Abstract:
A fluid powered linkage ( 12 ) has at least three side plates ( 18 ) of substantially equal width joined by connectors ( 17 ) to form a polygon of variable cross sectional area. An upper plate and a lower plate enclose a variable volume within the polygon. At least one port ( 37 ) allows fluid to enter into or leave from the enclosed variable volume in a controllable manner. Seals prevent fluid from entering or leaving the enclosed variable volume other than through the one or more ports. Two abutments ( 19, 11 ) are located on the side plates or connectors and the distance between the two abutments varies non-linearly with, but in the same direction as, the variable cross-sectional area. Optionally, an inner surface of one or more of the side plates defines a recess. A preferred linkage has a cross-section in the shape of a diamond or rhombus of varying internal angles, or a half or quarter thereof. In use, the obtuse angle preferably ranges from nearly 180 degrees to about 135 degrees. The linkage is used in an apparatus for producing a fluid output with altered pressure, volume or flow compared to a fluid input and a hydraulic motor.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention relates to fluid powered systems and in particular to fluid powered linkages and engines.  
         BACKGROUND OF THE INVENTION  
         [0002]    In many hydraulic or pneumatic systems, a master cylinder or pump is fluidly connected to a slave cylinder to transmit force or work to a remote location. When master and slave cylinders of unequal diameters are used, the force applied by the slave cylinder may be more or less than the force applied to the master cylinder. Similarly, the displacement of the slave cylinder may be more or less than the displacement of the master cylinder. In these systems, however, there is always a linear relationship between the force or displacement of the slave cylinder and the force or displacement of the master cylinder. Similarly, when a pump is used to drive a slave cylinder, the force exerted by the slave cylinder is always linearly related to the pressure produced by the pump. To achieve any other relationship requires additional mechanical linkages at one end. Similarly, the design of hydraulic or pneumatic engines using cylindrical linkages is limited by such linear relationships.  
         SUMMARY OF THE INVENTION  
         [0003]    An object of the present invention is to provide a fluid powered, preferably hydraulic, linkage with non-linear relationships between (a) the flow, volume or pressure of fluid added to the linkage and (b) the displacement of the linkage or the force applied by the linkage. Another object is to provide an apparatus for producing a fluid output with altered pressure, volume or flow compared to a fluid input. Yet another object of the present invention is to provide an engine using a linkage as mentioned above. These objects are met by the combination of features, steps or both found in the independent claims, the dependent claims disclosing further advantageous embodiments of the invention. The following summary may not describe all necessary features of the invention which may reside in a sub-combination of the following features or in a combination with features described in other parts of this document.  
           [0004]    In one aspect, the invention provides a fluid powered linkage having at least three sides of substantially equal width joined by connectors to form a polygon of variable cross sectional area. Side plates enclose a variable volume within the polygon. At least one port allows fluid to enter into or leave from the enclosed variable volume in a controllable manner. Seals prevent fluid from entering or leaving the enclosed variable volume other than through the one or more ports. Two abutments are located on the sides or connectors and the distance between the two abutments varies non-linearly with, but in the same direction as, the variable cross-sectional area. Optionally, an inner surface of one or more of the sides defines a recess.  
           [0005]    Preferred linkages have a cross-section in the shape of a diamond or rhombus of varying internal angles, or a half or quarter thereof. Where the cross-section is a diamond, four sides are connected by hinges. The four sides are of about equal length and the abutments are located substantially at the obtuse angles of the diamond. In use, the obtuse angle preferably ranges from nearly 180 degrees to about 135 degrees. A preferred seal is made of a resilient membrane forming a plenum which varies in volume as the membrane expands or contracts. The membrane is placed with the variable volume enclosed by the linkage and a port connects the interior of the plenum with the outside of the linkage.  
           [0006]    In another aspect, the invention relates to an apparatus for producing a fluid output with altered pressure, volume or flow compared to a fluid input. The apparatus comprises a linkage as described above and a piston movable in a cylinder to vary an enclosed volume in the cylinder. A cylinder port allows fluid to exit or enter the enclosed volume of the cylinder. A rod between one of the two abutments of the linkage and the piston ties the movement of one to the other. One or more spacing members to hold the other of the two abutments of the linkage at a constant spacing from the cylinder. Preferably, the area of the piston is equal to or slightly more than the area of each of a side of a diamond-shaped linkage and less than twice the area of a side of the diamond-shaped linkage.  
           [0007]    In yet another aspect, the invention relates to a fluid powered motor comprising the apparatus described above. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    Preferred embodiments of the present invention will now be described with reference to the following figures.  
