Torque transmission device, assembly method and motor vehicle seat

Abstract

Torque transmission device, assembly method and motor vehicle seat The torque transmission device (1) comprises: - a hub (3) rotating about an axis of rotation (X), the hub (3) having an orifice (5) delimited by an internal surface (7) carrying axial hub splines (9) distributed circumferentially around the axis of rotation (X); - a shaft (11) having a shaft end portion (13) delimited by an external surface (15) carrying shaft splines (17), the shaft splines (17) cooperating with the hub splines (9) to transmit the torque, the shaft end portion (13) being provided to be introduced into the orifice (5) by an open axial end (19) of said orifice (5); Each hub spline (9) terminates at the open axial end (19) with a point (23) and two chamfers (25) arranged on either side of the point (23). Figure for the abbreviation: 6

Description

Title of the invention: Torque transmission device, assembly method and motor vehicle seat

[0001] The invention relates generally to a torque transmission device, intended in particular to be implanted in a motor vehicle seat.

[0002] Such a torque transmission device may include:

[0003] - a hub rotating around an axis of rotation, the hub having an orifice delimited by an internal surface bearing axial hub splines distributed circumferentially around the axis of rotation;

[0004] - a tree having a tree tip portion delimited by an external surface bearing shaft splines, the shaft splines cooperating with the hub splines to transmit torque.

[0005] During the assembly of the torque transmission device, the shaft end portion is introduced into the orifice through an open axial end of said orifice.

[0006] When the insertion operation is performed on an automated production line, the device may be damaged. Damage can occur when the shaft splines are misaligned with respect to the hub splines. In particular, when the hub splines are aligned with the shaft splines, the engagement of the shaft end portion with the hub can lead to damage to one or both parts, or to a blockage that makes assembly impossible.

[0007] In this context, the invention aims to provide a torque transmission device that does not have this defect.

[0008] To this end, the invention relates to a torque transmission device comprising: - a hub rotating around an axis of rotation, the hub having an orifice delimited by an internal surface carrying axial hub splines distributed circumferentially around the axis of rotation;

[0009] - a tree having a tree tip portion delimited by an external surface bearing shaft splines, the shaft splines cooperating with the hub splines to transmit torque,

[0010] the shaft end portion being provided to be inserted into the orifice through an open axial end of said orifice;

[0011] each hub spline ending towards the axial end open by a point and two chamfers arranged on either side of the point.

[0012] Because each hub spline ends in a point and two chamfers arranged on either side of the point, the probability of the device being damaged The risk of jamming during insertion of the shaft end into the rotating hub is significantly reduced. Similarly, any risk of jamming during insertion is eliminated, preventing disruption to the assembly process.

[0013] Normally, the shaft splines each engage between two hub splines. If, at the time of insertion into the opening, the shaft splines are substantially aligned with the hub splines, the shaft splines will bear against the chamfers formed at the ends of the hub splines. These chamfers will circumferentially deflect the end portion of the shaft and guide the shaft splines so that each engages between two hub splines.

[0014] The torque transmission device may also have one or more of the following characteristics, considered individually or in all technically possible combinations:

[0015] - each hub spline having two turned lateral flanks circumferentially towards two adjacent hub grooves, the two chamfers connecting the two lateral sides to the point;

[0016] - each chamfer has a normal forming an angle with the axis of rotation between 30° and 80°;

[0017] - the first and second hub splines are provided to ensure a pre-orientation of the shaft end portion at the time of insertion into the orifice, the first and second hub splines being located on parts of the internal surface opposite to each other with respect to the axis of rotation, the tips of the first and second hub splines being offset towards the open axial end relative to the tips of the other hub splines, the tips of the first hub spline and the other hub splines being angularly regularly spaced around the axis of rotation, the second hub spline being located between two other hub splines, the tip of the second hub spline being angularly relatively closer to the tip of one of said two other hub splines than to the tip of the other of said two other hub splines;

[0018] - the tip of the first hub spline is axially relatively more close to the open axial end than the tip of the second hub spline;

[0019] - the hub includes a flexible tab that applies pressure to the end portion of the shaft towards the first hub spline at the time of insertion into the orifice.

