CRANKCASE FOR AN AIRCRAFT TURBOMACHINE

Abstract

The invention relates to a housing for an aircraft turbomachine, the housing comprising: - at least one annular body extending about a first axis (X), - sleeves (26) adapted to receive blades, the sleeves (26) being distributed about the first axis (X), each sleeve (26) having an annular wall (27) extending about a second axis (Y) oriented radially with respect to the first axis (X), characterized in that each sleeve (26) is connected to the body by a first radial link (L1) with respect to the first axis (X) and by a second radial link (L2) with respect to the first axis (X). Figure 2

Description

Title of the invention: Casing for an aircraft turbomachine Technical field of the invention

[0001] The invention relates to the field of housings for aircraft turbomachinery.

[0002] The invention relates in particular to the field of housings carrying fixed vanes, in particular with variable pitch angle, also known by the English acronym OGV for "Outlet Guided Vanes". Technical background

[0003] Among aircraft turbomachinery, there are unducted single-fan turbomachinery. This type of turbomachine offers high propulsive efficiency compared to ducted single-fan turbomachinery.

[0004] This type of turbomachine typically extends around and along a longitudinal axis and comprises, from upstream to downstream in the direction of the gas flow along this longitudinal axis, an unshod blower, a low-pressure compressor, a high-pressure compressor, a combustion chamber, a high-pressure turbine and a low-pressure turbine.

[0005] In contrast to enclosed fan turbomachines, the unenclosed fan turbomachine does not include a fan casing surrounding the fan.

[0006] The low pressure turbine is conventionally connected to the low pressure compressor and the blower by a low pressure shaft, and the high pressure turbine is connected to the high pressure compressor by a high pressure shaft.

[0007] The blower compresses an airflow. The compressed airflow splits into a primary airflow flowing in a primary channel of the turbomachine and a secondary airflow flowing in a secondary channel surrounding the primary channel. The primary airflow is compressed in the compressors and then burned in the combustion chamber. The combustion gases pass through the turbines, which then drive the blower and the low-pressure compressor.

[0008] Furthermore, the unshrouded turbomachine typically includes an air inlet casing arranged axially between the fan and the low-pressure compressor. The inlet casing is typically axially connected to a casing of the low-pressure compressor located downstream. The inlet casing includes, in a known manner, an inner shell centered on the longitudinal axis and an outer shell arranged coaxially around the inner shell. The outer shell internally delimits a portion of the secondary vein and the internal ferrule externally delimits a part of the primary vein.

[0009] To improve the performance of the turbomachine, the inlet casing carries fixed vanes, also known by the English acronym OGV for "Outlet Guided Vanes." Such vanes are regularly spaced around the longitudinal axis and compress the secondary airflow. These fixed vanes typically have a variable pitch angle, allowing their pitch angle to be adapted to the turbomachine's operating speeds.

[0010] In order to connect the blades to the inlet housing, the inlet housing typically includes support sleeves for these fixed blades, regularly distributed around the longitudinal axis and connected to the outer ferrule. Each support sleeve typically includes a hollow annular wall into which the fixed blades are inserted for their attachment to the inlet housing.

[0011] However, integrating these sleeves onto the inlet housing presents many challenges.

[0012] Indeed, the inlet casing absorbs forces generated by the upstream fan and forces generated by the downstream compressors. The inlet casing is also connected to a pylon linking the turbomachine to the aircraft, which ensures the transfer of axial thrust. Furthermore, the inlet casing must allow for the passage of service lines in areas close to the inlet casing.

[0013] The large number of stress points, constraints and air veins implies a complex geometric definition of this inlet housing and implies, for example, a connecting flange for the sleeves.

[0014] However, attaching the support sleeves for the fixed blades requires increasing the dimensions of the housing, reducing the space available for the passage of auxiliary lines. Furthermore, attaching the support sleeves to the inlet housing generates additional stresses on this inlet housing, necessitating reinforcement of the inlet housing against these additional stresses, for example by adding stiffeners, ultimately impacting the feasibility of this inlet housing.

[0015] There is therefore a need to provide a housing for an aircraft turbomachine, including variable pitch blade support sleeves, which are compact and whose load transfer is optimal. Summary of the invention

[0016] To this end, the invention proposes a housing for an aircraft turbomachine, the housing comprising:

[0017] - at least one annular body extending around a first axis,

[0018] - sleeves suitable for receiving blades, the sleeves being distributed around the first axis, each sleeve having an annular wall extending around a second axis oriented radially with respect to the first axis.

