MECHANICAL REDUCER FOR AN AIRCRAFT

Abstract

Mechanical reduction gear (28) for an aircraft, comprising: - a first sun gear (32) with external teeth (32a), - a fixed ring gear (38) with internal teeth (38d), - a movable ring gear (56) with internal teeth (56a), - planet gears (34) with double teeth (34a, 54a), and - a second sun gear (70) with external teeth (70a), the reduction gear being without planet carriers. Figure for the abbreviation: Figure 6

Description

Title of the invention: MECHANICAL REDUCER FOR AN AIRCRAFT Technical field of the invention

[0001] The present invention relates to a mechanical reducer for an aircraft and in particular for a drive device for at least one wheel of an aircraft landing gear. Technical background

[0002] An aircraft includes landing gear equipped with wheels for moving the aircraft on the ground on a tarmac. This taxiing, also called taxiing, can be achieved by propelling the aircraft using its turbomachinery.

[0003] To limit fuel consumption and environmental impact, it is known to perform this taxiing electrically. Electric taxiing is achieved by driving the wheels of a landing gear with an electric motor.

[0004] The present application proposes an improvement to existing technologies and thus relates to an electric motor device for driving at least one wheel of an aircraft landing gear.

[0005] A solution consisting of using a reducer to transmit the power of an electric motor to a wheel of a landing gear was proposed by the Applicant in document EP-A1-3 882 136.

[0006] 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.

[0007] In the distant field of aircraft turbomachinery, it is known to use a mechanical reducer to ensure power transmission between two rotating mechanical shafts.

[0008] There are many types of reducers, for example differential, planetary, epicyclic, intermediate line, series reduction stage, etc.

[0009] In the state of the art of turbofan engines, gearboxes are of the planetary or epicyclic type. Such a gearbox comprises a central pinion, called the sun gear, a ring gear, and gears called planet gears, which mesh between the sun gear and the ring gear. The planet gears are held by a frame called the planet carrier. The sun gear, ring gear, and planet carrier are planetary because their axes of revolution coincide with the longitudinal axis of the turbomachine. The planet gears each have a different axis of revolution, equally spaced on the same operating diameter around the axis of the planet gears. These axes are parallel to the longitudinal axis of the turbomachine.

[0010] There are several gearbox architectures. In other similar applications, there are so-called differential or "compound" architectures.

[0011] - On a planetary gearbox, the planet carrier is fixed and the ring gear constitutes the output shaft of the device which rotates in the opposite direction to the solar.

[0012] - On an epicyclic reducer, the ring gear is fixed and the planet carrier constitutes the output shaft of the device which rotates in the same direction as the solar panel.

[0013] - On a differential reducer, no element is fixed for rotation. The ring rotates in the opposite direction to the solar panel and the satellite carrier.

[0014] Reducers can be composed of one or more meshing stages. This meshing is achieved in various ways such as by contact, by friction or by magnetic fields.

[0015] In this application, the term "stage" or "toothing" means at least one series of meshing teeth with at least one series of complementary teeth. A toothing may be internal or external.

[0016] A satellite may comprise one or two gear stages. A single-stage satellite comprises teeth that may be straight, helical, or chevron-shaped, and whose teeth are located on the same diameter. These teeth cooperate with both the sun gear and the crown gear.

[0017] A two-stage satellite comprises two sets of teeth located on different diameters. A first set of teeth cooperates with the sun gear and a second set of teeth generally cooperates with the crown gear.

[0018] A double-stage gear reducer has the advantage of having a higher reduction ratio than a single-stage gear reducer of the same size.

[0019] In the context of a drive system for at least one landing gear wheel, the use of an electric motor and a gearbox to drive the wheel generates significant space constraints. The gearbox's outer diameter is limited by the wheel rim size, and its inner diameter is severely constrained by the wheel hub diameter. Furthermore, the use of an electric motor, which typically rotates at high speeds, necessitates a gearbox with a high reduction ratio to provide an output speed that matches the low rotational speed of the wheel. Epicyclic and planetary gear sets of current technology cannot achieve these levels of reduction within such a compact footprint.

