Resilient tires and wheels – Tires – resilient – Pneumatic tire or inner tube
Reexamination Certificate
2000-07-12
2002-09-03
Johnstone, Adrienne C. (Department: 1733)
Resilient tires and wheels
Tires, resilient
Pneumatic tire or inner tube
C152S539000, C152S542000, C152S543000
Reexamination Certificate
active
06443204
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 on 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 a meridian profile which is substantially rectilinear or even 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 which is placed along the carcass reinforcement upturn. Such an architecture results in relatively thick tire beads.
The problems of endurance referred to above, which are influenced by the operating temperature of the beads, have been solved to a very slight degree by a highly reinforced bead structure. French Patent 2 654 988 describes a tire, particularly suitable for heavy vehicles, having a radial carcass reinforcement which is formed of inextensible reinforcement elements and anchored within each bead. Said bead is reinforced by two plies of steel cables, a first ply turned up about the bead wire to form two strands, and a second ply arranged axially to the inside of the main part of the carcass reinforcement. Said problems can also be solved by what is called a “thinned” bead structure, obtained, for example, by the means described in French Patent 2 415 016 which, to this end, teaches to impart a relatively great concavity to the outer sidewall of the tire, between the point where said sidewall is no longer in contact with the rim and the point where said sidewall achieves its maximum distance relative to the equatorial plane, when the tire is mounted on its operating rim and inflated to the recommended pressure.
Such an arrangement becomes insufficient, in particular when the ratio of the height H on the rim to the maximum axial width S of the tire decreases, and requires improvement when the loads borne become greater, or the inflation pressures less, than the recommended loads and pressures.
Research has led to the conclusion that the thinning of the beads had to be effected not from the outside of the tire but from the inside, and that it needed to be effected in combination with specific reinforcement characteristics of said beads.
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, comprises 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 at least one bead wire to form an upturn, each bead B being reinforced by an additional reinforcement armature formed of metal elements. It is characterized in that, viewed in meridian section, the carcass reinforcement has a meridian profile, the trace of which between the point A of greatest axial width and the first point of tangency T with the virtually circular coating layer of the anchoring bead wire, is convex over its entire length, and such that the thickness &egr; of the bead B, measured on a line perpendicular to said meridian profile at a point C of height h
c
of between 30 and 40 mm and measured relative to the base of the bead YY′, is between 2.5 and 3.0 times the thickness e of the sidewall measured on the straight line D″, which is the line of greatest axial width, said carcass reinforcement being reinforced, in its non-upturned part, by the additional reinforcement armature formed of at least one ply of circumferential reinforcement elements which is arranged axially to the inside of said non-upturned part.
The point A of greatest axial width is, by definition, the point of the meridian profile of the carcass reinforcement corresponding to the point of greatest axial width of the carcass reinforcement when the tire is mounted on its operating rim, non-loaded and inflated to the recommended pressure, and the straight line D″ of greatest axial width is the straight line parallel to the axis of rotation and passing through A.
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°.
The convex trace of the meridian profile of the carcass reinforcement is generally formed of a plurality of adjacent arcs of a circle, the radii of curvature of which increase from the point A of greatest axial width to the point of tangency T with the virtually circular coating layer of the anchoring bead wire, but the trace between the point A and the point T may be convex and circular with a center of curvature located on the straight line of greates
Baker & Botts L.L.P.
Compagnie Generale des Etablissements Michelin--Michelin & Cie
Johnstone Adrienne C.
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