Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF THE INVENTION
This invention relates to hydraulic systems
of the type including one or more flow and pressure
compensated pumps for providing hydraulic fluid under
pressure to parallel hydraulic circuits, each
including a work performing means.
Increasingly, hydraulic systems having work
performing devices subjected to variable loading are
utilizing one or more flow and pressure compensated
pumps for the reason that such pumps maximize system
efficiency within their capacity and yet provide a
considerable reduction in energy requirements. In
the operation of many such systems, only infrequently
are the various work performing devices simultane-
ously subjected to maximum load conditions with the
result that it is uneconomical to provide pump capac-
ity that is sufficiently high that the fluid require-
ments of all work performing devices can be fully met
when all are simultaneously being subjected to
maximum load conditions. ~s a consequence, most
systems of this type are provided with a pump
capacity that is less than the theoretical maximum
required for the specific situation wherein all
components are subject to maximum load.
Nonetheless, during the operation of such
systems, this infrequently occurring happening will
take place periodically. And, where one of the work
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performing devices provides a relatively low resis-
tance to the passage of hydraulic fluid as opposed to
one or more of the other work performing devices, the
demand for fluid by the low resistance work per-
forming device will be substantially fully satisfiedwith the consequence that flow to the higher
resistance work performing devices will be severely
cut back thereby severely diminishing the ability of
the high resistance work perfo-ming device to perform
its intended function during the occurrence.
All too frequently, the nature of the system
will be such that, in the usual operation, the func-
tion produced by the low resistance work performing
device is one of lesser importance to the operation
being performed by the system while the function
being performed by the high resistance work per-
forming device is of considerably greater consequence
and importance.
As a resultl quite undesirably, a most
desirable function cannot be satisfactorily performed
while a function of less importance can be.
In order to solve the difficulty, the prior
art has suggested the provision of priority devices
whereby the demand of the work performing devices
performing the more important functions is first
satisfied, and only after such satisfaction has been
attained, is the demand of the work performing
devices performing functions of lesser importance
1~3~63ff
attended to. Typically, the priority determination is
accomplished by means contained within flow control valves
which directly interconnect the pump or pumps and the work
performing means. As a consequence, the priority
determining means are necessarily large since they are
interposed in hydraulic circuits having large flow rates
and must be designed to withstand the high pressures
typically associated with many hydraulic systems.
In addition, many such hydraulic systems employ
plural pumps, each for normally providing fluid under
pressure to an associated group of work performing
devices. In order to maximize efficiency, means have been
provided whereby the output of one pump may be transmitted
to work performing devices not normally associated
therewith so as to maximize the use of the total pumping
capacity employed in the system.
Heretofore, such transfer means have utilized
spool valves which tend to be rather expensive and which
tend to be relatively leaky as compared to other types of
known valves.
SUMMARY OF THE INVENTION
The present invention is directed to overcoming
one or more of the above problems.
25According to one aspect oE the invention, there
is provided a hydraulic system comprising a plurality of
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pressure and flow compensated pumps; a plurality of fluid
motors, each connected by a control valve to one of the
pumps; means for connecting each of the fluid motors to at
least another of the pumps in addition to the respective
one pump, the means includes a plurality of pilot-operated
poppet valves each having a first port connected to one oE
the pumps, second ports interconnected with each other, a
first pressure responsive surface in communication with
the first port, a second pressure responsive surface in
communication with the second port, a third pressure
responsive surface in communication with the fluid motor,
and restricted fluid passageways interconnecting the
second and third pressure responsive surfaces of the
poppet valves with the second ports; and a bleed valve
connected to the second ports of the plurality of poppet
valves whereby opening of the bleed valve causes the
plurality of poppet valves to open and provide cross
communication between the first ports, and when the bleed
valve is closed and a predetermined pressure difference
exists between the first ports, the highest pressure is
transmitted to the second pressure responsive surfaces of
the poppet valves causing the poppet valve with the lowest
pressure at its first port to close.
Other objects and advantages will become apparent
from the following specification taken in connection with
the accompanying drawings.
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DESCRIPTION OF THE DRAWINGS
The Figure is comprised of FigS. lA and lB
and is a schematic of a hydraulic system made
according to the invention, Fig. lB being adapted to
be placed to the right of Fig. lA.
