HYDRAULIC SYSTEM FOR ENERGY REGENERATION IN
A WORK MACHINE SUCH AS A WHEEL LOADER
Cross-Reference to Related Applications
This application is being filed on 13 December 2011, as a PCT International
Patent application in the name of Eaton Corporation, a U.S. national corporation,
applicant for the designation of all countries except the U.S., and, Kyle William
Schroeder, a citizen of the U.S., and Wade Leo Gehlhoff, a citizen of the U.S.,
applicants for the designation of the U.S. only, and claims priority to U.S. Patent
Application Serial No. 61/422,338 filed on 13 December 2010, U.S. Patent
Application Serial No. 61/422,346 filed on 13 December 2010, U.S. Patent
Application Serial No. 61/553,704 filed on 31 October 2011, and U.S. Patent
Application Serial No. 61/554,772 filed on 02 November 2011, the disclosures of
which are incorporated herein by reference in their entirety.
Technical Field
The present disclosure relates to systems and methods for capturing, storing,
and regenerating energy that would otherwise be wasted. More particularly, the
present disclosure is directed to a hydraulic system that uses an accumulator and
fluid flow control devices to capture, store, and regenerate energy. In addition, the
hydraulic system can provide suspension for a work attachment connected to a
mobile work machine.
Background
Work machines can be used to move material, such as ore, dirt, and/or
debris. Examples of work machines include wheel loaders, track loaders,
excavators, backhoes, bull dozers, telehandlers, etc. The work machines typically
include a work implement 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.
The movement of the work implement may be used to raise the work
implement and any material carried by the work implement against gravity. When
the work implement is raised, potential energy is imparted to the work implement.
When the work implement is lowered, the potential energy is typically lost to heat
via the pressurized hydraulic fluid being throttled across a valve. When the work
implement is moved, kinetic energy is imparted to the work implement. When the
work implement is slowed or stopped, the kinetic energy is typically lost to heat via
the pressurized hydraulic fluid being throttled across a valve.
The hydraulic system of the work machine may also be used to provide ride
control (i.e., suspension) to the work implement. When the work machine is driven
over uneven surfaces and/or obstacles, the work implement may place unwanted
dynamic loads on the work machine. These unwanted dynamic loads may be
reduced (i.e., softened) by a hydraulic accumulator that is fluidly connected to the
hydraulic actuator.

Summary
One aspect of the present disclosure relates to systems and methods for
effectively recovering and utilizing energy that would otherwise be wasted in a work
machine. The systems may be hydraulic systems, and the energy may be recovered
-from potential energy and kinetic energy of a work attachment of the work machine.
The systems may further provide suspension for the work attachment.
Another aspect of the present disclosure relates to a hydraulic suspension
system that provides suspension to a work implement connected to a mobile work
machine. The hydraulic suspension system includes a first hydraulic cylinder, a
hydraulic accumulator, and a first flow control valve. The first hydraulic cylinder
includes a first port that is fluidly connected to a head chamber of the first hydraulic
cylinder. The first hydraulic cylinder further includes a second port that is fluidly
connected to a rod chamber of the first hydraulic cylinder. The first hydraulic
cylinder further includes a piston that is positioned between the head chamber and
the rod chamber and further includes a rod that extends between a first end and a
second end and extends through the rod chamber. The first end of the rod is

connected to the piston and the second end of the rod is connected to a load of the
work implement. The hydraulic accumulator includes an inlet/outlet port. The first
flow control valve includes a first port and a second port. The first port of the first
flow control valve directly fluidly connects to the first port of the first hydraulic
cylinder by a first fluid line, and the second port of the first flow control valve
directly fluidly connects to the inlet/outlet port of the hydraulic accumulator by a
second fluid line. The hydraulic suspension system is adapted to capture energy
from the load of the work implement and store the energy in the hydraulic
accumulator. The hydraulic suspension system is adapted to reuse the energy in
lifting the work implement with the rod of the first hydraulic cylinder.
The hydraulic suspension system may further include a first flow control
device, a second flow control device, a second flow control valve, a hydraulic
junction, and a second hydraulic cylinder including a first port and a second port.
The first flow control device is fluidly connected between the second port of the first
hydraulic cylinder and the hydraulic junction. The second flow control device is
fluidly connected between the first port of the second hydraulic cylinder and the
hydraulic junction. The second flow control valve is fluidly connected between the
first port of the first hydraulic cylinder and the hydraulic junction. And, the
hydraulic suspension system is adapted to transform the energy from the load of the
work implement into actuation energy of the second hydraulic cylinder.
In certain embodiments, the first hydraulic cylinder is a boom cylinder of the
work implement, and the second hydraulic cylinder is a bucket cylinder of the work
implement. Transforming the energy from the load of the work implement into the
actuation energy may results in simultaneous movement of the boom cylinder and
the bucket cylinder.
In certain embodiments, the first flow control device and the second flow
control device are each check valves.
In certain embodiments, a fluid displacement rate of the head chamber is
between about 1.1 and 3 times larger than a fluid displacement rate of the rod
chamber when the piston is moved. In certain embodiments, the hydraulic
suspension system is adapted to fluidly connect the first and the second ports of the
first hydraulic cylinder and thereby amplify a hydraulic pressure generated by the
first hydraulic cylinder under the load of the work implement. The hydraulic

suspension system is adapted to charge the hydraulic accumulator with the amplified
hydraulic pressure.
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.
Brief Description of the Drawings
Figure 1 is a schematic diagram of a hydraulic system according to the
principles of the present disclosure;
Figure 2 is a schematic diagram of the hydraulic system of Figure 1 further
illustrating a control system of the hydraulic system;
Figure 3 is a schematic diagram of the hydraulic system of Figure 1 further
illustrating a first mode of the hydraulic system;
Figure 4 is a schematic diagram of the hydraulic system of Figure 1 further
illustrating a second mode of the hydraulic system;
Figure 5 is a schematic diagram of the hydraulic system of Figure 1 further
illustrating a third mode of the hydraulic system;
Figure 6 is a schematic diagram of the hydraulic system of Figure 1 further
illustrating a fourth mode of the hydraulic system;
Figure 7 is a schematic diagram of the hydraulic system of Figure 1 further
illustrating a fifth mode of the hydraulic system;
Figure 8 is a schematic diagram of the hydraulic system of Figure 1 further
illustrating a sixth mode of the hydraulic system;
Figure 9 is a schematic diagram of the hydraulic system of Figure 1 further
illustrating a seventh mode of the hydraulic system;
Figure 10 is a schematic diagram of the hydraulic system of Figure 1 further
illustrating a fifth mode of the hydraulic system;
Figure 11 is a schematic diagram of the hydraulic system of Figure 1 further
illustrating a sixth mode of the hydraulic system;

Figure 12 is a schematic diagram of the hydraulic system of Figure 1 further
illustrating a seventh mode of the hydraulic system;
Figure 13 is a schematic diagram of a hydraulic system that is a first subset
of the hydraulic system of Figure 1;
Figure 14 is a schematic diagram of a hydraulic system that is a second
subset of the hydraulic system of Figure 1;
Figure 15 is a perspective view of a work machine in which the hydraulic
systems of Figures 1,13, and/or 14 may be used;
Figure 16 is a side view of the work machine of Figure 15;
Figure 17 is a perspective view of another work machine in which the
hydraulic systems of Figures 1,13, and/or 14 may be used; and
Figure 18 is an example flow chart illustrating an operation of the control
system of Figure 2.
Detailed Description
Reference will now be made in detail to example embodiments of the present
disclosure. The accompanying drawings illustrate examples of the present
disclosure. When possible, the same reference numbers will be used throughout the
drawings to refer to the same or like parts.
Figure 1 schematically illustrates a hydraulic system 100. The hydraulic
system 100 is provided for use on a work machine. Example work machines may be
any machine that includes a hydraulically powered work implement. Figures 15 and
16 illustrate an example wheel loader 800 as the work machine. Figure 17 illustrates
an example wheel loader 800' as the work machine. Other work machines may be,
for example, an excavator, a bull dozer, a track loader, a back hoe, a telehandler, etc.
As will be described in detail below, the hydraulic system 100 is adapted to function
as a suspension system (e.g., a boom suspension system) for the work implement.
As will also be described in detail below, the hydraulic system 100 is adapted to
recover, store, and regenerate energy (e.g., kinetic and potential energy from and to
the work implement).
The hydraulically powered work implement may be any type of implement
... commonly connected to the work machine. Figures 15 and 16 illustrate a bucket
826 as the hydraulically powered work implement. Figure 17 illustrates a bucket

