PROPEL CIRCUIT AND WORK CIRCUIT COMBINATIONS
FOR A WORK MACHINE
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is being filed on 09 January 2013, as a PCT
International Patent application and claims priority to U.S. Patent Application Serial
No. 61/584,650 filed on 09 January 2012 and U.S. Patent Application Serial No.
61/584,630 filed on 09 January 2012, the disclosures of which are incorporated
herein by reference in their entireties.
BACKGROUND
[0002] Work machines can be used to move material, such as pallets, dirt, and/or
debris. Examples of work machines include fork lifts, wheel loaders, track loaders,
excavators, backhoes, bull dozers, telehandlers, etc. The work machines typically
include a work implement (e.g., a fork) connected to the work machine. The work
implements attached to the work machines are typically powered by a hydraulic
system. The hydraulic system can include a hydraulic pump that is powered by a
prime mover, such as a diesel engine. The hydraulic pump can be connected to
hydraulic actuators by a set of valves to control flow of pressurized hydraulic fluid
to the hydraulic actuators. The pressurized hydraulic fluid causes the hydraulic
actuators to extend, retract, or rotate and thereby cause the work implement to move.
[0003] The work machine may further include a propulsion system adapted to
propel the work machine. The propulsion system may include a hydraulic pump that
is powered by the prime mover. The propulsion system may include a hydrostatic
drive.
SUMMARY
[0004] One aspect of the present disclosure relates to a hydraulic circuit
architecture for a mobile work vehicle. The hydraulic circuit architecture includes a
drive hydraulic pump, a hydraulic work circuit, a hydraulic propel circuit, and a

circuit selector. The hydraulic circuit architecture may be adapted to include a
single pump as the drive hydraulic pump and thereby provide benefits of avoiding
the costs of buying and maintaining multiple pumps as well as benefits of space and
weight savings for the hydraulic work machine. The drive hydraulic pump is
adapted to be driven by a prime mover, and has a high pressure side and a low
pressure side. The hydraulic work circuit is adapted for connection to at least one
actuator for driving a work component of the mobile work vehicle. The hydraulic
propel circuit includes a propel hydraulic motor that is adapted to be connected to a
drive train of the mobile work vehicle. The hydraulic propel circuit also includes a
hydraulic accumulator. The circuit selector selectively connects the high pressure
side of the drive hydraulic pump to the hydraulic work circuit and the hydraulic
propel circuit. The hydraulic circuit architecture is operable in a first mode and a
second mode. In the first mode, the hydraulic propel circuit is connected to the high
pressure side of the drive hydraulic pump and the hydraulic work circuit is
disconnected from the high pressure side of the drive hydraulic pump. In the second
mode, the hydraulic work circuit is connected to the high pressure side of the drive
hydraulic pump and the hydraulic propel circuit is disconnected from the high
pressure side of the drive hydraulic pump. When the hydraulic circuit architecture is
in the second mode, stored energy from the hydraulic accumulator can be used to
drive the propel hydraulic motor to cause propulsion of the mobile work vehicle.
[0005] The hydraulic circuit architecture may be operable in at least one mode
where the hydraulic work circuit is hydraulically isolated from the hydraulic propel
circuit, and means for transferring energy from the hydraulic accumulator to the
hydraulic work circuit is provided.
[0006] A variety of additional aspects will be set forth in the description that
follows. These aspects can relate to individual features and to combinations of
features. It is to be understood that both the foregoing general description and the
following detailed description are exemplary and explanatory only and are not
restrictive of the broad concepts upon which the embodiments disclosed herein are
based.

DESCRIPTION OF THE DRAWINGS
[0007] Non-limiting and non-exhaustive embodiments are described with
reference to the following figures, which are not necessarily drawn to scale, wherein
like reference numerals refer to like parts throughout the various views unless
otherwise specified.
[0008] Figure 1 is a schematic diagram of a hydraulic system having features
that are examples according to the principles of the present disclosure;
[0009] Figure 2 is a schematic diagram of the hydraulic system of Figure 1
further illustrating a control system of the hydraulic system;
[0010] Figure 3 is the schematic diagram of Figure 1 further illustrating a first
mode of the hydraulic system;
[0011] Figure 4 is the schematic diagram of Figure 1 further illustrating a second
mode of the hydraulic system;
[0012] Figure 5 is the schematic diagram of Figure I further illustrating a third
mode of the hydraulic system;
[0013] Figure 6 is the schematic diagram of Figure 1 further illustrating a fourth
mode of the hydraulic system;
[0014] Figure 7 is the schematic diagram of Figure 1 further illustrating a fifth
mode of the hydraulic system;
[0015] Figure 8 is a schematic diagram of another hydraulic system having
features that are examples according to the principles of the present disclosure;
[0016] Figure 9 is a schematic top plan view of a work vehicle including the
hydraulic system of Figures 1 or 8 according to the principles of the present
disclosure;
[0017] Figure 10 is a schematic diagram of still another hydraulic system having
features that are examples according to the principles of the present disclosure; and
[0018] Figure 11 is a schematic diagram of a work circuit usable with the
hydraulic system of Figure 1.

