EP3898288A1

EP3898288A1 - Improved adapter and rolling assembly comprising such an adapter

Info

Publication number: EP3898288A1
Application number: EP19848931.2A
Authority: EP
Inventors: Daniel Walser; Bertrand Vedy
Original assignee: Compagnie Generale des Etablissements Michelin SCA
Current assignee: Compagnie Generale des Etablissements Michelin SCA
Priority date: 2018-12-20
Filing date: 2019-12-19
Publication date: 2021-10-27
Also published as: CA3121666A1; FR3090487A3; US20220144020A1; FR3090486B1; CN113195264A; FR3090486A1

Abstract

Disclosed is an adapter for a rolling assembly with an axis of rotation X-X' comprising a tyre (2), a rim (3), and an adapter (100), the adapter comprising an axially inner end (10), an axially outer end (11) and a body (12), in which the axially outer end comprises an outer reinforcing element (15) that is a structure that is substantially rotationally symmetrical about the axis X-X' comprising several windings of at least one wire arranged axially next to each other over several layers stacked radially on each other. According to the invention, the cross section of the outer reinforcement (15) has a ratio of the moments of inertia Ix/Iy greater than 1.3 for an axial width of between 6 and 9 mm, in which Ix is the moment of inertia around a first axis passing through its centre of gravity and parallel to the axis of rotation X-X' and Iy is the moment of inertia around a second axis passing through its centre of gravity and perpendicular to the first axis.

Description

IMPROVED EXTENSIONER AND ROLLING ASSEMBLY COMPRISING SUCH AN EXTENSIONER

The subject of the invention is an expander for a rolling assembly constituted by a tire and a rigid rim connected together by an expander capable of offering a certain elastic flexibility during an impact sustained during rolling, as well as a rolling assembly comprising it. . A tire comprises, as is known, two beads intended to be mounted on the seats of a rim. The present invention relates to rolling assemblies in which a tire bead is not mounted directly on a rigid rim, but is mounted on a flexible expander, which expander is itself mounted on a rigid rim.

A tire, a rim, as well as a stent which is involved in the present invention are usually described by a representation in a meridian plane, that is to say a plane containing the axis of rotation of the tire. All these products (the tire, the rim, the expander) are objects having a geometry of revolution relative to the axis of rotation of the tire. The radial and axial directions respectively designate the directions, the first, perpendicular to the axis of rotation of the tire, and the second, parallel to the axis of rotation of the tire. In what follows, the expressions “radially” and “axially” mean respectively “in a radial direction” and “in the axial direction”. The expressions “radially interior, respectively radially exterior” mean “closer, respectively farther, from the axis of rotation of the tire, in a radial direction”. A median plane is a plane perpendicular to the axis of rotation of the tire, positioned axially so as to cut the surface of the tread approximately halfway between the beads of a tire. The expressions “axially interior, respectively axially exterior” mean “closer, respectively farther, from the median plane of the tire, in the axial direction”. Furthermore, “radial section” or “radial section” means a section or section along a plane which contains the axis of rotation of the tire.

Document WO2016 / 046197 proposes to arrange a flexible expander between a bead of tire and a rim. The rolling assembly according to this document comprises a tire, a rim and two identical expanders. Considering the language conventions mentioned above, and referring to the way in which a stent is mounted on a rim, such a stent comprises, axially from the inside to the outside, an axially inner end called a bead of expander and intended to ensure the attachment of the expander to the rim. Such a stent also includes an axially outer end intended to receive and immobilize axially a bead of tire. A body connects the two ends respectively axially inner and axially exterior. The expanders are mounted on a rim which is mostly an aluminum part. The rim has on each side a rim hook intended in particular to immobilize in the axial direction of the expander.

A flexible expander must, on the one hand, have a certain elastic flexibility, for example during an impact against a sidewalk or when passing through a "pothole" and, on the other hand, it must have sufficient rigidity when driving in order to give correct behavior to the vehicle and to allow a wheel comprising it to pass the various validation tests, such as the high-pressure inflation test or the biaxial endurance test (generally known as ZWARP test). In order to satisfy all of these conditions, the ends of the expander are provided with reinforcing elements connected by at least one reinforcing ply, and more particularly the axially outer end of the expander is provided with an annular rod of section generally circular in shape generally made of a plurality of strands of steel wire.

