ROLLER DRIVE ELEMENT

Description

[0001] The present invention relates to a roller gear element, particularly but not exclusively of an aircraft motorized wheel. BACKGROUND OF THE INVENTION

[0002] In the field of aviation, it is now planned to equip aircraft with wheel rotation drive units to allow the aircraft to be moved on the ground without using its powertrains. In general, these drive units comprise an electric motor connected to a reduction gear whose output is equipped with a pinion. The pinion cooperates with a toothed crown secured to the aircraft wheel. In this way, the electric motor rotates the pinion, which in turn drives the toothed crown and therefore the wheel to move the aircraft.

[0003] Obviously, this type of drive requires the use of an electric motor associated with a reducer offering a particularly high torque. The gearing formed by the pinion and the crown gear must then be made without slippage and have the smallest possible play to withstand the torque of the motor, particularly during start-up where the torque is delivered relatively abruptly.

[0004] Such a type of meshing is known from document EP 3 048 044 and is made possible by the use of a roller pinion, which comprises a plurality of rollers intended to cooperate with the teeth of the crown gear. The rollers are generally supported and guided in rotation by bearings equipped with self-lubricated bushings to prevent slippage with the teeth of the crown gear. Thus, two rollers are at all times in contact with the same tooth of the crown gear, which allows a transmission without play with very high efficiency.

[0005] However, bearings are recognized as wear parts that should be replaced regularly to avoid premature wear of the rollers and teeth of the crown gear, which results in significant maintenance time and costs.

[0006] Furthermore, since the permissible load on the bearings is limited, the row of teeth of the crown gear and the row of rollers of the pinion are generally doubled. The pinion is then coupled to the output shaft of the reducer via a finger-joint type coupling device, ideally with elastic return to a neutral position, which allows both the torque to be transferred from the output shaft of the reducer to the pinion and guarantees simultaneous contact of the two rows of teeth with the two rows of rollers by allowing a slight inclination of said pinion relative to the crown gear. Such a coupling device results in additional mass and complexity. SUBJECT OF THE INVENTION

[0007] The object of the invention is therefore to propose a gear element making it possible to at least partially overcome the aforementioned problems. SUMMARY OF THE INVENTION

[0008] To this end, the invention provides a gear element comprising a support on which are mounted alternately first rollers and second rollers intended to cooperate with teeth of a neighboring gear element. Each roller comprises a longitudinal axis around which it is mounted to rotate via rotational guide means cooperating with end portions of the roller.

[0009] According to the invention, the means for guiding the rotation of the first rollers and the means for guiding the rotation of the second rollers are arranged in a staggered pattern in the vicinity of an external periphery of the support.

[0010] According to a preferred embodiment of the invention, the rotational guide means of the first rollers extend partially opposite the rotational guide means of the second rollers along an axis of rotation of the gear element, which makes it possible to maximize the number of rollers of the gear element with respect to the size of the rotational guide means.

[0011] In particular, the rotational guide means of the first rollers and the rotational guide means of the second rollers are identical.

[0012] In particular, the first rolls and the second rolls are identical.

[0013] According to a particular characteristic of the invention, the means for guiding the rotation of the first rollers and / or the means for guiding the rotation of the second rollers comprise at least one ball bearing.

[0014] As is known per se, ball bearings allow high radial loads, which allows the gear element to withstand high drive torques without necessarily doubling the row of rollers of the gear element.

[0015] Furthermore, it is recognized that ball bearings have a long service life, making it possible to limit the time and costs of maintenance of the gear element.

[0016] In particular, the ball bearing is a radial contact bearing.

[0017] According to another particular characteristic of the invention, the longitudinal axes of the first rollers and the second rollers are parallel to the axis of rotation of the gear element.

[0018] The invention also relates to a drive assembly for an aircraft wheel, comprising a first gear element rotatably connected to the wheel and a second gear element rotatably connected to a motor, at least one of the gear elements being of the preceding type.

[0019] The invention also relates to an aircraft comprising at least one wheel provided with such a drive assembly. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The invention will be better understood in light of the following description, which is purely illustrative and not limiting, and must be read in conjunction with the appended drawings, among which: there figure 1 is a perspective view of a gear element according to a particular embodiment of the invention, rollers of which cooperate with teeth of a toothed crown; figure 2 is a view of the gear element shown in figure 1 , in section through a plane passing through the axis of rotation of the gear element and the longitudinal axis of one of the rollers; the figure 3 is a side view of the gear element shown in figure 1 . DETAILED DESCRIPTION OF THE INVENTION

[0021] The invention is described here in application to a drive assembly for an aircraft wheel, comprising a first gear element rotatably connected to the wheel and a second gear element rotatably connected to a motor.

