Bead wire for a tire, tire and manufacturing method

Abstract

The bead wire (52) comprises several windings of wire and a basic hexagonal bead wire (56) comprising: two axially and radially external lateral rows (F1, F2) of N2 windings, two axially external and radially internal lateral rows (F3, F4) of N2 windings, where N1=N2+1 or N1=N2, two junctions (J1, J2), each formed by a winding that an axially and radially external lateral row (F1, F2) and an axially external and radially internal lateral row (F3, F4), have in common, each winding in common having no winding of wire axially on the outside of it. The bead wire (52) comprises two axially and radially external additional lateral rows (A1, A2) of N3 windings substantially parallel respectively to each axially and radially external lateral row (F1, F2).

Claims

1. A bead wire for a tire substantially of revolution about an axis comprising several windings of at least one wire which are arranged axially next to one another over N layers radially superposed on one another, comprising: a basic hexagonal bead wire comprising: a radially external layer of N1 windings, a radially internal layer of N1 windings, two axially and radially external lateral rows of N2 windings axially opposite one another, two axially external and radially internal lateral rows of N2 windings axially opposite one another, with N1=N2 +1 or N1=N2, and two junctions each one formed by a winding that an axially and radially external lateral row and an axially external and radially internal lateral row have in common, each winding in common forming each junction having no winding of the bead wire axially on the outside of it; and additional windings comprising: axially external and radially internal additional windings, the axially external and radially internal additional windings consisting exclusively of two pairs of axially external and radially internal additional lateral rows, each of the two pairs of axially external and radially internal additional lateral rows having a radially internal winding radially aligned with the radially internal layer of the basic hexagonal bead wire.

2. The bead wire according to claim 1, the additional windings further comprising: two axially and radially external additional lateral rows of N3 windings axially opposite one another, wherein each radially external winding of each axially and radially external additional lateral row is radially substantially aligned with the radially external layer of the basic hexagonal bead wire.

3. The bead wire according to claim 2, wherein, with each axially and radially external additional lateral row comprising N3 windings, N3+1=N2 or N3+2=N2.

4. The bead wire according to claim 1, further comprising at least one axially and radially external additional covering of windings in the overall shape of a U.

5. The bead wire according to claim 4, wherein the axially and radially external additional covering comprises: a radially external additional layer of N4 windings, and substantially parallel to the radially external layer of the basic hexagonal bead wire, and at least two axially and radially external additional lateral rows.

6. The bead wire according to claim 5, wherein N4=N1+1.

7. The bead wire according to claim 1, wherein max(L.sub.i)=N-1, max(L.sub.i)=N or max(L.sub.i)=N+1 where L.sub.i is the number of windings of each layer C.sub.i, i varying from 1 to N inclusive.

8. A bead wire for a tire substantially of revolution about an axis comprising several windings of at least one wire which are arranged axially next to one another over N layers radially superposed on one another, comprising: a basic hexagonal bead wire comprising: a radially external layer of N1 windings, a radially internal layer of N1 windings, two axially and radially external lateral rows of N2 windings axially opposite one another, two axially external and radially internal lateral rows of N2 windings axially opposite one another, with N1=N2+1 or N1=N2, and two junctions each one formed by a winding that an axially and radially external lateral row and an axially external and radially internal lateral row have in common, each winding in common forming each junction having no winding of the bead wire axially on the outside of it; and additional rows comprising: at least two pairs of axially external and radially internal additional lateral rows, each of the at least two pairs of axially external and radially internal additional lateral rows having a radially internal winding radially aligned with the radially internal layer of the basic hexagonal bead wire, the bead wire comprising at least one layer C.sub.k where k ]1, N[ such that L.sub.k+1>L.sub.k and L.sub.k <L.sub.k1.

9. A tire comprising: at least one bead comprising at least one bead wire according to claim 1; and a carcass reinforcement comprising at least one carcass ply anchored in each bead by a turnup around the bead wire.

