Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02747583 2011-07-29
DESCRIPTION
METHOD AND ARRANGEMENT FOR
ACTIVE MAKE-UP IN AN OVERRUNNING ACTUATOR
Technical Field
[0001] This disclosure relates generally to a hydraulic circuit for a double
acting actuator,
and, more particularly to arrangements for active fluid make-up in an
overrunning actuator.
Background
[0002] Dumping the load of a truck preferably occurs as a gradUial evacuation.
With certain
materials, however, such as the materials collected from the Canadian oil
sands, the contents of
the bed can adhere together, and dump as a single unit, or a small number of
relatively large
units. This phenomenon is referred to as loafing.
[0003] The dumping of a load is accomplished by way of a plurality of
actuators- In viewing
the structure of an actuator, a rod extends from the one side of the piston
and outward from the
cylinder. When dumping, the actuators extend, that is, hydraulic fluid is
evacuated from the rod
chamber of the actuator and hydraulic fluid is moved to the head chamber. As a
bed is moved to
start the dumping motion, the force of the load acts to compress the
actuators. As the load
continues to shift toward the dumping end of the bed, however, a situation
occurs that is
commonly referred to as an overrunning load if the load does not proceed
gradually to dump
from the bed. That is, if the load acts as a loaf, the force of the shifting
load causes a moment
that exerts a force on the actuator in the extending direction of the actuator-
[0004] If the flow of fluid to the head chamber is inadequate to meet the
demands of the
forcibly extending actuator, an undesirable severe voiding results in the head
end of the actuator.
In other words, a vacuum develops in the bead chamber as the volume of the
head chamber
extends beyond the volume of the hydraulic fluid flowing to the head chamber.
As a result,
when the load drops from the bed as a loaf, the vacuum formed in the head
chamber causes the
actuator to rapidly retract. This significant and undesirable dynamic event
can result in
discomfort, and even injury to a machine operator, or damage to the machine.
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[0005] In prior art arrangements, a hydraulic tank is provided as an external
source of make-
up flow to the hoist valve of the actuator. Unfortunately, however, this
passive arrangement is
often inadequate to meet the needs of an overrunning actuator, and an
alternative solution is
desirable-
Summary
[0006] In one aspect, there is disclosed a hydraulic system comprising an
actuator having a
piston disposed within a cylinder, and a rod extending from~the piston'and
extending out of the
cylinder. The piston defines a rod chamber and a head chamber within the
cylinder. The piston
and rod is adapted to move between a retracted position and an extended
position. The hydraulic
system also includes a first source of hydraulic fluid, and a first pump
adapted to provide
hydraulic fluid from the first source to the head chamber. The hydraulic fluid
from the first
pump is provided to the head chamber at a first pressure Ph. The hydraulic
system also includes
a second source of hydraulic fluid, and at least one selectively actuatable
valve fluidly coupled to
the second source. The second source is adapted to provide hydraulic fluid at
a second pressure
Pb_ The at least one valve provide hydraulic fluid from the second source to
supplement
hydraulic-fluid provided to the head chamber from the first pump when the
second pressure Pb is
greater than the first pressure Ph.
[0007) In another aspect, there is disclosed a machine for hauling a load. The
machine
comprises a chassis, and a bed pivotably mounted to the chassis and adapted to
pivot between
first position and a second position. The bed is disposed to hold a load in
the first position, and
to dump the load in the second position. The machine also includes a hydraulic
system having
an actuator, first and second sources of.hydraulic fluid, a first pump, and at
least one selectively
actuatable valve. The actuator has a piston disposed within a cylinder, and a
rod extending from
the piston and extending out of the cylinder. The piston defines a rod chamber
and a head
chamber within the cylinder. The actuator being adapted to;move between a
retracted position
and an extended position. The actuator being coupled to the chassis and the
bed and disposed to
move to the extended position to pivot the bed between the first and second
positions. The first
pump is adapted to provide hydraulic fluid from the first source to the head
chamber at a first
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pressure Ph. The second source of hydraulic fluid is adapted to provide
hydraulic fluid at a
second pressure Pb. The at least one valve is fluidly coupled to selectively
provide hydraulic
fluid from the second source to supplement hydraulic fluid provided to the
head chamber from
the first pump when the second pressure Pb is greater than the first pressure
Ph.
