U.S. patent number RE29,538 [Application Number 05/576,107] was granted by the patent office on 1978-02-14 for load responsive fluid control valve.
Invention is credited to Tadeusz Budzich.
United States Patent |
RE29,538 |
Budzich |
February 14, 1978 |
Load responsive fluid control valve
Abstract
A direction and flow control valve for use in a central fluid
power load responsive system having plurality of loads. The valve
maintains a selected constant flow level for control of both
positive and negative loads, irrespective of the change in the load
magnitude or change in the fluid pressure, supplied to the valve.
System is powered by a single variable volume pump equipped with a
load responsive control, which automatically maintains pump
discharge pressure at a level higher than the pressure required by
the system's largest load. Each direction and flow control valve is
equipped with a differential pressure regulating control, which is
responsive to the load pressure for controlling the negative loads
and preferably a second differential pressure regulating control
for controlling the positive loads.
Inventors: |
Budzich; Tadeusz (Moreland
Hills, OH) |
Family
ID: |
26880838 |
Appl.
No.: |
05/576,107 |
Filed: |
May 9, 1975 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
185146 |
Sep 30, 1971 |
03744517 |
Jul 10, 1973 |
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Current U.S.
Class: |
137/596.2;
137/596.1; 91/446 |
Current CPC
Class: |
F15B
11/0445 (20130101); F15B 13/04 (20130101); F15B
13/0402 (20130101); F15B 13/0417 (20130101); Y10T
137/87241 (20150401); Y10T 137/87233 (20150401) |
Current International
Class: |
F15B
11/00 (20060101); F15B 13/00 (20060101); F15B
11/044 (20060101); F15B 13/04 (20060101); F15B
013/02 (); F15B 013/08 () |
Field of
Search: |
;137/596,596.2,596.12,596.13,117,501,503,596.1
;91/461,468,445,446,448,421 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Cohan; Alan
Assistant Examiner: Michalsky; Gerald A.
Attorney, Agent or Firm: Hogg; William N.
Claims
What is claimed is:
1. A valve assembly comprising a housing having a fluid inlet
chamber, .[.a.]. .Iadd.at least one .Iaddend.fluid load chamber, a
fluid outlet chamber, and a fluid exhaust means, .Iadd.signal
passage means between said load chamber and said outlet chamber,
.Iaddend.first valve means for selectively interconnecting said
load chamber with said inlet chamber.Iadd., said load chamber with
said signal passage means, and said load chamber with said signal
passage means .Iaddend.and said outlet chamber to meter fluid flow
to and from said load chamber, and second valve means
interconnecting said outlet chamber and said exhaust means .Iadd.,
said second valve means having means responsive to pressure in said
signal passage means and pressure in said outlet chamber and
.Iaddend.operable to maintain a constant pressure difference
between said load chamber and said outlet chamber when said load
.Iadd.chamber, said signal passage means .Iaddend.and .Iadd.said
.Iaddend.outlet chamber.[.s.]. are interconnected and said load
chamber is pressurized. .[.2. A valve assembly as set forth in
claim 1 wherein said second valve means is operable directly
responsive to fluid pressure in said load
chamber..]. 3. .[.Valve.]. .Iadd.A valve .Iaddend.assembly as set
forth in claim 1 wherein said first valve means includes a valve
spool axially guided in a spool bore and movable from a neutral
position to at least one actuated position, said valve spool
isolating said load chamber .[.from.]..Iadd., .Iaddend.said fluid
inlet chamber and said fluid outlet chamber .[.and.]. .Iadd.from
each other and blocking said signal passage means from
.Iaddend.said second valve means when in .[.the.]. neutral
position. 4. A valve assembly as set forth in claim 3 wherein said
housing includes a pressure signal passage interconnecting said
spool bore and said second valve means, said valve spool when
displaced from its neutral position toward an actuated position
first interconnecting said load chamber with said second valve
means through said pressure signal passage and then interconnecting
said load chamber with said outlet chamber.
.[. A valve assembly as set forth in claim 1 wherein said second
valve means includes a control spool guided in a bore
interconnecting said outlet chamber and said exhaust means..].
