IL271693B1

IL271693B1 - Stirling-cycle cooling device with external rotor motor

Info

Publication number: IL271693B1
Application number: IL271693A
Authority: IL
Original assignee: Thales Sa
Priority date: 2018-12-28
Filing date: 2019-12-24
Publication date: 2023-06-01
Also published as: IL271693A; CN111379685B; SI3674625T1; EP3674625A1; IL271693B2; FR3091339B1; FR3091339A1; CN111379685A; US20200208883A1; EP3674625B1

Description

Stirling-cycle cooling device with external rotor motor The invention relates to a cooling device implementing a reverse Stirling-type thermodynamic cycle. Such a device is, for example, described in patent US4365982. Cooling is achieved by means of a coolant fluid circulating in a circuit comprising, principally, a compressor and a regenerator used as heat exchanger. The compressor comprises a piston that is movable in translation in a cylinder. The regenerator comprises a regeneration piston that is likewise movable in a second cylinder. The regenerator is sometimes called: "displacer". The two pistons are each driven by a connecting rod/crank arm, both actuated by a crankshaft. The crankshaft is driven in rotation by a rotary motor. In a known manner, the reverse Stirling cycle comprises the following four phases:  an isothermal compression of a fluid at high temperature, obtained by the movement of a compression piston in a compression cylinder;  an isochoric cooling of the fluid, from the high temperature to a low temperature, obtained by passage of the fluid through a regeneration piston, the piston moving in a regeneration cylinder and acting as a heat exchanger;  an isothermal expansion of the fluid at the low temperature, obtained by return of the compression piston in the compression cylinder; and  an isochoric heating of the fluid, from the low temperature to the high temperature, obtained by return of the regeneration piston in the regeneration cylinder. Conventionally, the regeneration piston and the compression piston are driven by the crankshaft, via a connecting rod articulated, on the one hand, on a crankpin and, on the other, on the piston in question. It is commonplace to use an internal rotor electric motor to drive the crankshaft. This type of motor is generally composed of an external stator and an internal rotor. More precisely, the stator has windings assembled in the form of a tube generating, inside the tube, a turning magnetic field. The rotor may have permanent magnets or windings. The rotor is arranged inside the stator and turns by engaging with the magnetic field generated by the stator. During the compression and expansion phases, the reciprocal movement of the pistons in their respective cylinder generates reciprocal and potentially out-of-phase axial forces. Via the connecting rod/crank arm systems, the forces exerted by the pistons are translated into a variable resistive torque at the level of the drive. More precisely, this torque exhibits considerable amplitude variations between a value close to zero and a maximum value achieved twice per revolution. Control of the electric motor makes it possible to adapt to these variations in torque but gives rise to electrical performance losses not only for the motor itself but also for the electronic device that controls it. Variations in toque give rise to variations in voltage and current in the electrical supply to the motor, potentially creating electromagnetic disturbances. Moreover, the variations in torque give rise to oscillations of the angular speed of the motor and of the crankshaft. These speed oscillations generate vibrations that may degrade the acoustic signature of the cooling device and potentially give rise to accelerated mechanical fatigue of the various components of the device. It is possible to limit the impact of these variations in resistive torque at the level of the drive with the aid of a flywheel added onto the drive shaft. However, the addition of this type of movable component gives rise to an increase in the volume, the mass and the cost of the cooling device. The invention aims to palliate all or some of the problems cited above by implementing an external rotor drive. The external rotor drive by construction exhibits a moment of inertia about its axis of rotation that is greater than in the case of an internal rotor configuration. In such a case it is thus possible to envisage being able to dispense with a flywheel. Moreover, for a given volume and performance, an external rotor motor may generate a torque greater than that of an internal rotor motor. Similarly, for a given torque, the use of an external rotor motor thus makes it possible to facilitate the miniaturization of the cooling device. Lastly, in a permanent magnet rotor motor, the magnets are arranged as close as possible to the stator. An internal rotor motor presents the risk of detachment of the magnets during rotation of the motor owing to the centrifugal force that tends to tear the magnets from their support. However, in an external rotor motor comprising magnets, the latter tend to be pressed against the bottom of their housing, thereby avoiding the implementation of specific means for holding the magnets, such as specific magnet holding rings. In an internal rotor motor, such holding means tend also to increase the gap between the rotor and the stator, which gives rise to a drop in the performance of the motor. To that end, a subject of the invention is a Stirling-cycle cooling device comprising a compressor with a reciprocal piston driven by an electric motor rotating about an axis via a crankshaft, wherein the electric motor comprises an internal stator and an external rotor and wherein the internal stator is connected to the crankshaft via a link with at least one degree of freedom in rotation about the axis of the electric motor. Advantageously, the internal stator has a solid cylindrical form extending along the axis of the electric motor. Advantageously, the stator has a cylindrical form comprising an axial opening and extending along the axis and wherein a drive shaft integral with the external rotor can turn. The axial opening partially or completely may traverse the stator. The external rotor is advantageously integral with a drive shaft carried by the link with at least one degree of freedom in rotation and the link with at least one degree of freedom in rotation is produced in two parts each arranged on one side of the motor along the axis . Each of the parts is, for example, formed by a bearing. A housing of the device advantageously comprises a tubular bearing surface extending along the axis, partially or completely traversing the stator, which is fixed on the exterior of the tubular bearing surface. The drive shaft extends inside the tubular bearing surface and the link with at least one degree of freedom in rotation connects the interior of the tubular bearing surface and the drive shaft. The device advantageously comprises a monoblock body integral with the stator. The link with at least one degree of freedom in rotation along