PROPELLER FOR A TURBINE ENGINE OF AN AIRCRAFT WITH A VARIABLE-PITCH VANE AND A GEARED COUNTERWEIGHT DEVICE

An assembly for a propeller of a turbine engine of an aircraft is provided. The assembly includes a variable-pitch vane having a blade connected to a root, the vane having a longitudinal axis aligned with a vane pitch axis which passes through the root, a base rigidly connected to the vane to rotate together with the vane about the axis and connected to a portion of a toothed wheel extending around the axis, and a counterweight device having a shaft which can rotate about an axis substantially perpendicular to the axis, the shaft being connected to at least one flyweight and to a pinion meshed with the toothed wheel portion. The toothed wheel portion can be attached to the base by at least one shear pin.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to the field of the aircraft turbine engines and in particular to the propulsive propellers of such turbine engines, which comprise variable-pitch vanes with a geared counterweight device.

TECHNICAL BACKGROUND

The prior art comprises in particular the documents FR-A1-3 009 710 and FR-A1-3 057 909.

An aircraft turbine engine propeller can be shrouded (FIG.1), as in the case of a fan for example, or unshrouded (FIG.2), as in the case of an open-rotor architecture for example.

A propeller comprises vanes which may be pitch variable. The turbine engine then comprises a mechanism allowing to modify the angle of pitch of the vanes in order to adapt the thrust generated by the propeller to different phases of flight. The angular pitch setting of the propeller vanes also allows to optimise the efficiency of the propeller as a function of the speed of the aircraft and to optimise the pumping margin of the turbine engine to reduce its fuel consumption in the different phases of flight.

As a reminder, the pitch angle of a propeller vane corresponds to the angle, in a longitudinal plane perpendicular to the axis of rotation of the propeller vane, between the vane chord and the plane of rotation of the fan or of the engine of the turbine engine.

The variable pitch propeller vanes can occupy a reverse thrust position in which they generate counter-thrust to help slow down the aircraft, and a feathered position in which, in the event of failure or breakdown, they allow to limit their aerodynamic resistance and/or drag. The consequences of this drag could be in terms of flight safety in the event of loss of control of the aircraft if its vertical stabilizer is not dimensioned for this, and could be in terms of performance for the possible duration of the single-engine diversion flight.

Numerous devices have been imagined to vary the pitch of the propeller vanes, which generally comprise a rotation of the vane about its main axis (corresponding to a pitch axis of the vane) by means of a control system located radially inside the roots of the vanes. This control system comprises, for example, an actuator which may be connected to the roots of the vanes by connecting rods and/or a linkage.

One of the stresses of the control system for controlling the pitch setting of the propeller vanes is to bring the vanes into the predetermined position, referred to as the “feathered position”, in the event of a failure of this pitch setting system. The feathering allows to minimise the aerodynamic drag.

Traditionally, the feathering is achieved by direct counterweight devices whose inertia, which is much greater than that of the propeller vanes, must ensure that the return of the latter to the pre-defined feathered position. A counterweight device is generally associated with each of the vanes. The counterweight device may comprise a shaft movable in rotation, for example, about an axis perpendicular to the pitch axis of the vane. Depending on the type of gearing used in the counterweight device, the gearing may be perpendicular and/or concurrent with the pitch axis of the vane. Conventionally, the conical pinion gearing of the counterweight device extends along an axis that at least coincides with the pitch axis of the vane. The movable shaft of the counterweight device is connected to a weight and therefore to a conical pinion, which is meshed with a portion of the toothed wheel that is secured in rotation with the vane (FIG.3). The shaft is generally centred and guided in rotation by at least one bearing, for example a ball bearing (FIG.4).

However, a seizure of the conical pinion or of one of the bearings of the counterweight device can cause the blocking of the kinematics of the counterweight device. To avoid blocking the assembly of the vane pitch setting mechanism, it may be necessary to add a section referedded to as a shear section. This shear section can be associated with the control system. By way of example, the shear section can be on one of the connecting rods for connecting to the actuator or on the rod for connecting to the actuator. However, this solution has the disadvantage of losing the actuation of one of the vanes, which remains blocked in its current operating position. This blockage can cause a mechanical and aerodynamic imbalance, and can lead to an active feathering and in-flight incidents such as an IFSD (In Flight Shut Down). This can generally limit the operability and the performances of the turbine engine and of the aircraft.

