Propeller for an aircraft turbo engine with an adjustable blade and a counterweight device with gear drive

Description

Domaine technique de l'invention

[0001] The present invention relates to the field of aircraft turbomachines and in particular to the propulsion propellers of these turbomachines which comprise variable-pitch blades with a geared counterweight device. Arrière-plan technique

[0002] The state of the art includes in particular documents FR-A1-3 009 710 and FR-A1-3 057 909.

[0003] An aircraft turbomachine propeller may be shrouded ( figure 1 ), as is the case with a blower for example, or not shrouded ( figure 2 ) as is the case with an open-rotor type architecture for example.

[0004] A propeller comprises blades that can be variable pitch. The turbomachine then comprises a mechanism for modifying the pitch angle of the blades in order to adapt the thrust generated by the propeller according to the different phases of flight. The angular pitch of the propeller blades also makes it possible to optimize the efficiency of the propeller according to the speed of the aircraft and to optimize the pumping margin of the turbomachine to reduce its fuel consumption in the different phases of flight.

[0005] As a reminder, the pitch angle of a propeller blade corresponds to the angle, in a longitudinal plane perpendicular to the axis of rotation of the propeller blade, between the blade chord and the plane of rotation of the fan or the turbomachine engine. Variable-pitch propeller blades can occupy a so-called reverse thrust position (known as "reverse") in which they generate counter-thrust to help slow down the aircraft and a feathering position in which, in the event of failure or breakdown, they limit their aerodynamic resistance and / or drag. The consequences of this drag can be of the order of flight safety in the event of loss of control of the aircraft if the aircraft's tail is not designed for it, and can be of the order of performance for the possible duration of the diversion flight on a single engine.

[0006] Multiple devices have been devised to vary the pitch of propeller blades, which generally involve rotating the blade around its main axis (corresponding to a blade pitch axis) by means of a control system located radially inside the blade roots. This control system comprises, for example, an actuator which can be connected to the blade roots by connecting rods and / or a linkage.

[0007] One of the constraints of the propeller blade pitch control system is to bring the blades into the predetermined position, known as the "flag position" in the event of a failure of this pitch system. Feathering helps to minimize aerodynamic drag.

[0008] Conventionally, the return to the feather position is ensured by so-called direct counterweight devices whose inertia, much greater than that of the propeller blades, must guarantee the return of the latter to the predefined feather position. A counterweight device is generally associated with each of the blades. The counterweight device may comprise a movable shaft rotating for example around an axis perpendicular to the blade setting axis. Depending on the type of gear of the counterweight device, the gear may be perpendicular and / or concurrent with the blade setting axis. Conventionally, the bevel gear of the counterweight device extends along an axis at least concurrent with the blade setting axis. The movable shaft of the counterweight device is connected to a flyweight and therefore to a bevel pinion which is meshed with a portion of toothed wheel integral in rotation with the blade ( figure 3 ). The shaft is generally centered and guided in rotation by at least one bearing, for example a ball bearing ( figure 4 ).

[0009] However, a seizure of the bevel gear or one of the counterweight device bearings can cause the counterweight device kinematics to jam. To avoid jamming the entire blade pitch change mechanism, it may be necessary to add a so-called fusible section. This fusible section can be associated with the control system. For example, the fusible section can be on one of the connecting rods to the actuator or on the connecting rod to the actuator. However, this solution has the disadvantage of losing the actuation of one of the blades which remains stuck in its current operating position. This jamming can cause mechanical and aerodynamic imbalance, and can lead to so-called active feathering and in-flight incidents such as an IFSD ( In Fligth Shut Down ). This can generally limit the operability and performance of the turbomachine and the aircraft.

[0010] In this context, it is interesting to overcome the drawbacks of the prior art, by integrating a simple and effective safety function on a variable-pitch blade and its counterweight device. Résumé de l'invention

[0011] The present invention provides a simple, effective and economical solution to at least some of the above-mentioned problems.