the axis connects the monoblock body and a drive shaft integral with the rotor and the piston of the compressor moves in a cylinder formed in the monoblock body. The body advantageously comprises the tubular bearing surface. Advantageously, only the link with at least one degree of freedom in rotation along the axis connects the body and the drive shaft. Furthermore, the link with at least one degree of freedom of rotation along the axis connects the body and the drive shaft directly. The rotor is integral with a drive shaft advantageously comprising a bearing surface extending along the axis and integral with the crankshaft, a tube segment inside which is fixed the rotor and a web connecting the tube segment and the bearing surface. The motor is advantageously arranged between the body and the web. The kinematic link with at least one degree of freedom in rotation along the axis comprises a link or a link assembly amongst:  a pivot link;  a sliding pivot link;  an annular linear link and a ball link associated in parallel;  two ball links associated in parallel;  a ball link and a rectilinear linear link (36) associated in parallel;  a sliding pivot link and a punctiform link (40) associated in parallel;  an annular linear link and a planar bearing link associated in parallel. The invention will be better understood and further advantages will become apparent upon reading the detailed description of embodiments given by way of example, which description is illustrated by the attached drawing, in which: Figures 1a to 1h show a first embodiment of an external rotor motor and different examples of kinematic links that can be used to connect the motor to the housing of a Stirling-cycle refrigeration device; Figures 2a to 2h show a second embodiment of an external rotor motor and different examples of kinematic links; Figure 3 shows a variant embodiment of the drive function of the refrigeration device implementing the first embodiment of an external rotor motor; Figure 4 shows a first variant embodiment of the drive function implementing the second embodiment of an external rotor motor; Figure 5 shows a second variant embodiment of the drive function implementing the second embodiment of an external rotor motor; Figure 6 shows a third variant embodiment of the drive function implementing the second embodiment of an external rotor motor; Figure 7 shows a fourth variant embodiment of the drive function implementing the second embodiment of an external rotor motor; Figure 8 shows a fifth variant embodiment of the drive function implementing the second embodiment of an external rotor motor; Figure 9 shows a sixth variant embodiment of the drive function implementing the second embodiment of an external rotor motor; Figure 10 shows a further view of the sixth variant embodiment. For the sake of clarity, the same elements will bear the same references in the different figures. An external rotor motor 10 is shown in Figures 1a to 1h. The motor comprises a stator 12 that has a solid cylindrical form extending along an axis 14 forming the axis of rotation of the motor 10. The stator 12 is fixed relative to a housing 16 of the refrigeration device. The stator comprises, for example, windings 18 that allow generation of a turning magnetic field extending radially relative to the axis 14 at the periphery of the stator 12. The motor 10 comprises a rotor 20 produced in the form of an axisymmetrical tube about the axis 14. The rotor 20 is arranged radially about the stator 12. The rotor 20 may comprise windings or permanent magnets designed to engage with the magnetic field generated by the stator windings. The use of permanent magnets makes it possible to dispense with the implementation of turning contacts, such as brushes or carbon brushes, for powering the rotor windings. Figures 1a to 1h show several examples of kinematic links that make it possible to connect the rotor 20 to the housing 16. The various arrangements presented to define the kinematic links all allow at least one degree of freedom in rotation about the axis 14. The figures shown do not constitute an exhaustive list of possible links. Possible links are characterized by all kinematic links that offer at least one degree of freedom in rotation about the axis 14. In Figure 1a, a pivot link 22 of axis 14 connects the rotor 20 to the housing 16. In Figure 1b, a sliding pivot link 24 of axis 14 connects the rotor to the housing 16. The sliding pivot link 24 has a supplementary degree of freedom in translation along the axis 14. For the operation of the motor 10, it is necessary to block the possible translation of the rotor 20 relative to the housing 16. This translation may be blocked in the compressor of the refrigeration device. Conserving a translational movement along the axis 14 at the level of the motor 10 makes it possible to prevent hyperstatism along this axis of rotation. It is thus possible to relax the manufacturing tolerances of the motor 10. Figure 1c shows the association of an annular linear link 26 and a ball link 28 for connecting the rotor 20 to the housing 16. The degree of freedom in translation of the annular linear link 26 is along the axis 14. This degree of freedom is eliminated by the ball link 28. Figure 1d shows the association of two ball links 30 and 32 for connecting the rotor 20 to the housing 16. The two ball links 30 and 32 are associated in parallel and the centres of rotation of the two ball links 30 and are arranged at a distance from one another and in line along the axis 14. In this association, translational movement along the axis 14 is blocked twice, once by each ball link. Although, generally, hyperstatism requires close tolerances, the hyperstatism of this association may be advantageous for stiffening the link between the rotor 20 and the housing 16. Figure 1e shows a ball link 34 and a rectilinear linear link associated in parallel to connect the rotor 20 to the housing 16. The rectilinear linear link 36 blocks translational movement along the axis 14 and rotation about the two other axes perpendicular to the axis 14 forming a trihedron. The degree of freedom in rotation about the axis 14 remains free. Figure 1f shows a sliding pivot link 38 and a punctiform link 40 still associated in parallel to connect the rotor 20 to the housing 16. The punctiform link 40 stops translational movement of the rotor 20 along the axis 14. Figure 1g shows an annular linear link 42 and a planar bearing link associated in parallel to connect the rotor 20 to the housing 16. The annular linear link 42 is similar to the link 24 in Figure 1c and the degree of freedom in translation thereof is along the axis 14. The planar bearing link 44 stops translational movement along the axis 14 and allows rotation about the axis 14. Figure 1h shows a pivot link 46 connecting the rotor 20 to the housing 16. This pivot link exhibits the same degree of freedom in rotation about the axis 14 as the link 22 in Figure 1a. In the link 22, the central part of the pivot link is connected to the