JP2023530922A - Synchronized hybrid clamping force controller for lift truck attachment - Google Patents

Abstract

The present invention provides an improved hydraulic control circuit that permits rapid and synchronized closure of opposing clamps toward a load and prevents damage to the load upon contact by the clamps. and A hydraulic control circuit is provided for selectively hydraulically coupling a first hydraulic actuator and a second hydraulic actuator and operable to bypass the hydraulic coupling. [Selection diagram] Fig. 1

Description

Cross-reference to related applications

[0001] This application claims the benefit of US Provisional Patent Application No. 63/041,014, filed June 18, 2020, the entire contents of which are incorporated herein by reference.

[0002] The subject matter of this application relates generally to improved systems and methods for operating lift truck attachments used to grip and move loads.

[0003] Material handling vehicles, such as lift trucks, are used to pick up and move loads from one location to another. Because lift trucks typically must transport many different types of loads, lift trucks usually include a mast that supports a vertically extendable carriage, each of which has a specific It can be selectively interconnected with any one of a variety of different hydraulically actuated lift truck attachments intended to securely engage and move types of loads. For example, certain lift truck attachments may include a pair of horizontally spaced forks intended to slide into respective slots of a pallet supporting the load to be moved. Another lift truck attachment may include a pair of opposed, vertically oriented clamps intended to firmly grip the sides of the load so that the lift truck can lift and move the load. .

[0004] Examples of this latter type of attachment include carton clamp attachments intended to grip boxes or other rectangular loads, paper roll clamps intended to grip cylindrical loads, and the like. included. Lift truck attachments, such as carton or roll clamp attachments, require hydraulic control systems designed to avoid damage to the load. As an example, a hydraulic control system for a clamp-type attachment must provide enough lateral force to securely grip the load so that it does not fall off during transport, but at the same time to provide a load that is not too large. It is necessary not to damage the load by applying force. Therefore, the hydraulic control system for the clamp attachment typically, together with the control system, automatically gradually increases the gripping fluid pressure from a relatively low initial pressure to just enough pressure to lift the load without slipping. It includes some sort of weight sensing mechanism that adjusts the gripping force by

[0005] However, using a low initial pressure limits the speed at which the load engaging surfaces can be closed into initial contact with the load, thereby limiting the productivity of the load clamping system. This problem arises because fast closing requires closing pressures higher than the desired low threshold pressure, and such higher pressures are trapped in the system by the fluid input check valve during initial closing. so that the desired lower threshold pressure is exceeded before automatic adjustment of the gripping pressure can be initiated.

[0006] Hydraulic control systems for clamp attachments also typically coordinate the movement of the clamps toward the load, resulting in one clamp prematurely impacting and damaging the load, or causing the load to strike the other. It does not slide towards the clamp of the To this end, such control systems typically utilize flow dividers, such as spool flow dividers and gear flow dividers, to divide hydraulic fluid evenly to each of the clamps. A spool-type flow divider divides the flow through a fixed pressure-compensated orifice, which ensures approximately equal flow through the orifices even with fluctuating inlet and/or outlet pressures. However, spool shunts must balance accuracy with the ability to withstand oil contamination without failure. Spool flow dividers are designed to divide flow accurately only within a narrow range of flow rates and because spool flow dividers use fixed orifices, when used below the rated flow rate of a given flow divider, An even split of the flow may not occur, and if the flow exceeds the valve rating, the large pressure drop across the valve will degrade performance and cause fluid heating. Gear diverters can operate over a wider range of operating flow rates than spool diverters, but are generally very expensive and require hydraulic pressure to prevent pressure build-up if one clamp is restricted in travel. The circuit must be properly designed.

[0007] The use of flow diverters, such as spool flow diverters and gear flow diverters, in hydraulic clamp control systems also tends to limit the closing speed at which the opposing clamp moves toward the load. Specifically, as mentioned above, because more pressure is required to increase the inward velocity of each clamp, and because each clamp is driven toward the load with the same pressure, the clamps are simultaneously The clamping force on a load can be very high when contacting the load. Thus, limiting the force on the load at the moment when the two opposing clamps are controlled by the fluid supplied through the flow diverter means limiting the closing pressure and thus the closing speed. To provide fast closing and low initial clamping force, a complex hydraulic control system may provide either manually or automatically selectable high and low relief settings depending on clamp closing speed.

[0008] Accordingly, an improved hydraulic control circuit is desired that allows rapid and synchronized closure of opposing clamps toward a load and prevents damage to the load upon contact by the clamps.

[0009] For a better understanding of the invention and to show how the same may be practiced, reference will now be made, by way of example, to the accompanying drawings.

4 illustrates an exemplary hydraulic control circuit using fluid supplied from the lift truck to actuate respective hydraulic cylinders each capable of driving respective clamps on the lift truck attachment. 2 shows the pressures and forces exerted by the hydraulic cylinders controlled by the circuit of FIG. 1; 2 illustrates the exemplary hydraulic control circuit of FIG. 1 connected to a pair of hydraulic cylinders used to actuate the pivot arm clamp; 2 illustrates a first exemplary synchronizing plunger that may be used in the hydraulic control circuit of FIG. 1; Figure 4 shows the synchronous plunger of Figure 3 in mid-stroke position and pressurized from the rod side; Figure 4 shows the synchronous plunger of Figure 3 in the end of stroke position and pressurized from the rod side; Figure 4 shows the synchronizing plunger of Figure 3 in the mid-stroke position and pressurized from the head side; 2 illustrates a second exemplary synchronizing plunger that may be used in the hydraulic control circuit of FIG. 1; Figure 6 shows the synchronous plunger of Figure 5 in mid-stroke position and pressurized from the rod side; Figure 6 shows the synchronous plunger of Figure 5 in the end of stroke position and pressurized from the rod side; Figure 6 shows the synchronous plunger of Figure 5 in mid-stroke position and pressurized from the head side; Figure 6 shows the synchronous plunger of Figure 5 in the end of stroke position and pressurized from the head side; Figure 4 shows an alternative control circuit used to control each hydraulically actuated motor of the lift truck attachment; Fig. 3 shows an alternative control circuit capable of coordinating movement of hydraulic actuators, such actuators being either coupled or uncoupled; Fig. 3 shows an alternative control circuit using a bi-directional relief valve and multiple sequence valves to resynchronize the hydraulic cylinders in the open position; Figure 3 shows a multi-load handler (MLH) attachment in single palette mode. Figure 3 shows a multi-load handler (MLH) attachment in double palette mode. Fig. 3 illustrates the operation of the MLH to move loads away from each other when in double pallet mode; Fig. 4 shows the operation of the MLH moving loads toward each other when in double pallet mode; 4 shows an exemplary hydraulic control circuit that may be used to control the MLH;

