Note: Descriptions are shown in the official language in which they were submitted.
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~ackground of th:e Inven-tion
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This invention relates generally to load responsi.ve
system controls, which permit variation in the level of
control differential between pump di`scharge pressure and the
load pressure si.gnal, while this control differential is
automatically maintained constant at each controlled level.
In more particular aspects this invention relates
to load responsive system controls, which permit variation
in the controlled pressure differential between pump discharge
pressure and the load pressure, in response to an external
control signal.
In still more particular aspects this invention
relates to signal modifying controls of a load resp~ive
~ system, which supply control signals to output flow control
;of a pump, to adjust and regulate the pressure differential
across an orifice positioned between thLe system pump and a
fluid motor operating a load.
. Load responsive systems, in which pump output flow
controls respond to load pressure signal to maintain a
20 constant pressure differelltial between pump discharge
pressure and load pressure, are well known in the art.
In such a control system flow through an orifice J positioned
~etween system pump and fluid ~otor operating a load, is
proport:ional to the area of the
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orifice and independent of system load. Such load
responsive systems are very desirable for a number of
reasons. Not only do they provide exceptional control
of a load, but they permit operation of the load at
very high system efficiency. Such load responsive
fluid control systems are shown in U.S. Patent
#2,892,312 issued to Allen et al and my U.S. Patent
#3,444,689 dated May 20, 1969. One disadvantage of
such systems is the fact that, once the control
pressure differential is selected and incorporated in~o
system design, it will remain constant under all
operating conditions of the system. Adjustment of the
controlled level of the system differential, in respect
to system flow, pressure, or specific conditions,
relating to control of a load, would not only improve
the control characteristics of the system, improve the
system efficiency, but would also make possible
independent adjustments in the system performance,
while the system load is controlled by a load
responsive direction control valve.
Summary of the Invention
It is therefore a principle object of this
invention to provide improved load responsive system
controls, which permit variation in the level of
control differential, between pump discharge pressure
and the load pressure, while this control dif~erential
is automatically maintained constant at each controlled
level.
Another object of this invention is to provide
load responsive system control, in which control of
system load can be either accomplished by variation in
area of orifice between the system pump and a ;Eluid
motor, while ~he pressure di~erential across this
ori~ice is maintained constant at a specific level, or
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by control or pressure differential, acting across this
orifice while area of the orifice remains constant.
- It is a further object of this invention to
provide load responsive system controls, which permit
variation in the controlled pressure differential
across a metering orifice in response to an external
control signal.
It is a further object of this invention to
provide load responsive system controls~ in which an
external control signal, at a minimum force level, can
adjust and control the pressure differential, acting
across a metering orifice of a load responsive
direction control valve, while the system load is being
controlled by variation in area oE the metering orifice.
It is a further object of this invention to
provide a control of a load responsive system, which
modifies control signals, supplied to output flow
control of a pump, to control the pressure differential
across an orifice, positioned between the system pump
and a fluid motor operating a load.
Briefly the foregoing and other additional
objects and advantages of this invention are
accomplished by providing novel load responsive system
controls to vary the level of control differential
~5 between pump discharge pressure and the load pressure
while this control differential is automatically
maintained constant at each controlled level by load
responsive pump control. This control action,
responsive to an external control signal can be
superimposed upon conventional constant pressure
differential control of a loacl responsive system,
providing a sys~em with dual parallel control inputs.
~n this way not only the level of the controllecl
pressure differelltial can be adjusted to any desired
value, during conventional mode oF operation o~ ~he
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load responsive control, but the load can be fully
controlled through change in the control differential,
in any control position of the load responsive
direction control valve.
Additional objects 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 Drawin~s
Fig. 1 is a diagrammatic representation of
load responsive control for adjustment in level of
control differential from a certain preselected level
to zero level, with fluid motor, system pump and pump
controls shown schematically;
Fig. 2 is a diagrammatic representation of the
differential pressure controller of Fig. 1 provided
with a fixed orifice;
Fig. 3 is a diagrammatic representation of
load responsive control for adjustment in the level of
control differential from a certain minimum preselected
value up to maximum level, with fluid motor, system
pump and pump controls sho~n schematically;
Fig. ~ is a diagrammatic representation of
combined load responsive controls of Figs~ 1 and 3 with
fluid motor, system pump and pump controls shown
schematically;
Fig. S is a diagrammatic representation of
another embodiment of load responsive control o~ E'ig.
1, with fluid motor, system pump and pump controls
shown schematlaally;
E'ig, 6 is a diagrammatic representation of
load responsive control of Fig. 5 in combination with
diagr~mmatically shown load responsive direction
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control ~alve and different type o~ differential
throttling valve;
Fig. 6a is a diagrammatic representation of
the differential pressure controller of Fig. 6 provided
with fixed preselected pressure differential;
Fig. 7 is a diagrammatic representation of one
arrangernent of load responsive pump controls;
Fig. 8 is a diagrammatic representation of
another arrangement of load responsive pump controls;
Fig. 9 is a diagrammatic representation of
still another arrangement of load responsive pump
controls;
Fig. 10 is a diagrammatic representation of
manual control input into load responsive controls of
Figs. 1, 3, 4 and 5;
Fig. 11 is a diagrammatic representation of
hydraulic control input into load responsive controls
of Figs. 1, 3, 4 and 5;
Fig. 12 is a diagrammatic representation of
electromechanical control input into load responsive
controls of Figs. 1, 3, 4 and 5;
Fig. 13 is a diagrammatic representation of
electrohydraulic control input into load responsive
controls of Figs 1, 3, 4 and 5; and
Fig. 14 is a diagrammatic representation of an
electromechanical control input into load responsive
system of Fig. 6.
