Mechanical reduction gear for an aircraft turbine engine

Abstract

The invention relates to a mechanical reduction gear (10) for an aircraft turbine engine (1), comprising a planet carrier (213) comprising a cage (220) in which a sun gear (11) and planet gears (12) and the bearings (8) thereof are mounted, the cage (220) comprising two disks (236, 238) connected by bridges (140), a first disk (236) comprising first bearing holes (292) which are able to receive first longitudinal ends (8a) of the bearings (8), and a second disk (238) comprising second bearing holes (294) which are able to receive covers (300) comprising third holes (302) which are able to receive second longitudinal ends (8b) of the bearings (8), these covers (300) forming eccentrics.

Description

[0001] DESCRIPTION

[0002] TITLE: MECHANICAL REDUCTION GEAR FOR AN AIRCRAFT TURBOMACHINE

[0003] Technical field of the invention

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

[0005] Technical Downstream Plan

[0006] The state of the art includes, in particular, documents FR-A1-2 987 416, FR-A1-2 853382, FR-A1-3 041 054, FR-A1-3 073 915, FR-A1-3 084428, USAI-2012 / 028754, EP-B1-2 831 391 and FR-A1-3 080 552. 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.

[0007] Newer generations of turbofan engines, particularly those with a high bypass ratio, incorporate a mechanical gearbox to drive the fan shaft. Typically, the gearbox's purpose is to transform the high rotational speed of the power turbine shaft into a slower rotational speed for the fan shaft.

[0008] Such a reduction gear comprises a central pinion, called the sun gear, a ring gear, and pinions called planet gears, which mesh between the sun gear and the ring gear. The planet gears are held by a frame called the planet carrier. The sun gear, ring gear, and planet carrier are planetary gears because their axes of revolution coincide with the longitudinal axis of the turbomachine. The planet gears each have a different axis of revolution and are evenly spaced on the same operating diameter around the axis of the planet gears. These axes are parallel to the longitudinal axis of the turbomachine.

[0009] REPLACEMENT SHEET (RULE J8) There are several gearbox architectures. In the state of the art for turbofan engines, gearboxes are of the planetary or epicyclic type. In other similar applications, there are so-called differential or "compound" architectures.

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

[0011] - on an epicyclic reducer, the ring 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 gearbox, no element is fixed in rotation. The ring rotates in the opposite direction to the solar and satellite carrier.

[0013] Gearboxes can consist of one or more meshing stages. This meshing is achieved in various ways, such as by contact, friction, or magnetic field. There are several types of contact meshing, such as with spur or herringbone teeth.

[0014] The satellite carrier can be a single unit or consist of a cage and a cage-bearing assembly. The cage comprises an internal cavity housing the solar array, the satellites, and their guidance bearings. The solar array has internal splines for coupling to a first shaft of the turbomachine, and the cage-bearing assembly has a cylindrical portion with external splines for coupling to another shaft.

[0015] The cage connection to the cage holder is generally rigid. Alternatively, a technology can be considered in which the cage is connected to the cage holder by "flexible" connections, as described in FRAI-2 853 382. In such a case, the cage holder comprises an annular row of axial fingers that carry first connecting elements. These first connecting elements cooperate with second connecting elements mounted in housings in the cage to form the flexible connections between the cage holder and the cage, which allow at least one degree of freedom.

[0016] During operation, the planet carrier is subjected to stresses that tend to deform it. This is the case for a one-piece planet carrier or a cage-and-cage type. These deformations cause the planets to tilt, leading to a degradation of the meshing and the risk of an asymmetrical oil film forming when using plain or hydrodynamic planetary guidance bearings, or the risk of roller tilting when using roller bearings for planetary guidance. These stresses and deformations must be rebalanced to limit or even eliminate these effects.

[0017] Satellite misalignment is an important point to monitor to avoid excessive stress on the gear teeth. To address this, the design of the satellite carrier can be optimized for flexibility to reduce or even eliminate this misalignment. Specifically, incorporating flexible zones into the carrier cage has already been proposed.

[0018] However, the introduction of such flexibility zones can compromise the mechanical strength of the reducer.

