Crown reinforcement for a tire for a heavy-duty civil engineering vehicle

Abstract

A tire for a heavy construction-type vehicle includes a tread, a radial carcass reinforcement, and a crown reinforcement. The crown reinforcement includes a working reinforcement and a hoop reinforcement. The working reinforcement includes two working layers, each of which includes inelastic metallic reinforcers that are crossed from one layer to a next layer and that make an angle in a range of from 15 to 40 with respect to a circumferential direction. The hoop reinforcement, which is a ply that is wound circumferentially to form a radial stack of at least two hooping layers, includes circumferential elastic metallic reinforcers that make an angle equal to at most 2.5 with respect to the circumferential direction. The hoop reinforcement is radially positioned between the working layers, and the circumferential metallic reinforcers of the hoop reinforcement have a force at break equal to at least 800 daN.

Claims

1. A tire for a heavy construction-type vehicle, the tire comprising: a tread structured to come into contact with a ground surface; a radial carcass reinforcement positioned radially inside relative to the tread, the radial carcass reinforcement including at least one carcass layer; and a crown reinforcement positioned radially inside relative to the tread, and positioned radially outside relative to the radial carcass reinforcement, the crown reinforcement including a working reinforcement and a hoop reinforcement, wherein the working reinforcement includes a plurality of working layers, each of the working layers including inelastic metallic reinforcers that: (a) are crossed from one working layer to another working layer, and (b) make an angle in a range of from at least 28 to at most 33 with respect to a circumferential direction, wherein the hoop reinforcement is formed of a circumferentially wound ply that includes circumferential elastic metallic reinforcers, the circumferential elastic metallic reinforcers making an angle equal to at most 2.5 with respect to the circumferential direction, the circumferentially wound ply being wound from a first circumferential end to a second circumferential end, so that the second circumferential end is located radially outside relative to the first circumferential end, and so that the circumferentially wound ply forms a radial stack of at least two hooping layers, wherein the hoop reinforcement is radially positioned between two of the working layers, and wherein the circumferential elastic metallic reinforcers of the hoop reinforcement have a force at break equal to at least 800 daN, wherein the circumferential elastic metallic reinforcers of the hoop reinforcement have a modulus of elasticity at 10% elongation in a range of from at least 70 GPa to at most 110 GPa, wherein the first and second circumferential ends of the circumferentially wound ply of the hoop reinforcement make an angle in a range equal to at least 25 with respect to an axial direction, and wherein a circumferential distance between the first circumferential end and the second circumferential end of the circumferentially wound ply of the hoop reinforcement is in a range of from at least 0.6 m to at most 1.2 m.

2. The tire according to claim 1, wherein a mean surface of the circumferentially wound ply of the hoop reinforcement, near the first circumferential end of the circumferentially wound ply, makes an angle equal to at most 45 with respect to the circumferential direction when measured in an equatorial plane.

3. The tire according to claim 1, wherein a mean surface of one of the working layers, near the second circumferential end of the circumferentially wound ply, makes an angle equal to at most 45 with respect to the circumferential direction when measured in an equatorial plane.

4. The tire according to claim 1, wherein an axial width of the hoop reinforcement is less than half an axial width of the tire.

5. The tire according to claim 1, wherein two of the working layers are coupled, in an axial direction, over a coupling portion having an axial width equal to at least 1.5% of an axial width of the tire.

6. The tire according to claim 1, wherein two of the working layers are coupled, in an axial direction, over a coupling portion having an axial width equal to at most 5% of an axial width of the tire.

7. The tire according to claim 5, wherein a radial distance between a first working layer of the two working layers, which is positioned radially inside relative to the hoop reinforcement, and the carcass reinforcement, measured at a center of the coupling portion of the two working layers, is equal to at least twice a radial distance between the first working layer and the carcass reinforcement, measured in an equatorial plane.

