Note: Descriptions are shown in the official language in which they were submitted.
~7~
~,
Description
_ad Responsive Sys~em Using Load
Responsive Pump ~ontrol of a Bypass Type
Background of the Invention
This invention generally relates to bypass
type flow control of a fixed displacement pump used in
a load responsive system.
In more particular aspects this invention
relates to unloading controls of a pump bypass type
control for use in load responsive systems.
In still more particular aspects this
invention relates to unloading controls for load
responsive bypass type pump controls, which reduc~ the
pump discharge pressure below the level of the control
pressure differential, when the control system is
maintained in a standby condition.
Load responsive controls of pump output flow
are widely used and are very desirable in load
responsive systems, since they improve the system
efficiency and the control characteristics of the
system valves. Such a load responsive pump control of
a bypass type is shown in U.S. Patent 3,488,953,
issued to Haussler. When using such a control the
minimum pump discharge pressure, even in standby
condition, is dictated by the value of the control
pressure differential, which may be in the order of
say 200 PSI and especially with large pumps represents
a high energy loss, with the system in standby
condition.
The efficiency of such a control can he
increased by providing an unloading control, which
permits reduction in the pump discharge pressure in
the standby condition to a level, below that
equivalent to the control pressure differential. Such
~'',
~ ,
:
68~g7-910
a control is shown in my United States Patent 3,~2,~96, issued
~lay ~3, 1975 and also in my United States Patent 4,159,72~, issued
July 3, 1979. Those unloading controls although very effective
suffer from one basic disadvantage. Since deactivation of ~he
unloading control is a~complished by the load pressure signal and
since the system may be controlling very small loads, the pump
discharge pressure, in its standby condition, can only be reduced
to a pressure level which will provide sufficient energy for
deactivaiion of the unloading control. This minimum pressure
level, although lower than the control pressure differential, must
still be of sufficient magnitude, so that it still represents a
very significant loss in standby condition. Also there is an
additional disadvantage ~o this approach and that is the
comparatively slow response of the unloading control, in
activation of the load responsive control of the pump. This
feature becomes especially important when the controlled load may
reverse direc~ion and therefore from being of positive type
becomes of a negative type. Under these conditions, during
negative load control, the unloading control becomes activated,
adversely affecting the response characteristics of the control
system operating such a load.
Summary of the Invention
The invention provides a fluid power load responsive
system comprising an actuator, a system pump, reservoir means and
at least one direction and flow con~ro:L valve means r said
~ direction and flow control valve means having a variable inflow
metering orifice means operably connected to said actuator, spring
B
. .
~L~7~
6~297-910
biasing means operable to bias said in~low metering orifice m~ans
towards a closed position and first actuatlng mean~ having first
force generating means responsive to a control slgnal and operable
to vary the flow area of said inflow metering orifice means above
a certain first predetermined energy level of said control signal,
bypass throttling means operable to maintain a relatively constant
control pressure differential between the discharge pressure of
said system pump and pressure downstream o~ said inflow metering
orifice means above said first predetermined energy level of said
control signal, and deactivating means of said bypass throttling
means having second force generating means responsive to said
control signal and operable to deactivate said bypass throttling
means below a certain second predetermined energy level of said
control signal, said first predetermined energy level of said
control signal being higher than said second predetermined energy
level whereby discharge pressure of said system pump can be
maintained below the level of said relatively constant pressure
differential when said control signàl drops below said second
predetermined energy level.
~0 The system can unload the minimum pump discharge
pressure virtually to atmospheric level, while the response of the
system controls is not affected. The unloading controls respond
to the control signals transmitted to the direc~ion and flow
control valve of the system, below a certain specific energy level
of such control signals.
The unloading control of the load responsive bypass type
pump controlr utilizes for its operation the energy derived from a
B
~7~
6~2g7-glO
source other than the syskem pump being controlled. It is
responsive to the control siynals to position the direction
control valves of the system and permits deactivation of the
unloading control, before the direction control spools of the
system are displaced from their neutral zero flo~7 position.
The unloading control may be responsive to electrically
or hydraulically transmitted control signals to the direction
control valves of the system below a certain speciPic minimum
energy level of those control signals.
The unloading control of a load responsive bypass type
pump control can be used in a system using multiple direction
control valves controlling multiple loads and provided with a
logic module, operable to selectively transmit control signals
used, in the control of the direction control valves of the
system, to the unloading control.
The novel unloading control of a load responsive pump
control permits
3a
, .......... . .
- `
.
,~
.
~ 27~
unloading o~ the pump discharye pressure virtually to
atmospheric lavel, without affectiny the response of
the system controls and which automatically deactivate
the pump unloadiny control, before the direction
control spools of the system valves are displaced ~rom
their neutral position, providing a feature of
anticipation whereby the pump control is fully
activated before the load controlling action can
begin.
