Reduction gearset

Abstract

A reduction gearset (10), in particular for an aircraft or an aircraft turbomachine, this reduction gearset (10) comprising: - a sun gear (26) able to rotate about an axis (X), the sun gear (26) comprising an external herringbone toothset, - a ring gear (28) extending around the axis (X) and the sun gear (26), the ring gear comprising an internal herringbone toothset, and - planet pinions (30) inserted between the sun gear (26) and the ring gear (28) and meshing with the sun gear (26) and the ring gear (28), the planet pinions (30) being borne by a planet carrier (32) and each comprising an external herringbone toothset, the ring gear (9) comprising two half-rings (9a, 9b) which comprise annular flanges (9ab, 9bb), the orifices (20, 22) of which differ in shape and / or dimensions.

Description

[0001] DESCRIPTION

[0002] REDUCER

[0003] Technical field of the invention

[0004] The present invention relates to a reducer, in particular for an aircraft or an aircraft turbomachine, as well as an aircraft or an aircraft turbomachine comprising such a reducer.

[0005] Technical approval plan

[0006] The state of the art includes in particular documents FR-A1 -2 987 416, FRAI -2 853 382, ​​FR-A1 -3 041 054, FR-A1 -3 073 915, FR-A1 -3 084 428, FR- A-1 -3 084 427, US-A1 -2020 / 166121 and W0-A1 -2020 / 021188.

[0007] The role of a mechanical reducer is to modify the speed ratio and torque between the input shaft and the output shaft of a mechanism.

[0008] New generations of dual-flow turbomachines, particularly those with a high bypass ratio, include a mechanical reducer to drive the shaft of a fan. Typically, the reducer's purpose is to transform the so-called fast rotation speed of a power turbine shaft into a slower rotation speed for the shaft driving the fan.

[0009] Such a reducer comprises a central pinion, called a sun gear, a crown gear and pinions called planet gears, which are meshed between the sun gear and the crown gear. The planet gears are held by a frame called a planet carrier. The sun gear, the crown gear and the planet carrier are planet gears because their axes of revolution coincide with the longitudinal axis of the turbomachine. The planet gears each have a different axis of revolution equally distributed over the same operating diameter around the axis of the planet gears. These axes are parallel to the longitudinal axis of the turbomachine. There are several reducer architectures. In the state of the art of double-flow turbomachines, the reducers are of the planetary or epicyclic type. In other similar applications, there are architectures called differential or "compound".

[0010] - on a planetary reducer, the planet carrier is fixed and the crown constitutes the output shaft of the device which rotates in the opposite direction to the solar.

[0011] - on an epicyclic reducer, the crown is fixed and the planet carrier constitutes the output shaft of the device which rotates in the same direction as the solar.

[0012] - on a differential reducer, no element is fixed in rotation. The crown rotates in the opposite direction to the sun and the planet carrier.

[0013] Gearboxes can be composed of one or more meshing stages. This meshing is ensured in different ways such as by contact, friction or even by magnetic field. There are several types of contact meshing such as with straight or herringbone teeth.

[0014] When the teeth are herringbone, it is common to form the crown by assembling two half-crowns, each of these half-crowns having an internal tooth forming one half of the chevrons, and the other of the half-crowns having an internal tooth forming the other half of the chevrons.

[0015] These half-crowns are assembled by clamping and comprise flanges which are applied axially one on the other. The flanges comprise orifices which are distributed around their periphery and which receive axial fixing means for assembling the crown, which are in practice generally screws.

[0016] Among these fixing means or screws, some have a function of tightening the flanges together and are called tightening means or screws. The other screws have a function of centering the flanges, and are called centering means or screws. These screws are used to axially position the half-crowns relative to each other. In practice, the number of centering screws can be at least two. The half-crowns, once positioned between them, must also be centered in the environment in which they are inserted. This positioning (or centering) can be achieved by shrinking into a shaft or a crown holder, for example.

[0017] The shrink fitting of half-crowns with parts external to the reducer, such as a crown carrier, can involve significant radial deformations at the level of the crown assembly flanges, in comparison with the clearances permitted at the level of the centering screws.

[0018] These greater deformations may mean that, during assembly, the centering screws work both in tension (tightening) and in shear (due to the different radial deformations of the half-crowns). This double stress must be avoided so as not to affect the service life of the crown.

[0019] The present invention provides a solution to this problem, which is simple, effective and economical.

