Abstract:
A novel and useful method and apparatus for generating power from pressure changes over time within a fluid. The apparatus comprises a housing ( 10 ), and a double-sided piston ( 12 ) subject to the forces brought about by the variations in pressure of the surrounding fluid and by a restoring force such as a spring ( 20 ) or other mechanism. The resulting motion of the piston is transferred to power a generator, or is used to directly perform work. The apparatus is particularly applicable to placement in the ocean or sea where the rise and fall of the tides create the variations of pressure that drive the piston within the housing. A rising tide presents a higher pressure against the face of the piston pushing it towards the back of the housing and opposing the restoring force mechanism. A falling tide presents a lower pressure against the face of the piston allowing the restoring force to move it towards the front of the housing. Energy is harvested from the movement of the piston in one or both directions either by connection to a turbine coupled to a generator or by a linkage attached to the piston that is connected to a mechanical load such as a generator, pump, etc.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Application Ser. No. 61/757,315, filed Jan. 28, 2013, incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     This application relates to the generation of power from pressure changes occurring over time in fluids. 
     BACKGROUND OF THE INVENTION 
     Power generation derived from variations in the earth&#39;s natural environments is in its early stages, and several technologies have been proposed. 
     A large number of prior art devices seek to harness the energy of ocean waves or the tides by measuring the varying height of the water through the use of floats. The float assembly is typically tied to a mechanical device in order to store energy, or to provide kinetic energy to an electric generator. One disadvantage of this approach is that it requires a mechanical connection from the float assembly to a stable reference point, usually the ocean floor. This could only be implemented in relatively shallow water environments where the risk of an apparatus breakup would be great. 
     Another group of prior art devices seeks to harness tidal energy by inserting turbines in the path of tidal currents. This solution will work only in a relatively small number of locations, and necessitate a thorough understanding of all forces at these locations, along with an assumption that these forces will not change over time. 
     Another group of prior art devices relies on the building of reservoirs at different levels and exploiting the movement of current between reservoirs. This solution is limited to near shore construction. 
     A reasonable alternative to the above mentioned approaches is to employ a power generating device which is completely submerged, and does not employ floats, or otherwise need to be in contact with the water surface. This type of device normally exploits the differences in hydrostatic pressure which occur as a result of tidal, wave, or other natural activity in the ocean. 
     One example of a submerged wave energy power generating device is U.S. Pat. No. 4,630,440 to Meyerand. In Meyerand, a constant pressure fluid reservoir positioned on land is connected by a hose to the submerged wave machine, which consists of a water filled outer housing and a fluid filled inner flexible bladder. The housing includes an opening to the ocean which includes a turbine driving an electrical generator. In this way, variances in hydrostatic pressure caused by the waves cause a filling and collapsing of the bladder, thereby increasing and decreasing the volume of water in the housing. This causes an inflow and outflow of water from the housing through the turbine, which is caused to turn to and fro. The turbine drives a generator, creating electrical power. This arrangement must be located near the shore, limiting the size of the apparatus and the amount of power it might produce. The hose would be susceptible to the difficult weather conditions sometimes found along the seashore. 
     A second example is U.S. Pat. No. 5,349,819 to Margittai. This apparatus employs a pump driven by hydrostatic pressure on the downside and a flexible member on the upside to drive pressurized water through 3 check valves to a collection tank for later use in driving a turbine. In this arrangement the pump plunger must move vertically and water flow takes place in one direction only. The need for a sealed air chamber would make this device difficult to produce and operate at significant depths. 
     Most prior art focuses on exploiting one particular phenomenon to the exclusion of others. In the case of the harnessing of ocean energy, for example, very few solutions, if any, seek to incorporate lower frequency tidal and higher frequency wave effects. Most proposed solutions are also applicable only to the particular environments for which they were originally designed. 