826' as the hydraulically powered work implement. Other examples of the
hydraulically powered work implement may include a blade, a fork, a shovel, a
basket, etc. When used in accordance with the principles of the present disclosure,
the hydraulic system 100 may capture energy that would otherwise be wasted, may
store the captured energy, and may regenerate energy from the stored energy for
further use. By capturing, storing, and/or regenerating energy, the hydraulic system
100 may increase an overall efficiency of the work machine. In addition, the
hydraulic system 100 may lower operating costs of the work machine, may reduce
emissions emitted by the work machine, may reduce a cooling load required by the
work machine, may allow a smaller prime mover to be used in the work machine,
may decrease a work cycle time of the work machine, may increase a working speed
of the work machine, and/or may reduce environmental impact of the work machine.
The hydraulic system 100 may capture and/or convert energy from potential
energy of the work implement (e.g., from the work implement's weight and
elevation acted on by gravity) and/or may capture and/or convert energy from
kinetic energy of the work implement (e.g., from the work implement's movement
relative to the work machine). The hydraulic system 100 may store the captured
energy in a hydraulic accumulator and/or may directly convert the captured energy
to other movement of the work implement (e.g., convert boom movement to bucket
movement). The hydraulic system 100 may further dynamically exchange and/or
dissipate energy as a suspension system of the work machine. For example, the
hydraulic system 100 may provide a spring-like characteristic between the work
implement and the work machine, may provide a damping characteristic between the
work implement and the work machine, may provide a shock absorbing
characteristic between the work implement and the work machine, etc.
In certain embodiments, components used in the hydraulic system 100 (e.g.,
a hydraulic accumulator 120) may be the same as or substantially the same as
corresponding components of a hydraulic suspension system used in a work machine
with a work implement suspension system but with no energy recovery system.
Certain of such work machines may be retrofitted with the hydraulic system 100 to
add energy recycling capability and/or other benefits, as mentioned in the preceding
paragraph. As the components typically used in the hydraulic suspension system are

further used in capturing energy, incremental cost of adding the energy recycling
capability is low.
Energy storage capacity of the hydraulic system 100 may be matched to a
work cycle of the work machine (e.g., a dig and dump cycle and/or an unloading
cycle). For example, energy captured during a boom lowering portion of the work
cycle may substantially fill the hydraulic accumulator 120 to capacity, and a boom
raising portion of the work cycle may substantially deplete the hydraulic
accumulator 120.
In preferred embodiments, the hydraulic system 100 should not perceivably
reduce performance of the work machine in comparison to performance of a similar
conventional work machine, and the work machine should have the same feel to an
operator as the conventional work machine. In certain embodiments, the
performance of the work machine will be improved and/or increased upon
implementing the hydraulic system 100.
As illustrated at Figure 1, the hydraulic system 100 includes a hydraulic
cylinder 130. The hydraulic cylinder 130 may be a lift cylinder, a boom cylinder, or
other type of hydraulic cylinder. The hydraulic cylinder 130 can be used to lift loads
against gravity. As illustrated at Figures 15 and 16, the hydraulic cylinder 130 may
be used as a boom cylinder 830. In the embodiment of Figures 15 and 16, a pair of
the boom cylinders 830 is included and work together to raise and lower a boom 824
of the wheel loader 800. Thus, as illustrated in the examples of Figures 1,15, and
16, the hydraulic cylinder 130 can be a single cylinder or a plurality of cylinders that
function as a set of cylinders. As illustrated at Figure 17, the hydraulic cylinder 130
may be used as a boom cylinder 830'. In the embodiment of Figure 17, a pair of the
boom cylinders 830' is included and work together to raise and lower a boom 824' of
the wheel loader 800'. Thus, as illustrated in the examples of Figures 1, 15, 16, and
17 the hydraulic cylinder 130 can be a single cylinder or a plurality of cylinders that
function as a set of cylinders.
The hydraulic cylinder 130 includes a cylinder housing 136, a piston 138,
and a rod 140 connected to the piston 138. The cylinder housing 136 includes a first
port 132 and a second port 134. Upon injecting hydraulic fluid into the first port
132, the rod 140 extends in a direction 152. Upon injecting hydraulic fluid into the
second port 134, the rod 140 retracts in a direction 154. The direction 152, as

depicted, is an extension direction, and the direction 154, as depicted, is a retraction
direction. The cylinder housing 136 extends between a head end 142 and a rod end
144. By selectively injecting hydraulic fluid into the first port 132 and/or the second
port 134, the hydraulic cylinder 130 can be controlled and selectively extended and
retracted, as desired. The hydraulic fluid injected into the hydraulic cylinder 130
may be provided by a hydraulic pump 110 and/or the hydraulic accumulator 120.
As depicted, a valve set 200 controls flow of the hydraulic fluid into the
hydraulic cylinder 130 from the hydraulic pump 110, and a second fluid flow control
device 224 controls flow of the hydraulic fluid into and out of the hydraulic cylinder
130 from and to the hydraulic accumulator 120. As depicted, the valve set 200
controls flow of the hydraulic fluid out of the hydraulic cylinder 130 to a tank 190
(e.g., by way of a hydraulic fluid flow junction 250). As depicted, the valve set 200
controls flow of the hydraulic fluid out of the hydraulic cylinder 130 to the hydraulic
fluid flow junction 250. As depicted, the head end 142 of the hydraulic cylinder 130
includes a functional cross-sectional area AH that is substantially equal to a cross-
sectional area of the piston 138 of the hydraulic cylinder 130, and the rod end 144 of
the hydraulic cylinder 130 includes a functional cross-sectional area AR that is
substantially equal to the cross-sectional area of the piston 138 minus a cross-
sectional area Ar of the rod 140 of the hydraulic cylinder 130. Thus, AR = AH - Ar
and AH - AR + Ar.
As depicted at Figures 15 and 16, the boom cylinder 830 is attached to a
chassis 816 of the wheel loader 800 at a first end. As depicted, the first end
corresponds to the head end 142 of the hydraulic cylinder 130. A first attachment
856 is thereby formed between the cylinder housing 136 of the hydraulic cylinder
130 and the chassis 816. A second attachment 858 is formed between a rod 840 of
the boom cylinder 830 and the boom 824 of the wheel loader 800. The boom 824
may thereby be actuated by the boom cylinder 830. As depicted at Figure 17, the
boom cylinder 830' is attached to a chassis 816' of the wheel loader 800' at a first
end. As depicted, the first end corresponds to the head end 142 of the hydraulic
cylinder 130. A first attachment 856' is thereby formed between the cylinder
-housing 136 of the hydraulic cylinder 130 and the chassis 816'. A second
attachment 858' is formed between a rod 840' of the boom cylinder 830' and the
boom 824' of the wheel loader 800'. The boom 824' may thereby be actuated by the

boom cylinder 830'. The boom cylinder 830, 830' may be powered by the hydraulic
pump 110 and/or the hydraulic accumulator 120. The hydraulic pump 110 may be
connected to a prime move 810 (e.g., a diesel engine, an electric motor, etc.) of the
wheel loader 800, 800'.
As illustrated at Figure 1, the hydraulic system 100 also includes a hydraulic
cylinder 160. The hydraulic cylinder 160 may be a tilt cylinder, a bucket cylinder,
or other type of hydraulic cylinder. The hydraulic cylinder 160 can be used to dump
the load carried by the boom 824, 824'. As illustrated at Figures 15-17, the
hydraulic cylinder 160 may be used as a bucket cylinder 860, 860'. In the
embodiments of Figures 15-17, a single bucket cylinder 860, 860' tilts the bucket
826, 826' of the wheel loader 800, 800'. In other embodiments, a pair of bucket
cylinders work together to tilt the bucket 826, 826'. Thus, the hydraulic cylinder 160
can be a single cylinder or a plurality of cylinders that function as a set of cylinders.
The hydraulic cylinder 160 includes a cylinder housing 166, a piston 168,
and a rod 170 connected to the piston 168. The cylinder housing 166 includes a first
port 162 and a second port 164. Upon injecting hydraulic fluid into the first port
162, the rod 170 extends in a direction 182. Upon injecting hydraulic fluid into the
second port 164, the rod 170 retracts in a direction 184. The direction 182, as
depicted, is an extension direction, and the direction 184, as depicted, is a retraction
direction. The cylinder housing 166 extends between a head end 172 and a rod end
174. By selectively injecting hydraulic fluid into the first port 162 and/or the second
port 164, the hydraulic cylinder 160 can be controlled and selectively extended and
retracted, as desired. The hydraulic fluid injected into the hydraulic cylinder 160
nray"be provided by the hydraulic pump 110 and/or the hydraulic cylinder 130. A
valve set 210 controls flow of the hydraulic fluid into and out of the hydraulic
cylinder 160.
As depicted at Figures 15 and 16, the bucket cylinder 860 is attached to the
chassis 816 of the wheel loader 800 at a first end. As depicted, the first end
corresponds to the head end 172 of the hydraulic cylinder 160. A first attachment
886 is thereby formed between the cylinder housing 166 of the hydraulic cylinder
160 and the chassis 816. A second attachment 888 is formed between a rod 870 of
the bucket cylinder 860 and a bucket linkage 828 of the wheel loader 800. The
bucket 826 may be actuated by the bucket linkage 828 in conjunction with the

