GB2106188A

GB2106188A - Hydraulic cylinder control

Info

Publication number: GB2106188A
Application number: GB08226771A
Authority: GB
Inventors: William W Dollison
Original assignee: Otis Engineering Corp
Current assignee: Otis Engineering Corp
Priority date: 1981-09-21
Filing date: 1982-09-20
Publication date: 1983-04-07
Also published as: CA1177726A; GB2106188B

Abstract

The outlets of two independent fixed volume pumps 20a, 20b, are connected to the two ends of a double-acting, large rod hydraulic cylinder 10. The outlets of the two pumps are also connected, through a three-position direction control valve 40, to tank. In the neutral position, both outlets are dumped to tank. In an extension control position, the valve restricts the dump line for one pump, thereby directing its outlet to the cap end of the cylinder; and in the retract control position the valve restricts the dump line for the other pump, thereby effecting flow to the rod end of the cylinder. The fluid line between each pump outlet and its respective cylinder end includes a check valve 24. A cross-piloted sequence valve 31 is connected in each fluid line between the respective cylinder end and check valve, and responsive to the pressure of the opposite fluid line. A control method includes the steps of supplying fluid to the two cylinder ends by respective independent pumps, flowing fluid from the pump outlets to tank and selectively restricting flow to tank from one pump to effect flow from that pump to the cylinder, and controlling fluid flow from the cylinder by cross-piloted sequence valves. <IMAGE>

Description

SPECIFICATION Hydraulic cylinder control This invention relates to an hydraulic power system, and more particularly to a system and method for controlling a double-acting hydraulic power cylinder.

The most common type of control circuit used to control the action of a double-acting large rod hydraulic cylinder includes a single fixed volume pump, a single relief valve, and a direction control valve. Depending on the area relationship existing between the rod end and the cap end of the cylinder, considerable speed and force differences may be experienced between the retracting and the extending action of the cylinder. While these differences may be overcome with different types of control circuits, such control circuits may be unduly complex and therefore more expensive, and yet may be less dependable than a more simple control circuit.

An object of this invention is to provide an improved system and method for controlling the action of a double-acting hydraulic cylinder.

Another object of this invention is to provide an improved system and method of controlling the action of a large rod, double-acting hydraulic cylinder.

A further object of this invention is to provide an improved system and method for controlling a double-action hydraulic cylinder, by supplying hydraulic fluid to the two cylinder ends at different selected pressures and volumes.

Still another object of this invention is to provide an improved system and method for controlling the action of a double-acting hydraulic cylinder, including control of acceleration and deceleration.

A still further object of this invention is to provide an improved system and method for controlling a double-acting hydraulic cylinder, including independent control of the maximum speed and maximum force of the cylinder rod, for each direction of movement thereof.

Another object of this invention is to provide an improved system and method for controlling the action of a double-acting hydraulic cylinder which is simple, economical to manufacture and very reliable in operation.

These objects are attained in a control system which includes first and second fixed volume pumps, supplied with hydraulic fluid from a fluid reservoir. A first conduit means connects the output of the first pump to the first hydraulic cylinder end; and a second conduit means connects the outlet of the second pump to the second hydraulic cylinder end. Check valve means in the respective conduit means permit flow only in one direction from the respective pumps. A direction control valve is connected between the first and second conduit means and the reservoir, for controlling the bypass flow of fluid from the outlets of both pumps to the reservoir and thereby to effect the flow of fluids selectively from each pump to its respective cylinder end.

These objects are further accomplished by a method which includes the steps: supplying fluid to the two cylinder ends by respective independent hydraulic pumps; and flowing fluid from the two pumps to a fluid reservoir by means of a direction contrdl valve for restricting selectively the flow from one pump and thereby effecting flow from that pump to its respective cylinder end.

The novel features and the advantages of the invention, as well as additional objects thereof, will be understood more fully from the following description when read in connection with the accompanying drawing.

The drawing is a schematic diagram of a double-acting hydraulic cylinder and an associated control system according to the invention.

The drawing illustrates schematically a hydraulic control system for a power cylinder, illustrated as a linear cylinder having a cap end and a rod end, where the rod has a relatively large diameter relative to the diameter of the piston.

While the control system of the invention is particularly useful for a large rod hydraulic cylinder, it will be understood that the control system may be used as well with other types of hydraulic cylinder apparatus, such as a rotary actuator for example.

The illustrated hydraulic cylinder 10 includes an elongated tubular housing 11 having a cap end 12 and a rod end 13, with a rod 14 extending through the rod end in sealing relation and having a piston 1 5 fixed thereto at its inner end. The hydraulic control system might be referred to as a parallel system, that is having parallel fluid paths for flowing fluid from the supply reservoir to the respective cylinder ends, and these paths including substantially identical components. In the following description, the fluid flow path and components for the cap end will be identified by reference numbers including the subscript a; and the flow path and components for the rod end will be identified by reference numbers including the subscript b.