[0012] To this end, the invention relates to an assembly for an aircraft turbomachine propeller, the assembly comprising: a variable-pitch vane comprising a blade connected to a root, the vane comprising a longitudinal axis coincident with a vane pitch axis A which passes through said root, a base integral in rotation with the vane around the pitch axis A and connected to a portion of toothed wheel extending around this pitch axis A, and a counterweight device comprising a shaft movable in rotation around an axis B substantially concurrent and perpendicular to said pitch axis A, this shaft being connected to at least one weight and to a portion of pinion meshed with the portion of toothed wheel.

[0013] According to the invention, the toothed wheel portion is fixed to said base by at least one shear screw.

[0014] The axis B may be substantially perpendicular and / or concurrent with the setting axis A.

[0015] The integration of at least one shear screw allows the toothed wheel portion to separate from the base integral in rotation with the variable-pitch blade in the event of failure of the counterweight device. More particularly, when the kinematics of the counterweight device are blocked (such as by seizure of the bevel pinion or the bearings), a significant force is applied to the meshed toothed wheel portion via the pinion of the counterweight device, so that the shear screw breaks. For example, the shear screw is dimensioned to break by a breaking overstress in shear and / or in tension which is exerted by the pinion of the blocked counterweight device. The breaking and the separation of the toothed wheel portion from the base makes it possible to release the pitch actuation kinematics of the set of blades so as not to block the entire pitch change mechanism.This prevents mechanical and aerodynamic imbalance on the blade caused by the blocked counterweight device. Consequently, the variable-pitch blade and its base are effectively secured in the event of failure of the associated counterweight device.

[0016] The assembly according to the invention may comprise one or more of the following characteristics, taken in isolation from one another, or in combination with one another: the toothed wheel portion is fixed to said base by several fusible screws; the or each fusible screw extends along a first elongation axis Y which is parallel to said setting axis A; the or each fusible screw comprises a first head bearing on said toothed wheel portion, and a first body which passes through first orifices of this portion and of the base; said first body comprises a first threaded section screwed into the first orifice of the base, which is tapped, and a second section defining a smaller section of the first body; the second section comprises an annular groove; -- said annular groove has a second or third diameter D2, D3 smaller than a first diameter of the first body and a first or second variable thickness, the diameters D1 to D3 being measured relative to an axis perpendicular to the Y axis and the thicknesses E1, E2 being measured relative to the Y axis; the second section comprises at least one hole; the assembly further comprises at least one screw for retaining the toothed wheel portion on the base, the or each retaining screw being non-functional as long as said at least one shear screw is not broken and the or each retaining screw being functional when said at least one shear screw is broken, the or each retaining screw comprises a second head which is configured, on the one hand, to be at a distance from the toothed wheel portion when said at least one shear screw is not broken, and on the other hand, to be able to come to bear and retain the toothed wheel portion when said at least one shear screw is broken; the or each retaining screw extends along a second elongation axis Z which is parallel to said setting axis A; the or each retaining screw comprises a second body which passes through second orifices of the toothed wheel portion and of the base;said second body comprises a third threaded section screwed into the second orifice of the base, which is tapped, and a fourth non-threaded section engaged in the second orifice of the toothed wheel portion; the fusible screws are staggered with the retention screws.;

[0017] The present invention also relates to a propeller for a turbomachine, in particular for an aircraft, comprising several assemblies as described above.

[0018] The propeller can be a shrouded propeller or an unshrouded propeller.

[0019] The present invention also relates to an unclaimed turbomachine, in particular for an aircraft, comprising at least one propeller or several assemblies as described above.