Description of the Preferred Embodiment
Referring now to Fig. 1 the hydraulic system
shown therein comprises a fluid pump 10, equipped with
a ELo~ changing mechanism 11, operated by all output
~low control 12. rrhe output flow control 12 regulates
delivery of the pump 10 into a load responsive circuit,
compo~ed oE a di~feren~ial con~rol, generally
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desi~nated as 13, regulating -the level of pressure
; differential developed across schematically shown
variable orifice 14, interposed between the pump 10 and
a fluid motor 15 operating load W. The pump 10 may be
of fixed or variable displacement type. With the pump
10 being of fixed displacement type, the output flow
control 12, in a well known manner r regulates, through
flow changing mechanism 11, delivery from pump -to load
responsive circuit, by bypassing part of the pump flow
to a system reservoir 16. With the pump 10 being of
.~ variable displacement type the output flow control 12,
in a well known manner, regulates through flow changing
mechanism 11 delivery from pump to load responsive
circuit, by changing the pump displacement. Although
in Fig. 1, for purposes of demonstration of the
principle of the invention, the differential control 13
is shown separated, in actual application the
.~ differential control 13 would be most likely an
integral part of pump output flow control 12. The
output flow control 12 may be supplied with fluid
energy from the pump 10 through discharge line 17 and
line 18, or from a separate source of fluid energy,
namely a pump 19 provided with a bypass valve 20.
Discharge line 17 of pump 12 is connected through a
load check 21, variable orifice 14 and line 22 to the
fluid motor 15 and through line 23 to a flui~ motor 24,
subjected to load Wl. Load pressure signal Pw is
transmitted through line 22 and a signal check valve 25
to fixed or variable orifice 26. Similarly, load
pressure signal from the fluid motor 24 is transmitted
through a signal check valve 27 and line 2~ to upstream
of fixed or variable orifice 26 and downstLeam of
si~nal check valve 25. qlhe differential control 13
communicates through line 29 with downstream of fixed
or var.iable ori:Eice 26 and throu~h linq 30 with -the
outpul: ~low control 12 of pump lQ.
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The differential control, generally desiynated
as 13, comprises a housing 31 having an inlet chamber
32, a control chamber 33 and an exhaust chamber 34,
interconnected by bore 35, guiding a control spool 36.
The control spool 36 is equipped with a land 37
provided with throttling slots 38 and positioned,
between control and inlet chambers, a land 39
separating inlet and exhaust chambers and a flange 40.
A control spring 41 is interposed in the exhaust
chamber between the flange 40 of control spool 36 and
the housing 31. The exhaust chamber 34 and the control ;~
chamber 33 are selectively interconnected by metering
orifice, created b~ a stem 43 guided in circular bore
42 and provided with metering slots 44. The stem 43 is
connected to an actuator 45, responsive to external
control signal 46.
Referring now to Fig. 2, a differential
pressure control 13a of Fig. 2 is identical to the
differential control 13 of Fig. 1, with the exception
that metering orifice 42 and the stem 43 with its
metering slots 44 were substituted by fixed orifice 42a.
Referring now to Fig. 3 the same components
used in Fig. 1 are designated by the same numerals.
The only difference between load responsive system
controls of Figs. 1 and 3 is the phasing of the
differential control 13 and the load pressure signals
from fluid motors 14 and 24 to the output flow control
12 of pump 10. In Fig. 2 the load pressure signal from
downstream of signal check valves 25 and 27 is ~irectly
transmitted through line 47 to the output flow control
12~ The discharge pressure signal from pump 10 is
transmitt~d to the output ~low control 12, through
discharge line 17, load check 21, ~i~ed or variahle
orifice 26 and line 30, with di~erential control 13
connected to this signal transmitting path.
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Referring now to Fig. 4 the same components
used in Figs 1 and 3 are designated by the same
numerals. The load responsive system o~ Fig. 4 shows
one differential control 13 connected to signal
transmitting line 30 in the same way as in the circuit
of Fig. 1 and a second differential control 13
connected to signal transmitting line 48 in the same
way as in the circuit of Fig. 3.
Referring now to Fig. 5, the same components
used in Fig. 1 are designated by the same numerals.
The basic load responsive circuit of Fig. 5 and all of
the system components, with the exception of
differential control assembly, generally designated as
50, are identical to those of Fig. 1. The differential
control assembly 50 of Fig. 4 is phased into the
circuit in the same way as the differential control 13
of Fig. 1 and performs an identical function. Although
the differential control assembly 50 is shown for
purpose of better demonstration, composed of two
components, those two components should be combined and
preferably incorporated into assembly of output flow
control 12. The differential control assembly 50
includes a variable orifice valve 51, provided with a
housing 52, having an inlet chamber 53, an outlet
chamber 54, circular bore 55, positioned between those
chambers and guiding a stem 56 equipped with metering
slot 57. The stem 56 is connected to the actuator 45
responsive to an external control signal 46. The
differential control assembly 50 also includes a flow
control valve 58, provided with a housing 59 having an
inlet chamber 60 and an exhaust chamber 61, connected
by bore 62, axlally guiding a meterillg pin 63, provided
with a metering slot 6~. The metering pin 63 is
provided with a stop 65 and is biased towards position
as shown by a spring 66, contained in the exhaust
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chamber. The inlet chamber 53 of variable orifice
valve 51 is connected by line 28 with downstream of
signal check valves 25 and 27, while the outlet chamber
54 is connected by line 67 with the inlet chamber 60,
of the flow control valve 58, which in turn is
connected by line 30 with the output flow control 12 of
pump 10.
