Mechanical reduction device for an aircraft turbomachine

Abstract

The invention relates to a mechanical reduction gear (6) of a turbomachine (1), in particular of an aircraft, comprising a sun gear (7), a ring gear (9) surrounded by a ring gear carrier (34), and planet gears (8) meshing with the sun gear (7) and the ring gear (9), the ring gear carrier (34) comprising an axial abutment (40) on which the ring gear is configured to be supported, and the ring gear comprising helical external splines (44) engaging with complementary internal splines (42) of the ring gear carrier (34) and configured to cooperate with these internal splines by sliding so as to force the ring gear to remain against the abutment (40) during operation.

Description

TECHNICAL FIELD

[0001] The present invention relates to the field of mechanical reduction gear for turbomachines, in particular for aircraft turbomachines, and in particular to a reduction gear equipped with a double planetary gear. BACKGROUND

[0002] The prior art notably includes documents WO-A1-2010 / 092263, FR-A1-2987416, FR-A1-3011901, FR-A1-3041054, FR-A1-3058493, US-A1-2017 / 122407 and US-A1-2010 / 292043.

[0003] The purpose of a mechanical reduction gear is to change the speed ratio and torque ratio between the input shaft and the output shaft of a mechanical system.

[0004] A new generation of double-flow turbomachines, in particular with a high bypass ratio, includes a mechanical reduction gear to drive the shaft of the fan. Generally, the purpose of the reduction gear is to convert the so-called fast rotation speed of the shaft of the power turbine into a slower rotation speed for the drive shaft of the fan.

[0005] Such a reduction gear comprises a central pinion called sun gear, a ring gear and pinions called planet gears, which are engaged between the sun gear and the ring gear. The planet gears are held in place by a frame called planet carrier. The sun gear, the ring gear and the planet carrier are planetary because their rotation axes coincide with the longitudinal axis X of the turbomachine. Each planet gear has a different rotation axis and is uniformly distributed around the axis of the planetary about the same running diameter. These axes are parallel to the longitudinal axis X.

[0006] There are various reduction gear architectures. In the prior art double-flow turbomachines, the reduction gear is planetary or epicyclic. In other similar applications, there are so-called differential or "compound" architectures.

[0007] For a planetary reduction gear, the planet carrier is fixed, the ring gear constitutes the output shaft of the device, the rotation direction of which is opposite to that of the sun gear.

[0008] For an epicyclic reduction gear, the ring gear is fixed, the planet carrier constitutes the output shaft of the device, the rotation direction of which is the same as that of the sun gear.

[0009] For a compound reduction gear, no element is fixed in rotation. The ring gear rotates in the opposite direction to the sun gear and the planet carrier.

[0010] The reduction device can comprise one or more gear stages. This engagement is achieved by various means, for example by contact, friction or by a magnetic field.

[0011] In the present disclosure, the term "stage" or "toothed section" is used to designate a series of meshing teeth relative to a series of complementary teeth. The toothed section can be internal or external.

[0012] A planetary gear can comprise one or more gear stages. A single-stage planetary gear comprises a toothed section which can be straight, helical or herringbone, and the teeth of the toothed section are located on the same diameter. This toothed section cooperates with both the sun gear and the ring gear.

[0013] A two-stage planetary gear comprises two toothed sections or two series of teeth located on different diameters. The first toothed section cooperates with the sun gear and the second toothed section cooperates with the ring gear.

[0014] One problem of mechanical reduction devices is the risk of misalignment of the planetary gears. This problem is particularly acute in the case of a two-stage planetary gear, since the toothed sections are located in two different planes perpendicular to the axis of the planet carrier, which makes the force take-up in the ring gear and in the planet carrier more complex.

[0015] The ring gear is subjected to forces in both the radial and axial directions, which can be significant during use of the reduction device, and must be limited to prevent the ring gear from moving.