10. A method of manufacturing a tire according to claim 9, wherein: the bead wire is placed on the carcass ply, a part of the carcass ply is folded around the bead wire, and the carcass ply and the bead wire are turned relative to one another.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be better understood from reading the following description, given solely by way of nonlimiting example and made with reference to the drawings in which:

(2) FIG. 1 is a view in radial section of a tire according to the invention;

(3) FIG. 2 is a detailed view in cross section of region I of the tire of FIG. 1;

(4) FIG. 3 is a view in cross section of a bead wire according to a first embodiment of the invention;

(5) FIGS. 4a, 4b, 4c and 4d are views in cross section illustrating various steps in the method of manufacture according to the invention;

(6) FIGS. 5 to 8 are views similar to that of FIG. 3 of bead wires respectively according to second, third, fourth and fifth embodiments;

(7) FIG. 9 is a view similar to that of FIG. 3 of a bead wire of the prior art;

(8) FIG. 10 is a view similar to that of FIG. 2 of a bead of a tire of the prior art comprising the bead wire of FIG. 9.

DETAILED DESCRIPTION OF THE DRAWINGS

(9) The tire according to embodiments of the invention has a toroidal overall shape about an axis of rotation. This axis of rotation defines the axial direction.

(10) When using the term radial it is appropriate to make a distinction between the various different uses made of this word by those skilled in the art when referring to tires.

(11) Firstly, the expression refers to a radius of the tire. It is in this sense that an element A is said to be radially inside an element B (or radially on the inside of the element B) if it is closer to the axis of rotation of the tire than is the element B. Conversely, an element C is said to be radially outside an element D (or radially on the outside of the element D) if it is further away from the axis of rotation of the tire than is the element D. Progress is said to be radially inwards (or outwards) when it is in the direction towards smaller (or larger) radii.

(12) Secondly, a reinforcing element or a reinforcement is said to be radial when the reinforcing element or the reinforcing elements of the reinforcement make an angle greater than or equal to 65 and less than or equal to 90 with the circumferential direction.

(13) Thirdly, a radial section or radial cross section here means a section or cross section on a plane containing the axis of rotation of the tire.

(14) An axial direction is a direction parallel to the axis of rotation of the tire. An element E is said to be axially inside an element F (or axially on the inside of the element F) if it is closer to the midplane of the tire than is the element F. Conversely, an element G is said to be axially outside an element H (or axially on the outside of the element H) if it is further from the midplane of the tire than is the element H.

(15) The midplane of the tire is the plane which is perpendicular to the axis of rotation of the tire and lies equal distances from the annular reinforcing structures of each bead.

(16) A circumferential direction is a direction which is perpendicular both to a radius of the tire and to the axial direction.

(17) Example of a Tire and Bead Wire According to the Invention

(18) The figures that follow depict directions X, Y, Z corresponding to the usual axial (X), radial (Y) and circumferential (Z) orientations of a tire.

(19) FIGS. 1 and 2 depict an example of a tire according to the invention and denoted by the general reference 10. The tire 10 is preferably intended for an industrial vehicle selected from motor vehicles of the passenger car type, SUVs (Sport Utility Vehicles), two-wheeled vehicles (notably bicycles, motorbikes), heavy vehicles such as heavy goods vehiclesi.e. metro vehicles, buses, road haulage vehicles (lorries, tractors, trailers), off the road vehiclesagricultural vehicles or construction plant vehicles, aircraft, other transport or handling vehicles. In this particular instance, the tire 10 is intended for an agricultural vehicle, for example a tractor.

(20) The tire 10 has a nominal rim diameter as defined by the ETRTO (European Tire and Rim Technical Organisation) of between 24 and 54 inches endpoints inclusive (between 60.96 cm and 137.16 cm). The tire 10 has a nominal aspect ratio as defined by the ETRTO of between 0.7 and 0.9, endpoints inclusive.

(21) The tire 10 comprises a crown 12 comprising a crown reinforcement 14 comprising one or more crown plies 16 of reinforcing elements. The crown reinforcement 14 is surmounted by a tread 18. The crown reinforcement 14 is arranged radially in the inside of the tread 18. Two sidewalls 20 extend the crown 12 radially inwards. The tire 10 comprises two beads 22 radially on the inside of the sidewalls 20 and each comprising an annular reinforcing structure 24.

