Synchronized Hybrid Clamp Force Controller for Lift Truck Attachments

Abstract

The present invention provides an improved hydraulic control circuit that allows for fast, synchronized closing of opposing clamps against a load while preventing damage to the load upon contact by the clamps. According to the present invention, a hydraulic control circuit is provided that is operable to selectively hydraulically couple and bypass a first hydraulic actuator and a second hydraulic actuator.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001]

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

[0002] FIELD OF THE DISCLOSURE

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

[0003] Material handling vehicles, such as lift trucks, are used to pick up and move loads from one location to another. Because lift trucks must typically transport many different types of loads, lift trucks usually include a mast supporting a vertically extendable carriage, which may be selectively interconnected to any one of a variety of different hydraulically actuated lift truck attachments, each intended to securely engage and move a particular type of load. For example, a particular lift truck attachment may include a pair of horizontally spaced apart forks intended to slide into respective slots in 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 a 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. 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 needs to provide enough lateral force to securely grip the load so that the load does not fall during transport, but at the same time not apply so much force to the load that it would be damaged. Thus, hydraulic control systems for clamp attachments typically include some sort of load-weight sensing mechanism that automatically adjusts the gripping force by gradually increasing the gripping fluid pressure from a relatively low initial pressure in conjunction with the control system to just enough pressure to lift the load without slipping.

[0005]

[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 occurs because high speed closure requires a closing pressure higher than the desired low threshold pressure, and such higher pressure is trapped within the system by the fluid input check valves during initial closure, resulting in the desired lower threshold pressure being exceeded before automatic adjustment of the gripping pressure can begin.

[0006]

[0006] Hydraulic control systems for clamp attachments also typically coordinate the movement of the clamps toward the load so that one clamp does not prematurely strike and damage the load or slide the load toward the other clamp. To this end, such control systems typically utilize flow dividers, such as spool and gear dividers, to split the hydraulic fluid evenly to each of the clamps. Spool-type flow dividers split the flow through a fixed, pressure-compensated orifice, which ensures approximately equal flow through the orifice even as inlet and / or outlet pressures vary. However, spool flow dividers must balance accuracy with the ability to withstand oil contamination without failure. Spool flow dividers are designed to split the flow precisely only within a narrow range of flow rates, and because spool flow dividers use fixed orifices, equal division of flow may not occur when used below the rated flow rate of a particular flow divider, and if the flow exceeds the rating of the valve, a large pressure drop across the valve can degrade performance and cause fluid heating. Gear diverters can operate over a wider range of operating flow rates than spool diverters, but are generally much more expensive and require proper design of the hydraulic circuit to prevent pressure build-up if one clamp becomes restricted in travel.

[0007]

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

[0008] Therefore, what is desired is an improved hydraulic control circuit which allows for fast and synchronized closing of opposing clamps against a load, while preventing damage to the load upon contact by the clamps.

[0009] For a better understanding of the present invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings in which: [Brief description of the drawings]

[0010] [Figure 1] 1 shows an exemplary hydraulic control circuit that uses fluid supplied from the lift truck to operate respective hydraulic cylinders, each of which may drive a respective clamp on the lift truck attachment. [Diagram 2] 2 illustrates the pressure and force exerted by a hydraulic cylinder controlled by the circuit of FIG. 1. [Diagram 3] 2 illustrates the example hydraulic control circuit of FIG. 1 connected to a pair of hydraulic cylinders used to actuate the pivot arm clamp. [Figure 4] 2 illustrates a first exemplary synchronized plunger that may be used in the hydraulic control circuit of FIG. 1. [Figure 5A] 4 shows the synchronized plunger of FIG. 3 in a mid-stroke position and pressurized from the rod end. [Figure 5B] 4 shows the synchronized plunger of FIG. 3 at the end of stroke and pressurized from the rod side. [Figure 5C] 4 shows the synchronized plunger of FIG. 3 in a mid-stroke position and pressurized from the head end. [Figure 6] 2 illustrates a second exemplary synchronized plunger that may be used in the hydraulic control circuit of FIG. 1. [Figure 7A] 6 shows the synchronized plunger of FIG. 5 in a mid-stroke position and pressurized from the rod end. [Figure 7B] 6 shows the synchronized plunger of FIG. 5 at the end of stroke and pressurized from the rod side. [Figure 7C] 6 shows the synchronized plunger of FIG. 5 in a mid-stroke position and pressurized from the head end. [Figure 7D] 6 shows the synchronized plunger of FIG. 5 at the end of its stroke and pressurized from the head side. [Figure 8] 1 illustrates an alternative control circuit that may be used to control each hydraulically actuated motor of a lift truck attachment. [Figure 9] 1 illustrates an alternative control circuit that can coordinate the movement of hydraulic actuators, such actuators being either coupled or uncoupled. [Figure 10] 1 shows an alternative control circuit using a two-way relief valve and multiple sequence valves that resynchronize the hydraulic cylinders in the open position. [Figure 11A] Shown is a Multi-Load Handler (MLH) attachment in single pallet mode. [Figure 11B] A multi-load handler (MLH) attachment in double pallet mode is shown. [Figure 12A] Shown is the action of the MLH moving the loads away from each other when in double pallet mode. [Figure 12B]1 shows the operation of the MLH to move loads towards each other when in double pallet mode. [Figure 13] 1 illustrates an exemplary hydraulic control circuit that may be used to control the MLH. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011]

