Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~ 29022
PROPORTIONAL FOLLOWER SPOOL VALVE SYSTEM
Background of the Invention
A. Field of the Invention
This invention relates generally to the field
of servo follower proportional control spool valves.
B. Background Art
Servo follower proportional control valves
are well known in the art and are generally described in
I980 - 81 Fluid Power Handbook and Directory, page A-
141 and in National Conference on Fluid Power, 1976
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Electro-proportional Position Controls - An Analysis for
Application on Various Hvdraulic Contro~ Function~ by
S D. W. Swaim.
Prior proportional control valves have left
much to be desired with respect to rapid response to
input commands which may be rapidly changing. In prior
spool valves, such rapid response was adversely af~ected
by the use of dynamic seals. The seals would enter the
space between the bore and the active valve element and
thus increase friction. In this way, such seals were
known to cause breakaway and running friction between
the valve element and bore, thereby decrea~ing the
ability to rapidly respond as well as decreasing ion
frequency tracking ability.
Another objectionable feature of prior pro-
portional control valves decreasing rapid response has
been the relatively large driving chamber volume. The
larqe chambers required a relatively large amount of
fluid to produce movement, which in turn required a
substantial amount of time. For example, ~ee U. S.
Patents 2,526,709 issued October 24, 1950 to W. O. Tait
and 2,555,755 issued June 5, lg51 to R. P. Moore.
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Many prior proportional valves are of the
electrohydraulic type which have flapper nozzles and
which produce valve spool movement. In these systems a
DC electrical signal to the coils of the pilot stage of
a force-balanced torque motor developis a torque moving
the armature-flapper either clockwise or counter clock-
wise between the nozzles. This movement restricts flow
out of one of the nozzles and eases flow out of the
other with the pressure unbalance driving the spool.
These flapper-nozzle proportional valves have left much
to be desired as a result of the constant leakage of
the valve including the time when the valve is at null.
This leakage at null is a serious disadvantage since
the valve may be at null for a long period of time and
would lose a substantial amount of energy, as for
example a quarter to four-tenths of a gallon per minute
per valve. For multiple valves the loss has been
considerable and has required cooling members to remove
the lost energy. Another problem with flapper-nozzle
proportional valves has been in their small orifices to
control the flapper as well as small spring feedback.
me small orifices are liable to clogging and the small
springs are liable to fatigue. Spool proportional
valves suffer from similar problem~ as they also have
small orifices and high null leakage. ~n such valves
the leakage at null undesirably increases a~ flow ln-
creases. The following is an example of a patent on
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1229022
spool within spool valves: U.S. Patent 3r53~r895
issued September 23, 1970 to A. A. Rothrock.
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Summary of the Inqenti~n
A proportional follower spool valve system
which provides output fluid flow proportional to a
positional control. The system includes a main spool
having an inner passage and a pilot spool which is
slidable in the passage. First fluid connections are
controlled by the main spool and they are effective to
control output fluid flow in accordance with the posi-
tion of the main spool. The pilot spool is moved from
a null position with the main spool in either a first
or second direction and in accordance with the posi-
tional control. First and a second driving chambers
are formed by the main spool each having a driving area
substantially less than the largest solid cross-
sectional area of the main spool. Second fluid con-
nections are controlled by the pilot spool for admit-
ting fluid under pressure (1) to the first chamber when
the pilot spool moves in the first direction away from
the first chamber and (2) to the second chamber when
the pilot spool moves in the second direction away from
the second chamber. In this manner, the main spool is
moved in the same direction as the pilot spool until a
null position is reached.
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Further in accordance with the invention, the
main spool is slidable in a main passage having end
chambers maintained at substantially return pressure.
Each of the first and second driving chambers are dis-
posed between a respective end chamber and return pres-
sure thereby to avoid dynamic seals on the main spooi.
Brief Description of the Drawings
Figs. 1-4 are detailed, elevational sectional
views of a proportional follower spool valve system of
the present invention, and
Fig. 5 is an exploded perspective view of the
elements of Figs. 1-4.
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Detailed Description of the Invention
Referring now to Fig. 1 there is shown a servo
follower proportional control spool valve 10 which
comprises a housing 15 having a cylindrical bore 15a for
slidably receiving a main spool 12. The main spool has
an open bore 12a for slidably receiving a pilot spool
11. Valve 10 may be coupled to a pump 17 for pumping
hydraulic fluid from a sump 16a through an inlet line
17a to an inlet passage 32 of valve 10.
A fluid operated actuator operated by valve 10
may be a piston 22a operating in a cylinder 22. ~ne end
of cylinder 22 is connected through a line 24 to an
outlet cylinder passage 27 of valve 10. The opposite
end of cylinder 22 is similarly connected through
another line 25 to another outlet cylinder passage 29.