rotor 20. However, in the link 46, the central part of the pivot link is connected to the housing 16. This difference in representation prefigures different embodiments for these two pivot links. To implement a device as shown schematically in Figure 1a, the rotor 20 is integral with a shaft turning inside the housing 16, whereas in a device shown schematically in Figure 1h the housing 16 comprises a fixed shaft about which the rotor 20 turns. In Figures 1c to 1g, the rotor 20 and the housing 16 are connected by means of two kinematic links. In each of these figures, the two links are shown on the same side of the motor 10. In practice, these two links may be implemented on the same side of the motor 10, but also in the form of one link on each side of the motor. By providing the implementation means of each link on either side of the motor 10, the loads supported by each of the two links are better distributed. In other words, the cantilever of the rotor 20 is reduced. It can perfectly well be envisaged to implement the invention with other link configurations that have not been shown previously in Figures 1a to 1h. The kinematics of the link between the rotor 20 and the housing 16 should be examined as a function of other links existing in the refrigeration device taken overall and, notably, in the compressor part not shown in Figures 1a to 1h. Figures 2a to 2h show another architecture of the external rotor motor 50. The stator 52 of the motor 50 differs from the stator 12 in that it has an open cylindrical form along the axis 14 of rotation of the motor. The rotor of the motor 50 is similar to that of the motor 10 and is thus given the reference 20. The axial opening 54 of the stator 52 makes it possible, notably, to cause the drive shaft integral with the rotor 20 to pass therethrough. Figures 2a to 2h refer again to the same kinematic links as those shown in Figures 1a to 1h. In Figures 2a to 2h, the different kinematic links are shown inside the axial opening 54. As above, Figures 2a to 2h do not constitute an exhaustive list of possible links. Possible links are characterized by all kinematic links offering at least one degree of freedom in rotation about the axis 14. Figure 3 shows a first embodiment of a refrigeration device according to the invention. The device comprises the external rotor motor 10, the stator 12 of which has a solid cylindrical form. The housing 16 of the device is produced in the form of a plurality of mechanical components belonging to the same equivalence class. In other words, the different components of the housing 16 have no degree of freedom between them. The housing comprises a body 60 of the compressor (not shown) and a cover 62 fixed to the body 60. The housing 16 forms a shell of the motor 10. The motor 10 has a globally cylindrical form about the axis 14. The body 60 comprises a tubular section 64 of axis 14 inside which the motor 10 is inserted. The cover 62 also comprises a tubular part 66 extending in the extension of the tubular section and fixed thereto. The cover 62 comprises a flank 68 extending perpendicularly to the axis 14. The flank 68 closes the tubular part 66. In practice, the tubular section 64 may extend as far as the flank 68. In this case, the tubular part disappears. Conversely, the tubular section 64 may disappear and the tubular part 66 thus extends as far as the part of the body 60 that is configured to support the compressor. More generally, the body 60 and the cover 62 form a shell of the motor 10. The drive shaft 70 turning about the axis 40 emerges from this shell. The stator 12 is assembled on the housing 16 and, more precisely, on the cover 62 in the example of Figure 3. The drive shaft 70 is integral with the rotor 20. More precisely, the drive shaft 70 comprises a tube 72 inside which the rotor 20 is fixed. The drive shaft 70 also comprises a bearing surface 74 extending along the axis 14, integral with the crankshaft (not shown) and a web 76 connecting the bearing surface 74 and the tube 72. The web 76 has the form of a disc centred on the axis 14. The drive shaft 70 makes it possible to increase the moment of inertia of the turning part of the device. More precisely, the inertia of the drive shaft is principally due to the presence of the tube 72. Indeed, the inertia of the turning part of the motor 10 is all the greater when it comprises mass at a distance from the axis 14. Thus, the tube 72 performs two functions: the mechanical holding of the rotor 20 and a significant share of the inertia of the turning part of the motor 10. A further significant share of the inertia is provided by the rotor 20. The inertia of such an assembly is much greater than that of an internal rotor motor, in which the essential part of the mass of the turning part of the motor is concentrated in the immediate vicinity of its axis of rotation. The kinematic link between the housing 16 and the rotor 20 is provided by two bearings 80 and 82. The bearing 80 is arranged between the bearing surface 74 of the drive shaft 70 and the body 60. The bearing 82 is arranged between the tube 72 and the tubular part 66 of the cover 62. The bearings 80 and 82 may, for example, be ball bearings. Certain types of bearing, when the rings are immobilized, may be likened to a ball link since, complementing rotation about the axis 14, they have a rotational mobility about two axes perpendicular to the axis 14. This assembly with two ball bearings may thus fulfil the function of the link shown in Figure 1d. For one of the bearings, it is also possible to preserve possible translational movement along the axis 14. This translational movement may be produced by leaving one ring of one of the two bearings free in rotation. With this translational mobility, the assembly may fulfil the function of the link shown in Figure 1c. Figure 3 shows bearings. It is also possible to implement other components that provide rotational mobility about the axis 14 such as, for example, plain bearings, magnetic bearings, pneumatic bearings or any other component providing any kinematic link that has at least one degree of freedom in rotation along the axis 14, as in the various examples of kinematic links shown in Figures 1a to 1h. Figure 4 shows a second embodiment of a refrigeration device according to the invention. The device comprises an external rotor motor, the stator of which has a cylindrical form that is in part open along the axis 14 of rotation of the motor. This form of the stator is intermediate between the schematic representations of Figures 1a to 1h on the one hand and those of Figures 2a to 2h. The references of Figures 2a to 2h are resumed for Figure 4: for the motor, 52 for the stator and 20 for the rotor. Here, the housing 16 is formed by the body 60 and the cover 62 on which the stator 52 is fixed. The motor 50 comprises a drive shaft 90 in which there is the tube 72 and the web 76. Unlike the drive shaft 70, the drive shaft 90 comprises a solid bearing surface 92 partially traversing the opening 53 of the stator 52.

