FR2728306A1 - Aircraft jet engine thrust reversal system - Google Patents

Abstract

The system comprises at least one flap (5,6) with its rear end pivoted in relation to the engine, with drives (9) to turn the flaps about their pivots, and a mechanism to shift the pivots axially. The forward ends of the flaps have radial stops (16) which cooperate with matching elements on the engine (1) and are designed to prevent deployment of the flaps while the flap's pivots are in their forward position. The distance between the forward and rear positions of the flaps' pivots is between 1 and 2 per cent of the motor's outlet diameter, and the axial movement mechanism for the pivots is in the form of guides and sliders.

Description

REACTION ENGINE HAVING INVERTER
OF IMPROVED PUSH.

 The invention relates to a jet engine equipped with an improved thrust reverser.

 Thrust reversers for jet engines are used to shorten the stopping distance when braking an aircraft, by reversing the direction of the gas jet delivered by the engine, which produces reverse braking thrust.

 In conventional manner, these thrust reversers comprise at least one door disposed in the extension of the nozzle and pivotally mounted around a transverse axis, each of said doors being associated with pivoting means arranged to pivot it between two extreme positions: a folded position where each door is profiled externally with the engine fairing, and internally forms the continuity of the nozzle, and a deployed position where each door intercepts the gas jet leaving the nozzle, then actively participating in the braking of the aircraft by inversion of said gas jet.

 Such thrust reversers, in particular described in patent FR 2 348 371, provide all satisfaction with regard to their reliability and their performance in the braking phase of the aircraft. However, they have a drawback in the flight phase of the aircraft, because these thrust reversers generate additional aerodynamic drag due to the large thickness of the base surface of the trailing edge of each door, which leads to loss of internal thrust as well as an increase in external drag.

 The external drag is, in addition, also increased due to the deformations of the doors under the effect of the internal pressures which they have to contain. These deformations cause, in fact, a mismatch between the external surfaces of the doors and the surfaces of the adjacent fixed structures.

 It should also be noted that despite the advantages they offer during the braking phase, the thrust reversers are sometimes also criticized for the extra weight they cause, and for the risk of incidents, even very small. which they can be the cause of by their mere presence.

 The present invention aims to overcome all of the above-mentioned drawbacks and has as its first objective to provide a jet engine equipped with a thrust reverser designed to lead to a reduction, on the one hand, in the thickness of the base surface, and on the other hand, external drag.

 Another object of the invention is to provide a jet engine equipped with a thrust reverser, the additional weight of which is minimized compared to a conventional engine, and the reliability of which, in particular in flight phase is increased.

 Another object of the invention is to provide a jet engine equipped with a thrust reverser, and the cross section of the outlet port of the engine gas jet is variable, in the folded position of the doors.

To this end, the invention relates to a jet engine, in particular of an aircraft, comprising a fixed upstream part composed of a nozzle extended by flanges, and of a fairing covering said nozzle and flanges, and a movable downstream part constituting said thrust reverser and comprising
- At least one door with a rear end face forming the trailing edge, arranged in the extension of the nozzle and carried by connecting pieces articulated around transverse pivots secured to the flanges, towards the rear end of these last,
- pivoting means of each door arranged to rotate it between two extreme positions:
a folded position where each door extends in the extension of the nozzle so as to be profiled externally with the fairing, and to form internally, with the flanges, the continuity of the nozzle,
a deployed position where each door is arranged so that its rear face is substantially parallel to the longitudinal axis of the motor (x).

According to the invention, this jet engine is characterized in that it comprises
means of displacement of each pivot, capable of making it possible to move each of said pivots by a predetermined distance along the longitudinal axis (x), between so-called advanced and retracted positions,
- radial stop means secured to the front end of each door, arranged to come to cooperate with conjugate stop means secured to the fixed upstream part, said stop means being adapted to prevent the deployment of the associated door in the position advanced pivots of the latter, and allow this deployment in the remote position of said pivots.

 The invention therefore consisted in producing a jet engine fitted with a thrust reverser, the doors of which are articulated around “semi-fixed” pivots, offering two main advantages.

 First, due to the movement of the doors to a remote position, it is possible to improve the design of the external fairing and the flanges so as to reduce the thickness of the residual base surface. In addition, this recoil also has the effect of reducing the harmful effects of the back pressure on the engine exhaust, caused by the proximity of the doors and the nozzle, and it therefore facilitates the integration of the thrust reverser. on the engine.

