AU2021213941A1

AU2021213941A1 - Optimized architecture of a heavy-duty tire of the agricultural or civil engineering type

Info

Publication number: AU2021213941A1
Application number: AU2021213941A
Authority: AU
Inventors: François BARBARIN; Lucas LAUBY; Philippe Mansuy; Gaël PATAUT; Olivier REIX
Original assignee: Compagnie Generale des Etablissements Michelin SCA
Current assignee: Compagnie Generale des Etablissements Michelin SCA
Priority date: 2020-01-29
Filing date: 2021-01-19
Publication date: 2022-07-14
Also published as: CN115003522A; FR3106529B1; CN115003522B; CL2022002026A1; WO2021152232A1; CA3163261A1; EP4096937A1; BR112022013272A2; EP4096937B1; FR3106529A1

Abstract

The invention relates to a radial tire (1) for a heavy vehicle, in which, on either side of the equatorial plane, a hyperelastic reinforcement ply (323), which is arranged radially outwards of the working layers, covers the axial end of the working layer with the smaller axial width (322), the axial ends of which are at a minimum axial distance (Ds/2) from said end, containing hyperelastic cords (50). Said cords comprise filamentary elements (54) on a single layer (52). The distance between the center of each filamentary element (54) of the layer (52) and the main axis (A) of the cord is equal to half of the helix diameter Dh and is substantially constant and equal for all the metal filamentary elements (54) of the layer (52), the metal filamentary elements (54) defining an internal arch (58) of the cord, having the diameter Dv. Each metal filamentary element (54) has a diameter Df and a helix radius of curvature Rf, such that: 9 ≤ Rf / Df ≤ 30, and 1.30 ≤ Dv / Df ≤ 4.5. Said hyperelastic cords are embedded in a rubber compound.

Description

OPTIMIZED ARCHITECTURE OF A TYRE OF THE HEAVY-DUTY VEHICLE, AGRICULTURAL OR CONSTRUCTION PLANT TYPE

[001] The subject of the present invention is a radial tyre, intended to equip a heavy vehicle of the construction plant, agricultural or goods transport type, and relates more particularly to the crown reinforcement of such a tyre, and even more particularly to its hoop reinforcement.

[002] Radial tyres intended to equip a heavy vehicle of the construction plant, agricultural or goods transport type are designated within the meaning of the European Tyre and Rim Technical Organization or ETRTO standard.

[003] For example, a radial tyre for a heavy vehicle of construction plant type, within the meaning of the European Tyre and Rim Technical Organization or ETRTO standard, is intended to be mounted on a rim with a diameter at least equal to 25 inches. Although not limited to this type of application, the invention is described for a radial tyre of large size, which is intended to be mounted on a dumper, in particular on vehicles for transporting materials extracted from quarries or surface mines, by way of a rim with a diameter at least equal to 35 inches, possibly as much as 57 inches, or even 63 inches.

[004] Since a tyre has a geometry exhibiting symmetry of revolution about an axis of rotation, the geometry of the tyre is generally described in a meridian plane containing the axis of rotation of the tyre. For a given meridian plane, the radial, axial and circumferential directions denote the directions perpendicular to the axis of rotation of the tyre, parallel to the axis of rotation of the tyre and perpendicular to the meridian plane, respectively. The circumferential direction is tangential to the circumference of the tyre.

[005] In the following text, the expressions "radially inner/radially on the inside" and "radially outer/radially on the outside" mean "closer to" and "further away from" the axis of rotation of the tyre, respectively. "Axially inner/axially on the inside" and "axially outer/axially on the outside" mean "closer to" and "further away from" the equatorial plane of the tyre, respectively, with the equatorial plane of the tyre being the plane that passes through the middle of the tread surface and is perpendicular to the axis of rotation. "An element A axially inside an element B by an axial distance Ds" means that the element A is closer to the equatorial plane than the element B and that the axial distance between the two elements is equal to the distance Ds. This type of sentence is generalizable with the radial and circumferential direction and the outer versus inner position of one or the other of the elements.

[006] Generally, a tyre comprises a tread intended to come into contact with the ground via a tread surface, the two axial ends of which are connected via two sidewalls to two beads that provide the mechanical connection between the tyre and the rim on which it is intended to be mounted.

[007] A radial tyre further comprises a reinforcement made up of a crown reinforcement radially on the inside of the tread and of a carcass reinforcement radially on the inside of the crown reinforcement.

[008] The carcass reinforcement of a radial tyre for a heavy vehicle of the construction plant, agricultural or goods transport type usually comprises at least one carcass layer comprising generally metal reinforcers, coated with a polymeric material of the elastomer or elastomeric type, obtained by mixing and called coating mixture. A carcass layer comprises a main part that joins the two beads together and is generally wound, in each bead, from the inside of the tyre to the outside, around a usually metal circumferential reinforcing element known as a bead wire so as to form a turn-up. The metal reinforcers of a carcass layer are substantially mutually parallel and form an angle of between 85 and 950 with the circumferential direction.

[009] The crown reinforcement of a radial tyre for a vehicle of the construction plant, agricultural or goods transport type comprises a superposition of crown layers extending circumferentially, radially outside the carcass reinforcement. Each crown layer is made up of generally metal reinforcers that are mutually parallel and are coated in a polymeric material of the elastomer or coating compound type.

[010] As regards the metal reinforcers, a metal reinforcer is mechanically characterized by a curve representing the tensile force (in N) applied to the metal reinforcer as a function of the relative elongation (in %) thereof, known as the force-elongation curve. Mechanical tensile characteristics of the metal reinforcer, such as the structural elongation As (in %), the total elongation at break At (in %), the force at break Fm (maximum load in N) and the breaking strength Rm (in MPa), are derived from this force-elongation curve, these characteristics being measured in accordance with the standard ASTM D 2969-04 of 2014.

[011] The total elongation At of the metal reinforcer is, by definition, the sum of its elastic and plastic structural elongations (At = As + Ae + Ap) and particularly at break where each of the elongations is non-zero. The structural elongation As results from the relative positioning of the metal threads making up the metal reinforcer under a low tensile force. The elastic elongation Ae results from the actual elasticity of the metal of the metal threads making up the metal reinforcer, taken individually, the behaviour of the metal following Hooke's law. The plastic elongation Ap results from the plasticity, i.e. the irreversible deformation beyond the yield point, of the metal of these metal threads taken individually. These various elongations and the respective meanings thereof, which are well known to a person skilled in the art, are described, for example, in the documents US5843583, W02005/014925 and W02007/090603.