DETAILED DESCRIPTION
[0019] Various embodiments will be described in detail with reference to the
drawings, wherein like reference numerals represent like parts and assemblies
throughout the several views. Reference to various embodiments does not limit the
scope of the claims attached hereto. Additionally, any examples set forth in this
specification are not intended to be limiting and merely set forth some of the many
possible embodiments for the appended claims.
[0020] The present disclosure relates generally to hydraulic circuit architectures
for use in work vehicles. A hydraulic circuit architecture, in accordance with the
principles of the present disclosure, can include a propel circuit and a work circuit.
In certain embodiments, the propel circuit and the work circuit can be powered by a
same hydraulic pump structure (e.g., a hydraulic pump or a hydraulic pump/motor).
In certain embodiments, the hydraulic pump structure includes a single drive pump
(e.g., only one pump, only one pumping rotating group, only one pump/motor, etc.).
In certain embodiments, the propel circuit can include a hydraulic accumulator and a
hydraulic propulsion pump/motor for powering propulsion elements (e.g., wheels,
tracks, etc.) of the work vehicle through a drivetrain. The work circuit can include
various actuators for powering work components such as lifts, clamps, booms,
buckets, blades, and/or other structures. The various actuators may include
hydraulic cylinders, hydraulic motors, etc. In a preferred embodiment, the hydraulic
architecture is used on a forklift 50 (see Figure 9) where the propulsion circuit
powers a drivetrain 114 coupled to drive wheels 54 of the forklift 50, and the work
circuit includes valving and actuators (e.g., hydraulic cylinders) for raising and
lowering a fork 52 of the forklift 50, for front-to-back tilting of the fork 52, and for
left and right shifting of the fork 52.
[0021] In certain embodiments, the hydraulic accumulator of the propulsion
circuit can be used to provide numerous functions and benefits. For example, the
provision of the hydraulic accumulator allows the hydraulic pump/motor and prime
mover powering the propulsion circuit to be consistently operated at peak efficiency
or near peak efficiency. Moreover, accumulated energy in the hydraulic
accumulator can be used to provide power for starting a power source (e.g., a prime
mover, a diesel engine, or other engine) used to drive the hydraulic pump/motor.

Additionally, the hydraulic accumulator can be used to provide propulsion
functionality even when the power source coupled to the hydraulic pump/motor is
not operating. Similarly, the hydraulic accumulator can be used to provide work
circuit functionality even when the power source coupled to the hydraulic
pump/motor is not operating. Furthermore, by operating the propulsion hydraulic
pump/motor as a motor during braking/deceleration events, energy corresponding to
the deceleration of the work vehicle can be back-fed and stored by the hydraulic
accumulator for later re-use to enhance overall efficiency of the work vehicle.
[0022] In certain embodiments, one (i.e., a single) hydraulic pump/motor (e.g., a
hydraulic pump/motor 102, shown at Figure 1) is used to power both the propulsion
circuit and the working circuit. In such an embodiment, a circuit selector (i.e., a
mode selector) can be provided for selectively placing a high pressure side of the
hydraulic pump/motor in fluid communication with either the propulsion circuit or
the working circuit. The circuit selector can include one or more valves.
Furthermore, a cross-over valve can be provided for selectively providing fluid
communication between the propulsion circuit and the work circuit. By opening the
cross-over valve, power from the hydraulic accumulator can be used to drive one or
more actuators of the work circuit thereby allowing for actuation of the actuators of
the work circuit, even when the power source is turned off. When the circuit
selector has placed the pump/motor in fluid communication with the propulsion
circuit for propelling the work vehicle, the various components of the work circuit
can be actuated by opening the cross-over valve. Additionally, when the circuit
selector has placed the pump/motor in fluid communication with the work circuit,
the hydraulic accumulator can be used to provide for propulsion and steering of the
work vehicle. It will be appreciated that a steering component is preferably
incorporated into the hydraulic propulsion circuit. When the power source is turned
off, the hydraulic accumulator can be used to power the steering component, power
the propulsion elements, and/or power the various components of the work circuit.
It will be appreciated that such activities can be conducted individually or
simultaneously. The cross-over valve can provide a variable size orifice.
[0023] In certain embodiments, the hydraulic pump/motor coupled to the power
source is an open circuit pump/motor having a rotating group and a swash plate that

is adjustable to control an amount of hydraulic fluid displaced by the pump/motor
per rotation of a pump/motor shaft by the power source. In certain embodiments,
the swash plate has an over-center configuration. When the pump/motor is
operating as a pump, the swash plate is on a first side of center and the power source
rotates the pump/motor shaft in a first direction such that hydraulic fluid is pumped
through the pump/motor from a low pressure side in fluid communication with a
reservoir/tank to a high pressure side in fluid communication with the circuit
selector. When the hydraulic pump/motor is operated as a motor, the swash plate
may be moved to a second side of center and hydraulic fluid from the hydraulic
accumulator is directed through the pump/motor from the high pressure side to the
low pressure side thereby causing the pump/motor shaft to rotate in the same
rotational direction that the pump/motor shaft rotates when driven by the power
source. In this way, hydraulic energy from the hydraulic accumulator can be used to
start modes including use of the power source.
[0024] The propulsion pump/motor can also be an open circuit pump/motor
having a low pressure side connected to the reservoir/tank and a high pressure side
that connects to the hydraulic pump/motor coupled to the power source through the
circuit selector. The propulsion pump/motor can include a rotating group and a
swash plate that can be adjusted to control displacement of the propulsion
pump/motor for each revolution of a shaft of the propulsion pump/motor. The
swash plate can be an over-center swash plate that allows for bi-directional rotation
of the shaft of the propulsion pump/motor. For example, when the swash plate is on
a first side of center, hydraulic fluid flow through the pump/motor from the high
pressure side to the low pressure side can drive the shaft in a clockwise direction. In
contrast, when the swash plate is on a second side of center, hydraulic fluid flow
through the propulsion pump/motor in a direction from the high pressure side to the
low pressure side causes rotation of the shaft in a counterclockwise direction. In this
way, the propulsion pump/motor can be used to drive the work vehicle in both
forward and rearward directions. Moreover, during a braking event, the propulsion
pump/motor can function as a pump and can direct hydraulic fluid from the reservoir
to the hydraulic accumulator to charge the hydraulic accumulator thereby capturing
energy associated with the deceleration. Thus, the propulsion pump/motor and the
hydraulic accumulator provide a braking/deceleration and energy storage function.

