Vehicle power steering system

A vehicle power steering system which effects steering with a pair of fluid actuated cylinders, one cylinder being operatively connected to each steerable wheel. Each cylinder is normally powered independently of the other cylinder so that both cylinders steer the vehicle. A pressurized fluid flow from a single source is divided for parallel flow along companion fluid flow paths to the indivdual cylinders. In response to a pre-determined pressure decrease sensed in one of those fluid flow paths a pressure responsive fluid diverter automatically diverts fluid flow from the reduced pressure flow path to the companion path so that all pressurized fluid in the system is then utilized to power one of the cylinders.

BACKGROUND OF THE INVENTION 
This invention relates generally to fluid power systems and more 
particularly to a fluid power assisted steering system for a vehicle. 
A prior art fluid power assisted vehicle steering system typically includes 
a pair of fluid actuated cylinders connected to vehicle wheels, a fluid 
reservoir, and a pump for pressurizing fluid in the system. An operator 
responsive control valve is in the system for controlling fluid flow to 
the cylinders selectively to effect vehicle steering. Fluid flow lines 
connect the system's components and define one or more continuous fluid 
circuits. 
There have been proposals for systems which will remain operative even 
though a portion of such system is either damaged and non-functioning or 
malfunctioning. A problem which these proposals have sought to overcome is 
rupture of a fluid line with consequent loss of all or substantially all 
of the pressurized fluid in the system. Such proposals have included 
independent fluid circuits or isolatable circuit sections. Should damage 
occur to one circuit or circuit section, that damaged circuit or section 
is to be isolated from the rest of the system. The remainder of the system 
is to remain integral and retain as much of the system's fluid as 
possible. There have been proposals for circuit isolation which take place 
either manually or automatically. 
One proposed power steering system incorporating an automatic cutoff for an 
independent circuit is disclosed in U.S. Pat. No. 3,865,211 issued to 
Liebert et al. Liebert et al discloses a two cylinder system where the 
cylinders are disposed in a series fluid flow relation. When the vehicle 
is steering, pressurized fluid is directed from the pump to only one of 
the cylinders and that cylinder powers the vehicle steering. 
During normal operation a primary circuit conducts pressurized fluid from 
the pressurized fluid source to one chamber of the appropriate one of the 
cylinders and a fluid reservoir receives fluid back from one chamber of 
the other cylinder. 
In response to pressurized fluid entering and leaving the cylinder chambers 
communicating with the pressurized fluid source, a secondary circuit acts 
as a slave circuit merely shifting fluid back and forth between the 
cylinder chambers which are not communicating with the pressurized fluid 
source. 
Should there be a rupture in a portion of the circuit conducting 
pressurized fluid between the pressurized fluid source and either of the 
cylinders, that circuit portion and the associated cylinder are 
automatically cut out of the circuit and the pressurized fluid normally 
conducted through that portion is diverted to the slave circuit and passes 
to the chamber of the other cylinder communicating with that slave 
circuit. 
SUMMARY OF THE INVENTION 
By this invention, fluid power system is provided which includes a pair of 
reversible actuators disposed in a parallel fluid flow arrangement. 
Normally, both actuators are simultaneously and independently powered by a 
source of pressurized fluid. A first pair of companion fluid flow paths 
connect the reversible actuators and the pressurized fluid source with 
each flow path being connected to a distinct one of the actuators. 
Pressurized fluid, to power each actuator flows along each flow path from 
the pressurized fluid source to its actuator. One form of actuation is 
produced. In response to fluid flow into the actuators, fluid is exhausted 
from the actuators along a similar second pair of parallel, companion flow 
paths. When reverse actuation is desired a control valve reverses flow in 
the fluid flow path pairs. Each pair of companion flow paths are 
interconnected with pressure responsive valves. 
If a substantial pressure decrease should occur in one flow path, the 
pressure responsive valve interconnecting that flow path and the companion 
flow path would sense the pressure decrease and divert pressurized fluid 
from the reduced pressure flow path to and through the companion flow path 
to the working actuator. Thus, one actuator ceases receiving fluid under 
pressure while the other actuator receives the combined pressurized fluid 
flows in the system and is capable of increased work output to maintain 
substantial power steering capability in the vehicle. 
