MOVEMENT TRANSMISSION DEVICE AND A SEAT

Abstract

A movement transmission device having a first assembly including a housing extending along a first axis, a second assembly configured to move in rotation and in translation along the first axis inside the housing, and a first elastic member. The first assembly includes a first axial stop and the second assembly includes a complementary first axial stop, a first axial clearance being formed between the first axial stop and the complementary first axial stop. The first elastic member is adapted to be deformed during translational movement of the second assembly along the first axis when an axial force greater than a first threshold is applied, the complementary first axial stop being axially supported by the first axial stop.

Claims

1. A movement transmission device (30) intended for an actuator (18), the device (30) comprising: a fixed first assembly (100), comprising a housing (110) extending along a first axis (B); a second assembly (200) arranged in said housing (110) and extending along the first axis (B), the second assembly (200) being configured to move in rotation about said first axis (B) and to move in translation along said first axis (B), inside said housing (110); and a first elastic member (300) installed inside said housing (110); wherein the first assembly (100) comprises a first axial stop (121) and the second assembly (200) comprises a complementary first axial stop (221), the first axial stop (121) and the complementary first axial stop (221) being axially facing each other, a first axial clearance (J1) being formed between the first axial stop (121) and the complementary first axial stop (221), wherein the first elastic member (300) is able of being deformed during translational movement of the second assembly (200) along the first axis (B) in a first direction when an axial force greater than a first threshold is exerted by the second assembly (200) on said first elastic member (300), the first axial clearance being progressively reduced until the complementary first axial stop (221) is axially supported on the first axial stop (121).

2. The device (30) according to claim 1, wherein the second assembly (200) comprises at least one shaft (210) and one helical pinion (230) which are integral with each other, the helical pinion (230) comprising the complementary first axial stop (221) and meshing with a complementary input pinion (240) of the device (30).

3. The device (30) according to claim 1, wherein a first bearing (270) is mounted in the housing (110), radially between the first assembly (100) and the second assembly (200), the first bearing (270) comprising a radially external ring (274) arranged facing the first assembly (100) and a radially internal ring (272) arranged facing the second assembly (200), the first elastic member (300) being axially supported on the radially external ring (274) of said first bearing.

4. The device (30) according to claim 3, wherein the first assembly (100) comprises a first shoulder (132) and the second assembly (200) comprises a complementary first shoulder (218), the radially external ring (274) of the first bearing (270) being axially supported on the first shoulder (132) of the first assembly (100), the radially internal ring (272) of the first bearing (270) being axially supported on the complementary first shoulder (218) of the second assembly (200).

5. The device (30) according to claim 1, further comprising a first preload element (124) for the first elastic member (300), able to adjust an axial preload force acting on the first elastic member (300).

6. The device (30) according to claim 5, further comprising a second elastic member (400) installed inside the housing (110), wherein the first assembly (100) comprises a second axial stop (123) and the second assembly comprises a complementary second axial stop (223), the second axial stop (123) and the complementary second axial stop (223) being axially facing each other, a second axial clearance (J2) being formed between the second axial stop (123) and the complementary second axial stop (223), wherein the second elastic member (400) is able to be deformed during translational movement of the second assembly (200) along the first axis in a second direction that is opposite to the first direction when an axial force greater than a second threshold is exerted by the second assembly (200) on said second elastic member (400), the second axial clearance (J2) being progressively reduced until the complementary second axial stop (223) is axially supported on the second axial stop (123).

7. The device (30) according to claim 6, further comprising a second bearing (280) mounted in the housing (110), radially between the first assembly (100) and the second assembly (200), the second bearing (280) comprising a radially external ring (284) arranged facing the first assembly (100) and a radially internal ring (282) arranged facing the second assembly (200), the second elastic member (400) being axially supported directly on the radially external ring (284) of said second bearing (280).

8. The device (30) according to claim 7, wherein the first assembly (100) further comprises a second shoulder (134) and the second assembly (200) further comprises a complementary second shoulder (220), the radially external ring (284) of the second bearing (280) being axially supported on the second shoulder (134) of the first assembly (100), the radially internal ring (282) of the second bearing (280) being axially supported on the complementary second shoulder (220) of the second assembly (200).

