Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF THE IN~ENTION
i The invention disclosed herein pertains generally to
i hydraulic control systems ror distributing fluid to a plurality
of fluid actuated devices, and more particularly to a hydraulic
control system which ensures that a particular fluid actuated
I device receives an adequ~te supply of fluid even when being used
in conjunction with one or more of the other of the plurality of
fluid actuated devices.
¦ It is frequently necessary for a single hydraulic pump to
lo Ij provide sufficient hydraulic fluid to operate a plurality of
fluid actuated devices. In the past it has been common to utilize¦
fixed displacement pumps in combination with open center control
valves to distribute the fluid to the various fluid actuated
I devices. Such systems have several drawbacks including the fact
, that they are energy inefficient because when the fluid actuated
~ devices utilize only a portion of the output of the fixed
¦ displacement pump, the remainder of the pump power is wasted.
To overcome 'he deficiencies associated with hydraulic
I control systems which utilize fixed clisplacement pumps, variable
I displacement pumps have been used in combination with closed
! center control valves to achieve better system efficiency. In
some applications the vari~ble displacement pumps have been
I provided with pressure compensated controls, and in other
! applications variable displacement pumps in combination with a
closed center control valve have been utilized in a load
sensitive system. ~he former systems have usually been character-
ized by large pressure drops which results in a very ineficient
use of energy. In the latter system, when a load is being
' lowered under the influence of gravity the load signal may
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l reverse, resulting in diminished pump output rather than the
desired increase in pump output.
The hydraulic control system disclosed in U.S. Patent No.
3,78B,077 to Johnson et al includes a variable displacement
pump, an open center type of control valve, and a fluid
actuated displacement control mechanism for the pump.
control pressure signal indicative of pump output pressure is
developed in the control valve, and this control signal is
eommunicated to the displacement control mechanism to regulate
pump displacement. Systems of this type generally lack the
responsiveness and sensitivity needed for the control of many
types of fluid actuated devices.
The hydraulic control system disclosed in U.S. Patent No.
4,197,7~5 to Westveer, overcomes many of the aforementioned
problems. This hydraulic control system includes a variable
displacement pump which supplies fluid to a control valve which
lncludes a plurality of control valves, each of which valves
regulates the flow of fluid to a fluid actuated device. Each
of the valves includes a relatively small, variable orifice in
its center. A relatively small fluid f:Low from the variable
displacement pump is supplied to the variable orifice of the
first valve, and the output from each variable orifice of each
valve is then directed to the input of the variable orifice of
each succeeding valve. The resulting pressure signal sensed at
a point downstream from the last of the variable orifices is
referred to as a center core signal and constitutes a control
signal. This control signal is comnunicated to a fluid
actuated displacement contrnl device which re~ulates the
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1 1, displacement of the variable displacement pump in response to
,l the magnitude of the control signal. As the plunger of any one
¦~ of the valves is moved from the neutral position toward an
operating position, indicating the need for a greater supply of
fluid to that valve, the size of the variable orifice of that
valve is reduced~ resulting in a decrease in the magnitude of the
control signal. As the plungers of the other valves are moved
from their neutral positions toward their operating positions,
I, the magnitude of the control signal is further reduced. The
~ displacement control device is suc~ that a decrease in the
' magnitude of the control signal results in a corresponding
I increase in the displacement of the variable displacement pump.
¦ While the hydraulic control system disclosed in U.S. Patent
! No 4,197,705 to Westveer i5 energy efficient and sufficiently
sensitive and responsive for the control of many types of fluid
- actuated devices~ neither this hydraulic control system nor any
of the other above-mentioned hydraulic control systems is
¦ capable of ensuring that one particuLLr fluid actuated device
1 will be supplied with an ade~uate flow of fluid when being used
20 ¦1 in conjunction with one or more other fluid actuated ~ievices.