[0008] In yet another aspect, there is disclosed a method of controlling a
hydraulic system in
a machine for hauling a load. The machine comprises a chassis with a bed
pivotably mounted to
the chassis and adapted to pivot between first position wherein the bed is
disposed to hold a load
and a second position wherein the bed is disposed to dump the load. The
machine additionally
includes a hydraulic system having an actuator, a first source of hydraulic
fluid, and a a first
pump. The actuator has a piston disposed within a cylinder, and a rod
extending from the piston
and extending out of the cylinder. The piston defines a rod chamber and a head
chamber within
the cylinder. The actuator is adapted to move between a retracted position and
an extended
position, the actuator being coupled to the chassis and the bed and disposed
to move from the
retracted position to the extended position to pivot the bed between the first
and second
positions. The first pump is adapted to provide hydraulic fluid from the first
source to the head
chamber. Hydraulic fluid from the first pump is provided to the head chamber
at a first pressure
Ph. The method comprising the steps of selectively fluidly coupling a second
source of
hydraulic fluid to at least one valve and the head chamber, and actuating the
at least one valve to
provide flow at a second pressure Pb .from the second source to supplement
hydraulic fluid
provided. to the head chamber from the first pump when the second pressure Pb
is greater than
the first pressure Ph.
Brief Description of the Drawing(s)
[0009] FIG. 1 is a side elevational view of a machine incorporating aspects of
this disclosure.
[0010] FIG. 2 is a fragmentary schematic view of a hydraulic system according
to a first
embodiment of this disclosure.
10011] FIG. 3 is a fragmentary schematic view of a hydraulic system according
to a second
embodiment of this disclosure.
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[0012] FIG. 4 is a fragmentary schematic view of a hydraulic system according
to a third
embodiment of this disclosure.
[0013] FIG. 5 is a fragmentary schematic view of a hydraulic system according
to a fourth
embodiment of this disclosure.
[0014] FIG. 6 is a flow diagram of a method according to the disclosure.
Detailed Description
100151 This disclosure relates to machines 100 that utilize hydraulic
actuators (identified
generally as 102) to control movement of moveable subassemblies of the
machine, such as
dumping beds, arms, booms, implement tools, or the like. More specifically,
the disclosure
relates to such machines 100 wherein the actuators 102 of the subassembly are
subject to
overrunning loads wherein the normal flow of hydraulic fluid under such
circumstances is
inadequate to meet the needs of the actuator 102. While the arrangement is
illustrated in
connection with a dumping truck 106, the arrangement disclosed herein has
universal
applicability in various other types of machines 100 as well. The term
"machine" may refer to
any machine that performs some type of operation associated with an industry
such as mining,
construction, farming, transportation, or any other industry known in the art.
For example, the
machine may be a wheel loader or a skid steer loader. Moreover, one or more,
implement tools
may be connected to the machine 100. Such implement tools may be utilized for
a variety of
tasks, including, for example, brushing, compacting, grading, lifting,*
loading, plowing, ripping,
and include, for example, augers, blades, breakers/hammer-s, brushes, buckets,
compactors,
cutters, forked lifting devices, grader bits and end bits, grapples, blades,
rippers, scarifiers,
shears, snow plows, snow wings, and others.
[0016] The truck 106 of FIG. 1 includes a cab 108 that is supported on a
chassis 110 that
includes motivators 112, such as wheels 114. It will be appreciated, however,
that the motivators
112 may alternately be a pair of tracks, or the like. The cab 108 includes an
operator station 116
from which an operator may control the operations of the machine 1.00.
