Motor assembly comprising at least one rotational guidance system allowing axial expansion

Abstract

Motor assembly comprising at least one rotational guidance system allowing axial expansion. The invention relates to a motor assembly comprising an electric motor (42) which includes a structure (44), a stator (46), a rotor (48), a hollow shaft (50) integral with the rotor (48) and coupled to an output shaft (64) and a rotational guidance system (52) connecting the structure (44) and the hollow shaft (50) and comprising first and second bearings (52.1, 52.2) immobilized in translation along an axial direction with respect to a first cylindrical wall among outer and inner cylindrical walls (56.1, 56.2) integral respectively with the structure (44) and the hollow shaft (50) and capable of translating along the axial direction with respect to a second cylindrical wall, different from the first cylindrical wall, among the outer and inner cylindrical walls (56.1, 56.2).This arrangement of the first and second bearings allows for the absorption of potential axial deformations due to expansion phenomena. Figure 3.

Description

Title of the invention: Motor assembly comprising at least one rotational guidance system allowing axial expansion

[0001] The present application relates to a motor assembly comprising at least one rotational guidance system allowing axial expansion.

[0002] According to embodiments visible in Figures 1 and 2, a motor assembly 10 comprises an electric motor 12 comprising a structure 14, a stator 16 fixed relative to the structure 14 and connected to the latter, a rotor 18 positioned inside the stator 16 as well as a hollow shaft 22 secured to the rotor 18 and connected to the structure 14 by a rotational guidance system 20. The hollow shaft 22 and the rotor 18 are coaxial and have a motor axis A12. The structure 14 is delimited by first and second transverse walls 14.1, 14.2 (substantially perpendicular to the motor axis A12), the stator 16, the rotor 18 and the hollow shaft 22 being positioned between the first and second transverse walls 14.1, 14.2. The hollow shaft 22 extends between first and second ends 22.1, 22.2 close respectively to the first and second transverse walls 14.1, 14.2.

[0003] The rotational guidance system 20 comprises first and second bearings 20.1, 20.2, such as rolling bearings for example, positioned close to the first and second ends 22.1, 22.2 of the hollow shaft 22, each interposed between the structure 14 and the hollow shaft 22. As illustrated in FIGS. 1 and 2, each of the first and second bearings 20.1, 20.2 is immobilized in translation in an axial direction (parallel to the motor axis A12), in two opposite directions, relative to the hollow shaft 22 and to the structure 14.

[0004] The motor assembly 10 also comprises a relatively long and flexible output shaft 24, which extends between first and second ends 24.1, 24.2, partially positioned in the hollow shaft 22, the first end 24.1 of the output shaft 24 being positioned projecting relative to the first transverse wall 14.1 of the structure 14 of the electric motor 12 and connected to a load 26 such as a propeller or a gearbox for example, the second end 24.2 of the output shaft 24 and the second end 22.2 of the hollow shaft 22 being located approximately in the same transverse plane.

[0005] According to one configuration, the load 26 is positioned against the first transverse wall 14.1 and connected to the structure 14.

[0006] According to a first embodiment visible in [Fig.l], the first end 24.1 of the output shaft 24 is connected to the load 26 by a coupling system 28 comprising male splines 28.1 located at the level of the first end 24.1 of the output shaft 24 and configured to cooperate with female splines of a sleeve secured to the load 26. In addition, the second end 24.2 of the output shaft 24 is connected to the second end 22.2 of the hollow shaft 22 by a rigid connection 30.

[0007] According to a second embodiment visible in [Fig. 2], the first end 24.1 of the output shaft 24 is connected to the load 26 by a rigid connection. In addition, the second end 24.2 of the output shaft 24 and the second end 22.2 of the hollow shaft 22 are connected by a coupling system 32 comprising male splines 32.1 located at the second end 24.2 of the output shaft 24 and configured to cooperate with female splines 32.2 provided at the second end 22.2 of the hollow shaft 22.

[0008] To remedy a possible malfunction of the electric motor 12, the motor assembly 10 comprises, in addition to the coupling system 28, 32, a disengageable coupling system, such as a freewheel for example, to uncouple the electric motor 12 and the load 26. According to one arrangement, the disengageable coupling system is positioned between the hollow shaft 22 and the load 26.

[0009] This disengageable coupling system must be regularly inspected and includes wear parts which must be regularly changed.

