Mechanically Decoupled Double Rod Linear Actuator

Abstract

The hydraulic circuit includes a first cylinder including a first rod and a second cylinder including a second rod. Additionally, the hydraulic circuit includes a primary energy source common to both the first and second cylinders, the primary energy source being sized to perform the intended operation of the circuit, and a secondary energy source common to both the first and second cylinders, the secondary energy source being sized to compensate for parasitic losses in the circuit. The first cylinder is electronically and fluidically coupled to the second cylinder, such that movement of the first rod relative to the first cylinder causes movement of the second rod relative to the second cylinder with an equal and opposite motion to that of the first rod.

Description

[Technical Field]

[0001] background Certain pumping applications, including but not limited to hydraulic fracturing or "fracking," require fluid pumps that deliver large volumes of fluid flow delivered at high fluid pressures. As shown in FIG. 1 , in the hydraulic fracturing market, a conventional pump 100 includes a mechanical plunger device 102, which provides linear motion at the fluid end via a crankshaft 104, displacing volumes back and forth to increase the pressure of an aqueous solution known as a slurry. Specifically, pressure is increased through a cover 108 from a charge pressure in a suction line 106 to the required formation fracturing pressure, as determined by the operating formation. The pump 100 is limited in stroke length and the force it can generate by mechanical limitations at its power end 110. Therefore, to increase flow, the pump 100, also known as a "short-stroke pump," can be operated at higher speeds, potentially resulting in high maintenance costs. To reduce operating and maintenance costs and increase the pump's durability and reliability, it is desirable to reduce the frequency at which a valve 112 integrated into the fluid end 114 opens and closes. Additionally, a longer, slower stroke is desirable to reduce the impact force on the fluid end 114. For reference, most commercially available fluid ends 114 have a stroke length of 8 inches.

[0002] overview Referring to FIG. 2, a linear actuator may be used to provide a pump with a longer stroke. In this case, actuator 201 is a hydraulic cylinder equipped with a variable, bidirectional hydraulic energy source 203. Energy source 203 directs a fluid, such as oil, between chambers 202 and 208 via first line 206, generating a force Fe and creating a pumping action in chamber 207. In this example, chamber 207 corresponds to the fluid end. In this simplified representation, those skilled in the art will recognize that there is a volume difference between chambers 202 and 208. This volume difference must be managed as rod 210 advances and retracts, but is not shown because numerous existing circuits exist to address this situation. Actuator 201 may be a ball screw or any other device capable of transmitting the necessary energy. For these purposes, the new device must reduce the number of strokes per minute required for a given flow rate compared to the device of FIG. 1. Fluid end 207 may be substantially the same as that of the conventional fracking pump of FIG. 1, but is not limited to this configuration. The idea and purpose of a linear long stroke is to provide a longer, gentler stroke and to displace a larger volume of fluid per stroke, e.g., about five times the volume per stroke. The design shown in Figure 2 is a very compact design, with the rod 210 of the actuator 201 acting as a plunger that enters the fluid end 207. In this case, the rod 210 displaces a volume, creating a pumping action. This can be a disadvantage because it can pull material from the slurry at the fluid end 207 back into the chamber 208, potentially contaminating the system.

[0003] Referring to FIG. 3, an alternative linear pump 300 has the same functionality as the pump 200 of FIG. 2, with the following exceptions. In FIG. 3, the actuator 201 is a hydraulic cylinder having a rod 310 separated into a first rod portion 313 and a second rod portion 309. The first rod portion 309 and the second rod portion 313 are coupled together to ensure that the distance between the fluid end 207 and the actuator 201 minimizes the possibility of slurry material entering the rod-side chamber 208. This is a less compact embodiment, but potentially more robust. An energy source 312 supplies fluid through a valve 311, ensuring that system pressure is maintained at all times. This is standard for all embodiments shown and should be understood by those skilled in the art.

[0004] One drawback of the pumps 200, 300 shown in Figures 2 and 3 is that no work is being done when the actuator 201 is retracting, i.e., when fluid is moving from the first port 204 to the second port 205. This means that the hydraulic energy source 203 is being used but is not doing any useful work, creating dead time in the cycle of this important asset.

[0005] 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 of the piston 214 and a second rod 210(2) protruding from a second side of the piston 214. This involves providing an extra (e.g., second) fluid end 407 that engages the second rod 210(2), such that as fluid moves from the first port 204 to the second port 205, the second fluid end 407 pumps and charges the first fluid end 207 with fluid. When the end of the stroke is reached and the energy source 203 reverses direction, fluid flows from the second port 205 to the first port 204. This causes the first fluid end 207 to pump and charge the second fluid end 407 with fluid. In this scenario, the energy source 203 is fully utilized 100% of the time, and the dead time is reduced to the time it takes to reverse direction. Note that the plunger rod orientation shown in FIG. 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 orientations of the first fluid end 207 and the second fluid end 407 are fixed at 180° to each other (e.g., linearly aligned and oriented in opposite directions). In some applications, it is desirable to achieve the same utilization of the energy source 203 without the linearly aligned orientation limitation imposed by this double-rod cylinder design.