.[.6. A valve assembly as set forth in claim 5 wherein said control
spool is biased in one direction both by pressure in said outlet
chamber and by spring means and in the other direction by pressure
in said load chamber..]. .[.7. A valve assembly comprising a
housing having a fluid inlet chamber, a fluid supply chamber, a
fluid load chamber, a fluid outlet chamber and fluid exhaust means,
first valve means for selectively interconnecting said fluid load
chamber with said fluid supply chamber and said fluid outlet
chamber to meter fluid flow to and from said load chamber, second
valve means interconnecting said outlet chamber and said exhaust
means operable to maintain a constant pressure difference between
said fluid outlet chamber and said fluid load chambe when said load
chamber is pressurized and connected to said outlet chamber, and
third valve means interconnecting said fluid inlet chamber and said
supply chamber and operable to maintain a constant pressure
difference between said fluid load chamber and said fluid supply
chamber when said chambers are interconnected by said first valve
means and said supply chamber is pressurized..]. .[.8. Valve
assembly as set forth in claim 7 wherein said second valve means is
operable responsive to fluid pressure in said load chamber when
said load chamber is connected to said outlet chamber by said first
valve means, and said third valve means is operable responsive to
fluid pressure in said load chamber when said load chamber is
connected to said supply chamber by said first valve means..].
.[.9. A valve assembly as set forth in claim 7 wherein said first
valve means includes a valve spool axially guided in a spool bore
and movable from a neutral position to at least one actuated
position, said valve spool isolating said load chamber from said
fluid supply chamber and said fluid outlet chamber and said second
valve means and said third valve means when in the neutral
position..]. .[.10. A valve assembly as set forth in claim 9
wherein said housing includes a first signal passage
interconnecting said spool bore and said second valve means and a
second signal passage interconnecting said spool bore and said
third valve means, said first and second signal passages being
positioned such that when said valve spool is displaced from the
neutral position in one direction it first interconnects said load
chamber with said second valve means through said first signal
passage and then interconnects said load chamber with said outlet
chamber and when said valve spool is displaced in other direction
it first interconnects said load chamber with said third valve
means through said second signal passage and then interconnects
said
load chamber with said supply chamber..]. 11. A valve assembly
comprising a housing having a fluid inlet chamber, a fluid supply
chamber, first and second fluid load chambers, a fluid outlet
chamber and fluid exhaust means, first valve means for selectively
interconnecting said fluid load chambers with said fluid supply
chamber and said fluid outlet chamber to meter fluid flow to and
from said load chambers, second valve means interconnecting said
outlet chamber and said exhaust means and operable to provide a
passage between said outlet chamber and said exhaust means open
above a preselected pressure level in the load chamber connected by
said first valve means to said supply chamber and progressively
reduce said passage opening upon pressure in said load chamber
connected by said first valve means to said supply chamber dropping
below said preselected pressure level, and third valve means
interconnecting said fluid inlet chamber and said supply chamber
operable to maintain a constant pressure difference between said
fluid supply chamber and said fluid load chamber
connected thereto. 12. A fourway fluid control valve assembly
comprising a housing having an outlet chamber, first and second
load chambers, an inlet chamber, a valve bore in direct
communication with said aforementioned chambers, said valve bore
axially guiding a valve spool having lands, said valve spool having
a neutral position in which said lands isolate said chambers, an
exhaust chamber in said housing, valve means interconnecting said
outlet chamber and said exhaust chamber and operable to maintain a
constant pressure differential between either one of said load
chambers which is pressurized and said outlet chamber when
connected thereto, said valve means including a control spool
guided in a control bore, fluid throttling means on said control
spool to control fluid flow between said outlet chamber and said
exhaust chamber, said control spool being biased in a direction to
increase fluid flow by pressure in said outlet chamber when said
control bore is connected thereto and by spring means and in the
other direction by pressure in one of said load chambers when the
control bore is connected thereto and said load chamber is
pressurized, first pressure signal passage interconnecting one
region of said valve bore between said outlet chamber and said
first load chamber and said control bore, second pressure signal
passage interconnecting another region of valve bore between said
outlet chamber and said second load chamber and said control bore,
said first and second pressure signal passages being blocked by
said valve spool in its neutral position, said valve spool when
displaced from its neutral position in one direction first
interconnecting said first load chamber through said first pressure
signal passage to said control bore and then connecting said first
load chamber to said outlet chamber and said second load chamber to
said inlet chamber, said valve spool when displaced from its
neutral position in the opposite direction first interconnecting
said second load chamber through said second pressure signal
passage to said control bore and then connecting said second load
chamber to said outlet chamber and said first load chamber to said
inlet chamber, whereby the valve will control a load under
negative
load conditions. 13. A fourway fluid control valve assembly
comprising a housing having an outlet chamber, first and second
load chambers, a supply chamber, a valve bore in direct
communication with said aforementioned chambers, said valve bore
axially guiding a valve spool having lands, said valve spool having
a neutral position in which said lands isolate said chambers, an
exhaust chamber in said housing, first valve means interconnecting
said outlet chamber and said exhaust chamber and operable to
maintain a constant pressure differential between either one of
said load chambers which is pressurized and said outlet chamber
when connected thereto, said first valve means including a first
control spool guided in a first control bore, first fluid
throttling means on said first control spool, said first control
spool being biased in one direction by pressure in said outlet
chamber when connected to said first control bore and by spring
means and in the other direction by pressure in one of said load
