EP0105783B1 - Coaxial multiple chamber hydraulic actuator and system provided with synchronised actuators of this type - Google Patents

Description

The invention relates to hydraulic cylinders comprising more than two chambers. Cylinders of this type include, for example, two cylinders, one of which, which can be called "working cylinder" encloses a piston intended to apply a displacement force to a mobile structure, and the other of which, may be called "pilot cylinder" encloses a piston mechanically or hydraulically linked to the piston of the working cylinder and is in particular used in a hydraulic circuit comprising the pilot cylinder of at least one other cylinder to impose synchronous strokes on all the pistons of the cylinders of job. Synchronization is indeed necessary in all sets of mobile structural elements whose mutual connections have little or no rigidity, and hydraulic synchronization of the control cylinders makes it possible to avoid the complications of a mechanical synchronization system.

• - un "cylindre de travail" dans lequel peut coulisser un premier piston sur lequel est fixée une tige cylindrique reliée à la structure mobile commandée,
• - un "cylindre pilote" formé à l'intérieur de ladite tige et contenant un second piston fixé entre deux conduits rigides dont l'un traverse une première chambre du "cylindre pilote" le premier piston et une première chambre du "cylindre de travail" et l'autre traverse la seconde chambre du "cylindre pilote" la seconde chambre annulaire du "cylindre de travail" entourant le "cylindre pilote" qui se déplace dans cette chambre en même temps que le premier piston séparant les deux chambres du "cylindre de travail".

Already known, in particular from FR-A-2433 661, such systems of hydraulic cylinders which are used to actuate thrust reversers of turbojets. In order to give such systems a minimum bulk and maximum rigidity, each cylinder is double cylinder and is of the type comprising:

• - a "working cylinder" in which a first piston can slide on which is fixed a cylindrical rod connected to the controlled mobile structure,
• - A "pilot cylinder" formed inside said rod and containing a second piston fixed between two rigid conduits, one of which crosses a first chamber of the "pilot cylinder", the first piston and a first chamber of the "working cylinder" and the other crosses the second chamber of the "pilot cylinder" the second annular chamber of the "working cylinder" surrounding the "pilot cylinder" which moves in this chamber at the same time as the first piston separating the two chambers of the "cylinder of"job".

In addition, each chamber of the "pilot cylinder" communicates through a passage in the second piston with the conduit fixed on its opposite face. According to these provisions, the differential thrust applied to the second piston under the effect of the hydraulic pressures which prevail respectively in the two chambers which this second piston separates is transmitted to the first piston linked to the rod of the jack.

We will see later, in the course of this description, why this embodiment of the prior art has drawbacks, namely the fragility of certain organs, a large longitudinal bulk and the necessary complication of the connections to be established between the rod of the jack. and the structure to move.

• - le corps du cylindre comporte intérieurement une paroi fixe cylindrique mitoyenne entre une enceinte cylindrique centrale et une enceinte annulaire,
• - un piston central est mobile dans l'enceinte centrale,
• - un piston annulaire coulisse dans l'enceinte annulaire et la sépare en deux chambres annulaires,
• - les pistons sont tous deux liés rigidement à une tige du vérin, liée elle-même à l'organe commandé,
• - le piston central sépare l'enceinte centrale en deux chambres cylindriques et la paroi mitoyenne est traversée par au moins un orifice qui fait communiquer la chambre cylindrique et la chambre annulaire, toutes deux situées du côté de la tige.

In addition, US-A-2,511,883 describes a double cylinder cylinder comprising a main working cylinder and an auxiliary cylinder of overdrive speed in which:

• the cylinder body internally comprises a fixed cylindrical wall adjoining between a central cylindrical enclosure and an annular enclosure,
• - a central piston is movable in the central enclosure,
• - an annular piston slides in the annular enclosure and separates it into two annular chambers,
• the pistons are both rigidly linked to a rod of the jack, itself linked to the controlled member,
• - The central piston separates the central enclosure into two cylindrical chambers and the dividing wall is crossed by at least one orifice which communicates the cylindrical chamber and the annular chamber, both located on the side of the rod.

