Resilient tires and wheels – Tires – resilient – Anti-skid devices
Reexamination Certificate
2001-08-08
2003-07-08
Johnstone, Adrienne C. (Department: 1733)
Resilient tires and wheels
Tires, resilient
Anti-skid devices
C152S455000, C152S526000, C152S528000, C152S531000, C152S534000
Reexamination Certificate
active
06588472
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention concerns radial tires whose crown is reinforced under the tread by means of superimposed plies of cords or cables which, in what follows, constitute the crown reinforcement. It also concerns a method for mounting a train of tires on a road vehicle.
As a general rule a tire for a passenger car comprises a radial carcass reinforcement anchored in two tire beads and covered radially by a crown reinforcement, itself covered radially by a tread designed to come into contact with the road during rolling. The crown reinforcement comprises at least two plies, known as working plies, each ply being composed of a plurality of cords or cables essentially parallel to one another within one ply, the cords or cables of one ply being crossed over relative to the cords or cables of the adjacent ply or plies.
To improve the general rolling characteristics of a vehicle fitted with tires, it is known to use tires having structural asymmetries.
To solve a wear problem on a vehicle rolling on a path with relatively small radii of curvature, FR 1.342.822 describes the formation of an asymmetrical crown reinforcement in which that the transverse rigidity of the tread decreases from one edge to the other with the less rigid portion facing outwards on the vehicle to which the said tire is fitted. To obtain this asymmetry, it is proposed among the examples described, to form a crown reinforcement with one ply extending across the full width of the tread and a second ply across only part of the said width, so as to confer on the said tread a greater transverse rigidity on one side than on the other.
Although interesting in terms of rolling behavior performance on the vehicle, the presence of asymmetrical rigidity in a tire has certain disadvantages and in particular that of drift when the said vehicle is rolling in a straight line (that is to say, a stress distribution in the tread essentially equivalent to that produced when going around a curve). This leads to contact forces which are detrimental from the standpoint of tire tread wear; the forces exerted by the road on the vehicle's tires also cause the vehicle to veer (that is, it deviates progressively from its path during rolling in a straight line).
To address this problem, FR 1.444.271 proposes a means to attenuate the effects of an asymmetrical structure when rolling in a straight line, by superimposing over the said structure a second asymmetry in order to counterbalance the effects of the first asymmetry while preserving good rolling behavior performance around bends for example, due to the presence of the first asymmetry. The examples described involve either the addition of a supplementary reinforcement element (carcass ply extending beneath the crown reinforcement), or additional thickness of the tread located over only part of the said tread.
SUMMARY OF THE INVENTION
The purpose of the present invention is to propose an asymmetrical tire structure that performs well both when rolling on bends and when travelling in a straight line, the said structure considerably reducing the lateral pull of a vehicle fitted with this type of tire and therefore avoiding the appearance of irregular wear linked for example to drift while rolling in a straight line. It has been found that by choosing particular values for a certain number of parameters, a considerable performance improvement can be obtained while preserving some asymmetry of the tire's structure without making the said tire any heavier.
This objective is achieved with a tire that has a preferred direction of fitting to a road vehicle. The tire comprises two tire beads, a crown and two side-walls that connect the beads and the crown, the said tire having a carcass reinforcement that extends from one bead to the other and, radially outside it, a crown reinforcement of width Ls formed by a stack of at least two crown plies, each of these crown plies having a width equal to or greater than Ls and comprising a plurality of cords or cables arranged parallel to one another along essentially the same direction, the said cables crossing over from one ply to the next.
This tire also comprises a meridian reinforcing ply arranged radially between the carcass reinforcement and the crown reinforcement, and comprising a plurality of cords or cables essentially parallel to one another and making with respect to the circumferential direction an average angle between 50° and 90°, the said ply being of width Lr measured between a first edge and a second edge, both edges being located on the same side relative to the equatorial plane of the tire.
The tire is characterized in that it comprises marking to indicate the side of the tire on which the meridian reinforcing ply is located (e.g., “inner side”), this marking enabling the said ply to be positioned on the inside of the vehicle when the tire is mounted on the said road vehicle.
The width Ls of the crown reinforcement is taken as the smallest of the widths of the crown plies, and corresponds to the effective width of the tire, that is, the width over which there is mechanical coupling between the crown plies.
While the state of the known prior art discloses tires with crowns comprising plies called triangulation plies and arranged symmetrically relative to the equatorial plane of the said tires, the present invention proposes a novel and not obvious solution which consists in associating the presence of a single meridian reinforcing ply with an indication of the necessary position of this ply relative to the vehicle, once the tire has been fitted to the vehicle, that will lead to good rolling performances both in a straight line and when rounding bends, without giving rise to undesirable wear and lateral pull effects.
Various marking means can be used, in particular marking on one side-wall of the tire to indicate the side on which the meridian reinforcing ply is located, a specific marking on the outside or inside surface of the tire indicating the side of the tire that must be positioned outwards or inwards on the vehicle, granted that the meridian reinforcing ply has to be on the inside.
With the tire according to the invention, the following characteristics can also be applied, alone or in combination:
the width Lr of the meridian reinforcing ply is between 15% and 45% of Ls;
the first edge of this meridian reinforcing ply is located a distance D
1
from the equatorial plane between 35% and 50% of Ls, while the second edge of the meridian reinforcing ply is located between the first edge and the equatorial plane of the tire;
the mean compression rigidity of the meridian reinforcing ply in the direction of the cords or cables of the said ply is higher than 1 Gpa, this rigidity being obtained by multiplying the compression rigidity of a single cord or cable by the number of cords or cables per unit length of the ply.
The combination of the parameters mentioned above makes it possible to benefit from the advantages of an asymmetrical tire structure without the need for additional means to counterbalance the effects of the drift induced during rolling in a straight line. The advantage of a tire according to the invention is significant, since the phenomena of irregular wear while rolling in a straight line (in the sense of wear localized in certain areas of the tread) are appreciably reduced.
If Lr is less than 15% of Ls, the reinforcing effect of the additional meridian reinforcing ply is insufficient for its effect on the tire to be measured; if Lr is more than 45% of Ls, when the tire is rotating at high speed effects are induced which can affect the tire's rolling performance adversely.
Similarly, to avoid any blockage in the radial direction of the median portion of the tire's crown when it is rotating about its axis, it is preferable to provide that the second edge of the meridian reinforcing ply is located at a distance D
2
from the equatorial plane larger than one-third of Lr.
When a tire according to the invention is rotating at a high speed, the presence of a meridian reinforcing ply ha
Baker & Botts L.L.P.
Johnstone Adrienne C.
Michelin & Recherche et Technique S.A.
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