liquid piston and electrical generation by reciprocal linear motion of magnets within a static coil. 
     Stirling engines in various embodiments are well known and can be generally described in their most common form as a heat engine that operates by cyclic expansion and contraction of a gas, often referred as the working fluid, at different temperatures. A Stirling engine is a thermo-dynamic, closed-cycle, regenerative heat engine wherein the gaseous working fluid is permanently retained within the system. An internal heat exchanger and thermal store, known as a regenerator, differentiates the Stirling engine from other closed cycle hot air engines. 
     Common Stirling engines suffer from problems relating to friction and wear, as moving seals are subject to degradation and failure over time. It is an object of this invention to provide a novel Stirling engine electrical generator that does not suffer the friction and wear problems found in other Stirling engines. 
     SUMMARY OF THE INVENTION 
     The invention in various embodiments comprises in general a liquid piston Stirling engine electrical generator, the generator being a linearly reciprocating electrical generator that is powered by a Stirling engine having a contained liquid, i.e., the liquid piston, that is displaced by the cyclic expansion and contraction of a gas, such as air, due to cyclic increases and decreases in the temperature of the gas. The liquid piston and some components of the linear generator are retained within a generally U-shaped tube or chamber, the tube being oriented to consist of two upwardly extending, first and second vertical segments joined by a horizontal segment. An essentially non-compressible liquid, such as oil or hydraulic fluid, forms the liquid piston and is present in sufficient quantity to fill the horizontal segment and extend upward into the vertical segments. 
     The cycle head of a Stirling engine is located on the upper end of the first vertical segment and retains a first volume of gas, the cycle head comprising a hot side heat exchanger structured to transfer heat energy to a gas occupying open areas within the hot side heat exchanger, a cold side heat exchanger structured to remove energy from s gas occupying open areas within the cold side heat exchanger, a displacer adapted to move the first volume of gas between the hot and cold side heat exchangers, a thermal barrier between the hot and cold side heat exchangers to prevent direct heat transfer from the hot side heat exchanger to the cold side heat exchanger, and a motor to move the displacer. Such Stirling engines are well known. The displacer may for example be a rotary displacer or a piston displacer. A high-pressure gas chamber is located at the upper end of the second vertical segment and contains a second volume of gas, the chamber acting as a gas spring relative to movement of the liquid within the U-shaped chamber. The first volume gas and the second volume gas are separated by the liquid piston. 
     Certain dynamic components of the linear generator reside in the horizontal segment of the U-shaped chamber and other static components are external to the horizontal segment of the U-shaped chamber. The linear generator comprises a translating slider on which are mounted permanent magnets, the slider moving within a stator that is preferably defined by the horizontal segment of the U-shaped chamber, the stator having a plurality of wire coils annularly disposed thereon. Reciprocating linear movement of the magnets on the slider within the wire coils of the stator generates an electrical current. The movement of the slider is caused by the expansion and contraction cycling of the first volume gas by the Stirling cycle head in combination with the compression and expansion cycling of the second volume gas within the gas spring chamber. 
     In alternative summarization, the invention is a liquid piston Stirling engine linear generator device comprising: a U-shaped chamber having a first vertical segment and a second vertical segment joined by a horizontal segment; a liquid piston comprising a liquid occupying said horizontal segment, a portion of said first vertical segment and a portion of said second vertical segment; a cycle head of a Stirling engine connected to and in fluid communication with said first vertical segment; a gas spring chamber connected to and in fluid communication with said second vertical segment; a first volume gas occupying said cycle head and in contact with said liquid occupying said first vertical segment, and a second volume gas occupying said gas spring chamber and in contact with said liquid occupying said second vertical segment; a slider disposed within said horizontal segment, said slider able to move in reciprocating manner within said horizontal segment; magnets disposed on said slider; and a stator comprising wire coils annularly encircling said horizontal segment; whereby expansion and contraction of said first volume gas upon operation of said cycle head results in reciprocal movement of said slider relative to said wire coils such that electrical current is generated. Furthermore, said slider having a transverse cross-sectional configuration and said horizontal segment having a transverse cross-sectional configuration, wherein said slider transverse cross-sectional configuration corresponds to said horizontal segment transverse cross-sectional configuration; wherein said slider transverse cross-sectional configuration and said horizontal segment transverse cross-sectional configuration preclude rotational movement of said slider within said horizontal segment; wherein said slider comprises a bridging member connecting two lobes to form a pair of channels, and wherein said magnets are disposed within said channels; wherein said liquid is chosen from the group of liquids consisting of hydraulic fluid and oil; wherein said cycle head comprises a rotary displacer; wherein said slider is disposed within said liquid piston; wherein said stator is disposed on said horizontal segment; and/or wherein said stator is comprised of a portion of said horizontal segment. 