[0020] The turbomachine can be a turbojet or a turboprop. Brève description des figures

[0021] Other characteristics and advantages will emerge from the following description of a non-limiting embodiment of the invention with reference to the appended drawings in which: [ Fig.1 ] there figure 1 is a partial schematic view in longitudinal section of an aircraft turbomachine comprising a ducted propeller, [ Fig.2 ] there figure 2 is a partial schematic view in longitudinal section of an aircraft turbomachine comprising two unducted propellers, [ Fig.3 ] there figure 3 is a schematic perspective view of an assembly comprising a counterweight device and a base of a propeller blade of the figure 1 or of the figure 2 , [ Fig.4 ] there figure 4 is a schematic longitudinal sectional view of the entire figure 3 , [ Fig.5a ] there figure 5a is a schematic perspective view of a fusible screw according to a first embodiment of the invention, [ Fig.5b ] there figure 5b is a schematic perspective view of a fusible screw according to a second embodiment of the invention, [ Fig.5c ] there figure 5c is a schematic perspective view of a fusible screw according to a third embodiment of the invention, [ Fig.6 ] there figure 6 is an enlarged and partial schematic view in longitudinal section of the fusible screw assembled in the assembly of the figure 4 according to a first embodiment of the invention, [ Fig.7 ] there figure 7 is a schematic perspective view of a retention screw according to the invention, [ Fig.8 ] there figure 8 is an enlarged and partial schematic view in longitudinal section of the fusible screw and the retention screw assembled in the assembly of the figure 4 according to a second embodiment of the invention, [ Fig.9 ] there figure 9 is a partial schematic perspective view of the entire figure 8 , [ Fig.10 ] there figure 10 is an enlarged and partial schematic view in longitudinal section of the fusible screw and the retention screw assembled in the assembly according to a third embodiment of the invention, [ Fig.11 ] there figure 11 is an enlarged and partial schematic view in longitudinal section of the fusible screw and the retention screw assembled in the assembly according to a fourth embodiment of the invention. Description détaillée de l'invention

[0022] By convention in the present application, the terms "inner" and "outer", and "internal" and "external" are defined radially relative to a longitudinal axis (which may correspond to a longitudinal axis X of a turbomachine). Thus, a cylinder extending along this longitudinal axis has an inner face facing the axis of the engine and an outer surface, opposite its inner surface. "Axial" or "axially" means any direction parallel to this longitudinal axis, and "transversely" or "transverse" means any direction perpendicular to this longitudinal axis. Similarly, the terms "upstream" and "downstream" are defined relative to the direction of air circulation in the turbomachine which is represented by an arrow F.

[0023] Typically, a turbomachine 1 ( figure 1 ou 2 ) comprises a gas generator G (or engine) upstream of which a fan module S is mounted. The turbomachine 1 extends along a longitudinal axis X.

[0024] Generally speaking and in the remainder of the description, the term "fan module" is used to designate either a fan or a propeller, the blades of the fan or the propeller being able to be shrouded (for example for the double-flow turbojets of the figure 1 ) or unducted (for example for turboprops of the figure 2 ).

[0025] THE figures 1 et 2 therefore illustrate two types of turbomachine 1 each intended to be mounted on an aircraft.

[0026] More specifically, the figure 1 schematically illustrates a double-flow turbomachine 1 comprising a fan module S having a ducted propulsive propeller. The gas generator G of the turbomachine 1 comprises, from upstream to downstream, a low-pressure compressor 3a, a high-pressure compressor 3b, an annular combustion chamber 4, a high-pressure turbine 5b, a low-pressure turbine 5a and an exhaust nozzle 6. The figure 2 schematically illustrates a turbomachine 1 of the “open-rotor” type comprising a fan module S having unducted propulsive propellers. On the example of the figure 2 , the fan module S is downstream of the gas generator G. Alternatively (not shown), the fan module S with a double propeller can be upstream of the gas generator G of the turbomachine. The gas generator G of the turbomachine 1 comprises, from upstream to downstream, a low-pressure compressor 3a, a high-pressure compressor 3b, an annular combustion chamber 4, a high-pressure turbine 5b, an intermediate-pressure turbine 5c, first and second free power turbines 5d, 5e and an exhaust nozzle 6. The first and second free turbines 5d, 5e form a doublet of counter-rotating turbines for driving the unducted propellers S in counter-rotation. First and second rotating structural devices 21, 22 are located axially between the first and second free turbines 5d, 5e. Each rotating structural device 21, 22 is connected to one of the propellers S and to a fixed shaft 20'.This fixed shaft 20' is centered on the X axis and forms a fixed housing for receiving the free turbines 5d, 5e. In the example of the . figures 1 et 2 , the high-pressure compressor 3b and the high-pressure turbine 5b are connected by a high-pressure shaft 50 and form with it a high-pressure (HP) body. The low-pressure compressor 3a and the low-pressure turbine 5a or the intermediate-pressure turbine 5c are connected by a low-pressure shaft 30 and form with it a low-pressure (LP) body.