(22) The tire 10 also comprises a radial carcass reinforcement 26. The carcass reinforcement 26 extends from the beads 22 through the sidewalls 20 towards the crown 12. The carcass reinforcement 26 comprises one or more carcass plies 28, at least one of these carcass plies 28 being anchored in each of the beads 22 by being folded 30 around the annular reinforcing structure 24 to form, within each bead 22, a main strand 32 extending radially between each bead 22 through the sidewalls 20 and the crown 12, and a turnup 34 extending radially from each bead 22 through each sidewall 20, the radially external end 36 of the turnup 34 being situated radially on the outside of the annular reinforcing structure 24 and axially on the outside of the main strand 32.

(23) The tire 10 also comprises an airtight inner ply 38 arranged radially and axially on the inside of the carcass reinforcement 26. The inner ply 38 extends between each bead 22, passing via the sidewalls 20 and the crown 12.

(24) Each bead 22 comprises, in addition to the annular reinforcing structure 24, a mass 40 of filling rubber arranged in a space delimited by the main strand 32 and the turnup 34. Each bead 22 also comprises a first mass 42 of cushioning rubber protecting the bead 22 around the folding 30 of the carcass reinforcement 26.

(25) In addition, each bead 22 also comprises a mass 44 of filling rubber arranged axially outside the carcass reinforcement 26, particularly axially outside the turnup 34. Each sidewall 20 comprises a mass 46 of axially external rubber delimiting an axially external surface 48 of the sidewall 20 and arranged axially on the outside of the mass 44 of filling rubber. Finally, each bead 22 comprises a second mass 50 of cushioning for the bead 22, arranged axially between the mass 44 of filling rubber and the axially external mass 46 of rubber of the sidewall 20.

(26) Each annular reinforcing structure 24 comprises an annular bead wire 52 coated in an encasing mass 54, for example containing rubber. The bead wire 52 is arranged radially on the inside of the mass 40 of filling rubber. The bead wire 52 is in accordance with a first embodiment of the invention.

(27) FIG. 3 depicts the bead wire 52 according to the first embodiment of the invention.

(28) The bead wire 52 has an overall shape of revolution about the axis of revolution of the tire 10 which is substantially parallel to the axial direction X.

(29) The bead wire 52 has an axial plane of symmetry Pa, namely a plane of symmetry that is perpendicular to the axial direction X (parallel to the midplane M).

(30) The bead wire 52 comprises P windings of at least one wire which are arranged axially next to one another over N layers C.sub.i radially superposed on one another. The bead wire 52 is obtained by successive superpositions of the N layers C.sub.i with i varying from 1 to N inclusive, each layer C.sub.i being obtained by axially successive windings of at least one wire. The total number of windings P of the bead wire 52 is greater than or equal to 30, preferably greater than or equal to 50, and more preferably, greater than or equal to 70 and here P=166.

(31) In the example of FIG. 3, the bead wire 52 comprises P windings of a single wire. For preference, the wire is made of metal, has a substantially circular cross section and advantageously a diameter of between 1 and 3.2 mm, preferably between 1.2 and 2.2 mm, and more preferably, between 1.2 and 2 mm, here a diameter equal to 1.55 mm. The wire is made of a carbon steel containing 0.7 wt % of carbon.

(32) The bead wire 52 thus comprises, starting from the radially innermost layer C.sub.1 to the radially outermost layer C.sub.N, N radially successive layers with N5, preferably N7 and more preferably N9, and here N=13.

(33) Table 1 below collates the number of windings L.sub.i of each layer C.sub.i. The maximum number of windings max(L.sub.i) of the N layers C.sub.i is such that max(L.sub.i)4, preferably max(L.sub.i)6, and more preferably, max(L.sub.i)9. Here, max(L.sub.i)=14. In addition, max(L.sub.i)=N1, max(L.sub.i)=N or max(L.sub.i)=N+1. Here, max(L.sub.i)=N+1.

