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Патент USA US3078684

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Feb. 26, 1963
3,078,674
A. F. ANDERSON
HYDRAULIC CONTROL SYSTEM FOR VARIABLE DISPLACEMENT PUMP
Filed Feb. 18, 1960
9 Sheets-Sheet 1
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INVENTOR.
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3,078,674
HYDRAULIC CONTROL SYSTEM FOR VARIABLE DISPLACEMENT PUMP
Filed Feb. 18, 1960
9 Sheets-Sheet 2
INVENTOR.
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Feb. 26, 1963
A. F.‘ ANDERSON
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Filed Feb. 18, 1960v
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Feb. 26, 1963
A. F. ANDERSON
3,078,674
HYDRAULIC CONTROL SYSTEM FOR VARIABLE DISPLACEMENT PUMP
Filed Feb. 18, 1960
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9 Sheets-Sheet 4
Feb. 26, 1963
A. F. ANDERSON
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HYDRAULIC CONTROL SYSTEM FOR VARIABLE DISPLACEMENT PUMP
' Filed Feb. 18, 1960
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HYDRAULIC CONTROL SYSTEM FOR VARIABLE DISPLACEMENT PUMP
Filed Feb. 18, 1960
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HYDRAULIC CONTROL SYSTEM FOR VARIABLE DISPLACEMENT PUMP
Filed Feb. 18, 1960
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United States Patent
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3,078,674
Patented Feb. '26, .1263
.2
3,078,674
HYDRAULIC CONTROL SYSTEMJFOR
VARIABLE DISPLACEMENT PUMP
_
"This is accomplished in the :system‘ of this invention. by
communicating the high pressure ‘?uid on the outputr'side
of the pump with the control ‘apparatus which‘actuatesi the
,
pump displacement control memberlsota‘s to ‘overpower the
control apparatus which isv maintaining the displacement
Arthur F. Anderson, Livonia, Mich., assignor -to Gar
Wood Industries, Inc., Wayne, ~Mich., a corporation of
Michigan
control mem-ber'in a~positive displacementposition. '
Another object-of this inventioniis to provide a control
system for a variable displacement ipumplwhichiincludes
a separate hydraulic control circuit. operable to actuate
This invention relates generally to pump control: systems 10 the pump so that it will pump ?uid? in either‘ofitwodirec
and more particularly to a hydraulic control system for
tions to the hydraulic device ‘which is being‘ controlled.
a' variable displacement pump.
‘A- further object of this invention is to provide a‘hy
In a system in which a variable displacement pump is
draulic control system for a variableldisplacementj'pump
‘used to operate a hydraulic device, a provision for actuat
‘and a hydraulic-device operated thereby?which;,.includes
Filed Feb. 18, 1960, Ser. No. 9,461
'29 Claims. (CI. 60-52)
ingthe pump to substantially “zero” displacement in the
limit positions of the hydraulic vdevice is desirable, because
a super-charge ‘circuit that replenishes the operating circuit
to maintain the operatingcircuitfsubstantially‘vfulllat all
this eliminates unnecessary heating of the system due to
times.
circulation of the hydraulic ?uid, and'makes it possible
,
Another object of this invention “is ‘to’ provide - in'f'a
to use the power required for operating the pump for
hydraulic ‘ control' system‘ 1 for *a ''variable ‘displacement
other useful purposes. By “limit position” is meant ‘a
pump, means for'automatically relieving thejj-pressure’in
position in which the hydraulic device cannot be moved
the‘ operating "circuit 'during ‘the time’ the epump'edispla'ce
in-a direction in which'?uid :from the-pump tends to
rnent control‘ member is ‘being 'movedtowa'r‘d‘ a ".“zero”
move it, either becauseof the structure of the hydraulic
"displacement or “neutral”-'position so ‘that the‘pre'ssure
device/or some external force applied to it. The‘invention
‘in the system does not exceed=a‘predetermined-maximum
‘is best understood by referring to a‘system in which a 25 pressure, thereby requiringcoriditiohing of Elie-‘system
variable displacement "pump of reciprocating vpiston type
‘for ‘withstanding only this predetermined maximum
operates a hydraulic cylinderassembly that raises and
pressure.
lowers a dozer blade mounted on 'the front-:end'of'a
Still ‘another object otithis yinventi'on'is to’provide 4a
tractor. 'In a pump of'this type,1which' is'idescri-bedtin
control system *for a‘ivariable displacement‘pump"which
detail ‘ in ‘my _ prior application Serial »No. ‘ 835,002," ?led
provides’ for movement of the vpump‘ displacement “con
August '20, 1959, and 'now abandoned, a'movable tilt
\box'is angularly adjustable relative to the'axis ‘of'rotation
of the cylinder barrel to control’the-displacement of the
'trol member to's’u-bstantially a-“neutral” "position‘fromra
positive displacementposition in either direction fromthe
“neutral” ' position without any “hunting” of ' the member
"pistons. When the tilt box is perp'endicularto‘ the-‘axis of
"cylinder barrel rotationf'thepistons ~have=noestroke= and
35
‘no’ ?uidis- pumped. ‘This is called'the “zero” displacement
or “neutral” position of the tilt box which'is" hereinafter
sometimes generally referredv to as the pumpdisplacernent
control member. When the tilt boxi'is movedin either
direction from the perpendicular‘ position ?uid- is'pumped
for the‘ “neutral”, position.
I
.
H
,
jFurther objects, features‘and'advantages of vthis inven
‘tion will become apparent :_from ya consideration v:of ‘the
following description, theiappended iclaimsrand 'the’a'e
companying drawing in which:
_
I
FIGURE ,1 is a' fragmentary‘ side ‘ elevationalyiew' of
a ‘tractor having a dozer blade“ which‘is, raised fand‘lowe
'Y‘by'the pump'in one or the other directions depending on
the‘ direction oflmovement'of'the tilt box. ‘The greater
'the'extent of movement of the 'tilt'b‘ox from 'the‘perpen
*dicular position, the'greater the stroke of the-pistons‘and,
‘by the control system of‘this' invention;
of engine power for unnecessary pump ‘operation is ‘to be
avoided if possible. Consequently, in‘ limit positions of the
hydraulic cylinder assembly it ‘is desirable to have the
.FIGURE 3 is a ‘diagrammatic viewofthe control‘sys
tem of thisinvention, shown associated-with a variable'dis
mu by a hydraulic cylinder'assembly .whichis actuated
' FIGURE‘Z is an enlarged fragmentary elevational view
of a portion of the vtractor vandnpurnp'mounting'shownjin
consequently, the greater the output of‘the pump. 'When 45 FIG.
1, with some parts. broken'away forjthe ‘purpose‘of
the pump is driven by the tractor; engine,'anyv diversion
clarity;
'
'
'tilt box moved from a full to substantially a “zero” Jdis 50
placement pump of reciprocating‘ piston type ‘and-the
.an. improvedhydraulic control vsystem for a variable dis
tion;
hydraulic cylinder‘ assembly shown'in' Fig. 1,- and illus
<placementposition so that substantially the full ‘power
strating the system‘is a “hold” condition, -namely,":a con
of the engine is available ‘for purposes other than'operat
dition for holding the ‘piston in the’cylinder-easser'nbly,
ring-the pump‘ at full pressure and unnecessarily‘ heating
and consequently the do'zer'blade, ‘in a‘ ?xed positioniwith
‘the control system. It is 'also't'desirable in systems of this
to the front‘ end of the tractor.
’’
type to provide for a flow of replenishing ?uid to'the 55 respect
FIGURE
4
‘is
a
diagrammatic
view‘
of
;the1"system
‘of
main pump circuit to replace the piston rod when it is
vthis inventiomlillustrated similarly to ‘FIG."3, showing'ithe
‘moving out of the cylinderassembly and to compensate
system in'a “raise” condition, in'which thejdozer'jblade
for leakage at the pump, which is a necessary characteristic
will be moved upwardly;
of pumps of this type since'a lubricating'layer ofl'?uid
FIGURE‘ 5 is a ‘diagrammatic view, illustratedisimil'arl-y
must be provided between the rotating cylinder barrel ‘and 60
‘to FIG. "4,‘ showing'the ‘system in-a"“raiseeoverload” ‘con
the adjacent stationary valve 'fa'ce through which ?uid
dition, namely, a condition in which the dozer ‘blade has
is supplied tothe pump and discharged from'the pump.
been raised to a limit position and‘ further effort bylthe
When the cylinder ismaintained‘substantially full/of’?uid
pump to raise thelblade has raised vitheipressure on5the
'at all times, an, immediate response‘ of thecylinder as
sembly to operation of the control (valve therefor is 65 output side'oi' the pump to-a predetermined safety limit at
which the system has operated to'move the pumpdisplaoe
insured.
'ment control memberto a substantially‘ “neutral” posi
It is an object ofthis invention, therefore, to provide
FIGURE 6 is a diagrammatic View ‘illustrated similarly
placement pump which provides __for an automatic actua
"tion of the pump displacement control member tosubstan~ 70 to~-FIG.' 3" showing the system 'in‘a “lower” condition,
tially a “zero” displacement position when theipump out
namely, a condition providing,for'downward-movement
put pressure exceeds a predetermined maximum‘pressure.
of the ‘dozer blade;
8,078,674
FIGURE 7 is a diagrammatic view illustrated simi
larly to FIG. 6, showing the system in a “lower-over
load” condition;
v
7 FIGURE 8 is a. diagrammatic view illustrated similarly
to FIG. 3, showing the system in a “?oat” condition;
FIGURES 9 and 10 are'enlarged sectional views of
one of the valves in the control system of this invention,
showing two positions of the valve;
4
valve 46 over which the pump 42 pumps to tank, a check
valve 48 which communicates with one side of the pump
12 and a pilot~operated check valve 50 which communi
cates with the opposite side of the pump 12. In the illus
trated embodiment of the invention the check valve 46 is
set to provide a pressure of about 50 psi. in this circuit
and the pump 42 is capable of pumping about 28 gallons
per minute.
