Note: Descriptions are shown in the official language in which they were submitted.
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Eull~ Compensaked Fluid Control Valve
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Background of the Invention
This invention relates generally to fluid
control valves provided with positive and negative load
compensation.
In more particular aspects this invention
relates to direction and flow control valves capable of
proportionally controlling a number of loads under
positive and negative load condi-tions.
In still more particular aspects -this
invention relates to pressure compensated direction and
flow control valves, the positive and negative load
compensators of which are controlled by a signal
amplifying pilot valve stage.
Closed center fluid control valves, pressure
compensated for control of positive and negative loads,
are desirable for a number of reasons~ They permit
load control with reduced power losses and therefore
increased system efficiency. They also permit
simultaneous proportional control of multiple positive
and negative loads. Such fluid control valves are
shown in my patent 4,180,098, issued December 5, 1979
and also in my patent 4,222,409, issued September 16,
1980. However, the valves of those patents, although
capable of proportional control of positive and
negative loads, use for such control the energy
directly transmitted through the load pressure sensing
ports, which not only attenuate the control signal, but
limit the response of the control.
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Summary of the Invention
It is therefore a princlpal object of this invention -to
provide an improved pressure compensated valve, equipped for
posi-tive and negative load compensation, in which the positive
and negative load compensa-tor is controlled by a single amplifying
pilot valve .stage.
According to the invention there is provided a valve
assembly supplied wïth.press.ure fluid ~y a pump, said valve
assembly comprising a housing havi.ng a fluid inlet chamber, a
fluid supply chamber, at least one load chamber, and fluid exhaust
means connected to reservoir means, first valve means for
selectively interconnecting said load chamber with said fluid
supply chamber and said fluid exhaust means, first variable
metering orifice means responsive to movement of said first
valve means and operable to meter fluid flow between said fluid
supply chamber and said load chamber, second variable metering
orifice means responsive to movement of said first valve means
and operable to meter fluid flow between said load chamber and
said fluid exhaust means, positive load fluid throttling means
between said fluid inlet chamber and said fluid supply chamber,
negative load fluid throttling means ~etween said load chamber
and said fluid exhaust means, con-trol means of said positive load
and said negative load fluid throttling means having pilot ampli-
flying valve means/ said pilot amplifying valve means having first
control force generating means responsive to pressure differential
across said first variable metering orifice means and second
control force generating means respons-ive to pressure differential
across said second variable metering orifice means, said pi.lot
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amplifying valve means operable through control of said positive
load fluid throttling means to maintain a relatively constant
pressure differential across ~aid first variable meteri.ng ori-
fice means or through control of said negative load fluid
throttling m~ans operable to maintain a relatively cons-tant
pressure differential across said second variable metering
orifice means.
Additional objects of this invention will become apparent
when referring to -the preferred embodiment of the invention as
shown in the accompanying drawing and described in the following
detailed description.
D crip-tion of the Drawi.ng
The drawing is a longitudinal sectional view of an
embodiment of a flow control valve provided with a single positive
and negative load compensator, also
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showing a longitudinal sectional view of an embodiment
of a pilot valve amplifying stage controlling the
compensator with system lines, second flow control
valve, system actuator~ system pump and system
reservoir shown diagrammatically.
Description of the Preferred Embodiment
Referring now to the drawing, an embodiment of
a flow control valve, generally designated as 10, is
shown interposed between diagrammatically shown fluid
motor 11 driving load W and a pump 12, of a fi~ed
displacement or variable displacement type, driven by a
prime mover, not shown. Fluid flow from the pump 12 to
flow control valve 10 and a circuit of diagrammatically
shown flow control valve 13 is regulated by pump flow
control 1~. If pump 12 is of a fixed displacement
type, pump flow control 14 is a differential pressure
relief valve, which, in a well known manner, by
~: bypassing ~luid from pump 12 to a reservoir 15,
maintains discharge pressure of pump 12 at a level,
higher by a constant pressure differential, than load
pressure developed in fluid motor 11. If pump 12 is of
a variable displacement type, pump flow control 14 is a
differential pressure compensator, well known in the
art, which by changing displacement of pump 12,
maintains discharge pressure of pump 12 at a level,
higher by a constant pressure differential, than load
pressure developed in fluid motor 11.
