RELATED APPLICATIONS
This application is being filed on 14 March 2014, as a PCT International
Patent application and claims priority to U.S. Patent Application Serial No. 61/791,895
filed on 15 March 2013, and U.S. Patent Application Serial No. 61/798,649 filed on 15
March 2013. The entireties of these applications are hereby incorporated by reference.
INTRODUCTION
Mobile pieces of heavy machinery (e.g., excavators, backhoe loaders,
wheel loaders, etc.) often include hydraulic systems having hydraulically powered
linear and rotary actuators used in conjunction with hydraulic transformers to power
various active machine components (e.g., swing, boom, dipper, bucket, linkages, tracks,
rotating joints, etc.). By accessing a user interface of a machine control system, a
machine operator controls the machinery to perform work (e.g., earth-moving).
In hybrid systems, hydraulic transformers are sometimes coupled to
external loads (e.g., via a shaft) which require precise speed control. Throughout the
work cycle, hydraulic transformers may provide a motoring function or a pumping
function where torque is transferred either to or from a shaft, an external load, and/or
energy storage devices (e.g., accumulator). Since pump motors have finite
displacement capabilities, a hydraulic system cannot always realize a high flow demand
at a specific rotational speed, such as, for example, when a system is utilized to lift or
move a work element (e.g., a boom) against a force of gravity. In such hybrid work
circuits, there is often a need to optimally achieve flow demand to one or more
hydraulic actuators when the flow is supplied by a hydraulic transformer and one or
more pump motors. In addition, such flow demand should be accomplished smoothly
so as to be transparent to an operator of the machinery to enable maximum fuel
efficiency and productivity.
SUMMARY
Aspects of the present disclosure relate to systems and methods for
effectively flow sharing in a hydraulic system between a hydraulic transformer and one
or more hydraulic pumps to achieve flow demands for high flow services.
One aspect is a hydraulic system including a tank, at least one system
pump, a first directional flow control valve, an accumulator, a hydraulic transformer, a
second load, and a controller. The at least one system pump is powered by at least one
prime mover and coupled to the tank. The first directional flow control valve is coupled
to the at least one system pump. The hydraulic transformer is in selective fluid
communication with the at least one system pump and includes first and second
displacement pump units connected to a shaft. The shaft is connected to a first load.
The first displacement pump unit includes a first side that selectively fluidly connects to
at least one of the at least one system pump and a second side that fluidly connects to
the tank. The second displacement pump unit includes a first side that fluidly connects
to the accumulator and a second side that fluidly connects with the tank. The second
load is driven by an actuator in selective fluid communication with the at least one
system pump and the hydraulic transformer. The controller is arranged and configured
to reduce dynamic responses in the hydraulic system by causing flow sharing between
the hydraulic transformer and the first directional flow control valve.
The controller has a memory with a set of instructions. The controller is
arranged and configured to execute the set of instructions to implement a method for
flow sharing. The method may include: receiving and reading operator inputs;
computing a load value indicative of the second load based on the pressure
measurements; computing a desired flow based on the load value; determining whether
the hydraulic transformer is sufficient to independently supply the desired flow; if the
hydraulic transformer is not sufficient to independently supply the desired flow:
computing a flow deficit; computing and sending a command to the first directional
flow control valve indicative of the flow deficit; and if the hydraulic transformer is
sufficient to independently supply the desired flow: computing a desired displacement
for the hydraulic transformer; and computing and sending a second transformer
command to the hydraulic transformer to realize the desired displacement.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a schematic diagram of a first hydraulic system in accordance
with the principles of the present disclosure;
Figure 2 is a schematic diagram of a second hydraulic system in
accordance with the principles of the present disclosure;
Figure 3 shows a mobile piece of excavation equipment that is an
example of one type of machine on which hydraulic systems in accordance with the
principles of the present disclosure can be used;
Figure 4 shows an alternate view of the mobile piece of excavation
equipment shown in Figure 3;
Figure 5 is an example logic flow chart for operating example control
systems that may be used to control certain hydraulic systems in accordance with the
principles of the present disclosure; and
Figure 6 is another example logic flow chart for operating example
control systems that may be used to control certain hydraulic systems in accordance
with the principles of the present disclosure.