[0017] The chassis 110 additionally supports a bed 118 that is pivotably
supported on the
chassis 110 at pivot location (shown generally as 120). It is noted that the
bed 118 may include a
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dumping gate (not illustrated) that pivots out of position to allow a load
contained within the bed
118 to dump from the bed 118 when the bed 118 is tilted. An alternate
arrangement, such as the
one illustrated need not include such a gate-
[00181 The machine 100 additionally includes components of a hydraulic system
122,
including hydraulic actuators 102. Although only one hydraulic actuator 102 is
visible in FIG. 1,
the illustrated hydraulic system 122 includes a plurality of hydraulic
actuators 102 that may be
extended to cause the bed 118 to pivot around pivot location 120 to dump a
load- As is
conventional, the hydraulic actuators 102 are pivotably coupled to the chassis
110 at one end
124, and to. the bed 118 at the other end. 126.
[0019] Referring to FIG. 2, which shows a fragmentary schematic of an
embodiment of the
hydraulic system 122 for operating the actuator 102, the actuators 102 may be
of a conventional
design, including a cylinder 130 in which a piston 132 is slidably disposed. A
rod 134 is secured
to the piston 132, and extends from the cylinder 130. In this way, the piston
132 divides the
interior of the cylinder 130 into a rod chamber 136 and a head chamber 138. In
operation, as the
actuator 102 is extended, hydraulic fluid flows out of the rod chamber 136 and
hydraulic fluid
flows into the head chamber 138 as the piston 132 and rod 134 slide within the
cylinder 130 to
telescope the rod 134 outward from the actuator 102. Conversely, as the
actuator 102 is
retracted, hydraulic fluid flows into the rod chamber 136 and hydraulic fluid
flows out of the
head chamber 138, as the piston 132 and'rod 134 slide within the cylinder 130
to retract the rod
134 into the cylinder 130. The actuator 102 may include, for example, a one or
a two stage rod,
although a single stage rod 1.34 is illustrated in this embodiment. Flow of
hydraulic fluid to and
from the rod and head chambers 136, 138 proceeds through a rod side fluid
connection 140 and a
head side fluid connection 142, respectively, that are fluidly coupled to
respective ports 144, 146
opening in the rod or head chambers 136, 138 in the cylinder 130. In an
embodiment of a
machine such as illustrated in FIG. 1, the ports 144, 146 may be both located
at the rod end of
the 124 of the actuator 102, flow to the head chamber 13 8 progressing through
a pipe (not
shown) contained in the rod 134. Ports 144, 146 also may be provided in
opposite ends of the
actuator 102, as illustrated in FIG- 2. To. dump a load contained within the
bed 118, the actuators
102 are extended to pivot the bed 118 about the pivot location 120 by
evacuating fluid from the
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rod chamber 136 and adding fluid to the head chamber 138. During extension of
the actuator
102, fluid under pressure is evacuated from the rod chamber 136 through the
port 144 and rod
side fluid connection 140 to, for example, a hoist valve 150. Simultaneously,
lower pressure
fluid flows from a first pump 152 through the head side fluid connection 142
and the port 146 to
the head chamber 13 8.
[00201. According to an embodiment of this disclosure, supplemental flow is
provided to the
head chamber 138 from an additional source 154 of pressurized fluid. In this
embodiment,
supplemental flow is provided from an existing pump 156 of an alternate
hydraulically operated
function or operation 158 that can tolerate an interruption in flow during the
hoisting operation.
In this embodiment, the flow is provided from a cooling pump 160, which,
during normal
operation, pumps hydraulic fluid from a fluid source 162, such as a sump 164,
to an oil cooler
J 66, by way of a plurality of conduits 168, 170, 172_ It is noted that when
fluid in conduit 170
reaches a preset pressure, poppet valve 173 may be triggered by a pilot
control line 174 to allow
fluid to be returned to the fluid source 162.
[00211 In order to control the flow of fluid from the pump 156 to the actuator
102 or the
alternate operation 158, a diverter valve 180 is provided. In this embodiment,
the diverter valve
is pilot operated and includes Hirst and. second poppet valves 182, 18'4_ Flow
from the additional
source 154, here, the pump 156, is provided through conduit 170 to poppet
valves . 182, 184,
which are both normally in their closed positions, as illustrated in FIG. 2.