The load (not shown) may be coupled to the shaft of
piston 22a in conventional manner. Further valve 10 has
a return passage 40 which is connected through a return
line 18 back to sump 16a.
Main spool 10 has cylindrically lands 60, 61, 67
and 68 spaced axially with respect to longitudinal axis
16. Chamfered main flow metering grooves or passages
64, 48a are formed on the left and right sides
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of land 60 and similar main flow metering grooves 48b,
65 are formed on the left and right sides of land 61,
Grooves 48a,b extend downwardly into spool 12 to define
a cylindrical pressure groove or reces~ 43. A trans-
verse inlet metering orifice 42 extends between groove43 and bore 12a in main spool 12. A cylindrical tank
groove or recess 70 is formed between main flow metering
groove 64 and land 67 with a restricted orifice 70a
formed between groove 70 and bore 12a. Similarly, a
cylindrical tank groove 71 is formed on spool 12 between
groove 65 and land 68 with a restricted orifice 71a
defined between groove 71 and bore 12a. Land 67 extends
into a reduced diameter cylindrical section 72 which
defines the left end of main spool 12 while land 68
extends into reduced diameter section 73 which defines
the right end of spool 12. Connecting passages 46, 47
are formed transverse of axis 16 and provide connecting
passages between bore 12a and chambers formed by the
outer surfaces of sections 46, 47 respectively.
Lands 60, 61, 67 and 68 on main spool 12 are
slidably but sealingly received in cylindrical bore
15a. This bore presents a cylindrical land surface 31
disposed between annular recess 30 leading to cylinder
passage 27 and annular pressure recess 44 leading to
pressure inlet passage 32. Similarly, cylindrical land
surface 33 of bore 15a is disposed between annular
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recess 35 which leads to cylinder passage 29 and
pressure recess or cavity ~4. In the spool 12
position shown in Fig. 1, recesses 43, 44 form an
annular pressure chamber 45. Further, bore 15a
presents cylindrical land surfaces 36 and 37. Land 36
is disposed between recess 30 and an annular return
recess 40a and land 37 is disposed between recess 35
and return recess 40b. Return recesses 40a,b lead to
return passage 40 and form annular return chambers with
recesses 70, 71 respectively in the spool 12 neutral
position.
At its left end, bore 15a forms an elongated
end recess 74 for receiving land 67 and a floating
annular spacer 50 which abutts an end wall of end cap
78. Spacer 50 has its inner cylindrically shaped bore
surface 50d ground to receive the outer surface of
section 72. A slot is formed on the outer surface of
spacer 50 to provide for an O-ring 50a for sealing
engagement between the spacer and recess 74. It is in
this manner that spacer 50 is effective to ~float"
within recess 74. In addition an annular slot 50b
leading to return passage 19 is undercut at the leEt en~
of spacer 50 which slot is coupled by way of a passage
50c to end chamber 55 formed by the inner hore oE spacer
55 and wall 78b. In this manner end chamber 55 is
referenced to tank. Wall 78b is formed by a left end
cap 78 which threadedly engages housing 15 to seal the
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bore 15a by way of an O-ring 78a. A left end driving
chamber 20 is formed by a right wall 20a of spacer 50, a
left wall 20b of land 67 and the upper surface of
section 72. The purpose and operation of driving
chamber 20 will later be described in detail.
It will be understood that the components as
shown within and adjacent to right end recess 75 o~ bore
15a are similar to those described with respect to
recess 74 and need not be further described in detail.
-These components comprise floating spacer 51, O-ring
51a, annular slot 51b, passage 51c, right wall 80b,
return passage l9a, chamber 56 and right end driving
chamber 21.
As previously described pilot spool 11 is re-
ceived within hore 12a of spool 12. Spool 11 has at
its center a V-groove piston 14 defined by a pair of
metering lands 14a, b where the V-groove 14c is formed
between the lands. In the null position of spool 11
with respect to spool 12 as shown in Figs. 1,
3, V-groove 14c is in communication with metering
orifice 42. Metering lands 14a, b each form a sharp
metering edge with a re.spective wall of orifice 42 and
sealingly engage bore 12a so that there is no flow of
fluid from orifice 42 into the left or right side of
bore 12a. Spool 11 also has two axially spaced
cylindrical lands llc, d formed at the left and right
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ends of the spool to sealingly engage the left and right
ends of open bore 12a in all positions of spool 11.