9. The device (30) according to claim 6, further comprising a second preload element (130) for the second elastic member (400), able to adjust an axial preload force acting on the second elastic member (400) independently of the axial preload force acting on the first elastic member (300).

10. A seat (2) for an aircraft, comprising: a fixed part intended to be fixed to a fixed part of the aircraft and a movable part able to be moved relative to the fixed part, and a movement transmission device (30) according to claim 1 mounted between the movable part and the fixed part, the first assembly (100) of the transmission device being connected to said fixed part of the seat (2), the second assembly (200) of the transmission device being adapted to be driven by a motor (20) to move in rotation about the first axis (B) and in translation along said first axis (B), the second assembly (200) being connected to said movable part of the seat (2).

Description

BRIEF DESCRIPTION OF DRAWINGS

[0101] Other features, details and advantages will become apparent from reading the detailed description below, and from analyzing the attached drawings, in which:

[0102] FIG. 1 shows a schematic side view of an aircraft seat provided with at least one actuator comprising a movement transmission device according to the invention.

[0103] FIG. 2 shows a schematic view in axial section of an actuator of the seat of FIG. 1.

[0104] FIG. 3 shows a schematic view in axial section of the movement transmission device of the seat of FIG. 1 according to one embodiment of the invention.

[0105] FIG. 4 shows a schematic view in axial section of the movement transmission device of the seat of FIG. 1 according to an alternative embodiment of the device of FIG. 3, the transmission device being in a first position.

[0106] FIG. 5 shows a schematic view in axial section of the movement transmission device of the seat of FIG. 1 according to the variant embodiment of FIG. 4, in a second position.

DESCRIPTION OF EMBODIMENTS

[0107] FIG. 1 shows a seat 2, in particular for an aircraft. Seat 2 comprises a seating part 4, a backrest 6, and a headrest 8. Seat 2 may further comprise a leg rest 10.

[0108] Seat 2 is intended to be connected to a fixed part of the aircraft, in particular to the floor. For this purpose, seat 2 may comprise feet 12 and a track 14. Track 14 comprises, for example, two rails fixed to the floor, each foot 12 being mounted on one of the rails so as to be able to slide along the respective rail. Seat 2 is thus able to move forwards or backwards.

[0109] Seat 2 comprises one or more electric drive systems 18, also referred to as actuators. Each actuator 18 is dedicated to moving one of the elements (seating part 4, backrest 6, headrest 8, leg rest 10, etc.) of seat 2 relative to the others. Alternatively, actuator 18 is dedicated to moving seat 2 in track 14.

[0110] In the following, the element of seat 2 that is moved is called the moving part, while the elements it moves relative to are called the fixed part. When seat 2 is moved in its entirety relative to the fixed part of the aircraft, the moving part is seat 2, and the fixed part is the fixed part of the aircraft.

[0111] As can be seen in FIG. 2, actuator 18 comprises a motor 20, an output shaft 22, a reduction gear train 23, a brake 24, and a casing 25.

[0112] Motor 20 is able of generating a movement of a shaft of the actuator, referred to as the input shaft or drive shaft (not illustrated). Motor 20 generates in particular a rotational movement of the input shaft about a longitudinal axis of this input shaft. Longitudinal is understood here to mean extending along its longest dimension. The input shaft is integral with a pinion 240, referred to as the upstream pinion or input pinion, which will be described further below with reference to FIG. 3.

[0113] Output shaft 22 is configured to be driven to rotate about its longitudinal axis A. In particular, output shaft 22 is rotated when the input shaft rotates about its longitudinal axis as indicated above. Advantageously, the longitudinal axes of output shaft 22 and input shaft are substantially parallel. As will be detailed below, output shaft 22 is integral with a pinion 260 referred to as the downstream pinion or output pinion. The rotation of output shaft 22 about axis A causes movement, in rotation and/or in translation, of the movable part of seat 2. Output shaft 22 is thus configured to convert the rotation of the input shaft into a movement adapted to move the movable part relative to the fixed part of the seat.

