U.S. patent number RE29,292 [Application Number 05/570,119] was granted by the patent office on 1977-07-05 for control valve means for fluid motors.
This patent grant is currently assigned to Sundstrand Corporation. Invention is credited to Francis H. Tennis.
United States Patent |
RE29,292 |
Tennis |
July 5, 1977 |
Control valve means for fluid motors
Abstract
A pressure reducing valve mechanism maintains pressure in one of
the service passages of a control valve at a desirably low value
except at times when the control valve element is actuated to a
position effecting flow of pressurized supply fluid to said service
passage for delivery to a motor governed by the control valve.
Inventors: |
Tennis; Francis H. (Oconomowoc,
WI) |
Assignee: |
Sundstrand Corporation
(Rockford, IL)
|
Family
ID: |
26842696 |
Appl.
No.: |
05/570,119 |
Filed: |
April 21, 1975 |
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
145137 |
May 20, 1971 |
03730219 |
May 1, 1973 |
|
|
Current U.S.
Class: |
137/596; 137/106;
91/420; 91/447; 137/596.1 |
Current CPC
Class: |
F15B
13/02 (20130101); Y10T 137/87169 (20150401); Y10T
137/87233 (20150401); Y10T 137/2554 (20150401) |
Current International
Class: |
F15B
13/02 (20060101); F15B 13/00 (20060101); F15B
013/04 () |
Field of
Search: |
;137/596,596.2,596.12,596.13,596.1,106,115,504
;91/421,447,445,420 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Cohan; Alan
Assistant Examiner: Michalsky; Gerald A.
Attorney, Agent or Firm: Jones; Ira Milton
Claims
The invention is defined by the following claims: .[.1. Valve
instrumentalities for governing operation of a fluid motor,
characterized by:
A. a control valve having a pair of service passages for connection
with the opposite sides of a fluid motor, and a valve element
movable through a number of metering positions to full flow
operating positions concurrently communicating either of the
service passages with pressure fluid supply means and the other
service passage with fluid return means in the valve, from a hold
position closing off said service passages from the fluid supply
and return means;
B. a pressure reducing valve mechanism for each service passage,
having a passageway through which exhaust fluid from the governed
motor flows to the fluid return means through the associated
service passage in one of said full flow operating positions of the
valve element, and a pressure responsive valve member actuatable in
a passageway restricting direction whenever the pressure of exhaust
fluid in the associated service passage is caused to exceed that of
fluid in the return means by a substantially small amount as a
result of the valve element occupying one of said metering
position, to thereby maintain the pressure of exhaust fluid in the
associated service passage at a substantially uniformly low value
above that of fluid in the return means;
C. and means cooperable with each pressure reducing valve mechanism
and rendered operative in response to pressure of fluid in said
pressure fluid supply means for effecting flow of such supply fluid
through the associated service passage to the governed motor
substantially without
interference from said pressure reducing valve mechanism..]. .[.2.
The combination of claim 1, wherein said last named means comprises
a chamber communicated with the pressure fluid supply passage
means, and a plunger which is connected with said valve member and
which operates in said chamber to be held by pressure of supply
fluid therein in a position blocking movement of said valve member
toward a passageway restricting position..]. .[.3. In combination
with a control valve for a fluid motor, having a valve element
movable to a first position to communicate a service passage with
supply passage means, and movable to a second position to provide
for flow of motor exhaust fluid through the service passage to
return passage means, said control valve element being movable
through a range of metering positions short of said second position
thereof to provide for restricted flow of motor exhaust fluid from
the service passage to the return passage means in an amount which
increases as the valve element approaches its said second
position:
A. a pressure reducing valve mechanism having
1. a passageway connecting with the service passage and through
which pressure fluid flows both to and from the governed motor,
2. a valve member actuatable in one direction to restrict flow of
motor exhaust fluid through said passageway,
3. and a spring to yieldingly urge the valve member toward an
inactive position affording substantially free flow of motor
exhaust fluid through said passageway;
B. means rendered operative in response to the rise in service
passage pressure produced by movement of the control valve element
to one of its said exhaust flow metering positions for effecting
actuation of the pressure reducing valve member in the flow
restricting direction an extent depending upon the magnitude of the
pressure present in the service passage;
C. and means rendered operative in response to the pressure of
supply fluid flowing to the service passage in said first position
of the control valve element, for effecting flow of such supply
fluid through said passageway and to the governed motor
substantially without interference from the
pressure reducing valve member..]. .[.4. The combination of claim
3, further characterized by:
A. said control valve element being movable to a load holding third
position to close off the service passage from the fluid supply and
return passage means:
B. and said pressure reducing valve mechanism also being operable
to maintain the pressure in the service passage at said low value
in said load holding position of the valve element..]. .[.5. The
combination of claim 3, wherein said last named means
comprises:
A. means connected with the service passage providing a bypass
around the pressure reducing valve mechanism, through which
pressure fluid can flow to the governed motor in said first
position of the valve element;
B. and a check valve in said bypass to block reverse flow of fluid
through the bypass..]. .[.6. Valve instrumentalities for governing
flow of pressure fluid to and from a fluid motor via a service line
connectable therewith, characterized by:
A. a directional control valve having fluid supply and return