[0016] There is therefore a need to improve the transmission of the forces to which the ring gear is subjected in a mechanical reduction device equipped with a two-stage planetary gear. SUMMARY

[0017] The invention relates to a mechanical reduction device of a turbomachine, in particular of an aircraft, comprising:

[0018] - a sun gear having an axis of rotation and comprising an external toothed section,

[0019] - a ring gear extending around the sun gear and comprising an internal toothed section, the ring gear being surrounded by a support of the ring gear which is fixed during use so as not to rotate around the axis,

[0020] - a plurality of planet gears, meshed with the sun gear and the ring gear, and each comprising a first toothing having an average diameter D1 and a second toothing having an average diameter D2, the average diameter D1 being different from the average diameter D2, the first toothing being meshed with the toothing of the sun gear, the second toothing being meshed with the inner toothing of the ring gear, the planet gears being held by a planet carrier, the planet carrier being movable in rotation around the axis during use,

[0021] The support of the ring gear comprises an annular axial abutment on which the ring gear is configured to be supported, and the ring gear comprises helical external splines which engage with complementary internal splines of the support of the ring gear, and the helical external splines are configured to cooperate with these internal splines by sliding so as to force the ring gear to remain against the abutment during operation.

[0022] Thus, the reduction device according to the application is designed to withstand the torques and axial forces to which the ring gear is subjected during operation. Thanks to the presence of the splines, the ring gear is able to move axially during operation. This movement is oriented towards the abutment due to the orientation of the helical splines depending on the direction of rotation of the planet gears around the axis, thus forcing the ring gear against this abutment and therefore maintaining this axial position during operation. Thus, the ring gear is axially fixed against this abutment thanks to the cooperation of the splines. The torques and axial forces acting on the ring gear are transmitted to the support of the ring gear via this abutment, which in turn can transmit them to the stator of the turbomachine.

[0023] The application is compatible with:

[0024] - a two-stage reduction device,

[0025] - a so-called sun-and-planet reduction device, the ring gear of which is fixed at the engine reference mark,

[0026] - straight or helical toothing,

[0027] - any type of planet carrier, whether monolithic or cage and cage support type,

[0028] - any type of planet gear bearing, whether it consists of rolling elements, hydrodynamic bearings, etc.

[0029] The reduction device according to the application can comprise one or more of the following features, which can be independent of each other or combined with each other:

[0030] - the carrier of the ring gear comprises a bearing support mounted on the shaft portion of the planet carrier, the bearing support housing a bearing for rotationally guiding the shaft portion of the planet carrier;

[0031] - the abutment portion and the shaft portion are located on the same side with respect to the planet gears;

[0032] - the carrier of the ring gear comprises a cylindrical wall comprising the internal splines and a frustoconical wall, the larger diameter end of the frustoconical wall being connected to the cylindrical wall, the abutment portion being located in the connection zone of the frustoconical wall and the cylindrical wall;

[0033] - a rolling bearing is located at the smaller diameter end of the carrier of the ring gear;

[0034] - the cylindrical wall is connected to a ring-shaped rim which extends radially outwards and forms a fixing flange;

[0035] - the ring-shaped rim extends in a plane perpendicular to the axis and the plane substantially passes through the centre of the ring gear and through the centre of a bearing (i.e. a rolling bearing) mounted between the planet carrier and the sun gear;

[0036] - the abutment portion is formed by a radially inner annular boss of the carrier of the ring gear;

[0037] - the boss comprises a radial face for supporting the ring gear;

[0038] - the radial face is connected to the internal splines of the carrier of the ring gear by an annular groove;

[0039] - the radial face is covered with a protective coating or the radial face cooperates with a protective coating located on the ring gear;

[0040] - the carrier of the ring gear comprises an oil film squeeze damper at least partially surrounding the ring gear;

[0041] - on the side opposite the abutment portion, the ring gear is axially held in opposition to the carrier of the ring gear by an open lock ring which engages in a radially inner annular groove of the carrier of the ring gear;

[0042] - the groove and the ring are located at the free axial end of the carrier of the ring gear and in particular at the cylindrical wall of the carrier of the ring gear;

[0043] - the internal splines of the carrier of the ring gear and the external splines of the ring gear extend over the entire axial dimension of the ring gear.

[0044] The application also relates to an aircraft turbomachine comprising a reduction gear as described above. BRIEF DESCRIPTION OF DRAWINGS

[0045] Other features and advantages will become apparent by reading the detailed description of non-limiting embodiments of the application, given by way of example only, with reference to the accompanying drawings, in which:

[0046] Figure 1 is a schematic axial section view of an aircraft turbomachine;

[0047] Figure 2 is an axial section view of a mechanical reduction gear,

[0048] Figure 3 is a schematic axial section view of a mechanical reduction gear equipped with a double planetary gear, and showing the prior art of the application;

[0049] Figure 4 is a schematic perspective view of a planet carrier of the reduction gear in Figure 3