We thus retain the teaching of two pistons located in the same plane.

However, such a jack which can be used when several different operating speeds are sought is unsuitable when it comes to obtaining improved synchronization of several jacks.

The object is to obtain a cylinder free of the drawbacks noted above and which also has the advantage of requiring only three liquid circulation pipes to control said cylinder, instead of four in the realization of the aforementioned prior art, which makes it possible to implement, in a system of synchronized jacks, a set of pipes with a smaller footprint and a simpler assembly.

A hydraulic cylinder according to the invention is characterized in that the section of the annular chamber situated on the fixed side opposite the rod is equal to the sum of the sections of the two chambers situated on the side of the rod, that said chambers situated on the side of the rod communicate with each other through said orifice whatever the position of the pistons and that each of the two annular chambers and the cylindrical chamber situated on the fixed side are provided respectively with a connection boss.

• - la tige est double et comporte une tige cylindrique liée au piston cylindrique et une tige de section annulaire entourant à distance la paroi mitoyenne et ladite tige cylindrique et liée au piston annulaire,
• - ces deux tiges émergent toutes deux du fond de vérin côté tige par des traversées étanches et sont liées par un fond étanche qui délimite avec ledit fond de vérin et avec la tige annulaire une cinquième chambre qui communique par un canal ménagé dans la longueur de la tige cylindrique et dans le piston cylindrique avec la chambre cylindrique située du côté dudit piston opposé à la tige cylindrique et
• - la tige de section annulaire est en outre traversée à proximité du piston annulaire par au moins un orifice qui met en communication les deux portions annulaires de chambre que ladite tige sépare dans la chambre de section annulaire qu'elle traverse.

Advantageously, with a view to increasing the thrust of the jack:

• the rod is double and comprises a cylindrical rod linked to the cylindrical piston and a rod of annular section surrounding at a distance the party wall and said cylindrical rod and linked to the annular piston,
• these two rods both emerge from the cylinder end of the cylinder on the rod side by watertight crossings and are linked by a watertight base which delimits with said cylinder base and with the annular rod a fifth chamber which communicates by a channel arranged in the length of the cylindrical rod and in the cylindrical piston with the cylindrical chamber situated on the side of said piston opposite to the cylindrical rod and
• - The rod of annular section is further crossed near the annular piston by at least one orifice which puts in communication the two annular chamber portions that said rod separates in the annular section chamber which it crosses.

Another object of the invention is a system of synchronized jacks which is essentially characterized in that it comprises at least two jacks according to the invention and means for bringing the annular section chamber of one of said jacks into communication. located on the side of the annular rod with respect to the annular piston with the annular section chamber of the other cylinder situated on the side opposite to the annular rod with respect to the annular piston.

• - la figure 1 est un schéma rappelant l'organisation générale d'un système de vérins synchronisés à double cylindre,
• - la figure 2 est un schéma de constitution d'un vérin à deux cylindres co-axiaux du genre connu par le FR-A-2 433 661 précitée,
• - la figure 3 est une section axiale d'un exemple de réalisation d'un vérin à deux cylindres co-axiaux conforme à l'invention,
• - la figure 4 est un schéma de constitutuion du même vérin,
• - la figure 5 est un schéma de l'organisation générale d'un système de vérins synchronisés à simple effet, conforme à l'invention,
• - la figure 6 est un schéma similaire à celui de la figure 5 dans lequel les vérins sont utilisés comme vérins à double effet et
• - la figure 7 est une demi-coupe longitudinalé d'une partie du piston annulaire d'un vérin conforme à l'invention, ce piston étant muni, conformément à l'invention, d'un dispositif de sécurité de fin de course.