[0020] - each shaft groove terminates at one end of the shaft with a point of shaft and two shaft chamfers arranged on either side of the shaft tip.

[0021] According to a second aspect, the invention relates to a motor vehicle seat comprising a seat, a backrest pivoting relative to the seat and at least one torque transmission device having the above characteristics linking the seat to the backrest.

[0022] According to a third aspect, the invention relates to a motor vehicle seat comprising: - a seat; - at least one rail fixed to a floor of the motor vehicle; - for each rail, a slide fixed to the seat and movable along said rail; and - a drive mechanism for translating the slide or each slide along the corresponding rail; the drive mechanism comprising: - a motor; - for each slide, a torque transmission device having the above characteristics, the hub of said torque transmission device being driven in rotation by the motor, - for each torque transmission device, a device for converting the rotational movement of the shaft into a translational movement of the slide along the rail.

[0023] According to a fourth aspect, the invention relates to a method of assembling a torque transmission device having the above characteristics, comprising engaging the shaft end part in the hub orifice by the open axial end of said orifice, the shaft splines fitting between the hub splines.

[0024] Other features and advantages of the invention will become apparent from the detailed description given below, by way of example and not limitation, with reference to the accompanying figures, among which: - [Fig.1] The [Fig.1] is a perspective view of a torque transmission device according to a first embodiment of the invention, with a partial section of the shaft and hub; - [Fig.2] The [Fig.2] is a perspective view of the hub of the torque transmission device of the [Fig.1]; - [Fig.3] The [Fig.3] is a front view of the hub of the [Fig.2]; - [Fig.4] [Fig.5] Figures 4 and 5 are perspective views of the hub and of the tree for a second embodiment of the torque transmission device of the invention; - [Fig.6] The [Fig.6] is an axial cross-sectional view of a variant of the torque transmission device of figures 4 and 5; - [Fig.7] The [Fig.7] is a schematic front view of the hub of the [Fig.6], with overlapping tree ribs in a potentially problematic situation; - [Fig. 8] [Fig. 8] is a partial representation of an early siege of motor vehicle implementing the torque transmission device of the invention; and - [Fig. 9] Fig. 9 is a partial perspective view of another seat of motor vehicle implementing the torque transmission device of the invention.

[0025] Device 1 shown in [Fig.1] is a torque transmission device, intended to be used, among other things, in motor vehicle seats.

[0026] The torque transmission device 1 comprises:

[0027] - a hub 3 rotating about an axis of rotation X, the hub 3 having an orifice 5 delimited by an internal surface 7 bearing axial hub splines 9 distributed circumferentially around the axis of rotation X;

[0028] - a tree 11 having a tree end portion 13 delimited by a surface external 15 carrying shaft splines 17, the shaft splines 17 cooperating with the hub splines 9 to transmit torque.

[0029] The shaft end portion 13 is intended to be introduced into the orifice 5 through an open axial end 19 of said orifice ([Fig.2]).

[0030] The shaft splines 17 fit into grooves 21, each delimited between two hub splines 9.

[0031] The internal surface 7 of the orifice 5 is cylindrical, as can be seen in particular in [Fig.3]. Perpendicular to the axis of rotation X, this internal surface 7 is circular.

[0032] In the example shown, the hub 3 has three hub splines 9. Alternatively, it has more than three hub splines 9, for example four, five or more than five hub splines 9.

[0033] The internal surface 5 is slightly flared at the open axial end 19, so as to facilitate the introduction of the shaft end part 13.

[0034] In the example shown, the tree 11 is hollow, and the external surface 15 is polygonal in shape.

[0035] The shaft end portion 13 has a number of shaft splines 17 equal to the number of hub splines 9.

[0036] The hub splines 9 are regularly distributed circumferentially around the axis of rotation X. They are all identical to each other.

[0037] Similarly, the shaft splines 17 are regularly distributed circumferentially around the axis of rotation X. They are all identical to each other.

[0038] The hub splines 9 are straight and parallel to each other.

[0039] Similarly, the shaft grooves 17 are straight and parallel to each other.

[0040] According to the invention, each hub spline 9 terminates towards the open axial end 19 by a point 23 and two chamfers 25 arranged on either side of the point 23.

