WO2024061722A1

WO2024061722A1 - Mechanically decoupled double rod linear actuator

Info

Publication number: WO2024061722A1
Application number: PCT/EP2023/075248
Authority: WO
Inventors: Royce Gerngross
Original assignee: Robert Bosch Gmbh
Priority date: 2022-09-20
Filing date: 2023-09-14
Publication date: 2024-03-28

Abstract

A hydraulic circuit includes a first cylinder including a first rod and a second cylinder including a second rod. In addition, the hydraulic circuit includes a primary energy source that is common to both the first cylinder and the second cylinder and is sized to perform the intended work of the circuit, and a secondary energy source that is common to both the first cylinder and the second cylinder and is sized to make up for parasitic losses of the circuit. The first cylinder is coupled to the second cylinder electronically and fluidly such that when the first rod moves relative to the first cylinder, the second rod moves relative to the second cylinder in a motion that is equal and opposite to the motion of the first rod.

Description

MECHANICALLY DECOUPLED DOUBLE ROD LINEAR ACTUATOR

BACKGROUND

[001 ] Certain pump applications, including but not limited to hydraulic fracturing or “fracking,” require fluid pumps that provide a high volume of fluid flow provided at high fluid pressure. As shown in Figure 1, in the hydraulic fracturing market, some conventional pumps 100 are comprised of a mechanical plunger device 102 making a linear motion in a fluid end displacing volume forward and backwards via a crank shaft 104 to raise the pressure of a water solution known as slurry. In particular, the pressure is raised from a charge pressure in the suction line 106 to a required formation-fracturing pressure determined by the formation being operated on via the cover 108. The pump 100 is limited in stroke length and force that is feasible to produce by the mechanical limitation of the power end 110. Therefore, to increase flow, the pump 100, also referred to as a “short stroke pump” may be operated at higher speeds introducing high maintenance costs into the operation. In order to reduce operating and maintenance costs and increase pump durability and reliability, it is desirable to lower the opening and closing frequency of the valves 112 that are incorporated into the fluid end 114. In addition, it is desirable to reduce impact forces on the fluid end 114 by making longer slower strokes. For reference, many market available fluid ends 114 have a stroke length of 8 inches.

SUMMARY

[002] Referring to Fig. 2, in order to provide a pump having a longer stroke, a linear actuator may be used. In this case, the actuator 201 is a hydraulic cylinder with a hydraulic energy source 203 that is variable and bi-directional. The energy source 203 directs a fluid such as oil between chambers 202 and 208 via a first line 206 to generate the force Fe and form a pumping action in chamber 207. In this example, the chamber 207 corresponds to the fluid end. In this simplified representation, those skilled in the art will recognize that there is a differential volume between chamber 202 and 208. The differential volume must be managed on advancement and retraction of the rod 210 but is not shown as there are many existing circuits to handle this situation. The actuator 201 may be a ball screw or any other device that can transmit the required energy. For these purposes the new device needs to lower the strokes per minute required for a given flow rate as compared to the device in Figure 1. The fluid end 207 may be roughly the same as that found in the conventional fracking pump in figure 1 but is not limited to this configuration. The idea and purpose of a linear long stroke is to provide longer, more gentle strokes and displace a greater fluid volume per stroke, for example approximately 5 times the volume per stroke. The design shown in Figure 2 is a very compact design having the rod 210 of actuator 201 acting as the plunger which enters fluid end 207. In this case, the rod 210 displaces the volume to form the pumping action. This can be a disadvantage as material from the slurry that resides in the fluid end 207 can be drawn back into chamber 208, contaminating the system.

[003] Referring to Fig. 3, an alternative linear pump 300 has a function that is identical to the pump 200 of Figure 2 with the following exception. In Fig. 3, the actuator 201 is a hydraulic cylinder that has a rod 310 that has been separated into a first rod portion 313 and a second rod portion 309. The first and second rod portions 309, 313 are coupled together in such a way that the distance between the fluid end 207 and the actuator 201 ensures that the chance of slurry material entering the rod-side chamber 208 is minimized. This is a less compact embodiment, but potentially more robust. An energy source 312 is supplying fluid through valves 311 to ensure system pressure is always maintained. This is standard in all embodiments shown and should be understood by those skilled in the art.

[004] One disadvantage of the pumps 200, 300 shown in figures 2 and 3 is that when the actuator 201 is retracting, i.e., fluid is moved from the first port 204 to the second port 205, is that there is no work being done. This means the hydraulic energy source 203 is being occupied but doing no useful work, creating dead time in the cycle for this important asset.

[005] Referring to Fig. 4, another alternative linear pump 400 addresses the above problem by using a double acting cylinder. In this embodiment, the actuator 201 includes a piston 214 having a first rod 210(1) protruding from a first side thereof and a second rod 210(2) protruding from a second side thereof. This involves installing an extra (e.g., second) fluid end 407 that is engaged with the second rod 210(2), but as fluid is moved from the first port 204 to the second port 205, the second fluid end 407 is pumping and the first fluid end 207 is charging with fluid. As the end of stroke is reached and energy source 203 reverses direction, fluid flows from the second port 205 to the first port 204. This results in the first fluid end 207 pumping and the second fluid end 407 charging with fluid. In this scenario, the energy source 203 is fully utilized 100% of the time reducing dead time to the time it takes to reverse direction. It should be known that the plunger rod orientations shown in Figure 3 can also be utilized in the double rod embodiment shown in Fig. 4. One limitation of the double-rod cylinder approach is that the orientation of the first fluid end 207 and the second fluid end 407 are fixed at 180 degrees from one another (e.g., are linearly aligned and pointing in opposite directions). In some applications, it is desired to achieve the same utilization of the energy source 203 without the limitation of the linearly-aligned orientation that is imposed by this double-rod cylinder design.

