CA1186594A - Fluid control circuit - Google Patents
Fluid control circuitInfo
- Publication number
- CA1186594A CA1186594A CA000400056A CA400056A CA1186594A CA 1186594 A CA1186594 A CA 1186594A CA 000400056 A CA000400056 A CA 000400056A CA 400056 A CA400056 A CA 400056A CA 1186594 A CA1186594 A CA 1186594A
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- Canada
- Prior art keywords
- fluid
- pilot
- valve
- supply
- dump
- Prior art date
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Abstract
ABSTRACT
A fluid control circuit is described which is for controll-ing the pressure applied by jacks (12) to an article such as an aircraft wing undergoing testing. Fluid supply lines (18,20) carry hydraulic fluid to and from the jacks (12) under control of a main control valve (23). Locking means (16) in the form of cutoff valves (25,26) are provided to close the supply lines (18,20) to fluid flow if a fault condition is detected. The cutoff valves (25,26) are pilot operated and normally hold lines (18,20) open. Pilot control valve (31) controls the supply of pilot fluid to the cutoff valves (25,26), Dump lines (37,38) are opened to pressure relieving fluid flow when dump control valves (39,40) are open. Bleed control valves (41,42) control the rate of such pressure relieving flow. Auxiliary valves (47,48) prevent leakage flow back through main control valve (23) when the dump lines (37,38) are open.
A fluid control circuit is described which is for controll-ing the pressure applied by jacks (12) to an article such as an aircraft wing undergoing testing. Fluid supply lines (18,20) carry hydraulic fluid to and from the jacks (12) under control of a main control valve (23). Locking means (16) in the form of cutoff valves (25,26) are provided to close the supply lines (18,20) to fluid flow if a fault condition is detected. The cutoff valves (25,26) are pilot operated and normally hold lines (18,20) open. Pilot control valve (31) controls the supply of pilot fluid to the cutoff valves (25,26), Dump lines (37,38) are opened to pressure relieving fluid flow when dump control valves (39,40) are open. Bleed control valves (41,42) control the rate of such pressure relieving flow. Auxiliary valves (47,48) prevent leakage flow back through main control valve (23) when the dump lines (37,38) are open.
Description
1.
FLUID CONTROL CIRCUIT
This invention relates to fluid control circuits for controlling the pressure applied to an article. The article may be a workpiece or a structure undergoing test-ing. The invention has been particularly designed for andwill ~e described with reference to testing aircraft wings to which stress is applied to simulate flight conditions although other uses are possible.
In prior test rigs for imposing stress on air-craft wings to simulate flight conditions hydraulic jackshave been used. Such jacks have been arranged in either of ~wo ways: (1) an open loop system in which all jacks are controlled through a single valve, or (2) a closed loop system in which each jack is controlled independently through its own control valve.
The closed loop system is preerred because it permits more accurate simulation of stress conditionsr but it has suffered some instability. In particular, it has been found that one or more of the jacks may apply abnormal loading thereby creating an undesirable stress condition which may damage the wing(s) under test~
It is an object of an aspect of the present inven-tion to provide a fluid control circuit for controlling the pressure applied to an article by a plurality o~ fluid operable thrusting means having a fail safe response to application of an abnormal pressure to the article.
According to the present invention there is pro-vided a structure testing apparatus for applying varying stresses to a structure undergoing testing, and including monitoring means for detecting an abnormal condition of the apparatus or structure, and a plurality of fluid operable thrusting means for applying time varying loading stresses to the structure, each thrusting means being drivable from a source of pressurized driving fluid, each thrusting ~eans having an associated fluid control circuit for controlling '~
~ 6~
FLUID CONTROL CIRCUIT
This invention relates to fluid control circuits for controlling the pressure applied to an article. The article may be a workpiece or a structure undergoing test-ing. The invention has been particularly designed for andwill ~e described with reference to testing aircraft wings to which stress is applied to simulate flight conditions although other uses are possible.
