Tire bead for aircraft

Abstract

Aircraft tire (1) comprising two beads (2). In each bead (2) portion (8) comprises surface layer (9) in contact with rim (3) via radially interior bead face (4) and having a shear stiffness K.sub.1. Portion (8) comprises a rigid layer (10), radially on the outside of and adjacent to the surface layer (9), having a shear stiffness K.sub.2 at least equal to five times the shear stiffness K.sub.1 of the surface layer (9), and a deformable layer (11), radially on the outside of and adjacent to the rigid layer (10) and radially on the inside of and adjacent to the carcass reinforcement portion (5) radially on the inside of the bead wire (7), having a shear stiffness K.sub.3 at most equal to 0.3 times the shear stiffness K.sub.1 of the surface layer (9).

Claims

1. An aircraft tire comprising: two beads respectively configured to come into contact with a rim via at least one radially interior bead face; a carcass reinforcement comprising at least one carcass layer connecting the two beads; the or each carcass layer, being wrapped, in each bead, around a circumferential reinforcing element having a meridian section of centre and diameter, referred to as a bead wire; in each bead, a portion clamped under the bead wire extending radially on the inside of a carcass reinforcement portion radially on the inside of the bead wire as far as the radially interior bead face; the portion clamped under the bead wire comprising a surface layer configured to come into contact with the rim via the radially interior bead face and having a shear stiffness K.sub.1, wherein the portion clamped under the bead wire comprises a rigid layer, radially on the outside of and adjacent to the surface layer, having a shear stiffness K.sub.2 at least equal to five times the shear stiffness K.sub.1 of the surface layer; and wherein the portion clamped under the bead wire comprises a deformable layer, radially on the outside of and adjacent to the rigid layer and radially on the inside of and adjacent to the carcass reinforcement portion radially on the inside of the bead wire, having a shear stiffness K.sub.3 at most equal to 0.3 times the shear stiffness K.sub.1 of the surface layer.

2. The aircraft tire according to claim 1, wherein the portion clamped under the bead wire has a radial thickness under the bead wire, in vertical alignment with the centre of the meridian section of the bead wire, at least equal to 2 mm and at most equal to 3.5 mm.

3. The aircraft tire according to claim 1, the surface layer, the rigid layer and the deformable layer having, in vertical alignment with the centre of the meridian section of the bead wire, respective radial thicknesses under the bead wire, wherein the radial thickness under the bead wire of the surface layer is at most equal to the radial thickness under the bead wire of the rigid layer, and wherein the radial thickness under the bead wire of the rigid layer is at most equal to the radial thickness under the bead wire of the deformable layer.

4. The aircraft tire according to claim 1, wherein the surface layer has a shear stiffness K.sub.1 at least equal to 4 N/mm.

5. The aircraft tire according to claim 1, wherein the surface layer is made of an elastomeric material having an elastic modulus M.sub.1 at 10% elongation at least equal to 5 MPa and at most equal to 9 MPa.

6. The aircraft tire according to claim 1, wherein the surface layer has a radial thickness under the bead wire at least equal to 0.125 times the radial thickness under the bead wire of the portion clamped under the bead wire.

7. The aircraft tire according to claim 1, wherein the rigid layer has a shear stiffness K.sub.2 at most equal to 17 times the shear stiffness K.sub.1 of the surface layer.

8. The aircraft tire according to claim 1, wherein the rigid layer is made of a material having an elastic modulus M.sub.2 at 10% elongation at least equal to 15 times the elastic modulus M.sub.1 at 10% elongation of the surface layer.

9. The aircraft tire according to claim 1, wherein the rigid layer is made of a material having an elastic modulus M.sub.2 at 10% elongation at most equal to 50 times the elastic modulus M.sub.1 at 10% elongation of the surface layer.

10. The aircraft tire according to claim 1, wherein the rigid layer is made of a fabric comprising reinforcers that are mutually parallel and coated in an elastomeric material.

11. The aircraft tire according to claim 10, wherein the reinforcers of the rigid layer are made of at least one textile material.

12. The aircraft tire according to claim 10, wherein the reinforcers of the rigid layer are made of at least one textile material of the aromatic polyamide type.

13. The aircraft tire according to claim 1, wherein the rigid layer has a radial thickness under the bead wire at least equal to 0.375 times the radial thickness under the bead wire of the portion clamped under the bead wire.

14. The aircraft tire according to claim 1, wherein the rigid layer has an axial width at least equal to the diameter of the bead wire and at most equal to twice the diameter of the bead wire.

