Hydro-mechanical failure detection and latching apparatus

A failure detection apparatus useful with a hydraulic system for maintaining fluid pressure signals present in the system to detect predetermined disparity therebetween. The apparatus includes a movable sleeve mounted within a housing and defining a central bore as well as transverse fluid flow passageways therethrough. A piston is mounted within the bore in the sleeve and normally blocks the fluid flow passageways defined within the sleeve. Fluid pressure signals to be monitored for detection of disparity therbetween are applied to opposite ends of the movable sleeve. Upon movement of the sleeve, fluid under pressure is applied through the passageways and through bores provided in the pistons thereby to cause movement of the piston to apply the fluid under pressure to a shut-off valve and a failure indicator mechanism. The piston latches in a limit position to retain the detection device and the shut-off valve in the actuated position. The operational portions of the system are isolated from the fluid pressures in the failure detection portions thereof.

BACKGROUND OF THE INVENTION 
It is often desirable to measure or compare two fluid pressure signals to 
ascertain disparity of a predetermined amount therebetween. If such 
disparity does occur, it is desirable to isolate the failed system from 
the remainder of the normally functioning system and to provide a signal 
which indicates such occurrence. The signal thus developed may be utilized 
for warning purposes or to operate additional equipment for a desired end 
result. It is further desired that once such disparity occurs the 
comparing apparatus is not permitted to return to a position such that the 
disparity indicating signal may be eliminated, that is the comparing 
apparatus should be latched once the disparity has been detected. 
Prior art apparatus for accomplishing such comparison and latching has, for 
the most part, included relatively complex electronic or electrical 
equipment and in those cases where fluid pressure systems have been 
involved, relatively complex mechanism has been required. In some 
instances, even though the complex equipment is not required, it has been 
detected that the equipment does not properly operate in all cases. Such 
improper operaton may result from differences in fluid leakage within the 
system as well as the possibility that system pressure may be applied to 
operational parts of the system resulting in damage thereto. 
The best prior art known to applicant at the present time is U.S. Pat. Nos. 
3,391,611, 3,406,702, 3,570,516, 1,986,084, 2,983,278. 
SUMMARY OF THE INVENTION 
A hydro-mechanical failure detection and latching apparatus in accordance 
with the present invention includes a sleeve slidably mounted within a 
housing and defining a longitudinal bore and transverse fluid passageway 
means therethrough. A piston is slidably disposed within the bore and 
normally blocks the fluid passageway means defined by the sleeve. Means is 
included for applying first and second pressure signals to be monitored to 
opposite ends of the sleeve to cause the sleeve to slide responsive to 
predetermined differences therebetween. Movement of the sleeve permits 
fluid pressure communication therethrough to move the piston to a limit 
position. 
In accordance with a more specific feature of the present invention there 
is also provided a shut-off valve which moves responsive to opening of the 
passageway means to fluid pressure and as a result of such movement, 
actuates a failure indicating means and may also shut-off a source of 
fluid under pressure normally provided to the operating apparatus from 
which the signals to be compared eminate.

By reference to FIG. 1 a simplified schematic version of a hydro-mechanical 
failure detection and latching apparatus constructed in accordance with 
the principles of the present invention is shown. Generally as pressure 
signals to be monitored reach a predetermined disparity a sleeve to which 
the signals are applied moves allowing application of system pressure to a 
spool. Movement of the spool communicates the system pressure to other 
devices and the spool is latched in its moved position. As is illustrated 
in FIG. 1, a housing 10 defines a bore 12 having a pair of enlarged end 
chambers 14 and 16 at each end thereof. Slidably positioned within the 
bore 12 is a sleeve 18. The sleeve 18 defines a passageway 20 which 
communicates with fluid under pressure (P.sub.s) from a source 22 thereof 
through a solenoid valve 24 and conduit means 26 extending through the 
housing 10. A reset means 28 is provided to deactivate the solenoid valve 
24 for purposes which will be described more fully hereinafter. Additional 
fluid passageways 30, 32, 34 and 36 are also provided through the sleeve 
18 and each communicates with an annular groove 38, 40, 42 and 46, 
respectively, formed in the body 10. It will also be noted that an 
additional annular groove 48 also communicates with the passageway 20 to 
which the fluid under pressure P.sub.s is connected. 
The sleeve 18 also defines a bore 50 therethrough. Slidably positioned 
within the bore 50 is a piston 52. The piston 52 is centered in the bore 
50 by a pair of springs 54 and 56 which are held in position by the spring 
guides 58 and 60, respectively. It will be noted that the piston 52 
contains a center land 62 and a pair of end lands 64 and 66 with a reduced 
diameter portion between the center lands 62 and each of the end lands, 
thus defining a pair of central chambers 53 and 55. Reentrant bores 68 and 
70 are provided in the end lands 64 and 66, respectively with transverse 
bores communicating therewith and into the central chambers 53 and 55 
defined by the reduced diameter portion between the center lands and the 
end lands. It will be noted that the center land 62 normally blocks the 
passageway 20 through which the fluid pressure is connected. 
