Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Description
Dual Control Input Flow Control Valve
Background of the Invention
This invention relates generally to flow
control valves regulating, irrespective of variations
in system pressure, the quantity of fluid flow to a
load.
In more particular aspects this invention
relates to flow control valves of a bypass type.
In still more particular aspects this
invention relates to flow control valves, in which the
bypass member is controlled by a pilot valve.
In still more particular aspects this
invention relates to pilot operated flow control valves
of a bypass type, which permit variation in the
controlled pressure differential between valve inlet
pressure and the load pressure, in response to an
external control signal.
The flow control valves of a throttling or
bypass type regulate the flow of fluid to a load by
automatically maintaining a constant pressure
differential across an orifice leading to the load.
The quantity of the flow is varied by the area of
orifice, each area corresponding to a specific flow to
the load, irrespective of the variations in the system
pressure. Beca!lse of the in.luence of flow forces on
the quantity of the controlled flow, the controlled
constant pressure differential is usually selected
quite high, providing a comparatively large throttling
loss and therefore affecting the system efficiency.
The forces necessary to vary the area of the orifice
vary with the size of the valve and are usually quite
high.
Summary oE the lnvention
It is therefore a princi.pal object of this invention to
provide a flow control valve of a bypass type, which permits
variation in the level of control differential between valve
supply pressure and load pressure, while this control diEferential
is automatically maintained constant at each controlled level.
According to one aspect of this invention there is
provided a valve assembly comprising a housing having an inlet
chamber connected to a pump and to a device supplied with
pressure fluid, a bypass chamber connected to fluid exhaust means,
control orifice means interposed between said inlet chamber and
said device supplied with pressure fluid, first valve means having
fluid throttling means between said inlet chamber and said bypass
chamber controllable by a pilot valve means and operable to
throttle fluid flow from said inlet chamber to said bypass chamber
to maintain a constant pressure differential at a preselected
constant level across said pilot valve means and to maintain a
constant pressure differential across said control orifice means,
and second valve means having means operable through said first
valve means to vary the level of said constant pressure
differential across said control orifice means while said
pressure differential across said pilot valve means remains
constant at said constant predetermined level.
According to a further aspect of this invention there
is provided a valve assembly comprising a housing having an inlet
chamber connected to a pump and to a device supplied with pressure
fluid, a bypass chamber connected to fluid exhaust means, control
orifice means interposed between said inlet chamber and said device
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supplied with pressure fluid, first and second control chambers
in said housing, first valve means having fluid throttling means
between said inlet chamber and said bypass chamber provided with
means responsive to pressure in said firs-t control chamber, and
pilot valve means cperable to control pressure in said first
control chamber having means responsive to pressure in said second
control chamber and to pressure in said inlet chamber, said first
valve means operable to throttle fluid flow from said inlet
chamber to said bypass chamber to maintain a constant pressure
differential at a preselected constant level between said inlet
chamber and said second control chamber and across said pilot
valve means and to maintain a constant pressure differential
across said control orifice means, pressure signal transmitting
means operable to transmit control pressure signal from downstream
of said control orifice means to said second control chamber,
and modifying ~eans of said control pressure signal operable
through said first valve means to vary the level of said constant
pressure differential controlled across said control orifice means
while said pressure differential between said inlet chamber and
said second control chamber remains constant at said constant
predetermined level.
Additional objects and aspects of this invention will
become apparent when referring to the preferred embodiments of
the invention as shown in the accompanying drawings and described
in the following detailed description.
Description of the Drawings
Figure 1 is a diagrammatic representation of a pilot
operated flow control valve provided with adjustment in the level
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of control differen-tial from a certain preselected level to zero
level, with fluid motor and system pump shown schematically; and
Figure 2 is a diagrammatic representation of another
embodiment of the pilot operated flow control valve of Figure 1,
with fluid motor and system pump shown schematically.
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Description of the Preferred Embodiments
Referring now to Fig. 1, -the hydraulic system
shown therein comprises a fluid pump 10, which may be
provided with an output flow control 11, connected to a
reservoir 12. The fluid pump 10 is preferably of a
fi~ed displacement type. The fluid pump 10 s~pplies
pressure fluid into a fluid power circuit, composed of
a differential bypass control, generally designated as
13, regulating the level of the pressure differential
developed across schematically shown variable orifice
14, interposed between the pump 10 and a fluid motor
15/ operating load W. With pump 10 being of ~ixed
displacement type the differential bypass control 13
bypasses a portion of flow delivered from the pump 10
to the reservoir 12, to regulate the pressure
differential across variable orifice 14. The output
flow control 11 of the pump 10 to the reservoir 12, to
regulate the pressure differential across variable
orifice 14. The output flow control 11 of the pump 10
may be a conventional maximum pressure relief valve,
well known in the art. The differential bypass control
13 is composed of bypass section, generally designated
as 15a~ a pilot section, generally designated as 16, a
flow control section, generally designated as 17 and a
signal throttling section, generally designated as 18.
