Abstract:
A system for conversion of hydrostatic pressure variations of sea waves into useful energy is disclosed. The system is comprised of a sealed casing ( 12 ) with a membrane-like cover ( 16 ). The cover operates piston ( 52 ) under the pressure of the waves. The piston compresses air into vessel ( 22 ), from which it is discharged ( 86 ) to drive turbine ( 24 ) and produce electric energy ( 26 ). The piston ( 52 ) is recoiled back upwards by second piston ( 56 ), reciprocable within cylinder  58.  The effective volume of the cylinder  58  is variable for counter-pressure adjustment purposes.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to systems for converting the energy of sea waves into useful energy. 
     Most of the state-of-the-art systems proposed and developed for the objective in question were designed for the exploitation of the kinetic energy of sea surf waves; all of these have failed due to technical and other reasons. 
     It is the object of the present invention to provide an off-shore, submerged energy generator utilizing the differential hydrostatic pressure prevailing between peaks and valleys of sea waves. 
     It is a further object of the invention that the generator be self-contained, i.e. working in closed cycles, without any external intervention, servicing, controls, etc. 
     SUMMARY OF THE INVENTION 
     Thus provided according to the present invention there is a system for the conversion of hydrostatic pressure variations such as generated by off-shore sea waves, into useful energy, comprising a casing hermetically sealed and submerged in the sea underneath the waves level, at least one wall of the casing being adapted to become displaced inwards and outwards of the casing under variable hydrostatic pressure applied thereon, a cylinder-and-piston system, (“the first system”) the piston being coupled to the said one wall to move in unison therewith, valve means associated with the first system so that on every stroke of the piston a quantity of a fluid supplied to the cylinder is compressed out of the cylinder into a pressurized fluid vessel and means for converting the energy of the pressurized fluid stored in the pressurized fluid vessel into useful energy. 
     Preferably the system further comprises a second cylinder-and-piston system (“the second system”), the piston thereof being coupled to the piston of the first system to move in unison therewith and means for controllably varying the effective volume of the cylinder of the second system. 
     The effective volume varying means may comprise a source of a liquid and means for introducing/evacuating the liquid into/from the said cylinder. 
     Further means may be provided for increasing the initial pressure in the said effective volume space. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and additional objects, advantages and constructional features of the invention will become more clearly understood in the light of the ensuing description of a preferred embodiment thereof, given by way of example only, with reference to the accompanying drawings, wherein: 
     FIG. 1 is a schematic view illustrating the underwater working location of the system and some of its sub-systems; and 
     FIG. 2 is a schematic representation of the system. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Shown in FIG. 1 is a portion of a sea body of water, between bottom A and surface B, waves C, forming peaks C 1  and valleys C 2 . It is the deferential hydrostatic pressure prevailing near the bottom A (or anywhere else below the surface B), namely the head balance (H 1 -H 2 ) that is harnessed to produce useful energy according to the principles to be explained below. 
     The energy generator generally denoted  10 , is comprised of a barrel-shaped casing  12 , with circular side wall  12   a,  bottom  12   b  and cover  14 . 
     The generator  10  is self-contained in the sense that it works in a closed loop and need not to cooperate with any other system; the functions of certain sub-systems are automatically controlled by feedback from relating other sub-systems, as will be seen later on. This stand-alone feature of the generator is regarded as one of the uniques of the present invention. 
     Furthermore, the generator  10  need not to rest on the sea bottom A, but can be held in buoyancy thereabove using suitable anchoring means (not shown). 
     As further schematically seen in FIG. 1 the cover  14  of the casing  12  is made as a membrane  16 , namely a rigid plate connected to the side wall  12   a  of the casing  12  intermediate a yeildable sheet  16   a,  thus allowing the displacement of the plate  16   a  up and down following changes in the differential pressures applied thereto (between the interior and the outer pressures as will be explained in detail below). 
     The general sub-systems of the generator  10  will be now identified for better understanding of the more detailed description given in conjunction with FIG. 2; these include: 
     First cylinder-and-piston assembly or system  18 ; 
     Second cylinder-and-piston system  20 ; 
     Pressurized fluid (air) accumulating vessel  22 ; 
     Turbine  24  drivingly coupled to electrical power generator  26 ; 
     Liquid supply source  28  for varying the volume of the cylinder of system  20 ; and 
     Interim fluid (air) supply vessel  30 , for supplying the cylinder of system  18 , and connected via conduit  32  to turbine  24  discharge port, thus closing the working loop of the fluid. 
     Referring now for more details to FIG. 2, it should be first noted that in order to function properly, the pressure prevailing within the casing  12  of the generator  10 , denoted Pg, must always be kept less than the minimum hydrostatic pressure applied by the waves B. namely under the water head H 2 ; otherwise, the membrane cover  16  will not respond to the differential pressure (H 1 -H 2 ), i.e. become displaced up and down as desired. 
     Therefore, outer pressure gauge  40  and inner pressure gauge  42  are provided for constantly measuring these pressures, and to govern the operation of an electrically operated, reversible suction pump  44  for lowering the internal pressure; relief valve  46  is associated with the high pressure vessel  22  for increasing the internal pressure, as the case may be. 