In prior test rigs for imposing stress on air-craft wings to simulate flight conditions hydraulic jackshave been used. Such jacks have been arranged in either of ~wo ways: (1) an open loop system in which all jacks are controlled through a single valve, or (2) a closed loop system in which each jack is controlled independently through its own control valve.
The closed loop system is preerred because it permits more accurate simulation of stress conditionsr but it has suffered some instability. In particular, it has been found that one or more of the jacks may apply abnormal loading thereby creating an undesirable stress condition which may damage the wing(s) under test~
It is an object of an aspect of the present inven-tion to provide a fluid control circuit for controlling the pressure applied to an article by a plurality o~ fluid operable thrusting means having a fail safe response to application of an abnormal pressure to the article.
According to the present invention there is pro-vided a structure testing apparatus for applying varying stresses to a structure undergoing testing, and including monitoring means for detecting an abnormal condition of the apparatus or structure, and a plurality of fluid operable thrusting means for applying time varying loading stresses to the structure, each thrusting means being drivable from a source of pressurized driving fluid, each thrusting ~eans having an associated fluid control circuit for controlling '~
~ 6~
2.
the loading stresses applied to the structuxe by the respect-ive thrus~ing means by means of control means for selectively switching driving fluid to the respective thrusting means, each fluid control circuit including an input supply line through which pressurized driving fluid from the source is supplied to the thrusting means and an output supply line for returning drivin~ fluid from the thrusting means, locking means operable in response to detection of the abnormal condition by said monitoring means to interrupt driving fluid supply to and from the respective thrusting means by closing both the input and output supply lines to fluid flow, thereby locking the respective Lhrusting means in its condition at the time when the monitoring means de~ects the abnormal condition.
Preferably, the locking means comprises a cutoff valve in eac~ fluid supply line, each cutoff valve being operable to close the respective fluid supply line to fluid 10w when the abnormal condition is detected. Each cutoff valve may be a pilot operable check valve operable to hold the respective fluid supply line open to fluid flow as long as a supply of pressuri~ed pilot fluid is connected thereto.
In this arrangement, each check valve is connected to the supply of pressurized pilot fluid by a respective pilot supply line, the pilot supply line including a pilot control valve for selectively disconnecting the supply of pilot fluid from the associated check valve. The pilot control valve is operable, when it disconnects the supply of pilot fluid from the associated check valve, to open the pilot supply line between the pilot control valve and the check valve to a sump to thereby relieve the pressure of pilot fluid at the check valve and cause the check valve to close the associated fluid supply line.
Each fluid supply line may be connected to a sump through a respective fluid dump line, each fluid dump line having a selectively operable dump valve therein which is operable to normally hold the dump line closed to fluid flow and to open the dump lines when pressure on the article is being relieved~ One or more of the fluid dump lines may be provided with a bleed control valve operable to ~ontrol the rate of fluid flow through the dump l:ine when the dump valve is open.
The thrusting means may be drivable in one direction and be adapted to return to their inoperative positions due to reaction of the article which is being worked upon.
In this arrangement the fluid supply line would be a single line to each thrusting means.
However in the pre~erred, more generally applicable arrangement, each thrusting means is positively drivable in both directions so that it can apply both compressive and tensile loads to the article. In this case each thrusting means is connected to a respective input fluid supply line and an output fluid supply line, the locking means being operable to close both input and output fluid supply lines to fluid flow when the abnormal condition is detected.
This latter arrangement using thrusting means drivable in both directions will now he further described with reference to the accompanying drawing which illustrates an hydraulic circuit diagram for one thrusting means of a control circuit according to a preferred embodiment of the present invention.
The fluid control circuit illustrated is operable to control the pressure applied to an article by a plurality of fluid operable thrusting means 10 drivable from a source of pressurized driving fluid (not shown). One thrusting means 10 is shown as an hydraulic jack 12 of generally known construction. The jack 12 is positively drivable in both directions for applying both compressive and tensile CM
~ ~ ~65~
loads to the article.
