Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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` POWER TRANSMISSION
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This inventio~ relates to power transmission and
particularly to hydraulic circuits for actuators such
- as are found in earth moving equipment including
excavators and cranes.
-` BACKGROU~D AND SU~MARY_OF TEE I~VE~TION
This invention relates to hydraulic systems for
controlling a plurality of actuators such as hydraulic
cylinders which are found, for e~ample, in earth moving
` 10 e~uipment such as excavators and cranes~ In such a
system, it is conventional to provide a pilot operated
` control valve for each actuator which is controlled
` by a manually operated controller through a pilot hy-
draulic circuit. The control valve functions to supply
hydraulic fluid to the actuator to control the speed
and direction of operation of the actuator. In addi-
tion, the control valve for each actuator controls the
flow of hydraulic fluid out of the actuator. It is also
common to provide counterbalance valves or fi~ed restric-
' 20 tions to control overrunning loads.
` In United States patent 4,201 052 having a common
assignee with the present application, there is disclosed
and claimed a hydraulic system for accurately controlling
the position and speed of operation of the actuators;
which system is simple and easy to make and maintain; which
- system is unaffected by change of load pressure of various
portions of the system or other actuators served by the same
` source; which system may not use flow from the pressure
source in the case of overrunning loads on the actuators;
wherein the control valves may be mounted adja~ent the
actuator for preventing loss of control of the load
in case of malfunction in the hydraulic lines to the
actuator; wherein the valves which control flow out
of the actuator function to control the velocity in the
case of ener~y generating loads; wherein the valve that
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controls flow into the actuator controls the velocity
in the case of energy absorbing loads; wherein the
valve system for each actuator can be mounted on its
respective ac.uator and incorporates means for pre-
venting uncontrolled lowering of the load in case of
pressure failure due to breaking of the lines to the
valve system; wherein the timing of operation of the
valve controlling flow into the actuator and out of
the actuator can be designed to accommodate the spe-
cific nature of the particular load.
It is an object of the present invention to provide
' a dual acting hydraulic control system havi~g dual
meter-in valves for controlling du~l-acting hydraulic
actuators.
Another object of the present invention is to
provide a dual acting hydraulic control system having
dual meter-in valves for providing control of dual-
acting hydraulic actuators in a regenerative mode.
A further object of the present invention is to
provide a single acting hydraulic control system for
` controlling single`acting hydraulic actuators.
The present invention comprises a hydraulic con-
trol system for use with a hydraulic actuator, a pilot
controller, and a pump. The actuator includes a
movable element and a pair of openings adapted to
function alternately as inlets or outlets for moving
the element in opposite directions. The pilot
controller supplies fluid to the system at pilot pres-
sure and the pump supplies fluid at pump pressure to
the actuator. The control system includes a line
adapted for connection to ea~h oE the openings and a
meter-out valve associated with each of the lines or
controlling fluid flow from the actuator. The meter-out
valves are each selectively pilot operated by pilot
pressure from the pilot controller. A meter-in valve
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; is positioned in each of the lines ~or controlling
fluid flow from the pump to the actuator with each
of the meter-in valves being selectively operable by
pilot pressure from the pilot controller.
In one embodiment of the present invention the
actuator includes a head end and a rod end associated
with each of the pair of openings and each of the lines
adapted to be connected therewith having a load drop
check valve associated with the head end and rod end,
respectively. A means for venting the load drop check
valve associated with the rod end and means for simul-
taneously opening the meter-in valves provide control
of fluid flow to the actuator in a regenerative mode.
Another embodiment of the invention comprises a
hydraulic control system for use with a hydraulic
actuator having a movable element and an opening
adapted to function alternately as an outlet and an
inlet for moving the element. A pilot controller con-
trols a supply of fluid at pilot pressure and a pump
supplies fluid at pump pressure to the actuator. The
hydraulic control system comprising a single line
adapted for connection to the opening of the actuator
and a single meter-out valve associated with the line
or controlling flow from th~ opening. The meter-out
valve being pilot operated by pilot pressure from the
pilot controller. A single meter-in valve is posi-
tioned in the line for controlling fluid flow from the
pump to the actuator with the meter-in valve being
operable by pilot pressure from the pilot controller.
