Delay valve, and circuit for supplying a cylinder comprising such a valve

Abstract

Hydraulic circuit for supplying a cylinder (Ve) comprising a delay valve (Vr, Vr', Vr'') having an inlet port (E), an outlet port (S) and at least one return port (R), the delay valve comprising a directional control valve comprising: - a supply port (A) connected to the inlet port; - a first service port forming the outlet port; - at least one second service port forming the return port; - a slide (Tr) which is movable between a pressure limitation position towards which it is automatically returned by a spring (Re) and in which the supply port is connected to the outlet port and to the return port, and a full pressure position in which the slide obstructs the return port; and - a control chamber (Ch) connected to the inlet port for the movement of the movable slide.

Description

[0001] DELAY VALVE AND SUPPLY CIRCUIT OF A CYLINDER COMPRISING SUCH A VALVE

[0002] The invention relates to valves for hydraulic circuits such as the supply circuits for the jacks of the attachment boxes such as those used in aircraft for retaining, in the retracted position, landing gear or hatches.

[0003] BACKGROUND OF THE INVENTION

[0004] Aircraft are known which are equipped with retractable landing gear, with bays for receiving these landing gear when the aircraft is in flight, and with hatches for closing these bays. The deployment and retraction of the landing gear, as well as the opening and closing of the hatches, are carried out using maneuvering actuators such as jacks.

[0005] When the landing gear reaches the retracted position, it is automatically held in this position by one or more latching boxes. The same applies when the hatch reaches the closed position.

[0006] In a manner known per se, the attachment housing comprises a hook mounted to pivot between a release position and a position for retaining an olive fixed to the landing gear or the hatch, and a locking member which is returned by a spring to a position for locking the hook when the latter is brought into the retaining position, and which is pushed back by an unlocking actuator to allow the hook to swing to a release position and thus release the olive.

[0007] The unlocking actuator generally comprises a hydraulic cylinder comprising a body inside which a rod associated with a piston can slide. The rod is arranged to act on the locking member in order to push it towards an unlocking position. The correct operation of the latching box, and in particular its unlocking performance, can be defined by the level of actuating force required by the cylinder to allow the olive to be released. This level of force is characterized in particular by the friction generated in the connections and contacts between the different parts making up the latching box (seals carried by the piston, pivot connection of the locking member and the hook, contact between the locking member and the hook, etc.).

[0008] It is known to minimize this friction by adding grease / lubricant to ensure the proper functioning of the attachment box but also its integrity in the face of wear. This addition requires opening the attachment box and is generally carried out according to a regular maintenance program corresponding to preventive maintenance carried out according to predetermined criteria (service life, number of cycles performed, etc.) and the objective of which is to reduce the probability of failure of the attachment box. This type of maintenance requires in particular knowledge of the behavior of the attachment box, its degradation modes and the average time of proper operation between two failures, and does not allow optimization of the maintenance operation frequencies of the attachment box.To do this, it would be necessary to precisely characterize the behavior of the attachment box in varied environments which are dependent on the operating conditions of the aircraft by the company which operates it.

[0009] To overcome these drawbacks, predictive maintenance was considered, consisting of measuring the pressure in the jack of the attachment box to monitor the actuation force in real time, and to define a pressure threshold from which a maintenance operation must be carried out.

[0010] However, the pressure rise speed of a hook box cylinder is generally very high (greater than 1000 bars per second). This is the result of a small volume of fluid compressed by the piston and results in very rapid unlocking of the hook. This speed makes it difficult to observe the time and pressure of hook unlocking.

[0011] Figures 1A and 1B illustrate two examples of pressure changes in a coupling housing cylinder. Figure 1A corresponds to a normal operating state of the coupling housing for which the unlocking time and pressure are respectively substantially equal to 1.07 seconds and 60 bars. Figure 1B corresponds to a degraded operating state of the coupling housing (friction has increased between internal parts making up the coupling housing following, for example, a lack of maintenance of said coupling housing) for which the unlocking time and pressure are respectively substantially equal to 1.16 seconds and 160 bars.

[0012] Between the normal operating state and the degraded operating state, the difference in unlocking time is less than 100 milliseconds, so that an observation frequency greater than 100 Hertz would be necessary at the landing gear computer level to guarantee relevant detection of the degradation of the attachment box.

[0013] However, the execution frequency of such a computer is generally approximately equal to 12.5 Hertz. Increasing it would have the effect of increasing the computer load (generally referred to as the CPU load from the English "Central Processing Unit") and therefore the size of the computer. It was therefore envisaged, during a sequence of releasing the hook immobilized in the retaining position by the locking member, to carry out the following steps:

[0014] - supply the cylinder with pressurized fluid with a law of evolution according to which the pressure of the fluid is, for a predetermined duration, less than full pressure, then equal to full pressure;

[0015] - determine a time of release of the hook and compare it to the time at which the predetermined duration ends; and

[0016] - deduce from this comparison a state of degradation of the hanging box.

[0017] By delaying the application of full pressure in the cylinder chamber, such a method makes it possible to diagnose a deterioration in the unlocking performance of the latching box before the complete loss of the unlocking function, and therefore to schedule maintenance of the latching box to prevent a latent failure of the latter.

[0018] However, no valve is known which can produce such a law of evolution of the pressure of the fluid supplying the cylinder.

[0019] SUBJECT OF THE INVENTION

[0020] More generally, such valves would be useful in any application where it is advantageous to delay the supply of a component to full pressure.

[0021] SUMMARY OF THE INVENTION

[0022] For this purpose, a delay valve is proposed having an inlet port intended to be connected to a source of pressurized fluid, an outlet port intended to be connected to a cylinder and at least one return port. According to the invention, the delay valve comprises a distributor comprising:

[0023] - a power port connected to the input port; - a first service port forming the output port;

[0024] - at least one second service port forming the return port;

[0025] - a slide movable between a pressure limiting position to which it is automatically returned by a spring and in which the supply port is connected to the outlet port and to the return port, and a full pressure position in which the slide obstructs the return port; and

[0026] - a pilot chamber connected to the input port for moving the movable drawer.

[0027] When a pressurized fluid enters the delay valve through the inlet port and the spool is in its pressure limiting position, the pressure of the fluid leaving through the outlet port S results from the pressure drop across the supply port and the return port, and is therefore lower than that entering through the inlet port. At the same time, the pressure in the pilot chamber tends to increase and therefore causes the spool to move towards its full pressure position. As the pressure increases in the pilot chamber, the spool eventually reaches its full pressure position in which it completely obstructs the return port. The pressure of the fluid leaving through the outlet port then results from the pressure drop across the supply port and thus becomes substantially equal to that entering through the inlet port.

[0028] It therefore appears that before becoming substantially equal to that entering through the inlet port, the pressure of the fluid leaving the outlet port is limited for a duration depending on the speed of movement of the slide.

[0029] In particular, the supply port is connected to the input port via a first restrictor.

[0030] In a special way, the pilot chamber is connected to the inlet port via a second restrictor.

[0031] In a special way, the supply port is connected to the return port via a third restrictor.

[0032] In particular, the delay valve comprises a first check valve allowing fluid to pass from the supply port to the inlet port.

[0033] In particular, the delay valve includes a second check valve allowing fluid to pass from the pilot chamber to the inlet port.

[0034] According to a particular embodiment, the delay valve comprises at least two return ports.

[0035] According to another particular embodiment, the drawer comprises an outer surface of truncated cone shape arranged so that said drawer, when it passes from the pressure limiting position to the full pressure position, obstructs the return port more gradually than if the outer surface were of cylindrical shape.

[0036] The invention also relates to a hydraulic circuit for supplying a cylinder comprising such a delay valve.

[0037] The invention also relates to an unlocking actuator comprising a hydraulic cylinder connected to such a hydraulic circuit.

[0038] The invention further relates to an aircraft comprising a latching box for retaining a retractable landing gear or a hatch closing a hold intended to receive the landing gear, the latching box comprising such an unlocking actuator.

[0039] BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The invention will be better understood in the light of the following description, which is purely illustrative and non-limiting, and must be read in conjunction with the appended figures, among which: [Fig. 1A] Figure 1A illustrates the evolution of the pressure in an unlocking cylinder equipping a hooking box according to the prior art, in a normal operating state;

[0041] [Fig.lB] Figure 1B is analogous to Figure 1A, the attachment box being in a degraded operating state;

[0042] [Fig.2] Figure 2 is a schematic view of a device for locking a hatch of an aircraft landing gear via a latching box;

[0043] [Fig.3] Figure 3 is a schematic view of a hydraulic circuit, according to a particular embodiment of the invention, for supplying a cylinder for unlocking a hooking box, for implementing the method illustrated in Figure 7;

[0044] [Fig. 4A] Figure 4A is a schematic front view of a hook housing, illustrated with the hook in the retaining position, the locking member being in the locking position.

[0045] [Fig.4B] Figure 4B is a view similar to that of Figure 4A, illustrating the hook in the release position, the locking member being in the unlocking position via the action of the jack;

[0046] [Fig.4C] Figure 4C is a view similar to that of Figure 4A, illustrating the hook in the release position, the locking member being in the unlocking position via the action of an emergency device;

[0047] [Fig.5] Figure 5 is a schematic view of an unlocking actuator according to a particular embodiment of the invention;

[0048] [Fig.6A] Figure 6A is a sectional view of the delay valve shown in Figure 5, in an at-rest condition;

[0049] [Fig.6B] Figure 6B is a view similar to Figure 6A, illustrating the valve in a limited pressure state; [Fig.6C] Figure 6C is a view similar to Figure 6A, illustrating the valve in a full pressure state;

[0050] [Fig.7] Figure 7 illustrates a method for diagnosing a state of degradation of a hanging box, according to a particular embodiment of the invention;

[0051] [Fig.8] Figure 8 illustrates the evolution of the pressure in the cylinder of the unlocking actuator illustrated in Figure 5, the cylinder being supplied with pressurized fluid with a first evolution law;

[0052] [Fig.9] Figure 9 illustrates a second law of evolution of the cylinder supply pressure;

[0053] [Fig.10] Figure 10 a sectional view of the delay valve allowing the second law of evolution of the supply pressure illustrated in Figure 9 to be carried out, in a state of rest.

[0054] [Fig.11] Figure 11 illustrates a third law of evolution of the cylinder supply pressure

[0055] [Fig.12] Figure 12 a sectional view of the delay valve allowing the third law of evolution of the supply pressure illustrated in Figure 11 to be achieved, in a state of rest.

[0056] DETAILED DESCRIPTION OF THE INVENTION

[0057] As illustrated in Figure 2, the invention is described here in relation to an aircraft 1 comprising a landing gear 10 articulated on a structure 2 of the aircraft 1 between a deployed position illustrated here and a retracted position in which the landing gear 10 is received in a hold 3 closable by a hatch 20.

[0058] With reference to Figure 3, a double-acting cylinder 11 is coupled to the landing gear 10 and allows it to be maneuvered between the retracted position and the deployed position. The landing gear 10 is held in the retracted position by a hooking box 13 provided with a hook 14 allowing an olive 15 secured to the landing gear 10 to be hooked when the latter reaches the retracted position. The unhooking of the hook 14 is controlled by a hydromechanical unlocking actuator 12.

[0059] Similarly, a double-acting cylinder 21 is coupled to the hatch 20 and allows it to be maneuvered between an open position allowing the deployment and retraction of the landing gear, and a closed position closing the hold 3. The hatch 20 is held in the closed position by a hooking box 23 secured to the structure of the aircraft 1. The hooking box 23 is provided with a hook 24 allowing an olive 25 secured to the hatch 20 to be hooked when said hatch 20 arrives in the closed position. The unhooking of the hook 24 is controlled by a hydromechanical unlocking actuator 22.

[0060] The hooking boxes 13, 23 are here of identical structures, as are the olives 15, 25 and the unlocking actuators 12, 22.

[0061] The cylinder 11 used to maneuver the landing gear 10 is controlled by a monostable distributor DU connected to a source of pressurized fluid P. The unlocking actuator 12 makes it possible to deactivate the attachment box 13 and is controlled by a monostable valve V12 connected to the source of pressurized fluid P.

[0062] The cylinder 21 used to operate the hatch 20 is controlled by a monostable distributor D21 connected to the source of pressurized fluid P. The unlocking actuator 22 makes it possible to deactivate the latching box 23 and is controlled by a monostable valve V22 connected to the source of pressurized fluid P.

[0063] A monostable isolation valve V± makes it possible to isolate, in particular during certain flight phases, the distributors D11, D21 and the valves V12, V22 from the source of pressurized fluid P in order to limit the risk of untimely deployment and retraction of the landing gear 10, but also of untimely opening and closing of the hatch 20.

[0064] It will be noted that in the event of failure of the attachment box 13, the undercarriage 10 would nevertheless be retained in the hold 3 by the hatch 20 locked in the closed position via the attachment box 23, so that the locking of the hatch 20 tends to limit any untimely deployment of the undercarriage 10.

[0065] The aircraft 1 also comprises a control unit UC arranged to control the distributors D21, D22 connected to the cylinders 11, 21 and the valves V12, V22 connected to the unlocking actuators 12, 22, so as to control the deployment and retraction of the landing gear 10, the locking of said landing gear 10 in the retracted position, the opening and closing of the hatch 20, and the locking of the hatch 20 in the closed position.

[0066] Referring to Figure 4A, the hanging boxes

[0067] 13, 23 comprise, in a manner known per se, a body 16, 26 carrying a first pivot and a second pivot defining parallel pivot axes XI, X2. The hook 14, 24 is pivotally mounted on the first pivot along the axis XI between a retaining position (figure 4A) and a release position towards which it is returned by a spring 17, 27 (figures 4B, 4C). The hook 14, 24 comprises a hooking part in which the olive 15, 25 of the landing gear 10 (or of the hatch 20) is intended to be retained by the hooking housing 13, 23 to immobilize said landing gear 10 in the retracted position (or said hatch 20 in the closed position). To do this, the landing gear 10 (or the hatch 20) is moved by the jack 11, 21 and the olive 15, 25 pushes the hook

[0068] 14, 24 to the retaining position in which it retains the olive 15, 25. For this purpose, a locking member 18, 28 is pivotally mounted on the second pivot along the axis X2 and comprises at one end a roller bearing on a cam profile of the hook 14, 24. The locking member 18, 28 pivots between a locking position to which it is automatically returned by the spring 17, 27 and which it reaches automatically when the hook 14, 24 arrives in the retaining position (figure 4A), and an unlocking position (figures 4B, 4C). In the locking position, the locking member 18, 28 blocks the hook 14, 24 in the retaining position. To release the olive 15, 25, the unlocking actuator 12, 22 pushes the locking member 18, 28 towards the unlocking position, which allows the hook 14, 24 to pivot towards the release position and therefore the olive 15, 25 to leave the hook 14, 24.

[0069] In a known manner, the hooking boxes 13, 23 also comprise a proximity sensor 19, 29 of the inductive type connected to the control unit UC and arranged to detect the presence of the hook 14, 24 in the retaining position.

[0070] The hooking boxes 13, 23 also comprise an emergency actuator 30 capable of unlocking the hook 14, 24 if the unlocking actuator 12, 22 is inoperative. For this purpose, an unlocking member 31 is pivotally mounted on a third pivot along an axis X3 parallel to the axes XI, X2, and comprises a roller at one end. The unlocking member 31 pivots between a rest position to which it is automatically returned by a spring 32 (FIGS. 4A, 4B), and an unlocking position in which the roller of the unlocking member 31 bears on the roller of the locking member 18, 28 (FIG. 4C).To release the olive 15, 25, the emergency actuator 30 pushes the unlocking member 31 which, upon reaching its unlocking position, in turn pushes the locking member 18, 28 towards its unlocking position, which allows the hook 14, 24 to pivot towards the release position and therefore the olive 15, 25 to leave the hook 14, 24.

[0071] With reference to Figure 5, the unlocking actuators 12, 22 comprise a cylinder V e hydraulic comprising a body in which a rod T± slides while being associated with a piston which defines a chamber with the body. The locking member 18, 28 is in the locking position when the rod T± is in the retracted position (figure 4A), and is in the unlocking position when the rod Ti is in the extended position (figure 4B).

[0072] The unlocking actuator 12, 22 also comprises a valve V rcalled "delay" connected to the chamber of cylinder V e . The delay valve V r understand :

[0073] - an inlet port E connected to the source of pressurized fluid P via the control valve V12, V22,

[0074] - an output port S connected to the cylinder chamber V e , And

[0075] - a return port R connected to a tank.