The circuit includes a fluid supply line 14 for carrying driving ~luid to and ~rom eachl thrusting means 10.
Locking means 16 is operable in response to detection of an abnormal condition to interrupt ~luid supply to or from each thrusting means 10 by closing each fluid supply line 14 to fluid flow and thereby locking the thrus~ing means 10 in their respective conditions when the abnormal condition is detected. In the case of jack 12 which can be positively driven in both directions, the jack 12 is connected to an input fluid supply line 18 connected to one side of the jack piston and output fluid supply line 20 connected to the other side and the locking means 1~ is operable to close both input and output fluid supply lines 18,20 to fluid flow when the abnormal condition is detected.
Control means 22 is provided for selectively switching supply of driving fluid to the thrusting means 10. The control means ?2 may comprise a control valve for simultaneously operating all the thrusting means 10. However as illustrated the control means 22 preferably comprises a selectively operable control valve 23 for each thrusting means 10 and located in the respective fluid supply line 14.
Each control valve 23 comprises a control servo valve having a valve member 24 with a supply position allowing supply of driving fluid to the respective thrusting means 10, a central cutoff position (as shown) in which the fluid supply line 14 is closed to fluid flow, and a drain position allowing draining of driving fluid from the thrusting means 10, the control servo valve being solenoid driven so as to allow selective changing of the position of the valve member CM
~6~
24~
~he valve member 24 is adapted to be positively driven by the solenoid(s) in either direction from its central cutoff position so that the valve 23 has a relatively S rapid response to electrical control signals. The rapid response characteristic may be used to provide an oscillating load to the article. For example in the case o~ aircraft wings, an oscillating load at a frequency of up to 2 hertz may be applied to the wings to simulate flight conditions.
The locking means 16 comprises a cutoff valve 25,26 in each of the 1uid supply lines 18,20 responsive to a predetermined fault condition to close the respective ~luid supply line 18,20 to fluid flow and hold the thrusting means in its condition at the instant of detection of the ~ault condition. Each cutoff valve is a selectively operable check valve. Each cutoff check valve is a pilot operable check valve 27,28 operable to hold the associated fluid supply line 18,20 open to ~luid flow as long as a supply of pressurized pilot fluid is connected to the check valve 27,28. In this embodiment there is provided a pilot supply line 29 to each cutoff check valve 27,28 associated with the thrusting means 10. In the illustrated case where two check valves 27,28 are provided for the jack 12, the pilot supply line 29 is divided at a T connection 3Q to supply the two check valves 27,2g. The pilot supply line 29 is provided with a pilot control valve 31 for selectively disconnecting the supply of pilot fluid from the cutoff check valves 27,28. The pilot control valve 31 is solenoid operated. As shown, the pilot control valve 31 ~M
is located in the common pilot supply line 29 and is arranged to maintain that line 29 open to the source of pressurized pilot fluid as long as the soleno.id is energized and to close that line on interruption of power to the solenoid thus providing a fail safe mod~ of operation.
Thus an electrical fault that interrupts power supply to the solenoid will result in closing the pilot supply line 29.
When the pilot control valve 31 closes it is arranged to open the pilot supply lines to the cuto~f valves 27,28 to a sump 32 to relieve the pressure of pilot fluid at the cutof~ valves 27,28 so that the cutoff valves 27,28 close - the fluid supply lines 18,20 to and from the jack 12 and thereby hold the jack 12 in its condition at the time the pilot control valve 31 is operat~d~
In use the fluid control circuit may be coupled to sensing means (not shown~ operative to detect the load .
applied to the article by each thrusting means 10. In the case of aircraft wing loading , the sensing means may include a plurality of transducers in the form of load cells.
2Q The outputs of the load cells may be fed to an electrical monitoring circuit for monitoring the load at each point of the aircraft wing where the thrusting means 10 is operating, the monitoring circuit being operative to detect any loading above a predetermined level to activate the looking means 16,.which in the preferred embodiment includes the solenoid operated pilot con-trol valves 31.
