Mechanical reduction gear for a turbine engine

Abstract

The invention relates to a mechanical reduction gear comprising a sun gear, a ring gear, planet gears, and a ring gear carrier, one of the members of the reduction gear, chosen from among the ring gear, the ring gear carrier and another annular element, comprising a primary flange (B1) for attachment to a secondary flange (B2) of the other member of the reduction gear via screws, the primary flange comprises first bearing faces (B10) configured to co-operate with corresponding second bearing faces (B20) of the secondary flange by bearing against one another, and first ramp faces (B12) configured to co-operate with second ramp faces (B22) of the secondary flange so that a torque transmitted by the ring gear in a second direction (D2) causes the flanges (B1, B2) to be axially spaced apart from each other and induces a tensile force on screws, which are configured to break when this tensile force is greater than a predetermined threshold.

Description

[0001]DESCRIPTION TITLE: MECHANICAL REDUCER FOR A TURBOMACHINE Field of the invention The present invention relates to the field of mechanical reducers for a turbomachine, in particular an aircraft turbomachine, as well as a turbomachine comprising such a mechanical reducer. Technical background The state of the art includes in particular documents US-A1-2018 / 038448, US-A1-2009 / 062058, FR-A1-3084427 and US-B2-10107378. The role of a mechanical reducer is to modify the speed and torque ratio between the input axis and the output axis of a mechanical system. The new generations of double-flow turbomachines, in particular those with a high bypass ratio, comprise a mechanical reducer to drive the shaft of a fan. Usually, the speed reducer is intended 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. Such aThe gearbox comprises a central pinion, called a sun gear, a crown gear and pinions called satellite gears, which are meshed between the sun gear and the crown gear. The satellite gears are held by a frame called a planet carrier. The sun gear, the crown gear and the planet carrier are planet gears because their axes of revolution coincide with the longitudinal axis X of the turbomachine. The satellite gears each have a different axis of revolution and are equally distributed over the same operating diameter around the axis of the planet gears. These axes are parallel to the longitudinal axis X. There are several gearbox architectures. In the state of the art of double-flow turbomachines, the gearboxes are of the planetary or epicyclic type. In other similar applications, there are architectures called differential or compound. On a planetary gearbox, the planet carrier is fixed and the crown gear constitutes the output shaft of the device which rotates in the opposite direction to the sun gear.On an epicyclic gearbox, the ring gear is fixed and the planet carrier constitutes the output shaft of the device which rotates in the same direction as the sun gear. · On a differential gearbox, no element is fixed in rotation. The ring gear rotates in the opposite direction to the sun gear and the planet carrier. Gearboxes 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 fields. There are several types of contact meshing such as with straight, helical or herringbone teeth. In operation, a failure of a planet bearing (hydrodynamic or rolling type) can cause the gearbox and the fan to jam. This can lead to an increase in the drag of the turbomachine and impair the maneuverability of the aircraft. To prevent such a jamming of the gearbox, it was proposed in document FR-A1-3066 004 to form thecrown by two half-crowns, the crown being intended to uncouple from the satellite when the satellite exerts on each half-crown a disengaging action whose amplitude is greater than a determined amplitude value. For this, this document proposes to integrate a fusible stop connected both to the crown holder and to one of the half-crowns which is intended to break by the disengaging action, in which the amplitude corresponds to a blockage of a component of the turbomachine (such as a blockage of a satellite bearing) and the axial force applied to the crown is oriented towards the outside of the reducer. However, this design can be complex to implement in particular because of the additional elements to be assembled in the reducer. In this context, it is interesting to overcome the drawbacks of the prior art, by proposing a solution making it possible to maintain the rotation of a fan during a blockage of a mechanical reducer of aturbomachine (resulting for example from a failure of a satellite bearing or a satellite for example). Summary of the invention The present invention provides a simple and economical solution to at least some of the aforementioned problems. To this end, the invention relates to a mechanical reducer for a turbomachine, in particular an aircraft one, this reducer comprising: - a sun gear having a first axis of rotation A, - a ring which extends around the sun gear and said first axis A, the ring comprising two annular half-rings which are fixed to each other respectively by first and second annular flanges, - satellites which are arranged around the first axis A, between the sun gear and the ring gear, and which are meshed with the sun gear and the ring gear, these satellites each having a second axis B of rotation parallel to the first axis A and being held by a planet carrier movable in rotation around said first axis A, - a ring carrier having a general shapeannular around the first axis A, the crown holder comprising a third annular flange for fixing to the first and second flanges, and a fourth annular