[0028] The present disclosure provides a hydraulic actuator on an industrial machine such as a lift truck or lift truck attachment in a first configuration in which the actuator is hydraulically coupled and a second configuration in which the actuator is not hydraulically coupled. Novel systems and methods are described that allow alternating between configurations. As used herein and in the claims, the term "hydraulic actuator" refers to any device having first and second fluid line connections where the differential fluid pressure across the connections is , are used to impart motion to the actuator. Examples of hydraulic actuators include, but are not limited to, hydraulic cylinders and hydraulically actuated motors. As used herein and in the claims, when referring to a hydraulic control circuit used to control one or more such actuators, the term "input port" refers to the operation of the control circuit. in which pressurized fluid is received from an external source, such as a lift truck, thereby pressurizing at least one output port of the control circuit, as defined below, while supplying unpressurized fluid to an external source, such as a lift truck. Refers to a pair of connections that can be put back on the track. Similarly, "output port" as used herein and in the claims when referring to a hydraulic control circuit is a pair of connections that during operation of the control circuit and Refers to a pair of connections that, when both are connected to a hydraulic actuator, can deliver fluid pressurized by the input port of the control circuit to the hydraulic actuator and simultaneously return fluid from the hydraulic actuator to the control circuit. . Also, as used herein and in the claims, the terms "hydraulically coupled," "hydraulically coupled," and similar when referring to two or more hydraulic actuators. The term means that the fluid pressure on the delivery side of the first actuator is in fluid communication with the input side of the second actuator, i.e. the hydraulically coupled actuators are connected in series. Further, as used herein and in the claims, the phrases "not hydraulically coupled", "not hydraulically coupled" and similar terms used in reference to two hydraulic actuators means that the fluid pressure on the delivery side of either actuator is not connected to the input side of the other actuator. Also, as used herein, the term "coordinated" when used in reference to two or more hydraulic actuators, hydraulic cylinders, clamps, etc. means that movement of such elements must occur together. while the term "uncoordinated" means that movement of one hydraulic actuator, hydraulic cylinder, clamp, etc. can occur independently of other such elements. . For the purposes of this disclosure, the specification will specifically refer to hydraulic cylinders, but those skilled in the art will appreciate that the expansion, contraction, rotation, or otherwise It will be appreciated that any fluid powered actuator whose movement causes the connected device to move can be used in the disclosed systems and methods.

[0029] As previously mentioned, materials handling vehicles that grip and move loads typically alternate between different modes of operation. As an example, a paper roll clamp or carton clamp would not only use a hydraulic actuator to force the clamp arm to apply a force against the load to positively lift the load, but would also force it to come together to initially contact the load. The clamp arms will be positioned by either moving toward or away to release the load. In such applications, efficiency is improved if the clamp arm is positioned at high speed and low force, but low speed and high force are desired so as not to damage the load while clamping it. As another example, some material handling equipment allows the gripped load to be rotated about an axis, so that the clamps are first rotated to align with the load and then the load is gripped. Requires rotation after Again, for efficient operation, it rotates at high speed and low torque when the load is not gripped, but to avoid damaging the load or imparting undue inertia to the vehicle, the load is gripped. It may be desirable to rotate at low speed and high torque when the As yet another example, sideshift forks often must move independently to provide the desired spacing between the forks, but again cooperate when sideshifting a load held on the forks. to move.

[0030] In each of these illustrative examples, the novel systems and methods disclosed by the present application advantageously allow a material handling vehicle, attachment, etc., to hydraulically operate an actuator during one mode of operation. and allows its hydraulic coupling to be released during another mode of operation. For example, referring to the clamp attachment described in the previous paragraph, when coordinating the movement of two clamps to or from a load, simultaneous actuation of the hydraulic cylinders or other actuators that move the clamps can be achieved at high speeds. It can be carried out in motion, but that high speed motion risks damaging the load after contact. This risk can be reduced by actuating the hydraulic cylinders in series, but this reduces the effective cylinder area used to generate the clamping force, making it less efficient for the clamp to grip the load. can decline. Accordingly, one embodiment of the disclosed system and method provides for the clamp to be positioned during clamp positioning, i.e., when the clamp is being moved outwardly, such as to release a load, and/or to clamp a load. is being moved inward toward the load, the effective cylinder area is increased and the clamp grips the load, at which point the hydraulic cylinder is no longer engaged so that clamp force control can be adjusted more efficiently. The cylinder is hydraulically connected until just before Other alternative embodiments of the disclosed systems and methods may, for example, hydraulically couple a cylinder that moves the clamp during the opening movement and bypasses the hydraulic coupling mechanism during the closing movement. Those skilled in the art will appreciate that similar benefits are achieved in other types of material handling applications, such as side shift fork attachments, rotor clamps, and the like.

[0031] Further, such benefits may preferably be achieved without the use of flow dividers. As previously mentioned, existing material handling equipment that engages and moves loads typically uses flow diverters to move clamps, forks, or other such members toward and away from each other. Designed to coordinate movements. Each such clamp, fork, etc. is typically driven by a respective fluid power actuator, e.g., a hydraulic cylinder, and a flow divider directs pressurized flow to each of the hydraulic actuators that move the respective clamp. used to divide equally. The flow divider therefore ensures that the opposing clamps move cooperatively toward or away from each other under essentially the same pressure, but which then provides a low pressure when the clamps first contact the load. The required initial pressure limits the speed at which the clamp moves. However, the disclosed systems and methods coordinate the movement of opposing clamps to and from each other without passing fluid through a flow divider by hydraulically coupling the fluid-powered actuators that move the clamps. can be used to

[0032] FIG. 1 includes a hydraulic control circuit 12 that operates hydraulic actuators 20 and 22 using pressurized fluid supplied, for example, from a lift truck or other industrial equipment having a pump or motor 14 and a reservoir 16. An exemplary system 10 is shown. Preferably, the hydraulic circuit 12 includes input ports having connections 19a and 19b, thus allowing fluid connection to a lift truck or other industrial equipment, so that fluid under pressure passes through the input connections 19a, 19b. while the depressurized fluid is returned to the lift truck via the other of the input connections 19a, 19b. Those skilled in the art will appreciate that during operation of the control circuit 12, each of the connections 19a and 19b are responsive to the direction in which fluid is flowing through the circuit, e.g., whether the cylinders 20, 22 are retracted or extended. will alternately receive pressurized fluid and discharge unpressurized fluid.

[0033] The hydraulic circuit 12 preferably includes a first output port having connections 21a, 21b and a second output port having connections 23a, 23b. Each output port is selectively connectable to a respective hydraulic actuator, such as one of cylinders 20, 22, so that the actuator can select which connection of the respective output port to pressurize. in a desired direction or other mode, while thereby allowing fluid expelled from the actuator to return to circuit 12 through other connections of the output port. For example, as shown in FIG. 1, when the connection portion 21a is connected to the rod side of the cylinder 20 and the connection portion 21b is connected to the head side of the cylinder 20, when the output connection portion 21a is pressurized, Fluid enters the rod side of the cylinder 20, then it retreats, and the fluid is discharged from the head side of the cylinder 20 and returns into the circuit 12 through the connection 21b. Alternatively, when output connection 21b is pressurized, fluid will flow to the head side of cylinder 20, which will expand to allow fluid to flow from cylinder 20 back into circuit 21 through connection 21a.

