Note: Descriptions are shown in the official language in which they were submitted.
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REGENERATION CIRCUIT
CROSS REFERENCES TO RELATED APPLICATIONS
[0001] This application claims the priority benefit of U.S. Provisional Patent
Application No. 60/216,041 filed on July 5, 2000.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH
[0002] Not Applicable
Back~,round Of The Invention
[0003] The present invention relates to regeneration circuits, and more
particularly to
hydraulic regeneration circuits in lift trucks.
[0004] Known lift trucks, such as Reach-Fork~ and Swing-Reach~ trucks
available
from The Raymond Corporation in Greene, New York, include a vertically
extendible mast
supporting a carriage having horizontally extendible forks. The trucks are
used with rack
systems for storing and retrieving loads such as pallets in the racks. Efforts
continue to
reduce the time to perform each store or retrieve operation, and thus increase
the efficiency
of the truck and operator.
[0005] Each store or retrieve operation requires similar steps. For example in
a
retrieve operation, the truck performs the following steps; raising the forks
vertically to a
level below the desired load , extending the forks horizontally underneath the
load, raising
the forks to lift the load off of the rack supports; and retracting the forks
horizontally. The
store operation is essentially the same except instead of extending the forks
underneath the
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load and then raising the forks, the forks are extended into the rack storage
location and then
lowered until the load is supported by the rack supports. Once the load is
supported by the
rack supports, the forks are then retracted without the load on board.
[0006] One method of decreasing the time required to perform these operations
is to
increase the vertical speed of the mast and the horizontal speed of the forks.
In hydraulic
systems, this can be accomplished by increasing the size of the hydraulic pump
and
hydraulic lines to handle the increase flow of hydraulic fluid, or providing
separate systems
sized for the maximum desired speed for individual functions. These
modifications,
however, increase the cost of the lift truck. Moreover, certain functions of
the lift truck, such
as retracting the forks horizontally with a load on board, is often limited
due to the potential
for tipping. As a result, increasing the top speed of certain functions does
not always provide
a reduction in cycle times.
[0007] Reducing the cycle time of an operation can often be accomplished by
increasing the speed of one particular function, such as horizontally
extending the forks
when a load is not on the forks. Horizontal fork movement is often
accomplished using one
or more double action hydraulic cylinders. As noted above, in the prior art,
increasing the
speed of one function, such as horizontal fork extension, may increase the
speed of another
function, such as horizontal fork retraction, beyond what is required.
Therefore, in a
hydraulic system for use in a lift truck, a need exists for economically
increasing the speed of
one function without increasing the speed of another related function.
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Summary Of The Invention
[0008] The present invention provides a regeneration hydraulic circuit which
increases the speed of one action of a double action cylinder. The hydraulic
circuit includes
first hydraulic line in fluid communication with one end of the double action
cylinder, and a
second hydraulic line in fluid communication with an opposing end of the
double action
cylinder. A third hydraulic Line connects the first hydraulic line and the
second hydraulic
line. A pilot check valve is disposed in the third hydraulic line, and has a
pilot line. The pilot
line is connected to the first hydraulic line, wherein the pilot check valve
is open when
hydraulic fluid flows through the first hydraulic line and into the one end of
the double
action cylinder The pilot check valve is closed when hydraulic fluid flows out
of the one end
of the double action cylinder and through the first hydraulic line. A check
valve is disposed
in the second hydraulic line, wherein hydraulic fluid flowing out of the
opposing end of the
double action cylinder is diverted into the third hydraulic line.
[0009] A general objective of the present invention is to increase the speed
of one
action of a double action cylinder without increasing the size of a pump
pumping hydraulic
fluid into the cylinder. This objective is accomplished by diverting hydraulic
fluid being
forced out of one end of the hydraulic cylinder to combine with fluid being
pumped into the
other end of the cylinder.
[0010] This and still other objects and advantages of the present invention
will be
apparent from the description which follows. In the detailed description
below, preferred
embodiments of the invention will be described in reference to the
accompanying drawings.
These embodiments do not represent the full scope of the invention. Rather the
invention
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may be employed in other embodiments. Reference should therefore be made to
the claims
herein for interpreting the breadth of the invention.