In document WO2017 / 191389, there is proposed such a flexible expander comprising an annular rod of globally polygonal section produced on the basis of a unitary metallic wire wound in contiguous fashion around a support at least three times in an axial direction and at minus twice in a radial direction. The bead wire is surrounded by sheets of rubber and forms therewith the axially outer end of the stent which supports the bead of the tire and is located axially outside of the latter.

The expanders are mounted on a metal rim which is mostly an aluminum part. The rim has on each side a rim hook intended in particular to immobilize in the axial direction of the expander. On a metal rim without expander for passenger vehicle wheels, type “J” hooks with a width of between 11 and 15 mm are most frequently encountered. However, the ETRTO standard (for European Tire and Rim Technical Organization) also defines “J-N” type hooks for an aluminum rim whose width is between 8 and 15 mm. Such a hook is less wide than a “J” type hook, which allows to gain mass but also to better protect the central part of the rim against sidewalk rasping.

However, in the case of a rolling assembly comprising a rim and a tire connected by a flexible expander, it has been found that the axially outer end of the expander protrudes relative to the rim hook of a fairly axial width. important, which means that it is more exposed to sidewalk grates. It is therefore necessary to reduce the axial width of the axially outer end of the stent. Thus, to solve this problem, starting from the solution described in document WO2017 / 191389, we would certainly have tried to increase the section of the unitary wire of the winding constituting the external reinforcement, while reducing the number of windings for a section of given shape, as described in this document. As the moment of inertia in bending of a circular section varies with the power four of the diameter of the wire whereas its section only varies with the square of this one, one could decrease the overall section of the reinforcement while retaining its moment of inertia in bending. In such a configuration, each wire would therefore be larger and present a greater moment of inertia in bending. This would nevertheless have the drawback of making the wire less able to regain its original shape after an imposed deformation. In other words, such a reinforcement would plasticize more easily during an impact against a sidewalk, which would have the consequence of deforming and therefore no longer being able to provide the elastic flexibility necessary during such an impact.

The object of the invention is to remedy the aforementioned drawbacks and to propose an expander for a rolling assembly produced so as to guarantee sufficient mechanical stability in rolling and to absorb shocks without being permanently deformed, while making it possible to protect its axially outer end during sidewalk grating.

The subject of the invention is therefore a stent for a rolling assembly with an axis of rotation XX ′ comprising a tire, having two beads and a rim, the stent being intended to ensure the junction between one of the beads and the rim, said stent comprising an axially inner end, an axially outer end and a body oriented mainly axially and disposed between said axially outer end and said axially inner end so that, when mounted within the assembly, said axially inner end is intended to be immobilized on said rim, said axially external end comprising an external reinforcement element is intended to receive a bead of tire, in which said external reinforcement is a structure substantially of revolution around the axis XX 'comprising several windings d '' at least one wire arranged axially next to each other on several radially s layers superimposed on each other, characterized in that the section of the external reinforcement has a ratio of the moments of inertia Ix / ly greater than 1.3 for an axial width of between 6 and 9 mm, where Ix is the moment of inertia around a first axis passing through its center of gravity and parallel to the axis of rotation XX 'and ly is the moment of inertia around a second axis passing through its center of gravity and perpendicular to the first axis.

In the operating position, when mounted within the rolling assembly, the expander is immobilized with its axially inner end on the rim while the other end forms a bearing surface or seat for the bead of the tire, the reinforcing element of the axially outer end being located axially outside the seat of the bead of tire. The reinforcing element of the axially outer end is designed so as to oppose a lot of flexural strength along an axis parallel to the axis of rotation of the rolling assembly in order to give it mechanical stability in rolling, but also to resist buckling stresses in compression and / or when the rolling assembly is under high inflation pressure. When it is subjected to a violent impact, such as an impact against a sidewalk for example, it has been observed that the axially outer end of the expander undergoes a rotational movement relative to the anchoring point at the rim. By turning, the axially outer end also rotates the outer reinforcing element around itself, a reinforcing element according to the invention which can then deform in bending along an axis having a lower moment of inertia, therefore opposing less resistance to deformation. In other words, the external reinforcing element of the expander of the invention is produced so that it has a greater moment of inertia Ix along a first axis substantially parallel to the axis of rotation of the rolling assembly and a lower moment of inertia ly along a second axis which is perpendicular to the first. Furthermore, for a limited axial width of the reinforcing element, width between 6 and 9 mm, it has been found that the ratio between Ix and ly is greater than 1.3. Thus, the geometry of the external reinforcing element of the expander makes it possible to limit the stresses seen by the windings of the reinforcement which have a purely elastic behavior in operation.