DESCRIPTION OF THE PREFERRED EMBODIMEMT
An exemplary embodiment of a hydraulic
system made according to the invention is illustrated
in Figs. lA and lB in the form of a system for
controlling the various work performing elements on a
vehicle such as an excavator. Major system com-
ponents include first and second flow and pressure
compensated pumps 10 and 12 of conventional con-
struction. AS will be seen, the pumps 10 and 12 are
of the type that will elevate the pressure of their
output in response to a decrease in the pressure of a
fluid signal applied thereto. However, it is to be
understood that, if desired, the pumps 10 and 12
could be of the type that increase the pressure of
their output in response to increasing pressure of a
control signal.
The system includes a source of pilot fluid
under pressure in the form of a pump 14. In addi-
tion, there are provided pilot operated main flow
valves and associated operator positioned valves
which control the pressure of pilot fluid to the main
flow valve for each of the differing work performing
means in the excavator.
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For example, there is provided an operator
positioned valve 16 which may be operated to apply
pilot pressure to the main flow valving system,
generally designated 18, which controls extension or
retraction of a hydraulic cylinder 20 which operates
the boom of the excavator. AS illustrated in Fig.
lB, various conventional components of the main flow
valving system 18 are eliminated for clarity. For
example, the valves illustrated provide for only uni-
10 directional operation of the cylinder 20 and are onlypartly shown. other conventionally oriented valves
are utilized to control operation of the cylinder 20
in the opposite direction.
The main flow valving system 18 includes a
valve 21 which is connected via a check 22 to the
output of the pump 12. A pilot operated metering
valve 24 meters flow to the cylinder 20 when the
valve 21 is opened while a pilot operated metering
valve 26 controls outflow from the cylinder 20 to a
further valve 28.
The system further includes an operator
positioned valve 30 for controlling the pressure of
pilot fluid to a bucket circuit 32 which will
generally be of the same nature as the circuit 18.
It will be observed that the bucket circuit 32 is
connected, in parallel, to the output of the pump 12
with respect to the circuit 18.
Other like components are illustrated in
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Fig. lA wherein there is illustrated an operator
positioned valve 34 for controlling the pressure of
pilot fluid to a stick circuit 36 for controlling the
stick of the excavator. A similar operator posi-
tioned valve 38 controls the pressure of pilot fluid
to a swing circuit 40 for controlling the position of
the turret of the excavator on the vehicle frame.
As seen in Fig. lB, right and left track
control, operator positioned valves 42 and 44 control
the pressure of pilot fluid to right and left track
circuits 46 and 48. As with the circuit 18, the cir-
cuit 46 is only fragmentarily shown, omitting many
conventional components for clarity.
Each of the circuits 18, 32 and 36 include
work performing means in the form of hydraulic cylin-
ders such as the cylinder 20. Each of the circuits
40, 46 and 48 include work performing means in the
form of bidirectional hydraulic motors such as the
motor 50 shown in the circuit 46.
As can be seen in Fig. lA, the circuits 36
and 40 are connected in parallel to the output of the
pump 10. The circuits 46 and 48 receive pressure
fluid from a port 52 of a multicomponent valve 54
which, in turn, has ports 56 and 58 connected respec-
tively to the outputs of the pumps 10 and 12 and in
parallel with respect to the other components con-
nected to such pumps.
Each of the pumps 10 and 12 is provided with
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a control input on line 60. The manner in which the
- signal is provided is the same for both the pumps 10
and 12, so only the components providing the signal
to the pump 12 will be described in detail.
- 5 Pilot fluid under pressure from the pump 14
is supplied to an inlet port 62 of a double piloted,
spring-assisted, metering valve 64. An outlet port
66 is connected to the line 60. The valve 64
includes a shiftable spool 68 provided with metering
10 slots (not shown) for controlling the flow of fluid
from the port 62 to the port 66, thereby providing a
controlled but variable pressure signal to the pump
12 to adjust its action, as is well known. One end
of the spool 68 is subject to pressure from the out-
15 put of the pump 12 through a line 70, while the otherend of the spool 68 is biased by a spring 72 as well
as being subjected to fluid under pressure from a
line 74. The pressure in the line 74 will be equal
to the highest pressure demanded by any of the work
20 performing means associated with the pump 12, as is
well known. It is derived via check valves, such as
check valve 76, connected between the work performing
means, such as the cylinder 20, and the pilot
controlled metering valve, such as the valve 24.
