REAR PART OF A TURBOCHARGER DRIVE WITH ENHANCED A9 / A8 NOZZLE AREA RATIO

Description

TECHNICAL FIELD

[0001] The present invention relates to the field of variable geometry nozzles for turbojets intended for aircraft propulsion. STATE OF THE PRIOR ART

[0002] Turbojets intended for supersonic flight generally include an afterburner channel whose outlet is delimited by an axisymmetric nozzle with variable geometry, i.e. capable of adapting its geometry to the different speeds at which such an aircraft is likely to fly.

[0003] For this purpose, such a nozzle comprises at least one set of movable internal flaps, called convergent flaps, distributed around the longitudinal axis of the turbojet engine and each having an upstream end articulated on an internal structure of the casing, each of the convergent flaps comprising a panel intended to channel the flow of exhaust gas within the nozzle. Such a nozzle further comprises a system for controlling the convergent flaps capable of causing the latter to pivot around their axes of articulation to the casing in a synchronized manner.

[0004] Very often, nozzles intended for supersonic flight further comprise another set of movable internal flaps, called diverging flaps, distributed around the longitudinal axis, each comprising a panel intended to channel the flow of exhaust gas within the nozzle, and having respective upstream ends articulated on downstream ends of the converging flaps, whereby such a nozzle is called a convergent-divergent nozzle.

[0005] In this case, the control system is further configured to control the positions of the diverging flaps to those of the converging flaps. Such a system thus makes it possible to continuously vary the respective inclinations of the converging flaps relative to the longitudinal axis of the turbojet engine, and to match the inclinations of the diverging flaps, relative to this axis, according to a determined unambiguous law. Such a nozzle thus makes it possible in particular to vary the position and shape of the nozzle throat.

[0006] It should be noted that the term "divergent" does not exclude the possibility that the shutters concerned may adopt orientations parallel to the longitudinal axis or even convergent in certain phases of operation.

[0007] Documents EP0833047A2 and EP0814253A1 disclose examples of known variable geometry nozzles.

[0008] An important parameter for the operation of such nozzles is the ratio A9 / A8, in which A8 denotes the nozzle section at the throat formed at the junction between the converging and diverging flaps, while A9 denotes the nozzle section at the downstream end of the diverging flaps.

[0009] The range in which this ratio A9 / A8 varies, for a given nozzle, depends on the configuration of the means implemented to control the positions of the diverging flaps to those of the converging flaps.

[0010] In this context, there is a need for a variable geometry nozzle whose control system for the movable internal flaps is efficient and space-saving in order to allow its integration in a limited space, while making it possible to maximize the range of possible values ​​for the A9 / A8 ratio. STATEMENT OF THE INVENTION

[0011] The invention aims in particular to respond to this need in a simple, economical and effective manner.

[0012] According to claim 1, the invention provides for this purpose a rear part of a turbojet, comprising: an upstream stator structure; a variable geometry convergent-divergent nozzle comprising a set of convergent flaps distributed around a longitudinal axis of the rear part of the turbojet engine, each comprising a panel intended to channel a flow of exhaust gas within the nozzle, and each having an upstream end articulated on the upstream stator structure, and further comprising a set of divergent flaps distributed around the longitudinal axis, each comprising a panel intended to channel the flow of exhaust gas within the nozzle, and each having an upstream end articulated on a downstream end of a corresponding convergent flap; a synchronization ring arranged around the set of convergent flaps or the upstream stator structure; motor means configured to move the synchronization ring in translation along the longitudinal axis, relative to the upstream stator structure;actuating means by which the synchronization ring acts on at least some of the converging flaps, called controlled converging flaps, to control a geometric variation of the nozzle; and means for controlling the positions of the diverging flaps to those of the converging flaps, comprising a first connecting rod having a first end portion articulated to the corresponding converging flap and a second opposite end portion, a second connecting rod having a first end portion articulated to the corresponding diverging flap and a second opposite end portion, and a third connecting rod having a first end portion articulated to the synchronization ring and a second opposite end portion; ; wherein the second end portion of the first connecting rod is hinged to at least one of the second end portion of the second connecting rod and the second end portion of the third connecting rod, and the second end portion of the third connecting rod is hinged to the second end portion of the second connecting rod.

