Note: Descriptions are shown in the official language in which they were submitted.
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Description
C trol for Load Sharing Pumps
Technical Field
This invention relates generally to fluid
systems having a plurality of pumps for supplying
working fluid to a plurality of fluid circuits. More
particularly the invention relates to the control and
coordination of variable output fluid sources in
systems where pump output that is not being used by
an associated circuit is made available to another
circuit served by another pump.
Background Art
. Fluid driven devices, such as rotary or
reciprocating fluid motors for example, are often
operated intermittently, at variable speeds, with
variable loading or under some combination of these
conditions. Demand for working fluid is therefore
variable with respect to both pressure and flow.
` Greater efficiency is realized under these
conditions if the source of working fluid is
controlled so that output pressure and preferably
output flow as well varies in accordance with demand.
Otherwise, the fluid source must be operated to
:` continually provide a high output pressure and high
flow adequate to meet the peak demands of the driven
devices. During periods when the demand is below
maximum, the fluid source needlessly consumes power
and needlessly contributes to heating and aeration
of the working fluid.
It is a known practice to avoid these
problems by feeding back a pressure signal from the
~`~ driven device to a control which adjusts the output
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pressure of the fluid source to match variations in
demand and which in some cases adjusts output flow
as well.
Fluid source control of this kind is
subject to a complication in systems in which a pump
supplies fluid to a plurality of devices. At any
given time, the feedback signal or control pressure
should correspond to the pressure within the one of
the several devices which is most highly pressurized
and different ones of the devices may become the most
highly pressurized one at different stages of
operation. Consequently the control system must
compare the pressures within each of the devices and
transmit the highest pressure to the pump control.
One known form of pump control for this
purpose uses a network of resolver valves to compare
pressures from several fluid driven devices in order
to communicate the most highly pressurized device,
at any given time, wi~h the fluid source control.
Pump output control by feedback of a control
pressure from a driven device becomes still more
complex in fluid systems that have more than one
pump each supplying an associated separate circuit
of fluid driven devices and which also have fluid
exchanging arrangements which make fluid from one
pump available to supplement another pump when the
pumping capacity of the one pump is not being fully
used by its own circuit. In such a system, the
pressure comparing function of the pump control of
the one circuit must be temporarily extended to
` include a pressure rom another circuit during
periods when fluid transfer is occurring.
To accomplish the conditional comparison of
pressures from devices served by separate fluid
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sources without intercommunicating such devices, prior
fluid source controls for systems of this kind include
check valves or the like in the control pressure lines
between the fluid source control and the several
devices. Thus the control pressure is transmitted to
the fluid source control through a one way flow path.
` Consequently pressure increases from the most highly
pressurized device are directly transmitted to the
fluid source control but pressure decreases are not.
To cause the control pressure to decrease when the
pressure at the most highly pressurized device
decreases, it has heretofore been necessary to provide
a continually open bleed orifice in the control
pressure line. This allows the control pressure to
drop following a decrease in pressure within the most
highly pressurized device since, owing to the bleed, a
continual input of fluid from that device, through the
check valve, is needed to maintain the control signal
pressure at any given level.
A continual bleeding or draining of fluid from
the fluid source control pressure line has several
undesirable effects. For example, the continual loss
" of working fluid which occurs at such bleed orifices
` can be substantial particularly in high pressure
- 25 systems. This discharging of pressurized fluid back to
drain through the orifice wastes a substantial amount
of power, and consequently the power source and pumps
must be of higher capacity than would otherwise be
~ necessary. Flow lines and other components of the
`' 30 system may necessarily be larger than would otherwise
; be the case.
The present invention is directed to
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overcoming one or more of the problems as set forth above.
