MECHANICAL REDUCTION GEARBOX FOR TURBO ENGINE OF AN AIRCRAFT

Description

Technical field of the invention

[0001] The present invention relates to the field of mechanical reducers for turbomachines, particularly aircraft, and in particular reducers equipped with double-stage meshing satellites. Technical background

[0002] The state of the art includes in particular documents WO-A1-2010 / 092263, FR-A1-2 987 416, FR-A1-3 011 901, FR-A1-3 041 054, FR-A1-3 058 493, US-A1-2017 / 122407 and US-A1-2010 / 292043.

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

[0004] New generations of dual-flow turbomachines, particularly those with a high bypass ratio, include a mechanical reducer to drive the shaft of a fan. Typically, the reducer's purpose is to transform the so-called fast rotation speed of a power turbine shaft into a slower rotation speed for the shaft driving the fan.

[0005] Such a reducer comprises a central pinion, called a sun gear, a crown gear and pinions called planet gears, which are meshed between the sun gear and the crown gear. The planet gears are held by a frame called a planet carrier. The sun gear, the crown gear and the planet carrier are planet gears because their axes of revolution coincide with the longitudinal axis X of the turbomachine. The planet 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.

[0006] There are several gearbox architectures. In the state of the art of double-flow turbomachinery, gearboxes are of the planetary or epicyclic type. In other similar applications, there are so-called differential or "compound" architectures. In a planetary gearbox, the planet carrier is fixed, and the ring gear forms the output shaft of the device, rotating in the opposite direction to the sun gear. In an epicyclic gearbox, the ring gear is fixed, and the planet carrier forms the output shaft of the device, rotating in the same direction as the sun gear. In a differential gearbox, no element is fixed for rotation. The ring gear rotates in the opposite direction to both the sun gear and the planet carrier.

[0007] Gearboxes can consist of one or more meshing stages. This meshing is achieved in various ways, such as by contact, friction, or magnetic fields.

[0008] In this application, the term "stage" or "teeth" means a series of teeth meshing with a series of complementary teeth. A toothing may be internal or external.

[0009] A satellite can have one or two gear stages. A single-stage satellite has teeth that can be straight, helical, or chevron-shaped, with teeth on the same diameter. These teeth cooperate with both the sun gear and the crown gear.

[0010] A two-stage satellite comprises two sets of teeth or two series of teeth located on different diameters. One set of teeth cooperates with the sun gear and a second set of teeth cooperates with the crown gear.

[0011] One of the problems with a mechanical gearbox concerns the risk of misalignment of the planet gears. This problem is amplified in the case of double-stage planet gears because the load transfers in the ring gear and the planet carrier are more complex due to the fact that the gear teeth are located in two different planes perpendicular to the axis of the planet carrier.

[0012] The crown is subjected to forces in the radial and axial directions which can be significant and which must be limited to avoid crown displacements when using the reducer.

[0013] There is therefore a need to improve the transmission of forces undergone by a crown in a mechanical reducer equipped with double-stage meshing satellites. Summary of the invention

[0014] The invention relates to a mechanical reducer for a turbomachine, in particular an aircraft, this reducer comprising: a sun gear having an axis of rotation and comprising external teeth, a crown which extends around the sun gear and which comprises internal teeth, the crown gear being surrounded by a crown carrier which is intended to be immobile in rotation around the axis in use, satellites which are meshed with the sun gear and the crown gear and which each comprise a first toothing of average diameter D2 meshed with the toothing of the sun gear, and a second toothing of average diameter D1, different from D2, meshed with the internal toothing of the crown gear, the satellites being held by a planet carrier which is intended to be mobile in rotation around the axis in use, the crown carrier comprising an annular axial stop on which the crown is configured to bear, and the crown comprising helical external splines which are engaged in complementary internal splines of the crown carrier and which are configured to cooperate by sliding with these internal splines so as to force the crown to be held against the stop in operation.

