TIRE COMPRISING A PAIR OF FLEXIBLE BEAD CORES

Abstract

A tire comprises a pair of flexible bead wires (51) of reduced mass. Each bead wire (51) has the form of a closed circumferential ring, bracing the bead of the tire (1) against the rim (100) and comprising a first part made of a first material M1 taking the form of textile cords (560), the first part interacting with a second part of the bead wire (51) made of a reinforcing second material M2; the tensile stiffness is comprised between 4.510.sup.5 N/m and 1.810.sup.6 N/m; the circumferential bending stiffness, Kf, is greater than or equal to Kr*(1000*D/(16*25.4)).sup.3, where D is the diameter of the wheel on which the tire is mounted, measured at the seat (110) of the rim (100) in meters, and where Kr is equal to 2.10.sup.2 N.m.sup.2; and the elastic elongation of the bead wire (51) is greater than or equal to 2%.

Claims

1.-16. (canceled)

17. A tire for a motor vehicle, comprising the following in a meridian plane: two beads intended to be mounted on a rim; two sidewall layers connected to the beads; a crown having a tread, the crown having a first side connected to a radially outer end of one of the two sidewall layers and a second side connected to a radially outer end of an other one of the two sidewall layers; at least one carcass reinforcement extending from the two beads as far as the crown, the at least one carcass reinforcement having a plurality of carcass reinforcing elements and being anchored in the two beads by way of a turn-up around a bead wire, so as to form a main part and a turn-up in each bead, wherein, in each bead, the bead wire has a form of a closed circumferential ring, bracing the bead of the tire against a rim and comprising a first part made up of a first material M1 taking a form of textile cords, the first part interacting with a second part of the bead wire made up of a reinforcing second material M2, wherein a tensile stiffness of the bead wire is comprised between 4.510.sup.5 N/m and 1.810.sup.6 N/m, wherein a circumferential bending stiffness of the bead wire, Kf, is greater than or equal to Kr*(1000*D/(16*25.4)).sup.3, where D is a diameter of a wheel on which the tire is mounted, measured at a seat of the rim in meters, and where Kr is equal to 2.10.sup.2 N.m.sup.2, and wherein an elastic elongation of the bead wire is greater than or equal to 2%.

18. The tire according to claim 17, wherein a tensile elastic modulus of the first material M1 is comprised between 10 GPa and 120 GPa.

19. The tire according to claim 17, wherein a compression elastic modulus of the second material M2 is comprised between 1 GPa and 10 GPa.

20. The tire according to claim 19, wherein the second part of the bead wire made up of the material M2 is wound around the first material M1 of the first part of the bead wire, so as to form a sheathing of the first material M1, and wherein the bead wire is obtained by a stack of layers of the cord thus sheathed.

21. The tire according to claim 17, wherein the second part of the bead wire made up of the material M2 is an internal core, and wherein the first part of the bead wire made up of the material M1, in the form of textile cords, is wound around the internal core.

22. The tire according to claim 5, wherein a geometry of the internal core in a meridian section of the bead wire is in a shape of a cross having 3 to 6 arms.

23. The tire according to claim 21, wherein a geometry of the internal core in a meridian section of the bead wire has an L shape, or a U shape or an H shape, or is circular, or polygonal with at least 3 sides.

24. The tire according to claim 21, wherein the second material M2 making up the internal core of the bead wire is of the thermoset type.

25. The tire according to claim 17, wherein the textile cord is obtained by twisting a twist T2 of N strands of a textile material in a given direction D1, with N1, each strand resulting from overtwisting a twist T1 of a spun yarn of the textile material in an opposite direction D2.

26. The tire according to claim 25, wherein the spun yarns are made up of a hybrid assembly of filaments of textile materials.

27. The tire according to claim 26, wherein the spun yarns are made up of an assembly of aramid filaments.

28. The tire according to claim 27, wherein the number N of strands for the twisting is comprised between 2 and 6.

29. The tire according to claim 28, wherein the overtwisting twist T1 and the twisting twist T2 are identical, and less than 500 turns per meter.

30. The tire according to claim 29, wherein an external layer around an internal core of the bead wire is made up of 15 to 70 aramid cords.

31. The tire according to claim 17, wherein the bead comprises at least one sidewall layer and one protective layer, and wherein the sidewall and protective layers of the bead are made up of the same elastomer material.

32. The tire according to claim 17, wherein a filler layer is made up of a composite material comprising textile filaments associated with an elastomer matrix.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0081] Further details and advantageous features of the invention will become apparent in the following text from the description of the exemplary embodiments of the invention, with reference to the figures, which represent schematic views of a tyre, and bead wires according to the embodiments of the invention. In order to make them easier to understand, the figures are not shown to scale.

[0082] FIG. 1 comprises a view 1-A which shows a cross section through a tyre of the invention in a meridian plane, and a view 1-B which represents an enlarged view of a portion of the meridian view 1-A surrounded by a dashed circle showing an enlarged view of the area of the bead containing a bead wire of a tyre of the invention.

