TIRE WITH A TREAD COMPRISING REINFORCING ELEMENTS

Abstract

In a tire with a tread that includes tread pattern elements, a circumferential reinforcement, and first and second circumferential grooves, the circumferential reinforcement is formed of a rubber mixture having a stiffness greater than a stiffness of a rubber mixture forming a remainder of the tread. The tire has an outer side on one side of a median plane of the tire, and an inner side on an opposite side of the median plane. The first circumferential groove is disposed axially toward the outer side relative to the second circumferential groove. The circumferential reinforcement includes a reinforcing element having a tapered shape positioned in each of a group of the tread pattern elements disposed axially toward the outer side relative to one of the first and second circumferential grooves, with the reinforcing elements being axially close to an outer-side face of that circumferential groove.

Claims

1-20. (canceled)

21. A tire having an axis of rotation, a median plane perpendicular to the axis of rotation, an outer side on one side of the median plane, and an inner side on an opposite side of the median plane, the tire comprising: two beads; two sidewalls, each of the two sidewalls being connected to a corresponding one of the two beads, and each of the two sidewalls including an end; and a crown connected to the ends of the two sidewalls, the crown including: a crown reinforcement, and a tread positioned at a radially outside position of the tire, the tread including: a plurality of tread pattern elements, each of the tread pattern elements having lateral faces and a contact face that is structured to come into contact with a road surface when the tire is rolling, a plurality of circumferential grooves, each of the circumferential grooves being delimited by a bottom and opposing lateral faces of adjacent elements of the tread pattern elements, with the opposing lateral faces of the adjacent elements being structured to face each other, and a circumferential reinforcement formed of a rubber mixture having a stiffness greater than a stiffness of a rubber mixture forming a remainder of the tread, wherein: the circumferential grooves include first and second circumferential grooves, with the first circumferential groove being positioned toward the outer side relative to the second circumferential groove, the circumferential reinforcement includes a first outer-side reinforcing element positioned in each of a first group of the tread pattern elements disposed axially toward the outer side relative to one of the first and second circumferential grooves, with the first outer-side reinforcing elements being disposed axially close to an outer-side face of the one of the first and second circumferential grooves, each of the first outer-side reinforcing elements extends radially from a radially outer surface of the crown reinforcement toward an outside portion of the tread and has an axial width that decreases gradually toward the outside portion of the tread over a partial or total height of a thickness of the tread, and for a group of the tread pattern elements disposed axially toward the inner side relative to the first circumferential groove and having lateral faces that delimit the first circumferential groove, none of the tread pattern elements of the group has a reinforcing element disposed axially close to an inner-side face of the first circumferential groove.

22. The tire according to claim 21, wherein the circumferential reinforcement further includes a second outer-side reinforcing element positioned in each of a second group of the tread pattern elements disposed axially toward the outer side relative to a remaining other one of the first and second circumferential grooves, with the second outer-side reinforcing elements being disposed axially close to an outer-side face of the remaining other one of the first and second circumferential grooves.

23. The tire according to claim 22, wherein the circumferential grooves further include a third circumferential groove, and the circumferential reinforcement further includes a third outer-side reinforcing element positioned in each of a third group of the tread pattern elements disposed axially toward the outer side relative to the third circumferential groove, with the third outer-side reinforcing elements being disposed axially close to an outer-side face of the third circumferential groove.

24. The tire according to claim 23, wherein the tread pattern elements include outer-side tread pattern elements positioned adjacent to the circumferential grooves, each of the outer-side tread pattern elements being disposed axially toward the outer side relative to an adjacent one of the circumferential grooves, the circumferential reinforcement includes an outer-side reinforcing element positioned in each of the outer-side tread pattern elements, with each of the outer-side reinforcing elements being disposed axially close to an outer-side face of an adjacent one of the circumferential grooves, and the outer-side reinforcing elements include the first, second, and third outer-side reinforcing elements.