[0028] The present disclosure describes a novel system and method that allows a hydraulic actuator on an industrial piece of equipment, such as a lift truck or lift truck attachment, to alternate between a first configuration in which the actuator is hydraulically coupled and a second configuration in which the actuator is not hydraulically coupled. As used herein and in the claims, the term "hydraulic actuator" refers to any device having first and second fluid line connections, where a difference in fluid pressure across the connections is 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 a pair of connections that, during operation of the control circuit, can receive pressurized fluid from an external source, such as a lift truck, thereby pressurizing at least one output port of the control circuit, as defined below, while simultaneously returning unpressurized fluid to the external source, e.g., the lift truck. Similarly, as used herein and in the claims, an "output port," when referring to a hydraulic control circuit, refers to a pair of connections that, during operation of the control circuit and when both are connected to a hydraulic actuator as defined above, 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 "hydraulic coupled," "hydraulically coupled," and similar terms, when referring to two or more hydraulic actuators, mean that the fluid pressure at the delivery side of a first actuator is in fluid communication with the input side of a second actuator, i.e., the hydraulically coupled actuators are connected in series. Additionally, as used herein and in the claims, the phrases "not hydraulically coupled," "not hydraulically coupled," and similar terms, when used in reference to two hydraulic actuators, mean that the fluid pressure at 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 purposes of this disclosure, the specification will refer specifically to hydraulic cylinders, but those skilled in the art will recognize that any fluid-powered actuator that moves a device to which it is connected by expanding, contracting, rotating, or otherwise moving as a result of changes in fluid pressure through the fluid-powered actuator may be used in the disclosed systems and methods.

[0012]

[0029] As previously mentioned, material 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 use a hydraulic actuator to have the clamp arm apply a force against the load to reliably lift the load, but would also position the clamp arm by either moving together to initially contact the load, or moving away to release the load. In such applications, efficiency is improved if the clamp arm is positioned with high speed and low force, but low speed and high force are desired to avoid damaging the load when clamping the load. As another example, some material handling equipment allows the gripped load to be rotated about an axis, thus requiring the clamp to first rotate to align with the load, and then rotate after the load is gripped. Again, it may be desirable to rotate at high speed and low torque when the load is not gripped for efficient operation, but at low speed and high torque when the load is gripped to avoid damaging the load or imparting excessive inertia to the vehicle. As yet another example, side shifting forks often must move independently to provide the desired spacing between the forks, yet move in unison when side shifting a load held on the forks.

[0013]

[0030] In each of these illustrative examples, the novel systems and methods disclosed by the present application advantageously enable material handling vehicles, attachments, and the like to hydraulically couple actuators during one mode of operation and disengage them during another mode of operation. For example, with reference to the clamp attachment described in the previous paragraph, when coordinating the movement of two clamps to or from a load, simultaneously actuating the hydraulic cylinders or other actuators moving the clamps can be performed at high speeds that risk damaging the load after contact. This risk can be reduced by operating the hydraulic cylinders in series, but this can reduce the efficiency with which the clamps grip the load by reducing the effective cylinder area used to generate the clamping force. Thus, one embodiment of the disclosed system and method hydraulically couples the cylinders during clamp positioning, i.e., when the clamp is being moved outward, such as to release the load, and / or when the clamp is being moved inward toward the load to clamp the load, until just before the clamp grips the load, at which point the hydraulic cylinders are no longer coupled, so that the effective cylinder area is increased and the clamping force control can be adjusted more efficiently. 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 linkage during the closing movement. Those skilled in the art will appreciate that similar advantages are achieved in other types of material handling applications, such as side shift fork attachments, rotor clamps, etc.

[0014]

[0031] Moreover, such benefits may preferably be achieved without the use of flow diverters. As previously mentioned, existing material handling equipment that engages and moves loads is typically designed to coordinate the movement of clamps, forks, or other such members toward and away from one another using flow diverters. Each such clamp, fork, etc. is typically driven by a respective fluid-powered actuator, e.g., a hydraulic cylinder, and a flow diverter is used to equally divide the pressurized flow toward each of the hydraulic actuators that move the respective clamps. Thus, the flow diverter ensures that opposing clamps move toward or away from one another in a coordinated manner under essentially the same pressure, but in so doing, the speed at which the clamps move is constrained due to the requirement for a lower initial pressure when the clamps first contact the load. However, the disclosed system and method may be used to coordinate the movement of opposing clamps toward and away from one another without passing fluid through a flow diverter by hydraulically coupling the fluid-powered actuators that move the clamps.

[0015]

[0032] 1 illustrates an exemplary system 10 including a hydraulic control circuit 12 that uses pressurized fluid supplied from, for example, a lift truck or other industrial equipment having a pump or motor 14 and a reservoir 16 to operate hydraulic actuators 20 and 22. Preferably, hydraulic circuit 12 includes input ports having connections 19a and 19b, thus allowing for fluid connection to the lift truck or other industrial equipment, such that fluid may be supplied under pressure to one of input connections 19a, 19b, while reduced pressure fluid is returned to the lift truck via the other of input connections 19a, 19b. Those skilled in the art will appreciate that during operation of control circuit 12, each of connections 19a and 19b alternately receives pressurized fluid and delivers unpressurized fluid depending on the direction fluid is flowing through the circuit, e.g., whether cylinders 20, 22 are retracted or extended.

[0016]

[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 the cylinders 20, 22, so that the actuator may be driven in a desired direction or other mode by selecting which connection of the respective output port to pressurize, while thereby allowing fluid discharged from the actuator to return to the circuit 12 from the other connection of the output port. For example, as shown in FIG. 1, when connection 21a is connected to the rod side of the cylinder 20 and connection 21b is connected to the head side of the cylinder 20, if output connection 21a is pressurized, fluid will flow into the rod side of the cylinder 20, which will then retract and fluid will be discharged from the head side of the cylinder 20 and return into the circuit 12 through connection 21b. Alternatively, when output connection 21b is pressurized, fluid will flow to the head side of cylinder 20 which will expand to force fluid out of cylinder 20 back into circuit 21 through connection 21a.