[0034] The hydraulic circuit 12 also determines whether the first output port 21a, 21b and the second output port 23a, 23b are actuated in series, as will be described in detail later herein. , preferably includes a selector such as the sequence valve 28 of FIG. One skilled in the art will recognize that the particular device or devices used as a selector may vary based on the type(s) of hydraulic device(s) being controlled by the circuit, but broadly the selector alternates whether the control circuit 12 interconnects the output ports so that fluid returned to the control circuit 12 from one hydraulic actuator is used to pressurize the port connection of another hydraulic actuator. It will be appreciated that any device or arrangement of devices configured within the hydraulic circuit 12 may be selected for. In some embodiments, the selector is configured such that the connected hydraulic actuator is connected in series with the input port of control circuit 12 or the connected hydraulic actuator is connected in parallel with the input port of control circuit 12, as described below. can be alternately selected to be connected to In other embodiments, the selector is such that the connected hydraulic actuators are connected in series with the input port of the control circuit 12, or one hydraulic actuator is pressurized by the input port of the control circuit and directed toward the input port. While expelling fluid, another hydraulic actuator may choose not to be pressurized by the input port and expel fluid toward the input port. Regardless of such variations, by selectively determining whether the hydraulic actuators are coupled in series, the control circuit 12 can be used in a variety of different hydraulically actuated devices, such as lift truck attachments, to can work more efficiently.

[0035] For example, the embodiment of Figure 1 shows a circuit 12 used to supply pressurized fluid to a pair of hydraulic cylinders 20 and 22 typical of a carton or roll clamp attachment, where Retraction of the rods of cylinders 20 and 22 brings the clamps together and extension of the rods of cylinders 20 and 22 moves the clamps apart. The open or closed movement of cylinders 20 and 22 is manually selectable by directional control valve 18 which, when moved left from the neutral position shown in FIG. When moved to the right from the neutral position shown in FIG. First, the clamp is opened away from the load by supplying pressurized fluid to port 19b of control circuit 12 and returning non-pressurized fluid to tank 16 through port 19a of control circuit 12. FIG. Typically, a pump or motor 14, a reservoir or tank 16, and a directional control valve 18 each supply pressurized fluid to the lift truck attachment via fluid lines that extend over the mast of the lift truck to the attachment. The attachment typically includes hydraulic cylinders 20 and 22 and their associated clamps and control circuit 12 used to actuate the attachment.

[0036] When the lift truck operator first moves the selector valve 18 to pressurize the port 19a of the control circuit 12, pressurized fluid is applied to maintain the load gripping force (pressure) in the primary cylinder 20. It will flow through the pilot operated check valve 24 used and through the output port connection 21a to the rod side of the primary cylinder 20, which will contract accordingly to pull its associated clamp inwards. , for example, toward the load. The fluid will then be discharged from the head side of the primary cylinder 20 through the output port connection 21 b of the control circuit 12 . A fluid sequence valve 28 (whose operation as the aforementioned selector will be described later) prevents fluid from returning to tank 16 through port 19b so that fluid discharged from primary cylinder 20 is directed through pilot operated check valve 26 through the output port connection 23a of the control circuit 12 and into the rod side of the secondary cylinder 22, which also contracts and pushes its associated clamp inward, e.g., toward the load. to move. Fluid is then discharged from the head side of secondary cylinder 22 into output port connection 23b and returns to tank 16 via port 19b of control circuit 12 . Thus, when the sequence valve 28 is maintained in the closed position as shown in FIG. 1, the cylinders 20 and 22 are connected in series and move inward toward the load before the clamp contacts the load. Movement of the clamps is coordinated during flow, resulting in improved clamping speeds without the use of shunts.

[0037] When the clamp contacts a load, pressure increases in line 30 to which sequence valve 28 is connected. when the pressure reaches the threshold setting of the sequence valve 28 indicating that the load is clamped, that valve opens to allow fluid to flow from the head side of the primary cylinder 20 into the non-pressurized tank 16; Therefore, the fluid is prevented from flowing into the rod side of the cylinder 22 . As the load is further clamped by primary cylinder 20, secondary cylinder 22 is locked in place and port 3 of pilot valve 26 is depressurized and port 1 is pressurized, thus allowing fluid to flow into secondary cylinder 22. The rod side cannot be entered to retract the rod, while the secondary cylinder 22 likewise cannot extend its rod because the pilot valve 26 blocks outflow from the rod side of the cylinder 22 . Thus, the sequence valve 28 sets the mode of operation of the primary and secondary cylinders 20, 22 during the closing movement to a first mode in which the primary and secondary cylinders 20, 22 are hydraulically coupled over a first range of motion of the primary cylinders. and a second mode of operation in which the primary and secondary cylinders 20, 22 are not hydraulically coupled over a second range of motion of the primary cylinders. Although FIG. 1 shows that the sequence valve 28 is actuated by an increase in pressure when the load is clamped, those skilled in the art will recognize that the clamp arm or cylinder may be extended or retracted beyond a certain point. to actuate sequence valves, such as by using valves that are actuated when the valve is actuated or by using sensor actuated solenoid valves, or to move cylinders 20 and 22 from the first hydraulic coupling mode to the second non-hydraulic mode. It will be appreciated that other means may be employed to switch to form-connection mode. In this way, for example, the primary and secondary cylinders may switch out of hydraulic engagement when the clamp reaches a location proximate to the load but has not yet contacted the load.

[0038] When the lift truck operator moves the selector valve 18 to the right relative to the position shown in FIG. to extend the rod. Port 3 of pilot-operated check valve 24 and port 3 of pilot-operated check valve 26 are each connected to a currently pressurized line 32 feeding secondary cylinder 22 so that check valve 24 and check valve 26 are Each of the stop valves 26 is now open and the pressure in line 32 applied to the spring force of sequence valve 28 will cause sequence valve 28 to close. Thus, as the secondary cylinder 22 extends, fluid is discharged from its rod side through the pilot operated check valve 26 and into the head side of the primary cylinder 20, causing the primary cylinder 20 to extend in unison with the secondary cylinder 22. , thereby moving the clamps away from each other in unison. As the primary cylinder 20 extends, fluid is discharged from its rod side through a pilot operated check valve 24 and back to tank 16 .

[0039] In this manner, the hydraulic control circuit 12 sets the operating modes of the primary and secondary cylinders 20, 22 to a clamp opening movement in which the cylinders 20 and 22 are hydraulically coupled and a clamping movement in which the cylinders 20 and 22 are closed. clamp closing movement that is not hydraulically coupled over at least a portion of the . Those skilled in the art will recognize that alternative embodiments may include hydraulic control circuits in which cylinders 20 and 22 are coupled during the entire opening movement and not coupled during the entire closing movement.

