US3707881A - Control system for hydraulic fluid-feed mechanism - Google Patents

Abstract

In a control for a hydraulic cylinder, incorporating a hydraulically actuated reversing valve, the reversing time at each end of the stroke is minimized by the use of pilot valves each of which is spring urged to its retracted position and is hydraulically urged to its extended position by hydraulic pressure applied to its piston and to the reversing valve by way of the other pilot valve. In operation, the retracting motion of a first pilot valve is initiated mechanically and completed by spring force as a second pilot valve releases the extending pressure as it is moved to extended position by hydraulic fluid flowing through the first pilot valve.

Description

United States Patent 91 Neuhaus et al.

[ 51 Jan. 2, 1973 154] CONTROL SYSTEM FOR HYDRAULIC FLUID-FEED MECHANISM [73] Assignee: Friedrich Uhde GmbH, Dortmund,

Germany [22] Filed: March 8, 1971 [21] Appl. No.: 121,713

[30] Foreign Application Priority Data March 12, 1970 Germany ..P 20 11 570.2

[52] US. Cl ..9l/306, 91/308 [51] Int. Cl ..F01l 25/06 [58] Field of Search ..91/308, 306, 305

[56] References Cited V UNITED STATES PATENTS 1,577,914 3/1926 Cain ..9l/308 2,296,647 9/1942 McCormick ..91/308 Witt ..9l/308 Pelisson ..9l/308 Primary Examiner-Paul E. Maslousky Attorney-Marshall & Yeasting [5 7 ABSTRACT In a control for a hydraulic cylinder, incorporating a hydraulically actuated reversing valve, the reversing time at each end of the stroke is minimized by the use of pilot valves each of which is spring urged to its retracted position and is hydraulically urged to its extended position by hydraulic pressure applied to its piston and to the reversing valve by way of the other pilot valve. In operation, the retracting motion of a first pilot ,valve is initiated mechanically and completed by spring force as a second pilot valve releases the extending pressure as it is moved to extended position by hydraulic fluid flowing through the first pilot valve. I

3 Claims, 5 Drawing Figures JIB PATENTEDJAHZ 1 7 Y 3.707.881

SHEET 2 OF 4 FIG. 3

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A T TOR NEYS PATENTEDJM 2 1915 saw 3 or 4 INVENTOR. HEI NZ NEUHAUS BY Wadi DR. HENNING PETERS ATTORNEYS CONTROL SYSTEM FOR HYDRAULIC FLUID- FEED MECHANISM BACKGROUND OF THE INVENTION The present invention relates to a control system for hydraulic fluid-feed mechanisms intended to produce straight-line reciprocating motions that are typical preferably for piston pumps and plunger pumps and machine tools.

Referring to hydraulic fluid-feed mechanisms, the hydraulic fluid, usually oil, passes through an open or a closed circuit and is admitted by a motor-driven variable-delivery or constant-delivery pump via a multiway or reversing valve alternately to the two sides of the working piston. The working piston moves towards the pressureless cylinder end and, by means of a rigid linkage, its motion is transferred to the working machine, for example to the plungers or pistons of pumps or to the carriages of machine tools.

Limit control valves or limit switches are intended to effect the change-over of the multiway valve. While fluid delivered by the hydraulic pump is admitted through the multiway valve into the cylinder to one side of the piston, the fluid on the other side of the piston leaves the cylinder at low pressure through the multiway valve into the return or reflux line.

The control system for hydraulic fluid-feed mechanisms, therefore, consists essentially of the two limit control valves or limit switches, the multiway valve and, possible, impulse amplifiers.

Referring to plunger pumps and reciprocating carriages of machine tools, it is known to make efforts to achieve a diagram of motion that features very short travels of acceleration and deceleration and also very short periods of acceleration and deceleration. Pressurizing and depressurizing at the points of reversal shall not be gradual, but rapid.

Referring to plunger pumps used for handling and metering liquids at high and supra-high pressures in industrial processes, this means that two plungers must be sufficient to achieve an almost continuous delivery and metering of the liquid at virtually constant pressure. Referring, for example, to processes for the manufacture of low-density polyethylene, the continuity of the temperature level in the process depends on the continuity ofliquid catalyst injection into the reaction chambers. The continuity of the temperature level, in turn, has an influence on the product quality.