chambers when connected thereto, an inlet chamber in said housing,
second valve means interconnecting said supply chamber and said
inlet chamber operable to maintain a constant pressure differential
between either of said load chambers when pressurized and said
supply chamber when connected thereto, said second valve means
including second control spool guided in a second control bore,
second throttling means on said second control spool to throttle
fluid flow between said inlet chamber and said supply chamber, said
second control spool being biased in a direction to lessen fluid
flow by pressure in said supply chamber when connected thereto and
in a direction to increase fluid flow by pressure in one of said
load chambers when connected thereto and spring means, first
pressure signal passage interconnecting one region of the valve
spool bore between said outlet chamber and said first load chamber
and said first control bore, second pressure signal passage
interconnecting another region of the valve spool bore between said
outlet chamber and said second load chamber and said first control
bore, a third pressure signal passage interconnecting another
region of valve spool bore between said first .[.second.]. load
chamber and said supply chamber and said second control spool,
.Iadd.a fourth pressure signal passage interconnecting another
region of the valve spool bore between said second load chamber and
said supply chamber and said second control spool, .Iaddend.said
first, second, third and fourth pressure signal passages being
blocked by said valve spool in its neutral position, said valve
spool when displaced from its neutral position in one direction
first interconnecting said first load chamber through said first
pressure signal passage to said first valve means and said second
load chamber through said fourth pressure signal passage to said
second valve means and then interconnecting said first load chamber
with said outlet chamber and said second load chamber with said
supply chamber, said valve spool when displaced from its neutral
position in opposite direction first interconnecting said second
load chamber through said second pressure signal passage to said
first valve means and said first load chamber through said third
pressure signal passage to said second valve means and then
interconnecting said second load chamber with said outlet chamber
and said first load chamber with said supply chamber, whereby the
valve will
control a load under both positive and negative load conditions.
14. A fourway fluid control valve assembly comprising a housing
having an outlet chamber, first and second load chambers, a supply
chamber, a valve bore in direct communication with said
aforementioned chambers, said valve bore axially guiding a valve
spool having lands, said valve spool having a position in which
said lands isolate said chambers, an exhaust chamber in said
housing, first valve means interconnecting said outlet chamber and
said exhaust chamber and operable to maintain passage between said
chambers open above preselected pressure level in said load chamber
connected to said supply chamber and progressively reduce said
passage upon pressure in said load chamber connected to said supply
chamber dropping below said preselected pressure level, said first
valve means including first control spool guided in a control bore,
first fluid throttling means on said first control spool, said
first control spool being biased in a direction to increase the
fluid passage by pressure in said load chamber connected to said
supply chamber and a direction to reduce fluid passage by spring
means, an inlet chamber in said housing, second valve means
interconnecting said supply chamber and said inlet chamber operable
to maintain a constant pressure differential between said load
chamber that is connected to the supply chamber and the supply
chamber, said second valve means including a second control spool
guided in a second control bore, second throttling means on said
second control spool, said second control spool being biased in a
direction to decrease fluid flow by pressure in said supply chamber
and in a direction to increase flow by pressure in the load chamber
and a spring means, first pressure signal passage interconnecting
an area of valve spool bore between said first load chamber and
said supply chamber and said second control spool, second pressure
signal passage interconnecting an area of valve spool bore between
said second load chamber and said supply chamber and said second
control spool, said first and second pressure signal passages being
blocked by said valve spool in its neutral position, said valve
spool when displaced from its neutral position in one direction
first interconnecting said first load chamber through said first
pressure signal passage to said second control spool and then
interconnecting said first load chamber to said supply chamber and
said second load chamber to said .[.second.]. outlet chamber, said
valve spool when displaced in opposite direction first
interconnecting said second load chamber with said supply chamber
and said first load chamber to said .[.first.]. outlet chamber,
whereby the valve assembly controls a load under both positive and
negative load conditions. .Iadd. 15. A fluid control valve assembly
comprising a housing having an outlet chamber, a load chamber, an
inlet chamber, a valve bore in direct communication with said
aforementioned chambers, said valve bore axially guiding a valve
spool having lands, said valve spool having a neutral position in
which said lands isolate said chambers, an exhaust chamber in said
housing, a valve means interconnecting said outlet chamber and said
exhaust chamber and operable to maintain a constant pressure
differential between said load chamber and said outlet chamber when
said load chamber is pressurized and connected thereto, said valve
means including a control spool guided in a control bore, fluid
throttling means on said control spool to control fluid flow
between said outlet chamber and said exhaust chamber, said control
spool being biased in a direction to increase fluid flow by
pressure in said outlet chamber and by spring means and in the
other direction by pressure in said load chamber when the control
bore is connected thereto and said load chamber is pressurized,
pressure signal passage interconnecting region of said valve bore
between said outlet chamber and said load chamber and said control
bore, said pressure signal passage being blocked by said valve
spool in its neutral position, said valve spool when displaced from
its neutral position in one direction first interconnecting said
load chamber through said pressure signal passage to said control
bore connecting said load chamber to said outlet chamber, said
valve spool when displaced from its neutral position in the
opposite direction interconnecting said load chamber to said inlet
chamber, whereby the valve will control a load under negative load
conditions. .Iaddend.