DETAILED DESCRIPTION
Reference will now be made in detail to aspects of the present disclosure
that are illustrated in the accompanying drawings. Wherever possible, the same
reference numbers will be used throughout the drawings to refer to the same or like
structure.
In general, the systems and methods below describe hybrid hydraulic
systems for increased fuel efficiency while maintaining operator transparency during
operation of machinery utilizing such hybrid hydraulic systems. In particular, operator
transparency may be achieved by reduction of undesirable dynamic responses due to
inadequate and/or inefficient scheduling of flow sources. In some embodiments, this is
accomplished by flow sharing between multiple sources, each capable of contributing
different amounts of flow.
Figure 1 shows a hydraulic system 10 in accordance with the principles
of the present disclosure. In general the hydraulic hybrid system 10 depicts includes
multiple variable displacement pumps 14, 16, directional control valves 24, 26, and a
hydraulic transformer 30. Systems and methods described herein are implemented
within the hydraulic system 10; however, it is understood that principles of the present
disclosure are applicable to any hydraulic system where flow from multiple sources is
combined to realize a desired flow rate.
The system 10 includes the variable displacement pumps 14, 16, driven
by a prime mover 18. In some examples, two prime movers can be used to drive the
variable displacement pumps 14, 16, respectively. Examples of the prime mover 18
include a diesel engine, a spark ignition engine, an electric motor or other power source.
It is understood that in some embodiments, only one prime mover is needed to power
both the variable displacement pumps 14, 16.
Each of the variable displacement pumps 14, 16 include inlets that draw
low pressure hydraulic fluid from a tank 22 (i.e., a low pressure reservoir). The variable
displacement pumps 14, 16 can include swash plates 15, 1 for controlling the pump
displacement volume per shaft rotation. The variable displacement pumps 14, 16 draw
the hydraulic fluid from the tank 22 and output pressurized hydraulic fluid for powering
a first load, which is controlled by a first hydraulic actuator 28 (e.g., boom cylinder), a
second load in the form of the hydraulic transformer 30 having a shaft 40 coupled to an
external load 42, and a third load, which is controlled by other actuators 29. The
variable displacement pumps 14, 16 include outlets through which the high pressure
hydraulic fluid is output. The outlets are preferably fluidly coupled (directly or
indirectly) to the plurality of different working load circuits, such as the first load, the
second load, and the third load. In the present embodiment, the directional control
valves 24, 26 control fluid flow between the load circuits (e.g., actuators or loads), the
variable displacement pumps 14, 16, and the tank 22. It is understood that in other
embodiments of the hydraulic system 10, more or less load circuits may exist in the
system.
In some examples where the system 10 is used to operate an excavator,
the first load includes a boom, which is actuated by the first actuator 28. The second
load (the external load 42) includes a swing, which is operated by the transformer 30.
The third load includes an arm, a bucket and a track motor, which are actuated by the
other actuators 29.
The second load circuit includes the hydraulic transformer 30 including a
first port 32, a second port 34, and a third port 35. The first port 32 of the hydraulic
transformer 30 is indirectly connected to the outlet of the variable displacement pumps
14, 16 via the outlet of the directional control valves 24, 26. The first port 32 is also
fluidly connected to the first actuator 28. The second port 34 is fluidly connected to the
tank 22. The third port 35 is fluidly connected to a hydraulic accumulator 36.
The hydraulic transformer 30 further includes an output/input shaft 38
that couples to the external rotational load 42. In some examples, a clutch 40 can be
used to selectively engage the output/input shaft 38 with the external load 42 and
disengage the output/input shaft 38 from the external load 42. When the clutch 40
engages the output/input shaft 38 with the external load 42, torque is transferred
between the output/input shaft 38 and the external load 42. In contrast, when the clutch
40 disengages the output/input shaft 38 from the external load 42, no torque is
transferred between the output/input shaft 38 and the external load 42. In some
embodiments, gear reductions may be provided between the clutch 40 and the external
load 42. It is understood that in some embodiments of the hydraulic transformer 30, a
clutch is not present.