[0006] Referring to Figure 5, it is desirable to achieve the benefits of the system of Figure 4 while decoupling the rods physically. Because the actuator rods are separated, there are no restrictions on the relative orientation of the rods. That is, the rods may be coaxial, parallel, offset, perpendicular, or at an acute angle.

[0007] In some aspects, the hydraulic circuit includes a first cylinder including a first rod and a second cylinder including a second rod, and additionally includes a primary energy source common to both the first and second cylinders, the primary energy source being sized to perform an intended task of the circuit, and a secondary energy source common to both the first and second cylinders.

[0008] The first cylinder is electronically and fluidly coupled to the second cylinder, and 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.

[0009] When the primary energy source induces motion in the first cylinder, causing the first rod to advance, the second rod will retract because the rod sides 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, causing the second rod to advance, the first rod will retract. Throughout the cycle defined by the forward and retract motion of the first rod, a secondary energy source can adjust the relative motion of the first and second cylinders with respect to the motion imparted by the primary energy source, as needed for a particular application.

[0010] In some aspects, the 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 and second cylinders and sized to perform the circuit's intended task. The hydraulic circuit includes a secondary energy source fluidly connected to both the first and second cylinders and configured to adjust the relative motion of the first and second cylinders in response to motion imparted to the first and second cylinders by the primary energy source. The first cylinder is electronically and fluidly coupled to the second cylinder, such that as the first rod moves relative to the first cylinder, the second rod moves relative to the second cylinder in an alternating motion such that as the first rod advances, the second rod retracts, and as the second rod advances, the first rod retracts.

[0011] In some embodiments, as the first rod moves relative to the first cylinder, the second rod moves relative to the second cylinder with an equal and opposite movement to that of the first rod.

[0012] In some embodiments, as the first rod moves relative to the first cylinder, the second rod moves relative to the second cylinder with a substantially equal and opposite movement of the first rod relative to the first cylinder.

[0013] In some embodiments, when the primary energy source induces motion in the first cylinder, causing the first rod to advance, the secondary energy source compensates for parasitic losses in the hydraulic circuit and the second rod retracts a distance equal to the stroke of the first rod, and when the primary energy source induces motion in the second cylinder, causing the second rod to advance, the secondary energy source compensates for parasitic losses in the hydraulic circuit and the first rod retracts a distance equal to the stroke of the second rod.

[0014] In some embodiments, the hydraulic circuit includes a charge pump configured to compensate for parasitic losses in the hydraulic circuit.

[0015] In some embodiments, the first cylinder includes a first piston separating the first cylinder into a first chamber and a second chamber. A first rod is secured to the first piston and disposed at least partially within the second chamber, and an end of the first rod is disposed outside the first cylinder and 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. Additionally, the second cylinder includes a second piston separating the second cylinder into a third chamber and a fourth chamber. A second rod is secured to the second piston and disposed at least partially within the fourth chamber, and an end of the second rod is disposed outside the second cylinder and 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.

[0016] In some embodiments, the hydraulic circuit includes a first fluid line providing communication between the primary energy source and the first chamber, a second fluid line providing communication between the primary energy source and the third chamber, a third fluid line providing communication between the second chamber and the fourth chamber, and a fourth fluid line providing communication between the third fluid line and each of the first and second fluid lines, where fluid flow in the fourth fluid line is unidirectional, such as from the third fluid line to the first fluid line or from the third fluid line to the second fluid line.

[0017] In some embodiments, a filter is disposed in the fourth fluid line.

[0018] In some embodiments, the hydraulic circuit includes a control device disposed in the fourth fluid line and configured to control fluid flow between the second chamber and the first chamber or between the fourth chamber and the third chamber.

[0019] In some embodiments, the control device is selected from the group of control devices including a control valve, a pressure control valve, and a variable pump.

[0020] In some embodiments, the hydraulic circuit includes a first fluid line providing communication between the primary energy source and the first chamber, a second fluid line providing communication between the primary energy source and the third chamber, a third fluid line providing communication between the second chamber and the fourth chamber, and a fourth fluid line providing 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 disposed in the fourth fluid line between the secondary energy source and the third fluid line.

[0021] In some embodiments, the hydraulic circuit includes a hydraulic accumulator connected to the third fluid line via a second valve, the hydraulic accumulator configured to allow expansion and contraction of volumes defined within the second chamber, the fourth chamber, and the third fluid line.

[0022] In some embodiments, the first rod is coaxial with the second rod.

[0023] In some embodiments, the first rod extends parallel to and is offset relative to the second rod.

[0024] In some embodiments, the first rod is perpendicular to the second rod.

[0025] In some embodiments, the first rod is at an acute angle to the second rod.

[0026] In some embodiments, the first rod has a first orientation in space, the second rod has a second orientation in space, and the first cylinder and the second cylinder are configured such that determination of the second orientation is not constrained based on the first orientation.