[0114] Reduction gear train 23 is for example a multi-stage reduction gear train. Reduction gear train 23 comprises a set of mechanical parts, such as gear assemblies or connecting rods, adapted to transmit movement of the input shaft to output shaft 22. More specifically, these mechanical parts connect the input shaft to output shaft 22. Among these mechanical parts, reduction gear train 23 comprises a movement transmission device 30, in particular for transmission of the movement of the input shaft, which will be described below with reference to FIGS. 3 to 5.

[0115] Reduction gear train 23 makes it possible to reduce the movement speed of the input shaft before transmission to output shaft 22. The reduction in the movement speed generated by motor 20 is linked to an increase in the output torque of actuator 18.

[0116] Brake 24 is configured to brake or prevent the input shaft's rotation generated by motor 20, so as to also brake or prevent the rotation of output shaft 22, and therefore the movement of the movable part of seat 2 relative to its fixed part.

[0117] As can be seen from FIG. 2, casing 25 houses motor 20, brake 24, and reduction gear train 23. Output shaft 22 is connected to reduction gear train 23 and traverses casing 25 in its longitudinal direction A. Casing 25 is connected to the fixed part of seat 2.

[0118] Transmission device 30 will now be described, with reference to FIGS. 3 to 5.

[0119] Transmission device 30 comprises a first assembly 100 and a second assembly 200.

[0120] First assembly 100 comprises a housing 110 extending along an axis B. Advantageously, axis B is substantially parallel to the longitudinal axes of the input shaft and output shaft 22 of actuator 18. Housing 110 is for example comprised in casing 25, casing 25 therefore forming part of first assembly 100. Housing 110 may be delimited by a radially internal wall 27 of casing 25.

[0121] Housing 110 may comprise a first end portion 112, a second end portion 114, and a central portion 116. Central portion 116 is arranged axially between first end portion 112 and second end portion 114. In particular, central portion 116 is delimited axially between a first face 118 of radially internal wall 27 of casing 25 and a second face 120 of radially internal wall 27 of casing 25. First face 118 and second face 120 extend substantially radially. First face 118 and second face 120 each comprise a hole which places central portion 116 in communication with, respectively, first end portion 112 and second end portion 114. First end portion 112 extends between first face 118 and a first end 112A, while second end portion 114 extends between second face 120 and a second end 114A that is axially opposite first end 112A.

[0122] Advantageously, first end portion 112, second end portion 114, and central portion 116 have a generally cylindrical shape. In the figures, first end portion 112 and second end portion 114 have substantially the same diameter, without this being limiting. Central portion 116 of housing 110 has a greater diameter than the diameter of first and second end portions 112, 114.

[0123] Housing 110 may be closed off at one of its ends. In particular, as can be seen in FIG. 3, an end wall 115 extending substantially radially at one of the ends of the housing, in this case at second end 114A, closes off housing 110. Alternatively, as in FIGS. 4 and 5, housing 110 may be open at both of its ends 112A, 114A.

[0124] First assembly 100 may further comprise a first preload element 124 and a second preload element 130. In FIG. 3, first preload element 124 comprises a plug which is sized to be at least partially insertable into first end portion 112 of housing 110. The plug is in particular a plug of which a radially external surface comprises a thread (not shown) complementary to a threaded hole 150 provided in a fraction of radially internal wall 27 of the casing delimiting first end portion 112 of housing 110. In FIGS. 4 and 5, first preload element 124 is a nut comprising a thread (not shown) on a radially external surface, complementary to threaded hole 150. By means of threaded hole 150 and the complementary thread provided on first preload element 124, first preload element may be removably connected to housing 110. In addition, the axial position of first preload element 124 inside housing 110 may be adjusted by advancing first preload element 124 along threaded hole 150, by a rotational movement of first preload element 124 about axis B. In FIG. 3, second preload element 130 is a plate which is connected to second face 120 of radially internal wall 27 of casing 25, preferably removably. For example, plate 130 may be screwed onto second face 120 of the radially internal wall by screws 152. Advantageously, plate 130 comprises a hole having a dimension greater than or equal to the hole in face 120 of radially internal wall 27, which allows the arrangement of the plate on face 120 to neither completely nor partially block the hole which places second end portion 114 and central portion 116 of housing 110 in communication. In FIGS. 4 and 5, second preload element 130 is a nut similar to the nut of first preload element 124. In order to connect this nut to second end portion 114 of housing 110, a threaded hole (not shown) complementary to the thread of the radially external surface of the nut may be provided in a fraction of radially internal wall 27 of the casing delimiting second end portion 114 of housing 110. Of course, first preload element 124 could be a plate similar to plate 130 described above, and second preload element 130 could be a plug similar to that of first preload element 124 of FIG. 3.