The flow control valve 10 is of a fourway type
and has a housiny 16 provided with a bore 17, axially
guiding a valve spool 18. The valve spool 18 is
equipped with lands 19, 20 and 21, which in neutral
position of the valve spool 18, as shown in the drawing
isolate a fluid supply chamber 22, load chambers 23 and
24 and outlet chambers 25 and 26. Lands 19, 20 and 21,
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of valve spool 18, are provided with metering slots 27,
28, 29 and 30 and control surfaces 31, 32, 33 and 340
Negative load sens:ing ports 35 and 36 are positioned
between load chambers 23 and 24 and outlet chambers 26
and 250 Positive load sensing ports 37 and 38 are
located between supply chambe.r 22 and load chambers 23
and 24. Negative load thrott:ling slots 39, of control
spool 40, equipped with throttling edges ~1, connect
outlet chambers 26 and 25 wi-th an exhaust chamber 42,
which in turn is connected to reservoir 15.
The pump 12, through its discharge line 43~ is
connected to an inlet chamber 44. The inlet chamber 44
is connected through positive load throktling slots 45,
on control spool 40, provided with throttling edges 46,
with the fluid supply chamber 22. Bore 47 axially
guides the control spool 40, which is biased by control
spring 48, contained in control space 49, -towards
position as shown. The control spool 40 at one end
projects into control space 49, the other end
projectiny into chamber 50, connected to the reservoir
15. A pilot valve assembly, generally designed as 51,
comprises a housing 52, provided with a bore 53,
slidably guiding spool 54 and free floating piston 55.
The spool 54 is provided with lands 56, 57 and 58,
defining annular spaces 59 and 60. Annular space 61 is
provided within the housing 52 and communicates
directly with bore 53. The free floating piston 55 is
provided with a land 62, which defines annular spaces
63 and 64 and is provided with extension 65,
selectively engageable with land 58 of the spool 54.
The spool 54 at one end projects into control space 66
and engages, with its land 56 and spring retainer 67, a
pilot valve spring 6~ Control space 66 communicates
through line 69 with check valves 70 and 71. The check
valve 70 is connected by passage 72 with positive load
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sensing ports 37 and 38. The check valve 71
communicates through line 73 with the outlet chamber
25. Annular space 61, of the pilot valve assembly 51,
communicates through line 74 with control space 49 and
also communicates, through leakage orifice 75, with
annular space 60, which in turn is connected to
reservoir 15. ~nnular space 59 communicates through
lines 76 and 77 with check valves 78 and 79. Check
valve 78 is connected to discharge line 43 and check
valve 79 is connected, through line 80, with outlet
chamber 26. Annular space 64 is connected by line 81
with the supply chamber 22. Annular space 63 is
connected by line 82 and passage 83 with negative load
sensing ports 36 and 35. Positive load sensing ports
37 and 38 are connected through passage 72, line 84 and
a check valve 85 and a signal line 86 with the pump
flow control 14. Control space 66 is connected through
a 1.eakage device 87 with the reservoir lS. Leakage
device 87 may be of a straight leakage orifice type, or
may be a flow control device, passing a constant -flow
from control space 66 to the reservoir 15. The load
chambers 2~ and 24 are connected, for one way fluid
flow, by check valves 89 and 90, to schematically shown
system reservoir, which also might be a pressurized
exhaust manifold of the entire control system, as shown
in the drawing~
The preferable se~uencing of lands and slots
of valve spool 13 i5 such, that when displaced in
either direction frol~ its neutral position, as shown in
the drawing, one of the load chambers 23 or 24 is
connected by control surfaces 32 or 33 to the positive
load sensing port 37 or 38, while the other load
chamber is simultaneously connected by control surface
31 or 34 with negative load sensing port 35 or 36, the
load chamber 23 or 24 still being isolated from the
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supply chamber 22 and outlet chambers 25 and 26.
Further displacement of valve spool 18 from its neutral
position connects load chamber 23 or 24 through
metering slot 28 or 2~ with the supply chamber 22,
while simultaneously connecting the other load chamber
through metering slot 27 or 30 with outlet chamber 25
or 26.
As previously described the pump flow control
14, in a well known manner, will regulate fluid flow,
delivered ~rom pump 12, to discharge line 43, ~o
maintain the pressure in discharge line 43 higher, by a
constant pressure differential, than the highest load
pressure signal transmitted through the check valve
system to signal line 86. Therefore, with the valve
spool 18, of flow control valve 10, in its neutral
position blocking posi-tive load sensing ports 37 and
38, signal pressure input to pump flow control 14 from
signal line 86 will be at minimum pressure level,
corresponding with the minimum standby pressure of the
pump 12.
