CROWN FOR A MECHANICAL REDUCER OF AN AIRCRAFT TURBOMACHINE

Abstract

Crown (9) for a mechanical reducer (6) of an aircraft turbomachine (1), comprising two independent half-crowns (9a, 9b) each comprising an external half-flange (9ab, 9bb), the external half-flanges (9ab, 9bb) of the two half-crowns (9a, 9b) being fixed to each other by screws which pass through orifices (9e) of the half-flanges (9ab, 9bb), oil passages being located between the half-flanges (9ab, 9bb), characterized in that it further comprises an oil passage ring (30) which is independent of the half-crowns (9a, 9b) and which is interposed between the half-flanges (9ab, 9bb) of the half-crowns (9a, 9b), the ring (30) comprising orifices (30e) aligned with the orifices (9e) half-flanges (9ab, 9bb) for the passage of said screws, and in that said passages are formed in said ring (30). Abstract figure: figures 7a

Description

Title of the invention: CROWN FOR A MECHANICAL REDUCER OF AN AIRCRAFT TURBOMACHINE Technical field of the invention

[0001] The invention relates to a crown for a mechanical reducer of an aircraft turbomachine, as well as a mechanical reducer comprising such a crown. Technical background

[0002] The state of the art includes in particular documents WO-A1-2010 / 092263, FR-A1-2 987 416 and FR-A1-3 041 054.

[0003] The role of a mechanical reducer is to modify the speed ratio and the torque between the input axis and the output axis of a mechanism.

[0004] New generations of dual-flow turbomachines, particularly those with a high bypass ratio, include a mechanical reducer to drive the shaft of a fan (also called a "fan"). Usually, the reducer aims to transform the so-called fast rotation speed of the shaft of a power turbine into a slower rotation speed for the shaft driving the fan.

[0005] Such a reducer comprises a central pinion, called a sun gear, a crown gear and pinions called satellites, which are engaged between the sun gear and the crown gear. The satellites are held by a frame called a planet carrier. The sun gear, the crown gear and the planet carrier are planetary gears because their axes of revolution coincide with the longitudinal axis of the turbomachine. The satellites each have a different axis of revolution equally distributed over the same operating diameter around the axis of the planetary gears. These axes are parallel to the longitudinal axis of the turbomachine.

[0006] There are several gearbox architectures. In the state of the art of dual-flow turbomachines, the gearboxes are of the planetary or epicyclic type. In other similar applications, there are so-called differential or "compound" architectures. - 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. - 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. - On a differential reducer, no element is fixed in rotation. The crown rotates in the opposite direction to the sun and the planet carrier.

[0007] The reducers can be composed of one or more meshing stages. This meshing is ensured in different ways such as by contact, by friction or even by magnetic field.

[0008] There are several types of contact meshing such as with straight or herringbone teeth.

[0009] The operation of reducers requires a particularly high oil flow rate to ensure the lubrication and cooling of its mechanical elements. However, this type of reducer has disadvantages linked to its lubrication and in particular to the evacuation of the lubricating oil.

[0010] In document FR-A1-3 084 427, the Applicant has proposed means for discharging lubricating oil which comprise an annular row of oil passages extending radially through the flange of the crown and configured to allow the circulation of oil radially towards the outside of this flange.

[0011] The crown comprises two half-crowns which comprise half-flanges assembled to form the crown flange. These half-flanges comprise through holes for mounting screws or bolts for fixing the half-flanges.

[0012] The oil passages comprise crescents formed in radial bearing faces of the half-flanges and extending radially over the entire height of these half-flanges.

[0013] The formation of these oil passages requires the machining of the lunules in the half-flanges of the half-crowns, during a complex and relatively expensive operation.

[0014] The present invention provides an improvement to this technology, which is simple, efficient and economical. Summary of the invention

[0015] To this end, the invention proposes a crown for a mechanical reducer of an aircraft turbomachine, this crown having an annular shape around an axis and comprising an internal annular toothing oriented towards the axis and an external annular flange oriented radially towards the outside of the axis, the crown comprising two half-crowns independent of each other and each comprising a part of the internal toothing and external half-flange, the external half-flanges of the two half-crowns together forming the flange of the crown and being fixed to each other by screws which are parallel to the axis and which pass through aligned orifices of the half-flanges, oil passages being oriented radially with respect to the axis being located between the half-flanges and regularly distributed around the axis, characterized in that it further comprises an oil passage ring which is independent of the half-crowns and which is interposed between the half-bridles of half-crowns,the ring comprising orifices aligned with the orifices of the half-flanges for the passage of said screws, and in that said oil passages are formed in said ring.