         [0009]    [0009]FIG. 1 is a schematic front-view representation of a system having a diamond-shaped linkage.  
         [0010]    [0010]FIG. 2 is a schematic side-view representation of the system of FIG. 1.  
         [0011]    [0011]FIG. 3 is a schematic side-view representation of a diamond-shaped linkage.  
         [0012]    [0012]FIG. 4 is a chart comparing displacement and volume for a diamond-shaped linkage.  
         [0013]    [0013]FIG. 5A shows a right angled triangle linkage.  
         [0014]    [0014]FIG. 5B shows a linkage in the shape of a segment of a cylinder.  
         [0015]    [0015]FIG. 6A shows an isosceles triangle linkage for which the base of the triangle has variable length.  
         [0016]    [0016]FIG. 6B shows an isosceles triangle linkage for which the sides of the triangle have variable length.  
         [0017]    [0017]FIG. 7 shows the fluid input and output of a system having an isosceles triangle linkage and a cylindrical linkage.  
         [0018]    [0018]FIG. 8 is a schematic representation of the system of FIG. 1 used in an engine.  
         [0019]    [0019]FIG. 9 is a schematic representation of the system of FIG. 1 with its output attached to a reservoir.  
         [0020]    [0020]FIG. 10 is a schematic representation of the system of FIG. 1 used to position a load depending on pressure in the diamond-shaped linkage.  
         [0021]    [0021]FIG. 11 are isometric representations of alternate sides of a diamond-shaped linkage.  
         [0022]    [0022]FIG. 12 is a schematic representation of the system of FIG. 1 used in another engine. 
     
    
     DETAILED DESCRIPTION OF EMBODIMENTS  
       [0023]    Referring now to FIGS. 1 and 2, a fluid powered system  10  has a diamond-shaped linkage  12  and a cylindrical linkage  14  connected by a solid rod  16 . The diamond-shaped linkage  12  has four sides  18 , preferably of about equal length and area, connected by connectors  17 , which are preferably hinges  20 , such that a side angle  22  can vary from nearly 0 degrees to 90 degrees. Preferably, however, the side angle  22  does not exceed about 45 degrees, the diamond-shaped linkage being apparently less efficient as the side angle  22  increases beyond the point where the obtuse angles of the diamond-shaped actuator are less than about 135 degrees. Side plates  24  enclose a variable volume inside of the four sides  18  of the diamond-shaped linkage  12  but do not prevent movement of the sides  18  parallel to side plates  24 . The volume contained in the diamond-shaped linkage  12  is surrounded and sealed by a membrane  26  located inside of the diamond-shaped linkage  12 . The membrane  26  is made of resilient material such as rubber which forms a plenum which varies in volume as the membrane expands or contracts. The membrane  26  is pre-stretched and lubricated with liquid silicone so that it requires little force to expand it once inside of the diamond-shaped linkage  12 . A thicker piece of rubber is preferably placed between the hinges  20  and the membrane  26  to reduce abrasion of the membrane  26 . Alternately, a system of hydraulic seals could be used to replace the membrane  26  such that the sides  18  and side plates  24  form a plenum directly.  
         [0024]    One of the hinges  20  or a part of one side  18  which is very close to one of the hinges provides a lower abutment  19  located substantially at an obtuse angle of the diamond-shaped linkage  12 . The lower abutment  19  and the side plates  24  are attached to a base plate  28  which allows the diamond-shaped linkage  12  to be attached to a machine etc.  
         [0025]    The cylindrical linkage  14  has a piston  30  sealed but slidable within a cylinder  32  attached to a mounting plate  34 . As the piston  30  moves within the cylinder  32  it varies a volume enclosed in the cylinder  32 . A cylinder port  31  allows fluid  39  to exit or enter the enclosed volume of the cylinder  32 .  
         [0026]    The rod  16  connects the piston  30  to the diamond-shaped actuator at an upper abutment  21  located substantially at an obtuse angle of the diamond-shaped linkage  12 . One or more spacing members  23  hold the mounting plate  34  at a constant spacing from the base plate  28  and thus hold the lower abutment  19  at a constant spacing from the cylinder  32 . Despite the use of the terms lower abutment  19  and upper abutment  21 , the diamond-shaped linkage  12  may also be placed in other orientations such as horizontally with the lower abutment  19  and upper abutment  21  spaced horizontally rather than vertically from each other. Similarly, the cylindrical linkage  14  and other components may be oriented in various ways.  