Description
BACKGROUND OF THE INVENTION
This invention relates generally to load responsive fluid control
valves and to fluid power systems incorporating such valves which
systems are supplied by a single variable displacement pump,
equipped with an automatic load responsive control, and in which
either one or a plurality of loads is individually controlled under
positive and negative load conditions by separate control
valves.
In more particular aspects this invention relates to direction and
flow control valves and load responsive fluid power systems
incorporating such valves capable of controlling simultaneously a
number of loads under both positive and negative conditions.
Closed center load responsive central hydraulic systems are very
desirable for a number of reasons. They permit load control with
minimum of power losses and therefore, at high system efficiency
and when controlling one load at a time provide a feature of flow
control, irrespective of the variation in the magnitude of the
load. In such a system a load responsive variable displacement pump
control automatically maintains pump discharge pressure at a level
higher, by constant pressure differential, than the pressure
required to sustain the load. A variable orifice, introduced
between pump and load, varys the flow supplied to the load, each
orifice area corresponding to a different flow level which is
maintained constant irrespective of variation in the magnitude of
the load. The application of such a system is, however, limited by
two basic system disadvantages. The pump control can maintain a
constant pressure differential and therefore constant flow
characteristics when operating only one load at a time. With two or
more loads, simultaneously controlled, only the highest of the
loads will retain the flow control characteristics, the speed of
actuation of the lower loads varying with the change in magnitude
of the highest load. This drawback can be overcome in part by the
provision of a proportional valve as disclosed in my U.S. Pat. No.
3,470,694, dated Oct. 7, 1969. However, while this valve is
effective in controlling positive loads it does not retain flow
control characteristics when controlling negative loads, which
instead of taking, supply the energy to the fluid system, and hence
the speed of actuation of such a load in a negative load system
will vary with the magnitude of the negative load. Especially with
so-called overcenter loads where a positive load may become a
negative load, such a valve will lose its speed control
characteristics in the negative mode.
.Iadd.Negative load can be controlled by valve disclosed in U.S.
Patent 3,534,774 issued to Tennis. However, this valve is capable
of controlling negative loads in one direction only and therefore
cannot be used with inertia type loads and loads driven by fluid
motors which require bi-directional control capability. Further,
the Tennis device does not isolate the load signal from the load
controller. .Iaddend.
SUMMARY OF THE INVENTION
It is therefore a principal object of this invention to provide an
improved valve for load responsive fluid power system, which will
retain system flow control characteristics when controlling both
positive and negative loads.
It is another object of this invention to provide improved valve
for load responsive fluid power system, in which multiplicity of
positive and negative loads can be controlled, while the system
speed control characteristics are retained.
It is a further object of the invention to provide an improved
valve for load responsive fluid power system, which converts the
energy of negative load by throttling, automatically maintaining a
constant pressure difference between the load pressure and the
valve outlet pressure.
.Iadd.It is a further object of this invention to provide an
improved valve capable of proportional control of negative loads in
both directions of motor operation.
It is a further object of this invention to provide a valve for
control of negative loads which when in neutral position will
isolate the valve controller from the negative load signal.
.Iaddend.
Briefly the foregoing and other additional objects and advantages
of this invention are accomplished by providing a novel flow
control valve, constructed according to the present invention, for
use in load responsive central hydraulic systems. A flow control
valve is positioned between variable pump and each motor. Each
valve has an automatic valve outlet throttling section; and, when a
plurality of valves are used, each also has an automatic inlet
throttling section. Since load responsive pump control can only
maintain a flow proportionality of one valve and one load at a time
and since it cannot control flow proportionality in control of
negative load, these valve inlet and outlet automatic throttling
controls provide a constant pressure differential across valve
spool, permitting retention of flow control characteristics, with
simultaneous control of all loads both positive and negative.
