DRIVE DEVICE FOR AT LEAST ONE WHEEL OF AN AIRCRAFT LANDING GEAR

Abstract

A device (10) for driving at least one wheel (12) of an aircraft landing gear (14), this device (10) comprising: - at least one landing gear wheel (12), this wheel (12) having a rim (16), - an electric motor (20) having 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 reduction gear (28) having: - a sun gear (32) fixed for rotation to the shaft of the motor (20), - a ring gear (38), and - planet gears (34) which are carried by a planet carrier (36) and which each have three external teeth (34a, 34b1, 34b2), including a central external tooth which meshes with a tooth (32a) of the sun gear, and two lateral external teeth (34b1, 34b2) which are respectively meshed with teeth (38d1, 38d2) of the crown (38). Figure for the abbreviation: Figure 1

Description

Title of the invention: DEVICE FOR DRIVING AT LEAST ONE WHEEL OF AN AIRCRAFT LANDING GEAR Technical field of the invention

[0001] The present invention relates to a device for driving 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 rolling, also called taxiing, can be achieved by propelling the aircraft using its turbomachines.

[0003] To limit fuel consumption and the impact on the environment, it is known to carry out this taxiing electrically. Electric taxiing is obtained by driving the wheels of a landing gear by 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 has been 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 axis and the output axis of a mechanical system.

[0007] In the distant field of aircraft turbomachines, 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, epicycloidal, with intermediate lines, with series reduction stages, etc.

[0009] In the state of the art of dual-flow turbomachines, the reducers are of the planetary or epicyclic type. Such a reducer comprises a central pinion, called a sun gear, a crown gear and pinions called satellites, which are meshed between the sun gear and the crown gear. The satellites are held by a frame called a planet carrier. The sun gear, the crown gear and the planet carrier are planetary gears because their axes of revolution coincide with the longitudinal axis of the turbomachine. The satellites each have a different axis of revolution equally distributed over the same operating diameter around the axis of the planetary gears. These axes are parallel to the longitudinal axis of the turbomachine.

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

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

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

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

[0014] The reducers can be composed of one or more meshing stages. This meshing is ensured in different ways such as by contact, by friction or even by magnetic fields.

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

[0016] A satellite can comprise one or two meshing stages. A single-stage satellite comprises a toothing which can 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.

[0017] A double-stage satellite comprises two sets of teeth which are 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.

[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 device for driving at least one wheel of a landing gear, the use of an electric motor and a reduction gear for driving the wheel generates significant space constraints. The outer diameter of the reduction gear is limited by the dimension of the wheel rim, and the inner diameter of the reduction gear is strongly constrained by the diameter of the wheel hub. In addition, the use of an electric motor generally rotating at high speeds requires the use of a reduction gear offering a large reduction ratio in order to provide an output speed which corresponds to the low rotational speed of the wheel. The epicyclic and planetary type gears of current technology do not allow these levels of reduction to be obtained in such a restricted space.

[0020] The invention provides 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 device for driving at least one wheel of an aircraft landing gear, this device comprising:

[0022] - at least one landing gear wheel, this wheel comprising a rim having a axis of rotation,

[0023] - an electric motor comprising a shaft,

[0024] - a mechanical transmission system between the motor shaft and the rim, this mechanical transmission system comprising a mechanical reducer,

[0025] characterized in that the mechanical reducer comprises:

[0026] - a solar unit rotating with the motor shaft, this solar unit being centered on the axis and comprising external teeth,

[0027] - a crown centered on the axis and which has two internal teeth, and

[0028] - satellites which are carried by a satellite carrier and which each have a median plane of symmetry perpendicular to the axis, each of the satellites comprising three external teeth, including a middle external tooth which is meshed with the tooth of the sun, and two lateral external teeth which are respectively arranged on either side of the middle external tooth and which are respectively meshed with the teeth of the crown.

[0029] The invention thus proposes a device for driving at least one wheel of an aircraft landing gear, which is equipped with a reduction gear with an epicyclic or planetary gear train whose satellites are symmetrical double-stage.

[0030] A first stage of each satellite, formed by the middle toothing of each satellite, meshes with the toothing of the sun gear.

[0031] A second stage of each satellite, formed by the two lateral teeth of each satellite, meshes with the crown which itself has two teeth.

[0032] In one embodiment, the crown is fixed and it is the planet carrier which is mobile in rotation and connected to the rim of the wheel. Alternatively, it is the opposite, the planet carrier is fixed and it is the crown which is mobile in rotation and connected to the rim of the wheel. The solar is connected to the rotor of the electric motor.