The bearing 80 lies between the bearing surface 92 and the body 60. In Figure 4, a second bearing 94 is arranged between the stator 52 and the bearing surface 92 in the bottom of the opening 53. This variant makes it possible to reduce the dimensions of the bearing 94 as compared with those of the bearing 82. Figure 5 shows a variant of Figure 4, in which the opening 54 of the stator is a through-opening. The motor 50 comprises a drive shaft 91 in which there is the tube 72 and the web 76. Unlike the drive shaft 90, the drive shaft comprises a solid bearing surface 93 longer than the bearing surface 92. The bearing surface 93 traverses the stator 52 via the opening 54 thereof and the second bearing 94 is arranged between the cover 62 and the bearing surface 93. The bearings 80 and 94 are arranged on either side of the motor along the axis 14, which makes it possible better to separate them and to properly distribute the radial forces exerted by the motor 50 on the drive shaft 91, avoiding the cantilever of the rotor 20. As in Figure 3, the bearings 80 and shown in Figures 4 and 5 may be ball bearings, (straight or tapered) roller bearings, or needle bearings. It is also possible to replace them with journals or any other component that provides at least one degree of freedom in rotation about the axis 14 and, notably, the various kinematic links shown in Figures 2a to 2h. In Figure 5, the stator 25 is fixed to the cover 62 by one of the lateral faces 96 thereof. This fixing method may present difficulties in terms of implementation owing to the presence of the windings 18 that may interfere with fixing. Figure 6 shows an alternative, proposing fixing the stator 52 to the cover via the opening 54. In other words, the cover 62 comprises a tubular bearing surface 98 extending along the axis 14. The stator 52 is fixed on the exterior of the tubular bearing surface 98 and the bearing surface 93 extends inside the tubular bearing surface 98 as far as the bearing 94. In Figure 6, the tubular bearing surface 98 completely traverses the opening 54 of the stator 52. Alternatively, it is possible to reduce the length of the bearing surface 98, thereby making it only partially traversing. Figure 7 shows a variant of Figure 6, in which the two bearings and 94 are both arranged between the cover 62 and the drive shaft 91 and, more precisely, between the tubular bearing surface 98 and the bearing surface 93.