These and other objects, advantages, and details
of the invention may be had from the following draw-
ings and description taken together with the accompany
ing claims.
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DESCRIPTION OF THE DRAWING
In the drawing:
Fig. 1 is a diagrammatic view of a hydraulic
control system embodying the invention;
Fig. la is a diagrammatic view of a control cir-
cuit used in conjunction with Fig. 1 along line A-A;
Fig, lb is a diagrammatic view of another control
circuit used in conjunction with Fig. 1 along line A-A;
Fig. 2 is a diagrammatic view of meter-in valves
utilized in the hydraulic control system of Fig. l;
` Fig. 3 is a diagrammatic view of a relief valve
and meter-out valve utilized in the hydraulic control
system of Fig. l;
Fig. 4 is a diagrammatic view of a meter-out valve
utilized in the hydraulic control system of Fig. l;
Fig. 5 is a diagrammatic view of another embodi-
ment of the hydraulic control system of the invention;
and
Fig. 5a is a diagrammatic view of a control circuit
used in con~unction with Fig. 5 along line B-B.
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`: DETA~ILED DESCRIPTION
Referring to Fig. 1 and Fig. la, the hydraulic
system embodying the invention comprises an actuator
` 20, herein shown as a hydraulic cylinder having a
movable rod 21, a head end 21a, a rod end 21b, and
a pair of openings A and B associated with head end
~ 21a and rod end 21b, respectively. Rod 21 is moved
;` in opposite directions by hydraulic fluid supplied
from a variable displacement pump system 22, Fig. la,
`~ 10 which has load sensing control in accordance with
conventional construction. The hydraulic system
` further includes a manually operated controller 23
`~ that directs a pilot pressure to a valve system 24
for controlling the direction of movement of the
actuator, as presently described. Fluid from the
pump 22 is directed to the pump pressure lines P and
passages 26 and 26a to a pair of meter-in valves 27a,
27b, that function to dirPct and control the flow
of hydraul1c fluid to one or the other end 21a, 21b,
of the actuator 20. Each meter-in valve 27a, 27b
is pilot pressure controlled by controller 23 movable
to direct pilot pressure through lines Cl or C2 to
passages 28 or 29 and passages 30a or 31a to one or the
' other of the meter-in valves. Depending upon which
~5 of the meter-in valves is actuated, hydraulic fluid passes
through passages, 32, 33 to one or the other end of the
actuator 200
` The hydraulic system further includes a meter-out
valve 34, 35 associated with each end of the actuator
in passages 32, 33 for controlling the flow o fluid
from the end of the actuator to which hydraulic fluid
is not flowing from the pump to a tank passage 36, as
presently described.
~` The hydraulic system further includes spring
loaded poppet valves 37, 38 in the lines 32, 33 and spring
loaded anti-cavitation valves 39, 40 which are adapted
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to open the lines 32, 33 to the tank passage 36. In
addition, spring loaded poppet valves 41,42 are asso-
; ciated with each meter-out valves 34, 35 as presently
described. A bleed line 47 having an orifice ~9 ex-
tends from passage 36 to meter-out valves 34, 35 and
to the pilot control lines 28, 29 through check valves
77~
The system also includes a back pressure valve
44, Fign la, associated ~ith the return or tank line.
Back pressure valve 44 functions to minimize cavita-
` ~ tion when an over-running or a lowering load tends to
drive the actuator down. A charge pump relief valve
45 is provided to take excess flow above the inlet
requirements of the pump 22 and apply it to the back
pressure valve 44 to augment the fluid available to
the actuator.
Referring to Fig. 2, each meter-in valve 27a, 27b
comprises a bore 50 in which a spool 51 is positioned
and in the absence of pilot pressure maintained in a
neutral position by springs 52. The spool 51 normally
blocks the flow from the pressure passages 26a, 26b to
the passages 32, 33. When pilot pressure is applied
to either passages 30a or 31a, the meter-in spool 51
of the respective meter-in valve is moved in the direc-
tion of the pressure until a force balance exists among
the pilot pressure, the spring load and the flow forces.
The direction of movement determines which of the
passages 32, 33 is provided with fluid under pressure
from passage 26a or 26b.