Metering land 14a and land llc are integrally inter-
connected by stem portion lla which defines an elongated
longitudinally directed annulus forming a longitudinal
passage which extends almost one-half of the length of
spool 11. Similarly, stem portion llb interconnects a
metering land 14b and land lld with an elongated longi-
tudinal annulus forming a passage extending almost half
the length of spool 11. Passage lla leads through to
passage 46 and to orifice 70a while passage llb leads
through to orifice 71a and to passage 47. The left end
of spool 11 terminates in an end portion lle which is
adapted to engage a stop 78c of end cap 78. Similarly,
a right end portion llf of spool 11 is adapted to engage
a stop 80c of right end cap 80. To provide axial move-
ment of pilot spool 11, there is provided an actuator 23
which is rigidly connected as shown through the center
of left end portion lle to the left section of spool
20 11. Actuator 23 extends through chamber 55 and through
the axis of end stop 78 and in sealing relation
thereto.
In operation, in the position shown in Fig. 1,
spools 11 and 12 are- in their center position within
bore 15a and the spools are in their null position with
respect to each other. In this position, main spool 12
is at a neutral position in hore 15a with land 60
sealingly engaging lands 36 and 31 and land 61 sealingly
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engaging lands 33 and 37. Accordingly, in this neutral
position of main spool 12 in bore 15a there is no flo~
of fluid from the inlet passage 32 to either outlet
passase 27 or 29. With spools 11 and 12 at null there
is no flow of fluid from passage 32 through metering
orifice 42 to either of chambers 20 or 21.
As shown in Fig. 2, when pilot spool 11 is moved
to the right, metering land 14a disengages from the left
wall of metering orifice 42 and fluid from inlet passage
32 flows through chamber 45, orifice 42 (~low 45a) and
then through annular passage lla and passage 46 to
chamber 20. The pressure in this chamber 20 is
effective between fixed wall 20a and moveable wall 20b
to move wall 20b of main spool 12 to the right to the
position shown in Fig. 3. As long as the opening be-
tween land 14a and the left wall of orifice 42 remains
open, there is pressure applied to chamber 20 to move
spool 12 to the right until that opening closes and
spools 11, 12 are at null one with the other. In this
position as shown in Fig. 3, spool 12 has moved out of
the neutral or central position with respect to the
lands in bore 15a. Specifically lands 61, 60 disengage
from lands 33, 36 respectively. Therefore fluid from
inlet passage 32 flows through chamber 45, metering
groove 48b, groove 35 and then to cylinder line 25. In
addition, return flow of fluid from cylinder line 24
flows through passage 27, recess 30, through metering
groove 64 to return groove 40a and thence to tank.
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It will now be understood that in this null
position between spools 11 and 12, as shown in Fig. 3,
there is a controlled flow through valve 10 in propor-
tion to the movement of pilot spool 11 from the neutral
position shown in Fig. 1. It is in this way that valve
10 provides an output hydraulic flow proportional to
actuator 25 movement or to an electrical signal where
the electrical signal is effective to move actuator 25
in a manner later to be described. In the control
position shown in Fig. 3 with spools 11, 12 at null,
there is no flow of fluid between the spools and thus
there is avoided loss of energy which in prior systems
would result from a continuous flow of fluid between the
spools.
Another example of the movement of pilot spool
11 is .shown in Fig. 4, in which main spool 12 is in its
position shown in Fig. 1 and the pilot spool is moved to
the let from its position in Fig. 1. Thus an opening
is formed between land 14b and the right wall of orifice
42. Accordingly, fluid flow 45b may he traced from
inlet passage 32, chamber 45, orifice 42, passage llh,
connecting passage 47 and thence to chamber 21. In the
manner previously described, pressure on wall 21b is
effective to move main spool 12 to the left until it
2S reaches a null position with pilot spool 11 at its new
control position. At this new control position ~not
shown) land 60 disengages from land 31 and land 61
disengages from land 37. Therefore fluid from inlet
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passage 32 flows past metering groove 48a to recess 30
and then through passage 27 to cylinder 22. Return flow
of fluid takes place by way of line 25 to passage 29 and
groove 35 and groove 65 to return 40b. It is in this
way that valve 10 operates as a servo follower and
proportional control valve.
It will be understood that in order to provide
for fast precise response of valve 10 to the movement of
pilot spool 11, it is preferred that each of end driving
chambers 20 and 21 have a minimum fluid volume. For
rapid response of valve 10 these chambers only require
sufficient volume to provide the ~orce required to move
main spool 12 to overcome the flow effects on the main
spool. ~ne of these flow effects is shown in Fig. 3 as
the flow from inlet 32 through chamber 45 and metering
groove 48b to recess 35 and outlet passage 29. As well
known by those skilled in the art, these flow effects
comprise the Bernoulli effect as well as other effects
of flow across main spool 12.
It will be seen that ring shaped chambers 2n and
21 are constructed having ~inimum volu~e by their
provision, in one dimension, of having an outer diameter
equal to bore 12a and an inner diameter equal to the
outer diameters of recesses 72, 73 respectively. In the
other dimension, chambers 20, 21 are constructed of
minimum volume by means of the sidewalls of floating
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spacers 50, 51 respectively and lands 67, 68 respective-
ly. It is in this manner that chambers 20, 21 operate
effectively and each have substantially less volume than
that of the spool end cha~bers 55~ 56 respectively.