8. The tire according to claim 5, further comprising: a first elastomeric material positioned radially inside relative to the coupling portion of the two working layers, the first elastomeric material being in contact with the coupling portion of the two working layers; and a second elastomeric material positioned axially outside relative to the first elastomeric material, the second elastomeric material being in contact with the first elastomeric material, wherein a modulus of elasticity at 10% elongation of the first elastomeric material is equal to at least a modulus of elasticity at 10% elongation of the second elastomeric material.

9. The tire according to claim 5, further comprising: a first elastomeric material positioned radially inside relative to the coupling portion of the two working layers, the first elastomeric material being in contact with the coupling portion of the two working layers; and an elastomeric material coating inelastic metallic reinforcers of a first working layer of the two working layers, the first working layer being positioned radially inside relative to the hoop reinforcement, wherein a modulus of elasticity at 10% elongation of the first elastomeric material is equal to at least equal a modulus of elasticity at 10% elongation of the elastomeric material coating the inelastic metallic reinforcers of the first working layer.

10. The tire according to claim 5, wherein, at the first and second circumferential ends of the circumferentially wound ply of the radial stack of at least two hooping layers, mean surfaces of the two working layers make angles in a range equal to at most 45 with respect to the axial direction.

11. The tire according to claim 5, further comprising: a third elastomeric material axially contained between each axial end of the hoop reinforcement and the coupling portion of the two working layers; and an elastomeric material coating inelastic metallic reinforcers of the two working layers, wherein a modulus of elasticity at 10% elongation of the third elastomeric material is equal to a modulus of elasticity at 10% elongation of the elastomeric material coating the inelastic metallic reinforcers of the two working layers.

12. The tire according to claim 5, wherein a width of a portion of a first working layer of the two working layers, which is positioned radially inside relative to the hoop reinforcement and which is axially contained between an outer axial end of the coupling portion and an outer axial end of the first working layer, is equal to at most half an axial width of the hoop reinforcement.

13. The tire according to claim 5, wherein an axial width of a portion of a second working layer of the two working layers, which is positioned radially outside relative to the hoop reinforcement and which is axially contained between an outer axial end of the coupling portion and an outer axial end of the second working layer, is equal to at most a width of a portion of a first working layer of the two working layers, which is positioned radially inside relative to the hoop reinforcement and which is axially contained between an outer axial end of the coupling portion and an outer axial end of the first working layer.

14. The tire according to claim 1, wherein in the hoop reinforcement, the circumferentially wound ply that forms a radial stack of at least two hooping layers includes two hooping layers in a first circumferential section and three hooping layers in a second circumferential section.

15. The tire according to claim 1, wherein the first circumferential end and the second circumferential end are not contained in the same meridian plane.

16. The tire according to claim 15, wherein the first circumferential end and the second circumferential end overlap over a circumferential portion of the periphery of the tire to ensure that the hoop reinforcement is present around the entire periphery of the tire, wherein the first circumferential end makes an angle with respect to the axial direction which is equal to and of the same sign as an angle that the second circumferential end makes with respect to the axial direction, the angle being greater than or equal to 25 so that the first circumferential end is not contained in a meridian plane and the second circumferential end is not contained in a meridian plane.

17. The tire according to claim 16, wherein an axial width of the hoop reinforcement is less than half an axial width of the tire, wherein two of the working layers are coupled, in an axial direction, over a coupling portion having an axial width equal to at least 1.5% of an axial width of the tire, wherein two of the working layers are coupled, in an axial direction, over a coupling portion having an axial width equal to at most 5% of an axial width of the tire, wherein two layers are coupled if the radial distance between geometric centers of two adjacent reinforcers is less than three times the mean radius of the reinforcers, and wherein a radial distance between a first working layer of the two working layers, which is positioned radially inside relative to the hoop reinforcement, and the carcass reinforcement, measured at a center of the coupling portion of the two working layers, is equal to at least twice a radial distance between the first working layer and the carcass reinforcement, measured in an equatorial plane.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further details and advantageous features of the invention will become apparent in the following from the description of the exemplary embodiments of the invention, with reference to FIGS. 1 to 7.

(2) In order to make them easier to understand, the figures are not shown to scale. The figures show only a partial view of a tire which extends symmetrically with respect to the axis XX that represents the circumferential median plane, or equatorial plane, of a tire.

