Valve with flow force compensator

A valve that directs flow from an inlet to at least two outlets, and which counterbalances flow induced forces that tend to restrict flow to one of its outlets. The valve has a valve chamber formed in a housing, and the inlet communicates fluid to the valve chamber. A valve member is movable in the valve chamber to communicate fluid from the inlet to the two outlets. The valve member has a land which fluid flows across as the fluid flows from the inlet to one of the outlets, and the fluid flowacross that land creates a force which acts on the valve member urging the valve member in a first direction in which flow across the land to the one outlet is restricted. Means communicates fluid pressure from the other outlet to the valve member to apply a force to the valve member that urges the valve member in a second direction that is opposite the first direction, to counterbalance the flow induced forces on the valve member.

BACKGROUND OF THE INVENTION 
This invention relates to a valve which directs fluid flow from an inlet 
port to a pair of outlet ports. The invention relates particularly to a 
priority valve which divides fluid flow from a pump between a vehicle 
steering circuit and an auxiliary fluid power circuit. 
A known priority valve for dividing fluid flow between a vehicle steering 
circuit and an auxiliary circuit is shown in U.S. application Ser. No. 
361,851, filed Mar. 25, 1982, and is assigned to the assignee of this 
invention. The known priority valve includes a movable valve spool which 
controls fluid flow to the vehicle steering circuit and the auxiliary 
fluid power circuit. The valve spool is spring biased to a priority 
position in which it directs all fluid from a fluid source to the steering 
circuit. The valve spool can move away from its priority position when a 
fluid pressure differential applied across the valve spool exceeds the 
spring bias thereon. 
The fluid pressure differential on the valve spool is produced by fluid 
pressures in a pilot fluid circuit that branches from the priority flow 
communicated to the steering circuit. Fluid pressure in the pilot circuit 
is controlled by a hydrostatic steering controller in the steering 
circuit, and can vary in accordance with the steering demand (i.e. the 
rate at which an operator steers and the resistance encountered by the 
vehicle's wheels). When the fluid flow and pressure directed to the 
steering circuit are sufficient to effect steering as demanded by an 
operator, the fluid pressure in the pilot circuit causes the priority 
valve spool to shift away from its priority position, and direct fluid 
that is not needed for steering to the auxiliary circuit where it is 
available for operating one or more auxiliary fluid power implements (e.g. 
back hoe, end loader) carried by the vehicle. When flow and pressure in 
the steering circuit are insufficient to effect steering as demanded by an 
operator, the priority valve spool is rapidly returned toward its priority 
position, so that more fluid is made available for steering until the 
steering demand is satisfied. 
In the system of U.S. patent application Ser. No. 361,851, the priority 
valve spool moves axially in a valve housing. The valve spool has lands 
that cooperate with surfaces of the housing to define variable size 
orifices for directing fluid to the steering and auxiliary circuits. The 
fluid flow to the steering and auxiliary circuits is across the lands that 
form the variable size orifices. 
Applicant has found that with a valve such as disclosed in Ser. No. 
361,851, when there is a high rate of flow across the lands of the valve 
spool to the priority port there are forces induced on the valve spool. 
The forces tend to urge the valve spool in a direction that restricts the 
priority flow. Such a condition can interfere with proper operation of a 
priority valve when the flow rate across the lands of the valve spool to 
the priority port is high and the auxiliary circuit is operating at a 
pressure that is significantly higher than the pressure in the steering 
circuit. The valve spool should assume and maintain its priority position 
to satisfy the steering demand, but the forces induced on the valve spool 
because of the increase in the pressure drop and the high rate of flow 
across those lands tend to urge it in a direction that restricts the flow 
to the priority port. Thus, the valve spool may not deliver the 
appropriate amount of priority flow to the steering circuit. 
SUMMARY OF THE INVENTION 
The present invention provides a valve in which a fluid pressure force is 
applied to a valve member that balances (neutralizes) the induced forces 
that would otherwise tend to move the valve member in a direction 
restricting flow to the priority outlet port. 
According to the invention, the valve has a valve chamber formed in a 
housing, and an inlet which communicates fluid to the valve chamber. A 
valve member is movable in the valve chamber to communicate fluid from the 
inlet to at least two outlets that also communicate with the chamber. The 
valve member has a land which, along with the housing, defines an orifice 
across which fluid flows from the inlet to one of the outlets. The fluid 
flow across the land can induce a force on the valve member which urges 
the valve member in a direction tending to reduce the size of the orifice. 