Referring now to Fig~ 6, the same components
used in Fig. 5 are designated by the same numerals.
The basic load responsive system of Fig. 6 is similar
to the system of Fig. 5, with the exception that
variable orifice 14 was substituted by a load
responsive direction control valve, generally
designated as 68 and a different type of a differential
valve 68a was used. The direction control valve 68
comprises a housing 69 having an inlet chamber 70,
first and second load chambers 71 and 72, first and
; second exhaust chambers 73 and 74, load pressure
sensing ports 75 and 76 and bore 77, guiding a valve
spool 78. The valve spool 78 has lands 79, 80 and 81
' provided with metering slots 82, 83, 84 and 85 and
- signal slots 86 and 87 and is actuated by control lever 88. Load pressure sensing ports 75 and 76 are
connected by line 89 to upstream of the signal check
valve 25. In an identical way load pressure sensing
ports of a load responsive direction control valve 90,
controlllng through fluid motor 91 load W2, are
connected by a line to upstream of the signal check
valve 27. Downstream of signal check valves 25 and 27
is connected by line 28 to inlet port 93 of
differential valve, generally designated as 68a. The
diEferential valv~ 68a comprises a housing 9~,
retaining a coil 95, guiding an armature 96 of a
solenoid, gen~rally designated as 97. ~he arrna~ure 96
is provided with a conical sur~ace 98 selectively
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engageable with the sealing edge 99 of the inlet port
93 and venting passage 100. A retaining spring 101 can
be interposed between the armature 96 and the housing
94. The coil 95 is connected by a sealed connector lOZ
to outside of the housing 94, external signal 46 being
applied to the sealed connector 102. The outlet port
103 of the differential valve 68a is connected by line
30 with the output flow control 12 and is also
connected by line 104 with orifice leading to the
reservoir 16. The orifice can be of a fixed or
variable type. If the orifice is of a variable type it
may be of a type and contained within the flow control
valve 58 of Fig. 5~ construction of which was described
in detail when referring to Fig. 5.
Referring now to Fig. 6a, a differential
pressure controller 68b is similar to the differential
controller 68a of Fig. 6, with the exception that the
throttling member 98, with its conical surface 98a
engaging sealing edge 99, is biased by a spring lOla
instead o~ by armature 96.
Referring now to Fig. 7 ~he variable output
flow pump 10 of Figs. 1, 3, 4, 5 and 6 is provided with
the flow changing mechanism 11 and the output flow
control 12. First pressure control signal is
transmitted from discharge line 17, through fixed or
variable orifice 26, line 29, the differential control
13 and line 30 to the output flow control 12, as per
control arrangement shown in E'ig. 3. A second pressure
control signal 105 is transmitted directly from the
largest system load to control space 106 of the output
flow control 12. The output flow control 12, well
known in the art, comprises a pilot val~e 107, guided
in a bore 10~ and equipped with lands 109, 110 and 111,
defining annular spaces 112, 113 and space 11~. The
pilot valve 107 is biased by a control spring 115,
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contained within control space 106. Bore 108 is
provided with an exhaust core 116, connected to the
syste~ reservoir 11 and a control core 117, connected
to a chamber 118 and through leakage orifice 119 also
connected to the exhaust core 116. The chamber 118
contains a piston 120 operating the flow changing
mechanism 11 and biased by a spring 121. ~nnular space
112 is connected by line 122 with discharge pressure of
the pump 19 and the flow changing mechanism 11 is
connected by line 123 with the system reservoir 16~
Referring now to Fig. 8 the basic arrangements
of the Elow changing mechanism 11 and the output flow
control 12 of the fluid pump 10 are the same, as those
shown in Fig. 7, however, the output flow control 12 of
Fig. 8 responds to different pressure control sig~als.
Space 114 is directly connected by line 125 with the
discharge line 17 and control space 106 is subjected to
control pressure signal 124, which is a load pressure
signal, modified by the differential control 13.
Referring now to Fig. 9, in Fig. 9 the basic
arrangement of Fig. 8 is shown with the fluid energy
for pump controls being supplied to annular space 112
,~ from separate pump 19, instead of using energy supplied
by the pump 10. Fig. 9 shows the pump controls
connected into basic system as shown in Fig. 1.
Referring now to Fig. 10 the ste~ 43 or 56 of
the actuator 45 of Figs. 1, 3~ 4 and 5 is biased by a
spring 126 towards position of zero orifice and is
directly operated by a lever 127, which provides the
external signal 46.
Re~qrrin~ now to Fig. 11, the stem ~3 or 56 of
the actuator ~5 of Figs. 1, 3, ~ and 5 is biased by a
sprin~ 128 towarcls position o~ æero orifice and is
clirectly op~rated by a piston 129. Fluid pressure is
supplied to the piston 129 Erom a pressure generator
130, operated by a lqv~r 131.