[0027] On the figure 1 , the blower S is driven by a blower shaft 20 which is coupled to the LP shaft 30 by means of a speed reducer 40. While in the figure 2 , gases from the primary vein escaping from the intermediate turbine 5c ensure the rotation of the free turbines 5d, 5e, the rotating structural devices 21, 22 and therefore the propellers S.

[0028] The invention applies generally to a propeller or fan S which is shrouded ( figure 1 ) or unfaired ( figure 2 ).

[0029] The propeller or fan S comprises a plurality of variable-pitch blades 2. Each blade 2 comprises a blade 20 connected to a root 22 ( figure 4 ). The blade 20 has an aerodynamic profile and comprises a lower surface and an upper surface which are connected by an upstream leading edge and by a downstream trailing edge (not shown). The blade 20 has an upper end which is free, called the tip, and a lower end which is connected to the root 22.

[0030] The root 22 defines a setting axis A which corresponds substantially to a longitudinal axis of the blade 2 and of the blade 20. The setting axis A is an axis around which the angular position of the blade 2 is adjusted. This axis A is also generally a radial axis (substantially perpendicular to the axis X) which therefore extends along a radius relative to the axis of rotation of the propeller S equipped with this blade 2.

[0031] The angular position of each of the blades 20 around their axis A can be ensured by a control system 200 of the propeller S. The control system 200 can comprise a single actuator for all the blades 2 of the propeller. For example, this actuator (not shown) can be connected to connecting rods at the roots 22 or to a rod which acts on pinions fixed on the blades 2, in particular by surrounding the roots 22.

[0032] The propeller S also comprises a polygonal ring C1 serving as support for the blades 20, this ring C1 forming a propeller hub ( figures 3 et 4 ). The polygonal ring C1 can be connected to a casing C2 or a fixed structure of the turbomachine 1. The ring C1 comprises a plurality of housings 74 spaced circumferentially from each other, these housings 74 being radial housings (relative to the axis X). Each of the housings 74 extends around the axis A and is configured to receive a support 76 for the blade root 22.

[0033] On the figure 4 , the support 76 comprises an annular wall 762. This annular wall 762 comprises a lower end 766 closed by a bottom wall 768, and an upper axial end 764 open and configured to allow the mounting of the root 22 of the blade 2 inside the housing 74. The bottom wall 768 is configured to cooperate by complementarity of shapes with a free end 24 of the root 22, so that the housing 74 is secured in rotation with the root 22 around the axis A.

[0034] First bearings 78 are interposed between each housing 74 and the annular wall 762 of the support 76 of the blade root, in particular to ensure the centering and guiding of the support 76 around the axis A with respect to the polygonal ring C1 and / or a fixed structure of the turbomachine 1.

[0035] In reference to the figures 3 et 4 , the propeller S comprises several assemblies 10. In the present application, an assembly 10 is understood to mean a part of the elements making up the propeller S. Thus, an assembly 10 comprises a variable-pitch blade 2, a base 70 and a counterweight device 8 associated with the blade 2.

[0036] The base 70 of each assembly 10 is configured to be integral in rotation with the blade 2 around the axis A. In the example of the figure 4 , the base 70 is mounted on the annular wall 762 of each support 76 and above each housing 74.

[0037] On the example of figures 6 , 8 And 9 , the base 70 comprises an extension 700 which extends substantially perpendicular to the axis A. This extension 700 is a radial extension (relative to the axis A) of the body of the base 70. The extension 700 comprises at least a first orifice 790 passing through a first plane PY ( figures 6 And 8). The extension 700 may also comprise at least one second orifice 792 passing through a second plane Pz ( figure 8 ). The first and second planes PY, Pz are substantially parallel to the axis A. The first plane PY can be upstream of the second plane Pz and / or vice versa.