The control circuit includes a gear pump 52 which is
FIGURE 11 is a fragmentary sectional view of a modi
?ed form of the control valve shown in FIGS. 9 and 10, 10 connected through a line 47 to one side of a check valve
54 that is connected on the opposite side by a line 49 to
showing the valve in assembly relation with the housing
the
supercharge circuit. In addition, the control circuit
for the variable displacement pump and illustrating the
includes the control valve 34 and a pair of substantially
valve in one position;
identical control valves 56 and 58 which control a pair of
FIGURE 12 is a fragmentary sectional view of the
tilt box actuating pistons 60 and 62, respectively, which
15
modi?ed valve shown in FIG. 11 illustrating the valve
‘are axially aligned and disposed on opposite sides of the
in another position; and
,
. pump 12 for moving the tilt box. In other words, con
FIGURE 13 is an enlarged view of the encircled por
trol ?uid can be directed through either one of the pilot
tion of FIG. 12 indicated by. the numeral 13.
valves
56 and 58 to extend either one of the pistons 60
, With reference to the drawing, the hydraulic control
system of this invention is illustrated in connection with a 20 and 62 to move the pump tilt box in a desired direction to
obtain the desired flow of ?uid from the pump 12. In
variable displacement pump 12, of reciprocating piston
the
illustrated embodiment of the invention, the pressure
type and described in detail in my prior application Serial
in the control circuit is about 400 p.s.i. and the pump 52
No. 35,35,002, ?led August 20, 1959, mounted on a
is capable of pumping about 8 gallons per minute.
tractor?14 for operating a hydraulic cylinder assembly 16
The pump 12, which is described in detail in my prior
to raise and lower a dozerzblade 18. However, it is to 25 application referred to above and is only shown diagram
be understood ‘that whilethe control system of this in
matically, includes a casing 61 having a tilt box 63
vendor} has particularputility in the illustrated installa
mounted
therein for rotatable movement in opposite direc
tion, the system has general utility in systems which in
tions about an axis perpendicular to the plane of the paper
clude ‘variable displacementnpumps. As used herein,
30 in FIGS. 4 and 6 between the limit positions illustrated
“variable displacement pump” means a positive displace
_
I ment
pump
which can be adjusted at a given speed 0
operation to vary the volumetric displacement.
.
‘The cylinder assembly 16 includes a cylinder member
therein in which the actuating pistons 62 and 60 bottom
in their respective cylinder supports. The tilt box 63 is
provided with an actuating arm 65 disposed between the
control pistons 60 and 62. A pair of spring assemblies
20 which is pivotally mounted on the front end of the
173 are associated with the pistons 60 and 62 and are
tractor, a piston 22 (FIG. 3), and a piston rod 24 which 35 initially
accurately adjusted so that they constitute yield
extends through the lower end of the cylinder and is con
able
abutments
which exert no force on the pistons 60 and
nected at its lower end to the dozer blade 18. A dozer
62 in the zero displacement position of the tilt box 63.
bladesupporting frame 26 which is pivotally supported at
Each spring assembly 173 will compress and yield so as
its rear end on shafts 28 carried by the tractor 14 has
the dozer blade 18 mounted on the front end thereof so 40 to permit retraction of its piston 60 or 62 when a retract
ing force is applied to the piston. The details of assembly
that the blade is forwardly of the front end of the tractor
of the spring assemblies 173 with the pump 12 are included
14. The pump 12 is hydraulically connected to the cyl
in my copending application referred to above.
_ inder assembly 16 for moving the dozer blade 18 between
, As shown in FIG. 2, the drive shaft 67 for the pump 12
‘ its upper position shown in broken lines and its lower
is driven by a tractor engine-driven shaft 69 disposed
position shown in full lines. A handle 30 mounted on
below the tank 44 which is mounted on the front end of
the tractor 14 at a position for convenient operation by
the tractor 14 and provided with a ?ll neck 45. The gear
the operator is connected to a control valve 34 which con
pumps 42 and 52 are driven from a common shaft and
trols the operation of the pump 12.
are mounted in a casing 55 located within the tank 44 and
The control system, which‘is indicated generally by
communicating with ?uid in the tank 44 through a ?lter
the-numeral 10 and is ‘illustrated diagrammatically in
53. The pump 12 is mounted on a valve block 71 at the
FIGS. 3-8, inclusive, is made up of three related circuits, 50 front
end of the tractor and a gear train 73 is provided on
namely, a main or cylinder operating circuit which in
the block 71 for transmitting driving power from the shaft
cludes the pump 12 and the cylinder assembly 16, a super
67 to the pumps 42 and 52. The check valve 54 is.
charge or makeup circuit which replenishes ?uid in the
mounted in a casing 57 disposed within the ?lter 53, the
main circuit to compensate for pump leakage and move
valve 46 is mounted on one side of the valve block
ment of the piston rod 24 into and out of the cylinder 20, 55 check
71, and a housing 59 which projects forwardly from the
and a control circuit which includes the valve 34 and
is provided for hydraulically actuating the pump 12 to
achieve the desired movement of the dozer blade 18.
' The main circ_uit includes, in addition to the pump 12
valve block 71 at a position above the pump 12 encloses.
the valves 36, 38, 40, 48 and 50 which communicate
through passages in the valve block 71 and the housing 59
and the cylinder assembly 16, -a pair of substantially ident 60 with the pump 12 and the tank 44 in a manner hereinafter described. The valves 56 and 58 are mounted on.
ical cylinder holding check valves 36 and 38 connected
the pump casing 61.
to the upper and lower ends, respectively, of the cylinder
While the pump 12 is normally controlled by the con
20 and a cylinder ?oat control valve 40 disposed between
trol circuit, under overload conditions the pump 12 is
the valves 36 and 38 and closed except in the “?oat” con
controlled by ?uid on the output side of the pump 12.
dition of the system 10. Each of the valves 36, 38 and
Under such conditions when the pressure on the output
40 is constructed for pilot operation, as will more clearly
side of the pump rises to a predetermined high pressure,
appear hereinafter. The pressure in the main circuit, in
?uid under pressure from the pump 12 is applied to one
the illustrated embodiment of the invention in which the
cylinder assembly 16 raises and lowers a dozer blade 18, 70. of the control pistons 60 and 62 so as to immediately
stroke the pump 12 toward a zero displacement position.
may be as high as 1500 psi. on the output side of the
As used herein, “stroking of the pump” refers to rotation
pump 12, which is capable of pumping 150 gallons or
more'of ?uid per minute.
_ d
_
The supercharge circuit'includes a gear pump 42 con
nected to a tank or reservoir 44 for the system 10, a check
‘ of the tilt box 63 in either direction so as to vary the stroke
of the pistons in the pump.
The operation of the system 10 can be better understood
5
33078374
6
if Ithe‘valves in thesystem are ?rst described in :detail.
The control valve 34 includes a'casing 64 in which a spool
v66 is mounted for reciprocal movementand which is con
nected ‘through ports 68, 70 and 72 to the tank 44. The
spool 66 has a stern 66a'which is connected to the handle
.30 so that the handle 30 is operable to reciprocate the
the pressure at the port 156‘ is sufficient to move the valve
memberv 148 in the opposite direction, the valve member
‘spool 66. The casing 64 has three outlets 74, 76 and 78
‘for ?uid under, pressure 'and Ya pair of ‘inlets 80 and 82.
The‘spool '66 is shiftable ‘longitudinally of the casing 44
‘between “holdj? “raise,” “lower” ‘and “?oat” \ positions,
shown in FIGS. 3, 4, 6 and 8, respectively, which are
.stantially identical only the valve 58, enlarged views of
which ares'hown inFIGS. 9 and lO,.will be described-in
As used herein, the term “line” refers to a passage,
‘shaped grooves 192 in the piston .186 are located so that
vvalve member toward the oppositeend of ‘the casing"
.against-‘the. pressure of¢?uid at'the .port .156. .Whenever
1481's movedto thepositionshown in FIG. 8 in which the
lines 142 and 144 are ?uid connected through the valve 40.
Since the tilt box control valves 56 and 58 are,-sub~
.detailwith alike numerals indicating like parts on the
‘valves. The valve 58 includes a casing_170 thathas a port
hereinafter described in detail in connection with a detailed
172 which communicates witha cylinder support 174 for
description of the operation of the-system.
:the ‘control piston'62. A port 176 in the casing'l170com
'The pilot-operated check valve 50 includes a valvestem
.municates through a line 178 with the outlet port 78in
90 which is guidably mounted in a casing 92 and is pro 115 .thescontrol valve 34. ._.A port 180win the casing1~70 com
vvided adjacent one end with a valve member 94. The
municates with tank 44. A pair ofspaced annular walls
opposite'end'of the stem engages a ball 96 which is urged
182 and 184 in the casing 170 separate the ports.172, 176
byfalspring'98 into a position closing'a valve passage. 100
and 7180. Apiston‘186 is slidablyusupported onthe walls
‘in the casing '92. The casing 92 hasv one end 91provided
.182 and 184 andis urged by a spring 188 toward aposition
with an opening that communicates with a line ‘104 and the :20 “engaged with an annular seat 191 which ‘surrounds. aport
'opposite end 93 of the casing ‘92 is closed.
{-190 at one end of the casing. Aplurality of keyway
conduit, tube or the like, through which ?uid can?ow
from one point to another.
When the'passage 100 is
theyextend across'the wall 184 (FIG. 9) whenthe piston
is engaged withvthe seat:191.
‘closed, comrnunication of a ?uid line 102 on one side of :25
The port .172 for the valve .56 communicates with a
passage 100 with the line 104 ‘on the opposite side is
supporting cylinder 175 for the control piston~60 and the
blocked. The line 102 connects to a line v106 extending
-port 176.communicates .throughaline194 with the outlet
between pump 42 and relief valve 46 and line 104 connects
_port 76 in the control valve 34.
I
.
to a line ‘108 which ‘extends between pump 12rand check
:The ports 19‘0,>which undercircuit overload conditions
valve 36. The portion of the casing 92 between-the closed I30 hereinafter described constitute inlet ports vfor ‘the valves
‘end 93 and the valve member 94 communicates with'one
56 and 58, are connected to the ends oflines 196 and 200,
:end of a line 110 connected at its opposite end to the valve
‘respectively. The oppositeend of the line 196 iscon
"36. When the pressure in‘the line 110 is above the pres
.nected to .the inlet port fora peakingrelief valvev 198. and
sure in line 104, the ?uid under pressure from line 110
.the opposite end of. the .line200 is connected to the inlet
"acting on valve member 94 will move the valve stem 90 ' “ . port for a peaking relief valve 202.
vso ‘as to move the ball v96 out of a position closing. the valve
passage 100, against the-pressure of spring '98, which-is
The peaking relief
vvalves 198, andr202 are identical, each including a casing
204 having an inlet port 206 and anoutlet. port 208' and
a valve member 210 urged by a spring 211 toward a seated
small.
Since the cylinder holding check valves 36 and 38 are
position closing the‘inlet port206. In the valve 198 the
‘substantially identical, only the valve .36 will vbe herein :40 port-i206 communicates with the .line 196 and the outlet
after describedin detail, with like numerals on the two
.port'208communicates with a line 212 which connects to
vvalves indicating like parts. The valve 36'consists of 'a
the line 108. In the-valve .202 the inlet port 206 com
casing 118. in' which a hollow elongated plunger member
-__municates with the line 200. and the port 208 communi
120, provided at one end with "a stem 122, is mounted
cates with‘ axline 214~which is connectedto -a line/216
for ‘reciprocal'movement. The stem 122 is formed inter
'that-extendslbetween
thepump 12 and the valve '38. vA
mediate its ends with a shoulder 124, and a disk 1% is 45 line 218'extends between the-line 216 and the line1110
*slidably supported on the‘valve stem 122 for .movement
which is in turn connected to the 1ine196 bya line 220
in one direction to a position engaged with one end1128 of
..for a pnrposeto appear‘ presently. A line 222 connects
"the casing 118' and in the opposite direction to ‘a position
the line 200 and the line 108 and a line 224 connects the
engaged with the shoulder 124. A spring 130 positioned
line 222 andv the valve 38 also for a purpose to-appear
.withinrthe hollow plunger 120and engaged with the op
posite end 132 of the casing 118 urges the plunger 120
'. in a direction to seat an inclined'surface 134 on the plunger
member 120 against a correspondingly inclined surface
presently.
