Shaft for an aircraft turbomachine

Abstract

The invention relates to a shaft (1) for an aircraft turbomachine (2), the shaft comprising a body (3) comprising an upstream portion (4) and a downstream portion (5) axially separated from one another by a bead (6), the bead (6) comprising an axial wall (7) arranged axially between two radial walls (8a, 8b) having an equivalent and constant thickness, the shaft (1) further comprising upstream and downstream attachment diaphragms (10a, 10b) which extend radially and respectively from the upstream and downstream portions (4, 5) of the body (3), each of the upstream and downstream diaphragms (10a, 10b) comprising a web (11) having a constant thickness arranged radially between an outer flange (12) and an inner base (13), a structurally critical diaphragm being determined from among the upstream and downstream diaphragms (10a, 10b), the quotient between the thickness (E1) of the radial walls (8a, 8b) of the bead (6) and the thickness (E2) of the web (11) of the critical diaphragm being greater than or equal to 1.5.

Description

[0001] DESCRIPTION

[0002] TITLE: TREE FOR AN AIRCRAFT TURBOMACHINE

[0003] Technical field of the invention

[0004] The present invention relates to a shaft for an aircraft turbomachine, as well as to an aircraft turbomachine comprising such a shaft.

[0005] Technical background

[0006] A turbomachine includes various shafts that allow the transmission of mechanical power (torque and speed) between a driving element (e.g., a turbine) and a receiving element (e.g., a propulsion blower), while accommodating existing misalignments.

[0007] A shaft is classically a single piece and annular. The shaft includes in particular a body which extends axially, and radial diaphragms (or radial flanges) each equipped with a flange, to clamp it to elements which are directly adjacent to it.

[0008] As part of the development of a turbomachine, engine manufacturers carry out various tests at different operating regimes, with the aim of validating or not certain technical solutions implemented.

[0009] To achieve this, engine manufacturers may need to instrument a shaft to perform certain measurements. They frequently choose to install the instrument(s) on a spacer placed in the central part of the shaft. However, engine manufacturers find that for some shafts, and more specifically shafts with large axially and radially close flanges, it is difficult (or even impossible) to install the instrument(s) on the spacer due to the limited available space. Furthermore, engine manufacturers note a need to mount the instrument(s) on a larger diameter support. A simple solution to meet the aforementioned needs could be to increase the diameter of the spacer. However, such a solution would significantly increase the shaft's mass, which is undesirable.

[0010] Engine manufacturers believe it might be beneficial to replace the excess thickness with a U-shaped ridge (or bellows) in its axial half-section. However, such a replacement would alter the shaft's mechanical properties, including its flexibility, axial compression under centrifugal force, mechanical strength, lifespan, and dynamic and vibrational behavior.

[0011] The objective of the present invention is therefore to provide a simple, effective, and economical solution to the aforementioned problem. Prior art also includes documents US2019 / 085890A1, US7926260B2, and US2013 / 065696A1.

[0012] Summary of the invention

[0013] The invention thus proposes a shaft for an aircraft turbomachine, the shaft being a single piece and annular around an axis X, the shaft comprising a body extending axially and having an upstream portion and a downstream portion separated axially from each other by a flange having a U-shape in axial half-section, the flange comprising an axial wall disposed axially between two radial walls of equivalent and constant thickness, each of the radial walls connecting the axial wall to one of the upstream and downstream portions of the body, the axial wall and the radial walls jointly and internally forming between them a cavity open towards the axis X, the shaft further comprising upstream and downstream fixing diaphragms which extend radially and respectively from the upstream and downstream portions of the body,each of the upstream and downstream diaphragms comprising a web of constant thickness arranged radially between an external flange and an internal base which is connected to the corresponding portion of the body, the upstream and downstream diaphragms each having an external diameter D1, D2 which is greater than the external diameter D3 of the axial wall of the rim, a structurally critical diaphragm is determined among the upstream and downstream diaphragms, the quotient between the thickness E1 of the radial walls of the rim and the thickness E2 of the web of the critical diaphragm is greater than or equal to 1.5.