Brief Description Of The Drawings
[0011] Fig. 1 is a perspective view of a lft truck incorporating the present
invention;
[0012] Fig. 2 is a hydraulic circuit schematic incorporating the present
invention; and
[0013] Fig. 3 is a detailed hydraulic circuit schematic showing the reach
regeneration
circuit of Fig. 2.
Detailed Description Of The Invention
[0014] As shown in Figs 1 and 2 a lift truck 1 includes an extendible multi-
stage
mast assembly 2 mounted thereon. The mast assembly 2 lifts a carriage 3 and a
pair of
rotatable and extendible forks 4 fixed to the carriage 3. The forks 4
vertically support a
pallet (not shown). The mast assembly 2 and forks 4 are actuated by a lift
truck hydraulic
circuit 10. The lift truck 1 can be any commercially available lift truck
having a mufti-stage
assembly, such as a Raymond Reach-Fork~, Easier Swing-Reach~, and Pacers Truck
available from Raymond Corporation, Greene, New York.
[0015] Refernng to Fig. 2, the mast assembly 2 includes hydraulic lift
cylinders 14
which lifts the carriage 3 and forks 4, to a predetermined height. An
auxiliary lift cylinder 15
can lift the forks 4 independently of the carriage 3. A second set of
hydraulic cylinders 16
extend and retract the forks 4. The forks 4 are rotated by a first rotary
actuator 18 which
rotates the forks in one direction, and a second rotary actuator 20 which
urges the forks in
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the opposite direction. Although the preferred embodiment of the present
invention is a
hydraulically actuated cylinder, other fluid actuators, such as a
pneumatically actuated
cylinder and the like, are within the scope of the invention.
[0016] The lift truck hydraulic circuit 10 includes a reservoir 12 for holding
hydraulic fluid which is pumped through hydraulic lines to actuate cylinders
14, 16 and
rotary actuators 18, 20. Various valves 22 direct the hydraulic fluid to the
cylinders 16, 18
and rotary actuators 18, 20 to actuate the desired cylinder 16, 18, or
actuator 18, 20. One
pump 24 pumps hydraulic fluid to the first set of cylinders 14, and a second
pump 26 pumps
hydraulic fluid to the carriage for operating the second set of cylinders I6
and rotary
actuators 18, 20 mounted on the carriage.
[0017] As shown in Figs. 2 and 3, the hydraulic circuit 10 includes a
regeneration
circuit 30 for actuating the double action second set of cylinders I6 which
extend and retract
the forks. Each double action cylinder 16 includes a cap end 32 and a rod end
34. The cap
end 32 and rod end 34 of each cylinder 16 are separated by a slidable
diaphragm 36 having a
rod 38 connected thereto. The rod 38 extends out of the cylinder 16, and is
linked to the
forks, such that as the rod 38 extends out of the cylinder 16 the forks
extend, and as the rod
38 is retracted into the cylinder 16 the forks retract. Hydraulic fluid pumped
in the cylinder
cap end 32 slidably moves the diaphragm 36 which urges fluid in the cylinder
rod end 34 out
of the cylinder 16. Conversely, hydraulic fluid pumped into the rod end 34
slidably moves
the diaphragm 38 which urges fluid in the cap end 32 out of the cylinder 16.
As the
diaphragm 38 moves toward the rod end 34, the rod 38 extends further out of
cylinder 16 to
extend the forks, and as the diaphragm 38 moves toward the cap end 32, the rod
38 retracts
into the cylinder 16 to retract the forks.
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[0018] The regeneration circuit 30 causes the forks 4 to extend faster than
the forks 4
can be extended without the regeneration circuit 30 by directing fluid being
forced out of the
cylinder rod end 34 back into the cap end 32. Referring to Fig. 2, in the
regeneration circuit
30, when extending the forks, hydraulic fluid flows into the cylinder cap end
32 through a
first hydraulic line 40, and out of the cylinder rod end 34 through a second
hydraulic line 42.