[0125] First assembly 100 may further comprise a first shoulder 132 and a second shoulder 134. First shoulder 132 is comprised in first end portion 112 of housing 110, while second shoulder 134 is comprised in second end portion 114 of housing 110.

[0126] In some cases, first shoulder 132 and/or second shoulder 134 are formed by a portion of casing 25 projecting radially inside housing 110 from radially internal wall 27. In other cases, first shoulder 132 and/or second shoulder 134 are formed from the arrangement of a piece not part of casing 25, inside housing 110, such that at least a portion of this piece not part of casing 25 projects radially relative to radially internal wall 27. In the illustrated case, first shoulder 132 is formed by a portion projecting radially inside first end portion 112 of housing 110, from radially internal wall 27 of casing 25. In FIG. 3, second shoulder 134 is comprised in a portion of plate 130, this portion of plate 130 being arranged radially inside second end portion 114 of housing 110. More specifically, in FIG. 3, second shoulder 134 is formed by a portion of plate 130 projecting axially relative to the rest of the plate so as to be insertable into second end portion 114 of housing 110. Advantageously, this projecting portion of the plate is sized so as to be radially in contact with radially internal wall 27 in second end portion 114 of housing 110. In FIGS. 4 to 5, second shoulder 134 is formed by a portion projecting radially inside second end portion 114 of housing 110, from radially internal wall 27 of casing 25.

[0127] First shoulder 132 and second shoulder 134 have an annular shape for example. First shoulder 132 may comprise an annular face 136 which, as will be detailed below, is axially supported by a first bearing 270. Second shoulder 134 may comprise an annular face 138 which, as will be detailed below, is axially supported by a second bearing 280.

[0128] As can be seen from FIGS. 3 to 5, a first elastic member 300 is housed in first end portion 112 of housing 110. A second elastic member 400 is housed in second end portion 114 of housing 110. First elastic member 300 and second elastic member 400 are arranged in housing 110 so as to be deformable in the axial direction, as will be detailed below.

[0129] In FIG. 3, first and second elastic members 300, 400 are a wave spring, without this being limiting.

[0130] Advantageously, first elastic member 300 and second elastic member 400 have a substantially hollow cylindrical shape or a substantially annular shape. A cavity or hole therefore axially traverses first and second elastic members 300, 400. A radially external diameter of first elastic member 300 is for example substantially equal to the diameter of first end portion 112 of the housing. A radially external diameter of second elastic member 400 is for example substantially equal to the diameter of second end portion 114 of the housing. A radially internal diameter of first elastic member 300 and a radially internal diameter of second elastic member 400 are advantageously chosen so as to allow at least a portion of second assembly 200 to move axially through first and second elastic members 300, 400, as will be detailed below.

[0131] As can be seen from FIGS. 3 to 5, second assembly 200 is housed in housing 110 of first assembly 100. Second assembly 200 comprises a shaft 210 and at least one helical pinion 230 which are housed in housing 110 of first assembly 100.

[0132] Shaft 210 has a generally cylindrical shape extending along axis B. Advantageously, shaft 210 has a substantially circular transverse cross-section. Traverse is understood here to mean comprised in a plane substantially perpendicular to axis B. Advantageously, the diameter of the cross-section of shaft 210 is, for the entire length of shaft 210, less than the diameter of first end portion 112 of housing 110, less than the diameter of second end portion 114 of housing 110, and less than the radially internal diameters of first and second elastic members 300, 400. Shaft 210 may thus move axially along each of end portions 112, 114 of housing 110, as well as along central portion 116 of housing 110.

