Device for driving 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) comprising a rim (16) having an axis of rotation (X), - an electric motor (20) comprising a shaft (30), - a system (22) for mechanical transmission between the shaft of the motor (20) and the rim (16), this mechanical transmission system (22) comprising a mechanical reduction gear (28) which has: - a movable ring gear (38) which rotates conjointly with the shaft of the motor (20), - a movable sun gear (32) which rotates conjointly with the rim (16), - a stationary sun gear (56) attached to a stator of the device (10), and - planet gears (34) which mesh with the ring gear and the sun gears.

Description

[0001] DESCRIPTION

[0002] TITLE: DEVICE FOR DRIVING AT LEAST ONE WHEEL OF AN AIRCRAFT LANDING GEAR

[0003] Technical field of the invention

[0004] The present invention relates to a device for driving at least one wheel of an aircraft landing gear.

[0005] Technical background

[0006] The technical background includes in particular document DE-A1 -10 2010 029823, US-A1 -2007 / 181357 and US-A1 -2008 / 070736.

[0007] An aircraft has 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 turbomachinery.

[0008] 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.

[0009] 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.

[0010] 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.

[0011] 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. In the distant field of aircraft turbomachinery, it is known to use a mechanical reducer to ensure power transmission between two rotating mechanical shafts.

[0012] There are many types of reducers, for example differential, planetary, epicyclic, intermediate line, series reduction stages, etc.

[0013] In the state of the art of turbofan engines, the gearboxes are planetary or epicyclic. Such a gearbox 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 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 planets. These axes are parallel to the longitudinal axis of the turbomachine.

[0014] There are several reducer architectures. In other similar applications, there are so-called differential or "compound" architectures.

[0015] - 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 to the solar.

[0016] - 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.

[0017] - On a differential reducer, no element is fixed in rotation. The crown rotates in the opposite direction to the sun and the planet carrier.

[0018] 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. 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 can be internal or external.

[0019] A satellite can have one or two meshing stages. A single-stage satellite has a toothing that 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.

[0020] A double-stage satellite consists of 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 generally cooperates with the crown.

[0021] A double-stage gear reducer has the advantage of having a higher reduction ratio than a single-stage gear reducer of the same size.

[0022] 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 that corresponds to the low rotational speed of the wheel. The epicyclic and planetary gears of current technology do not allow these reduction levels to be obtained in such a restricted space.

[0023] The invention provides a solution to at least some of these problems, which is simple, effective and economical.

[0024] Summary of the invention

[0025] The invention relates to a device for driving at least one wheel of an aircraft landing gear, this device comprising: - at least one landing gear wheel, this wheel comprising a rim having an axis of rotation,

[0026] - an electric motor comprising a shaft,

[0027] - a mechanical transmission system between the motor shaft and the rim, this mechanical transmission system comprising a mechanical reducer, characterized in that the mechanical reducer comprises:

[0028] - a movable crown centered on the axis and which has internal teeth, this movable crown being integral in rotation with the motor shaft,

[0029] - a mobile sun gear centered on the axis and which has external teeth, this mobile sun gear being integral in rotation with the rim,

[0030] - a fixed solar centered on the axis and which has external teeth, this fixed solar being configured to be fixed to a stator of the device, and

[0031] - satellites which are meshed with the crown and the sun gears, the satellites being carried by a planet carrier movable in rotation around the axis, each of the satellites comprising two external teeth meshed respectively with the teeth of the fixed and movable sun gears, one of these external teeth being furthermore meshed with the toothing of the crown. 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 independent double sun gears and having different functions. One of the sun gears is fixed and the other of the sun gears is movable in rotation. The movable sun gear forms a (torque) output of the reduction gear, the input of the reduction gear being formed by the crown. The planet carrier is also movable in rotation. It can be free in rotation and therefore independent of any rotor of the electric motor.

[0032] The invention is compatible with a multi-stage reducer as mentioned above. It is also compatible with any type of toothing (straight, helical, herringbone, etc.). The invention is further compatible with a planet carrier of the monobloc type or of the cage and cage carrier type. These different types of reducers are well known to those skilled in the art. The solution proposed below is compatible with any type of planet bearing, whether it is composed of rolling elements, a hydrodynamic bearing, etc.

