KRONE FOR AN AIRCRAFT MECHANICAL REDUCTION GEARBOX

Description

Technical field of the invention

[0001] The present invention relates to a crown for an aircraft mechanical reducer, and in particular for an aircraft turbomachine or for a drive system for a wheel of an aircraft landing gear. Technical background

[0002] The state of the art includes in particular documents FR-A1-3 025 780, FR-B1-3 066 792, FR-B1-3 071 023, FR-3 072 749, FR-B1-3 098 562, FR-B1-3 101 129 and WO-A1-2019 / 007915.

[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] A system for driving a wheel of a landing gear may further comprise a mechanical reducer, as proposed by the Applicant in document EP-A1-3 882 136.

[0006] 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 axis of the turbomachine or the wheel of a landing gear. The planet gears each have a different axis of revolution equally distributed over the same operating diameter around the axis of the planet gears. These axes are parallel to the longitudinal axis X.

[0007] There are several gearbox architectures. In the state of the art, gearboxes are planetary or epicyclic. In other similar applications, there are so-called differential or "compound" architectures. On a planetary gearbox, the planet carrier is fixed and the ring gear is 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 is 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.

[0008] Gearboxes can be composed of one or more meshing stages. This meshing is ensured in different ways such as by contact, friction or even magnetic fields. There are several types of contact meshing such as straight, helical or herringbone teeth.

[0009] Gearboxes can be composed of one or more meshing stages. This meshing is ensured in different ways such as by contact, friction or even magnetic fields.

[0010] A satellite may comprise one or two meshing stages. In this application, the term "stage" or "toothing" means a series of meshing teeth with a series of complementary teeth. A toothing may be internal or external. A single-stage satellite comprises a toothing which may be straight, helical or herringbone and whose teeth are located on the same diameter. This toothing cooperates with both the sun gear and the crown.

[0011] A double-stage satellite consists of two sets of teeth or two sets of teeth that are located on different diameters. One set of teeth cooperates with the sun gear and a second set of teeth cooperates with the crown gear.

[0012] There is also a configuration, called Wolfrom, in which the satellites are double-stage and have a first toothing that cooperates with the sun and a crown, and a second toothing that cooperates with a second crown. The reducer thus comprises two crowns, one of which is fixed and the other mobile.

[0013] In order to add flexibility to a reducer, a classic solution is to fix the fixed crown of the reducer by means of a crown holder having a "bellows" shape, as described by patent FR-B1-3 072 749. This solution is however difficult to integrate into a restricted space.

[0014] Other solutions have been developed to allow the crown to absorb vibrations and consist of integrating springs or elastomer pads into the crown. However, these solutions do not allow the meshing forces to be correctly supported without causing significant deformation in the crown teeth. Furthermore, the low stiffness of the pads does not allow their use in applications involving high power.

[0015] Document WO-A1-2019 / 007915 describes a crown whose flange includes radial notches for oil passage. These notches have no effect on the flexibility of the crown.

[0016] The invention makes it possible to provide a solution to at least some of these problems, in a simple, effective and economical manner. Summary of the invention

[0017] The invention relates to a crown for an aircraft mechanical reducer, this crown having an annular shape around an axis and comprising: an internal toothing at its internal periphery, an external annular flange or splines at its external periphery, and an annular web extending between the internal toothing and the external flange or splines, characterized in that the web comprises an annular row of arms which are distributed around said axis, these arms connecting the internal teeth to the external flange or splines and being formed in a single piece with the internal teeth and the external flange or splines.

[0018] The invention makes it possible to provide flexibility in the crown and therefore in the reducer, while maintaining a limited footprint. This is made possible by integrating this flexibility in the crown web, between its teeth and its flange or its splines. This flexibility is generated by the arms which are similar to spokes of a bicycle wheel for example. These arms make it possible to absorb the meshing forces by working in tension or compression, while allowing flexibility in the radial direction by working in bending.

[0019] The solution proposed below is compatible with a single-stage or multi-stage reducer. It is compatible with a so-called epicyclic, planetary, differential or Wolfrom type reducer. It is also compatible with straight, helical or chevron teeth. It is compatible with any type of planet carrier, and in particular with a single-piece planet carrier. It is also compatible with any type of bearing, whether it is composed of rolling elements, a hydrodynamic bearing, etc. It is compatible with the use of the crown and the reducer in a double-flow turbomachine, for example for driving a fan or a propeller. It is also compatible with the use of the crown and the reducer in a system for driving a wheel of a landing gear.

