Tire for vehicle of construction plant type

Abstract

The tire for a construction plant vehicle includes a tread and a crown reinforcement arranged radially internal to the tread. The crown reinforcement includes a protective reinforcement, a working reinforcement, and a hoop reinforcement. The protective reinforcement includes at least one protective ply that exhibits a force at break Fm.sub.NSP. The working reinforcement includes at least one working ply that exhibits a force at break Fm.sub.NST. The hoop reinforcement includes at least one hooping ply, each of which includes hoop reinforcing elements that make an angle at most equal to 10 with a circumferential direction of the tire. The working reinforcement is arranged radially internal to the protective reinforcement. A ratio Fm.sub.NSP/Fm.sub.NST is greater than or equal to 0.27 and less than or equal to 0.90.

Claims

1. A tire for a construction plant vehicle, the tire comprising: a tread; and a crown reinforcement arranged radially internal to the tread, the crown reinforcement including: (1) a protective reinforcement that includes at least one protective ply that exhibits a force at break Fm.sub.NSP and that is a reinforcement of the tire that is closest radially to the tread, wherein each of the at least one protective ply exhibits a force at break Fm.sub.NSP greater than or equal to 1300 daN.Math.cm.sup.1; (2) a working reinforcement that includes at least one working ply that exhibits a force at break Fm.sub.NST, the working reinforcement being arranged radially internal to the protective reinforcement, wherein each of the at least one working ply exhibits a force at break Fm.sub.NST greater than or equal to 2000 daN.Math.cm.sup.1; and (3) a hoop reinforcement that includes at least one hooping ply that exceeds a force at break Fm.sub.NSF greater than or equal to 1300 daN.Math.cm.sup.1, each of the at least one hooping ply including hoop reinforcing elements that make an angle at most equal to 10 with a circumferential direction of the tire, the hoop reinforcement being arranged radially internal to the working reinforcement, wherein the following condition is satisfied:
0.50Fm.sub.NSP/Fm.sub.NST0.70, and wherein the tire has a size according to a W R U type, where U49, and wherein each protective reinforcing element comprises a metal cord having a structure K(M+P), where K is a number of strands, and where each strand comprises (1) an internal layer comprising M internal threads and (2) an external layer comprising N external threads wrapped helically around the internal layer, and wherein each hoop reinforcing element comprises a metal cord having the same K(M+P) structure as the metal cord of the protective reinforcing element.

2. The tire according to claim 1, wherein each of the at least one protective ply exhibits a force at break Fm.sub.NSP greater than or equal to 1400 daN.Math.cm.sup.1.

3. The tire according to claim 1, wherein each of the at least one protective ply exhibits a force at break Fm.sub.NSP greater than or equal to 1500 daN.Math.cm.sup.1.

4. The tire according to claim 1, wherein each of the at least one protective ply exhibits a force at break Fm.sub.NSP greater than or equal to 1600 daN.Math.cm.sup.1.

5. The tire according to claim 1, wherein each of the at least one protective ply includes protective reinforcing elements, and each of the protective reinforcing elements exhibits a force at break (Fr) greater than or equal to 3000 N.

6. The tire according to claim 1, wherein each of the at least one protective ply includes protective reinforcing elements laid at a pitch that ranges from 1.2 mm to 6.5 mm.

7. The tire according to claim 1, wherein each of the at least one working ply exhibits a force at break Fm.sub.NST greater than or equal to 2500 daN.Math.cm.sup.1.

8. The tire according to claim 1, wherein each of the at least one working ply exhibits a force at break Fm.sub.NST greater than or equal to 3000 daN.Math.cm.sup.1.

9. The tire according to claim 1, wherein each of the at least one working ply exhibits a force at break Fm.sub.NST greater than or equal to 4000 daN.Math.cm.sup.1.

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

11. The tire according to claim 1, wherein each of the at least one working ply includes working reinforcing elements laid at a pitch that ranges from 2.5 mm to 7.5 mm.

12. The tire according to claim 1, wherein each of the at least one protective ply includes protective reinforcing elements, and the protective reinforcing elements make an angle at least equal to 10 with a circumferential direction of the tire.