[0040] FIG. 2 generally illustrates how pressure and force are transmitted through primary and secondary cylinders 20 and 22 and their associated clamps due to operation of hydraulic control circuit 12, as previously described. clearly shown. Preferably, the rod-side area _A1 of the primary cylinder 20 is designed to provide the required load-holding force at the expected input oil pressure. For example, if the required cylinder force is 4,180 lbs at 2000 psi input pressure, the required rod side area A ₁ is 2.09 in ² . This area can be achieved by using a 1.10 inch (28 mm) rod diameter and a 1.97 inch (50 mm) bore. The rod-side area _A3 of the secondary cylinder 22 is preferably designed to have an area equal or approximately equal to the head-side area _A2 of the primary cylinder. This matched area allows equal travel for each cylinder, ie, one inch of rod travel for primary cylinder 20 will result in one inch of travel for the rod of primary cylinder 22 . For example, using a primary cylinder 20 having dimensions of 1.10 inch (28 mm) rod diameter and 1.97 inch (50 mm bore diameter), the rod side area _A1 of the primary cylinder is 2.09 in ² , The head side area _A2 is 3.04 in ² . Therefore, the secondary cylinder 22 preferably has an equal lock area _A3 of 3.04 in ² . Such cylinders may be constructed with a rod diameter of 1.26 inches (32 mm) and a bore diameter of 2.34 inches (59.4 mm).

[0041] As can be determined _{from FIG .} The clamping force is doubled. Specifically, F _P and F _S must be equal because both forces act on the same stationary load, regardless of whether the cylinders are hydraulically coupled or not. , F _P equals P ₁ A ₁ -P ₂ A ₂ , F _S simply equals P ₃ A ₃ , and P ₄ equals 0 because it is connected to tank pressure. Further, given that _A2 is designed to equal _A3 , and that _P2 must equal _P3 due _to the hydraulic linkage, _{P2A2 equals P3A3} . There must be. Given these relationships,
F _P =F _S =P ₃ A ₃ =P ₂ A ₂
therefore,
F _P =P ₁ A ₁ -P ₂ A ₂ =P ₁ A ₁ -F _P.
By rearranging the formula
F _P =(1/2)P ₁ A ₁ .

[0042] However, when the actuation of the sequence valve 28 overrides the hydraulic linkage, _P4 and _P2 are both connected to tank and therefore zero,
P ₃ A ₃ = F _S = F _P = P ₁ A ₁
Therefore, when cylinders 20 and 22 are not hydraulically connected, _FP is double the value when cylinders 20 and 22 are hydraulically connected. Thus, by hydraulically coupling the cylinders during positioning, the movement of the clamp arm can be coordinated without the use of flow dividers (which would adversely limit inlet flow) so that the load is initially clamped. It can be done at high speeds while minimizing the forces on the load when it is loaded. When clamping occurs, the hydraulic linkage of cylinders 20 and 22 may be bypassed, allowing clamping forces to be applied more effectively.

[0043] Figure 3 illustrates an alternative embodiment in which the control circuit 12 of Figure 1 may be used to control hydraulic actuators or cylinders 27, 29 typically found in pivot arm clamps, where Extension of the cylinders 27,29 provides grip on the load and retraction of the cylinders 27,29 releases the load. Thus, unlike the embodiment of FIG. 1, the cylinders 27, 29 are connected to a control circuit so that, during the clamp closing movement, pressurized fluid is supplied to the head side of the primary cylinder 27 and the cylinder When discharged from the rod side of the cylinder 27 and hydraulically connected, the fluid discharged from the rod side of the cylinder 27 with the rod side of the cylinder 29 connected to the connection 23b and thus to 19b will flow into the head of the cylinder 29. supplied to the side. In this embodiment, the head side area of cylinder 29 is preferably equal to the rod side area of cylinder 27 to ensure equal movement of cylinders 27, 29 when hydraulically coupled.

[0044] Referring to Figures 1 and 3, as previously described, the sequence valve 28 opens, thereby bypassing the hydraulic linkage between the primary hydraulic cylinder 20 and the secondary hydraulic cylinder 22 to load the load. When clamping further, in some embodiments, secondary cylinder 22 may remain stationary while primary cylinder 20 applies additional clamping force. Due to this asynchronous behavior of the primary and secondary cylinders, if continued use of the hydraulic circuit 10 causes one of the cylinders 20, 22 to reach the end of their stroke before the other cylinder reaches , which can inhibit the ability of either the system to properly clamp loads or retract the clamps to their fully retracted position.

[0045] Thus, in some embodiments, the hydraulic circuit 10 preferably allows fluid to bypass the hydraulic linkage when one cylinder reaches the end of its stroke before the other. may include an optional resynchronization valve 25 that allows When the resynchronization valve 25 retracts the rods of the cylinders 20, 22, the pressure difference between the rod side of the primary cylinder 20 and the rod side of the secondary cylinder 22 reaches a threshold amount set by the spring setting of the resynchronization valve 25. is exceeded, oil is allowed to flow directly from the pressurized line 30 to the rod side of the secondary cylinder 22 . For example, if the rod of primary cylinder 20 were fully retracted while pressure was being provided to clamp port 19a, pressure would rise in line 30 until resynchronization valve 25 opened, pressurizing the fluid. Allowing flow from line 30 directly into the rod side of the secondary cylinder 22, the secondary cylinder 22 can continue to move to the fully retracted position to resynchronize the cylinders 20,22. Conversely, if the secondary cylinder 22 reaches the end of its stroke before the primary cylinder 20, the pressure increases in line 30 until the pressure setpoint of the sequencing valve 28 is reached and both cylinders are fully synchronized. Oil can be discharged from the head side of the primary cylinder 20 up to .

[0046] The spring setting of the resynchronization valve 25 ensures that the sequence valve 28 opens before the resynchronization valve 25 opens, and otherwise when the cylinders 20, 22 are hydraulically coupled. It must be high enough to both prevent the valve 25 from opening while positioned towards the load prior to clamping the load. In that case, since the head side of the primary cylinder 20 is connected to the rod side of the secondary cylinder 22, the spring pressure setting of the valve 25 is less than the maximum expected pressure drop across the primary cylinder 20 during positioning. It should be set to a high value, which in turn relates to the maximum intended positioning speed of the valve circuit 10 . When the primary cylinder 20 and secondary cylinder 22 are clamping on a load, both cylinders 20 and 22 are hydraulically coupled or not, and as long as the primary cylinder is not at the end of its stroke. The pressure on the rod side of the cylinder will be the same, so any spring setting of valve 25 that meets the above conditions will always keep the valve closed. In a preferred embodiment, the resynchronization valve 25 spring setting may preferably be set approximately 150 psi below the system pressure setting.