25. The tire according to claim 21, wherein the tread pattern elements include a group of inner-side tread pattern elements positioned adjacent to an inner side of one of the circumferential grooves other than the first circumferential groove, each of the inner-side tread pattern elements being disposed axially toward the inner side relative to the circumferential groove, and the circumferential reinforcement includes an inner-side reinforcing element positioned in each of the inner-side tread pattern elements, with each of the inner-side reinforcing elements being disposed axially close to an inner-side face of the one of the circumferential grooves.

26. The tire according to claim 21, wherein the circumferential grooves include at least four circumferential grooves, including a first inner-side circumferential groove and a second inner-side circumferential groove, with the first inner-side circumferential groove being closest to the inner side of the tire, and with the second-inner-side circumferential groove being second closest to the inner side of the tire, the tread pattern elements include a first group of inner-side tread pattern elements positioned adjacent to an inner side of the first inner-side circumferential groove, each of the inner-side tread pattern elements of the first group being disposed axially toward the inner side relative to the first inner-side circumferential groove, the tread pattern elements include a second group of inner-side tread pattern elements positioned adjacent to an inner side of the second inner-side circumferential groove, each of the inner-side tread pattern elements of the second group being disposed axially toward the inner side relative to the second inner-side circumferential groove, the circumferential reinforcement includes a first inner-side reinforcing element positioned in each of the first inner-side tread pattern elements, with each of the first inner-side reinforcing elements being disposed axially close to an inner-side face of the first inner-side circumferential groove, and the circumferential reinforcement includes a second inner-side reinforcing element positioned in each of the second inner-side tread pattern elements, with each of the second inner-side reinforcing elements being disposed axially close to an inner-side face of the second inner-side circumferential groove.

27. The tire according to claim 21, wherein the circumferential reinforcement includes first inner-side reinforcing elements, and the first outer-side reinforcing elements and the first inner-side reinforcing elements are disposed symmetrically with respect to the median plane.

28. The tire according to claim 27, wherein a central circumferential groove of the circumferential grooves is positioned such that the median plane passes through the central circumferential groove, the circumferential reinforcement includes a reinforcing element in each of the tread blocks positioned adjacent an inner-side face of the central circumferential groove and in each of the tread blocks positioned adjacent an outer-side face of the central circumferential groove, and the reinforcing elements in the tread blocks positioned adjacent the central circumferential groove are disposed axially close to the median plane.

29. The tire according to claim 21, wherein the reinforcing elements have two lateral walls, and an angle of each of the two lateral walls relative to a radial direction of the tire is between 35 degrees and 45 degrees.

30. The tire according to claim 21, wherein each of the reinforcing elements has a base part and a top part, with a radial height of the base part being strictly less than a radial distance between a bottom of an adjacent one of the circumferential grooves and the radially outer surface of the crown reinforcement, and with the top part extending radially outwards towards the outside portion of the tread to at least half a height of lateral faces of the adjacent circumferential groove.

31. The tire according to claim 30, wherein the top part of each of the reinforcing elements forms at least a part of one of the lateral faces of the adjacent circumferential groove.

32. The tire according to claim 30, wherein the top part of each of the reinforcing elements is disposed at an axial distance in a range of 1 mm to 8 mm from one of the lateral faces of the adjacent circumferential groove.

33. The tire according to claim 30, wherein the base part of each of the reinforcing elements extends axially under at least a portion of the bottom of the adjacent circumferential groove.

34. The tire according to claim 30, wherein the base part of each of the reinforcing elements extends axially away from the adjacent circumferential groove and under a corresponding one of the tread pattern elements in which the reinforcing element associated with the base part is positioned.

35. The tire according to claim 30, wherein the base parts of the reinforcing elements are axially contiguous with each other and extend axially over at least 50% of an axial width of the tread.

36. The tire according to claim 35, wherein the base parts extend axially over at most an axial width of the crown reinforcement.

37. The tire according to claim 21, wherein the tread includes a first rubber mixture disposed axially on top of a second rubber mixture, the first and second rubber mixtures being different rubber mixtures.

38. The tire according to claim 30, wherein the tread includes a first rubber mixture disposed axially on top of a second rubber mixture, the first and second rubber mixtures being different rubber mixtures, and the base parts of the reinforcing elements extend axially between the radially outer surface of the crown reinforcement and the first and second two rubber mixtures of the tread.

