AU2019291191A1

AU2019291191A1 - Double-layer multi-strand cord with improved penetrability

Info

Publication number: AU2019291191A1
Application number: AU2019291191A
Authority: AU
Inventors: Marianna CHEVALLEY; Emmanuel Clement; Alexandre GIANETTI; Stéphane LAURENT; Rémi PINAUT
Original assignee: Compagnie Generale des Etablissements Michelin SCA
Current assignee: Compagnie Generale des Etablissements Michelin SCA
Priority date: 2018-06-20
Filing date: 2019-06-04
Publication date: 2021-01-21
Also published as: WO2019243688A1; CA3102888A1; CN112469861A; EP3810848A1

Abstract

The disclosed cord (50) comprises K > 1 helically wound inner strands (TI) and L > 1 outer strands (TE). Each inner strand (TI) comprises: - an inner layer (C1) consisting of Q = 2, 3 or 4 inner wires (F1); - an intermediate layer (C2) consisting of M intermediate wires (F2) wound at a pitch p2; - an outer layer (C3) consisting of N outer wires (F3) wound at a pitch p3. The average inter-strand distance E between two adjacent outer strands is at least 30 µm. p1 is different from p2 and/or the direction of the inner layer (C1) of each inner strand (TI) is different from the direction of the intermediate layer (C2) of each inner strand (TI). The intermediate layer (C2) of each inner strand (TI) is desaturated, and the outer layer (C3) of each inner strand (TI) is desaturated. The following applies to pitches p2 and p3: 0.33 ≤ (p3-p2)/p3 ≤ 0.45 if Q=2; 0.35 ≤ (p3-p2)/p3 ≤ 0.42 if Q=3; 0.28 ≤ (p3-p2)/p3 ≤ 0.43 if Q=4.

Description

Double-layer multi-strand cord with improved penetrability

[001] The invention relates to multi-strand cords that can be used notably for reinforcing tyres, particularly tyres for heavy industrial vehicles.

[002] Atyre having a radial carcass reinforcement comprises a tread, two inextensible beads, two sidewalls connecting the beads to the tread and a belt, or crown reinforcement, arranged circumferentially between the carcass reinforcement and the tread. The carcass reinforcement and the crown reinforcement comprise a plurality of plies made of elastomeric compound, possibly reinforced with reinforcing elements such as cords or monofilaments, of the metal or textile type.

[003] The carcass reinforcement is anchored in each bead and surmounted radially by the crown reinforcement. The carcass reinforcement comprises a carcass ply comprising carcass reinforcing metal filamentary elements. Each carcass reinforcing metal filamentary element makes an angle of between 80 and 90 with the circumferential direction of the tyre.

[004] The crown reinforcement generally comprises at least two superposed crown plies, sometimes referred to as working plies or crossed plies, the, generally metal, reinforcing elements of which are placed virtually parallel to one another within a ply but crossed from one ply to the other, that is to say inclined, symmetrically or asymmetrically, with respect to the median circumferential plane, by an angle which is generally comprised between 10° and 45°. The working plies generally comprise reinforcing elements that exhibit very low elongation so as to perform their function of guiding the tyre.

[005] The crown reinforcement may also comprise various other auxiliary plies or layers of elastomeric compound, with widths that may vary as the case may be, and which may or may not contain reinforcing elements. Mention may be made by way of example of what are known as protective plies which have the role of protecting the remainder of the belt from external attacks or perforations, or also of what are known as hooping plies which contain reinforcing elements that are oriented substantially in the circumferential direction (what are known as zero-degree plies), whether these be radially on the outside or on the inside with respect to the working plies. The protective plies generally comprise reinforcing elements that exhibit a high elongation so that they deform under the effect of a stress applied by an indenter, for example a rock.

[006] A reinforcing element for the plies described hereinabove and comprising a two layer multi-strand metal cord as disclosed in the examples of W02011064065, W02016202622 and W02009048054 is known from the prior art. These cords comprise an internal layer of the cord made up of an internal strand and an external layer of the cord made up of six external strands wound in a helix around the internal layer of the cord.

[007] Each internal and external strand comprises an internal layer of the strand which layer is made up of two, three or four internal threads, an intermediate layer made up of seven to nine intermediate threads and an external layer made up of twelve to fifteen external threads. The intermediate and external layers of the internal strand are wound in the Z-direction around the internal and intermediate layers of the internal strand respectively. The intermediate and external layers of each external strand are wound in the Z-direction around the internal and intermediate layers of each external strand respectively. The external strands are wound in a helix around the internal strand in a direction of winding up the cord, this being the S-direction.

[008] A tyre of a heavy industrial vehicle, notably of construction plant type, is subjected to numerous attacks. Specifically, this type of tyre usually runs on an uneven road surface, sometimes resulting in perforations of the tread. These perforations allow the entry of corrosive agents, for example air and water, which oxidize the metal reinforcing elements of the various reinforcements, in particular of the crown plies, and considerably reduce the service life of the tyre.

[009] One solution for increasing the service life of the tyre is to combat the spread of these corrosive agents. Provision may thus be made to cover each internal and intermediate layer with an elastomer compound during the manufacture of the cord. During this process, the elastomer compound present penetrates the capillaries that are present between each layer of each strand and thus prevents the corrosive agents from spreading. Such cords, generally referred to as cords rubberized in situ, are well known from the prior art.

[010] Another solution for increasing the service life of the tyre is to increase the cord's breaking strength. In general, the breaking strength is increased by increasing the diameter of the threads that make up the cord and/or by increasing the number of threads and/or the individual strength of each thread. However, increasing the diameter of the threads still further, for example beyond 0.50 mm, of necessity leads to a lowering of the flexibility of the cord, and this is not desirable. Increasing the number of threads usually leads to a lowering of the ability of the elastomer compound to penetrate the strands. Finally, increasing the individual strength of each thread entails significant investments in the installations used to manufacture the threads.

[011] The object of the invention is a cord exhibiting better penetrability of each internal strand by the elastomer compound, as compared with the cord of the prior art, thus making it possible to reduce the ingress and spread of corrosive agents into and along the cord.

[012] CORD ACCORDING TO THE INVENTION To this end, one subject of the invention is a two-layer multi-strand cord comprising: - an internal layer of the cord made up of K>1 internal strands wound in a helix, each internal strand being a three-layer strand and comprising: • an internal layer made up of Q=2, 3 or 4 internal threads wound with a pitch p1, the internal layer being wound in an internal-layer direction of each internal strand, * an intermediate layer made up of M intermediate threads, wound around the internal layer with a pitch p2, the intermediate layer being wound in an intermediate-layer direction of each internal strand, and * an external layer made up of N external threads wound around the intermediate layer with a pitch p3, - an external layer of the cord made up of L>1 external strands wound around the internal layer of the cord, each external strand being an at least two-layer strand and comprising: * an internal layer made up of Q' internal thread(s) and * an external layer made up of N' external threads wound around the internal layer, wherein: - the mean inter-strand distance E separating two adjacent external strands is greater than or equal to 30 pm, - p1 is different from p2 and/or the internal-layer direction of each internal strand is different from the intermediate-layer direction of each internal strand; - the intermediate layer (C2) of each internal strand (TI) is desaturated; - the external layer (3) of each internal strand (TI) is desaturated; and - the pitches p2 and p3 satisfy the relationship: - 0.33:5 (p3-p2)/p35 0.45 in instances in which Q=2, - 0.355 (p3-p2)/p3 0.42 in instances in which Q=3, - 0.285 (p3-p2)/p3 0.43 in instances in which Q=4.

[013] It will be recalled that, as is known, the pitch of a strand represents the length of this strand, measured parallel to the axis of the cord, after which the strand that has this pitch has made a complete turn around the said axis of the cord. Similarly, the pitch of a thread represents the length of this thread, measured parallel to the axis of the strand in which it is located, after which the thread that has this pitch has made a complete turn around the said axis of the strand.

[014] What is meant by the direction of winding of a layer of strands or of threads is the direction that the strands or the threads form with respect to the axis of the cord or of the strand. The direction of winding is commonly designated by the letter Z or S.

[015] The pitches, directions of winding, and diameters of the threads and of the strands are determined in accordance with standard ASTM D2969-04 of 2014.

[016] According to the invention, the external layer of the cord is desaturated.

[017] By definition, a desaturated layer of strands is one such that there is enough space left between the strands to allow an elastomer compound to pass. An external layer of strands that is desaturated means that the external strands do not touch and that there is enough space between two adjacent external strands to allow an elastomer composition to pass as far as the internal strands. By contrast, a layer of strands that is saturated is one such that there is not enough space between the strands of the layer to allow an elastomer compound to pass, for example because each pair of two strands of the layer touch one another.

[018] According to the invention, the inter-strand distance of the external layer of external strands, defined, on a cross section of the cord perpendicular to the main axis of the cord, as being the shortest distance separating, on average, the circular envelopes in which two adjacent external strands are inscribed, is greater than or equal to 30 pm.

[019] As a preference, the mean inter-strand distance E separating two adjacent external strands is greater than or equal to 70 pm, more preferably than/to 100 pm, more preferably still than/to 150 pm and highly preferably than/to 200 pm.

[020] What is meant by "at least two layers" is that each external strand may, in certain embodiments, comprise two layers, which means to say that each external strand comprises only two layers, but does not comprise just one, or three, of them; and that in other embodiments, each external strand may comprise three layers, which means to say that each external strand comprises only three layers but does not comprise just two, or four, of them.

[021] In the invention, the cord has two layers of strands, which means to say that it comprises an assembly made up of two layers of strands, neither more nor less, which means to say that the assembly has two layers of strands, not one, not three, but only two. The external layer of the cord is wound around the internal layer of the cord in contact with the internal layer of the cord.

[022] The cord according to the invention exhibits improved penetrability in comparison with a cord in which the ratio (p3-p2)/p3 is outside of the range of ratios conforming to the invention. The inventors instigating the invention postulate the hypothesis that this ratio makes it possible to obtain relatively large radial windows for the passage of the elastomer compound within each internal strand. The radial passage windows are defined as being the intersection between, on the one hand, the space projected onto a plane parallel to the main axis of the cord between two adjacent threads of the external layer of each internal strand and, on the other hand, the space projected onto a plane parallel to the main axis of the cord between two adjacent threads of the intermediate layer of each internal strand. Such a radial passage window is illustrated in Figure 25.

[023] In addition, thanks to the fact that the external layer of the cord is desaturated, the cord according to the invention has spaces between the external strands that allow the elastomer compound to pass. Cords having a relatively high breaking strength because the external layer of the cord is saturated (the external strands are in contact with one another in pairs), thereby forming an arch that absorbs the tensile forces applied to the cord, are known from the prior art. In the cord according to the invention, although the arch around the internal layer is broken, the high penetrability of each internal strand rendered possible by the ratio (p3-p2)/p3 and the desaturated nature of the external layer of the cord allows the elastomer compound to penetrate, on the one hand, between the external strands and, on the other hand, between the external strands and each internal strand. In this way, the arch is at least partially restored and the drop in breaking strength of the cord is therefore limited while at the same time giving the cord its excellent penetrability. Furthermore, this feature allows the elastomer compound to infiltrate between the external layers of the internal and external strands so as to create a cushion of elastomer compound that at least partially absorbs the radial component of the force between the internal and external strands.

[024] In a cord of the prior art comprising an internal layer of the cord which layer is made up of a single internal strand, significant desaturation of the external layer of the cord for the purposes of promoting the penetrability of the cord leads to a significant drop in the mass of metal and therefore to a relatively substantial reduction in the breaking strength of the cord. In the cord of the invention, significant desaturation of the external layer of the cord for the purposes of promoting the penetrability of the cord leads, because of the presence of K internal strands, to a less significant drop in the mass of metal and therefore to a controlled reduction in the breaking strength, unlike the cords of the prior art in which the contribution made by each external strand to the breaking strength is greater than in the cords according to the invention.

[025] Asa result of the invention and the relationship between p2 and p3 and because of the relationship between p1 and p2 and the directions of the internal and intermediate layers of each internal strand, each internal strand has layers that are cylindrical. Very advantageously, each external strand is a strand with cylindrical layers regardless as to whether this external strand has two layers or three. A strand with cylindrical layers is very highly penetrable, unlike a strand with compact layers in which the pitches of all the layers are the same and the directions of winding of all the layers are the same and exhibits far lower penetrability.