[0050] Figure 5 is a schematic axial section view of a mechanical reduction gear equipped with a double planetary gear, and showing an embodiment of the application;

[0051] Figure 6 is an enlarged view of a part of Figure 5 ; and

[0052] Figure 7 is a partial schematic perspective view of the reduction gear in Figure 5 DETAILED DESCRIPTION

[0053] Figure 1 A turbomachine 1 is shown, which generally comprises a rotation axis X, a fan S, a low pressure compressor la, a high pressure compressor lb, a combustion annular chamber lc, a high pressure turbine Id, a low pressure turbine le and an exhaust nozzle lh. The high pressure compressor lb and the high pressure turbine Id are connected by a high pressure shaft 2 and form a high pressure (HP) body. The low pressure compressor lb and the low pressure turbine le are connected by a low pressure shaft 3 and form a low pressure (LP) body.

[0054] The fan S is driven by a fan shaft 4, which is driven by the LP shaft 3 through a reduction gear 6. Said reduction gear 6 is generally of planetary type or epicyclic type.

[0055] The following description relates to a planetary reduction gear, in which the ring gear is rotatable.

[0056] ​​The reduction gear 6 is located in the upstream portion of the turbomachine. Here, schematically, the fixed structure comprising the upstream portion 5a and the downstream portion 5b (constituting the engine casing or stator 5) is arranged to form an enclosure E around the reduction gear 6. This enclosure E is closed upstream at the bearing which allows the fan shaft 4 to pass through, by a seal, and downstream by a grommet at which the LP shaft 3 passes through.

[0057] Figure 2 The reduction gear 6 is shown, which can be designed in different architectures depending on whether some components are fixed or rotating. On the input side, the reduction gear 6 is connected to the LP shaft 3, for example via internal splines 7a. The LP shaft 3 thus drives a planetary gear called sun gear 7. Conventionally, the rotation axis of the sun gear 7 is identical to the axis X of the turbomachine, the sun gear driving a series of gears called planet gears 8, which are uniformly distributed around the rotation axis X on the same diameter. This diameter is equal to twice the operating center distance between the sun gear 7 and the planet gears 8. The number of planet gears 8 is generally limited to between three and seven for this type of application. The set of planet gears 8 is held together by a frame called planet carrier 10. Each planet gear 8 rotates around its own axis Y and engages with a ring gear 9.

[0058] In this planetary architecture, the set of planet gears 8 is held by the planet carrier 10 attached to the engine casing or stator 5. Each planet gear drives a ring gear attached to the fan shaft 4 through a support 12 of the ring gear.

[0059] Each planet gear 8 is mounted freely rotatably by means of a bearing 11, for example a rolling bearing or a hydrodynamic bearing. Each bearing 11 is mounted on one of the shafts 10b of the planet carrier 10, and all the shafts are positioned relative to each other by one or more structural frames 10a of the planet carrier 10. The number of shafts 10b and the number of bearings 11 is equal to the number of planet gears. The shafts 10b and the frames 10a can be divided into several parts for reasons of operation, assembly, manufacturing, inspection, maintenance or spare parts.

[0060] For the same reasons as those described above, the toothed part of the reduction gear can be divided into several spirals, each having a central plane P. In the example shown, the ring gear is divided into two ring gear halves:

[0061] The upstream ring gear half 9a is composed of a rim 9aa and a fastening flange half 9ab. The upstream spiral of the toothed part of the reduction gear is located on the rim 9aa. Said upstream spiral engages with the spiral of the planet gears 8, which engage with the spiral of the sun gear 7.

[0062] The downstream ring gear half 9b is composed of a rim 9ba and a fastening flange half 9bb. The downstream helix of the toothed connection of the reduction gear is located on the rim 9ba. Said downstream helix meshes with the helix of the planet gears 8, which meshes with the helix of the sun gear 7.

[0063] The fastening flange half 9ab of the upstream ring gear 9a and the fastening flange half 9bb of the downstream ring gear 9b form a fastening flange 9c of the ring gear. By way of example, the ring gear 9 is attached to the ring gear carrier by assembling the fastening flange 9c of the ring gear and the fastening flange 12a of the ring gear carrier of the ring gear carrier together using a bolt assembly.