; Disclosure of the Invention
In one aspect of the present invention, a fluid
system comprises, a first pressurized fluid source having
5 first control means for varying output pressure in
response to variations of a control pressure, a first
plurality of fluid motors, a first plurality of motor
control valves each being connected between said first
fluid source and an associated individual one of said
first plurality of motors, a second pressurized fluid
source having second control means for varying output
pressure in response to variations of a control pressure,
a second plurality of fluid motors, a second plurality of
motor control valves each being connected between said
second fluid source and an associated individual one of
said second plurality of motors, a crossover conduit
interconnecting one of the motor control valves of said
first plurality thereof with at least one of said motor
control valves of said second plurality thereof, a
plurality of resolver valves including an initial one and
a final one thereof, each of said plurality of resolver
valves having a pair of inlet passages and an outlet
passage, one inlet passage of each of said plurality of
resolver valves being connected to an associated
~" 25 individual one of said first plurality of motors and the
other inlet passage of each of said plurality of resolver
valves other than said final one thereof being connected
to said outlet of a subsequent one thereof, said outlet of
said initial one of said plurality of resolver valves
being connected to said first control means, and means for
communicating said other inlet passage of said final one
of said plurality of resolver valves with said one of said
motors of said second plurality thereof at least while
said crossover conduit is transmi.tting fluid to said one
of said motors of said second plurality thereof.
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The fluid system precisely varies pump output
pressure, and preferably output flow as well, to match the
requirements of the most heavily loaded one of an
associated group of devices under conditions where the
associated group of devices may at times be extended to
include one of another group of devices having another
supply pump. The fluid system does not require a
continuous bleed of fluid from the pump control pressure
line. Consequently, power savings are realized and, at
least in some cases, pumps, fluid lines and other
- components of reduced capacity or size may be used in
certain parts of the system. As a two way or reversible
pump control pressure flow path is provided, the pump
responds more precisely to pressure demand variations than
is the case where bleed orifices are needed in order to
respond to decreasing pressures in the devices supplied by
a pump.
Brief Description of the Drawin~
Figure l is a schematic view of a plural circuit,
plural pump fluid system including an embodiment of the
present invention.
Figure 2 is a fluid circuit diagram further
illustrating a portion of the system of Figure l.
Figure 3 is a fluid circuit diagram illustrating
an alternate embodiment of the portion of the system shown
in Figure 2.
Best Mode for Carrying Out the Invention
Referring initially to Figure l a fluid
system 11 is initially depicted in schematic form to best
illustrate certain significant features of the
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invention. Examples of suitable more detailed
const~ructions for portions of the system 11 will
be hereinafter described.
The invention is adaptable to a variety
of different specific fluid systems 11 of the
general type which have a plurality of fluid sources
12A and 12B each primarily supplying pressuri~ed
fluid to an associated one of a plurality of fluid
circuits 13A and 13B and in which each of the
circuits 13A and 13B includes a plurality of fluid
operated devices such as fluid motors 14A, 15A and
16A of the first circuit 13A and motors 14B, 15B and
16B of the second circuit 13B in this particular
example. Fluid systems 11 of the type to which the
invention is applicable are further characterized
by load sharing or crossover means 17 for making
working fluid which is not being utilized by one of
the circuits 13A, 13B available to the other circuit
to supplement the output of the fluid source 12A,
12B of the other circuit.
For purposes of example the fluid system
11 depicted in Figure 1 is of the type used in a
hydraulic excavator vehicle of the form described
~- in U.S. Patent 3,987,623 issued to Donald L.
Bianchetta and dated October 26, 1976. In this
context, fluid motor 14A drives the right crawler
track of the vehicle, fluid motor l5A pivots the
bucket and fluid motor 16A raises and lowers the
boom of the excavator. Fluid motor 14B drives the
left side crawler track, motor 15B swings the boom
horizontally and motor 16B pivots the stick of the
excavator.
The devices or motors 14A, 15A and 16A of
first circuit 13A are supplied with working fluid by
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the first fluid source 12A which in this example in-
cludes a first variable displacement pump 18A. Pump
18A is provided with first control means l9A for vary-
ing the pump output in response to variations of a
first control pressure received through a first control
pressure line 21A. Control means l9A, which may be of
known construction, increases or decreases the dis-
` placement of pump 18A in response to decreases and
increases respectively of the control pressure in line
21A to vary both the pump output pressure and outputflow in response to variations in demand for working
fluid. Alternately, the fluid source 12A may be of the
other known type which employs a constant displacement
pump and in which the control means l9A is a modulated
relief valve that diverts a portion of the pump output
flow back to tank to the extent necessary to vary out-
put pressure in accordance with variations of the
control pressure. A variable displacement pump 18A as
used in this example is often preferable since it
matches output flow as well as output pressure with
demand changes. Power savings are realized as little,
if any, working fluid is discharged to tank prior to
being utilized by a motor.