         [0027]    The base plate  28  and mounting plate  34  are fixed relative to each other. A fluid  36  flows through an inlet pipe  38  sealed in communication with the membrane  26  in the diamond-shaped linkage  12  through a port  37  such that fluid  36  can leave or enter the plenum of the membrane  26  enclosing the variable volume of the diamond-shaped linkage  12 . The membrane  26  provides a seal around the variable volume of the diamond-shaped linkage  12  which prevents fluid  36  from entering or leaving the variable volume of the diamond-shaped linkage other than through the port  37 . As fluid  36  enters the diamond-shaped linkage  12  it forces it open, increasing the side angle  22  and the distance between the lower abutment  19  and the upper abutment  21  which pushes the rod  16  away from the base plate  28 . The rod  16  in turn pushes the piston  30  driving driven fluid  39  out of the cylindrical linkage  14  through an outlet pipe  40 .  
         [0028]    In the fluid powered system  10 , the cylindrical linkage  14  serves to convert the movement of the rod  16  from mechanical force to a pressurised volume of driven fluid  39 . By choosing a larger or smaller diameter cylindrical linkage  14 , the pressure or displacement of driven fluid  39  in the outlet pipe  40  may also be modified as in a conventional master-slave hydraulic or pneumatic system. These conversions, however, are linear in nature. It is the action of the rod  16  compared to the flow of fluid  36  into the diamond-shaped linkage  12  that is primarily of interest.  
         [0029]    One characteristic of concern is the relationship between the displacement of the rod  16  and the volume of fluid  36  entering the diamond-shaped linkage  12  which is equal to the change in volume within the diamond-shaped linkage  12 . Referring now to FIG. 3, a diamond shaped linkage  12  is divided into four quadrants  42 . The sides  18  of the diamond shaped linkage  12  have length L and width W, width W extending out of the page in FIG. 3. Each quadrant  42  has an angle A, a displacement D and a volume V. Accordingly,  
           D= 2 ·L ·sin  A ; and,  (1)  
           V= 2 ·W·L  sin  A·L  cos  A.   (2)  
         [0030]    By selecting different values of A between 0 and 45 degrees, a chart comparing volume and displacement of the diamond shaped linkage  12  can be drawn. Such a chart is shown in FIG. 4 for a diamond-shaped linkage  12  of the size indicated. At very small volumes V, increases in D are nearly proportional to increases in V. At larger volumes, however, D increases faster than V.  
         [0031]    Referring to FIGS. 1 and 2, the combination of a diamond shaped linkage  12  with a cylindrical linkage  14  creates an apparatus for producing a fluid output with altered pressure, volume or flow characteristics compared to a fluid input. In such an apparatus, it is preferred if the volume displaced by the cylindrical linkage for a selected movement of the rod  16  is greater than the volume added to the diamond shaped linkage  12  to produce the selected movement of the rod  16 . This occurs over the entire range of movement of the diamond shaped linkage  12  if the area of the piston  30  is at least equal to the area of a side  18 . For example, a diamond shaped linkage  12  having four equal sides  18  each 1″ by 10″ in size is connected by a rod  16  to a cylindrical linkage  14  having a piston  30  of 10 square inches in area. To displace 10 cubic inches of fluid in the cylindrical linkage requires the rod to move 1″ which can be achieved by filling the diamond shaped linkage  12  with just under 10 cubic inches of fluid of the appropriate pressure. To displace 70 cubic inches of fluid in the cylindrical linkage requires the rod to move 7″ which can be achieved by filling the diamond shaped linkage  12  with about 65 cubic inches of fluid of the appropriate pressure. To displace 140 cubic inches of fluid in the cylindrical linkage requires the rod to move 14″ which can be achieved by filling the diamond shaped linkage  12  with about 100 cubic inches of fluid of the appropriate pressure. The area of the piston  30  is preferably less than twice the area of a side  18  and more preferably between 1.0 and 1.1 times the area of a side  18 .  
         [0032]    Linkages in the shape of one or two quadrants  42  of the diamond shaped linkage  12  can also be constructed and will have similar characteristics. These linkages use three sides  18  (although the sides  18  may also be given other names) and at least two connectors  17  which provide a sliding connection. In FIG. 5A, a right angled linkage  44  has a single side  18  and an end plate  46 . Grooves  48  in the side plates  24  accept pins  50  attached to the ends of the side  18  and allow the side  18  to move as would a single quadrant  42  of the diamond-shaped actuator  12 . In FIG. 6A, an isosceles triangle linkage  52  has two sides  18  having pins  50  on their distal ends. The isosceles triangle linkage  52  has the characteristics of two quadrants  42  of the diamond-shaped actuator  12  and can be used with a rod  16  as shown with a solid line or with a rod  16 ′ as shown with a dashed line.  