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

[0020] Summary of the invention

[0021] The invention relates to a mechanical gearbox for an aircraft turbomachine, this gearbox comprising:

[0022] - a solar panel centered on a central axis,

[0023] - a corona centered on the central axis and extending around the sun,

[0024] - satellites guided in rotation by bearings centered on bearing axes that are parallel to the central axis, the satellites being meshed with the sun and the corona, and

[0025] - a satellite carrier comprising a cage in which the solar array and the satellites and their bearings are mounted, the cage comprising: - a first disk centered on the central axis and extending perpendicularly to this central axis, this first disk comprising first bearing orifices centered respectively on the bearing axes and which are suitable for receiving first longitudinal ends of the bearings,

[0026] - a second disc centered on the central axis and extending parallel and axially at a distance from the first disc, this second disc having second bearing ports which are suitable for receiving covers having third ports suitable for receiving second longitudinal ends of the bearings, and

[0027] - bridges which extend between the first and second discs and connect them together, characterized in that said second orifices are offset with respect to the bearing axes and in that the covers form eccentrics each comprising a cylindrical portion which is engaged in one of the second bearing orifices and which is offset with respect to the third orifice of this cover.

[0028] It is therefore understood that the second holes of the second disk are not aligned with the first holes of the first disk. The satellite bearings are mounted in the third holes of covers attached to the second holes on the second disk. In the current technique, a cover is centered on the bearing axis of its corresponding first hole, and its third hole is also centered on this bearing axis. According to the invention, a misalignment is intentionally created between the cover and its third hole. The cover comprises a cylindrical portion engaged in the second hole of the second disk, and this cylindrical portion is offset from the axis of the third hole of the cover. It is therefore understood that, depending on the position of each cover in its corresponding second hole, the first and third holes will be aligned or not. The present invention is compatible with:

[0029] - of a multi-stage reducer;

[0030] - of a planetary, epicyclic or differential reducer; - of straight or herringbone gears.

[0031] The reducer according to the invention may comprise one or more of the following features, taken individually or in combination with each other:

[0032] - after assembly of the reducer, the bearing shaft of the first orifice and the shaft of the third orifice are misaligned;

[0033] - after assembly of the reducer, the bearing axis of the first orifice and the axis of the third orifice are offset by a distance corresponding to twice the center distance between the cylindrical portion and the third orifice of each cover;

[0034] - each of the covers includes at least one external tab or external collar, which includes at least one through hole for the passage of a fastening element which is suitable for passing through a hole in the second disc or for being screwed into a hole in the second disc;

[0035] - the number of holes in the entire lid is equal to the number of holes in the second disc;

[0036] - the number of holes in all the lids is greater than the number of holes in the second disc;

[0037] - the number of holes in all the lids is less than the number of holes in the second disc;

[0038] - each of the covers and / or the second disc includes, for each of the covers, at least one reference mark allowing visualization in which position, around the axis of the second bearing orifice, the bearing axis of the first orifice and the axis of the third orifice are aligned;

[0039] - the reducer further includes an eccentric ring associated with each of the covers, each ring defining the second receiving bearing orifice of this cover and being engaged in a fourth orifice of the second disc which is axially aligned with the first bearing orifice of the first disc;

[0040] -- each of the second orifices has a diameter greater than the diameter of each of the first orifices; -- each of the third orifices has a diameter identical to the diameter of each of the first orifices;

[0041] -- each of the fourth orifices has a diameter greater than the diameter of each of the second orifices.

[0042] The present invention also relates to an aircraft turbomachine comprising a reducer as described above.

[0043] The present invention also relates to a method of assembling a reducer as described above, comprising the following steps: a) inserting the satellites and their bearings inside the cage and engaging the first longitudinal ends (8a) of the bearings (8) in the first orifices of the first disc, b) engaging the cylindrical portions of the covers in the second orifices of the second disc, and the second longitudinal ends of the bearings in the third orifices of these covers, so that the third orifices are aligned with the first orifices, c) creating a misalignment between the bearing axes of the first orifices and the axes of the third orifices.