Discharge line 19 of pump 10 is connected to
port 20 of differential bypass control 13 and through a
check valve 21, line 22r variable orifice 14 and line
23 is also connected to the fluid motor 15. The fluid
motor 15 is also connected by lines 23 and 69 with the
differential bypass control, generally designated as 13.
The bypass s~ction 15a of the differ~ntial
bypass control 13 comprises a housing 25 having an
inlet chamber 26, a bypass chamber 27, a first control
chamber 28 and an exhaust chamber 29, all of those
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chambers being connected by bore 30, slidably guiding a
bypass spool 31. The bypass spool 31, equipped with
lands 32 and 33 and stop 34, is provided with
throttling slots 35, terminated in cut-of:E edges 36,
between the inlet chamber 26 and the bypass chamber
27. One end oE the bypass spool 31 projects into the
first control chamber 28, while the other end projects
into the exhaust chamber 29 and is biased by a control
spring 37. The exhaust chamber 29 is connected by
passage 38 with the bypass chamber 27 and therefore
with the system reservoir 12. The first control
chamber 28 is connected by passage 39 with annular
space 40 of the pilot valve section, generally
designated as 16. Bore 41 connects annular space 40
with port 42 and a second control chamber 43 and
axially guides a pilot valve spool 44. The pilot valve
spool 44, equipped with metering land 45 and land 46,
which define annular space 47, communicates with port
42 and projects into the second control chamber 43,
where it engages a spring 48. Annular space 47 is
connected by passage 49 with the exhaust chamber 29 and
therefore the system reservoir 12. The second control
chamber 43 is connected through passage 50 with the
signal throttling section, generally designated as 18
and is also connected through passage 51 with the flow
control section, generally designated as 17. Passage
51 connects the second control chamber 43 with a supply
chamber 52, connected by bore 53 with a third control
chamber 54 and an exhaust chamber 55. Bore 53 slidably
guides a control spool 56, equipped with land 57,
provided with throttling slots 58 and positioned
between the supply chamber 52 and the third control
chamber 54, a land 59 separating the supply chamber 52
and the exhaust chamber 55. The third control chamber
54 is connected by orifice 60 and passage 61 with the
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exhaust chamber 55, which contains a spring 62~ biasing
the control spool 56 and is connected by passage 63
with the exhaust chamber 29. The second con-trol
chamber 43 is connected by passage 50 with chamber 64,
which is selectively :interconnected by metering orifice
created by a stem 65 guided in bore 66 and provided
with metering slots 67, with signal chamber 68. Signal
chamber 6~ is connected by line 69 with the fluid motor
15. The stem 65 is connected to an actuator 70,
responsive to external control signal 71. Exhaust
chambers 55 and 29, connected to the system reservoir
12 are also connected by passages 63 and 49 and orifice
72 with passage 39.
Referring ilOW to Fig. 2 the differential
bypass control, generally designated as 13, has bypass
section 15a, pilot section 16 and flow control section
17 identical to those as shown in Fig. 1. A signal
throttling section of Fig. 2, generally designated as
73, is different from the signal throttling section 18
of Fig. 1. The same components used in Figs. 1 and 2
are designated by the same numerals. The second
exhaust chamber 43 is connected by passage 50 to
chamber 74 of the signal throttling section, generally
designated as 73. The signal throttling section 73
comprises a coil 75 retained in the housing, which
guides an armature 76 of a solenoid, generally
designated as 77. The armature 76 is provided with
conical surface 78, selectively engageable with sealing
edge 79 of inlet port 80 and venting passage 81,
terminating in bore 82, guiding a reaction pin 83. The
coil 75 is connected by sealed connector 84 to outside
of housing 25, external control signal 85 being applied
t~ the sealed connector 84.