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Referring now to Fig. 12 the stem 43 or 56 of
the actuator 45 of Figs. 1, 3, 4 and 5 is biased by a
spring 132 towards position of zero orifice and is
directly operated by a solenoid 133, connected by a
line to an input current control 134, operated by a
lever 135 and supplied from an electrical power source
136.
Referring now to Fig. 13, the stem 43 of the
differential control 13 is biased by a spring 137
towards position, where it isolates the inlet chamber
33 from the exhaust chamber 3~ and is controlled by a
solenoid 138. The electrical control signal, amp:Lified
by amplifier 139, is transmitted from a logic circuit
or a microprocessor 140, subjected to inputs 1~ 2
and 143.
Referring now to Fig. 14, a logic circuit or a
microprocessor 144, supplied with control signals 145,
146 and 147 transmits an external control signal to the
differential control 68a through an amplifier 148.
Referring now to Fi~. 1 the output flow from
the fluid pump 10 to the fluid motor 15 is regulated by
the output flow control 12 in response to Pl and P2
pressure signals through the flow changing mechanism
11. If pump 10 is of a Eixed displacement type, output
flow control 12 is a differential pressure r~lief
valve, which in a well known manner, by bypassing fluid
from the pump 10 to the reservoir 16, maintains
discharge pressure Pl of pump tO at a level, higher
by a constant pressure differential, than P2 pressure
signal delivered to the output ~low control 12. If
pump 10 is of a variable displacement type, pump flow
con~rol 16 is a di~ferential pressure compensator~ well
known in the art, which by changing displacement of
pump 10 maintains dlscharge pressure Pl of pump 10 at
a level, higher by a constant pressure differential,
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than P2 pressure signal delivered to the output flow
control 12. Therefore irrespective of the
characteristics of pump 10 the load responsive output
flow control 12 will always automatically maintain,
between two of its control inputs, namely P2 and P
pressurest a preselected constant pressure
differential, irrespective of the variation in its
discharge pressure level. Such load responsive output
flow controls either in the form of differential
pressure relief valve, or in the form of differential
pressure compensator, are well known in the art and
will be described in greater detail when referring to
Figs. 7, 8 and 9.
In a conventional load responsive system using
the differential pressure relief valve, or the
differential pressure compensator, the P2 pressure is
always the maximum load pressure Pw, developed in one
of the fluid motors subjected to maximum load.
Therefore, in a conventional load responsive system the
pump output flow control will always maintain a
constant pressure differential between the pump
discharge pressure Pl and the maximum load pressure
Pw, irrespective of the magnitude of Pw pressure,
maintaining the relationship oE ~P = Pl - Pw =
constant. Such a system will always maintain a
constant pressure differential ~P across orifice 14,
positioned between system pump and fluid motor. With
constant pressure differential acting across the
orifice, flow through the orifice will be proportional
to the area of the orifice and independent of the
pressure level ln the fluid motor~ ~hqrefore, by
varying the area of variahle orifice 14 the fluid flow
to the fluid motor: 15 and velocity of the load W can be
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controlled, each specific area of variable orifice 14
corresponding to a specific velocity of load Wy which
will remain constant, irrespective of the variation in
. magnitude of load W.
In the arrangement of Fig. 1 the relationship
between load pressure Pw and signal pressure P2 is
controlled by the differential control, generally
designated as 13 and orifice 26. Assume that the stem
43, positioned by the actuator 45 in response to
external control signal 46, as shown in Fig. 1, 'olocks
completely the metering orifice, isolating the control
chamber 33 from the exhaust chamber 34. The control
spool 36, with its land 37 protruding into the control
chamber 33, will generate pressure in the control
chamber 33, equivalent ~o the preload of control spring
41. Displacement of the stem 43 to the right will move
metering slots 40 out of circular bore 4~, creating an
orifice area, through which fluid flow will take place
from the control chamber 33 to the exhaust chamber 34.
The control spool 36, biased by the control spriny 41,
will move from right to left, connecting by throttling
slots 38 the inlet chamber 32 with the control chamber
33. Rising pressure in the control chamber 33,
reacting on cross-sectional area of control spool 36,
~5 will move it back into a modulating position, in which
sufficient flow of pressure fluid will be throttled
from the inlet chamber 32 to the control chamber 33, to
maintain the control chamber 33 at a constan~ pressure,
equivalent to preload in the control spring 41. When
displacing metering slots 44 in respect to circular
bore ~, the area of the metering oriEice will be
vari~d. Since constant pressure ~ifferent.ial is
automatically maintained between the exhaust chamber 34
and the control chamber 33 and there~ore across the
meterin~ slots 44 by the control spool 36 each specific
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area of metering slots 44 will correspond to a specific
constant flow level from the control chamber 33 to the
exhaust chamber 3~ and from the inlet chamber 32 to the
control chamber 33, irrespective of the magnitude of
the pressure in the inlet chamber 32. Thereore each
specific position of stem 43, within the zone of
metering slots 44, will correspond to a specific flow
level and therefore a specific pressure drop ~Px
through fixed orifice 26, irrespective of the magnitude
of the load pressure Pw. When referring to Fig. 1 it
can be seen that Pl - Pw = ~Py, Pl P2 = ~P'
maintained constant by pump control and Pw - P2 =
~ Px. From the above equations, when substituting and
eliminatin~ 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
differential control 13, 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 the control
signal 46, pressure differential ~Py can be 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 14 the pressure
differential, acting across orifice 14 and the flow
through orifice 14 can be controlled from maximum to
minimum by the differential control 13, each flow level
automatically being controlled constant by the output
flow contol 12, irrespective of the variation in the
load pressure Pw. From inspection o the basic
equation ~Py = ~P - ~Px it becomes apparent that
wit~ Q P~ - 0, ~Py = ~P and that the system will.
