Fully compensated fluid control valve

A direction flow control valve for control of positive and negative loads equipped with a positive and negative load compensator controlled by a single pilot valve stage responsive to positive and negative load pressure signals. The positive and negative load compensator is provided with two sets of negative load throttling slots, one set of negative load throttling slots for each actuator port.

BACKGROUND OF THE INVENTION 
This invention relates generally to direction and flow control valves 
capable of proportionally controlling a number of loads under positive and 
negative load conditions. 
In more particular aspects this invention relates to fluid control valves 
provided with positive and negative load compensation. 
In still more particular aspects this invention relates to negative load 
compensation, of a direction and flow control valve, in which fluid flow 
from each of the actuator ports is individually compensated. 
Closed center fluid control valves, pressure compensated for control of 
positive and negative loads, are desirable for a number of reasons. They 
permit load control with reduced power losses and therefore increased 
system efficiency. They also permit simultaneous proportional control of 
multiple positive and negative loads. Such fluid control valves are shown 
in my U.S. Pat. No. 4,180,098, issued Dec. 5, 1979 and also in my U.S. 
Pat. No. 4,222,409, issued Sept. 16, 1980. The negative load compensation 
of the valves of those patents suffers from certain unobvious 
disadvantages. 
In the valve of U.S. Pat. No. 4,180,098 the flow of fluid, under negative 
load pressure, is delivered from one load chamber, through passage leading 
past two transfer tubes in the comparatively long transverse core, to the 
negative load compensator and therefore is subjected to a substantial 
pressure drop, before it enters the compensator, while the fluid flow from 
the other load chamber directly enters the compensator. This factor 
influences the magnitude of the control pressure differential in a 
different way for each of the load chambers and is therefore undesirable. 
The existance of large resistance to flow in the exhaust branch of the 
circuit also decreases efficiency, when controlling a positive load while 
the valve size becomes larger and the transfer tubes themselves create an 
additional cost. 
In the valve of U.S. Pat. No. 4,222,409 the flow of fluid, under negative 
load pressure is delivered from one load chamber, through a passage 
provided in the hollow spool, to the negative load compensator providing 
large resistance to flow, large unbalance in control pressure 
differentials, severe limitation in maximum fluid flow through the valve, 
large throttling and therefore efficiency loss, increase in valve length 
and increase in cost. 
SUMMARY OF THE INVENTION 
It is therefore a principle object of this invention to provide a pressure 
compensated valve with an identical fluid flow path and identical minimum 
resistance to flow from both load chambers to the negative load 
compensator, resulting in identical control differential at minimum 
efficiency loss. 
Another object of this invention is to provide a pressure compensated valve 
with two identical negative load throttling circuits, in which fluid flow 
from each load chamber, subjected to negative load pressure is 
individually controlled. 
It is a further object of this invention to provide a pressure compensated 
valve with a simplified low resistance exhaust circuit, adaptable to 
negative load compensation by a compensator provided with two sets of 
individual negative load throttling slots. 
Briefly the foregoing and other additional objects and advantages of this 
invention are accomplished by providing novel negative load compensation 
for a flow control valve, in which fluid under negative load pressure, 
from each actuator port, is individually throttled to provide an identical 
control pressure differential, while also providing an exhaust circuit 
with greatly reduced resistance to flow. 
Additional objects of this invention will become apparent when referring to 
the preferred embodiment of the invention as shown in the accompanying 
drawing and described in the following detailed description.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to the drawing, an embodiment of a flow control valve, 
generally designated as 10, is shown interposed between diagrammatically 
shown fluid motor 11 driving load W and a pump 12, of a fixed displacement 
or variable displacement type, driven by a prime mover, not shown. Fluid 
flow from the pump 12 to flow control valve 10 and a circuit of 
diagrammatically shown flow control valve 13 is regulated by pump flow 
control 14. If pump 12 is of a fixed displacement type, pump flow control 
14 is a differential pressure relief valve, which, in a well known manner, 
by bypassing fluid from pump 12 to a reservoir 15, maintains discharge 
pressure of pump 12 at a level, higher by a constant pressure 
differential, than load pressure developed in fluid motor 11. If pump 12 
is of a variable displacement type, pump flow control 14 is a differential 
pressure compensator, well known in the art, which by changing 
displacement of pump 12, maintains discharge pressure of pump 12 at a 
level, higher by a constant pressure differential, than load pressure 
developed in fluid motor 11. 
