PNEUMATIC TIRE FEATURING A CARCASS REINFORCEMENT MADE OF LOW PERMEABILITY METAL CABLES

Abstract

The invention relates to a tire (1) with a radial carcass reinforcement (2), consisting of at least one layer of metallic reinforcing elements, said tire comprising a crown reinforcement (5), itself radially capped by a tread (6), said tread being joined to two beads (3) by means of two sidewalls. According to the invention, the reinforcing elements of at least one layer of the carcass reinforcement are metallic cables (21) exhibiting, in the so-called permeability test, an average flow rate of between 1 and 7 cm³ / min, and the maximum difference in flow rate, measured according to the permeability test carried out according to ASTM D2692-98, between two average flow rate measurements on sampling areas of said reinforcing elements distributed along the length of said reinforcing elements is less than 5 cm³ / min. Figure for the abstract: Fig 2

Description

Title of the invention: TIRE COMPRISING A CARCASS REINFORCEMENT MADE OF ME CABLES LOW PERMEABILITY TALLICS

[0001] The present invention relates to a tire, with a radial carcass reinforcement and more particularly to a tire intended to equip vehicles carrying heavy loads and traveling at sustained speed, such as, for example, trucks, tractors, trailers or road buses.

[0002] Generally, in heavy-duty tires, the carcass reinforcement is anchored on both sides in the bead area and is radially surmounted by a crown reinforcement consisting of at least two superimposed layers formed of parallel wires or cables in each layer and crossed from one layer to the next at angles between 10° and 45° with the circumferential direction. These working layers, forming the working reinforcement, may also be covered by at least one protective layer formed of advantageously metallic and extensible reinforcing elements, known as elastic elements.It may also include a layer of low-extensibility wires or cables forming an angle of between 45° and 90° with the circumferential direction. This layer, known as the triangulation layer, is radially positioned between the carcass reinforcement and the first crown layer, known as the working layer, which is formed of parallel wires or cables having angles of no more than 45° in absolute value. The triangulation layer, together with at least the aforementioned working layer, forms a triangulated reinforcement which exhibits little deformation under the various stresses it is subjected to. The essential role of the triangulation layer is to resist the transverse compression forces exerted on all the reinforcing elements in the crown area of ​​the tire.

[0003] In the case of tires for "Heavy Goods Vehicles", a single protective layer is usually present, and its protective elements are, in most cases, oriented in the same direction and at the same absolute angle as those of the reinforcing elements of the outermost, and therefore radially adjacent, working layer. In the case of off-road tires intended for use on more or less uneven terrain, the presence of two protective layers is advantageous, the reinforcing elements being intersected from one layer to the next, and the reinforcing elements of the inner radial protective layer being intersected with the inextensible reinforcing elements of the outermost, radially adjacent working layer. dialement interne.

[0004] The circumferential direction of the tire, or longitudinal direction, is the direction corresponding to the periphery of the tire and defined by the rolling direction of the tire.

[0005] The transverse or axial direction of the tire is parallel to the axis of rotation of the tire.

[0006] The radial direction is a direction intersecting the axis of rotation of the tire and perpendicular to it.

[0007] The axis of rotation of the tire is the axis around which it rotates in normal use.

[0008] A radial or meridian plane is a plane that contains the axis of rotation of the tire.

[0009] The circumferential median plane, or equatorial plane, is a plane perpendicular to the axis of rotation of the tire and which divides the tire into two halves.

[0010] Some current tires, known as "road" tires, are designed for high-speed driving and increasingly long journeys, due to improvements in the road network and the growth of the motorway network worldwide. The overall conditions under which such a tire is expected to operate undoubtedly allow for an increase in the number of kilometers traveled, as tire wear is reduced; however, its durability is compromised. To allow for one or even two retreadings of such tires in order to extend their lifespan, it is necessary to maintain a structure, and in particular a carcass reinforcement, whose durability properties are sufficient to withstand these retreadings.

[0011] Prolonged driving under particularly severe conditions of tires thus constructed does indeed reveal limits in terms of the endurance of these tires.

[0012] The carcass reinforcement elements are subjected to bending and compression stresses during rolling, which are detrimental to their durability. The cords that constitute the reinforcement elements of the carcass layers are indeed subjected to significant stresses during tire rolling, particularly repeated bending or changes in curvature, inducing friction at the cord level, and therefore wear, as well as fatigue; this phenomenon is known as "fatigue-fretting".

[0013] To fulfill their function of reinforcing the carcass reinforcement of the tire, said cables must first of all exhibit good flexibility and high endurance in bending, which implies in particular that their wires have a relatively small diameter, preferably less than 0.28 mm, more preferably less than 0.25 mm, generally smaller than that of the wires used in conventional cables for the crown reinforcements of tires.

[0014] The carcass reinforcement cables are also subject to so-called "fatigue-corrosion" phenomena due to the very nature of the cables, which facilitate the passage or even the drainage of corrosive agents such as oxygen and moisture. Indeed, air or water that penetrates the tire, for example during damage from a cut or simply due to the permeability, however low, of the tire's inner surface, can be conducted through the channels formed within the cables by virtue of their structure.

[0015] All these fatigue phenomena, which are generally grouped under the generic term "fatigue-fretting-corrosion", cause a progressive degeneration of the mechanical properties of the cables and can affect their lifespan under the most severe rolling conditions.

[0016] To improve the durability of these carcass reinforcement cords, it is known to increase the thickness of the rubber layer that forms the inner wall of the tire cavity in order to minimize the permeability of said layer. This layer is usually partly composed of butyl in order to increase the tire's airtightness. This type of material has the disadvantage of increasing the cost of the tire.

[0017] It is also known to modify the construction of said cables in order in particular to increase their penetration by the rubber, and thus limit or even eliminate the passage of oxidizing agents through the channels formed within the cables.

[0018] It is also known in particular from document EP 1699973 Al of three-layer cable constructions during the manufacture of which a layer of rubbery mixture is deposited around the intermediate layer to plug the gaps between all the metal wires constituting this cable.

[0019] Tires made with such cables have, however, highlighted problems of air pocket formation during tire manufacturing.

[0020] Indeed, the various manufacturing stages lead to the formation of occluded air pockets. In the case of tires with a carcass reinforcement made of cords whose structure forms channels capable of conducting air, these air pockets disappear due to the diffusion of air into the materials, particularly through said channels existing within the cords. In the case of tires with a carcass reinforcement made of cords whose structure is heavily penetrated by the rubber, or of cords into which the rubber is introduced during the cord manufacturing process itself, these air pockets remain after the manufacturing stages. Only a displacement of these air pockets occurs during the tire curing stage, as they are moved towards areas where low pressure is exerted.Air movement occurs along the frame structure following existing passages between the reinforcing elements, the layers of rubber mixture. A layer of reinforcing material covering the reinforcement elements forms recessed areas parallel to the reinforcement elements before the tire curing stage. These recessed areas allow air to move slightly depending on the pressure exerted on the regions where the air pockets are located. Pressure or pressure variations occur particularly during the tire curing stage or during the shaping stage, if one exists.

[0021] The appearance of these air pockets is most often a deal-breaker depending on their location and may necessitate the disposal of the tires, as they can become areas of weakness in the tire. Manufacturing costs then become unacceptable simply due to poor production yields.

[0022] The inventors have thus set themselves the task of providing tires for heavy vehicles of the "Heavy Goods Vehicle" type, whose endurance performance is improved in particular with regard to the phenomena of "fatigue-corrosion" or "fatigue-fretting-corrosion", whatever the driving conditions in particular in terms of inflation and whose manufacturing cost remains acceptable.

[0023] This goal has been achieved according to the invention by a tire with a radial carcass reinforcement, consisting of at least one layer of reinforcing elements, said tire comprising a crown reinforcement, itself radially capped with a tread, said tread being joined to two beads by means of two sidewalls, the reinforcing elements of at least one layer of the carcass reinforcement being metal cables exhibiting in the so-called permeability test an average flow rate of between 1 and 7 cmVmin and, the maximum difference in flow rate, measured according to the permeability test carried out according to ASTM D2692-98, between two average flow rate measurements on sampling areas of said reinforcing elements distributed over the length of said reinforcing elements being less than 5 cmVmin.

[0024] The so-called permeability test determines the longitudinal air permeability of the tested cables by measuring the volume of air passing through a test specimen under constant pressure over a given time. The principle of such a test, well known to those skilled in the art, is to demonstrate the effectiveness of a cable treatment to make it airtight; it has been described, for example, in ASTM D2692-98 and STP694-1978.

[0025] The test is carried out on cables extracted directly, by peeling, from the vulcanized rubber sheets which they reinforce, therefore penetrated by the cooked rubber.

[0026] The test is carried out on a 2 cm length of cable, therefore coated by its surrounding rubber composition (or coating rubber) in the cooked state, as follows: air is sent to the inlet of the cable, under a pressure of 1 bar, and the volume of air at the outlet is measured, using a flow meter (calibrated for example from 0 to 500 cm3 / min). During the measurement, the cable sample is blocked in a compressed airtight seal (for example a dense foam or rubber seal) in such a way that only the amount of air passing through the cable from one end to the other, along its longitudinal axis, is taken into account by the measurement; the tightness of the airtight seal itself is checked beforehand using a solid rubber test piece, i.e. without cable.

[0027] The measured airflow rate is lower the higher the longitudinal impermeability of the cable. Since the measurement is made with an accuracy of ± 0.2 cmVmin, measured values ​​less than or equal to 0.2 cmVmin are considered to be zero; they correspond to a cable that can be described as airtight (completely airtight) along its axis (i.e., in its longitudinal direction).

[0028] This permeability test also provides a simple means of indirectly measuring the penetration rate of the cable by a rubber compound. The measured flow rate is lower the higher the penetration rate of the cable by the rubber.

[0029] Cables exhibiting a flow rate of less than 10 cm3 / min in the so-called permeability test have a penetration rate greater than 66%.

[0030] Cables exhibiting a flow rate of less than 2 cm3 / min in the so-called permeability test have a penetration rate greater than 90%.

[0031] The average yield of reinforcement elements in at least one layer of the carcass reinforcement is the result of 70 measurements taken on 10 cables taken from a tire. First, four tire sectors with a circumferential length between 10 and 15 centimeters are cut along radial planes. These four sectors are centered on radial planes spaced every 90° along the tire's rotation. Cables are taken from each of these sectors at a rate of two or three per sector.

[0032] On each of the cables, the so-called permeability test is carried out as described above. The seven sampling zones of the two centimeters of cables are distributed as follows: a first sampling corresponds to a position centered on the circumferential median plane, two second samplings correspond to positions, on either side of the circumferential plane, centered on the intersection of a radial line, passing through an outermost end of the top reinforcement, and the carcass reinforcement layer, two third samplings correspond to positions, on either side of the circumferential plane, centered on the intersection of an axial line, passing through the end of the turn of the carcass reinforcement layer, and the carcass reinforcement layer.The two fourth samples are, on either side of the circumferential median plane, centered on a point of the carcass frame located radially at mid-distance between the centers of the samples of a second and a third sample.

[0033] The maximum difference in flow rate between two average flow rate measurements, each average being established in each of the seven sampling zones as defined above, is the maximum observable difference between any two of the seven average flow rate measurements. Each of the seven average flow rate measurements is established on the basis of ten measurements taken on each of the ten cables described above.

[0034] To establish this maximum difference in flow rate between two average flow rate measurements, we begin by calculating an average of the flow rates measured in each of the seven sampling zones. Each of these average flow rate measurements is the average of ten flow rate measurements taken in the same sampling zone across the ten cables. From these seven average flow rate measurements, defined for each sampling zone, we determine the maximum difference between any two of these seven average flow rate measurements.

[0035] The inventors have demonstrated that a tire manufactured according to the invention leads to very significant improvements in terms of the trade-off between durability and manufacturing costs. Indeed, the durability properties of such a tire are lower than those of tires whose three-layer carcass cords have a layer of rubber compound deposited around the intermediate layer, but higher than those of more conventional cords, i.e., those not having a rubber layer applied during cord manufacturing, which are more susceptible to corrosion. The presence of metallic cords exhibiting an average flow rate of between 1 and 7 cmVmin in at least one layer of the carcass cord in the so-called permeability test helps to limit the risks associated with corrosion.Furthermore, the permeability test measurement of the maximum flow difference between two average flow measurements taken from sampling points on the reinforcement elements, distributed along their length and less than 5 cmVmin, indicates the presence of an incomplete but relatively homogeneous rubber compound within the cables. This suggests the presence of a rubber compound within the metallic cables, leaving gaps that allow for the circulation, or at least the temporary storage, of air, particularly during tire manufacturing.The inventors demonstrated that the presence of these spaces within the cords not filled with rubber compound allows for the drainage of air trapped during tire manufacturing, thus leading to better production quality than that previously observed with tires whose three-layer carcass cords have a layer of rubber compound deposited around the intermediate layer, and therefore at a lower cost. The tests carried out confirmed these results. The performance of tires using such metal cables according to the invention in at least one layer of the carcass reinforcement is incomparable to that obtained with carcass reinforcement layers made of cables such as those mentioned previously, in which a layer of rubber compound is deposited around the intermediate layer of a three-layer cable to fill the gaps between all the metal wires constituting that cable. Indeed, the production of tires according to the invention has made it possible to retain almost all of the tires manufactured in this way and thus reduce the unit manufacturing cost to acceptable levels.

[0036] The inventors have further demonstrated that, compared with metal cables, also mentioned previously, which are designed to increase their penetration by rubber, and thus limit or even eliminate the passage of oxidizing agents through the channels formed within the cables, the tires according to the invention lead to superior endurance performance.

[0037] In the case of a carcass reinforcement comprising several layers of reinforcing elements, each of said layers may conform to the invention. Advantageously, according to the invention, the reinforcing elements of at least the outermost radial layer of the carcass reinforcement are metallic cables exhibiting, in the so-called permeability test, an average flow rate of between 1 and 7 cmVmin, and the maximum difference in flow rate, measured according to the permeability test performed according to ASTM D2692-98, between two average flow rate measurements on sampling areas of said reinforcing elements distributed along the length of said reinforcing elements is less than 5 cmVmin. This choice is particularly advantageous for ensuring complete evacuation of air pockets that form during tire manufacturing, these appearing primarily on the outermost axial and / or radial surface of the carcass reinforcement during manufacturing..

[0038] Preferably according to the invention, said reinforcement elements of at least one layer of the carcass reinforcement are metal cables exhibiting, in the so-called permeability test, an average flow rate greater than 2 cmVmin. Such average flow rate values ​​of the reinforcement elements further improve the evacuation of air pockets during tire manufacturing.

[0039] Preferably, according to the invention, said reinforcement elements of at least one layer of the carcass reinforcement are metal cables exhibiting, in the so-called permeability test, an average flow rate less than or equal to 5.5 cmVmin. Such average flow rate values ​​of the reinforcement elements further improve the tire's performance in terms of durability.

[0040] According to an advantageous embodiment of the invention, in a meridional cross-section of the tire, the maximum flow difference, measured according to the permeability test Performed according to ASTM D2692-98, the average flow rate between two measurements taken from sampling points on said reinforcement elements, distributed along the length of said reinforcement elements, is less than or equal to 3.5 cmVmin. Such values ​​indicate an even more homogeneous distribution of the rubber compound within the cables.

[0041] According to a preferred embodiment of the invention, the reinforcement elements of said at least one carcass reinforcement layer are three-layer metal cables, the inner layer of said three-layer cables being sheathed with a layer made of a polymeric composition such as a non-crosslinkable, crosslinkable or crosslinked rubber composition, preferably based on at least one diene elastomer.

[0042] According to an advantageous embodiment of the invention, to further improve the tire's endurance performance and, more specifically, to further limit the risk of oxidation of the reinforcement elements of the carcass reinforcement layer, at least the wires constituting the intermediate layer of a three-layer cord are zinc-coated. The wires of the third layer are advantageously coated with brass to facilitate bonding with the rubber compounds of the calendered layers forming the carcass reinforcement layer. Advantageously still according to the invention, the wire(s) of the first layer of the reinforcement elements of the carcass reinforcement layer are also brass-coated.

[0043] By the expression "composition based on at least one diene elastomer", it is understood in a known way that the composition comprises in a major proportion (i.e. according to a mass fraction greater than 50%) this or these diene elastomers.

[0044] It will be noted that the sheath according to the invention extends continuously around the layer it covers (that is to say that this sheath is continuous in the "orthoradial" direction of the cable which is perpendicular to its radius), so as to form a continuous sleeve of cross-section which is advantageously practically circular.

[0045] It should also be noted that when the rubber composition of this sheath is crosslinkable or crosslinked, it includes by definition a crosslinking system adapted to allow the crosslinking of the composition during its cooking (i.e., its hardening and not its melting); thus, this rubber composition can be described as infusible, since it cannot be melted by heating at any temperature.

[0046] By "diene" elastomer or rubber, we understand in a known way an elastomer derived at least in part (i.e. a homopolymer or a copolymer) from diene monomers (monomers bearing two carbon-carbon double bonds, conjugated or not).

[0047] Diene elastomers can be classified in a known manner into two categories: those called "essentially unsaturated" and those called "essentially saturated". Generally speaking, an "essentially unsaturated" diene elastomer is understood here to be a diene elastomer derived at least in part from conjugated diene monomers, having a proportion of diene motifs or units (conjugated dienes) greater than 15% (mole percent). Thus, for example, diene elastomers such as butyl rubbers or diene-alpha-olefin copolymers of the EPDM type do not fall under the preceding definition and can, in particular, be described as "essentially saturated" diene elastomers (low or very low proportion of diene motifs, always less than 15%).In the category of "essentially unsaturated" diene elastomers, a "highly unsaturated" diene elastomer is defined in particular as a diene elastomer having a proportion of diene-derived motifs (conjugated dienes) greater than 50%.

[0048] Having given these definitions, the term "diene elastomer capable of being used in the cable of the invention" refers more specifically to: (a) any homopolymer obtained by polymerization of a conjugated diene monomer having from 4 to 12 carbon atoms; (b) any copolymer obtained by copolymerization of one or more dienes conjugated together or with one or more aromatic vinyl compounds having from 8 to 20 carbon atoms; (c) a ternary copolymer obtained by copolymerization of ethylene, of an α-olefin having 3 to 6 carbon atoms with an unconjugated diene monomer having 6 to 12 carbon atoms, such as, for example, elastomers obtained from ethylene, propylene with an unconjugated diene monomer of the aforementioned type such as, in particular, hexadiene-1,4, ethylidene norbomene, dicyclopentadiene; (d) a copolymer of isobutene and isoprene (butyl rubber), as well as halogenated versions, in particular chlorinated or brominated, of this type of copolymer.

[0049] Although applicable to any type of diene elastomer, the present invention is primarily implemented with essentially unsaturated diene elastomers, in particular of type (a) or (b) above.

[0050] Thus, the diene elastomer is preferentially chosen from the group consisting of polybutadienes (BR), natural rubber (NR), synthetic polyisoprenes (IR), various butadiene copolymers, various isoprene copolymers, and mixtures of these elastomers. Such copolymers are more preferentially chosen from the group consisting of butadiene-styrene copolymers (SBR), isoprene-butadiene copolymers (BIR), isoprene-styrene copolymers (SIR), and isoprene-butadiene-styrene copolymers (SBIR).

[0051] Preferably, according to the invention, the chosen diene elastomer is majori tarily (i.e. for more than 50 pc) made of an isoprene elastomer. By "isoprene elastomer", we mean in a known way a homopolymer or a copolymer of isoprene, in other words a diene elastomer chosen from the group consisting of natural rubber (NR), synthetic polyisoprenes (IR), the various isoprene copolymers and mixtures of these elastomers.

[0052] According to an advantageous embodiment of the invention, the chosen diene elastomer is exclusively (i.e. per 100 pc) made up of natural rubber, synthetic polyisoprene or a mixture of these elastomers, the synthetic polyisoprene having a cis-1,4 bond ratio (molar %) preferably greater than 90%, more preferably greater than 98%.

[0053] According to a particular embodiment of the invention, blends (mixtures) of this natural rubber and / or these synthetic polyisoprenes could also be used with other highly unsaturated diene elastomers, in particular with SBR or BR elastomers as mentioned above.

[0054] The rubber sheath of the cable of the invention may contain one or more diene elastomer(s), the latter being able to be used in association with any type of synthetic elastomer other than diene, or even with polymers other than elastomers, for example thermoplastic polymers, these non-elastomer polymers then being present as a minor polymer.

[0055] Although the rubber composition of said sheath is preferably devoid of any plastomer and comprises only a diene elastomer (or mixture of elastomers) as a polymeric base, said composition could also comprise at least one plastomer in a mass fraction xp less than the mass fraction xe of the elastomer(s). In such a case, the following relationship preferably holds: 0 < xp < 0.5 xe, and more preferably: 0 < xp < 0.1 xe.

[0056] Preferably, the crosslinking system for the rubber sheath is a so-called vulcanization system, i.e., based on sulfur (or a sulfur-donating agent) and a primary vulcanization accelerator. Various known secondary accelerators or vulcanization activators can be added to this basic vulcanization system. Sulfur is used at a preferential rate of between 0.5 and 10 parts per million (ppm), more preferably between 1 and 8 ppm. The primary vulcanization accelerator, for example a sulfenamide, is used at a preferential rate of between 0.5 and 10 ppm, more preferably between 0.5 and 5.0 ppm.

[0057] The rubber composition of the sheath according to the invention comprises, in addition to said crosslinking system, all the usual ingredients usable in tire rubber compositions, such as reinforcing fillers based on carbon black and / or an inorganic reinforcing filler such as silica, anti-aging agents, for example antioxidants, extending oils, plasticizers or agents facilitating the implementation of raw compositions, methylene acceptors and donors, resins, bismaleimides, known adhesion-promoting systems of the "RFS" (resorcinol-formaldehyde-silica) type or metallic salts, including cobalt salts.

[0058] Preferably, the composition of this sheath is chosen to be identical to the composition used for the rubber matrix that the cables according to the invention are intended to reinforce. Thus, there is no problem of potential incompatibility between the respective materials of the sheath and the rubber matrix.

[0059] Preferably, said composition is based on natural rubber and includes carbon black as a reinforcing filler, for example a carbon black of grade (ASTM) 300, 600 or 700 (for example N326, N330, N347, N375, N683, N772).

[0060] According to a variant of the invention, said metallic reinforcement elements of at least one layer of the carcass reinforcement are metal cables with construction layers [L+M+N], comprising a first layer Cl of L wires of diameter di with L ranging from 1 to 4, surrounded by at least one intermediate layer C2 of M wires of diameter d2 wound together in a helix with a pitch p2 with M ranging from 3 to 12, said layer C2 being surrounded by an outer layer C3 of N wires of diameter d3 wound together in a helix with a pitch p3 with N ranging from 8 to 20, and a sheath made of a non-crosslinkable, crosslinkable or crosslinked rubber composition based on at least one diene elastomer, covers said first layer Cl.

[0061] Preferably, the diameter of the wires of the first layer (Cl) is between 0.10 and 0.5 mm and the diameter of the wires of the intermediate (C2) and outer (C3) layers is between 0.10 and 0.5 mm.

[0062] Preferably, the helix pitch of winding said wires of the outer layer (C3) is between 8 and 25 mm.

[0063] For the purposes of the invention, the pitch represents the length, measured parallel to the axis of the cable, at the end of which a wire having this pitch makes a complete turn around the axis of the cable; thus, if the axis is cut by two planes perpendicular to said axis and separated by a length equal to the pitch of a wire of a constituent layer of the cable, the axis of this wire has in these two planes the same position on the two circles corresponding to the layer of the wire considered.

[0064] Advantageously, layer C3 is a saturated layer, that is to say, there is not enough space in this layer to add at least one (N+1)th wire of diameter d3, N then representing the maximum number of wires that can be wound in a layer around layer C2.

[0065] Advantageously, the intermediate layer C2 preferably comprises six or seven wires, and the cable according to the invention then has the following preferred characteristics (db d2, d3, p2 and p3 in mm): - (i) 0.10 <d1<0,28 ; - (ii) 0.10 <d2< 0,25 ; - (iii) 0.10 <d3< 0,25 ; - (iv) M = 6 or M = 7; - (v) 5 Jt (d^ d2) < p2 < p3 < 5 ir (d^ 2d2 + d3); - (vi) the yarns of said layers C2, C3 are wound in the same direction of twist (S / S or Z / Z).

[0066] Preferably, the characteristic (v) is such that p2 = p3, so that the cable is said to be compact taking into account the characteristic (vi) (wires of layers C2 and C3 wound in the same direction).

[0067] According to feature (vi), all the wires in layers C2 and C3 are wound in the same direction of twist, that is, either in the S direction (arrangement "S / S") or in the Z direction (arrangement "Z / Z"). Winding layers C2 and C3 in the same direction advantageously minimizes friction between these two layers C2 and C3 in the cable according to the invention, and therefore the wear of the wires that constitute them (since there is no longer any cross-contact between the wires).

[0068] Preferably, said metallic reinforcing elements of at least one layer of the carcass reinforcement are cables with construction layers noted 1+M+N, that is to say that the inner layer Cl consists of a single wire.

[0069] Advantageously still, the ratios (di / d2) are preferably fixed within given limits, according to the number M (6 or 7) of wires in layer C2, as follows: for M = 6: 0.9 < (di / d2) < 1.3; for M = 7: 1.3 < (di / d2) < 1.6.

[0070] Too low a value for the d / d2 ratio can be detrimental to wear between the inner layer and the wires of layer C2. Too high a value can, on the other hand, impair the compactness of the cable, for a level of resistance that is ultimately little modified, as well as its flexibility; the increased rigidity of the inner layer Cl due to an excessively large diameter di could also be detrimental to the very feasibility of the cable during cabling operations.

[0071] The wires in layers C2 and C3 may have the same or different diameters from one layer to the other. Wires of the same diameter (d2=d3) are preferably used, particularly to simplify the wiring process and reduce costs.

[0072] The maximum number Nmax of wires that can be wound in a single saturated layer C3 around the layer C2 is of course a function of many parameters (diameter di of the inner layer, number M and diameter d2 of the wires of the layer C2, diameter d3 of the wires of the layer C3).

[0073] Said metallic reinforcing elements of at least one layer of the frame reinforcement are preferably chosen from structural cables 1+6+10, 1+6+11, 1+6+12, 1+7+11, 1+7+12 or 1+7+13.

[0074] For a better compromise between resistance, feasibility and flexural strength of the cable, on the one hand, and penetration by the rubber, on the other hand, it is preferable that the diameters of the wires of layers C2 and C3, identical or not, be between 0.12 mm and 0.22 mm.

[0075] In such a case, the following relations are more preferably verified: 0.14 <d!< 0,22; 0.12 < d2 < d3 < 0.20; 5 < p2 < p3 < 12 (reduced mm pitch) or 20 < p2 < p3 < 30 (large mm pitch).

[0076] A diameter less than 0.19 mm reduces the stress experienced by the wires during significant cable bending, whereas diameters greater than 0.16 mm are preferred, particularly for reasons of wire strength and industrial cost.

[0077] An advantageous embodiment consists for example of choosing p2 and p3 between 8 and 12 mm, advantageously with 1+6+12 structural cables.

[0078] Generally speaking, said metallic reinforcing elements of at least one layer of the frame reinforcement according to the invention can be made of any type of metal wire, in particular steel, for example carbon steel wire and / or stainless steel wire. Carbon steel is preferably used, but it is of course possible to use other steels or other alloys.

[0079] When a carbon steel is used, its carbon content (% by weight of steel) is preferably between 0.1% and 1.2%, more preferably between 0.4% and 1.0%; these contents represent a good compromise between the mechanical properties required for pneumatics and the feasibility of the wire. It should be noted that a carbon content between 0.5% and 0.6% makes such steels ultimately less expensive because they are easier to draw. Another advantageous embodiment of the invention may also consist, depending on the intended applications, of using low-carbon steels, for example between 0.2% and 0.5%, due in particular to a lower cost and greater ease of drawing.

[0080] Said metallic reinforcement elements of at least one layer of the carcass reinforcement according to the invention may be obtained according to different techniques known to the person skilled in the art, for example in four steps, firstly a first operation of cabling or twisting of the first layer Cl consisting of L wires, then a second step of sheathing via an extrusion head of the layer Cl, followed in a third step by an operation of cabling or twisting the M wires of the layer C2 around the layer Cl thus sheathed and finally a fourth step of cabling or twisting the N wires of the layer C3 around the layer C2.

[0081] Preferably, according to the invention, said layer, consisting of a polymeric composition sheathing the first layer of said three-layer cables, has, particularly in the case of a first layer of the three-layer cable made of a single wire, a thickness of less than 50 microns. Such a thickness of the layer consisting of a polymeric composition sheathing the first layer promotes the preservation of free space within the cables.

[0082] Preferably also according to the invention, said layer, consisting of a polymeric composition sheathing the first layer of said three-layer cables, has a thickness greater than 30 microns. A thinner sheath made of a polymeric composition is insufficient to observe a significant effect on the tire's endurance performance.

[0083] According to one embodiment of the invention, the crown reinforcement of the tire is formed of at least two working crown layers of inextensible reinforcing elements, crossed from one layer to the other making angles with the circumferential direction between 10° and 45°.

[0084] According to other embodiments of the invention, the top reinforcement also includes at least one layer of circumferential reinforcing elements.

[0085] A preferred embodiment of the invention further provides that the top reinforcement is completed radially on the outside by at least one additional layer, called a protective layer, of so-called elastic reinforcing elements, oriented with respect to the circumferential direction with an angle between 10° and 45° and in the same direction as the angle formed by the inextensible elements of the working layer which is radially adjacent to it.

[0086] According to any one of the embodiments of the invention mentioned above, the top reinforcement can be further completed, radially inside between the carcass reinforcement and the radially inner working layer closest to said carcass reinforcement, by a triangulation layer of inextensible metallic steel reinforcing elements making, with the circumferential direction, an angle greater than 60° and in the same direction as that of the angle formed by the reinforcing elements of the layer radially closest to the carcass reinforcement.

[0087] Other advantageous details and features of the invention will become apparent from the description of the exemplary embodiments of the invention with reference to Figures 1 to 4, which represent: - [Fig. 1], a meridian view of a diagram of a tire according to an embodiment of the invention, - [Fig.2], a schematic representation of a cross-sectional view of an example of a cable of at least one layer of the carcass reinforcement of the tire of [Fig.1], - [Fig. 3], a schematic representation of a cross-sectional view of a second cable of reference, - [Fig.4], a schematic representation of a cross-sectional view of a third reference cable.

[0088] The figures are not shown to scale to simplify understanding.

[0089] In [Fig. 1], the tire 1, size 315 / 80 R 22.5, comprises a Radial carcass reinforcement 2 anchored in two ridges 3, around rods 4. The carcass reinforcement 2 is formed of a single layer of wire cables. The carcass reinforcement 2 is bounded by a top reinforcement 5, itself capped with a tread 6. The top reinforcement 5 is formed radially from the inside out: - a first working layer made of inextensible 9.35 unfretted metal cables, continuous across the entire width of the layer, oriented at an angle of 26°, - a second working layer formed of inextensible 9.35 non-fretched metal cables, continuous across the entire width of the layer, oriented at an angle of 18° and crossed with the metal cables of the first working layer, - a protective layer made of 6x35 elastic metal cables.

[0090] The entirety of these layers constituting the vertex 5 reinforcement is not shown in detail in the figures.

[0091] Figure 2 illustrates a schematic representation of the cross-section of a carcass reinforcement cable 21 of the tire 1 of Figure 1. This cable 21 is a 1+6+12 structure layer cable, not crimped, consisting of a first layer formed of one wire 22, an intermediate layer formed of six wires 23 and an outer layer formed of twelve wires 24.

[0092] It has the following characteristics (d and p in mm): - structure 1+6+12; - di = 0.20 (mm); - d2 = 0.18 (mm); - p2 = 10 (mm) - d3 = 0.18 (mm); - p3 = 10 (mm), -(d2 / d3)=l; with d2, p2, respectively the diameter and helix pitch of the intermediate layer and d3 and p3, respectively the diameter and helix pitch of the wires of the outer layer.

[0093] The first layer formed by the wire 22 is sheathed by a rubber composition 25 based on unvulcanized diene elastomer (in its raw state). The sheathing is obtained via an extrusion head of the core formed by the wire 22, followed by twisting or cabling operations of the six wires 23, of the intermediate layer, and the 12 wires 24, of the outer layer, around the sheathed wire 22. The layer of rubbery mixture that surrounds wire 22 has a thickness of 42 microns.

[0094] The cable 21 has a diameter of 0.9 mm.

[0095] The elastomeric composition constituting the rubber sheath 25 is made from a composition as described above and in this case has the same formulation, based on natural rubber and carbon black, as that of the calendering layers of the carcass reinforcement which the cables are intended to reinforce.

[0096] Tests were carried out with tires made according to the invention in accordance with the representation in Figures 1 and 2 and others with so-called reference tires.

[0097] Some initial reference tires, not shown in the figures, differ from the tires according to the invention by a carcass reinforcement whose reinforcing elements are cables such as those shown in [Fig.2] but which do not have a sheathing layer.

[0098] Second reference tires differ from the tires according to the invention by a carcass reinforcement whose reinforcing elements are cables 31 such as those shown in [Fig.3], identical to the cables of [Fig.2] but which have a sheathing layer 35 surrounding the central core of the cable formed by the wire 32 and the intermediate layer formed by six wires 33.

[0099] Third reference tires differ from the tires according to the invention by a carcass reinforcement whose reinforcing elements are cables 41 such as those shown in [Fig. 4]. This cable 41 is a 1+6+11 structure layer cable, not coiled, consisting of a first layer formed of one wire 42, an intermediate layer formed of six wires 43 and an outer layer formed of eleven wires 44.

[0100] It has the following characteristics (d and p in mm): - structure 1+6+11; - di = 0.20 (mm); - d2 = 0.18 (mm); - p2 = 7 (mm) - d3 = 0.18 (mm); - p3 = 10 (mm), - (d^ d2) — 1.11; with d2, p2, respectively the diameter and helix pitch of the intermediate layer and d3 and p3, respectively the diameter and helix pitch of the wires of the outer layer.

[0101] The wires 43 and 44 wound around the wire 42 are arranged in two adjacent and concentric, tubular layers (a first layer of thickness substantially equal to d2, then an outer layer of thickness substantially equal to d3).

[0102] During the manufacture of these tires, only some of the second reference tires, i.e. those having a sheathing layer in a rubber compound placed around the intermediate layer of the cable, have appearance defects due to air pockets trapped during manufacturing which require these tires to be discarded.

[0103] None of the other tires, whether the tires according to the invention or the first and third reference tires, have any appearance defect attributable to the presence of air or moisture.

[0104] Flow measurements, carried out in accordance with the permeability test described above, are performed on the cords of the carcass reinforcement layer of the tires according to the invention and of reference tires. For each type of tire, the measurements are carried out on three tires in accordance with the description of the measurements described above, resulting in 70 measurements on each tire.

[0105] The results of the flow rate and flow rate difference measurements are thus presented in the following table as an average of several measurements and expressed in cm3 / min: Pneumatics according to the invention: First reference pneumatics, Second reference pneumatics, Third reference pneumatics, Average flow rate: 3.9, 35.2, 0, 10.8, Maximum difference in flow rate between two average measurements: 3.5, 35.2, 0, 15.1

[0106] Endurance tests in a rolling road were carried out on a test machine subjecting the tires to a load of 4415 daN and a speed of 40 km / h, with the tires inflated using oxygen-enriched tires. The tests were performed on the tires according to the invention under conditions identical to those applied to the reference tires. The rolling tests were stopped as soon as the tires showed any damage to the carcass reinforcement.

[0107] The tests thus carried out showed that the distances covered during these tests with the tires according to the invention are approximately 20% lower compared to the second reference tires. The third reference tires exhibit performance approximately 10% lower than the tires according to the invention, and the first reference tires exhibit performance approximately 30% lower than the tires according to the invention.

Claims

Demands

1. A tire (1) with a radial carcass reinforcement (2), consisting of at least one layer of reinforcing elements, said tire comprising a crown reinforcement (5), itself radially capped with a tread (6), said tread being joined to two beads (3) by means of two sidewalls, characterized in that the reinforcing elements of at least one layer of the carcass reinforcement (2) are metal cables (21) exhibiting in the so-called permeability test, carried out according to ASTM D2692-98, an average flow rate of between 1 and 7 cmVmin and in that, the maximum difference in flow rate, measured according to the permeability test carried out according to ASTM D2692-98, between two average flow rate measurements on sampling areas of said reinforcing elements distributed over the length of said reinforcing elements is less than 5 cmVmin.

2. Pneumatic (1) according to claim 1, characterized in that said reinforcement elements of at least one layer of the carcass reinforcement are metal cables (21) exhibiting in the so-called permeability test an average flow rate greater than 2 cmVmin.

3. Pneumatic (1) according to claim 1 or 2, characterized in that said reinforcement elements of at least one layer of the carcass reinforcement are metal cables (21) exhibiting in the so-called permeability test an average flow rate less than or equal to 5.5 cmVmin.

4. Pneumatic (1) according to any one of claims 1 to 3, characterized in that the maximum difference in flow rate, measured according to the permeability test carried out according to ASTM D2692-98, between two average flow rate measurements on sampling areas of said reinforcement elements distributed over the length of said reinforcement elements is less than or equal to 3.5 cmVmin.

5. Pneumatic (1) according to any one of claims 1 to 4, the reinforcing elements of said at least one carcass reinforcement layer being three-layer metal cables (21), characterized in that the inner layer (22) of said three-layer cables (21) is sheathed with a layer (25) made of a polymeric composition such as a non-crosslinkable, crosslinkable or crosslinked rubber composition, preferably based on at least one diene elastomer.

6. Pneumatic (1) according to claim 5, characterized in that said metallic reinforcing elements of at least one layer of the carcass reinforcement are metal cables (21) with construction layers [L+M+N], comprising a first layer Cl of L wires of diameter di with L ranging from 1 to 4, surrounded by at least one intermediate layer C2 of M wires of diameter d2 wound together helically in a pitch p2 with M ranging from 3 to 12, said layer C2 being surrounded by an outer layer C3 of N wires of diameter d3 wound together helically in a pitch p3 with N ranging from 8 to 20, and in that a sheath made of a non-crosslinkable, crosslinkable or crosslinked rubber composition based on at least one diene elastomer, covers said first layer Cl.

7. Pneumatic (1) according to claim 6, characterized in that the diameter of the wires of the first layer Cl is between 0.10 and 0.5 mm, and in that the diameter of the wires of layers C2, C3 is between 0.10 and 0.5 mm.

8. Pneumatic (1) according to claim 6 or 7, characterized in that the helix pitch of winding said wires of the outer layer C3 is between 8 and 25 mm.

9. Pneumatic (1) according to any one of claims 5 to 8, characterized in that the diene elastomer is selected from the group consisting of polybutadienes, natural rubber, synthetic polyisoprenes, butadiene copolymers, isoprene copolymers, and mixtures of these elastomers.

10. Pneumatic (1) according to any one of claims 5 to 9, the reinforcing elements of said at least one carcass reinforcement layer being three-layer metal cables (21), the first layer (22) being made of a single wire, characterized in that said layer (25) made of a polymeric composition sheathing the first layer (22) of said three-layer cables has a thickness of less than 50 microns and preferably greater than 30 microns.

Images