[0016] The invention thus proposes to form the oil passages through the crown, in a ring that is inserted between the half-flanges of the half-crowns. It is therefore no longer necessary to provide for the formation of these passages in the half-flanges, which are simpler and more economical to produce. The ring is dedicated to the evacuation of the oil and is sized and designed to perform this function.

[0017] The solution proposed below is compatible with a single-stage or multi-stage reducer. It is compatible with a so-called epicyclic, planetary or differential reducer. It is compatible with straight, helical or herringbone teeth. It is compatible with any type of planet carrier, whether monobloc or cage and cage carrier type. It is compatible with any type of satellite bearing, whether it is composed of a rolling element, a hydrodynamic bearing, etc.

[0018] The crown 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: - the oil passages are formed by channels formed within the ring, lunules or slits formed on sides of the ring, and / or honeycomb or lattice portions of the ring; it is understood that the honeycomb or lattice portions of the ring comprise open cells which communicate with each other to allow the passage of oil between the cells and through these portions; - the ring comprises a first annular bearing face on one of the half-flanges, and a second annular bearing face on the other of the half-flanges, the orifices of the ring opening onto these first and second faces, the ring further comprising a radially internal annular edge and a radially external annular edge; - the internal channels are formed in the middle of the ring, at a distance from its first and second faces, and open onto the internal and external edges of the ring; - the lunules or slits are formed on at least one of the first and second faces of the ring; - the lunules or slits extend over the entire radial dimension of the ring; - the ring holes are formed in rigid blocks which are distributed around the axis and which are secured to each other by an annular honeycomb or lattice structure of the ring, the honeycomb or lattice portions of this structure located between the blocks forming said oil passages; - the blocks are all identical and have a diamond shape for example; - Danneau_int is between 0.9.Dbride_int and l.l.Dbride_int and Danneau_ext is between 0.9.Dbride_ext and l.l.Dbride_ext, Danneau_int and Danneau_ext being respectively the internal and external diameters of the ring, and Dbride_int and Dbride_ext being respectively the internal and external diameters of the crown flange.

[0019] The present invention also relates to a mechanical reducer for an aircraft turbomachine, comprising a crown as described above, a sun gear centered on the axis of the crown and surrounded by the crown, and satellites mounted between the sun gear and the crown and meshed with the sun gear and the crown. Brief description of the figures

[0020] 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:

[0021] [Fig-1] [Fig.l] is a schematic axial sectional view of a turbomachine aircraft,

[0022] [Fig.2] [Fig.2] is a partial schematic view in axial section of a mechanical reducer,

[0023] [Fig.3] [Fig.3] is a partial schematic view in axial section of a mechanical reducer,

[0024] [Fig.4] [Fig.4] is a schematic sectional and perspective view of the reducer of [Fig.3],

[0025] [Fig.5] [Fig.5] is a partial schematic view of a crown of the reducer of [Fig.3],

[0026] [Fig.6] [Fig.6] is a partial schematic view of a half-flange of a half-crown of the reducer of [Fig.3],

[0027] [Fig.7a] [Fig.7a] is a schematic half-view in axial section of a crown according to an embodiment of the invention,

[0028] [Fig.7b-7c] Figures 7b and 7c are views similar to that of [Fig.7a] and illustrate other embodiments of the invention,

[0029] [Fig.8] [Fig.8] is a schematic perspective view of a ring according to a first embodiment,

[0030] [Fig.9a] [Fig.9a] is another schematic perspective view of the ring of [Fig.8],

[0031] [Fig.9b] [Fig.9b] is an enlarged view of part of [Fig.9a],

[0032] [Fig. 10a] [Fig. 10a] is a schematic perspective view of a ring according to a second embodiment,

[0033] [Fig. 10b] [Fig. 10b] is an enlarged view of part of [Fig. 10a],

[0034] [Fig.11a] [Fig.11a] is a schematic perspective view of a ring according to a third embodiment,

[0035] [Fig. 11b] [Fig. 11b] is an enlarged view of part of [Fig. 11a]. Detailed description of the invention

[0036] [Fig. 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 1c and an exhaust nozzle 1h. 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 low-pressure compressor 1a and the low-pressure turbine 1c are connected by a low-pressure shaft 3 and form with it a low-pressure (LP) body.