Fluid pressure
provided to the poppet valves 182, 184 will be at pressure Pb, that is, the
pressure Pb as fluid
leaves the pump 156 and travels along conduit 170.
[0022] In operation, a pilot signal is provided by way of pilot line 1.86 from
the rod. side fluid
connection 140 connected to the rod chamber 136. The pilot line 186 is coupled
to a pair of pilot
valves 190, 192, valve 190 being normally open, and valve 192 being normally
closed. In this
way, pressure from the rod side fluid connection 140 is provided as pressure
Pr to valves 190,
192, that is, the pressure Pr of the fluid leaving the rod side chamber 136
and traveling through
conduit 140.
10023] In operation, if pressure Pr provided to pilot line 186 from the rod
side fluid
connection 140 is relatively low, pilot valve 190 remains in the open
position, and pilot valve
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192 remains in a closed position. A bleed orifice 194 allows any residual
pressure in the pilot
line 186 to vent to a drain 196. It is noted that drain 196 and sump 164 may
be the same
structure or otherwise connected. With the pilot valve 190 in the open
position as illustrated,
when pressure Pb builds in conduit 170, a pilot line 198 from conduit 200
extending from
conduit 170 applies pressure Pb to the poppet valve 182 to move the poppet
valve 182 from the
illustrated closed position to an open position. As the poppet valve 182 moves
from the closed to
the open position against the force of a spring 202, pressure within line 204
is vented through the
pilot valve 190 to the drain 196.
(0024] Turning to the poppet valve 184, with the pilot valve 192 in the closed
position,
pressure on the backside of the poppet valve 184 is unable to vent, and pilot
line 206 does not
move the poppet valve 184 to an open position against the force of spring 208.
As a result, all of
the flow from conduit 170 proceeds to conduit 200, flowing through open poppet
valve 182 to
conduit 172, and on to the alternate operation 158, here, an oil cooler 166.
It will be appreciated
by those of skill in the art that the structure various acting surfaces of the
valves 182, 184 may be
designed such that the force of fluid on the surfaces results in movement
providing the desired
flow direction.
[00251 As the pressure Pr within pilot line 186 builds, however, pilot valve
190 shifts to its
closed position, terminating the vent from line 204 to the drain 196, but
continuing to allow
venting to drain 196 through orifice 194. With pilot valve 190 in the closed
position, pressure Pb
from conduit 200 additionally is transmitted through pilot line 210 and
orifice 212 such that the
forces, including that of the spring 202, move the poppet valve 182 to the
illustrated closed
position, shutting off flow to the alternate operation 158, i.e., the oil
cooler 166.
[0026] As pressure continues to build, the pilot valve 192 is also shifted
from its nonn.ally
closed position illustrated to its open position, connecting the backside of
the poppet valve 184 to
conduit 214 by way of line 216. It will be appreciated that pressure Ph from
the first pump 152
is applied to one side of the pilot valve 192 by way of conduits 142, 214,
line 216, and pilot line
218. In this way, pressure Ph, which is the pressure Ph of fluid leaving the
first pump 152 and
traveling through head side fluid connection 142, along with the force of
biasing spring 220 act
on one end of the pilot valve 192, while pressure Pr from pilot line 186 acts
on the other side of
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pilot valve 192. Here, pressure Pr from pilot line 186 is the same as pressure
exiting the rod
chamber 136 and traveling through the rod side fluid connection 140. Thus,
when Pr exceeds
Ph, pilot valve 192 shifts from the closed to the open position.