         [0033]    [0033]FIGS. 5B and 6B show related linkages. In FIG. 5B, a first end of a side  18  pivots on a hinge  20  while a second end of the side  18  rotates through an arc creating a linkage with the shape of a segment of a cylinder. A curve  108  in the end plate  46  and a seal  110  restrain the membrane  26  in the proper shape. This linkage is similar to the linkage in FIG. 5A but with a different relationship of pressure, volume and force produced by the rod  16 . The linkage of FIG. 5A may be more efficient because it has no internal forces acting on the second end of the side  18 . In FIG. 6B, two sides are connected to each other by a hinge  20  and to the base plate  28  by a linear bearing  112  connected to a pivot  114 . This linkage is similar to the one in FIG. 6A but with a different relationship of pressure, volume and force produced by the rod  16  because the sides  18 , rather than the base of the triangle, are of varying length.  
         [0034]    Now referring to FIG. 7, a second fluid powered system  54  has an isosceles triangle linkage  52  coupled by a rod  16  to a cylindrical linkage  14 . In the particular example shown, the sides  18  of the isosceles triangle linkage  52  are 10 inches long and 1 inch wide for an area of 10 square inches. The cross-sectional area of the cylindrical linkage  14  is also 10 square inches. The volume and displacement of the isosceles triangle linkage  52  and the cylindrical linkage  14  are shown at various points of displacement of the rod  16 . At each of these points of displacement, the volume of driven fluid  39  displaced by the cylindrical linkage  14  is compared to the volume of fluid  36  entering the isosceles triangle linkage  52 . As suggested by FIG. 4, the volume of driven fluid  39  leaving the second fluid powered system  54  increases faster than the volume of fluid  36  entering the second fluid powered system  54  as displacement increases.  
         [0035]    Now referring to FIG. 8, an engine  56  has diamond-shaped linkages  12  coupled to a cylindrical linkages  14  as in FIG. 1. In the example shown, the diamond-shaped linkages  12  have each a maximum volume of 100 cubic inches, a maximum displacement of 14 inches and springs  57  to return them to a nearly volume-less position. The cylindrical linkages  14  have an area of 10 square inches and thus move 140 cubic inches of liquid when operated by the diamond-shaped linkages  12 . Other sizes of linkages may be used, but the volume of fluid moved by a cylindrical linkage  14  is greater than the maximum volume of its corresponding diamond-shaped linkage  12 . The engine  56  also has check valves  58 , normally closed valves  60  (which open when pressed), and hydraulic actuators  62 . The hydraulic actuators  62  have internal springs which drive a piston as well as plungers attached to the piston for triggering the normally closed valves  60 . The hydraulic actuators  62  are provided in pairs of a high range actuator  64  and a low range actuator  66 , referring to the average force of the internal spring. Despite the difference in average force of their internal springs, however, the range of force of the high range actuators  64  and low range actuators  66  in a pair overlap. For example, high range actuators  64  having a spring varying from 5 to 10 pounds force over their stroking range and corresponding low range actuators  66  having a spring varying from 3 to 7 pounds force over their stroking range are appropriate for use with the linkages described above. Preferably, the high range actuators  64  displace a volume similar to the maximum volume of the next downstream diamond-shaped linkage  12  when moving through their stroking range. Further preferably, the low range actuators  66  displace a volume when moving through their stroking range similar to the difference between the volume of fluid moved by the next downstream cylindrical linkage  14  and the maximum volume of the next downstream diamond-shaped linkage  12 . Also provided in the engine  56  are shut off valves  68 , a start valve  70 , an inlet  72  for pressurize fluid, turbines  74  to extract energy from the engine  56  and an outlet  76 .  
         [0036]    To operate the engine  56 , a first pair  78  of actuators  62  are filled with pressurized fluid from the inlet  72  to their capacity and the system filled and vented. When, the start valve  70  is opened the first pair  78  of actuators  62  fill the next downstream diamond-shaped actuator  12  extending it to its maximum volume. Excess fluid flows through a by-pass line  84  as permitted by the relevant valves  60  as they open. As the diamond-shaped actuator  12  fills, it displaces driven fluid  39  in the corresponding cylindrical linkage  14  which fills a second pair  80  of actuators  62 , filling the high range actuator  64  first. When the second pair  80  of actuators  62  are filled, valves  60  are opened providing a path for fluid in the by-pass line  84  and allowing the springs  57  to retract the diamond-shaped linkage  12 . Before liquid is released from the second pair  80  of actuators  62 , however, the cylindrical linkage  14  is filled with liquid  36  from the diamond-shaped linkage  12  and the excess liquid from the first pair  78  of actuators  62  as it similarly retracts. Once the cylindrical linkage  14  is refilled, the second pair  80  of actuators  62  are release to flow liquid through a turbine  74  to produce mechanical or electrical energy. Once the liquid flows through the turbine  74  it is released through an outlet  76 , preferably with minimal pressure or velocity. Alternately, the liquid passing through the turbine  74  may be used to drive a second diamond-shaped actuator  12  as shown.  
