Coupling part and mechanical coupling device comprising it

Abstract

The invention relates to a coupling part (1) for a mechanical coupling device (2) for coupling two rotating elements (3, 5) to each other. It comprises a body part (6), to be secured to a first element (3), and an engagement part (7) comprising at least one pair of torque transmission and obstacle pinching fingers (8), forming between them a groove (9) open at one end and deformable for pinching a radial obstacle (40) secured to the second element (5) and received in the respective groove (9). The fingers (8) project from the body part (6) and are located on the periphery of a receiving space (10) for the second rotating element (5). Figure to be published with the abstract: Figure 5

Description

Title of the invention: Coupling part and mechanical coupling device comprising it

[0001] The technical field of the invention is that of mechanical couplings, and in particular that of coupling devices used to mechanically transmit a rotational torque between two rotating elements to be coupled.

[0002] The coupling device according to the present invention is particularly suitable for coupling a weapon capable of rotating about an elevation axis and an associated angular position encoder in order to measure changes in angular position of the weapon about its elevation axis. It should however be emphasized that the coupling device according to the present invention is applicable to the coupling of any two elements mounted rotatably about a common axis of rotation.

[0003] There are many types of mechanical couplings for transmitting torque between two elements, including torsionally rigid couplings, such as bellows couplers, and flexible couplings, such as elastomer couplers.

[0004] A bellows coupling, such as that disclosed in European patent application EP1923588, has the advantage of being relatively compact, having high torsional rigidity and allowing compensation for axial, lateral and angular misalignments. However, such a rigid coupling cannot be assembled blindly.

[0005] An elastomer coupler, such as that disclosed in European patent EP3084247, is a coupling having an elastomer insert placed between two half-hubs. It has the advantage of allowing compensation for axial, lateral and angular misalignments. However, such a flexible coupling cannot be assembled blindly.

[0006] However, in certain applications, it is not possible to visually access the mounting area of ​​the coupling device or to intervene with tools when mounting the coupling device, for example, to screw in a fixing member, the mounting then having to be done blind. In this case, it is necessary to have a coupling device allowing easy blind mounting.

[0007] As an example of such an application, the coupling of an angular position encoder with the elevation axis of a turret, and therefore of a weapon, can be indicated. Such a coupling requires easy blind mounting, but also high precision in the transmission of the rotational movement between the weapon and the angular position encoder. For such an application, the coupling device must allow the correction of an eccentricity defect, for example of the order of ±0.4 mm, be compact with a small external diameter, for example an external diameter not exceeding 14 mm, be torsionally rigid, for example the angular defect must not exceed 0.07 degrees for 0.05 Nm, and be assemblable with a high axial dispersion, for example of the order of ±0.5 mm.

[0008] There are also coupling devices which have the advantage of allowing blind assembly, having significant torsional rigidity and allowing compensation for misalignments, such as miniature bellows couplings. However, these couplings are not compact, the outside diameter being too large.

[0009] Finally, US patent 3,286,489 A discloses a mechanical coupling device comprising a coupling part and a transmission part each intended to be mounted on the free end of a respective one of first and second rotary elements. The coupling part and the transmission part each comprise a cylindrical body in which a blind hole is formed, opening into a first axial side of the body and in which the free end of the respective rotary element is received. The coupling part also has two diametrically opposed grooves on the circumferential surface of the body and two U-shaped springs are fixed on the distal axial side of the body, each U-shaped spring having two flat elastic blade portions forming two fingers each extending into a groove of the body, such that each groove receives a pair of elastic fingers facing each other.The transmission part also comprises two pins extending axially from the second axial side of the body and whose free ends are sphere-shaped. In the position of use, each of the pins is engaged in the gap between a respective pair of fingers and elastically pinched by the latter.

[0010] This coupling device has the advantage of allowing blind assembly and clearance compensation.

[0011] However, it is relatively axially uncompact.

[0012] Furthermore, when the driving element begins to rotate, each pin deforms one of the elastic fingers at its base region, by which it is fixed to the body, until this finger comes into contact against a flank of the respective groove and it is only after this contact has been established that the rotational movement will be transmitted to the driven element. In other words, the fingers do not constitute torque transmission means here, this transmission being ensured by the pins and the flanks of the grooves. This coupling device therefore does not have, as a whole, a torsional rigidity which is acceptable for applications requiring high precision in the transmission of the rotational movement, such as for example coupling an angular position encoder to the elevation axis of a weapon.