revert to the mode o~ operat:ion of conventional load
responsive system~ with maximum constant ~P of the
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output flow control 12. When ~Px = ~P, ~Py becomes
zero, pump discharge pressure Pl will be equal to
load pressure Pw and the flow through variable orifice
14 will become ~ero, with ~Px larger than ~P pump
pressure Pl will beco~e smaller than load pressuxe 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
differential control 13 through the output flow control
12, 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 differential control 13 through the
output flow control 12, 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 the 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 khe load
pressure. Action of one control can be superimposed
upon 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 siynal 46 ~rom a computing device,
acting through the dif:~erential control 13.
So far in the above considerations it wa5
assumed ~hat the system pump will respond to the load
p~essure oE ~luid motor 15. As is well know in the
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art, the load pressure signals from fluid motors 15 and
24 are transmitted through the check valve logic system
of check valves 25 and 27 and only the highest of the
load pressures will be transmitted to system controls.
With both motors controlled simultaneously, only the
fluid motor controlling the higher load will receive
proportionally controlled fluid flow.
Referring now to Fig. 2, a differential
control, generallly designated as 13a, is similar to
the differential control 13 of Fig. 1. The variable
metering orifice, operated by actuator ~5 of Fig. 1 was
substituted by fixed metering orifice ~2a, the pressure
regulating section of both controls remaining the
same. The differential control 13a, of Fig. 2 will
generate a constant ~Px across fixed orifice 26
decreasing, by exactly the same amount, the control
pressure differential of the load responsive system.
The arrangement of Fig. 2 is very useful to reduce
comparatively large controlled pressure differential o~
output flow control 12 to a lower level, thus
increasing system efficiency, while response of output
flow control 12 is not affected~
Referring now to Fig. 3, the differential
control 13 is identical to the differential control 13
~5 of Fig. 1 and performs in an identical way, by
modifying a control signal transmitted to the output
flow control 12 of pump 10. ~Iowever, the differential
control 13 of Fig. 3 modifies the control signal o~
pump discharge pressure Pl instead of modifying the
control signal of load pressure Pw, as shown in the
system o~ Fig. ]. In Fig. 3 the control load pressure
51gllal Pw i8 traIlsmittqd directly from ~luid motors 15
and 2~, ~hrough logic ~ystem o~ signal check valvqs ~S
and 27 and line ~7 to the output flow control 12.
q'hen, as can be sqen in Fig. 2I Pl - Pw = ~Py,
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Pl - P2 = f~Px and P2 ~ Pw = ~P which; in a
manner as previously described~ is maintained constant
by pump control. From the above ecluations, when
substituting and eliminating Pl and P2, the basic
relationship of ~Py = ~P + ~Px can be obtained.
Since ~Px can be varied and maintained constant at any
level so can ~Py, acting across variable orifice 14,
be varied and maintained constant at any level. From
inspection of the basic equation ~Py = ~P ~ a Px it
becomes apparent that with f~Px = 0, ~Py = ~P and
that the system will revert to the mode of operation of
conventional load responsive system, with minimum
constant ~P equal to the pressure differential of
output flow control 12. Any value of ~Px other than
zero will increase the pressure differential ~Py,
acting across variable metering orifice 14 above the
level of constant pressure differential ~P of output
flow control 12. Therefore, the load responsive
control arrangement of Fig. 1 will control ~Py in a
range between ~P and zero, will the load responsive
control arrangement of Fig. 3 will control ~Py in a
range above the level of constant pressure
differential ~P of ou-tput flow control 12.
Referring now to Fig. 4 the load responsive
control systems of Fig. 1 and Fig. 3 have been combined
into a single system. With one differential control 13
made inactive in response to external control signal 49
the other difEerential control 13, responding to
e~ternal control signal ~6, by modifying load pressure
signal, will perform in an identical way, as previously
described when re~erring to the load responsive control
of Fig~ 1, var~ing the level o~ control pressure
differential ~Py ~rom maximum level o~ Q P to zero.
Conversely, Wit}l the dif~erential control 13 made
inactive Ln response to external control sic~n~l ~6, the
~,:
: : .
,.
: - . . . .. . . :., -: : : . .
3.~
, -19-
:, ,
other differential control 13, responding to external
control signal 49, by modifying pump discharge pres~ure
signal will perform in an identical way, as previously
described when referring to the load responsive control
of Fig. 3, varying the level of control pressure
differential ~P ~rom minimum level of ~P to any
desired higher level. Therefore, combined load
responsive control oE Fig. 4 is capable of controlling
the pressure differential ~Py from zero to any desired
maximum value.
Referring now to Fig. 5 the load responsive
system is identical to the load responsive system of
; ~ig. 1 with the exception of a differential control 50,
which although different in construction performs in a
; 15 very similar way as the differential control 13 of Fig.