The first fluid circuit 13A as depicted in
Figure 1 is of the priority form in which working fluid
from source 12A is made available to the motors 14A,
15A and 16A in sequence with the requirements of
initial motor 14A taking precedence over those of
motors 15A and 16A and in which the requirements of
motor lSA in turn take precedence over the requirements
of the final motor 16A. For this purpose an output
line 22A of pump 18A is connected to a motor control
valve 23A of the
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initial motor 14A through a ~low control valve 24A.
Motor control valve 23A, which will
hereinafter be described in more detail, is operated
by a pilot pressure received from a manually actuated
S pilot valve 26A and controls fluid flow to motor 14A
to start, stop and reverse the motor and to control
motor speed.
Flow control valve 24A, which will also be
hereinafter described in more detail, maintains a
constant flow of fluid to motor 14A, as selected by
the setting of motor con~rol valve 23A, if pressure
variations occur within the pump output line 22A.
` Flow control valve 24A also delivers working fluid
which is not needed by motor 14A to a bypass line
27A.
The sec~nd motor 15A is operated by working
fluid received from bypass line 27A through another
, flow control valve 28A and another motor control
valve 29A which is operated by pilot pressures from
another manual pilot valve 31A. The bypass line 32A
of flow control valve 28A delivers fluid to still
another flow control valve 33A which may in turn
transmit such fluid to the final motor 16A through
another motor control valve 34A responsive to pilot
pressures from another manually operated pilot valve
36A. The bypass line 37A of the final flow control
valve 33A connects with a first crossover line 17A
of crossover means 17 which will be hereinafter
described in more detail.
Aside from the different functions served
by the three motors 14B, 15B and 16B, the second
fluid circuit 13B is essentially similar to the
first circuit 13A as described above and has similar
components which are designated in Figure 1 by
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` similar reference numerals ~ollowed by the letter B
instead of the letter A. Thus a second variable
displacement pump 18B having second control means
l9B responsive to a second control pressure in a
second control signal line 21B may supply fluid to
motors 14B, 15B and 16B through a second set of
components similar to those previously described.
A bypass line 37s of the final ~low control valve
; 33B of second fluid circuit 13B connects with a
~~ 10 second crossover line 17B.
Thus in either of the two circuits 13A
and 13B, motors 14A, 14B, 15A, 15B, 16A and 16B may
be operated singly or at the same time. Considering
first circuit 13A for example, owing to the starting
and stopping of the several motors at different times
and the load variations w~ich may be experienced by
each of the motors the demand for working fluid of
the circuit 13A as a whole, both with respect to
pressure and flow, is variable. To control the
output of pump 18A to match demand variations, a
fluid pressure is fed back to control pressure line
21A and is caused to vary in accordance with
variations of pressure in the particular one of the
motors l~A, 15A and 16A which is the most highly
pressurized one at any given time.
In particular, first pressure comparing or
resolving means 38A are provided for establishing a
` two way control pressure flow path between control
pressure line 21A and the most highly pressurized
one of motors 14A, 15A and 16A. Pressure comparing
means 38A includes a first plurality of resolver
valves 39A, 40A and 41A each being of the type which
has a pair of inlet passages 42A and 43A and an
outlet passage 44A and which maintains the outlet
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passage 44A in communication with the most highly
pressurized inlet passage 42A or 43A while sealing
off the other inlet passage. First inlet passages
42A of resolver valves 39A, 40A and ~lA are connected
to motors 14A, 15A and 16A respectively, during
operation of the associated motor, through motor
control valves 23A, 29A and 34A respectively. The
second inlet passage 43Aof the initial resolver
valve 39Ais connected to the outlet 44A of ~he
succeeding resolver valve 40A which in turn has
; the second inlet passage 43A connected with the
outlet passage 44A of the final resolver valve 41A.
The outlet passage 44A of the initial resolver
valve 39Ais connec~ed with the control pressure
signal line 21A while the second inlet passage 43A
of the final resolver valve 41A connects with
resolver control means 46 to be hereinafter described
in more detail.