[0041] As can be seen in [Fig. 3], each hub spline 9 has two lateral flanks 27 circumferentially facing two adjacent hub splines 9. Each groove 21 is thus delimited by two lateral flanks 27, belonging to the two hub splines 9 adjoining the groove 21.

[0042] In the example shown, each side 27 extends along the entire length of the hub spline 9. Each side 27 is connected to the internal surface 7 along an axial line. The sides 27 are substantially perpendicular to the internal surface 7 along the connecting line.

[0043] Each hub spline 9 is also delimited towards the axis of rotation X by an intermediate face 29. The intermediate face 29 extends over the entire length of the hub spline 9. It connects the two flanks 27 to each other, and is located between the two flanks 27.

[0044] The two chamfers 25 connect the two lateral sides 27 to the point 23.

[0045] The point 23 corresponds to the edge along which the two chamfers 25 connect to each other. This edge extends substantially in a plane containing the axis of rotation X. The edge originates from the intermediate face 29 and extends from it radially towards the internal surface 7 and axially towards the open axial end 19, up to the internal surface 7. The edge extends in a radial median plane of the hub spline 9.

[0046] Each chamfer 25 is delimited radially on one side by the internal surface 7, and on the other side by the intermediate face 29. Circumferentially, it is delimited on one side by the edge constituting the point 23, and on the other side by the flank 27.

[0047] When following the chamfer 25 from the edge constituting the point 23 to the flank 27, one moves away axially from the open axial end 19.

[0048] Each chamfer 25 has a normal N forming an angle between 30° and 80° with the axis of rotation X. This angle is preferably between 50° and 75°, and is, for example, 70° ([Fig. 2]). This angle is chosen according to the angular and radial error value between the shaft and the hub.

[0049] The shaft splines 17 have sections chosen to be able to fit into the grooves 21. In section in a plane perpendicular to the axis of rotation X, they each have a section complementary to that of the groove 21.

[0050] Each shaft groove 17 is delimited by two flanks 31 connected to each other by a summit surface 33.

[0051] The summit surfaces 33 are arched and have shapes adapted to bear against the area of ​​the internal surface 7 forming the bottom of the grooves 21.

[0052] The flanks 31 have orientations adapted to bear against the flanks 27 of the hub splines 9.

[0053] The assembly of the torque transmission device 1 is carried out by engaging the shaft end part 13 in the orifice 5 of the hub through the open end 19 of said orifice.

[0054] The shaft splines 17 fit between the hub splines 9.

[0055] If the shaft splines 17 are not axially aligned with the grooves 21 defined between the hub splines 9, each shaft spline 17 bears against a chamfer 25 of one of the hub splines 9. Due to the orientation of the chamfer 25, the shaft spline 17 is guided towards one of the grooves 21. The end portion of the shaft 13 then undergoes both axial and circumferential movement, causing it to engage correctly in the grooves 21 separating the hub splines 9.

[0056] A second embodiment of the invention will now be described, with reference to figures 4 to 7.

[0057] Only the points by which the second embodiment differs from the first will be detailed below. Identical elements or elements performing the same function will be designated by the same reference numerals in both embodiments.

[0058] In the second embodiment, the hub 3 has a large number of hub splines 9. In the example shown, the hub 3 has ten hub splines 9. Alternatively, it has fewer or more than ten hub splines 9.

[0059] Similarly, the shaft 11 has a large number of shaft splines 17. This number of shaft splines is equal to the number of hub splines.

[0060] According to a first aspect of the second embodiment, each shaft groove 17 terminates towards an end 35 of the shaft by a shaft point 37 and two shaft chamfers 39 arranged on either side of the shaft point 37.

[0061] The end 35 of the shaft has a generally conical shape, and terminates in a flat nose 41.

[0062] The tips 37 of the shaft splines 17 converge towards the nose 4L

[0063] More specifically, and as can be seen in Figures 5 and 7, each shaft groove 17 is delimited by two shaft sides 31 turned towards the neighboring grooves, and a summit surface 33 connecting the two shaft sides 31 to each other.

[0064] Each shaft tip 37 extends axially from the apex surface 33 to the nose 41. The shaft chamfers 39 are placed circumferentially on either side of the shaft tip 37. The shaft tip 37 constitutes the edge of junction of the two shaft chamfers 39.