[0037] 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 is generally of the planetary or epicycloidal type.

[0038] Although the following description concerns a planetary or epicycloidal 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.

[0039] The reducer 6 is positioned in the front 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.

[0040] [Fig.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 axis X 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.

[0041] The set of satellites 8 is held by a chassis called a planet carrier 10. Each satellite 8 rotates around its own Y axis, and meshes with the crown 9.

[0042] At the output of the reducer, we have: • in an epicyclic configuration, all 8 satellites drive in rotation of the planet carrier 10 around the X axis of the turbomachine. The crown 9 is fixed to the engine casing or stator 5 via a crown carrier 12 and the planet carrier 10 is fixed to the fan shaft 4. • in a planetary configuration, all of the planet gears 8 are held by a planet gear carrier 10 which is fixed to the engine casing or stator 5. Each planet gear 8 drives the crown gear 9 which is attached to the fan shaft 4 via a crown gear carrier 12.

[0043] 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.

[0044] The teeth of a reducer can be separated into several helices.

[0045] The crown 9 is separated into two half-crowns 9a, 9b: • a front half-crown 9a consisting of a rim 9aa and a half-fixing flange 9ab. On the rim 9aa is the front helix of the reduction gear teeth. This front helix meshes with that of the satellite 8 which meshes with that of the solar 7. • a rear half-crown 9b consisting of a rim 9ba and a half-fixing flange 9bb. On the rim 9ba is the rear helix of the reduction gear teeth. This rear helix meshes with that of the satellite 8 which meshes with that of the solar 7.

[0046] The fixing half-flange 9ab of the front half-crown 9a and the fixing half-flange 9bb of the rear half-crown 9b form the fixing flange 9c of the crown 9. 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. In the following, a half-flange may be called a flange.

[0047] The arrows in [Fig.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 port 13d of the bearing 11. The oil then circulates through the shaft 10b in one or more buffer zones 10c and then exits through ports 10d in order to lubricate the bearings 11 of the satellites.

[0048] In the examples of Figures 3 and 4, each axis 10b is surrounded by two bearings 17a, 17b which are roller bearings in the example shown. The bearings 17a, 17b are coaxial and arranged next to each other, each bearing being located in a median plane PI, P2 passing substantially through the median plane of a toothing or helix 8d of the satellite 8 and through the median plane of a toothing or helix 9d of a half-crown 9a, 9b. The planes PI and P2 are parallel to each other and perpendicular to the axes X and Y. The number of bearings 17a, 17b may be different from the example shown. It does not necessarily depend on the number of helices 8d, 9d.

[0049] Each satellite 8 has an internal rolling track. To reduce the precise surface to be machined to the exact need, this internal cylindrical surface is divided into several tracks of reduced axial width, the number of which is equal to the number of bearings 17a, 17b. This makes it possible to obtain an annular groove 8e for recovering oil between the tracks, to reduce the mass because the satellite is subjected to less stress at this location and to reduce the difficulty of production on elements requiring very high precision because several tracks are produced independently of each other and the total high-precision surface is smaller with the grooves between each track. An annular row of radial holes 19 are formed at the bottom of this groove 8e and allows, in operation, the flow of the lubricating oil from the bearings to an annular space E2 located between the two half-rings 9a, 9b.

[0050] The flange 12a of the crown carrier 12 is applied axially on one of the sides of the flange 9c, namely on the upstream side in the example shown. The crown carrier 12 is centered axially on the crown 9 using a cylindrical rim 12ab located at the external periphery of the flange 12a (figures 3 and 4). Once positioned, the crown carrier 12 extends around the crown 9 (or the half-crown 9a in our example) and the area delimited between these two parts defines the annular space El for oil circulation.