[0019] The housing according to the invention is remarkable in that each sleeve is connected to the body by a first radial link with respect to the first axis and by a second radial link with respect to the first axis.

[0020] By "radial connection" is meant a connection involving at least two bearing surfaces extending in a plane parallel to the first axis and cooperating together.

[0021] Thanks to this double radial link connecting each sleeve to the body of the housing, the distribution of forces is improved.

[0022] This makes it possible to eliminate the need for stiffeners and the connecting flange, which simplifies the geometry of the housing and therefore its manufacture. Furthermore, the overall size of the housing is reduced, facilitating the routing of auxiliary components.

[0023] Finally, optimizing the distribution of forces in the sleeve makes it possible to reduce the deformation of the housing during operation.

[0024] The invention may comprise one or more of the following features, taken individually or in combination with each other:

[0025] - each sleeve comprises a first connecting arm extending from the wall and connected to the body by the first link,

[0026] - each first connecting arm has a bearing surface which is oriented radially inwards and which cooperates radially with a body support surface that is oriented radially outwards, the support surfaces extending in a plane parallel to the first axis and held tightly together to form the first bond,

[0027] - each sleeve includes a second connecting arm extending from the wall and connected to the body by the second connection,

[0028] - the second connecting arm comprises a first portion which extends substantially parallel to the first axis and a second portion which extends substantially radially and is connected to the body, the first and second portions being connected to each other by an intermediate curved portion,

[0029] - the first and second arms are diametrically opposed with respect to the second axis,

[0030] - among the sleeves, at least one first sleeve and one adjacent second sleeve to the first sleeve, are connected to each other,

[0031] - the walls of the first and second sleeves are connected to each other by a first connecting bar,

[0032] - the second arms of the first and second sleeves are connected to each other by a second connecting bar,

[0033] - the second connecting bar is radially supported on the body, relative to the first axis,

[0034] - the body comprises a first annular ferrule which extends around the first axis and a second annular ferrule which extends around the first axis, the first and second ferrules being axially connected to each other, each sleeve being connected to the first ferrule by the first connection and to the second ferrule by the second connection.

[0035] The invention also relates to a turbomachine for an aircraft, comprising a casing according to any one of the preceding characteristics. Brief description of the figures

[0036] Other features and advantages will become apparent from the following description of a non-limiting embodiment of the invention with reference to the accompanying drawings in which:

[0037] [Fig.1] is a schematic axial cross-sectional representation of half an aircraft turbomachine;

[0038] [Fig.2] is a schematic representation of part of a casing according to the invention comprising first and second ferrules connected to a blade support sleeve;

[0039] [Fig.3] is a perspective view of a sleeve fitting the housing of [Fig.2];

[0040] Figure 4 is a perspective view of a housing according to the invention comprising sleeves connected together according to an embodiment of the invention;

[0041] [Fig.5] is a perspective view of two sleeves connected together and which can be fitted to the housing of [Fig.4],

[0042] [Fig.6] is a perspective view of a housing according to the invention comprising sleeves connected together according to another embodiment of the invention. Detailed description of the invention

[0043] An example of a turbomachine 1 is illustrated in [Fig. 1]. The turbomachine 1 extends around and along a first axis X.

[0044] In the remainder of the application, unless otherwise indicated, the terms "longitudinal", "longitudinally", "axial", "axially", "radial", "radially", are understood to be in relation to the first X axis of the turbomachine 1.

[0045] The terms "exterior", "interior" are understood in relation to the distance of the first X axis along a radial axis.

[0046] The terms "upstream" and "downstream" are understood with respect to the circular direction of an airflow F in the turbomachine 1 along the first axis X.

[0047] The turbomachine 1 comprises from upstream to downstream a blower 2, a low pressure compressor 3, a high pressure compressor 4, a combustion chamber 5, a high pressure turbine 6, a low pressure turbine 7.

[0048] The fan 2 comprises movable blades 2a regularly distributed around the first axis X. The blades 2a are free to rotate about this first axis X. Advantageously, the blades 2a have a variable pitch angle. They are connected to a pitch-changing system 2b to vary the pitch angle of these blades 2a according to the operating conditions of the turbomachine 1.

