Resilient tires and wheels – Tires – resilient – Pneumatic tire or inner tube
Reexamination Certificate
1998-12-22
2002-07-02
Johnstone, Adrienne C. (Department: 1733)
Resilient tires and wheels
Tires, resilient
Pneumatic tire or inner tube
C152S531000, C152S532000, C152S549000, C152S555000, C152S557000
Reexamination Certificate
active
06412533
ABSTRACT:
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 having a high weight.
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 road behavior both in straight stretch and in curve, stability of the vehicle at high speed, kilometric yield, wear uniformity and regularity, and low weight.
In order to satisfy this need, tires for two-wheeled vehicles have been manufactured for a long time with a carcass structure comprising a couple of plies made of rubberized fabric reinforced with cords symmetrically inclined with respect to the equatorial plane of the tire—usually known as cross-plies carcass—and possibly an intermediate structure (breaker), also realized with couples of strips made of rubberized fabric provided with cords arranged at an angle with respect to the equatorial plane of the tire. 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 to a removal of bulk portions of rubber, according to a phenomenon known in the art by the term of: “chunking”.
To try to prevent these drawbacks, it was then suggested to use a tire comprising a carcass structure of the so-called “radial” type, i.e. a tire provided with reinforcing cords essentially perpendicular to the equatorial plane of the tire, on which structure a belt structure comprising at least one couple of strips made of rubberized fabric provided with cords placed at an angle with respect to the equatorial plane of the tire or, alternatively, a cord winding, preferably made of metal, oriented in a circumferential direction and known in the art by the term of: zero-degree cords, is coaxially associated.
Even though the tires provided with a radial carcass have improved the situation in terms of comfort and vehicle straight-away stability at high speed with a substantial elimination of chunking phenomena—to such an extent that they are considered top range products by those skilled in the art—they are not suitable for use in the so-called “touring” motor-bikes having a high-weight and a high performance.
Actually, the motor-cycles of this type equipped with a tire having a radial carcass are particularly subject to an undesired “floatation” effect while running along a curve, also 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 instances, 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 road behavior, both in straight stretches and along curves, stability of the vehicle at high speeds, kilometric yield, wear regularity, 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 a radially outer layer comprising a plurality of zero-degree cords and a radially inner layer comprising at least one sheet made of an elastomeric material.
In other words, the Applicant has become aware of the fact that the aforesaid problem can be effectively solved by renouncing to use the radial carcass, i.e., the very structure that is unanimously considered by those skilled in the art as the “top” of the available technology, provided that the carcass equipped with reinforcing inclined cords is adequately separated from the belt layer comprising the zero-degree cords, by interposing a sheet made of an elastomeric material.
Hence, the present invention provides a tire comprising:
a) 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;
b) a belt structure coaxially extending around the carcass structure, including:
i) a radially inner layer comprising at least one sheet made of an elastomeric material;
ii) a radially outer layer including a plurality of circumferential coils, axially arranged side by side, of at least one inextensible cord, circumferentially wound at a substantially null angle with respect to the equatorial plane of the tire;
c) a tread, coaxially extending around the belt structure.
According to the invention, the Applicant has in particular and unexpectedly found that by interposing a sheet made of an elastomeric material between the carcass structure and the radially outer layer provided with zero-degree cords of the belt structure, it is possible to achieve at the same time both the desired features of road holding and curve stability imparted to the tire by the carcass structure, and the desired features of comfort, wear regularity and uniformity and stability of the vehicle at high speeds in straight stretches, imparted to the tire by the zero-degree cord layer of the belt structure.
More particularly, the Applicant has unexpectedly found that said sheet made of an elastomeric material allows the carcass structure and the zero-degree cords of the belt structure to exercise the aforesaid effects substantially independently from one another, preventing at the same time the zero-degree cords from damaging the reinforcing cords of the underlying carcass structure.
Thanks to the structural features of the carcass structure, the tire of the invention is able to develop high camber thrusts quite sufficient to balance the centrifugal thrust affecting the motor-bike, with a very homogeneous curve behavior.
According to the invention, it has also been found that camber and drift thrusts developed by the tire are increased by the combination of one or more carcass plies provided with reinforcing cords crown-forming a suitable angle with respect to the equatorial plane of the tire, with the radially outer layer incorporating the zero-degree cords of the belt.
Thanks to this feature, it was observed that a motor-bike equipped with a couple of tires having such a structure shows advantageous features of neutral driving, so that the driver can travel the curvilinear trajectory by simply inclining the vehicle and without correcting its trim, in particular the steering angle of the handlebar.
Besides, it was found that the cross-plies carcass lends the tire advantageous features of 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 tire ground-contacting area, i.e. the area of contact with the ground, in all of the operating conditions of the tire.
Thanks to this feature, both the stresses due to scraping on the road and the stresses due to hysteresis dissipation in the rubber composition of the tread are reduced, with a substantial reduction in tire overheating due to the centrifugal force which develops during running, counter-balanced by the substantial inextensibility of the radially outer layer provided with zero-degree cords of the belt structure.
The adopti
Armellin Giancarlo
Kronthaler Peter
Zoller Thomas
Finnegan Henderson Farabow Garrett & Dunner LLP
Johnstone Adrienne C.
Pirelli Pneumatici S.p.A.
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