[0064] Figure 2 The arrows in the figure show the oil supply in the reduction gear 6. The oil enters the reduction gear 6 from the stator part 5 through various ways of distribution 13, which will not be specified in this view, as they are directed to one or more types of architecture. The distribution is divided into two parts, each part being typically repeated with the same number of planet gears. The injectors 13a have the function of lubricating the toothed connection, while the arms 13b have the function of lubricating the bearings. The oil is fed to the injectors 13a and flows out through the end 13c to lubricate the toothed connection. The oil is also fed to the arms 13b and flows through the supply orifices 13d of the bearings. The oil then passes through the shaft into one or more buffer zones 10c and flows out through the orifices 10d to lubricate the bearings of the planet gears.

[0065] Figure 3 and Figure 4 A reduction gear 6 of an aircraft turbomachine according to the prior art is shown.

[0066] The reduction gear 6 comprises a planet carrier 10 configured to be rotatable about an axis X and is monolithic, i.e. formed in one piece.

[0067] The planet carrier 10 comprises a cage 14 and a shaft portion 15.

[0068] The shaft portion 15 has a generally tubular shape and is elongated along the axis X and comprises a free longitudinal end (here, located on the left of the figure) and an opposite longitudinal end connected to the cage 14.

[0069] The shaft portion 15 comprises an external toothed connection 15a for engaging, for example, with a fan.

[0070] The cage 14 comprises two annular flanges 14a, 14b parallel and spaced apart from each other and extending perpendicularly to the axis X. The flanges 14a, 14b have a generally circular shape and are centered on the axis X.

[0071] The flange 14a on the left in the figure, called first flange, is connected to the shaft portion 15. The other flange 14b is called second flange.

[0072] The flanges 14a, 14b are connected to each other by a material bridge 16 between which a flange housing 18 configured to accommodate the planetary gears 8 is defined. The housing 18 opens radially outward at the outer periphery of the cage 14 and also radially inward through the inner tubular wall 20 of the cage 14. The material bridge 16 can be solid or partially hollow, as shown. Figure 5

[0073] The wall 20 extends from the first flange 14a towards the second flange 14b around the axis X. There, it extends substantially along the axial prolongation of the shaft portion 15. This wall 20 defines on the inside a space 22 for accommodating the sun gear 7.

[0074] This space 22 comprises two adjacent portions. A first portion 22a is surrounded by the wall 20 which comprises an inner cylindrical surface 22a for mounting a bearing 23 for guiding one end of the sun gear 7. A second portion 22b, located at the level of the outlet of the housing 18, receives the opposite end of the sun gear 7 which comprises an outer toothed interface 7b for engaging with the planetary gears 8. The sun gear 7 also comprises an inner toothed interface 7a for coupling to a shaft, for example of a turbomachine.

[0075] Each housing 18 comprises a first portion 18a located on the side of the first flange 14a and a second portion 18b located on the side of the second flange 14b. The housing 18 opens at the outer periphery of the cage 14 at the level of the two portions 18a, 18b of the housing and at the inner periphery of the cage 14 only at the level of the second portion 18b.

[0076] The flanges 14a, 14b comprise aligned holes or orifices 24 for mounting the planetary gears 8 and in particular the plain bearings 26 of these planetary gears 8. Each bearing 26 has a substantially cylindrical shape which extends parallel to the axis X and the longitudinal end of which comprises an extension 26a which is accommodated in the orifice 24 forming a seat.

[0077] As is known, each bearing 26 can comprise an internal bore 26b for the circulation of oil which is generally in communication with an oil supply duct to the outer cylindrical surface 26c of the bearing so as to form an oil film on this surface 26c.

[0078] The planetary gears 8 are of the double-stage engagement type as described above and each comprise a tubular body 8a equipped with a first outer toothed interface 28 and connected to a second outer toothed interface 32 by a web 30.

[0079] ​The toothed interfaces 28, 32 are arranged next to each other and in particular in two planes perpendicular to the axis X, respectively.

[0080] The first toothed interface 28, located on the left side of the figure, is located on the side of the first flange 14a and thus on the first portion 18a of the housing. As Figure 3 indicated, this toothed interface 28 meshes with the ring gear 9.

[0081] The second toothed interface 32, on the right-hand side of the figure, is located on the side of the second flange 14b and thus on the second portion 18b of the housing. As Figure 3 indicated, this toothed interface 32 meshes with the toothed interface of the sun gear 7.