[0049] The blower 2 allows the aspiration of an airflow F which divides downstream of the blower 2 into a primary airflow Fl and a secondary airflow F2. The primary airflow Fl flows into an annular primary vein vl and the secondary airflow F2 flows into an annular secondary vein v2 surrounding the primary air vein vl.

[0050] The primary airflow Fl is compressed within the low pressure and high pressure compressors 3, 4. Then the primary airflow Fl is mixed with a fuel within the combustion chamber 5. The gases from the combustion flow into the high pressure and low pressure turbines 6, 7.

[0051] The secondary airflow F2 flows into the secondary vein v2 and provides propulsion.

[0052] The turbomachine 1 further comprises an upstream casing 8 arranged downstream of the blower 2.

[0053] The turbomachine 1 further advantageously comprises an inter-compressor casing 9 arranged axially between the low and high pressure compressors 3, 4, an inter-turbine casing 10 arranged axially between the high and low pressure turbines 6, 7 and an exhaust casing 11 of the gases located downstream of the low pressure turbine 7.

[0054] The turbomachine 1 further comprises a low pressure shaft 12 centered on the first axis X and a high pressure shaft 13 arranged coaxially around the low pressure shaft 12.

[0055] The low pressure shaft 12 mechanically connects the low pressure compressor 3 to the low pressure turbine 7 and the high pressure shaft 13 mechanically connects the high pressure compressor 4 to the high pressure turbine 6.

[0056] Advantageously, the turbomachine 1 further comprises a blower shaft 14 connecting the blower 2 to the low-pressure shaft 12, in particular via a mechanical speed reducer 15.

[0057] The blower shaft 14 is guided in rotation by a first bearing 16a. The first bearing 16a is, for example, a double ball bearing. The first bearing 16a is, for example, arranged between the upstream housing 8 and the blower shaft 14.

[0058] The low-pressure shaft 12 is guided in rotation upstream by second and third bearings 16b, 16c. The second and third bearings 16b, 16c are ball and / or roller bearings. The second bearing 16b is, for example, arranged between the upstream housing 8 and the low pressure shaft 12. The third bearing, 16c, is for example arranged between the inter-compressor housing 9 and the low pressure shaft 12.

[0059] The low-pressure shaft 12 is guided in rotation downstream by a fourth bearing 16d and a fifth bearing 16e. This fourth bearing 16d is, for example, a roller bearing. The fourth bearing 16d is, for example, located between the inter-turbine housing 10 and the low-pressure shaft 12, and the fifth bearing is, for example, located between the exhaust housing 11 and the low-pressure shaft 12.

[0060] The high-pressure shaft 13 is guided in rotation upstream by a sixth bearing 16f, for example of the double type, and downstream by a seventh bearing 16g. The sixth and seventh bearings 16f and 16g are, for example, roller and / or ball bearings. The sixth bearing 16f is, for example, located between the inter-compressor housing 9 and the high-pressure shaft 13, and the seventh bearing 16g is, for example, located between the inter-turbine housing 10 and the high-pressure shaft 13.

[0061] In order to allow optimal lubrication of the bearings, the turbomachine 1 further includes lubrication chambers in which said bearings for the rotational guidance of the shafts are arranged.

[0062] The turbomachine 1 includes for example an upstream enclosure 17a in which the first and second bearings 16a, 16b and the speed reducer 15 are arranged. The upstream enclosure 17a is for example located in the upstream casing 8.

[0063] The turbomachine 1 may include an intermediate housing 17b in which the third and sixth bearings 16c, 16f are arranged. The intermediate housing 17b is, for example, located in the inter-compressor casing 9.

[0064] The turbomachine 1 may include a first downstream chamber 17c in which the fourth and seventh bearings 16d, 16g are arranged, and a second downstream chamber 17d in which the fifth bearing 16e is arranged. The first downstream chamber 17c is, for example, located in the inter-turbine casing 10 and the second downstream chamber 17d is, for example, located in the exhaust casing 11.

[0065] The number of bearings and enclosures may vary depending on the configuration of the turbomachine 1.

[0066] According to the invention, the turbomachine 1 further comprises fixed blades 18 distributed around the first axis X. These blades 18 are advantageously fixed against rotation about the first axis X. These blades 18 are located axially between the fan 2 and the low-pressure compressor 3. They are also known by the English acronym OGV for "Outlet Guided Vanes". These blades 18 improve the propulsive efficiency of the turbomachine 1.