[026] As an option and a preference, in one embodiment, the cord does not have any polymer compound, notably the cord does not have any sheath of any polymer compound covering each internal strand. In another embodiment, the cord does not have any elastomer compound, notably the cord does not have any sheath of any elastomer compound covering each internal strand.

[027] Advantageously, the cord is made of metal. The term "metal cord" is understood by definition to mean a cord formed of threads made up predominantly (i.e. for more than 50% of these threads) or entirely (for 100% of the threads) of a metallic material. Such a metal cord is preferably implemented with a steel cord, more preferably a cord made of pearlitic (or ferritic-pearlitic) carbon steel referred to as "carbon steel" below, or else made of stainless steel (by definition, steel comprising at least 11% chromium and at least 50% iron). However, it is of course possible to use other steels or other alloys.

[028] When a carbon steel is advantageously used, its carbon content (% by weight of steel) is preferably between 0.4% and 1.2%, in particular between 0.5% and 1.1%; these contents represent a good compromise between the mechanical properties required for the tyre and the feasibility of the threads.

[029] The metal or the steel used, whether it is in particular a carbon steel or a stainless steel, may itself be coated with a metallic layer which improves for example the workability properties of the metallic cord and/or of its constituent elements, or the use properties of the cord and/or of the tyre themselves, such as properties of adhesion, corrosion resistance or resistance to ageing. According to a preferred embodiment, the steel used is covered with a layer of brass (Zn-Cu alloy) or of zinc.

[030] For preference, the threads of the one same layer of a predetermined (internal or external) strand all have substantially the same diameter. Advantageously, the external strands all have substantially the same diameter. What is meant by "substantially the same diameter" is that the threads or the strands have the same diameter to within the industrial tolerances.

[031] Advantageously, each thread of each strand has a diameter ranging from 0.15 mm to 0.60 mm, preferably from 0.20 mm to 0.50 mm, more preferentially from 0.22 mm to 0.40 mm, and more preferably still from 0.24 mm to 0.35 mm.

[032] What is meant by a polymer compound or a polymeric compound is that the compound contains at least one polymer. For preference, such a polymer may be a thermoplastic, for example a polyester or a polyamide, a thermosetting polymer, an elastomer, for example natural rubber, a thermoplastic elastomer or a combination of these polymers.

[033] What is meant by an elastomer compound or an elastomeric compound is that the compound contains at least one elastomer or one rubber (the two terms being synonyms) and at least one other component. For preference, the elastomer compound also contains a vulcanization system and a filler. More preferentially, the elastomer is a diene elastomer.

[034] Advantageously: - 0.365 (p3-p2)/p3, preferably 0.385 (p3-p2)/p3 in instances in which Q=2, - 0.365 (p3-p2)/p3, preferably 0.385 (p3-p2)/p3 in instances in which Q=3, - 0.325 (p3-p2)/p3, preferably 0.365 (p3-p2)/p3 in instances in which Q=4.

[035] The higher the ratio (p3-p2)/p3 or, in other words, the greater the difference between p3 and p2, the better the architectural stability of each internal strand. Specifically, the greater the extent to which the pitches of the intermediate and external layers of each internal strand differ, the greater the crossing of the intermediate and external threads with respect to one another (contacts between the intermediate and external threads are then relatively point-like contacts), the better the external threads will mechanically hold the intermediate threads and the better will be the penetrability of each internal strand, the threads of the intermediate and external layers of which will then be evenly distributed within each intermediate and external layer. This mechanical integrity makes it possible to avoid, on the one hand, during manufacture of the cord, all the threads of the intermediate layer grouping together all in contact with one another under the effect of the mechanical forces exerted by the assembly tools and, on the other hand, during manufacture of a ply containing the cord or of the tyre containing the cord, all the threads of the intermediate layer grouping together all in contact with one another under the effect of the pressure of the elastomer compound penetrating the cord.

[036] Furthermore, for a given pitch p3, by increasing the ratio (p3-p2)/p3, the inter thread distance of the intermediate layer of each internal strand is reduced. A person skilled in the art would expect to see a drop in the penetrability of each internal strand. Yet, entirely unexpectedly, as the comparative tests described hereinafter show, by increasing the ratio (p3-p2)/p3, the inter-thread distance of the intermediate layer of each internal strand is admittedly reduced, but the size of the radial passage windows for the elastomer compound is increased which means that the penetrability of each internal strand is appreciably improved.

[037] Advantageously: - (p3-p2)/p3 5 0.42 and preferably (p3-p2)/p3 5 0.40 in instances in which Q=2, - (p3-p2)/p3 0.40 in instances in which Q=3, - (p3-p2)/p3 5 0.40 and preferably (p3-p2)/p3 0.38 in instances in which Q=4. Below these values, the size of the radial passage windows for the elastomer compound is at a maximum and makes it possible to optimize the penetrability of each internal strand.

[038] Advantageously, the pitch p1 is such that 3 mm5 p1 5 16 mm, preferably 4 mm 5 p1 5 13 mm and more preferably 5 mm5 sp1 5 10 mm.

[039] Advantageously, the pitch p2 is such that 8 mm5 p2 20 mm, preferably 9 mm 5 p2 5 18 mm and more preferably 10 mm5 sp2 5 16 mm.

[040] Advantageously, the pitch p3 is such that 10 mm 5 p3 5 40 mm, preferably 12 mm5 p35 30 mm and more preferably 15 mm5 p35 25 mm.

[041] Pitches p1, p2 and p3 within these preferred ranges make it possible to obtain a cord that exhibits mechanical properties compatible with tyre use, a relatively low cost and a relatively low linear cord weight.

[042] Advantageously, K=2, 3 or 4, and preferably K=3 or 4.

[043] In oneembodiment, Lis equal to 7, 8, 9 or 10, preferably L=8, 9 or 10 and more preferably L=8 or 9.

[044] In a first variant, K=2 and L=7 or 8.

[045] In a second variant, K=3 and L=7, 8 or 9, and preferably K=3, L=8 or 9. Instances in which L=8 favour the desaturation of the external layer of the cord and therefore the penetrability of the cord between the external strands. Instances in which L=9 maximize the number of external strands and therefore the breaking strength of the cord.

[046] In a third variant, K=4 and L=7, 8, 9 or 10, and preferably K=4, L=9 or 10.

[047] In these embodiments, notably those in which K=3 or4, there is a risk of seeing a highly significant spread of corrosive agents between the K=3 or 4 internal strands which delimit a central capillary which very much encourages them to spread along the cord, when the cord is insufficiently penetrated. This disadvantage can be overcome by rendering the cord capable of being penetrated by the elastomer compound which then prevents the corrosive agents from accessing the central capillary and, in the best of cases in which the central capillary is itself penetrated, prevents these corrosive agents from spreading along the cord.

[048] As already explained hereinabove, as the cords according to the invention have an architecture in which K>1, the most severe transverse loadings applied to the cord when the latter is tensioned are the transverse loadings applied between the internal strands, unlike in a cord in which K=1 and in which the most severe transverse loadings are the transverse loadings applied by the external strands to the internal strands. Cords exhibiting an architecture in which K>1 and comprising a number of external strands such that the external layer of the cord is saturated so as to maximize the breaking strength by adding a maximum number of external strands are known from the prior art. Here, thanks to the fact that the external layer of the cord is desaturated, the cord has, on the one hand, spaces between the external strands that allow the elastomer compound to pass, therefore allowing the cord to be rendered less sensitive to corrosion. On the other hand, although the number of external strands is reduced, the desaturation of the external layer of the cord allows the elastomer compound to penetrate, on the one hand, between the external strands and, on the other hand, between the internal strands so as to form a cushion of elastomer compound that at least partially absorbs the transverse loads applied between the internal strands. Thus, by comparison with a similar cord having a saturated external layer of the cord, a better compromise between breaking strength and corrosion resistance is achieved.

[049] In an embodiment that promotes the penetrability of the cord, the external layer of the cord is completely unsaturated.

[050] By definition, a completely unsaturated layer of strands is, as opposed to an incompletely unsaturated layer, such that there is sufficient space in this layer to add in at least one (X+1)th strand having the same diameter as the X strands of the layer, it thus being possible for a plurality of strands to be, or not to be, in contact with one another. In this particular instance, there is enough space in the external layer of the cord to add in at least one (L+1)th strand having the same diameter as the L external strands of the external layer of the cord.

[051] Thus, advantageously, the sum SIE of the inter-strand distances E of the external layer of the cord is such that SIE > DE. The sum SIE is the sum of the inter strand distances E separating each pair of adjacent strands in the layer. The inter strand distance of a layer is defined, in a section of the cord perpendicular to the main axis of the cord, as being the shortest distance which, on average, separates two adjacent strands of the layer. Thus, the inter-strand distance E is calculated by dividing the sum SIE by the number of spaces separating the strands in the layer.

[052] In another embodiment that promotes the compromise between penetrability and breaking strength, the external layer of the cord is incompletely unsaturated.

[053] A layer that is incompletely unsaturated with strands is such that there is not enough space in this layer to add in at least one (X+1)th strand having the same diameter as the X strands of the layer. In this particular instance, there is not enough space in the external layer to add in at least one (L+1)th external strand having the same diameter as the L external strands of the external layer of the cord.

[054] By definition, the diameter of an internal strand DI is the diameter of the smallest circle inside which the internal strand is circumscribed. The diameter of an external strand DE is the diameter of the smallest circle inside which the external strand is circumscribed.

[055] In one preferred embodiment, the internal layer of the cord is wound in a helix with a non-zero pitch pi, and the external layer of the cord is wound in a helix around the internal layer of the cord with a non-zero pitch pe.

[056] In one embodiment that is particularly advantageous for the penetrability of the cord, the internal layer of the cord is wound in a helix in a cord internal-layer direction with a pitch pi, the external layer of the cord is wound in a helix in a cord external-layer direction with a pitch pe, and the cord satisfies one and/or the other of the following features: - the cord internal-layer direction is different from the cord external-layer direction, - pi is different from pe.

[057] In this embodiment, the cord has a cylindrical-layers structure (as opposed to a compact structure), promoting the penetrability of the cord.

[058] In another embodiment, the internal layer of the cord is wound in a helix in a cord internal-layer direction with a pitch pi, the external layer of the cord is wound in a helix in a cord external-layer direction with a pitch pe, and the cord satisfies the following features: - the cord internal-layer direction is identical to the cord external-layer direction, - pi is equal to pe.

[059] In this embodiment, despite the compact structure of the cord, which is difficult to penetrate, the high penetrability of the internal strands nevertheless makes it possible to obtain a cord exhibiting satisfactory penetration.

[060]

[061] Optionally, each external thread of each internal strand has a diameter d3 greater than or equal to the diameter d3' of each external thread of each external strand, for preference each external thread of each internal strand has a diameter d3 greater than the diameter d3' of each external thread of each external strand. Preferably, by virtue of the characteristic d3>d3', each external thread of each internal strand may be able to withstand the radial component of the force exerted by the external strands on each internal strand when the cord is under tension. This characteristic d3>d3' makes it possible to restore, or even to improve, the breaking strength of the cord by comparison with a cord comprising an arch formed by the external strands or by comparison with a cord in which d3sd3'. For preference, 1 < d3/d3' 5 2, more preferably 1 < d3/d3' 5 1.5 and more preferably still 1 < d3/d3' 5 1.25 or 1.25 < d3/d3' 5 1.5.

[062] In one advantageous embodiment, the external layer of the cord is wound around the internal layer of the cord in a cord external-layer direction of winding, and each external layer of each internal and external strand is wound respectively around the intermediate and internal layer of each internal and external strand respectively in a same direction of winding that is the opposite to the direction of winding of the cord. In this embodiment, the direction of winding of the cord that is the opposite to the directions of winding of each external layer of each internal and external strand gives the cord better penetrability, notably between the external strands. The inventors postulate the hypothesis that, by virtue of these directions of winding, the external threads of the external strands cross the external threads of each internal strand to form a relatively point-like contact zone unlike cords in which the direction of winding of the cord is identical to the directions of winding of the external layers of each internal and external strand and in which the external threads of the external strands cross the external threads of the internal strand to form a less point-like and more linear contact zone, preventing the elastomer compound from passing as far as the internal strand.

[063] Internal strand of the cord according to the invention

[064] In some embodiments, M=7, 8, 9 or 10, N=12, 13, 14 or 15.