[0027] In some embodiments, the energy production capacity of the primary energy source is greater than the energy production capacity of the secondary energy source.

[0028] In some aspects, the hydraulic circuit includes a primary energy source configured to generate a working fluid flow 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 having a first cylinder and a first piston-side port of 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 of the first cylinder and a first piston disposed within the first cylinder. The first piston separates an interior space of the first cylinder into a first chamber connected to the first piston-side port and a second chamber connected to the first rod-side port. Additionally, the first actuator includes a first rod disposed within the second chamber, the first rod having a first end connected to one side of the first piston and a second end 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 of 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 separating the interior space of the second cylinder into a third chamber connected to the second piston-side port and a fourth chamber connected to the second rod-side port. Additionally, the second actuator includes a second rod disposed in the second chamber, the second rod having a first end connected to one side of the second piston and a second end configured to be connected to a second load. The hydraulic circuit includes a secondary energy source 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.Additionally, the hydraulic circuit includes a valve disposed in a fourth fluid line between the secondary energy source and the third fluid line. A subvolume of fluid in the hydraulic circuit is defined by the second chamber, the third fluid line, and the fourth chamber. When the primary energy source induces motion in the first cylinder, the first rod advances or retracts a first distance, and the second rod advances or retracts a second distance. The second distance is equal to the first distance due to the volume of fluid in the subvolume at the time the motion is induced. The secondary energy source is configured to supply fluid to the subvolume through the valve, and the valve is configured to adjust the amount of fluid in the subvolume to allow the motion of the second rod to lag or lead the motion of the first rod.

[0029] In some embodiments, the first rod has a first orientation in space, the second rod has a second orientation in space, and the first cylinder and the second cylinder are configured such that determination of the second orientation is not constrained based on the first orientation.

[0030] In some embodiments, the energy production capacity of the primary energy source is greater than the energy production capacity of the secondary energy source.

[0031] In some embodiments, the hydraulic circuit includes a charge pump configured to compensate for parasitic losses in the hydraulic circuit. [Brief explanation of the drawings]

[0032] [Figure 1] FIG. 1 is a diagram of a prior art frac pump. [Figure 2] FIG. 1 is a schematic diagram of a linear pump. [Figure 3] FIG. 1 is a schematic diagram of a linear pump with isolated chambers. [Figure 4] FIG. 1 is a schematic diagram of a double-acting hydraulic cylinder. [Figure 5] FIG. 1 is a schematic diagram of a split hydraulic cylinder. [Figure 6] FIG. 1 is a schematic diagram of a hydraulic circuit including a double-rod linear actuator with separated rods. [Figure 7] FIG. 10 is a schematic diagram of a hydraulic circuit of an alternative embodiment including a double-rod linear actuator with separated rods. [Figure 8] 8 is a schematic diagram of the hydraulic circuit of FIG. 7 showing the separated rods in alternative relative orientations. [Figure 9] FIG. 8 is a schematic diagram of the hydraulic circuit of FIG. 7 showing the separated rods in another alternative relative orientation. [Figure 10] FIG. 8 is a schematic diagram of the hydraulic circuit of FIG. 7 showing the separated rods in another alternative relative orientation.

[0033] Detailed Description Referring to FIGS. 4-6, a hydraulic circuit 650 includes a double-rod linear actuator 600, in which rods 616 and 618 are decoupled. In the decoupled double-rod linear actuator 600, a first primary energy source 603 supplies power to two hydraulic actuators 601 and 602, which drive the rods 616 and 618 to move forward and backward. The primary energy source 603 may be, for example, a variable-speed bidirectional pump. Although the two hydraulic actuators 601 and 602 are mechanically decoupled as shown in FIG. 5, they hydraulically operate and function as a single actuator as shown in FIG. 4. Additionally, the hydraulic circuit 650 includes a secondary energy source 608, which is used to adjust the relative motion of the hydraulic actuators 601 and 602, allowing one rod to lead or lag the other rod during intermediate motion. Because the hydraulic actuators are uncoupled, they can fully utilize the primary energy source 603 while at the same time providing the freedom to individually orient the rods 616, 618 and corresponding fluid ends 207, 407 as needed. Additionally, the secondary energy source 608 allows for adjustment of the relative alternating motion of the rods 616, 618. The decoupled double rod linear actuator 600 will now be described in detail.

[0034] The first actuator 601 includes a first cylinder 624 and a first actuator piston-side port 606 of 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 rod-side port 609 of the first cylinder 624 and a first piston 614 disposed within the first cylinder 624. The first piston 614 forms a seal with the inner surface of the first cylinder 624, separating the interior space of the first cylinder 624 into a first chamber 604(1) connected to the first actuator piston-side port 606 and a second chamber 604(2) connected to the first actuator rod-side port 609. Additionally, the first cylinder 624 includes a first rod 616 disposed within the second chamber 604(2). The first rod 616 has a first end connected to one side of the first piston 614 and a second end configured to be connected to a first load, for example, the first fluid end 207.