[0014] The integration of such a bead provides a large-diameter support for the measuring instrument(s), simplifying their installation and meeting the evolving needs of engine manufacturers. The bead also provides a large-diameter measuring surface, further simplifying the measurement process.

[0015] Such an E1 / E2 ratio also allows the shaft to have mechanical properties equivalent to those of a prior art shaft with an extra thickness.

[0016] Furthermore, such integration does not have a negative impact on the mass of the tree, and may even prove beneficial for some of them.

[0017] Finally, such a tree can be easily manufactured using conventional manufacturing processes such as turning.

[0018] The tree according to the invention may comprise one or more of the following features, taken individually or in combination with each other:

[0019] - the ratio between the internal diameter D4 of the upstream portion of the body and the internal diameter D5 of the axial wall of the ridge is greater than or equal to 0.3;

[0020] - the ratio between the internal diameter D6 of the downstream portion of the body and the internal diameter D5 of the axial wall of the ridge is greater than or equal to 0.3;

[0021] - the length L1 between the downstream face of the upstream diaphragm wall and the upstream end of the axial wall is greater than or equal to the height H1 between the external surface of the axial wall and the external surface of the upstream portion of the body; - the length L2 between the upstream face of the downstream diaphragm wall and the downstream end of the axial wall is greater than or equal to the height H2 between the external surface of the axial wall and the external surface of the downstream portion of the body;

[0022] - the thickness E3 of the axial wall of the bead is greater than or equal to the thickness E1 of the radial walls of the bead;

[0023] - the length L3 of the axial wall is greater than or equal to the length L1 between the downstream face of the upstream diaphragm wall and the upstream end of the axial wall;

[0024] - the length L3 of the axial wall is greater than or equal to the length L2 between the upstream face of the downstream diaphragm wall and the downstream end of the axial wall;

[0025] - the ratio between the external diameter D1 of the upstream diaphragm and the external diameter D7 of the upstream portion of the body is greater than or equal to 3; - the ratio between the external diameter D2 of the downstream diaphragm and the external diameter D8 of the downstream portion of the body is greater than or equal to 3;

[0026] - the ratio between the external diameter D3 of the axial wall of the rim and the external diameter D7 of the upstream portion of the body is greater than or equal to 2; - the ratio between the external diameter D3 of the axial wall of the rim and the external diameter D8 of the downstream portion of the body is greater than or equal to 2; - the thickness E4 of the structurally non-critical diaphragm wall is between 0.8 and 1 times the thickness E2 of the critical diaphragm wall, the structurally non-critical diaphragm corresponding to the diaphragm not chosen among the upstream and downstream diaphragms.

[0027] The present invention also relates to an aircraft turbomachine comprising a shaft as described above.

[0028] The turbomachine according to the invention may comprise one or more of the following features, taken individually or in combination with each other:

[0029] - the turbomachine includes a fan driven in rotation by the shaft via a speed reducer, the shaft itself being driven in rotation by a low-pressure shaft of a low-pressure body of the turbomachine; -- the turbomachine further includes one or more measuring instruments which are arranged around the axial wall of the shaft flange;

[0030] - the measuring instrument(s) are opposite and at a distance from the axial wall of the ridge;

[0031] - the measuring instrument(s) are mounted (or installed) on the axial wall of the bead;

[0032] - the measuring instrument(s) are each a torque meter (for example inductive) or a speed sensor;

[0033] - the speed reducer is an epicyclic gear reducer;

[0034] -the epicyclic gear reducer includes at least one reduction stage comprising a sun gear, a ring gear, satellites and a satellite carrier; -the reducer includes an input element which corresponds to the sun gear, the sun gear being rotationally linked with an input shaft which is itself rotationally linked with the shaft;

[0035] - the reducer includes an output element which is chosen from the crown and the planet carrier, the output element being rotationally linked with the blower.

[0036] Brief description of the figures

[0037] The invention will be better understood and other details, features and advantages of the invention will become more apparent upon reading the following description, given by way of non-limiting example and with reference to the accompanying drawings in which:

[0038] [Fig.1] Figure 1 is a half-axial cross-sectional view of a shaft for an aircraft turbomachine according to the invention;

[0039] [Fig.2] Figure 2 is a view similar to Figure 1 on which different parameters of the shaft are represented; [Fig.3] Figure 3 is a schematic axial half-section view of an aircraft turbomachine including a shaft, according to a first embodiment;

[0040] [Fig.4] Figure 4 is a schematic axial half-section view of an aircraft turbomachine comprising a shaft, according to a second embodiment.