[0033] The proposed solution is therefore similar to a device equipped with a mechanical reducer of the “inverted” Wolfrom type, this reducer comprising two sun gears, respectively fixed and mobile, instead of two crowns, respectively fixed and mobile, in a conventional Wolfrom type reducer. The device according to the invention may comprise one or more of the following characteristics, taken in isolation from each other, or in combination with each other:

[0034] - the teeth of the fixed and mobile solar panels have the same diameter;

[0035] - the teeth of the fixed and mobile solar panels have different diameters;

[0036] - the teeth of fixed and mobile solar panels have different numbers of teeth;

[0037] - the teeth of the crown and the teeth of the mobile sun gear are meshed with the same teeth of each of the satellites;

[0038] - the teeth of the crown and the teeth of the fixed sun gear are meshed with the same teeth of each of the satellites;

[0039] - the crown is meshed with one of the teeth of each of the satellites and extends around the other tooth of each of the satellites;

[0040] - all teeth are chosen from straight, helical or herringbone teeth;

[0041] - the motor has an annular shape centered on the axis and is arranged axially between the wheel and the reducer;

[0042] - the motor extends at least partly around the mobile solar;

[0043] - the teeth of each of the satellites have different diameters, the teeth of the smallest diameter of each of the satellites meshing with the teeth of the fixed sun, and the teeth of the largest diameter of each of the satellites meshing with the teeth of the mobile sun;

[0044] - the electric motor is arranged on the side of the crown and on the side opposite the fixed solar; -- the teeth of each of the satellites have identical diameters and different numbers of teeth;

[0045] -- the teeth of each of the satellites have different diameters, the teeth of the smallest diameter of each of the satellites meshing with the teeth of the mobile sun, and the teeth of the largest diameter of each of the satellites meshing with the teeth of the fixed sun;

[0046] - the electric motor is located on the fixed solar side;

[0047] - the mobile sun is centered and guided by two bearings, the first bearing of which is located in line with the teeth of the sun, and a second bearing is axially offset from these teeth;

[0048] - the second bearing is located to the right of said motor, and radially inside it;

[0049] - the motor shaft is centered and guided by two bearings which are arranged radially inside a rotor of said motor;

[0050] - the second bearing is arranged radially inside the guide bearings of the motor shaft, and is located axially between these bearings; each of the satellites is centered and guided by two bearings which are located respectively in line with the teeth of this satellite;

[0051] -- the satellites are each centered and guided by two roller bearings carried by the planet carrier, the teeth of each of the satellites being located between these roller bearings;

[0052] -- the satellites are each centered and guided by two needle bearings carried by the planet carrier, each of the needle bearings being radially aligned with one of the teeth of the satellite.

[0053] Brief description of the figures

[0054] 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:

[0055] [Fig.1] Figure 1 is a schematic perspective view of a wheel of an aircraft landing gear and a device for driving this wheel, [Fig.2] Figure 2 is a partial axial sectional view of a mechanical reducer,

[0056] [Fig.3] Figure 3 is a very schematic partial axial sectional view of a reducer for a device according to one embodiment of the invention,

[0057] [Fig. 4] Figure 4 is seen similar to that of Figure 3 and illustrates an alternative embodiment of the device;

[0058] [Fig.5] Figure 5 is a view similar to that of Figure 3 and illustrates another alternative embodiment of the device;

[0059] [Fig.6] Figure 6 is a schematic axial sectional view of a wheel of an aircraft landing gear and of a device for driving this wheel according to one embodiment of the invention,

[0060] [Fig.7] Figure 7 is an enlarged view of part of Figure 6, and

[0061] [Fig.8] Figure 8 is a schematic perspective view of the reducer of the drive device of Figure 6.

[0062] Detailed description of the invention

[0063] Figure 1 shows a device 10 for driving at least one wheel 12 of an aircraft landing gear 14.

[0064] 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.

[0065] 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.

[0066] 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 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 reduce 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.