It will be appreciated that in other embodiments (e.g., an embodiment illustrated at
Figure 8), valving can be used in combination with non-over-center pump/motors to
provide the same or similar functionality as the over-center pump/motors described
above. The non-over-center pump/motors and the valving can be used as the
hydraulic pump/motor coupled to the power source, as shown at Figure 8, and/or can
be used as the propulsion hydraulic pump/motor that is coupled to the drivetrain.
[0025] According to the principles of the present disclosure and as illustrated at
Figures 1-7, a hydraulic system 100 (i.e., a hydraulic circuit architecture) is adapted
to power the drivetrain 114 of the work machine 50 (i.e., a work vehicle, a mobile
work vehicle, a forklift, a lift truck, a fork truck, a wheel loader, a digger, an
excavator, a backhoe loader,' etc.). The hydraulic system 100 may be further adapted
to power a work circuit 300 of the work machine 50. The hydraulic system 100 may
be adapted to power a steering control unit 600 (e.g., a hydraulic steering circuit) of
the work machine 50. As depicted at Figure 9, the work machine 50 includes a work
attachment 52 (e.g., the fork, a work component, etc.), at least one drive wheel 54,
and at least one steer wheel 56. In certain embodiments, one or more drive wheel 54
may be combined with one or more steer wheel 56. In certain embodiments, the
work machine 50 may include only a single drive hydraulic pump.
[0026] The hydraulic system 100 is adapted to recover energy and store the
energy in a hydraulic accumulator 116 for reuse. For example, when the work
machine 50 is decelerated, the drivetrain 114 may deliver kinetic energy to the
hydraulic system 100 and thereby store the energy in the hydraulic accumulator 116.
The hydraulic system 100 is also adapted to quickly start a prime mover 104 (e.g.,
the internal combustion engine) of the work machine 50 with the energy stored in
the hydraulic accumulator 116. The hydraulic system 100 may be adapted to power
the drivetrain 114, the work circuit 300, and/or the steering control unit 600 without
the prime mover 104 running by drawing hydraulic power from the hydraulic
accumulator 116. In certain embodiments, the prime mover 104 may drive only a
single hydraulic pump. In certain embodiments, the prime mover 104 may drive
only a single hydraulic pump that powers the drivetrain 114 and the work circuit
300. In certain embodiments, the prime mover 104 may drive only a single
hydraulic pump that powers at least the drivetrain 114 and the work circuit 300. In

certain embodiments, the prime mover 104 may drive only a single hydraulic pump
that powers the drivetrain 114, the work circuit 300, and the steering control unit
600. In certain embodiments, the prime mover 104 may drive only a single
hydraulic pump that at least powers the drivetrain 114, the work circuit 300, and the
steering control unit 600.
[0027] The hydraulic system 100 operates in various modes depending on
demands placed on the work machine 50 (e.g., by an operator). A control system
500 monitors an operator interface 506 of the work machine 50 and also monitors
various sensors 510 and operating parameters of the hydraulic system 100. As
illustrated at Figure 2, signal lines 508 may facilitate communication within the
control system 500. The control system 500 evaluates input received from the
operator interface 506. In certain embodiments, an electronic control unit 502
monitors the various sensors 510 and operating parameters of the hydraulic system
100 to configure the hydraulic system 100 into the most appropriate mode. The
modes include a work circuit primary mode 82, as illustrated at Figure 3; a hybrid
propel mode 84, as illustrated at Figures 4 and 5, and a hydrostatic mode 86, as
illustrated at Figures 6 and 7. The electronic control unit 502 may monitor the
operator interface 506, the prime mover 104, and environmental conditions (e.g.
ambient temperature). Memory 504 (e.g., RAM memory) may be used within the
electronic control unit 502 to store executable code, the operating parameters, the
input from the operator interface, etc.
[0028] In the work circuit primary mode 82 (see Figure 3), power from the
prime mover 104 is directly supplied to the work circuit 300 by the hydraulic system
100, and power from the hydraulic accumulator 116 is delivered to the drivetrain
114 by the hydraulic system 100. In certain embodiments, power for the steering
control unit 600 is also taken from the hydraulic accumulator 116 in the work circuit
primary mode 82. The work circuit primary mode 82 may be selected when power
demands by the drivetrain 114 are low, relatively low, and/or are anticipated to be
low, and power demands and/or hydraulic flow demands by the work circuit 300 are
high, relatively high, and/or are anticipated to be high. Such conditions may occur,
for example, when the work machine 50 is moving slowly or is stationary and the
work attachment 52 is being used extensively and/or with high loading. In the work

circuit primary mode 82, the steering control unit 600 may receive power from the
hydraulic accumulator 116.
[0029] The hybrid propel mode 84 (see Figures 4 and 5) may be used when the
power demand from the drivetrain 114 is dominate over the power demand of the
work circuit 300. The hybrid propel mode 84 may also be used when it is desired to
recapture energy from the deceleration of the work machine 50. The hybrid propel
mode 84 may further be used to power the work machine 50 without the prime
mover 104 running or running full time. For example, the hybrid propel mode 84
allows the prime mover 104 to be shut down upon sufficient pressure existing in the
hydraulic accumulator 116. Upon depletion of the hydraulic accumulator 116 to a
lower pressure, the hybrid propel mode 84 hydraulically restarts the prime mover
104 thereby recharging the hydraulic accumulator 116 and also providing power to
the work machine 50 from the prime mover 104. In the hybrid propel mode 84, the
steering control unit 600 may receive power from the hydraulic accumulator 116
and/or the prime mover 104.
[0030] The hydrostatic mode 86 (see Figures 6 and 7) may be used when the
demands of the drivetrain 114 are high, relatively high, and/or are anticipated to be
high. For example, when the work machine 50 is driven at a high speed, when the
work machine 50 is driven up an incline, and/or when the drivetrain 114 is under a
high load. The hydrostatic mode 86 may be used when the demands of the
drivetrain 114 are sufficiently high to require a pressure within the hydraulic
accumulator 116 to be in excess of a pressure rating and/or a working pressure of the
hydraulic accumulator 116. The pressure rating and/or the working pressure of the
hydraulic accumulator 116 can correspondingly be lowered in a hydraulic system
that can switch between a mode (e.g., the hydrostatic mode 86) where the hydraulic
accumulator 116 is isolated and a mode (e.g., the hybrid propel mode 84) where the
hydraulic accumulator 116 is connected. In the hydrostatic mode 86, the steering
control unit 600 may receive power from the prime mover 104.
[0031] The control system 500 may rapidly switch between the work circuit
primary mode 82, the hybrid propel mode 84, and/or the hydrostatic mode 86 to