flange for fixing to a fifth annular flange of another annular element extending around the first axis A, said first, second and third flanges being axially tightened against each other by first screws parallel to the first axis, and said fourth and fifth flanges being axially tightened against each other by second screws parallel to the first axis. According to the invention, one of the flanges, called primary flange, among the first, second and third flanges, or among the fourth and fifth flanges, comprises first bearing faces which are distributed around the first axis A and first ramp faces which are distributed around the first axis A, the first bearing faces being configured to cooperate by bearing in a tangential direction with second facescorresponding support faces of another of said flanges, called secondary flange, which is in axial support against the primary flange, so as to transmit a torque transmitted by the crown in a first direction D1 around the first axis A, and the first ramp faces being configured to cooperate with second ramp faces of said secondary flange so that a torque transmitted by the crown in a second direction D2 around the first axis A, opposite to the first direction D1, causes an axial separation of the flanges from each other and a tensile force on the first and / or second screws which are configured to break when this tensile force is greater than a predetermined threshold. The invention thus proposes to modify the crown holder so as to maintain the rotation of a fan of the turbomachine during a blockage of a component of the reducer (for example of a satellite bearing or of the satellite). For this, the crown holder integratesfirst bearing faces cooperating with second bearing faces and first ramp faces cooperating with second ramp faces on the primary and secondary flanges. Thus, in normal operation of the mechanical reducer, the first bearing and ramp faces are, on the one hand, in circumferential support respectively with the corresponding secondary bearing and ramp faces, and on the other hand, the primary and secondary flanges are axially tightened by screws. This maintains the connection between the primary and secondary flanges. In addition, this configuration makes it possible to transmit a torque transmitted by the crown in a first direction D1 around the first axis A. In abnormal operation of the mechanical reducer (for example in the event of failure of the satellite bearing(s) or the satellite), the bearing faces are in circumferential support and the first and second ramp faces are able to move axially apart from each other (in particular bycam effect) when the torque transmitted by the crown is greater than a predetermined threshold and in a second direction D2 around the first axis A, opposite to the first direction D1. Indeed, the direction of transmission of the torque by the crown to the crown carrier is reversed, for example, during a failure of the planet bearing. This reversal of the direction of torque transmission generates additional forces on the ramp faces which causes tensile forces on the screws. These tensile forces, when they are greater than the predetermined threshold (for example, due to a failure of the planet bearing), cause the axial separation of the ramp faces from each other and also a breakage of the screws, so as to break the connection between the primary and secondary flanges. This makes it possible to first separate the connection between the primary and secondary flanges. The rotation of the satellite(s) having the failure remains blocked. In this way, thesolar directly drives the planet carrier and / or the ring gear through the blocked planet gear(s), so that the fan (connected to the planet carrier and / or the ring gear, for example, via a drive shaft) of the turbomachine can continue to rotate. Consequently, in the event of a satellite blockage (for example, during a satellite bearing failure), the fan blockage is prevented. The problems of drag of the turbomachine on aircraft wings and of hindrance to the maneuverability of the aircraft are therefore limited. The first and second ramp faces thus make it possible to provide a mechanical fuse function (in abnormal operation described above) while allowing a rigid system to be provided when the satellites are not blocked (in normal operation). The mechanical reduction gear also comprises one or more of the following features, taken alone or in combination: - the primary flange comprises a rowannular of first axial teeth which are axially engaged between second axial teeth of the secondary flange, to form a dog connection between the primary and secondary flanges; - the first and second axial teeth of each of the primary and secondary flanges are regularly distributed around said first axis A; - the first and second axial teeth of each of the primary and secondary flanges are identical; - first and second axial teeth of each of the primary and secondary flanges respectively comprise said first and second bearing faces on a first side, and said first and second ramp faces on a second side, opposite the first side; - each of the primary and secondary flanges comprises a number of teeth between 25 and 50; - the first and second axial teeth each have a generally parallelepiped shape; - the first axial teeth of the primary flange, respectively of the secondary flange,each comprise a radial face perpendicular to said first axis A and extending between the bearing face and the ramp face of this first tooth, this radial face being configured to bear axially between the second axial teeth of the secondary flange, respectively of the primary flange; - the first and / or second screws