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1 SUMMARY OF THE INVENTION
i The present invention is directed to a hydraulic control
system for regulating a flow of fluid from a variable displacement ¦
pump to a plurality of fluid actua~ed devices, which control
! system ensures that a particular fluid actuated device receives
an adequate supply of fluid even when being used in conjunction
~with one or more of the other fluid actuated devices. The
present invention may, for example, be used as a hydraulic control
svstem for a combination loader and backhoe vehicle to ensure that
10 the swi~gvalve of the backhoe valve receives an adequate supply of
fluid from the variable displacement pump of the hydraulic control
system even when being used in conjunction with one or more o~
the other backhoe valves.
Accordingly, a primary object of the present invention is
to ?rovide a hydraulic control system for a plurality of fluid
actuated devices which ensures that a particular fluid actuated
device receives an adequate supply of fluid even when being used
in conjunction with one or more of the other fluid actuated
devices.
Another object of the present invention is to provide a
hydraulic control system for a plurality of fluid actuated
devices which employs a modified cent~r core signal system,
modified to enable the system to provide an adequate supply of
fluid to a particular fluid actuated device even when this
device is used in conjunction with one or more of the other
fluid actuated devices.
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1 I Yet another object of the present invention is to provide
i a hydraulic control system for a combination loader and backhoe
` vehicle which will prevent the variable displacement pump of the
! present invention from increasing its displacement to maximum
displacement in order to meet the flow demands of the loader
valve when this valve is fully actuated and the vehicle is in
' motion.
I Thus, a hydraulic control system, according to the present
! invention, includes a fluid reservoir and a variable displacement ¦
1~ pump having a fluid input in fluid communication with the fluid
I reservoir and a fluid output. The present control system also
includes a first control valve having a fluid input in fluid
communication with the fluid output of the variable displacement
pump, the first control valve being adapted to regulate a flow
of fluid to a first fluid actuated device and including first
means for developing a first pressure signal. At least a second
control valve is included having a fluid input in fluid
communication with the fluid output of the variable displacement
l pump, the second control valve also being adapted to regulate a
flow of fluid to a second fluid actuated device and including
second means for developing a second pressure signal. A selector
~means senses the first and second pressure signals and provides a
'i control pressure signal which is the smaller of the first and
! second pressure signals. Finally, the present invention includes
a fluid actuated displacement control means in fluid communication
, with the selector means, for sensing the control pressure signal
i provided by the selector means and for regulating the displace-
ment of the pump in response to the magnitude of the control
pressure signal.
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1 BRIEF DESCRIPTION OF THE DRAWING
A preferred embodiment of the present invention is
described with reference to the single accompanying drawing
which is a schematic diagram of a hydraulic control system
according to the present invention as used in a combination
loader and backhoe.
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1 ., DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
With reference to the single accompanying figure, a preferred
¦ embodiment of a hydraulic contxol system 10, according to the
present invention, for controlling the distribution of fluid to
a plurality of fluid actuated devices on a combination loader and
backhoe vehicle, includes a variable displacement pump 12. The
. variable displacement pump 12 has i;ts fluid input in fluid
communication with a fluid reservoir 14. The pump 12 is provided
~ with a fluid actuated displacement control mechanism 16 for
lo controlling the displacement of the pump 12. The displacement
control mechanism 16 includes a displacement control cylinder 18
. which is mechanically linked to the pump 12, and a sensor valve
22 which communicates with both the displacement control cylinder
18 and the reservoir 14.
The displacement control cylinder 18 includes a spring biased
piston 20 which is mechanically linked to the pump 12. A spring
l9 biases the piston 20 to the left (as shown in the single
~igure) so that the displacement of the pump 12 is initially at
maximum displacement. The sensor valve 22 is a meterin~ valve
; having first operative positions 24, a neutral position 26, and
second operative positions 28. A spring 30, on the right side
of the sensor valve 22, biases the sensor valve 22 toward the
il first operative positions 24 in which the high pressure side of
¦ the displacement control cylinder 18 communicates with, and is
vented to, the reservoir 14. As is conventional with metering
valves, the further the sensor valve 22 is moved from the neutral ¦
position 26 toward the first operative positions 24, the smaller
will be the reslstance to fluid flow through the valve and the
greater will be the fluid flow through the valve, and the more
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1 1iquickly the high pressure side of the displacement control
cylinder 18 will be vented to the reservoir 14. In the neutral
position 26 fluid flow through the sensor valve 22 is blocked
and the displacement control cylinder 18 is hydraulically locked.
