Flexible truncated cone input shaft

Abstract

The present invention relates to a shaft (15) for a propulsion system (1), the shaft being configured to rotate a reduction gear (12) around a rotation axis (X), the shaft (15) comprising: a first end (16), the first end being configured to engage with an input gear (14) of the reduction gear (12), a first waveform (17) and a second waveform (18), the first waveform (17) and the second waveform (18) being rotationally symmetrical around the rotation axis (X), the first waveform (17) extending between the first end (16) and the second waveform (18), and a truncated cone-shaped body (19), the truncated cone-shaped body mechanically connecting the first waveform (17) and the second waveform (18).

Description

Technical Field

[0001] The present invention relates to the field of aviation propulsion systems, and more specifically, to a dual-flow propulsion system having a speed reduction mechanism for driving a fan. Background Art

[0002] In the flow direction of the gas, the dual-flow propulsion system generally includes a fan, a primary annular flow space, and a secondary annular flow space from upstream to downstream, and the secondary annular flow space is outside relative to the mainstream. Therefore, the mass of air sucked in by the fan is divided into a mainstream and a secondary flow, the mainstream circulates in the primary flow space, and the secondary flow is concentric with the mainstream and circulates in the secondary flow space. The fan (or spiral portion) may have a duct and be fixed in the fan housing, or as a variation, the fan is of the unducted single fan (USF) type. The fan blades may be fixed or have a variable pitch angle, and the uniform field is adjusted by the pitch change mechanism according to the flight phase.

[0003] The main flow space passes through a body that includes one or more compressor stages (e.g., a low-pressure compressor (or booster) and a high-pressure compressor), a combustion chamber, one or more turbine stages (e.g., a high-pressure turbine and a low-pressure turbine), and a gas discharge nozzle. Typically, the high-pressure turbine drives the high-pressure compressor to rotate through a first shaft (referred to as the high-pressure shaft), while the low-pressure turbine drives the low-pressure compressor and the fan to rotate through a second shaft (referred to as the low-pressure shaft). Typically, the low-pressure shaft is housed in a specific section of the high-pressure shaft.

[0004] In order to increase the propulsion output of the propulsion system and reduce the specific consumption of the propulsion system and the noise emitted by the fan, a propulsion system with a high bypass ratio is proposed, the bypass ratio being the ratio of the flow rate of the secondary flow to the flow rate of the mainstream. Here, a high bypass ratio means a bypass ratio greater than 10, such as about 15 or 20, or even higher, such as about 40 or 80 in the case of a turbine whose fan is a non-ducted turbine.

[0005] In order to achieve this bypass ratio, the fan is decoupled from the low-pressure turbine, so that the rotational speeds of the fan and the low-pressure turbine are optimized independently and effectively. Usually, the decoupling is achieved by a reduction mechanism (such as an epicyclic reduction mechanism or a planetary reduction mechanism), which is arranged between the upstream end of the low-pressure shaft and the fan. The fan is driven by the low-pressure shaft through the reduction mechanism and an additional shaft (called the fan shaft), which is fixed between the reduction mechanism and the disk of the fan.

[0006] This decoupling therefore reduces the speed and pressure ratio of the fan and increases the power extracted by the low-pressure turbine.

[0007] As is known per se, such a reduction mechanism generally comprises:

[0008] - a central pinion gear, called the sun gear, to which the propulsion system's drive shaft (usually the low-pressure shaft) can be connected,

[0009] - a ring gear, which is coaxial with the sun gear, and

[0010] - Planetary gears, which are mounted on a planet carrier, each planetary gear meshing with the sun gear on the one hand and with the ring gear on the other hand.

[0011] In particular, the output shaft (usually the fan shaft) can be driven to rotate by one of the ring gear or the planet carrier, and the other is fixed relative to the housing of the reduction mechanism.

[0012] However, the propulsion system including the reduction mechanism may encounter some difficulties that need to be coordinated at the interface:

[0013] - An appropriate level of rigidity / flexibility limits overloads inside the components of the reduction mechanism, overloads generated partly by external misalignments (managing misalignment issues), in particular misalignments between the drive shaft and the sun gear.

[0014] - Good mechanical strength of the components of the reduction mechanism that are subject to specific stresses associated with misalignment, in particular the rotor components (and rotational bending type stresses combined with torsion associated with torque movements).

[0015] - The mechanical strength of the joint (eg teeth of the sun gear, planet gears and ring gear or grooves of the shaft) and the contribution of the joint to the recovery of misalignment.