pass through first orifices formed in the first teeth of the primary flange, respectively of the secondary flange, and second orifices formed between the second teeth of the secondary flange, respectively of the primary flange; - each of the first and second ramp faces has an angle of inclination relative to a plane passing through said first axis A, which is between 5° and 75°; - the first and second axial teeth each have an extent around the first axis A which is between 5° and 10°; - said first bearing faces are located in planes passing through the first axis A; -- the other elementannular is a turbomachine stator or a drive shaft (such as a fan shaft) of a turbomachine. The invention further relates to a turbomachine, in particular an aircraft turbomachine, comprising a mechanical reducer according to one of the features of the invention. The invention further relates to an aircraft equipped with such a turbomachine. Brief description of the figures The invention will be better understood, and other aims, details, characteristics and advantages thereof will appear more clearly on reading the detailed explanatory description which follows, of embodiments of the invention given by way of purely illustrative and non-limiting examples, with reference to the appended schematic drawings in which: Figure 1 is a schematic half-view in axial section of an example of a turbomachine according to the invention; Figure 2 is a schematic half-view in axial section of an example of an epicyclic type mechanical reducer of the turbomachine of Figure 1; TheFigure 3 is a schematic half-view in axial section of an example of a differential-type mechanical reducer of the turbomachine of Figure 1; Figure 4 schematically represents in perspective a primary flange and a secondary flange of the mechanical reducer of Figure 2 or 3; Figure 5 schematically represents an enlarged and perspective view of the primary flange of Figure 4; Figure 6 schematically represents an enlarged and perspective view of the secondary flange of Figure 4; Figure 7 schematically represents a first example of a dog connection between the primary and secondary flanges of the mechanical reducer of Figure 2 or 3; Figure 8 schematically represents a second example of a dog connection between the primary and secondary flanges of the mechanical reducer of Figure 2 or 3; Figure 9 schematically represents a third example of a dog connection between the primary and secondary flanges of the mechanical reducer of Figure 2 or3; Figure 10 is a half schematic axial sectional view illustrating the different possibilities of dog connection in the mechanical reducer of Figure 2; Figure 11a schematically represents normal operation of the mechanical reducer of Figure 2 or 3; Figure 11b schematically represents abnormal operation of the mechanical reducer of Figure 2 or 3; Figure 12a is a partial schematic axial sectional view of a dog connection between the primary and secondary flanges of the mechanical reducer of Figure 2 or 3, in normal operation; Figure 12b is a partial schematic axial sectional view of the dog connection of Figure 12a in abnormal operation. The elements having the same functions in the different implementations have the same references in the figures. Detailed description of the invention By convention, in the description below, the terms “longitudinal” and “axial” qualify the orientation of elementsstructural elements extending in the direction of a longitudinal axis (such as a turbomachine). The terms "radial" or "vertical" describe an orientation of structural elements extending in a direction perpendicular to the longitudinal axis. The terms "inner" and "outer", and "internal" and "external" are used with reference to a positioning relative to the longitudinal axis. Thus, a structural element extending along the longitudinal axis has an inner face facing the longitudinal axis and an outer surface, opposite its inner surface. Similarly, by convention in the present application, the terms "upstream" and "downstream" are defined relative to the direction of flow of the gases in the turbomachine. Figure 1 shows a partial axial sectional view of a turbomachine 1, in particular an aircraft turbomachine, with a longitudinal axis X which comprises a mechanical reducer 3. The turbomachine 1 illustrated is a double-flow turbomachine intended to be mountedon an aircraft. Of course, the turbomachine can be a single-flow turbojet or can be a turboprop equipped with a single unducted propeller or a pair of counter-rotating, unducted propellers, known by the English expression "open rotor". The invention can be applied to other fields in which a mechanical speed reducer is used. The turbomachine 1 comprises, in a conventional manner and, from upstream to downstream, 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 1f. The high-pressure compressor 1b and the high-pressure turbine 1d are connected by a high-pressure shaft 1bd and form with it a high-pressure (HP) body. The low pressure compressor 1a and the low pressure turbine 1e are connected by a low pressure shaft 1ae and together form a low pressure (LP) body.The fan S is shrouded by a fan casing 2s carried by an external nacelle 2. The fan S generates, from an air flow F entering the fan, a primary air flow which circulates in a primary vein V1 opening into the exhaust nozzle 1f and a secondary air flow which circulates in a secondary vein V2, around the primary vein V1, opening into an ejection nozzle 2f of the nacelle 2. The fan S is driven by a fan shaft 1s which is driven to the low pressure shaft 1ae by means of a mechanical reducer 3. The mechanical reducer 3 can be of the epicyclic or differential