continuously adjust the hydraulic system 100 to the demands of the work machine
50.
[0032] Turning now to Figure 1, the hydraulic system 100 is illustrated as a
schematic diagram. The hydraulic system 100 is powered by the prime mover 104
which is connected to a pump/motor 102. In certain embodiments, the pump/motor
102 may be replaced with a pump. As depicted, the hydraulic system 100 allows the
hydraulic pump/motor 102 to be a single pump/motor (or a single pump) that powers
the drivetrain 114, the work circuit 300, and/or the steering control unit 600. By
configuring the hydraulic system 100 with the single pump/motor (or the single
pump), a cost of the hydraulic system 100 may be reduced, a weight of the hydraulic
system 100 may be reduced, the efficiency of the hydraulic system 100 may be
increased by reducing the parasitic losses of additional components, and/or a
packaging size of the hydraulic system 100 may be reduced.
[0033] As depicted, the hydraulic pump/motor 102 and the prime mover 104
may be assembled into an engine pump assembly 106. In certain embodiments, the
prime mover 104 turns in a single rotational direction (e.g., a clockwise direction),
and thus, the hydraulic pump/motor 102 may also rotate in the single rotational
direction of the prime mover 104. Power may be transferred between the hydraulic
pump/motor 102 and the prime mover 104 by a shaft (e.g., an input/output shaft of
the hydraulic pump/motor 102 may be connected to a crankshaft of the prime mover
104). The power is typically transferred from the prime mover 104 to the hydraulic
pump/motor 102 when the hydraulic pump/motor 102 is supplying hydraulic power
to the hydraulic accumulator 116, the drivetrain 114, the work circuit 300, and/or the
steering control unit 600. The power may be transferred from the hydraulic
pump/motor 102 to the prime mover 104 when the hydraulic pump/motor 102 is
starting the prime mover 104, during engine braking, etc.
[0034] The hydraulic pump/motor 102 may be a variable displacement
pump/motor. The hydraulic pump/motor 102 may be an over-center pump/motor.
The hydraulic pump/motor 102 includes an inlet 1021 (i.e., a low pressure side) that
receives hydraulic fluid from a tank 118 via a low pressure line 440, and the
hydraulic pump/motor 102 includes an outlet 102h (i.e., a high pressure side) that is

connected to a high pressure line 400 of the hydraulic pump/motor 102. When the
prime mover 104 supplies power to the hydraulic pump/motor 102, hydraulic fluid is
drawn from the tank 118 into the inlet 1021 of the hydraulic pump/motor 102 and
expelled from the outlet 102h of the hydraulic pump/motor 102 at a higher pressure.
In certain embodiments, power may be delivered from the hydraulic pump/motor
102 to the prime mover 104 when a swash plate of the hydraulic pump/motor 102 is
positioned over center and high pressure hydraulic fluid from the high pressure line
400 is driven backwards through the hydraulic pump/motor 102 and ejected to the
low pressure line 440 and to the tank 118. Alternatively, as illustrated at Figure 8, a
reversing valve 103 of a hydraulic system 100' can be used to cause the prime mover
104 to be backdriven with a hydraulic pump/motor 102', similar to the hydraulic
pump/motor 102.
[0035] A flow control device 202 (e.g., a relief valve) includes a connection to
the high pressure line 400. Upon hydraulic fluid pressure within the high pressure
line 400 reaching a predetermined limit, the flow control device 202 opens and
dumps a portion of the hydraulic fluid to the tank 118 and thereby protecting the
high pressure line 400 from reaching an over pressure condition.
[0036] A flow control device 206 is connected between the high pressure line
400 and a high pressure line 406 of the work circuit 300. In the depicted
embodiment, the flow control device 206 is a work circuit valve.
[0037] A flow control device 208 is connected between the high pressure line
400 and a high pressure line 402. As depicted, the high pressure line 402 may be
connected to an inlet 108h (i.e., a high pressure side) of a pump/motor 108. The
flow control device 208 may be an isolation valve. In certain embodiments, the flow
control device 206 and the flow control device 208 may be combined into a single
three-way valve 207 (see Figure 8).
[0038] The high pressure line 402 is connected to the hydraulic accumulator 116
by a fluid flow control device 210. In the depicted embodiment, the fluid flow
control device 210 is an isolation valve for the hydraulic accumulator 116. In the
depicted embodiment, the fluid flow control device 210 and the hydraulic
accumulator 116 are connected by an accumulator line 404.

[0039] The high pressure line 402 is further connected to the high pressure line
406 by a flow control device 212 and another flow control device 224. In the
depicted embodiment, the flow control device 212 is a Valvistor® proportional flow
control device, and the flow control device 224 is a check valve that prevents
hydraulic fluid from the high pressure line 406 from entering the high pressure line
402. In the depicted embodiment, the flow control devices 212 and 224 are
connected in series along a cross-over flow line 408 that connects the high pressure
line 402 and the high pressure line 406. In other embodiments, a single flow control
device may be used along the cross-over flow line 408.
[0040] Certain aspects of the propulsion system of the work machine 50 will
now be described. The propulsion system includes the pump/motor 108 that both
transmits and receives power to and from the drivetrain 114 via an output shaft 110.
In particular, the output shaft 110 is connected to a gear box 112. As illustrated at
Figure 9, the gear box 112 may include a differential connected to a pair of the drive
wheels 54. In other embodiments, a hydraulic pump/motor may be included at each
of the drive wheels 54, and the differential may not be used. When sending power
to the drivetrain 114, the pump/motor 108 may accelerate the work machine 50, may
move the work machine 50 up an incline, and/or may otherwise provide overall
movement to the work machine 50. When the work machine 50 decelerates and/or
travels down an incline, the pump/motor 108 may receive energy from the drivetrain
114. When the hydraulic system 100 is in the hybrid propel mode 84 or the work
circuit primary mode 82, the pump/motor 108 may send hydraulic energy to the
hydraulic accumulator 116. In particular, the pump/motor 108 may receive
hydraulic fluid from the tank 118 via the low pressure line 440 and pressurize the
hydraulic fluid and send it through the high pressure line 402 through the fluid flow
control device 210 and the accumulator line 404 and into the hydraulic accumulator
116.
[0041] The pump/motor 108 may be driven by hydraulic power from the
hydraulic accumulator 116 or the hydraulic pump/motor 102. In particular, when
the hydraulic system 100 is in the work circuit primary mode 82, the pump/motor
108 receives the hydraulic power from the hydraulic accumulator 116, as illustrated
at Figure 3. When the hydraulic system 100 is in the hybrid propel mode 84, as