[0016] -Optimization of the axial volume of the reduction mechanism (influence on motor length).

[0017] - Functional clearances between the different components of the reduction mechanism.

[0018] -Optimal installation and modularity conditions.

[0019] -The ability to manufacture the flexible part taking into account its overall complex form.

[0020] In order to compensate for any possible misalignment between the drive shaft and the reduction mechanism, it has been suggested to add a shaft called a flexible shaft between the drive shaft and the input pinion, which is configured to respond to flexibility specifications consistent with the overload of the reduction mechanism and the dynamic conditions of the motor assembly. To this end, the shaft includes two straight corner joints separated by a tubular barrel, and the tubular barrel and the corner joints are integral, that is, integral. The corner joints act as springs, each corner joint has flexibility relative to the theoretical rotation axis of the corner joint in the bending rotation of the shaft, while the barrel is rigid (non-deformable when rotating and bending under use conditions). The shaft also includes an upstream end and a downstream end, the upstream end bearing grooves and configured to engage with teeth associated with the sun gear, and the downstream end is configured to be fixed to the drive shaft, for example, close to the bearing of the propulsion system. Since the barrel is rigid, the shaft is able to transmit the torque applied by the drive shaft of the propulsion system (usually a low-pressure shaft driven by a low-pressure turbine). However, this transmission of torque generates a mechanical load on the shaft called a "static" mechanical load or an "average" mechanical load. Furthermore, the corner joints are configured to compensate for misalignments between the drive shaft (in the region of the downstream end of the shaft) and the sun gear of the reduction mechanism (in the region of the upstream end of the shaft). These misalignments, however, generate on the shaft a rotational bending behavior with a large number of cycles, as well as alternating loads known as “dynamic” loads (because they vary with the rotation of the shaft).

[0021] The dimensioning of the shaft must therefore take into account these dynamic and static loads by finding the best compromise from the point of view of the shaft geometry and the distribution of inertia between the barrel and the fillet, in order to optimize the mechanical strength and the service life margin of the shaft. More precisely, the barrel must be rigid enough to limit the static loads, while the fillet must be soft enough to limit the dynamic loads.

[0022] However, it seems that the static maximum load and the maximum dynamic load are concentrated in the same area of ​​the shaft, in particular in the interface area between the upstream end of the shaft and the adjacent corner joint (see attached Figure 7 Static and dynamic loads concentrated on the same shaft position significantly reduce the shaft life margin. Summary of the invention

[0023] The object of the present invention is to propose a solution to the above-mentioned drawbacks, in particular to provide robustness in the mechanical strength of the shaft and still comply with the flexibility specifications.

[0024] To this end, according to a first aspect of the present invention, a shaft for a propulsion system is proposed, the shaft being configured to drive a reduction mechanism to rotate around a rotation axis, the shaft comprising:

[0025] - a first end portion configured to engage with an input pinion of a reduction mechanism,

[0026] a first corner joint and a second corner joint, the first corner joint and the second corner joint being rotationally symmetrical about the axis of rotation, the first corner joint extending between the first end and the second corner joint, and

[0027] A barrel portion mechanically connecting the first corner joint and the second corner joint.

[0028] In particular, the barrel portion of the shaft is frustoconical when at rest (ie without any external stress).

[0029] Some preferred but non-limiting characteristics of the shaft according to the first aspect are as follows, these features being taken individually or in combination:

[0030] The half angle at the vertex of the truncated cone defined by the truncated cone-shaped barrel is greater than or equal to 5° and less than or equal to 25°.

[0031] The barrel has a first diameter close to the first corner joint and a second diameter close to the second corner joint, the second diameter being strictly smaller than the first diameter.

[0032] The maximum diameter of the first corner joint is between 80% and 120% of the maximum diameter of the second corner joint.

[0033] The first corner connection is attached to the first end portion by a first fillet, the first fillet having a radius of curvature greater than or equal to 10 mm and less than or equal to 20 mm.

[0034] - A portion of the first end portion is frustoconical.

[0035] The second corner connection is connected to the barrel in the region of a second rounded corner, the radius of curvature of the second rounded corner being greater than or equal to 10 mm and less than or equal to 15 mm.

[0036] The barrel has a first diameter close to the first corner joint and a second diameter close to the second corner joint, the second diameter being strictly greater than the first diameter.

[0037] The first end comprises a groove configured to engage with a tooth of the input pinion.