[0013] It is therefore the aim of the present invention to propose a coupling device making it possible to correct angular and coaxiality defects, to take up clearances, easily assembled blindly, rigid in torsion and compact both radially and axially, and which will therefore be suitable, for example, for an application to the coupling of an angular position encoder with the elevation axis of a weapon.

[0014] The invention thus relates to a coupling part for a mechanical coupling device used to couple two cylindrical rotating elements to each other, each mounted to rotate about an associated axis of rotation, said coupling part comprising a body part and an engagement part, the body part having a central axis, a first axial side, called proximal, a second axial side, called distal, opposite the proximal side along the central axis, and securing means for securing the coupling part to a free end of a first of the rotating elements such that the latter is then on the proximal side, and said engagement part being configured to engage, in the position of use, in which the rotating elements are coupled by the mechanical coupling device, at least one obstacle which is secured to a second of the rotating elements,the coupling part being characterized in that the engagement part comprises torque transmission and radial obstacle pinching fingers, fingers by which a torque applied to one or other of the first and second rotary elements, around the respective axis of rotation, is directly transmitted between the at least one obstacle and the body part by the fingers alone, the fingers projecting from the body part and their longitudinal axes belonging to an imaginary cylinder whose axis is coaxial with the central axis of the body part, the fingers being located on the periphery of a receiving space capable of receiving, in the position of use, a free end of the second rotary element, the fingers of the same pair forming a groove having a closed proximal end and an open distal end through which a radial obstacle, integral with the second rotary element,is introduced so as to be received in the groove and pinched by the fingers in said position of use, and the fingers being elastically deformable in the radial direction.

[0015] In other words, the fingers of the same pair are deformable at their base region adjacent to the body part and have a rigidity in the circumferential direction which is sufficiently high so that in the position of use a torque is transmitted between the rotating elements via said radial obstacle, without the fingers deforming, in the circumferential direction, by a magnitude greater than the maximum permissible angular deformation in the application considered, and without being so high as to prevent said radial obstacle from being introduced in the groove and thus the engagement part to be engaged around said free end of the second rotating element, and a rigidity in the radial direction which allows elastic deformation of the fingers ensuring compensation for possible angular and coaxial deviations between the driven and driving elements.

[0016] Thus, the coupling part can be mounted on the first element using the securing means, then be blindly engaged on the second element.

[0017] Furthermore, given that in the position of use the engagement part surrounds the free end of the second rotary element, the coupling part makes it possible to obtain a more compact coupling device, in particular axially, than the device of US patent 3,286,489 A.

[0018] Furthermore, unlike the blade parts forming elastic fingers of the device of US patent 3,286,489 A, due to the torque transmission and radial obstacle pinching fingers, the coupling part according to the present invention allows transmission of a rotation of the driving element to the driven element from the start of the rotational movement (in any case, within the limits of the maximum permissible angular deformation), and therefore high precision in the transmission of the rotational movement, while allowing tolerance to angular and coaxial deviations between the driven and driving elements.

[0019] In the case of the angular position encoder application discussed in the introduction, the maximum permissible angular deformation will simply be the minimum permissible angular error for measuring changes in angular position. Those skilled in the art will be able to take into account the resistive torque when dimensioning the coupling part.

[0020] In practice, a person skilled in the art can simply use calculation software, for example finite element calculation software, to design the coupling part meeting the requirements related to the application in question (maximum permissible angular deformation in the circumferential direction, maximum permissible eccentricity defect, maximum axial dispersion at assembly), in particular to choose the materials used, the dimensions of the fingers (cross sections, lengths), etc.

[0021] In particular in the case of the angular position encoder application discussed above, the stiffness of the fingers in the circumferential direction can advantageously be 140N / mm ± 40N / mm and / or the stiffness of the fingers in the radial direction is 40N.m / rd ± 5N / mm.

[0022] Advantageously, the engagement part comprises at least two pairs of fingers, in particular three pairs of fingers, the grooves being distributed in an angularly equidistant manner.

[0023] In particular, the presence of three pairs of fingers spaced 120 degrees apart from each other allows for reliable and precise torque transmission.

[0024] Each finger may advantageously have a free end which is bevelled so as to widen the groove at the distal end thereof. This facilitates the introduction of a radial obstacle into the groove and therefore the blind positioning of the coupling part on the second rotating element.

