METALLIC REINFORCING CORD FOR TYRES FOR VEHICLE WHEELS AND TYRE COMPRISING SAID METALLIC REINFORCING CORD

Abstract

The invention relates to a metallic reinforcing cord (10) for tyres for vehicle wheels, comprising a single metallic wire (11) extending along a substantially helical path to form a helix having a predetermined pitch (Pw) and, in at least some cross sections thereof, an inner diameter (Di) greater than, or equal to, 0.7 mm.

Claims

1-10. (canceled)

11. A metallic reinforcing cord for tyres for vehicle wheels, comprising: a single metallic wire extending along a substantially helical path to form a helix having a predetermined winding pitch (Pw) and, in at least some cross sections of the helix, an inner diameter (Di) greater than, or equal to, 0.7 mm.

12. The metallic reinforcing cord according to claim 11, wherein the inner diameter (Di) is less than, or equal to, 4 mm.

13. The metallic reinforcing cord according to claim 12, wherein the inner diameter (Di) ranges from 1.5 mm to 3 mm.

14. The metallic reinforcing cord according to claim 11, wherein the metallic reinforcing cord consists of the single metallic wire.

15. The metallic reinforcing cord according to claim 11, wherein the metallic wire has a diameter less than, or equal to, 0.35 mm.

16. The metallic reinforcing cord according to claim 11, wherein the metallic wire has a diameter greater than, or equal to, 0.08 mm.

17. The metallic reinforcing cord according to claim 11, wherein the winding pitch (Pw) is greater than, or equal to, 2 mm.

18. The metallic reinforcing cord according to claim 11, wherein the winding pitch (Pw) is less than, or equal to, 35 mm.

19. A tyre for vehicle wheels, comprising: at least one reinforcing layer delimited by two opposite interface surfaces (S1, S2) and a plurality of metallic reinforcing cords arranged between the two opposite interface surfaces (S1, S2), wherein at least some of the metallic reinforcing cords are metallic reinforcing cords according to claim 11.

20. The tyre according to claim 19, wherein in at least some cross sections of the at least one reinforcing layer the metallic wire is spaced apart from one of the opposite interface surfaces (S1, S2) by a distance less than or equal to the diameter of the metallic wire.

Description

DESCRIPTION OF THE FIGURES

[0104] Further features and advantages of the present invention will become clearer from the following detailed description of a preferred embodiment thereof, made with reference to the attached drawings.

[0105] In such drawings:

[0106] FIG. 1 is a schematic partial half-cross section view of a portion of an embodiment of a tyre in which a metallic reinforcing cord in accordance with the present invention can be used;

[0107] FIG. 2 is a photo of a segment of an embodiment of a metallic reinforcing cord in accordance with the present invention;

[0108] FIG. 3 is a photo of a textile yarn used to make the metallic reinforcing cord of FIG. 2;

[0109] FIG. 3a is a photo of an elongated element used to make a metallic reinforcing cord in accordance with the present invention, such an elongated element comprising the textile yarn of FIG. 3;

[0110] FIG. 4 is a schematic view of a first embodiment of an apparatus for making the metallic reinforcing cord in accordance with the present invention, such an apparatus carrying out a continuous process;

[0111] FIGS. 5a and 5b illustrate a second embodiment of an apparatus for making the metallic reinforcing cord in accordance with the present invention, such an apparatus carrying out a discontinuous process;

[0112] FIG. 6 shows an example of conventional metallic reinforcing cord and various examples of metallic reinforcing cords made in accordance with the present invention; some cross sections of each of the aforementioned reinforcing cords in a respective structural component of the tyre are also illustrated.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0113] For the sake of simplicity, FIG. 1 shows only one side of an embodiment of a tyre 100 for vehicle wheels, the remaining side, which is not represented, being substantially identical and being arranged symmetrically with respect to the equatorial plane M-M of the tyre.

[0114] The tyre 100 illustrated in FIG. 1 is, in particular, a tyre for four-wheeled vehicles.

[0115] More in particular, the tyre 100 is an HP or UHP tyre for sports and/or high or ultra-high performance vehicles.

