BALANCING SYSTEM FOR VARIABLE PITCH BLADE FAN MODULE

Abstract

The invention relates to a balancing system for a fan module (1) having several blade pitch configurations that differ from one another, each generating an unbalance, the balancing system comprising: - a first balancing disc (110) and a second balancing disc (120), each movable in rotation about a main axis (C) and having a center of gravity eccentric with respect to the main axis, - at least one first rotary actuator (115) and at least one second rotary actuator (125), each configured respectively to rotate the first and second balancing discs about the main axis, - a control system (130) configured to control each actuator (115, 125) to rotate the first and second discs (110, 120) of the balancing system so as to compensate for the unbalance generated by the blade pitch configuration of the fan module. Figure for abstract: Figure 4

Description

Title of the invention: BALANCING SYSTEM FOR A VARIABLE-PITCH BLADE FAN MODULE Technical field

[0001] The present invention relates to a variable-pitch fan module for a propulsion unit, and more specifically to a balancing system adapted to such a fan as well as a method for balancing such a variable-pitch fan module. Prior art

[0002] A fan equipped with variable pitch blades (known by the English acronym VPF for "Variable Pitch Fan") makes it possible to adjust the pitch of the blades, and more precisely the pitch angle of the blades, according to the flight parameters, and thus to optimize the operation of the fan, and generally of the propulsion unit in which such a fan is integrated. As a reminder, the pitch angle of a blade corresponds to the angle, in a longitudinal plane perpendicular to the axis of rotation of the blade, between the chord of the blade and the plane of rotation of the fan.

[0003] It is known to have pitch change systems adapted to propulsion units or turbomachines generally comprising a shrouded fan or an unshrouded propeller equipped with variable pitch moving blades.

[0004] In the category of turbomachines with at least one unducted propeller, also called by the English term "open rotor" or "unducted fan", there are those having a single unducted propeller and a rectifier comprising several stator blades (known by the English acronym USF for "Unducted Single Fan").

[0005] An “open rotor” type turbine engine mainly comprises, inside a fixed cylindrical casing carried by the structure of the aircraft, a coaxial “gas generator” part and a “propulsion” part. The gas generator part can be arranged upstream or downstream of the propulsion part. The terms “upstream” and “downstream” are defined in relation to the circulation of gases in the turbine engine. The propulsion part comprises at least one propeller driven in rotation by a turbine, in particular a low-pressure turbine, of the gas generator part via a reduction gear, for example, with epicyclic gear trains. In certain cases, the propulsion part can comprise two coaxial and counter-rotating propellers, respectively upstream and downstream, which are driven, in rotation opposite to each other, by the turbine of the gas generator via the reduction gear. The propeller(s) extend substantially radially with respect to the transmission shaft with a longitudinal axis outside the casing.

[0006] Generally, the or each propeller comprises a substantially cylindrical rotating casing carrying an outer polygonal ring hub rotatably received around the longitudinal axis in the stator of the turbomachine. The ring comprises radial cylindrical housings distributed on its periphery around the longitudinal axis. Shafts with radial axes, perpendicular to the longitudinal axis of the turbomachine, integral with the roots of the blades are received in the housings of the polygonal rings and also pass through radial passages of the cylindrical casing.

[0007] To enable the turbine engine to operate optimally according to the different flight phases encountered, the propeller blades can rotate in the radial housings of the polygonal rings. For this, they are rotated around their respective pivot axes, called the pitch axis, by an appropriate system making it possible to vary the pitch of the blades during flight, i.e. the pitch of the propellers.

[0008] This system for changing the pitch of the propeller blades covers an angular range of rotation between two extreme positions, namely an extreme position called thrust reversal or "reverse" for which the blades protrude for example by 30° the plane transverse to the axis of the turbine engine (the direction of advance of the aircraft) to participate in the braking of the aircraft, in the manner of conventional thrust reversers, and an extreme position called "feathering" for which the blades are then retracted as much as possible relative to the direction of advance, for example, in the event of engine failure or during a failure (or breakdown) of the blade pitch control device (for example a failure of a hydraulic actuator) so that the latter offer the least resistance (drag) possible.

[0009] Generally, a system for changing the pitch of the blades of a propeller comprises a control device and a linkage mechanism connecting the control device to each blade of the propeller to ensure the desired angular pivoting of the blades.

[0010] In addition, a passive feathering system is provided to compensate for a failure of the hydraulic system or the cylinder. The feathering of the blades is generally carried out via counterweights. Usually, the counterweights are placed on the root of each blade and are potentially very heavy depending on the available space and come to load centrifugally and therefore increase the constraints of the root of the blades and the bearings of the root of the blades already under heavy stress.

[0011] Different solutions have been proposed for changing the pitch of the blades of a fan and for feathering the blades on “open rotor” or other type turboshaft engines.

[0012] For example, document FR 3 066 559 discloses a blade pitch change system comprising a single annular cylinder arranged on a fixed casing or stator. internal to the fan hub and a connecting mechanism comprising a transfer bearing, better known by the English acronym LTB for "Load Transfer Bearing", fixed on one side to the moving part of the cylinder and cooperating, on the other side, with a means of connecting the mechanism to the blades of the rotating hub, in such a way that the load transfer bearing of the mechanism driven in rotation transmits the translational movement of the moving part of the fixed cylinder, by means of connecting the rotating mechanism to change the orientation of the propeller blades. This pitch change system further comprises a blade feathering device comprising counterweights with a lever mechanism arranged in the rotating reference, connected to the outer ring of the load transfer bearing by a connecting rod.The use of counterweights with a lever mechanism acting on the cylinder makes it possible to multiply the force and to take advantage of an empty space to reduce the mass of the counterweights and not to stress the base of the blades. Having a linear actuator in a fixed reference makes it easier to supply it with oil and to reduce the rotating masses.

[0013] However, after assembly, the lever feathering device and consequently the engine requires balancing at the end of production. This balancing is typically done by installing balancing weights on the fan disc at the upstream cone. This balancing makes it possible to compensate for the residual unbalance of the fan. It is based on the assumption that this residual unbalance is always the same regardless of the operating point of the engine. Consequently, compensation for this residual unbalance on the ground is sufficient to balance the fan in all operating modes of the engine.

[0014] This assumption is no longer valid in the case of a variable-pitch fan or propeller. Indeed, changing the pitch of the fan blades or propeller blades changes the position of their center of gravity which, in particular for wide-chord blades / blades, is not exactly on the pivot axis. This results in an unbalance resulting from the bladed wheel which varies with the pitch. If this variation is too great, it is then impossible to guarantee acceptable balancing of the engine at all operating points. However, poor balancing of the engine can lead to discomfort linked to vibrations in the cabin, or even to excessive loads.

[0015] The objective of the present invention is thus to propose a blower module making it possible to overcome at least some of these drawbacks. Summary of the invention

[0016] To this end, the invention relates to a balancing system for a fan module with variable-pitch blades, the fan module having an axis longitudinal and several blade pitch configurations different from each other, each pitch configuration generating an imbalance.

[0017] According to the invention, the balancing system comprises: - a first balancing disc and a second balancing disc, each movable in rotation about a main axis intended to be collinear with the longitudinal axis and each having a center of gravity eccentric with respect to the main axis, - at least one first rotary actuator and at least one second rotary actuator, each configured respectively to rotate the first and second balancing discs about the main axis, - a control system configured to control each first actuator and each second actuator to rotate the first and second discs of the balancing system so as to compensate for the imbalance generated by the pitch configuration of the blades of the fan module.

[0018] The invention thus proposes a balancing system for any fan module with variable pitch blades allowing it to be balanced at all operating points of the engine. This is intended to be integrated into the fan module.