Additional objects of this invention will
become apparent when referring to the preferred
embodiments of this invention as shown in the
accompanying drawings and described in the following
detailed description.
Description of the Drawin~
Fig. 1 is a longitudinal sectional view of
two direction control valve assemblies, together with
a sectional view of pump bypass control, provided with
one type of unloading control, with system pump,
reservoir, signal generators, power transmitting lines
and signal transmitting lines shown schematically;
Fig. 2 is a longitudinal sectional view of
two direction control valve assemblies together with a
sectional view of pump bypass control provided with
another type of unloading control with system pump,
reservoir, signal generators, power transmitting lines
and signal transmitting lines shown schematically;
Fig. 3 shows identical system components as
those of Fig. 1, with schematically shown hydraulic
signal amplifying valve interposed between the
hydraulic control signal generating system and the
unloading control;
Fig. 4 is a longitudinal sectional view of
two solenoid controlled direction control valve
assemblies together with a sectional view of the pump
:..
,
. .
, :
~;~'7~
bypass control and electrically solenoid operated
unloading control, with system pump ~lectrical control
signal generating controls, ~luid transmitting lines
and electric signal transmitting lines shown
schematically;
Fig. 5 is a longitudinal sectional view of
two direction control valve assemblies provided with
electro-hydraulic controls together with a sectional
view of pump bypass control and hydraulic operated
unloading control with electrical signal generating
control, power amplifying valve responsive to an
electrical control signal, system pump, separate
control pump, fluid transmitting lines and electrical
signal transmitting lines shown schematically.
Description of the Preferred Embodiments
Referring now to the drawings and for the
present to Fig. l, direction and flow control valve
means 10 include identical direction and flow control
~alves ll and 12.
The direction and flow control valve 11 is
interposed between an actuator 13 subjected to load W
and a system pump 14 and reservoir means 15. The
direction and flow control valve ll is provided with
spring biasing means 16 operable to bias spool means
17, which include a direction and flow control spool
18, towards its neutral flow isolatin~ position. The
direction and flow control valve 11 is also provided
with first actuating means 19 including first force
generating means 20, subjected to control signal
generally designated as C1 and C2, which in the
embodiment of Fig. 1 consists of force generated by
hydraulic pressure of signals Pl, P2, P3 and P4,
acting on the cross-sectional area 21 of the direction
and flow control spool 18. The direction and flow
control spool 18 of the direction and flow control
.
'
,
~7~
valve 11, axially guide~ in a bore 22 of a housing 23
and provided with lands 24, 25 and 26, which ~e~ine
load chambers 27 and 28, is operationally connected to
spring biasing means 16. The housing 23 is provided
with exhaust chambers 29 and 30 connected to reservoir
means 15 and a supply chamber 31 connect~d through
supply line 32a with the system pump 14. The land 25
of the direction and flow control spool 18 is provided
with inflow metering orifice means 32, which includes
metering slots 33 and 34. The land 25 also
selectively interconnects the load chambers 27 and 28
with load pressure sensing ports 35 and 36, which,
together with shuttle valves 37 and 38, constitute
load pressure signal shuttle logic means 39, ~ell
known in the art. The load sensing ports 35 and 36 of
the direction and flow control valve 11 are connected
with identical load sensing ports oP the direction and
flow control valve 12 to the shuttle valve 37 by lines
40 and 41. The land 24 of the direction and flow
control spool 18 protrudes into a control chamber 42,
~hile the land 26 protrudes into a control chamber 43.
Control signal generating means 44 include
first control signal generator 45, second control
signal generator 46, a source of energy 47a, which in
the embodiment of Fig. 1 includes second pump means 47
and means responsive to an external control signal 48
including control levers 49 and 50.
The first control signal generator 45 is
connected by signal line 51, transmitting a control
pressure signal Pl, to the control chamber 43, while
also being connected by signal line 52, transmitting a
control pressure signal P~, to the control chamber 42.
In a similar way the second control signal generator
46 is connected by signal lines 53 and 54, which
transmit P3 and P4 control pressure signals, to the
.
", :'
; ~ .
~L~7~
control chambers 42 and 43 of the direction and ~low
control valve 12.
A shuttle valve 55, interposed between
signal lines 51 and 52 is connected to a shuttle valve
56 by a line 57. In an identical way a shuttle valve
58 is interposed between signal lines 53 and 54 and is
connected to the shuttle valve 56. The shuttle valves
55,56 and 58 in the embodiment o~ Fig. 1 fonstitute
control signal logic means 59, which, in its fluid
power form, in a well known manner, is operable to
transmit the highest o~ the control pressure signals
Pl, P2, P3 or P4 to line 60 connected to the shuttle
valve 56.