[006] Referring to Fig. 5, it is desirable to attain the advantages of the system in figure 4 while breaking the physical coupling of the rods. Since the rods of the actuator are decoupled, there are no limitations on the relative orientations of the rods. That is, the rods may be coaxial, parallel and offset, perpendicular, or acutely angled.

[007] In some aspects, the hydraulic circuit includes a first cylinder including a first rod and a second cylinder including a second rod. In addition, the hydraulic circuit includes a primary energy source that is common to both the first cylinder and the second cylinder and is sized to perform the intended work of the circuit, and a secondary energy source that is common to both the first cylinder and the second cylinder.

[008] The first cylinder is coupled to the second cylinder electronically and fluidly such that when the first rod is driven to move relative to the first cylinder by the primary energy source, the second rod moves relative to the second cylinder in a motion that alternates with the motion of the first rod.

[009] When the primary energy source induces motion in the first cylinder such that the first rod advances, the second rod retracts because the rod sides of each of the first and second cylinders are associated with a common fixed volume. Similarly, when the primary energy source induces motion in the second cylinder such that the second rod advances, the first rod retracts. Throughout the cycle defined by the advancing and retracting motion of the first rod, the secondary energy source, if required by the specific application, may adjust the relative motion of the first and second cylinders relative to the motion imposed by the primary energy source.

In some aspects, a hydraulic circuit includes a first cylinder including a first rod, a second cylinder including a second rod, and a primary energy source. The primary energy source is fluidly connected to both the first cylinder and the second cylinder and is sized to perform the intended work of the circuit. The hydraulic circuit includes a secondary energy source that is fluidly connected to both the first cylinder and the second cylinder and is configured to adjust the relative motion of the first cylinder and the second cylinder relative to the motion imposed on the first cylinder and the second cylinder by the primary energy source. The first cylinder is coupled to the second cylinder electronically and fluidly such that when the first rod moves relative to the first cylinder, the second rod moves relative to the second cylinder in an alternating motion in which the first rod advances as the second rod retracts and the second rod advances as the first rod retracts.

In some embodiments, when the first rod moves relative to the first cylinder, the second rod moves relative to the second cylinder in a motion that is opposite and equal to the motion of the first rod.

In some embodiments, when the first rod moves relative to the first cylinder, the second rod moves relative to the second cylinder in a motion that is opposite and substantially equal to the motion of the first rod relative to the first cylinder.

In some embodiments, when the primary energy source induces motion in the first cylinder such that the first rod advances, the secondary energy source compensates for parasitic losses in the hydraulic circuit such that the second rod retracts a distance that is equal to the stroke of the first rod, and when the primary energy source induces motion in the second cylinder such that the second rod advances, the secondary energy source compensates for parasitic losses in the hydraulic circuit such that the first rod retracts a distance that is equal to the stroke of the second rod.

In some embodiments, the hydraulic circuit includes a charge pump configured to compensate for parasitic losses in the hydraulic circuit.

In some embodiments, the first cylinder includes a first piston that segregates the first cylinder into a first chamber and a second chamber. The first rod is fixed to the first piston and is at least partially disposed in the second chamber and an end of the first rod is disposed outside the first cylinder and is configured to be connected to a first load. The first rod is isolated from the first chamber via a seal between the first piston and the first cylinder. In addition, the second cylinder includes a second piston that segregates the second cylinder into a third chamber and a fourth chamber. The second rod is fixed to the second piston and is at least partially disposed in the fourth chamber and an end of the second rod is disposed outside the second cylinder and is configured to be connected to a second load. The second rod is isolated from the third chamber via a seal between the second piston and the second cylinder.

In some embodiments, the hydraulic circuit includes a first fluid line that permits communication between the primary energy source and the first chamber, a second fluid line that permits communication between the primary energy source and the third chamber, a third fluid line that permits communication between the second chamber and the fourth chamber, and a fourth fluid line that permits communication between the third fluid line and each of the first fluid line and the second fluid line. Fluid flow in the fourth fluid line flows in only one direction so as to flow from the third fluid line to the first fluid line or from the third fluid line to the second fluid line.

In some embodiments, a filter is disposed in the fourth fluid line.

In some embodiments, the hydraulic circuit includes a control device that is disposed in the fourth line and is configured to control fluid flow between the second and first chamber or the fourth and third chamber.

In some embodiments, the control device is selected from a group of control devices that includes a control valve, a pressure control valve and a variable pump.

In some embodiments, the hydraulic circuit includes a first fluid line that permits communication between the primary energy source and the first chamber, a second fluid line that permits communication between the primary energy source and the third chamber, a third fluid line that permits communication between the second chamber and the fourth chamber, and a fourth fluid line that permits communication between the third fluid line and the secondary energy source. Fluid flow in the fourth fluid line is controlled by a first valve that is disposed in the fourth fluid line between the secondary energy source and the third fluid line.

In some embodiments, the hydraulic circuit includes a hydraulic accumulator that is connected to the third fluid line via a second valve and is configured to permit expansion and contraction of a volume defined within the second chamber, the fourth chamber and the third fluid line. In some embodiments, the first rod is coaxial with the second rod.

In some embodiments, the first rod extends in parallel to, and is offset relative to, the second rod.

In some embodiments, the first rod is perpendicular to the second rod.

In some embodiments, the first rod is acutely angled relative to the second rod.

In some embodiments, the first rod has a first orientation in space, the second rod has a second orientation in space, and the first and second cylinders are configured so that the determination of the second orientation is free of a restriction that is based on the first orientation.

In some embodiments, the energy producing capacity of the primary energy source is greater than that of the secondary energy source.

