Resilient tires and wheels – Tires – resilient – Pneumatic tire or inner tube
Patent
1998-09-03
2000-10-10
Knable, Geoffrey L.
Resilient tires and wheels
Tires, resilient
Pneumatic tire or inner tube
152560, 156134, B06C 902
Patent
active
061291293
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention concerns radial tires and the reinforcement of the carcasses thereof.
It is known that such carcass reinforcement includes at least one layer of ply, hereinafter called a radial ply or radial carcass ply, prepared in the form of a semi-finished product of essentially an elastomeric matrix reinforced by cross-threads. These reinforcement threads, hereinafter called radial threads, are arranged parallel to one another and at regular intervals in an essentially radial direction, i.e., a direction making an angle of approximately 90.degree..+-.10.degree. with the tangent to the circumference of the tire.
Each radial ply normally takes the form of a continuous annular element formed during the fabrication of the carcass reinforcement on a drum by cutting widths or strips of rubberized tire fabric and then joining together the two edges of the fabric thus cut on the drum, by means of a joint also known as a weld splice, which enables those edges to be joined. The strips of tire fabric are usually cut between and parallel to two radial threads to avoid cutting them.
Two types of joints or splices are currently in use: the so-called butt splice obtained by abutment of the two edges without overlap, and the so-called overlapping splice, i.e., one involving overlap of the two edges. In the case of radial tire for touring vehicles whose carcass is reinforced with non-metallic threads, notably by textile threads, a overlapping splice is the more usual.
The present invention relates to an improvement to overlapping splices of the radial ply constituting the carcass reinforcement of radial tires.
As its name suggests, the overlapping splice technique involves covering one edge of the cut fabric with its other edge over a certain distance, and joining the two together by the application of pressure. After curing of the tire carcass, this type of splice shows great strength because of the considerable area of mutual adhesion between the overlapped portions.
However, this overlapping splice has disadvantages. Because of the double thickness of tire fabric, the density of the radial threads is in effect doubled in the overlap zone. The term "density of threads", is a term which denotes the number of threads per unit length of ply in a direction normal to the axis of the threads. Because of the presence of this double layer, and notably under the effect of the inflation pressure of the tire and therefore the tensioning of the radial carcass ply, each radial thread in the seam is stressed and elongated about half as much as a thread outside the overlapped zone. Moreover, and in a known way, if the radial threads are thermo-shrinking they will contract differently during the curing of the tire, depending on whether they are within or outside the overlap.
The above phenomena result in a discontinuity of the properties of the carcass ply in the region of the overlap, notably its rigidity, such that the tire produced is not uniform. This discontinuity and non-uniformity, which are very localized, may be particularly harmful for the appearance, the external aspect of the tire, because they will in general result in the formation of a more or less pronounced hollow in the sidewalls of the inflated tire. It is known that this depression or deformation of the sidewall, also described as an indentation, is the more marked the lower is the tensile modulus of the reinforcing thread used.
The above appearance defect, which is well known and particularly visible when using threads of polyester with a low tensile modulus, is sometimes prejudicial to the marketability of the tire. If the defect is deemed too pronounced, it may even prevent any sales of the manufactured tire, resulting in the eventual destruction thereof, a destruction all the more regrettable from the functional standpoint since the unattractive appearance is not associated with any compromise of safety at all. Moreover, it is known that this non-uniformity of the tire sidewalls can have an adverse effect on the rolling reg
REFERENCES:
patent: 4466473 (1984-08-01), Matyja et al.
patent: 5658405 (1997-08-01), Iseki
Patent Abstracts of Japan, English Abstract for JP 61-083,025, Apr. 1986.
Billieres Jean
Chandezon Pierre
Compagnie Generale des Etablissements Michelin - Michelin & Cie
Knable Geoffrey L.
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