Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Description
Metering Slo~ Configuration for A Valve Spool
Technical Field
This invention relates to fluid control valves
and more particularly to a meteriny slot configuration
in which flow forces generated by fluid flowing
thereacross are relatively low while providing a
metering area which increases in size rather quickly
with small increments of movement of the valve spool~
Background Art
Fluid control or metering slots are commonly
formed in a valve spool to interconnect a groove and an
adjacent control land in the spool to provide good
modulation of fluid flow through the control valve.
One of the problems associated with any metering slot
configuration is its effect on flow forces generated by
the fluid passing therethrough. It is known that
generally flow forces generated by a metering slot
react differently dependent upon whether the slot is
controlling fluid flow in a "meter in" or "meter out"
condition. For example, metering slots in the form of
shallow, cylindrical pockets formed by plunge cutting
with an end mill cutter or the like directed radially
inwardly and at a slight angle with respect to the
spool provides low rlow forces in a meter out
condition. The problem with such cylindrical pocket is
that the metering area of the slot increases rather
slowly with respect to spool travel and in some cases
does not provide the desired modulating
characteristic. On the other hand, while the key
cutter type metering slo~s can effectively provide the
desired modulation by opening a substantial metering
,
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area very quickly, the ~low forces generated thereby in
a meter out condition are rather high. These high flow
forces then require centering springs having higher
preloads and result in higher lever efforts by the
operator causing undue fatigue.
The present invention is directed to
overcoming one or more of the problems as set forth
above.
Disclosure of the Invention
In one aspect of the present invention, a
fluid control valve includes a body having a bore
therein and an annulus communicating with the bore. A
valve spool is slida~ly disposed in the bore and has a
cylindrical land and an intersecting control face for
controlling fluid flow between the bore and the
annulus. The spool has a metering slot in the control
face and land formed by causing relative movement
between the spool and a rotating end mill cutter to
plunge cut into the control face to a preselected depth
cutting away a portion of the cylindrical land adjacent
the control face and ~y then causing relative
transversing movement between the spool and the cutter
so that the cutter cuts laterally across the control
face and cylindrical land to establish a preselected
width of the metering slot. The cutter is maintained
at an acute angle relative to the control face to
undercut the cylindrical land defining a flow control
edge of the metering slot.
The present invention provides an improved
metering slot configura~ion for a control valve spool
in which the flow forces generated by the fluid passing
through the slot in a fluid flow metering position of
the spool are relatively low. The lateral width of the
3~ subject throttling slot permits a metering area of the
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slot to increase in size very quickly relative -to the
travel distance of the spool to minimize the
restriction to fluid flow thereacross in the fluid flow
metering position of the spool travel.
Brief Description oE the Drawin~
Fig. 1 is a sectional view through a control
valve illustrating an embodiment of the present
invention in combination with a diagrammatic
illustration of a fluid circuit;
Fig. 2 is a somewhat enlarged plan view of a
portion of FigO 1.
Fig. 3 is a cross-sec~ional view taken along
lines III-III of Fig. 2;
Fig. 4 is a sectional view taken along lines
IV-IV of Fig. 3;
Fig. 5 is a somewhat enlarged sectional view
taken along lines V-V of Fig. 1;
Fig. 6 is a plan view of another embodiment of
the present invention; and
Fig. 7 is a sectional view taken along line
VII-VII of Fig. 6.
Bes~ Mode for Carrying Out the Invention
Referring to the drawings, a control valve 10
is connected to a pump 11 via a supply conduit 12 and
to the head end and rod end of a hydraulic cylinder 13
via a pair of motor conduits 14 and 16. The rod of the
hydraulic cylinder 13 is connected to a blade 17
pivotally mounted on a tractor 18 in the conventional
manner. The supply conduit 12 is also connected to a
pressure compensated bypass valve 19 which is connected
to a tank 21 via a drain conduit 22.
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The control valve 10 includes a valve ~ody 23
having a longitudinally extending bore 24 therein and a
plurality of axially spaced annuluses 26-30
intersecting the bore. An inlet port 32 connects the
supply conduit 12 to the center annulus 28. A pair of
motor ports 33,34 connect the motor conduits 14,16 with
the annuluses 27,29. A pair of exhaust ports 36,37
connect the annuluses 26 and 30 with the tank 21. A
pair of signal ports 38,3g intersect with the bore 24
adjacent the annuluses 27,28 and are connected to a
single signal outlet port 41 throu~h a resolver 42.
The control valve 10 also includes a valve
spool 46 slidably disposed in the bore 24 and is
movable between Raise, Neutral and Lower positions.
The spool 46 has a pair oE spaced apart cylindrical
lands 47,48 which cooperate with the bore 24 when the
valve spool 46 is in the Neutral position shown to
block the annulus 28 from the adjacent annuluses 27 and
29. Each of the lands 47,48 has an annular control
face 49 and a pair of metering slots, one shown at 51,
recessed into the control face. The metering slots 51
are of the conventional key cutter type commonly used
in a meter in condition. The valve spool 46 also has a
pair of cylindrical lands 52,53 at opposite ends of the
spool and which cooperate with the bore 24 to block the
annuluses 27l29 from the annuluses 26,30 respectively
at the Neutral position. A pair of diametrically
opposed flat surfaces or chordal recesses, one shown at
54, are prov ded adjacent the land 52 and intersect
with a pair of control faces~ one shown at 560
Similarly, a pair of diametrically opposed flat
surfaces, one shown at 57, are provided adjacent the
land 53 and intersect with a pair of control faces, one
shown at 58.