Referring now to Fig. 1, the differential
bypass control 13 is introduced into a circuit between
the pump 10 and fluid motor 15 and controls the fluid
flow and pressure -therebetween. The fluid motor 15 can
be substituted by any device to which fluid flow must
be controlled. The differential bypass control 13 is
composed of the bypass section 15a, the pilot section
16, the flow control section 17 and the signal
throttling section 18. The bypass section 15a with its
bypass spool 31 throttles with throttling slots 35
fluid flow between the inlet chamber 26, connected by
discharge line 19 to the pump 10 and the bypass chamber
27, connected to the system reservoir 12 to
automatically maintain a constant pressure differential
across variable orifice 14, connected by line 23 with
the fluid motor 15. This control action is
accomplished in the following way. Fluid from upstream
Of variable orifice 14 of Pl pressure is supplied to
port 4~ where, reacting on the cross-sectional area of
the pilot valve spool 44, generates a force tending to
move the pilot valve spool 44 upward, to connect Pl
pressure through annular space 40 and passage 39 to the
first control chamber 28 and therefore to increase the
pressure level in the first control chamber 28. Fluid
at load pressure Pw, which is the pressure acting
downstream of variable orifice 14, is supplied by line
69 to the signal throttling section 18. With the stem
65 displaced to the right and the signal chamber 68
connected to the chamber 64 by metering slots 67 the
fluid under P2 pressure, which approximately equals
Pw pressure, is supplied through passage 50 to the
second control chamber 43 where, reacting on the
30 cross-sectional area of the pilot valve spool 44, it
generates a force tending to move the pilot valve spool
44 downward, to connect the reservoir pressure from
annular space 47 to annular space 40, passage 39 and to
the first control chamber 28 and therefore to decrease
the pressure level in the first control chamber 28.
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This force, due ~o pressure in the second control
chamber 43, is supplemented by the biasing force of the
spring 48. Increase in pressure level in the first
control chamber 28, above the level, equivalent to
preload of the control spring 37, reacting on the
cro~s-sectional area of the bypass spool 31, will
generate a force tending to move the bypass spool 31
from right to left, in the direction of opening of the
flow area through the throttling slots 35 and therefore
in the direction of increasing the bypass flow by the
throttling action of the bypass spool 31. Conversely,
a decrease in pressure level in the first control
chamber 28, below the level equivalent to preload of
control spring 37, will result in the control spring 37
moving the bypass spool 31 from left to right, in the
direction of decreasing the flow area through the
throttling slots 35 and therefore in direction of
decreasing the bypass flow by the throttling action of
the bypass spool 31. Therefore by regulating the
pressure level in the first control chamber 28 the
pilot valve spool 44 will control the bypass action of
the bypass spool 31 and the quantity of fluid flowing
through variable orifice 14. Assume that the stem 65
is fully displaced to the right, providing a minimum
resistance to the fluid flow from line 69 to the second
control chamber 43. The pilot valve spool 44,
subjected to Pl and P2 pressures and the biasing
force of spring 48 will reach a modulating position, in
which by throttling action of metering land 45 will
regulate the pressure in the first control chamber 28
and therefore the bypass action of the bypass spool 31
to regulate the pump Pl pressure which is higher, by
a constant pressure differential ~ P, than P2
pressure and equal to the quotient of the biasing force
of spring 48 and the cross-sectional area of the pilot
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valve spool 44. In this way the pilot valve spool 44,
subjected to low energy pressure signals, will act as
an amplifying stage using the energy derived from the
pump 10 to control the position and therefore the
bypass action of the bypass spool 31. Leakage orifice
72~ connecting the first control chamber 28 through
passage 49 and the exhaust chamber 29 to the reservoir
12, is used, in a well known manner, to increase the
stability of the pilot valve spool 44. If P2
pressure is approximately equal to Pw pressure which is
the case when the stem 65 is in the position fully
displaced to the right from the as shown in Fig. 1, the
bypass section 15a, by throttling fluid flow from the
inlet chamber 26 to the bypass chamber 27, wi.ll
automatically maintain a constant pressure
differential ~ P between the pump pressure Pl and
P2 pressure in the second control chamber 43 and
with Q Py becoming ~ P, will also maintain a constant
pressure differential across variable orifice 14. With
constant pressure differential, acting across an
orifice, the flow through an orifice will be
proportional to the area of the orifice and independent
of pressure in the fluid motor. Therefore, by varying
the area of variable orifice 14, the Eluid flow to the
fluid motor 15 and velocity of the load W can be
controlled, each specific area of variable orifice 14
corresponding to a specific velocity of load W, which
will remain constant, irrespective of the variation in
the magnitude of the load W.