Referring to Fig. 4, each meter-out valve 34, 35
is of identical construction and, for purposes of
clarity, only valve 34 is described. The meter-out
valve 34 includes a bore 60 in which a poppet 61 is
positioned. The poppet 61 includes one or more pas-
sages 64 extending from an area 63 within the poppet
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to the tank passage 36. A stem 65 normally closes
the connection between the chamber 63 and passages
64 under the action of a spring 66. The pressure in
area or chamber 63 equalizes with the pressure in
- 5 line 32 and the resulting force unbalance keeps
poppet 61 seated. The valve further includes a pis-ton
67 surrounding the stem 65 yieldingly urged by a
spring 68 to the left as viewed in Fig. 4. The pilot
line 28 from the controller 23 extends through a
passage 69 to a chamber 70 that acts against the
piston 67. When pilot pressure is applied to passage
28, the piston 67 is moved to the left as viewed in
Fig. 4 moving the stem 65 to the left permitting
chamber 63 to be vented to tank passage 36 via passage
64. The resulting force unbalance causes poppet 61 to
~` move to the left connecting line 32 to passage 36~
It can thus be seen that the same pilot pressure
which functions to determine the direction of opening
~` of a meter-in valve also functions to determine and
` 20 control the opening of the appropriate meter-out valve
so that the fluid in the actuator can return to the
tank line.
Referring to Fig. 3, each of the meter-out valves
has associated therewith a spring loaded pilot spool
71 which functions when the load pressure in passage
32 exceeds a predetermined value to open a flow path
from the load through a control orifice 62 to the tank
passage 36 through an intermediate passage 73. This
bleed flow reduces the pressure and closing force on
the left end of the poppet valve 61 permitting the
valve 61 to move to the left and allowing flow from
passage 32 to the return or tank line 36. In order
to prevent overshoot when the pressure rises rapidly,
an orifice 72 and associated chamber 72a are provided
so that there is a delay in the pressure build-up to
the left of poppet valve 71. As a result, poppet
valves 71 and 61 will open sonner and thereby control
the rate of pressure rise and minlmize overshoot~
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Referring to Fig. 1 and la, in the case of an
energy absorbing load, when the controller 23 is moved
to operate the actuator 20 in a predetermined direc-
tion, pilot pressure applied through line 29 and pas-
sages 30a, 31a moves the spool of the respective meter-
in valve to the right causing hydraulic fluid under
pressure to flow through passage 33 opening poppet
' valve 38 and continuing to opening B assoclated with
rod end 21b of actuator 20. The same pilot pressure
is applied to the meter-out valve 34 permitting the
~` flow of fluid out of opening A associated with head
end 21a of the actuator 20 to the return or tank pas-
sage 36~
Referring to FigsO 1 and la, when the controller
23 is moved to operate the actuator, for example, or
an- overrunning or lowering a load, the controller 23
- is moved to Cl so that pilot pressure is applied to
passage 31a and to passage 28. The meter-out valve
34 opens before the respective meter-in valve 27a
under the influence of pilot pressure. The load on
the actuator forces hydraulic fluid through the open--
i ing A of the actuator past the meter-out valve 34 to
the return or tank passage 36. At the same time, the
poppet valve 40 is opened permitting return of some
of the ~luid to the other end of the actuator through
opening B thereby avoiding cavitation~ Thus, the
fluid is supplied to the other end of the actuator
without opening the meter-in valve 27b and without
utilizing fluid from the pump.
To achieve a float position, the controller 23 is
bypassed and pilot pressure is applied to both pilot
pressure lines 28, 29. This is achieved, for example,
by the use of solenoid opera-ted valves which bypass
controller 23 when energized and apply the fluid from
pilot pump directly to lines 28, 29 causing both meter-
out valves 34 and 35 to open and thereby permit both
ends of the actuator to be connected to tank pressure.
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In this situation, the meter-out valves function
` in a manner that the stem of each is fully shifted
permitting fluid to flow back and forth between
opposed ends of the cylinder.