39. The tire according to claim 21, wherein the rubber mixture forming the circumferential reinforcement has a dynamic modulus G* greater than 20 MPa, the dynamic modulus G* being measured at 60 C. at 10 Hz and under an alternating shear stress of 0.7 MPa.

40. The tire according to claim 21, wherein the rubber mixture forming the remainder of the tread has a dynamic modulus G* less than or equal to 1.3 MPa, the a dynamic modulus G* being measured at 60 C. at 10 Hz and under an alternating shear stress of 0.7 MPa.

Description

DESCRIPTION OF THE FIGURES

[0045] The subjects of the invention will now be described with the aid of the appended drawing, in which:

[0046] FIG. 1 very schematically shows (without being drawn to any particular scale) a radial cross section through a tire according to one embodiment of the invention;

[0047] FIGS. 2 to 13 depict treads of tires according to different embodiments of the invention in radial cross section; and

[0048] FIG. 14 shows the embodiment of the tested tread in radial cross section.

DETAILED DESCRIPTION OF THE INVENTION

[0049] FIG. 1 schematically shows a radial cross section of a pneumatic tire or tire incorporating a circumferential reinforcement 20 according to one embodiment of the invention.

[0050] The tire 1 has an outer side E intended to be positioned towards the outside of a vehicle and an inner side I intended to be positioned towards the inside of a vehicle. This tire thus exhibits tread asymmetry.

[0051] FIG. 1 also indicates the axial X, circumferential C and radial Z directions and also the median plane EP (plane perpendicular to the axis of rotation of the tire which is situated halfway between the two beads 4 and passes through the middle of the crown reinforcement 6).

[0052] This tire 1 has a crown 2 reinforced by a crown reinforcement or belt 6, two sidewalls 3 and two beads 4, each of these beads 4 being reinforced with a bead wire 5. The crown reinforcement 6 is surmounted radially on the outside by a rubber tread 9. A carcass reinforcement 7 is wound around the two bead wires 5 in each bead 4, the turn-up 8 of this reinforcement 7 being, for example, disposed towards the outside of the tire 1. In a manner known per se, the carcass reinforcement 7 is made up of at least one ply reinforced by what are known as radial cords, for example of textile or metal, that is to say that these cords are disposed virtually parallel to one another and extend from one bead to the other so as to form an angle of between 80 and 90 with the median circumferential plane EP. An airtight layer 10 extends from one bead to the other radially on the inside with respect to the carcass reinforcement 7.

[0053] The tread 9 has four grooves 11, 12, 13 and 14 from the outer side E to the inner side I. Each groove has an outer face 11.1, 12.1, 13.1 and 14.1, a groove bottom 11.2, 12.2, 13.2 and 14.2 and an inner face 11.3, 12.3, 13.3 and 14.3.

[0054] This tread 9 also has a circumferential reinforcement 20 made up of a reinforcing element 22 disposed adjacently to the outer wall 12.1 of the second groove 12. This reinforcing element 20 bears against the radially outer wall of the crown reinforcement 6 and has a substantially triangular cross section. This reinforcing element partially forms the outer wall 12.1 of the groove 12.

[0055] The circumferential reinforcement 20 opposes the rocking and shearing of the rib externally adjacent to the groove 12 during strong transverse loads on the tire that are oriented axially from the outside to the inside, for example during cornering of the vehicle on which the tire is mounted in the direction of the inner side of the tire.

[0056] FIGS. 2 to 9 depict radial cross sections of treads according to different embodiments of the invention in the case of tread patterns with three circumferential grooves.

[0057] The tread 30 in FIG. 2 has three grooves 11, 12 and 13 and also a circumferential reinforcement 32 comprising two circumferential reinforcing elements 34 and 36. The circumferential reinforcing element 34 is disposed as in FIG. 1, adjacently to the outer wall 12.1 of the second groove 12. This circumferential reinforcing element 34 bears against the radially outer wall of the crown reinforcement 6 and partially forms the outer wall 12.1 of the groove 12.

