GB2095759A

GB2095759A - Energy-conserving apparatus for a piston cylinder arrangement

Info

Publication number: GB2095759A
Application number: GB8206089A
Authority: GB
Original assignee: Rexnord Inc
Current assignee: Rexnord Inc
Priority date: 1981-03-26
Filing date: 1982-03-02
Publication date: 1982-10-06
Also published as: DE3211232A1

Abstract

An energy-conserving apparatus is provided for use with a first controlled pressure source 16, a second (lower) controlled pressure source 18, and a piston-cylinder combination 2, 3. The piston-cylinder combination has a piston 3 which reciprocates within a cylinder 2. The cylinder 2 defines two variable- volume working chambers 8 and 14 on opposite sides of the piston 3. The energy-conserving apparatus is constituted by conduits 22, 26, 30 and 34 providing fluid communication among the working chambers 8 and 14 and the first and second controlled pressure sources 16 and 18, so that the fluid provided by the first controlled pressure source is used to cause the piston 3 to execute a working stroke, and some of the same fluid is reused to cause the piston to execute a return stroke. <IMAGE>

Description

SPECIFICATION Energy-conserving apparatus for a piston-cylinder combination This invention relates to a piston-cylinder combination which is operated by gas or air pressure and, more particularly, to an energy-saving apparatus for use with such a piston-cylinder combination.

In such a piston-cylinder combination, the piston reciprocates within the cylinder creating a first variable-volume working chamber between a first end of the cylinder and a first end of the piston, and a second variable-volume working chamber between a second end of the cylinder and a second end of the piston. Generally, high gas or air pressure is applied to the first working chamber, and the second working chamber is exhausted to atmosphere, thereby pushing the piston towards the second end of the cylinder. A piston rod is attached to the piston, and a load is applied to the end of the piston rod, so that movement of the piston towards the second end of the cylinder causes work to be done against that load. This movement is called the working stroke.

Typically, as a means for returning the piston to its original position, a spring is placed between the second end of the piston and the second end of the cylinder.

When high pressure is applied to the first working chamber to push the piston towards the second end of the cylinder, it also causes work to be done against the biasing force of the spring. This results in the spring being compressed, thereby storing energy in the spring. When the high pressure is removed from the first working chamber, usually by exhausting it to atmosphere, the spring acts to return the piston to its original position, using the energy stored in it. Thus, the spring requires the working fluid to be at a high enough pressure to overcome the biasing force of the spring in addition to the work load. This results in more work being done during each working stroke than is demanded by the work load alone.

In another typical method of operation, high pressure is applied alternately to the first and second ends of the cylinder to push the piston back and forth. When the work load on the piston rod is essentially only in one direction, the cylinder and piston absorb the force exerted by the high pressure fluid on the return stroke. This absorption results in some additional deterioration of the cylinder and in waste of energy.

Some thought has been given in the past to returning the piston by reusing the same pressurised fluid that was used to push the piston during its working stroke. However, in order for such a system to work, the pressurised fluid in the second working chamber must act on a larger surface area of the piston than that acted on by the fluid in the first working chamber. For example, one known pistoncylinder combination has two pistons, the initial work being done on a piston having a relatively small surface area, and the return work being done on a piston having a relatively large surface area. The two working chambers of such a piston-cylinder combination are connected together, so that both are subjected to the same pressure.Although both pistons are acted on by the same pressure, since the force applied to a surface is equal to PressurexArea, the force applied to the larger area piston is greater than the force applied to the smaller area piston, thereby causing the piston to be returned.

Unfortunately, this type of piston-cylinder combination is not very practical, because it requires two pistons and cylinders and special valving. Also, it can only do work in one direction. The working fluid must push on the smaller area piston to do the work, and the larger area piston must be used for the return stroke.

The aim of the invention is to provide an energy-conserving apparatus which can be used with a standard piston-cylinder combination having a single cylinder and a single piston, and in which the same pressurised fluid which is used for the working stroke can a;so be used for the return stroke.

The present invention provides an energy-conserving apparatus for use with a first controlled pressure source, a second controlled pressure source, and a piston-cylinder combination, the pistoncylinder combination having a piston reciprocable within a cylinder, and having a first variable-volume working chamber between a first end of the cylinder and a first end of the piston and a second variablevolume working chamber between a second end of the cylinder and a second end of the piston, the apparatus comprising a first conduit for selectively providing fluid communication between the first working chamber and the first controlled pressure source, a second conduit for selectively providing fluid communication between the first working chamber and the second working chamber, a third conduit for selectively providing fluid communication between the first working chamber and the second controlled pressure source, a fourth conduit for se!ectively providing fluid communication between the second working chamber and the second controlled pressure source, and a controller for opening and closing the conduits, the controller being such as to open the first and fourth conduits and to close the second and third conduits, then to close the first, third and fourth conduits and to open the second conduit, and finally to close the first, second and fourth conduits and to open the third conduit, whereby fluid provided by the first controlled pressure source is used to move the piston in a working stroke and is then recirculated for use in a return stroke.

Advantageously, a shuttle valve is provided in the first conduit, the shuttle valve being effective to open and close the first conduit. Preferably, the first and second conduits intersect, and the shuttle valve lies in both the first and second conduits, the shuttle valve being such as to change position in - response to pressure changes and alternately to open the first conduit and close the second conduit, and then to close the first conduit and open the second conduit.

A non-return valve may be provided in the second conduit, the non-return valve being effective to permit fluid flow in only one direction between the first and second working chambers.