[0013] As a result, the means used to control the shutters can have a limited size and mass at best, while allowing a wide range of values ​​for the A9 / A8 ratio.

[0014] In preferred embodiments of the invention, the second end portion of the first connecting rod is jointly articulated to the second end portion of the second connecting rod and to the second end portion of the third connecting rod, about a common articulation axis.

[0015] In other preferred embodiments of the invention, the second end portion of the third connecting rod is hinged to the second end portion of the second connecting rod about a fifth hinge axis, and the second end portion of the first connecting rod is hinged to the second end portion of the second connecting rod about a sixth hinge axis located between the fifth hinge axis and the first end portion of the second connecting rod.

[0016] Preferably, a ratio A9 / A8, equal to the quotient of a section A9 of the nozzle at a downstream end of the diverging flaps by a section A8 of the nozzle at a neck formed at a junction between the converging flaps and the diverging flaps, varies in a range of greater than 0.35.

[0017] The invention also relates to a turbojet engine for an aircraft, comprising a rear part of the type described above. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The invention will be better understood, and other details, advantages and characteristics thereof will appear on reading the following description given by way of non-limiting example and with reference to the appended drawings in which: there figure 1 is a schematic half-view in axial section of a turbojet engine comprising a variable geometry nozzle; the figure 2 is a schematic half-view in axial section of a rear part of a turbojet engine of a known type; the figure 3 is a schematic half-view in axial section of a rear part of the turbojet of the figure 1 , according to an embodiment of the invention, in a configuration of low convergence of the converging flaps; the figure 4 is a schematic half-view in axial section of the rear part of the turbojet of the figure 1 , in a configuration of strong convergence of the converging flaps; the Figure 5is a schematic perspective view of certain elements making up the rear part of the turbojet engine of the figure 1 , intended for controlling the converging shutters; the figures 6 And 7 are larger-scale schematic perspective views of some of the elements visible on the Figure 5 . there figure 8 is a partial schematic perspective view of a rear part of a turbojet according to an alternative embodiment, illustrating elements intended for controlling the divergent flaps of the nozzle.

[0019] Throughout these figures, like references may designate identical or similar elements. DETAILED DISCLOSURE OF PREFERRED EMBODIMENTS

[0020] There figure 1illustrates a turbojet 10, for example a twin-spool, twin-flow turbojet, intended for the propulsion of an aircraft capable of supersonic flight, and therefore intended in particular to be installed in the fuselage of such an aircraft. The invention is of course applicable to other types of turbojets.

[0021] Throughout this description, the axial direction X is the direction of the longitudinal axis 11 of the turbojet engine. Unless otherwise stated, the radial direction R is at all points a direction orthogonal to the longitudinal axis 11 and passing through the latter, and the circumferential direction C is at all points a direction orthogonal to the radial direction R and to the longitudinal axis 11. Unless otherwise stated, the terms “internal” and “external” refer respectively to a relative proximity, and a relative distance, of an element relative to the longitudinal axis 11. Finally, the qualifiers “upstream” and “downstream” are defined by reference to a general direction D of the flow of gases in the turbojet engine 10.

[0022] By way of illustration, such a turbojet engine 10 comprises, from upstream to downstream, an air inlet 12, a low-pressure compressor 14, a high-pressure compressor 16, a combustion chamber 18, a high-pressure turbine 20, a low-pressure turbine 22, an afterburner duct 26, and a nozzle 28 with variable geometry, for example of the convergent-divergent type. These components of the turbojet engine are all centered along the longitudinal axis 11 of the turbojet engine.

[0023] In a well-known manner, the high-pressure compressor 16, the combustion chamber 18, and the high-pressure 20 and low-pressure 22 turbines define a primary flow path PF. The latter is surrounded by a secondary flow path SF of the turbomachine which extends from upstream to downstream from an outlet of the low-pressure compressor. Thus, in operation, air F1 which has entered through the air inlet 12 and which has been compressed by the low-pressure compressor 14, then divides into a primary flow F2 which circulates in the primary flow path and a secondary flow F3 which circulates in the secondary flow path. The primary flow F2 is then further compressed in the high-pressure compressor 16, then mixed with fuel and ignited in the combustion chamber 18, before undergoing expansion in the high-pressure turbine 20 and then in the low-pressure turbine 22.