Assume that the load chamber 23 is subjected
to a positive load and that the control pressure
: differential of the pilot valve assembly 51 is higher
than the control pressure differential of the pump flow
control 14. The pilot valve assembly 51 is shown on
the drawing with the spool 54 in its equilibrium
modulating position and with land 57 blocking the
annular space 61. With the control system at rest the
pilot valve spring 68 will move the spool 54 all the
way to the left, connecting annular space 60 with
annular space 61 and therefore connecting control space
49 with system reservoir~ Under those conditions the
control spool 40 will be maintained by the control
spring 48 in the position as shown in the drawing. The
initial displacement of the valve spool 18 to the right
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will connect, in a manner as previous:Ly described, the
load chamber 23, subjected to positive load pressure,
with positive load sensing port 37, while also
connecting the load chamber 2~ with negative load
sensing port 35. The positive load pressure signal
from positive load sensing port 37 will be transmitted
through passage 72 t line 84, check valve 85 and signal
line 86 to the pump flow control 14 and, in a manner as
previously described, will ralse the discharge pressure
of the pump 12 to a level, higher by a constant
pressure differential, than the positive load pressure
existing in the load chamber 23.
Further displacement oE the valve spool 18 to
the right will create a metering orifice through
metering slot 29, between the load chamber 23 and the
supply chamber 22, while also creating through metering
slot 27 a similar metering orifice between the load
chamber 24 and the outlet chamber 25. Therefore, fluid
flow from the supply chamber 22 to the load chamber 23
will take place at a constant pressure differential,
automatically maintained by the pump flow control 18,
with the control spool 40 remaining in the position as
shown in the drawing and with spool 54 in a position
all the way to the left. Therefore th'e flow into the
load chamber 23 will be proportional to the area of the
metering orifice and therefore to the displacement of
the valve spool 18 from its neutral position and
independent of the magnitude of the load W~
Assume that while controlling positive load W
through the flow control valve 10, a higher load
pressure signal is transmitted from the schematically
shown flow control valve 13 through the check valve 88
and signal line 86 to the pump flow control 14. The
discharge pressure o~ the pump 12 will proportionally
increase, increasing the pressure differential between
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the supply chamber 22 and the load chamber 23. The
spool 54, of the pilot valve assembly 51, is subjected
to the pressure difEerential between supply chamber 22
and the load chamber 23, since the annular space 64 is
connected by line 81 to the supply chamber 22 and the
control space 66 is connected by line 69, the check
valve 70, passage 72 and positive load sensing port 37
to the load chamber 23. The increasing pressure
differential between the pressure in the supply chamber
22 and the pressure in the load chamber ~3 will move
the spool 54 from left to right, against the biasing
force of the pilot valve spring 58, into a modulating
position, as shown in the drawing, increasing pressure
in the control space 49, which will move the control
spool 40 from right to left, into a position in which
it will throttle fluid flow between the inlet chamber
44 and the supply chamber 22. Therefore, the spool 54,
in its modulating position, will automatically
throttle, by control spool 40, the fluid flow from the
inlet chamber 44 to the supply chamber 22 to maintain
the pressure differential between the supply chamber 22
and the load chamber 23, at a constant predetermined
level, equivalent to preload in the pilot valve spring
68 and higher than the constant pressure differential
of the pump flow control 14~ Therefore, irrespective
of the pump pressure level, the pilot valve assembly 51
will automatically control the throttling action of the
control spool 40, to maintain a constant pressure
differential between the supply chamber 22 and the load
chamber 23, and across the metering orifice, created by
displacement of the metering slot 29. During this
control action the free floating piston 55 will be
subjected to the pressure differential between the
supply chamber 22 and the load chamber 24, which is
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subjected to minimum pressure and therefore it will be
maintained in a position all -the way to the left, out
of contact with the spool 540
Assume that load chamber 23 is subjected to
negative load pressure and that the valve spool 18 was
moved to the left, connecting the negative load
pressure with the negative load sensing port 36, while
also connecting the pressure at minimum level in the
load chamber 24 with the positive load sensing port
38. The negative load pressu:re, from the negative load
sensing port 36, will be transmitted through passage 83
and line 82 to annular space 63, where it will react on
the cross-sectional area o the free floating piston
55, moving the spool 54 to the right, against the
biasing force of the pilot valve spring 68, connecting
annular space 59 with annular space 61 and therefore
connecting annular space 59 with control space 49. The
pump discharge pressure in control space 49 will move
the control spool 40 all the way from right to left,
isolating with throttling edges 41 the outlet chamber
26 from the exhaust chamber 42~
Further displacement o~ the valve spool 18 to
the left will create a metering flow orifice through
metering slot 30, between the load chamber 23 and the
outlet chamber 26, while also creating a similar
metering orifice, through metering slot 28, between the
load chamber 24 and the supply chamber 22, the supply
chamber 22 being completely isolated from the inlet
chamber 44 by the position oE the throttling edges 46.