[0065] The shaft splines 17 define a plurality of shaft grooves 43. Each shaft chamfer 39 extends axially between the nose 41 and one of the flanks 31 of the shaft spline 17. Circumferentially, it extends between the tip 37 of the shaft spline and the bottom of the shaft groove 43 located on the same side.

[0066] According to a second aspect, illustrated in figures 6 and 7, the first and second hub splines 45 and 47 are provided to ensure a pre-orientation of the shaft end part 13 at the time of insertion into the orifice 5.

[0067] The first and second hub splines 45, 47 are located on parts of the internal surface 7 opposite to each other with respect to the axis of rotation X.

[0068] When the hub 5 has an even number of hub splines 9, the first and second hub splines 45, 47 are advantageously diametrically opposed, as illustrated in [Fig.7].

[0069] As can be seen in [Fig.6], the points 23 of the first and second hub splines 45, 47 are offset towards the open axial end 19 of the orifice 5 relative to the points 23 of the other hub splines 9.

[0070] In other words, the first and second hub splines 45, 47 extend further than the other hub splines 9 towards the open axial end 19.

[0071] Consequently, at the time of the introduction of the shaft end part 13 into the orifice 5, this shaft end part 13 will first encounter the first and second hub splines 45, 47, before encountering the other hub splines 9.

[0072] The tip 23 of the first hub spline 45 is axially relatively closer to the open axial end 19 than the tip 23 of the second hub spline 47.

[0073] As can be seen in particular in [Fig.7], the hub splines 9, including the first and second hub splines 45, 47, are circumferentially regularly distributed around the axis of rotation X.

[0074] The points 23 of the first hub spline 45 and of the other hub splines 9 are angularly regularly spaced around the axis of rotation X.

[0075] The second hub spline 47 is located between two of the other hub splines 9, referenced 9' and 9” on the [Fig.7].

[0076] The tip 23 of the second hub spline 47 is angularly relatively closer to the tip 23 of the hub splines 9' than to the tip 23 of the hub spline 9”.

[0077] In other words, the tip 23 of the second hub spline 47 is circumferentially offset towards the tip of one of the neighboring hub splines, and relatively further away from the tip of the other of the two neighboring hub splines.

[0078] In the example shown in [Fig.7], where the first hub spline 45 and the second hub spline 47 are diametrically opposed, the point 23 of the second hub spline 47 is not located opposite the point 23 of the first hub spline 45.

[0079] Consequently, the second hub spline 47 has two chamfers 25 of unequal sizes. One of the chamfers 25 is relatively smaller and the other chamfer 25 is relatively larger.

[0080] The chamfer located circumferentially on the side of the hub spline 9' is smaller, and the one located circumferentially on the side of the hub spline 9" is larger. The tip 23 of the second hub spline 47 is not located in the median axial plane of the second hub spline 47. It is circumferentially offset to one side of this plane.

[0081] On the contrary, for the first hub spline 45 and all other hub splines 9, the tip 23 is located in the median axial plane of the corresponding spline.

[0082] Furthermore, as can be seen in [Fig.6], the hub 5 has a flexible tab 49 which forces the shaft end part 13 towards the first hub spline 45 when the shaft end part 13 is inserted into the orifice 5.

[0083] The flexible leg 49 extends axially from an edge of the open axial end 19. It carries, at its free end 51, a bead 53. In projection into the plane of the open axial end 19, that is to say in projection along the axial direction in a plane perpendicular to the axial direction, the bead 53 protrudes towards the inside of the open axial end 19.

[0084] The flexible leg 49 is located opposite the first hub spline 45 with respect to the axis of rotation X.

[0085] It is flexible in the sense that it is capable of deforming radially, outwards from the orifice 5, as illustrated in [Fig.6].

[0086] The pre-orientation function of the shaft end part 13 will now be detailed.

[0087] When the shaft end portion 13 is inserted into the orifice 5, the shaft end portion 13 is displaced axially towards the open axial end 19. The shaft end part 13 is deflected by the flexible leg 49 radially towards the first hub spline 45.