The provisions of the invention and the advantages which result therefrom will be better understood on reading the descriptions of exemplary embodiments which follow and which refer to the appended drawings in which:

• FIG. 1 is a diagram recalling the general organization of a system of synchronized double-cylinder jacks,
• FIG. 2 is a diagram of the construction of a jack with two co-axial cylinders of the type known from the aforementioned FR-A-2 433 661,
• FIG. 3 is an axial section of an exemplary embodiment of a jack with two co-axial cylinders according to the invention,
• - Figure 4 is a diagram of constitutuion of the same cylinder,
• FIG. 5 is a diagram of the general organization of a system of synchronized single-acting cylinders, according to the invention,
• FIG. 6 is a diagram similar to that of FIG. 5 in which the jacks are used as double-acting jacks and
• - Figure 7 is a longitudinal half-section of a portion of the annular piston of a cylinder according to the invention, this piston being provided, in accordance with the invention, a safety device for end of travel.

The arrows carried by the pipes indicate the direction of circulation of the liquid requiring the extension of the jack or jacks represented.

• - dans un cylindre 10, un piston 11 lié par une tige 12 à la structure ST à mouvoir et divisant la capacité dudit cylindre en deux chambres, à savoir une chambre B située du côté de la face dudit piston liée à ladite tige et munie d'un raccord d'adduction b et une chambre A située du côté de la face opposée et munie d'un raccord d'adduction a;
• - dans un cyclindre 15, un piston 16 lié par une tige 17 et par une traverse 18 à la tige 12 et divisant la capacité dudit cylindre en deux chambres, à savoir une chambre D située du côté de la face dudit piston liée à ladite traverse et munie d'un raccord d'adduction d et une chambre C située du côté de la face opposée et munie d'un raccord d'adduction c; le côté du cylindre opposé à la sortie de la tige 17 est traversé par une contretige 17' du même diamètre.

Figure 1 therefore shows a plurality of double cylinder cylinders, namely, in the example considered, three identical cylinders VI, V2 and V3. Each of them includes:

• - In a cylinder 10, a piston 11 linked by a rod 12 to the structure ST to move and dividing the capacity of said cylinder into two chambers, namely a chamber B located on the side of the face of said piston linked to said rod and provided with 'a supply connection b and a chamber A located on the side of the opposite face and provided with a supply connection a;
• - In a cylinder 15, a piston 16 linked by a rod 17 and by a cross member 18 to the rod 12 and dividing the capacity of said cylinder into two chambers, namely a chamber D located on the side of the face of said piston linked to said cross member and provided with a supply connection d and a chamber C situated on the side of the opposite face and provided with a supply connection c; the side of the cylinder opposite the outlet of the rod 17 is crossed by a counter-rod 17 'of the same diameter.

The cylinder 10 and the cylinder 15 of each jack are rigidly linked to each other and to a common frame, which has been symbolized by hatching. All the connections a are connected in parallel by pipes R to one of the supply ports of a hydraulic control unit U, while all the connections b are connected in parallel by pipes S to the other port d 'adduction of said unit. The cylinders VI, V2 and V3 therefore operate as double-acting cylinders. From the direction of the arrows carried by the pipes, it can be seen that the case envisaged in the figure is that where the pipes R discharge the liquid into the chambers A while the pistons 11 push the liquid from the chambers B into the pipes S.

As for the connection d of each cylinder, it is connected by a pipe T to the connection c of the cylinder, the index of which follows, observing the rules of circular permutation.

• - le raccord d de VI est connecté au raccord c de V2,
• - le raccord d de V2 est connecté au raccord c de V3 et
• - le raccord d de V3 est connecté au raccord c de VI.

For example, in the case of the three cylinders considered:

• - connection d of VI is connected to connection c of V2,
• - connection d of V2 is connected to connection c of V3 and
• - connection d of V3 is connected to connection c of VI.

Due to the incompressibility of the liquid in chambers C and D, it follows that the pistons 16 impose on each other the same position in their cylinders 15 and that each of them imposes this position on the corresponding piston 11 in its cylinder 10. The cylinders 10 can be called "working cylinders" because each of them exerts, by means of its piston 11, a differential thrust, positive or negative, resulting from the pressures admitted into chambers A and B respectively. cylinders 15 can be called "pilot cylinders" because the differential thrust that each exerts on the rod 12 of the corresponding cylinder 10 constitutes a term of thrust correction which is added algebraically to the thrust exerted by the piston 11 to obtain an identical elongation of all cylinders. All the points of the structure ST linked to the rods 12 therefore undergo an identical translation.

