Pitch-changing mechanism with locking device comprising an articulation forming a pinned ball joint

Abstract

This pitch-changing mechanism (70) comprises a frame (72), a moving part (102) which is translationally movable along a longitudinal axis (X), and a locking device (160). The locking device (160) comprises a screw / nut system (164), with a screw (176) mounted for rotational movement about the longitudinal axis (X) and a nut (178) secured to the moving part (102), and a blocking mechanism (200) for preventing the screw (176) from rotating in at least one direction. The locking device (160) also comprises an articulation (242) forming a pinned ball joint between the nut (178) and the moving part (82).

Description

[0001] Pitch changing mechanism with locking device comprising a joint forming a ball joint to a finger

[0002] FIELD OF INVENTION

[0003] The present invention relates to the general field of gas turbine engines equipped with at least one fan with variable pitch blades, and more particularly to the control of the orientation of the fan blades of these gas turbine engines.

[0004] A key area of ​​application for the invention is that of unducted fan turbojets (better known by their English names "propfan", "open fan", "open rotor" and "unducted fan"). However, the invention also applies to turboprops with one or more pusher propellers.

[0005] TECHNOLOGICAL BACKGROUND

[0006] Climate change is a major concern, and there is an urgent need to reduce carbon emissions globally. Ambitious standards have been adopted to restrict emissions from civil aviation. Technological research efforts have led to significant improvements in aircraft energy efficiency. These efforts focus on new generations of aircraft engines, aircraft weight reduction through the use of lighter materials and onboard equipment, and the development of electric propulsion technologies.

[0007] One of the avenues currently being explored to improve the specific consumption of civil aircraft engines and thus reduce their emissions is the development of turbojets with unshod fans, such as the one described in document FR 2 941 493. These turbojets include a conventional turboshaft engine gas generator, one or more turbine stages of which drive one or more unshod fans of large diameter, extending outside the engine nacelle.

[0008] One disadvantage of these large diameter blowers is that they have a reduced rotational speed and compression ratio and generate aerodynamic instabilities.

[0009] One solution to counter these instabilities is to equip these fans with variable-pitch blades, as in conventional turboprops. This means blades whose angular position (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 perpendicular to the blade's pivot axis, between the blade chord at 75% of the fan's radius and a plane perpendicular to the fan's rotation axis. It can vary from 0°, corresponding to a "sail" or "flat" blade position, to 90°, corresponding to a "flap" blade position. It can also take a value strictly less than 0°, typically around -5°, corresponding to a "reverse" blade position.

[0010] As is well known, this adjustment of the fan blade pitch angle during flight allows the engine thrust to be varied and the fan efficiency to be optimized according to the aircraft's speed. Indeed, the fan speed is almost constant throughout all phases of operation, and it is the blade pitch that varies the thrust. Thus, during cruise flight, the blades are angled to adjust the thrust while minimizing the power drawn from the turbine shaft and fuel consumption, and optimizing efficiency. Conversely, during takeoff, the blades are angled to maximize thrust in order to accelerate and then lift off.

[0011] The blade pitch control is commonly achieved using a pitch control mechanism comprising a control cylinder that rotates directly onto the fan hub. This control cylinder has a fixed section, which moves linearly with the fan hub, and a movable section that moves linearly along the fan axis. The movable section is connected to the blade by a linkage system, converting the translation of the movable section into a rotation of the variable-pitch blade. This control cylinder is generally a hydraulic cylinder supplied with fluid from a main source attached to the engine casing.This primary source comprises, in a conventional manner, a pump for pressurizing the fluid, driven by the high-pressure housing of the gas turbine via a gearbox, and a control unit for selectively directing the pressurized fluid exiting the pump to one or the other chamber of the control cylinder. A rotating fluid transfer mechanism ensures the transfer of the pressurized fluid between the housing and the blower rotor.

[0012] One difficulty encountered with variable-pitch blades is that, in the event of a malfunction of the primary power source, these blades tend, under their own centrifugal force, to move into a sail position. However, a blade stuck in this position generates little resistive torque and risks causing the engine to overspeed, with potential risks of engine damage. Furthermore, a blade stuck in this position also risks generating excessive and unacceptable drag, compromising the aircraft's controllability and / or its range in the event of a diversionary mission. To overcome this difficulty, it is known to employ safety systems capable of returning the blades to a feathered position and / or preventing the variable-pitch blades from moving towards a small pitch (i.e., towards the sail position) in the event of a failure of the blade pitch control system.Such systems are for example known from EP 1 832 509 and EP 3 400 169.

[0013] The safety system described in EP 1 832 509 employs a ball screw-nut system coupled with a locking nut. In normal operation, the nut of the ball screw system follows the movements of the cylinder controlling the blade orientation, thus causing the screw to rotate around its axis, while the locking nut follows the screw's threads without ever touching them (the locking nut's threads are designed to allow slight play with the screw threads). In the event of a malfunction in the blade orientation control system, the screw of the ball screw system is immobilized (its rotation is blocked), and the locking nut engages with the screw, thus preventing the blades from pivoting to the small pitch position.

[0014] This safety system, however, is not entirely satisfactory. Indeed, for it to function correctly, it requires very precise alignment of the screw axis with that of the cylinder. Such alignment is costly to achieve. Without this alignment, the safety system generates parasitic forces leading to premature wear.

[0015] DESCRIPTION OF THE INVENTION

[0016] One objective of the invention is to provide an economical system capable of counteracting the movement of a variable-pitch blade towards smaller pitches. Other objectives are that this system be reliable, precise, lightweight, and easy to manufacture.

[0017] To this end, the invention relates, according to a first aspect, to a pitch-changing mechanism for adjusting the angular position of at least one variable-pitch blade around a blade pivot axis, said pitch-changing mechanism being of the type comprising:

[0018] a fixed frame relative to the pivot axis,

[0019] a control cylinder comprising a fixed part attached to the frame and a movable part that moves in translation along a longitudinal axis relative to the fixed part, the movable part being mechanically connected to the variable-pitch blade such that a displacement of the movable part relative to the fixed part causes a rotation of the variable-pitch blade around the pivot axis, and

[0020] a pitch locking device suitable for blocking the translation of the moving part relative to the fixed part in at least one direction, wherein the pitch locking device comprises:

[0021] a screw-nut system with:

[0022] • a screw mounted substantially parallel to the longitudinal axis and free to rotate about the longitudinal axis relative to the frame, and

[0023] • a nut fixed in translation to the moving part along the longitudinal axis and coaxial with the screw, the nut cooperating with the screw such that a translation of the nut along the longitudinal axis causes the screw to rotate about the longitudinal axis, a locking mechanism having a screw immobilization configuration to prevent the screw from rotating relative to the frame in at least one direction, and a screw release configuration, and

[0024] a first joint forming a ball joint to a finger between the nut and the moving part.