Bypass throttling means 61 is interposed
between ~upply chambers 31 of direction and flow
control valve 11 and 12, the system pump 14 and
reservoir means 15 and is operable to maintain a
relatively constant control pressure differential
between discharge pressure of said system pump 14 and
pressure upstream of said inflow metering orifice
means 32. Bypass throttling means 61 includes a
throttling and bypass spool 62, provided with lands 63
and 64, which are connected by a stem 65 and are
slidably guided in bore 66 in a housing 67. The
housing 67 is provided with an inlet chamber 68, an
exhaust chamber 69, a load pressure chamber 70 and
discharge pressure chamber 71, all of said chambers
being interconnected by the bore 66. The throttling
and bypass spool 62 protrudas with the land 64 into
the load pressure chamber 70 and with land 63 into the
discharge pressure chamber 71 and is biased towards
position as shown in Fig. 1 by a control spring 72.
The land 64 is provided with throttling ports 73,
which are operable to selectively interconnect the
inlet chamber 68 with the exhaust chamber 690 The
inlet ~hamber 68 is connected through lines 73a and 74
3l ~7V~
--8--
with the system pump 14, while also being connected
through lines 75 and 76 with the supply chambers 31 of
the direction and Elow control valves 11 and 12. The
e~haust chamber 6~ is connected by line 77 to
reservoir mPans 15. The load pressure chamber 70 is
connected by line 78 to load signal shuttle logic
means 39. The shuttle valve 38 may be a part of load
signal shuttle logic means 39 and may be connected by
line 79 to a separate schematically shown load
pressure sensing system 80. The discharge pressure
chamber 71 is connected by lines 81 and 74 with the
inlet chamber 68.
The housing 67 also includes a bore 82 which
interconnects the inlet chamber 68, the exhaust
chamber 69, an unloading chamber 83 and an exhaust
chamber 84 and slidably guides an unloading spool 85,
biased towards position as shown by an unloading
spring 86, which is located in the exhaust chamber 84.
The unloading spool 85 is provided with a land 87,
which protrudes into the unloading chamber 83 and is
provided with a cross-sectional area 88, which also
being provided with a land 89, which protrudes into
the exhaust chamber 84. The exhaust chambers 69 and
84 are interconnected by passage 90, provided in the
unloading spool 85. A web 91 intersected by bore 82
is positioned between the inlet chamber 68 and the
exhaust chamber 69 and is selectively engageable by
cut-off surface 92 provided on the land 87. The
unloading spool 85 is also provided with a stop 93.
The unloading chamber 83 is subjected to the actuating
pressure P5, which is supplied by line 60 from control
signal logic means 59. Deactivating means 9~, in the
configuration of Fig. 1, includes the unloading spool
85, which is operable to selectively open annular
space 95, defined by a stem 96 and bore 82, which
interconnects the inlet chamber 68 and the exhaust
.
.
: . `
~;~'7~
chamber 69 and constitutes connectiny means 95.
Deactivating means 94 is provided with second force
generating means 97, which in Fig. 1 includes ~orce
generated on the cross-sectional area 88 by P5
pressure and opposed by the biasing force of the
unloading spring 86. The housing 67 includes assembly
of throttling and bypass spool 62 and unloading spool
85, both of those assemblies being generally
designated a control assembly 67a.
Referring now to Fig. 2, like components are
designated by like numerals. The basic control
components, including the direction and flow control
valves 11 and 12, control signal logic means 59, the
pump 14, the reservoir 15 and control signal
generating means 44 of Fig. 2 are identical to those
of Fig. 1. Bypass throttling means 98 are
functionally identical to bypass throttling means 61
of Fig. 1 with passage 99 in the throttling and bypass
spool 100 of Fig. 2 being equivalent to line 81 of
Fig. 1. The throttling and hypass spool 100 and a
force piston 101 are slidably guided in bore 66
provided in a housing 102. A land 103 of the force
piston 101 defines chambers 104 and 105. The force
piston 101 protrudes with its circular extension 106
into the load pressure chamber 70, engaging the
control spring 72, while also protruding with a
circular extension 107 into a chamber 108, which is
connected by passage 109 in the force piston 101 with
the load pressure chamber 70. Deactivating means 110
of Fig. 2 accomplishes the same end results as
deactivating means 94 of Fig. 1, but in the embodiment
of Fig. 2 includes the force generating piston 101,
operable to change the biasing force of the control
spring 72. Second force generating means 97a of the
embodiment of Fig. 2 includes force generated on the
annular area 111 of the land 1023 of the force piston
' ' ,~
- . , .
. .