Additional objects of the invention will become apparent when
referring to the preferred embodiment of the invention as shown in
the accompanying drawings and described in the following detailed
description.
DESCRIPTION OF THE DRAWING
FIG. 1 is a longitudinal sectional view of one embodiment of a flow
control valve including the control mechanism used in control of
negative loads with system lines, pump and pump control shown
diagramatically;
FIG. 2 is a sectional view taken substantially along the plane
designated by the line 2--2 of FIG. 1;
FIG. 3 is a longitudinal sectional view of another embodiment of a
flow control valve including two control mechanisms used in control
of multiple positive and negative loads with additional valve,
pump, and power lines shown diagramatically; and
FIG. 4 is a longitudinal sectional view of still another embodiment
of flow control valve.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to the drawings, and for the present to FIG. 1,
embodiment of a flow control valve, generally designated as 10, is
shown interposed between diagramatically shown fluid motor 11
driving a load L and a variable flow pump 12, equipped with a
conventional displacement changing mechanism (not shown). The
output of the pump is regulated by a differential pressure
compensator control 13. This preferably is of the type shown in my
U.S. Pat. No. 3,444,689. The variable flow pump 12 is driven
through shaft 14 by a suitable prime mover, not shown.
The flow control valve 10 is a four-way type and has a housing 15
provided with a bore 16, axially guiding a valve spool 17. The
valve spool 17 is equipped with lands 18, 19 and 20, which in the
position shown will isolate fluid inlet chamber 21, load chambers
22 and 23 and outlet chambers 24 and 25 formed in the housing 15.
The outlet chambers 24 and 25 are cross-connected through passage
26 and are connected through passage 27 and bore 28 and guiding
control spool 29, to exhaust chamber 30.
The outlet of the pump 12 is connected through discharge line 31 to
inlet chamber 21. The inlet of pump 12 is connected through line 32
to diagramatically shown reservoir 33. Reservoir 33 is also
connected by line 34 to the exhaust chamber 30. Pressure sensing
passages 35 and 36 communicate with the bore 16 between inlet
chamber 21 and load chambers 22 and 23 respectively and are blocked
by land 19 of the valve spool 17 in its neutral position, as shown
in FIG. 1. The pressure sensing passages 35 and 36 are connected
through line 37 to differential pressure compensator 13. Movement
of the valve spool 17 to the right, from the position as shown,
will connect first the pressure sensing passage 35 to the load
chamber 22 and then connect the load chamber 22 with the inlet
chamber 21. Movement of the control spool 17 to the left will first
connect the pressure sensing passage 36 to the load chamber 23 and
then connect the load chamber 23 with the inlet chamber 21.
As described in U.S. Pat. No. 3,444,689, the differential pressure
compensator control adjusts pump flow to regulate the pump
discharge pressure in response to the load pressure signal
transmitted through line 37. In absence of any signal,
corresponding to the blocked position of sensing passages 35 and 36
as shown in FIG. 1, the pump control automatically brings the
variable pump into zero flow condition, at a minimum preselected
pressure level, thus operating at minimum standby power loss.
Movement of the land 19 of valve spool 17 to right will connect
pressure sensing passage 35 to load chamber 22 and transmit the
load pressure signal through line 37 to differential pressure
compensator control 13. The differential pressure compensator
control 13 will then automatically adjust the displacement of
variable pump 12 to maintain its discharge pressure and therefore
pressure in the inlet chamber 21 at a level higher, by a fixed
pressure differential, than the load signal pressure in the load
chamber 22.
Further movement of land 19 to the right will connect inlet chamber
21 to load chamber 22, resulting in a fluid flow from chamber 21
through line 22A to the fluid motor. Since the pressure in chamber
21 is maintained at a fixed pressure differential with respect to
load chamber 22 by the variable pump control, the volume of flow
per unit time will be proportional to the area of the orifice
opened between chambers 21 and 22 and constant for each specific
area, irrespective of the actual pressure level in the load chamber
22. Since the area of the orifice between chambers 21 and 22 is
proportional to the travel of the valve spool 17, the fluid flow
from inlet chamber 21 to load chamber 22 will also be proportional
to the displacement of the valve spool 17, each specific position
of the valve spool 17 corresponding to a specific constant fluid
flow level, irrespective of the magnitude of the pressure level
required to operate the load.