Advantageously, a valve is provided in the third conduit, said valve being effective to open and close the third conduit. Preferably, the valve in the third conduit comprises a main chamber in which the first, second and third conduits intersect, a stem in the main chamber, the stem having a top end and a bottom end, an opening in the main chamber leading to a conduit which can be put in fluid communication with the second controlled pressure source, a poppet attached to the bottom end of the stem and lying in said opening, the poppet being such as to close off said opening when the stem moves away from said opening and to permit fluid communication through said opening when the stem moves towards said opening, and a diaphragm having top and bottom sides, the bottom side of the diaphragm being adjacent to the main chamber, and the top side of the diaphragm being adjacent to a second chamber which is in fluid communication with a conduit which can be put in fluid communication with the second working chamber, the diaphragm being attached to the top end of the stem, such that movement of the diaphragm towards said opening causes the poppet to move so as to open fluid communication through said opening.

A valve may be provided in the fourth conduit, said valve being effective to open and close the fourth conduit. The valve in the fourth conduit may be a pressure-controlled valve. Advantageously, the valve in the fourth conduit is attached by a shaft to the shuttle valve so that, when the shuttle valve opens the first conduit and closes the second conduit, it also causes the valve in the fourth conduit to open the fourth conduit; and, when the shuttle valve closes the first conduit and opens the second conduit, it also causes the valve in the fourth conduit to close the fourth conduit.

In a preferred embodiment, the first, second, third and fourth conduits are constituted by conventional spool valves.

Preferably, the controller is a time-sensitive controller. Where spool valves constitute the conduits, the time sensitive controller may control the positions of the spool valves.

The invention also provides an energy-conserving method of operating a piston-cylinder combination having a piston reciprocable within a cylinder, and having a first variable-volume working chamber between a first end of the cylinder and a first end of the piston and a second variable-volume working chamber Detween a second end of the cylinder and a second end of the piston, the method comprising the steps of placing the first working chamber in fluid communication with a first controlled pressure source and the second working chamber in fluid communication with a second, lower controlled pressure source thereby creating a pressure differential between the first and second working chambers and causing the piston to make a working stroke and move towards the end of the cylinder which is at a lower pressure; then closing the fluid communication between the second working chamber and the second controlled pressure source, removing the first working chamber from fluid communication with the first controlled pressure source and placing the first working chamber in fluid communication with the second working chamber, so that the pressure in the first working chamber is substantially in equilibrium with the pressure in the second working chamber; and then closing the fluid communication between the first and second working chambers and placing the first working chamber in fluid communication with the second controlled pressure source so that the pressure in the first working chamber approaches the pressure of the second controlled pressure source, and the pressure differential between the first and second working chambers causes the piston to make a return stroke.

The present invention provides an energy-conserving apparatus which may be used with a first controlled pressure, a second controlled pressure, and a piston-cylinder combination in which the piston reciprocates within the cylinder, creating a first variable volume between a first end of the cylinder and a first end of the piston and a second variable volume between a second end of the cylinder and a second end of the piston. The invention provides conduits which selectively provide fluid communication among the variable volumes and the controlled pressures, such that the fluid provided by the first controlled pressure is used to move the piston towards one end for the work stroke and is then reused in the return stroke.

Four arrangements, each of which shows a piston-cylinder combination and a different form of energy-conserving apparatus constructed in accordance with the invention, will now be described, by way of example, with reference to the accompanying drawings, in which: Figs. 1 a, 1 b and 1 C are schematic representations showing a piston-cylinder combination and a first form of energy-conserving apparatus in various stages of its operation; Figs. 2a, 2b and 2c are cross-sectional views showing a piston-cylinder combination and a second form of energy-conserving apparatus in various stages of its operation; Fig. 2d is a diagram showing the pressures in the two working chambers of the cylinder during operation of the arrangement shown in Figs. 2a, 2b and 2c; ; Fig. 3 is a cross-sectional view showing a piston-cylinder combination and a third form of energy conserving apparatus in various stages of its operation; and Figs. 4a, 4b and 4c are schematic representations showing a piston-cylinder combination and a fourth form of energy-conserving apparatus in various stages of its operation.

Referring to the drawings, Figs 1 a, 1 b and 1 C show a piston-cylinder combination having a cylinder 2. and a piston 3 reciprocable within the cylinder. A first end 4 of the cylinder 2 and a first end 6 of the piston 3, define a first variable-volume working chamber 8. A second end 10 of the cylinder 2 and a second end 12 of the piston 3 define a second variable-volume working chamber 14. The second working chamber 14 is sealed off from the first working chamber 8, so there is no fluid communication therebetween inside the cylinder 2. A piston rod 13 is attached to the second end 12 of the piston 3. It is also possible for the piston rod 13 to be attached to the first end 6 of the piston 3.The piston rod 13 is adapted to be attached to a load (not shown) outside the cylinder 2, and to do work on that load by moving back and forth as the piston 3 reciprocates within the cylinder.

Figs. 1 a, 1 b and 1 C also show a first controlled pressure source 16, a second controlled pressure source 18, and a reservoir 20; the first controlled pressure source 1 6 being a high pressure source, such as a pump, and the second controlled pressure source 1 8 being a low pressure sink. In most applications, the second controlled pressure source 1 8 would be an opening to the atmosphere. The reservoir 20 is in fluid communication with the second working chamber 14. The reservoir 20 is simply a volume in which fluid may accumulate, even when the piston 3 is extended as far towards the second end 10 of the cylinder 2 as it will go.If there are stops inside (or outside) the cylinder 2 which maintain the piston 3 at least a specified distance away from the end 10 at all times, then the free volume in the cylinder beyond the stops may serve as the reservoir 20. The reservoir 20 may be a separate volume outside the cylinder 2 which is in fluid communication with the second working chamber 14 (as shown in Fig. 1) or it may just comprise the volume of the conduits which provide fluid communication with the second working chamber.