Second, essentially similar pressure
comparing means, 38B, including additional resolver
valves 39Br40B and 41B, are provided in the second
fluid circuit 13B, elements of the second pressure
comparing means being designated in the drawings by
reference numerals corresponding to the reference
numerals of the corresponding element of the first
fluid circuit 13A but which are followed by the
letter B instead oE the letter A.
Crossover means 17 enables working fluid
from first source 12A, that is not required by any
30 of the devices of the first circuit 13A to be
delivered to at least one device or motor 16B of
the second circuit 13B if it is needed by the second
circuit motor at that time. In this example,
; crossover means 17 also enables the transmitting of
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fluid that is not required by the devices of the
second circuit 13B to at least one device 16A of
the first circuit 13A. Thus either pump 18A and
18B may assist the other at times when the full
output of a particular pump is not being used by
the associated fluid circui~ 13A or 13B. This
enables more productive use of the available
pumping capacity.
In the hydraulic excavator vehicle example
of this embodiment the boom motor 16A of the first
circuit 13A and the stick motor 16B of the second
circuit 13B are ~he particular devices mos~ likely
to experience the highest working fluid demand.
Accordingly the crossover means 17 make surplus
fluid from first circuit 13A available ko the stick
motor 16B only of the second circuit 13B and makes
surplus fluid from second circuit 13B available to
the boom motor 16A only of the first circuit. In
; other usages of the i~vention the fluid supplementing
arrangement may be extended to include others of
the devices of each circuit 13A and 13B by adding
one or more resolver valves to means 38A and 38B.
In the present example crossover means 17
includes a check valve 47A in bypass line 32A of
the first circuit 13A, the check valve being
oriented to block flow towards flow control valve
28A. A check valve 47B is similarly situated in
bypass line 32B of the second fluid circuit 13B.
The first crossover flow llne 17A connects
bypass line 37A of first circuit 13A with the
portion of bypass line 32B of second circuit 13B
which is between check valve 47B and flow control
valve 33B. Similarly the second crossover flow
line 17B interconnects bypass line 37B of second
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circuit 13B with bypass line 32A of the first circuit
at a point between check valve 47A and the final flow
control valve 33A.
; During periods when working 1uid not
needed by :Eirst circuit 13Ais being transmitted to
second circuit 13B, the pressure comparing function
performed by resolver valves 39A, 40A and 41A of
the first circuit is extended to include the
pressure from the motor 16B of the second circuit to
which the surplus fluid is being made available.
This assures that the control pressure transmitted
to first pump control l9A of the first circuit 13A
is always indicative of pressure at the most highly
pressurized device currently being supplied with
15 working fluid by that pump. Similarly, second
circuit pump control l9B may respond to a pressure
from the first circuit 13A when working fluid from
the second circuit is being supplied to first circuit.
Resolver control means 46 for this purpose
includes first and second resolver control valves
51A and 51B. First resolver control valve 51Aisa
two position pilot operated valve which is spring
biased to a normal position at which the valve
` closes a pressure transmitting line 49A connected to
25 first inlet passage 42A of the final resolver valve
41A of first circuit 13A while venting another
pressure transmitting line 50A which connects with
second inlet passage 43B of the final resolver valve
41B of the second circuit 13B.A pilot line 52Aof
first resolver control valve 51Ais communicated with
pilot valve36A and is pressurized at the same time
". that motor control valve 34A of the first circuit i5
opened to operate motor 16A in a predetermlned
direction of motor operation, the predetermined
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direction being the boom raising mode of motor
operation in this hydraulic excavator vehicle
example.
Pressurization of pilot line 52A shifts
5 valve 51A to an alternate position at which pressure
transmitting lines 49A and 50A are communicated with
each other.
Second resolver control valve 51Bis a
similar two position valve spring biased to a normal
position at which a pressure transmitting line 53B,
connected to first inlet passage 42B of the final
resolver valve 41B of the second circuit 13B, is
~` closed while a line 54B to the second inlet passage
.` 43A of the final resolver valve 41A of the first
15 circuit is vented. Pilot line 56B of second resolver
control valve 51B communicates with pilot valve 36B
of second circuit 13B and is pressurized when the
motor control valve 34Bis opened to operate motor
16B in one of the two directions of motor operation,
20 specifically the stick advancing direction of motor
operation in this hydraulic excavator vehicle
example of the invention. Pressurization of pilot
line 56B shifts second resolver control valve 51B to `
the alternate position at which pressure transmitting
25 lines 53B and 54B are intercommunicated.