[0067] The mechanical transmission system 22 comprises a mechanical reducer 28, an exemplary embodiment of which is illustrated in FIG. 2.

[0068] 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 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.

[0069] The set of satellites 34 is held by a frame called a satellite carrier 36. Each satellite 34 rotates around its own Y axis, and meshes with a crown 38.

[0070] At the output we have:

[0071] ■ 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.

[0072] ■ In another planetary configuration, the set of planet gears 34 is held by a planet carrier 36 which is fixed to a stator. Each planet gear drives the ring gear 38 which is connected to the shaft 42 via a ring gear carrier 40.

[0073] ■ 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.

[0074] 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 are 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.

[0075] 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:

[0076] ■ An upstream ring 38a consisting of a rim 38aa and a fixing half-flange 38ab. On the rim 38aa is the front 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.

[0077] ■ 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.

[0078] 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.

[0079] Figure 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.

[0080] 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.

[0081] The present invention proposes, in a reduced size, to increase the reduction ratio of a mechanical reducer within the framework of a device 10 for driving at least one wheel of an aircraft landing gear, as illustrated in FIG. 1.

[0082] The reducer 28 of the device 10 according to the invention comprises all of the characteristics described above to the extent that they are not contrary to or do not contradict what follows.

[0083] The references used in figures 3 and following and already used in figures 1 and 2 therefore designate identical or similar elements.

[0084] Figures 3 to 5 illustrate embodiments of a reducer 28 for a device 10 according to the invention, which comprises:

[0085] - a movable crown 38 centered on the X axis and movable around this axis, the movable crown 38 comprising internal teeth 38d,

[0086] - a mobile sun 32 centered on the X axis and mobile around this X axis, the mobile sun 32 comprising an external toothing 32a,

[0087] - a fixed solar 56 centered on the X axis and which comprises an external toothing 56a, this fixed solar 56 being configured to be fixed to a stator of the device 10, and

[0088] - satellites 34 which are meshed with the sun gears 32, 56 and the crown 38, the satellites 34 being carried by a partially shown satellite carrier 36 which is rotatable around the X axis.

[0089] Each of the satellites 34 has two external teeth 34a, 34b meshed respectively with the teeth 32a, 56a of the fixed 32 and mobile 56 sun gears. One of these external teeth 34a, 34b is further meshed with the tooth 38d of the crown 38.

[0090] In the context of the present invention, the crown 38 is coupled with the shaft 30 of the electric motor 20. The mobile solar 32 is coupled to the shaft 42 of the rim 16 or to the rim 16 directly. The invention is also compatible with a decoupling system between the output of the reducer and the rim (for example via a mobile dog clutch).

[0091] Each of the satellites 34 is meshed with the sun gears 32, 56 and the crown 38 and comprises a first external toothing 34a of average diameter D1, and a second external toothing 34b of average diameter D2, different from D1. In the example shown, D1 is greater than D2. Alternatively, the teeth 34a and 34b could have equal diameters D1 and D2 and different numbers of teeth, so as to have different modules.

[0092] In the embodiment of figure 3, the toothing 34a of diameter D1 of each satellite 34 is meshed with the toothing 32a of the mobile sun 32 and the toothing 38d of the crown 38. The toothings 32a, 34a and 38d are thus in the same plane P1 perpendicular to the axis X. The toothing 34b of diameter D2 of each satellite 34 is meshed with the toothing 56a of the fixed sun 56.

[0093] In the embodiment of figure 4, the toothing 34a of diameter D1 of each satellite 34 is meshed with the toothing 56a of the fixed sun 56 and the toothing 38d of the crown 38. The toothing 34b of diameter D2 of each satellite 34 is meshed with the toothing 32a of the mobile sun 32. The toothings 56a, 34a and 38d are thus in the same plane P1 perpendicular to the axis X.

[0094] In the embodiment of figure 5, the toothing 34a of diameter D1 of each satellite 34 is meshed with the toothing 32a of the mobile sun 32. The toothing 34b of diameter D2 of each satellite 34 is meshed with the toothing 56a of the fixed sun 56 and with the toothing 38d of the crown 38. The toothings 56a, 34b and 38d are thus in the same plane P1 perpendicular to the axis X.