         [0037]    Now referring to FIG. 9, a diamond-shaped linkage  12  is coupled to a cylindrical linkage  14  as in FIGS. 1 and 8. The outlet of the cylindrical linkage  14 , however, is connected to a storage tank  86 . The storage tank  86  has a large horizontal cross-sectional area such that driven fluid  39  (which is a liquid in this example) in it has a near constant height despite movement of driven fluid  39  by the linkages. Such a storage tank  86  may be used in place of the actuators  62  downstream of a cylindrical linkage  14  in FIG. 8 to provide a more nearly constant pressure against the driven liquid  39 . This alleviates a disadvantage of the actuators  62  that the force required to fill the actuators  62  increases with displacement. Contrarily, force in the rod  16  produced by the diamond-shaped actuator  12  decreases with displacement for a given pressure of liquid  36 . Advantageously, a very tall cylindrical linkage  14  having a very small horizontal cross-sectional area used in the arrangement of FIG. 8 will require less force to move driven liquid  39  into the storage tank  86  as displacement increases.  
       EXAMPLE 1  
       [0038]    Now referring to FIG. 10, a diamond-shaped linkage  12  is used to position a hanging mass  88  of 50 pounds. In this case, however, the diamond-shaped linkage  12  is powered by compressed air. An air compressor  90  supplies pressurized air (through suitable reducing valves and restrictors if required) to the inlet pipe  38 . Air pressure gauge  92  and pressure controller  94  (operable to bleed air from the inlet pipe  38 ) are used to control and measure pressure in the diamond-shaped linkage  12 . The rod  16  is supported by linear motion bearing  96  and attached to a cable  98  wrapped around a pulley  100  such that the cable  98  is very nearly parallel to the rod  16  before contacting the pulley  100 . The remainder of the cable  98  hangs downwards and is attached to the mass  88 . Scales  102  measure the displacement of the rod  16  and mass  88 . The sides  18  of the diamond-shaped linkage  12  are 9 inches long and 2.625 inches wide. A stop  104  prevents the total displacement  106  from being less than 1.938 inches. Air pressures of less than 5 psi were used. The gauge  92  is stated to be accurate to 0.05 psi and all measurements are relative to atmospheric pressure.  
         [0039]    At a pressure of 1.2 psi, the rod  16  (and mass  88 ) started to move and advanced {fraction (1/32)} inches. Pressure was increased to 2.5 psi and the rod  16  moved to a displacement of 1{fraction (15/16)} inches. Pressure was lowered to 1.75 psi and the rod  16  moved to a displacement of 1{fraction (9/16)} inches. Pressure was raised to 2.05 psi and the rod  16  moved to a displacement of 1⅝ inches. The mass  88  was stable at all of these positions. In comparison, with a cylindrical linkage, holding the mass  88  in a stable position would only occur at one pressure setting and would require very accurate pressure maintenance. To move the mass  88  would require a precise momentary application of a different pressure and then a return to precisely the first pressure setting.  
       EXAMPLE 2  
       [0040]    A triangular linkage as shown in FIG. 6B powered by an air compressor was linked by a rod to a 4 inch low friction pneumatic actuator fed by a second compressor at 10.75 psig, or a total force of 135 pounds force. Different sides  18 A, B and C as shown in FIG. 11 were used. Sides  18 B and  18 C have cavities or recesses  120  carved into the faces which contact the membrane. With side C, a hose from the air compressor was connected to the membrane in contact with side  18 CI and a second hose was connected to a second membrane in contact with the inside cavity of side  18 CII. The second membrane inside of side  18 CII was not in contact with the membrane which contacts side  18 CI. Both hoses had a common source of air pressure.  