[0035] The second actuator 602 includes a second cylinder 626 and a second actuator piston-side port 607 of 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 within the second cylinder 626. The second piston 615 forms a seal with the inner surface of the second cylinder 626, separating the interior space of the second cylinder 626 into a third chamber 605(1) connected to the second actuator piston-side port 607 and a fourth chamber 605(2) connected to the second actuator rod-side port 610. Additionally, the second cylinder 626 includes a second rod 618 disposed within the fourth chamber 605(2), the second rod 618 having a first end connected to one side of the second piston 615 and a second end configured to be connected to a second load, for example, the second fluid side end 407.

[0036] The hydraulic circuit 650 includes a secondary energy source 608. The secondary energy source 608 may be, for example, a variable-speed, unidirectional pump. The secondary energy source 608 can draw fluid from a reservoir 620 and is connected to a third fluid line 3 at a location between a piston-side port 609 of the first actuator 601 and a piston-side port 610 of the second actuator 602. The secondary energy source 608 may be a charge pump that operates to maintain a preset 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 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 the fluid flow in the hydraulic circuit 650 to maintain the cylinders 624, 626 in sequence or to allow a small lead or lag in their relative motion, as described in more detail below.

[0037] A control valve 611 is disposed in the fourth fluid line 4. The fourth fluid line 4 connects the third fluid line 3, and thus 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 Figure 6, the one-way check valves are referred to collectively using the reference numeral 612.

[0038] To achieve the orientational freedom of actuator 600, first hydraulic actuator 601 and second hydraulic actuator 602 comprising actuator 600 must be mechanically decoupled, as shown in FIG. 6. However, it is desirable to generate motion using primary energy source 603, with motion of first actuator 601 generating corresponding motion of second actuator 602. In the illustrated embodiment, primary energy source 603 and secondary energy source 608 operate synergistically to achieve the relative alternating motion of actuators 601, 602, with forward-reverse motion of first actuator 601 generating corresponding reverse-reverse motion of second actuator 602. Second chamber 604(2) is connected to fourth chamber 605(2) via third fluid line 3, and the relative alternating motion occurs naturally because these structures together define a fixed volume.

[0039] When the primary energy source 603 induces motion in the first cylinder 624, causing the first rod 616 to advance, the second rod 618 will retract because the rod sides of each of the first cylinder 624 and second cylinder 626 are associated with a common, fixed volume. Similarly, when the primary energy source 603 induces motion in the second cylinder 626, causing the second rod 618 to advance, the first rod 616 will retract. Throughout the cycle defined by the forward and retract motion of the first rod 616, the secondary energy source 608 can adjust the relative motion of the first cylinder 624 and second cylinder 626 with respect to the motion imparted by the primary energy source 603, as needed for a particular application.

[0040] In some embodiments, the movement of the first actuator 601 generates a corresponding movement of the second actuator 602 that is opposite and equal to (e.g., "180 degrees out of phase") the movement of the first actuator 601. Note that the term "opposite" as used herein refers to retraction compared to advancement, not to a specific absolute direction, and the rods may not be parallel or aligned when the rods are separated. In other embodiments, the corresponding movement of the second actuator 602 may be opposite and substantially equal to the movement of the first actuator 601. The term "substantially equal" as used herein means that, within the relative magnitude of the secondary energy source 608 compared to the primary energy source 603, the movement 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 by a period of time during a given advance-retract cycle of a given rod 616 or rod 618. The amount of lead or delay that can be achieved depends on the size of the secondary energy source 608 and is determined by the requirements of a particular application. In some embodiments, the amount of lead or delay is quite small, for example, in the range of 1% to 10% of the distance traveled by the actuator rods 616, 618 during forward motion. Advantageously, the secondary energy source 608 may be small relative to the primary energy source 603, since the amount of lead or delay can be quite small relative to the distance traveled by the actuator rods 616, 618.

[0041] During movement, the actuators 601, 602 are controlled by the secondary energy source 608 to move in exactly opposite directions, or alternatively to lead or lag each other. However, after one complete cycle, the second actuator 602 is 180° out of phase with the first actuator 601. This is because the secondary energy source 608 is extremely small relative to the primary energy source 603.

[0042] This configuration allows the actuator 600 to behave similarly from a kinematic standpoint to the double-acting actuator shown in Figure 4, and further provides the advantage of achieving "substantially equal" motion. In operation, the hydraulic circuit 650 operates the first or primary energy source 603 to transfer fluid force 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 operation when force is being transferred to the first actuator 601, the primary energy source 603 draws fluid from the second actuator piston-side port 607 and compresses it into the first actuator piston-side port 606. As a result, the rod 616 of the first actuator 601 extends (e.g., moves forward), displacing a volume at the first fluid-side end 207.