[0044] The process according to the invention may comprise one or more of the following features or steps, taken individually or in combination with each other:

[0045] - step c) is carried out by rotating the lids around the axes of the cylindrical portions;

[0046] - step c) is carried out by rotating the rings in the fourth holes;

[0047] - the rotation is carried out over an angle of 180°;

[0048] - the rotation is carried out until the axis of the third orifice of each of the lids is as close as possible to a theoretical position determined by calculation;

[0049] - At the end of step c), the bearing axis of the first orifice and the axis of the third orifice are offset by a distance corresponding to twice the center distance between the cylindrical portion and the third orifice of each cover. Brief description of the figures

[0050] Other features and advantages will become apparent from the following description of a non-limiting embodiment of the invention with reference to the accompanying drawings in which:

[0051] [Fig.1] Figure 1 is a schematic axial cross-sectional view of a turbomachine using the invention;

[0052] [Fig.2] Figure 2 is a schematic axial cross-sectional view of a mechanical reducer;

[0053] [Fig.3] Figure 3 is a perspective view of a cage and cage-carrier assembly forming a mechanical reducer planet carrier;

[0054] [Fig.4] Figure 4 is an axial and partial cross-sectional view of part of the satellite carrier of Figure 3;

[0055] [Fig.5] Figure 5 is a detail view of Figure 4;

[0056] [Fig.6] Figure 6 is a schematic front view of the satellite carrier in Figure 3;

[0057] [Fig.7] Figure 7 is a partial schematic axial cross-sectional view of a mechanical reducer;

[0058] [Fig.8] Figure 8 is a schematic perspective view of a cover for a mechanical reducer;

[0059] [Fig.9] Figure 9 is a partial schematic axial cross-sectional view of a mechanical reducer according to one embodiment of the invention;

[0060] [Fig.10a-10c] Figures 10a to 10c show different mounting configurations for the reducer of Figure 9, depending on the position of a cover;

[0061] [Fig. 11 a-11 b] Figures 11 a and 11 b show other mounting configurations for a reducer according to the invention; and

[0062] [Fig. 12a-12b] Figures 12a and 12b are partial schematic axial cross-sectional views of a mechanical reducer according to an embodiment of the invention, and show two mounting configurations for this reducer. Detailed description of the invention

[0063] Figure 1 depicts a turbomachine 1 which conventionally comprises 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 high-pressure compressor 1b and the high-pressure turbine 1d are connected by a high-pressure shaft 2 and together form a high-pressure (HP) housing. The low-pressure compressor 1a and the low-pressure turbine 1e are connected by a low-pressure shaft 3 and together form a low-pressure (LP) housing.

[0064] The blower S is driven by a blower shaft 4 which is connected to the BP shaft 3 by means of a mechanical reducer 10. This reducer 10 is generally of the planetary or epicyclic type.

[0065] Although the following description relates to a planetary or epicycloidal type reducer, it also applies to a mechanical differential in which its three essential components, namely the planet carrier, the ring and the sun gear, are mobile in rotation, the rotational speed of one of these components depending in particular on the difference in speeds of the other two components.

[0066] The gearbox 10 is positioned in the upstream part of the turbomachine. A fixed structure schematically comprising, here, an upstream part 5a and a downstream part 5b which make up the motor or stator housing 5 is arranged to form an enclosure E surrounding the gearbox 10. This enclosure E is closed upstream by seals at the level of a bearing allowing the passage of the blower shaft 4, and downstream by seals at the level of the passage of the BP shaft 3.

[0067] Figure 1 shows part of a gearbox 10, which can take different forms depending on whether certain parts are fixed or rotating. At the input, the gearbox 10 is connected to the shaft BP 3, for example, via splines 7. Thus, the shaft BP 3 drives a planetary gear called the sun gear 11. Typically, the sun gear 11, whose axis of rotation coincides with the X-axis of the turbomachine 1, drives a series of gears called sun gears 12, which are equally spaced circumferentially on the same diameter around the X-axis of rotation. This diameter is equal to twice the operating center distance between the sun gear 11 and the sun gears 12. The number of sun gears 12 is generally defined as between three and seven for this type of application.

[0068] The set of satellites 12 is held by a frame called the satellite carrier 12. Each satellite 12 rotates around its own Y axis, and meshes with the ring 14.

[0069] At the output of the gearbox 10, we have: In an epicyclic configuration, the set of planet gears 12 drives the planet carrier 13 in rotation around the X-axis of the turbomachine. The ring gear 14 is fixed to the motor or stator housing 5 via a ring carrier 15, and the planet carrier 12 is fixed to the fan shaft 4. In a planetary configuration, the set of planet gears 12 is held by a planet carrier 12, which is fixed to the motor or stator housing 5. Each planet gear drives the ring gear, which is connected to the fan shaft 4 via a ring carrier 15.