' Referring to the carriages of machine tools carrying a workpiece to be machined, short travels and periods, respectively, of acceleration and deceleration mean a substantial reduction of dead periods and machining time.

Consequently, optimum process conditions and economical machine-shop fabrication are conditional upon the right selection and design of the control system.

Limit control elements may operate upon the multiway valve either mechanically or through hydraulic, pneumatic or electric transmission.

Where mechanical limit control elements are used, the multiway valve must be located in the vicinity of said elements because they operate directly on the multiway valve. The disadvantage of these mechanical limit control elements is that they do not open quickly the entire necessary cross-sectional area in the multiway valve for the hydraulic fluid; instead, the rate of opening is proportional to the speed of the reciprocating machine element. Where hydraulic, pneumatic or electric limit control elements are used, the multiway valve may be located at a distance from said elements. The conventional hydraulically or pneumatically operating limit control valves have, however, the disadvantage that the control piston is actuated through its entire stroke by the reciprocating machine element; this means that the control piston moves at a speed that corresponds to the speed of the reciprocating machine element. This speed, however, is insufficient for the reversing action.

Referring to pneumatically controlled hydraulic fluid-feed mechanisms, the reversing action can be shortened by using a pneumatic limit control valve with a very short travel followed by a series of pneumatic amplifiers of progressively upward rating depending on the rating of the hydraulic multiway valve. Obviously, this system is necessarily very expensive.

A quick reversing action can also be achieved by using an electrically operating control system consisting of limit control element and multiway valve. However, electric control devices also have inherent disadvantages, such as wear of contactors, faulty contacts, difficulties in locating faults in the electric system and an expensive design for use in areas or plants where explosion hazards are encountered.

For delivery pumps or metering pumps it is frequent practice to use a multicylinder dual arrangement, for example, with four orsix cylinders. In this way, the total delivery of, for example, 60 liters/hr. can be split for being handled by three dual pumps of 20 liters/hr.

each. This method makes it possible to disconnect pairs of cylinders for periods of part-loads or repair. For fullload service of such a pump at the necessary synchronized travel of the various pairs of pistons it has so far been necessary to install expensive synchronizing devices.

SUMMARY OF THE INVENTION the action of force of the return spring is opposed to the direction of motion of the control piston when the interlocking pressure becomes effective. It is another feature of the invention that the working piston of two or more mechanisms can be connected in parallel in that the limit control valves of one side, i.e., of the same direction of motion, of several mechanisms are interconnected through the interlocking lines of these limit control valves. The limit control valves for the opposite direction of motion are not interconnected.

The invention incorporates the particular advantage that, referring to the limit control valve, a minute initiating stroke measuring a fraction of a millimeter is sufficient to achieve a rapid control stroke of several millimeters and, consequently, to cause a quick breakdown of the pressure on one side of the working piston and a quick build-up of pressure on the opposite side of the piston. Referring to piston pumps and plunger pumps, this method makes it possible to obtain an almost ideal rectangular discharge diagram. The pressure on the working piston remains effective until the piston has reached its end position, then breaks down suddenly while becoming fully effective on the opposite side. Referring to carriages of machine tools, the use of the subject control system results in very short dead periods and, consequently, reduced machining time.

Another advantage of the invention is that the control cam on the working piston rod will contact the head of the control piston for a short time only and move it a fraction of a millimeter into the valve. The return spring then acts to draw the head of the control piston away from the control cam. The limit control valve cannot be damaged by the control cam or the working piston rod.

Referring to multicylinder dual pumps, full synchronism of the mechanisms can be achieved simply by interlocking the limit control valves for one direction of motion of all mechanisms. One or several connecting lines only are necessary. There is no need for additional synchronizing facilities that might be a source of disturbances.

BRIEF DESCRIPTION OF THE DRAWINGS Examples of application of the invention are illustrated in the accompanying drawings.

