Crown Reinforcement for a Tire for a Heavy Vehicle of Construction Plant Type

Abstract

A radial tire for a heavy vehicle of construction plant type, and aims to increase the resistance of the crown thereof to attack The tire (1) for a heavy vehicle of construction plant type has a crown reinforcement (3) radially on the inside of a tread (2) and radially on the outside of a carcass reinforcement (4), the crown reinforcement (3) has, radially from the outside to the inside, a protective reinforcement (5) and a working reinforcement (6). The protective reinforcement (5) has at least one protective layer (51, 52) comprising elastic metal reinforcers that have a breaking strength Fm and a section of diameter D and are spaced apart in pairs by a spacing P at least equal to the diameter D. According to the invention, the ratio A=(PD)/D is at least equal to 0.25 and at most equal to 1, the ratio B=(Fm/P)/1000 is at least equal to 1.1 and at most equal to 2, Fm being expressed in N and P being expressed in mm, and the elastic metal reinforcers of the protective layer (51, 52) are multistrand ropes of structure 1N comprising a single layer of N strands wound in a helix.

Claims

1. A tire for a heavy vehicle of construction plant type, comprising a crown reinforcement radially on the inside of a tread and radially on the outside of a carcass reinforcement, the crown reinforcement comprising, radially from the outside to the inside, a protective reinforcement and a working reinforcement, the protective reinforcement comprising at least one protective layer comprising metal reinforcers that are coated in an elastomeric material, are mutually parallel and form an angle at least equal to 10 with a circumferential direction tangential to the circumference of the tire, the metal reinforcers of the protective layer each having a section of diameter D and being spaced apart in pairs by a spacing P at least equal to the diameter D, the metal reinforcers of the protective layer being elastic and having a breaking strength Fm, wherein the ratio A=(PD)/D is at least equal to 0.25 and at most equal to 1, and the ratio B=(Fm/P)/1000 is at least equal to 1.1 and at most equal to 2, Fm being expressed in N and P being expressed in mm, and the elastic metal reinforcers of the protective layer are multistrand ropes of structure 1N comprising a single layer of N strands wound in a helix, each strand comprising an internal layer of M internal threads wound in a helix and an external layer of K external threads wound in a helix around the internal layer, in that M=3.

2. The tire according to claim 1, wherein the ratio A=(PD)/D is at least equal to 0.3.

3. The tire according to claim 1, wherein the diameter D is at least equal to 3 mm, the force at break Fm is at least equal to 5900 N, and the spacing P is at least equal to 4 mm.

4. The tire for a heavy vchicic of construction plant typc according to claim 1, wherein N=3.

5. (canceled)

6. The tire according to claim 1, wherein K=7, 8, 9, 10 or 11.

7. The tire according to claim 1, wherein the metal reinforcers of the protective layer form an angle at least equal to 15 and at most equal to 35 with the circumferential direction Ng.

8. The tire according to claim 1, wherein the protective reinforcement comprises two protective layers, the respective metal reinforcers of which are crossed from one protective layer to the next.

9. The tire according to claim 1, wherein the working reinforcement comprises two working layers, the respective metal reinforcers of which, which are inextensible, are coated in an elastomeric material, are mutually parallel and form an angle at least equal to 15 and at most equal to 45 with the circumferential direction, are crossed from one working layer to the next.

10. The tire according to claim 1, wherein the crown reinforcement comprises, radially on the inside of the working reinforcement, a hoop reinforcement comprising two hooping layers, the respective metal reinforcers of which, which are coated in an elastomeric material, are mutually parallel and form an angle at most equal to 10 with the circumferential direction, are crossed from one hooping layer to the next.

