Tire for heavy industrial vehicle

Abstract

A tire includes a tread and a crown reinforcement arranged radially internal to the tread. The crown reinforcement includes a protective reinforcement and a working reinforcement. The protective reinforcement includes a protective ply that exhibits a force at break greater than or equal to 1300 daN.Math.cm.sup.1. The protective ply includes protective reinforcing elements, each of which exhibits a force at break greater than or equal to 3000 N. The working reinforcement is arranged radially internal to the protective reinforcement and includes a working ply. The working ply includes working reinforcing elements, each of which includes a working cord formed of at least a strand that includes an external layer of unsaturated threads.

Claims

1. A tire comprising: a tread; and a crown reinforcement arranged radially internal to the tread, the crown reinforcement including: (a) a protective reinforcement that includes at least one protective ply, wherein each of the at least one protective ply exhibits a force at break (Fm) greater than or equal to 1400 daN.Math.cm.sup.1, wherein each of the at least one protective ply includes protective reinforcing elements, wherein each of the protective reinforcing elements exhibits a force at break (Fr) greater than or equal to 3000 N and comprises (1) an internal layer comprising a plurality of internal strands and (2) an external layer comprising a plurality of external strands, the external strands being wrapped helically around the internal layer, and wherein each internal strand comprises (i) an internal layer comprising a plurality of internal threads and (ii) an external layer comprising a plurality of external threads, and (b) a working reinforcement that includes at least one working ply, the working reinforcement being arranged radially internal to the protective reinforcement, wherein each of the at least one working ply includes working reinforcing elements, wherein each of the working reinforcing elements includes a working cord that includes at least one strand, wherein each of the at least one strand has a total of two layers of threads, the two layers of threads being (i) an internal layer of threads and (ii) an external layer of threads wrapped helically around the internal layer of threads, wherein the external layer of threads is unsaturated and an inter-thread distance between threads of the external layer of threads is greater than or equal to 40 m, wherein the protective reinforcing elements make an angle at least equal to 10 with a circumferential direction of the tire, wherein the protective reinforcement is interposed radially between the tread and the working reinforcement, wherein the inter-thread distance is greater than or equal to 50 m, wherein in the at least one strand, threads of the internal layer of threads and threads of the external layer of threads are wrapped in the same wrapping direction, wherein the at least one protective ply has a different construction from the at least one working ply, wherein in the at least one strand, the number of threads of the external layer of threads is equal to 7, wherein in the at least one strand, diameters of the threads of the internal layer of threads and of the threads of the external layer of threads are the same, wherein the at least one strand comprises a plurality of strands, and wherein the plurality of strands comprises one or more internal strands and a plurality of external strands wrapped helically around a layer comprising the one or more internal strands, a pitch of the threads of the internal layer of threads of each of the plurality of external strands being different from a pitch of the threads of the internal layer of threads of each of the one or more internal strands, and a pitch of the threads of the external layer of threads of each of the plurality of external strands being different from a pitch of the threads of the external layer of threads of each of the one or more internal strands.

2. The tire according to claim 1, wherein the force at break (Fm) of each of the at least one protective ply is greater than or equal to 1500 daN.Math.cm.sup.1.

3. The tire according to claim 1, wherein the force at break (Fm) of each of the at least one protective ply is greater than or equal to 1600 daN.Math.cm.sup.1.

4. The tire according to claim 1, wherein the force at break (Fr) of each of the protective reinforcing elements is greater than or equal to 3500 N.

5. The tire according to claim 1, wherein the force at break (Fr) of each of the protective reinforcing elements is greater than or equal to 4500 N.

6. The tire according to claim 1, wherein the force at break (Fr) of each of the protective reinforcing elements is greater than or equal to 5500 N.

7. The tire according to claim 1, wherein a pitch at which the protective reinforcing elements are laid ranges from 1.2 mm to 6.5 mm.

8. The tire according to claim 1, wherein, for each of the working cords of the working reinforcing elements of the at least one ply, the working cord includes at least one internal cord layer and an external cord layer, wherein: each of the at least one internal cord layer includes at least one internal strand, the external cord layer includes a plurality of external strands, with each of the external strands including at least one internal layer of threads and an external layer of threads wrapped helically around the at least one internal layer of threads, and with the external layer of threads being unsaturated.