[0133] The shaft comprises a first end portion 212, a second end portion 214, and a central portion 216. As can be seen from the figures, the diameter of the cross-section of shaft 210 in first end portion 212 and in second end portion 214 is less than the diameter of the cross-section of the shaft in central portion 216. Also, a first shoulder 218 is formed at the interface between first end portion 212 and central portion 216. Similarly, a second shoulder 220 is formed at the interface between second end portion 214 and central portion 216 of shaft 216. Alternatively, the cross-sections of first end portion 212, second end portion 214, and central portion 216 all have the same diameter. In this case, first shoulder 218 is formed by a portion of the shaft projecting radially relative to the remainder of shaft 210 at the interface between first end portion 212 and central portion 216 of shaft 210, and second shoulder 220 is formed by a portion of the shaft projecting radially relative to the remainder of shaft 210 at the interface between second end portion 214 and central portion 216 of shaft 210.

[0134] First shoulder 218 and second shoulder 220 have, for example, an annular shape. First shoulder 218 may comprise an annular face 222 which, as will be detailed below, axially supports first bearing 270. Second shoulder 220 may comprise an annular face 224 which, as will be detailed below, axially supports second bearing 280.

[0135] First shoulder 218 of the shaft is complementary to first shoulder 132 of first assembly 100. Complementary is understood here to mean that in a rest position of device 30, annular face 222 of first shoulder 218 of shaft 210 is preferably aligned in the radial direction with annular face 136 of first shoulder 132 of first assembly 100. Similarly, second shoulder 220 of shaft 210 is complementary to second shoulder 134 of first assembly 100. In the rest position of device 30, annular face 224 of second shoulder 220 of shaft 210 is therefore preferably aligned in the radial direction with annular face 138 of second shoulder 134 of first assembly 100. As will be detailed below, the rest position of device 30 corresponds to a position in which no axial force is exerted on first elastic member 300 and/or on second elastic member 400 by second assembly 200.

[0136] Helical pinion 230 is arranged around shaft 210. In the figures, helical pinion 230 is arranged around central portion 216 of shaft 210. Helical pinion 230 advantageously has an annular shape, with a hole (not visible) of a diameter substantially equal to the diameter of central portion 216 of shaft 210 axially traversing helical pinion 230. Shaft 210 is thus press-fitted or adjusted to fit tightly into the hole of helical pinion 230, which makes it possible to make integral the movements of shaft 210 and the helical pinion, as will be detailed below. Pinion 230 comprises a first face 231A and a second face 231B which are axially opposed.

[0137] Helical pinion 230 is in particular arranged in central portion 116 of housing 110. In the figures, helical pinion 230 is arranged between first face 118 of radially internal wall 27 of casing 25 and an intermediate wall 119 projecting radially into central portion 116 of housing 110 from radially internal wall 27 of the casing. Wall 119 comprises a first face 119A which is axially directly opposite first face 118 of radially internal wall 27 when second assembly 200 is not installed in housing 110.

[0138] A radially external diameter of helical pinion 230 is chosen such that at least a portion of first face 231A of helical pinion 230 is axially facing first face 118 of radially internal wall 27 of the casing. Similarly, the radially external diameter of helical pinion 230 is chosen so that at least a portion of second face 231B of helical pinion 230 is axially facing first face 119A of intermediate wall 119.

[0139] Advantageously, first face 118 of radially internal wall 27 and first face 119 of intermediate wall 119 are separated by a distance allowing, in the rest position of device 30, the formation of a first axial clearance J1 and a second axial clearance J2 between pinion 230 and faces 118, 119A. In particular, as can be seen in FIGS. 3 and 4, first axial clearance J1 is formed axially between first face 231A of pinion 230 and first face 118 of radially internal wall 27 of casing 25. Second axial clearance J2 is formed axially between second face 231B of pinion 230 and first face 119A of intermediate wall 119.