[012] Also defined, at each point on the force-elongation curve of a metal reinforcer, is a tensile modulus expressed in GPa, which represents the gradient of the straight line tangential to the force-elongation curve at this point. In particular, the tensile modulus of the elastic linear part of the force-elongation curve is referred to as the tensile elastic modulus or Young's modulus.

[013] Among the metal reinforcers, a distinction is usually made between elastic metal reinforcers, such as those used in the protective layers, and non-extensible or inextensible metal reinforcers.

[014] An elastic metal reinforcer, in its non-rubberized state, is characterized by a structural elongation As at least equal to 1% and a total elongation at break At at least equal to 4%. Moreover, an elastic metal reinforcer has a tensile elastic modulus at most equal to 180 GPa, and usually between 40 GPa and 150 GPa.

[015] For example, a metal cord comprising a single layer ofN=5 metal filamentary elements wound in a helix is known from the prior art. Each metal filamentary element is made up of a steel monofilament and has a diameter equal to 0.38 mm. Each metal filamentary element is wound at a pitch P, here P=6.7 mm, and is individually preformed before the final helical assembly step of the metal filamentary elements. The metal filamentary elements define an internal enclosure of the cord, making it possible to define an enclosure diameter Dv. The preforming and internal enclosure give the cord, once assembled, relatively significant aeration, in other words a relatively large space between each pair of adjacent metal filamentary elements. Such aeration causes structural elongation As of the cord equal to 2.3%. Such a cord is intended in particular to be used in tyres, for example tyres for a heavy duty type vehicle.

[016] An inextensible metal reinforcer is characterized by a total elongation At, under a tensile force equal to 10% of the force at break Fm, at most equal to 0.2%. Moreover, an inextensible metal reinforcer has a tensile elastic modulus usually between 150 GPa and 200 GPa.

[017] Among the crown layers, a distinction is usually made between the protective layers, constituting the protective reinforcement and radially outermost, which are generally elastic, and the inextensible working layers (W02007/003562A1), constituting the working reinforcement and radially comprised between the protective reinforcement and the carcass reinforcement.

[018] The protective reinforcement, which comprises at least one protective layer, essentially protects the working layers from mechanical or physicochemical attacks, which are likely to spread through the tread radially towards the inside of the tyre.

[019] The protective reinforcement often comprises two radially superposed protective layers formed of elastic metal reinforcers that are mutually parallel in each layer and crossed from one layer to the next, forming angles at least equal to 10 with the circumferential direction.

[020] The working reinforcement, comprising at least two working layers, has the function of belting the tyre and ensuring its stiffness and road-holding. It absorbs both mechanical inflation stresses, which are generated by the tyre inflation pressure and transmitted by the carcass reinforcement, and mechanical stresses caused by running, which are generated as the tyre runs over the ground and are transmitted by the tread. It is also intended to withstand oxidation, impacts and perforation, by virtue of its intrinsic design and that of the protective reinforcement.

[021] The working reinforcement usually comprises two radially superposed working layers formed of inextensible metal reinforcers that are mutually parallel in each layer and are crossed from one layer to the next, forming angles at most equal to 60, and preferably at least equal to 15° and at most equal to 45, with the circumferential direction. To reduce the shearing of the rubber compounds at the axial ends of the working layers, it is customary to axially shift the position of said ends relative to one another. The crown reinforcement therefore usually comprises a working layer of greatest axial width and a working layer of smallest axial width. The shearing of the rubber compounds is maximum at the end of the working layer of smallest axial width. Specifically, this maximum shearing due to the displacements of the end of the working layer of smallest axial width is distributed over the radial thickness of rubber compounds between the working layer of smallest axial width and the working layer of greatest axial width. This shearing is amplified by the deformations of the working layer of greatest axial width. Specifically, given the angle of the metal reinforcers crossed with the metal reinforcers of the working layer of smallest width, the working layer of greatest axial width deforms in another direction, which increases the deformations of the rubber compounds. These shearing maxima are generally reduced by adding a decoupling rubber between the end of the working layer of smallest axial width and the working layer of largest axial width. The end of the working layer of greatest axial width is also subjected to strong shearing but generally of lesser amplitude given that for this end, the thickness of the rubber compounds is greater and the deformations are no longer amplified by the presence of the other working layer.

[022] To reduce the mechanical inflation and running stresses transmitted to the working reinforcement and the shearing of the rubber compound which covers them, it is known to arrange, radially outside the carcass reinforcement, a hoop reinforcement. The hoop reinforcement, the function of which is to at least partially absorb the mechanical inflation stresses, improves the endurance of the crown reinforcement by stiffening the crown reinforcement. The hoop reinforcement may be positioned radially on the inside of the working reinforcement, between the two working layers of the working reinforcement, or radially on the outside of the working reinforcement.

[023] In construction plant type applications, the hoop reinforcement can comprise two hooping layers, radially superimposed, formed of metal reinforcers, parallel to one another in each layer and crossed from one layer to the next, forming, with the circumferential direction, angles at most equal to 10.

[024] In heavy-duty vehicle type applications for load transport, the hoop reinforcement usually comprises a hooping layer produced by the circumferential winding of a hooping wire or a continuous hooping strip by forming, with the circumferential direction, angles at most equal to 5°.

[025] In both cases, the hooping layers are of smaller axial width than the working layer of smallest axial width. Specifically, the stresses due to running at the end are very high in tension and compression and lead to the rupture of the metal reinforcers arranged around the ends of the working layers. Document W02014/095099 discloses a shoulder covering strip whose width is limited due to these stresses. Even using elastic cords, known in the prior art, the phenomenon of buckling during running and the high consumption of the As of the reinforcer during the moulding of tyres for tyres for heavy vehicles render these solutions unsatisfactory. Specifically, tyres for heavy vehicles have a significant tread height at least equal to 10 mm for heavy-duty vehicle tyres and sometimes much more for agricultural and construction plant tyres, in particular at the shoulders of the tyre. It is necessary for moulding to press the rubber compound of the tread into the mould. For this, before curing, the tyre is at a smaller diameter and the moulding pressure displaces the crown by a radius close to the tread height. The working layers deform easily due to the angle of the reinforcers, the rubber compound of the working layers absorbing the deformation. For the hooping layers, their deformation is facilitated by using elastic metal reinforcers or by using hooping layers with discontinuous metal reinforcers. However, at the shoulder, it is necessary to have greater elastic properties than at the centre and the proposed solution must be improved to be really advantageous.