• - l'encombrement latéral et longitudinal de chaque vérin double,
• - la complication de l'usinage et du montage,
• - le manque de rigidité des liaisons entre les deux tiges de pistons d'un même vérin,
• - etc...

If its operating principle is flawless, the embodiment of Figure 1 has significant drawbacks, namely:

• - the lateral and longitudinal dimensions of each double cylinder,
• - the complication of machining and assembly,
• - the lack of rigidity of the connections between the two piston rods of the same cylinder,
• - etc ...

The double jack proposed by the aforementioned patent application, illustrated by FIG. 2, does not have these drawbacks, because the cylinders are co-axial. The chambers and fittings which perform the same functions as in the double jacks in FIG. 1 are designated by the same letters as in this one.

The working cylinder 20, which carries the connector a (communicating with the chamber A) and the connector b (communicating with the chamber B) houses the piston 21. The latter carries a rod 22 in the form of a bell which emerges from the bottom of the cylinder 20 by a sealed crossing and which plays both the role of rod transmitting the force of the jack and the role of pilot cylinder. In fact, a piston 23, around which the bell 22 slides, is supported, on the side of the bottom 24 of the cylinder 20 opposite the bell, by a hollow shaft 25 carrying the connection c and tightly connected to said bottom 24 and, from the side of the bell, by a hollow shaft 26 which carries the connector d and which passes through the bell by a sealed passage.

The pilot cylinder constituted by the bell 22 is therefore mobile relative to the working cylinder 20 while the piston 23, housed in this pilot cylinder, is mobile relative to the latter but fixed relative to the working cylinder 20.

The piston 23 is traversed by orifices c ′ and through which, respectively, the hollow shaft 25 puts the connection c in communication with the chamber C (portion of the bell 22 which surrounds the hollow shaft 26) while the 'hollow shaft 26 puts the connection d in communication with the chamber D (portion of the bell 22 which surrounds the hollow shaft 25). Consequently, as in the examples of double cylinders in FIG. 1, the differential thrust exerted on the piston 21 by the pressures which prevail on the one hand in the chamber A, connected to a pipe R by the connector a and d on the other hand in the chamber B, connected to a pipe S by the fitting b, is corrected by the differential thrust due to the pressures which prevail respectively in the rooms C and D, one of which is connected to a pipe T by the fitting c and the other to another pipe T 'through the fitting d.

• - encombrement longitudinal sensiblement plus grand en tous cas, côté tige de commande que celui des vérins doubles de la figure 1 en raison de la présence de l'arbre creux 26,
• - difficulté de réalisation de l'accrochage de la tige 22 à la structure à mouvoir (non représentée) car, pour centrer les poussées sur l'axe général du vérin, il est nécessaire de prévoir des points d'accrochage multiples (représentés par des oreilles 27) symétriques par rapport à l'arbre 26 et de lier ces points d'accrochage à la structure par des liaisons dont la longueur dépasse celle de l'arbre 26.

Examination of FIG. 2 shows that this embodiment of double cylinders of the prior art has the following drawbacks, which can be very troublesome:

• in longitudinal case, substantially larger in all cases, on the control rod side than that of the double jacks of FIG. 1 due to the presence of the hollow shaft 26,
• - difficulty in achieving the attachment of the rod 22 to the structure to be moved (not shown) because, to center the thrusts on the general axis of the jack, it is necessary to provide multiple attachment points (represented by ears 27) symmetrical with respect to the shaft 26 and to link these attachment points to the structure by links whose length exceeds that of the shaft 26.

We now consider Figure 3 which shows the detailed constitution of a double cylinder cylinder of the invention, in which these drawbacks have disappeared.

