Resilient tires and wheels – Tires – resilient – Pneumatic tire or inner tube
Reexamination Certificate
2000-07-12
2002-10-08
Johnstone, Adrienne C. (Department: 1733)
Resilient tires and wheels
Tires, resilient
Pneumatic tire or inner tube
C152S539000, C152S543000
Reexamination Certificate
active
06460589
ABSTRACT:
BACKGROUND OF INVENTION
The present invention relates to a tire with radial carcass reinforcement which is intended to bear heavy loads, and more particularly to a “heavy-vehicle”-type tire, intended to be fitted on vehicles such as, for example, lorries, road tractors, buses, trailers and others, and more particularly to the novel reinforcement structure for the beads of said tire.
Generally, a tire of the type in question comprises a carcass reinforcement formed of at least one ply of metal cables, which is anchored in each bead to at least one bead wire, forming an upturn. The carcass reinforcement is radially surmounted by a crown reinforcement, composed of at least two plies of metal cables which are crossed from one ply to the next, forming angles of between 10° and 45° with the circumferential direction. The carcass reinforcement upturns are generally reinforced by at least one bead reinforcement ply formed of metal cables which are oriented at a small angle relative to the circumferential direction, generally of between 10° and 30°.
In the case of the presence of a single bead reinforcement ply, the latter is generally located axially to the outside, along the carcass reinforcement upturn, with a radially upper end located above or below the radially upper end of the carcass reinforcement upturn. As for the radially lower end of such a reinforcement ply, it is generally located beneath a straight line parallel to the axis of rotation and passing approximately through the center of gravity of the meridian section of the anchoring bead wire of the carcass reinforcement.
The known solution aims to avoid deradialization of the cables of the carcass reinforcement upturn and to minimize the radial and circumferential deformations to which the end of said upturn and the outer rubber layer covering the bead and providing the connection to the rim are subjected.
The life of “heavy-vehicle” tires, owing to the progress achieved, and to the fact that certain types of travel are made less of a handicap as far as wear of the tread is concerned, has become such that it is also necessary to improve the endurance of the beads. Said improvement must focus on the degradation of the rubber layers at the level of the ends of the carcass reinforcement upturn and the radially outer ends of the bead reinforcement plies. More particularly in the case of tires which are subject to prolonged travel, which travel frequently induces a high temperature of the beads, owing to the temperatures which the mounting rims reach, the rubber mixes in contact with the rim are then subject to a reduction in their rigidity, and to more or less slow oxidation, hence the very marked tendency of the carcass reinforcement to unwind from around the bead wire under the action of the internal inflation pressure, despite the presence of one or more bead reinforcement plies. There then arise bead wire movements and shearing deformations at all the ends of the plies, resulting in the destruction of the bead. Said improvement must also, and primarily, focus on this second possibility of degradation.
The carcass reinforcement of a radial tire, mounted on its operating rim and inflated to the recommended pressure, has in one sidewall a regularly convex meridian profile between approximately the zones of connection with the meridian profile of the crown reinforcement and with the bead. In particular, starting from the radius where the carcass reinforcement is subject to the influence of the bead reinforcement ply (plies), said reinforcement has in the bead a meridian profile which is either substantially rectilinear or curved in the opposite direction to the curvature in the sidewalls, that is to say, substantially parallel to the curvature of the rim flanges starting from a point of inflection located radially approximately at the level of the radially upper end of the bead reinforcement ply placed along the carcass reinforcement upturn.
Such a meridian profile of the carcass reinforcement does not appear favourable to good endurance of the beads, which requires improvement when the loads borne become greater, or the inflation pressures lower, than the recommended loads and pressures.
French Patent 2 604 396, in order to improve the durability of a radialtire bead intended for intensive travel, proposes reinforcing the main part of the carcass reinforcement with two bead reinforcement armatures: one, located axially to the outside of the carcass reinforcement, being formed of layers of metal cables inclined relative to the meridian direction, the other, located axially to the inside of the carcass reinforcement, also being formed of layers of metal cables which are inclined in the opposite direction to the direction of inclination of the cables of the first layers, so as to obtain a triangulated overall reinforcement with the radial cables of the carcass reinforcement.
Research has led to the conclusion that the meridian profile of the carcass reinforcement in the region of the change of curvature within the bead needed to be reinforced by at least one bead reinforcement armature of circumferential reinforcement elements.
SUMMARY OF THE INVENTION
In order to improve the endurance of the beads of a tire, for a vehicle intended to bear heavy loads, said tire, according to the invention, comprising at least one radial carcass reinforcement which is formed of at least one ply of inextensible reinforcement elements and is anchored within each bead B to a bead wire to form an upturn, each bead B being reinforced by at least one additional reinforcement armature formed of metal elements, the non-upturned part of the carcass reinforcement, in the region of the bead located on either side of the point of inflection, where the trace of its meridian profile changes curvature to become rectilinear or concave, being reinforced, at least axially to the inside, by an additional reinforcement armature of at least one ply formed of metal reinforcement elements, the radially lower end of which is radially below the straight line D′ which is parallel to the axis of rotation and passes through that point of the coating layer of the anchoring bead wire which is farthest from the axis of rotation, but above the straight line D which is parallel to the axis of rotation and passes through that point of the coating layer of the anchoring bead wire which is radially closest to the axis of rotation, and the radially upper end of which is located at a radial distance from the straight line D which lies between a quantity equal to half the radial distance between the straight lines D and D″ increased by half the radial distance between the straight lines D and D′ and a quantity equal to half the distance between the straight lines D and D″ reduced by half the radial distance between the straight lines D and D′, the straight line D″ being the straight line at the point of greatest axial width, is characterized in that the reinforcement elements of the additional armature are lengths or assemblies of lengths of circumferential cables, of a circumferential length of between 0.2 and 0.4 times the circumferential length of the reinforcement armature (
6
A), measured upon the laying of said ply.
The straight line D″ at the point of greatest axial width is, by definition, the straight line parallel to the axis of rotation and passing through the point in the meridian profile of the carcass reinforcement which corresponds to the point of greatest axial width when the tire is mounted on its operating rim, non-loaded and inflated to the recommended pressure.
The elements of the additional reinforcement armature are said to be circumferential if the angle which they form with the circumferential direction is between +5° and −5°.
This structure thus permits partial takeup of the tensile forces to which the carcass reinforcement is subjected, and thus minimizes the radial deformations at the ends of the carcass reinforcement upturn, whatever the conditions of travel.
The takeup of the forces will be all the gr
Baker & Botts L.L.P.
Compagnie Generale des Etablissements Michelin--Michelin & Cie
Johnstone Adrienne C.
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