[0051] An annular oil collector 22 surrounds the half-crown 9b and comprises an annular flange 22a for fixing to the flange 9c of the crown 9. The flange 22a is applied axially to one of the sides of the flange 9c, namely on the downstream side in the example shown. The oil collector 22 is axially centered on the crown 9 using a cylindrical rim 22ab located at the external periphery of the flange 22a ( [Fig.4]). The area delimited between the collector 22 and the crown 9 defines the annular space E3 for oil circulation.

[0052] In order to ensure that the position is maintained, the flanges 9ab, 9bb of the crown 9 and the flanges 12a, 22a of the crown carrier 12 and of the collector 22 respectively comprise tively an annular row of through holes 9e, 12b and 22b. These through holes serve as passage for fixing means 21 of the screw-nut type or the like.

[0053] Once the crown 9, the crown holder 12, and the collector 22 are assembled, their flanges applied to each other, the orifices 9e, 12b and 22b receive the fixing means 21 to ensure that the three elements which now form the crown assembly are held in position.

[0054] The crown assembly constitutes a fairing for the reducer 6. Although it is not watertight, the assembly will have the function of capturing a maximum of oil to limit its recirculation in the motor whether it is fixed or mobile depending on the type of reducer. The oil will thus be recovered at three internal locations of the crown assembly which are the annular spaces E1, E2 and E3 to then be evacuated into the annular space E4 (figures 4 and 8) located radially outside the flanges 12a, 9c, 22a.

[0055] The first oil passages are here formed by a first annular row of passages or, as in our example, of substantially radial lunules 25 formed in the flange 9c of the crown 9. The lunules 25 of the first row are made at a distance from the orifices 9e for the passage of the fixing means 21.

[0056] The lunules 25 are in fluid communication, at their radially internal ends, with the space E2, and at their axially external ends with oil outlet notches 27, 27' provided on the cylindrical rims 12ab, 22ab located at the external periphery of the flanges 12a, 22a ([Fig.4]).

[0057] Second oil passages are further formed by annular rows of passages or, as in our example, substantially radial lunules 28, 28' formed in the radial bearing surfaces of the flanges 12a, 22a ([Fig.4]). The lunules 28, 28' are made at a distance from the orifices 12b, 22b for the passage of the fixing means 21 and communicate with orifices 29 provided at the bottom of the lunules 25 of the flanges 9ab, 9bb.

[0058] The oil which passes through the orifices 10d of the axis 10b of the planet carrier 10 (arrows fl), lubricates the bearings 17a, 17b and must then flow radially outside of them. This is also the case for the lubricating oil for the gears of the reducer. The lubricating oil of the reducer can follow several paths as illustrated by the arrows f2 to f5.

[0059] In the case shown in Figures 5 and 6, the lunules 25 for discharging oil through the flange 9c are formed directly in the radial faces bearing on the half-flanges 9ab, 9bb of the half-crowns 9a, 9b.

[0060] The invention proposes an improvement to this technology, embodiments of which are shown in Figures 7a to 7c and detailed in the following figures.

[0061] Generally, the crown 9 has an annular shape around the axis X and comprises an internal annular toothing 9d oriented towards the axis X and an external annular flange 9c oriented radially towards the outside of the axis X.

[0062] The crown 9 comprises two half-crowns 9a, 9b independent of each other and each comprising a part of the internal toothing 9d and an external half-flange 9ab, 9bb.

[0063] The external half-flanges 9ab, 9bb of the two half-crowns 9a, 9b together form the flange 9c of the crown 9 and are fixed to each other by fixing means 21 of the screw-nut type or the like which are parallel to the axis X and which pass through aligned orifices 9e of the half-flanges 9ab, 9bb.

[0064] Oil passages are located between the half-flanges 9ab, 9bb and regularly distributed around the axis X. These oil passages are oriented radially with respect to the axis X for the evacuation of the lubricating oil from the reducer radially towards the outside.

[0065] According to the invention, the crown 9 further comprises an oil passage ring 30 which is independent of the half-crowns 9a, 9b and which is interposed between the half-flanges 9ab, 9bb of the half-crowns 9a, 9b.

