Note: Descriptions are shown in the official language in which they were submitted.
POST-PRESSURE-COMPENSATED UNITARY HYDRAULIC VALVE
Background And Summary
The invention relates to pressure compensated
hydraulic valves, wherein a fixed di~ferential pressure
is maintained, to maintain a uniform flow rate.
In a hydraulic valve having a reciprocal
spool for communicating hydraulic fluid to work ports,
it is known to create a fixed differential pressure
across the spool by controlling the pressure before the
~low has passed through the spool. For example in
Wilke U.S. Patent 3,881,512, the hydraulic fluid is
preconditioned before it flows across control spool 13
by an initial pressure compensating valve mechanism 15
which divides flow from inlet 18 to either feeder 20 or
bypass 19 to keep the flow through work port 22 con-
stant for any given position of spool 13 regardless of
fluxuations in pump or load pressure.
~ In the present invention, a fixed differ-
ential pressure is created by controlling pressure
after hydraulic flo~ has passed through the spool~
The present invention evolved from cost re-
duction efforts to minimize the number and complexity
of parts, particularly those requiring machining. This
is accomplished in part by marrying certain open flow
circuit structure with pressure compensated circuit
structure. In an open flow circuit, the flow rate
changes in response to load pressure. Unitary open
flow hydraulic valves are known having check valves in
the same housing as the control spool, typically in the
area of a bridge passage between work ports through the
spool.
The present invention provides a unitary
pressure compensated hydraulic valve, eliminating a
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separate dlscreet pressure compensatlng module. The pressure
compensatlng means of the Inventlon Is In the same houslng as the
control spool. Furthermore, the Inventlon enables known check
valve structure and locatlon from open flow clrcultry to be
applled and used In pressure compensatIng and shuttle clrcuits.
Thls facllltates economy o~ manufacture by enablIng use of
exlstlng manufacturlng steps and assembly llne sequences for as
much of the valve as posslble. The use of check valve structure
for pressure compensatlng and shuttle clrcults Is further
deslrable because It typlcally Invo~ves a less expenslve stamplng
operatlon, as opposed to machlnlng or the llke.
Thus accordlng to one asepct thereof the present
Inventlon provldes a closed center hydraullc control valve
assembly comprlsed of a pluralIty of control valve sectlons
~olned In a bank and for use wlth a varla~le dlsplacement pump
havlng output and pressure senslng ports, each of sald control
valve sectlons havlng thereln a valve spool movable to an
operatlng posltlon for selectlvely dlrectlng pressure fluld from
a supply passage to one of a palr of workports vla a feeder
passage havln~ upstream and downstream branches wlth a connectlng
passage therebetween and wlth sald downstream feeder branch
havlng a U-shaped brId~e passage havln~ a palr of le~s
selectlvely respectively communlcable wlth sald workports by sald
valve spool, the Improvement whlch comprlses a check valve blased
In one dlrectlon toward a posltlon closlng sald connectlng
passage and adapted to be moved In the opposlte dlrectlon to a
posltlon openlng sald connectlng passage~ under force exerted on
sald check valve In sald upstream feeder branch; meterlng means
on sald spool for establIshlng a predetermlned pressure
dlfferentlal across sald spool In sald operatlng posltlon; means
for translatlng workport pressure Into force on sald check valve
and also tendlng to move sald check valve In sald closlng one
dlrectlon whereby sald check valve can act to hold a load In the
absence of pressure In sald upstream feeder branch; means In sald
houslng to communlcate ~orkport pressure wlth sald senslng Input
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port of sald variable dlsplacement pump havlng sald Olltput port
connected wlth sald supply passage, whereby sald check valve acts
as a pressure compensatlng valve and moves back and forth to vary
the degree of communlcatlon between sald feeder branches in
response to varlatlons In the forces of opposlng fluld pressures
actlng thereon, to thereby malntaln sald predetermlned pressure
dlfferentlal across sald spool and shuttle means operable to
effect suJectlon of each sald check valve to t~le hlghest pressure
o~ any sald workport In sald bank, sald shuttle means comprlslng
0 a senslng shuttle passage In each sa~d contro~s sectlon between
the respective sald brldge passage and a shuttle check valve, and
a through shuttle PaSsage between sald shuttle check valve of Its
control sectlon and the shuttle check valve of the next control