‘T
Operation
The operation of the control System10 can now be
.136 formed in the casing 118. An opening ‘138 in'the
understood by‘ explaining'how the va'riouselements of the
casing 146 having a valve ‘member 148‘ disposed therein
since nopressure‘is' being applied to the control pistons
60 and 62 the tilt box ‘63 is in a “zero” displacement posi
plunger 120 provides for a ‘constant communication-,ofthe 65 system react to movement of the control'valve 34 to the
“hold,” “raise,” “lower” and “float” positions illustrated
“spring urged side of the plunger 120 with a port 140 in the
'in FIGS. 3L8, inclusive.
“casing 118. The port 140 communicates with'a line 142
-' First assume that the valve 34 is moved to its “hold”
‘extending between the valve 40 and the closed. end of the
position illustrated in'FIG. 3'for the purpose of: main
'cylinder 20. The corresponding'port 140 in the valve38
communicates with a line 144 which-extends between the 60 taining itheblade'lS in a'?xed vertical position with re
spect to‘the-front end ‘of the tractor 14. In this position
-~valve 40 andthe piston‘ rod end of the cylinder .20.
of vthe- valve 34, the control pump 52 is supplying ?uid
The cylinder ?oat control valve ~40'thus communicates
--to the valveinlet ports 80 and 82 both of which’ com
‘.011 one side through the line v142 with the cylinder 20 ,on
rnunicate through the‘valve’casing 64 with the tank port
the top side of the piston 22 and 'on the opposite ‘side
‘70 so that no pressure is being developed by the control
through the line 144 with the cylinder 20 on thebottom
pump 52 and the relief valve 54 is closed. Consequently,
side of the piston 22. The control valve40 consists of .a
'and provided at one end 154 with a port 150 which com
‘tion and no oil is being pumped by the pump 12. ‘The
municates through a line 152 with the’line 106 which is
connected to the output side of the supercharge pumpv42. 70 supercharge pump 42 is pumping over the relief valve 46
‘to tank 44 so the pressurerequired to open thev valve
,A port 156 at the opposite end of'lthe casing 146 com~
146 determines the pressure developed by the pump '42.
municates through a line 158 with the outlet port 74 in "the
"Theva'lves 48 and 50 are set to open at a pressure vb'elow
control valve 34. A spring 160 :extends between the eas
' this pressure‘ and'the volume outputof pump 42 is “such
ing end 154 and the valve member 148' forurging='the 75 'that'the full-volume of ?uid ‘from? pump 42 is“ greater than
3,078,674
.
7
will ?ow through valves 48 and 50 at a pressure below
the pressure at which relief vale 46 opens. At this pres
sure su?icient ?uid will ?ow through relief valve 46 under
all conditions to prevent a pressure rise in the supercharge
circuit above the pressure at which valve 46 opens, which
"is hereinafter referred to as “supercharge pressure.”
Fluid under a supercharge pressure is supplied to both
8
The pump 12 has two ports ‘or openings, shown dia
grammatically at 230 and 232, either one of which can
function as the pump inlet or outlet depending on the
direction of tilt of the tilt box 63, as described in my
copending application hereinbefore referred to, and in
the position of the tilt box 63 shown in FIG. 4 the valve
port 230 communicates with the cylinder bores (not
shown) in the pump 12 when the pistons in these bores
the cylinder holding check valves 36 and 38, and in the
are on their suction stroke. Consequently, the port 230
illustrated embodiment of the invention this pressure on
functions as the inlet port for the pump 12 and the other
the valve members 120 is not sui?cient to overcome the 10 pump port 232, which communicates with the cylinder
force of the springs 130. This is because the springs 130
bores during the time the cylinders in these bores are on
are strong to insure quick and positive closing of the check
their discharge stroke, functions as the pump outlet.
Fluid under pressure from the pump port 232 flows
invention, a spring 130 exerts a force of about one
through the line 216 to the valve 38 and moves the
15
hundred pounds on its valve member 120. However, even
plunger 120 off its seat 136 so that ?uid ?ows through
if the springs 130 were weak enough to permit opening
the valve 38 and line 144 into the lower end of the cyl
valves 36 and 38. In the illustrated embodiment of the
of a valve 36 or 38 under supercharge pressure, the sys
tern 10 would work satisfactorily so long as the weight
inder 20 so as to raise the piston 22. Fluid from line
216 ?ows through a line 234 to the relief valve 48 and
of the dozer blade 18 is suf?cient to maintain the pressure
on the spring side of valve member 120 in valve 38 closed 20 keeps the valve closed.
Fluid in the cylinder 20 above the piston 22 is ex
against supercharge pressure on the opposite side. If the
hausted
through the line 142 and is returned to the pump
valve 36 opens under supercharge pressure, there will
12
through
the open valve 36 and the line 108. The
only be enough ?ow therethrough to ?ll the cylinder 20 on
valve 36 is maintained open by ?uid under pressure from
the top side of piston 22, following which the valve mem
the pump 12 supplied through the line 218 to a pilot port
ber 120 will seat because the pressures on opposite sides
219 in valve 36 so as to move the disk 126 toward the
thereof will be equal.
right as viewed in FIG. 4 to unseat the valve plunger 120.
Normally, the cylinder 20 is full and the cylinder hold
ing check valves 36 and 38 are closed and prevent move
The volume of ?uid exhausted from the closed end of
the cylinder 20, during upward travel of the piston 22,
ment of the piston 22 in either direction in the cylinder,
exceeds the volume of ?uid being supplied to the piston
and the shut-off valve 40 blocks communication of oppo 30 rod end of the cylinder 20 because of the space in the
site ends of the cylinder 20.
,
cylinder 20 occupied by the piston rod 24. Consequently,
Since the piston 22 is unbalanced in the system of this
the volume of ?uid ?owing toward the inlet port 230 ex
invention, meaning that the areas on opposite sides
ceeds the volume of ?uid being pumped out of the pump
thereof are unequal, it must be weighted su?iciently to
12 through the outlet port 232. The excess ?uid ?owing
35
raise the pressure on the small area side enough to main
to the pump inlet 230 ?ows back to the tank 44 through
tain the valve 38 closed against supercharge pressure, in
the pilot operated check valve 50 which is maintained
the event the spring 130 will not accomplish this purpose,
in an open position, illustrated in FIG. 4, by ?uid under
to prevent the piston 22 from moving downwardly when
main pump outlet pressure supplied to the valve 50
valve 34 is in a hold position. In the use of the system
of this invention with a piston 22 which is not weighted,
and with a spring 130 which will not hold the valve 38
closed against supercharge pressure, the piston 22 must
be balanced, as by extending the piston rod 24 completely
through the cylinder 20, if the piston 22 is to be main
through the line 110 so as to move the valve member 94
in a direction to unseat the ball 96. A restriction 111
is provided in the line 110 to prevent a surge of ?uid to
the valve 50 tending to move the (valve parts so rapidly
as to decrease the wear life thereof.
The spring 188 in the pump control valve 56 is ad
tained in a ?xed position in cylinder 20 in the “hold” ~ justed to prevent unseating of the piston 186 when the
position of the control valve 34. The valves 48 and 50 45 pressure of ?uid on the outlet side of pump 12 is at or
are shown open but of course as soon as the lines 108
and 216 are ?lled with ?uid from the pump 42, the valves
48 and 50 will close since the ?uid pressures on both sides
of each valve will be the same, and the full output of ?uid
£12111: pump 42 will ?ow through the relief valve 46 to
ta
.
It can thus be seen that in the “hold” position of the
below the predetermined maximum pump operating pres
sure, which in the illustrated embodiment is about 1500
p.s.i. This pressure is determined by the capabilities of
the pump 12 and the other components of the system 10
and is adequate for moving the blade 18 to accomplish
the usual work operations for which the tractor and dozer
valve 34, the dozer blade 18 is held in a ?xed position
assembly is intended.
relative to the front end of the tractor 14.
When it is desired to raise the dozer blade 18, the con
struction which prevents raising movement of the blade
However, in the event the blade 18 encounters an ob
18 or, as more often happens, in the event the piston 22
trol valve 34 is moved to its “raise” position shown in
engages the closed end of the cylinder 20, continued oper
FIG. 4 in which ?uid from the pump 52 supplied to the
ation of the pump 12 causes an immediate rise of the pump
inlet port 80 is blocked by the spool 66 against travel out
pressure to a pressure above the predetermined maximum
of the casing 64 and ?uid supplied to the inlet port 82
?ows through the casing 64 to the outlet port 78. Line 60 pressure which is high enough to unseat the piston 186 in
the valve 56 as shown in FIG. 5. Fluid then ?ows into
194 is now in communication with tank port 68 since in
valve 56 through port 190 and from valve 56 into the cyl
this position of the control valve ?uid may pass around
inder support 175 for piston 60 through port 172 so as to
the upper end of the spool 66, as well as through the
extend the depressed pump operating piston 60 and move
grooves thereat, as can be seen in FIGURE 4. Fluid
the tilt box 63 toward its “zero” displacement position.
from the outlet port 78 ?ows through the line 178 to the
Since some time is involved in moving the tilt box 63 to
inlet port 176 in the valve 58. Since the piston 186 is
substantially its “zero” displacement position, and since
seated, ?uid from the port 176 ?ows through the piston
the pressure in the system 10 on the output side of the
grooves 192 to the valve outlet 172 and into the support
pump 12 is continually rising during this time, the peak~
cylinder 174 for the pump control piston 62. The con
ing relief valve 198 is provided to limit the pressure. In
trol piston 62 is extended by this ?uid to thereby tilt the
the illustrated embodiment of this invention, the spring
tilt box 63 in a clockwise direction to the limit position
211 in valve 198 is adjusted so that the valve member 210
shown in FIG. 4. Excess ?uid from pump 52, over and
above that required to extend piston 62, ?ows through the
check valve 54 and the line 49 into the line 106 in the
supercharge circuit.
. moves off its seat at a peak pressure of about 1700 psi.
Consequently, the valve 198 will open to dump enough
76 ?uid from the pump outlet line 216 to the inlet line 108 to
9
10
lower the pump output pressure to below 1700 p.s.i. v'To
accomplish this it is not necessary-thatthearelief valve
is "maintained in fthegpositio-n "at which‘ raisingixmovem'ent
i-‘WaSP-StOPPEd.