In prior art hydraulic circuits, the hydraulic fluid exiting the cylinder rod
end 34 is returned
to the reservoir 12. However, in the present invention, the hydraulic fluid
exiting the
cylinder rod end 34 is diverted into the first hydraulic line 42 to increase
the speed of the
fork extension, and not back to the reservoir 12.
[0019] The hydraulic fluid is diverted to the first hydraulic Line 40
supplying the
cylinder cap end 32 by check valves 44, 46. The first check valve 44 prevents
hydraulic fluid
from exiting the regeneration circuit 30 through the second hydraulic line 42.
The second
check valve is a pilot check valve 46 in a connecting hydraulic line 48
connecting the first
hydraulic line 40 to the second hydraulic line 42. A pilot line 50 of the
pilot check valve 46
is connected to the first hydraulic line 40, such that the pilot check valve
46 is open when the
first hydraulic line 40 is supplying hydraulic fluid to the cylinder cap end
32, and closed
when the second hydraulic line 42 is supplying hydraulic fluid to the cylinder
rod end 34.
[0020] In operation, when hydraulic fluid is being supplied to the cylinder
cap end 32
through the first hydraulic Iine 40, the pilot check valve 46 is open, and the
first check valve
44 is closed which causes hydraulic fluid exiting the cylinder rod end 34 to
flow from the
second hydraulic line 42 through the connecting line 48 and into the first
hydraulic line 40.
The hydraulic fluid exiting the rod end 34 combines with the fluid pumped by
the carriage
pump 26 being supplied to the cap end 32 to increase the volumetric flow of
hydraulic fluid
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into the cylinder cap end 32. Increasing the volumetric flow of hydraulic
fluid by diverting
the fluid exiting the cylinder rod end 38 increases the extension speed of the
forks over the
speed which would be attained by hydraulic fluid pumped by the carriage pump
26 alone.
Advantageously, the fork extension speed is increased without increasing the
pump size.
[0021] When the forks are retracted, hydraulic fluid is supplied to the
cylinder rod
end 34 by the second hydraulic line 42, and fluid exits the cylinder cap end
32 through the
first hydraulic line 40 and into the reservoir 12. The pilot check valve 46
prevents the flow of
hydraulic fluid into first hydraulic line 40, and forces the fluid flowing
through the second
hydraulic line 42 into the cylinder rod end 34.
[0022] Advantageously, the present invention can provide a simple modification
to
an existing hydraulic circuit to increase the speed of one actuation direction
of a double
actuation cylinder, or other circuitry, such as in use with a torque motor,
valves, and the like,
without increasing the pump size. The modification includes providing a
connection
hydraulic line which connects a hydraulic line which supplies hydraulic fluid
to the cap end
of a cylinder and a hydraulic line which receives hydraulic fluid from the rod
end of the
hydraulic cylinder. A check valve is installed in the hydraulic line supplying
fluid to the rod
end of the cylinder, such that hydraulic fluid exiting the cylinder rod end is
diverted into the
connection hydraulic line. A pilot check valve is installed in the connecting
hydraulic line
with a pilot line connected to the hydraulic line supplying hydraulic fluid to
the cap end of
the cylinder, such that the pilot check valve is open when fluid is being
supplied to the cap
end of the cylinder, and the pilot check valve is closed when fluid is exiting
the cylinder cap
end. Of course, the portion of the hydraulic line downstream of the merging
point of the
connection line and the hydraulic line supplying fluid to the cap end of the
cylinders (i.e. the
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portion of the hydraulic line between the merging point and the cap end) must
be sized to
accommodate the hydraulic fluid from the pump and the rod end of the
cylinders.
[0023] Another advantage of the present invention, is that a circuit
incorporating the
present invention prevents a cylinder from "overrunning." Overrunning exists
when a
cylinder load tries to pull, or extend the cylinder rods. This can occur in a
lift truck carrying
a Ioad on extendible forks when braking.
[0024] While there has been shown and described what are at present considered
the
preferred embodiments of the invention, it will be obvious to those skilled in
the art that
various changes and modifications can be made therein without departing from
the scope of
the invention defined by the appended claims. For example, a different fluid,
such as air,
can be used.
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