Tyre including a carcass reinforcement consisting of metal cords with low permeability

Abstract

The invention relates to a tyre (1) having a radial carcass reinforcement (2) consisting of at least one ply of metal reinforcing elements, the tyre comprising a crown reinforcement (5), which in turn is radially covered with a tread (6), the tread being joined to two beads (3) via two sidewalls. According to the invention, the reinforcing elements of at least one ply of the carcass reinforcement are metal cords (21) having, in the so-called permeability test, an average flow rate of between 1 and 7 cm3 / min, and the maximum flow rate difference, measured according to the permeability test carried out in accordance with standard ASTM D2692-98, between two average flow rate measurements from sampling areas of the reinforcing elements distributed over the length of the reinforcing elements is less than 5 cm3 / min.

Description

TIRE COMPRISING A CARCASS REINFORCEMENT MADE OF LOW PERMEABILITY METAL CABLES

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

[0002] Generally speaking, in heavy-duty tires, the carcass reinforcement is anchored on both sides in the bead area and is surmounted radially by a crown reinforcement consisting of at least two layers, superimposed and formed of parallel wires or cables in each layer and crossed from one layer to the next, making angles of between 10° and 45° with the circumferential direction. Said working layers, forming the working reinforcement, may also be covered with at least one so-called protective layer and formed of advantageously metallic and extensible reinforcement elements, called elastic.It may also comprise a layer of low-extensibility metal wires or cables forming an angle of between 45° and 90° with the circumferential direction, this ply, called the triangulation ply, being radially located between the carcass reinforcement and the first crown ply, called the working ply, formed of parallel wires or cables having angles at most equal to 45° in absolute value. The triangulation ply forms with at least said working ply a triangulated reinforcement, which, under the various stresses to which it is subjected, exhibits little deformation, the triangulation ply having the essential role of absorbing the transverse compression forces to which all the reinforcing elements are subjected in the area of ​​the crown of the tire.

[0003] In the case of tires for "Heavy Goods Vehicles" vehicles, a single protective layer is usually present and its protective elements are, in most cases, oriented in the same direction and with the same angle in absolute value as those of the reinforcing elements of the radially outermost and therefore radially adjacent working layer. In the case of Earthmover tires intended for driving on more or less uneven ground, the presence of two protective layers is advantageous, the reinforcing elements being crossed from one layer to the next and the reinforcing elements of the radially inner protective layer being crossed with the inextensible reinforcing elements of the radially outer working layer and adjacent to said radially inner protective layer.

[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 tire's axis of rotation.

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

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

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

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

[0010] Some current tires, called "road tires", are intended to travel at high speeds and on increasingly long journeys, due to the improvement of the road network and the growth of the motorway network in the world. All the conditions under which such a tire is called upon to travel, undoubtedly allow an increase in the number of kilometers traveled, the wear of the tire being less; on the other hand, the endurance of the latter is penalized. To allow one or even two retreads of such tires in order to extend their lifespan, it is necessary to maintain a structure and in particular a carcass reinforcement whose endurance properties are sufficient to withstand said retreads.

[0011] Prolonged driving in particularly severe conditions of tires thus constructed actually reveals limits in terms of endurance of these tires.

[0012] The elements of the carcass reinforcement are particularly subject to bending and compression stresses during rolling which are detrimental to their endurance. The cables that constitute the reinforcing elements of the carcass layers are in fact subject to significant stresses when the tires are rolling, in particular to repeated bending or variations in curvature inducing friction at the level of the wires, and therefore wear, as well as fatigue; this phenomenon is called "fatigue-fretting".

[0013] To fulfil their function of reinforcing the carcass reinforcement of the tyre, said cables must first of all have 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 tyres.

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

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

[0016] To improve the endurance of these carcass reinforcement cables, it is known to increase the thickness of the rubber layer that forms the inner wall of the tire cavity to limit the permeability of said layer as much as possible. This layer is usually partly composed of butyl in order to increase the airtightness of the tire. 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 penetrability by the rubber, and thus limit or even eliminate the passage of oxidizing agents through the channels formed within the cables.

[0018] Also known in particular from document EP 1699973 A1 are three-layer cable constructions during the manufacture of which a layer of rubber mixture is deposited around the intermediate layer to fill the gaps between all the metal wires constituting this cable.