In some embodiments, the other actuators 29 are fluidly connected
between the variable displacement pumps 14, 16 and the directional control valves 24,
26. As the other actuators 29 run, the other actuators 29 change the pressures at the
outlet of the variable displacement pumps 14, 16. In this configuration, by detecting the
pressures changed by the other actuators 29, which are, for example, monitored by
pressure sensors (P_pumpl) 3 1 and (P_pump2) 33 (Figure 2), the stream of the working
fluid can be controlled to ensure a flow continuity, as described below in further detail.
The system 10 further includes an electronic controller 44 that interfaces
with the variable displacement pumps 14, 16, the directional control valves 24, 26, and
the hydraulic transformer 30. It will be appreciated that the electronic controller 44 can
also interface with various other sensors and other data sources provided throughout the
system 10. For example, the electronic controller 44 can interface with pressure sensors
incorporated into the system 10 for measuring the hydraulic pressure in the accumulator
36, the hydraulic pressure provided by the variable displacement pumps 14, 16 to the
plurality of actuators or loads in the system 10, the pressures at the pump and tank sides
of the hydraulic transformer 30 and other pressures. Moreover, the controller 44 can
interface with a rotational speed sensor that senses a speed of rotation of the
output/input shaft 38 and the rotational speed of the transformer shaft. In some
examples, the electronic controller 44 operates to control the variable displacement
pumps 14, 16 by, for example, controlling the position of the swash plates 15, 17. In
other examples, the electronic controller 44 can be used to monitor a load on the prime
mover 18 and can control the hydraulic fluid flow rate across the variable displacement
pumps 14, 16 at a given rotational speed of a drive shaft, for example, the drive shafts
19, powered by the prime mover 18. Thus, in some embodiments, the prime mover 18
is connected to the drive shafts 19. In one embodiment, the hydraulic fluid
displacement across the variable displacement pumps 14, 16 per shaft rotation can be
altered by changing positions of the swash plates 15, 1 of the variable displacement
pumps 14, 16, respectively. The controller 44 can also interface with the clutch 40 for
allowing an operator to selectively engage and disengage the output/input shaft 38 of
the hydraulic transformer 30 with respect to the external load 42.
The electronic controller 44 includes a user interface 48 and a memory
46. A controller of the hydraulic system 10 may interact with the user interface 48 to
control movement of the various machine components connected to the system, such as,
the loads or actuators. In some embodiments, the user interface 48 may be arranged and
configured to accept controller commands which determine the overall operation of the
machine components. The user interface 48 may be any electronic or mechanical
device capable of receiving commands from an operator, such as, for example, a
computer, a joystick, and/or the like. The memory 46 can include various algorithms
and control logic that is utilized by the electronic controller 44 in controlling the
operation of the system 10. The memory 46 can also include one or more look-up
tables that help in the computation of certain measurements, such as, for example, the
desired flow of a system.
In some embodiments, the electronic controller 44 can control operation
of the hydraulic transformer 30 so as to provide a load leveling function that permits the
prime mover 18 to be run at consistent operating conditions (i.e., a steady operating
condition) thereby assisting in enhancing an overall efficiency of the prime mover 18.
The load leveling function can be provided by efficiently storing energy in the
accumulator 36 during periods of low loading on one or more of the prime mover 18,
and efficiently releasing the stored energy during periods of high loading on one or
more of the prime mover 18. This allows the prime mover 18 to be sized for an average
power requirement rather than a peak power requirement.
Figure 2 depicts an alternate embodiment of the system 10 of Figure 1,
equipped with a hydraulic transformer 30a having a plurality of pump/motor units
connected by a common shaft. For example, the hydraulic transformer 30a includes
first and second variable volume positive displacement pump/motor units 100, 102
connected by a shaft 104. The shaft 104 includes a first portion 106 that connects the
first pump/motor unit 100 to the second pump/motor unit 102, and a second portion 108
that forms the output/input shaft 38. The first pump/motor unit 100 includes a first side
100a that is fluidly (and indirectly) connected to the variable displacement pumps 14,
16 and a second side 100b fluidly connected to the tank 22. The second pump/motor
unit 102 includes a first side 102a fluidly connected to the accumulator 36 and a second
side 102b fluidly connected to the tank 22.