[0066] The ring 30 has orifices 30e aligned with the orifices 9e of the half-flanges 9ab, 9bb for the passage of the fixing means 21.

[0067] The aforementioned passages are formed in this ring 30 and FIGS. 7a to 7c show three variant embodiments of the ring 30 and of these passages.

[0068] The passages can be formed:

[0069] - by channels 32 formed inside the ring 30 as illustrated in [Fig.7a], and / or

[0070] - by alveolar or lattice portions 34 of the ring 30 as illustrated in Figure 7b, and / or

[0071] - by lunules 36 or slits formed on the sides of the ring 30 as is shown in Figure 7c.

[0072] In all of these embodiments, it is noted that the ring 30 preferably comprises a first annular face 30a for bearing on one of the half-flanges 9ab, and a second annular face 30b for bearing on the other of the half-flanges 9bb. The orifices 30e of the ring 30 open onto these faces 30a, 30b.

[0073] The ring 30 further comprises a radially inner annular edge 30c and a radially outer annular edge 30d.

[0074] We define by Danneau_int and Danneau_ext respectively the internal and external diameters of the ring 30, which can be measured at the edges 30c and 30d, respectively.

[0075] We further define by Dbride_int and Dbride_ext respectively the internal diameters and external of the flange 9c of the crown 9 (and of each of the half-flanges 9ab, 9bb).

[0076] Preferably, Danneau_int is between 0.9.Dbride_int and 1.1.Dbride_int and Danneau_ext is between 0.9Dbride_ext and 1.1Dbride_ext. This means that the ring 30 preferably has radial dimensions close to those of the flange 9c, or even identical to those of the flange 9c, as can be seen in the drawings.

[0077] We now refer to figures 8, 9a and 9b which illustrate a more concrete example of the production of a ring 30 comprising lunules 36 or slots formed on the sides of the ring 30, as in figure 7c.

[0078] The lunules 36 or slots are formed on at least one of the first and second faces 30a, 30b of the ring 30. In the example shown, they are formed on only one of these faces 30a, 30b. The number of lunules 36 is equal to the number of orifices 30e. Each lunule 36 is arranged between two adjacent orifices 30e and each orifice 30e is arranged between two adjacent lunules 36.

[0079] In the example shown, the lunules 36 or slots extend over the entire radial dimension of the ring 30 and thus open onto the edges 30c, 30d of the ring 30.

[0080] Each of the lunules 36 may have a generally parallelepiped shape as in the example shown and have an elongated shape in the radial direction.

[0081] The lunules 36 of the ring 30 can be produced by machining for example. Their dimensions and their number depend in particular on the volume of oil to be evacuated during operation.

[0082] We now refer to figures 10a and 10b which illustrate a more concrete example of the production of a ring 30 comprising alveolar or lattice portions 34, as in figure 7b.

[0083] The orifices 30e of the ring are preferably formed in rigid blocks 38 which are distributed around the axis X and which are secured to each other by an annular cellular or lattice structure 40 of the ring 30.

[0084] The alveolar or lattice portions 34 of this structure 40 comprise open cells which communicate with each other to allow the passage of oil between the cells and through these portions. The alveolar or lattice portions 34 are located between the blocks 38 and therefore form the aforementioned passages.

[0085] The blocks 38 may all be identical and have a diamond shape, for example, as in the example shown. Due to this diamond shape, each of the portions 34 has, in the example shown, a convergent then divergent shape, moving radially outwards from the axis.

[0086] The number of blocks 38 is preferably equal to the number of orifices 30e. Each portion 34 is arranged between two adjacent orifices 30e and therefore two blocks 38, and each orifice 30e and each block 38 is arranged between two adjacent portions 34.

[0087] The blocks 38 may extend over only a portion of the radial dimension of the ring 30 or over the entire radial extent of the ring 30.

[0088] The ring 30, and in particular its structure 40 and / or its blocks 38, can be produced by additive manufacturing. With these configurations, the ring 30 can also have a function of separating air from oil, the passage of oil through the structure 40 promoting this separation.

[0089] We now refer to Figures 11a and 11b which illustrate a more concrete example of the production of a ring 30 comprising channels 32 formed inside the ring 30, as in [Fig.7a].