[0024] The exhaust gas flow F4, consisting of the mixture of combustion gases from the primary stream and the secondary flow F3, then circulates in the post-combustion channel 26, then escapes from the turbojet 10 through the nozzle 28.

[0025] In afterburner operation, for example to propel an aircraft to supersonic speeds, fuel is mixed with the exhaust gas flow F4 within the afterburner channel 26, and the mixture thus formed is ignited within this afterburner channel, in order to generate additional thrust.

[0026] There figure 2 illustrates on a larger scale a rear part of a turbojet engine in a configuration known from the prior art, and in particular allows the movable internal flaps of the nozzle to be seen.

[0027] The movable internal flaps consist, upstream, of a set of converging flaps 30 distributed around the longitudinal axis 11, and, downstream, of a set of diverging flaps 32 also distributed around the longitudinal axis 11.

[0028] These movable internal flaps each comprise a panel 31, 33 contributing to externally delimiting an exhaust gas circulation channel 34 defined in the extension of the post-combustion channel 26. The movable internal flaps 30, 32 thus make it possible to channel the flow of exhaust gas F4 at the outlet of the turbojet engine 10, in operation.

[0029] The converging flaps 30 are articulated at their upstream ends 36 on a stator structure 38 of the rear part of the turbojet, in this case on internal yokes 40 of beams 42 belonging to said stator structure, so that the converging flaps 30 are movable in rotation around first articulation axes A1 subject to the stator structure 38.

[0030] The diverging flaps 32 are articulated, at their upstream ends 44, on downstream ends 46 of the converging flaps 30, so that the diverging flaps 32 are movable in rotation around second articulation axes A2 subject to the converging flaps 30 and generally parallel to the first axes A1. The diverging flaps 32 are further articulated, at their downstream ends 48, on first ends 50A of connecting rods 50 having opposite second ends 50B articulated on the stator structure 38, in this case on external yokes 54 of the beams 42.

[0031] A system for controlling movable internal flaps comprises motor means configured to act on at least some of the converging flaps, which will be referred to as controlled converging flaps in the following. In the case where other converging flaps are only subject to the action of the motor means via the controlled converging flaps, these other converging flaps are referred to as follower converging flaps, in a well-known manner.

[0032] The motor means are typically constituted by jacks 56 each having a static part, for example their body 56A, fixed to the stator structure 38, and a movable part, for example their rod 56B, secured to a corresponding roller holder 58, on which is mounted a roller 60 bearing rollingly on a cam 62 formed by a structure 64 secured to the panel 31 of a corresponding convergent flap 30, the roller holder 58 being further secured to a retaining finger 66 cooperating with the structure 64 to radially retain the convergent flap 30 and in particular prevent the flap from lowering under the effect of gravity when the turbojet is stopped. The assembly of the movable internal flaps 30 and 32 thus forms, with the stator structure 38, an isostatic system.

[0033] A translational movement of the movable part of each cylinder 56 thus makes it possible to cause a movement of the converging flaps 30 in rotation around the first articulation axes A1, which is accompanied by a movement of the diverging flaps 32 in rotation around the second articulation axes A2, during which the travel of the diverging flaps is determined by the connecting rods 50. Such movements of the movable internal flaps 30, 32 lead to modifying the profile of the nozzle and in particular the section of the neck thereof at the junction between the converging flaps and the diverging flaps.

[0034] The nozzle further comprises movable external flaps 70 having upstream ends 72 articulated on the stator structure 38, for example on the external yokes 54 of the beams 42, and downstream ends 74 secured to the downstream ends 48 of the diverging flaps 32, for example by means of roller 76 and slide 78 connecting devices.

[0035] The variable geometry configuration of the nozzle 28 makes it possible to adapt the latter to the different phases of flight. Thus, in subsonic mode, the converging internal flaps are for example maintained in a weakly convergent configuration, while in supersonic mode, the converging internal flaps adopt a more convergent configuration.