9. The tire according to claim 1, wherein each of the at least one working ply exhibits a force at break (FmNST) greater than or equal to 2000 daN.Math.cm.sup.1.

10. The tire according to claim 1, wherein each of the at least one working ply exhibits a force at break (FmNST) greater than or equal to 3500 daN.Math.cm.sup.1.

11. The tire according to claim 1, wherein each of the at least one working ply exhibits a force at break (FmNST) greater than or equal to 4000 daN.Math.cm.sup.1.

12. The tire according to claim 1, wherein each of the working reinforcing elements of the at least one working ply exhibits a force at break (Fr) greater than or equal to 15000 N.

13. The tire according to claim 1, wherein a pitch at which the working reinforcing elements of the at least one working ply are laid ranges from 3.5 mm to 7.5 mm.

14. The tire according to claim 1, wherein the working reinforcing elements of the at least one working ply make an angle at most equal to 60 with a circumferential direction of the tire.

15. The tire according to claim 1, wherein the crown reinforcement includes a hoop reinforcement that includes at least one hooping ply.

16. The tire according to claim 15, wherein each of the at least one hooping ply includes hoop reinforcing elements that make an angle at most equal to 10 with a circumferential direction of the tire.

17. The tire according to claim 16, wherein the hoop reinforcement is arranged radially internal to the working reinforcement.

18. The tire according to claim 15, wherein the hoop reinforcement is arranged radially internal to the working reinforcement.

19. The tire according to claim 1, wherein the protective reinforcement comprises another protective ply that has a different construction from the at least one protective ply and that is disposed radially internal with respect to the at least one protective ply.

20. The tire according to claim 1, wherein each of the protective reinforcing elements comprises a cord having an unsaturated exterior.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be better understood from reading the following description, given solely by way of non-limiting example and with reference to the drawings in which:

(2) FIG. 1 is a simplified view in section of a tire according to a first embodiment of the invention;

(3) FIG. 2 is a detail view of the part I of the tire in FIG. 1;

(4) FIG. 3 is a view in section perpendicular to the axis of the protective reinforcing element (presumed to be rectilinear and at rest) of a reinforcing element of a protective ply of the tire in FIG. 1;

(5) FIG. 4 is a view similar to that in FIG. 3 of a reinforcing element of a protective ply of the tire in FIG. 1; and

(6) FIG. 5 is a view similar to that in FIG. 3 of a reinforcing element of a working ply of the tire in FIG. 1.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

(7) Examples of Tires According to the Invention

(8) In the following description, when the term radial is used, it is appropriate to make a distinction between several different uses of the word by a person skilled in the art. Firstly, the expression refers to a radius of the tire. It is within this meaning that a point, ply or reinforcement P1 is said to be radially inside a point, ply or reinforcement P2 (or radially on the inside of the point P2) if it is closer to the rotation axis of the tire than the point, ply or reinforcement P2. Conversely, a point, ply or reinforcement P3 is said to be radially outside a point, ply or reinforcement P4 (or radially on the outside of the point, ply or reinforcement P4) if it is further away from the rotation axis of the tire than the point, ply or reinforcement P4. Progress will be said to be radially inwards (or outwards) when it is in the direction of smaller (or larger) radii. It is this sense of the word that applies also when radial distances are being discussed.

(9) On the other hand, a reinforcing element or a reinforcement is said to be radial when the reinforcing element or the reinforcing elements of the reinforcement make an angle greater than or equal to 65 and less than or equal to 90 with the circumferential direction.

(10) An axial direction is a direction parallel to the axis of rotation of the tire. A point, ply or reinforcement P5 is said to be axially inside a point, ply or reinforcement P6 (or axially on the inside of the point, ply or reinforcement P6) if it is closer to the median plane M of the tire than the point, ply or reinforcement P6. Conversely, a point, ply or reinforcement P7 is said to be axially outside a point P8 (or axially on the outside of the point, ply or reinforcement P8) if it is further away from the median plane M of the tire than the point, ply or reinforcement P8. The median plane M of the tire is the plane which is normal to the axis of rotation of the tire and which is situated equidistantly from the annular reinforcing structures of each bead.

(11) A circumferential direction is a direction which is perpendicular both to a radius of the tire and to the axial direction.