[0019] Such a balancing system advantageously makes it possible to generate a corrective unbalance making it possible to compensate for an unbalance generated by the variable pitch of the blades of the fan module regardless of the pitch configuration of the blades, i.e. regardless of the pitch angle of the blades. Thus, this corrective unbalance compensates for the unbalance resulting from the bladed wheel which varies with the pitch at any operating point.

[0020] For this purpose, the balancing system according to the invention comprises two rotating balancing discs with an eccentric center of gravity, the simultaneous rotation of which is guided by the pitch angle of the blades. Indeed, according to the invention, the rotation of the two balancing discs is advantageously either programmed as a function of the pitch angle of the blades, or automated as a function of the pitch angle of the blades

[0021] Although the unbalance correction is passive since there is no feedback loop, it adapts to the different blade pitches.

[0022] The balancing system 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 according to all technically possible combinations: - the first balancing disc has a first corrective unbalance, the second balancing disc has a second corrective unbalance, the second corrective unbalance being equal to the first corrective unbalance, and the control system is configured to control the first actuator and the second actuator to: drive the first and second discs of the balancing system in common rotation while maintaining a relative position of the first and second balancing discs so that that the sum of the first corrective unbalance and the second corrective unbalance has an orientation opposite to an orientation of the unbalance generated by the configuration of the blade pitch; and rotating the first and second discs of the balancing system symmetrically with respect to each other with respect to the orientation of the unbalance generated by the variation of the blade pitch so that the sum of the first corrective unbalance and the second corrective unbalance has an intensity minimizing the unbalance generated by the configuration of the blade pitch; - each of the first and second balancing discs supports at least one balancing weight on the periphery or at least one orifice on the periphery; - the rotations of the first and second balancing discs are carried out simultaneously; - for each wedging configuration, the generated imbalance has an orientation and an intensity; the control system comprises a storage memory storing a database, the database comprising predefined data for each wedging configuration, the predefined data comprising at least the orientation and the intensity of the imbalance generated by said wedging configuration; and the control system is configured to control the first actuator and the second actuator to rotate the first and second discs of the balancing system according to the predefined data in the database relating to the wedging configuration; - the balancing system comprises a shaft supporting the first and second balancing discs, the shaft being intended to be secured to a fan shaft of the fan module supporting the variable-pitch blades; and at least one vibration sensor configured to measure vibrations of the shaft of the balancing system when the latter is secured to the fan shaft, the vibrations being linked to the sum of the unbalance generated by the blade pitch configuration and corrective unbalances generated by the first and second balancing discs, the at least one vibration sensor being connected to the control system; - the control system is configured to control the first actuator and the second actuator to rotate the first and second discs of the balancing system so as to minimize the vibrations measured by the at least one vibration sensor when the shaft of the balancing system is secured to the fan shaft.

[0023] The invention also relates to a fan module with variable-pitch blades for a propulsion unit with a longitudinal axis, said module comprising: - a casing rotating around the longitudinal axis and carrying the blades, and - a blade pitch change system comprising a control device and a connecting mechanism, the control device comprising a annular actuator centered on the longitudinal axis having a fixed body attached to the rotating casing and a movable body movable relative to the fixed body, the movable body being coupled to a synchronization ring of the connecting mechanism, said synchronization ring being connected to the blades and configured to be driven in rotation around the longitudinal axis by the movable body so as to change the pitch of the blades.

[0024] According to the invention, the module further comprises a balancing system according to the invention and as described previously.

[0025] According to one embodiment, the first balancing disc and the second balancing disc are advantageously arranged upstream of the rotating casing.

[0026] The invention also relates to a propulsion assembly comprising at least one fan module with variable-pitch blades according to the invention and as described previously.

[0027] The invention also relates to a method for balancing a fan with variable pitch blades using a balancing system according to the invention and as described previously, the method comprising a step of rotating the first balancing disc by the first rotary actuator and the second balancing disc by the second rotary actuator so as to compensate for the imbalance generated by the pitch configuration of the blades.

[0028] The balancing method 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 in all technically possible combinations: - the rotation step comprises: a common rotation of the first and second balancing discs while maintaining a relative position of the first and second balancing discs so that the sum of the first corrective unbalance and the second corrective unbalance has an orientation opposite to an orientation of the unbalance generated by the blade pitch configuration; and a rotation of the first and second discs of the balancing system symmetrically to each other with respect to the orientation of the unbalance generated by the variation in the blade pitch so that the sum of the first corrective unbalance and the second corrective unbalance has an intensity minimizing the unbalance generated by the blade pitch configuration; - the rotations of the first and second balancing discs are carried out simultaneously; - the first and second balancing discs are rotated respectively by the first and second rotary actuators according to the predefined data in the database relating to the timing configuration; - the balancing method comprises: a preliminary step of determining for each calibration configuration data relating to the unbalance generated by said shimming configuration, the data comprising at least an orientation and an intensity of the imbalance; and a step of storing the determined data in the storage memory; - the balancing process includes the following steps: — generating a test unbalance by rotating the first balancing disc by the first rotary actuator and the second balancing disc by the second rotary actuator; — determining an orientation of the assembly formed by the first and second balancing discs when the latter generates the test unbalance while minimizing vibrations measured by the at least one vibration sensor when the shaft of the balancing system is secured to the fan shaft; and — from the determined orientation of the assembly, the first and second balancing discs are rotated symmetrically with respect to each other so as to minimize the vibrations measured by the at least one vibration sensor when the shaft of the balancing system is secured to the fan shaft; - the test unbalance has a lower intensity than that of the unbalance generated by the blade pitch configuration of the fan module. Brief description of the drawings

[0029] The present invention will be better understood and other details, characteristics and advantages of the present invention will appear more clearly on reading the description of a non-limiting example which follows, with reference to the appended drawings in which: - [Fig.l] is an axial (or longitudinal) half-sectional view of a fan module to which the invention applies, the module comprising a balancing system and a blade feathering device, in a first position corresponding to a blade feathering position, along an axial plane passing through the axis of rotation of a fan blade; - [Fig.2] is a three-dimensional view of a blade whose center of gravity is eccentric relative to its axis of rotation; - [Fig.3a]-3b is a schematic view of the displacement of the center of gravity of the blade as a function of its pitch angle; - [Fig.4] is a schematic view in longitudinal section of a balancing system according to a first embodiment of the invention; - [Fig.5] schematically represents a balancing system according to the invention; - Figures 6a-6d illustrate examples of balancing configurations making it possible to obtain different correction levels at different correction angles; - [Fig.7] is a schematic view in longitudinal section of a balancing system according to a second embodiment of the invention; - [Fig.8] is a flowchart of a balancing method according to the invention; - [Fig.9] is a flowchart of a balancing method according to a first embodiment of the invention; - [Fig. 10] is a flowchart of a preliminary calibration step of the balancing process of [Fig.9]; - Figures 11a-11c illustrate steps in the balancing process of [Fig.9]; - [Fig. 12] is a flowchart of a balancing method according to a second embodiment of the invention; - Figures 13a-13c illustrate steps of the balancing process of [Fig. 12]; - [Fig. 14] represents an enlarged view in longitudinal section of a balancing system according to the invention; and - [Fig. 15] represents a cross-sectional view of the balancing system of [Fig. 14],

[0030] Elements having the same functions in different implementations have the same references in the figures.

[0031] In the figures, the scales and proportions are not strictly respected, for the purposes of illustration and clarity.

[0032] In the description and the claims, the terminology axial, radial and transverse will be adopted without limitation with reference to the trihedron A, R, T indicated in the figures. Description of the embodiments

[0033] The invention applies to a propulsion unit intended to be mounted on an aircraft. The aircraft comprises a fuselage and at least two wings extending on either side of the fuselage along the axis of the fuselage. At least one propulsion unit is mounted, for example, under each wing. The propulsion unit may be a turbojet, for example a propulsion unit equipped with a ducted fan (turbofan) or a turboprop, for example a propulsion unit equipped with an unducted propeller ("open rotor", "USF" for "Unducted Single Fan" or "UDF" for "Unducted Fan"). Of course, the invention applies to other types of propulsion units, for example comprising two coaxial and counter-rotating propellers.

[0034] Generally speaking and in the remainder of the description, the term “blower” is used to designate either a blower or a propeller.

[0035] In [Fig.l] is shown a fan module 1 or fan of a propulsion unit 2 with longitudinal axis X. The fan 1 comprises a rotating casing or rotor 3 movable around the axis X relative to a fixed casing. The rotor 3 carries a series of blades 5 with variable pitch. The fan 1 is here placed upstream of the engine part of the propulsion unit 2 which comprises, for example, successively from upstream to downstream, a gas generator and a power turbine which drives the rotor 3 of the fan 1 via a speed reducer.

[0036] By convention, in the present application, the terms “upstream” and “downstream” are defined relative to the direction of circulation of the gases in the fan 1 (or propulsion unit 2). Similarly, by convention in the present application, the terms “internal” and “external”, “interior” and “exterior” are defined radially relative to the longitudinal (or axial) axis X of the propulsion unit 2, which is in particular the axis of rotation of the rotors of the compressors and turbines of the gas generator.

[0037] The rotating casing 3 comprises an internal annular shaft, called the fan shaft 4, centered on the X axis which, in operation, is driven by the power turbine via the speed reducer. The rotating casing 3 further comprises a ring or disc 16 for supporting the blades 5.

[0038] More precisely, each blade 5 comprises a foot which is for example in the form of a bulb-shaped attachment, this foot being integral with a pivot 18 mounted in a housing 19 of a base 20 projecting from the ring 16 in a movable manner in rotation about a substantially radial axis Y via two rolling bearings. The rolling bearings placed in each housing 19 are generally lubricated with grease.

[0039] The fan comprises a system 22 for changing the pitch of the blades 5 or a system for setting the blades 5 around their axis Y, and more precisely the setting angle of the blades 5 which corresponds for a blade 5 to the angle, in a longitudinal plane perpendicular to the axis Y, between the chord of the blade 5 and the plane of rotation of the fan 1.

[0040] The blades 5 are positioned in the flag position in [Fig.l]. In the flag position, the pitch angle is positive and generally equal to 90°. This position of the blades 5 makes it possible to limit the resistance (drag) generated by the latter.

[0041] According to the embodiment illustrated in [Fig.l], the pitch change system 22 of the blades 5 comprises a linear annular control device or actuator 23, centered on the X axis, common to all the blades 5 and a connecting mechanism 24 connected to each blade 5, this connecting mechanism 24 making it possible to transform the linear movement initiated by the actuator 23 into a rotational movement of the corresponding blade 5.

[0042] More precisely, the linear actuator 23 comprises a fixed annular body 25 attached to an annular support (centered on X) of the rotor 3 by means of fixing screws 89, it is therefore arranged in the rotating frame linked to the rotor. In other words, the fixed body 25 is integral in rotation with the rotor 3. The linear actuator 23 further comprises a movable body 27, the latter being movable in translation relative to the fixed body 25 along the axis X in the example illustrated in particular in [Fig.l]. Advantageously, the linear actuator 23 is hydraulic. Preferably, the actuator 23 is a hydraulic cylinder comprising a fixed cylinder secured to the shaft of the rotor 3 forming the fixed body 25 of the actuator and a rod forming the movable body 27 of the actuator.

[0043] The connecting mechanism 24 of the pitch change system 22 further comprises a synchronization ring 34 secured to the movable body 27 of the actuator 23. In particular, a ferrule 81 makes it possible to fix the synchronization ring 34 to the movable body 27 of the actuator via screws 82. The synchronization ring 34 is centered on the longitudinal axis X and is intended to drive the setting of blades 5 simultaneously.

[0044] The connecting mechanism 24 for transforming the linear movement of the actuator into a rotational movement of the blade 5 further comprises, for each blade 5, a connecting rod 35. One of the ends of the connecting rod 35 is mounted so as to rotate freely along a substantially radial axis A1 with the synchronization ring 34 via a yoke and the other end is mounted so as to rotate freely with an eccentric 36 connected to the pivot 18 which orients the root of the corresponding blade 5 via, for example, a splined connection. The axis A1 is offset relative to the rotational axis Y of the blade 5. The connecting rod 35 and the eccentric 36 make it possible to multiply the force required to adjust the setting of the corresponding blade 5.

[0045] The linear movement of the movable body 27 of the actuator 23 makes it possible to adjust the timing of all the blades 5 in a synchronized manner, in particular via the synchronization ring 34.

[0046] The fan 1 also comprises a device 38 for feathering the blades 5, in particular in the event of failure (or breakdown) of the pitch change device 22, and for example a failure in the hydraulic supply of the linear actuator 23. As a reminder, the flag position corresponds to a positive setting generally substantially equal to 90°.

[0047] The feathering device 38 comprises at least one mechanism 39 comprising a lever 40 articulated by a pivot connection 80 around an axis A2, called the articulation axis, fixed relative to the rotor 3. The articulation axis A2 is here rectilinear and perpendicular to the axis X. The lever 40 has a first end 41 and a second end 42. A flyweight 43 is integral with the first end 41 and the second end 42 is coupled to the synchronization ring 34 via a connecting rod 60. The flyweight 43 is capable, under the centrifugal effect, of being moved into a position (see [Fig.l]) in which the synchronization ring 34 imposes a flag position on the blades 5. The mechanisms 39 of the feathering device 38 are distributed angularly in a regular manner around the axis X. Thus, the assembly weights 43 form an annular row centered on the longitudinal axis X and spaced angularly in a regular manner.

[0048] According to the embodiment illustrated in [Fig. 1], for each mechanism 39, the lever 40 has a V shape in axial section. Each lever 40 comprises two arms spaced angularly and connected at the level of the articulation of the lever at A2, a first arm 44 supporting the weight 43 and a second 45 coupled to the synchronization ring 34 via the connecting rod 60. The two arms 44, 45 are fixed relative to each other. The length of the first branch 44 is greater than the length of the second branch 45, approximately twice as long in the present case. This length ratio makes it possible to multiply the force supplied by each weight 43, and in other words to minimize their mass, and more generally, the mass of all the weights 43.

[0049] The lever 40 is articulated relative to the rotating casing at A2 by a pivot connection, preferably formed by a needle bearing or by two ball bearings.

[0050] Advantageously, the distance between the articulation axis A2 of the lever 40 and the longitudinal axis X is greater than or equal to the distance between a radially inner edge of the synchronization ring and the longitudinal axis X, the radially inner edge allowing attachment to the movable body 27 of the actuator by means of the ferrule 81.

[0051] The second end 42 of the lever 40 and an upstream axial end of the connecting rod 60 are coupled by a first ball joint around an axis A4. Similarly, a downstream axial end of the connecting rod 60 is articulated in a yoke of the synchronization ring 34 preferably by a second ball joint around an axis A5.

[0052] When the propulsion unit 2 is operating normally (no failure), the feathering device 38 is subordinate to the system 22 for changing the pitch of the blades 5, and more precisely to the linear actuator 23. It is noted that when the blades 5 are in the “thrust reversal” position, the weights 43 of the mechanisms 39 of the feathering device 38 of the blades 5 are close to the longitudinal axis X of the rotor 3.

[0053] In the event of a failure (need to position the blades 5 in the flag position), for example a failure in the hydraulic supply of the linear actuator 23, the system 22 for setting the blades 5 then becomes subordinate to the feathering device 38, and more precisely the weights 43 which, under the centrifugal effect, find themselves further away from the longitudinal axis X of the rotor 3 as illustrated in [Fig.l], to impose a flag position on the blades 5.