 In addition, the radial stop means preventing the deployment of the doors in the advanced position of the latter, constitute locking means which, on the one hand, offer protection against the risks of accidental opening in flight, and on the other hand on the other hand, guarantee a perfect flush with fixed and mobile surfaces, thereby eliminating a source of increase in external drag attributable to the inverter.

 According to another characteristic of the invention, the means for moving the pivots are arranged to be actuated by the pivoting means of the door hinged around said pivots.

 Furthermore, according to a preferred embodiment of the invention, the means of displacement of each pivot comprise a disc carried by an axis of rotation secured to a flange, on which said pivot is fixed eccentrically, and a system of bracing applied by elastic stop means, associated with said disc and adapted, on the one hand, to give the latter two stable positions corresponding respectively to the advanced and retracted positions of the pivot, and on the other hand, to allow a change of position of this disc under the effect of a force greater than a given threshold determined by the elastic stop means.

 The advantage of such displacement means is that it prevents accidental backing of the doors, without requiring an auxiliary hydraulic, pneumatic or electric control system which would lead to a significant additional mass and the risk of breakdowns.

 In addition, the bracing system of each disc advantageously comprises a link articulated, towards one of its ends, eccentrically on the disc, and towards its other end, on a rod capable of moving axially along a parallel axis. to the axis (x), said rod being urged by a spring stop capable of opposing its axial displacement.

 In addition, in the most common case where the thrust reverser comprises two symmetrical and opposite doors, each bracing system preferably comprises a rod extending substantially in the plane of symmetry of the engine, and two symmetrical connecting rods each rod to a pivot door disc of a door.

 Furthermore, the radial abutment means may simply consist of the front edge of the doors shaped so as to engage at least locally under the rear edge of the fixed upstream part in the advanced position of said doors.

 As a variant, these radial abutment means may also consist of pins projecting longitudinally relative to the front edge of the doors, and housings formed axially relative to the rear edge of the fixed upstream part and each capable of accommodating a pin.

 In either case, protection against an accidental backing of the doors can be ensured by the bracing system described above, by a conventional locking system with auxiliary control, or by the combination of these two solutions.

 Another solution aimed at improving protection against accidental backing of the doors without however having to resort to an auxiliary control system advantageously consists in providing radial stop means comprising, for each door, at least one stop element integral with the end. front of said door, arranged to cooperate with a receptacle integral with the fixed upstream part, said abutment element and receptacle having a cam profile adapted to generate a reaction comprising a longitudinal component capable of opposing the recoil of the door.

Such radial abutment means allow the aerodynamic forces acting naturally on the doors to be used when the latter form an integral part of the nozzle, as described for example in the patent.
US 4,182,501, this design being the most common in terms of thrust reverser.

 In this case, in fact, the average pressure acting on the internal surface of the doors is not only higher than that acting on the external surface, but is all the more important as the engine speed and the speed of the airplane are high. . As an indication, this overpressure can vary from 0.1 to 0.5 hectobars and consequently generate significant forces.

 Under these conditions, the cam profile can be designed to create an additional locking force such that the folded position of the doors is not only stable but also impossible to unlock under the action of the pivoting means of the doors, outside the conditions of deliberately limited theft.

 In practice, these cam profiles, of specific shape for each application, are adjusted so that an accidental or controlled reversal leading to deployment of the doors is only possible for an engine speed close to idle and for a speed of 1 aircraft slightly higher than the approach speed.

 It should be noted, moreover, that the total protection thus obtained against the risks of deployment in flight, during the take-off, climb, cruise, descent and go-around phases in the event of a refused landing, is all the more remarkable, in terms of reliability and weight saving, that it is obtained without requiring the addition of any additional device.

It should be noted, however, that this solution does not apply to thrust reversers provided with reversing doors arranged around and behind the propellant nozzle, as described in particular in the patent.
US 4,147,027. In fact, the average pressures acting on the internal and external faces are then both close to the ambient pressure. In this case, the mechanical locking of the recoil requires, in addition to the arching system, a conventional locking system.

 According to another characteristic of the invention aimed at a thrust reverser provided with bracing systems according to the invention, each receptacle is extended towards the rear by a radial abutment face parallel to the longitudinal axis (x) capable of serving as a stop for the corresponding stop element when the door is brought into its folded position, so as to tilt the bracing systems.