'7
--10--
101 by P5 pressure, opposed by the biasing force of
the control spring 72. The land 103 of the force
piston 101 is provided with surface 112 selectively
engaging a rib 113, provided in the housing 102 and
line llla connects chamber 104 to the exhaust means
15. Second force generating means 97a is included in
deactivating means 110, which also is provided with
pressure differential reducing means llOa, operable to
increase the biasing force of said con~rol spring 72.
Referring now to Fig~ 3, like components are
designated by like numerals. The basic circuit
components namely direction and flow control valves 11
and 12, control signal logic means 59, control signal
generating means 44 and control assembly 67a of Fig. 3
are identical to those of Fig. 1. The only difference
between Figs. 1 and 3 is that in Fig. 3 a three way
valve assembly 114, well known in the art, is
interposed between the shuttle valve 56 and the
control assembly 67a for selectively interconnecting,
in response to P5 pressure, the second pump means 47
and the unloading chamber 83. The three way valve
assembly 114 is provided with means 115 responsive to
P5 pressure and constitutes power amplifyin~ valve
means 116. The three way valve assembly 114 in a well
known manner is connected to second pump means 47 and
reservoir means 15 and constitutes the interconnecting
means 117.
Referring now to Fig 4, like components are
desi~nated by like numerals. Direction and flow
control valves llB and 119 are identical and perform
in an identical way to control the fluid power as the
direction and flow control valves 11 and 12 of Fig. 1.
However, direction and flow control valves 11~ and 119
are provided with direction and flow control spools 18
directly operated by proportional solenoids 120, 121,
122 and 123, which, in a well known manner, provide a
.., ~, . ...
...... ..... ... .
..
.
' ;. ' ! .
. .
. '
J~7~
mechanical displacement proportional to th~ enery~ of
th~ electrical input signals Sl, S2, S3 and S4. The
electrical input or control siynals S1, S2, S3 and S4
are generated by control signal generating -rneans 44,
5 which in the embodiment of Fig. 4 include ~irst
electrical signal generator 124 and second electrical
signal generator 125, which are provided with control
levers 49 and 50, which together constikute means
responsive to an external control signal 48. The
10 electrical signal generators 124 and 125, in a well
known manner, are supplied with energy from the source
of electrical power 126. First electrical signal
generator 124 is connected by electrical signal
transmitting lines 127 and 128 wilth proportional
solenoids 122 and 123, while the second electrical
generator 125 is connected by electrical signal
transmitting lines 129 and 130 with the proportional
solenoids 120 and 121. The basic configuration of the
control assembly 67a of Fig. 4 is similar to that of
Figs. 1 and 3 the only dif~erence being that the
unloading spool 85 is directly operated by an
electrical solenoid 131, well known in the art. The
solenoid 131 is provided with a coil 132, provided
with electrical power from the source of electrical
25 power 126 through a relay 133, well known in the art.
The relay 133, in a well known manner, in response to
an electrical signal from electric logic 134, either
connects or disconnects the coil 132 of the electrical
solenoid 131 from the source of electrical power 126.
In the embodiment of Fig. 4 in the presence of S1, S2,
S3 or S4 electrical signals the electrical relay 133
connects the coil 132 with the source of electrical
power 126, resulting in displacement of the unloading
spool 85 against the biasing force of the unloading
spring 86.
. .
:. :, ,: '`'
:'
~a~
--12
Referring now to Fig. 5, like components are
designated by like numerals. The direction control
spools 18 of the direction and flow control valves 135
and 136 are displaced in a manner identical to that as
referred to in Fig. 1 by control pressures generated
by electro-hydraulic valves 137, 138, 139 and 140,
well known in the art, which in response to electrical
control signals Sl, S2, S3 and S4 will produce
proportional pressure signals P1, P2, P3 and P~ in the
control chambers 42 and 43. In a manner similar to
that as shown in Fig. 3, the power amplifying valve
means 116 is interposed between electric logic means
134 and deactivating means 94 of the control assembly
67a. Power amplifying valve means 116 is provided
with a three way valve 141, well known in the art,
which will, in a well known manner, connect unloading
chamber 83 with a source of hydraulic power 47, when
actuated by a solenoid 142 supplied with an electrical
power signal 143. The solenoid 142, responding to
electrical power signal 143 constitutes the means 144,
responsive to electrical signal from electric logic
134.
Referring now back to Fig. 1, a fluid power
and control system of this invention is interposed
between the system pump 14 and system actuators 13 and
13a controlling load W. The control system of Fig. 1
will control a single actuator, while also being
adaptable to the control of multiple actuators, when
using a single system pump.