[0015] The gearbox according to the invention is thus designed to handle the torque and axial forces to which the ring gear is subjected during operation. Due to the presence of splines, the ring gear is able to move axially during operation. Thanks to the orientation of the helical splines, which depends on the direction of rotation of the planet gears around the axis, this movement is directed towards the thrust bearing so that the ring gear is forced to bear against this bearing and thus maintain this axial position during operation. The ring gear is therefore axially immobilized against this bearing due to the interaction of the splines. The torque and axial forces acting on the ring gear are thus transmitted via this bearing to the ring carrier, which can in turn transmit them to a stator of the turbomachine.

[0016] This invention is compatible: of a double-stage reducer, of a so-called epicyclic reducer, i.e. one whose crown is fixed in the motor reference frame, of straight or helical teeth, of any type of planet carrier whether monobloc or cage and cage carrier type, of any type of satellite bearing, whether it is composed of rolling elements, of a hydrodynamic bearing, etc.

[0017] The reducer according to the invention may comprise one or more of the following features, taken individually or in combination with each other: the crown carrier comprises a bearing support mounted on a shaft portion of the planet carrier, the bearing support receiving a bearing for guiding the rotation of the shaft portion of the planet carrier; the stop and the shaft portion are located on the same side relative to the planets; the crown carrier comprises a cylindrical wall comprising said internal grooves and a frustoconical wall whose larger diameter end is connected to this cylindrical wall, said stop being located in a connection zone of the frustoconical and cylindrical walls; -- the rolling bearing is located at the smaller diameter end of the crown carrier; the cylindrical wall is connected to an annular rim extending radially outwards and forming a fixing flange;the annular rim extends in a plane perpendicular to said axis which passes substantially through the middle of the crown and through the middle of a bearing, for example a roller bearing, mounted between the planet carrier and the solar array; the stop is formed by an annular boss radially internal to the crown carrier; the boss includes a radial bearing face for the crown; the radial face is connected to the internal splines of the crown carrier by an annular groove; the radial face is covered with a protective coating or is intended to cooperate with a protective coating located on the crown; the crown carrier includes an oil film compression damper which surrounds at least part of said crown; on the side opposite the stop, the crown is held axially vis-à-vis the crown carrier by means of a split locking ring which is engaged in an annular groove radially internal to the crown carrier;The groove and the ring are located at the level of a free axial end of the crown holder, and in particular of its cylindrical wall; the internal grooves of the crown holder and the external grooves of the crown extend over the entire axial dimension of the crown.

[0018] The present invention also relates to an aircraft turbomachine, comprising a reducer as described above. Brief description of the figures

[0019] 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: [ Fig. 1 ] there figure 1 is a schematic axial cross-sectional view of an aircraft turbomachine, [ Fig. 2 ] there figure 2 is a partial axial view of a mechanical reducer, [ Fig.3 ] there figure 3is a schematic axial cross-sectional view of a mechanical reducer equipped with double-stage meshing satellites, and illustrates the prior art of the invention, [ Fig. 4 ] there figure 4 is a schematic perspective view of the planet carrier of the gearbox of the figure 3 , [ Fig.5 ] there Figure 5 is a schematic axial cross-sectional view of a mechanical reducer equipped with double-stage meshing satellites, and illustrates one embodiment of the invention, [ Fig.6 ] there figure 6 is a larger-scale schematic view of part of the Figure 5 , And [ Fig.7 ] there figure 7 is a partial schematic perspective view of the reducer of the Figure 5 . Detailed description of the invention

[0020] There figure 1This describes a turbomachine 1 which conventionally comprises a rotation shaft X, 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) unit. 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) unit.

[0021] The blower S is driven by a blower shaft 4 which is driven to the LP shaft 3 by means of a reducer 6. This reducer 6 is generally of the planetary or epicyclic type.

[0022] The following description concerns a planetary type reducer in which the crown is rotatable.

[0023] The reducer 6 is positioned in the upstream part of the turbomachine. A fixed structure comprising schematically, here, an upstream part 5a and a downstream part 5b which composes the motor casing or stator 5 is arranged so as to form an enclosure E surrounding the reducer 6. This enclosure E is here closed upstream by seals at the level of a bearing allowing the fan shaft 4 to pass through, and downstream by seals at the level of the passage of the LP shaft 3.