 Furthermore, the jet engine according to the invention has the advantage of being able to be easily completed in order to form, in direct jet, a two-position nozzle, the advantages of which are well known and whose certain embodiments have in particular been described in U.S. Patent 4,966,327.

 To this end, the jet engine according to the invention simply needs to be equipped with means for auxiliary displacement of the pivots able to move said pivots between their advanced position called, in this case, take-off, and a position, called cruising , located in front of the take-off position and in which the nozzle has an outlet orifice of smaller cross-section than that of said outlet orifice in the take-off position of the pivots, the radial abutment means being adapted to allow this movement forward pivots.

 In addition, according to a preferred embodiment making it possible to obtain the smallest nozzle section in the cruise position of the pivots, and an upper section in the take-off position of these pivots, the latter are fixed on a portion of disc. offset forward with respect to a transverse plane passing through the axis of rotation of said disc and orthogonal to the longitudinal axis (x), the auxiliary displacement means being adapted to move each of said pivots along a path included in a sector dial located at the front of the aforementioned transverse plane.

 According to another characteristic of the invention, the auxiliary displacement means comprise, for each rod carrying rods, a single-acting cylinder provided with a body arranged so as to be biased by the spring stop, and with a piston carrying the rod holder rod, said cylinder being connected to supply means capable of allowing it to be brought into an deployed state corresponding to the cruise position of the pivots in which the rods form a buttoning arc, and comprising elastic means capable to urge the piston to a retracted state corresponding to the take-off position of the pivots, in the absence of supply and when the force of said elastic means is able to break the bracing.

 The nozzle section variations are therefore achieved by means of a single-acting cylinder pressurized only to bring the pivots into their cruising position in which they are then held mechanically, under the effect of aerodynamic forces, without requiring the pressure maintenance of the jack.

 The backward movement of the pivots towards their take-off position is obtained automatically when the aerodynamic forces decrease, when the taring force of the elastic means urging the piston turns out to be sufficient to break the bracing. This automatic reversing therefore simply requires an adequate adjustment of the calibration of the elastic means.

 Furthermore, the maintenance of the pivots in their cruising position being ensured mechanically, it is not necessary, in this position, for the radial abutment means to generate a reaction comprising an axial component.

 This data advantageously allows each receptacle to be shaped so that it comprises, at the front of the cam profile, a front portion for guiding the stop element during the movements of the pivots between their cruising and take-off position, said guide portion being adapted to bring about a displacement of the stop element along a rectilinear trajectory substantially inclined relative to the longitudinal axis (x) so as to generate a lowering of the upstream part of the doors during a movement towards the 'rear of said stop member.

 In this way, and by adjusting the inclination as a function of the position of the receptacles relative to the plane of symmetry of the door, one obtains a lowering of the front part of said door during the retraction of the pivots, which prevents the appearance of an extra drag.

Other characteristics, objects and advantages of the invention will emerge from the detailed description which follows, with reference to the appended drawings which show by way of nonlimiting examples three preferred embodiments as well as two alternative embodiments. In these figures which form an integral part of the present description
FIG. 1 is a schematic perspective view of a jet engine according to 1 invention on which the locations of the radial stop means conforming to two of the preferred embodiments are shown,
FIG. 2 is a longitudinal view, partially in section, of the rear part of the doors of a thrust reverser according to a first embodiment, in the advanced position of the pivots,
FIG. 3 is a longitudinal view similar to that of FIG. 2, in the retracted position of the pivots,
FIG. 4a is a perspective view of the radial stop means equipping this first embodiment,
FIG. 4b is a longitudinal section through a plane A of these radial abutment means mounted on a motor according to the invention,
FIG. 5 is a longitudinal section of the radial stop means in accordance with a second preferred embodiment,
FIG. 6 is a longitudinal section of a variant of radial stop means which can be fitted to an engine according to the invention,
FIG. 7a represents, in schematic top view, a jet engine according to the invention equipped with a second variant of the radial stop means, in the advanced position of the pivots,
FIG. 7b is a schematic longitudinal section through a plane B in FIG. 7a,
FIGS. 8a and 8b correspond respectively to FIGS. 7a and 7b, in the retracted position of the pivots,
FIG. 9a is a longitudinal view partially in section of the rear part of the doors of a thrust reverser according to a third embodiment, in the pivoting position of the pivots,
FIG. 10a is a longitudinal view similar to that of FIG. 9a, in the position of takeoff of the pivots,
FIG. 1a is a longitudinal view similar to that of FIGS. 9a and 10a, in the retracted position of the pivots,
FIGS. 9b, 1Ob, îîb are diagrams respectively corresponding to FIGS. 9a, 10a, and 11a, representing a thrust reverser seen in longitudinal half-section, FIG. 11b further representing this thrust reverser after tilting of the doors,
- And Figures 9c, 10c are longitudinal sections of the radial stop systems fitted to this third embodiment, in positions corresponding respectively to Figures 9a and 1Oa.