In one embodiment, each of the first and second pump/motor units 100,
102 includes a rotating group (e.g., cylinder block and pistons) that rotates with the
shaft 104, and a swash plate 110 that can be positioned at different angles relative to the
shaft 104 to alter the amount of pump displacement per each shaft rotation. The volume
of hydraulic fluid displaced across a given one of the pump/motor units 100, 102 per
rotation of the shaft 104 can be changed by varying the angle of the swash plate 110
corresponding to the given pump/motor unit. Varying the angle of the swash plate 110
also changes the torque transferred between the shaft 104 and the rotating group of a
given pump/motor unit. When the swash plates 110 are aligned perpendicular to the
shaft 104, no hydraulic fluid flow is directed through the pump/motor units 100, 102.
The swash plates 110 can be over-center swash plates that allow for bi-directional
rotation of the shaft 104. The angular positions of the swash plates 110 are individually
controlled by the electronic controller 44 based on the operating condition of the system
10. Thus, by controlling the positions of the swash plates 110, the controller 44 can
operate the system 10 in several operating modes.
By controlling the displacement rates and displacement directions of the
pump/motor units 100, 102, fluid power (pressure times flow) at a particular level can
be converted to an alternate level, or supplied as shaft power used to drive the external
load 42. When a deceleration of the external load 42 is desired, the hydraulic
transformer 30a can act as a pump taking low pressure fluid from the tank 22 and
directing it either to the accumulator 36 for storage, to the first actuator 28 connected
indirectly to the variable displacement pumps 14, 16 via the directional control valves
24, 26, or a combination of the two. In some examples, similarly to the clutch 40 in
Figure 1, a clutch can be used to selectively disengage the output/input shaft 38 from
the external load 42. In this configuration, the hydraulic transformer 30a can function
as a stand-alone hydraulic transformer (e.g., a hydraulic transformer) when no shaft
work is required to be applied to the external load 42. This is achieved by taking energy
from the system 10 at whatever pressure is dictated by the other associated system loads
(e.g., the first actuator 28) and storing the energy, without throttling, at the current
accumulator pressure. In the same way, un-throttled energy can also be taken from the
accumulator 36 at its current pressure and supplied to the system 10 at the desired
operating pressure. Proportioning of power flow by the hydraulic transformer 30a can
be controlled by controlling the positions of the swash plates 110 on the pump/motor
units 100, 102. In certain embodiments, as depicted in Figure 2, aspects of the present
disclosure can be used in systems without a clutch for disengaging a connection
between the output/input shaft 38 and the external load 42.
In some examples, the system 10 includes a rod-to-tank valve 116, which
is fluidly connected between the rod side of the first actuator 28 and the tank 22. When
power is drawn from the accumulator 36 to operate the second pump/motor unit 102 as
a motor, the swash plate 110 rotates and the first pump/motor unit 100 operates to pump
the working fluid from the tank 22 to the system loads (e.g., the first actuator 28). In
particular, when the directional control valves 24, 26 are closed, the working fluid is
supplied to the first actuator 28, which is operated to actuate a load, such as a boom. In
this case, the working fluid contained in the top cavity of the first actuator 28 is drawn
back from the rod side of the actuator 28 to the tank 22 through the rod-to-tank valve
116 as the actuator 28 works to actuate the load.
Figures 3 and 4 depict an example embodiment of mobile excavation
equipment which incorporates hydraulic circuit configurations of the type described
above with reference to Figures 1 and 2. In particular, Figures 3 and 4 show an
example excavator 200 including an upper structure 212 supported on an undercarriage
210. The undercarriage 210 includes a propulsion structure for carrying the excavator
200 across the ground. For example, the undercarriage 210 can include left and right
tracks. The upper structure 212 is pivotally movable relative to the undercarriage 210
about a pivot axis 208 (i.e., a swing axis). In certain embodiments, transformer
input/output shafts of the type described above can be used for pivoting the upper
structure 212 about the swing axis 208 relative to the undercarriage
The upper structure 212 can support and carry the prime mover (e.g.,
prime mover 18) of the machine and can also include a cab 225 which may include an
operator interface, such as, for example, the user interface 48. A boom 202 is carried by
the upper structure 212 and is pivotally moved between raised and lowered positions by
a boom cylinder 202c. An arm 204 is pivotally connected to a distal end of the boom
202. An arm cylinder 204c is used to pivot the arm 204 relative to the boom 202. The
excavator 200 also includes a bucket 206 pivotally connected to a distal end of the arm
204. A bucket cylinder 206c is used to pivot the bucket 206 relative to the arm 204. In
some embodiments, the boom cylinder 202c, the arm cylinder 204c, and the bucket
cylinder 206c may be part of system load circuits of the type described above. In some
embodiments, the first load 28 can function as the boom cylinder 402c.
