Stabilizer for priority flow divider valve

The present invention is a stabilizer for steering priority flow divider valves. The present invention prevents the variable displacement pump of the steering hydraulic system from destroking to zero displacement when the steering hydraulic demand rapidly varies from a high level to a low level of demand. The use of the present invention is especially advantageous in hydraulic systems which are close centered with pressure and flow compensation.

BACKGROUND OF THE INVENTION 
Mobile vehicles such as tractors and other farm vehicles usually have 
hydraulically powered steering systems. The hydraulic steering system is 
comprised of a hydraulic pump, a hydraulic cylinder mounted to pivot the 
vehicle wheel, a directional flow control valve (or steering valve) for 
controlling flow from the pump to the cylinder. In most instances the pump 
will also power auxiliary hydraulic systems such as cylinders or hydraulic 
motors which control the implements on the vehicle, therefore a steering 
priority flow divider valve is provided in the hydraulic system. An 
example of a flow divider valve is illustrated in U.S. Pat. No. 3,916,932 
issued to Thorson. 
The priority valve divides the hydraulic flow between the steering system 
and the auxiliary systems of the vehicle. Safety considerations mandate 
that the priority valve give priority to the flow demands of the steering 
system over the flow demand of the auxiliary systems. When the total flow 
demand of the vehicle hydraulic system is beyond the capacity of the pump, 
the flow demand of the steering system is met first before any flow is 
delivered to the auxiliary systems. 
Often the pump utilized in such a hydraulic system as described above, is a 
variable displacement pump. In some hydraulic systems the variable 
displacement pump will have a compensator, wherein the variable 
displacement pump will only supply the combined flow demanded by the 
steering system, auxiliary system and leakage. The compensator senses the 
load pressure of the complete hydraulic system and maintains the variable 
displacement pump output pressure at a preset level above the load 
pressure. When there is no load the variable displacement pump idles at 
the preset standby pressure. However, due to internal flow characteristics 
of the compensator, the standby pressure usually jumps to a level beyond 
the preset level when the pump displacement (or the swash angle) is very 
close to zero. 
There are two main problems associated with the above noted system. If the 
steering wheel is rapidly turned to the left, then to the right, then to 
left again, such as in an avoidance maneuver, the variable displacement 
pump will first stroke towards maximum displacement, then rapidly destroke 
to almost zero displacement, and then again stroke towards maximum 
displacement. 
In the above maneuver the compensator will rapidly go from a lower preset 
pressure differential to a higher pressure differential pressure as the 
variable displacement pump's displacement approaches zero. The 
aforementions fluctuation in compensator differential pressure causes an 
instantaneous pressure imbalance at the priority valve which is felt as a 
pulsation in the pump, steering system and the hydraulic lines feeding the 
steering system. The above noted pressure pulsation is highly undesirable. 
When the auxiliary system is also demanding pump flow, the pulsation is 
significantly diminished because the variable displacement pump is not 
allowed to go to zero displacement even during an avoidance maneuver. 
The priority valve, which is constantly trying to supply the steering 
system with whatever flow is demanded, can often experience unstable 
operation. The above instability is manifested in the form of a pressure 
pulsation which is felt in the vehicle tires during steering operation. 
The pressure pulsation in the tires is undesirable. 
SUMMARY OF THE INVENTION 
To overcome the prior noted problems, of priority flow divider valves the 
present invention is brought forth. The present invention is a priority 
valve which has the added feature of a stabilizer. The valve comprises 
three major components. The first component is a housing with a plurality 
of bores and passages. The second major component is a supply valve spool 
which is slideably mounted within a longitudinal bore within the housing. 
The third component is a bypass valve spool which is slideably mounted 
within another bore of a housing. The valve functions in such a manner 
that rapid changes and steering system demand are not allowed to 
immediately cause the displacement of the variable displacement pump to go 
to zero. The above is accomplished by delaying or retarding the hydraulic 
signal which causes pump displacement go to zero in instances of rapid 
changes in steering system demand. The priority valve supply spool is 
designed in a manner to stabilize flow demands, to decrease or eliminate 
pressure pulsation when the steering system is in operation. 