[0025] The fingers of the same pair may each have a polygonal cross-section and each have a flat lateral face belonging to a plane to which said central axis belongs, the groove being delimited in the circumferential direction by the two lateral faces of the fingers.

[0026] According to a particular embodiment, the body part comprises a bore opening on the proximal side and capable of receiving the free end of said first element, and the securing means comprise at least one threaded through hole extending radially and having a first end opening outside the body part and a second end opening into said bore, the threaded hole being capable of receiving a fixing member, in particular a set screw.

[0027] The present invention also relates to a mechanical coupling device for coupling to each other two cylindrical rotating elements each mounted to rotate about an associated axis of rotation, characterized in that it comprises a coupling part as defined above, intended to be made integral with the free end of a first of the rotating elements, and a transmission part integral or intended to be integral with the free end of a second of the rotating elements, the transmission part comprising at least one radial obstacle which, in the position of use, extends radially projecting from the free end of the second rotating element so as to be received in the groove formed by a pair of fingers of the coupling part and pinched by said fingers.

[0028] Advantageously, the at least one radial obstacle is formed by a radial pin, preferably a split elastic pin.

[0029] The transmission part may further comprise, for each pair of fingers, an axial stop intended to extend, in the position of use, radially projecting from the free end of the second rotary element and opposite the radial obstacle so as to form an axial stop against which the corresponding pair of fingers can come into abutment when said free end is introduced into the receiving space of the coupling part.

[0030] The present invention will be better understood on reading the following description of a particular embodiment, a description made in light of the appended drawings, drawings in which:

[0031] [Fig-1] is a side perspective view of a coupling part according to a mode of particular embodiment of the present invention;

[0032] [Fig.2] is a perspective view from behind of the coupling part of the [Fig.l];

[0033] [Fig.3] is a schematic diagram of the coupling device according to the present invention;

[0034] [Fig.4] is a partial schematic cross-sectional view of a transmission portion of the coupling device according to the particular embodiment of the present invention;

[0035] [Fig.5] is a top perspective view of the coupling device according to the particular embodiment of the present invention; and

[0036] [Fig.6] is a side view of the coupling device of [Fig.5].

[0037] Referring firstly to Figures 1 to 3, it can be seen that there is shown a coupling part 1 of a coupling device 2 according to a particular embodiment of the present invention, which coupling part 1 is intended to be made integral with a first rotatably mounted element 3, for example a driven element such as an angular position encoder, and to interact with a transmission part 4 integral with a second rotatably mounted element 5, for example a driving element such as the elevation axis of a turret, as shown in Figures 5 and 6.

[0038] The coupling part 1 comprises a body part 6 and an engagement part 7, formed in one piece.

[0039] The body part 6 is intended to be fixed to the first element 3 and for this purpose comprises securing means 60 making it possible to secure the coupling part 1 to the first element 3 both in translation and in rotation.

[0040] The body part 6 is in the form of a cylindrical body 61 having a central axis A1 and a small external diameter, in particular an external diameter less than or equal to 14 mm. The body 61 has a first axial side 61a intended to be oriented towards the first element 3 once the coupling part 1 is secured thereto, and a second axial side 61b opposite. A bore 62 is provided in the body 61 and opens into the first axial side 61a so as to receive the free end of the first element 3.

[0041] The securing means 60 comprise at least one threaded through hole 63 formed radially in the wall of the body 61 and thus opening both outside the body 61 and into the bore 62. The threaded hole 63 is intended to receive a fixing member (not shown), in particular a set screw, by which the body part 6 is made integral with the free end of the first element 3 received in the bore 62. Such securing by set screw is an economical and rapid fixing solution, particularly suitable for low torques. It should be noted that this securing could be ensured by any other appropriate means.

[0042] After being secured to the first element 3, the central axis A1 of the body part 6 is coaxial with the axis of rotation of the first element 3.

[0043] Alternatively, the body part 6 could be in two parts and comprise two body part halves assembled to each other.

[0044] The engagement part 7 is carried by the body part 6 and extends outwards from the second axial side 61b of the body 61. The engagement part 7 comprises at least one pair of longitudinal fingers 8 for transmitting torque and pinching a radial obstacle, at least one longitudinal groove 9 formed between the fingers 8 and a receiving space 10, all intended to cooperate with the transmission part 4.