     Alternatively, the invention is a liquid piston Stirling engine linear generator device comprising: a U-shaped chamber having a first vertical segment and a second vertical segment joined by a horizontal segment, said U-shaped chamber structured to retain a liquid; a liquid piston comprising an essentially non-compressible liquid occupying said horizontal segment, a portion of said first vertical segment and a portion of said second vertical segment; a cycle head of a Stirling engine connected to and in fluid communication with said first vertical segment, said cycle head comprising a hot side heat exchanger, a cold side heat exchanger and a displacer; a gas spring chamber connected to and in fluid communication with said second vertical segment; a first volume gas occupying said cycle head and in contact with said liquid occupying said first vertical segment, and a second volume gas occupying said gas spring chamber and in contact with said liquid occupying said second vertical segment; slider disposed within said horizontal segment and within said liquid piston, said slider retaining magnets and able to move in reciprocating manner within said horizontal segment; and a stator disposed on or formed as part of said horizontal segment, said stator comprising wire coils annularly encircling said horizontal segment and surrounding said slider; said slider having a transverse cross-sectional configuration and said horizontal segment having a transverse cross-sectional configuration, wherein said slider transverse cross-sectional configuration corresponds to said horizontal segment transverse cross-sectional configuration; whereby expansion and contraction of said first volume gas upon operation of said cycle head results in reciprocal movement of said liquid piston within said U-shaped chamber and reciprocal movement of said slider relative to said wire coils such that electrical current is generated. Furthermore, wherein said slider transverse cross-sectional configuration and said horizontal segment transverse cross-sectional configuration preclude rotational movement of said slider within said horizontal segment; wherein said slider comprises a bridging member connecting two lobes to form a pair of channels, and wherein said magnets are disposed within said channels; wherein said liquid is chosen from the group of liquids consisting of hydraulic fluid and oil; wherein said cycle head comprises a rotary displacer; wherein said stator is disposed on said horizontal segment; and/or wherein said stator is comprised of a portion of said horizontal segment. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  a schematic representational view of an embodiment of the invention. 
         FIG. 2  is a cross-sectional view of the horizontal segment of the embodiment of  FIG. 1  taken along line  2 - 2 , the view showing the stator, slider and magnets mounted in channels on the slider. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In various embodiments the invention comprises in general a liquid piston Stirling engine electrical generator, the generator being a linearly reciprocating electrical generator that is powered by a Stirling engine having a liquid, referred to as a liquid piston, that is displaced by the cyclic expansion and contraction/compression in volume of a gas, such as air, as illustrated in  FIG. 1 . 
     The liquid piston  51  and dynamic components of the linear generator  30  are retained within a liquid piston assembly  20  comprising a U-shaped tube or chamber  21 , the chamber  21  being oriented in use to consist of a two upwardly extending, first and second vertical segments  23  and  24  connected to a linear horizontal segment  22 , the combination providing a continuous opening to receive a quantity of an essentially non-compressible liquid, such as water, oil or hydraulic fluid, which defines the liquid piston  51  and which is present in sufficient quantity to fill the horizontal segment  22  and extend upward into the vertical segments  23 / 24  of the U-shaped chamber  21 . In this manner the U-shaped chamber  21  acts as a trap to preclude movement of gas into and through the horizontal segment. The gas is present as a first volume gas  52  and a second volume gas  53 . The first volume gas  52  resides in the first vertical segment  23  and cycle head  10 . The second volume gas  53  resides in the second vertical segment  24  and the gas spring chamber  25 . The first volume gas  52  and a second volume gas  53  may be identical or may differ in composition. 