The structural elements to which the jack must impart a relative movement are not shown. The bottom 31 on the foot side of the double cylinder 30 is for example fixed to one of these elements by an ear 32. The external rod 64 of the double piston 60 (see below), which emerges from the bottom 33 on the head side of the cylinder, is for example fixed to the other element by an ear 66.

The annular median wall 34 is adjoining the central cavity 51 of the cylinder and the peripheral cavity 52 which is delimited externally by the external wall 35. The latter bears near the bottom 31 a coupling boss 36 and near the bottom 33 a boss 37. These two drilled bosses allow the connection of the cavity 52 with pipes not shown. The bottom 31 carries a drilled boss 38 which allows the connection of the cavity 51 with a third pipe, not shown.

• - d'une part, par le piston central 61 qui coulisse dans la cavité centrale 51 et porte la tige 63 qui émerge du fond 33 par une ouverture centrale 41,
• - d'autre part, par le piston annulaire 62 qui coulisse dans la cavité annulaire 52 et qui porte la tige périphérique 64, en forme de virole, qui émerge du fond 33 par une ouverture annulaire 42.

In the middle wall 34, near the bottom 33, lights 39 allow communication between the two cavities 51 and 52. As for the double piston 60, it consists

• on the one hand, by the central piston 61 which slides in the central cavity 51 and carries the rod 63 which emerges from the bottom 33 through a central opening 41,
• - on the other hand, by the annular piston 62 which slides in the annular cavity 52 and which carries the peripheral rod 64, in the form of a ferrule, which emerges from the bottom 33 by an annular opening 42.

Outside the cylinder, the rods 63 and 64 are linked by a bottom 65 which closes the cavity of the rod 64 to form a sealed bell and which carries the ear 66.

The circumference of the central piston 61, the inner and outer edges of the annular piston 62, the edge of the opening 41 and the outer and inner edges of the opening 42 carry O-rings.

An axial channel 71 is drilled in the central piston 61 and in the central rod 63 and communicates with at least one lumen 72 which opens into the periphery of the rod 63 near the bottom 65. Lights 73 pass through the peripheral rod 64 nearby piston 62.

• - une chambre A délimitée par le fond 31, le piston central 61 et la paroi annulaire médiane 34,
• - une chambre B délimitée par le piston central 61, la tige centrale 63, la paroi médiane 34 et le fond 33
• - une chambre C délimitee par le fond 31, le piston annulaire 62, la paroi médiane 34 et la paroi externe 35,
• - une chambre D délimitée par le piston annulaire 62, le fond 33 et les parois 34 et 35 (les lumières 73 permettant l'équilibrage des pressions de part et d'autre de la paroi mobile constituée par la tige 64) et
• - une chambre E délimitée par le fond de cylindre 33, les tiges 63 et 64 et le fond de tige 65.

The double piston 60 thus cooperates with the cylinder 30 to delimit five chambers, namely:

• a chamber A delimited by the bottom 31, the central piston 61 and the middle annular wall 34,
• a chamber B delimited by the central piston 61, the central rod 63, the central wall 34 and the bottom 33
• a chamber C delimited by the bottom 31, the annular piston 62, the central wall 34 and the external wall 35,
• a chamber D delimited by the annular piston 62, the bottom 33 and the walls 34 and 35 (the ports 73 allowing the pressures to be balanced on either side of the movable wall formed by the rod 64) and
• - A chamber E delimited by the cylinder bottom 33, the rods 63 and 64 and the rod bottom 65.

The chambers A and E which communicate by the channel 71 and by the lights 72, are therefore both in communication with a tube possibly connected to the bore of the central boss 38. The chambers B and D, which communicate through the lights 39, are both in communication with a tube possibly connected to the bore of the boss 37. The chamber C is the only one to communicate with a tube possibly connected to the bore of the boss 36.

• s1: section intérieure délimitée par la paroi externe 35
• s2: section extérieure occupée par la paroi médiane 34
• s3: section extérieure occupée par la tige annulaire 64
• s4: section intérieure délimitée par la paroi médiane 34
• s5: section extérieure de la tige centrale 63 et
• s6: section intérieure délimitée par la tige annulaire 64.