In this context, it is interesting to overcome the disadvantages of the prior art, by integrating a simple and effective safety function on a variable vane and its counterweight device.

SUMMARY OF THE INVENTION

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

To this end, the invention relates to an assembly for an aircraft turbine engine propeller, the assembly comprising:a variable pitch vane comprising a blade connected to a root, the vane comprising a longitudinal axis coincident with a pitch axis A of the vane which passes through said root,a base secured in rotation to the vane about the pitch axis A and connected to a toothed wheel portion extending about this pitch axis A, anda counterweight device comprising a shaft movable in rotation about a substantially concurrent axis B perpendicular to said pitch axis A, this shaft being connected to at least one weight and to a pinion portion geared with the toothed wheel portion.

According to the invention, the toothed wheel portion is attached to said base by at least one shear bolt.

The axis B may be substantially perpendicular to and/or concurrent with the pitch axis A.

The incorporation of at least one shear bolt allows the toothed wheel portion to become disengaged from the base, which is secured in rotation to the variable pitch vane in the event of failure of the counterweight device. More specifically, when the kinematic of the counterweight device is blocked (such as by a seizure of the conical pinion or the bearings), a significant force is applied to the portion of the toothed wheel geared by means of the pinion of the counterweight device, so that the shear bolt breaks. By way of example, the shear bolt is dimensioned to break as a result of shear and/or tensile overstress exerted by the pinion of the blocked counterweight device. The breaking and the disengagement of the toothed wheel portion of the base allows to free the pitch actuation kinematic of the assembly of the vanes, so that the assembly of the pitch change mechanism is not blocked. This allows to prevent a mechanical and aerodynamic imbalance on the vane due to the blocked counterweight device. As a result, the variable pitch vane and its base are effectively protected in the event of failure of the associated counterweight device.

The assembly according to the invention may comprise one or more of the following characteristics, taken alone from each other, or in combination with each other:the toothed wheel portion is attached to said base by several shear bolts;the or each shear bolt extends along a first axis of elongation Y which is parallel to said pitch axis A;the or each shear bolt comprises a first head bearing on said toothed wheel portion, and a first body which passes through first orifices in this portion and in the base;said first body comprises a first segment threaded and screwed into the first orifice of the base, which is tapped, and a second segment defining a smaller section of the first body;the second segment comprises an annular groove;said annular groove has a second or third diameter D2, D3smaller than a first diameter of the first body and a variable first or second thickness, the diameters D1to D3being measured with respect to an axis perpendicular to the axis Y and the thicknesses E1, E2being measured with respect to the axis Y;the second segment comprises at least one hole;the assembly further comprises at least one retention screw for retaining the toothed wheel portion on the base, the or each retention screw being non-functional as long as the at least one shear bolt is unbroken and the or each retention screw being functional when said at least one shear bolt is broken,the or each retention 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 bolt is not broken, and on the other hand, to be capable of coming to bear on and retaining the toothed wheel portion when said at least one shear bolt is broken;the or each retention screw extends along a second axis of elongation Z which is parallel to said pitch axis A;the or each retention screw comprises a second body which passes through second orifices in the toothed wheel portion and in the base;said second body comprises a third segment threaded and screwed into the second orifice of the base, which is tapped, and a fourth non-threaded segment engaged in the second orifice of the toothed wheel portion;the shear bolts are staggered with the retention screws.

The present invention also relates to a propeller for a turbine engine, in particular of an aircraft, comprising several assemblies as described above.

The propeller can be either a shrouded propeller or an unshrouded propeller.

The present invention also relates to a turbine engine, in particular for an aircraft, comprising at least one propeller or several assemblies as described above.

The turbine engine may be a turbojet or a turboprop.

DETAILED DESCRIPTION OF THE INVENTION

By convention in the present application, the terms “inside” and “outside”, and “internal” and “external” are defined radially with respect to a longitudinal axis (which may correspond to a longitudinal axis X of a turbine engine). A cylinder extending along this longitudinal axis therefore comprises an inner face facing the axle 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 “transversal” means any direction perpendicular to this longitudinal axis. Similarly, the terms “upstream” and “downstream” are defined in relation to the direction of air flow in the turbine engine, which is represented by an arrow F.