In the arrangement of Fig. 1 the relationship
between load pressure Pw and signal pressure P2 is
controlled by the combined action of the flow control
section 17 and the signal throttling section 18~ Fluid
under P2 pressure is conducted through passage 51 to
the supply chamber 52 of the flow control section 17,
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from where it is throttled by throttliny slots 58 on
its way to the third control chamber 54. The control
spool 56 will automatically assume a modulating
position, in which it will sufficiently throttle fluid
at P2 pressure to a constant pressure level in the
third control chamber 54, equivalent to the preload of
the spring 62. Since a constant pressure level is
automatically maintairled in the third control chamber
54 and since the exhaust chamber 55 is maintained at a
constant atmospheric pressure level, constant flow will
take place through orifice 60, independent of P2
pressure level. Therefore the flow control section 17
will automatically maintain a constant preselected flow
level from the second control chamber 43. Therefore,
in a well known manner, for each specific area of
orifice, caused by displacement of metering slots 67, a
constant specific pressure drop ~ Px will be maintained
between Pw pressure and P2 pressure, irrespective of
the variation in Pw pressure. Under those conditions
each specific position of stem 65 will correspond to a
specific value of ~ Px, which can be varied from Pw
pressure level to zero pressure, each specific value
of ~ Px being maintained constant and independent of Pw
pressure. When referring to Fig. 1 it can be seen that
Pl Pw ~ Py, Pl ~ P2 = ~ P~ maintained
constant by the pass section 15a and Pw - P2 = ~ Px.
From the above equations, when substituting and
eliminating Pl and P2 a basic relationship of
~Py = ~ P - ~ Px is obtained. Since ~ Px can be
varied and maintained constant at any level by the
signal throttling section 18, so can ~ Py, acting
across variable orifice 14, be varied and maintained
constant at any level. Therefore with any specific
constant area of variable orifice 14, in response to
control signal 71, pressure differential ~ Py can be
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varied from maximum to zero, each specific level of
Py being automatically controlled constant,
irrespective of variation in the load pressure Pw.
Therefore, for each specific area of variable orifice
1~ the pressure difEerential, acting across orifice 14
and the flow through orifice 14 can be controlled from
maximum to minimum by the signal modifying section
composed of constant flow control section 17 and signal
throttling section 18, each flow level automatically
being controlled constant by the differential bypass
control 13, irrespective of the variation in the load
pressure Pw. From inspection of the basic equation
Py = ~ P - ~ Px it becomes apparent that with ~ Px =
0, ~ Py = ~ P and that the system will revert to the
mode of operation of conventional load responsive
systeml with maximum constant ~ P of the differential
throttling control 13. When ~ Px = ~ P, ~ Py becomes
zero, outlet pressure from the differential throttling
control 13 Pl will be equal to load pressure Pw and
the flow through variable orifice 14 will become zero.
With ~ Px larger than ~ P, pressure Pl will become
smaller than load pressure Pw and the load check 21
will seat.
In the load responsive system of Fig. 1 for
each specific value of ~ Py, maintained constant by the
signal throttling section 18 through the bypass section
15a of the differential bypass control 13, the area of
variable orifice 14 can be varied, each area
corresponding to a specific constant flow into the
fluid motor 15, irrespective of the variation in the
magnitude in the load pressure Pw. Conversely, for
each specific area of the variable orifice 14 pressure
differential ~ Py, acting across orifice 14, can be
varied by the signal throttling section 18, through the
bypass section 15a of the differential bypass control
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13, each specific pressure differential ~ Py
corresponding to a specific constant flow into the
fluid motor 15, irrespective of the variation in the
magnitude of the load pressure Pw. Therefore fluid
flow into fluid motor 15 can be controlled either by
variation in area of variable orifice 14~ or by
variation in pressure differential ~ Py, each of those
control methods displaying identical control
characteristics and controlling flow~ which is
independent of the magnitude of the load pressure.
Action of one control can be superimposed on the action
of the other, providing a unique system, in which, for
example, a command signal from the operator, through
the use of variable orifice 14 can be corrected by
signal 71 from a computing device, acting through the
signal throttling section 18.
