Resilient tires and wheels – Tires – resilient – Pneumatic tire or inner tube
Reexamination Certificate
2000-07-12
2002-10-15
Johnstone, Adrienne C. (Department: 1733)
Resilient tires and wheels
Tires, resilient
Pneumatic tire or inner tube
C152S539000, C152S540000, C152S542000, C152S543000, C152S545000, C152S550000, C152S552000
Reexamination Certificate
active
06463975
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 a 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°.
The bead reinforcement ply 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.
U.S. Pat. No. 3,301,303, in order to improve the endurance of the bead zone of a tire bearing heavy loads, claims a carcass reinforcement which is wound in a precise trace around two bead wires which are practically axially adjacent: the carcass reinforcement is first anchored by turning up about the axially innermost bead wire, passing radially from the outside to the inside, then axially from the inside to the outside, then passing radially below the second bead wire, which is arranged axially to the outside, to wind about said second bead wire, passing radially from the inside to the outside then axially from the outside to the inside to form an upturn which comes back radially beneath the first bead and possibly winds around said bead wire to then be arranged along the axially outer face of the carcass ply.
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 firstly with the meridian profile of the crown reinforcement and secondly with the bead. In particular, starting from the radius where the carcass reinforcement is subject to the influence of the bead reinforcement 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 an arrangement associating two bead wires within a bead with a meridian profile having a point of inflection in the region of the bead significantly improves the endurance of the beads in the case of travel on a heated rim, but becomes insufficient, however, in the case of travel where the supported loads become greater, or the inflation pressures less, than the recommended loads and pressures, and more particularly when the ratio of the height H on rim to the maximum axial width S of the tire becomes less than 0.8.
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.
SUMMARY OF THE INVENTION
In order to improve the endurance of the beads of a tire having an HIS form ratio of less than 0.8, intended to be fitted on a vehicle bearing heavy loads, said tire, according to the invention, comprises at least one radial carcass reinforcement, formed of at least one ply of inextensible reinforcement elements, anchored within each bead B to at least two bead wires which are close to each other, which is turned up about the first and then wound around the second to form an upturn, and it is characterized in that, viewed in meridian section, an additional reinforcement armature, formed of at least one ply of circumferential reinforcement elements, is placed along the carcass reinforcement, at least axially to the inside, in the bead region where the trace of the meridian profile of said carcass reinforcement changes curvature to become rectilinear or concave at the point of tangency T with the virtually circular coating layer of the first anchoring bead wire, said reinforcement armature having its radially lower end radially beneath the straight line D′ which is parallel to the axis of rotation and passes through that point of the coating layer of the first anchoring bead wire which is radially 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 first anchoring bead wire which is radially closest to the axis of rotation.
The additional reinforcement armature will preferably have its radially upper end 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 radial 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.
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 that 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 and inflated to the recommended, non-loaded 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°.
Whatever the path
Baker & Botts L.L.P.
Compagnie Generale des Etablissements Michelin--Michelin & Cie
Johnstone Adrienne C.
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