[0043] If there are no leaks in the hydraulic circuit 650, the rod 618 of the second actuator 602 retracts at the same rate as the extension of the rod 616 of the first actuator 601. This, in turn, causes a constant volume of fluid to exit the first port 607 of the second actuator 602 and be supplied to the primary energy source 603 along with the fluid being forced into the first port 606 of the first actuator 601. Unfortunately, all hydraulic systems intentionally have leaks to allow for lubrication and cooling. These leaks are referred to as parasitic losses. Thus, some portion of the volume of fluid exiting ports 609 and 607 returns to the reservoir 620. As a result, unless the lost fluid is replenished, the rod 618 of the second actuator 602 will not retract in sync with the advancement of the rod 616 of the first actuator 601.

[0044] When used in conventional hydraulic circuits, a charge pump is typically not used as part of a control circuit and operates in an uncontrolled manner to replenish displaced fluid. In hydraulic circuit 650 shown in FIG. 6, secondary energy source 608 functions as a charge pump and is also used as part of the control circuit. Primary energy source 603 is coupled in a closed loop with the position feedback device of first actuator 601, while secondary energy source 608 is coupled in a closed loop with the feedback device of second actuator 602. By implementing position / velocity control of second actuator 602 via secondary energy source 608, it is ensured that any fluid leaving hydraulic circuit 650 due to, for example, parasitic losses, is accurately replenished by secondary energy source 608 drawing from reservoir 620. This allows the secondary energy source 608 to accurately deliver sufficient flow to the control valve 611 and one-way check valve 612 so that the volume entering port 610 and exiting piston side port 607 is approximately equal to the volume exiting rod side port 609 and entering first port 606, synchronizing the motion of the two actuators 601, 602.

[0045] To control the movement, control valve 611 sets a pressure differential between rod-side port 610 and piston-side port 607 of second actuator 602, causing second actuator 602 to retract as fluid exits piston-side port 607. Check valve 612 ensures that fluid exiting control valve 611 enters the low-pressure side of primary energy source 603.

[0046] In some embodiments, a filtration module 622 can be placed in the fourth fluid line 4, either at the control valve 611 (shown) or at the check valve 612, to ensure that any contaminants that may enter the hydraulic circuit 650 from the fluid end slurry are captured before entering the main circuit. This can be applied to any application where the working stroke is unidirectional and required continuously.

[0047] In hydraulic circuit 650, when primary energy source 603 induces motion in first cylinder 624, causing first rod 616 to move forward, second rod 618 moves back a distance equal to the stroke of first rod 616 because parasitic losses in hydraulic circuit 650 are compensated for by secondary energy source 608.

[0048] Referring to FIGS. 4-5 and 7, an alternative embodiment of a hydraulic circuit 750 includes a double-rod linear actuator 700 with decoupled rods 716, 718. In the decoupled double-rod linear actuator 700, a first primary energy source 703 provides power to two hydraulic actuators 701, 702, which drive the rods 716, 718 to move forward and backward. The primary energy source 703 may be, for example, a variable-speed bidirectional pump. Although the two hydraulic actuators 701, 702 are mechanically decoupled as shown in FIG. 5, they hydraulically operate and function as a single actuator as shown in FIG. 4. Additionally, the hydraulic circuit 750 includes a secondary energy source 708 and a control valve 711, which are used to adjust the relative motion of the hydraulic actuators 701, 702, allowing one rod to lead or lag the other rod during intermediate motion. Because the hydraulic actuators are uncoupled, they can fully utilize the primary energy source 703 while at the same time providing the freedom to individually orient the rods 716, 718 and corresponding fluid ends 207, 407 as needed. Additionally, the secondary energy source 708 and control valve 711 cooperate to allow for adjustment of the relative alternating motion of the rods 716, 718. The decoupled double rod linear actuator 700 will now be described in detail.

[0049] The first actuator 701 includes a first cylinder 724 and a first actuator piston-side port 706 of 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 rod-side port 709 of the first cylinder 724 and a first piston 714 disposed within the first cylinder 724. The first piston 714 forms a seal with the inner surface of the first cylinder 724, separating the interior space of the first cylinder 724 into a first chamber 704(1) connected to the first actuator piston-side port 706 and a second chamber 704(2) connected to the first actuator rod-side port 709. Additionally, the first cylinder 724 includes a first rod 716 disposed within the second chamber 704(2). The first rod 716 has a first end connected to one side of the first piston 714 and a second end configured to be connected to a first load, for example, the first fluid end 207.

[0050] The second actuator 702 includes a second cylinder 726 and a second actuator piston-side port 707 of 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 of 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 within the second cylinder 726. The second piston 715 forms a seal with the inner surface of the second cylinder 726, separating the interior space of the second cylinder 726 into a third chamber 705(1) connected to the second actuator piston-side port 707 and a fourth chamber 705(2) connected to the second actuator rod-side port 710. Additionally, the second cylinder 726 includes a second rod 718 disposed within the fourth chamber 705(2), the second rod 718 having a first end connected to one side of the second piston 715 and a second end configured to be connected to a second load, for example, the second fluid side end 407.