[0041] Detailed description of the invention

[0042] Figure 1 shows a half-axial section of a shaft 1 for an aircraft turbomachine 2, such as an airplane.

[0043] Turbomachine 2, for example, is a turbomachine known by the English acronym USF for "Unducted Single Fan" or by the English term "RISE Open Fan." Such a turbomachine includes, in particular, an unducted fan, an unducted rectifier, and a gas generator. A USF turbomachine with a high bypass ratio offers the advantage of excellent efficiency, notably with reduced fuel consumption and carbon dioxide emissions.

[0044] More specifically, the unshod fan comprises an annular array of blades with fixed or variable pitch. The fan is driven in rotation by a power turbine from the gas generator via a gear reducer, which is conventionally an epicyclic gear reducer.

[0045] The unshrouded stator is fixed in rotation and positioned axially downstream of the blower. The stator straightens at least a portion of the airflow generated by the blower. The stator comprises an annular array of guide vanes with fixed or variable pitch.

[0046] The gas generator includes, from upstream to downstream following the gas flow, an air inlet, a low-pressure compressor, a high-pressure compressor, a combustion chamber, a high-pressure turbine, a power turbine (or low-pressure turbine), and an exhaust nozzle. According to the invention, the shaft 1 is a single piece (or monobloc) and annular about an axis X. The shaft 1 includes a body 3 extending axially and having an upstream portion 4 and a downstream portion 5 separated axially from each other by a bulge 6 (or bellows) having a U-shape in axial half-section. The bulge 6 comprises an axial wall 7 arranged axially between two radial walls 8a, 8b (or radial diaphragms) of equivalent and constant thickness, each of the radial walls 8a, 8b connecting the axial wall 7 to one of the upstream and downstream portions 4, 5 of the body 3.The axial wall 7 and the radial walls 8a, 8b jointly and internally form a cavity 9 open towards the axis X. The shaft 1 further includes upstream and downstream fixing diaphragms (or flanges) 10a, 10b which extend radially from the upstream and downstream portions 4, 5 of the body 3, respectively. Each of the upstream and downstream diaphragms 10a, 10b comprises a web 11 of constant thickness arranged radially between an external flange 12 and an internal base 13 which is connected to the corresponding portion 4, 5 of the body 3. The upstream and downstream diaphragms 10a, 10b each have an external diameter (or external radial dimension) D1, D2 which is greater than the external diameter D3 of the axial wall 7 of the flange 6. A structurally critical diaphragm is determined (or chosen) from among the upstream and downstream diaphragms 10a, 10b.The ratio between the thickness E1 of the radial walls 8a, 8b of the bulge 6 and the thickness E2 of the veil 11 of the critical diaphragm is greater than or equal to 1.5.

[0047] The integration of such a 6-inch bead provides a large-diameter support for the measuring instrument(s), simplifying their installation and meeting the evolving needs of engine manufacturers. The bead's integration also creates a large-diameter measuring surface, further simplifying the measurement process.

[0048] Such a ratio E1 / E2 also allows shaft 1 to have mechanical properties equivalent to those of a prior art shaft with an added thickness. In addition, such integration has no negative impact on the mass of shaft 1, and may even prove beneficial for some of them.

[0049] Finally, such a tree 1 can be easily manufactured using conventional manufacturing processes such as turning.

[0050] Tree 1 is defined along the X axis which corresponds in particular to its axis of rotation and its axis of symmetry.

[0051] The structurally critical diaphragm is determined (or chosen) from among the upstream and downstream diaphragms 10a and 10b by analyzing the external forces (force and torque) applied to shaft 1. The critical diaphragm is thus the one that is structurally most mechanically stressed. This result can be determined by performing a numerical simulation using calculation software.