Each fluid supply line 18,20 is connected to a sump 35,36 through a respective fluid dump line 37,38 each fluid dump line 37,38 having a selectively operable dump valve 39,40 therein which is operable to normallyhol~th'edumplline (~M .
31~ 38 closed to fluid flow and to open the dump lines 37,38 when pressure on the article is being relieved. Each fluid dump line 37,38 extends from a point between the cutoff valve 27,28 and control valve 23 to the sump 35,36. Each dump valve 39,40 is a pilot operated check dump valve 43,44 coupled to a respective or, as illustrated~ a common dump pilot supply line 45. The pressure in the common dump supply line 45, and hence at all the dump valves 43,44 may be contro:Lled by a central dump control valve (not shown) to selectively open and close the dump valves 43~44. During relief of pressure on the article the dump valves 39,40 are opened enabling pressure relieving~- flow from the pressurized side`
the jac]c piston and fluid take-up from the sump on the other side of the piston to prevent cavitation in the fluid supply lines on the latter side. The central dump control valve may be operated simultaneously with the pilot con~rol valve 31 to relieve any pressure that may build up in the fluid supply lines 18,20 between the cutoff valves 27,28 and control valves 24. Also simultaneously the control valves 24 may be operated to return to their cutoff conditions.
Each fluid d~p line 37,38 includes a bleed control valve 41,42 operable to control the rate of fluid flow through the dump line 37,38 when the dump valve 39,40 are open. The ; bleed control valve 41,42 loacted in the fluid dump line 37,38 are temperature and pressure compensating so that the rate of discharge of fluid through the bleed valves 41,42 may be controlled. For example, in the case of aircraft wing testing, different pressures may be exerted on the various jacks by the wings during pressure relief and it is desirable to be able to individually control or set the rate o~
CM
8.
discharge of each jack so that a wing is not damaged.
Similarly fluid temperature can ~ary particularly when an oscillating load is applied and this can affect the viscosity of the fluid and hence its discharge rate.
Each fluid supply line 18,20 includes an auxiliary check valve 47,48 operable, when the associated ~ump line 37,38 is open, to close the 1uid supply line 18,20 against leakage flow other than through the bleed contr~l valve 41,42.
In some cases it may occur that leakage flow through the con-trol valve 23 negates the setting of the bleed control valves 41,42. The auxiliary check valves 4i,48 prevent such leakage flow and ensure that pressure relieving flow is controlled as desired by the bleed control valves 41,42. The auxiliary check valves 47, 48 as shown can be ope~ated from the common dump supply line 45 so that the auxiliary check valves 47,48 close when the dump valves ~3,44 open.
In operation of the illustrated fluid control circuit according to the preferred embodiment of the present invention when used for loading~aircraft wings, the h~draulic jack 12 is connected to a source of pressurized li~uid through the associated control valve 23. The control valve 23 is open in response to an electrical signal from a central control location to commence the loading operation of the respective jacks and this may occur simultaneously for all jacks. Each jack 12 has associated therewith a sensing means (not shown) which is connected to the electrical monitoring circuit (not shown) so that the loaded condition of the jack 12 or stress on the wing can be monitored and controlled through the control valve 23. In the event of a failure in the electrical control circuit or hydraulic fault in any , ~8659~
jack or any other event to cause a jack to apply an abnormal load, the pilot control valves 31 will operate to interrupt pilot fluid supply to the cutof~ valves 25,26 in the fluid supply lines 18ll9 of the jacks 12. The jacks 12 therefore will be held in the active or load applying condition. For example if one jack "sticks" while all the other jacks are relieving pressure on the aircraft wing the detection of the abnormal stress at the sticking jack will initiate locking of all t~ jacks in the condition at the instant the fault is detectea. The faulty jack may then be inspected and serv-iced so that it will operate correctly. The pilot control - valve associated with the ~aulty jack may be independently operated to ensure that -that jack is then operating correctly. While the jacks are being held in their load applying condition any excess pressure in the circuit on the side of the cutoff valves 25,26 remc~te from the jacks 12 can be purged through the dump lines 37,38 through operation of the pilot opera~ted dump valves 37,40.