[0070] Each satellite 12 is mounted to rotate freely around a Y-axis using a bearing 8. The Y-axis rotations of the satellites 12 are distributed around and parallel to the X-axis. The bearings 8 are, for example, of the roller bearing or hydrodynamic bearing type. Each bearing 8 is mounted on a physical axis 13a of the satellite carrier 12, and all these physical axes 13a are positioned relative to each other using one or more structural frames of the satellite carrier 12. There is a number of physical axes 13a and bearings 8 equal to the number of satellites 12. For operational, assembly, manufacturing, inspection, repair, or replacement purposes, the axes 13a and the frame may be separated into several parts.

[0071] For the same reasons mentioned previously, the teeth of a reduction gear can be separated into several helices. In our example, we detail the operation of a multi-helix reduction gear 10 with a ring gear divided into two half-rings: A front half-ring 14a consisting of a rim 14aa and a mounting flange half 14ab. The front helix of the reduction gear teeth is located on the rim 14aa. This front helix meshes with that of the satellite gear 12, which meshes with that of the solar gear 11. A rear half-ring 14b consisting of a rim 14ba and a mounting flange half 14bb. The rear helix of the reduction gear teeth is located on the rim 14ba. This rear helix meshes with that of the satellite gear 12, which meshes with that of the solar gear 11.

[0072] The front sprocket 14a mounting bracket half-flange 14ab and the rear sprocket 14b mounting bracket half-flange form the sprocket mounting bracket 14c. The sprocket 14 is attached to the sprocket carrier 15 by joining the sprocket mounting bracket 14c and the sprocket carrier mounting bracket 15a using, for example, a bolted assembly. In the following, a half-flange may be referred to as a flange.

[0073] The arrows in Figure 1 describe the oil flow within the gearbox 10. The oil enters the gearbox 10 from the stator section 5 into the distributor 16 by various means, which will not be detailed in this view as they are specific to one or more types of architecture. The distributor 16 is divided into two parts, each generally repeated with the same number of planetary gears. The injectors 17a lubricate the gear teeth, and the arms 17b lubricate the bearings 8. The oil is supplied to the injector 17a and exits through the end 17c to lubricate the gear teeth. The oil is also supplied to each arm 17b and flows through the supply mouth 17d of the bearing 8. The oil then flows through the shaft 13a into one or more buffer zones 13b and then out through ports 13c to lubricate the bearings 8 of the satellites.

[0074] The satellite carrier 13 in Figure 2 is formed from a single piece in the example shown. In Figures 3 to 5, the elements already described above are designated by the same reference numerals plus one hundred.

[0075] Figures 3 to 5 represent a particular satellite carrier technology 113, this satellite carrier comprising a cage 120 and a cage carrier 122 connected by ball joints.

[0076] The cage 120 comprises two radial annular discs or walls 136, 138 which are parallel to each other and perpendicular to the X axis, as well as a cylindrical wall 140 which extends between the external peripheries of these discs walls 136, 138.

[0077] The cylindrical wall 140 is of the double-skinned type and comprises an outer skin 140a interrupted by openings 143 and an inner skin 140b interrupted by the same openings 143. The outer skin 140a, separated by five openings 143, forms five outer brackets, and the inner skin 140b, separated by five openings 143, forms five inner brackets. Each pair of lower and upper brackets forms a clevis to receive the finger 182 of the cage holder 122. In other words, the brackets of each pair define a recess 180 for receiving a finger 182 of the cage holder 122. The brackets provide the structural connection between the walls 136 and 138. Oblong openings 180a are made in at least one of the walls 136 and 138 to allow the finger 182 to pass between the inner and outer brackets. These 180a lights open into the 180 housing units.

[0078] The cage 120 thus comprises an annular row of housings 180. These housings 180 receive the axial fingers 182 which are integral with an annular wall 182a substantially radial to the cage holder 122. The wall 182a is located at an axial end of the cage holder 122. The fingers 182 extend axially from the wall 182a and are engaged by axial translation in the housings 180.

[0079] Each finger 182 includes, substantially in its middle, a mounting ring 184 for the ball joint 186, designed to be traversed by a cylindrical pin 188 carried by the cage 120. The ring 184 has a substantially radial orientation with respect to the X-axis. It has a generally cylindrical shape. The cage 120 and the ball joint 186 have a thickness, measured in a radial direction with respect to the X-axis, that is less than the inter-bridge distance or the radial thickness of the oblong slot 180a, so that they can be engaged in this housing concurrently with the finger 182 supporting these parts.