[0047] The resynchronization valve 25, which is configured to resynchronize the cylinders 20 and 22 by moving the rods of both cylinders to the fully retracted position, instead, for example, directs the input of the resynchronization valve 25 to line 30. Moving the rods of both cylinders to the fully extended position by connecting line 32 instead and connecting the output of resynchronization valve 25 to the head side of primary cylinder 20 instead of the rod side of secondary cylinder 22. It will be appreciated by those skilled in the art that the cylinders 20 and 22 may be configured to resynchronize by.

[0048] As an alternative to using a resynchronization valve 25, one or both of the primary and secondary cylinders 20, 22 are designed to allow oil to flow from the rod side of the cylinder to the head side when the cylinder reaches the end of stroke position. may be configured to selectively operate as a valve to enable resynchronization by allowing flow to and vice versa. For example, referring to FIG. 4, either or both primary or secondary cylinders 20 or 22 have a cylinder shell 42 that encloses at least a portion of a sliding cylinder rod 44 that is secured to a threaded bore 48 in a sliding piston 46. synchronizing cylinder 40 having a Piston 46 preferably includes wear bands 50 and piston seals 52 to provide sealed sliding movement of the piston within cylinder shell 42 . Cylinder rod 44 may define a conduit for pressurized oil to flow back and forth between the rod-side area of cylinder 40 (ie area A ₁ or A ₃ in FIG. 2) and the interior of piston 46 . For example, the cylinder rod 44 has a first portion extending axially inwardly from the end of the rod 44 embedded in the piston 46 to a second portion including a plurality of radial passages around the circumference of the cylinder rod 44. may include a conduit 53 having a passageway with a . The piston side of conduit 53 may be selectively sealed by check ball 58 mounted on spring 56 urging check ball 58 toward the first axial portion of conduit 53 . The end of the spring 56 opposite the non-return ball 58 is also rigidly fixed around the flange of the sliding plunger 54 . The flange of plunger 54 prevents oil inside piston 46 from entering the head side area of cylinder 40 (i.e. area A ₂ or A ₄ in FIG. It fits within the seat of retainer 59 so that it is sealed from flowing in the opposite direction when it is on.

[0049] Referring to FIG. 5A, when the cylinder 40 is pressurized from the rod side to retract the rod and is not at the end of stroke position, the pressurized oil will flow radially from the rod side area of the cylinder 40. A portion and then an axial portion of the passageway 52 to push the non-return ball 58 inward and allow the oil to reach the internal cavity of the piston 46 . However, spring 56 forces plunger 54 against the seat of retainer 59 , thus preventing oil from entering the head side area of cylinder 40 . However, as seen in FIG. 5B, when the cylinder 40 has retracted the rod a sufficient distance to reach the end-of-stroke position of the rod, the plunger 54 engages the flange of the plunger 54 and the unseated check. Between the balls 58, the plunger 54 contacts the cylinder head 57 which compresses the spring 56 out of the seat of the retainer 59, allowing oil to flow from the rod side area of the cylinder 40 into the interior of the piston 46 and further head-side area and eventually through porting 55 to the other cylinder 20 or 22 (or tank 16), allowing resynchronization. As shown in FIG. 5C, when the cylinder 40 is pressurized from the head side, at the mid-stroke position, the pressurized oil pushes the plunger 54 out of the seat of the retainer 59 causing oil to flow inside the piston 46. However, the plunger 54 pushes the non-return ball 58 against the spring 56 to seal the conduit 53 so that oil may not flow into the rod side area of the cylinder 40 .

[0050] FIG. 6 shows an alternative synchronization cylinder 60 that can be resynchronized at either the fully retracted end-of-stroke position or the fully extended end-of-stroke position of the rod of the cylinder 60. As shown in FIG. Specifically, the cylinder 60 may comprise a cylinder shell 62 in which a piston 66 is slidably and sealably secured via a seal 74 and one or more wear bands 72 . The end of cylinder rod 64 that slides with piston 66 is rigidly attached within first bore 65 of piston 66, for example by a heat shrink connection. Piston 66 also defines a second bore 67 that houses a spool 68 that substantially conforms to the shape of second bore 67 such that the outer surface of spool 68 and the inner surface of second bore 67 are aligned. A gap is defined between. Both the second bore 67 and the spool 68 have a central region having a diameter/width greater than the opposing peripheral regions of the second bore 67 and the spool 68 respectively, the central region of the spool 68 being the same as the second bore. Second bore 67 and spool 68 are shorter than the length of 67 and have a first extreme end where one peripheral region of spool 68 extends out from an associated peripheral region of second bore 67 and spool 68 The central region of the spool 68 extends back and forth within the central region of the second bore 67 between the second extreme regions of the second bore 67 extending out from its associated peripheral region. are co-molded so that they can slide against each other. In some embodiments, the second bore 67 surrounds one peripheral region of the spool 68 to facilitate forming the second bore 67 shaped to closely surround the spool 68 . , may be formed at one end using a retainer plug 70 secured within the piston 66 by a heat shrink connection.

[0051] Referring to FIG. 7A, when the cylinder 60 is pressurized from the rod side, the spool 68 is forced into the second bore 67 causing oil to enter the gap between the second bore 67 and the rod side of the spool 68. However, as the spool 68 is forced into the head side peripheral region of the second bore 67 and closes off, entry of oil into the head side of the cylinder 60 is blocked. However, when the retracting rod reaches the end of stroke position shown in FIG. Or 52 , or cylinder head 76 pushes spool 67 inwards so that it can escape to tank 16 .

[0052] As can be seen in Figures 7C and 7D, this action is reversed when the cylinder 60 is pressurized from the head side, and during the mid-stroke position, the spool 68 allows oil to spool from the head side of the cylinder 60. It slides to block oil from entering the rod side area of cylinder 60 while allowing it to flow into the area between 68 and second bore 67 . When the extending rod 64 reaches its end-of-stroke position, pressurized oil enters the rod-side peripheral region of the second bore 67 and passes through porting 82 to another cylinder 50 or 52 or tank 16 . Cylinder retainer 80 pushes spool 67 inward so that it can escape into the air.

[0053] The embodiments shown in FIGS. 1 and 3 provide a first mode in which the hydraulic actuators are connected in series for coordinated movement and a first mode in which movement of the hydraulic actuators is uncoordinated, e.g. A control circuit 12 intended to alternately actuate the hydraulic actuators in a second mode, locked in one position while the other is moved, is used. Figure 8 shows an alternative control circuit 84 for a rotor dual drive motor, where the control circuit 84 has a selector 88a that can alternately drive the two hydraulic motors 86a, 86b in series or in parallel. , 88b, the motion of the motors being coordinated in both instances. Specifically, the control circuit 84 includes, for example, a clamp selector valve 18 intended to alternately clamp and release a load as previously described, and a clamp by moving the valve to the left or right of the center position. a rotor selector valve 83 used to selectively rotate about the axis in a desired direction or to keep the angular orientation of the clamp fixed by moving the valve 83 to a centered position; It may include input ports 19a, 19b that are selectively connectable to pump 14 and reservoir 16 on lift trucks that have both.