[0038] According to a second aspect, the invention proposes a drive assembly for a propulsion system, the assembly comprising a shaft according to the first aspect and a reduction gear comprising an input pinion, a first end of the shaft being engaged with the input pinion of the reduction gear to drive the input pinion in rotation about a rotation axis.

[0039] According to a third aspect, the invention proposes a propulsion system comprising a drive assembly according to the second aspect and a turbine section attached to a shaft to drive the shaft in rotation about a rotation axis.

[0040] According to a fourth aspect, the invention proposes an aircraft comprising a propulsion system according to the third aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Other characteristics, objectives and advantages of the invention will emerge from the following description, which is purely illustrative and non-limiting and must be considered with respect to the accompanying drawings, in which:

[0042] Figure 1 An example of an aircraft propulsion system including a ducted fan according to an embodiment of the invention is schematically shown.

[0043] Figure 2 is a partial cross-sectional view of an embodiment of a shaft for a propulsion system according to a first embodiment, wherein the concentration points of static and dynamic loads have been indicated by boxes.

[0044] Figure 3 is a partial cross-sectional view of an embodiment of a shaft for a propulsion system according to a second embodiment, wherein the concentration points of static and dynamic loads have been indicated by boxes.

[0045] Figure 4 yes Figure 2 A perspective view of a shaft showing the dynamic load field when the shaft is in an operating propulsion system.

[0046] Figure 5 yes Figure 2 A perspective view of a shaft showing the static load field when the shaft is in an operating propulsion system.

[0047] Figure 6 is a top plan view of an example of an aircraft that can include a propulsion system according to the invention.

[0048] Figure 7 This is a partial cross-sectional view of a conventional shaft, in which the concentration points of static and dynamic loads have been framed.

[0049] Figure 8 According to the third embodiment, Figure 7 A partial cross-sectional view of an embodiment of a shaft for a propulsion system in an example of a variant embodiment of the embodiment shown in FIG.

[0050] Fig. 9 is Figure 2 An example of a modified embodiment of the first embodiment is shown in FIG.

[0051] Fig.10 is Figure 3 An example of a modified embodiment of the second embodiment is shown in FIG.

[0052] Similar elements have the same reference numerals throughout the drawings. DETAILED DESCRIPTION

[0053] In the present application, upstream and downstream are defined relative to the normal flow direction of gases in the fan through the propulsion system.

[0054] The propulsion system 1 for an aircraft 100 generally includes a fan 2 and a main body. In the flow direction of the gas of the propulsion system 1, the main body includes: an inlet passage extending immediately downstream of the fan 2, a low-pressure compressor 4 (or booster), a high-pressure compressor 5, a combustion chamber, a high-pressure turbine 7, a low-pressure turbine 9, and a gas discharge nozzle. The high-pressure turbine 7 drives the high-pressure compressor 5 to rotate through the high-pressure shaft 8, and the low-pressure turbine 9 drives the low-pressure compressor 4 and the fan 2 to rotate through the low-pressure shaft 10.

[0055] The fan 2 comprises a fan disc 43 having fan blades 11 arranged at its outer circumference, which guide the air flow in the primary flow space and the secondary flow space of the propulsion system 1 when the fan blades are set in rotation.

[0056] The invention is applicable to any type of aviation dual-flow propulsion system 1, whether the fan 2 is ducted or unducted, with fixed blades or blades with variable pitch.

[0057] The propulsion system 1 has a high bypass ratio. Here, a high bypass ratio refers to a bypass ratio greater than or equal to 10, for example a bypass ratio between 10 and 80 (including orders of magnitude for the case where the fan is a motor without a ducted fan). To this end, the fan 2 is decoupled from the low-pressure turbine 9 to independently optimize the respective rotational speeds of the fan and the low-pressure turbine by means of a reduction mechanism 12, the reduction mechanism being arranged between the upstream end of the low-pressure shaft 10 (relative to the flow direction of the gas in the propulsion system 1) and the fan 2. Therefore, the fan 2 is driven by the low-pressure shaft 10 through the reduction mechanism 12 and the fan shaft 13, and the fan shaft is fixed between the reduction mechanism 12 and the disk of the fan 2. The fan shaft 13 can rotate and move around an axis of rotation X, which is coaxial with the axis of rotation X of the low-pressure shaft 10.

[0058] To calculate the bypass ratio, the secondary and primary flows are measured when the propulsion system 1 is stationary in standard atmosphere (defined by the International Civil Aviation Organization (l'Organisation de l'aviation civile internationale, OACI) Guidelines, Doc 7488 / 3 3rd edition) and in an oceanic area at take-off rated power.