[0067] These blades 18 advantageously have a variable pitch angle. The blades 18 are thus free to rotate about a pitch axis Y extending radially by relative to the first X axis. Such a characteristic makes it possible to improve the propulsive efficiency of the turbomachine 1 according to the operating conditions of the turbomachine 1.

[0068] To vary the pitch angle of the fixed blades 18, the turbomachine 1 includes a pitch changing system 19 connected to these blades 18.

[0069] The blades 18 are carried by a housing according to the invention.

[0070] This housing according to the invention will now be described in detail.

[0071] As more clearly seen in [Fig. 2], the housing comprises an annular body centered on the first X-axis. This body preferably comprises a first ferrule 20 and a second ferrule 21 axially connected to each other. The first ferrule 20, also called the upstream ferrule, is annular and centered on the first X-axis. The second ferrule 21, also called the downstream ferrule, is annular and centered on the first X-axis.

[0072] The first ferrule 20 is fixed around the first axis X. It extends longitudinally between an upstream annular end 22 and a downstream annular end 23. The upstream annular end 22 has an upstream annular flange 22a and the downstream annular end 23 has a downstream annular flange 23a. The upstream annular flange 22a is, for example, connected to the upstream housing 8.

[0073] The second ferrule 21 is, for example, rotationally fixed. It also extends longitudinally between an upstream annular end 24 and a downstream annular end 25. The upstream and downstream annular ends 24, 25 have, respectively, an upstream and downstream annular flange 24a, 25a. The downstream annular flange 25a is, for example, connected to the inter-compressor housing 9.

[0074] The first and second ferrules 20, 21 are axially connected to each other. For example, the downstream flange 23a of the first ferrule 20 is connected to the upstream flange 24a of the second ferrule 21. Connecting rods, such as screws, can hold the downstream and upstream flanges 23a, 24 together. These connecting rods are evenly spaced around the first axis X.

[0075] Furthermore, according to the invention, the housing comprises sleeves 26 for supporting the blades 18. Each blade 18 is supported by a respective sleeve 26. There are therefore as many sleeves 26 as there are blades 18. The sleeves 26 are regularly distributed around the first axis X.

[0076] Each sleeve 26 comprises an annular wall 27 and an internal housing 28 delimited by the annular wall 27 and receiving a fixed blade 18. The annular wall 27 extends around a second axis Y extending radially with respect to the first axis X. The second axis Y thus corresponds to the alignment axis of the blades 18. The annular wall 27 has a circular cross-section with respect to the second axis Y.

[0077] According to the invention, each sleeve 26 is connected to the body of the housing by a first radial link L1 with respect to the first axis X and a second radial link L2 with respect to the first axis X.

[0078] By "radial connection" is meant a connection involving at least two bearing surfaces extending in a plane parallel to the first axis X and connected to each other. In particular, these bearing surfaces are connected by a set of means for securing the housing body to the sleeve 26 located in a plane perpendicular to the first axis X.

[0079] Preferably, each sleeve 26 is connected to the first ferrule 20 by the first link L1 and to the second ferrule 21 by the second link L2. According to this preferred embodiment of the invention, each sleeve 26 is therefore connected to both the first ferrule 20 and the second ferrule 21.

[0080] Each sleeve 26 comprises a first connecting arm 29 and a second connecting arm 30. Each first and second connecting arm 29, 30 connects a sleeve 26 to the housing body. In particular, each first connecting arm 29 connects the annular wall 27 of the sleeve 26 to the first ferrule 20, and each second connecting arm 30 connects the annular wall 27 of the sleeve 26 to the second ferrule 21.

[0081] Each first connecting arm 29 extends from the annular wall 27 of the sleeve 26 to the housing body, in particular to the first ferrule 20. Each first connecting arm 29 extends, for example, radially or substantially radially towards the interior of the housing. Each first connecting arm 29 comprises a first end fixed to the annular wall 27 of the sleeve 26 and a second end connected to the housing body by the first connection L1. Each first connecting arm 29 further comprises a tab 31 located on the second end of the first connecting arm 29. The tab 31 has an axial bearing surface 31a extending in a plane parallel to the first axis X. The axial bearing surface 31a of the tab 31 is oriented inwards. This axial bearing surface 31a cooperates radially with a corresponding axial bearing surface of the housing body, in particular of the first ferrule 20.This corresponding axial bearing surface of the body is oriented outwards and extends in a plane parallel to the first X-axis. These bearing surfaces 31a are radially connected to each other by screwing to form the first LL connection. The lug 31, for example, has at least one orifice 31b which has an axis perpendicular to the first X-axis. A screw (not shown) passes through the orifice to connect the first connecting arm 29 to the housing body. The screw has an elongation axis perpendicular to the first X-axis.