In one embodiment the pressure responsive valve comprises a two position 
3-way flow control valve disposed in each of the companion fluid flow 
paths.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIG. 1, a fluid power system is illustrated which incorporates 
features of this invention. Generally, the system is seen to comprise a 
pair of reversible actuators 10, 11 in the form of hydraulic cylinders 
which are connected in a parallel fluid flow relationship with respect to 
each other and with respect to a source of pressurized fluid, generally 
indicated at 12. Pressurized fluid flows to the actuators 10, 11 from the 
source 12, first by way of a control valve 20, and then by way of either 
one of two diverter valves 22, 24 which are connected in series fluid flow 
relationship with the control valve 20. The control valve 20 controls 
which one of the two diverter valves 22, 24 receives the pressurized fluid 
flowing from the source. 
Each diverter valve is capable of dividing such flow between two companion 
flow paths. Each such flow path communicates with a distinct one of the 
actuators 10, 11. When the control valve 20 sends pressurized fluid 
through the diverter valve 22 to both the actuators, those actuators 
produce one type action. When the control valve 20 sends the pressurized 
fluid through the other diverter valve 24 to the actuators, those 
actuators produce the reverse action. Each diverter valve is responsive to 
a pre-determined decrease in pressure in each of its companion flow paths. 
Such a pressure decrease causes the diverter valve to divert pressurized 
fluid from the reduced pressure flow path to its companion flow path and 
to the actuator connected to that companion flow path. Thus, in the event 
of a rupture of a fluid conduit transporting fluid to one of the 
actuators, the inoperability of that actuator does not prevent the system 
from functioning and fluid loss is minimized. In addition, increased power 
output of the other actuator is achieved by combining the diverted fluid 
flow with the pressurized fluid normally flowing to that operable actuator 
and obtaining an increased work output from it. 
In one application the fluid power system incorporating features of this 
invention may be embodied in a vehicle steering apparatus. Each of the 
actuators 10, 11 is connected to a wheel of a vehicle. Each of the 
actuators 10, 11 comprises a fluid cylinder defining non-communicating 
chambers 10a, 10b and 11a, 11b at opposed ends of the cylinder. The 
cylinders 10, 11 are connected to their respective vehicle wheels so that 
the simultaneous delivery of pressurized fluid to a particular chamber in 
each cylinder causes both cylinders to produce steering action. 
The fluid pressure source 12 includes a reservoir 16 which is connected to 
the control valve 20 by a conduit 30. A pump 18 is disposed in the conduit 
30 to pressurize fluid passing through the conduit 30 to the control valve 
20. A conduit 32 conducts fluid exiting the control valve 20 back through 
a check valve to the reservoir and to the conduit 30. The control valve 20 
is a 4-way, 3 position valve which controls which of the diverter valves 
receives the pressurized fluid flowing from the source 12. The valve has a 
neutral position and a pair of fluid conducting positions. One of the 
fluid conducting positions conducts pressurized fluid from conduit 30 to 
the diverter valve 22 and returns fluid from diverter valve 24 to the 
conduit 32. The other fluid conducting position conducts pressurized fluid 
from the conduit 30 to the diverter valve 24 and returns fluid from the 
diverter valve 22 to the conduit 32. 
The control valve 20 is shiftable between its three positions in response 
to the rotation of a steering wheel 26 which may be operatively 
interconnected with said valve 20 in any suitable manner. Operators 28, 29 
interconnecting the steering wheel 26 and the valve 20 are illustrated. 
The diverter valves 22, 24 are identical valves which divide any 
pressurized fluid passing to them from the control valves along a pair of 
companion fluid flow paths. One path of each pair is connected to a port 
of one of the actuators and the companion path of the pair is connected to 
a port of the other actuator. 
The diverter valve 22 is connected to the control valve 20 by a conduit 40. 
The conduit 40 intersects a conduit 50 which connects a pair of similar 
two position, three way pressure responsive flow control valves 60, 70 and 
which divides fluid flow from the conduit 40 between the valves 60, 70. 
The valve element in the valve 60 is movable between a first position 
wherein the conduit 50 communicates with a conduit 80 and a second 
position wherein the conduit 50 communicates with a conduit 86. The valve 
element in the valve 70 is similarly movable between a first position 
wherein the conduit 50 communicates with a conduit 90 and a second 
position wherein the conduit 50 communicates with a conduit 96. 