The following cross sections have been represented in FIG. 3, in the form of lines of diametrical dimensions:

• s1: inner section delimited by the outer wall 35
• s2: outer section occupied by the middle wall 34
• s3: outer section occupied by the annular rod 64
• s4: inner section delimited by the middle wall 34
• s5: outer section of the central rod 63 and
• s6: inner section delimited by the annular rod 64.

The values of these sections will be used later to determine the conditions making it possible to ensure correct synchronization of the movements of several cylinders according to the invention in a system of synchronized cylinders.

We now consider FIG. 4 which represents the jack of FIG. 3, in accordance with the invention, in a schematic form analogous to that already used in FIGS. 1 and 2 relating to double cylinder jacks of prior art. There are pistons 61 and 62 which separate, the first, chambers A and B and, the second, Chambers C and D. There is also the additional piston constituted by the bottom 65 which connects the central rod 63 and the annular rod 64. The connections a, c and d respectively allow the connection of pipes with the chamber A (boss 38 of FIG. 3), the chamber C (boss 36) and the chamber D (boss 37).

It should be noted that in the preferred solution and shown, the two pistons are arranged in the same transverse plane in order to avoid the presence of residual volumes at the end of the stroke.

Although designed to constitute, with other identical jacks, a system of synchronized jacks, the jack of the invention can be used as an isolated jack. To use it as a single-acting insulated cylinder, it is sufficient to connect fittings a and c to the same pressure source and to connect fitting d to the open air (if chambers B and D are empty) or to a tarpaulin (if chambers B and D contain liquid). The pressure in chambers A, C and E causes the extension of the jack and the cancellation of this pressure causes retraction under the effect of the reaction of the load applied to the ear 66.

To use the jack of the invention as a double-acting insulated jack, one can, to obtain the extension, switch the pressure source on chambers A and E (connection a) or on chambers A, C and E (connections a and c). The retraction is obtained by switching the pressure source to chambers B and D (connection d).

We now consider Figures 5 and 6 relating to a synchronized cylinder system implementing a number N of cylinders according to the invention. These figures show four jacks, respectively marked V'l, V'2, V'3 and V'4. FIG. 5 illustrates the case where these jacks are used as single-acting jacks and FIG. 6 illustrates the case where they are used as double-acting jacks. The pressure source is represented by a distributor making it possible to switch the connection pipes either on a pressure tank or on a tank to thus constitute a control unit U.

In both use cases, the extension of the cylinders is obtained by injecting the pressurized liquid into the fittings a (chambers A and E) supplied in parallel by pipes R.

For single-acting use, the connection d of each cylinder is connected to the connection c of the cylinder which follows it in the order of the indices and marks, using the rules of circular permutation. More precisely, if we denote by c (J) and d (J) the connections c and d of a jack V "(J), J taking the discrete values from 1 to N, any connection d (J) is connected by means of a pipe T to connection c (J + 1), with the exception of connection d (N) - here, connection d of the jack V'4 - connected to connection c (1) - here, the connection c of the jack V'I - by means of the line T1, the jacks are thus connected to each other in a closed loop and controlling each other.

For double-acting use, as shown in FIG. 6, the pipes T remain and a pipe T2 connects the connection d (N) to the control unit U to allow the circulation of the pump liquid. Connection c (1) is supplied by means of a T3 pipe in parallel with connection a (1). The passage from extension to retraction is obtained by reversing the direction of circulation of the hydraulic fluid by acting on the distributor.

• c'est-à-dire que:

In both cases, in order to obtain synchronous strokes to the rods 60 linked to the structure ST, the active section of the chamber C must be equal to the sum of the active sections of the chambers B and D. In other words, if we refer in FIG. 3, it can be seen that the dimensions of the organs in play must be such that:

• which means:

This condition is easily achievable by assigning adequate values to the inside diameter of the middle wall 34, to the diameter of the central rod 63 and to the outside and inside diameters of the annular rod 64.