[0036] An important parameter for the operation of such a nozzle is the ratio A9 / A8, in which A8 designates the section of the nozzle at the neck 79A formed at the junction between the converging flaps 30 and the diverging flaps 32, while A9 designates the section of the nozzle at the downstream end 79B of the diverging flaps 32. Such a ratio A9 / A8 generally has a value between 1.1 and 1.8.

[0037] The range of values ​​in which the ratio A9 / A8 varies, for a given nozzle, depends on the configuration of the means implemented to control the positions of the diverging flaps 32 to those of the converging flaps 30. In the example described above, this range is thus determined by the characteristics of the connecting rods 50 and by the method of connection of the latter to the diverging flaps 32 and to the stator structure 38, and typically has a range of 0.15.

[0038] The rear part of the turbojet engine of the figure 1 , according to an embodiment of the invention, which will now be described in more detail with reference to figures 3 to 7 , aims to obtain a wider range of values ​​for the A9 / A8 ratio.

[0039] For illustration purposes, a preferred control mode for converging flaps will first be described in the following.

[0040] According to this preferred embodiment, the controlled converging flaps 30 each comprise a lever 80 secured to the panel 31 of the flap. Such a lever 80 of course extends in a direction away from the longitudinal axis 11, from the panel 31 or, in the example illustrated, from a stiffening structure 81 arranged on the external face of the panel 31 and secured to the latter.

[0041] In a manner similar to that described above, the rear part of the turbojet engine comprises motor means comprising a movable part which can be moved axially on command relative to the upstream stator structure 38. By way of illustration, the motor means are, here again, made up of cylinders 56, and all of the rods 56B of the cylinders constitute said movable part.

[0042] In order to allow the movable part of the motor means to act on the lever 80 of at least one of the controlled converging flaps 30, said lever 80 is arranged axially between an upstream support wall 90 and a downstream support wall 92, which are rigidly secured to the movable part of the motor means, so that the lever 80 is free to move relative to the upstream 90 and downstream 92 support walls at least in the radial direction R relative to the longitudinal axis 11.

[0043] In this way, during a downstream movement of the mobile part of the motor means (consisting of the rods 56B), the upstream support wall 90 pushes the lever 80 downstream and thus causes a pivoting of the convergent flap 30 along the corresponding first articulation axis A1, leading to the downstream end 46 of the flap being brought closer to the longitudinal axis 11.

[0044] Conversely, during an upstream movement of the movable part of the engine means, at least if the turbojet engine is stopped, the downstream support wall 92 pushes the lever 80 upstream and thus causes the convergent flap 30 to pivot about the corresponding first articulation axis A1, leading to the downstream end 46 of the flap being moved away from the longitudinal axis 11. If the turbojet engine is in operation, it is possible that the thrust of the gases on the convergent flap 30 is sufficient to cause the latter to pivot even before the downstream support wall 92 comes into contact with the lever 80. As a result, it is advantageously provided that the upstream support wall 90 has increased rigidity compared to the downstream support wall 92.For this purpose, the upstream support wall 90 may be thicker than the downstream support wall 92, or the upstream support wall 90 may have stiffening ribs; the downstream support wall 92 may be devoid of such stiffening ribs.

[0045] The lever 80 is provided with a support roller 96 of cylindrical shape of revolution, mounted freely in rotation on the lever 80 along an axis 94 parallel to the corresponding first articulation axis A1, arranged between the upstream 90 and downstream 92 support walls, so that any contact of any one of the upstream 90 and downstream 92 support walls on the lever 80 is a cylinder / plane contact.

[0046] Thus, during a pivoting maneuver of the convergent flap under the effect of a thrust force applied to the support roller 96 by one of the upstream 90 and downstream 92 support walls, the radial displacement of the support roller 96 relative to the support wall concerned is carried out by means of rolling of the support roller 96 on said support wall.

[0047] The axial spacing between the upstream 90 and downstream 92 support walls is greater than the diameter of the support roller 96, so that an axial clearance permanently exists between the support roller 96 and the support wall opposite the support wall exerting the thrust on the support roller 96.