In some aspects, a hydraulic circuit includes a primary energy source that is configured to generate flow of hydraulic fluid within the hydraulic circuit. The primary energy source includes a primary energy source A port and a primary energy source B port. The hydraulic circuit includes a first actuator that has a first cylinder and a first piston-side port in the first cylinder. The first piston-side port is connected to the primary energy source A port via a first fluid line. The first actuator includes a first rod-side port in the first cylinder and a first piston disposed in the first cylinder. The first piston segregates an interior space of the first cylinder into a first chamber that is connected to the first piston-side port and a second chamber that is connected to the first rod-side port. In addition, the first actuator includes a first rod disposed in the second chamber and having a first rod first end that is connected to one side of the first piston, and a first rod second end that is configured to be connected to a first load. The hydraulic circuit includes a second actuator having a second cylinder and a second piston-side port in the second cylinder. The second piston-side port is connected to the primary energy source B port via a second fluid line. The second actuator includes a second rod-side port in the second cylinder. The second rod-side port is connected to the first rod-side port via a third fluid line. The second actuator includes a second piston disposed in the second cylinder, the second piston segregating an interior space of the second cylinder into a third chamber that is connected to the second pistonside port and a fourth chamber that is connected to the second rod-side port. In addition, the second actuator includes a second rod disposed in the second chamber and having a second rod first end that is connected to one side of the second piston, and a second rod second end that is configured to be connected to a second load. The hydraulic circuit includes a secondary energy source that is connected to the third fluid line via a fourth fluid line, the secondary energy source configured to maintain a predetermined minimum fluid pressure in the hydraulic circuit. In addition, the hydraulic circuit includes a valve disposed in the fourth fluid line between the secondary energy source and the third fluid line. A sub-volume of fluid in the hydraulic circuit is defined by the second chamber, the third line and the fourth chamber. When the primary energy source induces motion in the first cylinder such that the first rod does one of advances and retracts through a first distance, the second rod does the other of advances and retracts through a second distance. The second distance is equal to the first distance due to the volume of fluid in the sub-volume at the time the motion is induced. The secondary energy source is configured to provide fluid to the subvolume via the valve, and the valve is configured to adjust the amount of fluid in the sub-volume to permit the motion of the second rod to lag or lead the motion of the first rod.

BRIEF DESCRIPTION OF THE FIGURES

[0010] Fig. 1 is an illustration of a prior art frack pump.

[0011] Fig. 2 is a schematic illustration of a linear pump.

[0012] Fig. 3 is a schematic illustration of a linear pump with an isolated chamber.

[0013] Fig. 4 is a schematic illustration of a double acting hydraulic cylinder.

[0014] Fig. 5 is a schematic illustration of a split hydraulic cylinder. [0015] Fig. 6 is a schematic illustration of a hydraulic circuit including a double rod linear actuator in which the rods are decoupled.

[0016] Fig. 7 is a schematic illustration of an alternative embodiment hydraulic circuit including a double-rod linear actuator in which the rods are decoupled.

[0017] Fig. 8 is a schematic illustration of the hydraulic circuit of Fig. 7 illustrating the decoupled rods in an alternative relative orientation.

[0018] Fig. 9 is a schematic illustration of the hydraulic circuit of Fig. 7 illustrating the decoupled rods in another alternative relative orientation.

[0019] Fig. 10 is a schematic illustration of the hydraulic circuit of Fig. 7 illustrating the decoupled rods in another alternative relative orientation.

DETAILED DESCRIPTION

[0020] Referring to Figs. 4-6, a hydraulic circuit 650 includes a double-rod linear actuator 600 in which the rods 616, 618 are decoupled. In the decoupled double-rod linear actuator 600, a first, primary energy source 603 provides power to two hydraulic actuators 601, 602 and drives the two hydraulic actuators to 601, 602 to advance and retract the rods 616, 618. The primary energy source 603 may be, for example, a variable speed, bi-direction pump. The two hydraulic actuators 601, 602are mechanically decoupled as shown in Figure 5 but will operate and function due to a hydraulic scheme as a single actuator as shown in Figure 4. In addition, the hydraulic circuit 650 includes a secondary energy source 608 that is used to adjust the relative motion of the hydraulic actuators 601, 602 in such a way as to permit mid-motion relative lead or lag of one rod relative to the other. Because the hydraulic actuators are not coupled, the primary energy source 603 may be fully utilized while at the same time providing the freedom to orient the rods 616, 618 and corresponding fluid ends 207, 407 individually, however desired. In addition, the secondary energy source 608 permits adjustment in the relatively alternating motion of the rods 616, 618. The decoupled double-rod linear actuator 600 will now be described in detail.

[0021] The first actuator 601 includes a first cylinder 624 and a first actuator piston-side port

606 in the first cylinder 624. The first actuator piston-side port 606 is connected to the first energy source A port via a first fluid line 1. The first actuator 601 includes a first actuator rodside port 609 in the first cylinder 624 and a first piston 614 disposed in the first cylinder 624. The first piston 614 forms a seal with the inner surface of the first cylinder 624 and segregates an interior space of the first cylinder 624 into a first chamber 604(1) that is connected to the first actuator piston-side port 606 and a second chamber 604(2) that is connected to the first actuator rod-side port 609. In addition, the first cylinder 624 includes a first rod 616 disposed in the second chamber 604(2). The first rod 616 has a first rod first end that is connected to one side of the first piston 614, and a first rod second end that is configured to be connected to a first load, for example the first fluid end 207.