[0140] A radially external face 232 of helical pinion 230 comprises a plurality of teeth oriented so as to form an angle with axis B, referred to as the helix angle, that is not 0 or 90. When device 30 is installed in actuator 18, radially external face 232 of helical pinion 230 is meshed with a complementary input pinion 240, in particular with a radially external face 242 of input pinion 240. As it is clear from FIG. 3, radially external face 240 of the input pinion is provided with teeth. The helix angle of input pinion 240 is advantageously equal to the helix angle of helical pinion 230 in order to ensure correct meshing between helical pinion 230 and input pinion 240. Input pinion 240 is in particular a pinion connected to the drive shaft of actuator 18, so that input pinion 240 moves integrally with the drive shaft.

[0141] Second assembly 200 may further comprise a second pinion 250 press-fitted or adjusted to fit tightly around shaft 210. The movements of shaft 210 and second pinion 250 are thus integral. Second pinion 250 may have an annular shape similar to the shape of helical pinion 230, but, as can be seen from the figures, it may have a radially external diameter that is smaller than the radially external diameter of helical pinion 230.

[0142] A radially external face 252 of second pinion 250 comprises a plurality of teeth. Second pinion 250 may be a helical pinion (helix angle that is not 0 or) 90 or a spur pinion. In the case of a spur pinion, the teeth of radially external face 252 form, with axis B, an angle equal to 0 or 90.

[0143] When second pinion 250 is a helical pinion, the helix angle of second pinion 250 may be equal to or different from the helix angle of helical pinion 230. Preferably, the helix angle of helical pinion 230 and of pinion 250 are in opposite directions, without this being limiting.

[0144] As can be seen in FIG. 3, when device 30 is installed in actuator 18, radially external face 252 of second pinion 250 meshes with a complementary output pinion 260, in particular with a radially external face 262 of output pinion 260. As is clear from FIG. 3, radially external face 262 of output pinion 260 is provided with teeth. The angle formed between the teeth of output pinion 260 and axis B is advantageously equal to the angle formed between the teeth of second pinion 250 and axis B, in order to ensure correct meshing between second pinion 250 and output pinion 260. Output pinion 260 is in particular a pinion connected to output shaft 22 of actuator 18, such that output pinion 260 moves integrally with output shaft 22.

[0145] Second assembly 200 may further comprise first bearing 270 and second bearing 280. First bearing 270 comprises a radially internal ring 272 and a radially external ring 274. A plurality of rolling elements 276 are arranged circumferentially between rings 272 and 274 of first bearing 270. Second bearing 280 comprises a radially internal ring 282 and a radially external ring 284. A plurality of rolling elements 286 are arranged circumferentially between rings 282 and 284 of second bearing 280. In the figures, bearings 270, 280 comprise a single circumferential row of rolling elements 276, 286, but several rows of radially-distributed rolling elements may be provided.

[0146] First bearing 270 is arranged around first end portion 212 of shaft 210. In the rest position of device 30, radially external ring 274 of first bearing 270 is axially supported on first shoulder 132 of the first assembly, in particular on annular face 136 of first shoulder 132. Radially internal ring 272 of first bearing 270 is axially supported on complementary first shoulder 218 of shaft 210, in particular on annular face 222. In the rest position of device 30, radially external ring 284 of second bearing 280 is axially supported on second shoulder 134 of the first assembly, in particular on annular face 138 of said second shoulder 134. Radially internal ring 282 of second bearing 280 is axially supported on complementary second shoulder 220 of shaft 210, in particular on annular face 224.

[0147] Radially internal ring 272, 282 of each bearing 270, 280 may be configured to rotate integrally with shaft 210 about axis B.

[0148] As is clearly apparent from FIGS. 3 to 5, first elastic member 300 is axially supported on radially external ring 274 of first bearing 270, and second elastic member 400 is axially supported on radially external ring 284 of second bearing 280.

[0149] In FIG. 3, first elastic member 300 is arranged axially between first preload element 124 and first bearing 270, while second elastic member 400 is arranged axially between second bearing 280 and end wall 115 of housing 110. In FIGS. 4 and 5, first elastic member 300 is arranged similarly to FIG. 3, but second elastic member 400 is arranged axially between second bearing 280 and second preload element 130.

