TIRE COMPRISING A TREAD CONTAINING CIRCUMFERENTIAL REINFORCING ELEMENTS IN THE SUBLAYER

Abstract

A tire (1) comprises two beads (4), two sidewalls (3) connected to the beads and a crown (2) connected to the ends of the two sidewalls, the crown comprising a crown reinforcement (6) and a tread (5) radially outside the crown reinforcement (6), said tread (7) comprising a plurality of tread pattern blocks (71), at least two radially superposed layers: a sublayer (7S) covering the crown reinforcement (6), and a main layer (7P) radially above the crown reinforcement (6), the sublayer comprising a plurality of circumferential reinforcing elements (73) being formed of a rubber compound having greater stiffness than the stiffness of the rubber compound of the rest of the sublayer, the circumferential reinforcing elements (73) extending radially from the radially exterior surface of said crown reinforcement (6) in the direction of the interface between the sublayer (7S) and the main layer (7P), said circumferential reinforcing elements having an axial width which decreases gradually with increasing radial proximity to the outside.

Claims

1.-8. (canceled)

9. A tire comprising a crown reinforcement and a tread radially outside the crown reinforcement, the tread comprising: at least two grooves extending at least partially circumferentially, each groove being delimited radially toward the inside by a groove bottom, the tread having a contact face intended to come into contact with the roadway when the tire is being driven on and a wear limit level situated radially on the outside of the groove bottom; a plurality of tread pattern blocks, two axially adjacent blocks being axially separated by one of the at least two grooves; at least two radially superposed layers including a sublayer covering the crown reinforcement and a main layer radially above the crown reinforcement, wherein the sublayer comprises at least two circumferential reinforcing elements arranged axially between two axially consecutive grooves, wherein the circumferential reinforcing elements are formed of a rubber compound having greater stiffness than the stiffness of a rubber compound of the rest of the sublayer, and wherein the circumferential reinforcing elements extend radially from a radially exterior surface of the crown reinforcement in the direction of an interface between the sublayer and the main layer, each circumferential reinforcing element having an axial width which decreases gradually, with increasing radial proximity to an exterior of the tread, until a radial end thereof.

10. The tire according to claim 9, wherein the dynamic shear modulus G* of the rubber compound of the circumferential reinforcing elements is at least two times greater than the dynamic shear modulus G* of the rubber compound of the rest of the sublayer.

11. The tire according to claim 9, wherein the sublayer extends radially substantially as far as the wear limit level.

12. The tire according to claim 9, wherein the radial end of each circumferential reinforcing element is situated radially below or substantially at the wear limit level.

13. The tire according to claim 9 comprising at least three circumferential reinforcing elements distributed axially between two grooves.

14. The tire according to claim 9, wherein the sublayer comprises a base layer directly covering the crown reinforcement, formed of a same material as the circumferential reinforcing elements, the base layer extending radially over a height equal to less than 10% of a radial thickness h of the sublayer.

15. The tire according to claim 9, wherein each circumferential reinforcing element forms a triangle, viewed in meridional section, and an angle of lateral walls of the triangle is between 35 and 45.

16. The tire according to claim 9, wherein the rubber compound of the circumferential reinforcing elements has a dynamic shear modulus G*, measured at 60 C. at 10 Hz and under an alternating shear stress of 0.7 MPa, of greater than 3 MPa, and a rubber compound constituting the main layer has a dynamic shear modulus G*, measured at 60 C. at 10 Hz and under an alternating shear stress of 0.7 MPa, of less than 1.6 MPa.

Description

DESCRIPTION OF THE FIGURES

[0029] The objects of the invention will now be described with the aid of the appended drawing, in which:

[0030] FIG. 1 depicts, highly schematically (without being true to a specific scale), a meridional section through a tyre in accordance with one embodiment of the invention;

[0031] FIGS. 2 to 4 depict, in meridional section, tyres according to different embodiments of the invention;

[0032] FIG. 5 depicts different variant embodiments of an element according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0033] FIG. 1 shows a tyre 1 comprising a crown 2, two sidewalls 3 each connected to a bead 4. The crown 2 is connected on each side to the radially exterior end of each of the two sidewalls. The crown 2 comprises a tread 5. FIG. 1 indicates an equatorial plane CP, which plane is perpendicular to the axis of rotation of the tyre, situated mid-way between the two beads 4 (mounted on rim) and passing through the middle of the axial width of the crown 2; FIG. 1 also indicates, by arrows placed just above the tread 5, on the equatorial plane CP, the axial X, circumferential C and radial Z directions.