[0020] The invention proposes a solution to at least some of these problems, which is simple, effective and economical. Summary of the invention

[0021] The invention relates to a mechanical reducer for an aircraft, comprising:

[0022] - a first mobile solar element rotating about a first axis and comprising a external dentition,

[0023] - a fixed crown centered on the first axis and comprising internal teeth,

[0024] - a movable crown centered on the axis and comprising internal teeth, and

[0025] - satellites that are geared with the first solar and the two coronas and which are mobile in rotation around second axes parallel to the first axis, each of the satellites having a first external toothing meshed with the toothing of the fixed ring and a second external toothing meshed with the toothing of the mobile ring, one of the first and second toothings of each of the satellites being meshed with the external toothing of the first solar,

[0026] characterized in that it further comprises a second free solar element rotating around the first axis and having external teeth, the other of the first and second teeth of each of the satellites being meshed with the external teeth of the second solar element,

[0027] and in that it is devoid of satellite carriers, the satellites being held solely by the meshing of their first and second teeth with the teeth of the first and second solars and the teeth of the crowns.

[0028] The reducer is of the independent double-ring type. One of the rings is fixed and the other is rotatable. It is therefore understood that the rotatable ring forms a torque output of the reducer, the input of the reducer being formed by the first solar element.

[0029] One of the distinctive features of the invention is that the gearbox includes a second solar element. This second solar element does not form a torque input or output since it is free to rotate. It is used to cooperate with the gears of the satellites that are not meshed with the first solar element in order to prevent imbalance of the satellites during operation. Each of the satellite gears is therefore meshed with two gears, one of a ring gear and one of the solar elements respectively, which ensures that the satellites are held securely in place.

[0030] The other particularity of the invention is related to the fact that the reducer does not include or no longer includes planet carriers since the planets are sufficiently held and balanced by their double meshing on each tooth.

[0031] The invention is compatible with a multi-stage reducer as mentioned above. It is also compatible with gears of any type (straight, helical, herringbone, etc.).

[0032] The reducer according to the invention may comprise one or more of the following features, taken individually or in combination with each other: • the first toothing of each of the satellites is meshed with the toothing of the fixed ring and with the toothing of the first solar, and the second toothing of each of the satellites is meshed with the toothing of the movable ring and with the toothing of the second solar; • the first toothing of each of the satellites is meshed with the toothing of the fixed crown and with the toothing of the second solar, and the second toothing of each of the satellites is meshed with the toothing of the movable crown and with the toothing of the first solar; • the second solar panel is mounted freely to rotate on and around the first solar panel; • the second solar panel is guided in rotation on the first solar panel by at least one bearing; • each of the satellites comprises a cylindrical body which carries the said first and second teeth; • the cylindrical body of each of the satellites is solid; • the cylindrical body of each of the satellites has an axial bore internal which is not crossed by a guide axis; • each of the satellites includes, between its first and second teeth, a radially external annular veil; • said radially external annular veil is able to cooperate by axial stop with at least one of the rings in order to axially retain the satellites; • said radially external annular sail is capable of cooperating by axial stop with at least one of the solars in order to axially retain the satellites. • all the teeth are straight and parallel to the first axis; • at least some of the teeth are helical or chevron; • the second solar element is axially intercalated between the teeth of the first solar element and an internal periphery of the fixed ring.

[0033] The present invention further relates to a drive device for at least one wheel of an aircraft landing gear, this device comprising:

[0034] - at least one landing gear wheel, this wheel comprising a rim having a first axis of rotation,

[0035] - an electric motor comprising a shaft,

[0036] - a mechanical transmission system between the engine shaft and the rim, this mechanical transmission system comprising a mechanical reducer as described above, the first solar part of the reducer being rotationally fixed to the motor shaft, the fixed ring being fixed to a stator of the device, and the moving ring being rotationally fixed to the rim. Brief description of the figures

[0037] 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:

[0038] [Fig-1] [Fig.1] is a schematic perspective view of a train wheel aircraft landing gear and a drive device for this wheel,

[0039] [Fig.2] [Fig.2] is a partial axial cross-sectional view of a mechanical reducer,

[0040] [Fig. 3] [Fig. 3] is another partial axial cross-sectional view of a reducer mechanical,