The left side of the sensor valve 22 is biased by a control
~pressure signal 32 toward the second operative positions 28 in
jwhich the control pressure signal is communicated to the displace-
ment control cylinder 18 in order to urge the piston 20 to move
'to the right, to thereby reduce the displacement of the variable
displacement pump 12. Again, the further the sensor valve 22 is
moved from the neutral position 26 toward the second operative
~'positions 28, th~ smaller will be the resis~ance to fluid flow
through the valve. The control pressure signal 32, which is
discussed more fully below, is communicated to the input of the
~sensor valve 22 through a line 34 and is communicated to the left j
side of the sensor valve 22 through a line 33 which branches off
from the line 34 upstream from the sensor valve 22.
The output of the pump 12 is communicated through a line
44 to a priority valve 46. The priority valve 46 communicates
through a line 48 with a steering valve 50, and through a line
58 with a loader valve 60. The loader valve 60, in turn,
communicates with a stabilizer valve 70 through a line 67. The
priority valve 46, the steering valve 50, the loader valve
'l60, and the stabilizer valve 70, are conventional, and need not
be discussed in detail here. The function of the priority valve
46 is to give fluid flow priority to the steering valve 50
over the loader valve 60 and the stabilizer valve 70, as well
as over the other valves in the hydraulic control system down-
stream from the line 58 discussed below.
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1 A portion oî the fluid flowing through the line 58 to the
loader valve 60 is diverted from the loader valve through a line
80 which intersects the line 58 upstream from the loader valve.
The line 80 contains a flow control valve 82 which includes a
variable orifice 84. The line 80 leads, through a line 81, to a
,'~ swing valve and a backhoe valve, described below. One function
of the line 80 and flow control valve 82, as is explained more
-ully below, is to divert a relatively small amount of flow from
the loader valve 60 and stabilizer valve 70 to the line 80. This ¦
lo small amount of flow is used to define a pressure signal, large
compared to the pressure downstream from the loader and stabilizer
valves when these valves are fully actuated, which pressure signal
is communicated to the pump 12 in order to prevent the pump from
soing to maximum displacement when the loader cr stabilizer valves¦
are rully actuated. Yet another function of the flow control valvq
82 is to limit the amount of flow diverted from the loader valve 60
and stabilizer valve 70 through the line 80, in order to assure
the loader valve and stabilizer valve an adequate supply of flow
when these valves are actuated. The flow control valve 82
accomplishes this function by presenting a greater resistance to
fluid flow through the line 80 than the resistance to fluid flow
.hrough the lines 58 and 67 created by the actuation of the loader
valve 60 and stabilizer valve 70.
The loader valve 60, may, for example, include two valves
arranged serially with respect to one another, each open center
metering valve containing a variable orifice in its center. The
line 58 from the priority valve 46 would communicate with the
input of the first of these valves as ~ell as with the input to
the variable orifice in the center of this valve. In addition,
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1 the o~tput from the variable orifice in the center of the first
of these valves would communicate with the input to the second
of these valves as well as with the input to the variable orifice
, in this second valve. If each of the valves is actuated by a
plunger which moves the valve from a neutral position to an
operating position, then the cross-sectional area of he variable
orifice in the center of each of the valves would be reduced as
; the plunger of that valve moves from the neutral position to an
operating position, and the pressure downstream from each of the
o variable orifices would be correspondingly reduced. Thus, the
pressure downstream from the second of the variable orifices would
be indicative of the total flow demanded by the loader valve 60.