[0052] By convention in this application, the terms "upstream" and "downstream" define the axial positions of the elements of shaft 1 relative to each other with reference to the arrangement of shaft 1 illustrated in the figures, this arrangement corresponding to the arrangement of shaft 1 in position in the turbomachine.

[0053] Furthermore, "axial" or "axially" means any direction parallel to the X-axis, and "radial" or "radially" means any direction perpendicular to the X-axis.

[0054] Finally, the terms "internal" and "external" are defined radially with respect to the X-axis.

[0055] Advantageously, as illustrated in Figure 2, the ratio between the internal diameter (or internal radial dimension) D4 of the upstream portion 4 of the body 3 and the internal diameter D5 of the axial wall 7 of the flange 6 is greater than or equal to 0.3. Such a dimensioning allows the passage of the machining tool inside the shaft 1 to machine the cavity 9 of the flange 6.

[0056] Advantageously, as illustrated in Figure 2, the ratio between the internal diameter (or internal radial dimension) D6 of the downstream portion 5 of the body 3 and the internal diameter D5 of the axial wall 7 of the bead 6 is greater than or equal to 0.3. Similarly, such a dimensioning allows the passage of the machining tool inside the shaft 1 to machine the cavity 9 of the bead 6.

[0057] Advantageously, as illustrated in Figure 2, the length (or axial dimension) L1 between the downstream face 14 of the web 11 of the upstream diaphragm 10a and the upstream end 15 of the axial wall 7 is greater than or equal to the height (or radial dimension) H1 between the external surface 16 of the axial wall 7 and the external surface 17 of the upstream portion 4 of the body 3. Such dimensioning allows the passage of the machining tool going to machine the fillet of connection between the internal base 13 of the upstream diaphragm 10a and the upstream portion 4 of the body 3.

[0058] Advantageously, as illustrated in Figure 2, the length (or axial dimension) L2 between the upstream face 18 of the web 11 of the downstream diaphragm 10b and the downstream end 19 of the axial wall 7 is greater than or equal to the height (or radial dimension) H2 between the external surface 16 of the axial wall 7 and the external surface 20 of the downstream portion 5 of the body 3. Similarly, such dimensioning allows the passage of the machining tool going to machine the fillet of connection between the internal base 13 of the downstream diaphragm 10b and the downstream portion 5 of the body 3.

[0059] Advantageously, as illustrated in Figure 2, the thickness E3 of the axial wall 7 of the bead 6 is greater than or equal to the thickness E1 of the radial walls 8a, 8b of the bead 6.

[0060] Advantageously, as illustrated in Figure 2, the length (or axial dimension) L3 of the axial wall 7 is greater than or equal to the length L1 between the downstream face 14 of the veil 11 of the upstream diaphragm 10a and the upstream end 15 of the axial wall 7.

[0061] Advantageously, as illustrated in Figure 2, the length (or axial dimension) L3 of the axial wall 7 is greater than or equal to the length L2 between the upstream face 18 of the veil 11 of the downstream diaphragm 10b and the downstream end 19 of the axial wall 7.

[0062] Advantageously, as illustrated in Figure 2, the ratio between the external diameter (or external radial dimension) D1 of the upstream diaphragm 10a and the external diameter D7 of the upstream portion 4 of the body 3 is greater than or equal to 3.

[0063] Advantageously, as illustrated in Figure 2, the ratio between the external diameter (or external radial dimension) D2 of the downstream diaphragm 10b and the external diameter D8 of the downstream portion 5 of the body 3 is greater than or equal to 3.

[0064] Advantageously, as illustrated in Figure 2, the ratio between the external diameter (or external radial dimension) D3 of the axial wall 7 of the bead 6 and the external diameter D7 of the upstream portion 4 of the body 3 is greater than or equal to 2

[0065] Advantageously, as illustrated in Figure 2, the ratio between the external diameter (or external radial dimension) D3 of the axial wall 7 of the bead 6 and the external diameter D8 of the downstream portion 5 of the body 3 is greater than or equal to 2.

[0066] Advantageously, the thickness E4 of the veil 11 of the structurally non-critical diaphragm is between 0.8 and 1 times the thickness E2 of the veil 11 of the critical diaphragm. The structurally non-critical diaphragm corresponds to the diaphragm not selected from the upstream and downstream diaphragms 10a, 10b.

