Radial tire with crown reinforcement including radial ply

Details Radial tire with crown reinforcement including radial ply Radial tire with crown reinforcement including radial ply

2000-11-08

2002-10-29

Johnstone, Adrienne C. (Department: 1733)

Resilient tires and wheels

Tires, resilient

Pneumatic tire or inner tube

C152S534000, C152S535000

Reexamination Certificate

active

06470939

ABSTRACT:

BACKGROUND OF INVENTION
The present invention relates to a tire with radial carcass reinforcement anchored on either side to at least one bead wire and having a crown reinforcement formed of at least two so-called working plies, superposed and made of wires or cables which are parallel in each ply and are crossed from one ply to the next, forming angles of at most 45° in absolute value with the circumferential direction of the tire.
It relates more particularly to a tire of the “heavy vehicle” type, the ratio of the height above rim H to the maximum axial width S of which is at most 0.80, and which is intended to be fitted on a medium- or high-tonnage vehicle, such as a lorry, bus, trailer, etc.
Some current tires, called “highway” tires, are intended to travel at high speed and on longer and longer journeys, owing to the improvement in the road network and the growth of the motorway network throughout the world. All the conditions under which such a tire is required to travel without doubt make it possible to increase the number of kilometers traveled, the wear of the tire being less; on the other hand, the endurance of the latter and in particular of the crown reinforcement is adversely affected.
U.S. Pat. No. 4,271,890 discloses that although the type of tire in question, with a low H/S ratio, has numerous advantages, it also has a certain number of disadvantages, such as poor adhesion of the equatorial zone of the tread or localization of high pressures in the region of the edges of the tread, which pressures are due to the shortening of the area of contact in the longitudinal direction of the tire. In order to overcome said disadvantages, the cited Patent advocates arranging between the carcass reinforcement and the radially inner working ply, in two zones distant from the equatorial plane, two limiting blocks each formed of two superposed plies of inextensible cables, crossed from one ply to the other, forming opposed angles with the circumferential direction which are at most equal in absolute value to half the smallest angle used in the working plies, and other than 0°.
The application of the solution set forth above, and the application thereof to a tire of H/S form ratio of at most 0.80, in particular at most 0.60, intended to be fitted on a heavy vehicle, does not make it possible to obtain satisfactory endurance of the crown reinforcement. The lack of endurance relates both to the fatigue resistance of the crown plies, and in particular the resistance to separation between ends of plies, and to the fatigue resistance of the cables of the portion of carcass reinforcement located beneath the crown reinforcement, the first deficiency being greatly influenced by the operating temperature at the edges of the working plies, whether traveling in a straight line or under drift.
The object of U.S. Pat. No. 5,738,740 is to improve the endurance of the crown reinforcement of a “heavy vehicle” tire, of a form ratio of at most 0.60, said reinforcement comprising at least two working crown plies of inextensible cables, crossed from one ply to the next, forming angles of between 10° and 45° with the circumferential direction, said plies having widths at least equal to 80% of the maximum axial width S
0
of the carcass reinforcement. It proposes arranging, firstly between the carcass reinforcement and the working ply radially closest to the axis of rotation, an axially continuous ply formed of inextensible metal cables forming with the circumferential direction an angle of at least 60° and the axial width of which is at least equal to the axial width of the shortest working crown ply, and, secondly between the two working crown plies, an additional ply formed of metallic elements oriented substantially parallel to the circumferential direction, the axial width of said ply being at least 0.7 S
0
, and the modulus of elasticity upon traction of which being at most equal to the modulus of the same name of the most extensible working ply.
Although the problems relating to the separation between working plies and the fatigue resistance of the carcass reinforcement cables would appear to be solved in one case, if the operating temperatures are greatly reduced in the other case, on the other hand prolonged travel of the tires thus constructed causes fatigue failure of the cables of the additional ply, and more particularly of the edges of said ply, whether or not the so-called triangulation ply is present.
It is always possible to change the reinforcement elements concerned, and in particular to select cables of a different construction or cables of greater tensile strength. The solution above, while admittedly simple, is still costly.
In order to overcome the above drawbacks and to improve the endurance of the crown reinforcement of the type of tire in question, U.S. Pat. No. 6,401,778 B1 has proposed a tire with radial carcass reinforcement of maximum axial width S
0
, comprising a crown reinforcement formed of at least two working crown plies of inextensible reinforcement elements, crossed from one ply to the other, forming angles of between 10° and 45° with the circumferential direction, said plies having axial widths at least equal to 80% of the width S
0
, and, arranged radially between said working plies, an additional ply of reinforcement elements substantially parallel to the circumferential direction, said working plies having widths greater than the width of the additional ply by at least 16% of the width S
0
, and, on either side of the equatorial plane and in the immediate axial extension of the additional ply, being coupled over an axial distance at least equal to 3.5% of the width S
0
, then being decoupled by profiled members of rubber mix at least over the remainder of the width common to said two working plies.
The choice of circumferential reinforcement elements for the additional ply of inextensible elements, such that the modulus of elasticity under traction of said additional ply is at most equal to the modulus of the same name of the most extensible working ply, and preferably low for a relative elongation of between 0% and 0.4%, and at most equal to the greatest modulus of elasticity upon traction of the most extensible working ply, for relative elongations greater than 0.4%, does not make it possible to obtain the best price/quality ratio, since the optimum fatigue strength of the circumferential elements requires a minimum density of the elements at the edges of the ply and a minimum tensile strength of said elements.
SUMMARY OF THE INVENTION
The object of the invention is to improve the endurance of the crown reinforcement of the type of tire in question, without being faced with problems of fatigue of reinforcement elements. In the context of coupling the two working plies radially on either side of the additional ply of reinforcement elements, the solution consisting in selecting said elements as being circumferential has unexpectedly not proved to be the best solution.
The tire according to the invention, with a radial carcass reinforcement of maximum axial width S
0
, comprising a crown reinforcement formed of at least two working crown plies of inextensible reinforcement elements, crossed from one ply to the other, forming angles of between 10° and 45° with the circumferential direction, said plies having axial widths at least equal to 80% of the width S
0
, and greater by at least 16% of the width S
0
than the width of an additional ply of reinforcement elements, arranged radially between said working plies, said working plies, on either side of the equatorial plane and in the immediate axial extension of the additional ply, being coupled over an axial distance at least equal to 3.5% of the width S
0
, then being decoupled by profiled members of rubber mix at least over the remainder of the width common to said two working plies, is characterized in that the reinforcement elements of the additional ply are inextensible and substantially radial.
The thickness of the decoupling profiled members between working plies, measured at the ends of the least wide

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