; The stabilizer valve 70 may/ for example, include two
serially arranged valves, with each valve containing a variable
orifice in its center. The line 67 would communicate the output
,rom the second of the variable orifices in the loader valve 60
to the input of the first of the valves of the stabilizer valve
70 as well as to the input of the variable orifice in the first
of these valves. The output from the variable orifice in the
first valve of the stabilizer valve 70 would be communicated to the
input of the variable orifice in the second valve, whose output
would then be communicated through a line 79 to a line 81 which
extends from the point of intersection of the lines 79 and 80,
which line 80 branches off from the line 58 feeding the loader
valve 60. If each of the valves of the stabilizer valve 70 is
actuated by a plunger which moves the valve from a neutral position
to an operating position, then as these plungers are moved to
their respective operating positions, the flow demanded by the
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1 stabilizer valve and by the loader valve would be reflected by
the pressure in the line 79 downstream from the second of the
variable orifices in the stabilizer valve 70.
It is often common to use the loader valve 60 when the
combined loader and backhoe vehicle is in motion. The stabilizer
valve 70 and the backhoe valve section, described below, being
used when the vehicle is stationary~ If the loader valve 60 and
stabilizer valve 70 were fully actuated, then the pressure
downstream from these valves communicated to the line 81 through
the line 79 would necessarily be relatively low. This relatively
low pressure would then be communicated through the center core
signal system described below to the displacement control
mechanism 16, which mechanism would act to drive the pump 1~ ¦
toward maximum displacement. However, the flow control valve 82
prevents this from happening by generating a relatively large
pressure signal which is communicated through the line 80 and
added to the relatively low pressure signal in the line 79 from
the fully actuated loader or stabilizer valves to produce a
combined pressure signal in the line 81 to prevent the pump 12
~o from going to maximum displacement.
- The backhoe valve section 89 of hydraulic control system 10
of the present invention includes a swing valve 90 and at least
one other valve. The backhoe valve section 89 is usually used
only when the combined loader and backhoe vehicle is stationary. I
The backhoe valve section may, for e~ample, include a bucket
valve 100. In addition, the backhoe valve section may also
include a dipper valve, a boom valve, and a dipper extension
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1 Ivalve arranged serially with respect to the bucket ~alve. Each
¦of the swing and backhoe valves is preferably an open center
¦metering valve. The swing and bucket valves also include a
modified center core signal system which ensures that the swing
valve 30 always gets an adequate supply of fluid even when being
jused in conjunction with the other backh~e valves. This modified
Icenter core signal system includes a variable orifice in the
l¦center of each of the swing and other backhoe valves. That is,
¦Ithe swing valve 90 includes a relatlvely small, variable orifice
~92 in its center. Similarly, the bucket valve 100 of ~he backhoe
Ivalve section includes a relatively small, variable orifice 102
in its center, while each of the dipper, boom, and dipper
lextension valves, if included in the backhoe valve section, would
¦also include a relatively small, variable orifice in its center.
I The swing valve 90 includes a fluid input 93 which is in
'fluid communication with the flow line 81 through a flow line 94
~Iwhich branches off from the flow line 81, and through a flow line
ilg5. In addition, the input to the variable orifice 92 o~ the swing
¦valve 90 also communicates with the flow line 81 through a flow
lline 98 which branches off from the flow line 81 at a point down- ¦
stream from where the flow line 94 branches off from the flow line
81. Because the swing valve 90 (and other backhoe valves~ are
typically used only when the combined loader and backhoe vehicle is~
stationary and the loader valve 60 and stabilizer valve 70 are in
their neuiral positions, the input 93 of the swing valve 90
receives its supply of working fluid from the pump 12 through the
lines 44 and 58, almost without any resistance to flow through the
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'lines 67 and 79 (when the loader and stabilizer valves are in their'
neutral positions), and then through the lines 81, 94, and 95. of
course, a portion of the relatively small pressure signal flow
diverted through the flow control 82 is also supplled to he
~input 93 through the flow lines 80, 81, 94, and 95. The input to
¦ithe vaxiable orifice 92 receives a portion of the fluid flowing
through the loader valve 60, line 67, stabilizer valve 70, and
,line 79, via the flow lines 81 and 98. In addition, a portion
Iiof the relatively small pressure signal flow diverted through
,',the flow control valve 82 is also supplied to the input of the
"variable orifice 92 through the flow lines 80, 81, and 98.
