Resilient tires and wheels – Tires – resilient – With wear indicating feature
Reexamination Certificate
1997-10-16
2001-10-23
Johnstone, Adrienne C. (Department: 1733)
Resilient tires and wheels
Tires, resilient
With wear indicating feature
C152S209100, C152S209500, C152S209800, C152S209180, C152S209190, C152S209260, C152S454000, C152S526000, C152S527000, C152S531000, C152S538000, C264S326000
Reexamination Certificate
active
06305450
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a high-performance tire, which mitigates the aqua planing effect and increases wear-resistance, as well as to the manufacturing method and mold thereof.
More particularly, the tire of the invention is of the type comprising a tread band provided with at least one large-sized, extended circumferential cavity, preferably but not exclusively disposed at a central position, for quickly ejecting water collected on the ground so as to counteract the effect currently referred to as “aquaplaning”. Aquaplaning occurs when a vehicle loses ground contact, particularly at high speed, due to the continuous water film interposed between the tire and the ground.
Tires of the above type, in which the tread substantially comprises two distinct axial portions separated from each other by a wide circumferentially-extended cavity, are well-known and have been described in several patents briefly mentioned hereinafter.
2. Description of the Related Art
For instance, patent EP 0 503 404 discloses a tread comprising circumferential and transverse S-shaped grooves, crossed with each other so as to form a plurality of blocks, and provided with a central cavity of a width corresponding to 10%-20% of the tread width and a depth corresponding to 78%-80% of the overall tread thickness.
Patent EP 0 503 405, in addition to the above, gives particular values for the angle of inclination of the entrance and exit walls of the blocks relative to the ground-contacting area. Patent EP 0 503 406 also illustrates particular connecting arcs of the side walls of the different tread band blocks.
Other details concerning the geometrical and operating features of the grooves and blocks in the tread pattern are described in U.S. Pat. Nos. 5,176,766; 4,700,762; and 4,785,863.
U.S. Pat. No. 4,796,683 refers to a tread pattern comprising a circumferentially-directed cavity and transverse grooves of great inclination to the cavity so as to promote water draining. In this tread pattern blocks are formed that have acute and obtuse angles. Close to the acute angles where stiffness is lower, the greatest abrasion can be found. Elimination of this drawback is suggested by forming particular chamfers in the blocks so as to increase the block stiffness at aimed areas. U.S. Pat. No. 4,289,182 refers to a motorcycle tire adapted for high speed and provided with a tread pattern having a circumferentially-directed cavity and two sets of rectilinear transverse grooves at each side of the cavity. Between the grooves of the two sets, a zigzag rib is formed.
The Applicant has noticed that the known tires of the above type generally exhibit a marked wear of the tread band at the central area thereof, close to the cavity along the equatorial plane, which takes place early and continues over time. The remaining tread portions outside of the central area exhibit slower wear, and therefore, the overall lifetime of the tire is reduced as compared to possible lifetime of an evenly wearing tire.
It is a current hypothesis that this type of wear depends on a greater flexibility and deformability of the carcass by effect of the wide central cavity in the tread pattern.
U.S. Pat. No. 4,687,037, directed to a tire comprising a carcass, a belt and a tread band having a circumferential cavity in the middle, the width of which corresponds to 20% of the tread width, attempts to find a solution to this problem by imparting a particular rigidity to the belt. Actually the belt comprises a plurality of reinforcing layers having cords crossed with each other following known techniques, partly substantially extended over the whole width of the tread band, and partly axially concentrated on given preferential areas.
In particular, the belt structure has four layers of mutually crossed cords of a width corresponding to the tread band width and two further reinforcing layers of a width as large as or slightly larger than the width of the central cavity. These further layers of reduced width are disposed below the cavity, the first layer between the two pairs of layers of a width as large as that of the tread band and the second layer immediately under the cavity, respectively.
Radially projecting outwardly from the cavity bottom, in such a manner as to nearly constitute a link between the two distinct tread band portions, there is a rib of elastomeric material extending over the whole cavity length.
SUMMARY OF THE INVENTION
The Applicant believes that the known solutions are not capable of providing an adequate solution to the problem because each is based on an incorrect perception. In particular, in accordance with the invention, it has been understood that said early and localized wear depended on the anomalous expansion of the belt at the central cavity, where this expansion was made possible by the reduced structural strength of the tread due to a lack of material at this area.
This expansion was not sufficiently inhibited by the addition of new belt layers because all layers are fairly expandible in a circumferential direction due to a rotation of the reinforcing cords in the lying plane of the cords themselves and due to the typical elasticity of the rubberizing material forming the layers.
In accordance with the present invention, the Applicant proposes to solve the problem by trying to achieve reinforcing-belt stability in the area of thinner tread below the cavity and exerting a control on the anomalous belt expansion. The resulting tire has a better performing tread band in terms of wear, and therefore the tire has a longer lifetime.
Accordingly, a first aspect the invention relates to a tire for motor-vehicle wheels comprising a toroidal carcass provided with axially opposite sidewalls and beads for anchoring the tire to a corresponding mounting rim, a tread band disposed crown-wise to said carcass and a belt structure interposed between said carcass and said tread band, axially extended in a continuous manner between the sidewalls, said tread band being molded with a raised pattern having at least one circumferential groove, characterized in that, in a non-operating condition, that is in the absence of load and inflating pressure, said belt structure, seen in right section in the plane containing the tire axis, has an axial profile comprising three distinct portions, two side portions and one central portion respectively, said central portion being interposed between said side portions, said side portions being concave at a radially internal position, in which the concavity is defined for each portion by a respective center and a respective radius of curvature, said central portion being concave at a radially external position, the concavity center of the central portion lying in the center line plane of the circumferential groove, in which the depth, S, of the outer concavity is capable of being canceled under the effect of the normal inflating pressure of the tire.
In a convenient embodiment of the invention, the center line plane of said groove is coincident with the equatorial plane of the tire.
Preferably in this case the depth S of said concavity is defined by the relation:
S=R
1
−R
0
wherein:
R
1
corresponds to the radius of a known tire as measured at the equatorial plane when the tire is mounted to the respective rim and inflated to the normal running pressure. This tire is identical in its structure and size to the tire of the present invention except for the fact that its belt structure under any condition and seen in right section exhibits a continuously concave profile in a radially internal position;
R
0
corresponds to the radius of the same known tire, still measured at the equatorial plane, under non-working conditions.
Therefore, the depth S of the concavity of the central portion is precisely the depth required to negate the expanding effect at the equatorial plane exhibited by known tires. Upon inflation of the tire of the present invention, the concavity of the central portion of Applicant's tire having a depth S is reversed
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Johnstone Adrienne C.
Pirelli Coordinamento Pneumatici S.p.A.
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