     BRIEF SUMMARY OF THE INVENTION 
     The apparatus for generating power from pressure changes occurring over time in a fluid, in one embodiment, comprises a housing divided into two chambers separated by a moveable wall. The housing is submerged in the surrounding fluid. The first chamber is exposed to this fluid and thus the face of the moveable wall exposed to the first chamber is subject to the force resulting from the fluid pressure, which varies with the pressure of the fluid. This varying force is opposed by a restoring force in the second chamber which presses upon the moveable wall in the opposing direction. The resulting motion of the moveable wall is transmitted to a generator, which translates mechanical motion to electrical power. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS FIGURES 
         FIG. 1A  is a cross sectional view of an embodiment directing fluid through a turbine and which employs a spring as the restoring force. It shows the fluid and piston motion resulting from increasing fluid pressure. 
         FIG. 1B  is a cross sectional view of an embodiment directing fluid through a turbine and which employs a spring as the restoring force. It shows the fluid and piston motion resulting from decreasing fluid pressure. 
         FIG. 2A  is a cross sectional view of an embodiment type used to direct fluid through a turbine and which employs a compressible liquid or gas as the restoring force. It shows the fluid and piston motion resulting from increasing fluid pressure. 
         FIG. 2B  is a cross sectional view of an embodiment type used to direct fluid through a turbine and which employs a compressible liquid or gas as the restoring force. It shows the fluid and piston motion resulting from decreasing fluid pressure. 
         FIG. 3A  is a cross sectional view of an embodiment type used to direct fluid through a turbine and which employs a compressible liquid or gas within a bladder as the restoring force. It shows the fluid and piston motion resulting from increasing fluid pressure, 
         FIG. 3B  is a cross sectional view of an embodiment type used to direct fluid through a turbine and which employs compressible liquid or gas within several bladders as the restoring force. It shows the fluid and piston motion resulting from increasing fluid pressure. 
         FIG. 3C  is a cross sectional view of an embodiment type used to direct fluid through a turbine and which employs a material with the required elasticity as the restoring force. It shows the fluid and piston motion resulting from increasing fluid pressure. 
         FIG. 3D  is a cross sectional view of an embodiment type used to direct fluid through a turbine and which employs a compressible liquid or gas within a bladder as the restoring force. It shows the fluid and piston motion resulting from decreasing fluid pressure. 
         FIG. 3E  is a cross sectional view of an embodiment type used to direct fluid through a turbine and which employs compressible liquid or gas within several bladders as the restoring force. It shows the fluid and piston motion resulting from decreasing fluid pressure. 
         FIG. 3F  is a cross sectional view of an embodiment type used to direct fluid through a turbine and which employs a material with the required elasticity as the restoring force. It shows the fluid and piston motion resulting from decreasing fluid pressure. 
         FIG. 4A  is a cross sectional view of an embodiment type employing a linkage and which employs a compressible liquid or gas within several bladders as the restoring force. It shows the fluid and piston motion resulting from increasing fluid pressure. 
         FIG. 4B  is a cross sectional view of an embodiment type employing a linkage and which employs a spring within the fluid chamber as the restoring force. It shows the fluid and piston motion resulting from increasing fluid pressure. 
         FIG. 4C  is a cross sectional view of an embodiment type employing a linkage and which employs repelling magnets to provide the restoring force. It shows the fluid and piston motion resulting from increasing fluid pressure 
         FIG. 4D  is a cross sectional view of an embodiment type employing a linkage and which employs a compressible liquid or gas within several bladders as the restoring force. It shows the fluid and piston motion resulting from decreasing fluid pressure. 
         FIG. 4E  is a cross sectional view of an embodiment type employing a linkage and which employs a spring within the fluid chamber as the restoring force. It shows the fluid and piston motion resulting from decreasing fluid pressure 
         FIG. 4F  is a cross sectional view of an embodiment type employing a linkage and which employs repelling magnets to provide the restoring force. It shows the fluid and piston motion resulting from decreasing fluid pressure. 
     