According to the invention, the ratio between Ix and ly is greater than 1.3, preferably greater than 1.30 and more preferably greater than or equal to 1.35 and even more preferably greater than or equal to 1.38.

The stent of the invention therefore has sufficient bending stiffness, which makes it possible to impart sufficient rigidity under normal rolling conditions to the rolling assembly which it equips, while having sufficient radial elastic flexibility to allow it to absorb the shocks undergone by rolling while being elastically deformed, and while limiting the axial width of its axially outer end which is intended to support the bead of a tire of the rolling assembly.

The section of the external reinforcement of the stent of the invention has an axial width I and a radial height h and can have a form factor h / l greater than 1.3 and preferably between 1.3 and 2.

The section of the external reinforcement of the stent of the invention has main moments of inertia of concurrent axes 11 and 12 which can make a non-zero angle with Ix, respectively ly. By main moments of inertia of a section we understand, in a manner known in the resistance of materials, the moments of inertia having the greatest value for 11 and respectively the smallest value for 12. The main axes of inertia are always perpendicular to each other.

The ratio between the main moments of inertia 11 and 12 can be greater than 2.

The windings of at least one strand of the stent of the invention form a radially innermost alignment and at least a second adjacent alignment superimposed on the first called lines in which the axis passing through the centers of the lines are parallel to each other and the wires of the most axially inward alignments form a first column and the axially adjacent axially outward alignments form at least a second column where the axes passing through the centers of the wires of the columns are parallel to each other and where the axis passing through the center of the windings of a line makes an angle b with the axis passing through the center of the windings of a column of wire, angle b which can be different from 90 °.

The windings of the external reinforcement of the stent of the invention may comprise at least two windings arranged axially next to each other on at least three layers radially superposed on each other. The windings of the external reinforcement of the expander can be produced on the basis of a metallic unitary wire with a diameter between 2 and 5 mm and preferably between 2.15 and 3 mm.

The windings of the external reinforcement of the stent can be produced on the basis of a metallic unitary wire coated with a polymeric composition, preferably an elastomeric composition.

The external reinforcement of the expander can be arranged so that the main axis of its section is inclined with respect to an axis perpendicular to the axis XX '.

The invention also relates to a rolling assembly with an axis of rotation X-X 'comprising a tire having two beads, a rim and a stent of the invention.

The invention is described below using figures la to 3b, given only by way of illustration:

- Figure la is a partial meridian section of a rolling assembly with a stent according to the state of the art,

FIG. 1b is an enlargement of the external reinforcement element of the expander of FIG. 1a,

FIG. 2a is a partial meridian section of a rolling assembly with a stent according to a first embodiment of the invention,

FIG. 2b is an enlargement of the external reinforcement element of the expander of FIG. 2a,

- Figure 2c is an enlargement of an outer reinforcing element according to a variant of realization of the assembly of FIG. 2a,

FIG. 3a is a partial meridian section of a rolling assembly with a stent produced according to a second embodiment of the invention,

- Figure 3b is an enlargement of the external reinforcing element of the expander of Figure 3a.

In the different figures, identical or similar elements have the same reference. Their description is therefore not systematically repeated.

The figure shows a partial view of a rolling assembly 1 according to the prior art. This assembly has an axis of rotation X-X ', an axis YY' perpendicular to the first and included in a median plane, it comprises two identical expanders 100 (only one being illustrated in the figure), a tire 2 and a rim 3. The tire 2 has two beads 21. The rim 3 has two seats on the rim 31, each extended by a rim flange 32. The rim flange 32 has a radially outer support face 33 intended to serve as a support for the body of the expander. The bearing face 33 of the rim flange 32 is in contact with the stent 100 when the tire is mounted on the stents and when these are mounted on the rim, the tire being inflated to nominal pressure.

