Protective Reinforcement For A Tire For A Heavy Civil Engineering Vehicle

Abstract

The present invention concerns a radial tire (1) for a heavy civil-engineering vehicle, and aims to increase the resistance to repeated impact of its crown reinforcement (3), when driving over stones, while maintaining good resistance to attacks. The tire (1) comprises a protective reinforcement (5) comprising at least one protective layer (51, 52) comprising elastic metal reinforcers, and a working reinforcement (6) comprising two working layers (61, 62) comprising non-extensible metal reinforcers, the elastic metal reinforcers of the radially innermost protective layer (51) have a elastic modulus in extension of at least 100 GPa and a diameter D of at least 3 mm, and are distributed axially at an axial pitch P at least 1.2 times the diameter D.

Claims

1. A tire for a heavy duty civil engineering type vehicle, 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 elastic metal reinforcers having a tensile elastic modulus at most equal to 150 GPa, coated in an elastomeric material, which are mutually parallel and which form, with a circumferential direction (XX′) tangential to the circumference of the tire, an angle at least equal to 10°, the working reinforcement comprising two working layers respectively comprising inextensible metal reinforcers having a tensile elastic modulus greater than 150 GPa and at most equal to 200 GPa, coated in an elastomeric material, which are mutually parallel and which form, with the circumferential direction (XX′), an angle at least equal to 15° and at most equal to 45° and which are crossed from one working layer to the next, the protective reinforcement comprising a radially innermost protective layer having an axial width LP1, the working reinforcement comprising a radially innermost working layer having an axial width LT1 at most equal to the axial width LP1, the radially innermost protective layer comprising elastic metal reinforcers having a diameter D distributed axially at an axial spacing P, wherein the elastic metal reinforcers of the radially innermost protective layer have a tensile elastic modulus at least equal to 100 GPa and a diameter D at least equal to 3 mm, and are axially distributed at an axial spacing P at least equal to 1.2 times the diameter D.

2. The tire according to claim 1, wherein the elastic metal reinforcers of the radially innermost protective layer have a diameter D at at most equal to 6 mm.

3. The tire according to claim 1, wherein the elastic metal reinforcers of the radially innermost protective layer are distributed axially at an axial spacing P at most equal to 1.5 times the diameter D.

4. The tire according to claim 1, wherein the elastic metal reinforcers of the protective layer are multistrand ropes of structure 1×N 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.

5. The tire according to claim 4, wherein the single layer of N strands, wound in a helix, comprises N=3 or N=4 strands.

6. The tire according to claim 4, wherein the internal layer of M internal threads, wound in a helix, of each strand comprises M=3, 4, or 5 internal threads.

7. The tire according to claim 4, wherein the external layer of K external threads, wound in a helix around the internal layer of each strand, comprises K=7, 8, 9, 10 or 11 external threads.

8. 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 (XX′).

9. The tire according to claim 1, wherein the radially innermost protective layer has an axial width LP1 at least equal to 1.05 times and at most equal to 1.25 times the axial width LT1 of the radially innermost working layer.

10. The tire according to claim 1, wherein the elastic metal reinforcers of the radially innermost protective layer form, with the circumferential direction (XX′), an angle equal to that formed by the inextensible metal reinforcers of the radially innermost working layer.

11. 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.

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

Description

[0046] The features of the invention are illustrated in the FIGS. 1 and 2, which are schematic and not to scale, with reference to a tire of size 53/80R63:

[0047] FIG. 1 is a meridian cross section through a crown of a tire for a heavy duty vehicle of dumper type according to the invention.

[0048] FIG. 2 is a meridian cross section through a portion of the radially innermost protective layer according to the invention.

[0049] FIG. 1 shows a meridian cross section through a tire 1 for a heavy duty civil engineering type vehicle of size 53/80R63, 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 elastic metal reinforcers that are coated in an elastomeric material, are mutually parallel and form an angle equal to 330 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), of which the respective metal reinforcers, which are inextensible, are coated in an elastomeric material, are mutually parallel and form with the circumferential direction XX′ angles respectively equal to 33°, in the case of the radially innermost working layer 61, and 24°, in the case of the radially outermost working layer 62, are crossed from one working layer to the next. The radially innermost protective layer 51 protrudes axially beyond the radially innermost working layer 61, which is to say that the radially innermost protective layer 51 has an axial width LP1 greater than the axial width LT1 of the radially innermost working layer 61. In the case depicted, the axial width LP1 is equal to 1.2 times the axial width LT1. The hoop reinforcement 7 comprises two hooping layers (71, 72), of which the respective metal reinforcers, which are coated in an elastomeric material, are mutually parallel and form an angle of between 6° and 10 with the circumferential direction XX′, are crossed from one hooping layer to the next.

[0050] FIG. 2 shows a meridian cross section through a portion of the radially innermost protective layer 51. The protective layer metal reinforcers each have a cross section of diameter D and are spaced apart one from the next by an axial spacing P at least equal to 1.2 times the diameter D, the axial spacing P being the axial distance between the respective centres of the circular cross sections of two consecutive reinforcers.

[0051] The inventors have compared a tire according to the invention, I, against a reference tire R, for the tire size 53/80R63, the respective technical features of which are given in Table 1 below:

TABLE-US-00001 TABLE 1 Dimension 53/80R63 Tire according to the Reference tire R invention I Type of reinforcer 24.26 = 4*(1 + 5)*26 44.35 = 4*(3 + 8)*35 Tensile elastic modulus 110 GPa 130 GPa M of a reinforcer Diameter D of a 1.9 mm 3.8 mm reinforcer Axial spacing P of a 2.5 mm 4.9 mm reinforcer Axial width LP1 1120 mm 1120 mm Axial width LT1 1000 mm 930 mm

[0052] The reference tire R has a radially innermost protective layer that has an axial width LP1 equal to 1120 mm, which is 120 mm greater than the axial width LT1 of the radially innermost working layer. The elastic metal reinforcers of the radially innermost protective layer are multistrand ropes of structure 24.26, namely made up of N=4 strands, each strand comprising an internal layer of M=1 internal thread and an external layer of K=5 external threads wound in a helix around the internal layer, the threads having a section of diameter d=0.26 mm. In addition, these reinforcers have a tensile elastic modulus equal to 110 GPa, a diameter D equal to 1.9 mm, and are axially distributed at an axial spacing P equal to 2.5 mm, namely equal to 1.32 times the diameter D.

[0053] The tire according to the invention, I, has a radially innermost protective layer that has an axial width LP1 equal to 1120 mm, which is 190 mm greater than the axial width LT1 of the radially innermost working layer, and therefore equal to 1.2 times the axial width LT1. The elastic metal reinforcers of the radially innermost protective layer are multistrand ropes of structure 44.35, namely made up of 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. In addition, these reinforcers have a tensile elastic modulus equal to 130 GPa, which is therefore higher than 100 GPa, a diameter D equal to 3.8 mm, which is therefore higher than 3 mm, and are axially distributed at an axial spacing P equal to 4.9 mm, namely equal to 1.3 times the diameter D, and therefore greater than 1.2 times the diameter D.

[0054] The inventors have demonstrated by finite-element numerical simulations that the shear in the elastomeric compounds positioned between the metal reinforcers of the axial end portions of the radially innermost working layer, and in the elastomeric compounds positioned radially on the inside or on the outside of the said axial end portions, was reduced by 15% to 25% for the tire according to the invention I as compared with the reference tire R. The inventors have also demonstrated, through experimental running via the client base, that the service life of the tire according to the invention, I, before being removed from the vehicle, was increased by approximately 12% with respect that the reference tire R.