If the operator decides that it is safe to unload a jack the pilot supply to the cutoff valves 25,26 is reconnected by energizing the solenoid of the pilot control valve 31.
During relief of pressure on the aircraft wing the cutoff valves 25,26 in the supply lines 18,20 are still maintained open and the fluid dump valves 39,40 are opened so that pressure relieving flow to and from the respective sumps 35,36 can take place. The pilot control valve 31 will still be operative in response to detection of a fault condition to close the fluid supply lines 18,20 to pressure relieving flow so tha-t -the circuit can operate to protect the aircraft wing at all stages throughout the CM
10.
the testing operatio~.
the loading stresses applied to the structuxe by the respect-ive thrus~ing means by means of control means for selectively switching driving fluid to the respective thrusting means, each fluid control circuit including an input supply line through which pressurized driving fluid from the source is supplied to the thrusting means and an output supply line for returning drivin~ fluid from the thrusting means, locking means operable in response to detection of the abnormal condition by said monitoring means to interrupt driving fluid supply to and from the respective thrusting means by closing both the input and output supply lines to fluid flow, thereby locking the respective Lhrusting means in its condition at the time when the monitoring means de~ects the abnormal condition.
Preferably, the locking means comprises a cutoff valve in eac~ fluid supply line, each cutoff valve being operable to close the respective fluid supply line to fluid 10w when the abnormal condition is detected. Each cutoff valve may be a pilot operable check valve operable to hold the respective fluid supply line open to fluid flow as long as a supply of pressuri~ed pilot fluid is connected thereto.
In this arrangement, each check valve is connected to the supply of pressurized pilot fluid by a respective pilot supply line, the pilot supply line including a pilot control valve for selectively disconnecting the supply of pilot fluid from the associated check valve. The pilot control valve is operable, when it disconnects the supply of pilot fluid from the associated check valve, to open the pilot supply line between the pilot control valve and the check valve to a sump to thereby relieve the pressure of pilot fluid at the check valve and cause the check valve to close the associated fluid supply line.
Each fluid supply line may be connected to a sump through a respective fluid dump line, each fluid dump line having a selectively operable dump valve therein which is operable to normally hold the dump line closed to fluid flow and to open the dump lines when pressure on the article is being relieved~ One or more of the fluid dump lines may be provided with a bleed control valve operable to ~ontrol the rate of fluid flow through the dump l:ine when the dump valve is open.
The thrusting means may be drivable in one direction and be adapted to return to their inoperative positions due to reaction of the article which is being worked upon.
In this arrangement the fluid supply line would be a single line to each thrusting means.
However in the pre~erred, more generally applicable arrangement, each thrusting means is positively drivable in both directions so that it can apply both compressive and tensile loads to the article. In this case each thrusting means is connected to a respective input fluid supply line and an output fluid supply line, the locking means being operable to close both input and output fluid supply lines to fluid flow when the abnormal condition is detected.
This latter arrangement using thrusting means drivable in both directions will now he further described with reference to the accompanying drawing which illustrates an hydraulic circuit diagram for one thrusting means of a control circuit according to a preferred embodiment of the present invention.
The fluid control circuit illustrated is operable to control the pressure applied to an article by a plurality of fluid operable thrusting means 10 drivable from a source of pressurized driving fluid (not shown). One thrusting means 10 is shown as an hydraulic jack 12 of generally known construction. The jack 12 is positively drivable in both directions for applying both compressive and tensile CM
~ ~ ~65~
loads to the article.
The circuit includes a fluid supply line 14 for carrying driving ~luid to and ~rom eachl thrusting means 10.