Referring now to E'ig. 2 the flow control valve
is similar in construction and performs in a similar
way as that of Fig. 1. The bypass section, the pilot
2Q section and the flow control section of Figs. 1 and 2
are identicalO The signal throttling sections of Figsr
1 and 2 represent different embodiments of the control,
which provides similar control characteristics. The
signal throttling section of Fig. 2, generally
designated as 73, contains the solenoid, generally
designated as 77, which consists of coil 75, secured in
the housing 25 and the armature 76, slidably guided in
the coil 75. The armature 76 is provided with conical
surface 78, which, in cooperation with sealing edge 79,
regulates the pressure differential ~ Px between inlet
port 80 and passage 50. The sealed connector 84, in
the housing 25, well known in the art, connects the
coil 75 with external terminals, to which the external
signal 85 can be applied. A solenoid is an
electro-mechanical device, using the principle of
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electro-magnetics, to produce output forces from
electrical input signals. The force developed on the
solenoid armature 76 is a function of the input
current. As the current is applied to the coil 75,
each specific current level will correspond to a
specific force level, transmitted to the armature.
Therefore, the contact force between the conical
surface 78 of the armature 76 and sealing edge 79 to
housing 25 will vary and be controlled by the input
current. This arrangement will then be equivalent to a
type of differential pressure throttling valve, varying
automatically the pressure differential ~ Px between
inlet port 80 and second control chamber 43, in
proportion to the force developed in the armature 76,
in respect to the area enclosed by the sealing edge 79
and therefore proportional to the external signal 85,
of the input current supplied to the solenoid 77. The
pressure forces acting on the armature 76, within the
housing 25, are completely balanced with the exception
of the pressure force due to the pressure differential
~ Px acting on the enclosed area of sealing edge 79.
This force is partially balanced by the reaction force,
developed on the cross-sectional area of the reaction
pin 83, guided in a bore 82, which is connected through
venting passage 81 with inlet port 80. The
cross-sectional area of the reaction pin 83 must always
be smaller than the area enclosed by sealing edge 79,
so that a positive force, due to the pressure
differential ~ Px, opposes the force developed by the
solenoid 77. The reaction pin 83 permits use of larger
flow passages, while also permitting a very significant
reduction in the size of solenoid 77, also permitting
the solenoid 77 to work in the higher range of ~ Px.
The second control chamber 43 is connected to the flow
control section 17.
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The schematically shown actuator 70 of Fig. 1
may respond to many types of external control signals
71. The stem 65 can be manually operated through a
mechanical linkage. The actuator 70 may be of a
hydraulic or pneumatic type, responding to a hydraulic
or pneumatic external control signal r it may be a
solenoid or a torque motor r respondiny to an electrical
input current signal, or it may be a stepper motor,
responding to a digital electrical external control
signal.
Figs. 1 and 2 show a dual input flow control
system supplying a fluid motor operating a load W. In
such a system the check valve 21, preventing reverse
flow from the fluid motor may be of some value. It
should be noted that location of the check valve 21, in
the position as shown, or in line 22 past port 42, will
to some degree change the operating conditions of the
flow control. With the check valve 21 in position as
shown in Figs. 1 and 2, variable orifice 14 open and
~ Px larger than ~ P, the pilot section 16 will be
operated by power derived from load W and Pl will
equal zero, with the pump 10 completely unloaded. With
the check valve 21 mounted in the other position the
port 42 will be isolated from Pw, when ~ Px is larger
than ~ P and the pump pressure will be Pl = Pw - ~ Px
~ ~ P. When Pw = ~ Px, Pl becomes equal to ~ P, this
being the lowest operating pressure of the pump 10.
With variable orifice 14 closed or with load W becoming
zero, irrespective of the position of the check valve
21, pump pressure Pl will automatically drop to the
fixed value of ~ P. The flow control valves of Figs. 1
and 2 may control the fluid flow to other devices than
fluid motor, for example fuel flow to fuel nozzle or
flow of fluid used in a chemical process or mixing
operation. In such instances the flow to the device
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can be controlled, at all Pw pressure levels, at
constant ~ Py by variation in flow area of orifice 14.
The flow can also be controlled by variation in ~ Py,
but that can be accomplished at Pw pressure levels
higher than ~ P. If control of ~ Py at Pw values lower
than ~ P, a constant pressure differential throttling
device/ in the form for example of a spring loaded
check, located downstream of variable orifice 14 and
throttling the fluid flow to the device, at a level
higher than ~ P, can be inserted in line 23. In this
way Pw can not drop below the minimum value of ~ P.
Although the preferred embodiments of this
invention have 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
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.
