Tire with simplified crown reinforcement

Details Tire with simplified crown reinforcement Tire with simplified crown reinforcement

1998-03-31

2001-03-13

Johnstone, Adrienne C. (Department: 1733)

Resilient tires and wheels

Tires, resilient

Pneumatic tire or inner tube

C152S526000, C152S537000, C152S548000, C152S558000, C152S564000

Reexamination Certificate

active

06199612

ABSTRACT:

BACKGROUND OF INVENTION
The invention relates to the crowns of tires and especially to the cushion compounds in contact with the cords that reinforce these crowns.
The crowns of tires usually comprise a carcass reinforcement, belting, usually with at least two reinforcing plies, and a tread. These crowns are in contact with the ground and transmit to the wheels, via the sidewalls and the beads, the transverse forces necessary for steering the vehicles. For the on-road behavior of the vehicles to be satisfactory, it is necessary for the crowns to be very rigid relative, for example, to the sidewalls. An on-going goal is to attempt to obtain this kind of high rigidity simply and in the most economical way possible.
It is well known that the cushion compounds that bind the reinforcing cords of the belting play a part in obtaining a high rigidity. This is why these cushion compounds usually have a high modulus of elasticity. By contrast, the cushion compounds for the carcass cords usually have a low modulus of elasticity because they need to withstand without damage the high amounts of deformation they experience in the sidewalls of the tires.
Furthermore, there is a great deal of research currently being carried out in an attempt to reduce the fuel consumption of road vehicles. To this end, the desire is to design tires which have a very low rolling resistance while keeping the other properties, namely of wear, adherence, behavior, etc. the same, and to do so in the most economical way possible.
SUMMARY OF THE INVENTION
The subject of the invention is a tire in which the crown structure is improved to make it easier to manufacture and thus make it more economical, as well as to improve its quality and performance.
Another subject of the invention is, in a first alternative form, an embodiment of the tire according to the invention designed chiefly to improve the rigidity of the crown and, according to a second alternative form, an embodiment intended chiefly to lower the rolling resistance.
In that which follows, the term “cord” is understood to mean both monofilaments and multifilaments, or assemblies, such as ply cords, twisted cords, or alternatively any kind of equivalent assembly, this being irrespective of the material and treatment of these cords which may, for example, have a surface treatment or be coated or pre-coated with adhesive to encourage them to stick to the rubber.
For a given reinforcing ply, the term “layer of cushion compound” is understood to be the rubber blend in contact with these ply-reinforcing cords, which sticks to these cords and fills the gaps between adjacent cords. In common industrial practice, for a given carcass-reinforcing ply, the same type of cushion compound is used for the various regions of the tire. “Contact” between a cord and a layer of cushion compound is understood to mean that at least some of the external circumference of the cord is in close contact with the rubber blend forming the cushion compound.
The “modulus of elasticity” of a rubber blend is understood to be a secant extension modulus obtained at a deformation in uni-axial extension of the order of 10% at room temperature.
When a rubber blend is stressed sinusoidally, for example for a given deformation &egr;*=&egr;
0
e
j&ohgr;t
, the steady-state response of this blend is itself also sinusoidal and phase-shifted by an angle &dgr;, &sgr;*=&sgr;
0
e
j(&ohgr;+&dgr;)
. A complex modulus G*=&sgr;*/&egr;*=&sgr;
0
/&egr;
0
e
j&dgr;
=G′+jG″ is defined, with &sgr; representing the stress in MPa. A “dynamic modulus” G′ and a “dynamic loss modulus” G″ are defined. The ratio tan &dgr;=G″/G′ is termed the damping factor. Measurements are taken under cyclic shear stress at a frequency of 10 Hz, at a temperature of 60° C. and for a peak-to-peak dynamic deformation of 10%.
The tire according to the invention comprises a tread extended by two sidewalls and two beads, and a carcass reinforcement anchored in the two beads. The tire is composed, in the region under the tread, at least of belting and of the carcass reinforcement. The carcass reinforcement in the region under the tread consists of cords such that:
a) the cords of the carcass reinforcement which are arranged furthest toward the inside of the tire are in contact with a first layer of cushion compound of low modulus of elasticity which is radially on the inside relative to these cords; and
b) the cords of the carcass reinforcement which are arranged furthest toward the outside of the tire are in contact with a second layer of cushion compound that is radially on the outside relative to these cords, this second layer of cushion compound also being in contact with the cords of the belting which are arranged radially furthest toward the inside of the tire.
The tire according to the invention has the advantage that under the tread, it has just one layer of cushion compound that is between the carcass reinforcement and the first crown ply of the belting. This makes it possible for the properties and nature of this layer of single cushion compound to be specially chosen to suit the objectives of the tire designer. This also simplifies manufacture as hitherto it was always considered necessary to have a specific cushion compound with which to impregnate the cords of the carcass reinforcement and another specific one for impregnating the cords of the belting.
By way of example, a high modulus of elasticity of between 7 and 25 MPa and preferably between 9 and 15 MPa may be selected for this second layer of single cushion compound.
This gives a crown whose rigidity is very high, giving it excellent strength at high speeds.
In another alternative form, a low modulus of elasticity, of less than 6 MPa and preferably of between 2 and 5 MPa may be selected for this second layer of single cushion compound. This makes it possible to reduce the hysteresis energy expended during running and thus to reduce the resistance to travel of the tire in question.
In a preferred embodiment, a blend with very low hysteresis is selected, for example, one that has a damping factor tan &dgr; value of less than 0.08.


REFERENCES:
patent: 3392774 (1968-07-01), Le Bosse
patent: 1039382 (1958-09-01), None
patent: 0620129 (1994-10-01), None
patent: 0705717 (1996-04-01), None

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