[0010] To be able to access the disengageable coupling system, it is necessary to separate the electric motor 12 and the load 26 and to extract the output shaft 24 from the hollow shaft 22. Consequently, this disengageable coupling system is difficult to access, making the inspection and maintenance phases difficult.

[0011] To limit the risks of premature wear of some of its elements, the motor assembly 10 comprises a lubrication system for lubricating, among other things, the coupling system 28, 32. Due to a friction phenomenon, in particular of the lubricant, the motor assembly 10 is subjected to significant temperature variations which cause different expansions between the structure 14, the hollow shaft 22 and the output shaft 24. These expansion phenomena generate significant axial loads at the bearings 20.1, 20.2 of the rotational guidance system 20 which must be sized accordingly, which leads to an increase in the mass of the motor assembly 10 and to a reduction in the total efficiency of the transmission chain due to significant losses at the bearings.

[0012] The present invention aims to remedy all or part of the drawbacks of the prior art.

[0013] To this end, the invention relates to an engine assembly comprising: a. an electric motor which comprises a structure having first and second transverse faces, a stator fixed relative to the structure, a rotor coaxial with the stator, a hollow shaft secured to the rotor and a system of rotating guide connecting the structure and the hollow shaft, b. an output shaft, extending between first and second ends, partially positioned in the hollow shaft, the first end of the output shaft projecting from the first transverse face of the structure and configured to be connected to a load, c. at least one coupling system connecting the hollow shaft and the output shaft, d. the rotational guidance system comprising first and second bearings positioned on either side of the rotor as well as, for each of the first and second bearings, outer and inner cylindrical walls respectively integral with the structure and the hollow shaft, each of the first and second bearings comprising outer and inner parts in contact respectively with the outer and inner cylindrical walls.

[0014] According to the invention, the first and second bearings are immobilized in translation in an axial direction relative to a first cylindrical wall among the outer and inner cylindrical walls and can translate in the axial direction relative to a second cylindrical wall, different from the first cylindrical wall, among the outer and inner cylindrical walls.

[0015] The fact that the first and second bearings of the engine assembly are mounted floating relative to one of the outer and inner cylindrical walls makes it possible to tolerate possible axial displacements between the output shaft and the structure, due for example to expansion phenomena. Thus, this results in a reduction of friction losses resulting from the stresses linked to these axial displacements. It is therefore not necessary to oversize the first and second bearings so that they can take up the stresses linked to these axial displacements.

[0016] According to another characteristic, the motor assembly comprises, for each first or second bearing, a pair of first and second axial stops secured to the first cylindrical wall among the outer and inner cylindrical walls, spaced apart by a distance substantially equal to a dimension taken in the axial direction of the first and second bearing so as to immobilize it in the axial direction relative to the first cylindrical wall.

[0017] According to another characteristic, the engine assembly comprises: a. third and fourth axial stops integral with the second cylindrical wall among the outer and inner cylindrical walls, positioned on either side of the first and second bearings or between the first and second bearings, spaced from the first and second bearings, b. at least one first elastically deformable element interposed between the first or second bearing and the third or fourth axial stop.

[0018] According to another characteristic, the engine assembly comprises a first element elastically formable between the first bearing and the third axial stop and a second elastically deformable element interposed between the second bearing and the fourth axial stop.

[0019] According to another characteristic, the first and second cylindrical walls correspond respectively to the inner and outer cylindrical walls.

[0020] According to another characteristic, the motor assembly comprises, for each bearing, a seal interposed between the bearing and the rotor, in contact simultaneously with the outer and inner cylindrical walls.

[0021] According to another characteristic, the coupling system is positioned at or near the second transverse face of the structure in order to facilitate accessibility of the coupling system, said second transverse face comprising an orifice positioned in the extension of the hollow shaft.

[0022] According to another characteristic, the coupling system is interposed between first and second extensions passing through the orifice, secured respectively to the hollow shaft and the output shaft.

[0023] According to another characteristic, the first extension comprises: a. a tubular body, in which the coupling system is positioned, which extends between first and second ends, the first end being connected to the hollow shaft, b. a transverse wall closing the second end of the tubular body.

[0024] According to another characteristic, the motor assembly comprises a set of axial stops configured to immobilize in translation in the axial direction the coupling system relative to the hollow shaft and to the output shaft.