To best illustrate basic aspects of the
fluid system 11, certain components are depicted
in Figure 1 by means of generalized symbols and as
being interconnected by single fluid flow lines which
as a practical matter would provide only for one
way operation of the several motors 14A, 15A, 16A,
14B, 15B and 16B. In most usages of the invention
two way or reversible motor operation i9 needed.
~` Figure 2 schematically depicts suitable detail for
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the flow control valve 33A, motor control valve 34A,
pilot valve 36A, resolver valve 41A and
interconnec~ions and associated components, for
controlling motor 16A in particular. Essentially
similar detailed interconnections may be utilized
to control each of the other motors 14A, 15A, 14B,
15B and 16Bof the fluid circuits 13A and 13B of
Figure 1.
Referring to Figure 2, flow control valve
10 33A receives working fluid through the previously
described bypass line 32A and is spring biased
towards a position at which the bypass line 32Ais
communicated with the fluid supply line 57 to motor
control valve 34A. Motor control valve 34Ais a
15 three position pilot operated valve spring biased to
a centered position at which lines 58 and 59to
the associated motor 16A are closed but which may be
operated to deliver fluid to either of such lines
while communicating the other with a drain line 61.
20 The motor control valve 34Ais operated by shifting
a manual pilot valve 36A which is supplied with
pilot pressure from a suitable source 64. Upon
being shifted in either direction from the centered
position, pilot valve 36A selectively pressurizes
; 25 pilot line 62 or pilot line 63 to controllably shift
motor control-valve 34A. Pressurization of pilot
line 63 in particular also pressurizes the pilot
line 52A of the first resolver control valve 51Aof
Figure 1, as line 52Ais connected to line 63.
`~ 30 Referring again to Figure 2, a signal
;"~ line 66 connects to motor control valve 34A to
"` receive a pressure corresponding to that being
; supplied to motor drive line 5~ or 59 except when
the control valve is at the centered position, the
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signal line being vented to drain line 61 at the
centered position of the control valve. Signal
line 66 also connects to first inlet 42A of the
previously described resolver valve 41A through a
flow orifice 67 and thus delivers a control pressure
to resolver valve 41A that is indicative of the
pressure in motor 16A. This control pressure is
delivered to outlet 44A of the previously described
resolver valve 41A except when another control
pressure received at the other inlet passage 43A of
resolver valve 41A is greater.
Signal line 66 also communicates with one
pilot line 68 of flow control valve 33A, the
opposite pilot line 69 being connected to fluid
supply 57.
The fluid circuits 13A and 13B as
hereinbefore described with reference to Figures 1 ;
and 2 provide a priority system in which working
fluid is made available to the several motors of each
circuit in sequence and thus the fluid requirements
of a given one of the motors of either circuit take
precedence over subsequent ones of the motors of
the same circuit. In Figure 2, the flow control
valve 33A transmits working fluid to outgoing
bypass line 37A only to the extent that such fluid
is not needed to fully meet the requirements of
motor 16A as determined by the operator's adjustment
~` o pilot valve 36A. The invention is also adaptable
to parallel systems in which the available supply of
; 30 working fluid of either circuit 13A or 13B is made
equally available to all motors of that circuit. As
illustrated in Figure 3 this may be accomplished by
utilizing a modified form of flow control valve 72.
In the parallel system modification of
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Figure 3, a fluid input line 73 to all flow control
valves, such as valve 72, of a given circuit 13A is
communicated directly with the pump output line 22A
of the circuit. The flow control valve 72 in this
embodiment is of the known two way form as it need
not perform a bypass function as in the previously
described example. All other portions of the circuit
as depicted in Figure 3 may be similar to the
previously described circuit of Figure 2.