More particularly, the drive area of chamber 20 defined
by wall 20b is substantially less than the transverse
solid or metal cross sectional area of main spool 12
itself at its largest diameter. That largest cross
sectional area may be that taken at land 67 perpendic-
ular to axis 16. The remaining cross sectional areadefined by the end of section 72 is at return pressure
in chamher 55. Similarly, wall 21b is of substantially
less area than the largest solid cross sectional area
of spool 12. The end of section 73 is at return
pressure.
In addition, as previously described, spacers
50, 5] provide the walls of one side of chambers 20, 21
respectively without imposing side loads on the system.
Spacers 50, 51 effectively float in main bore 15a and
20 allow the ends of both spools 11, 12 in chambers 55, 56
to operate at tank or exhaust pressure. It is in this
way that the ends of spools 11, 12 do not play any role
in the movement.
It will be understood that driving chamber 20 is
positioned adjacent the left end section of spool 12
between tank groove 40a and end chamber 55 also at tank
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or return pressure. In this manner, any minimal leakage
from drive chamber 20 flows harmlessly to tank rather
than flowing to and adversely affecting a control port
such as port 30. Similarly, chamber 21 is between
groove 40b and end chamber 56. Thus any leakage flows
harmlessly to tank rather than adversely affecting
control port 35. It is in this way that valve 10 does
not require dynamic seals on spools 11 and 12. In this
way, valve 10 rapidly follows rapidly changing step
functions, for example, slow movements for accurate
positioning resolution.
Further, annular passages lla, llb are sized to
provide minimum volume passageways between orifice 42
and chambers 20, 21 thereby to minimize compressibility
losses in the trapped volume.
It will be understood that if, in the example
shown in Fig. 2, pilot spool 11 is moved rapidly to the
right in a step movement of relatively large magnitude
then passage 42 is completely opened. The resultant
relatively large opening of orifice 42 allows a
relatively large magnitude of flow of fluid from chamber
4S to chamber 20. Thus the resultant rapid step func-
tion of pressure developed in chamber 20 is effective to
quickly move main spool 12 to the right in a direction
to close that large opening. It is in this way there is
produced an initial rapid change in pressure in chamber
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20 which is effective to rapidly tend to close the
opening of orifice 42. This rapid change in pressure
decreases to a finite metering as passage 42 is closed~
On the other hand if, in the example shown in Fig. 2,
spool 11 were only moved a relatively small distance to
the right, a small secant opening would only be provided
between land 14a and the left wall of the orifice. The
forsgoing also applies for spool 11 movement to the left
as in the example of Fig. 4. Thus only a finite move-
ment of spool 12 to the right would be effected untilthat opening would be closed. Thus, valve 10 achieves
high magnitude response to big step functions in the
movement of pilot spool 11 and small magnitude response
as the step function decreases.
It will be understood that bleed orifice 70a is
provided in order to bleed off fluid from chamber 20.
This chamher is being compressed as in Fig. 4 when main
spool 12 moves to the left. Similarly, bleed orifice
71a is provided to bleed off fluid from chamber 21 when
this chamber is compressed by movement of spool 12 to
the right as shown in Figs. 2 an~ ~. The size of
orifices 70a, 71a is a factor in determining the
dynamics of the system of valve 10 since the compression
of the respective chambers 20 and 21 i~5 determined by
the size of that ori~ice. In another embodiment of the
invention, the flow from bleed orifice~ 70a, 71a
through return recesses 40a, 40b may be returned to tank
separately from return passages 19, 19a. ~urther,
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orifices 70a, 71a may be connected (not shown) through
the center of spool 11 to respective end chambers 55, 56
which are in turn connected to tank.
It will further be understood that pilot spool
11 is pressure balanced so that it may be moved by a
very light force applied to actuator 23. ~y pressure
balance, it is meant that there is no spring biasing
applied to pilot spool 11 and end chambers 55, 56 within
which the pilot spool reciprocates and is halanced at
tank or drain. Such a light force to actuator 23 may be
applied by a digital drive motor such as a bi-
directional linear actuator Series 9200 made by Airpax,
Cheshire, Connecticut 06410. ~uch a linear actuator
provides a half a thousandths linear motion for each
applied digital pulse. In this manner, for a digital
input to the linear actuator, pilot spool 11 is
accordingly moved and is accurately followed by main
spool 12. It is in this way that valve 10 provides
accurate and repeatable flow from pressure input 32 to
20 cylinder ports 27, 29. In another example, actuator 23
may be moved manually or may be moved by a linear
solenoid of the proportional or on/off type which is
coupled to each end of spool 11.