1. Although the major components of the differential
control 5~, namely a variable orifice valve 51 and a
flow control valve 58, for purposes of better
demonstration are shown separated, in actual design
they woul~ be combined together and preferably placed
within the output flow control 12. The flow control
valve 58, of differential control 50, is provided with
the housing 59 guiding the metering pin 63, which is
subjected to inlet pressure in the inlet chamber 60, to
the reservoir pressure in the exhaust chamber 61 and to
the biasing force of spring 66. Subjected to pressure
in the inlet chamber 60 the metering pin 63 will move
from left to right, each specific pressure level
corresponding to a specific position of metering pin
63, in respect to the housing 59 and also corresponding
to the specific biasing ~orce of spring 66. Each
speci~ic position of metering pin 63~ in re~pect to the
housing 59, will correspond to a specific flow area Of
mekerlng slot 6~, interconnecting the inlet chamber 60
with the e~haust chamber 61. rrhe shape Oe metering
;
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- ~:. . . . . .
-20-
slot 64 and the characteristics of biasing spring 66
are so selected that variation in the effective orifice
area of metering slot 6~, in respect to pressure in the
inlet chamber 60, will provide a relatively constant
flow from the inlet chamber 60 to the exhaust chamber
61. To obtain special control characteristics oE the
load responsive control the shape of metering slot 64
may be so selected, that any desired relationship
between the flow from the inlet chamber 60 and its
pressure level can be obtained. Assume that the flow
control 58 provides a constant flow from the inlet
chamber 60, irrespective of its pressure level. Then,
in a well known manner, the flow control 58 could be
substitued by a conventional flow control valve, well
known in the art. Constant flow to the inlet charnber
60 is supplied from fluid motors 15 or 24 through a
logic system of signal check valves 21 and 25, the
variable orifice valve 51 and line 67. The variable
orifice valve 51, upstream of flow control valve 58, is
provided with circular bore 55, guiding a stem 56,
provided with metering slots 57. Displacement of
: metering slots 57 past circular bore 55 creates an
orifice, the effective area of which can be varied by
positioning of stem 56 by the actuator 45, in response
to external control signal 46. With stem 56 engaging
circular bore 55 flow area of variable orifice valve 51
becomes zero. There~ore, in response to external
control signal 46, the effective flow area through the
variable orifice valve 51 can be varied from zero to a
selected maximum value. Since the flow through the
variable ori~ice valve is maintairled constant by the
~low control valve 5~, each specific area of :~low
throu~h the variable or:L:Eice valve 51, in a well known
manner, will correspond to a specific constant pressure
drop ~Px, irrespective Oe the varia~ion in the load
- : :
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-21--
pressure Pw. Therefore, the load pressure signal can
be modified on its way to the output flow control 12,
each value of pressure drop ~Px, maintained constant
hy the differential control 50, corresponds to a
specific value of pressure differential ~Py, following
the basic relationship of ~Py = ~P - ~Px~
~herfore, the control characteristics of the load
responsive control of Fig. 5 will be identical to those
described when referring to Fig. 1~ the pressure
differential ~Py being varied and maintained constant
at each specific level by the differential control 50
in response to external control signal 46 between
maximum value equal to ~P and zero.
In a manner as previously described the shape
of metering slot 64 and the biasing force
characteristics of spring 66 can be so selected, that
any desired relationship between pressure in the lnlet
chamber 60 and the fluid flow through the variable
orifice valve 51 can be obtained. For better purposes
of illustration assume that the variable orifice valve
51 of Fig. 5 was substituted by the fixed orifice 42a
of Fig. 2. Then controlled increase in flow through
fixed orifice 42a, with increase in the load pressure,
will proportionally increase the pressure differential
~Px and therefore proportionally decrease the
pressure differential ~Py, effectively decreasing the
gain of the load responsive control with increase in
the load pressure. Conversely, a controlled decrease
in flow through fixed orifice 42a with increase in the
load pressure will proportionally decrease the pressure
differential ~Px and therefore proportionally increase
the pressure dlfferential ~Py, eeEectively increasing
the gain oE the load responsive control, with increase
in the load pressure. As is well known in the art, the
~tability margin of most fl-lid flow and pressure
.
~.~L5~
-22-
controllers decreases with increase in system
pressure. Therefore, the capability of adjustiny the
system gain, in respect to system pressure, is of
primary importance. With the flow control valve 58 the
rate of change of pressure differential ~Py in respect
to load pressure does not have to be constant and can
be varied in any desired way.
Referring now to Fig. 6 the load responsive
system of Fig. 6 is similar to that of Fig. 5 with the
exception that variable orifice 14 of Fig. 5 was
substituted in Fig~ 6 by a load responsive four way
valve, generally designated as 68 and a different type
of a differential valve 68a was used. The differential
control 68a, which can be substituted by the
differential control 13 of Fiy. 1, or the diferential
control 50 of Fig. 5, is connected to load pressure
sensing ports 75 and 76 of four way valve 68. With the
valve spool 78 in its neutral position, as shown in
Fig. 6 load pressure sensing ports 75 and 76 are
blocked by the land 80 and therefore effectively
isolated from the load pressure existing in load
chamber 71 or 72. Under those conditions, in a well
known manner, the output flow control 12 will
automatically maintain the discharge pressure of pump
10 at a minimum level equal to the load responsive
system a P. Displacement of the valve spool 78 from
its neutral position in either direction first connects
with signal slot 86 or 87 load chamber 71 or 72 with
load pressure sensing port 75 or 76, while load
chambers 71 and 72 are still isolated by the valve
spool 78 from the inlet chamber 70 and first and second
exhaus~ chambers 73 and 74. With the variable oriEice
valve 51 open, the load pressure signal will be
transmikted to the OlltpUt ~low control 12, permitting
3S it to react, beEore metering oriice i5 open to the
: : : , . :~ .