[0020] Summary of the invention

[0021] The invention relates to a reducer, in particular for an aircraft or an aircraft turbomachine, this reducer comprising:

[0022] - a mobile sun rotating around an axis, the sun comprising external herringbone teeth,

[0023] - a crown extending around the axis and the sun, the crown having internal herringbone teeth, and

[0024] - satellites interposed between the sun and the crown and meshed with the sun and the crown, the satellites being carried by a planet carrier and each comprising an external herringbone toothing, the crown comprising two half-crowns which are annular and coaxial, the half-crowns comprising annular flanges which extend radially outwards relative to the axis and which are mounted axially against each other, these flanges comprising axial through-orifices for the passage of axial fixing means for assembling the crown, these axial fixing means comprising clamping means which pass through a part of the axial orifices of the flanges and which serve to fix the flanges against each other, and centering means which pass through another part of the orifices of the flanges and which serve to center the flanges with respect to each other,characterized in that the axial orifices crossed by the clamping means differ in their shape and / or their dimensions from the axial orifices crossed by the centering means.,

[0025] Having different shapes and / or dimensions for the mounting holes of the clamping means and for the mounting holes of the centering means is advantageous for dimensioning these shapes and / or dimensions according to the functions of these means. For example, the receiving holes of the centering means could be oversized compared to the receiving holes of the clamping means so as to allow deformations and displacements of the half-crowns, one relative to the other, without losing radial and angular positioning precision. In the case where the oversizing of the receiving holes of the centering means is carried out in the radial direction relative to the axis of the reducer, deformations and displacements of the half-crowns in the radial direction are authorized, in particular during radial compression of one crown relative to the other.

[0026] The passage holes of the centering means and these centering means are dimensioned so as to allow less movement between the half-crowns than that allowed by the clamping means for angular and radial positioning. The object of the invention is thus to allow more radial movement and deformation between the half-crowns than angular movement while remaining more restrictive than the clamping means.

[0027] The present invention is compatible:

[0028] - a single-stage or multi-stage reducer;

[0029] - a so-called epicyclic, planetary or differential reducer.

[0030] - preferably herringbone teeth; - any type of single-piece planet carrier or cage and cage carrier type;

[0031] - any type of satellite guide bearings, such as rolling elements or hydrodynamic.

[0032] The reducer according to the invention may comprise one or more of the following characteristics, taken in isolation from one another, or in combination with one another:

[0033] - the axial orifices crossed by the clamping means are circular and their centers are located on the same circumference;

[0034] - the axial orifices crossed by the centering means are non-circular;

[0035] - the axial orifices crossed by the centering means have an oblong or elliptical shape;

[0036] - the axial orifices crossed by the centering means have an elongated shape in the radial direction;

[0037] - the axial orifices crossed by the centering means have a radial dimension which is greater than a circumferential dimension of these orifices, the difference between the radial dimension and the circumferential dimension of these orifices being between 0.01 mm and 3 mm, preferably between 0.01 mm and 2 mm, and more preferably between 0.5 and 2 mm;

[0038] - the axial orifices crossed by the centering means have a circumferential dimension equal to or less than a diameter or a transverse dimension of the axial orifices crossed by the clamping means;

[0039] - the axial orifices crossed by the centering means have centers which are located on the same circumference, which can pass through centers of the axial orifices crossed by the clamping means;

[0040] - the axial orifices are distributed in series of axial orifices, each of the flanges comprising several series of axial orifices, the axial orifices of each series being separated from each other by a circumferential pitch, and the series of axial orifices being circumferentially spaced from each other by a distance greater than this pitch;

[0041] -- each series of axial orifices comprises at least one axial orifice for the passage of the centering means and any number of axial orifices for the passage of the clamping means;

[0042] -- the axial orifices for the passage of the centering means are regularly distributed around the axis;

[0043] -- the axial holes for the passage of the clamping means are regularly distributed around the axis;

[0044] - each series of axial orifices comprises at least two axial orifices for the passage of the centering means and at least three or four axial orifices for the passage of the clamping means, each of the axial orifices for the passage of the centering means being located between two axial orifices for the passage of the clamping means;

[0045] - each series of axial orifices comprises at least two axial orifices for the passage of the centering means and at least two orifices for the passage of the clamping means arranged on each side of each of these axial orifices for the passage of the centering means;

[0046] - each series of axial orifices has a symmetry with respect to a median plane passing through the axis and through the middle of the series;