bucket cylinder 860. The bucket cylinder 860 may be powered by the hydraulic
pump 110 and/or the boom cylinder(s) 830.
As depicted at Figure 17, the bucket cylinder 860' is attached to the chassis
816' of the wheel loader 800' at a first end. As depicted, the first end corresponds to
the head end 172 of the hydraulic cylinder 160. A first attachment 886', similar to
the first attachment 886, is thereby formed between the cylinder housing 166 of the
hydraulic cylinder 160 and the chassis 816'. A second attachment 888' is formed
between a rod 870' of the bucket cylinder 860' and a bucket linkage 828' of the
wheel loader 800'. The bucket 826' may be actuated by the bucket linkage 828' in
conjunction with the bucket cylinder 860'. The bucket cylinder 860' may be
powered by the hydraulic pump 110 and/or the boom cylinder(s) 830'.
The hydraulic pump 110 may be a variable displacement hydraulic pump.
The hydraulic pump 110 may include an inlet 112 and an outlet 114. Hydraulic
fluid may be supplied from the tank 190 to the hydraulic pump 110. As depicted, an
inlet/outlet 192 of the tank 190 is fluidly connected to the inlet 112 of the hydraulic
pump 110. The outlet 114 of the hydraulic pump 110 may be fluidly connected to
the valve set 200, the valve set 210, and a valve set 220, described in detail below.
The hydraulic accumulator 120 includes an inlet/outlet 122. The inlet/outlet
122 is fluidly connected to the valve set 220. As depicted at Figures 1-12, the valve
set 220 includes a first fluid flow control device 222, the second fluid flow control
device 224, and a third fluid flow control device 226. The fluid flow control devices
222, 224, 226 can be valves, proportional valves, on-off valves, check valves,
variable orifices, etc. The first fluid flow control device 222 is fluidly connected
between the outlet 114 of the hydraulic pump 110 and the inlet/outlet 122 of the
hydraulic accumulator 120. As mentioned above, the second fluid flow control
device 224 fluidly connects the inlet/outlet 122 of the hydraulic accumulator 120 to
the first port 132 of the hydraulic cylinder 130 by way of a fluid passage 150. As
depicted, the fluid passage 150 does not pass through any fluid flow control device
of the valve set 200. As depicted, the fluid passage 150 passes through the second
fluid flow control device 224 of the valve set 220, and the second fluid flow control
device 224 regulates fluid flow through the fluid passage 150, including shutting off
fluid flow across the fluid passage 150. in particular, a first line 146 of the fluid
passage 150 is connected between the first port 132 of the hydraulic cylinder 130

and a first port 224a of the second fluid flow control device 224, and a second line
148 of the fluid passage 150 is connected between the inlet/outlet 122 of the
hydraulic accumulator 120 and a second port 224b of the second fluid flow control
device 224 (see Figure 1). The third fluid flow control device 226 is fluidly
connected between the inlet/outlet 122 of the hydraulic accumulator 120 and the
inlet/outlet 192 of the tank 190.
As depicted, the valve set 200 includes a first fluid flow control device 202, a
second fluid flow control device 204, a third fluid flow control device 206, and a
, fourth fluid flow control device 208. The fluid flow control devices 202, 204, 206,
20J5 can also be valves, proportional valves, on-pff valves, check valves, variable
drifices, etc. The first fluid flow control device 202 of the valve set 200 is fluidly
connected between the outlet 114 of the hydraulic pump 110 and the first port 132 of
the hydraulic cylinder 130. The first fluid flow control device 202 may be directly
connected to the first port 132 of the hydraulic cylinder 130, may be connected to
the first port 132 of the hydraulic cylinder 130 by way of the first line 146, may be
connected to the first port 132 of the hydraulic cylinder 130 by way of a separate
line, or may be connected to the first port 132 of the hydraulic cylinder 130 by way
of a shared line with the connection of the second fluid flow control device 204 to
the first port 132, as described in detail below. The second fluid flow control device
204 is fluidly connected between the first port 132 of the hydraulic cylinder 130 and
the hydraulic fluid flow junction 250. The second fluid flow control device 204 may
be directly connected to the first port 132 of the hydraulic cylinder 130, may be
connected to the first port 132 of the hydraulic cylinder 130 by way of the first line
146, may be connected to the first port 132 of the hydraulic cylinder 130 by way of a
separate line, or may be connected to the first port 132 of the hydraulic cylinder 130
by way of the shared line with the connection of the first fluid flow control device
202 to the first port 132. The third fluid flow control device 206 is fluidly connected
between the outlet 114 of the hydraulic pump 110 and the second port 134 of the
hydraulic cylinder 130. And, the fourth fluid flow control device 208 is fluidly
connected between the second port 134 of the hydraulic cylinder 130 and the
hydraulic fluid flow junction 250.
The valve set 210 includes a first fluid flow control device 212, a second
fluid flow control device 214, a third fluid flow control device 216, and a fourth

fluid flow control device 218. The fluid flow control devices 212,214, 216, 218 can
alslf be valves, proportional valves, on-off valves, check valves, variable orifices,
etc. The first fluid flow control device 212 is fluidly connected between the outlet
114 of the hydraulic pump 110 and the first port 162 of the hydraulic cylinder 160.
The second fluid flow control device 214 is fluidly connected between the first port
162 of the hydraulic cylinder 160 and the hydraulic fluid flow junction 250. The
third fluid flow control device 216 is fluidly connected between the outlet 114 of the
hydraulic pump 110 and the second port 164 of the hydraulic cylinder 160. And, the
fourth fluid flow control device 218 is fluidly connected between the second port
164 of the hydraulic cylinder 160 and the hydraulic fluid flow junction 250.
The hydraulic system 100 includes a valve set 230. The valve set 230 is
fluidly connected between the inlet/outlet 192 of the tank 190 and the hydraulic fluid
flow junction 250. As depicted, the valve set 230 includes a fluid flow control
device 232 and a relief valve 234. The fluid flow control device 232 can also be a
valve, a proportional valve, an on-off valve, a check valve, a variable orifice, etc.
The fluid flow control device 232 is fluidly connected between the hydraulic fluid
flow junction 250 and the inlet/outlet 192 of the tank 190. The relief valve 234 is
fluidly connected between the hydraulic fluid flow junction 250 and the inlet/outlet
192 of the tank 190.
Turning now to Figure 2, an example control system is illustrated for the
hydraulic system 100. As depicted, the control system includes a plurality of
pressure sensors 260, at least one temperature sensor 262, a plurality of position
sensors 264, a controller 270, an operator interface 272, memory 274, and a wiring
harness 280. As depicted, the controller 270 is connected to the other various
components of the control system by the wiring harness 280. In certain
embodiments, the controller 270 may include distributed controllers connected to the
various components of the control system. For example, a controller area network
bus system may be used to control the hydraulic system 100. The various
components of the control system may establish one-way communication with the
controller 270, and/or the various components may establish two-way
communication with the controller 270. For example, the hydraulic pump 110 may
receive a control signal from the controller 270. Alternatively, the hydraulic pump
110 may both receive a control signal from the controller 270 and also send a