The arrangement is such that, within limits
of its capacity, the pump 12 will always provide
fluid at a pressure a substantially fixed margin, as,
for example, 200 psi above the pressure demanded by
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the work performing means. When the predetermined
margin is met, pressure in the line 74 and the spring
bias provided by the spring 72 will balance the force
applied by pressure in the line 70. Conversely, when
the margin is exceeded, the spool 68 will shift to
the right, increasing flow to the pump 12 to cause
the same to decrease its output pressure. When the
margin is not met, the spool 68 will shift to the
left to decrease pilot flow to the pump 12, thereby
10 causing the same to increase its output pressure.
The system also includes a shutoff valve 77
which, when a predetermined pressure at the output of
the pump 12 is exceeded, will open to direct high
pressure to the line 60 to cause the pump 12 to
15 decrease its output pressure.
As mentioned, a similar circuit is provided
for the pump 10 and the same is given the designation
SUPPLY MARGIN CIRCUIT in Fig. lA.
In many systems of the general type des-
20 cribed, the capacity of the pumps 10 or 12 is notsuch as to be able to fully satisfy the demand of
each of the associated work performing means, as
generally alluded to previously. When maximum pump
capacity is approached, and the pressure of the load
signal on line 74 continues to increase, the valve 68
will shift to the left to signal the pump 12 to
increase its capacity. However, because the pump's
maximum capacity is met, or almost approached, very
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little, if any, increase in output pressure can be
attained with the result that one or more of the work
performing means will be partly or wholly starved of
hydraulic fluid under pressure. To ensure that when
such occurs, the more important one or ones of the
work performing means are not starved, a DEMAND
MARGIN CIRCUIT is provided for each of the pumps 10
and 12. The two are identical and, accordingly, only
the demand margin circuit associated with the pump 12
10 will be described.
The same includes a spool valve 80 which is
double-piloted and spring-associated. One end of the
spool 82 receives pump pressure through a line 84
while the other end receives load pressure from the
15 line 74 and is also biased by a spring 86. The valve
80 includes an inlet port 88 connected to the pilot
pump 14 and an outlet port 90 which is conected to
some, but not all, of the operator positicned
valves. As shown in Fig. lB, the port 90 is con-
20 nected only to the valves 16 and 30 and not to thevalves 42 and 44.
In an excavator system, it is generally
desirable that the fluid demands of the track circuit
be satisfied before the fluid demands of the boom,
25 bucket, stick and turret are met.
So long as the predetermined margin between
supply pressure and load pressure is maintained
through action of the valve 64, no problem exists.
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~13~t~;38
However, when that margin cannot be maintained, the
demand margin circuit including the valve 80 reduces
the flow demand of the selected work performing
means, here, the boom and the bucket, to ensure that
the demands of the track circuits are met.
As the load signal in the line 74 begins to
increase, the spool 82 will begin to shift to the
left, as viewed in Fig. lB, with the consequence that
metering slot 94 will begin to throttle the incoming
flow of pilot fluid through the port 88 while other
metering slots 96 will establish fluid communication
with an outlet port lO0 connected to tank. Conse-
quently, pilot pressure to the operator positioned
valves 16 and 30 will be decreased. AS a conse-
quence, pilot pressure provided by the valves 16 or
30 to the pilot operated metering valves, such as the
valves 24 and 26 associated with the corresponding
work performing means will be decreased, thereby
reducing the flow of pressurized fluid to the
associated work performing means from the pump 12.
Thus, the demand margin circuits act as priority
determining means to ensure that the needs of desired
circuits, such as the track circuits, are met within
pump capacity before the fluid needs of other, less
important circuits are met to avoid starving of
higher priority circuits.
If desired, the system may be provided with
a priority sequencing feature through the inclusion
i~39~
of a valve 102 which may be identical, save in one
respect, to the valve 80. The valve 102 receives a
pump pressure signal at a port 104 via a line 106 and
a load signal from the line 74T. The valve 102 is
operative to control the supply of pilot fluid from
the pilot pump 14 to the operator positioned valves
42 and 44 for the right and left track circuits.
The difference between the valve 102 and the
valve 80 is the fact that the valve 102 has a biasing
10 spring 108 which is lighter than the spring 86. Con-
sequently, metering of the pilot fluid by the valve
102 will not occur until the difference between
supply pressure and load pressure is considerably
smaller than that required to initiate operation of
15 the valve 80.