The flow control valve 10 is of a fourway type and has a housing 16 
provided with a bore 17, axially guiding a valve spool 18. The valve spool 
18 is equipped with lands 19, 20 and 21, which in neutral position of the 
valve spool 18, as shown in the drawing isolate a fluid supply chamber 22, 
load chambers 23 and 24 and outlet chambers 25 and 26. Lands 19, 20 and 
21, of valve spool 18, are provided with metering slots 27, 28, 29 and 30 
and timing slots 31, 32, 33 and 34. Negative load sensing ports 35 and 36 
are positioned between load chambers 23 and 24 and outlet chambers 26 and 
25. Positive load sensing ports 37 and 38 are located between supply 
chamber 22 and load chambers 23 and 24. Negative load throttling slots 39, 
of control spool 40, equipped with throttling edges 41, connect the outlet 
chamber 26 with an exhaust chamber 42, which in turn is connected to 
reservoir 15, while negative load throttling slots 39a, equipped with 
throttling edges 41a, connect the outlet chamber 25 with an exhaust 
chamber 42a, which in turn is connected to reservoir 15. 
The pump 12, through its discharge line 43, is connected to an inlet 
chamber 44. The inlet chamber 44 is connected through positive load 
throttling slots 45, on control spool 40, provided with throttling edges 
46, with the fluid supply chamber 22. Bore 47 axially guides the control 
spool 40, which is biased by control spring 48, contained in control space 
49, towards position as shown. The control spool 40 at one end projects 
into control space 49, the other end projecting into chamber 50, connected 
to the reservoir 15. A pilot valve assembly, generally designated as 51, 
comprises a housing 52, provided with a bore 53, slidably guiding spool 54 
and free floating piston 55. The spool 54 is provided with lands 56, 57 
and 58, defining annular spaces 59 and 60. Annular space 61 is provided 
within the housing 52 and communicates directly with bore 53. The free 
floating piston 55 is provided with a land 62, which defines annular 
spaces 63 and 64 and is provided with extension 65, selectively engageable 
with land 58 of the spool 54. The spool 54 at one end projects into 
control space 66 and engages, with land 56 and spring retainer 67, a pilot 
valve spring 68. Control space 66 communicates through line 69 with check 
valves 70 and 71. The check valve 70 is connected by passage 72 with 
positive load sensing ports 37 and 38. The check valve 71 communicates 
through line 73 and check valves 71a and 71b with the outlet chambers 25 
and 26. Annular space 61, of the pilot valve assembly 51, communicates 
through line 74 with control space 49 and also communicates through 
leakage orifice 75, with annular space 60, which in turn is connected to 
reservoir 15. Annular space 59 communicates through lines 76 and 77 which 
check valves 78 and 79. Check valve 78 is connected to discharge line 43 
and check valve 79 is connected through line 80, with outlet chambers 25 
and 26. Annular space 64 is connected by line 81 with the supply chamber 
22. Annular space 63 is connected by line 82 and passage 83 with negative 
load sensing ports 36 and 35. Positive load sensing ports 37 and 38 are 
connected through passage 72, line 84 and a check valve 85 and a signal 
line 86 with the pump flow control 14. Control space 66 is connected 
through a leakage device 87 with the reservoir 15. Leakage device 87 may 
be of a straight leakage orifice type, or may be a flow control device, 
passing a constant flow from control space 66 to the reservoir 15. The 
leakage device 87 comprises a housing 88, provided with bore 89 guiding a 
spool 90, which defines spaces 91, 92 and 93. The spool 90 is provided 
with throttling slots 94, leakage orifice 95 and is biased by a spring 96. 