[0033] The invention is compatible with a multi-stage reducer as mentioned above. It is also compatible with a reducer whose planet carrier or crown is rotatable such as an epicyclic, planetary or differential reducer. It is also compatible with teeth of any type (straight, helical, chevron, etc.). The invention is furthermore compatible with a planet carrier of the monobloc type or of the cage and cage carrier type. These different types of reducer are well known to those skilled in the art. The solution proposed below is compatible with any type of satellite bearing, whether it is composed of rolling elements, a hydrodynamic bearing, etc.

[0034] The device according to the invention may comprise one or more of the characteristics following, taken in isolation from each other, or in combination with each other: - the crown is fixed and is attached to a stator of the device, and the planet carrier is rotatable around the axis and is attached to the rim; - the crown is rotatable around the axis and is fixed to the rim, and the planet carrier is fixed and is fixed to a stator of the device; - the crown teeth are identical; - the toothing of the sun gear and the external median toothing of each of the satellites are chevron-shaped; - the lateral external teeth of each of the satellites and the teeth of the crown are helical; - the motor has an annular shape centered on the axis and is arranged next to the reducer; - the engine is arranged next to and at the level of the satellites; - the middle tooth has a diameter greater than the diameter of the teeth lateral; - the planet carrier comprises a single transverse wall which is perpendicular to the axis and on which the satellites are mounted in a cantilever. - the planet carrier comprises two transverse walls which are perpendicular to the axis and between which the satellites are mounted, at least one of these transverse walls or even both of them has a central orifice for the passage of the motor shaft; - the satellites are each centered and guided by:

[0035] + two roller bearings carried by the planet carrier, the teeth of each of the sa tellites being located axially between these roller bearings,

[0036] + or three needle bearings carried by the planet carrier, each of the needle bearings needles being radially in line with one of the teeth of the satellite. Brief description of the figures

[0037] 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:

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

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

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

[0041] [Fig.4] [Fig.4] is a schematic axial sectional view of a double reducer symmetrical meshing stage for a device according to the invention,

[0042] [Fig.5] [Fig.5] is a schematic perspective view of a reducer of the type shown in [Fig.4];

[0043] [Fig.6] [Fig.6] is a schematic axial sectional view of a device according to the invention equipped with the reducer of [Fig.4],

[0044] [Fig.7] [Fig.7] is a schematic view in axial section of an alternative embodiment of a device according to the invention,

[0045] [Fig.8] [Fig.8] is a schematic axial sectional view of another alternative embodiment of a device according to the invention,

[0046] [Fig.9] [Fig.9] is a schematic view in axial section of a satellite and guide bearings of this satellite; and

[0047] [Fig. 10] [Fig. 10] is a schematic view in axial section of a satellite and guide bearings of this satellite. Detailed description of the invention

[0048] [Fig.l] shows a device 10 for driving at least one wheel 12 of an aircraft landing gear 14.

[0049] The wheel 12 comprises a rim 16 which has an axis of rotation X. Conventionally, this rim 16 has a generally tubular or disc shape and carries a tire 18 at its periphery.

[0050] The device 10 comprises 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.

[0051] In the example shown, the motor 20 and the system 22 each have a generally annular shape and are centered on the axis X. They are arranged next to each other and the system 22 is installed between the motor 20 and the rim 16. A part of the system 22, or even also a part of the motor 20, could be housed in the rim 16 to limit the size of the device 10. The motor 20 and the system 22 can be protected by an external cylindrical cover 26 projecting on one side of the rim 16 or the tire 18.

[0052] The mechanical transmission system 22 comprises a mechanical reducer 28, examples of embodiment of which are illustrated in FIGS. 2 to 5.

[0053] [Fig.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 sun gear 32. Conventionally, the sun gear 32 drives a series of pinions called satellites 34, which are equally distributed over the same diameter around the axis X of rotation of the sun gear 32. This diameter is equal to twice the operating center distance between the sun gear 32 and the satellites 34. The number of satellites 34 is generally defined between three and seven.

[0054] The set of satellites 34 is held by a frame called a planet carrier 36. Each satellite 34 rotates around its own Y axis, and meshes with a crown 38.

[0055] At the output we have: • In this epicyclic configuration, the set of satellites 34 drives the planet carrier 36 in rotation around the X axis. The crown 38 is fixed to a stator via a crown carrier 40 and the planet carrier 36 is fixed to another shaft 42. • In another planetary configuration, all of the planet gears 34 are held by a planet carrier 36 which is fixed to a stator. Each planet gear drives the crown 38 which is connected to the shaft 42 via a crown carrier 40. • In another differential configuration, all of the satellites 34 are held by a planet carrier 36 which is connected to the shaft 30. Each satellite 34 drives the crown 38 which is attached to the shaft 42 via a crown carrier 40.