30 The negative load pressure from the load chamber 23,
will be transmitted through created metering orifice to
the outlet chamber 26, which is completely isolated
from the exhaust chamber 42 by the position of control
spool 40. The pressure in the outlet chambers 26 and
25 will rise, will open check valve 71~ close check
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valve 7n and will be transmitted through l.ine 69 to -the
control space 66, where it will react on the
cross-sectional area of spool 54. The rising pressure
.in control space 66 will move the spool 54 and piston
55 into a modulating position, as shown in the drawing,
regulating the pressure in control space 49 and
therefore also regulating the position of the control
spool 40. The control spool 40 will move from left to
right into a throttling position, in which fluid flow
from the outlet chamber 26 to the exhaust chamber 42
will be sufficiently throttled, to maintain a constant
pressure differential between the load chamber 23 and
the outlet chamber 26. The magnitude of this constant
pressure differential, the same as that developed when
controlling a positive load, is dictated by the preload
of the pilot valve spring 68. Therefore the pilot
valve assembly 51 will automatically con-trol the
throttling action of the control spool 40, to maintain
a constant pressure differential between the load
chamber 23 and the outlet chamber 26, irrespective of
the magnitude of the negative load. ~ince during
control of negative load the supply chamber 22 is
completely isolated from the inlet chamber 44, the
make-up fluid flow into the load chamber 24 will be
supplied, either from the pressurized exhaust manifold
or from the system reservoir by the check valve 89.
While controlling negative load annular space 59 is
connected, through check valve 79, with the outlet
chamber 26. If the pump discharge pressure is greater
than the negative load pressure in the outlet chamber
26, the check valve 78 will open, the check valve 79
will close and annular space 59 will be subjected to
pump pressure, the energy from the pump being utilized
to control position of the control spool 40. If the
pump is at its standby pressure, which is usually the
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case when controlling a negative load, the higher
negative load pressure will open the check valve 79,
close the check valve 7B and be transmitted to annular
space 59. Therefore under those conditions the energy
to control the position of the control spool 40 will be
supplied from the negative load.
The leakage device 87 connects control space
66 with the system reservoir. The leakage device 87
may take the form of a straight orifice, or may take
the Eorm of a simple flow control valve, permitting a
constant flow, at a very low flow level, from control
space 66. Such a leakage flow is necessary to permit
the spool 54 to move from left to right~ Such a
movement will close the check valves 70 and 71, the
displaced Eluid from control space 66 being passed by
the leakage device 87.
The leakage orifice 75 is provided between
annular space 61 and system reservoir. Use of such a
leakage orifice, well known in the art, increases the
stability margin of the pilot valve control.
The pilot valve assembly 51 is phased into the
control circuit of the flow control valve 10 in such a
way, that it is used to control the throttling action
of control spool 40 during control of both positive and
negative loads. This arrangement provides not only a
less expensive but a more stable control, with
identical pressure differential, while controlling
positive and negative loads.
The pilot valve assembly 51 utilizes the
energy supplied either by the pump or by the negative
load in control of control spool 40. This two stage
type control uses minimum flows through the load
sensing ports and therefore provides a very fast
responding control, completely eliminating the
influence of the flow forces acting on the control
spool 40.
The single stage controls, well known in the
art, must control the positiion of the control spool 40
utilizing the energy transmitted through the load
sensing ports. Since the resistance of those load
sensing ports to high rates of flow is comparitively
large, not only the control pressure signals are
severely attentuated, but the response of the control
is limited. Also since the throttling spool is
directly subjected to the load pressure signals and
since the flow forces transmitted to the throttling
spool will vary with flow and pressure differential,
the control pressure differential of the single stage
control will not be constant and will vary with the
magnitude of the flow forces. Those above mentioned
Eactors become especially important when using large
valves handling large flows. The use of the pilot
valve stage eliminates all of those drawbacks and
provides a fast responding control, without control
signal attenuation and completely independent of the
magnitude of the flow forces.
The free floating piston 55 is one of the
factors permitting the use of a single pilot valve
control is control of both positive and negative
loads. During control of positive load the free
floating piston 55 is forceably maintained out of
contact with the spool 54 7 by the developed pressure
differential. During control of negative load the free
floating piston 55 works all the time in contact with
the spool 54, the free floating piston 55 and the spool
54 acting as an integral pilot valve spool.
Although the preferred embodiment of this
invention has been shown and described in detail it is
recognized that the invention is not limited to the
precise form and structure shown and various
modifications and rearrangements as will occur to those
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skilled in the art upon full comprehension of this
invention may be resorted to wlthout departing from the
scope of the invention as defined in the claims.