The invention also contemplates the provi-
sion of means whereby pressure fluid from either of
the pumps 10 and 12 may be directed to any of the
components. As will be appreciated from the fore-
20 going description, the boom and bucket circuits
normally are associated only with the pump 12 while
the stick and swing circuits are normally only
associated with the pump 10. As will be seen, the
track circuits are associated with both.
In some instances, when only, for example,
the boom and ~he bucket are being utilized, it may be
desirable to utilize part of the capacity of the pump
10 for operating such components in addition to the
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1139~8
capacity of the pump 12. Conversely, occasions may
arise when only the swing and/or stick circuits are
being utilized and it is desired to supplement the
capacity of the pump 10 with the capacity of the pump
12.
The multi-component valve 54 provides for
cross connection of the outputs of the pumps 10 and
12 so that either pump may be connected to a work
performing means not normally associated therewith
10 when such occasions arise. The valve 54 also directs
the output of one or the other of the pumps 10 and
12, or both, to the track circuits, as previously
mentioned.
The valve 54 is composed of two poppet
15 valves having poppets 120 and 122, respectively.
Each of the poppets 120 and 122 have a pressure
responsive surface 124 and 126, respectively, in
fluid communication with the ports 56 and 58, respec-
tively. Valve seats 128 are provided for the poppets
20 120 and 122 to seat against. Downstream of the valve
seats 128 from the ports 56 and 58, there are pro~
vided annular spaces 130 for each of the poppets 120
and 122 and the two annular spaces are connected to
each other by a conduit 132 which, in turn, connects
25 to the port 52.
Within each of the annular spaces 130, each
poppet 122 includes an enlarged shoulder 134 which
faces the same direction as the associated pressure
responsive surface 124 and 126.
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Each of the poppets 120 and 122 further
includes an associated pressure responsive surface
136 and 138, respectively, which are in bucking rela-
tion to the surfaces 124 and 126. Finally, each
poppet 120 and 122 is provided with a restricted
fluid passage 140 which establishes fluid communi-
cation between the annular spaces 130 and the
corresponding pressure responsive surfaces 136 and
138.
In the case where both the pumps 10 and 12
are providing substantially the same output pressure,
flow therefrom will be directed against the pressure
responsive surfaces 124 and 126 to cause both poppets
120 and 122 to move away from their seats 128. The
15 flow from both pumps will enter the annu-lar spaces
130 and be directed to the port 52 by the conduit 132
to provide fluid under pressure to the track cir-
cuits. Upon initial opening of the poppets 120 and
122, any fluid abutting the surfaces 136 and 138
20 tending to preclude poppet movement will be vented
via the passages 140 to the annular spaces 13a and
thus to the track circuits.
The flow of pressurized fluid through the
valves will, at the same time, be directed against
25 the shoulders 134 to maintain both poppets open.
In another situation, it may be assumed that
the operator positioned valve 16 for the boom has
been manipulated to increase demand for fluid for the
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~:13963~3
boom to a level above that demanded by the work per-
forming means normally associated with the pump 12.
A line 150 connected to the output of the valve 16
directs pressure against one end of a spool 152 of a
valve 154 to cause the same to move to the left, as
viewed in Fig. lA, against the bias of a spring 156.
When this occurs, a flow path from an inlet 158 of
the valve 154 is established to an outlet 160. The
inlet 158 is connected to the pilot pump 14.
A similar valve 170 is connected to the out-
put of the stick control valve 34 and when subject to
pilot pressure from the valve 34, will open to estab-
lish a flow path between an inlet 172, also connected
to the pilot pump 14, and an outlet 174.
The degree to which each of the valves 154
and 170 opens will be dependent upon the pilot pres-
sure applied to each. A double-piloted spool valve
176 has one pilot 178 connected to the outlet 160 of
the valve 154 and its other pilot 180 connected to
20the outlet 174 of the valve 170. The valve 176 is
spring centered to the position shown and when
neither pilot 178 and 180 are pressurized, or when
both are receiving the same pressure, the spool 182
of the valve 176 will be in the position shown.