[0054] The control circuit 84 preferably includes a first output port having connections 21a, 21b and a second output port having connections 23a, 23b each selectively connectable to respective hydraulic motors 86a, 86b. and an output port of Thus, when connected as shown in FIG. 8, the motor 86a is one-stop by pressurizing connection 21a and allowing fluid to drain back into the control circuit 84 from the motor through connection 21b. It can be driven in one direction and can be driven in the opposite direction by pressurizing connection 21b and draining fluid from the motor back into control circuit 84 through connection 21a. Motor 86b can be similarly driven via connections 23a and 32b.

[0055] The control circuit 84 preferably has a selector, shown in this example as comprising first and second solenoid valves 88a, 88b, to control the pressurized fluid received through the input ports 19a, 19b. Motors 86a, 86b may be used in series (e.g., useful for rotating the clamp at high speed when a load is not gripped) or in parallel (e.g., rotating the clamp at low speed but high torque when a load is gripped). It is used to determine whether to drive (useful for rotating). Specifically, when solenoids 88a and 88b are each in a de-energized state, pressurized fluid is sent from pump 14 to connections 21a and 23a when input connection 19a is pressurized, Pressurized fluid present in either of the input port connections drives motors 86a, 86b in parallel by directing pressurized fluid from pump 14 to connections 21b and 23b when 19b is pressurized. It will happen. In both situations, each of the non-pressurized output connections to motors 86a and 86b are independently connected to reservoir 16, allowing the motors to expel fluid directly towards reservoir 16.

[0056] However, when both solenoids are energized, the connection 23b to the control circuit output port to the motor 86b is connected to the control circuit output port to the motor 86a so as to rotate the motors 86a, 86b in series. It is connected to the connection portion 21a. In this configuration, when connection 19a is pressurized by pump 14, pressurized fluid flows from connection 23a into motor 86b, which forces fluid back into connection 23b and through connection 21a. It is discharged to the motor 86a. Fluid from motor 86a returns into control circuit 84 through connection 21b and flows from control circuit 84 to tank 16 through input connection 19b. The pressurizing connection 19b, while both solenoids are energized, conversely maintains the series connection of the motors 86a, 86b, but otherwise resists the rotation that occurs when the connection 19a is energized. Rotate them in the direction of Although FIG. 8 shows two solenoids 88a, 88b as selectors for alternating the control circuit 84 between parallel and series configurations, other embodiments may include different selectors, e.g. Those skilled in the art will appreciate that pilot control valves with variable configuration may also be used.

[0057] FIG. 9 illustrates yet another embodiment of a control circuit that coordinates movement of hydraulic actuators that selectively alternates between one of a series configuration and a parallel configuration. Specifically, the hydraulic control circuit is used to move the clamps toward and away from the load using, for example, pressurized fluid supplied to connections 19a, 19b of the input ports of the hydraulic control circuit. The movements of the hydraulic cylinders 92 and 94 to be moved respectively are coordinated. As can be seen in FIG. 9, the control circuit 90 includes all the elements of the control circuit 12 shown in FIGS. Also included is a pressure actuated valve 98 .

[0058] When pressurized fluid is supplied to the input port connection 19b of the control circuit 90, the control circuit 90 operates similarly to the control circuit 12 of FIG. Connected in series to extend the rod, fluid flows from the control circuit 90 into the head side of the cylinder 94, from the rod side of the cylinder 94 back into the control circuit 90, and from the control circuit 90 into the head side of the cylinder 92. It flows in, exits the rod side of the cylinder 92, returns into the control circuit, and then delivers fluid into the tank 16. However, when pressurized fluid is supplied to input port connection 19 a of control circuit 90 , the pressurized fluid is distributed by flow divider 96 in a manner determined by the position of pressure actuated valve 98 . Specifically, the flow divider 96 diverts the fluid supplied from the connection 19 a through a first path or line toward the connection 21 a connected to the rod side of the cylinder 92 and a second path or line toward the pressure operated valve 98 . route or line. Pressure actuated valve 98 is spring biased to a position where it recombines the flow split by flow divider 96 so that the entire flow pressurizes port 21a which again causes the control circuit to switch to control circuit 12 of FIG. It behaves in exactly the same way, ie cylinders 92 and 94 are connected in series to position the clamps in a coordinated closing movement towards the load. When the clamp contacts a load, pressure at port 19a causes pressure actuated valve 98 to divert fluid from the second path through one-way check valve 99 to the rod side of cylinder 94, as just described. Pressure builds up to a moving level, whereby pressure provided through input port connection 19a of control circuit 90 actuates cylinders 92 and 94 in parallel when a load is clamped.

[0059] Coordinated operation of cylinders 92 and 94, when hydraulically coupled to each other in series, requires that the head side area of cylinder 92 coincides with the rod side area of cylinder 94, so that the The rod side area can typically be smaller than the rod side area of cylinder 94 . Therefore, to equalize the forces exerted by cylinders 92 and 94 and to coordinate the movement of cylinders 92 and 94 when cylinders 92 and 94 are not hydraulically coupled and controlled in parallel, flow dividers 96 preferably divides the flow from input connection 19a unevenly in an amount proportional to the rod side area of the cylinder driven by each divided fluid flow. Thus, in the illustrative example of FIG. 9 where cylinder 92 has a rod side area of 2.09 in ² and cylinder 94 has a rod side area of 3.04 in ² for a total area of 5.13 in ² , the flow diverter 96 directs 41% of the flow into the cylinder 92 (i.e. 2.09 in ² /5.13 in ² ) and 59% of the flow into the cylinder 94 (i.e. , 3.04 in ² /5.13 in ² ). This ensures that each flow into cylinders 92 and 94 causes the same linear retraction of the rod in each respective cylinder.

[0060] One of the advantages of control circuit 90 compared to control circuit 12 is that control circuit 90, when used to actuate clamps on a load, reduces the need for resynchronization valve 25 or FIGS. The use of valves in hydraulic cylinders, such as shown in , can be reduced or even eliminated. Cylinders 92 and 94 move in concert both during clamp positioning and while the load is clamped so that each cylinder 90 and 92 reaches the end of its stroke before the other cylinder does. Much less likely.

[0061] FIG. 10 shows a control circuit 100, which is an alternative embodiment of the control circuit shown in FIG. Control circuit 100 may optionally include a bi-directional relief valve 102 for limiting pressure during opening and closing of 27 and 29 to protect against structural damage to itself or surrounding objects. Additionally, in the control circuit of FIG. Possible pilot pressure may be exceeded. To accommodate this possibility, control circuit 100 replaces pilot-operated check valve 24 shown in FIG. During closing, pressure through port 19a causes fluid to bypass counterbalance valve 104 via check valve 105, which then pressurizes the rod side of cylinder 27. During the closing operation, pressure through port 19b opens pilot operated control valve 26 and also opens counterbalance valve 104, thereby allowing fluid to exit through port 19a.