End chambers 33 and 35 are defined respectively between the end land 64 and 
the spring guide 58 and the end land 66 and the spring guide 60. 
The spring guides 58 and 60 each also retain in position a spring 72 and 
74, respectively. 
A first pressure signal from a first signal source 80 is connected through 
a conduit 82 to the end chamber 14 while a second pressure signal from a 
second source 84 thereof is connected by a conduit 86 to the end chamber 
16. 
When the piston 52 is in the position shown in FIG. 1 blocking the 
passageway 20, system return 100 is connected by way of conduit 102 to the 
annular grooves 38 and 46 and from there through the passageways 30 and 36 
to the chambers 33 and 35. System return is further applied through the 
reentrant bores 68 and 70 to the central chambers 53 and 55 from which it 
is also connected to the annular grooves 40 and 42 through the passageways 
32 and 34. The annular grooves 40 and 42 are also connected through the 
conduit 104 to the end chamber 106 defined by a bore 108 within which 
there is disposed a valve means 110 having lands 112, 114 and 116 disposed 
therein. The valve 110 is spring loaded toward the left as viewed in FIG. 
1 by the spring 118. 
It will be noted that the bore 108 also has connected thereto a plurality 
of conduits as follows: a conduit 120 which is connected to the source 22 
of system pressure (P.sub.s), a conduit 122 which connects to the second 
pressure signal from second source 84, a conduit 124 which connects the 
first pressure signal from the first source 80, as well as the conduits 
126 and 128 which are also connected to system return 100. 
A failure indication means such as a switch 130 is provided. When the valve 
110 moves toward the right, as viewed in FIG. 1, the rod 132 will engage 
the switch 130 thus providing a signal which may be used for any purpose 
desired and as will be more fully described hereinafter. 
In operation of the device as illustrated in FIG. 1, the pressure signals 
from the sources 80 and 84 are applied simultaneously to the chambers 14 
and 16. The pressure signals in turn are applied to each end of the sleeve 
18 positioned within the bore 12. The springs 72 and 74 provide a 
predetermined preload to the sleeve 18 thereby preventing any movement of 
the sleeve until such a time as a threshold level is reached. The 
threshold level is determined by the force of the springs 72 and 74. When 
the signal pressure differential reaches the threshold level the sleeve 
moves to the left or right as viewed in FIG. 1 depending upon the larger 
of the two pressure signals applied to the chambers 14 and 16. 
Assuming for purposes of description that the larger pressure signal is 
from the second source 84 the sleeve moves toward the left as viewed in 
FIG. 1. As the sleeve moves toward the left the passageway 20 is carried 
toward the left but remains in communication with the annular groove 48 
which communicates fluid pressure from source 22 to the passageway 20. 
When the passageway 20 reaches the central chamber 53 between the lands 62 
and 64 system fluid pressure (P.sub.s) is applied through the reentrant 
bore 68 and to the end chamber 33. The restriction orifice 31 in the 
passageway 30 creates a pressure drop thereacross thereby generating a 
pressure in the end chamber 33 within which the spring 54 is positioned. 
This force operates against the land 64 and moves the piston 52 toward the 
right until it stops againt the spring guide 60 thus positioning the 
piston in a first limit position. In this limit position fluid pressure 
maintains its communication from the source 22 through the conduit 
passageway 20, the reentrant bore 68, the chamber 33, the passageway 30 
and from there to system return 100. At the same time, the build-up in 
pressure which occurs as a result of the restriction orifice 31 is also 
communicated through the passageway 32 and the annular groove 40 to the 
conduit 104 and into the chamber 106. The build-up in pressure in chamber 
106 operates against the land 112 and translates the slide valve 110 
toward the right as viewed in FIG. 1 against the force of the spring 118. 
Such movement of the valve 110 accomplishes several results. 
First, the land 112 blocks communication of the conduit 120 with the bore 
108 thereby precluding the application of fluid pressure (P.sub.s) from 
the source 22 through the conduit 121 to any apparatus to which it may be 
connected and in turn system return 100 is connected through conduit 126 
thereto. Second, the first and second signal sources 80 and 84 are 
connected together in the space between land 114 and 116 thereby 
effectively bypassing the apparatus generating these two signal sources 
and rendering such apparatus inoperable. It will also be noted that since 
the chambers 14 and 16 are effectively connected together that the sleeve 
18 will return to the position shown in FIG. 1. However, the piston 52 
will remain latched in its first limit position because system pressure 
remains applied to the central chamber 53. Third, and as above indicated, 
when such translation occurs the rod 132 also contacts the failure 
indication switch 130 to provide an output signal which typically is of an 
electrical nature that may be utilized to warn the operator of the device 
or to effectuate other activities as may be required in a particular 
application. 