[0025] According to particular embodiments of the invention, the pitch change mechanism has one or more of the following characteristics, taken individually or in any technically possible combination(s):

[0026] the first joint includes a universal joint;

[0027] The cardan joint comprises a first yoke attached to the moving part, a second yoke attached to the nut, and a cross joint articulated to the first yoke by a first pivot joint along a first axis substantially orthogonal to the longitudinal axis and articulated to the second yoke by a second pivot joint along a second axis substantially orthogonal to the first axis and to the longitudinal axis;

[0028] the crossbar is hollow in its center;

[0029] the pitch locking device also includes a support member, fixed in rotation relative to the frame around any axis orthogonal to the longitudinal axis, and a second joint forming a ball joint between the screw and the support member;

[0030] the second articulation comprises two angular contact bearings mounted in X, said angular contact bearings being made up of angular contact ball bearings or tapered roller bearings;

[0031] Each angular contact bearing comprises an inner ring, an outer ring, and a plurality of rolling elements arranged between said inner and outer rings and exerting contact forces on the inner and outer rings converging at a point called the "pressure peak", the pressure peaks of the two angular contact bearings being substantially coincident;

[0032] the second joint includes a spherical ball joint;

[0033] the second joint also includes a bearing assembly, consisting of at least one bearing

[0034] the bearing assembly is kinematically interposed between the screw and the spherical ball joint;

[0035] the center of the spherical ball joint is substantially coincident with the axis of the bearing assembly;

[0036] the screw is approximately coaxial with the control cylinder; and

[0037] the support element is mounted to move in translation along the longitudinal axis relative to the frame.

[0038] The invention also relates, according to a second aspect, to a blower rotor for a gas turbine engine comprising a hub and a plurality of variable pitch blades each pivotable relative to the hub around its own pivot axis, the rotor further comprising a pitch change mechanism according to the first aspect, the frame of which is integral with said hub to adjust an angular position of each of the variable pitch blades around its respective pivot axis.

[0039] The invention also relates, according to a third aspect, to a gas turbine engine comprising a blower rotor according to the second aspect.

[0040] The invention also relates, according to a fourth aspect, to an aircraft comprising at least one gas turbine engine according to the third aspect.

[0041] BRIEF DESCRIPTION OF THE FIGURES

[0042] Other features and advantages of the invention will become apparent from the following description, given solely by way of example and with reference to the accompanying drawings, in which:

[0043] Figure 1 is a top view of an aircraft according to an exemplary embodiment of the invention.

[0044] Figure 2 is a simplified partial longitudinal cross-sectional view of a gas turbine engine from the aircraft in Figure 1.

[0045] Figure 3 is a schematic representation of a pitch change mechanism for the gas turbine engine shown in Figure 2.

[0046] Figures 4 and 5 are simplified longitudinal sectional views along two orthogonal cutting planes of a part of the pitch change mechanism of Figure 3; Figure 6 is a view of a detail marked VI of Figure 4 showing a joint of the pitch change mechanism of Figure 3.

[0047] Figure 7 is a view similar to that of Figure 6 showing a variant of said joint,

[0048] Figure 8 is a view similar to that of Figure 6 showing another variant of the joint, and

[0049] Figure 9 is a view similar to that of Figure 6 showing yet another variant of the joint.

[0050] DETAILED DESCRIPTION OF A PROJECT EXAMPLE

[0051] The aircraft 10 shown in Figure 1 includes gas turbine engines 12 for propulsion.

[0052] In the example shown, aircraft 10 is an airplane. It conventionally comprises a fuselage 14, a tail assembly 16, and two wings 18. The gas turbine engines 12 are two in number and are each housed under a respective wing 18. Alternatively (not shown), the gas turbine engines 12 are arranged along the fuselage 14, for example, near the tail assembly 16. In yet another alternative (also not shown), aircraft 10 comprises a single gas turbine engine 12 or at least three gas turbine engines 12.

[0053] One of the gas turbine engines 12 is shown in Figure 2.

[0054] As can be seen in this Figure, the gas turbine engine 12 is elongated along a longitudinal axis X. It typically exhibits angular symmetry about said longitudinal axis X, that is to say, there is at least one angle for which the gas turbine engine is invariant under rotation about the longitudinal axis X.

[0055] Here and in the following, the terms "interior" and "exterior", "internal" and "external", as well as their variations, are understood in 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 in the opposite direction to the X axis.

[0056] The gas turbine engine 12 conventionally comprises a casing 20, an internal channel 22 for circulating an airflow through the casing 20, a combustion chamber 24 housed in the channel 22, an engine body 26 and a gas exhaust nozzle 28.

[0057] In the following, the terms "upstream" and "downstream" are understood to refer to the direction of flow of an airflow through vein 22.

[0058] The engine body 26 comprises a compressor 30, a turbine 32, and a drive shaft 34 coupling the turbine 32 to the compressor 30 for driving the compressor 30 by the turbine 32. The compressor 30 is located upstream of the combustion chamber 24 and supplies the combustion chamber 24 with compressed air. The turbine 32 is located downstream of the combustion chamber 24 and receives the exhaust gases exiting the combustion chamber 24.

[0059] The transmission shaft 34 has the longitudinal axis X as its axis of rotation.

[0060] The transmission shaft 34 is guided in rotation relative to the housing 20 by means of bearings (not shown).

[0061] In the example shown, the gas turbine engine 12 is a multi-body gas turbine engine, in particular a double-body, comprising a low-pressure body 40 in addition to the power body 26. The power 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 drive shaft 34 being a high-pressure shaft.

[0062] 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.

[0063] The low-pressure compressor 42 is located upstream of the high-pressure compressor 30 and supplies the latter with compressed air. The low-pressure turbine 44 is located downstream of the high-pressure turbine 32 and receives the exhaust gases exiting the latter.

[0064] The low-pressure shaft 46 is guided in rotation relative to the housing 20 by means of bearings (not shown).

[0065] 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.

