Tire with prestressed radial carcass reinforcement

Claim 1

A tire formed of a tread, two shoulders, two sidewalls and two beads and having a carcass reinforcement capped by a tread reinforcement, the carcass reinforcement consisting essentially of at least one ply of radial wires or cables anchored to at least on bead ring in each bead, the tread reinforcement consisting of at least two plys of wires or cables which are parallel to each other in each ply and crossed from one ply to the other, the tire being characterized by the fact that, the tire being considered in radial cross-section, mounted on its service rim and not under load, (a) the mean meridian fiber of the carcass reinforcement of the uninflated tire and the mean meridian fiber of the carcass reinforcement of the tire inflated to its service pressure have a point of intersection (E i ) which is located between a point (E') of the mean meridian fiber of the carcass reinforcement of the uninflated tire and a point (E") of the mean meridian fiber of the carcass reinforcement of the inflated tire at which said points (E', E") the mean meridian fibers have a common tangent perpendicular to the axis of rotation of the tire, (b) the mean meridian fiber of the carcass reinforcement of the uninflated tire has an upper segment, contained between the point (S) where the carcass reinforcement becomes parallel to the tread reinforcement and said point of intersection (E i ), which is located radially and axially outward of a corresponding upper segment of the mean meridian fiber of the carcass reinforcement of the inflated tire, (c) the mean meridian fiber of the carcass reinforcement of the uninflated tire has a lower segment, contained between said point of intersection (E i ) and the point (J' T ) where the carcass reinforcement becomes parallel to the bead ring, which is located radially outward and axially inward of a corresponding lower segment of the mean meridian fiber of the carcass reinforcement of the inflated tire, (d) the mean meridian fiber of the carcass reinforcement follows traces defined by the relationship cos φ=(R 2 -R e 2 )/(R s 2 -R e 2 ), at least between the point (S) where the carcass reinforcement becomes parallel to the tread reinforcement and the zone of the bead, the traces of the mean meridian fiber of the uninflated tire and of the tire inflated to its service pressure having, on the one hand, in common the point (S) where the carcass reinforcement becomes parallel to the tread reinforcement, these traces being furthermore located at the same axial distance from the equatorial plane of the tire to said points (E', E") where they have a common tangent perpendicular to the axis of rotation of the tire, and these traces or their extensions furthermore passing into the zone of the bead via points (J', J") located at the same axial distance from the equatorial plane of the tire but at a radial distance from the axis of rotation of the tire, with respect to the point (J") corresponding to the mean meridian fiber of the tire inflated to its service pressure, which is less than the radial distance of the point (J') corresponding to the mean meridian fiber of the uninflated tire; said terms φ, R, R e and R s being as defined in the foregoing specification, (e) the difference in the radial distances from the axis of rotation of the tire to the points (J', J") of the traces or of the extensions of the traces of the mean meridian fibers, which are located at the same axial distance from the equatorial plane of the tire, in the zone of the bead, is between 2% and 20% of the height of the tire on its service rim, (f) the shape of the tire, and more particularly the shape of its carcass reinforcement, mounted on its service rim, not inflated and not under load, is obtained by vulcanizing the tire on a rim of a width equal to or less than the width of its service rim in a vulcanization mold corresponding to said shape, (g) the carcass reinforcement, at least between the point (S) where it becomes parallel to the tread reinforcement and the point (J' T ) where it becomes parallel to the bead ring, has a relative elongation of less than 0.5%, and preferably less than 0.2%, under a tensile force equal to 10% of its ultimate tensil strength, and (h) the length of the mean meridian fiber of the carcass reinforcement of the uninflated tire and the length of the mean meridian fiber of the carcass reinforcement of the inflated tire differ from each other by at most 1%, at least between the point (S) where the carcass reinforcement becomes parallel to the tread reinforcement and points (J' T ) and (J" T ), respectively, where the carcass reinforcement becomes parallel to the bead ring.