The expander 100 has an axially inner end 10 intended to be mounted on one of said seats on a rim 3. It has an axially outer end 11 as well as a body 12 oriented substantially axially and disposed between said axially outer end 11 and said axially inner end 10. The axially inner end 10 of the expander has an axial positioning face substantially perpendicular to the axis of rotation XX ", and is immobilized by being pressed axially against the rim flange 32, under the effect the inflation pressure of the tire 2 and a particular geometry of the rim flange. The axially outer end 11 has a shoulder 16 forming a face substantially perpendicular to the axis of rotation XX ′. Said expander 100 comprises a seat on stent 14 for the tire bead 21. The bead 21 is immobilized by being pressed axially on said seat 14 against said shoulder 16 of the ext axially outer remnant 11 of the expander, under the effect of the inflation pressure of the tire. The expander thus produced has a shape of revolution around a central axis. When in the unassembled state on the rolling assembly, the expander has a generally annular shape. After its assembly within the rolling assembly, its central axis becomes identical to the axis XX 'of the rolling assembly.

The axially inner end 10 of the stent includes an inner reinforcing element 17 connected to the outer reinforcing element 15 by a reinforcing ply 19 made from reinforcing threads embedded in an elastomeric composition. The reinforcing ply 19 forms with the elements of reinforcement 15, 17 an internal structure of the stent. Other external elastomeric layers surround the internal structure of the stent.

The assembly of the assembly is done by arranging each expander 100 on the rim 3 and then mounting the tire 2 on the expander 100. Once the assembly has been carried out, the bead of the tire imposes a circumferential contraction of the expander 100. The attached figures illustrate the rolling assembly with the elements assembled.

Figure lb illustrates the reinforcing element 15 of the expander of Figure la on an enlarged scale. In the example illustrated in Figure 1, the width of the axially outer end 11 is 18.7 mm, it is obtained with an annular reinforcement or rod produced by several windings of a metal wire 4 having a diameter of 2 , 15mm. More particularly, such a rod is obtained by winding the metal wire on six radially superposed layers, the first most radially inner layer has 4 windings, it is followed by a second having 5

windings, a third having 4 windings, a fourth having five windings, a fifth having 4 windings and finally the last layer which has three windings. The windings of two adjacent layers are offset axially with respect to each other, and they form parallel lines between them corresponding to the axial windings and the windings of the radially superposed layers form columns parallel to each other. The windings are produced in a known manner, so that the axis passing through the center of the windings of a line is perpendicular to the axis of the windings of a column. The section of the rod thus obtained has a width "I" equal to 10.8 mm and a height "h" equal to 11.5 mm. The calculated moments of inertia of the section of the rod, in particular the moment Ix calculated according to a first axis xx 'which is parallel to the axis of rotation XX' of the assembly and passing through the center of gravity of the section is equal to 854 mm4 and the moment of inertia ly along a second axis perpendicular to the first and passing through the center of gravity of the section is equal to 647 mm4. The main moments of inertia 11 and 12 are equal to Ix respectively ly. The rolling assembly of the figure operating it to satisfaction, it has however been noted that the axially outer end 11 of the expander is too protruding (it has an axial width of 18.7 mm in the example of FIG. ), it was exposed to sidewalk grates and was in danger of being damaged while driving.

The invention provides a solution according to the examples illustrated in Figures 2a to 3b.

Figure 2a shows in partial meridian section an embodiment of a stent 100 according to a first embodiment of the invention. This expander differs from that illustrated in FIG. 1a by an axial end 11 having a reduced axial width, of the order of 16.9 mm, while having an excellent ability to deform elastically during an impact, such as the impact of the wheel against the pavement, for example. This reduced axial width is obtained using a rod or external reinforcing element 15 whose section has an advantageous geometry.