The valves 60, 70 are maintained in their first position when the lines 40, 
80, and 90 are normally pressurized. Position control passages in the form 
of pilot lines 41a, 41b extend from the conduit 40 to the valves 60, 70. A 
system sensing flow passage in the form of a pilot line 81 extends from 
the conduit 80 to the valve 60. Another system sensing flow passage in the 
form of a pilot line 91 extends from the conduit 90 to the valve 70. The 
pilot pressure in the pilot line 81 and a resilient member 82 act in 
concert on the valve 60 and in opposition to the pilot pressure in the 
pilot line 41a. The pilot pressure in the pilot line 91 acts in concert 
with a resilient member 92 on the valve 70 and in opposition to the pilot 
pressure in the line 41b. When the conduits 40, 80, 90 are normally 
pressurized, the forces generated by the pilot pressures in the pilot 
lines 81, 91 in combination with their resilient members 82, 92, 
respectively, are sufficient to overcome, the forces generated by the 
pilot pressures in the lines 41a, 41b. 
Should the pilot pressure in either of the lines 81, 91 be reduced below 
some predetermined limit, the pilot pressure in the other pilot line 41a, 
41b acting on that same valve 60, 70 will be sufficient to move the valve 
60, 70 into its second position. 
The conduits 80, 90 form a companion pair of conduits arranged in parallel 
fluid flow relation with respect to each other. They are provided to 
connect each of the valves 60, 70 to a separate one of the cylinders 10, 
11. The conduit 80 is connected to a chamber 11b in one end of the 
cylinder 11 while the conduit 90 is connected to a chamber 10a in one end 
of the cylinder 10. 
Crossover conduits 86, 96 are provided to communicate each of the valves 
60, 70 in the conduits 80, 90 with the companion conduit 90, 80 when the 
valves 60, 70 are in their second positions. 
To assure that the valves 60, 70 are shiftable, sequencing valves 88, 98 
are preferably disposed in the respective conduits 80, 90. These 
sequencing valves are utilized to generate a bias pressure. Such valves 
normally will block the conduits 80, 90 until sufficient pressure is 
generated in the pilot lines of 89, 99 to shift the sequencing valves from 
a fluid conduit obstructing position to a fluid conduit conducting 
position. 
A check valve bypass is provided around each of the valves 60, 70 and their 
sequencing valves, 88, 98 to provide return flow paths through the 
diverter valve 22 for fluid exhausted from the cylinders 10, 11. The 
bypasses each comprise check valves 100, 102 disposed in bypass conduits 
101, 103. The conduits 101, 103 each intersect the respective conduits 80, 
90 intermediate the sequencing valves 88, 98 and the cylinders 11, 10 and 
intersect the conduit 40 intermediate the control valve 20 and the valves 
60, 70. 
Referring to the diverter valve 24, a similar arrangement is shown. The 
conduit 42 communicates with a conduit 150 which connects a pair of 
similar two position, three way pressure responsive flow control valves 
160, 170 and which divides fluid flow from the conduit 42 between the 
valves 160, 170. 
The valve element in the valve 160 is movable between a first position 
wherein the conduit 150 communicates a conduit 180 and a second position 
wherein the conduit 50 communicates with a conduit 186. The valve element 
in the valve 170 is similarly movable between a first position wherein the 
conduit 150 communicates with a conduit 190 and a second position wherein 
the conduit 150 communicates with a conduit 196. 
A pair of position control passages in the form of pilot lines 141a, 141b 
extend from the conduit 42 to the respective valves 160, 170 and tend to 
urge those valves into their second position. A pair of system sensing 
flow passages in the form of pilot lines 181, 191 extend from the conduits 
180, 190 to the respective valves 160, 170 and act in concert with 
resilient members 182, 192 to urge the respective valves 160, 170 toward 
their first position. When the conduits 180, 190 are normally pressurized, 
the valves 160, 170 are in their first positions, and the conduit 150 
communicates with the conduits 180, 190. When the conduits 180, 190 are 
not normally pressurized the valves 160, 170 communicate with the conduits 
190, 180 respectively through a pair of crossover conduits 186, 196. 