[0022] The second actuator 602 includes a second cylinder 626 and a second actuator piston-side port 607 in the second cylinder 626. The second actuator piston-side port 607 is connected to the first energy source B port via a second fluid line 2. The second actuator 602 includes a second actuator rod-side port 610 in the second cylinder 626 and the second actuator rod-side port 610 is connected to the first actuator rod-side port 609 via a third fluid line 3. The second actuator 602 includes a second piston 615 disposed in the second cylinder 626. The second piston 615 forms a seal with an inner surface of the second cylinder 626 and segregates an interior space of the second cylinder 626 into a third chamber 605(1) that is connected to the second actuator pistonside port 607 and a fourth chamber 605(2) that is connected to the second actuator rod-side port 610. In addition, the second cylinder 626 includes a second rod 618 that is disposed in the fourth chamber 605(2) and has a second rod first end that is connected to one side of the second piston 615, and a second rod second end that is configured to be connected to a second load, for example the second fluid end 407.

[0023] The hydraulic circuit 650 includes the secondary energy source 608. The secondary energy source 608 may be, for example, a variable speed, single direction pump. The secondary energy source 608 may draw fluid from a reservoir 620 and is connected to the third fluid line 3 at a location between the piston-side ports 609, 610 of the first and second actuators 601, 602. The secondary energy source 608 may be a charge pump that operates to maintain a predetermined minimum fluid pressure in the circuit despite parasitic losses. The secondary energy source 608 provides a relatively small amount of energy to the hydraulic circuit as compared to the primary energy source 603. In addition to charging the circuit, the secondary energy source 608, in combination with a control valve 611, controls fluid flow in the hydraulic circuit 650 to keep the cylinders 624, 626 in sequence or to permit a small lead or lag in relative motion, as discussed in detail below.

[0024] The control valve 611 is disposed in a fourth fluid line 4. The fourth fluid line 4 connects the third fluid line 3, and thus also the output of the secondary energy source 608, to the first fluid line 1 via a first one-way check valve and to the second fluid line 2 via a second one-way check valve. In Fig. 6, the one-way check valves are referred to collectively using reference number 612.

[0025] To achieve freedom of orientation of the actuator 600, the first and second hydraulic actuators 601, 602 that constitute the actuator 600 must be mechanically decoupled as depicted in Figure 6. However, it is desired to use the primary energy source 603 to produce movement such that a movement in the first actuator 601 produces a corresponding movement in the second actuator 602. In the illustrated embodiment, the primary energy source 603 and the secondary energy source 608 operate synergistically to achieve a relatively alternating movement of the actuators 601, 602 such that an advancing-retracting movement in the first actuator 601 produces a corresponding retracting-advancing movement in the second actuator 602. Because the second chamber 604(2) is connected to the fourth chamber 605(2) via the third fluid line 3, and because these structures together define a fixed volume, the relatively alternating movement is generated naturally.

[0026] When the primary energy source 603 induces motion in the first cylinder 624 such that the first rod 616 advances, the second rod 618 retracts because the rod sides of each of the first and second cylinders 624, 626 are associated with a common fixed volume. Similarly, when the primary energy source 603 induces motion in the second cylinder 626 such that the second rod 618 advances, the first rod 616 retracts. Throughout the cycle defined by the advancing and retracting motion of the first rod 616, the secondary energy source 608, if required by the specific application, may adjust the relative motion of the first and second cylinders 624, 626 relative to the motion imposed by the primary energy source 603.

[0027] In some embodiments, the movement in the first actuator 601 produces a corresponding movement in the second actuator 602 that is opposite and equal (e.g., “180 degrees out of phase”) to that of the first actuator 601. As used herein, the term “opposite” refers to retracting as compared to advancing rather than any particular absolute direction, keeping in mind that the rods may not be parallel or aligned in their decoupled state. In other embodiments, the corresponding movement in the second actuator 602 may be opposite and substantially equal to that of the first actuator 601. As used herein, the term “substantially equal” means that within the confines of the relative size of the secondary energy source 608 compared to the primary energy source 603, the motion of the second actuator 602 may be 180 degrees out of phase with the first actuator 601, or alternatively may lead or lag the first actuator for a period of time during a given advancing -and-retracting cycle of a given rod 616 or 618. The amount of the lead or lag that can be achieved depends on the sizing of the secondary energy source 608 and is determined by the requirements of the specific application. In some embodiments, the amount of lead or lag may be very small, e.g., in a range of one percent to ten percent of the distance traveled by the actuator rods 616, 618 during an advancing motion. Advantageously, since the amount of lead or lag may be very small relative to a distance traveled by the actuator rods 616, 618, the secondary energy source 608 may be small relative to the primary energy source 603.

[0028] Throughout the movement, the actuators 601, 602 are controlled by the secondary energy source 608 to be exactly opposed, or alternatively to lead or lag each other. However, after one complete cycle the second actuator 602 will be 180 degrees out of phase with the first actuator 601. This is due to the secondary energy source 608 being very small relative to the primary energy source 603.

[0029] By this configuration the actuator 600 behaves, from a motion standpoint, like the double-acting actuator shown in Figure 4, with the further advantage of being able to implement a motion that is “substantially equal”. Operationally, the hydraulic circuit 650 operates with the first or primary energy source 603 operating to transfer fluid power between the first actuator piston-side port 606 of the first actuator 601 and the second actuator piston-side port 607 of the second actuator 602. During an operation where power is being transferred to the first actuator 601, the primary energy source 603 draws fluid from the second actuator piston-side port 607, compressing it into the first actuator piston-side port 606. As a result, the rod 616 of the first actuator 601 extends (e.g., advances), displacing volume in the first fluid end 207.

[0030] If there are no leakages in the hydraulic circuit 650, the rod 618 of the second actuator 602 will retract at the same rate the rod 616 of the first actuator 601 extends. Likewise, this will cause a volume of fluid to exit the first port 607 of the second actuator 602 and supply the primary energy source 603 with fluid to be pushed into the first port 606 of the first actuator 601. Unfortunately, all hydraulic systems have leakages intentionally created to allow for lubrication and cooling. These leakages are referred to as parasitic losses. Therefore, of the volume of fluid leaving the ports 609 and 607, some portion will return to a reservoir 620. As a result, the rod 618 of the second actuator 602 will not retract in synchrony with the advancement of the rod 616 of the first actuator 601 unless the lost fluid is replaced.

