Pressure-balance valve for balancing fluid feed to actuator cylinders of a servo-control for controlling rotor blades of a rotorcraft

Abstract

A pressure-balance valve for balancing the pressures of fluids admitted into the pressure-balance valve via respective second ducts. The pressure-balance valve has both a chamber for guiding movement in translation of a piston, and also fluid flow paths, each comprising a said second duct and a first duct for admitting a fluid coming from the same fluid source as the fluid flowing in its second duct. Each of the first ducts is provided with a shutter co-operating with a ramp arranged on the piston. Movement of the piston in translation as a result of a pressure difference between the fluids respectively admitted into the second ducts causes one of the shutters to slide along the corresponding ramp and consequently allows additional fluid to be delivered from a first duct to the second duct of the same fluid flow path.

Claims

1. A pressure-balance valve for balancing the pressures of different fluids flowing respectively in a plurality of double-acting actuator cylinders of at least one servo-control suitable for driving a member for varying flight attitude of an aircraft, the valve including a valve cylinder comprising at least: a chamber for guiding a piston to move in translation along an axial extension direction of the chamber; two first ducts opening out into the chamber and each serving to convey a flow of a respective fluid between the outside and the inside of the valve; two second ducts opening out into the chamber and each serving to convey a flow of a respective fluid between the outside and the inside of the valve; two passages, each passage for individually conveying a flow of a respective fluid into the inside of the valve between one of the first ducts and an accompanying one of the second ducts; and at least one bleed duct for the draining fluids admitted into the inside of the chamber; wherein the pressure-balance valve has two fluid flow paths, each fluid flow path for conveying a respective fluid, each fluid flow path including a respective one of the first ducts, one of the passages, and one of the second ducts placed mutually in fluid flow communication; wherein for each of the fluid flow paths, the first duct is provided at its outlet to the chamber with a movable shutter that co-operates with a respective ramp formed on the piston, sliding of the shutter along the ramp caused under the effect of the piston moving in translation inside the chamber disengaging the shutter from the outlet of the first duct and consequently placing the first and second ducts in fluid flow communication with each other via the passage, the first duct and the second duct in fluid flow communication with each other delivering additional fluid through the passage from the first duct to the second duct.

2. A pressure-balance valve according to claim 1, wherein for each of the fluid flow paths, the passage is formed by an axial end segment of the chamber into which the first and second ducts open out.

3. A pressure-balance valve according to claim 1, wherein: the valve cylinder is subdivided into two valve cylinder blocks that are axially assembled together, the blocks providing the respective fluid flow paths by including respective chamber segments on a common axis; and the piston is subdivided into two structurally distinct piston segments, the piston segments being housed respectively in the chamber segments and bearing axially one against the other.

4. A pressure-balance valve according to claim 1, wherein the at least one bleed duct is arranged as a drain isolated from the fluid flow paths by seals interposed between the piston and the chamber, the bleed duct collecting lost fluid and discharging it from the valve, which lost fluid comes from any residue of respective fluids in at least one of the two fluid flow paths that has infiltrated past the seals.

5. A pressure-balance valve according to claim 4, wherein the bleed duct is common to collecting and discharging lost fluid coming from respective fluids in at least one of the two fluid flow paths.

6. A pressure-balance valve according to claim 4, wherein the seals comprise gaskets interposed axially between the bleed duct and respective axial ends of the chamber.

7. A pressure-balance valve according to claim 4, further comprising a warning device for giving a warning concerning malfunctioning of the valve by evaluating the quantity of lost fluid discharged from the bleed duct.

8. A pressure-balance valve according to claim 1, wherein the valve is configured to hydraulically damp the movement of the piston inside the chamber.

9. A pressure-balance valve according to claim 1, wherein the valve has hydraulic damper means for damping the movement of the piston inside the chamber, wherein the hydraulic damper means are formed by blind sockets opening out into respective end walls of the axial ends of the chamber and co-operating with respective axial extensions of the piston, the sockets respectively receiving the extensions as a result of the piston moving axially inside the chamber, clearance being arranged respectively between each socket and the extension co-operating therewith to leave controlled discharge channels for discharging the fluids from the sockets to the chamber.

10. A pressure-balance valve according to claim 1, wherein when the piston is in a stabilized axial position inside the chamber under the effect of balanced thrusts exerted on the axial end faces of the piston by each of the fluids respectively, axial gaps are left between the shutters and the respective ramps with which the shutters co-operate.