198 be of a large size su?icient to carry thelentire pump
In the event "downward movement-'ofithe vblade 18. is'de
I output. ' It is only necessary that the'valve-198 be capable
of carrying about 30 to 40 gallons per minute of ?uid.
'Since no relief has beenprovided for the ?uid on'the
:Isired,~ the. control'valve34 is moved. to'its ‘.-‘down”' position
:. shown in :FIG. .6, in .which .the valve spool "66' isgintra
I'jpOSltiOH'lIl which the‘i'nlet port 82 is' blocked'and'the inlet
~ outputside of the pump 12, otherithan to prevent‘ the pres
' sure from rising above 1700 p.s.i., a pump output pressure
I of’ about 1500 psi is maintained. ‘Since'there is no'?ow
~port/'74communicateswith the tank-port 68 and theoutlet
:..port . 80 communicates with. the. outlet’port 76. “The. outlet
:port '78communicates with the tank port 72. ’ Fluid-under
through'valve 38, it closes tightly to trap ?uid in cylinder Y'110 -.';pressure :from the-port. 7.6. ?ows through‘. line .194 ito . the
20 which is on the underside of the piston 22 and which
sinlet-tport 176-in valvec56rjfor ?ow. outtheiport 172:.into
d-sat-about ‘the 1500‘ psi. pressureso that the blade 18
does not fall.
i the cylinder 175. so .as to extend the'control piston 60 and
;rotate-_the~_tilt box- 63 .in-aa counterclockwise jdirection,ias
viewed _,~in;.-FI'G.; 6. .‘Some: of ‘the. ?uid in .the cylinder.174
'When the piston 186 is unseated (FIG. 10) some of the
?uid suppliedthrough poi-1:190 to valve‘ 56 ?ows through P15 j~is~exhausted,~during1 retraction of piston 62,.through the
‘the grooves 192 to the port .176-and'into line 194which
communicates with the tank port~68 in control valve 34.
~The grooves'192 are located relative toithewall 184-and
valve 58,_the.line 178 and the control valve tank port 72.
Assume that the blade 18 is encountering an obstacle,"such
.-?as the ground. surface which resists wits downward ~move
are of a-size such that theycon-stitute: a restriction to ?ow
..ment so that the piston r0d'24 isiunder compression.
I through the valve'56 from port 190 to tank when the, pump 5.20
The pump 12 now'operates-so that the ‘port-230 func
v12*is pumping at full volume capacity. Consequently,
.,tions.as theoutlet port and the port 232 functions asthe
rsorne i?uid entering. valve .56 through portl190?ows out
‘inlet'port. Fluid is pumped out of the port ~230..and
through port 172 into cylinder'175 and causes arise in the
.travels through‘ the. line ‘108 to thecheck valve 36,'where
pressure‘in cylinder 175 until vthe combined force of the
.it, unseats the. valveplunger 120 and‘ travels out the .‘port
'w?uid. and spring assembly 173 tending to extend pistoni60 V25 140 and through the line,142 to the closed end. of the‘ cylin
exceeds the oppositely directed force on piston 62. so that
..der..20. so as to exert a. pressure on the'top-side ofpiston
the piston 60 is extended. ‘During extension of piston 60,
T22 which moves-the piston downwardly, to infturn move
the tilt .box 63 is rotated toward its neutral position.
the dozer~blade<18 downwardly. .»Since the ?oat: control
This causes a corresponding reduction in the volume of
.shut-o?valve 40 is closed no ?uid under pressure is. sup
‘?uid being pumped by the pump 12 through the port 190 f» 30. plied tothepiston rod‘ end of the cylinder 20.
*for valve 56, until at someposition of piston 60 short/‘of
.As the-piston22-moves downwardly, ?uid is ‘exhausted
-.a centered position of tilt'box 63, the volume of ?uid being
‘from the cylinder 20 through the line 144, theiopen valve
pumped into valve ‘56 through port‘190-equals the volume
.>_38..and .the line “216. to -_the_,;pump inlet >232. Thevalve 38
of'?uid ?owing through the~grooves 192. .In: this equi
is .maintainedopen by ?uid under pump. outletgpressnre
'Jibrium position of the piston 186 in valve 56,'the-force 35 . supplied to.,the pilotinlet>219 for the valve 38. through the
exerted on the piston by the compressed spring188 is "b'al
...1ines.222 and.224. Thisf?uidlmoves the (1181(‘126'011'1116
~.ance'd by an equal and oppositely directed force-exerted
on the piston 186 by the ?uid entering through‘ port 190‘.
. stem .122 into engagement with__the shoulder :124; so ':as
the lower pressure existingat port_172 and in cylinder175
.,.the_spring-u_rged sidegplunger 120. toprov-ide for opening
,to. move the plungerlZG-to an unseated position.
‘ .The' flow throughport 190 in this equiblibrium position of
Theiarea of the disk126 ‘subjected to pressuresby?uid
piston 186 at a pressure drop-of from about 1500 p;.-s.i.:to $40 entering port 219,is-su?icientlygreater.than, the :‘area on
equals the '?OW: through the grooves, 192 »' at,lthe_ pressure
of valve 438 at :a pressure considerably below Ether limit
drop existing between ports 172 and 176. ‘By forming the
,pressureuo'f 1500. psi-"when thejpressureof ?uid. trapped
valve .56 so that "a ~?owjthrough grooves .192;is;.insured
.in cylinder.ZOonthe-underside of ‘piston v22,is 1'S00;p;sli.
‘when the valve member 186 is unseated,-a-movement'gof
‘the pumptilt box 63 ton substantially~zerojdisplacement
positionwithout any “hunting” is insured.
‘All-of ‘the above ‘described action of valve 56 ‘during
»rnovernent of tilt box 63 toward a substantially ‘zero dis
‘The ratio of this area of =disk~.126. to the areafo'f‘thet spring
.urgedside of,plunger.-12‘0> is greater than . the 'ratioxof the
.areas. on the. topand .bottornsides _ of piston 22‘ to‘ prevent
_a,bu.ildup.of thevforce on the plunger 120'resisting' opening
__fast_er than, the buildup ofthe force on the-disk 126 'in'the
.conditionof “thev system .10 shown in FIG. .6 followingaa
1 placement position takes place very quickly. In the event :
the piston 186 should momentarilymove against the spring
‘188 to a position‘ in which the-grooves 192 are closed ;-by
condrtionsuchas shown in FIG. 5 in which ?uid is trapped
. in cylinder 20 on the underside of the piston .22. 1In the
the ‘wall 184, as in'the case of a sudden pressure above
v‘illustrated embodiment of'the invention, the ratio :of ‘.the
1700 p.s.i., the quick response of thertilt -box"63 toppro
areaof disk.126 to the area of the spring-urged sideofthe
- vide for a reduced pump output and the action of the
_ plunger
‘peaking relief valve 198 provide‘ for a reduced pressure at
120 is about 2 to 1 and the ¢ratiooffthe :area ‘of
the
_ . top. side of . thev piston .22rto the area ofithesbottom
‘port190 so that the spring 188 again moves the piston 186
to‘ its ‘equilibrium position. The spring 188 is of a strength
such that at pressures at port 190 between the equilibrium
'sideof piston .22 is less than this.
In a free fallcondition of the dozer blade 18, namely,
a condition .in which there is no external force resisting
downward travel of; the blade 18 so that the piston rod124
pressure in the cylinder 20 ‘below the
In the equilibrium position'of piston 186 in valve 56, the 6 ,1s_1n,tens1on,'the
‘piston '22 willv riseqand the pressureabove thelpiston ‘22
pump 12 will pump su?icient ?uid to take careof ?ow
willf’vfall. Consequently,_,the.plunger 120'in the valve.38
through grooves 19-2, leakage at the pump 12 and allother
will-be moved by the .pressure‘on the‘cunderside of ‘the
leakage in the system parts communicating with the pump
.piston v2,2 toward a seated position against'the pressure
outlet. The supercharge pump 42 supplies ‘this, amount
applied to.the disk 126, which latter .pressure- is the same
of ?uid to the pump 12. Thus the pump 12 is’ not stroked
"pressurethat
vexists on the top side of the piston 22, .by
to an absolute zero displacement condition, only a sub
-virtue of the connectionof'line 108 with valve 38 by
stantially zero displacement condition.
means of lines 222 and 224. As soon as the plunger 120
It can thus beseen that if raising movement-of the blade
:seats
against the seat 136, the pressure onvthe top ‘side
_‘18 is prevented and the control valve 34is in the “raise”
of thepiston 22 will rise, because of 'the resistance to
position, the tiltbox 63 is automatically moved to a sub—
-downwar'd movement of the piston 22 created-by the ‘?uid
vstantially “zero” displacement position, by theaction of
.trappe'd‘in cylinder ‘20 below‘the piston 22. ‘This will
valve 56, so that very little power is required from‘ the
:zcausethe Ydisk 126 mm move'd in-adirection to open ‘the
tractor engine to operate the pump 12,.and the blade‘ 18 75 >1valvei38. lThe result-of this ‘type of operation is that‘the
pressure and the peaking relief pressure ?uid can " ?ow
‘ through grooves ~192-to tank.
a
0'
.
.
.
.
dozer blade 18 tends to “hunt” during its downward move
ment. In other words, the downward movement of the
1 blade 18'is a start and stop type of movement.
cuit,'but it is advantageous to utilize the control circuit
?uid to increase the volume of ?uid available in the
supereharge circuit.
In the event the downward movement of the piston 22
In order to overcome this tendency of the system 10 to
is
stopped, because it engages the lower end of the cyl
operate so that the dozer blade 18 moves downwardly in a,
inder 20 (FIG. 7), the pump operating pressure immedi
this manner when the piston rod 24 is under tension, the
ately rises above the predetermined maximum pressure
line 194 which is connected to the port 176 in the control
for which the valve 58 is set, 1500 p.s.i. in the example,
valve 56 is also connected to the inlet port 254 in a one~
resulting in unseating of the piston member 186, so that
way check valve 250 that includes a casing 252 having an
outlet port 256 which is connected by a line 258 to the 10 ?uid ?owing to port 190 in valve 58 is supplied to the
cylinder 174 so as to extend the control piston 60 and
line 224 communicating with the pilot port 219 in the
stroke the tilt box 63 toward its neutral position. The
valve 38. The check valve 250 has a ball member 260
valve 58 operates like the valve 56 previously described
therein which is urged by a spring 262 toward a seated
to insure stroking of the pump to a substantially zero
position closing the inlet port 254. There is a restriction
displacement position without any hunting.
‘
264 in the line 224 at a position between the line 222 and
The peaking relief valve 202 bleeds of! enough ?uid
the connection of the line 258 to the line 224 for a purpose
to appear presently.