In some instances, hybrid hydraulic systems, such as the ones shown in
Figures 1 and 2, require extra functionality to achieve increased fuel efficiency. It is
desirable for this extra functionality to be transparent to an operator of the system, such
as the operator of the excavation equipment shown in Figures 3 and 4. In other words,
transitions between operating modes of the system should be smooth instead of sporadic
and jerky so that the operator is unaware of mode transitions. A primary cause of
undesirable dynamic responses that create such problems during mode transitions is the
scheduling of flow sources. For example, as the system is recovering energy from an
overrunning load (e.g., when actuators allow the load to free fall when the directional
valve that controls the actuator shifts to lower the load), flow may need to move through
the hydraulic transformer 30a to enable energy recover and storage. However, if the
swing is rotating at a set speed, the hydraulic transformer may not be sufficient to
supply all of the flow necessary to maintain the desired boom speed. In this instance, it
is beneficial for at least some of the flow to be sent through the alternate sources, such
as, for example, the directional control valves 24, 26.
Now referring to Figures 5 and 6, example logic flow charts depicting
method 300 and 400 for operating a hydraulic system with flow sharing are shown. It is
understood that a control system, such as the electronic controller 44 is arranged and
configured to control the hydraulic system, such as the hydraulic system 10. The
methods 300 and 400 are example methods of operation of the control system. A
primary goal of the control logic/architecture is to improve operator transparency during
operation of the hybrid hydraulic system or machinery that implements the hybrid
hydraulic system. In particular, the methods 300 and 400 are example methods of
reducing dynamic responses due to inadequate and/or inefficient scheduling of flow
sources by causing flow sharing between multiple sources. The methods 300 and 400
will be described with reference to the hybrid hydraulic system 10 described in Figure
2; however, the methods 300 and 400 may be implemented in any hydraulic system.
It is further understood that the controller 44 may be any device suitable
to process digital and/or analog instructions, such as, for example, a computing device,
and implement the methods 300 and 400. In some embodiments, the controller 44
includes at least some form of computer-readable media. Computer readable media
includes any available media that can be accessed by the controller 44. By way of
example, computer-readable media include computer readable storage media and
computer readable communication media.
Computer readable storage media includes volatile and nonvolatile,
removable and non-removable media implemented in any device configured to store
information such as computer readable instructions, data structures, program modules or
other data. Computer readable storage media includes, but is not limited to, random
access memory, read only memory, electrically erasable programmable read only
memory, flash memory or other memory technology, compact disc read only memory,
digital versatile disks or other optical storage, magnetic cassettes, magnetic tape,
magnetic disk storage or other magnetic storage devices, or any other medium that can
be used to store the desired information and that can be accessed by the controller 44,
such as, for example, the memory 46 which may include a plurality of instructions for
operating the system 10, control algorithms, stored measurements, and the like.
Computer readable communication media typically embodies computer
readable instructions, data structures, program modules or other data in a modulated
data signal such as a carrier wave or other transport mechanism and includes any
information delivery media. The term "modulated data signal" refers to a signal that
has one or more of its characteristics set or changed in such a manner as to encode
information in the signal. By way of example, computer readable communication
media includes wired media such as a wired network or direct-wired connection, and
wireless media such as acoustic, radio frequency, infrared, and other wireless media.
Combinations of any of the above are also included within the scope of computer
readable media.