(34) TABLE-US-00001 TABLE 1 Number of the Number of layer Ci windings Li C1 12 C2 13 C3 14 C4 13 C5 14 C6 13 C7 14 C8 13 C9 14 C10 13 C11 12 C12 11 C13 10

(35) The bead wire 52 comprises at least one layer C.sub.k where k ]1, N[ such that L.sub.k+1>L.sub.k and L.sub.k<L.sub.k1. In addition, for i varying from 1 to N inclusive, |L.sub.k+1L.sub.k|=1. Furthermore, for each layer C.sub.k, where k ]1, N[ such that L.sub.k+1>L.sub.k and L.sub.k<L.sub.k1, L.sub.k+1=L.sub.k+1 and L.sub.k+1=L.sub.k1. Here, each layer C.sub.4, C.sub.6 and C.sub.8 comprises L.sub.4=L.sub.6=L.sub.8=13 windings and each layer C.sub.3, C.sub.5, C.sub.7 and C.sub.9 comprises L.sub.3=L.sub.5=L.sub.7=L.sub.9=14 windings.

(36) The bead wire 52 comprises a base bead wire 56 of which the windings are depicted in the various FIGS. 3 and 5-8 by circles filled with a pattern of crosshatching. The bead wire 56 has an axial plane of symmetry Pa, namely a plane of symmetry perpendicular to the axial direction X (parallel to the midplane M). The bead wire 56 also has a radial plane of symmetry Pr, namely a plane of symmetry perpendicular to the radial direction Y.

(37) The base bead wire 56 has a hexagonal shape, namely a shape comprising six sides each one defined by a layer or a row of windings each one meeting the next at six junctions J1 to J6 each one formed by a winding that a layer and a row or two rows that form the corresponding junction have in common.

(38) Thus, the base bead wire 56 comprises a radially internal side defined by a radially internal layer C.sub.inf of N1 windings and a radially external side defined by a radially external layer C.sub.sup of N1 windings. The base bead wire 56 also comprises two radially external axial sides each one defined by an axially and radially external lateral row F1, F2 of N2 windings. The base bead wire 56 additionally comprises two radially internal axial sides each one defined by an axially external and radially internal lateral row F3, F4 of N2 windings. The pairs of radially external and internal axial sides are axially opposite one another, namely face one another about the axial direction X.

(39) N1=N2+1 or N1=N2 and here N1=N2+1. Specifically, N1=8 and N2=7.

(40) Each junction J1, J2 is formed by a winding that each axially and radially external lateral row F1, F2 and each axially external and radially internal lateral row F3, F4 have in common. Each winding in common that forms each junction J1, J2 has no winding of the wire axially on the outside of it.

(41) Each junction J3, J4 is formed by a winding that each axially and radially external lateral row F1, F2 and the radially external layer C.sub.sup have in common.

(42) Each junction J5, J6 is formed by a winding that each axially external and radially internal lateral row F3, F4 and the radially external layer C.sub.inf have in common.

(43) The bead wire 52 also comprises at least two axially and radially external additional lateral rows A1, A2 of N3 windings. Each axially and radially external additional lateral row A1, A2 is substantially parallel respectively to each axially and radially external lateral row F1, F2.

(44) Each axially and radially external additional lateral row A1, A2 is arranged axially on the outside respectively of each axially and radially external lateral row F1, F2. Here N3=5.

(45) In this embodiment, each axially and radially external additional lateral row A1, A2 comprises a radially external winding a1, a2 radially substantially aligned with the radially external layer C.sub.sup.

(46) N3N2 and for preference N3=N2, N3+1=N2 or N3+2=N2. In this instance, N3+2=N2.

(47) In this embodiment, the bead wire 52 also comprises at least two axially external and radially internal additional lateral rows B1, B2, B3, B4. The bead wire 52 comprises two pairs of axially external and radially internal additional lateral rows, B1, B2 on the one hand, and B3, B4 on the other hand, of N5 and N6 windings respectively. Each axially external and radially internal additional lateral row B1, B3 on the one hand, and B2, B4 on the other hand, is substantially parallel respectively to each axially external and radially internal lateral row F3, F4.