When ?uid under control pressure is supplied through
in the line 200 to prevent the pressure from exceeding
a predetermined maximum pressure. In the illustrated
embodiment of the invention this pressure is about 1700
the line 194 to the check valve 250, in response to move
p.s.i., and as previously explained, the peaking relief
ment of valve 34 to a “down” position (FIGS. 6 and 7.),‘ 20
valve 202 functions to prevent undue pressure rise in
the ball member 260 is unseated so that ?uid under con
trol pressure is supplied through the line 258 to the pilot
the system 10 during the time involved in moving the
tilt box 63 to a substantially zero displacement position.
Since there is no ?ow through the valve 36 the piston
126 against the valve stem shoulder 124 and unseat the
120 is moved by the spring 130 to a position engaged
25
The
restriction
264
prevents
free
?ow
of
plunger 120.
with
the seat 136 to there-by hold the pressure on the
this valve actuating ?uid into the main pump operating
. top side of piston 22. In this position of the tilt box,
circuit. When the pressure in the line 108 exceeds the
the pump 12 pumps enough ?uid to take care of leakage
pressure in line 258, the check valve 250 is closed. The
' at the pump, ?ow through the valve 58, and any other
valve opens again only if the pressure in line 108 drops
leakage in the system on the output side of the pump.
below the pressure in the control circuit. At such time 30 In the event the pressure falls below the pressure neces
valve 250 opens to prevent hunting of the piston 22 during
sary to maintain the piston member 186 in valve 58 in an
port 219 in the valve 38 so as to ‘move the disk member
-
downward movement.
unseated position, for any reason, the piston member 186
The area of the disk 126 in valve 38 is proportioned
- moves to the seated position shown in FIG. 9 in which
with respect to the area on the underside of the piston 22
35 the cylinder 174 communicates with the tank port 176 in
and the weight of the blade 18 so that the total force
the valve 58, and the control pressure in the cylinder
exerted on the disk 126 by the ?uid under control pressure
v175 again extends the piston 60 to provide for tilting of
is suf?cient to maintain the plunger 120 in an unseated
the tilt box 63 to a position in which the pumping of
position against the combined forces in the opposite direc
an increased volume of ?uid out the pump outlet 230 is
tion exerted by the ?uid communicating with the under 40 resumed
to again raise the pressure at the port 190 to
side of the plunger 120 and the spring 130.
the
predetermined
maximum.
It is seen, therefore, that the ?uid from the control
In FIGS. 11-13, a valve 58a is illustrated which may
circuit is used to insure an open position of the valve
38 when the pressure in line 108 is not high enough to
be substituted for the valves 56 and 58, and is shown
main closed as shown in FIG. 6. The volume of ?uid be
835,002. The spring assembly 173 is positioned in the
associated with the cylinder 174 only for purposes of illus
keep the valve 38 open during a powered movement of
tration, it being understood that an identical valve may
45
the dozer blade 18 downwardly.
be mounted on the opposite side of the tilt box 63 and
When the pump 12 is operating to pump ?uid into
associated with the cylinder 175 if desired. The valve
the upper end of the cylinder 20, to move the dozer blade
58a includes an elongated casing 300 which is provided
18 downwardly, ?uid under operating pressure from the
‘ with a longitudinally extending bore 302 and is integrally
pump 12 is supplied from the line 108 through the line
formed with the cylinder 174 which is at substantially right
104 to the pilot operated check valve 50 so as to main 50 angles to the bore 302. The valve 58a is assembled with
tain the ball member 96 in a seated position. Fluid under
the pump 12, only fragmentary portions of which are
operating pressure is supplied from the line 222 to the line
shown in FIG. 11, by inserting the cylinder 174 in an
200 which communicates with the control valve 58 and
opening 304 in the pump casing 61. The cylinder 175 is
the peaking relief valve 202, and so long as the pressure
similarly inserted on the diametrically opposite side of
55
of this ?uid does not exceed the maximum normal oper
the casing 61 so that it is in substantial alignment with
ating pressure, about 1500 p.s.i. in the illustrated embodi
the cylinder 174, as shown in FIGS. 3-8, and as de
ment of the invention, the valve members 58 and 202 re
scribed in detail in my copending application Serial No.
ing supplied to the pump inlet 232 through the line 216
cylinder 174 and engaged with the piston 62 so that the
is less than the volume of ?uid which must be supplied 60 spring assembly constitutes a yieldable abutment which
to the cylinder 20 on the top side of the piston 22 to keep
exerts no force on the piston 62 in the neutral position
the cylinder 20 full because the piston rod 24 is moving
of the tilt box 63 in which the actuating arm 65 is cen
out of the cylinder 20. The necessary additional volume
tered between the pistons 60 and 62. The spring assembly
of ?uid is supplied to the inlet port 232 from the super
173 will compress and yield so as to permit retraction of
65
charge pump 42 which pumps through the open check
its piston 62 when a retracting force is applied to the
valve 48 to the line 216. So long as replenishing ?uid is
piston and of course the more the spring assembly 173
required at the pump inlet 232, the pressure in the line
is compressed the greater the force it exerts on the
216 will be below supercharge pressure so that the valve
piston 62.
48 will be open. The communication of the relief valve
The valve casing 300 is secured, such as by bolts
54 in the control circuit with the line 106 provides ‘for
(not shown) to the pump casing 61 so as to maintain
the cylinder 174 in the position shown in FIGS. 11 and 12.
a dumping of control circuit ?uid into the supercharge
A spool sleeve 306 is threaded into the bore 302 in
circuit as a precaution against the creation of voids in
the casing 300 and is provided with an axial bore 308
the cylinder 20 above the piston 22. The valve 54 can
be connected to tank, instead of to the supercharge cir 75 which extends inwardly from the inner end 309 of the
1:114
‘sleeve 306 and has‘ its inner end''3101ocatedintermediate
‘163 _is jcentered, thevolume OfJ?uid'Ibeing pumpedlinto
} the ‘ends of the sleeve 306. 'l‘hree-sets'of~ radially ex
:lthejvalve 584 ,through 'theopenings’312equals the volume
,tudinally spaced positions‘in magnet/@5396 and intersect
vof'?uid-j?owing out the va’lvef58athrough tank‘port 176.
“In; an‘ equilibrium ,position vofjthe vspool 318, shown in
‘IQ-and’ ‘13, ‘the amount“ of T?uid ?owing past land
tending openings 312, 314’ and .316, ‘are formed'at‘v'longi
__the
borebore308.
308 so'thatAthespool
inner’end
318 isF'slidably
§20thereofsupported‘in?the
isilspacedjfrom
[2:28 to, the jopeiiingsfiilyt'ifor cylinder "174i equals'the
the bore end 310. An axialpassagethe: spool
'amountfo‘f‘?uidj ?owing 'from'the openings 314' past land
318 at the end 320 thereof is in, constant :?uid' communi
$528; to tank'port-176. fAsl‘shown-in FIG. l3,'-the'land
cation with the sleevel‘opening 312‘vthrough; thejspace I‘ 328 is slightly‘ to "the right" of :a centered position relative
between the spool end 3’20..an'd_ theubo're en'df3l0."'The= 10 ‘to the ‘openings3'1‘i4, ~ in the equilibrium ipo'sition ofv spool
spool 318 is formed with three longitudinally spaced
I 318, hecausefthe pressure dropgin the illustrated embodi
lands 326 V328 and 330‘and the: passage.'32'2ihas,_a_ trans
211161“ ofjthe- inventionyvis greater’ between "the ?uid ion'the
‘_ rightlhand' side‘of land4'32’8 and :the'?uidin openings’ 31-14
sects'the outer surface of the ‘spool;318'_be,t_ween the lands
landpylindergl?’than ‘thejfdrop-between' the ?uid in open
326 and 328.
V
"15, ings f§>141and 'the‘?uidron' the left-hand! side of landv 328,
versely extending portion 332 at_its'pinner_end_
inter
.The opposite end of the spool'_i318;hasva reduced ‘diam
v whichfeommnnicates with tank port ‘176. In ‘this'position
v oftheiftiltv box-‘63,?theivolum'e' of ?uid being pumped‘ by
theypnnipf12is‘si1i?cient to take care of the ?ow" through
eter extension,_334. which :supports a. guide 336;, for the
spring 188 that extends'be'tween the ‘inner’ end of the
' bore-302 and the guide ‘336. :The springll88 urges .the
"the; vaIve'lSi‘Safan'd' leakage atjithe pump 12, as~well= as any
‘spool 318 toward the rightas viewed'in FIGSgllpand ‘1'2 e20 other" leakage in the portion of ?the@system;10~'communi
tothe position, shown in FIG.~1,11 in which anend?ange ;eatingjwith'fthe output-side o?‘th'e-pump 11,2. vAt a pres
337 on the guide336 engages ‘the inner'endofjthesleeve “ sure of the ?uid at'the‘openings 3l2labove theequilibrium
‘pressure ?lldjbélOW the peaking'pressure of 1700 p;s.i.,
‘ the "spool 3181 is ‘moved ‘slightly? to the left-of- the ‘position
In use,vthe valve 58a is connectedtin the control system
10 so't‘hat the sleeve openings “312 communicatew'ithlthe “25 ‘shown ,in "FIGS. Hand 713' ‘to ;a posit-ion -in-' which ?uid
end of line 200 opposite the.fl'aeaykinglv relief.=valv'e 202,
‘leaks ' past" the "land-‘328"totank" and around the land 328
the s1eeveopenings314 communicate ‘with ‘the connecting
atothe?port7,172?and intovthe cylinder 174 so as toiextend
port 172 between the cylinderv 1/74and'the. ‘bore.30,8,iand
I‘ the; piston 62 torotate‘ theytilt box 63" to~a- position in
t the openings "316vcommunicatesthrongh'theportil76iinithe ,
_ which} the amount'of ?uid pumped is'insu?icient! to main
tain the pressure above “the equilibrium- pressure. ' Con
weasing300 with the ‘line .178 iwhiehzistconnectedtitoithe
port 78 in the control, valve .34."