[065] In a first variant, Q=2, M=7 or 8 and N=12 or 13. Instances in which M=7 and/or N=12 favour the desaturation of the intermediate or external layer of each internal strand and therefore the penetrability of each internal strand. Instances in which M=8 and/or N=13 maximize the number of intermediate or external threads and therefore the breaking strength of the cord.

[066] In a second variant, Q=3, M=8 or 9 and N=13 or 14. Instances in which M=8 and/or N=13 favour the desaturation of the intermediate or external layer of each internal strand and therefore the penetrability of each internal strand. Instances in which M=9 and/or N=14 maximize the number of intermediate or external threads and therefore the breaking strength of the cord.

[067] In a third variant, Q=4, M=9 or 10 and N=14 or 15. Instances in which M=9 and/or N=14 favour the desaturation of the intermediate or external layer of each internal strand and therefore the penetrability of each internal strand. Instances in which M=10 and/or N=15 maximize the number of intermediate or external threads and therefore the breaking strength of the cord.

[068] In these embodiments, notably those in which Q=3 or 4, there is a risk of seeing a highly significant spread of corrosive agents between the Q=3 or 4 internal threads which delimit a central capillary which very much encourages them to spread along the strand, when the strand is insufficiently penetrated. This disadvantage can be overcome by rendering the strand capable of being penetrated by the elastomer compound which then prevents the corrosive agents from accessing the central capillary and, in the best of cases in which the central capillary is itself penetrated, prevents these corrosive agents from spreading along the strand.

[069] Advantageously, the sum S12 of the inter-thread distances of the intermediate layer is such that S12 < d3 where d3 is the diameter of each external thread of each internal strand, preferably S12 5 0.8 x d3. The sum S12 is the sum of the inter-thread distances separating each pair of adjacent threads in the intermediate layer. The inter thread distance of a layer is defined, in a section of the cord perpendicular to the main axis of the cord, as being the shortest distance which, on average, separates two adjacent threads of the layer. Thus, the inter-thread distance is calculated by dividing the sum S12 by the number of spaces separating the threads in the intermediate layer. Because the diameter d3 of the external threads of the external layer of each internal strand is preferably greater than the sum S12, the external threads are prevented from penetrating the intermediate layer. This then ensures good architectural stability, thereby additionally reducing the risk of alteration to the radial passage windows for the elastomer compound and therefore the risk of degrading the good penetrability of each internal strand.

[070] Advantageously, the intermediate layer of each internal strand is desaturated.

[071] By definition, a layer of threads that is desaturated with threads is one such that there is enough space left between the threads to allow an elastomer compound to pass. Thus, a layer that is desaturated means that the threads in this layer do not touch and that there is enough space between two adjacent threads in the layer to allow an elastomer compound to pass through the layer. By contrast, a layer of threads that is saturated is such that there is not enough space between the threads of the layer to allow an elastomer compound to pass, for example because each pair of two threads ofthe layer touch one another.

[072] Advantageously, the inter-thread distance of the intermediate layer of each internal strand is greater than or equal to 5 pm. For preference, the inter-thread distance in the intermediate layer of each internal strand is greater than or equal to 15 pm, more preferably greater than or equal to 35 pm, more preferably still greater than or equal to 50 pm and highly preferably greater than or equal to 60 pm.

[073] The fact that the intermediate layer of each internal strand is desaturated advantageously makes it easier for the elastomer compound to pass as far as the centre of each internal strand, and thus render each internal strand less sensitive to corrosion.

[074] In an embodiment that promotes the compromise between penetrability of each internal strand and breaking strength, the intermediate layer of each internal strand is incompletely unsaturated.

[075] By definition, a layer that is incompletely unsaturated threads is such that there is not enough space in this layer to add in at least one (X+1)th thread having the same diameter as the X threads of the layer. In this particular instance, there is not enough space in the intermediate layer to add in at least one (M+1)th intermediate thread having the same diameter as the M intermediate threads of the intermediate layer. In other words, what is meant by an incompletely unsaturated intermediate layer of an internal strand is that the sum S12 of the inter-thread distances 12 of the intermediate layer is less than the diameter d2 of the intermediate threads of the intermediate layer. Thus, advantageously, the sum S12 of the inter-thread distances of the intermediate layer of each internal strand is such that S12 < d2.

[076] The fact that the intermediate layer of each internal strand is incompletely unsaturated makes it possible to ensure architectural stability of the intermediate layer. This then reduces the risk of seeing an external thread penetrate the intermediate layer, something which would alter the radial passage windows for the elastomer compound and therefore degrade the good penetrability of each internal strand. Furthermore, the fact that the intermediate layer of each internal strand is incompletely unsaturated makes it possible to ensure that each internal strand comprises a relatively high number of intermediate threads and therefore exhibits a relatively high breaking strength.

[077] In another embodiment that promotes the penetrability of each internal strand, the intermediate layer of each internal strand is completely unsaturated.

[078] By definition, a completely unsaturated layer of threads is such that there is sufficient space in this layer to add in at least one (X+1)th thread having the same diameter as the X threads of the layer, it thus being possible for a plurality of threads to be in contact, or not in contact, with one another. In this particular instance, there is enough space in the intermediate layer of each internal strand to add in at least one (M+1)th intermediate thread having the same diameter as the M intermediate threads of the intermediate layer. In other words, what is meant by a completely unsaturated intermediate layer of an internal strand is that the sum S12 of the inter-thread distances 12 of the intermediate layer is greater than or equal to the diameter d2 of the intermediate threads of the intermediate layer. Thus, advantageously, the sum S12 of the inter-thread distances of the intermediate layer of each external strand is such that S12 d2.

[079] Advantageously, the external layer of each internal strand is desaturated, preferably completely unsaturated. In a way similar to the case with the intermediate layer, the fact that the external layer of each internal strand is desaturated advantageously makes it easier for the elastomer compound to pass into and through each internal strand, and thus render each internal strand less sensitive to corrosion.

[080] Advantageously, the inter-thread distance of the external layer of each internal strand is greater than or equal to 5 pm. For preference, the inter-thread distance of the external layer of each internal strand is greater than or equal to 15 pm, more preferably greater than or equal to 35 pm, more preferably still greater than or equal to 50 pm and highly preferably greater than or equal to 60 pm.

[081] By definition, a completely unsaturated layer of threads is such that there is sufficient space in this layer to add in at least one (X+1)th thread having the same diameter as the X threads of the layer, it thus being possible for a plurality of threads to be in contact, or not in contact, with one another. In this particular instance, there is enough space in the external layer of each internal strand to add in at least one (N+1)th external thread having the same diameter as the N external threads of the external layer. In other words, what is meant by a completely unsaturated external layer of an internal strand is that the sum S13 of the inter-thread distances 13 of the external layer is greater than or equal to the diameter d3 of the external threads of the external layer. Thus, advantageously, the sum S13 of the inter-thread distances of the external layer of each internal strand is such that S13 1 d3. The sum S13 is the sum of the inter-thread distances separating each pair of adjacent threads in the external layer. The inter thread distance of a layer is defined, in a section of the cord perpendicular to the main axis of the cord, as being the shortest distance which, on average, separates two adjacent threads of the layer. Thus, the inter-thread distance is calculated by dividing the sum S13 by the number of spaces separating the threads in the external layer.

[082] The fact that the external layer of each internal strand is completely unsaturated makes it possible to maximize the penetration of the elastomer compound into each internal strand, and thus to render each internal strand even less sensitive to corrosion.

[083] In some preferred embodiments, each internal thread of each internal strand has a diameter d1 greater than or equal to the diameter d2 of each intermediate thread of each internal strand, and highly preferably 15d1/d251.10. The use of diameters such that d1>d2 makes it possible to promote the penetrability of the elastomer compound through the intermediate layer. When dl>d2, then very preferably d1/d251.10, which makes it possible, on the one hand, to control the architectural stability of the intermediate layer and, on the other hand, to render the present invention even more beneficial because of the relatively small amount of desaturation created by the difference between dl and d2. The use of diameters such that dl=d2 makes it possible to limit the number of different threads to be managed in the manufacture of the cord, but also makes it possible to render the present invention even more beneficial because of the lack of desaturation created by the equality between dl and d2.

[084] In some preferred embodiments, each internal thread of each internal strand has a diameter dl greater than or equal to the diameter d3 of each external thread of each internal strand, and highly preferably 1 dl/d351.10. The use of diameters such that d1>d3 makes it possible to promote the penetrability of the elastomer compound through the external layer.When dl>d3,then very preferably d1/d351.10, which makes it possible, on the one hand, to control the architectural stability of the external layer and, on the other hand, to render the present invention even more beneficial because of the relatively small amount of desaturation created by the difference between dl and d3. The use of diameters such that dl=d3 makes it possible to limit the number of different threads to be managed in the manufacture of the cord, but also makes it possible to render the present invention even more beneficial because of the lack of desaturation created by the equality between dl and d3.

[085] In some preferred embodiments, each intermediate thread of each internal strand has a diameter d2 equal to the diameter d3 of each external thread of each internal strand. The use of diameters such that d2=d3 makes it possible to limit the number of different threads to be managed in the manufacture of the cord.

[086] Advantageously, each internal strand is of the type not rubberized in situ. What is meant by not rubberized in situ is that, prior to the assembly of the external layer of the cord, and prior to the assembly of the cord, each internal strand is made up of the threads of the various layers and does not have any polymer compound, notably any elastomer compound.

[087] External strands of the cord according to the invention

[088] Advantageously, the external layer of each external strand is desaturated, preferably completely unsaturated. The fact that the external layer of each external strand is desaturated advantageously makes it easier for the elastomer compound to pass as far as the centre of each external strand, and thus render each external strand less sensitive to corrosion.

[089] Advantageously, the inter-thread distance of the external layer of each external strand is greater than or equal to 5 pm. For preference, the inter-thread distance of the external layer of each external strand is greater than or equal to 15 pm, more preferably greater than or equal to 35 pm, more preferably still greater than or equal to 50 pm and highly preferably greater than or equal to 60 pm.

[090] The external layer of each external strand is preferably completely unsaturated.

[091] By definition, a completely unsaturated layer of threads is such that there is sufficient space in this layer to add in at least one (X'+1)th thread having the same diameter as the X' threads of the layer, it thus being possible for a plurality of threads to be in contact, or not in contact, with one another. In this particular instance, there is enough space in the external layer to add in at least one (N'+1)th thread having the same diameter as the N' threads of the external layer. In other words, what is meant by a completely unsaturated external layer of an external strand is that the sum S3' of the inter-thread distances 13' of the external layer is greater than or equal to the diameter d3' of the external threads of the external layer. Thus, advantageously, the sum S3' of the inter-thread distances of the external layer of each external strand is such that S3'> d3'. The sum S3' is the sum of the inter-thread distances separating each pair of adjacent threads in the external layer. The inter-thread distance of a layer is defined, in a section of the cord perpendicular to the main axis of the cord, as being the shortest distance which, on average, separates two adjacent threads of the layer. Thus, the inter-thread distance is calculated by dividing the sum S3' by the number of spaces separating the threads in the external layer.

[092] The fact that the external layer of each external strand is completely unsaturated makes it possible to maximize the penetration of the elastomer compound into each external strand, and thus to render each external strand even less sensitive to corrosion.

[093] In some preferred embodiments, each internal thread of each external strand has a diameter dl'greater than or equal to the diameter d3' of each external thread of each external internal strand, and highly preferably 1 d1'/d3'1.10. The use of diameters such that dl'>d3' makes it possible to promote the penetrability of the elastomer compound through the external layer. When dl'>d3', then very preferably d1'/d3'1.10, which makes it possible, on the one hand, to control the architectural stability of the external layer and, on the other hand, to render good penetrability of each external strand even more beneficial because of the relatively small amount of desaturation created by the difference between d1'and d3'. The use of diameters such that dl'=d3' makes it possible to limit the number of different threads to be managed in the manufacture of the cord, but also makes it possible to render the present invention even more beneficial because of the lack of desaturation created by the equality between d1'and d3'.

[094] In one embodiment, each external strand is of the type rubberized in situ. Such a strand comprises, prior to assembly of the cord, a layer of a polymer compound, notably an elastomer compound, arranged between at least two radially adjacent layers of threads, possibly between each of the radially adjacent layers of threads. Such a strand that is rubberized in situ is notably described in W02010054790.