The swing valve 90 includes a neutral position 90a in which
fluid communication between the variable displacement pump 12
(through the flow lines 44, 58, 67, 79, 81, 94, and 95) and the
fluid actuated device regulated by the swing valve 90, is blocked.
The swing valve 90 also includes flrst operating positions 90b,
and second operating positions 90c. When a plunger 97 of the
swing valve 90 is used to move the swing valve 90 from the
neutral position 90a toward one of the operating positions, the
extent of which motion corresponds to the flow demands of the
swing valve 90, the cross-sectlonal area of the variable orifice
~92 is progressively reduced during the motion of the plunger
and the pressuxe downstream from the variabl~ orifice 92 is
indicative of the flow demands of the swing valve 90. The
pressure at the outlet of the variable orifice 92 in the swing
valve 90, which pressure constitutes a first pressure signal 140,
''is communicated through a line 150 to a selector valve 160, which
,is described more fully below.
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1The output from the variable orifice 92 in the swing valve
90 is communicated through a flow line 101 to the input of the
'variable orifice 102 in the bucket valve 100. In addition, the
input to the bucket valve 100 receives its fluid supply through
a line 105 which branches of from a node 104 o~ the flow line
94~ Thus, the input to the bucket valve 100 communicates with the
variable displacement pump 12 through the flow lines 44, 58, 67,
79, 81, 94, and 105. In addition, fluid communication is provided
Ilbetween the flow line 94 and the flow line 101 by a flow line 108
`which hranches off from the flow line 94 at a node 107 which is
~arranged upstream from the node 104~ In order to regulate the
amount of flow going to the input 103 of the bucket valve 100,
as compared to the amount of flow going to the input 93 of the
swing valve 90, a flow control valve 180 is arranged in the flow
line 94 between the nodes 96 and 107. The flow control valve 180
includes a variable orifice 182. The flow control valve 180
provides a means for regulating the amount of flow going to the
- bucket valve 100, thereby helping to ensure that the swing valve
j 90 receives some flow even when being used in conjunction with
. the bucket valve.
The bucket valve 100 includes a neutral position lOOa
in which fluid communication is blocked between the pump 12 and '.
the fluid actuated device regulated by the bucket valve 100.
, The bucket valve 100 also includes first operating positions
lOOb, and second operating positions lOOc. When a plunger 109
of the bucket valve 100 is used to move the valve from the neutral
:position lOOa toward one of the operating positions, the cross-
sectional area of the variable orifice 102 is progressively
:reduced. The pressure at the outlet of the variable orifice 102
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1 . of the bucket valve 100 will, of course, be reduced as the
.cross-sectional area of the variable orifice 102 is reduced, and
will thus be indicative of the flow demands of the bucket valve
!102.
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If the backhoe valve section 89 of the present invention were ¦
to include additional valves such as a dipper valve, a boom valve~
and a dipper extension valve, then these could, for example, be 'I
~similar to the bucket valve 100 and serially arranged with respect
to one another, each bearing a flow relationship to the preceding
valve similar to the flow relationship between the bucket valve
..100 and the swing valve 90. That is, the input of the variable
iorifice of each of these additional backhoe valves would communi-
cate with the output of the variable orifice of the previous
valve, and the inputs to each of these valves would be supplied
with fluid through flow lines branching off from the line 94.
Of course, the output of the variable orifice of the last of these
valves would then communicate with the selector valve 160,
described below, rather than the output of the variable orifice
102 of the bucket valve 100.