[026] The inventors have set themselves the objective, for a radial tyre for a vehicle of the construction plant, heavy-duty vehicle or agricultural type, to reduce the risk of cracking of the rubber compounds at the ends of the working layers of the tyre when running while reducing the risks of breakage of the reinforcing elements of a radially outer hooping layer.

[027] This objective has been achieved, according to the invention, by a tyre for a vehicle of the heavy-duty vehicle, construction plant or agricultural type, comprising:

* a median circumferential plane, called the equatorial plane, perpendicular to the axis of rotation of the tyre and dividing the tyre into two substantially symmetrical half-torus shapes, * a crown reinforcement, radially on the inside of a tread and radially on the outside of a carcass reinforcement; • the crown reinforcement comprising at least one working reinforcement, the crown reinforcement comprising at least two working layers, one of greatest axial width and one of smallest axial width, * each working layer comprising inextensible reinforcing elements parallel to one another, forming, with the circumferential direction, oriented angles at least equal to 15° and at most equal to 40°, the two angles of the two working layers being of opposite sign,

• an axial distance Ds being the maximum value of the axial distances measured on either

side of the equatorial plane between the axial end of the working layer of smallest axial width and the axial end of the working layer of greatest axial width, * the crown reinforcement comprising, on either side of the equatorial plane, at least one hooping layer radially on the outside of the radially outermost working layer, called the hyperelastic radially outer hooping layer, of which the axially outermost axial end is axially outside the axial end of the working layer of smallest axial width by an axial distance at least equal to Ds/2 and of which the axially innermost point is axially inside the axial end of the working layer of smallest axial width, by an axial distance at least equal to Ds/2, * said hyperelastic radially outer hooping layer, on either side of the equatorial plane, comprising hyperelastic metal reinforcers, parallel to one another and forming, with a circumferential direction (XX') of the tyre, an angle at most equal to 5, each hyperelastic metal reinforcer comprising at least one cord, called hyperelastic cord, • said hyperelastic cords comprising a single layer consisting of N metal filamentary elements wound in a helix and having an external diameter D, each metal filamentary element of the layer describing, when the cord extends in a substantially rectilinear direction, a trajectory in the form of a helix around a main axis (A) substantially parallel to the substantially rectilinear direction, so that, in a section plane substantially perpendicular to the main axis (A), the distance between the centre of each metal filamentary element of the layer and the main axis (A) is equal to half the helix diameter Dh and is substantially constant and equal for all the metal filamentary elements of the layer, the metal filamentary elements defining an internal enclosure of the cord of diameter Dv, each metal filamentary element having a diameter Df and a helix radius of curvature Rf defined by Rf=P/(R x Sin(2a)) with P the pitch of each metal filamentary element expressed in millimetres and a the helix angle of each metal filamentary element, characterized in that, with Dh, D, Dv, Df and Rf being expressed in millimetres: • 9<Rf/Df 30,and • 1.30 < Dv / Df < 4.5, • said hyperelastic cords being embedded in a rubber compound.

[028] The inventors have reduced the risk of cracking of the rubber compounds of the crown without degrading the other performance, by using as metal reinforcer of a radially outer hooping layer either directly a hyperelastic cord or a multi-strand of hyperelastic cords, said hyperelastic cords having particular geometric characteristics. The hooping layer is said to be radially outer because it is always radially outside the working layers. It is said to be hyperelastic because its metal reinforcers are hyperelastic.

[029] The enclosure diameter Dv of the hyperelastic metal reinforcers of the hyperelastic radially outer hooping layer must be large enough compared with the diameter of the metal filamentary elements Df to allow compression deformation improving the resistance to buckling and small enough to define the thickness of the hyperelastic radially outer hooping layer compatible with the objectives of limiting the mass of the tyres and therefore the material resources necessary for their production. Similarly, the helix radius of curvature Rf must be sufficiently small compared with the diameter of the metalfilamentary elements Df to give a significant structural elongation which will be used during the moulding of the tyre and sufficiently large to obtain a linear rupture strength of the hyperelastic radially outer hooping layer adequate not to break under the stress when running in particular under a transverse force under cornering.

[030] Such cords have the advantage over conventional hybrid or non-hybrid elastic cords of having not only high tensile elasticity but also good resistance to buckling. Specifically, the region of the ends of the working layer is, in particular during cornering, under transverse force, longitudinally stressed in tension and in compression on either side of the equatorial plane.

[031] The values of the characteristics Df, Dv and Rf and of the other characteristics described below are measured on or determined from cords either directly after they have been manufactured, that is to say before any step of embedding in an elastomeric matrix, or once they have been extracted from an elastomeric matrix, for example of a tyre, and have thus undergone a cleaning step during which any elastomeric matrix is removed from the cord, in particular any material present inside the cord. In order to ensure an original state, the adhesive interface between each metal filamentary element and the elastomeric matrix has to be eliminated, for example by way of an electrochemical process in a bath of sodium carbonate. The effects associated with the shaping step of the method for manufacturing the tyre that are described below, in particular the elongation of the cords, are eliminated by the extraction of the ply and of the cord which, during extraction, substantially regain their characteristics from before the shaping step.

[032] The cord according to the invention comprises a single layer of helically wound metal filamentary elements. In other words, the cord according to the invention comprises one layer, not two or more than two layers, of helically wound metal filamentary elements. The layer is made up of metal filamentary elements, that is to say a plurality of metal filamentary elements, not just one metal filamentary element. In one embodiment of the cord, for example when the cord has been obtained from its manufacturing process, the cord according to the invention consists of the layer of wound metal filamentary elements.

[033] The cord according to the invention has a single helix. By definition, a single-helix cord is a cord in which the axis of each metalfilamentary element of the layer describes a single helix, in contrast to a double-helix cord, in which the axis of each metalfilamentary element describes a first helix about the axis of the cord and a second helix about a helix described by the axis of the cord. In other words, when the cord extends in a substantially rectilinear direction, the cord comprises a single layer of metalfilamentary elements wound together in a helix, each metal filamentary element of the layer describing a path in the form of a helix around the substantially rectilinear direction so that the distance between the centre of each metal filamentary element of the layer and the axis of the substantially rectilinear direction is substantially constant and equal for all the metal filamentary elements of the layer. By contrast, when a double-helix cord extends in a substantially rectilinear direction, the distance between the centre of each metal filamentary element of the layer and the substantially rectilinear direction is different for all of the metal filamentary elements of the layer.

[034] The cord according to the invention does not have a central metal core. This is also referred to as a cord of structure 1xN, in which N is the number of metalfilamentary elements, or as an open cord.