[095] In another embodiment, each external strand is of the type not rubberized in situ. What is meant by not rubberized in situ is that, prior to the assembly of the cord, each external strand is made up of the threads of the various layers and does not have any polymer compound, notably any elastomer compound.

[096] Two-layer external strands

[097] In one embodiment which favours the compromise between the diameter of the cord and the breaking strength, each external strand has two layers. In this embodiment, the external layer of each external strand is wound around the internal layer of the external strand in contact with the internal layer of the external strand. In this embodiment, each external strand comprises a collection of threads which is made up of two layers of threads, neither more nor less, which means to say that the collection of threads has two layers of threads, not one, not three, but only two.

[098] In preferred embodiments, Q'=1, 2, 3or4.

[099] In one embodiment, Q'=1, N'=5 or 6, preferably Q'=1, N'=6.

[0100] In preferred embodiments that make it possible to increase the breaking strength of the cord with respect to the embodiment in which Q'=1, Q=2', 3 or 4, preferably Q'=3 or 4. Unlike in the embodiment in which Q'=1 and in which there is a risk of seeing the internal thread of each external strand pop radially out of each external strand and even out of the cord, under the effect of the repeated compressive loadings applied to the cord, the presence of several threads in the internal layer of each internal strand (Q'>1) makes it possible to reduce this risk as the compressive forces are then distributed over the plurality of threads of the internal layer.

[0101] In these embodiments in which Q'>1, advantageously each external strand has cylindrical layers, that is to say is a strand in which the Q' internal threads wound with a pitch p1' and in an internal-layer direction of each external strand and the N' external threads are wound around the intermediate layer with a pitch p3' and in an external layer direction of each external strand, p1' being different from p3' and/or the internal layer direction of each external strand being different from the external-layer direction of each internal strand.

[0102] In these preferred embodiments in which Q'>1, notably those in which Q'=3 or 4, there is a risk, when the strand is insufficiently penetrated, of seeing a highly significant spread of corrosive agents between the Q'=3 or 4 internal threads which delimit a central capillary which very much encourages them to spread along each strand. This disadvantage can be overcome by rendering the strand capable of being penetrated by the elastomer compound which then prevents the corrosive agents from accessing the central capillary and, in the best of cases in which the central capillary is itself penetrated, prevents these corrosive agents from spreading along the strand.

[0103] In preferred embodiments in which Q'>1, N'=7, 8, 9 or 10, for preference N'=8, 9 or 10 and more preferably N'=8 or 9.

[0104] In a first variant, Q'=2 and N'=7 or 8, for preference Q'=2, N'=7.

[0105] In a second variant, Q'=3 and N'=7, 8 or 9, for preference Q'=3, N'=8.

[0106] In a third variant, Q'=4 and N'=7, 8, 9 or 10, for preference Q'=4, N'=9.

[0107] In a first embodiment of the cord, the intermediate layer of each internal strand is wound around the internal layer of each internal strand in a direction of winding identical to the direction of winding of the cord.

[0108] Advantageously, the internal layer of the cord is wound in a cord internal-layer direction, and each intermediate layer and external layer of each internal strand is wound in the same direction of winding as the cord internal-layer direction.

[0109] Advantageously, the external layer of the cord is wound in a cord external-layer direction, and each internal layer (when Q'>1), intermediate layer and external layer of each external strand is wound in the same direction of winding as the cord external layer direction.

[0110] In one embodiment, the internal-layer direction of the cord and the external layer direction of the cord are the same. In this embodiment, manufacture is relatively easy because, unlike in the previous embodiment, there is no need to differentiate between the directions of winding of the internal and external layers of the cord. Nevertheless, contacts between the external threads of the external layers of the internal and external strands are relatively long and this may, with certain combinations of pitch, diameter and architecture of the cords, give rise to assembly defects caused, for example, by undesired slippage of the external strands in the grooves formed between the internal strands.

[0111] In another embodiment, the internal-layer direction of the cord and the external layer direction of the cord are opposite directions. In this embodiment, the risk of potential undesired slippage of the external strands in grooves formed between the internal strands as a result of a crossing between the internal and external strands is reduced.

[0112] Three-layer external strands

[0113] In another particularly advantageous embodiment that improves the breaking strength of the cord, each external strand has three layers and comprises: * an internal layer made up of Q'1 internal threads, • an intermediate layer made up of M'>1 intermediate threads wound around the internal layer, and * an external layer made up of N'>1 external threads wound around the intermediate layer.

[0114] In this embodiment, the external layer of each external strand is wound around the intermediate layer of the external strand in contact with the intermediate layer of the external strand and the intermediate layer of the external strand is wound around the internal layer of the external strand in contact with the internal layer of the external strand. In this embodiment, each internal strand comprises a collection of threads which is made up of three layers of threads, neither more nor less, which means to say that the collection of threads has three layers of threads, not two, not four, but only three.

[0115] In preferred embodiments, Q'=1, 2, 3 or 4.

[0116] In some embodiments, Q'=1. In the embodiment in which Q'=1, and when the cord is insufficiently penetrated, there is a risk of seeing the internal thread of each external strand radially leave each external strand and even the cord, under the effect of the repeated compressive loadings applied to the cord. By virtue of good penetration of each external strand and despite the fact that Q'=1, the elastomer compound acts like a wrapping layer around each external strand, notably around the external and intermediate layers of each external strand, preventing the internal thread from popping out, even under the repeated compressive loadings.

[0117] In these embodiments in which Q'=1, advantageously each external strand has cylindrical layers, that is to say is a strand in which the M' intermediate threads are wound around the internal layer with a pitch p2' and in an external strand intermediate layer direction and the N' external threads are wound around the intermediate layer with a pitch p3' and in an external strand external-layer direction, p2' is different from p3' and/or the external strand intermediate-layer direction is different from the external strand external-layer direction.

[0118] In one embodiment, Q'=1, M'=5 or 6 and N'=10, 11 or 12, for preference Q'=1, M'=5 or 6 and N'=10 or 11 and more preferably Q'=1, M'=6 and N'=11.

[0119] In preferred embodiments that make it possible to increase the breaking strength of the cord with respect to the embodiment in which Q'=1, Q'=2, 3 or 4, preferably Q'=3 or 4.

[0120] In these embodiments in which Q'>1, advantageously each external strand has cylindrical layers, that is to say is a strand in which the Q' internal threads are wound with a pitch p1' and in an external strand internal-layer direction, the M' intermediate threads are wound around the internal layer with a pitch p2' and in an external strand intermediate-layer direction, the N'external threads are wound around the intermediate layer with a pitch p3' and in an external strand external-layer direction, p1', p2' and p3' are each different one from another and/or the directions of the adjacent layers of the external strand are different.

[0121] In addition, for preference, the M' intermediate threads are wound around the internal layer with a pitch p2' and the N' external threads are wound around the intermediate layer with a pitch p3', the pitches p2' and p3' satisfying: - 0.33:5 (p3'-p2')/p3' 0.45 in instances in which Q'=2, - 0.355 (p3'-p2')/p3' 0.42 in instances in which Q'=3, - 0.285 (p3'-p2')/p3' 0.43 in instances in which Q'=4.

[0122] Such a ratio (p3'-p2')/p3' makes it possible to obtain relatively large radial passage windows for the elastomer compound within each external strand.

[0123] Advantageously, the pitches p2' and p3' satisfy the relationship: - 0.365 (p3'-p2')/p3', preferably 0.385 (p3'-p2')/p3'in instances in which Q=2, - 0.365 (p3'-p2')/p3', preferably 0.385 (p3'-p2')/p3'in instances in which Q'=3, - 0.325 (p3'-p2')/p3', preferably 0.365 (p3'-p2')/p3'in instances in which Q'=4.

[0124] In a similar way to the internal strand, the higher the ratio (p3'-p2')/p3' or, in other words, the greater the difference between p3'and p2', the better the architectural stability of each external strand.

[0125] Advantageously, the pitches p2' and p3' satisfy the relationship: - (p3'-p2')/p3' 5 0.42 and preferably (p3'-p2')/p3' 5 0.40 in instances in which Q'=2, - (p3'-p2')/p3' 0.40 in instances in which Q'=3, - (p3'-p2')/p3' 5 0.40 and preferably (p3'-p2')/p3' 5 0.38 in instances in which Q'=4.

[0126] Below these values, the size of the radial passage windows for the elastomer compound is at a maximum and makes it possible to optimize the penetrability of each external strand.

[0127] Advantageously, the pitch p1' is such that 3 mm 5 p1' 5 16 mm, preferably 4 mm5 p1' 13 mm and more preferably 5 mm5 sp1' 10 mm.

[0128] Advantageously, the pitch p2' is such that 8 mm 5 p2' 5 20 mm, preferably 9 mm5 p2' s 18 mm and more preferably 10 mm5 sp2' s 16 mm.

[0129] Advantageously, the pitch p3'is such that 10 mm5 p3' 540 mm, preferably 12 mm5 p3'5 30 mm and more preferably 15 mm5 p3' 25 mm.

[0130] Pitches p1', p2' and p3'within these preferred ranges make it possible to obtain a cord that exhibits mechanical properties compatible with tyre use, a relatively low cost and a relatively low linear cord weight.

[0131] In these preferred embodiments in which Q'>1, notably those in which Q'=3 or 4, there is a risk, when the strand is insufficiently penetrated, of seeing a highly significant spread of corrosive agents between the Q'=3 or 4 internal threads which delimit a central capillary which very much encourages them to spread along each strand. This disadvantage can be overcome by rendering the strand capable of being penetrated by the elastomer compound which then prevents the corrosive agents from accessing the central capillary and, in the best of cases in which the central capillary is itself penetrated, prevents these corrosive agents from spreading along the strand.

[0132] In preferred embodiments in which Q'>1, Q'=2, 3 or 4, M'=7, 8, 9 or 10, N'=13, 14 or 15, preferably Q'=3 or 4, M'=8, 9 or 10, N'=14 or 15, more preferably Q'=3, M'=8 or 9 and N'=14 or 15 and more preferably still Q'=3, M'=9 and N'=15.

[0133] Advantageously, the sum SI2' of the inter-thread distances of the intermediate layer is such that SI2' < d3' where d3' is the diameter of each external thread of each external strand, preferably SI2'5 0.8 x d3'. In a similar way to the internal strand, because the diameter d3' of the external threads of the external layer of each external strand is preferably greater than the sum SI2', the external threads are prevented from penetrating the intermediate layer. This then ensures good architectural stability, thereby reducing the risk of alteration to the radial passage windows for the elastomer compound and therefore the risk of degrading the good penetrability of each external strand. The sum SI2' is the sum of the inter-thread distances separating each pair of adjacent threads in the intermediate layer. The inter-thread distance of a layer is defined, in a section of the cord perpendicular to the main axis of the cord, as being the shortest distance which, on average, separates two adjacent threads of the layer. Thus, the inter-thread distance is calculated by dividing the sum SI2' by the number of spaces separating the threads in the intermediate layer.

[0134] Advantageously, the intermediate layer of each external strand is desaturated.

[0135] Advantageously, the inter-thread distance of the intermediate layer of each external strand is greater than or equal to 5 pm. For preference, the inter-thread distance in the intermediate layer of each external strand is greater than or equal to

15 pm, more preferably greater than or equal to 35 pm, more preferably still greater than or equal to 50 pm and highly preferably greater than or equal to 60 pm.

[0136] The fact that the intermediate layer of each external strand is desaturated advantageously makes it easier for the elastomer compound to pass as far as the centre of each external strand, and thus render each external strand less sensitive to corrosion.

[0137] In an embodiment that promotes the compromise between penetrability of each external strand and breaking strength, the intermediate layer of each external strand is incompletely unsaturated.

[0138] By definition, a layer that is incompletely unsaturated with threads is such that there is not enough space in this layer to add in at least one (X'+1)th thread having the same diameter as the X' threads of the layer. In this particular instance, there is not enough space in the intermediate layer to add in at least one (M'+1)thintermediate thread having the same diameter as the M' intermediate threads of the intermediate layer. In other words, what is meant by an incompletely unsaturated intermediate layer of an external strand is that the sum SI2' of the inter-thread distances 12' of the intermediate layer is less than the diameter d2' of the intermediate threads of the intermediate layer. Thus, advantageously, the sum SI2' of the inter-thread distances of the intermediate layer of each external strand is such that SI2' < d2'.