[0051] Hydraulic circuit 750 includes a charge pump 730 that operates to maintain a preset minimum fluid pressure in hydraulic circuit 759 despite parasitic losses by pumping fluid through check valve 712 into first fluid line 1 and second fluid line 2. Charge pump 730 may be a single-speed, unidirectional pump and can draw fluid from reservoir 720.

[0052] Hydraulic circuit 750 includes a secondary energy source 708, which may be, for example, a variable speed, unidirectional pump. Secondary energy source 708 may draw fluid from reservoir 720 and is connected to third fluid line 3 at a location between piston-side port 709 of first actuator 701 and piston-side port 710 of second actuator 702. Secondary energy source 708, in combination with control valve 711, controls fluid flow in hydraulic circuit 750 to maintain cylinders 724, 726 in sequence or to allow a small lead or lag in their relative motion, as described in more detail below.

[0053] The secondary energy source 708 is in fluid communication with the third fluid line 3 via a fourth fluid line 4. A 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 the fluid flow from the secondary energy source 708.

[0054] To achieve the orientational freedom of actuator 700, first hydraulic actuator 701 and second hydraulic actuator 702 comprising actuator 700 must be mechanically decoupled, as shown in FIG. 7. However, it is desirable to generate motion using primary energy source 703, with motion of first actuator 701 generating corresponding motion of second actuator 702. In the illustrated embodiment, primary energy source 703 and secondary energy source 708 operate synergistically to achieve the relative alternating motion of actuators 701, 702, with forward-backward motion of first actuator 701 generating a corresponding opposite motion, e.g., backward-forward motion, of second actuator 702. Second chamber 704(2) is connected to fourth chamber 705(2) via third fluid line 3, and the relative alternating motion occurs naturally because these structures together define a fixed volume. The fixed volume is referred to as the rod side chamber 780, and the fixed volume includes the sum of the volumes of fluid within the second chamber 704(2), the fourth chamber 705(2) and the third fluid line 3.

[0055] When the primary energy source 703 induces motion in the first cylinder 724, causing the first rod 716 to advance, the second rod 718 will retract because the rod sides of each of the first cylinder 724 and second cylinder 726 are associated with a common, fixed volume defined within the rod side chamber 780. Similarly, when the primary energy source 703 induces motion in the second cylinder 726, causing the second rod 718 to advance, the first rod 716 will retract. Throughout the cycle defined by the forward and retract motion of the first rod 716, the secondary energy source 708 can adjust the relative motion of the first cylinder 724 and second cylinder 726 with respect to the motion imparted by the primary energy source 703, as needed for a particular application.

[0056] In some embodiments, the movement of the first actuator 701 generates a corresponding movement of the second actuator 602 that is opposite and equal to (e.g., "180 degrees out of phase") the movement of the first actuator 601. In other embodiments, the corresponding movement of the second actuator 602 may be opposite and substantially equal to the movement of the first actuator 601. As noted above, the term "substantially equal" means that, within the relative size of the secondary energy source 708 compared to the primary energy source 703, the movement 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 by a period of time during a given forward-retract cycle of a given rod 716 or rod 718. The amount of lead or lag that can be achieved depends on the size of the secondary energy source 708 and is determined by the requirements of a particular application. In some embodiments, the amount of lead or lag is very small, for example, in the range of 1% to 10% of the distance traveled by the actuator rods 716, 718 during forward motion. Advantageously, because the amount of lead or lag is very small relative to the distance traveled by the actuator rods 716, 718, the secondary energy source 708 may be small relative to the primary energy source 703.

[0057] During movement, actuators 701, 702 are controlled by secondary energy source 708 to move in exactly opposite directions, or alternatively to lead or lag each other. However, after one complete cycle, second actuator 702 is 180° out of phase with first actuator 701. This is due to the fact that secondary energy source 708 is extremely small relative to primary energy source 703.

[0058] With this configuration, actuator 700 behaves kinematically similarly to the double-acting actuator shown in Figure 4. In operation, hydraulic circuit 750 operates first or primary energy source 703 to transfer fluid force between first actuator piston side port 706 of first actuator 701 and second actuator piston side port 707 of second actuator 702. During operation when force is being transferred to first actuator 701, primary energy source 703 draws fluid from second actuator piston side port 707 and compresses it into first actuator piston side port 706. As a result, rod 716 of first actuator 701 extends (e.g., moves forward), displacing a volume at first fluid side end 207.

[0059] If there are no leaks in hydraulic circuit 750, the total volume of fluid in rod-side chamber 780 remains constant. Thus, rod 718 of second actuator 702 retracts at the same rate as rod 716 of first actuator 701 extends. This, in turn, causes a constant volume of fluid to exit first port 707 of second actuator 702 and be supplied to primary energy source 703 along with the fluid being forced into first port 706 of first actuator 701. Unfortunately, all hydraulic systems intentionally have leakage, e.g., parasitic losses, to allow for lubrication and cooling. Most of these leakage occurs in primary energy source 703. In this embodiment, volume losses in first fluid line 1 and second fluid line 2 are replenished via check valve 712 and charge pump 730.