illustrated at Figures 4 and 5, the pump/motor 108 may receive hydraulic power
from either the hydraulic pump/motor 102, the hydraulic accumulator 116, or both
the hydraulic pump/motor 102 and the hydraulic accumulator 116. When the
hydraulic system 100 is in the hydrostatic mode 86, as illustrated at Figures 6 and 7,
the pump/motor 108 receives power from the hydraulic pump/motor 102. However,
the pump/motor 108 may deliver power to the hydraulic pump/motor 102 and the
prime mover 104 may thereby provide engine braking.
[0042] A relief valve 214 may be connected between the high pressure line 402
and the tank 118. Feedback from the high pressure line 402 may be given to the
hydraulic pump/motor 102 by way of a pump/motor control pressure valve 220 (e.g.
a pressure reducing valve). In particular, a point of use filter device 222 is
connected between the high pressure line 402 and the pump/motor control pressure
valve 220. The pump/motor control pressure valve 220 may feed a pressure signal
to the hydraulic pump/motor 102 and thereby control the hydraulic pump/motor 102
in certain embodiments and/or in certain modes.
[0043] In the depicted embodiment, the steering control unit 600 receives
hydraulic power from the high pressure line 402. In particular, an intermediate
pressure steering line 420 is connected to the high pressure line 402 via a steering
feed valve 218 (e.g., a flow control valve) and a steering feed valve 216 (e.g., a
pressure reducing valve). A return line 422 is connected between the steering
control unit 600 and the tank 118.
[0044] Various components may be included in a manifold block 200. For
example, the flow control device 202, the flow control device 206, the flow control
device 208, the fluid flow control device 210, the flow control device 212, the relief
valve 214, the pump/motor control pressure valve 220, the device 222, and/or the
flow control device 224 may be included in the manifold block 200.
[0045] Turning now to Figure 2, a schematic diagram of the control system 500
is shown with a schematic diagram of the hydraulic system 100. As can be seen, the
hydraulic system 100 monitors a plurality of sensors indicating the state of the
hydraulic system 100. The control system 500 further monitors the operator
interface 506 thereby allowing an operator to take control of the hydraulic system

100 and thereby take control of the work machine 50. The electronic control unit
502 of the control system 500 may perform calculations that model the hydraulic
system 100 in the various modes and thereby determine the optimal mode and
thereby select the optimal mode for the given working conditions and the given
operator input. Under certain conditions, the mode of the hydraulic system 100 is
selected to maximize fuel efficiency of the work machine 50. In other conditions,
the mode of the hydraulic system 100 is selected to maximize performance of the
hydraulic system 100 and thereby the work machine 50. The electronic control unit
502 may learn a working cycle that the work machine 50 repeatedly undertakes. By
learning the working cycle, the electronic control unit 502 can maximize efficiency
for the working cycle and identify when the work machine 50 is in the working
cycle. The electronic control unit 502 may switch modes differently depending on
which working cycle the work machine 50 is in. By switching modes throughout
the working cycle, various parameters of the hydraulic system 100 can be optimized
for efficiency or performance. For example, charge pressure of the hydraulic
accumulator 116, swash plate angle of the hydraulic pump/motor 102 and/or the
pump/motor 108, and/or the timing of starting and stopping the prime mover 104
may be determined based on the working cycle of the work machine 50. The control
system 500 may emulate a conventional work machine such that the work machine
50 behaves and feels like the conventional work machine to the operator.
[0046] Turning now to Figure 3, the work circuit primary mode 82 is illustrated.
The work circuit primary mode 82 is selected by the control system 500 when the
work attachment 52 is under heavy use, sustained use, and/or use that requires high
volumetric flow rates of hydraulic fluid. The drivetrain 114 of the work machine 50
is operational in the work circuit primary mode 82. In particular, the hydraulic
accumulator 116 can supply power to and receive power from the pump/motor 108.
Upon the hydraulic accumulator 116 being depleted to a given level, the control
system 500 may quickly switch the hydraulic system 100 into the hybrid propel
mode 84 to recharge the hydraulic accumulator 116. Upon the hydraulic
accumulator 116 being recharged to a given pressure level, the control system 500
may return the hydraulic system 100 to the work circuit primary mode 82.