The load chambers 23 and 24 are connected, for one way fluid flow, by 
check valves 97 and 98, to schematically shown system reservoir, which 
also might be a pressurized exhaust manifold of the entire control system, 
as shown in the drawing. 
The preferable sequencing of lands and slots of valve spool 18 is such, 
that when displaced in either direction from its neutral position, as 
shown in the drawing, one of the chambers 23 or 24 is connected by timing 
slots 32 or 33 to the positive load sensing port 37 or 38, while the other 
load chamber is simultaneously connected by timing slots 31 or 34 with 
negative load sensing port 35 or 36, the load chamber 23 or 24 being 
isolated from the supply chamber 22 and outlet chambers 25 and 26. Further 
displacement of valve spool 18 from its neutral position connects load 
chamber 23 or 24 through metering slot 28 or 29 with the supply chamber 
22, while simultaneously connecting the other load chamber through 
metering slot 27 or 30 with outlet chamber 25 or 26. 
As previously described the pump flow control 14, in a well known manner, 
will regulate fluid flow, delivered from pump 12, to discharge line 43, to 
maintain the pressure in discharge line 43 higher, by a constant pressure 
differential, than the highest load pressure signal transmitted through 
the check valve system to signal line 86. Therefore, with the valve spool 
18 of flow control valve 10, in its neutral position blocking positive 
load sensing ports 37 and 38, signal pressure input to pump flow control 
14 from signal line 86 will be at minimum pressure level, corresponding 
with the minimum standby pressure of the pump 12. 
Assume that the load chamber 23 is subjected to a positive load and that 
the control pressure differential of the pilot valve assembly 51 is higher 
than the control pressure differential of the pump flow control 14. The 
pilot valve assembly 51 is shown on the drawing with the spool 54 in its 
equilibrium modulating position and with land 57 blocking the annular 
space 61. With the control system at rest the pilot valve spring 68 will 
move the spool 54 all the way to the left, connecting annular space 60 
with annular space 61 and therefore connecting control space 49 with 
system reservoir. Under those conditions the control spool 40 will be 
maintained by the control spring 48 in the position as shown in the 
drawing. The initial displacement of the valve spool 18 to the right will 
connect, in a manner as previously described, the load chamber 23, 
subjected to positive load pressure, with positive load sensing port 37, 
while also connecting the load chamber 24 with negative load sensing port 
35. The positive load pressure signal from positive load sensing port 37 
will be transmitted through passage 72, line 84, check valve 85 and signal 
line 86 to the pump flow control 14 and, in a manner as previously 
described, will raise the discharge pressure of the pump 12 to a level, 
higher by a constant pressure differential, than the positive load 
pressure existing in the load chamber 23. 
Further displacement of the valve spool 18 to the right will create a 
metering orifice through metering slot 29, between the load chamber 23 and 
the supply chamber 22, while also creating through metering slot 27 a 
similar metering orifice between the load chamber 24 and the outlet 
chamber 25. Therefore, fluid flow from the supply chamber 22 to the load 
chamber 23 will take place at a constant pressure differential, 
automatically maintained by the pump flow control 18, with the control 
spool 40 remaining in the position as shown in the drawing and with spool 
54 in a position all the way to the left. Therefore the flow into the load 
chamber 23 will be proportional to the area of the metering orifice and 
therefore to the displacement of the valve spool 18 from its neutral 
position and independent of the magnitude of the load W. 