[0080] Each housing 180 is traversed by a pin 188 which has a substantially radial orientation with respect to the X-axis. Each pin 188 comprises a cylindrical body 188a connected at an axial end, here radially internal, to an external annular collar 188b. The pin 188 is engaged by radial translation from the inside through radial holes in the bridges, its collar 188b being designed to bear radially against a flat face 191 of the outer bridge of the cage 120. After insertion of the pin 188 into the holes in the bridges, until the collar 188b bears against the outer bridge, the collar 188b is fixed to this bridge, for example by screwing.

[0081] Figure 6 shows a detail of the disks or walls 136, 138 of the planet carrier 113. In these figures, it can be seen that each of the walls 136, 138 includes first orifices 192, 194 centered respectively on the Y axes of rotation of the planets of the gearbox. In the example shown, there are five orifices 192, 194 on each of the walls 136, 138.

[0082] The invention provides a mechanical gearbox for an aircraft turbomachine. As in the examples described above, the mechanical gearbox 10 according to the invention comprises:

[0083] - a solar 11 centered on a central axis X,

[0084] - a ring 14 centered on the central axis X and extending around the solar element - satellites 12 guided in rotation by bearings 8 centered on bearing axes Y which are parallel to the central axis X, the satellites 12 being meshed with the solar element 11 and the ring 14, and

[0085] - a satellite carrier.

[0086] The satellite carrier is preferably of the monobloc type as illustrated in figure 2.

[0087] The preceding descriptions in relation to Figures 2 to 6 may be used to illustrate and describe the invention insofar as they do not contradict or are contrary to what follows.

[0088] The invention relates to a gearbox whose satellite carrier is equipped with covers for mounting the satellites and, in particular, their bearings. This type of gearbox and cover is illustrated in Figures 7 and 8.

[0089] The satellite carrier 213 includes a cage 220 in which the solar array and the satellites 12 and their bearings 8 are intended to be mounted.

[0090] The cage 220 is formed in one piece with a cage holder 222 which has a portion-of-a-tree shape and may include external grooves for coupling to another tree.

[0091] Cage 220 includes:

[0092] - a first disk 236 centered on the X axis, called the first axis or central axis, and extending perpendicularly to this X axis, this first disk 236 having first bearing orifices 292 centered respectively on the Y axes, called bearing axes or second axes, which are parallel to the X axis and arranged around this X axis,

[0093] - a second disk 238 centered on the X-axis and parallel to and at a distance from disk 236, this second disk 238 having second bearing ports 294, and

[0094] - bridges (not visible) extending between and connecting the discs 236 and 238, these bridges being formed as a single piece with the discs 236 and 238, and the bridges being circumferentially separated from each other by openings 243 intended for the passage of the planetary gears 12 for their engagement with the reduction gear ring. The first disc 236 is, for example, a front or upstream disc, and the second disc 238 is, for example, a rear or downstream disc, with reference to the position of the reduction gear in the turbomachine and the gas flow within the turbomachine.

[0095] The first disk 236 is preferably the disk connected to the cage carrier 222. The ports 292, 294 are used to mount the satellites 12 and in particular the bearings 8 for guiding the satellites 12, in the satellite carrier 213. The bearings 8 have longitudinal ends 8a, 8b which are housed in these ports 292, 294. The bearings 8 are plain (hydrodynamic) or rolling bearings for example.

[0096] As can be seen in Figure 7, the longitudinal ends 8a of the bearings are mounted directly in the first orifices 292 of the first disc 236 while their longitudinal ends 8b are mounted in third orifices 302 of covers 300 which are themselves mounted in the second orifices 294 of the second disc 238.

[0097] Figure 8 shows an example of a cover 300 which includes a cylindrical portion 300a suitable for being engaged in one of the second orifices 294 of the second disc 238, and at least one tab 300b or collar having one or more through holes 304 for passage of fastening element(s).

[0098] The lug 300b or the collar is intended to be axially pressed against a radial face of the second disc 238, opposite the first disc 236, and one or more fixing element(s) are mounted through the hole(s) 304 and engaged or screwed into corresponding holes (not shown) of the second disc 238.

