Inverted kinematic pitch change mechanism

Abstract

This pitch-changing mechanism (70) comprises a frame (72) and a control cylinder (74) having a movable part (102) that moves in translation relative to the frame (72). It also comprises a linkage system (78) capable of converting a translation of the movable part (102) in a first direction into a rotation of the variable-pitch blade (56) towards the sail position, and a translation of the movable part (102) in a second direction into a rotation of the variable-pitch blade (56) towards the flag position. This linkage system (78) comprises a first hinge (144) integral with the movable part (102) and a second hinge (146) integral with the variable-pitch blade (56). The first hinge (144) is located upstream of the second hinge (146), the first direction being from upstream to downstream. Figure for the abbreviation: Fig. 3

Description

Title of the invention: Inverted kinematics pitch change mechanism Field of the invention

[0001] The present invention relates to the general field of turbomachines equipped with at least one fan provided with variable-pitch blades, and more particularly to the control of the orientation of the fan blades of these turbomachines.

[0002] A preferred field of application of the invention is that of turbojets with unducted fans (better known under the English names "propfan", "open fan", "open rotor" and "unducted fan"). However, the invention also applies to turboprops with one or more propulsive propellers. Technological background

[0003] One of the avenues currently being explored to improve the specific consumption of civil aircraft engines is the development of unducted fan turbojets, such as that described in document FR 2 941 493. These turbojets comprise a conventional turboshaft engine gas generator, one or more turbine stages of which drive one or more unducted fans extending outside the engine nacelle.

[0004] The blades of this or these fans are, as in the case of conventional turboprops, with variable pitch, that is to say that the angular position of these blades (called the pitch angle) can be modified during 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 rotation axis of the fan and the chord of the blade at 75% of the radius of the fan. 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.

[0005] As is known, this modification of the pitch angle during flight makes it possible to change the engine thrust and optimize the efficiency of the fan as a function of the aircraft speed. Indeed, the fan speed is almost constant over all operating phases, and it is the pitch of the blades that varies the thrust. Thus, in the cruising flight phase, the blades are oriented so as to adjust the thrust by minimizing the power taken from the turbine shaft and consumption and by optimizing efficiency. Conversely, during takeoff, the blades are oriented so as to maximize the thrust in order to accelerate and then take off the aircraft.

[0006] Controlling the orientation of the blades is commonly achieved by means of a pitch change mechanism comprising a control cylinder having a part that can move in translation along the axis of the fan and a connecting system connecting the moving part to the blade so as to convert the translation of the moving part into rotation of the variable-pitch blade. Often, said connecting system comprises a first pin secured to the moving part, a second pin secured to the blade, away from its pivot axis, and a connecting rod connecting the two pins to each other. Such a pitch change mechanism is for example known from FR 2 980 770 A1 and WO 2017 / 118793 A1.

[0007] A difficulty encountered with variable pitch vanes is that they are forced, under their own centrifugal effect, towards the sail position. This induces significant stresses in the connection system connecting the moving part to the vane, requiring the parts to be dimensioned appropriately to withstand these stresses. Most often, this dimensioning has a negative effect on the weight of the connection system. Presentation of the invention

[0008] One objective of the invention is to allow a lightening of the connection system of a pitch change mechanism controlling the orientation of variable-pitch blades. Other objectives are to facilitate the assembly of 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 variable-pitch blades.

[0009] To this end, the invention relates, according to a first aspect, to a pitch change mechanism for adjusting an angular position of at least one variable-pitch blade around a pivot axis of the blade, the variable-pitch blade being movable around its pivot axis between a sail position and a flag position, said pitch change mechanism comprising: - a frame fixed 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, and - a connection system connecting the moving part to the variable-pitch blade so as to convert: • a translation of the moving 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 • a translation of the moving part along the longitudinal axis in a second direction opposite to the first direction in a rotation of the blade to variable timing around the pivot axis towards the flag position,

[0010] said connecting system comprising 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, in which the first articulation is arranged upstream, respectively downstream, of the second articulation, the first direction going from upstream to downstream, respectively from downstream to upstream.

[0011] 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 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 chord and containing the pivot axis; - the pitch change mechanism comprises a pitch locking device capable of blocking the translation of the movable part relative to the fixed part at least in the first direction; - the step locking device includes: • a support member, movable in translation relative to the frame along the longitudinal axis between an operating position and a locking position, • a return device urging the support member towards its locking position, • a holding device for holding the support member in its operating position under normal operating conditions, and • a screw-nut system with: • a screw integral in translation with the support member and mounted to move 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 bearing against the frame when the support member is in the locking position, and • a nut secured to the moving part of the jack and coaxial with the screw, the nut cooperating with the screw so that a translation of the nut along the longitudinal axis causes the screw to rotate around the longitudinal axis,

[0012] the abutment surface being oriented in the first direction; - the support member moves from its operating position to its locking position by translation in the first direction; - the frame comprises a stop against which the stop surface of the screw comes to bear when the support member is in the locking position, the control cylinder and the stop being arranged longitudinally on the same side of the nut; - the stop surface is provided at a downstream end of the screw, respectively at an upstream end; - 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 fluid chambers each containing a control fluid for controlling the movement of the movable part relative to the fixed part; - the cylinder is continuous; - the fluid chambers are contiguous; - each fluid chamber is delimited at least in part by an external peripheral surface of the frame; - the fluid chambers are closed at each of the longitudinal ends of the cylinder; - the step locking device is outside said fluid chambers; - the pitch change mechanism includes a fluid-insulating seal specifically the fluid chambers of the pitch lock device; - one of the two fluid chambers is in fluid communication with the interior of the casing, the control fluid constituting a lubricating fluid for the locking device; - at least a portion of the pitch locking device extends longitudinally away from the cylinder; - the pitch locking device is longitudinally cantilevered relative to the frame; - the pitch change mechanism comprises a ferrule connecting the nut to the movable part of the jack, said ferrule projecting longitudinally, in particular upstream, from the jack; - the locking device comprises a guide system guiding the support member relative to the frame, the control cylinder and the system of

[0013]

[0014]

[0015]

[0016]

[0017]

[0018] guide 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 casing at least partially delimits an enclosure for circulation of a lubricating fluid for the pitch 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 an internal face of the external cylinder, the external cylinder and the casing together delimiting an enclosure for the circulation of a lubricating fluid for the locking device; - the pitch change mechanism comprises a device for guiding the nut relative to the frame, said guiding 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 so as 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 variable-pitch blades 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 at least one turbomachine according to the third aspect. Finally, the invention relates, according to a fifth aspect, to 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 about its respective pivot axis by means of a pitch changing mechanism according to the first aspect.

[0019] 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

[0020] Other characteristics and advantages of the invention will appear on reading the description which follows, given solely by way of example and with reference to the appended drawings, in which: - [Fig.l] is a top view of an aircraft according to an exemplary embodiment of the invention, - [Fig.2] is a simplified view in partial longitudinal section of a turbomachine of the aircraft of [Fig.l], - [Fig.3] is a simplified longitudinal sectional view of a part of a pitch change mechanism of the turbomachine of [Fig.2], according to a first embodiment, the pitch change mechanism being in a first configuration, - [Fig.4] is a view similar to that of [Fig.3], the pitch change mechanism being in a second configuration, - [Fig.5] is a view similar to that of [Fig.3] of a first variant of the pitch change mechanism of [Fig.3], - [Fig.6] is a view similar to that of [Fig.3] of a second variant of the pitch change mechanism of [Fig.3], - [Fig.7] is a view similar to that of [Fig.3] of a third variant of the pitch change mechanism of [Fig.3], - [Fig.8] is a simplified view along a radial axis of a rotating arm of a variable-pitch blade of the turbomachine of [Fig.2], - [Fig.9] is a perspective and partial sectional view of a satellite roller screw of the pitch change mechanism of [Fig.3], and - [Fig. 10] is a simplified longitudinal sectional view of a part of a pitch change mechanism of the turbomachine of [Fig. 2] according to a second embodiment. Detailed description of an example of implementation

[0021] The aircraft 10 shown in [Fig.l] comprises turbomachines 12 to propel it.

[0022] In the example shown, the aircraft 10 is an airplane. This comprises, in a manner conventional, a fuselage 14, a tailplane 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 tailplane 16. As a further variant (also not shown), the aircraft 10 comprises a single turbomachine 12 or at least three turbomachines 12.

[0023] One of the turbomachines 12 is shown in [Fig.2].

[0024] As visible in this Figure, the turbomachine 12 is elongated along a longitudinal axis X. It typically has an angular symmetry around said longitudinal axis X, that is to say that there is at least one angle for which the turbomachine is invariant by rotation around the longitudinal axis X.

[0025] Here and hereinafter, the terms "interior" and "exterior", "internal" and "external", as well as their variations, are understood with reference to the X axis, an element described as "interior" or "internal" being oriented towards the X axis while an "exterior" or "external" element is oriented opposite the X axis.

[0026] 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, an engine body 26 and a gas exhaust nozzle 28.

[0027] In the following, the terms “upstream” and “downstream” are understood to refer to a direction of flow of an air flow through the vein 22.

[0028] 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.

[0029] The transmission shaft 34 has the longitudinal axis X as its axis of rotation.

[0030] The transmission shaft 34 is guided in rotation relative to the nacelle 20 by means of bearings (not shown).

[0031] In the example shown, the turbomachine 12 is a multi-body turbomachine, in particular a double-body turbomachine, 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.

[0032] The low pressure body 40 comprises 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.

[0033] 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.

[0034] The low pressure shaft 46 is guided in rotation relative to the nacelle 20 by means of bearings (not shown).

[0035] 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 high pressure shaft 34.

[0036] The turbomachine 12 also comprises a fan 50 for driving the air flow in an external circulation vein 52 surrounding the nacelle 20. A primary air flow A (hot) is thus distinguished, consisting of the portion of the air flow driven in the internal circulation vein 22, and a secondary air flow B (cold), consisting of the portion of the air flow driven in the external circulation vein 52.

[0037] 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 ([Fig. 3]) provided with fan blades 56 extending substantially radially outwards from the hub 55. These blades 56, when they are rotated, drive the air flow in the external circulation vein 52.

[0038] As seen in [Fig.8], each blade 56 comprises a leading edge 57A, a trailing edge 57B and a chord C connecting the leading edge 57A to the trailing edge 57B.

[0039] Returning to [Fig. 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, that is to say that the fan rotor 54 is integral in rotation with the low pressure shaft 46. In a variant (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.

[0040] 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 duct 52, along a plane orthogonal to the longitudinal axis X. This fan stator 58 is here arranged downstream of the fan rotor 54. As a variant (not shown), the fan 50 comprises, instead of the fan stator 58, a counter-rotating fan rotor.

[0041] Advantageously, the fan 50 is, as shown, unducted, 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, as a variant, by a turboprop. As a variant (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 dilution ratio (in English “bypass ratio”), the dilution ratio 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).

[0042] 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 vein 22 and also drives the air flow in the latter. In 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.

[0043] The blades 56 of the fan rotor 54 are 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.

[0044] Each blade 56 is in particular able to pivot about 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 X. Preferably, each blade 56 is also able to pivot beyond the sail position, to a so-called reverse position, in which 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. Since the blades 56 are most often twisted, the chord C taken as a reference for measuring the pitch angle is, by convention, constituted by the chord of the blade at 75% of the radius of the fan rotor 54.

[0045] For this purpose, each blade 56 is secured, as visible in [Fig. 3], to an attachment piece 60 arranged at the blade root. This attachment piece 60 is rotatably mounted relative to the hub 55 around the pivot axis P. More precisely, the attachment piece 60 is rotatably mounted inside a housing 62 formed in the hub 55 by means of balls 64 or other rolling elements.

[0046] The fan 50 further comprises a pitch change mechanism 70 for adjusting 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 flight phases.

[0047] With reference to [Fig. 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.

[0048] 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.

[0049] The frame 72 comprises a base 80. This base 80 is centered on the longitudinal axis X. Here, it is crossed by the pivot axes P.

[0050] 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.

[0051] 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 X. This cavity 86 is in particular cylindrical, typically cylindrical of revolution, and centered on the axis X. It is interposed between the upstream face 88 and the housing 82.

[0052] 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.

[0053] In the example shown, the frame 72 also comprises 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 of revolution.

[0054] Here, the frame 72 also 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.

[0055] 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.

[0056] Alternatively, as shown in [Fig.5], the frame 72 does not include the cylinder 94.

[0057] As a further variant, as shown in [Fig.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.

[0058] Returning to [Fig. 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 X relative to the fixed part 100 between a retracted position, shown in [Fig. 3], and a deployed position shown in [Fig. 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°.

[0059] The control cylinder 74 comprises in particular a continuous cylinder 104, forming one of the fixed part 100 and the mobile part 102 and a piston 106 forming the other of the fixed part 100 and the mobile part 102. Here, the cylinder 104 forms the mobile part 102 and the piston 106 forms the fixed part 100. In a variant (not shown), it is the opposite: the cylinder 104 forms the fixed part 100 and the piston 106 forms the mobile part 102.

[0060] 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 collar 108 secured to the frame 72 extending radially outwards from the external peripheral surface 88 to the cylinder 104.

[0061] The cylinder 104 defines 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 constituted by an oil, for controlling the movement of the movable part 102 relative to the fixed part 100. This control fluid is at a first pressure in the first fluid chamber 112 and at a second pressure in the second fluid chamber 114. The first and second fluid chambers 112, 114 are arranged such that the relative increase in the first pressure (i.e., relative to the second pressure) causes the piston 110 to move towards its deployed position, the relative increase in the second pressure (i.e., relative to the first pressure) causes the piston 110 to move towards its retracted position.

[0062] Here, each of the fluid chambers 112, 114 is delimited internally by the external peripheral surface 88 of the frame 72 and externally by the cylinder 104. The first fluid chamber 112 is furthermore delimited at its downstream end by the piston 106 and the second fluid chamber 114 is delimited at its upstream end by the piston 106.

[0063] The control cylinder 74 is thus particularly compact, which makes it possible to lighten it.

[0064] In the example shown in [Fig. 3], the movable part 102 also comprises an upstream guide ring 116 and a downstream guide ring 118 each integral with the cylinder 104 and extending radially inward 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 fluid chamber 114.

[0065] In the example shown in [Fig. 3], each of the upstream and downstream guide rings 116, 118 constitutes a sealing ring and longitudinally closes the first fluid chamber 112, respectively the second fluid chamber 114. The fluid chambers 112, 114 are thus closed at each of the longitudinal ends of the control cylinder 74.

[0066] Alternatively, as shown in [Fig.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.

[0067] As a further variant, as shown in [Fig.5], the movable part 102 does not include an upstream guide ring 118.

[0068] Returning to [Fig. 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 fluid chambers 112, 114 by means of the third pressure, and a return line 136 for discharging the depressurized control fluid. The control system 76 also comprises a main reservoir 133, a backup circuit 134 and a control module 135.

[0069] 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 pressure relief valve 139A makes it possible to evacuate a portion of the control fluid to the return line 136 when the pressure of the control fluid downstream of the pressure generator 130 exceeds the third pressure.

[0070] The pressure control unit 132 is supplied with control fluid at the third pressure by the pressure generator 130. It is fluidically connected to the first fluid chamber 112 and to the second fluid chamber 114 via the oil transfer bearing 106. It is able to distribute the control fluid between the first fluid chamber 112 and the second fluid 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 extended positions. It is also able to discharge control fluid from the first and second fluid chambers 112, 114 into the return line 136.

[0071] The main reservoir 133 is configured to collect depressurized control fluid from the return line 136. It supplies the pressure generator 130.

[0072] 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. For this purpose, the emergency circuit 134 comprises an auxiliary reservoir 137 and an auxiliary pump 138. In the example shown, it also comprises an auxiliary pressure relief valve 139B.

[0073] The auxiliary tank 137 is configured to collect depressurized control fluid 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 from the return line 136 passing through the auxiliary tank 137 before reaching the main tank 133.

[0074] The auxiliary pump 138 is capable of pumping the control fluid into the auxiliary reservoir 137 to bring it to the third pressure. It is fluidically 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 to the first fluid chamber 112.

[0075] The pressure relief valve 139B is adapted to discharge a portion of the control fluid to the return line 136 when the pressure of the control fluid downstream of the auxiliary pump 138 exceeds the third pressure.

[0076] The control module 135 is configured to receive a timing instruction (not shown) and deduce therefrom 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.

[0077] The control module 135 is also configured to transmit to the emergency circuit 134, more particularly to its auxiliary pump 138, a start instruction in the event of failure of the pressure generator 130.

[0078] The connecting 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 and, where appropriate, the rotation of the movable part 102 around the longitudinal axis X into a rotation of each blade 56 around its pivot axis P. In particular, the connecting 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 first direction into 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 X in a second direction opposite to the first direction in a rotation of the variable-pitch blade 56 around the pivot axis P towards the flag position.

[0079] For this purpose, the connection system 78 comprises a synchronization ring 140 secured to the mobile part 102 and, for each of the blades 56, a mechanism 142 for connecting the blade 56 to the synchronization ring 140.

[0080] The synchronization ring 140 extends in a radial plane around the mobile part 102. It is in particular fixed to an upstream end 143 of the mobile part 102.

[0081] Each connecting mechanism 142 comprises a first articulation 144 secured to the movable part 102, a second articulation 146 secured to the blade 56, at a distance of the pivot axis P of said blade 56, and a connecting member 148 connecting the first articulation 144 to the second articulation 146.

[0082] The first articulation 144 is carried by the synchronization crown 140. Here it is constituted by a ball joint.

[0083] The second articulation 146 is also constituted by a ball joint. It is eccentric relative to the pivot axis P.

[0084] 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 setting angle of each blade 56 by the pitch change mechanism 70.

[0085] The connecting member 148 is here constituted by a connecting rod 153.

[0086] In the example shown, each connecting mechanism 142 also comprises 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.

[0087] In the example shown in [Fig. 3], the first direction is 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 is 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 a rotation of each blade 56 towards its flag position. In addition, the first articulation 144 is arranged upstream of the second articulation 146.

[0088] For this purpose, the second articulation 146 is, as visible in [Fig.8], placed opposite the trailing edge 57B relative to a plane Q orthogonal to the chord C and containing the pivot axis P.

[0089] This particular arrangement allows, 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 tension 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 to lighten the pitch change mechanism 70.

[0090] The pitch change mechanism 70 also comprises a pitch locking device 160 suitable for blocking the translation of the movable part 102 of the jack of command 74 in the first direction, that is to say here towards its retracted position.

[0091] This locking device 160 comprises a support member 162 and a screw-nut system 164.

[0092] 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 in [Fig. 3], by translation from upstream to downstream. In other words, the operating position of the support member 162 is arranged upstream of its locking position.

[0093] The support member 162 comprises a body 166 elongated along the longitudinal axis X and centered on the longitudinal axis X. Said body 166 has a first longitudinal end 168, in particular a downstream longitudinal end, engaged through the orifice 90 of the frame 72, and a second free longitudinal end 170. The body 166 is here solid.

[0094] 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.

[0095] 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.

[0096] The screw-nut system 164 comprises a screw 176 and a nut 178.

[0097] The screw 176 extends around the body 166 of the support member 162 and is coaxial said body 166. It is integral in translation with the support member 162 and mounted to move in rotation around the longitudinal axis X relative to the support member 162. For this purpose, the screw 176 is assembled to the support member 162 by means of 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.

[0098] The screw 176 has a second longitudinal end portion 184 opposite the end portion 182. This second longitudinal end portion 184 defines a radial stop 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 in abutment against the stop 92 of the frame 72 when the support member 162 is in the locking position.

[0099] Here, the second longitudinal end portion 184 flares from a threaded body 190 of the screw 176 to the stop surface 186. Thus, the contact surface between the stop surface 186 and the stopper 92 is increased, which increases the friction forces between the stop surface 186 and the stopper 92 and allows better transmission of the braking and locking forces.

[0100] The abutment surface 186 and the stopper 92 are each smooth here. Alternatively (not shown), the abutment surface 186 and / or the stopper 92 has / have asperities, so as to further increase the friction forces between the abutment surface 186 and the stopper 92 and allow for even greater transmission of forces.

[0101] The stop surface 186 extends in particular substantially radially. It is oriented in the first direction, that is to say, in the example shown in [Fig. 3], downstream. Here, it is provided at a downstream end of the screw 176.

[0102] The threaded body 190 extends from one to the other of the end portions 182, 184. It has an external thread 192 at its circumference.

[0103] The threaded body 190 and the nut 178 are housed inside the cylinder 94 of the frame 72.

[0104] The nut 178 is integral with the mobile part 102 of the jack 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 X relative to the screw 176 causes the screw 176 to rotate around the longitudinal axis X relative to the support member 162.

[0105] The nut 178 has an internal thread 194.

[0106] 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 longitudinal axis X.

[0107] As visible in [Fig.9], each roller 196 has a thread 198 engaged with the external thread 192 of the screw 176 and the internal tapping 194 of the nut 176. It further comprises external teeth 199 located at its ends and extended by smooth journals 200.

[0108] The satellite roller screw system 195 also has, in a conventional manner, a device 202 for guiding and holding the rollers 196. This guiding and holding device 202 comprises roller holders 204 (also called spacer rings) which are mounted coaxially with the screw 176, between the latter and the nut 178, with notches 206 receiving the journals 200 of the rollers 196. It also comprises a synchronizing toothing 210 in which the external toothing 198 located at the respective ends of the rollers 196 mesh.This gearing of the external teeth 198 in the synchronization teeth 210 forms a planetary gear whose role is to ensure synchronization of the satellite movement, also called planetary or epicyclic, of the rollers 196, thus smoothing the movement of the rollers 196 by helping them to roll easily, with the least possible slippage, on the thread 192 of the screw 176 and the tapping 194 of the nut 178.

[0109] 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 teeth of synchronization 210 is constituted by the internal toothing 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.

[0110] 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 toothing 210 is then constituted by two external toothings 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.

[0111] 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 A2, or by a rolling roller screw system such as, for example, that described in document EP 168 942 A1 or that described in document EP 671 070 A1.

[0112] This feature 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 allows the nut 178 to be immobilized 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 the manufacturing and reduces the costs of the mechanism, while increasing its reliability and minimizing its mass.

[0113] 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.

[0114] Returning to [Fig. 3], the pitch locking device 160 is, in the example shown in this Figure, outside the fluid chambers 112, 114 of the control cylinder 74. This arrangement makes it possible to assemble the pitch locking device 160 and the cylinder 74 to the frame 72 separately from each other, which facilitates the assembly of the pitch change mechanism 70 and thus reduces costs.

[0115] As can be seen in [Fig. 3], a portion of the pitch locking device 160 even extends longitudinally away from the cylinder 74. In other words, there is a radial plane beyond which a portion of the pitch locking device 160 extends without the cylinder 74 extending beyond said radial plane. In particular, said portion of the pitch locking device 160 extends upstream of the cylinder 74.

[0116] To allow 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. 193A, attached to the jack 74, to its upstream end 193B, attached to the nut 178.

[0117] In the example shown in [Fig. 3], the pitch locking device 160 is also longitudinally cantilevered relative to the frame 72. In other words, the entire portion of the frame 72 supporting the locking device 160 is located longitudinally on the same side, here downstream, of the locking device 160; the locking device 160 is not framed longitudinally by the portion of the frame 72 supporting it. Thanks to this arrangement, a support arranged upstream of the locking device 160 is saved, which facilitates access to the pitch change mechanism 70 and more particularly to the connecting system 78.

[0118] Thus, the control cylinder 74 is, in the example shown in [Fig. 3], arranged longitudinally on the same side of the nut 178, here the downstream side, as the guide device 172 and the stopper 92.

[0119] To ensure good support of 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 guiding 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.

[0120] 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.

[0121] The external cylinder 224 is here constituted by the cylinder 94 of the frame 72.

[0122] The pitch locking device 160 requires lubrication. For this purpose, the locking device 160 comprises a casing 230 at least partially delimiting an enclosure for circulation of 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.

[0123] 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 circulation of a lubricating fluid of the locking device 160. This enclosure 238 is fluidically isolated from the fluid chambers 112, 114 of the jack 74 by the seal 234 and the upstream guide ring 116. The seal 234 and the guide ring 116 thus form seals of the change mechanism 70 fluidly isolating the locking device 160 from the fluid chambers 112, 114 of the jack 74. not 160 the fluidic chambers 112, 114 of cylinder 74.

[0124] Advantageously, the lubricating fluid of the locking device 160 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.

[0125] In the example of [Fig. 5], where the external cylinder 224 and the upstream guide ring 116 are absent, as well as in [Fig. 7], where the internal cylinder 222 and the upstream guide ring 116 are pierced, 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 fluid chamber 112 is then in fluid communication with the interior of the casing 230, the control fluid constituting the lubricating fluid of the locking device 160.

[0126] This variant makes it possible to do without the use of an accumulator. However, it requires a pump 130 with a higher flow rate than in the variant of Figures 3, 4 and 6.

[0127] The locking device 160 also comprises a return device 240 urging the support member 162 towards its locking position and a holding device 242 for holding the support member 162 in its operating position when the pitch change mechanism 70 is in normal operating conditions.

[0128] 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.

[0129] The holding device 242 comprises a counterbalancing cylinder 250 having a counterbalancing piston 252 and a counterbalancing chamber 254.

[0130] The counterbalancing piston 252 is mounted to move in translation along the longitudinal axis X relative to the frame 72. It is in particular coaxial with the support member 162. In the example shown, it is arranged in the longitudinal extension of the support member 162, between the support member 162 and the counterbalancing chamber 254.

[0131] 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 guide 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.

[0132] The counterbalancing chamber 254 is fluidically 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 stress of the return device 240 when this supply is active.

[0133] 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 stress 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 of the return device 240.

[0134] Thus, when the supply of the chamber 254 with control fluid at the third pressure is active, the stress on the return device 240 is canceled and the support member 162 is maintained in the operating position.

[0135] In the example shown, the pressure control unit 132 is fluidly interposed between the pressure generator 130 and the fluidic connection circuit 256. It has a first configuration, in which it isolates the fluidic connection circuit 256 from the return line 136, and a second configuration, in which it fluidly connects the fluidic connection circuit 256 to the return line 136.

[0136] 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.

[0137] A method of changing the pitch of the blades 56, implemented by the pitch changing mechanism 70, will now be described.

[0138] During a first step of this method, 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. As the fluid pressure in the first chamber 112 increases, the movable part 102 of the cylinder 74 moves in the second direction, towards its deployed position, which, via the connecting system 78, causes the blades 56 to pivot towards the large pitches (i.e. towards the flag position).

[0139] Once the mobile part 102 has reached an equilibrium position, it stabilizes, the blades 56 maintaining a fixed orientation.

[0140] During a second step of the pitch change method, 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 pressure control unit 132 a control signal intended to increase the fluid pressure in the second chamber 114. As the fluid pressure in the second chamber 114 increases, the movable part 102 of the cylinder 74 moves in the first direction towards its retracted position, which, via the connecting system 78, causes the blades 56 to pivot towards the small pitches (i.e. towards the sail position).

[0141] Once the mobile part 102 has reached an equilibrium position, it stabilizes, the blades 56 maintaining a fixed orientation.

[0142] Optionally, the pitch change method also comprises, following the first or second step, a step of controlled locking of the orientation of the blades 56.

[0143] During this step, the control module 135 transmits a pitch locking 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, causing 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 of the return device 240, which thus causes the support member 162 to move towards its locking position.

[0144] During this movement, the screw 176, while translating, rotates around the longitudinal axis X under the effect of the resistance imposed by the assembly of the nut 178 and the rollers 194 (which are kept immobile in translation by the control cylinder 74) until its stop 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 X.

[0145] The blades 56 are thus blocked in their orientation even in the event of loss of fluid pressure in the first chamber 112.

[0146] In the event of a loss of pressure in the second chamber 114 only, the movable part 102 of the jack 74 is moved in the second direction under the effect of the pressure difference between the two chambers 112, 114, carrying with it the screw 176 and the support member 162, which returns to its operating position. The movable part 102 is therefore no longer immobilized and can continue to move in the second direction until the blades 56 are in the flag position.

[0147] In the event of a malfunction of the control system 76, typically in the event of failure of the pressure generator 130, the pitch change method comprises an additional step of non-controlled locking of the orientation of the blades 56.

[0148] 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 of the return device 240, which thus causes the support member 162 to move towards its locking position.

[0149] During this movement, the screw 176 carries with it the nut 178 and the rollers 194, which are no longer kept 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 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 X.

[0150] The pivoting of the blades 56 towards the small pitches is then prevented by the locking device 160.

[0151] 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 fluid 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, carrying with it the screw 176 and the support member 162, which returns to its operating position. The movable part 102 is therefore no longer immobilized and can continue to move downstream until the blades 56 are in the flag position.

[0152] It will be noted that these different steps can be implemented independently of one another.

[0153] Thus, thanks to the embodiments described above, it is possible to lighten the connection system 78 of the pitch change mechanism 70 thanks to the use of less resistant and therefore lighter connection members 148.

[0154] The weight of the pitch change mechanism 70 is thus reduced, this weight saving being further reinforced by the compactness of the control cylinder 74.

[0155] Furthermore, the assembly of the pitch change mechanism 70 is made easier, and its cost reduced.

[0156] The embodiments described above also make it possible to avoid the use of a locking nut separate from the nut 178 of the screw-nut system 164. This results in a locking device 160 and, as a result, a pitch change mechanism 70 whose manufacture is simplified, the costs reduced and the reliability increased.