[035] The enclosure of the cord according to the invention is delimited by the metal filamentary elements and corresponds to the volume delimited by a theoretical circle that is, on the one hand, radially on the inside of each metal filamentary element and, on the other hand, tangent to each metal filamentary element.

[036] A filamentary element means an element extending longitudinally along amain axis and having a section perpendicular to the main axis, the largest dimension G of which is relatively small compared with the dimension L along the main axis. The expression "relatively small" means that L/G is greater than or equal to 100, preferably greater than or equal to 1000. This definition covers both filamentary elements with a circular section and filamentary elements with a non-circular section, for example a polygonal or oblong section. Very preferably, each metal filamentary element has a circular section.

[037] By definition, the term metal means a filamentary element made up mostly (i.e. more than 50% of its weight) or entirely (100% of its weight) of a metal material. Each metal filamentary element is preferably made of steel, more preferably pearlitic or ferritic-pearlitic carbon steel, commonly referred to as carbon steel by a person skilled in the art, or made of stainless steel (by definition steel comprising at least 10.5% chromium).

[038] The helix angle a is a parameter that is well known to a person skilled in the art and can be determined using the following iterative calculation comprising three iterations and wherein the index i indicates the number of the iteration 1, 2 or 3. Knowing the structural elongation As expressed in %, the helix angle a(i) is such thata(i)=Arcos [ (100/(100+As) x Cos [ Arctan ( (R x Df) / (P x Cos(a(i-1)) x Sin(R/N)) ] ], in which formula P is the pitch expressed in millimetres at which each metal filamentary element is wound, N is the number of metal filamentary elements in the layer, Df is the diameter of each metal filamentary element expressed in millimetres, Arcos, Cos and Arctan and Sin denote the arccosine, cosine, arctangent and sine functions, respectively. For the first iteration, that is to say for the calculation of a(1), a(0)=0. At the third iteration, a(3)=a is obtained with at least one significant digit after the decimal point when a is expressed in degrees.

[039] The helix diameter Dh, expressed in millimetres, is calculated using the relationship Dh=P x Tan(a) / u, in which P is the pitch expressed in millimetres at which each metal filamentary element is wound, a is the helix angle of each metalfilamentary element determined above, and Tan is the tangent function. The helix diameter Dh corresponds to the diameter of the theoretical circle passing through the centres of the metalfilamentary elements of the layer in a plane perpendicular to the axis of the cord.

[040] The enclosure diameter Dv, expressed in millimetres, is calculated using the relationship Dv=Dh-Df, in which Df is the diameter of each metal filamentary element and Dh is the helix diameter, both expressed in millimetres.

[041] The radius of curvature Rf, expressed in millimetres, is calculated according to the relationship Rf=P/(u x Sin(2a)) in which P is the pitch expressed in millimetres, a is the helix angle of each metal filamentary element and Sin is the sine function.

[042] It will be recalled that the pitch at which each metalfilamentary element is wound is the length covered by this filamentary element, measured parallel to the axis of the cord in which it is located, after which the filamentary element that has this pitch has made a complete turn about said axis of the cord.

[043] The optional features described below could be combined with one another in so far as such combinations are technically compatible.

[044] In an advantageous embodiment, all the metal filamentary elements have the same diameter Df.

[045] The orientation of an angle means the direction, clockwise or anticlockwise, in which it is necessary to rotate from a reference straight line, in this instance the circumferential direction of the tyre, defining the angle in order to reach the other straight line defining the angle.

[046] In preferred embodiments, 9 < Rf / Df < 25. In one embodiment of a cord intended to reinforce a tyre for industrial vehicles chosen from vans, heavy-duty vehicles, for example light rail vehicles, buses, heavy road transport vehicles (lorries, tractors, trailers), 9 < Rf/Df < 15.

[047] In one embodiment of a cord intended to reinforce a tyre for industrial vehicles chosen from vans, heavy-duty vehicles, for example light rail vehicles, buses, heavy road transport vehicles (lorries, tractors, trailers), 1.70 < Dv/Df < 2.50.

[048] Advantageously, the helix radius of curvature Rf is such that 2 mm < Rf < 7 mm. In one embodiment of a cord intended to reinforce a tyre for industrial vehicles chosen from vans, heavy-duty vehicles, for example light rail vehicles, buses, heavy road transport vehicles (lorries, tractors, trailers), 4 mm < Rf < 6 mm and preferably 4 mm < Rf < 5 mm.

[049] In one embodiment of a cord intended to reinforce a tyre for off-road vehicles, for example agricultural or construction plant vehicles, 4 mm < Rf < 7 mm and preferably 4.5 mm < Rf < 6.5 mm.

[050] Advantageously, the helix diameter Dh of each metal filamentary element is such that 0.40 mm < Dh < 1.60 mm.

[051] In one embodiment of a cord intended to reinforce a tyre for industrial vehicles chosen from vans, heavy-duty vehicles, for example light rail vehicles, buses, heavy road transport vehicles (lorries, tractors, trailers), 0.85 mm < Dh < 1.60 mm and preferably 0.90 mm < Dh

< 1.60 mm.

[052] In one embodiment of a cord intended to reinforce a tyre for off-road vehicles, for example agricultural or construction plant vehicles, 0.95 mm < Dh < 1.40 mm and preferably 1.00 mm < Dh < 1.35 mm.

[053] Advantageously, Df is such that 0.10 mm < Df < 0.50 mm.

[054] In one embodiment of a cord intended to reinforce a tyre for industrial vehicles chosen from vans, heavy-duty vehicles, for example light rail vehicles, buses, heavy road transport vehicles (lorries, tractors, trailers), 0.22 mm < Df < 0.50 mm and preferably 0.25 mm < Df < 0.45 mm.

[055] In one embodiment of a cord intended to reinforce a tyre for off-road vehicles, for example agricultural or construction plant vehicles, 0.32 mm <Df < 0.50 mm and preferably 0.35 mm < Df < 0.50 mm.

[056] Advantageously, Dv is such that Dv > 0.46 mm, and more preferably 0.50 mm < Dv < 1.20 mm.

[057] In one embodiment of a cord intended to reinforce a tyre for industrial vehicles chosen from vans, heavy-duty vehicles, for example light rail vehicles, buses, heavy road transport vehicles (lorries, tractors, trailers), 0.65 mm < Dv < 0.80 mm.

[058] In one embodiment of a cord intended to reinforce a tyre for off-road vehicles, for example agricultural or construction plant vehicles, 0.55 mm < Dv < 1.00 mm.