    
    
     
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
               
               
                 REFERENCE NUMERAL TABLE 
               
             
          
           
               
                   
                 Reference 
                   
                 Reference 
                   
               
               
                   
                 Numeral 
                 Description 
                 Numeral 
                 Description 
               
               
                   
                   
               
             
          
           
               
                   
                 10 
                 Housing 
                 26 
                 Power 
               
               
                   
                   
                   
                   
                 Conditioning 
               
               
                   
                   
                   
                   
                 Unit 
               
               
                   
                 12 
                 Piston or 
                 30 
                 Minimum Mark 
               
               
                   
                   
                 Moveable Wall 
                   
                   
               
               
                   
                 16 
                 Opening 
                 32 
                 Maximum Mark 
               
               
                   
                 17 
                 Linkage 
                 34 
                 Elastic Material 
               
               
                   
                 20, 60 
                 Spring 
                 40 
                 Fluid Chamber 
               
               
                   
                 21 
                 Compressible 
                 42 
                 Restoring Force 
               
               
                   
                   
                 Liquid and/or 
                   
                 Chamber 
               
               
                   
                   
                 Gas 
                   
                   
               
               
                   
                 22 
                 Turbine 
                 44 
                 Load 
               
               
                   
                 23 
                 Bladder 
                 46 
                 Fastener 
               
               
                   
                 24 
                 Generator 
                 48, 49 
                 Magnet 
               
               
                   
                 54 
                 Fluid Surface 
                   
                   
               
               
                   
                   
               
             
          
         
       
     
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIG. 1A , the apparatus for generating power comprises a rigid housing  10  containing a restoring force in the form of spring  20  next to which is placed a moveable wall, moveable double sided seal, or double sided piston  12 . The term “piston”  12  will henceforth be used in this document to mean moveable wall, moveable double sided seal, or double sided piston. The chamber  42  containing the means of producing the restoring force and bordering the piston  12  will be referred to as the restoring force chamber. A piston shaft and piston shaft guide (not shown) may be needed in order to keep piston  12  stable in certain implementations. They need not be considered for understanding how the apparatus functions and are not pictured. 
     The installed apparatus is shown in a horizontal position in  FIG. 1A  and  FIG. 1B , but is not limited to that orientation. The range between a minimum mark  30  and a maximum mark  32  is a recommended range of travel of the piston  12 . The term “fluid” will refer to the fluid in which the apparatus resides. For example, the fluid is seawater when the apparatus is operated in the sea. The surface of the surrounding body of fluid (e.g., the ocean or sea) is referenced  54  in the  FIGS. 1A and 1B  but is not shown for clarity sake in the subsequent Figures. 