[0017]

[0034] The hydraulic circuit 12 also preferably includes a selector, such as the sequence valve 28 of FIG. 1, that determines whether the first output ports 21a, 21b and the second output ports 23a, 23b are operated in series, as described in more detail later in this specification. Those skilled in the art will appreciate that the particular device or devices used as a selector may vary based on the type or types of hydraulic device being controlled by the circuit, but broadly, a selector is a device or arrangement of devices configured within the hydraulic circuit 12 that allows the control circuit 12 to alternately select whether or not to interconnect output ports such that fluid returned from one hydraulic actuator to the control circuit 12 is used to pressurize the connection of a port of another hydraulic actuator. In some embodiments, as described below, the selector may alternately select whether the connected hydraulic actuators are connected in series to the input ports of the control circuit 12 or whether the connected hydraulic actuators are connected in parallel to the input ports of the control circuit 12. In other embodiments, the selector may select whether the connected hydraulic actuators are connected in series to the input port of the control circuit 12, or whether one hydraulic actuator is pressurized by the input port of the control circuit and discharges fluid toward the input port while another hydraulic actuator is not pressurized by the input port and does not discharge fluid toward the input port. Regardless of such variations, by selectively determining whether the hydraulic actuators are connected in series, the control circuit 12 may be used in a variety of different hydraulically operated devices, such as lift truck attachments, to operate more efficiently.

[0018]

[0035] For example, the embodiment of Figure 1 shows circuit 12 being used to supply pressurized fluid to a pair of hydraulic cylinders 20 and 22 typical of a carton clamp 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 opening and closing movement of cylinders 20 and 22 is manually selectable by directional control valve 18 which, when moved to the left from the neutral position shown in Figure 1, closes the clamp towards the load by supplying pressurized fluid to port 19a of control circuit 12 and returning unpressurized fluid to tank 16 through port 19b of control circuit 12, and when moved to the right from the neutral position shown in Figure 1, opens the clamp away from the load by supplying pressurized fluid to port 19b of control circuit 12 and returning unpressurized fluid to tank 16 through port 19a of control circuit 12. Typically, a pump or motor 14, a reservoir or tank 16, and a directional control valve 18 are each located on the lift truck which supply pressurized fluid to the lift truck attachment via fluid lines that extend over the mast of the lift truck to the attachment, which typically includes hydraulic cylinders 20 and 22 and their associated clamps used to operate the attachment, and control circuitry 12.

[0019]

[0036] When the lift truck operator first moves selector valve 18 to pressurize port 19a of control circuit 12, pressurized fluid will flow through pilot operated check valve 24, used to maintain load gripping force (pressure) in primary cylinder 20, through output port connection 21a to the rod side of primary cylinder 20, which will correspondingly contract to move its associated clamp inward, e.g., toward the load. Fluid will then be discharged from the head side of primary cylinder 20 through output port connection 21b of control circuit 12. Fluid sequence valve 28 (operating as the aforementioned selector as described below) prevents fluid from returning to tank 16 through port 19b, so that fluid discharged from primary cylinder 20 will flow through pilot operated check valve 26, through output port connection 23a of control circuit 12, to the rod side of secondary cylinder 22, which will also contract to move its associated clamp inward, e.g., toward the load. Fluid is then discharged from the head side of secondary cylinder 22 into output port connection 23b and returned to tank 16 via port 19b of control circuit 12. Thus, when sequence valve 28 is maintained in the closed position as shown in FIG. 1, cylinders 20 and 22 are connected in series, coordinating clamp movement as the clamp moves inward toward the load before contacting the load, resulting in improved clamping speed without the use of a flow diverter.

[0020]

[0037] When the clamp contacts the load, pressure increases in line 30 to which sequence valve 28 is connected. When pressure reaches a threshold setting for sequence valve 28 indicating a load is clamped, that valve opens to allow fluid to flow from the head side of primary cylinder 20 into non-pressurized tank 16, thus preventing fluid from flowing into the rod side of cylinder 22. As the load is further clamped by primary cylinder 20, secondary cylinder 22 is locked in position and port 3 of pilot valve 26 is depressurized and port 1 is pressurized so that fluid cannot enter the rod side of secondary cylinder 22 to retract the rod, while pilot valve 26 blocks flow from the rod side of cylinder 22 so that secondary cylinder 22 cannot extend its rod. Thus, the sequence valve 28 operates to alternate the operating modes of the primary and secondary cylinders 20, 22 during the closing movement between a first operating mode in which the primary and secondary cylinders 20, 22 are hydraulically coupled over a first range of motion of the primary cylinder, and a second operating mode in which the primary and secondary cylinders 20, 22 are not hydraulically coupled over a second range of motion of the primary cylinder. Although FIG. 1 shows the sequence valve 28 being actuated by a rise in pressure when a load is clamped, those skilled in the art will recognize that other means may be employed to actuate the sequence valve or switch the cylinders 20 and 22 from a first hydraulically coupled mode to a second non-hydraulic coupled mode, such as using a valve that is actuated when the clamp arm or cylinder extends or retracts beyond a certain location, or using a sensor-activated solenoid valve. In this manner, for example, the primary and secondary cylinders may switch from hydraulically coupled when the clamp reaches a location proximate to the load but has not yet contacted the load.

[0021]

[0038] When the lift truck operator moves the selector valve 18 to the right relative to the position shown in Figure 1 and pressurizes port 19b of the control circuit 12, pressurized fluid will flow to the head side of the secondary cylinder 22 to extend its rod. Because 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 supplying the secondary cylinder 22, each of the check valves 24 and 26 will now open, and the pressure in line 32 added to the spring force of the sequence valve 28 will close the sequence valve 28. Thus, as the secondary cylinder 22 extends, fluid is discharged from its rod side through the pilot operated check valve 26 into the head side of the primary cylinder 20, which extends in concert with the secondary cylinder 22, thereby moving the clamps apart in concert with each other. As the primary cylinder 20 extends, fluid is discharged from its rod side through the pilot operated check valve 24 and back to tank 16.