[0099] In the prior art, the first orifices 292 are aligned with the bearing axes Y and the second orifices 294 are also aligned with these bearing axes Y. The third orifice 302 and the cylindrical portion 300a of each cover 300 are aligned and are also aligned with the corresponding second orifice 294.

[0100] The invention proposes, on the contrary, to offset the second orifices 294 of the second disk 238 with respect to the axes of the Y bearings, as illustrated in Figure 9, and furthermore to use eccentric covers 300. Each of these covers 300 comprises a cylindrical portion 300a which is engaged in one of the second orifices 294 and which is offset with respect to the third orifice 302 of that cover.

[0101] The invention allows for several mounting configurations, which will be described below, and which notably allow for the intentional creation of a misalignment between the first and third ports 292 and 302 during assembly. Since the longitudinal ends 8a, 8b of the bearings 8 are aligned in the unstressed state, the misalignment between the first and third ports 292, 302, which receive these longitudinal ends 8a, 8b, will induce stress on the bearings 8, particularly torsion. This preload can be advantageous during the assembly of the gearbox and when the gearbox is stationary. Preferably, this preload is designed to be completely released during gearbox operation, when the forces transmitted through the bearings tend to deform them in the opposite direction to the torsion experienced during assembly.In other words, the satellite bearings are mounted pre-loaded so that this preload disappears during operation. The forces transmitted through the bearings and deforming them in torsion are thus used to release this preload and prevent the satellites themselves from deforming in torsion, which could lead to misalignment of their gear teeth. These forces can be calculated before the gearbox is assembled. It is therefore possible to anticipate the forces to which the bearings will be subjected before they are mounted. These calculations can be used to determine the necessary offset between the first and third ports 292, 302 so that the forces during operation perfectly compensate for these forces and the associated deformations.

[0102] Advantageously, therefore, after assembly of the reducer, the bearing axis Y of the first orifice 292 and the axis of the third orifice 302 are offset for each of the covers 300. Figures 10a to 10c illustrate a kinematic assembly of a cover 300 according to the invention and a method of assembling a reducer according to the invention.

[0103] In a first step a), the satellites and their bearings, which are not shown in the drawings, are inserted inside the cage. To do this, they can be moved through the second orifices 294, which generally have a larger diameter than the first orifices 292.

[0104] During this step, the first longitudinal ends 8a of the bearings 8 are engaged in the first orifices 292 of the first disc 236.

[0105] In a second step b) of the process, which is illustrated in figure 10a (left drawings), the cylindrical portions 300a of the lids 300 are engaged in the second orifices 294 of the second disc 238.

[0106] The aforementioned second longitudinal ends 8b of the bearings 8 are engaged in the third orifices 302 of the covers 300.

[0107] At the end of this step, and as illustrated in figure 10a, the third orifices 302 of the lids are aligned with the first orifices 292.

[0108] For each of the covers 300, we note A, the offset between the bearing axis Y, i.e. the axis of the first orifice 292, and the axis Z of the cylindrical portion 300a of the cover 300. The axis Z of the cylindrical portion 300a corresponds to the axis of the second orifice 294 so the axis of the second orifice 294 is also designated by Z in what follows.

[0109] In a subsequent step c) illustrated in figure 10b (center drawings), a misalignment is created between the bearing axes Y of the first orifices 292 and the Z axes of the third orifices 302.

[0110] In the embodiment shown, this is achieved by rotating the covers 300 around the Z axes of the cylindrical portions 300a. This movement can be carried out using a tool. As mentioned above, this movement will induce stress on the bearing 8. In the example shown, and preferably, the rotation is performed through an angle α of 180°.

[0111] At the end of this step c), the bearing axis Y of the first orifice 292 and the axis W of the third orifice 302 are offset by a distance 2A corresponding to twice the aforementioned center distance A.

[0112] Figure 10c on the right of the drawing shows the state of the cover 300 during operation. It can be seen that the forces F applied to the cage 220 during operation cause a torsion of this cage around the X-axis and a relative circumferential displacement of the discs 236, 236, which compensate for and cancel out the preload. During operation, the orifices 302 of the covers 300 are then aligned with the orifices 292 of the first disc so that the planetary bearings are not subjected to any torsional stress likely to cause misalignment of the planetary gear teeth.