[0116] In FIG. 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 rotation axis of the tyre 100.

[0117] The tyre 100 comprises at least one support structure 100a and, in a radially outer position with respect to the support structure 100a, a tread band 109 made of elastomeric material.

[0118] The support structure 100a comprises a carcass structure 101, which in turn comprises at least one carcass layer 111.

[0119] Hereinafter, for the sake of simplicity of presentation, reference will be made to an embodiment of the tyre 100 comprising a single carcass layer 111, nevertheless being understood that what is described has analogous application in tyres comprising more than one carcass layer.

[0120] The carcass layer 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 intended to allow the tyre 100 to be anchored on a corresponding mounting rim, not illustrated.

[0121] The carcass layer 111 comprises a plurality of reinforcing cords 10 coated with elastomeric material or incorporated in a matrix of cross-linked elastomeric material.

[0122] The carcass structure 101 is of the radial type, i.e. the reinforcing cords 10 are located on planes comprising the rotation axis R-R of the tyre 100 and substantially perpendicular to the equatorial plane M-M of the tyre 100.

[0123] Each annular reinforcing structure 103 is associated with the carcass structure 101 by folding back (or turning) the opposite end edges of the at least one carcass layer 111 around the bead core 102 and the possible elastomeric filler 104, so as to form the so-called turns 101a of the carcass structure 101.

[0124] In an embodiment, the coupling between carcass structure 101 and annular reinforcing structure 103 can be done through a second carcass layer (not shown in FIG. 1) applied in a radially outer position with respect to the carcass layer 111.

[0125] An anti-abrasion strip 105 is arranged at each annular reinforcing structure 103 so as to wrap around the annular reinforcing structure 103 along the axially inner, axially outer and radially inner areas of the annular reinforcing structure 103, thus being interposed between the latter and the rim of the wheel when the tyre 100 is mounted on the rim. Such an anti-abrasion strip 105 may however not be provided.

[0126] The support structure 100a comprises, in a radially outer position with respect to the carcass structure 101, a crossed belt structure 106 comprising at least two belt layers 106a, 106b arranged in radial juxtaposition over one another.

[0127] The belt layers 106a, 106b respectively comprise a plurality of reinforcing cords 10a, 10b. Such reinforcing cords 10a, 10b have an orientation 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, such an angle is equal to 30.

[0128] The reinforcing cords 10a, 10b of a belt layer 106a, 106b are parallel to each other and have a crossed orientation with respect to the reinforcing cords 10b, 10a of the other belt layer 106b, 106a.

[0129] In ultra-high-performance tyres, the belt structure 106 can be a turned crossed belt structure. Such a belt structure is made by arranging at least one belt layer on a support element and turning the opposite lateral end edges of said at least one belt layer. Preferably, a first belt layer is initially deposited on the support element, then the support element is radially expanded, then a second belt layer is deposited on the first belt layer and finally the opposite axial end edges of the first belt layer are turned onto the second belt layer to at least partially cover the second belt layer, which is the radially outermost one. In some cases, it is possible to arrange a third belt layer on the second belt layer. Advantageously, the turning of the axially opposite end edges of a belt layer on another belt layer radially outside of it provides the tyre with greater reactivity and responsiveness when tackling a bend.

[0130] The support structure 100a comprises, in a radially outer position with respect to the crossed belt structure 106, at least one zero degrees reinforcing layer 106c, commonly known as zero degrees belt. It comprises reinforcing cords 10c oriented in a substantially circumferential direction. Such reinforcing cords 10c thus 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.

[0131] The tread band 109 made of elastomeric material is applied in a radially outer position with respect to the zero degrees belt layer 106c.

[0132] Respective sidewalls 108 made of elastomeric material are also applied on the opposite lateral 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 lateral edges of the tread band 109 up to the respective annular reinforcing structure 103.

[0133] The anti-abrasion strip 105, if present, extends at least up to the respective sidewall 108.

[0134] In some specific embodiments, like the one illustrated and described herein, the rigidity of the sidewall 108 can be improved by providing a stiffening layer 120, generally known as flipper or additional strip-like insert, which has the function of increasing the rigidity and integrity of the annular reinforcing structure 103 and of the sidewall 108.