Industrial Applicability
The invention has been described above and
depicted in the drawings in the context of the fluid
system 11 for controlling a plurality of motors 14A,
15A, 16A, 14~, 15B and 16B on a hydraulic excavator
vehicle. It should be understood that the invention
is equally adaptable to many other fluid systems
. having plural motors or other fluid actuated devices
which exhibit a variable demand for fluid and which
have a plurality of pumps for supplying the working
fluid.
With reference to Figure 2, the operator
initiates operation of a selected one of the motors
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such as motor 16A by shifting the associated pilot
~; valve 36A to supply pilot fluid to the associated
motor control valve 34A. This shifts the motor control
valve 34A to supply fluid under pressure to one drive
line 58 or 59 of the motor 16A while venting the
other motor drive line to drain line 61. Motor 16A
` thus operates at a speed determined by the degree to
~`~'` 30 which the operator has shifted pilot valve 36A.
. Signal line 66 communicates the pressurized one of
the motor supply lines 58 and 59 with resolver
valve 41A through orlfice 67. During this opera~ion
of the motor 16A, flow control valve 33A self-adjusts
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as necessary, in the known manner, to maintain a
constant flow through motor control valve 34A as
selected by the adjustment of pilot valve 36A and
thus maintains a constant selected motor speed
notwithstanding variations in loading of the motor
which may occur.
The modified fluid circuit of Figure 3
operates in an essentially similar manner in
response to operator actuation of the pilot valve
36A except insofar as the flow control valve 72
does not pass fluid, not needed by the associated
motor 16A, into a bypass line leading to a
subsequent motor flow control valve. This is
unnecessary in the Figure 3 modification as the
flow control valve 72 for all motors in the parallel
system connect directly with the pump output line
22A.
; In both forms of the circuit depicted in
: 20 Figures 2 and 3, inlet passage 42A of resolver valve
41A receives a pressure which increases and
decreases in correspondence with increases and
decreases of the pressure within the motor 16A.
~ ~eferring again to Figure 1, the resolver valve 41A
.' 25 transmits this pressure to the inlet 43A of
resolver valve 40A except at such times as a higher
pressure is being received through ~he other inlet
., 43A of resolver valve 41A in which case that higher
pressure is transmitted to resolver valve 40A.
Referring still to Figure 1, each of the
additional resolver valves 40A and 39A of the first
circuit 13A similarly compare the pressures being
; received at inlets 42A and 43A and transmit the
higher pressure to the next resolver valve except
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that the initial resolver valve 39A transmits the
highest received pressure to pump control 19A.
; Thus the resolver valves 39A, 40A and 41A
- of the first circuit 13A continually compare the
pressures within a pr~determined group of devices,
mo~ors 14A, 15A, 16A, that may be receiving fluid
from pump 18A and transmit the highest of these
pressures to pump control l9A. Pump control l9A
responds by adjusting the displacement of pump 18A
to match output pressure to that within the most
highly pressurized one of the motors 14A, 15A, 16A
and to match output flow with the totalized demand
from the several motors.
The resolver valves 39B, 40B and 41B of
the second circuit 13B similarly compare pressures
from a predetermined group of devices, motors 14B,
15B and 16B, and transmit a control pressure to the
: second pump control l9B, from the most highly
pressurized motor, to adjust the displacement of
` 20 second pump 18B in a similar manner.
The composition of the predetermined
group of devices or motors from which pressures are
compared to obtain control pressure for the first
pump control l9A changes when pilot valve 36B of the
second circuit 13B is shifted to actuate motor 16B
and to supply pilot pressure to line 56~. Second
resolver control valve 51B then shifts to transmit
motor line pressure from motor 16B to the second
inlet 43A of resolver valve 41A of the first circuit
13A. The predetermined group of devices from which
pressures are compared to obtain a control pressure
~- for first pump control l9A now includes motor 16B
of the second circuit 13B as well as the motors 14A,
15A and 16A of the first circuit itself. This is
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desirable since second circuit motor 16B may receive
working fluid from the ~irst circuit 13A through
crossover line 17A and may at times be the most
highly pressurized device being supplied with fluid
by the first circuit pump 18A.
Thus if the second circuit motor 16B is
operating wholly or in part with working fluid
received from the first circuit 13A through line
17A, pump control 19A of the first circuit receives
a control pressure corresponding to the pressure in
the second circuit motor 16B at such times as that
pressure is higher than the pressures in any of the
motors 14A, 15A and 16A of the first circuit 13A
itself.
