Resilient tires and wheels – Tires – resilient – Anti-skid devices
Reexamination Certificate
1999-04-15
2001-06-12
Johnstone, Adrienne C. (Department: 1733)
Resilient tires and wheels
Tires, resilient
Anti-skid devices
C152S454000, C152S458000, C152S526000, C152S531000, C152S532000, C152S533000, C152S548000, C152S556000
Reexamination Certificate
active
06244315
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a tire with a high transverse curvature coefficient, in particular suitable for fitting to motorcycles.
The invention relates in particular to tires for two-wheeled vehicles, in which the transverse curvature coefficient, which in any case has a value of not less than 0.15, is greater in the front tire than that of the corresponding rear tire.
Even more particularly the invention relates to tires which have a carcass with a radial structure and preferably have a cross-sectional ratio (H/C)<80% and/or are mounted on a mounting rim with a width>60% than the nominal chord of the tire.
Generally tires for motorcycles comprise a torus-shaped carcass with a central peripheral crown and two sidewalls terminating in a pair of beads for securing the tire to a corresponding mounting rim, a tread extending coaxially around the peripheral crown and a belt structure arranged between the carcass and the tread.
The carcass in turn comprises at least one rubberized fabric ply provided with reinforcing cords which moreover are of the textile type.
The textile cords are identified by a numerical abbreviation which represents the count of the fibre used and the number of strands which combine to form the cord. “Strand” is understood as being a bundle of filaments or single filaments which are twisted together; “count” is understood as being the weight in grammes of a length of 10,000 meters of fibre, expressed in dtex units.
As is known, a two-wheeled vehicle, when travelling along a curved trajectory, inclines on the sidewall inside the bend at an angle, called the camber angle, the value of which can reach a value as high as 65° with respect to the plane perpendicular to the ground; this inclination produces on the part of the tires a (camber) thrust which opposes the centrifugal force acting on the vehicle.
It is also known that, with an increase in speed and a decrease in the radius of curvature of the trajectory, the inclination of the vehicle alone is no longer sufficient to compensate for the effect of the centrifugal force, ensuring the stability of travel of the vehicle itself: an increase in the thrust exerted by the tires is required, and this increase is obtained by varying the position of the vehicle with a manoeuvre, performed by the rider via the handlebars, usually known to experts as “push steering”, i.e. inclining the rolling plane of the front tire with respect to the direction tangential to the curved trajectory at an angle, called “slip angle”, directed in the opposite direction to the curvature of the trajectory.
This therefore produces a total thrust which is the sum of a camber thrust resulting from the inclination of the equatorial plane of the tire with respect to the vertical and a slip thrust caused by the angular variation in the rolling plane of the front wheel.
The value to be assigned to the slip angle depends on the structural and performance characteristics of the front tire, i.e. on the relationship which the tire is able to express between the value of the slip angle and that of the slip thrust, in combination with its camber thrust and that exerted by the rear tire.
In particular, in order to control steering of a motorcycle in the aforementioned conditions, it is preferred to modify the structural characteristics of the tires represented by the structure and the associated belt reinforcing elements.
A known tire for motorcycles comprises a carcass structure formed by a pair of rubberized fabric plies reinforced with cords which are symmetrically inclined with respect to the equatorial plane of the tire, usually known as a cross-ply carcass, and if necessary a belt structure which is also formed with pairs of rubberized fabric strips, with cords which are arranged angled both with respect to the equatorial plane of the tire and the circumferential direction thereof.
The abovementioned tire structure is able to generate considerable camber thrusts, but gives rise to problems relating to comfort, stability and road-holding power of the vehicle as well as fatigue on the part of the rider, caused by the excessive rigidity of these tires.
These drawbacks have been partly overcome by a tire which has appeared on the market more recently, comprising a radial carcass combined with a belt structure consisting of textile or metal cords: in particular the tire for use on the rear wheel is provided with a belt structure comprising, and sometimes in an exclusive manner, a wound arrangement of cords which are preferably metallic and oriented in the circumferential direction, while the tire for use on the front wheel retains the belt structure with radially superimposed strips of inclined cords, indicated above.
This pair of tires has undoubtedly improved the situation from the point of view of riding comfort and stability, particularly during travel on straight roads.
The improvement in the behaviour along straight roads has, however, given rise to a new problem, consisting in the fact that the radial carcass of the tire, in combination with a belt of cords arranged circumferentially (at 0°), during travel around bends is not always able to produce a camber thrust which is suited to requirements, also taking into account the increasingly higher performances of vehicles.
More precisely, the rear tire provides a thrust which is quantitatively less than and qualitatively different from—i.e. is of a linear rather than a curvilinear nature—that of the front tire and this fact makes steering of the vehicle around bends even more critical.
Other tires for motorcycles, together with their structural characteristics, are for example described in the European Patent Applications EP 756,949 and EP 808,730 in the name of the Applicants, to which reference should be made for further more precise details.
Patent Application EP 756,949 describes a tire, in particular for use on the front wheels, which comprises a radial twin-ply carcass containing nylon cords with a count of 940/2 dtex and two radially superimposed belt strips provided with nylon cords with a count of 940/2 dtex arranged symmetrically intersecting with one another in the two strips and with respect to the equatorial plane of the tire. The belt structure further comprises one radially external layer of steel cords, with the constructional characteristics 3×4×0.20 HE HT, where the cords are distributed with a density which continuously increases from the centre towards the ends of the belt.
Basically, according to the technical solution described in this patent application, it is possible to obtain a belt which at the same time is flexible in the centre, in order to absorb and dampen the vibrations due to the roughness of the ground, and rigid laterally, so as to generate notable slip thrusts, by providing a central portion which is mainly provided with cords at zero degrees, in combination with a low density or total absence of reinforcing elements oriented in the transverse direction, and two side portions provided both with cords at zero degrees and with reinforcements oriented in an intersecting direction with respect to the equatorial plane.
These tires, compared to tires which have a radial twin-ply carcass made of nylon 940/2 dtex and a single pair of belt strips with cords intersecting with one another in the two strips, have provided better results with regard to the capacity for absorption of the roughness of the road surface (contact feeling), the behaviour of the vehicle (ease of handling) and the stopping distance (braking capacity).
Patent Application EP 808,730 describes a pair of tires for a motorcycle, i.e. a front tire and a rear tire.
More specifically, the front tire comprises a radial twin-ply carcass with textile cords made of a material having a higher count than that of the tire according to the preceding application, i.e. rayon 1220/2 dtex instead of nylon 940/2 dtex.
The belt consists of a radially external layer of metal cords, which are oriented circumferentially and have an axial variable density, and a radially int
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Johnstone Adrienne C.
Pirelli Pneumatici S.p.A.
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