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

(13) FIGS. 1 and 2 show a tire for a construction plant-type vehicle, for example of the dumper type, denoted by the overall reference 10. Thus, the tire 10 has a size of the W R U type, for example 40.00 R 57 or 59/80 R 63.

(14) In a manner known to a person skilled in the art, W: when it is in the form H/B, denotes the nominal aspect ratio H/B as defined by the ETRTO (H being the height of the section of the tire and B being the width of the section of the tire) and, 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 tire is intended to be mounted, and R denotes the type of carcass reinforcement of the tire, in this case radial. U35, preferably U49 and more preferably U57.

(15) The tire 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 a bead wire 20. The crown 12 is surmounted by a tread 22. The crown reinforcement 14 is arranged radially on the inside of the tread 22. A carcass reinforcement 24, arranged radially on the inside of the crown reinforcement 14, is anchored in each bead 18, in this case wrapped around each bead wire 20 and comprises a turn-up 26 disposed towards the outside of the tire 10, which is shown mounted on a rim 28 here.

(16) The carcass reinforcement 24 comprises at least one carcass ply 30 comprising reinforcing elements known as carcass reinforcing elements (not shown). The carcass reinforcing elements make an angle greater than or equal to 65, preferably greater than or equal to 80 and more preferably in the range from 80 to 90, with the circumferential direction of the tire. The carcass reinforcing elements are arranged substantially parallel to one another and extend from one bead 18 to the other. Examples of such carcass reinforcing elements are described in the documents

(17) The tire 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 tire 10 and which is intended to protect the carcass ply 30 from the diffusion of air coming from the space inside the tire 10.

(18) The crown reinforcement 14 comprises, radially from the outside to the inside of the tire 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 a hoop reinforcement 39 arranged radially on the inside of the working reinforcement 38. Thus, the protective reinforcement 36 is interposed radially between the tread 22 and the working reinforcement 38.

(19) The protective reinforcement 36 comprises first and second protective plies 42, 44, the first protective ply 42 being arranged radially on the inside of the second protective ply 44.

(20) The working reinforcement 38 comprises first and second working plies 46, 48, the first working ply 46 being arranged radially on the inside of the second working ply 48.

(21) The hoop reinforcement 39, also known as limiting block, the function of which is to partially absorb the mechanical stresses due to inflation, comprises first and second hopping plies 40, 41, the first hooping ply 40 being arranged radially on the inside of the second hooping ply 41.

(22) FIGS. 3, 4 and 5 show a first protective reinforcing element 50 of the first protective ply 42, a second protective reinforcing element 52 of the second protective ply 44 and a working reinforcing element 54, 56 of the first and second working plies 46, 48, respectively. In a variant, the working reinforcing elements 54, 56 of the first and second working plies 46, 48 can be different.

(23) Each of these elements 50, 52, 54, 56 comprises a metal cord.

(24) The term metal cord is understood by definition to mean a cord formed of wires made up predominantly (i.e. more than 50% of these wires) or entirely (100% of the wires) of a metallic material. The invention 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.

(25) When a carbon steel is used, its carbon content (% by weight of steel) is preferably between 0.7% and 0.9%. These contents represent a good compromise between the required mechanical properties of the tire and the feasibility of the threads. The metal or steel used is covered with a metal layer, in this case a layer of brass (ZnCu alloy) or zinc.

(26) Protective Reinforcement

(27) With reference to FIG. 3, each first protective reinforcing element 50 of the first protective ply 42 comprises a metal cord 58, known as a protective metal cord, of structure K(M+P).

(28) Each protective metal cord 58 comprises K strands 60 wrapped helically at a pitch p. Each strand 60 comprises an internal layer 62 of the strand and an external layer 64 of the strand. The internal layer 62 is made up of M internal thread(s) 66 wrapped helically at a pitch p1. The external layer 64 is made up of P external threads 68 wrapped helically around the internal layer 62 at the pitch p2.

(29) The P external threads 68 are wrapped in the same direction as the K strands 60. In a variant, they are wrapped in different directions.

(30) The external layer 64 is unsaturated.

(31) In the example in FIG. 3, K=4, M=1 and P=5.