The invention provides means which communicates fluid pressure from the 
other outlet to the valve member to apply a force to the valve member that 
opposes the induced force on the valve member, thus balancing the induced 
force on the valve member. 
According to the preferred embodiment, a biasing spring acts on one end of 
the valve member and biases the valve member toward a priority position in 
which it directs fluid from the inlet across the land and through an 
orifice to the one outlet and blocks communication between the inlet and 
other outlet. The valve member can move away from its priority position 
when a differential fluid pressure applied to the valve member exceeds the 
biasing force of the spring. The valve member, as it moves away from its 
priority position, (i) progressively restricts the flow area from the 
inlet across the land and through the orifice to the one outlet, and (ii) 
establishes and then progressively increases the flow area of an orifice 
between the inlet and the other outlet. When the flow to the one outlet 
induces forces that tend to move the valve member further away from its 
priority position, fluid pressure from the other outlet is communicated 
with the valve member and acts on the valve member in opposition to the 
flow induced forces that act on the valve member. Thus, that fluid 
balances (neutralizes) the flow-induced forces that would otherwise urge 
the valve member away from its priority position.

DESCRIPTION OF PREFERRED EMBODIMENT 
FIG. 1 shows a hydrostatic vehicle steering system in which fluid from a 
pump 10 is directed through a priority valve 12 to a primary steering 
circuit 14 and an auxiliary circuit 16. The pump 10 is driven by the 
vehicle's engine 18 and delivers fluid to the inlet port 20 of the 
priority valve 12. The priority valve 12 directs the fluid that is needed 
for steering to a priority outlet port 22 connected to the steering 
circuit 14, and directs excess flow, beyond that need for steering, to an 
auxiliary outlet port 24 connected to the auxiliary circuit 16. 
In the steering circuit 14, a hydrostatic steering controller 26, of the 
type disclosed in U.S. Ser. No. 243,497, meters the flow, and directs the 
metered flow to a steering actuator 28. In the auxiliary circuit 16, the 
flow from the auxilary port 24 is available to operate a actuator 25 
associated with a fluid power implement such as a backhoe, loader, etc. 
carried by the vehicle. 
The steering controller 26 is operated by the vehicle's steering wheel 50, 
and includes a directional control valve 30 and a positive displacement 
metering unit 32. The controller 26 has an inlet port 46 connected with 
the priority outlet port of the priority valve 22, a pair of working ports 
38, 40 connected to opposite chambers of the steering actuator 28, a 
return port 42 connected to a reservoir 44, and a steering load sense port 
36. The control valve 30 is spring biased to a neutral position in which 
it blocks flow from inlet port 46 to the metering unit 32. In response to 
a steering effort, the control valve 30 shifts away from the neutral 
position and to an operating position where it (i) directs fluid from the 
inlet port 46 to the metering unit 32, (ii) directs metered flow from the 
metering unit to one chamber of the steering actuator 28, and (iii) 
exhausts fluid from the other chamber of the steering actuator 28 to the 
reservoir 44. 
The priority valve 12 controls flow to the steering circuit 14 and to the 
auxiliary circuit(s) 16. It operates to insure that during steering all 
flow that is needed to cause steering is made available to the steering 
circuit 14. When there is no steering, or when the flow and pressure to 
the steering circuit 14 are more than sufficient to cause the steering 
maneuver demanded, the priority valve 12 makes excess fluid available to 
the auxiliary circuit(s) 16. 
During a steering manuever, the steering controller 26 provides a fluid 
pressure signal at its load sense port 36 which indicates a demand for 
flow and pressure. The signal causes the priority valve 12 to shift to its 
priority position (and if pump 10 is of the variable displacement type, 
causes the displacement of the pump 10 to increase) in order to bring flow 
and pressure delivered to the controller 26 to levels which are sufficient 
to cause the steering demanded. When no steering is taking place, the 
control valve 30 in controller 26 is biased to its neutral position, and 
the pressure at the load sense port 36 causes the priority valve 12 (and 
pump 10) to be in a condition in which flow and pressure communicated with 
the controller's inlet port 46 are maintained at minimum standby levels. 