[0062] FIG. 10 also shows relief valves 106a and 106b that together allow resynchronization of cylinders 27 and 29. FIG. Specifically, during the opening operation, if cylinder 29 reaches the end of its stroke before cylinder 27 , relief valve 106 a will open, allowing fluid to enter the piston side of cylinder 27 . Conversely, if cylinder 27 reaches the end of its stroke before cylinder 29, relief valve 106b will open, allowing fluid to be delivered from the rod side of cylinder 29.

[0063] Referring to FIGS. 11A and 11B, multi-load handlers (MLHs) are arranged laterally relative to each other to allow the lift truck to alternately engage one or two pallet loads. A type of lift truck attachment that includes four slidable forks. In a first configuration shown in FIG. 11A, the four forks may be split into two pairs of adjacent forks such that each pair can slide into respective openings of a single pallet. . A second configuration, shown in FIG. 11B, arranges the forks in two spaced pairs of forks, each pair arranged to engage and move a respective pallet.

[0064] Thus, the MLH has two different actions for laterally positioning the forks. The first action is to position the forks between "single" pallet mode and "double" pallet mode, as shown in FIGS. 11A and 11B. This movement requires little actuator force and is preferably fast with precise synchronization between the two different pairs of forks. A second operation performed in "double" mode positions each set of forks laterally relative to each other, as shown in FIGS. 12A and 12B. This is commonly referred to as "snapping" when closing and "unfolding" when opening. This operation requires high actuator forces and low speeds, and is also preferably accompanied by precise synchronization between the left and right fork sets.

[0065] Because the MLH mode of operation operates between a first mode characterized by high speed and low force and a second mode characterized by low speed and high force, as previously described, the hybrid clamp It is desirable to employ a force control circuit. However, unlike the previously described system, where high force motion occurs when clamping around a single load, and therefore synchronization of movement between hydraulic cylinders during clamping occurs through force transmission through the load. Unlike, in the MLH attachment, each cylinder is moving an independent load, so the control circuit must also provide synchronization between the cylinders. This is especially true when different bore cylinders are used, as the same pressure can generate different forces in the cylinder, resulting in different travel speeds.

[0066] Figure 13 shows a control circuit 110 that receives and delivers fluid from inlet ports 114a, 114b and through first outlet ports 116a, 116b and second output ports 118a, 118b. . Although FIG. 13 shows first outlet ports 116a, 116b connected to small bore cylinder 120 and second outlet ports 118a, 118b connected to large bore cylinder 122, those skilled in the art will recognize this. It will be appreciated that the configuration may be reversed.

[0067] During high speed, low force operation of the MLH attachment, such as when the forks are positioned between double pallet mode and single pallet mode, the cylinder can be actuated in either the closing or opening movement. In the open movement, selector valve 112 may be moved to pressurize connection 114a, thereby supplying flow diverter 124 with fluid. One side of the flow divider is directly connected to the connection 116a feeding the rod side of the small bore cylinder 120, while the other side of the flow divider is connected to a pilot operated directional control valve 126 with spring bias. , the spring bias sets the pilot operated directional control valve 126 to the default position at low force operation which also supplies fluid to the rod side connection 116a of the small bore cylinder 120, i.e. at low force operation All fluid in the shunt exits connection 116a into the rod side of cylinder 120, and cylinder 120 contracts to discharge fluid back to control circuit 110 through connection 116b. The pressurized fluid opens the pilot operated control valve 132 so that it again exits the control circuit into the rod side of the large bore cylinder 122 which contracts to force the fluid through connection 118b. It dispenses into the control circuit and then out of the control circuit 110 through the inlet connection 114a. In this manner, during high speed, low force operation, cylinders 120 and 122 are coupled so that the output of one cylinder supplies fluid to the input of the other cylinder.

[0068] However, during high force slow action closing movements, such as when loaded pallets are snapped toward each other, this coupling mechanism is interrupted and the control circuit is operated in a non-coupling mode. Specifically, selector valve 112 is set to pressurize connection 114a again, but when the loaded pallets are moved by cylinders 120, 122, sequence valve 134 opens, thus pilot-operated directional control valve Pressurize the pilot line to port 1 of 126. Accordingly, valve 126 moves to a position in which a portion of the flow through flow divider 124 is directed to output connection 118a instead of being directed to output connection 116a, so that each cylinder 120, . 122 are driven independently. At the same time, the pilot line to port 1 of sequence valve 136 is also pressurized by actuation of valve 134, thereby allowing fluid to exit cylinder 120 into connection 116b and out of connection 114b. In some embodiments, the setting of sequence valve 114 may be approximately 2000 psi.

[0069] The flow splitter 124 splits and recombines the flow in a ratio corresponding to the size difference between the cylinders 120 and 122 . For example, a primary (small) actuator with a bore size of 40mm and a rod size of 25mm has a rod side working area of 766mm^2 and a corresponding secondary (large) actuator has a bore size of 50mm and a rod size of 30mm. The rod size has a rod side working area of 1257 mm^2. Therefore, the flow divider preferably splits 38% of the flow to the primary (small) actuator and 62% of the flow to the secondary (large) actuator according to the following equations to achieve synchronized movement: should:
Primary Actuator = Volume 1 = A1 * Stroke Secondary Actuator - Volume 3 - A3 * Total Stroke Volume = Volume 1 + Volume 3

Flow divider = specification port 2 distribution = volume 1 / total volume = 766 * stroke / (766 + 1257) * stroke = 38%
Port 4 distribution = volume 3 / total volume = 1257 * stroke / (766 + 1257) * stroke = 62%

[0070] Given that each cylinder is moving an independent load, as described above, and given that cylinders 120 and 122 have different bore sizes, control circuit 110 determines that cylinders 120 and 122 It preferably includes a synchronization mechanism to ensure that it moves at speed. Accordingly, control circuit 110 preferably includes an increased pressure relief valve 130 positioned between directional control valve 126 and output port 118a. The pressure boost relief valve 130 provides a pressure drop due to the action of the fluid against the spring of the valve 130 and the spring resistance is set so that the force exerted by the large bore cylinder is the same as the small bore cylinder. This causes the two cylinders 120, 122 to move at the same speed. For example, assuming cylinder 120 has a 40 mm bore with 25 mm rods, cylinder 122 has a 50 mm bore and 30 mm rods), and an equal load is supported on both pallets, the small bore A load that requires 2200 psi at rpm may require only 1400 psi to achieve the same force. Therefore, valve 130 is set at 800 psi to compensate for the difference, thereby allowing the flow divider to operate more accurately. In some embodiments, the booster relief valve may have variable settings to accommodate different loads, different cylinders, and/or different configurations. Preferably, the spring force of valve 130 is set low enough so that valve 130 will open against the spring whenever the system switches to uncoupled mode, i.e. sequence valve 134 actuates valve 126. It has a higher spring resistance than the pressure relief valve 130 so that any pressure in the port 114a that is large enough to actuate the valve 130 will be large enough.