The direction and flow control valves 11 and
12 of the system are of a conventional type, well
known in the art, and are provided with metering slots
33 and 34 and load pressure sensing ports 35 and 36,
which are connected through a logic system of shuttle
valves 37 and 38 to the bypass and throttling means
61, well known in the art~
'
-~3-
The direction and flow control spools 18 of
the direction and flow control valve 11 and 12 are
displaced against the centering force of spriny
biasing means 16 by control signals, remot~ly
generated by control signal generating means 4~ and in
a well known manner, in a proportional way, vary the
flow area of the metering slots 33 and 34, while also
transmitting the load pressure signals to the
throttling and bypass spool 62.
In a well known manner the throttling and
bypass spool 62, subjected to pump discharge pressure
in chamber 71 and positive load pressure, transmitted
through the load pressure sensing and logic circuit,
to the load pressure chamber 70, while also being
subjected to the biasing force of the control spring
72, will assume a modulating position throttling
through throttling ports 73 fluid flow from the inlet
chamber 68 to the exhaust chamber 69, to maintain a
relatively constant pressure differential between the
pump discharge pressure and the highest positive load
system pressure, this pressure differential being
equivalent to the preload in the control spring 72.
In the system of Fig. 1, since while
controlling any of the system loads, with constant
pressure differential being automatically maintained
constant across the metering slots 33 and 34, by the
bypass throttling means 61, the fluid flow into the
fluid motor 13 or 13a will become proportional to the
displacement of the valve spool 18, irrespective of
the magnitude of the system load W. Since, as
previously described, the displacement of the
direction and flow control spool 18 is in turn
proportional to the magnitude of the control signal,
generated by the control signal generating means 44,
very precise control of the load W can be obtained.
~7~
-14-
As is w~ll known in the art, one of the
basic characteristics of bypass throttling means 61 is
that in the absence of a load pressure signal and
therefore in standby condition it will generate and
maintain a minimum discharge pressure of the pump 14,
which is equivalent to the preload of the control
spring 72, which minimum system pressure, in
conventional operating systems, usually exceeds 100
PSI, which especially in a system utilizing the system
pump 14 of a large size represents a large parasitic
loss, associated with such control systems.
In the embodiment of Fig. 1 in the absence
of P5 control pressure, the unloading spool 85,
subjected to the biasing force of the unloading spring
86 will be maintained in position as shown in Fig. 1,
providing a bypass path for fluid flow through annular
space 95, from the inlet chamber 68 to the exhaust
chamber 69, maintaining, in standby condition, the
discharge pressure of pump 14 at near atmospheric
level and therefore maintaining the system losses in a
standby condition to a minimum level.
With control pressure P5 provided to
unloading chamber 83 at a level high enough to
generate force, to overcome the preload of the
unloading spring 86, the unloading spool 85 is moved
all the way from right to left with the cut-off
surface 92, in combination with we~ 91, isolating the
inlet chamber 68 ~rom the exhaust chamber 69. Under
those conditions the bypass throttling means 61 will
automatically assume its modulating position,
maintaining, in a manner as previously described, the
discharge pressure of the pump 14 at a constant level,
equivalent to the preload of the control spring 72 and
equal to the control pressure differential of the load
responsive system.
. ~ ' ~',
. ~ '' "' ,.
..,., :;
,
7~
-15-
In the embodiment o~ Fig. 1 the control
pressure signals Pl, P2, P3 and P4 are generated by
the first and second control signal generators 45 and
46, using energy derived from source of energy 47a,
which in this embodiment is second pump means 47.
The generated control pressure signal P1,
P2, P3 or P4 reacts on the cross-sectional area of the
direction and flow control spool 18 and will start
displacing it in either direction at a pressure level
equivalent to the centering force of the spring
biasing means 16. Therefore, until a specific level
of the control pressure, as dictated by the centering
force of the spring biasing means 16, is reached, the
direction and flow control spools 18 will remain in
lS the centered position, as shown in Fig. 1, isolating
inlets and outlets of the actuators 13 or 13a.
However, the very fact that the control pressure
signal is generated by the first or second control
signal generators 45 or 46, automatically establishes
the intention of the operator to control the load W.
The P5 pressure level, to fully actuate the
unloadinq spool 85, is selected well below the minimum
pressure level of the control pressures P1, P2, P3 and
P4, which would displace the direction control spools
18.
The first and second control signal
generators 45 and 46, which in the embodiment of Fig.
l are of a hydraulic type, are connected by fluid
conducting lines 51, 52, 53 and 54 to the direction
and flow control valves 11 and 12 respectively, while
control signal logic means 59, including the shuttle
valves 55, 56 and 58, connect by line 60 the highest
of the control pressures Pl, P2, P3 or P4 to the
unloading chamber 83. To facilitate the description
of the operation of Fig. 1 the maximum load pressure
signal generated by control signal generating means 4
.