As noted earlier, the flow control valve 180 in the line 94
regulates the total amount of flow going to the input of the bucket
valve 100, as well as to any additional valves included in the back-
backhoe valve section, as compared to the flow going to the input of
of the swing valve 90 throush the line 95. This is a consequence of
~of the fact that the input of each of the additional backhoe valves
receives its flow from a line which branches off from the successive
nodes along the line 94 downstream from the flow control valve 180.
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1 ¦ The pressure at the output of the variable orifice 102
,of the bucket valve 100, which constitutes a s~-ond pressure
l signal 155, is communicated through a line 156 to the selector
!Ivalve 160 referred to above. In addition, and as noted earlier,
¦Ithe pressure at the outlet of the variable ori~ice 92 of the
¦Iswing valve 90, which constitutes the first pressure signal 140,
is also communicated to the selector valve 160 through the line
150. The selector valve 160 is a two-position valve intended
Ito select, and communicate, a control pressure signal which is
lo the lower of the first and second pressure signals 140 and 155
communicated to the selector valve 160 through the lines 150
and 156. This control pressure signal is the control pressure
signal 32 which is communicated by the selector valve 160 to the
sensor valve 22 through the line 34.
The seli~ctor valve 160 includes a first operative position
160a, the top-most position (as shown in the figure), and
a second operative position 160b which is the bottom-most
operative position. A spring 162, arranged on the top side
of the selector valve 160, biases the selector valve to the
' position 160a. In addition, the second pressure signal 155
is also communicated to the top side of the selector valve
160 througn a line 164 which branches off from the line 156,
and is also used to bias the selector valve 160 to the operative
,position 160a in conjunction with the spring 162. On the other
hand, the first pressure signal 140 is communicated to the bottom
side of the selector valve 160 through the line 150 to oppose
¦ the biasing force exerted by the spring 162 and the first
l pressure signal 155. That is, the first pressure signal 140 acts
I I to bias the selector valve 160 to the second operative position
1 160b.
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1 When the first pres~ure si~nal 140 is smaller in magnitude
than the second pressure signal 155, the selector valve 160 is
biased by the spring 162 and the second pressure signal 155 to
the first operative position 160a. In this first operative
position, the first pressure signal 140 is communicated through
a line 158 which branches off from the line 150 to the input
of the selector valve 160, and is transmitted through the line
34 as the control pressure signal 32. On the other hand, when
the first pressure signal 140 is greater in magnitude than the
second pressure signal 156 and exerts a biasing force greater
than the biasing force exerted by the spring 162 and the second
pressure signal 155, then the selector valve 160 is pushed
to the second operative position 160b, and in this position the
second pressure signal 155 is transmitted by the selector valve
as the control pressure signal 32. Thus, the selector valve 160
acts like a logic device, which selects and provides a control
pressure signal 32 which is the smaller of the first and second
pressure signals 140 and 155 communicated to the selector valve. I
The operation of the hydraulic control system 10 of the
present invention is as follows. When the prime mover of the
combined loader and backhoe vehicle in which the present invention
is incorporated is started, which prime mover powers the variable
displacement pump 12, the spring biased piston 20 of the
displacement control cylinder 18 initially biases the pump 12 to
maximum displacement. If all of the valves downstream from the
pump 12 are in their neutral positions, and no flow is being
demanded of the pump 12, then the pressure drops across the
variable orifices in the various valves of the hydxaulic control
system 10 will be relatively small, and thus the control pressure
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1 Isignal 32 communicated to the sensor valve 22 will be relatively
high. The relatively high control pressure signal 32 which is
communicated through the lines 34 and 33 to the left side of the
sensor valve 22 will be high enough to overcome the biasing force
exerted by the spring 30 and force the sensor valve 22 toward
the second operative positions 28 so that the control pressure
siignal 32 can be communicated to the displacement control cylinder
l18 in order to force the piston 20 to move to the right to thereby
Ireduce the displacement of the pump 12.