Locking means 16 is operable in response to detection of an abnormal condition to interrupt ~luid supply to or from each thrusting means 10 by closing each fluid supply line 14 to fluid flow and thereby locking the thrus~ing means 10 in their respective conditions when the abnormal condition is detected. In the case of jack 12 which can be positively driven in both directions, the jack 12 is connected to an input fluid supply line 18 connected to one side of the jack piston and output fluid supply line 20 connected to the other side and the locking means 1~ is operable to close both input and output fluid supply lines 18,20 to fluid flow when the abnormal condition is detected.
Control means 22 is provided for selectively switching supply of driving fluid to the thrusting means 10. The control means ?2 may comprise a control valve for simultaneously operating all the thrusting means 10. However as illustrated the control means 22 preferably comprises a selectively operable control valve 23 for each thrusting means 10 and located in the respective fluid supply line 14.
Each control valve 23 comprises a control servo valve having a valve member 24 with a supply position allowing supply of driving fluid to the respective thrusting means 10, a central cutoff position (as shown) in which the fluid supply line 14 is closed to fluid flow, and a drain position allowing draining of driving fluid from the thrusting means 10, the control servo valve being solenoid driven so as to allow selective changing of the position of the valve member CM
~6~
24~
~he valve member 24 is adapted to be positively driven by the solenoid(s) in either direction from its central cutoff position so that the valve 23 has a relatively S rapid response to electrical control signals. The rapid response characteristic may be used to provide an oscillating load to the article. For example in the case o~ aircraft wings, an oscillating load at a frequency of up to 2 hertz may be applied to the wings to simulate flight conditions.
The locking means 16 comprises a cutoff valve 25,26 in each of the 1uid supply lines 18,20 responsive to a predetermined fault condition to close the respective ~luid supply line 18,20 to fluid flow and hold the thrusting means in its condition at the instant of detection of the ~ault condition. Each cutoff valve is a selectively operable check valve. Each cutoff check valve is a pilot operable check valve 27,28 operable to hold the associated fluid supply line 18,20 open to ~luid flow as long as a supply of pressurized pilot fluid is connected to the check valve 27,28. In this embodiment there is provided a pilot supply line 29 to each cutoff check valve 27,28 associated with the thrusting means 10. In the illustrated case where two check valves 27,28 are provided for the jack 12, the pilot supply line 29 is divided at a T connection 3Q to supply the two check valves 27,2g. The pilot supply line 29 is provided with a pilot control valve 31 for selectively disconnecting the supply of pilot fluid from the cutoff check valves 27,28. The pilot control valve 31 is solenoid operated. As shown, the pilot control valve 31 ~M
is located in the common pilot supply line 29 and is arranged to maintain that line 29 open to the source of pressurized pilot fluid as long as the soleno.id is energized and to close that line on interruption of power to the solenoid thus providing a fail safe mod~ of operation.
Thus an electrical fault that interrupts power supply to the solenoid will result in closing the pilot supply line 29.
When the pilot control valve 31 closes it is arranged to open the pilot supply lines to the cuto~f valves 27,28 to a sump 32 to relieve the pressure of pilot fluid at the cutof~ valves 27,28 so that the cutoff valves 27,28 close - the fluid supply lines 18,20 to and from the jack 12 and thereby hold the jack 12 in its condition at the time the pilot control valve 31 is operat~d~
In use the fluid control circuit may be coupled to sensing means (not shown~ operative to detect the load .
applied to the article by each thrusting means 10. In the case of aircraft wing loading , the sensing means may include a plurality of transducers in the form of load cells.
2Q The outputs of the load cells may be fed to an electrical monitoring circuit for monitoring the load at each point of the aircraft wing where the thrusting means 10 is operating, the monitoring circuit being operative to detect any loading above a predetermined level to activate the looking means 16,.which in the preferred embodiment includes the solenoid operated pilot con-trol valves 31.
Each fluid supply line 18,20 is connected to a sump 35,36 through a respective fluid dump line 37,38 each fluid dump line 37,38 having a selectively operable dump valve 39,40 therein which is operable to normallyhol~th'edumplline (~M .