[0088] The shaft end part 13 comes into contact with the bead 53, which has the effect of moving this shaft end part 13 radially.

[0089] The shaft end part 13 then continues its axial movement, and comes to rest against the end of the first hub spline 45.

[0090] If the shaft splines 17 are circumferentially offset with respect to the hub splines 9, the first hub spline 45 will circumferentially deflect one of the shaft splines 17 so that it engages in one of the grooves 21. The other shaft splines 17 will engage in the other grooves 21.

[0091] The contact between the first hub spline 45 and the shaft spline 17 which comes into contact with it produces both a circumferential movement of the shaft end part 13 and a radial movement towards the center of the orifice 5.

[0092] When the shaft end part 13 continues its movement, the axis of the shaft end part 13 is aligned with the axis of the orifice 5, and the flexible leg 49 is deformed by bending outwards from the orifice 5.

[0093] In the case where the shaft end portion 13 is positioned in front of the open axial end 19 with an orientation in which the shaft splines 17 are perfectly aligned with the hub splines 9, as illustrated in [Fig. 7], the contact between the first hub spline 45 and the shaft spline 17 coming into contact with it will not produce a circumferential deflection. This contact will cause, as illustrated by arrow Fl in [Fig. 6], an axial and radial displacement, forcing the shaft end portion 13 to come into contact with the second hub spline 47.

[0094] When the axial movement of the shaft end portion 13 towards the inside of the orifice 5 is prolonged, due to the circumferential offset of the tip 23 of the second hub spline 47 towards the hub spline 9', one of the shaft splines 17 will come into contact with the chamfer 25 of the larger area of ​​the second hub spline 47. The shaft end portion 13 is then deflected circumferentially as illustrated by the arrow F2 of [Fig.7]. The shaft spline 17 in contact with the larger surface chamfer 25 will be guided by this chamfer to engage in the groove 21 located between the second hub spline 47 and the shaft spline 9”. The other shaft splines 17 will then be oriented appropriately to engage in the other grooves 21 of the hub 3.

[0095] The radial deviation of the shaft end portion 13 towards the second hub spline 47 will cause the lug 49 to bend outwards from the orifice, as illustrated in [Fig.6].

[0096] When the number of hub splines 9 is odd, the second hub spline 47 is not arranged diametrically opposite the first hub spline 45. It is circumferentially offset by half a pitch from the position illustrated in [Fig. 7]. A pitch corresponds to the circumferential distance between two hub splines 9. Its shape is similar to that illustrated in [Fig. 7]: the point 23 is offset towards the adjacent spline 9'. It has two chamfers 25 of different sizes, the chamfer 25 facing the spline 9' being smaller and the chamfer 25 facing the spline 9" being larger.

[0097] A first example of a motor vehicle seat using the torque transmission device 1 described above is shown in [Fig.8].

[0098] The seat 55 comprises a seat 57, a backrest 59 and at least one torque transmission device 1 linking the seat 57 to the backrest 59.

[0099] In the example shown, the seat 55 has two torque transmission devices 1, each linking the seat 57 to the backrest 59. Alternatively, the seat 55 has only one torque transmission device 1.

[0100] The shaft 11 is common to both torque transmission devices 1. In contrast, the hubs 3 are separate.

[0101] The or each torque transmission device 1 constitutes a pivoting joint by which the backrest 59 is linked to the seat 57.

[0102] The hub 3 of each torque transmission device 1 is mounted on a plate 61 intended to be rigidly fixed to the seat 57. The two plates 61 are transversely separated from each other and placed transversely opposite each other.

[0103] The file 59 includes a frame 63 having an upper crossbar 65, a lower crossbar 67 and two lateral uprights 69.

[0104] The end parts 13 of the shaft 11 are engaged in the holes 5 of the hubs 3 at the time of the assembly of the frame 63.

[0105] As illustrated in [Fig.8], before assembly, the shaft 11 is fixed to the lower cross member 67. The plates 61 are connected to the two lateral uprights 69.

[0106] The frame 63 is assembled by moving the side uprights 69 transversely relative to the lower cross member 67, and typically also relative to the upper cross member 65. The side uprights 69 are moved in opposite directions, as illustrated in [Fig.8].