Assume that while controlling positive load W through the flow control 
valve 10, a higher load pressure signal is transmitted from the 
schematically shown flow control valve 13 through the check valve 99 and 
signal line 86 to the pump flow control 14. The discharge pressure of the 
pump 12 will proportionally increase, increasing the pressure differential 
between the supply chamber 22 and the load chamber 23. The spool 54, of 
the pilot valve assembly 51, is subjected to the pressure differential 
between supply chamber 22 and the load chamber 23, since the annular space 
64 is connected by line 81 to the supply chamber 22 and the control space 
66 is connected by lines 69 and 69a, the check valve 70, passage 72 and 
positive load sensing port 37 to the load chamber 23. The increasing 
pressure differential between the pressure in the supply chamber 22 and 
the pressure in the load chamber 23 will move the spool 54 from left to 
right, against the biasing force of the pilot valve spring 68, into a 
modulating position, as shown in the drawing, increasing pressure in the 
control space 49, which will move the control spool 40 from right to left, 
into a position in which it will throttle fluid flow between the inlet 
chamber 44 and the supply chamber 22. Therefore, the spool 54, in its 
modulating position, will automatically throttle, by control spool 40, the 
fluid flow from the inlet chamber 44 to the supply chamber 22 to maintain 
the pressure differential between the supply chamber 22 and the load 
chamber 23, at a constant predetermined level, equivalent to preload in 
the pilot valve spring 68 and higher than the constant pressure 
differential of the pump flow control 14. Therefore, irrespective of the 
pump pressure level, the pilot valve assembly 51 will automatically 
control the throttling action of the control spool 40, to maintain a 
constant pressure differential between the supply chamber 22 and the load 
chamber 23, and across the metering orifice, created by displacement of 
the metering slot 29. During this control action the free floating piston 
55 will be subjected to the pressure differential between the supply 
chamber 22 and the load chamber 24, which is subjected to minimum pressure 
and therefore it will be maintained in a position all the way to the left, 
out of contact with the spool 54. 
Assume that load chamber 23 is subjected to negative load pressure and that 
the valve spool 18 was moved to the left, connecting the negative load 
pressure with the negative load sensing port 36, while also connecting the 
pressure at minimum level in the load chamber 24 with the positive load 
sensing port 38. The negative load pressure, from the negative load 
sensing port 36, will be transmitted through passage 83 and line 82 to 
annular space 63, where it will react on the cross-sectional area of the 
free floating piston 55, moving the spool 54 to the right, against the 
biasing force of the pilot valve spring 68, connecting annular space 59 
with annular space 61 and therefore connecting annular space 59 with 
control space 49. The pump discharge pressure in control space 49 will 
move the control spool 40 all the way from right to left, isolating with 
throttling edges 41 the outlet chamber 26 from the exhaust chamber 42, 
while also isolating with throttling edges 41a the outlet chamber 25 from 
the exhaust chamber 42a. 
Further displacement of the valve spool 18 to the left will create a 
metering flow orifice through metering slot 30, between the load chamber 
23 and the outlet chamber 26, while also creating a similar metering 
orifice, through metering slot 28, between the load chamber 24 and the 
supply chamber 22, the supply chamber 22 being completely isolated from 
the inlet chamber 44 by the position of the throttling edges 46. The 
negative load pressure from the load chamber 23, will be transmitted 
through created metering orifice to the outlet chamber 26, which is 
completely isolated from the exhaust chamber 42 by the position of control 
spool 40. The pressure in the outlet chamber 26 will rise, will open check 
valves 71a and 71, close check valves 71b and 70 and will be transmitted 
through line 69 to the control space 66, where it will react on the 
cross-sectional area of spool 54. The rising pressure in control space 66 
will move the spool 54 and the free floating piston 55 into a modulating 
position, as shown in the drawing, regulating the pressure in control 
space 49 and therefore also regulating the position of the control spool 
40. The control spool 40 will move from left to right into a throttling 
position, in which fluid flow from the outlet chamber 26 to the exhaust 
chamber 42 will be sufficiently throttled, to maintain a constant pressure 
differential between the load chamber 23 and the outlet chamber 26. The 
magnitude of this constant pressure differential, the same as that 
developed when controlling a positive load, is dictated by the preload of 
the pilot valve spring 68. Therefore the pilot valve assembly 51 will 
automatically control the throttling action of the control spool 40, to 
maintain a constant pressure differential between the load chamber 23 and 
the outlet chamber 26, irrespective of the magnitude of the negative load. 