[0135] The flipper 120 is wound around a respective bead core 102 and the elastomeric filler 104 so as to at least partially surround the annular reinforcing structure 103. In particular, the flipper 120 wraps around the annular reinforcing structure 103 along the axially inner, axially outer and radially inner areas of the annular reinforcing structure 103.

[0136] The flipper 120 is arranged between the turned end edge of the carcass layer 111 and the respective annular reinforcing structure 103. Usually, the flipper 120 is in contact with the carcass layer 111 and the annular reinforcing structure 103.

[0137] In some specific embodiments, like the one illustrated and described herein, the bead structure 103 can also comprise a further stiffening layer 121 that is generally known by the name chafer, or protective strip, and which has the function of increasing the rigidity and integrity of the annular reinforcing structure 103.

[0138] The chafer 121 is associated with a respective turned end edge of the carcass layer 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.

[0139] The flipper 120 and the chafer 121 comprise reinforcing cords 10d (in the attached figures those of the chafer 121 are not visible) coated with an elastomeric material or incorporated in a matrix of cross-linked elastomeric material.

[0140] The tread band 109 has, in a radially outer position, a rolling surface 109a configured to make contact with the ground. Circumferential grooves (not represented in FIG. 1) are formed on the rolling surface 109a, said grooves being connected by transversal notches (not represented in FIG. 1) so as to define on the rolling surface 109a a plurality of blocks of various shapes and sizes (not represented in FIG. 1).

[0141] A sub-layer 107 can be arranged between the zero degrees belt layer 106c and the tread band 109.

[0142] In some specific embodiments, like the one illustrated and described herein, a strip 110 consisting of elastomeric material, commonly known as mini-sidewall, can possibly be provided in the connection area between the sidewalls 108 and the tread band 109. The mini-sidewall 110 is generally obtained through co-extrusion with the tread band 109 and allows an improved mechanical interaction between the tread band 109 and the sidewalls 108.

[0143] Preferably, an end portion of the sidewall 108 directly covers the lateral edge of the tread band 109.

[0144] In the case of tubeless tyres, a layer of elastomeric material 112, generally known as liner, can also be provided in a radially inner position with respect to the carcass layer 111 to provide the necessary impermeability to the inflation air of the tyre 100.

[0145] The carcass layer 111, the crossed belt layers 106a, 106b, the zero degrees belt layer 106, the flipper 120 and the chafer 121 define reinforcing layers of the tyre 100.

[0146] As illustrated in FIG. 2, each of such reinforcing layers comprises opposite interface surfaces S1, S2 that delimit the reinforcing layer with respect to other structural and non-structural components of the tyre 100. The reinforcing cords of each of such reinforcing layer are arranged between the respective opposite interface surfaces.

[0147] Depending on the type of tyre 100, the reinforcing cords 10a and of the belt layers 106a and 106b, the reinforcing cords 10c of the zero degrees belt layer 106c and the reinforcing cords 10d of the chafer 121 can be metallic reinforcing cords 10 made in accordance with the present invention. Such metallic reinforcing cords 10 can also be used in the carcass or belt structure of tyres for motorcycle wheels.

[0148] An example embodiment of a metallic reinforcing cord 10 in accordance with the present invention is illustrated in FIG. 2.

[0149] With reference to such a figure, the metallic reinforcing cord 10 comprises a single metallic wire 11 extending along a longitudinal direction L according to a helical geometry defined by a respective helix having a predetermined winding pitch Pw. The metallic reinforcing cord thus extends longitudinally along a helical path with the aforementioned predetermined winding pitch Pw.

[0150] Basically, the metallic cord 10 consists of the metallic wire 11.

[0151] With reference to FIGS. 3 and 3a, a metallic reinforcing cord in accordance with the present invention is obtained by twisting together, in a conventional twisting machine, the metallic wire 11 and a textile yarn (for example of the type illustrated in FIG. 3) with a twisting pitch equal to the aforementioned winding pitch Pw, to form an elongated element 15 (for example of the type illustrated in FIG. 3a).