[0020] The crown according to the invention may comprise one or more of the following characteristics, taken in isolation from one another, or in combination with one another: the arms are separated from each other by spaces, or delimit spaces between them; each or at least part of said spaces has a general parallelepiped, trapezoidal, triangular, or diamond shape; said spaces are formed by circular or oblong orifices; the veil comprises a first annular row of orifices located on a first circumference, and a second annular row of orifices located on a second circumference whose diameter is greater than that of the first circumference, the orifices of the first row being located circumferentially between the orifices of the second row; said spaces are empty, that is to say passing axially through; said spaces are filled by blocks made of a material different from the main material of the crown, and for example of polymer;the arms are inclined obliquely with respect to a radial direction and have an inclination orientation in the same circumferential direction; the arms are all oriented in the same way; a first series of arms is oriented in a first way, and a second series of arms is oriented in a second way, different from the first way; the arms of the first series are intersected with the arms of the second series; the arms are all inclined with respect to radii to said axis; the arms are all located in the same plane perpendicular to said axis; the number of arms is greater than 2, for example greater than 5 or 10, preferably greater than 20, and more preferably between 20 and 100; this number depends for example on the diameter of the crown. ;

[0021] The present invention also relates to a mechanical reducer for an aircraft, this reducer comprising: a mobile sun rotating about an axis, a crown as described above, mounted around the sun and said axis, and satellites mounted between the sun and the crown and meshed with the sun and the crown, these satellites having axes of rotation parallel to said axis.

[0022] The invention further relates to a turbomachine or a system for driving a landing gear wheel, in particular an aircraft wheel, comprising at least one crown or mechanical reducer as described above. Brief description of the figures

[0023] Other characteristics and advantages will emerge from the following description of a non-limiting embodiment of the invention with reference to the appended drawings in which: [ Fig. 1 ] there figure 1 is a schematic axial sectional view of an aircraft turbomachine, [ Fig. 2 ] there figure 2is a partial schematic view in axial section of a mechanical reducer, [ Fig. 3 ] there figure 3 is a schematic front view of a crown according to a first embodiment of the invention, [ Fig. 4 ] there figure 4 is another schematic perspective view of the crown of the figure 3 , [ Fig. 5 ] there Figure 5 is a partial schematic perspective view of the crown of the figure 3 , [ Fig. 6 ] there figure 6 is a view similar to that of the Figure 5 and illustrates an alternative embodiment of the invention, [ Fig. 7 ] there figure 7 is a view similar to that of the Figure 5 and illustrates another alternative embodiment of the invention, [ Fig. 8 ] there figure 8 is a view similar to that of the Figure 5 and illustrates another alternative embodiment of the invention, [ Fig. 9 ] there figure 9 is a view similar to that of the Figure 5and illustrates another alternative embodiment of the invention, [ Fig. 10 ] there figure 10 is a schematic perspective view of a wheel of an aircraft landing gear and a drive system for this wheel. Detailed description of the invention

[0024] There figure 1 describes a turbomachine 1 which comprises, in a conventional manner, a fan S, a low-pressure compressor 1a, a high-pressure compressor 1b, an annular combustion chamber 1c, a high-pressure turbine 1d, a low-pressure turbine 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 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 3 and form with it a low-pressure (LP) body.

[0025] The blower S is driven by a blower shaft 4 which is rotated with the LP shaft 3 by means of a reducer 6. This reducer 6 is generally of the planetary or epicyclic type.

[0026] Although the following description concerns a planetary or epicyclic type reducer, it also applies to a mechanical differential in which the three components, namely the planet carrier, the crown wheel and the sun gear, are mobile in rotation, the rotation speed of one of these components depending in particular on the difference in speeds of the other two components. It also applies to the particular case of a double-stage reducer of the Wolfrom type.

[0027] 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.

[0028] 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 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.

[0029] The set of satellites 8 is held by a satellite carrier 10. Each satellite 8 rotates around its own Y axis, and meshes with the crown 9.

[0030] At the output we have: ▪ in an epicyclic configuration, the set of planet gears 8 rotates the planet carrier 10 around the axis X of the turbomachine. The ring gear is fixed to the engine casing or stator 5 via a ring gear carrier 12 and the planet carrier 10 is fixed to the fan shaft 4. ▪ in a planetary configuration, the set of planet gears 8 is held by a planet carrier 10 which is fixed to the engine casing or stator 5. Each planet gear drives the ring gear which is attached to the fan shaft 4 via a ring gear carrier 12.