[0022] In reference to the figure 1 , the invention comprises a gear element 1 which is in contact with a ring gear 2 having a row of teeth. The gear element 1 has an axis of rotation X parallel to an axis of rotation of the ring gear 2.

[0023] The gear element 1 comprises a support 3 on which are mounted alternately a plurality of first rollers 10a and second rollers 10b symmetrically distributed around the axis of rotation X.

[0024] The support 3 comprises a central core 4 whose shape is comparable to that of a straight tube whose longitudinal axis coincides with the axis of rotation X of the gear element. The central core 4 has ends provided respectively with a first flange 5 and a second flange 6. The first flange 5 and the second flange 6 have a general shape of a circular ring with a central axis coincident with the axis of rotation X. The first flange 5 and the second flange 6 extend in radial projection towards the outside of the central core 4 and therefore have substantially identical external diameters which are greater than the external diameter of the central core 4. The first flange 5 and the second flange 6 thus delimit between them a groove whose bottom is formed by the external surface of the central core 4.

[0025] The first flange 5 has an external face on which open identical bores 5a distributed symmetrically around the axis of rotation X in the vicinity of the external periphery of said first flange 5. Each of the bores 5a is cylindrical in shape with an axis parallel to the axis of rotation X. The centers of the bores 5a are inscribed on the same circle, the center of which is located on the axis of rotation X.

[0026] The first flange 5 also comprises an internal face on which identical bores 5b open, symmetrically distributed around the axis of rotation X in the vicinity of the external periphery of said first flange 5. Each of the bores 5b is cylindrical in shape with an axis parallel to the axis of rotation X. The centers of the bores 5b are inscribed on the same circle, the center of which is located on the axis of rotation X and the diameter of which is identical to that of the circle on which the centers of the bores 5a are inscribed.

[0027] The number of bores 5b is the same as the number of bores 5a and the diameter of bores 5b is the same as that of bores 5a.

[0028] Furthermore, the bores 5b are angularly offset relative to the bores 5a so that when the support 3 is viewed along the axis of rotation X, the bores 5b appear to be uniformly interposed between the bores 5a, the central axis of each of the bores 5b being equidistant from the central axes of the two neighboring bores 5a and each of the bores 5b extending partially opposite the two neighboring bores 5a.

[0029] Similarly, the second flange 6 has an inner face and an outer face on which respectively bores 6a and bores 6b open which are respectively opposite the bores 5a and the bores 5b of the first flange 5. The bores 6a, 6b are of identical shape and diameter to the bores 5a, 5b. Thus, the bores 6a, 6b are of cylindrical shape and are symmetrically distributed around the axis of rotation X in the vicinity of the outer periphery of the second flange 6. In the same way, the centers of the bores 6a, 6b are inscribed on the same circle whose center is located on the axis of rotation X.

[0030] In each bore 5a, 5b of the first flange 5 is mounted tightly a radial contact ball bearing 20 which is immobilized in translation via locking rings 30. The bearings 20 mounted in the bores 5a, 5b are thus arranged in a staggered pattern, each of these bearings being axially offset relative to its two neighbors and extending partially opposite, along the axis of rotation, the two neighboring bearings 20.

[0031] Preferably, the bearings 20 comprise on each side a lateral protection formed for example by a flange or a synthetic rubber seal making it possible to ensure lifetime lubrication of said bearings 20.

[0032] In reference to the figure 2 , the first rollers 10a and the second rollers 10b are identical. They comprise a main section 11 having one end provided with a radially projecting collar 12 defining a first shoulder 13 and another end provided with a cylindrical bearing surface of larger diameter which is extended by a threaded portion 14 and which is connected to the main section by a second shoulder 15 and a third shoulder 16 forming a stop. The diameters of the collar 12 and of the cylindrical bearing surface are substantially identical.

[0033] Each cylindrical bearing extended by the threaded portion 14 receives a ball bearing 20 which is held in position against the shoulder 16 via a nut 17 screwed onto said threaded portion 14.

[0034] The gear element 1 shown in the figure 1 comprises six rollers 10a and six rollers 10b, making a total of twelve rollers. The rollers 10a, 10b are inserted into the support 3 by the housings 6a, 6b following a translation along the longitudinal axis X' of each of the rollers 10a, 10b, from the second flange 6 to the first flange 5.

[0035] The collars 12 of the rollers 10a are then introduced into the inner rings of the bearings 20 mounted tightly in the bores 5a of the first flange 5 while the bores 6a of the second flange 6 receive the outer rings of the bearings 20 mounted on the threaded portions 14 of the rollers 10a.

[0036] Likewise, the collars 12 of the rollers 10b are then introduced into the inner rings of the bearings 20 mounted tightly in the bores 5b of the first flange 5 receive the collars 12 of the rollers 10b while the bores 6b of the second flange 6 receive the outer rings of the bearings 20 mounted on the threaded portions 14 of the rollers 10b.