A first conduit 22 connects the first controlled pressure source 1 6 and the first working chamber 8. The conduit 22 is provided with closure means 24 for selectively providing fluid communication between the first controlled pressure source 1 6 and the first working chamber 8. A second conduit 26 connects the first working chamber 8 and the second working chamber 1 4. The conduit 26 is provided with closure means 28 for selectively providing fluid communication between the two working chambers 8 and 14.A third conduit 30 connects the first working chamber 8 and the second controlled pressure source 1 8. The conduit 30 is provided with closure means 32 for selectively providing fluid communication between the first working chamber 8 and the second controlled pressure source 1 8. A fourth conduit 34 connects the second working chamber 14 and the second controlled pressure source 1 8. The conduit 34 is provided with closure means 36 for selectively providing fluid communication between the second working chamber 1 4 and the second controlled pressure source 1 8.

The conduits 22, 26, 30 and 34 may be tubes, hoses, closed channels, or anything through which a fluid may flow. The closure means 24, 28, 32 and 36 may be anything that can open and close the conduits 22, 26, 30 and 34. For example, if 9 given conduit is a hose, its closure means may be a hose clamp; and, if a given conduit is a pipe, its closure means may be any kind of valve which will serve to open and close the pipe. In the drawings, whenever a closure means is shown by an "X", that shows it is closed; and, when a closure means is shown by an "O", it is open. The closure means 24, 28, 32 and 36 may be operated manually, by an electronic controller, by a pressure-sensitive controller or otherwise.

The arrangement shown in Figs. 1 a,1 b and 1 C operates as follows: First, as shown in Fig. 1 a, the closure means 24 and the closure means 36 are opened, while the closure means 32 and 28 are closed. This enables a high pressure fluid to flow from the first controlled pressure source 16, through the conduit 22, and into the first working chamber 8 so as to act on the end surface 6 of the piston 3. Since the pressure acting on the other end surface 12 of the piston 3 is lower than the pressure from the first controlled pressure source 16, there is an unbalanced force acting on the piston 3, tending to push it towards the end 10 of the cylinder 2.If this force is great enough to overcome the internal friction, the work load attached to piston rod 13, and any other forces associated with the moving piston 3, the piston will be pushed towards the end 10 of the cylinder 2 (as indicated by the arrow 38), thereby accomplishing the desired work function. This is called the working stroke. As mentioned above, the piston rod 1 3 may extend out of the cylinder end 4 instead of the end 10, in which case work would be done by piston rod retraction rather than by piston rod extension as shown in Fig. 1.

Next, as shown in Fig. 1 b, the closure means 24 and 36 are closed, and the closure means 28 is opened, while the closure means 32 remains closed. This permits the high pressure fluid, which was previdusly supplied to the first working chamber 8, to flow through the conduit 26 and the reservoir 20 and into the second working chamber 14, so that approximately equilibrium pressure conditions prevail. At that point, the fluid in the conduit 26 and the reservoir 20, and in the first and second working chambers 8 and 14, is substantially at equilibrium pressure. This equilibrium pressure is lower than the pressure of the first controlled pressure source 16, and higher than the pressure of the second controlled pressure source 1 8. This is called the equilibration step.

Next, as shown in Fig. 1 c, the closure means 28 is closed and the closure means 32 is opened, while the closure means 24 and 36 remain closed. Since the conduit 30 is open, the first working chamber 8 is in fluid communication with the lower pressure of the second controlled pressure source 18, and the fluid in the first working chamber 8 will rapidly escape. Thus, the pressure in the first working chamber 8 will rapidly approach the low pressure of the second controlled pressure source 18.

Since the second working chamber 14 is at equilibrium pressure, which is higher than the low pressure provided by the second controlled pressure source 1 8, the pressure acting on the end 12 of the piston 3 is greater than the pressure acting on the end 6 of the piston. If the force acting on the end 12 is sufficiently higher than the force acting on the end 6, so as to overcome friction and the other forces present, the piston 3 will be moved towards the cylinder end 4 (as shown by the arrow 40). This is called the return stroke.

As the piston 3 moves towards the end 4 of the cylinder 2, the volume of the second working chamber 14 increases, and the fluid in the reservoir 20 expands to fill the increasing volume, so that the pressure acting on the piston end 12 is gradually reduced. Thus, the force pushing the piston 3 towards the cylinder end 4 is reduced as the piston approaches that cylinder end. If the equilibrium pressure is not high enough, and the amount of fluid in the reservoir 20 is not large enough, the pressure may be reduced so that the piston 3 will not be returned all the way to its initial position.

However, if the equilibrium pressure is high enough, and the reservoir 20 is large enough, the piston 3 will be returned to its initial position. The following example illustrates the theoretical relationship between the pressures and volumes of the arrangement shown in Fig. 1.

Assuming the fluid supplied by the first controlled pressure source 1 6 is an ideal gas, the ideal gas law applies, that is to say P1V1 P2V2 T, T2 where P is absolute pressure and T is absolute temperature.

Now, assuming the processes are isothermai, P1V,=P2V2.

Given: AH=the area of the piston end 6 The area of the piston end 12 P,N=the high pressure of the first controlled pressure source 16 VH=the volume of the first working chamber 8 at the end of the working stroke PEx=the low pressure provided by the second controlled pressure source 1 8 VROd=the volume of the piston rod 13 inside the cylinder 2 at the end of the return stroke The volume of the reservoir 20 PEQ=the pressure in the reservoir 20, and in the first and second working chambers 8 and 14 at the end of the equilibration step PF=the pressure in the second working chamber 14 at the end of the return stroke.

Applying the ideal gas law for the equilibration step, PV before equilibration=PV after equilibration: PINVH+PEXVR=PEQ[VH+VR] Solving for the equilibrium pressure: PINVH+PEXVR PEa VH+VR Assume that, before the return stroke, the volume of the second working chamber 14 is negligibly small. Also assume that, at the end of the return stroke, the volume of the second working chamber 14 is equal to V,--V,,,.