The hydrostatic controller 26 can take various forms, but is preferably the 
type shown and described in U.S. application Ser. No. 243,497, which is 
assigned to the assignee of this invention, and incorporated herein by 
reference. The controller 26 has a rotatable input member 48 connected to 
the vehicle's steering wheel 50. The metering unit 32 is of the gerotor 
gear type having relatively rotatable and orbital gerotor gears. The 
directional control valve 30 comprises a control valve member that is 
rotated away from a neutral position by torque transmitted through the 
gerotor gear metering unit PG,10 32. The control valve 30 can rotate 
through a range of motion away from its neutral position, and in that 
range of motion, the extent of its movement is proportional to the 
steering demand (which demand is a function of the rate the operator 
rotates the steering wheel 50 and the resistance to movement of the 
vehicle's ground wheels). As the control valve 30 rotates away from its 
neutral position, it first establishes a main flow control orifice 51 that 
communicates its inlet port 46 with the metering unit 32. Once the orifice 
51 is established, its flow area varies in proportion to the extent of 
movement of the valve away from its neutral position. Thus, the flow area 
of orifice 51 varies as a function of the steering demand. 
The priority valve 12 comprises a housing 52, an axially extending fluid 
chamber 54, and an axially movable valve spool 56 movable in the chamber 
54. The housing 52 has three inlet cavities 58, 60, 62 which communicate 
between the valve's inlet port 20 and the fluid chamber 54. The housing 52 
also has a priority outlet cavity 64 which communicates fluid chamber 54 
with the priority outlet port 22, and an auxiliary outlet cavity 66 which 
communicates fluid chamber 54 with the auxiliary outlet port 24. 
The priority valve 12 has several variable orifices that control fluid flow 
to the priority port 22 and the auxiliary port 24. Those orifices are 
formed by lands on the valve spool 56 that move relative to respective 
surfaces of the housing 52. A pair of lands 68, 70 on the valve spool 56 
move relative to respective surfaces 68a, 70a (FIG. 2) of the housing 52 
to define therewith variable orifices directing fluid from the inlet 
cavities 58, 60 to the priority outlet port 22. Another pair of lands 72, 
74 on the valve spool 56 move relative to respective surfaces 72a, 74a 
(FIG. 2) of the housing 52 to define therewith variable orifices directing 
fluid flow from the inlet cavities 60,62 to the auxiliary outlet port 24. 
When the priority valve spool 56 is in its priority position (FIG. 3), the 
flow area of the orifices which communicate the inlet port 20 with the 
priority outlet port 22 is a maximum value, and communication between the 
inlet port 20, and the auxiliary port 24 is blocked by the lands 72,74. In 
this condition maximum flow across the lands 68, 70 to the priority port 
22 is possible, and the auxiliary port 24 is blocked. As the valve spool 
56 moves away from its priority position (i.e., rightward from the 
position shown in FIG. 3) the lands 68, 70 progressively close off the 
flow area of the orifices directing fluid to the priority port 22 and the 
lands 72, 74 establish, and progressively increase, the flow areas of the 
orifices directing fluid to the auxiliary port 24. In accordance with the 
specific teachings of U.S. Ser. No. 361,851, the lands 72, 74 are designed 
for a specific, staged type of movement, so that land 72 first opens to 
direct a small amount of flow to the auxiliary circuit, and land 74 then 
opens to provide larger flows to the auxiliary circuit. FIGS. 1 and 2 
illustrate the valve spool in a position in which it has moved rightwardly 
from its priority position to a position in which there is flow across the 
lands 68, 70 to the priority port, and there is also flow across the land 
72 to the auxiliary port. 
A passageway 78, having a fixed size orifice 80, is formed in the housing 
52, and communicates the priority outlet port 22 with a fluid cavity 82 at 
the lefthand side of the priority valve spool 56. A conduit 84 is formed 
in the housing 52, and communicates the fluid cavity 64, through a fixed 
size orifice 86, with a fluid cavity 88 on the other side of the priority 
valve spool 56. The fluid cavity 88 communicates through a fixed size 
orifice 90 with a pilot port 76 formed in the housing 52. 
A biasing spring 94 biases the valve spool 56 toward its priority position. 
When there is flow in the pilot circuit, the pressures in the fluid 
cavities 82, 88 are different, due to the pilot flow through the fixed 
size orifice 86. Thus, there is a differential fluid pressure across the 
valve spool 56. When that differential fluid pressure exceeds the biasing 
force of spring 94, the valve spool 56 moves rightwardly away from the 
priority position of FIG. 3. As the valve spool 56 moves away from its 
priority position, it (i) progressively restricts the flow area of the 
variable orifice directing flow across the lands 68, 70 to the steering 
circuit 14, and (ii) establishes and then progressively increases the flow 
area(s) of the variable orifices communicating fluid flow across the 
land(s) 72 (74) and to the auxiliary circuit 16. When the fluid pressure 
differential does not exceed the spring force, the spring 94 biases the 
valve spool 56 to its priority position (FIG. 3). 