[0031] A charge pump, when used in a conventional hydraulic circuit is normally not used as part of the control circuit and operates to make up displaced fluid in an uncontrolled fashion. In the hydraulic circuit 650 illustrated in Fig. 6, the secondary energy source 608 serves as a charge pump and is also used as part of the control circuit. While the primary energy source 603 is coupled closed loop with a position feedback device on the first actuator 601, the secondary energy source 608 is coupled closed loop with the feedback device on the second actuator 602. By enforcing position/velocity control on the second actuator 602 via the secondary energy source 608, it is ensured that all fluid leaving the hydraulic circuit 650, for example due to parasitic losses, is exactly replaced by the secondary energy source 608, which draws from the reservoir 620. This allows the secondary energy source 608 to deliver precisely enough flow to control valve 611 and one-way check valves 612 so that the volumes entering port 610 and exiting the piston-side port 607 approximately equal those exiting the rod-side port 609 and entering the first port 606, synchronizing the motion of the two actuators 601, 602.

[0032] To control the motion, the control valve 611 sets the pressure difference between the rodside port 610 and piston-side port 607 of the second actuator 602 so that the second actuator 602 will retract when fluid is vacated from the piston-side port 607. The check valves 612 ensure that the fluid leaving the control valve 611 will enter the low-pressure side of primary energy source 603.

[0033] In some embodiments, a filtration module 622 is disposed the fourth fluid line 4 disposed in either the control valve 611 (shown) or the check valve 612 to ensure that any contamination that may enter the hydraulic circuit 650 from the fluid end slurry can be trapped before entering the main circuit. This can be applied for any application where the work stroke is in one direction and is needed continuously. [0034] In the hydraulic circuit 650, the primary energy source 603 induces motion in the first cylinder 624 such that the first rod 616 advances, the second rod 618 retracts a distance that is equal to the stroke of the first rod 616 because parasitic losses of the hydraulic circuit 650 are compensated for by the secondary energy source 608.

[0035] Referring to Fig. 4-5 and 7, an alternative embodiment hydraulic circuit 750 includes a double-rod linear actuator 700 in which the rods 716, 718 are decoupled. In the decoupled double-rod linear actuator 700, a first, primary energy source 703 provides power to two hydraulic actuators 701, 702 and drives the two hydraulic actuators to 701, 702 to advance and retract the rods 716, 718. The primary energy source 703 may be, for example, a variable speed, bi-direction pump. The two hydraulic actuators 701, 702 are mechanically decoupled as shown in Figure 5 but will operate and function due to a hydraulic scheme as a single actuator as shown in Figure 4. In addition, the hydraulic circuit 750 includes a secondary energy source 708 and a control valve 711 that are used to adjust the relative motion of the hydraulic actuators 701, 702 in such a way as to permit mid-motion relative lead or lag of one rod relative to the other. Because the hydraulic actuators are not coupled, the primary energy source 703 may be fully utilized while at the same time providing the freedom to orient the rods 716, 718 and corresponding fluid ends 207, 407 individually, however desired. In addition, the secondary energy source 708 and the control valve 711 cooperate to permit adjustment in the relatively alternating motion of the rods 716, 718. The decoupled double-rod linear actuator 700 will now be described in detail.

[0036] The first actuator 701 includes a first cylinder 724 and a first actuator piston-side port 706 in the first cylinder 724. The first actuator piston-side port 706 is connected to the first energy source A port via a first fluid line 1. The first actuator 701 includes a first actuator rodside port 709 in the first cylinder 724 and a first piston 714 disposed in the first cylinder 724. The first piston 714 forms a seal with the inner surface of the first cylinder 724 and segregates an interior space of the first cylinder 724 into a first chamber 704(1) that is connected to the first actuator piston-side port 706 and a second chamber 704(2) that is connected to the first actuator rod-side port 709. In addition, the first cylinder 724 includes a first rod 716 disposed in the second chamber 704(2). The first rod 716 has a first rod first end that is connected to one side of the first piston 714, and a first rod second end that is configured to be connected to a first load, for example the first fluid end 207.

[0037] The second actuator 702 includes a second cylinder 726 and a second actuator piston-side port 707 in the second cylinder 726. The second actuator piston-side port 707 is connected to the first energy source B port via a second fluid line 2. The second actuator 702 includes a second actuator rod-side port 710 in the second cylinder 726 and the second actuator rod-side port 710 is connected to the first actuator rod-side port 709 via a third fluid line 3. The second actuator 702 includes a second piston 715 disposed in the second cylinder 726. The second piston 715 forms a seal with an inner surface of the second cylinder 726 and segregates an interior space of the second cylinder 726 into a third chamber 705(1) that is connected to the second actuator pistonside port 707 and a fourth chamber 705(2) that is connected to the second actuator rod-side port 710. In addition, the second cylinder 726 includes a second rod 718 that is disposed in the fourth chamber 705(2) and has a second rod first end that is connected to one side of the second piston 715, and a second rod second end that is configured to be connected to a second load, for example the second fluid end 407.

[0038] The hydraulic circuit 750 includes a charge pump 730 that operates to maintain a predetermined minimum fluid pressure in the hydraulic circuit 759 despite parasitic losses by pumping fluid into the first and second fluid lines 1,2 via check valves 712. The charge pump 730 may be a single speed, single direction pump and draws fluid from a reservoir 720.