[0022]

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

[0023]

[0040] FIG. 2 generally illustrates how pressure and force are transferred through the primary and secondary cylinders 20 and 22 and their associated clamps due to operation of the hydraulic control circuit 12, as previously described. Preferably, the rod side area A1 of the primary cylinder 20 is designed to provide the required load gripping force at the expected input hydraulic pressure. For example, if the required cylinder force is 4,180 lbs at an input pressure of 2000 psi, the required rod side area A1 is 2.09 in. 2This area can be achieved by using a rod diameter of 1.10 inches (28 mm) and a bore of 1.97 inches (50 mm). The rod side area A3 of the secondary cylinder 22 is preferably designed to have an area equal or nearly equal to the head side area A2 of the primary cylinder. This matched area allows for equal movement of each cylinder, i.e., one inch of rod movement of the primary cylinder 20 will result in one inch of rod movement of the primary cylinder 22. For example, using a primary cylinder 20 having dimensions of a rod diameter of 1.10 inches (28 mm) and a bore of 1.97 inches (50 mm), the rod side area A1 of the primary cylinder will be 2.09 in. 2 and the head side area A2 is 3.04in 2 Therefore, the secondary cylinder 22 is preferably 3.04 in. 2 Such a cylinder may be constructed with a rod diameter of 1.26 inches (32 mm) and a bore diameter of 2.34 inches (59.4 mm).

[0024]

[0041] As can be seen from FIG. 2, assuming that the rod side area A3 of the secondary cylinder 22 is equal to the head side area of ​​the primary cylinder 20, the actuation of the sequence valve 28 causes the load F P , F S Specifically, whether the cylinder is hydraulically coupled or not, both forces act on the same stationary load, so F P and F S must be equal to F if hydraulically connected. P is equal to P1A1-P2A2, and F S is simply equal to P3A3, and P4 is equal to 0 because it is connected to tank pressure. Furthermore, A2 is designed to be equal to A3, and considering that P2 must be equal to P3 due to the hydraulic linkage, P2A2 must be equal to P3A3. Given these relationships, F P =F S =P3A3=P2A2 therefore, F P =P1A1-P2A2=P1A1-F P It is. Rearranging the formula, we get F P =(1 / 2)P1A1.

[0025]

[0042] However, when the actuation of sequence valve 28 disables the hydraulic linkage, P4 and P2 will be zero since they are both connected to tank. P3A3=F S =F P =P1A1 Therefore, if cylinder 20 and cylinder 22 are not hydraulically connected, F P is twice as high as when cylinders 20 and 22 are hydraulically coupled. Thus, by hydraulically coupling the cylinders during positioning, movement of the clamp arm can be coordinated without the use of flow diverters (which would adversely limit inlet flow rate) and can be accomplished at high speeds while minimizing the forces on the load when it is initially clamped. Once clamping has occurred, the hydraulic coupling of cylinders 20 and 22 can be bypassed, allowing the clamping force to be applied more effectively.

[0026]

[0043] Figure 3 shows 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 a gripping force on a load and retraction of the cylinders 27, 29 releases the load. Thus, unlike the embodiment of Figure 1, the cylinders 27, 29 are connected to the control circuit so that, during a closing operation of the clamp, pressurized fluid is supplied to the head side of the primary cylinder 27 and discharged from the rod side of the cylinder 27, and when hydraulically coupled, fluid discharged from the rod side of the cylinder 27 is supplied to the head side of the cylinder 29 with the rod side of the cylinder 29 connected to connection 23b and therefore 19b. In this embodiment, the head side area of ​​the cylinder 29 is preferably equal to the rod side area of ​​the cylinder 27 to ensure equal movement of the cylinders 27, 29 occurs when hydraulically coupled.

[0027]

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

[0028]

[0045] Thus, in some embodiments, hydraulic circuit 10 may preferably include an optional resynchronization valve 25 that allows fluid to bypass the hydraulic linkage when one cylinder reaches the end of its stroke before the other cylinder. The resynchronization valve 25 allows oil to flow directly from the pressurized line 30 to the rod side of the secondary cylinder 22 when retracting the rods of cylinders 20, 22 whenever the pressure difference between the rod side of primary cylinder 20 and the rod side of secondary cylinder 22 exceeds a threshold amount set by the spring setting of the resynchronization valve 25. For example, if the rod of primary cylinder 20 is fully retracted while pressure is provided to clamp port 19a, pressure will rise in line 30 until the resynchronization valve 25 opens, allowing fluid to flow directly from the pressurized line 30 into the rod side of secondary cylinder 22 so that secondary cylinder 22 can continue to move to the fully retracted position to resynchronize cylinders 20, 22. Conversely, if the secondary cylinder 22 reaches the end of its stroke before the primary cylinder 20, pressure will increase in line 30 until the pressure setpoint of the sequencing valve 28 is reached, allowing oil to be bled out of the head side of the primary cylinder 20 until both cylinders are fully synchronized.

[0029]

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

[0030]

[0047] It will be understood by those skilled in the art that resynchronization valve 25, which is configured to resynchronize cylinders 20 and 22 by moving the rods of both cylinders to a fully retracted position, may instead be configured to resynchronize cylinders 20 and 22 by moving the rods of both cylinders to a fully extended position, for example by connecting the input of resynchronization valve 25 to line 32 instead of line 30, 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.