[0082] The second connecting arm 30 is radially opposite to the first connecting arm with respect to the second Y-axis. The second connecting arm 30 extends from the wall annular 27 of the sleeve 26 up to the body of the housing, in particular up to the second ferrule 21.

[0083] Each second connecting arm 30 comprises a first portion 32, a second portion 33, and an intermediate portion 34 connecting the first and second portions 32 and 33. The first portion 32 extends substantially parallel to the first axis X from the annular wall 27.

[0084] The second portion 33 extends substantially radially to the first axis X and is connected to the housing body, in particular to the second ferrule 21. The second portion 33 has an inwardly oriented tab 35 with an axial bearing surface 35a extending in a plane parallel to the first axis X. The axial bearing surface 35a is oriented inward. The axial bearing surface 35a cooperates radially with a corresponding axial bearing surface of the housing body, in particular of the second ferrule 21. The corresponding axial bearing surface of the body is oriented outward. These bearing surfaces 35a are radially connected to each other by screwing to form the second connection L2. For example, the leg 35 has at least one orifice, and advantageously two orifices 35b, each of which has an axis perpendicular to the first axis X. A screw (not shown) passes through the orifice to connect the second connecting arm 30 to the body of the housing.The screw has an elongation axis perpendicular to the first X axis.

[0085] The intermediate portion 34 of the second arm 30 connects the first and second portions 32, 33. The intermediate portion 34 is curved. The intermediate portion 34 thus has a concave internal surface 34a. This feature allows for radial space E between the second arm 30 and the housing body. This space E can be used for the passage of auxiliary lines or other equipment. Furthermore, this curved shape concentrates stresses related, for example, to bird ingestion, within the intermediate portion 34. This curved shape also increases the flexibility of the sleeve 26 and thus limits deformations of the second ferrule 21. This helps to minimize clearances between the inter-compressor housing 9 and the downstream rotor.

[0086] The second arm 30 may include a recess 30a. This recess 30a may be located at the first portion 32. It may have a generally triangular shape. Such a recess 30a makes it possible to reduce the total mass of each sleeve 26.

[0087] As more clearly seen in [Fig.3], the second bond L2 is located more radially closer to the first X axis than the first bond LL. Advantageously, the first bond L1 is located radially closer to the second Y axis than the second bond L2, the term "radially" being understood with respect to the second Y axis.

[0088] As shown in [Fig. 3], advantageously, each sleeve 26 comprises a dial 36 surrounding the annular wall 27. Each dial 36 has a shape, for example, polygonal, such as square or rectangular. The dial 36 of each sleeve 26 has openings 36a.

[0089] Each sleeve 26 may further include a tab 37 for example connected to the second connecting arm 30. Each tab 37 may be connected to the pitch changing system.

[0090] According to an advantageous embodiment of the invention, with reference to Figures 4, 5 and 6, among the sleeves 26, the first and second and optionally third adjacent sleeves 26a, 26b, 26c are connected to each other. In particular, the annular walls 27 of the first, second and optionally third sleeves 26a, 26b, 26c are connected to each other in pairs by a first connecting bar 38. Thus, a first connecting bar 38 connects the two adjacent sleeves 26.

[0091] Each first connecting bar 38 extends perpendicularly to the first and second axes X, Y. Each first connecting bar 38 has a polygonal shape, such as rectangular or square.

[0092] The first connecting bars 38 can be connected to the dial 36 and fixed to the latter via the ports 36a.

[0093] According to an embodiment illustrated in [Fig. 4], each first connecting bar 38 includes a fixing bracket 38a. Each bracket 38a extends radially with respect to the first X-axis and parallel to the second Y-axis. Each bracket 38a includes an opening 38b. The brackets 38a allow the housing to be connected to components of the turbomachine 1, such as flow duct covers.