[0039] The hydraulic circuit 750 includes the secondary energy source 708. The secondary energy source 708 may be, for example, a variable speed, single-direction pump. The secondary energy source 708 may draw fluid from the reservoir 720 and is connected to the third fluid line 3 at a location between the piston-side ports 709, 710 of the first and second actuators 701, 702. The secondary energy source 708, in combination with a control valve 711, controls fluid flow in the hydraulic circuit 750 to keep the cylinders 724, 726 in sequence, or to permit a small lead or lag in relative motion, as discussed in detail below.

[0040] The secondary energy source 708 is in fluid communication with the third fluid line 3 via a fourth fluid line 4. The control valve 711 is disposed in the fourth fluid line 4 at a location between the secondary energy source 708 and the third fluid line 3. The control valve 711 controls fluid flow from the secondary energy source 708. [0041] To achieve freedom of orientation of the actuator 700, the first and second hydraulic actuators 701, 702 that constitute the actuator 700 must be mechanically decoupled as depicted in Figure 7. However, it is desired to use the primary energy source 703 to produce movement such that a movement in the first actuator 701 produces a corresponding movement in the second actuator 702. In the illustrated embodiment, the primary energy source 703 and the secondary energy source 708 operate synergistically to achieve a relatively alternating movement of the actuators 701, 702 such that an advancing-retracting movement in the first actuator 701 produces a corresponding opposite movement, e.g., a retracting— advancing movement in the second actuator 702. Because the second chamber 704(2) is connected to the fourth chamber 705(2) via the third fluid line 3, and because these structures together define a fixed volume, the relatively alternating movement is generated naturally. The fixed volume will be referred to as the rod side chamber 780, which includes the sum of fluid volumes within the second chamber 704(2), the fourth chamber 705(2) and the third fluid line 3.

[0042] When the primary energy source 703 induces motion in the first cylinder 724 such that the first rod 716 advances, the second rod 718 retracts because the rod sides of each of the first and second cylinders 724, 726 are associated with a common fixed volume as defined within the rod side chamber 780. Similarly, when the primary energy source 703 induces motion in the second cylinder 726 such that the second rod 718 advances, the first rod 716 retracts. Throughout the cycle defined by the advancing and retracting motion of the first rod 716, the secondary energy source 708, if required by the specific application, may adjust the relative motion of the first and second cylinders 724, 726 relative to the motion imposed by the primary energy source 703.

[0043] In some embodiments, the movement in the first actuator 701 produces a corresponding movement in the second actuator 602 that is opposite and equal (e.g., “180 degrees out of phase”) to that of the first actuator 601. In other embodiments, the corresponding movement in the second actuator 602 may be opposite and substantially equal to that of the first actuator 601. As previously discussed, the term “substantially equal” means that within the confines of the relative size of the secondary energy source 708 compared to the primary energy source 703, the motion of the second actuator 702 may be 180 degrees out of phase with the first actuator 701, or alternatively may lead or lag the first actuator 701 for a period of time during a given advancing- and-retracting cycle of a given rod 716 or 718. The amount of the lead or lag that can be achieved depends on the sizing of the secondary energy source 708 and is determined by the requirements of the specific application. In some embodiments, the amount of lead or lag may be very small, e.g., in a range of one percent to ten percent of the distance traveled by the actuator rods 716, 718 during an advancing motion. Advantageously, since the amount of lead or lag may be very small relative to a distance traveled by the actuator rods 716, 718, the secondary energy source 708 may be small relative to the primary energy source 703.

[0044] Throughout the movement, the actuators 701, 702 are controlled by the secondary energy source 708 to be exactly opposed, or alternatively to lead or lag each other. However, after one complete cycle the second actuator 702 will be 180 degrees out of phase with the first actuator 701. This is due to the fact that the secondary energy source 708 is very small relative to the primary energy source 703.

[0045] By this configuration the actuator 700 behaves, from a motion standpoint, like the double-acting actuator shown in Figure 4. Operationally the hydraulic circuit 750 operates with the first or primary energy source 703 operating to transfer fluid power between the first actuator piston-side port 706 of the first actuator 701 and the second actuator piston-side port 707 of the second actuator 702. During an operation where power is being transferred to the first actuator 701, the primary energy source 703 draws fluid from the second actuator piston-side port 707, compressing it into the first actuator piston-side port 706. As a result, the rod 716 of the first actuator 701 extends (e.g., advances), displacing volume in the first fluid end 207.

[0046] If there are no leakages in the hydraulic circuit 750, the total volume of fluid in the rod side chamber 780 remains fixed. Therefore, the rod 718 of the second actuator 702 will retract at the same rate the rod 716 of the first actuator 701 extends. Likewise, this will cause a volume of fluid to exit the first port 707 of the second actuator 702 and supply the primary energy source 703 with fluid to be pushed into the first port 706 of the first actuator 701. Unfortunately, all hydraulic systems have leakages intentionally created to allow for lubrication and cooling, e.g., parasitic losses. Most of these leakages occur in the primary energy source 703. In this embodiment, volumetric losses in the first and second fluid lines 1, 2 are replaced via check valves 712 and the charge pump 730.

[0047] In the hydraulic circuit 750 illustrated in Fig. 7, the secondary energy source 708 is separate from the charge pump 730 and is used as part of the control circuit. The second energy source provides a relatively small amount of energy to the hydraulic circuit 750 as compared to the primary energy source 703.

[0048] In the hydraulic circuit 750, while the primary energy source 703 is coupled closed-loop with a position feedback device on the first actuator 701, the secondary energy source 708 is coupled closed-loop with the feedback device on the second actuator 702 via the control valve 711. By enforcing position/velocity control on the second actuator 702 via the secondary energy source 708 and control valve 711, it is ensured that the fluid volume of the rod side chamber 780 is controlled, maintaining the synchronization between the first and second actuators 701 and 702.

