U.S. patent number 3,707,881 [Application Number 05/121,713] was granted by the patent office on 1973-01-02 for control system for hydraulic fluid-feed mechanism.
This patent grant is currently assigned to Friedrich Uhde GmbH. Invention is credited to Heinz Neuhaus, Henning Peters.
United States Patent |
3,707,881 |
Neuhaus , et al. |
January 2, 1973 |
CONTROL SYSTEM FOR HYDRAULIC FLUID-FEED MECHANISM
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.
Inventors: |
Neuhaus; Heinz (Am Hoing 21,
DT), Peters; Henning (Am Kamp 24, DT) |
Assignee: |
Friedrich Uhde GmbH (Dortmund,
DT)
|
Family
ID: |
5764803 |
Appl.
No.: |
05/121,713 |
Filed: |
March 8, 1971 |
Foreign Application Priority Data
|
|
|
|
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Mar 12, 1970 [DT] |
|
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P 20 11 570.2 |
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Current U.S.
Class: |
91/306;
91/308 |
Current CPC
Class: |
F04B
9/113 (20130101); F16K 11/0716 (20130101); F01L
25/063 (20130101); F01L 15/08 (20130101) |
Current International
Class: |
F16K
11/065 (20060101); F16K 11/07 (20060101); F01L
15/08 (20060101); F01L 25/06 (20060101); F04B
9/00 (20060101); F01L 15/00 (20060101); F04B
9/113 (20060101); F01L 25/00 (20060101); F01l
025/06 () |
Field of
Search: |
;91/308,306,305 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Maslousky; Paul E.
Claims
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 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.
Description
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 of
liquid 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 or six
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 full-load
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 object of the invention is to provide a control system without
the inherent disadvantages described above and which features
extremely short travels of acceleration and deceleration while the
full pressure acts upon the working piston.
Surprisingly, the problem was solved by attaching a return spring
to the control piston of each limit control valve and by tying-in
to the leak-oil connection the interlocking line for the control
fluid between the second limit control or pilot valve and the
multiway valve. The return spring is attached to the control piston
so that 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
a pressure 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 10 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 two
dual 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 1a, 1b 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'a, 3'b 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 shut-off 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.
* * * * *