[0031] Each satellite 8 is mounted to rotate freely using a bearing 11, for example of the rolling bearing or hydrodynamic plain bearing type. In the case of a plain bearing, the bearing 11 comprises a bearing body 10b and the bearing bodies 10b of the different plain bearings are positioned relative to each other and are carried by walls 10a1, 10a2 of the planet carrier 10.

[0032] The walls 10a1, 10a2 have an annular shape and are perpendicular to the X axis. They are axially spaced from each other and receive between them the bearings 11, the satellites 8 and the solar 7.

[0033] There are a number of bearings 11 equal to the number of satellites 8. For reasons of operation, assembly, manufacturing, control, repair or replacement, the bearings 11 (and in particular the bearing bodies 10b) and the walls 10a1, 10a2 can be separated into several parts.

[0034] For the same reasons mentioned above, the 8d toothing of a reducer can be separated into several helices, each having a median plane P. In our example, we detail the operation of a multi-helix reducer with a crown separated into two half-crowns: ▪ an upstream half-crown 9a consisting of a rim 9aa and a fixing half-flange 9ab. On the rim 9aa is the upstream helix of the gear teeth. This upstream helix meshes with that of the satellite 8 which meshes with that of the sun gear 7. ▪ a downstream half-crown 9b consisting of a rim 9ba and a fixing half-flange 9bb. On the rim 9ba is the downstream helix of the gear teeth. This downstream helix meshes with that of the satellite 8 which meshes with that of the sun gear 7.

[0035] If the propeller widths vary between the sun gear 7, the satellites 8 and the crown 9 because of the tooth overlaps, they are all centered on a median plane P for the upstream propellers and on another median plane P for the downstream propellers.

[0036] 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.

[0037] Alternatively, the flange 9c of the crown 9 could be replaced by splines.

[0038] 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 the distributor 13 by different means which will not be specified in this view because they are specific to one or more types of architecture. The distributor is separated into two parts, generally each repeated by the same number of satellites. The injectors 13a have the function of lubricating the teeth and the arms 13b have the function of lubricating the bearings 11. The oil is brought to injectors 13a to exit through ends 13c in order to lubricate with oil the teeth of the satellites 8, of the sun 7 and also of the crown 9. The oil is also brought to the arm 13b and circulates via the supply mouth 13d of the bearing body 10b in an internal cavity 10c of the latter.The oil then circulates in this cavity 10c to supply oil passage orifices 10d to an external cylindrical guide surface of the corresponding satellite.

[0039] The present invention relates to a crown for a mechanical reduction gear 6 of an aircraft. This reduction gear 6 may be of the type described above or of another type, for example a double-stage reduction gear of the Wolfrom type. Furthermore, this reduction gear 6 may be used in a turbomachine 1 such as that illustrated in figure 1 , for driving a fan S, or in another context such as in a wheel drive system for an aircraft landing gear (cf. figure 10 ).

[0040] It should be noted that the crown according to the invention may be the only crown of the reducer 6, and may be a fixed or movable crown. Alternatively, the reducer 6 could comprise two crowns according to the invention. One of these crowns could be fixed and the other could be movable. The two crowns could furthermore be fixed or movable. For example, each of these two crowns could be similar to a half-crown as illustrated in figure 2 , the two crowns (or half-crowns) then being fixed together and to a crown holder by their flanges or grooves.

[0041] THE figures 3 to 5 illustrate a first embodiment of a crown 90 according to the invention, and the figures 6 and following illustrate variants of the embodiment of this crown 90.

[0042] The 90 crown is preferably metallic. Its main material is therefore a metal alloy.

[0043] The 90 crown of figures 3 to 5 has a ring shape around the X axis and includes: an internal toothing 92 at its internal periphery, an external annular flange or splines 94 at its external periphery, and an annular web 96 extending between the internal toothing 92 and the external flange or splines 94.

[0044] The particularity of this crown 90 is that its web 96 comprises an annular row of arms 98 which are distributed around the axis X, these arms connecting the internal teeth 92 to the flange or the splines 94 and being formed in a single piece with the internal teeth 92 and the flange or the splines 94. The teeth 92 are straight in the example shown but could alternatively be helical.

[0045] In the example shown, the flange 94 comprises a plurality of axial orifices 100 for the passage of fixing elements of the screw or bolt type. These orifices 100 are formed in radially external ears 102 of the flange 94. These ears 102 are distributed around the axis X. Alternatively, the orifices 100 could be formed in a continuous annular wall of the flange 94.

