Resilient tires and wheels – Tires – resilient – Anti-skid devices
Reexamination Certificate
2001-04-30
2004-05-18
Maki, Steven D. (Department: 1733)
Resilient tires and wheels
Tires, resilient
Anti-skid devices
C152S209190, C152S209210, C152S209220, C152S209270, C152S902000, C152SDIG001
Reexamination Certificate
active
06736175
ABSTRACT:
The present invention relates to motor vehicle tyres, particularly for lorries and the like, intended for heavy-haulage.
The invention is particularly concerned with tyres intended for use on the live axle of trucks or articulated lorries on mid-length journeys, i.e. on routes which, as is well known, impose severer demands and generate more wear than long journeys, which generally take place on motorways.
DESCRIPTION OF THE RELATED ART
Tyres designed to be mounted on live axles usually have a tread of elastomeric material containing a relief pattern comprising circumferential grooves intersected by transverse grooves so as to form a plurality of blocks, hence the name “block” tyres, to distinguish them from “ribbed” tyres formed from continuous circumferential ribs having poorer grip properties.
In the remainder of the description and in the claims that follow, the expression “elastomeric material” is used to indicate the rubber compound in its entirety, that is the total mixture composed of one or more base polymers suitably amalgamated with reinforcing fillers and other product additives and process additives such as accelerators, retardants, anti-ageing agents, plasticizers, cross-linking agents and so forth.
Furthermore, the term “tread” is used to indicate the strip of elastomeric material provided with a sheet of a different compound laid on the radially innermost surface of the said strip to promote the adhesion of the tread when cold to the underlying elements of the carcass, in particular the belt layers.
Tyres for live axles have to satisfy multiple requirements: in particular they must provide good grip on both dry surfaces and wet and/or snow-covered surfaces.
In addition, both the market and many national legislations are increasingly demanding quiet-running tyres, whereas the use of “block” tyres generally produces more noise than “ribbed” tyres.
The tread must also wear evenly and offer high mileage.
On top of this, treads are required to have a pattern capable of efficiently expelling stones and small fragments that become trapped in the grooves of the tread, since if such stones or fragments were to remain in the tread they could perforate the tread as the tyre wears down and so damage the underlying belt structure.
The prior art already includes tyres capable of confronting these problems and offering a solution to them.
For example, Italian Patent 1,245,773 by the Applicant discloses a tread comprising at least four rows of blocks defined by at least three circumferential grooves of different widths, the axially innermost groove being wider and the two lateral grooves on either side of the equatorial plane of the tyre being narrower, and by a plurality of oblique transverse grooves connecting pairs of circumferentially adjacent grooves.
In this solution the narrow groove that separates the two lateral rows of blocks on each half of the tyre is characterized by the fact that its width is no greater than 2.5 mm and its depth not greater than that of the confluent transverse grooves while the blocks of the two lateral rows are circumferentially staggered relative to each other so that every block of each row is next to two consecutive blocks of the adjacent row.
This patent describes other solutions comprising, for example, two additional axially internal circumferential grooves defining a pair of circumferential ribs, in the walls of which there are oblique transverse grooves extending as far as the equatorial plane, so that the ribs have the appearance of two adjacent rows of blocks.
The blocks of all rows have an ordered configuration, the longitudinal sides of the blocks of any one row lying along two lines parallel to the equatorial plane.
In another solution the two rows of blocks of the two central ribs can be joined together to form a single row straddling the equatorial plane and in another solution the blocks of the central row may be of roughly hexagonal shapes.
Also known is a tyre comprising a “block”-type tread composed of four, that is two lateral and two central, circumferential grooves of equal width, and a plurality of transverse grooves that together define five rows of blocks, that is two axially external shoulder rows, two axially internal intermediate rows and a central row of blocks passing through the equatorial plane of the tyre.
The blocks of the central row and of the intermediate rows are all of identical “Z” shapes defined by two longitudinal sides and two transverse end sides, while the shoulder blocks are defined by two longitudinal sides and two transverse end sides, one at the front and one at the rear, both in the form of arrows and complementary to each other.
The longitudinal sides of the blocks of all rows are parallel with each other and inclined to the equatorial plane while the transverse end sides of the blocks of the central and intermediate rows are parallel with each other and slightly inclined to a plane perpendicular to the equatorial plane.
The blocks of the adjacent rows are also circumferentially offset relative to each other.
SUMMARY OF THE INVENTION
The Applicant was convinced that the performance of tyres of the prior art with “block”-type treads could be improved, particularly as regards protection against the penetration of stones towards the belt in the central zone of the tread, which is usually at greater risk, without this improvement triggering negative changes to other characteristics such as resistance to stone penetration in the lateral zones of the tread, grip, wear resistance and quiet running, but instead if possible introducing further improvements.
It was thought that it would be possible to achieve this result by employing a “block”-type tread comprising a widening of the central circumferential grooves disposed between the central row and the intermediate rows of blocks while nonetheless maintaining the width of the lateral circumferential grooves within the range of a predetermined value that would still be useful in protecting against the penetration by stones.
It was realized that the accomplishment of this task could depend on achieving a particular ratio between the widths of the circumferential, lateral and central grooves.
It was then felt that although the reduction in the width of the blocks of the intermediate rows, necessary to permit both widening of the central grooves and a predetermined width of the lateral grooves, would introduce a consequent poorer rigidity of the intermediate blocks, this effect could be compensated for by increasing the rigidity of the blocks of the central rows and by providing an elastic linkage between the blocks of the shoulder and intermediate rows.
The idea, in fact, was to liken the central, intermediate and shoulder rows of blocks to three parallel springs under load so that by giving the blocks of the central rows a more rigid shape than that of the other blocks it was possible to create in the central spring a greater elastic reaction which would protect the other rows of blocks.
It was also felt that it should be possible to reinforce the resistance to bending deformations of the intermediate and shoulder rows by means of a mutual elastic linkage so that these rows in combination could present an increased resistance to bending deformations.
In order to achieve satisfactorily quiet running the characteristics of inclining all the longitudinal sides of the blocks to the equatorial plane, and the circumferential staggering of the blocks of one row relative to the next, have been maintained.
In an initial aspect the invention therefore relates to a vehicle wheel tyre comprising a carcass structure that includes a central crown portion and two sidewalls terminating in two beads for fixing the tyre to a wheel rim; a belt structure coaxially fixed to the carcass structure; and a tread extending coaxially around the belt structure, its thickness being defined between the outer surface intended to contact the ground and the inner surface in contact with the said belt structure, having a tread pattern which comprises four, that is two lateral and two ce
Campana Luigi
Carra Alberto
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Maki Steven D.
Pirelli Pneumatici S.P.A.
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