[0060] 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 compared to the primary energy source 703.

[0061] In hydraulic circuit 750, primary energy source 703 is coupled in a closed loop to the position feedback device of first actuator 701, while secondary energy source 708 is coupled in a closed loop to the feedback device of second actuator 702 via control valve 711. By implementing position / velocity control of second actuator 702 via secondary energy source 708 and control valve 711, the volume of fluid in rod-side chamber 780 is controlled, ensuring that synchronization between first actuator 701 and second actuator 702 is maintained.

[0062] Optionally, it may be desirable to control the first actuator 701 and the second actuator 702 so that their relative motions are opposite and equal or substantially equal. In the hydraulic circuit 750, this can be accomplished in several ways. In FIG. 7 , the control valve 711 can be used to vent fluid from the third fluid line 3 to the reservoir 720, reducing 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 can retract. 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 a previous synchronization setting or to allow the actuator 702 to retract a greater distance than the actuator 701 can extend. In this example, equal or substantially equal synchronization is maintained between the actuators 701 and 702.

[0063] In a second example, the use of a hydraulic accumulator 740 in hydraulic circuit 750 can achieve equal or substantially equal opposite motion between the two actuators 701, 702. The hydraulic accumulator 740 is connected to the third fluid line 3 via a valve 741. This configuration allows for the expansion and contraction of the volume of fluid in the rod-side chamber 780, allowing for differential motion between actuators 701, 702. This may be particularly useful for pressure reduction. When actuator 701 reaches the end of its forward stroke, actuator 702 is fully retracted. Under load, the fluid in first chamber 704(1) must be depressurized before first rod 716 and first piston 714 begin to retract. This pressure reduction is achieved by moving a volume of fluid from first chamber 704(1) to third chamber 705(1). To accomplish this, second piston 715 and second rod 718 must be slightly extended. Because the first rod 716 and first piston 714 cannot yet retract, the volume of fluid in the rod end chamber 780 must be reduced. This can be done temporarily by displacing a small volume of fluid into the accumulator 740. After the pressure is reduced and the system equalizes, the volume of fluid in the rod end chamber 780 returns to its original state, and fluid leaving the accumulator 740 re-enters the rod end chamber 780.

[0064] In the hydraulic circuits 650, 750 described above with respect to Figures 6 and 7, the rods 616, 618, 716, 718 of the actuators 600, 700 are separated, and there are no limitations on the relative orientation of the rods 616, 618, 716, 718. For example, in some embodiments, the cylinders 624, 626, 724, 726 are arranged such that the first rod 616, 716 is coaxial with the second rod 618, 718 (Figure 8). In other embodiments, the cylinders 624, 626, 724, 726 are arranged such that the first rod 616, 716 extends parallel to, but is non-coaxial with, the second rod 618, 718 (Figure 9). In yet other embodiments, the cylinders 624, 626, 724, 726 are arranged such that the first rod 616, 716 is at an angle to the second rod 618, 718, which may be an acute angle (FIG. 10), a right angle, or an obtuse angle. In the orientation shown here, the rods 616, 618, 716, 718 are coplanar, but are not limited to this configuration.

[0065] Although hydraulic circuits are described herein as applied to hydraulic fracturing, they are not limited to this application. For example, hydraulic circuits can be used in many other applications, including, but not limited to, drives for cryogenic fluid pumps, gas compressors, mud pumps, or any application driven by a crankshaft connected to a piston. Furthermore, hydraulic circuits are not limited to applications requiring high fluid flow rates and / or high pressures. Advantages of hydraulic circuits include, but are not limited to, the ability to reduce strokes per minute to reduce wear, modify the discharge frequency of pumping pulses, and modify the motion profile of the pump strokes.

[0066] Although exemplary primary energy sources are described as being variable speed bidirectional pumps and secondary energy sources as being variable speed unidirectional pumps, the energy sources are not limited to these types of pumps. The type of pump employed will be determined by the particular application. Additionally, other energy sources, such as hydraulic motors (e.g., when run in reverse), can also be used.

[0067] Selected exemplary embodiments of the hydraulic circuit are described in detail above. It should be understood that only that structure deemed necessary to clarify the hydraulic circuit is described herein. Other conventional structures of the hydraulic circuit, and structures of associated and auxiliary components, are assumed to be known and understood by those skilled in the art. Furthermore, while exemplary working examples of the hydraulic circuit are described above, the hydraulic circuit is not limited to the exemplary working examples described above, and various design modifications can be made without departing from the hydraulic circuit as set forth in the claims.