         [0041]    For each side  18 , the linkage was first set up with no pressure in the membrane and the sides  18  parallel to each other. Pressure in the membrane was increased until the sides  18  moved against the pneumatic actuator. With side  18 A, the actuator started to move with a pressure of 6 to 7 psig in the linkage. With side  18 B, the actuator started to move with a pressure of 3.5 to 4 psig in the linkage. With side  18 C, the actuator started to move with a pressure of 2 to 2.5 psig in the linkage.  
       EXAMPLE 3  
       [0042]    A diamond-shaped linkage was mounted vertically so as to have a highest and a lowest abutment located at the obtuse angles of the diamond-shaped linkage and vertically above each other. Each side plate of the diamond-shaped linkage was 9.125 inches by 2.625 inches or about 23.95 square inches in area. The lowest abutment was secured to a fixed and stable platform. A rod extended upwards from the highest abutment. A scale was used to temporarily hold the rod and the diamond-shaped linkage at a slight displacement with the lowest abutment still secured to the platform. The scale registered a weight of 10 pounds and was then released. Weighed separately, the diamond-shaped linkage weighs 4.2 pounds and the rod weighed 4.9 pounds. An additional 50 pound mass was placed on top of the rod. Compressed air was fed into the diamond-shaped actuator through a pressure reducer and control valves. The gauge pressure of the air inside of the diamond shaped linkage was measured in inches of water. The following results were recorded.  
                                             Approximate Gauge Pressure in           Inches of Water   Inches of Displacement of the Rod                                56   1       59   2       61   2.4       62   2.5       63   2.7       66   2.9                  
 
         [0043]    More accurately, at a displacement of the rod of 2.5 inches, the gauge pressure was 61.8 inches of water and the internal volume of diamond shaped linkage was 59.3 cubic inches.  
       EXAMPLE 4  
       [0044]    The apparatus of Example 3 was used as described in Example 3 except that different air pressures were applied. At 30 inches of water gauge pressure, the rod was displaced by 0.02 mm. Gauge pressures of 51, 54, 57 and 59 inches of water produced displacements of 0.4, 0.5, 0.6 and 0.8 mm respectively. The uppermost two sides of the diamond-shaped linkage were then removed and their inner faces routered to provide an inner surface defining recesses. The apparatus was then reassembled. After re-assembly, a gauge pressure of 24 inches of water produced a displacement of 0.02 mm. Gauge pressures of 51, 54, 57 and 59 inches of water produced displacements of 0.7, 0.8, 0.9 and 1.1 mm respectively. ie. greater displacements than those produced at the same pressures before the sides were recessed.  
       EXAMPLE 5  
       [0045]    [0045]FIG. 12 shows a schematic representation of a hydraulic engine  199 . A diamond shaped linkage  12  having sides of 7.5 inches by 1.6 inches and a cross-sectional area of 12.4 square inches is oriented with its upper abutment  21  spaced horizontally from its lower abutment  19 . The upper abutment  21  is connected by a rod  16  to a cylindrical linkage  14  oriented horizontally and located at the same elevation as the diamond-shaped linkage  12 . One or more spacing members (not illustrated) hold the lower abutment  19  of the diamond-shaped linkage  12  at a constant spacing from a cylinder  32  of the cylindrical linkage  14 . The design of the hydraulic engine  199  is based on the area of the sides  18  of the diamond shaped linkage  12  being equal to or slightly less than the area of the piston  30  of the cylindrical linkage  14 . In this example, this is achieved by the piston  30  having an area of 12.6 square inches or 1.5% more area than each of the sides  18 .  
         [0046]    A cylinder port  31  communicates with a normally closed (meaning that it remains closed until energized) first solenoid valve  210  and a first solenoid switching valve  211 . The solenoid switching valves are shown in FIG. 12 as having a common (“C”), normally closed (“NC”) and normally open (“NO”) port. When not energized, these valves allow flow from the C to NO ports. When energized, these valves allow flow from the C to NC ports. Flow from the NO to NC ports is not permitted in either position.  
         [0047]    The first solenoid valve  210  communicates with a cushion tank  209  pressurized by a compressed air supply  140  acting through a first pressure reducing valve  200  and a first hand valve  204 . The first solenoid valve  210  also communicates with a first check valve  215  (which permits flow only in the direction of the arrow) and the common port of a second solenoid switching valve  212 . The normally closed port of the first solenoid switching valve  211  communicates with the normally open port of the second solenoid switching valve  212 . The normally closed port of the second solenoid switching valve  212  communicates with the normally closed port of a third solenoid switching valve  213 . The normally open port of the first solenoid switching valve  211  communicates with the normally open port of a third solenoid switching valve  213 . The common port of the third solenoid switching valve  213  communicates with a second hand valve  208  which communicates with the port  37  of the diamond-shaped linkage  12 . The common port of the third solenoid switching valve  213  also communicates with a normally open second solenoid valve  214  which in turn connects with a second check valve  216 . The first check valve  215  and second check valve  216  communicate with each other and with a second cylindrical port  331  of a second cylindrical linkage  314 .  