[0047] Turning now to Figure 4, the hybrid propel mode 84 is illustrated. In
particular, a hybrid mode 84a is illustrated. The hybrid mode 84a allows the
exchange of energy between the hydraulic pump/motor 102, the hydraulic
accumulator 116, and the pump/motor 108. In particular, the hydraulic pump/motor
102 may supply hydraulic power to the hydraulic accumulator 116 for the purpose of
recharging the hydraulic accumulator 116. The hydraulic pump/motor 102 may
separately or simultaneously supply power to the pump/motor 108 to propel the
work machine 50. The hydraulic accumulator 116 may supply power to the
hydraulic pump/motor 102 for the purpose of starting the prime mover 104.
Separately or simultaneously, the hydraulic accumulator 116 may supply power to
the pump/motor 108 to propel the work machine 50. The pump/motor 108 may
supply hydraulic fluid power to the hydraulic accumulator 116 and thereby charge
the hydraulic accumulator 116. Separately or simultaneously, the pump/motor 108
may provide power to the hydraulic pump/motor 102. The power supply to the
hydraulic pump/motor 102 can be used to start the prime mover 104 and/or to
provide engine braking (e.g., upon the hydraulic accumulator 116 being full). When
the hydraulic system 100 is in the hybrid mode 84a, the work circuit 300 may be cut
off from hydraulic fluid power. In this case, the work circuit 300 may have no
demand for hydraulic power.
[0048] Turning now to Figure 5, the hybrid propel mode 84 is again illustrated.
In particular, a hybrid mode 84b is illustrated. The hybrid mode 84b is similar to the
hybrid mode 84a except that the cross-over flow line 408 is open allowing hydraulic
fluid power from the high pressure line 402 to be supplied to the work circuit 300.
In the hybrid mode 84b, the hydraulic pump/motor 102, the hydraulic accumulator
116, and/or the pump/motor 108 may supply hydraulic power to the work circuit
300.
[0049] The hybrid propel mode 84 may be preferred when the work machine 50
is undergoing a moderate workload, and/or when high efficiency and/or energy
recovery from the drivetrain 114 is desired.
[0050] Turning now to Figure 6, the hydrostatic mode 86 is illustrated. In
particular a hydrostatic mode 86a is illustrated. The hydrostatic mode 86a may be

used when the drivetrain 114 of the work machine 50 is under heavy load. For
example, when the work machine 50 is driven at high torque/power and/or when the
work machine 50 is driven up an incline. When the hydraulic system 100 is
operated in the hydrostatic mode 86a, hydraulic pressure within the high pressure
line 400 and the high pressure line 402 may exceed a working pressure and/or a
rated pressure of the hydraulic accumulator 116. By switching between the hybrid
propel mode 84 and the hydrostatic mode 86, the hydraulic system 100 may
undertake tasks that result in high pressures in the high pressure line 402 without
exposing the hydraulic accumulator 116 to the high pressures. Thus, the benefits of
the hybrid propel mode 84 can be enjoyed without requiring that the accumulator
116 have a pressure rating that matches the maximum pressure rating of the
hydraulic pump/motor 102. By bypassing (e.g., isolating) the accumulator 116 with
the fluid flow control device 210, the hydraulic system 100 does not need to wait for
the accumulator 116 to be pressurized up to the desired working pressure. When the
hydraulic system 100 is in the hydrostatic mode 86a, the work circuit 300 may be
cut off from hydraulic fluid power. In this case, the work circuit 300 may have no
demand for hydraulic power.
[0051] Turning now to Figure 7, the hydrostatic mode 86 is further illustrated.
In particular, a hydrostatic mode 86b is illustrated. The hydrostatic mode 86b is
similar to the hydrostatic mode 86a, except that the cross-over flow line 408 is open
allowing hydraulic fluid power from the high pressure line 402 to be supplied to the
work circuit 300. In the hydrostatic mode 86b, the hydraulic pump/motor 102
and/or the pump/motor 108 may supply hydraulic power to the work circuit 300.
[0052] Turning now to Figure 8, a system forming a second embodiment of the
principles of the present disclosure is presented. The system includes the hydraulic
system 100', mentioned above. As many of the concepts and features are similar to
the first embodiment, shown at Figures 1-7, the description for the first embodiment
is hereby incorporated by reference for the second embodiment. Where like or
similar features or elements are shown, the same reference numbers will be used
where possible. The following description for the second embodiment will be
limited primarily to the differences between the first and second embodiments. In
the hydraulic system 100', the flow control device 206 and the flow control device

208 of the hydraulic system 100 have been replaced by the single three-way valve
207. In addition, the flow control device 212 and the flow control device 224 of the
hydraulic system 100 has been replaced by an on-off electrically controlled valve
212' and a constant flow valve 2241. The substitution of the on-off electrically
controlled valve 212' and the constant flow valve 224' can be further made in other
embodiments of the present disclosure. Likewise, the flow control device 212 and
the flow control device 224 can be substituted in the present embodiment.
[0053] Turning now to Figure 9, a schematic layout of the work machine 50 is
illustrated. In the depicted embodiment, the work machine 50 is a fork truck.
[0054] Turning now to Figure 10, a system forming a third embodiment of the
principles of the present disclosure is schematically illustrated. The system includes
a hydraulic system 100". As with the hydraulic system 100, the hydraulic system
100" similarly powers the work circuit 300. However, in the hydraulic system 100"
a hydraulic pump 107 is used to provide hydraulic power to the work circuit 300.
The hydraulic pump 107, in turn, is connected by a shaft 109 to a pump/motor 102".
A clutch 105 is operably connected between the prime mover 104 and the hydraulic
pump/motor 102". A low pressure accumulator 117 (i.e., a storage accumulator) is
further included connected to a low pressure side of the hydraulic pump/motor 102".
[0055] By placing the hydraulic pump/motor 102" at a zero swash plate
displacement angle, power can flow from the prime mover 104 through the clutch
105 and into the hydraulic pump 107. Thus, power from the prime mover 104 can
directly power the work circuit 300. While the prime mover 104 is directly
powering the work circuit 300, the hydraulic accumulator 116 can be both supplying
and receiving power from the pump/motor 108. Thus, the hydraulic system 100" has
a mode similar to the work circuit primary mode 82, illustrated at Figure 3.
[0056] Hydraulic power from the hydraulic accumulator 116 can be used to start
the prime mover 104. In particular, hydraulic power flows from the hydraulic
accumulator 116, through fluid flow control device 210, and into the hydraulic
pump/motor 102". The clutch 105 can be engaged and thereby the hydraulic
pump/motor 102" can start the prime mover 104.