(48) Each axially external and radially internal additional lateral row, B1, B3 on the one hand, and B2, B4 on the other hand, is arranged axially on the outside respectively of each axially external and radially internal lateral row B3, F4. Each axially external and radially internal additional lateral row B3, B4 is arranged axially on the outside respectively of each axially external and radially internal additional lateral row B1, B2.

(49) In this embodiment, each axially external and radially internal additional lateral row B1, B2, B3, B4 comprises a radially internal winding b1, b2, b3, b4 radially substantially aligned with the radially internal layer C.sub.inf.

(50) N5N6, preferably N5>N6 and here N5=N6+2 with N5=5 and N6=3. Also, N5N2, preferably N5=N2, N5+1=N2 or N5+2=N2 and here N5+2=N2.

(51) Also, max(L.sub.i)N16.

(52) The windings of the additional lateral rows A1, A2, B1, B2, B3 and B4 are depicted as circles filled with a pattern of parallel hatching.

(53) Example of the Method According to the Invention

(54) A method of manufacturing a tire according to the invention will now be described with reference to FIGS. 4a to 4d.

(55) First of all, in a first tire-building phase, the various plies, masses of rubber and other elements described hereinabove are built up to form a green tire on a tire-building drum already known to those skilled in the art.

(56) Thus, the first mass 42 of cushioning rubber, airtight inner ply 38, one or more carcass plies 28 intended to be anchored in the bead 20, the mass 40 of filling rubber and the annular reinforcing structure 24 comprising the bead wire 52 and the encasing mass 54 are laid in succession and in that order. Thus, the bead wire 52 has been placed on the carcass ply or plies 28. This results in the intermediate green tire form depicted in FIG. 4a.

(57) The first mass 42 of cushioning rubber and part of the carcas ply or plies 28, in this instance the turnup 34, is then folded around the annular reinforcing structure 24. This then results in the intermediate green tire form depicted in FIG. 4b.

(58) Next, the mass 44 of filling rubber, the second cushioning mass 50 and finally the axially external mass 46 of rubber delimiting the axially external surface 48 of the sidewall 20 are placed in succession and in that order. This then results in the intermediate green tire form depicted in FIG. 4c.

(59) Finally, the carcass ply or plies 28 and the bead wire 52 are turned relative to one another. In this instance, the entire intermediate green tire form with the exception of the annular reinforcing structure 24 is turned about the latter which remains substantially fixed during rotation. As an alternative, the bead wire 52 could be turned keeping the remainder of the green tire form fixed. This then results in the intermediate green tire form depicted in FIG. 4d. It may be noted that following the rotation, the bead wire 52 has the same orientation that it had before rotation and that the various plies and masses of rubber have not been deformed under the effect of the rotation.

(60) In a subsequent second finishing phase, the crown 12 and the tread 18 are added to the intermediate green tire form previously obtained.

(61) In a third, curing, phase, the final green tire is cured in order to obtain the cured tire.

(62) Other Examples of Bead Wires According to the Invention

(63) FIGS. 5, 6, 7 and 8 depict bead wires according to other embodiments of the invention. In these figures, elements similar to those of FIG. 3 are denoted by identical references.

(64) FIG. 5 depicts a bead wire according to a second embodiment of the invention.

(65) Unlike the bead wire according to the first embodiment, the bead wire 52 according to the second embodiment comprises N=10 layers and P=83 windings.

(66) Table 2 below collates the number of windings L.sub.i of each layer C.sub.i. max(L.sub.i)=N=10.

(67) TABLE-US-00002 TABLE 2 Number of the Number of layer Ci windings Li C1 6 C2 7 C3 8 C4 9 C5 10 C6 9 C7 10 C8 9 C9 8 C10 7

(68) The bead wire 52 comprises at least one layer C.sub.k where k ]1, N[ such that L.sub.k+1>L.sub.k and L.sub.k<L.sub.k1. Furthermore, for each layer C.sub.k where k ]1, N[ such that L.sub.k+1>L.sub.k and L.sub.k<L.sub.k1, L.sub.k+1=L.sub.k+1 and L.sub.k+1=L.sub.k1. Here, the layer C.sub.6 comprises L.sub.6=9 windings and each layer C.sub.5, C.sub.7 comprises L.sub.5=L.sub.7=10 windings.