type. In the present embodiment, the turbomachine 1 is equipped with the mechanical reducer 3 formed by a gear train and known by the English acronym RGB for "Reduction Gear Box". The mechanical reducer 3 is positioned in the upstream part of the turbomachine 1 following the circulation of the gases of the turbomachine. A fixed structure 4schematically comprising, here, an upstream part 4a and a downstream part 4b, composes a stator 5 (or a casing) of a turbomachine is arranged so as to form an enclosure 40 surrounding the mechanical reducer 3. The stator 5 can be for example the inlet casing of the turbomachine. A lubricant mist reigns in the enclosure 40. This enclosure 40 is advantageously but not limitatively closed upstream by seals at the level of an upstream bearing P allowing the fan shaft 1s to pass through, and downstream by seals at the level of the crossing of the low pressure shaft 1ae. With reference to figure 2, the mechanical reducer 3 is here of the epicyclic type. The latter comprises three components which are a sun pinion 31, planet pinions 32 and a planet carrier 33 which are rotatable. The rotation speed of one of these components depends in particular on the difference in speeds of the other two components. At the input, the mechanical reducer isconnected to the low pressure shaft 1ae, for example by means of splines. Thus the low pressure shaft 1ae drives the sun gear 31 (or internal planetary gear). Conventionally, the sun gear 31, whose first axis of rotation A is the same as that of the longitudinal axis X of the turbomachine, drives the satellites 32, which are equally distributed over the same diameter around the first A. This diameter is equal to twice the operating center distance between the sun gear and the satellites. The number of satellites is generally defined between three and seven for this type of application. The sun gear 31 is rotationally fixed to the low pressure shaft 1ae and the satellite carrier 33 is rotationally fixed to the fan shaft 1s. The set of satellites 32 is held by a frame called a planet carrier 33. Each satellite 32 rotates around its own second axis of rotation B. Each second axis B is parallel to the first axis A. Each satellite 32 meshes with a crown 35(or external planetary). The crown 35 is preferably fixed or immobile in rotation relative to the first axis A. The mechanical reducer 3 may comprise an annular deflector 6 extending around the first axis A. This deflector 6 may be fixed to the crown 35 and configured to convey oil exiting radially towards the outside of the crown thanks to centrifugal effects. At the output of the epicyclic reducer, the set of satellites 32 drives the planet carrier 33 in rotation around the first axis A. The crown 35 is fixed to the stator 5 via a crown carrier 36. The planet carrier 33 is fixed and integral in rotation with the fan shaft 1s. Although the above description concerns an epicyclic type reducer, it also applies to a differential type reducer in which the three components (planet carrier, crown and sun) are mobile in rotation, the rotation speed of one of these components depending in particular on thespeed difference of the other two components. Consequently and alternatively, the mechanical reducer 3 can be of the differential type. In this case, the input of the mechanical reducer 3 of the turbomachine 1 of FIG. 1 can be coupled to the low pressure shaft 1ae while the output of the mechanical reducer 3 can be coupled to the fan shaft 1s. In particular, at least one of the planet carrier 33 and / or the ring gear 35 is rotationally fixed to the fan shaft 1s around the first axis A. In the differential mechanical reducer 3 in operation, the sun gear 31 is driven by the low pressure shaft 1ae at a first speed. The planet gears 32 are rotated by the sun gear 31 around their second axis B at a second rotational speed. Figure 3 illustrates a non-limiting configuration of the differential mechanical reducer 3, in which the set of satellites 32 drives the satellite carrier 33 in rotation.around the first axis A which can be connected to a first member of the turbomachine. The planet carrier 33 rotates at a third speed. The ring gear 35 can be connected to the fan shaft 1s. The ring gear 35 which is meshed with the planet gears 32, is driven in rotation around the first axis A and drives the fan shaft 1s. The ring gear 35 rotates at a fourth rotation speed and in a direction opposite to that of the sun gear 31. In the case of the epicyclic or differential mechanical reducer 3, each planet gear 32 is mounted to rotate freely using a bearing 34, for example of the rolling bearing or hydrodynamic bearing type. Generally, a hydrodynamic bearing is supplied with “low” pressures (usually less than 10 bars). The rotation of the bearing makes it possible to increase the pressure of the oil wedge and to separate the planet gears and the bearings. Each bearing is mounted on one of the axes of the planet carrier 33 and all the axes are positionedrelative to each other using one or more structural frames of the planet carrier 33. Each planet 32 ​​meshes with external teeth of the sun 31 and internal teeth of the crown 35. The internal teeth of the crown 35 can be straight (parallel to the longitudinal axis) or chevron-shaped. There is a number of axes and bearings equal to the number of planets. For reasons of operation, assembly, manufacturing, control, repair or replacement, the axes and the frame can be separated into several parts. For the same reasons mentioned above, the teeth of a reducer 3 can be separated into several helices. Still with reference to Figure 2, the crown 35 is separated into two half-crowns 35a, 