feedback signal to the controller 270. The pressure sensors 260 may monitor
hydraulic pressures of the hydraulic system 100 at various locations.
^ As depicted, the first port 132, the second port 134, the first port 162, the
second port 164, the inlet/outlet 122, the outlet 114, the hydraulic fluid flow junction
250, and the inlet 112 may each include one of the pressure sensors 260. The
pressure sensors 260 are optional at any or all of the aforementioned locations. The
at least one temperature sensor 262 may monitor temperature of compressed gas
within the hydraulic accumulator 120. The position sensors 264 may monitor a
relative position between the rod 140 and the cylinder housing 136. Likewise, the
position sensors 264 may monitor a relative position between the cylinder housing
r«466 and the rod 170. As depicted at Figures 15 and 16, the wheel loader 800
includes an operator station 818. As depicted at Figure 17, the wheel loader 800'
includes an operator station 818'. The operator interface 272 may be mounted
within the operator station 818, 818'. The operator may thereby operate the
hydraulic system 100 and thereby the wheel loader 800, 800' by interacting with the
operator interface 272.
Turning now to Figure 3, an energy capturing mode 102 of the hydraulic
system 100 is depicted. In the energy capturing mode 102, energy is recovered from
the hydraulic cylinder 130 and stored in the hydraulic accumulator 120. In
particular, a load, such as the boom 824 and various loads imposed thereon, moves
the rod 140 in the direction 154. This, in turn, forces hydraulic fluid from the first
port 132. The hydraulic fluid from the first port 132 may flow through the fluid
passage 150, including the second fluid flow control device 224, toward the
hydraulic accumulator 120 and thereby charge the hydraulic accumulator 120. In
addition, the hydraulic fluid from the first port 132 may flow through the second
fluid flow control device 204 and the fourth fluid flow control device 208 and
thereby enter the second port 134. In addition, the hydraulic fluid from the first port
- 132 may flow through the second fluid flow control device 204 and through the
second fluid flow control device 214 and into the first port 162 and thereby actuate
" (e.g., extend) the hydraulic cylinder 160 in the direction 182. The hydraulic fluid
from the first port 132 may flow through the second fluid flow control device 204,
through the hydraulic fluid flow junction 250, and through the second fluid flow
control device 214 and into the first port 162 and thereby actuate (e.g., extend) the

hydraulic cylinder 160. The actuation (e.g., extension) of the hydraulic cylinder 160
may cause hydraulic fluid to exit the second port 164. Upon exiting the second port
164, the hydraulic fluid may flow through the fourth fluid flow control device 218
and the second fluid flow control device 214 and into the first port 162 of the
hydraulic cylinder 160. In certain embodiments, time periods, and/or
configurations, the second fluid flow control device 214 and/or the fourth fluid flow
control device 218 may be closed and/or the hydraulic cylinder 160 may remain
stationary.
When hydraulic fluid pressure within the hydraulic accumulator 120 is below
a pre-determined pressure and/or when the hydraulic fluid pressure within the
hydraulic accumulator 120 is below the pressure within the hydraulic cylinder 130
an&an energy capturing mode (e.g., the energy capturing mode 102) is active, the
second fluid flow control device 224 may open and thereby recover hydraulic
energy from the hydraulic cylinder 130. When the hydraulic fluid pressure within
the hydraulic accumulator 120 is above a pre-determined pressure and/or when the
hydraulic fluid pressure within the hydraulic accumulator 120 is above the pressure
within the hydraulic cylinder 130 and an energy capturing mode is active, the second
fluid flow control device 224 may close.
Assuming negligible friction (e.g., between the piston 138 and the cylinder
housing 136) and pressure drop across the second fluid flow control device 204, the
fourth fluid flow control device 208, and the various hydraulic lines, a given net
force F, acting on the rod 140, produces a hydraulic fluid pressure of F/Ar = F/(AH -
AR) at the head end 142 of the hydraulic cylinder 130 and thereby at the first port
132 in the energy capturing mode 102. The hydraulic fluid pressure F/(AH - AR)
may be delivered from the hydraulic cylinder 130 to the hydraulic accumulator 120
via the fluid passage 150.
Turning now to Figure 10, an energy capturing mode 102p of the hydraulic
system 100 is depicted. In the energy capturing mode 102p, energy is recovered
from the hydraulic cylinder 130 and stored in the hydraulic accumulator 120. In
particular, the load, such as the boom 824, 824' and various loads imposed thereon,
moves the rod 140 in the direction 154. This, in turn, forces hydraulic fluid from the
first port 132. The hydraulic fluid from the first port 132 may flow through the fluid
passage 150, including the second fluid flow control device 224, toward the

hydraulic accumulator 120 and thereby charge the hydraulic accumulator 120. The
movement of the hydraulic cylinder 130 may cause hydraulic fluid to enter the
second port 134 of the hydraulic cylinder 130. In particular, the hydraulic fluid may
be drawn from the tank 190 by way of the fourth fluid flow control device 208, the
hydraulic fluid flow junction 250, and the fluid flow control device 232.
Assuming negligible friction and pressure drop across the fourth fluid flow
control device 208 and the various hydraulic lines, a given net force F, acting on the
rod 140, produces a hydraulic fluid pressure of F/AH at the head end 142 of the
hydraulic cylinder 130 and thereby at the first port 132 in the energy capturing mode
102p. The hydraulic fluid pressure F/AH may be delivered from the hydraulic
cylinder 130 to the hydraulic accumulator 120 via the fluid passage 150.
Turning now to Figure 9, an energy capturing mode 102r of the hydraulic
system 100 is depicted. In the energy capturing mode 102r, energy is recovered
from the hydraulic cylinder 130 and stored in the hydraulic accumulator 120. In
particular, the load, such as the boom 824, 824' and various loads imposed thereon,
moves the rod 140 in the direction 154. In addition, hydraulic fluid from the pump
110 may enter the second port 134 of the hydraulic cylinder 130. In particular, the
hydraulic fluid is drawn by the hydraulic pump 110 from the tank 190 through the
inlet/outlet 192 and the inlet 112. The hydraulic pump 110 pressurizes the hydraulic
fluid and pumps the hydraulic fluid out of the outlet 114. The hydraulic fluid may
then flow through the third fluid flow control device 206 and into the second port
134 of thfeJ^ydKauIic cylinder 130. The load on the rod 140 in combination with the
hydraulic fluid flow from the pump 110 force hydraulic fluid from the first port 132.
The hydraulic fluid from the first port 132 may flow through the fluid passage 150,
including the second fluid flow control device 224, toward the hydraulic
accumulator 120 and thereby charge the hydraulic accumulator 120.
Assuming negligible friction and pressure drop across the third fluid flow
"control device 206 and the various hydraulic lines, a given net force F, acting on the
rod 140, produces a hydraulic fluid pressure of F/AH at the head end 142 of the
hydraulic cylinder 130 and thereby at the first port 132 in the energy capturing mode
102r, and pump pressure Pp from the hydraulic pump 110 produces a hydraulic fluid
pressure Pc = Pp x (AR/AH) at the head end 142 of the hydraulic cylinder 130 and
thereby at the first port 132 in the energy capturing mode 102r. In combination, a

total pressure Pt = F/AH + Pc = F/AH + Pp x (AR/AH) is produced at the head end
142 of the hydraulic cylinder 130 and thereby at the first port 132 in the energy
capturing mode 102r. The total pressure F/AH + Pp x (AR/AH) may be delivered
from the hydraulic cylinder 130 to the hydraulic accumulator 120 via the fluid
passage 150.
When employed on the example wheel loaders 800, 800', the energy
capturing modes 102, 102p, 102r may provide several functions. These functions
may include capturing kinetic and/or potential energy from the boom 824, 824' and
storing at least a portion of the captured energy in the hydraulic accumulator 120. In
addition, hydraulic fluid may be supplied to the second port 134 to prevent
cavitation of the hydraulic cylinder 130, 830, 830'. In addition, by actuating the
hydraulic cylinder 160, 860, 860' the bucket 826, 826' may be simultaneously
actuated with a portion of the energy.
As depicted at Figure 4, the hydraulic cylinder 160 is extended by the portion
of the energy. As depicted at Figures 15 and 16, extending the hydraulic cylinder
160, 860 tilts the bucket 826 downward. In other embodiments, the hydraulic
valving may be rearranged and thereby the portion of the energy can cause the
hydraulic cylinder 160, 860 to retract (i.e., the rod 170 moves in the direction 184, as
illustrated at Figure 1). As depicted at Figure 17, extending the hydraulic cylinder
160, 860' (e.g., by moving the rod 170, 870' in the direction 182) tilts the bucket
826-' hran upward direction 825 as the boom 824' moves in a downward direction in
conjunction with the rod 840' moving in the direction 154. The bucket linkage 828'
may be a "Z-bar" bucket linkage, as depicted at Figure 17, that transforms extension
of the hydraulic cylinder 160, 860' (i.e., the rod 170, 870' moves in the direction
182) intojtilting of the bucket 826' in the upward direction 825. Such simultaneous
movements are particularly useful when the work machine is the wheel loader 800'.
The "Z-bar" bucket linkage includes a rocking member 827 rotatably mounted on
the boom 824' between a first end 827a and a second end 827b. The first end 827a
includes the second attachment 888'. The second end 827b is rotatably connected to
a bucket link 829 at a second end 829b of the bucket link 829. A first end 829a of
the bucket link 829 is rotatably connected to the bucket 826'. Extending the
hydraulic cylinder 160-860' (e.g., by moving the rod 170, 870' in the direction 182)
rocks the rocking member 827 in a direction 823.