[0025] According to another characteristic, the coupling system is a disengageable coupling system configured to occupy a first state in which the disengageable coupling system immobilizes the first and second extensions in rotation relative to each other as well as a second state in which the disengageable coupling system allows the first and second extensions to pivot relative to each other.

[0026] According to another characteristic, the engine assembly comprises a plug configured to close the orifice provided at the level of the second transverse face of the structure as well as fixing elements connecting the plug and the second transverse face.

[0027] According to another characteristic, the motor assembly comprises at least one sensor configured to determine at least one characteristic of the rotational movement of the output shaft.

[0028] According to another characteristic, the sensor is positioned between the plug secured to the structure and a first extension secured to the hollow shaft.

[0029] The invention also relates to an aircraft comprising at least one assembly engine according to one of the preceding characteristics.

[0030] Other characteristics and advantages will emerge from the description of the invention which follows, a description given by way of example only, with reference to the appended drawings, among which:

[0031] [Fig-1] is a schematic section of an engine assembly illustrating a first mode of implementation of the prior art,

[0032] [Fig.2] is a schematic section of an engine assembly illustrating a second embodiment of the prior art,

[0033] [Fig.3] is a schematic section of an engine assembly illustrating an embodiment according to the invention,

[0034] [Fig.4] is a schematic section of an engine assembly illustrating another embodiment according to the invention.

[0035] According to an embodiment visible in [Fig. 3], a motor assembly 40 comprises an electric motor 42 comprising a structure 44, a stator 46 fixed relative to the structure 44 and connected to the latter, a rotor 48 coaxial with the stator 46, a hollow shaft 50 secured to the rotor 48 as well as a rotational guidance system 52 connecting the structure 44 and the hollow shaft 50.

[0036] The hollow shaft 50 and the rotor 48 are coaxial and have a motor axis A42.

[0037] For the remainder of the description, an axial direction is parallel to the motor axis A42 and a transverse plane is perpendicular to the motor axis A42.

[0038] According to one embodiment, the structure 44 comprises a tubular body 44.1 as well as first and second transverse walls 44.2, 44.3 positioned at each end of the tubular body 44.1, the tubular body 44.1 as well as the first and second transverse walls 44.2, 44.3 being connected to each other.

[0039] Of course, the invention is not limited to this embodiment for the structure 44. Whatever the embodiment, the structure 44 is delimited by first and second transverse faces 54.1, 54.2, the stator 46, the rotor 48 and the hollow shaft 50 being positioned between the first and second transverse faces 54.1, 54.2.

[0040] The hollow shaft 50 extends between first and second ends 50.1, 50.2 close respectively to the first and second transverse faces 54.1, 54.2. According to one arrangement, the first and second ends 50.1, 50.2 of the hollow shaft 50 pass respectively through the first and second transverse faces 54.1, 54.2 of the structure 44.

[0041] The rotational guidance system 52 comprises first and second bearings 52.1, 52.2, such as rolling bearings for example, positioned near the first and second ends 50.1, 50.2 of the hollow shaft 50, on either side of the rotor 48. According to one arrangement, each of the first and second bearings 52.1, 52.2 is composed of a single bearing. According to another arrangement, at least one of the first and second levels 52.1, 52.2 is composed of several levels.

[0042] For each of the first and second bearings 52.1, 52.2, the rotational guidance system 52 comprises outer and inner cylindrical walls 56.1, 56.2 secured respectively to the structure 44 and to the hollow shaft 50. Each of the first and second bearings 52.1, 52.2 of the rotational guidance system 52 comprises an outer part 58.1 in contact with the outer cylindrical wall 56.1 as well as an inner part 58.2 in contact with the inner cylindrical wall 56.2.

[0043] According to one embodiment, the motor assembly 40 comprises, for each bearing 52.1, 52.2, a seal 60.1, 60.2 interposed between the bearing 52.1, 52.2 and the rotor 48 in contact simultaneously with the outer and inner cylindrical walls 56.1, 56.2.

[0044] According to one embodiment, the motor assembly 40 comprises at least a first lubrication system 62 configured to lubricate at least the rotational guidance system 52, in particular the first and second bearings 52.1, 52.2. This first lubrication system 62 is designed so that the lubricant is not in contact with the rotor 48 in order to limit its heating.