[0082] As Figure 3 indicated, the material bridge 16 extends radially between the housings 18 from the inner periphery of the wall 20 and the flanges 14a, 14b to the outer periphery of the flanges.

[0083] The ring gear 9 is carried by a ring gear carrier not shown in the figure.

[0084] The invention provides a solution to ensure that the torque and axial forces to which the ring gear 9 is subjected during operation are taken up by the ring gear carrier.

[0085] Figure 5 to Figure 7 A preferred embodiment of a reduction gear 6 according to the invention is shown. This reduction gear 6 comprises all the features described above in relation to Figure 3 and Figure 4 as far as they are not contrary or incompatible with the features below.

[0086] Thus, the reference signs used in Figure 5 to Figure 7 and already used in Figure 4 and Figure 5 denote identical or similar elements.

[0087] The sun gear 7 is similar to the sun gear 7 described above and is centered and rotationally guided in the planet carrier 10 by rolling bearings 23, here comprising two rings 23a, 23b between which two rows of adjacent rolling elements 23c are arranged.

[0088] The inner ring 23a is mounted on one axial end of the sun gear 7, while the outer ring 23b is mounted in the inner wall 20 of the planet carrier 10.

[0089] The planet carrier 10 itself is centered and rotationally guided in the ring gear carrier 34 by bearings 36, which can be rolling bearings and comprise for example rollers. The bearings 36 are located on the shaft portion 15 of the planet carrier 10, for example approximately in the middle thereof.

[0090] The bearing 36 can comprise an inner ring mounted on the shaft portion 15 or integrated directly into the shaft portion 15. Similarly, the outer ring of the bearing 36 can be mounted in or integrated into the carrier 34 of the ring gear.

[0091] In the example shown, the carrier 34 of the ring gear has a substantially annular shape around the axis X and extends axially around a portion of the shaft portion 15 and around the ring gear 9.

[0092] The carrier 34 of the ring gear substantially comprises two axial portions, namely a frustoconical upstream portion 34a and a cylindrical downstream portion 34b.

[0093] The frustoconical portion 34a flares towards the downstream and has an upstream end of smaller diameter which extends around the bearing 36 to support said bearing. It can thus be understood that the carrier 34 of the ring gear has the function of supporting the bearing 36.

[0094] The cylindrical portion 34b has an average diameter D3 measured with respect to the axis X. Dl is the average diameter of the toothed interface 28 and D2 is the average diameter of the toothed interface 32. In the example shown, Dl is less than D2, where Dl and D2 are measured with respect to the axis Y of the planetary gear 8.

[0095] The cylindrical portion 34b comprises an annular rim 38 which extends radially outwards and forms an annular flange for fixing the carrier 34 of the ring gear to the stator of the turbomachine. For example, this rim 38 comprises a row of annularly arranged holes (not shown), each hole being axially oriented and configured to receive a fastening screw.

[0096] At the connection between the frustoconical portion 34a and the cylindrical portion 34b, the carrier 34 of the ring gear comprises an annular abutment 40 which extends radially inwards. This abutment 40 is in the form of a projecting annular boss. This abutment 40 is located at an axial end of the ring gear 9 (here the upstream end) and extends in an axially opposite manner to the ring gear so that the ring gear can be supported on the abutment 40.

[0097] The abutment 40 comprises a downstream radial face 40a which supports the upstream end of the ring gear 9 (here the upstream end). In the example shown, the axial section of the abutment 40 is substantially triangular, thus comprising an upstream face 40b which slopes and flares outwards from downstream towards upstream. Figure 6 ) In the example shown, the axial section of the abutment 40 is substantially triangular, thus comprising an upstream face 40b which slopes and flares outwards from downstream towards upstream.

[0098] The cylindrical portion 34b of the carrier 34 of the ring gear comprises internal splines 42 in which complementary external splines 44 of the ring gear 9 engage. In the example shown, the external splines 44 of the ring gear 9 extend over the entire axial dimension of the ring gear 9, as do the internal toothing portions 9d of the ring gear, and the internal splines 42 of the cylindrical portion 34b extend over at least 80% of the axial dimension of the cylindrical portion.

[0099] The internal splines 42 are connected to the face 40a of the abutment portion 40 by an annular groove 46 formed in the carrier 34 of the ring gear at the bottom or periphery of the abutment portion 40. This groove 46 can be radially oriented and open radially inwards; or can be inclined and open radially inwards (inwardly oriented from upstream to downstream), as shown in the example. Figure 6

[0100] According to the application, better illustrated in Figure 7 , the splines 42, 44 are helical and can slide inside each other in the axial direction. It will be understood that, due to the helical shape of the splines, this movement is similar to the movement of a screwdriver.