[0139] The fact that the intermediate layer of each external strand is incompletely unsaturated makes it possible to ensure architectural stability of the intermediate layer. Furthermore, the fact that the intermediate layer of each external strand is incompletely unsaturated makes it possible to ensure that the external strand comprises a relatively high number of intermediate threads and therefore exhibits a relatively high breaking strength.

[0140] In another embodiment that promotes the penetrability of each external strand, the intermediate layer of each external strand is completely unsaturated.

[0141] By definition, a completely unsaturated layer of threads is such that there is sufficient space in this layer to add in at least one (X'+1)th thread having the same diameter as the X' threads of the layer, it thus being possible for a plurality of threads to be in contact, or not in contact, with one another. In this particular instance, there is enough space in the intermediate layer of each external strand to add in at least one (M'+ 1)th intermediate thread having the same diameter as the M' intermediate threads of the intermediate layer. In other words, what is meant by a completely unsaturated intermediate layer of an external strand is that the sum SI2' of the inter-thread distances 12' of the intermediate layer is greater than or equal to the diameter d2' of the intermediate threads of the intermediate layer. Thus, advantageously, the sum SI2' of the inter-thread distances of the intermediate layer of each external strand is such that S2' > d'2.

[0142] In some preferred embodiments, each internal thread of each external strand has a diameter dl'greater than or equal to the diameter d2'of each intermediate thread of each external strand, and highly preferably 1 d1'/d2' 1.10. The use of diameters such that d1'>d2' makes it possible to promote the penetrability of the elastomer compound through the intermediate layer. When d1'>d2', then very preferably d1'/d2'1.10, which makes it possible, on the one hand, to control the architectural stability of the intermediate layer and, on the other hand, to render good penetrability of each external strand even more beneficial because of the relatively small amount of desaturation created by the difference between d1'and d2'. The use of diameters such that dl'=d2' makes it possible to limit the number of different threads to be managed in the manufacture of the cord, but also makes it possible to render the present invention even more beneficial because of the lack of desaturation created by the equality between d1'and d2'.

[0143] In some preferred embodiments, each intermediate thread of each external strand has a diameter d2' equal to the diameter d3' of each external thread of each external strand. The use of diameters such that d2'=d3' makes it possible to limit the number of different threads to be managed in the manufacture of the cord.

[0144] TYRE ACCORDING TO THE INVENTION

[0145] Another subject of the invention is a tyre comprising a cord as defined above.

[0146] The cord is most particularly intended for industrial vehicles selected from heavy vehicles such as "heavy-duty vehicles" - i.e. underground trains, buses, road haulage vehicles (lorries, tractors, trailers), off-road vehicles, agricultural vehicles or construction plant vehicles, or other transport or handling vehicles.

[0147] As a preference, the tyre is for a vehicle of the construction plant type. The tyre has a size of the W R U type in which, as is known to those skilled in the art, W denotes: - the nominal aspect ratio H/B as defined by the ETRTO, when it is in the form H/B, H being the cross-sectional height of the tyre and B being the cross-sectional width of the tyre, - H.00 or B.00 when it is in the form H.00 or B.00, in which H=B, H and B being as defined above, U represents the diameter, in inches, of the rim seat on which the tyre is intended to be mounted, and R denotes the type of carcass reinforcement of the tyre, in this case radial. Examples of such dimensions are, for example, 40.00 R 57 or else 59/80 R 63.

[0148] Preferably, U 35, more preferably U 49 and even more preferably U57.

[0149] In one embodiment, the tyre has a carcass reinforcement anchored in two beads and surmounted radially by a crown reinforcement which is itself surmounted by a tread, the crown reinforcement being joined to the said beads by two sidewalls, the carcass reinforcement comprising at least one cord as defined above.

[0150] In another embodiment, the tyre has a carcass reinforcement anchored in two beads and surmounted radially by a crown reinforcement which is itself surmounted by a tread, the crown reinforcement being joined to the said beads by two sidewalls, and comprising at least one cord as defined above.

[0151] Advantageously, the carcass reinforcement comprises at least one carcass ply comprising filamentary metal carcass reinforcing elements, each filamentary metal carcass reinforcing element making an angle of between 80 and 90 with the circumferential direction of the tyre.

[0152] Advantageously, the crown reinforcement comprises a working reinforcement comprising at least one cord as defined hereinabove.

[0153] Advantageously, the working reinforcement comprises at least one working ply comprising filamentary metal working reinforcing elements arranged substantially parallel to one another, each filamentary metal working reinforcing element making an angle at most equal to 60°, preferably ranging from 15° to 40°, with the circumferential direction of the tyre and being formed of a cord as defined hereinabove.

[0154] In one advantageous embodiment, the working reinforcement comprises at least a first and a second working ply, each first and second working ply respectively comprising first and second filamentary metal working reinforcing elements arranged substantially parallel to one another in each first and second working ply, each first and second filamentary metal working reinforcing element making an angle at most equal to 60°, preferably ranging from 15° to 40°, with the circumferential direction of the tyre and being formed of a cord as defined hereinabove. Optionally, the first and second filamentary metal working reinforcing elements are crossed from one working ply to the other, which is to say that the orientation of the angle made by the first filamentary metal working reinforcing elements with the circumferential direction of the tyre is the opposite to the orientation of the angle made by the second filamentary metal working reinforcing elements with the circumferential direction of the tyre.

[0155] Advantageously, the crown reinforcement comprises a protective reinforcement comprising at least one protective ply comprising filamentary metal protective reinforcing elements arranged substantially parallel to one another, each filamentary metal protective reinforcing element making an angle at least equal to 10, preferably ranging from 100 to 350 and preferentially from 150 to 300, with the circumferential direction of the tyre.

[0156] In one advantageous embodiment, the protective reinforcement comprises a first and a second protective ply, each first and second protective ply respectively comprising first and second filamentary metal protective reinforcing elements arranged substantially parallel to one another in each first and second protective ply, each first and second filamentary metal protective reinforcing element making an angle at least equal to 100, preferably ranging from 100 to 350 and preferentially from 150 to 300, with the circumferential direction of the tyre.

[0157] In a preferred embodiment, the protective reinforcement is interposed radially between the tread and the working reinforcement.

[0158] Advantageously, the crown reinforcement comprises an additional reinforcement comprising at least one additional ply comprising additional filamentary metal reinforcing elements arranged substantially parallel to one another in the additional ply, each additional filamentary metal reinforcing element making an angle at most equal to 100, preferably ranging from 50 to 100, with the circumferential direction of the tyre.

[0159] In one advantageous embodiment, the additional reinforcement comprises a first and a second additional ply, each first and second additional ply respectively comprising first and second additional filamentary metal reinforcing elements arranged substantially parallel to one another in each first and second additional ply, each first and second additional filamentary metal reinforcing element making an angle at most equal to 100, preferably ranging from 50 to 100, with the circumferential direction of the tyre.

[0160] The invention will be understood better from reading the following description, which is given solely by way of non-limiting example and with reference to the drawings, in which: - Figure 1 is a view in cross section perpendicular to the circumferential direction of a tyre according to the invention; - Figure 2 is a detail view of the region II of Figure 1; - Figures 3, 4 and 5 are schematic views in cross section perpendicular to the axis of the cord (which is assumed to be straight and at rest) of cords according to first, second and third embodiments of the invention, respectively; - Figures 6, 7 and 8 are views similar to those of Figures 3, 4 and 5 of cords according to fourth, fifth and sixth embodiments of the invention, respectively;

- Figures 9, 10 and 11 are views similar to those of Figures 3, 4 and 5 of cords according to seventh, eighth and ninth embodiments of the invention, respectively; - Figures 12, 13 and 14 are views similar to those of Figures 3, 4 and 5 of cords according to tenth, eleventh and twelfth embodiments of the invention, respectively; - Figures 15, 16 and 17 are views similar to those of Figures 3 and 4 of cords according to thirteenth, fourteenth and fifteenth embodiments of the invention, respectively; - Figure 18 is a schematic view in projection onto a plane containing the axis of an external strand prior to assembly of the cord according to the first embodiment of the invention; and - Figure 19 is a detail view of the region XVlI depicting a radial passage window delimited by threads of an intermediate layer and threads of an external layer of each internal strand of Figure 24.

[0161] Any range of values denoted by the expression "between a and b" represents the range of values extending from more than a to less than b (namely excluding the end-points a and b), whereas any range of values denoted by the expression "from a to b" means the range of values extending from the end-point "a" as far as the end point "b", namely including the strict end-points "a" and "b".

[0162] EXAMPLE OF A TYRE ACCORDING TO THE INVENTION

[0163] A frame of reference X, Y, Z corresponding to the usual respectively axial (X), radial (Y) and circumferential (Z) orientations of a tyre has been depicted in the figures.

[0164] The "median circumferential plane" M of the tyre is the plane which is normal to the axis of rotation of the tyre and which is situated equidistant from the annular reinforcing structures of each bead and passes through the middle of the crown reinforcement.

[0165] Figures 1 and 2 depict a tyre according to the invention and denoted by the general reference 10.

[0166] The tyre 10 is for a heavy vehicle of construction plant type, for example of "dumper" type. Thus, the tyre 10 has a dimension of the type 53/80R63.

[0167] The tyre 10 has a crown 12 reinforced by a crown reinforcement 14, two sidewalls 16 and two beads 18, each of these beads 18 being reinforced with an annular structure, in this instance a bead wire 20. The crown reinforcement 14 is surmounted radially by a tread 22 and connected to the beads 18 by the sidewalls 16. A carcass reinforcement 24 is anchored in the two beads 18 and is in this instance wound around the two bead wires 20 and comprises a turnup 26 positioned towards the outside of the tyre 20, which is shown here fitted onto a wheel rim 28. The carcass reinforcement 24 is surmounted radially by the crown reinforcement 14.

[0168] The carcass reinforcement 24 comprises at least one carcass ply 30 comprising filamentary metal carcass reinforcing elements 31 and extending from one bead 18 to the other so as to form an angle of between 80 and 90 with the circumferential direction Z of the tyre 10.

[0169] The tyre 10 also comprises a sealing ply 32 made up of an elastomer (commonly known as "inner liner") which defines the radially internal face 34 of the tyre 10 and which is intended to protect the carcass ply 30 from the diffusion of air coming from the space inside the tyre 10.

[0170] The crown reinforcement 14 comprises, radially from the outside towards the inside of the tyre 10, a protective reinforcement 36 arranged radially on the inside of the tread 22, a working reinforcement 38 arranged radially on the inside of the protective reinforcement 36 and an additional reinforcement 80 arranged radially on the inside of the working reinforcement 38. The protective reinforcement 36 is thus interposed radially between the tread 22 and the working reinforcement 38. The working reinforcement 38 is interposed radially between the protective reinforcement 36 and the additional reinforcement 80.

[0171] The protective reinforcement 36 comprises first and second protective plies 42, 44, the first ply 42 being arranged radially on the inside of the second ply 44. Each first and second protective ply 42, 44 respectively comprises first and second filamentary metal protective reinforcing elements 43, 45 arranged substantially parallel to one another in each first and second protective ply 42, 44. Each first and second filamentary metal protective reinforcing element 43, 45 makes an angle at least equal to 10, preferably ranging from 10 to 35 and more preferably from 15 to 30, with the circumferential direction Z of the tyre.

[0172] The working reinforcement 38 comprises first and second working plies 46, 48, the first ply 46 being arranged radially on the inside of the second ply 48. Each first and second working ply 46, 48 respectively comprises first and second filamentary metal working reinforcing elements 47, 49 arranged substantially parallel to one another in each first and second working ply 46, 48. Each first and second filamentary metal working reinforcing element 47, 49 makes an angle at most equal to 60, preferably ranging from 15 to 40, with the circumferential direction Z of the tyre 10. Optionally, the first and second filamentary metal working reinforcing elements 47, 49 are crossed from one working ply to the other, which is to say that the orientation of the angle made by the first filamentary metal working reinforcing elements 47 with the circumferential direction Z of the tyre 10 is the opposite to the orientation of the angle made by the second filamentary metal working reinforcing elements 49 with the circumferential direction Z of the tyre 10.