[0047] - the number of axial passage holes for the centering means of each flange is less than the number of axial passage holes for the clamping means of this flange;

[0048] -- the number of axial orifices for the passage of the centering means is at least equal to two;

[0049] -- the number of axial passage holes for the centering means comprises between three and one third of the number of axial passage holes for the fixing means; - the number of axial passage holes for the centering means of each flange represents half the number of axial passage holes for the clamping means of this flange;

[0050] -- the number of axial passage holes for the centering means of each flange represents one third of the number of axial passage holes for the clamping means of this flange;

[0051] - an annular element such as a shaft or a crown carrier surrounds one of the half-crowns and is fixed, for example by shrinking, to this half-crown;

[0052] - the centering means are or include centering screws and / or the clamping means are or include clamping screws.

[0053] The invention further relates to a turbomachine or an aircraft, comprising a reducer as described above.

[0054] Brief description of the figures

[0055] Other characteristics and advantages will emerge from the following description of a non-limiting embodiment of the invention with reference to the appended drawings in which:

[0056] [Fig.1] Figure 1 is a half schematic view in axial section of an aircraft turbomachine,

[0057] [Fig.2] Figure 2 is a half schematic view in axial section of a speed reducer,

[0058] [Fig.3] Figure 3 is a very schematic half-view in axial section of a reducer crown and its environment;

[0059] [Fig.4a] Figure 4a is a view similar to that of Figure 3, the section plane passing through a clamping screw;

[0060] [Fig.4b] Figure 4b is a view similar to that of Figure 3, the section plane passing through a centering screw;

[0061] [Fig.4c] Figure 4c is a very schematic view of the screw passage holes of a reducer crown flange; [Fig.5] Figure 5 is a very schematic view of a series of screw passage holes of a crown flange of the prior art;

[0062] [Fig.6] Figure 6 is a very schematic view of a series of screw passage holes of a crown flange according to the invention; and

[0063] [Fig.7] Figure 7 is a partial schematic view of a flange of the reducer crown.

[0064] Detailed description of the invention

[0065] Figure 1 describes a turbomachine 1 which comprises, in a conventional manner, a fan S, a low-pressure compressor 1a, a high-pressure compressor 1b, an annular combustion chamber 1c, a high-pressure turbine 1d, a low-pressure turbine 1e and an exhaust nozzle 1h. The rotors of the high-pressure compressor 1b and the high-pressure turbine 1d are connected by a high-pressure shaft 2 and form with it a high-pressure (HP) body. The rotors of the low-pressure compressor 1a and the low-pressure turbine 1e are connected by a low-pressure shaft 3 and form with it a low-pressure (LP) body.

[0066] The blower S is driven by a blower shaft 4 which is connected to the LP shaft 3 by means of a reducer 6. This reducer 6 is generally of the planetary or epicyclic type.

[0067] Although the following description concerns a planetary or epicyclic type reducer, it also applies to a mechanical differential in which its three essential components, namely the planet carrier, the crown and the sun gear, are mobile in rotation, the rotation speed of one of these components depending in particular on the difference in speeds of the other two components.

[0068] The reducer 6 is positioned in the upstream part of the turbomachine. A fixed structure comprising schematically, here, an upstream part 5a and a downstream part 5b which compose the motor casing or stator 5 is arranged so as to form an enclosure E surrounding the reducer 6. This enclosure E is here closed upstream by seals at the level of a bearing allowing the fan shaft 4 to pass through, and downstream by seals at the level of the passage of the LP shaft 3.

[0069] Figure 2 shows a part of a reducer 6 which can take the form of different architectures depending on whether certain parts are fixed or rotating. At the input, the reducer 6 is connected to the LP shaft 3, for example via splines 7a. Thus, the LP shaft 3 drives a planetary pinion called the sun gear 7. Conventionally, the sun gear 7, whose axis of rotation coincides with the X axis of the turbomachine, drives a series of pinions called satellites 8, which are equally distributed over the same diameter around the axis of rotation X. This diameter is equal to twice the operating center distance between the sun gear 7 and satellites 8. The number of satellites 8 is generally defined between three and seven for this type of application.

[0070] All of the satellites 8 are held by a frame called a satellite carrier 10. Each satellite 8 rotates around its own Y axis, and meshes with the crown 9.