[0066] The gas turbine engine 12 also includes a blower 50 to drive the airflow into an external circulation channel 52 surrounding the casing 20. Thus, a primary airflow A (hot), consisting of the portion of the airflow driven into the internal circulation channel 22, and a secondary airflow B (cold), consisting of the portion of the airflow driven into the external circulation channel 52, are distinguished.

[0067] The blower 50 includes a blower rotor 54. This blower rotor 54 is rotatably mounted relative to the housing 20 about the longitudinal axis X. It includes a hub 55 provided with blower blades 56 extending substantially radially outwards from the hub 55. These blades 56, when rotated, drive the airflow into the external circulation channel 52.

[0068] Each blade 56 comprises, in a known manner, a leading edge, a trailing edge, and a chord connecting the leading edge to the trailing edge. The blower rotor 54 is driven in rotation by the low-pressure turbine 44, via the low-pressure shaft 46. Preferably, this drive is achieved via a reduction gear (not shown) allowing the blower rotor 54 to rotate at a speed lower than that of the low-pressure shaft 46. Alternatively (not shown), this drive is direct, i.e., the blower rotor 54 is rotationally fixed to the low-pressure shaft 46.

[0069] In the example shown, the blower 50 also includes a blower stator 58 comprising fixed blades 59 arranged at the periphery of the casing 20, in the external circulation vein 52, along a plane orthogonal to the longitudinal axis X. This blower stator 58 is arranged here downstream of the blower rotor 54. In an alternative (not shown), the blower 50 includes, instead of the blower stator 58, a counter-rotating blower rotor.

[0070] Advantageously, the fan 50 is, as shown, unshod, meaning that the external circulation duct 52 has no peripheral delimitation. The gas turbine engine 12 then consists, as shown, of a turbojet with an unshod fan or, alternatively, of a turboprop. Alternatively (not shown), the external circulation duct 52 is defined between the casing 20 and a nacelle surrounding the fan 50; the gas turbine engine 12 then typically consists of a turbojet with a high bypass ratio, the bypass ratio being defined as the ratio of the secondary flow rate B (cold) to the primary flow rate A (hot).

[0071] In the example shown, the gas turbine engine 12 is specifically of the "puller" type, meaning that the fan 50 is positioned upstream of the internal circulation channel 22 and also drives the airflow into it. Alternatively (not shown), the gas turbine engine 12 is of the "pusher" type, meaning that the fan 50 is positioned around the downstream half of the casing 20.

[0072] The blades 56 of the blower rotor 54 have variable pitch, meaning that each blade 56 is mounted to pivot relative to the hub 55 around its own pivot axis P. This pivot axis P extends along the direction of elongation of the blade 56. It is orthogonal to the longitudinal axis X.

[0073] Each blade 56 is specifically capable of pivoting about the axis P relative to the hub 55 between a so-called "flag" position, in which the chord of the blade 56 is substantially orthogonal to a plane of rotation of the fan rotor 54 (and is therefore substantially parallel to the longitudinal axis X), and a so-called "sail" position, in which the chord of the blade 56 is substantially contained within said plane of rotation of the fan rotor (and is therefore substantially orthogonal to the longitudinal axis X). Preferably, each blade 56 is also capable of pivoting beyond the sail position, to a so-called "reverse" position, in which the chord of the blade 56 forms an angle, for example substantially equal to -5°, with the plane of rotation of the fan rotor 54, on the side of said plane opposite to that in which the "flag" position is located.Since the blades 56 are most often twisted, the chord taken as a reference for measuring the pitch angle is, by convention, constituted by the blade chord at 75% of the radius of the blower rotor 54.

[0074] To this end, each blade 56 is fixed, as shown in Figure 3, to a mounting piece 60 located at the blade's base. This mounting piece 60 is rotatably mounted relative to the hub 55 around the pivot axis P. More precisely, the mounting piece 60 is rotatably mounted within a housing 62 formed in the hub 55 by means of bearings 64.

[0075] With reference to Figure 3, the gas turbine engine 12 also includes 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 gas turbine engine 12 to the different phases of flight.

[0076] The pitch change mechanism 70 includes a frame 72, a control cylinder 74, a linkage system 76 and a control system 78 for the cylinder 74.

[0077] The frame 72 is integral with the hub 55 and is typically made up of a part of the hub 55. It is thus fixed relative to the pivot axes P and mobile in rotation relative to the housing 20.

[0078] Here, the frame 72 includes a base 80. This base 80 is centered on the longitudinal axis X. In the example shown, it is crossed by the pivot axes P.

[0079] The base 80 also defines a cavity 82 communicating with the outside of the base 80 through an orifice 86 opening into an upstream face 84 of the base 80 and which is here centered on the X axis. This cavity 82 is in particular cylindrical, typically cylindrical of revolution, and centered on the X axis.

[0080] The base 80 defines a stop 88 oriented upstream. This stop 88 is here formed by a part of the upstream face 84. It extends substantially radially and is in particular arranged around the opening 86.

[0081] In the example shown, the frame 72 also includes a cylinder 90 projecting upstream from the base 80. This cylinder 90 is centered on the X axis and open at its upstream end 92. It extends around the stop 88. It is typically cylindrical of revolution.

[0082] The base 80 and the cylinder 90 together define an external peripheral surface 94 of the frame 72. This external peripheral surface 94 is substantially cylindrical and centered on the X-axis. It is oriented radially outwards. The control cylinder 74 comprises a fixed part 100, integral with the frame 72, and a movable part 102 that moves in translation along the longitudinal axis X relative to the fixed part 100 between a first and a second position. Optionally, the movable part 102 is also movable in rotation about the longitudinal axis X through a small angle, for example, on the order of 5°, relative to the fixed part 100.

[0083] The control cylinder 74 is typically substantially centered on the longitudinal axis X. The control cylinder 74 therefore has the longitudinal axis X as its axis.

[0084] The control cylinder 74 includes in particular an internal portion 104 forming one of the fixed part 100 and the moving part 102 and an external portion 106 forming the other of the fixed part 100 and the moving part 102. Here, the internal portion 104 forms the fixed part 100 and the external portion 106 forms the moving part 102.

[0085] The external portion 106 delimits an internal cavity 110. The internal portion 104 includes at least one partition 108 housed within said internal cavity 110 and delimiting with the external portion 106 two fluidic chambers 112, 114 within the internal cavity 110. Each contains a control fluid, typically consisting of an oil, to control the movement of the moving 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 of the first pressure (i.e. relative to the second pressure) causes the moving part 102 to move in a first direction, the relative increase of the second pressure (i.e. relative to the first pressure) causes the moving part 102 to move in a second direction opposite to the first direction.