(3) FIG. 1 shows a cutaway perspective view of the crown of a tire according to the prior art, having:

(4) a tread 10,

(5) sidewalls 20,

(6) a carcass reinforcement 30 comprising a carcass layer, the reinforcers of which form an angle of close to 90 with the circumferential direction XX,

(7) a hoop reinforcement 40 comprising two hooping layers 41 and 42, the reinforcers of which respectively form angles of 8 to 15 with the circumferential direction XX,

(8) a working reinforcement 50 comprising two working layers 51 and 52 and radially on the outside of the hoop reinforcement 40,

(9) a protective reinforcement 60 comprising two protective layers 61 and 62.

(10) FIG. 2 shows a meridian section through the crown of a tire according to the invention, having:

(11) a tread 10,

(12) a carcass reinforcement 30,

(13) a crown reinforcement 100 comprising a working reinforcement 50 comprising two working layers 51 and 52, a hoop reinforcement 70 comprising a winding of two turns of circumferential reinforcers 71 and 72 having an axial width L1 and a protective reinforcement 60 comprising two protective layers 61 and 62,

(14) a coupling zone of the working layers 51 and 52, having an axial width L2,

(15) a free end portion of the radially inner working layer 51 having an axial width L3,

(16) a free end portion of the radially outer working layer 52 having an axial width L4,

(17) a first elastomeric compound Z1, radially on the inside of the coupling zone of the working layers 51 and 52 and having a maximum radial thickness E1,

(18) a second elastomeric compound Z2, radially on the inside of the radially inner working layer 51 and axially on the outside of the coupling zone of the working layers 51 and 52,

(19) a third elastomeric compound Z3, radially contained between the working layers 51 and 52 and axially contained between the hoop reinforcement 70 and the coupling zone of the working layers 51 and 52.

(20) FIG. 3 shows a cutaway perspective view of the crown of a tire according to the invention. It differs substantially from FIG. 1, showing the prior art, by way of a hoop reinforcement 70 comprising a winding of two turns of circumferential reinforcers 71 and 72, the radially outermost circumferential end 74 of which makes an angle (A) with the axial direction.

(21) FIG. 4 shows a cutaway perspective and partial view of the crown of a tire according to the invention, notably having:

(22) the carcass reinforcement 30,

(23) the radially innermost working layer 51,

(24) the radially innermost circumferential end 73 of the hoop reinforcement 70 making an angle (A) with the axial direction.

(25) FIG. 5 shows a circumferential section, in the equatorial plane, of the circumferential portion of overlap of the hoop reinforcement 70. In the main section, the hoop reinforcement 70 comprises a radial superposition of two layers 71 and 72. In the zone of overlap having a circumferential length L5, the hoop reinforcement comprises a radial superposition of three layers. At its radially inner first circumferential end 73, the hoop reinforcement 70 makes an angle A2 with the circumferential direction XX. At the radially outer second circumferential end 74 of the hoop reinforcement 70, the radially outer working layer 52 makes an angle A3 with the circumferential direction XX.

(26) FIG. 6 shows a section through the crown, in a meridian plane, at the axial ends of the hooping layers 71 and 72, where the radially inner 51 and radially outer 52 working layers make angles A4 and A5, respectively, with the axial direction YY. It shows in particular the radial thickness E1 of the first elastomeric compound Z1, radially contained between the carcass reinforcement 30 and the radially innermost working layer 51 radially on the inside of the coupling zone of the working layers 51 and 52, and the radial thickness E2 of the elastomeric compound radially contained between the radially inner working layer and the carcass reinforcement 30, measured in the equatorial plane.