In a similar fashion, with movement of the valve spool 17 in
opposite direction, the fluid from inlet chamber 21 to load chamber
23 is controlled and supplied to the opposite end of the fluid
motor through line 23A. The foregoing regulation is in the positive
load mode and does not per se constitute the present invention. The
regulation in the negative load mode will now be described.
Additional pressure sensing passages 38 and 39 are provided in the
bore 16 between the load chamber 22 and outlet chamber 24 and
between load chamber 23 and outlet chamber 25 respectively. The
pressure sensing passages 38 and 39 are connected by passage 40
with a fluid receiving space 41. Control spool 29, guided in bore
28, is equipped with longitudinally extending grooves 42
terminating in metering edge 43 providing communication between
outlet chamber 25, passage 26, outlet chamber 24, passages 27, and
exhaust chamber 30. (See also FIG. 2) Movement of control spool 29
from right to left will gradually reduce the effective area of the
grooves 42, eventually metering edge 43 cutting off communication
between passage 27 and exhaust chamber 30.
Movement of the control spool 29 from right to left is opposed by
differential spring 44, normally biasing control spool 29 into the
fully open position shown in FIG. 1. Space 41 is connected through
resistance orifice 45, drillings 46 and 47 to exhaust chamber 30.
Movement of the valve spool 17 from left to right will open at
first pressure sensing passage 35 to load chamber 22 and pressure
sensing passage 39 to load chamber 23. Pressure in load chamber 22,
transmitted through pressure sensing passage 35 will activate,
through line 37, the differential pressure compensator 13, in the
manner as previously described. Simultaneously, pressure signal
from load chamber 23 will be supplied through sensing passage 39
and will be transmitted to space 41 through passage 40.
Assume that the positive load generates a positive sustaining
pressure in load chamber 22. Then the load chamber 23 will be at
zero pressure and therefore zero pressure signal is transmitted
through pressure sensing passage 39 to space 41. Further movement
of valve spool 17 from left to right will connect load chamber 22
to inlet chamber 21 and load chamber 23 to outlet chamber 25. Since
in the position as shown control spool 29 connects outlet chamber
25 with exhaust chamber 30, the fluid flows from inlet chamber 21
to load chamber 22 and through line 22A to fluid motor 11 and out
of fluid motor 11 through line 23A to load chamber 23 and outlet
chamber 25, which through passage 26, outlet chamber 24, passage
27, and control spool 29 is connected to exhaust chamber 30, which
in turn through line 34 is connected to reservoir 33. For the
positive load condition as just described the speed of the fluid
motor is fully controlled by the area of the orifice between the
inlet chamber 21 and load chamber 22 and the fixed pressure
differential, maintained between these two chambers, by the
differential pressure compensator control.
However, assume that during the above actuation of the fluid motor
the load characteristics changed from positive to negative. With
the valve spool 17 displaced to the right the pressure in the load
chamber 22 would drop to zero. This pressure signal, transmitted
through the pressure sensing passage 35, would bring the pump
discharge pressure to the minimum standby level through the
differential pressure compensated control, the pump automatically
supplying required flow at this minimum pressure level. Due to the
action of the negative load the pressure would be generated in load
chamber 23 and this pressure signal transmitted through pressure
signal passage 39 and passage 40 to space 41. Also, the pressure in
the load chamber 23, reacting on the cross-section area of control
spool 29, overcomes the preload force of differential spring 44,
moving the control spool 29 from right to left. This movement will
reduce the effective area of grooves 42 as the metering edge 43
approaches cut-off face 50. Resistance to flow through grooves 42
will raise the pressure in the passage 27 and outlet chamber 25
until a condition of force equilibrium is achieved. Under this
condition of equilibrium, force generated due to pressure in load
chamber 23 transmitted to space 41 through passage 40, reacting on
the cross-section area of valve spool 29, is balanced by the force
generated due to the pressure in passage 27, acting on the
cross-section area of control spool 29 plus the biasing force of
differential spring 44. Therefore under these conditions, control
spool 29 will automatically assume a throttling position,
maintaining a constant pressure differential between load chamber
23 and outlet chamber 25. This constant pressure differential is
equal to preload of differential spring 44 divided by cross-section
area of the control spool 29.
Since modulating control spool 29 maintains by throttling action a
constant pressure differential between load chamber 23 and outlet
chamber 25, flow between these two chambers will be directly
proportional to the area of orifice created by valve spool 17
between these chambers and constant for each particular value of
this area irrespective of the pressure level in load chamber 23
sustaining the negative load. Preload in the differential spring 44
can be so selected that the equivalent constant pressure
differential is the same as the constant pressure differential,
regulated by the pump control. In this way the flow control
characteristics of the valve can be maintained in both directions
of fluid motor operation irrespective of the magnitude of the
positive or negative load.