[0024] There figure 2shows a reducer 6 which can take the form of different architectures depending on whether certain parts are fixed or rotating. At the input, the reducer 6 is connected to the LP shaft 3, for example via internal splines 7a. Thus the LP shaft 3 drives a planetary pinion called the sun gear 7. Conventionally, the sun gear 7, whose axis of rotation is the same as that of the turbomachine X, drives a series of pinions called satellites 8, which are equally distributed over the same diameter around the axis of rotation X. This diameter is equal to twice the operating center distance between the sun gear 7 and the satellites 8. The number of satellites 8 is generally defined between three and seven for this type of application.

[0025] All of the satellites 8 are held by a frame called a planet carrier 10. Each satellite 8 rotates around its own Y axis, and meshes with the crown 9. ▪ In this planetary configuration, the set of satellites 8 is held by a satellite carrier 10 which is fixed to the motor housing or stator 5. Each satellite drives the ring which is brought to the blower shaft 4 via a ring carrier 12.

[0026] Each satellite 8 is mounted to rotate freely using a bearing 11, for example, a roller bearing or hydrodynamic bearing. Each bearing 11 is mounted on one of the axes 10b of the satellite carrier 10, and all the axes are positioned relative to each other using one or more structural frames 10a of the satellite carrier 10. There is a number of axes 10b and bearings 11 equal to the number of satellites. For operational, assembly, manufacturing, inspection, repair, or replacement purposes, the axes 10b and the frame 10a may be separated into several parts.

[0027] For the same reasons mentioned above, the teeth of a gearbox can be separated into several helices, each with a median plane P. In the example shown, the ring gear is separated into two half-ring gears: ▪ An upstream half-crown 9a consisting of a rim 9aa and a mounting flange half 9ab. The upstream helix of the reduction gear teeth is located on the rim 9aa. This upstream helix meshes with that of the satellite gear 8, which meshes with that of the solar gear 7. ▪ A downstream half-crown 9b consisting of a rim 9ba and a mounting flange half 9bb. The downstream helix of the reduction gear teeth is located on the rim 9ba. This downstream helix meshes with that of the satellite gear 8, which meshes with that of the solar gear 7.

[0028] The half-clamp 9ab of the upstream crown 9a and the half-clamp 9bb of the downstream crown 9b form the crown mounting flange 9c. The crown 9 is fixed to a crown carrier by assembling the crown mounting flange 9c and the crown carrier mounting flange 12a using a bolted assembly for example.

[0029] The arrows of the figure 2describe the routing of the oil in the reducer 6. The oil arrives in the reducer 6 from the stator part 5 in a distributor 13 by different means which will not be specified in this view because they are specific to one or more types of architecture. The distributor is separated into 2 parts, generally each repeated by the same number of satellites. The injectors 13a have the function of lubricating the teeth and the arms 13b have the function of lubricating the bearings. The oil is brought to the injector 13a to exit through the end 13c in order to lubricate the teeth. The oil is also brought to the arm 13b and circulates via the supply mouth 13d of the bearing. The oil then circulates through the axis in one or more buffer zones 10c to then exit through the orifices 10d in order to lubricate the bearings of the satellites.

[0030] THE figures 3 And 4represent a 6-speed gearbox for an aircraft turbomachine according to prior art.

[0031] The reducer 6 includes a planet carrier 10 which is configured to be mobile in rotation around the X axis and which is of the monobloc type, i.e. formed from a single piece.

[0032] This satellite carrier 10 includes a cage 14 and a shaft portion 15.

[0033] The portion of the shaft 15 has a general tubular shape and is elongated along the X axis and includes a free longitudinal end, here on the left in the drawings, and an opposite longitudinal end for connection to the cage 14.

[0034] The shaft portion 15 includes an external gear 15a for meshing, for example with a blower.

[0035] The cage 14 has two annular flanges 14a, 14b which are parallel and spaced apart and extend perpendicularly to the X axis. The flanges 14a, 14b have a general circular shape and are centered on the X axis.

[0036] The flange 14a, called the first flange, on the left in the drawing, is connected to the shaft portion 15. The other flange 14b is called the second flange.