[0152] Such an elongated element 15 has a space inside the helix of the metallic wire 11 that is occupied by the textile yarn 20 (which will then be removed). Such a space increases, keeping all other parameters the same, as the diameter of the textile yarn 20 increases (and therefore as the number of filaments and/or pieces that constitute the textile yarn 20 increases) and as the twisting pitch decreases.

[0153] In each cross section of the metallic wire 11 the aforementioned space defines the inner diameter Di of the helix defined by the metallic wire 11. Such an inner diameter Di corresponds to the diameter of the textile yarn 20 in that cross section.

[0154] In the example of FIG. 2, the aforementioned inner diameter Di remains substantially constant in all of the cross sections of the helix defined by the metallic wire 11.

[0155] Such an inner diameter Di is preferably comprised between 0.7 mm and 4 mm, more preferably between 0.8 mm and 3.5 mm, even more preferably between 0.9 mm and 3 mm.

[0156] As will be described hereinafter with reference to FIGS. 4 and 5a, 5b, the textile yarn 20 is intended to be removed from the elongated element 15. After such removal, the metallic wire 11 keeps the same helical geometry that it had before the removal of the textile yarn 20.

[0157] The metallic wire 11 is preferably made of steel. The metallic wire 11 can be made of NT (Normal Tensile) steel, HT (High Tensile) steel, ST (Super Tensile) steel or UT (Ultra Tensile) steel.

[0158] The metallic wire 11 has a carbon content lower than or equal to 1, preferably lower than or equal to 0.9%.

[0159] Preferably, the carbon content is greater than or equal to 0.7%.

[0160] In preferred embodiments, the carbon content is comprised between 0.7% and 1%, preferably between 0.7% and 0.9%.

[0161] The metallic wire 11 is typically coated with brass or another corrosion-resistant coating (for example Zn/Mn).

[0162] The metallic wire 11 has a diameter preferably comprised between 0.08 mm and 0.35 m, more preferably between 0.1 mm and 0.30 mm.

[0163] The textile yarn 20 is preferably made of a water-soluble synthetic polymeric material, even more preferably a polyvinyl alcohol (PVA). Such a textile yarn 20 can be acquired from specialized producers, like for example Kuraray Co., Ltd or Sekisui Specialty Chemicals, or be made by twisting together a plurality of filaments of PVA in a conventional twisting machine.

[0164] The textile yarn 20 has a count preferably greater than, or equal to, 200 dtex, more preferably greater than, or equal to, 700 dtex.

[0165] The textile yarn 20 has a count preferably lower than, or equal to, 4400 dtex, more preferably lower than, or equal to, 1670 dtex.

[0166] In preferred embodiments, the textile yarn 20 has a count comprised between 200 dtex and 4400 dtex, preferably between 700 dtex and 1670 dtex.

[0167] The elongated element 15 can comprise more than one textile yarn 20.

[0168] The metallic wire 11 can be twisted on itself, in the same direction as, or in the opposite direction to, the direction in which it is twisted on the textile yarn 20.

[0169] The winding pitch Pw is preferably comprised between 2 mm and mm, preferably between 5 mm and 35 mm, even more preferably between 10 and 35 mm.

[0170] The metallic wire 11 is twisted together with the textile yarn 20 with the aforementioned winding pitch Pw to form metallic reinforcing cords 10 having different geometries, like for example those illustrated in FIG. 6.

[0171] As illustrated in FIG. 2, the metallic wire 11 of the reinforcing cord 10 is separated from at least one of the interface surfaces S1 and S2 of the respective structural component by a distance lower than or equal to the diameter of the metallic wire 11.

[0172] With reference to FIG. 4, an embodiment of an apparatus and of a process for making the metallic reinforcing cord 10 in accordance with the present invention is described.

[0173] The textile yarn 20 and the metallic wire 11 are taken from respective reels 40 and 30 and fed to a twisting device 60 to be twisted to one another, so as to form the elongated element 15. The twisting device 60 is therefore arranged downstream of the reels 40 and 30 with reference to a feeding direction indicated with A in FIG. 4.

[0174] The elongated element 15 is fed, along said feeding direction A, to a removal device 70 in which the textile yarn 20 is removed from the elongated element 15, thus making the metallic reinforcing cord 10. The removal device 70 is therefore arranged downstream of the twisting device 60 with reference to the feeding direction A.

[0175] In a preferred embodiment of the invention, the removal device 70 comprises a device 73 for feeding a hot water jet configured to hit the elongated element 15, with a hot water jet indeed, in counter-current while the elongated element 15 moves along the feeding direction A. The hot water jet dissolves the textile yarn 20 while such a jet is crossed by the metallic wire 11, which remains the only constituent element of the metallic reinforcing cord 10.

[0176] Preferably, the metallic reinforcing cord 10 thus formed then passes through a drying device 75 to be wound subsequently in a respective collection reel 50, from which it can be taken during the building of the specific structural component of the tyre 100 of interest. The drying device 75 is therefore arranged downstream of the removal device 70 with reference to the feeding direction A.

[0177] In the process described above with reference to FIG. 4, the making of the metallic reinforcing cord 10 takes place without solution of continuity with the making of the elongated element 15 (and therefore with the removal of the textile yarn 20). The metallic reinforcing cord 10 is thus made through a continuous process that, in a time sequence without interruptions or stops, comprises making the elongated element 15 by twisting together the metallic wire 11 and the textile yarn 20, moving the elongated element 15 thus made along the feeding direction A, removing the textile yarn 20, possibly drying the metallic reinforcing cord 10 thus formed and winding it in the collection reel 50.

[0178] It is however possible to make the metallic reinforcing cord 10 in two distinct operative steps, i.e. through a discontinuous process like for example the one illustrated in FIGS. 5a, 5b. Such a process differs from the one described above with reference to FIG. 4 only in that the elongated element 15, once made, is collected in a service reel 45 (FIG. 5a), from which it can be taken when desired to proceed with making the metallic reinforcing cord 10 as described earlier (FIG. 5b). The service reel 45 is thus intended to be arranged downstream of the twisting device 60 when the elongated element 15 is made and upstream of the removal device 70 when the textile yarn 20 is removed from the elongated element 15 to make the metallic reinforcing cord 10.

[0179] The metallic reinforcing cords 10 are intended to be incorporated in a piece of elastomeric material through conventional calendaring processes in conventional rubber-coating machines, thus making the various structural components of the tyre 100 described above.

[0180] The metallic reinforcing cord 10 can be made with different helical geometries depending on the particular intended application (type of tyre of interest or structural component thereof of interest). In order to change the helical geometry it is possible to intervene on one or more of the following parameters: inner diameter of the helix defined by the metallic wire 11, diameter of the metallic wire 11, diameter (or count) of the textile yarn 20 (dependent on the number of filaments and/or ends that constitute the textile yarn 20), winding pitch Pw, number of textile yarns 20.

[0181] Depending on the predetermined helical geometry the metallic reinforcing cord 10 will have different mechanical behavior that provide, in a load-elongation graph, a different curve. All of these curves will have a knee that differentiates the mechanical behavior of the metallic reinforcing cord 10 at low loads and that at high loads.

[0182] It is thus possible to make metallic reinforcing cords 10 having different rigidities, breaking loads, elongations at break and part load elongations.

[0183] In particular, it is possible to make metallic reinforcing cords 10 having part load elongations even equal to 12% and elongations at break even equal to 15%. These values are much higher than those that can be obtained with conventional single-wire metallic reinforcing cords; indeed, the latter typically have part load elongation values not greater than 1.5% and elongation at break values not greater than 4%, in the case of single-wire metallic reinforcing cords subjected to deformation through preforming.

[0184] FIG. 6 illustrates, as an example, two conventional single-wire metallic reinforcing cords, indicated with STD, and respective metallic reinforcing cords 10 made in accordance with the present invention.