[0019] Tires made with such cables, on the other hand, have shown problems with the appearance of air pockets during the manufacture of the tire.

[0020] Indeed, the various manufacturing stages lead to the formation of occluded air pockets. In the case of tires comprising a carcass reinforcement formed of cables whose structure forms channels that can conduct air, these air pockets disappear due to the diffusion of air in the materials, in particular through said channels existing within the cables. In the case of tires comprising a carcass reinforcement formed of cables whose structure is heavily penetrated by rubber or cables into which the rubber is introduced during the actual manufacture of the cable, these air pockets remain at the end of the manufacturing stages. Only a displacement of these air pockets appears during the curing stage of the tire, these being displaced towards areas where low pressure is exerted.The air moves along the carcass reinforcement through existing passages between the reinforcement elements, the layers of rubber compound covering the reinforcement elements forming recessed areas parallel to the reinforcement elements before the tire curing stage. These recessed areas thus allow the air to move slightly depending on the pressure exerted on the regions where the air pockets are located. The pressure or pressure variations occur in particular during the tire curing stage or during the shaping stage if one exists.

[0021] The appearance of these air pockets is most often prohibitive depending on their location and may require the tires to be scrapped, as they can become areas of weakness in the tire. Manufacturing costs then become unacceptable simply because of poor production yields.

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

[0023] This aim 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 presenting in the so-called permeability test an average flow rate of between 1 and 7 cm 3 / min and, the maximum difference in flow rate, measured according to the permeability test carried out according to standard 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 cm 3 / min.

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

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

[0026] The test is carried out on a 2 cm length of cable, coated by its surrounding rubber composition (or coating gum) in the cooked state, in the following manner: air is sent to the cable inlet, 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 cm 3 / min). During the measurement, the cable sample is clamped in a compressed seal (e.g. 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 seal itself is checked beforehand using a solid rubber test piece, i.e. without cable.

[0027] The measured air flow rate is lower the higher the longitudinal impermeability of the cable. The measurement is made with an accuracy of ± 0.2 cm. 3 / min, measured values ​​less than or equal to 0.2 cm 3 / min are considered zero; they correspond to a cable which can be described as airtight (totally airtight) along its axis (i.e., in its longitudinal direction).

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

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

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

[0031] The average flow rate of the reinforcing elements of at least one layer of the carcass reinforcement is the result of 70 measurements taken on 10 cords taken from a tire. First, four tire sectors are made with a length measured in the circumferential direction between 10 and 15 centimeters, cut according to radial planes. These four sectors are centered on radial planes distributed every 90° according to the tire's wheel circumference. The cords 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 straight line, passing through the outermost end of the crown 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 straight line, passing through the end of the turn-up 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 reinforcement located radially midway between the centers of the samples of a second and a third sample.

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

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

[0035] The inventors were able to demonstrate that a tire thus produced according to the invention leads to very interesting improvements in terms of compromise between endurance and manufacturing costs. Indeed, the endurance properties with such a tire are lower than those of tires whose three-layer cables of the carcass reinforcement include a layer of rubber compound deposited around the intermediate layer but higher than those of more usual cables in their design, that is to say not including a rubber layer put in place during the manufacture of the cable, and which are more sensitive to corrosion phenomena. The presence of metal cables presenting in the so-called permeability test an average flow rate of between 1 and 7 cm 3 / min in at least one layer of the carcass reinforcement helps limit the risks associated with corrosion. In addition, the measurement according to the permeability test of the maximum difference in flow rate between two average flow rate measurements on sampling areas of said reinforcement elements distributed over the length of said reinforcement elements less than 5 cm 3 / min indicate the presence of rubber compound within the cables incomplete but with a relatively homogeneous distribution. This reflects the presence of rubber compound within the metal cables leaving free spaces which allow the circulation or at least the temporary storage of air, in particular during the manufacture of the tire. The inventors were able to demonstrate that the presence of these spaces within the cables not filled with rubber compound can allow the drainage of the air occluded during the manufacture of the tire and therefore leads to a better production quality than that mentioned previously with tires whose three-layer cables of the carcass reinforcement include a layer of rubber compound deposited around the intermediate layer and therefore to more attractive costs.The tests carried out have confirmed that the results obtained with such metal cables according to the invention in at least one layer of the carcass reinforcement are not comparable with those obtained with layers of carcass reinforcement made up of cables such as those mentioned above in which a layer of rubber mixture is deposited around the layer. intermediate layer of a three-layer cable to fill the gaps between all the metal wires constituting this cable. Indeed, the production of tires according to the invention made it possible to keep almost all of the tires thus manufactured and therefore reduce the unit manufacturing cost to acceptable values.