Now referring to Figure 5, the method 300 begins at operation 302 when
the controller 44 receives, reads, and processes operator inputs and measurements. In
particular, the operator may request actions via the user interface 48. In addition, an
operator input may be, for example, the pilot pressure delta generated by a hydraulic
joystick acting on each directional control valve 24, 26 or other pressure changes
generated by movement of the joystick by the operator. The controller 44 may also read
measurements, such as the head-side pressure, and /or temperature, at the actuator to
compute the load. In some embodiments, a head-side pressure transducer 112 can be
used to measure the head-side pressure at the actuator, and a head-side temperature
transducer 114 can be used to measure the head-side temperature at the actuator. In
other embodiments, a rod-side pressure transducer may be read for precise load
estimation.
After completing the operation 302, the method 300 moves to operation
304 at which the controller 44 computes the desired flow based on the operator's inputs,
measurements, and load estimation. For example, based on the operator's joystick
commands and the estimation of the actuator load, the controller 44 retrieves and
utilizes a look-up table. Based on the information retrieved from the look-up table, the
controller 44 computes the desired flow.
The method 300 then moves to operation 306 at which the controller 44
determines whether the hydraulic transformer 30a is sufficient to independently supply
the desired flow computed at the operation 304. To properly make the determination,
the controller 44 takes one or more measurements to determine the maximum flow that
could pass through the hydraulic transformer 30a without negative dynamic responses.
At the operation 306, the controller 44 compares the desired flow with the maximum
flow to determine whether the maximum flow is sufficient to meet the desired flow.
If the maximum flow is not sufficient to meet the desired flow, the
method 300 moves to operation 308. At the operation 308, the transformer is set to its
maximum flow and the controller 44 computes a flow deficit that needs to be
supplemented by alternate sources. The flow deficit is the amount of flow that is
needed beyond the maximum flow of the hydraulic transformer 30a and is the amount
that will be mitigated by flow from other sources, such as, for example, the directional
control valves 24, 26.
At operations 310 and 312, the flow deficit is converted into a command
that is sent from the controller 44 to the directional control valves 24, 26. The amount
of flow requested from each of the directional control valves 24, 26, can be either the
same or different amounts. The command is received at the directional control valves
24, 26 and the requested amount of flow is supplied to the system.
If, however, the maximum flow of the hydraulic transformer 30a is
sufficient to supply the computed desired flow, the method 300 moves to operation 314
instead of the operation 308. At the operation 314, the controller 44 computes the
displacement required to achieve the desired flow and converts this desired flow into a
command. At the operation 316, this command is sent to the hydraulic transformer 30a
which realizes the requested displacement and supplying the desired flow for the action.
Upon completing either the operation 312 or the operation 316, the
method 300 ends at operation 318. In some embodiments of the method 300, the
controller 44 may continuously operate in accordance with the method 300 within a
predetermined or arbitrary amount of time. In yet other embodiments, the controller 44
may begin the operation 300 again only after receiving new inputs from the operator via
the user interface 48.
Now referring to Figure 6, the method 400 begins at operation 402 at
which the controller 44 reads operator commands. As stated above with reference to
the operation 302 in the method 300, the controller 44 receives, reads, and processes
operator inputs such as the ones described herein.
At operation 404, the controller 44 reads pressure measurements at the
actuator. Such pressure measurements include the head-side pressure at the actuator,
and can be read utilizing a head-side pressure transducer, a rod-side pressure transducer,
or the like.
In some examples, at operation 405, the controller 44 also reads
temperature measurements at the actuator. Such temperature measurements can include
the head-side temperature at the actuator, and can be read utilizing a head-side
temperature transducer 114, a rod-side temperature transducer, or the like.
The method 400 then moves to operation 406 at which the controller 44
computes the load based on the pressure and/or temperature measurements read at the
operation 404.
At operation 408, the controller retrieves and utilizes a lookup table for
the purpose of computing a desired flow. The lookup table may be an operation map
that correlates certain measurements, such as, load estimations to flow. The controller
44 may, based on the operator commands read at the operation 402, the measurements
read at the operation 404, and/or the computed load estimation at the operation 406,
utilize the lookup table to correlate one or more of these inputs with a flow. In some
embodiments, this flow is the desired flow.