[0056] Each satellite 34 is mounted to rotate freely using a bearing 44, for example of the rolling bearing or hydrodynamic bearing type. Each bearing 44 is mounted on one of the axes 36b of the planet carrier 36 and all the axes 36b are positioned relative to each other using one or more structural frames 36a of the planet 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, control, repair or replacement, the axes 36b and the frame 36a can be separated into several parts.

[0057] For the same reasons cited above, the toothing 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 series of chevron teeth cooperating with a crown 38 separated into two half-crowns: • An upstream ring 38a consisting of a rim 38aa and a fixing half-flange 38ab. On the rim 38aa is the front helix meshed with a helix of the toothing 34a of each satellite 34. The helix of the toothing 34a also meshes with that of the sun 32. • A downstream ring 38b consisting of a rim 38ba and a half-fixing flange 38bb. On the rim 38ba is the rear propeller meshing with a propeller of the toothing 34a of each satellite 34. The propeller of the toothing 34a also meshes with that of the sun 32.

[0058] If the helix widths vary between the sun gear 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.

[0059] [Fig.2] thus illustrates the case of a single-stage gear reducer, that is to say that the same toothing 34a of each satellite 34 cooperates with both the sun gear 32 and the crown 38. Even if the toothing 34a comprises two series of teeth, these teeth have the same average diameter and form a single toothing called a chevron.

[0060] The fixing half-flange 38ab of the upstream ring 38a and the fixing half-flange 38bb of the downstream ring 38b form the fixing flange 38c of the crown. The crown 38 is fixed to the crown carrier 40 by assembling the fixing flange 38c of the crown 38 and a fixing flange 40a of the crown carrier 40 using a bolted assembly for example.

[0061] [Fig. 3] shows another example of a reduction gear architecture, called a double meshing stage, in which each satellite 34 comprises two separate teeth 34al, 34a2 configured to cooperate respectively with the crown 38 and the sun gear 32.

[0062] In this [Fig.3], the elements already described in the above are designated by the same references.

[0063] The toothing 34al for meshing with the crown 38 has an average diameter denoted D2 and is located in a median plane P. The toothing 34a2 for meshing with the sun 32 has an average diameter denoted DI and is located in another median plane P'. The median planes P, P' are parallel to each other and perpendicular to the axis X. The diameter D2 is less than the diameter DI. Finally, each toothing 34al, 34a2 here comprises a single helix.

[0064] Figures 4 to 6 show a reducer 28 with symmetrical double teeth as well as a device 10 for driving at least one wheel of an aircraft landing gear.

[0065] In the example shown, the reducer 28 is of the epicyclic gear type and comprises:

[0066] - a solar 32 having an axis of rotation X,

[0067] - a crown 38 which extends around the solar 32 and which is configured to be stationary in rotation around the X axis, and

[0068] - satellites 34 which are meshed with the sun 32 and the crown 38 and which are held by a planet carrier 36 which is configured to be rotatable about the X axis.

[0069] The plane H is defined as being a median plane perpendicular to the axis X and passing substantially through the middle of the reducer 28.

[0070] The sun gear 32 comprises an external toothing 32a for meshing with the satellites 34. The toothing 32a may be of the herringbone type and have two sets of adjacent teeth. The toothing 32a is symmetrical with respect to the plane H, its teeth being located on either side of the plane H.

[0071] In the example shown, the solar 32 comprises a shaft 32c which may be that of the motor 20 or which can be connected to the shaft of the motor 20, and a pinion comprising at its external periphery the external toothing 32a.

[0072] The crown 38 is formed by two independent rings 38a, 38b and comprises two internal teeth 38dl, 38d2 carried respectively by the two rings 38a, 38b.

[0073] The teeth 38dl, 38d2 may each be of the helical type. The teeth 38dl, 38d2 are symmetrical with respect to the plane H.

[0074] 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 crown holder 40 which is fixed to a stator of the device 10.

[0075] As is the case with the crown 38, the crown carrier 40 has a symmetry with respect to the plane H which intersects the crown carrier 40 in its middle.

[0076] Each satellite 34 comprises a median external toothing 34a of average diameter DI for meshing with the sun gear 32, and two lateral external toothings 34b 1, 34b2 of diameter D2, different from DI and in particular less than D1, for meshing with the toothings 38d1, 38d2 of the crown 38.

[0077] These diameters are average diameters 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.

[0078] The teeth 34bl, 34b2 are identical, as are the teeth 38dl, 38d2.