[0045] The motor assembly 40 comprises a relatively long output shaft 64, which extends between first and second ends 64.1, 64.2, partially positioned in the hollow shaft 50, the first end 64.1 of the output shaft 64 being positioned projecting relative to the first transverse face 54.1 of the structure 44 of the electric motor 42 and configured to be connected to a load 66, the second end 64.2 of the output shaft 64 and the second end 50.2 of the hollow shaft 50 being located approximately in the same transverse plane. Guide bearings 65 may be provided between the hollow shaft 50 and the output shaft 64, as illustrated in [Fig.4].

[0046] According to one arrangement, the load 66 is positioned against the first transverse face 54.1 of the structure 44 and connected to the latter by at least one fixing element 66.1.

[0047] According to one application, the load 66 is a propeller and / or a gearbox of a propulsion assembly of an aircraft. Thus, an aircraft comprises at least one engine assembly 40 as illustrated in [Fig.3].

[0048] The motor assembly 40 comprises at least one coupling system 68 connecting the hollow shaft 50 and the output shaft 64. According to one embodiment, the coupling system 68 is positioned at or near the second transverse face 54.2 of the structure 44 and connects, directly or indirectly, the second ends 50.2, 64.2 of the hollow shaft 50 and the output shaft 64. In addition, the second transverse face 54.2 of the structure 44 comprises an orifice 70 positioned in the extension of the second end 50.2 of the hollow shaft 50 to make the coupling system 68 accessible. Positioning the system coupling 68 at or near the second transverse face 54.2 of the structure 44 helps to facilitate accessibility of the coupling system 68 for its maintenance.

[0049] The hollow shaft 50 comprises a first extension 72 which passes through the second transverse face 54.2 of the structure 44, projecting relative to the latter. According to a first configuration, the hollow shaft 50 and the first extension 72 are made in one piece. According to a second configuration, the hollow shaft 50 and the first extension 72 are two separate elements. According to this second configuration, the first extension 72 comprises a tubular body 74 which has a cylindrical inner surface and extends between first and second ends, the first end being oriented towards the hollow shaft 50 and connected to the latter. The first extension 72 comprises an outer collar 76, integral with the first end of the tubular body 74, configured to be pressed against the hollow shaft 50 and connected to the latter by fixing elements 78.The first extension 72 comprises a transverse wall 80 configured to close the second end of the tubular body 74. Whatever the configuration, the first extension 72 is integral with the hollow shaft 50.

[0050] The output shaft 64 comprises a second extension 82 which passes through the second transverse face 54.2 of the structure 44, projecting relative to the latter. According to one configuration, the output shaft 64 and the second extension 82 are made in one piece. According to a second configuration, the output shaft 64 and the second extension 82 could be two separate elements connected to each other. The second extension 82 comprises a cylindrical outer surface substantially coaxial with the cylindrical inner surface of the first extension 72.

[0051] The coupling system 68 is interposed between the first and second extensions 72, 82 passing through the orifice 70, secured respectively to the hollow shaft 50 and the output shaft 64.

[0052] According to an embodiment visible in [Fig. 4], the output shaft 64 comprises several sections 64a, 64b and 82 placed end-to-end and coupled together. A compression spring 83 may be provided between the transverse wall 80 of the first extension 72 and the second extension 82 of the output shaft 64 to keep the sections 64a, 64b and 82 coupled. Providing an output shaft 64 in several sections 64a, 64b and 82 makes it possible to reduce the clearance required for its disassembly. According to one arrangement, the second extension 82 comprises a housing 83.1 for housing a portion of the compression spring 83.

[0053] According to one configuration, the coupling system 68 is a disengageable coupling system, such as a freewheel for example, configured to occupy a first state in which the disengageable coupling system immobilizes in rotation the first and second extensions 72, 82 relative to each other as well as a second state in which the disengageable coupling system allows the first and second extensions 72, 82 to pivot relative to each other. In the case of a freewheel, the latter immobilizes in rotation the first and second extensions 72, 82 in a first direction of rotation and allows them to pivot relative to each other in a second direction of rotation (opposite to the first direction of rotation).