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

14. The tire according to claim 1, wherein the angle that the hoop reinforcing elements make with the circumferential direction of the tire is in a range from 5 to 10.

15. The tire according to claim 1, wherein each of the at least one protective ply exhibits a force at break Fm.sub.NSP greater than or equal to 1400 daN.Math.cm.sup.1, and wherein each of the at least one working ply exhibits a force at break Fm.sub.NST greater than or equal to 2500 daN.Math.cm.sup.1.

16. The tire according to claim 1, wherein each of the at least one protective ply exhibits a force at break Fm.sub.NSP greater than or equal to 1600 daN.Math.cm.sup.1, and wherein each of the at least one working ply exhibits a force at break Fm.sub.NST greater than or equal to 4000 daN.Math.cm.sup.1.

17. The tire according to claim 16, wherein the at least one protective ply are plural in number, wherein each of the at least one protective ply comprises protective reinforcing elements, and each of the protective reinforcing elements exhibits a force at break (Fr) greater than or equal to 3500 N, wherein the protective reinforcing elements are laid at a pitch that ranges from 2.5 mm to 5.0 mm, wherein the at least one working ply are plural in number, wherein each of the at least one working ply comprises working reinforcing elements, and each of the working reinforcing elements exhibits a force at break (Fr) greater than or equal to 15000 N, wherein the working reinforcing elements are laid at a pitch that ranges from 3 mm to 7 mm, wherein the at least one hooping ply are plural in number, wherein each of the at least one hooping ply exhibits a force at break Fm.sub.NSF greater than or equal to 1500 daN.Math.cm.sup.1, wherein each of the hoop reinforcing elements exhibits a force at break (Fr) greater than or equal to 2500 N, wherein the hoop reinforcing elements are laid at a pitch that ranges from 1.8 mm to 6.5 mm, and wherein U57.

18. The tire according to claim 17, wherein each of the protective reinforcing elements exhibits a force at break (Fr) greater than or equal to 5500 N, wherein the protective reinforcing elements are laid at a pitch that ranges from 3.5 mm to 4.5 mm, wherein the working reinforcing elements are laid at a pitch that ranges from 3.5 mm to 6.5 mm, wherein each of the at least one hooping ply exhibits a force at break Fm.sub.NSF greater than or equal to 2000 daN.Math.cm.sup.1, wherein each of the hoop reinforcing elements exhibits a force at break (Fr) greater than or equal to 6500 N, and wherein the hoop reinforcing elements are laid at a pitch that ranges from 3.7 mm to 4.8 mm.

19. The tire according to claim 18, wherein each of the hoop reinforcing elements exhibits a force at break (Fr) greater than or equal to 8500 N, wherein the protective reinforcing elements make an angle in the range of 15 to 35 with the circumferential direction of the tire, wherein each of the M internal threads and the N internal threads of the metal cord of the protective reinforcing element have a diameter in the range of from 0.10 mm to 0.35 mm, wherein either (1) each working reinforcing element comprises a metal cord having a structure (J+Q)(A+B) and comprising an internal layer comprising J internal strands, an external layer comprising Q external strands wrapped helically around the internal layer, each of the J internal strands and the Q external strands comprising an internal layer comprising A internal threads and an external layer comprising B external threads wrapped helically around the internal layer, with each of the A internal threads and the B external threads having a diameter in the range of from 0.10 mm to 0.35 mm, or (2) each working reinforcing element comprises a metal cord having a structure (J+Q)(A+C+B) and comprising an internal layer comprising J internal strands, an external layer comprising Q external strands wrapped helically around the internal layer, each of the J internal strands and the Q external strands comprising an internal layer comprising A internal threads, an intermediate layer comprising C intermediate threads wrapped helically around the internal layer, and an external layer comprising B external threads wrapped helically around the intermediate layer, wherein the angle that the hoop reinforcing elements make with the circumferential direction of the tire is in a range from 5 to 10.

20. The tire according to claim 19, wherein K=4, M=4, and P=9, and wherein (1) J=1, Q=6, A=3, and B=9 or (2) J=1, Q=6, A=3, C=9, and B=15.

