Resilient tires and wheels – Tires – resilient – Pneumatic tire or inner tube
Reexamination Certificate
1998-12-22
2002-06-04
Johnstone, Adrienne C. (Department: 1733)
Resilient tires and wheels
Tires, resilient
Pneumatic tire or inner tube
C152S527000, C152S531000, C152S532000, C152S533000, C152S549000, C156S117000
Reexamination Certificate
active
06397911
ABSTRACT:
DESCRIPTION
Background of the Invention
In its more general aspect, the present invention relates to a high transverse-curvature tire for two-wheeled vehicles.
More particularly, the invention relates to a tire preferably, though not exclusively, usable in the so-called high-performance “touring” motor-bikes, of the type comprising:
a carcass structure including at least one ply provided with reinforcing cords essentially parallel to one another and oriented along directions inclined with respect to the equatorial plane of the tire;
a belt structure coaxially extending around the carcass structure and including a radially inner layer comprising at least one strip made of an elastomeric material including a plurality of reinforcing cords essentially parallel to one another and oriented along directions inclined with respect to the equatorial plane of the tire;
a tread, coaxially extending around the belt structure.
KNOWN ART
In the field of production of tires for two-wheeled vehicles, and in particular, those intended for equipping the so-called “touring” motor-bikes generally having a swept volume exceeding 1000 cm
3
, a high weight and a high torque, the need is increasingly felt of providing ever higher performances in terms of stability of the vehicle at high speed, kilometric yield, wear uniformity and regularity, road behavior both in straight stretch and in curve, and low weight.
In order to fulfill this need, 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 equatorial plane of the tire—which carcass structure is also known as cross-plies carcass—and possibly an intermediate structure (breaker), also realized with couples of strips of rubberized fabric provided with cords arranged at an angle with respect to the tire equatorial plane.
Even though this tire structure could ensure an extremely regular curve behavior of the motor-bike, the use of this type of tires involved problems of comfort, stability of the vehicle at high speed, and especially of irregular wear of the tread, often associated with removal of bulk portions of rubber according to a phenomenon referred to in the art by the term: “chunking”.
To try to prevent these drawbacks, it has been suggested to use a tire having a radial carcass and provided with a belt structure comprising at least a couple of strips of rubberized fabric with cords arranged at an angle with respect to the equatorial plane of the tire or, alternatively, a coil of cords, preferably made of metal, oriented in a circumferential direction and known in the art by the term of: zero-degree cords.
Even though this type of tire has improved the situation as concerns comfort and stability of the vehicle at high speed along a straight-away with a substantial elimination of chunking phenomena—their low stiffness in the transverse direction markedly penalize their curve behavior.
Actually, the motor-bikes equipped with this type of tire are particularly subject to an undesired “floatation” effect while running along a curve, otherwise known by the term of “pudding effect”, which causes the motor-bike to undergo a swaying phenomenon that would not be easily damped and that, in some cases, may be even self-amplifying. In extreme conditions, this phenomenon may even lead drivers to lose control of the vehicle, with obviously deleterious consequences.
SUMMARY OF THE INVENTION
According to the present invention, the Applicant has now understood that the problem of achieving adequate performances in terms of vehicle stability at high speeds, kilometric yield, wear regularity and uniformity, road behavior, both in straight stretches and in curves, and low weight can be solved by combining a carcass structure having at least one ply provided with reinforcing cords inclined with respect to the equatorial plane of the tire, with a belt structure including, in combination, at least one strip made of an elastomeric material incorporating a plurality of reinforcing cords inclined with respect to the equatorial plane of the tire and a radially outer layer comprising a plurality of zero-degree cords wound on the strip according to a preferred winding direction.
In a first aspect, the present invention therefore provides a tire of th e aforementioned type, which is characterized in that the belt structure further comprises a radially outer layer including a plurality of circumferential coils, axially arranged side by side, of at least one circumferentially inextensible cord wound at a substantially null angle with respect to the equatorial plane of the tire according to a winding direction adapted to compression-stress elastomeric material portions interposed between consecutive reinforcing cords incorporated in said at least one strip of the radially inner layer.
More specifically, the Applicant has found that the best results are obtained when the winding direction of said circumferentially inextensible cord, at the starting end of the winding, forms with the reinforcing cords of the radially inner belt layer an acute angle, measured moving away from the equatorial plane of the tire, having a value not lower than 25°.
According to the invention, the Applicant has in particular found that such tire structure achieves at the same time both the desired properties of comfort, wear regularity and uniformity and stability of the vehicle at high speeds along a straight-away and the desired properties of road holding, curve stability and low weight.
Thanks to the structural features of the carcass structure, in fact, the tire of the invention can develop high camber thrusts quite sufficient to balance the centrifugal thrust affecting the motor-bike, with a very homogeneous curve behavior.
Thanks to this feature, it was observed that a motor-bike equipped with a couple of tires having such a structure affords neutral driving behavior, so that the driver can travel the curvilinear trajectory by simply inclining the vehicle and without correcting its trim, in particular without correcting the steering angle of the handlebar.
According to the invention, furthermore, it was also unexpectedly found that, thanks to the structural features of the belt structure, the tire of the invention achieves on the one hand curvature thrusts and drift adequate to the requirements, provided by the combination of carcass plies with a suitable crown angle with the radially inner belt layer incorporating inclined cords and the outer belt layer incorporating the zero-degree cords, and on the other hand a uniform and regular wear provided by the radially outer belt layer comprising zero-degree cords wound on the radially inner layer according to a preferred winding direction.
Advantageously, the cross-plies carcass lends the tire transverse strength and curve stability, while the aforesaid belt structure lends the tire dimensional stability, directional stability and lower energy absorption, achieving at the same time a low rolling resistance and a substantial disappearance of the chunking phenomenon.
In particular, it was observed that the presence in the belt structure of a radially outer layer provided with zero-degree cords allows to increase both the directional stability and the ground-contacting area of the tire, i.e. the area of contact with the ground, in all the operating conditions of the tire.
Thanks to this feature, both the stresses due to scraping on the ground and the stresses due to hysteresis dissipation in the rubber composition of the tread are reduced, with a substantial reduction of the tire overheating due to the centrifugal force which develops during the running, counter-balanced by the substantial inextensibility of the radially outer layer provided with zero-degree cords of the belt structure.
Furthermore, the adoption of such a combination of carcass and belt structures contributes to reduce the tire weight, with all of the ensuing advantages in terms of reduction of the inertia effects due to the nonsuspen
Armellin Giancarlo
Kronthaler Peter
Zoller Thomas
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Johnstone Adrienne C.
Pirelli Pneumatici S.p.A.
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