In the steering circuit 14, the pilot port 76 communicates with a conduit 
92 that leads to the load sense port 36 of the hydrostatic steering 
controller 26 in the steering circuit. Normally, if there is no steering, 
the fluid at the load sense port 36 flows through the steering controller 
26 and to the reservoir 44. The spring 94 requires a certain differential 
fluid pressure to exist across the priority valve spool 56 before the 
valve spool 56 can move away from its priority position. When that 
differential pressure exists, indicating there is sufficient flow in the 
steering circuit, the valve spool 56 can move away from its priority 
position, against the bias of the spring 94, to a position in which it 
directs fluid from the inlet 20 to both the steering and the auxiliary 
circuits (FIGS. 1, 2). The valve spool 56 can continue to move away from 
its priority position, to increase flow to the auxiliary circuit 16, as 
long as the differential fluid pressure exceeds the bias of spring 94. If 
the differential fluid pressure is high enough, the valve spool 56 can 
move to a position where virtually all fluid is communicated to the 
auxiliary circuit 16 and only a minimum standby flow and pressure is 
maintained in the steering circuit 14. 
When an operator begins to steer, the steering controller 26 restricts the 
pilot flow to the reservoir 44, before the main flow control orifice 51 in 
the controller is established. A pressure surge is created in the pilot 
conduit 92. That surge communicates with pressure cavity 88, and, along 
with spring 94, acts on the priority valve spool 56 to urge the priority 
valve spool rapidly to its priority position. Thus sufficient fluid is 
made available to the steering circuit 14 to complete the steering 
maneuver. 
During steering, the pilot fluid pressure in the spring cavity 88 varies in 
accordance with variations in the variable main flow control orifice 51 in 
the hydrostatic steering controller 26. As discussed above, variations in 
the main flow control orifice 51 are proportional to the steering demand. 
Thus, the flow in the pilot circuit, and the pressure in cavity 88, is 
proportional to steering demand. The pressure in cavity 88, along with the 
force of spring 94, determines the amount of fluid flow and pressure which 
must exist at the priority port 22 before the valve spool 56 can move away 
from its priority position, and begin directing fluid to the auxiliary 
port. Thus, the pilot fluid pressure in the spring cavity 88 is 
proportional to and reflects the steering demand. 
The pump 10 is preferably a variable displacement swash plate pump, and the 
pressure signal in the pilot circuit also controls the displacement of the 
pump. A device is provided for adjusting the position of the swash plate 
of the pump depending on the fluid pressure in the pilot circuit. Pressure 
from the pilot conduit 92 is communicated to the device 91 through an 
orifice 93 and a check valve 94 that are in parallel with each other (FIG. 
1). In addition, the auxiliary circuit 16 is also designed to provide a 
pressure signal to the device 91 that controls the displacement of the 
variable displacement pump. That fluid pressure signal is through a 
conduit 95 having a valve 96. Further, as seen from FIG. 1, the conduit 95 
communicates with one side of orifice 93, so that some of the fluid in the 
auxiliary conduit 95 is bled to the pilot conduit 92. The foregoing 
concept applies the teachings of U.S. patent application Ser. No. 345,546, 
filed Feb. 3, 1982, entitled "Load Sense Hydrostatic Vehicle Steering 
System", which is assigned to the assignee of this application, and 
incorporated herein by reference. 
When the priority valve spool 56 is directing fluid to both the steering 
circuit 14 and the auxiliary circuit 16, a condition may arise in which 
there is a need for a significant rate of flow to the steering circuit 14, 
but the fluid pressure required in the steering circuit is relatively low 
in comparison to the fluid pressure in the auxiliary circuit. Thus, there 
may be a significant rate of flow to the steering circuit 14, and a 
relatively high pressure differential between the steering circuit 14 and 
the auxiliary circuit 16. Applicant has found that in such a condition, 
the priority valve spool 56 may not respond to the demand for fluids by 
the steering circuit 14, due to forces on the valve spool 56 which are 
induced by the high pressure drop across the lands 68, 70 to the priority 
port 22. Specifically, if the auxiliary circuit 16 is under high pressure, 
there is a high pressure at the priority valve's inlet port 20. That 
pressure means that the pressure drop across the lands 68, 70 and to the 
priority port is very high. At high pressure drops across the lands 68, 
70, forces are induced on the valve spool 56 that tend to urge the valve 
spool in a direction (depicted by the arrow 97 in FIG. 2) in which flow to 
the priority port 22 is further restricted. Those flow induced forces 
impede the ability of the priority valve to move to a position that 
insures a proper amount of priority flow to the steering circuit at the 
proper pressure drop. 