(69) The base bead wire 56 is such that N1=N2+1. Specifically, N1=6, N2=5.

(70) Unlike the bead wire of the first embodiment, the bead wire 52 according to the second embodiment comprises at least one axially and radially external additional covering D.sub.sup of windings in the overall shape of a U. The windings of the axially and radially external additional covering D.sub.sup are depicted as circles filled with a pattern of parallel hatching.

(71) The windings of the axially and radially external additional covering D.sub.sup are arranged axially on the outside of each axially external lateral row and radially on the outside of the radially external layer C.sub.sup.

(72) The axially and radially external additional covering D.sub.sup comprises a radially external additional layer E.sub.sup of N4 windings, substantially parallel to the radially external layer C.sub.sup. The additional layer E.sub.sup is radially arranged on the outside of the radially external layer C.sub.sup. The bead wire 52 according to the second embodiment is such that N4=N1+1.

(73) The axially and radially external additional covering D.sub.sup also comprises two axially and radially external additional lateral rows A1, A2 of N3 windings. Each additional lateral row A1, A2 is substantially parallel respectively to each axially and radially external lateral row F1, F2. Each axially and radially external additional lateral row A1, A2 is arranged axially on the outside respectively of each axially and radially external lateral row F1, F2.

(74) Here, N3=4. N3N2 and here N3+1=N2.

(75) Also, max(L.sub.i)N16.

(76) FIG. 6 depicts a bead wire according to a third embodiment of the invention.

(77) The bead wire 52 according to the third embodiment comprises N=7 layers and P=42 windings.

(78) Table 3 below collates the number of windings L.sub.i of each layer C.sub.i. max(L.sub.i)=N=7.

(79) TABLE-US-00003 TABLE 3 Number of the Number of layer Ci windings Li C1 5 C2 6 C3 7 C4 6 C5 7 C6 6 C7 5

(80) The bead wire 52 comprises at least one layer C.sub.k where k ]1, N[ such that L.sub.k +1>L.sub.k and L.sub.k<L.sub.k1. Furthermore, for each layer C.sub.k where k ]1, N[ such that L.sub.k+1>L.sub.k and L.sub.k<L.sub.k1, L.sub.k+1=L.sub.k+1 and L.sub.k+1=L.sub.k1. Here, the layer C4 comprises L.sub.4=6 windings and each layer C.sub.3, C.sub.5 comprises L.sub.3=L.sub.5=7 windings.

(81) The bead wire 52 according to the third embodiment is such that N1=N2+1. Specifically, N1=4 and N2=3. Additionally, N3N2 and here N3=N2=3. Furthermore, N4=N1+1 with N4=5 and N1=4.

(82) Unlike the bead wire according to the second embodiment, the bead wire 52 according to the third embodiment comprises at least one axially external and radially internal additional covering D.sub.inf of windings in the overall shape of a U. The windings of the axially external and radially internal additional covering D.sub.inf are depicted as circles filled with a pattern of parallel hatching.

(83) The windings of the axially external and radially internal additional covering D.sub.inf are arranged axially on the outside of each axially internal and radially external lateral row and radially on the inside of the radially internal layer C.sub.inf.

(84) The axially external and radially internal additional covering D.sub.inf comprises a radially internal additional layer E.sub.inf of N7 windings substantially parallel to the radially internal layer C.sub.inf. The radially internal additional layer E.sub.inf is arranged radially on the inside of the radially internal layer C.sub.inf.

(85) The axially external and radially internal additional covering D.sub.inf also comprises two axially external and radially internal additional lateral rows B1, B2 of N5 windings. This axially external and radially internal additional lateral row B1, B2 is substantially parallel respectively to each axially external and radially internal lateral row F3, F4. Each axially external and radially internal additional lateral row B1, B2 is axially arranged on the outside respectively of each axially external and radially internal lateral row F3, F4.