¦ Once one or more of the various valves of the control system
¦il0 are actuated, for example, the loader valve 60 and the
istabilizer valve 70, then the displacement control system 16 will
!appropriately vary the displacement of the pump 12 to meet the
iflow demands of these actuated valves. That is, as the pressure
Idrops across the variable orifices in the actuated valves of the
¦ hydraulic control system 10 begin to increase, then the control
!I pressure signal 32 communicated to the sensor valve 22 will begin
to decrease. This ~ontrol pressure signal will then no longer
be able to overcome the biasing force exerted by the spring 30
ao land the sensor valve 22 will be pushed toward the first operative
Ipositions 24 wherein the high pressure side of the displacement
I control cylinder 18 will be vented to the reservoir 14, the piston
20 pushed to the left by the biasing spring 19, and the displace-
ment of the pump 12 increased to meet the increased flow needs
of the actuated valves. Thusi, a decrease in the magnitude of the
control pressure signal 32 results in an increase in the displace-
ment of the pump 12.
If the steering valve 50 is actuated, then the priority
llvalve 46 will ensure that all of the flow demands of the steering
¦valve 50 are met, even at the expense of the various other valves
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in the hydraulic control system 10. As the flow demands of the
steering valvP S0 are reduced, the priority valve 46 will operate
to allow more and more fluid to pass through the line 58 to the
loader valve 60 and the stabilizer valve 70. Of course, a
. portion of the fluid flowing through the line 58 will be diverted
Il to the line 80 across the flow control valve 82.
I Typically, the loader valve 60 is only actuated when the
: combined loader and backhoe vehicle is in motion. As the flow
. I demands of the loader valve 60 or the stabilizer valve 70 begin
1~ : to increase, then the pressure in the line 79 downstream from the
variable orifices in these valves will begin to decrease. If the
pressure signal generated by the flow control valve %2 is
momentarily ignored, then it follows that the pressure in the line
79 is communicated to the variable orifices in the backhoe valve
section 89 through the line 81. Because the swing valve 90 and
the other backhoe valves are usually not used when the vehicle is :
in motion, the variable orifices 92 and 102 in the swing valve 90
and the bucket valve 100 will be fully open, and thus little or
- no pressure drop will occur across these orifices. Thus, the
~0 decreasing pressure in the line 79 will be communicated, almost
unchanged, through the orifice 92 and the line 150 as the first
pressure signal 140 to the bottom of the selector valve 160, while
the decreasing pressure in the line 79 will also be communicated,
almost unchanged, through the orifices 92 and 102 and the lines
156 and 164 to the top of the selector valve 160. Since the first
and second pressure signals will necessarily be virtually e~ual in
magnitude, the first pressure signal 140 will be communicated as
the control pressure signal 32 to the displacement control
mechanism 16 by the selector valve 160 because the biasing force
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;l exerted by the first pressure signal 140 will necessarily be less ¦
than the biasing force exerted by the nearly equal second
pressure signal 155 and the spring 162. Because the control
pressure signal 32 will be virtually equal to the decreasing
¦ pressure in the line 79, the displacement control mechanism 16
will act to increase the displacement of the variable displace-
ment pump 12 to meet the increasing flow demands of the loader
valve 60 or the stabilizer valve 70 in response to the decreasing ¦
~ control pressure signal 32.
If the loader valve 60 or the stabilizer valve 70 were to
be fully actuated, and if there were no flow line 80 and flow
. control valve 82, then the relatively low pressure in the line 79 ¦
would be transmitted, virtually unchanged, through the line 81 and¦
through the modified center core slgnal system of the present
- invention, as the control pressure signal 32, driving the pump 12
to maximum displacement. The existence of the flow control valve
82 in the line 80, however, prevents the increasing flow demands
of the loader valve 60 and stabilizer valve 70 from driving the
pump 12 to maximum displacement. ~hat is, the relatively small
amount of flow diverted from the line 58 through the line 80 and
across the flow control valve 82, results in a pressure signal
which, together with the relatively low pressure in the line 79,
is transmitted through the line 81 and through the modified center¦
core signal system of the present invention as the control
; pressure signal 32. Since this combined pressure signal is always¦
greater in magnitude than the pressure in the line 79, the pump
12 is never driven to maximum displacement.