[0058] The additional circumferential reinforcing element 36 is disposed adjacently to the outer wall 11.1 of the first groove 11. Through its presence, it opposes the shearing and rocking of the tread pattern elements externally adjacent to the first groove 11 and thus cooperates with the action of the circumferential reinforcing element 34 during strong transverse loads on the tire.

[0059] The circumferential reinforcement 42 of the tread 40 in FIG. 3 comprises three circumferential reinforcing elements 44, 46 and 48. The additional circumferential reinforcing element 48 with respect to the circumferential reinforcement 42 is disposed adjacently to the outer wall 13.1 of the third groove. The three circumferential reinforcing elements of this tread cooperate so as to oppose the rocking and shearing of the tread pattern elements externally adjacent to the three grooves during strong transverse loads oriented from the outside to the inside.

[0060] FIG. 4 shows an embodiment of a tread 50 according to one of the subjects of the invention, in which the circumferential reinforcement 52 comprises, as in FIG. 3, three elements 54, 56 and 58 and an additional circumferential reinforcing element 59. This circumferential reinforcing element 59 is disposed adjacently to the inner wall 13.3 of the groove 13. This circumferential reinforcing element 59 opposes the rocking and shearing of the tread pattern elements internally adjacent to the third groove 13 during transverse loads oriented from the inside to the outside. In such a case, taking into account the dynamics of vehicles when cornering, the loads oriented from the inside to the outside are markedly less strong than those oriented in the other direction and it is unnecessary to add further circumferential reinforcing elements. In a bend at the limits of grip, the tire disposed on the vehicle inside the bend is strongly unloaded, taking into account the dynamics of vehicles when cornering. This tire on the inside of the bend nevertheless contributes towards transverse grip through its leading shoulder, situated towards the vehicle. The presence of a reinforcement in this leading shoulder makes it possible to increase the overall thrust at the axle, resulting from the thrust of the two tires on the same axle.

[0061] In FIG. 5, the tread 60 comprises a circumferential reinforcement 62 made up of four circumferential reinforcing elements 64, 66, 68 and 69 disposed in a similar manner to FIG. 4. These four circumferential reinforcing elements have a base 61 and a top part 63. In the embodiment shown, the bases 61 extend under the ribs or tread pattern elements adjacent to the three grooves. These extensions enhance the stiffening provided by the various circumferential reinforcing elements. The radial height of the bases 61 is strictly less than the radial position of the bottoms of the grooves. The bottom of the ribs is thus always formed only by the mixture of the tread.

[0062] In FIG. 6, the tread 70 comprises a circumferential reinforcement 72 made up, as in FIG. 5, of four circumferential reinforcing elements 74, 76, 78 and 79. These circumferential reinforcing elements have top parts 73 and bases 71 and are such that their bases 71 extend under the adjacent grooves. As before, these extensions enhance the stiffening provided by the various circumferential reinforcing elements.

[0063] In FIG. 7, the tread 80 has a circumferential reinforcement 82 made up of four circumferential reinforcing elements 84, 86, 88 and 89 such that their bases 81 are axially contiguous and extend continuously from one side of the tread to the other. This base 81 is thus in continuous direct contact with the radially outer surface of the crown architecture 6 of the tire for which the tread is intended and has a marked action of stiffening the entire crown 2 of this tire.

[0064] The axial width of the axially contiguous bases 81 covers at least half the axial width of the tread and at most the axial width W of the crown reinforcement 6. The fact that the bases are continuous enhances the resistance to rocking of the entire crown block during transverse loads and the fact that they do not extend beyond the axial width of the crown reinforcement 6 promotes the flattening the shoulders and limits the rolling resistance of the tire.

[0065] 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.

[0066] In the examples depicted, the angle made by these two lateral walls is around 40 degrees, i.e. between 35 and 45 degrees.

[0067] The radial height of the circumferential reinforcing elements may reach the contact face of the tread pattern elements when the tire is new, but may also be smaller. It should not be less than half the height of the tread pattern elements in order to be able to act throughout the life of the tire.