[0048] The support roller 96 is advantageously arranged at a free end of the lever 80, so as to maximize the lever arm exerted by the upstream 90 and downstream 92 support walls on the converging flap 30 concerned.

[0049] Thus, the support roller 96 is for example mounted on an axis carried by two lateral arms 80A, 80B forming a terminal fork of the lever 80 ( Figure 5 ).

[0050] Furthermore, one of the support walls, in this case the downstream support wall 92, is connected to the mobile part of the motor means via the other of the support walls, in this case the upstream support wall 90.

[0051] For this purpose, an external connecting wall 98 connects to each other respective radially external ends of the upstream 90 and downstream 92 support walls.

[0052] The above description, concerning the operation of the lever of one of the controlled converging flaps, is preferably also valid for the other controlled converging flaps.

[0053] Thus, in the illustrated embodiment, the upstream support wall 90 arranged opposite each lever 80 is circumferentially spaced from the upstream support walls 90 arranged opposite the two levers 80 closest to the lever in question, and the downstream support wall 92 arranged opposite each lever 80 is circumferentially spaced from the downstream support walls 92 arranged opposite the two levers 80 closest to the lever in question ( Figure 5 ). The upstream 90 and downstream 92 support walls thus form an annular row of support devices 100 spaced apart from each other, each support device 100 comprising a corresponding pair of support walls comprising one of the upstream support walls 90 and one of the downstream support walls 92.

[0054] The rear part of the turbojet engine further comprises a synchronization ring 82 arranged around the set of converging flaps 30 or, as a variant, arranged a little further upstream around the upstream stator structure 38, and by which each of the support devices 100 is connected to the mobile part of the motor means, that is to say to the set of rods 56B of the cylinders 56.

[0055] In particular, the movable part of the motor means is connected to the synchronization ring 82 so as to be able to move the latter in translation along the longitudinal axis 11. For this purpose, the rods 56B of the jacks 56 are articulated to first yokes 84 of the synchronization ring 82. Such first yokes 84 are formed projecting from a main body 86, for example toroidal in shape, of the synchronization ring 82. The first yokes 84 extend for example upstream from the main body 86.

[0056] It should be noted that the main body 86 of the synchronization ring may have a more complex shape, comprising for example an alternation of parts projecting radially inward and parts projecting radially outward and / or an alternation of parts projecting upstream and parts projecting downstream. In all cases, the main body 86 of the synchronization ring extends all around the longitudinal axis 11 of the turbojet and thus has a generally annular shape.

[0057] Each of the support devices 100 is connected to the synchronization ring 82, for example by means of three arms 102 spaced circumferentially from each other and each connecting the synchronization ring 82 to the downstream support wall 92.

[0058] The support devices constitute an example of actuating means by which the synchronization ring 82 acts on the controlled converging flaps 30, to control a geometric variation of the nozzle.

[0059] In the illustrated example, within each support device 100, one of which is visible on the figure 6 , a first connecting side wall 104 connects together respective first circumferential ends of the upstream 90 and downstream 92 support walls, and a second connecting side wall 106 connects together respective second circumferential ends of the upstream 90 and downstream 92 support walls, opposite the first circumferential ends. The first and second connecting side walls 104, 106 thus make it possible to connect the upstream support wall 90 to the downstream support wall 92 and therefore to the synchronization ring 82, and via the latter, to the mobile part of the motor means.

[0060] In operation, a deployment of the rod 56B of each cylinder 56, or more generally a deployment downstream of the mobile part of the motor means, causes a downstream movement of the synchronization ring 82, which drives each upstream 90 and downstream 92 support wall downstream. Each upstream support wall 90 is thus brought into contact with the support roller 96 of the corresponding lever 80. Each upstream support wall 90 then pushes the support roller 96, and therefore the lever 80, downstream, and causes the corresponding flap to pivot in the direction of the longitudinal axis 11, which increases the convergence of the converging flaps 30. The support roller 96 rolls on the upstream support wall 90 during the pivoting of the flap, such rolling being permitted due to the clearance existing between the roller 96 and the other support wall, in this case the downstream support wall 92.