     The cycle head  10  of the Stirling engine is located on the upper end of the first vertical segment  23  and retains the first volume of gas  52 , the cycle head  10  comprising a hot side heat exchanger  11  structured to transfer heat energy to a gas of lower temperature occupying open areas within the hot side heat exchanger  11 , a cold side heat exchanger  12  structured to remove or receive energy from a gas of higher temperature occupying open areas within the cold side heat exchanger  12 , a displacer  13  adapted to move the first volume of gas  52  between the hot and cold side heat exchangers  11 / 12 , a thermal barrier  14  between the hot and cold side heat exchangers  11 / 12 , and a motor (not shown) to move the displacer  13 . Stirling engines are well known. The displacer  13  may be of various known types, such as for example be a rotary displacer or a piston displacer. With cycle heads  10  comprising a rotary displacer  13 , the rotary displacer  13  in a preferred embodiment is of the type having semi-circular blades mounted onto a rotatable shaft. As the blades are rotated they pass through open sub-chambers or voids defined by fins in the hot and cold side heat exchangers  11 / 12 , the movement of the blades displacing hot or cool air from the sub-chambers in cycling manner as needed. A rotary displacer  13  is preferred over a piston displacer  13 , as the large number of blades on the displacer  13  and the fins formed in the hot and cold side heat exchangers  11 / 12  increase the surface area available for heat exchange. The displacer  13  is motor operated, such as by an electrical motor which rotates the displacer shaft. 
     A high-pressure gas spring chamber  25  is located at the upper end of the second vertical segment  24  of the U-shaped chamber  21  and retains the second volume of gas  53 , the chamber  25  acting as a gas spring against the liquid piston  51 , the combination of the cycle head  10  and the gas spring chamber  25  producing reciprocating movement of the liquid piston  51  within the U-shaped chamber  21  as the first volume of gas  52  expands and contracts and the second volume of gas  53  is compressed and then expands. 
     The linear generator  30  comprises the combination of dynamic components and static components. The dynamic components comprise a horizontally translating or reciprocating slider  31  on which are mounted permanent magnets  32 , the slider  31  being configured and sized in transverse cross-section to correspond to the configuration and size of the interior of horizontal segment  22  of the U-shaped chamber  21 , effectively acting in the manner of a moving plug which reciprocates linearly within the horizontal segment  22  of the U-shaped chamber  21  as the liquid piston  51  moves in reciprocating manner. Mounted onto, encircling or formed as or from an integral component of the horizontal segment  22  is a static stator  34  having annular wire coils  35  encircling the horizontal segment  22 . 
     Preferably, the slider  31  is configured to comprise a thin bridging member  62  extending between two lobes  61 , the combination defining a pair of longitudinal channels  63 , as shown in  FIG. 2 . The magnets  32  are paired vertically, separated by the bridging member  62  of the slider and occupying the longitudinal channels  63 . With more than two magnets  32 , the magnets  32  are separated horizontally by spacers  33 . The magnet pairs  32  are oriented such that the like poles point in the same direction, for example both N poles on top and both S poles on the bottom. 
     The static components of the linear generator  30  comprise a stator  34  having wire coils  35  annularly disposed thereon, the wire coils  35  encircling a portion of the horizontal segment  22  of the U-shaped chamber  21 . The stator  34  may be a separately defined component encircling all of a portion of the horizontal segment  22  of the U-shaped chamber  21 , or the stator  34  may be defined by, formed integrally with or constitute all or a portion of the horizontal segment  22 . 
     The external configuration of the slider  31  and the internal configuration of the horizontal segment  22  or the stator  34  in transverse cross-section are preferably designed such that movement of the slider  31  in any direction other than along the longitudinal axis, i.e., rotational movement, is precluded, and further such that only a minimum gap necessary to allow for movement is present. In this manner the slider  31  easily reciprocates in response to movement of the liquid piston  51 , which also serves to provide lubrication between the slider  31  and the interior wall of the horizontal segment  22 . With this structure, reciprocating linear movement of the slider  31  within the stator  34  generates an electrical current as the magnets  32  oscillate within the coils  35 . Electrical current produced by the linear generator  30  is delivered for use or battery storage in known manner. 
     The liquid comprising the liquid piston  51  is present on both sides of the dynamic slider  31 , fills the horizontal segment  22  and extends partially up each of the first and second vertical segments  23 / 24 , thereby creating a lower seal for the first volume gas  52  within the first vertical segment  23  of the U-shaped chamber  21  and a lower seal for the second volume gas  53  within the second vertical segment  24 . The movement of the slider  31  is caused by the expansion and contraction cycling of the first volume gas  52  by the cycle head  10  combined with the compression and expansion cycling, in opposite sequence, of the second volume gas  53  within the gas spring chamber  25 . 
     In operation, the hot side heat exchanger  11  of the cycle head  10  receives heat energy from an external source. With the displacer  13  positioned so as to occupy the open volume of the cold side heat exchanger  12 , the first volume gas  52  present in the cycle head  10  is in contact with the surface of the hot side heat exchanger  11  and expands as it absorbs heat from the hot side heat exchanger  11 . This expanded gas  52  presses against and lowers the portion of the liquid piston  51  present in the first vertical segment  23  of the U-shaped chamber  21 . The liquid piston  51 , being non-compressible, then presses against the end of the slider  31  and shifts it in the direction of the second vertical segment  24 , thereby moving the magnets  32  in the longitudinal axial direction relative to the coils  35  of the stator  34 . The movement of the slider  31  forces the portion of the liquid piston  51  present in the second vertical segment  24  upward, thereby compressing the second volume gas  53  within the gas spring chamber  25 . Once pressure is equalized, the displacer  13  is then moved from the cold side heat exchanger  12  to occupy the open volume of the hot side heat exchanger  11 , thereby allowing the first volume gas  52  to contact the surface of the cold side heat exchanger  12 . The heat energy present in the first volume gas  52  is now transferred to the cold side heat exchanger  12 , acting as heat sink, thereby lowering the temperature and reducing the volume of the first volume gas  52  as well as the pressure being applied to the liquid piston  51  present in the first vertical segment  23 . The compressed second volume gas  53  in the gas spring chamber  25  is then able to expand, moving the liquid piston  51  in the second vertical segment  24  downward to press against the slider  31 , thereby forcing the slider  31  back in the direction of the first vertical segment  23 , which moves the magnets  32  in the opposite direction relative to the wire coils  35 . The movement of the slider  31  in this direction forces the liquid piston  51  in the first vertical segment  23  upward, the now cooler first volume gas  52  in the cold side heat exchanger  12  having a reduced volume. Once pressure is equalized, the displacer  13  than is then moved back to occupy the open volume of the cold side heat exchanger  12 , shifting the cooled first volume gas  52  back to the hot side heat exchanger  11 . This cycle is then continuously repeated to produce reciprocal movement of the slider  31  within the stator  34  and generate electricity. 
     The liquid piston Stirling engine linear generator as described provides a simple design with very high gas pressures and low friction, thereby keeping manufacturing and operational costs low. The rotary displacer  13  operates with very low energy, as it can be operated by an electric motor, and allows for heat regeneration as well as being highly efficient in displacing the first volume gas  52 . Because of the liquid piston  51 , only static seals are required for the device, as there is no requirement for seals to be in contact with the dynamic slider  31 . The device produces high AC power output and maintains low operational temperatures. 
     It is understood that equivalents and substitutions for certain elements set forth above may be obvious to those of skill in the art, and therefore the true scope and definition of the invention is to be as set forth in the following claims.