Thus, as best seen in FIG. 2b, an external reinforcement element 15 has been produced which is a structure substantially of revolution around the axis XX 'comprising several windings of a wire 4 arranged axially next to each other on several layers radially superimposed on each other and whose section geometry is such that the ratio of the moments of inertia Ix / ly is greater than 1.3. More particularly, the external reinforcement 15 was obtained on the basis of a metal wire 4 of round section, the diameter of the wire being equal to 2.4 mm and by making four windings arranged axially next to each other on three radially layers superimposed on each other and comprising a fourth radially outer layer with three windings. These windings thus form four lines 41 of wire parallel to each other and four columns 4c of wire parallel to each other. According to the invention, the axis passing through the centers of the wires of a line 41 forms an angle b with the axis passing through the centers of the wires of a column 4c, an angle which is different from 90 °. More particularly, the angle b is equal to 60 °.

The section of the external reinforcement element 15 of FIG. 2b thus obtained has an axial width "I" equal to 8.9 mm and a radial height "h" equal to 11.8 mm. The moments of inertia calculated from the section of the reinforcing element, in particular the moment Ix calculated along a first axis xx 'which is parallel to the axis of rotation XX' of the assembly and passing through the center of gravity of the section is equal to 525 mm4 and the moment of inertia ly along a second axis perpendicular to the first and passing through the center of gravity of the section is equal to 379 mm4. The main moments of inertia of concurrent axes 11 and 12 make an angle cp equal to 30 ° with the axes of the moments of inertia Ix, respectively ly and their values calculated for the section of Figure 2b are 619 mm4 for Il and 285 mm 4 for 12. By main moments of inertia of a section, we understand, in a manner known in the resistance of materials, the moments of inertia having the largest value for 11 and respectively the smallest value for 12. The main axes of inertia associated 1-1 and 2-2 are always perpendicular to each other.

Such an external reinforcing element 15 is produced on the basis of a metal wire, such as a steel wire, preferably comprising a steel core preferably covered with brass, the wire being coated with a polymeric composition, preferably a elastomeric composition to ensure cohesion between the threads. The winding is done by slicing, layer by layer on a support in inclined plane shape. More precisely, we choose a support inclined at an angle 90 ° -b = 30 ° in this case and we start by making a first radially inner layer 41 on starting from the end with the smallest diameter, then we continue with make the second layer radially superimposed on the first by winding the same wire from the end corresponding to that of the last winding of the first layer, by slicing in the opposite direction to the first. One thus continues to carry out windings of wire by cutting in one direction, then in the other to carry out four radially superimposed layers of which the first three comprise four windings and the last only three windings so as to obtain the section represented in figure 2b .

A variant of this embodiment is shown in Figure 2c. More particularly, the external reinforcement 15 was obtained on the basis of a metallic wire 4 of round section, the diameter of the wire being equal to 2.3 mm and by producing a first radially inner layer of three

windings arranged axially next to each other, followed by three other radially superimposed layers each having four windings arranged axially against each other out of three and which ends with a fifth layer radially superimposed on the preceding ones and three windings arranged axially against each other other. These windings thus form five lines 41 of wire parallel to each other and four columns 4c of wire parallel to each other. According to the invention, the axis passing through the centers of the wires of a line 41 forms an angle b with the axis passing through the centers of the wires of a column 4c, an angle which is different from 90 °. More particularly, the angle b is equal to 60 °.

The section of the external reinforcement element 15 of FIG. 2c thus obtained has an axial width "I" equal to 8.6 mm and a radial height "h" equal to 12.6 mm. The moments of inertia calculated from the section of the reinforcing element, in particular the moment Ix calculated along a first axis xx 'which is parallel to the axis of rotation XX' of the assembly and passing through the center of gravity of the section is equal to 703 mm4 and the moment of inertia ly along a second axis perpendicular to the first and passing through the center of gravity of the section is equal to 369 mm4. The main moments of inertia of concurrent axes 11 and 12 make an angle cp equal to 14 ° with the axes of the moments of inertia Ix, respectively ly and their values calculated for the section of Figure 2b are 727 mm4 for Il and 345 mm4 for 12.