passage means, a service passage for connection with the service
line to form a part thereof, and a valve element movable from a
hold position to first and second operating positions to
respectively communicate the service passage with the fluid supply
and return passage means, said valve element being movable through
a range of metering positions to provide for return flow of motor
exhaust fluid from the service passage to the return passage means
in an amount which increases with movement of the valve element
toward said second position thereof and reaches maximum
thereat;
B. a pressure reducing valve mechanism having a valve member to
regulate flow of motor exhaust fluid through the service line to
the service passage, said valve member being urged by a spring
toward a normally inactive position but being actuatable out of
said position in a direction to restrict return flow of motor
exhaust fluid through said service line to the service passage
under force exerted on the valve member counter to the force of its
spring;
C. means for monitoring the pressure of fluid present in the
service passage and rendered operative by the valve element in said
metering positions thereof to translate said monitoring pressure
into said actuating force on the valve member whenever said
monitored pressure rises to a predetermined value above that of
fluid in the return passage means;
D. and means rendered operative by supply fluid pressure, in said
first operating position of the valve element, for assuring
substantially free flow of pressure fluid through the service line
to a fluid motor connected therewith..]. .[.7. The valve
instrumentalities of claim 6 wherein said last named means
comprises:
A. means defining a piston connected with said valve member and
which can be held by fluid pressure force in a position blocking
movement of the valve member toward its active position;
B. and means for translating pressure of supply fluid into said
force on the piston..]. .[.8. The valve instrumentalities of claim
6, wherein said last named means comprises:
A. a passage connecting with the service passage and through which
supply fluid can flow in bypass relation to said valve member in
said first operation position of the control valve element;
B. and a check valve in said bypass passage to block flow of
exhaust fluid therethrough to the return means in said second
operating position of the control valve element..]. .[.9. The valve
instrumentalities of claim 6, further characterized by:
A. said pressure reducing valve mechanism comprising a pair of
chambers, one of which is communicated with said service passage to
be pressurized by motor exhaust fluid therein;
B. said valve member having portions disposed in said chambers, and
being movable toward an active position restricting said passageway
in response to pressure of motor exhaust fluid in said one
chamber;
C. and means venting the other of said chambers..]. .[.10. The
combination of claim 9, wherein said last named means comprises a
vent line at all times connecting said other chamber with pressure
fluid supply passage means in the control valve..]. .[.11. The
combination of claim 9, wherein said venting means communicates
with the pressure fluid supply passage means in the control
valve..]. .[.12. The combination of claim 9, wherein said venting
means comprises a duct at all times communicated with the fluid
return means..]. .[.13. The combination of claim 9, wherein said
venting means comprises a duct which communicates with the pressure
fluid supply passage means in the control valve and further
comprises a passage in the control valve element effective only in
the hold position thereof to communicate the pressure fluid supply
passage with the fluid return means..]. .[.14. The combination of
claim 9, wherein said venting means comprises a duct communicating
said other chamber with the pressure fluid supply passage means,
and wherein passage means in the control valve element communicates
the pressure fluid supply passage means with the return means in
the hold position of the valve element..]. .Iadd. 15. Valve
instrumentalities for governing flow in a service line connectable
with a fluid motor of pressure fluid to the motor and return fluid
therefrom, said valve instrumentalities being of the type
comprising a directional control valve having a service passage for
connection with the service line to form a part thereof, fluid
supply passage means, return passage means, and a valve element
movable from a hold position blocking communication between the
service passage and both of said passage means to a pair of
operating positions, in one of which the service passage is
communicated with the fluid supply passage means and in the other
of which the service passage is communicated with the return
passage means, through a range of metering positions at which the
valve element restricts flow of fluid between the service passage
and a passage means to an extent that decreases with movement of
the valve element towards an operating position, said valve
instrumentalities comprising:
A. a pressure reducing valve mechanism for said service passage
(1) having a single passageway through which all fluid that flows
in said service line must pass,
(2) having a valve member movable in one direction to an open
position and movable in the opposite direction to a restricting
position throttling flow of fluid through said passageway, said
valve member being arranged to be urged in said opposite direction
with a force that depends upon pressure of fluid in the service
passage,
(3) a chamber separate from said passageway, and
(4) means responsive to pressure of fluid in said chamber and
operatively associated with the valve member for imposing a biasing
force on said valve member that is in said one direction and of a
magnitude that depends upon pressure of fluid in said chamber and
is sufficient to maintain the valve member in its open position
when fluid pressure in the service passage does not exceed pressure
of fluid in said chamber; and
B. means at all times communicating said chamber with the fluid
supply passage means, so that said valve member is held in its open
position whenever pressure fluid is flowing from the pressure fluid
source to the motor through the service passage. .Iaddend. .Iadd.