Claims

1. A hydraulic circuit, a first cylinder including a first rod; a second cylinder including a second rod; a primary energy source fluidly connected to both the first cylinder and the second cylinder, the primary energy source sized to perform the intended operation of the hydraulic circuit; a secondary energy source fluidly connected to both the first cylinder and the second cylinder, the secondary energy source configured to adjust relative motion of the first cylinder and the second cylinder with respect to motion imparted to the first cylinder and the second cylinder by the primary energy source; Equipped with The first cylinder is electronically and fluidly coupled to the second cylinder, and as the first rod moves relative to the first cylinder, the second rod moves relative to the second cylinder in an alternating motion such that as the first rod moves forward, the second rod moves backward, and as the second rod moves forward, the first rod moves backward. Hydraulic circuit.

2. 2. The hydraulic circuit of claim 1, wherein movement of said first rod relative to said first cylinder causes said second rod to move relative to said second cylinder in an equal and opposite movement to said movement of said first rod.

3. 2. The hydraulic circuit of claim 1, wherein movement of said first rod relative to said first cylinder causes said second rod to move relative to said second cylinder in a substantially equal and opposite movement to said movement of said first rod relative to said first cylinder.

4. when the primary energy source induces motion in the first cylinder, causing the first rod to advance, the secondary energy source compensates for parasitic losses in the hydraulic circuit, causing the second rod to retract a distance equal to the stroke of the first rod; When the primary energy source induces motion in the second cylinder to advance the second rod, the secondary energy source compensates for parasitic losses in the hydraulic circuit, causing the first rod to retract a distance equal to the stroke of the second rod. The hydraulic circuit according to claim 1.

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

6. the first cylinder includes a first piston separating 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 within the second chamber; an end of the first rod is disposed outside the first cylinder and 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 separating 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 within the fourth chamber; an end of the second rod is disposed outside the second cylinder and 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; The hydraulic circuit according to claim 1.

7. a first fluid line providing communication between the primary energy source and the first chamber; a second fluid line providing communication between the primary energy source and the third chamber; a third fluid line providing communication between the second chamber and the fourth chamber; a fourth fluid line that allows communication between the third fluid line and each of the first fluid line and the second fluid line; Equipped with the fluid flow in the fourth fluid line is unidirectional, such as from the third fluid line to the first fluid line or from the third fluid line to the second fluid line; 7. The hydraulic circuit according to claim 6.

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

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

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

11. a first fluid line providing communication between the primary energy source and the first chamber; a second fluid line providing communication between the primary energy source and the third chamber; a third fluid line providing communication between the second chamber and the fourth chamber; a fourth fluid line providing communication between the third fluid line and the secondary energy source; and Equipped with fluid flow in the fourth fluid line is controlled by a first valve disposed in the fourth fluid line between the secondary energy source and the third fluid line; 7. The hydraulic circuit according to claim 6.

12. 12. The hydraulic circuit of claim 11, comprising a hydraulic accumulator connected to the third fluid line through a second valve, the hydraulic accumulator configured to allow expansion and contraction of volumes defined within the second chamber, the fourth chamber, and the third fluid line.

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

14. The hydraulic circuit of claim 1 , wherein the first rod extends parallel to the second rod 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 said first rod is at an acute angle relative to said second rod.

17. 2. The hydraulic circuit of claim 1, wherein a first rod has a first orientation in space and the second rod has a second orientation in space, and the first cylinder and the second cylinder are configured such that determination of the second orientation is not constrained based on the first orientation.

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

19. A hydraulic circuit, a primary energy source configured to generate a working fluid flow 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, a first cylinder; a first piston-side port of 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 of the first cylinder; a first piston disposed in the first cylinder, the first piston separating an internal space of the first cylinder into a first chamber connected to the first piston-side port and a second chamber connected to the first rod-side port; a first rod disposed within the second chamber, the first rod having a first end connected to one side of the first piston and a second end configured to be connected to a first load; a first actuator including: a second actuator, a second cylinder; a second piston-side port of 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 of 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 within the second cylinder, the second piston separating an internal space of the second cylinder into a third chamber connected to the second piston-side port and a fourth chamber connected to the second rod-side port; a second rod disposed within the second chamber, the second rod having a first end connected to one side of the second piston and a second end configured to be connected to a second load; a second actuator including: a secondary energy source 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; a valve disposed in the fourth fluid line between the secondary energy source and the third fluid line; Equipped with a subvolume of fluid in the hydraulic circuit is defined by the second chamber, the third fluid line, and the fourth chamber; when the primary energy source induces motion in the first cylinder and the first rod advances or retracts a first distance; the second rod advances or retracts the other of a second distance equal to the first distance due to a volume of fluid in the sub-volume at the time the movement is induced; the secondary energy source is configured to supply fluid to the sub-volume via the valve, the valve being configured to adjust the amount of fluid in the sub-volume to allow the movement of the second rod to lag or lead the movement of the first rod. Hydraulic circuit.

20. 20. The hydraulic circuit of claim 19, wherein the first rod has a first orientation in space and the second rod has a second orientation in space, and the first cylinder and the second cylinder are configured such that determination of the second orientation is not constrained based on the first orientation.

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

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

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