[0057] The hydraulic pump/motor 102", the hydraulic accumulator 116, the
pump/motor 108, and the prime mover 104 can operate in a hybrid propel mode
similar to the hybrid propel mode 84. When hydraulic power is required by the
work circuit 300, the hydraulic pump 107 can receive power from the hydraulic
pump/motor 102" via the shaft 109. Thus, the hydraulic system 100" has a mode
similar to the hybrid mode 84b, illustrated at Figure 5.
[0058] The hydraulic accumulator 116 can be isolated from the pump/motor 108
by closing the fluid flow control device 210. In this way, the hydraulic system 100"
can operate in a hydrostatic mode similar to the hydrostatic mode 86. If the work
circuit 300 requires hydraulic power, the hydraulic pump 107 may receive power
from the hydraulic pump/motor 102" via the shaft 109.
[0059] Turning now to Figure 11, a detailed schematic diagram of the example
work circuit 300 is shown. The work circuit 300 is for activating the work
attachment 52 of the work machine 50. In the embodiment shown, the work circuit
300 has a pump port 302 for connecting to the pump/motor 102 via the high pressure
line 406. The work circuit 300 also has a tank port 304 for connecting to the
reservoir or tank 118 (e.g., via the low pressure line 440).
[0060] The work circuit 300 also includes a first valve 306 for enabling a work
attachment lift function, a second valve 308 for enabling a work attachment tilt
function, and a third valve 310 for enabling a work attachment side shift function.
In the particular embodiment shown, the valves 306, 308, 310 are proportional
valves of the spool and sleeve type.
[0061] The first valve 306 is configured and arranged to selectively provide
pressurized fluid from the port 302 to one or both of hydraulic lift cylinders 312, 314
which are mechanically coupled to the work attachment 52. The operation of the
valve 306 causes the work attachment 52 to be selectively raised or lowered in a
lifting function. The lifting speed of the lift cylinders 312,314 is a result of the flow
through the valve 306. Flow through the valve 306 can be controlled by a pair of
variable solenoid actuators 322, 326 acting on each end of the spool of the valve
306. The variable solenoid actuators 322, 326 can be operated by the control system

500 via control lines 324, 328, respectively. Alternatively, in certain embodiments,
flow through the valve 306 can be controlled by a lever.
[0062] The second valve 308 is configured and arranged to selectively provide
pressurized fluid from the port 302 to one or both of hydraulic tilt cylinders 316,318
which are mechanically coupled to the work attachment 52. The operation of the
valve 308 causes the work attachment 52 to be selectively tilted forward and
backward in a tilting function. Flow through the valve 308 can be controlled by a
pair of variable solenoid actuators 330, 334 acting on each end of the spool of the
valve 308. The variable solenoid actuators 330, 334 can be operated by the control
system 500 via control lines 332, 336, respectively. Alternatively, in certain
embodiments, flow through the valve 308 can be controlled by a lever.
[0063] The third valve 310 is configured and arranged to selectively provide
pressurized fluid from the port 302 to a side shift hydraulic cylinder 320 which is
mechanically coupled to the work attachment 52. The operation of the valve 310
causes the work attachment 52 to be selectively moved from side to side in a side
shift function. Flow through the valve 310 can be controlled by a pair of variable
solenoid actuators 338, 342 acting on each end of the spool of the valve 310. The
variable solenoid actuators 338, 342 can be operated by the control system 500 via
control lines 338, 342, respectively. Alternatively, in certain embodiments, flow
through the valve 310 can be controlled by a lever.
[0064] In certain embodiments, the functions or sets of functions described
above may be accomplished with a single drive pump component (e.g., a single
pump, a single pump/motor, a single pumping rotating group, etc.). As used herein,
the term "pump" indicates the ability to transfer fluid from a lower pressure to a
higher pressure over a duration sufficient to power a function. The single drive
pump may include a charge pump. As used herein, the terms "drive pump" and
"drive hydraulic pump" indicate a pump or pump/motor that is driven by the prime
mover (e.g., directly mechanically driven).
[0065] The various embodiments described above are provided by way of
illustration only and should not be construed to limit the claims attached hereto.
Those skilled in the art will readily recognize various modifications and changes that

may be made without following the example embodiments and applications
illustrated and described herein, and without departing from the true spirit and scope
of the disclosure.

We Claim:
1. A hydraulic circuit architecture for a mobile work vehicle, the hydraulic
circuit architecture comprising:
a drive hydraulic pump adapted to be driven by a prime mover, the drive
hydraulic pump having a high pressure side and a low pressure side;
a hydraulic work circuit adapted for connection to at least one actuator for
driving a work component of the mobile work vehicle;
a hydraulic propel circuit including a propel hydraulic motor adapted to be
connected to a drive train of the mobile work vehicle, the hydraulic propel circuit
also including a hydraulic accumulator; and
a circuit selector for selectively connecting the high pressure side of the drive
hydraulic pump to the hydraulic work circuit and the hydraulic propel circuit;
wherein the hydraulic circuit architecture is operable in: a) a first mode
where the hydraulic propel circuit is connected to the high pressure side of the drive
hydraulic pump and the hydraulic work circuit is disconnected from the high
pressure side of the drive hydraulic pump; and b) a second mode where the
hydraulic work circuit is connected to the high pressure side of the drive hydraulic
pump and the hydraulic propel circuit is disconnected from the high pressure side of
the drive hydraulic pump; and
wherein when the hydraulic circuit architecture is in the second mode, stored
energy from the hydraulic accumulator can be used to drive the propel hydraulic
motor to cause propulsion of the mobile work vehicle.
2. The hydraulic circuit architecture of claim 1, further comprising a cross-over
hydraulic flow line that provides fluid communication between the hydraulic work
circuit and the hydraulic propel circuit, wherein a cross-over valve is provided for
opening and closing the cross-over hydraulic flow line.
3. The hydraulic circuit architecture of claim 2, wherein the cross-over valve
controls a flow rate through the cross-over hydraulic flow line.
4. The hydraulic circuit architecture of claim 2, wherein the cross-over
hydraulic flow line allows the stored energy from the hydraulic accumulator to be
used to drive the at least one actuator of the hydraulic work circuit.