[0036] The inventors have also been able to demonstrate that in comparison with metal cables, also mentioned previously, the production of which is designed to increase their penetrability by the 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 be in accordance with the invention. Advantageously according to the invention, the reinforcing elements of at least the radially outer layer of the carcass reinforcement are metal cables exhibiting in the so-called permeability test an average flow rate of between 1 and 7 cm. 3 / min, and the maximum difference in flow rate, measured according to the permeability test carried out according to standard 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 cm 3 / min. This choice is particularly advantageous for ensuring complete evacuation of air pockets that form during tire manufacturing, these appearing mainly on the axially and / or radially outer surface of the carcass reinforcement during manufacturing.

[0038] Preferably according to the invention, said reinforcing 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 cm 3 / min. Such values ​​of the average flow rate of the reinforcing elements further improve the evacuation of air pockets during the manufacture of the tire.

[0039] More preferably according to the invention, said reinforcing 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 cm 3 / min. Such values ​​of the average flow rate of the reinforcing elements further improve the tire's endurance performance.

[0040] According to an advantageous embodiment of the invention, in a meridian section of the tire, the maximum difference in flow rate, measured according to the permeability test carried out according to standard ASTM D2692-98, between two average flow rate measurements on sampling zones of said reinforcement elements distributed over the length of said reinforcement elements is less than or equal to 3.5 cm. 3 / min. Such values ​​mark an even more homogeneous distribution of the rubber mixture within the cables.

[0041] According to a preferred embodiment of the invention, the reinforcing elements of said at least one layer of carcass reinforcement are three-layer metal cables, the inner layer of said three-layer cables being sheathed with a layer consisting 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 endurance performance of the tire and more specifically to further limit the risks of oxidation of the reinforcing elements of the carcass reinforcement layer, at least the wires constituting the intermediate layer of a three-layer cable are coated with zinc. The wires of the third layer are advantageously covered with brass to facilitate bonding with the rubber mixtures of the calendering layers forming the carcass reinforcement layer. Advantageously still according to the invention, the wire(s) of the first layer of the reinforcing elements of the carcass reinforcement layer are also covered with brass.

[0043] By the expression "composition based on at least one diene elastomer", it is understood in a known manner that the composition comprises in the majority (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 that it covers (i.e. 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 by definition comprises a crosslinking system adapted to allow the crosslinking of the composition during its curing (i.e., its hardening and not its fusion); thus, this rubber composition can be described as infusible, because it cannot be melted by heating at any temperature.

[0046] By "diene" elastomer or rubber, we mean, in a known manner, an elastomer derived at least in part (i.e. a homopolymer or a copolymer) from diene monomers (monomers carrying 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, here we mean by "essentially unsaturated" diene elastomer a diene elastomer derived at least in part from conjugated diene monomers, having a content of units or patterns of diene origin (conjugated dienes) which is greater than 15% (mol %). Thus, for example, diene elastomers such as butyl rubbers or copolymers of dienes and alpha-olefins such as EPDM do not fall within the preceding definition and can be described in particular as "essentially saturated" diene elastomers (low or very low content of patterns of diene origin, always less than 15%).In the category of "essentially unsaturated" diene elastomers, a "highly unsaturated" diene elastomer is understood to mean in particular a diene elastomer having a content of units of diene origin (conjugated dienes) which is greater than 50%.

[0048] Given these definitions, the term diene elastomer capable of being used in the cable of the invention is understood more particularly to mean: (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 conjugated dienes with each other 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 a non-conjugated diene monomer having from 6 to 12 carbon atoms, such as for example elastomers obtained from ethylene, of propylene with a non-conjugated diene monomer of the aforementioned type such as in particular hexadiene-1,4, ethylidene norbornene, dicyclopentadiene; (d) a copolymer of isobutene and isoprene (butyl rubber), as well as halogenated, in particular chlorinated or brominated, versions 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 blends 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] More preferably according to the invention, the diene elastomer chosen is predominantly (i.e. for more than 50 pce) made up of an isoprene elastomer. By "isoprene elastomer" is meant, in a known manner, 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 diene elastomer chosen is exclusively (i.e. for 100 pce) made up of natural rubber, synthetic polyisoprene or a mixture of these elastomers, the synthetic polyisoprene having a rate (mol%) of cis-1,4 bonds preferably greater than 90%, more preferably still greater than 98%.