[0059] As known per se, as mentioned above, the speed reduction mechanism 12 comprises:

[0060] a sun gear 14 which is mounted in the center of the reducer so as to be movable in rotation about the axis of rotation X,

[0061] - a ring gear, which is coaxial with the sun gear 14, and

[0062] - Planetary gears, which are mounted on a planet carrier, each planetary gear meshing with a central pinion on the one hand and with a ring gear on the other hand.

[0063] In order to provide the low-pressure shaft with robustness of mechanical strength to connect the low-pressure shaft with the reduction mechanism 12 while complying with the flexibility specification, the propulsion system 1 comprises a shaft 15 called a flexible shaft, which is configured to drive the reduction mechanism 12 in rotation about the rotation axis X and comprises:

[0064] a first end 16 or upstream end 16 which is configured to engage with the sun gear 14 of the reduction mechanism 12 ,

[0065] a first corner connection 17 and a second corner connection 18 which are rotationally symmetrical about the axis of rotation X, the first corner connection 17 extending between the first end 16 and the second corner connection 18,

[0066] a barrel 19 which mechanically connects the first corner joint 17 and the second corner joint 18, and

[0067] - A second end 20 or downstream end 20, which extends opposite the upstream end 16 downstream of the second corner 18 and is configured to be fixed to a bearing of the propulsion system 1, typically the front bearing of the low-pressure shaft 10. The range of having such a bearing is Figure 2 In the drawing, this bearing is designated 20P and typically supports the downstream end of the shaft 15 and upstream of the low-pressure shaft.

[0068] The barrel 19 of the shaft 15 is truncated cone-shaped so that the position of maximum static load (indicated by box A) is unrelated to the position of maximum dynamic load (indicated by box B), as shown in FIG. Figure 4 and Figure 5 . Thus, the barrel 19 of the shaft 15 is truncated cone-shaped when at rest (i.e. without any external stress). Thus, the maximum static load is located at the junction between the second fillet 18 and the barrel 19, while the maximum dynamic load is located at the junction between the first fillet 17 and the upstream end 16 of the shaft 15. Thus, the service life margin of the shaft 15 is significantly improved compared to a shaft having a through tubular barrel 19.

[0069] The angle of inclination and the direction of the truncated cone forming the barrel 19 are determined according to the absolute misalignments that may exist upstream and downstream of the shaft 15. Absolute misalignments are understood here to mean misalignments that are caused only by the movement of the shaft 15 upstream (respectively, downstream), as opposed to relative misalignments of the shaft 15, which correspond to the sum of the absolute misalignments observed by the shaft 15.

[0070] In particular, when, in a given propulsion system 1, the absolute misalignment is greater upstream of the shaft 15 (i.e., in the region of the reduction mechanism 12) than downstream (i.e., in the region of the bearing on the upstream side of the low-pressure shaft), the truncated cone-shaped barrel portion 19 converges from upstream to downstream. In other words, the diameter of the truncated cone-shaped barrel portion 19 is greater in the region of the first corner joint 17 than in the region of the second corner joint 18 ( Figure 2 ).

[0071] However, in a given propulsion system 1, when the absolute misalignment is more significant downstream of the shaft 15 than upstream, the truncated cone barrel portion 19 flares out from upstream to downstream. In other words, the diameter of the truncated cone barrel portion 19 is smaller in the region of the first corner 17 than in the region of the second corner 18 ( Figure 3 ).

[0072] In this case, the diameter is understood to be the diameter measured in a plane perpendicular to the axis X of rotation.

[0073] In the following, more particularly, the invention will be described in the case of a converging truncated cone shaft 15, ie the largest diameter of the truncated cone shaft being located close to the downstream side of the first corner joint 17. As just explained, this is not restrictive, since the truncated cone shaft 15 may be divergent, as in Figure 3 Therefore, unless otherwise stated in this specification, the present description applies mutatis mutandis to such a splayed shaft 15 simply by inverting the described construction.

[0074] In the embodiment, the half angle at the vertex of the inclined portion of the truncated cone forming the cylindrical portion 19 is between 5° and 25°. Here, the half angle at the vertex refers to the angle formed between the rotation axis X and the outer surface of the cylindrical portion 19.

