Patent Publication Number: US-2002000157-A1

Title: Manually-operated synchronizing valve for paired hydraulic cylinders

Description:
FIELD OF THE INVENTION  
       [0001] The present invention relates generally to hydraulic systems. In particular, the invention is a hydraulic system including a manually-operated synchronizing valve for evenly distributing hydraulic fluid flow between paired cylinders.  
       BACKGROUND OF THE INVENTION  
       [0002] Many hydraulic systems use two or more cylinders or other actuators to drive a load. In these applications the “paired” cylinders are typically connected in a parallel hydraulic circuit to the work section of a single control valve. Hydraulic fluid flow from the control valve is thereby distributed to each of the cylinders. In-line flow dividers or orifices are sometimes incorporated into systems of this type to divide the fluid flow between the cylinders in desired proportions (e.g., equally). However, these dividers are subject to tolerance variations and system differentials which can cause the flow between the cylinders to vary from the desired proportions.  
       [0003] By way of example, hydraulic systems used to raise and lower ramps or platforms which are used to support relatively heavy objects (e.g., ramps on trucks used to transport cars and other vehicles) often have a pair of transversely-spaced hydraulic cylinders connected to a common control valve. If the loads supported by these ramps or platforms are unevenly distributed, or if the mechanical efficiencies of the cylinder linkages vary or change, the pressures required to drive the cylinders will be different. Since fluid will flow to the lightest load first in these hydraulic systems, the uneven load distribution can cause the platform to twist. This action may continue until a binding occurs, and the force required to continue movement of the advancing cylinder equalizes with that of the trailing cylinder. In addition to other potential consequences, this action results in the uneven raising and lowering of the ramp or platform.  
       [0004] It is evident that there is a continuing need for improved approaches for controlling the relative flow of hydraulic fluid between paired cylinders actuated by a common control valve. To be commercially viable, any such system should be effective and capable of being efficiently implemented. A system of this type which can be controlled by an operator would be especially desirable.  
       SUMMARY OF THE INVENTION  
       [0005] The present invention is a synchronizing valve arrangement for controlling the flow of hydraulic fluid between a tank and a set of hydraulic cylinders or other actuators. It enables an operator to easily and accurately synchronize or otherwise control the relative speed of two actuators powered by a single control valve work section. The valve arrangement is also capable of being efficiently implemented.  
       [0006] One embodiment of the valve arrangement includes a set of at least two actuator ports, a primary control valve and a synchronizing control valve. Each actuator port of the set couples hydraulic fluid flow to one of a set of at least two hydraulic actuators. The primary control valve commonly controls the flow of hydraulic fluid between the tank and all the actuator ports of the set. The synchronizing valve individually controls the flow of hydraulic fluid between each actuator port of the set and the tank, to synchronize the primary control valve-controlled flow of hydraulic fluid through the actuator ports. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0007]FIG. 1 is a schematic diagram of a hydraulic valve system in accordance with the present invention. The valve system is shown interconnected to two pairs of hydraulic cylinders and to a hydraulic fluid supply system. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     [0008] One preferred embodiment of the hydraulic valve system  10  of the present invention is illustrated in FIG. 1. In this particular embodiment the valve system  10  is configured for interconnection to first and second sets of double acting hydraulic cylinders (i.e., actuators)  12 A,  12 B and  14 A,  14 B, respectively. The valve system  10  is also interconnected to hydraulic fluid supply system  16 . Although not shown, each set of cylinders  12 A,  12 B and  14 A,  14 B can be mounted to and operated to raise and lower a ramp or platform, or to otherwise actuate a structure or device. First primary control valve  18  is connected to the first set cylinders  12 A and  12 B in a parallel hydraulic circuit and operated to simultaneously control both cylinders of the first set. Similarly, second primary control valve  20  is connected to the second set cylinders  14 A and  14 B in a parallel hydraulic circuit and operated to simultaneously control both cylinders of the second set. A synchronizing valve  22  is connected between each set of cylinders  12 A,  12 B and  14 A and  14 B and the associated primary control valve  18  and  20 , respectively. By operating the synchronizing valve  22  when one or both of the primary control valves  18  and  20  is also being operated to extend or retract the associated set of cylinders  12 A,  12 B and/or  14 A and  14 B, an operator can synchronize or otherwise control the relative travel speeds of the two cylinders of the set. This functionality enables an operator to manually adjust for travel speed differences and provide improved positioning control.  