[0150] Due to first preload element 124, it is possible to create a first axial preload force which acts on first elastic member 300. In particular, when first preload element 124 is a plug or a nut as described above, the first axial preload force may be created and adjusted by the movement of first preload element 124 along threaded hole 150. When first preload element 124 is moved along threaded hole 150 towards first elastic member 300, first elastic member 300 is compressed, which increases the first axial preload force acting on elastic member 300. Conversely, when first preload element 124 is moved along threaded hole 150 in the opposite direction to first elastic member 300, first elastic member 300 relaxes, which reduces the first axial preload force acting on elastic member 300. If first preload element 124 is a plate such as the plate described above with reference to FIG. 3, the plate is sized so as to induce a given value of the first axial preload force when the plate is installed in housing 110. More precisely, the length of a portion of the plate projecting axially for insertion into first end portion 112 of housing 110 may be chosen so as to subject first elastic member 300 to the predetermined value of the first axial preload force.

[0151] Similarly, by means of second preload element 130, it is possible to create a second axial preload force which acts on second elastic member 400. In particular, when second preload element 130 is a plug or a nut as described above, the second axial preload force may be created and adjusted by the movement of second preload element 130 along the threaded hole provided in second end portion 114 of housing 110. If second preload element 130 is the plate of FIG. 3, the plate is sized so as to induce a given value of the second axial preload force when the plate is installed in housing 110. More precisely, the length of the portion of the plate projecting axially for insertion into the second end portion of housing 110 may be chosen so as to subject second elastic member 400 to the predetermined value of the second axial preload force.

[0152] One will note that the first axial preload force and the second axial preload force may be different from each other.

[0153] An operating mode of transmission device 30 will now be explained.

[0154] As indicated above, input pinion 240 moves integrally with the drive shaft of actuator 18. As was also explained, input pinion 240 and helical pinion 230 are two complementary helical pinions which engage in a helical meshing. Such meshing generates an axial force on the pinions which interact when torque is transmitted between these pinions.

[0155] When the drive shaft is driven by motor 20 to rotate about its longitudinal axis, input pinion 240 is also driven to rotate about this axis. The meshing of input pinion 240 with helical pinion 230 causes the helical pinion to also be rotated about axis B when input pinion 240 rotates. As shaft 210 is integral with helical pinion 230, shaft 210 is also driven to rotate about axis B.

[0156] Because the meshing between helical pinion 230 and input pinion 240 is helical, transmission of torque from input pinion 240 to helical pinion 230 generates an axial force in helical pinion 230 which causes axial movement of helical pinion 230 in the direction of this axial force. The helical meshing may also generate an opposite axial force in input pinion 240 which causes axial movement of input pinion 240 in a direction opposite to the direction of the axial force generated in helical pinion 230.

[0157] When the axial force generated in helical pinion 230 of second assembly 200 is oriented towards first elastic member 300, second assembly 200 moves axially towards first elastic member 300. The contact between first shoulder 218 and radially internal ring 272 of the first bearing causes the axial force generated in helical pinion 230 to be transmitted to first bearing 270. In particular, the axial force is transmitted to radially internal ring 274 of bearing 270. Radially internal ring 272 is then moved axially, integrally with second assembly 200. The axial force is then transmitted to radially external ring 274 of the first bearing, through rolling elements 276.

[0158] As indicated above, first elastic member 300 is axially supported on radially external ring 274 of first bearing 270. As was also indicated above, a first axial preload force acts on first elastic member 300. When the axial force generated in helical pinion 230 and transmitted to radially external ring 274 of the first bearing is less than or equal to the first axial preload force, first elastic member 300 opposes the axial movement of radially external ring 274 of first bearing 270 due to the axial force. The axial movement of second assembly 200 is thus stopped. When the axial force generated in helical pinion 230 and transmitted to radially external ring 274 of the first bearing is greater than the first axial preload force, first elastic member 300 cannot oppose the axial movement of radially external ring 274 of first bearing 270 due to the axial force generated in helical pinion 230. Radially external ring 274 therefore moves axially, which compresses first elastic member 300. The first axial preload force thus defines a first axial preload force threshold beyond which first elastic member 300 is compressed due to the axial movement of second assembly 200 under the effect of the axial force generated in helical pinion 230.

