Resilient tires and wheels – Tires – resilient – Anti-skid devices
Reexamination Certificate
1997-07-23
2001-11-06
Johnstone, Adrienne C. (Department: 1733)
Resilient tires and wheels
Tires, resilient
Anti-skid devices
C152S209180, C152S209240, C152S454000, C152S458000, C152S526000, C152S527000, C152S531000, C152S533000, C152S536000, C152S540000, C152S903000
Reexamination Certificate
active
06311747
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a high-transverse-curvature tire, in particular for use in motor-vehicles, comprising:
a carcass structure of toric form having a high transverse curvature and provided with a central crown portion and two sidewalls ending in a couple of beads for anchoring onto a corresponding mounting rim;
a belt structure, circumferentially inextensible, coaxially extended around the carcass structure;
a tread band coaxially extended around the belt carcass and comprising a plurality of rubber blocks defined between a plurality of grooves extending along a direction substantially transverse to the running direction of the tire, the tread band being, free from any groove extending along a direction substantially parallel to the running direction of the tire, said grooves comprising a bottom connected to opposite inlet and outlet lateral walls, extending substantially perpendicularly to said bottom.
In the following description and in the appended claims, the expression: “lateral walls substantially perpendicular to the groove bottom”, is intended to indicate walls so shaped as to form—with respect to a plane perpendicular to the bottom—an angle varying from 0° to 40°.
More particularly, the invention relates to a rear tire for two-wheeled motor-vehicles, wherein the transverse curvature value—as defined by the ratio between the height of the tread crown from a line passing through the tread axial ends, said line being measured at the equatorial plane or “camber” of the tread band, on the one hand, and the distance between said tread ends on the other hand is not lower than 0.15.
In the following description and in the appended claims, said ratio will be indicated by the term: “curvature ratio”.
BACKGROUND OF THE INVENTION
As is known, tires for two-wheeled vehicles have been manufactured for a long time with a carcass structure comprising a couple of plies of rubberized fabric reinforced with cords symmetrically inclined with respect to the tire equatorial plane, which structure is usually known as cross-plies carcass, and possibly a belt structure also comprising couples of strips of rubberized fabric provided with cords inclined with respect to the tire equatorial plane.
While such tire structure could ensure an extremely regular curve holding of the motor-vehicle, the use of this type of tires involved problems of comfort, stability, road holding of the vehicle and weariness of the driver, due to their excessive stiffness.
The structure of these tires , in fact, accumulated—under the effect of an imposed deformation—elastic energy which was given back almost instantaneously upon termination of the stress, amplifing the unevennesses transmitted by the road surface layer, with ensuing stability loss of the vehicle.
To try to obviate these problems, the use of radial carcass tires with a belt structure of textile or metal cords has been recently introduced: in particular, the rear tire is provided with a belt structure comprising, sometimes exclusively, a winding of circumferentially-oriented cords, preferably metal cords, also indicated by the term: zero-degree cords.
This belt structure of the tires has unquestionably improved the situation in terms of comfort and driving stability: since the rear tire has a remarkable dampening effect, in fact, the vehicle oscillations at straightaway high speeds have in practice disappeared.
However, regardless of which belt structure type is adopted for the tires, no adequate solution has been found so far in connection with the problem of an extremely irregular and dishomogeneous wear of the edges of the grooves defining the rubber blocks formed in the tire tread, often associated with removal of bulk portions of rubber referred to in the art by the term: “chunking”.
The causes of such phenomenon, particularly marked in case of tires to be mounted on the rear wheel of a motor-vehicle, are in general ascribed both to the rubbing effect of the groove edges with the road, and to the excessive mobility of the rubber blocks positioned upstream of the inlet edges of the grooves towards the rolling direction of the tire.
In this regard, it has been found that such excessive mobility causes a local overheating of the rubber composition of the tire tread, due to a high energy dissipation by hysteresis, which overheating causes in its turn a degradation of the rubber composition, facilitating the aforesaid chunking phenomenon.
SUMMARY OF THE INVENTION
In the light of the lack in the art of any suggestion for remedying to such phenomenon, the Applicant has now realized that the problem now identified can be overcome by a tread band having:
a relatively low mobility of the rubber blocks positioned upstream of the grooves located in the central part or equatorial zone of the tire, stressed during the prevailing running of the vehicle (straight road), and
a relatively higher mobility of the rubber blocks located in opposite side portions of the tire tread, so as to ensure while travelling over a curvilinear path the energy dissipation by hysteresis necessary to obtain an adequate grip between tire and road.
Therefore, the invention provides a tire for two-wheeled vehicles of the type mentioned hereinabove, which is characterized in that in an equatorial zone of the tread band the inlet wall of said grooves is inclined with respect to said bottom towards the rolling direction of the tire and forms with respect to a plane tangent to said bottom an angle (&agr;) of from 50° to 80°.
In the following description and in the appended claims, the terms: “inlet” and “outlet” are intended to indicate—with reference to the structural characteristics of the grooves—those parts of the grooves which are stressed first or get in touch first with the ground during the tire rolling and, respectively, those parts of the grooves which are stressed after a predetermined angular rotation of the wheel.
In the same way, in the following description and in the appended claims, the terms: “upwards” and “downwards” are intended to indicate—with reference to the position of the grooves—parts of the tread band, for instance the rubber blocks, that are stressed or get in touch with the ground during the tire rolling before and, respectively, after said grooves.
In the following description and in the appended claims, furthermore, all the angular values measured starting from a plane (&pgr;) tangent to the groove bottom will be measured in counterclockwise direction.
According to the invention, when the value of angle a formed by the inlet wall of the grooves is within the range of values mentioned hereinabove, it has been noticed a rigidity increase of the rubber blocks positioned upwards of the grooves in the very zone of the tread band subject to greater stresses during the straightaway running—the equatorial zone—with a substantial disappearance of the aforementioned chunking phenomenon.
Advantageously, it has also been found:
a) an increased wear resistance of the tire tread, with the ensuing advantageous possibility of reducing the tire weight, and consequently of reducing both the disturbing effects on vehicle stability caused by impacts or ground roughness and the braking distance because of the lower inertia of the tire;
b) a greater wear uniformity of the tire tread, with an ensuing advantageous road holding increase of the same;
c) a lower rolling resistance of the tire, with an ensuing wear reduction.
Preferably, angle (&agr;) has a value of from 60° to 70° and still more preferably, it is equal to about 65°: in fact, an optimum rigidity of the rubber blocks positioned upstream of the grooves has been found within such range of values, while under 60° the tire has shown an undesired progressive loss of traction capacity, a wear increase and a rolling unevenness.
Preferably, the equatorial zone of the tread band interested by the desired inclination of the inlet walls of the grooves extends on either side of the equatorial plane of the tire for a portion having a width of from 10% to 35% of the axial development of said tread ba
Armellin Giancarlo
Kronthaler Peter
Johnstone Adrienne C.
Pirelli Coordinamento Pneumatici SpA
Stevens Davis Miller & Mosher LLP
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