sectlon, such that If the workport pressure In sald brldge
passage Is greater than the workport pressure In the brldge
passage In the prevlous sectlon, then sald shuttle ~heck valve In
the present sectlon closes the through shuttle passage of the
prevlous sectlon and opens the senslng shuttle passage of the
present sectlon to the through shuttle passage of the present
sectlon such that the workport pressure In the brldge passage of
the present sectlon Is passed through the senslng shuttle passage
of the present sectlon to the next sectlon, and such that If the
workport pressure In the bridge passage of the present sectlon Is
less than the workport pressure In the brldge passage of the
prevlous sectlon, then the shuttle check valve of the present
sectlon closes the sensing shuttle passage o~ the present sectlon
such that the workport pressure of the prevlous sectlon flows
through the shuttle passage of the prevlous sectlon and Into the
through shuttle passage of the present sectlon and Into the next
sectlon, such that the hlghest workport pressure Is communlcated
to sald pump and to the other slde of each of sald pressure
compensatlng check valves In sald sectlons. Sultably sald valve
spool Is axlally reclprocal In sald houslng, and whereln sald
through shuttle passage Includes a flrst portlon ~xtendlng
3~ axlally In sald houslng from said houslng from sald shuttle check
valve and a second portlon extendlng dlagonally transversely
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across sald houslng to sald shuttle check valves o~ the next
sectlon, sald shuttle valves of the present and next sectlons
belng substan~lally allgned along a lateral dlrectlon
subs~ant~ally orthogonal to sald axls of axla~ reclproca-tlon of
sald vaIve spool, saId flrst portlons of saId through shuttle
passages of the present and next sectlons also belng
substantlally allgned along sald lateral dlrectlon. Deslrably
sald second portlon of sald through shuttle passage has flrst and
second ends, ~he ~Irst end of sald second portlon of sald through
shuttle passage of the present sectlon belng axlally offset from
the second end of sald second portlon of sald through shuttle
passage of the next sectlon and laterally allgned wlth an end of
sald senslng shuttle passage o~ the next sectlon at sald shuttle
check valve of sald next sectlon, the second end of sald second
1~ portlon of sald through shuttle passage of the present sectlon
belng axlally offset from an end of sald sendlng shuttle passage
of the present sectlon, and belng axlally offset from the flrst
end of sald second portlon of sald through shuttle passage of the
precedlng sectlon, sald end of sald senslng shuttle passage oF
the present sectlon belng laterally allgned wlth sald flrst end
of sald second portlon of sald through shuttle passage of the
precedlng sectlon at sald shuttle check valve of the present
sectlon. Preferably sald senslng shuttie passage of each sald
sectlon extends dlagonally transversely In sald houslng parallel
to sald second portlon of sald through shuttle passage In Its
respectlve sald sectlon.
In another aspect thereof the present Inventlon
provldes a hydraullc control valve for use wlth a varlable
dlsplacement pump havlng output and pressure senslng ports,
comprlslng a houslng havïng thereln a valve spool movable In a
bore to an operat7ng posltlon at whlch It dlrects pump output
fluld from a pressure fluid supply passage In the bore to a
workport characterlzed by: A means In the houslng provldlng a
3~ feeder passage havlng an Inlet branch whlch has Its orlgln In the
bore to recelve supply pressure fluld ~rom the supply passage
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whenever the valve spool Is In sald operatlng posltlon ~hereof,
sald feeder passage havlng an outlet branch adJacent to the
workport to be communlcated therewlth through the bore by the
valve spool In Its sald operatlng posltlon; B. means In the
houslng deflnlng a check valve chamber, one end portlon of whlch
Is sltuated between sald branches of the feeder passage and to
whlch the Inlet branch thereof opens to recelve supply pressure
fluld therefrom; C. means In the houslng provldlng a connectlng
passage to communlcate sald one end portlon of the check valve
chamber wlth the outlet branch of the feeder passage and by whlch
sald feeder passage branches are communlcable wlth one another;
D. a load holdlng check valve In sald chamber blased In a closlng
dlrectlon toward a posl~lon In said one end portlon of Its
chamber at whlch It blocks fluld flow to sald outlet branch of
1~ the feeder passage, sald chec~ valve belng movable In the openlng
dlrectlon under force exerted thereon by pressure of supply fluld
In the Inlet branch of the feeder passage to provlde for flow of
such supply fluld to the outlet branch of the feeder passage; E.