The conduits 180, 190 form a companion pair of conduits arranged in 
parallel fluid flow relation with respect to each other. They are provided 
to connect each of the valves 160, 170 to a separate one of the cylinders 
10, 11. The conduit 180 communicates with the chamber 11a of the cylinder 
11 while the conduit 190 communicates with the end 10b of the cylinder 10. 
Sequencing valves 188, 198 are disposed in the conduits 180, 190. Check 
valve bypasses are also provided around each of the valves 160, 170 and 
their sequencing valves 188, 198. The bypasses comprise check valves 200, 
202 disposed in bypass conduits 201, 203 which communicate the conduits 
180, 190 with conduit 42. 
In the operation of this system, when the control valve 20 is in its 
neutral position, no pressurized fluid is conducted from the source 12 to 
the circuit. When the steering wheel 26 is turned in one direction the 
control valve 20 is moved to one of its conducting positions and 
pressurized fluid is conducted from the pump 18 through the conduit 30 to 
the conduit 40 and into the diverter valve 22. That pressurized fluid is 
divided by the conduit 50 and passes through both of the companion valves 
60, 70 to the respective conduits 80, 90. Sufficient pressure is generated 
in the conduits 80, 90 to pressurize the pilot lines 89, 99 and shift the 
sequencing valves 88, 98 from a flow obstructing to a flow enabling 
position. Pressurized fluid flow then passes along the respective conduits 
80, 90 to the cylinder chambers 11b, 10a. 
Simultaneously with fluid entering the cylinder chambers 11b, 10a other 
fluid will be evacuated from the cylinder chambers 10b, 11a through the 
conduits 190, 180 and the bypasses 201, 203 in the diverter valve 24. The 
two flowing portions of evacuated fluid will combine in the conduit 42 and 
pass through the valve 20 to the conduit 32 for recirculation. This fluid 
flow through the diverter valves causes the vehicle to turn in one 
direction. 
When the steering wheel 26 in the opposite direction, the valve 20 is moved 
to the other of its conducting positions. Fluid then flows in the opposite 
direction through the diverter valves to the cylinders. 
If there is a rupture of one of the fluid conduits conducting fluid to the 
cylinders 10, 11 the fluid in that conduit will be diverted to the 
companion conduit which is continuously conducting fluid to its own 
cylinder. The result of course, is that an increased amount of pressurized 
fluid will be conveyed to the operating cylinder to increase its work 
output and maintain steering of the vehicle until it can be brought to a 
stop. Only a minimal amount of fluid will be lost because of a rupture. 
The operation of the system in the event of a fluid conduit rupture is 
illustrated by assuming that the control valve 20 is conducting 
pressurized fluid from the conduit 30 into the conduit 40 and the diverter 
valve 22. The conduit 80, would normally conduct pressurized fluid to the 
cylinder chamber 11b. If the conduit 80 ruptures at some point between the 
diverter valve 22 and the cylinder 11, the diverter valve 22 will divert 
the pressurized fluid in the conduit 80 to the companion conduit 90. Thus, 
the diverted pressurized fluid will combine with the pressurized fluid 
normally flowing in the companion conduit 90 and flow to the cylinder 10 
to maintain vehicle steering capability. 
More specifically, when a rupture takes place in the conduit 80, the pilot 
pressure in the pilot line 81 is substantially reduced and the pilot 
pressure in the pilot line 41a causes the valve 60 to be shifted from its 
first position to its second position. Fluid in the conduit 40 is directed 
by the valve 60 into the conduit 86 which carries the diverted fluid to 
the companion conduit 90 where these fluids join and together flow to the 
chamber 10a of the cylinder 10. 
Similarly if a break should appear in the conduit 90 between the diverter 
valve 22 and the cylinder 10, a similar diverting action would be carried 
out by the three way flow control valve 70 to direct fluid through the 
conduit 96 to the conduit 80 to combine with other pressurized fluid 
flowing through that conduit into the cylinder chamber 11b. 
An analgous fluid diverting action is performed in the diverter valve 24 if 
the fluid exiting the control valve 20 should pass to the valve 24 and if 
a conduit rupture should occur in either of the companion conduits 180, 
190. 
Although the invention has been described in its preferred form with a 
certain degree of particularity, it is understood that the present 
disclosure of the preferred form has been made only by way of example and 
that numerous changes in the details of construction and the combination 
and arrangement of parts may be resorted to without departing from the 
spirit and the scope of the invention as hereinafter claimed.