Resilient tires and wheels – Tires – resilient – Pneumatic tire or inner tube
Reexamination Certificate
2000-03-30
2004-06-29
Aftergut, Jeff H. (Department: 1733)
Resilient tires and wheels
Tires, resilient
Pneumatic tire or inner tube
C152S531000, C152S533000, C152S209110, C152S209240, C152S903000
Reexamination Certificate
active
06755227
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a high-transverse-curvature tire, having a curvature ratio not lower than 0.3, 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 sidewalls extending substantially perpendicularly to said bottom.
In the following description and in the appended claims, the expression: “sidewalls substantially perpendicular to the groove bottom” is used to indicate walls that form—with respect to a plane perpendicular to the bottom—an angle varying from 0° to 40°.
More particularly, the invention relates to a front tire for two-wheeled motor-vehicles, wherein the high transverse curvature is defined by particular values of the ratio between the height of the tread crown from the line passing through the tread axial ends or “camber” of the tread band, said line being measured at the equatorial plane, on the one hand, and the distance between said tread band ends on the other hand. Said value, preferably not lower than 0.3, is anyhow higher than the value related to the corresponding rear tire, usually not lower than 0.15.
In the following description and in the appended claims, said ratio will be indicated by the term: “curvature ratio”.
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.
BACKGROUND DISCUSSION
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, amplifying the unevennesses transmitted by the road surface layer, with ensuing stability loss of the vehicle.
In particular, during the straightaway running such excessive stiffness causes, at low speeds, high frequency (8-10 Hz) oscillations on the front tire (shimmy effect), causing driving to be precarious.
To try to obviate these problems, it has recently been proposed in co-pending patent application Ser. No. 08/857,305, filed on May 16, 1996 by the same assignee, the use of a radial-ply tire provided with a belt structure comprising circumferentially-oriented cords, preferably metal cords, also indicated by the term: zero-degree cords.
This type of tire has unquestionably improved the situation in terms of comfort and driving stability: in fact, the oscillations of the vehicle at straightaway high speeds have disappeared and in particularly the shimmy effect has been substantially eliminated.
However, even if improvements as to the comfort and reduction of the driver's weariness have been achieved, the tires of the aforesaid type have not allowed, at least so far, neither to improve the wet grip of the vehicle nor to increase the wear resistance and, consequently, the kilometric yield of the tread band.
SUMMARY OF THE INVENTION
According to the present invention, the inventors have now realized that the problem of achieving such desired characteristics can be solved by combining a belt structure having zero-degree cords and a particular pattern of the tire tread, such as to provide a given ratio between the area occupied by the rubber blocks and the area occupied by the grooves (or solid/hollow area ratio).
Therefore, the present invention provides a tire of the type indicated hereinabove, which is characterized in that:
a) said belt structure comprises at least a radially external layer including a plurality of circumferential coils, axially arranged side by side, of a cord wound at a substantially zero angle with respect to the equatorial plane of the tire; and in that
b) the area occupied by said rubber blocks in a portion of tread band having a length equal to a pitch of the tread pattern and a width equal to the axial development of the tread band is between 70% and 90% of the total area of said portion.
According to the invention, the Applicant has found that by adopting a belt structure with zero-degree cords it is possible to obtain a higher degree of freedom in the design of the tread pattern, substantially overcoming the limit represented by the need of having a large solid area (i.e. a large area occupied by the rubber blocks) to ensure an adequate wear resistance of the tire.
According to the invention, in fact, it has surprisingly been found that by adopting a belt structure with zero-degree cords, it is possible to reduce the area of the rubber blocks, and therefore the solid/hollow area ratio, with respect to that of the tires of the prior art without affecting the wear resistance of the tire and achieving at the same time the following important advantages:
a) an improvement of tire capacity of draining off the water present under the tire ground-contacting area (aquaplaning);
b) an improvement of shimmy behavior of the tire in spite of the presence of a greater hollow area under the tire ground-contacting area;
c) maintenance of a high directional stability of the tire, whatever the use conditions, and especially while traveling over a curvilinear path;
d) an improvement of braking behavior of the vehicle with a reduction of the vehicle braking distance.
More particularly, according to the invention, such characteristics are achievable when, as indicated hereinabove, the area occupied by the rubber blocks formed in a portion of the tread band having a length equal to the pitch of the tread pattern and a width equal to the axial development of the tread band, is between 70% and 90% of the total area of said portion.
In the following description and in the appended claims, the term: axial development of the tread band, is used to indicate the extension in width of the latter as measured along the peripheral surface of the tire.
In the following description and in the appended claims, the term: pitch of the tread pattern, is used to indicate the length, measured along the circumferential development of the tread band, of a portion of the tread pattern which periodically repeats for a finite number “n” of times throughout the whole circumferential development of the tread band.
In the present case, therefore, the pitch of the tread pattern is equal to the distance between the starting points of two subsequent repetitive portions of the tread pattern, measured along the circumferential development of the tread band.
Preferably, the solid area is between 80% and 85%, and, still more preferably, it is equal to about 83% of the total area of said portion having a length equal to the pitch of the tread pattern and a width equal to the axial development of the tread band.
Advantageously, furthermore, the adoption of a belt structure with zero-degree cords in a radially external layer of the same allows to increase both the directional stability and the tire ground-contacting area, i.e. the area where the tire gets in touch with the ground, in any use cond
Armellin Giancarlo
Kronthaler Peter
Aftergut Jeff H.
Fischer Justin
Pirelli Coordinamento Pneumatici S.p.A.
Stevens Davis Miller & Mosher LLP
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