means In the houslng for translatlng workport pressure Into force
on sald check valve In opposltlon to sald valve openlng force and
capable of movlng It In sald closlng dlrectlon whereby sald check
valve can act to hold a load In the event of pressure drop In the
Inlet branch of the feeder passage; and F. means In the houslng
to communlcate workport pressure wlth sald senslng port of a
varlable dlsplacement pump havlng Its output port connected wlth
sald supply passage, whereby sald chec~ valve can act as a
pressure compensatlng valve to move back and forth and thus vary
the degree of communlcatlon between the feeder passage branches
In response to Varlatlons In the opposlng fluld pressure forces
actlng thereon. to thereby malntaln a predetermlnable dlfference
In pressure between fluld In the suPply passage and that In the
Inlet branch of the feeder passage. Sultably sald houslng Is
provlded wlth two workports; the outlet branch of the feeder
passage comprlses a U-shaped brldge passage whlch spans that
portlon of the bore at whlch the supply passage and the orlgln of
the feeder passage are located, sald brldge passage having a palr
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of legs selectlvely respectlvely communlcable wlth sald wor~ports
by the valve spool; one of sald legs belng In communlcatlon wIth
sald connectlng passage; and the check valve chamber and chec~
valve thereln belng substantlally embraced by ~he U-shaped brldge
passage.
The present Inventlon wlll be Illustrated by reference
to the accompanylng drawlngs. In whlch:-
Flg. 1.is a sectlonal slde vlew of a valve constructed
In accordance wlth the Inventlon; and
Flg. 2 Is a sectlonal top vlew of the valve of Flg. 1.
Referrlng to Flg. 1, valve 2 Includes a houslng 4
havlng a reclprocal control spool 6 moveable left-rlght for
communlcatlng hydraullc fluld to work ports 8 and 10. Spool 6 Is
shown In the neutral posltlon, and brldge passage 12 Is vented to
reservolr passage or tank 14 throu~h brldge vent passage 16 In
the control spool as shown at dashed llne vent passages 16a,16b
and 16c.
When spool 6 Is moved leftwardly by the operator,
brldge vent passage 16 Is blocked, and brldge Passage 12 Is
placed In communlcatlon wIth workport 8 through control spool
passage 20, such that the workport pressure Is sensed In brldge
passage 12 by
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hydraulic fluid flow through the spool. This applied
work port pressure pressurizes a pilot system for load
sensing and pressure compensation.
Bridge passage 12 is in communication with a
S sensing shuttle passage 22, FIG. 2. If the valve is a
single section or monoblock valve, the hydraulic flow
in passage 22 continues past shuttle check valve 24 and
into crossing passage 26 and through-shuttle passage
28. If the valve is a multi-section valve, then a
plurality of identical valve sections are aligned side
by side, for example as shown cut away at 30 and 32.
If the work port pressure of central section 31 in
sensing shuttle passage 22 is greater than the work
port pressure in through-shuttle passage 34 of the
lS previous section 30, then shuttle check valve 24 moves
downwardly to close passage 34 and the higher pressure
from passage 22 is communicated through crossing pas-
sage 26 to through shuttle passage 28. If the work
port pressure in sensing shuttle passage 22 of present
~ valve section 31 is less than the work port pressure in
the through-shuttle passage 34 of the previous section
30, then shuttle check valve 24 moves upwardly to close
passage 22 and enable the higher pressure in passage 34
to be communicated to through-shuttle passage 28.