In the modified form of the hydraulic system
shown in Fig. lb taken in conjunction with Fig. 1,
a remote controlled circuit is provided wherein the
system may be operated in the normal fashion as des-
cribed above with reference to Fig. 1 and la or in a
10 regenerative mode as presently described. In the
regenerative mode fluid from the rod end 21b of actuator
20 is permitted to flow to the head end 21a via line
33, vented load drop check valve 38a, presently
described, meter-in valve 27b, and to pump pressure
15 lines P wherein the fluid flow from rod end 21b joins
` fluid flow from the pump to head end 21a.
In the modified circuit three remote controlled
two-position valves, such as solenoid operated valves,
are provided to control the flow of pilot pressure
to meter-in valves 27a, 27b and meter~out valves 34,
35, shown in Fig~ 1. In addition a fourth remote
controlled two-position valve is provided to vent a
modified load drop check valve 38a, Fig. lb.,as des-
cribed below.
A first of the two-position valves 75a, is con-
nected to a remote hydraulic pilot controller through
lines Cl, C2 which provide fluid flow at pilot pressure
thereto. First valve 75a is connected to a second
valve 75b and a third valve 75c of the two-position
valves through control pressure lines C1 and C2, res-
pectively. Second and third valves 75b, 75c are in
turn connected through lines Cl and C2 to passages
28, 30, 30a and 29, 31, 31a, respectively, of the
hydraulic control system of Fig. 1. The fourth two-
position or on-off valve 75d is connected between
check valve 38a and tank.
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;~ The modified load check valve 38a, Fig. lb, in-
cludes an orifice 76 and a passage 78 connected to on-
off valve 75do The orifice 76 provides a means of
limiting the amount of flow being vented to the tank.
~ 5 In normal operation on-off valve 75d, is closed
; in the spring offset position and valves 75a, 75b, and
;; 75c are also in the spring offset position permitting
`i control pressure flow in the manner heretofore des-
cribed with regard to the arrangement of Figs. 1 and
la.
When a regenerative function is desired valves
75a, 75b, 75c and 75d are energized. On-off valve
` 75d vents load drop check valve 38a to tank, cpntrol
pressure to both meter-out valves 34, 35, Fig. 1, is
shut-off, and at the same time control pressure applied
~` ~ simultaneously opens both meter-in valves 27a and
27b. The opening of check valve 38a and meter-in
valves 27a and 27b with meter-out valve 34 and 35
` being closed permit fluid flow in the regenerative
mode as described above. Thus, this circuit arrange-
ment permits operation in the normal mode or in the
`regenerative mode, the latter being used where a more
rapid movement of the actuator element 21 is desired.
Where the pressure in the return from end A of the
actuator is excessive, the pilot spool 71 functions
to permit the poppet valve 61 to open and thereby
compensate for the increased pressure as well as
permit additional flow to the actuator 20 through
opening of the poppet valve 40 extending to the passage
which extends to the other end of the actuator.
By varying the spring forces and the areas on the
meter-in valves 27a, 27b and the meter-out valves 34,
35, the timing between these valves can be controlled.
Thus, for example, if the timing is adjusted so that
the meter-out valve leads the meter-in valve, the res-
pective meter-in valve will control flow and speed in
the case where the actuator is being driven. In such
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an arranyement with an overhauling load, the load-
generate~ pressure will result in the meter-out valve
controlling flow and speed. In such a situation,
the anti-cavitation check valves 39, 40 will permit
fluid to flow to the supply side of the actuator so
that no pump flow is needed to fill the actuator in
an overhauling load mode or condition.
With this knowledge of independent control of the
n~eter-out and meter-in valves, varying metering ar-
rangements can be made to accommodate the type of
loading situation encountered by the particular ac-
` tua-tor. Thus, where there are primarily energy ab-
sorbing or driving loads, the spring and areas of the
meter-out valve can be controlled so that the meter-
' 15 out valve opens quickly before the meter-in valve
opens. In the case of primarily overrunning loads,
the meter-out valve can be caused to open gradually
` but much sooner than the meter-in valve so that the
meter-out valve is the primary control~
As shown in Figs. 1 and la, a check valve 77
r` is provided in a branch 78 of each pilot line 28r 29adjacent each meter-out valve 34, 35. The valves 77
allow fluid to bleed from the high tank pressure in
passage 36, which fluid is relatively warm, and to
` 25 circulate through pilot lines 28, 29 back to the con-troller 23 and the fluid reservoir when no pilot
pressure is applied to the pilot lines 2~, 29. When
pilot pressure is applied to a pilot line, the res-
pective check valve 77 closes isolating the pilot
pressure from the tanlc pressure.