[0027] With the pilot valve 192 in the open position, as pressure Pb from the
alternate source
154 increases, pressure Pb is applied to the poppet valve 184 through conduits
170,.222 and pilot
line 206. As pressure Pb builds, the pressure Pb asserted on poppet valve 184,
including by way
of conduit 222 and pilot line 206, overcomes the pressure Ph from the first
pump 152 asserted on
the poppet valve 184. The poppet valve 184 then moves from the closed position
illustrated to
the open position, connecting flow from conduit 222 to conduit 214 to provide
flow
supplemental to the head chamber 138 by way of conduit 142 and port 146. This
flow to the
head chamber 138 from the first pump 152 and the supplemental source 154 is a
relatively high
flow at a relatively low pressure, while the flow from the rod chamber 136 is
at a relatively high
pressure, providing maximum tension force in the cylinder 130. It will be
appreciated by those
of skill in the art, that this supplemental flow to the head chamber 13 8
provides fluid to the void
that may otherwise be created in the head chamber 138 as a result of an
ovenunniag situation-
[0028] Turning now to the embodiment of FIG. 3, the same numbers preceded by
the number
1XXX are utilized to identify the various elements. Those elements identified
by such
corresponding numbers in FIG. 3 that are not explained in detail below may. be
the same or
similar to the structure explained with regard to FIG. 2. It is noted,
however, that flow of
hydraulic fluid to and from the rod and head chambers 1136, 1138 proceeds
through a rod side
fluid connection 1140 and a head side fluid connection 1142, respectively, but
the respective
ports 1144, 1146 opening in the rod or head chambers 1136, 1138 are both
disposed in the rod
end 1124 of the actuator 1102, flow to the head chamber 1138 progressing
through a pipe (not
shown) contained in the rod 1134. As with the first embodiment, to dump a load
contained
within the bed 118, the actuator 1102 is extended by evacuating fluid from the
rod chamber 1136
and adding fluid to the head chamber 1138.
[0029] During extension of the actuator 1102, fluid under pressure is
evacuated from the rod
chamber 1136 through the port 1144 and rod side fluid connection 1140 to a
hoist valve 1150,
from which the fluid may be directed, for example, to a tank 1164 via conduit
1141
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Simultaneously, a first pump 1152 pumps lower pressure fluid through the hoist
valve 1150 to
the head side fluid connection 1142 and the port 1146 to the head chamber
1138.
[00301 According to this embodiment, supplemental flow is provided to the head
chamber
1138 from the fluid source 1162, or tank 1164 from an additional fluid source
(shown generally
as 1154) by way at least one existing pump 1156 from an alternate operation
1158 that can
tolerate an interruption in flow during the hoisting operation. In this
embodiment, flow is
provided from a pair of cooling pumps 1160 that service the rear brakes 1166.
In this
embodiment, low and high pressure valves 1182, 1184 may be provided
separately, as opposed
to being contained in a single diverter valve 180, such as the one illustrated
in the embodiment of
FIG. 2.
[00311 As with the first embodiment, flow from the additional source 1154,
here, the pumps
1156, is provided through conduit 1170 to low and high pressure poppet valves
1182, 1184 by
way of conduits 1200, 1222, respectively. Fluid pressure provided to the
poppet valves 1182,
1184 by way of conduits 1200, 1222 will be at pressure Pb, that is, the
pressure of the hydraulic
fluid leaving existing pumps 1156 and traveling through conduit 1200.
[00321 A pilot connection 1186 from the rod connection 1140 connected to the
rod chamber
1136 provides pressure Pr to the poppet valves 1182, 1184 by way of pilot
connections 1187,
1188. Pressure Pr in this embodiment is the pressure of fluid leaving the rod
chamber 1136 and
traveling through the rod side fluid connection 1140. As with the poppet
valves 182, 184 of FIG.
2, the high pressure poppet valve 1184 will be closed and the low pressure
poppet valve 1182
will be open to provide passage of hydraulic fluid when pressure Pr provided
by way of pilots
1186, 1187, 1188 is relatively low. That is, when the pressure Pr in the rod
side fluid connection
1140 is low, as in normal operation, fluid from the at least one existing pump
1156 will be
directed to its operation 1158 through the open low pressure poppet valve
1182, i. e., fluid from
the cooling pumps 1160 will be directed from conduit 1200 through open poppet
valve 1182 and
conduit 1172 to the rear brakes 1166.
[00331 Conversely, when the pressure provided by the pilots 1186, 1187, 1188
is increases,
the low pressure poppet valve 1182 closes and the high pressure poppet valve
1184 opens.