[0068] FIG. 8 depicts a tread 100 with a circumferential reinforcement 102 having three circumferential reinforcing elements 104, 106 and 108 disposed, as in FIG. 3, close to the three grooves and on the outside. However, in this example, the inner lateral walls of the three circumferential reinforcing elements do not form part of the outer faces of the ribs but are offset axially towards the outside so as to be spaced apart from these outer faces of the ribs by a distance a of 1 to 8 mm and preferably from 2 to 5 mm. This offset makes it possible not to disrupt the moulding of the ribs during the vulcanization of the tires without decreasing the effectiveness of the circumferential reinforcing elements.

[0069] In this FIG. 8, it can also be seen that the top part of the circumferential reinforcing element 104 extends radially as far as the outer face of the tread pattern element. This makes it easier for electrostatic charges to be discharged on account of the conductive nature of the mixture of the circumferential reinforcing element.

[0070] FIG. 9 depicts a tread 90, the circumferential reinforcement 92 of which consists of three circumferential reinforcing elements 94, 96 and 98 as illustrated in FIG. 3. This tread 90 is made up of a first rubber mixture 91 that is disposed radially on the outside and forms notably the contact faces of the tread pattern elements. This tread 90 also comprises a second rubber mixture 93 that is radially on the inside and intended to be in contact with the radially outer surface of the crown architecture 6. This second mixture 93 forms an underlayer. It should be noted that the three circumferential reinforcing elements are always in direct contact with the radially outer surface of the crown architecture of the tire to be joined to this tread.

[0071] Depending on the objective of the tire designer, the mixture of this underlayer may be of low hysteresis and thus improve the rolling resistance of the tire or be stiffer than the other mixture that forms the tread; in this case the underlayer has a stiffening action on the crown of the tire. All the particular reinforcement features cited above are compatible with the use of this underlayer. This underlayer is situated above the base of the reinforcing elements when the base exists, such that the reinforcement bears directly and primarily on the crown reinforcement. That is to say on the skim layer of the radially outermost ply of the crown architecture.

[0072] FIGS. 10 and 11 depict embodiments according to a subject of the invention in which the tread has an underlayer.

[0073] FIG. 10 depicts a tread 140 similar to that of FIG. 5 and having an underlayer 115. As indicated above, this underlayer is disposed radially on the outside of the bases 61 of the reinforcement 62.

[0074] FIG. 11 depicts a tread 150 similar to that of FIG. 7 and having an underlayer 115. As indicated above, this underlayer is disposed radially on the outside of the bases 81 of the reinforcement 82.

[0075] FIGS. 12 and 13 depict another embodiment of a tire according to a subject of the invention in which the circumferential reinforcements are disposed symmetrically in the tread.

[0076] The tread 120 of FIG. 12 has three grooves 11, 12 and 13 and also a circumferential reinforcement 122. In this embodiment according to one of the subjects of the invention, the circumferential reinforcement 122 comprises four circumferential reinforcing elements 124, 126, 128 and 129 disposed symmetrically with respect to the median plane EP. The three circumferential reinforcing elements 124, 126, and 128 are disposed like the reinforcing elements 54, 56 and 59 in FIG. 4. By contrast, the reinforcing element 129 is disposed axially on the inside with respect to the groove 12 and thus forms at least part of the inner face 12.3 of this groove. The circumferential reinforcement 122 thus does not add any asymmetry to the tread 120, thereby making it easier to mount such a tire when it does not have any other asymmetry. Such a symmetrical tire may thus have its outer side mounted towards the outside or inside of a vehicle, these inner and outer sides being only a geometric reference in this case.

[0077] FIG. 13 depicts a tread 130 with four grooves 11, 12, 13, 14 and a circumferential reinforcement 132. This circumferential reinforcement 132 has four circumferential reinforcing elements 134, 136, 138 and 139. As in the embodiment in FIG. 12, these four circumferential reinforcing elements are disposed symmetrically with respect to the median plane EP of the tire. The reinforcing elements 134 and 136 are disposed axially on the outside with respect to the grooves 12 and 11, respectively; the reinforcing elements 138 and 139 are disposed axially on the inside with respect to the grooves 14 and 13, respectively.