[0101] The handedness of the helix of the splines 42, 44 is important and depends on the direction of rotation of the planetary gear 8 about its axis. This is because the splines 42, 44 must be configured so that, during operation, the ring gear 9 is axially loaded in the upstream direction and can thus be held against the abutment portion 40. The person skilled in the art is capable of choosing the handedness of the splines 42, 44 depending on the direction of rotation of the planetary gear 8.

[0102] In the particular example shown in Figure 7 , the sun gear 7 rotates about the axis X in the direction of the arrow F1. The sun gear drives the planetary gear 8 to rotate about the axis Y in the direction of the arrow F2, which in turn drives the planet carrier 10 to rotate about the axis X in the direction of the arrow F3. With the helical splines 44 of the ring gear, the ring gear 9 is axially loaded in the direction of the arrow F4.

[0103] In order to prevent wear (e.g. fretting wear) of the abutment portion 40 or of the ring gear 9, the side face 40a of the abutment portion can be covered with a protective coating. This coating can be a hard material, i.e. a material harder than the material of the abutment portion 40, or can be an anti-friction material.

[0104] Alternatively, the coating can be located on the ring gear 9 (e.g. at the upstream end of the ring gear) and cooperate with the face 40a of the abutment portion 40.

[0105] ​In a variant not shown, an oil film squeeze damper can be fitted to the ring gear carrier 34 and mounted preferably around the ring gear 9. The function of this damper is to dampen the vibrations undergone by the ring gear 9 during operation.

[0106] On the side opposite the abutment 40, i.e. downstream in the example shown, the ring gear 9 is held axially opposite the ring gear carrier 34 by an open locking ring 50, which can be seen more clearly in Figure 6 The ring 50 engages in a radially inner annular groove 52 of the ring gear carrier 34, at which point the annular groove 52 is formed at the free downstream end of the ring gear carrier 34.

Claims

1. A mechanical speed reduction device (6) for a turbine (1), the mechanical speed reduction device comprising: - Sun gear (7), which has a rotation axis (X) and includes an external toothed portion (7a). - A ring gear (9) extending around the sun gear (7) and including an internal toothed portion (9d), the ring gear (9) being surrounded by a ring gear support (34) that is fixed in use and does not rotate about the axis of rotation (X). - A plurality of planetary gears (8) mesh with the sun gear (7) and the ring gear (9), and each includes a first toothed portion (32) having an average diameter D1 and a second toothed portion (28) having an average diameter D2, the average diameter D1 being different from the average diameter D2. The first toothed portion meshes with the outer toothed portion (7a) of the sun gear (7), and the second toothed portion meshes with the inner toothed portion (9d) of the ring gear (9). The planetary gears (8) are held by a planet carrier (10) which is movably rotatable about the axis of rotation (X) during use. The support (34) of the ring gear includes an annular axial abutment (40), the ring gear (9) is configured to be supported on the annular axial abutment (40), and the ring gear (9) includes a helical external spline (44) that engages with complementary internal splines (42) of the support (34) of the ring gear, and the helical external spline (44) is configured to slide and engage with these internal splines (42) to force the ring gear (9) to remain against the annular axial abutment (40) during operation. The annular axial abutment portion (40) is formed by the radially inner annular boss of the support (34) of the annular gear. The radial inner annular boss includes a radial surface (40a) for supporting the annular gear (9), and the radial surface (40a) is connected to the inner spline (42) of the bracket (34) of the annular gear through an annular groove (46).

2. The mechanical reduction device (6) according to claim 1, wherein, The support (34) of the ring gear includes a bearing support (36) mounted on the shaft (15) of the planetary carrier (10), the bearing support (36) accommodating a bearing for rotatably guiding the shaft (15) of the planetary carrier (10).

3. The mechanical speed reduction device (6) according to claim 2, wherein, The annular axial abutment portion (40) and the shaft portion (15) are located on the same side relative to the planetary gear (8).

4. The mechanical speed reduction device (6) according to any one of claims 1 to 3, wherein, The support (34) of the ring gear includes a cylindrical wall (34b) and a truncated conical wall (34a), the cylindrical wall including the internal spline (42), the larger diameter end of the truncated conical wall being connected to the cylindrical wall (34b), and the annular axial abutment (40) being located in the connection area between the truncated conical wall (34a) and the cylindrical wall (34b).