(27) FIG. 7 shows the movements in mm of the points of the tread surface, which are situated in a meridian plane, during the inflation of the tire to the pressure recommended by the manufacturer in the three following cases:

(28) a prior art tire A comprising two narrow hooping layers, having the advantage of limiting the rising at the shoulders and thus the risk of cleavage of the working layers, but having the drawback of stiffening the center, thereby making it sensitive to impacts,

(29) a prior art tire B without a hoop reinforcement, and thus with a crown that is flexible at the center and has good impact resistance, but is also flexible at the shoulders, with the consequence of a high working temperature at the crown, which can lead to cleavage of the working layers,

(30) a tire C of the invention, comprising a hoop reinforcement made up of two circumferential reinforcer layers radially positioned between the working layers, having both the advantage of limiting the rising at the shoulders and of being flexible at the center, allowing improved impact resistance.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

(31) The invention has been realized on a tire for a heavy vehicle of construction plant type of the size 40.00R57, with a maximum axial width equal to 1115 mm. The reference tire, according to the prior art, is made up of a carcass layer having metallic reinforcers, of two narrow hooping layers with a width equal to 400 mm, having reinforcers that made an angle equal to 8 with the circumferential direction and are crossed from one layer to the next, of two working layers with respective widths equal to 740 mm and 680 mm and having reinforcers that form respective angles equal to 33 and 19 with the circumferential direction, and two protective layers having reinforcers that make an angle equal to 24 with the circumferential direction and are crossed from one layer to the next.

(32) The tire according to the invention differs from the prior art tire by way of the working reinforcement having two working layers, the respective reinforcers of which make an angle equal to 33 with the circumferential direction, and by way of the hoop reinforcement. Disposed between the working layers is the hoop reinforcement made up of the circumferential winding of two turns of a ply having an axial width equal to 350 mm and comprising elastic metallic circumferential reinforcers having a breaking strength equal to 900 daN and a modulus of elasticity equal to 90 GPa, these mechanical characteristics being measured on reinforcers extracted from the tire.

(33) Moreover, the circumferential ends of the hoop reinforcement of the tire according to the invention form an angle equal to 30 with the axial direction and the circumferential length of overlap of the hoop reinforcement is equal to 1 m. Disposed at these ends are transverse strips of elastomeric material identical to the compound coating the reinforcers of the working layers and of triangular cross section, having a circumferential width equal to 15 mm and a radial height equal to the diameter of the reinforcers of the hoop reinforcement. These strips bring about an angle equal to 18 between the hooping layer radially on the outside of the radially inner circumferential end and the circumferential direction, at the radially innermost first circumferential end of the hoop reinforcement, and between the working layer radially on the outside of the hoop reinforcement and the circumferential direction at the radially outermost second circumferential end of the hoop reinforcement.

(34) The two working layers are coupled over an axial width of 25 mm. The radial distance between the carcass reinforcement and the radially innermost working layer is equal to 4.6 mm in the equatorial plane and is equal to 13 mm under the coupling zone of the working layers. The elastomeric materials of the different zones around the coupling zone are identical to the elastomeric material coating the reinforcers of the working layers. The length of the working layer radially on the inside of the hoop reinforcement, measured from the outer axial end of the coupling zone to the outer axial end of said working layer, is equal to 107 mm and the length of the working layer radially on the outside of the hoop reinforcement, measured from the outer axial end of the coupling zone to the outer axial end of said working layer, is equal to 70 mm.

(35) The endurance performance with regard to cleavage of the crown is measured in tests on a dumper vehicle having 60 t of load per tire, inflated in the cold state to 6 bar and rolling for 640 hours at 17 km/h. Following this use, the tires are cut into 6 sectors, the tread is removed in order to extract the working layers and to detect any cracks present between these two layers. The endurance performance with regard to cleavage of the crown is estimated in proportion to the widths of the cleavage cracks. The tire according to the invention reveals a level of cleavage damage 20% lower than that for the tire according to the prior art.

(36) For tires of this size, the crown impact resistance of the different versions of tires is tested directly in use at client premises. These in situ experiments have demonstrated that tires without a hoop reinforcement, which are more flexible at the crown, have better impact resistance than those that have narrow hooping layers in accordance with the prior art, while the latter are better in terms of endurance with regard to cleavage of the crown. The tire according to the invention exhibits both impact resistance at least equal to that of a tire without a hoop reinforcement and an improvement in cleavage of the crown of 30% compared with a tire comprising a hoop reinforcement according to the prior art.