[0061] Conversely, a retraction of the rod 56B of each cylinder 56, or more generally a retraction upstream of the mobile part of the motor means, causes an upstream movement of the synchronization ring 82, which drives each upstream 90 and downstream 92 support wall upstream. If the turbojet is stopped, each downstream support wall 92 is thus brought into contact with the support roller 96 of the corresponding lever 80. Each downstream support wall 92 then pushes the support roller 96, and therefore the lever 80, upstream, and causes the corresponding flap to pivot in the direction opposite to the longitudinal axis 11, which reduces the convergence of the converging flaps 30. The support roller 96 rolls on the downstream support wall 92 during the pivoting of the flap, such rolling being again permitted due to the clearance existing between the roller 96 and the other support wall, in this case the upstream support wall 90.On the other hand, if the turbojet is in operation, it is possible that the thrust of the gases on the convergent flap 30 is sufficient to cause the latter to pivot even before the downstream support wall 92 comes into contact with the lever 80.

[0062] The cylinders 56 thus work in the direction of deployment of their rod 56B during a maneuver to increase the convergence of the converging flaps, which is advantageous from a mechanical point of view. Indeed, at least in the preferred case in which the cylinders 56 are hydraulic cylinders, the deployment of the rod of such a cylinder results from hydraulic pressure exerted on the entire surface of the piston of the cylinder, while the retraction of the rod results from hydraulic pressure exerted on the surface of the piston reduced by the section of the rod. For this reason at least, the deployment of the rod generally offers increased power compared to the retraction of the rod.

[0063] In addition, all of the elements involved in controlling the internal flaps, consisting of the levers 80, the upstream 90 and downstream 92 support walls, and the means connecting the latter to the mobile part of the motor means, can thus have limited size and mass.

[0064] Furthermore, the lever 80 of each of the controlled converging flaps 30 is advantageously arranged at an upstream end of the flap, again so as to limit as much as possible the size and mass of the flap control system.

[0065] In such a case, it is advantageous for the synchronization ring 82 to be arranged downstream of the lever 80 of each of the controlled converging flaps 30.

[0066] It should be noted that the bodies 56A of the jacks 56 can be rigidly fixed to the stator structure 38, in the same way as in the known example illustrated in the figure 2 and described above.

[0067] In alternative embodiments, the upstream bearing walls 90 may be connected to each other to form a unitary upstream bearing structure extending 360 degrees. Similarly, the downstream bearing walls 92 may be connected to each other to form a unitary downstream bearing structure extending 360 degrees.

[0068] Such support structures may be directly integrated into the body 86 of the synchronizing ring 82.

[0069] The means implemented to control the positions of the diverging flaps 32 to those of the converging flaps 30 will be described in the following.

[0070] For each divergent flap 32, these means comprise a first connecting rod 120 having a first end portion 120A articulated to the corresponding convergent flap 30 and an opposite second end portion 120B, a second connecting rod 122 having a first end portion 122A articulated to the corresponding divergent flap 32 and an opposite second end portion 122B, and a third connecting rod 124 having a first end portion 124A articulated to the synchronizing ring 82 and an opposite second end portion 124B. In addition, the second end portion 120B of the first connecting rod 120 is hinged to at least one of the second end portion 122B of the second connecting rod 122 and the second end portion 124B of the third connecting rod 124. Finally, the second end portion 124B of the third connecting rod 124 is hinged to the second end portion 122B of the second connecting rod 122.

[0071] In the example illustrated on the figures 3 to 7, the second end portion 120B of the first connecting rod 120 is jointly articulated to the second end portion 122B of the second connecting rod 122 and to the second end portion 124B of the third connecting rod 124, along a common articulation axis AC.

[0072] In addition, the first end portion 120A of the first connecting rod 120 is articulated to the stiffening structure 81 secured to the panel 31 of the converging flap, along a third articulation axis A3 which is advantageously closer to the first articulation axis A1 than to the second articulation axis A2. In the example illustrated, the third articulation axis A3 is also closer to a center line LM, located midway between the first axis A1 and the second axis A2, than to the first axis A1. The first end portion 122A of the second connecting rod 122 is articulated to a yoke 126 secured to the panel 33 of the diverging flap, along a fourth articulation axis A4 which is advantageously located substantially midway between the second articulation axis A2 and the downstream end 79B of the diverging flap. Finally, the first end portion 124A of the third connecting rod 124 is articulated to a second yoke 128 of the synchronizing ring 82.Such second yokes 128 are formed projecting from the main body 86 of the synchronizing ring 82 and extend, for example, downstream and radially outward from the main body 86.