Likewise, shuttle check valve 36 of the next section 32
operates to apply the higher pressure of through-
shuttle passage 28 of the present section 31 and sens-
ing shuttle passage 38 of the next section 32 to the
through-shuttle passage 40 of next section 32. In this
manner, the highest work port pressure of all the valve
sections is communicated to a sense line 42 connected
to the input 44 of hydraulic pump 46 and to a communi-
cation passage 48 which extends through all of the
valve sections, as shown through respective passages
50, 52 and 54.
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. Transfer passage 52 communicates through
cross passage 56 with a pressure compensating check
valve 58, such as a spring biased poppet. The bottom
side 60 of check valve 58 is thus applied with the
pressure from passage 52, which is the highest work
port pressure of the valve sections. The top side 62
of valve 58 is of the same area as the bottom side and
thus the same pressure is applied in passage 64 above
valve 58. Passage 64 around the top of valve 58 is a
feeder passage which also has a section around spool 6,
FIG. 1. The pressure in feeder passage 64 is thus the
highest work port pressure of the multiple valve sec-
tions.
The above noted description e~plains pressur-
ization of the system in response to initial movement
of spool 6. This pressurization occurs before metering
notch or passage 66 in the spool and comes into commun-
ication with feeder passsage 64.
Further leftward movement of spool 6 brings
2~ metering passage 66 into communication with feeder
passage 64. Supply passage 68 then communicates with
feeder passage 64 through metering passage 66.
Metering passage 70 and supply passage 72, effective
during rightward movement of spool 6, are comparable.
~5 Supply passages 68 and 72 are supplied from pump ~6
which outputs hydraulic flow pressure on output 74
which is a predetermined amount greater than the flow
pressure input to the pump at 44. Since the pressure
at 44, FIGS. 1 and 2, is the highest work port pressure
of the valve sections, the pressure in supply passages
68 and 72 is the noted predetermined amount greater
than the highest work port pressure. As above noted,
the initial pressurization of the system causes the
pressure in feeder passage 64 to be the same as the
highest work port pressure. There is thus a fixed
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differential pressure across metering passage 66 from
supply passage 68 to feeder passage 64.
Hydraulic fluid can flow from supply passage
68 through metering passage 66 to feeder passage 64.
Feeder passage 64, FIG. 2, communicates with the left
side of bridge passage 12 through cross passage 76 and
an orifice 78 opened by downward movement of pressure
compensating check valve 58. The flow rate in feeder
passage 64 is such as to provide sufficient fluid to
~ afford the same amount of pressure on the top side 62
as on the bottom side 60 of valve 58. Valve 58 can
move up and down to control the size of orifice 78,
such that should the load increase, causing work port
pressure to increase r the shuttle system communicates
1~ the need for increased fluid to be delivered from the
pump through the pressure compensating mechanism into
the bridge and the work port until balance is achieved
in the system. The fluid trans~erred into passage 76
flows through bridge 12 to the right side of the
~ latter, FIGo 1~ and through spool passage 20 to work
port 8, to supply the additionally required fluid.
Load 80 is raised via outlet and inlet work
ports 8 and 10 and their respective connection lines 82
and 84. Further leftward movement of spool 6 by the
~5 operator further raises load 80 by increasing the area
of metering passage 66 which is exposed to feeder pas-
sage 64. Flow rate is equal to the product of the area
and the square root of the differential pressure.
Since the differential pressure across metering passage
66 is constant, flow rate is a direct linear function
of the area of metering passage 66 which is in communi-
cation with feeder passage 64. This area is increased
during further leftward movement of spool 6, thus
supplying more fluid and raising load 80. Standard
pressure relief valves 86 and 88 are provided for the
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work ports and reservoir passage. A standard spring
centering mechanism 90 is provided on the end of spool
6 Eor locating the latter's neutral positionO