In Figure 7, the bearing surface 98 completely traverses the stator 52. Figure 8 shows a variant of Figure 7, in which the cover 62 comprises a bearing surface 99 that does not completely traverse the stator 52. The axial distance between the bearings 80 and 94 is less than in Figure 7. Figure 8, however, is advantageous in terms of increasing the useful volume of the stator in the vicinity of the axis 14, which makes it possible to make the motor more compact. Figures 9 and 10 further show another variant implementing the motor 50, the stator 52 of which has an open cylindrical form. Figure 9 is a sectional view in a plane containing the axis 14, and Figure 10 is a sectional view in a plane perpendicular to the axis 14. The compressor 100 of the refrigeration device is shown in Figure 9. The compressor 100 comprises a piston 102 moving in a cylinder 104 formed in the body 60. The body 60 is monoblock and comprises a tubular bearing surface 106 extending along the axis 14. The drive shaft, here, bears the reference 108 and the bearings 80 and 94 are arranged between the drive shaft 108 and the tubular bearing surface 106. As previously, the bearings may be replaced by other mechanical components such as smooth bearings. More generally, the link allows at least rotational mobility along the axis 14 and connects the body 60 and the drive shaft 108 directly. No other link connects the body 60 and the drive shaft 108. The link is arranged directly in the tubular bearing surface 106. The monoblock body 60 is advantageously produced without assembly. In the method for manufacturing the body 60, an assembly may be accepted provided the cylinder 104 and also the tubular bearing surface 106 receiving the link are machined after assembly. This machining made after assembly makes it possible to avoid the assembly tolerances being added to that connecting the cylinder 104 and the tubular bearing surface 106. In other words, "monoblock" is understood to mean a mechanical component of which the manufacturing tolerances are not impacted by any assembly that might arise during the method for manufacturing same. Similarly, arranging the link in the body 60 directly makes it possible to limit the dimensional chains between the cylinder 104 and the drive shaft 108. In this embodiment, the function of the cover 62 is only to form a shell of the motor 50 and it no longer supports the stator 52. The stator 52 is fixed to the exterior of the tubular bearing surface 106. The arrangement of the bearings 80 and 94 between the body and the drive shaft simplifies the dimensional chain passing via the body, the drive shaft, the crankshaft 110, the connecting rod 120, and the piston 102, thereafter returning towards the bodies 60. This dimensional chain does not pass via the cover as in the embodiments shown in Figures 4, 5 and 6, where at least one of the bearings is carried by the cover. In this embodiment, the drive shaft 108 comprises a solid bearing surface 112 extending along the axis 14, and on which the bearings 80 and are mounted. The crankshaft 110 is formed by the end of the bearing surface 112 and a crankpin 113 integral with the bearing surface 112 and extending in the extension thereof. The piston 102 is driven by the drive shaft 108 via the crankpin 113 and a connecting rod 120. The drive shaft 108 further comprises a tube segment 114 similar to the tube segment 72 and carrying the external rotor 20 and also a web 116 connecting the bearing surface 112 and the tube segment 114. The web 116 has the form of a disc centred on the axis 14. In the embodiments of Figures 3 to 8, the web 76 is located between the body 60 and the motor 10 or 50. This arrangement of the web distances the motor from the compressor, which increases the length of the bearing surface. Conversely, in the embodiment of Figure 9, the web 116 is not arranged between the motor and the body. In other words, the motor 50 is arranged between the body and the web 116, which makes it possible to bring the motor 50 closer to the compressor 100. Figure 10 shows the regenerator 122 of the cooling device. The regenerator comprises a regeneration piston 124 moving in a cylinder 126 also formed in the monoblock body 60. The regeneration piston 24 is driven by the drive shaft 108 via the crankpin 113 and a connecting road 128. The crankshaft 110 may comprise a single crankpin 113, as shown in Figures 9 and 10. Alternatively, the crankshaft 110 may comprise two crankpins, each driving one of the connecting rods 120 and 128. Alternatively, the two connecting rods 1and 128 may be located in one and the same single plane. In Figure 10, the axis of movement of the regeneration piston 124 is perpendicular to the axis of movement of the piston 102 of the compressor 100. It is also possible to produce a cooling device according to the invention with other relative orientations of the two axes.