[0031]

[0048] As an alternative to using a resynchronization valve 25, one or both of the primary and secondary cylinders 20, 22 may be configured to selectively operate as a valve to enable resynchronization by allowing oil to flow from the rod side to the head side of the cylinder, or vice versa, when the cylinder reaches an end-of-stroke position. For example, with reference to FIG. 4, either or both of the primary or secondary cylinders 20 or 22 may comprise a synchronizing cylinder 40 having a cylinder shell 42 surrounding at least a portion of a sliding cylinder rod 44 secured in a threaded bore 48 of a sliding piston 46. The piston 46 preferably includes a wear band 50 and a piston seal 52 to provide sealed sliding movement of the piston within the cylinder shell 42. The cylinder rod 44 may define a conduit for pressurized oil to flow back and forth between the rod side area of ​​the cylinder 40 (i.e., areas A1 or A3 in FIG. 2) and the interior of the piston 46. For example, the cylinder rod 44 may include a conduit 53 with a passageway having a first portion extending axially inward from the end of the rod 44 embedded in the piston 46 to a second portion including a plurality of radial passageways to the circumference of the cylinder rod 44. The piston side of the conduit 53 may be selectively sealed by a check ball 58 mounted on a spring 56 that urges the check ball 58 toward the first axial portion of the conduit 53. The end of the spring 56 opposite the check ball 58 is also fixedly secured around a flange of the sliding plunger 54. The flange of the plunger 54 fits within a seat of the retainer 59 such that oil inside the piston 46 is sealed from entering the head side area of ​​the cylinder 40 (i.e., areas A2 or A4 in FIG. 2) or flowing in the opposite direction when the flange of the plunger 54 rests within the seat of the retainer 59.

[0032]

[0049] 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 can flow from the rod side area of ​​the cylinder 40 through the radial portion and then the axial portion of the passage 52 to push the check ball 58 inward and allow the oil to reach the internal cavity of the piston 46. However, the spring 56 presses the plunger 54 against the seat of the retainer 59, thus preventing the oil from flowing into the head side area of ​​the cylinder 40. However, as seen in Figure 5B, when the cylinder 40 has retracted the rod far enough to reach the end of the rod stroke position, the plunger 54 contacts the cylinder head 57 which compresses the spring 56 between the flange of the plunger 54 and the unseated check ball 58 so that the plunger 54 is unseated from its seat in the retainer 59, allowing oil to flow from the rod side area of ​​the cylinder 40 to the inside of the piston 46, out to the head side area of ​​the cylinder 40, and finally to the other cylinder 20 or 22 (or tank 16) through porting 55, allowing resynchronization. As shown in Figure 5C, when the cylinder 40 is pressurized from the head side, in the mid-stroke position, the pressurized oil pushes the plunger 54 out of its seat in the retainer 59, allowing oil to flow into the inside of the piston 46, but the plunger 54 pushes the check ball 58 against the spring 56 to seal the conduit 53, so that oil cannot flow into the rod side area of ​​the cylinder 40.

[0033]

[0050] 6 illustrates an alternative synchronizing cylinder 60 that can be resynchronized at either the end of a fully retracted stroke or the end of a fully extended stroke of the rod of the cylinder 60. Specifically, the cylinder 60 can include 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. An end of a cylinder rod 64 that slides with the piston 66 is rigidly mounted within a first bore 65 of the piston 66, for example by a heat shrink connection. The piston 66 also defines a second bore 67 that accommodates a spool 68, the spool 68 substantially conforming to the shape of the second bore 67 such that a gap is defined between an outer surface of the spool 68 and an inner surface of the second bore 67. 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 shorter than the length of the second bore 67, and the second bore 67 and the spool 68 being co-molded such that the central region of the spool 68 may slide back and forth within the central region of the second bore 67 between a first extreme end where one peripheral region of the spool 68 extends out from its associated peripheral region of the second bore 67 and a second extreme end where the opposing peripheral region of the spool 68 extends out from its associated peripheral region of the second bore 67. In some embodiments, to facilitate the formation of the second bore 67 molded to closely surround the spool 68, the second bore 67 may be formed at one end using a retainer plug 70 secured securely within the piston 66 by a heat shrink connection to surround one peripheral region of the spool 68.

[0034]

[0051] 7A, when the cylinder 60 is pressurized from the rod side, the spool 68 is forced into the second bore 67 to allow oil to flow through the gap between the second bore 67 and the rod side of the spool 68, but the spool 68 is forced into and blocks the head side peripheral area of ​​the second bore 67, blocking the ingress of oil to the head side of the cylinder 60. However, when the retracting rod reaches the end of stroke position shown in FIG. 7B, the cylinder head 76 pushes the spool 67 inward so that pressurized oil can enter the head side peripheral area of ​​the second bore 67 and escape via porting 78 to the other cylinder 50 or 52, or to tank 16.

[0035]

[0052] 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 slides to allow oil to flow from the head side of the cylinder 60 into the area between the spool 68 and the second bore 67, but blocks oil from entering the rod side area of ​​the cylinder 60. When the extending rod 64 reaches an end-of-stroke position, the cylinder retainer 80 pushes the spool 67 inward to allow pressurized oil to enter the rod side peripheral area of ​​the second bore 67 and escape via porting 82 to the other cylinder 50 or 52, or to tank 16.

[0036]

[0053] The embodiment shown in Figures 1 and 3 uses a control circuit 12 intended to alternately operate the hydraulic actuators in a first mode in which the hydraulic actuators are connected in series to move in a coordinated manner, and a second mode in which the movement of the hydraulic actuators is not coordinated, e.g., one hydraulic actuator is locked in place while the other moves. Figure 8 shows an alternative control circuit 84 for a rotor dual drive motor, in which the control circuit 84 includes selectors 88a, 88b that can alternately drive two hydraulic motors 86a, 86b in series or in parallel, with the movement of the motors being coordinated in both instances. In particular, the control circuit 84 may include input ports 19a, 19b selectively connectable to a pump 14 and reservoir 16 on a lift truck having both a clamp selector valve 18 intended to alternately clamp and release a load as described above, and a rotor selector valve 83 used to selectively rotate the clamp about an axis in a desired direction by moving the valve to the left or right of a center position, or the angular orientation of the clamp remains fixed by moving the valve 83 to a center position.

