Delay valve and supply circuit of a cylinder including such a valve

Abstract

A delay valve having an inlet port, an outlet port, and at least one return port, and the delay valve comprising a distributor including: - a supply port connected to the inlet port; - a first service port forming the outlet port; - at least one second service port forming the return port; - a spool moving 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 and return ports, and a full-pressure position in which the spool obstructs the return port; and - a pilot chamber connected to the inlet port for the movement of the spool. Hydraulic supply circuit of a cylinder comprising such a delay valve (Vr, Vr', Vr''). FIGURE IN ABRIDGED DIAGRAM: Fig. 6A

Description

Title of the invention: Delay valve and supply circuit of a cylinder comprising such a valve

[0001] The invention relates to valves for hydraulic circuits such as the supply circuits for the cylinders of the latching boxes such as those used in aircraft for retaining, in the retracted position, landing gear or hatches.

[0002] BACKGROUND OF THE INVENTION

[0003] Aircraft equipped with retractable landing gear, cargo bays for storing these landing gear when the aircraft is in flight, and hatches for closing these bays are known. The deployment and retraction of the landing gear, as well as the opening and closing of the hatches, are carried out using operating actuators such as hydraulic cylinders.

[0004] When the lander reaches the retracted position, it is automatically held in this position by one or more latching housings. The same is true when the hatch reaches the closed position.

[0005] In a manner known per se, the hooking housing comprises a hook mounted pivoting between a release position and a retention position of an olive fixed on the landing gear or hatch, and a locking member which is returned by a spring to a locking position of the hook when the latter is brought into the retention position, and which is pushed back by a release actuator to allow the hook to pivot to a release position and thus release the olive.

[0006] The unlocking actuator generally comprises a hydraulic cylinder having 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 back to an unlocked position.

[0007] The proper functioning of the hooking housing, and in particular its unlocking performance, can be defined by the level of actuation force required by the cylinder to release the olive. This level of force is characterized in particular by the friction generated in the connections and contacts between the various parts composing the hooking housing (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 that these frictions can be minimized by applying grease / lubricant to ensure the proper functioning of the latching mechanism and its resistance to wear. This application requires opening the latching mechanism and is generally carried out according to a regular maintenance schedule. Preventive maintenance is performed according to predetermined criteria (service life, number of cycles performed, etc.) and aims to reduce the probability of failure of the latching mechanism. This type of maintenance requires, in particular, knowledge of the latching mechanism's behavior, its degradation modes, and the mean time between failures, and does not allow for optimizing the maintenance frequency of the latching mechanism. For that, a precise characterization of the latching mechanism's behavior in various environments, which depend on the aircraft's operating conditions as defined by the operating company, would be necessary.

[0009] To overcome these drawbacks, predictive maintenance was envisaged, consisting of measuring the pressure in the cylinder of the mounting housing to monitor the actuation force in real time, and defining a pressure threshold from which a maintenance operation must be carried out.

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

[0011] Figures IA and IB illustrate two examples of pressure evolution in a coupling housing cylinder. Figure IA corresponds to a normal operating state of the coupling housing, for which the unlocking time and pressure are approximately 1.07 seconds and 60 bar, respectively. Figure IB corresponds to a degraded operating state of the coupling housing (friction has increased between internal parts of the coupling housing, for example, due to a lack of maintenance of said coupling housing), for which the unlocking time and pressure are approximately 1.16 seconds and 160 bar, respectively.

[0012] Between the normal operating state and the degraded operating state, the difference in unlocking time is less than 100 milliseconds, so an observation frequency greater than 100 Hertz would be required at the level of the landers' computer to ensure relevant detection of the degradation of the docking housing.

[0013] However, the execution frequency of such a computer is generally approximately 12.5 Hertz. Increasing it would result in an increase in the computer's load (generally referred to as CPU load, from the English "Central Processing Unit") and therefore in the computer's size.

[0014] It was therefore envisaged, during a sequence of releasing the hook immobilized in the retained position by the locking member, to carry out the following steps: • supply the cylinder with pressurized fluid with a law of evolution according to which the fluid pressure is, for a predetermined time, less than full pressure, then equal to full pressure; • determine a release time for the hook and compare it to the time the predetermined duration ends; and • deduce from this comparison a state of degradation of the mounting housing.

[0015] By delaying the application of full pressure in the cylinder chamber, such a method makes it possible to diagnose a degradation of the unlocking performance of the latching box before the complete loss of the unlocking function, and therefore to program maintenance of the latching box to protect against a latent failure of the latter.

[0016] However, no valve is known to enable such a law of evolution of the pressure of the fluid supplying the cylinder.

[0017] SUBJECT OF THE INVENTION

[0018] More generally, such valves would be useful in any application in which it is advantageous to delay the supply of a component at full pressure. Summary of the invention

[0019] To this end, a delay valve is proposed having an inlet port for connection to a pressurized fluid source, an outlet port for connection to a cylinder, and at least one return port. According to the invention, the delay valve comprises a distributor including: - a power port connected to the input port; - a first service port forming the exit port; - at least one second service port forming the return port; - a sliding spool that moves 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 and return ports, and a full-pressure position in which the spool obstructs the return port; and - a pilot chamber connected to the input port for the movement of the mobile drawer.

[0020] 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 exiting through the outlet port S results from the pressure drop across the supply and return ports, 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 This 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, where it completely blocks the return port. The fluid pressure exiting through the outlet port then results from the pressure drop across the supply port and thus becomes approximately equal to the pressure entering through the inlet port.

[0021] It therefore appears that before becoming substantially equal to that entering through the inlet port, the pressure of the fluid exiting the outlet port is limited for a period depending on the speed of movement of the spool.

[0022] In particular, the power supply port is connected to the input port via a first restrictor.

[0023] In particular, the pilot chamber is connected to the inlet port via a second restrictor.

[0024] In particular, the supply port is connected to the return port via a third restrictor.

[0025] In particular, the delay valve includes a first check valve allowing fluid to pass from the supply port to the inlet port.

[0026] In particular, the delay valve includes a second check valve allowing fluid to pass from the pilot chamber to the inlet port.

[0027] According to a particular embodiment, the delay valve includes at least two return ports.

[0028] According to another particular embodiment, the spool has an outer surface of frustoconical shape arranged so that said spool, when passing from the pressure limiting position to the full pressure position, obstructs the return port more progressively than if the outer surface were cylindrical in shape.

[0029] The invention also relates to a hydraulic supply circuit for a cylinder comprising such a delay valve.

[0030] The invention also relates to an unlocking actuator comprising a hydraulic cylinder connected to such a hydraulic circuit.

[0031] The invention further relates to an aircraft comprising a latching housing for retaining a retractable landing gear or a hatch closing a cargo bay intended to receive the landing gear, the latching housing comprising such a release actuator. Brief description of the drawings

[0032] The invention will be better understood in the light of the following description, which is purely illustrative and not limiting, and should be read in conjunction with the accompanying figures, among which:

[0033] [Fig.1A] [Fig.1A] illustrates the evolution of the pressure in a release cylinder equipping a prior art locking housing, in a normal operating state;

[0034] [Fig.1B] [Fig.1B] is analogous to [Fig.1A], the latching box being in a degraded operating state;

[0035] [Fig.2] [Fig.2] is a schematic view of a locking device for a landing gear hatch of an aircraft via a latching housing;

[0036] [Fig.3] [Fig.3] is a schematic view of a hydraulic circuit, according to a particular embodiment of the invention, to supply a unlocking cylinder of a hooking box, to implement the method illustrated in [Fig.7];

[0037] [Fig.4A] [Fig.4A] is a schematic front view of a hook housing, shown with the hook in the retaining position and the locking member in the locked position.

[0038] [Fig.4B] [Fig.4B] is a view analogous to that of [Fig.4A], illustrating the hook in the release position, the locking member being in the unlocking position via the action of the cylinder;

[0039] [Fig.4C] [Fig.4C] is a view analogous to that of [Fig.4A], illustrating the hook in the release position, the locking member being in the unlocking position via the action of a rescue device;

[0040] [Fig.5] [Fig.5] is a schematic view of an unlocking actuator according to a particular embodiment of the invention;

[0041] [Fig.6A] [Fig.6A] is a cross-sectional view of the delay valve illustrated in [Fig.5], in a resting state;

[0042] [Fig.6B] [Fig.6B] is a view analogous to [Fig.6A], illustrating the valve in a limited pressure state;

[0043] [Fig.6C] [Fig.6C] is a view analogous to [Fig.6A], illustrating the valve in a state of full pressure;

[0044] [Fig.7] [Fig.7] illustrates a method for diagnosing a state of degradation of a hanging housing, according to a particular embodiment of the invention;

[0045] [Fig.8] [Fig.8] illustrates the evolution of the pressure in the cylinder of the unlocking actuator illustrated in [Fig.5], the cylinder being supplied with pressurized fluid with a first law of evolution;

[0046] [Fig.9] [Fig.9] illustrates a second law of evolution of the supply pressure of the cylinder;

[0047] [Fig. 10] the [Fig. 10] a cross-sectional view of the delay valve enabling the second law of evolution of the supply pressure illustrated in [Fig.9] to be carried out in a rest state.

[0048] [Fig. 11] Figure 11 illustrates a third law of evolution of the supply pressure of the cylinder

[0049] [Fig. 12] the [Fig. 12] a cross-sectional view of the delay valve enabling the third law of evolution of the supply pressure illustrated in [Fig.11], in a rest state. DETAILED DESCRIPTION OF THE INVENTION

[0050] As illustrated in [Fig.2], the invention is here described 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 compartment 3 which can be closed by a hatch 20.

[0051] Referring to [Fig. 3], a double-acting cylinder 11 is attached to the lander 10 and allows it to be maneuvered between the retracted and deployed positions. The lander 10 is held in the retracted position by a latching housing 13 equipped with a hook 14 that engages a lug 15 attached to the lander 10 when the latter reaches the retracted position. The release of the hook 14 is controlled by a hydromechanical release actuator 12.

[0052] Similarly, a double-acting cylinder 21 is attached to the hatch 20 and allows it to be maneuvered between an open position, enabling the deployment and retraction of the landing gear, and a closed position, closing the cargo bay 3. The hatch 20 is held in the closed position by a latching housing 23 attached to the structure of the aircraft 1. The latching housing 23 is equipped with a hook 24 for engaging a latch 25 attached to the hatch 20 when said hatch 20 reaches the closed position. The release of the hook 24 is controlled by a hydromechanical unlocking actuator 22.

[0053] The latching housings 13, 23 are here of identical structures, as are the olives 15, 25 and the unlocking actuators 12, 22.

[0054] The cylinder 11 used to maneuver the lander 10 is controlled by a monostable distributor DI 1 connected to a pressurized fluid source P. The unlocking actuator 12 allows the latching housing 13 to be deactivated and is controlled by a monostable valve V12 connected to the pressurized fluid source P.

[0055] The cylinder 21 used to operate the hatch 20 is controlled by a monostable distributor D21 connected to the pressurized fluid source P. The unlocking actuator 22 allows the latching housing 23 to be deactivated and is controlled by a monostable valve V22 connected to the pressurized fluid source P.

[0056] A monostable isolation valve V allows the distributors DU, D21 and the valves V12, V22 to be isolated, particularly during certain phases of flight, from the pressurized fluid source P in order to limit the risk of untimely deployment and retraction of the lander 10, but also of untimely opening and closing of the hatch 20.

[0057] It should be noted that in the event of failure of the latching box 13, the lander 10 would nevertheless be held in the hold 3 by the hatch 20 locked in the closed position via the latching box 23, so that the locking of the hatch 20 tends to limit any untimely deployment of the lander 10.

[0058] Aircraft 1 also includes a control unit UC arranged to control distributors D21, D22 connected to cylinders 11, 21 and valves V12, V22 connected to 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.