[0045] In the embodiment shown, the engagement portion 7 comprises six fingers 8, namely three pairs of fingers 8.

[0046] The fingers 8 extend in a direction parallel to the central axis A1 of the body 61. Each finger 8 has a base region 80 adjacent to the body 61 and at which the finger 8 is connected to the body 61, and an opposite free end 81.

[0047] In particular, the fingers 8 are positioned such that their longitudinal axes belong to an imaginary cylinder whose axis is coaxial with the central axis A1, and they thus surround the receiving space 10.

[0048] In the embodiment shown, each finger 8 has a substantially trapezoidal cross-section, the small and large sides 82, 83 of which are in fact portions of a cylinder whose axis is coaxial with the central axis AL. The diameter of the large side 83 is equal to the external diameter of the body 61 and the diameter of the small side 82 is at least slightly greater than the diameter of the free end of the second element 5. The two lateral sides of each arm 8 each have a flat lateral face 84 which belongs to a plane in which the central axis AL extends. Each groove 9 is delimited laterally by two lateral faces 84 of a pair of fingers 8.

[0049] The free end 81 is beveled so as to have at least one end surface 81a inclined both with respect to the plane of the respective lateral face 84 and with respect to a transverse plane perpendicular to the central axis Al so as to widen the respective groove 9 at the entrance of the latter and to be turned towards the central axis AL

[0050] As indicated above, two fingers 8 of the same pair are spaced from each other in the circumferential direction of the body part 6 so as to delimit a groove 9 between them.

[0051] Thus, in the embodiment shown, the engagement portion 7 comprises three grooves 9. Each groove 9 has a proximal end 90 closed on the body portion 6 side and a distal end 91 open at the free ends 81 of the fingers 8. Due to the beveled shape of said free ends 81, each groove 9 has a widened distal end 91.

[0052] The pairs of fingers 8, and therefore the grooves 9, are distributed at regular angular intervals along the circumference of the body part 6. Thus, the grooves 9 are angularly spaced from each other by 120 degrees. It should be emphasized that, in the case where the engagement portion 7 would have two pairs of fingers 8, the grooves 9 would preferably be diametrically opposed, with an angular spacing of 180 degrees between them. Similarly, in the case where the engagement portion 7 would have four pairs of fingers 8, the grooves 9 would preferably be angularly spaced by 90 degrees.

[0053] Each groove 9 is intended to receive an obstacle oriented radially outwards and secured to the second element 5. The two fingers 8 of the same pair are defined to pinch this radial obstacle between them.

[0054] The spacing between the fingers 8 of the same pair as well as the elastic deformation and stiffness properties of the fingers 8 are provided so that each finger 8 has a high transverse rigidity and a lower radial rigidity.

[0055] It is emphasized here that “transverse rigidity” means the rigidity of a finger 8 in the circumferential direction, and it can be considered that it is equivalent to the rigidity in the direction tangent to said imaginary cylinder to which the longitudinal axis of the finger 8 belongs, which tangent is taken at a point belonging to said longitudinal axis, and that “radial rigidity” means the rigidity of a finger 8 in a direction passing through the central axis A1 and the longitudinal axis of the finger 8 and belonging to a transverse plane perpendicular to the central axis A1

[0056] The high transverse rigidity makes it possible to obtain the pinching of a radial obstacle received in the groove 9 while avoiding a deformation of the fingers 8 in the circumferential direction during the transmission of a rotational movement of the driving element to the driven element. The lower radial rigidity allows the fingers 8 to deform elastically radially, in other words towards the outside of the coupling part 1, which promotes tolerance to angular and coaxial deviations.

[0057] These characteristics can be determined, depending on the application considered, by a person skilled in the art using calculation software, for example finite element calculation, well known in the art.

[0058] The pairs of fingers 8 are positioned on the periphery of the receiving space 10 inside the engagement part 7. The receiving space 10 is therefore a cylindrical space whose central axis coincides with the central axis A1 of the body part 6. This receiving space 10 has an open end on the free end side 81 of the fingers 8.

[0059] Preferably, the coupling part 1 is made of spring steel, type 45 SCD 6 for example.

[0060] If we refer to Figures 3 to 6, we can see that the coupling device 2 is shown there, in the position of use in Figures 3, 5 and 6, in which the coupling part 1, made integral with the first element 3, cooperates with the part transmission 4 made integral with the second element 5 and thus able to rotate around an axis of rotation A2 coaxial with the axis of rotation of the second element 5.