[0107] This movement causes the shaft end portions 13 to engage in the hubs 3 carried by the plates 61. They also allow positioning correctly the side uprights 69 in relation to the lower and upper cross members 65, 67.

[0108] After this transverse displacement, causing the shaft end parts 13 to engage in the holes 5, the frame elements are fixed to each other.

[0109] Finally, the plates 61 are rigidly fixed to the seat 57.

[0110] The assembly of the frame 63 can be carried out automatically, i.e., by means of a robot. Consequently, the engagement of the shaft end sections 13 in the hubs 3 is also performed automatically, without operator intervention. Due to the design of the torque transmission devices 1, the engagement of the shaft end sections 13 in the ports 5 is achieved with an extremely low failure rate. This engagement can be performed even if the shaft splines 17 are initially substantially aligned transversely with the hub splines 9.

[0111] Another example of a motor vehicle seat implementing the device of The torque transmission 1 described above is illustrated in [Fig.9].

[0112] Seat 71 comprises:

[0113] - a seat 73;

[0114] - at least one rail 75 fixed to a floor of the motor vehicle;

[0115] - for the rail or each rail, a slide 77 fixed to the seat and movable along said rail 75; and

[0116] - a translational drive mechanism 79 of the or each slide 77 along of the corresponding rail 75.

[0117] The drive mechanism 79 comprises: - an 81 engine; and

[0118] - for the slide or each slide 77, a torque transmission device 1 such that as described above, the hub 3 of said torque transmission device 1 being driven in rotation by the motor 81.

[0119] The drive mechanism 79 also includes, for the or each torque transmission device 1, a device 83 for converting the rotational movement of the shaft 11 into a translational movement of the slide 77 along the rail 75.

[0120] Typically, the seat 71 comprises two rails 75 parallel to each other. It also comprises two slides 77, two torque transmission devices 1 and two conversion devices 83. Only one rail, one slide and one torque transmission device are shown in [Fig.9].

[0121] The motor 81 has two output shafts 85, each carrying a pinion 87 for cooperating with the hub 3 of one of the two torque transmission devices 1. The axis of rotation of the hub 3 is perpendicular to the output shaft 85, but extends parallel to the corresponding rail 75. The hub 3 has an external helical thread, cooperating with the pinion 87. The hub 3 functions as a worm gear.

[0122] In the example shown, the conversion device 83 is of the screw-nut type. In other words, it comprises a nut 89 cooperating with a screw 91 fixed to the shaft 11. The nut 89 has a thread that is complementary to that of the screw 91. The nut 89 is locked in a nut holder 92. The nut holder 92 is rigidly fixed to the rail 75. The screw 91 is fixed in translation longitudinally relative to the slide 77 and free in rotation relative to the slide 77. The hub 3 drives the shaft 11 and the screw 91 in rotation, which causes the screw 91 to move axially relative to the nut 89 and the slide 77 relative to the rail 75.

[0123] The motor 81 and the output shafts 85 are mounted in a transverse cradle 93, which is integral with the base 73. The hubs 3 are mounted at the two opposite transverse ends of the cradle 93. The rails 75 are longitudinally oriented.

[0124] The torque transmission device described above has multiple advantages.

[0125] The fact that each hub spline has two lateral flanks circumferentially turned towards two adjacent hub splines, with the two chamfers connecting the two lateral flanks at the tip, means that the shaft splines are adequately guided by the two chamfers when the shaft end portion engages in the open axial end of the bore. The chamfers deflect the shaft splines towards the grooves located on either side of the hub splines.

[0126] The fact that each chamfer has a normal forming with the axis of rotation an angle between 30° and 80° contributes to the accuracy of the guidance towards the corresponding groove.

[0127] The first and second hub splines allow for pre-orientation of the shaft end portion upon insertion into the bore, regardless of the circumferential orientation of the shaft splines relative to the hub splines. Even if the shaft splines are perfectly aligned with the hub splines when the shaft end portion enters the bore, the arrangement of the first and second hub splines ensures that the shaft splines are correctly oriented to engage in the grooves defined between the hub splines.