     [0009] In the embodiment shown, primary control valve  18  is a manually-actuated, double-acting, closed center spool valve in block  24 . Valve block  24  has a set of first and second base ports B 1  and B 2  (i.e., a first set of base ports) which are adapted to be connected to the base ends of cylinders  12 A and  12 B, respectively, and a set of first and second rod ports R 1 , and R 2  (i.e., a first set of rod ports) which are adapted to be connected to the rod ends of cylinders  12 A and  12 B, respectively. The working section of primary control valve  18  has a supply side pressure port P s  (i.e., an input port) connected to the pressure port P of the hydraulic fluid supply system  16  and a supply side tank port T s  connected to the tank port T of the hydraulic fluid supply system. On the cylinder side of the control valve  18 , the working section has a pressure port P c  (i.e., an output port) which is connected in parallel from junction J to both base ports B 1  and B 2  through orifices O 1  and O 2  and check valves C 1  and C 2 , respectively. Both rod ports R 1  and R 2  of the valve block  24  are connected to the tank port T c  (also an output port) on the cylinder side of the working section of the valve  18 . The sensing port S of the valve  18  is connected to the sensing input SI of an unloader valve  30  in the hydraulic fluid supply system  16 . Check valves C 1  and C 2  prevent load-induced drift-down of cylinders  12 A and  12 B, and in the embodiment shown are pilot-operated devices which have their sensing inputs connected to the rod port R 2  of valve block  24 . Orifices O 1  and O 2  can be used to enhance the accuracy of the differential fluid flow to the ports B 1  and B 2 . Port restrictions O 3  and O 4  can be included in valve block  24  adjacent to rod ports R 1 , and R 2 , respectively, to enhance the stability of system  10  when lowering heaving loads.  
     [0010] Synchronizing valve  22  also is a manually-actuated, double acting spool valve in the embodiment shown, and can be mounted within a valve block such as  26 . In this configuration the cylinder side of the working section of the synchronizing valve  22  has a pair of ports P 1  and P 2  (i.e., input ports) which are connected to base ports B 1  and B 2 , respectively, of the valve block  24 . This connection is made at locations between the respective check valves C 1  and C 2  and orifices O 1  and O 2  in the embodiment shown. A pair of check valves C 4  and C 5  are included in the fluid flow paths between the ports P 1  and P 2  of synchronizing valve  22  and base ports B 1  and B 2 , respectively, of the valve block  24 . A tank port T s  (i.e., an output port) of the synchronizing valve  22  is connected to the tank port T of the hydraulic fluid supply system  16  through the valve block  24 .  
     [0011] The second primary control valve  20  is a manually-actuated, double-acting, closed center spool valve mounted within the valve block  26  in the embodiment shown. Valve block  26  has a set of first and second base ports B 1  and B 2  (i.e., a second set of base ports) which are adapted to be connected to the base ends of cylinders  14 A and  14 B, respectively, and a set of first and second rod ports R 1  and R 2  (i.e., a second set of rod ports) which are adapted to be connected to the rod ends of cylinders  14 A and  14 B, respectively. The working section of primary control valve  20  has a supply side pressure port P s  connected to the pressure port P of the hydraulic fluid supply system  16  and a supply side tank port T s  connected to the tank port T of the hydraulic fluid supply system, both through the valve block  24 . On the cylinder side of the control valve  20 , the working section has a pressure port P c  which is connected in parallel from junction J to both base ports B 1  and B 2  through orifices O 1  and O 2  and check valves C 1  and C 2 , respectively. Both rod ports R 1  and R 2  of the valve block  26  are connected to the tank port T c  on the working section cylinder side of the valve  20 . The sensing port S of the valve  20  is connected to the sensing input SI of the unloader valve  30  in the hydraulic fluid supply system  16  through the valve block  24 . Check valves C 1  and C 2  prevent load-induced drift-down of cylinders  14 A and  14 B, and in the embodiment shown are pilot-operated devices which have their sensing inputs connected to the rod port R 2  of valve block  26 .  