At operations 410, 412, and 414, the controller 44 reads speed sensors at
the transformer shaft 38, reads one or more position sensors connected to the lower
pump-motor swash plate, and calculates a maximum flow that could pass through the
lower pump-motor of the hydraulic transformer 30a based on the speed and
displacement position measurements taken in the operations 410 and 412. In some
embodiments, at the operation 414, the controller 44 calculates the maximum flow by
multiplying the speed read from the speed sensor by a maximum possible displacement
of the hydraulic transformer 30a.
At operation 416, the controller 44 determines whether the maximum
flow calculated in the operation 414 is sufficient to meet the desired flow calculated in
the operation 408. If the maximum flow is not sufficient to meet the desired flow, the
method 400 moves to operation 418. At the operation 418, in some embodiments, the
controller 44 computes a flow deficit by subtracting an actual flow at the current speed
and swash angle from the desired flow. This is the flow deficit that must be mitigated
by flow across the directional control valves 24, 26.
At the operation 420, the flow deficit is converted into a command that is
sent to the directional control valves 24, 26, which in turn, supply the flow deficit to the
system 10. The command sent to the directional control valves 24, 26 may differ based
on the status and/or configuration of the system 10 and/or valves 24, 26. For example,
in some embodiments, one of the directional control valves 24, 26 is coupled to the tank
22 and the other is blocked for at least one of a number of reasons. In the case of flow
recovery, a pilot pressure command can be computed utilizing an orifice equation as
shown in Equation 1 below. In particular, using the orifice equation, the controller 44
computes a desired orifice area needed to achieve the desired flow based on head-side
pressure and tank pressure measurements taken from sensors.
(1) A DESIRED = Q DEFICIT/ (Cd* SQRT ([P HEAD - P_TANK]*(2/RHO))),
where A DESIRED is a desired orifice area, Q DEFICIT is the flow deficit, Cd is the
discharge coefficient, P HEAD is the head-side actuator pressure, P TANK is tank
pressure, and RHO is fluid density.
A lookup table, which correlates orifice area to pilot pressure delta, is
then used to determine the pilot pressure delta for the orifice connected head-side to the
tank 22. In some embodiments, the lookup table is a computerized function which can
be utilized to tabulate the pilot pressure delta that is required for a given orifice area,
such as, in this case, the orifice connecting head-side to tank). An example of such a
function is shown in Equation 2 below.
(2) X DCV = F PP (A DESIRED),
where X DCV is the pilot pressure delta, F PP (A) is the lookup table, which in this
case, accepts the desired orifice area calculated via Equation 1 as an input. This desired
pilot pressure delta across the boom directional flow control valve is achieved using
electronically controlled pressure control valves.
In an alternate configuration, both of the directional control valves 24, 26 have
orifices connecting their respective pumps 14, 16 to the head-side of the actuator. The
controller 44 may utilize an optimization-based algorithm to compute the optimum pilot
pressure command to send to both of the control valves 24, 26. In this example, the
command is based on pressure sensor measurements at the head-side of the actuator, the
outlet of the pump 14, the outlet of the pump 16. In particular, Equations 3, 4, and 5, in
conjunction with lookup tables created using test data prior to system commissioning,
may be utilized to determine the optimum pilot pressure in a flow supply case as
described above.
(3) X DCV - ARGMIN X (A1(X) + A2(X)*SQRT (DP2)/SQRT (DP1)-
Q DEFICIT/ (Cd*SQRT (DPl*2/RHO))},
(4) DPI = P PUMPl - P HEAD,
(5) DP2 = P PUMP2 - P HEAD,
where ARGMIN X is the function that retrieves the value of X that minimizes the
function, A1(X) is the area-versus-pilot pressure delta map for the orifice on the DCV
connecting pump 14 to head-side, and A2(X) is the area-versus-pilot pressure delta map
for the orifice on the other DCV connecting pump 16 to head-side. The X DCV
command is realized at the directional control valves 24, 26 pilot ports via pressure
control, for example, using electro-proportional pressure relief valves in closed loop
control. The computed command, in either scenario, is sent to the actuators, and the
algorithm concludes at the end operation 426.