[0076] The delay valve V r also includes a distributor D comprising:

[0077] - a supply port A connected to the inlet port E via a first restrictor RI and a first non-return valve Cl arranged in parallel with each other, the first non-return valve Cl allowing the fluid to pass from the supply port A to the inlet port;

[0078] - a first service port forming the output port S,

[0079] - a second service port forming the return port R,

[0080] - a T drawer r mobile between a rest position called “pressure limitation” to which it is automatically returned by a spring R e and in which the supply port A is connected to the outlet port S and to the return port R via a third restrictor R3, and a so-called “full pressure” position in which it obstructs the return port R; and - a pilot chamber CH for the movement of the spool T r , connected to the inlet port E via a second restrictor R2 and a second non-return valve C2 arranged in parallel with each other, the second non-return valve C2 allowing the fluid to pass from the pilot chamber CH to the inlet port E.

[0081] The operation of the delay valve V r is the following.

[0082] When a pressurized fluid enters the delay valve V r through the input port E and that the drawer T ris in its rest position (figure 6A), the fluid tends to reach, almost simultaneously, the outlet port S via the first restrictor RI, the return port R via the first restrictor RI and the third restrictor R3, and the pilot chamber CH of the distributor D via the second restrictor R2. The pressure of the fluid leaving through the outlet port S then results from the pressure drop across the first restrictor RI and the third restrictor R3, and is therefore lower than that entering through the inlet port E. At the same time, the pressure prevailing in the pilot chamber CH tends to increase and therefore to cause a movement of the spool T r towards its full pressure position (figure 6B). This speed of movement of the spool T r is defined by the second restrictor R2 .

[0083] As the pressure increases in the pilot chamber CH, the spool T rends up reaching its full pressure position in which it completely obstructs the return port R (figure 6C). The pressure of the fluid leaving through the outlet port S then results from the pressure drop across the first restrictor RI and thus becomes substantially equal to that entering through the inlet port E.

[0084] It therefore appears that before becoming substantially equal to that entering through the inlet port E, the pressure of the fluid leaving the outlet port S is limited for a duration depending on the speed of movement of the slide T r , which is itself defined by the second restrictor R2.

[0085] When the inlet port E of the delay valve V r is no longer supplied with pressurized fluid, the pressure prevailing in the pilot chamber CH tends to decrease and therefore to cause a movement of the spool T r towards its pressure limiting position under the effect of spring Re The depressurization of the pilot chamber CH is done through the second non-return valve C2, and that of the outlet port S through the first non-return valve Cl.

[0086] In order to monitor the integrity of the attachment box 13, 23 and thus protect against a latent failure thereof, the control unit UC is arranged to implement, via the delay valve V r , a method for diagnosing a state of degradation of the attachment box 13, 23. With reference to figures 7 and 8, the different stages of the method will now be detailed.

[0087] During an unlocking sequence of the landing gear 10 or the hatch 20, the valve V12, V22 is first controlled to connect, from an instant to, the unlocking actuator 12, 22 to the source of pressurized fluid P. The pressure of the inlet port E of the unlocking actuator is then substantially equal to the pressure Ps of the source of pressurized fluid P which is generally equal to 206 bars or 350 bars depending on the nominal pressure of the aircraft's hydraulic generation, and which is here equal to 206 bars.

[0088] Up to a time ti (corresponding to a first phase), the pressure of the outlet port S, and therefore that of the chamber of the cylinder V e , is lower than that of the inlet port E and is limited by the delay valve V r . The delay valve V r and, in particular, its first and third restrictors RI, R3 are arranged so that the pressure of the outlet port S is, until the instant ti, at most equal to a pressure Pi im slightly higher than a maximum unlocking pressure P ma x representative of a maximum level of effort required to release the hook 14, 24 via the cylinder V e under nominal greasing / lubricating conditions of the attachment box 13, 23. The pressure Pma x is generally between 70 bars and 90 bars, and here is equal to 85 bars. The pressure Pü m is generally between 90 bars and 110 bars, and here is equal to 95 bars.

[0089] The instants to and ti define a duration T corresponding approximately to the time taken by the drawer T r of the delay valve V r to move from its pressure limit position to its full pressure position. The delay valve V r and in particular its second restrictor R2 are arranged so that the duration T is greater than a duration Tmax representative of a maximum unlocking time required to release the hook 14, 24 via the jack V e under nominal greasing / lubricating conditions of the attachment box 13, 23. The duration T is here between 0.5 seconds and 1 second.

[0090] After the instant ti (corresponding to a second phase), the pressure of the outlet port S, and therefore that of the chamber of the cylinder V e , tend to become substantially equal to the pressure Ps of the source P.

[0091] The pressure of the outlet port S is thus, during the duration T, substantially constant and equal to the pressure Pn m , then equal to the pressure P s .

[0092] During the unlocking sequence of the landing gear 10 (or the hatch 20), the control unit UC determines, via the proximity sensor 19, 29, the instant t when the hook 14, 24 leaves the retaining position, in other words the instant t when the rod T± of the cylinder V e has substantially finished pushing the locking member 18, 28 towards its unlocking position. The instant t corresponds to the moment when the pressure in the chamber of the cylinder V e reaches a minimum after falling sharply when moving the rod T±.

[0093] Time t is then compared to time tl.

[0094] If time t is before time tl as shown in Figure 8, then the unlocking pressure Pdev required by cylinder V e to release the hook 14, 24 is less than or equal to the maximum unlocking pressure P ma x representative of the maximum force level required to release the hook 14, 24 under nominal greasing / lubricating conditions of the hooking housing 13, 23. It can be deduced from this that the hooking housing 13, 23 is in a nominal greasing / lubricating state and does not require the addition of grease or lubricant.

[0095] On the contrary, if the instant t is after the instant tl, then the unlocking pressure Pdev required by the cylinder V e to release the hook 14, 24 is greater than the maximum unlocking pressure P max representative of the maximum force level required to release the hook 14, 24 under nominal greasing / lubricating conditions of the hooking housing 13, 23. It can be deduced from this that the hooking housing 13, 23 is in a degraded state and requires the addition of grease or lubricant.

[0096] It will be understood that by delaying the application of full pressure in the chamber of the cylinder V eduring the duration T, such a method makes it possible to diagnose a deterioration in the unlocking performance of the hooking box 13, 23 before the complete loss of the unlocking function, and therefore to program maintenance of the hooking box 13, 23 making it possible to protect against a latent failure thereof (addition of lubricant / grease, disassembly of the box for inspection and / or replacement of a part of said box, etc.). The detection of the deterioration in the unlocking performance of the hooking box 13, 23 is based solely on the release time of the hook 14, 24 and does not require the use of a pressure sensor.

[0097] A level of degradation state Nd of the unlocking performance of the latching box 13, 23 can further be calculated by the control unit UC via Or :

[0098] - tmax defines with to the duration Tmax; and

[0099] - you is a predefined moment beyond which a maintenance operation is required (aircraft 1 is no longer authorized to fly).

[0100] Expressed as a percentage, the level of degradation state Nd is recorded in a memory of the control unit UC in order in particular to be able to observe a change in the level of degradation state Nd of the attachment box 13, 23 during several successive unlocking sequences of the landing gear 10 (or of the hatch 20) and thus estimate a maximum number of unlocking sequences authorized before carrying out a maintenance operation.

[0101] Although the supply pressure of the cylinder V e is here substantially constant during the duration T (corresponding to the first phase), it can also increase in stages. For example, the supply pressure of the cylinder V e can, during the duration T, be equal to a first pressure lower than the pressure Pn m, then be equal to a second pressure greater than the first pressure and less than the pressure Pn m , then be equal to the pressure Pii m (figure 9). Such a law of evolution of the supply pressure of the cylinder V e can be achieved via a V valve r ' distinguishing itself from the V valve r in that it comprises not one but three return ports R each equipped with a third restrictor R3.1, R3.2, R3.3 (figure 10).

[0102] When a pressurized fluid enters the delay valve V r ' through the input port E and that the drawer T ris in its rest position (shown in Figure 10), the fluid tends to reach, almost simultaneously, the outlet port S via the first restrictor RI, the return ports R via the first restrictor RI and the third restrictors R3.1, R3.2, R3.3, and the pilot chamber CH of the distributor D via the second restrictor R2. The pressure of the fluid leaving through the outlet port S then results from the pressure drop across the first restrictor RI and the third restrictors R3.1, R3.2, R3.3, and is therefore lower than that entering through the inlet port E. At the same time, the pressure prevailing in the pilot chamber CH tends to increase and therefore to cause a movement of the spool T r to its full pressure position (not shown). This speed of movement of the spool T r is defined by the second restrictor R2.

[0103] As the pressure increases in the pilot chamber CH, the spool Tr moves to reach its full pressure position by obstructing in turn the third restrictors R3.1, R3.2, R3.3, so that the pressure of the fluid exiting through the outlet port S results;

[0104] - firstly, the pressure loss through the first restrictor RI and the third restrictors R3.1, R3.2, R3.3 (the drawer T r obstructs any of the three return ports R);

[0105] - secondly, the pressure loss through the first restrictor RI and the third restrictors R3.2, R3.3 (the drawer T r obstructs one of the three return ports R, more precisely the return port R equipped with the restrictor R3.1);

[0106] - thirdly, the pressure loss through the first restrictor RI and the third restrictor R3.3 (the drawer T robstructs two of the three return ports R, more precisely the return ports R equipped with restrictors R3.1, R3.2); and

[0107] - in a fourth step, the pressure loss through the first restrictor RI (the drawer T r obstructs all the return ports R) and thus becomes substantially equal to that entering through the input port E.

[0108] It therefore appears that before becoming substantially equal to the pressure entering through the inlet port E, the pressure of the fluid leaving the outlet port S is limited to a first pressure then to a second pressure for a duration depending on the speed of movement of the slide T r , which is itself defined by the second restrictor R2.

[0109] When the inlet port E of the delay valve V r' is no longer supplied with pressurized fluid, the pressure prevailing in the pilot chamber CH tends to decrease and therefore to cause a movement of the spool T r towards its pressure limiting position under the effect of spring R e The depressurization of the pilot chamber CH is done through the second non-return valve C2, and that of the outlet port S through the first non-return valve Cl.

[0110] It can also be provided that the supply pressure of the cylinder V e increases continuously. For example, the supply pressure of cylinder V e can, during the duration T, increase linearly until reaching the pressure Pii m (figure 11). Such a law of evolution of the supply pressure of the cylinder V e can be achieved via a V valve r ' ' distinguishing itself from the V valve r in that the drawer T r has an outer surface S eof truncated cone shape arranged so that said drawer T r obstructs, when passing from the pressure limiting position to the full pressure position, the return port R more gradually than if the outer surface S e was cylindrical in shape (for a given speed of movement of the drawer Tr).

[0111] When a pressurized fluid enters the delay valve V r ' ' through the input port E and that the drawer T ris in its rest position (figure 12), the fluid tends to reach, almost simultaneously, the outlet port S via the first restrictor RI, the return port R via the first restrictor RI and the third restrictor R3, and the pilot chamber CH of the distributor D via the second restrictor R2. The pressure of the fluid leaving through the outlet port S then results from the pressure drop across the first restrictor RI and the third restrictor R3, and is therefore lower than that entering through the inlet port E. At the same time, the pressure prevailing in the pilot chamber CH tends to increase and therefore to cause a movement of the spool T r towards its full pressure position. This speed of movement of the spool T r is defined by the second restrictor R2 .

[0112] As the pressure increases in the pilot chamber CH, the spool T rtends to reach its full pressure position by progressively obstructing the return port R until it is completely obstructed. The pressure of the fluid leaving through the outlet port S then results from the pressure loss across the first restrictor RI and thus becomes substantially equal to that entering through the inlet port E. It therefore appears that before becoming substantially equal to the pressure entering through the inlet port E, the pressure of the fluid leaving the outlet port S increases linearly for a duration depending on the speed of movement of the slide T r , which is itself defined by the second restrictor R2.

[0113] When the inlet port E of the delay valve V r ' ' is no longer supplied with pressurized fluid, the pressure prevailing in the pilot chamber CH tends to decrease and therefore to cause a movement of the spool T r towards its pressure limiting position under the effect of spring Re The depressurization of the pilot chamber CH is done through the second non-return valve C2, and that of the outlet port S through the first non-return valve Cl.

[0114] By determining the instant t of release of the hook 14, 24, it is then possible, with such laws of evolution of the supply pressure of the cylinder V e , to go back to the unlocking pressure Pdev, and to determine the level of degradation state Nd of the performance of the attachment box 13, 23 and to schedule maintenance of said attachment box 13, 23 in accordance with its degradation state. For example, an unlocking pressure Pdev slightly lower or higher than the maximum unlocking pressure P ma x may be representative of a lubrication / greasing defect in the attachment housing. Conversely, an unlocking pressure Pdev significantly higher than the maximum unlocking pressure Pma x may be representative of a lubrication / greasing defect in the attachment housing or of a tearing off of a surface coating of a part making up the attachment housing 13, 23.

[0115] By determining the instant t of release of the hook 14, 24 during several unlocking sequences of the landing gear 10 (or of the hatch 20), it is also possible to determine a change in said instant t of release and therefore to refine the programming of the maintenance of the attachment box 13, 23. For example, stability of the instant t of release may make it possible to delay the maintenance of the attachment box 13, 23. Conversely, an increasing change in the instant t of release may make it possible to precisely program the maintenance of the attachment box 13, 23. Also, a significant decrease in the instant t of release may confirm a tearing of a surface coating of a part composing the attachment box 13, 23.

[0116] By determining the evolution of the level of degradation state Nd of the unlocking performance of the attachment box 13, 23 during several unlocking sequences of the landing gear 10 (or of the hatch 20), it is also possible to refine the programming of the maintenance of the attachment box 13, 23. For example, a significant increase in the level of degradation state Nd may generate a maintenance operation even if the instant t is less than tmax.

[0117] Of course, the invention is not limited to the embodiments described but encompasses any variant falling within the scope of the invention as defined by the claims.

[0118] Although here the method is described in application to the unlocking actuator, it can also be described in application to the emergency actuator.

[0119] Actuators can be single or double acting cylinders.

[0120] The delay valve can be integrated into the V cylinder e .

[0121] The invention is applicable to any locking box that can be used, for example, for locking hatches on vehicles other than aircraft or on buildings. More broadly, the invention is applicable to any hydraulic circuit element for which it is advantageous to delay the supply to full pressure. For example, the invention may be used on hydraulic systems of thrust reversers for which the simultaneous pressurization of deployment actuators and unlocking devices results in the application of temporary forces to the locking devices.

Claims

DEMANDS 1. Hydraulic supply circuit for a cylinder (Ve) comprising a delay valve (Vr, Vr', Vr'') having an inlet port (E) intended to be connected to a pressurized fluid source (P), an outlet port (S) intended to be connected to the cylinder (Ve) and at least one return port (R), the delay valve comprising a distributor (D) including: - a power port (A) connected to the input port; - a first service port forming the exit port; - at least one second service port forming the return port; - a drawer (T r ) mobile between a pressure limiting position to which it is automatically returned by a spring (R e ) and in which the supply port is connected to the output port and the return port, and a full-pressure position in which the drawer obstructs the return port; and - a pilot chamber (Ch) connected to the input port for the movement of the mobile drawer.

2. Hydraulic circuit according to claim 1, wherein the supply port (A) is connected to the inlet port (E) via a first restrictor (RI).

3. Hydraulic circuit according to any one of the preceding claims, wherein the pilot chamber (Ch) is connected to the inlet port (E) via a second restrictor (R2) 4. Hydraulic circuit according to any one of the preceding claims, wherein the supply port (A) is connected to the return port (R) via a third restrictor (R3, R3.1, R3.2, R3.3).

5. Hydraulic circuit according to any one of the preceding claims, comprising a first non-return valve (Cl) allowing fluid to pass from the port power supply (A) to input port (E).

6. Hydraulic circuit according to any one of the preceding claims, comprising a second check valve (C2) allowing fluid to pass from the pilot chamber (Ch) to the inlet port (E).

7. Hydraulic circuit according to any one of the preceding claims, wherein the spool (T r ) has an exterior surface (S e ) of truncated conical shape arranged so that said spool, when passing from the pressure limiting position to the full pressure position, obstructs the return port (R) more progressively than if the outer surface were cylindrical in shape.

8. Unlocking actuator (12, 22) comprising a cylinder (V e ) hydraulic connected to a hydraulic circuit according to any one of the preceding claims.

9. Aircraft comprising a latching housing (13, 23) for retaining a retractable landing gear (10) or a hatch (20) closing a cargo bay intended to receive the landing gear, the latching housing comprising a release actuator (12, 22) according to claim 8.

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