16. The valve instrumentalities of claim 15, further characterized
by:
C. means at all times imposing upon said valve member a biasing
force in said one direction that is of substantially constant
magnitude and is in addition to the biasing force imposed upon said
means responsive to pressure of fluid in said chamber, so that
movement of the valve member in said opposite direction requires
that the biasing force exerted on the valve member by fluid in the
service passage exceed the sum of the forces in said one direction.
.Iaddend..Iadd. 17. The valve instrumentalities of claim 15,
further characterized by:
C. means operative in the hold position of said valve element for
communicating the fluid supply passage means with the return
passage means, for venting of said chamber when the valve element
is moved to its hold position. .Iaddend. .Iadd. 18. The valve
instrumentalities of claim 17, further characterized by:
D. said valve element and said valve member being so arranged that
in the restricting position of the latter leakage of return fluid
thereacross does not exceed leakage of return fluid from the
service passage to the return passage means across the valve
element in its hold position. .Iaddend..Iadd. 19. The valve
instrumentalities of claim 15, wherein there is a second service
line connectable with a fluid motor to provide for reversible
actuation of the same and the directional control valve has a
second service passage for connection with said second service line
to form a part thereof, further characterized by:
C. a second pressure reducing valve mechanism for the second
service passage, substantially identical to said first mentioned
pressure reducing valve mechanism; and
D. means at all times communicating the chamber of the second
pressure reducing valve mechanism with the fluid supply passage
means, to enable the two pressure reducing valve mechanisms to
cooperate for coordination of fluid flows through the respective
service lines. .Iaddend. .Iadd. 20. Valve instrumentalities for
governing operation of a fluid motor, characterized by:
A. a control valve having a pair of service passages for connection
with the opposite sides of a fluid motor, and a valve element
movable through a number of metering positions to full flow
operating positions concurrently communicating either of the
service passages with pressure fluid supply means and the other
service passage with fluid return means in the valve, from a hold
position closing off said service passages from the fluid supply
and return means;
B. a pressure reducing valve mechanism for each service passage,
having a passageway through which exhaust fluid from the governed
motor flows to the fluid return means through the associated
service passage and through which same passageway supply fluid from
the pressure fluid supply means must flow to reach the governed
motor, each of said pressure reducing valve mechanisms having a
chamber separate from said passageway but communicated with the
pressure fluid supply means and further having a pressure
responsive valve member actuatable in a direction to restrict the
passageway to an extent depending upon the pressure of motor
exhaust fluid in the associated service passage whenever the
pressure of said exhaust fluid exceeds that of fluid at the
pressure fluid supply means during times the valve element is in
one of said metering positions, to thereby maintain the pressure of
exhaust fluid in the associated service passage at a substantially
uniformly low value above that of fluid in the return means;
C. and means located in said chamber of each pressure reducing
valve mechanism operatively connected with the valve member thereof
and rendered operative in response to pressure of supply fluid in
said chamber for preventing movement of said valve member in said
direction when fluid pressure in the associated service passage
does not exceed that of fluid at the pressure fluid supply means,
to thus permit flow of supply fluid through the associated service
passage to the governed motor substantially without interference
from said pressure reducing valve mechanism. .Iaddend. .Iadd. 21.
The combination of claim 20, wherein said last named means
comprises a plunger which is connected with said valve member and
which operates in said chamber to be biased by pressure of supply
fluid therein towards a position preventing movement of said valve
member in said direction. .Iaddend. .Iadd. 22. Valve
instrumentalities for governing flow of pressure fluid to and from
a fluid motor via a service line connectable therewith,
characterized by:
A. a directional control valve having fluid supply and return
passage means, a service passage for connection with the service
line to form a part thereof, and a valve element movable from a
hold position to first and second operating positions to
respectively communicate the service passage with the fluid supply
and return passage means, said valve element being movable through
a range of metering positions to provide for return flow of motor
exhaust fluid from the service passage to the return passage means
in an amount which increases with movement of the valve element
toward said second position thereof and reaches maximum
thereat;
B. a pressure reducing valve having
(1) a pair of chambers, and
(2) a valve member to regulate flow of motor exhaust fluid through
the service passage, said valve member having opposing portions
respectively disposed in said chambers and being urged by a spring
in one direction toward a normally inactive position but being
movable in the opposite direction toward an active position
restricting return flow of motor exhaust fluid through said service
line to the service passage;
C. monitoring means rendered operative by the valve element in said
metering positions thereof to translate pressure of fluid present
in the service passage into a force on the valve member that moves
it in said opposite direction whenever pressure of fluid in said
service passage exceeds that of fluid in the return passage means
by more than a predetermined difference, said monitoring means
comprising means communicating one of said chambers with said
service passage; and
D. communication means comprising duct means by which the other of
said chambers is at all times communicated with the fluid supply
passage means in the control valve, said communication means being
rendered effective to vent said other chamber in consequence of the
valve element of the directional control valve being in its hold
position, and being rendered operative by fluid pressure in the
supply passage means when the valve element is in its first
operating position to pressurize said other chamber and thus
maintain the valve member in its inactive position at which said
valve member allows substantially free flow of pressure fluid
through the service line to a motor connected therewith. .Iaddend.
.Iadd. 23. The valve instrumentalities of claim 22 wherein said
communication means further comprises a passage in the control
valve element effective only in the hold position thereof to
communicate the fluid supply passage means with the return fluid
passage means. .Iaddend. .Iadd. 24. Valve instrumentalities for
governing flow of pressure fluid to and from a fluid motor via a
service line connectable therewith, characterized by:
A. a directional control valve having fluid supply and return
passage means, a service passage for connection with the service
line to form a part thereof, and a valve element movable from a
hold position to first and second operating positions to
respectively communicate the service passage with the fluid supply
and return passage means, said valve element being movable through
a range of metering positions to provide for return flow of motor
exhaust fluid from the service passage to the return passage means
in an amount which increases the movement of the valve element
toward said second position thereof and reaches maximum
thereat;
B. a pressure reducing valve having
(1) a pair of chambers, and
(2) a valve member to regulate flow of motor exhaust fluid through
the service passage, said valve member having opposite portions
respectively disposed in said chambers and being urged by a spring
in one direction toward a normally inactive position but being
movable in the opposite direction toward an active position
restricting return flow of motor exhaust fluid through said service
line to the service passage;
C. monitoring means rendered operative by the valve element in said
metering positions thereof to translate pressure of fluid present
in the service passage into a force on the valve member that moves
it in said opposite direction whenever pressure of fluid in said
service passage exceeds that of fluid in the return passage means
by more than a predetermined difference, said monitoring means
comprising means communicating one of said chambers with said
service passage;
D. communication means at all times communicating the other of said
chambers with the fluid supply passage means in the control valve,
to pressurize said other chamber from fluid pressure in the supply
passage means when the valve element is in its first operating
position and thus maintain the valve member in its inactive
position at which said valve member allows substantially free flow
of pressure fluid through the service line to a motor connected
therewith; and
E. duct means rendered operative to vent said other chamber in
consequence of the valve element of the directional control valve
being in its hold position. .Iaddend..Iadd. 25. The valve
instrumentalities of claim 24 wherein said duct means comprises a
passage in the control valve element effective only in the hold
position thereof to communicate the fluid supply passage means with
the return fluid passage means. .Iaddend.
Description
BACKGROUND OF THE INVENTION
This invention relates to control valves for governing the
operation of fluid motors, and it has more particular reference to
valve instrumentalities by which the speed of motor operation can
be closely controlled despite load influences which tend to drive
the motor at rates faster than desired.
The tendency for fluid motors such as hydraulic cylinders to be
driven by the load thereon is well known. The booms of backhoes and
front end loaders, for example, constitute heavy loads which are
customarily raised and lowered by hydraulic cylinders at the
dictate of control valves therefor. During lowering of such a boom,
the control valve for its cylinder directs pressure fluid from a
pump into one end of the cylinder and conducts fluid expelled from
the other end thereof to the reservoir line of the system. The
boom, aided by gravity, tends to descend rapidly at an accelerating
and uncontrolled rate, and the boom usually attains a speed such
that the expanding end of its cylinder cannot be kept filled with
fluid from the pump. When that occurs, a void is drawn in the
expanding end of the cylinder, and positive control over the boom
is lost until its cylinder is refilled with fluid.
In situations where the load is swingable from side to side, as is
the case with the boom of a backhoe, the load can actually drive
the cylinder in each direction. This makes it extremely difficult
to control the speed with which the boom is swung, and positive
control over the boom at all times cannot be had.
Elaborate and costly throttling schemes have been proposed in the
past in an effort to achieve controlled movement of heavy loads by
their hydraulic cylinders. This invention provides an exceptionally
simple and low cost solution to that problem.
SUMMARY OF THE INVENTION
It is the primary object of this invention to provide a control
valve instrumentality for a fluid motor, wherein exceptionally good
control over the speed of motor operation is achieved by means
which comprises fluid pressure responsive mechanism to effectively
throttle the flow of motor return fluid in one or in both service
passages of the valve.
More specifically, it is an object of the invention to so combine
with a more or less conventional control valve a fluid pressure
.[.responsive.]. responsive exhaust throttling device which can
comprise a simple pressure reducing valve mechanism for one or for
both service passages of the control valve to maintain pressure
therein at a substantially uniformly low value above that of fluid
in the return passages of the control valve.
It is also a purpose of the invention to provide fluid motor
control instrumentalities such as described in the preceding object
with means to render the pressure reducing valve mechanism or
mechanisms ineffective at times when pressure fluid is being
directed to the service passage associated therewith for flow to
the governed motor.
A further objective of the invention is to so combine a pressure
reducing valve mechanism with a control valve for a fluid motor as
to minimize leakage of fluid past the control spool of the valve to
the return passages thereof from one or both of its service
passages in the neutral position of the control valve element.
With these observations and objectives in mind, the manner in which
the invention achieves its purpose will be appreciated from the
following description and the accompanying drawings, which
exemplify the invention, it being understood that changes may be
made in the specific apparatus disclosed herein without departing
from the essentials of the invention set forth in the appended
claims.
The accompanying drawings illustrate two complete examples of the
embodiments of the invention constructed according to the best
modes so far devised for the practical application of the
principles thereof, and in which:
FIG. 1 is a sectional view of a hydraulic control valve embodying
this invention;
FIG. 2 is a fragmentary sectional view corresponding to the left
hand portion of FIG. 1 but showing an operating position of the
control valve spool; and
FIG. 3 is a fragmentary sectional view corresponding to a portion
of FIG. 1 but showing a modified embodiment of the invention.
Referring now to the accompanying drawings, the numeral 5 generally
designates a hydraulic control valve of more or less conventional
construction except as to features to be described hereinafter. The
control valve comprises a body 6 having a bore 7 therein and a
valve spool 8 slidable axially in the bore. The spool can be
shifted in either direction from the neutral or hold position
thereof seen in FIG. 1 to a pair of operating positions, one of
which is seen in FIG. 2, to connect either of a pair of service
passages 9 and 10 of the valve with the pressure fluid inlet
thereof (not shown) through what can be termed a high pressure
supply or bridge passage 11, and to concurrently connect the other
service passage with a reservoir port (not shown) through an
exhaust passage adjacent thereto.
In the valve shown, the exhaust passages 12 and 13, open to the
bore at widely spaced locations along its length. The bridge
passage 11 is U-shaped, and has legs 11a and 11b which open to the
bore 7 at zones spaced axially inwardly from the junctions between
the exhaust passages and the bore. Each service passage connects
with the bore at a zone between one of the exhaust passages and the
leg of the bridge passage adjacent thereto.