It suffices to compare the diagrams of FIGS. 1 or 2, on the one hand, and 5 or 6, on the other hand, to note that, owing to the fact that the jack of the invention has only three connections, the jack systems synchronized that it allows to constitute implement connecting pipes in a smaller number and are of a simpler assembly than the system of actuators of the prior art.

• - encombrement longitudinal plus réduit,
• - raccourcissement des liaisons entre la tige et la structure à mouvoir,
• - suppression d'organes fragiles et peu rigides.

Just compare the diagrams in Figures 2 and 4 to find that, compared with the jack of the aforementioned French patent, the jack of the invention actually has the following advantages, due to the elimination of the hollow shafts 25 and 26:

• - reduced longitudinal dimensions,
• - shortening of the connections between the rod and the structure to be moved,
• - removal of fragile and not very rigid organs.

In such complex cylinders, slight synchronization faults in the cylinder system can result from small leaks at the joints. Of course, these leaks can be compensated for by a known means, such as that shown for example in FIG. 7. The piston 62 of the pilot cylinder of each jack comprises a device automatically balancing the pressures which prevail on both sides at the end of the stroke. other of this piston. This device can consist, for example, of a valve 81 housed in an orifice 80 formed in the piston. This valve is held against its seat by a spring 83 and carries a pusher 82 oriented towards the wall 33 which pushes it back at the end of the stroke. If the jack is intended to operate in double effect, it is advantageous to accommodate in the same piston a second valve identical but whose pusher is oriented towards the wall 31 (Figure 3).

Claims (3)

1. Hydraulic actuator of the type comprising chambers (A B,C D E) more than two in number in which:

- the cylindrical body (35) comprises internally a fixed cylindrical wall (34) intermediate a cylindrical central enclosure (51), and an annuler enclosure (52)

- a central piston (61) is movable within the central enclosure (51),

- an annular piston (62) slides within the annular enclosure (52) and separates it into two annular chambers (C and D)

- the pistons (61, 62) are both rigidly connected to a rod of the actuator (63,64,65), itself connected to the control member,

- the central piston (61) divides the central enclosure into two cylindrical chambers (A and B) and the intermediate wall (34) is traversed by at least one orifice (39) which enables communication between the cylindrical chamber (B) and the annular chamber (D), both being disposed on the side of the rod (63, 64, 65) characterized in that the section of the annular chamber (C) located on the fixed side (31) opposite to the rod (63, 64, 65) is equal to the sum of the sections of the two chambers (B and D) disposed on the side of the rod, that the said chambers (B and D) disposed on the side of the rod intercommunicate through the said orifice (39) whatever the position of the pistons (61, 62), and that each of the two annular chambers (C and D) and the cylindrical chamber (A) located on the fixed side (31) are provided respectively with a connecting boss (38, 36, 37).

2. Hydreulic actuator according to claim 1, characterized in that:

- the rod is in two parts and comprises a cylindrical rod (63) connected to the cylindrical piston (61) and an annular section rod (64) connected to the annular piston (62)

- these two rods extend from the bottom of the actuator (33) on the side of the rod through sealed passages (41,42) and are connected by a fluid-tight base (65) which defines with the said base of the actuator and with the annular rod a fifth chamber (E) which communicates with the cylindrical chamber (A) located on the side of the cylindrical piston opposite to the rod through a duct (71, 72) traversing the said piston and extending along the length of the said cylindrical rod and

- the rod of annular section (64) is traversed adjacent to the annular piston by at least one orifice (73) which places in communication the two annular portions of the chamber which the said rod separates within the annular chamber (D) which it traverses.

3. Synchronised actuator system, characterized in that it comprises et least two actuators (V'1,V'2) according to any one of claims 1 and 2 and means (T) for providing communication between the chamber of annuler section (D) of the said actuators (V'1) disposed on the side of the annular rod (64) with respect to the annular piston with the chamber of annular section (C) of the other actuator (V'2) disposed on the opposite side to the annular rod (64) with respect to the annular piston (62).

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