A typical cycle of the wheel loader 800, 800' includes the wheel loader 800,
800' driving into a pile of material followed by the boom 824, 824' raising the
bucket 826, 826'. The wheel loader 800, 800' is then driven to a dumping location
(e.g., a hauling truck) with the bucket 826, 826' above an elevation of the dumping
location. The bucket cylinder 160, 860, 860' is then moved in the direction 182 to
tilt the bucket 826, 826' via a connection through the bucket linkage 828, 828'.
Upon the bucket 826, 826'being emptied of the material at the dumping location,
the wheel loader 800, 800' is moved clear of the dumping location, and the boom
824, 824' is lowered to return the bucket 826, 826' to a loading (e.g., a digging)
configuration. The downward movement of the boom 824, 824' and the upward
movement of the bucket 826, 826' occur simultaneously, and the movement of the
bucket 826, 826' is provided by the energy from the boom cylinder 130, 830, 830'.
Such a coordinated movement may be referred to as a "return to dig" movement or a
"return to dig" operation. The "return to dig" operation may be a pre-defined
position based movement. The "return to dig" movement may be activated, for
example, when the boom 824, 824' is fully up and the bucket 826, 826' is fully
down.
Turning now to Figure 4, a variation of the energy capturing mode 102 is
illustrated. As depicted, a mode 102s is similar to the energy capturing mode 102,
but includes provisions to accommodate a full hydraulic accumulator 120. In
addition, or separately, the mode 102s may include a provision for when the
hydraulic cylinder 160 cannot accept all of the flow through the hydraulic fluid flow
junction 250. In particular, the hydraulic fluid flow through the fluid passage 150
can be at least partially diverted through the third fluid flow control device 226 and
into the tank 190 through the inlet/outlet 192. Similarly, the hydraulic fluid flow
through the hydraulic fluid flow junction 250 may at least partially be diverted
through the fluid flow control device 232 and into the tank 190 via the inlet/outlet
192.
As illustrated at Figures 3 and 4, the energy capturing mode 102 and the
energy capturing mode 102s may channel hydraulic fluid flow from the first port
132 through the second fluid flow control device 204 and the fourth fluid flow
control device 208 into the second port 134. The head end 142 has a higher
hydraulic fluid displacement rate than the rod end 144 when the piston 138 is moved

as a result of the functional cross-sectional area AH being greater than the functional
cross-sectional area AR. When the rod 140 is moved in the direction 154, the
connection between the first port 132 and the second port 134 increases the pressure
generated at the first port 132 under a given load at the rod 140 in the direction 154
(e.g., the given net force F). In particular, the hydraulic fluid pressure F/(AH - AR)
when the first port 132 and the second port 134 are connected may be greater than
the hydraulic fluid pressure F/AH when the first port 132 and the second port 134 are
disconnected and the second port 134 is connected, for example, to the tank 190.
The increased hydraulic fluid pressure F/(AH - AR) can thereby charge the
hydraulic accumulator 120 at a higher pressure given the same load (e.g., the given
net force F) at the rod 140 in the direction 154. The increased hydraulic fluid
pressure, F/(AH - AR) = F/Ar, results from an effective area of the hydraulic cylinder
130 becoming the cross-sectional area Ar of the rod 140 (see Figure 1). In certain
embodiments, the hydraulic fluid displacement rate of the head end 142 can be
higher than the hydraulic fluid displacement rate of the rod end 144 by a factor that
ranges between about 1.1 to 1.5 or about 1.1-3. In certain embodiments, the cross-
sectional area AH of the head end 142 can be higher than the cross-sectional area AR
of the rod end 144 by a factor that ranges between about 1.1 to 1.5 or about 1.1-3.
The pressure at the first port 132 is thereby amplified by connecting the first port
132 to the second port 134, via the second fluid flow control device 204 and the
fourth fluid flow control device 208, in comparison to the pressure that would
otherwise be generated at the first port 132 from a load placed on the rod 140 in the
direction 154.
Figures 5 and 6 illustrate a mode 104 and a mode 104m, respectively. The
modes 104,104m result in charging and/or precharging the hydraulic accumulator
120. The hydraulic accumulator 120 may be normally pressurized (i.e., precharged)
to a pre-defined value. When energy capturing modes 102,102s, 102r, 102p are
activated, the hydraulic accumulator 120 may be allowed to gain more pressure than
the pre-defined value and thereby may be filled above the normal resting capacity.
Any excess flow to the hydraulic accumulator 120 may be passed to the tank 190 via
the third fluid flow control device 226.
In the depicted embodiment, the hydraulic pump 110 is used to charge and/or
precharge the hydraulic accumulator 120. The precharging can be done

simultaneously with the actuation of the hydraulic cylinder 130. As illustrated at
Figure 5, hydraulic fluid is drawn by the hydraulic pump 110 from the tank 190
through the inlet/outlet 192 and the inlet 112. The hydraulic pump 110 pressurizes
the hydraulic fluid and pumps the hydraulic fluid out of the outlet 114. At least a
portion of the hydraulic fluid flows through the first fluid flow control device 222
and into the inlet/outlet 122 of the hydraulic accumulator 120 and thereby charges
the hydraulic accumulator 120. Another portion of the hydraulic fluid from the
hydraulic pump 110 may flow through the first fluid flow control device 202 and
into the first port 132 of the hydraulic cylinder 130. The hydraulic fluid flow into
the hydraulic cylinder 130 causes the hydraulic cylinder 130 to extend and expel
hydraulic fluid from the second port 134. The expelled hydraulic fluid from the
second port 134 flows through the fourth fluid flow control device 208, through the
hydraulic fluid flow junction 250, and through the fluid flow control device 232 into
the inlet/outlet 192 of the tank 190.
Figure 6 is similar to Figure 5 except for hydraulic fluid flow from the first
fluid flow control device 202 also flowing through the second fluid flow control
device 224 and into the inlet/outlet 122 of the hydraulic accumulator 120. The mode
104m can be used to equalize hydraulic fluid pressure between the head end 142 and
the hydraulic accumulator 120.
As illustrated at Figure 7, a mode 106 of the hydraulic system 100
regenerates (i.e., recycles) hydraulic fluid energy stored in the hydraulic accumulator
120 and uses the energy to extend the hydraulic cylinder 130 (e.g., when boom lift is
commanded). In particular, when hydraulic fluid pressure within the hydraulic
accumulator 120 is above a pre-determined pressure and/or when the hydraulic fluid
pressure within the hydraulic accumulator 120 is above the pressure required by the
hydraulic cylinder 130, the second fluid flow control device 224 may open and
thereby relieve hydraulic load from the hydraulic pump 110. A signal (e.g., a digital
signal) may be sent to a load sense controller of the hydraulic pump 110 to
coordinate the opening of the second fluid flow control device 224 (e.g., subtracting
the accumulator supplied flow).
,, As illustrated at Figures 15-17, extending the hydraulic cylinder 130, 830,
830', raises the boom 824, 824' and thereby raises the bucket 826, 826'. The
hydraulic pump 110 may be used to supplement hydraulic fluid flow into the

hydraulic cylinder 130 and thereby assist in extending the hydraulic cylinder 130. In
particular, hydraulic fluid flows from the inlet/outlet 122 of the hydraulic
accumulator 120 and through the fluid passage 150, including the second fluid flow
control device 224, and into the first port 132 of the hydraulic cylinder 130.
Additional hydraulic fluid flow may be transferred from the inlet/outlet 192 of the
tank 190 into the inlet 112 of the hydraulic pump 110. The hydraulic pump 110
pressurizes the hydraulic fluid and forces the hydraulic fluid through the outlet 114
and the first fluid flow control device 202 and into the first port 132. As the
hydraulic cylinder 130 extends, hydraulic fluid is expelled from the rod end 144
through the second port 134, the fourth fluid flow control device 208, the hydraulic
fluid flow junction 250, and the fluid flow control device 232, and into the tank 190
through the inlet/outlet 192. When hydraulic fluid pressure within the hydraulic
accumulator 120 reaches a pre-determined pressure and/or when the hydraulic fluid
pressure within the hydraulic accumulator 120 reduces to below the pressure
required by the hydraulic cylinder 130, the second fluid flow control device 224 may
close and thereby transfer hydraulic load to the hydraulic pump 110. A signal (e.g.,
a digital signal) may be sent to the load sense controller of the hydraulic pump 110
to coordinate the closing of the second fluid flow control device 224 (e.g., adding
back the accumulator supplied flow that is now depleted).
As illustrated at Figure 8, a mode 107 of the hydraulic system 100 retracts
the hydraulic cylinder 130 under hydraulic fluid pressure from the pump 110. In
particular, hydraulic fluid flow may be transferred from the inlet/outlet 192 of the
tank 190 into the inlet 112 of the hydraulic pump 110. The hydraulic pump 110
pressurizes the hydraulic fluid and forces the hydraulic fluid through the outlet 114
and the third fluid flow control device 206 and into the second port 134 of the
hydraulic cylinder 130. As the hydraulic cylinder 130 retracts with the piston 138
moving in the direction 154, hydraulic fluid is expelled from the head end 142
through the first port 132, the second fluid flow control device 204, the hydraulic
fluid flow junction 250, and the fluid flow control device 232, and into the tank 190
through the inlet/outlet 192.
As illustrated at Figure 11, the hydraulic system 100 includes a mode 108m.
The mode 108m may be used to set hydraulic fluid pressure of the hydraulic
accumulator 120 to a desired value. In particular, the mode 108m may be used to