[0185] To the left of each of the reinforcing cords illustrated, portions of some cross sections of the structural component that incorporates the respective reinforcing cord are shown and, to the left of such cross sections, the specific construction of the reinforcing cord is shown. Pt indicates the twisting pitch in mm of the reinforcing cords STD, whereas PW indicates the winding pitch in mm of the reinforcing cords 10. In the latter, before the symbol+the number of filaments or pieces that constitute the textile yarn 20 used to make the reinforcing cords 10 is indicated in brackets.

[0186] All the reinforcing cords illustrated in FIG. 6 comprise an UT steel wire having a diameter equal to 0.30 mm.

[0187] The first three reinforcing cords in FIG. 6 have a twisting pitch Pt equal to 10 mm, whereas the last three reinforcing cords have a winding pitch Pw equal to 20 mm. It should be noted that, keeping the other parameters the same, as the twisting/winding pitch Pt/Pw and the inner diameter of the helix increase, the geometry of the reinforcing cord and the position thereof in the structural component of the tyre change.

[0188] In particular, the two reinforcing cords indicated with STD have a slightly wavy geometry (such cords are substantially rectilinear), such geometry being obtained by feeding the metallic wire to a twisting device in which a predetermined twisting pitch Pt is preset, whereas the reinforcing cords 10 have a helical geometry, obtained through the process described above in which use is made, in the step of making the reinforcing cord, of the textile yarn 20.

[0189] Keeping the winding pitch Pw and diameter of the metallic wire the same, the two reinforcing cords 10 differ from one another only due to the different inner diameter of the helix defined by the respective metallic wire (equal to the diameter of the textile yarn 20 used to make the reinforcing cords 10). In particular, keeping the winding pitch Pw and diameter of the metallic wire the same, in one case such an inner diameter is equal to 0.9 mm and is obtained using, in the step of making the reinforcing cord 10, a textile yarn 20 having 18 filaments, whereas in the other case the inner diameter is equal to 1.2 mm and is obtained using, in the step of making the reinforcing cord 10, a textile yarn having 36 filaments.

[0190] It can be noted that the reinforcing cords 10 are more distributed over the entire volume of the structural component, going close to the opposite interface surfaces of the structural component. Differently, the two reinforcing cords STD are always distributed in a same central area of the structural component.

[0191] The Applicant has carried out some comparative tests on samples of the metallic reinforcing cords illustrated in FIG. 6 in order to evaluate the mechanical behavior of such cords. In particular, the breaking load (BL), the elongation at break (AT) and the part load elongation (PLE) were measured by subjecting such cords to a traction test carried out according to methods BISFA E6 and BISFA E7.

[0192] The result of such tests is given in Table 1 below.

TABLE-US-00001 TABLE 1 BL AT PLE (N) (%) (%) 0.30 UT 248 2.3 0.30 P = 10 18 + 0.30 UT 243 2.8 0.70 P = 10 36 + 0.30 UT 238 4.4 1.615 P = 10 0.30 UT 250 2.3 0.32 P = 20 18 + 0.30 UT 246 2.4 0.459 P = 20 36 + 0.30 UT 247 2.8 0.752 P = 20

[0193] It can be noted that, keeping the twisting/winding pitch Pt/Tw and the diameter of the metallic wire the same, the reinforcing cords 10 in accordance with the present invention have a part load elongation much greater than that of conventional metallic reinforcing cords, substantially for the same breaking load. It can also be noted that there is an increase in the elongation at break.

[0194] Such tests confirm the opinion of the Applicant that the metallic reinforcing cords made in accordance with the present invention make it possible to achieve part load elongations and elongations at break higher than those of conventional single-wire metallic reinforcing cords. This is due to the different geometry of the metallic reinforcing cords of the invention with respect to that of conventional single-wire metallic reinforcing cords. The helical geometry also allows the metallic reinforcing cords of the invention to adhere better to the surrounding elastomeric material, substantially reducing the risk for the cords to protrude out of the structural component that incorporates them, even if such cords are arranged closer to the interface surfaces of the structural component.

[0195] The present invention has been described with reference to some preferred embodiments. Different modifications can be brought to the embodiments described above, still remaining within the scope of protection of the invention, defined by the following claims.