[0041] [Fig.4] [Fig.4] is a schematic axial cross-sectional and perspective view of a two-stage reducer with symmetrical meshing,

[0042] [Fig.5] [Fig.5] is another schematic axial cross-sectional view of the reducer of [Fig.4];

[0043] [Fig.6] [Fig.6] is a very schematic partial axial cross-sectional view of a mechanical reducer according to an embodiment of the invention,

[0044] [Fig.7] [Fig.7] is a schematic perspective view of a reducer according to the invention;

[0045] [Fig.8] [Fig.8] is a schematic axial cross-sectional view of the reducer of [Fig.7]. Detailed description of the invention

[0046] Fig. 1 shows a drive device 10 for at least one wheel 12 of an aircraft landing gear 14.

[0047] The wheel 12 has a rim 16 which has an axis of rotation X. In a conventional manner, this rim 16 has a general tubular or disc shape and carries a tire 18 on its periphery.

[0048] The device 10 includes an electric motor 20 and a mechanical transmission system 22 between a shaft of the motor 20 and the rim 16 of the wheel 12.

[0049] In the example shown, the motor 20 and the system 22 each have a generally annular shape and are centered on the X-axis. They are arranged side by side, and the system 22 is installed between the motor 20 and the rim 16. Part of the system 22, or even part of the motor 20, could be housed in the rim 16 to optimize the size of the device 10. The motor 20 and the system 22 can be protected by an external cylindrical cover 26 projecting from one side of the rim 16 or the tire 18.

[0050] The mechanical transmission system 22 includes a mechanical reducer 28, examples of which are illustrated in figures 2 to 5.

[0051] Figure 2 shows an epicyclic reducer 28. At the input, the reducer 28 is connected to a shaft 30, for example via internal splines 32a. Thus, the shaft 30 drives a planetary pinion called the solar 32. Classically, the solar 32 drives a series of pinions called satellites 34, which are equidistant on the same diameter around the X axis of rotation of the solar 32. This diameter is equal to twice the operating center distance between the solar 32 and the satellites 34. The number of satellites 34 is generally defined between three and seven.

[0052] The set of satellites 34 is held by a frame called satellite carrier s 36. Each satellite 34 rotates around its own Y axis, and meshes with a ring 38.

[0053] The output we have: • In this epicyclic configuration, the set of satellites 34 drives the satellite carrier 36 in rotation around the X axis. The ring 38 is fixed to a stator via a ring carrier 40 and the satellite carrier 36 is fixed to another shaft 42. • In another planetary configuration, the set of satellites 34 is held by a satellite carrier 36 which is fixed to a stator. Each satellite drives the ring gear 38 which is connected to the shaft 42 via a ring gear carrier 40. • In another differential configuration, the set of satellites 34 is held by a satellite carrier 36 which is connected to the shaft 30. Each satellite 34 drives the ring 38 which is brought to the shaft 42 via a ring carrier 40.

[0054] Each satellite 34 is mounted to rotate freely by means of a bearing 44, for example, a roller bearing or hydrodynamic bearing. Each bearing 44 is mounted on one of the axes 36b of the satellite carrier 36, and all the axes 36b are positioned relative to each other by means of one or more structural frames 36a of the satellite carrier 36. There is a number of axes 36b and bearings 44 equal to the number of satellites 34. For reasons of operation, assembly, manufacturing, inspection, repair, or replacement, the axes 36b and the frame 36a may be separated into several parts.

[0055] For the same reasons mentioned above, the teeth 34a of a satellite 34 can be separated into several helices or teeth, each having a median plane P, P'. In the example shown, each satellite 34 comprises two sets of chevron teeth cooperating with a ring 38 separated into two half-rings: • An upstream ring 38a consisting of a rim 38aa and a half-flange for fixing 38ab. On the rim 38aa is the front helix meshed with a helix of the teeth 34a of each satellite 34. The helix of the teeth 34a also meshes with that of the solar 32. • A downstream ring 38b consisting of a rim 38ba and a half-flange for mounting 38bb. The rear propeller, meshed with a, is located on the rim 38ba. helix of the teeth 34a of each satellite 34. The helix of the teeth 34a also meshes with that of the solar 32.