     As will be shown, changes in fluid pressure in time, usually caused by a variety of natural factors, drive the operation of the apparatus. The fluid chamber  40  is in contact with the fluid, which is anticipated to be seawater in many cases, and is filled with this fluid through opening  16 . The piston  12  provides an effective separation between the fluid chamber  40  and the restoring force chamber  42 . The opening  16  in fluid chamber  40  is connected via pipe  50  to one side of turbine  22 . The other side of turbine  22  is connected via pipe  52  to the surrounding fluid. Turbine  22  drives an electrical power generator  24 . The output from the electrical power generator  24  is sent to the load  44  via the power conditioning unit  26 . The power conditioning unit  26 , if needed, modifies the electrical output of the generator  24 . The turbine  22 , the generator  24 , and the power conditioning unit  26  may be installed in close proximity to or at a distance from housing  10 . The load  44  may be an electrical distribution facility or storage unit, or one or more machines that consume electrical power. 
     The Regarding installation, the parameters of the apparatus are preferably optimally set for the particular installation. The location within the fluid at which the apparatus will be installed and the resulting average fluid pressure at that location are preferably understood through analysis or direct measurement. During installation, fluid chamber  40  is filled with fluid. In the case of seawater, the apparatus will typically be installed on the sea floor, or at some fixed distance from the sea floor. The tension of spring  20  is preferably such that piston  12  will travel freely in housing  10  within the range between minimum mark  30  and maximum mark  32  once the apparatus is installed. As the fluid pressure increases, piston  12  travels toward maximum mark  32 . As the fluid pressure decreases, piston  12  travels toward minimum mark  30  because of the restoring force of spring  20 . 
     The restoring force exerted by the spring  20  is in opposition to the force exerted by the fluid. In the case of the fluid being seawater, the force exerted by the fluid is proportional to the fluid pressure, which varies in proportion to the depth at which the apparatus resides within the fluid. At a fluid depth of 1 kilometer, for example, a much stronger force would be generated by the fluid pressure than at a fluid depth of 10 meters. The spring type must have the characteristics which will enable it to compress and expand such as to cause the piston  12  to travel between minimum mark  30  and maximum mark  32  under the pressures found at the installation depth. 
     Typical operation of the apparatus will now be described. As fluid pressure increases, as would happen in the case of seawater when the tide rises which would cause the level of the surface  54  to rise, pressure rises in fluid chamber  40  to equal the pressure outside the apparatus in the nearby fluid. Fluid flows into pipe  52 , and then into turbine  22 , causing it to rotate. The fluid then flows into pipe  50  and into fluid chamber  40  via opening  16 . Piston  12  is pushed in the direction of maximum mark  32 , compressing spring  20 . When the pressure of the surrounding fluid decreases, as would happen with a falling tide causing the level of the surface  54  to fall, pressure decreases in fluid chamber  40 , and the force of the now compressed spring  20  pushes the piston  12  back toward the minimum mark  30 . The force exerted by spring  20  may be calculated using well-known in the art Hooke&#39;s Law. Fluid flows out from the fluid chamber  40  via opening  16  to pipe  50  and then into the turbine  22 , causing the turbine to rotate in the opposite direction, and then out through pipe  52 . The rotation of the turbine  22  causes rotation of the attached generator  24 , producing electric power. 
     The amount of power produced depends on several factors:
         (a) All other factors being constant, the greater the sum of the pressure variations in a given time interval, the greater is the amount of power produced. For example, in the case where the fluid is seawater, a large change in tidal level and thus greater fluid pressure variation would generate more power than a small change in the tidal level, where the fluid pressure variation is less.       