[0159] Because of the compression of first elastic member 300, the second assembly may continue its axial movement towards first elastic member 300. First axial clearance J1 is thus progressively reduced until first face 118 of radially internal wall 27 of casing 25 and first face 231A of helical pinion 230 come into contact with each other, as illustrated in FIG. 5. First face 118 therefore comprises a first axial stop 121, and first face 231A of helical pinion 230 therefore comprises a complementary first axial stop 221. The contact between first axial stop 121 and complementary first axial stop 221 makes it possible to dissipate some or all of the axial force generated in helical pinion 230, through casing 25.

[0160] When the axial force generated in helical pinion 230 of second assembly 200 is oriented towards second elastic member 400, the operation of the transmission device is similar to when the axial force generated in helical pinion 230 is oriented towards first elastic member 300. However, in such case, second assembly 200 is moved axially towards second elastic member 400. The contact between second shoulder 220 and radially internal ring 282 of second bearing 280 causes the axial force generated in helical pinion 230 to be transmitted to second bearing 280. In particular, the axial force is transmitted to radially internal ring 282 of bearing 280. Radially internal ring 282 is then moved axially, integrally with second assembly 200. The axial force is then transmitted to radially external ring 282 of the second bearing, through rolling elements 286.

[0161] When the axial force generated in helical pinion 230 and transmitted to radially external ring 282 of the second bearing is less than or equal to the second axial preload force, second elastic member 400, which as explained is axially supported on radially external ring 282 of second bearing 280, opposes the axial movement of radially external ring 282 under the effect of the axial force. The axial movement of second assembly 200 is thus stopped. When the axial force generated in helical pinion 230 and transmitted to radially external ring 282 of the second bearing is greater than the second axial preload force, second elastic member 400 cannot oppose the axial movement of radially external ring 282 of second bearing 280 under the effect of the axial force generated in helical pinion 230. Radially external ring 282 therefore is moved axially so as to compress second elastic member 400. The second axial preload force thus defines a second axial preload force threshold beyond which second elastic member 400 is compressed because of the axial movement of second assembly 200 under the effect of the axial force generated in helical pinion 230.

[0162] Due to the compression of second elastic member 400, the second assembly can continue its axial movement towards second elastic member 400. Second axial clearance J2 is thus progressively reduced until first face 119A of intermediate wall 119 and second face 231B of helical pinion 230 come into contact with each other. First face 119A therefore comprises a second axial stop 123, and second face 231B of helical pinion 230 therefore comprises a complementary second axial stop 223. The contact between second axial stop 123 and complementary second axial stop 223 makes it possible to dissipate some or all of the axial force generated in helical pinion 230, through casing 25.

[0163] One will note that any reduction in first axial clearance J1 implies an increase in second axial clearance J2, as can be seen in FIG. 5. Similarly, any reduction in second axial clearance J2 implies an increase in first axial clearance J1.

[0164] By means of the device described above, the axial forces generated within actuator 18 are dissipated through first assembly 100 of transmission device 30 when the forces are very significant, in particular when they exceed the first or second axial force threshold described above. The percentage of the forces generated in actuator 18 which reach brake 24 is therefore reduced or even zero. Consequently, the risks of wear and/or breakage of brake 24 are limited.

[0165] This disclosure is not limited to the examples of transmission devices described above solely by way of example, but encompasses all variants conceivable to a person skilled in the art within the context of the protection sought

[0166] For example, as indicated above, the transmission device could comprise a single elastic member. In this case, only one preload element and one bearing are included in device 30. Furthermore, first axial stop 121 and second axial stop 123 could project axially relative to the remainder of respective wall 118 and wall 119A which comprises them. Similarly, complementary first axial stop 221 and complementary second axial stop 223 could project axially relative to the remainder of respective wall 231A and wall 231B which comprises them. According to another variant, at least one among the first axial stop and the complementary first axial stop and/or at least one among the second axial stop and the complementary second axial stop may comprise a friction surface containing roughnesses and/or axially projecting elements, for example a dog system. As indicated above, by means of the roughnesses and/or radially protruding elements, dissipation of the axial force through first assembly 100 is increased.