[0061] In the embodiment shown, the transmission part 4 comprises three radial obstacles 40 and three axial stops 41. The transmission part 4, thus composed, can be intended to be fixed to the free end 50 of the second element 5 by any appropriate securing means.

[0062] As a variant, the transmission part 4 further comprises a cylindrical shaft 42, on which the radial obstacles 40 and the axial stops 41 are mounted or formed, and which is made integral with the second element 5, in which case the shaft 42 constitutes said free end 50.

[0063] The outer diameter of said free end 50 is at least slightly smaller than the diameter of the receiving space 10, such that said free end 50 is able to be received in the receiving space 10 with the fingers 8 possibly sliding along it.

[0064] Each radial obstacle 40 projects radially outwardly from the circumferential surface of said free end 50. The three radial obstacles 42 are formed in the same transverse plane and are spaced apart so that each can be inserted into a respective groove 9. Consequently, they are here spaced apart from each other by the same angular distance of 120 degrees. It should be noted that, in the case where the transmission part 4 comprises two radial obstacles 40, these will preferably be diametrically opposed, namely angularly spaced apart by 180 degrees.

[0065] Preferably, the radial obstacles 40 are pins 43 mounted in radial bores provided for this purpose in said free end 50. Even more preferably, the pins 43 are split elastic pins, namely having a cylindrical wall of revolution made of steel and having a longitudinal slot, known under the commercial name “Mécanindus”, which allows easy mounting, by force, even in an imprecise bore.

[0066] The axial stops 41 are located behind the radial obstacles 40 when considering the direction of engagement of the engagement part 7 on said free end 50. In other words, the radial obstacles 40 are located between the end face of said free end 50 and the axial stops 4L. Each axial stop 41 is in the form of a block extending radially from the circumferential surface of said free end 50 and is opposite a radial obstacle 40. The width of each axial stop 41, namely its dimension in the circumferential direction, corresponds substantially to the width, in the circumferential direction, of a pair of fingers 8. Thus, in the position of use, each axial stop 41 is in alignment with a pair of fingers 8. The introduction of each radial obstacle 40 into the corresponding groove 9 can therefore be, if necessary, stopped by the contact of each stop axial 41 with the free ends 81 of the pair of fingers 8 opposite this axial stop 41.

[0067] With such a coupling device 2, the assembly can be carried out blindly in an easy manner. Indeed, it is sufficient to axially insert the coupling part 1 onto the free end 50 of the second element so that the radial obstacles 40 are introduced into the corresponding grooves 9. The beveled shape of the free ends 81 of the fingers 8 facilitates this axial blind assembly. It is also possible to arrange an elastomer element in the non-functional intervals between two successive fingers not belonging to the same pair of fingers, in order to facilitate the blind assembly of the coupling part 1.

[0068] In the position of use, as shown in Figures 5 and 6, the radial obstacles 40 will rotate jointly with the second element 5 around its axis of rotation, and the radial obstacles 40 being in rigid engagement between the pairs of fingers 8 by pinching, the rotational movement is transmitted to the coupling part 1, and therefore to the first element 3, by pressing on the fingers 8, whatever the direction of rotation of the second element 5.

[0069] Due to the radial elastic deformation capacity of the fingers 8 at their base regions, the coupling device 2 makes it possible to compensate for any play between the first and second elements 3, 5 in the event that they are not perfectly coaxial.

[0070] Due to the transverse rigidity of the fingers 8, the coupling device 2 has a high torsional rigidity, essential in the case of an alternating rotational movement.

[0071] Since, in the use position, the free end 50 of the second element 5 is received inside the receiving space 10 and the radial obstacles 40 extend between the fingers 8, the coupling device 2 is very compact both radially and axially. Such an arrangement also allows for easy mounting of the engaging part 7 around said free end 50.

[0072] Furthermore, the coupling device 2 is of the obstacle type and is thus less sensitive to vibrations. Such a property is particularly useful when it is desired to connect a rotating element to a delicate component, such as an angular position encoder, since the appearance of vibrations can cause abnormal operation of the component.

[0073] It is understood that the particular embodiment which has just been described has been given for informational purposes and is not limiting, and that modifications may be made without departing from the present invention.