[0056] If the helix widths vary between the solar 32, the satellites 34 and the crown 38 because of the tooth overlaps, they are all centered on a median plane P for the upstream teeth and on another median plane P' for the downstream teeth.

[0057] Fig. 2 thus illustrates the case of a single-stage gear reducer, that is to say, the same toothing 34a of each satellite 34 cooperates with both the solar 32 and the ring 38. Even though the toothing 34a comprises two sets of teeth, these teeth have the same average diameter and form a single toothing called a chevron.

[0058] The mounting half-flange 38ab of the upstream ring 38a and the mounting half-flange 38bb of the downstream ring 38b form the mounting flange 38c of the crown. The crown 38 is fixed to the crown carrier 40 by assembling the mounting flange 38c of the crown 38 and a mounting flange 40a of the crown carrier 40 using a bolted assembly, for example.

[0059] Fig. 3 shows another example of a reducer architecture, called a double-stage geared reducer, in which each satellite 34 comprises two separate gears 34al, 34a2 configured to cooperate respectively with the crown 38 and the sun 32.

[0060] In this [Fig.3], the elements already described above are designated by the same references.

[0061] The meshing teeth 34a1 with the ring gear 38 have an average diameter denoted D2 and are located in a median plane P. The meshing teeth 34a2 with the sun gear 32 have an average diameter denoted DI and are located in another median plane P'. The median planes P and P' are parallel to each other and perpendicular to the X-axis. The diameter D2 is smaller than the diameter DI. Finally, each meshing tooth 34a1, 34a2 comprises a single helix.

[0062] Figures 4 and 5 show a symmetrical double-gear reducer 28, which comprises:

[0063] - a solar 32 having an axis of rotation X,

[0064] - a crown 38 which extends around the solar element 32 and which is configured to be stationary, rotating around the X-axis, and

[0065] - satellites 34 which are meshed with the solar 32 and the corona 38 and which are held by a satellite carrier 36 which is configured to be mobile in rotation around the X axis.

[0066] We define the plane H as a median plane perpendicular to the axis X and passing substantially through the middle of the reducer 28 ([Fig.5]).

[0067] The solar element 32 comprises internal splines 32b for coupling with the shaft 30 and external teeth 32a for meshing with the satellites 34. The teeth 32a has two sets of adjacent chevron-shaped teeth, separated from each other by an annular groove 46 oriented radially outwards. The teeth 32a are symmetrical with respect to plane H, its teeth being located on either side of plane H which passes through groove 46.

[0068] The crown 38 is formed by two independent rings 38a, 38b and includes a toothing which is separated into two series of chevron teeth 38dl, 38d2 carried respectively by the two rings.

[0069] The rings 38a, 38b are arranged symmetrically with respect to the plane H, which therefore extends between these rings. The rings 38a, 38b are connected and fixed to a ring carrier 40 by means of connecting annular flanges 48. The flanges 48 are independent of each other, each flange having a general S-shaped axial cross-section providing it with a certain radial flexibility through elastic deformation during operation.

[0070] Each ring 38a, 38b extends around the X axis and is fixed to the corresponding flange 48 by its outer periphery. Its inner periphery includes one of the teeth 38d1, 38d2.

[0071] The crown carrier 40 has a generally annular shape around the X-axis and, more specifically, a biconical shape. It thus comprises a first upstream or left-hand section in the drawing, with an upstream end of smaller diameter, and a downstream end of larger diameter which is connected to the upstream end of larger diameter of the other section, downstream or right-hand in the drawing. The larger-diameter ends of the sections are therefore connected to each other, and their smaller-diameter ends form the axial ends of the crown carrier 40.

[0072] The upstream end of the crown carrier 40 extends around the planet carrier 36 or a shaft 42 connected to this planet carrier, and is centered and guided in rotation on the planet carrier or the shaft by means of at least one bearing 50. In the same way, the downstream end of the crown carrier 40 extends around the planet carrier 36 or a shaft connected to this planet carrier, and is centered and guided in rotation on the planet carrier or the shaft by means of at least one other bearing 52.