[0054] The lever counterweight mechanism thus acts on the cylinder which is kinematically linked with the actuating mechanism to the blades. The number of lever counterweight is thus independent of the number of blades. The lever counterweight mechanism imposes the direction of the flag position on the pitch actuation kinematics.

[0055] Generally, after assembly, the lever feathering device and consequently the engine requires balancing at the end of production. This balancing is typically done by installing balancing weights on the fan disc at the upstream cone. This balancing makes it possible to compensate for the residual unbalance of the fan. It is based on the assumption that this residual unbalance is always the same regardless of the engine operating point. Consequently, compensation for this residual unbalance on the ground is sufficient to balance the fan in all engine operating modes.

[0056] This assumption is no longer valid in the case of a variable-pitch fan or propeller. Indeed, changing the pitch of the fan blades or propeller blades changes the position of their center of gravity which, in particular for wide-chord blades / blades, is not located exactly on the Y pivot axis.

[0057] [Fig.2] represents a three-dimensional view of a blade with a complex profile which has a center of gravity G which is not aligned with its pitch rotation axis denoted Y. The location of the center of gravity therefore has a radial component denoted r along the R axis, an axial component denoted a along the A axis and a tangential component denoted t along the T axis. [Fig.3a] represents the position of the center of gravity G in a tangential plane, that is to say perpendicular to the R axis, the axial a and tangential t components are clearly visible. [Fig.3b] represents the position of the center of gravity G in the same tangential plane as [Fig.3a] after a modification of its pitch angle [3.

[0058] This results in an unbalance resulting from the bladed wheel which varies with the pitch angle of the blades. The change in pitch thus results in a significant modification of the recorded vibration levels. If this variation is too significant, it is then impossible to guarantee acceptable balancing of the engine at all operating points. However, poor balancing of the engine can lead to discomfort linked to vibrations in the cabin, or even to excessive loads.

[0059] To date, the balancing techniques provided for propulsion systems with variable pitch vanes are carried out using a correction that only allows acceptable vibration levels to be achieved that meet all the requirements established for the healthy operation of the engine, the good performance of the parts and the preservation of the machine's service life. This classic and unique balancing therefore consists of finding a compromise between all the possible balancings for each blade pitch configuration. An unbalance close to the average of the unbalances recorded in the system is therefore corrected so that, regardless of the configuration of used, the residual unbalance is always close enough to maintain acceptable and not ideal vibration levels. Once the corrective unbalance value has been determined, the necessary masses are installed in locations provided for this purpose in the structure of the fan module. This conventional balancing technique therefore does not allow for the reduction of vibrations in the engine as much as possible, throughout its use.

[0060] The invention proposes a balancing system for any fan module with variable pitch blades allowing it to be balanced at all operating points of the engine. This advantageously makes it possible to generate a corrective unbalance making it possible to compensate for the unbalance generated by the variable pitch of the blades of the fan module regardless of the pitch configuration of the blades, i.e. regardless of the pitch angle [3 of the blades.

[0061] According to the invention, the blower module 1 further advantageously comprises a balancing system 100 which will be described in detail with reference to the figures.

[0062] In particular, [Fig. 4] schematically represents a first embodiment of the balancing system 100 equipping a fan module. For the sake of clarity, only the fan disc 16 and the variable-pitch blades 5 are shown.

[0063] The balancing system 100 is arranged with a large radius near the housings 19 of the pivot 18. The large radius layout has the advantage of limiting the mass of the weights for the same unbalance generated.

[0064] The balancing system 100 comprises a first balancing disc 110 and a second balancing disc 120. The first balancing disc 110 is rotatable about a main axis denoted C. Similarly, the second balancing disc 120 is rotatable about the main axis C. The main axis C of the balancing system is intended to be collinear with the longitudinal axis X when the fan module is equipped with the balancing system as shown in [Fig.4].

[0065] The main axis C passes through the geometric center of the first balancing disc 110 and by the geometric center of the second balancing disc 120.

[0066] The balancing system 100 comprises a shaft 105 supporting the first and second balancing discs 110, 120. The shaft 105 is intended to be secured to the fan shaft 4 of the fan module 1 supporting the variable-pitch blades 5.

[0067] For example, each balancing disc 110, 120 has for this purpose an orifice 121 centered on the main axis C allowing the insertion of the shaft 105.

[0068] The second balancing disc 120 will be described more precisely hereinafter and in particular with reference to [Fig. 14]. The first balancing disc 110 is arranged in a mirror image relative to the second balancing disc 120 in a plane transverse to the shaft 105 supporting them.

[0069] Preferably and as illustrated in Figures 1, 4 and 7, when the balancing system equips a fan module 1, the first balancing disc 110 and the second balancing disc 120 are arranged upstream of the rotating casing 3 in the direction of flow of the fluids.

[0070] The first balancing disc 110 has an eccentric center of gravity denoted Gl, that is to say not aligned with the main axis C. Similarly, the second balancing disc 120 has an eccentric center of gravity denoted G2, that is to say not aligned with the main axis C.

[0071] [Fig. 5] schematically represents an exploded view of the balancing system 100. In order to easily visualize the position of the centers of gravity G1 and G2, the balancing discs 110, 120 are represented with protrusions 112, 122 extending from the periphery of the balancing discs 110, 120 radially outward. Each protrusion 112, 122 indicates the direction in which the centers of gravity G1 and G2 of the balancing discs 110, 120 are respectively located. By direction of a center of gravity of a balancing disc is meant the straight line passing through the center of gravity of the disc and through the geometric center of the balancing disc.

[0072] The two balancing discs 110, 120 have common characteristics, in particular they have the same mass and the same eccentricity of their center of gravity. However, their dimensions may be different. Similarly, the materials which form them and / or their density may be different.

[0073] For example, the first and second balancing discs 110, 120 have a diameter between 40 cm and 100 cm.

[0074] A disc with an eccentric center of gravity can be produced by a disc on which a balancing weight is placed on its rim called eccentricity by adding mass or by drilling its rim called eccentricity by removing mass.

[0075] For example, each of the first and second balancing discs 110, 120 supports at least one balancing weight 114, 124 at the periphery in order to produce an eccentricity of the center of gravity relative to the main axis C. Each balancing weight 114, 124 is arranged at the periphery respectively of the first disc 110 and of the second disc 120 at a predetermined angular position.

[0076] Alternatively, the first disc 110 comprises several orifices, through or not, distributed angularly around the periphery of the first disc, preferably in a regular manner. Thus, the orifices are arranged close to an external peripheral edge of the first disc 110. In other words, the orifices are closer to the external peripheral edge than to the main axis C. The orifices of the first disc 110 are intended to receive balancing weights. In operation, some of the orifices of the first disc 110 actually house balancing weights while others are empty.

[0077] Similarly, the second disc 120 comprises several orifices, through or not, distributed angularly around the periphery of the second disc, preferably in a regular manner. Thus, the orifices are arranged close to an external peripheral edge of the second disc. In other words, the orifices are closer to the external peripheral edge than to the main axis C. The orifices of the second disc 120 are intended to receive balancing weights. In operation, as for the first disc 110, some of the orifices of the second disc actually house balancing weights while others are empty.

[0078] The balancing weights 114, 124 are for example screws, nuts, braked screws or other dedicated masses whose mass is known and calibrated.

[0079] For example, the mass of each balancing weight is between 5 g and 25 g.

[0080] The number of balancing weights 114, 124, their respective angular positions on the first disc 110 or the second disc 120, their materials and their masses depend on the characteristics of the blades of the fan module to be balanced. In particular, all of the above parameters: the number of balancing weights on each balancing disc, their respective angular positions on each balancing disc, their materials and their masses depend in particular on the radial, tangential and axial weight-moments of the blades of the fan module used during their distribution when assembling the module.

[0081] Alternatively, each eccentric center of gravity balancing disc may be achieved by beveling the disc to a predefined angle.

[0082] The minimum correction unbalance of such a balancing system 100 according to the invention depends on the angular pitch between the two balancing discs 110, 120. When the two discs are arranged so that their center of gravity G1, G2 are diametrically opposed ([Fig. 6d]), the corrective unbalance is zero. With an angular positioning error of the order of 2°, it is possible to obtain a minimum correction of 10 cmxg.

[0083] The maximum balancing capacity of such a balancing system 100 according to the invention varies between 20,000 cmxg and 100,000 cmxg.

[0084] The balancing system 100 further comprises a first and a second rotary actuator. The first rotary actuator 115 is configured to rotate the first balancing disc 110 about the main axis C. The second rotary actuator 125 is configured to rotate the second balancing disc 120 about the main axis C.

[0085] For example, and preferably, each rotary actuator 115, 125 is an electric servomotor rotating around the shaft 105. An electric servomotor has the advantage of preventing any involuntary rotation, i.e. not electrically controlled. Thus, this type of rotary actuator makes it possible to lock the angular position of the balancing discs and therefore ensure that the balancing is maintained over time. Each servomotor is preferably powered and controlled by a single- or multi-channel induced current device.

[0086] [Fig. 14] represents an enlarged view of a part of the balancing system 100 and in particular the second balancing disc 120 and the second rotary actuator 125 supported by the shaft 105. The first balancing disc 110 is arranged in a mirror image relative to the second balancing disc 120 along a plane transverse to the shaft 105 supporting them.

[0087] According to the example illustrated, in particular in [Fig. 14], the second rotary actuator 125 is rigidly fixed to the shaft 105 by one of its ends. Furthermore, the second rotary actuator 125 is configured to rotate the second balancing disc 120 about the main axis C by drive means. In the example illustrated, the drive means of the second rotary actuator 125 comprise a splined wheel 127 for driving the rotation of the second balancing disc 120. The splined wheel 127 has radially external splines configured to cooperate with internal splines arranged on the second balancing disc 120.

[0088] Preferably, each balancing disc 110, 120 advantageously comprises several rotary actuators configured to rotate the first balancing disc 110 around the main axis C. For each balancing disc 110, 120, the rotary actuators of a balancing disc are arranged regularly on the periphery of the shaft 105 so as to avoid adding a parasitic unbalance on the shaft 105.

[0089] [Fig. 15] illustrates a front view of the balancing system 100 of [Fig. 4]. In the illustrated example, the balancing system 100 comprises three second rotary actuators 125 configured to rotate the second balancing disc 120 around the main axis C. The three second rotary actuators 125 are arranged regularly on the periphery of the shaft 105 so as to avoid adding a parasitic unbalance on the shaft 105. Of course, the balancing system 100 also comprises three first rotary actuators 115 configured to rotate the first balancing disc 110 around the main axis C.

[0090] In addition, the balancing system 100 comprises a control system 130 configured to control the first actuator 115 and the second actuator 125 to drive the first and second discs 110, 120 of the balancing system in rotation respectively so as to compensate for the imbalance generated by the pitch configuration of the blades of the fan module 1.

[0091] Thus, each of the first and second rotary actuators 115, 125 is electrically connected to the control system 130.

[0092] Preferably, the rotations of the first and second balancing discs are performed simultaneously. Alternatively, they may be consecutive.

[0093] Such a balancing system is thus adapted to generate a corrective unbalance making it possible to compensate for the unbalance generated by the variable pitch of the blades of the fan module regardless of the pitch configuration of the blades, i.e. regardless of the pitch angle [3 of the blades. Indeed, because of the eccentricity of the center of gravity G1 of the first balancing disk 110, the latter has an unbalance called hereinafter the first corrective unbalance and represented by an arrow F1. Similarly, the second balancing disk 120 has an unbalance due to the eccentricity of its eccentric center of gravity called hereinafter the second corrective unbalance and represented by an arrow F2.

[0094] Figures 6a-6d illustrate examples of balancing configurations making it possible to obtain different correction levels at different correction angles. The corrective unbalance is shown diagrammatically by the arrows Fc in each figure 6a-6d. Thus, if the centers of gravity G1 and G2 of the balancing discs 110, 120 are angularly separated by an angle of 45°, the corrective unbalance will be oriented with a direction at an angle of 27.5° relative to each of the balancing discs 110, 120, and more precisely the centers of gravity G1 and G2 (case of [Fig.6a]).

[0095] The examples illustrated in Figures 6b to 6d show balancing configurations making it possible to obtain different corrective unbalance intensities for the same vertical orientation thereof, respectively a corrective unbalance of maximum intensity (case of [Fig.6b]), of average intensity (case of [Fig.6c]) and of very low or even zero intensity (case of [Fig.6d]).

[0096] Advantageously, the control system 130 is configured to control each first actuator 115 and each second actuator 125 for: - on the one hand, driving in rotation, called common rotation, the first and second discs 110, 120 of the balancing system while maintaining a relative position of the first and second balancing discs so that the sum of the first corrective unbalance F1 and the second corrective unbalance F2 has an orientation opposite to an orientation of the unbalance generated by the configuration of the blade pitch and represented by an arrow F; and - on the other hand, driving in rotation, called relative rotation, the first and second balancing discs 110, 120 symmetrically to each other with respect to the orientation of the unbalance generated by the variation in the pitch of the blades so that the sum of the first corrective unbalance F1 and the second corrective unbalance F2 has an intensity minimizing the unbalance F generated by the configuration of the pitch of the blades.

[0097] By "common rotation" is meant that the assembly formed by the first and second balancing discs 110, 120 is rotated while maintaining the angle between the first and second balancing discs and more precisely the angle between the directions of the centers of gravity G1 and G2. In other words, the two discs 110, 120 move together in such a way that the projection of their respective unbalance is aligned with the necessary correction angle. This rotation will always be in the direction of the shortest path (angle less than 180°) in order to always reduce the residual unbalance with the movement of the discs.

[0098] By "relative rotation" is meant that the first and second balancing discs 110, 120 are set in counter-rotational rotation, that is to say that they rotate in opposite directions by the same angle in order to maintain the direction of the corrective unbalance generated by the assembly formed by the first and second balancing discs 110, 120, more precisely by the sum of the first and second corrective unbalances and shown diagrammatically by an arrow Fc in the figures concerned. In other words, the two discs move away from or towards each other so that the combined value of the projection of their respective unbalance reaches the necessary correction value.

[0099] During a relative rotation, the rotations of the first and second balancing discs 110, 120 are preferably carried out simultaneously. Alternatively, they may be consecutive.

[0100] According to the first embodiment of the balancing system according to the invention, the control system 130 comprises a storage memory 132 storing a database. The database comprises predefined data for each pitch configuration generating an unbalance F, that is to say for each pitch angle of the blades.

[0101] The predefined data include at least the orientation and the intensity of the unbalance F generated by each possible pitch configuration of the fan blades.

[0102] In this case, the control system 130 is configured to control each first actuator 115 and each second actuator 125 to drive the first and second balancing discs 110, 120 in rotation according to the predefined data in the database relating to the timing configuration.

[0103] These predefined data are advantageously determined beforehand during a calibration step, for example when mounting the blades or vanes and as described below.

[0104] A second embodiment of a balancing system 200 according to the invention equipping a fan module will now be detailed with reference to [Fig.7]. For the sake of clarity, only the fan disc 16 and the variable-pitch blades 5 are shown.

[0105] In this embodiment, the balancing system 200 comprises a vibration sensor 240 secured to the shaft 105 of the balancing system. The vibration sensor 240 is secured to the shaft 105 of the balancing system and configured to measure vibrations of the shaft 105 of the balancing system when the latter is secured to the fan shaft.

[0106] Preferably, the balancing system 200 comprises several vibration sensors 240, each secured to the shaft 105 of the balancing system. The vibration sensors 240 are arranged on the periphery of the shaft 105 of the balancing system. They are distributed angularly in a regular manner in the same plane transverse to the shaft 105 of the balancing system in order to avoid creating a parasitic unbalance.

[0107] Alternatively, the vibration sensor(s) may be placed on a motor bearing support in the stator portion on the passage of the force path. In this case, the vibrations will rise in the bearing support, via the bearing and the influence of the balancing will be measured directly. Each vibration sensor is thus configured to measure vibrations of the shaft 105 of the balancing system indirectly. An advantage of placing the sensor(s) on a stator portion is to avoid adding an additional unbalance on the shaft of the balancing system.

[0108] In operation, the measured vibrations are linked to the sum of the unbalance F generated by the blade setting configuration and the corrective unbalances F1, F2 generated by the first and second balancing discs 110, 120.

[0109] Each vibration sensor 240 is connected to the control system 130 and configured to transmit the measured data relating to the vibrations.

[0110] According to this second embodiment, the control system 130 is configured to control the first actuator 115 and the second actuator 125 to drive the first and second balancing discs 110, 120 in rotation respectively so as to minimize the vibrations measured by the at least one vibration sensor 240 when the shaft 105 of the balancing system is secured to the fan shaft 4.

[0111] A method of balancing a variable-pitch fan using a balancing system according to the invention and as described previously will now be described with reference to [Fig.8].

[0112] Following a change in the pitch of the blades of the fan module 1, i.e. following a change from a first pitch configuration generating a first unbalance, in particular corrected, to a second pitch configuration generating a second unbalance to be corrected, the method comprises a step S10 of rotating the first balancing disc 110 by the first rotary actuator 115 and the second balancing disc 120 by the second rotary actuator 125 so as to compensate for the new (i.e. the second) unbalance F generated by the new (i.e. the second) configuration of the pitch of the blades.

[0113] Following this step, the fan module 1 is balanced again. In other words, the fan module is balanced for the new and second timing configuration generating the second unbalance F.

[0114] More precisely, the rotation step S10 comprises two steps: - a step of “common rotation” S12 of the first and second balancing discs 110, 120 while maintaining a relative position of the first and second balancing discs 110, 120 so that the sum of the first corrective unbalance F1 and the second corrective unbalance F2 has an orientation opposite to an orientation of the unbalance F generated by the new blade pitch configuration; and - a rotation S14, called “relative rotation”, of the first and second balancing discs 110, 120 symmetrically to each other with respect to the orientation of the unbalance F generated by the variation in the blade pitch so that the sum of the first corrective unbalance F1 and the second corrective unbalance F2 has an intensity minimizing the unbalance F generated by the new blade pitch configuration.

[0115] The common rotation step S12 is performed before the relative rotation step S14.

[0116] Alternatively, the steps of common rotation S12 and relative rotation S14 can be carried out simultaneously, that is to say in parallel with each other. This simultaneity is possible as long as the median correction axis of the two discs 110 and 120 takes the “shortest path” towards the angle to be corrected so as not to further aggravate the dynamic situation by passing through the maximum engine unbalance resulting from the sum of the unbalance to be corrected and the correction unbalance of the balancing discs having their centers of gravity aligned.

[0117] As indicated previously, by “common rotation” is meant that the assembly formed by the first and second balancing discs 110, 120 is rotated while maintaining the angle between the first and second balancing discs and more precisely the angle between the directions of the centers of gravity G1 and G2.

[0118] This common rotation makes it possible to align the geometric center G of the assembly formed by the first and second balancing discs 110, 120 with the direction of the unbalance F to be corrected generated by the new blade setting configuration. This direction corresponds to the bisector, also called the median angle, of the angle between the directions of the centers of gravity G1 and G2 of the first and second balancing discs 110, 120. It is recalled that, by direction of a center of gravity of a balancing disc, we mean the straight line passing through the center of gravity of the disc and through the geometric center of the balancing disc or axis of rotation of the disc.

[0119] As indicated previously, by “relative rotation” is meant that the first and second balancing discs 110, 120 are put into counter-rotation, that is to say that they turn in opposite directions by the same angle, in order to maintain the direction of the corrective unbalance generated by the assembly formed by the first and second balancing discs 110, 120, more precisely by the sum of the first and second corrective unbalances and shown diagrammatically by an arrow Fc in the figures concerned. During a relative rotation, the rotations of the first and second balancing discs 110, 120 are preferably carried out simultaneously. Alternatively, they may be consecutive. The center of gravity G of the assembly formed by the first and second balancing discs 110, 120 remains on the direction line relative to the median angle determined in the common rotation step S12.

[0120] Whether during the common rotation step S12 or during the relative rotation step S14, the first balance disc 110 and the second balance disc 120 preferably rotate simultaneously.

[0121] In the case where the balancing system is a balancing system according to the first embodiment of the invention and as illustrated in [Fig.4], this balancing system 100 is adapted to implement the balancing method as described above and in particular the balancing method of which a flowchart is represented in [Fig.9].

[0122] According to this first embodiment of the balancing method, the first and second balancing discs 110, 120 are rotated respectively by the first and second rotary actuators 115, 125 as a function of the data predefined in the database relating to the timing configuration and stored in the storage memory 132 of the control system 130.

[0123] As indicated previously, the predefined data include at least one orientation and one intensity of the unbalance F generated by any possible pitch configuration of the blades of the fan module 1.

[0124] More precisely, from the predefined data relating to the new timing configuration, instructions are determined and transmitted to the first rotary actuator 115 and to the second rotary actuator 125 by the control system 130 during a step S16 so as to be able to carry out the steps of common rotation S12 and relative rotation S14 of the first balancing disc 110 and of the second balancing disc 120.

[0125] The first embodiment of the balancing method advantageously comprises a prior step of determining, for each setting configuration, data relating to the unbalance generated by said setting configuration and a step of storing the determined data in the storage memory 132 of the control system 130. These steps are carried out according to a calibration method as illustrated in [Fig. 10] preferably after the assembly of the fan module and in particular the assembly of the blades or vanes.

[0126] With reference to [Fig. 10], this calibration method S20 is carried out for each possible pitch configuration of the fan module blades.

[0127] Thus for a blade pitch configuration, the fan module is balanced by a conventional balancing method during a step S22, preferably using the balancing system according to the invention.

[0128] When the fan module is balanced, the median angle between the two balancing discs is measured during a step S24. The median angle corresponds to the orientation of the corrective unbalance Fc opposite to the orientation of the unbalance F generated by the wedging configuration. In other words, the direction of the center of gravity G of the assembly formed by the two balancing discs in the balancing position of the fan module is measured.

[0129] In addition, when the fan module is balanced, the inter-disc angle is measured during a step S26. The inter-disc angle corresponds to the angle between the direction of the center of gravity G1 of the first balancing disc 110 and the direction of the center of gravity G2 of the second balancing disc 120. In other words, the intensity of the corrective unbalance Fc adapted to compensate for the unbalance F generated by the calibration configuration is measured.

[0130] Finally, these data (median angle and inter-disc angle) are recorded in the storage memory 132 of the control system 130 during a step S28.

[0131] Steps S22, S24, S26 and S28 of the calibration method S20 are carried out for each possible pitch configuration of the blades of the fan module.

[0132] Figures 1 la-1 le illustrate steps of the balancing method of [Fig.9] and represent a sectional view in a plane transverse to the main axis C of the balancing system. For clarity, the second balancing disc 120 is offset relative to the first balancing disc 110.

