Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
2000-03-24
2003-12-02
Maki, Steven D. (Department: 1733)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C152S209180, C152S209260, C152S209270, C152S209280, C152S904000, C152SDIG003
Reexamination Certificate
active
06656300
ABSTRACT:
BACKGROUND OF THE INVENTION
In its more general aspect, the present invention relates to a tire for vehicles.
More particularly, the invention relates to a very high performance tire for vehicles having a curvature ratio not greater than 0.1, the tire being preferably, however not exclusively, used in motor-vehicles capable of providing a high torque and reaching high speeds both in straight and curve.
The known tires of this type comprise:
a carcass structure including a central crown portion and two sidewalls ending in a couple of beads for anchoring to a rim of a wheel;
a belt structure, coaxially associated to the carcass structure;
a tread, coaxially extending around the belt structure, on the tread being defined:
i) an equatorial zone extending on either side of the equatorial plane of the tire, and
ii) two shoulder zones in axially opposite positions with respect to said equatorial zone;
said tread comprising a plurality of transversal grooves including a first shoulder portion and a second equatorial portion.
Definitions
In the following description and in the appended claims, the terms:
“groove” and “slit” are intended to indicate grooves formed on the tire tread having a width greater than and, respectively, equal to or lower than 2 mm;
“longitudinal” and “longitudinally” are intended to indicate entities measured along the circumferential development of the tire;
“axial” and “axially” are intended to indicate entities measured along the peripheral surface of the tire in a direction perpendicular with respect to the equatorial plane of the same.
Finally, in the following description and in the appended claims, the various geometrical entities will be measured with reference to the median axis of the elements present on the tread.
PRIOR ART
As is known, in the production of tires and in particular of tires of the so called very high performance type to be mounted on high-powered sports-cars, the need has always been felt of ensuring an adequate performance of the tire, in spite of the extreme stresses it has to withstand in use, particularly when the same is a sports use.
The Applicant believes that the difficulty of fully satisfying the above requirement is essentially related to the difficulty of limiting the mobility of the blocks (meaning by this term the tread portions delimited between consecutive grooves, both along the axial and along the circumferential direction) present on the tread as the blocks warm up during use.
Up to now the attempts made in the art for ensuring the desired high performance levels of the tire and based on the design of treads provided with variously inclined grooves and variously shaped blocks have not allowed to achieve entirely satisfactory results.
In fact, during the tire rolling, the blocks present on the tread are submitted to a full range of thermal-mechanical stresses, mainly due to the warming of the rubber composition caused by friction and to the compression and shear stresses which tend to bend and deform the blocks, modifying their geometry and causing a degradation of tire performances, in particular during the so-called “boundary” driving.
Besides, in the tires of the known art, a performance degradation of the same after a certain wear of the tread takes place almost always, since the thermal-mechanical stresses imparted to the blocks increasingly modify the geometry thereof which, in its turn, causes an increasingly marked deviation from the desired road behavior.
Tires having no longitudinal grooves are known in the field of motor-cycle tires, for instance as described in copending European patent applications Nos. 97 202 112.5 and 97 202 113.3, i.e. tires showing a high transverse curvature with respect to the corresponding motor-vehicle tires.
As is known, in a tire the transverse curvature is defined by the value of the ratio between the distance of the tread crown from the line passing through the tread end points as measured on the equatorial plane, also known as “camber” of the tread, and the distance between said end points of the tread. In motor-cycles tires, such ratio, indicated in the following as “curvature ratio” usually has a value not lower than 0.15. The curvature ratio of a conventional tire for motor-vehicles has a value equal to about 0.05 and in any case it is never higher than 0.1.
However, in a motor-cycle tire, the limited width of the tread and the particular curvature ratio define a ground-contacting area which is remarkably narrower than a corresponding tire for motor-vehicle. This means that the problems of wet ground grip and aquaplaning, directly related to the size of the ground-contacting area of the tread on the ground, affect the tires in a different way and are therefore solved in a different way according to the type of tire concerned.
In particular, the Applicant has sensed that a tread pattern for motor-cycles, optimized to solve the specific problems of this type of tire (for instance, the excessive wear of the equatorial zone of the tread), but not other much less felt problems (for instance, water draining off), can be adopted as a reference to realize a tread pattern for motor-vehicles.
In fact, the Applicant has understood that the realization of a tire with a tread pattern having no longitudinal grooves might be very advantageous, and in contrast to the constant teaching of the prior art, it has surprisingly found that, by suitably modifying a tread pattern which was considered to be fit for use only in motor-cycles, it was possible to satisfy the different more specific requirements of a tire for motor-vehicles, such as for instance the grip on wet ground and aquaplaning.
SUMMARY OF THE INVENTION
The technical problem underlying the present invention is that of providing a tire having structural and functional features adapted not only to ensure an adequate performance of the tire, but also to maintain substantially constant—independently of the wear conditions of the tread—the performances of the tire in general and, in particular, grip on dry and wet ground, tractivity, side stability and noisiness.
According to a first aspect of the invention, this problem is solved by a tire of the aforementioned type, which is characterized in that said transversal grooves are circumferentially distributed along the tread in groups alternately extending from said shoulder zones of the tread, said groups of grooves defining in the equatorial zone of the tread a plurality of substantially continuous portions of the tread ending at the equatorial portion of a same transversal groove of the axially opposed group of grooves.
According to a second aspect of the invention, this problem is solved by a tread for vehicle tires, in particular a premolded tread for covering worn tires, comprising a plurality of transversal grooves including a first shoulder portion and a second equatorial portion formed in an equatorial zone of the tread extending on either side of the equatorial plane of the tire and along at least one of two adjoining shoulder zones defined in axially opposed parts with respect to said equatorial zone, which tread is characterized in that said transversal grooves are circumferentially distributed in groups alternately extending from said shoulder zone of the tread, said groups of grooves defining in the equatorial zone of the tread a plurality of substantially continuous portions of the tread terminating at the equatorial portion of a same transversal groove of the axially opposed group of grooves.
In the following description and in the appended claims, the term: “substantially continuous tread portion” is intended to indicate a portion of the tread which is not interrupted by grooves even though it is crossed by slits however oriented.
According to the invention, the Applicant has found in particular that the aforesaid groups of substantially continuous tread portions alternately extending from opposite shoulder zones towards the equatorial plane of the tire, form a sort of “grid” or “matrix” of elastomeric material portions fitted in with one another and substantially devoid
Cesarini Riccardo
Colombo Gianfranco
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Maki Steven D.
Pirelli Pneumatici S.p.A.
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