[0059] With reference to [Fig. 4A], the latching housings 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 about the axis XI between a retaining position ([Fig. 4A]) and a release position to which it is returned by a spring 17, 27 (Figs. 4B, 4C). The hook 14, 24 includes a hooking portion in which the olive 15, 25 of the lander 10 (or of the hatch 20) is intended to be retained by the latching housing 13, 23 to immobilize said lander 10 in the retracted position (or said hatch 20 in the closed position). To do this, the lander 10 (or the hatch 20) is moved by the cylinder 11,21 and the olive 15, 25 pushes the hook 14, 24 towards the retaining position in which it holds the olive 15, 25.For this purpose, a locking member 18, 28 is pivotally mounted on the second pivot along axis X2 and has at one end a roller bearing against a cam profile of the hook 14, 24. The locking member 18, 28 pivots between a locked position, to which it is automatically returned by the spring 17, 27 and which it automatically reaches when the hook 14, 24 arrives in the retained position ([Fig. 4A]), and an unlocked position (Figures 4B, 4C). In the locked position, the locking member 18, 28 holds the hook 14, 24 in the retained 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 thus the olive 15, 25 to leave the hook 14, 24.

[0060] In a known manner, the hooking boxes 13, 23 also include an inductive proximity sensor 19, 29 connected to the control unit UC and arranged to detect the presence of the hook 14, 24 in the retention position.

[0061] The latching housings 13, 23 also include a backup 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 about an axis X3 parallel to the axes XI, X2, and has a roller at one end. The unlocking member 31 pivots between a rest position to which it is automatically returned by a spring 32 (Figures 4A, 4B), and an unlocked position in which the roller of the unlocking member 31 bears against the roller of the locking member 18, 28 ([Fig. 4C]).To release the olive 15, 25, the emergency actuator 30 pushes back the unlocking member 31 which, upon reaching its unlocking position, in turn pushes back the locking member 18, 28 towards its unlocking position, which allows the hook 14, 24 to pivot towards the release position and thus the olive 15, 25 to leave the hook 14, 24.

[0062] With reference to [Fig. 5], the unlocking actuators 12, 22 comprise a hydraulic cylinder Ve including a body in which a rod T; slides, being associated with a piston which defines a chamber with the body. The locking member 18, 28 is in the locked position when the rod T; is in the retracted position ([Fig. 4A]), and is in the unlocked position when the rod T; is in the extended position ([Fig. 4B]).

[0063] The unlocking actuator 12, 22 also includes a so-called "delay" valve Vr connected to the cylinder chamber Ve. The delay valve Vr comprises: - an inlet port E connected to the pressurized fluid source P via the control valve V12, V22, - an output port S connected to the cylinder chamber Ve, and - a return port R connected to a reservoir.

[0064] The delay valve Vr also includes a distributor D comprising: - a supply port A connected to the inlet port E via a first restrictor RI and a first check valve Cl arranged in parallel with each other, the first check valve Cl allowing the fluid to pass from the supply port A to the inlet port;

[0065] - a first service port forming the output port S,

[0066] - a second service port forming the return port R,

[0067] - a movable Tr drawer between a rest position known as the "pressure limiting" position to which it is automatically returned by a spring Re and in which the supply port A is connected to the output port S and 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

[0068] - a CH pilot chamber for the movement of the Tr drawer, connected to the port inlet E via a second restrictor R2 and a second non-return valve C2 arranged in parallel with each other, the second check valve C2 allows the fluid to pass from the pilot chamber CH to the inlet port E.

[0069] The operation of the delay valve Vr is as follows.

[0070] When a pressurized fluid enters the delay valve Vr through the inlet port E and the spool Tr is in its rest position ([Fig. 6A]), the fluid tends to flow almost simultaneously to 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 exiting through the outlet port S 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 in the pilot chamber CH tends to increase, thus causing the spool Tr to move towards its full-pressure position ([Fig. 6B]). This rate of movement of the spool Tr is defined by the second restrictor R2.

[0071] As the pressure increases in the pilot chamber CH, the spool Tr eventually reaches its full-pressure position in which it completely obstructs the return port R ([Fig. 6C]). The pressure of the fluid exiting 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.

[0072] It therefore appears that before becoming substantially equal to that entering through the inlet port E, the pressure of the fluid exiting the outlet port S is limited for a period depending on the speed of movement of the spool Tr, which is itself defined by the second restrictor R2.

[0073] When the inlet port E of the delay valve Vr is no longer supplied with pressurized fluid, the pressure in the pilot chamber CH tends to decrease, thus causing the spool Tr to move towards its pressure-limiting position under the effect of the spring Re. The pilot chamber CH is depressurized through the second check valve C2, and the outlet port S is depressurized through the first check valve CL

[0074] In order to monitor the integrity of the latching housing 13, 23 and thus guard against a latent failure thereof, the control unit UC is arranged to implement, via the delay valve Vr, a method for diagnosing a state of degradation of the latching housing 13, 23. With reference to figures 7 and 8, the different steps of the method will now be detailed.

[0075] During a landing gear 10 or hatch 20 unlocking sequence, valve V12, V22 is first controlled to connect, from a time 10, the unlocking actuator 12, 22 to the pressurized fluid source P. The pressure The inlet port E of the unlocking actuator is then substantially equal to the pressure Ps of the pressurized fluid source P, which is generally equal to 206 bar or 350 bar depending on the nominal pressure of the aircraft's hydraulic generation, and which here is equal to 206 bar.

[0076] Up to a certain instant 1 (corresponding to a first phase), the pressure of the outlet port S, and therefore that of the cylinder chamber Ve, is lower than that of the inlet port E and is limited by the delay valve Vr. The delay valve Vr and, in particular, its first and third restrictors RI, R3 are arranged so that the pressure of the outlet port S is, up to instant 1i, at most equal to a pressure Piim slightly higher than a maximum unlocking pressure Pmax representative of a maximum level of force required to release the hook 14, 24 via the cylinder Ve under nominal greasing / lubrication conditions of the hook housing 13, 23. The pressure Pmax is generally between 70 bar and 90 bar, and is here equal to 85 bar. Piim pressure is generally between 90 bars and 110 bars, and here is equal to 95 bars.

[0077] Instants 10 and 1; define a duration T corresponding substantially to the time it takes for the spool Tr of the delay valve Vr to move from its pressure limit position to its full pressure position. The delay valve Vr, and in particular its second restrictor R2, are arranged so that the duration T is greater than a duration T representing the maximum unlocking time required to release the hook 14, 24 via the cylinder Ve under nominal greasing / lubrication conditions of the hook housing 13, 23. The duration T is here between 0.5 seconds and 1 second.

[0078] After time 1; (corresponding to a second phase), the pressure of the outlet port S, and therefore that of the cylinder chamber Ve, tends to become substantially equal to the pressure Ps of the source P.

[0079] The pressure of the outlet port S is thus, during the duration T, substantially constant and equal to the pressure Piim, then equal to the pressure Ps.

[0080] 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 retention position, in other words, the moment t when the rod T of the cylinder Ve has substantially finished pushing the locking member 18, 28 back towards its unlocking position. The instant t corresponds to the moment when the pressure in the chamber of the cylinder Ve reaches a minimum after having dropped sharply during the movement of the rod T.

[0081] Time t is then compared to time tl.

[0082] If time t is before time tl as illustrated in [Fig.8], then the unlocking pressure Pdev required by the cylinder Ve to release the hook 14, 24 is less than or equal to the maximum unlocking pressure Pmax representing the maximum level of effort required to release the hook 14, 24 under nominal greasing / lubrication conditions of the hook housing 13, 23. It follows that the hook housing 13, 23 is in a nominal state of greasing / lubrication and does not require the addition of grease or lubricant.

[0083] On the contrary, if time t is after time tl, then the unlocking pressure Pdev required by the cylinder Ve to release the hook 14, 24 is greater than the maximum unlocking pressure Pmax representing the maximum level of effort required to release the hook 14, 24 under nominal greasing / lubrication conditions of the hooking housing 13, 23. It is deduced that the hooking housing 13, 23 is in a degraded state and requires an application of grease or lubricant.

[0084] It will be understood that by delaying the application of full pressure in the cylinder chamber Ve for a duration T, such a method makes it possible to diagnose a degradation in the unlocking performance of the latching housing 13, 23 before the complete loss of the unlocking function, and thus to schedule maintenance of the latching housing 13, 23 to prevent a latent failure (application of lubricant / grease, dismantling of the housing for inspection and / or replacement of a part of said housing, etc.). The detection of the degradation in the unlocking performance of the latching housing 13, 23 is based solely on the release time of the hook 14, 24 and does not require the use of a pressure sensor.