[0086] In the example shown, the first direction goes from downstream to upstream and the second direction goes from upstream to downstream.

[0087] Here, the external portion 106 includes a cylinder 115 extending around the external peripheral surface 94 of the frame 72, coaxially with the latter. It also includes an upstream guide ring 116 and a downstream guide ring 118, each integral with the cylinder 104 and extending radially inwards from the cylinder 104 to the outer peripheral face 94 of the frame 72. The upstream guide ring 116 is positioned upstream of the partition 108 and defines an upstream end of the first fluidic chamber 112. The downstream guide ring 118 is positioned downstream of the partition 108 and defines a downstream end of the second fluidic chamber 114. In the example shown, each of the upstream and downstream guide rings 116, 118 constitutes a sealing ring and longitudinally closes the first fluidic chamber 112, and the second fluidic chamber 114, respectively.

[0088] Here, the partition 108 is annular and extends radially outwards from the external peripheral surface 94 to the cylinder 115.

[0089] Thus, in the example shown, each of the fluidic chambers 112, 114 consists of an annular chamber delimited internally by the external peripheral surface 94 of the frame 72 and externally by the cylinder 104. The first fluidic chamber 112 is further delimited at its downstream end by the partition 108 and at its upstream end by the upstream guide ring 116, and the second fluidic chamber 114 is delimited at its upstream end by the partition 108 and at its downstream end by the downstream guide ring 118.

[0090] The linkage system 76 connects the moving part 102 to each blade 56 so as to convert the translation of the moving part 102 along the longitudinal axis X and, where applicable, the rotation of the moving part 102 about the longitudinal axis X into a rotation of each blade 56 about its pivot axis P. In particular, the linkage system 76 connects the moving part 102 to each blade 56 so as to convert:

[0091] the translation of the moving part 102 along the longitudinal axis X in the first direction by a rotation of the variable-pitch blade 56 around the pivot axis P towards the flag position, and

[0092] the translation of the moving part 102 along the longitudinal axis X in the second direction in a rotation of the variable pitch blade 56 around the pivot axis P towards the sail position.

[0093] Thus, the relative increase in the first pressure causes the blades 56 to rotate towards their flag position, and the relative increase in the second pressure causes the blades 56 to rotate towards their sail position. The first fluidic chamber 112 will therefore be referred to hereafter as the "large pitch chamber" since the increase in fluid pressure in said chamber causes the blades 56 to rotate towards higher pitch angles, and the second fluidic chamber 114 will be referred to as the "small pitch chamber" since the increase in fluid pressure in said chamber causes the blades 56 to rotate towards smaller pitch angles.

[0094] For this purpose, the linking system 76 includes a synchronizing ring 120 attached to the moving part 102 and, for each of the blades 56, a linking mechanism 122 of the blade 56 to the synchronizing ring 120.

[0095] The synchronizing ring 120 extends in a radial plane around the moving part 102. Each linkage mechanism 122 here comprises a first joint 126 fixed to the moving part 102, a second joint 128 fixed to the blade 56, away from the pivot axis P of said blade 56, a linkage member 130 connecting the first joint 126 to the second joint 128, and a crank 132 connecting the attachment piece 60 to the second joint 128.

[0096] The first joint 126 is carried by the synchronizing ring 120. It is, for example, made up of a ball joint.

[0097] The second joint 128 is also made up of a ball joint. It is eccentric relative to the pivot axis P.

[0098] The connecting member 130 has a first end (not referenced) articulated to the first joint 126 and a second end (not referenced) articulated to the second joint 128. The connecting member 130 is typically rigid.

[0099] The crank 132 is rigid and integral with the attachment piece 60. It extends at least in part along a direction orthogonal to the pivot axis P. It forms an arm for rotating the blade 56.

[0100] Alternatively (not shown), each linkage mechanism 122 is made by any suitable mechanism to convert the translation of the synchronizing ring 120 along the longitudinal axis X into a rotation of the blade 56 associated with the linkage mechanism 122 around its pivot axis P.

[0101] The control system 78 includes a fluidic system 134 to supply the fluidic chambers 112, 114 with control fluid and to collect control fluid exiting said fluidic chambers 112, 114.

[0102] This fluidic system 134 includes a main source 136 of pressurized fluid, for example a pump, comprising a low pressure inlet 138 and a high pressure outlet 140. This main source 136 is configured to draw control fluid at a low pressure lower than each of the first and second pressures, typically less than or equal to 20 bar, at the low pressure inlet 138 and to bring this control fluid to a high pressure greater than each of the first and second pressures, typically greater than or equal to 100 bar, at its high pressure outlet 140.

[0103] The fluidic system 134 also includes a fluidic circuit 142 configured to selectively supply one of the fluidic chambers 112, 114 with high-pressure control fluid and to collect the control fluid exiting the other fluidic chamber 112, 114 so as to supply the main source 136 with the control fluid thus collected. For this purpose, the fluidic system 134 includes, for example, a valve system (not shown) to selectively connect the high-pressure outlet 140 of the main source 136 to one of the fluidic chambers 112, 114, the low-pressure inlet 138 being connected to the other fluidic chamber 112, 114. Alternatively, the main source 136 is reversible, its low-pressure inlet 138 and its high-pressure outlet 140 being able to be interchanged.

[0104] In the example shown, the fluidic system 134 also includes an auxiliary source 144. This auxiliary source 144 is configured to supply control fluid at high pressure. For this purpose, it includes, for example, a pump or a pressurized fluid reservoir (not shown). The fluidic circuit 142 typically includes a valve (not shown) to fluidly connect this auxiliary source 144 to the large pitch chamber 112 in the event of a failure of the main source 136. This valve is, for example, a servovalve. Alternatively, it is controlled by the pressure of the control fluid at the outlet of the auxiliary source 144.

[0105] The control system 78 also includes an electronic control module 146 to control the fluidic system 134. This electronic control module 146 is configured to receive a pitch instruction 147 and a measurement 148 of the pitch angle of the blades 56. It is also configured to deduce from this instruction 147 and this measurement 148 a control signal 149 for the fluidic system 134.

