Wireless bead for a tire

#The invention relates to a tire comprising at least one tread joined to two beads by means of two sidewalls and a carcass reinforcement, said tire being able to be used with or without an independent inner tube and being intended, after mounting on a standardized rim and after inflation, to be fitted on any vehicle capable of rolling.

#Application FR A 2 771 150, filed Nov. 14, 1997, describes a tire which is intended to be mounted on a rim of axial width L, with rim seats forming an angle γ with the axis of rotation such that 0°≦γ≦16°, and rim flanges with rounded hooks. Said tire comprises a tread joined to two beads by two sidewalls and at least one carcass reinforcement formed of at least one ply of reinforcement elements, each bead being devoid of a bead wire, and said carcass reinforcement having in each bead a meridian profile which is curved axially and radially from the outside to the inside to form an axially inner edge located in an angle α open axially and radially towards the inside, one of the sides of which is parallel to the axis of rotation, and of a value of at most 25°. Said carcass reinforcement is reinforced in each bead, at least radially to the outside and axially to the inside, by at least one first continuous additional layer of meridian profile substantially parallel to the meridian profile of said carcass reinforcement in the bead and comprising at least one first section composed of at least one ply formed of inextensible reinforcement elements forming an angle of between −2.5° and +2.5° with the circumferential direction, the radially upper end of said additional ply being distant from the axis of rotation by an amount at least equal to 0.96 times the distance between said axis and that point of the corresponding flange of the mounting rim which is farthest from said axis of rotation, and the axially inner end being distant from the equatorial plane by an amount at most 0.43 times the width L of the mounting rim.

#It is then possible better to control the distribution of the contact pressures between the rim and the tire at the level of the respective rim and bead seats while permitting an improvement in the resistance to unwinding of the carcass reinforcement in the event of a high degree of heating of the beads without using anchoring bead wires for the carcass reinforcement.

#FIG. 1 is a schematic, viewed in meridian section, of a bead of a “heavy vehicle” tire embodying the invention.

#The “heavy vehicle” tire of dimension 385/65 R 22.5 (FIG. 1), intended to be mounted on a drop center rim having rim seats inclined at 15°, comprises a tread joined to two beads 3 by two sidewalls 2. A carcass reinforcement, formed of a single ply 1 of radial metal cables, made of steel, reinforces said tire, and is surmounted by a crown reinforcement (not shown) formed of at least two plies of metal cables made of steel which are parallel to each other in each ply and are crossed from one ply to the next, forming angles of between 10° and 35° with the circumferential direction.

#The meridian profile of the geometric center line of the carcass ply 1, viewed in meridian section, said profile being considered radially to the inside of a straight line XX′ parallel to the axis of rotation of the mounting rim and of the tire passing through the point of the rim flange, corresponding to the bead in question, farthest from the axis of rotation, is formed by a first, concave, arc of a circle AB, forming a tangent at A to the meridian profile of the carcass reinforcement in the sidewall 2 and at B to a second, convex, arc of a circle BC, which itself is extended tangentially and axially to the inside by a straight line segment CD forming an angle of 20° with the axis of rotation, and D being the end of the carcass reinforcement 1. The point A is distant from the equatorial plane by an amount equal to 149 mm, or 0.5 times the width L of the 11.75 rim on which the tire is mounted, whereas the point D is distant from the same plane by an amount equal to 0.3 times the same rim width. The arc of a circle AB, as can be seen in the figure, is not of the maximum possible length, owing to the specific form of the meridian profile of the flange of the 15° seat rim, the point B not being the point of tangency with a straight line perpendicular to the axis of rotation. Said meridian profile is therefore curved axially and radially from the outside to the inside to form an axially inner edge SD, located in an angle which is open axially and radially towards the inside, one of its sides forming an angle of 25° with the axis of rotation, being at a tangent to the second arc of a circle BC at S, and its other side, starting from S, being parallel to said axis of rotation.

#The first radially outer and axially inner additional layer 6 is composed of three plies 61, 62 and 63 of metal 68×23 cables made of steel, oriented circumferentially, the breaking load of which is at least 700 daN. The radially lower ends of the three plies are farther from the equatorial plane than the end of the carcass ply and the radially stepped radially upper ends are radially to the inside of the straight line XX′, except for the ply 61 which is closest to the carcass ply 1.