When the *pressure Pr is relatively high, the high pressure poppet valve 1184
will be open to
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allow passage of hydraulic fluid and the low pressure poppet valve 1182 will
be closed to
prevent passage. That is, when pressure Pr in the rod side fluid connection
1140 is relatively
high, as during an overrunning load situation, fluid from the at least one
existing pump 1156 will
be directed to the head chamber 1138 through the open high pressure poppet
valve 1184, i.e.,
fluid from the cooling pumps 1160 will be directed to the head chamber 113 8
through conduit
1222, open poppet valve 1184, conduit 1214, and head side fluid connection
1142 to supplement
the flow from the first pump 1152.
[0034] Turning now to FIG. 4, the same numbers preceded by the number 2XXX are
utilized
to identify the various elements. Those elements identified by such
corresponding numbers in
FIG. 4 that are not explained in detail below may be the same or similar to
the structure
explained with regard to FIGS. 2 and/or 3. FIG. 4 illustrates an example of a
pilot valve 2180 in
conjunction with a make-up valve 2184. The pilot valve 2180 is of a spool type
in this
embodiment, while the make-up valve 2184 is of a poppet type.
[0035] In the implementation of FIG. 4, a spool 2230 is provided within a
valve body 2232,
and biased to the illustrated position by spring 2202. in the position
illustrated, the spool 2230 is
disposed to direct flow through port 2200 from an existing pump 2156 to port
2172 and on to an
alternate operation 2158, here, from a brake cooling.pump 2160 to an oil
cooler 2166. In this
way, pressure Pb is applied at port 2200, pressure Pc is applied at port 2172,
that is, the pressure
Pb from the existing pump 2156 is applied at port 2200, and the pressure Pc
from the alternate
operation 2158 is applied at port 2172, In order to shift the spool 2230 from
the illustrated
position against the force of the spring 2202 and existing flow through the
valve body 2232, a
pilot signal of pressure Pr is applied to a spool 2230 at port 2186_ Thus,
when pilot pressure Pr is
relatively low, the spool 2230 will be disposed in the illustrated position,
directing flow from the
existing pump 2156 to the alternate operation 2158. When pilot pressure Pr
builds, however, the
spool 2230 will shift from the illustrated position to cut off flow to the
alternate operation 2158,
and direct flow to the port 2221, through conduit 2222, and on to make-up
valve 2184. It will be
appreciated that, once in the shifted position, the pressure at port 2221 and
in conduit 2222 will
be the same as the pressure Pb entering the valve body 2232 at port 2200.
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[0036) In this way, pressure Pb is applied at port 2223 of, the make-up valve
2184. The
outlet port 2214 of the make-up valve 2184 is open to the flow to the actuator
(not illustrated in
this embodiment). Consequently, the pressure applied at port 2214 is the
pressure Ph from the
first pump (not illustrated in this embodiment). As pressure Pb applied to
make-up valve 2184 at
port 2223 builds and eventually becomes greater than the force applied by the
spring 2185 and
pressure Ph, the make-up valve 2184 opens to allow flow to port 2214. That is,
when make-up
valve 2184 opens, flow through valve 2180 from the existing pump 2156-is
directed supplement
flow to the cap chamber (not illustrated in this embodiment) during an
overrunning operation.
100371 Turning now to FIG. 5, the same numbers preceded by the number 3XXX are
utilized
to identify the various elements. Those elements identified by such
corresponding numbers in
FIG. 5 that are not explained in detail below may be the same or similar to
the structure
explained with regard to FIG. 3. FIG. 5 illustrates an example of a
regenerative system wherein
an accumulator 3156 is utilized as an additional source of pressurized fluid
3154 to supplement
flow from a first pump 3152. As in the embodiment of FIG. 3, the first pump
3152 directs fluid
from a tank 3164 to the head chamber 313 8 by way of a hoist valve 3150 and
head side fluid
connection 3142. It is noted that the cooling pumps 3160 in this embodiment
direct fluid to the
oil cooler 3166, but are not involved in the provision of supplemental fluid
to the head chamber
3138.