     A central computerized unit CPU is included, which controls the various operational parameters of the generator sub-systems as will be explained below. 
     The first cylinder-and-piston system  18  comprises cylinder  50  and piston  52  with piston rod  54 , which extends upwards where it is rigidly connected to the plate  16 , as well as downwards out of the cylinder  50 , where it becomes the rod of piston  56  of the second cylinder-and-piston system  20 , provided with cylinder  58 . Thus defined are upper and lower effective spaces denoted S 1  and S 2 . 
     The system  18  acts as a double-stroke air pump, compressing air supplied from vessel  30  to vessel  22 . There are provided two unidirectional inlets  60 ,  62  connected to the vessel  30  on the one hand, and two unidirectional outlets  64 ,  66 , leading to the vessel  22 , as shown. Reciprocation of the piston  52  in either direction will therefore pressurize air into the vessel  22 . 
     Referring to the second cylinder-and-piston system  20 , it will be noted that the stroke of the piston  52  is opposed by that of the piston  56 , both being mounted to a common rod  54 . 
     The cylinder  58  is of a variable effective volume (space S 3 ), achieved by filling it partly, to a controlled amount, with liquid  70 , such as oil, through pump  72  from container  28 . 
     The variable space S 3  within the cylinder  58  underneath the piston  56  is also adapted to be charged with pre-determined, variable pressure to be supplied from pressurized air vessel  22  via control valve  80  and pressure regulator  82 . 
     The turbine (or air motor)  24  is operated by the pressurized air stored in vessel  22 , via control valve  84  and pressure regulator  86 . 
     As already explained, the discharge port of the turbine  24  is connected by conduit  32  and control valve  88  to the interim air supply vessel  30 . 
     Finally, a rechargeable battery  90  recharged by the generator  26  (through voltage regulator  92 ) is included for supplying electric power to operate the CPU, the suction pump  44 , the oil pump  72  and all the control valves and other devices as apparent from the foregoing description. 
     The operation of the generator  10  proceeds as follows. As already mentioned, the internal pressures Pg is pre-set and maintained to a value less to a certain extent, than the value of the external hydrostatic pressure to which the membrane cover  16  is subjected. Otherwise, should the internal pressure exceed the external pressure, the membrane cover would not respond to, i.e. become displaced downwards under the external pressure represented by the water head H 1 ; and if the internal pressure is too low, again the membrane  16  will not function, but remain stationary at its lowermost position, irrespective of a reduced water head H 2 . 
     Regulation of the pressures is maintained by the suction pump  44 , or the relief valve  46  (controlled by pressure gauges  40 ,  42 ), in accordance with the actual working conditions, taking into account, among other parameters, the height of the sea waves B at any given time. 
     Supposing that the internal pressure has been properly adjusted, the piston  52  is at its uppermost position, and the generator is first subjected to the increased hydrostatic pressure proportional to a wave peak C 1 , then, under such elevated pressure the membrane cover  10  will descend. The piston will move down and a quantity of air (space S 2 ) will be compressed into the vessel  22 . 
     Simultaneously, a pressure will be built-up in the space S 3 . This counter-pressure is essential in order to achieve the upwards stroke of the piston  52  along with the lifting of the membrane cover  16 , after the wave peak C 1  has passed away and a lower hydrostatic pressure, related to head H 2 , prevails. 
     The appropriate adjustment of the counter pressure, which is of major importance for starting and maintaining the cyclic operation of the unit, is achieved by adjusting at least one of the following variants: Changing the effective volume S 3 , and/or charging extra pressure thereinto. The first variant is accomplished in the present example by the filling/evacuating the oil  70  into/out of the lower part of the cylinder  58 ; and the second variant is adjusted by partly directing compressed air from the vessel  22 , though pressure regulated valve  82  into the space S 3 . 
     The combination of the two variants, each being individually controllable by the CPU, along with suitable calculation of the area of the piston  56  relative to that of the piston  52  ensure the availability of a wide range of changeable factors required for achieving the desired result, namely, effectively, lifting the piston  56  when a relative relief of force is sensed by the membrane  16 , caused by the decreased hydrostatic pressure H 2 , with minimum loss of energy. 
     As the compression cycles continue, the pressure will be built-up within the vessel  22 . Upon reaching a level sufficiently high, pressure regulator  86 , by a command of the CPU, will open and the compressed air will drive the turbine  24  for as long as the pressure remains effective for that purpose. Again controlled by the CPU, the valve  84  will close and a new cycle will be started. 
     Low pressure air is directed through conduit  32  from the outlet port of the turbine  24  to the vessel  30 , and therefrom to the cylinder  50 . The air is therefore recycled in a closed working loop (except for a portion either expelled from the relief valve  46 , or sucked by suction pump  44 —as already mentioned above). 
     It goes without saying that a plurality of generators as herein described, are readily adapted to work in parallel, thus compensating for the inherent operating pauses of each one of them. 
     Once installed, no maintenance or servicing is requested for a long period (say, for replacing the batteries  90 ). It is thus suitable for use along coasts of deserted areas, where the supply of conventionally produced electricity is too expensive. 
     Those skilled in the art will readily understand that various changes, modifications and variations may be applied to the invention as above exemplified without departing from the scope of the invention as defined in and by the appended claims.