11. A pressure-balance valve according to claim 1, wherein the valve is configured to brake the movement of the piston inside the chamber.

12. A pressure-balance valve according to claim 1, wherein the valve includes braking means for braking the movement of the piston inside the chamber, wherein the braking means are formed by at least one of the following arrangements: the ramps having slopes at an angle relative to the extension axis of the piston lying in the range 5 to 60; seals mounted so that they are a tight fit along the piston under the effect of the piston moving axially; and axial gaps are left between the shutters and the respective ramps with which the shutters co-operate.

13. A pressure-balance valve according to claim 1, wherein the valve is provided with a detector for detecting the position of the piston inside the chamber, the detector generating a warning signal in the event of detecting an axial stroke of the piston greater than a predetermined acceptable stroke.

14. A pressure-balance valve according to claim 13, wherein the detector generates a variation in the warning signal as a function of the axial position of the piston inside the chamber.

15. A pressure-balance valve according to claim 13, wherein the detector is formed by at least one set of components that co-operate by exchange of waves, the set of components comprising at least a first component placed at an axial end of the piston that is associated therewith and a second component placed at the end of the chamber facing said any axial end of the piston.

16. A pressure-balance valve according to claim 15, wherein said at least one first component may be placed equally well at either axial end face of the piston or on either of said extensions.

17. A pressure-balance valve according to claim 15, wherein the detector is of the type that make use of the Hall effect, the first component and the second component being formed by magnets that generate between them a magnetic field that is crossed by a third component mounted on the cylinder of the valve and producing a voltage that generates said warning signal at a predefined setpoint voltage.

18. A pressure-balance valve according to claim 1, wherein the shutters are bodies of revolution and wherein the ramps are arranged at respective ends of the piston.

19. A pressure-balance valve according to claim 1, wherein each of the first ducts is provided with a perforated seat for retaining the shutter with which it is associated against the shutter escaping to the inside of the first duct under the effect of thrust exerted by the fluid present in the chamber at a pressure that is higher than the pressure of the fluid admitted into the first duct.

20. A pressure-balance valve according to claim 1, wherein the valve is configured to control axial movement of the piston prior to admitting fluids into the inside of the valve.

21. A pressure-balance valve according to claim 1, wherein the valve is provided with control means for controlling axial movement of the piston prior to admitting fluids into the inside of the valve, wherein the piston is subdivided into two piston segments on a common axis bearing axially one against the other, said control means being formed by an elastically deformable member interposed axially between the piston segments and urging them towards the axial ends of the chamber respectively facing said piston segments.

22. A hydraulic installation suitable for driving a member for varying flight attitude of an aircraft, the hydraulic installation comprising two distinct hydraulic circuits preventing communication between respective fluids conveyed by the hydraulic circuits between respective fluid sources for said fluids and respective double-acting actuator cylinders of at least one servo-control suitable for driving said member for varying flight attitude of an aircraft, each hydraulic circuit including a hydraulic directional-control valve controlling the flow of the fluid through an end chamber and through a head chamber of an actuator cylinder fed with fluid under the control of the hydraulic directional-control valve of a given hydraulic circuit, the hydraulic directional-control valves being actuatable jointly under the effect of a flight control generated by a pilot of the aircraft and simultaneously controlling the flow of the various fluids inside the actuator cylinders, wherein the hydraulic installation is fitted with pressure-balance valves each in accordance with claim 1, a first pressure-balance valve balancing the respective pressures of the fluids flowing through the respective end chambers of each of the actuator cylinders and a second pressure-balance valve balancing the respective pressures of the fluids flowing through the respective head chambers of each of the actuator cylinders.

23. A hydraulic installation according to claim 22, wherein the concepts upstream and downstream are considered relative to the flow direction of the fluids from the fluid sources to the actuator cylinders; wherein the first ducts of each of the pressure-balance valves are in fluid flow communication upstream from the hydraulic directional-control valves with the respective fluid sources; wherein the second ducts of each of the pressure-balance valves are in fluid flow communication downstream from the hydraulic directional-control valves, for a first pressure-balance valve with the respective end chambers of the actuator cylinders, and for a second pressure-balance valve with the respective head chambers of the actuator cylinders; and wherein each of the pressure-balance valves opens out to the surrounding air via said at least one bleed duct with which each of the pressure-balance valves is provided.