[0054] When the disengageable coupling system 68 is a freewheel, it comprises an outer ring 68.1 in contact with the first extension 72, an inner ring 68.2 in contact with the second extension 82, third and fourth bearings 68.3, 68.4 interposed between the outer and inner rings 68.1, 68.2 as well as a cage of locking rollers 68.5 interposed between the outer and inner rings 68.1, 68.2 and positioned between the third and fourth bearings 68.3, 68.4. In addition, the motor assembly 40 comprises a first rotational coupling 84 immobilizing in rotation the first extension 72 and the outer ring 68.1 relative to each other as well as a second rotational coupling 86 immobilizing in rotation the second extension 82 and the inner ring 68.2 relative to each other.

[0055] According to the embodiments, each of the first and second rotational couplings 84, 86 is an obstacle coupling such as a keyway, a set of male and female splines or the like.

[0056] Of course, the invention is not limited to this embodiment for the coupling system 68. The latter may not comprise outer and inner rings 68.1, 68.2. In this case, the third and fourth bearings 68.3, 68.4 are interposed between the first extension 72 and the second extension 82. In addition, the first rotational coupling 84 is provided between the first extension 72 and the locking roller cage 68.5 and the second rotational coupling 86 is provided between the second extension 82 and the locking roller cage 68.5.

[0057] When it comprises a transverse wall 80, the first extension 72 forms a housing in which the coupling system 68 is positioned. This embodiment provides better protection for the coupling system 68.

[0058] According to one embodiment, the motor assembly 40 comprises a second lubrication system 88 configured to lubricate the coupling system 68. According to one embodiment, this second lubrication system 88 comprises a lubricant supply 88.1 positioned between the hollow shaft 50 and the output shaft 64.

[0059] According to one embodiment, the first and second lubrication systems 62, 88 form a single lubrication system adapted to lubricate the coupling system 68 and the rotational guidance system 52.

[0060] According to one embodiment, the engine assembly 40 comprises a plug 90, configured to close the orifice 70 which passes through the second transverse face 54.2 of the structure 44, as well as fixing elements 92 connecting the plug 90 and the second transverse face 54.2. The structure 44 and the plug 90 form a casing in which the lubricant of the first and second lubrication systems 62, 88 is confined. This casing may comprise, in the lower part, a low point 94 for collecting the lubricant by gravity. A seal 106 may be interposed between the first extension 72 and the plug 90 to limit the spread of the lubricant.

[0061] As illustrated in [Fig.4], the plug 90 can be made in several parts assembled together.

[0062] According to one embodiment, the motor assembly 40 comprises at least one sensor 96 configured to determine at least one characteristic of the rotational movement of the output shaft 64. By way of example, the sensor 96 is a resolver configured to determine the angular position of the output shaft 64. According to one configuration, the sensor 96 is positioned between the plug 90 secured to the structure 44 and the first extension 72 secured to the hollow shaft 50. According to one arrangement, the plug 90 comprises an orifice having a first cylindrical wall. In addition, the first extension 72 has a cylinder shape 91, projecting relative to the transverse wall 80, providing a second cylindrical wall coaxial with the first cylindrical wall, the sensor 96 being interposed between the first and second cylindrical walls and immobilized in translation in the axial direction relative to the first and second cylindrical walls.This arrangement improves the accessibility of the sensor 96. .

[0063] Of course, the invention is not limited to this type of sensor 96 or to this positioning for the sensor 96.

[0064] In the presence of a sensor 96, the cap 90 may comprise a first part 90.2 configured to house the coupling system 68 and the first extension 72 as well as a second part 90.1 configured to house the sensor 96.

[0065] According to one embodiment, the motor assembly 40 comprises a set of first, second, third and fourth axial stops 100.1 to 100.4 configured to immobilize in translation in the axial direction, in two opposite directions, the coupling system 68 relative to the hollow shaft 50 and to the output shaft 64. According to one configuration, the first axial stop 100.1 corresponds to a shoulder provided at the output shaft 64 and the second axial stop 100.2 corresponds to an elastic ring or a nut mounted on the output shaft 64, the first and second axial stops 100.1, 100.2 being separated by a distance substantially equal to the length (dimension taken in the axial direction) of the coupling system 68. In addition, the third axial stop 100.3 corresponds to a shoulder of the hollow shaft 50 or to its end or to an elastic ring secured to the first extension 72 and the fourth axial stop 100.4 corresponds to a shoulder provided at the level of the cylindrical interior surface of the first extension 72 or to an elastic ring secured to the first extension 72, the third and fourth axial stops 100.3, 100.4 being separated by a distance substantially equal to the length of the coupling system 68.