Since the fluid in the reservoir 20 expands to fill the new volume of the second working chamber 14 during the return stroke, PV before expansion=PV after expansion: P EQVA=P F{VH VRO D ) + P FVR P F(VH VROD+VR) Solving for PF.

PEQVR PF= VHVROD+VR In this example, assume: VH=1.0 unit of volume AH=3 in2 VR=0.8 unit of volume AR=2.5 in2 PIN=l 14.7 psia Pew=14.7 psia VAOD=O.2 unit of volume PINVH+PEXVR PEn VH+VR 1 14.7x1.0+14.7x0.8 1.0+0.8 =70.2 psia P EQVR PF= VH-VROD+VR 70.2 x0.8 1.0-0.2+0.8 =35.1 psia The forces acting on the piston 3 due only to fluid pressures within the cylinder 2 will be as follows: Force (Fw) due to the pressure on the piston 3 during the working stroke:: FW=P1NAHPEXAR =114.7 psia x 3 in2-14.7 psiax2.5 in =307.4 pounds Force (FR) due to the pressure on the piston 3 at the beginning of the return stroke: FR=P EoAAP ExAH =70.2 psiax2.5 in2-14.7 psia x3 in =131.4 pounds Force (FF) due to the pressure on the piston 3 at the end of the return stroke: FF=PFAA-PEXAH =35.1 psiax2.5 in2-14.7 psia 3 in =43.6 pounds The previous calculations were repeated, solving for PEa and PF while varying VR.For these calculations, it was assumed that: PIN=1 14.7 psia (100 psig supply pressure) PEX=14.7 psia (0 psig, atmospheric pressure) VH=1.0 unit of volume VROt)=O.2 unit of volume AH=3 in2 At2.5 in The foliowing table lists the theoretical results: VR PEQ(psia) PF(Psia) Fibs. FRlbs. Fibs.

.6 77.2 33.1 307.4 148.9 38.6 .8 70.2 35.1 307.4 131.4 43.6 1.0 64.7 35.9 307.4 117.6 45.6 1.2 60.2 36.1 307.4 106.4 46.2 1.4 56.4 35.9 307.4 96.9 45.6 Figs. 2a, 2b and 2c illustrate a piston-cylinder combination and a practical form of energy conserving apparatus in the form of a group of valves and channels in a single housing 42. This group of valves and channels is adapted to operate with a first controlled pressure source 1 6 (which is a high pressure fluid supplied by, for example, a pump), with a second controlled pressure source 18 (which is a lower pressure such as atmospheric pressure), with a four-way valve 44, and with a piston 3 and cylinder 2 combination similar to the combination shown in Figs. 1 a, 1 b and 1 c.

It should be noted that, although the valves and conduits shown in Figs. 2a, 2b and 2e are all in a single housing 42, the same arrangement of valves and conduits would operate equally well if the valves were in separate housings interconnected by conduits. The single housing 42 is used for convenience and economy of manufacture. The housing 42 is made in two pieces 42a and 42b, a nonporous, flexible piece of material 43 is placed between the pieces 42a and 42b, and the pieces 42a and 42b are then bolted together, clamping the material 43 into place. Portions of the material 43 will be described in more detail later, when the valves and diaphragms formed by the material 43 are described.

It should be noted that, as in Figs. 1 a, 1 b and 1 c, the reservoir 20 is simply a volume in which fluid may accumulate, even when the piston 3 is extended as far towards the end 10 of the cylinder 2 as it will go. If there are stops inside (or outside) the cylinder 2 which maintain the piston 3 at least a specified distance away from the cylinder end 10 at all times, then the free volume within the cylinder 2 beyond the stops may serve as the reservoir 20. The reservoir 20 may be a separate volume outside the cylinder 2 which is in fluid communication with the second working chamber 14 (as shown in Figs.

2a, 2b and 2c), or it may just comprise the volume of the conduits which provide fluid communication with the second working chamber.

The four-way valve 44 has two positions. In its first position, shown in Fig. 2a, it connects the first controlled pressure source 1 6 to a channel 46 in the housing piece 42b and it connects the second controlled pressure source 1 8 to a channel 48 in the housing piece 42b. In its second position, shown in Fig. 2b, it reverses the connections, so that the first controlled pressure source 1 6 communicates with the channel 48 and the second controlled pressure source 1 8 communicates with the channel 46.

The four-way valve 44 may be moved from one position to the other manually, by use of a solenoid, by use of a hydraulically-operated device, or by other known means.

The channel 46 leads to a shuttle valve 50. The shuttle valve 50 has two positions, and communicates with three channels 46, 52 and 54. In its first position, shown in Fig. 2a, the shuttle valve 50 puts the channel 46 in fluid communication with the channel 52, which is in fluid communication with the first working chamber 8. At the same time, the shuttle valve 50 closes the fluid communication between the channel 54 and the channels 52 and 46. The channels 52 and 46, together with the shuttle valve 50, thus comprise a conduit adapted to provide selective fluid communication between the first working chamber 8 and the first controlled pressure source 1 6.

In its second position, shown in Fig. 2b, the shuttle valve 50 puts the channel 52 in fluid communication with the channel 54, and closes communication between the channels 52 and 46. The shuttle valve 50 is made from part of the material 43 which has been partially cut away so as to form a flap, the flap being attached to the housing 42. The movement of the flap of the shuttle valve 50 is controlled by the relative pressures in the channels, as will be described below.

The conduit 54 communicates with a non-return valve 56. The non-return valve 56 permits fluid to flow from the channel 54 to a channel 58, but does not permit fluid to flow in the opposite direction.