match the hydraulic fluid pressure of the hydraulic accumulator 120 to the hydraulic
fluid pressure in the head end 142. Matching the hydraulic pressures between the
hydraulic accumulator 120 and the head end 142 may be done in preparation for the
hydraulic system 100 going into a mode 108, described in detail below. To increase
the hydraulic fluid pressure of the hydraulic accumulator 120, hydraulic fluid can be
drawn from the tank 190 through the inlet/outlet 192 into the inlet 112 of the
hydraulic pump 110. The hydraulic pump 110 pressurizes the hydraulic fluid and
pumps the hydraulic fluid through the outlet 114 and through the first fluid flow
control device 222 into the inlet/outlet 122 of the hydraulic accumulator 120. To
lower the hydraulic fluid pressure of the hydraulic accumulator 120, hydraulic fluid
can be released from the hydraulic accumulator 120 through the inlet/outlet 122 and
the third fluid flow control device 226 and into the inlet/outlet 192 of the tank 190.
The hydraulic fluid pressure difference between the hydraulic accumulator 120 and
the head end 142 of the hydraulic cylinder 130 can be balanced before the second
fluid flow control device 224, and thereby the fluid passage 150, is opened.
As illustrated at Figure 12, the hydraulic system 100 can provide suspension
to the work machine in the suspension mode 108. As illustrated at Figures 15-17,
the hydraulic cylinder 130, 830, 830' supports the boom 824, 824' and thereby
supports the bucket 826, 826'. As the wheel loader 800, 800' moves across uneven
ground or other obstacles, dynamic movement of the boom 824, 824' and the bucket
826, 826' may occur. By connecting the hydraulic cylinder 130, 830, 830' to the
hydraulic accumulator 120 via the fluid passage 150, the hydraulic cylinder 130 can
provide a spring-like behavior between the first attachment 856, 856' and the second
attachment 858, 858'. The spring-like behavior allows the boom 824, 824' to
accommodate the wheel loader 800, 800' as the wheel loader 800, 800' moves over
uneven terrain and/or other obstacles. In addition to the spring-like behavior, the
second fluid flow control device 224 can provide damping of the movement of the
boom 824, 824' as hydraulic fluid flows through the fluid passage 150. In particular,
hydraulic fluid flowing through the second fluid flow control device 224 may be
throttled in one or in both flow directions and thereby dissipate energy to dampen
the hydraulic cylinder 130, 830, 830'. In particular, the hydraulic cylinder 130, 830,
830' may move in the directions 152, 154. This movement of the rod 140 of the
hydraulic cylinder 130 causes hydraulic fluid to be transferred between the head end

142 and the hydraulic accumulator 120 through the first port 132, the fluid passage
150 including the second fluid flow control device 224, and the inlet/outlet 122. The
fluid passage 150 can be directly fluidly connected to the inlet/outlet 122 and also be
directly fluidly connected to the first port 132. The second fluid flow control device
224 of the fluid passage 150 can be a single hydraulic fluid flow control device. The
second fluid flow control device 224 may be the sole hydraulic fluid flow control
device along the fluid passage 150.
According to the principles of the present disclosure, a hydraulic system 400
can be derived as a subset of the hydraulic system 100 and function, in certain
modes, independent of a pump. In particular, as illustrated at Figure 13, the
hydraulic system 400 includes a hydraulic cylinder 430 similar to the hydraulic
cylinder 130 and a hydraulic cylinder 460 similar to the hydraulic cylinder 160. The
hydraulic cylinder 430 includes a first port 432 similar to the first port 132 and a
second port 434 similar to the second port 134. Likewise, the hydraulic cylinder 460
includes a first port 462 similar to the first port 162 and a second port 464 similar to
the second port 164.
The hydraulic system 400 further includes a hydraulic accumulator 420
similar to the hydraulic accumulator 120. In the illustrated embodiment of Figure
13, the hydraulic accumulator 420 includes a first hydraulic accumulator 420a and a
second hydraulic accumulator 420b. In other embodiments, the hydraulic
accumulator 120 may include two or more hydraulic accumulators. In other
embodiments, the hydraulic accumulator 420 may include three or more hydraulic
accumulators. In other embodiments, the hydraulic accumulator 420 may include a
single hydraulic accumulator. The hydraulic accumulator 420 includes an
inlet/outlet 422 similar to the inlet/outlet 122. The first hydraulic accumulator 420a
can have a different spring and/or gas charge than the second hydraulic accumulator
420b. The first hydraulic accumulator 420a can be charged and discharged in
different stages than the second hydraulic accumulator 420b. The charging and
discharging stages of the first hydraulic accumulator 420a and the second hydraulic
accumulator 420b can overlap each other or can be substantially sequential. By
having the first hydraulic accumulator 420a and the second hydraulic accumulator
420b, the hydraulic system 400 can match various and varying loads of the hydraulic
cylinder 430. By having the first hydraulic accumulator 420a and the second

hydraulic accumulator 420b, the hydraulic system 400 can match modes (e.g., mode
102 and 102p and/or a high pressure mode and a low pressure mode) with the first
hydraulic accumulator 420a and the second hydraulic accumulator 420b.
The hydraulic system 400 further includes a tank 490 similar to the tank 190.
The tank 490 includes an inlet/outlet 492 similar to the inlet/outlet 192. The
hydraulic system 400 includes a fluid flow control device 504 similar to the fluid
flow control device 204, a fluid flow control device 508 similar to the fluid flow
control device 208, a fluid flow control device 514 similar to the fluid flow control
device 214, a fluid flow control device 524 similar to the fluid flow control device
224, a fluid flow control device 526 similar to the fluid flow control device 226, and
a fluid flow control device 532 similar to the fluid flow control device 232. The
hydraulic system 400 further includes a hydraulic fluid flow junction 550 similar to
the hydraulic fluid flow junction 250 and a relief valve 534 similar to the relief valve
234. The hydraulic system 400 further includes a fluid passage 450 similar to the
fluid passage 150. The fluid passage 450 similarly includes a first line 446, similar
to the first line 146, and a second line 448, similar to the second line 148. In the
present paragraph, the term similar indicates a similar component and a similar
function within the hydraulic system 400. The fluid flow control device 508 and the
fluid flow control device 514 are illustrated at Figure 13 as check valves.
According to the principles of the present disclosure, a hydraulic system 600
can be derived as a subset of the hydraulic system 100. In particular, as illustrated at
Figure 14, the hydraulic system 600 includes a hydraulic pump 610 similar to the
hydraulic pump 110. The hydraulic pump 610 includes an inlet 612 and an outlet
614 similar to the inlet 112 and the outlet 114, respectively. The hydraulic system
600 further includes a hydraulic cylinder 630 similar to the hydraulic cylinder 130.
The hydraulic cylinder 630 includes a first port 632 similar to the first port 132 and a
second port 634 similar to the second port 134. The hydraulic system 600 further
includes a hydraulic accumulator 620 similar to the hydraulic accumulator 120. The
hydraulic accumulator 620 includes an inlet/outlet 622 similar to the inlet/outlet 122.
The hydraulic system 600 includes a tank 690 similar to the tank 190. The tank 690
includes an inlet/outlet 692 similar to the inlet/outlet 192. The hydraulic system 600
includes a fluid flow control device 708 similar to the fluid flow control device 208,
a fluid flow control device 722 similar to the fluid flow control device 222, a fluid