[0133] [Fig.11a] represents an example of a first configuration in which the unbalance generated by this wedging configuration is represented by the arrow F and the corrective unbalance generated by the balancing system 100 is represented by the arrow Fc. The corrective unbalance Fc is obtained when the first balancing disc 110 is in the position P11 and the second balancing disc 120 is in the position P12.

[0134] In the example illustrated, the position P11 corresponds to an orientation of the center of gravity G1 of the first balancing disc 110 having an angle of 150° with a reference direction, here the vertical direction, i.e. the radial axis R. The position P12 corresponds to an orientation of the center of gravity G2 of the second balancing disc 120 having an angle of 120°. The direction of the center of gravity of the assembly of the first and second balancing discs thus has a median angle equal to 135°.

[0135] [Fig. 1 le] represents an example of a second configuration in which the unbalance generated by this wedging configuration is represented by the arrow F' and the corrective unbalance generated by the balancing system 100 is represented by the arrow Fc'. corrective unbalance Fc' is obtained when the first balancing disc 110 is in position P21 and the second balancing disc 120 is in position P22.

[0136] In the example illustrated, the position P21 corresponds to an orientation of the center of gravity G1 of the first balancing disc 110 having an angle of 265° with a reference direction, here the vertical direction, i.e. the radial axis R. The position P22 corresponds to an orientation of the center of gravity G2 of the second balancing disc 120 having an angle of 135°. The direction of the center of gravity of the assembly of the first and second balancing discs thus has a median angle equal to 200°.

[0137] These data relating to the position of the first and second balancing discs form instructions and are obtained from the data (median angle and inter-disc angle) recorded in the storage memory 132 of the control system 130.

[0138] [Fig. 11b] represents the transition from the first pitch configuration to the second pitch configuration of the blades of the fan module and more precisely to step S10 of the balancing method during which the instructions associated with each rotary actuator 115, 125 are sent to them by the control system in order to carry out: - on the one hand a common rotation according to the arrow RI in order to adjust the median angle of the assembly formed by the first and second balancing discs 110, 120, and - on the other hand a relative rotation according to the arrow R2 in order to adjust the inter-disc angle between the first and second balancing discs 110, 120.

[0139] In the example illustrated, the common rotation RI makes it possible to move the assembly formed by the first and second balancing discs 110, 120 so that the orientation of the center of gravity G of the assembly changes from an angle of 135° to an angle of 200°.

[0140] Advantageously and preferably, the transition from corrective unbalance 1 to corrective unbalance 2 is done in parallel with the transition from the first blade setting configuration to the second configuration in order to minimize the residual unbalance.

[0141] In the case where the balancing system is a balancing system according to the second embodiment of the invention and as illustrated in [Fig. 7], this balancing system 200 is adapted to implement the balancing method as described above and in particular the balancing method of which a flowchart is represented in [Fig. 12].

[0142] This second embodiment of the balancing method will be described with reference to [Fig.12] and to figures 13a-13c which illustrate steps of the method.

[0143] This method may advantageously include a preliminary step S30 of measuring by at least one vibration sensor 240 the vibrations generated by the unbalance F generated by the new blade pitch configuration. If the vibration response is acceptable, i.e. less than a threshold of vibrations tolerated for the proper functioning of the fan module and the corresponding propulsion assembly, then the fan module is considered balanced.

[0144] Otherwise, the method comprises a step S32 of generating a test unbalance by rotating the first balancing disc 110 by the first rotary actuator 115 and the second balancing disc 120 by the second rotary actuator 125. This step is illustrated in [Fig. 13a] and the text unbalance is represented by the arrow Ft. In this example, the test unbalance has a vertical orientation representing the median angle of the assembly formed by the first and second balancing discs 110, 120.

[0145] Preferably, the test unbalance Ft has a much lower intensity than that of the unbalance generated by the pitch configuration of the blades of the fan module, making it possible to test the vibration response measured by the vibration sensor over 360°, without the risk of obtaining a resulting unbalance that is too large when the disks are aligned with the unbalance generated by the pitch configuration.

[0146] Thus, the inter-disc angle between the first and second balancing discs 110, 120 is slightly less than 180°.

[0147] The balancing method further comprises a step of determining an orientation of the assembly formed by the first and second balancing discs 110, 120 when the latter generates the test unbalance Ft while minimizing vibrations measured by the at least one vibration sensor 240 when the shaft of the balancing system 105 is secured to the fan shaft 4.

[0148] To do this, the assembly formed by the two balancing discs 110, 120 undergoes a common rotation during a step S12 by a predetermined angle. For each angle, and consequently, for each “angular” position of the assembly formed by the two balancing discs 110, 120, the resulting vibrations of the test unbalance Ft and of the unbalance F generated by the setting configuration are measured by at least one vibration sensor 240. The “angular” position of the assembly formed by the two balancing discs 110, 120 making it possible to obtain a minimum vibration response corresponds to the median angle of the balancing system making it possible to generate a corrective unbalance Fc adapted to compensate for the unbalance generated by the setting configuration of the blades of the fan module.

[0149] The result of this step is illustrated in [Fig.13b]. In the illustrated example, the unbalance to be corrected is represented by the arrow F and is in a direction making an angle of 210° with the vertical. The assembly formed by the two balancing discs 110, 120 has undergone several common rotations spaced apart from each other by 30°. The result, i.e. the sum of the test unbalance Ft and the unbalance F generated by the blade pitch configuration, is represented for each position of the assembly by the arrows Ftc. The size of the arrows is a function of the intensity of the vibrations measured and therefore of the resulting unbalance measured, i.e. the sum of the test unbalance Ft and the unbalance F generated by the blade pitch configuration.

[0150] In this example, an orientation of the assembly formed by the two balancing discs 110, 120 at 30° from the vertical gives minimal vibrations, which corresponds well to a direction opposite to that of the unbalance generated by the blade pitch configuration.

[0151] In this determined orientation of the assembly formed by the two balancing discs 110, 120, i.e. for this determined median angle, the first and second balancing discs are then rotated symmetrically with respect to each other with respect to this orientation during step S14 so as to minimize the vibrations measured by the at least one vibration sensor 240 when the shaft of the balancing system 105 is secured to the fan shaft 4.

[0152] During this step S14, the two balancing discs 110, 120 rotate by the same angle but in opposite directions in order to find the minimum vibration response corresponding to an intensity of the corrective unbalance adapted to compensate for that of the unbalance generated by the blade pitch configuration.

[0153] This step is illustrated in [Fig. 13c], the first balancing disc rotates from the intermediate position P1i to the final position P1f while simultaneously the second balancing disc rotates from the intermediate position P2i to the final position P2f. When the first and second balancing discs 110, 120 are in the respective angular positions P1f and P2f, the measured vibrations are minimal. The corrective unbalance thus generated by the balancing system has an intensity and an orientation adapted to compensate for the unbalance generated by the blade pitch configuration.

[0154] The invention as described above makes it possible to provide a balancing system adjusted to the assembly of the blades / vanes and making it possible, by a mechanical movement, to correct the variations in unbalance caused by the variations in pitch of the blades / vanes.

[0155] Each blade setting configuration corresponds to an associated balancing configuration. In this way, there is no longer any need to compromise by proposing a single balancing solution to correct all the unbalances.

[0156] The balancing system and the balancing method according to the first embodiments make it possible to individually balance each unbalance to optimally reduce the vibrations of each blade pitch configuration using predetermined corrective unbalances. Such a balancing system is said to be programmed. The corrective unbalance to be applied for each different blade pitch configuration can be determined using conventional balancing methods known at the end of the assembly of the fan module blades.

[0157] The balancing system and the balancing method according to the second embodiments make it possible to individually balance each unbalance to optimally reduce the vibrations of each blade setting configuration thanks to corrective unbalances in real time and in an automated manner. Such a balancing system is thus said to be automated.