[0067] The shaft 1 according to the invention is, for example, machined on a numerically controlled lathe.

[0068] According to the embodiment illustrated in Figures 1 and 2, the upstream and downstream portions 4 and 5 of the body 3 are each cylindrical and of constant thickness. The ratio D4 / D5 is approximately 0.4. The ratio D6 / D5 is approximately 0.45.

[0069] The bead 6 provides flexibility to the shaft 1. Thus, the geometric and dimensional characteristics associated with the bead 6 allow control of the flexibility of the shaft 1.

[0070] The external surface 16 of the axial wall 7 of the bead 6 is here a working surface. The working surface can be an instrumentation surface on which one or more measuring instruments are installed (e.g., torque meter(s) (e.g., inductive) and / or speed sensor(s)). Alternatively, the working surface can be a measuring surface on which one or more measurements are performed.

[0071] The axial wall 7 of the bead 6 is cylindrical here. The length L3 of the axial wall 7 is greater than the lengths L1 and L2 defined above. The ratio D3 / D7 is approximately 2.5. The ratio D3 / D8 is approximately 2.3.

[0072] The upstream and downstream radial walls 8a, 8b are each frustoconical. More precisely, the upstream radial wall 8a of the bulge 6 flares upstream from the downstream end 22 of the upstream portion 4 of the body 3 to the upstream end 15 of the axial wall 7 of the bulge 6. The downstream radial wall 8b of the bulge 6 flares upstream from the upstream end 23 of the downstream portion 5 of the body 3 to the downstream end 19 of the axial wall 7 of the bulge 6. The frustoconical geometry of the radial walls 8a, 8b minimizes contraction under the effect of centrifugal forces. Alternatively, the upstream and downstream radial walls 8a, 8b could, for example, be purely radial (or vertical).

[0073] The upstream radial wall 8a has an external end 25 which is connected to the upstream end 15 of the axial wall 7, and an internal end 26 which is connected to the downstream end 22 of the upstream portion 4 of the body 3. The downstream radial wall 8b has an external end 27 which is connected to the downstream end 19 of the axial wall 7, and an internal end 28 which is connected to the upstream end 23 of the downstream portion 5 of the body 3.

[0074] The axial wall 7 of the rim 6 forms the bottom of the cavity 9 and the internal ends 26, 28 of the radial walls 8a, 8b form the opening 29 of the cavity 9. The bottom of the cavity 9 is radially external with respect to the opening 29 of the cavity 9. The axial dimension of the cavity 9 decreases radially from the bottom to the opening 29 of the cavity 9.

[0075] The upstream and downstream diaphragms also provide flexibility to shaft 1. Thus, the geometric and dimensional characteristics associated with the diaphragms also allow control of the flexibility of shaft 1.

[0076] The critical diaphragm here is the upstream diaphragm 10a. This result was determined by a numerical simulation. The ratio E1 / E2 is approximately equal to 2. The non-critical diaphragm is therefore the downstream diaphragm 10b.

[0077] According to the embodiment illustrated in Figures 1 and 2, the upstream diaphragm 10a is located axially at an upstream end 21 of the upstream portion 4 of the body 3, and in other words, the internal base 13 of the upstream diaphragm 10a is connected to the upstream end 21 of the upstream portion 4 of the body 3. The downstream diaphragm 10b is located axially at a downstream end 24 of the downstream portion 5 of the body 3, and in other words, the internal base 13 of the downstream diaphragm 10b is connected to the downstream end 24 of the downstream portion 5 of the body 3. The flange 12 of the upstream diaphragm 10a can be fixed, for example, to a ring carrying the blower blades or to an inlet shaft. The flange 12 of the downstream diaphragm 10b can be fixed to an element of the gear speed reducer (for example a ring gear or a planet carrier) or to a pressure-passing shaft of a low-pressure body of the turbomachine.

[0078] The shaft 1 further includes an upstream tail 30 which projects axially from the upstream end 21 of the upstream portion 4 of the body 3. The upstream tail 30 can be used to carry a sealing element. The shaft 1 further includes a downstream tail 31 which projects axially from the downstream end 24 of the downstream portion 5 of the body 3. Like the upstream tail 30, the downstream tail 31 can be used to carry a sealing element.

