Crown reinforcement for heavy duty tires

Details Crown reinforcement for heavy duty tires Crown reinforcement for heavy duty tires

2000-04-17

2002-06-11

Ball, Michael W. (Department: 1733)

Resilient tires and wheels

Tires, resilient

Pneumatic tire or inner tube

C152S531000, C152S532000, C152S538000, C152S535000

Reexamination Certificate

active

06401778

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention concerns a tire with radial carcass reinforcement anchored on both sides to at least one bead wire and having a crown reinforcement consisting of at least two superimposed working plies composed of parallel cords or cables in each ply and crossing from one ply to the next at angles with respect to the circumferential direction of the tire of at most 45° in absolute value.
More particularly it concerns a “Heavy Duty” type of tire, whose ratio of height at rim H to maximum axial width S is equal to at most 0.80, and is intended to be fitted to medium to high tonnage vehicles, such as lorries, buses, trailers, etc.
Some present-day so-termed “highway” tires are designed to run at high speeds and over increasingly long distances, due to improved road networks and the world-wide growth in motorway networks. The overall conditions under which such a tire is called upon to operate undoubtedly allows a greater number of kilometres to be covered, since the tire wear is less severe; on the other hand, the fatigue strength of the tire and of the crown reinforcement in particular are taxed more severely.
Patent FR 2 419 185 makes it clear that the type of tire in question, with a low H/S ratio, while offering numerous advantages, also has a number of drawbacks, such as poor adhesion of the equatorial area of the tread or a concentration of high pressures in the area of the edges of the tread, due to reduced contact area in the longitudinal direction of the tire. In order to overcome the said drawbacks, the above-mentioned French patent recommends the provision between the carcass reinforcement and the radially internal working ply, in two areas remote from the equatorial plane, of two limiting blocks each composed of two superimposed plies of inextensible cables, crossing from one ply to the next at opposing angles with respect to the circumferential direction, the said angles being equal in absolute value to at most one-half of the smallest angle used in the working plies and above 0°.
The implementation of the solution outlined above, its application to a tire with a shape ratio H/S equal to at most 0.80, in particular equal to at most 0.6, and intended to be fitted to a “heavy goods vehicle”, does not allow a crown reinforcement with a satisfactory fatigue strength to be obtained.
The lack of fatigue strength relates to both the fatigue strength of the crown plies, and in particular the resistance to separation between the edges of the plies, and the fatigue strength of the cables in the part of the carcass reinforcement situated below the crown reinforcement, the former deficiency being heavily influenced by the operating temperatures prevailing at the margins of the working plies, whether the tire is running in a straight line or cornering.
The objective of French patent application 94/015736 is to improve the fatigue strength of the crown reinforcement of a “heavy goods vehicle” tire having a shape ratio equal to at least 0.60. the said reinforcement comprising at least two working crown plies made from inextensible cables, crossing from one ply to the next at angles of between 10° and 45° to the circumferential direction, the said plies having widths equal to at least 80% of the maximum axial width S
0
of the carcass reinforcement. It proposes to make provision, firstly, between the carcass reinforcement and the working ply radially closest to the axis of rotation, for an axially continuous ply formed from inextensible metallic cables making an angle of at least 60° with respect to the circumferential direction, and whose axial width is equal to at least the axial width of the shortest working crown ply, and secondly between the two working crown plies an additional ply formed from metallic elements and arranged essentially parallel to the circumferential direction, the axial width of the said ply being equal to at least 0.7 S
0
, and its modulus of elasticity in tension being at most equal to the modulus of elasticity of the most extensible working ply.
French patent application FR 96/02178, which aims to lower the operating temperature of a “heavy goods vehicle” type of tire with radial carcass reinforcement, while offering a solution that is at once effective and economical, recommends adding to the said carcass reinforcement a crown reinforcement comprising at least two working crown plies made from inextensible cables, crossing from one ply to the next at angles of between 10° and 45° to the circumferential direction, and comprising in addition, in the absence of any ply formed from inextensible cables at an angle greater than 45° to the circumferential direction, an axially continuous additional ply formed from metal elements arranged essentially parallel to the circumferential direction and positioned radially between the working plies, the said additional ply having an axial width equal to at least 1.05 times the axial width of the widest working crown ply.
While the problems of separation between the working plies and the fatigue strength of the cables in the carcass reinforcement appear to be resolved in one case, and while the operating temperatures are greatly reduced in the other, the long haulage distances covered by tires constructed in this way lead to the appearance of fatigue fractures in the cables of the additional ply and more especially at the edges of the said ply, whether or not the so-termed triangulation ply is present.
It is always possible to change the reinforcing elements, and in particular to choose cables of a different construction or cables with a higher tensile strength. The above solution, while certainly simple, is always costly.
SUMMARY OF THE INVENTION
To overcome the above drawbacks and to improve the fatigue strength of the crown reinforcement of the type of tire in question without raising its cost, the tire with radial carcass reinforcement having a maximum axial width S
0
, according to the invention, comprising a crown reinforcement composed of at least two working crown plies of inextensible reinforcing elements crossing, from one ply to the next at angles of between 10° and 45° to the circumferential direction, the said plies having axial widths equal to at least 80% of the width S
0
and, arranged radially between the said working plies, an additional ply of reinforcing elements essentially parallel to the circumferential direction, is characterized by the fact that the working plies of widths greater than the width of the additional ply by at least 16% of the width S
0
are, on both sides of the equatorial plane and in the immediate axial extension of the additional ply, coupled over an axial distance equal to at least 3.5% of width S
0
, thereafter being separated by sections of a rubber mix over at least the remainder of the width common to the said working plies.
The thickness of the separating profiles between the plies, measured opposite the ends of the narrowest working ply, are equal to at least 2 mm and preferably greater than 2.5 mm.
The term ‘coupled plies’ should be understood to mean plies whose respective reinforcing elements are separated radially by at most 1.5 mm, the said thickness of rubber being measured radially between respectively the upper and lower generatrices of the said reinforcing elements.
The term ‘inextensible element’ should be understood to mean an element, cable or monofilament, that has a relative elongation of less than 0.2% when subjected to a tensile force equal to 10% of the breaking load. In the case of the tire considered, the inextensible reinforcing elements are preferably inextensible steel cables.
Reinforcing elements, cords or cables, arranged essentially parallel to the circumferential direction, are elements that form angles with the said direction in the range +2.5° to −2.5° with respect to 0°.
The additional ply advantageously has a modulus of elasticity in tension at most equal to the modulus of elasticity in tension of the most extensible working ply. A modulus of elasticity in tension of a ply of cables results from the

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