[00381 In the embodiment of FIG. 5, return flow from the rod chamber 3136 may
be directed
by rod side fluid connection 3140 through the hoist valve 3150 and conduit
3141 to the tank
3164. Return flow from the rod chamber 3136 may alternatively or additionally
be directed from
rod side fluid connection 3140 through conduit 3186 and check valve 3185 to
the accumulator
3156. A flow limiter 3183, illustrated here as a compensated orifice, may be
disposed in the path
of charge conduit 3186.
[00391 In operation, supplemental flow from the accumulator 3156 may be may be
directed
to head side fluid connection 3142 by way of operation of valves 3192 and
31.84. Turning first
to the operation of the valve 3184, pressure Ph from head side fluid
connection 3142 is applied to
valve 3184 by way of conduit 3214, while pressure Pr from rod side fluid
connection 3140 as a
result of flow from the iod chamber 3136 is applied to valve 3184 by way of
pilot line 3188.
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Generally speaking, when the pilot pressure Pr at pilot line 3188 is greater
than pressure resulting
from flow to the head chamber 3138, valve 3184 will open to permit flow
therethrough.
[0040] With valve 3184 in the open position, pressure Ph will be applied to
one side of the
valve 3192, while pressure Pa from the accumulator 3156 will be applied to the
other side of
valve 3192. When the pressure Ph from the valve 3184 applied to the valve 3192
drops, pressure
applied at pilot line 3218 drops, allowing the valve 3192 to move under the
force of spring 3220
from the normally closed position illustrated to an open flow position. With
valve 3192 in the
open position, fluid from, the accumulator 3156 passes through the conduit
3222, valve 3192,
valve 3184, and conduit 3214-to the bead side fluid connection 3142, and onto
the head chamber
3138 through port 3146. Valve 3192 maybe a pressure reducing valve such that
valve 3192
reduces the pressure of fluid flowing from the accumulator 3156 before passing
the fluid on to
valve 3184- It will be appreciated by those of skill in the art that valve
3184 and, consequently,
valve 3192 will return to their respective closed position when the difference
between the
pressure Ph applied at conduit 3214 and the pressure Pr applied at pilot line
31.88 reduces.
Industrial Applicability
[0041] The present disclosure is applicable to machines 100 that haul
materials that are
subject to massing together as one or more larger units. The disclosure may be
particularly
applicable to machines 100 which experience high forces that may result in
overrunning and
potential voiding in the head chamber of 138 of an actuator 102 during
extension. The present
disclosure may be applicable to such machines that are otherwise susceptible
to rapid removal of
such high forces, as may occur with "loafing" during unloading of a load. The
systems and
method disclosed herein may reduce or minimize the possibility of such
loafing. The systems
and method may also minimize or reduce the effects of such loafing on
machinery components,
as well as on the operator-
[0042] It will be appreciated that the foregoing description provides examples
of the
disclosed system and technique. However, it is contemplated that other
implementations of the
disclosure may differ in detail from the foregoing examples. All references to
the disclosure or
examples thereof are intended to reference the particular example being
discussed at that point
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and are not intended to imply any limitation as to the scope of the disclosure
more generally- All
language of distinction and disparagement with respect to certain features is
intended to indicate
a lack of preference for those features, but not to exclude such from the
scope of the disclosure
entirely unless otherwise indicated.
[00431 Recitation of ranges of values herein are merely intended to serve as a
shorthand
method of referring individually to each separate value falling within the
range, unless otherwise
indicated herein, and each separate value is incorporated into the
specification as if it were
individually recited herein. All methods described herein can be performed in
any suitable order
unless otherwise indicated herein or otherwise clearly contradicted by
context.
[0044] Accordingly, this disclosure includes all modifications and equivalents
of the subject
matter recited in the claims appended hereto as permitted by applicable law.
Moreover, any
combination of the above-described elements in all possible variations thereof
is encompassed by
the disclosure unless otherwise indicated herein or otherwise clearly
contradicted by context,