The control systems includes two fixed volume pumps 20a and 20b each selected to have the desired parameters with respect to volume and pressure to enable it to perform its desired function. As seen in the drawing, the pump 20a is associated with the cap end of the cylinder 10, while the pump 20b is associated with the rod end of the cylinder. As illustrated in the drawing, the two pumps are coupled to be driven by a common drive shaft 21 and a single power source (not shown); however, if desired, the pumps could have independent drives. A hydraulic fluid reservoir or tank 22 provides the source of hydraulic fluid for both pumps; and this tank is indicated schematically with respect to several returns of the system.

Referring now to the portion of the system for supplying fluid to the cylinder cap end 12, the outlet of the pump 20a is connected to the cap end by a fluid line 23a which includes a check valve 24a allowing flow only in the direction toward the cylinder. A pressure relief valve 25a is connected in a line 26a branching from the line 23a and dumping to the tank 22. This relief valve responds to the pressure in the line 23a and will open to dump fluid to the tank when the maximum selected pressure for that line is achieved. This valve then limits the maximum fluid pressure available to the cap end of the cylinder.

The portion of the system for supplying fluid to the rod end 13 of the cylinder includes substantially identical components, namely the pump 20b coupled to the rod end by the line 23b and a check valve 24b. Since the effective piston area of the piston-rod assembly in the rod end of the cylinder is quite different from that of the cap end, the parameters of the pump 20b may be quite different from those of pump 20a. This system is also provided with a pressure relief valve 25b for dumping fluid through the line 26b to tank at a selected maximum pressure; and the selected maximum pressure for the valve 25b will likely be different from that for the valve 25a.

The control system includes sequence valves 31 a and 31 b associated respectively with the cap end and rod end of the cylinder 1 0. These sequence valves are connected at cross-piloted sequence valves to prevent the cylinder rod from "over-running" in the event that the resistance to movement of the rod should reverse for some reason. In the schematic drawing, the sequence valve 31 a is connected between the line 23a and the tank 22 by a line 32a; and, similarly the valve 31 b is connected between the line 23b and the tank by a line 32b. It will be understood that these sequence valves may be mounted directly on the cylinder 10, so that there may be no rupturable flexible fluid line between the valve and the cylinder, for example.The sequence valve 31 a for the cap end is connected to the line 23b for the rod end by a pilot line 33a; and accordingly this valve is opened in response to the pressure in the line 23b. Correspondingly the sequence valve 31 b associated with the rod end is connected to the line 23a by a pilot line 33b; and this valve responds to the pressure in the line 23a. The opening pressures for the sequence valves are selected as desired. In the operation of these sequence valves, when it is desired to move the rod 14 to the left for example, the pressure will build up in the cap end, but the rod and piston cannot move until the pressure of fluid in the rod end is released.

This release occurs when the pressure in the cap end reaches a selected value to effect the opening of the sequence valve 31 b and allow the fluid from the rod end to dump to tank through the line 32b. The operation is similar for moving the rod in the opposite direction; however the release pressure for the valve 31 a may be different from that selected for the valve 31 b.

The directional control of the rod 14 is accomplished by means of a direction control valve 40 connected between the outlets of the two pumps 20a and 20b and the tank 22. While the valve 40 is depicted in the drawing as a spool type valve, it may be of any suitable design such as a plug valve, shear seal valve, double poppet valve, or rotary valve. The direction control valve 40 is a three position valve having a neutral position in which the outlets of both pumps are communicated with the tank 22 so that both pumps are effectively "unloaded". The valve has two direction positions for effecting the flow of fluid from a respective pump to its respective cylinder end.

Referring to the control for the cap end, the outlet of the pump 20a is connected to the valve 40 by means of a line 41 a; and with the valve in a neutral position the outlet of the pump 20a is dumped to tank. Similarly the outlet of the pump 20b is connected to the valve 40 by a line 41 b; and in the neutral position of the valve the outlet of the pump 20b is dumped to tank. To move the rod 14 to the left (in the drawing) the control valve 40 is shifted to the right (in the drawing) wherein the line 41 a is blocked at the valve, but the line 41 b remains open and continues to dump fluid from the pump 20b to the tank. With the line 41 a blocked, the output from the pump 20a necessarily flows through the line 23a to the cap end of the cylinder to move the rod to the left.

Similarly for movement of the rod to the right, the valve 40 is shifted to the left to block the line 41 b, while the line 41 a is open to tank. Fluid from the pump 20b then flows to the rod end of the cylinder 10.

It will be seen that the acceleration or deceleration of the piston and cylinder rod assembly will be directly related to the manner in which the direction control valve 40 is shifted.

With appropriate manipulation of the direction control valve, it is possible to cause the cylinder rod 14 to emulate simple harmonic motion in the pattern of acceleration and deceleration it experiences. For both directions of movement of the rod, the speed of movement will be proportional to the discharge rate of the respective pump, and the maximum force applied to the piston will be limited by the setting of the respective pressure relief valve.

The operation of the control system is believed apparent from the foregoing description.

