Resilient tires and wheels – Tires – resilient – Pneumatic tire or inner tube
Reexamination Certificate
1999-02-18
2001-11-13
Johnstone, Adrienne C. (Department: 1733)
Resilient tires and wheels
Tires, resilient
Pneumatic tire or inner tube
C152S526000, C152S531000, C152S532000, C152S533000, C152S534000, C152S538000
Reexamination Certificate
active
06315019
ABSTRACT:
The present invention relates to a tire for vehicle wheels and, more particularly, to a tire of the radial type which has an improved belt structure.
A radial tire usually comprises a torus-shaped carcass, a tread band located at the top of said carcass and moulded with a suitable pattern in relief, the so-called tread pattern, and a belt structure located between the carcass and tread.
The carcass is formed by at least one ply of rubberized fabric incorporating reinforcing elements, usually textile or metal cords, axially extending from one bead to the other one; in carcasses of the radial type, these cords lie in radial planes.
The belt structure in turn comprises radially superimposed strips of rubberized fabric which extend axially substantially over the entire width of the tread and incorporate reinforcing elements, usually textile or metal cords arranged parallel to one another in each strip and intersecting with those of the adjacent strip.
More specifically the invention relates to belt structures suitable for tires of heavy transportation vehicles, i.e. with a high load-carrying capacity, mainly for lorries, buses and the like, comprising reinforcing elements made of material with a high modulus, generally metal cords having breakage elongation values of between 2% and 3%.
Some of these structures are characterized by the fact that they have their ends inserted in a pair of rings of rubberized fabric, called “bands” hereinbelow, incorporating reinforcing elements, usually high-elongation metal cords extending in a direction substantially parallel to the equatorial plane of the tire.
The expression “high elongation” is used to indicate the capacity of the reinforcing elements to lengthen under strain to a substantial degree, at least initially, owing to the use of special materials and/or predetermined, specially chosen, geometrical shapes, so as to be able to satisfy particular stages of manufacture of the tire. and/or operating conditions thereof.
These reinforcing elements may therefore be wires or cords with high elongation properties which are arranged in linear form, or wires or cords with low elongation properties which are arranged in a form other than a linear form, for example in a zigzag or undulating form.
In particular these reinforcing elements may be made with the known metal cords of the “HE” (high elongation) type, having a breakage elongation value of between 4% and 10%, the characteristics of which have already been described in detail, for example in European Patent No. 0,461,646 in the name of the same Applicant.
The function of these bands is to achieve both correct moulding of the tread pattern, controlling expansion of the tire inside the vulcanization mould, and optimum behaviour during use, stopping expansion of the ends of the belt structure owing to the centrifugal effect.
More particularly, the function of the lateral bands is that of preventing the movements of the ends of the cords of the underlying belt strips, reducing to a minimum the shearing stresses caused by said movements, the effect of which would result in tearing of the rubber with consequent separation of the belt strips from one another and from the carcass ply.
In known tires provided with this type of belt, the lateral bands comprise two radially superimposed layers of metal cords wound onto a pair of belt strips with the axially external edge of the bands aligned with the edge of one of the two belt strips, for example with that of the radially innermost strip.
A tire of the type mentioned is described in the patent GB 2,061,202.
The presence of dual-layer bands in the belt results from the need to ensure a high strength of the structure in severe stress conditions created by running in bends.
In fact, during the run in bends, the impression area of the tire may be transformed from the elliptical configuration, which is typical of run in a straight line, into a “bean” type configuration.
Consequently, in each band, the metal cords arranged on the outside of the bend, with reference to the trajectory of the neutral axis, are subject to pulling force, while those in the axially opposite position, i.e. on the inside of the bend, are subject to compression.
In this situation, the cords of the bands may be able to withstand adequately the compressive stresses, without collapse as a result of the extreme load, only owing to the considerable cross-section of the band, resulting from the presence of at least two radially superimposed layers of cords.
However, the tire has a high vertical rigidity owing to the fact that these bands, formed by the said layers, are equivalent in practice to two non-deformable metal rims.
Moreover, the top portion of the tire has a sudden and high increase in rigidity, in the transition area between the sidewall zone and the tread zone, from the rigidity of the carcass structure to the rigidity of the belt structure, said increase being concentrated in the plane parallel to the equatorial plane in which the edge of at least one belt strip is aligned with that of the band.
This sudden increase in rigidity has a negative effect on the comfort of the tire.
The patent GB 2,064,445 also discloses a tire comprising bands applied onto the ends of a pair of belt strips, in which a third belt strip is arranged between the two layers of each band and a fourth belt strip covers the entire set of underlying strips.
In this solution, the presence of lateral bands formed by two individual layers of cords separated from one another by a belt strip results in a worse effect as regards the comfort since both the overall rigidity and the sudden increase in rigidity, in particular on the edges, are increased considerably, as a result of having increased the overall number of belt strips. Radial tires are also known, having a relative distance between the axially external portions of the belt strips in order to reduce the shearing deformations at the ends of the structure, as for example described in the patent U.S. Pat. No. 4,696,335 and in the patent application EP 0,719,659.
More particularly, the patent U.S. Pat. No 4,696,335 relates to a radial tire comprising a belt structure formed by a plurality of superimposed strips reinforced with metal cords inclined with respect to the circumferential direction.
The ends of the adjacent strips are separated from one another by means of the insertion of special rubber fillings. The belt structure described in this patent does not have any lateral bands with circumferentially directed reinforcing elements.
The patent application EP 0,719,659, in turn, describes a radial tire comprising a belt formed by two strips of rubberized fabric incorporating reinforcing elements inclined relative to the equatorial plane, and by two lateral bands formed by at least one layer with circumferential reinforcing elements.
The ends of the second strip are radially spaced from the ends of the first strip, i.e. the radially innermost one, and the width of the first strip is greater than that of the second strip.
Both the load-bearing strips have their central portion, delimited between the axially internal edges of the bands, extending in the radial direction outwards, assuming, in cross-section, a wave-like configuration with a point of inflection at each of said axially internal edges.
At the axially external edges of the bands the second strip has a further point of inflection, from which the divergence between the ends of the two belt strips commences.
In a particular embodiment, criticized by the same owner of the application for the inadequate fatigue resistance of the belt, the bands are formed by a single layer of metal cords: in this case the structural strength of the belt is recovered by reverting to the conventional solution with bands consisting of two superimposed layers of metal cords, where the second layer extends over the entire width of the belt.
The state of the art described does not offer any teaching useful for determining a belt structure which allows a reduction in the masses involved and the rigidity of the known metall
Garlaschelli Carlo
Lo Presti Gaetano
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Johnstone Adrienne C.
Pirelli Pneumatici S.p.A.
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