In the operation of the,valve,58_>a,- when thegtiltyjbox
,sequentlyi the pressure > at; the ‘openings'312-quickly' falls
_]to" ‘the, equilibrium ‘pressure: and ‘the spring 188 moves the
63 is to‘b‘e rotated to the‘pos'ition shown in FIG. 44o; raise
,spool i318 _ to _j_the "equilibrium ;_ position. ’
the dozer blade 18, ?uid under controlrpressurefrom the
jfInrthe 'equilibriuin' position [of the“ spool?l'sfshown in
valve 34 is supplied through the'line'178i to the‘lbore
‘ Bl_GS._ _12 "and i 13, "the ‘force exerted on the'spool‘ Lbylthe
302, through the openings 316, around thejlspool§l8sand
\ compressedjspring- "18.8 is" ‘balanced by» an ‘ equal ‘and op
through the ports‘ 314 and 172 int'orth'e cylinder_\'174iso
“positely ,directed?'forceexerted on -'the spool 318%»by-1the
as to extend thepiston 62, spool ,318‘ being titlthepo-si
uf?luidsupplied‘through the openings 312. -~'lfhe~eonstruc
.tion shown'tin'FIG. 1'1. '_Wheri the components of‘the
system to are'in ‘the ‘position showniniFlG. Feminine
dozer blade 18 is being.‘moved-downwardlL'the valve
"tion of "the valve =58a‘ ‘to ~ provide for {a continual > ?ow
‘around the f land ‘I328, insures vstroking of the" pump {12
I to‘ a ‘substantially zero ‘displacement; position awithoutaany
58a is still in the position'shown in;'FlG.._1"1,fhoweverz the
iihugtiugfi
line 178 which communicatestwithi thersleegeopenings 316
connects through the control valve 394 withjthe. tank 144,
‘for? movement of the tilt "box ~-‘63 " to 'a» substantially jcen
\Thejabovejdescribedhaction'ofethe valve 58a to provide
teredpositionjtakesjplace very‘quicklyeridthe pump '12
of the pump "1'2,i_andthefltilt.box operating‘tpistony?lis" v‘responds'very ,quickly tOTédUQéf the volume *of‘?uid'fbeing
the sleeve openings~312i communicate with; the outputside _v
depressed by the’ action of 'pis'tonf60l
*purnpe'djsinee'thedistance ‘the actuating 'arm '65 inustibe
v'lmoved'totcenter'lthe tilt'bQX w63 is‘srnall. ‘In the-event
fthejpuinp “output 'pressure 'at the ‘openings-3'12 should
,
When. theipiston" 522vengagjes “ the. bottom‘ end ofjthe cyl
inder 20',(FIG. '7‘)".so that continued operationnof _'the
pump 12 causes an immediaterisetoifjth'e pump pressure
_.
a
,
.
.
vA50
to a pressure above thepredeternnned. maximum operat
ing pressure, which in theillustratedleinbodirnentlof ‘the
invention is about 1500 v_p.sy.i., wthejlffoyrce ‘of ,Hthe ?uid fat
the openings 312 is su?icientelto “move .;the .t spool .0318
momentarilyijbeihigh :enough tomove the spool~>3118 ‘ to
a,‘ position__ inlwhich the‘ land 1328 v blocks [?ow of‘ ?uid-p to
‘the tanklopenings v1316, "the ' quickv response » ofthe- tilt vbox
f_6‘3;_t_o< extension ‘of ‘the piston v'6Zrrto- 'pr'ovide‘for a reduced
vvolume v‘ of” ?uidf beingpurnped : by ‘ the‘ pump v12 'and‘jthe
vvvagainst'the force vof the spring;_1'88 ‘to lei-position inhyvhich .155 voperation “of the jpeakingj relief valve, provide "for an im
,mediatej_reduotion gof the’presslure'of the‘ ?uid at the open
the land 3278; is positioned‘relativeitorthetsleeve penings
‘
314 such-that‘?uid supplied ‘throng
‘passage "22510 _.ings 312.
“The valve "58a ‘thus operates in "conjunction 'with the
the. space between -' the . lands Q26 v and 1328412311 ‘.‘?iow Tout
the openings 314 to; the cylinder porttl7ziandcaifoundithe
I peaking relief j valve 202 "to ‘provide for movement of ‘the
vland
the tank.
328 totFluidesupplied-fthronghithe.épvort
the openingsC3-16liwhichlcoinrnnnieatet
_»17,:2§‘to.:,_the "
‘.tilt" box 1163 to 'a substantially neutral'position, in' response
‘cylinder 174, extends the depressedgpump pperating piston
162 and moves the tiltboxiqfautowardeazpositionfcentered
' gtrated'e-mubodiment of the.invention,_this pressure‘ is ‘about
:202 .will open totpreventtheipressv'ure ong‘thve outputlside ;
spring‘188. vlf‘theHsprin_g_‘l1_88"is of ‘a slightly "reduced
_ ‘strength, ‘this ‘pressure ' ‘will '_'be slightly lower .‘and 'if the
between the pistons 60and62§ fIhelpeakingajreliefsvalve
of the pump 12 fromtrising above-‘the_1700rp.s.i..: pressure
during the time involvedin moving the-'tiltfboi??ttoward
a neutral position.
This varrangement provides ‘for "a continual i?ow 50f
?uid through the valve 58atottianik‘, during itheyiit‘irnen-tl‘he .
valve 58a is in aposition providing-for;a¢?qw.ofdiuid ‘
to extend the piston '62. Duringentension i,ofgtheepist‘on
62, the volume of ?uid being; pnrnpediby their-pump vv12 is
:eontinually ' being reducedv andtat (some :position 30f piston
62, short of a fully extended ‘position’.v in'whichjthetilt box $75
_'to a riseiin theipressure'qon'the ontpnt‘si‘de of thepump
§1500;p;s;_i., and is {determinedbyfthe strength ‘of "the
spring is ofaslightly greater; strength, this :pressure will
be slightly higher. The ‘size "of the openings '_3\14‘relative
,to. the.land‘ti3r28mdeterminesthe volumetof?uid which will
fileaktpast the land?” to tankvan‘dthessmaller this vqlurne
iis-fth'ef less work thatfis‘requiredItromthe pump 12 in-the
.v substantially ‘I zero i displacement position of -,the tilt ,box
‘6:3. '_1n,the illustrated, embodiment. of theinvention about
19116 new?“ aallqn in?ltiiiinnte leaks east :the. land 1628
8,078,674
15
, the port 74, which is connected by the line 158 to the
valve 40 is connected to tank, so that the ?uid under
of the tractor 12, the valve member 34 is moved to the
?oat position illustrated in FIG. 8 in which the valve
supercharge pressure supplied through the line 152 to the
port 150 in the valve 40 is operative to close the valve 40.
From the above description, it is seen that this inven
spool 66 is in a position blocking the inlet port 82 and
providing for communication of the inlet port 80 with
the outlet ports 74 and 76 which are blocked by the spool
66 against communication with the tank port 68. The
outlet port 78 communicates with the tank port 72.
Fluid from the outlet port 74 ?ows through the line
158 to the inlet port 156 in the
?oat control shut-off
valve?
‘
_
16
from the “?oat" position (FIG. 8) to any other position,
move freely up and down with respect to the front end
tion provides a hydraulic system in which the piston 22,
, which constitutes a work member, can be raised, lowered,
held, or ?oated, without requiring unnecessary operation
10 of the pump 12 while still providing for quick response of
40 and operates to move the valve member 148 against
the pressure of spring 160 to a position in which the lines
the piston 22 to manipulation of the control valve 34.
As a result, the power required for operation of the pump
12 is then made available for other useful purposes re
142 and 144 on opposite sides of valve 40 are communi
quired in the particular installation of the pump. The
cated, by a groove 149 in the valve member 148 as shown
supercharge pump 42 provides the ?uid necessary to main
15
in FIG. 8, to provide for a ?uid communication of op
tain the main circuit full at all times with the check valves
posite ends of the cylinder 20. The piston 22 is thus free
to ?oat up and down in the cylinder 20 as the dozer blade
18 moves over the ground surface, since the ?uid is free
to ?ow from one side to the other of the piston 22, com
48 and 50 separating the supercharge and main circuits
when no ?uid is to be added to or taken from the main
circuit. The use of control circuit ?uid to open the valve
38 prevents “hunting” of the piston 22 during the time the
plicated only by the fact that during movement of the 20 piston 22 is being powered down, and if desired control
piston rod 24 into the cylinder 20 some of the ?uid being
forced out of the upper end of the cylinder 20 must be
bled off because it is more than enough to ?ll the opposite
end and during movement of the piston rod out of one
circuit ?uid may be similarly utilized to open the valve
36 if there is any tendency for the piston 22 to hunt in the
opposite direction. In the illustrated system this is not a
problem and in a system where hunting of the piston 22 is
end of the cylinder, additional ?uid must be supplied 25 not objectionable, use of control ?uid to open either or
to the opposite end of the cylinder if it is to be kept full
both of the valves 36 and 38 is not necessary.
of ?uid.
_
It will be understood that the speci?c construction of
Fluid from the control valve outlet 76 is 'supphed
the improved control system for variable displacement
through line, 194 to the valve 56, and through the valve
pumps and similar devices which is herein disclosed and
56 into the cylinder 175 so as to extend the control piston 30 described is presented for purposes of explanation and
60 and rotate the tilt box 63 in a counterclockwise direc
illustration and is not intended to indicate limits of the
tion as shown in FIG. 8. The pump 12 thus pumps its
invention," the scope of which is de?ned by the following
full volume of ?uid out the port 230 'and through line 108
claims.
to holding valve 36. However, since the piston 22 1S
?oating in the cylinder 20, the only pressure developed in as What is claimed is:
line 108 is that required to overcome line loss and open
valves 36 and 38, as shown in FIG. 8, and provide a
,1. In a hydraulic control system for a variable dis
placement pump having an actuating member for varying
complete circuit for the ?uid from the pump outlet port
230 through the line 108, valves 36, 40 and 38 and the
_ displacement, and a hydraulically actuable device operable
the, control circuit supplied through the open check valve
, moving said'actuating member to and from a ?rst posi
by ?uid from said pump: actuating means movable in
line 216 to the inlet port 232. Fluid under pressure from 40 response to a supply of ?uid under pressure thereto for
250 to the valve 38 maintains the valve 38 open at all
times in the “?oat” position of control valve 34 so that
the piston 22 can move downwardly without “hunting?
tion in ‘which the displacement of said pump is zero and
a second position in which said displacement is maximum;
During downward ?oating movement ‘of the piston 22
?uid supply and return lines connecting said pump and
said device; means independent of said pump for supply
move the valve member 94 to open the pilot valve 50 so
in response to a supply of ?uid under pressure thereto for
in the cylinder 20, the pressure in line 216 falls because 45 ing ?uid at a control pressure; valve means for com
municating said ?uid at control pressure to said actuating
there is insu?icient ?uid ?owing out of the lower end 'of
means to move said member to increase the displacement
cylinder 20 to supply the pump 12 with enough ?uid to
and ‘hence output of said pump, and means responsive to
?ll the upper end thereof since the piston rod 24 is moving
the pressure of the output ?uid from said pump in said
out of the cylinder 20. Consequently, the ?uid under
supply line to communicate said output ?uid to said actuat
supercharge pressure in line 106 opens the check valve
ing means to move said member in the opposite direction
48 and enough of this ?uid ?ows into the pump inlet 232
' to decrease the displacement of said pump to a substan
to insure ?lling of the upper end of the cylinder 20. Dur
ing upward movement of the piston 22 a greater volume ‘ tially zero-?ow equilibrium position when said output
pressure reaches a predetermined high pressure.
of ?uid is forced out of the top end of cylinder 20 than
2. In a hydraulic ‘control system for a variable dis
is required to ?ll the cylinder 20 on the underside of piston 55
22 because the piston rod 24 is moving into cylinder 20. ' placement pump having an actuating member for varying
This additional ?uid in the main circuit causes a rise win '_ displacement, and a- hydraulically actuable device oper
the pressure in line 216 su?icient ‘to close valve 48 and 1 able ‘by’ ?uid from said pump: actuating means movable
that a volume ‘of. ?uid equal to the volume of the ?uid 60 moving said actuating member to and from a ?rst at-rest
position in which the displacement of said pump is zero
displaced in the cylinder .20 by the piston rod 24 can ?ow
through the valve ‘50. to tank; For this reason the area of ‘I and a second position in which said‘ displacement is
maximum; spring means for resisting movement of said
the surface of valve'member 94 exposed to pressure ?uid
“member by said actuating means away from said ?rst posi~
from line 110 is proportioned tothe area of ball 96 to
tion, said spring means being restrained and prestressed
. insure unseating of ball 96 when the ?uidpressures‘applied
so as to allow movement of said member away from said
to the ball from line 104 and to the valve member 94from
the line 110 are substantially equal.v
' .