[0073] As is the case with the crown 38, the crown carrier 40 has a symmetry with respect to the plane H which cuts the crown carrier 40 in its middle and therefore passes through the ends of the largest diameter of the aforementioned sections.

[0074] Each satellite 34 has a first tooth 34a of average diameter DI for meshing with the solar 32, and a second tooth 54aa of average diameter D2, different from DI and in particular less than Dl, for meshing with the ring 38. The average diameters are measured from the Y axis of each satellite 34 and represent the average between the maximum diameter and the minimum diameter of a tooth of this satellite.

[0075] Each satellite 34 comprises a cylindrical sleeve 58 and an annular web 60 extending substantially radially outwards from the middle of this sleeve 58. The teeth 54aa are separated into two series of chevron teeth 54al, 54a2 which are located respectively on the axial ends of the sleeve 58. The teeth 34aa comprise two series of chevron teeth 34al, 34a2 which are located on the outer periphery of the web 60 and which are separated from each other by an annular groove 55 opening radially outwards with respect to the Y axis.

[0076] The teeth 34aa are crossed in their middle by the plane H which passes through the groove 55, the teeth 34al, 34a2 being therefore arranged on either side of the plane H. The teeth 54al, 54a2 are also arranged symmetrically with respect to the plane H.

[0077] The teeth 34aa and the outer periphery of the veil 60 have an axial dimension which is less than the axial distance between the rings 38a, 38b, as well as between the flanges 48, so that each satellite 34 can freely rotate in the crown carrier 40 and between the rings 38a, 38b and the flanges 48.

[0078] Each of the satellites 34 is guided in rotation by a hydrodynamic bearing 44 which includes a cylindrical body 44a which passes through the satellite 34, and in particular its sleeve 58, and which is configured to form a guiding oil film inside the satellite.

[0079] The body 44a of a bearing 44 extends along the Y axis and includes at its longitudinal ends extensions 44b housed in orifices forming seats for the planet carrier 36.

[0080] The body 44a is generally tubular and includes an internal oil circulation bore which generally communicates with oil supply channels to an external cylindrical surface of the body for the purpose of forming the oil film between this surface and an internal cylindrical surface of the satellite 34.

[0081] The present invention proposes in particular a simplified reducer ensuring good support of the satellites in operation.

[0082] The reducer 28 of the device 10 according to the invention comprises all the features described above in relation to Figures 3, 4 and 5, with one exception, insofar as they are not contrary to or contradict what follows. The exception concerns the fact that the reducer does not include planet carriers, in particular.

[0083] The references used in Figures 6 and following and already used in Figures 3, 4 and 5 therefore designate identical or similar elements.

[0084] Figures 6 to 8 illustrate embodiments of a reducer 28 according to the invention, which comprises:

[0085] - a first solar element 32 which is mobile in rotation about the X-axis and which comprises an external dentition 32a,

[0086] - a fixed crown 38 which extends around the X axis and which has teeth internal 38d,

[0087] - a movable crown 56 which extends around the X axis and which has teeth internal 56a, this movable ring 56 being independent of the fixed ring 38, and

[0088] - satellites 34 which are meshed with the solar element 32 and the rings 38 and 56, the satellites 34 being mobile in rotation around Y axes which are parallel to the X axis.

[0089] In the context of the present invention, the first solar element 32 is coupled to the shaft 30 of the electric motor 20. The movable ring 56 is coupled to the shaft 42 of the rim or directly to the rim 16. The fixed ring 38 is fixed to a stator of the device 10,

[0090] The special feature of the reducer 26 is that it includes a second solar element 70.

[0091] The second solar 70 is free to rotate around the X axis and has an external toothing 70a.

[0092] Each of the satellites 34 is meshed with the solar elements 32, 70 and the crowns 38, 56 and comprises a first external toothing 34a of average diameter D1, and a second external toothing 54a of average diameter D2, different from DL

[0093] In the example shown, Dl is greater than D2. Alternatively, the teeth 34a and 54a could have equal diameters Dl and D2 and different numbers of teeth, so as to have different modules.

[0094] In the embodiment of [Fig. 6], the toothed gear 54a of diameter D2 of each satellite 34 meshes with the toothed gear 32a of the solar element 32 and the toothed gear 56a of the movable ring 56. The toothed gears 32a, 54a, and 56a are thus in the same plane PI perpendicular to the X-axis.