[0173] The additional reinforcement 80, also referred as the limiting block, the function of which is to partially absorb the mechanical stresses of inflation, comprises first and second additional plies 82, 84, each first and second additional ply 82, 84 respectively comprising first and second additional filamentary metal reinforcing elements 83, 85 arranged substantially parallel to one another in each first and second additional ply 82, 84. Each first and second additional filamentary metal reinforcing element 83, 85 makes an angle at most equal to 100, preferably ranging from 50 to 100, with the circumferential direction Z of the tyre 10. The additional filamentary metal reinforcing elements are, for example, as described in FR 2 419 181 or FR 2 419 182.

[0174] In one embodiment, each first and second filamentary metal working reinforcing element 47, 49 is formed by a cord according to the invention, for example the cord 50 described hereinbelow.

[0175] In another embodiment, each filamentary metal carcass reinforcing element 31 formed by a cord according to the invention, for example the cord 50 described hereinbelow.

[0176] In yet another embodiment, each first and second filamentary metal working reinforcing element 47, 49 and each filamentary metal carcass reinforcing element 31 is formed by a cord according to the invention, it being possible for these cords to be identical or different according to whether they are filamentary metal reinforcing elements 31, 47 or 49.

[0177] CORD ACCORDING TO A FIRST EMBODIMENT OF THE INVENTION

[0178] Figure 3 depicts the cord 50 according to a first embodiment of the invention.

[0179] The cord 50 is metal and is of the multi-strand type with two cylindrical layers. Thus, it is understood that there are two layers, not more, not less, of strands of which the cord 50 is made. The layers of strands are adjacent and concentric. The cord 50 is devoid of polymer compound and of elastomer compound when it is not integrated into the tyre.

[0180] The cord 50 comprises an internal layer CI of the cord 50, and an external layer CE of the cord 50. The internal layer CI is made up of K>1 internal strands TI wound in a helix. The external layer CE is made up of L>1 external strands, which means to say a plurality of external strands TE. In this instance, K=2, 3 or 4, preferably K=3 or 4 and here K=3. The external layer CE is made up of L>1 external strands TE wound around the internal layer CI of the cord. In this particular instance, L=7, 8, 9 or 10, preferably L=8, 9 or 10 and more preferably L=8 or 9 and in this particular instance L=9. The cord 50 also comprises a wrapper F made up of a single wrapping wire.

[0181] The internal layer CI of the cord is wound in a helix in a cord internal-layer direction, in this instance Z, with a pitch pi, and here pi=80 mm, and the external layer CE is wound in a helix in a cord external-layer direction, in this instance Z, with a pitch pe, and here pe=100 mm. Because pi is different from pe, the cord has layers which are cylindrical.

[0182] The wrapper F is wound around the external layer CE in a direction of winding of the wrapper, in this instance opposite to the direction of winding of the cord, in this instance in the S-direction. The wrapping wire is wound in a helix around the external strands TE with a pitch pf such that 2 mm5 pf 10 mm and, for preference, 3 mm5 pf 5 8 mm. Here, pf=5.1 mm.

[0183] The assembly made up of the internal CI and external CE layers, which means to say the cord 50 without the wrapper F, has a diameter D. Here, D=6.0 mm.

[0184] The external layer CE of the cord 50 is desaturated. The mean inter-strand distance E separating two adjacent external strands TE is greater than or equal to 30 pm, preferably greater than or equal to 70 pm, more preferably greater than or equal to 100 pm, more preferably still greater than or equal to 150 pm and highly preferably greater than or equal to 200 pm. In this embodiment, the inter-strand distance of the external layer of external strands is greater than or equal to 200 pm. Here, E=271 pm.

[0185] Each internal strand TI has a diameter DI and each external strand TE has a diameter DE. In this particular instance, DI=1.56 mm and DE=1.32 mm.

[0186] The external layer CE of the cord 50 is incompletely unsaturated. Specifically, SIE=9 x 0.271=2.44 mm, which is a value higher than DE=1.32 mm.

[0187] External strands TE of the cord 50

[0188] Each external strand TE has at least two layers. In this particular instance, each external strand TE is a three-layered strand. Each external strand TE comprises, in this instance is made up of, three layers, not more, not less.

[0189] Each external strand TE comprises an internal layer Cl' made up of Q' internal thread(s) F1', an intermediate layer C2'made up ofM'intermediate threads F2'wound in a helix around the internal layer C', and an external layer C3'made up of N' external threads F3' wound in a helix around the internal layer Cl' and around and in contact with the intermediate layer C2'.

[0190] Q'=1, 2, 3 or 4 and more preferably here Q'=1.

[0191] Where Q'=1, M'=5 or 6 and N'=10, 11 or 12, for preference Q'=1, M'=5 or 6 and N'=10 or 11 and here Q'=1, M'=6 and N'=11.

[0192] The internal thread Fl' has an infinite pitch.

[0193] The intermediate layer C2' of each external strand TE is wound around the internal layer C1' of the external strand TE in an external strand intermediate-layer direction of winding, in this instance in the direction Z, which is opposite to the direction of winding of the cord, S. The M' intermediate threads F2'are wound in a helix around the internal thread Fl'with a pitch p2' such that 8 mm 5 p2' 5 20 mm, for preference 9 mm5 p2' 18 mm, and more preferably 10 mm5 sp2' 16 mm. Here, p2'=14 mm.

[0194] The external layer C3' of each external strand TE is wound around the internal C1'and intermediate C2'layers of the external strand TE in an external strand external layer direction of winding, in this instance in the direction Z, which is opposite to the direction of winding of the cord, S, and in the same direction Z as the intermediate layer C2' of each external strand TE. The N external threads F3'are wound in a helix around the M' intermediate threads F2' with a pitch p3' such that 10 mm 5 p3' 5 40 mm, for preference 12 mm 5 p3'5 30 mm, and more preferably 15 mm5 p3'5 25 mm. Here, p3'=20 mm.

[0195] Because p1' is different from p2' and p2' is different from p3', each external strand TE has layers which are cylindrical.

[0196] The intermediate layer C2' of each external strand TE is desaturated and incompletely unsaturated. The inter-thread distance 12' of the intermediate layer C2' which on average separates the M' intermediate threads is advantageously greater than or equal to 5 pm and is here equal to 9 pm. Because the intermediate layer C2' is incompletely unsaturated, the sum SI2' of the inter-thread distances 12' of the intermediate layer C2' is less than the diameter d2' of the intermediate threads F2' of the intermediate layer C2'. Here, the sum S12'=6 x 0.009=0.05 mm, which is a value strictly less than d2'=0.26 mm.

[0197] The sum SI2' of the inter-thread distances 12' of the intermediate layer C2' is less than the diameter d3' of the external threads F3' of the external layer C3' and preferably less than or equal to 0.8 x d3'. Here, the sum S12'=6 x 0.009=0.05 mm, which is a value strictly less than d3'=0.26 mm.

[0198] The external layer C3'of each external strand TE is desaturated and completely unsaturated. The inter-thread distance 13' of the external layer C3' which on average separates the N' external threads is advantageously greater than or equal to 5 pm, preferably greater than or equal to 15 pm, more preferably greater than or equal to 35 pm, and is here equal to 36 pm. The sum S3' of the inter-thread distances 13 of the external layer C3' is greater than the diameter d3' of the external threads F3' of the external layer C3'. Here, the sum S13'=11 x 0.036=0.39 mm, which is a value strictly greater than d3'=0.26 mm.

[0199] Each internal, intermediate and external thread of each external strand TE respectively has a diameter d1', d2' and d3'. Each internal thread diameter d1', intermediate thread diameter d2' and external thread diameter d3' of each external strand TE ranges from 0.15 mm to 0.60 mm, preferably from 0.20 mm to 0.50 mm, more preferably from 0.22 mm to 0.40 mm, and more preferably still from 0.24 mm to 0.35 mm.

[0200] The internal thread Fl' of each external strand TE has a diameter d1' greater than or equal to the diameter d2'of each intermediate thread F2'of each external strand TE, and very preferably 1 d1'/d2'1.10. The internal thread Fl'of each external strand TE has a diameter dl'greater than or equal to the diameter d3' of each external thread F3' of each external strand TE, and very preferably 1d1'/d3' 1.10. Each diameter d2' of each intermediate thread F2' of each external strand TE and each diameter d3' of each external thread F3' of each external strand TE are such that d2'=d3'.

[0201] In this instance, d1'>d2' and d1'>d3', d1'/d2'=d1'/d3'=1.08 and d1'=0.28 mm, d2'=d3'=0.26 mm.

[0202] Internal strand TI of the cord 50

[0203] Each internal strand TI has three layers. Thus, each internal strand TI comprises, in this instance is made up of, three layers, not more, not less.

[0204] Each internal strand TI comprises an internal layer C1 made up of Q=2, 3 or 4 internal threads, an intermediate layer C2 made up of M intermediate threads F2 wound in a helix around the internal layer C1, and an external layer C3 made up of N external threads F3 wound in a helix around the internal layer C1 and around and in contact with the intermediate layer C2.

[0205] M=7, 8, 9 or 10, N=12, 13, 14 or 15 and here Q=2, M=7 or 8 and N=12 or 13. In this instance, the cord 50 is such that Q=2, M=7 and N=12.

[0206] The internal layer C1 of each internal strand TI is wound in a helix in an internal layer direction of winding for each internal strand, in this instance in the direction Z, which is opposite to the direction of winding S of the cord. The Q internal threads F1 are wound in a helix with a pitch p1 such that 3 mm5 p1 5 16 mm, for preference 4 mm 5 p1 5 13 mm, and more preferably 5 mm5 sp1 5 10 mm. Here, p1=6 mm.

[0207] The intermediate layer C2 of each internal strand TI is wound around the internal layer C1 of each internal strand TI in an intermediate-layer direction of winding for each internal strand, in this instance in the direction Z, which is opposite to the direction of winding S of the cord. The M intermediate threads F2 are wound in a helix around the internal threads F1 with a pitch p2 such that 8 mm 5 p2 5 20 mm, for preference 9 mm ! p2 5 18 mm, and more preferably 10 mm 5 p2 5 16 mm. Here, p2=11 mm.

[0208] The external layer C3 of each internal strand TI is wound around the intermediate layer C2 of each internal strand TI in an external-layer direction of winding for each internal strand TI, in this instance in the direction Z, which is opposite to the direction of winding S of the cord and in the same direction Z as the internal layer C1 and intermediate layer C2 of each internal strand TI and in the same direction Z as the external layer C3' of each external strand TE. The N external threads F3 are wound in a helix around the M intermediate threads F2 with a pitch p3 such that 10 mm 5 p3 5 40 mm, for preference 12 mm 5 p3 5 30 mm, and more preferably 15 mm 5 p3 5 25 mm. Here, p3=18 mm.

[0209] The pitches p2 and p3 satisfy 0.335 (p3-p2)/p3 0.45.

[0210] 0.365 (p3-p2)/p3, preferably 0.385 (p3-p2)/p3.

[0211] (p3-p2)/p3 0.42 and for preference (p3-p2)/p3 0.40.

[0212] In this instance, (p3-p2)/p3=0.39.

[0213] Because p1 is different from p2 and p2 is different from p3, each internal strand has layers which are cylindrical.

[0214] The intermediate layer C2 of each internal strand TI is desaturated and in this instance completely unsaturated. The inter-thread distance 12 of the intermediate layer C2 which on average separates the M intermediate threads is advantageously greater than or equal to 5 pm, preferably greater than or equal to 15 pm, more preferably greater than or equal to 35 pm, and more preferably still than/to 50 pm, and in this embodiment, the inter-thread distance 12 is very preferably greater than or equal to 60 pm, and is here equal to 75 pm. Because the intermediate layer C2 is completely unsaturated, the sum S12 of the inter-thread distances 12 of the intermediate layer C2 is less than the diameter d2 of the intermediate threads F2 of the intermediate layer C2. Here, the sum S12=7 x 0.075 = 0.52 mm, which is a value strictly greater than d2=0.26 mm.

[0215] The external layer C3 of each internal strand TI is desaturated and completely unsaturated. The inter-thread distance 13 of the external layer C3 which on average separates the N external threads is advantageously greater than or equal to 5 pm, preferably greater than or equal to 15 pm, more preferably greater than or equal to 35 pm, and more preferably still than/to 50 pm, and in this embodiment, the inter-thread distance 12 is very preferably greater than or equal to 60 pm, and is here equal to 71 pm. The sum S13 of the inter-thread distances 13 of the external layer C3 is greater than the diameter d3 of the external threads F3 of the external layer C3. Here, the sum S13=12 x 0.071=0.85 mm, which is a value strictly greater than d3=0.26 mm.