35b: - an annular half-crown, called "front", 35a consisting of a rim 35aa and a first annular fixing flange 35ab (hereinafter called first flange). On the rim 35aa is the front helix of the toothingof the reducer. This front helix meshes with that of the satellite 32 which meshes with that of the solar 31. - an annular half-crown, called "rear", 35b consisting of a rim 35bb and a second annular fixing flange 35ba (hereinafter called second flange). On the rim is the rear helix of the teeth of the reducer. This rear helix meshes with that of the satellite 32 which meshes with that of the solar 31. The first 35ab and second 35ba flanges extend radially outwards. In a variant (not illustrated), the first flange 35ab of the front crown and the second flange 35ba of the rear crown can form a single fixing flange 350 of the crown 35. This fixing flange 350 is annular and extends radially outwards. Still referring to Figure 2 or Figure 3, the epicyclic or differential mechanical reducer 3 comprises a crown carrier 36. The crown carrier 36 is annular and centered on the firstaxis A. For this purpose, the crown carrier 36 comprises a third annular fixing flange 362 (hereinafter called third flange) to the crown 35, in particular to the second flange 35ba (or the fixing flange 350), using a bolted assembly for example. This third flange 362 can extend radially inwards. Alternatively, the third flange 362 extends radially outwards. The crown carrier 36 comprises a fourth annular fixing flange 364 (hereinafter called fourth flange). This fourth flange 364 can extend radially outwards. Alternatively, the fourth flange 364 extends radially inwards. The crown carrier 36 may comprise an annular portion 366 capable of connecting the third flange 362 and the fourth flange 364. The third and fourth flanges 362, 364 and the annular portion may be in one piece (i.e., made in one piece). Advantageously, the crown carrier 36 mayinclude flexibility means (not shown in the figures) which are configured so as, on the one hand, to limit overloads in the turbomachine due to the movements of certain components thereof and / or of the mechanical reducer 3, and on the other hand, to obtain a uniform and stable distribution of dynamic loads. The flexibility means may comprise at least one bellows. The crown carrier 36 may comprise a portion provided with several bellows. With reference to FIG. 2, the crown carrier 36 may connect the crown 35 to the stator 5 of the turbomachine, for example in the configuration of the epicyclic mechanical reducer 3. Thus, the fourth flange 364 may be intended to be fixed to an annular flange 50 for fixing the stator 5 using a bolted assembly, for example. The crown carrier 36 makes it possible to transfer the torque from the mechanical reducer 3 to the stator 5 of the turbomachine. Referring to Figure 3, the crown carrier may connect the crown 35 to the shaft offan 1s. Thus, the fourth flange 364 may be intended to be fixed to an annular flange for fixing the fan shaft 1s, using a bolted assembly for example. As a variant of the mechanical reducer 3 of FIG. 3, the crown carrier may connect the crown 35 to a second member of the turbomachine (not illustrated in the figures). The second member may be one of the upstream or downstream propellers of an unducted turbomachine. The fourth flange 364 may be intended to be fixed to an annular flange for fixing the second turbomachine member, using a bolted assembly for example. The turbomachine stator 5, the fan shaft 1s and / or the second turbomachine member may or may correspond generally to an “other annular element” E of the present application. Thus, the annular flange(s) for fixing the stator 5, the fan shaft 1s and the second member form(s) one (or a plurality of) fifth annular flange(s).fixing flange E0 (hereinafter called fifth flange). In this way, the fourth flange 364 of the crown carrier 36 is connected to the fifth flange E0 of the other element E, using a bolted assembly for example. In the case of the epicyclic or differential mechanical reducer 3, the first 35ab, second 35ba and third 362 flanges are axially tightened against each other by first screws 72 parallel to the first axis A. The fourth 364 and fifth E0 flanges are axially tightened against each other by second screws 74 parallel to the first axis A. The mechanical reducer 3 may comprise one or more flange(s) called primary(s) B1 and one or more secondary flange(s) B2 which is axially supported against the corresponding primary flange B1. The primary flange B1 may be at least one of the first 35ab, second 35ba and third 362 flanges (or the fourth 364 and fifth E0 flanges). The secondary flange B2 thus corresponds tothe fixing flange (i.e. among the first 35ab, second 35ba, third 362, fourth 364 and fifth E0 flanges) to the primary flange B1. Figure 4 illustrates, in a non-limiting manner, an exemplary embodiment of a primary flange B1. The primary flange B1 may comprise an annular row of first axial teeth T1. The first axial teeth T1 may be distributed around the first axis A. The first axial teeth T1 may be identical to each other. The primary flange B1 may comprise a number of first axial teeth T1 of between 25 and 50. The first axial teeth T1 may each have a generally parallelepiped shape. The first axial teeth T1 may each have a first angular extent βD1 around the first axis A. This first angular extent βD1 may be between 1° and 10°. Figure 5 illustrates, in a non-limiting manner, an exemplary embodiment of a secondary flange B2. The second flange B2 may includesecond axial teeth T2. The second axial teeth T2 may be distributed around the first axis A. The second axial teeth T2 may be