[0038] The base 70 is connected to a portion of toothed wheel 72 which also extends around the axis A. In the example of the figure 3 , this portion 72 may be an angular sector extending circumferentially around the axis A. The angular sector of the portion 72 may be between 30° and 150°, preferably between 90° and 130°. The angular sector of the portion 72 may vary depending on the setting range of the blade setting axis depending on a shrouded propeller or an unshrouded propeller. The toothed wheel portion 72 may comprise teeth configured to mesh with teeth of the counterweight device 8. This portion 72 may therefore be conical.

[0039] On the example of figures 6 , 8 And 9 , the portion 72 comprises at least one first orifice 791 passing through the first plane PY. The portion 72 may also comprise at least one second orifice 793 passing through the second plane Pz. In the examples, the first orifices 790, 791 of the base 70 and of the portion 72 are aligned with respect to the first plane PY and the second orifices 792, 793 are aligned with respect to the second plane Pz. The counterweight device 8 of each assembly 10 comprises a shaft 80 connected to at least one weight 82 and to a pinion portion 84.

[0040] The pinion portion 84 (or pinion 84) may be conical in shape. In the example of the figure 4 , the pinion portion 84 comprises a cylindrical upstream section 842 and a downstream section 844 flared towards the base 70. The upstream section 842 therefore has a smaller diameter than the downstream section 844. The pinion portion 84, and in particular the downstream section 844, may comprise teeth capable of meshing with the teeth of the toothed wheel portion 72, in particular conical. Thus, the assembly 10 may comprise a toothed pinion portion 72 of the support 76 of the blade root and a toothed pinion portion 84 on the shaft 80 of the counterweight device. The proportion of the pinion portions may be equal to the reduction ratio (or transmission ratio) between the rotation speeds of the shaft of the counterweight device and the blade.

[0041] The shaft 80 is rotatable about an axis B which is substantially perpendicular to the axis A (and substantially parallel to the axis X). In the example of the figure 4 , the shaft 80 is a hollow cylindrical part. The shaft 80 comprises a first cylindrical portion 802 and a second cylindrical portion 804. The upstream section 842 of the pinion portion 84 extends inside the first and second portions 802, 804. Second bearings 86 are interposed between the second portion 804 of the shaft 80 and the upstream section 842 of the pinion portion 84. A third bearing 88 is interposed between the first portion 802 of the shaft 80 and the upstream section 842 of the pinion 84. The second and third bearings 86, 88 are arranged around the upstream section 842 of the pinion portion 84. The second bearings 86 and / or the third bearing 88 may be of the ball bearing type ( figure 4 ), needle roller bearings or other bearing technology. Needle roller bearings are smaller and lighter in relation to the stresses of the counterweight device shaft. These bearings 86, 88 allow the shaft 80 and the pinion portion 84 to be centered and guided around the axis B with respect to the polygonal ring C1. The shaft 80 may be flanged to the ring C1 by a flange 806 which extends radially inward of the axis X.

[0042] On the example of figures 3 et 4 , the weight 82 is connected to the shaft 80 and to the pinion 84 by a clip 820. The weight 82 extends radially outwards from the axis B.

[0043] One of the particularities of the invention is that the portion 72 of the toothed wheel is fixed to the base 70 by at least one or more shear screws 90. The figures 5a à 5c illustrate several embodiments of the fusible screw 90.

[0044] There figure 5a illustrates a first embodiment of the fusible screw 90. The fusible screw 90 is a cylindrical part of revolution extending around a first elongation axis Y. This axis Y corresponds to a screwing axis of the fusible screw 90. This axis Y is substantially parallel to the axis A. The fusible screw 90 comprises a first head 900 and a first body 902. The first body 902 has a cylindrical shape and has a first external diameter D1. The external diameter D1 is measured relative to a radial axis perpendicular to the axis Y. The body 902 comprises a first section 904 and a second section 906 (also called by the term “barrel”). The first section 904 may comprise a thread 905. The second section 906 may have a first length L1 measured relative to the Y axis. The second section 906 is therefore configured to form a preferred zone of rupture in shear and / or in tension.More particularly, the second section 906 may have a smaller section than the first body 902. For this, the second section 906 may comprise an annular groove 908a. This annular groove 908a has a second external diameter D2 less than D1. The annular groove 908a has a first thickness E1 measured relative to the Y axis.

[0045] There figure 5b illustrates a second embodiment of the fusible screw 90. This fusible screw 90 of the figure 5b differs from that of the figure 5a by the second section 906. The second section 906 of the second embodiment also comprises an annular groove 908b which is deep. This annular groove 908b has a third external diameter D3 less than D2. The annular groove 908b has a second thickness E2 greater than E1.

[0046] There figure 5b illustrates a third embodiment of the fusible screw 90. This fusible screw 90 of the figure 5c differs from that of the figures 5a et 5b also by the second section 906. The second section 906 of the third embodiment comprises at least one hole 908c of variable dimension.

[0047] The present application now describes the fusible screw 90 mounted in the assembly 10 of the invention with reference to the figure 6 . Alternatively, several fusible screws 90 may connect the base 70 and the toothed wheel portion 72. For example, the fusible screws 90 may be two to ten in number. Preferably, the portion 72 and the base 70 are connected by approximately two or three fusible screws 90 ( figure 9 ).

[0048] More particularly, the fusible screw(s) 90 are screwed into the first orifices 790, 791 of the base 70 and of the toothed wheel portion 72. The Y axis of each fusible screw 90 is therefore coincident with the first plane PY of each of the first orifices 790, 791.

[0049] The first head 900 of the shear screw 90 bears on the portion 72 of the toothed wheel. The first body 902 passes through the first orifices 790, 791. More particularly, the second section 906 is mounted in the first orifice 791 of the portion 72 of the toothed wheel, and the first section 904 is mounted in the first orifice 790 of the base 70, in particular of the extension 700. By way of example, the first threaded section 904 is screwed in a manner complementary to the tapping of the first orifice 790 of the base 7. In a variant illustrated in the figures 10 et 11 , the first section 904 is mounted in the first orifice 790 and a first clamping nut 94 can be screwed onto the thread 905 of the first section 904 to lock the assembly.

[0050] In this configuration of the figure 6 , the first head 900 is in direct contact with the portion 72 of the toothed wheel, the second section 906 (having the fusible section) is assembled in the portion 72 also and the first section 904 is mechanically linked to the base 7. In the event of blocking of at least one of the elements of the counterweight device 8, the portion 72 meshed by the pinion portion 84 of the counterweight device 8 transmits a torque (or a stress) greater than the tightening torque of the fusible screw 90. In particular, the contact adhesion between the first head 900 and the portion 70 causes the fusible section of the second section 906 to break during the transmission of torque from the portion 72 to the fusible screw 90. This makes it possible to separate the base 70 from the blocked portion 72 of the toothed wheel and the counterweight device 8. This also prevents the base 70, which is integral in rotation with the blade 2, and the entire pitch change mechanism of the blade 2 from being blocked.

[0051] Another feature of the invention lies in the fact that in addition to at least one shear screw 90, the base 70 and the toothed wheel portion 72 are fixed by at least one retention screw 92 (or fixing or retaining screw).

[0052] In reference to the figure 7 , the retention screw 92 is also a cylindrical part of revolution extending around a second elongation axis Z. This axis Z corresponds to a screwing axis of the retention screw 92. This axis Z is substantially parallel to the axes A and Y. The retention screw 92 comprises a second head 920 and a second body 922 of cylindrical shape. The second body 922 comprises a third section 924 and a fourth section 926 (also called by the term “barrel”). The third section 924 may comprise a second thread 925. The fourth section 926 may comprise an annular shoulder 928. This shoulder 928 is located opposite the second head 920 and connected to the third section 924. The fourth section 926 may have a second length L2 measured relative to the axis Z. Preferably, the second length L2 is greater than the first length L1.The second head 920 is configured to form a preferred zone for holding the portion 72 of the toothed wheel in the event of the counterweight device 8 becoming blocked and the portion 72 becoming detached from the base 70.