24. A hydraulic installation according to claim 23, wherein the lost fluid collected and discharged by said at least one bleed duct of each of the pressure-balance valves is collected in a common storage volume for evaluation of the quantity of lost fluid that has been collected by the storage volume.

25. A hydraulic installation according to claim 22, wherein the actuator cylinders are distinct actuators formed from separated cylinders incorporated in a single servo-control having multiple actuator cylinders or actuator cylinders incorporated in servo-controls having respective single actuator cylinders.

26. An aircraft, wherein said aircraft includes at least a hydraulic installation according to claim 22.

27. An aircraft, wherein said aircraft includes at least: two pressure-balance valves, each pressure-balance valve according to claim 1.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

(1) Embodiments of the present invention are described with reference to the figures of the accompanying sheets, in which:

(2) FIG. 1 shows an example of architecture for a hydraulic installation of the present invention;

(3) FIGS. 2 to 5 are diagrams showing a pressure-balance valve in a preferred embodiment of the present invention, showing how such a pressure-balance valve operates;

(4) FIG. 6 is a diagram of a pressure-balance valve in a particular arrangement in accordance with the present invention;

(5) FIG. 7 is a diagram of a pressure-balance valve in another particular arrangement in accordance with the present invention; and

(6) FIG. 8 shows an example of architecture for a hydraulic installation of the present invention, similar to the one of FIG. 1 but with distinct actuators formed from separated cylinders incorporated in a single servo-control having multiple actuator cylinders.

DETAILED DESCRIPTION OF THE INVENTION

(7) For a better understanding of the explanations below, members that are common and shown in various figures are respectively identified in the description relating specifically to those figures using the same reference numbers and/or letters, but without that meaning that they are shown individually in each of the figures.

(8) In FIG. 1, a hydraulic installation is dedicated to pivotally moving the blades 1 of a rotary wing aircraft AC. In this example, the rotary wing aircraft AC is a rotorcraft having blades 1 that pivot about their respective pitch variation axes A1.

(9) Conventionally, such a hydraulic installation comprises two distinct hydraulic circuits 2 and 2 causing respective fluids F1 and F2 to flow between fluid sources S1 and S2 associated with respective ones of the hydraulic circuits 2 and 2, and respective actuator cylinders C1 and C2 of a servo-control 3.

(10) The hydraulic installation also typically includes hydraulic directional-control valves D1 and D2 each placed in fluid flow communication with one or the other of the hydraulic circuits 2 and 2. The hydraulic directional-control valves D1 and D2 are operable jointly by a common control member 4 actuated in compliance with flight commands issued by a pilot, which may equally well be a human pilot or an autopilot.

(11) In the embodiment shown, the hydraulic directional-control valves D1 and D2 are of the type having at least one slide and preferably of the safe type having two slides. Naturally, the hydraulic directional-control valves D1 and D2 may be of any other structure that provides at least the same functions, such as hydraulic directional-control valves arranged as rotary valves, for example.

(12) The hydraulic directional-control valves D1 and D2 distribute the combined flow of the fluids F1 and F2 through each of the hydraulic circuits 2 and 2 in order to feed fluid selectively to the end chambers 5, 5 and to the head chambers 6, 6 of the various actuator cylinders C1, C2 with which the hydraulic directional-control valves are respectively associated. Relative movement between the actuator cylinders C1, C2 and a rod 7 slidably mounted inside the actuator cylinders C1 and C2 serves to vary the pitch of the blades 1 of the rotor.

(13) In the embodiment shown, these actuator cylinders C1, C2 are incorporated in a single hydraulic actuator 10 having two actuator cylinders C1, C2 of the servo-control 3. The actuator cylinders C1 and C2 co-operate jointly with a common rod 7 having anchor means 8 for anchoring to a structure 9 of the rotorcraft, with the hydraulic actuator 10 being provided with fastener means 11 for fastening to a drive member 12 for driving the blades 1 about their respective pitch variation axes A1.

(14) In a possible variant embodiment providing the same relative movement between the actuator cylinders C1, C2 and the rod 7, the hydraulic actuator 10 could be provided conversely with anchor means for anchoring to the structure of the rotorcraft, while the rod 7 could be provided with fastener means for fastening to the drive member 12 of a blade 1.