[0157] Said exemplary embodiments also make it possible to save on a support arranged upstream of the locking device 160, which facilitates access to the pitch change mechanism 70, and more particularly to the connection system 78, once it is assembled.

[0158] These embodiments finally allow great precision in controlling the pitch angle of the blades 56, which allows the close implantation on the hub 55 of large blades 56 with complex geometry, thus making it possible to increase the efficiency of the turbomachine 12.

[0159] It will be noted that although the embodiments described above all relate to a case in which the first direction goes from upstream to downstream, the first articulation 144 being arranged upstream of the second articulation 146, the invention is not limited to this single variant. The invention in fact also extends to the case in which the first direction goes from downstream to upstream, the first articulation 144 being arranged downstream of the second articulation 146. The second articulation 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. Such a variant is presented in [Fig. 10], in which the reference signs used previously have been used to designate identical elements.

Claims

1.

2.

3. Claims Pitch change mechanism (70) for adjusting an angular position of at least one variable pitch vane (56) about a pivot axis (P) of the vane (56), the variable pitch vane (56) being movable about its pivot axis (P) between a sail position and a flag position, said pitch change mechanism (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 (72) and a movable part (102) movable in translation along a longitudinal axis (X) relative to the fixed part (100) between a retracted position and a deployed position, and - a connecting system (78) connecting the moving part (102) to the variable-pitch blade (56) so as to convert: • a 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 • a translation of the movable part (102) along the longitudinal axis (X) in a second direction opposite to the first direction in a rotation of the variable-pitch blade (56) around the pivot axis (P) towards the flag position, said connecting system (78) comprising a first articulation (144) secured to the movable part (102), a second articulation (146) secured to the variable-pitch blade (56), away from the pivot axis (P), and a connecting member (148) connecting the first articulation (144) to the second articulation (146), wherein the first articulation (144) is arranged upstream, respectively downstream, of the second articulation (146), the first direction going from upstream to downstream, respectively from downstream to upstream. The pitch change mechanism (70) of claim 1, wherein the connecting member (148) is a connecting rod (153). A pitch change mechanism (70) according to claim 1 or 2,

4.

5. wherein the variable pitch vane (56) comprises a leading edge (57A), a trailing edge (57B) and a chord (C) connecting the leading edge (57A) to the trailing edge (57B), the second articulation (146) being placed opposite the trailing edge (57B) relative to a plane (Q) orthogonal to the chord (C) and containing the pivot axis (P). Pitch change mechanism (70) according to any one of the preceding claims, comprising a pitch locking device (160) capable of blocking the translation of the movable part (102) relative to the fixed part (100) at least in the first direction. The pitch change mechanism (70) of claim 4, wherein the pitch locking device (160) comprises: - 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) urging the support member (162) towards its locking position, - a holding device (202) for holding 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 to move in rotation around the longitudinal axis (X) relative to the support member (162), the screw (176) having a stop surface (186) which is at a distance from the frame (72) when the support member (162) is in the operating position and bearing against the frame (72) when the support member (162) is in the locking position, and • a nut (178) secured to the movable part (102) of the jack 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), the abutment surface (186) being oriented in the first direction.

6. The pitch change mechanism (70) of claim 5, wherein the support member (162) moves from its operating position to its locking position by translation in the first direction.

7. A pitch change mechanism (70) according to claim 5 or 6, wherein the frame (72) comprises a stop (92) against which the stop surface (186) of the screw (176) bears when the support member (162) is in the locking position, the control cylinder (74) and the stop (92) being arranged longitudinally on the same side of the nut (178).

8. A fan rotor (54) for a turbomachine comprising a hub (55) and a plurality of variable pitch vanes (56) each pivotable relative to the hub (55) about 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) about its respective pivot axis (P).

9. A turbomachine (12) comprising a fan rotor (54) according to claim 8.

10. Aircraft (10) comprising at least one turbomachine (12) according to claim 9.

11. A method of changing the pitch of blades (56) of a fan rotor (54) for a turbomachine, each of which is pivotable relative to a hub (55) of the fan rotor (54) about a specific pivot axis (P), said method comprising adjusting an angular position of each of said blades (56) about its respective pivot axis (P) by means of a pitch changing mechanism (70) according to any one of claims 1 to 7.

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