[0079] The ratio D1 / D7 is approximately 3.7. The ratio D2 / D8 is approximately 3.8.

[0080] Figures 3 and 4 represent aircraft turbomachines 2, each comprising a shaft 1 as described previously. As illustrated in Figures 3 and 4, the turbomachine 2 comprises a fan 32 driven in rotation by the shaft 1 via a speed reducer 33. The shaft 1 is itself driven in rotation by a low-pressure shaft 34 of a low-pressure body 35 of the turbomachine 2.

[0081] More specifically, the fan 32 is rotatable about the X-axis, which here corresponds to the longitudinal axis of the turbomachine 2. The fan 32 comprises an annular array of blades 36 with variable or fixed pitch. The fan 32 may be shrouded or unshrouded. An unshrouded fan lacks a fairing that externally surrounds the fan blades.

[0082] The gearbox 33 reduces the rotational speed of the fan 32 relative to that of the shaft 1 or the low-pressure shaft 34. The gearbox 33 is a planetary gear reducer, which allows for a high speed reduction in a compact space. Typically, the gearbox 33 comprises at least one reduction stage including a sun gear 37 (or planetary gear), a ring gear 38, satellite gears 39, and a satellite carrier 40. The gearbox 33 can be configured in various ways depending on the requirements, as illustrated in Figures 3 and 4.

[0083] As illustrated in Figures 3 and 4, the input element of the reducer 33 is commonly the solar 37. The solar 37 is rotationally linked with an input shaft 41 which is itself rotationally linked with the shaft 1. The input shaft 41 includes a downstream flange 42 which is fixed to the flange 12 of the upstream diaphragm 10a of the shaft 1 via an annular row of bolts (not shown).

[0084] Furthermore, the output element of the reducer 33 differs from one embodiment to another. In Figure 3, the output element of the reducer 33 is the ring gear 38, which is thus rotationally linked with the blower 32. In Figure 4, the output element of the reducer 33 is the planet carrier 40, which is thus rotationally linked with the blower 32. The low-pressure body 35 comprises a low-pressure compressor 43 and a low-pressure turbine 44 (or power turbine). The low-pressure compressor 43 is driven in rotation by the low-pressure turbine 44 via the low-pressure shaft 34. The low-pressure shaft 34 includes an upstream flange 45 which is fixed to the flange 12 of the downstream diaphragm 10b of the shaft 1 via an annular row of bolts (not shown).

[0085] As illustrated in Figures 3 and 4, the turbomachine further includes a measuring instrument 46 arranged around the axial wall 7 of the flange 6 of the shaft 1, for taking measurements. The measuring instrument 46 is positioned opposite and at a distance from the outer surface 16 of the axial wall 7. Alternatively, the measuring instrument 46 could be mounted or installed on the outer surface 16 of the axial wall 7. The measuring instrument 46 is a torque meter (e.g., inductive) or a speed sensor. The turbomachine 2 could, of course, include several measuring instruments 46 arranged around the axial wall 7 of the flange 6 of the shaft 1.

Claims

DEMANDS 1. Shaft (1) for an aircraft turbomachine (2), the shaft (1) being a single piece and annular about an axis (X), the shaft (1) comprising a body (3) extending axially and having an upstream portion (4) and a downstream portion (5) separated axially from each other by a flange (6) having a U-shape in axial half-section, the flange (6) comprising an axial wall (7) disposed axially between two radial walls (8a, 8b) of equivalent and constant thickness, each of the radial walls (8a, 8b) connecting the axial wall (7) to one of the upstream and downstream portions (4, 5) of the body (3), the axial wall (7) and the radial walls (8a, 8b) jointly and internally forming a cavity (9) open towards the axis (X), the shaft (1) further comprising mounting diaphragms upstream and downstream (10a, 10b) which extend radially and respectively from the upstream and downstream portions (4, 5) of the body (3), each of the upstream and downstream diaphragms (10a,10b) comprising a web (11) of constant thickness arranged radially between an external flange (12) and an internal base (13) which is connected to the corresponding portion (4, 5) of the body (3), the upstream and downstream diaphragms (10a, 10b) each having an external diameter (D1, D2) which is greater than the external diameter (D3) of the axial wall (7) of the rim (6), a structurally critical diaphragm is determined among the upstream and downstream diaphragms (10a, 10b), the quotient between the thickness (E1) of the radial walls (8a, 8b) of the rim (6) and the thickness (E2) of the web (11) of the critical diaphragm is greater than or equal to 1.