15. The aircraft tire according to claim 1, wherein the deformable layer is made of an elastomeric material having an elastic modulus M.sub.3 at 10% elongation at most equal to the elastic modulus M.sub.1 at 10% elongation of the surface layer.

16. The aircraft tire according to claim 1, wherein the deformable layer is made of an elastomeric material having an elastic modulus M.sub.3 at 10% elongation at least equal to 0.5 times the elastic modulus M.sub.1 at 10% elongation of the surface layer.

17. The aircraft tire according to claim 1, wherein the deformable layer has a radial thickness under the bead wire at least equal to 0.5 times the radial thickness under the bead wire of the portion clamped under the bead wire.

Description

BRIEF DESCRIPTION OF THE SINGLE DRAWING

(1) The features and other advantages of the invention will be better understood with the aid of the FIGURE which depicts a meridian section of a tire bead according to the invention.

(2) The FIGURE has not been drawn to scale. Not all of the elements have necessarily been depicted.

DETAILED DESCRIPTION OF THE SINGLE DRAWING

(3) The FIGURE shows a bead 2 of an aircraft tire 1 intended to come into contact with a rim 3 via at least one radially interior bead face 4. In the bead 2, two carcass layers 6 that make up a carcass reinforcement 5 are wound respectively from the inside towards the outside and from the outside towards the inside around a bead wire 7 having a meridian section of centre O and diameter D. A portion 8 clamped under the bead wire extends radially on the inside of a carcass reinforcement portion 5 radially on the inside of the bead wire 7 as far as the radially interior bead face 4.

(4) The portion 8 clamped under the bead wire comprises three layers extending radially from the inside to the outside: a surface layer 9, a rigid layer 10 and a deformable layer 11 which, in vertical alignment with the centre O of the meridian section of the bead wire 7, has respective radial thicknesses E.sub.1, E.sub.2 and E.sub.3 under the bead wire. The portion 8 clamped under the bead wire has a radial thickness E under the bead wire equal to the sum of the respective radial thicknesses E.sub.1, E.sub.2 and E.sub.3 under the bead wire. In the embodiment depicted, the radial thickness E.sub.1 under the bead wire of the surface layer 9 is less than the radial thickness E.sub.2 under the bead wire of the rigid layer 10, itself less than the radial thickness E.sub.3 under the bead wire of the rigid layer 11. In addition, the rigid layer 10 has an axial width L greater than the diameter D of the bead wire 7.

(5) Embodiments of the invention have been developed more particularly for an aircraft tire having a radial carcass reinforcement of size 4617.0R20, used on an airliner, and the nominal pressure of which is 15.9 bar, the nominal load of which is 20642 daN and the maximum speed of which is 378 km/h.

(6) In the example studied, the surface layer is made of an elastomeric material having an elastic modulus M.sub.1 at 10% elongation equal to 8 MPa, and having a radial thickness E.sub.1 under the bead wire of 0.4 mm. The rigid layer is made up of a fabric the circumferentially oriented reinforcers of which are made of an aromatic polyamide of the aramid type and having an elastic modulus equal to 120 MPa, and has a radial thickness E.sub.2 under the bead wire equal to 1.1 mm. Finally, the deformable layer is made of an elastomeric material having an elastic modulus M.sub.3 at 10% elongation equal to 4 MPa, and a radial thickness E.sub.3 under the bead wire equal to 1.5 mm. Therefore the portion clamped under the bead wire has a total radial thickness E under the bead wire equal to 3 mm.

(7) In the example studied, numerical simulations by finite element calculation have shown that the movements in the surface of contact between the radially interior face of the bead and the rim seat were appreciably reduced for a tire according to the invention in comparison with the reference tire according to the prior art. Moreover, comparative tests of mounted assemblies comprising tires respectively according to the prior art and according to the invention have shown a significant reduction in the number of defects observed on the rim seat.

(8) The invention is not restricted to a portion clamped under the bead wire that comprises three layers. It may be extrapolated to a portion clamped under the bead wire comprising more than three layers, at least two of which are deformable, in so far as the at least two deformable layers radially on the outside of the rigid layer constitute a shear stiffness gradient in which the shear stiffnesses decrease radially towards the outside, i.e. as they come radially closer to the bead wire. The stack of three layers may also be reduced, if appropriate, to two layers, when the surface layer is thin enough to be incorporated into the compound with which the textile reinforcers of the rigid layer are coated: in that case, the coating compound of the rigid layer, situated radially on the inside of the textile reinforcers, acts as a surface layer.