[0094] According to another advantageous embodiment illustrated in [Fig. 5], each first connecting bar 38 has a recess 38'. The recess 38' has a generally polygonal shape such as square or rectangular. The recess 38' is, for example, centered on the first connecting bar 38.

[0095] The connection of the sleeves 26 to each other in pairs makes it possible to improve the distribution of forces and to reduce the stresses in the sleeves 26. Also, such a connection makes it possible to take up the moment related to the aerodynamic forces which are applied in the blades 8, and therefore to reduce the displacements at the top of the blades 8.

[0096] According to an advantageous embodiment illustrated in [Fig. 6], the second connecting arms 30 of the first, second, and optionally third sleeves 26a, 26b, 26c are connected in pairs by a second connecting bar 39. Preferably, the second connecting bar 39 connects the lugs 35 of the second connecting arms 30 in pairs. Each second connecting bar 39 bears radially on the body of the upstream housing 8, relative to the first axis X. Each second connecting bar 39 can be held tightly against the second ferrule 21. Each second connecting bar 39 can therefore present a bearing surface which extends in a plane parallel to the first axis X and which cooperates with a corresponding bearing surface of the second ferrule 21. The two bearing surfaces can be held tightly together by connecting elements, such as a set of screws and nuts.

[0097] The first and second radial links L1, L2 distribute the forces within the housing sleeve. Since the distribution of forces within the housing 8 according to the invention is optimal, the deformation of the support 32 during operation is reduced.

[0098] Also, thanks to such a solution, it is possible to do away with stiffeners, which simplifies the geometry of the inlet housing 8 and therefore its manufacture.

[0099] Finally, the size of the inlet casing 8 is reduced, which facilitates the passage of the servicing.

Claims

Demands

1. Casing for an aircraft turbomachine (1), the casing comprising: - at least one annular body extending around a first axis (X), - sleeves (26) adapted to receive blades (18), the sleeves (26) being distributed around the first axis (X), each sleeve (26) having an annular wall (27) extending around a second axis (Y) oriented radially with respect to the first axis (X), characterized in that each sleeve (26) is connected to the body by a first radial link (L1) with respect to the first axis (X) and by a second radial link (L2) with respect to the first axis (X).

2. Housing according to the preceding claim, characterized in that each sleeve (26) comprises a first connecting arm (29) extending from the wall (27) and connected to the body by the first connection (L1).

3. Carter according to the preceding claim, characterized in that each first connecting arm (29) has a bearing surface (31a) which is oriented radially inwards and which cooperates radially with a bearing surface of the body which is oriented radially outwards, the bearing surfaces extending in a plane parallel to the first axis (X) and held tightly together to form the first connection (Ll).

4. Housing according to any one of the preceding claims, characterized in that each sleeve (26) comprises a second connecting arm (30) extending from the wall (27) and connected to the body by the second connection (L2).

5. Carter according to the preceding claim, characterized in that the second connecting arm (30) comprises a first portion (32) which extends substantially parallel to the first axis (X) and a second portion (33) which extends substantially radially and which is connected to the body, the first and second portions (32, 33) being connected to each other by a curved intermediate portion (34).

6. Carter according to any one of claims 2 to 3 in combination with any one of claims 4 to 5, characterized in that the first and second arms (29, 30) are diametrically opposed with respect to the second axis (Y).

7. Carter according to any one of the preceding claims, characterized in that, among the sleeves (26), at least a first sleeve (26a) and a second sleeve (26b) adjacent to the first sleeve (26a), are connected to each other.

8. Housing according to the preceding claim, characterized in that the walls (27) of the first and second sleeves (26a, 26b) are connected to each other by a first connecting bar (38).

9. Carter according to claim 7 or 8 in combination with one of claims 5 to 7, characterized in that the second arms (30) of the first and second sleeves (26a, 26b) are connected to each other by a second connecting bar (39).

10. Housing according to the preceding claim, characterized in that the second connecting bar (39) is radially supported on the body, with respect to the first axis (X).

11. Carter according to any one of the preceding claims, characterized in that the body comprises a first annular ferrule (20) extending around the first axis (X) and a second annular ferrule (21) extending around the first axis (X), the first and second ferrules (20, 21) being axially connected to each other, each sleeve (26) being connected to the first ferrule (20) by the first link (L1) and to the second ferrule (21) by the second link (L2).

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