Obviously the system is designed for continuous drive of the two pumps 20a and 20b.

Applicant's invention is aiso concerned with a method for controlling a double-acting hydraulic cylinder; and that method includes, broadly, the steps: supplying fluid to the two cylinder ends by respective independent hydraulic pumps; and flowing fluid from the two pumps to a fluid reservoir by means of a direction control valve for restricting, selectively, the flow of fluid from one of the pumps to the reservoir, thereby effecting fluid flow from that one pump to its respective cylinder end.The method may include one or more of the following steps; controlling the flow of fluid from the cylinder ends by respective cross-piloted control valves, each controlled by the fluid pressure delivered to the opposite cylinder end; supplying fluid to the cylinder ends by means of a fixed volume pumps; driving the pumps from a single power source; selectively flowing fluid from both the pumps to the fluid reservoir by means of a direction control valve, to unload both pumps simultaneously; controlling the maximum pressure applied to each cylinder by means of a pressure relief valve connected to the output of each pump; and controlling the acceleration and deceleration of the cylinder rod by means of the direction control valve.

What has been described is a unique system and method for controlling a double-acting fluid power cylinder.

A particular advantage of this invention is that it enables the selection of widely differing parameters, such as pump volume and pump pressure, for the two ends of the cylinder. This is accomplished, of course, by the use of two independent pumps which may or may not be driven from a common power source. A related advantage is that this flexibility of control is provided in a system which is quite simple and economic to manufacture and which is very reliable.

Another important feature and advantage of the invention is that it enables precise control of the power cylinder, including control of acceleration and deceleration.

An important feature of the system with respect to economy of manufacture and reliability, is that the system features a completely hydraulic logic circuit.

While the preferred embodiment of the invention has been illustrated and described, it will be understood by those skilled in the art that changes and modifications may be resorted to without departing from the spirit and scope of the invention.

Claims

1. A control system for a hydraulic cylinder having opposed first and second cylinder ends, said system comprising first and second pumps; a fluid reservoir for supplying hydraulic fluid to the inlets of said pumps; a first conduit means connecting the outlet of said first pump to said first cylinder end; a second conduit means connecting the outlet of said second pump to said second cylinder end; a direction control valve connected between said first and second conduit means and said reservoir, for controlling flow of fluid from the outlets of said first and second pumps to said reservoir, and thereby to effect fluid flow selectively from said pumps to respective cylinder ends.

2. A control system as set forth in Claim 1 a pressure relief valve connected in each of said first and second conduit means, to control the maximum pressures delivered by each pump to a respective cylinder end.

3. A control system as set forth in Claim 1 said pumps being coupled to a common drive source.

4. A control system as set forth in Claim 1 check valve means in each of said conduit means, permitting fluid flow only in one direction from the pump to the cylinder end; first and second piloted sequence valves connected with respective first and second cylinder ends, for controlling fluid flow from said respective cylinder ends; said first sequence valve being responsive to the pressure applied to said second cylinder end; and said second sequence valve being responsive to the pressure applied to said first cylinder end.

5. A control system as set forth in Claim 1 said direction control valve having a neutral position for passing fluid from both of said conduit means to said reservoir, having a first control position for restricting the flow of fluid from said first conduit means to said reservoir to effect fluid flow from said first pump to said first cylinder end, and having a second control position for restricting the flow of fluid from said second conduit means to said reservoir to effect fluid flow from said second pump to said second cylinder end.

6. A control system as set forth in Claim 1 said hydraulic cylinder comprising a doubleacting cylinder.

7. A control system as set forth in Claim 1 said hydraulic cylinder comprising a single large rod, double-acting hydraulic cylinder.

8. A method for controlling a double-acting hydraulic cylinder comprising supplying fluid to the two cylinder ends by respective independent hydraulic pumps; flowing fluid from said two pumps to a fluid reservoir by means of a direction control valve for restricting, selectively, the flow from one of said pumps to said reservoir, thereby effecting fluid flow from said one pump to its respective cylinder end.

9. A method as set forth in Claim 8 including the step controlling the flow of fluid from said cylinder ends by respective cross-piloted control valves, each controlled by the fluid pressure delivered to the opposite cylinder end.

10. A method as set forth in Claim 8 including the step supplying fluid to said cylinder ends by means of fixed volume pumps.

11. A method as set forth in Claim 8 including the step driving said pumps for a single power source.

12. A method as set forth in Claim 8 including the step selectively flowing the fluid from both said first and second pumps to said fluid reservoir by means of said direction control valve, to unload both pumps simultaneously.

13. A method as set forth in Claim 8 including the step controlling the maximum pressure applied to each cylinder end by means of a pressure relief valve connected to the output of each pump.

14. A method as set forth in Claim 8 including the step controlling the acceleration and deceleration of the cylinder rod by means of said direction control valve.

1 5. A control system substantially as described with reference to, or as shown in, the drawing.

1 6. A method of controlling a double-acting hydraulic cylinder, substantially as described.