31~ 38 closed to fluid flow and to open the dump lines 37,38 when pressure on the article is being relieved. Each fluid dump line 37,38 extends from a point between the cutoff valve 27,28 and control valve 23 to the sump 35,36. Each dump valve 39,40 is a pilot operated check dump valve 43,44 coupled to a respective or, as illustrated~ a common dump pilot supply line 45. The pressure in the common dump supply line 45, and hence at all the dump valves 43,44 may be contro:Lled by a central dump control valve (not shown) to selectively open and close the dump valves 43~44. During relief of pressure on the article the dump valves 39,40 are opened enabling pressure relieving~- flow from the pressurized side`
the jac]c piston and fluid take-up from the sump on the other side of the piston to prevent cavitation in the fluid supply lines on the latter side. The central dump control valve may be operated simultaneously with the pilot con~rol valve 31 to relieve any pressure that may build up in the fluid supply lines 18,20 between the cutoff valves 27,28 and control valves 24. Also simultaneously the control valves 24 may be operated to return to their cutoff conditions.
Each fluid d~p line 37,38 includes a bleed control valve 41,42 operable to control the rate of fluid flow through the dump line 37,38 when the dump valve 39,40 are open. The ; bleed control valve 41,42 loacted in the fluid dump line 37,38 are temperature and pressure compensating so that the rate of discharge of fluid through the bleed valves 41,42 may be controlled. For example, in the case of aircraft wing testing, different pressures may be exerted on the various jacks by the wings during pressure relief and it is desirable to be able to individually control or set the rate o~
CM
8.
discharge of each jack so that a wing is not damaged.
Similarly fluid temperature can ~ary particularly when an oscillating load is applied and this can affect the viscosity of the fluid and hence its discharge rate.
Each fluid supply line 18,20 includes an auxiliary check valve 47,48 operable, when the associated ~ump line 37,38 is open, to close the 1uid supply line 18,20 against leakage flow other than through the bleed contr~l valve 41,42.
In some cases it may occur that leakage flow through the con-trol valve 23 negates the setting of the bleed control valves 41,42. The auxiliary check valves 4i,48 prevent such leakage flow and ensure that pressure relieving flow is controlled as desired by the bleed control valves 41,42. The auxiliary check valves 47, 48 as shown can be ope~ated from the common dump supply line 45 so that the auxiliary check valves 47,48 close when the dump valves ~3,44 open.
In operation of the illustrated fluid control circuit according to the preferred embodiment of the present invention when used for loading~aircraft wings, the h~draulic jack 12 is connected to a source of pressurized li~uid through the associated control valve 23. The control valve 23 is open in response to an electrical signal from a central control location to commence the loading operation of the respective jacks and this may occur simultaneously for all jacks. Each jack 12 has associated therewith a sensing means (not shown) which is connected to the electrical monitoring circuit (not shown) so that the loaded condition of the jack 12 or stress on the wing can be monitored and controlled through the control valve 23. In the event of a failure in the electrical control circuit or hydraulic fault in any , ~8659~
jack or any other event to cause a jack to apply an abnormal load, the pilot control valves 31 will operate to interrupt pilot fluid supply to the cutof~ valves 25,26 in the fluid supply lines 18ll9 of the jacks 12. The jacks 12 therefore will be held in the active or load applying condition. For example if one jack "sticks" while all the other jacks are relieving pressure on the aircraft wing the detection of the abnormal stress at the sticking jack will initiate locking of all t~ jacks in the condition at the instant the fault is detectea. The faulty jack may then be inspected and serv-iced so that it will operate correctly. The pilot control - valve associated with the ~aulty jack may be independently operated to ensure that -that jack is then operating correctly. While the jacks are being held in their load applying condition any excess pressure in the circuit on the side of the cutoff valves 25,26 remc~te from the jacks 12 can be purged through the dump lines 37,38 through operation of the pilot opera~ted dump valves 37,40.
If the operator decides that it is safe to unload a jack the pilot supply to the cutoff valves 25,26 is reconnected by energizing the solenoid of the pilot control valve 31.