     (b) All other factors being constant, the larger the apparatus, the greater the amount of power that can be generated. A larger cross-sectional area of the piston  12  and a greater distance of travel of piston  12  will result in a greater volume of fluid passing through the turbine  22  and a greater amount of generated power. 
     Referring to  FIG. 2A  and  FIG. 2B , a second embodiment consists of the same type of housing  10 , but the restoring force within restoring force chamber  42  is a compressible liquid, compressible gas, or a combination of liquid and gas, henceforth identified as compressible liquid and/or gas  21 . The piston  12  provides an effective seal between the fluid chamber  40  and the restoring force chamber  42  containing the compressible liquid and/or gas  21 . In  FIG. 2A  and  FIG. 2B , the walls in chambers  40  and  42  are drawn to show that they need not be parallel. Piston  12 , however, must be capable of adjusting to the varying widths of the chambers  40  and  42 , and provide an effective seal at its points of travel. 
     Consideration must be given to the location in the fluid at which the apparatus is to be installed. Fill restoring force chamber  42  in the housing  10  with the quantity and pressure of compressible liquid and/or gas  21  such that the following requirement is met: At the installation location, and as with the previous embodiment of  FIGS. 1A and 1B , the range of travel of piston  12  during operation is preferably between minimum mark  30  and maximum mark  32 . 
     With the apparatus installed, operation begins in similar fashion to the previous embodiment of  FIGS. 1A and 1B , but with the compressible liquid and/or gas  21  providing the restoring force instead of spring  20 . As fluid pressure increases, as would happen in the seawater case with a rising tide, fluid pressure increases in fluid chamber  40  to equal the pressure outside the apparatus in the nearby fluid. The resulting force on piston  12  drives it toward maximum mark  32 , compressing the compressible liquid and/or gas  21 . As fluid pressure decreases, pressure decreases in fluid chamber  40  and the force exerted by the now expanding compressible liquid and/or gas  21  moves piston  12  back toward minimum mark  30 . The flow of fluid into and out of fluid chamber  40 , and the resulting power production through turbine  22  are as previously described. 
     The distance traveled by piston  12 , and the restoring force produced, can be calculated, given the materials used as the compressible liquid and/or gas  21 , the dimensions of the apparatus, and the pressure variations of the fluid. 
     Referring to the embodiments shown in  FIGS. 3A ,  3 D and  FIGS. 3B ,  3 E, the compressible liquid and/or gas  21  is enclosed in one (see  FIGS. 3A and 3D ) or more (see  FIGS. 3B and 3E ) sealed bladders  23 . The bladder or bladders  23  are in restoring force chamber  42 . The use of a single bladder  23  presents some advantages over the previous, bladderless embodiment as the risk of leakage of the compressible liquid and/or gas  21  past piston  12  is reduced, and the use of a bladder  23  may simplify the construction and configuration of the apparatus. Furthermore, the use of multiple bladders may present advantages over the use of a single bladder: (a) The use of multiple bladders may be called for when there is the possibility of bladder leakage. With multiple bladders, leakage in a single bladder would not be as detrimental to the overall operation of the apparatus as it would in an apparatus equipped with a single bladder. (b) The use of multiple bladders would permit a mix of compressible liquids and gases to be used in the bladders. (c) The use of multiple bladders would be advantageous when housing  10  is very large, or of a certain geometry. (d) Several smaller bladders are typically easier to produce reliably than a single larger bladder. 
     The one or more bladders  23  containing the compressible liquid and/or gas  21  are in restoring force chamber  42 . As the surrounding fluid pressure increases, as would happen in the seawater case with a rising tide, fluid pressure in fluid chamber  40  increases to equal the pressure outside the apparatus in the nearby surrounding fluid. The resulting force on piston  12  drives it toward maximum mark  32 , compressing the one or more bladders containing compressible liquid and/or gas  21 . As the surrounding fluid pressure decreases, pressure in fluid chamber  40  decreases and the force exerted by the now expanding bladder or bladders move piston  12  back toward minimum mark  30 . Fluid entering or exiting the fluid chamber  40  causes turbine  22  to turn, driving electrical generator  24 . 
     The embodiments described thus far differ in the type of restoring force they employ. The types of restoring force described are the spring  20  based type (shown in  FIGS. 1A and 1B ), the type based on compressible liquid and/or gas  21  (shown in  FIGS. 2A and 2B ), and the type based on one or more bladders  23  (shown in  FIGS. 3A ,  3 B,  3 D and  3 E) containing a compressible liquid and/or gas  21 . Other materials, such as many metals, possess spring-like characteristics internally as described by their elasticity and may also be used to supply the restoring force. The use of such materials, labeled as elastic material  34 , is represented in  FIG. 3C  and  FIG. 3F , where it is shown affixed at each end to housing  10  and piston  12 . Piezoelectric materials may also provide the restoring force. Piezoelectric materials are further able to directly generate electric power from the changes in pressure. 