[059] Advantageously, each metal filamentary element is wound at a pitch P such that 3 mm < P < 15 mm.

[060] In one embodiment of a cord intended to reinforce a tyre for industrial vehicles chosen from vans, heavy-duty vehicles, for example light rail vehicles, buses, heavy road transport vehicles (lorries, tractors, trailers), 7 mm < P < 15 mm and preferably 7.5 mm < P < 11 mm.

[061] In one embodiment of a cord intended to reinforce a tyre for off-road vehicles, for example agricultural or construction plant vehicles, 9 mm < P < 15 mm.

[062] Advantageously, the cord has a diameter D such that D < 2.10 mm.

[063] The diameter or visible diameter, denoted D, is measured by means of a thickness gauge, the diameter of the contacts of which is at least equal to 1.5 times the winding pitch P of the filamentary elements (the model JD50 from Kaefer may be mentioned for example, which makes it possible to achieve a precision of 1/100 of a millimetre, is equipped with a type a contact, and has a contact pressure of around 0.6 N). The measurement protocol consists of three repetitions of a set of three measurements (carried out perpendicularly to the axis of the cord and under zero tension), wherein the second and third of these measurements are carried out in a direction offset angularly from the previous measurement by one third of a turn, by rotation of the measurement direction about the axis of the cord.

[064] In one embodiment of a cord intended to reinforce a tyre for industrial vehicles chosen from vans, heavy-duty vehicles, for example light rail vehicles, buses, heavy road transport vehicles (lorries, tractors, trailers), 1.15 mm < D < 1.55 mm.

[065] In one embodiment of a cord intended to reinforce a tyre for off-road vehicles, for example agricultural or construction plant vehicles, 1.5 mm < D < 2 mm.

[066] In one embodiment, each metal filamentary element comprises a single metal monofilament. Here, each metal filamentary element is advantageously made up of a metal monofilament. In a variant of this embodiment, the metal monofilament is directly coated with a layer of a metal coating comprising copper, zinc, tin, cobalt or an alloy of these metals, for example brass or bronze. In this variant, each metal filamentary element is then made up of the metal monofilament, made for example of steel, forming a core, which is directly coated with the metal coating layer.

[067] In this embodiment, each metal elementary monofilament is, as described above, preferably made of steel, and has a mechanical strength ranging from 1000 MPa to 5000 MPa. Such mechanical strengths correspond to the steel grades commonly encountered in the field of tyres, namely the NT (Normal Tensile), HT (High Tensile), ST (Super Tensile), SHT (Super High Tensile), UT (Ultra Tensile), UHT (Ultra High Tensile) and MT (Mega Tensile) grades, the use of high mechanical strengths potentially allowing improved reinforcement of the matrix in which the cord is intended to be embedded and lightening of the matrix reinforced in this way.

[068] Advantageously, with the layer being made up of N helically wound metalfilamentary elements, N ranges from 3 to 18, preferably from 5 to 12, more preferably from 6 to 9.

[069] The objective of said hyperelastic radially outer hooping layer is to reduce the maximum shearing in the rubber compounds near the end of the working layer of smallest axial width. To reduce these stresses, the designers separate the two ends of these working layers by a length Ds. The length Ds is therefore such that if this distance is observed between the ends, the overstresses linked to the two ends are not added in a damaging manner. Ds/2 is therefore of the order of magnitude of the influence distance of the overstresses at the ends. It is therefore advantageous for the hyperelastic radially outer hooping layer to be positioned on either side of the end of the working layer of smallest axial width over a distance of at least Ds/2 to reduce the shearing over this entire region.

[070] Advantageously, on either side of the equatorial plane, the axially outermost axial end of the hyperelastic radially outer hooping layer is axially outside the axial end of the working layer of greatest axial width, by a distance at least equal to Ds/2 so as to reduce the shearing also at the end of the working layer of greatest axial width. In such a configuration, with the hyperelastic radially outer hooping layer reducing the risks of cracking of the rubber compounds around the ends of the working layers and being composed of a hyperelastic cord or strand capable of withstanding large deformations such as those due to obstacles on the the ground on which the tyre is running that are capable of causing crown ruptures, it can act as a protective layer in this region. Therefore, to reduce the mass of the protective layer of a tyre comprising a protective reinforcement radially outside the working reinforcement comprising at least one protective layer and therefore of the tyre, it is advantageous, if the hyperelastic radially outer hooping layer comprises an axially inner end, that, on either side of the equatorial plane, the axial end of the protective layer of greatest axial width is axially inside the axially innermost axial end of the hyperelastic radially outer hooping layer.

[071] On the axially outer part of the hyperelastic radially outer hooping layer, there is necessarily an end of this layer. On the axially inner part of the hyperelastic radially outer hooping layer, it is possible to arrange a hyperelastic radially outer hooping layer which runs without interruption from a first axially outer end, crossing the equatorial plane to the other axially outer end located on the other side of the equatorial plane of the tyre. In this case, on each side of the equatorial plane, the axially innermost point is located on the equatorial plane, although there is no axially inner end of the radially outer hooping layer.

[072] Although the hyperelastic radially outer hooping layer does not comprise an axially inner end and is therefore of full width, it is advantageous, depending on the type of tyres and the stresses to which they are subjected, either to remove the protective layer or to reduce the number thereof.

[073] Advantageously, the ratio K of the pitch P to the diameter Df of each metal filamentary element of said hyperelastic cords is such that 19 < K < 44, preferably 20 < K < 40 and more preferably 23 < K < 39, P and Df being expressed in millimetres. In one embodiment of a cord intended to reinforce a tyre for industrial vehicles chosen from vans, heavy-duty vehicles, for example light rail vehicles, buses, heavy road transport vehicles (lorries, tractors, trailers), 19 < K < 35 and preferably 23 < K < 30.

[074] Advantageously, the helix angle a of each metal filamentary element is such that 130 < a < 30°, preferably 17° < a < 26°. In one embodiment of a cord intended to reinforce a tyre for industrial vehicles chosen from vans, heavy-duty vehicles, for example light rail vehicles, buses, heavy road transport vehicles (lorries, tractors, trailers), 18.5° < a< 30° and preferably 18.5° < a < 26°.

[075] In the case of values of the ratio K that are too high or in the case of values of the helix angle that are too low, the longitudinal compressibility of the cord is reduced. In the case of values of the ratio K that are too low or in the case of values of the helix angle that are too high, the longitudinal stiffness of the cord and thus its reinforcement capacity are reduced.

[076] Advantageously, the cord has a structural elongation As such that As > 1%, preferably As > 2.5%, more preferably As > 3%.

[077] Lastly, the relative radial clearance Jr is representative of the distance separating each pair of adjacent metal filamentary elements brought to within the length available for positioning the metal filamentary elements on the layer. More precisely, Jr =N/(R*(D-Df)) x (Dh x Sin(R/N) - (Df / Cos(a x /180))), a being the helix angle, expressed in degrees, of

each metal filamentary element (54) and Dv=Dh-Df. Thus, the greater Jr, the greater the space separating two adjacent metal filamentary elements relative to the maximum number of metal filamentary elements that the layer could accommodate. Conversely, the smaller Jr, the smaller the space separating two adjacent metal filamentary elements relative to the maximum number of metal filamentary elements that the layer could accommodate. Within the range according to the invention, Jr makes it possible to maximize the number of metal filamentary elements present on the layer and therefore the reinforcing capacity of the cord but not at the expense of the capacity to adapt to longitudinal compressive deformations.

[078] Advantageously, the relative radial clearance between two adjacent filamentary elements, Jr of said hyperelastic cords included in the elastic metal reinforcers of the hyperelastic radially outer hooping layer is such that 0.10 < Jr < 0.60, preferably 0.30 < Jr < 0.60. The relative radial clearance between two adjacent filamentary elements makes it possible to adjust the ventilation of the cord and the balance in this type of application. A cord that is too poorly ventilated will behave similarly to conventional cords and will not provide the same level of performance gain. A cord that is too ventilated, beyond a relative clearance of 0.6, will deform easily but will not put up resistance to longitudinal forces in tension or compression.

[079] Depending on the type of tyre designed, depending on the need for tensile strength for each specific use, i.e. vans, heavy-duty vehicles or construction plant vehicles, whose dimensions vary from 16 inches to 63 inches, each metal reinforcer of the hyperelastic radially outer hooping layer consists of a single hyperelastic cord as defined above or is composed of a plurality of said cords, assembled together, namely is a strand of hyperelastic cords. Specifically, the assembly of a plurality of hyperelastic cords retains the compression properties of the hyperelastic cord.

[080] Preferably, for correct endurance performance of the metal reinforcers of the hyperelastic radially outer hooping layer, the hyperelastic metal reinforcers of said hyperelastic radially outer hooping layer have a secant modulus at 2% elongation at most equal to 80 GPa and an elongation at break at least equal to 4%.

[081] Advantageously, for correct endurance performance of the reinforcements of the hyperelastic radially outer hooping layer, the hyperelastic metal reinforcers of said hyperelastic radially outer hooping layer have a compression buckling deformation value at least equal to 2%.

[082] Preferably on either side of the equatorial plane, the hyperelastic radially outer hooping layer is formed by the circumferential winding of a hyperelastic metal reinforcer or of a strip consisting of a plurality of hyperelastic metal reinforcers, which makes it possible to reduce, by comparison with a layer of non-continuous reinforcements, the number of ends of cords or strands which are so many likely points of initiation of a crack and to use all the resistance potential of the metal reinforcers circumferentially.

[083] For tyres for heavy vehicles of the construction plant type, according to a preferred embodiment of the protective layers, the elastic metal reinforcers of the protective layers form, with the circumferential direction, an angle at least equal to 15° and at most equal to 350.

[084] For tyres for heavy vehicles of the construction plant type, a preferred embodiment comprises two protective layers comprising elastic or hyperelastic metal reinforcers. More advantageously, the respective metal reinforcers of the two protective layers are crossed from one protective layer to the next. More advantageously for productivity gains, the metal reinforcers of the radially innermost protective layer form with the circumferential direction (XX') an angle equal in absolute value to the angle formed by the metal reinforcers of the radially outermost protective layer with the circumferential direction (XX'). And more advantageously, to have homogeneous behaviour in the distribution of the forces taken up by each of the layers of the crown reinforcement, the absolute value of the angles formed by the metal reinforcers of the protective layers with the circumferential direction is substantially equal to the average of the absolute values of the angles formed by the metal reinforcers of the working layers with the circumferential direction (XX').

[085] The tyre may comprise a protective reinforcement radially outside the working reinforcement comprising at least one protective layer. According to a preferred embodiment of the crown reinforcement, to improve the hammering performance, namely the cracking of the rubber materials, the radially innermost protective layer has an axial width LP1 at least equal to 1.05 times and at most equal to 1.25 times the maximum axial width LTmax of the working layer having the greatest axial width. Below 1.05 times the axial width LTmax, the radially innermost protective layer does not project sufficiently beyond the working layer of greatest axial width to be able to provide effective protection against hammering. Above 1.25 times the axial width LTmax, the axial end of the radially innermost protective layer is very close to the axial end of the tread, thereby increasing the risk of cracking between the axial end of said protective layer and the axial end of the tread.

[086] According to a preferred embodiment of the crown reinforcement of a construction plant tyre, the crown reinforcement comprises a hoop reinforcement comprising two hooping layers radially inside the radially outermost working layer, the respective metal reinforcers of which, coated in an elastomeric material, parallel to one another and forming, with the circumferential direction, an angle at most equal to 100, are crossed from one hooping layer to the next. A distinction is usually made between angled hooping layers, with reinforcers that form angles at least equal to 5° and at most equal to 8°, and circumferential hooping layers, with reinforcers that are substantially circumferential and form angles close to 0° and at most equal to 5°. The metal reinforcers of the hooping layer may be either elastic or inextensible. The hoop reinforcement can be positioned radially inside the working reinforcement, between the two working layers of the working reinforcement.

[087] The features of the invention are illustrated in the schematic Figures 1 to 4, which are not to scale, with reference to a tyre of size 53/80R63: • Figure 1: meridian cross section of a tyre crown according to the invention. • Figure 2: meridian cross section of a tyre crown according to the invention. • Figure 3: meridian cross section of a tyre crown according to the invention. • Figure 4: cross section of a hyperelastic cord making up all or part of the metal reinforcers of the protective reinforcement according to the invention.

[088] Figure 1 shows a meridian cross section through a tyre 1 for a heavy vehicle of construction plant type comprising a crown reinforcement 3 radially on the inside of a tread 2 and radially on the outside of a carcass reinforcement 4. The crown reinforcement 3 comprises, radially from the outside to the inside, a protective reinforcement 31, a working reinforcement 32 and a hoop reinforcement 33. The protective reinforcement 31 comprises two protective layers (311, 312) comprising elastic metal reinforcers that are coated in an elastomeric material, are mutually parallel and form an angle equal to 24 with a circumferential direction XX' tangential to the circumference of the tyre, the respective metal reinforcers of each protective layer being crossed from one protective layer to the next. The working reinforcement 32 comprises two working layers 321, 322 whose respective inextensible metal reinforcers that are coated in an elastomeric material, are mutually parallel and form, with the circumferential direction XX', angles respectively equal to 330, for the radially innermost working layer 321 which is also circumstantially the working layer of greatest axial width, and 19, for the radially outermost working layer 322 which is also circumstantially the working layer of smallest axial width, are crossed from one working layer to the next. The working reinforcement also comprises a hyperelastic radially outer hooping layer 323 comprising hyperelastic cords, of an axial width at least equal to Ds and arranged such that the axially outermost axial end is axially outside the axial end of the working layer of smallest axial width (322) by an axial distance at least equal to Ds/2 and that the axially innermost end is axially inside the axial end of the working layer of smallest axial width (322), by an axial distance at least equal to Ds/2. The hyperelastic metal reinforcers of the hyperelastic radially outer hooping layer are a circumferential winding of a hyperelastic cord forming an angle of 0.5° with the circumferential direction. The radially innermost protective layer 311 projects axially beyond the working layer of greatest axial width, here the radially innermost working layer

321. In the case represented, the axial width LP1 is equal to 1.15 times the axial width LTmax. The hoop reinforcement 33 comprises two hooping layers 331, 332, the respective metal reinforcers of which, which are coated in an elastomeric material, are mutually parallel and form an angle of between 5° and 10 with the circumferential direction XX', are crossed from one hooping layer to the next.

[089] Figure 2 is a variant of the invention where the axially outermost axial end of the hyperelastic radially outer hooping layer (323) is axially outside the axial end of the working layer of greatest axial width (321), by a distance at least equal to Ds/2.

[090] Figure 3 is a variant of the invention where the axially outermost axial end of the hyperelastic radially outer hooping layer (323) is axially outside the axial end of the working layer of greatest axial width (321), by a distance at least equal to Ds/2 and the axial end of the protective layer of greatest axial width (311) is axially inside the axially innermost axial end of the hyperelastic radially outer hooping layer.

[091] Figure 4 illustrates the cords involved in the production of the reinforcing elements of the hyperelastic radially outer hooping layers either constituting the reinforcing elements, or being one of the cords of the strand which constitutes the reinforcing element of said hooping layer. The cord 50 according to the invention comprises a single layer 52 of metal filamentary elements 54 wound helically. In this instance, the cord 50 is made up of the single layer 52, in other words the cord 50 does not comprise any other metal filamentary element than those of the layer 52. The layer 52 consists of 9 metal filamentary elements wound in a helix and being embedded in the rubber compound matrix of the hyperelastic radially outer hooping layer, the internal enclosure 58 itself being filled with said rubber compound.

[092] The invention has been simulated on calculation tools and will be tested on tyres of size 24.00R35. The simulations make it possible to evaluate the mechanical and thermal stresses on tyres by the technique of finite elements under large movement and large deformation, taking into account the mechanical and hysteretic characteristics of the materials. The tyres are also compared in running tests on drums 22 m in circumference. The same test protocol is applied to the tyres according to the invention and to the reference tyres according to the prior art.

[093] A first test consists in running at a zero cornering angle at a load corresponding to the load index at the recommended pressure. The speed of the test is 30 km/h. The result of the test is the mileage of the tyre before its loss of pressure or delamination of the crown. This first test evaluates the endurance capacity of the crown to withstand the running cycles which generate a cyclic shearing stress on the region of the ends of the working layers with a high and increasing thermal stress which essentially stresses the rubber compounds in this region.

[094] A second test consists in running with transverse force imposed on the load corresponding to the load index at the recommended pressure. The transverse force is equal to 30% of the load, alternated over cycle times of 10 min. The speed of the test is 15 km/h. The result of the test is the mileage of the tyre before its loss of pressure or delamination of the crown. This test evaluates the endurance capacity of the crown to withstand running cycles under cornering which generate a high tensile/compressive cyclic stress on the region of the ends of the working layers with less thermal stress than the previous one, and thus more stress on the metal reinforcers.

[095] The reference tyres and those according to the invention are identical except for the crown reinforcement due to the presence of a hyperelastic radially outer hooping layer on the tyre according to the invention. They have the same tread pattern and the same reinforcers for the carcass layer (4), the hooping layers (331, 332), the working layers (321, 322) and the protective layers and the same rubber compounds for the different parts of the tyre.

[096] For the reference tyre, the crown reinforcement is composed radially from the outside towards the inside of two protective layers, two working layers and two hooping layers. The radially outermost protective layer is 400 mm wide, and its metal reinforcers make an angle with the circumferential direction of 24. The radially innermost protective layer is 520 mm wide, and its metal reinforcers make an angle with the circumferential direction of -24°. The radially outermost working layer is 380 mm wide, and its metal reinforcers make an angle with the circumferential direction of 190. The radially innermost working layer is 450 mm wide, and its metal reinforcers make an angle with the circumferential direction of 330. The radially outermost hooping layer is 200 mm wide, and its metal reinforcers make an angle with the circumferential direction of 80. The radially outermost hooping layer is 240 mm wide, and its metal reinforcers make an angle with the circumferential direction of -8°. The metal reinforcers of the working and hooping layers are inextensible 26.30 metal reinforcers, namely cords of 26 threads of 30 hundredths of a mmin diameter, arranged in three layers, the central layer comprising 3 threads, the second comprising 9 threads and the outer layer comprising 14 threads. Said strands are arranged at a pitch of 3.4 mm. The elastic metal reinforcers of the protective reinforcement of the reference tyre are 24.26 cords, namely strands of 4 cords 6 threads of 26 hundredths of a mm in diameter. Said strands are arranged at a pitch of 2.5 mm.

[097] The tyre according to the invention comprises, in addition to the crown reinforcement of the reference tyre, on either side of the equatorial plane, a hyperelastic radially outer hooping layer, the metal reinforcers of which are hyperelastic. On either side of the equatorial plane, the hyperelastic radially outer hooping layer has an axial width of 35 mm, equal to Ds, and is centred on the axial end of the radially outermost working layer which is also the working layer of smallest axial width.