When starting with a negative load, displacement of the valve spool
17 in appropriate direction will transmit first a zero pressure
signal to the pump control and a load sustaining pressure signal to
the control spool 29. Since at that time the load chamber
sustaining the negative load pressure is still isolated from the
outlet chamber, the control spool 29 will move all the way from
right to left under the generated load pressure, isolating passage
27 from the exhaust chamber 30. Further movement of valve spool 17
will connect the pressurized load chamber with the outlet chamber,
gradually increasing the pressure in passage 27, until control
spool 29 moves to its modulating position maintaining a constant
pressure differential in a manner as already described. In this way
flow control feature will be retained during operation of negative
load.
Movement of the valve spool 17 from right to left from the position
shown will actuate the fluid motor 11 in the opposite direction,
with the chamber 23 becoming the inlet chamber and chamber 24
becoming the outlet chamber. Thus the valve is double acting in
that it controls negative loads in either direction of
movement.
To allow for leakage and increase stability of the control a
resistance orifice 45 is provided which connects space 41 through
passages 46 and 47 with exhaust chamber 30. The area of resistance
orifice 45 is very much smaller than the area of pressure signal
passages 38 and 39.
Referring now to FIG. 3, another embodiment of a flow control
valve, generally designated as 51, is shown interposed between
fluid motor 11 and variable displacement pump 12. A second similar
schematically shown flow control valve 52 is interposed between a
second fluid motor 53 and the variable displacement pump 12. The
general configuration of the flow control valve 51, including the
valve spool 17, control spool 29, position of the outlet and load
chambers and location of the pressure sensing passages are
identical to FIG. 1 and the valve operates in an identical manner
to control negative loads. However this valve will also control
positive loads. The mechanism for this function is as follows.
Supply chamber 21A is connected through passages 54 and 55, of
inlet control valve 55A, to inlet chamber 56, through which line 57
is connected to the outlet port of the pump. Load sensing line 37,
in communication with load sensing passages 35 and 36, is connected
through check valve 57A and line 60 to differential pressure
compensator 13. Similarly, control valve 52 is connected through
load sensing line 58 and check valve 59 and line 60 to the
differential pressure compensator control. Load sensing line 37 is
connected through line 60A to space 61. The control valve 55A which
extends into space 61 is biased towards position as shown by
differential spring 62. (As noted above, the operation of control
valve 29 of FIG. 3 is identical to operation of control valve 29 of
FIG. 1, the control valve maintaining a constant pressure
differential between appropriate load chamber and outlet chambers
24 and 25 and passage 27.)
Assume the flow control valve 51 is actuated, the flow control
valve 52 remaining in its neutral position. Assume that when
actuating the flow control valve 51 the spool valve 17 was moved
from left to right, connecting load sensing passage 35 to load
chamber 22. Assume that load chamber 22 is subjected to pressure
sustaining positive load. Pressure signal from load sensing passage
35 will be transmitted through lines 37 and through check valve 57A
and line 60 to differential pressure compensator control 13, which
in a manner as previously described, will adjust the displacement
control of variable volume pump 12 to maintain inlet chamber 56 at
a pressure higher by a fixed pressure differential than the
pressure in load chamber 22.
The pressure signal from line 37 will also be transmitted through
line 60A to space 61. Control valve 55A is then subjected to pump
discharge pressure, transmitted through passages 55 and 54 to
supply chamber 21A, acting on the cross-sectional area of the
control valve 55A in one direction and the pressure existing in
load chamber 22, connected to space 61, acting on the cross-section
of control valve 55A, plus the preload of the differential spring
62 in the opposite direction. As already mentioned the pressure in
space 61 is always smaller by a constant pressure differential than
the discharge pressure of the pump and therefore pressure in inlet
chamber 56 and supply chamber 21A. The preload in the differential
spring 62 is so selected that it equals this constant pressure
differential, multiplied by the cross-section area of control valve
55A so the control valve 55A, subjected to these forces, will
remain in position as shown in FIG. 3. Therefore as long as
differential pressure compensated control 13 controls the variable
flow pump 12 to maintain a constant pressure differential between
pump discharge pressure and the appropriate load chamber pressure,
the control valve 55A will remain inactive. Under these conditions
flow control valve 51 will perform in an identical way as control
valve 10 of FIG. 1, when controlling both positive and negative
loads.
However, assume that the flow control valves 51 and 52 are actuated
simultaneously. In this case the flow control valve, having the
highest load controls the output pressure from the pump due to well
known action of check valves 57A and 59 whereby the higher load
pressure signal will be transmitted from control valve 52 to
differential pressure compensator control 13.
