Resilient tires and wheels – Tires – resilient – Pneumatic tire or inner tube
Reexamination Certificate
2001-11-14
2003-09-02
Aftergut, Jeff H. (Department: 1733)
Resilient tires and wheels
Tires, resilient
Pneumatic tire or inner tube
C152S529000, C152S531000, C152S532000, C152S535000, C152S536000, C152S538000
Reexamination Certificate
active
06612353
ABSTRACT:
BACKGROUND OF THE 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 H above rim 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.
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 travelling in a straight line or under drift.
A first solution has been described in French Application FR 2 728 510, and proposes arranging, firstly between the carcass reinforcement and the crown reinforcement working ply radially closest to the axis of rotation, an axially continuous ply formed of inextensible metal cables forming an angle of at least 60° with the circumferential direction 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
.
The problems relating to the separation between working plies and the fatigue resistance of the carcass reinforcement cables have been solved, and the operating temperatures reduced; on the other hand, prolonged travel of the tires thus constructed has caused fatigue breaking 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, 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.
Thus, in order to overcome these above new drawbacks and to improve the endurance of the crown reinforcement of the type of tire in question, French Application FR 97/14011, which has not been published to date, has chosen another solution, and proposes, on either side of the equatorial plane and in the immediate axial extension of the additional ply of reinforcements which are substantially parallel to the circumferential direction, to couple, over a certain axial distance, the two working crown plies formed of reinforcement elements crossed from one ply to the next, then to decouple them by profiled members of rubber mix at least over the remainder of the width common to the said two working plies.
The fatigue strength of the circumferential elements is not optimal, unless the minimum density of the elements at the edges of the ply and a minimum rupture resistance of said elements are respected, which involves a high cost price for material.
In order to improve the endurance of the crown reinforcement of the type of tire in question, without being faced with problems of fatigue of the reinforcement elements, French application FR 98/06000 radically modifies the orientation of the inextensible reinforcement elements of the additional ply which is arranged radially between said working plies, said elements then being radial.
The shearing stresses between the two working crown plies are very great, more particularly in the case of coupling of said two working plies, which results in delamination between the plies as the tire becomes fatigued. In order to overcome the above disadvantages and to improve the endurance of the crown reinforcement of the type of tire in question, the invention proposes ingeniously to reconcile the advantages of radial orientation with those of circumferential orientation of the reinforcements elements of the additional ply located radially between the two working crown plies.
SUMMARY OF THE INVENTION
According to a first variant, the tire according to the invention, 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 L
32
, L
34
at least equal to 80% of the width S
0
, is characterized in that an additional ply formed of at least one ply of reinforcement elements, of width L
33
less by at least 15% of the width S
0
than the width L
32
(L
33
) of the least wide working ply, arranged radially between said working plies, is axially composed of three parts, a central part in the form of a ply formed of inextensible, substantially radial, metallic reinforcement elements, said ply having an axial width L′
33
equal to at least 45% of the width S
0
, and two lateral parts in the form of strips, each formed of circumferential elastic metallic reinforcement elements, the modulus of elasticity upon traction per unit of width of a lateral strip being at most equal to the modulus of elasticity upon traction, measured under the same conditions, of the most extensible working ply, and the width L″
33
of each strip being at most 10% of the width S
0
.
“Inextensible element” is to be understood to mean an element, cable or monofilament which 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 in question, the inextensible reinforcement elements are preferably inextensible metal cables made of steel.
Metallic elements oriented substantially parallel to the circumferential direction are elements which form angles within the range +2.5°, −2.5° of said 0° direction.
Substantially radial reinforcement elements, cords or cables are elements which form angles within the range +5°, −5° of the 0° meridian direction.
Metallic reinforcement elements are said to be elastic if they have a relative elongation greater than 2% when they are subjected to a tensile force equal to 10% of their breaking load. They have a curve of tensile stress as a function of the relative elongation which has shallow gradients for the slight elongations and a substantially constant, steep gradient for the greater elongations, the change of gradient taking place in a range of relative elongation of between 0.2% and 0.8%. Owing to this, said elements may be referred to as “bimodular” elements.
A modulus of elasticity E upon traction of a ply per unit of width results from the tensile stress &sgr; exerted in the direction of the reinforcement elements and over a unit of width to obtain a relative elongation &egr;. “Elasticity modulus of the lateral part of the additional ply which is at most equal to the same modulus of the most extensible working ply” is to be understood to mean that the modulus of said part of the additional ply, whatever the relative elongation, is at most equal to the modulus of the most extensible working ply whatever the relative elongation, the most extensible ply being the ply w
Baker & Botts LLP
Fischer Justin
Michelin & Recherche et Technique S.A.
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