Conventionally, a turbine engine1(FIG.1or2) comprises a gas generator G (or engine) upstream of which is mounted a fan module S. The turbine engine1extends along a longitudinal axis X.

In general, and for the remainder of the description, the term “fan module” is used to refer either to a fan or a propeller, and the vanes of the fan or of the propeller may be shrouded (for example, in the turbofan engines shown inFIG.1) or unshrouded (for example, in the turboprop engines shown inFIG.2).

FIGS.1and2illustrate two types of turbine engine1, each intended to be mounted on an aircraft.

More specifically,FIG.1schematically illustrates a double flow turbine engine1comprising a module of fan S with a shrouded propulsive propeller. The gas generator G of the turbine engine1comprises, from upstream to downstream, a low-pressure compressor3a, a high-pressure compressor3b, an annular combustion chamber4, a high-pressure turbine5b, a low-pressure turbine5aand an exhaust nozzle6.

FIG.2provides a schematic illustration of an open-rotor turbine engine1comprising a fan module S with unshrouded propulsive propellers. In the example shown inFIG.2, the fan module S is downstream of the gas generator G. Alternatively (not illustrated), the fan module S with doublet propeller can be upstream of the gas generator G of the turbine engine. The gas generator G of the turbine engine1comprises, from upstream to downstream, a low-pressure compressor3a, a high-pressure compressor3b, an annular combustion chamber4, a high-pressure turbine5b, an intermediate-pressure turbine5c, first and second free power turbines5d,5eand an exhaust nozzle6.

The first and second free turbines5d,5eform a doublet of counter-rotating turbines to drive the unshrouded propellers S in counter-rotation. First and second rotating structural devices21,22are located axially between the first and second free turbines5d,5e. Each rotating structural device21,22is connected to one of the propellers S and to a stationary shaft20′. This stationary shaft20′ is centred on the axis X and forms a stationary casing for the free turbines5d,5e. In the example shown inFIGS.1and2, the high-pressure compressor3band the high-pressure turbine5bare connected by a high-pressure shaft50and together form a high-pressure (HP) body. The low-pressure compressor3aand the low-pressure turbine5aor the intermediate-pressure turbine5care connected by a low-pressure shaft30and together form a low-pressure (LP) body.

InFIG.1, the fan S is driven by a fan shaft20which is coupled to the LP shaft30by means of a speed reducer40. Whereas inFIG.2, gases from the primary duct escaping from the intermediate turbine5crotate the free turbines5d,5e, the rotating structural devices21,22and therefore the propellers S.

The invention is generally applicable to a propeller or a fan S which is either shrouded (FIG.1) or unshrouded (FIG.2).

The propeller or the fan S comprises a plurality of variable pitch vanes2. Each vane2comprises a blade20connected to a root22(FIG.4). The blade20has an aerodynamic profile and comprises an intrados and an extrados which are connected by an upstream leading edge and a downstream trailing edge (not shown). The blade20has an upper end which is free, referred to as summit, and a lower end which is connected to the root22.

The root22defines a pitch axis A which corresponds substantially to a longitudinal axis of the vane2and of the blade20. The pitch axis A is an axis about which the angular position of the vane2is adjusted. This axis A is also generally a radial axis (substantially perpendicular to the axis X) which therefore extends along a radius in relation to the axis of rotation of the propeller S equipped with this vane2.

The angular position of each of the blades20about their axis A can be ensured by a control system200for controlling the propeller S. The control system200may comprise a single actuator for all the vanes2of the propeller. By way of example, this actuator (not shown) can be connected to connecting rods at the roots22or to a rod which acts on pinions attached to the vanes2, in particular by surrounding the roots22. The propeller S also comprises a polygonal annulus C1to support the blades20, this annulus C1forming a propeller hub (FIGS.3and4). The polygonal annulus C1can be connected to a casing C2or a stationary structure of the turbine engine1. The annulus C1comprises a plurality of housings74spaced circumferentially from one another, these housings74being radial housings (with respect to the axis X). Each of the housings74extends around the axis A and is configured to receive a support76for the root22of vane.