identical to each other. The second flange B2 may comprise a number of second axial teeth T2 of between 25 and 50. The second axial teeth T2 may each have a generally parallelepiped shape. The second axial teeth T2 may each have a second angular extent βD2 around the first axis A. This second angular extent βD2 may be between 1° and 10°. One of the particularities of the invention is that the primary flange B1 comprises first bearing faces and first ramp faces, and that the secondary flange B2 comprises second bearing faces and second ramp faces. As illustrated in Figures 4 and 5, the first and second bearing faces are distributed around the first axis A. The first bearing faces may be located in planes passing through the first axis A.The second bearing faces may be located in planes passing through the first axis A. The first and second ramp faces may also be distributed around the first axis A. In particular, the first axial teeth T1 of the primary flange B1 may comprise the first bearing faces B10 on a first side and the first ramp faces B12 on a second side which is opposite the first side. The first ramp faces B12 may each be inclined by a first inclination angle αB12 relative to a plane passing through the first axis A. This first inclination angle αB12 may be between 5° and 75°. For example, the first inclination angle αB12 is approximately 25°. The first axial teeth T1 may each comprise a first radial face B14. These first radial faces B14 are perpendicular to the first axis A. Each of the first radial faces B14 extends between the first bearing face B10 and the first ramp face B12of the corresponding first tooth T1. According to the configuration of Figure 4, the first radial faces B14 may each comprise a first orifice B18. These first orifices B18 are configured to receive at least a portion of the first 72 or second 74 screws. The primary flange B1 may comprise first hollow faces B16. Each first hollow face B16 may extend between a first bearing face B10 and a first ramp face B12. Each first hollow face B16 may be located between two adjacent first radial faces B14. In other words, each first hollow face B16 may be located between two adjacent first axial teeth T1. In a variant not illustrated, the first orifices B18 can be provided in the first hollow faces B16, instead of the first radial faces B14 (or between two adjacent first axial teeth T1), for example in the case of the second orifices B28 aligned with the first orifices B18 are provided in thesecond radial bearing faces B24 of the secondary flange B2. The first hollow faces B16 may each have a third angular extent βB16 around the first axis A. This third angular extent βB16 may be between 1° and 10°. The first angular extent βD1 may be identical to or different from the third angular extent βB16. The second axial teeth T2 of the secondary flange B2 may comprise the second bearing faces B20 on a first side and the second ramp faces B22 on a second side which is opposite the first side. The second ramp faces B22 may each be inclined by a second angle of inclination αB22 relative to a plane passing through the first axis A. This second angle of inclination αB22 may be between 5° and 75°. For example, the second angle of inclination αB22 is approximately 25°. The second axial teeth T2 may each comprise a second radial face B24. These second radial faces B24 areperpendicular to the first axis A. Each of the second radial faces B24 extends between the second bearing face B20 and the second ramp face B22 of the corresponding second tooth T2. The secondary flange B2 may comprise second hollow faces B26. Each second hollow face B26 may extend between a second bearing face B20 and a second ramp face B22. Each second hollow face B26 may be located between two adjacent second radial faces B24. In other words, each second hollow face B26 may be located between two adjacent second axial teeth T2. According to the configuration of FIG. 5, second orifices B28 may be formed between the second axial teeth T2. In particular, these second orifices B28 are provided in each of the second hollow faces B24. These second orifices B28 are configured to receive at least a portion of the first 72 or second 74 screws. In a variant not shown, the second orifices B28 can be provided in thesecond radial faces B24, instead of the second hollow faces B24, for example in the case where the first orifices B18 aligned with the second orifices B28 are provided in the first hollow faces B14 of the primary flange B1. The second hollow faces B26 may each have a fourth angular extent βB26 around the first axis A. This fourth angular extent βB26 may be between 1° and 10°. The second angular extent βD2 may be identical to or different from the fourth angular extent βB26. The primary and secondary flanges B1, B2 are configured to bear axially against each other. For this, the first bearing faces B10 are configured to cooperate by bearing in the tangential direction with the corresponding second bearing faces B20 of the secondary flange B2. The first ramp faces B12 are configured to cooperate with second ramp faces B22. The first and second axial teeth T1, T2 can be complementary betweenthem. The first and second angular extents βD1, βD2 may be identical or different. The first and second inclination angles αB12, αB22 may be identical or different. Thus, advantageously, the first axial teeth T1 may be axially engaged between the second axial teeth T2 to form a dog connection between the primary flange B1 and secondary flange B2. Figures 7 to 10 illustrate schematically and in a non-limiting manner, the different possibilities and positions of dog connection in the mechanical reducer 3. For