Claims

Claims

1. Coupling part (1) for a mechanical coupling device (2) for coupling to each other two cylindrical rotating elements (3, 5) each mounted to rotate about an associated axis of rotation, said coupling part (1) comprising a body part (6) and an engagement part (7), the body part (6) having a central axis (A1), a first axial side (61a), called proximal, a second axial side (61b), called distal, opposite the proximal side (61a) along the central axis (A1), and securing means (60) for securing the coupling part (1) to a free end of a first (3) of the rotating elements (3, 5) such that the latter is then located on the proximal side (61a), and said engagement part (7) being carried by the body part (6) and configured to engage, in the position of use, in which the elements rotary (3, 5) are coupled by the mechanical coupling device (2),at least one obstacle (40) which is integral with a second (5) of the rotating elements (3, 5), the coupling part (1) being characterized in that the engagement part (7) comprises fingers (8) for transmitting torque and for pinching the radial obstacle (40), fingers (8) by which a torque applied to one or other of the first and second rotating elements (3, 5), around the respective axis of rotation, is directly transmitted between the at least one obstacle (40) and the body part (6) by the fingers (8) alone, the fingers (8) projecting from the body part (6) and their longitudinal axes belonging to an imaginary cylinder whose axis is coaxial with the central axis (A1) of the body part (6), the fingers (8) being located on the periphery of a receiving space (10) capable of receiving, in the position of use, a free end (50) of the second rotating element (5),the fingers (8) of the same pair forming a groove (9) having a closed proximal end (90) and an open distal end (91) through which a radial obstacle (40), integral with the second rotary element (5), is introduced so as to be received in the groove (9) and pinched by the fingers (8) in said position of use, and the fingers (8) being elastically deformable in the radial direction.,

2. Coupling part (1) according to claim 1, characterized in that the rigidity of the fingers (8) in the circumferential direction is 140N.m / rd ± 40N / mm.

3. Coupling part (1) according to any one of claims 1 and 2, characterized in that the rigidity of the fingers (8) in the radial direction is 40N.m / rd ± 5N / mm.

4. Coupling part (1) according to any one of claims 1 to 3, characterized in that the engagement part (7) comprises at least two pairs of fingers (8), in particular three pairs of fingers (8), the grooves (9) being distributed in an angularly equidistant manner.

5. Coupling part (1) according to any one of claims 1 to 4, characterized in that each finger (8) has a free end (81) which is beveled so as to widen the groove (9) at the distal end (91) of the latter.

6. Coupling part (1) according to any one of claims 1 to 5, characterized in that the fingers (8) of the same pair each have a polygonal cross-section and each have a flat lateral face (84) belonging to a plane to which said central axis (Al) belongs, the groove (9) being delimited in the circumferential direction by the two lateral faces (84) of the fingers (8).

7. Coupling part (1) according to any one of claims 1 to 6, characterized in that the body part (6) comprises a bore (62) opening onto the proximal side (61a) and capable of receiving the free end of said first rotary element (3), and the securing means (60) comprise at least one threaded through hole (63) extending radially and having a first end opening outside the body part (6) and a second end opening into said bore (62), the threaded hole (63) being capable of receiving a fixing member, in particular a set screw.

8. Mechanical coupling device (2) for coupling to each other two cylindrical rotating elements (3, 5) each mounted to rotate about an associated axis of rotation, characterized in that it comprises a coupling part (1) according to any one of claims 1 to 7, intended to be made integral with the free end of a first (3) of the rotating elements (3, 5), and a transmission part (4) integral or intended to be integral with the free end (50) of a second (5) of the rotating elements (3, 5), the transmission part (4) comprising at least one radial obstacle (40) which, in the position of use, extends radially projecting from the free end (50) of the second rotating element (5) so as to be received in the groove (9) formed by a pair of fingers (8) of the coupling part (1) and pinched by said fingers (8).

9. Mechanical coupling device (2) according to claim 8, characterized in that the at least one radial obstacle (40) is formed by a radial pin (43), preferably a split elastic pin.

10. Mechanical coupling device (2) according to any one of claims 8 and 9, characterized in that the transmission part (4) further comprises, for each pair of fingers (8), an axial stop (41) intended to extend, in the position of use, radially projecting from the free end (50) of the second rotary element (5) and opposite the radial obstacle (40) so as to form an axial stop against which the corresponding pair of fingers (8) can come into abutment when introducing said free end (50) into the receiving space (10) of the coupling part (1).

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