[0071] At the output of the reducer 6, we have: o in an epicyclic configuration, the set of planet gears 8 rotates the planet carrier 10 around the axis X of the turbomachine. The ring gear 9 is fixed to the engine casing or stator 5 via a ring gear carrier 12 and the planet carrier 10 is fixed to the fan shaft 4. o in a planetary configuration, the set of planet gears 8 is held by a planet carrier 10 which is fixed to the engine casing or stator 5. Each planet gear drives the ring gear which is attached to the fan shaft 4 via a ring gear carrier 12.

[0072] Each satellite 8 is mounted to rotate freely using a bearing 11, for example of the rolling bearing or hydrostatic bearing type. Each bearing 11 is mounted on one of the axes 10b of the planet carrier 10 and all the axes are positioned relative to each other using one or more structural frames 10a of the planet carrier 10. There is a number of axes and bearings equal to the number of satellites. For reasons of operation, assembly, manufacturing, control, repair or replacement, the axes 10b and the frame 10a can be separated into several parts.

[0073] For the same reasons mentioned above, the teeth of a reducer can be separated into several helices.

[0074] According to the invention, the teeth of the sun gear 7, the satellites 8 and the crown 9 are herringbone, that is to say that they each comprise helices each formed of teeth, the teeth of one of the helices being inclined relative to the teeth of the other helix.

[0075] In our example we detail the operation of a herringbone reduction gear with a crown separated into two half-crowns. A front half-crown 9a comprises a rim 9aa and a half-fixing flange 9ab. On the rim 9aa is the front helix of the herringbone teeth of crown 9. This front helix meshes with that of the satellite 8 which meshes with that of the solar 7.

[0076] A 9b rear half-crown consists of a 9ba rim and a 9bb mounting half-flange. On the 9ba rim is the rear helix of the herringbone toothing of crown 9. This rear helix meshes with that of satellite 8 which meshes with that of sun 7.

[0077] The half-fixing flange 9ab of the front crown 9a and the half-fixing flange 9bb of the rear crown 9b form the fixing flange 9c of the crown. The crown 9 is fixed to the crown carrier 12 by assembling the fixing flange 9c of the crown and the fixing flange 12a of the crown carrier using a bolted assembly for example. Furthermore, the crown carrier 12 can be fixed, for example by shrink fitting, on one of the half-crowns 9a, 9b.

[0078] The arrows in Figure 2 describe the routing of the oil in the reducer 6. The oil arrives in the reducer 6 from the stator part 5 in the distributor 13 by different means which will not be specified in this view because they are specific to one or more types of architecture. The distributor 13 is separated into two parts, generally each repeated by the same number of satellites. The injectors 13a have the function of lubricating the teeth, and the arms 13b have the function of lubricating the bearings 11. The oil is brought to the injector 13a to exit through the end 13c in order to lubricate the teeth. The oil is also brought to each arm 13b and circulates via the supply mouth 13d of the bearing 11. The oil then circulates through the axis 10b in one or more buffer zones 10c and then exits through orifices 10d in order to lubricate the bearings 11 of the satellites.

[0079] As is very schematically illustrated in Figures 3 and 4a to 4c, the half-crowns 9a, 9b comprise annular flanges 9ab, 9bb which are oriented radially outwards relative to the axis X and which are applied axially against each other. These flanges 9ab, 9bb comprise axial through-holes 20, 22 for the passage of axial fastening means for assembling the crown 9. Preferably, these axial fastening means comprise or are assembly screws 24. For convenience, the assembly screws 24 will be used in the following to describe these axial fastening means.

[0080] The assembly screws 24 are of two types and comprise clamping means or screws 24a which pass through a part of the orifices 20 of the flanges 9ab, 9bb and which serve to fix the flanges 9ab, 9bb against each other, and centering means or screws 24b which pass through another part of the orifices 22 of the flanges 9ab, 9bb and which serve to center the flanges 9ab, 9bb with respect to each other.

[0081] Furthermore, the crown carrier 12 comprises a flange 12a which is applied to the flanges 9ab, 9bb, and in particular assembled to the flanges 9ab, 9bb with the same assembly screws 24.

[0082] The crown carrier 12 can further be shrunk onto one of the half-crowns 9a, 9b, and in particular onto the body or one of the rims 9aa, 9ba of these half-crowns.

[0083] As seen in Figure 4c, the centering screws 24b are distributed around the X axis. In the current technique, the orifices 20, 22 all have a circular shape. Furthermore, the clearance J2 between the centering screws 24b and the orifices 22 is less than the clearance J1 between the clamping screws 24a and the orifices 20, so that it is the screws 24b which cooperate in priority with the edges of the orifices 24 for the centering of the half-crowns 9a, 9b.