         [0048]    A second piston  330  of the second cylindrical linkage  314  is connected to a second rod  316 . A second cylinder  332  of the second cylindrical linkage  314  sweeps through a volume of about 7.4 cubic inches. With the second cylinder  332  at its lowest volume, the second rod  316  contacts and opens a normally closed first push button valve  218 . When open, the first push button valve  218  vents the common port of second push button valve  219  and the pilot of an air valve  220  to atmosphere. Without pressurized air on the pilot of the air valve  220 , the common port of the air valve  220  is vented to atmosphere through the normally open port of the air valve  220 . When pressurized air is supplied to the pilot of the air valve  220 , air can flow from the common port to the normally closed port. With the second cylinder  332  at its highest volume, the second rod  316  contacts and opens a normally closed second push button valve  219 . The common port of the second push button valve  219  communicates with the pilot of the air valve  220  while the normally closed port of the second push button valve  219  communicates with a second compressed air supply  142  through a second pressure reducing valve  225 . The second compressed air supply  142  also communicates, through a third pressure regulator  202  with the normally closed port of the air valve  220 . The common port of the air valve  220  communicates with a sealed volume of the second cylindrical linkage  314  on the dry side of the second cylindrical linkage  314  which is on the opposite side of second piston  330  from the second cylinder  332 .  
         [0049]    The rod  16  has a linkage  227  attached to it. When the diamond shaped linkage  12  is at its lowest volume of about 12.2 cubic inches, the linkage  227  contacts a normally open push button switch  223  and a normally open first end switch  221 . When the diamond shaped linkage  12  is at its highest volume of about 15.7 cubic inches, the linkage  227  contacts a normally closed second end switch  222 . A return spring  226  extends as the diamond-shaped linkage  12  increases in volume and retracts the diamond-shaped linkage  12  to its lowest volume when pressure to the port  37  of the diamond-shaped linkage  12  is released. A control relay  224  and control relay contacts  230  are provided. The various electrical components are wired to a circuit as shown in the upper left hand corner of FIG. 12.  
         [0050]    After the components are assembled as described above, the hydraulic engine  199  is filled with hydraulic fluid and all air is vented. With the diamond-shaped linkage  12  at its minimum volume, the cylindrical linkage  14  contains about 50 cubic inches of fluid, the cushion tank contains about 2.5 liters of fluid and the second cylindrical linkage  314  is substantially empty. Second hand valve  208  is closed to prevent the hydraulic engine from starting until second hand valve  208  is opened. The hydraulic engine  199  may be started in any position, but will be described for example starting with the diamond-shaped linkage  12  at its lowest volume and the linkage  227  holding the push button switch  223  closed and the first end switch  221  closed.  
         [0051]    The cushion tank  209  is pressurized via the first pressure reducing valve  200  by opening the first hand valve  204 . After the cushion tank  209  is pressurized, the first hand valve  204  is closed. The first pressure reducing valve  200  (ie. the pressure in the cushion tank  209 ) controls the speed of operation and power output for the hydraulic engine  199 . The higher the pressure setting of the first pressure reducing valve  200 , the more power is generated. In this example, the hydraulic motor  199  was operated with the cushion tank  209  initially set at pressures ranging from 55 PSIG to 85 PSIG but a higher pressure is preferred, up to the mechanical limit of the components of the hydraulic motor. The third pressure reducing valve  202  is set for 20 PSIG above the setting of the first pressure reducing valve  200 . The second pressure reducing valve  225  is set to satisfy the pilot requirements of air valve  120  without damaging the air valve  220 . In this example, the second pressure reducing valve  225  is set to about 95% of the pressure in the cushion tank  209 .  
         [0052]    To operate the hydraulic motor  199 , a 24 volt potential is applied to the electric circuit the second hand valve  208  is opened. The contacts of push buttton switch  223  are closed which energizes the relay  224  causing it to pull the control relay contacts  230  closed to keep valves  210 ,  212 ,  213  and  214  energized even after push button switch  223  opens its contacts. Hydraulic fluid in the cushion tank  209  communicates with and pressurizes the diamond-shaped linkage  12  and the cylinder  32  of the cylindrical linkage  14 . A small amount of fluid may flow into the diamond-shaped linkage as its membrane compresses.  