[0216] Each internal, intermediate and external thread of each internal strand TI respectively has a diameter dl, d2 and d3. Each internal thread diameter dl, intermediate thread diameter d2 and external thread diameter d3 of each internal strandTI rangesfrom 0.15 mm to0.60 mm, preferablyfrom 0.20 mmto0.50 mm, more preferably from 0.22 mm to 0.40 mm, and more preferably still from 0.24 mm to 0.35 mm.

[0217] The internal thread F1 of each internal strand TI has a diameter dl greaterthan or equal to the diameter d2 of each intermediate thread F2 of each internal strand TI, and highly preferably 1d1/d251.10. The internal thread F1 of each internal strand TI has a diameter dl greater than or equal to the diameter d3 of each external thread F3 of each internal strand TI, and highly preferably 1 d1/d351.10. Each diameter d2 of each intermediate thread F2 of each internal strand TI and each diameter d3 of each external thread F3 of each internal strand TI are such that d2=d3.

[0218] In this instance, d1=d2=d3 and d1=d2=d3=0.26 mm.

[0219] Each external thread F3 of each internal strand TI has a diameter d3 greater than or equal to the diameter d3' of each external thread F3 of each external strand TE. Here, d3=0.26 mm=d3'=0.26 mm.

[0220] Each thread has a breaking strength, denoted Rm, such that 2500 5 Rm 3100 MPa. The steel for these threads is said to be of SHT ("Super High Tensile") grade. Other threads may be used, for example threads of an inferior grade, for example of NT ("Normal Tensile") or HT ("High Tensile") grade, just as may threads of a superior grade, for example of UT ("Ultra Tensile") or MT ("Mega Tensile") grade.

[0221] METHOD FOR MANUFACTURING THE CORD ACCORDING TO THE INVENTION

[0222] The cord according to the invention is manufactured using a method comprising steps well known to those skilled in the art.

[0223] Each aforementioned internal strand is manufactured according to known methods involving the following steps, preferably performed in line and continuously: - first of all, a first step of assembling, by cabling, the Q internal threads F1 of the internal layer C1 at the pitch p1 and in the Z-direction to form the internal layer C1 at a first assembling point; - followed by a second step of assembling, by cabling or by twisting, the M intermediate threads F2 around the Q internal threads F1 of the internal layer C1 at the pitch p2 and in the Z-direction to form the intermediate layer C2 at a second assembling point; - followed by a third step of assembling, by cabling or by twisting, the N external threads F3 around the M intermediate threads F2 of the intermediate layer C2 at the pitch p3 and in the Z-direction to form the external layer C3 and each internal strand TI at a third assembling point; - preferably a final twist-balancing step.

[0224] In a step for manufacturing the external strands using the following steps, preferably carried out in line and continuously: - first of all, in instances in which Q'>1, a first step of assembling, by cabling, the Q internal threads F1 of the internal layer C1 at the pitch p1 and in the Z-direction to form the internal layer C1 at a first assembling point; in embodiments in which Q'=1, the first assembling step is omitted; - followed by a second step of assembling, by cabling, the M' intermediate threads F2' around the Q' internal threads F1' of the internal layer Cl' at the pitch p2' and in the Z direction to form the intermediate layer C2' at a first assembling point; - followed by a third step of assembling, by cabling, the N'external threads F3' around the M' intermediate threads F2' of the intermediate layer C2'at the pitch p3' and in the Z-direction to form the external layer C3' and each external strand TE at a second assembling point; - preferably a final twist-balancing step.

[0225] What is meant here by "twist balancing" is, as is well known to those skilled in the art, the cancellation of the residual torque (or the elastic return of the twist) applied to each thread of the strand, in the intermediate layer as in the external layer.

[0226] After this final twist-balancing step, the manufacture of the strand is complete. Each strand is wound onto one or more receiving reels, for storage, prior to the later operation of assembling the elementary strands by cabling in order to obtain the multi strand cord.

[0227] In a step of manufacturing the internal layer CI, the K internal strands TI are assembled by cabling at the pitch pi and in the Z-direction to form the internal layer CI at a first assembling point.

[0228] Then, in a later manufacturing step, the L external strands TE are assembled by cabling around the internal layer CI at the pitch pe and in the Z-direction to form the assembly of the layers CI and CE. Possibly, in a last assembly step, the wrapper F is wound, at the pitch pf and in the S-direction, around the assembly previously obtained.

[0229] The cord is then incorporated by skimming into composite fabrics formed from a known composition based on natural rubber and carbon black as reinforcing filler, conventionally used for manufacturing crown reinforcements of radial tyres. This compound essentially contains, in addition to the elastomer and the reinforcing filler (carbon black), an antioxidant, stearic acid, an extender oil, cobalt naphthenate as adhesion promoter, and finally a vulcanization system (sulfur, accelerator and ZnO).

[0230] The composite fabrics reinforced by these cords have an elastomeric compound matrix formed from two thin layers of elastomeric compound which are superposed on either side of the cords and which have a thickness of between 1 and 4 mm, inclusive, respectively. The skim-coating pitch (the pitch at which the cords are laid in the elastomeric compound fabric) ranges from 4 mm to 8 mm.

[0231] These composite fabrics are then used as working ply in the crown reinforcement during the method of manufacturing the tyre, the steps of which are otherwise known to a person skilled in the art.

[0232] CORD ACCORDING TO A SECOND EMBODIMENT OF THE INVENTION

[0233] Figure 4 depicts a cord 50' according to a second embodiment of the invention. Elements similar to those of the first embodiment are denoted by identical references.

[0234] Unlike in the first embodiment described hereinabove, the cord 50' according to the second embodiment is such that is such that K=2 and L=8.

[0235] CORD ACCORDING TO A THIRD EMBODIMENT OF THE INVENTION

[0236] Figure 5 depicts a cord 50" according to a third embodiment of the invention. Elements similar to those of the first embodiment are denoted by identical references.

[0237] Unlike in the first embodiment of the cord 50 described hereinabove, the cord 50" according to the third embodiment is such that is such that K=4 and L=10.

[0238] Table A below summarizes the characteristics of the various cords 50, 50' and 50".

Cords 50 50' 50" Q/M/N 2/7/12 2/7/12 2/7/12 dl/d2/d3 0.26/0.26/0.26 0.26/0.26/0.26 0.26/0.26/0.26

direction for C1/pitch Z/6 Z/6 Z/6 p1 (mm) TI direction2 for C2/pitch Z/11 Z/11 Z/11 p (mm) direction for C3/pitch Z/18 Z/18 Z/18 p3 (mm) (p3-p2)/p3 0.39 0.39 0.39

12 (pm)/SI2 (mm) 75/0.52 75/0.52 75/0.52

13 (pm)/S13 (mm) 71/0.85 71/0.85 71/0.85 DI (mm) 1.56 1.56 1.56 Q'/M'/N' 1/6/11 1/6/11 1/6/11 dl'/d2'/d3' 0.28/0.26/0.26 0.28/0.26/0.26 0.28/0.26/0.26

direction for C1'/pitch -/Inf -/Inf -/Inf p1' (mm) direction for C2'/pitch Z/14 Z/14 Z/14 p2'(mm) TE direction for C3'/pitch Z/20 Z/20 Z/20 p3'(mm) (p3'-p2')/p3' 0.3 0.3 0.3

12'(pm)/S12'(mm) 9.0/0.05 9.0/0.05 9.0/0.05

13'(pm)/S13'(mm) 36.0/0.39 36.0/0.39 36.0/0.39

DE (mm) 1.32 1.32 1.32 K 3 2 4 L 9 8 10 D (mm) 6.0 5.8 6.4 E (pm) 271 373 239 SIE (mm) 2.44 3.98 2.39

Direct oof winding of the Z/Z 80/100 Z/z 80/100 Z/Z 80/100 cord/pitch pi/pe

Table A

[0239] CORDS ACCORDING TO THE FOURTH TO FIFTEENTH EMBODIMENTS OF THE INVENTION

[0240] Figures 6 to 17 depict the cords 51, 51', 51", 52, 52', 52", 60, 60', 60", 61, 61' and 61" according to the fourth to fifteenth embodiments of the invention.

[0241] The features of the various cords 51, 51', 51", 52, 52', 52", 60, 60', 60", 61, 61' and 61" according to the fourth to fifteenth embodiments of the invention have been summarized in Tables B and C hereinbelow.

CNN C

N4 rn 0) CC:) 0- 5 0 C 6l ci- C)~? N 00 rl C:)~ 00

d -)

(0 (0 CN CO (0 0 . r 0C 0 00

'o 006 C0 C

(0 (0 CC CN (0 . (00 0 CC~ .0 0 coC) C)

.n N- j )j0 C Ec) N- j EN (0 Co C) C)

(0 (0 CN CN 0 o .O E O .) CY) 0I) (0 O0 COO C )0 *C~

(0 (0f)C CN CNJ Ln- Nl ji ji jD04

(0 00 ) -(0 C C5 C504CN _ C C? ~~ 04 (0-~ 60 co C))O ' N e c c 0-- ~ o oC c, c iz es 6 )

If) 0 PR (0 LOIf o C) CJ

(0 co 2 00 0) m o (0 C) Ce N O CN CN CY) CIf)rIC)L O0) c o 00 CO ) m r 0 (0 C) '

(Y) |-CI-O : C.0 .

CN C C o CN? 04C 0 N

c o LO 0 0 0

CL CLJ~ CL) c E E CL ;--- E'j- E

- :*- - :- :- E E~

(D C14 C 'a E_ jE ' 0E 0E 0E

Uj A :5 :;- .c N. )

w c0

.,o CN )ce0o o0 6 m er; o0 00 6 N j:; j: 6 - .6

! -Y er- NNO dO -I cf U o o co rN j

NN jY N-I C C:) 0) ~~~(0 0 0 ) C:

0 0o (0= co) o © o) U)oo

N C) CY)

CNN e LL)O

o . O C 66C ON( CO) N WLO 6 Nf LO~6 +-• C 0 - C E --- --- C 0 ' 6 6E - 3 (0 U oC) CY) Lo r-j cor 0 )-o(0 o )0 r (0 -) (0 _ CO 0) O0,© CO T CO(0-- 6- . -- OC5 ok- 0 .6C 0 00 . 6 N C:

! N CN H~ -10 U' N 4) 4 CY)

(0 LO 04 CNY) Eo -~ z C) CN U )E ' -;T- Yi 00 to r- (0 66 nm -- 0C) ~ ( . CY 00 ~0) N0 LO CC? 0O L

N CC)

r-o 0 toCo ).6c) 0 r.0N0. 04 -- E 04' C')

E 0 ~ 4)~E z EE E E~ c,4 co :i) CM CL EOcOcE E E 5CY 4

0 0) 0C 0C C \I E E 0 0 L4- .-) 0

0

00 r I~w. irLo 00

0

cI 00 0O 00N~ * 0

NN .6 ~fm( oo

L60 0

NN

N- M CI 0 E~ 0~ EN -N&

0

-~ -~00

[0242] COMPARATIVE TESTS

[0243] Indicator of the penetrability of the strands by an elastomeric compound

[0244] The ability of a strand to be penetrated by an elastomeric compound was determined in the following tests by simulating the size of the radial passage windows formed by two adjacent threads F2 of the intermediate layer C2 and by two adjacent threads F3 of the external layer C3. Such windows are illustrated in Figure 18 which depicts a schematic view of each internal strand along its main axis P and in Figure 19 which depicts the radial passage window S defined hereinabove.