[0084] In practice, the orifices 22 may have a dimension in the transverse direction which is smaller than that of the orifices 20. The screws 24a, 24b may then have similar or even identical transverse dimensions. Alternatively, the orifices 20, 22 all have the same diameter and the centering screws 24b are oversized in the transverse direction to reduce the clearance with their receiving orifices 22 (see FIG. 5).

[0085] According to the invention, the orifices 20 crossed by the clamping screws 24a differ in their shape and / or their dimensions from the orifices 22 crossed by the centering screws 24b.

[0086] Preferably, the orifices 20 crossed by the clamping screws 24a are circular and their centers are located on the same circumference C1, as illustrated in figure 6.

[0087] Preferably, the orifices 22 crossed by the centering screws 24b are non-circular, as also illustrated in FIG. 6.

[0088] The holes 22 crossed by the centering screws 24b may have an oblong or elliptical shape for example.

[0089] The orifices 22 crossed by the centering screws 24b advantageously have an elongated shape in the radial direction.

[0090] The orifices 22 may have a radial dimension R1 which is greater than a circumferential dimension E1 of these orifices 22. The difference between the radial dimension R1 and the circumferential dimension E1 of these orifices 22 is for example between 0.01 mm and 3 mm, preferably between 0.01 mm and 2 mm, and more preferably between 0.5 and 2 mm.

[0091] The orifices 22 may have a circumferential dimension E1 less than or equal to a diameter D1 or to a transverse dimension of the orifices 20 crossed by the clamping screws 24a. The orifices 22 may have centers which are located on the same circumference C2, which may pass through the centers of the orifices 24. In other words, the centers of the orifices 20, 22 may be located on a single circumference C1, C2.

[0092] In the example shown in Figures 6 and 7, the orifices 20, 22 are distributed in series of orifices S1, S2, ...Sn. Each of the flanges 9ab, 9bb comprises several series of orifices S1, S2, ...Sn, the orifices 10, 22 of each series being separated from each other by a circumferential pitch P1, and the series of orifices S1, S2, ...Sn being circumferentially spaced from each other by a distance H1 greater than this pitch P1.

[0093] Each series of orifices S1, S2, ...Sn may comprise at least one orifice 22 for the passage of a centering screw 24b and any number of orifices 20 for the passage of a clamping screw 24a.

[0094] Each series of orifices S1, S2, ...Sn may comprise at least two centering orifices 24b and at least three or four orifices 20 for the passage of the clamping screws 24a, as illustrated in the drawings. Each of the orifices 22 for the passage of the centering screws 24b is preferably located between two orifices 20 for the passage of the clamping screws 24a.

[0095] In other words, each series of orifices S1, S2, ..., Sn comprises at least two orifices 22 for the passage of the centering screws 24b and at least two orifices 20 for the passage of the clamping screws 24a arranged on each side of each of these orifices 22 for the passage of the centering screws 24b.

[0096] As seen in the figures, each series of orifices S1, S2, ..., Sn has a symmetry with respect to a median plane Q passing through the X axis and through the middle of the series.

[0097] The number of holes 22 for the passage of centering screws 24b of each flange 9ab, 9ab is preferably at least equal to two. It is for example between three and one third of the number of holes 20 for the passage of fixing screws 24a. The number of holes 22 for the passage of centering screws 24b of each flange 9ab, 9ab is preferably less than the number of holes 20 for the passage of tightening screws 24a of this flange.

[0098] The number of holes 22 for the passage of the centering screws 24b of each flange 9ab, 9bb represents for example a third of the number of holes 20 for the passage of the clamping screws 24a of this flange.

[0099] In the drawings, the shapes and dimensions of the orifices may be exaggerated from practice for the purpose of better understanding the invention.