FIG. 1 is a schematic diagram of a hydraulic cylinder control system constructed according to the invention with the parts shown in neutral positions.

FIG. 2 is a cross section of a limit control valve or pilot valve used in the control system of FIG. 1, with the valve stem in extended position.

FIG. 3 is similar to FIG. 2 with the valve stem in retracted position.

FIG. 4 is a schematic diagram similar to FIG. 1 showing the valve positions as a transfer or reversal of the power cylinder is being completed.

FIG. 5 is a schematic diagram of two control systems connected for synchronous operation.

DESCRIPTION OF A PREFERRED EMBODIMENT Referring to FIG. 1, the hydraulic fluid-feed mechanism consists essentially of the system comprising the mechanism and the control and interlocking facilities. In the fluid-feed mechanism A, the fluid is admitted through multiway valve 1 alternately to the two sides of working piston 2 by means of a pump that has been omitted from the drawing for better clarity. The fluid returns from the depressurized cylinder end through the multiway valve 1 to a pump suction tank. The pump for the control system S the pump has also been omitted from the drawing --produces the constant control pressure ahead of limit control or pilot valves 3 and 3'. Through these valves, the control pressure acts alternately upon the two sides of the multiway valve to produce a reciprocating motion of its piston 4. The interlocking system V consists of the limit control valves with the control lines between limit control valves 3 and 3 and multiway valve 1. Return lines R on the limit control valves are provided to achieve an alternate pressure release on piston 4 in the multiway valve.

Each of the two limit control valves, as shown in FIGS. 2 and 3, consists essentially of a valve body 5, two covers 6 and 7, control sleeve 8, control piston 9 and return spring 10. Valve body 5 is provided with a pressure control-fluid connection B, a return connection C and a connection D for an interconnecting line between the limit control valve 3 and the multiway valve 1. Each cover 6 is provided with a connection E for one of the interlocking lines V. Referring to known control systems, this connection serves for leak oil discharge- The limit control valve has two stable positions: a working position and a zero position. In the working position, as shown in FIG. 2, the control piston 9 extends from the valve in position to be actuated by the moving machine, for example a plunger pump. In the zero position, the return spring has drawn the control piston into the valve. Regarding the control system with reference to the limit control valves there is a static state, i.e., with one valve in the working position while the second valve is in the zero position, and a dynamic state, i.e., in which the control piston of one valve is traveling from the working position into the zero position while the control piston of the second valve is moving from the zero position into the working position. The sequence of control actions accomplishing the change from the working position to the zero position and vice versa may be described as follows:

Referring to FIGS. 2, 3, and 4, the control piston is forced into the extended or working position by the pressure in one line of the interlocking system and against the force of the return spring, the pressure being admitted through connection E. The return spring is being compressed. Connections D and C are communicating with return line R through piston recess 11 and are, therefore, pressureless. Control line 12 connected at D and leading to the multiway valve is also pressureless. The control pressure admitted to connection B remains ineffective because the flow from B through piston recess 13 is obstructed. As soon as a cam 14 on the working piston rod contacts piston head roller 15 of the control piston, the latter will start moving into the valve and establish communication between connection B and connection D through piston recess 13 as may be noted from FIG. 3.

Referring to limit control valve 3 of FIG. 4, the pressure becomes'effective from B through D, and control line 16 upon piston 4 of multiway valve 1 and through interlocking line 17 and connection E of limit control valve 3. The pressure acting upon piston 4 in the multiway valve effects a reversal of the direction of flow of the fluid-feed for the mechanism. In limit control valve 3, the control piston is caused to move up into the working position against the force of the spring 10. Through the displacement of the control edges, the existing connection from B to D is interrupted while the communication between D and C is being established. From C, the fluid is released into the return line.At the same time, there is apressure release in line 12 and interlocking line 18 with a consequent drop in the pressure beneath the spring 10 of valve .3 and an immediate expansion of the spring moving the control piston into zero position. Pressure build-up in lines 16 and 17 and pressure release in lines 12 and 18 take place simultaneously.