21. The tire according to claim 20, wherein J=1, Q=6, A=3, C=9, and B=15.

22. The tire according to claim 20, wherein J=1, Q=6, A=3, and B=9.

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 the invention;

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

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Example of Tires According to the Invention

(4) 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.

(5) 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.

(6) 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.

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

(8) 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.

(9) 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.

(10) 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.

(11) 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.

(12) 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 respect to 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 EP0602733 and also EP0383716.

(13) 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.

(14) 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.

(15) 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.

(16) 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.

(17) 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 hooping plies 40, 41, the first hooping ply 40 being arranged radially on the inside of the second hooping ply 41.

(18) Protective Reinforcement

(19) The first and second protective plies 42, 44 comprise reinforcing elements known as protective reinforcing elements (not shown). In this case, the reinforcing elements of each first and second protective ply 42, 44 are identical. In this case, each protective reinforcing element of the protective reinforcement 36 comprises a metal cord. The protective reinforcing elements are arranged side by side parallel to one another in a main direction substantially perpendicular to the overall direction in which these reinforcing elements extend. The protective reinforcing elements are crossed from one protective ply 42, 44 to the other.

(20) Each protective reinforcing element, in this case the overall direction in which these reinforcing elements extend, makes an angle at least equal to 10, preferably in the range from 10 to 35 and more preferably from 15 to 35, with the circumferential direction Z of the tire 10. In this case, the angle is equal to 24.

(21) In this case, each protective reinforcing element is a metal cord of the type 52.26 for example as described in the document FR 2 959 517. This cord has a structure K(M+P), where K=4, M=4 and P=9 in this case, comprising a single layer made of up 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.
Each individual metal thread has a diameter in the range from 0.10 mm to 0.35 mm and in this case equal to 0.26 mm.

(22) Each protective reinforcing element exhibits a force at break Fr greater than or equal to 3000 N, preferably greater than or equal to 3500 N, more preferably greater than or equal to 4500 N and more preferably greater than or equal to 5500 N. In this case, the force at break of the cord 52.26 is equal to 6038 N.

(23) The pitch at which the protective reinforcing elements of each protective ply 42, 44 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.

(24) Each protective ply 42, 44 exhibits a force at break Fm.sub.NSP1, Fm.sub.NSP2, respectively, greater than or equal to 1300 daN.Math.cm.sup.1, preferably greater than or equal to 1400 daN.Math.cm.sup.1, more preferably greater than or equal to 1500 daN.Math.cm.sup.1 and even more preferably greater than or equal to 1600 daN.Math.cm.sup.1 and in this case Fm.sub.NSP1=Fm.sub.NSP2=Fm.sub.NSP=1632 daN.Math.cm.sup.1.

(25) Working Reinforcement

(26) The first and second working plies 46, 48 comprise reinforcing elements known as working reinforcing elements (not shown). In this case, the reinforcing elements of each first and second working ply 46, 44 are identical. In this case, each working reinforcing element of the working reinforcement 38 comprises a metal cord. The working reinforcing elements are arranged side by side parallel to one another in a main direction substantially perpendicular to the overall direction in which these reinforcing elements extend. The working reinforcing elements are crossed from one working ply 46, 48 to the other.

(27) Each working reinforcing element, in this case the overall direction in which these reinforcing elements extend, makes an angle at most equal to 60, preferably in the range from 15 to 40, with the circumferential direction Z of the tire 10. In this case, the angle of the reinforcing elements of the first working ply is equal to 19 and the angle of the reinforcing elements of the second working ply is equal to 33.

(28) In this case, each working reinforcing element is a metal cord of the type 84.26. This cord has a structure (J+Q)(A+B), where J=1, Q=6, A=3 and B=9, and comprises: an internal layer of the cord made up of J internal strand(s), an external layer of the cord made up of Q external strands wrapped helically around the internal layer of the cord,

(29) each internal and external strand comprising: an internal layer of the strand made up of A internal thread(s) and an external layer of the strand made up of B external threads wrapped helically around the internal layer of the strand.
Each individual metal thread has a diameter in the range from 0.10 mm to 0.35 mm and in this case equal to 0.26 mm.

(30) Each working reinforcing element 84.26 exhibits a force at break Fr equal to 12 251 N.