As further shown in Figs. 1 and la, provision
is made for sensing the maximum load pressure in
one of a series of valve systems 24 controlling a
plurality of actuators and applyirlq that hlgner
pressure to the load sensitive variable displacement
pump 22. Each valve system 24 includes a line 79
extending to a shuttle valve ~0 that receives load
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pressure from an adjacent actuator through line 81
Shuttle valve 80 senses which of the two pressures
- is greater and shifts to apply the same to a shuttle
valve 82 through line 83. A line 84 extends from
passage 32 to shuttle valve 82~ - Shuttle valve 82
senses which of the pressures is greater and shifts
to apply the higher pressure to pump 22. Thus, each
valve system in succession incorporates shuttle valves
80, 82 which compare the load pressure therein with the
load pressure of an adjacent valve system and transmit
the higher pressure to the adjacent valve system in
succession and finally apply the highest load pressure
to pump 22.
The provision of the load sensing system and
the two load drop check valves 37, 38 provide for
venting of the meter-in valves in neutral SG that no
orifices are required in the load sensing lines which
would result in a horsepower loss during operation
which would permit flow from the load during build up
of pressure in the sensing lines. In addition, there
will be no cylinder drift if other actuators are in
operation. Further, the load drop check valves 37, 38
eliminate the need for close tolerances between the
spool 51 and the bore 50.
In practice, the various components of valve
assembly 24 are preferably made as a part of a valve
which is mounted directly on actuator 20 so that the
need for long flow lines from the valve assembly to
the actuator is obviated.
Although the system has been described in connecton
with a variable displacement pump with load sensing
control, the system can also be utilized with a fixed
displacement pump having a load sensing variable relief
valve. In such an arrangement, the pressure Erom line
81a is applied to the variable relief valve associated
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with the fixed displacement pump rather than the
variable displacement pump with load sensing control.
` It will be apparent to those skilled in the art
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that many changes may be made to the described inven-
tion without departing from the spirit and scope
thereof and of the appended claims.
An example of such changes is in the form of the
i~vention shown in FigsO 5 and 5a. The hydraulic
" control system of Fig. 1 is modified for use with a
` 10 single acting hydraulic actuator 20a shown as a hydrau-
lic cylinder having a rod 21a. Rod 21a is moved only
` in one direction by hydraulic fluid supplied from
pump system 22, Fig. 5a, and may be moved in the
` opposite direction mechanically or by gravity.
In the modified single acting hydraulic system, as
` shown, only the elements of the right half of the double
--acting system shown in Fig~ 1 are utilized to control
actuator 20a.
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In the case of an energy absorbing load, when con-
troller 23, Fig. 5a, is moved to operate the actuator
20a, the controller 23 is moved to Cl so that the pilot
pressure is applied through passage 28 and passage 31a.
The applied pilot pressure moves the spool of the meter-
~` in valve 27b to the right, as viewed in Fig. 5, causing
hydraulic fluid under pressure to flow through passage33 opening poppet valve 38 and continuing to inlet B
of actuator 20a.
- When the controller 23 is moved to operate the
actuator for a lowering load, the controller is moved
to C2 so that pilot pressure is applied to passage
29 and the meter-out valve 35 opens. The load on the
actuator forces hydraulic fluid through opening B past
the meter-out valve 35 to tank passage 36.
~` When large actuators are required, for example, in
large fork lift trucks and off-highway equipment having a
large double acting cylinder and high area ratios exist,
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an appropriately sized large volume single acting
system may be used to control the head end of the
.cylinder and an appropriately sized small volume
single acting system may be used to control the
rod end of the cylinder.
.When, in the interest of safety, an absolute
~`load lock is required and no piping is allowed
between the head end and the rod end of a cylinder
subject to overrunning loads in both directions~
a pair of single acting systems may be placed at
each end of the cylinder.