-16-
and transmitted by the control signal lo~ic means 59
to the unloading chamber 83, is denoted as P5.
Therefore, at any preselected P5 pressure
level of P1, P2, P3 and P4 control pressures, which is
selected well below the control pressure level,
capable of actuating the direction and flow control
spools 18, through the action of unloading spool 88,
the load responsive circuit of Fig. 1 is activated, in
anticipation of controlling action of load W, while
the direction and flow control spools 18 remain in
neutral position isolating the port of fluid motors 13
and 13a.
Any further increase in the pressure level
of the signals P1, P2, P3 and P~, above that
equivalent to that of the spool centering forces, will
displace the spools 18 in either direction, with the
fully activated load responsive system control
automatically providing a well known proportional
control feature of system loads.
Any reduction in control pressure signals to
P5 level will first permit spring biasing means 16 to
return the direction and flow control spools 1~ to
their neutral isolating position, while also
permitting after this sequence of events is
accomplished, movement of the unloading spool 85 under
action of the unloading spring 86 to its fully bypass
position, as shown in Fig. 1, thus lowering the pump
discharge pressure to a minimum level.
Therefore, the embodimant of Fig. 1 permits
unloading of the system for a minimum system loss in
standby condition, while also providing activation of
the load responsive system controls, before the
direction control spools of the system are displaced
and therefore before the control action of the system
loads can take place, providing a unique anticipation
-17-
feature, high system response and minimum system loss
in bypass condition.
Referring now back to Fig. 2, identical
direction and flow control valves 11 and 12 are
providPd with an identical load sensing sys~em,
control signal generating means 44 and control signal
logic means 55 as used in Figs. 1 and 2. As described
when referring to Fig. 1 bypass throttling means 98
performs an identical function as the bypass
throttling means 61 of Fig. 1, in maintaining a
constant pressure differential between the inlet
chamber 68 and the load pressure signal, by the
throttling and bypassing action of the throttling
ports 73. In a well known manner this constant
pressure differential is proportional to the preload
in the control spring 72.
However, in the arrangement of Fig. 2, in
standby condition, in a manner well known in the art,
the preload in control spring 72 is reduced to a
certain preselected minimum level, which automatically
reduces the control pressure differential and the pump
discharga pressure in standby condition, thus
substantially reducing the parasitic system loss in
standby condition. In the systems of prior art this
minimum pressure level and minimum pressure
differential, in standby condition, can be reduced
only to a certain minimum level, since the minimum
pump discharge pressure, in standby condition, must be
sufficiently high to self-energize the control
circuit. With such a control not only the system
loss, although substantially reduced, is still
comparatively high, but because of the low energy
levels, used in energizing the control system, the
response of the energizing controls is very slow.
In the present invention with the force
piston 101, in the position as shown in Fig. 2, the
,
: . ;
.
:
;,; ~
-18-
preload in the conkrol spring 72 is completely
eliminated and the bypass and throttling spool 100
mov~s to the left, interconnecting the inlet chamber
68 with the exhaust chamber 69 through a very large
flow area of the throttling port 73. In this way, in
standby condition the pump discharge pressure can be
reduced to a very low level, corresponding to a very
small system loss. The force piston 101 is provided
with two circular extensions 106 and 107, having
identical cross-sectional areas, with passage 109
interconnecting the chamber 108 with the load pressure
chamber 70, providing a balanced type configuration of
the force piston, which does not respond to the
pressure level of the positive load pressure existing
15 in the load pressure chamber 70. With the chamber 104
connected by line llla to the system reservoir 15, any
pressure in the chamber 105 generates, in a well known
manner, a force equal to the product of the pressure
and the annular area 111. This annular area 111 is so
selected that when subjected to P5 pressure it will
move the force piston 101 all the way from left to
right through a preselected distance, which will
produce a preselected preload in the control spring
72, equivalent to the relatively constant control
pressure differential of the load responsive system.
Therefore, in a different way the embodiment of Fig. 2
produces identical control characteristics as that of
the embodiment of Fig. 1.
In the absence of P5 pressure, or with P5
pressure below a certain specific preselected level,
the control of the pressure differential of the system
is deactivated and the discharge pressure of the pump
14 is brought to a minimum level, corresponding to a
minimum standby loss.
In a manner as fully described when
referring to Fig. 1, the presence of control signals
. I ... .
q~
--19--
P1, P2, P3 and P~ at P5 pressure level will eneryize,
through the control signal logic means 59, thP
pressure differential reducing means llOa,
automatically restoring the constant pressure
differential control action of bypass throttling means
98. Therefore, the system load responsive control
becomes activated before the direction and flow
control spools 18 are displaced from their neutral
position, providing an anticipation feature identical
to that of Fig. l~ The activation of the control of
the constant pressure differential takes place through
control signal logic means 59, using the energy
derived from second pump means 47/ permitting the pump
14 to work at minimum pressure level in its standby
condition.