Since during control of negative load the supply chamber 22 is completely 
isolated from the inlet chamber 44, the make-up fluid flow into the load 
chamber 24 will be supplied, either from the pressurizing exhaust manifold 
or from the system reservoir by the check valve 98. While controlling 
negative load annular space 59 is connected, through check valves 79 and 
71a, with the outlet chamber 26. If the pump discharge pressure is greater 
than the negative load pressure in the outlet chamber 26, the check valve 
78 will open, the check valve 79 will close and annular space 59 will be 
subjected to pump pressure, the energy from the pump being utilized to 
control position of the control spool 40. If the pump is at its standby 
pressure, which is usually the case when controlling a negative load, the 
higher negative load pressure will open the check valve 79, close the 
check valve 78 and be transmitted to annular space 59. Therefore under 
those conditions the energy to control the position of the control spool 
40 will be supplied from the negative load. While controlling a negative 
load from the load chamber 23 the outlet chamber 26 will be pressurized by 
the throttling action of negative load throttling slots 39 and the outlet 
chamber 25, isolated from the load chamber 24 by the land 19, will be 
connected through negative load throttling slots 39a to the exhaust 
chamber 42a, which in turn is connected to reservoir 15. The check valve 
71b will remain closed isolating the outlet chamber 25 from the negative 
load pressure in outlet chamber 26. 
Assume that the load chamber 24 is subjected to negative load pressure and 
that the valve spool 18 was moved to the right, connecting through signal 
slot 31 the negative load pressure with the negative load sensing port 35, 
while also connecting the pressure at minimum level in the load chamber 23 
with the positive load sensing port 37. The negative load pressure, from 
the negative load sensing port 35, will be transmitted through passage 83 
and line 82 to annular space 63, where it will react on the 
cross-sectional area of the free floating piston 55, moving the spool 54 
to the right, against the biasing force of the pilot valve spring 68, 
connecting annular space 59 with annular space 61 and therefore connecting 
annular space 59 with control space 49. The pump discharge pressure in 
control space 49 will move the control spool 40 all the way from right to 
left, isolating with throttling edges 41 the outlet chamber 26 from the 
exhaust chamber 42, while also isolating with throttling edges 41a the 
outlet chamber 45 from the exhaust chamber 42a. 
Further displacement of the valve spool 18 to the left will create a 
metering flow orifice through metering slot 27, between the load chamber 
24 and the outlet chamber 25, while also creating a similar metering 
orifice, through metering slot 28, between the load chamber 23 and the 
supply chamber 22, the supply chamber 22 being completely isolated from 
the inlet chamber 44 by the position of the throttling edges 46. The 
negative load pressure from the load chamber 24 will be transmitted 
through created metering orifice to the outlet chamber 25, which is 
completely isolated from the exhaust chamber 42a by the position of 
control spool 40. The pressure in the outlet chamber 25 will rise, will 
open check valves 71b and 71, close check valves 71a and 70 and will be 
transmitted through line 69 to control space 66 where it will react on the 
cross-sectional area of spool 54. The rising pressure in control space 66 
will move the spool 54 and the free floating piston 55 into a modulating 
position, as shown in the drawing, regulating the pressure in control 
space 49 and therefore also regulating the position of the control spool 
40. The control spool 40 will move from left to right into a throttling 
position, in which fluid flow from the outlet chamber 25 to the exhaust 
chamber 42 will be sufficiently throttled, to maintain a constant pressure 
differential between the load chamber 24 and the outlet chamber 25. The 
magnitude of this constant pressure differential, the same as that 
developed when controlling a positive load is dictated by the preload of 
the pilot valve spring 68. Therefore the pilot valve assembly 51 will 
automatically control the throttling action of the control spool 40, to 
maintain a constant pressure differential between the load chamber 24 and 
the outlet chamber 25, irrespective of the magnitude of the negative load. 