When the combined loader and backhoe vehicle comes to rest
and has been stabilized, the loader valve 60 and the stabilizer
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valve 70 will usually have been .returned to their neutral
positions, while the swing valve 90 and the backhoe valves will
be actuated. Because the loader valve 60 and the st~bili2er
valve 70 are in their neutral positions, the variable orifices
in these valves will be open, and the inputs to the swing valve 90
and the bucket valve 100 (as well as any other valves included in
the backhoe valve section) will receive their flow supply, almost
without restriction, through the line 58, the loader valve 60, the
line 67 the stabilizer valve 70, the line 73, the line 81, and the
line 94.
The flow control valve 180 in the line 94 acts to regulate
the amount of 10w going to the input of the bucket valve 100
(as well as the inputs of any other valves included in the backhoe
valve section) as compared to the amount of flow going to the
input of the swing valve 90. Furthermore, the modified center
core signal system acts to ensure that the input to the swing
valve 90 always receives at least a certain minimum amount of the
flow even when the swing valve 90 is being used in conjunction
with the bucket valve (or any other valve included in the backhoe
valve section). That is, as the swing valve 90 is moved from its
netural position 90a toward one of its operating positions, the
first pressure signal 140 at the outlet of the variable orifice 92
in the swing valve 90 will correspondingly decrease, and this
first pressure signal will be communicated to the selector valve
160. This first pressure signal 140 is also communicated through
the line 101 to the input of the variable orifice 102 in the
bucket valve 100. If the bucket valve 100 is moved from its
neutral position lOOa to one oE its operating pOSitiGns, then the
pressure at the outlet of the bucket valve 100, that is, the
second pressure signal 155, will be correspondingly reduced below ¦
.
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that of the first pressure signal 140. The selector valve 160
~will then pass the lowex of the two pressure signals communicated
to it, that is, the second pressure signal 155, which will
constitute the control p.ressure signal 132 communicated to the
sensor valve 22.
Thus, the greater the movement of the bucket valve 100 from
its neutral position to one of its operating positions, the
smaller in magnitude will be the control pressure signal 32. If
this control pressure signal 32 is of relatively small magnitude,
lo ,then it will not be sufficient to overcome the opposed biasing
force exerted by the spring 30 on the sensor valve 22, and the
.sensor valve ~2 will remain in one of the operative positions 24.
Thus, the high pressure side of the piston 20 in the displacement
control cylinder 18 will be vented to the fluid reservoir 14, and
the displacement of the variable displacement pump 12 will
increase in order to meet the flow demands of the bucket valve
(as well as any other valves included in the backhoe valve section).
In this fashion, the modified center core signal system acts to
increase the displacement of the pump 12 in order to meet the
flow demands of the backhoe valve, and to thereby ensure that the
swing valve 90 receives at least a certain minimum amount of flow.
The hydraulic control system of the present invention is
.advantageous because the modified center core signal system
incorporated within the present invention operates to ensure
th~t the swing valve receives at least a certain minimum amount
~of flow even when being used in conjunction with one of the
backhoe valves.
. The hyd.raulic control system of the present invention is
also advantageous because it operates to prevent the loader valve
and the stabilizer valve from using an excessive amount of fluid.
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1 ~ The principles, preferred embodiments and modes of operation
of the present invention have been described in the foregoing
specifiation. The invention which is intended to be protected
herein, however, is not to be construed as limited to the
particular forms disclosed, since these are to be regarded as
illustrative rather than restrictive. Variations and changes
lmay be made by those skilled in the art without departing from
,! the spirit of the present invention;
10 '.
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