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As best shown in Figs. 2-~ a fluid control or
metering slot 61 is recessed into each of the control
faces 56 of the valve spool 46. The metering slot 61
is formed by positioning a rotating ball-end end mill
c~ltter 6Q at a preselected acute angle relative to the
control face 56 and at a preselected distance o~fcenter
from the longitudinal axis of the spool. The rotating
cut~er is then advanced along its longitudinal axis to
plunge cut into the control face 5~ and flat surface 54
to a preselected depth to form a hemispherical shaped
recess ~herein. The cutter also cuts away a por~ion of
the peripheral surface oE the cylindrical land 52. The
cutter is then moved transversely relative to the spool
so that the cutter cuts a laterally extending
semicylindrical-shaped groove across the control face,
flat surface, and cylndrical land to establish a
preselected width of the metering slot. The cutter is
maintained at the preselected angle as it traverses the
control face to undercut the peripheral surface of the
land and deEine a flow control edge 62 of the metering
slot. The major portion of the metering slot has a
substantially semicylindrical surface with the lateral
ends of the metering slot being spherically shaped~
Moreover, the flow control edge 62 has a wavy or
~ndulating shape as viewed in Figs. 1 and 2.
As best shown in Figs. 1 and 5, fluid control
or metering slot 6~ is also recessed into each of the
control faces 58 and cylindrical land 53 of the valve
spool ~6. The metering slot 63 is formed in a manner
as described above with the primary difference being
that the diameter of the end mill cutter is slightly
smaller so that the bottom surface of the metering slot
is contiguous with the flat surface 57.
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The preselected angle of the cutter is chosen
so that the exit angle oE the flow control edge 62 of
the metering slots 61,63 is approximately 30
relative to the associated control faces 56,58. In
this embodiment the preselected angle of the cutter is
about 30.
The above-described process of forming the
metering slots sets forth that the cutter 60 is moved
relative to the spool 46. However, it is recognized
that identical metering slots can be formed by moving
the spool relative to the rotating ball-end end mill
cutter. The valve spool 46 also has a pair of axial
elongate signal transmitting slots 66,67 in the
peripheral surface of the cylindrical lands 52,53
respectively.
An alternate embodiment of a metering slot
configuration of the present invention is disclosed in
Figs. 6 and 7. It is noted that the same reference
numerals of the Eirst embodiment are used to designate
similarly constructed counterpart elements of this
embodiment. In the embodiment, however, the flat
surfaces adajacent the land 53 have been replaced with
a reduced diameter cylindrical portion 68 so that the
control face 56 is an annular shoulder. A metering
slot 69 is formed in the annular control face 58 and
cylindrical portion 68 by the same process described
above.
Industrial Applicability
In operation, the blade 17 is raised by
shifting the valve spool 46 leftward from the position
shown toward the Raise position. In so doing, the
signal slot 67 establishes communication between the
annulus 29 and the signal port 39, the annulus 28 is in
communication with the annulus 29, and the annulus 27
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is in communication with the annulus 26. Establishing
comMunication between the annulus 29, and the signal
port 39 causes a load signal to be directed to the
bypass valve 19 to shift it to the left to resist or
block fluid flow from the supply conduit 12 to the
tank~ With the annulus 28 in communication with the
annulus 29, fluid from the supply conduit 12 is
directed th~ough the motor conduit 16 to the rod end of
the hydraulic cylinder 13 causing the hydraulic
cylinder to retract. The fluid exhausted from the head
end o the hydraulic cylinder 13 passes through the
metering slot 61 in a meter out direction and is
returned to the tank 21.
Due to the area difference between the head
end and rod end of the hydraulic cylinder, the volume
of fluid exhausted from the head end of the cylinder is
approximately 150~ of the volume being directed into
the rod end. The metering slot 61 provides a metering
area which increases in size very quickly as the valve
spool 46 is moved to the operating position to minimize
the pressure drop across the valve spool. Moreover,
the profile of the metering slot 61 minimizes the flow
forces generated by the Eluid passing therethrough and
past the flow control edge 62. In a direct comparison
with a key cutter slot (similar to the metering slot
51) under identical operating conditions, the flow
forces generated by the present metering slot
configuration were reduced to less than half the flow
forces generated by the key cutter metering slot. The
reduction in flow forces is attributed primarily to the
e~it angle of the flow control edge 62 of the metering
slot which causes the fluid to exit from the slot at an
angle opposite to the direction of the fluid entering
the slot and at an acute angle relative to the control
face.
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~ hen the blade 17 is dropped from a hiyh
height by shifting the valqe spool 46 rightward to the
Lower position, a large volume of Eluid is forced from
the rod end of the hydraulic cylinder 13 and must pass
througn the metering slot 63. However, the metering
slot 63 also provides a rather large area which opens
ver~ quickly as the spool is moved rightward to the
Lower position and thereby minimizes the pressure drop
across the spool~ The proile of the metering slot 63
also minimizes the flow forces generated ~y the large
flow passing therethrough in the manner described
above. The wavy shape of the flow control edge 62
provides fine control over fluid flow through the
metering slot at the initial opening of the metering
lS slot when fine modulated control of the speed of the
hydraulic cylinder i5 desired.
In view of the above~ it is readily apparent
that the structure of the present invention provides an
improved metering slot conficJuration capable of precise
~O modulation of high fluid flows while minimizing the
generation of flow forces. The profile of the control
edge of the metering slot provides for the opening of a
rather large metering area with a relatively short
travel distance of the spool to minimize the
restriction of flow therethrough. The profile of the
metering slot also causes the fluid to exit from the
metering slot at an angle which minimizes the flow
forces acting on the spool.
Other aspects, objects and advantages of this
invention can be obtained Erom a study of the drawingst
the disclosure and the appended claims.