[0037]

[0054] The control circuit 84 preferably has a first output port having connections 21a, 21b and a second output port having connections 23a, 23b each selectively connectable to a respective one of the hydraulic motors 86a, 86b. Thus, when connected as shown in Figure 8, the motor 86a may be driven in one direction by pressurizing connection 21a and allowing fluid to be evacuated from the motor back into the control circuit 84 through connection 21b, and may be driven in the opposite direction by pressurizing connection 21b and allowing fluid to be evacuated from the motor back into the control circuit 84 through connection 21a. The motor 86b may be similarly driven via connections 23a and 32b.

[0038]

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

[0039]

[0056] However, when both solenoids are energized, connection 23b of the output port of the control circuit to motor 86b is connected to connection 21a of the output port of the control circuit to motor 86a so as to rotate motors 86a, 86b in series. In this configuration, when connection 19a is pressurized by pump 14, pressurized fluid flows from connection 23a to motor 86b, which causes fluid to flow back into connection 23b and out through connection 21a to motor 86a. Fluid from motor 86a flows back into control circuit 84 through connection 21b and from control circuit 84 through input connection 19b to tank 16. Pressurizing connection 19b while both solenoids are energized conversely maintains the series connection of motors 86a, 86b but rotates them in the other direction relative to the rotation that occurs when connection 19a is pressurized. Although FIG. 8 shows two solenoids 88a, 88b as selectors that alternate the control circuit 84 between parallel and series configurations, one skilled in the art will appreciate that other embodiments may use different selectors, such as a pilot controlled valve that changes configuration based on detected clamp pressure.

[0040]

[0057] Figure 9 illustrates yet another embodiment of a control circuit that coordinates the movement of hydraulic actuators that selectively alternate between one of a series and a parallel configuration. Specifically, the hydraulic control circuit is used to coordinate the movement of hydraulic cylinders 92, 94 that move the clamp toward and away from the load, respectively, using pressurized fluid supplied to input port connections 19a, 19b of the hydraulic control circuit, for example. As can be seen in Figure 9, the control circuit 90 includes all of the elements of the control circuit 12 shown in Figures 1 and 3, but also includes a flow divider 96 and a pressure operated valve 98 interposed between input port connection 19a and the control circuit 90.

[0041]

[0058] When pressurized fluid is provided to connection 19b of the input port of control circuit 90, control circuit 90 operates similarly to control circuit 12 of FIG. 1, with cylinders 92 and 94 connected in series to cooperate to extend the rods of the cylinders, and fluid flows from control circuit 90 into the head side of cylinder 94, back into control circuit 90 from the rod side of cylinder 94, flows from control circuit 90 into the head side of cylinder 92, flows out the rod side of cylinder 92 and back into the control circuit, and then delivers the fluid into tank 16. However, when pressurized fluid is provided to connection 19a of the input port of control circuit 90, the pressurized fluid is distributed by flow diverter 96 in a manner determined by the position of pressure operated valve 98. Specifically, flow diverter 96 divides the fluid provided from connection 19a into a first path or line to connection 21a connected to the rod side of cylinder 92 and a second path or line to pressure operated valve 98. Pressure operated valve 98 is spring biased into a position to recombine the flows separated by flow divider 96, thereby pressurizing port 21a, which again causes the control circuit to behave exactly like control circuit 12 of Figure 1, i.e., cylinders 92 and 94 are connected in series to position the clamp in a coordinated closing movement toward the load. When the clamp contacts the load, pressure at port 19a rises to a level which moves pressure operated valve 98 to divert fluid from the second path, as just described, through one-way check valve 99 to the rod side of cylinder 94, whereby pressure provided through input port connection 19a of control circuit 90 operates cylinders 92 and 94 in parallel when a load is being clamped.

[0042]

[0059] Because coordinated movement of cylinders 92 and 94 requires that the head side area of ​​cylinder 92 match the rod side area of ​​cylinder 94 when hydraulically connected in series with one another, the rod side area of ​​cylinder 92 will typically be less than the rod side area of ​​cylinder 94. Thus, 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 connected and controlled in parallel, flow divider 96 preferably unequally divides the flow from input connection 19a in amounts proportional to the rod side areas of the cylinders driven by each divided fluid flow. Thus, when cylinder 92 is 2.09 in 2 and the cylinder 94 has a rod side area of ​​3.04 in 2 rod side area for a total area of ​​5.13in 2 In the illustrative example of FIG. 9, the flow diverter 96, when clamped on the load, diverts 41% of the flow into the cylinder 92 (i.e., 2.09 in 2 / 5.13in 2 ), and 59% of the flow is directed into cylinder 94 (i.e., 3.04 in 2 / 5.13in 2 ) which ensures that flow into cylinders 92 and 94 each causes the same linear retraction of the rods in each respective cylinder.

[0043]

[0060] One advantage of control circuit 90 over control circuit 12, when used to actuate a clamp on a load, is that control circuit 90 may reduce or possibly eliminate the need for resynchronization valve 25 or the use of valves in the hydraulic cylinders as shown in Figures 4 and 6. Because cylinders 92 and 94 move in coordination both during positioning of the clamp and while a load is clamped, each of cylinders 90 and 92 is much less likely to reach the end of its stroke before the other cylinder does.