[0113] Figures 10a to 10c show that each of the covers 300 includes at least one external tab 300b or external flange, which includes at least one through hole 304, as mentioned above, for the passage of a fastener that is suitable for passing through a hole 306 in the second disk 238 or for being screwed into a hole 306 in the second disk 238. Advantageously, the position of the cover 300 around the axis W in which the axis of its orifice 302 is aligned with the axis of the bearing Y is marked on the cage 220 and in particular on the second disk 238. The cage 220 includes, for example, a marker G, such as an arrow, indicating the required position of the tab 300b of the cover 300 with respect to the Z axis.

[0114] Also advantageously, the position of the cover 300 around the Z axis in which the offset between the Y bearing axis and the W axis of the third orifice 302 is equal to 2A is marked on the cage 220 and in particular on the second disc 238 thanks to the presence of the hole 306. It is therefore understood that the alignment of the hole 304 with the hole 306 makes it possible to confirm that the cover 300 is in its correct position to have the expected offset 2A.

[0115] To avoid the risk of error and incorrect assembly, the number of holes 306 on all the covers 300 can be equal to the number of holes 306 on the second disc 238, as is the case in the example shown. There is only one hole per cover 300. The number of holes 304 therefore corresponds to the number of covers 300 and the number of holes on the disc 238.

[0116] Alternatively, the number of holes 304 in all the lids 300 can be greater than the number of holes 306 in the second disk 238. This is the case, for example, when using a lid 300 equipped with several holes 304 as illustrated in Figure 8. The number of holes 304 in all the lids then represents a multiple of the number of lids 300.

[0117] In yet another variant shown in Figures 11a and 11b, the number of holes 304 in all the covers 300 is less than the number of holes 306 in the second disc 238. This configuration allows for more possible fixing positions of the covers 300 on the second disc 238.

[0118] Within the framework of the present invention, in addition to determining by calculation the deformation undergone by a satellite bearing during operation due to the torsional forces applied to this bearing, it is possible to determine by calculation the impact of manufacturing tolerances of the parts (such as machining errors) on this deformation.

[0119] Figure 11a shows the theoretical position P1 that the X-axis of the third hole 302 of the cover 300 should have during assembly, according to the aforementioned calculations. It can be seen that, for this position, there is a hole 306 on the second disc 238 which is perfectly aligned with the hole 304 in the tab of the cover 300.

[0120] When manufacturing tolerances are taken into account in the calculations, it becomes clear that the theoretical position P2 that the X-axis of the third hole 302 of the cover 300 should have during assembly is slightly offset from position P1. Therefore, increasing the number of holes 306 makes it possible to fix the cover 300 in a different position around the Z-axis, in which there is a hole 306 on the second disc 238 that is well aligned with the hole 304 in the tab of the cover 300.

[0121] The process described above can thus consist, in step c) for example, of rotating the covers 300 until the Z axis of the third orifice 302 of each of the covers 300 is as close as possible to a theoretical position determined by calculation.

[0122] Figures 12a and 12b illustrate a variant embodiment of the invention which differs from the previous embodiment in that the second orifices 294 are formed by eccentric rings 400.

[0123] Each ring 400 is engaged in a fourth orifice 402 of the second disc 238 and includes the second orifice 294 which is offset from this fourth orifice 402. Each fourth orifice 402 is aligned with one of the first orifices 292 and therefore with one of the Y bearing axes.

[0124] In this case, it is this ring 400 which is preferably rotated around the axis of bearing Y to offset the third holes 302 with respect to the axes of bearing Y and thus to pre-load the bearings.

[0125] It is therefore understood that, in the aforementioned process of the invention, step c) is carried out by rotating the rings 400 in the fourth orifices 402.

[0126] As in the example described above, this rotation can be carried out over an angle a of 180°.

[0127] At the end of step c) of the process, the bearing axis Y of the first orifice 292 and the axis W of the third orifice 302 can be offset by a distance 2A corresponding to twice the center distance D between the orifices 294, 402.