 The jet engine with thrust reverser shown in FIG. 1 comprises, in a conventional manner, a nozzle 1 extended by two flanges such as 2 diametrically opposite.

 The fairing 3 of this engine is interrupted in line with the flanges 2, and comprises two fairing strips such as 4 coming in the extension of the main body of this fairing so as to each cover one of said flanges 2.

 The thrust reverser of this jet engine has two identical doors 5, 6 mounted tilting around transverse pivots such as 7.

 Each of these doors 5, 6 is carried by two connecting fittings such as 8 arranged in line with the rear corners of said doors, and articulated around the transverse pivots 7.

These doors 5, 6 also have a rear face extending in an oblique plane with respect to the longitudinal axis of said doors and are associated with pivoting means able to pivot them between two extreme positions.
- A folded position where these doors 5, 6 extend in the extension of the fairing body 3, so as to profile externally with this fairing body 3 and the fairing strips 4, and to form internally, with the flanges 2 , the continuity of the nozzle 1. Furthermore, in this folded position, the rear faces of the doors 5, 6 delimit an oblique cut whose shape is defined in English by an expression whose literal translation is "fish mouth
- a deployed position where the doors 5, 6 are in abutment against one another by their rear face, and where said doors are arranged so as to intercept and reverse the gaseous jet leaving the nozzle 1.

 The pivot means of these doors 5, 6 comprise, at each flange 2, a central jack disposed longitudinally between said flange 2 and the corresponding fairing strip 4 (this jack being masked in FIG. 1 by the associated fairing strip ), and two connecting rods such as 9 articulated on the central jack and each on a connecting piece 8.

 The elements described above being conventional and known, they will not be described in more detail in the present application.

 According to the invention, and firstly, each transverse pivot 7 is mounted, eccentrically on a disc such as 10, carried by an axis of rotation integral with a flange 2, so that it can be moved longitudinally along d 'a circular sector, during deployment or withdrawal of the central cylinder.

 In addition, each disc 10 is associated with a bracing system with a spring stop arranged to confer two stable positions on this disc, and consequently, two stable positions on the transverse pivots 7.

 This bracing system comprises a rod 11 extending coaxially to the longitudinal axis (x), on the rear end of which are articulated two rods 12, 13 connecting said rod to the disks 10 associated respectively with doors 5 and 6, arranged to allow said doors to be moved simultaneously.

 Towards its opposite end, this rod 11 comprises a head îîa housed in a cylindrical body 35 provided with a rear front wall 36 pierced with an orifice through which extends said rod. This cylindrical body 35 contains, in addition, a spring stop 14 consisting for example of a stack of Belleville washers, arranged so that the head of the rod 11 is positioned between an elastic front stop that constitutes this spring stop 14 and a fixed rear stop consisting of the rear front wall 36 of the cylindrical body 35.

 As shown in Figures 2, 3, the articulation point of the links 12, 13 on the discs and the arrangement of the spring stop 14 are adapted so that said links take two distinct positions of bracing between which the discs 10 undergo a rotation of the order of one third to two thirds of a circle causing a longitudinal displacement of the doors 5, 6.

 According to the invention, the thrust reverser further comprises radial stop means capable of preventing the deployment of the doors 5, 6 in the advanced position of the pivots 7 (FIG. 2), and of authorizing this deployment in the retracted position of said pivots (Figure 3).

 As shown in Figures 4a and 4b, these stop means comprise receptacle elements 15 intended to be secured to the fixed upstream part and stop elements 16 arranged to engage in the receptacles and intended to be secured to the front end of doors 5, 6.

 Firstly, the elements 15 forming a receptacle comprise a plate 17 arranged to be secured to a square-shaped frame 18 for reinforcing the downstream part of the nozzle 1. This plate 17 also carries a receptacle wall 19 orthogonal to said plate, provided with a notch 20 inclined upwards, delimited frontally by an inclined upper internal face.

 In addition, this receptacle wall 19 forms, in the lower continuity of the notch 20, an appendage 21 extending in the rear extension of said wall and comprising an upper face arranged to serve as a bottom stop for a radial stop element 16 secured to a door 5, 6 at the end of folding of the latter, so as to allow the rear bracing of the links 12, 13 to be "broken".

 The abutment elements comprise, for their part, a support plate 22 in the form of a square arranged to be secured to a U-shaped frame 23 for reinforcing the front end of the doors 5, 6. This support plate 22 carries a yoke 24 extending orthogonally relative to one of its wings, housing a transverse pin 25 arranged to penetrate into the notch 20 of a receptacle element 15.

 As shown in FIG. 1, such abutment means can be distributed around the circumference of the rear end of the nozzle 1 and of the front end of the doors 5, 6 so as to obtain a correct distribution of the forces.

 Due to the shape of the notch 20, such abutment means are adapted to generate, when the pins 25 are housed in the notches 20, a reaction comprising a longitudinal component tending to oppose any recoil of the doors 5, 6, even in the event of an attempt to deploy the central jack, and this as long as the aerodynamic forces acting on these doors are greater than a given threshold representative of a landing phase of the aircraft.

 Once the aerodynamic forces are below this threshold, the deployment of the central jack makes it possible to "break" the rear bracing of the rods 12, 13 by compression of the spring stop 14, causing the discs 10 to rotate and consequently a recoil of doors 5, 6.

 Maintaining the doors 5, 6 in this remote position allowing the subsequent folding of the doors 5, 6 is then ensured by the front bracing of the links 12, 13 obtained automatically during the rotation of the discs 10.

 At the end of folding, in addition, and as indicated above, the links 12, 13 return to the rear bracing position allowing the doors 5, 6 to be brought back to their advanced position, thanks to the appendix 21 of the radial stop element.

 FIG. 6 represents a second embodiment aiming at a variant of radial abutment means the objective of which is the same as that of the radial abutment means described above, namely to prohibit the recoil of the doors 5, 6 outside of conditions specific to the landing phase.

 These radial abutment means are in this case, not carried by fittings, such as the fittings 17, 22 described above, but by reinforcing strips 37, 39 respectively secured to the rear end of the fixed upstream part , and from the front end of doors 5, 6.

 Note that it is not necessary for these reinforcing strips 37, 39 to extend over the entire periphery of the doors 5, 6, and that it suffices, in general, to arrange them over a sector of 20 at 30 degrees on either side of the plane of symmetry of said doors.

 The radial abutment means carried by these reinforcing bands 37, 39 have the general form of hooks 39, 40 provided with cooperation surfaces inclined relative to the horizontal, adapted to create a reaction comprising a longitudinal component tending to oppose at any retreat from doors 5, 6.

 In addition, the hook 40 secured to the doors 5, 6 has a chamfered front face 40a allowing the engagement of this hook with the hook 39 vis-à-vis during the advancement of the doors 5, 6.

 With such radial abutment means, the "rupture" of the rear bracing of the links 12, 13 is obtained by any abutment means known per se used to limit the rotation of the doors 5, 6 during their folding.

 FIG. 6 represents a variant according to which the radial stop means generate a simple reaction orthogonal to the longitudinal axis (x), according to which either the force to be exerted by the bracing must be sufficient to guarantee stable positioning in the advanced position doors 5, 6, or additional locking means must be provided.

 According to this variant, the receptacle elements 15 comprise, in place of the receptacle wall 19, a longitudinal sleeve 26, and the abutment elements 16 comprise a longitudinal finger 27 capable of coming to engage axially in the sleeve 26.

 Figures 7 and 8 show a second variant according to which the reaction generated by the stop means is also strictly orthogonal to the longitudinal axis (x).

 As shown in these figures, the doors 5, 6 have a front edge 28 which bends in the direction of the axis of the motor, so as to come to engage, at least in its major portion, under the rear edge of the nozzle 1, in the advanced position of said doors 5, 6.

 Figures 9, 10, 11 show a third embodiment of the same design as that described with reference to Figures 2 and 3, supplemented by auxiliary displacement means adapted to allow the section of the nozzle to be varied in direct jet. (For the sake of simplification and because of this similarity in design, the elements of these two embodiments having the same function bear the same reference numeral).

 These auxiliary displacement means comprise a hydraulic cylinder 29 designed to come to be interposed between the spring stop 14 and the rod 11.

 To this end, the body 30 of this jack 29 comprises a head 30a housed in the cylindrical body 35 so as to be urged by the spring stop 14 and to come into abutment against the front wall 36. In addition, the piston 31 of this jack 29 is secured to the rear end of the rod 11.

 The cylinder 29 is, moreover, supplied by means of a hydraulic line 32 communicating with a passage formed in the head 30a of the body 30 of this cylinder, in order to allow the piston 31 to be moved rearward. The reverse movement is obtained by means of an internal helical spring 33 mounted around the rod 11, capable of bringing the piston 31 to a front stop position.

 As shown in Figure 9a, the articulation point of the links 12, 13 on the discs 10 and the arrangement of the hydraulic cylinder 29 and the spring stop 14 are adapted so that the links have a third arc position -buttin obtained after deployment of the hydraulic cylinder 29, and corresponding to a position of the pivots 7 said to be cruising where the latter are in front with respect to the previously defined advanced position then becoming the take-off position.

 In addition, the articulation point of the links 12, 13 is adapted so that, in this third bracing position, the distance separating the pivots 7 facing the two doors 5, 6 is less than that separating said pivots in the retracted position of the hydraulic cylinder 29.

 Therefore in the deployed position of the hydraulic cylinder 29, the outlet section of the nozzle is smaller than that obtained in the retracted position of this verlan.

 In addition, once the links 12, 13 are in this third bracing position, this positioning remains stable as long as the aerodynamic forces counteract the action of the spring 33.

 Furthermore, according to this embodiment, the notches 20 are extended by a rectilinear opening 34 with a longitudinal axis inclined rearward relative to the longitudinal axis (x) adapted to guide the pins 25, during the passage of the cruise position to take-off position, so as to obtain a lowering of the upstream part of the doors 5, 6.

 It should be noted that, identically, the hooks 39 of the radial abutment means described with reference to FIG. 5 may include a guide surface making it possible to obtain a result similar to that described above.

Claims (13)