example, the mechanical reducer 3 may comprise at least one or more of the following dog connections: - a first dog connection L1 between the first and second flanges 35ab, 35ba (figure 7), - a second dog connection L2 between one of the first and second flanges 35ab, 35ba and third 362 flanges (figure 8), and - a third dog connection L3 between the fourth and fifth flanges 364, E0 (figure 9), inin which one of the flanges forms the primary flange B1 and the other of the flanges forms the secondary flange B2 which have been described above with reference in particular to figures 4 and 5. Figure 10 illustrates an example of an epicyclic mechanical reducer 3 which may comprise these three dog connections L1, L2 and L3. The differential mechanical reducer 3 may also comprise at least one of the dog connections L1, L2 and L3. The operation of the mechanical reducer 3 of the invention will now be described with reference to figures 11a, 11b, 12a and 12b. According to the invention, the first bearing faces B10 of the primary flange B1 are configured to cooperate by bearing in a tangential direction with the corresponding second bearing faces B20 of the secondary flange B2, which is in axial bearing against the primary flange B1, so as to transmit a torque transmitted by the crown 35 in a first direction D1 around the first axis A. The first radial faces B14 of the primary flange B1can be configured to bear axially between the second axial teeth T2 of the secondary flange B2, in particular on the second hollow faces B26. Alternatively, the second radial faces B24 of the secondary flange B2 can be configured to bear axially between the first axial teeth T1 of the primary flange B1, in particular on the first hollow faces B16. According to the invention, the first ramp faces B12 of the primary flange B1 are configured to cooperate with second ramp faces B22 of the secondary flange B2, so that a torque transmitted by the crown 35 in a second direction D2 around the first axis A, opposite to the first direction D1, causes, on the one hand, an axial separation of the primary and secondary flanges B1, B2 from each other, and on the other hand, a tensile force on the screws 72, 74 which are configured to break when this tensile force is greater than a predetermined threshold.by "predetermined threshold", the moment when the torque transmitted by the crown 35 to the crown carrier 36 is in the first direction D1 in normal operation of the mechanical reducer 3. For example, this predetermined threshold is exceeded when the crown carrier 36 is subjected to a torque in the second direction D2, in particular in the event of failure of the satellite bearing 34. Figures 11a and 12a schematically represent the normal operation of the mechanical reducer 3, and in particular the forces exerted on each of the components of the mechanical reducer 3 (illustrated by simple arrows in the figures). As described above with reference to the mechanical reducer 3 of Figure 2 or Figure 3, the rotation of the sun gear 31 (driven by the low pressure shaft 1ae) drives the satellites 32 into rotation inside the crown 35 which is stationary or rotating. The rotation of the satellites 32 drives in rotation either the satellite carrier 33 or the crown 5,so as to rotate the fan S via the fan shaft 1s. The rotating satellites 32 transmit an axial force to the crown 35 which is directed towards the outside of the mechanical reducer. The crown 35 in turn transmits a torque to the crown carrier 36 in the first direction D1 around the first axis A. In this first direction D1 (illustrated by double arrows in the figures) of torque transmission, the first bearing and ramp faces B10, B12 are, on the one hand, in circumferential support respectively with the corresponding secondary bearing and ramp faces B20, B22, and on the other hand, the primary and secondary flanges B1, B2 are axially tightened by screws 72, 74. This maintains the connection between the primary and secondary flanges B1, B2 in a robust manner. The first and second bearing faces B10, B20 allow the torque transmitted by the crown 35 to be taken up. Figures 11b and 12b schematically represent theabnormal operation of the mechanical reducer 3, and in particular the forces exerted on each of the components of the mechanical reducer. For example, in the event of failure of the satellite bearing(s) 34, the direction of transmission of the torque by the crown 35 to the crown carrier 36 is reversed. Thus, the crown 35 transmits a torque to the crown carrier 36 in the second direction D2 around the first axis A. This second direction D2 (illustrated by double arrows in FIG. 11b and 12b) of torque transmission can generate additional forces (illustrated by dotted arrows in FIG. 11b) on the first and second ramp faces B12, B22 which causes tensile forces on the first and / or second screws 72, 74. These tensile forces when they are greater than the predetermined threshold (for example a failure of the satellite bearing), cause the axial separation of the ramp faces B12, B22 from each other and also a breakage ofthese screws 72, 74, so as to break the connection between the primary and secondary flanges B1, B2. This makes it possible to separate the connection between the primary and secondary flanges B1, B2 (for example the half-rings 35a, 35b, the ring 35, 35a, 35b and the ring carrier 36 and / or between the ring carrier 36 and the other element E). The rotation of the satellite(s) having the fault remains blocked. In this way, the solar 31 makes it possible to directly drive the planet carrier 33 or the ring 35 in rotation through the blocked satellite(s) 32, to rotate the fan S (via the fan shaft 1s).