         [0053]    The cushion tank  209  causes hydraulic fluid at a constant pressure to be exerted at the port  37  and cylinder port  31 . The total force generated at the upper abutment  21  of the diamond-shaped linkage  12  pushes rod  16  forward to force the piston  30  to displace fluid out of the cylindrical linkage  14 . The linkage  227  advances which causes push button switch  223  to open its contacts and first end switch  221  to open its contacts. As mentioned above valves  210 ,  212 ,  213  and  214  remain energized. Fluid displaced travels from the cylindrical linkage  14  flows through first solenoid valve  210 , through second solenoid switching valve  212 , through third solenoid switching valve  213 , through second hand valve  208  and into the diamond-shaped linkage  12 . Any difference in volume of fluid displaced from the cylindrical linkage  14  and flowing into the diamond-shaped linkage is compensated for by the cushion tank  209 . The diamond-shaped linkage  12  continues to fill with hydraulic fluid until the linkage  227  opens the contacts of second end switch  222 .  
         [0054]    Opening the contacts of second end switch  222  de-energizes valves  210 ,  212 ,  213  and  214  and control relay  224 . Control relay contacts  230  open causing valves  210 ,  212 ,  213  and  214  to remain in their de-energized position. This isolates the cushion tank  209  from the diamond-shaped linkage  12 , the cylindrical linkage  14  and the second cylindrical linkage  314 . When the second solenoid valve  214  opens, it depressurizes the diamond-shaped linkage  12  and the cylindrical linkage  14  by allowing a very small volume of fluid to enter the second cylindrical linkage  314 . The amount of fluid entering the second cylindrical linkage  314  depends in part on the elasticity of the membrane of the cylindrical linkage  314 . In this example, the second cylindrical linkage  314  reached its maximum volume every two or three cycles. The return springs  226  can then pull the diamond-shaped linkage  12  and the cylindrical linkage  14  back toward their starting point.  
         [0055]    As the diamond-shaped linkage  12  retracts (ie. decreases in volume), the cylindrical linkage  14  is refilled with fluid formerly held in the diamond-shaped linkage  12 . A small difference in the volume leaving the diamond-shaped linkage  12  and entering the cylindrical linkage  14  is believed to be compensated for temporarily by the elasticity of the membrane of the diamond-shaped linkage  12 . Then, as the linkage  227  nears its initial position, first end switch  221  closes its contacts to energize first solenoid switching valve  211  to allow the surplus volume stored in the cushion tank  209  to return to the cylindrical linkage  14 . If more or earlier compensation is required, alternate means of connecting the cushion tank  209  to the cylindrical linkage  14  may be devised. When the cylindrical linkage  14  has been completely refilled, push button switch  223  (which the linkage  227  contacts slightly after contacting first end switch  221 ) closes its contacts again and the cycle repeats.  
         [0056]    As mentioned above, the second cylindrical linkage takes in fluid with each cycle. After a number of cycles, the second rod  316  moves towards and contacts the second push button valve  219  which opens its pneumatic port to pass pressurized air to the pilot port of air valve  220 . Air valve  220  passes compressed air into the dry side of the second cylindrical linkage  314  at a pressure about 20 PSIG higher than the pressure of cushion tank  109 . Second check valve  216  prevents the fluid flow out of the second cylindrical linkage  314  from flowing backwards through second solenoid valve  214 . First check valve  215  allows the fluid to flow out of the second cylindrical linkage  314  into the cushion tank  209  to be stored for future cycles. When the second cylindrical linkage  314  is empty, the second rod  316  pushes the plunger of first push button valve  218  to remove the pilot signal to air valve  220 . This releases the pressure from the dry side of the second cylindrical linkage  314  to allow the second cylindrical linkage  314  to receive fluid to de-pressurize the diamond-shaped linkage  12  and the cylindrical linkage  14  in future cycles. Alternately, other hydraulic pumping mechanism could be used to return the fluid which enters the second cylindrical linkage in this example to the cushion tank  209 .  
         [0057]    The hydraulic motor  199  was operated for many cycles with the duration of each cycle being about 15 to 20 seconds.  
         [0058]    It is to be understood that what has been described are preferred embodiments to the invention. The invention nonetheless is susceptible to certain changes and alternative embodiments fully comprehended by the spirit of the invention as described above, and the scope of the claims below. For example, although the terms “hydraulic” or “pneumatic” may be used in places and examples may describe operation with pressurized gases or liquids, the invention is adaptable to use with fluids generally although use with fluids is preferred.