 1 / - Jet engine, in particular of an aircraft, comprising a fixed upstream part composed of a nozzle (1) extended by flanges (2), and a fairing (3, 4) covering said nozzle and flanges, and a movable downstream part constituting said thrust reverser and comprising  - at least one door (5, 6) provided with a rear end face forming the trailing edge, arranged in the extension of the nozzle (1) and carried by connecting pieces (8) articulated around transverse pivots (7) secured to the flanges (2), towards the rear end of the latter,  - pivoting means (9) of each door (5, 6) arranged to rotate it between two extreme positions  a folded position where each door (5, 6) extends in the extension of the nozzle (1) so as to be profiled externally with the fairing (3, 4), and to form internally, with the flanges (2), the continuity of the nozzle,  a deployed position where each door (5, 6) is arranged so that its rear face is substantially parallel to the longitudinal axis of the engine (x), said jet engine being characterized in that it comprises  means (10-14) for moving each pivot (7), capable of allowing each of said pivots to be displaced by a predetermined distance along the longitudinal axis (x), between so-called advanced and retracted positions,  - radial stop means (16; 39, 40; 27; 28) integral with the front end of each door (5, 6), arranged to cooperate with conjugate stop means (15; 37, 38; 26 ) integral with the fixed upstream part (1, 2), said abutment means being adapted to prohibit the deployment of the door (5, 6) associated in the advanced position of the pivots (7) of the latter, and authorize this deployment in the retracted position of said pivots.  2 / - Jet engine according to claim 1, characterized in that the displacement means (10-14) of the pivots (7) are arranged to be actuated by the pivoting means (9) of the door (5, 6) articulated around said pivots.  3 / - Jet engine according to one of claims 1 or 2, characterized in that the means for moving each pivot (7) comprise a disc (10) carried by an axis of rotation secured to a flange (2) , on which said pivot is fixed eccentrically, and a bracing system (11-13) urged by elastic stop means (14), associated with said disc and adapted, on the one hand, to give this last two stable positions corresponding respectively to the advanced and retracted positions of the pivot (7), and on the other hand, to allow a change of position of this disc (10) under the effect of a force greater than a given threshold determined by the elastic stop means (14).  4 / - Jet engine according to claim 3, characterized in that the arching system of each disc (10) comprises a link (12, 13) articulated, towards one of its ends, eccentrically on the disc (10 ), and towards its other end, on a rod (11) able to move axially along an axis parallel to the axis (x), said rod being urged by a spring stop (14) capable of opposing its axial displacement.  5 / - Jet engine according to claim 4 comprising two doors (5, 6) substantially symmetrical and opposite, characterized in that, for each flange (2) of the fixed upstream part, the arching system comprises a rod (11 ) extending substantially in the plane of symmetry of the motor, and two symmetrical connecting rods (12, 13) each connecting the rod (11) to a disc (10) pivot door (7) of a door (5, 6).  6 / - Jet engine according to one of the preceding claims, characterized in that it comprises means (29-33) for auxiliary displacement of the pivots (7) able to move said pivots between their advanced position, called in this case take-off, and a so-called cruise position located in front of the take-off position and in which the nozzle has an outlet orifice of smaller cross-section than that of said outlet orifice in the pivots take-off position (7), the means radial stop (15, 16; 37-40; 26, 27; 28) being adapted to allow this forward movement of the pivots.  7 / - jet engine according to one of claims 3 to 5 and claim 6 taken together, characterized in that each pivot (7) is fixed on a disc portion (10) offset forwardly relative to a transverse plane passing through the axis of rotation of said disc and orthogonal to the longitudinal axis (x), the auxiliary displacement means (29-33) being adapted to move each of said pivots along a trajectory included in a dial sector located at the front of the aforementioned transverse plane.  8 / - Jet engine according to claims 4 and 7 taken together, characterized in that the auxiliary displacement means comprise, for each rod (11) rod holder (12, 13), a single-acting cylinder (29) provided with 'a body (30) arranged so as to be biased by the spring stop (14), and a piston (31) carrying the rod (11) carrying the rods, said jack being connected to supply means ( 32) capable of allowing it to be brought into a deployed state corresponding to the cruise position of the pivots (7) in which the rods (12, 13) form a bracing, and comprising elastic means (33) capable of urging the piston (31) to a retracted state corresponding to the take-off position of the pivots (7), in the absence of supply and when the force of said elastic means is found capable of breaking the bracing.  9 / - Jet engine according to one of the preceding claims, characterized in that the radial stop means consist of the front edge (28) of the doors (5, 6) shaped so as to come to engage at least locally under the rear edge of the fixed upstream part (1, 2) in the advanced position of said doors.  10 / - Jet engine according to one of claims 1 to 8, characterized in that the radial stop means consist of pins (27) projecting longitudinally relative to the front edge of the doors (5, 6), and housings (26) arranged axially relative to the rear edge of the fixed upstream part (1, 2) and capable of each housing a pin (27).  11 / - Jet engine according to one of claims 1 to 8, characterized in that the radial stop means comprise, for each door (5, 6), at least one stop element (25; 40) integral with the front end of said door, arranged to cooperate with a receptacle (19, 20; 38) integral with the fixed upstream part (1, 2), said stop element and receptacle having a cam profile adapted to generate a reaction comprising a longitudinal component capable of opposing the recoil of the door.  12 / - Jet engine according to claims 6 and 11 taken together, characterized in that each receptacle (19, 20) comprises, at the front of the cam profile, a front portion (34) for guiding the element of stop (25) during movements of the pivots (7) between their cruising and take-off position, said guide portion being adapted to bring about a movement of the stop element (25) along a rectilinear trajectory substantially inclined relative to the longitudinal axis (x) so as to generate a lowering of the front end of the doors (5, 6) during a rearward movement of said stop element.  13 / - Jet engine according to one of claims 11 or 12 and claim 3 taken together, characterized in that each receptacle (19, 20) is extended rearward by a face (21) of radial stop parallel to the longitudinal axis (x) capable of serving as a stop for the corresponding stop element (25) when the door (5, 6) is brought into its folded position, so as to tilt the bracing systems ( 10-14).