[0066] According to a feature of the invention, the first and second bearings 52.1, 52.2 are mounted floating relative to a cylindrical wall among the outer and inner cylindrical walls 56.1, 56.2 so as to be able to tolerate possible axial deformations between the output shaft 64 and the structure 44, due for example to expansion phenomena.

[0067] According to one configuration, the first and second bearings 52.1, 52.2 are immobilized in translation in the axial direction, in two opposite directions, relative to a first cylindrical wall among the outer and inner cylindrical walls 56.1, 56.2 and can translate in the axial direction relative to a second cylindrical wall, different from the first cylindrical wall, among the outer and inner cylindrical walls 56.1, 56.2.

[0068] For this purpose, the motor assembly 40 comprises, for each first or second bearing 52.1, 52.2, a pair of first and second axial stops 102.1, 102.2 secured to the first cylindrical wall among the outer and inner cylindrical walls 56.1, 56.2, spaced apart by a distance substantially equal to the length (dimension taken in the axial direction) of the first and second bearing 52.1, 52.2 so as to immobilize it in the axial direction, in two opposite directions, relative to the first cylindrical wall.

[0069] In addition, the engine assembly 40 comprises: a. third and fourth axial stops 102.3, 102.4, cooperating respectively with the first and second bearings 52.1, 52.2, integral with the second cylindrical wall among the outer and inner cylindrical walls 56.1, 56.2, positioned on either side of the first and second bearings 52.1, 52.2 or between the first and second bearings 52.1, 52.2, spaced from the first and second bearings 52.1, 52.2, b. at least one first elastically deformable element 104.1 interposed between the first or second bearing 52.1, 52.2 and the third or fourth axial stop 102.3, 102.4.

[0070] According to one embodiment, the motor assembly 40 comprises a first elastically deformable element 104.1 between the first bearing 52.1 and the third axial stop 102.3 as well as a second elastically deformable element 104.2 interposed between the second bearing 52.2 and the fourth axial stop 102.4.

[0071] The first and second elastically deformable elements 104.1, 104.2 allow axial movements to be tolerated between the hollow shaft 50 and the structure 44. Consequently, it is no longer necessary to oversize the first and second bearings 52.1, 52.2 of the rotational guidance system 52 to absorb any axial deformations generated due to expansion phenomena.

[0072] According to one configuration, the first cylindrical wall corresponds to the inner cylindrical wall 56.2. Thus, each of the first and second bearings 52.1, 52.2 is immobilized in translation in the axial direction, in two opposite directions, relative to the hollow shaft 50. According to one embodiment, the first axial stop 102.1 corresponds to a shoulder provided at the level of the inner cylindrical wall 56.2 of the hollow shaft 50 and the second axial stop 102.2 corresponds to an elastic ring or a nut mounted on the hollow shaft 50.

[0073] In addition, the second cylindrical wall corresponds to the outer cylindrical wall 56.1. According to one embodiment, the outer cylindrical wall 56.1 comprises two shoulders positioned on either side of the first and second bearings 52.1, 52.2 corresponding to the third and fourth axial stops 102.3, 102.4.

[0074] According to one embodiment, each first or second elastically deformable element 104.1, 104.2 is a compression spring or a stack of elastic washers.

Claims

Claims

1. Engine assembly comprising: a. an electric motor (42) which comprises a structure (44) having first and second transverse faces (54.1, 54.2), a stator (46) fixed relative to the structure (44), a rotor (48) coaxial with the stator (46), a hollow shaft (50) secured to the rotor (48) as well as a rotational guidance system (52) connecting the structure (44) and the hollow shaft (50), b. an output shaft (64), which extends between first and second ends (64.1, 64.2), partially positioned in the hollow shaft (50), the first end (64.1) of the output shaft (64) being projecting relative to the first transverse face (54.1) of the structure (44) and configured to be connected to a load (66), c. at least one coupling system (68) connecting the hollow shaft (50) and the output shaft (64), d. the rotational guidance system (52) comprising first and second bearings (52.1, 52.2) positioned on either side of the rotor (48) as well as, for each of the first and second bearings (52.1, 52.2), outer and inner cylindrical walls (56.1, 56.2) secured respectively to the structure (44) and to the hollow shaft (50), each of the first and second bearings (52.1, 52.2) comprising outer and inner parts (58.1, 58.2) in contact respectively with the outer and inner cylindrical walls (56.1, 56.2), e. characterized in that the first and second bearings (52.1, 52.2) are immobilized in translation in an axial direction relative to a first cylindrical wall among the outer and inner cylindrical walls (56.1, 56.2) and can translate in the axial direction relative to a second cylindrical wall, different from the first cylindrical wall, among the outer and inner cylindrical walls (56.1, 56.2).

