Resilient tires and wheels – Tires – resilient – Anti-skid devices
Reexamination Certificate
1999-07-30
2002-11-26
Maki, Steven D. (Department: 1733)
Resilient tires and wheels
Tires, resilient
Anti-skid devices
C152S209180, C152S209220, C152S211000, C152S212000, C152SDIG003, C156S110100, C156S123000, C156S127000, C156S128100, C156S129000
Reexamination Certificate
active
06484772
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to treads for the manufacture of new tires or for the recapping of tires, and in particular to the patterns for said treads which comprise a large number of cutouts in the form of grooves and/or incisions. It also relates to a production method making it possible to produce such treads.
In order to adapt the performance of tires to the increasingly improved performance of new vehicles, it is becoming necessary, inter alia, to increase the level of the adhesion performance of the tires on a wet road, without for all that adversely affecting the other types of performance thereof. “Adhesion” is understood to mean both the adhesion properties of the tire in the direction transverse to the displacement of the vehicle (cornering ability) and those of the tire in the direction longitudinal to the displacement of the vehicle (possibility of transmitting a braking or driving force to the ground).
In order to increase the adhesion potential of a tread of a tire traveling on a road covered with water, it is known to provide this tread with a pattern formed of a plurality of cutouts formed at greater or lesser depths in said tread, said cutouts opening on to the surface of said tread in contact with the road (this surface is called the rolling surface).
“Cutout” quite obviously means formed in the tread, be it by removing material once the tread has been vulcanized or be it by molding in a mold for molding said strip and comprising molding elements which project on the molding surface of said mold, each molding element having a geometry identical to the geometry of the desired cutout. As a general rule, a cutout made in a tread is defined by at least two walls of rubber which face one another, said walls being separated by an average distance representing the width of the cutout, the intersection of said walls with the rolling surface forming rubber ridges. Several types of cutout can be distinguished, for example:
grooves or furrows characterized by a width greater than about 10% of the thickness of the tread;
incisions of relatively low width compared with the thickness of the tread; under certain conditions of stress, these incisions may close, at least partially, in contact with the road;
the walls facing one another come into contact with one another at least over a more or less large part of the surfaces of said walls (the ridges formed by an incision on the rolling surface are in contact, which causes the incision to close).
Some cutouts may open into at least one other cutout. The trace of a cutout on the rolling surface of a tread follows an average geometric profile determined as the geometric profile located at an average distance from the ridges formed by the walls of said cutout on the rolling surface. The center axis of the trace of a cutout on the rolling surface corresponds to the straight line of the least-error squares of the distances of the points of the average profile from the trace of said cutout. Furthermore, it is usual to define the groove ratio of a pattern as the following ratio: area of the cutouts on the rolling surface divided by the total area of contact between the tire and the road.
By effecting a plurality of cutouts which open on to the rolling surface, a plurality of rubber ridges is created to break up the layer of water which may be present on the road, so as to keep the tire in contact with the ground and to create cavities forming channels intended to collect and remove the water present in the zone of contact of the tire with the road since they are arranged so as to open outside the zone of contact.
An example of such a pattern is found in U.S. Pat. No. 1,452,099, which describes a tread provided with a plurality of regularly spaced incisions of transverse orientation.
However, the increase in the number of cutouts rapidly results in a substantial decrease in the rigidity of the tread, which has an adverse effect on the performance of the tire, and even on the adhesion. “Rigidity of the tread” is understood to mean the rigidity of the tread under the combined actions of compressive stresses and shearing stresses in the region affected by the contact with the road. Conjointly, the presence of numerous cutouts forming channels for evacuating water results in a level of traveling noise on a dry road which is nowadays considered as a nuisance which it is desired to reduce to as great an extent as possible, very particularly on vehicles of recent design. This traveling noise is amplified by the cyclical movements of closing and opening of the cutouts which are associated with the friction of the walls of said cutouts when they are closed.
In French Patent 1 028 978, a solution to this problem is, proposed which consists in providing the tread with a plurality of circumferential incisions of low depth over the rolling surface of the new tread so as to increase the flexibility of said tread solely in the vicinity of the rolling surface.
However, since the tire, once mounted on a vehicle, is intended to provide good performance during the entire life of said tire (that is to say, until its tread has worn down to a level corresponding at least to the legally permitted level), it is necessary to provide a tread having a pattern which ensures the lasting quality of the adhesion performance on wet ground.
SUMMARY OF THE INVENTION
The object of the present invention is to develop a tread for a tire which manages to combine a very good level of adhesion to a wet road and to a dry road with a low emission of noise while traveling when new and during at least a major part of the life of said tread. Complementary, one of the objects of the invention is to control the evolution of the performance with the wear of the tread.
According to the invention, a tread is proposed, of thickness E in a rubber mix, intended to be placed radially on the outside of a tire, said tread being provided with a rolling surface which is intended to come into contact with the road during the travel of the tire. The tread is provided with a large number of cutouts such that a plurality of cutouts is affected by the zone of contact of the tire with the road. Each cutout is defined by the space enclosed mainly between two opposing walls, said walls being perpendicular to or oblique to the rolling surface, and each cutout has a depth at most equal to the thickness E of the tread, the depth of said cutout being measured as the distance in a radial direction between the points of the contour of said cutout which are farthest from the rolling surface of the new tire and said rolling surface. Furthermore, two main walls of at least one cutout located in the part of the tread affected by the loading on the ground of the tire during travel are connected by at least one rubber connecting element.
The reference S
E
is given to the total connection surface on each of the walls of said cutout equal either to the total intersection surface of the connecting element in the case of a single element or to the total of the intersection surfaces of all the connecting elements in the case of several elements, and the total surface of each of the main walls of said cutout is referenced S
T
.
The tread according to the invention is characterized in that:
the two main walls of at least one cutout located in the part of the tread affected by the loading on the ground of the tire during travel are connected by at least one rubber connecting element, the connecting element(s) having with each of the walls a connection surface S
E
corresponding to the total of the intersection surfaces of each connecting element, said surface S
E
on each of the walls being at least 10% of the surface S
T
of said wall,
all the points of the outer contour of the surface of intersection of at least one connecting element with one of the walls are located at a distance from the rolling surface which is strictly less than the depth of the cutout,
and in that, on each of the main walls, the connection surface S
E
is at most 80% of the surface S
G
, the surface S
G
being equal to
De Labareyre Bertrand Garnier
Lopez José Merino
Baker & Botts L.L.P.
Compagnie Generale des establissements Michelin-Michelin & Cie
Maki Steven D.
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