.
,1
It can ‘thus be seen that the-check- valves ‘48 and '50
function to continuously maintain the cylinder 20 full vof
?uid. As a result, if downward movement of the blade
18 is desired, when the control valve‘ 34 is in ‘the ?oat
' position, it is only necessaryto move the control valve
" '?rst'posi‘tionl-only when a substantial force is applied
,_ thereto ,by sa1d actuating means; ?uid supply and return
‘lines connectingsaid pump and said device; means in
dependent of said pump for supplying ?uid at a control
pressure; valve means for communicating said ?uid at
controlv pressure to said actuating means to move said
34 to the “down” position shown in’FI'GS'. 6'and 7 and
‘ member to increase the displacement and hence output of
‘ the piston 22 will be immediately moved downwardly
without any time delay. 3As soon as-the valve 34 is moved
~-output~?uidifrom-said pump in said supply line to com
said pump, and means responsive to the pressure of the
17
3,078,674
municate said output ?uid to said actuating means to move
said member in the opposite direction to decrease thedis
placement of said pump to a substantially zero-?ow equie
librium position when said output pressure reaches a pre
determined high pressure.
18
saidpump- in either said one-or said opposite directions
respectively, and means responsive ‘to the pressure of the
output ?uid from said pump in said supply line to corn~
municate said output ?uid to the side of said piston unit
not subject to control pressure to move said member to
3. In a hydraulic control system for a variable dis
placement pump having an actuating member for vary
decrease the displacement of said pump to a substantially
zero-?ow equilibrium position when said output pressure
reaches a predetermined high pressure.
ing displacement, and a hydraulically actuable device
operable by ?uid from said pump: actuating meansyin
7. in a hydraulic control system for a reversible vari
cluding a double-acting piston unit movable in response 10 able displacement pump having an actuating member for
to a supply of ?uid under pressure thereto for moving
varying displacement, and a hydraulically actuable device
said actuating member to and from a position in which
the displacement of said pump is zero and a position in
which said displacement is maximum; ?uid supply and
operable by ?uid from said pump: actuating means in
cluding a double-acting. piston unit movable in response
to a supply of ?uid under pressure thereto for moving
return lines connecting said pump and said device; a ?uid 15 said actuating member through an at-rest zero displace
reservoir; means independent of said pump for supplying
ment position to and from a position in which the dis-.
?uid from said reservoir at a control pressure; and valve
placement of said pump is maximum for one direction
means operable in a ?rst position to communicate said
of ?ow and a position in which said displacement is maxi
?uid at control pressure to one side of said double-acting
mum for the opposite direction of flow; spring means for
piston unit to move said member to increase the displace
resisting movement of said member by said double-acting
ment and hence output of said pump, said valve means
piston unit in either direction away from said at-rest
being responsive to the pressure of the output ?uid from
said pump in said supply line and operable in a second
position to communicate said output ?uid to the opposite
side of said double-acting piston unit to
zero-displacement position, said spring means being re
strained and prestressed so as to allow movement of said
member away from said zero displacement position in
move said mem 25
either direction only when a substantial force is applied
the displacement
theretoby said actuating means, ?uid supply and return
equilibrium posi
lines connecting said pump and said device; a ?uid reser~
a predetermined
ber in the opposite direction to decrease
of said pump to a substantially zero-?ow
tion when said output pressure reaches
voir; means independent of said pump for supplying ?uid
high pressure.
4. A system as claimed in claim 3, wherein said valve 30 from said reservoir at a control pressure; and valve means
for selectively communicating said ?uid at control pres
means is operable in said ?rst position to communicate
sure
to one side-or the other side of said piston unit to
said opposite side of said double-acting piston unit with
move said member to increase the displacement and hence
said reservoir, and in said second position to substantially
output of said pump ineither said one or said opposite
block communication between said opposite side and said
directions respectively, said valve means being responsive
reservoir.
35
to the pressure of the output ?uid from said pump in said
5. A system as claimed in claim 3, wherein said valve
means comprises a housing having a bore therein, a pas
supply line to communicate said output ?uid to the side of
pressure is maintained and a limited ?ow is provided
pressure to one side or the other side of said piston unit
through said valve for said unit.
and said reservoir with the opposite side thereof to move
said member to increase the displacement and hence out
said piston unit not subject to control pressure to move
sageway connecting said bore to the side of said double
said member to decrease the displacement of said pump
acting piston unit not subject to control pressure, a spool
having a land slidable in said bore relative to said pas 40 to a substantially zero-?ow equilibrium position when said
output pressure reaches a predetermined high pressure.
sageway, said bore adapted to communicate on one side
8. In a hydraulic control system for a reversible vari
of said land with said supply line and on the other side
able displacement pump having an actuating member for
of said land with said reservoir, said spool land normally
varying displacement, and a hydraulically'actuable device
blocking communication between said passageway and
said supply line and being movable from said normal posi 4.5 operable by ?uid from said pump: actuating means in
cluding a double-acting piston unit movable in response
tion to progressively restrict communication between said
to a supply of ?uid under-pressure thereto for moving
passageway and said reservoir and progressively admit
said actuating member through an :at-rest ‘zero displace,
?uid from said supply line to said passageway in response
ment'positionto and from a position in which the dis?
to a predetermined high pressure in said supply line,
whereby said spool assumes an equilibrium position in 59 placement of said pump is maximum for one direction of
?ow and a- position in which said displacement is maxi,‘
which the amount of ?uid ?owing into said passageway
mum for the opposite direction of ?ow; ?uid supply and
from said supply line substantially equals the amount of
return lines connecting-said pump and said device; a ?uid
?uid ?owing from said passageway to said reservoir and
reservoir; means independent of said pump for supplying
the total forces exerted on said unit are substantially
balanced to maintain said pump in an equilibrium positive 5,5 ?uid from said reservoir at-a control pressure; and valve
displacement position in which said predetermined high
means for selectively communicating said ?uid at control
6. In a hydraulic control system for a reversible vari
able displacement pump having an actuating member for 60 put of said pump in either said one or said opposite direc
varying displacement, and a hydraulically actuable device
operable by ?uid from said pump; actuating means in
cluding a double-acting piston unit movable in response to
a supply of ?uid under pressure thereto for moving said
tions respectively,_said valve means being responsive‘to
the pressure of the output ?uid from said pump in said
supply line to substantially block said communication be;
tween said reservoir'and the side ofsaid'piston unit not
actuating member through an at-rest zero displacement 65 subject to control pressure and to communicate said out;
position to and from a position in which the displacement
put ?uid thereto to move said member to decrease the
of said pump is maximum for one direction of ?ow and a
displacement of said pump to a substantially zero-?ow
position in which said displacement is maximum for the
equilibrium position when said output pressure reaches
opposite direction of ?ow; ?uid supply and return lines
a predetermined high pressure;
connecting said, pump and said device; a ?uid reservoir; 70
9. A system as claimed in claim 7, wherein said valve
means independent of said pump for supplying ?uid from
means comprises a housing having a bore therein, a pas,
said reservoir at a control pressure; valve means for selec
sageway connecting said bore to the side of said doubles
tively communicating said ?uid at control pressure to one
acting piston unit‘not subject to control pressure, a spool
side or the other side of said piston unit to move said
having a land slidable in said bore relative to said passages.
member to increase the displacement and hence output of 75 way, said bore adapted to communicate on one side of
8,078,674
said land with said supply line and on the other side of said
20
passage means extending between said other one of said
land with said reservoir, said spool land normally blocking
communication between said passageway and said supply
line and being movable from said normal position to pro
gressively restrict communication between said passage
way and said reservoir and progressively admit ?uid from
said supply line to said passageway in response to a prede
termined high pressure in said supply line, whereby said
ports and the opposite end of said cylinder, a ?rst pilot
operated check valve in said ?rst passage means operable
in response to the pressure of ?uid from said pump in said
?rst passage means to admit said ?uid to said cylinder to
move said piston in one direction, a pilot line‘ connecting
said ?rst check valve and said second passage means for
opening said ?rst check valve in response to a predeter
mined high pressure in said second passage means, a sec
‘spool assumes an equilibrium position in which the amount
of ?uid ?owing into said passageway from said supply 10 ond pilot-operated check valve in said second passage
means operable in response to the pressure of ?uid from
line substantially equals the amount of ?uid ?owing from
said passageway to said reservoir and the total forces ex
erted on said unit are substantially balanced to maintain
said pump in said second passage means to admit ?uid to
said cylinder to move said piston in the opposite direction,
means for opening said second check valve when a pre
said pump in an equilibrium positive displacement position
high pressure exists in said ?rst passage means,
in which said predetermined high pressure is maintained 15 adetermined
pilot-operated ?oat-control valve connected to opposite
and a limited ?ow is provided through said valve for said
ends of said cylinder, a pilot line communicating with said
unit.
?oat-control
valve, and means for selectively supplying
10. In a hydraulic control system for a reversible vari
?uid under pressure to said ?oat-control pilot line to open
able displacement pump and a reversible hydraulically
said ?oat-control valve, whereby when all of said valves
actuatable device operable by ?uid from said pump: a 20 are closed said piston is ?uid-locked against movement in
member that is movable in opposite directions to control
either direction in said cylinder, when said ?oat-control
the direction and magnitude of the pump displacement;
hydraulically operable means for moving said member
valve is open said piston is freely movable in said cylin
der, and when said ?oat-control valve is closed and said
in opposite directions between a zero pump displacement
pump is pumping ?uid under pressure through said ?rst
position and a maximum pump displacement position for 25 passage means said piston is moved in said one direction
each direction of ?ow; spring means arranged to resist
and when said pump is pumping ?uid under pressure
movement of said member by said hydraulically operable
through said second passage means said piston is moved in
means in either direction away from said zero pump dis
direction.
placement position, said spring means being restrained 30 said13.opposite
In a hydraulic control system for a variable dis
and prestressed so as to allow movement of said mem
ber away from said zero displacement position in either
direction only when a substantial force is applied thereto
by said hydraulically operable means; and means includ
ing a control valve operable in one position to supply 35
?uid to said hydraulically operable means to move said
member in one direction against said spring means to
increase the displacement of said pump in one direction
and in a second position to supply ?uid to said hydrauli
cally operable means to move said member in an opposite
direction against said spring means to increase the dis
placement of said pump in the opposite direction.