(32) The pitch p is greater than or equal to 3 mm and less than or equal to 15 mm, preferably greater than or equal to 5 mm and less than or equal to 10 mm. In this case, p=8 mm. The pitch p1 is infinite here. The pitch p2 is greater than or equal to 3 mm and less than or equal to 10. In this case, p2=5 mm.

(33) The diameter D1, D2 of the internal thread(s) 66 and external threads 68, respectively, is greater than or equal to 0.10 mm and less than or equal to 0.50 mm, preferably greater than or equal to 0.15 mm and less than or equal to 0.35 mm, in this case equal to 0.26 mm.

(34) Thus, in line with conventional nomenclature, the cord 58 is known as a 24.26 cord.

(35) The force at break Fr.sub.NSP1 of each first protective reinforcing element 50 is equal to 2550 N. The pitch at which the first protective reinforcement elements 50 are laid is equal to 2.5 mm. The force at break Fm.sub.NSP1 of the first protective ply 42 is equal to 1020 daN.Math.cm.sup.1.

(36) With reference to FIG. 4, each second protective reinforcing element 52 of the second protective ply 44 comprises a metal cord 70, known as a protective metal cord, of structure (K+L)(M+P). Thus, in this embodiment, each metal cord 70 comprises an internal layer 71 of the cord made up of K internal strands 73 and an external layer 75 of the cord made up of L>1 external strands 77 wrapped helically around the internal layer 71. Preferably, K>1.

(37) The external layer 75 of the cord is unsaturated.

(38) Each internal strand 73 and external strand 77 comprises an internal layer 74 made up of M internal threads 78 and an external layer 76 made up of P external threads 80. The external layer 76 of each internal strand 73 and external strand 77 is unsaturated.

(39) For the cord 70 in FIG. 4, K=3, L=8, M=2 and P=3.

(40) The M internal threads 78 of each of the K internal strands 73 are wrapped helically at a pitch p1i, where p1i=7.5 mm. The P external threads 80 of each of the K internal strands 73 are wrapped helically at a pitch p2i, where p2i=5 mm.

(41) The M internal threads 78 of each of the L external strands 77 are wrapped helically at a pitch p1e, where p1e=15 mm here. The P external threads 80 of each of the L external strands 77 are wrapped at a pitch p2e, where p2e=7.5 mm here.

(42) The internal strands 73 are wrapped helically at a pitch pi, where pi equals 7.5 mm here. The external strands 77 are wrapped helically around the internal layer 71 at a pitch pe, where pe=15 mm here.

(43) The M internal threads 78 are wrapped in the same direction as the P external threads 80 and in the same direction as the K strands 73. In a variant, the M internal threads 78 are wrapped in the same direction as the P external threads 80 and in the opposite wrapping direction to the K strands 73.

(44) The K internal strands 73 and the L external strands 77 are wrapped in the same twisting direction.

(45) The diameter D1, D2 of the internal thread(s) 78 and external threads 80, respectively, is greater than or equal to 0.10 mm and less than or equal to 0.50 mm, preferably greater than or equal to 0.15 mm and less than or equal to 0.35 mm, in this case equal to 0.26 mm.

(46) Thus, in line with conventional nomenclature, the cords 70 are known as 55.26 cords.

(47) The force at break Fr.sub.NSP2 of each second protective reinforcing element 52 is greater than or equal to 3000 N, or even 3500 N, preferably greater than or equal to 4500 N and more preferably greater than or equal to 5500 N. In this case, Fr.sub.NSP2=6325 N.

(48) The pitch at which the second protective reinforcing elements 52 are laid ranges from 1.2 to 6.5 mm, preferably from 2.5 to 5.0 mm, and more preferably from 3.5 to 4.5 mm and in this case is equal to 3.7 mm.

(49) The force at break Fm.sub.NSP2 of the second protective ply 44 is greater than or equal to 1300 daN.Math.cm.sup.1, or even greater than or equal to 1400 daN.Math.cm.sup.1, preferably greater than or equal to 1500 daN.Math.cm.sup.1 and more preferably greater than or equal to 1600 daN.Math.cm.sup.1. In this case, Fm.sub.NSP2=1709 daN.Math.cm.sup.1.