[0095] The toothed portion 34a of diameter Dl of each satellite 34 meshes with the toothed portion 38d of the fixed ring 38 and with the toothed portion 70a of the sun gear 70. The toothed portions 34a, 38d, and 70a are thus in the same plane P2 perpendicular to the X-axis and distant from the plane PL

[0096] In the embodiment shown in Figures 7 and 8, a different configuration is represented. The teeth 54a of diameter D2 of each satellite 34 mesh with the teeth 70a of the sun gear 70 and the teeth 56a of the movable ring 56. The teeth 32a, 54a, and 70a are thus in the same plane PI perpendicular to the X-axis. The teeth 34a of diameter D1 of each satellite 34 mesh with the teeth 38d of the fixed ring 38 and with the teeth 32a of the sun gear 32. The teeth 34a, 38d, and 32a are thus in the same plane P2 perpendicular to the X-axis and distant from the plane PL

[0097] In the configuration shown in Figure 7, where the solar element 32 and the movable ring gear 56 mesh with the same teeth of the satellite gears 34, the output (torque) of the reducer can be said to be aligned with its input. In the configuration shown in Figures 7 and 8, where the solar element 32 and the movable ring gear 56 mesh with different teeth of the satellite gears 34, the output (torque) of the reducer can be said to be opposite to its input.

[0098] The number of teeth on the movable ring 56 differs from the number of teeth on the fixed ring 38 so that the two rings have different diameters. Alternatively, the diameters may be equal, provided that the two rings have different modules. The direction of rotation of the movable ring 56 may depend on the relative diameters of the two rings 38 and 56. For example, when the number of teeth on the movable ring 56 is greater than that on the fixed ring 38, the reduction gear 28 is counter-rotating, meaning that the movable ring 56 rotates in the opposite direction to the sun gear 32. When the number of teeth on the movable ring 56 is less than that on the fixed ring 38, the reduction gear 28 is co-rotating, meaning that the ring 56 and the sun gear 32 rotate in the same direction.

[0099] The solar element 70 can be mounted freely for rotation on and around the solar element 32, as in the examples shown. The solar element 70 can be guided in rotation on the solar element 32 by at least one bearing 72, such as a plain bearing or a roller bearing, for example, a needle bearing.

[0100] Each of the satellites 34 comprises a cylindrical body 74 which carries the teeth 34a, 54a and which may be solid or hollow. In the case where they are hollow, each of the satellites has an internal axial bore which is not traversed by a guide shaft insofar as there are no guide shafts for the satellites or satellite carriers as in the prior art.

[0101] Advantageously, each of the satellites 34 comprises, between its teeth 34a, 54a, a radially external annular web 76 ([Fig. 6]). The web 76 serves to provide axial retention of the corresponding satellite 34.

[0102] The veil 76 of each satellite 34 is for example able to cooperate by axial stop with at least one of the rings, and preferably both in order to axially retain the satellites in two opposite directions along the X axis.

[0103] In [Fig.6], we see that the veil 76 of the satellite 34 could come to axial support at Cl against the fixed ring 38 and at C2 against the mobile ring 56.

[0104] Still in [Fig.6], the sail 76 of the satellite 34 could come into axial support at C3 against the solar 70 and at C4 against the solar 32.

[0105] This configuration with the sails 76 of the satellites 34 is particularly useful when the gear teeth are straight and parallel to the X axis. In this case, the satellites 34 are not held by the teeth and are likely to move axially by axial sliding of the teeth against each other.

[0106] Alternatively, at least some of the teeth are helical or herringbone to avoid radial displacements of the operating satellites and the presence of the sails 76

[0107] In the embodiment variant of figures 7 and 8, it can be seen that the solar 70 is axially intercalated between the teeth 32a of the first solar 32 and an internal periphery 38e of the fixed ring 38.