Claims

1./ 0269914061-01 CLAIMS 1. Stirling-cycle cooling device comprising a compressor with a reciprocal piston driven by an electric motor rotating about an axis via a crankshaft, characterized in that the electric motor comprises an internal stator and an external rotor and in that the internal stator is connected to the crankshaft via a link with at least one degree of freedom in rotation about the axis of the electric motor.

2. Device according to Claim 1, characterized in that the internal stator has a solid cylindrical form extending along the axis of the electric motor.

3. Device according to Claim 1, characterized in that the stator has a cylindrical form comprising an axial opening and extending along the axis and wherein a drive shaft integral with the external rotor can turn.

4. Device according to Claim 3, characterized in that the axial opening partially or completely traverses the stator.

5. Device according to Claim 4, characterized in that the external rotor is integral with a drive shaft carried by the link with at least one degree of freedom in rotation and in that the link with at least one degree of freedom in rotation is produced in two parts each arranged on one side of the motor along the axis.

6. Device according to Claim 5, characterized in that each of the parts is formed by a bearing.

7. Device according to one of the preceding claims, characterized in that a housing of the device comprises a tubular bearing surface extending along the axis, partially or completely traversing the stator, in that the stator is fixed on the exterior of the tubular bearing surface, in that the drive shaft extends inside the tubular bearing surface and in that the link with at least one degree of freedom in rotation connects the interior of the tubular bearing surface and the drive shaft.

8. Device according to one of the preceding claims, characterized in that it comprises a monoblock body integral with the stator, in that the link with 271693/ 0269914061-01 at least one degree of freedom in rotation along the axis connects the body and a drive shaft integral with the rotor and in that the piston of the compressor moves in a cylinder formed in the body.

9. Device according to Claims 7 and 8, characterized in that the monoblock body comprises the tubular bearing surface.

10. Device according to Claim 9, characterized in that only the link with at least one degree of freedom in rotation along the axis connects the body and the drive shaft and in that the link with at least one degree of freedom in rotation along the axis connects the body and the drive shaft directly.

11. Device according to one of the preceding claims, characterized in that the rotor is integral with a drive shaft comprising a bearing surface extending along the axis and integral with the crankshaft, a tube segment inside which is fixed the rotor and a web connecting the tube segment and the bearing surface.

12. Device according to Claim 11, characterized in that the motor is arranged between the body and the web.

13. Device according to one of the preceding claims, characterized in that the kinematic link with at least one degree of freedom in rotation along the axis comprises a link or a link assembly amongst: • a pivot link; • a sliding pivot link; • an annular linear link and a ball link associated in parallel; • two ball links associated in parallel; • a ball link and a rectilinear linear link associated in parallel; • a sliding pivot link and a punctiform link associated in parallel; • an annular linear link and a planar bearing link associated in parallel.