Essentially similar operation occurs
with respect to controlling the pump 18B of the
second circuit 13B. Resolver control valve pilot
line 52A is not pressurized and resolver control
valve 51A vents the second inlet 43B of resolver
valve 41B of the second circuit except when motor
.. 16A of the first circuit is operating in one
predetermined direction as previously described.
Accordingly, when motor 16A is not operating in the
; predetermined direction, resolving means 38B
compares only the pressures for motors 14B, 15B and
. 16B of the second circuit to obtain a control
pressure for second circuit pump control l9B.
If motor 16A of the first circuit 13A is
~` then actuated to operate in the predetermined
direction, first resolver control valve 51A is
piloted to transmit motor line pressure from the
first circuit motor 16A to inlet 43B of resolver
:~ valve 41B of the second circuit 13B. Thus the
predetermined group of devices from which pressures
are compared to obtain a control pressure for
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second circuit pump control l9B is temporarily
extended to include a motor 16A of the first
circuit 13A.
Accordingly, when the pump 18A or 18B of
either fluid circuit 13A or 13B is supplying fluid
only to the motors of that particular circuit, the
control pressure for the pump control l9A or l9B of
that particular circuit matches the most highly
pressurized one of the motors of that circuit. At
other times, when fluid from the pump 18A or 18~ of
either circuit is also being utilized by a device
or motor 16A or 16B of the other circuit, the control
pressure for each circuit may be derived from a
device of the other circuit when that device is more
highly pressurized.
The intercommunication of either pump
control l9A or l9B with the most highly pressurized
one of a predetermined group of devices, the
composition of which group may be different at
different stages of operation, is always a two way
or reversible flow path through the pressure comparing
means 38A or 38B. Thus the control signal lines 21A
and 21B do not require a continuous bleed of fluid
through orifices in order to track pressure decreases.
As a result the pump controls l9A and 19B respond
quickly and precisely to decreases of control
pressure as well as to increases of pressure at the
; most highly pressurized device. Power waste, from
- continually pumping high pressure fluid through a
" 30 bleed orifice, is thereby avoided. As the demand
for fluid from the pumps 18A and 18B is reduced by
the absence of bleed orifices, in some cases pumps
18A and 18B, the power source and other components
of the fluid system 11 may be of smaller capacity
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then would otherwise be required.
The fluid system 11 as described above for
purposes of example is one in which underutilized
pumping capacity at either of the two component
circuits 13A and 13BiS made available to the other
circuit under predetermined operating conditions.
The invention may also be employed in fluid
systems in which only a one way working fluid
sharing function is needed. For example, the system
11 may be converted to one in which output capacity
; of the second pump 18B that is not being utilized
by the second circuit 13B is made available to the
first circuit 13A but in which no reverse transfer
of fluid from first circuit 13A to second circuit
15 13Bis provided for. This may be accomplished by
eliminating the first crossover line 17A, the second
control pressure transmitting line 53B and first
- resolver control valve 51B and pressure transmitting
~` line 54B. The second outlet 43A of resolver valve
20 41A of the first circuit 13A may then be ven~ed to
~` drain or the resolver valve 41A may simply be
removed entirely with second inlet 43A of the
preceding resolver valve 40A being connected to
signal llne 66 of motor control valve 34A.
In the embodiments herein described, a
crossover of working fluid from one circuit 13A or
", 13B to the other and a comparison of load signals
from both circuits occurs only during operation of
motor 16A or 16B in one of the ~wo different
30 directions of motor operation. In embodiments of
this kind, resolver control valves 51A and 51B
conserve power by preventing an unnecessarily
high control pressure from reaching pump control 19A
or l9B during periods when motor operation is in the
~L.~J4~ ~ 3
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opposite direction and no actual crossover of
working fluid is occuring. In instances where it is
desired that sharing of fluid between circuits 13A
and 13B occur regardless of the direction of motor
;.5 operation, resolver control valves 51A and 51B may
be eliminated as described above.
Other aspects, objects and advantages of
:this invention can be obtained from a study of the
drawings, the disclosure and the appended clalms.
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