11. In a hydraulic control system for a variable dis
placement pump having a pair of ports operable to pump
?uid in either of two directions so that when the pump is
pumping in one direction one port functions as an inlet
port and the other port functions as an outlet port and
when the pump is pumping in the opposite direction said
other port functions as an inlet port and said one port
functions as an outlet port, and wherein said pump is
connected to a hydraulic cylinder assembly including a
cylinder having a working piston slidably mounted there
in: ?rst passage means extending between one of said
ports and one end of said cylinder, second passage means
extending between said other one of said ports and the op
posite end of said cylinder, a ?rst pilot-operated check
placement pump having inlet and outlet ports and a hy
valve in said ?rst passage means operable in response to
draulically actuatable cylinder assembly consisting of a 45 the pressure of ?uid from said pump in said ?rst pas
cylinder, a piston, and a piston rod projecting through
sage means to admit said ?uid to said cylinder to move
one end of the cylinder, ?rst passage means communicat
said piston in one direction, a ?rst pilot line connecting
ing the inlet and outlet ports on said pump with opposite
said ?rst check valve to said second passage means for
ends of said cylinder, a supercharge circuit including a
opening said ?rst check valve in response to a predeter
second pump, second passage means connecting said sec 50 mined high pressure in said second passage means, a
ond pump and said ?rst passage means, check valve means
in said second passage means movable to an open posi
tron when the pressure in said second passage means is
above the pressure in said ?rst passage means to provide
for ?ow of ?uid from said second pump into said ?rst 55
passage means when said piston rod is moving out of
said cylinder, tank means communicating with said second
passage means, second check valve means in said second
passage means, and means responsive to ?uid pressure in
second pilot-operated check valve in said second passage
means operable in response to the pressure of ?uid from
said pump in said second passage means to admit ?uid to
said cylinder to move said piston in the opposite direc
tion, a second pilot line communicating with said second
check valve, a hydraulic control circuit operatively as
sociated with said pump for controlling the direction in
which said pump pumps, means connecting said control
circuit with said second pilot line to communicate ?uid
the rod end of said cylinder for moving said second ‘check 60 thereto to open said second check valve when said pump
valve means to an open position to provide for ?ow of
?uidtherethrough to said tank when said piston‘rod is
is pumping into said ?rst passage means to move said
piston in said one direction, a pilot-operated ?oat-control
moving into said cylinder.
valve connected to opposite ends of said cylinder, a pilot
‘
>
12. In a hydraulic control system for a variable dis
line communicating with said ?oat-control valve, and
placement pump having a pair of ports operable to pump 65 means for selectively supplying ?uid under pressure to
?uid in either of 'two directions so that when the pump is
said ?oat-control pilot line to open said ?oat-control valve,
pumping in one direction one port functions as an inlet
whereby when all of said valves are closed said piston is
port and the other port functions as an outlet port and
?uid-locked against movement in either direction in said
when the pump is pumping in the opposite direction said
cylinder, when said ?oat-control valve is open said piston
other ‘port functions asan inlet port and said one port 70 is freely movable in said cylinder, and when said ?oat
functions as an outlet port, and wherein said pump is con
control valve is closed and said pump is pumping ?uid
nected to a hydraulic cylinder assembly‘ including a cylin
under pressure through said ?rst passage means said
piston is moved in said one direction and when said pump
der having a working piston slidably mounted therein, said
is pumping ?uid under pressure through said second pas
system comprising ?rst passage means extending between
one of said ports and one end of said cylinder, second 75 sage means said piston is moved in said opposite direction.
El
3,078,674
14. In a hydraulic control system for a variable dis
22
?oat control valve for supplying ?uid under pressure/to
placement pump having a pair of ports and operable to
the ?oat control valve so as to open the valve, and means
pump ?uid in either of two directions so that when the
for selectively supplying ?uid under pressure to said pilot
pump is pumping in one direction one port functions as
line, whereby when all of said valves are open said piston
an inlet port and the other port functions as an outlet port
is freely movable in said cylinder, when all of said valves
and when the pump is pumping in an opposite direction
are closed the piston is ?uid-locked against movement in
said other port functions as an inlet port and said one
either direction in said cylinder, when said ?oat control
port functions as an outlet port, and wherein said pump
valve is closed and said pump is pumping ?uid under
is connected to a hydraulic cylinder assembly which in
pressure through said ?rst passage means to said one end
cludes a cylinder having a piston mounted therein and 10 of the cylinder the piston is moved toward the opposite
a load carrying piston rod attached to the piston and ex
end of the cylinder, and when said pump is pumping ?uid
tending through one end of the cylinder, said system com
under pressure through said second passage means to said
prising ?rst passage means extending between said one
other end of the cylinder the piston is moved toward said
of said ports and said one end of said cylinder, second
one end of the cylinder, a hydraulic control circuit oper
passage means extending between said other one of said 15 atively associated with said pump for actuating the pump
ports and the opposite end of said cylinder, a ?rst pilot
to determine the direction of ?ow in said ?rst and second
operated check valve in said ?rst passage means operable
passage means and means connecting said control circuit
in response to the pressure of ?uid from said pump to
and said ?rst pilot line to provide for a flow of ?uid into
admit said ?uid to said cylinder, a ?rst pilot line ex
said ?rst pilot line so as to open said ?rst check valve
tending between said ?rst check valve and said second pas 20 when said variable displacement pump is pumping ?uid
sage means providing for opening of said check valve in
in said second direction.
response to a predetermined high pressure in said sec
16. In a hydraulic control system for a variable dis
ond passage means, a second pilot-operated check valve
placement pump connected by a main circuit to opposite
in said second passage means operable in response to
ends of a hydraul’c cylinder having a piston therein and
the pressure of ?uid from said pump to admit ?uid to said 25 a piston rod connected thereto and extending through one
cylinder, 21 second pilot line extending between said sec—
end of the cylinder, and wherein said main circuit in
ond check valve and said ?rst passage means providing
cludes a ?rst line extending between one pump port and
for opening of said second check valve in response to a
the closed end of said cylinder and a second line extend
predetermined high pressure in said ?rst passage means,
ing between another pump port and the rod end of'said
a pilot-operated ?oat control valve connected to opposite 30 cylinder, a ?uid reservoir, a supercharge circuit connected
ends of said cylinder, a third pilot line connected to said
?oat control valve for supplying ?uid under pressure to
the ?oat control valve so as to open the valve, and means
for selectively supplying ?uid under pressure to said
third pilot line, whereby when all of said valves are open
said piston is freely movable in said cylinder, when all of
said valves are closed the piston is ?uid-locked against
movement in either direction in said cylinder, when said
?oat control valve is closed and said pump is pumping
?uid under pressure out of said ?rst port and through said
?rst passage means to said one end of the cylinder the
piston is moved toward the opposite end of the cylinder,
to said reservoir and said second line in said main circuit
for supplying ?uid from the reservoir to the main circuit
when said p'ston rod is moving out of said cylinder, means
providing a path from said ?rst line to said reservoir for
?uid displaced by the piston rod during movement of
the rod into the cylinder, said supercharge circuit includ,
ing a pump connected to said reservoir, a ?rst check valve
communicating on one side with said supercharge pump
and on the opposite side with said second main circuit
line and movable to an open position by a high pressure
on said one side, a normally closed pilot-operated check
valve in said path and communicating on one side with
sa'd reservoir and on the opposite side with said ?rst line,
and when said pump is pumping ?uid under pressure out
a pilot line communicating said pilot-operated check valve
said second port and through said second passage means
to said other end of the cylinder the piston is moved 45 with said cylinder on the piston rod side of said piston so
that when ?uid under pressure is supplied to said cylinder
toward said one end of the cylinder.
so as to move the piston in a d’rection moving the piston
15. In a hydraulic control system for a variable dis
rod into the cylinder the pressure in the pilot line main
placement pump wherein said pump is connected to a
tains said pilot-operated check valve in an open position
hydraulic cylinder assembly which includes a cylinder
so that excess ?uid in the main circuit can ?ow through
hav'ng a piston mounted therein and a load-carrying pis
the pilot-operated check valve to the reservoir.
ton rod attached to the piston and extending through one
17. In a hydraulic control system for a variable dis
end of the cylinder, said system comprising ?rst passage
placement pump having a pair of inlet and outlet ports and
means extending between said pump and said one end
a hydraulically acuatable device operable by ?uid from
of said cylinder, second passage means extending between
said pump, a member that is movable from a zero dis
said pump and the opposite end of said cylinder, said
pump being operable to pump ?uid in a ?rst direction
placement position to control the pump displacement,
such that it travels out said ?rst passage means for return
through said second passage means and in a second di
rection such that it travels out said second passage means
means engaged with one side of said movable member
for urging the member in one direction to a position cor,
responding to a ?rst positive displacement condition of
for return through said ?rst passage means, a ?rst pilot 60 said pump in which ?uid is pumped out one of said ports,
a piston and cylinder unit engaged with the opposite side
operated check valve in said ?rst passage means operable
of said movable member, means associated with said unit
in response to the pressure of ?uid from said pump to ad
for resisting retraction thereof on movement of said mov~
mit said ?u'd to said cylinder, a ?rst pilot line extending
able member in said one direction, said unit ‘being ex
‘between said first check valve and said second passage
tendible by ?uid under pressure supplied thereto to there
means providing for opening of said check valve in re
sponse to a predetermined high pressure in said second 65 move said movable pump member in an opposite direc
tion to a position corresponding to a second positive dis
passage means, a second pilot-operated check valve in
placement condition of said pump in which ?uid is pumped
said second passage means operable in response to the
out another one of said ports, a reservoir for ?uid, a
pressure of ?uid from said pump to admit ?u’d to said
valve for said unit controlling communication between
cylinder, a second pilot line extending between said sec
said unit and the outlet port for said pump and commu
ond check valve and said ?rst passage means providing
nication between said unit and said, reservoir when said
for opening of said second check valve in response to a
pump is in said ?rst positive displacement condition, said
predetermined high pressure in said ?rst passage means,
valve including a member formed with a bore and an
a pilot-operated ?oat control valve connected to oppo
opening communicating with said bore and said unit,
site ends of said cylinder, a pilot line connected to said 75 a spool member having a land slidable in said bore rela
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