[0245] Such an indicator of the penetrability of the strand is an image of the impermeability of the strand to air. Specifically, the larger the size of the windows, the higher the penetrability indicator, the more elastomer compound is liable to penetrate the strand and the more impermeable the strand is to air. The permeability could also be determined using the permeability test that makes it possible to determine the longitudinal permeability to air of the strands or cords tested, by measuring the volume of air passing along a test specimen under constant pressure over a given period of time. The principle of such a test, which is well known to those skilled in the art, is to demonstrate the effectiveness of the treatment of a strand or of a cord to make it impermeable to air; it has been described for example in standard ASTM D2692-98. Such a test is carried out on as-manufactured and non-aged strands or cords. The raw strands or cords are coated on the outside beforehand with an elastomeric compound referred to as coating compound. For this purpose, a series of 10 strands or cords laid parallel (distance between cords: 20 mm) is placed between two layers or "skims" (two rectangles measuring 80 x 200 mm) of a diene elastomeric compound in the raw state, each skim having a thickness of 5 mm; all of this is then immobilized in a mould, with each of the strands or cords being kept under sufficient tension (for example 3 daN) to guarantee that it lies straight as it is being placed in the mould, using clamping modules; it is then vulcanized (cured) for around 10 to 12 hours at a temperature of around 120°C and at a pressure of 15 bar (rectangular piston measuring 80 x 200 mm). After that, the entirety is removed from the mould and 10 test specimens of strands or cords thus coated are cut out, for characterizing, in the shape of parallelepipeds measuring 7x7x60 mm. The compound used as a coating elastomeric compound is a diene elastomer compound conventionally used in tyres, based on natural (peptized) rubber and carbon black N330 (65 phr), also containing the following usual additives: sulfur (7 phr), sulfenamide accelerator (1 phr), ZnO (8 phr), stearic acid (0.7 phr), antioxidant (1.5 phr), cobalt naphthenate (1.5 phr) (phr meaning parts by weight per hundred parts of elastomer); the El0 modulus of the coating elastomeric compound is around 10 MPa. The test is carried out on a 6 cm length of strand or cord, which is therefore coated with its surrounding elastomeric compound (or coating elastomeric compound) in the cured state, in the following way: air is injected into the inlet end of the strand or cord at a pressure of 1 bar and the volume of air at the outlet end is measured using a flow meter (calibrated for example from 0 to 500cm 3 /min). During the measurement, the sample of strand or cord is immobilized in a compressed airtight seal (for example, a seal made of dense foam or of rubber) so that only the amount of air passing along the strand or cord from one end to the other, along its longitudinal axis, is taken into account by the measurement; the airtightness of the airtight seal itself is checked beforehand using a solid elastomeric-compound test specimen, that is to say one devoid of both strand and cord. The higher the longitudinal impermeability of the strand or cord, the lower the mean air flow rate measured (averaged over the ten specimens). As the measurement is taken with a precision of ±0.2 cm3/min, measured values of less than or equal to 0.2 cm3/min are considered to be zero; they correspond to a strand or cord that can be described as airtight (completely airtight) along its axis (i.e. in its longitudinal direction).

[0246] Nevertheless, for the sake of the speed at which the strands can be evaluated, the inventors favoured simulation and calculation of the windows S over the permeability test.

[0247] Evaluation of the penetrability indicator for the external strands according to the pitch p3 of the cord 50

[0248] Various internal strands analogous to the internal strand of the cords 50, 51 and 52 according to the invention were simulated by varying the value of p2 for various values of p3, with all the other structural features of the cord remaining unchanged in comparison with the above description.

[0249] The results of these simulations are collated in the various Tables 50.1 to 52.6 in base 100 with respect, in each instance, to a control strand such that (p3 p2)/p3=0.31 for Q=2, (p3-p2)/p3=0.33 for Q=3 and (p3-p2)/p3=0.25 for Q=4. Thus, for a window size value St for the tested strand and for a window size value SO for the control strand, the penetrability indicator is equal to St*100/SO. Thus, a result higher than 100 means that the strand tested exhibits superior penetrability to the corresponding control strand. It is estimated that the size of the windows is significantly higher when the penetrability indicator is greater than or equal to 120, which means to say when the size of the windows in the strand tested is 20% higher than that of the control strand.

[0250] Each Table 50.1 to 52.6 respectively corresponds to a pitch p3 equal to 12, 14, 16, 18, 20 and 23 mm.

[0251] It will be noted that, although the inter-thread distance 12 increases when p2 increases, the maximum value for the radial passage windows is obtained for 12 values which are not necessarily the highest values. Thus, before carrying out the invention, a person skilled in the art, starting from the assumption that the lower 12, the lower the penetrability of the strand, would have difficulty in predicting a maximum penetrability for p2 values that yield relatively low values for 12.

[0252] Within the interval for the ratio (p3-p2)/p3 that ranges from 0.33 to 0.45 in instances in which Q=2, that ranges from 0.35 to 0.42 in instances in which Q=3 and that ranges from 0.28 to 0.43 in instances in which Q=4, and for each p3 value tested, the value for the penetrability indicator is significantly higher than that obtained for the corresponding control strand.

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[0253] Evaluation of the penetrability indicator for the internal strands of the cords 50', 50", 51', 51", 52', 52", 60, 60', 60", 61, 61' and 61"

[0254] In a way similar to the cords 50, 51 and 52, various external strands of the cords 60 and 61 according to the various embodiments of the invention were simulated by varying the value of p2 while fixing the value of p3 to the value described hereinabove, with all the other structural features of each cord remaining unchanged in comparison with the above description.

[0255] Since the external strands of the cords 50', 50", 51', 51", 52' and 52" are respectively identical to those of the cords 50 in the case of cords 50' and 50", 51 in the case of cords 51' and 51", and 52 in the case of cords 52' and 52", the conclusion remains the same, namely that the interval for the ratio (p3'-p2')/p3' ranging from 0.33 to 0.45 in instances in which Q'=2, ranging from 0.35 to 0.42 in instances in which Q'=3, and ranging from 0.28 to 0.43 in instances in which Q'=4.

[0256] The results of these simulations are collated in the various Tables 60 and 61 in base 100 with respect, in each instance, to a control strand such that (p3-p2)/p3=0.31 for Q=2, and (p3-p2)/p3=0.33 for Q=3. Thus, for a window size value St for the tested strand and for a window size value SO for the control strand, the penetrability indicator is equal to St*100/SO. Thus, a result higher than 100 means that the strand tested exhibits superior penetrability to the corresponding control strand. It is estimated that the size of the windows is significantly higher when the penetrability indicator is greater than or equal to 120, which means to say when the size of the windows in the strand tested is 20% higher than that of the control strand.

[0257] It will be noted that, although the inter-thread distance 12 increases when p2 increases, the maximum value for the size of the radial passage windows is obtained for 12 values which are not necessarily the highest values. Thus, before carrying out the invention, a person skilled in the art, starting from the assumption that the lower 12, the lower the penetrability of the strand, would have difficulty in predicting a maximum penetrability for p2 values that yield relatively low values for 12.

[0258] Within the interval for the ratio (p3-p2)/p3 that ranges from 0.33 to 0.45 in instances in which Q=2, that ranges from 0.35 to 0.42 in instances in which Q=3 and that ranges from 0.28 to 0.43 in instances in which Q=4, and for each p3 value tested, the value for the penetrability indicator is significantly higher than that obtained for the corresponding control strand.

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[0259] Tables 60 and 61 show that, for varying cord constructions, the penetration of the elastomeric compound into the external strands, and therefore the ability this elastomeric compound has to access each internal strand, is significantly improved for a ratio (p3-p)/p3 that ranges from 0.33 to 0.45 in instances in which Q=2, that ranges from 0.35 to 0.42 in instances in which Q=3, and that ranges from 0.28 to 0.43 in instances in which Q=4, by comparison with the control cords for which (p3 p2)/p3=0.31 for Q=2, (p3-p2)/p3=0.33 for Q=3 and (p3-p2)/p3=0.25 in instances in which Q=4.

[0260] Of course, the invention is not restricted to the exemplary embodiments described above.

[0261] For reasons of industrial feasibility, of cost and of overall performance, it is preferable to implement the invention with linear threads, that is to say straight threads, having a conventional circular cross section.

[0262] It will also be possible to combine the characteristics of the various embodiments described or envisaged above, with the proviso that these characteristics are compatible with one another.

Claims

1. Two-layer multi-strand cord (50), characterized in that it comprises: - an internal layer (CI) of the cord made up of K>1 internal strands (TI) wound in a helix, each internal strand (TI) being a three-layer (C1, C2, C3) strand and comprising: • an internal layer (Cl) made up of Q=2, 3 or 4 internal threads (Fl) wound with a pitch p1, the internal layer (Cl) being wound in an internal layer (Cl) direction of each internal strand (TI), * an intermediate layer (C2) made up of M intermediate threads (F2), wound around the internal layer (Cl) with a pitch p2, the intermediate layer (C2) being wound in an intermediate-layer (C2) direction of each internal strand (TI), and * an external layer (C3) made up of N external threads (F3) wound around the intermediate layer (C2) with a pitch p3, - an external layer (CE) of the cord made up of L>1 external strands (TE) wound around the internal layer (CI) of the cord, each external strand (TE) being an at least two-layer (C1', C3') strand and comprising: • an internal layer (Cl) made up of Q' internal thread(s) (Fl'), and * an external layer (C3') made up of N' external threads (F3') wound around the internal layer (Cl'), wherein: - the mean inter-strand distance E separating two adjacent external strands is greater than or equal to 30 pm; - p1 is different from p2 and/or the internal-layer (C1) direction of each internal strand (TI) is different from the intermediate-layer (C2) direction of each internal strand (TI); - the intermediate layer (C2) of each internal strand (TI) is desaturated; - the external layer (C3) of each internal strand (TI) is desaturated; and - the pitches p2 and p3 satisfy the relationship: - 0.33:5 (p3-p2)/p35 0.45 in instances in which Q=2, - 0.355 (p3-p2)/p3 0.42 in instances in which Q=3, - 0.285 (p3-p2)/p3 0.43 in instances in which Q=4.

2. Cord (50) according to the preceding claim, in which the mean inter strand distance E separating two adjacent external strands is greater than or equal to 70 pm, more preferably than/to 100 pm, more preferably still than/to 150 pm and highly preferably than/to 200 pm.

3. Cord (50) according to either one of the preceding claims, in which: - 0.36 (p3-p2)/p3, preferably 0.38 5 (p3-p2)/p3 in instances in which Q=2, - 0.36 (p3-p2)/p3, preferably 0.38 5 (p3-p2)/p3 in instances in which Q=3, - 0.32 (p3-p2)/p3, preferably 0.36 5 (p3-p2)/p3 in instances in which Q=4.

4. Cord (50) according to any one of the preceding claims, in which: - (p3-p2)/p3 5 0.42 and preferably (p3-p2)/p3 5 0.40 in instances in which Q=2, - (p3-p2)/p3 0.40 in instances in which Q=3, - (p3-p2)/p3 5 0.40 and preferably (p3-p2)/p3 5 0.38 in instances in which Q=4.

5. Cord (50) according to any one of the preceding claims, in which the pitch p1 is such that 3 mm5 p1 5 16 mm, for preference 4 mm5 p1 5 13 mm and more preferably 5 mm 5 p1 5 10 mm.

6. Cord (50) according to any one of the preceding claims, in which the pitch p2 is such that 8 mm5 p25 20 mm, for preference 9 mm5 p25 18 mm and more preferably 10 mm5 sp2 16 mm.

7. Cord (50) according to any one of the preceding claims, in which the pitch p3 is such that 10 mm 5 p3 5 40 mm, for preference 12 mm 5 p35 30 mm and more preferably 15 mm5 p35 25 mm.

8. Cord (50) according to any one of the preceding claims, in which K=2, 3 or 4, and preferably K=3 or 4.

9. Cord (50) according to any one of the preceding claims, in which L=7, 8, 9 or 10, preferably L=8, 9 or 10 and more preferably L=8 or 9.

10. Cord (50) according to any one of the preceding claims, in which the internal layer (CI) of the cord is wound in a helix in a cord internal-layer direction with a pitch pi, the external layer (CE) of the cord is wound in a helix in a cord external-layer direction with a pitch pe, and the cord satisfies one and/or the other of the following features: - the cord internal-layer direction is different from the cord external-layer direction, - pi is different from pe.

11. Cord (50) according to any one of the preceding claims, in which M=7, 8, 9 or 10 and N=12, 13, 14 or 15.

12. Cord (50) according to any one of the preceding claims, in which the sum S12 of the inter-thread distances (12) of the intermediate layer (C2) of each internal strand (TI) is such that S12 < d3 where d3 is the diameter of each external thread (F3) of each internal strand (TI), preferably S12 5 0.8 x d3.

13. Cord (50) according to any one of the preceding claims, in which the external layer (C3) of each internal strand (TI) is completely unsaturated.

14. Cord (50) according to any one of the preceding claims, in which the external layer (C3') of each external strand (TE) is desaturated, preferably completely unsaturated.

15. Tyre (10), characterized in that it comprises the cord (50) according to any one of the preceding claims