Resilient tires and wheels – Tires – resilient – Anti-skid devices
Reexamination Certificate
1999-06-18
2001-07-24
Maki, Steven D. (Department: 1733)
Resilient tires and wheels
Tires, resilient
Anti-skid devices
C152S209220, C152S209230, C152S210000, C152S211000, C152SDIG003
Reexamination Certificate
active
06263934
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to tire treads, and in particular to a structure of a new incision geometry, imparting improved properties of adherence to said treads while postponing the occurrence of irregular wear.
The invention relates to treads intended for the fabrication of new tires or to the retreading of tires, and in particular to tread structures for said tires, comprising a large number of cut-outs in the form of grooves and/or incisions. By incision is meant, in this description, a cut-out of width less than or equal to 2 mm, while a groove is a cut-out of width greater than 2 mm.
It is known, for example in U.S. Pat. No. 2,100,084, that incisions may be made whose trace on the tread surface of a tire is of closed circular shape, providing active edges in all directions tangent to the tread surface. Each such incision bounds and isolates a rubber element (of small size compared to the tread width) joined to the tread at its base only. This rubber element, under the action of forces of rolling contact with the ground, has a tendency to deform both in shear and in bending (stresses tangential to the surface of the isolated element coming into contact with the ground) and in compression under the load supported by the tire. Considering the size of the isolated elements and of the stresses to which they are subjected, it may happen that these elements are torn away from the rolling tread.
To remedy this drawback, it is known, for example in U.S. Pat. No. 2,938,560, that the walls of the isolated element may be provided with rubber connecting elements joining said element to the rest of the tread. U.S. Pat. No. 2,938,560 describes a tread provided with a structure made up of a plurality of wave-shaped incisions, said incisions being arranged under as to isolate rubber studs; these studs are joined to the tread by four supports arranged on the tread surface, each support rising beneath the rolling surface in new condition and extending in a direction perpendicular to said surface, as far as the full depth of said incisions. By stud is meant in the description a small isolate rubber element.
However, such incisions may lead to irregular wear, that is, wear occurring preferentially in certain areas of the tread and amplified in rolling so as to lead usually to premature discard of the tire; in some cases, the edges formed by the incisions in the tread may be preferential locations of initiation of such wear, especially in applications having a large tread thickness (for example in tires for heavy loads).
Furthermore, the incisions proposed in U.S. Pat. No. 2,938,560 have another disadvantage relating to the entry of pebbles into the tread.
It often happens that the ground on which the tire rolls is covered with gravel or other objects that may get into the incisions. In many cases, these introduced objects are ejected under the action of centrifugal force due to rotation of the tire; all the same, it will happen that some of these foreign bodies remain imprisoned in said incisions and may travel towards the bottom of the incisions until they attack the tire structure. It is likewise possible that these included objects may cut the rubber studs bounded by each closed-curve incision, with the result that the rubber will tear, forming holes in the tread and thus increasing the likelihood of penetration by foreign bodies.
SUMMARY OF THE INVENTION
To avoid both the occurrence of abnormal wear near edges formed by said incisions of closed or nearly closed outline on the contact surface of a tread, and reduce the likelihood of introduction of foreign matter into the incision, the invention proposes a tire tread provided with a rolling surface and a plurality of incisions opening upon said surface. Wear is termed abnormal when it occurs locally at certain places in the structure of a tread and not uniformly over the structure as a whole.
Each incision is defined by the space bounded principally between two main walls facing each other, said walls being perpendicular or oblique with respect to the rolling surface.
The tread is provided with at least one rubber stud, of principal orientation XX′ perpendicular or inclined with respect to the rolling surface, bounded by at least one incision, said stud comprising an outer end wall and a side wall perpendicular or inclined with respect to the rolling surface. The end wall, corresponding to the stud wall located nearest the rolling surface, is intended to come into contact with the ground when the tread equips a tire rolling over the ground.
The stud thus bounded is joined to the tread by its base (portion of stud located farthest inside the said tread) and by at least one rubber connecting element joining the side wall of said stud to the rest of the tread. The tread according to the invention is characterized in that:
Each connecting element of each rubber stud has a surface of intersection, bounded by two principal geometrical lines of like course, with the side walls of said rubber stud.
The projected length, on the rolling surface of the tread in new condition and in the direction XX′ of the principal geometrical lines of the surfaces of intersection of all the connecting elements of each rubber stud represents at least 80 percent of the contour perimeter of each rubber stud measured on the same surface.
The sum of the lengths of the intersections, with any surface substantially parallel to the rolling surface of the tread in new condition and located inside of the said tread, of the surfaces of intersection of all the connecting elements of one and the same rubber stud, represents at most 50 percent of the contour perimeter of said rubber stud measured on the same said surface substantially parallel to the rolling surface of the tread in new condition and located inside of the tread.
By mean direction XX′ of a rubber stud bounded by an incision is meant the direction connecting the geometric center of gravity of the base of said stud to the center of gravity of the end wall (this direction makes an angle of 90 degrees with said surface when the incision bounding that element is perpendicular to that surface).
A connecting or bridging element is defined as a rubber portion projecting from the side wall of an isolated rubber stud, said side wall forming one of the principal walls of an incision; said connecting element is moreover joined to the other principal wall of the incision bounding said rubber stud. Each connecting element, with the side wall of the stud, has a surface of intersection geometrically defined by a contour having two principal geometrical lines with traces fairly close together.
By a similar trace is meant that the principal geometrical lines bounding a surface of intersection of a connecting element have geometrical shapes virtually superposable over much of their extent.
Preferably, said traces are substantially parallel, which is to say that the mean distances between said lines are nearly constant. The distance between two geometrical lines of one and the same surface of intersection of a connecting element of a stud is measured on said lateral surface of said stud as the length of the curve obtained by intersection of said surface of intersection with a virtual surface parallel to the rolling surface of the tread in new condition.
The projected length corresponds to the length measured on the contour of the rubber stud, corresponding to the projections of the principal geometrical lines of the totality of surfaces of intersection of the connecting elements of said stud; if two principal geometrical lines have the same projection, then the projected length is equal to the length of that projection. By convention, the projected length is at most equal to the contour perimeter of the stud, and in this latter case, to each point of the said contour there corresponds at least one point of at least one principal geometrical line.
A tread configuration comprising incisions bounding rubber studs according to the invention has the advantage of having a long length of active rub
Auxerre Pascal
de Labareyre Bertrand Garnier
Lopez José Merino
Baker & Botts L.L.P.
Maki Steven D.
Michelin Recherche ET Technique S.A.
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