For the situation wherein the boom control
valve 16 has been operated to cause a greater demand
for the boom circuit than is called for by the stick
circuit, the valve 154 will direct a greater pressure
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1~3'36~3
to the pilot 178 than will be directed to the pilot
180 by the valve 170. The spool 182 will, accord-
ingly, move to the left with a first land 184 opening
a flow path between an inlet 186 and an outlet 188.
The outlet 188 is connected to drain while the inlet
186 is in fluid communication with the pressure
responsive surfaces 136 and 138. Consequently, the
valve 176 provides a bleed path for the poppets 120
and 122. At the same time, a land 190 on the spool
10 182 will establish a flow path between two ports 192
and 194.
The port 192 is connected to the load
sensing line 74 associated with the stick and swing
circuits, designated 74L in Fig. lA, while the port
15 194 is connected to the load sensing line 74 associ-
ated with the boom and bucket circuits and this line
is designated 74R in Fig. lA only. The load sensing
line for the track circuits, designated 74T, is
connected to the junction 200 of two opposed checks
20 202 and 204 which are respectively connected to the
line 74L and the line 74R. As can be seen, the
checks 202 and 204, while openable to permit a high
pressure signal from the junction 200 to be directed
to the margin circuits for either or both of the
25 pumps 10 and 12, preclude fluid communication between
the lines 74L and 74R. However, when the land 190 of
the valve 176 opens a flow path as mentioned
previously, the check valves 202 and 204 are bypassed
-17
~13'~6~8
now establishing fluid communication between the
lines 74L and 74R.
As a consequence, the increased demand for
fluid by the boom caused by the previously mentioned
actuation of the boom control valve 16 which will
have resulted in an increased pressure in the line
74R will be fed to the supply margin circuit for the
pump 10 causing the same to increase its output.
Because the pressure responsive surfaces 136 and 138
10 have been simultaneously vented, notwithstanding the
fact that a pressure differential may momentarily
exist across the ports 56 and 58 of the valve 54,
both poppets 120 and 122 will open to allow the now
increased pressure and/or flow from the pump 10 to be
15 directed to the boom by a flow path entering the port
56 and exiting the port 58. This will cc,ntinue so
long as the greater demand in the entire system is
called for by the boom control 16.
The opposite action will occur should the
20 stick control 34 be set such that the stick circuit
36 has greater demands than the boom.
It is to be observed that neither the bucket
nor the swing control valves 30 and 38 can be opera-
ted to cause one of the pumps 10 or 12 to assist the
25 bucket circuit or the swing circuit with which it is
not normally associated. The purpose of this con-
struction is unique to an excavator in that, typi-
cally, the bucket and swing circuits have large flow
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requirements with relatively low loading with the
consequence that, in some situations, they could
utili~e almost the entire flow capacity of both
pumps, thereby starving other system components.
Consequently, when either the swing circuit or the
bucket circuit is being operated, it is desired to
isolate the pumps 10 and 12. In this situation, the
bleed path through the valve 176 will be closed and
because of the low loading of the bucket, for
example, a relatively low pressure will be present at
the port 58 with respect to the pressure present at
the port 56. Assuming both poppets 120 and 122 to be
open to allow the combining of the outputs of both
pumps, when this pressure difference occurs, the pop-
pet 120 will be maintained open and initially, fluid
will flow from the high pressure side to the low
pressure side, namely, from the port 56 through the
conduit 132 to the port 58. A pressure drop will
occur during such flow in the conduit 132 with the
consequence that a relatively higher pressure will be
applied to the pressure responsive surface 138 due to
its fluid communication with the left-hand annular
space 130 via the flow passage 140 in the poppet
120. As a result, the poppet 122 will close thereby
halting the combining of the output of both the pumps.
Should the swing circuit be calling for a
high flow rate, the reverse of the foregoing action
will occur with the poppet 120 closing to halt the
combining of the outputs of the two pumps.
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In either event, pressurized fluid will con-
tinue to be directed to the track circuit through
whichever one of the poppet valves 120 and 122 that
remains open.
From the foregoing, it will be appreciated
that a hydraulic system made according to the inven-
tion assures priority of application of fluid under
pressure to those system components having the more
important functions when pump capacity is approached
10 or exceeded by load demand. It will also be appreci-
ated that the invention provides a means of sequenc-
ing priorities if desired. Finally, it will be
appreciated that the invention provides a unique
means whereby the discharge of plural pumps may be
15 selectively combined or isolated as system components
require.
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