[0079] 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 helical teeth 34bl, 34b2 are located respectively on the axial ends of the sleeve 58. The herringbone teeth 34a are located at the external periphery of the web 60.

[0080] The teeth 34a are crossed in their middle by the plane H. The teeth 34b 1, 34b2 are also arranged symmetrically with respect to the plane H.

[0081] The toothing 34a and the external periphery of the web 60 have an axial dimension which is less than the axial distance between the rings 38a, 38b, so that each satellite 34 can freely rotate in the crown carrier 40 and between the rings 38a, 38b.

[0082] Each of the satellites 34 is mounted on a cylindrical body 44a which passes through the satellite 34, and in particular its sleeve 58, and which is fixed to the planet carrier 36.

[0083] The body 44a of a bearing 44 extends along the axis Y and comprises at least one of its longitudinal ends an extension 44b housed in an orifice forming a seat of the planet carrier 36.

[0084] The body 44a is generally tubular and includes an internal oil circulation bore which generally communicates with oil supply conduits to a external cylindrical surface of the body for the formation of the oil film between this surface and an internal cylindrical surface of the satellite 34.

[0085] In the context of the present invention, the solar 32 is coupled with the shaft 30 of the electric motor 20. The crown 38 is fixed and the planet carrier 36 is connected to the rim 16 of the wheel 12.

[0086] [Fig.6] shows that the motor 20 has an annular shape centered on the X axis and is arranged next to the reducer 28. Preferably, the motor 20 is arranged next to and at the level of the satellites 34.

[0087] In the example shown in [Fig.4], the planet carrier 36 comprises a single transverse wall 36c 1 which is perpendicular to the axis X and on which the satellites 34 are mounted in a cantilevered manner. The aforementioned cylindrical bodies 44a are thus mounted by only one of their ends in orifices of this transverse wall 36c 1.

[0088] The planet carrier 36 further comprises a shaft 36d or a portion of shaft connected to the rim 16. This connection can be made by a clutch system which is capable of adopting two positions: a first position in which the output shaft of the reducer 28, and in particular the shaft 36d, is coupled to the rim 16 or to the shaft of the rim, and a second position in which this output shaft is uncoupled from the rim 16 which is then in freewheel mode.

[0089] In the case of [Fig.5], the transverse wall 36c is replaced by radial arms extending from the shaft 36d to the cylindrical bodies 44a. The number of these arms is equal to the number of satellites 34 and the arms are preferably regularly distributed around the axis X.

[0090] As seen in [Fig.4], the shafts 32c, 36d are centered and guided in rotation around the X axis by bearings 50.

[0091] [Fig. 6] shows that the motor 20 of the device 10 comprises a rotor 20a and a stator 20b. The rotor 20a here has an annular shape and is connected to the shaft 32c. The stator 20b has an annular shape and extends around the rotor 20a and also on a side of the rotor 20a opposite the reduction gear 28. The ring gear 38 can be fixedly connected to the stator 20b.

[0092] In the embodiments of Figures 7 and 8, the reducer 28 is of the planetary gear type and differs from the previous embodiment essentially in that its planet carrier 36 is fixed and its crown 38 is movable.

[0093] It is therefore the crown 38 which is fixed to the rim 16 of the wheel 12. For this, the crown carrier 40 is connected to the rim 16 or comprises a portion of shaft 40a for connection to the rim 16.

[0094] The planet carrier 36 is fixed to the stator 20b of the electric motor 20 for example.

[0095] The other features described above in relation to Figures 4 to 6 apply to the embodiments of Figures 7 and 8.

[0096] In the case of [Fig.7], it can be seen that the stator 20b of the motor 20 comprises a rod 20c which is centered on the X axis and which extends along the X axis successively crossing the reducer 28 and the rim 16.

[0097] In the case of [Fig.8], it can be seen that the planet carrier 36 comprises two transverse walls 36c 1, 36c2 which are perpendicular to the X axis and between which the satellites 34 are mounted. At least one of these transverse walls 36c 1, 36c2 or even both, comprises a central orifice for the passage of the shaft portion 32c of the solar 32. Each of the transverse walls 36c 1, 36c2 could be replaced by a series of radial arms as mentioned above. The cylindrical bodies 44a for mounting the satellites 34 would then be connected to two arms via their two axial ends.

[0098] [Fig. 9] shows an example of guidance of the satellites 34 of the reducer 28. The satellites 34 are guided by rolling bearings 45 which are here more particularly roller bearings. The guide bearings 45 of each satellite 34 are two in number and are mounted around the longitudinal ends of this satellite, between these ends and the planet carrier 36. Each of the bearings 45 comprises an internal ring 45a carried by the satellite 34 or integrated into the latter, and an external ring 45b carried by the planet carrier 36. The rollers 45c are mounted between the rings 45a, 45b.