If the signal from the first source 80 is the greater of the two exactly 
the opposite movement of the sleeve occurs and the piston will move to the 
left and stop against the guide 58 in its second limit position with 
similar results as a result of the restriction orifice 37 in the 
passageway 36. 
After the indication of a particular failure has occurred the operator may, 
if desired, check the unit to be certain that a malfunction has occurred 
in the device generating the first and second signals. Such resetting may 
be accomplished by activating the reset means or switch 28 which causes 
the solenoid valve to remove the supply of system pressure 22 from the 
passageway 20. When such occurs the springs 54 and 56 again center the 
piston 52 into the position shown in FIG. 1, thereby blocking the supply 
of system pressure in the manner above-referred to. Upon removal of the 
fluid pressure (P.sub.s) from source 22 the spring 118 returns the valve 
110 to the position shown in FIG. 1 thereby once again applying the fluid 
pressure 22 through the conduit 121 to the original desired operational 
status. Under these ciurcumstances the sources 80 and 84 again will 
generate the desired signals which will have the effect of applying the 
same to the chambers 14 and 16 in accordance with normal operation. If, in 
fact, a malfunction has occurred thereby generating the signals from the 
sources 80 and 84 having the disparity to create a threshold differential 
equal to the threshold pressure, the entire system will operate as above 
indicated. Thus, the piston 52 will be latched in one of its limit 
positions and valve 110 will be translated thereby cutting off the system 
supply source, bypassing the two signals as well as providing the failure 
indication signal again thereby clearly indicating a failure in that part 
of the system containing the pressure signal source 80 and 84. 
At times it becomes desirable to compare a plurality of pressure signals 
and by reference to FIG. 2, there is disclosed an implementation of 
apparatus constructed in accordance with the principles of the present 
invention for that purpose. As is seen in FIG. 2, the output pressure 
signals appearing across a pair of actuators are compared to detect a 
predetermined discrepancy therebetween in a manner similar to that 
discussed with respect to the apparatus of FIG. 1. As will be noted by 
investigation of the apparatus disclosed in FIG. 2, the pressure signals 
from one side of each of the actuators are compared to each other while 
the pressure signals form the opposite side of each of the actuators are 
compared to each other by applying the pressure signals across the movable 
sleeve as hereinabove described. As will be appreciated by those skilled 
in the art the two electrohydraulic servovalves (EHSV A and EHSV B) will 
have the same signals applied thereto and under normal operating 
conditions will generate equal signals for application to the two 
actuators. Only a general description of the apparatus and its operation 
will be provided since the detailed description was set forth with respect 
to the apparatus contained in FIG. 1. 
First and second electrohydraulic servovalves 202 and 204, designated as 
EHSV A and EHSV B, respectively, are provided for generating pressure 
signals which will be applied to the actuators and then compared to detect 
any discrepancies therebetween. Typically the EHSV's A and B will be 
provided with identical input signals and will, under normal operating 
circumstances, provide identical output signals for operation of devices 
connected thereto such as the actuators. The movable sleeve 200 is 
positioned and designed so as to provide chambers 206 and 208 at opposite 
ends thereof to receive output signals A1 and B1. Also provided are 
additional annular chambers 210 and 212 to which are applied the output 
signals B2 and A2. It will thus be seen that the output signals A1 and B1 
are compared across equal area portions of the sleeve 200 while the output 
pressure signals A2 and B2 are also compared across equal area portions of 
the sleeve 200. It will be appreciated by those skilled in the art that 
when the pressure difference between A1 plus B2 and A2 plus B1 is 
sufficiently great enough to exceed the predetermined threshold level, 
sleeve 200 will move thereby providing communication of system pressure 
(P.sub.s) to move the piston 214 with the same results as previously 
described. The slide valve 220 operates similar to that shown and 
described with respect to FIG. 1 with the exception that the valve is also 
designed to detect system pressure (P.sub.s) failure and if such does 
occur the spring 222 will move the slide valve toward the right as is 
viewed in FIG. 2 as if there had been a failure of one of the valves EHSV 
A or EHSV B. In addition thereto, it will be appreciated that the valve 
shown makes provision for bypassing or short circuiting the output signals 
A1 and A2 from EHSV A as well as B1 and B2 from EHSV B. 
As will be recognized by those skilled in the art the system of the present 
invention may also be used in a redundant hydraulic system. For example, 
signals A1 and A2 from one hydraulic system within a control system may be 
compared while B1 and B2 are likewise compared. The threshold would 
necessarily be set somewhat higher but otherwise the apparatus of the 
present invention would function as described in conjunction with FIG. 1. 
In all other respects the construction and operation of the apparatus 
illustrated in FIG. 2 is the same as that illustrated in FIG. 1 and thus 
any additonal detailed description is not believed to be required herein.