[0073] In the variant illustrated on the figure 8 , the second end portion 124B of the third connecting rod 124 is articulated to the second end portion 122B of the second connecting rod 122 along a fifth articulation axis A5, and the second end portion 120B of the first connecting rod 120 is articulated to the second end portion 122B of the second connecting rod 122 along a sixth articulation axis A6 located between the fifth articulation axis A5 and the first end portion 122A of the second connecting rod 122.

[0074] In operation, the first, second and third connecting rods 120, 122, 124 determine the orientation of the diverging flaps 32 according to a univocal law as a function of the orientation of the converging flaps 30.

[0075] This method of controlling the positions of the diverging flaps makes it possible to extend the value range of the A9 / A8 ratio. The extent of this range can thus typically be increased to 0.35, or even more.

Claims

1. A turbojet engine rear portion, comprising: - an upstream stator structure (38); - a convergent-divergent nozzle with a variable geometry (28) comprising a set of convergent flaps (30) distributed around a longitudinal axis (11) of the rear portion of the turbojet engine, each comprising a panel (31) intended to channel an exhaust gas flow (F4) within the nozzle, and each having an upstream end (36) hinged on the upstream stator structure, and further comprising a set of divergent flaps (32) distributed around the longitudinal axis (11), each comprising a panel (33) intended to channel the exhaust gas flow within the nozzle, and each having an upstream end (44) hinged on a downstream end (46) of a corresponding convergent flap; - a synchronisation ring (82) arranged around the set of convergent flaps (30) or the upstream stator structure (38); - drive means configured to move the synchronisation ring (82) in translation according to the longitudinal axis (11), relative to the upstream stator structure (38); - actuating means by which the synchronisation ring (82) acts on at least some of the convergent flaps (30), called controlled convergent flaps, to control a geometric variation of the nozzle; and - means for controlling the positions of the divergent flaps on the basis of those of the convergent flaps, comprising a first connecting rod (120) having a first end portion (120A) hinged to the corresponding convergent flap (30) and an opposite second end portion (120B), a second connecting rod (122) having a first end portion (122A) hinged to the corresponding divergent flap (32) and an opposite second end portion (122B), and a third connecting rod (124) having a first end portion (124A) hinged to the synchronisation ring (82) and an opposite second end portion (124B); characterized in that the second end portion (120B) of the first connecting rod (120) is hinged to at least one amongst the second end portion (122B) of the second connecting rod (122) and the second end portion (124B) of the third connecting rod (124), and the second end portion (124B) of the third connecting rod (124) is hinged to the second end portion (122B) of the second connecting rod (122).

2. The turbojet engine rear portion according to claim 1, wherein the second end portion (120B) of the first connecting rod (120) is hinged together to the second end portion (122B) of the second connecting rod (122) and to the second end portion (124B) of the third connecting rod (124), according to a common hinge axis (AC).

3. The turbojet engine rear portion according to claim 1, wherein the second end portion (124B) of the third connecting rod (124) is hinged to the second end portion (122B) of the second connecting rod (122) according to a fifth axis (A5), and the second end portion (120B) of the first connecting rod (120) is hinged to the second end portion (122B) of the second connecting rod (122) according to a sixth hinge axis (A6) located between the fifth hinge axis (A5) and the first end portion (122A) of the second connecting rod (122).

4. The turbojet engine rear portion according to any one of claims 1 to 3, wherein an A9 / A8 ratio, equal to the quotient of a section A9 of the nozzle at a downstream end of the divergent flaps by a section A8 of the nozzle at a neck formed at a junction between the convergent flaps and the divergent flaps, varies within a range wider than 0.35.

5. A turbojet engine for an aircraft, comprising a rear portion according to any one of claims 1 to 4.