It is an object of the present invention to provide a priority valve which 
maintains the flow required by the steering system of a vehicle. It is a 
desire of the present invention to provide a priority valve which aids in 
preventing the displacement of a variable displacement pump (with a 
compensator) from going to zero displacement in a rapid avoidance type 
maneuver by the steering system. It is a desire of the present invention 
to provide a priority valve with increased stability when used in 
conjunction with steering operations. It is another desire of the present 
invention to provide a priority flow divider valve with increased 
stabilization without allowing hydraulic load flow to be a function of the 
pump pressure, thereby retaining load sensing characteristics of the 
hydraulic system. 
Other objects, desires and advantages of the present invention will become 
apparent to those skilled in the art as the nature of the invention is 
better understood from the accompanying drawings and the detailed 
description.

DETAILED DESCRIPTION OF THE DRAWINGS 
FIG. 1 is a sectional view of an embodiment of the present invention. The 
priority flow divider valve 1 has three main components, the housing 100, 
the supply valve spool 8 and the bypass valve spool 42. Housing 100 has a 
plurality of bores and passages including a first bore 10 and a second 
bore 46. In most instantances the first bore 10 and the second bore 46 
will be comprised of a plurality of diameters and the first bore 10 will 
be generally longitudinal. Second bore 46 fluid communicates with the 
first bore 10 and is usually intersecting with first bore 10. Housing 100 
has a first fluid inlet passage 4, a first fluid outlet passage 18, a 
second fluid outlet passage 20 and a third fluid outlet passage 40. 
Housing 100 also has a first signal passage 48 and a bypass passage 6 
which intersects with the first inlet passage 4 and said second bore 46. 
First inlet passage 4, first outlet passage 18, second outlet passage 20, 
and first signal passage 48, all intersect with the first bore 10. In the 
embodiment illustrated in FIG. 1 the second bore 46 also intersects with 
the first bore 10, and the second bore 46 is essentially coterminous with 
the third outlet passage 40. 
Priority flow divider valve 1, is fluidly connected to the steering valve 
22 via the first outlet passage 18 and the signal passage 48. Steering 
valve 22 is a variable resistance control valve for the primary demand 
hydraulic circuit (in this case the steering system). In most steering 
applications the steering valve is a directional control type valve. 
The first bore 10 is sealed by the first seal 16 and the second seal 26. In 
an alternative embodiment to the present invention either first seal 16 or 
second seal 26 may be formed from the housing 100 itself, in lieu of the 
double insertable seals as shown in FIG. 1. 
Second outlet passage 20 is provided for connection to auxiliary components 
on the vehicle or tractor, such as hydraulic cylinders, motors and other 
various components. Third outlet passage 40 is provided for connection to 
the low pressure lubrication, reservoir or to the hydraulic system drain. 
In an alternative embodiment a drain may be added which intersects with 
the second bore 46. First inlet passage 4 is connected to the output of a 
source of pressurized hydraulic fluid, usually a variable displacement 
piston hydraulic pump with pressure and flow compensation. 
Supply valve spool 8 is slideably mounted within the first bore 10 between 
first and second seals 16 and 26 respectively. Movement of the supply 
valve spool 8 allows for selective fluid communication between the first 
inlet passage 4 and the first and second outlet passages 18 and 20 
respectively. Valve spool 8 also has a first interior passage 12 which 
allows fluid communication between the first inlet passage 4 and the first 
outlet passage 18. Chamber 14 is defined by the first bore 10 and said 
first seal 16. Valve spool 8 also has a second interior passage 80 which 
allows fluid communication between the steering valve 22 and the second 
bore 46 via first signal passage 48 and second pressure chamber 24. Second 
chamber 24 is defined by the second seal 26 and the first bore 10. Spring 
32, captured in the second chamber 24 pushes the supply valve spool 8 to 
the right to bias the supply valve spool 8 to a preselected position. 
Supply valve spool first interior passage 12 is comprised of a generally 
first axial bore 28 and the intersecting first radial bore 34 and radial 
metering orifices 38. In the embodiment illustrated in FIG. 1, the supply 
valve spool 8 is provided with a plurality of generally radial metering 
orifices 38. 
Dividing first bore 28 is plug member 29. Plug 29 allows a first pressure 
chamber 14 to be formed between first seal 16 and first bore 10. Supply 
valve spool third radial orifice 36 allows the pressure of first outlet 18 
to interact within first pressure chamber 14. 