[0083] FIG. 2-A is a metallic bead wire of the prior art. FIGS. 2-B, 2-C and 2-D show embodiments of the invention with cross-sectional views through the bead wire in a meridian plane. In these embodiments, an annular base element is made of the first material of the first part of the bead wire, that is to say a textile cord which occupies the interior space. The second material occupies the peripheral space, so as to form a sheath around the textile-cord material.

[0084] FIGS. 3-A, 3-B, 3-C and 3-F represent further embodiments of the invention, showing textile cords associated with a stiff homogeneous material of variable geometric shape making up a core around which the textile cords are wound.

DETAILED DESCRIPTION OF THE INVENTION

[0085] The invention was implemented on a passenger vehicle tyre of size 245/45R18 in accordance with the specifications of the ETRTO (European Tyre and Rim Technical Organisation) standard. Such a tyre can carry a load of 800 kilos, inflated to a pressure of 250 kPa.

[0086] In FIG. 1-A, the tyre of overall reference 1 comprises a carcass reinforcement 90 consisting of reinforcers coated in a rubber composition, and two beads 50 in contact with a rim 100. A region 49 delimited by a dashed circle defines a lower region of the tyre, an enlarged view of which is given in FIG. 1-B. The carcass reinforcement 90 is anchored in each of the beads 50. The tyre further comprises a crown reinforcement 20 comprising two working layers 21, 22 and a hooping layer 23. Each of the working layers 21 and 22 is reinforced by filamentary reinforcing elements which are parallel within each layer and crossed from one layer to the next, forming angles of between 10 and 70 with the circumferential direction. The hooping layer 23 is positioned radially outside the crown reinforcement 20, this hooping layer 23 being formed of reinforcing elements oriented circumferentially and wound in a spiral. A tread 10 is placed radially on the outside of the hooping layer 23; it is this tread 10 which provides the contact between the tyre 1 and the ground. The tyre 1 depicted is a tubeless tyre: it comprises an inner liner 95 made from a rubber composition impermeable to the inflation gas, covering the inner surface of the tyre.

[0087] The part of the rim 100 that interacts with the tyre within the scope of the invention is axisymmetric relative to the axis of rotation of the tyre.

[0088] In a meridian plane, the rim 100 comprises at least one flange 120 located at one axial end and connected to a seat 110 that is intended to receive the radially innermost face of the bead. A rectilinear portion 130 that connects the rim flange 120 to the seat 110 via fillets is located between the seat 110 and the flange 120. The flange 120 of the rim extended by the rectilinear portion 130 axially limits the movement of the beads during inflation.

[0089] FIG. 1-B shows a lower region of overall reference 55 containing the sidewall layer 30 and the bead 50. The contour of the lower region follows the outer contours of at least part of the sidewall layer 30 and the outer contour of the bead 50.

[0090] Said bead 50 partially comprises a carcass reinforcement 90 that comprises a main part 52, and is then wrapped around a bead wire 51 to form a turn-up 53. A filler layer 70 is positioned between the main part 52 of the carcass reinforcement 90 and its turn-up 53.

[0091] Depending on the embodiment, the bead 50 can comprise a lateral reinforcing layer 60, positioned axially outside the turn-up 53 and axially inside the sidewall layer 30. Axially innermost from the bead 50, an airtight layer 95 forms the inner wall in contact with the internal inflation air.

[0092] Said bead 50 also comprises a protective layer 80 that is in axially outer contact with a rectilinear portion 130 of the rim so as to limit the axial movement of the bead. Said protective layer 80 also comprises a portion intended to be in contact with the rim on the rim seat 110. A sidewall layer 30 interacts with the bead 50 and forms an outer lateral wall.

[0093] FIG. 2-A represents a meridian section of a bead wire 51 of the prior art, made up of a steel central core 520 surrounded by metallic cords 510.

[0094] FIG. 2-B represents a bead wire of the invention of hexagonal cross section. The textile cords 560 are surrounded by a sheath made of the second material 550. A transverse winding method is used to manufacture the bead wire from the sheathed cord. The bead wire is obtained by winding a turn around a support with lateral movement by a distance equal to the diameter of the sheathed cord. At the end of the process, the bead wire results from the assembly of multiple layers of sheathed cords which are bonded to one another, giving the bead wire a certain stiffness.

[0095] FIG. 2-C shows an enlarged view of the sheathed cord. The sheath 550 surrounds the cord 560.

[0096] FIG. 2-D shows a bead wire of the invention in which the first material M1 in the form of textile spun yarns is dispersed in a matrix made of the second material M2. The matrix may be made of a polylactic polymer (PLA), or a nylon (polyamide 6-6: PL66), or vinyl ester. PA66 has a compression modulus of 2.7 GPa and an elongation at break of 70%.