Such an external reinforcement element 15 of FIG. 2c is produced in the same manner as that described with reference to the reinforcement element of FIG. 2b, by slicing in one direction, then in the other, on a support inclined at starting from the end with the smallest diameter to get five radially superimposed layers, the first having three windings, the following three each having four windings and the last three axial windings.

Figures 3a and 3b illustrate a second embodiment of a stent according to the invention. Indeed, the particular geometry of the section of the external reinforcing element 15 makes it possible to obtain a stent 100 with a very reduced axial width, being equal to 14.3 mm, which ensures good protection of the stent during sidewalk rasping, while giving it excellent capacity to deform elastically during an impact, such as the impact of the wheel against the sidewalk for example, and mechanical stability in rolling.

Thus, as best seen in FIG. 3b, an external reinforcing element 15 has been produced which is a structure substantially of revolution around the axis XX ′ and comprises several windings of a metallic wire 4 of round section and of a diameter equal to 3 mm, the structure comprising two windings arranged axially next to each other on four layers radially superposed on each other. These windings thus form four lines 41 of wire parallel to each other and two columns 4c of wire parallel to each other. According to the invention, the axis passing through the centers of the wires of a line 41 forms an angle b with the axis passing through the centers of the wires of a column 4c, an angle which is different from 90 °. More particularly, the angle b is equal to 60 °.

The section of the external reinforcing element 15 of FIG. 3b thus obtained has an axial width "I" equal to 8.2 mm and a radial height "h" equal to 12.5 mm. The moments of inertia calculated from the section of the reinforcing element, in particular the moment Ix calculated along a first axis xx 'which is parallel to the axis of rotation XX' of the assembly and passing through the center of gravity of the section is equal to 634 mm4 and the moment of inertia ly along a second axis perpendicular to the first and passing through the center of gravity of the section is equal to 193 mm4. The main moments of inertia of concurrent axes 11 and 12 make an angle cp equal to 20.4 ° with Ix, respectively ly and their values calculated for the section of Figure 3b are 705 mm4 for 11 and 122 mm4 for 12.

Such an external reinforcing element 15 of FIG. 3b is produced in a similar manner to that previously described, by making windings of metal wire coated with elastomeric composition side by side on a support inclined at an angle 90 ° -b, by slicing in one direction, then in the other, on an inclined support starting from the end having the smallest diameter to obtain four radially superposed layers, each having two axial windings.

In a variant, not illustrated in the figures, the reinforcing element of FIG. 3b is modified. Thus, the last radially outer layer superimposed on the previous three comprises only one winding, the last winding axially outside being omitted, while the other layers below each include two windings, as in Figure 3b. This makes it possible to have a reinforcing element with a smaller radial size, while retaining the required mechanical properties.

As illustrated in FIGS. 2a, 2b, 2c, 3a and 3b, the moment of inertia along the axis Ix is different from the moment of inertia along the main axis 11 and the moment of inertia along the axis ly is different from the moment of inertia along the main axis 12. More particularly, the main axes 1-1 and 2-2 of the main moments 11 and 12 make an angle cp with the axes xx 'respectively yy' of the moments Ix, respectively ly. This angle of inclination cp is present from the completion of the windings of the external reinforcement and is such that the intersection between the extension of the axis 2-2 with the axis XX 'of the wheel is on the inner side of the wheel or in other words, it makes it possible to arrange the external reinforcement so that the longitudinal direction of the windings of the external reinforcement 15 is oriented towards the outside when the expander is in place within the rolling assembly in order to anticipate the movement of rotation which takes the section of the external reinforcement in the event of a violent shock suffered by the assembly. By longitudinal direction of the windings is understood a direction parallel to the largest dimension of the section of the reinforcement.

More particularly, the external reinforcement 15 is arranged so that the direction

longitudinal of the windings is inclined outwards with respect to an axis perpendicular to the axis of rotation XX 'of the rolling assembly when the expander is in the mounted position within the assembly. Such an outward inclination makes it possible to anticipate the rotational movement undergone by the external reinforcement element during an impact and therefore to help the external reinforcement element to initiate the rotational movement when it undergoes a violent shock.