[0106] In particular, control module 128 is configured so that control signal 149 commands:

[0107] an increase in fluid pressure in the large pitch chamber 112 when the angle measurement 148 is less than the calibration instruction 147, an increase in fluid pressure in the small pitch chamber 114 when the angle measurement 148 is greater than the calibration instruction 147, and the supply of pressurized control fluid from the auxiliary source 144 to the large pitch chamber 112 in case of failure of the main source 136.

[0108] For this purpose, the control signal 149 typically acts on the active components of the fluidic system 134, such as pumps and servovalves.

[0109] With reference to Figures 4 and 5, the pitch change mechanism 70 also includes a pitch locking device 160 designed to block the translation of the moving part 102 of the control cylinder 74 in the second direction, i.e. in the direction causing the pivoting of the blades 56 towards the small pitches.

[0110] This locking device 160 comprises a support member 162 and a screw-nut system 164. The support member 162 is fixed in rotation relative to the frame 72 around any axis orthogonal to the longitudinal axis X. It is also fixed in translation relative to the frame 72 along any axis orthogonal to the longitudinal axis X.

[0111] 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, linked to the frame 72, and a second free longitudinal end 170.

[0112] The first longitudinal end 168 is here engaged through the orifice 86 of the frame 72. The first longitudinal end 168 and the orifice 86 of the frame 72 together form a guide system 172 guiding the support member 162 in translation along the longitudinal axis X relative to the frame 72. The support member 162 is thus mounted movable in translation relative to the frame 72 along the longitudinal axis X between a first position, shown in Figures 3 to 6, and a second position (not shown).

[0113] The screw-nut system 164 includes a screw 176 and a nut 178.

[0114] The screw 176 and the nut 178 are housed inside the cylinder 90 of the frame 72.

[0115] The screw 176 is mounted substantially parallel to the longitudinal axis X, that is to say that its axis of elongation is substantially parallel to the longitudinal axis X. In particular, the screw 176 extends around the body 166 of the support member 162 and is coaxial with said body 166. In the example shown, it is also substantially coaxial with the control cylinder 74, that is to say that the axis of the screw 176 and that of the control cylinder 74 form an angle of less than 5° and are less than 10 mm apart.

[0116] The screw 176 comprises a body 180 and a longitudinal end portion 182. The body 180 is threaded. It has an external thread 184 and a substantially constant diameter.

[0117] The longitudinal end portion 182 defines a bearing surface 186. This bearing surface 186 extends, in particular at least partially radially, and is oriented in the second direction, that is to say, in the example shown, downstream. Here, the said bearing surface 186 is radial, that is to say, it is substantially parallel to a plane orthogonal to the longitudinal axis X, and it is delimited by a longitudinal end of the screw 176, here the downstream end.

[0118] The longitudinal end portion 182 is here without threads. In the example shown, it flares out from the body 180 of the screw 176 to the bearing surface 186.

[0119] The screw 176 is mounted to rotate freely around the longitudinal axis X relative to the frame 72, while being fixed in translation relative to the frame 72 along any axis orthogonal to the longitudinal axis X. In particular, it is fixed in translation to the support member 162 and mounted to rotate freely around the longitudinal axis X relative to the support member 162.

[0120] The nut 178 is fixed in translation to the movable part 102 of the cylinder 74 along the longitudinal direction X. It is also 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.

[0121] Nut 178 has an internal thread (not shown).

[0122] The screw-nut system 164 is here formed by a reversible satellite roller screw system 190. In a conventional manner, this satellite roller screw system 190 comprises, in addition to the screw 176 and the nut 178, a plurality of rollers 192 interposed between the screw 176 and the nut 178, each roller 192 being elongated parallel to the longitudinal axis X and having a thread (not shown) engaging with the external thread 184 of the screw 176 and the internal thread of the nut 176.

[0123] This feature ensures efficient transmission of forces from nut 178 to screw 176 via the screw-nut system 164, while maintaining a small pitch in the helical connection of the screw-nut system 164. In particular, if screw 176 becomes blocked from rotating, it allows nut 178 to be immobilized relative to screw 176 even without a separate locking nut. This eliminates the need for a separate locking nut, simplifying manufacturing and reducing the cost of the mechanism, while simultaneously increasing its reliability and minimizing its weight.

[0124] As an alternative (not shown), the screw-nut system 164 is formed by a reversible ball screw system.

[0125] As a further alternative (still not shown), the screw-nut system 164 consists of a screw-nut system similar to that described in EP 1 832509.

[0126] The locking device 160 also includes a locking mechanism 200 for selectively immobilizing and releasing the screw 176 relative to the frame 72.

[0127] This mechanism 200 includes a locking piece 202. It also includes a mechanism 203 for moving the screw 176 and the locking piece 202 relative to each other between a first configuration (not shown), in which the screw 176 is engaged with the locking piece 202 so as to prevent the rotation of the screw 176 relative to the frame 72 in at least one direction, and a second configuration, shown in the Figures, in which the screw 176 is separated from said locking piece 202 in a blocking direction so as to be free to rotate about the longitudinal axis X. The locking mechanism 200 thus has a locking configuration of the screw 176 corresponding to the first configuration mentioned above and a release configuration of the screw 176 corresponding to the second configuration mentioned above.

[0128] The blocking direction here is constituted by a direction parallel to the longitudinal axis X.

[0129] In particular, in the first configuration, the bearing surface 186 is in contact with a friction surface 204 of the locking piece 202. In the second configuration, the bearing surface 186 is away from the friction surface 204 along the locking direction.

[0130] Thanks to the flared shape of the longitudinal end portion 182, the size of the bearing surface 186, and therefore the size of the contact area between the bearing surface 186 and the friction surface 202, is increased. This increases the friction forces between the bearing surface 186 and the friction surface 202 and allows for better transmission of braking and locking forces between these two surfaces.

[0131] Preferably, the bearing surface 186 and / or the friction surface 204 have asperities, so as to further increase the friction forces between the bearing surface 186 and the friction surface 204 and thus allow for even greater force transmission. Alternatively, the bearing surface 186 and the friction surface 204 are each smooth.

[0132] Preferably, one of the screw 176 and the locking piece 202, hereafter referred to as the moving part 206, is free to move in translation relative to the frame 72 along the locking direction, and the other of the screw 176 and the locking piece 202, hereafter referred to as the fixed part 208, is fixed in translation to the frame 72 along said locking direction. The displacement mechanism 203 then consists of a mechanism for moving the moving part 206 relative to the frame 72.