flow control device 724 similar to the fluid flow control device 224, and a fluid flow
control device 726 similar to the fluid flow control device 226. The hydraulic
system 600 further includes a fluid passage 650 similar to the fluid passage 150.
The fluid passage 650 similarly includes a first line 646, similar to the first line 146,
and a second line 648, similar to the second line 148. In the present paragraph, the
term similar indicates a similar component and a similar function within the
hydraulic system 600.
As illustrated at Figure 18, the controller 270 can control the hydraulic
system 100 and thereby switch between the various modes of the hydraulic system
100. A flowchart 900 includes a group of steps 902. The group of steps 902
represents a normal operation of the controller 270 in controlling the hydraulic
system 100. The group of steps 902 can be initiated from the operator interface 272
by the operator. Other operations may include service operations, diagnostic
operations, calibrations, etc. When the controller 270 is controlling the hydraulic
system 100 under normal operation, control flow may begin at step 904, for
example, upon start up of the wheel loader 800, 800'. Upon start up, the controller
270 puts the hydraulic system 100 in an inactive state 906. The controller 270
periodically checks, as represented by flow line 908, the status of an external input
switch 9T0. The external input switch 910 can be set by the operator to either an on
position or an off position. If the external input switch 910 is set to the off position,
the state of the hydraulic system 100 returns to inactive as represented by flow line
912. Upon the external input switch 910 being switched to the on position, the state
of the hydraulic system 100 switches to an active state 916, as represented by flow
line 914. The active state 916 may include the hydraulic system 100 operating in the
mode 108.
The controller 270 periodically checks for a passive lift command 918 and a
regeneration command 940. If the passive lift command 918 is yes, the controller
270 reads accumulator pressure as indicated by flow line 922. If the passive lift
command 918 is no, then the controller 270 checks the status of the regeneration
command 940, as indicated by flow line 920. The accumulator pressure is checked
at step 924. If the accumulator pressure is greater than the pressure within the head
end 142, mode 106 is implemented as indicated by flow line 926. If the accumulator
pressure is less than the pressure within the head end 142, then mode 104 and/or

mode 104m is implemented as indicated by flow line 928. As indicated by box 930,
mode 106, mode 104, mode 104m, energy capturing mode 102, and mode 102s are
in a special modes group. Upon control flow arriving in the special modes group,
the controller 270 periodically checks the accumulator pressure as indicated by flow
line 932 moving control to step 934. In step 934, the controller 270 resumes the
current mode in box 930 if the accumulator pressure is less than a set point, as
indicated by flow line 938. At step 934, the controller 270 transfers control flow to
the group of steps 902 upon the accumulator pressure being equal to or great than
the set point.
Upon control flow being at the group of steps 902, the controller 270
periodically checks the passive lift command 918 and the regeneration command
940. Upon the passive lift command 918 being no, the regeneration command 940
is checked. If the regeneration command 940 is yes, then the controller 270 checks
accumulator pressure as indicated by flow line 942. If the regeneration command
940 is no, the controller 270 passes control flow to the group of steps 902, as
illustrated by flow line 944. Upon the accumulator pressure being checked at step
946, the controller 270 transfers control flow to the box 930 and puts the hydraulic
system 100 in the energy capturing mode 102 and/or the mode 102s, as indicated by
flow line 948. If the accumulator pressure is found to be greater than the pressure at
the head end 142, the controller 270 returns control flow to the group of steps 902 as
indicated by flow line 950.
The controller 270 may switch the hydraulic system 100 between modes to
maximize or improve efficiency of the hydraulic system 100. In certain
embodiments, mechanical and/or electrical hardware may automatically switch the
hydraulic system 100 between modes to maximize or improve the efficiency of the
hydraulic system 100. For example, the mode 102p may result in the hydraulic
cylinder 130 charging the hydraulic accumulator 120 more efficiently when the
hydraulic accumulator 120 is at a low charge, and the mode 102 may be required for
the hydraulic cylinder 130 to charge the hydraulic accumulator 120 when the
hydraulic accumulator 120 is at a high charge or a higher charge. Also, various
modes of the hydraulic system 100 may result in the hydraulic cylinder 130
discharging the hydraulic accumulator 120 more efficiently when the hydraulic
accumulator 120 is at the low charge, and other modes may be more efficient when

the hydraulic cylinder 130 discharges the hydraulic accumulator 120 when the
hydraulic accumulator 120 is at the high charge or the higher charge. The charging
and the discharging of the accumulator 120 by the hydraulic cylinder 130 may be
staged to increase efficiency and/or performance of the hydraulic system 100.
Various modifications and alterations of this disclosure will become apparent
to those skilled in the art without departing from the scope and spirit of this
disclosure, and it should be understood that the scope of this disclosure is not to be
unduly limited to the illustrative embodiments set forth herein.

WE CLAIM
1. A hydraulic system for actuating a work attachment of a mobile work
machine, the hydraulic system comprising:
a first hydraulic cylinder configured to actuate the work attachment, the first
hydraulic cylinder including a piston connected to a rod, the piston positioned
between a head chamber and a rod chamber of the first hydraulic cylinder, and the
rod extending through the rod chamber;
an accumulator;
a first flow control device fluidly connected between the accumulator and the
head chamber of the first hydraulic cylinder; and
a second flow control device fluidly connected between the head chamber
and the rod chamber of the first hydraulic cylinder;
wherein hydraulic fluid flow from the head chamber of the first hydraulic
cylinder charges the accumulator when the work attachment compresses the first
hydraulic cylinder and the first flow control device is open; and
wherein a hydraulic pressure of the hydraulic fluid flow is amplified by
opening the second flow control device between the head chamber and the rod
chamber of the first hydraulic cylinder.
2. A method of using the hydraulic system of claim 1, the method comprising:
opening the first flow control device; and
compressing the head chamber by moving the piston and rod of the first
hydraulic cylinder with the work attachment and thereby charging the accumulator
with the hydraulic fluid flow.
3. The method of claim 2, further comprising amplifying the hydraulic pressure
and charging the accumulator with the amplified hydraulic pressure by fluidly
connecting the rod chamber of the first hydraulic cylinder to the head chamber with
the second flow control device.

4. The method of claim 2, further comprising reusing energy captured by the
charging of the accumulator by discharging the accumulator and thereby actuating
the work attachment.
5. The method of claim 2, further comprising simultaneously actuating a second
hydraulic cylinder by opening the hydraulic fluid flow through a third flow control
device connected between the second hydraulic cylinder and the head chamber of
the first hydraulic cylinder.
6. The method of claim 2, wherein the moving of the piston and rod is at least
partly done by gravity acting on mass of the work attachment.
7. The method of claim 2, wherein the moving of the piston and rod is at least
partly done by decelerating mass of the work attachment.
8. The hydraulic system of claim 1, wherein the mobile work machine is a
wheel loader and the first hydraulic cylinder is connected to a boom of the work
attachment.
9. The hydraulic system of claim 8, wherein the first hydraulic cylinder, the
accumulator, and the first flow control device belong to a suspension system of the
wheel loader.
10. The hydraulic system of claim 8, further comprising a bucket cylinder of the
work implement and a third flow control device connected between the bucket
cylinder and the head chamber of the first hydraulic cylinder, wherein simultaneous
movement of the first hydraulic cylinder and the bucket cylinder occurs from the
work attachment compressing the first hydraulic cylinder.
11. The hydraulic system of claim 1, wherein a fluid displacement rate of the
head chamber is between about 1.1 and 3 times larger than a fluid displacement rate
of the rod chamber when the piston is moved.

12. The hydraulic system of claim 1, further comprising:
a pump;
a valve set including a plurality of valves, the valve set fluidly connected
between the head chamber of the first hydraulic cylinder and the pump and also
fluidly connected between the rod chamber of the first hydraulic cylinder and the
pump, the valve set adapted to direct fluid flow from the pump to the head chamber
to extend the first hydraulic cylinder and the valve set adapted to direct the fluid
flow from the pump to the rod chamber to retract the first hydraulic cylinder; and
a fluid passage fluidly connected between the head chamber of the first
hydraulic cylinder and the hydraulic accumulator, the fluid passage not passing
through any of the plurality of valves of the valve set, the fluid passage including the
first flow control device connected to the head chamber of the first hydraulic
cylinder by a first fluid line of the fluid passage and to the hydraulic accumulator by
a second fluid line of the fluid passage.
13. The hydraulic system of claim 12, further comprising a tank, wherein the
valve set is fluidly connected between the head chamber of the first hydraulic
cylinder and the tank and also fluidly connected between the rod chamber of the first
hydraulic cylinder and the tank.
14. The hydraulic system of claim 1, wherein the hydraulic system is adapted to
capture energy from the work attachment and store the energy in the accumulator
and wherein the hydraulic system is adapted to reuse the energy by actuating the
work implement with the rod of the first hydraulic cylinder.
15. The hydraulic system of claim 1, wherein the hydraulic system is adapted to
actuate the work attachment by lifting the work attachment with the rod of the first
hydraulic cylinder.
16. A hydraulic suspension system for providing suspension to a work
implement connected to a mobile work machine, the hydraulic suspension system
comprising:

a first hydraulic cylinder including a first port fluidly connected to a head
chamber of the first hydraulic cylinder, a second port fluidly connected to a rod
chamber of the first hydraulic cylinder, a piston positioned between the head
chamber of the first hydraulic cylinder and the rod chamber of the first hydraulic
cylinder, and a rod extending between a first end of the rod and a second end of the
rod and through the rod chamber, the first end of the rod connected to the piston and
the second end of the rod connected to a load of the work implement;
a pump;
a valve set including a plurality of valves, the valve set fluidly connected
between the first port of the first hydraulic cylinder and the pump and also fluidly
connected between the second port of the first hydraulic cylinder and the pump, the
valve set adapted to direct fluid flow from the pump to the first port to extend the
first hydraulic cylinder and the valve set adapted to direct the fluid flow from the
pump to the second port to retract the first hydraulic cylinder;
a hydraulic accumulator including an inlet/outlet port; and
a fluid passage fluidly connected between the first port of the first hydraulic
cylinder and the inlet/outlet port of the hydraulic accumulator, the fluid passage not
passing through any of the plurality of valves of the valve set, the fluid passage
including a first flow control valve fluidly connected to the first port of the first
hydraulic cylinder by a first fluid line of the fluid passage and to the inlet/outlet port
of the hydraulic accumulator by a second fluid line of the fluid passage;
wherein the hydraulic suspension system is adapted to capture energy from
the load of the work implement and store the energy in the hydraulic accumulator;
and
wherein the hydraulic suspension system is adapted to reuse the energy by
actuating the work implement with the rod of the first hydraulic cylinder.
17. The hydraulic suspension system of claim 16, further comprising a tank,
wherein the valve set is fluidly connected between the first port of the first hydraulic
cylinder and the tank and also fluidly connected between the second port of the first
hydraulic cylinder and the tank.

18. The hydraulic suspension system of claim 16, wherein the hydraulic
suspension system is adapted to actuate the work implement by lifting the work
implement with the rod of the first hydraulic cylinder.
19. The hydraulic suspension system of claim 16, further comprising a first flow
control device of the valve set, a second flow control device, a second flow control
valve of the valve set, a hydraulic junction, and a second hydraulic cylinder
including a first port and a second port, wherein the first flow control device is
fluidly connected between the second port of the first hydraulic cylinder and the
hydraulic junction, wherein the second flow control device is fluidly connected
between the first port of the second hydraulic cylinder and the hydraulic junction,
wherein the second flow control valve is fluidly connected between the first port of
the first hydraulic cylinder and the hydraulic junction, and wherein the hydraulic
suspension system is adapted to transform the energy from the load of the work
implement into actuation energy of the second hydraulic cylinder.
20. The hydraulic suspension system of claim 19, wherein the first hydraulic
cylinder is a boom cylinder of the work implement and the second hydraulic
cylinder is a bucket cylinder of the work implement, wherein transforming the
energy from the load of the work implement into the actuation energy results in
simultaneous movement of the boom cylinder and the bucket cylinder.
21. The hydraulic suspension system of claim 19, wherein the first flow control
device and the second flow control device each include check valves.
22. The hydraulic suspension system of claim 16, wherein a fluid displacement
rate of the head chamber is between about 1.1 and 3 times larger than a fluid
displacement rate of the rod chamber when the piston is moved, wherein the
hydraulic suspension system is adapted to fluidly connect the first and the second
ports of the first hydraulic cylinder and thereby amplify a hydraulic pressure
generated by the first hydraulic cylinder under the load of the work implement, and
wherein the hydraulic suspension system is adapted to charge the hydraulic
accumulator with the amplified hydraulic pressure.

23. The hydraulic suspension system of claim 16, wherein the mobile work
machine is a wheel loader.
24. A method of reusing energy of a work attachment of a work machine, the
method comprising:
opening hydraulic fluid flow through a first flow control device, the first
flow control device fluidly connected between an accumulator and a head chamber
of a first hydraulic cylinder;
- compressing the head chamber by moving a piston and rod of the first
hydraulic cylinder with the work attachment and thereby charging the accumulator
with the hydraulic fluid flow; and
simultaneously actuating a second hydraulic cylinder by opening hydraulic
fluid flow through a second flow control device connected between the second
hydraulic cylinder and the head chamber of the first hydraulic cylinder.
25. The method of claim 24, wherein the moving of the piston and rod is at least
partly done by gravity acting on mass of the work attachment.
26. The method of claim 24, wherein the moving of the piston and rod is at least
partly done by decelerating mass of the work attachment.
27. The method of claim 24, wherein the first hydraulic cylinder, the
accumulator, and the first fluid flow control device belong to a suspension system of
the work machine.
28. The method of claim 24, wherein the work machine is a wheel loader and the
first hydraulic cylinder is connected to a boom of the work attachment.
29. The method of claim 28, wherein the first hydraulic cylinder, the
accumulator, and the first fluid flow control device belong to a boom suspension
system of the wheel loader.

30. The method of claim 24, wherein the first hydraulic cylinder further includes
a rod chamber and a second flow control device fluidly connects the head chamber
to the rod chamber and thereby amplifies a hydraulic pressure generated within the
first hydraulic cylinder and used to charge the accumulator.
31. A method of reusing energy of a work attachment of a work machine, the
method comprising:
opening hydraulic fluid flow through a first flow control device, the first
flow control device fluidly connected between an accumulator and a head chamber
of a first hydraulic cylinder;
compressing the head chamber by moving a piston and rod of the first
hydraulic cylinder with the work attachment and thereby charging the accumulator
with the hydraulic fluid flow; and
amplifying a hydraulic pressure generated within the first hydraulic cylinder
and used to charge the accumulator by fluidly connecting a rod chamber of the first
hydraulic cylinder to the head chamber with a second flow control device.
32. The method of claim 31, wherein the moving of the piston and rod is at least
partly done by gravity acting on mass of the work attachment.
33. The method of claim 31, wherein the moving of the piston and rod is at least
partly done by decelerating mass of the work attachment.
34. The method of claim 31, wherein the first hydraulic cylinder, the
accumulator, and the first fluid flow control device belong to a suspension system of
the work machine.
35. The method of claim 31, wherein the work machine is a wheel loader and the
first hydraulic cylinder is connected to a boom of the work attachment.
36. The method of claim 35, wherein the first hydraulic cylinder, the
accumulator, and the first fluid flow control device belong to a boom suspension
system of the wheel loader.

37. The method of claim 31, further comprising simultaneously actuating a
second hydraulic cylinder by opening hydraulic fluid flow through a second flow
control device connected between the second hydraulic cylinder and the head
chamber of the first hydraulic cylinder.
38. A method of reusing energy of a work attachment of a work machine, the
method comprising:
opening hydraulic fluid flow through a first flow control device, the first
flow control device fluidly connected between an accumulator and a head chamber
of a first hydraulic cylinder;
compressing the head chamber by moving a piston and rod of the first
hydraulic cylinder with the work attachment and thereby charging the accumulator
with the hydraulic fluid flow through the first flow control device, the hydraulic
fluid flow substantially equal to a head chamber hydraulic fluid flow from the head
chamber of the first hydraulic cylinder;
opening head chamber to rod chamber hydraulic fluid flow through a second
flow control device, the second flow control device fluidly connected between the
head chamber of the first hydraulic cylinder and a rod chamber of the first hydraulic
cylinder; and
compressing the head chamber by moving the piston and rod of the first
hydraulic cylinder with the work attachment and thereby charging the accumulator
with the hydraulic fluid flow through the first flow control device, the hydraulic
fluid flow substantially equal to the head chamber hydraulic fluid flow minus the
head chamber to rod chamber hydraulic fluid flow through the second flow control
device.
39. The method of claim 38, wherein the moving of the piston and rod is at least
partly done by gravity acting on mass of the work attachment.
40. The method of claim 38, wherein the moving of the piston and rod is at least
partly done by decelerating mass of the work attachment.

41. The method of claim 38, wherein the first hydraulic cylinder, the
accumulator, and the first fluid flow control device belong to a suspension system of
the work machine.
42. The method of claim 38, wherein the work machine is a wheel loader and the
first hydraulic cylinder is connected to a boom of the work attachment.
43. The method of claim 42, wherein the first hydraulic cylinder, the
accumulator, and the first fluid flow control device belong to a boom suspension
system of the wheel loader.
44. The method of claim 38, further comprising simultaneously actuating a
second hydraulic cylinder by opening actuating hydraulic fluid flow through a third
flow control device connected between the second hydraulic cylinder and the head
chamber of the first hydraulic cylinder.