[0078] The circumferential reinforcing elements should serve as a bearing point for opposing the shearing and rocking of the tread pattern elements which contain them. For this purpose, the mixture of which these circumferential reinforcing elements are made is preferably very substantially stiffer than that of the tread. Preferably, the dynamic modulus G*, measured at 60 C. at 10 Hz and under an alternating shear stress of 0.7 MPa, is greater than 20 MPa and very preferentially greater than 30 MPa.

[0079] Such mixtures are described in particular in the Applicants' application WO 2011/045342 A1.

[0080] Table 1 below gives an example of such a formulation.

TABLE-US-00001 TABLE 1 Constituent C. 1 NR (1) 100 Carbon black (2) 70 Phenol-formaldehyde resin (3) 12 ZnO (4) 3 Stearic acid (5) 2 6PPD (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).

[0081] This formulation makes it possible to obtain mixtures of high stiffness, in particular by virtue of the combined action of an epoxy resin and an amine-comprising curing agent. The shear modulus G* measured under an alternating shear stress of 0.7 MPa at 10 Hz and 60 degrees Celsius is 30.3 MPa.

[0082] This very stiff material for circumferential reinforcements is preferably used in treads of low stiffness with dynamic moduli G* of less than 1.3 MPa and preferably less than or equal to 1.1 MPa.

[0083] The following 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% stirene, 1,2-butadiene: 5%, cis-1,4: 15%, trans-1,4: 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) Antioxidant Santoflex 6PPD from Solutia (g) Accelerator Santocure CBS from Solutia Phr: parts by weight per 100 parts of elastomer.

[0084] The dynamic modulus after vulcanization is 0.9 MPa.

[0085] A person skilled in the art, who is a tire designer, should be able to adapt the number and the position of the circumferential reinforcing elements in order to obtain optimum resistance to the rocking and shearing of the ribs and tread pattern elements, specifically for tires which are asymmetrical or not.

Tests

[0086] The rubber mixtures are characterized as follows.

[0087] The dynamic mechanical properties are well known to those skilled in the art. These properties are measured on a viscosity analyser (Metravib VA4000) with test specimens moulded from uncured mixtures or test specimens bonded together from vulcanized mixtures. The test specimens used are described in the standard ASTM D 5992-96 (the version published in September 2006 but initially approved in 1996 is used) in Figure X2.1 (circular test specimens). The diameter d of the test specimens is 10 mm (the circular cross section is thus 78.5 mm.sup.2), the thickness L of each portion of mixture is 2 mm, giving a d/L ratio of 5 (as opposed to the standard ISO 2856, mentioned in paragraph X2.4 of the ASTM standard, which recommends a d/L value of 2).

[0088] The response of a sample of vulcanized composition subjected to a simple alternating sinusoidal shear stress at a frequency of 10 Hz is recorded. The maximum shear stress imposed is 0.7 MPa.

[0089] The measurements are made with a temperature change of 1.5 C. per minute, from a minimum temperature lower than the glass transition temperature (Tg) of the mixture or rubber to a maximum temperature greater than 100 C. Before the test begins, the test specimen is conditioned at the minimum temperature for 20 minutes to ensure good homogeneity of temperature in the test specimen.

[0090] The result used is notably the value of the dynamic modulus G* at a temperature of 60 C.

[0091] The performance of the tires according to the subjects of the invention were measured during the following tests: [0092] Longitudinal braking distance: the distance required to go from 80 to 20 km/h on wet ground is measured. [0093] Cornering stiffness: the axial lateral thrust force of the tire is measured during rolling for a given drift angle. [0094] Speed test on Charade circuit: the test consists of four laps and the performance selected is the average of the four timings. A test is carried out with control tires at the beginning and at the end of the tests in order to be able to correct a possible drift associated for example with a change in the air temperature and ground temperature conditions.

Trials

[0095] FIG. 14 very schematically depicts a cross section of the tread of the tires used for vehicle tests.