[0133] Here, the moving part 206 is the screw 176, and the fixed part 208 is the locking piece 202. The locking piece 202 is, in particular, formed by a portion of the frame 72, with the stop 88 constituting the friction surface 204. The movement of the screw 176 relative to the frame 72 between the first and second configurations of the locking mechanism 200 is enabled by the translation of the support member 162 relative to the frame 72 along the X-axis. The support member 162 thus forms part of the displacement mechanism 203. It has a locking position (not shown), corresponding to the immobilization configuration of the locking mechanism 200, in which the bearing surface 186 is in contact with the stop 88, and an operating position, shown in the Figures and corresponding to the release configuration of the locking mechanism 200, in which the bearing surface 186 is at the gap of the stop 88.The support member 162 moves from its operating position to its locking position by translation in the second direction, that is, in the example shown, by translation from upstream to downstream. In other words, the operating position of the support member 162 is located upstream of its locking position.

[0134] The displacement mechanism 203 also includes an actuator 210 for selectively bringing the screw 176 and the locking piece 202 closer together and further apart.

[0135] This actuator 210 includes a return device 211 that forces the screw 176 and the locking piece 202 towards each other in the direction of locking. It also includes a retaining device 212 for holding the screw 176 and the locking piece 202 apart when the pitch change mechanism 70 is in normal operating conditions.

[0136] The return device 211 is here constituted by a compression spring compressed between a first surface 214 fixed in translation to the moving part 206 along the blocking direction and a second surface 216 fixed in translation to the fixed part 208 along the blocking direction.

[0137] The holding device 212 includes a counterbalancing cylinder 220 comprising a counterbalancing piston 222 and a counterbalancing chamber 224.

[0138] The counterbalancing piston 222 is mounted to move in translation along the blocking direction relative to the frame 72. It is fixed in translation to the moving part 206 along the blocking direction.

[0139] The counterbalancing chamber 224 is delimited between the counterbalancing piston 222 and the frame 72. It is fluidically connected to the main source 136 by the fluidic circuit 142 so as to be supplied with control fluid at the high pressure provided by said main source 136. It is intended to counterbalance the stress on the return device 211 when this supply is active.

[0140] To this end, the counterbalancing cylinder 220 is arranged so that the pressure exerted on the piston 222 by the fluid contained in the chamber 224 is oriented in the blocking direction, in a direction opposite to that of the force exerted by the return device 211 on the moving part 206. Furthermore, the counterbalancing piston 222 and the counterbalancing chamber 224 are dimensioned so that, when the chamber 224 is supplied with high-pressure control fluid, the force exerted by the control fluid on the piston 222 is greater than the force exerted by the return device 211. Thus, when the supply of high-pressure control fluid to the chamber 224 is active, the force exerted on the return device 211 is canceled and the screw 176 and the locking part 202 are kept apart from each other.In the example shown, the counterbalancing piston 222 is integral with the support member 162 along the longitudinal direction X. In particular, it is coaxial with the support member 162 and is arranged in the longitudinal extension of the support member 162, between the support member 162 and the counterbalancing chamber 224.

[0141] In the example shown, the counterbalancing piston 222 is also housed in the cavity 82. It divides the cavity 82 in a sealed manner into a first part 226 and a second part 228.

[0142] The first part 226 is delimited along the longitudinal direction X between the piston 222 and a first wall 230 of the cavity 82 into which the orifice 86 opens. The return device 211 is housed in said first part 226, the first surface 214 being constituted by the face of the piston 222 oriented towards the first part 226 and the second surface 216 being delimited by the first wall 230.

[0143] The second part 228 is delimited along the longitudinal direction X between the counterbalancing piston 222 and a second wall 232 of the cavity 82 longitudinally opposite to the first wall 230. Said second part 228 constitutes the counterbalancing chamber 224.

[0144] The counterbalancing piston 222 is thus interposed between the counterbalancing chamber 224 and the first surface 214, and the first surface 214 is interposed between the piston 222 and the return device 211. This allows the pressure exerted on the piston 222 by the fluid contained in the chamber 224 to be oriented along the blocking direction, in a direction opposite to that of the stress on the return device 211 on the moving part 206.

[0145] The locking device 160 also includes a guide device 234 for the nut 178 relative to the frame 72, to guide the nut 178 in translation along the longitudinal direction X. This guide device 234 has an internal cylinder 236 attached to the nut 178 and an external cylinder 238 attached to the frame 72, the internal cylinder 236 cooperating with the external cylinder 238 so as to slide longitudinally inside the latter.

[0146] Here, the internal cylinder 236 extends around the nut 178, the nut 178 being mounted on an internal face of said internal cylinder 236. In an alternative (not shown), the internal cylinder 236 is formed as a single piece with the nut 178.

[0147] The external cylinder 238 is here constituted by the cylinder 90 of the frame 72.

[0148] The locking device 160 further includes a connecting device 240 for the nut 178 to the moving part 102 of the control cylinder 74, such that the nut 178 is fixed in translation to the moving part 102 of the cylinder 74 along the longitudinal direction X. This connecting device 240 includes a joint 242 forming a ball-and-pin connection between the nut 178 and the moving part 102. In the example shown, the connecting device 240 also includes an inner ferrule 244 and an outer ferrule 246.

[0149] The joint 242 is in particular formed by a cardan joint 250. This cardan joint 250 includes a cross 252, a first clevis 254 integral with the movable part 102 and a second clevis 255 integral with the nut 178.

[0150] The cross member 252 is articulated to the first yoke 254 by a first pivot joint 256 (Figure 4) along a first axis Y substantially perpendicular to the longitudinal axis X. It is articulated to the second yoke 255 by a second pivot joint 257 (Figure 5) along a second axis Z substantially perpendicular to the first axis Y and to the longitudinal axis Z. Here and in the following, "substantially perpendicular" means that two axes are substantially orthogonal to each other and that they are substantially concurrent.

[0151] Each of the first and second pivot joints, respectively 256, 257, is here a pure pivot joint, that is to say that it has no other degree of freedom than the degree of freedom in rotation around the first axis Y, respectively around the second axis Z. As an alternative (not shown), at least one of the first and second pivot joints 256, 257 is constituted by a sliding pivot joint.

[0152] In the example shown, the cross 252 is hollow in its center. In particular, it includes a ring 260, a pair of primary axes 262 (Figure 4) and a pair of secondary axes 264 (Figure 5).