Since during control of negative load the supply chamber 22 is completely 
isolated from the inlet chamber 44 the make-up fluid flow into the load 
chamber 23 will be supplied, either from the pressurized exhaust manifold 
or from the system reservoir by the check valve 97. While controlling 
negative load annular space 59 is connected, through check valves 79 and 
71b, with the outlet chamber 25. If the pump discharge pressure is greater 
than the negative load pressure in the outlet chamber 25, the check valve 
78 will open, the check valve 79 will close and annular space 59 will be 
subjected to pump pressure, the energy from the pump being utilized to 
control the position of the control spool 40. If the pump is at its 
standby pressure, which is usually the case when controlling a negative 
load, the higher negative load pressure will open the check valve 79, 
close the check valve 78 and be transmitted to annular space 59. Therefore 
under those conditions the energy to control the position of the control 
spool 40 will be supplied from the negative load. While controlling a 
negative load from the load chamber 24 the outlet chamber 25 will be 
pressurized by the throttling action of negative load throttling slot 39a 
and the outlet chamber 26, isolated from the load chamber 23 by the land 
21, will be connected through negative load throttling slots 39 to the 
exhaust chamber 42, which in turn is connected to reservoir 15. The check 
valve 71a will remain closed isolating the outlet chamber 26 from the 
negative load pressure in outlet chamber 25. 
During control of negative load the control arrangement, as shown in the 
drawing, uses two identical individual circuits, each of them throttled by 
separate negative load throttling slots. The control of negative load from 
the load chamber 23 uses metering slot 30, the outlet chamber 26, negative 
load throttling slots 39 and the exhaust chamber 42. The control of 
negative load from the load chamber 24 uses metering slot 27, the outlet 
chamber 25, negative load throttling slots 39a and the exhaust chamber 
42a. Since the configuration and resistance to flow of passages 
interconnecting individual load chambers to the individual negative load 
throttling slots is identical and since the two sets of the negative load 
throttling slots, positioned on the control spool 40, are identical, the 
control characteristics of the negative load control from individual load 
chambers is identical, providing a unique negative load control system for 
a fully compensated flow control valve. In this way not only the position 
of the valve spool 18 provides identical flow control characteristics, in 
control of bidirectional negative loads, making it ideally suited for 
control of a load using a microprocessor without load position feedback, 
but the resistance to the flow of the exhaust passages becomes minimal in 
control of positive load and the cored exhaust passages of the valve 
become simple and inexpensive. 
The leakage device 87 connects control space 66 with the system reservoir. 
The leakage device 87 may take the form of a simple orifice, or may be of 
a compensated type, as shown in the drawing, permitting a constant flow, 
at a very low flow level, from control space 66. Such a leakage flow is 
necessary to permit the spool 54 to move from left to right. Such a 
movement will close the check valves 70 and 71, the displaced fluid from 
control space 66 being passed by the leakage device 87. The spool 90 of 
the leakage device 87, in a well known manner throttles, by throttling 
slots 94, the fluid flow from space 92 to space 93, to maintain space 93 
at a constant pressure, equivalent to preload in the spring 96. Since 
space 93 is maintained at constant pressure and since space 91 is 
connected to system reservoir, there exists a constant pressure 
differential across leakage orifice 95, corresponding to a constant flow 
from control space 66 and independent of the pressure level in control 
space 66. 
The leakage orifice 75 is provided between annular space 61 and system 
reservoir. Use of such a leakage orifice, well known in the art, increases 
the stability margin of the pilot valve control. 
The pilot valve assembly 51 is phased into the control circuit of the flow 
control valve 10 in such a way, that it is used to control the throttling 
action of control spool 40 during control of both positive and negative 
loads. This arrangement provides not only a less expensive but a more 
stable control, with identical pressure differential, while controlling 
positive and negative loads. 
The pilot valve assembly 51 utilizes the energy supplied either by the pump 
or the negative load in control of control spool 40. This two stage type 
control uses minimum flows through the load sensing ports and therefore 
provides a very fast responding control, completely eliminating the 
influence of the flow forces acting on the control spool 40. 
Although the preferred embodiment of this invention has been shown and 
described in detail it is recognized that the invention is not limited to 
the precise form and structure shown and various modifications and 
rearrangements as will occur to those skilled in the art upon full 
comprehension of this invention may be resorted to without departing from 
the scope of the invention as defined in the claims.