[0037] The flanges 14a, 14b are connected to each other by material bridges 16 which define, both between themselves and with the flanges, housings 18 configured to receive the satellites 8. The housings 18 open radially outwards at the outer periphery of the cage 14, and also radially inwards by passing through an internal tubular wall 20 of the cage 14. The material bridges 16 may be solid or partially hollow, as illustrated in the Figure 5 .

[0038] The wall 20 extends around the X axis, from the first flange 14a towards the second flange 14b. Here it extends substantially in the axial continuation of the portion of shaft 15. This wall 20 internally delimits a space 22 for housing the solar element 7.

[0039] This space 22 comprises two adjacent parts. The first part 22a is surrounded by the wall 20 which includes an internal cylindrical surface 22a for mounting a bearing 23 for guiding one end of the solar element 7. The second part 22b, located at the openings of the housings 18, receives the opposite end of the solar element 7, which includes an external toothed gear 7b for meshing with the satellites 8. The solar element 7 further includes an internal toothed gear 7a for coupling to a shaft, for example, of a turbine.

[0040] Each housing unit 18 comprises a first part 18a, located on the side of the first flange 14a, and a second part 18b, located on the side of the second flange 14b. Housing units 18 open onto the outer periphery of shaft 14, at the level of its two parts 18a and 18b, and onto the inner periphery of shaft 14, at the level of the second part 18b only.

[0041] The flanges 14a, 14b comprise aligned holes or orifices 24 for mounting the satellites 8 and in particular the plain bearings 26 of these satellites 8. Each bearing 26 has a generally cylindrical shape which extends parallel to the axis X and the longitudinal ends of which comprise extensions 26a housed in the orifices 24 forming seats.

[0042] As is known, each bearing 26 may include an internal oil circulation bore 26b which generally communicates with oil supply channels to the external cylindrical surface 26c of the bearing for the purpose of forming an oil film on this surface 26c.

[0043] The satellites 8 are of the double-stage meshing type, as mentioned above, and each comprise a tubular body 8a equipped with a first external toothing 28 and connected by a web 30 to a second external toothing 32.

[0044] The teeth 28, 32 are arranged next to each other and more particularly are located respectively in two planes perpendicular to the X axis.

[0045] The first tooth 28, located on the left in the drawings, is situated on the side of the first flange 14a and therefore at the level of the first part 18a of the housing. As can be seen in the figure 3 , this toothing 28 is meshed with the crown 9.

[0046] The second toothing 32, located on the right in the drawings, is situated on the side of the second flange 14b and therefore at the level of the second part 18b of the housing. As can be seen in the figure 3 , this toothing 32 is meshed with the toothing 7b of the solar 7.

[0047] As seen in the figure 3 , the material bridges 16 extend radially, between the housings 18, from the wall 20 and the inner periphery of the flanges 14a, 14b to the outer periphery of the flanges.

[0048] Crown number 9 is carried by a crown bearer who is not shown in the drawings.

[0049] The invention proposes a solution to guarantee the recovery of the torque and axial forces to which the crown 9 is subjected in operation, by the crown carrier.

[0050] THE figures 5 to 7illustrate a preferred embodiment of a reducer 6 according to the invention. This reducer 6 comprises all the features described above in relation to the figures 3 And 4 to the extent that they do not contradict or conflict with what follows.

[0051] The references used in the figures 5 to 7 and already used in the figures 4 And 5 therefore designate identical or similar elements.

[0052] The solar 7 is similar to that described above and is centered and guided in rotation in the satellite carrier 10 by means of a bearing 23 which here comprises two rings 23a, 23b between which are arranged two adjacent rows of balls 23c.

[0053] The inner ring 23a is mounted on an axial end of the solar 7 and its outer ring 23b is mounted in the inner wall 20 of the satellite carrier 10.

[0054] The planet carrier 10 is itself centered and guided in rotation in a crown carrier 34 by means of a bearing 36 which may be a rolling bearing and which comprises, for example, rollers. The bearing 36 is located on the shaft portion 15 of the planet carrier 10, for example substantially in its middle.

[0055] The bearing 36 may comprise an inner ring mounted on the shaft portion 15 or directly integrated therein. Similarly, the outer ring of the bearing 36 may be mounted in the crown carrier 34 or integrated therein.