[0075] Each fillet 17, 18 has an upstream side and a downstream side. The upstream side 21 of the first fillet 17 is attached to the upstream end 16 of the shaft 15 by a first upstream fillet 22, and the downstream side 23 of the first fillet is connected to the barrel 19 by a first downstream fillet 24. Similarly, the upstream side 25 of the second fillet 18 is connected to the barrel 19 by a second upstream fillet 26, and the downstream side 27 of the second fillet is attached to the downstream end 20 of the shaft 15 by a second downstream fillet 28.

[0076] In an embodiment, since the barrel 19 has a larger diameter in the region of the downstream side 23 of the first corner joint 17, the maximum diameter D1 of the first corner joint 17 can be increased compared to a conventional shaft, so that the first corner joint 17 remains sufficiently flexible. In fact, the flexibility of the corner joint depends on the first order of the maximum radial extent of the corner joint (i.e. the height of the corner joint, given by the diameter at the apex of the corner joint compared to the diameter of the shaft at the radially inner side of the downstream side 21 of said first corner joint 17). Therefore, the radii of curvature of the first upstream fillet 22 and the first downstream fillet 24 can also be increased, so as to reduce the static loads in these first fillets 22, 24.

[0077] Typically, the maximum diameter D1 of the first corner joint 17 is between 80% and 120% of the maximum diameter D2 of the second corner joint 18 , for example, between 90% and 100% of the maximum diameter of the second corner joint.

[0078] In addition, the radius of curvature of the first upstream fillet 22 may be greater than or equal to 10 mm and less than or equal to 20 mm. The radius of curvature of the first downstream fillet 24 may be greater than or equal to 5 mm and less than or equal to 15 mm.

[0079] In particular, it should be noted that the larger the half angle of the truncated cone forming the barrel 19, the larger the maximum diameter D1 of the first corner joint 17 (in order to maintain the same flexibility and comply with the compromise between the mechanical strength of the shaft 15 and the flexibility specifications relative to the propulsion system without changing the length of the shaft 15), and the larger the radii of curvature of the first upstream fillet 22 and the first downstream fillet 24 can be.

[0080] Optionally, in order to further reduce the static loads in the region of the first upstream fillet, the upstream end 16 may include a truncated cone-shaped portion 222 (see in particular the attached Figures 8 to 10 ). Preferably, when the upstream end 16 carries the groove 29, the groove is configured to engage with the shaft 15 through the sun gear 14 of the speed reduction mechanism 12, and the truncated cone portion 222 extends between the first upstream fillet 22 and the groove 29 (the portion including the groove 29 generally remains tubular). Therefore, the radius of curvature of the first upstream fillet 22 can be increased more than that of a conventional shaft.

[0081] refer to Figure 2, in the region of the second corner joint 18, the result of the truncated cone shape of the shaft 15 is a reduction in the angular range of the radius of curvature of the second upstream fillet 26, thereby increasing the static load in this region. In fact, this portion of the barrel 19 has a smaller diameter. However, the applicant has noticed that, since this second upstream fillet 26 only concentrates the maximum static loads (dynamic loads are small), the dimensioning of this second upstream fillet is more flexible. Therefore, the increase in the static load in the region of the second upstream fillet 26 does not affect the increase in the service life margin caused by the truncated cone shape of the barrel 19.

[0082] As in Figure 2 As shown in the figure, the shaft has a truncated cone-shaped barrel portion 19 which opens from downstream to upstream. Therefore, in the area (indicated by box A) of the second fillet 18, on the side of the second upstream fillet 26, the shaft 15 is subjected to a considerable static load but a minimum dynamic load, and in the area (indicated by box B) of the first fillet 17, on the side of the first upstream fillet 22, the shaft is subjected to a minimum static load and an average dynamic load, thereby significantly improving the service life margin.

[0083] In an embodiment, the shaft 15 is made of steel (e.g. stainless steel), or of a high temperature alloy based on nickel and including chromium, iron, niobium and molybdenum (e.g. about 19 or 20 percent nickel, and also 19 or 20 percent chromium, and similarly 19 or 20 percent iron, and, for example, small amounts of niobium and molybdenum). In the case of a shaft 15 made of such an alloy with a ratio of NiCr19Fe19Nb5Mo3, the thickness of the barrel 19 can be, for example, between 4.0 mm and 8.0 mm, and the thickness of the fillet can be about 2.5 mm to 5.0 mm, close to 10%. The maximum diameter D1 of the first fillet 17 can be greater than 170 mm, for example less than 250 mm, and remain, for example, greater than the maximum diameter D2 of the second fillet 18. The maximum diameter D2 of the second fillet 18 can be greater than or equal to 150 mm and, for example, less than 240 mm, and remain, for example, less than the maximum diameter D1 of the first fillet. The radius of curvature of the second upstream fillet 26 can be between 5 mm and 10 mm. The radius of curvature of the second downstream fillet 28 may also be between 5 mm and 10 mm. Generally, the fillet adjacent to the barrel at the end with the largest diameter may have a larger maximum outer diameter than the fillet adjacent to the barrel at the end with the smallest diameter.