[0097] FIGS. 3-A, 3-B, 3-C and 3-D are embodiments in which the bead wire has a core of variable geometry in a meridian section. The core made of the material M2 is referenced 555, and the textile cords are referenced 560. FIG. 3-F is a view in the circumferential direction showing the winding of the textile cords around an internal core.

[0098] Configurations of tyres of the invention were tested in order to clearly highlight the performance offered by the invention. The results of these tests were compared with those obtained on control tyres.

[0099] The results for the tyre of the invention were compared with those of a control having the same size and provided with a braided metallic bead wire.

[0100] The bead wire of the control T comprises a mild steel core with 0.1% carbon, and a layer of metallic cords twisted around said core. The threads of the cords are made of steel with 0.7% carbon. The core has a diameter of 215 hundredths of a millimeter and each metallic cord around the core has a diameter of 130 hundredths of a millimeter. The total diameter of the bead wire (core+layers of cords included) is 4.79 mm. The mass of such a bead wire is 169 g. It is illustrated in FIG. 2-A.

[0101] The first tyre P1 in accordance with the invention reprises the specifications of the control T, but the bead wire is composed of sheathed textile cords. The cord is obtained after twisting two strands each having a linear density of 167 tex. Each strand is the result of overtwisting a spun yarn with 315 turns per meter. The twist during the twisting phase is also 315 turns per meter.

[0102] The sheath of the cord is made of polyamide 6-6, and the geometry of the bead wire is hexagonal as depicted in FIG. 2-B. The cross section of the sheathed cord is 0.55 mm.sup.2, and the total cross section of the bead wire is 24 mm.sup.2. The bead wire is obtained after a transverse winding operation of 45 turns. The mass of this bead wire is 35 grammes.

[0103] Lastly, the second tyre P2 in accordance with the invention contains a pair of bead wires each made up of multiple layers of textile cords made of aramid that are wound around an internal core made of a PLA polymer. The cords are identical to those used for P1, and the internal core of the bead wire made of PLA has a diameter of 5.5 mm.

[0104] The cross section of the central core is 24 mm.sup.2, and the total cross section of the bead wire is 41 mm.sup.2. In a meridian plane, a cross section of the bead wire is hexagonal, as depicted in FIG. 3-E. The core is extruded by a known method and then cut, curved and bonded to itself to form a ring. The mass of the bead wire is 60 grammes.

[0105] The following table summarizes the various configurations tested:

TABLE-US-00001 TABLE 1 Control T P1 P2 Bead wires (FIG. 2-A) (FIG. 2-B) (FIG. 3-E) Solution Metallic core Sheathed cord Internal core + cords 215 + 8x130 Core diameter: 5.5 mm Breaking strength 16.5 kN, minimum 22 kN 22 kN 26 kN, maximum Interior 1466 mm 1450 mm 1450 mm development Diameter 4.79 mm 5.5 mm 7.2 mm Mass of bead 169 g 35 g 60 g wire Tensile stiffness 2990 kN 700 kN 700 kN (Young's modulus x S) Bending stiffness 5.10.sup.5 10.sup.5 2.10.sup.5 (N .Math. mm.sup.2) Cross-sectional 18.1 mm.sup.2 24 mm.sup.2 41 mm.sup.2 area of bead wire

[0106] The control tyre and those of the invention were tested and compared for performance criteria affected by the influence of the bead wires.

[0107] As seen above, the bead wires contribute to the handling performance of the vehicle. The influence of the bead wires on the handling can be assessed by analysing the transverse cornering stiffnesses.

[0108] The transverse cornering stiffness was measured on dedicated measuring machines, such as those sold by MTS.

[0109] The bead wire also contributes to the quality of the mounting of the bead on a rim. The test of mountability on a rim consists in giving a result for the overall mountability on the basis of a breakdown of the mounting into elementary operations, which notably comprise: passing through the rim flanges, pressure tapping, crossing of humps on the rim, placing the bead by compression, the tightness below the rim seat, debeading and dismounting. To perform this test, means are necessary such as a semi-automatic mounting machine, or else means

[0110] A result greater than (respectively less than) 100% indicates an improvement (respectively a diminution) in the performance criterion under consideration.

[0111] The results obtained are summarized in Table 2 below:

TABLE-US-00002 TABLE 2 Mass of Burst bead Unseating Mountability pressure Mass of tyre wire pressure on rim T1 100 100 100 100 100 P1 90 105 500 100 99 P2 90 103 300 100 98

[0112] The tyres of the invention have a burst pressure comparable with that of the control. The flexibility of the bead wires of the invention does not affect their burst strength much. The mass of the bead wires of the invention is significantly less than that of the control T.

[0113] Moreover, the performance of a metallic bead wire is reprised, which would not be the case for the textile bead wires of the prior art.

[0114] The inventors have designed a tyre provided with a pair of bead wires that have reduced mass while still performing the many expected functions of bead wires. The inventors have also proposed bead wires for which the industrial manufacturing cost is kept under control in relation to the prior art.