[0095] In the embodiment of Figure 5, it is further noted that the crown 38 or the shaft 30 to which it is connected extends around the teeth 34a of the satellites 34.

[0096] In the configuration of Figure 3 where the sun gear 32 and the movable crown 38 mesh with the same teeth 34a of the planet gears 34, it can be said that the output (torque) of the reducer is aligned with its input. In the configuration of Figures 4 and 5 where the sun gear 32 and the movable crown 38 mesh with different teeth 34a, 34b of the planet gears 34, it can be said that the output (torque) of the reducer is opposite to its input.

[0097] The number of teeth of the mobile sun gear 32 may be different from the number of teeth of the fixed sun gear 56 so as to have different diameters on the two sun gears. Alternatively, the diameters may be equal provided that different modules are available on the two sun gears 32, 56. The direction of rotation of the mobile sun gear 32 may depend on the relative diameter of the two sun gears 32, 56. For example, when the number of teeth of the mobile sun gear 32 is greater than that of the fixed sun gear 56, the reduction gear 28 is counter-rotating, that is to say that the mobile sun gear 32 rotates in the opposite direction to the ring gear 38. When the number of teeth of the mobile sun gear 32 is less than that of the fixed sun gear 56, the reduction gear 28 is co-rotating, that is to say that the ring gear 38 and the sun gear 32 rotate in the same direction.

[0098] Figures 6 to 8 illustrate in a more concrete manner an embodiment of a device 10 for driving a wheel 12 of a landing gear 14. Figure 6 further shows the position of the motor 20 next to, and in particular to the right, of the reduction gear 28. Alternatively, the motor 20 could be located to the left of the reduction gear 28.

[0099] The motor 20 has an annular shape and is arranged next to the ring gear 38 and on the side opposite the fixed sun gear 56. The motor 20 extends at least partly around the mobile sun gear 32 or the shaft 42 connected to this sun gear.

[0100] The crown 38 and the motor 20 are located on circumferences of the same diameter or of close diameters. The references 20a and 20b respectively designate the rotor and the stator of the motor 20, both annular. The stator 20b is fixed on or carried by the cowling 26 and the rotor 20a is guided in rotation by rolling bearings 46 on the stator or the cowling.

[0101] The shaft 30, and in particular the rotor 20a, of the motor 20 is centered and guided by two bearings 46 which are arranged radially inside the rotor 20a. The mobile sun gear 32 is centered and guided by two bearings 48, 50, a first bearing 48 of which is located in line with the toothing 32a of the sun gear 32, and a second bearing 50 is axially offset from this toothing 32a.

[0102] The second bearing 50 can be located to the right of the motor 20, and radially inside it.

[0103] In the example shown, the second bearing 50 is arranged radially inside the bearings 46 for guiding the shaft 30 of the motor 20, and is located axially between these bearings 46.

[0104] The planet carrier 36 carries the bearings 44 for guiding the planets 34. The planet carrier 36 is independent, which means that it is not connected to the rest of the engine by any torque transmission. It can be supported by any bearing with the crown 38 or the sun 32. It can also be completely free without support and simply balanced by the planets 34. The teeth 34a, 34b of each of the planets have different diameters, the tooth 34b of smaller diameter of each of the planets 34 meshes with the tooth 56a of the fixed sun 56. The tooth 34a of larger diameter of each of the planets 34 meshes with the tooth 32a of the mobile sun 32 and the tooth 38d of the crown 38. We therefore find the configuration of Figure 3.

[0105] Alternatively, the teeth 34a, 34b could have identical diameters with different numbers of teeth.

[0106] The number of satellites 34 of the reducer is equal to five in this example. The satellites 34 can be guided by rolling bearings 44 which are two in number per satellite 34 and are mounted around the longitudinal ends of each satellite, between these ends and the planet carrier 36.

[0107] The bearings 44 may be roller bearings carried by the planet carrier 36, the teeth 34a, 34b of each of the planets 34 being located between these bearings 44. Alternatively, the bearings 44 may be needle bearings carried by the planet carrier 36, each of the needle bearings being radially aligned with one of the teeth 34a, 34b of the planet 34 for example, as in the example illustrated.