InFIG.4, the support76comprises an annular wall762. This annular wall762comprises a lower end766closed by a bottom wall768, and an upper axial end764which is open and configured to allow the root22of the vane2to be mounted inside the housing74. The bottom wall768is configured to cooperate in a form-fitting manner with a free end24of the root22, so that the housing74is secured in rotation with the root22about the axis A.

First bearings78are interposed between each housing74and the annular wall762of the support76of the vane root, in particular to ensure the centring and the guiding of the support76about the axis A with respect to the polygonal annulus C1and/or a stationary structure of the turbine engine1.

With reference toFIGS.3and4, the propeller S comprises several assemblies10. In the present application, an assembly10is taken to mean some of the elements making up the propeller S. Thus, an assembly10comprises a variable-pitch vane2, a base70and a counterweight device8associated with the vane2.

The base70of each assembly10is configured to be secured in rotation with the vane2about the axis A. In the example shown inFIG.4, the base70is mounted on the annular wall762of each support76and above each housing74.

In the example shown inFIGS.6,8and9, the base70comprises an extension700which extends substantially perpendicular to the axis A. This extension700is a radial extension (relative to the axis A) of the body of the base70. The extension700comprises at least one first orifice790passing through a first plane Py (FIGS.6and8). The extension700may also comprise at least one second orifice792passing through a second plane Pz (FIG.8). The first and second planes PY, Pz are substantially parallel to the axis A. The first plane Py may be upstream of the second plane Pz and/or vice versa.

The base70is connected to a toothed wheel portion72which also extends around the axis A. In the example shown inFIG.3, this portion72may be an angular sector extending circumferentially around the axis A. The angular sector of the portion72may be between 30° and 150°, preferably between 90° and 130°. The angular sector of the portion72can vary according to the pitch range of the pitch axis of the vane, depending on a shrouded propeller or on an unshrouded propeller. The toothed wheel portion72may comprise toothings configured to gear with toothings of the counterweight device8. This portion72may therefore be conical.

In the example shown inFIGS.6,8and9, the portion72comprises at least one first orifice791passing through the first plane Py. The portion72may also comprise at least one second orifice793passing through the second plane Pz. In the examples, the first orifices790,791of the base70and of the portion72are aligned with respect to the first plane Py and the second orifices792,793are aligned with respect to the second plane Pz.

The counterweight device8of each assembly10comprises a shaft80connected to at least one weight82and to a pinion portion84.

The pinion portion84(or pinion84) can be conical in shape. In the example shown inFIG.4, the pinion portion84comprises a cylindrical upstream segment842and a downstream segment844flared towards the base70. The upstream segment842therefore has a smaller diameter than the downstream segment844. The pinion portion84, and in particular the downstream segment844, may comprise toothing suitable for gearing with the toothings of the toothed wheel portion72, in particular conical. For example, the assembly10may comprise a toothed pinion portion72on the support76of the vane root and a toothed pinion portion84on the shaft80of the counterweight device. The proportion of the pinion portions can be equal to the reduction ratio (or transmission ratio) between the rotational speeds of the shaft of the counterweight device and of the vane.

The shaft80is movable in rotation about an axis B which is substantially perpendicular to the axis A (and substantially parallel to the axis X). In the example shown inFIG.4, the shaft80is a hollow cylindrical part. The shaft80comprises a first cylindrical portion802and a second cylindrical portion804. The upstream segment842of the pinion portion84extends inside the first and second portions802,804. Second bearings86are interposed between the second portion804of the shaft80and the upstream segment842of the pinion portion84. A third bearing88is interposed between the first portion802of the shaft80and the upstream segment842of the pinion84. The second and third bearings86,88are arranged around the upstream segment842of the portion of the pinion84. The second bearings86and/or the third bearing88can be of the ball bearing type (FIG.4), needle rollings or other bearing technology. The needle rolling bearings are smaller and lighter in relation to the stresses on the shaft of the counterweight device. These bearings86,88allow the shaft80and the pinion portion84to be centred and guided about the axis B with respect to the polygonal annulus C1. The shaft80can be flanged to the annulus C1by a flange806which extends radially inwards from the axis X.