3;3.~
-23-
fluid motor 15. Further displacement of the valve
spool 78 in either direction will create, in a well
known manner, through metering slot 83 or 84 a metering
orifice between one of the load chambers and the inlet
chamber 70, while connecting the other load cham~er,
through metering slot 82 or 85, with one of the exhaust
chambers, in turn connected to the system reservoir
16. The metering orifice can be varied by displacement
of valve spool 78, each position corresponding to a
specific flow level into fluid motor 15l irrespective
of the magnitude of the load Wl. Upon this control,
in a manner as previously described when referring to
Fig. 1, can be superimposed the control action of the
differential control 63a. The differential valve,
generally designated as 68a, contains the solenoid,
generally designated as 97, which consists of the coil
95 secured in the housing 94 and the armature 96,
slidably guided in the coil 95. The armature 96 is
provided with conical surface 98; which, in cooperation
with sealing edge 99, regulates the pressure
differential ~Px between inlet port 93 and outlet port
103. The comparatively weak spring 101 can be
interposed between the armature 96 and the housing 94,
to permit a back flow under deenergized condition f the
coil 95 from outlet port 103 to inlet port 93. This
feature may be of importance, when using a shuttle
valve logic system instead of the check valve logic
system o~ Fig. 6. The sealed connector 102 in the
housing 94, well known in the art, connects the coil 95
with external terminals, to which the external signal
46 can be applied. A solenoid is an electromechanical
device, using the principle of electromagnetics, to
produce output forces ~om electrical input signals.
The force developed on the solenoid armature 96 is a
~unction of input current. As the current is applied
: ,
;
33~11
-24-
to the coil 95, each specific current level will
correspond to a specific force level transmitted to the
armature. Therefore the contact force between the
conical surface 98 of the armature 96 and sealing edge
99 o~ the housing 94 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 93 and outlet port
103, in proportion to the force developed in the
,armature 96, in respect to the area enclosed by the
sealing edge 99 and therefore proportional to the
external signal 46 of the input current supplied to the
solenoid 97. The pressure forces acting on the
armature 96, within the housing 94, are completely
balanced with the exception of the pressure force due
, to the pressure differential ~Px, acting on the
' enclosed area of sealing edge 99. Since the outlet
flow control 12, which will be described in greater
detail when referring to Fig. 7, 8 and 9, contains a
bidirectional moving pilot valve, the flow out of the
output flow control 12 into line 30 is passed through
line 104 and a metering orifice to the reservoir 16.
; In a well known manner, the flow through the fixed
orifice will vary with the load pressure, providing a
slow response of the control at low load pressures and
high energy loss at high load pressures. Therefore,
the orifice in line 104 most likely will be the flow
control valve 58, described in detail, when referring
to Fig. 5, which will automatically pass a
preselectable flow, which may be a Eunction oE, or
independent of the load pressure, depending on the
desired gain o~ the output flow control 12. When using
a logic system o~ shuttle valves instead of check
valves o~ ~'ig, 6, line 10~ and the ~low control valve
-25-
58 are not necessary. To simplify the demonstration of
the principle of operation of differential control 68a
the armature 96 is shown hydraulically unbalanced. In
a well known manner venting passage lO0 can be
connected directly through the cone of conical surface
98 with inlet port 93 and the lower end of venting
passage 100 enlarged, to slidably engage a balancing
pin, of diameter smaller than diameter of inlet port
93. In this way the eEfecti~e area subjected to
pressure differential is greatly reduced, permitting
reduction in the size of the solenoid 97. Such an
arrangement is shown by dotted lines in the armature 96
of Fig. 6, the balancing pin being unnumbered.
With the valve spool 78 displaced to any
specific position, corresponding to any specific area
of metering orifice, the load Wl can be
proportionally controlled by action of differential
control 68a, each value of pressure differential ~Py
being automatically maintained at a constant level by
the output flow control 12 and corresponding to a
specific flow level into fluid motor 15, irrespective
of the magnitude of the load Wl. The load W2 is
controlled by the direction control valve 90, which may
be identical to the direction control valve 68.
Referring now to Fig. 6a a differential
pressure controller, generally designated as 68B,
performs a similar function as the differential
pressure controller 68a, but is capable of providing,
in a well known manner, a fixed pressure differential
between inlet port 93 and outlet port 103, this
pressure diE~erential being proportional to preload in
the spring lnla. Control ~P o~ the system will be
reduced by thi~ pressure differential provicling the
controlling pressure differential ~Py of a much
smaller valuq. The arrant3ement of Fig. 6a is very
''
; ' ' , :
-26-
useful to reduce comparatively large controller
pressure differential of output flow control 12 to a
lower level, thus increasing system efficiency~ while
response of output flow control 12 is not affected.