2. Engine assembly according to claim 1, characterized in that the engine assembly (40) comprises, for each first or second bearing (52.1, 52.2), a pair of first and second axial stops (102.1, 102.2) integral with the first cylindrical wall among the outer and inner cylindrical walls (56.1, 56.2), spaced apart by a distance such that the first and second stops (102.1, 102.2) immobilize the first or second bearing (52.1, 52.2) in the axial direction relative to the first cylindrical wall.

3. Motor assembly according to one of the preceding claims, characterized in that the motor assembly (40) comprises: a. third and fourth axial stops (102.3, 102.4) integral with the second cylindrical wall among the outer and inner cylindrical walls (56.1, 56.2), positioned on either side of the first and second bearings (52.1, 52.2) or between the first and second bearings (52.1, 52.2), spaced from the first and second bearings (52.1, 52.2), b. at least one first elastically deformable element (104.1) interposed between the first or second bearing (52.1, 52.2) and the third or fourth axial stop (102.3, 102.4).

4. Motor assembly according to the preceding claim, characterized in that the motor assembly (40) comprises a first elastically deformable element (104.1) between the first bearing (52.1) and the third axial stop (102.3) as well as a second elastically deformable element (104.2) interposed between the second bearing (52.2) and the fourth axial stop (102.4).

5. Engine assembly according to one of the preceding claims, characterized in that the first and second cylindrical walls correspond respectively to the inner and outer cylindrical walls (56.2, 56.1).

6. Motor assembly according to one of the preceding claims, characterized in that the motor assembly (40) comprises, for each bearing (52.1, 52.2), a seal (60.1, 60.2) interposed between the bearing (52.1, 52.2) and the rotor (48), in contact simultaneously with the outer and inner cylindrical walls (56.1, 56.2).

7. Engine assembly according to one of the preceding claims, characterized in that the coupling system (68) is positioned at or near the second transverse face (54.2) of the structure (44) in order to facilitate accessibility of the coupling system (68), said second transverse face (54.2) comprising an orifice (70) positioned in the extension of the hollow shaft (50).

8. Motor assembly according to the preceding claim, characterized in that the coupling system (68) is interposed between first and second extensions (72, 82) passing through the orifice (70), secured respectively to the hollow shaft (50) and the output shaft (64).

9. Motor assembly according to the preceding claim, characterized in that the first extension (72) comprises: a. a tubular body (74), in which the coupling system (68) is positioned, which extends between first and second ends, the first end being connected to the hollow shaft (50), b. a transverse wall (80) closing the second end of the tubular body (74).

10. Motor assembly according to one of claims 7 to 9, characterized in that the motor assembly (40) comprises a set of axial stops (100.1 to 100.4) configured to immobilize in translation in the axial direction the coupling system (68) relative to the hollow shaft (50) and to the output shaft (64).

11. Engine assembly according to one of claims 7 to 10, characterized in that the coupling system (68) is a disengageable coupling system configured to occupy a first state in which the disengageable coupling system (68) immobilizes the first and second extensions (72, 82) in rotation relative to each other as well as a second state in which the disengageable coupling system (68) allows the first and second extensions (72, 82) to pivot relative to each other.

12. Motor assembly according to one of claims 7 to 11, characterized in that the motor assembly (40) comprises a plug (90) configured to close the orifice (70) provided at the level of the second transverse face (54.2) of the structure (44) as well as fixing elements (92) connecting the plug (90) and the second transverse face (54.2).

13. Motor assembly according to one of the preceding claims, characterized in that the motor assembly (40) comprises at least one sensor (96) configured to determine at least one characteristic of the rotational movement of the output shaft (64).

14. Motor assembly according to claims 12 and 13, characterized in that the sensor (96) is positioned between the plug (90) secured to the structure (44) and a first extension (72) secured to the hollow shaft (50).

15. Aircraft comprising at least one engine assembly according to one of the preceding claims.

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