[0053] Furthermore, the second head 920 of the retention screw 92 can be offset relative to the portion 72 to ensure that the forces nominally pass through the fusible screws 90 and that in the event of seizure it is indeed the fusible screws 90 which break. Finally, to ensure during assembly that the second retention screw head does not come into contact with the portion 72, it is possible to put either a shoulder 928 on the screw 92, or to go to the bottom of the thread of the base 70.

[0054] The present application now describes the retention screw 92 mounted in the assembly 10 of the invention with reference to the figures 8 And 9. Alternatively, several retention screws 92 may connect the extension 700 of the base 70 and the toothed wheel portion 72. Preferably, the assembly 10 comprises the same number of fusible screws 90 and retention screws 92. For example, the retention screws 92 may be two to ten in number. figure 9 illustrates the portion 72 and the base 70 connected by three retention screws 92 and three fusible screws 90.

[0055] More particularly, the retention screw(s) 92 are screwed into the second orifices 792, 793 of the base 70 and of the toothed wheel portion 72. The axis Z of each shear screw 90 is therefore coincident with the second plane Pz of each of the second orifices 792, 793.

[0056] The second head 900 of the shear screw 90 is distant from the toothed wheel portion 72. Indeed, each retention screw 92 is mounted in the second orifices 792, 793 with a minimum clearance J between the second head 900 and the toothed wheel portion 72. For example, the clearance J is between 1 and 5 mm. Preferably, the clearance J is approximately 2 mm. This clearance J may be a compromise to have a minimum of unbalance so that it is detectable, and a maximum to avoid damaging the turbomachine. Thus, the clearance J may depend on the rotational speed and the radial position of the counterweight device. The second body 922 passes through the second orifices 792, 793. More particularly, the fourth section 926 is mounted in the second orifice 793 of the toothed wheel portion 72, and the third section 924 is mounted in the second orifice 792 of the base 70.For example, the third threaded section 924 is screwed in a complementary manner to the threading of the second orifice 792 of the base 70. In a variant illustrated in the . figures 10 et 11 , the third section 924 is mounted in the second hole 792 and a second clamping nut 96 can be screwed onto the thread 925 of the third section 924 to lock the assembly.

[0057] In reference to the figure 9 , the fusible screws 90 are arranged in a staggered pattern relative to the retention screws 92. This makes it possible to form a sufficient support polygon to ensure a balance of loads in the screws 90, 92 and to obtain a reduced size.

[0058] In this configuration of the figure 8 or of the figure 9 , the second head 920 is not in direct contact with the portion 72 of the toothed wheel, the fourth section 926 is mounted in the portion 72 with the annular shoulder 928 bearing on the base 70 and the third section 924 is mechanically connected to the base 70. When the fusible screw(s) 90 are unbroken and intact (in particular in normal operation without blocking of the counterweight device 8), the second head 920 is distant from the portion 72 of the toothed wheel. When the fusible screw(s) 90 are broken (in particular in the event of blocking of at least one of the elements of the counterweight device 9), the portion 72 becomes detached from the base 70. The detached portion 72 comes into abutment against the second head 920. The second head 920 is therefore able to retain the detached portion 72. This prevents the detached portion 72 (then considered to be debris) from being released and projected into the operating turbomachine.

[0059] THE figures 10 et 11 illustrate two other variants of the assembly 10 of the figure 8 .

[0060] Set 10 of the figure 10 differs from set 10 of the figure 8 by the use of the first 94 and second 96 tightening nuts, respectively, of the first section 904 of the fusible screw 90 and of the third section 924 of the retention screw 92. In the example of the figure 10 , the threads 905, 925 of the first 904 and third 924 sections and the first 94 and second 96 nuts are arranged outside the base 70.