In either operating position of the control valve spool .[.9.].
.Iadd.8.Iaddend., pressure fluid from the valve inlet is diverted
into the high pressure bridge passage 11 through a load holding
check valve 13 in a conventional way. It should be noted, however,
that the check valve is held in place in the valve body by means of
a threaded plug 14 which extends down into the body and has a well
15 therein opening to the bridge passage. A stem 16 on the check
valve projects up into the well 15 to be guided thereby for opening
and closing motion axially of the well. As is customary, the check
valve stem has an angled passageway 17 therein to communicate the
inner portion of the well 15 with the bridge passage and thus
enable fluid to be readily expelled to the latter during opening
motion of the check valve. A light spring (not shown) is ordinarily
accommodated in the well to yieldingly urge the check valve toward
closed position.
Mounted on the body 6 of the control valve directly over the mouths
of its service passages 9 and 10, are pressure reducing valve
mechanism 20 and 21, respectively. Since the pressure reducing
valve mechanisms are identical, a description of the left hand
mechanism 20 will suffice for both.
The pressure reducing valve mechanism 20 comprises a body 22 having
a bore 23 therethrough, closed at its opposite ends by means of
plugs 24 and 25. Those portions of the bore which are axially
inwardly adjacent to the plugs 24 and 25 provide chambers 26 and
27, respectively. Slidably mounted in the bore 23 with its opposite
end portions received in the chambers 26 and 27 is a fluid pressure
sensitive plunger 29 having a circumferential groove 30 therein
intermediate its ends to normally provide communication through the
bore 23 between two branches 31 and 32 of a passageway that forms a
continuation of the associated service passage 9. The branch 31
communicates directly with service passage 9 and with the bore 23
at a location spaced axially a short distance from the junction of
the other branch 32 with said bore. Hence, the service passage 9
and the two branches 31 and 32 of the passageway in the pressure
reducing valve mechanism constitute continuous portions of a
service line through which pressure fluid can flow to and from a
fluid motor.
A spring 34 confined between the plug 25 and an adjacent end
portion of the plunger 29 urges the latter toward a normal or
inactive position defined by the plug 24. In this normal position
of the plunger, its circumferential groove 30 spans the junctions
between the bore and both passage branches 31 and 32 and thus
communicates the branch 32 with the associated service passage
9.
The chamber 26 at the left hand end of the plunger 29 is
communicated with the branch passage 31 and hence with the service
passage 9 by means of a passageway in the plunger. That passageway
has an axial branch 36 which opens to the chamber 26 and a radial
branch 37 which opens to the branch passage 31 and at all times
communicates with the service passage 9. Accordingly, the chamber
26 will contain fluid at a pressure corresponding to that in the
service passage 9.
The chamber 27 at the other end of the plunger 29 is vented so that
the plunger can move to the right in response to pressure of fluid
in chamber 26. Chamber 27 can be communicated in any desired
fashion with the reservoir of a system of which the control valve
forms a part, or it can be vented to the bridge passage .[.10.].
.Iadd.11 .Iaddend.in the interior of the control valve body 6 as by
means of a vent line 40 shown diagrammatically as connecting with
the plugs 14 and 25 in communication with axial ports 41 and 42,
respectively, in said plugs. The vent line 40 thus serves to
communicate the chamber 27 with the well in the interior of the
plug 14, and with the high pressure bridge 11 through the angled
passage 17 in check valve 13.
One of the features of this invention resides in providing the
control spool 8 with a passageway 44 having axially spaced radial
branches 45 to communicate one leg 11a of the high pressure bridge
passage 11 with the return passage 12 in the neutral or hold
position of the control valve spool 8. By such venting of the
bridge passage, the chamber 27 of the pressure reducing valve
mechanism is also vented in the hold position of the valve spool 8,
and the plunger 29 can respond to load pressurized fluid in the
chamber 26 and be actuated to the right thereby and thus effect
reduction of pressure in the service passage 9 to a value
determined by the force of the spring 34 opposing such response of
the plunger.