[0037] The bearings 20 mounted on the cylindrical bearing surfaces extended by the threaded portions 14 of the rollers 10a, 10b are thus arranged in a staggered pattern, each of these bearings being axially offset relative to its two neighbors and extending partially opposite, along the axis of rotation, the two neighboring bearings 20.

[0038] Therefore, the rollers 10a, 10b are mounted to move in rotation on the support 3 around their longitudinal axis X' and are arranged in a staggered pattern in the vicinity of the periphery of the flanges 5, 6 of said support.

[0039] The rollers 10a, 10b are held in the support 3 by locking rings 31 which immobilize in translation along the longitudinal axis X' the outer ring of the bearings 20 received in the bores 6a, 6b of the second flange.

[0040] The rotation of the gear element 1 around its axis X then in turn causes the rotation of the toothed crown 2, the rollers 10a, 10b successively coming into contact with the teeth of the toothed crown 2. The rollers 10a, 10b in fact make it possible to cooperate without sliding with the row of teeth of the toothed crown 2. Ideally, the teeth of the toothed crown 2 are shaped to cooperate without play with the rollers 10a, 10b.

[0041] The gear element 1 and the toothed crown 2 thus form a conventional spur gear in which the rollers 10a, 10b rotate around the axis of rotation X of the gear element 1 but also around their longitudinal axis X'.

[0042] Of course, the invention is not limited to the embodiments described but encompasses any variant falling within the scope of the invention as defined by the claims.

[0043] Although the gear element 1 may be similar to a pinion in terms of the figure 1 , the diameter of the gear element 1 may be greater than that of the toothed crown 2.

[0044] Although the gear element 1 cooperates here with a ring gear 2, the gear element 1 can, for example, cooperate with a rack.

[0045] Although the bore diameters are identical here, these can vary from one flange to another provided that they do not hinder the possibility of mounting the rollers on the gear element support.

[0046] The bearings 20 may be of a different type than that illustrated in the figure 2 .

[0047] The immobilization of the bearings in translation can be ensured in a different way to that illustrated in figure 2 .

[0048] The support can be made from a single piece, by machining, or in several pieces. In the latter case, the flanges are for example attached to the central core and then welded to it; or assembled in a removable manner, for example by providing grooves for the rotational immobilization of the flanges relative to the central core and threaded / tapped elements for their axial immobilization.

[0049] Although the gear element has been described in application to an aircraft wheel drive assembly, the invention is applicable to any type of gear train.

[0050] Although the bearings 20 here are ball bearings, other types of bearings can be considered, including tapered roller bearings or needle roller bearings.

[0051] The first rollers 10a and the second rollers 10b may be different, in particular with regard to their dimensions. For example, the main section of the first rollers 10b may have a different length from that of the second rollers 10b. The same applies to the length of the collars and that of the cylindrical bearing surfaces.

Claims

1. Gear element (1) comprising a support (3) on which first rollers (10a) and second rollers (10b) are alternately mounted, which are intended for engaging with the teeth of a neighbouring gear element (2), each rollers (10a, 10b) being mounted for rotation about its longitudinal axis (X') via rotary guide means (20) cooperating with end portions of the rollers (10a, 10b), characterised in that the rotary guide means (20) of the first rollers (10a) and the rotary guide means (20) of the second rollers (10b) are staggered in the vicinity of an outer periphery of the support (3).

2. Gear element (1) according to claim 1, wherein the rotary guide means (20) of the first rollers (10a) partially extend facing the rotary guide means (20) of the second rollers (10b) about the axis of rotation (X) of the gear element (1).

3. Gear element (1) according to any one of the preceding claims, wherein the rotary guide means (20) of the first rollers (10a) and the rotary guide means (20) of the second rollers (10b) are identical.

4. Gear element (1) according to any one of the preceding claims, wherein the first rollers (10a) and the second rollers (10b) are identical.

5. Gear element (1) according to any one of the preceding claims, wherein the rotary guide means (20) of the first rollers (10a) and / or the rotary guide means (20) of the second rollers (10b) comprise at least one ball bearing.

6. Gear element (1) according to claim 5, wherein the ball bearing (20) is a radial rolling-element bearing.

7. Gear element (1) according to claim 2, wherein the longitudinal axes (X') of the first rollers (10a) and of the second rollers (10b) are parallel to the axis of rotation (X) of the gear element (1).

8. Assembly for driving an aircraft wheel, comprising a first gear element (1) connected in rotation to the wheel and a second gear element (2) connected in rotation to a motor, at least one of the gear elements (1, 2) being according to any one of the preceding claims.

9. Aircraft comprising at least one wheel provided with a drive assembly according to claim 8.