[0056] In the example shown, the crown carrier 34 has a generally annular shape around the axis X, and extends axially around a part of the shaft portion 15 and around the crown 9.

[0057] The crown carrier 34 essentially comprises two axial parts, namely an upstream frustoconical part 34a and a downstream cylindrical part 34b.

[0058] The truncated cone-shaped portion 34a is flared downstream and its upstream end of smaller diameter extends around the bearing 36 in order to support it. It is thus understood that the crown carrier 34 has a function of supporting the bearing 36.

[0059] The cylindrical part 34b has an average diameter D3 measured relative to the X axis. D1 is the average diameter of the toothing 28 and D2 is the average diameter of the toothing 32. D1 is less than D2 in the example shown, D1 and D2 being measured relative to the Y axis of the satellites 8.

[0060] The cylindrical portion 34b comprises an annular rim 38 extending radially outwards and forming an annular flange for fixing the crown carrier 34 to a stator of the turbomachine. This rim 38 comprises, for example, an annular row of orifices (not shown) which each have an axial orientation and which are configured to receive fixing screws.

[0061] At the junction between the frustoconical part 34a and the cylindrical part 34b, the crown carrier 34 includes an annular stop 40 that extends radially inwards. This stop 40 is in the form of a projecting annular boss. This stop 40 is located at an axial end, here the upstream end, of the crown 9 and extends axially opposite this crown so that the crown can bear against the stop 40.

[0062] The stop 40 comprises a downstream radial face 40a for supporting the upstream end of the crown 9 ( figure 6). In the example shown, the stop 40 has a generally triangular axial section shape and therefore comprises a face 40b on the upstream side which is inclined and flared from downstream to upstream towards the outside. The cylindrical part 34b of the crown carrier 34 comprises internal splines 42 in which are engaged external splines 44 complementary to the crown 9. In the example shown, the external splines 44 of the crown 9 extend over the entire axial dimension of the crown 9, like its internal toothing 9d, and the internal splines 42 of the cylindrical part 34b extend over at least 80% of the axial dimension of this part.

[0063] The internal grooves 42 are connected to the face 40a of the stop 40 by an annular groove 46 formed in the crown carrier 34, at the base or at the external periphery of the stop 40. This groove 46 can be oriented radially and open radially inwards, or be inclined and open radially inwards, being oriented from upstream to downstream inwards, as in the example shown in figure 6 .

[0064] According to the invention, more clearly visible at the figure 7 , the grooves 42, 44 are helical and are able to slide one inside the other in the axial direction. It is understood that this movement is similar to that of screwing due to the helical shapes of the grooves.

[0065] The winding direction of the helices in the splines 42 and 44 is important and depends on the direction of rotation of the satellites 8 around their axes. Indeed, the splines 42 and 44 must be configured so that, during operation, the ring 9 is axially driven upstream and can therefore be held against the stop 40. Choosing the winding direction of the splines 42 and 44 based on the direction of rotation of the satellites 8 is within the capabilities of someone skilled in the art.

[0066] In the particular example shown in the figure 7 The solar array 7 rotates around the X-axis in the direction of arrow F1. It drives the satellites 8 around the Y-axes in the direction of arrows F2, which in turn drive the satellite carrier 10 around the X-axis in the direction of arrow F3. Thanks to its helical grooves 44, the ring 9 is axially stressed in the direction of arrows F4.

[0067] To prevent wear on the stop 40 or the ring 9 (for example, wear of the type fretting ), it is possible to cover its face 40a with a protective coating. This coating can be a hard material, i.e. harder than the material of the stop 40, or an anti-friction material.

[0068] Alternatively, this coating could be located on the ring 9, for example at its upstream end, and cooperate with the face 40a of the stop 40.

[0069] In an unrepresented variant, an oil film compression damper could be fitted to the crown carrier 34 and preferably mounted around the crown 9. This damper would have the function of damping the vibrations to which the crown 9 would be subjected during operation.