[098] The hyperelastic metal reinforcers of the hyperelastic radially outer hooping layer of the tyre 1 according to the invention are 18.45, namely strands according to the invention, composed of 3 cords comprising 6 threads with a diameter Df of 45 hundredths of a mm. Said strands are arranged at a pitch of 4.8 mm. The enclosure diameter Dv of said threads is equal to 1.11 mm. The helix radius of curvature Rf is equal to 4.2 mm. Jr, the relative radial clearance between two adjacent filamentary elements, is equal to 0.35.

[099] The hyperelastic strands have a structural elongation As at least equal to 3% and a total elongation at break at least equal to 8%.

[0100] According to the finite element calculations, the tyre 1 according to the invention leads to a gain of about 15% in performance in mileage before tyre failure through the cracking of the rubber compounds around the axial ends of the working layers compared with the reference tyre. The invention as proposed therefore makes it possible to improve the endurance of the tyre.

Claims

1. Tyre (1) for a vehicle of the heavy-duty, construction plant or agricultural type, comprising: • a median circumferential plane, called the equatorial plane, perpendicular to the axis of rotation of the tyre and dividing the tyre into two substantially symmetrical half-torus shapes, * a crown reinforcement (3), radially on the inside of a tread (2) and radially on the outside

of a carcass reinforcement (4); • the crown reinforcement (3) comprising at least one working reinforcement (32), the crown reinforcement comprising at least two working layers (321, 322), one of greatest axial width (321) and one of smallest axial width (322), • each working layer (321, 322) comprising inextensible reinforcing elements parallel to one another, forming, with the circumferential direction, oriented angles at least equal to 150 and at most equal to 40°, the two angles of the two working layers being of opposite sign, * an axial distance Ds being the maximum value of the axial distances measured on either

side of the equatorial plane between the axial end of the working layer of smallest axial width (322) and the axial end of the working layer of greatest axial width (321), • the crown reinforcement comprising on either side of the equatorial plane at least one hooping layer (323) radially on the outside of the radially outermost working layer (321, 322), called the hyperelastic radially outer hooping layer, of which the axially outermost axial end is axially outside the axial end of the working layer of smallest axial width (322) by an axial distance at least equal to Ds/2 and of which the axially innermost point is axially inside the axial end of the working layer of smallest axial width (322), by an axial distance at least equal to Ds/2, * said hyperelastic radially outer hooping layer (323), on either side of the equatorial plane, comprising hyperelastic metal reinforcers, parallel to one another and forming, with a circumferential direction (XX') of the tyre, an angle at most equal to 5°, each hyperelastic metal reinforcer comprising at least one cord, called hyperelastic cord (50):

* characterized in that said hyperelastic cords (50) comprise a single layer (52) consisting of N metal filamentary elements (54) wound in a helix and having an external diameter D, each metal filamentary element (54) of the layer (52) describing, when the cord (50) extends in a substantially rectilinear direction, a trajectory in the form of a helix around a main axis (A) substantially parallel to the substantially rectilinear direction, so that, in a section plane substantially perpendicular to the main axis (A), the distance between the centre of each metal filamentary element (54) of the layer (52) and the main axis (A) is equal to half the helix diameter Dh and is substantially constant and equal for all the metal filamentary elements (54) of the layer (52), the metalfilamentary elements (54) defining an internal enclosure (58) of the cord of diameter Dv, each metal filamentary element (54) having a diameter Df and a helix radius of curvature Rf defined by Rf=P/(R x Sin(2a)) with P the pitch of each metal filamentary element expressed in millimetres and a the helix angle of each metalfilamentary element (54), characterized in that, with Dh, D, Dv, Df and Rf being expressed in millimetres: • 9SRf/DfS30,and • 1.30 < Dv / Df < 4.5,

* said hyperelastic cords being embedded in a rubber compound. 2. Tyre (1) according to Claim 1, in which the ratio K of the pitch P to the diameter Df of each metal filamentary element (54) of said hyperelastic cords is such that 19 < K < 44, preferably 20 < K < 40 and more preferably 23 < K < 39, P and Df being expressed in millimetres. 3. Tyre (1) according to one of Claims 1 or 2, in which there is a relative radial clearance, Jr, between two adjacent filamentary elements of said hyperelastic cords, Jr =N/(*(D Df)) x (Dh x Sin(7/N) - (Df / Cos(a x /180))), a being the helix angle, expressed in degrees, of each metal filamentary element (54) and Dv=Dh-Df, and Jr of the elastic metal reinforcers of the hooping layer (311) being such that 0.10 < Jr < 0.6. 4. Tyre (1) according to any one of the preceding claims, in which each hyperelastic metal reinforcer of said hyperelastic radially outer hooping layer (323) is a hyperelastic cord. 5. Tyre (1) according to any one of Claims I to 3, in which each hyperelastic metal reinforcer of said hyperelastic radially outer hooping layer (323) is a strand of hyperelastic cords.

6. Tyre (1) according to any one of the preceding claims, in which the hyperelastic metal reinforcers of said hyperelastic radially outer hooping layer (323) have a secant modulus at 2% elongation at most equal to 80 GPa and an elongation at break at least equal to 4%.

7. Tyre (1) according to any one of the preceding claims, in which the hyperelastic metal reinforcers of said hyperelastic radially outer hooping layer (323) have a compression buckling deformation value at least equal to 2%.

8. Tyre (1) according to any one of the preceding claims, in which on either side of the equatorial plane, the hyperelastic radially outer hooping layer (323) is formed by the circumferential winding of a strip made up of a plurality of hyperelastic metal reinforcers.

9. Tyre (1) according to any one of the preceding claims, in which on either side of the equatorial plane, the axially outermost axial end of the hyperelastic radially outer hooping layer (323) is axially outside the axial end of the working layer of greatest axial width (321), by a distance at least equal to Ds/2.

10. Tyre (1) according to any one of the preceding claims, comprising a protective reinforcement (31) radially outside the working reinforcement (32), comprising at least one protective layer (311, 312), in which the radially innermost protective layer (311) has an axial width LP1 at least equal to 1.05 times and at most equal to 1.25 times the maximum axial width LTmax of the working layer with the greatest axial width (321).

11. Tyre (1) according to any one of Claims 1 to 9, comprising a protective reinforcement (31) radially outside the working reinforcement (32), comprising at least one protective layer (311, 312), said tyre comprising, on either side of the equatorial plane, a hyperelastic radially outer hooping layer (323) comprising an axially inner end, in which on either side of the equatorial plane, the axial end of the protective layer of greatest axial width (311) is axially inside the axially innermost axial end of the hyperelastic radially outer hooping layer (323).