[0046] The flange or splines 94 is / are located in a plane H which is perpendicular to the axis X and which passes through the middle of the toothing 92 in the example shown.

[0047] The arms 98 preferably extend in this plane H.

[0048] In the embodiment of the figures 3 to 5, we see that the arms 98 are regularly distributed around the X axis and are at a distance from each other. They all have the same orientation and are inclined in the same direction relative to rays to the X axis. The angle α of inclination of each arm is for example between 20 and 70°.

[0049] In the case where the satellites meshed with the crown 90 rotate in the direction of the arrow F1, each of the arms 98 would undergo traction work in a direction which would be aligned with the axis of elongation of this arm 98 (arrow F11 - Figure 5 ). In the case where the satellites meshed with the crown 90 rotate in the direction of the arrow F2, each of the arms 98 would undergo compression work in a direction which would be aligned with the axis of elongation of this arm (arrow F21 - Figure 5 ). Furthermore, the veil 96 and therefore the crown 90 have flexibility in the radial direction according to the arrow F3.

[0050] The arms 98 define between them spaces 104 which are empty and here have a general parallelepiped shape.

[0051] Each of the arms 98 comprises a first radially external end for connection to the flange or the splines 94, and a second radially internal end for connection to the teeth 92. These ends can be widened relative to the rest of the arm and in particular to the middle part of the arm, as can be seen in the Figure 5 .

[0052] Generally, due to the spaces 104 created between the arms 98, these arms can be oversized to withstand the forces in operation, without significantly impacting the mass of the crown 90. This oversizing can be done for example in a direction parallel to the X axis, the arms 98 having for example a width in this direction which is greater than the width of a crown web of the prior art.

[0053] Furthermore, the arms 98 may have any cross-sectional shape, for example square, rectangular, round, elliptical, etc. This cross-sectional shape may also vary along the axis of elongation of the arm 98.

[0054] The variant of the realization of the figure 6 differs from the previous embodiment in that one set, e.g., half, of the arms 98, 98a is oriented in a first way, and a second set, e.g., half, of the arms 98, 98b is oriented in a second way, different from the first way.

[0055] The arms 98, 98a are for example inclined at a positive angle +β with respect to rays on the X axis, and the arms 98, 98b are for example inclined at a negative angle -β with respect to rays on the X axis.

[0056] The arms 98 define between them spaces 104 which are empty and here have a generally trapezoidal shape. A first series of trapezoids have their small bases located outside their large bases, and the other series of trapezoids, arranged between the trapezoids of the first series, have their small bases located inside their large bases.

[0057] The ends of the 98 arms are also widened.

[0058] The variant of the realization of the figure 7 differs from the previous embodiment in that the arms 98, 98a of the first series are intersected with the arms 98, 98b of the second series.

[0059] The arms 98 define between them spaces 104, 106 which are empty and here have general triangular and diamond shapes. A pair of intersecting arms 98a, 98b together define two triangular spaces 106 located respectively inside and outside the arms 98a, 98b. Two adjacent pairs of arms 98a, 98b define between them a diamond-shaped space 104.

[0060] The variant of the realization of the figure 8 differs from previous embodiments in that the empty spaces 104 between the arms 98 are formed by circular orifices 108a, 108b.

[0061] The web 96 comprises a first annular row of orifices 108a located on a first circumference, and a second annular row of orifices 108b located on a second circumference whose diameter is greater than that of the first circumference, the orifices 108a of the first row being located between the orifices 108b of the second row.

[0062] The variant of the realization of the figure 9 differs from the first embodiment in that the spaces 104 are filled with blocks 110 which are made of a material different from the main material of the crown, and which are for example made of polymer. The polymer is for example chosen from: polyetheretherketone, polyamide, polyimide, bismaleimide, epoxy, phenoplasts (eg, polystyrene), polyesters, polyurethanes, silicone rubbers, nylons, copolymers, mixture of polymers, etc.

[0063] The blocks 110 can be designed to take up part of the meshing forces, and thus reduce the section of the arms 98 for the purpose of saving mass.

[0064] The spaces 104, 106 between the arms 98 of the other variant embodiments of figures 6 to 8 could also be filled with similar 110 blocks.

[0065] The number of arms 98 of the crown 90 is for example greater than 2, 5 or 10, preferably greater than 20, and more preferably between 20 and 100. This number depends in particular on the level of loading of the teeth 92 of the crown 90 in operation. A lightly loaded crown 90 will have a lower number of arms 98 than a more heavily loaded crown in operation. In the same way, the inclination of the arms 98 will depend on the loading of the crown 90 and the desired flexibility.