[0053] It would also be possible to use, according to a particular embodiment of the invention, blends (mixtures) of this natural rubber and / or these synthetic polyisoprenes 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 polymers other than elastomers then being present as a minority polymer.

[0055] Although the rubber composition of said sheath is preferably free of any plastomer and only comprises one diene elastomer (or mixture of elastomers) as polymer base, said composition could also comprise at least one plastomer according to a mass fraction x p less than the mass fraction x e of the elastomer(s). In such a case, we preferably have the following relationship: 0 < x p < 0.5. x e , and more preferably: 0 < x p < 0.1. x e .

[0056] Preferably, the crosslinking system of 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 may be added to this basic vulcanization system. The sulfur is used at a preferential rate of between 0.5 and 10 pce, more preferably between 1 and 8 pce, the primary vulcanization accelerator, for example a sulfenamide, is used at a preferential rate of between 0.5 and 10 pce, more preferably between 0.5 and 5.0 pce.

[0057] The rubber composition of the sheath according to the invention comprises, in addition to said crosslinking system, all the usual ingredients usable in rubber compositions for tires, such as reinforcing fillers based on carbon black and / or a reinforcing inorganic filler such as silica, anti-aging agents, for example antioxidants, extender oils, plasticizers or agents facilitating the processing of the compositions in the raw state, methylene acceptors and donors, resins, bismaleimides, known adhesion promoting systems of the "RFS" (resorcinol-formaldehyde-silica) type or metal salts, in particular 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 possible incompatibility between the respective materials of the sheath and the rubber matrix.

[0059] Preferably, said composition is based on natural rubber and it comprises 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 metal reinforcing elements of at least one layer of the carcass reinforcement are metal cables with [L+M+N] construction layers, comprising a first layer C1 with L wires of diameter di with L ranging from 1 to 4, surrounded by at least one intermediate layer C2 with M wires of diameter d? wound together in a helix at a pitch p2 with M ranging from 3 to 12, said layer C2 being surrounded by an external layer C3 of N wires of diameter d3 wound together in a helix at 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 C1.

[0061] Preferably, the diameter of the wires of the first layer (C1) is between 0.10 and 0.5 mm and the diameter of the wires of the intermediate (C2) and external (C3) layers is between 0.10 and 0.5 mm.

[0062] More preferably, the helix pitch of winding of said wires of the external 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 sectioned 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 that 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 preferential characteristics (di, d2, ds, p2 and ps in mm): - (i) 0.10 < di < 0.28; - (ii) 0.10 < d2 < 0.25 ; - (iii) 0.10 < d3 < 0.25 ; - (iv) M = 6 or M = 7; - (v) 5% (di + d2) < p2< p3< 5 7i (di + 2d2+ d3); - (vi) the wires of said layers C2, C3 are wound in the same direction of twist (S / S or Z / Z).

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

[0067] According to feature (vi), all the wires of layers C2 and C3 are wound in the same direction of twist, i.e. either in the S direction ("S / S" arrangement) or in the Z direction ("Z / Z" arrangement). Winding layers C2 and C3 in the same direction advantageously makes it possible, in the cable according to the invention, to minimize friction between these two layers C2 and C3 and therefore 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 layered cables of construction noted 1+M+N, that is to say that the internal layer Cl is made up of a single wire.

[0069] Advantageously, 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 of the di / d2 ratio can be detrimental to wear between the inner layer and the wires of layer C2. Too high a value can be detrimental to the compactness of the cable, for a level of resistance that is ultimately little modified, as well as to its flexibility; the increased rigidity of the inner layer Cl due to a diameter di that is too high could also be detrimental to the feasibility of the cable itself, during cabling operations.

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

[0072] The maximum number N max of wires that can be wound in a single saturated layer C3 around the layer C2 is of course a function of numerous parameters (diameter di of the internal 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 carcass 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 bending strength of the cable, on the one hand, and penetrability by the rubber, on the other hand, it is preferred that the diameters of the wires of layers C2 and C3, whether identical or not, be between 0.12 mm and 0.22 mm.

[0075] In such a case, we have more preferentially the following relations which are verified: 0.14 < di < 0.22 ; 0.12 < d2< d3< 0.20 ; 5 < p2< p3< 12 (reduced mm steps) or 20 < p2< p3< 30 (high mm steps).

[0076] A diameter of less than 0.19 mm makes it possible to reduce the level of stresses experienced by the wires during significant variations in cable curvature, while diameters greater than 0.16 mm are preferably chosen 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 cables of structure 1+6+12.

[0078] Generally speaking, said metal reinforcing elements of at least one layer of the carcass reinforcement according to the invention can be made with 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 the tire and the feasibility of the wire. It should be noted that a carbon content of between 0.5% and 0.6% ultimately makes such steels less expensive because they are easier to draw. Another advantageous embodiment of the invention may also consist, depending on the intended applications, in using steels with a low carbon content, for example between 0.2% and 0.5%, in particular due to a lower cost and greater ease of drawing.

[0080] Said metal reinforcing elements of at least one layer of the carcass reinforcement according to the invention may be obtained using various techniques known to those skilled in the art, for example in four steps, firstly a first operation of cabling or twisting the first layer C1 made up of L wires, then a second step of sheathing via an extrusion head of the layer C1, a step followed in a third step by an operation of cabling or twisting the M wires of the layer C2 around the layer C1 thus sheathed and finally a fourth step of cabling or twisting the N wires of the layer C3 around the layer C2.

[0081] More preferably according to the invention, said layer consisting of a polymeric composition sheathing the first layer of said three-layer cables has, in particular in the case of a first layer, of the three-layer cable, consisting 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 conservation of free space within the cables.

[0082] Also preferably 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 lower thickness of the sheath consisting of a polymeric composition is insufficient to observe a notable effect on the endurance performance of the tire.

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

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

[0085] A preferred embodiment of the invention also provides that the crown reinforcement is completed radially on the outside by at least one additional layer, called a protective layer, of so-called elastic reinforcing elements, oriented relative to the circumferential direction with an angle of 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 of the embodiments of the invention mentioned above, the crown reinforcement can also be supplemented, 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 characteristics of the invention will emerge below from the description of the exemplary embodiments of the invention with reference to Figures 1 to 4 which represent: Figure 1, a meridian view of a diagram of a tire according to an embodiment of the invention, Figure 2, a schematic representation of a sectional view of an example of a cable of at least one layer of the carcass reinforcement of the tire of Figure 1, Figure 3, a schematic representation of a sectional view of a second reference cable, Figure 4, a schematic representation of a sectional view of a third reference cable.

[0088] Figures are not drawn to scale to simplify understanding.

[0089] In Figure 1, the tire 1, of dimension 315 / 80 R 22.5, comprises a radial carcass reinforcement 2 anchored in two beads 3, around rods 4. The carcass reinforcement 2 is formed of a single layer of metal cables. The carcass reinforcement 2 is hooped by a crown reinforcement 5, itself capped with a tread 6. The crown reinforcement 5 is formed radially from the inside to the outside: of a first working layer formed of non-hooked inextensible metal cables 9.35, continuous over the entire width of the ply, oriented at an angle equal to 26°, of a second working layer formed of non-hooked inextensible metal cables 9.35, continuous over the entire width of the ply, oriented at an angle equal to 18° and crossed with the metal cables of the first working layer, of a protective layer formed of elastic metal cables 6x35.

[0090] All of these layers constituting the crown reinforcement 5 are not shown in detail in the figures.

[0091] Figure 2 illustrates a schematic representation of the 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 hooped, consisting of a first layer formed of a wire 22, an intermediate layer formed of six wires 23 and an external 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 the helix pitch of the intermediate layer and d3 and P3, respectively the diameter and the helix pitch of the wires of the external layer.

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

[0094] Cable 21 has a diameter equal to 0.9 mm.

[0095] The elastomeric composition constituting the rubber sheath 25 is produced from a composition as described previously and in the present case has the same formulation, based on natural rubber and carbon black, as that of the calendering layers of the carcass reinforcement that 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] First 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 Figure 2 but which do not include 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 Figure 3, identical to the cables of Figure 2 but which comprise a sheathing layer 35 surrounding the central core of the cable formed from the wire 32 and the intermediate layer formed from 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 Figure 4. This cable 41 is a cable with a 1+6+11 structure layer, not hooped, consisting of a first layer formed of a wire 42, an intermediate layer formed of six wires 43 and an external 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), (di / d2) = 1.11; with d2, p2, respectively the diameter and the helix pitch of the intermediate layer and d3 and P3, respectively the diameter and the helix pitch of the wires of the external 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 external layer of thickness substantially equal to d3).

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

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

[0104] Flow rate measurements, carried out in accordance with the so-called permeability test previously described, are carried out on the cables of the carcass reinforcement layer of the tires according to the invention and of the reference tires. For each of the types of tires, the measurements are carried out on three tires in accordance with the description of the measurements described previously, leading to 70 measurements being taken on each of the tires.

[0105] The results of the flow rate and flow difference measurements are presented in the following table as an average of several measurements and expressed in cm 3 / min:

[0106] Endurance tests on the steering wheel were carried out on a test machine imposing a load of 4415 daN on the tires and a speed of 40 km / h, with oxygen-doped tire inflation. The tests were carried out for the tires according to the invention with conditions identical to those applied to the reference tires. Rolling is stopped as soon as the tires show damage to the carcass reinforcement.

[0107] The tests thus carried out have shown that the distances traveled during these tests with the tires according to the invention are lower by around 20% compared to the second reference tires. The third reference tires have lower performances by around 10% compared to the tires according to the invention and the first reference tires have lower performances by around 30% compared to the tires according to the invention.

Claims

CLAIMS 1 - Tire (1) with 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) presenting in the so-called permeability test, carried out according to standard ASTM D2692-98, an average flow rate of between 1 and 7 cm 3 / min and in that the maximum difference in flow rate, measured according to the permeability test carried out according to standard 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 cm 3 / min. 2 - Tire (1) according to claim 1, characterized in that said reinforcing elements of at least one layer of the carcass reinforcement are metal cables (21) presenting in the so-called permeability test an average flow rate greater than 2 cm 3 / min. 3 - Tire (1) according to claim 1 or 2, characterized in that said reinforcing elements of at least one layer of the carcass reinforcement are metal cables (21) presenting in the so-called permeability test an average flow rate less than or equal to 5.5 cm 3 / min. 4 - Tire (1) according to 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 standard ASTM D2692-98, between two average flow rate measurements on sampling zones of said reinforcing elements distributed over the length of said reinforcing elements is less than or equal to 3.5 cm 3 / min. 5 - Tire (1) according to one of claims 1 to 4, the reinforcing elements of said at least one layer of carcass reinforcement 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) consisting of a polymeric composition such as a non-crosslinkable, crosslinkable or crosslinked rubber composition, preferably based on at least one diene elastomer. 6 - Tire (1) according to claim 5, characterized in that said metallic reinforcing elements of at least one layer of the carcass reinforcement are cables metallic (21) with [L+M+N] construction layers, comprising a first layer Cl with L wires of diameter di with L ranging from 1 to 4, surrounded by at least one intermediate layer C2 with M wires of diameter d? wound together in a helix at a pitch p2 with M ranging from 3 to 12, said layer C2 being surrounded by an external layer C3 of N wires of diameter ds wound together in a helix at a pitch ps 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 - Tire (1) according to claim 6, characterized in that the diameter of the wires of the first layer C1 is between 0.10 and 0.5 mm, and in that the diameter of the wires of the layers C2, C3 is between 0.10 and 0.5 mm. 8 - Tire (1) according to claim 6 or 7, characterized in that the helix pitch of winding of said wires of the external layer C3 is between 8 and 25 mm. 9 - Tire (1) according to one of claims 5 to 8, characterized in that the diene elastomer is chosen from the group consisting of polybutadienes, natural rubber, synthetic polyisoprenes, butadiene copolymers, isoprene copolymers, and mixtures of these elastomers. 10 - Tire (1) according to one of claims 5 to 9, the reinforcing elements of said at least one layer of carcass reinforcement being three-layer metal cables (21), the first layer (22) being made up of a single wire, characterized in that said layer (25) made up 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.

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