[0034] Each bead has a bead wire 40. A carcass ply 41 is wrapped around each bead wire 40. The carcass ply 41 is radial and is, in a manner known per se, made up of cords; in this implementation, textile cords; these cords are arranged substantially parallel to one another and extending from one bead to the other in such a way that they form an angle of between 80 and 90 with the equatorial plane CP.

[0035] From a geometrical perspective, the tread 5 comprises a plurality of tread pattern blocks 71. Two axially adjacent tread pattern blocks 71 are separated by a groove 72 extending at least partially circumferentially; each groove 72 is delimited radially towards the inside by a groove bottom 721 and lateral groove walls 722. The tread has a contact face 51 intended to come into contact with the roadway when the tyre is being driven on and a wear limit level 52 situated radially on the outside of said groove bottom 721.

[0036] From the perspective of the constituent materials, the tread 5 comprises two radially superposed layers: one sublayer 7S directly covering the crown reinforcement 6, and a main layer 7P radially directly above the sublayer 7S (considering the thin layer of calendering materials of the cords or threads of the crown reinforcement 6 to form part of said crown reinforcement layer). Sublayer usually refers to the layer of rubber compound which is not part of the wear layer of the tread, said wear layer being referred to in the present document as main layer. The limit between the sublayer 7S and the main layer 7P is shown as a dashed line. The sublayer 7S extends radially substantially at the level of said wear limit 52.

[0037] It can be seen in FIG. 1 that the tyre comprises three circumferential reinforcing elements 73 distributed axially between two grooves 72. Said circumferential reinforcing elements 73 comprise a radial end 730. Said circumferential reinforcing elements 73 are arranged axially facing a tread pattern block 71. The tyre also comprises four circumferential reinforcing elements 73 distributed axially between each of the shoulders 21 of the tyre and each of the axially outermost grooves 72; each group of four circumferential reinforcing elements 73 is also arranged axially facing a tread pattern block 71, that which is the radially outermost of the tread. It should be noted that, in the variant embodiment illustrated in FIG. 1, the sublayer 7S is formed of the same rubber compound as the main layer 7P.

[0038] The variant embodiment illustrated by means of FIG. 2 differs from the preceding embodiment in that the sublayer 7S is formed of a rubber compound that is different from the rubber compound of the main layer 7P (hatched section in FIG. 2), with all the other aspects being identical, meaning that it is not necessary to describe them again.

[0039] FIG. 3 shows a variant embodiment of the tyre according to the invention, in which it can be seen that a portion of the sublayer is formed of a base layer 7S1 directly covering the crown reinforcement 6, formed of the same material as the circumferential reinforcing elements 72. Said base layer extends radially over a height equal to less than 10% of the radial thickness h of said sublayer 7S. The rest of the sublayer is formed of the same rubber compound as the main layer 7P.

[0040] FIG. 4 shows a variant embodiment of the tyre according to the invention, in which the sublayer comprises a base layer 7S1 (formed as described above) and a second layer 7S2, formed, like the sublayer of FIG. 2, of a rubber compound that is different both from the rubber compound forming the circumferential reinforcing elements 73 and from the rubber compound of the main layer 7P, for example a rubber compound stiffer than that of the main layer 7P and less stiff than that forming the circumferential reinforcing elements 73.

[0041] In terms of the radial height h of the circumferential reinforcing element 73, it may vary from approximately 30% of the thickness p of the sublayer to 120% of said thickness p. This makes it possible to obtain a significant reinforcing effect. It should further be noted that, in all the embodiments illustrating the invention, the radial end 730 of said circumferential reinforcing elements 73 is located radially at the level of said wear limit. More generally, it is suitable for the radial end 730 of said circumferential reinforcing elements 73 to be situated radially below or substantially at the level of said wear limit.