(86) N5N2, and here, N5=N2=3 and N7=N1+1 with N7=5.

(87) Also, max(L.sub.i)N16 and preferably max(L.sub.i)N12.

(88) FIG. 7 depicts a bead wire according to a fourth embodiment of the invention.

(89) The bead wire 52 according to the fourth embodiment comprises N=7 layers and P=35 windings.

(90) Table 4 below collates the number of windings L.sub.i of each layer C.sub.i. max(L.sub.i)=N1=6.

(91) TABLE-US-00004 TABLE 4 Number of the Number of layer Ci windings Li C1 4 C2 5 C3 6 C4 5 C5 6 C6 5 C7 4

(92) The bead wire 52 comprises at least one layer C.sub.k where k ]1, N[ such that L.sub.k+1>L.sub.k and L.sub.k<L.sub.k1. Furthermore, for each layer C.sub.k where k ]1, N[ such that L.sub.k+1>L.sub.k and L.sub.k<L.sub.k1, L.sub.k+1=L.sub.k+1 and L.sub.k+1=L.sub.k1. Here, the layer C.sub.4 comprises L.sub.4=5 windings and each layer C.sub.3, C.sub.5 comprises L.sub.3=L.sub.5=6 windings.

(93) Unlike the bead wire 52 according to the third embodiment, N1=N2=3. In addition, N3N2 and here N3=N2=3. Furthermore, N4=N1+1 with N4=4 and N1=3. Also, N5N2 and here N5=N2=3 and N7=N1+1 with N7=4. Also, max(L.sub.i)N16 and preferably N1max(L.sub.i)2.

(94) FIG. 8 depicts a bead wire according to a fifth embodiment of the invention.

(95) The bead wire 52 according to the fifth embodiment comprises N=12 layers and P=35 windings. N1=N2=6.

(96) Table 5 below collates the number of windings L.sub.i of each layer C.sub.i. max(L.sub.i)=N=12.

(97) TABLE-US-00005 TABLE 5 Number of the Number of layer Ci windings Li C1 10 C2 11 C3 12 C4 11 C5 12 C6 11 C7 12 C8 11 C9 10 C10 9 C11 8 C12 7

(98) The bead wire 52 comprises at least one layer C.sub.k where k ]1, N[ such that L.sub.k+1>L.sub.k and L.sub.k<L.sub.k1. Furthermore, for each layer C.sub.k, where k ]1, N[ such that L.sub.k+1>L.sub.k and L.sub.k<L.sub.k1, L.sub.k+1=L.sub.k+1 and L.sub.k+1=L.sub.k1. Here, each layer C.sub.4, C.sub.6 comprises L.sub.4=L.sub.6=11 windings and each layer C.sub.3, C.sub.5, C.sub.7 comprises L.sub.3=L.sub.5=L.sub.7=12 windings.

(99) In a similar way to the bead wire according to the second embodiment of FIG. 5, the bead wire 52 according to the fifth embodiment comprises an axially and radially external additional covering D.sub.sup of windings in the overall shape of a U.

(100) The axially and radially external additional covering D.sub.sup comprises a radially external additional layer E.sub.sup of N4 windings, substantially parallel to the radially external layer C.sub.sup. The radially external additional layer E.sub.sup is radially arranged on the outside of the radially external layer C.sub.sup.

(101) The axially and radially external additional covering D.sub.sup also comprises two axially and radially external additional lateral rows A1, A2 of N3 windings substantially parallel respectively to each axially and radially external row F1, F2. Each axially external and radially internal additional lateral row A1, A2 is axially arranged on the outside respectively of each axially external and radially internal lateral row F1, F2.

(102) The bead wire 52 according to the second embodiment is such that N3N2 and here N3=N2=6. Furthermore N4=N1+1 with N4=7 and N1=6.

(103) In a similar way to the bead wire according to the first embodiment, the bead wire 52 according to the fifth embodiment also comprises two pairs of axially external and radially internal additional lateral rows, B1, B2 on the one hand, and B3, B4 on the other hand, respectively of N5 and N6 windings.