[0061] In reference to the figure 11 , the toothed wheel portion 72 of the assembly 10 may further comprise first 910 and second 930 counterbores. The first counterbore(s) 910 are configured to receive the first head 900 of the fuse screws 90. The second counterbore(s) 930 are configured to receive the second head 920 of the retention screws 92. In the example of the figure 11, the first counterbore(s) 910 comprise an annular groove 980 (relative to the Y axis). The annular groove 980 is preferably located above and distant from the first head 900 of screw 90. This groove 980 may comprise a circlip (or elastic ring), so as to prevent the first head 900 of shear screw 90, once it has been separated from the base 70, from being thrown out of the assembly 10 into the compartment of the turbomachine.

Claims

1. An assembly (10) for a propeller (S) of a turbine engine of an aircraft, this assembly (10) comprising: - a variable-pitch vane (2) comprising a blade (20) connected to a root (22), the vane (2) comprising a longitudinal axis coincident with a pitch axis (A) of the vane (2) which passes through said root (22), - a base (70) secured in rotation to the vane (2) about the pitch axis (A) and connected to a toothed wheel portion (12) extending about this pitch axis (A), and - a counterweight device (8) comprising a shaft (80) movable in rotation about a substantially concurrent axis (B) perpendicular to said pitch axis (A), this shaft (80) being connected to at least one weight (82) and to a pinion portion (84) geared with the toothed wheel portion (72), characterised in that the toothed wheel portion (72) is attached to said base (70) by at least one shear bolt (90).

2. The assembly (10) according to claim 1, characterised in that the toothed wheel portion (72) is attached to said base (70) by a plurality of shear bolts (90).

3. The assembly (10) according to claim 1 or 2, characterised in that the or each shear bolt (90) extends along a first axis of elongation (Y) which is parallel to said pitch axis (A).

4. The assembly (10) according to any one of the preceding claims, characterised in that the or each shear bolt (90) comprises a first head (900) bearing on said toothed wheel portion (72), and a first body (902) which passes through first orifices (790, 791) of this portion (72) and of the base (70).

5. The assembly (10) according to the preceding claim, characterised in that said first body (902) comprises a first segment (904) threaded and screwed into the first orifice (790) of the base (70), which is tapped, and a second segment (906) defining a smaller section of the first body (902).

6. The assembly (10) according to the preceding claim, characterised in that the second segment (906) comprises an annular groove (908a).

7. The assembly (10) according to claim 5, characterised in that the second segment (906) comprises at least one hole (908c).

8. The assembly (10) according to any one of the preceding claims, characterised in that it further comprises at least one retention screw (92) for retaining the toothed wheel portion (72) on the base (70), the or each retention screw (92) being non-functional as long as said at least one shear bolt (90) is unbroken and the or each retention screw (92) being functional when said at least one shear bolt (90) is broken.

9. The assembly (10) according to the preceding claim, characterised in that the or each retention screw (92) comprises a second head (920) which is configured, on the one hand, to be at a distance from the toothed wheel portion (72) when said at least one shear bolt (90) is not broken, and, on the other hand, to be able to come to bear on and retain the toothed wheel portion (72) when said at least one shear bolt (90) is broken.

10. The assembly (10) according to claim 8 or 9, characterised in that the or each retention screw (92) extends along a second axis of elongation (Z) which is parallel to said pitch axis (A).

11. The assembly (10) according to any one of claims 8 to 10, characterised in that the or each retention screw (92) comprises a second body (922) which passes through second orifices (792, 793) in the toothed wheel portion (72) and in the base (70).

12. The assembly (10) according to the preceding claim, characterised in that said second body (922) comprises a third segment (924) threaded and screwed into the second orifice (792) of the base (70), which is tapped, and a fourth non-threaded segment (926) engaged in the second orifice (793) of the toothed wheel portion (72).

13. The assembly (10) according to any one of claims 8 to 12, characterised in that the shear bolts (90) are staggered with the retention screws (92).

14. A propeller (S) for a turbine engine (1), in particular for an aircraft, comprising several assemblies (10) according to any one of the preceding claims.