(15) As shown in FIG. 8, the actuator cylinders C1, C2 may equally well be separate and distinct actuator cylinders 10, 10 incorporated in a single servo-control 3 having multiple actuator cylinders or actuator cylinders incorporated in servo-controls having respective single actuator cylinders.

(16) In the configuration shown in FIG. 1 of the hydraulic installation, the operating positions of the hydraulic directional-control valves D1, D2 cause the fluids F1 and F2 to be admitted respectively into one or the other of the end chambers 5, 5 of the actuator cylinders C1, C2 via the hydraulic circuits 2, 2 respectively associated with passing flows of the fluids F1, F2 through one or other of the actuator cylinders C1, C2.

(17) Such fluid admission causes relative movement between the rod 7 and the actuator cylinders C1, C2, and consequently causes the fluids F1, F2 to be expelled from the head chambers 6, 6 of the actuator cylinders C1, C2 towards the fluid sources S1, S2 via the hydraulic circuits 2, 2 respectively associated with passing flows of the fluids F1, F2 through one or the other of the actuator cylinders C1, C2.

(18) Naturally, in an inverse operating configuration of the hydraulic installation, admission of the fluids F1, F2 into the head chambers 6, 6 of the actuator cylinders C1, C2 causes the fluids F1, F2 to be expelled from the end chambers 5, 5 towards the fluid sources S1, S2, as indicated by the dot-dash style arrows in FIG. 1.

(19) The hydraulic installation also has a pair of pressure-balance valves V1, V2 placed in the respective hydraulic circuits 2 and 2. A first pressure-balance valve V1 serves to balance the pressures of the fluids F1, F2 flowing respectively through the head chambers 6, 6 of the actuator cylinders C1, C2, and a second pressure-balance valve V2 serves to balance the pressure of the fluids F1, F2 flowing respectively through the end chambers 5, 5 of the actuator cylinders C1, C2.

(20) In FIGS. 1 to 7, each of the pressure-balance valves V1, V2 comprises a valve cylinder 13 providing a chamber 14 for guiding movement in translation of a piston 15 along an axial extension direction A2 of the chamber 14. First ducts 16, 16 open out radially into the chamber 14, each at an axial end of the chamber 14 that is associated therewith. Second ducts 17, 17 open out to respective axial ends of the chamber 14, such that the fluids F1, F2 conveyed by the second ducts 17, 17 exert opposing axial thrusts against the piston 15 via its axial end faces.

(21) Each of the pressure-balance valves V1, V2 has a pair of distinct fluid flow paths, each fluid flow path comprising a first duct 16 or 16 and a second duct 17 or 17 opening out into the same axial end of the chamber so as to provide a passage 18 or 18 for fluid between the first duct 16 or 16 and the second duct 17 or 17.

(22) In FIG. 1, the first ducts 16, 16 of each of the pressure-balance valves V1, V2 are in fluid flow communication with a respective fluid source S1, S2. Fluid flow communication between the first ducts 16, 16 and the fluid sources S1, S2 is established upstream from the hydraulic directional-control valves D1, D2 relative to a flow direction of the fluids F1, F2 from the fluid sources S1, S2 to the actuator cylinders C1, C2.

(23) The second ducts 17, 17 of each of the pressure-balance valves V1, V2 are in fluid flow communication, respectively with the end chambers 5, 5 of the actuator cylinders C1, C2 for one of the pressure-balance valves V1, V2 and with the head chambers 6, 6 of the actuator cylinders C1, C2 for the other one of the pressure-balance valves V2, V1.

(24) The second ducts 17, 17 are put into fluid flow communication with the chambers of the actuator cylinders C1, C2 downstream from the hydraulic directional-control valves D1, D2 relative to the flow direction of the fluids from the fluid sources S1, S2 to the actuator cylinders C1, C2.

(25) More specifically, in FIGS. 2 to 7 and for any given pressure-balance valve V1 or V2 (only one pressure-balance valve V1 is shown in FIGS. 2 to 7), the outlet 19, 19 of each first duct 16, 16 into a chamber 14 is provided with a shutter 20, 20 preventing the fluids F1, F2 from flowing from the first duct 16, 16 to the chamber 14 under the effect of the pressure of the fluids F1, F2 conveyed from the fluid sources S1, S2 to the first ducts 16, 16.