Claims

CLAIMS 1. Mechanical reducer (3) for a turbomachine (1), in particular for an aircraft, this reducer comprising: - a sun gear (31) having a first axis of rotation (A), - a ring gear (35) which extends around the sun gear and said first axis (A), the ring gear comprising two annular half-rings which are fixed to each other respectively by first and second annular flanges (35ab, 35ba), - satellites (32) which are arranged around the first axis (A), between the sun gear and the ring gear, and which are meshed with the sun gear (31) and the ring gear (35), these satellites (32) each having a second axis (B) of rotation parallel to the first axis (A) and being held by a planet carrier (33) movable in rotation around said first axis (A), - a ring gear carrier (36) having a generally annular shape around the first axis (A), the ring gear carrier (36) comprising a third annular fixing flange (362) to the first and second flanges (35ab, 35ba),and a fourth annular fixing flange (364) to a fifth annular flange (E0) of another annular element extending around the first axis (A), said first, second and third flanges (35ab, 35ba, 362) being axially clamped against each other by first screws (72) parallel to the first axis (A), and said fourth (364) and fifth (E0) flanges being axially clamped against each other by second screws (74) parallel to the first axis, characterized in that one of the flanges, called primary flange (B1), among the first, second and third flanges (35ab, 35ba, 362), or among the fourth and fifth flanges (362, E0), comprises first bearing faces (B10) which are distributed around the first axis (A) and first ramp faces (B12) which are distributed around the first axis (HAS),the first bearing faces (B10) being configured to cooperate by bearing in a tangential direction with corresponding second bearing faces (B20) of another of said flanges, called secondary flange (B2), which is in axial bearing against the primary flange (B1), so as to transmit a torque transmitted by the crown (35) in a first direction (D1) around the first axis (A), and the first ramp faces (B12) being configured to cooperate with second ramp faces (B22) of said secondary flange (B2) so that a, torque transmitted by the crown (35) in a second direction (D2) around the first axis (A), opposite to the first direction (D1), causes an axial separation of the flanges (B1, B2) from each other and a tensile force on the first and / or second screws (72, 74) which are configured to break when this tensile force is greater than a predetermined threshold.

2. Reducer according to claim 1, characterized in that the primary flange (B1) comprises an annular row of first axial teeth (T1) which are axially engaged between second axial teeth (T2) of the secondary flange (B2), to form a dog connection (L1, L2, L3) between the primary and secondary flanges (B1, B2).

3. Reducer according to claim 2, characterized in that the first and second axial teeth (T1, T2) of each of the primary and secondary flanges (B1, B2) are regularly distributed around said first axis (A). 4.Reducer according to claim 2 or 3, characterized in that the first and second axial teeth (T1, T2) of each of the primary and secondary flanges (B1, B2) are identical.

5. Reducer according to any one of claims 2 to 4, characterized in that the first and second axial teeth (T1, T2) of each of the primary and secondary flanges (B1, B2) respectively comprise said first and second bearing faces (B10, B20) on a first side, and said first and second ramp faces (B12, B22) on a second side, opposite the first side.

6. Reducer according to any one of claims 1 to 5, characterized in that each of the primary and secondary flanges (B1, B2) comprises a number of teeth between 25 and 50.

7. Reducer according to any one of claims 2 to 6, characterized in that the first and second axial teeth (T1, T2) each have a generally parallelepiped shape.

8. Reducer according to any one of claims 2 to 7, characterized in that the first axial teeth (T1) of the primary flange (B1), respectively of the secondary flange (B2), each comprise a radial face (B14, B24) perpendicular to said first axis (A) and extending between the bearing face (B10, B20) and the ramp face (B12, B22) of this first tooth (T1), this radial face (B14, B24) being configured to bear axially between the second axial teeth (T2) of the secondary flange (B2), respectively of the primary flange (B1).

9. Reducer according to any one of claims 2 to 8, characterized in that the first (72) and / or second (74) screws pass through first orifices (B18) formed in the first teeth (T1) of the primary flange (B1), respectively of the secondary flange (B2), and second orifices (B28) formed between the second teeth (T2) of the secondary flange (B2), respectively of the primary flange (B1). 10.Reducer according to any one of the preceding claims, characterized in that each of the first and second ramp faces (B12, B22) has an angle of inclination (αB12, αB22) relative to a plane passing through said first axis (A), which is between 5° and 75°.

11. Reducer according to any one of claims 2 to 10, characterized in that the first and second axial teeth (T1, T2) each have an angular extent (βT1, βT2) around the first axis (A) which is between 5° and 10°.

12. Reducer according to any one of the preceding claims, characterized in that said first bearing faces (B10) are located in planes passing through the first axis (A).

13. Turbomachine, in particular for an aircraft, comprising a mechanical reducer according to any one of the preceding claims.

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