[0042] The shape of the circumferential reinforcing elements depicted is triangular, but this shape may vary and the lateral walls may be concave, convex or in the form of a staircase, notably without departing from the scope of this invention. The reader may refer to FIG. 5 in which a circumferential reinforcing element 738a viewed in meridional section has the shape of a triangle as used in all the earlier illustrations, the lateral walls, viewed in meridional section, therefore being straight lines. Preferably, the angle formed by the two lateral walls of the circumferential reinforcing element(s) is between 35 and 45 degrees. Below 35 degrees, the effectiveness of the bearing point is reduced, and beyond 45 degrees, the volume of the circumferential reinforcing element becomes too great.

[0043] The walls of this circumferential reinforcing element may be concave, convex or in the form of a staircase. Thus, in the variant formed by the circumferential reinforcing element 738b, the meridional section thereof is a trapezium. In the variant formed by the circumferential reinforcing element 738c, the lateral walls viewed in meridional section are straight-line segments, the angle that each of these segments forms with the radial direction varying from one segment to the next (decreasing with increasing radial proximity to the outside in the figure). In the variant formed by the circumferential reinforcing element 738d, the lateral walls viewed in meridional section are curved, convex; they could be concave. In the variant formed by the circumferential reinforcing element 738e, the lateral walls viewed in meridional section form staircases. These variations in the shape of the meridional section can be used with all the variants described hereinabove.

[0044] The circumferential reinforcing elements need to serve as a bearing point for opposing the shearing of the sublayer. For this purpose, the compound constituting these circumferential reinforcing elements is very stiff.

[0045] Table 1 below gives an example of such a formulation.

TABLE-US-00001 TABLE 1 Constituent C. 1 (in phr) NR (1) 100 Carbon black (2) 70 Phenol-formaldehyde resin (3) 12 ZnO (4) 3 Stearic acid (5) 2 6-PPD (6) 2.5 HMT (7) 4 Sulfur 3 CBS (8) 2 (1) Natural rubber; (2) Carbon black N326 (name according to standard ASTM D-1765); (3) Phenol-formaldehyde novolac resin (Peracit 4536K from Perstorp); (4) Zinc oxide (industrial grade - Umicore); (5) Stearin (Pristerene 4931 from Uniqema); (6) N-(1,3-dimethylbutyl)-N-phenylparaphenylenediamine (Santoflex 6-PPD from Flexsys); (7) Hexamethylenetetramine (from Degussa); (8) N-cyclohexylbenzothiazolesulfenamide (Santocure CBS from Flexsys).

[0046] This formulation makes it possible to obtain compounds with high stiffness. The dynamic shear modulus G* measured under an alternating shear stress of 0.7 MPa at 10 Hz and 60 degrees Celsius is 30.3 MPa.

[0047] This very stiff material for the circumferential reinforcements is preferably used with treads of low stiffness, of which table 2 gives an example of a suitable formulation:

TABLE-US-00002 TABLE 2 Composition B1 (phr) SBR (a) 100 Silica (b) 110 Coupling agent (c) 9 Liquid plasticizer (d) 20 Resin plasticizer (e) 50 Black 5 Zinc oxide 3 Stearic acid 2 Antioxidant (f) 2 Accelerator (g) 2 DPG 2 Sulfur 1 The formulations are given by weight. (a) SBR with 27% styrene, 1,2-butadiene: 5%, cis-1,4-butadiene: 15%, trans-1,4-butadiene: 80%; Tg = 48 C. (b) Zeosil1165MP silica from Solvay with BET surface area of 160 m.sup.2/g (c) SI69 TESPT silane from Evonik (d) Flexon 630 TDAE oil from Shell (e) Escorez 2173 resin from Exxon (f) Santoflex 6PPD antioxidant from Solutia (g) Santocure CBS accelerator from Solutia phr: parts by weight per 100 parts of elastomer.

[0048] The dynamic shear modulus G* after vulcanization is 0.9 MPa.