(26) Furthermore, at its axial ends, the piston 15 has respective ramps 21, 21 for thrusting the shutters 20, 20 towards the insides of the first ducts 16, 16 where the shutters 20, 20 shut off respectively their outlets 19, 19 to the chamber 14.

(27) These arrangements are such that moving the piston 15 axially inside the chamber 14 causes sliding thrust to be engaged between one or the other of the shutters 20, 20 along the associated ramp 21, 21 in the axial travel direction of the piston 15 inside the chamber 14. The effect of such sliding thrust engagement is to push the shutter 20, 20 towards the inside of the first duct 16, 16 and consequently to release, at least in part, the outlet 19, 19 from the first duct 16, 16 so that it is no longer shut by the shutter 20, 20.

(28) The resulting disengagement of the outlet 19, 19 of the first duct 16, 16 then allows the fluid F1, F2 admitted into the first duct 16, 16 to flow towards the second duct 17, 17 opening out into the same passage 18, 18 into which the first duct 16, 16 also opens out.

(29) Furthermore, the passages 18, 18 arranged respectively at the axial ends of the chamber 14 are isolated from being put into fluid flow communication with each other by sealing means 22, 22. Such sealing means 22, 22 are formed by a pair of gaskets interposed respectively between said passages 18, 18 and a bleed duct 23 opening out into the chamber 14 in an axial middle zone of the chamber 14.

(30) It should be observed that advantage may be taken of the friction conditions between the sealing means 22, 22 and the piston 15 or the chamber 14 in order to slow down the movement of the piston 15 and thereby avoid sudden movements of the piston 15 and violent variations in the pressure of the fluids F1, F2 as admitted respectively into each of the passages 18, 18.

(31) Such a bleed duct 23 is constituted by a drain collecting any fluid residue that might infiltrate past the sealing means 22, 22 under the effect of repeated movements in translation of the piston 15. Such fluid residues are lost, with the lost fluid 24 collected by the bleed duct 23 being discharged to the outside of the pressure-balance valve V1, V2, since the bleed duct 23 opens out to the surrounding atmosphere.

(32) Furthermore, the actuator cylinder 13 is preferably subdivided axially into two pressure-balance valve cylinder blocks 44, 44 that are assembled together. The blocks 44, 44 provide respective fluid flow paths and respective chamber segments lying on a common axis and making up the chamber 14.

(33) The piston 15 is possibly formed by a one-piece unit that is guided to move axially by both of the chamber segments. Nevertheless, in the preferred embodiment as shown, the piston 15 is subdivided into two piston segments 32, 33 that bear axially against each other.

(34) With reference to FIGS. 2 and 3 in succession, the pressure-balance valve V1 is suitable for mutually balancing the pressures of the fluids F2, F1 as conveyed respectively towards the second ducts 17, 17 and consequently makes it possible to balance the thrust forces exerted on the rod 7 by the fluids F1, F2 as admitted respectively into each of the actuator cylinders C1, C2, as shown in FIG. 1.

(35) More particularly in FIG. 2, the piston 15 is in a stabilized axial position inside the chamber 14 under the effect of the axial thrusts exerted against the respective axial end faces of the piston 15 by the respective fluids F1 and F2 as admitted into the two second ducts 17, 17. A stabilized axial position is obtained for the piston 15 because of the mutual balance between the pressures of the fluids F1 and F2 as admitted respectively into the two second ducts 17, 17.

(36) In this situation, each of the shutters 20, 20 is pressed against the corresponding outlet 19, 19 into the chamber 14 from the first duct 16, 16 that houses that shutter. Since the outlets 19, 19 of the first ducts 16, 16 are completely shut by the shutters 20, 20, it is not possible for the fluids F1, F2 that are admitted into the first ducts 16, 16 to flow towards the chamber 14.

(37) With the piston in a stabilized position, axial gaps, E, E are left between the ramps 21, 21 and the shutters 20, 20 that co-operate respectively with the ramps 21, 21.

(38) Such axial gaps E, E make it possible, whether the piston 15 is in the stabilized position to be certain that the shutters 20, 20 are bearing in leaktight manner against the outlets 19, 19 of the first ducts 16, 16.

(39) Said axial gaps E, E also make it possible to allow for an acceptable pressure difference between the fluids F1, F2 flowing respectively in the various fluid flow paths 16, 17, 18 or 16, 17, 18. Such provisions serve to avoid continuous and inappropriate movements of the piston 15 seeking to correct small pressure differences between the fluids F1 and F2 admitted respectively into the second ducts 17, 17.

(40) Furthermore, the pressure-balance valve, which is designed to be installed on board the rotorcraft in an environment close to the rotor, is subjected to particularly high levels of vibration. Such vibration is likely to cause the piston 15 to oscillate randomly in its axial movement direction. Under such conditions, said axial gap E, E serve to filter out the unwanted movements of the piston 15 caused by the vibration to which the pressure-balance valve is subjected.

(41) As explained below, such axial gaps E, E can also be used to advantage for braking and stabilizing the movement in translation of the piston 15 prior to sliding thrust engagement between the shutters 20, 20 and the ramps 21, 21 with which the shutters 20, 20 co-operate respectively. The shutters 20, 20 and the ramps 21, 21 are thus protected against coming into contact violently, and sustained and pointless movements of the shutters 20, 20 driven by the piston 15 are avoided.

(42) In FIG. 3, excess pressure of the fluid F1 admitted into one of the second ducts 17, 17 compared with the pressure of the fluid F2 admitted into the other one of the second ducts 17, 17 causes the piston 15 to move in translation.

(43) The shutter 20 in the first duct 16 situated axially opposite from the second duct 17 with excess pressure then comes into sliding thrust engagement against the ramp 21 with which the shutter 20 co-operates, thereby releasing at least in part the outlet 19 of the first duct 16 housing the shutter 20.

(44) The first duct 16 that has its outlet 19 disengaged is then put into fluid flow communication with the chamber 14. In this situation, the fluid F2 admitted into this first duct 16 having its outlet 19 disengaged flows towards the passage 18 to which this first duct 16 leads, thereby having the effect of increasing the pressure of the fluid F2 present in this passage 18. The piston 15 is then pushed back in translation until it reaches a stabilized position when equilibrium is reestablished between these pressures of the fluids F1 and F2 respectively admitted into the second ducts 17, 17.

(45) In FIGS. 2 to 7, the pressure-balance valve V1 is provided with detector means 25, 25 for detecting the axial position of the piston 15 inside the chamber 14.

(46) In the embodiments shown, such detector means 25, 25 are of the type that exchange waves within at least components 26, 26 and 27, 27 in at least one set of components installed at either of the axial ends of the chamber 14 and of the piston 15.

(47) A first component 26, 26 is installed at one of the axial ends of the piston 15 and a second component 27 is installed at the axial end of the chamber 14 facing the axial end of the piston 15 having the first component 26, 26. The detector means 25, 25 preferably comprise two sets of components in which the components 26, 26 and 27, 27 are placed respectively at each of the axial ends of the piston 15 and at each of the axial ends of the chamber 14.

(48) As shown in FIG. 4, an excessive stroke in translation of the piston 15 compared with a predefined acceptable stroke for the piston 15 causes a warning signal 28 to be generated as a result of co-operation between the components 26, 26 and 27, 27 of one of the sets of components.

(49) Such a warning signal 28 is transmitted to signaling means 29 that operate an indicator light, for example, informing the pilot of the rotorcraft that there is a potential malfunction of the hydraulic installation.

(50) More particularly, an excessive stroke of the piston 15 is indicative of potential malfunction of at least one of the hydraulic members of the hydraulic installation. An excessive stroke of the piston 15 reveals that there is an excessive pressure difference between the fluids admitted into the end chambers 5, 5 and into the head chambers 6, 6 of each of the actuator cylinders C1, C2.

(51) As shown in FIG. 1, it should be understood that the first ducts 16, 16 of the pressure-balance valves V1, V2 are preferably in fluid flow communication with the fluid sources S1, S2 upstream from the hydraulic directional-control valves D1, D2 and that the second ducts 17, 17 of the pressure-balance valves V1, V2 are in fluid flow communication respectively with the end chambers 5, 5 or the head chambers 6, 6 of one or the other of the actuator cylinders C1, C2.

(52) Under such conditions, the detector means 25, 25 fitted to the pressure-balance valves V1, V2 are suitable for indicting a malfunction of any one at least of the hydraulic members of the hydraulic installation, having the effect of generating a pressure difference between the fluids F1 and F2 as admitted respectively into the head chambers 6, 6 and/or into the end chambers 5, 5 of each of the actuator cylinders C1, C2.

(53) In the embodiment shown in FIG. 6, the detector means 25, 25 comprise at least one set of components that co-operate with each other by means of the Hall effect. Each set of components has a first component 26, 26 installed on the piston 15, and a second component 27, 27 installed at the end of the chamber 14 in the manner of the embodiment shown in FIGS. 2 to 5.

(54) The first component 26, 26 and the second component 27, 27 are formed by magnets that co-operate with each other to generate a magnetic field passing through a third component 30, 30 installed on the valve cylinder 13. The third component 30, 30 then generates a voltage from which the warning signal 28 is derived. The intensity of the warning signal 28 may vary depending on the variation in the voltage generated by the third component 30 as a function of the distance between the first component 26, 26 and the second component 27, 27 representative of the axial position of the piston 15.

(55) Such arrangements serve to provide variable information to the pilot about the operating state of the pressure-balance valves V1 and V2 and thus about the hydraulic installation.

(56) Furthermore, in the embodiment shown in FIG. 6, each of the pressure-balance valves V1, V2 has means for controlling the ability of the piston 15 to move axially prior to admitting the fluids F1, F2 into the insides of the pressure-balance valves V1, V2. Such control means 31 are used in particular on exit from the workshop in which a pressure-balance valve V1 is fabricated, or at least prior to the pressure-balance valve V1 being mounted in the hydraulic installation.

(57) Said control means 31 comprise subdividing the piston 15 into two piston segments 32, 33 along its axial extent and interposing an elastically deformable member 34, e.g. arranged as a compression spring, axially between the two piston segments 32 and 33.

(58) These provisions are such that the two piston segments 32 and 33 bear axially against each other via the elastically deformable member 34. In the absence of any admission of fluids F1, F2 into the pressure-balance valve V1, the elastically deformable member 34 pushes the piston segments 32, 33 against the respective axial ends of the chamber 14, thereby having the effect of activating the detector means 25, 25. A warning signal 28 as then generated by the detector means 25, 25 indicates that the piston 15 made up of two piston segments 32 and 33 is suitable for moving axially without major obstacle inside the chamber 14.

(59) Naturally, said elastically deformable member 34 is rated to deliver an axial thrust force that is just sufficient to move the piston segments 32, 33 against friction inside the chamber and in the absence of the pressure-balance valve V1 having the fluids F1, F2 fed thereto. When the pressure-balance valve V1 is fed with the fluids F1, F2, the fluids F1, F2 admitted into the passages 18, 18 urge the piston segments 32, 33 axially towards each other against the opposing forces exerted by the elastically deformable member 34 against the piston segments 32, 33.

(60) It should thus be understood that the elastically deformable member 34 is inoperative when the pressure-balance valve V1 is installed in a chamber installation and is in use, in the sense that the elastically deformable member 34 cannot be the cause of a potential malfunction of the pressure-balance valve V1.

(61) It should also be observed that independently of the pressure-balance valve V1 being fitted with said control means 25, 25, subdividing the piston 15 into two piston segments 32, 33 and the cylinder 13 into two cylinder blocks 44, 44 serves to prevent any cracks propagating from one of the blocks 44, 44 to the other and makes it easier to assemble the component elements of the pressure-balance valve V1 by contributing to making its structure simple.

(62) In the embodiments shown in FIGS. 1 to 7, the shutters 20, 20 fitted to the respective outlets 19, 19 of the first ducts 16, 16 are each in the form of a sphere. For each of the first ducts 16, 16, the shutter 20, 20 is mounted to move towards the inside of the end of the first duct 16, 16 opening out into the chamber 14 between the outlet 19, 19 of the first duct 16, 16 into the chamber 14 and a perforated seat 36, 36 for retaining the shutter 20, 20 and fitted to the first duct 16, 16.

(63) As shown in FIG. 5, and taking a given first duct 16, 16 into consideration, the perforated seat 36, 36 has an opening 37, 37 formed therethrough, for example. The fluid F1, F2 admitted into the inside of the first duct 16, 16 is suitable for flowing through said opening 37, 37 from the first duct 16, 16 towards the chamber 14. The perforated seat 36, 36 forms an abutment for retaining the shutter 20, 20 against escaping into the inside of the first duct 16, 16. Such an escape could potentially be caused under the effect of thrust exerted by the fluid F1, F2 present in the chamber 14 in the event of the fluid F1, F2 being at a pressure that is excessive relative to the fluid F1, F2 admitted into the first duct 16 from the corresponding fluid source S1, S2.

(64) Such a situation might arise in the context of proper operation of the hydraulic installation. Nevertheless, under such circumstances, the operation of the pressure-balance valve V1, V2 is inhibited, which is not desired, even if inhibiting the operation of the pressure-balance valve V1, V2 does not prevent the servo-control 3 from operating correctly.

(65) In order to avoid such a situation of the pressure-balance valve continuing to remain inhibited, pushing the shutter 20, 20 towards the perforated seat 36, 36 serves to cause the shutter 20, 20 to shut the opening 37, 37 in the perforated seat 36, 36, and consequently to prevent fluid being admitted from the first duct 16, 16 into the chamber 14.

(66) When the pressure of the fluid F1, F2 admitted from the second duct 17, 17 towards the passage 18, 18 into which the first duct 16, 16 opens out is lower than the pressure of the fluid F1, F2 admitted to the first duct 16, 16, the shutter 20, 20 is pushed back towards the outlet 19, 19 of the first duct 16, 16 into the chamber 14 by the fluid F1, F2 admitted into the first duct 16, 16 and then flowing through the opening 37, 37 in the perforated seat 36, 36.

(67) Returning to FIGS. 2 to 7, the pressure-balance valve V1 is also fitted with a warning device 38 for warning of a possible malfunction of the pressure-balance valve V1 as a result of excessive wear of its sealing means 22, 22. More particularly, the bleed duct 23 opens out to the surrounding atmosphere into a storage volume 39 that collects the lost fluid 24 picked up by the bleed duct 23.

(68) The storage volume 39 includes means 40 for evaluating the quantity of lost fluid 24 that has been collected, e.g. formed by a window forming part of the storage volume 39. Such a window can then be used to enable an operator performing a maintenance operation to verify the operating state of the pressure-balance valve V1, and more particularly the wear state of the sealing means 22, 22.

(69) In FIG. 7, the pressure-balance valve is preferably provided with hydraulic means for damping the movement of the piston 15 inside the chamber 14.

(70) For this purpose, blind sockets 41, 41 are formed in the end wall at each of the axial ends of the chamber 14. Each of the sockets 41, 41 opens out at a respective end of the chamber 14. More particularly, the sockets 41, 41 open out into the fluid passages 18, 18 from which the sockets 41, 41 are fed with fluid.

(71) The sockets 41, 41 co-operate with respective axial extensions 42, 42 of the piston 15, said extensions 42, 42 projecting axially from the respective ends of the piston 15 facing the sockets 41, 41. More particularly, in the preferred situation where the piston 15 is subdivided into two respective piston segments 32, 33 as shown, the extensions 42, 42 are arranged respectively at the ends of the piston segments 32, 33 facing the sockets 41, 41 with which the extensions 42, 42 co-operate respectively.

(72) In a given direction of axial movement of the piston 15 inside the chamber 14, as shown by way of example in FIG. 7, one of the extensions 42 travels inside the socket 41 with which the extension 42 co-operates. The insertion of the extension 42 into the inside of the socket 41 is braked by the fluid present in the socket 41 opposing counterthrust against the extension 42 moving inside the socket 41, and consequently opposing counterthrust against the movement of the piston 15.

(73) As the piston 15 continues to move, the fluid present in the socket 41 is expelled progressively into the chamber 14, and more particularly into the passage 18 between the first duct 16 and the second duct 17, and consequently as the extension 42 penetrates progressively into the socket 41.

(74) For this purpose, discharge channels are provided to enable the fluid to be discharged from the sockets 41 into the chamber 14. In the preferred example as shown and contributing to simplifying the structure of the pressure-balance valve, the channels for discharging fluid out from the socket are advantageously formed by dimensional clearance J arranged between the extension 42 and the respective socket 41 co-operating therewith.

(75) Furthermore, in the embodiment shown in FIG. 7, the first components 26, 26 of said detector means 25 may be installed respectively on the extensions 42, 42, and the second components 27, 27 of said detector means 25 may be installed respectively on the walls defining the sockets 41, 41.

(76) The invention is naturally not limited to the embodiments described, but covers any technically feasible combination of their characteristics.