In the example shown inFIGS.3and4, the weight82is connected to the shaft80and to the pinion84by a clip820. The weight82extends radially outwards from the axis B.

One of the particularities of the invention is that the toothed wheel portion72is attached to the base70by at least one or more shear bolts90.FIGS.5ato5cillustrate several different embodiments of the shear bolt90.

FIG.5ashows a first embodiment of the shear bolt90. The shear bolt90is a cylindrical revolution part extending around a first axis of elongation Y. This axis Y corresponds to a screwing axis of the shear bolt90. This axis Y is substantially parallel to the axis A. The shear bolt90comprises a first head900and a first body902. The first body902is cylindrical in shape and has a first external diameter D1. The external diameter D1is measured with respect to a radial axis perpendicular to the axis Y. The body902comprises a first segment904and a second segment906(also referred to as the “barrel”).

The first segment904may comprise a thread905. The second segment906may have a first length L1measured with respect to the axis Y. The second segment906is therefore configured to form a preferred shear and/or tensile fracture area. In particular, the second segment906may have a smaller section than the first body902. To achieve this, the second segment906may comprise an annular groove908a. This annular groove908ahas a second external diameter D2smaller than D1. The annular groove908ahas a first thickness E1measured with respect to the axis Y.

FIG.5billustrates a second embodiment of the shear bolt90. This shear bolt90inFIG.5bdiffers from that inFIG.5ain the second segment906. The second segment906of the second embodiment also comprises a deep annular groove908b. This annular groove908bhas a third external diameter D3smaller than D2. The annular groove908bhas a second thickness E2greater than E1.

FIG.5billustrates a third embodiment of the shear bolt90. This shear bolt90inFIG.5calso differs from that inFIGS.5aand5bin the second segment906. The second segment906of the third embodiment comprises at least one hole908cof variable size.

The present application now describes the shear bolt90mounted in the assembly10of the invention with reference toFIG.6. Alternatively, several shear bolts90can connect the base70and the toothed wheel portion72. For example, there may be between two and ten shear bolts90. Preferably, the portion72and the base70are connected by approximately two or three shear bolts90(FIG.9).

More particularly, the shear bolt or bolts90are screwed into the first orifices790,791of the base70and the toothed wheel portion72. The axis Y of each shear bolt90therefore coincides with the first plane Py of each of the first orifices790,791.

The first head900of the shear bolt90rests on the toothed wheel portion72. The first body902passes through the first orifices790,791. More particularly, the second segment906is mounted in the first orifice791of the toothed wheel portion72, and the first segment904is mounted in the first orifice790of the base70, in particular of the extension700. By way of example, the first threaded segment904is screwed in a complementary manner to the tapping of the first orifice790in the base7. Alternatively, as shown inFIGS.10and11, the first segment904is mounted in the first orifice790and a first tightening nut94can be screwed onto the thread905of the first segment904to lock the assembly.

In this configuration shown inFIG.6, the first head900is in direct contact with the toothed wheel portion72, the second segment906(with the fusible section) is also assembled in the portion72and the first segment904is mechanically linked to the base7. If at least one of the elements of the counterweight device8blocks, the portion72geared by the pinion portion84of the counterweight device8transmits a torque (or a stress) greater than the tightening torque of the shear bolt90. In particular, the contact adhesion between the first head900and the portion70causes the fusible section of the second segment906to break when torque is transmitted from the portion72to the shear bolt90. This allows the base70to be disengaged from the locked toothed wheel portion72and the counterweight device8. This also prevents the base70, which is secured in rotation to the vane2, and the assembly of the pitch change mechanism for changing the pitch of the vane2from being blocked.

Another particularities of the invention lies in the fact that, in addition to at least one shear bolt90, the base70and the toothed wheel portion72are attached by at least one retention screw92(or attachment or retaining screw).

With reference toFIG.7, the retention screw92is also a cylindrical revolution part extending around a second axis of elongation Z. This axis Z corresponds to the screwing axis for screwing the retention screw92. This axis Z is substantially parallel to the axes A and Y. The retention screw92comprises a second head920and a second cylindrical body922. The second body922comprises a third segment924and a fourth segment926(also referred to as the “barrel”). The third segment924may comprise a second thread925. The fourth segment926may comprise an annular shoulder928. This shoulder928is located opposite the second head920and connected to the third segment924. The fourth segment926may have a second length L2measured with respect to the axis Z. Preferably, the second length L2is greater than the first length L1. The second head920is configured to form a preferred area for holding the toothed wheel portion72in the event of the counterweight device8blocking and the portion72becoming disengaged from the base70.