[0066] There figure 10 shows a system 210 for driving at least one wheel 212 of an aircraft landing gear 214.

[0067] The wheel 212 comprises a rim 216 which has an axis of rotation X. Conventionally, this rim 216 has a generally tubular or disc shape and carries a tire 218 at its periphery.

[0068] The system 210 comprises an electric motor 220 and a mechanical transmission system 222 between a shaft of the motor 220 and the rim 216 of the wheel 212.

[0069] In the example shown, the motor 220 and the system 222 each have a generally annular shape and are centered on the X axis. They are arranged next to each other and the system 222 is installed between the motor 220 and the rim 216. A part of the system 222, or even also a part of the motor 220, could be housed in the rim 16 to reduce the size of the system 210. The motor 220 and the system 222 can be protected by an external cylindrical cover 226 projecting on one side of the rim 216 or the tire 218.

[0070] The mechanical transmission system 222 comprises a mechanical reducer 228 similar to the reducer 6 described above.

Claims

1. A ring gear (90) for an aircraft mechanical gearbox (6, 228), this ring gear (90) having an annular shape about an axis (X) and comprising: - an internal toothing (92) at its internal periphery, - an external annular flange or splines (94) at its external periphery, and - an annular web (96) extending between the internal toothing (92) and the external flange or splines (94), characterised in that the web (96) comprises an annular row of arms (98) which are distributed around said axis (X), these arms (98) connecting the internal toothing (92) to the external flange or splines (94) and being formed in a single piece with the internal toothing (92) and the external flange or splines (94).

2. The ring gear (90) as claimed in claim 1, wherein the arms (98) are separated from one another by spaces (104, 106), or delimit spaces (104, 106) between them.

3. The ring gear (90) as claimed in claim 2, wherein each or at least a portion of said spaces (104, 106) is generally parallelepipedal, trapezoidal, triangular or diamond-shaped.

4. The ring gear (90) as claimed in claim 2, wherein said spaces are formed by circular or oblong orifices (108a, 108b).

5. The ring gear (90) according to claim 4, wherein the web (96) comprises a first annular row of orifices (108a) located on a first circumference, and a second annular row of orifices (108b) located on a second circumference whose diameter is greater than that of the first circumference, the orifices (108a) of the first row being located circumferentially between the orifices (108b) of the second row.

6. The ring gear (90) according to one of claims 2 to 5, wherein said spaces (104, 106) are empty.

7. The ring gear (90) according to one of claims 2 to 5, wherein said spaces (104) are filled by blocks (110) made of a material different from the main material of the ring gear, for example polymer.

8. The ring gear (90) according to one of claims 1 to 7, wherein the arms (98) are inclined obliquely to a radial direction and have an inclination orientation in the same circumferential direction.

9. The ring gear (90) according to one of claims 1 to 8, wherein a first series of the arms (98a) is oriented in a first way, and a second series of the arms (98b) is oriented in a second way, different from the first way.

10. The ring gear (90) as claimed in claim 9, wherein the arms (98a) of the first series are intertwined with the arms (98b) of the second series.

11. The ring gear (90) according to one of claims 1 to 10, wherein the arms (98) are all located in the same plane (P) perpendicular to said axis (X).

12. The ring gear (90) according to one of claims 1 to 11, wherein the number of arms (98) is greater than 2, for example greater than 5 or 10, preferably greater than 20, and more preferably between 20 and 100.

13. The ring gear (90) according to any of claims 1 to 12, wherein the arms (98) are all oriented in the same way, and in particular they are all inclined with respect to radii of said axis.

14. A mechanical gearbox (6, 228) for an aircraft, the gearbox (6, 228) comprising: - a sun gear (7) movable in rotation about an axis, - a ring gear (90) according to one of the preceding claims, mounted around the sun gear (7) and said axis (X), and - planet gears (8) mounted between the sun gear (7) and the ring gear (90) and meshed with the sun gear and the ring gear, these planet gears (8) having axes of rotation (Y) parallel to said axis (X).

15. A turbomachine (1), in particular for an aircraft, comprising at least one ring gear (90) according to one of claims 1 to 13 or a mechanical gearbox (6, 228) according to claim 14.

16. A drive system (210) for driving a wheel (212) of a landing gear (214), in particular of an aircraft, comprising at least one ring gear (90) according to one of claims 1 to 13 or a mechanical gearbox (228) according to claim 14.