(50) The first protective reinforcing elements 50 and second protective reinforcing elements 52 make, within each first protective ply 42 and second protective ply 44, respectively, at least equal to 10, preferably in the range from 10 to 35 and more preferably 15 to 35, with the circumferential direction Z of the tire 10, and in this case equal to 24. The protective reinforcing elements 50, 52 are substantially parallel to one another within each protective ply 42, 44 and are crossed from one protective ply 42, 44 to the other.

(51) Working Reinforcement

(52) With reference to FIG. 5, each working reinforcing element 54, 56 of the first and second working plies 46, 48 respectively comprises a metal cord 82, 84, known as a working metal cord, of structure (J+Q)(A+B).

(53) Each cord 82, 84 comprises an internal layer 86 of the cord made up of J internal strand(s) 88 and an external layer 90 of the cord made up of Q external strands 92 wrapped helically around the internal layer 86. When J>1, the J internal strands are wrapped helically at the pitch pi. The Q external strands are wrapped at the pitch pe.

(54) Each internal strand 88 and external strand 92 comprises an internal layer 94 made up of A internal strand(s) 96 and an external layer 98 made up of B external strands 100 wrapped helically around the internal layer 94. When A>1, the A internal strands 96 are wrapped helically.

(55) In the example in FIG. 5, J=1, Q=6, A=2, B=7.

(56) The A internal threads 96 of each of the J internal strands 88 are wrapped helically at a pitch p1i, where p1i=7.5 mm here. The B external threads 100 of each of the Q internal strands 88 are wrapped helically at a pitch p2i, where p2i=5 mm here.

(57) The A internal threads 96 of each of the Q external strands 92 are wrapped helically at a pitch p1e, where p1e=15 mm here. The B external threads 100 of each of the Q external strands 92 are wrapped at a pitch p2e, where p2e=7.5 mm here.

(58) The internal strands 88 are wrapped helically at a pitch pi, where pi=7.5 mm here. The external strands 92 are wrapped helically around the internal layer 86 at a pitch pe, where pe=15 mm here.

(59) Each diameter D1, D2 of the internal threads 96 and external threads 100 is greater than or equal to 0.15 mm and less than or equal to 0.45 mm, preferably greater than or equal to 0.20 mm and less than or equal to 0.40 mm, more preferably greater than or equal to 0.22 mm and less than or equal to 0.38 mm, in this case equal to 0.35 mm.

(60) Thus, in line with conventional nomenclature, each cord 82, 84 is known as a 63.35 cord.

(61) The external layer 98 of B external threads 100 is unsaturated. The inter-thread distance d3 between the external threads 100 of the external layer 98 is greater than or equal to 25 m, or even greater than or equal to 30 m, preferably greater than or equal to 40 m and more preferably greater than or equal to 50 m. In this case, d3=75 m. The A internal threads 96 and the B external threads 100 are wrapped in different wrapping directions. In a variant, they are wrapped in identical wrapping directions.

(62) The force at break Fr.sub.NST1, Fr.sub.NST2 of each working reinforcing element 54, 56 is greater than or equal to 15 000 N. In this case, Fr.sub.NST1=Fr.sub.NST2=17 400 N. In other embodiments, the force at break Fr.sub.NST1, Fr.sub.NST2 of each working reinforcing element 54, 56 is greater than or equal to 20 000 N and more preferably greater than or equal to 25 000 N.

(63) The pitch at which each first and second working reinforcing element 54, 56 is laid ranges from 3.5 to 7.5 mm, preferably from 4.0 to 7.0 mm, and more preferably from 4.5 to 6.5 mm and in this case is equal to 5.5 mm.

(64) The force at break Fm.sub.NST1, Fm.sub.NST2 of each first and second working ply 46, 48 is greater than or equal to 2000 daN.Math.cm.sup.1. In this case, Fm.sub.NST1=Fm.sub.NST2=3164 daN.Math.cm.sup.1. In other embodiments, the force at break Fm.sub.NST1, Fm.sub.NST2 of each first and second working ply 46, 48 is greater than or equal to 3500 daN.Math.cm.sup.1 and more preferably greater than or equal to 4000 daN.Math.cm.sup.1.