[0108] The present invention makes it possible to obtain a high reduction ratio in a small footprint compared to other more conventional architectures (epicyclic or planetary gearset), and can be integrated more easily into certain systems than a conventional Wolfrom gearset. In the particular case of a conventional Wolfrom, for example, access to solar energy could be more complicated for a large diameter motor.

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 (30), - 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 movable crown (38) centered on the axis (X) and which comprises internal teeth (38d), this movable crown (38) being integral in rotation with the motor shaft (20), - a mobile sun (32) centered on the axis (X) and which comprises external teeth (32a), this mobile sun (32) being integral in rotation with the rim (16), - a fixed solar (56) centered on the axis (X) and which comprises external teeth (56a), this fixed solar (56) being configured to be fixed to a stator of the device (10), and - satellites (34) which are meshed with the crown and the sun gears, the satellites (34) being carried by a stellite carrier (36) movable in rotation around the axis (X), each of the satellites (34) comprising two external teeth (34a, 34b) meshed respectively with the teeth (32a, 56a) of the fixed and mobile sun gears (32, 56), one of these external teeth (34a, 34b) being further meshed with the tooth (38a) of the crown (38).

2. Device (10) according to claim 1, in which the teeth (32a, 56a) of the fixed and mobile sun gears (32, 56) have the same diameter.

3. Device (10) according to claim 1, in which the teeth (32a, 56a) of the fixed and mobile sun gears (32, 56) have different diameters.

4. Device (10) according to one of claims 1 to 3, in which the teeth (32a, 56a) of the fixed and mobile sun gears (32, 56) have different numbers of teeth.

5. Device (10) according to one of claims 1 to 4, in which the teeth (38d) of the crown (38) and the teeth (32a) of the mobile sun gear (32) are meshed with the same teeth (34a, 34b) of each of the satellites (34).

6. Device (10) according to one of claims 1 to 4, in which the teeth (38d) of the crown (38) and the teeth (56a) of the fixed sun gear (56) are meshed with the same teeth (34a, 34b) of each of the satellites (34).

7. Device (10) according to one of the preceding claims, in which the crown (38) is meshed with one of the teeth (34a, 34b) of each of the satellites (34) and extends around the other tooth (34b, 34a) of each of the satellites (34).

8. Device (10) according to one of the preceding claims, in which all the teeth (32a, 34a, 34b, 38d, 56a) are chosen from straight, helical or herringbone teeth.

9. 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 axially between the wheel and the reducer (28).

10. Device (10) according to one of the preceding claims, in which the motor (20) extends at least partly around the mobile solar (32).

11. Device (10) according to one of the preceding claims, in which the teeth (34a, 34b) of each of the satellites (34) have different diameters (D1, D2), the teeth (34b) of smaller diameter (D2) of each of the satellites (34) meshing with the teeth (56a) of the fixed sun (56), and the teeth (34a) of larger diameter of each of the satellites (34) meshing with the teeth (32a) of the mobile sun (32).

12. Device (10) according to one of the preceding claims, in which the electric motor (20) is arranged on the side of the crown (38) and on the side opposite the fixed solar (56).

13. Device (10) according to one of the preceding claims, in which the mobile sun (32) is centered and guided by two bearings (48, 50) of which a first bearing (48) is located in line with the teeth (32a) of the sun, and a second bearing (50) is axially offset from this teeth (32a).

14. Device according to the preceding claim, in which the second bearing (50) is located in line with said motor (20), and radially inside it.

15. Device (10) according to one of the preceding claims, in which the shaft (30) of the motor (20) is centered and guided by two bearings (46) which are arranged radially inside a rotor (20a) of said motor.

16. Device according to all of claims 14 and 15, in which the second bearing (50) is arranged radially inside the bearings (48, 50) for guiding the shaft (30) of the motor (20), and is located axially between these bearings (48, 50).

17. Device (10) according to one of the preceding claims, in which each of the satellites (34) is centered and guided by two bearings (44) which are located respectively in line with the teeth (34a, 34b) of this satellite.

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