Referring now to Fig. 7, a load responsive
output flow control of a pump is shown. If the pump 10
is of a fixed displacement type, the flow changing
mechanism 11 becomes a differential pressure relief
~alve, ~ell known in the art. If the pump 10 is of a
variable displacement type, the flow changing mechanism
11 becomes a differential pressure compensator, well
known in the art. The pilot valve 107 on one side is
subjected to a load pressure signal 105, together with
the biasing force of control spring 115 and on the
other side to pump discharge pressure signal whih, as
shown in Fig. 7, can be modified by the differential
control 13. Subjected to those ~orces, in a well know
manner, the pilot valve 1~7 will reach a modulating
position, in which it will control the position of
piston 120, to regulate the discharge pressure in
discharge line 17, to maintain a constant pressure
differential between pressure in space 114 and pressure
in control space 106. This constant pressure
differential is dictated by the preload in the control
spring 115 and is e~ual to the quotient of this preload
and cross-sectional area oE the pilot valve 107. The
pilot valve 107, in control of flow changing mechanism
11, uses energy supplied by the pump 19.
Referring now to Fig. ~, space 114 is directly
supplied from discharge line 17, while the flow
changing mechanism 11 uses energy supplied from the
pump 12. In convenkional control oP load responsive
sys~em pressure sigrlal 124 is directly supplied from
~hq system load ~nd a small leakage is provided Prom
control space 94. In the load responsive system oP
:; ;: . ,. : . :
;. . . :.
3~
-27-
this invention load pressure signal is modified by the
differential control 13 and becomes pressure signal 124.
Referring now to Fig. 9, the pump control of
Fig. 9 is identical to that as shown in Fig. 8, but
uses energy supplied from the pump 19. Fig. 9 shows -
the pump controls connected into a basic system as
shown in Fig. 1. The differential control 13 is
connected to space 106 and as described when referring
to Fig. 1 modifies the control signal to vary the
effective pressure differential across an orifice
connecting the pump 10 and the load. As previously
described in Figs. 1 and 3-5 the differential control
13 is shown separately connected to the schematically
shown output flow control of the pump. As shown in
Fig. 9 the components of the differential control 13
would become an integral part of the output flow
control of the pump 10.
Referring now to Fig. 10, the stem 43 or 56 of
the actuator 45 of Figs. 1, 3, 4 and 5 is biased by a
23 spring 126 towards position of zero orifice and is
directly operated by a lever 127, which provides the
external signal 46 in the form of manual input.
Referring now to Fig. 11, the stem 43 or 56 of i~
the actuator 45 of Figs. 1, 3, ~ and 5 biased by a
spring 128 towards position of zero orifice and is
directly operated by a piston 129. Fluid pressure is
supplied, in a well know manner, to the piston 129 from
a pressure generator 130, operated by a lever 131.
Therefore the arrangement of Fig. 11 provides the
external signal ~6 in the form of a fluid pressure
; signal.
~eferring no~ to Flg. 12, the stem ~3 or 56 of
~he actuator ~5 o~ Figs. 1, 3, ~ and 5 is biased by a
spring 132 towarcls position of æero orifice and is
directly operated, in a well known manner, by a
~", ,
3~t
-28
solenoid 133r connected by a line to an input current
control 134, operated by a lever 135 and supplied from
an electrical power source 136. Therefore the
arrangement of Fig. 12 provides the external signal 46
in the form of an electric current, proportional to
displacement of lever 123.
Referring now to Fig. 13, the stem 43 of the
differential control 13 is biased by a spring 137
towards position, where it isolates the inlet chamber
33 from the exhaust chamber 3~. The stem 43 is
completely pressure balanced, can be made to operate
through a very small stroke and controls such low
flows, at such low pressures, that the influence of
flow forces is negligible. In any event, if the area
of metering slots 44 is so selected that it provides a
linear function in respect to displacement of the stem
43 and a constant pressure is maintained in front of
the orifice, the flow force will also be linear and
will add to the spring force, changing slightly the
combined rate of the spring. The stem 43 is directly
coupled to a solenoid 138. A solenoid is an
electromechanical device using the principle of
electromagnetics to produce output forces from
electrical input signals. The position of solenoid
armature, when biased by a spring, is a function of the
input current. ~s the current is applied to the coil,
the resulting magnetic forces generated move the
armature from its deenergized position to its energiæed
position. When biased by a spring, for each specific
current level there is a corresponding particular
- position, which the solenoid will attain. As the
current i8 v~ried ~rom æero ~o maxlmum rating, the
arma~ure will move one way Erom a ~ully retracted ~o a
fully extended position in a predictable ~a~hion,
dependlng on the speci~ic level o~ current at any one
: . . , ~ . : ,~ , ..
.:
3~
-29-
instant. Since the forces developed by solenoid 126
are very small, so is the input current which is
controlled by a logic circuit or a microprocessor 128.
The microprocessor 128 will then, in response to
different types of ~ransducers, either directly control
the s~stem load, in respect to speed, force and
position, or can superimpose its action upon the
control function of an operator, to perform the
required work in minimum time, with a minimum amount of
energy, within the maximum capability of the structure
of the machine and within the envelope of its
horsepower.
Referring now to Fig. 14l the control signal
from a logic circuit or microprocessor 144, in a
similar way as described in Fig. 13, is directly
transmitted through the amplifier 148 to the
differential pressure control 68a, where, through a
solenoid and throttling valve combination, in a manner
as previously described, regulates the pressure
differential in response to input current.
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.
.: . ...
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