[0158] It is noted that the examples illustrated in the figures are in no way limiting, the blade pitch change system according to the invention could for example be incorporated into the rotor of a propeller of a turboprop or even into the rotor of each of the two propellers of a turbomachine comprising two counter-rotating propellers, better known by the English designation "Open Rotor". In the definition of the invention, the term "fan" also covers the propeller or propellers of such turbomachines.

[0159] Furthermore, in the examples illustrated in the figures, the cylinder body is connected to the rotor (in the rotating frame of reference) and the cylinder rod, which is fixed to the fixed frame of reference connected to the casing, is movable in translation relative to the cylinder body, the synchronization ring being connected to the cylinder rod. However, the invention could also be applied to a system in which the cylinder body would be fixed to the synchronization ring and movable in translation relative to the cylinder rod. Thus, depending on the configuration of the cylinder, the entire feathering device is supported by a casing connected directly to the cylinder or to the structure of the engine.

[0160] Such a balancing system applies more generally to any turbomachine comprising a blade pitch control device. In particular, the invention also applies to a blade pitch change system comprising a single annular cylinder arranged on a fixed casing and a connecting mechanism comprising a transfer bearing or whose linear actuator is an electric cylinder.

Claims

1.

2. Claims Balancing system (100; 200) for a fan module (1) with variable-pitch blades, the fan module having a longitudinal axis (X) and several blade pitch configurations different from each other, each pitch configuration generating an unbalance, the balancing system comprising: - a first balancing disc (110) and a second balancing disc (120), each movable in rotation about a main axis (C) intended to be collinear with the longitudinal axis (X) and each having a center of gravity eccentric with respect to the main axis, - at least one first rotary actuator (115) and at least one second rotary actuator (125), each configured respectively to rotate the first and second balancing discs around the main axis, - a control system (130) configured to control each first actuator (115) and each second actuator (125) to drive the first and second discs (110, 120) of the balancing system in rotation so as to compensate for the imbalance generated by the pitch configuration of the blades of the fan module (1). Balancing system (100; 200) according to claim 1, wherein the first balancing disc (110) has a first corrective unbalance (F1), the second balancing disc (120) has a second corrective unbalance (F2), the second corrective unbalance (F2) being equal to the first corrective unbalance (F1), and the control system (130) is configured to control the first actuator (115) and the second actuator (125) to: - driving the first and second discs (110, 120) of the balancing system in common rotation while maintaining a relative position of the first and second balancing discs so that the sum of the first corrective unbalance (F1) and the second corrective unbalance (F2) has an orientation opposite to an orientation of the unbalance (F) generated by the configuration of the blade pitch; and - driving the first and second discs (110, 120) of the balancing system in rotation symmetrically to each other with respect to the orientation of the unbalance generated by the variation of the blade pitch so that the sum of the first corrective unbalance and the second corrective unbalance presents an intensity minimizing the unbalance generated by the blade pitch configuration.

3. A balancing system (100; 200) according to claim 1 or 2, wherein each of the first and second balancing discs (110, 120) supports at least one peripheral balancing weight (114, 124) or at least one peripheral orifice.

4. A balancing system (100; 200) according to any preceding claim, wherein the rotations of the first and second balancing discs (110, 120) are performed simultaneously.

5. Balancing system (100) according to any one of the preceding claims 1 to 4, wherein: - for each wedging configuration, the generated unbalance (F) has an orientation and an intensity; - the control system (130) comprises a storage memory (132) storing a database, the database comprising predefined data for each wedging configuration, the predefined data comprising at least the orientation and the intensity of the unbalance generated by said wedging configuration; and - the control system (130) is configured to control the first actuator and the second actuator to rotate the first and second discs of the balancing system according to the predefined data in the database relating to the wedging configuration.

6. Balancing system (200) according to any one of claims 1 to 4, comprising: - a shaft supporting the first and second balancing discs, the shaft being intended to be secured to a fan shaft of the fan module supporting the variable-pitch blades; and - at least one vibration sensor configured to measure vibrations of the shaft of the balancing system when the latter is secured to the fan shaft, the vibrations being linked to the sum of the unbalance generated by the blade pitch configuration and corrective unbalances generated by the first and second balancing discs, the at least one vibration sensor being connected to the control system; and wherein the control system is configured to control the first actuator and the second actuator to drive in rotation the first and second discs of the balancing system so as to minimize the vibrations measured by the at least one vibration sensor when the shaft of the balancing system is secured to the fan shaft.

7. Fan module (1) with variable pitch blades for a propulsion unit with a longitudinal axis (X), said module comprising: - a casing (3) rotating around the longitudinal axis (X) and carrying the blades (5), and - a system for changing the pitch (22) of the blades comprising a control device (23) and a connecting mechanism (24), the control device comprising an annular actuator centered on the longitudinal axis (X) having a fixed body (25) attached to the rotating casing and a movable body (27) movable relative to the fixed body, the movable body being coupled to a synchronization ring (34) of the connecting mechanism, said synchronization ring being connected to the blades (5) and configured to be driven in rotation around the longitudinal axis (X) by the movable body so as to change the pitch of the blades; the module being characterized in that it comprises a balancing system (100;200) according to any one of the preceding claims.;

8. Fan module (1) according to the preceding claim, wherein the first balancing disc (110) and the second balancing disc (120) are arranged upstream of the rotating casing (3).

9. Propulsion assembly (2) comprising at least one variable-pitch fan module according to claim 7 or 8.

10. A method of balancing a variable-pitch fan using a balancing system according to any one of claims 1 to 6, the method comprising a step of rotating (S 10) the first balancing disc (110) by the first rotary actuator (115) and the second balancing disc (120) by the second rotary actuator (125) so as to compensate for the unbalance (F) generated by the blade pitch configuration.

11. A balancing method according to claim 10 when dependent on claim 2, wherein the rotating step (S 10) comprises: - a common rotation (S 12) of the first and second balancing discs (110, 120) while maintaining a relative position first and second balancing discs so that the sum of the first corrective unbalance (F1) and the second corrective unbalance (F2) has an orientation opposite to an orientation of the unbalance generated by the blade pitch configuration; and - a rotation (S 14) of the first and second discs (110, 120) of the balancing system symmetrically to each other with respect to the orientation of the unbalance (F) generated by the variation in the blade pitch so that the sum of the first corrective unbalance (F1) and the second corrective unbalance (F2) has an intensity minimizing the unbalance generated by the blade pitch configuration.

12. A balancing method according to claim 10 or 11, wherein the rotations of the first and second balancing discs (110, 120) are performed simultaneously.

13. A balancing method according to any one of the preceding claims 10 to 12 in combination with claim 5, wherein the first and second balancing discs (110, 120) are rotated respectively by the first and second rotary actuators (115, 125) according to the predefined data in the database relating to the timing configuration.

14. Balancing method according to the preceding claim, comprising: - a prior step of determining for each calibration configuration data relating to the unbalance (F) generated by said calibration configuration, the data comprising at least one orientation and one intensity of the unbalance; and - a step of storing the determined data in the storage memory (132).

15. A balancing method according to any one of the preceding claims 10 to 12 in combination with claim 6, comprising the following steps: - generating a test unbalance (Ft) by rotating the first balancing disc (110) by the first rotary actuator (115) and the second balancing disc (120) by the second rotary actuator (125); - determining an orientation of the assembly formed by the first and second balancing discs (110, 120) when the latter generates the test unbalance while minimizing vibrations measured by the at least one vibration sensor (240) when the shaft of the balancing system (105) is secured to the fan shaft (4); and wherein, from the determined orientation of the assembly, the first and second balancing discs (110, 120) are rotated symmetrically with respect to each other so as to minimize the vibrations measured by the at least one vibration sensor (240) when the shaft of the balancing system (105) is secured to the fan shaft (4).

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