(65) The first working reinforcing elements 54 and second working reinforcing elements 56 make, within each first working ply 46 and second working ply 48, respectively, an angle at most equal to 60, preferably in the range from 15 to 40, with the circumferential direction Z of the tire 10, and in this case equal to 19 for the first ply 46 and 33 for the second ply 48. The working reinforcing elements 54, 56 are substantially parallel to one another within each working ply 46, 48 and are crossed from one working ply 46, 48 to the other.

(66) Hoop Reinforcement

(67) Each hooping ply 40, 41 comprises metal hoop reinforcing elements (not shown), for example metal cords identical to the protective reinforcing elements, that make an angle at most equal to 10, preferably in the range from 5 to 10, with the circumferential direction Z of the tire 10. In this case, the angle is equal to 8. The hoop reinforcing elements are crossed from one hooping ply 40, 41 to the other. Thus, in the embodiment illustrated, apart from the angle made by the reinforcing elements of each ply, the hooping plies and protective plies are identical.

(68) Preferably, whether or not it is identical to the protective reinforcing elements, each hoop reinforcing element is made up of a metal cord that has a structure K(M+P), comprising a single layer made up of K strands, each strand comprising: an internal layer of the strand made up of M internal thread(s) and an external layer of the strand made up of N external threads wrapped helically around the internal layer of the strand.

(69) Each individual metal thread has a diameter in the range from 0.10 mm to 0.35 mm.

(70) Each hoop reinforcing element exhibits a force at break Fr greater than or equal to 2500 N, preferably greater than or equal to 4000 N, more preferably greater than or equal to 6000 N and even more preferably greater than or equal to 8500 N.

(71) The pitch at which the hoop reinforcing elements of each hooping ply 42, 44 are laid ranges from 1.8 to 6.5 mm, preferably from 3.0 to 5.5 mm, and more preferably from 3.7 to 4.8 mm.

(72) Each hooping ply 40, 41 exhibits a force at break Fm.sub.NSF1, Fm.sub.NSF2, respectively, greater than or equal to 1300 daN.Math.cm.sup.1, preferably greater than or equal to 1500 daN.Math.cm.sup.1, more preferably greater than or equal to 1800 daN.Math.cm.sup.1 and even more preferably greater than or equal to 2000 daN.Math.cm.sup.1.

(73) In a variant, use may be made of hoop reinforcing elements different from those of the protective reinforcement.

(74) A second embodiment of the invention as described below is also conceivable.

(75) In contrast to the tire according to the first embodiment, the mechanical characteristics of the first and second protective plies 42, 44 are substantially identical. This is because, in contrast to the tire according to the first embodiment, each first and second protective ply 42, 44 comprises first and second protective reinforcing elements 50, 52, respectively, comprising protective metal cords 58, 70 that are identical and, in line with conventional nomenclature, are known as 55.26 cords.

(76) The force at break Fr.sub.NSP1 of each protective metal cord 58 is greater than or equal to 3000 N, or even 3500 N, preferably greater than or equal to 4500 N and more preferably greater than or equal to 5500 N. In this case, Fr.sub.NSP1=Fr.sub.NSP2=6050 N.

(77) The pitch at which the first protective reinforcing elements 50 are laid ranges from 1.2 to 6.5 mm, preferably from 2.5 to 5.0 mm, and more preferably from 3.5 to 4.5 mm.

(78) The force at break Fm.sub.NSP1 of the first protective ply 42 is greater than or equal to 1300 daN.Math.cm.sup.1, or even greater than or equal to 1400 daN.Math.cm.sup.1, preferably greater than or equal to 1500 daN.Math.cm.sup.1 and more preferably greater than or equal to 1600 daN.Math.cm.sup.1. In this case, Fm.sub.NSP1=Fm.sub.NSP2=1709 daN.Math.cm.sup.1.

(79) Example of a Method For Manufacturing Cords of the Tires According to the Invention

(80) The metal cords 58, 70, 82, 84 are manufactured by cabling or else by twisting, using conventional methods known to a person skilled in the art.

(81) Comparative Tests

(82) A prior art tire T0, two control tires T1 and T2 and the tire 10 according to the first embodiment were compared below.

(83) In contrast to the tire 10 according to the invention, each first and second protective ply of the prior art tire T0 comprises metal reinforcing elements comprising 24.26 metal cords described above.