(31) The pitch at which the working reinforcing elements of each working ply 46, 48 are laid ranges from 2.5 to 7.5 mm, preferably from 3.0 to 7.0 mm, and more preferably from 3.5 to 6.5 mm and in this case is equal to 3.8 mm.

(32) Each working ply 46, 48 exhibits a force at break Fm.sub.NST1, Fm.sub.NST2, respectively, greater than or equal to 2000 daN.Math.cm.sup.1, preferably greater than or equal to 2500 daN.Math.cm.sup.1, more preferably greater than or equal to 3000 daN.Math.cm.sup.1 and in this case Fm.sub.NST1=Fm.sub.NST2=Fm.sub.NST=3224 daN.Math.cm.sup.1. In other embodiments using other cords or a smaller laying pitch, the force at break Fm.sub.NST is greater than or equal to 4000 daN.Math.cm.sup.1.

(33) In another embodiment, each working cord is of the type 189.23 and of the structure (J+Q)(A+C+B), where J=1, Q=6, A=3, C=9 and B=15, and comprises: an internal layer of the cord made up of J internal strand(s), an external layer of the cord made up of Q external strands wrapped helically around the internal layer of the cord,

(34) each internal and external strand comprising: an internal layer of the strand made up of A internal thread(s), an intermediate layer of the strand made up of C intermediate threads wrapped helically around the internal layer of the strand, and an external layer of the strand made up of B external threads wrapped helically around the intermediate layer of the strand.
There is then a force at break greater than or equal to 15 000 N, preferably greater than or equal to 20 000 N and more preferably greater than or equal to 25 000 N.

(35) Hoop Reinforcement

(36) 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.

(37) 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 NI P external threads wrapped helically around the internal layer of the strand.

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

(39) 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 more preferably greater than or equal to 8500 N.

(40) 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.

(41) 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.

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

(43) Example of a Method for Manufacturing Cords of the Tires According to the Invention

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

(45) Comparative Tests

(46) A prior art tire T0, a control tire T1 and several tires P1 to P5 according to the invention were compared below. All of the tires T0 and P1 to P5 comprise two protective plies comprising protective reinforcing elements that are identical from one protective ply to the other, two working plies comprising working elements that are identical from one working ply to the other, and two hooping plies comprising hoop elements that are identical from one hooping ply to the other. The tire P1 is identical to the tire 10 described above. The tires P2 to P5 correspond to embodiments in which only the laying pitches of the protective and/or working reinforcing elements have been varied in order to vary the values of Fm.sub.NSP1=Fm.sub.NSP2=Fm.sub.NSP and Fm.sub.NST1=Fm.sub.NST2=Fm.sub.NST. For each tire Pi, the relative percentage N of variation in Fm.sub.NST equal to 100.Math.(Fm.sub.NST(T1 or Pi)Fm.sub.NST(T0))/Fm.sub.NST(T0) has been indicated. In contrast to the tire T0 and to the tires P1 to P5, the tire T1 does not have a hoop reinforcement.

(47) Each tire was tested in a working ply breakage test in which the tire was made to pass over an indenting feature having a hemispherical head with a diameter of several centimetres. On each passage, the indenting feature was raised by 5 mm until one of the working plies broke. The greater the height at which one of the working plies breaks (maximum height Hm), the more the tire is resistant to the action of the indenting feature. The maximum heights Hm measured are benchmarked against the maximum height Ho measured for the tire T0. The percentage given R is equal to the value 100.Math.(HmHo/)Ho.

(48) The characteristics of the various tires T0, T1 and P1 to P5 and the results of the breakage tests are collated in the following Table 1.