[0044]

[0061] FIG. 10 illustrates a control circuit 100 that is an alternative embodiment of the control circuit shown in FIG. 3. The control circuit 100 may optionally include a bidirectional relief valve 102 to limit 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. 3, the pilot operated check valve 26 may open before the check valve 24, causing a pressure build-up at port 1 of the valve 24 that may exceed the pilot pressure available to open the valve 24. To address this possibility, the control circuit 100 replaces the pilot operated check valve 24 shown in FIG. 3 with a counterbalance valve 104. During a closing operation, pressure through port 19a causes fluid to bypass the counterbalance valve 104 via the check valve 105, which then pressurizes the rod side of the cylinder 27. During a closing operation, pressure through port 19b opens the pilot operated control valve 26 and also opens the counterbalance valve 104, thereby allowing fluid to be exhausted through port 19a.

[0045]

[0062] 10 also shows relief valve 106a and relief valve 106b, which together allow for resynchronization of cylinders 27 and 29. Specifically, during opening, if cylinder 29 reaches the end of its stroke before cylinder 27, relief valve 106a 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 exit the rod side of cylinder 29.

[0046]

[0063] 11A and 11B, a multi-load handler (MLH) is a type of lift truck attachment that includes four forks that can slide laterally relative to one another to allow the lift truck to alternately engage one or two pallet loads. In a first configuration, shown in FIG. 11A, the four forks may be split into two pairs of adjacent forks, with each pair capable of sliding into a respective opening in a single pallet. A second configuration, shown in FIG. 11B, arranges the forks into two pairs of spaced-apart forks, with each pair positioned to engage and move a respective pallet.

[0047]

[0064] The MLH therefore has two different actions for laterally positioning the forks. The first action is to position the forks between the "single" and "double" pallet modes, as shown in Figures 11A and 11B. This action requires little actuator force and is preferably performed at high speed with precise synchronization between the two different pairs of forks. The second action, performed in the "double" mode, laterally positions each set of forks relative to each other, as shown in Figures 12A and 12B. This is commonly referred to as "snap" when closing and "spread" when opening. This action requires high actuator force and low speed, and again preferably with precise synchronization between the left and right set of forks.

[0048]

[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, it is desirable to employ a hybrid clamping force control circuit. However, unlike the previously described systems in which high force operation occurs when clamping around a single load, and therefore synchronization of movement between the hydraulic cylinders during clamping occurs through transmission of force through the load, in an 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 cylinders of different bores are used, since the same pressure may generate different forces in the cylinders, resulting in different rates of movement.

[0049]

[0066] Figure 13 shows a control circuit 110 receiving and delivering fluid from inlet ports 114a, 114b and through first outlet ports 116a, 116b and second output ports 118a, 118b. Figure 13 shows the first outlet port 116a, 116b connected to a small diameter cylinder 120 and the second outlet port 118a, 118b connected to a large diameter cylinder 122, although one skilled in the art will appreciate that this configuration may be reversed.

[0050]

[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 a closed or open movement. In the open movement, the selector valve 112 can be moved to pressurize the connection 114a, thereby supplying fluid to the flow diverter 124. One side of the flow diverter is directly connected to the connection 116a that supplies the rod side of the small bore cylinder 120, while the other side of the flow diverter is connected to a pilot operated directional control valve 126 that has a spring bias that also supplies fluid to the connection 116a on the rod side of the small bore cylinder 120, setting the pilot operated directional control valve 126 to a default position, i.e., in low force operation all fluid in the flow diverter exits the connection 116a and enters the rod side of the cylinder 120, and the cylinder 120 retracts to discharge fluid back to the control circuit 110 through the connection 116b. The pressurized fluid opens pilot operated control valve 132 so that the pressurized fluid again leaves the control circuit and enters the rod side of large bore cylinder 122 which contracts and discharges fluid into the control circuit through connection 118b and then out of control circuit 110 through 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.

[0051]

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

[0052]

[0069] The flow diverter 124 splits and recombines the flows in a ratio that corresponds to the difference in size between cylinders 120 and 122. For example, a primary (small) actuator with a 40mm bore size and a 25mm rod size has a rod side working area of ​​766mm^2, and a corresponding secondary (large) actuator with a 50mm bore size and a 30mm rod size has a rod side working area of ​​1257mm^2. Thus, the flow diverter should preferably split 38% of the flow to the primary (small) actuator and 62% of the flow to the secondary (large) actuator to achieve synchronized movement according to the following equation: Primary actuator = Volume1 = A1 * Stroke Secondary actuator-volume3-A3*stroke Total Volume = Volume 1 + Volume 3 Shunt = Specifications 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%

[0053]

[0070] As mentioned above, given that each cylinder is moving an independent load, and given that the cylinders 120 and 122 have different bore sizes, the control circuit 110 preferably includes a synchronization mechanism that ensures that the cylinders 120 and 122 move at the same speed. Accordingly, the control circuit 110 preferably includes a pressure intensifier relief valve 130 positioned between the directional control valve 126 and the output port 118a. The pressure intensifier relief valve 130 provides a pressure drop due to the action of the fluid against a spring in the valve 130, the spring resistance being set so that the force exerted by the larger diameter cylinder is the same as the smaller diameter cylinder. This allows the two cylinders 120, 122 to move at the same speed. For example, assuming that the cylinder 120 has a 40 mm bore with a 25 mm rod and the cylinder 122 has a 50 mm bore and a 30 mm rod, and equal loads are supported on both pallets, a load requiring 2200 psi in the smaller bore may only require 1400 psi to achieve equal force. Therefore, valve 130 is set at 800 psi to compensate for the difference, thereby allowing the flow divider to operate more precisely. In some embodiments, the boost 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 that valve 130 will open against the spring whenever the system switches to uncoupled mode, i.e., sequence valve 134 has a higher spring resistance than boost relief valve 130 so that any pressure in port 114a that is large enough to actuate valve 126 will also be large enough to actuate valve 130.

[0054]

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

[0055]

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

[0056]

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

[0057]

[0074] It will be understood that the present invention is not limited to the particular embodiments described, but that variations are possible therein without departing from the scope of the invention as defined in the appended claims, as interpreted in accordance with general legal principles, including the doctrine of equivalents or any other doctrine that expands the enforceable scope of the claims beyond their literal scope. Unless the context dictates otherwise, reference in a claim to the number of instances of an element, whether a reference to one instance or to more than one instance, requires at least the recited number of instances of the element, but is not intended to exclude from the scope of the claim structures or methods having more instances of that element than are recited. When used in the claims, the word "comprises" or its derivatives are used in a non-exclusive sense that is not intended to exclude the presence of other elements or steps in the claimed structure or method.

Claims

1. an input port configured to receive pressurized input fluid from the pump and return unpressurized fluid to the reservoir; a first output port and a second output port, each of the first output port and the second output port being connectable to a corresponding hydraulic actuator, each of the first output port and the second output port being configured to deliver pressurized fluid to a hydraulic actuator connected to each of the first output port and the second output port, while simultaneously receiving fluid delivered from the hydraulic actuator; a selector capable of selectively using fluid delivered from one hydraulic actuator to pressurize fluid delivered to another hydraulic actuator; A hydraulic control circuit comprising:

1. A hydraulic control circuit in which the fluids supplied to each hydraulic actuator are at different pressures from one another by a valve that determines whether to rejoin the input fluid output from a flow divider when no fluid is being delivered from one hydraulic actuator to pressurize the fluid delivered to the other hydraulic actuator, and the one hydraulic actuator and the other hydraulic actuator extend and retract synchronously even though the fluid supplied to one hydraulic actuator is at a different pressure than the fluid supplied to the other hydraulic actuator.

2. 2. The hydraulic control circuit of claim 1, wherein the selector selectively uses fluid delivered from one hydraulic actuator to automatically pressurize fluid delivered to another hydraulic actuator based on a magnitude of fluid pressure supplied to the hydraulic control circuit.

3. 2. The hydraulic control circuit of claim 1, wherein the selector selectively uses fluid delivered from one hydraulic actuator to automatically pressurize fluid delivered to another hydraulic actuator based on which connection of an input port receives pressurized fluid.

4. 10. The hydraulic control circuit of claim 1, wherein the hydraulic control circuit is connected to a lift truck attachment having a clamp, and the selector selectively uses fluid delivered from one hydraulic actuator to automatically pressurize fluid delivered to the other hydraulic actuator when the clamp engages a load.

5. 2. The hydraulic control circuit of claim 1, wherein the selector selectively uses fluid delivered from one hydraulic actuator to automatically pressurize fluid delivered to another hydraulic actuator during an opening movement of the hydraulic actuator.

6. 2. The hydraulic control circuit of claim 1, wherein the selector selectively uses fluid delivered from one hydraulic actuator to automatically pressurize fluid delivered to another hydraulic actuator during a portion of a closing movement of the hydraulic actuator and during an opening movement of the hydraulic actuator.

7. 2. The hydraulic control circuit of claim 1, wherein the selector alternates the control circuit between a first mode in which the hydraulic actuators are connected in series and a second mode in which the hydraulic actuators are not connected in series.

8. The hydraulic control circuit of claim 7 , wherein in the second mode, the hydraulic actuators are driven in parallel.

9. The hydraulic control circuit of claim 7 , wherein in the second mode, one hydraulic actuator is moved by the control circuit while the other hydraulic actuator is prevented from moving by the control circuit.

10. a hydraulic control circuit configured to receive pressurized input fluid from a pump and return unpressurized fluid to a reservoir, The hydraulic control circuit includes a selector operable alternately between a first state and a second state when the control circuit is connected to a first hydraulic actuator and a second hydraulic actuator, wherein in the first state, the first hydraulic actuator and the second hydraulic actuator are hydraulically connected, and in the second state, the first hydraulic actuator and the second hydraulic actuator are not hydraulically connected; The hydraulic control circuit is configured such that when fluid is not being delivered from one hydraulic actuator to pressurize the fluid delivered to the other hydraulic actuator during simultaneous and synchronous operation of the first hydraulic actuator and the second hydraulic actuator, the fluid supplied to each hydraulic actuator is at different pressures from one another by a valve that determines whether to rejoin the input fluid output from a flow divider.

11. The hydraulic control circuit of claim 10 , wherein the selector automatically alternates between the first state and the second state based on a magnitude of fluid pressure supplied to the hydraulic control circuit.

12. The hydraulic control circuit of claim 10 , wherein the selector automatically alternates between the first state and the second state based on which connection of an input port receives pressurized fluid.

13. The hydraulic control circuit of claim 10 including a resynchronization valve operable to resynchronize the first hydraulic actuator with the second hydraulic actuator.

14. The hydraulic control circuit of claim 10 included in a lift truck attachment having said first hydraulic actuator and said second hydraulic actuator.

15. 15. The hydraulic control circuit of claim 14, wherein at least one of the first hydraulic actuator and the second hydraulic actuator operates as a valve to selectively allow fluid to pass between a rod side and a head side of the corresponding hydraulic actuator.

16. The hydraulic control circuit of claim 15 , wherein at least one of the valves is a resynchronization valve configured to resynchronize the first hydraulic actuator with the second hydraulic actuator.

17. 17. The hydraulic control circuit of claim 16, wherein at least one of the valves allows fluid to pass between a rod side and a head side of a corresponding hydraulic actuator at an end of stroke of a closing movement.

18. 20. The hydraulic control circuit of claim 17, wherein at least one of the valves allows fluid to pass between the rod side and the head side of a corresponding hydraulic actuator at an end of a stroke of an opening movement.

19. The hydraulic control circuit of claim 15 , wherein at least one of the valves allows fluid to pass between the rod side and the head side of a corresponding hydraulic actuator at an end of a stroke of a closing movement.

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