[0128] The flexible tab that directs the shaft end portion towards the first hub spline at the time of insertion into the orifice helps to ensure that the shaft end portion will first come into contact with the first hub spline, which makes it easier and more reliable to insert the shaft end portion into the orifice.

[0129] The fact that the tip of the first hub spline is axially relatively closer to the open axial end of the orifice than the tip of the second hub spline contributes to making the introduction of the shaft end portion into the orifice easier and therefore more reliable.

[0130] The fact that each shaft groove terminates at one end of the shaft with a shaft tip and two shaft chamfers arranged on either side of the shaft tip, contributes to making the introduction of the shaft end part into the orifice easier and more reliable.

Claims

Demands

1. Torque transmission device (1), comprising: - a hub (3) rotating about an axis of rotation (X), the hub (3) having an orifice (5) delimited by an internal surface (7) carrying axial hub splines (9) distributed circumferentially around the axis of rotation (X); - a shaft (11) having a shaft end portion (13) delimited by an external surface (15) carrying shaft splines (17), the shaft splines (17) cooperating with the hub splines (9) to transmit the torque, the shaft end portion (13) being provided to be introduced into the orifice (5) by an open axial end (19) of said orifice (5); each hub groove (9) ending towards the open axial end (19) by a point (23) and two chamfers (25) arranged on either side of the point (23).

2. Torque transmission device according to claim 1, in which each hub spline (9) has two lateral flanks (27) circumferentially turned towards two adjacent hub splines (9), the two chamfers (25) connecting the two lateral flanks (27) to the tip (23).

3. Torque transmission device according to claim 2, wherein each chamfer (25) has a normal forming with the axis of rotation (X) an angle between 30° and 80°.

4. A torque transmission device according to any one of the preceding claims, wherein first and second hub splines (45, 47) are provided to ensure pre-orientation of the shaft end portion (13) upon insertion into the orifice (5), the first and second hub splines (45, 47) being located on portions of the internal surface (7) opposite to each other with respect to the axis of rotation (X), the tips (23) of the first and second hub splines (45, 47) being offset towards the open axial end (19) with respect to the tips (23) of the other hub splines (9), the tips (23) of the first hub spline (45) and the other hub splines (9) being angularly and regularly spaced around the axis of rotation (X), the second hub spline (47) being located between two other hub splines (9', 9"), the tip (23) of the second hub spline (47) being angularly relatively closer to the tip (23) of one of said two other hub splines (9', 9") than to the tip (23) of the other of said two other hub splines (9', 9").

5. Torque transmission device according to claim 4, wherein the tip (23) of the first hub spline (45) is axially relatively closer to the open axial end (19) than the tip (23) of the second hub spline (47).

6. Torque transmission device according to claim 4 or 5, wherein the hub (3) has a flexible tab (49) that forces the shaft end portion (13) towards the first hub spline (45) at the time of insertion into the orifice (5).

7. Torque transmission device according to any one of the preceding claims, wherein each shaft spline (17) terminates towards one end (35) of the shaft (11) by a shaft tip (37) and two shaft chamfers (39) arranged on either side of the shaft tip (37).

8. Motor vehicle seat (55) comprising a seat (57), a backrest (59) pivoting relative to the seat (57) and at least one torque transmission device (1) according to any one of the preceding claims, linking the seat (57) to the backrest (59).

9. A motor vehicle seat (71) comprising: - a seat (73); - at least one rail (75) fixed to a floor of the motor vehicle; - for the rail or each rail (75), a slide (77) integral with the seat (73) and movable along said rail (75); and - a mechanism (79) for driving the slide or each slide (77) in translation along the corresponding rail (75); the drive mechanism (79) comprising: - a motor (81); - for the slide or each slide (77), a torque transmission device (1) according to any one of claims 1 to 7, the hub (3) of said torque transmission device (1) being driven in rotation by the motor (81); - for the torque transmission device (1), a device (83) for converting the rotational motion of the shaft

10. (11) of said torque transmission device (1) in a translational movement of the corresponding slide (77) along the rail (75). Method of assembling a torque transmission device (1) according to any one of claims 1 to 7, comprising engaging the shaft end portion (13) in the orifice (5) of the hub (3) by the open axial end (19) of said orifice (5), the shaft splines (17) fitting between the hub splines (9).

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