[0090] In the example shown, the internal channels 32 are formed in the middle of the ring 30, at a distance from its faces 30a, 30b. The channels 32 open onto the edges 30c, 30d of the ring 30.

[0091] The channels 32 can have any shape in section and for example oval as in the example shown.

[0092] The number of channels 32 is preferably equal to the number of orifices 30e. Each channel 32 is arranged between two adjacent orifices 30e, and each orifice 30e is arranged between two adjacent channels 32.

[0093] The channels 32 of the ring 30 can be produced by machining for example. Their dimensions and their number depend in particular on the volume of oil to be evacuated during operation.

Claims

Claims

1. Crown (9) for a mechanical reducer (6) of an aircraft turbomachine (1), this crown (9) having an annular shape around an axis (X) and comprising an internal annular toothing (9d) oriented towards the axis (X) and an external annular flange (9c) oriented radially towards the outside of the axis (X), the crown (9) comprising two half-crowns (9a, 9b) independent of each other and each comprising a part of the internal toothing (9d) and an external half-flange (9ab, 9bb), the external half-flanges (9ab, 9bb) of the two half-crowns (9a, 9b) together forming the flange (9c) of the crown (9) and being fixed to each other by screws which are parallel to the axis (X) and which pass through aligned orifices (9e) of the half-flanges (9ab, 9bb), oil passages oriented radially with respect to the axis (X) being located between the half-flanges (9ab, 9bb) and regularly distributed around the axis (X),characterized in that it further comprises an oil passage ring (30) which is independent of the half-crowns (9a, 9b) and which is interposed between the half-flanges (9ab, 9bb) of the half-crowns (9a, 9b), the ring (30) comprising orifices (30e) aligned with the orifices (9e) of the half-flanges (9ab, 9bb) for the passage of said screws, and in that said oil passages are formed in said ring (30).,

2. A crown (9) according to claim 1, wherein the oil passages are formed by channels (32) formed within the ring (30), lunules (36) or slots formed on sides of the ring (30), and / or honeycomb or lattice portions (34) of the ring (30).

3. Crown (9) according to claim 1 or 2, in which the ring (30) comprises a first annular face (30a) for bearing on one of the half-flanges (9ab), and a second annular face (30b) for bearing on the other of the half-flanges (9bb), the orifices (30e) of the ring (30) opening onto these first and second faces (30a, 30b), the ring (30) further comprising a radially internal annular edge (30c) and a radially external annular edge (30d).

4. Crown (9) according to all of claims 2 and 3, in which the internal channels (32) are formed in the middle of the ring (30), at a distance from its first and second faces (30a, 30b), and open onto the internal and external edges (30c, 30d) of the ring (30).

5. Crown (9) according to all of claims 2 and 3, in which the lunules (36) or slots are formed on at least one of the first and second faces (30a, 30b) of the ring (30).

6. A crown (9) according to claim 5, wherein the lunules (36) or slots extend over the entire radial dimension of the ring (30).

7. Crown (9) according to all of claims 2 and 3, in which the orifices (30e) of the ring (30) are formed in rigid blocks (38) which are distributed around the axis (X) and which are secured to each other by an annular cellular or lattice structure (40) of the ring (30), the cellular or lattice portions (34) of this structure (40) located between the blocks (38) forming said oil passages.

8. Crown (9) according to claim 7, in which the blocks (38) are all identical and have a diamond shape for example.

9. Crown (9) according to one of the preceding claims, in which Danneau_int is between 0.9.Dbride_int and l.l.Dbride_int and Danneau_ext is between 0.9.Dbride_ext and l.l.Dbride_ext, Danneau_int and Danneau_ext being respectively the internal and external diameters of the ring (30), and Dbride_int and Dbride_ext being respectively the internal and external diameters of the flange (9c) of the crown (9).

10. Mechanical reducer (6) for an aircraft turbomachine (1), comprising a crown (9) according to one of the preceding claims, a sun gear (7) centered on the axis (X) of the crown (9) and surrounded by the crown (9), and satellites (8) mounted between the sun gear (7) and the crown (9) and meshed with the sun gear (7) and the crown (9).

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