While controlling he load W reduction of the
pressure of the control pressure signals P1, P2, P3
and P4, to a level equivalent to the centering force
of the spring biasing means 16, permits the return of
the direction control spools 18 to their neutral
isolating position, while the load sensing control is
still active. A further reduction in control pressure
to or below the P5 pressure level automatically
signifies the intention of the operator to discontinue
control of the load W and also signifies standby
condition. In a manner as described when referring to
Fig. 1, a drop in control pressure signal below P5
pressure level automatically unloads the system pump
14 to a minimum standby discharge pressure level.
Referrin~ now back to Fig. 3, all of the
basic control components of Fig. 1 are identical to
those of Fig. 3 and perform in an identical way. The
only difference between Fig. 1 and Fiy. 3 is the
introduction of power amplifying valve mans 116 in the
form of well known three way valve assembly 14, which
is intarposed between the shuttle valve 56 and the
, -
;.
: ~
-20
unloading chamber 83. The three way valve 114 is
provided with means responsive to P5 pressure 115,
which is in the form of a hydraulic actuator spring,
biased towards position as shown in Fig. 3. In this
position the unloading chamber 83 is directly
connected to reservoir 15 and the deactivating means
94 automatically unloads the discharye pressure of the
pump 14 to near atmospheric level, in a manner as
described in detail when referring to Fig. 1.
Once control signal generating means 44
generates a control signal at a pressure level equal
to or exceeding P5 pressure, in a well known manner
the three way valve 114 is moved into a position, in
which P pressure of second pump means 47 is directly
conn~cted to the unloading chamber 83. The presence
of high pressure in the unloading chamber 83, in a
manner as described when referring to Fig. l, moves
the unloading spool 85 from right to left, isolating
the inlet chamber 68 from the exhaust chamber 69 and
therefore automatically activating the load responsive
constant pressure differential control - bypass
throttling means 61O
Once control signal generating means 44
generates a control signal at a pressure level equal
to or exceeding P5 pressure, in a well known manner
the three way valve 114 is moved into a position, in
which P pressure of second pump means ~7 is directly
connected to the unloading chamber 83. The presence
of high pressure in the unloading chamber 83, in a
manner as described when referring to Fig. 1, moves
the unloading spool 85 from right to left, isolating
the inlet chamber 68 from the exhaust chamber 69 and
therefore automatically activating the load responsive
constant pressure differential control - bypass
throttling means 61.
,~
.
,
. . . .
7 ~
-21-
Although the basic operation of the cGntrol
circuits of Figs. 1 and 3 are identical, there is a
difference in response of the unloading control
between the embodiments of Figs. 1 and 3.
In Fig. 1 the energy of the control pressure
signal P1, P2, P3 or P4 is used to displace the
unloading spool 85. This requires larger capacity
signal generators 45 and 46 and larger capacity
control signal logic means and slows down
significantly the response of the control.
In Fig. 3, through the use of power
amplifying valve means 116, which responds to pressure
at minimum flow, permits direct use of the energy
developed by second pump means 47 in displacement of
the unloading spool 85, not only sig~ificantly
reducing the required flow capacity of the signal
generators 45 and 46 and flow transmitting capacity of
the control signal logic means 59, but results in a
much faster responding controls, which is still
provided with the feature of anticipation.
Referring now back to Fig. 4 the direction
and flow control valves 118 and 119, as far as the
fluid power and transmission circuit are concerned,
are identical to direction and flow control valves 11
and 12 of Fig. 1. The only difference between
direction and flow controls 118 and 119 of Fig. 4 as
compared to those of Fig. 1 is in the way in which the
direction control spools 18 are displaced, in response
to the control signals S1, S2, S3 and S4. The
direction and flow control spools 18 of Fig. 4 are
spring biased by spring biasing means 16, towards
neutral position and displaced from neutral position
by the proportional solenoids 120, 121, 122 and 123,
well known in the art, which are supplied with
electrical control signals S1, S2, S3 and S4, from
control signal generating means 44, which, in the
.
:
. .
--22--
embodimerlt of Fig. 4, consists of electrical signal
generators 124 and 125, well known in the art, and
supplied with electrical energy from the source of
electrical power 126. The electrical signal
generators 12~ and 125 generate electrical control
signals in response to the displacement of the control
levers 49 and 50. Although the electrical control
signals Sl, S2, S3 and S4 can be proportional to the
displacement of the control levers 49 and 50, in
10 either direction from their neutral position, as is
well known in the art, those signals can be
conditioned to include the solenoid temperature
compensation and may include the so-called spring bias
eliminator which, with the control levers 49 and 50
15 displaced from neutral position, generate an
electrical signal at an energy level e~uivalent to the
preload of the centering spring biasing means 16.