During relief of pressure on the aircraft wing the cutoff valves 25,26 in the supply lines 18,20 are still maintained open and the fluid dump valves 39,40 are opened so that pressure relieving flow to and from the respective sumps 35,36 can take place. The pilot control valve 31 will still be operative in response to detection of a fault condition to close the fluid supply lines 18,20 to pressure relieving flow so tha-t -the circuit can operate to protect the aircraft wing at all stages throughout the CM
10.
the testing operatio~.
Claims (10)
1. A structure testing apparatus for applying varying stresses to a structure undergoing testing, and including monitoring means for detecting an abnormal condition of the apparatus or structure, and a plurality of fluid operable thrusting means for applying time varying loading stresses to the structure, each thrusting means being drivable from a source of pressurized driving fluid, each thrusting means having an associated fluid control circuit for controlling the loading stresses applied to the structure by the respect-ive thrusting means by means of control means for selectively switching driving fluid to the respective thrusting means, each fluid control circuit including an input supply line through which pressurized driving fluid from the source is supplied to the thrusting means and an output supply line for returning driving fluid from the thrusting means, locking means operable in response to detection of the abnormal condition by said monitoring means to interrupt driving fluid supply to and from the respective thrusting means by closing both the input and output supply lines to fluid flow, thereby locking the respective thrusting means in its condition at the time when the monitoring means detects the abnormal condition.
2. Apparatus according to claim 1, wherein the locking means comprises two cutoff valves, one in each of said input and output supply lines.
3. Apparatus according to claim 2, wherein each cutoff valve is a pilot operable check valve operable to hold the respective supply line open to fluid flow as long as a supply of pressurized pilot fluid is connected thereto.
4. Apparatus according to claim 3 wherein each check valve is connected to the supply of pressurized pilot fluid by a respective pilot supply line, the pilot supply line including a pilot control valve for selectively disconnecting the supply of pilot fluid from the associated valve check.
5. Apparatus according to claim 4, wherein the pilot control valve is operable, when it disconnects the supply of pilot fluid from the associated check valve to open the pilot supply line between the pilot control valve and the check valve to a sump to thereby relieve the pressure of pilot fluid at the check valve and cause the check valve to close the associated supply line.
6. Apparatus according to claim 1, wherein each said control means comprises a selectively operable control valve.
7. Apparatus according to claim 6, wherein each thrust-ing means is positively drivable in two opposite directions, and each said selectively operable control valve comprises a control servo valve having a valve member with a supply position allowing supply of driving fluid through the input supply line and return of driving fluid through the output supply line, a central cutoff position in which the input and output supply lines are closed to fluid flow, and a drain position allowing return of driving fluid from the thrusting means through the input supply line and supply of driving fluid through the output supply line, the control servo valve being solenoid driven so as to allow selective changing of the position of the valve member.
8. Apparatus according to claim 1, wherein each of said input and output supply lines is connected to a sump through a respective fluid dump line, each fluid dump line having a selectively operable dump valve therein which is operable to normally hold the dump line closed to fluid flow and to open the dump line when loading stress on the structure is being relieved following locking of the thrust-ing means.
9. Apparatus according to claim 8 wherein at least one said fluid dump line includes a bleed control valve operable to control the rate of fluid flow through the dump line when the dump valve is open.
10. Apparatus according to claim 9, wherein each of said input and output supply lines includes an auxiliary check valve operable, when the associated dump line is open, to close the respective one of said input and output supply lines against leakage flow other than through the bleed control valve.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000400056A CA1186594A (en) | 1982-03-31 | 1982-03-31 | Fluid control circuit |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000400056A CA1186594A (en) | 1982-03-31 | 1982-03-31 | Fluid control circuit |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1186594A true CA1186594A (en) | 1985-05-07 |
Family
ID=4122465
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000400056A Expired CA1186594A (en) | 1982-03-31 | 1982-03-31 | Fluid control circuit |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1186594A (en) |
-
1982
- 1982-03-31 CA CA000400056A patent/CA1186594A/en not_active Expired
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |