WO2025032450A1

WO2025032450A1 - Reinforcing cord for tyres for vehicle wheels and tyre comprising said reinforcing cord

Info

Publication number: WO2025032450A1
Application number: PCT/IB2024/057493
Authority: WO
Inventors: Giacomo DE FERRARI; Simone Agresti; Thomas HANEL
Original assignee: Pirelli SpA; Pirelli Tyre SpA
Current assignee: Pirelli and C SpA; Pirelli Tyre SpA
Priority date: 2023-08-04
Filing date: 2024-08-02
Publication date: 2025-02-13
Anticipated expiration: 2026-02-04

Abstract

A reinforcing cord (10) for tyres for vehicle wheels, comprising at least two elongated elements (11a, lib) made of non-metallic material and twisted together, the reinforcing cord (10) extending along a non- rectilinear longitudinal trajectory, in particular an undulating longitudinal trajectory.

Description

Reinforcing cord for tyres for vehicle wheels and tyre comprising said reinforcing cord

DESCRIPTION

The present invention relates to a reinforcing cord for tyres for vehicle wheels.

The invention also relates to a tyre for vehicle wheels comprising such a reinforcing cord.

The reinforcing cord of the invention has a geometry suitable for achieving a high part load elongation.

PRIOR ART

US 10,618,353 B2 describes textile reinforcing cords comprising two or more yarns twisted together and made of aramid fibres. The high modulus of the aramid fibres provides these reinforcing cords with the desired stiffness. In order to increase the part load elongation, while making such reinforcing cords the yarns are spaced apart from each other and a RFL adhesive composition is inserted between them. When these reinforcing cords are subjected to traction, the yarns approach each other, compressing the adhesive composition and achieving the desired part load elongation. As the load increases, the elongation is counteracted by the high modulus of the aramid fibres.

WO 2012/083148 Al, US 2017/0274706 Al and US 4,155,394 A describe textile reinforcing cords comprising elongated elements made of a high modulus and low elongation material (aramid), twisted to elongated elements made of a low modulus and high elongation material (nylon).

KR 20110061110 A describes a reinforcing cord comprising at least one high elongation elongated element made of nylon, at least one medium elongation elongated element made of a material selected among polyester, polyvinyl, PVA, rayon, lyocell, PEN and at least one low elongation elongated element made for example of aramid, carbon fibres or glass fibres.

SUMMARY OF THE INVENTION

In this description and in the subsequent claims, when reference is made to certain angle values, these values are to be deemed as absolute values, i.e. both positive and negative values with respect to a reference plane or direction, unless otherwise specified.

Moreover, when reference is made to any range of values comprised between a minimum value and a maximum value, the aforesaid minimum and maximum values are deemed to be included in the aforesaid range, unless expressly stated to the contrary.

Moreover, all of the ranges include any combination of the described minimum and maximum values and include any intermediate range, even if not specifically expressly described.

Even if not expressly indicated, any numerical value is deemed to be preceded by the term "about" to also indicate any numerical value that differs slightly from the one described, for example to take into account the dimensional tolerances typical of the sector of reference.

Hereinafter, the following definitions apply.

The term "green tyre" is used to indicate a tyre obtained from the manufacturing process and not yet moulded and vulcanized.

The term "tyre" or "finished tyre" is used to indicate a tyre obtained by subjecting a green tyre to a moulding and vulcanization process in a vulcanization mould.

The term "footprint area" of the tyre is used to indicate the portion of the tyre in contact with the ground or road surface when the tyre is mounted on a wheel rim and a predetermined vertical load is exerted on the tyre.

The term "parallel" is used to indicate not only a condition of perfect parallelism, but also a condition in which there is a slight deviation from the perfect parallelism, for example by an angle of no more than 5°.

The term "perpendicular" is used to indicate not only a condition of perfect perpendicularity or orthogonality, but also a condition in which there is a slight deviation from the perfect perpendicularity or orthogonality, for example by an angle of no more than 5°.

The term "equatorial plane" of the tyre is used to indicate a centreline plane perpendicular to the axis of rotation of the tyre. The equatorial plane subdivides the tyre into two parts that typically are symmetrically equal.

The term "elastomeric material" or "elastomer" is used to indicate a material comprising a vulcanizable natural or synthetic polymer and a reinforcing filler, wherein said material, at room temperature and after being subjected to vulcanization, is susceptible to deformations caused by a force and is capable of rapidly and energetically recovering the substantially original shape and dimensions after elimination of the deforming force (according to the definitions of ASTM D1566-11 Standard Terminology Relating To Rubber).

The terms "upstream" and "downstream" are used with reference to a predetermined direction and to a predetermined reference. Therefore, assuming for example a direction from left to right and a reference taken along said direction, a position "downstream" with respect to the reference indicates a position to the right of said reference and a position "upstream" with respect to the reference indicates a position to the left of said reference.

The terms "circumferential" and "circumferentially" are used, when referred to a tyre, with reference to the rolling direction of the tyre, which corresponds to a direction lying on a plane coincident with or substantially parallel to the equatorial plane of the tyre. The same terms, when referred to a reinforcing cord, are used with reference to a direction that, in any cross section of the reinforcing cord, turns around the centre of the reinforcing cord.

The terms "radial", "radially inner" and/or "radially outer" are used, when referred to a tyre, with reference to a direction substantially parallel to the equatorial plane of the tyre, i.e. to a direction substantially perpendicular to the axis of rotation of the tyre. The same terms, when referred instead to a reinforcing cord, are used with reference to a direction substantially perpendicular to the longitudinal direction of the reinforcing cord.

The terms "axial", "axially inner" and/or "axially outer" are used, when referred to a tyre, with reference to a direction substantially perpendicular to the equatorial plane of the tyre, i.e. to a direction substantially parallel to the axis of rotation of the tyre. The same terms, when referred instead to a reinforcing cord, are used with reference to a direction substantially parallel to the longitudinal direction of the reinforcing cord.

The terms "longitudinal trajectory" and "longitudinal direction" of a reinforcing cord are used to indicate the trajectory and the direction, respectively, along which the centres of the circumferences circumscribing all the cross sections of the reinforcing cord follow each other.

A longitudinal trajectory is intended as being "non-rectilinear" when, being fixed a reference straight line tangent to the reinforcing cord at the radially outermost point of the reinforcing cord and directed along the longitudinal direction of the reinforcing cord, the distance of the aforesaid centres from said reference straight line varies along the longitudinal direction of the reinforcing cord in such a way that the difference between the maximum distance and the minimum distance is greater than 150 pm.

The term "substantially axial direction" is used to indicate a direction inclined, with respect to the equatorial plane of the tyre, by an angle comprised between 70° and 90°.

The term "substantially circumferential direction" is used to indicate a direction oriented, with respect to the equatorial plane of the tyre, at an angle comprised between 0° and 10°.

The term "reinforcing cord", or more simply "cord" is used to indicate a long-shaped element comprising several elongated elements possibly covered by, or incorporated in, a matrix of elastomeric material.

The term "elongated element" is used to indicate a wire or yarn.

The term "wire" is used to indicate an elongated element consisting of a single filament. Therefore, the term "monofilament" is also used to refer to a "wire".

The term "yarn" is used to indicate an elongated element consisting of the aggregation of a plurality of filaments twisted to each other. Therefore, the term "multifilament" is also used to refer to a "yarn".

Each filament can also be referred to as "fibre".

An elongated element may therefore consist of a single wire or of a single yarn or of several yarns twisted together.

In the case of yarns, the elongated elements can be identified with an abbreviation that represents the textile material, the linear density of the fibre used and the number of yarns that form the elongated element. For example, an elongated element made of PET (polyethylene terephthalate) identified with PET 1672 indicates an elongated element comprising PET fibres having a linear density of 1670 dtex, formed by two yarns twisted together.

The term "strand" is used to indicate an assembly consisting of at least two elongated elements. The strand may itself define a reinforcing cord or be intended to be twisted to at least another elongated element or to at least another strand to make a reinforcing cord. The term "hybrid strand" is used to indicate a strand consisting of at least two elongated elements made of different materials.

In this description and in the subsequent claims, any reference to a particular plastic material is to be understood as extending both to a plastic material of fossil origin and to a corresponding recycled or biobased material, if any. Thus, for example, when mention is made of PET it is foreseen that such a PET may be of fossil or recycled origin.

The term "recycled material" is used to indicate a plastic material obtained starting from waste or industrial waste products made of a corresponding plastic material (typically, although not necessarily, of fossil origin) and subjected to appropriate mechanical and/or chemical and/or thermal treatments in order to be able to obtain reusable products.

The term "non-recycled material" is used to indicate a plastic material of fossil origin.

The term "bio-based material" is used to indicate a material that is not of fossil origin and is not obtained starting from waste or industrial waste products, but is obtained from renewable sources, such as for example agricultural and forestry products that are cultivated and/or used by the human being for purposes other than those of human or animal nutrition.

The term "diameter" of a wire is used to indicate the diameter measured as prescribed by the BISFA E10 method (The International Bureau For The Standardization Of Man-Made Fibres, Internationally Agreed Methods For Testing Steel Tyre Cords, 1995 edition).

By "diameter" of a yarn is intended to mean the diameter of an ideal circumference that circumscribes all the filaments defining the yarn.

The term "breaking load" of a reinforcing cord is used to indicate the load at which the breakage of the reinforcing cord occurs, evaluated in accordance with the BISFA standard (Bureau International pour la Standardisation des Fibres Artificielles) relating to the material under test as per definition herein below.

The term "part load elongation" of a reinforcing cord is used to indicate the difference between the percentage elongation obtained by subjecting the reinforcing cord to a traction of 50 N and the percentage elongation obtained by subjecting the reinforcing cord to a traction of 2.5 N. The part load elongation is evaluated with the BISFA E7 method (The International Bureau For The Standardization Of Man-Made Fibres, Internationally Agreed Methods For Testing Steel Tyre Cords, 1995 edition).

The term "modulus" is used to indicate the ratio between load (or force) and elongation measured at any point of a load-elongation curve according to the BISFA standard. Such a curve is drawn by calculating the first derivative of the load-elongation function that defines the aforesaid curve, normalized to the linear density expressed in Tex. The modulus is therefore expressed in cN/Tex or Mpa. In a load-elongation graph, the modulus is identified by the slope of the aforesaid curve with respect to the X-axis.

The term "initial modulus" is used to indicate the modulus calculated at the origin point of the load-elongation curve, i.e. for an elongation equal to zero.

The term "final modulus" is used to indicate the modulus calculated close to the breaking load, before any sudden failure.

In the context of the present invention, the term "high modulus" is used to indicate a modulus higher than 5 Mpa, while the term "low modulus" is used to indicate a modulus lower than 5 Mpa.

The term "linear density" or "count" of yarn is used to indicate the weight of the cord/elongated element per unit of length. The linear density is measurable in dtex (grams per 10 km of length).

For the measurement of the linear density and for the determination of the tensile properties (such as for example the breaking load), flat yarns are referred to, without twists applied during the test phase, according to the tests regulated by the BISFA standard. In particular:

- for aramid fibres (AR.) reference is made to para-aramidic yarn test methods - 2002 edition:

• Determination of linear density - Chapter 6;

• Determination of tensile properties - Chapter 7 - Test Procedure - Paragraph 7.5 - procedure with initial pre-tensioning;

- for Nylon (NY), reference is made to BISFA - Testing methods for polyamide yarns - 2004 edition:

• Determination of linear density - Chapter 6 - Procedure A;

• Determination of tensile properties - Chapter 7 - Procedure A;

• Preparation of laboratory samples: Preparation of samples under relaxation - paragraph 7.4.1.1 => preparation of samples on collapsible spool;

• Preparation of laboratory samples and carrying out the test: Manual test - paragraph 7.5.2.1 => c);

• Start of procedure => e) pretension at start of procedure;

• Tractions performed with Zwick - Roell Z010 dynamometer;

- for Polyester (PET), reference is made to BISFA - Methods for testing polyester yarns - 2004 edition:

• Determination of linear density - Chapter 6 - Procedure A;

• Determination of tensile properties - Chapter 7 - Procedure A;

• Start of procedure => e) pretension at start of procedure;

• Tractions performed with Zwick - Roell Z010 dynamometer.

Hereinafter, when the adhesion to the elastomeric material of a reinforcing cord or of an elongated element thereof is mentioned, reference is made to the adhesion capacity conferred to the reinforcing cord/elongated element solely by its shape or structure, therefore without considering surface coating treatments through adhesive compositions, such as for example the Resorcinol-Formaldehyde-Latex (RFL) composition typically used in the tyre production sector.

The term "structural component" of a tyre is used to indicate any tyre ply or layer containing reinforcing cords, such as, for example, a carcass ply of car or motorcycle tyres, or a belt ply of car tyres, or a zerodegree reinforcing layer (or a cross-belt structure) of a motorcycle tyre, or a stiffening layer associated with a carcass ply of car tyres at or close to a respective turned-up end edge of the carcass ply and further below indicated with the terms "flipper" and "chafer".

The term "mechanical behaviour" of a reinforcing cord or of an elongated element thereof or of a strip-like element that incorporates the cord is used to indicate the reaction offered by the reinforcing cord/strip- like element when subjected to a load (or force). In the case of a traction load, such a load causes an elongation that is variable depending on the amount of the load according to a function identified by a particular loadelongation curve.

A tyre for vehicle wheels comprises a carcass structure comprising a plurality of reinforcing cords, typically textile. Such reinforcing cords may be incorporated in a single carcass ply or in multiple carcass plies (preferably no more than two) radially superimposed on each other.

The carcass structure has a crown portion extended on opposed sides with respect to the equatorial plane and at which the reinforcing cords extend along a substantially axial direction, and two side portions extended on opposed sides with respect to the crown portion, each one in proximity to a respective sidewall of the tyre.

In a radially outer position with respect to the carcass structure a crown structure comprising a belt structure is provided and, in a radially outer position with respect to the belt structure a tread band made of elastomeric material is provided.

The belt structure may comprise a cross-belt structure and/or a zero-degree reinforcing layer.

The cross-belt structure, typically provided in car tyres, comprises several belt layers radially overlapping each other. In particular, it may be provided a first belt layer including reinforcing cords, typically textile or metallic, substantially parallel to each other and inclined, with respect to the equatorial plane of the tyre, by a predetermined angle and at least one second belt layer arranged in a radially outer position with respect to the first belt layer and including reinforcing cords, typically textile or metallic, substantially parallel to each other but oriented, with respect to the equatorial plane of the tyre, with an inclination opposite to that of the reinforcing cords of the first belt layer.

The "zero-degree reinforcing layer" comprises a plurality of textile reinforcing cords arranged on the belt structure (in the case of car tyres) or on the crown portion of the carcass structure (in the case of motorcycle tyres) according to a substantially circumferential winding direction. In motorcycle tyres, the zero-degree reinforcing layer may itself define the "belt structure" of such tyres or may be replaced by two overlapping reinforcing layers that define a cross-belt structure.

Typically, the reinforcing cords of the zero-degree reinforcing layer are incorporated into a rubberized fabric strip-like element. This strip-like element is spirally wound on the crown portion of the carcass structure from one end to the other end thereof with a predetermined deposition pulling force.

The production cycle of a tyre for vehicle wheels generally comprises at first a process for building a green tyre in which the various structural components of the tyre are built and assembled. The green tyre thus shaped is subsequently subjected to a moulding and vulcanization process aimed at defining the structure of the finished tyre according to a desired geometry and tread design.

Typically, the building and assembling of the various structural components of the tyre takes place on special forming drums having a substantially cylindrical shape. These drums are radially contractible/expandable.

In particular, the carcass structure is built on a first forming drum, known as first-stage drum, and the crown structure is built on a second forming drum, known as auxiliary or second-stage drum.

The assembling of the carcass structure to the crown structure may take place on the first forming drum, in which case the first-stage drum is called single stage or "unistage" drum, or on a different forming drum, known as shaping drum. This assembling comprises, after having positioned the crown structure in a coaxially centred and radially outer position with respect to the carcass structure, shaping the green tyre by radially expanding the first-stage and/or shaping drum. This shaping allows the radially outer surface of the carcass structure to be associated with the radially inner surface of the crown structure and the green tyre to take a toroidal configuration.

The Applicant has observed that during the shaping of the green tyre, the reinforcing cords of the zero-degree reinforcing layer arranged at the axially central portion of the drum (hereinafter also indicated with "centre" of the drum) undergo an elongation greater than that of the reinforcing cords arranged at the opposed shoulder portions of the drum (hereinafter also indicated with "shoulders" of the drum). In other words, during the shaping of the green tyre, the strip-like element that incorporates the aforesaid reinforcing cords elongates more at its portion wound around the centre of the drum (hereinafter indicated with "central portion" of the strip-like element) and less at its opposed side portions wound around the shoulders of the drum (hereinafter indicated with "shoulder portions" of the strip-like element).

Consequently, at the end of the shaping the strip-like element is more pulled, and thus stiffer, at its central portion and less pulled, and thus less stiff, at its opposed shoulder portions. In particular, the Applicant has found a difference in elongation, and therefore in stiffness, between central portion and shoulder portions of the strip-like element of abpu 2-3%.

The Applicant has observed that it would instead be desirable the strip-like element to have, at the end of the shaping, a substantially uniform stiffness in the axial direction, so as to avoid an undesired nonuniformity of mechanical behaviour of the zero reinforcing layer in the axial direction at the tyre footprint area.

The Applicant has considered that a suitable measure to limit the aforesaid difference in elongation or stiffness, thus moving towards the desired uniformity of stiffness in the axial direction, is to wind the striplike element on the drum with a deposition pull force which varies between the shoulders and the centre of the drum. In particular, it is possible to have a greater deposition pull force at the shoulders of the drum and a smaller one at the centre of the drum. In this way, at the end of the deposition of the strip-like element on the drum and before the shaping of the green tyre, the strip-like element is more pulled, and thus stiffer, at the shoulders of the drum and less pulled, and thus less stiff, at the centre of the drum.

However, the Applicant has found that the textile reinforcing cords used in the tyre strip-like elements currently on the market have a limited elongation at low loads (such as those which the strip-like element is subjected to as a result of the aforesaid deposition pull force). Therefore, the provision of a deposition pull force that is lower at the centre of the drum and greater at the shoulders of the drum allows to only partially reduce the difference in stiffness typically present at the end of the shaping between central portion and shoulder portions of the strip-like element.

The Applicant has therefore thought to make reinforcing cords having high part load elongations, so as to be able to achieve a significant elongation of the shoulder portions of the strip-like element when the latter is wound on the drum with a deposition pull force that is greater at the shoulders of the drum and lower at the centre of the drum. In this way, before the shaping of the green tyre, the strip-like element would be more pulled (and thus stiffer) at its shoulder portions and less pulled (and thus less stiff) at its central portion, thus being able to compensate for the inevitable difference in elongation in the axial direction that occurs during the shaping of the green tyre. The desired uniformity of stiffness of the strip-like element in the axial direction would thus be achieved at the end of the shaping of the green tyre.

Wishing also to contain the rolling resistance of its tyres, in order to reduce CO2 emissions in the atmosphere, the Applicant has oriented itself towards making reinforcing cords that are as light as possible and has therefore decided to use elongated elements made of non-metallic material.

The Applicant has found that in order to achieve high part load elongations, it is possible to configure the reinforcing cords in such a way that they extend along a non-rectilinear longitudinal, preferably an undulating trajectory. In this way, when subjected to traction and before this stress is counteracted by the resistance offered by the material from which the elongated elements are made, the reinforcing cords can elongate until they become straight. This initial elongation allows the desired high part load elongation to be achieved.

The Applicant has verified that it is possible to make non- rectilinear reinforcing cords by twisting their elongated elements, either individually or after having twisted two or more elongated elements together to form semi-finished products in the form of strands, in conventional twisting apparatuses typically used for twisting metallic wires or textile elongated elements and by appropriately controlling the twisting process carried out in such twisting apparatuses. This control comprises, for example, properly feeding the various elongated elements to the twisting apparatus and setting the latter so that, during twisting, each of them is arranged in a desired position with respect to the others (e.g. so that some elongated elements are arranged in a radially inner position with respect to other elongated elements and the latter are wound around the first ones along respective helical paths, or so that all elongated elements are wound on each other along respective helical paths without some of them being arranged in a radially inner position with respect to others), adjusting the twisting pitch (corresponding to the helix pitch in the reinforcing cord), adjusting the force with which the individual elongated elements or semi-finished products are pulled, applying a predetermined braking force to the individual elongated elements or semi-finished products, possibly applying a predetermined degree of deformation to the reinforcing cord (through the measure, known as preforming or pleating, that is typically provided in metallic wire twisting devices in order to space apart the metallic wires from each other).

Therefore, in a first aspect thereof the present invention relates to a reinforcing cord for tyres for vehicle wheels, comprising at least two elongated elements made of non-metallic material.

Preferably, said at least two elongated elements are twisted together.

Preferably, the reinforcing cord extends along a non-rectilinear longitudinal trajectory.

In a second aspect thereof, the invention relates to a tyre for vehicle wheels comprising a plurality of cords in accordance with the first aspect of the invention.

According to the Applicant, the reinforcing cords of the invention allows the desired uniformity of stiffness of the strip-like element in the axial direction at the end of the shaping of the green tyre to be achieved. This is obtained thanks to the fact that when the strip-like element is wound on the drum with a deposition pull force that is greater at the shoulders of the drum and lower at the centre of the drum, the shoulder portions of the strip-like element can elongate significantly, thus resulting more pulled and stiffer than the central portion of the strip-like element and thus compensating for the greater elongation/pull of the central portion of the strip-like element with respect to the shoulder portions during the shaping of the green tyre.

The greater stiffness of the shoulder portions of the strip-like element before the shaping of the green tyre causes an increase in stiffness of the entire crown portion of the tyre and, therefore, a uniform and effective transfer of forces between the tyre and the road surface at the tyre footprint area, to the benefit of the tyre's performance and rolling resistance.

In addition, the high part load elongation of the reinforcing cords of the invention allows the strip-like element that incorporates them to withstand high pull forces during the shaping of the green tyre, making it possible to deposit the strip-like element on drums having diameters smaller than those typically provided, without any risk of breaking through the belt structure on which the strip-like element is wound.

The Applicant has observed that depending on the type of elongated elements used in the reinforcing cord (wires, yarns and/or any combination of one or more wires with one or more yarns) and of the non-metallic material (low modulus material, high modulus material or any combination of such materials) it is possible to make reinforcing cords in accordance with the present invention and having characteristics such as to make the reinforcing cords suitable for being used also in structural components of car and motorcycle tyres other than the zero-degree reinforcing layer. In particular:

- with the same material and diameter, the wires are more suitable than the yarns to withstand compressive stresses and to reduce hysteresis caused by mutual friction between wires and/or filaments of the yarns, while the yarns are more suitable than the wires to withstand bending stresses and to adhere to the surrounding elastomeric material;

- with the same type of elongated elements and diameter, a high modulus material allows to increase the stiffness, and/or the breaking load, while a low modulus material allows to maximize the part load elongation and/or the elongation at break.

According to the Applicant, it is preferable to maximize the stiffness and/or the breaking load when the reinforcing cord of the invention are used in the cross-belt structures of the tyres, or in the reinforcing structures of the bead, indicated further below with the terms "chafer" and "flipper", or in the carcass structures of the tyres, while it is preferable to maximize the part load elongation and/or the elongation at break when the reinforcing cord of the invention are used in the zerodegree reinforcing layer.

In at least one of the aforesaid aspects, the present invention may have at least one of the preferred features described below.

Preferably, said longitudinal trajectory is substantially undulating. In this way, the desired part load elongation can be achieved by limiting the radial dimension of the reinforcing cord, and thus, the thickness of the strip-like element (and thus also of the structural component) incorporating this reinforcing cord.

Preferably, said substantially undulating longitudinal trajectory has a substantial periodicity measurable by an undulation pitch greater than 2 mm, more preferably greater than 3 mm, even more preferably greater than 4 mm.

Preferably, the undulation pitch is less than 25 mm, more preferably less than 20 mm, even more preferably less than 12.5 mm.

In preferred embodiments, the undulation pitch is comprised between 2 mm and 25 mm, preferably between 3 mm and 20 mm, even more preferably between 4 mm and 12.5 mm.

In some preferred embodiments, at least one first elongated element of said at least two elongated elements extends along a helical path with a predetermined helix pitch around at least one second elongated element of said at least two elongated elements.

In this case, a core portion arranged in a radially inner position and a crown portion arranged in a radially outer position and extended around the core portion are identifiable in the reinforcing cord. The at least one second elongated element is arranged in the core portion and the at least one first elongated element extends, along said helical path and with said predetermined helix pitch, in the crown portion and therefore around the at least one second elongated element.

In other preferred embodiments, at least one first elongated element of said at least two elongated elements extends along a respective helical path with a predetermined helix pitch and at least one second elongated element of said at least two elongated elements extends along a respective helical path with said predetermined helix pitch.

In this case, the at least two elongated elements of the reinforcing cord are helically wound on each other and are arranged side by side. Preferably, said at least one second elongated element is twisted to said at least one first elongated element with said predetermined helix pitch. In this case, said at least two elongated elements define at least one first strand.

Preferably, the predetermined helix pitch is greater than 2 mm, more preferably greater than 3 mm, even more preferably greater than 4 mm.

Preferably, the predetermined helix pitch is less than 25 mm, more preferably less than 20 mm, even more preferably less than 12.5 mm.

In preferred embodiments, the predetermined helix pitch is comprised between 2 mm and 25 mm, preferably between 3 mm and 20 mm, even more preferably between 4 mm and 12.5 mm.

The Applicant has found that in this case the part load elongation and the elongation at break of the reinforcing cords can be maximized, the other parameters being the same.

In these embodiments, the predetermined helix pitch substantially corresponds to the aforesaid undulation pitch of the undulating trajectory of the cord.

Preferably, said at least one first elongated element is defined by at least one yarn.

Preferably, said at least one first elongated element comprises a single yarn or two or three yarns.

In some embodiments, said two or three yarns are twisted together.

Preferably, said at least one second elongated element is defined by at least one wire or yarn.

In some preferred embodiments, said at least one second elongated element comprises a single wire or two wires twisted together.

In other preferred embodiments, said at least one second elongated element comprises a single yarn. In some preferred embodiments, the reinforcing cord comprises a single first strand.

Preferably, said single strand comprises a single wire twisted to a single yarn.

In other preferred embodiments, the reinforcing cord comprises two first strands twisted to each other and extending along respective helical paths with respective helix pitches.

Said two first strands may be equal to each other or different from each other.

Preferably, said two first strands are equal to each other.

Said respective helix pitches may be equal to or different from said predetermined helix pitch.

Preferably, said respective helix pitches are equal to said predetermined helix pitch.

Preferably, each of said two first strands comprises at least one respective wire twisted to at least one respective yarn.

Even more preferably, each of the two first strands comprises a single wire twisted to a single yarn.

In some embodiments, said at least one first elongated element and said at least one second elongated element are made of the same non-metallic material.

In this case, preferably, said at least two elongated elements are defined by at least one wire and by at least one yarn, respectively, or by at least two wires that may or may not have the same diameter or by respective yarns that may or may not have the same linear density.

In preferred embodiments, said at least one first elongated element is made of a first non-metallic material and said at least one second elongated element is made of a second non-metallic material different from said first material. In this case, said at least two elongated elements, when twisted to each other, define at least one first hybrid strand.

In preferred embodiments, said first material and second material are selected among: nylon, rayon, PET, aramid, glass.

Preferably, said first material is selected among nylon, rayon, PET, aramid, glass.

Preferably, said second material is selected among nylon, rayon, PET.

Preferably, one elongated element is made of a low modulus material and another elongated element is made of a material having a higher modulus than that of the other elongated element.

Preferably, one elongated element is made of a low modulus material and another elongated element is made of a high modulus material, so as to achieve, in addition to the desired part load elongation, a high stiffness at higher loads.

The characteristic "double modulus" mechanical behaviour typical of the hybrid reinforcing cords is thus obtained, which translates, in a load-elongation graph, into a curve defined by two segments separated by a connecting knee, in which the segment to the left of the knee (indicative of the part load elongations, which is particularly high in the reinforcing cord of the invention) has an inclination with respect to the axis of the abscissa that is much lower than that of the segment to the right of the knee (indicative of the stiffness). At part load, the mechanical behaviour of the reinforcing cord is influenced by the stretching of the reinforcing cord, initially extending along a non-rectilinear trajectory, as well as dictated by the reaction offered by the low modulus material, while at high load the mechanical behaviour of the reinforcing cord is mainly dictated by the reaction offered by the high modulus material.

Preferably, said at least one first elongated element is defined by at least one aramid or glass or PET yarn.

Preferably, said at least one second elongated element is defined by at least one nylon or rayon or PET wire.

In some specific embodiments, the at least one first elongated element and the at least one second elongated element are defined by nylon yarns. In this case, the greater part load elongation with respect to the conventional reinforcing cords defined by two nylon elongated elements is obtained only as a result of the stretching of the reinforcing cord, initially extending along a non-rectilinear trajectory.

In some specific embodiments, the at least one first elongated element and/or the at least one second elongated element are defined by PET wires or yarns. PET provides the reinforcing cord with a greater stiffness than that of the conventional reinforcing cords defined by nylon elongated elements.

In some preferred embodiments, the reinforcing cord comprises at least one third elongated element made of non-metallic material and twisted to said at least one first elongated element.

In this case, the at least one first elongated element and the at least one third elongated element define at least one strand that is wound around the at least one second elongated element with said predetermined helix pitch.

Preferably, said at least one third elongated element is arranged, together with said at least one first elongated element, in the crown portion of the reinforcing cord.

Said at least one third elongated element may be made of a non- metallic material equal to or different from that of said at least one first elongated element.

Preferably, said at least one third elongated element is made of a non-metallic material different from that of said at least one first elongated element.

Preferably, said at least one third elongated element is made of a material selected among nylon, rayon, PET. Preferably, said at least one third elongated element is made of the same material as said at least one second elongated element.

In some embodiments, said at least one third elongated element is defined by at least one wire.

In some preferred embodiments, said at least one third elongated element comprises a single wire or two wires twisted together.

In some preferred embodiments, the reinforcing cord comprises at least one fourth elongated element made of non-metallic material and arranged in a radially inner position with respect to said at least one first elongated element and, if present, also with respect to said at least one third elongated element.

Preferably, said at least one fourth elongated element is twisted to said at least one second elongated element.

The reinforcing cords of such embodiments thus have at least two elongated elements at the respective radially inner or core portions, and, when the at least one third elongated element is also present, at least two elongated elements at their respective radially outer or crown portions.

Said at least one fourth elongated element may be made of a non- metallic material which is the same of or different from that of said at least one second elongated element.

Preferably, said at least one fourth elongated element is made of a non-metallic material different from that of said at least one second elongated element.

In this case, said at least one second elongated element and at least one fourth elongated element define at least one second hybrid strand, which is preferably arranged in a radially inner position with respect to the first hybrid strand.

Preferably, said at least one fourth elongated element is made of the same material as said at least one first elongated element. Said second hybrid strand may be equal to or different from said first hybrid strand.

Preferably, said second hybrid strand is equal to said first hybrid strand.

In some preferred embodiments, the reinforcing cord comprises a single second hybrid strand.

Preferably, said single second hybrid strand comprises a single wire twisted to a single yarn.

Preferably, said at least one fourth elongated element is made of a material selected among nylon, rayon, PET, aramid, glass.

Preferably, said at least one fourth elongated element is defined by at least one yarn.

Preferably, said at least one third elongated element is defined by at least one nylon or rayon or PET wire and said at least one fourth elongated element is defined by at least one aramid or glass yarn.

More preferably, said at least one third elongated element is defined by a single nylon or rayon or PET wire and said at least one fourth elongated element is defined by a single aramid or glass yarn.

Preferably, the reinforcing cord has an initial modulus and a final modulus such that the ratio between final modulus and initial modulus is greater than or equal to 9.

Preferably, the ratio between final modulus and initial modulus is greater than, or equal to, 12, even more preferably greater than, or equal to, 20, even more preferably greater than, or equal to, 30.

Preferably, the/each wire has a diameter greater than, or equal to, 0.10 mm, more preferably greater than, or equal to, 0.16 mm, even more preferably greater than, or equal to, 0.23 mm.

Preferably, the/each wire has a diameter less than, or equal to, 0.8 mm, more preferably less than, or equal to, 0.5 mm, even more preferably less than, or equal to, 0.35 mm. In preferred embodiments, the/each wire has a diameter comprised between 0.10 mm and 0.8 mm, more preferably comprised between 0.16 mm and 0.5 mm, even more preferably comprised between 0.23 mm and 0.35 mm.

Preferably, the/each yarn has a linear density greater than or equal to 235 dtex, more preferably greater than or equal to 500 dtex, even more preferably greater than or equal to 940 dtex.

Preferably, the/each yarn has a linear density less than or equal to 3300 dtex, more preferably less than or equal to 2700 dtex, even more preferably less than or equal to 2200 dtex.

Preferably, the/each yarn has a linear density comprised between 235 dtex and 3300 dtex, more preferably comprised between 500 dtex and 2700 dtex, even more preferably comprised between 940 dtex and 2200 dtex.

Preferably, the reinforcing cords of the invention are used in the zero-degree reinforcing layer of the tyre.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Further characteristics and advantages of the tyre of the present invention will become clearer from the following detailed description of preferred embodiments thereof, made with reference to the appended drawings. In such drawings:

- figure 1 is a schematic partial half-cross section view of a portion of an embodiment of a tyre comprising reinforcing cords in accordance with the present invention;

- figure 2-5 are photos of segments of various embodiments of a reinforcing cord in accordance with the present invention;

- figures 2a-5a are schematic cross-sectional views of the reinforcing cords of figures 2-5 taken at the section plane A-A indicated in figures 2-5;

- figures 6 and 7 show two load-elongation graphs of a conventional textile reinforcing cord and of reinforcing cords made in accordance with the present invention.

For the sake of simplicity, figure 1 shows only a part of an exemplary embodiment of a tyre 100 in accordance with the present invention, the remaining part, which is not shown, being substantially identical and being arranged symmetrically with respect to the equatorial plane M-M of the tyre.

The tyre 100 shown in figure 1 is, in particular, an exemplary embodiment of a tyre for four-wheeled vehicles.

Preferably, the tyre 100 is an HP or UHP tyre for sports and/or high and ultra high performance vehicles. This tyre allows to reach speeds higher than 190 km/h, up to over 300 km/h and has one of the following speed codes: "T", "U", "H", "V", "Z","W", "Y", according to the E.T.R.T.O. standard (European Tyre and Rim Technical Organisation). It has a section width equal to or higher than 185 mm, preferably comprised between 195 mm and 385 mm, more preferably comprised between 195 mm and 355 mm and is intended to be mounted on rims having fitting diameters equal to or higher than 13 inches, preferably not higher than 24 inches, more preferably comprised between 16 inches and 23 inches.

In figure 1 "a" indicates an axial direction, "c" indicates a radial direction, "M-M" indicates the equatorial plane of the tyre 100 and "R-R" indicates the axis of rotation of the tyre 100.

The tyre 100 comprises a carcass structure 101, in turn comprising at least one carcass ply 111.

Hereinafter, for the sake of simplicity of disclosure, reference will be made to an embodiment of the tyre 100 comprising a single carcass ply 111. H what is described has analogous application in tyres comprising more than one carcass ply.

The carcass ply 111 has axially opposite end edges engaged with respective annular anchoring structures 102, called bead cores, possibly associated with an elastomeric filler 104. The area of the tyre 100 comprising the bead core 102 and the possible elastomeric filler 104 forms an annular reinforcing structure 103 called "bead structure" and configured to allow the anchoring of the tyre 100 on a corresponding mounting rim, not shown.

The carcass ply 111 comprises a plurality of reinforcing cords 10' coated with an elastomeric material or incorporated in a matrix of crosslinked elastomeric material.

The carcass structure 101 is of the radial type, i.e. the reinforcing cords 10' are arranged on planes comprising the axis of rotation R-R of the tyre 100 and are substantially perpendicular to the equatorial plane M-M of the tyre 100.

Each annular reinforcing structure 103 is associated with the carcass structure 101 by folding up (or turning up) the opposite end edges of the at least one carcass ply 111 about the bead core 102 and the possible elastomeric filler 104, so as to form the so-called turnings 101a of the carcass structure 101.

A crown structure is arranged in a radially outer position with respect to the carcass structure 101. The crown structure comprises a cross-belt structure 106 and a zero-degree reinforcing layer 106c, commonly known as a "zero-degree belt".

The cross-belt structure 106 comprises at least two belt layers 106a, 106b radially overlapping each other.

The belt layers 106a, 106b respectively comprise a plurality of reinforcing cords 10", 10'". Such reinforcing cords 10", 10'" have an orientation that is inclined with respect to the circumferential direction of the tyre 100, or to the equatorial plane M-M of the tyre 100, by an angle comprised between 15° and 45°, preferably between 20° and 40°. For example, this angle is equal to 30°.

The reinforcing cords 10", 10'" of one belt layer 106a, 106b are parallel to each other and have a cross orientation with respect to the reinforcing cords 10"', 10" of the other belt layer 106b, 106a.

The zero-degree reinforcing layer 106c comprises reinforcing cords oriented in a substantially circumferential direction. These reinforcing cords therefore form an angle of a few degrees (typically less than 10°, for example comprised between 0° and 6°) with respect to the equatorial plane M-M of the tyre 100.

A tread band 109 made of elastomeric material is applied in a radially outer position with respect to the zero-degree reinforcing layer 106c.

Respective sidewalls 108 made of elastomeric material are also applied on the side surfaces of the carcass structure 101, in an axially outer position with respect to the carcass structure 101 itself. Each sidewall 108 extends from one of the side edges of the tread band 109 up to the respective annular reinforcing structure 103.

In some specific embodiments, like the one illustrated and described here, the stiffness of the sidewall 108 can be improved by providing a stiffening layer 120, generally known as "flipper" or additional strip-like insert and which has the function of increasing the stiffness and integrity of the annular reinforcing structure 103 and of the sidewall 108.

The flipper 120 is wound around a respective bead core 102 and elastomeric filler 104 so as to at least partially surround the annular reinforcing structure 103. In particular, the flipper 120 wraps the annular reinforcing structure 103 along the axially inner, axially outer and radially inner zones of the annular reinforcing structure 103.

The flipper 120 is arranged between the turned-up end edge of the carcass ply 111 and the respective annular reinforcing structure 103. Usually, the flipper 120 is in contact with the carcass ply 111 and the annular reinforcing structure 103.

In some specific embodiments, like the one illustrated and described here, the bead structure 103 can also comprise a further stiffening layer 121 that is generally known by the term "chafer", or protective strip, and which has the function of increasing the stiffness and integrity of the annular reinforcing structure 103.

The chafer 121 is associated with a respective turned-up end edge of the carcass ply 111 in an axially outer position with respect to the respective annular reinforcing structure 103 and extends radially towards the sidewall 108 and the tread band 109.

The flipper 120 and the chafer 121 comprise reinforcing cords 10* (in the attached figures those of the flipper 120 are not visible).

In the tyre of figure 1, at least some of the reinforcing cords of the zero-degree reinforcing layer 106c (preferably all the cords of the zero-degree reinforcing layer 106c) are reinforcing cords 10 in accordance with the present invention.

A first embodiment of such reinforcing cords 10 is shown in figures 2 and 2a.

This reinforcing cord 10 comprises, in a crown portion thereof, i.e. in a radially outer position, two elongated elements 11a made of non- metallic material and twisted on each other and, in a core portion thereof, and therefore in a radially inner position, two elongated elements lib made of non-metallic material, the latter being also twisted on each other and of a different type with respect to the two elongated elements 11a.

The elongated elements 11a are twisted to the elongated elements lib and extend around the elongated elements lib along a helical path with a predetermined helix pitch E. In figure 2, the longitudinal direction L of extension of the individual elongated elements 11a and therefore of the reinforcing cord 10 is indicated.

The reinforcing cord 10 extends along the longitudinal direction L with a non-rectilinear, preferably undulating, trajectory. This trajectory has a periodicity measurable by an undulation pitch. The helix pitch E and the undulation pitch are comprised between 2 mm and 25 mm, preferably between 3 mm and 20 mm, more preferably between 4 mm and 12.5 mm.

Preferably, the helix pitch E is substantially equal to the undulation pitch.

In an embodiment of the reinforcing cord 10 of figures 2 and 2a, each of the two elongated elements 11a is defined by a respective yarn, while each of the two elongated elements lib is defined by a respective wire.

Each wire has a diameter comprised between 0.10 mm and 0.8 mm, preferably comprised between 0.16 mm and 0.5 mm, more preferably comprised between 0.23 mm and 0.35 mm.

Each yarn has a linear density comprised between 235 dtex and 3300 dtex, preferably comprised between 500 dtex and 2700 dtex, more preferably comprised between 940 dtex and 2200 dtex.

Each wire is made of a material selected among nylon, rayon, PET.

Each yarn is made of a material selected among nylon, rayon, PET, aramid, glass.

Preferably, each wire is made of a low modulus material, in particular nylon or rayon or PET, and each yarn is made of a high modulus material, in particular aramid or glass.

In those cases where each wire is made of nylon or rayon or PET, each yarn can be made of PET.

The reinforcing cords 10 are intended to be incorporated into a strip-like element made of elastomeric material and intended to be used for making the zero-degree reinforcing layer 106c of the tyre 100.

In all the reinforcing cords 10 in accordance with the present invention, preferably both at least one elongated element made of a low modulus material and at least one elongated element made of a high modulus material are provided. In particular, the ratio between final modulus and initial modulus is greater than, or equal to, 9.

An example of a reinforcing cord 10 of the type shown in figures

2 and 2a has the following construction:

2 x 0.28 NY + 1 x AR 1672

This reinforcing cord comprises two elongated elements lib defined by respective nylon wires having a diameter equal to 0.28 mm twisted to two elongated elements 11a defined by respective aramid yarns having a linear density equal to 1670 dtex.

Another example of reinforcing cord 10 in accordance with the present invention is shown in figures 3 and 3a.

This reinforcing cord 10 differs from that of figures 2 and 2a only in that it comprises, in the crown portion thereof, instead of two elongated elements 11a, a strand 11 comprising an elongated element 11a made of non-metallic material twisted to an elongated element 11c made of non-metallic material different from that of the elongated element 11a.

The strand 11 extends around the two elongated elements lib along a helical path with a predetermined helix pitch E.

The elongated element 11a of the strand 11 is like the one described above with reference to figures 2, 2a.

The elongated element 11c of the strand 11 is defined by a respective wire having a diameter comprised between 0.10 mm and 0.8 mm, preferably between 0.16 mm and 0.5 mm, more preferably between 0.23 mm and 0.35 mm.

The elongated element 11c is made of a material selected among nylon, rayon, PET.

An example of a reinforcing cord 10 of the type shown in figures

3 and 3a has the following construction:

2 x 0.23 NY + 1 x (AR1680 + NY 0.23)

This reinforcing cord comprises two elongated elements lib defined by respective nylon wires having a diameter equal to 0.23 mm, twisted to a strand 11 (hereinafter indicated with "crown strand") comprising an elongated element 11a defined by an aramid yarn having a linear density equal to 1680 dtex twisted to an elongated element 11c defined by a nylon wire having a diameter equal to 0.23 mm. Also in this case the two elongated elements lib are arranged in the core portion of the reinforcing cord 10. The strand 11 is instead arranged in the crown portion of the reinforcing cord 10.

An example, not shown, of a reinforcing cord 10 in accordance with the present invention differs from that of figures 3 and 3a only in that the elongated element lib provided in the core portion thereof is twisted to another elongated element to form a strand (hereinafter indicated with "core strand") which is then twisted to the crown strand described above to form the reinforcing cord 10.

Preferably, the core strand is identical to the crown strand.

A further example, not shown, of reinforcing cord in accordance with the present invention differs from that of figures 2 and 2a only in that it comprises, in the crown portion thereof, instead of two elongated elements 11a, a conventional hybrid strand comprising two aramid yarns each having a linear density equal to 1330 dtex twisted to a nylon yarn having a linear density equal to 1400 dtex. This conventional hybrid strand corresponds to the reinforcing cord which, in the description below with reference to figures 6 and 7, is indicated with STD and has the following construction: 2 x AR.1330 / NY1400.

Another example of reinforcing cord 10 in accordance with the present invention is shown in figures 4 and 4a.

This reinforcing cord 10 differs from that of figures 2 and 2a only in that it comprises, in the core portion thereof, instead of two elongated elements lib, a single elongated element lib which, in the specific case, is defined by a yarn made of a material selected among nylon, rayon, PET, Aramid, Glass.

The elongated elements 11a are of the type described above with reference to figures 2, 2a.

An example of a reinforcing cord 10 of the type shown in figures 4 and 4a has the following construction:

1 x NY1400 + 2 x AR.1670

This reinforcing cord 10 comprises an elongated element lib defined by a nylon yarn having a linear density equal to 1400 dtex twisted to two elongated elements 11a defined by respective aramid yarns having a linear density equal to 1670 dtex. The elongated element lib is arranged in the core portion of the reinforcing cord 10, while the two elongated elements 11a are arranged in the crown portion of the reinforcing cord 10.

The reinforcing cords of the examples discussed hereinabove thus have at least one elongated element in the core portion and at least one elongated element in the crown portion. These reinforcing cords are made by feeding the aforesaid elongated elements to a twisting apparatus typically used for twisting metallic wires and by appropriately controlling the twisting process.

In the specific case in which in the core portion and/or in the crown portion there are several elongated element, the twisting process firstly comprises forming one or more semi-finished products in which all the elongated elements of the core portion (hereinafter indicated with "first elongated elements") and/or of the crown portion (hereinafter indicated with "second elongated elements") are pre-twisted. These semi-finished products and possible individual elongated elements are fed to the twisting apparatus, where they are twisted together by arranging the first elongated elements in a radially inner position with respect to the second elongated elements.

The twisting process is controlled by adjusting the force with which the elongated elements/semi-finished products are pulled, by applying a predetermined braking force to only some of the aforesaid elongated elements/semi-finished products and by applying a predetermined degree of deformation (preforming or pleating) to the reinforcing cord. The application of the braking force allows to brake some elongated elements/semi-finished products with respect to others, thus creating an abundance of some elongated elements with respect to others per unit of length of the reinforcing cord. In particular, an abundance of the elongated elements made of a stiffer material with respect to those made of a less stiff material is created in order to initially make the elongated elements made of a less stiff material work under traction, so as to obtain the desired high part load elongation, and subsequently those made of the stiffer material, so as to also achieve adequate stiffness at higher loads. The desired degree of deformation (preforming or pleating) can be obtained by passing the elongated elements on a plurality of cylinders having a small diameter (for example comprised between 1 and 5 mm) with a predetermined pull force. This makes it possible to provide the reinforcing cord with a high curvature and therefore with the desired undulation.

After twisting the semi-finished products, the reinforcing cord thus obtained is subjected to an adhesion process in order to maintain the desired geometry.

Another example of a reinforcing cord 10 in accordance with the present invention is shown in figures 5, 5a.

This reinforcing cord 10 differs from that of figures 4 and 4a only in that in this case the various elongated elements 11a, lib that make up the reinforcing cord 10 are not splitted between the core portion and the crown portion but are all twisted together so as to be arranged side by side along respective helices having the same helix pitch.

An example of a reinforcing cord 10 of the type shown in figures 5 and 5a has the following construction:

1 x NY940 + 2 x AR.1670

This reinforcing cord 10 comprises an elongated element lib defined by a nylon yarn having a linear density equal to 940 dtex twisted to two elongated elements 11a defined by respective aramid yarns having a linear density equal to 1670 dtex. The two elongated elements 11a and the elongated element lib are helically wound on each other.

The reinforcing cord of figures 5 and 5a can be made by feeding the aforesaid elongated elements to a twisting apparatus typically used for twisting textile yarns and by appropriately controlling the twisting process. Semi-finished products or pre-twisted elongated elements are not provided. The parallel filaments of the individual elongated elements 11a, lib are fed directly to the twisting apparatus which provides for mutually twisting them in a single phase. At first the individual elongated elements are twisted in one direction and subsequently, after the twisting of these elongated elements, the reinforcing cord thus formed is twisted, with consequent de-twisting of the individual elongated elements.

In this case, the twisting process is controlled by adjusting the force with which the elongated elements are pulled and by applying a predetermined braking force to only some of the aforesaid elongated elements, similar to what was discussed above.

After twisting the individual elongated elements, the reinforcing cord is subjected to an adhesion process in order to maintain the desired geometry.

The Applicant has made some comparative tensile tests according to the BISFA standard between various reinforcing cords in accordance with the present invention and a conventional reinforcing cord typically used in the zero-degree reinforcing layer of the tyres.

The conventional reinforcing cord comprised two aramid yarns each having a linear density equal to 1330 dtex twisted to a nylon yarn having a linear density equal to 1400 dtex. This cord is indicated herein with STD and has the following construction: 2 x AR.1330 / NY1400.

The reinforcing cords in accordance with the present invention had the following constructions:

2 x 0.28 NY + 1 x AR. 1672, herein indicated with INV1 (this is the example described above with reference to figures 2 and 2a);

2 x 0.23 NY + 1 x (AR1680 + NY 0.23), herein indicated with INV2 (this is the example described above with reference to figures 3 and 3a);

2 x NY 0.23 + 2 x AR1330 / NY1400, herein indicated with INV3 (this is the example described above wherein a conventional hybrid strand having construction 2 x AR1330/ NY1400 is provided in the crown portion of the reinforcing cord);

1 x NY1400 + 2 x AR1670, herein indicated with INV4 (this is the example described above with reference to figures 4 and 4a).

The results of these comparative tests are shown in figure 6.

It can be noted that, with the same other parameters, the reinforcing cords in accordance with the present invention have a part load elongation much greater than that of the conventional reinforcing cord and also have the characteristic "double modulus" mechanical behaviour, thus guaranteeing, in addition to the desired part load elongation, a high stiffness at higher loads. In particular, the reinforcing cord INV3 has a mechanical behaviour herein indicated as "three- modulus", characterized at first by a high part load elongation which is a consequence of both the stretching of the initially non-rectilinear reinforcing cord and of the reaction offered by the nylon wires present in the core portion of the reinforcing cord, then (after a first knee) by a slight increase in stiffness (and consequent slight reduction in elongation) which is a consequence of the reaction offered by the nylon wire present in the crown portion of the reinforcing cord, and subsequently (after a second knee) by a strong increase in stiffness (and consequent strong reduction in elongation) which is a consequence of the reaction offered by the aramid yarns present in the crown portion of the reinforcing cord.

The Applicant has carried out further comparative tensile tests according to the BISFA standard between a further reinforcing cord in accordance with the present invention and the conventional reinforcing cord discussed above with reference to figure 6.

The reinforcing cords in accordance with the present invention had the following construction:

1 x NY1400 + 2 x AR.1670, herein indicated with INV5 (this is the example described above with reference to figures 5 and 5a).

The results of these comparative tests are shown in figure 7.

Also in this case it can be noted that, with the same other parameters, the reinforcing cords in accordance with the present invention has a part load elongation much greater than that of the conventional reinforcing cord as well as the characteristic "double modulus" mechanical behaviour discussed above.

The present invention has been described with reference to some preferred embodiments. Various modifications can be made to the embodiments described above, still remaining within the scope of protection of the invention as defined by the following claims.

Claims

1. Reinforcing cord (10) for tyres for vehicle wheels, comprising at least two elongated elements (11a, lib) made of non-metallic material and twisted together, wherein the reinforcing cord (10) extends along a non-rectilinear longitudinal trajectory.

2. Reinforcing cord (10) according to claim 1 wherein said longitudinal trajectory is substantially undulating.

3. Reinforcing cord (10) according to claim 1 or 2, wherein at least one first elongated element (11a) of said at least two elongated elements (11a, lib) extends along a helical path with a predetermined helix pitch (E) around at least one second elongated element (lib) of said at least two elongated elements (11a, lib).

4. Reinforcing cord (10) according to claim 1 or 2, wherein at least one first elongated element (11a) of said at least two elongated elements (11a, lib) extends along a respective helical path with a predetermined helix pitch (E) and at least one second elongated element (lib) of said at least two elongated elements (11a, lib) extends along a respective helical path with said predetermined helix pitch (E).

5. Reinforcing cord (10) according to claim 3 or 4, wherein said at least one first elongated element (11a) is defined by at least one yarn and said at least one second elongated element (lib) is defined by at least one wire or yarn.

6. Reinforcing cord (10) according to any one of claims 3 to 5, wherein said at least one first elongated element (11a) is made of a first non-metallic material and said at least one second elongated element (lib) is made of a second non-metallic material different from said first material.

7. Reinforcing cord (10) according to claim 6, wherein said first material and second material are selected among : nylon, rayon, PET, aramid, glass.

8. Reinforcing cord (10) according to claim 6 or 7, wherein said first material is selected among nylon, rayon, PET, aramid, glass and said second material is selected among nylon, rayon, PET.

9. Reinforcing cord (10) according to claim 3 or any one of claims 5 to 8 when depending on claim 3, further comprising at least one third elongated element (11c) made of non-metallic material and twisted to said at least one first elongated element (11a).

10. Reinforcing cord (10) according to claim 9, wherein said at least one third elongated element (11c) is defined by at least one wire.

11. Reinforcing cord (10) according to claim 9 or 10, wherein said at least one third elongated element (11c) is made of a material different from that of said at least one first elongated element (11a).

12. Reinforcing cord (10) according to any one of claims 9 to 11, wherein said at least one third elongated element (11c) is made of a material selected among nylon, rayon, PET.

13. Reinforcing cord (10) according to any one of claims 9 to 12, wherein said at least one third elongated element (11c) is made of the same material as said at least one second elongated element (lib).

14. Reinforcing cord (10) according to any one of the previous claims, wherein said reinforcing cord (10) has an initial modulus and a final modulus such that the ratio between final modulus and initial modulus is greater than, or equal to, 9.