Thus, with a 200 p.s.i. spring, for example, the pressure reducing
valve mechanism will function to reduce pressure to about 200
p.s.i. in the service passage 9, whereas the pressure therein might
otherwise reach a value as high as 3,000 p.s.i. if the governed
cylinder is heavily loaded. Consequently, with zero pressure in the
adjacent exhaust passage 12, the leakage of fluid thereto along the
wall of the spool receiving bore 7 from the service passage 9 when
such reduced pressure obtains in the latter could be as much as
one-fifteenth .[.less than.]. .Iadd.of .Iaddend.the leakage that
would occur if a non-reduced pressure of 3,000 p.s.i. were allowed
to remain in the service passage in the hold position of the valve
spool 8. In other words, the leakage would be far greater with a
3,000 p.s.i. pressure differential between the exhaust passage 12
and service passage 9 than it is with only a 200 p.s.i. pressure
differential between said passages.
The pressure reducing valve mechanism 20 will maintain this
desirably low pressure differential between passages 9 and 12 in
the neutral position of the valve spool 8 as long as seepage past
the left hand land of plunger 29 to the service passage 9 is no
greater than the leakage from service passage 9 to the adjacent
exhaust passage 12 across the control valve spool 8. .[.This can
normally be taken care of.]. .Iadd.Since plunger clearance in its
bore and wall area of the latter engaged by the left hand land on
the plunger are factors that determine the amount of fluid at a
given pressure that will seep past the plunger in neutral, it is
obvious that such seepage can be reduced to a very low level either
by minimizing plunger clearance, or .Iaddend.by assuring adequate
land length along the wall of the bore 23 between its junctions
with passage branches 31 and 32 .[...]. .Iadd.for encircling
engagement with the left hand land of the plunger in what can be
considered its closed position. It will also be obvious that
plunger clearance in its bore need not be critical if its left hand
land were enlarged and formed like a poppet, with a conical surface
to engage a similarly surfaced seat formed in that portion of the
bore between passage branches 31 and 32. .Iaddend.
It will thus be seen that the pressure reducing valve mechanism
will function to minimize leakage of pressure fluid from either
service passage to the adjacent exhaust passage, past the control
valve spool 8 in the neutral or hold position of the latter.
The control valve spool 8 is shown in an operating position in FIG.
2 which, for the sake of discussion, can be considered as
permitting pressure fluid to exhaust to passage 12 from a single
acting hydraulic cylinder, via service passage 9. The valve spool
has not been moved to a full .[.operation.]. .Iadd.operating
.Iaddend.position to the left of neutral, but is in a partial
operating position at which it meters flow of exhaust fluid to the
return passage 12. This situation represents the heretofore
commonly accepted way of governing the speed of motor operation, in
this case, the rate at which the load on the cylinder is allowed to
descend.
If the load on the governed cylinder is a heavy one that tends to
descend at an increasing rate, exhaust fluid will be forced through
the metering orifice set up by the control valve spool at
correspondingly faster rates. Under such conditions, the valve
spool 8 can only effect throttling over a very narrow range,
through the metering notches ordinarily provided in the spool lands
governing exhaust flow.
This problem is solved by the pressure reducing valve mechanism 20
for service passage 9. Again let it be assumed that the spring 34
exerts a 200 p.s.i. force upon the plunger 29 tending to hold it in
its wide open or inactive position allowing free flow of fluid to
service passage 9 from branch passage 32. The plunger 29 will then
respond to increase in pressure in service passage 9 to a value
above 200 p.s.i. and be moved to the right by such pressure in
chamber 26, toward a closed position restricting communication
between passage branch 32 and the service passage 9 whatever extent
is necessary to restore the desired 200 p.s.i. differential in the
pressures of fluid in the service passage 9 and in the adjacent
exhaust passage 12. Any tendency for increase in pressure in
service passage 9 due to the tendency for the load on the governed
cylinder to descend at an accelerating rate will thus be manifested
in further automatic adjustment of the plunger 29 in the passage
closing direction, to keep the pressure in service passage 9 at a
constant low value predetermined by the strength of spring 34.
Other advantages result from the use of the pressure reducing valve
mechanisms described. For example, with only a 200 p.s.i. pressure
differential between passages 9 and 12, the axial jet forces
reacting upon the valve spool as the result of high speed fluid
flow past the spool to the exhaust passage are dramatically
reduced. Equally as significant, however, is the fact that the
range of spool throttling movement is greatly increased.