(84) Moreover, in contrast to the tire 10 according to the invention, each first and second working ply of the tire T0 comprises metal reinforcing elements comprising metal cords known as 189.23 cords of structure (J+Q)(A+B+C), where J=1, Q=6, A=3, B=9 and C=15, and in which all of the threads have a diameter equal to 0.23 mm. The external layer of the C threads of each 189.23 cord is saturated. Specifically, the inter-thread distance d3 of the external layer of each strand of the 189.23 metal cords is equal to 6 m.

(85) In contrast to the tire 10 according to the invention, each first and second protective ply of the control tire T1 comprises metal reinforcing elements comprising 24.26 metal cords as described above.

(86) In contrast to the tire 10 according to the invention, each first and second working ply of the tire T2 comprises metal reinforcing elements comprising 189.23 metal cords as described above.

(87) The characteristics of the various cords described below are collated in the following Table 1.

(88) TABLE-US-00001 TABLE 1 Cord 24.26 55.26 189.23 63.35 Ply in question NSP1 NST1 Laying pitch (mm) 2.5 3.7 5.5 5.5 Fm of the ply (daN .Math. cm.sup.1) 1050 1709 3636 3164 Fr (N .Math. mm.sup.2) 2550 6325 20000 17400 Lack of saturation external layer No Yes Inter-thread distance d3 (m) 6 75

(89) A significant number of each tire T0, T1, T2 and 10, in this case between 10 and 20, were run on different types of uneven ground, for example extraction mines. Thus, on a first type of ground, a significant number of tires of the prior art T0 were compared with a significant number of control tires T1. On a second type of ground, the same comparison was carried out between the tires T0 and T2. Finally, on a third type of ground, the same comparison was carried out between the tires T0 and 10.

(90) The proportion of tires that had to be removed following an attack on the crown reinforcement that made it impossible to continue running the tire, and in which the wear U on removing the tire was less than 95% at the centre of the tread of the tire, was thus counted.

(91) The proportion of tires for which it was possible to use virtually the entire tread, that is to say in which the wear U on removing the tire was greater than or equal to 95%, was also counted.

(92) The results are summarized in Table 2 below. From experience, the monitors of these tests consider that, for a difference to be significant, a difference of at least 10 points has to be observed.

(93) TABLE-US-00002 TABLE 2 Removal with attack to the crown rein- Removal forcement and with U < 95% U 95% Tire Tire NST1 NST2 NSP1 NSP2 T0 tested T0 tested T0 189.23 189.23 24.26 24.26 T1 63.35 63.35 24.26 24.26 47% 55% 17% 10% T2 189.23 189.23 55.26 55.26 33% 37% 33% 37% 10 63.35 63.35 24.26 55.26 21% 0% 54% 100%

(94) The comparison between the tires T0 and T1 does not show any significant difference in the proportion of tires that have to be removed with wear less than 95%, or in the proportion of tires that attain wear greater than or equal to 95%, which remains relatively low. Thus, only changing the working reinforcement does not make it possible to maximize the use of the tread.

(95) The comparison between the tires T0 and T2 leads to the same conclusion. Only changing the protective reinforcement, in this case the two protective plies, does not make it possible to maximize the use of the tread, either.

(96) The comparison between the tires T0 and 10 shows that the combination both of a protective reinforcement comprising at least one ply that exhibits a particularly high force at break, in this case greater than or equal to 1300 daN.Math.cm.sup.1, and comprising cords that exhibit a force at break that is likewise high, in this case greater than or equal to 3000 N, and of a working reinforcement comprising cords that are able to be penetrated to a high degree, in this case a strand comprising an unsaturated external layer of threads, makes it possible to maximize the use of the tread. Thus, even if each protective reinforcement and working reinforcement is effective independently of one another, the combination of the two reinforcements gives the tire according to the invention surprising resistance to attack.

(97) A person skilled in the art will easily conclude from the results above that the tire 10 according to the second embodiment, in which each protective ply 42, 44 comprises 55.26 cords 58, 70, exhibits a performance greater than that of the tire according to the first embodiment.

(98) The invention is not limited to the embodiments described above.

(99) Tires comprising metal cords having layers comprising a single strand may also be employed.

(100) Different reinforcing elements of the metal cords described above are also conceivable.

(101) Working cords and/or protective cords comprising a wrapping thread are also conceivable, regardless of whether this wrapping thread is metal or textile.