Supply valve spool 8 is also provided with the metering notches (sometimes 
referred to as landings) 58 allowing fluid communication between the first 
inlet passage 4 and the second outlet passage 20 when the valve spool 8 is 
in a preselected position. (Note the preselected positions mentioned 
herein relate to design criteria. The preselected position of the supply 
spool valve 8 which allows fluid communication between the first inlet 
passage 4 and the outlet passage 20, need not be identical with the 
preselected position which allows fluid communication through the metering 
orifice 38 or the neutral position of valve spool 8 due to biasing of the 
spring 32. 
Supply valve spool second interior passage 80 is comprised of a generally 
axial bore 82 with a plurality of diameters which intersects with a 
generally radial bore 70. 
Check valve 60 is provided to allow fluid communication from the second 
chamber 24 (steering valve 22) to second bore 46, while at the same time 
preventing flow in the opposite direction. In the embodiment illustrated 
in FIG. 1 the check valve 60 comprises a ball valve biased by a spring 
captured in the supply valve spool second interior passage 80. 
Referring to FIGS. 1 and 2, bypass valve spool 42 is slideably mounted 
within the second bore 46. Bypass valve spool 42 has a generally second 
radial bore 50 which intersects with the bypass valve spool axial bore 92. 
Bypass valve spool axial bore 92 communicates with the third outlet 40. In 
its neutral position, bypass valve spool 42 is biased by the coil spring 
78, wherein bypass valve spool second radial bore 50 is biased out of 
alignment with bypass passage 6 to prevent fluid communication between the 
bypass passage 6 and the third outlet 40. 
Bypass valve spool 42 has a flow channel which provides for restricted 
fluid communication between the first bore 10 and the third fluid outlet 
40. In the embodiment illustrated in FIG. 1 the flow channel comprises the 
helical grooves 72 along the bypass valve spool 42 circumferential 
surface, and bypass valve spool first radial bore 90 and axial bore 92. 
In operation, pump flow is received through the first inlet passage 4. Via 
the first bore 10 and the first oulet passage 18, pump flow is fed to the 
primary demand valve or steering valve 22. Pump flow is delivered to the 
auxiliary functions from the second fluid outlet 20. The steering valve 22 
has a variable orifice 74 which is proportional to the displacement of the 
supply valve spool 8 as will be explained. The pressure at the supply side 
of the steering valve 22 is equal to the pressure in the first pressure 
chamber 14. The pressure of the demand side of the steering valve 22 is 
equal to the pressure in the second pressure chamber 24. 
When the steering valve 22 is in neutral, the pressure in the second 
chamber 24 is zero. Orifice 74 is essentially blocked and a very small 
leakage flow is usually allowed in the steering valve in neutral. The 
pressure in the first chamber 14 will exceed the pressure in the second 
chamber 24 by the extent of the pressure force exerted upon the supply 
valve spool 8 by coil spring 32. When it is desired to increase the flow 
rate of hydraulic fluid to the steering system from neutral by opening the 
steering valve 22 and the variable orifice 74, the demand side pressure 
will increase and will tend to be equal to the pressure in chamber 14, the 
spring 32 will cause the supply valve spool 8 to be displaced to the 
right. The movement of the supply valve spool 8 to the right increases the 
amount of fluid flowing into the first outlet 18 from the metering 
orifices 38. Supply valve spool 8 will come to an equilibrium when flow to 
the steering cylinder causes enough pressure drop across orifice 74 to 
balance spring 32. 
If the variable orifice 74 is open further, the supply valve spool 8 will 
move slightly further to the right, opening more of metering orifice 38, 
and increasing flow to first outlet passage 18 and maintaining a constant 
pressure differential across orifice 74 in the steering valve 22. Since 
pressure differential over the steering valve 22 remains constant, flow is 
a function of the setting of the differential orifice 74 and the spring 
load of the spring 32. Therefore, flow to the steering system (i.e. 
cylinder) is not dependent upon pump pressure or load pressure. Of course 
the above is true only when the pressure of the pump is sufficiently 
higher than the pressure of the load for the system to operate properly. 
After the flow demands of the steering system have been met, the variable 
orifice 74 is closed and the supply valve spool 8 shifts to the left to 
increase available hydraulic supply available to the auxiliary systems via 
the metering notches 58 and the second fluid outlet 20. 