[0085] A degradation state level Nd of the unlocking performance of the latching housing 13, 23 can further be calculated by the control unit UC via the following equation:

[0086] 2V —

[0087] where: - t max is defined with t0 as the duration T max; and - t M is a predefined instant beyond which a maintenance operation is required (aircraft 1 is no longer authorized to fly).

[0088] Expressed as a percentage, the degradation state level Nd is recorded in a memory of the control unit UC in order in particular to be able to observe an evolution of the degradation state level Nd of the hooking box 13, 23 during several successive unlocking sequences of the lander 10 (or of the hatch 20) and thus estimate a maximum number of unlocking sequences allowed before carrying out a maintenance operation.

[0089] Although the supply pressure of the cylinder Ve is substantially constant during the time interval T (corresponding to the first phase), it can also increase in steps. For example, the supply pressure of the cylinder Ve can, during the time interval T, be equal to a first pressure lower than the pressure Piim>, then be equal to a second pressure higher than the first pressure and lower than the pressure Piim>, and then be equal to the pressure PUm ([Fig.9]).

[0090] Such a law of evolution of the supply pressure of the cylinder Ve can be achieved via a valve Vr' which differs from the valve Vr in that it includes not one but three return ports R each equipped with a third restrictor R3.1, R3.2, R3.3 ([Fig. 10]).

[0091] When a pressurized fluid enters the delay valve Vr' through the inlet port E and the spool Tr is in its rest position (shown in [Fig. 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 exiting 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 in the pilot chamber CH tends to increase and thus causes the spool Tr to move towards its full-pressure position (not shown). This speed of movement of the drawer Tr is defined by the second restrictor R2.

[0092] As the pressure increases in the pilot chamber CH, the spool Tr moves to reach its full pressure position by successively obstructing the third restrictors R3.1, R3.2, R3.3, so that the pressure of the fluid exiting through the outlet port S results; - initially, pressure loss through the first restrictor RI and the third restrictors R3.1, R3.2, R3.3 (the Tr drawer does not obstruct any of the three return ports R); - secondly, the pressure loss through the first restrictor RI and the third restrictors R3.2, R3.3 (the Tr spool obstructs one of the three return ports R, more precisely the return port R equipped with the restrictor R3.1); - in a third step, the pressure drop across the first restrictor RI and the third restrictor R3.3 (the Tr spool obstructs two of the three return ports R, more precisely the return ports R equipped with restrictors R3.1, R3.2); and - in a fourth step, the pressure loss through the first restrictor RI (the spool Tr obstructs all the return ports R) thus becomes substantially equal to that entering through the inlet port E.

[0093] It therefore appears that before becoming substantially equal to the pressure entering through the inlet port E, the pressure of the fluid exiting the outlet port S is limited to a first pressure and then to a second pressure for a duration depending on the speed of movement of the spool Tr, which is itself defined by the second restrictor R2.

[0094] When the inlet port E of the delay valve Vr' is no longer supplied with pressurized fluid, the pressure in the pilot chamber CH tends to decrease, thus causing the spool Tr to move towards its pressure-limiting position under the effect of the spring Re. The pilot chamber CH is depressurized through the second check valve C2, and the outlet port S is depressurized through the first check valve CL

[0095] It can also be provided that the supply pressure of the cylinder Ve increases continuously. For example, the supply pressure of the cylinder Ve can, during the time interval T, increase linearly until it reaches the pressure Piim ([Fig. 11]).

[0096] Such a law of evolution of the supply pressure of the cylinder Ve can be achieved via a valve Vr' ' differing from the valve Vr in that the spool Tr has an external surface Se of frustoconical shape arranged so that said spool Tr obstructs, when passing from the pressure limiting position to the full pressure position, the return port R more progressively than if the external surface Se were cylindrical in shape (for a given speed of movement of the spool Tr).

[0097] When a pressurized fluid enters the delay valve Vr'' through the inlet port E and the spool Tr is in its rest position ([Fig. 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 exiting 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 in the pilot chamber CH tends to increase and thus causes the spool Tr to move towards its full-pressure position. This rate of movement of the spool Tr is defined by the second restrictor R2.

[0098] As the pressure increases in the pilot chamber CH, the spool Tr tends to return to its full-pressure position, progressively obstructing the return port R until it is completely blocked. The pressure of the fluid exiting through the The output port S then results from the pressure loss through the first restrictor RI and thus becomes substantially equal to that entering through the input port E.

[0099] It therefore appears that before becoming substantially equal to the pressure entering through the inlet port E, the pressure of the fluid exiting the outlet port S increases linearly over a period depending on the speed of movement of the spool Tr, which is itself defined by the second restrictor R2.

[0100] When the inlet port E of the delay valve Vr” is no longer supplied with pressurized fluid, the pressure in the pilot chamber CH tends to decrease, thus causing the spool Tr to move towards its pressure-limiting position under the effect of the spring Re. The pilot chamber CH is depressurized through the second check valve C2, and the outlet port S is depressurized through the first check valve CL

[0101] By determining the time t of release of the hook 14, 24, it is then possible, with such laws governing the evolution of the supply pressure of the cylinder Ve, to determine the release pressure Pdev, and to determine the level of degradation Nd of the performance of the hook housing 13, 23 and to schedule maintenance of said hook housing 13, 23 in accordance with its state of degradation. For example, a release pressure Pdev slightly lower or higher than the maximum release pressure Pmax may indicate a lubrication / greasing defect in the hook housing. Conversely, a release pressure Pdev significantly higher than the maximum release pressure Pmax may indicate a lubrication / greasing defect in the hook housing or the removal of a surface coating from a component of the hook housing 13, 23.

[0102] By determining the release time t of the hook 14, 24 during several unlocking sequences of the lander 10 (or the hatch 20), it is also possible to determine an evolution of said release time t and thus refine the maintenance programming of the latching housing 13, 23. For example, a stable release time t could allow for delaying the maintenance of the latching housing 13, 23. Conversely, an increasing evolution of the release time t could allow for precise programming of the maintenance of the latching housing 13, 23. Also, a significant decrease in the release time t could confirm the detachment of a surface coating from a component of the latching housing 13, 23.

[0103] By determining the evolution of the degradation state level Nd of the unlocking performance of the latching housing 13, 23 during several unlocking sequences of the lander 10 (or the hatch 20), it is also possible to refine the programming of maintenance for the latching box 13, 23. For example, a significant increase in the degradation state level Nd may trigger a maintenance operation even if time t is less than t

[0104] 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.

[0105] Although here the method is described in application to the unlocking actuator, it can also be described in application to the backup actuator.

[0106] The actuators can be single-acting or double-acting cylinders.

[0107] The delay valve can be integrated into the Ve cylinder.

[0108] The invention is applicable to any locking housing usable, for example, for the hatch locking on vehicles other than aircraft or on buildings.

[0109] 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 can be used on hydraulic thrust reverser systems for which the simultaneous pressurization of deployment actuators and unlocking devices results in the application of temporary forces on the locking devices.

Claims

Claims

1. Hydraulic circuit comprising a cylinder (Ve) and a delay valve (Vr, Vr', Vr”) supplying the cylinder with pressurized fluid, the delay valve having an inlet port (E) connected to a source of pressurized fluid (P), an outlet port (S) connected to the cylinder (Ve) and at least one return port (R), the delay valve comprising a distributor (D) 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 valve (Tr) movable between a pressure limiting position to 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 valve obstructs the return port; and - a pilot chamber (Ch) connected to the inlet port for moving the movable slide valve.

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

3. A hydraulic circuit according to any preceding claim, wherein the pilot chamber (Ch) is connected to the inlet port (E) via a second restrictor (R2)

4. A hydraulic circuit according to any preceding claim, 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 supply port (A) to the inlet port (E).

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

7. Hydraulic circuit according to any one of the preceding claims, in which the spool (Tr) comprises an outer surface (Se) of truncated cone shape arranged so that said spool, when it passes from the pressure limiting position to the full pressure position, obstructs the return port (R) more gradually than if the outer surface were of cylindrical shape.

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

9. Aircraft comprising a latching box (13, 23) for retaining a retractable landing gear (10) or a hatch (20) closing a hold intended to receive the landing gear, the latching box comprising an unlocking actuator (12, 22) according to claim 8.

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