[0049] Optionally, it may be desirable to control the first and second actuators 701, 702 such that the relative movement is opposite and equal or substantially equal. In the hydraulic circuit 750 this can be accomplished in multiple ways. In Fig. 7, the control valve 711 can be used to discharge fluid from the third fluid line 3 to a reservoir 720, thus decreasing the total volume of the rod side chamber 780. This allows the first actuator 701 to extend a greater distance than the second actuator 702 retracts. Using the control valve 711 and the secondary energy source 708, the volume of the rod side chamber 780 can be increased to return the actuators 701 and 702 to the previous set synchronization, or to allow actuator 702 to retract a greater distance than 701 extends. In this example, equal or substantially equal synchronization is maintained between actuator 701 and 702.

[0050] In a second example, opposite and equal or substantially equal movement between the two actuators 701, 702 may be accomplished by employing a hydraulic accumulator 740 in the hydraulic circuit 750. The hydraulic accumulator 740 is connected to the third fluid line 3 via a valve 741. This configuration allows for an expansion and contraction of the volume of fluid within the rod side chamber 780, allowing for a differential movement between actuator 701 and 702. This can be particularly useful for decompression. When actuator 701 reaches the end of its advancing stroke, the actuator 702 is fully retracted. Under load, the fluid in the first chamber 704(1) must be decompressed before the first rod 716 and the first piston 714 can begin to retract. This decompression is accomplished by moving a volume of fluid from the first chamber 704(1) to the third chamber 705(1). For this to take place, the second piston 715 and the second rod 718 must extend slightly. Since the first rod 716 and the first piston 714 cannot yet retract, it

Y1 is necessary to allow the volume of fluid within the rod side chamber 780 to be reduced. By displacing a small volume of fluid into accumulator 740, the volume of fluid within the rod side chamber 780 can be temporarily reduced. After decompression and the system equalizes, the volume of the fluid within the rod side chamber 780 will return to its original state with fluid exiting accumulator 740 re-entering the rod side chamber 780.

[0051] In the hydraulic circuits 650, 750 described above with respect to Figs. 6 and 7, the rods 616, 618, 716, 718 of the actuators 600, 700 are decoupled, whereby there are no limitations on the relative orientations of the rods 616, 618, 716, 718. For example, in some embodiments, the cylinders 624, 626, 724, 726 are arranged so that the first rod 616, 716 is coaxial with the second rod 618, 718 (Fig. 8). In other embodiments, the cylinders 624, 626, 724, 726 are arranged so that the first rod 616, 716 extends in parallel to, and is non-coaxial with, the second rod 618, 718 (Fig. 9). In still other embodiments, the cylinders 624, 626, 724, 726 are arranged so that the first rod 616, 716 is angled relative to the second rod 618, 718, where the angle may be acute (Fig. 10), normal or obtuse. Although in the orientations illustrated herein the rods 616, 618, 716, 718 are coplanar, they are not limited to this configuration.

[0052] Although the hydraulic circuit has been described herein as having application in hydraulic fracturing, the hydraulic circuit is not limited to this application. For example, the hydraulic circuit may be used in many other applications, including, but not limited to, as a driver for cyrogenic fluid pumps, gas compressors, mud pumps or any application that is driven by a crank shaft that is connected to pistons. Moreover, the hydraulic circuit is not limited to applications requiring high fluid flow and/or high pressure. Advantages of the hydraulic circuit include, but are not limited to, permitting a reduction in strokes per minute to reduce wear, changing the discharge frequency of pumping pulses, and the ability to vary the motion profile of the pump stroke.

[0053] Although the exemplary primary energy source is described as being a variable speed, bidirection pump and the secondary energy source is described as being a variable speed, single direction pump, the energy sources are not limited to being these types of pumps. The type of pump employed will be determined by the specific application. Moreover, other energy sources may be used, such as hydraulic motors (for example, when run in reverse). [0054] Selective illustrative embodiments of the hydraulic circuit are described above in some detail. It should be understood that only structures considered necessary for clarifying the hydraulic circuit have been described herein. Other conventional structures, and those of ancillary and auxiliary components of the hydraulic circuit, are assumed to be known and understood by those skilled in the art. Moreover, while a working example of the hydraulic circuit has been described above, the hydraulic circuit is not limited to the working example described above, but various design alterations may be carried out without departing from the hydraulic circuit as set forth in the claims.

Claims

What is claimed is,

1. A hydraulic circuit comprising: a first cylinder including a first rod, a second cylinder including a second rod, and a primary energy source that is fluidly connected to both the first cylinder and the second cylinder and is sized to perform the intended work of the circuit, and a secondary energy source that is fluidly connected to both the first cylinder and the second cylinder and is configured to adjust the relative motion of the first cylinder and the second cylinder relative to the motion imposed on the first cylinder and the second cylinder by the primary energy source, wherein the first cylinder is coupled to the second cylinder electronically and fluidly such that when the first rod moves relative to the first cylinder, the second rod moves relative to the second cylinder in an alternating motion in which the first rod advances as the second rod retracts and the second rod advances as the first rod retracts.

2. The hydraulic circuit of claim 1 , wherein when the first rod moves relative to the first cylinder, the second rod moves relative to the second cylinder in a motion that is opposite and equal to the motion of the first rod.

3. The hydraulic circuit of claim 1, wherein when the first rod moves relative to the first cylinder, the second rod moves relative to the second cylinder in a motion that is opposite and substantially equal to the motion of the first rod relative to the first cylinder.

4. The hydraulic circuit of claim 1 , wherein when the primary energy source induces motion in the first cylinder such that the first rod advances, the secondary energy source compensates for parasitic losses in the hydraulic circuit such that the second rod retracts a distance that is equal to the stroke of the first rod, and when the primary energy source induces motion in the second cylinder such that the second rod advances, the secondary energy source compensates for parasitic losses in the hydraulic circuit such that the first rod retracts a distance that is equal to the stroke of the second rod.

5. The hydraulic circuit of claim 1, comprising a charge pump configured to compensate for parasitic losses in the hydraulic circuit.

6. The hydraulic circuit of claim 1 , wherein the first cylinder includes a first piston that segregates the first cylinder into a first chamber and a second chamber, the first rod is fixed to the first piston and is at least partially disposed in the second chamber, an end of the first rod is disposed outside the first cylinder and is configured to be connected to a first load, the first rod is isolated from the first chamber via a seal between the first piston and the first cylinder, the second cylinder includes a second piston that segregates the second cylinder into a third chamber and a fourth chamber, the second rod is fixed to the second piston and is at least partially disposed in the fourth chamber, an end of the second rod is disposed outside the second cylinder and is configured to be connected to a second load, and the second rod is isolated from the third chamber via a seal between the second piston and the second cylinder.

7. The hydraulic circuit of claim 6, comprising a first fluid line that permits communication between the primary energy source and the first chamber, a second fluid line that permits communication between the primary energy source and the third chamber, a third fluid line that permits communication between the second chamber and the fourth chamber, and a fourth fluid line that permits communication between the third fluid line and each of the first fluid line and the second fluid line, wherein fluid flow in the fourth fluid line flows in only one direction so as to flow from the third fluid line to the first fluid line or from the third fluid line to the second fluid line.

8. The hydraulic circuit of claim 7, wherein a filter is disposed in the fourth fluid line.

9. The hydraulic circuit of claim 7, comprising a control device that is disposed in the fourth line and is configured to control fluid flow between the second and first chamber or the fourth and third chamber.

10. The hydraulic circuit of claim 9, wherein the control device is selected from a group of control devices that includes a control valve, a pressure control valve and a variable pump.

11. The hydraulic circuit of claim 6, comprising a first fluid line that permits communication between the primary energy source and the first chamber, a second fluid line that permits communication between the primary energy source and the third chamber, a third fluid line that permits communication between the second chamber and the fourth chamber, and a fourth fluid line that permits communication between the third fluid line and the secondary energy source, wherein fluid flow in the fourth fluid line is controlled by a first valve that is disposed in the fourth fluid line between the secondary energy source and the third fluid line.

12. The hydraulic circuit of claim 11, comprising a hydraulic accumulator that is connected to the third fluid line via a second valve and is configured to permit expansion and contraction of a volume defined within the second chamber, the fourth chamber and the third fluid line.

13. The hydraulic circuit of claim 1, wherein the first rod is coaxial with the second rod.

14. The hydraulic circuit of claim 1, wherein the first rod extends in parallel to, and is offset relative to, the second rod.

15. The hydraulic circuit of claim 1, wherein the first rod is perpendicular to the second rod.

16. The hydraulic circuit of claim 1, wherein the first rod is acutely angled relative to the second rod.

17. The hydraulic circuit of claim 1, wherein first rod has a first orientation in space, the second rod has a second orientation in space, and the first and second cylinders are configured so that the determination of the second orientation is free of a restriction that is based on the first orientation.

18. The hydraulic circuit of claim 1, wherein the energy producing capacity of the primary energy source is greater than that of the secondary energy source.

19. A hydraulic circuit, comprising: a primary energy source that is configured to generate flow of hydraulic fluid within the hydraulic circuit, the primary energy source including a primary energy source A port and a primary energy source B port; a first actuator that includes a first cylinder, a first piston-side port in the first cylinder, the first piston-side port being connected to the primary energy source A port via a first fluid line, a first rod-side port in the first cylinder, a first piston disposed in the first cylinder, the first piston segregating an interior space of the first cylinder into a first chamber that is connected to the first piston-side port and a second chamber that is connected to the first rod-side port, and a first rod disposed in the second chamber and having a first rod first end that is connected to one side of the first piston, and a first rod second end that is configured to be connected to a first load; a second actuator that includes a second cylinder, a second piston-side port in the second cylinder, the second piston-side port being connected to the primary energy source B port via a second fluid line, a second rod-side port in the second cylinder, the second rod-side port being connected to the first rod-side port via a third fluid line, a second piston disposed in the second cylinder, the second piston segregating an interior space of the second cylinder into a third chamber that is connected to the second pistonside port and a fourth chamber that is connected to the second rod-side port, and a second rod disposed in the second chamber and having a second rod first end that is connected to one side of the second piston, and a second rod second end that is configured to be connected to a second load; a secondary energy source that is connected to the third fluid line via a fourth fluid line, the secondary energy source configured to maintain a predetermined minimum fluid pressure in the hydraulic circuit; and a valve disposed in the fourth fluid line between the secondary energy source and the third fluid line, wherein a sub-volume of fluid in the hydraulic circuit is defined by the second chamber, the third line and the fourth chamber, and when the primary energy source induces motion in the first cylinder such that the first rod does one of advances and retracts through a first distance, the second rod does the other of advances and retracts through a second distance, where the second distance is equal to the first distance due to the volume of fluid in the sub-volume at the time the motion is induced, and the secondary energy source is configured to provide fluid to the subvolume via the valve, and the valve is configured to adjust the amount of fluid in the sub- volume to permit the motion of the second rod to lag or lead the motion of the first rod.

20. The hydraulic circuit of claim 19, wherein the first rod has a first orientation in space, the second rod has a second orientation in space, and the first and second cylinders are configured so that the determination of the second orientation is free of a restriction that is based on the first orientation.

21. The hydraulic circuit of claim 19, wherein the energy producing capacity of the primary energy source is greater than that of the secondary energy source.

22. The hydraulic circuit of claim 19, comprising a charge pump configured to compensate for parasitic losses in the hydraulic circuit.