WO2024089376A1

WO2024089376A1 - Pitch-change mechanism with actuating cylinder and pitch-locking device outside the chambers of the actuating cylinder

Info

Publication number: WO2024089376A1
Application number: PCT/FR2023/051701
Authority: WO
Inventors: Christophe Marcel Lucien Perdrigeon; Clément Cottet; Régis Eugène Henri Servant; Jean Charles Olivier Roda
Original assignee: Safran Aircraft Engines
Priority date: 2022-10-28
Filing date: 2023-10-27
Publication date: 2024-05-02
Also published as: FR3141443A1

Abstract

The invention relates to a pitch-change mechanism (70), which comprises a frame (72), an actuating cylinder (74), and a locking device (160). The actuating cylinder (74) comprises a cylinder block (104) and a piston (106), of which one is stationary and the other is translatable relative to the frame (72). The cylinder block (104) defines an internal cavity (110) and the piston (106) divides the internal cavity (110) into two fluid chambers (112, 114) each containing a control fluid for controlling the movement of the cylinder block (104) and the piston (106) relative to each other. The pitch-locking device (160) is outside the fluid chambers (112, 114).

Description

DESCRIPTION

TITLE: PITCH CHANGE MECHANISM WITH CONTROL CYLINDER AND PITCH LOCKING DEVICE OUTSIDE THE CYLINDER CHAMBERS

FIELD OF INVENTION

The present invention relates to the general field of turbomachines equipped with at least one fan equipped with variable pitch blades, and more particularly to controlling the orientation of the fan blades of these turbomachines.

A privileged area of application of the invention is that of turbojet engines with unducted fans (better known by the English names “propfan”, “open fan”, “open rotor” and “unducted fan”). However, the invention also applies to turboprop engines with one or more propulsive propellers.

TECHNOLOGICAL BACKGROUND

One of the ways currently explored to improve the specific consumption of civil aircraft engines consists of the development of turbojet engines with unducted fans, such as that described in document FR 2 941 493. These turbojet engines include a gas generator of conventional turboshaft engine, one or more turbine stages of which drive one or more unducted fan(s) extending outside the engine nacelle.

The blades of this or these fan(s) are, as in the case of conventional turboprops, with variable pitch, that is to say that the angular position of these blades (called pitch angle) can be modified during the flight. . As a reminder, the pitch angle of a blade corresponds to the angle, in a plane orthogonal to the pivot axis of the blade, between the axis of rotation of the fan and the chord of the blade at 75% of the fan radius. It can vary from a value equal to 90°, corresponding to a so-called “sail” or “flat” position of the blade, to a value equal to 0°, corresponding to a so-called “flag” position of the blade. . It can also take a value strictly greater than 90°, typically substantially equal to 95°, corresponding to a so-called “reverse” position of the blade.

As is known, this modification of the pitch angle during the flight makes it possible to change the thrust of the engine and optimize the efficiency of the fan as a function of the speed of the aircraft. In fact, the fan speed is almost constant over all operating phases, and it is the setting of the blades which causes the thrust to vary. Thus, in the cruise flight phase, the blades are oriented so as to adjust the thrust by minimizing the power taken from the turbine shaft and consumption and optimizing efficiency. Conversely, during takeoff, the blades are oriented to maximize thrust in order to accelerate and then take off the plane.

The orientation of the blades is commonly controlled by means of a pitch change mechanism comprising a control cylinder comprising a part movable in translation along the axis of the fan and a connection system connecting the movable part to the blade so as to convert the translation of the movable part into rotation of the variable-pitch blade.

A difficulty encountered with variable pitch blades is that, in the event of a malfunction in the systems controlling their orientation, said blades tend, under their own centrifugal effect, to move into sail position. However, a blade blocked in this position generates little resistive torque and risks causing the motor to overspeed, with potential risks of engine damage. Furthermore, a blade blocked in this position also risks generating excessive and unacceptable drag for the controllability of the aircraft and/or its range of action in the case of a diversion mission.

To remedy this difficulty, it is known to use safety systems capable of preventing the movement of the variable pitch blades towards small pitches (that is to say towards the sail position) in the event of failure of the blade orientation control system. Such a system is for example known from EP 3 400 169.

In particular, we know of a safety system integrating into the cylinder controlling the orientation of the blades a screw-nut system of the ball screw type coupled to a locking nut. In normal operation, the nut of the screw-nut system follows the movements of the control cylinder, thus causing the rotation of the screw around its axis, while the locking nut follows the thread of the screw without ever touching it ( the thread of the locking nut is designed to provide slight play with the screw thread). In the event of a malfunction in the blade orientation control system, the screw of the screw-nut system is immobilized (its rotation is blocked) and the locking nut engages with said screw, thus preventing the blades from pivoting towards the little steps.

However, this security system is not entirely satisfactory. Indeed, it is complex to assemble it to the control cylinder. In addition, it requires a control cylinder with a particular geometry making it heavy and bulky. In addition, it makes access to the connection system connecting the blade to the moving part of the cylinder difficult once the control system is installed. Furthermore, for proper operation, it requires precise and complex management of the clearances between the locking nut and the screw thread. STATEMENT OF THE INVENTION

An objective of the invention is to facilitate the assembly of a pitch change mechanism controlling the orientation of variable pitch blades when said pitch change mechanism comprises a pitch locking device. Other objectives are to allow a reduction in the pitch change mechanism, to allow a simplification of the pitch change mechanism, and to facilitate access to the pitch change mechanism when it is assembled to a set of blades. with variable timing.

To this end, the subject of the invention is, according to a first aspect, a pitch change mechanism for adjusting an angular position of at least one blade with variable pitch around a pivot axis of the blade, said mechanism step change comprising: a fixed frame relative to the pivot axis, a control cylinder comprising a fixed part secured to the frame and a movable part movable in translation along a longitudinal axis relative to the fixed part between a retracted position and a deployed position, a connection system connecting the mobile part to the variable pitch blade so as to convert the translation of the mobile part along the longitudinal axis into a rotation of the variable pitch blade around the pivot axis , and a pitch locking device capable of blocking the translation of the movable part relative to the fixed part in at least one direction, in which the control cylinder comprises a cylinder forming one of the fixed part and the movable part and a piston forming the other of the fixed part and the movable part, the cylinder delimiting an internal cavity and the piston dividing said internal cavity into two fluidic chambers each containing a control fluid to control the movement of the movable part relative to the fixed part, the pitch locking device being outside said fluidic chambers.

According to particular embodiments of the invention, the pitch change mechanism also has one or more of the following characteristics, taken in isolation or in any technically possible combination(s): the cylinder is continuous ; the fluidic chambers are contiguous; each fluidic chamber is delimited at least in part by an external peripheral surface of the frame; at least part of the pitch locking device extends longitudinally away from the control cylinder. the pitch change mechanism includes a seal fluidly isolating the fluid chambers of the pitch locking device. the pitch locking device comprises: o a support member, movable in translation relative to the frame along the longitudinal axis between an operating position and a locking position, o a return device urging the support member towards its position locking device, o a holding device to maintain the support member in its operating position under normal operating conditions, and o a screw-nut system with:

■ a screw secured in translation to the support member and mounted movable in rotation around the longitudinal axis relative to the support member, the screw having a stop surface which is at a distance from the frame when the support member is in the operating position and resting against the frame when the support member is in the locking position, and

■ a nut integral with the movable part of the control cylinder and coaxial with the screw, the nut cooperating with the screw so that a translation of the nut along the longitudinal axis causes the rotation of the screw around the longitudinal axis; the pitch change mechanism comprises a ferrule connecting the nut to the movable part of the control cylinder, said ferrule projecting longitudinally, in particular upstream, from the control cylinder; the abutment surface is provided at a downstream end of the screw; the fluidic chambers are closed at each of the longitudinal ends of the control cylinder; the connection system comprises a first articulation secured to the movable part, a second articulation secured to the variable-pitch blade, away from the pivot axis, and a connecting member connecting the first articulation to the second articulation ; the link system is suitable for converting: o a translation of the movable part along the longitudinal axis in a first direction in a rotation of the variable-pitch blade around the pivot axis towards the sail position, and o a translation of the movable part along the axis longitudinal in a second direction opposite the first direction in a rotation of the variable-pitch blade around the pivot axis towards the flag position; the first joint is arranged upstream, respectively downstream, of the second joint, the first direction going from upstream to downstream, respectively from downstream to upstream; the abutment surface is oriented in the first direction; the support member moves from its operating position to its locking position by translation in the first direction; the connecting member is constituted by a connecting rod; the variable pitch blade comprises a leading edge, a trailing edge and a chord connecting the leading edge to the trailing edge, the second articulation being placed opposite the trailing edge relative to a plane orthogonal to the rope and containing the pivot axis; the frame comprises a stopper against which the abutment surface of the screw comes to rest when the support member is in the locking position, the control cylinder and the stopper being arranged longitudinally on the same side of the nut; the control cylinder comprises a cylinder forming one of the fixed part and the movable part and a piston forming the other of the fixed part and the movable part, the cylinder delimiting an internal cavity and the piston dividing said internal cavity in two fluidic chambers each containing a control fluid to control the movement of the movable part relative to the fixed part; the pitch locking device is longitudinally cantilevered relative to the frame; the locking device comprises a guiding system guiding the support member relative to the frame, the control cylinder and the guiding system being arranged longitudinally on the same side, preferably a downstream side, of the nut; the pitch locking device comprises a casing secured to the nut and surrounding the nut, the screw and the support member; the pitch change mechanism comprises an enclosure for containing and/or circulating a fluid for lubricating the pitch locking device; the casing at least partially delimits said enclosure; the enclosure is a closed enclosure; one of the two fluid chambers is in fluid communication with the interior of the casing, the control fluid constituting a lubricating fluid of the locking device; the casing comprises an internal cylinder carrying the nut on an internal face and cooperating with an external cylinder secured to the frame so as to slide longitudinally inside the latter, the internal cylinder having at its periphery a seal in contact with one face internal of the external cylinder, the external cylinder and the casing together delimiting an enclosure for the circulation of a lubricating fluid of the locking device; the pitch change mechanism comprises a device for guiding the nut relative to the frame, said guide device comprising an internal cylinder secured to the nut and an external cylinder secured to the frame, the internal cylinder cooperating with the external cylinder in such a manner to slide longitudinally inside the latter; and the longitudinal axis is substantially orthogonal to the pivot axis.

The invention also relates, according to a second aspect, to a fan rotor for a turbomachine comprising a hub and a plurality of vanes with variable pitch each pivotable relative to the hub around a specific pivot axis, the rotor further comprising a pitch change mechanism according to the first aspect for adjusting an angular position of each of the variable pitch blades around its respective pivot axis.

According to a particular embodiment of the invention, the fan rotor also has the following characteristic: the longitudinal axis constitutes an axis of rotation of the rotor.

The invention also relates, according to a third aspect, to a turbomachine comprising a fan rotor according to the second aspect.

According to a particular embodiment of the invention, the turbomachine also has the following characteristic: the longitudinal axis constitutes an axis of elongation of the turbomachine.

The invention also relates, according to a fourth aspect, to an aircraft comprising a turbomachine according to the third aspect. Finally, the subject of the invention, according to a fifth aspect, is a method for changing the pitch of the blades of a fan rotor for a turbomachine, each pivotable relative to a hub of the fan rotor around a specific pivot axis, said method comprising adjusting an angular position of each of said blades around its respective pivot axis by means of a pitch change mechanism according to the first aspect.

According to a particular embodiment of the invention, the method also has the following characteristic: the method comprises an additional step of locking the orientation of the blades by means of the pitch locking device.

BRIEF DESCRIPTION OF THE FIGURES

Other characteristics and advantages of the invention will appear on reading the description which follows, given solely by way of example and made with reference to the appended drawings, in which:

- Figure 1 is a top view of an aircraft according to an exemplary embodiment of the invention,

- Figure 2 is a simplified view in partial longitudinal section of a turbomachine of the aircraft of Figure 1,

- Figure 3 is a simplified view in longitudinal section of part of a pitch change mechanism of the turbomachine of Figure 2 according to a first variant, the pitch change mechanism being in a first configuration,

- Figure 4 is a view similar to that of Figure 3, the pitch change mechanism being in a second configuration,

- Figure 5 is a simplified view in longitudinal section of part of a pitch change mechanism of the turbomachine of Figure 2 according to a second variant,

- Figure 6 is a simplified view in longitudinal section of part of a pitch change mechanism of the turbomachine of Figure 2 according to a third variant,

- Figure 7 is a simplified view in longitudinal section of part of a pitch change mechanism of the turbomachine of Figure 2 according to a fourth variant, - Figure 8 is a simplified view along a radial axis of an arm for rotating a variable-pitch blade of the turbomachine of Figure 2, and

- Figure 9 is a perspective view and partial section of a satellite roller screw of the pitch change mechanism of Figure 3.

DETAILED DESCRIPTION OF AN EXAMPLE OF WORK

The aircraft 10 shown in Figure 1 includes turbomachines 12 to propel it.

In the example shown, the aircraft 10 is an airplane. This comprises, in a conventional manner, a fuselage 14, a tail unit 16 and two wings 18. The turbomachines 12 are here two in number and are each housed under a respective wing 18. As a variant (not shown), the turbomachines 12 are arranged along the fuselage 14, for example near the empennage 16. As a further variant (also not shown), the aircraft 10 comprises a single turbomachine 12 or at least three turbomachines 12.

One of the turbomachines 12 is shown in Figure 2.

As visible in this Figure, the turbomachine 12 is elongated along a longitudinal axis X. It typically has angular symmetry around said longitudinal axis by rotation around the longitudinal axis

Here and in the following, the terms “interior” and “exterior”, “internal” and “external”, as well as their variations, are understood with reference to the X axis, an element qualified as “interior” or “internal » being oriented towards the X axis while an “outer” or “external” element is oriented opposite the X axis.

The turbomachine 12 comprises, in a conventional manner, a nacelle 20, an internal vein 22 for circulating an air flow through the nacelle 20, a combustion chamber 24 housed in the vein 22, a motor body 26 and a nozzle gas exhaust 28.

In the following, the terms “upstream” and “downstream” are understood with reference to a direction of flow of an air flow through the vein 22.

The engine body 26 comprises a compressor 30, a turbine 32 and a transmission shaft 34 coupling the turbine 32 to the compressor 30 for driving the compressor 30 by the turbine 32. The compressor 30 is arranged upstream of the combustion chamber 24 and supplies the combustion chamber 24 with compressed air. The turbine 32 is arranged downstream of the combustion chamber 24 and receives the exhaust gases leaving the combustion chamber 24.

The transmission shaft 34 has the longitudinal axis X as its axis of rotation. The transmission shaft 34 is guided in rotation relative to the nacelle 20 by means of bearings (not shown).

In the example shown, the turbomachine 12 is a multi-body turbomachine, in particular a double body, comprising a low pressure body 40 in addition to the engine body 26. The engine body 26 then constitutes a high pressure body, the compressor 30 being a high pressure compressor, the turbine 32 being a high pressure turbine and the transmission shaft 34 being a high pressure shaft.

The low pressure body 40 includes a low pressure compressor 42, a low pressure turbine 44 and a low pressure shaft 46 coupling the low pressure turbine 44 to the low pressure compressor 42 for driving the low pressure compressor 42 by the low pressure turbine 44.

The low pressure compressor 42 is arranged upstream of the high pressure compressor 30 and supplies the latter with compressed air. The low pressure turbine 44 is arranged downstream of the high pressure turbine 32 and receives the exhaust gases leaving the latter.

The low pressure shaft 46 is guided in rotation relative to the nacelle 20 by means of bearings (not shown).

The low pressure shaft 46 is coaxial with the high pressure shaft 34. It therefore also has the longitudinal axis X as its axis of rotation. In particular, the low pressure shaft 46 extends inside the shaft high pressure 34.

The turbomachine 12 also includes a fan 50 to drive the air flow in an external circulation vein 52 surrounding the nacelle 20. We thus distinguish a primary air flow À (hot), constituted by the portion of the air flow entrained in the internal circulation vein 22, and a secondary air flow B (cold), constituted by the portion of the air flow entrained in the external circulation vein 52.

The fan 50 comprises a fan rotor 54. This fan rotor 54 is rotatably mounted relative to the nacelle 20 around the longitudinal axis X. It comprises a hub 55 (Figure 3) provided with fan blades 56 extending substantially radially outwards from the hub 55. These blades 56, when rotated, drive the air flow in the external circulation vein 52.

As visible in Figure 8, each blade 56 comprises a leading edge 57À, a trailing edge 57B and a chord C connecting the leading edge 57À to the trailing edge 57B.

Returning to Figure 2, the fan rotor 54 is driven in rotation by the low pressure turbine 44, via the low pressure shaft 46. In the example shown, this drive is direct, i.e. that is to say that the fan rotor 54 is integral in rotation with the low pressure shaft 46. Alternatively (not shown), this Drive is done via a reduction gear allowing the fan rotor 54 to rotate at a speed lower than that of the low pressure shaft 46.

In the example shown, the fan 50 also comprises a fan stator 58 comprising fixed blades 59 arranged at the periphery of the nacelle 20, in the external circulation vein 52, along a plane orthogonal to the longitudinal axis Fan stator 58 is here arranged downstream of the fan rotor 54. Alternatively (not shown), the fan 50 comprises, in place of the fan stator 58, a counter-rotating fan rotor.

Advantageously, the fan 50 is, as shown, not ducted, that is to say that the external circulation vein 52 has no peripheral delimitation. The turbomachine 12 is then constituted, as shown, by a turbojet with an unducted fan or, alternatively, by a turboprop. Alternatively (not shown), the external circulation vein 52 is defined between the nacelle 20 and a fan casing surrounding the fan 50; the turbomachine 12 is then typically constituted by a turbojet with a high bypass ratio, the dilution rate being defined as the ratio of the flow rate of the secondary flow B (cold) to the flow rate of the primary flow A ( hot).

In the example shown, the turbomachine 12 is in particular of the "puller" type, that is to say that the fan 50 is arranged upstream of the internal circulation stream 22 and also drives the air flow in this last. As a variant (not shown), the turbomachine is of the “pusher” type, that is to say that the fan 50 is placed around the downstream half of the nacelle 20.

The blades 56 of the fan rotor 54 have variable pitch, that is to say that each blade 56 is pivotally mounted relative to the hub 55 around a specific pivot axis P. This pivot axis P extends in the direction of elongation of the blade 56. It is orthogonal to the longitudinal axis X.

Each blade 56 is in particular capable of pivoting around the axis P relative to the hub 55 between a so-called flag position, in which the chord C of the blade 56 is substantially parallel to the longitudinal axis X, and a so-called sail position. , in which the chord C of the blade 56 is substantially orthogonal to the longitudinal axis the chord C of the blade 56 forms an angle strictly greater than 90°, for example substantially equal to 95°, with the longitudinal axis X. The blades 56 being most often twisted, the chord C taken as a reference for the measurement of the pitch angle is, by convention, constituted by the chord of the blade at 75% of the radius of the fan rotor 54. To this end, each blade 56 is secured, as visible in Figure 3, to a fastening part 60 arranged at the base of the blade. This attachment part 60 is rotatably mounted relative to the hub 55 around the pivot axis P. More precisely, the attachment part 60 is rotatably mounted inside a housing 62 provided in the hub 55 by via balls 64 or other rolling elements.

The fan 50 further comprises a pitch change mechanism 70 to adjust the pitch angle of each blade 56 around its pivot axis P so as to adapt the performance of the turbomachine 12 to the different phases of flight.

With reference to Figure 3, this pitch change mechanism 70 comprises a frame 72, a control cylinder 74, a system 76 for controlling the cylinder 74 and a connection system 78.

The frame 72 is integral with the hub 55 and is typically constituted by a part of the hub 55. It is thus fixed relative to the pivot axes P.

The frame 72 includes a base 80. This base 80 is centered on the longitudinal axis X. Here, it is crossed by the pivot axes P.

In the example shown, the base 80 delimits a housing 82 open downstream. This housing 82 is in particular cylindrical, typically cylindrical of revolution, and centered on the axis X. An oil transfer bearing 84 is received in said housing 82.

The base 80 also delimits a cavity 86 opening into an upstream face 88 of the base 80 through an orifice 90 which is here centered on the axis axis X. It is interposed between the upstream face 88 and the housing 82.

The base 80 has a stopper 92 oriented upstream. This stopper 92 is here formed by a part of the upstream face 88. It extends substantially radially and is in particular arranged around the orifice 90.

In the example shown, the frame 72 also includes a cylinder 94 projecting upstream from the base 80. This cylinder 94 is centered on the axis X and open at its upstream end 95. It extends around the stopper 92. It is typically cylindrical in revolution.

Here, the frame 72 further comprises a peripheral cylinder 96, coaxial with the cylinder 94 and surrounding the latter, projecting upstream from the base 80. This cylinder 96 is open at its upstream end 97. It is typically cylindrical of revolution.

The base 80 and the peripheral cylinder 96 together delimit an external peripheral surface 88 of the frame 72. This external peripheral surface 88 is substantially cylindrical and centered on the axis X. It is oriented radially outwards. Alternatively, as shown in Figure 5, the frame 72 does not include the cylinder

94.

As a further variant, as shown in Figure 6, the frame 72 does not include the peripheral cylinder 96. The external peripheral surface 88 is then delimited by the base 80 and the cylinder 94.

Returning to Figure 3, the control cylinder 74 comprises a fixed part 100, integral with the frame 72, and a movable part 102 movable in translation along the longitudinal axis Figure 3, and a deployed position shown in Figure 4. Optionally, the movable part 102 is also movable in rotation around the longitudinal axis X over a restricted angle, for example of the order of 5°.

The control cylinder 74 comprises in particular a continuous cylinder 104, forming one of the fixed part 100 and the movable part 102 and a piston 106 forming the other of the fixed part 100 and the movable part 102. Here , the cylinder 104 forms the movable part 102 and the piston 106 forms the fixed part 100. Alternatively (not shown), it is the reverse: the cylinder 104 forms the fixed part 100 and the piston 106 forms the movable part 102 .

Thus, in the example shown, the cylinder 104 extends around the external peripheral surface 88 of the frame 72, coaxially with the latter, and the piston 106 is constituted by a flange 108 secured to the frame 72 extending radially towards the 'outside from the outer peripheral surface 88 to the cylinder 104.

The cylinder 104 delimits an internal cavity 110. The piston 106 divides said internal cavity 110 into two contiguous fluid chambers 112, 114. Each contains a control fluid, typically consisting of an oil, to control the movement of the movable part 102 relative to the fixed part 100. This control fluid is at a first pressure in the first fluidic chamber 112 and at a second pressure in the second fluidic chamber 114. The first and second fluidic chambers 112, 114 are arranged so that the relative increase in the first pressure (that is to say relative to the second pressure) causes the piston 110 to move towards its deployed position, the relative increase in the second pressure (that is to say relative to the first pressure) causing the movement of the piston 110 towards its retracted position.

Here, each of the fluidic chambers 112, 114 is delimited internally by the external peripheral surface 88 of the frame 72 and externally by the cylinder 104. The first fluidic chamber 112 is also delimited at its downstream end by the piston 106 and the second fluidic chamber 114 is delimited at its upstream end by the piston 106. The control cylinder 74 is thus particularly compact, which makes it lighter.

In the example shown in Figure 3, the movable part 102 also comprises an upstream guide ring 116 and a downstream guide ring 118 each secured to the cylinder 104 and extending radially inwards from the cylinder 104 to the external peripheral face 88 of the frame 72. The upstream guide ring 116 is arranged upstream of the piston 106 and delimits an upstream end of the first fluid chamber 112. The downstream guide ring 118 is arranged downstream of the piston 106 and delimits a downstream end of the second fluidic chamber 114.

In the example shown in Figure 3, each of the upstream and downstream guide rings 116, 118 constitutes a sealing ring and longitudinally closes the first fluidic chamber 112, respectively the second fluidic chamber 114. The fluidic chambers 112, 114 are thus closed at each of the longitudinal ends of the control cylinder 74

Alternatively, as shown in Figure 7, only the downstream guide ring 118 constitutes a sealing ring. The upstream guide ring 118 has holes 119 allowing the control fluid to flow through the upstream guide ring 118.

As a further variant, as shown in Figure 5, the movable part 102 does not include an upstream guide ring 118.

Returning to Figure 3, the control system 76 comprises a pressure generator 130 for bringing the control fluid to a third pressure higher than the first and second pressures, a pressure control unit 132 for adjusting the pressure of the control fluid in the first and second fluidic chambers 112, 114 by means of the third pressure, and a return line 136 to discharge the depressurized control fluid. The control system 76 also includes a main tank 133, an emergency circuit 134 and a control module 135.

The pressure generator 130 comprises for example a pump capable of pumping the fluid to bring it to the third pressure, for example 100 bars. A main relief valve 139À makes it possible to evacuate part of the control fluid towards the return line 136 when the pressure of the control fluid downstream of the pressure generator 130 exceeds the third pressure.

The pressure control unit 132 is supplied with control fluid at the third pressure by the pressure generator 130. It is fluidly connected to the first fluidic chamber 112 and to the second fluidic chamber 114 via the oil transfer bearing 106. It is capable of distributing the control fluid between the first fluidic chamber 112 and the second fluidic chamber 114 so as to adjust the fluid pressure inside each of these chambers 112, 114 and, thus, adjust the position of the piston 110 between its retracted and deployed positions. It is also capable of evacuating control fluid coming from the first and second fluidic chambers 112, 114 into the return line 136.

The main tank 133 is configured to collect depressurized control fluid from the return line 136. It feeds the pressure generator 130.

The emergency circuit 134 is capable of supplying the first fluid chamber 112 with control fluid so as to move the piston 110 towards its deployed position in the event of failure of the pressure generator 130. To this end, the emergency circuit 134 comprises a auxiliary tank 137 and an auxiliary pump 138. In the example shown it also includes an auxiliary pressure relief valve 139B.

The auxiliary tank 137 is configured to collect depressurized control fluid coming from the return line 136. It supplies the auxiliary pump 138. In the example shown, it also supplies the main tank 133, the depressurized control fluid coming from the return line 136. return line 136 passing through the auxiliary tank 137 before reaching the main tank 133.

The auxiliary pump 138 is capable of pumping the control fluid into the auxiliary tank 137 to bring it to the third pressure. It is fluidly connected to the pressure control unit 132 so as to supply it with control fluid at the third pressure, the pressure control unit 132 being configured to redirect all of the control fluid coming from the auxiliary pump 138 towards the first fluidic chamber 112.

The pressure relief valve 139B is capable of evacuating part of the control fluid towards the return line 136 when the pressure of the control fluid downstream of the auxiliary pump 138 exceeds the third pressure.

The control module 135 is configured to receive a timing instruction (not shown) and deduce a control signal transmitted to the pressure control unit 132. In particular, the control module 135 is configured to transmit to the pressure control unit 132 a control signal intended to increase the fluid pressure in the first chamber 112 when the timing instruction aims to increase the pitch of the blades 56, and to transmit to the pressure control unit 132 a control signal intended to increase the fluid pressure in the second chamber 114 when the timing instruction aims to reduce the pitch of the blades 56. The control module 135 is also configured to transmit to the emergency circuit 134, more particularly to its auxiliary pump 138, a start-up instruction in the event of failure of the pressure generator 130.

The connection system 78 connects the movable part 102 to each blade 56 so as to convert the translation of the movable part 102 along the longitudinal axis X in a rotation of each dawn 56 around its pivoting axis P. In particular, the 78 link system connects the mobile part 102 to each dawn 56 so as to convert:

- the translation of the movable part 102 along the longitudinal axis X in a first direction in a rotation of the variable pitch blade 56 around the pivot axis P towards the sail position, and

- the translation of the movable part 102 along the longitudinal axis

For this purpose, the connection system 78 comprises a synchronization ring 10 secured to the movable part 102 and, for each of the blades 56, a mechanism 142 for connecting the blade 56 to the synchronization ring 140.

The synchronization ring 140 extends in a radial plane around the movable part 102. It is in particular fixed to an upstream end 143 of the movable part 102.

Each connecting mechanism 142 comprises a first articulation 144 secured to the movable part 102, a second articulation 146 secured to the blade 56, away from the pivot axis P of said blade 56, and a connecting member 148 connecting the first joint 144 to the second joint 146.

The first articulation 144 is carried by the synchronization ring 140. It is here constituted by a ball joint.

The second articulation 146 is also constituted by a ball joint. It is eccentric relative to the pivot axis P.

The connecting member 148 has a first end 150 articulated to the first articulation 144 and a second end 152 articulated to the second articulation 146. Advantageously the connecting member 148 is rigid and of adjustable length, that is to say that the distance between the first and second ends 150, 152 can be modified, which makes it possible to precisely adjust the length when stopped so as to allow the control of the pitch angle of each blade 56 by the mechanism of step change 70.

The connecting member 148 is here constituted by a connecting rod 153.

In the example shown, each connecting mechanism 142 also includes a crank 154 connecting the attachment part 60 to the second articulation 146. This crank 154 is rigid and integral with the attachment part 60. It extends at least partly in a direction orthogonal to the pivot axis P. It forms an arm for rotating the blade 56.

In the example shown, the first direction goes from upstream to downstream, that is to say that the movement of the movable member 102 towards the stopper 92 (in other words towards its retracted position) causes a rotation of each blade 56 towards its sail position, and the second direction goes from downstream to upstream, that is to say that the movement of the movable member 102 away from the stopper 92 ( in other words towards its deployed position) causes each blade 56 to rotate towards its flag position. In addition, the first joint 144 is arranged upstream of the second joint 146.

For this purpose, the second articulation 146 is, as visible in Figure 8, placed opposite the trailing edge 57B relative to a plane Q orthogonal to the chord C and containing the pivot axis P.

As a variant (not shown), the first direction goes from downstream to upstream, the first joint 144 being arranged downstream of the second joint 146. The second joint 146 is then placed on the same side of the trailing edge 57B relative to the plane Q orthogonal to the chord C and containing the pivot axis P.

These particular arrangements allow, when the pitch change mechanism 70 is immobilized, that the natural stresses of the blade 56 towards its sail position cause the connecting member 148 to work in traction and not in compression. The risk of buckling of the connecting member 148 is therefore very low, so that it is possible to use a relatively weak connecting member 148 and thus lighten the pitch change mechanism 70.

The pitch change mechanism 70 also comprises a pitch locking device 160 capable of blocking the translation of the movable part 102 of the control cylinder 74 in the first direction, that is to say here towards its retracted position.

This locking device 160 comprises a support member 162 and a screw-nut system 164.

The support member 162 is movable in translation relative to the frame 72 along the longitudinal axis X between an operating position, shown in Figures 3 to 7, and a locking position (not shown). The support member 162 moves from its operating position to its locking position by translation in the first direction, that is to say, in the example shown, by translation from upstream to downstream. In other words, the operating position of the support member 162 is arranged upstream of its locking position. The support member 162 comprises a body 166 elongated along the longitudinal axis of the frame 72, and a second free longitudinal end 170. Body 166 is here full.

The first longitudinal end 168 and the orifice 90 of the frame 72 together form a guide system 172 guiding the support member 162 relative to the frame 72. This guide system 172 is here arranged on a downstream side of the screw-nut system 164.

The support member 162 also comprises a skirt 174 secured to the body 166 and arranged around the second longitudinal end 170 of the body 166.

The screw-nut system 164 includes a screw 176 and a nut 178.

The screw 176 extends around the body 166 of the support member 162 and is coaxial with said body 166. It is integral in translation with the support member 162 and mounted movable in rotation around the longitudinal axis the support member 162. For this purpose, the screw 176 is assembled to the support member 162 via a bearing 180. This bearing 180 is here interposed between the skirt 174 of the support member 162 and an end portion 182 of the screw 176, housed between the body 166 and the skirt 174.

The screw 176 has a second longitudinal end portion 184 opposite the end portion 182. This second longitudinal end portion 184 defines a radial abutment surface 186. This stop surface 186 is at a distance from the frame 72 when the support member 162 is in the operating position and rests against the stop 92 of the frame 72 when the support member 162 is in the locking position.

Here, the second longitudinal end portion 184 flares from a threaded body 190 of the screw 176 to the abutment surface 186. Thus, the contact surface between the abutment surface 186 and the stopper 92 is increased, which increases the friction forces between the abutment surface 186 and the stopper 92 and allows better transmission of braking and blocking forces.

The abutment surface 186 and the stopper 92 are each smooth here. As a variant (not shown), the abutment surface 186 and/or the stopper 92 presents asperities, so as to further increase the friction forces between the abutment surface 186 and the stopper 92 and allow transmission of the further increased efforts.

The abutment surface 186 extends in particular substantially radially. It is oriented in the first direction, that is to say, in the example shown, downstream. Here, it is provided at a downstream end of screw 176.

The threaded body 190 extends from one end portion 182, 184 to the other. It has an external thread 192 at its circumference.

The threaded body 190 and the nut 178 are housed inside the cylinder 94 of the frame 72. The nut 178 is integral with the movable part 102 of the cylinder 74 and coaxial with the screw 176. It cooperates with the screw 176 so that a translation of the nut 178 along the longitudinal axis the rotation of the screw 176 around the longitudinal axis X relative to the support member 162.

Nut 178 has an internal thread 194.

The screw-nut system 164 is in particular formed by a reversible satellite roller screw system 195. Conventionally, this satellite roller screw system 195 comprises, in addition to the screw 176 and the nut 178, a plurality of rollers 196 interposed between the screw 176 and the nut 178, each roller 196 being elongated parallel to the axis longitudinal

As visible in Figure 9, each roller 196 has a thread 198 engaging with the external thread 192 of the screw 176 and the internal thread 194 of the nut 176. It further comprises external teeth 199 located at its ends and extended of smooth pins 200.

The satellite roller screw system 195 also presents, always in a conventional manner, a device 202 for guiding and holding the rollers 196. This guiding and holding device 202 includes roller holders 204 (also called spacer rings) which are mounted coaxially with the screw 176, between it and the nut 178, with notches 206 accommodating the pins 200 of the rollers 196. It also includes a synchronization toothing 210 in which the external teeth 198 located at the respective ends of the rollers 196. This gearing of the external teeth 198 in the synchronization teeth 210 forms a planetary train whose role is to ensure synchronization of the satellite movement, also called planetary or epicyclic, of the rollers 196, thus making the movement of the rollers more fluid. rollers 196 helping them to roll easily, with as little slip as possible, on the thread 192 of the screw 176 and the tapping 194 of the nut 178.

In the example shown, the satellite roller screw system 195 is of the standard type, the rollers 196 being integral in translation with the nut 178. The synchronization teeth 210 is constituted by the internal teeth of crowns 208 integral with the nut 178 and mounted respectively at each longitudinal end of the nut 178, the latter having a longitudinal extension substantially equal to that of the threaded portion of the rollers 196 and less than that of the threaded body 190 of the screw 176.

As a variant (not shown), the satellite roller screw system 195 is of the inverted type, the rollers 196 being integral in translation with the screw 176. The synchronization teeth 210 are then constituted by two external teeth of the screw 176 at each longitudinal end of the threaded body 190, the latter having a longitudinal extension substantially equal to that of the threaded portion of the rollers 196 and less than that of the nut 178.

As a further variant, the satellite roller screw system 195 is constituted by a recirculated satellite roller screw system such as for example that described in document EP 275 504 À2, or by a rolling roller screw system such as by example that described in document EP 168 942 À1 or that described in document EP 671 070 À1.

This characteristic allows good transmission of the forces from the nut 178 to the screw 176 by the screw-nut system 164, while maintaining a small pitch in the helical connection of the screw-nut system 164. In particular, in the event of blocking of the rotation of the screw 176, it makes it possible to immobilize the nut 178 relative to the screw 176 even in the absence of a separate locking nut. It is thus possible to avoid the use of a separate locking nut, which simplifies manufacturing and reduces the costs of the mechanism, while increasing its reliability and minimizing its mass.

As a variant (not shown), the screw-nut system 164 is constituted by a screw-nut system similar to that described in EP 1 832 509.

Returning to Figure 3, the pitch locking device 160 is here outside the fluidic chambers 112, 114 of the control cylinder 74, that is to say that none of the parts of the pitch locking device 160 are is housed inside one of said fluidic chambers 112, 114. This arrangement makes it possible to assemble the pitch locking device 160 and the cylinder 74 separately from each other to the frame 72, which facilitates the mounting of the pitch change mechanism 70 and thus reduces costs. Here, the pitch locking device 160 is even away from the fluidic chambers 112, 114 of the control cylinder 74, that is to say that, in addition to being outside the fluidic chambers 112, 114, no parts of the pitch locking device 160 do not contribute to delimiting one of these chambers 112, 114.

As visible in Figure 3, part of the pitch locking device 160 even extends longitudinally away from the cylinder 74. In other words, there is a radial plane beyond which extends part of the pitch locking device 160 without the cylinder 74 extending beyond said radial plane. In particular, said part of the pitch locking device 160 extends upstream of the cylinder 74.

To enable this arrangement, the pitch locking device 160 comprises a ferrule 193 connecting the nut 178 to the movable part 102 of the cylinder 74. This ferrule 193 here projects longitudinally upstream from the control cylinder 74. It is in particular frustoconical, its diameter decreasing from its downstream end 193À, attached to the cylinder 74, to its upstream end 193B, attached to the nut 178. In the example shown, the pitch locking device 160 is also longitudinally cantilevered relative to the frame 72. In other words, the entire part of the frame 72 supporting the locking device 160 is located longitudinally of the same side, here downstream, of the locking device 160; the locking device 160 is not framed longitudinally by the part of the frame 72 supporting it. Thanks to this arrangement, we save on a support placed upstream of the locking device 160, which facilitates access to the pitch change mechanism 70 and more particularly to the connection system 78.

Thus, the control cylinder 74 is arranged longitudinally on the same side of the nut 178, here the downstream side, as the guide device 172 and the stopper 92.

To ensure good support for the locking device 160 despite this overhang, the pitch change mechanism 70 comprises a device 220 for guiding the nut 178 relative to the frame 72. This guide device 220 comprises an internal cylinder 222 secured to the nut 178 and an external cylinder 224 secured to the frame 72, the internal cylinder 222 cooperating with the external cylinder 224 so as to slide longitudinally inside the latter.

The nut 178 is in particular mounted on an internal face 226 of the internal cylinder 222. The internal cylinder 222 has an upstream end 228 to which the upstream end 193B of the ferrule 193 is fixed.

The external cylinder 224 is here constituted by the cylinder 94 of the frame 72.

The 160 pitch lock device requires lubrication. For this purpose, the locking device 160 comprises a casing 230 at least partially delimiting a circulation enclosure for a lubricating fluid of the pitch locking device 160. This casing 230 is integral with the nut 178 and surrounds the nut 178, the screw 176 and the support member 162.

This enclosure makes it possible to confine said lubricating fluid around the pitch locking device 160.

In the examples of Figures 3, 4 and 6, the casing 230 comprises the internal cylinder 222 and a plug 232 closing one end of the internal cylinder 222 opposite the frame 72, here the upstream end 228. The internal cylinder 222 has at its periphery a seal 234 in contact with an internal face 236 of the external cylinder 224. Thus, the external cylinder 224 and the casing 230 together delimit an enclosure 238 for circulating a lubricating fluid of the locking device 160. This enclosure 238 is fluidically isolated fluidic chambers 112, 114 of the cylinder 74 by the seal 234 and the upstream guide ring 116. The seal 234 and the guide ring 116 thus form seals of the pitch change mechanism 70 fluidly insulating from the pitch locking device 160 the fluidic chambers 112, 114 of the cylinder 74.

The enclosure 238 is then a closed enclosure, that is to say that the interior of the enclosure 238 is fluidically isolated from the elements external to the latter.

As a variant (not shown), in particular when the frame 72 does not include the cylinder 74, the casing 230 is constituted by the ferrule 193 and by a plug closing the upstream end 193B of the ferrule 193. The enclosure 238 is then fluidly isolated from the fluidic chambers 112, 114 of the cylinder 74 only by the upstream guide ring 116. The enclosure 238 is then, again, a closed enclosure.

In these variants where the enclosure 238 is a closed enclosure, the lubricating fluid of the locking device 160 consists of a lubricant distinct from the control fluid. Advantageously, said lubricating fluid consists of an oil. The pitch locking device 160 then comprises an accumulator (not shown) allowing the storage of the lubricating fluid when the cylinder 74 is in the retracted position and the transfer of the lubricating fluid into the enclosure 238 when the cylinder 74 moves towards its deployed position. Alternatively, the lubricating fluid of the locking device 160 consists of a grease deposited on the screw 176 and the bearings of the bearing 180.

In the example of Figure 5, where the outer cylinder 224 and the upstream guide ring 116 are absent, as well as in Figure 7, where the inner cylinder 222 and the upstream guide ring 116 are drilled, the casing 230 is constituted by the ferrule 193 and by a plug 239 closing the upstream end 193B of the ferrule 193. The first fluidic chamber 112 is then in fluidic communication with the interior of the casing 230, the control fluid constituting the lubricating fluid of the device locking 160.

This variant allows you to avoid the use of an accumulator. However, it requires a pump 130 with a greater flow rate than in the variant of Figures 3, 4 and 6.

The locking device 160 also includes a return device 240 urging the support member 162 towards its locking position and a holding device 242 for maintaining the support member 162 in its operating position when the pitch change mechanism 70 is under normal operating conditions.

The return device 240 is here constituted by a compression spring compressed between the frame 72 and a shoulder 244 secured to the support member 162. It is in particular housed in the cavity 86, between the shoulder 244 and the orifice 90.

The holding device 242 comprises a counterbalancing cylinder 250 comprising a counterbalancing piston 252 and a counterbalancing chamber 254. The counterbalancing piston 252 is mounted movable in translation along the longitudinal axis support member 162, between the support member 162 and the counterbalancing chamber 254.

The counterbalancing chamber 254 is delimited between the counterbalancing piston 252 and the frame 72. In particular, the counterbalancing chamber 254 is delimited between the counterbalancing piston 252 and a bottom 255 of the cavity 86 opposite the orifice 90; the guiding system 172, the return device 240 and the holding device 250 are thus all arranged longitudinally on the same side, here the downstream side, of the screw-nut system 164 and therefore in particular of the nut 178.

The counterbalancing chamber 254 is fluidly connected to the pressure generator 130 by a fluid connection circuit 256 so as to be supplied with control fluid at the third pressure. It is intended to counterbalance the demand on the recall device 240 when this power supply is active.

For this purpose, the counterbalancing cylinder 250 is arranged so that the pressure exerted on the piston 252 by the fluid contained in the chamber 254 is oriented in a direction opposite to that of the bias of the return device 250: in the example shown, the counterbalancing piston 252 is interposed between the chamber 254 and the shoulder 244 and the shoulder 244 is interposed between the piston 252 and the return device 240. In addition, the counterbalancing piston 252 and the counterbalancing chamber 254 are dimensioned so that, when the chamber 254 is supplied with control fluid at the third pressure, the force exerted by the control fluid on the piston 252 is greater than the stress on the return device 240.

Thus, when the supply of control fluid to the chamber 254 at the third pressure is active, the bias on the return device 240 is canceled and the support member 162 maintained in the operating position.

In the example shown, the pressure control unit 132 is fluidly interposed between the pressure generator 130 and the fluid connection circuit 256. It has a first configuration, in which it isolates the fluid connection circuit 256 from the line return line 136, and a second configuration, in which it fluidly connects the fluidic connection circuit 256 to the return line 136.

The pressure control unit 132 is configured to be normally in its first configuration and to switch to its second configuration upon receipt of a control instruction transmitted by the control module 135.

A method of changing the pitch of the blades 56, implemented by the pitch changing mechanism 70, will now be described. During a first step of this process, the control module 135 first receives a setting instruction aimed at increasing the pitch of the blades 56. The control module 135 then transmits to the pressure control unit 132 a control signal intended to increase the fluid pressure in the first chamber 112. The fluid pressure in the first chamber 112 increasing, the movable part 102 of the cylinder 74 moves in the second direction, towards its deployed position, which, via the connection system 78, causes the vanes 56 to pivot towards the large pitches (that is to say towards the flag position).

Once the mobile part 102 arrives in an equilibrium position, it stabilizes, the blades 56 maintaining a fixed orientation.

During a second step of the pitch change process, the control module 135 first receives a setting instruction aimed at reducing the pitch of the blades 56. The control module 135 then transmits to the control unit pressure 132 a control signal intended to increase the fluid pressure in the second chamber 114. The fluid pressure in the second chamber 114 increasing, the movable part 102 of the cylinder 74 moves in the first direction towards its retracted position, this which, via the connection system 78, causes the vanes 56 to pivot towards the small steps (that is to say towards the sail position).

Optionally, the pitch change method also includes, following the first or second step, a step of controlled locking of the orientation of the blades 56.

During this step, the control module 135 transmits a pitch lock command to the pressure control unit 132. Under the effect of this command, the pressure control unit 132 fluidly connects the fluid connection circuit 256 to the return line 136, resulting in a drop in the fluid pressure in the counterbalancing chamber 254. The fluid pressure in said chamber 254 is then insufficient to counterbalance the stress on the return device 240, which thus causes the support member 162 to move towards its locking position.

During this movement, the screw 176, while translating, rotates around the longitudinal axis by the control cylinder 74) until its abutment surface 186 comes to bear against the stop 92 of the frame 72, blocking the rotation of the screw 176 around the longitudinal axis X and its translation along the same axis . The blades 56 are thus blocked in their orientation even in the event of loss of fluid pressure in the first chamber 112.

In the event of a loss of pressure in the second chamber 114 only, the movable part 102 of the cylinder 74 is moved in the second direction under the effect of the pressure difference between the two chambers 112, 114, bringing with it the screw 176 and the support member 162, which returns to its operating position. The mobile part 102 is therefore no longer immobilized and can continue to move in the second direction until the blades 56 find themselves in the flag position.

In the event of a malfunction of the control system 76, typically in the event of a breakdown of the pressure generator 130, the pitch change process includes an additional step of uncontrolled locking of the orientation of the blades 56.

During this step, the malfunction of the control system 76 causes a drop in the fluid pressure in the counterbalancing chamber 254, typically because the pressure generator 130 is no longer able to bring the control fluid to the third pressure. The fluid pressure in said chamber 254 is then insufficient to counterbalance the stress on the return device 240, which thus causes the support member 162 to move towards its locking position.

During this movement, the screw 176 carries with it the nut 178 and the rollers 194, which are no longer held immobile in translation due to the loss of power to the control cylinder 74. The blades 56 therefore pivot slightly towards the small steps, until the stop surface 186 of the screw 176 comes to rest against the stop 92 of the frame 72, blocking the rotation of the screw 176 around the longitudinal axis X and its translation along the same axis .

The pivoting of the blades 56 towards the small pitches is then prevented by the locking device 160.

The non-controlled locking step is followed by a step of securing the blower 50. During this step, the emergency circuit 134 is activated and supplies the first fluidic chamber 112 with control fluid so as to increase the fluid pressure in this chamber. Under the effect of this increase in pressure, the movable part 102 moves in the second direction, taking with it the screw 176 and the support member 162, which returns to its operating position. The mobile part 102 is therefore no longer immobilized and can continue to move downstream until the blades 56 find themselves in the flag position.

It will be noted that these different steps can be implemented independently of each other. Thus, thanks to the exemplary embodiments described above, the assembly of the pitch change mechanism 70 is facilitated, and its cost reduced.

Furthermore, it is possible to lighten the pitch change mechanism 70 thanks to the compactness of the control cylinder 74 and the use of less resistant and therefore lighter connecting members 148.

The exemplary embodiments described above still make it possible to dispense with the use of a locking nut distinct from the nut 178 of the screw-nut system 164. This results in a locking device 160 and, therefore, , a pitch change mechanism 70 whose manufacturing is simplified, costs reduced and reliability increased. Said exemplary embodiments also make it possible to save on a support placed upstream of the locking device 160, which facilitates access to the pitch change mechanism 70, and more particularly to the connection system 78, once that it is assembled.

These exemplary embodiments finally allow great precision in controlling the pitch angle of the blades 56, which allows on the hub 55 the close installation of blades 56 of large size and complex geometry, thus making it possible to increase the efficiency of the turbomachine 12.

Claims

1. Pitch change mechanism (70) for adjusting an angular position of at least one variable pitch blade (56) around an axis (P) of pivoting of the blade (56), said pitch change mechanism step (70) comprising: a frame (72) fixed relative to the pivot axis (P), a control cylinder (74) comprising a fixed part (100) secured to the frame and a movable part (102) movable in translation along a longitudinal axis (X) relative to the fixed part (100) between a retracted position and an deployed position, a connection system (78) connecting the movable part (102) to the variable pitch blade (56) so to convert the translation of the movable part (102) along the longitudinal axis (X) into a rotation of the variable-pitch blade (56) around the pivot axis (P), and a pitch locking device (160) capable of blocking the translation of the movable part (102) relative to the fixed part (100) in at least one direction, in which the control cylinder (74) comprises two fluidic chambers (112, 114) delimited between the fixed part (100) and the mobile part (102), these fluidic chambers (112, 114) each containing a control fluid to control the movement of the mobile part (102) relative to the fixed part (100), the device for pitch lock (160) being outside said fluidic chambers (112, 114).

2. Pitch change mechanism (70) according to claim 1, wherein at least part of the pitch locking device (160) extends longitudinally away from the control cylinder (74).

3. Pitch change mechanism (70) according to claim 1 or 2, comprising a seal (116, 234) fluidically isolating the fluidic chambers (112, 114) from the pitch locking device (160).

4. Pitch change mechanism (70) according to any one of the preceding claims, wherein the pitch locking device (160) comprises: TJ a support member (162), movable in translation relative to the frame (72) along the longitudinal axis (X) between an operating position and a locking position, a return device (200) biasing the support member (162) towards its locking position, a holding device (202) for maintaining the support member (162) in its operating position under normal operating conditions, and a screw-nut system (164) with:

• a screw (176) integral in translation with the support member (162) and mounted movable in rotation around the longitudinal axis (X) relative to the support member (162), the screw (176) having a abutment surface (186) which is at a distance from the frame (72) when the support member (162) is in the operating position and bears against the frame (72) when the support member (162) is in position locking, and

• a nut (178) integral with the movable part (102) of the control cylinder (74) and coaxial with the screw (176), the nut (178) cooperating with the screw (176) so that a translation of the nut (178) along the longitudinal axis (X) causes the rotation of the screw (176) around the longitudinal axis (X).

5. Pitch change mechanism (70) according to claim 4, comprising a ferrule (193) connecting the nut (178) to the movable part (102) of the control cylinder (74), said ferrule (193) projecting longitudinally, in particular upstream, from the control cylinder (74).

6. Pitch change mechanism (70) according to claim 4 or 5, wherein the abutment surface (186) is provided at a downstream end of the screw (176).

7. Pitch change mechanism (70) according to any one of the preceding claims, wherein the pitch locking device (160) is lubricated by a lubricant distinct from the control fluid.

8. Pitch change mechanism (70) according to claim 7, comprising an enclosure (238) for confinement and/or circulation of said lubricant.

9. Pitch change mechanism (70) according to claim 8 in combination with any one of claims 4 to 6, wherein the pitch locking device (160) comprises a casing (230) secured to the nut ( 178) and surrounding the nut (178), the screw (176) and the support member (162), the casing (230) at least partially delimiting the enclosure (238).

10. Pitch change mechanism (70) according to any one of the preceding claims, wherein the fluidic chambers (112, 114) are closed at each of the longitudinal ends of the control cylinder (74).

11. Pitch change mechanism (70) according to any one of the preceding claims, wherein the pitch locking device (160) is away from the fluidic chambers (112, 114) of the control cylinder (74) .

12. Fan rotor (54) for a turbomachine comprising a hub (55) and a plurality of variable pitch blades (56) each pivotable relative to the hub (55) around a specific pivot axis (P), the rotor (54) further comprising a pitch change mechanism (70) according to any one of the preceding claims for adjusting an angular position of each of the variable pitch vanes (56) around its respective pivot axis (P).

13. Turbomachine (12) comprising a fan rotor (54) according to claim 12.

14. Aircraft (10) comprising a turbomachine (12) according to claim 13.

15. Method for changing the pitch of the blades (56) of a fan rotor (54) for a turbomachine, each pivotable relative to a hub (55) of the fan rotor (54) around a pivot axis (P) own, said method comprising adjusting an angular position of each of said vanes (56) around its respective pivot axis (P) by means of a pitch change mechanism (70) according to any one of claims 1 to 11.