A bias spring 60 holds the non-return valve 56 in its proper position inside the channel 58. The channel 58 is in fluid communication with the second working chamber 14. When the shuttle valve 50 is in a position such that it provides fluid communication from the channel 52 to the channel 54, and when the fluid in the channel 54 is at a higher pressure than the fluid in the channel 58 (so that it can flow past the non-return valve 56), fluid may flow from the first working chamber 8 through the channels 52, 54 and 58, to the second working chamber 14. Thus, the channels 52, 54 and 58, together with the shuttle valve 50 and the non-return valve 56, comprise a conduit adapted to provide selective fluid communication between the first and second working chambers 8 and 14.

The channel 48 ieads to a diaphragm 62 which is a portion of the material 43. The edges of the diaphragm 62 are fixed to the housing 42, and the diaphragm is adapted to respond to the relative pressures surrounding it by moving in the direction of lower pressure. The conduit 48 is on one side of the diaphragm 62, and the channel 58 and an opening 63 are on the other side of the diaphragm. The opening 63 lead to a channel 64 which communicates with the second controlled pressure source 1 8.

When the channel 48 is in fluid communication with the first controlled pressure source 16, the diaphragm 62 is acted on by a higher pressure on the side adjacent to the channel 48, and moves away from that high pressure, closing off the opening 63 to the channel 64, and closing fluid communication between the channel 58 and the channel 64.

When the channel 48 is in fluid communication with the second controlled pressure source 18, the diaphragm 62 is acted on by a lower pressure on the side adjacent to the channel 48 and moves towards the channel 48, moving away from the opening 63, and thereby opening fluid communication between the channel 58 and the channel 64. When the diaphragm 62 moves away from the opening 63, there is fluid communication between the second working chamber 14, the channel 58, the channel 64, and the second controlled pressure source 18; and, when the diaphragm 62 moves towards the opening 63, it closes fluid communication between the second working chamber 14 and the second controlled pressure source 1 8.Thus, the channels 58 and 64, together with the diaphragm 62, comprise a conduit adapted to provide selective fluid communication between the second working chamber 14 and the second controlled pressure source 18.

In the channel 52, which is in fluid communication with the first working chamber 8, there is an opening 66 leading to a channel 68 which is in fluid communication with the second controlled pressure source 18. A poppet 70, which is part of a valve 72, is provided in the opening 66. The poppet 70 is attached to the bottom of a stem 74, the stem being located in the channel 52. The top end of the stem 74 is attached to a diaphragm 76, having a top side 78 and a bottom side 80. The diaphragm 76 is another portion of the material 43. The bottom side 80 of the diaphragm 76 is adjacent to the channel 52, and the top side 78 of the diaphragm 76 is adjacent to a chamber 82, which is in fluid communication with the conduit 58 and the second working chamber 14 through a channel 83. A bias spring 84 is attached to the top side 78 of the diaphragm 76, and to the housing piece 42b.Pressure acts on the top and bottom sides 78 and 80 of the diaphragm 76, and on the top and bottom sides 86 and 88 of the poppet 70. The diaphragm 76 is flexible, and responds to changes in the pressure acting on its opposite sides by moving the attached poppet 70 of the valve 72 either towards or away from, the opening 66. When the diaphragm 76 moves towards the opening 66, it pushes the stem 74 towards the opening 66, and the stem 74 in turn pushes the poppet 70 out of the opening 66, thereby opening fluid communication between the channel 52 and the channel 68. In other words, it opens fluid communication between the first working chamber 8 and the second controlled pressure source 1 8.

Thus, the channels 52 and 68, together with the valve 72, comprise a conduit adapted to provide selective fluid communication between the first working chamber 8 and the second controlled pressure source 18. When the forces on the sides 78, 80, 86 and 88 are such as to push the diaphragm 76 away from the opening 66, then the poppet 70 moves in a direction to seal off fluid communication through the opening 66.

The operation of the embodiment of the invention shown in Figs. 2a, 2b and 2e is as follows: To initiate the working stroke, the four-way control valve 44 is moved to its first position, so that high pressure fluid flows into the channel 46. Since the pressure in the channel 46 is higher than the pressure in the channel 54, the shuttle valve 50 is forced down, opening the channel 46 to the channel 52 and closing the channel 54. This puts the first controlled pressure source 1 6 in fluid communication with the first working chamber 8.

At the same time, the four-way valve 44 puts the second controlled pressure source 1 8 in fluid communication with the channel 48. Since the pressure in the channel 48 is lower than the pressure in the channel 58 as the piston 3 starts to travel towards the cylinder end 10, the diaphragm 62 moves towards the channel 48, thereby opening fluid communication between the second working chamber 14 and the second control'wed pressure source 1 8 through the channels 58 and 64. This arrangement permits the diaphragm 62 and its surrounding channels to operate as a quick exhaust valve for the second working chamber 14.

The valve 72 is in a closed position, because the pressure in the chamber 82, which is approximately the same as the second controlled pressure source 18, is substantially lower than the pressure in the channel 52, which is approximately the same as the first controlled pressure source 1 6.

This pressure difference causes the diaphragm 76 to move up, causing the poppet 70 to seal against the opening 66, closing it off. Since the first working chamber 8 is in fluid communication with the higher pressure of the first controlled pressure source 16, and the second working chamber 14 is in fluid communication with the lower pressure of the second controlled pressure source 1 8, the piston 3 will be pushed towards the cylinder end 10, just as it was in the working stroke shown in Fig. 1 a.

To initiate the equilibration step shown in Fig. 2b, the four-way valve 44 is moved to its second position, in which the first controlled pressure source 16 is put in fluid communication with the channel 48, and the second controlled pressure source 1 8 is put in fluid communication with the channel 46.