     [0012] The fluid supply system  16  includes the unloader valve  30 , pump  40  and relief valve  42 . The unloader valve  30  is shown mounted within a block  44 . Valve blocks  24 , 26  and  44  are mounted together in a bank in the embodiment shown. Pressurized hydraulic fluid from pump  40  is coupled to the pressure port P of supply system  16  though the block  44 . The tank port T of the supply system  16  is coupled to a tank  46  of hydraulic fluid through the block  44 . As shown, unloader valve  30  is also connected to both the pressure port P and tank  46  of hydraulic fluid supply system  16 .  
     [0013] During the operation of valve system  10 , the pump  40  will provide a continuous supply of pressurized hydraulic fluid to pressure port P. As long as both primary control valves  18  and  20  are not actuated, their sensing ports S causes the unloader valve  30  to be in an open state, shunting the supply of pressurized fluid back to the tank  46 . However, if either or both of primary control valves  18  and  20  are actuated to raise or lower their respective set of cylinders  12 A,  12 B and  14 A,  14 B, the associated sensing port S will cause the unloader valve  30  to switch to its closed state, and thereby supply fluid to the supply side pressure port P s  of the actuated control valve(s). The control valves  18  and/or  20  can thereby be operated to control the flow of fluid, in a parallel hydraulic circuit, to the associated base ports B 1  and B 2  or rod ports R 1  and R 2 , and thereby raise and/or lower the respective set of cylinders  12 A,  12 B, and/or  14 A,  14 B.  
     [0014] Synchronizing valve  22  can be actuated by the operator during the actuation of primary control valves  18  and/or  20  to synchronize the motion of the cylinders  12 A,  12 B and/or  14 A,  14 B, respectively, being driven. By operating the synchronizing valve  22 , fluid flow to a selected one of cylinders  12 A and  12 B (if primary control valve  18  is being actuated) and/or a selected one of cylinders  14 A and  14 B (if primary control valve  20  is being actuated) is shunted or bled off and returned to tank port T. By way of example, if the primary control valve  18  is actuated in such a manner that its supply side pressure port P s  is fluidly connected to the cylinder side pressure port P c , thereby providing pressurized hydraulic fluid to the base ends of cylinders  12 A and  12 B through ports B 1  and B 2 , respectively, the relative travel speed of cylinder  12 A can be slowed with respect to that of cylinder  12 B by actuating synchronizing valve  22  in such a manner as to connect its cylinder side port P 1  to its tank port T s . This action will cause some of the pressurized hydraulic fluid that would otherwise flow to the base end of the cylinder  12 A through port B 1  to instead flow to the tank  46 . In a similar manner, the relative speed of cylinder  12 B can be slowed with respect to cylinder  12 A if the primary control valve  18  is actuated in the manner described above by actuating the synchronizing valve  22  in the opposite direction to connect its cylinder side port P 2  to its tank port T s . The relative speed of cylinders  14 A and  14 B can be controlled by synchronizing valve  22  in a similar manner when the second primary control valve  20  is being actuated to drive the cylinders  14 A and  14 B. Synchronizing valve  22  can also be operated to synchronize the motion of cylinders  12 A and  12 B and/or  14 A and  14 B when the respective primary control valves  18  and/or  20  are actuated to supply pressurized hydraulic fluid to the rod ends of the cylinders.  
     [0015] The synchronizing valve offers a number of important advantages. It allows an operator to relatively easily and accurately synchronize the motion of a pair of cylinders or other hydraulic actuators. Positioning control can thereby be enhanced. The system can also be efficiently implemented. One synchronizing valve can be used to provide the synchronizing function to one or more cylinders (i.e., it can be incorporated into a multiple section valve bank).  
     [0016] Although the present invention has been described with reference to preferred embodiments, those skilled in the art will recognize that changes can be made in form and detail without departing from the spirit and scope of the invention. For example, valve control and synchronization can be accomplished with lever, solenoid, pneumatic spool or other valve configurations. Open center and other valve configurations can also be used. Although shown in connection with cylinders, the synchronization approach can be used with other hydraulic actuators such as motors. The system can also be configured to synchronize the relative travel speed of a set of three or more actuators.