[0071] During the opening movement, the selector valve may pressurize connection 114b, which provides all pressurized fluid to port 118b, causing the control circuit to operate in coupled mode. Because ports 114b are pressurized, the pilot lines to port 3 of pilot operated control valve 132 open each, thereby allowing fluid from cylinder 122 to flow into cylinder 120 and fluid from cylinder 120 to flow into cylinder 120. can flow through shunt 124 and back to port 114a.

[0072] In some embodiments, the control circuit 110 may include a crossover relief valve 128 across the output of the shunt 124. When in coupled mode, the crossover relief valve has no effect on control circuit 110, but when in uncoupled mode, the crossover relief will open when the pressure differential exceeds the setting of valve 124. FIG. This allows flow to bypass the flow divider and resynchronize when the forks are in the fully closed position.

[0073] In some embodiments, the control circuit 110 vents any trapped pressure in the pilot portion of the circuit and normalizes the pressure between the pilot port of the sequence valve 136 and the directional control valve 126. may include a pilot discharge orifice 138 to maintain both normal conditions. When the inlet pressure exceeds the setting of sequence valve 134 , that valve will open, allowing flow/pressure to steer sequence valve 136 and directional control valve 126 . The orifice is sized such that it cannot exhaust pressure faster than the sequence valve 134 can supply.

[0074] The invention is not limited to the particular embodiments described, but encompasses the doctrine of equivalents or any other doctrine that extends the enforceable scope of the claims beyond their literal scope. It will be understood that modifications may be made therein without departing from the scope of the invention defined in the appended claims, as construed in accordance with general principles of law. Unless the context dictates otherwise, any reference to the number of instances of an element in a claim, whether a reference to one instance or to more than one instance, requires at least the stated number of instances of the element. However, it is not intended to exclude from the scope of a claim any structure or method having more instances of that element than recited. The word "comprising" or its derivatives, when used in the claims, is used in its non-exclusive sense, not intended to exclude the presence of other elements or steps in the claimed structure or method. .

Claims (20)

an input port configured to receive pressurized fluid from the pump and return non-pressurized fluid to the reservoir;
a first output port and a second output port, wherein the first output port is connectable to a first hydraulic actuator and the second output port is connectable to a second hydraulic actuator; , each of said first output port and said second output port simultaneously delivering pressurized fluid to a hydraulic actuator connected to each of said first output port and said second output port; a first output port and a second output port configured to receive fluid delivered from
a selector operable to selectively use fluid delivered from said first hydraulic actuator to pressurize fluid delivered into said second hydraulic actuator, said hydraulic control circuit comprising:
Fluid supplied to the first hydraulic actuator is supplied to the second hydraulic actuator when fluid is not delivered from the first hydraulic actuator to pressurize fluid delivered into the second hydraulic actuator. A hydraulic control circuit that is at a different pressure than the supplied fluid. The selector selectively used fluid delivered from the first hydraulic actuator to be delivered into the second hydraulic actuator based on the amount of fluid pressure supplied to the hydraulic control circuit. 2. The hydraulic control circuit of claim 1, which automatically pressurizes the fluid. the selector selectively using fluid delivered from the first hydraulic actuator to automatically pressurize fluid delivered into the second hydraulic actuator to thereby provide an input port connection; 2. The hydraulic control circuit of claim 1, wherein receives pressurized fluid. The selector selectively uses fluid delivered from the first hydraulic actuator to automatically add fluid delivered into the second hydraulic actuator when the clamp engages a load. 2. The hydraulic control circuit of claim 1, wherein the hydraulic control circuit presses. the selector selectively uses fluid delivered from the first hydraulic actuator to automatically pressurize fluid delivered into the second hydraulic actuator during an opening movement of the hydraulic actuator; 2. The hydraulic control circuit of claim 1. The selector selectively uses fluid delivered from the first hydraulic actuator to move the second hydraulic actuator during a portion of a closing movement of the hydraulic actuator and during an opening movement of the hydraulic actuator. 2. The hydraulic control circuit of claim 1, which automatically pressurizes fluid delivered therein. 2. The hydraulic control of claim 1, wherein said selector alternates said control circuit between a first mode in which said hydraulic actuators are connected in series and a second mode in which said hydraulic actuators are not connected in series. circuit. 8. The hydraulic control circuit of claim 7, wherein in said second mode said hydraulic actuators are driven in parallel. 9. The hydraulic control circuit of claim 8, including a second selector for controlling flow from the shunt. 8. The hydraulic control circuit of claim 7, wherein in said second mode one hydraulic actuator is moved by said control circuit while the other hydraulic actuator is prevented from moving by said control circuit. A hydraulic control circuit configured to receive pressurized fluid from a pump and return non-pressurized fluid to a reservoir, the hydraulic control circuit being adapted to apply pressure to a first hydraulic actuator and a second hydraulic actuator. a selector operable alternately between a first state and a second state when connected, wherein the first hydraulic actuator and the second hydraulic actuator are hydraulically operated in the first state; in the second state, the first hydraulic actuator and the second hydraulic actuator are not hydraulically connected, and the first hydraulic cylinder and the second hydraulic cylinder are hydraulically connected to A hydraulic control circuit that is supplied with fluid at different pressures when uncoupled. 12. The hydraulic control circuit of claim 11, wherein said selector automatically alternates between said first state and said second state based on the amount of fluid pressure supplied to said hydraulic control circuit. 12. The hydraulic control circuit of claim 11, wherein said selector automatically alternates between said first state and said second state based on which connection of an input port receives pressurized fluid. 12. The hydraulic control circuit of claim 11, including a resynchronization valve operable to resynchronize said first hydraulic cylinder with said second hydraulic cylinder. 12. The hydraulic control circuit of claim 11 included in a lift truck attachment having said first hydraulic actuator and said second hydraulic actuator. at least one of the first hydraulic actuator and the second hydraulic actuator operates as a valve that selectively allows passage of fluid between a rod side and a head side of the respective hydraulic actuator; 16. A hydraulic control circuit as claimed in claim 15. 17. The hydraulic control circuit of claim 16, wherein said valve is a resynchronization valve configured to resynchronize said first hydraulic actuator with said second hydraulic actuator. 18. The hydraulic control circuit of claim 17, wherein the valve allows fluid to pass between the rod side and the head side of the respective hydraulic actuator at the end of stroke of closing travel. 19. The hydraulic control circuit of claim 18, wherein said valve allows fluid to pass between said rod side and said head side of said respective hydraulic actuator at the end of a stroke of opening travel. 17. The hydraulic control circuit of claim 16, wherein said valve allows fluid to pass between said rod side and said head side of said respective hydraulic actuator at the end of a stroke of closing travel.

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