In accordance with the invention, the pilot conduit system is communicated 
with the auxiliary port in such a way that forces will be applied to the 
valve spool 56 to counteract and balance (neutralize) the flow induced 
forces that would otherwise tend to urge the valve spool in a direction 
which restricts the flow to the priority port. As shown in FIGS. 1 and 2, 
a pilot conduit 100 is provided in the housing 52, and extends between the 
inlet cavity 62 and the pilot conduit 84 in pressure area 88. The conduit 
100 communicates the optional inlet cavity 62 through a fixed size orifice 
102, with the downstream side of the fixed size orifice 86 in the pilot 
conduit 84. A one-way check valve 104 is provided in conduit 100, between 
the orifice 102 and the pilot conduit 84 to prevent loss of pilot fluid to 
the auxiliary port. Thus, the auxiliary outlet cavity 66 communicates with 
the pressure area 88 when the check valve 104 is open. 
In the pilot conduit system, the fluid in pilot conduit 84 originates from 
the fluid communicated to the priority steering port 22. Thus, the 
pressure in pilot conduit 84, even on the downstream side of orifice 86, 
is related to the pressure in the steering circuit taken at the priority 
port 22. It changes as the pressure at the priority port 22 changes. 
The orifice 102 and the check valve 104 allow fluid from the auxiliary port 
to be communicated to the pilot conduit 84, downstream of the orifice 86, 
when the pressure in the auxiliary port is sufficiently greater than the 
pressure in the pilot conduit to open the check valve 104 and to provide 
flow across orifice 102. Thus, the orifice 102 and the check valve 104 
effectively sense a pressure differential that is related to the pressure 
differential between the auxiliary port 24 and the priority steering port 
22. They communicate fluid pressure from the auxilary port 24 to the pilot 
conduit 84 when a predetermined pressure differential exists between the 
pressure at the auxiliary port 24 and the pressure at the priority port 
22. When that pressure differential exists, the amount of flow and 
pressure in the pilot conduit 84 is likely to be insufficient to enable 
the valve spool to maintain a position in which it delivers adequate fluid 
to the priority port 22. When such a condition exists, additional flow and 
pressure is communicated from the auxiliary port 24 to the pilot conduit 
100. The fluid pressure in the pilot conduit 84 increases, and the 
pressure in the cavity 88, which biases the priority valve spool 56 toward 
its priority position also increases. The increased pressure in cavity 88 
balances (neutralizes) the forces on the valve spool that tend to urge the 
valve spool 56 in a direction which would restrict flow to the priority 
port 22. In FIG. 2, arrow 109 depicts the direction of the balancing 
(neutralizing) force applied to the valve spool 56. 
The orifice 102 is sized, in relation to the remainder of the pilot orifice 
system, to allow that flow at a certain pressure differential between the 
steering and auxiliary circuits but which does not adversely affect pilot 
conduit system regulation of the valve spool 56. Also, the check valve 104 
prevents flow from the pilot conduit 84 to the auxiliary port 24 when the 
auxiliary port 24 is operating under a lower pressure than the pressure in 
conduit 84. 
The pilot conduit 100 may extend between the auxiliary cavity 66 or between 
the inlet cavity (60, 62 or 58) and the pilot conduit 84. In FIG. 1, the 
conduit 100 is shown extending from the inlet cavity 62. 
With the invention, when there is a flow to the steering circuit, and a 
sufficiently large differential pressure exists between the steering and 
the auxiliary circuits, the pressure from the auxiliary circuit is made 
available to the pilot conduit system. That pressure balances 
(neutralizes) the flow induced forces that would otherwise tend to close 
the valve 56. Thus, the valve 36 should always be able to maintain a 
priority position to direct the intended amount of fluid to the steering 
circuit. 
Thus, applicants have provided what is believed to be a useful way of 
balancing (neutralizing) flow induced forces that might otherwise impede 
the ability of the priority valve.