Bead core for agricultural tire

1. A bead core for a tire which is substantially rotationally symmetrical about an axis, the bead core comprising a plurality of windings of at least one metallic wire with diameter d arranged next to one another in a direction P forming an angle α with an axial direction in a radial sectional half-plane R, on N layers superposed on one another in a radial direction,

wherein α ranges from 0° to 10°,

wherein, in the sectional half-plane R, the windings of the bead core form a structure consisting of a base structure and a cap structure, where a radially inner base structure is directly in contact in the radial direction with a radially outer cap structure,

wherein the base structure of I layers Ci superposed on one another in the radial direction, wherein I is odd and I≥3, comprises:

the radially innermost layer C 1 and the radially outermost layer C I comprising L windings,

wherein i is an integral number ranging from 1 to I−2, L i =L i+2 and |L i −L i+1 |=1, wherein L i is the number of windings of the layer Ci and Max(L i )=L with:

when i is odd, each axially outermost winding of the layers Ci is arranged in contact with a first outer side, which is a straight line parallel to the radial direction and tangent to the axially outermost winding of the layer C 1 in the radial sectional half-plane R, and

when i is even, the axially outermost winding of the layers Ci is arranged in contact with the two axially outermost windings of the immediately lower layer,

wherein the cap structure of J layers Cj superposed on one another in the radial direction comprises:

the layer C I+1 of L−1 windings superposed on layer C I of the base structure in the radial direction and the axially outermost winding being in contact with the two axially outermost windings of the immediately lower layer, and

or when j is an integral number between 1 and J, the layer C I+j is such that:

when j is even, L I+j =L I+(j−1) ,

when j is odd, L I+j =L−(j+1)/2,

such that when j is odd, the layer C I+j is formed from L I+j windings and the axially outermost winding is arranged in contact with the two axially outermost windings of the immediately lower layer, and

when j is even, the layer C I+j comprises L I+j windings arranged next to one another in the direction P from the first outer side,

or when j ranges from 1 to J, the layer C I+j is such that: L I+j =L−j,

wherein a product of the diameter d times L ranges from 13.0 mm to 25.0 mm,

wherein N, I and J are integral numbers not equal to zero, such that N=I+J is less than or equal to 16, and

wherein a radially outermost layer of the cap structure has less windings than any layer in the base structure.

2. The bead core according to claim 1 , wherein the product of the diameter d times L is less than or equal to 24.5 mm.

3. The bead core according to claim 1 , wherein the product of the diameter d times L is greater than or equal to 14.5 mm.

4. The bead core according to claim 1 , wherein the angle α is less than or equal to 8°.

5. The bead core according to claim 1 , wherein the angle α is greater than or equal to 3°.

6. The bead core according to claim 1 , wherein the diameter d ranges from 0.95 mm to 3.00 mm.

7. The bead core according to claim 1 , wherein max(L k )=max(L i )=L is strictly greater than N, with C k being a layer of the bead core selected from N layers, and L k is the number of windings of each layer C k , k being an integral number between 1 and N.

8. The bead core according to claim 1 , wherein N ranges from 7 to 16.

9. The bead core according to claim 1 , wherein 1 ranges from 5 to 13.

10. The bead core according to claim 1 , wherein J ranges from 2 to 3.

11. A method for manufacture of a bead core for a tire which is substantially rotationally symmetrical about an axis, the bead core comprising a plurality of windings of at least one wire with diameter d arranged next to one another in a direction P forming an angle α with an axial direction in a radial sectional half-plane R, on N layers superposed on one another in a radial direction, the method comprising:

placing a winding in contact with a laying surface of a channel at a radially inner end and unwinding the winding toward a first outer side, which is a straight line parallel to the radial direction and tangent to an outermost winding of the layer, in order to form the layer C 1 such that a product of the diameter d times L is strictly less than 25.0 mm;

superposing I layers Ci on one another in the radial direction, wherein I is odd and I≥3, so as to form a base structure in the sectional half-plane R such that the radially innermost layer C 1 and the radially outermost layer C I comprise L windings,

wherein i is an integral number ranging from 1 to I−2, L i =L i+2 and |L i −L i+1 |=1, wherein L i is the number of windings of the layer Ci and Max(L i )=L with:

when i is odd, each axially outermost winding of the layers Ci is arranged in contact with the first outer side, which is a straight line parallel to the radial direction and tangent to the axially outermost winding of the layer C 1 in the radial sectional half-plane R, and

when i is even, the axially outermost winding of the layers Ci is arranged in contact with the two axially outermost windings of the immediately lower layer;

superposing J layers Cj on one another in the radial direction so as to form a cap structure in the sectional half-plane R such that:

the layer C I+1 of L−1 windings superposed on layer C I of the base structure in the radial direction, and

or when j is an integral number between 1 and J, the layer C I+j is such that:

when j is even, L I+j =L I+(j−1) ,

when j is odd, L I+j =L−(j+1)/2,

such that when j is odd, the layer C I+j is formed from L I+j windings and the axially outermost winding is arranged in contact with the two axially outermost windings of the immediately lower layer, and

when j is even, the layer C I+j comprises L I+j windings arranged next to one another in the direction P from the first outer side,

or when j ranges from 1 to J, the layer C I+j is such that: L I+j =L−j,

wherein N, I and J are integral numbers not equal to zero, such that N=I+J is less than or equal to 16, and

wherein a radially outermost layer of the cap structure has less windings than any layer in the base structure.

12. The method according to claim 11 , wherein the bead core is covered with at least one fabric comprising filamentary elements comprising at least one multifilament strand comprising several monofilaments, each made up of a material selected from the group consisting of a polyester, a polyamide, a polyketone, a polyurethane, a natural fiber, a mineral fiber, and an assembly of these materials.

13. A tire for an agricultural or forestry vehicle comprising:

at least one bead comprising a bead core according to claim 1 ; and

a carcass reinforcement comprising at least one carcass ply anchored in each bead by a return around the bead core.

14. The tire according to claim 13 , wherein the carcass reinforcement consists of a single carcass ply anchored in each bead by a return around the bead core.