[0084] It is also obvious that the truncated cone shape of the shaft 15 makes the manufacturing conditions of the shaft easier. In fact, the corners 17, 18 are usually manufactured by removing material from the inside of the barrel 19 using tools, which constitutes a delicate operation. The truncated cone shape of the barrel 19 makes it easier to access the internal area of ​​the shaft 15 and clears space for the machining tools.

[0085] As a variant, for example, Figure 3 As shown in the figure, the shaft 15 has a truncated cone-shaped barrel portion 19 which flares from upstream to downstream, so that in the region (indicated by box A) of the second fillet 18, on the side of the second upstream fillet 26, the shaft is subjected to a considerable static load but a small dynamic load, and in the region (indicated by box B) of the first fillet 17, on the side of the first downstream fillet 24, the shaft is subjected to a small static load and an average dynamic load, which significantly increases the service life margin.

[0086] The present invention is shown as involving a double-flow ducted motor (see Figure 1 ), but the invention is also applicable to corresponding shafts within the range of motors of the open secondary flow type, such as USF (Unducted Single Fan), wherein the module of the USF comprising the fan rotor blade arrangement and its downstream rectifier blade arrangement is unducted.

Claims

1. A shaft (15) for a propulsion system (1), the shaft being configured to drive a reduction mechanism (12) to rotate about a rotation axis (X), the shaft (15) comprising: a first end portion (16) configured to engage with an input pinion (14) of the speed reduction mechanism (12), a first corner joint (17) and a second corner joint (18), the first corner joint (17) and the second corner joint (18) being rotationally symmetrical about the rotation axis (X), the first corner joint (17) extending between the first end (16) and the second corner joint (18), and A cylindrical portion (19) mechanically connects the first corner joint (17) and the second corner joint (18), and the shaft (15) is characterized in that the cylindrical portion (19) is truncated cone-shaped.

2. The shaft (15) according to claim 1, wherein A half angle (α) at ​​the vertex of a truncated cone defined by the truncated cone-shaped barrel portion (19) is greater than or equal to 5° and less than or equal to 25°.

3. The shaft (15) according to claim 1 or 2, wherein: The barrel (19) has a first diameter close to the first corner (17) and a second diameter close to the second corner (18), the second diameter being strictly smaller than the first diameter.

4. The shaft (15) according to claim 1 or 2, wherein: The maximum diameter (D1) of the first corner joint (17) is between 80% and 120% of the maximum diameter (D2) of the second corner joint (18).

5. The shaft (15) according to claim 1 or 2, wherein: The first corner joint (17) is attached to the first end portion (16) via a first fillet (22), the radius of curvature of the first fillet (22) being greater than or equal to 10 mm and less than or equal to 20 mm.

6. The shaft (15) according to claim 1 or 2, wherein: A portion of the first end portion (16) is frustoconical.

7. The shaft (15) according to claim 1 or 2, wherein: The second corner connection (18) is connected to the cylindrical portion (19) in the region of a second rounded corner (26), the curvature radius of the second rounded corner (26) being greater than or equal to 10 mm and less than or equal to 15 mm.

8. The shaft (15) according to claim 1 or 2, wherein: The barrel (19) has a first diameter close to the first corner (17) and a second diameter close to the second corner (18), the second diameter being strictly larger than the first diameter.

9. The shaft (15) according to claim 1 or 2, wherein: The first end (16) includes a groove (29) configured to engage with teeth of the input pinion (14).

10. A drive assembly for a propulsion system (1), the assembly comprising a shaft (15) according to any one of claims 1 to 9 and a reduction mechanism (12) comprising an input pinion (14), the first end (16) of the shaft (15) being engaged with the input pinion (14) of the reduction mechanism (12) to drive the input pinion to rotate around the rotation axis (X).

11. A propulsion system (1) comprising a drive assembly according to claim 10 and a turbine section (7, 8) attached to the shaft (15) to drive the shaft in rotation about the rotation axis (X).

12. An aircraft (100) comprising a propulsion system (1) according to claim 11.

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