In addition, the second head920of the retention screw92can be offset relative to the portion72to ensure that the nominal forces pass through the shear bolts90and that, in the event of seizure, it is the shear bolts90that break. Finally, to ensure during assembly that the second retention screw head is not brought into contact with the portion72, it is possible to fit either a shoulder928on the screw92, or to go to the bottom of the tapping of the base70.

The present application now describes the retention screw92mounted in the assembly10of the invention with reference toFIGS.8and9. Alternatively, several retention screws92can connect the extension700of the base70and the toothed wheel portion72. Preferably, the assembly10comprises the same number of shear bolts90and retention screws92. For example, there may be between two and ten retention screws92.FIG.9shows the portion72and the base70connected by three retention screws92and three shear bolts90.

More specifically, the retention screw or screws92are screwed into the second orifices792,793of the base70and into the toothed wheel portion72. The axis Z of each shear bolt90is therefore coincident with the second plane Pz of each of the second orifices792,793.

The second head900of the shear bolt90is at a distance from the toothed wheel portion72. Each retention screw92is mounted in the second orifices792,793with a minimum clearance J between the second head900and the toothed wheel portion72. By way of example, the clearance J is between 1 and 5 mm. Preferably, the clearance J is about 2 mm. This clearance J may be a compromise between having a minimum of unbalance so that it is detectable, and a maximum to avoid damaging the turbine engine. In this way, the clearance J can depend on the speed of rotation and on the radial position of the counterweight device. The second body922passes through the second orifices792,793. More particularly, the fourth segment926is mounted in the second orifice793of the toothed wheel portion72, and the third segment924is mounted in the second orifice792of the base70. By way of example, the third threaded segment924is screwed in a complementary manner to the tapping of the second orifice792in the base70. Alternatively, as shown inFIGS.10and11, the third segment924is mounted in the second orifice792and a second tightening nut96can be screwed onto the thread925of the third segment924to lock the assembly.

With reference toFIG.9, the shear bolts90are staggered in relation to the retention screw92. This allows to form a polygon of sustentation sufficient to ensure a balance of loads in the screws90,92and to obtain a reduced overall dimension.

In this configuration ofFIG.8orFIG.9, the second head920is not in direct contact with the toothed wheel portion72, the fourth segment926is mounted in the portion72with the annular shoulder928bearing on the base70and the third segment924is mechanically linked to the base70. When the shear bolt or bolts90are unbroken and intact (in particular in normal operation without blocking the counterweight device8), the second head920is at a distance from the toothed wheel portion72. When the shear bolt or bolts90are broken (in particular if at least one of the elements of the counterweight device9is blocked), the portion72becomes disengaged from the base70. The disengaged portion72comes into abutment against the second head920. The second head920is therefore able to retain the disengaged portion72. This prevents the disengaged portion72(considered as a debris) from being released and projected into the turbine engine during operation.

FIGS.10and11illustrate two other variants of embodiment of the assembly10shown inFIG.8.

The assembly10inFIG.10differs from the assembly10inFIG.8by the use of the first94and second96nuts for tightening, respectively, the first segment904of the shear bolt90and the third segment924of the retention screw92. In the example shown inFIG.10, the threads905,925of the first904and third924segments and the first94and second96nuts are arranged outside the base70.

With reference toFIG.11, the toothed wheel portion72of the assembly10may further comprise first910and second930counterbores. The first counterbore or counterbores910are configured to receive the first head900of the shear bolt90. The second counterbore or counterbores930are configured to receive the second head920of the retention screws92. In the example shown inFIG.11, the first counterbore or counterbores910comprise an annular gorge980(relative to the axis Y). The annular gorge980is preferably located above and at a distance from the first head900of screw90. This gorge980may comprise a circlip (or elastic annulus), so as to prevent the first head900of shear bolt90, once it has been disengaged from the base70, from being projected out of the assembly10into the compartment of the turbine engine.