Resilient tires and wheels – Tires – resilient – Anti-skid devices
Reexamination Certificate
2001-05-18
2004-08-17
Maki, Steven D. (Department: 1733)
Resilient tires and wheels
Tires, resilient
Anti-skid devices
C152S209170, C152S209280
Reexamination Certificate
active
06776204
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
According to a general aspect thereof, the present invention relates to a tyre for vehicles, and in particular to its tread pattern.
2. Description of the Related Art
As is known, a tyre in its most general form comprises a torus-shaped carcass with a central crown and two side walls terminating in a pair of beads for fixing the tyre onto a corresponding mounting rim, a tread band coaxially extending around the crown and a belt structure arranged between the carcass and the tread band.
On its external surface the tread band comprises a raised pattern which, together with the physico-chemical properties of the compound from which it is made, is especially suitable for providing the road-handling properties of the tyre, in particular the tractional power.
Generally the tread pattern is formed by several circumferentially and/or transversely directed grooves which result in voids and solid areas of rubber of different shapes and sizes which are usually called “blocks”.
As is known, in the sector of tyre production, a long-standing requirement has been that of ensuring an adequate performance of the tyre, despite the extremely high stresses to which it is subject during use, in particular when it is of the racing type.
Therefore the Applicants have considered the problem of obtaining a tread which is able to optimize the driving performance and grip.
U.S. Pat. No. 4,641,696 describes a tread of the directional type which is suitable for high-power vehicles and for extreme conditions of use. The tread pattern consists of a plurality of blocks which have a substantially rhomboidal shape and are arranged in at least six circumferential rows each other separated by straight circumferential grooves and by slanting transverse grooves.
The Applicants consider that the difficulty of fully satisfying the abovementioned requirement with the type of tread described is essentially related to the difficulty of limiting the mobility of the blocks present on the tread band as the blocks warm up during use.
Hitherto the attempts made in the art to ensure the desired high performance levels of the tyre, based on the design of tread bands provided with grooves having different inclinations and blocks of different shapes, have been unable to achieve fully satisfactory results.
During rolling of the tyre, in fact, the blocks present on the tread band are subjected to a whole series of thermo-mechanical stresses—mainly due to the heating of the compound as a result of friction and to the compressive and shearing forces—which tend to cause flexing and deformation of the blocks. These stresses modify the geometry of the blocks and cause a decline in the performance of the tyre, in particular during the so-called “extreme” driving conditions.
Another problem arises from the presence of straight circumferential grooves on the tread pattern since said latter grooves represent concentrated zones which are subject to deformation under high transverse loads that give rise to a “circumferential hinge” effect. Therefore said grooves modify the tyre footprint when drifting and therefore the grip.
The Applicants have considered in particular the problem of finding a tread pattern which is suitable both for dry and wet grounds.
A tread band, or a portion thereof, is characterized by the value of the “solid/void” ratio which depends on the quantity of rubber which is removed from the tread band owing to the presence of the grooves.
High values of the “solid/void” ratio result in good tractional properties on dry ground, but low road-holding values on wet ground.
Numerous examples of tread patterns which have been especially designed to achieve optimum performance of the tyre on dry and wet ground are already known.
For example, U.S. Pat. No. 4,700,762 describes a tyre provided with a tread pattern formed by a large-width circumferential groove which is located along the equatorial plane and by a plurality of grooves which are extended substantially in the transverse direction on either side of the central groove up to the shoulders of the tyre.
Each transverse groove forms an angle of 45° at the point where it meets with the central groove and then gradually curves until it assumes an orientation substantially perpendicular to the equatorial plane in the end zone of the tread on the shoulder of the tyre.
Therefore, the central groove and the plurality of transverse grooves produce on the sides of the equatorial plane two series of blocks each one extending from the centre to the shoulders of the tyre.
In a further embodiment, the tread pattern has a plurality of circumferential grooves which are parallel to the central groove and which intersect the transverse grooves.
Said further embodiment results in a plurality of circumferential adjacent rows of rhomboidal blocks on each side of the equatorial plane.
The tread pattern is designed so that three to five transverse grooves are present underneath the tyre footprint, each of said grooves being sized in order not to close when the tread comes into contact with the ground; therefore, as a result of said geometric features, the water which is accumulated in the centre of the tyre footprint is conveyed through the transverse grooves towards the shoulders of the tyre and here discharged ensuring driving stability and tractional properties even on wet surfaces.
A tyre marketed by the Applicants under the name “P ZERO C” and comprising a tread pattern formed by two distinct parts which are each other circumferentially located alongside, i.e. an external part and an internal part with respect to the mounting position of the tyre on the vehicle, is known too.
The external part of the tread comprises, from the central zone towards the corresponding end, a continuous longitudinal rib which is defined between two circumferential grooves and comprises on both sides substantially axial incisions partially extending in the direction of the width of the rib. In an axially external position, the abovementioned rib has, arranged alongside it, another shoulder-type rib which is substantially smooth, except for an ordered series of small blind incisions extending circumferentially in succession on the internal side.
Said first part of the pattern has a very high solid/void ratio so as to ensure good tractional properties on dry ground.
The second part of the tread, i.e. the internal part, comprises, from the centre towards the corresponding end, a longitudinal rib defined between two central grooves and cut by transverse grooves which are directed substantially in the form of a herring-bone pattern and, in a more axially external position, it comprises a row of substantially rhomboidal shoulder blocks.
Said second part of the pattern has a solid/void ratio which is lower than that of the first part so as to provide good tractional properties also on wet ground.
It should also be pointed out that in the market there is a great demand for tyres with optimum performance features both on dry and on wet ground in order to satisfy a certain category of clients who own powerful cars in particular for use on racing tracks or in any case for racing purposes.
SUMMARY OF THE INVENTION
The Applicants, in the light of the state of the art described above, have set themselves the task of realizing a tread provided with a pattern which is suitable both for dry and wet grounds and having features in order to ensure driving stability not only to cars intended for ordinary use but also to powerful cars used for racing purposes and the like.
The Applicants have thought to specialize the tread pattern by using a system of grooves intended for a specific purpose (in place of the known multi-purpose grooves), some of which are specifically suitable for providing an optimum performance on wet ground, while others, different from the first ones, are suitable for ensuring an optimum performance on dry ground. The Applicants have realized that it was possible to solve the problem by using any combination of grooves on condition that they were distributed i
Cerizza Ernesto
Cesarini Riccardo
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Maki Steven D.
Pirelli Pneumatici S.p.A.
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