[0070] On the opposite side to the stop 40, i.e. downstream in the example shown, the crown 9 is held axially vis-à-vis the crown carrier 34 by means of a split locking ring 50, more clearly visible in Fig. 6. The ring 50 is engaged in an annular groove 52 radially internal to the crown carrier 34, which is here formed at the free downstream end of the crown carrier 34.

Claims

1. A mechanical reduction gear (6) of a turbomachine (1), in particular of an aircraft, this reduction gear comprising: - a sun gear (7) having an axis (X) of rotation and comprising an external toothing (7a), - a ring gear (9) which extends around the sun gear (7) and which comprises an internal toothing (9d), the ring gear (9) being surrounded by a ring gear carrier (34) which is intended to be immobile in rotation about the axis (X) in use, - planet gears (8) which are in mesh with the sun gear (7) and the ring gear (9) and which each comprise a first toothing (32) of mean diameter D2 meshed with the toothing (7a) of the sun gear (7), and a second toothing (28) of mean diameter D1, different from D2, meshed with the internal toothing (9d) of the ring gear (9), the planet gears (8) being held by a planet carrier (10) which is intended to be movable in rotation about the axis (X) in use, the ring gear carrier (34) comprising an annular axial abutment (40) on which the ring gear (9) is configured to bear, and the ring gear (9) comprising external splines (44) which are engaged in complementary internal splines (42) of the ring gear carrier (34), characterized in that said external splines are helical and configured to co-operate by sliding with these internal splines (42) so as to force the ring gear (9) to be held against the abutment (40) during operation.

2. The reduction gear (6) according to claim 1, wherein the ring gear carrier (34) comprises a bearing support (36) mounted on a shaft portion (15) of the planet carrier (10), the bearing support (36) receiving a bearing for rotationally guiding the shaft portion (15) of the planet carrier (10).

3. The reduction gear (6) according to claim 2, wherein the abutment (40) and the shaft portion (15) are located on the same side with respect to the planet gears (8).

4. The reduction gear (6) according to one of the preceding claims, wherein the ring gear carrier (34) comprises a cylindrical wall (34b) comprising said internal splines (44) and a frustoconical wall (34a) whose larger diameter end is connected to this cylindrical wall (34b), said abutment (40) being located in a connecting zone of the frustoconical (34a) and cylindrical (34b) walls.

5. The reduction gear (6) according to the preceding claim, wherein the cylindrical wall (34b) is connected to an annular edge (38) extending radially outwards and forming a fixing flange.

6. The reduction gear (6) according to the preceding claim, wherein the annular edge (38) extends in a plane perpendicular to said axis (X) and which passes substantially through the centre of the ring gear (9) and through the centre of a bearing (23) mounted between the planet carrier (10) and the sun gear (7).

7. The reduction gear (6) according to one of the preceding claims, wherein the abutment (40) is formed by a radially inner annular boss of the ring gear carrier (34).

8. The reduction gear (6) according to one of the preceding claims, wherein the boss comprises a radial face (40a) for supporting the ring gear (9), this radial face (40a) being connected to the internal splines (42) of the ring gear carrier (34) by an annular groove (46).

9. The reduction gear (6) according to the preceding claim, wherein the radial face (40a) is covered with a protective coating or is intended to cooperate with a protective coating located on the ring gear (9).

10. The reduction gear (6) according to one of the preceding claims, wherein, on the side opposite the abutment (40), the ring gear (9) is held axially opposite the ring gear carrier (34) by means of a split locking ring (50) which is engaged in a radially inner annular groove (52) of the ring gear carrier (34).

11. The reduction gear (6) according to the preceding claim, wherein the groove (52) and the ring (50) are located at a free axial end of the ring gear carrier, and in particular its cylindrical wall (34b).

12. The reduction gear (6) according to any of the preceding claims, wherein the ring gear carrier (34) comprises an oil film compression damper which at least partially surrounds said ring gear (9).

13. The reduction gear (6) according to any of the preceding claims, wherein the internal splines (42) of the ring gear carrier (34) and the external splines (44) of the ring gear (9) extend over the entire axial dimension of the ring gear (9).

14. An aircraft turbomachine (1) comprising a reduction gear (6) according to one of the preceding claims.