While the pressure reducing valve mechanism 20 thus serves to
improve the throttling action and regulation of the speed of
descent of a single acting cylinder, (or of the speed of rotation
of a rotary fluid motor supplied with pressure fluid from the other
service passage .[.13.]. .Iadd.10.Iaddend.), it should not
interfere with flow of pump fluid to a cylinder or other motor when
the valve spool 8 is actuated to an operating position
communicating the service passage 9 with the adjacent leg of the
high pressure bridge passage 11, and the load is to be raised. For
that purpose, the vent line 40 which connects the spring chamber 27
of the pressure reducing valve mechanism with the high pressure
bridge passage 11 also serves to render the plunger 29
non-responsive to the high pressure of pump fluid flowing through
the service passage 9 to the cylinder. This results from the fact
that fluid in spring chamber 27 will then be maintained at the same
high pressure as obtains in the bridge passage 11, and the plunger
29 will be held thereby in its wide open limit of motion defined by
its engagement with plug 24.
Pressure reducing valve mechanisms 20 and 21, such as seen in FIG.
1, are useful for both service passages of a control valve
governing the operation of reversible fluid motors such as double
acting hydraulic cylinders. The operation of the pressure reducing
valve 21, of course, is the same as that of the pressure reducing
valve mechanism 20 described above. It will function to maintain a
desirably low pressure in service passage .[.13.]. .Iadd.10
.Iaddend.in the neutral position of valve spool 8 as well as when
the spool is in a position communicating service passage 10 with
the adjacent branch 13 of the exhaust passage; but its vent line
connection with the bridge passage 11 renders it ineffective at
times when its associated service passage 10 is communicated with
the leg 11b of the bridge passage by the control valve spool.
Another important feature of the invention which results from
venting the chambers 27 of the two pressure reducing valves 20 and
21 to the high pressure bridge or supply passage 11 of the control
valve, is that this expedient permits the pressure reducing valves
to achieve a counter balancing or flow coordinating function such
as is ordinarily possible only with far more sophisticated
counterbalance valve mechanisms.
For example, let it be assumed that the control spool 8 is in a
left hand operating position directing pump fluid from the supply
bridge 11 to service passage 10 for flow to one end of a hydraulic
cylinder while providing for return flow of fluid from the other
end of the cylinder to exhaust passage 12 through service passage 9
and the pressure reducing valve 20 therefor. At that time, the
pressure of supply fluid is manifested in the spring chambers 27 of
both pressure reducing valves through the venting lines 40, 41 and
42 and the angled passage 17 in load check 13. Hence, the pressure
will immediately rise in the supply bridge 11 if and when the
plunger of valve 20 occupies a restricting position at which it
will not allow flow of fluid out of the exhausting end of the
governed cylinder at a high enough rate to match the flow of pump
fluid into its other end. Such rise in pressure, of course, is also
manifested in the chambers 27 of both pressure reducing valves 20
and 21. As a result, the pressures in the chambers 26 and 27 of
valve 21 will be in balance at the increased pressure and the
spring 34 thereof will hold the valve plunger in its open position;
but the increased pressure in the spring chamber 27 of the pressure
reducing valve 20 on the return side will cause the plunger thereof
to be moved in the valve opening or flow coordinating direction to
allow exhaust flow from the governed cylinder as fast as pump fluid
is allowed to flow thereinto in any given setting of the control
spool 8.
FIG. 3 shows another way of assuring flow of high pressure fluid
from the pump out through either service passage 9 or 10 of the
control valve to a fluid motor governed thereby, without
interference from the associated pressure reducing valve mechanism,
at times when the spring chambers 27 thereof are vented to a
reservoir or to the opposite service passage 10, instead of to the
bridge passage 11. As diagrammatically seen in FIG. 3, a check
valve controlled bypass line 50 can then be provided to connect the
branch passages 31 and 32, in bypass relation to the plunger 29.
The check valve 51 in the bypass line is oriented to permit
pressure fluid to flow substantially freely from the branch passage
31 to the branch passage 32, regardless of the position of the
plunger 29 of the pressure reducing valve mechanism, while
precluding reverse flow through the bypass line.
As will be appreciated, the bypass line 50 and its check valve 51
can be incorporated in the body of the pressure reducing valve
mechanism if desired. Similarly, the pressure reducing valve
mechanisms can be incorporated in the body 6 of the control valve,
or secured thereto by screws, whichever is preferred.
From the foregoing description, together with the accompanying
drawings, it will be readily apparent to those skilled in the art
that this invention provides an exceptionally simple but
efficacious way of utilizing pressure reducing valve mechanisms to
help govern the speed at which fluid motors are operated by their
control valves.
* * * * *