(49) TABLE-US-00001 TABLE 1 Fm.sub.NSP Fm.sub.NST Fm.sub.NSP/ Hoop N R (daN .Math. cm.sup.1) (daN .Math. cm.sup.1) Fm.sub.NST reinforcement (%) (%) T0 616 2406 0.26 Yes 0 0 T1 1016 3224 0.31 No 34 17 P1 1632 3224 0.51 Yes 34 39 P2 1016 2574 0.39 Yes 7 19 P3 850 2406 0.35 Yes 0 15 P4 1016 2189 0.46 Yes 9 12 P5 1016 1660 0.61 Yes 31 1

(50) It will be noted that the tires P1 to P5 according to the invention are all such that Fm.sub.NSP/Fm.sub.NST0.27 and even such that Fm.sub.NSP/Fm.sub.NST0.30 or even such that Fm.sub.NSP/Fm.sub.NST0.35, even such that Fm.sub.NSP/Fm.sub.NST0.41, or even such that Fm.sub.NSP/Fm.sub.NST0.50. Moreover, the tires P1 to P5 according to the invention are all such that Fm.sub.NSP/Fm.sub.NST0.90 or even such that Fm.sub.NSP/Fm.sub.NST0.70.

(51) The results of the breakage tests on the tire P1 show that, for a relatively large rise in the value of Fm.sub.NST (34%), a relatively large rise in the maximum height is also obtained by increasing the value of Fm.sub.NSP such that Fm.sub.NSP/Fm.sub.NST0.27.

(52) Moreover, the results of the breakage tests on the tires P2 and P3 show that, for a relatively small rise, or no rise in the value of Fm.sub.NST (7% et 0%), a significant rise in the maximum height (19% et 15%) is obtained by increasing the value of Fm.sub.NSP such that Fm.sub.NSP/Fm.sub.NST0.27.

(53) In addition, the results of the breakage tests on the tire P4 show that, for a moderate drop in the value of Fm.sub.NST (9%), a substantial rise in the maximum height (12%) is nevertheless obtained by increasing the value of Fm.sub.NSP such that Fm.sub.NSP/Fm.sub.NST0.27.

(54) Finally, the results of the breakage tests on the tire P5 show that, for a relatively large drop in the value of Fm.sub.NST (31%), there is virtually no impact on the maximum height (1%) by increasing the value of Fm.sub.NSP such that Fm.sub.NSP/Fm.sub.NST0.27.

(55) The comparison of the results of the breakage tests between the tires T0 and P3 shows that, for a fixed value of Fm.sub.NST, the increase in the ratio Fm.sub.NSP/Fm.sub.NST allows an increase in the maximum height of 15%. The comparison of the results of the breakage tests between the tires T0 and P4 shows that, for a drop in the value of Fm.sub.NST, the increase in the ratio Fm.sub.NSP/Fm.sub.NST nevertheless allows an increase in the maximum height of 12%.

(56) The comparison of the tire T1 with the tires P3 and P4 shows that, although the Fm.sub.NST of the tires P3 and P4 are significantly lower than the Fm.sub.NST of the tire T1, a comparable maximum height is obtained for the same value of Fm.sub.NSP (case of P4) or for a value similar to the ratio Fm.sub.NSP/Fm.sub.NST (case of P3).

(57) Thus, in conclusion, a tire according to the invention exhibiting a ratio Fm.sub.NSP/Fm.sub.NST greater than or equal to 0.27 associated with a hoop reinforcement makes it possible to increase the mechanical strength of the working plies with respect to indenting features while limiting the increase, or maintaining and even decreasing the mechanical strength of these working plies.

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

(59) Specifically, a protective reinforcement comprising several protective plies, only one of which exhibits a force at break Fm.sub.NSP such that the ratio Fm.sub.NSP/Fm.sub.NST is greater than or equal to 0.27 may be conceivable within the scope of the invention.

(60) Still within the scope of the invention, a working reinforcement comprising several working plies, only one of which exhibits a force at break Fm.sub.NST such that the ratio Fm.sub.NSP/Fm.sub.NST is greater than or equal to 0.27 may be conceivable.

(61) Still within the scope of the invention, a tire comprising: a protective reinforcement comprising several protective plies, at least two of which exhibit different forces at break, for example by virtue of different reinforcing elements, and a working reinforcement comprising several working plies, at least two of which exhibit different forces at break, for example by virtue of different reinforcing elements, may be conceivable, at least one protective ply exhibiting a force at break Fm.sub.NSP and at least one working ply exhibiting a force at break Fm.sub.NST such that the ratio Fm.sub.NSP/Fm.sub.NST is greater than or equal to 0.27.