Resilient tires and wheels – Tires – resilient – Anti-skid devices
Reexamination Certificate
1999-07-13
2002-07-09
Maki, Steven D. (Department: 1733)
Resilient tires and wheels
Tires, resilient
Anti-skid devices
C152S209180, C152S209210, C152S209220, C152S209270, C152S209280, C152SDIG003
Reexamination Certificate
active
06415834
ABSTRACT:
DESCRIPTION
In its more general aspect, this invention relates to a tire for vehicles comprising:
a carcass structure including a central crown portion and two sidewalls ending into 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, comprising a plurality of blocks, located on opposite parts of an equatorial plane of the tire between a longitudinal groove formed astride said equatorial plane and a couple of longitudinal grooves, said blocks being circumferentially spaced by a plurality of first slits extending in a direction substantially perpendicular to the rolling direction of the tire.
More particularly, the invention refers to a tire which is preferably, however not exclusively, used on driving wheels of heavy vehicles adapted to cover long travels in motorways.
In the following description and in the appended claims, the term: “block” is used to indicate a tread portion comprised between consecutive grooves or slits either in the axial or in the circumferential direction.
In the following description and in the appended claims, the terms: “grooves” and “slits” are used to indicate channels formed in the tire tread and having a width greater than and, respectively, equal to or smaller than 1 mm.
In the following description and in the appended claims, furthermore, the terms: “longitudinal” and “longitudinally”, are used to indicate quantities measured along the circumferential development of the tire.
Lastly, in the following description and in the appended claims, the terms: “axial” and “axially” are intended to indicate quantities measured along the peripheral surface of the tire in a direction perpendicular to the equatorial plane of the same.
As is known, in the field of tire production, intended or not for use on heavy vehicles, the need has always been felt of reducing as much as possible the rolling resistance of the tire.
It is also known that the difficulty of fully satisfying the above need is essentially related to the difficulty of reducing the tire rolling resistance without substantially affecting its performances in terms of kilometric yield, good traction capacity, stability on wet or snow grounds, and good lateral stability.
Until now all the attempts made in the art aiming at reducing the rolling resistance of the tire have brought about a more or less marked worsening of one or more of the above-identified features.
So, for instance, it was recently proposed to form in the blocks located in an equatorial zone of the tread a plurality of slits extending in a direction substantially perpendicular to the rolling direction of the tire.
In such case, however, the desired reduction in rolling resistance was obtained at the expense of the traction characteristics of the tire, which have undergone a corresponding worsening.
Therefore, the technical problem underlying the present invention is to provide a tire having structural and functional features which allow to reduce the tire rolling resistance while keeping the tire performances at a very satisfactory level in terms of kilometric yield, good traction and stability on wet or snow grounds, and good performances of lateral stability.
According to a first aspect of the invention, this problem is solved by a tire of the type indicated above, which is characterised in that the tread further comprises a plurality of transversal grooves, pitchwise spaced from one another and extending parallel to said first slits, said grooves being provided with respective second slits extending from a bottom portion thereof.
According to a second aspect of the invention, this problem is solved by a tread for vehicle tires, in particular a pre-moulded tread for cold-covering worn tires, comprising a plurality of blocks located in opposite sides of the equatorial plane of a tire between a longitudinal groove formed astride said equatorial plane and a couple of longitudinal grooves, said blocks being axially crossed by a plurality of first slits extending in a direction substantially perpendicular to the rolling direction of the tire, which is characterised in that it further comprises a plurality of transversal grooves, pitchwise spaced from one another and extending parallel to said first slits, said grooves being provided with respective second slits extending from a bottom portion thereof.
According to the invention, the Applicant has found in particular that by forming, in an equatorial zone of the tread, transversal grooves provided with slits downwardly extending therefrom, it is advantageously possible to achieve both adequate traction characteristics and the desired lower rolling resistance, essentially associated to the overall lower mobility of the tread blocks under the tire ground-contacting area due to the mutual contact of adjoining blocks caused by a closure of the slits.
In the following description and in the appended claims, the blocks located in the equatorial zone of the tread will be indicated for the sake of simplicity by the term: “equatorial blocks”.
Preferably, the equatorial zone of the tread concerned by the transversal grooves provided with slits in their lower part extends astride the equatorial plane of the tire and up to the middle of the longitudinal grooves for a length comprised between 40% and 70% of the axial development of the tire tread.
Still more preferably, such equatorial zone extends astride the equatorial plane of the tire for a length comprised between 50% and 60% of the axial development of the tread.
Thanks to the presence of the slits, the tread portions in which the equatorial blocks are formed, are so-to-say embedded into one another under the ground-contacting area of the tire, because of the strains which the tread undergoes during tire rolling.
The ensuing stiffness increase reduces the energy dissipation phenomena due both to the mobility of the blocks and to the physical-mechanical characteristics of the rubber composition of the tread, with a reduction of rolling resistance during running.
A further and important advantageous effect attained by the particular structure of the transversal grooves is represented by the achievement of a better wear regularity, which is also associated to some extent to the stiffness increase of the tread equatorial blocks.
Preferably, the tread is circumferentially provided with a couple of longitudinal slits extending in opposite parts of the equatorial plane of the tire, which slits axially separate the equatorial blocks and split the transversal grooves formed therein into two portions proximal and, respectively, distal with respect to the equatorial plane of the tire. A depth of the longitudinal slits is substantially equal to a sum of depths of the transversal grooves and the second slits, and a depth of the first slits is substantially equal to a sum of the depths of the transversal grooves and the second slits.
Advantageously, the longitudinal slits contribute both to increase the tire road holding in the axial direction, whenever the same is stressed in a transversal direction with respect to the rolling direction, and to prevent the triggering of phenomena of irregular wear of the blocks.
Preferably, the longitudinal slits extend along substantially the whole circumferential development of the tire according to an essentially zigzag path, which advantageously enhances the embedding between axially adjoining blocks, with a further reduction in energy dissipation phenomena due to block mobility in the longitudinal direction.
In the tire of the invention, the transversal grooves preferably have a reduced depth compared to the tires of the known art, and such as not to exceed 18 mm together with the slits downwardly extending from their bottom.
Such a reduced depth of the grooves allows to achieve several important advantages.
Firstly, it allows to effectively contribute to reduce the rolling resistance of the tire, thanks to the reduction in the volume of the rubber composition required to form the tread and, along t
Campana Luigi
Carra Alberto
Finnegan Henderson Farabow Garrett & Dunner LLP
Maki Steven D.
Pirelli Pneumatici S.p.A.
LandOfFree
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