5. The hydraulic circuit architecture of claim 2, wherein the hydraulic circuit
architecture is operable in a third mode where both the hydraulic work circuit and
the hydraulic propel circuit receive no hydraulic fluid flow from the high pressure
side of the drive hydraulic pump, and wherein the cross-over hydraulic flow line
allows the stored energy from the hydraulic accumulator to be used to drive the at
least one actuator of the hydraulic work circuit and the stored energy from the
hydraulic accumulator drives the propel hydraulic motor.
6. The hydraulic circuit architecture of claim 1, wherein the propel hydraulic
motor is a variable displacement hydraulic pump/motor, wherein the hydraulic
circuit architecture is operable in a charge mode where hydraulic fluid pumped by
the variable displacement hydraulic pump/motor is used to charge the hydraulic
accumulator.
7. The hydraulic circuit architecture of claim 6, wherein kinetic energy of the
mobile work vehicle is transformed into added stored energy that is stored in the
hydraulic accumulator when the mobile work vehicle decelerates.
8. The hydraulic circuit architecture of claim 1, wherein the drive hydraulic
pump is a hydraulic pump/motor, and wherein hydraulic fluid from the hydraulic
accumulator can be used to drive the hydraulic pump/motor.
9. The hydraulic circuit architecture of claim 8, wherein the hydraulic
pump/motor may start the prime mover when the hydraulic pump/motor is driven by
the hydraulic fluid from the hydraulic accumulator.
10. The hydraulic circuit architecture of claim 1, wherein the circuit selector
includes a valve.
11. The hydraulic circuit architecture of claim 1, wherein the circuit selector
includes a plurality of valves.
12. The hydraulic circuit architecture of claim 1, further comprising an isolator
valve for selectively isolating the hydraulic accumulator from the hydraulic propel
circuit.

13. The hydraulic circuit architecture of claim 1, further comprising a hydraulic
steering circuit in fluid communication with the hydraulic propel circuit.
14. The hydraulic circuit architecture of claim 1, wherein the mobile work
vehicle is a fork lift, wherein the prime mover is a combustion engine mechanically
coupled to the drive hydraulic pump, wherein the hydraulic work circuit is
hydraulically coupled to the at least one actuator, and wherein the at least one
actuator includes a first hydraulic cylinder for lifting a fork of the fork lift, a second
hydraulic cylinder for tilting the fork, and a third hydraulic cylinder for laterally
moving the fork.
15. The hydraulic circuit architecture of claim 14, wherein the first hydraulic
cylinder is a main stage cylinder, wherein the at least one actuator further includes a
secondary stage set of hydraulic cylinders that includes at least one second stage
cylinder for lifting the fork of the fork lift.
16. The hydraulic circuit architecture of claim 12, wherein a maximum working
pressure of the hydraulic propel circuit is higher than a working pressure of the
hydraulic accumulator.
17. The hydraulic circuit architecture of claim 12, wherein a maximum working
pressure of the hydraulic propel circuit is higher than a rated pressure of the
hydraulic accumulator.
18. The hydraulic circuit architecture of claim 1, wherein the drive hydraulic
pump is an only drive hydraulic pump of the hydraulic circuit architecture.
19. The hydraulic circuit architecture of claim 18, wherein the drive hydraulic
pump includes a charge pump.
20. A hydraulic circuit architecture for a mobile work vehicle, the hydraulic
circuit architecture comprising:
a hydraulic work circuit adapted for connection to at least one actuator for
driving a work component of the mobile work vehicle; and

a hydraulic propel circuit including a propel hydraulic motor adapted to be
connected to a drive train of the mobile work vehicle, the hydraulic propel circuit
also including a hydraulic accumulator;
wherein the hydraulic circuit architecture is operable in at least one mode
where the hydraulic work circuit is hydraulically isolated from the hydraulic propel
circuit, and wherein the hydraulic circuit architecture includes means for transferring
energy from the hydraulic accumulator of the hydraulic propel circuit to the
hydraulic work circuit.
21. The hydraulic circuit architecture of claim 20, further comprising a drive
hydraulic pump adapted to be driven by a prime mover, and a work circuit hydraulic
pump adapted to be driven by the prime mover, wherein the means for transferring
the energy from the hydraulic accumulator of the hydraulic propel circuit to the
hydraulic work circuit includes shaft power being transferred from the drive
hydraulic pump to the work circuit hydraulic pump.
22. The hydraulic circuit architecture of claim 21, further comprising a clutch
operably connected between the prime mover and the drive hydraulic pump, wherein
the clutch may decouple the prime mover from the drive hydraulic pump when the
shaft power is being transferred from the drive hydraulic pump to the work circuit
hydraulic pump.
23. The hydraulic circuit architecture of claim 20, further comprising a cross-
over hydraulic flow line that provides fluid communication between the hydraulic
work circuit and the hydraulic propel circuit, wherein a cross-over valve is provided
for opening and closing the cross-over hydraulic flow line.
24. The hydraulic circuit architecture of claim 23, wherein the means for
transferring the energy from the hydraulic accumulator of the hydraulic propel
circuit to the hydraulic work circuit includes opening the cross-over hydraulic flow
line.
25. The hydraulic circuit architecture of claim 21, wherein the drive hydraulic
pump is an only drive hydraulic pump of the hydraulic circuit architecture.

26. The hydraulic circuit architecture of claim 25, wherein the drive hydraulic
pump includes a charge pump.
27. A hydraulic circuit architecture for a mobile work vehicle, the hydraulic
circuit architecture comprising:
a work circuit adapted for connection to at least o le actuator for driving a
work component of the mobile work vehicle, the work circuit being hydraulically
powered by a first rotating group mounted on a first rotatable shaft; and
a hydraulic propel circuit that is not in fluid communication with the work
circuit, the hydraulic propel circuit including a propel hydraulic motor adapted to be
connected to a drive train of the mobile work vehicle, the hydraulic propel circuit
also including a hydraulic accumulator, and the hydraulic propel circuit being
hydraulically powered by a second rotating group mounted on the first rotatable
shaft, the second rotating group being a pump/motor, wherein by operating the
second rotating group as a motor, energy from the accumulator can be transferred
through the first rotatable shaft to the first rotating group to hydraulically power the
work circuit.