Claims

CLAIMS 1. Reducer (10), in particular for an aircraft or an aircraft turbomachine, this reducer (10) comprising: - a sun (26) movable in rotation around an axis (X), the sun (26) comprising external herringbone teeth, - a crown (28) extending around the axis (X) and the sun (26), the crown comprising internal herringbone teeth, and - satellites (30) interposed between the sun (26) and the crown (28) and meshed with the sun (26) and the crown (28), the satellites (30) being carried by a planet carrier (32) and each comprising an external herringbone toothing, the crown (9) comprising two half-crowns (9a, 9b) which are annular and coaxial, the half-crowns (9a, 9b) comprising annular flanges (9ab, 9bb) which extend radially outwards relative to the axis (X) and which are mounted axially against each other, these flanges (9ab, 9bb) comprising axial through-orifices (20, 22) for the passage of axial fixing means (24) for assembling the crown, these axial fixing means comprising clamping screws (24a) which pass through a part of the axial holes (20) of the flanges (9ab, 9bb) and which serve to fix the flanges against each other, and centering screws (24b) which pass through another part of the holes (22) of the flanges (9ab,9bb) and which serve to center the flanges (9ab, 9bb) with respect to each other, characterized in that the axial orifices (20) crossed by the clamping screws (24a) differ in their shape and / or their dimensions from the axial orifices (22) crossed by the centering screws (24b)., 2. Reducer (10) according to claim 1, in which the axial orifices (20) crossed by the clamping screws (24a) are circular and their centers are located on the same circumference (C1).

3. Reducer (10) according to claim 1 or 2, in which the axial orifices (22) crossed by the centering screws (24b) are non-circular.

4. Reducer (10) according to one of the preceding claims, in which the axial orifices (22) crossed by the centering screws (24b) have an oblong or elliptical shape.

5. Reducer (10) according to one of the preceding claims, in which the axial orifices (22) crossed by the centering screws (24b) have an elongated shape in the radial direction.

6. Reducer (10) according to claim 5, in which the axial orifices (22) crossed by the centering screws (24b) have a radial dimension (R1) which is greater than a circumferential dimension (E1) of these orifices, the difference between the radial dimension (R1) and the circumferential dimension (E1) of these orifices being between 0.01 mm and 3 mm, preferably between 0.01 mm and 2 mm, and more preferably between 0.5 and 2 mm.

7. Reducer (10) according to claim 6, in which the axial orifices (22) crossed by the centering screws (24b) have a circumferential dimension (E1) less than or equal to a diameter (D1) or to a transverse dimension of the axial orifices (20) crossed by the clamping screws (24a).

8. Reducer (10) according to one of claims 5 to 7, in which the axial orifices (22) crossed by the centering screws (24b) have centers which are located on the same circumference (C2), which can pass through centers of the axial orifices (20) crossed by the clamping screws (24a).

9. Reducer (10) according to one of the preceding claims, in which the axial orifices (20, 22) are distributed in series of axial orifices (S1, S2, ..., Sn), each of the flanges (9ab, 9bb) comprising several series of axial orifices, the axial orifices (20, 22) of each series being separated from each other by a circumferential pitch (P1), and the series of axial orifices being circumferentially spaced from each other by a distance (H1) greater than this pitch (P1).

10. Reducer (10) according to claim 9, in which each series of axial orifices (S1, S2, ..., Sn) comprises at least two axial orifices (22) for the passage of the centering screws (24b) and at least three or four orifices (20) for the passage of the clamping screws (24a), each of the orifices (22) for the passage of the centering screws (24b) being located between two axial orifices (20) for the passage of the clamping screws (24a).

11. Reducer (10) according to claim 9, in which each series of axial orifices (S1, S2, ..., Sn) comprises at least two axial orifices (22) for the passage of the centering screws (24b) and at least two orifices (20) for the passage of the clamping screws (24a) arranged on each side of each of these axial orifices (22) for the passage of the centering screws (24b).

12. Reducer (10) according to one of claims 9 to 11, in which each series of axial orifices (S1, S2, ..., Sn) has a symmetry with respect to a median plane (Q) passing through the axis (X) and through the middle of the series.

13. Reducer (10) according to one of the preceding claims, in which the number of axial orifices (22) for the passage of the centering screws (24b) of each flange (9ab, 9bb) is less than the number of axial orifices (20) for the passage of the clamping screws (24a) of this flange.

14. Reducer (10) according to claim 13, in which the number of axial orifices (22) for the passage of the centering screws (24b) of each flange (9ab, 9bb) represents half the number of axial orifices (20) for the passage of the clamping screws (24a) of this flange.

15. Reducer (10) according to one of the preceding claims, in which an annular element such as a shaft or a crown carrier (12) surrounds one of the half-crowns (9a, 9b) and is shrunk onto this half-crown.

16. Turbomachine or aircraft, comprising a reducer (10) according to one of the preceding claims.

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