Claims

Demands

1. A mechanical reducer (28) for an aircraft, comprising: - a first sun gear (32) rotatable about a first axis (X) and having external teeth (32a), - a fixed ring gear (38) centered on the first axis (X) and having internal teeth (38d), - a movable ring gear (56) centered on the axis (X) and having internal teeth (56a), and - planet gears (34) that are meshed with the first sun gear (32) and the two ring gears and that are rotatable about second axes (Y) parallel to the first axis (X), each of the planet gears (34) having a first external toothed gear (34a) meshed with the teeth (38d) of the fixed ring gear (38) and a second external toothed gear (54a) meshed with the teeth (56a) of the movable ring gear (56), one of the first and second toothed gears (34a, 54a) of each of the satellites (34) being meshed with the external teeth (32a) of the first solar (32),characterized in that it further comprises a second solar element (70) free to rotate about the first axis (X) and having an external toothing (70a), the other of the first and second toothings (34a, 54a) of each of the satellites (34) being meshed with the external toothing (70a) of the second solar element (70), and in that it is devoid of satellite carriers, the satellites (34) being held solely by the meshing of their first and second toothings (34a, 54a) with the toothings (32a, 70a) of the first and second solar elements (32, 70) and the toothings (38d, 56a) of the crowns (38, 56).

2. Reducer (28) according to claim 1, wherein the first toothing (34a) of each of the satellites (34) is meshed with the toothing (38d) of the fixed ring (38) and with the toothing (32a) of the first solar (32), and the second toothing (54a) of each of the satellites (34) is meshed with the toothing (56a) of the movable ring (56) and with the toothing (70a) of the second solar (70).

3. Reducer (28) according to claim 1, wherein the first toothing (34a) of each of the satellites (34) is meshed with the toothing (38d) of the fixed ring (38) and with the toothing (70a) of the second sun gear (70), and the second toothing (54a) of each of the satellites (34) is meshed with the teeth (56a) of the movable crown (56) and with the teeth (32a) of the first solar (32).

4. Reducer (28) according to any one of claims 1 to 3, wherein the second solar (70) is mounted freely in rotation on and around the first solar (32).

5. Reducer (28) according to any one of claims 1 to 4, wherein the second solar (70) is guided in rotation on the first solar (32) by at least one bearing (72).

6. Reducer (28) according to any one of claims 1 to 5, in which each of the satellites (34) comprises a cylindrical body (74) which carries said first and second teeth (34a, 56a).

7. Reducer (28) according to claim 6, wherein the cylindrical body (74) of each of the satellites (34) is solid.

8. Reducer (28) according to claim 6, wherein the cylindrical body (74) of each of the satellites (34) has an internal axial bore which is not traversed by a guide shaft.

9. Reducer (28) according to any one of claims 1 to 8, wherein each of the satellites (34) comprises, between its first and second teeth (34a, 56a), a radially external annular veil (76).

10. Reducer (28) according to claim 9, wherein said radially external annular veil (76) is able to cooperate by axial stop with at least one of the rings (38, 56) in order to axially retain the satellites (34).

11. Reducer (28) according to claim 9, wherein said radially external annular sail (76) is able to cooperate by axial stop with at least one of the solars (32, 70) in order to axially retain the satellites (34).

12. Reducer (28) according to claim 10 or 11, wherein all the teeth (32a, 70a, 38d, 56a) are straight and parallel to the first axis (X).

13. Reducer (28) according to any one of claims 1 to 9, wherein at least some of the teeth (32a, 70a, 38d, 56a) are helical or herringbone.

14. Reducer (28) according to any one of claims 1 to 13, wherein the second solar (70) is axially intercalated between the teeth (32a) of the first solar (32) and an internal periphery (38e) of the fixed ring (38).

15. A device (10) for driving at least one wheel (12) of an aircraft landing gear (14), said device (10) comprising: - at least one landing gear wheel (12), said wheel (12) comprising a rim (16) having a first axis of rotation (X), - an electric motor (20) comprising a shaft, - a mechanical transmission system (22) between the shaft of the motor (20) and the rim (16), this mechanical transmission system (22) comprising a mechanical reducer (28) according to any one of the preceding claims, the first solar (32) of the reducer (28) being rotationally fixed to the shaft of the motor (20), the fixed ring (38) being fixed to a stator of the device (10), and the movable ring (56) being rotationally fixed to the rim (16).