5.

2. Shaft (1) according to claim 1, characterized in that the ratio between the internal diameter (D4) of the upstream portion (4) of the body (3) and the internal diameter (D5) of the axial wall (7) of the bead (6) is greater than or equal to 0.

3.

3. Shaft (1) according to any one of the preceding claims, characterized in that the ratio between the internal diameter (D6) of the downstream portion (5) of the body (3) and the internal diameter (D5) of the axial wall (7) of the bead (6) is greater than or equal to 0.

3.

4. Shaft (1) according to any one of the preceding claims, characterized in that the length (L1) between the downstream face (14) of the web (11) of the upstream diaphragm (10a) and the upstream end (15) of the axial wall (7) is greater than or equal to the height (H1) between the external surface (16) of the axial wall (7) and the external surface (17) of the upstream portion (4) of the body (3).

5. Shaft (1) according to any one of the preceding claims, characterized in that the length (L2) between the upstream face (18) of the web (11) of the downstream diaphragm (10b) and the downstream end (19) of the axial wall (7) is greater than or equal to the height (H2) between the external surface (16) of the axial wall (7) and the external surface (20) of the downstream portion (5) of the body (3).

6. Shaft (1) according to any one of the preceding claims, characterized in that the thickness (E3) of the axial wall (7) of the bead (6) is greater than or equal to the thickness (E1) of the radial walls (8a, 8b) of the bead (6).

7. Shaft (1) according to any one of the preceding claims, characterized in that the length (L3) of the axial wall (7) is greater than or equal to the length (L1) between the downstream face (14) of the web (11) of the upstream diaphragm (10a) and the upstream end (15) of the axial wall (7).

8. Shaft (1) according to any one of the preceding claims, characterized in that the length (L3) of the axial wall (7) is greater than or equal to the length (L2) between the upstream face (18) of the web (11) of the downstream diaphragm (10b) and the downstream end (19) of the axial wall (7).

9. Shaft (1) according to any one of the preceding claims, characterized in that the ratio between the external diameter (D1) of the upstream diaphragm (10a) and the external diameter (D7) of the upstream portion (4) of the body (3) is greater than or equal to 3.

10. Shaft (1) according to any one of the preceding claims, characterized in that the ratio between the external diameter (D2) of the downstream diaphragm (10b) and the external diameter (D8) of the downstream portion (5) of the body (3) is greater than or equal to 3.

11. Shaft (1) according to any one of the preceding claims, characterized in that the ratio between the external diameter (D3) of the axial wall (7) of the bead (6) and the external diameter (D7) of the upstream portion (4) of the body (3) is greater than or equal to 2.

12. Shaft (1) according to any one of the preceding claims, characterized in that the ratio between the external diameter (D3) of the axial wall (7) of the bead (6) and the external diameter (D8) of the downstream portion (5) of the body (3) is greater than or equal to 2.

13. Shaft (1) according to any one of the preceding claims, characterized in that the thickness (E4) of the web (11) of the structurally non-critical diaphragm is between 0.8 and 1 times the thickness (E2) of the web (11) of the critical diaphragm, the structurally non-critical diaphragm corresponding to the diaphragm not chosen from the upstream and downstream diaphragms (10a, 10b).

14. Aircraft turbomachine (2) comprising a shaft (1) according to any one of the preceding claims.

15. Aircraft turbomachine (2) according to the preceding claim, characterized in that the turbomachine (2) comprises a fan (32) driven in rotation by the shaft (1) via a speed reducer (33), the shaft (1) itself being driven in rotation by a low-pressure shaft (34) of a low-pressure body (35) of the turbomachine (2).

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