The shape of the section of the external reinforcing element according to the invention has a radial height "h" markedly greater than its axial width "I", for a form factor h / l greater than 1.3. The ratio of moments of inertia Ix / ly is also greater than 1.3. Sufficient rigidity is thus obtained during ovalization and therefore mechanical stability in normal operation of the rolling assembly (characterized by the moment of inertia about an axis parallel to that of rotation of the rolling assembly). During an impact against a sidewalk, for example, the rolling assembly equipped with the expander of the invention leads to an elastic deformation of the latter which is a progressive pouring of the section of the external reinforcement in the plane of the impact. Thus, the greater the deformation, the more this reinforcement rotates around itself and the more the inertia around the axis x-x 'decreases, thus making it possible to limit the stress seen by the wires which enter into the constitution of the reinforcement.

In addition, the external reinforcement thus produced allows gains in mass and size. Other variants and embodiments of the invention can be envisaged without departing from the scope of its claims. Thus, the external reinforcement whose section has a general shape of

the parallelogram in FIG. 3b can have a generally rectangular cross section whose moments of inertia are ll = lx and I2 = ly. In a variant, a metal wire not covered with a polymer composition is used. In yet another variant, metallic wires of different diameters are used to make the windings constituting the external reinforcement of the expander of the invention.

Claims

1. Expander for a rolling assembly with an axis of rotation XX 'comprising a tire (2), having two beads (21) and a rim (3), the expander (100) being intended to ensure the junction between one beads (21) and the rim (3), said stent (100) comprising an axially inner end (10), an axially outer end (11) and a body (12) oriented mainly axially and disposed between said axially outer end ( 11) and said axially inner end (10), so that, when mounted within the assembly, said axially inner end (10) is intended to be immobilized on said rim, said axially outer end comprising an element of external reinforcement (15) is intended to receive a bead (21) of tire (2), in which said external reinforcement (15) is a structure substantially of revolution around the axis XX 'comprising several windings of at least one wire arranged axially alongside the others on several layers radially superposed on each other, characterized in that the section of the external reinforcement (15) has a ratio of the moments of inertia Ix / ly greater than 1.3 for an axial width of between 6 and 9 mm, where Ix is the moment of inertia around a first axis passing through its center of gravity and parallel to the axis of rotation XX 'and ly is the moment of inertia around a second axis passing through its center of gravity and perpendicular to the first axis.

2. A stent according to claim 1, in which the section of the external reinforcement (15) having an axial width I and a radial height h has a form factor h / l greater than 1.3.

3. Expander according to one of the preceding claims, characterized in that the section of the external reinforcement (15) has main moments of inertia of concurrent axes 11 and 12 which form a non-zero angle with Ix, respectively ly.

4. Extender according to claim 3, in which the ratio between the moments of inertia

main 11 and 12 is greater than 2.

5. Expander according to one of the preceding claims, in which the wire windings form a radially innermost alignment and at least one second adjacent alignment superimposed on the first called lines (41) in which the axis passing through the centers of the lines (41) are parallel to each other and the wires of the most axially inside alignments form a first column (4c) and the axially adjacent alignments outside form at least a second column (4c) where the axes passing through the centers column wires (4c) are parallel to each other and where the axis passing through the center of the windings of a line (41) makes an angle b with the axis passing through the center of the windings of a column (4c) of wire and in which the angle b is different from 90 °.

6. A stent according to any one of the preceding claims, wherein said

windings of the external reinforcement (15) comprise at least two windings arranged axially next to each other on at least three layers radially superposed on each other.

7. Expander according to one of the preceding claims, in which said windings of the external reinforcement (15) are produced on the basis of a metallic unitary wire of diameter between 2 and 5mm.

8. Extender according to one of the preceding claims, in which said windings of the external reinforcement are produced on the basis of a unitary metal wire coated with a polymeric composition.

9. Stent according to any one of the preceding claims, characterized in that said external reinforcement (15) is arranged so that the main axis of its section is inclined relative to an axis perpendicular to the axis X- X '.

10. Rolling assembly of axis of rotation X-X 'comprising a tire (2), having two

beads (21) a rim (3) and a stent (100) according to one of the preceding claims intended to ensure the junction between one of the beads (21) and the rim (3).