The hydraulic circuits of Figs. 1 and 4,
including direction control valves 118 and 119, the
20 load shuttle logic means 39, which may include load
pressure sensing ports 35 and 36 and the control
assembly 67a, including the bypass throttling means 61
and the unloading spool 85 are identical, the one
basic difference between Figs. 1 and 4 is in
25 generation of the electrical signals Sl, S2, S3 and S4
versus hydraulic pressure control signals Pl, P2, P3
and P4 and the displacement mechanism of the spool 85.
In Fig. 4 the unloading spool 85 is displaced by the
armature of the electrical solenoid 131, contained
30 within the coil 132. The solenoid 131 is provided
with energy from the source of electrical power 126,
through an electrical re]ay 133, which is activated by
a signal from electric logic 134, in response to
electrical signals Sl, S2, S3 and S4, generated by the
35 electrical signal generators 124 and 125.
~'
.. . . .
.
`: '`
-23-
The electrical solanoid 131 of Fiy. 4~ from
a functional standpoint, is equivalent to the second
force generating means 97 of Fig. l, while the
electrical signal generators 124 and 125 of control
signal generating means 44 of Fig. 4, are equivalent
to the control signal yenerators 45 and 46 of Fig. 1,
all of those generators being responsive to the
displacement of the control levers 49 and 50, while
the control signal logic means 59 are equivalent to
the electric logic 134 combined with electrical relay
133.
In a manner as described when referring to
Fig. 1, in standby condition the system pump 14 is
fully unloaded by the unloading spool 85.
Generation of an electrical control signal
at a first power level, through the electric logic 134
and the relay 133, actuates the unloading spool 85 by
the solenoid 131, in a manner as previously described,
activating the bypass throttling means ~1, while the
proportional solenoids 120, 121, 122 and 123 generate
a force, lower than that equivalent to the centering
force of the spring biasing means 16, with the
direction control spools 18 remaining in their load
isolating position.
Further increase in the power level of the
electrical control signals S1, S2, S3 and S4
proportionally displaces, through the proportional
solenoids 120, 121, 122 and 123, the valve spools 18
from their neutral position, proportionally
controlling the velocities of the load W, irrespective
of the magnitude of the load. The control aspects of
the load responsive control of Fig. 4, from a fluid
power standpoint, were fully described when referring
to Fig. 1 and the control characteristics, advantages
and the features of anticipation are retained in both
of those controls.
. ~:
. . .
p~
~L O ~
-~4-
Referring now back to Fig. 5, the control
characteristics of the direction and flow control
valves 135 and 136 are identical to the direction and
flow control valves 118 and 119 of Fig. 4, the one
difference being that instead of using the eleckrical
proportional solenoids 120, 121, 122 and 123 of Fiy. 4
the electro-h~draulic valves 137, 138, 139 and 140 are
used. Both the proportional solenoids and the
electro-hydraulic valves respond to the electrical
control signals S1, S2, S3 and S4, generated by
similar electric signal generators 124 and 125, which
constitute control signal generating means 44. The
embodiments of Figs. 4 and 5 use similar electric
logic 134 and relay 133, responsive to the electrical
control signals S1, S2, S3 and S4.
The basic difference between the embodiments
of Figs. 4 and 5 is in actuation of the unloading
spool 85. In Fig. 5 the unloading spool 85 is
actuated in an identical way as the unloading spool 85
of Fig. 3, through the action of power amplifying
valve means 116, which include identical three way
valves 114 and 141, the only difference between those
three way valves being that the three way valve 114 of
Fig. 3 has means responsive to P5 pressure 115 and is
operated by hydraulic pressure, while the three way
valve 141 of Fig. 5 is operated directly by solenoid
142, in response to an electrical power signal 143.
The embodiment of the control of Fig. 5 has
much faster response characteristics, since the
response of the electro-hydraulic valves 137, 138, 139
and 140 is much faster than the response of
proportional electrical solenoids 120, 121, 122 and
123 of Fig~ ~, but also the response of the unloading
spool 85 of Fig. 5 is much faster than the solenoid
operated version of Fig. 4, since, in a manner as
described when referring to Fig. 3, it is utilizing
-25-
the energy developed in the second pump means 47, to
move the unloading spool 85.
All the basic control characteristics of
Figs. 1 - 5 are identical, with most of the same
common advantages of saving energy an~ the feature of
anticipation, when converting from standby condition
to operational condition.
Although the preferred embodiments of this
inventions have been shown and described in detail it
is recognized that the invention is not limited to the
precisa 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.
, .
.
,, .