Thus by means of return spring whose force acts against the pressure at connection E, a short mechanically indicated stroke and a short initiating control period are transformed into a long effective stroke at a very short effective control period. The cross-sectional areas for the passage of the fluid in all of the control elements are thus opened suddenly and independently of the speed of the working piston. After reversal, the full control pressure of system S is admitted rapidly upon the piston of the multiway valve. The fluid-feed for the mechanism passes at full pressure and full flow through alternate routes of the multiway valve into the cylinder of the working piston. The rapid reversal of the piston in the multiway valve effects a sudden and simultaneous loading and unloading of the working piston in either end position.

The control system for a multicylinder mechanism, for example twodual pumps, may comprise a plurality of systems as shown in FIG. 5 interconnected to operate in synchronism. In this figure a first system similar to that shown in FIGS. 1 and 4 is shown in the upper part of the figure and the parts identified with corresponding numerals with a suffix a. A second similar system is shown in the lower part of the figure and the parts identified with corresponding numerals with a suffix b. The two systems and any others to be operated in synchronism therewith are connected by leads b and c. The pump for the fluid-feed is adequately sized to permit simultaneous operation of both working pistons. The several fluid-feed mechanisms A are connected to the pump discharge line at a. One multiway valve la, lb and two limit control valves 3a, 3'a; 3b, 3'b with control system and interlocking system are associated with each working piston. The two control systems are fed from one pump and are interconnected through connection b. Synchronous operation of the two working pistons is achieved by interconnecting the two control lines 12a, 12b through connection c.

Through the connection of control lines 12a, 12b, the interlocking lines 18a, 18b are also connected to each other. The two limit control valves 3'0, 3b for the opposite direction of travel are not interconnected or interlocked since the pressure changes in the lines 12a, 12b; 18a, 18b as a result of operating one pair of limit control valves can hydraulically operate the other interconnected pairs of valves.

Depending on the size of the fluid-feed pump, several systems can be served as shown in FIG. 5, and the total discharge flow rate increased. The installation of shutoff valves or change-over valves on the interconnecting lines makes it possible to disconnect individual systems, for example for part-load operation or repair work.

We claim:

1. A control system for a hydraulically actuated valve of a hydraulic power cylinder assembly comprising, in combination, a pair of limit control valves, a spring in each limit control valve for urging the valve in a first direction, a piston and cylinder in each limit valve for urging the valve in a second direction, means responsive to approach of the power cylinder assembly to an end of its stroke for initiating movement of one of the limit control valves, ports in each limit control valve and fluid conduit means connecting a source of contro fluid through the ports in one limit control valve to the piston and cylinder of the other limit control valve and to an end of the hydraulically actuated valve, said piston and cylinder and said spring cooperating to position the limit control valve in response to control fluid supplied through the other limit control valve following an initial movement of one of the limit control valves.

2. A limit control valve according to claim 1 in which the spring urges the valve toward its inactive position and the fluid pressure admitted through the other valve to the piston and cylinder urges the valve toward its working position.

3. A limit control valve system according to claim 1 including fluid conduit means interconnecting first ones of a plurality of pairs of limit control valves in parallel for synchronous operation.

Claims (3)

1. A control system for a hydraulically actuated valve of a hydraulic power cylinder assembly comprising, in combination, a pair of limit control valves, a spring in each limit control valve for urging the valve in a first direction, a piston and cylinder in each limit valve for urging the valve in a second direction, means responsive to approach of the power cylinder assembly to an end of its stroke for initiating movement of one of the limit control valves, ports in each limit control valve, and fluid conduit means connecting a source of control fluid through the ports in one limit control valve to the piston and cylinder of the other limit control valve and to an end of the hydraulically actuated valve, said piston and cylinder and said spring cooperating to position the limit control valve in response to control fluid supplied through the other limit control valve following an initial movement of one of the limit control valves.

2. A limit control valve according to claim 1 in which the spring urges the valve toward its inactive position and the fluid pressure admitted through the other valve to the piston and cylinder urges the valve toward its working position.

3. A limit control valve system according to claim 1 including fluid conduit means interconnecting first ones of a plurality of pairs of limit control valves in parallel for synchronous operation.

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