(104) In this embodiment, each axially external and radially internal additional lateral row B1, B2, B3, B4 comprises a radially internal winding b1, b2, b3, b4 radially substantially aligned with the radially internal layer C.sub.inf.

(105) The axially external and radially internal additional lateral rows, B1, B2, on the one hand, and B3, B4 on the other hand, are respectively substantially parallel to each axially external and radially internal row F3, F4. Each axially external and radially internal additional lateral row, B1, B2 on the one hand, and B3, B4 on the other hand, is axially arranged on the outside respectively of each axially external and radially internal lateral row F3, F4.

(106) N5N96, preferably N5>N6 and here N5=N6+2 with N5=5 and N6=3. Also, N5N2 and here N5+1=N2.

(107) Also max(L.sub.i)N16.

COMPARATIVE TESTS AND TRIALS

(108) Performance of the Method of Manufacture

(109) FIG. 9 depicts a bead wire 100 of the prior art. This bead wire has none of the features essential to the invention that allow easy relative rotation of the bead wire with respect to the carcass ply.

(110) FIG. 10 depicts a tire 200 of the prior art comprising a bead wire 100 and manufactured by employing steps similar to the steps described with reference to FIGS. 4a to 4d. The tire 200 has defects that have been deliberately exaggerated for the purposes of illustrating the advantages of the invention.

(111) Note the presence of the region in which the turnup 34 and the masses of rubber 44, 46 and 50 arranged axially on the outside of the turnup have been placed in compression. The overtensioning of the main strand 32 causes the windings in contact with the main strand 32 but also those in contact with the turnup 34 to become disorganized. In addition, the relative rotation falls short by an angle .

(112) Comparing FIG. 2 (or 4d) and 10, it may be noted that use of the method of manufacture according to the invention leads to a tire that does not have the potential defects unlike the tire 200.

(113) Tire-Rim Slip Performance

(114) The tire-rim slip performance of each tire was tested. Specifically, in order for the tire to be able to transfer all of the force applied by the engine or motor of the vehicle to the ground, it is preferable that the tire-rim slip be as low as possible.

(115) The co-efficient of friction between the rim and tire is therefore measured. To do so, use is made of a vehicle with a total mass of 2 tonnes provided with two tires to be tested. A weight of equal mass, in this instance 2 tonnes, is then hauled over bitumen. Between the weight that is to be hauled and the vehicle is positioned a dynamometric sensor that enables the force F, expressed in kg applied by the vehicle to the weight to be hauled to be measured as the tire begins to slip relative to the rim. Thus, for a force F=500 kg applied in order to cause the tire to slip relative to the rim, a co-efficient of friction =0.5 is obtained. A score of between 0 and 5.0 is assigned according to the force recorded, zero indicating a tire exhibiting a great deal of tire-rim slip and 5 indicating a tire with the best possible tire-rim slip performance. The results of these tests are collated in Table 6 below.

(116) TABLE-US-00006 TABLE 6 Bead wire Score 100 5 52 - FIG. 3 5 52 - FIG. 5 3 52 - FIG. 6 5 52 - FIG. 7 4 52 - FIG. 8 5

(117) The scores of 4 and 5 are considered to indicate a low tire-rim slip and therefore that the corresponding tires meet the required tire-rim slip performance criterion. Note that all the tires according to the invention, with the exception of the tire according to the second embodiment, have a score of 4 or higher.

(118) Thus, the tires according to the invention of FIGS. 3, 6, 7 and 8 make it possible to avoid the need to take special precautions during the method of manufacture and exhibit low tire-rim slip.

(119) The invention is not restricted to the embodiments described hereinabove.

(120) Thus, the axially and radially external additional covering D.sub.sup may comprise several radially external additional layers E.sub.sup substantially parallel to the radially external layer C.sub.sup as well as several pairs of axially and radially external additional lateral rows.

(121) The features of the various embodiments described hereinabove may be combined in so far as they are mutually compatible.