[0096] The tread 110 has four grooves 11, 12, 13 and 14. Two mixtures make up the tread, the mixture 113 radially on the outside and the underlayer 115. It also has a circumferential reinforcement 112 comprising five circumferential reinforcing elements 114, 116, 117, 118 and 119. The circumferential reinforcing elements 114, 116 and 118 are each disposed adjacently to an outer face of one of the three ribs disposed furthest towards the outside. The circumferential reinforcing elements 119 and 120 are for their part disposed adjacently to an inner face of one of the two ribs disposed furthest towards the inside. The third rib is thus reinforced by two circumferential reinforcing elements. Each circumferential reinforcing element has a substantially triangular shape and is intended to be in direct contact with the radially outer surface of the architecture of the crown of the tire of which the tread is intended to form part, and one of its lateral walls partially forms a lateral face of a rib. The underlayer is interrupted by the circumferential reinforcing elements. In the present case, the underlayer has a dynamic alternating shear modulus at 60 C. of around 7 MPa.

[0097] The tread 110 of the test tires was produced in a hand-made manner. A length profile corresponding to a multiple of the perimeter of a test tire of the two mixtures of which the tread 113 and the underlayer 115 are made was obtained by coextrusion. This profile had four grooves.

[0098] Profiles of the same length corresponding to the four circumferential reinforcing elements were also produced by extrusion.

[0099] Then, four mixture volumes, each corresponding to the volume and shape of a circumferential reinforcing element, were removed from the coextruded profile of the two mixtures of the tread with a heated chisel and the four circumferential reinforcing elements were placed manually in the four volumes thus prepared.

[0100] The treads thus assembled were then placed on the crown of a tire in a manner well known to a person skilled in the art to complete it. The complete tires were then vulcanized as usual in a curing press.

[0101] The reference tires are Michelin tires of the Pilot Sport 3 type, size 225/45 R17, pressure 2.3 bar at the front and 2.7 bar at the rear, and the test vehicle is a Renault Clio Cup.

[0102] These reference tires R1 have a tread with a mixture having a dynamic shear modulus G* at 60 C. of 1.4 MPa.

[0103] Other reference tires R2 were also produced. The tread of these tires is identical to that of FIG. 10 except for the four circumferential reinforcing elements and the underlayer, which are absent. These tires have a tread pattern formed only by the four circumferential grooves indicated.

[0104] The tread mixture of the reference tires R2 has a G* value at 60 C. of 0.9 MPa.

[0105] The test tires E1 have a tread mixture with a G* value of 0.9 MPa and the circumferential reinforcing elements are produced with a mixture with a G* value of 30 MPa. These tires E1 have a circumferential reinforcement corresponding to that of FIG. 10, but no underlayer.

[0106] Other tires E2 according to the invention were produced with a tread and a circumferential reinforcement such as E1, but additionally an underlayer with a dynamic modulus G* equal to 5 MPa. This underlayer is interrupted by the four circumferential reinforcing elements as indicated in FIG. 10.

[0107] The circumferential reinforcing elements have an angle of 40 degrees between their lateral walls.

TABLE-US-00003 TABLE 3 Braking on wet ground 80-20 km/h Cornering stiffness R1 100 100 R2 115 85 E1 110 100

[0108] The use of a tread of lower stiffness normally reduces the cornering stiffness of the tire and improves the braking performance on wet ground.

[0109] The tire tested according to the invention makes it possible to obtain a gain of 10 points in the braking performance on wet ground while having a cornering stiffness comparable to that of the control R1.

TABLE-US-00004 TABLE 4 Timing Timing gain R1 2 min 18 s R2 2 min 17.7 0.3 s E1 2 min 17.2 0.8 s E2 2 min 17.0 1.0 s

[0110] A gain is considered significant starting from 0.3 s on this circuit.

[0111] It can be seen that the use of a tread with a much less stiff mixture results in only a barely significant gain whereas the results obtained with the tires having circumferential reinforcements according to the invention are very marked.

[0112] The presence of the circumferential reinforcements in the tread thus makes it possible to make full use of the grip potential of tread mixtures of lower stiffness.

[0113] By combining the choice of mixture of the tread, the choice of mixture of the underlayer and the circumferential reinforcements, it is then possible for the tire designer to offset the compromises between grip and, respectively, behaviour and rolling resistance, this not being attainable through the choice of a single material of the tread.