[0153] The ring 260 is interposed between the first yoke 254 and the second yoke 255. In particular, it is radially framed by the first yoke 254 and it radially frames the second yoke 255. By the fact that a first part "radially frames" a second part, it is understood here and in the following that there is at least one axis perpendicular to the longitudinal axis X along which the first part frames the second part.

[0154] The primary axes 262 are diametrically opposed with respect to the ring 260. Each is fixed to the ring 260, extends substantially along the first axis Y and is engaged in a complementary primary recess 266 (Figure 4), formed in the first yoke 254. The cooperation of the primary axes 262 with the recesses 266 in which they are engaged forms the first pivot joint 256.

[0155] Here, each primary axis 262 extends radially outwards from the ring 260.

[0156] The secondary axes 264 are diametrically opposed with respect to the ring 260. Each is fixed to the ring 260, extends substantially along the second axis Z and is engaged in a complementary secondary recess 268 (Figure 5), formed in the second yoke 255. The cooperation of the secondary axes 264 with the recesses 268 in which they are engaged forms the second pivot joint 257.

[0157] Here, each secondary axis 264 extends radially inwards from the ring 260.

[0158] In an alternative (not shown), the primary axes 262 and secondary axes 264 are integral with the cleats 254, 255 and cooperate with recesses made in the cross member 252.

[0159] As described above, the first yoke 254 includes primary recesses 266 cooperating with the primary axes 262 of the cross 250 to form the first pivot joint 256. These primary recesses 266 are each oriented along the first Y axis and are diametrically opposed to each other.

[0160] As described above, the second yoke 255 includes secondary recesses 268 cooperating with the secondary axes 264 of the cross 250 to form the second pivot joint 256. These secondary recesses 268 are each oriented along the second Z axis and are diametrically opposed to each other.

[0161] In variants (not shown), the joint 242 is formed by any other type of joint forming a ball joint to finger connection, for example a ball joint to finger or a tripod joint.

[0162] This joint 242 compensates for any misalignments between the moving part 102 of the cylinder 74 and the nut 178. The two degrees of rotational freedom provided by the joint 242 allow the nut to translate in a direction forming a slight angle with the direction of translation of the moving part 102. This limits the forces between the nut 178 and parts that may not be perfectly aligned with the direction of translation of the moving part 102, such as the screw 176 and the external cylinder 238 of the nut 178 guide system 234, thus reducing the risk of seizing and wear of the screw-nut system 164.

[0163] The inner ferrule 244 has a downstream end 270 for connection to the nut 178, here via the inner cylinder 236, and an opposing upstream end 272. It projects longitudinally upstream from said downstream end 270. It is oriented along the longitudinal axis X and is centered on this axis.

[0164] The inner ferrule 244 is formed as a single piece with the inner cylinder 236. The outer ferrule 246 has a downstream end 274 for connection to the moving part 102 of the cylinder 74 and an opposing upstream end 276. It projects longitudinally upstream from said downstream end 274. It is oriented along the longitudinal axis X and is centered on this axis.

[0165] The outer ferrule 246 extends around the inner ferrule 244. The inner ferrule 244 and the outer ferrule 246 are linked to each other by their upstream ends 272, 276. They thus define between them an annular space 278 open downstream suitable for receiving the cylinder 90. This allows the nut 178 to move inside the cylinder 90 while being held fixed against translation to the moving part 102 of the control cylinder 74.

[0166] In the example shown, the inner ferrule 244 and the outer ferrule 246 are connected to each other by the joint 242. Thus, the first yoke 254 is integral with the outer ferrule 246 and located at its upstream end 276, and the second yoke 255 is integral with the inner ferrule 244 and located at its upstream end 272. Here, the first yoke 254 is formed as a single piece with the outer ferrule 246, and the second yoke 255 is a separate piece from the inner ferrule 244 and is fixed to it. Alternatively (not shown), the first yoke 254 is a separate piece from the outer ferrule 246 and is fixed to it, and / or the second yoke 255 is formed as a single piece with the inner ferrule 244.

[0167] The pitch locking device 160 requires lubrication. For this purpose, the locking device 160 includes a housing 280 that at least partially encloses a container 282 for the lubrication of the pitch locking device 160. This housing 280 is integral with the nut 178 and surrounds the nut 178 and the screw 176.

[0168] Here, the housing 280 includes the inner cylinder 236 and the inner ferrule 244. It also includes a plug 284 closing the inner ferrule 244 at its upstream end 272. Furthermore, a seal 286 is provided at the interface between the inner cylinder 236 and the outer cylinder 238. Thus, the outer cylinder 238 and the housing 280 together define the enclosure 282 containing the lubricating fluid of the locking device 160.

[0169] Here, the 280 crankcase is formed from a single piece.

[0170] Advantageously, the lubricating fluid for the locking device 160 is an oil. The pitch locking device 160 then includes an accumulator (not shown) that stores the lubricating fluid when the cylinder 74 is in a position corresponding to the sail position of the blades 56, and transfers the lubricating fluid into the housing 282 when the cylinder 74 moves to drive the blades 56 towards the large pitch position. Alternatively, the lubricating fluid for the locking device 160 is grease deposited on the screw 176.

[0171] The locking device 160 finally includes a joint 288 through which the screw 176 is assembled to the support member 162. This joint 288 has one degree of rotational freedom about the longitudinal axis X so as to allow the screw 176 to rotate about the longitudinal axis X relative to the support member 162. In particular, it is interposed between the support member 162 and the longitudinal end portion 182 of the screw 176. Here, it is housed between the screw 176 and the body 166 of the support member 162.

[0172] The joint 288 forms a ball joint between the screw 176 and the support member 162. In addition to the rotational degree of freedom around the longitudinal axis X, it provides two further rotational degrees of freedom around two axes orthogonal to the longitudinal axis X. This compensates for any misalignment between the nut 178 and the support member 162. These two additional degrees of freedom facilitate the alignment of the screw 176 with the nut 178 in the event of misalignment of the nut 178 with the support member 162. The parasitic forces exerted by the nut 178 on the screw 176 are thus reduced, thereby minimizing the risk of seizing and wear of the screw-nut system 164.

[0173] Referring to Figure 6, in the first variant of Figures 4 to 6, the joint 288 is formed by a bearing 290 comprising two angular contact bearings 292 mounted in an X configuration. In the example shown, these angular contact bearings 292 are angular contact ball bearings. In an alternative (not shown), they are tapered roller bearings.