Assuming that the load from motor 53 is higher the check valve 59
passes the signal but check valve 57A isolates the higher pressure
signal from lines 37 and 60A. In a manner as previously described,
the differential pressure compensator control 13 will respond to
the load control signal from flow control valve 52, the flow
control valve 52 fully retaining flow control features in control
of the higher load. However in the case of valve 51 the pump
discharge pressure in line 57 will exceed the control fixed
pressure differential, disturbing the equilibrium of the control
valve 55A. Under the action of unbalanced forces, control valve 55A
will move from right to left, gradually moving metering edge 63 of
control valve 55A toward face 64, thus reducing the effective area
between inlet chamber 56 and supply chamber 21A. The movement will
continue which will reduce the pressure in chamber 21A until
equilibrium is restored. Since, as previously described, the
preload in the differential spring 62 is equal to the product of
the constant differential pressure of the pump control and
cross-section area of the control valve 55A, the control valve 55A
will modulate, throttling the excess pressure in the inlet chamber
56 and maintain the supply chamber 21A at a fixed pressure
differential above the load signal from the appropriate load
chamber. If the load should become negative, the pressure in the
load chamber 22 would drop to or near zero. This would cause the
valve 55A to move further from right to left, throttling most of
the pressure of chamber 56 to maintain constant pressure
differential between supply chamber 21A and load chamber 22.
Simultaneously the pressure in the load chamber 23 would increase
actuating the valve 29 as previously described to control the
negative load.
In this way both valves 52 and 51 when operated simultaneously will
fully retain the flow control characteristics in control of both
positive and negative loads. Valve 51 also is double acting and
will control both positive and negative loads in either direction
depending upon the direction of movement of valve spool 17.
Referring now to FIG. 4, yet another flow control valve generally
designated as 65 is shown. This valve is similar to that of FIG. 3
with respect to control of positive loads but has a modified
negative load control section. A negative control spool 66 is
located in a bore 67 connecting outlet chambers 25 and 24 and an
exhaust chamber 68. In its normal position control valve 66, under
action of differential spring 69, maintains the passage between
outlet chambers and exhaust chamber 68 closed. Space 70 is
connected with pressure sensing passages 35 and 36 through lines 37
and 71.
Assume that valve spool 17 was moved from left to right connecting
first pressure sensing passage 35 to pump differential pressure
compensator control and then connecting load chamber 22 with supply
chamber 21A and load chamber 23 with outlet chamber 25. Assume also
that chamber 22 is subjected to pressure of a positive load. In a
manner as previously described, a pressure signal from the
compensator control will be supplied through pressure sensing
passage 35 to the pump control, adjusting it accordingly. A
pressure signal will also be supplied from the compensator control
to space 70. Pressure in space 70 acting on cross-sectional area of
control valve 66 will move it from right to left against preload of
differential spring 69, opening the passage between exhaust chamber
68 and outlet chambers 25 and 24 and will maintain it open as long
as a positive load is operated from load chamber 22.
Assume that midway through the actuation the positive load would
become a negative load and the pressure in the load chamber 22
would start dropping to zero level. The differential pressure
compensator control will still maintain a constant pressure
differential between supply chamber 21A and load chamber 22.
However, since load chamber 23 is connected to outlet chamber 25
and since load chamber 23 is now pressurized, due to the action of
negative load, the speed of actuation of the negative load will
tend to increase, further reducing pressure in the load chamber 22.
Since load chamber 22 is connected with space 70 through pressure
sensing passage 35 and lines 37 and 71, the differential spring 69
will move the control valve 66 from left to right. This will
restrict the passage opening around bore 67 thus increasing the
pressure in the outlet chamber 25. This increase in pressure in
outlet chamber 25 will reduce the pressure differential between
load chamber 23 and outlet chamber 25, proportionally reducing the
flow between these two chambers. This in turn will tend to increase
the pressure in the load chamber 22 and therefore pressure in space
70, modulating the throttling action of the control valve 66, to
maintain flow control during operation of negative load. In this
way control valve 65 of FIG. 4 is capable of controlling in a
multiple load system both positive and negative loads. This valve
also is double acting in that it can control in either direction of
movement of the motor.
Although preferred embodiments of this invention have been shown
and described in detail it is recognized that the invention is not
limited to the precise forms and structure shown and various
modifications and rearrangements as will readily occur to those
skilled in the art upon full comprehension of this invention may be
resorted to without departing from the scope of the invention as
defined in the claims.
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