Since the diaphragm 62 now is acted on by a higher pressure in the channel 48, it moves down, closing off the opening fi3. The fluid in the channels 46 and 54 is roughly at the same pressure, namely the pressure of the second controlled pressure source 18. However, the fluid in the channel 52 is at a higher pressure, about equal to the pressure of the first controlled pressure source 1 6, and it begins to flow at high velocity past the shuttle valve 50 and into the channel 46. This rapid movement of fluid picks up the edge of the shuttle valve 50, permitting the high pressure fluid in the channel 52 to react on the underside of the shuttle valve 50.

Once the high pressure fluid reacts on the underside of the shuttle valve 50, the pressure difference causes the shuttle valve to move towards the channel 46, closing off the channel 46 and opening the channel 54. The high pressure fluid in the channel 52 then moves into the channel 54, through the non-return valve 56, into the channel 58, and finally into the reservoir 20 and the second working chamber 14. This permits the pressure in the first working chamber 8, the reservoir 20 and the second working chamber 1 4 to approach equilibrium, as in the equilibration step shown in Fig.1 b. The velocity at which fluid flows through a channel depends on the area of the channel. By reducing the area of the channel 58 at the point where the conduit 83 enters (this reduced area being designated 58A), the fluid velocity is thereby increased at that point, and this results in a reduction in the value of the pressure in the reduced channel area 58A. This same reduced pressure communicates with the chamber 82 via the channel 83. Thus, when fluid flows from the chamber 8 into the chamber 1 4 through the reduced area 58A, the pressure in 58A, the channel 83 and the chamber 82 is reduced as compared with the pressure in the channel 52 acting on the underside of the diaphragm 76.Thus the diaphragm 76, with reduced pressure on its top side, stays in its uppermost position, keeping the poppet 70 against the opening 66, while there is fluid flowing from the chamber 8 to the chamber 14, passing through the reduced area channel 58A in the process of "pressure equalisation". It is desirable for the pressure in the chamber 82 to mirror the pressure in the second working chamber 14, so that the valve 72 does not open too soon before equilibrium fluid flow approaches zero. An adjustable needle valve may be inserted into the channel 83 to slow the flow of fluid into the chamber 82, and cause the change of pressure in the chamber 82 to mirror the change of pressure in the second working chamber 14.When the pressure approaches equilibrium, and equalisation flow approaches zero, the pressure on the surfaces 78, 80 and 86 will be approximately the same equilibrium pressure, and the pressure on the surface 88 will be lower than the equilibrium pressure, namely the pressure of the second controlled pressure source 1 8. At a time, somewhere before equilibrium pressure is reached, depending on the relative areas of the surfaces 78, 80, 86 and 88, the valve 72 will pop open, permitting fluid in the channel 52 to flow into the second controlled pressure source 1 8. Fluid will begin to flow from the channel 58 towards the channel 54 and the channel 52, but the non-return valve 56 will close to prevent the escape of that fluid.The fluid in the second working chamber 14, the reservoir 20, the channel 58, the channel 83 and the chamber 82 will thus remain at equilibrium pressure while the fluid pressure in the first working chamber 8 and the channel 52 approaches the lower second controlled pressure. Since the pressure on the surface 78 of the diaphragm 76 remains at equilibrium pressure while the pressure on the surface 80 decreases, the valve 72 will open more and more once it has opened even a small amount. It should be noted that the valve 72 also serves as a quick exhaust valve, permitting the fluid in the first working chamber 8 to exhaust rapidly to the second controlled pressure source 18 without having to flow through long conduits.

At this point, the valves are in the positions shown in Fig. 2c to begin the return stroke. First, the working chamber 8 is in fluid communication with the second controlled pressure source 18; and the reservoir 20 and the second working chamber 14 are closed off from fluid communication with any other volume. Now, the end 6 of the piston 3 is acted on by the second controlled pressure source 1 8, which is lower than the equilibrium pressure acting on the end 12 of the piston 3. If the force acting on the piston end 12 is sufficiently higher than the force acting on the piston end 6, so as to overcome friction and the other forces present, the piston 3 will be moved towards the cylinder end 4, as was the case in the return stroke shown in Fig. 1 c.As the piston 3 moves towards the cylinder end 4, the volume of the second working chamber 14 increases, and fluid in the chamber 14 and in the reservoir 20 expands to fill the increasing volume, so that the pressure acting on the piston end 12 is gradually reduced. Thus, the force pushing the piston 3 towards the cylinder end 4 is reduced as the piston approaches that end. If the equilibrium pressure is not high enough, and the amount of fluid in the reservoir 20 is not large enough, the pressure may be reduced so that the piston 3 will not be returned all the way to its initial position. However, if the equilibrium pressure is high enough, and the reservoir 20 is large enough, the piston 3 will be returned to its initial position, thereby returning the piston by re-using some of the pressurised fluid which had initially been used to push the piston in the working stroke.If the four-way valve 44 is returned to its first position, another working stroke will begin, and the cycle shown in Figs. 2a, 2b and 2e will be repeated.

Figure 2d shows a pressure readout from an actual test of the embodiment shown in Figs. 2a, 2b and 2c. The cylinder 2 used for the test was a Hanna Cylinder having a 12.2 inch stroke and a 2.0 inch diameter. The diameter of the piston rod 1 3 was 0.75 inches. The pressure of the first controlled pressure source 1 6 was 84 psig (98.7 psia), and the second controlled pressure source 1 8 was 0 psig (14.7 psia). Pressure readings were taken in the first working chamber 8 and the second working chamber 14 during the working stroke, equilibration, and the return stroke. The pressure readings show that, when the four-way control valve 44 moves to its first position for the working stroke at time tj, the pressure in the first working chamber 8 rapidly increases.At the same time ta, the pressure in the second working chamber 14 shows no change. This indicates stiction in the cylinder 2, with a pressure of approximately 42 psig being required in the first working chamber 8 in order to begin to move the piston 3. Once the piston 3 begins to move, the pressure in the first working chamber 8 suddenly drops, with a corresponding sudden rise in pressure in the second working chamber 14, as the fluid in the second working chamber 14 4 is compressed by the moving piston 3 faster than it can escape to the second controlled pressure source 1 8. The quick successions of peaks in the pressure in both the first and second working chambers 8 and 14 indicates a somewhat jerky movement of the piston 3, with the fluid in the first working chamber 8 having to overcome small amounts of stiction in order to move the piston towards the end 10 of the cylinder 2. Stiction refers to friction which results in a stick-slip phenomenon generally caused by lack of lubrication between packings and the surfaces they rub against. This sort of stiction is typical in most cylinders. If a cylinder with a rolling diaphragm piston seal were used. that sort of stiction would not be present.

At time t2, the working stroke has been completed. The, pressure in the first working chamber 8 is 84 psig, and in the second working chamber 14 is 0 psig. At a time shortly before t3, the four-way control valve 44 is moved to its second position. The pressure readings indicate that the equilibration step is taking place, with the pressure in the first working chamber 8 decreasing while the pressure in the second working chamber 14 increases. At time t3, the equilibration step ends, with the pressure in the first working chamber 8 equal to 44 psig, and the pressure in the second working chamber 14 equal to 36 psig. At time ts, the return stroke begins, with the pressure in the first working chamber 8 rapidly dropping as the fluid escapes to atmosphere.The pressure in the second working chamber 14 gradually decreases, with the fluid expanding to fill the increasing volume created when the piston 3 moves back towards the end 4 of the cylinder 2 in its return stroke.

Fig. 3 shows another embodiment of the invention, which is similar to the embodiment shown in Fig. 2. The differences between the embodiments of Figs. 2 and 3 involve the valve used to open and close the conduit from the second working chamber 14 to the second controlled pressure source 1 8. In Fig. 2, that valve includes the diaphragm 62. In Fig. 3 that valve is a poppet valve 90. The poppet valve 90 is attached to the shuttle valve 50 by a shaft 92 so that, when the shuttle valve moves up to close off the channel 46 from fluid communication with the channel 52 and to open the channel 54, it causes the shaft 92 to move up, thereby moving the poppet valve 90 so that it seals off the opening 63, and closes fluid communication between the second working chamber 14 and the second controlled pressure source 1 8.When the shuttle valve 50 moves down to close off the channel 54, and open the channel 46, it causes the poppet valve 90 to move down and permit fluid communication through the opening 63.

Since the poppet valve 90 is controlled by the movement of the shuttle valve 50, rather than by the pressures around the poppet valve 90, it does not require the channel 48 or the alternate communication with the first and second controlled pressure sources 1 6 and 1 8 as were required in Fig. 2. This means that the four-way valve 44 may be replaced by a three-way valve 94 which communicates with the first and second controlled pressure sources 1 6 and 18, and with the channel 46.

In Fig. 3, the non-return valve 56 is mounted on the shaft 92, but moves independently of the movement of the shaft 92. The shuttle valve 50 of Fig. 3 is structurally somewhat different from the shuttle valve 50 of Figs. 2a, 2b and 2c. In Fig. 3, the shuttle valve 50 is not a flap of flexible material, but rather is a more rigid member. The increased rigidity is necessary in order for the shuttle valve 50 to operate the shaft 92 which controls the poppet valve 90. Also, the shuttle valve 50 in Fig. 3 is not mounted in the housing 42. That is not necessary in Fig. 3, because mounting the shuttle valve 50 on the shaft 92 is enough to keep it in place. A guide 91 on the shaft 92 restricts the movement of the shuttle valve 50 to mostly an axial movement with very little movement perpendicular to the shaft 92.

Another difference between the embodiments of Figs. 2 and 3 is that the channel 64 communicates with the channel 68 which communicates with the second controlled pressure source 18, rather than having direct fluid communication between the channel 64 and the second controlled pressure source 1 8. This permits one less connection to ba made to the housing 42, thereby reducing complexity and cost. The operation of the embodiment of Fig. 3 is essentially the same as that of Fig. 2, with the same conduits open at the same times. The basic difference in operation is that the poppet valve 90 is controlled by the shuttle valve 50 rather than by fluid pressure.

Figs. 4a, 4b and 4c show another embodiment, in which two conventional valves 100 and 102 (such as spool valves) are in fluid communication with the first and second controlled pressure sources 16 and 18, and with the first and second working chambers 8 and 14, to provide the same conduits and permit the same order of opening and closing of fluid communication as shown in the earlier embodiments. However, with this arrangement, the movement of the valves 100 and 1 02 is controlled by a time-sensitive controller, rather than by sensing pressure as in Figs. 2 and 3. The valve 100 is a two-way valve having two positions, and the valve 102 is a five-way valve having three positions.In its first position, the valve 100 puts the first controlled pressure source 1 6 in fluid communication with a conduit 101 which is in communication with the valve 102; and, in its second position, it closes fluid communication between the conduit 101 and the first controlled pressure source 1 6. In its first position, shown in Fig. 4a, the valve 102 puts the conduit 101 in fluid communication with the first working chamber 8, and puts the second working chamber 14 in fluid communication with the second controlled pressure source 1 8. In its second position, shown in Fig. 46, the valve 102 puts the first working chamber 8 in fluid communication with the second working chamber 14.In its third position, shown in Fig. 4c, the valve 102 puts the first working chamber 8 in fluid communication with the second controlled pressure source 18, and closes communication with the second working chamber 14.

The valves 100 and 102 are solenoid controlled. Alternatively, the valves 100 and 102 are controlled by controllers which receive a signal depending on the passage of time. The valves 100 and 102 move together so that the valve 100 is in its first position when the valve 102 is in its first position. Next, the valve 100 is in its second position and the valve 102 is in its second position.

Finally, the valve 100 is in its second position and the valve 102 is in its third position. This embodiment provides the same order of fluid communication as the other embodiments.

While the figures show a horizontal cylinder and valves which move in a vertical plane, the invention will operate with any orientation of the cylinder and the valves.

Claims

1. An energy-conserving apparatus for use with a first controlled pressure source, a second controlled pressure source, and a piston-cylinder combination, the piston-cylinder combination having a piston reciprocable within a cylinder, and having a first variable-volume working chamber between a first end of the cylinder and a first end of the piston and a second variable-volume working chamber between a second end of the cylinder and a second end of the piston, the apparatus comprising a first conduit for selectively providing fluid communication between the first working chamber and the first controlled pressure source, a second conduit for selectively providing fluid communication between the first working chamber and the second working chamber, a third conduit for selectively providing fluid communication between the first working chamber and the second controlled pressure source, a fourth conduit for selectively providing fluid communication between the second working chamber and the second controlled pressure source, and a controller for opening and closing the conduits, the controller being such as to open the first and fourth conduits and to close the second and third conduits, then to close the first, third and fourth conduits and to open the second conduit, and finally to close the first, second and fourth conduits and to open the third conduit, whereby fluid provided by the first controlled pressure source is used to move the piston in a working stroke and is then recirculated for use in a return stroke.

2. Apparatus as claimed in claim 1, wherein a shuttle valve is provided in the first conduit, the shuttle valve being effective to open and close the first conduit.

3. Apparatus as claimed in claim 2, wherein the first and second conduits intersect, and the shuttle valve lies in both the first and second conduits, the shuttle valve being such as to change position in response to pressure changes and alternately to open the first conduit and close the second conduit, and then to close the first conduit and open the second conduit

4. Apparatus as claimed in any one of claims 1 to 3, wherein a non-return valve is provided in the second conduit, the non-return valve being effective to permit fluid flow in only one direction between the first and second working chambers.

5. Apparatus as claimed in any one of claims 1 to 4, wherein a valve is provided in the third conduit, said valve being effective to open and close the third conduit

6. Apparatus as claimed in claim 5, wherein the valve in the third conduit comprises a main chamber in which the first, second and third conduits intersect, a stem in the main chamber, the stem having a top end and a bottom end, an opening in the main chamber leading to a conduit which can be put in fluid communication with the second controlled pressure source, a poppet attached to the bottom end of the stem and lying in said opening, the poppet being such as to close off said opening when the stem moves away from said opening and to permit fluid communication through said opening when the stem moves towards said opening, and a diaphragm having top and bottom sides, the bottom side of the diaphragm being adjacent to the main chamber, and the top side of the diaphragm being adjacent to a second chamber which is in fluid communication with a conduit which can be put in fluid communication with the second working chamber, the diaphragm being attached to the top end of the stem, such that movement of the diaphragm towards said opening causes the poppet to move so as to open fluid communication through said opening.

7. Apparatus as claimed in any one of claims 1 to 6, wherein a valve is provided in the fourth conduit, said valve being effective to open and close the fourth conduit.

8. Apparatus as claimed in claim 7, wherein the valve in the fourth conduit is a pressurecontrolled valve.

9. Apparatus as claimed in either of claims 6 and 7 when appendant to claim 2, wherein the valve in the fourth conduit is attached by a shaft to the shuttle valve so that, when the shuttle valve opens the first conduit and closes the second conduit, it also causes the valve in the fourth conduit to open the fourth conduit; and, when the shuttle valve closes the first conduit and opens the second conduit, it also causes the valve in the fourth conduit to close the fourth conduit.

1 0. Apparatus as claimed in claim 1, wherein the first, second, third and fourth conduits are constituted by conventional spool valves.

11. Apparatus as claimed in any one of claims 1 to 10, wherein the controller is a time-sensitive controller.

12. Apparatus as claimed in claim 11 when appendant to claim 10, wherein the time-sensitive controller controls the positions of the spool valves.

1 3. Energy-conserving apparatus substantially as hereinbefore described with reference to, and as shown by, Figs. 1 a, 1 b and 1 C, Figs. 2a, 2b and 2c, Fig. 3 or Figs. 4a, 4b and 4e of the accompanying drawings.

14. An energy-conserving method of operating a piston-cylinder combination having a piston reciprocable within a cylinder, and having a first variable-volume working chamber between a first end of the cylinder and a first end of the piston and a second variable-volume working chamber between a second end of the cylinder and a second end of the piston, the method comprising the steps of placing the first working chamber in fluid communication with a first controlled pressure source and the second working chamber in fluid communication with a second, lower controlled pressure source thereby creating a pressure e differential between the first and second working chambers and causing the piston to make a working stroke and move towards the end of the cylinder which is at a lower pressure; then closing the fluid communication between the second working chamber and the second controlled pressure source, removing the first working chamber from fluid communication with the first controlled pressure source and placing the first working chamber in fluid communication with the second working chamber, so that the pressure in the first working chamber is substantially in equilibrium with the pressure in the second working chamber; and then closing the fluid communication between the first and second working chambers and placing the first working chamber in fluid communication with the second controlled pressure source so that the pressure in the first working chamber approaches the pressure of the second controlled pressure source, and the pressure differential between the first and second working chambers causes the piston to make a return stroke.

1 5. An energy-conserving method of operating a piston-cylinder combination, the method being substantially as hereinbefore described with reference to the accompanying drawings.