11. The tire according to claim 1, wherein N=4.

12. The tire according to claim 1, wherein K=8.

Description

[0050] The features of the invention are illustrated in the schematic FIGS. 1 and 2, which are not to scale, with reference to a tire of size 40.00R57:

[0051] FIG. 1 is a meridian cross section through a crown of a tire for a heavy vehicle of dumper type according to the invention

[0052] FIG. 2 is a meridian cross section through a portion of protective layer according to the invention

[0053] FIG. 1 shows a meridian cross section through a tire 1 for a heavy vehicle of construction plant type of size 40.00R57, comprising a crown reinforcement 3 radially on the inside of a tread 2 and radially on the outside of a carcass reinforcement 4. The crown reinforcement 3 comprises, radially from the outside to the inside, a protective reinforcement 5, a working reinforcement 6 and a hoop reinforcement 7. The protective reinforcement 5 comprises two protective layers (51, 52) comprising metal reinforcers that are coated in an elastomeric material, are mutually parallel and form an angle equal to 24 with a circumferential direction XX tangential to the circumference of the tire, the respective metal reinforcers of each protective layer being crossed from one protective layer to the next. The working reinforcement 6 comprises two working layers (61, 62), the respective metal reinforcers of which, which are inextensible, are coated in an elastomeric material, are mutually parallel and form angles respectively equal to 33 and 19 with the circumferential direction XX, are crossed from one working layer to the next. The hoop reinforcement 7 comprises two hooping layers (71, 72), the respective metal reinforcers of which, which are coated in an elastomeric material, are mutually parallel and form an angle of between 6 and 8 with the circumferential direction XX, are crossed from one hooping layer to the next.

[0054] FIG. 2 shows a meridian cross section through a portion of protective layer (51, 52). The metal reinforcers of the protective layer (51, 52) each have a section of diameter D and are spaced apart in pairs by a spacing P at least equal to the diameter D. The inter-reinforcer distance between two consecutive reinforcers is PD. Moreover, the metal reinforcers of the protective layer (51, 52) are elastic and have a breaking strength Fm.

[0055] Two types of metal reinforcers of the protective layer (51, 52) were studied in more detail: a multistrand rope of structure 52.26 and a multistrand rope of structure 44.35. The rope 52.26 is a multistrand rope having N=4 strands, each strand comprising an internal layer of M=4 internal threads wound in a helix and an external layer of K=9 external threads wound in a helix around the internal layer, the threads having a section of diameter d=0.26 mm. The rope 44.35 is a multistrand rope having N=4 strands, each strand comprising an internal layer of M=3 internal threads wound in a helix and an external layer of K=8 external threads wound in a helix around the internal layer, the threads having a section of diameter d=0.35 mm.

[0056] Table 1 presents the respective changes in the ratio A=(PD)/D and the ratio B=(Fm/P)/1000 as a function of the spacing P, for an elastic metal multistrand rope of structure 52.26 having a diameter D=3.1 mm and a force at break Fm=5950 N.

TABLE-US-00001 TABLE 1 P (mm) 3.15 3.5 3.7 4.1 4.4 4.8 5 5.5 6 6.5 A = (P D)/D 0.02 0.13 0.19 0.32 0.42 0.55 0.61 0.77 0.94 1.10 B = (Fm/P)/1000 1.9 1.7 1.6 1.45 1.4 1.2 1.2 1.1 1.0 0.9

[0057] For an elastic metal multistrand rope of structure 52.26 having a diameter D=3.1 mm and a force at break Fm=5950 N, values of the spacing P of between 4.1 mm and 5.5 mm ensure that the essential features of the invention are complied with.

[0058] Table 2 presents the respective changes in the ratio A=(PD)/D and the ratio B=(Fm/P)/1000 as a function of the spacing P, for an elastic metal multistrand rope of structure 44.35 having a diameter D=3.8 mm and a force at break Fm=9500 N.

TABLE-US-00002 TABLE 2 P (mm) 3.8 4.4 4.8 5 5.5 6 6.5 A = (P D)/D 0 0.15 0.26 0.31 0.44 0.57 0.71 B = (Fm/P)/1000 2.5 2.2 2.0 1.9 1.7 1.6 1.5

[0059] For an elastic metal multistrand rope of structure 44.35 having a diameter D=3.8 mm and a force at break Fm=9500 N, values of the spacing P of between 4.8 mm and 6.5 mm ensure that the essential features of the invention are complied with.

[0060] The inventors carried out comparative analyses of the state of the interface between the protective reinforcement and the tread for tires according to the invention and for tires of the prior art that have been driven on by customers. They found that the extent of the areas of corrosion, in particular perpendicularly to the elastic metal reinforcers of the protective layer, were significantly smaller for the tires according to the invention compared with the tires of the prior art, resulting in a significant improvement in terms of resistance of the crown to attack.