[0099] It can be seen in [Fig.9] that the teeth 34, 34b 1, 34b2 of the satellites 34 are located between the bearings 45. This assembly makes it possible to balance as best as possible the moments applied to the satellites 34 by the meshing.

[0100] Alternatively and as shown in [Fig.10], the satellites 34 are guided by needle bearings 47. These bearings 47 are three in number and are mounted radially between the satellites 34 and the bodies 44a. Each of the bearings 47 is aligned radially with one of the teeth 34a, 34b1, 34b2 of the satellite 34. This assembly makes it possible to reduce the axial size.

[0101] Each of the bearings 47 may have an axial length or dimension L1, L2, L3 measured along the Y axis, which represents at least 80% of the axial length or dimension L4, L5, L6 of the corresponding toothing 34a, 34b1, 34b2.

[0102] In yet another variant not shown, the guide bearings of the satellites 34 are smooth bearings or hydrodynamic bearings.

[0103] The reducer 28 as described above allows a large reduction ratio compared to the reducers of the prior art, and has a small footprint, these two parameters being important for the use of this reducer in a device for driving at least one wheel of an aircraft landing gear.

Claims

Claims

1. Device (10) for driving at least one wheel (12) of an aircraft landing gear (14), this device (10) comprising: - at least one landing gear wheel (12), this wheel (12) comprising a rim (16) having an axis of rotation (X), - an electric motor (20) comprising a shaft, - a mechanical transmission system (22) between the motor shaft (20) and the rim (16), this mechanical transmission system (22) comprising a mechanical reducer (28), characterized in that the mechanical reducer (28) comprises: - a sun gear (32) integral in rotation with the motor shaft (20), this sun gear (32) being centered on the axis (X) and comprising an external toothing (32a), - a crown (38) centered on the axis (X) and which comprises two internal toothings (38dl, 38d2), and - satellites (34) which are carried by a stellite carrier (36) and which each have a median plane of symmetry perpendicular to the axis (X),each of the satellites (34) comprising three external teeth (34a, 34b 1, 34b2), including a middle external tooth which is meshed with the tooth (32a) of the sun gear, and two lateral external teeth (34b 1, 34b2) which are respectively arranged on either side of the middle external tooth (34a) and which are respectively meshed with the teeth (38dl, 38d2) of the crown (38).,

2. Device (10) according to claim 1, wherein the crown (38) is fixed and is fixed to a stator of the device (10), and the planet carrier s (36) is rotatable about the axis (X) and is fixed to the rim (16).

3. Device (10) according to claim 1, wherein the crown (38) is rotatable about the axis (X) and is fixed to the rim (16), and the planet carrier (36) is fixed and is fixed to a stator of the device (10).

4. Device (10) according to one of the preceding claims, in which the teeth (38dl, 38d2) of the crown (38) are identical.

5. Device (10) according to one of the preceding claims, in which the toothing (32a) of the sun gear (32) and the median external toothing (34a) of each of the satellites (34) are chevron-shaped.

6. Device (10) according to one of the preceding claims, in which the lateral external teeth (34b 1 , 34b2) of each of the satellites (34) and the teeth of the crown (38) are helical.

7. Device (10) according to one of the preceding claims, in which the motor (20) has an annular shape centered on the axis (X) and is arranged next to the reducer (28).

8. Device (10) according to one of the preceding claims, in which the motor (20) is arranged next to and at the level of the satellites (34).

9. Device (10) according to one of the preceding claims, in which the middle toothing (34a) has a diameter greater than the diameter of the lateral toothings (34b 1, 34b2).

10. Device (10) according to one of the preceding claims, in which the planet carrier (36) comprises a single transverse wall (36cl) which is perpendicular to the axis (X) and on which the satellites (34) are mounted in a cantilever manner.

11. Device (10) according to one of claims 1 to 7, in which the planet carrier (36) comprises two transverse walls (36c 1, 36c2) which are perpendicular to the axis (X) and between which the satellites (34) are mounted, at least one of these transverse walls (36c 1, 36c2) or even both comprising a central orifice for the passage of the motor shaft (20).

12. Device (10) according to one of the preceding claims, in which the satellites (34) are each centered and guided by: - two roller bearings (45) carried by the planet carrier (36), the teeth (34a, 34b 1, 34b2) of each of the satellites (34) being located axially between these roller bearings (45), - or three needle bearings (47) carried by the planet carrier (36), each of the needle bearings (47) being radially in line with one of the teeth (34a, 34b 1, 34b2) of the satellite (34).

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