5. The mechanical speed reduction device (6) according to claim 4, wherein, The cylindrical wall (34b) is connected to the annular edge (38), which extends radially outward and forms a fixed flange.

6. The mechanical speed reduction device (6) according to claim 5, wherein, The annular edge (38) extends in a plane perpendicular to the axis of rotation (X), and the plane passes substantially through the center of the ring gear (9) and through the center of the bearing (23) mounted between the planet carrier (10) and the sun gear (7).

7. The mechanical speed reduction device (6) according to claim 1, wherein, The radial surface (40a) is covered with a protective coating, or the radial surface is adapted to engage with the protective coating located on the ring gear (9) by means of a support.

8. The mechanical speed reduction device (6) according to any one of claims 1 to 3, wherein, The ring gear (9) is axially held between the axial abutment of the ring and the open locking ring (50), the open locking ring engaging in the radial inner annular groove (52) of the support (34) of the ring gear.

9. The mechanical speed reduction device (6) according to claim 8, wherein, The radial inner annular groove (52) and the open locking ring (50) are located at the free axial end of the support of the annular gear.

10. The mechanical speed reduction device (6) according to any one of claims 1 to 3, wherein, The internal spline (42) of the support (34) of the ring gear and the external helical spline (44) of the ring gear (9) extend over the entire axial dimension of the ring gear (9).

11. The mechanical speed reduction device (6) according to claim 1, wherein, The turbine in question is the turbine of the aircraft.

12. The mechanical speed reduction device (6) according to claim 9, wherein, The radial inner annular groove (52) and the open locking ring (50) are located at the cylindrical wall (34b) of the support of the annular gear.

13. A turbine (1) comprising a mechanical reduction gear (6) according to any one of claims 1 to 12.

14. A mechanical reduction gear for a turbine of an aircraft, the mechanical reduction gear comprising: - A sun gear, which has a rotation axis and includes an external toothed portion. - A ring gear extending around the sun gear and including an internal gear engagement, the ring gear being surrounded by a ring gear support that is fixed during use and does not rotate about the axis of rotation. - A plurality of planetary gears, which mesh with the sun gear and the ring gear, and each including a first toothed portion having an average diameter D1 and a second toothed portion having an average diameter D2, the average diameter D2 being different from the average diameter D1; the first toothed portion meshes with the outer toothed portion of the sun gear, and the second toothed portion meshes with the inner toothed portion of the ring gear; the planetary gears are held by a planet carrier, which is movably rotatable about the axis of rotation during use. The ring gear's support includes an annular axial abutment portion, the ring gear being configured to be supported on the annular axial abutment portion, and the ring gear including a helical external spline that engages with complementary internal splines of the ring gear's support, the helical external spline being configured to slide and engage with these internal splines to force the ring gear to remain against the annular axial abutment portion during operation. The ring gear is axially held between the axial abutment portion of the ring and the open locking ring, the open locking ring engaging in the radial inner annular groove of the support of the ring gear.

15. A mechanical reduction gear for a turbine of an aircraft, the mechanical reduction gear comprising: - A sun gear, which has a rotation axis and includes an external toothed portion. - A ring gear extending around the sun gear and including an internal gear engagement, the ring gear being surrounded by a ring gear support that is fixed during use and does not rotate about the axis of rotation. - A plurality of planetary gears, which mesh with the sun gear and the ring gear, and each including a first toothed portion having an average diameter D1 and a second toothed portion having an average diameter D2, the average diameter D2 being different from the average diameter D1; the first toothed portion meshes with the outer toothed portion of the sun gear, and the second toothed portion meshes with the inner toothed portion of the ring gear; the planetary gears are held by a planet carrier, which is movably rotatable about the axis of rotation during use. The ring gear's support includes an annular axial abutment portion, the ring gear being configured to be supported on the annular axial abutment portion, and the ring gear including a helical external spline that engages with complementary internal splines of the ring gear's support, the helical external spline being configured to slide and engage with these internal splines to force the ring gear to remain against the annular axial abutment portion during operation. Wherein, the annular axial abutment portion and the bracket of the annular gear are integrally formed, and During operation, the ring gear remains in direct contact with the axial abutment portion of the ring.

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