If, however, the maximum flow is sufficient to meet the desired flow, the
method 400 moves to the operations 422 and 424. The operations 422 and 424 of the
method 400 are the same or substantially the same as the operations 314 and 316 of the
method 300. Upon completing either the operation 420 or the operation 424, the
method 400 ends at operation 426. In some embodiments of the method 400, the
controller 44 may continuously operate in accordance with the method 400 and repeat
the method at sample times. In yet other embodiments, the controller 44 may begin the
operation 400 again only after receiving new inputs from the operator via the user
interface 48.

What is claimed is:
1. A hydraulic system comprising:
a tank;
at least one system pump powered by at least one prime mover and coupled to
the tank;
a first directional flow control valve coupled to the at least one system pump;
an accumulator;
a hydraulic transformer in selective fluid communication with the at least one
system pump, the hydraulic transformer including first and second displacement pump
units connected to a shaft, the shaft being connected to a first load, the first
displacement pump unit including a first side that selectively fluidly connects to at least
one of the at least one system pump and a second side that fluidly connects to the tank,
the second displacement pump unit including a first side that fluidly connects to the
accumulator and a second side that fluidly connects with the tank;
a second load driven by an actuator in selective fluid communication with the at
least one system pump and the hydraulic transformer; and
a controller arranged and configured to reduce dynamic responses in the
hydraulic system by causing flow sharing between the hydraulic transformer and the
first directional flow control valve, the controller having a memory with a set of
instructions, wherein the controller is arranged and configured to execute the set of
instructions to implement a method for flow sharing, the method comprising:
receiving and reading operator inputs;
computing a load value indicative of the second load based on the
pressure measurements;
computing a desired flow based on the load value;
determining whether the hydraulic transformer is sufficient to
independently supply the desired flow;
if the hydraulic transformer is not sufficient to independently supply the
desired flow:
computing a flow deficit;
computing and sending a command to the first
directional flow control valve indicative of the flow deficit; and
if the hydraulic transformer is sufficient to independently supply the
desired flow:
computing a desired displacement for the hydraulic transformer;
and
computing and sending a second transformer command to the
hydraulic transformer to realize the desired displacement.
2. The hydraulic system of claim 1, further comprising:
a second system pump powered by the at least one prime mover and coupled to
the tank; and
a second directional flow control valve coupled to the second system pump.
3. The hydraulic system of claim 2, wherein the method implemented by the
controller further comprises:
computing and sending a second valve command to the second directional flow
control valve indicative of at least a portion of the flow deficit.
4. The hydraulic system of claim 1, wherein the method implemented by the
controller further comprises:
reading pressure measurements at the actuator.
5. The hydraulic system of claim 1, wherein the method implemented by the
controller further comprises:
reading temperature measurements at the actuator.
6. The hydraulic system of claim 1, wherein when the system is recovering energy
from an overrunning load, the command is computed based on a desired orifice area.
7. The hydraulic system of claim 6, wherein the memory further comprises:
a look-up table, and
the method implemented by the controller further comprises:
retrieving the look-up table; and
utilizing the desired orifice area as an input to the look-up table to
determine at least a portion of the command.
8. The hydraulic system of claim 1, wherein the method implemented by the
controller further comprises:
reading speed measurements at the shaft.
9. The hydraulic system of claim 1, wherein the method implemented by the
controller further comprises:
reading displacement position measurements of at least one of the first and
second displacement pump units.
10. The hydraulic system of claim 1, wherein determining whether the hydraulic
transformer is sufficient to independently supply the desired flow comprises:
calculating a maximum flow that can be supplied by the hydraulic transformer.
11. The hydraulic system of claim 1, wherein computing the flow deficit comprises:
subtracting an actual flow at a current speed and current position from the
desired flow.
12. The hydraulic system of claim 1, further comprising a third load driven by a
second actuator in selective fluid communication with the at least one system pump.
13. The hydraulic system of claim 1, further comprising a third load driven by a
second actuator in selective fluid communication with the at least one system pump and
the hydraulic transformer, the second actuator is connected between the at least one
system pump and the first directional flow control valve.
14. The hydraulic system of claim 1, wherein the first directional flow control valve
and the desired displacement for the hydraulic transformer are controlled to enable the
hydraulic system to share flow smoothly between multiple power sources, loads, and
energy storage elements.