Claims

DEMANDS 1. Mechanical gearbox (10) for an aircraft turbomachine (1), this gearbox comprising: - a solar (11) centered on a central axis (X), - a corona (14) centered on the central axis (X) and extending around the solar (11), - satellites (12) guided in rotation by bearings (8) centered on bearing axes (Y) which are parallel to the central axis (X), the satellites (12) being meshed with the solar element (11) and the corona (14), and - a satellite carrier (213) comprising a cage (220) in which the solar array (11) and the satellites (12) and their bearings (8) are mounted, the cage (220) comprising: - a first disk (236) centered on the central axis (X) and extending perpendicularly to this central axis (X), this first disk (236) having first bearing orifices (292) centered respectively on the bearing axes (Y) and which receive first longitudinal ends (8a) of the bearings (8), - a second disk (238) centered on the central axis (X) and extending parallel and axially at a distance from the first disk (236), this second disk (238) having second bearing ports (294) which receive covers (300) having third ports (302) which receive second longitudinal ends (8b) of the bearings (8), and - bridges extending between the first and second discs (236) and connecting them, characterized in that said second orifices (294) are offset with respect to the bearing axes (Y) and in that the covers (300) form eccentrics, each comprising a cylindrical portion (300a) engaged in one of the second bearing orifices (294) and offset with respect to the third orifice (302) of this cover (300), the bearing axis (Y) of the first orifice (292) and the axis (W) of the third orifice (302) being misaligned.

2. Reducer (10) according to claim 1, in which the bearing axis (Y) of the first orifice (292) and the axis (W) of the third orifice (302) are offset by a distance (2A) corresponding to twice a center distance (A) between the cylindrical portion (300a) and the third orifice (302) of each cover (300).

3. Reducer (10) according to any one of the preceding claims, in which each of the covers (300) comprises at least one external tab (300b) or external collar, which comprises at least one through hole (304) for the passage of a fastening element which passes through a hole (306) of the second disc (238) or to be screwed into a hole (306) of the second disc (238).

4. Reducer (10) according to claim 3, wherein the number of holes (304) in all the covers (300) is equal to the number of holes (306) in the second disc (238).

5. Reducer (10) according to claim 3, wherein the number of holes (304) of all the covers (300) is greater than the number of holes (306) of the second disc (238).

6. Reducer (10) according to claim 3, wherein the number of holes (304) of all the covers (300) is less than the number of holes (306) of the second disc (238).

7. Reducer (10) according to any one of the preceding claims, wherein each of the covers (300) and / or the second disc (238) comprises, for each of the covers, at least one marker (G) enabling visualization in which position, around the axis (Z) of the second bearing orifice (294), the bearing axis (Y) of the first orifice (292) and the axis (W) of the third orifice (302) are aligned.

8. Reducer (10) according to any one of the preceding claims, wherein it further comprises an eccentric ring (400) associated with each of the covers (300), each ring (400) defining the second bearing orifice (294) for receiving this cover (300) and being engaged in a fourth orifice (402) of the second disk (238) which is axially aligned with the first bearing orifice (292) of the first disk (236).

9. Turbomachine (1), in particular for aircraft, comprising a reduction gear (10) according to any one of the preceding claims.

10. A method for assembling a reducer (10) according to any one of claims 1 to 8, comprising the following steps: a) inserting the satellites (12) and their bearings (8) inside the cage (220) and engaging the first longitudinal ends (8a) of the bearings (8) in the first holes (292) of the first disc (236), b) engaging the cylindrical portions (300a) of the covers (300) in the second holes (294) of the second disc (238), and the second longitudinal ends (8b) of the bearings (8) in the third holes (302) of these covers (300), so that the third holes (302) are aligned with the first holes (292), c) creating a misalignment between the bearing axes (Y) of the first holes (292) and the axes (W) of the third holes (302).

11. Method according to claim 10, the reducer (10) being as defined in any one of claims 1 to 8, wherein step c) is carried out by rotating the covers (300) around the axes (Z) of the cylindrical portions (300b).

12. Method according to claim 10, the reducer (10) being as defined in claim 9, wherein step c) is carried out by rotation of the rings (400) in the fourth orifices (402).

13. Method according to claim 11 or 12, wherein the rotation is carried out over an angle of 180°.

14. Method according to claim 11 or 12, wherein the rotation is carried out until the axis (W) of the third orifice (302) of each of the covers (300) is in a theoretical position determined by calculation.

15. A method according to any one of claims 10 to 14, wherein, at the end of step c), the bearing axis (Y) of the first orifice (292) and the axis (W) of the third orifice (302) are offset by a distance (2A) corresponding to twice one center distance (A) between the cylindrical portion (300a) and the third orifice (302) of each cover (300).

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