The present invention as illustrated in FIG. 1 improves stability for 
standard steering maneuvers because metering of hydraulic fluid which 
flows through the first outlet passage 18 is accomplished through the 
radial orifices 38 in lieu of metering lands. With the radial orifices 38, 
flow forces are low and the pressure drop across the metering edge is kept 
small by maintaining a relatively high spring load for the spring 32. The 
priority valve 1 remains a true load sensing valve since only load 
pressure is fed to the second chamber 24. 
An important feature of this priority valve 2 is the time delay bypass 
arrangement which prevents the pump from complete de-swashing, even in an 
avoidance maneuver. Whenever the vehicle steering is operated by use of 
the steering valve 22, the pressure in the signal passage 48 and the 
second chamber 24 rises. The increase in pressure causes the check valve 
60 to open up, allowing fluid to flow through the supply valve spool 
second interior passage 80 and cause the bypass valve spool 42 to move 
upwardly, aligning the bypass valve spool second radial bore 50 with the 
bypass passage 6. When the bypass valve spool second radial bore 50 aligns 
with the bypass passage 6, a bypass flow is created between the first 
inlet passage 4 and the third outlet passage 40. If during the steering 
maneuver the pressure in second chamber 24 drops to zero, the bypass valve 
spool 42 will attempt to come back to the lower position, being biased by 
the spring 78. However, the check valve 60 prevents the free downward 
travel of the bypass spool valve 42. The hydraulic fluid trapped at the 
lower end of the supply valve spool 42 slowly escapes to the third fluid 
outlet 40 via flow channel helical grooves and annulus 72 on the outer 
circumference of supply valve spool 42 and supply valve spool first radial 
and axial passages 90 and 92 respectively. The bypass of the first 
interior passage 6 will continue until bypass valve spool second radial 
bore 50 is covered up. This will take some period of time depending on 
specific design criteria and helical groove 72 sizing, therefore complete 
de-swashing of the variable displacement pump will be delayed. Thus, 
during very quick steering maneuvers the bypass will be maintained. This 
is similar to creating an artificial auxiliary flow demand which always 
smooths out the steering. The check valve 60 is set to open at a 
predetermined pressure high enough to prevent false triggering of supply 
valve spool 42. 
FIG. 3 illustrates an alternative embodiment of the present invention. With 
this embodiment, bypass flow is eliminated when there is an auxiliary 
load, therefore lowering flow demand of the system when the steering and 
auxiliary circuits are simultaneously in operation. The priority valve 3 
has added to the housing an auxiliary signal inlet passage 56. The bypass 
valve spool 63 has a first axial bore 65 with intersecting first and 
second radial bores 31 and 51 respectively. Bypass valve spool first 
landing or preferably annulus 41 allows fluid comunication between the 
auxiliary signal inlet passage 56 and the bypass valve spool axial bore 
65. Slideably mounted within the bypass valve spool axial bore 65 is an 
auxiliary piston 61. Auxiliary piston 61 is biased to allow flow through 
the bypass valve spool second radial orifice 51. Pressure in the auxiliary 
signal input passage 56 will act to cause the auxiliary piston 61 move up 
and to block off the bypass valve spool second radial orifice 51, thereby 
preventing bypass flow when an auxiliary system is being utilized. 
Auxiliary piston return spring 33 is sufficiently strong to prevent false 
triggering of the auxiliary piston 61. It is apparent to those skilled in 
the art of the various modifications in bypass spool construction, means 
of biasing, location of biasing devices and diameter modifications of the 
second bore 46 which can be utilized to achieve the same function as 
illustrated in the embodiments of FIGS. 1 and 3. 
The present invention has been explained mainly in environments of 
hydraulic steering systems for mobile vehicles, however, the present 
invention can be utilized on many other hydraulic systems where flow 
priority is essential. As discussed in this disclosure the primary flow 
control valve is a steering valve, however, it is apparent to those 
skilled in the art that the primary flow control valve may be other than a 
steering valve as mentioned in this application. 
While a few embodiments of the present invention have been explained, it 
will be apparent to those skilled in the art of the various modifications 
which can be made to the present invention without departing from the 
spirit or scope of this application as encompassed by the folowing claims.