[0174] Each angular contact bearing 292 comprises an inner ring 294, an outer ring 295, and a plurality of rolling elements 296 arranged between said rings 294, 295 and exerting contact forces on the rings 294, 295. These contact forces converge at a point called the "pressure peak" 297, 298. The pressure peaks 297, 298 of the two angular contact bearings 292 are substantially coincident. This maximizes the angular amplitude of the spherical joint formed by the bearing 290.

[0175] In the example shown, for each bearing 292, the inner ring 294 is integral with the support member 162 and the outer ring 296 is integral with the screw 176.

[0176] With reference to Figure 7, in the second variant shown in this figure, the joint 288 includes a spherical ball joint 300 and a bearing assembly 301.

[0177] Typically, the spherical ball joint 300 comprises an inner ring 302 and an outer ring 304. The inner ring 302 has a convex spherical outer profile. The outer ring 304 has a concave spherical inner profile. The inner ring 302 is embedded inside the outer ring 304, with the outer and inner profiles of the two rings 302 and 304 coinciding with each other.

[0178] The bearing assembly 301 comprises at least one, here two, bearing(s) 306. Each bearing 306 conventionally comprises an inner ring 308, an outer ring 310, and a plurality of rolling elements 312 arranged between said rings 308, 310. The outer ring 310 is here integral with the screw 176. In the example shown, the center of the spherical ball joint 300 is substantially coincident with the axis of the bearing assembly 301. This arrangement is particularly compact.

[0179] Here, the bearing assembly 301 is kinematically interposed between the spherical ball joint 300 and the screw 176. In particular, the inner ring 302 of the spherical ball joint 300 is integral with the support member 162. Furthermore, the spherical ball joint 300 is housed within the bearing assembly 301, the outer ring 304 of said spherical ball joint 300 being integral with the inner ring 308 of each bearing 306 composing the bearing assembly 301. This arrangement minimizes the inertia of the screw 176.

[0180] In an alternative (not shown), the reverse is true: the bearing assembly 301 is kinematically interposed between the spherical ball joint 300 and the support member 162. In particular, the outer ring 304 of the spherical ball joint 300 is integral with the screw 176. Furthermore, the bearing assembly 301 is housed inside the spherical ball joint 300, the inner ring 302 of the spherical ball joint 300 being integral with the outer ring 310 of each bearing 306 composing the bearing assembly 301.

[0181] With reference to Figure 8, in the third variant shown in this figure, the joint 288 is formed by a spherical ball bearing 314.

[0182] With reference to Figure 9, in the fourth variant shown in this figure, the joint 288 is formed by a spherical roller bearing 316.

[0183] Thus, thanks to the invention described above, parasitic stresses in case of misalignment of the parts are reduced. It is therefore possible to be less rigorous during manufacturing and assembly and to have wider manufacturing tolerances. This makes it easier to produce the 70 pitch change mechanism, which reduces its cost without compromising its weight, precision, or reliability.

Claims

24 DEMANDS 1. Pitch change mechanism (70) for adjusting the angular position of at least one variable-pitch blade (56) about a blade pivot axis (P) of the blade (56), said pitch change mechanism (70) comprising: a fixed frame (72) relative to the pivot axis (P), a control cylinder (74) comprising a fixed part (100) integral with the frame (72) and a movable part (102) movable in translation along a longitudinal axis (X) relative to the fixed part (100), the movable part (102) being mechanically connected to the variable-pitch blade (56) such that a displacement of the movable part (102) relative to the fixed part (100) causes a rotation of the variable-pitch blade (56) around the pivot axis (P), and a pitch locking device (160) adapted to block the translation of the moving part (102) relative to the fixed part (100) in at least one direction, the step locking device (160) comprising: a screw-nut system (164) with: • a screw (176) mounted substantially parallel to the longitudinal axis (X) and free to rotate about the longitudinal axis (X) relative to the frame (72), and • a nut (178) fixed in translation to the movable part (102) along the longitudinal axis (X) and coaxial with the screw (176), the nut (178) cooperating with the screw (176) such that a translation of the nut (178) along the longitudinal axis (X) causes the screw (176) to rotate around the longitudinal axis (X), and a locking mechanism (200) having a screw (176) immobilization configuration, to prevent the screw (176) from rotating relative to the frame (72) in at least one direction, and a screw (176) release configuration, in which the pitch locking device (160) also includes a first joint (242) forming a finger ball joint between the nut (178) and the moving part (82).

2. Pitch changing mechanism (70) according to claim 1, wherein the first articulation (242) comprises a universal joint (250).

3. Pitch changing mechanism (70) according to claim 1 or 2, wherein the pitch locking device (160) also includes a support member (162), fixed in rotation relative to the frame (72) around any axis orthogonal to the longitudinal axis (X), and a second joint (288) forming a ball joint between the screw (176) and the support member (162).

4. Pitch changing mechanism (70) according to claim 3, wherein the second articulation (288) comprises two angular contact bearings (292) mounted in X, said angular contact bearings (292) being made up of angular contact ball bearings or tapered roller bearings.

5. Pitch changing mechanism (70) according to claim 4, wherein each angular contact bearing (292) comprises an inner ring (294), an outer ring (295) and a plurality of rolling elements (296) arranged between said inner and outer rings (294, 295) and exerting on the inner and outer rings (294, 295) contact forces converging at a point called "pressure peak" (297, 298), the pressure peaks (297, 298) of the two angular contact bearings (292) being substantially coincident.

6. Pitch changing mechanism (70) according to claim 3, wherein the second joint (288) comprises a spherical ball joint (300).

7. Pitch changing mechanism (70) according to claim 6, wherein the second articulation (288) also includes a bearing assembly (301), consisting of at least one bearing (306).

8. Blower rotor (54) for gas turbine engine comprising a hub (55) and a plurality of variable pitch blades (56) each pivotable relative to the hub (55) about its own pivot axis (P), the rotor (54) further comprising a pitch changing mechanism (70) according to any one of the preceding claims, the frame (72) of which is integral with said hub (55) for adjusting an angular position of each of the variable pitch blades (56) about its respective pivot axis (P).

9. Gas turbine engine (12) comprising a blower rotor (54) according to claim 8.

10. Aircraft (10) comprising at least one gas turbine engine (12) according to claim 9.

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