     Additional embodiments of the present invention will now be described in detail. In  FIGS. 4A ,  4 B and  4 C, housing  10  comprises a cavity divided into two chambers by piston  12 . These two chambers include (a) the restoring force chamber  42 , which contains the restoring force and (b) the fluid chamber  40 , which is connected to the fluid surrounding the apparatus. As before, the connection of fluid chamber  40  to the surrounding fluid may be through one or more openings  16  in the wall of the fluid chamber  40 . The restoring force may be of several types, including those described supra. 
     In these embodiments, a turbine is not employed. Instead, as shown in  FIGS. 4A ,  4 B and  4 C, a linkage  17  is connected to piston  12 , or otherwise attached thereto in order to transfer the motion of piston  12 . The linkage  17  serves to transfer the motion of piston  12  to do work. It can drive a linear electric generator, or more commonly, its motion can be converted to rotary motion, through a screw arrangement, or other means known to those skilled in the art, to drive a rotary electric generator. The linkage  17  may also be used to do direct work such as driving a pump. The flexibility of the use of linkage  17  would likely make this embodiment particularly useful in a wide variety of applications. The linkage  17  may comprise a mechanical linkage as shown in  FIGS. 4A ,  4 B and  4 C, or may use different material characteristics such as magnetism to transfer the motion of piston  12  at a distance. 
     In  FIG. 4B , spring  60  resides in the fluid chamber  40  and is affixed to piston  12  on one end and to housing  10  on the other end with fasteners  46 . In this embodiment, spring  60  stretches as fluid pressure increases. It is the consequent compression of spring  60  when fluid pressure decreases that provides the restoring force. 
       FIG. 4C  shows one example of the use of magnetism to provide the restoring force. A first magnet  48  is affixed to piston  12  and a second magnet  49  is affixed to the end of restoring force chamber  42 . Assuming like poles of magnets  48 ,  49  face each other, repelling force between these two magnets provides the restoring force. 
     The embodiments described thus far may be combined in various ways to yield embodiments of greater complexity but which nevertheless are based upon the same principles. Examples include embodiments employing two pistons  12  within a single housing  10 , sandwiching a fluid chamber  40  between two restoring force chambers  42 , or sandwiching a restoring force chamber  42  between two fluid chambers  40 . 
     As the surrounding fluid pressure increases, the pressure in fluid chamber  40  increases to equal the pressure outside the apparatus in the nearby surrounding fluid. The resulting force on piston  12  drives it toward maximum mark  32 . In the embodiment of  FIGS. 4A ,  4 B and  4 C, the provider of the restoring force in restoring force chamber  42  is compressed. In the embodiment of  FIG. 4B , the provider of the restoring force is stretched. As fluid pressure decreases, pressure decreases in fluid chamber  40  and the force exerted by the restoring force moves piston  12  back toward minimum mark  30 . The resulting back and forth motion of piston  12  is transferred to linkage  17  which in turn transfers that motion to perform work, either directly or by driving an electric generator. 
     From the description provided supra, several advantages of the described embodiments include the following: 
     (a) The apparatus is capable of operating on its own without external control. It can be used to provide power in remote locations, such as powering buoys in the ocean. 
     (b) The apparatus is self-contained in that it does not require floats or other references to operate. 
     (c) The apparatus is scalable. A larger unit should be able to produce more power. 
     (d) The methods and apparatus described herein are applicable to diverse fluid environments that experience changes in pressure, such as in the sea and the atmosphere. 
     As described in detail supra, the operation of the apparatus is based upon the countering of the force brought about by the fluid pressure with a restoring force. Subsystems which can provide this restoring force include those based on springs, compressible liquids, gasses, magnetic materials, or any combinations of materials and structures possessing the required elasticity. 
     In general, electrical power is presented to the load device in a manner consistent with the requirements of the load device. For example, a load such as a charging battery may require the electrical power to be in the form of a positive direct current. In some cases, a mechanical means of controlling the motion of the generator may be used to present the desired form of electrical power to the load. More generally, however, a power conditioning unit employing circuitry is used to convert the electrical output from the generator to the desired form. The particular implementation of the circuitry used will depend on the generator used as well as the particular requirements of the load device. The design and usage of power conditioning units and their circuitry is well known to those skilled in the art and it not described in detail herein. 
     Most of the discussion and examples in this document have focused on the operation of the apparatus in a fluid such as seawater. It is noted that an apparatus constructed based on this discussion and the corresponding drawings may be operated in other fluids. The atmosphere is a prominent example. In this case, the fluid is the local atmosphere and operation would be based on changes in barometric pressure instead of seawater pressure. A suitable embodiment for producing power from changes in the barometric pressure might comprise an embodiment described supra, such as an apparatus employing compressible gas within one or more bladders as the restoring force, and employing a linkage attached to the piston to drive an electric generator as shown in  FIGS. 4A and 4D . 
     A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims.